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Rational Design of Reactive M=X (X = N, CR and MLn) Fragments Supported by Trianionic Pincer Ligands Relevant to Atom Tr...

Permanent Link: http://ufdc.ufl.edu/UFE0043676/00001

Material Information

Title: Rational Design of Reactive M=X (X = N, CR and MLn) Fragments Supported by Trianionic Pincer Ligands Relevant to Atom Transfer, Bond Activation and Metathesis Chemistry
Physical Description: 1 online resource (196 p.)
Language: english
Creator: Sarkar, Soumya
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: activation -- alkylidyne -- bond -- metathesis -- nitride -- pincer -- polymerization -- trianionic
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Trianionic pincer ligands are an emerging class of ligands that constrain three anionic donors in a meridional plane and are capable of supporting coordinatively and electronically unsaturated metal complexes. This thesis details the synthesis of trianionic pincer-supported metal-nitride and metal-alkylidyne complexes and their applications as atom transfer reagent and catalyst for polyalkyne synthesis. The synthesis and metalation of the NCN-trianionic pincer ligand precursors are described. Treating 3,5-Me2NCNH2Br (2-13) with 3.0 equiv. of MeLi provides access to the trilithio salt 3,5-MeNCNLi22Li2(DME)6 (2-15), which on subsequent metalation with HfCl4 provides the trianionic-pincerate complex (3,5-MeNCN)2HfLi2(DME)2 (2-16). Alternatively, salt metathesis of known {2,6-iPrNCHNLi2}2 (2-17) with Zr(NMe2)2Cl2(THF)2 provides 2,6-iPrNCHNZr(NMe2)2 (2-18). Finally treating {2,6-iPrNCNLi3}2 (2-9) with HfCl4 and subsequent alkylation of in situ generated 2,6-iPrNCNHfCl2Li(DME)3 (2-10) allows access to the trianionic pincerate complex 2,6-iPrNCNHfMe2Li(DME)2 (2-20) in good yield and purity. The terphenyl diol tBuOCOH3 (3-4) reacts with Mo(NMe2)4 with remarkable ease to produce tBuOCOMo(NMe2)(NHMe2)2 (3-5). Complex 3-5 react with NaN3 to provide a rare nitrido anion dimer {tBuOCOMo=N(NMe2)Na(DMF)}2 (3-10). Unlike other metal nitrides, the anionic Mo-nitride behave as a nucleophile with a variety substrates of the form RL (where R is a mild electrophile and L is a leaving group) to produce Mo(VI), d0 metal-imido complexes tBuOCOMo=NR(NMe2) (3-11-R). Complex 3-10 readily transfers the N-atom to acid chlorides to generate the corresponding nitriles and the oxo-amide tBuOCOMo=O(NMe2) (3-14). Detailed mechanistic studies reveal that slow cyclometalation and DMF dissociation precede the fast nitrile extrusion. 2 equiv. tBuOCOH3 react with W2(NMe2)6 at 80 °C for 3 d, producing tBuOCHOW(µ-NMe2)(µ-NMe)(µ-CH)WtBuOCHO (4-6), and liberating 4 equiv. of NHMe2. The formation of this product marks an unprecedented combination of reactions; a C-N and double C-H bond activation across a W-W triple bond. Detailed spectroscopic investigations indicate that one equiv. of ligand reacts with the metal precursor to give tBuOCHOW(NMe2)W(NMe2)3 (4-7). Heating 4-7 in the absence of ligand indicates that multiple bond activations occur prior to addition of the second ligand. A combination of multinuclear NMR, IR, and Mass spectroscopic data elucidate the sequential events. Finally, tBuOCOH3 reacts with (OtBu)3W=C(tBu) to form tBuOCHOW=CC(CH3)3 (OtBu)(THF) (5-1). Treating with mild base PPh3=CH2 and subsequent alkylation with MeOTf provide access to the neutral trianionic pincer supported metal-alkylidyne tBuOCOW=CC(CH3)3(THF)2 (5-4). Complex (5-4) is an active catalyst for polymerization of phenyl acetylenes with TON>4000.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Soumya Sarkar.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Veige, Adam S.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043676:00001

Permanent Link: http://ufdc.ufl.edu/UFE0043676/00001

Material Information

Title: Rational Design of Reactive M=X (X = N, CR and MLn) Fragments Supported by Trianionic Pincer Ligands Relevant to Atom Transfer, Bond Activation and Metathesis Chemistry
Physical Description: 1 online resource (196 p.)
Language: english
Creator: Sarkar, Soumya
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: activation -- alkylidyne -- bond -- metathesis -- nitride -- pincer -- polymerization -- trianionic
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Trianionic pincer ligands are an emerging class of ligands that constrain three anionic donors in a meridional plane and are capable of supporting coordinatively and electronically unsaturated metal complexes. This thesis details the synthesis of trianionic pincer-supported metal-nitride and metal-alkylidyne complexes and their applications as atom transfer reagent and catalyst for polyalkyne synthesis. The synthesis and metalation of the NCN-trianionic pincer ligand precursors are described. Treating 3,5-Me2NCNH2Br (2-13) with 3.0 equiv. of MeLi provides access to the trilithio salt 3,5-MeNCNLi22Li2(DME)6 (2-15), which on subsequent metalation with HfCl4 provides the trianionic-pincerate complex (3,5-MeNCN)2HfLi2(DME)2 (2-16). Alternatively, salt metathesis of known {2,6-iPrNCHNLi2}2 (2-17) with Zr(NMe2)2Cl2(THF)2 provides 2,6-iPrNCHNZr(NMe2)2 (2-18). Finally treating {2,6-iPrNCNLi3}2 (2-9) with HfCl4 and subsequent alkylation of in situ generated 2,6-iPrNCNHfCl2Li(DME)3 (2-10) allows access to the trianionic pincerate complex 2,6-iPrNCNHfMe2Li(DME)2 (2-20) in good yield and purity. The terphenyl diol tBuOCOH3 (3-4) reacts with Mo(NMe2)4 with remarkable ease to produce tBuOCOMo(NMe2)(NHMe2)2 (3-5). Complex 3-5 react with NaN3 to provide a rare nitrido anion dimer {tBuOCOMo=N(NMe2)Na(DMF)}2 (3-10). Unlike other metal nitrides, the anionic Mo-nitride behave as a nucleophile with a variety substrates of the form RL (where R is a mild electrophile and L is a leaving group) to produce Mo(VI), d0 metal-imido complexes tBuOCOMo=NR(NMe2) (3-11-R). Complex 3-10 readily transfers the N-atom to acid chlorides to generate the corresponding nitriles and the oxo-amide tBuOCOMo=O(NMe2) (3-14). Detailed mechanistic studies reveal that slow cyclometalation and DMF dissociation precede the fast nitrile extrusion. 2 equiv. tBuOCOH3 react with W2(NMe2)6 at 80 °C for 3 d, producing tBuOCHOW(µ-NMe2)(µ-NMe)(µ-CH)WtBuOCHO (4-6), and liberating 4 equiv. of NHMe2. The formation of this product marks an unprecedented combination of reactions; a C-N and double C-H bond activation across a W-W triple bond. Detailed spectroscopic investigations indicate that one equiv. of ligand reacts with the metal precursor to give tBuOCHOW(NMe2)W(NMe2)3 (4-7). Heating 4-7 in the absence of ligand indicates that multiple bond activations occur prior to addition of the second ligand. A combination of multinuclear NMR, IR, and Mass spectroscopic data elucidate the sequential events. Finally, tBuOCOH3 reacts with (OtBu)3W=C(tBu) to form tBuOCHOW=CC(CH3)3 (OtBu)(THF) (5-1). Treating with mild base PPh3=CH2 and subsequent alkylation with MeOTf provide access to the neutral trianionic pincer supported metal-alkylidyne tBuOCOW=CC(CH3)3(THF)2 (5-4). Complex (5-4) is an active catalyst for polymerization of phenyl acetylenes with TON>4000.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Soumya Sarkar.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Veige, Adam S.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043676:00001


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1 X = N, CR AND ML n ) FRAGMENTS SUPPORTED BY TRIANIONIC PINCER LIGAND S RELEVANT TO ATOM TRANSFER, BOND ACTIVATION AND METATHESIS CHEMISTRY By SOUMYA SARKAR A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011

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2 2011 Soumya Sarkar

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3 To my parents and all my teachers

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4 ACKNOWLEDGMENTS A s I am getting close to finishing my PhD at the Department of C hemistry in University of Florida, it is time to look back. There are several people who made my expedition enjoya ble, educational and gratifying. If I have to go back in time, I will have no to redo my PhD. I thank you from the bottom of my heart for accepting me in your group in Fall, 2006. You have spent more time than anyone else to refine me to be a better scientist. I am honored to inherit your en thusiasm for making new molecules and I will cherish those days when you used to spend almost an entire day sitting in a chair beside me and explaining where my product should be (residue or filtrate). I am grateful to you for being patient and for your c onstant encouragement for making this possible. You have been a perfect advisor who kept a balance between giving away freedom and at the same time setting defined targets so that I could be productive. I will try my best to stand up to the training and advices you gave me. I would like to thank Maa and Baba for supporting me all these years with love and compassion and more importantly passing me the values to be a better person. I am blessed to be your son and I am happy to make you proud. Jethu, I es teem you for the blessings and I adore you for keeping all the adversities away from me so that I could remain calm and focused on my job. Shreya, you are my strength and motivation and I thank you for being the person who is always there for me. This j ourney would have been very difficult without you and at no cost I want to change that. Four other people who also deserve special mention are Gary, Natalie, Ranjan and Rashmi. Your friendship is precious and I am going to miss you all.

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5 I would like to thank my committee members Dr. Talham, Dr. Murray, Dr. Aponick, and Dr. Weaver for your input in getting this degree and your kind help in context to my future endeavors. This dissertation would be incomplete without the help of Dr. Abboud. You have enr iched this document with your invaluable contribution in getting all the X ray crystal lographic data I thank you for being so committed with several of the air sensitive crystals. I also appreciate the effort from the X ray team (past and present) inclu ding Patrick, Antonio, Dan and Yousoon. I thank Dr. Ghiviriga and his team (especially Robert and David) for the contribution with all the 2D NMR data and my questions. I would also like to thank Dr. Dem p sey Hyatt for taking the time to teach me prelimin ary DFT calculations, and sharing his zeal about chemistry with me All the Veige group members you are awesome. Melanie, I acknowledge you for making the OCO ligand which is why I am able to write this dissertation and also for your generosity for edit in g this document. Roxy and Matt I thank you for welcoming me Matias; thank you all for your friendship support and most notably the critical inputs during the group meeti ngs that has helped me in my research. You people have created a wonderful work atmosphere and I wish you all the best in future. I am also privileged to work with several undergraduate students. Joe, Jeff, Trevor and Jorma I appreciate your hard work a nd the significant contributions that you made in my publications. I am proud to be your mentor. read this section of my dissertation to just to find t of it!

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ .......... 10 LIST OF ABBREVIATIONS ................................ ................................ ........................... 16 ABSTRACT ................................ ................................ ................................ ................... 17 CHAPTER 1 BACKGROUND INFORMATION ................................ ................................ ............ 19 1.1 Introduction ................................ ................................ ................................ ....... 19 1.2 Chemistry of Terminal Metal Nitrides ................................ ................................ 20 1.2.1 Nitroge n Fixation ................................ ................................ ..................... 20 1.2.2 Catalytic Dinitrogen Fixation Under Ambient Conditions ......................... 21 1.2.3 N atom Transfer Reactions from Metal Nitrides ................................ ...... 22 1.3 Chemistry of Metal Alkylidynes ................................ ................................ ......... 25 1.3.1 Synthetic Rou tes to High Oxidation State Metal Alkylidynes ................... 26 1.3.2 General Reactions of High Oxidation State Metal Alkylidynes ................ 28 1.4 Our Goal ................................ ................................ ................................ ........... 29 1.5 Chemistry of Traditional Pincer Ligands ................................ ........................... 30 2 SYNTHESIS AND CHARACTERIZATION OF GROUP 4 METAL COMPLEXES WITH NCN 3 Trianionic P INCER LIGANDS ................................ ............................ 39 2.1 Introduction ................................ ................................ ................................ ....... 39 2.1.1 Metalation Strategies: Direct Metalation ................................ .................. 39 2.1.2 Metalation Strategies: Salt Metathesis ................................ .................... 40 2.2 Results and Discussion ................................ ................................ ..................... 41 2.2.1 The Strategy ................................ ................................ ............................ 41 2.2.2 Synthesis and Reactivity of [3,5 Me 2 NCN]H 3 (2 11) ............................... 42 2.2.3 Synthesis and Characterization of [3,5 Me 2 NCN]H 2 Br (2 13) ................. 42 2.2.4 Synthesis and Characterization of {3,5 MeNCNLi 2 } 2 {Li 2 (DME) 6 } (2 15) ................................ ................................ ................................ ................. 43 2.2.5 Structural Description of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] (2 15) .................. 44 2.2.6 Synthesis and Characterization of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] (2 16) ................................ ................................ ................................ ................. 45 2.2.7 Structural Description of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] (2 16) ................ 46 2.2.8 Synthesis and Characterization of [2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18) ........ 46 2.2.9 Structural Description of [2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18) ....................... 47 i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) ................................ ................................ ................................ ................. 48 i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) .............. 49

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7 2.3 Experimental Section ................................ ................................ ........................ 50 2.3.1 General Considerations ................................ ................................ ........... 50 2.3.2 Synthesis of 3,5 Me NCNH 2 Br (2 13) ................................ ...................... 50 2.3.3 Synthesis of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] (2 15) ................................ ..... 51 2.3.4 Synthesis of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] (2 16) ................................ ... 52 2.3.5 Synthesis of [2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18) ................................ ........... 52 2.3.6 Synthesis of [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) ................................ ... 53 2.3.7 X ray Experimental Details for {3,5 Me 2 NCHNLi 2 (THF) 2 } 2 (2 14) ........... 54 2.3.8 X ray Experimental Details for [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] (2 15) ........ 55 2.3.9 X ray Experimental Details for [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] (2 16) ...... 55 2.3.10 X ray Experimental Details for [2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18) ........... 56 2.3.11 X ray Experimental Details for i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) ... 57 2.4 Conclusions ................................ ................................ ................................ ...... 57 3 SYNTHESIS AND REACTIVITY OF AN ANIONIC MOLYBDENUM NITRIDE SUPPORTED BY AN OCO 3 TRIANIONIC PINCER LIGAND ................................ 72 3.1 Introduction ................................ ................................ ................................ ....... 72 3.2 Resul ts and Discussion ................................ ................................ ..................... 73 3.2.1 Synthesis and Characterization of [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 (3 7) ...... 74 3.2.2 Structural Description of [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 (3 7) ..................... 75 3.2.3 Synthesis and Characterization of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 (3 8) .... 75 3.2.4 Structural Description of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 (3 8) ................... 76 3.2.5 Comparison of Structural Features, Magnet ic Moment and Reactivity between (3 5), (3 6), (3 7) and (3 8) ................................ ............................. 77 3.2.6 Initial Attempts to Synthesize a Terminal Mo nitride ................................ 78 3.2.7 Synthesis and Characterization of {[ t 2 )Na(DMF)} 2 (3 10) ................................ ................................ ................................ ............ 79 3.2.8 Structural Description of {[ t 2 )Na(DMF)} 2 (3 10) ........ 80 3.2.9 Reactivity of {[ t 2 )Na(DMF)} 2 (3 10) with Mild Electrophiles ................................ ................................ ................................ .. 81 3.2 .10 Reactivity of [ t 2 )Na(DMF)} 2 (3 10) with Protons ..... 82 3.2.11 Structural Description of [ t 2 ) (3 12) .............. 83 3.2.12 Nitrile Synthesis via N atom Transfer to Acid Chlorides ........................ 83 3.2.13 Structural Description of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 )(DMF) (3 13 t Bu) ................................ ................................ ................................ ................ 85 3.2.14 Proposed Mechanism for N atom Transfer ................................ ............ 86 3.3 Exp erimental Section ................................ ................................ ........................ 87 3.3.1 General Considerations ................................ ................................ ........... 87 3.3.2 Synthesis of [ t BuOC O]Mo(OTf)(NHMe 2 ) 2 (3 7) ................................ ........ 88 3.3.3 Synthesis of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 (3 8) ................................ ...... 88 3.3.4 Synthesis of {[ t 2 )Na(DMF)} 2 (3 10) ........................... 8 9 3.3.5 Synthesis of [ t BuOCO]Mo=NSiMe 3 (NMe 2 ) (3 11 SiMe 3 ) ......................... 90 3.3.6 Synthesis of [ t 2 ) (3 12) ................................ .. 91 3.3.7 Synthesis of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) (3 13 t Bu) .......................... 91 3.3.8 Synthesis of [ t BuOCO]Mo=O(NMe 2 ) (3 14) ................................ ............. 92 3.3.9 NMR Tube Reactions ................................ ................................ .............. 93

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8 3.3.9.1 Excess MeI and 3 10 to form [ t BuOCO]Mo=NMe(NMe 2 ) (3 11 Me) ................................ ................................ ................................ ......... 93 3.3.9.2 t BuCOCl and 3 10 to form 3 14 and t ................................ .. 94 3.3.9.3 PhCOC l and 3 10 to form 3 ................................ ... 94 3.3.9.4 MeCOCl and 3 10 to form 3 ................................ 95 3.3.10 X ray Experimental Details for [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 (3 7) ......... 95 3.3.11 X ray Experimental Details for [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 (3 8) ....... 96 3.3.12 X ray Ex perimental Details for {[ t 2 )Na(DMF)} 2 (3 10) ................................ ................................ ................................ ................. 97 3.3.13 X ray Experimental Details for [ t 2 ) (3 1 2) .... 98 3.3.14 X ray Experimental Details for [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) (3 13 t Bu) ................................ ................................ ................................ ................ 98 3.4 Conclusions ................................ ................................ ................................ ...... 99 4 UNIQUE PR IMARY CARBON NITROGEN BOND SCISSION ACROSS A W W MULTIPLE BOND AND METHYL DEHYDROGENATION ................................ .. 118 4.1 Introduction ................................ ................................ ................................ ..... 118 4.2 Original Motivation ................................ ................................ .......................... 119 4.3 Results and Discussion ................................ ................................ ................... 119 4.3.1 Characterization of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] (4 6) ................................ ................................ ................ 120 4.3.2 Structural Description of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] (4 6) ................................ ................................ ................ 121 4.3.3 Confirmation of Methyl Dehydrogenation Event and Fate of Hydrogen Atoms ................................ ................................ ................................ .......... 122 4.3.4 Synthesis and Characterization of [ t BuOCHO](NMe 2 2 ) 3 (4 7) ................................ ................................ ................................ ................. 123 4.3.5 Synthesis and Characterization of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W(NMe 2 ) 2 (4 8) ................................ ................................ ...................... 125 4.4 Experimental S ection ................................ ................................ ...................... 126 4.4.1 General Considerations ................................ ................................ ......... 126 4.4.2 Synthesis of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] (4 6) 127 4.4.3 Synthesis of [ t BuOCHO]W(NMe 2 )W(NMe 2 ) 3 (4 7) ................................ 128 4.4 .4 X ray Experimental Evidence for [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] (4 6) ................................ ................................ ................ 129 4.5 Conclusions ................................ ................................ ................................ .... 130 5 SYNTHESIS AND REACTIVITY OF AN OCO 3 TRIANIONIC PINCER TUNGSTEN ALKYLIDYNE ................................ ................................ ................... 142 5.1 Introduction ................................ ................................ ................................ ..... 142 5.2 Results and Discussion ................................ ................................ ................... 144 5.2.1 Synthesis and Characterization of [ t BuOCHO] 3 ) 3 (O t Bu)(THF) (5 1) ................................ ................. 144 5.2.2 Structural Description of [ t BuOCHO] 3 ) 3 (O t Bu)(THF) (5 1) ..... 145

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9 5.2.3 Synthesis and Characterization of { [ t BuOCO] 3 ) 3 (O t Bu)}{PPh 3 CH 3 } (5 2) ................................ .......... 146 5.2.4 Synthesis and Characterization of [ t BuOCO] 3 ) 3 (Et 2 O) (5 3) .. 147 5.2.5 Structural Descriptio n of [ t BuOCO] 3 ) 3 (Et 2 O) (5 3) ................. 148 5.2.6 Synthesis and Characterization of [ t BuOCO] 3 ) 3 (THF) 2 (5 4) 148 5.2.7 Structural Description of [ t BuOCO] 3 ) 3 (THF) 2 (5 4) ................ 149 5.2.8 Polymerization of Alkynes using [ t BuOCO] 3 ) 3 (THF) 2 (5 4) .... 150 5.3 Experimental Section ................................ ................................ ...................... 150 5.3.1 General Considerations ................................ ................................ ......... 150 5.3.2 Synthesis of [ t 3 ) 3 (O t Bu)(THF) (5 1) .......................... 151 5.3.3 Synthesis of {[ t BuOCO] 3 ) 3 (O t Bu)}{Ph 3 PCH 3 } (5 2) ................ 152 5.3.4 Synthesis of [ t BuOCO] 3 ) 3 (Et 2 O) (5 3) ................................ .... 153 5.3.5 Synthesis of [ t BuOCO] 3 ) 3 (THF) 2 (5 4) ................................ ... 153 5.3.6 General Procedure for Polymerization Reactions ................................ .. 154 5.3.7 X Ray Experimental Details for [ t 3 ) 3 (O t Bu)(THF) (5 1) ................................ ................................ ................................ ................. 154 5.3.8 X ray Experimental Details for [ t BuOCO] 3 ) 3 (Et 2 O) (5 3) ........ 155 5.3.9 X ray Experimental Details for [ t BuOCO] 3 ) 3 (THF) 2 (5 4) ....... 156 5.4 Conclusions ................................ ................................ ................................ .... 157 APPENDIX: CRYSTAL DATA AND REFINEMENT PARAMETER ............................. 166 LIST OF REFERENCES ................................ ................................ ............................. 181 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 196

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10 LIST OF TABLES Table page 3 1 Experimentally determined magnetic moments for the Mo(IV) metal complexes 3 5 3 6 3 7 and 3 8 ................................ ................................ ...... 101 3 2 Experimentally determined thermodynamic parameters for the equilibration of 3 11 SiMe 3 3 13 t Bu and 3 14 ................................ ....................... 101 4 1 1 H and 13 C chemical shifts assignments for [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) ................................ ................................ ..................... 131 4 2 1 H and 13 C chemical shifts assignments for [ t BuOCHO]W(NMe 2 )W(NMe 2 ) 3 ( 4 7 ). ................................ ................................ ................................ ................. 132 5 1 Polymerization of alkynes using [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) ............... 158 A 1 Data and refinement for {3,5 Me 2 NCHNLi 2 (THF) 2 } 2 ( 2 14 ) .............................. 166 A 2 Data and refinement for [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) ............................ 167 A 3 Data and refinement for [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) .......................... 168 A 4 Data and refinement for [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) ................................ 169 A 5 i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) ......................... 170 A 6 Data and refinement for [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 ( 3 7 ) ............................... 171 A 7 Data and refinement for [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 ( 3 8 ) ............................. 172 A 8 Data and refinement for [ t 2 )(DMF) ( 3 9 ) .......................... 173 A 9 Data and refinement for {[ t 2 )Na(DMF)} 2 ( 3 10 ) .................. 174 A 10 Data and refinement for [ t 2 ) ( 3 12 ) ......................... 175 A 11 Data and refinement for [ t BuOCO]Mo=NC(O) t Bu(NMe 2 )(DMF) ( 3 13 t Bu ) ....... 176 A 12 Data for [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) ................... 177 A 13 Data and refinement for [ t BuOCHO] 3 ) 3 (O t Bu)(THF) ( 5 1 ) ................ 178 A 14 Data and refinement for [ t 3 ) 3 (Et 2 O) ( 5 3 ) ............................. 179 A 15 Data and refinement for [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) ............................ 180

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11 LIST OF FIGURES Figure page 1 1 A simplified catalytic cycle to incorporate small molecules into organic substrates ................................ ................................ ................................ ........... 31 1 2 Representation of active site of FeMo cofactor, and the overall nitrogen fixation reaction ................................ ................................ ................................ .. 31 1 3 (a) The active catalyst [Mo(HIPTN 3 N)N 2 ] ( 1 1 ), (b) intermediates in the reduction of N 2 at Mo by stepwise addition of protons and electrons. ................ 32 1 4 (a) Synthesis of {Mo(PNP)(N 2 ) 2 } 2 ( 1,2 N 2 ) ( 1 2 ), (b) Proposed catalytic cycle for dinitrogen fixation at ambient temperature. ................................ ................... 32 1 5 Reductive cleavage of dinitrogen by Mo(N t Bu(3,5 MeC 6 H 3 ) 3 ( 1 3 ) ..................... 33 1 6 Synthesis and subsequent chemistry of complex 1 5 ................................ ......... 33 1 7 N atom transfer to olefins form high oxidation state Mn nitride. .......................... 33 1 8 Nitrile alkyne cros s metathesis using a terminal W nitride ................................ .. 33 1 9 Metal mediated N atom transfer to acid chlorides, where the N atom is derived from dinitrogen ................................ ................................ ....................... 34 1 10 Synthesis of first high oxidation state metal alkylidyne 1 6 ................................ 34 1 11 Synthesis of (ArO) 2 ( t BuCH 2 t Bu ( 1 7 ) ................................ ......................... 34 1 12 t Bu fragment. ............. 35 1 13 General route to synthesize X 3 1 9 ) ................................ .............. 35 1 14 3 1 10 ) ............ 35 1 15 t Bu)Ar] 3 ( 1 11 ) ................... 35 1 16 Possible mechanisms for alkyne metathesis (AM) ................................ ............. 36 1 17 Reaction of metal alkylidyne with nitriles ................................ ............................ 36 1 18 General 1,2 ................................ ............ 36 1 19 ................................ ................................ ................................ 37 1 20 Target molecules with [ArNCN] ( 1 14 ) and [ t BuOCO] ( 1 15 ) ligand frameworks ................................ ................................ ................................ ......... 37

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12 1 21 Lowest unoccupied molecular orbital (LUMO) of [ t 1 15 ) ............ 38 1 22 Potential modification sites available in the pincer architecture to enable precise control over the metal complex property ................................ ................ 38 2 1 Library of NCN pincer ligands ................................ ................................ ............. 5 9 2 2 Synthesis of (a) ( [ i PrNCHN]){Zr(NMe 2 ) 3 } 2 ( 2 6 ), (b) {( 3,5 CF 3 N C CH C N)Zr(NMe 2 ) 2 NHMe 2 } 2 ( 2 7 ), and (c) ( 3,5 CF 3 N C CH anth C N){Hf (NMe 2 ) 3 NHMe 2 } 2 ( 2 8 ) ................................ ................................ ........................ 60 2 3 Solid state molecular structure of (a) {2,6 i PrNCNLi 3 } 2 ( 2 9 ), (b) [2,6 i PrNCNHfCl 2 ] [Li(DME) 3 ] ( 2 10 ), the solvated lithium counter ion is not in shown in the picture. ................................ ................................ ........................... 61 2 4 Synthesis of [3,5 Me 2 NCN]H 3 ( 2 11 ) and attempted synthesis of {2,6 Me 2 NCNLi 3 } 2 ( 2 12 ). ................................ ................................ ........................... 61 2 5 Synthesis of [3,5 Me 2 NCN]H 2 Br ( 2 13 ) ................................ .............................. 61 2 6 Synthesis of {3,5 Me 2 NCHNLi 2 (THF) 2 } 2 ( 2 14 ) ................................ ................... 62 2 7 Solid state molecular structure of {3,5 Me 2 NCHNLi 2 (THF) 2 } 2 ( 2 14 ). The h ydrogen atoms are omitted for clarity. ................................ .............................. 62 2 8 Synthesis of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) ................................ ................ 63 2 9 Solid state molecular structure of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ). The hydrogen atoms, lithium counter ions and DME are omitted for clarity. .............. 63 2 10 Synthesis of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) ................................ .............. 64 2 11 Solid state molecular structure of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ). The hydrogen atoms are omitted for clarity. ................................ .............................. 64 2 12 Synthesis of [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) ................................ ...................... 65 2 13 Solid state molecular structure of [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ).The hydrogen atoms (excluding C ipso H) are omitted for clarity. ................................ 65 2 14 Attempted synthesis of [2,6 i PrNCN]Zr(NMe 2 )(py) ( 2 19 ) ................................ ... 65 2 15 Synthesis of [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) ................................ .............. 66 2 16 Solid state molecular structure of i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ). The hydrogen atoms are omitted for clarity. ................................ .............................. 66 2 17 1 H NMR spectrum of 3,5 MeNCNH 2 Br ( 2 13 ) in C 6 D 6 ................................ ........ 67

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13 2 18 1 H NMR spectrum of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) in C 6 D 6 ...................... 68 2 19 1 H NMR spectrum of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) in C 6 D 6 .................... 69 2 20 1 H NMR spectrum of [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) in C 6 D 6 ........................... 70 2 21 1 H NMR spectrum of [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) i n CDCl 3 ................. 71 3 1 Comparison of two trianionic pincer ligands (a) [ArNCN]H 3 and (b) [ t BuOCO]H 3 ................................ ................................ ................................ ...... 101 3 2 Synthesis of [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) and [ t BuOCO]MoCl (NHMe 2 ) 2 ( 3 6 ) ................................ ................................ ................................ .. 101 3 3 Four step synthesis of 3,3'' di tert butyl 1,1':3',1'' terphenyl 2,2'' diol [ t BuOCO]H 3 ( 3 4 ) ................................ ................................ .............................. 102 3 4 Synthesis of [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 ( 3 7 ) ................................ ................. 102 3 5 Solid state molecular structure of [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 ( 3 7 ). The hydrogen atoms are omitted for clarity. ................................ ............................ 103 3 6 Synthesis of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 ( 3 8 ) ................................ ............... 103 3 7 Solid state molecular structure of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 ( 3 8 ). The hydrogen atoms and DME are omitted for clarity. ................................ ............. 104 3 8 Solid state structures of [ t BuOCO]Mo(IV) metal complexes, exhibiting C s and C 2 symmetric structures. ................................ ................................ ................... 104 3 9 Attempted synthesis of a trianionic pincer su pported molybdenum nitride ....... 105 3 10 Solid state structure of [ t 2 )(DMF) ( 3 9 ) ............................ 105 3 11 Synthesis of {[ t 2 )Na(DMF)} 2 ( 3 10 ) ................................ .... 105 3 12 Solid state structure of {[ t 2 )Na(DMF)} 2 ( 3 10 ), in which the asymmetric unit is displayed. The hydrogen atoms and the DMF molecule are removed for clarity. ................................ ................................ ...... 106 3 13 Addition of mild electrophiles to {[ t 2 )Na(DMF)} 2 ( 3 10 ) ...... 106 3 14 Synthesis of [ t 2 ) ( 3 12 ) ................................ ............ 107 3 15 Solid state structure of [ t 2 ) ( 3 12 ) ........................... 107 3 16 Addition of acid chlorides to synthesize acylimido complexes 3 13 R .............. 107 3 17 Synthesis of [ t BuOCO]Mo=O(NMe 2 ) ( 3 14 ) ................................ ...................... 108

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14 3 18 Solid state structure of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 )(DMF) ( 3 13 t Bu ). The hydrogen atoms are removed of clarity. ................................ ........................... 108 3 19 Eyring plot for the equilibration of N Me 2 resonance in the 1 H NMR spectrum for complex 3 11 SiMe 3 3 14 and 3 13 t Bu ................................ ..................... 109 3 20 Mechanism of N tom transfer from 3 13 R to acid chlorides to form nitriles. .... 109 3 21 Selected region of 1 H NMR spectrum featuring conversion of the pivaloyl imido complex 3 13 t Bu to oxo imido complex 3 14 over time at 40C ............ 110 3 22 Eyring plot for the decay of 3 13 t Bu ................................ ................................ 110 3 23 1 H NMR spectrum of [ t 2 )(DMF)( 3 9 ) and mixture of compounds in C 6 D 6 ................................ ................................ ......................... 111 3 24 1 H NMR spectrum of [ t 2 )Na(DMF)} 2 ( 3 10 ) in C 6 D 6 ........... 112 3 25 1 H NMR of [ t BuOCO]Mo=NSiMe 3 (NMe 2 ) ( 3 11 SiMe 3 ) in C 6 D 6 ........................ 113 3 26 1 H NMR of [ t BuOCO]Mo=NMe(NMe 2 ) ( 3 11 Me ) in C 6 D 6 ................................ 114 3 27 1 H NMR of [ t BuOCHO]Mo N(Cl)(NMe 2 ) ( 3 12 ) in CDCl 3 ................................ 115 3 28 1 H NMR of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) ( 3 13 t Bu ) in C 6 D 6 ......................... 116 3 29 1 H NMR of [ t BuOCO]Mo=NC(O)Ph(NMe 2 ) ( 3 13 Ph ) in C 6 D 6 .......................... 117 4 1 Motivation for making group 6 metal alkylidyne supported by trianionic pincer ligand ................................ ................................ ................................ ................ 133 4 2 Synthesis of (a) [ t BuOCO]W=CH t Bu(O 2,6 i PrC 6 H 3 ) ( 4 1 ), (b) [( t BuOCO) W=CH t Bu ( t BuOCHO)W=CH t Bu( t BuOCO)] ( 4 2 kin and 4 2 therm ) and, (c) [ t BuOCHO] W C( t Bu)Cl ( 4 3 ) ................................ ................................ ........... 134 4 3 Synthetic strategy towards [ t BuOCO]W CR(S) ( 4 5 ) ................................ ....... 135 4 4 Synthesis of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) ............ 135 4 5 (a) Selected region of 1 H NMR spectrum of complex 4 6 (CDCl 3 500 MHz), (b) Selected region of an HMQC spectrum of complex 4 6 .............................. 135 4 6 Molecular structure of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ). Hydrogen atoms (except H1), a benzene molecule, and disordered NMe groups are removed for clarity. ................................ ................................ ......... 136 4 7 Gas chromatograph of the reaction headspace ................................ ................ 136 4 8 Synthesis of [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ) ................................ .......... 137

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15 4 9 Variable temperature 1 H NMR spectra of [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ) (toluene d 8 ). ................................ ................................ ................................ .. 137 4 10 Formation of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W(NMe 2 ) 2 ( 4 8 ) ................. 138 4 11 Overall sequence of reactions that contribute to the formation of 4 6 via 4 7 and 4 8 ................................ ................................ ................................ ............. 138 4 12 Position numbering in compound 4 6 for 2D NMR assignment ....................... 139 4 13 Position numbering in compound 4 7 for 2D NMR assignment ....................... 139 4 14 1 H NMR spectrum of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) in CDCl 3 ................................ ................................ ................................ ....... 140 4 15 1 H NMR spectra of [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ) in C 6 D 6 at 25 C ....... 141 5 1 Ring expansion mechanism for poly acetylene formation using metal alkylidynes ................................ ................................ ................................ ........ 158 5 2 Synthesis of [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) ................................ .. 158 5 3 Solid state molecular structure of [ t BuOCHO] 3 ) 3 (O t Bu)(THF) ( 5 1 ). The hydrogen atoms, except H 12a, are omitted for clarity. ............................. 159 5 4 Synthesis of { [ t BuOCO] 3 ) 3 (O t Bu)}{PPh 3 CH 3 } ( 5 2 ) ........................... 159 5 5 Synthesis of [ t 3 ) 3 (Et 2 O) ( 5 3 ) ................................ ............... 159 5 6 Solid state molecular structure of [ t 3 ) 3 (Et 2 O) ( 5 3 ). The hydrogen atoms are omitted for clarity. ................................ ............................ 160 5 7 Synthesis of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) ................................ .............. 160 5 8 Solid state molecular structure of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ). The hydrogen atoms are omitted for clarity. ................................ ............................ 161 5 9 General polymerization reaction with [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) ....... 161 5 10 1 H NMR spectrum of [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) in C 6 D 6 ........... 162 5 11 1 H NMR spectrum of {[ t BuOCO] 3 ) 3 (O t Bu)}{Ph 3 PCH 3 } ( 5 2 ) .............. 163 5 12 1 H NMR spectrum of crude [ t BuOCO] 3 ) 3 (Et 2 O) ( 5 3 ) and {PPh 3 CH 3 }{OTf} ................................ ................................ ................................ 164 5 13 1 H NMR spectrum of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) in C 6 D 6 .................... 165

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16 LIST OF ABBREVIATION S ACM alkyne cross metathesis C 6 D 6 benzene d 6 CDCl 3 chloroform d DCM dichloromethane DFT density functional theory DME 1,2 dimethoxyethane DMF dimethyl formamide Et 2 O diethyl ether FT IR fourier transform infra red gDQCOSY g radient double quantum filtered correlation gHMBC g radient heteronuclear multiple bond coherence gHMQC g radient heteronuclear multiple quantum coherence HDN hydrodenitrogenation HOMO highest occupied molecular orbital LUMO lowest unoccupied molecular orbit al mmol millimoles NACM nitrile alkyne cross metathesis NCN N,N' (1,3 phenylenebis(methylene))diarylamine NMR nuclear magnetic resonance NOE nuclear over Hauser effect OCO 3,3'' di tert butyl [1,1':3',1'' terphenyl] 2,2'' diol PPA poly(phenylacetylene) ppm parts per million THF tetrahydrofuran

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17 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy RATIONAL DESIGN OF REACTIVE X = N, CR AND ML n ) FRAGMENTS SUPPORTED BY TRIANIONIC PINCER LIGAND S RELEVANT TO ATOM TRANSFER, BOND ACTIVATION AND METATHESIS CHEMISTRY By Soumya Sarkar December 2011 Chair: Adam S. Veige Major: Chemistry This dissertation details the synthesis of trianionic pincer supported metal nitride and metal alkylidyne complexes and their application s as atom transfer reagent and catalyst for polyalkyne synthesis. The synthesis and metalation of the NCN trianionic pincer ligand pre cursors are described. Treating [3,5 Me 2 NCN]H 2 Br ( 2 13 ) with 3.0 equiv of MeLi provide s access to the trilithio salt [ 3,5 MeNCNLi 2 ] 2 [ Li 2 (DME) 6 ] ( 2 15 ), which on subsequent metalation with HfCl 4 provides the trianionic pincerate complex [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ). Alternatively, s alt metathesis of known {[2,6 i PrNCHN]Li 2 } 2 ( 2 17 ) with Zr(NMe 2 ) 2 Cl 2 (THF) 2 provide s [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) Finally treating {[2,6 i PrNCN]Li 3 } 2 ( 2 9 ) with HfCl 4 and subsequent alkylation of in situ generated [2,6 i PrNCNHfCl 2 ][Li(DME) 3 ] ( 2 10 ) allows access to the trianionic pincerate complex i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) in good yield and purity. The terphenyl diol [ t BuOCO]H 3 ( 3 4 ) react s with Mo(NMe 2 ) 4 with remarkable ease to produce [ t BuOCO]Mo(NMe 2 )(NH Me 2 ) 2 ( 3 5 ). Complex 3 5 react with NaN 3 to provide a rare nitrido anion dimer {[ t 2 )Na(DMF)} 2 ( 3 10 ). Unlike other metal

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18 nitrides, the anionic Mo nitride behave as a nucleophile with a variety substrates of the form RL (where R is a mild electrophile and L is a leaving group) to produce Mo(VI), d 0 metal imido complexes [ t BuOCO]Mo=NR(NMe 2 ) ( 3 11 R ). Complex 3 10 readily transfer s the N atom to acid chlorides to generate the corresponding nitriles and the oxo amide [ t BuOCO]Mo= O (NMe 2 ) ( 3 14 ) Detailed mechanistic studies reveal that slow cyclometalation and DMF dissociation precede the fast nitrile extrusion. 2 equiv [ t BuOCO]H 3 react with W 2 (NMe 2 ) 6 at 80 C for 3 d, producing [ t BuOCHO]W( NMe 2 )( NMe)( CH)W[ t BuOCHO] ( 4 6 ), and liberating 4 equiv. of NHMe 2 The formation of this product marks an unprecedented combination of reactions; a C N and double C H bond activation across a W W triple bond. Detailed spectroscopic investigation s indicate that one equiv of ligand react s with the meta l precursor to give [ t BuOCHO]W(NMe 2 )W(NMe 2 ) 3 ( 4 7 ). Heating 4 7 in the absence of ligand indicate s that multiple bond activations occur prior to addition of the second ligand. A combination of multinuclear NMR, IR, and Mass spectroscopic data elucidate t he sequential events. Finally, [ t BuOCO]H 3 react s with (O t Bu) 3 t Bu) to form [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) Treating with mild base PPh 3 =CH 2 and subsequent alkylation with MeOTf provide access to the neutral trianionic pincer supported metal alkylidyne [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) Complex ( 5 4 ) is a n active catalyst for polymerization of phenyl acetylenes with TON>4000.

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19 CHAPTER 1 BACKGROUND INFORMATI ON 1.1 Introduction A sustainable future relies on the critical balance of energy supply and demand. With an expanding world population, the development of new energy efficient technologies is paramount. 1,2 Modern chemists have set lofty goals to solve the global energy crisis. Among them are methods to c onver t naturally abundant small molecules to chemically higher value molecules and the discovery of reagents and pathways for bre aking inert chemical bonds 3,4 Catalysis plays a vital role towards these goals 5,6 and Figure 1 1 illustrates an abridged catalytic cycle 7,8 via which small molecules such as dinitrogen (N 2 ), dioxygen (O 2 ), carbon monoxide ( CO), carbon dioxide (CO 2 ) can be incorporated in an atom economic, selective and eco friendly manner into synthetic schemes. According to Figure 1 1, the transition metal complex is multiply bonded to X ( X = N, O, etc.) and is a key intermediate in the c atalytic cycle. Such transition metal complexes as a consequence, have received extensive attention for last four decades. 9 14 Multiply pivotal roles in biology, 15,16 materials, 17,18 catalysis, 19 21 small molecule activation, 22,23 bond activation, 24 atom transfer reactions, 25 and several other reactions. 26,27 This dissertation focuses on such complexes; specifically group 6 (Mo and W) nitrides and alkylidynes. The novelty of this work is the incorporation of trianion ic pincers as ancillary ligands to stabilize these high oxidation state metal fragments. Transition metal complexes bearing trianionic pincer ligands offer an opportunity to examine the effects of a constrained geometry ligand and its ability to create co ordinative and

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20 electronic unsaturation. The following section will discuss the chemistry of M nitrides and M alkylidynes. 1. 2 Chemistry of Terminal Metal N itrides 1.2.1 Nitrogen Fixation Nitrogen is one of the most abundant elements in biological organism s and is an essential building block for life, in particular the biochemical synthesis of amino acids and nucleic acids. 28 The largest reserve of nitrogen is in the form of dinitrogen, comp osing ~78% of the air that we breathe. Despite its ready availability, this simple diatomic molecule is inert, and as a result its utility as a feedstock chemical presents a challenge. 29 The inherent stability of N 2 originates from factors suc triple bond (226 kcal/mol) ; the lack of a dipole moment ; and particularly the large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). 30 The latter explains why N 2 is so difficult to reduce and oxidize. The Haber Bosch process fixes atmospheric dinitrogen and produces ammonia on an industrial scale. 31 33 Strikingly, this single reaction is responsible for the consumption of ~2% of the total energy consumption. Such massive energy requirement stems from the extreme reaction conditions ( 350 550 C and 150 350 atm ) required for the production of ammonia from atmospheric nitrogen and hydrogen. Despite the ma ssive energy consumption, this reaction is indispensable to sustain life and a global economy. This provides impetus for chemists to design systems that are capable of catalytic dinitrogen fixation at ambient conditions. 34 In contrast to the Haber Bosch process, nature formulated a recipe to produce ammonia from nitrogen under ambient temperature and pressure, in a process

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21 commonly known as biological nitrogen fixation 35 Since 1960 it has been recognized that the nitrogenase enzyme carries out this important chemical transformation to fix dinitrogen and produce ammonia. 36 Einsle et al. reported the X ray structural model that indicates the active site is composed of a Fe 7 MoS 7 cluster (Figure 1 2). 37 Although the precise mechanism through which this enzyme functions is a matter of debate, 38 the reaction takes pla ce by the consumption of 16 ATP s and the combination of eight protons and eight electrons with dinitrogen to produce 2 equiv. of ammonia and 1 equiv. of hydrogen. 1.2.2 Catalytic Dinitr ogen Fixation Under Ambient C ondition s Following the model provided by nature, chemists started developing transition metal complexes to synthesize homogeneous systems that are capable of fixing dinitrogen under ambient conditions. 39 43 An initial lead came from Chatt and coworkers who utilized low oxidation state g roup 6 metal centers supported by ancillary phosphane ligands to create monometallic dinitrogen complexes. 44,45 Although th ese systems were not catalytic, they react ed with reducing agents and protons to yield reduced nitrogen compounds such as hydrazine and ammonia. Thi s discovery was vital and paved the way for future chemistry in this field. In 2003, Schrock and coworkers reported a remarkable homogeneous catalytic system for dinitrogen fixation. 46 Figure 1 3(a) depicts the Mo(III) catalyst in which synchronized proton coupled electron transfer occurs to a coordinated dinitrogen ligand, ultimately generating ammonia. 47 Key to the success of this system is the well engineered ligand architecture in the metal complex Mo(HIPT N 3 N)N 2 ( 1 1 ) The use of significantly bulky hexaisopropylterphenyl ( HIPT ) groups on the amide substituents of the triamidoamine motif resists the coordination of a second metal center to the bound

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22 nitrogen in an end on fashion. It generates a suitable cavity in which only small moieties (such as dinitrogen, protons, and electrons) can access the molybdenum center. 48,49 Although, the catalyst is active for only four turnovers, this discovery represented the best homogeneous syste m to fix dinitrogen. Recently, Nishibayashi and coworkers reported a dimolybdenum dinitrogen complex 1 2 bearing a PNP pincer ligand as an effective catalyst for dinitrogen fixation. 50 This system produces 12 equiv. of ammonia per metal c enter (TON = 6), and as such demonstrates a slight improvement over the Schrock system. Complex 1 2 is the pre catalyst for the system, which forms via three electron reduction of the Mo(PNP)Cl 3 lyst bears a dinitrogen ligand coordinated to a molybdenum d 0 metal center. Sequential protonation and reduction produces two equivalents of ammonia per catalytic cycle. The authors claim that the PNP pincer ligand is crucial for this result; however a d etailed mechanism for the catalytic cycle and the precise role of the ligand remains elusive. 1.2.3 N atom Transfer Reactions from Metal N itrides The Schrock and Nishibayashi system describe ammonia production via sequential proton and electron addition to the terminal nitrogen coordinated to a single molybdenum center. However, if sufficient bulk is not present around the metal center, such dinitrogen coordinated systems swif tly convert to the corresponding nitrido complex. An example was provided by Cummins et al. in 1995, who utilized an analogous Mo(III) center supported by three monodentate amide ligands The complex Mo[N( t Bu)Ar] 3 ( 1 3 ) in the presence of 1 atm dinitroge n reductive ly cleav es the substrate even at C. Figure 1 5 depicts the reaction sequence which features the facile 51

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23 Initially, N 2 coordinates to th e Mo[ N( t Bu)Ar] 3 to form N 2 Mo( N( t Bu)Ar ) 3 This is followed by coordination of a second Mo [ N( t Bu)Ar ] 3 to form an intermediate dimer with N 2 bridging end on to both Mo centers. The dinitrogen bond then cleaves to form 2 equiv t Bu)Ar] 3 The barrier to cleavage has been measured to be 97 kJ mol and the overall reaction is exothermic by ~ 84 kcal mol 52,53 The same Mo[N( t Bu)Ar] 3 can also cleave N 2 O which contains a stronger N N bond t Bu)Ar] 3 54 T hese reports establish that bases and are capabl e of back bonding into the high orbitals of dinitrogen. 55 The driving force for such reactions is the formation of the very stable (155 kcal/mol) 56 which makes the extension of such systems into catalytic cycles difficult. 57 The nitride ligand however is not inert and c hemists have been designing various methodologies to incorporate the N atom in to organic and inorganic substrates. The following section highlights some examples that detail the activation of the M nitride bond and ultimately achieve complete N atom transfer. In the 1970 s Van Tamlen and coworkers reported a metal mediated N atom transfer to synthesize organic nitriles from an ill occurs when acid chlorides are allowed to react in a system containing the reduced Cp 2 Ti and an atmosphere of N 2 58,59 Reminiscent to this work Chirik and coworkers report that ( 5 C 5 Me 4 H) 2 ZrCl 2 upon reduction in an atmosphere of nitrogen produces the dinuclear N 2 complex ( 1 5 ), with ( 2 : 2 2 N 2 ) side on coordination. 60 Complexes of this type have been utilized to demonstrate diverse functionalization chemistry (Figure 1

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24 6). 61,62 Fryzuk et al. utilizes the P 2 N 2 ligand ( where P 2 N 2 = PhP(CH 2 SiMe 2 NSiMe 2 CH 2 ) 2 PPh ) to do similar chemistry with side on functionalized dinitrogen. 63 However, such bimetallic systems are beyond the scope of discussion in this dissertation The reactivity of the nitride ligand depends on the following factors: the transition metal ; the oxidation state of the transition metal ; and the nature of the ancillary ligands. 64 Typically the nitr ido ligand is considered a closed shell 3 ligand that donates 10 Most of the reactivity is derived from the extent of the inte raction between the p orbitals of the ligand and the d orbitals orbitals of the metal Generally, the nitride ligand is nucleophilic when attached to an early transition m etal in a high oxidation state, and electrophilic if attached to a late transition m etal. 65 While terminal nitrido ligands are inherently stable, Groves and Takashi demonstrated that w hen activated by an excess of a strong electrophile such as triflic anhydride (CF 3 CO) 2 O, an N atom transfer to electron rich olefins (Figure 1 7) is possible. 66 Carreira and coworkers extended the N atom transfer chemistry to various olefins, silyl enol ethers and glycols. However, the N atom transfers only occur from an activated Mn imido complex not the M nitride. 67 Apart f rom activation by electrophiles, Johnson et al. demonstrated that a [2+2] cycloaddition reaction is also possible between the terminal W nitride in (RO) 3 C(CF 3 ) 2 CH 3 ) and alkynes. 68 70 In a closely related system, Chisholm et al. demonstrated N atom ex change reaction between (RO) 3 studies. 71 Key to the success of this reaction relies on the use of electron poor alkoxide

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25 ligands, which make the metal center highly Lewis acidic. In fact, this system is catalytic and introduces terminal metal nitrides as an entry point to alkyne (AM) and nitrile alkyne cross metathesis (NACM) reactions. A major roadblock to the catalytic version of the reaction is the high energy azametallacyclobutadiene intermediate (Figure 1 8). 72 The system reacts slowly, demands sacrificial alkynes, high temperature and has low functional group toleran ce. Moore et al. utilized the Lewis acid B(C 6 F 5 ) 3 to activate such metal nitrides toward metathesis with alkynes with a noticeable increase in the reaction rate. 73 Finally, Cummins et al. estab lished a well defined system for benzonitrile extrusion via EPh ( E= S, Se, and Te) elimination from [Ar( t Bu)N] 3 Mo N=CPh(EPh). 74 The same group i Pr)Ar) 3 (Ar = 3,5 Me 2 C 6 H 3 ) can be used as a reagent for the transformation of acid chlorides into organic nitriles. 75,76 The reaction exemplifies an intriguing example of an isovalent N for the (O)Cl exchange process. Subsequently a complete cycle that incorporates dinitrogen into nitriles was reported for the molybdenum c omplex [Ar( t Bu)N] 3 ( Figure 1 9 ). 77 Terminal metal nitrides and metal alkylidynes are related, since N 3 and CR 3 are isolobal. As such, bonding of an alkylidyne ligand to a metal cente r is similar to the bonding of terminal nitrides. A key difference is the much lower electronegativity of carbon compared with that of nitrogen; the CR 3 donor. The following section briefly outlines the general methodologies to sy nthesize high oxidation state metal alkylidynes, and their applications. 1. 3 Chemistry of Metal A lkylidynes

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26 tremendous attention due to their application in the field of alkyne metathesis (AM). For the last 40 years significant research efforts have been dedicated to this field, and notable achievements include several natural product and macromolecule syntheses. 78 84 with nitriles (NACM), carbonyls, and bond activations. 85 The research described in this dissertation is restricted to high oxidation state metal alkylidyne complexes of the early transition metals. 1.3.1 S ynthetic R o utes to H igh O xidation State M etal A lkylidynes Unlike terminal oxo and nitrido ligands which could be derived directly from O 2 and N 2 respectively, alkylidyne ligands require different methodologies for their synthesis. The first high oxidation state metal alkylidyne complex was synthesized by C H hydrogen atoms of the precursor alkylidene complex and subsequent stabi donors. Figure 1 10 displays 3 )Cl(PMe 3 ) 2 ( 1 6 ), starting from CpTa(=CHMe 3 )Cl 2 86 Following this lead, analogous routes were discovered, in which bu lky alkyl groups were utilized as internal ba with subsequent release of steric crowding via alkane elimination and formation of metal alkylidynes. 87 This route is elimination. Schrock et al. reported a high yield synthesis of (ArO) 2 ( t BuCH 2 t Bu ( 1 7 ) (where Ar = 2,6 i PrC 6 H 3 ) by treating (ArO) 3 WCl 3 with four equivalents of Grignard reagent (Figure 1 11). 88 The exact order in which the alkylation and abstraction steps occur in these systems is not currently known. Similarly, Mindiola et al. reported access t 1 8 ) supported by a PNP pincer ligand, which could subsequently be trapped by bulky nitriles (Figure 1 12). 89

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27 An alternative synthesis of high oxidation state metal alkylidynes came from Mayr et al. who converted previously known monohalotetracar bonyl(alkylidyne) complexes of molybdenum and tungsten to the corresponding trihalo(alkylidene) complexes, via an oxidative pathway (Figure 1 13) 90 This route allows access to the compounds of the formula X 3 1 9 ) starting from the hexacarbonyl M 0 (M = Mo, W) precursors. Recently Frstner and coworkers revisited this synthetic protocol and extended the synthesis further by substituting the chlorides in complex 1 9 with bulky siloxides, to produce air stable Mo and W alkylidynes that can be used as AM catalysts. 83 The most co nvenient way to access compounds of the type (RO) 3 1 10 ), is by metathesis of methyl 3 3 91 This remarkable reaction is a rare 6e oxidation of two metal centers in the W( II I III ) complex. The product is 2 equiv. of the W(VI) alkylidyne complex in near quantitative yield. Compound 1 10 is a commercially available alkyne metathesis catalyst which has demonstrated excellent activity in metathesis reactions at ambient condi tions with diverse alkynes and with a wide range of functional group tolerance. The yield of the reaction (Figure 1 14) largely depends upon the extent of removal of 2 butyne. Independent reports by Frstner and Moore describe different methods to remove 2 butyne and maximize the efficiency of metathesis reactions. 92,93 Figure 1 15 depicts a reductive recycle strategy to make Mo[N( t Bu) Ar ] 3 ( 1 11 ) developed by Frstner and Moore, in which gem di molybdenum tris anilide ( 1 3 ), to give ClMo[N( t Bu) Ar ] 3 and [ N ( t Bu ) Ar ] 3 However in the presence of magnesium, ClMo[N( t Bu) Ar ] 3 is selectively reduced to regenerate 1 3

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28 to provide an overall high yield of the catalyst 1 11 94 96 1.3.2 General R eactions of High Oxidation State Metal A lkylidynes High oxidation state metal alkylidynes are capable of triple bond metathesis with alkynes. This reaction is known as alkyne metathesis (AM), which interconverts organic 80 Figure 1 16 shows two mechanisms for this reaction based on the orientation of the metal alkylidyne and the alkyne. 97,98 Independent reports have demonstrated isolation of the metalacyclobutadiene 99,100 and metalatetrahedrane 97,101 i ntermediates. However, combined experimental and theoretical studies suggest AM proceeds via the metalacyclobutadiene intermediate. 102,103 ond in metal alkylidynes is polarized in a M ) CR fashion and thus a Wittig type [2+2] cyclo addition reaction is possible. Figure 1 17 displays that nitriles react with tungsten alkylidynes to give the corresponding terminal nitrid e and alkynes. 104 Johnson et al. later developed the reverse reaction of nitrile alkyne cross metathesis (NACM) and demonstrated that terminal nitrides could be a valuable entry point for triple bond metathesis reactions 69 Similar reactions are observed when complex 1 12 is treated with polar unsaturated molecules. Figure1 18 represents the generic reaction in which the nucleophile attacks the electropositive metal center and undergoes bond cleavage via metalacyclobutene intermediates. 105,106 Apart from metathesis reactions, terminal metal alkylidynes are also known to demonstrate bond activation chemistry. Mindiola et al. utilizes the PNP pincer type pyridine

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29 activations respectively. 24,107 109 This research is of paramount importance in the fields of hydrodenitrogenation, hydrodefluorination, and in the development of reaction acr oss M X multiple bonds 1. 4 Our G oal Figure 1 20 presents target molecules, that feature a n and CR) fragment supported by a trianionic pincer ligand. The goal is to probe the fixation portion of Figure 1 1 and, more specifically co ntribute to the field of N atom transfer chemistry by synthesizing terminal group 6 metal nitrides bearing trianionic reasons. Firstly, the rigid pincer architecture permi ts exclusive meridional coordination, and as a consequence the metal center is forced to adopt a constrained four coordinate geometry, compared to the electronically and spatially favored trigonal coordination geometry observed in most of the examples abov e. Secondly, o ur pincer ligands carry a 3 charge which will stabilize the Mo/W in the 6 + oxidation state. The ligand occupies three coordination sites but can contribute a maximum of ten electrons (formal oxidation state method) thus enabling access to electronically unsaturated species. 110,111 Also t he tridentate ligand compared to three individual monoanionic ligands may suppress undesirable ligand degradation /hydrolysis Figure 1 21 depicts the result of a spin restricted DFT calculation 112 114 on our target molecule [ t BuOCO] ( 1 15 ) The nitrido ligand in the four coordinate metal complex occupies the apical position creating an open coordination site trans to the antibonding orbital is a major contributor to the LUMO of [ t BuOCO] ( 1 15 ) This presents an ideal site for substrate binding during the

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30 metathesis reaction. The following section highlights the important aspects of pincer ligands and the chemistry of pincer ligated metal complexes 1.5 Chemistry of Traditional Pincer L igands Amidst a myriad of ligands developed and utilized with transition metals, only a 115 sin ce they are used widely throughout the periodic table, and their metal complexes have found applications in diverse fields. Pincer ligands have earned this distinction and their broad utility is derived from an inherent modular architecture, thereby enabl ing precise control over both the steric and electronic coordination environment of metals. 116 Pincer ligated metal complexes have emerged as efficient catalysts, 117,118 sensors 119,120 and even building blocks for supramolecular motifs 121,122 and several reviews have been published in this area. 123 128 Bernard Shaw synthesized the first PCP tridentate ligand in the late 1970s w hich was metallated with nickel. 129,130 Lat class of ligands, in late 1980 s. 13 1 between the ligand and the metal center, rendering stability to the metal complexes. Additionally, many metal complexes bearing pincer ligands are thermally stable and even purified by sublimation. 132 To date a variety of modifications have been made to the ligand framework to impart different properties to the metal complexes. Figure 1 2 2 illustrates the sites available for modification. Since their discovery, pincer ligands are mostly monoanionic and are predominantly utilized with late transition metals. Early and late transition metals have distinct structural and electronic prope rties which are manifested in their different reactivities. We intend to introduce trianionic

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31 pincer ligands in early transition metal chemistry and study the reactivity properties of such metal complexes containing a trianionic pincer ligand. This diss ertation describes an approach to metallate different trianionic pincer n ) multiply bonded fragments relevant to atom transfer, metathesis, and bond activation chemistry with the corresponding high oxidation state metal complexes. Figure 1 1. A simplified catalytic cycle to incorporate small molecules into organic substrates Figure 1 2. Representation of active site of FeMo cofactor, and the overall nitrogen fi xation reaction

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32 Figure 1 3 (a) The active catalyst [Mo(HIPT N 3 N)N 2 ] ( 1 1 ) ( b) intermediates in the reduction of N 2 at Mo by stepwise addition of protons and electrons. Figure 1 4. (a) Synthesis of {Mo(PNP)(N 2 ) 2 } 2 ( 1,2 N 2 ) ( 1 2 ), (b) Proposed catalytic cycle for dinitrogen fixation at ambient temperature.

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33 Figure 1 5. Reductive cleavage of dinitrogen by Mo(N t Bu(3,5 MeC 6 H 3 ) 3 ( 1 3 ) Figure 1 6. Synthesis and subsequent chemistry of complex 1 5 Figure 1 7. N atom transfer to olefins form high oxidation state Mn nitride. Figure 1 8 Nitrile alkyne cross metathesis using a terminal W nitride

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34 Figure 1 9. Metal mediated N atom transfer to acid chlorides, where the N atom is derived from dinitrogen Figure 1 10. Synthesis of first high oxida tion state metal alkylidyne 1 6 Figure 1 11. Synthesis of (ArO) 2 ( t BuCH 2 t Bu ( 1 7 )

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35 Figure 1 t Bu fragment. Figure 1 13. General route to synthesize X 3 1 9 ) Figure 1 3 1 10 ) Figure 1 15. Re ductive recycle strategy to form make Mo[N( t Bu) Ar ] 3 ( 1 11 )

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36 Figure 1 16 P ossible mechanisms for alkyne metathesis (AM) Figure 1 17 Reaction of metal alkylidyne with nitriles Figure 1 18 General 1,2 addition

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37 Figure 1 a transient Figure 1 20. Target molecules with [ArNCN] ( 1 14 ) and [ t BuOCO] ( 1 15 ) ligand frameworks

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38 Figure 1 21. Lowest unoccupied molecular orbital (LUMO) of [ t BuOCO] ( 1 15 ) Figure 1 22. Potential modification sites available in the pincer architecture to enable precise control over the metal complex property

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39 CHAPTER 2 SYNTHESIS AND CHARAC TERIZATION OF GROUP 4 METAL COMPLEXES WI TH NCN 3 TRIANIONIC PINCER LI GANDS 2.1 Introduction T he most common pincer ligand framew ork comprises the ortho, ortho disubstituted monoanionic aryl ring, which covalently binds to the metal center via a bond. The ortho substituents are typically neutral heteroatom E ( E = N, P, As, O, S and Se) donors which form dative bonds to the metal, thus satisfying the 3 meridional coordination of the ligand. 125 We pursued a straight forward modification of the heteroatom donors from neutral to monoanionic, such as 2 amine s to attain a ligand capable of providing three anionic donors in a meridional fashion. The trianioni c pincer ligand precursor [2,6 i PrNCN]H 3 ( 2 1 ) was chosen for initial studies. The key features of this trianionic pincer ligand are as follows: ( a) the chelate and constrained arrangement of atoms promotes meridional coordination ; ( b) the secondary amine upon deprotonation provides a hard anionic linkage ; ( c) the bulky 2,6 diisopropyl groups suppress two ligands binding to one metal center; ( d) the ligand framework is modular; and ( e) convenient one step ligand synthesis. The m ajority of work is centered on the [ArNCN]H 3 framework due to its ease of synthesis. 133,134 To vary the pincer pocket size and incorporate rigidity in to the architecture four other ligand motifs [3,5 CF 3 N C C C N]H 3 ) ( 2 2 ), 135,136 [3,5 CF 3 N C C anth C N]H 3 ( 2 3 ) 136 ([2,4,6 Me 3 C 6 H 2 NC anth N]H 3 ) ( 2 4 ), 137 and [2,4,6 Me 3 C 6 H 2 NC TP N]H 3 ) ( 2 5 ) 137 were also synthesized by colleagues (Figure 2 1). To obtain desired metal complexes multiple metalation strategies were pursued 2.1.1 Metalation Strategies: Direct Metalation The most logical approach to proceed towards metal complex synthesis is direct

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40 metalation. 138,139 with metal precursors such as MR x M(NR 2 ) x M(OR) x (where M is any metal from group 4, 5 and 6) under a variety of reaction conditions, via elimination of alkane, amine and alcohol respectively, were unsuccessful. Figure 2 2 depicts the few examples in which isolable group 4 metal complexes were observed. In all the examples provided, the metalations rely on aminolysis as the thermodynamic impetus, which ultimately leads to dinuclear complexes. 133,136 There are two rationales for the formation of such dinuclear complexes. First, two arms of the ligand could attach to two different metal centers prior to the formation of a mononuclea r complex. Secondly, a reversible aminolysis under such reaction conditions could occur to form the thermodynamically stable dinuclear complex. As such, an irreversible salt metathesis route was sought. 140 144 2.1.2 Metalation Strategies: Salt Metathesis A different approach to incorporate a metal inside the pincer cavity is to use a trilithio salt. Refluxing the parent ligand [2,6 i PrNCN]H 3 ( 2 1 ) with 3.5 equiv of MeLi in toluene provides the trilithio salt { 2,6 i PrNCNLi 3 } 2 ( 2 9 ). Figure 2 3(a) features the result of an X ray diffraction experiment. The core comprises of six lithium ions attached to two ligands, highlighting o ne LiC ipso LiC ipso 145 and two LiNLiN rhombi Access to similar trilithio starting materials with ligand systems 2 2 2 3 2 4 and 2 5 were unfruitful. Recall in C hapter 1 we sought group 6 metal nitrides and alkylidynes Salt metathesis reactions of trilithio salt { 2,6 i PrNCNLi 3 } 2 ( 2 9 ) with MCl n (M = Mo and W) often provided intractable mixtures, and ultimately free parent ligand [2,6 i PrNCN]H 3 ( 2

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41 1 ) This is presumably due to single electron transfer (SET). To access less reducing salts, our group also synthesized a series of dianionic ligand precursors with a variety of structural motifs and composition. 136 Unfortunately transmetalation s with even the dilithio salts were unsuccessful. Fortunately, group 4 complexes have been synthesized starting from the trilithio salt { 2,6 i PrNCNLi 3 } 2 ( 2 9 ) and metal halides. T he hafnium dichloride anion [2,6 i PrNCNHfCl 2 ][Li(DME) 3 ] ( 2 10 ) wa s synthesized by treating the trilithio salt { 2,6 i PrNCNLi 3 } 2 ( 2 9 ) with HfCl 4 (THF) 2 in DME The c omplex 2 10 is the first trianionic NCN 3 pincer ligand supported metal complex. 110 Depicted in Figure 2 3(b) is the X ray crystal structure of 2 10 which reveals the trianionic pincer ligand chelates in a meridional fashion as intended, and suggests the ligand design is appropriate. While this result wa s encouraging, the synthesis of 2 10 is restricted to milligram quantities due to isolation complications arising from the presence of LiCl with identical solubility We are also able to attach the pincer ligand to other group 4 metals, but only the hafniu m pincerate complex could be obtained reproducibl y To improve metalation certain modifications of the ligand are possible. Th e following section details approaches to improve the synthesis of trianionic pincer supported metal complexes of group 4. 2.2 R esults and D iscussion 2.2.1 The Strategy The anionic donors are held tightly inside the trilithio dimer 2 9 Figure 2 3(a) suggests that the hexalithio core is surrounded by non polar organic functional groups. Alteration of the substitution pattern in t he pendant aromatic groups may favorably affect the solubility properties of the trilithio salt. C lose inspection of the molecular

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42 structure of 2 10 suggests that chelation to the m etal center occurs at the cost of steric repulsion between the bulky 2,6 d iisopropyl groups. During metalation, i f electron transfer precedes chelation, t he yields may be compromised due to the formation of reduced metal s pecies Moving substituents on the aryl ring from the 2 6 positions to 3,5 positions may provide reduced s te ric repulsion during metalation. 2.2.2 Synthesis and Reactivity of [3,5 Me 2 NCN]H 3 ( 2 11 ) Direct N alkylation of one equivalent of 1,3 bis(bromomethyl)benzene, with two equivalents of 3,5 dimethylaniline allows access to the N N (1,3 p henylenebis(methyle ne))bis 2,6 methylaniline [3,5 Me 2 NCN]H 3 ( 2 11 ) ligand (Figure 2 7) During t he synthesis of the trilithio salt [2,6 i PrNCNLi 3 ] 2 ( 2 9 ) the product was generated in a one step triple deprotonation reaction. A similar synthesis of [3,5 C H 3 C 6 H 3 ]Li 3 ( 2 12 ) with 3.5 equiv of MeLi was attempted ( Figure 2 4 ). However, based on 1 H NMR studies, instead of deprotonation of the backbone C ipso the methylene protons are deprotonated This suggests that the 2,6 diisopropyl groups play a pivotal role in the deprotonation chemistry, and in the stabilization of the trilithio salt. Clearly, the C ipso H bond is too difficult to deprotonate in 2 11 To solve this problem we synthesized the C ipso Br derivative [3,5 Me 2 ArNCN]H 2 Br ( 2 13 ). 2.2. 3 Synthesis and Characterization of [3,5 Me 2 NCN]H 2 Br (2 13) The synthesis of 2 13 involves N alkylation of 2 bromo 1,3 bis(bromomethyl)benzene, with 2 equiv of 3,5 dimethyl aniline ; in the presence of 2 equiv of n BuLi (Figure 2 5 ). Compound 2 13 precipitates as a tan microcrystalline solid by slow cooling of a saturated hot hexane solution in 52% yield. 1 H NMR spectroscopy confirms the identity of compound 2 13 The 3,5 Me groups resonate at 2.10 ppm as twelve protons. The methylene protons re sonate at 4.25 ppm as four protons and the

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4 3 NH protons resonate as a triplet ( J = 6 .0 Hz) at 3.52 ppm. The aromatic resonance at 6.14 ppm corresponds to the four protons ortho to the NH groups, while the para protons in the same ring resonate at 6.35 ppm. The proton para to the ipso Br resonates as a triplet ( J = 6 .0 Hz) at 6.86 ppm while the protons meta to the ipso Br resonates at 7.14 ppm. The mass spectroscopic analysis exhibits a parent ion [M + H] + peak at (m/z ) = 423.142. 2.2. 4 Synthesis and C haracterization of { 3,5 MeNCNLi 2 } 2 {Li 2 (DME) 6 } ( 2 15 ) We anticipated that starting with a C ipso Br bond might require milder conditions to generate the trilithio salt. Unfortunately, treating compound 2 13 with three equivalents of n BuLi in THF at room te mperature generates a dilithio salt { 2,6 i PrNC H NLi 3 } 2 ( 2 14 ) (Figure 2 6) A single crystal amenable to X ray diffraction experiments is obtained from a concentrated THF solution of 2 14 7 depicts the molecular structure of the {3,5 Me 2 NC H NLi 2 (THF) 2 } 2 ( 2 14 ) dimer The core comprises four lithium ions. Two nitrogen atoms from two different ligands coordinate to each of the lithium ions inside the core creating an eight membered ring, and the third coordination com es from the THF mol ecule is 135.4(3) This result indicates that an undesirable H atom abstraction might be occurring during the reaction. However, if the reaction is performed in DME the corresponding trilithio salt forms cleanly upon slow addition of three equivalents of n BuLi to a cold solution of 2 13 ( Figure 2 8 ). B right yellow [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) precipitates from the reaction mixture as it warms to room temperature. X ray quality crystals grow by slow evaporation of a hot, concentrated benzene solution of 2 15

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44 As shown in Figure 2 9 the trilithio salt [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) forms as a dimer. 133 The core consists of four lithium ions instead of the six observed for 2 9 The other two lithium ions are each solvated by three DME molecules and serve as counter ions to balance the overall charge. The molecule exhibits pseu d o D 2 d symmetry in both the solid and solution states A combination of 1 H NMR, 13 C {1H} NMR spectroscopy, combustion analysis and X ray crystallography confirm the identity and composition of the trilithio salt 2 15 In the 1 H NMR spectrum of 2 15 the twenty four 3,5 Me protons resonate at 2.19 ppm. The methyl ether protons of the coordinated DME resonate at 2.90 ppm as a broad singlet, while the methylene protons on DME resonate at 2.83 ppm. The methylene protons of the ligand shift downfield t o 4.78 ppm compared to 2 9 A broad aromatic resonance at 6.06 ppm corresponds to the remaining six protons corresponds to the protons of the aryl ring. Additional data to co nfirm the identity of compound 2 15 comes from a water quench experiment. The C 6 D 6 solution of compound 2 15 turns cloudy upon addition of a drop of water. The 1 H NMR spectrum of this cloudy solution indicates the formation of [3,5 Me 2 Ar NCN ]H 3 ( 2 11 ), instead of [3,5 Me 2 ArNCN]H 2 Br ( 2 13 ). This confirms the successful installation of the C ipso Li bond in compound 2 15 2.2. 5 Structural D escription of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] (2 15) Figure 2 5 depicts the results of a single crystal X ray diffraction experiment performed on compound 2 15 Compound 2 15 crystallizes in a tetragonal crystal system in the P 2 1 c space group. Compared to compound 2 9 the structure of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) represents a tetralithio core. There are two other

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45 [Li 2 (DME) 6 ] 2+ counter cations outside the core. The aryl rings on the pendant arm s in each of the ligands remain nearly coplanar with the pincer plane comprising the N1 C1 C2 C5 atoms, with an average dihedral angle of ~13 T he pincer planes (N1 C1 C2 C 5) of the two ligands are perpendicular to each other, exhibiting an overall pseudo D 2d symmetry which complements the 1 H NMR data As shown in Figure 2 9 each of the lithium atoms inside the core is coordinated to two nitrogen atoms from two different ligands, and the third coordination comes from the C ipso atom. distance ranges from 1.968(4) to 1.981(4) which is shorter compared to compound 2 9 ipso distance of 2 .714(4) is longer than that in compound 2 9 by 2.219(4) 2.2. 6 Synthesis and C haracterization of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) Slow addition of a yellow solution of 2 15 in benzene to a suspension of HfCl 4 in benzene at room temperature results in the formation of a colorless solution from which a white precipitate forms After filtering, adding the resulting colorless benzene filtrate to cold pentane precipitates the product as a white microcrystalline solid The precipitate is collected by fi ltration and the crude yield of the metal complex is 54%, which is significantly higher than that of complex 2 10 The 1 H NMR spectrum of 2 10 reveals a broad resonance at 5.56 ppm for four protons, which is diagnostic of formation of a metal complex with at least C 2v symmetry. The twenty four 3,5 Me protons resonate upfield at 2.00 ppm. Two DME molecules solvate two lithium ions, with the twelve methyl ether protons ( OC H 3 ) resonat ing at 2.89 ppm as a broad singlet, while the methylene protons (MeO(C H 2 ) 2 OMe) resonat e at 2.78 ppm. The four aromatic protons in the aryl ring para to the amide donor resonate at 6.16 ppm, while the other eight protons ortho to the amide donor resonate at 7.01 ppm. The six aromatic protons

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46 from the backbone ring resonate at 7.45 ppm. Another downfield resonance at 204.28 ppm in the 13 C { 1 C pincer bond. 146 2.2.7 Structural D escription of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] (2 16) A single crystal X ray crystallography experiment identifie s the pseudo D 2d sym metric dianionic hafnium pincerate complex and is displayed in Figure 2 11 The compound crysta l lizes in a monoclinic crystal system with a P2 1 / n space group. The asymmetric unit contains two crystallographically independent molecules. Two trianionic pi ncer ligands coordinate to the Hf(IV) metal center in a meridional fashion creating a distorted octahedral coordination sphere about the metal. T he Hf1 C1A and Hf1 C25A bond distances are both 2.277(4) T pincer bonds are trans to each other which is manifested in a 0.06 longer bond compared to complex 2 10 in which the Hf(IV) ion has a si milar coordination environment. The amide donors from the pincer ligand coordinate to the metal center creat ing very small bite angles for both the NCN 3 ligands; = = 144.07(12). The lithium atoms bridge a pair of nitrogen atoms from the opposed ligands and are each coordinated by a molecule of DME. The stark contrast between 2 10 and 2 16 is the orie ntation of the N aryl groups. In complex 2 10 the N aryl rings contain 2,6 diisopropyl substit uents. Due to steric repulsion both the pendant arm aryl rings remain perpendicular to the CH 2 N Hf atoms. In complex 2 16 the N aryl rings remain nearly coplanar with an average dihedral angle of ~ 16 with the plane. Clearly by locating the smaller methyl substituents in the 3,5 positions the N aryl groups are able to rotate and allow a second ligand to approach and bind to the hafnium ion 2.2. 8 Synthesis and C haracterization of [ 2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18)

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47 Having established that the original [2,6 i PrNCN]H 3 ( 2 1 ) ligand is crucial for successful isolation of trianionic pincer complex es with early transition metals we decided to reassess the reaction strategies to achieve a high yield synthesis compared to 2 10 We sought a mild metalation strategy which combines a double salt metathesis with C ipso 111,147 Lappert and coworkers reported the synthesis of the dilithio salt {[2,6 i PrNCHN]Li 2 } 2 ( 2 17 ). 133 According to Figure 2 12 treating 2 17 with known Zr(NMe 2 ) 2 Cl 2 (THF) 2 148 in diethyl ether re sults in a pale yellow solution with the formation of a white precipitate which is removed by filtration. After removing all volatiles the resulting crude mixture was dissolved in a minimal amount of Et 2 O/pentane f [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ). The room temperature 1 H NMR spectrum of compound 2 18 reveals several diagnostic resonances for a mononuclear metal complex with a pincer ligand attached in a dianionic fashion. The isopropyl methyl protons appear as fou r unique doublets ( J = 6.0 Hz) at 1.42, 1.41, 1.35, and 1.24 ppm clearly indicating a low symmetry species. The corresponding septets for the methine protons appear at 3.92 and 3.70 ppm. Two sets of diastereotopic methylene arm protons appear as doublets at 4.83 and 4.01 ppm ( J =15.0 Hz). Finally, the C ipso H proton resonates significantly downfield at 9.34 ppm, 149 confirming the dianionic attachment of the pincer ligand. The two N Me 2 ligands freely rotate around the Zr N bond and as such two singlets appear at 2.49 and 2.06 ppm. 2.2. 9 Structural D escription of [2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18) Figure 2 C s consistent with the solution state characterization. The Zr(I V) metal center displays a highly distorted trigonal bipyramidal geometry in which the pincer ligand binds via the

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48 anionic amide donors in a dianionic fashion occupying two equatorial sites. 150 The Zr1 C29 distance of 2.656(2) is short and clearly indicates an agostic interaction (interaction of coordinatively unsaturated metal with C H bond) consistent with the w ell downfield resonance for H29A in the 1 H NMR spectrum. The N aryl groups are nearly orthogonal to the plane containing the N1 C35 C30 plane with a dihedral angle ~78. The back bone ring also twists out of the pincer plane by ~54. The crystal structur e and 1 H NMR spectrum of 2 18 indicates that the C ipso is intact and in close proximity to the metal center. However, heating compound 2 18 for extended hours failed to attach the pincer ligand in its trianionic form to the metal. donors such as pyridine or phosphine to replace potentially liberated dimethyl amine and drive the equilibrium to stabilize 2 19 did not lead to the desired compound (Figure 2 14). 149 2.2. 10 Synthesis and C i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) In complex 2 1 6 the metal center is coordinatively saturated from the chelation of two less sterically demanding pincer ligands. Pursuit of a ny metal mediated chemical transformation starting from complex 2 1 6 demands a complicated selective dechelation of one of the ligands, prior to further reaction. Alternatively, complex 2 10 contains most of the prerequisites to form an active species in catalytic reactions. The major shortcoming towards utilizing complex 2 10 for future reactions is its poor yield. Part of the problem is that the synthesis is restricted to milligram quantities due to s eparation complications arising from the presence of LiCl. A possible solution is to alkylate the chlorides of the pincerate complex, and alter the solubility prior to isolation. Figure 2 15 demonstrates a new strategy, wherein 2 10 is generated in situ and add ing 2 equiv of MeLi to provide colorless [(2,6 i PrNCN)HfMe 2 ][Li(DME) 2 ] ( 2 20 ) in

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49 35% yield The 1 H NMR spectrum of the crude material suggests a C 2v species is present in solution. The isopropyl methyl protons appear as two unique doublets at 1.41 and 1.39 ppm ( J = 6Hz) indicating a r estricted rotation across the N C aryl bond. The corresponding methine proton resonates downfield at 4.26 ppm ( J = 6Hz) as a septet. Only one resonance for the methylene arm protons, at 5.21 ppm, confirms a high symmetry species. A singlet at 0.49 ppm f or six protons arises from methyl groups coordinated to the Hf center. The most downfield signal in the 13 C{ 1 H} NMR (CDCl 3 ) spectrum of 2 20 at 205.7 ppm is attributable to the C pincer Hf carbon. The corresponding C pincer in the dichloride complex 2 10 resonates slightly upfield at 201.5 ppm and for [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) it appears at 204.3 ppm. Symmetric Hf C H 3 carbons appear at 50.6 ppm Two DME molecules solvate the Li + counter ion and the corresponding resonances appear as broad single ts at 3.66 and 3.51 ppm which is different from free DME in CDCl 3 (3.55 and 3.40 ppm). 2.2. 11 Structural D escription of i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) A single crystal amenable for an X ray diffraction experiment is obtained from a concentrated DME sol ution of 2 20 16 displays the solid state structure which confirms the trianionic form of the ligand and is consistent with C 2v Analogous to complex 2 10 most of the distortion comes from the pincer arms where the amido donors fail to span 180 with a bipyramidal geometry with the axis occupied by the amide donors from th e ligand. The dimethyl groups create a 108.09(8) angle between them but they are not symmetrically situated around the

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50 me tal center. A 11.54(9) difference results between C1 Hf1 C33 (131.72(7)) and C1 Hf1 C34 (120.18(7)) in addition to a difference of 0.0245(19) bond length. A possible explanation could be the proximity of the Li(DME) 3 counter ion to C34. The closes t distances between C34 Li and C33 Li are 4.9 and 6.0 respectively. 2.3 Experimental Section 2.3.1 General Considerations Unless specified otherwise, all manipulations were performed under an inert atmosphere using standard Schlenk or glovebox technique s. Pentane, hexanes, toluene, diethyl ether, tetrahydrofuran, and 1,2 dimethoxyethane were dried using a GlassContour drying column. C 6 D 6 (Cambridge Isotopes) was dried over sodium benzophenone ketyl, distilled or vacuum transferred and stored over molec ular sieves. Sublimed HfCl 4 was purchased from Strem Chemicals and used without further purification. ZrCl 2 (NMe 2 ) 4 (THF) 2 was prepared according to literature procedure. 148 MeLi, ( 1.6 M in diethyl ether ) was purchased from Acros. NMR spectra were obtained on Gemini (300 MHz), VXR (300 MHz), or Mercury (300 MHz) spectrometers. Chemical For 1 H and 13 C NMR spectra, the residual solvent peak was used as an internal reference GC/MS spectra were record ed on an Agilent 6210 TOF MS instrument. 2.3. 2 Synthesis of 3,5 MeNCNH 2 Br ( 2 13 ) To a solution of 3,5 dimethlyaniline, (8.26 mL, 66 mmol) in of THF ( 125 mL ) was added n BuLi solution (2.5 M in hexanes, 26.7 mL, 66 mmol) via syringe at 0 C. The solution w as allowed to warm to room temperature and then 2 bromo 1,3 bis(bromomethyl)benzene (11.4 g, 33 mmol) was added as a THF (30 mL) solution. The solution quickly turned dark brown and was refluxed for 20 h. After removing all

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51 volatiles the resulting brown oil was taken up in diethyl ether and washed with H 2 O (2 x 10 mL). The organic layer was dried over MgSO 4 filtered, and all vol atiles were removed under vacuo The resulting light brown solid was recrystallized from hot hexanes to provide 2 13 as a tan microcrystalline solid; yield 7.31 g (17.3 mmol, 52%). 1 H NMR (300 MHz, C 6 D 6 (ppm) ): 7.14 (d, J = 6 Hz, 2H, Ar H ), 6.86 (t, J = 6 Hz, 1H, Ar H ), 6.36 (s, 2H, Ar H ), 6.14 (s, 4H, Ar H ), 4.25 (d, J = 6 .0 Hz, 4H, C H 2 ), 3.52 (t, J = 6 .0 Hz, N H ), 2.10 (s, 12H, C H 3 ). 13 C{ 1 H} NMR (75.36, C 6 D 6 (ppm) ): 22.02 (s, C H 3 ), 49.28 (s, C H 2 ), 111.5 (s, C aromatic), 120.4 (s, C aromatic), 124.3 (s, C Br, aromatic), 127.9 (s, C aromatic), 128.3 (s, C aromatic), 139.1 (s, C aromatic), 139.9 (s, C aromatic), 148.6 (s, N C aromatic). ESI MS ( m / z ): [M + H] + C alcd for C 24 H 27 BrN 2 423.144; found, 423.142. Anal. Calcd for C 24 H 27 BrN 2 : C, 68.08; H, 6.43; N, 6.62. Found: C, 67.92; H, 6.61; N, 6.62. 2.3. 3 Synthesis of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) To an orange DME (3 mL ) solution of 2 13 (500 mg, 1.18 mmol) was added 3.3 equiv of n BuLi solution (1.56 mL, 2.5 M in hexanes, 3.89 mmol) via syringe at 35 C. Upon warming to room temperature a bright yellow precipitate formed. After stirring for 5 min the solution was filtered to provide a yellow solid that was washed with DME All volatiles were removed in vacuo to provide 2 15 as a yellow microcrystalline solid; yield 366 mg (0.58 mmol, 50% ) The yellow salt can be further purified by recrystallization from hot ben zene in necessary. 1 H NMR (300 MHz, C 6 D 6 (ppm) ): 7.50 (s, 4H, Ar H ), 7.50 (s, 2H, Ar H ), 6.08 (br s, 4H, Ar H ), 6.06 (s, 8H, Ar H ), 4.78 (s, 8H, C H 2 ), 2.90 (br s, 36H, DME/ OC H 3 ), 2.83 (br s, 24H, DME/ C H 2 O), 2.19 (s, 24H, C H 3 ). 13 C{ 1 H} NMR (75.36, toluene d 8 (ppm) ): 22.1 (s, C H 3 ), 58.9 (s, DME/ O C H 2 ), 60. 9 (s, C H 2 ), 70.9 (s, DME/ O C H 3 ), 111.9 (br s, C Li, aromatic), 113.5 (s, C aromatic), 123.8 (s, C

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52 aromatic), 126. 2 (s, C aromatic), 138.0 (s, C aromatic), 142.4 (s, C aromatic), 156.9 (s, C aromatic), 160.5 (s, N C aromatic). Anal. Calcd for C 72 H 110 Li 6 N 4 O 12 : C, 68.34; H, 8.76; N, 4.43. Found: C, 68.12; H, 8.49; N, 4.55. 2.3. 4 Synthesis of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) Benzene solutions of 2 15 (300 mg, 0.24 mmol) and HfCl 4 (76 mg, 0.24 mmol) were combined at room temperature. The initial suspension quickly dissolved and then a white precipitate formed which was removed by filtration. The product was precipitated as a white microcrystalline solid by addition of the filtrat e (5 mL) to cold pentane (100 mL) ; yield 7.31 g (0.13 mmol, 54%). 1 H NMR (300 MHz, C 6 D 6 (ppm) ): 7.45 (s, 4H, Ar H ), 7.45 (s, 2H, Ar H ), 7.01 (s, 8H, Ar H ), 6.16 (s, 4H, C Ar H ), 5.56 (br s, 8H, C H 2 ), 2.89 (br s, 12H, DME/ OC H 3 ), 2.78 (br s, 8H, DME/ C H 2 O), 2.00 (s, 24H, C H 3 ). 13 C{ 1 H} NMR (75.36, C 6 D 6 (ppm) ): 21.97 (s, C H 3 ), 59.2 (s, DME/ O C H 2 ), 69.2 (s, C H 2 ), 71.5 (s, DME/ O C H 3 ), 117.0 (s, C aromatic), 118.7 (s, C aromatic), 119.68 (s, C aromatic), 127.6 (s, N C aromatic), 137.6 (s, C aromatic), 154.8 (s, C aromatic), 156.9 (s, C aromatic), 204.2 (s, Hf C aromatic). Anal. Calcd for C 56 H 70 HfLi 2 N 4 O 4 : C, 63.72; H, 6.68; N, 5.31. Found: C, 61.69; H, 6.52; N, 5.31. 2.3.5 Synthesis of [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18) ZrCl 2 (NMe 2 ) 4 (THF) 2 (168 mg, 0.426 mmol) in Et 2 O (3 mL) was added to {[2,6 i PrNCHN]Li 2 } 2 ( 2 17 ) (200 mg, 0.426 mmol) in Et 2 O (3 mL) at 35 C with stirring. As the solution was warmed to room temperature and stirred for 1 h, the color changed to pale yellow with the formati on of a white precipitate. The solution was filtered and the resulting pale yellow filtrate was concentrated in vacuo Pentane (1 mL) was added to the solution and the product was obtained as yellow crystals ov er a period of 3 days at 35 C, y ield (114 mg, 42 %). 1 H NMR (300 MHz, C 6 D 6 ) : 9.34 (s, 1H, Ar H ),

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53 7.20 (m, 4H, Ar H ), 7.12 (m, 3H, Ar H ), 6.93 (d, 2H, J = 6 .0 Hz, Ar H ), 4.83 (d, 2H, J = 15 .0 Hz, Ar C H 2 N), 4.01 (d, 2H, J = 15 .0 Hz, Ar C H 2 N), 3.93 (sept, 2H, J = 9Hz, C H (CH 3 ) 2 ), 3.70 (sept, 2H, J = 9 .0 Hz, C H (CH 3 ) 2 ), 2.50 (s, 6H, N( C H 3 ) 2 ), 2.06 (s, 6H, N( C H 3 ) 2 ), 1.42 (d, 6H, J = 9 .0 Hz, CH(C H 3 ) 2 ), 1.41 (d, 6H, J = 9 .0 Hz, CH(C H 3 ) 2 ), 1.35 (d, 6H, J = 9 .0 Hz, CH(C H 3 ) 2 ), 1.25 (d, 6H, J = 9 .0 Hz, CH(C H 3 ) 2 ). 13 C{ 1 H} NMR (75.36 Hz, C 6 D 6 ) : 150.3 (s, C aromatic), 146.7 (s, C aromatic), 146.3 (s, C aromatic), 145.1 (s, C aromatic), 133.7 (s, C aromatic), 127.0 (s, C aromatic), 125.4 (s, C aromatic), 124.6 (s, C aromatic), 124.2 (s, C aromatic), 63.7 (s, Ar C H 2 N), 44.0 (s, N( C H 3 ) 2 ), 41.4 (s, N( C H 3 ) 2 ), 29.3 (s, C H(CH 3 ) 2 ), 27.8 (s, C H(CH 3 ) 2 ), 27.3 (s, CH( C H 3 ) 2 ), 26.9 (s, CH( C H 3 ) 2 ), 25.8 (s, CH( C H 3 ) 2 ), 25.0 (s, CH( C H 3 ) 2 ). Anal. Calcd for C 36 H 54 N 4 Zr: C, 68.19; H, 8.58; N, 8.84. Found: C, 68.08; H, 8.64; N, 8.76 2.3.6 Synth esis of [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20) HfCl 4 (202 mg, 0.630 mmol) in THF (3 mL) was added to {[2,6 i PrNCN]Li 3 } 2 ( 2 9 ) (300 mg, 0.316 mmol) in THF (3 mL) at 35 C with stirring. As the solution was warmed to room temperature and stirred for 45 min, the color changed from colorless to pale yellow. MeLi (0.78 mL, 1.6 M, 1.26 mmol) in Et 2 O was added to the reaction mixture and the stirring continued for an additional 30 min. The solution was filtered and all volatiles were removed in vacuo. The residu e was triturated and washed with pentane and the remaining solid was extracted into DME (2 x 3 mL). The organic layers were combined, filtered and the product was obtained as a pale yellow powder afte r removing the solvent in vacuo, y ield (189 mg, 35%). Single crystals for X ray diffraction were obtained by diffusing Et 2 O into a saturated DME solution of 2 20 at 35 C for 4 d. 1 H NMR (300 MHz, CDCl 3 ) : 7.19 7.31 (m, 9 H, Ar H ), 5.21 (s, 4H, C H 2 N), 4.26 (sept, 4H, J = 6 .0 Hz, C H (CH 3 ) 2 ), 3.66 (s, 12H, CH 3 OC H 2 C H 2 O CH 3 ), 3.51 (s, 18H,

PAGE 54

54 C H 3 OCH 2 CH 2 OC H 3 ), 1.41 (d, 12H, J = 3 .0 Hz, CH(C H 3 ) 2 ), 1.39 (d, 12H, J = 3 .0 Hz, CH(C H 3 ) 2 ), 0.49 (s, 6H, Hf ( C H 3 ) 2 ). 13 C{ 1 H} NMR (75.36 Hz, CDCl 3 ) : 205.6 (s, Hf C aromatic), 155.6 (s, C aromatic), 154.3 (s, C aromatic), 148.4 (s, C aromatic), 124.6 (s, C aromatic), 123.0 (s, C aromatic), 122.6 (s, C aromatic), 117.4 (s, C aromatic), 72.5 (s, Ar C H 2 N), 71.0 (s, CH 3 O C H 2 C H 2 O CH 3 ), 59.6 (s, C H 3 OCH 2 CH 2 O C H 3 ), 50.6 (s, Hf C H 3 ), 28.8 (s, CH( C H 3 ) 2 ), 27.0 (s, C H(CH 3 ) 2 ), 24.5 (s, CH( C H 3 ) 2 ). Anal. Calcd for C 42 H 67 HfLiN 2 O 4 : C, 59.39; H, 7.95; N, 3.30. Found: C, 59.17; H, 7.92; N, 3.08 2.3.7 X ray E xperimental D etails for {3,5 Me 2 NCHNLi 2 (THF) 2 } 2 (2 14) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the scan method (0.3 frame width). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the d irect m ethods in SHELXTL6 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions an d were riding on their respective carbon atoms. The Li tetramers are located on 4bar symmetry elements thus the asymmetric unit consists of only a quarter of the complex. The proton on the central aryl ring was located from a Difference Fourier map and r efined without any constraints. A total of 166 parameters were refined in the final cycle of refinement using 1848 reflections with I > 2 (I) to yield R 1 and wR 2 of 5.55% and 13.62%, respectively.

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55 Refinement was done using F 2 2.3. 8 X ray E xperimental D e tails for [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with a 0.71073 ). Cell parameters were refined using up to 8192 re flections. A full sphere of scan method (0.3 frame width). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1%). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the d irect m ethods in SHELXTL6, 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. The structure consists of a core of [ Li 4 ] +4 (located on 4 symmetry elements) coordinated to two triply deprotonated ligand [ L 2 ] 6 and two Li(DME) 3 +1 cations located on two fold rotation axes along the z axis. Thus the asymmetric unit consists of a cation and a half anion. The counter cation is fully disord ered a nd sits on two fold rotation symmetry, thus, all atoms are refined with 50% occupancy. Two DME ligands were constrained during refinement to geometries similar to the third, well behaved, DME ligand. A total of 277 parameters were refined in the fi nal cycle of refinement using 2745 1 and wR 2 of 4.93% and 12.21%, respectively. Refinement was done using F 2 2.3. 9 X ray E xperimental D etails for [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) Data were collected at 173 K on a Si emens SMART PLATFORM equipped with a CCD area detector and a grap hite monochromator utilizing Mo

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56 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data scan me thod (0.3 frame width). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1%). Absorption corrections by integration were applied based on measured indexed cryst al faces. The structure was solved by the d irect m ethods in SHELXTL6, 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. The asymmetric unit consists of two chemically equivalent but crystallographically independent complexes. A total of 1207 parameters were refined in the final cycle of refine ment using 13830 1 and wR 2 of 4.22% and 6.60%, respectively. Refinement was done using F 2 2.3. 10 X ray E xperimental D etails for [2,6 i PrNCHN]Zr(NMe 2 ) 2 (2 18) Data were collected at 173 K on a Siemens SMART PLATFORM e quipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the scan method (0.3 frame widt h). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The struct ure was solved by the d irect m ethods in SHELXTL6, 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. A total of 12504 parameters were refined in the final cycle of

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57 refinement using 7445 reflections with I > 2 (I) to yield R 1 and wR 2 of 3.37% and 9.50%, respectively. Refinement was done using F 2 2.3. 11 X ray E xperimental D etails for i PrNCNHfMe 2 ][Li(DME) 2 ] (2 20) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with a ). Cell parameters we re refined using up to 9999 reflections. A full sphere of data scan method (0.3 frame width). A hemisphere of data was collected using the w scan method (0.5 frame width). Absorption corrections by integration w ere applied based on measured indexed crystal faces. The structure was solved by the d irect m ethods in SHELXTL6 151 and refined using full matrix least squares. The non H atoms were treated anisotropical ly, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. A total of 521 parameters were refined in the final cycle of refinement using 10208 1 and wR 2 of 1.82% and 4.43%, respectively. Refinement was done using F 2 2.4 Conclusions Reported here are several methods to metalate NCN trianionic pincer ligand precursors. The NCN pincer ligand is modular and a variety of ligand precursors is synthesized to accommoda te different sizes of metallacycles Direct metalation between the protonated ligand precursors and group 4 metal amides produces dinuclear metal complexes in which the dianionic diamide ligand bridge two metal ce nters bridged via the a mide donors This recommends that the C ipso H proton require removal prior to metalation. Access to the NCN 3 trilithio salts is possible, however even

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58 the most reduction resistant metal substrates are susceptible to SET when treated with the NCN 3 trilithio salts Fortunately, group 4 metal halides react with the NCN 3 trilithio salt s to form the corresponding trianionic pincerate complexes 2 10 and 2 16 In both of these complexes the trianionic ligand bind s to the metal center in the desired meridional fashion Interestingly the geometry and composition of the metal complex es is determined by the sterics of N aryl substituents In a different metalation strategy the dilithio ligand salt reacts with ZrCl 2 (NMe 2 ) 2 to provide the monomeric [2,6 i PrNCHN]Zr(NMe 2 ) 2 in which the ligand functions as a diamide with an intact aromatic C ipso H bond Finally, the trianionic pincer complex [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) form when {[2,6 i PrNCN]Li 3 } 2 ( 2 9 ) reacts with HfCl 4 (THF) 2 in THF followed by alkylation with MeLi. T he yield and scale improve over the previous synthesis of the dichloride complex [(2,6 i PrNCN)HfCl 2 ][Li(DME) 3 ] ( 2 10 ) because 2 20 is insoluble in Et 2 O. 2 20 cleanly precipitate from DME upon slow addition of Et 2 O whereas 2 10 stay dissolved. Future reaction involves conversion of 2 10 to a neutral alkyl complex. Meanwhile, the discovery of an OCO 3 trianionic terphenyl pincer ligand backbone led to a promising area of research. Chapter 3 describe s the results involving the OCO 3 trianionic terphenyl pincer ligand backbone.

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59 Figure 2 1. Library of NCN pincer ligands

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60 Figure 2 2. Synthesis of (a) ( [ i PrNC H N]){Zr(NMe 2 ) 3 } 2 ( 2 6 ), (b) {( 3,5 CF 3 N C CH C N)Zr(NMe 2 ) 2 NHMe 2 } 2 ( 2 7 ), and (c) ( 3,5 CF 3 N C CH anth C N){Hf (NMe 2 ) 3 NHMe 2 } 2 ( 2 8 )

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61 Figure 2 3. Solid state molecular structure of (a) { 2,6 i PrNCNLi 3 } 2 ( 2 9 ), the hydrogen atoms and isopropyl groups are removed for clarity. (b) [2,6 i PrNCNHfCl 2 ][Li(DME) 3 ] ( 2 10 ) the solvated lithium counter ion is not in shown in the picture. Figure 2 4 Synthesis of [3,5 Me 2 NCN]H 3 ( 2 11 ) and attempted synthesis of { 2,6 Me 2 NCNLi 3 } 2 ( 2 12 ). Figure 2 5. Synthesis of [3,5 Me 2 NCN]H 2 Br ( 2 13 )

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62 Figure 2 6 Synthesis of {3,5 Me 2 NC H NLi 2 (THF) 2 } 2 ( 2 14 ) Figure 2 7. Solid state molecular structure of {3,5 Me 2 NC H NLi 2 (THF) 2 } 2 ( 2 14 ) The h ydrogen atoms are omitted for clarity.

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63 Figure 2 8 Synthesis of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) Figure 2 9. Solid state molecular structure of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) The h ydrogen atoms, lithium counter ions and DME are omitted for clarity.

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64 Figure 2 10 Synthesis of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) Figure 2 11. Solid state molecular structure of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) The h ydrogen atoms are omitted for clarity.

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65 Figure 2 12 Synthesis of [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) Figure 2 13. Solid state molecular structure of [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ). The h ydrogen atoms (excluding C ipso H) are omitted for clarity. Figure 2 14 Attempted synthesis of [2,6 i PrNC N]Zr(NMe 2 ) (py) ( 2 19 )

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66 Figure 2 15 Synthesis of [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) Figure 2 16. Solid state molecular structure of i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ). The h ydrogen atoms are omitted for clarity.

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67 Figure 2 1 7 1 H NMR spectrum of 3,5 MeNCNH 2 Br ( 2 13 ) in C 6 D 6

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68 Figure 2 1 8 1 H NMR spectrum of [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) in C 6 D 6

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69 Figure 2 19. 1 H NMR spectrum of [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) in C 6 D 6

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70 Figure 2 20. 1 H NMR spectrum of [ 2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) in C 6 D 6

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71 Figure 2 2 1 1 H NMR spectrum of [2,6 i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) i n CDCl 3

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72 CHAPTER 3 SYNTHESIS AND REACTI VITY OF AN ANIONIC MOLYBDENUM NITRIDE SUPPORTED BY AN OCO 3 TRIANIONIC PINCER LI GAND 3 1 Introduction Initial studies using the NCN 3 pincer ligand suggest th at formation of a trianionic pincer complex requires removal of the C ipso H proton prior to metalation. Metalation via salt metathesis was complicated presumably due to single electron transfer (SET) reductions which either yielded parent ligand or metal complexes in very low yields. Alternatively, direct metalation reactions between the parent ligand pre cursor and M(NMe 2 ) 4 ( M =Zr and Hf) led to dinuclear metal complexes. A potential solution to furnish the desired metal complex is to change the aniline moiety to the more acidic phenol moiety. To promote chelation a new ligand [ t BuOCO]H 3 ( 3 4 ) with an OC O 3 donor combination on a rigid terphenyl framework was synthesized (Figure 3 1b ). 111,152,153 The m terphenyl architecture has been widely used to stabilize highly reactive low coordinate metal centers. 154,155 T he t Bu groups are located in close proximity to the metal coordination sphere to prevent binding of two ligands to a single metal center. Another design benefit is the ligand creates t w o six membered met allacycles upon binding a metal ion, this is in contrast to the constrained five membered metallacycles that form with the NCN derivatives (Figure 3 1). 156 We thought that the combination of all these factors might result in easy metalation. I nitial metalation studies focused on direct metalation (Figure 3 2) employing the parent protonated derivative M etalation of 3 4 with Mo(NMe 2 ) 4 occurs with remarkable ease via combined O H and C H bond activation forming [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) in 80% yield 157 Synthesis of comp lex 3 5 allows us for the first time to investigate the impact of the trianionic pincer ligand on the reactivity properties of metal complexes.

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73 For example, facile substitution of the amide ligand in 3 5 is possible (Figure 3 2). Complex 3 5 reacts with 2,6 lutidine HCl in benzene to form [ t BuOCO]MoCl(NHMe 2 ) 2 ( 3 6 ) 158 Both 3 5 and 3 6 contain d 2 metal centers. Their 1 H NMR spectra contain broad resonances that preclude solution phase structural assignment. However, a combination of single crystal X diffraction and combustion analysis allows for their unambiguous identification. The following section details a compari son of the structural features and reactivity of a series of metal complexes featuring Mo(IV) metal centers bearing the OCO trianionic pincer ligand. 3.2 Results and D iscussion The original synthesis of 3 4 was modified to avoid column chromatography and e mploy an improved step involving lithiation with t BuLi discovered by Agapie and Bercaw. 111 Figure 3 2 depicts the modified four step synthetic sequence for the [ t BuOCO]H 3 ( 3 4 ) ligand. The first step involves ortho bromination of commercially available 2 tert butylphenol with N bromodimethylami d e in toluene to provide 2 bromo 6 tert butylphenol ( 3 1 ). 159 Pure 3 1 is a colorless liquid after fractional distillation Treating compound 3 1 with methyl iodide pro duces 1 bromo 3 tert butyl 2 methoxybenzene ( 3 2 ). C rystallization from a concentrated isopropanol solution at 15 C provides pure 3 2 Palladium catalyzed coupling between 1,3 dibromobenzene and 2 equiv of 3 2 provide s 3,3'' di tert butyl 2,2'' dimeth oxy 1,1':3',1'' terphenyl ( 3 3 ). Crystallization from isopropanol affords the clean terphenyl bismethylether 3 3 Finally treating 3 3 with excess boron tribromide generate s 3,3'' di tert butyl 1,1':3',1'' terphenyl 2,2'' diol [ t BuOCO]H 3 ( 3 4 ). Hot hex ane solutions of 3 4 precipitate analytically pure ligand as a

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74 white microcrystalline solid when cooled to 15 C Compared to the synthesis of 2 1 the current ligand synthesis requires four steps However, it can be synthesize d on a multigram scale. The salient features in t he 1 H NMR spectrum of 3 4 (C 6 D 6 ) are: (a) the distinct aliphatic resonance for the eighteen t Bu protons at 1.56 ppm ; and (b) t he phenol protons ( O H ) resonat ing as a broad singlet at 5.19 ppm. These two distinctive peaks are ofte n monitored by 1 H NMR spectroscopy to probe metalation progress. Synthesis of complex 3 5 was a major breakthrough since it provides convenient access to an analytically pure metal complex in multi gram yield. In an attempt to test the substitution reacti vity of complex 3 5 it was treated with neutral donor ligands such as pyridine, THF, and phosphines. However, such reactions to substitute the dimethyl amine ligands remain unsuccessful. Analogous to the synthesis of complex 3 6 substitution of the NMe 2 is effected by alkylation or salt metathesis. 3.2.1 Synthesis and Characterization of [ t BuOCO]Mo (OTf) (NHMe 2 ) 2 ( 3 7 ) The dimethylamide group is a and donor ligand which binds strongly to the Mo(IV) center. One approach to access an even more el ectron deficient metal center is to replace the dimethylamide with a non coordinating ligand such as triflate or tetrafluoroborate. Dark orange toluene solution of [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) when treated with one equivalent of trimethylsilyltriflate (TMSOTf) at room temperature, gradually change to purple over the course of 30 min. After removing all volatiles in vacuo the resulting crude mixture i s dissolved in a minimal amount of Et 2 O, and cooling C overnight affords single crystals of [ t BuOCO]Mo (OTf) (NHMe 2 ) 2 ( 3 7 ). The 1 H NMR spectra (C 6 D 6 ) display typical paramagnetic resonances spread over a wide spectral window that hinders precise structural assignment.

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75 3.2.2 Structural D escription of [ t BuOCO]Mo (OTf) (NHMe 2 ) 2 ( 3 7 ) A single crystal X ray crystallography experiment reveals that the asymmetric unit contains two crystallographically independent molecules. Figure 3 5 depicts the solid state molecular structure of the pseudo C s symmetric complex 3 7 The compound crystallizes in a triclin ic crystal system with a P space group The structure consists of an octahedral Mo(IV) center in which the pincer ligand binds in a terdentate meridional fashion. The phenolate donors span a bite angle of 170.47(12) (O1 Mo O2) with the average Mo O pincer bond length of 1.945(3) The Mo and imparts a strong trans influence on the triflate ligand which is manifested in a long is found i n metal complexes such as N(B Ph 3 ) (OTf)(syn Me 8 [16]aneS 4 ) 160 (dMo OTf = 2.375(2) ) and Mo(OTf) 2 (NNPh 2 ) 2 (py) 2 161 (dMo OTf = 2.203(7) and 2.266(6) ). The triflate ligands in those examples also experience similar trans influence s from the nitrido and hydrazinido ligands respectively. The dimethyl amine groups are trans to each other with a near bond distance of 2.2343(2) Similar to complex 3 5 the pincer backbone is twisted in a pseudo C s fashion and, as such, the central ring creates a dihedral angle of ~33 b etween the aryl rings. 3.2.3 Synthesis and Characterization of [ t BuOCO]Mo (NCO) (NHMe 2 ) 2 ( 3 8) A salt metathesis reaction is another option to displace the NMe 2 ligand in complex 3 5 To install an isocyanate ligand, [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) is treated with solid sodium isocyanate at room temperature (Figure 3 6). Since no distinct color change occurs, the stirring is continued overnight to ensure reaction

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76 completion. The reaction mixture is filtered and the crude product is obtained as an orange powder after removing all volatiles in vacuo. Dissolving the resulting crude mixture C for 3 d affords single crystals of [ t BuOCO]Mo (NCO) (NHMe 2 ) 2 ( 3 8 ). The 1 H NMR spectrum is again indicative of a paramagnetic compound. Key information is available from the IR spectrum in which the signature stretching frequencies for the NCO ligand appear at 2219 and 2190 cm 1 which are significantly shifted from that of free NaNCO at 2232 cm 1 3.2.4 Structural D escription of [ t BuOCO]Mo (NCO) (NHMe 2 ) 2 ( 3 8) A single crystal X ray crystallography experiment identified a Mo(IV) metal center attached to the pincer ligand, two dimethyl amines and an isocyanate ligand. The compound crystallizes in a triclinic crystal system with a P space group and the asymmetric unit contains two crystallographically independent complexes and two DME molecules (Figure 3 7) Bound in its trianionic form, the pincer ligand with its terphenyl backbone now twists along the C33 Mo N5 axis exhibiting over all C 2 symmety, in contrast to the C s symmetry in 3 7 The vector containing the atoms O3 C32, and N5 is collinear with the Mo C33 axis. This suggests an N5 p Mo d overlap. The bond lengths in the isocyanate ligands are C32 O3 = 1.255(6) and C32 N5 =1.048(6) which is consistent with known terminal Mo NCO fragments. However, to the best of our knowledge, the Mo N5 bond distance is the longest (2.229(3) ) for a terminal isocyanate ligand attached to a molybdenum ion. This is even larger than t he bent isocyanate ligand in Cp*Mo(CO) 2 (NCO)(PPh 3 ), 162 (dMo N = 2.175(1) and Mo N CO= 150.10(2) ) in whic h the N p Mo d overlap is minimal. Such elongation is presumably due to a

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77 strong trans influence imposed by the Mo C33 bond, which is 2.135(3) The phenolate donors span a bite angle of 166.76(9) (O6 Mo O5) with the average Mo O bond length of 1.946(4) and the remaining coordination comes from the trans 3.2.5 Comparison of Structural Features, Magnetic Mom ent and Reactivity between (3 5), (3 6), (3 7) and ( 3 8) The metal complexes 3 5 3 6 3 7 and 3 8 have several similar features. They all contain the [ t BuOCO] 3 pincer ligand bound to the Mo(IV) metal center in a meridional fashion. Table 3 1 summarizes the result of Evans method NMR experiments 163 which are indicative of two unpaired electrons. The calculated value for two unpaired elctrons is Another noticeable similarity between these molecules is that each molecule co ntains two coordinated dimethyl amine ligands. The key difference is the addi tional anionic ligand which seems to have an influence on the configuration of the pincer backbone adopting either a C 2 or a C s configuration. A logical explanation is as follows: if the ancillary ligand X (X = NCO, Cl) is capable of donating to the me tal d xy orbital, the Mo O pincer bonding is minimal, which allows the ligand arms to adopt the C 2 configuration (Figure 3 8). In contrast, if X cannot donate (X = NHMe 2 OTf) into the d xy orbital, the Mo O pincer interaction is necessary to compensate for the electronic unsaturation. In this case, the ligand adopts a C s configuration. This is consistent with the findings of Tonks and Bercaw et al. 164 The dimethylamine ligands on each of the metal complexes above are tightly bound to the metal center. Attempts to substitute the dimethylamine ligands with THF,

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78 DME or CO even at elevated temperature (80 C) remain unsuccessful A ttempts to reduce the Mo(IV) center with Na/Hg amalgam or to alkylate the fourth anionic ligand with alkyl Grignard reagents were unsuccessful, and provid ed only intractable mixtures and protonated ligand. The following section details a method to oxidize the Mo(IV) and synthesize a terminal molybdenum nitride. 3 .2.6 Initial Attempts to Synthesize a Terminal Mo nitride The chloride complex [ t BuOCO]MoCl(NHMe 2 ) 2 ( 3 6 ) did not react with Me 3 SiN 3 or NaN 3 in refluxing THF. Instead, the more polar solvent DMF had to be used (Figure 3 9) 158 A red solution of 3 6 in DMF turns yellow orange when treated with NaN 3 at 25C, with concomitant release of N 2 After removing all volatiles under reduced pressure, a 1 H NMR spectrum of the crude material in C 6 D 6 indicate s the presence of multiple products. The products proved to be inseparable which thwarted future studies. Fortunately a single crystal of one species is obtained from a mixture of solids and was identified as the yellow Mo(VI) nitride complex [ t BuOCHO]M 2 )(DMF) ( 3 9 Figure 3 9 ). I nspection of the 1 H NMR spectrum of the crude mixture indicates the possib le presence of at least three different compounds. The 1 H NMR spectrum displays a resonance at 1.40 ppm which is attributable to the t Bu protons of 3 9 Corresponding diastereotopic amido methyl protons resonate at 3.50 and 4.03 ppm. However, a similar set of resonances appear at 1.65, 2.59 and 4.20 ppm. Clearly, an isostructural compound of 3 9 is present. Figure 3 10 displays the crystal str ucture of 3 9 The complex consists of a square pyramidal Mo(VI) center. The apical position The basal plane is comprised of trans phenolate s from the dianionic pincer The other basal

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79 position are occupied by trans DMF and dimethyl 1.940(3) which is longer than documented terminal Mo N fragments 73 backbone detaches from the metal center. One explanation involves intramolecular protonation from the coordinated amines. As the metal center is oxidized to Mo(VI), the 2 pincer 3 5 in which the dimethyl amine is attached to a lower oxidation state Mo(IV) center, however is stable. An at tempt to make the molybdenum nitride by treating [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 ( 3 7 ) with NaN 3 results in a mixture of compounds, and the 1 H NMR spectra of the crude mixture reveals a downfield peak at 8.76 ppm, which is suggestive of a dianionic pincer complex akin to 3 9 3 9 is obtained as a part of an intractable mixture; as such subsequent chemistry with this terminal Mo nitride is thwarted. 3.2. 7 Synthesis and Characterization of {[ t 2 )Na(DMF)} 2 ( 3 10 ) The unsatisfactory yield and purity of 3 9 necessitated the exploration of alternative routes to nitrido species. Using 3 5 as the starting material prove s fruitful. Treating 3 5 with excess NaN 3 in DMF results in rapid color change from dark orange to yellow with the expulsion of N 2 Rem oving all volatiles under vacuo provides a black tacky material. This time { [ t 2 )Na(DMF)} 2 ( 3 10 ) is exclusively extracted from the black material by washing with Et 2 O (3 x 1 mL). Combining the Et 2 O washes and removing all volatiles, provides 3 10 in excellent yield (86%) and purity. This result is promising because : ( a ) the Mo C pincer bond remains intact ; ( b ) the synthesis gives desired product in high yield and purity; and ( c ) complex 3 10 The e ighteen t Bu protons of the pincer

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80 ligand resonate at 1.53 ppm. The coordinated DMF exhibits two distinct amido methyl resonances at 1.86 and 2.05 ppm respect ively. The amidomethyl groups are diastereotopic d ue to restricted rotation about the Mo NMe 2 bond, and resonate at 2.60 and 4.10 ppm. The aromatic proton trans to the Mo C pincer resonates as a triplet ( J = 6 Hz) at 7.41 ppm, while the protons trans to t he phenoxide resonate as a triplet ( J = 6 Hz) at 6.75 ppm. The remaining aromatic protons appear as three sets of doublets ( J = 6 Hz) at 7.26, 7.50 and 7.73 ppm respectively. Finally, the aldehyde proton from the coordinated DMF resonates as a broad sing let at 6.94 ppm. The IR spectrum of 3 10 exhibits a broad band at 1039 cm 1 consistent with a terminal 165 3.2. 8 Structural D escription of {[ t 2 )Na(DMF)} 2 ( 3 10 ) Slow evaporation of a concentrated benzene solution of 3 10 provides X ray quality single crystals. Figure 3 12 displays the solid state structure of 3 10 that consists of the complex anion, and a sodium ion. The pincer ligand binds in the desired triden tate fashion. The nitride occupies the apical position of the distorted square 2 The phenoxide donors from the ligands are trans to each other and create a bite angle (O1 Mo1 O2) of 154.80(5). Unlike in 3 9 the Mo C pin cer bond is intact and is trans to the dimethyl amide ligand. The Mo C1 bond length is 2.188( 2 ) and the 13 C{ 1 H} NMR spectrum exhibits a resonance at 172.7 ppm, characteristic of C sp 2 166 The overall charge of the complex anion is balanced by a solvated sodium ion situated 2.445( 2 ) from the nitride. The t Bu groups creat e steric congestion and exert c onsiderable strain on the pincer backbone. As a result, the phenoxide rings twist out of the pincer backbone plane and describe a dihedral angle of ~67 As discussed previously, terminal me tal nitrides are stable and as su ch,

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81 incorporation of the N atom to organic substrates requires prior activation with harsh electrophiles. The following section describes the reactivity of 3 10 with mild electrophiles and a metal mediated N atom transfer to acid chlorides. 3.2. 9 Reactivity of { [ t 2 ) Na(DMF)} 2 (3 10) with Mild Electrophiles The combination of a constrained geometry by the pincer ligand around the metal center and the location of an anionic charge on the nitrido ligand should enhance the reactivity of co mplex 3 10 towards electrophiles Indeed, mild electrophiles such as Me 3 SiCl and MeI add to the nitrido fragment to generate the corresponding imido complexes [ t BuOCO]Mo=NSiMe 3 (NMe 2 ) ( 3 11 SiMe 3 ) and [ t BuOCO]Mo=NMe(NMe 2 ) ( 3 11 Me ) respectively (Figure 3 13) 167 A yellow THF solution of 3 10 changes rapidly to orange at 25 C upon addition of Me 3 SiC l Removal of all volatiles in vacu o provides t he silyl imido derivative 3 11 SiMe 3 as an analytically pure orange solid in 71% yield. A 1 H NMR spectrum (C 6 D 6 ) of 3 11 SiMe 3 reveals distinct amido methyl resonances at 4.14 and 2.95 ppm while the silyl methyl protons resonate s upfield at 0.21 ppm. The eighteen t Bu protons appear as a singlet at 1.62 ppm indicating the C s 3 11 SiMe 3 in solution. In contrast 3 11 Me is generated in a seal able NMR tube by treating 3 10 with excess MeI followed by heating at 60 C for 10 h. Attempts to isolate 3 11 Me led only to intractable mixtures, thus precluding combustion analysis. However 3 11 Me is stable in solution even in the presence of excess MeI and is well characterized by 1 H and 13 C{ 1 H} NMR spectroscopy. In the 1 H NMR spectrum t wo distinct singlets for the diastereotopic Me 2 protons appear at 4.23 and 3.59 ppm, and a third singlet is for the imido methyl is located at 2.86 ppm indicating electrophile addition to the nitride and

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82 formation of an imido methyl group The eighteen t Bu protons resonate at 1.68 ppm. A resonance at 1.41 ppm indicates the excess MeI in the reaction mixture Prompted by the reactivity of { [ t 2 ) Na(DMF)} 2 ( 3 10 ) towards mild electrophiles we attempted the reaction of 3 10 with less reactive electrophiles such as aryl halides and vinyl halides Complex 3 1 0 d id not exhibit reactivity with substrates having C sp 2 even at elevated temperatures (80 C) nor did it react with CO 2 or CO. 26 Fortunately, preliminary investigation suggests 3 10 reacts rapidly at room temperature with other electrophiles such as PPh 3 CH 2 Br, cyanuril chloride and even Cp 2 ZrCl 2 168 Research is in progress to identify the products of these reactions and to further elucidate additional substrat e scope for the rare molybdenum nitride. 3.2. 10 Reactivity of [ t 2 ) Na(DMF)} 2 (3 10) with Protons In context synchronized addition of protons and electrons is required to functionalize a terminal 3 10 the terminal molybdenum nitride bears an anio nic charge. To determine at which site a proton will add, { [ t 2 )Na(DMF)} 2 ( 3 10 ) is treated with 2,6 lutidinine HCl. Deep purple [ t BuOC H (Cl) (NHMe 2 ) ( 3 12 ) forms within 15 min at 23 C. The 1 H NMR spectrum (CDCl 3 ) of 3 12 contains a doublet at 2.36 ppm ( J = 6 Hz), which integrates as the six NH Me 2 protons while the corresponding N H Me 2 appears at 3.75 ppm The t Bu protons resonate as a singlet at 1. 66 ppm. The aromatic proton trans to the C pincer resonates at 7.86 ppm as a tri plet ( J = 10 Hz) while the protons trans to the phenoxide resonate as a triplet ( J = 7.6 Hz) at 7.11 ppm. The remaining aromatic protons appear as three sets of doublets at 7.52 7. 40, and 7.29 ppm. Finally a

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83 resonance at 7.45 ppm stem from the C ipso proton that correlates to a carbon signal at 118.4 ppm in a gHMQC experiment. 3.2. 11 Structural D escription of [ t 2 ) (3 12) A single crystal amenable to an X ray diffraction experiment is obtained from a concentrated benzene solution of 3 12 over a period of 7 d. Compound 3 12 crystallizes in a monoclinic crystal system with a P2 1 /c space group. Figure 3 15 displays the result of the single crystal X ray diffraction experiment and indicates 3 12 contains a square pyramidal Mo(VI) center A nitride ligand resides in the apical 157.18(2) in the basal plane. The coordin ation sphere is completed by the trans 2.400(7) This result suggests that if the Mo metal center is in the +6 oxidation state, the pincer bond is susceptible to protonation from acids or coordinated amine. Although this seems to be detrimental to the progress of trianionic pincer supported metal nitrides, our group has already synthesized ONO 3 pincer ligands 169 that permit us pincer pincer bond. Though the Mo N pincer bond can be proton ated it is much easier to subsequently deprotonate with a mild base. 3.2.12 Nitrile S ynthesis via N atom T ransfer to A cid C hlorides The facile reactivity of 3 10 towards electrophiles encouraged exploration of its utility as an N atom transfer reagent. 170 The anionic nitride { [ t 2 ) Na(DMF)} 2 ( 3 10 ) reacts instantaneously with acid chlorides at room temperature to

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84 provide the corresponding a c yl imido complexes 3 13 R (R = t Bu, Ph, Me) as illustrated in Figure 3 16. The reactions are performed in seal able NMR tubes. A bright orange solution forms within minutes upon combination of a yellow C 6 D 6 solution of 3 10 and pivaloyl chloride. The 1 H NMR spectrum of the reaction mixture indicates t he formation of the p ivaloylimido complex [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) (DMF) ( 3 13 t Bu ). In particular, the spectrum reveals a C s symmetric species in solution, evidenced by a resonance for the eighteen t Bu protons as a singlet at 1.63 ppm, while the nine t Bu protons of the pivaloylimido group appear at 0.83 ppm. Two broad resonances at 4.06 and 1.96 ppm correspond to the coordinated amide and DMF ligands, respectively. The IR spectrum of 3 13 t Bu reveals a strong band at 1648 cm 1 ( C=O) which is consiste nt with the coordinated DMF molecule. The benzoylimido ( 3 13 Ph ) and methoylimido ( 3 13 Me ) complexes are o btained in a similar fashion in situ when PhC(O)Cl and MeC(O)Cl are employed. Gentle heating prompts N atom transfer and nitrile expulsion. The reaction is m onitored for each derivative of 3 13 R by 1 H NMR spectroscopy. Clear differences are found in the time required for complete nitrile formation 3 13 Me (1.5 h) < 3 13 Ph (3 h) < 3 13 t Bu (7.5 h), which reflect the size of the acid chlorid e. Concomitant with nitrile expulsion is the growth of a new compound assigned as the oxo amide [ t BuOCO]Mo=O(NMe 2 ) ( 3 14 ; Figure 3 17 ). Each imido complex generates the corresponding free nitrile and the same oxo amide complex [ t BuOCO]Mo=O(NMe 2 ) ( 3 14 ) Diagnostic resonances for complex 3 14 are the eighteen t Bu protons at 1.49 ppm and broad N Me 2 resonances at 3.70 and 2.47 ppm, indicating a C s

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85 3.2. 13 Structural D escription of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) (DMF) ( 3 13 t Bu) The pivaloylimido complex [ t BuOCO]Mo=NC(O) t Bu (NMe 2 ) (DMF) ( 3 13 t Bu ) is isolated as a bright orange powder. Slow evaporation of a concentrated diethyl ether solution of 3 13 t Bu provides thin dark orange plates. Figure 3 18 depicts the solid state structu re of 3 13 t Bu The asymmetric unit consists of two chemically equivalent but crystallographically independent molecules The OCO 3 trianionic pincer ligand coordinates in a tridentate fashion with the Mo C pincer intact (d(Mo1 C1) = 2.164(11) ). The metal center features a distorted octahedral coordination geometry. The amide group is oriented trans to the Mo C bond with a Mo1 N1 bond length equal to 1.985(8) while the pivaloylimido group and a DMF molecule occup y the axial coordination sites The Mo1 N3 bond length is 3 10 This is consistent with the conversion of a nitrido to imido functionality. The O4 C32 bond length is 1.27(2) characteristic of a C=O bond and the 13 C{ 1 H} NMR spectrum of 3 13 t Bu exhibits a resonance at 184.12 ppm indicat ive of a carbonyl group. A DMF molecule is coordinated to the metal center with a Mo1 O3 bond length of 2.221(7) Cummins et al report a similar metal mediated N atom transfer from a ter minal nitrido complex to acid chlorides. 171 The proposed reaction mechanism involves an azametallocyclobutene intermediate, although it could not be detected prior to nitrile expulsion. 75,76,172 The successful isolation of the pivaloylimido complex 3 13 t Bu provides an opportu nity to examine the mechanistic detail s for nitrile expulsion. The following section details the NMR spectroscopic experiments used to investigate the mechanism of N atom transfer.

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86 3.2. 14 Proposed Mechanism for N atom Transfer The 1 H NMR spectrum (25 C C 6 D 6 ) of silylimido complex 3 11 SiMe 3 and oxo amide 3 14 exhibits distinct diastereotopic resonances for the amido methyl protons indicating restricted rotation about the Mo NMe 2 bond. In contrast, the pivaloyl imido complex 3 13 t Bu exhibits a broad resonance for the six amido methyl protons at 4.06 ppm This prompted us to determine the thermodynamic parameters for the Mo NMe 2 bond rotation in each molecule Variable temperature NMR experiments are conducted for 3 11 SiMe 3 3 13 t Bu and 3 14 Line shape analysis 173 of the N Me 2 resonances over a temperature range of at least 60 ) for rotation about the Mo NMe 2 bond (Figure 3 19 ). S (cal/molK, 273K) values for 3 11 SiMe 3 = 0.6(2) and 3 14 = 2.5(3) are small and negative; this suggest minimal entropy change which fits a simple rotation around the Mo NMe 2 bond. A different mechanism must operate for 3 13 t Bu since S = 24.8(2) (cal/molK, 273K) is large and positive. The value of +24 is attributa ble to DMF dissociation since simple rotation in 3 11 SiMe 3 and 3 14 provides a value near zero. Table 3 2 summarizes the thermodynamic parameters and the coalescence 2 resonances. Figure 3 20 provides the proposed mechanism of the metal mediated N atom transfer reaction to form nitriles and the corresponding oxo amide comp lex 3 14 The key steps include initial dissociation of a DMF molecule and simultaneous formation of aza metallocyclobutene intermediate. Following this, a reverse cycloaddition reaction occurs leading to nitrile extrusion in a fast step to generate oxo amide complex 3 14 The mechani sm is consistent with the kinetic studies performed on 3 13 t Bu Examining the entropy change for the overall reaction provides support for a rate

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87 determining cyclometalation. The rate of decay of 3 13 t Bu is monitored by 1 H NMR (toluene d 8 ) spectroscopy using hexamethyldisiloxane (0.11 ppm) as an internal standard over a 40 C temperature range and indicates complex 3 14 and free pivalonitrile form The overall reaction follows first order kinetics with respect to 3 13 t Bu Figure 3 22 depicts the Ey ring plot, from which the entropy of activation is determined to be + 1.5(3) cal/molK. This suggests that the increase in entropy during DMF loss ( + 24 cal/molK) is probably followed by an approximately equal decrease in entropy associated with the cyclomet alation. Nitrile loss must be post rate determin ing because additional entropy associated with nitrile release is expected to be large and positive. These kinetic studies add direct evidence for the presence of a cyclometalated intermediate during the metal mediated N atom transfer to acid chlorides from a terminal molybdenum nitride. 3.3 Experimental Section 3.3.1 General Considerations Unless specified otherwise, all manipulations were performed under an inert atmosphere using standard Schlenk or glov e box techniques. Pentane, hexanes, toluene, diethyl ether, tetrahydrofuran, and 1,2 dimethoxyethane were dried using a GlassContour drying column. C 6 D 6 and toluene d 8 (Cambridge Isotopes) w ere dried over sodium benzophenone ketyl, distilled or vacuum tr ansferred and stored over 4 molecular sieves. THF d 8 (Cambridge Isotopes) was stored over 4 sieves. Mo(NMe 2 ) 4 and the ligand 3 4 w ere prepared according to published procedures. 152,174 Pivaloyl chloride ( t BuCOCl), benzoyl chloride (PhCOCl), and acetyl chloride (MeCOCl) were purchased from Aldrich or Acros and distilled over anhydrous MgSO 4 and stored

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88 over 4 sieves. Trimethylsilylchloride (TMSCl) and methyl iodide (MeI) were purchased from Fluka and Fisher respectively, distilled and stored over 4 sieves prior to use. NMR spectra were obtained on Varian Mercury Broad Band 300 MHz, or Varian 1 H and 13 C{ 1 H} NMR spectra, the residu al solvent peak was used as an internal reference Elemental analyses were performed at Complete Analysis Laboratory Inc., Parsippany, New Jersey. FT IR spectra were recorded on a Thermoscientific instrument. 3.3.2 Synthesis of [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 (3 7) In a nitrogen filled glove box a vial was charged with 3 5 ( 100 mg, 0.144 mmol ) and 2 mL of toluene was added. The reaction mixture was cooled to 35 C for 15 min. The solution was stirred vigorously and TMSOTf ( 26 L, 0.144 mmol ) was added drop wis e. As the solution was allowed to warm to room temperature its color changed from dark orange to purple S tirring was continued for 3 h. All volatil es were removed under vacuo and the solid was washed thoroughly wi th pentane. The product is obtained as a dark purple powder (91 mg, 88%). X ray quality single crystals were obtained by dissolving 3 7 in minimal diethyl ether and cooling to 35 C. 1 H NMR (300 MHz, C 6 D 6 113.72 (bs, = 25.98 Hz), 72.99 (bs, = 18.22 Hz), 19.29 (bs, = 17.45 Hz), 2.40 (bs, = 5.7 Hz), 1.13 (bs, = 16.08 Hz), 6.58 (bs, = 13.36Hz), 19.00 (bs, = 13.36Hz). Anal. Calcd for C 31 H 41 F 3 MoN 2 O 5 S: C, 52.69; H, 5.85; N, 3.96. Found: C, 52.62; H, 5.97; N, 4.04. 3.3.3 Synthesis of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 (3 8) In a nitrogen filled glove box a vial was charged with 3 5 ( 112 mg, 0.162 mmol ) and NaNCO ( 42 mg, 0.647 mmol ). DME (2 mL) was added and the reaction mixture was stirred for 24 h. The solution was filtered through a bed of celite and all volatile s

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89 were removed from the filtrate. The resulting red orange powder was triturated with pentane (3x2 mL). Finally the residue was washed with pentane to obtain crude 3 8 as a bright orange microcrystalline solid ( 69 mg, 61% ). X ray quality single crystal s were obtained by dissolving 3 8 in minimal diethyl ether and cooling to 35 C. 1 H NMR (300 MHz, C 6 D 6 75.67 (bs, = 136.49 Hz), 11.79 (br, = 32.39 Hz), 3.34 (br, = 33.5 Hz), 3.15 (br, = 44.35 Hz), 1.24(br, = 38.27Hz), 9.84(br, = 35.96). Selected IR data of 3 8 (neat film, cm 1 ): 2219 (s, NC ), 2190 (s, CO ). 3.3.4 Synthesis of {[ t 2 )Na(DMF)} 2 (3 10) In a nitrogen filled glove box a 10 mL flask was charged with 3 5 (250 mg, 0.416 mmol), NaN 3 (108 mg, 1.66 mmol) and a stirbar, and a needle valve adapter was attached. The apparatus was affixed to a Schlenk line and the system was purged with a rgon. Under counter a rgon flow DMF (2 mL) was added via syringe and the solution was stirred. After 2 min N 2 began to evolve from solution and the color changed from orange to yellow. After heating at 50 C for 30 min all vol atiles were removed under vacuo to provide a yellow orange solid. The solid residue was triturated and washed with pentane The soild was taken u p in Et 2 O and filtered to remove salts. The filtrate was evaporated to dryness to provide 3 10 as a yellow powder (232 mg, 86%). 1 H NMR (500 MHz, C 6 D 6 ): 7.74 (d, J = 10 .0 Hz, 2H, Ar H ), 7.49 (d, J = 10 .0 Hz, 2H, Ar H ), 7.41 (t, J = 10 .0 Hz, Ar H ) 7.26 (d, J = 10 .0 Hz, 2H, Ar H ), 6.94 (br s, 1H, O=C H N(CH 3 ) 2 ), 6.75 (t, J = 10 .0 Hz, 2H, Ar H ), 4.10 (s, 3H, MoN(C H 3 ) 2 ), 2.60 (s, 3H, MoN(C H 3 ) 2 ), 2.05 (br s, 3H, O=CHN(C H 3 ) 2 ), 1.86 (br s, 3H, O=CHN(C H 3 ) 2 ), 1.53 (s, 18 H, t Bu). 13 C{ 1 H} NMR (75.36, Hz, C 6 D 6 (ppm) ): 172.69 (s, Mo C ), 163.99 (s, C aromatic), 162.22 (s, O= C HN(CH 3 ) 2 ), 143.16 (s C aromatic), 138.81 (s, C aromatic), ),

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90 134.33 (s, C aromatic), 127.84, (s, C aromatic), 126.40 (s, C aromatic), 125.60 (s, C aromatic), 124.97 (s, C aromatic) 117.83 (s, C aromatic), 57.47 (s, MoN( C H 3 ) 2 ), 43.15 (s, MoN( C H 3 ) 2 ), 36.36 (s, O=CHN( C H 3 ) 2 ), 35.82 (s, C (CH 3 ) 3 ), 31.36 (s, O=CHN( C H 3 ) 2 ), 30.96 (s, C( C H 3 ) 3 ). Selected IR data of 3 10 (neat film cm 1 ): 1655 (s, (C=O)), 1039 (w, for C 66 H 84 Mo 2 N 6 O 6 Na 2 : C, 61.20; H, 6.54; N, 6.49. Found: C, 61.82; H, 6.90; N, 6.89. 3.3.5 Synthesis of [ t BuOCO]Mo=NSiMe 3 (NMe 2 ) (3 11 SiMe 3 ) In a nitrogen filled glove box 3 10 (100 mg, 0.160mmol) was dissolved in dry THF (2 mL) and cooled to 35 C. In a separate vial TMSCl (0.02 mL, 1.1 equiv., 0.176 mmol) was dissolved in THF (2 mL) and cooled to 35 C. The solution of 3 10 was added drop wise to the TMSCl solution and the mixture was stirred vigorously. As the reaction warmed to room temperature a color change from light yellow to dark orange was observed. The orange solution was filtered and the filtrate was concentrated to provide an orange solid. The solid was triturated and wash ed with pentane and the volatiles were removed under vacuo to give on orange powder (68 mg, 71%). 1 H NMR (300 MHz, C 6 D 6 J = 9 .0 Hz, 2H, Ar H ), 7.79 (dd, J = 9 .0 Hz, J = 3 .0 Hz, 2H, Ar H ), 7.43 (t, J = 9 .0 Hz, 1H, Ar H overlapping signa l ), 7.40 (dd, J = 9 .0 Hz, J = 3 Hz, 2H, Ar H overlapping signal), 6.98 (t, J = 9 Hz, 2H, Ar H ), 4.14 (bs, 3 H, N Me ), 2.95 (bs, 3 H, N Me ), 1.62 (s, 18 H, t Bu), 0.21 (s, 9H, Si Me 3 ). 13 C{ 1 H} NMR (75.36 Hz, C 6 D 6 C Mo), 160.18 (s, C O), 139.98 (s, C aromatic), 137.37 (s, C aromatic), 133.04 (s, C aromatic), 129.42 (s, C aromatic), 126.78 (s, C aromatic), 126.56 (s, C aromatic), 125.97 (s, C aromatic), 119.78 (s, C aromatic), 57.58 (s, N( C H 3 ) 2 ), 42.82 (s, N( C H 3 ) 2 ), 35.82 (s, C (CH 3 ) 3 ), 30.93 (s, C( C H 3 ) 3 ), 0.64 (s, Si( C H 3 ) 3 )

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91 Anal. Calcd for C 31 H 42 MoN 2 O 2 Si: C, 62.19, H, 7.07, N, 4.68. Found C, 62.08, H, 7.08, N, 4.82. 3.3. 6 Synthesis of [ t 2 ) (3 12) In a nitrogen filled glove box 3 10 ( 102 mg 0.163 mmol) was dissolved in THF (2 mL) and cooled to 35 C. In a separate vial 2,6 lutidineHCl ( 26 mg 1.1 equiv, 0.180 mmol) was dissolved in THF (2 mL) and cooled to 35 C. The solution of 3 10 was added dropwise to the lutidineHCl solution and stirred vigoro usly. As the reaction warmed to room temperature a color change from light yellow to intense purple was observed. The purple solution was filtered and all volatiles were removed under vacuo to provide a tacky purple solid. A concentrated THF solution of the purple solid was added to 15 mL of cold pentane and filtered quickly The residue was washed with cold pentane, and volatiles were removed to provide 3 12 as a purple powder (31 mg, 36 %). 1 H NMR ( 500 MHz, C DCl 3 (ppm)): 7. 70 ( t J = 7.5 Hz 1H, Ar H ), 7. 51 (d, J = 7.5 Hz, 2H, Ar H ), 7.45 (s, 1H, Ar H ), 7.40 (d, J = 7.5 Hz, 2H, Ar H ), 7.28 (t, J = 7.5 Hz, 2H, Ar H ), 7.11 ( t J = 7.5 Hz 2H, Ar H ) 3.75 (bs, 1H, H NMe 2 ), 2.40 (d, J = 8 Hz, 6H, H N Me ), 1. 66 (s, 18 H, t Bu). 13 C{ 1 H} NMR (75.36 Hz, THF d 8 (ppm)): 164.08 (s, Mo C ), 143.07 (s, O C ), 140.10 (s, C, aromatic), 133.56 (s, C, aromatic), 132.63 (s, C aromatic), 130.07 (s, C aromatic), 128.43 (s, C aromatic), 127.96 (s, C aromatic), 124.50 (s, C aromatic), 119.13 (s, C aromatic), 46.28 (s, NH( C H 3 ) 2 ), 36.56(s, C (CH 3 ) 3 ), 31.37 (s, C( C H 3 ) 3 ). Anal. Calcd for C 28 H 33 MoN 2 O 2 : C, 63.87; H, 6.51; N, 5.32. Found C, 63.45; H, 6.36; N, 5.24 3.3. 7 Synthesis of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) (3 13 t Bu) In a nitrogen filled glove box 3 10 ( 50 mg, 0.08 mmol) was dissolved in 2 mL of dr y

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92 benzene and cooled to 35 C. A dditional 1 mL dr y benzene was then layered onto the frozen solution and cooled again. t added to the frozen solution via a micro pipette and the reaction mixture was allowed to thaw slowly. As the reaction warmed to room temperature a color change from light yellow to dark orange was observed. The dark orange solution was quickly filtered and all volatiles were removed in vacuo to provide a tacky solid. The solid was triturated, washed wit h pentane and dried in vacuo to give an orange brown powder (49 mg, 99% yield). 1 H NMR (300 MHz, C 6 D 6 J = 6 Hz, 2H, Ar H ), 7.72 (d, J = 9 Hz, 2H, Ar H ), 7.38 (d, J = 9 Hz, 2H, Ar H overlapping signal), 7.37 (t, J = 6 Hz, 1H, Ar H overlapping signal), 6.94 (t, J = 6 Hz, 2H, Ar H ), 4.07 (bs, 6H, N Me ), 1.96 (br s, 3H, O=CHN(C H 3 ) 2 ), 1.64 (s, 18 H, t Bu), 0.83 (s, 9H, NC=O t Bu). 13 C{ 1 H} NMR (75.36 Hz,C 6 D 6, C (O) t Bu ), 179.91 (s, C Mo), 161.61 (s, C (O)H), 139.22 (s, C aromatic), 137.96 (s, C aromatic), 133.52 (s, C aromatic), 126.47 (s, C aromatic), 126.43 (s, C aromatic), 126.03 (s, C aromatic), 125.73 (s, C aromatic), 122.72 (s, C aromatic), 119.51 (s, C a romatic), 42.14 (s, Mo N( C H 3 ) 2 ), 35.72 (s, HC(O)N( C H 3 ) 2 ), 31.26 (s, HC(O)N( C H 3 ) 2 ), 30.83 (s, =NC(O)C( C H 3 ) 3 ), 26.77 (s, =NC(O) C (CH 3 ) 3 ). Selected IR data of 3 10 t Bu (neat film): 1648 (s, (C=O)), 1409 (s), 1268 (w), 1241 (m), 1177 (s), 1109 (w), 940 (w), 863 (m). Anal. Calcd for C 36 H 49 MoN 3 O 4 : C, 63.24, H, 7.22, N, 6.15. Found C, 62.98, H, 7.17, N, 5.98. 3.3. 8 Synthesis of [ t BuOCO]Mo=O(NMe 2 ) (3 1 4 ) A J Young tube was charged with 3 10 t Bu ( 35 mg, 0.06 mmols) and 0.5 mL of C 6 D 6 The tube was heated (60 C) for 8 h and monitored periodically by 1 H NMR spectroscopy to determine the endpoint. The solution turned from orange brown to brown as the nitrile wa s extruded. The solvent and all volatiles were removed to

PAGE 93

93 provide a brown tacky solid which was triturated with pentane The resulting brown solid was suspended in pentane and isolated by filt ration The solid was washed with pentane (3 x 0.5 mL) to provide analytically pure 3 1 4 (20 mg, 66%). 1 H NMR (300 MHz, C 6 D 6 ) (ppm) ) : 7.78 (d, J = 9 Hz, 2H, Ar H ), 7.73 (d, J = 6 Hz, 2H, Ar H ), 7.38 (m, 3H, overlapping signals ), 6.99 (t, J = 9 Hz, 2H, Ar H ), 3.70 (bs, 3 H, N Me ), 2.47 (bs, 3H, N Me ), 1.49 (s, 18 H, t Bu). 13 C{ 1 H} NMR (75.36 Hz, C 6 D 6 ) (ppm) ) : 174.35 (s, C Mo), 157.52 (s, C aromatic), 138.10 (s, C aromatic), 137.05 (s, C aromatic), 131.67 (s, C aromatic), 128.83 (s, C aromatic ), 127.04 (s, C aromatic), 126.36 (s, C aromatic), 121.44 (s, C aromatic), 35.79 (s, C (CH 3 ) 3 ), 30.85 (s, ( C H 3 ) 3 ). Anal. Calcd for C 28 H 33 MoN O 3 : C, 63.75, H, 6.31, N, 2.66. Found C, 63.66, H, 6.43, N, 2.79. 3.3. 9 NMR T ube R eactions 3.3. 9 .1 Excess MeI and 3 10 to form [ t BuOCO]Mo=NMe(NMe 2 ) ( 3 11 Me) In a nitrogen filled glove box a J young tube was charged with 3 10 (33 mg, 0.06 mmol) and C 6 D 6 (0.3 mL) The tube was cooled to 35 C then C 6 D 6 ( 0.1 mL ) was layered onto the frozen solution and again cooled 0.3mmol) was added to the frozen solution and the reaction mixture was allowed to thaw slowly. The NMR tube was sealed and heat ed at 60 C for 10 h. 1 H NMR (300 MHz, C 6 D 6 (ppm)): 7.93 (d, J = 9 Hz, 2H, Ar H ), 7.75 (d, J = 9 Hz, 2H, Ar H ), 7.44 (t, J = 9 Hz, 1H, Ar H ), 7.35 (d, J = 9 Hz, 2H, Ar H ), 6.90 (t, J = 9 Hz, 2H, Ar H ), 4.23 (bs, 3 H, N Me ), 3.59 (bs, 3 H, N Me ), 2.86 (s, =N Me ), 1.69 (s, 18 H, t Bu), 1.42 (s, 9H, excess Me I). 13 C{ 1 H} NMR (75.36 Hz, C 6 D 6 ) (ppm) ) : 177.25 (s, C Mo), 162.37 (s, C O), 139.38 (s, C aromatic), 138.21 (s, C aromatic), 134.01 (s, C aromatic), 127.44 (s, C aromatic), 126.11 (s, C aromatic), 125.87 (s, C aromatic), 124.99 (s, C aromatic), 118.17 (s, C aromatic), 59.49 (s, N( C H 3 ) 2 ), 51.95 (s, =N C H 3 ), 48.16 (s, N( C H 3 ) 2 ), 35.80 (s, C (CH 3 ) 3 ), 30.91 (s,

PAGE 94

94 C( C H 3 ) 3 ). 3.3. 9 .2 t BuCOCl and 3 10 to form 3 1 4 and t In a nitrogen fille d glove box a J young tube was charged with 3 10 (15 mg, 0.02 mmol) and dissolved in 0.3 mL of C 6 D 6 The solution was cooled to 35 C then C 6 D 6 (0.1 mL) was layered onto the frozen solution and again cooled. t equiv, 0.03 mmol) was added to the frozen solution. The solution changed from yellow to orange in color as it warmed to room temperature. The tube was heated at 60 C for 7.5 h and the progress of the reaction was monitored periodical ly by 1 H NMR spectroscopy. At time = 0 resonances attributed to 3 13 t Bu were observed. As the tube was heated, growth of peaks corresponding to the oxo amide complex 3 14 was observed concomitant with the appearance of a signal indicating formation of o ne equivalent t 3.3. 9 .3 Ph COCl and 3 10 to form 3 1 4 In a nitrogen filled glove box a J yo ung tube was charged 3 10 (14 mg, 0.02 mmol) and 0.3 mL of C 6 D 6 The tube was cooled to 35 C; and C 6 D 6 ( 0.1 mL) was layer ed onto the frozen solution which was mmol) was then added to the frozen solution. The solution changed from yellow to dark orange in color as it warmed to room temperature. The reaction mixture was heated a t 60 C for 3 h and the progress of the reaction was monitored periodically by 1 H NMR spectroscopy. At time = 0 resonances attributed to 3 13 Ph were observed. After continued heating growth of peaks corresponding to oxo amide complex 3 14 w ere observed concomitant with the appearance of signals indicating formation of one 3 13 Ph : 1 H NMR (300 MHz, C 6 D 6 (ppm)): 7.86 (d, J = 6 .0 Hz, 2H, Ar H ), 7.74 (d, J = 6 .0 Hz,

PAGE 95

95 2H, Ar H ), 7 .53 (d, J = 9 .0 Hz, 2H, Ar H ), 7.38 (t, J = 6 .0 Hz, 2H, Ar H overlapping signal), 7.33 (d, J = 9 .0 Hz, 2H, Ar H overlapping signal), 6.87 (t, J = 9 .0 Hz, 1H, Ar H overlapping signal), 6.82 (t, J = 6 .0 Hz, 2H, Ar H overlapping signal), 6.73 (t, J = 6 .0 Hz, 2H, Ar H overlapping signals), 4.35 (bs, v 1/2 = 312 Hz, 6H, N Me ), 1.66 (s, 18 H, t Bu). 3.3. 9 .4 MeCOCl and 3 10 to form 3 1 4 In a nitrogen filled glove box a J young tube was charged with 3 10 (12 mg, 0.02 mmol) and 0.3 mL of C 6 D 6 The solution was cooled to 35 C ; and C 6 D 6 (0.1 mL) was layered onto the frozen solution and again cooled mmol) was then added to the frozen solution. The solution changed from yellow to brown in color as it warmed to room temperature. The reaction mixture was heated at 60 C for 1.5 h and the progress of the reaction was monitored periodically by 1 H NMR spectroscopy. At time = 0 resonances attributed to 3 13 Me were observed. After continued heating growt h of resonances attributed to the oxo amide complex 3 14 was observed concomitant with the appearance of a signal indicating formation of one equivalent 3 13 Me : 1 H NMR (300 MHz, C 6 D 6 (ppm)): 7.93 (d, J = 9 .0 Hz, 2H, Ar H ), 7.70 (d, J = 9 .0 Hz, 2H, Ar H ), 7.41 (t, J = 6 .0 Hz, 2H, Ar H overlapping signal), 7.34 (d, J = 9 .0 Hz, 2H, Ar H overlapping signal), 6.88 (t, J = 6 .0 Hz, 1H, Ar H ), 4.79 (bs, v 1/2 = 84 Hz, 3H, N Me ), 3.77 (bs, v 1/2 = 84 Hz, 3H, N Me ), 1.63 (s, 18 H, t Bu), 1.22 (s, 3H, NC=O Me ). 3.3.10 X ray Experimental Details for [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 (3 7) X Ray i ntensity data were collected at 100 K on a Bruker DUO diffractometer using MoK radiation ( = 0.71073 ) and an APEXII CCD area detector. Raw data

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96 frames were rea d by the program SAINT and integrated using 3D profiling algorithms. The resulting data were reduced to produce hkl reflections and their intensities and estimated standard deviations. The data were corrected for Lorentz and polarization effects and nume rical absorption corrections were applied based on indexed and measured faces. The structure was solved and refined in SHELXTL6.1, 151 using full matrix least squares refinement. The non H atoms were refined with anisotropic thermal parameters and all of the H atoms were calculated in idealized positions and refined riding on their parent atoms. The asymmetric unit consists of two chem ically equivalent but crystallographically independent complexes. All four amino protons were obtained from a Difference Fourier map and refined freely. In the final cycle of refinement, 15094 used to refine 811 parameters and the resulting R 1 wR 2 and S (goodness of fit) were 2.66 %, 5.62 % and 0.925 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 wa s calculated to provide a refere nce to the conventional R value but its function wa s not minimized. 3.3.11 X ray Experimental Details for [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 (3 8) X Ray Intensity data were collected at 100 K on a Bruker DUO diffractometer using MoK radiation ( = 0.71073 ) and an APEXII CCD area detector. Raw data frames were read by program SAINT and integrated using 3D profiling algorithms. The resulting data were reduced to produce hkl reflections and their intensities and stimated standard deviations. Th e data were corrected for Lorentz and polarization effects and numerical absorption corrections were applied based on indexed and measured faces.

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97 The structure was solved and refined in SHELXTL6.1, 151 us ing full matrix least squares refinement. The non H atoms were refined with anisotropic thermal parameters and all of the H atoms were calculated in idealized positions and refined riding on their parent atoms. There are two chemically equivalent but cry stallographically independent complexes in the asymmetric unit, two DME solvent molecules. All four amino protons were obtained from a Difference Fourier maps and refined freely. In the final cycle of refinement, 15770 reflections (of which 8974 are obse 1 wR 2 and S (goodness of fit) were 4.15 %, 9.25 % and 0.845 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 wa s calcu lated to provide a reference to the conventional R value but its function wa s not minimized 3.3.12 X ray Experimental Details for {[ t 2 )Na(DMF)} 2 (3 10) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK ). Cell parameters were refined using up to 8192 reflections. A full sphere of data scan method (0.3 frame width). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the Dir ect Methods in SHELXTL6, 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on thei r

PAGE 98

98 respective carbon atoms. The asymmetric unit consists of the complex anion, a sodium cation and a molecule of dimethylformam ide ( DMF ). A total of 354 parameters were refined in the final cycle of refinement using 5783 d R 1 and wR 2 of 2.70% and 6.62%, respectively. Refinement was done using F 2 3.3. 13 X ray Experimental Details for [ t 2 ) (3 12) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the scan method (0.3 frame width). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6, 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atom s. The asymmetric unit consists of two chemically equivalent but crystallographically independent complexes and a benzene solvent molecule. A total of 683 parameters were refined in the final cycle of refinement using 9996 ield R 1 and wR 2 of 3.92% and 7.84%, respectively. Refinement was done using F 2 3.3. 14 X ray Experimental Details for [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) (3 1 3 t Bu) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073

PAGE 99

99 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data scan method (0.3 frame width). The first 50 frames were re measure d at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6, 151 and refined using full matrix least squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. The asymmetric unit consists of two molecules that are chemically equivalent but crystallographically independent, and an ether solvent molecule. The latter was disordered and could not be modeled properly, thus program SQUEEZE, 175 a part of the PLATON package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. One of the molecules has its keto oxygen atoms disordered and was refined in two parts. The other has the N3 ligand disordered and was also refined in two parts with their site occupation factors dependently refined. A total of 804 parameters were refi ned in the final cycle of refinement using 5483 1 and wR 2 of 7.10% and 16.66%, respectively. Refinement was done using F 2 3.4 Conclusions The [ OCO ] 3 trianionic pincer ligand contains more acidic phenolic groups compa red to the NCN ligand precursors that contain aniline moieties. Consequently, metalation of the terphenyl diol with OCO donors occurs with group 6 metal amides for the first time, furnishing [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) in high yield and purity A series of d 2 metal complexes are synthesized by displacing the dimethylamide ligand to

PAGE 100

100 form compounds with general formula [ t BuOCO]Mo( X )(NHMe 2 ) 2 ( X = Cl, NCO, OTf). Furthermore, two electron oxidation of 3 5 with NaN 3 provides a rare nitrido anion dimer { [ t 2 )Na(DMF)} 2 ( 3 10 ) The trianionic pincer ligand serves dual purpose; firstly, it stabilizes the +6 oxidation state of the molybdenum nitride and secondly, it binds in a meridional fashion creating an uncomfortable geometry around the met al center. Consequently, the reactivity of the nitrido functionality is enhanced allowing easy functionalization with mild electrophiles (MeI and Me 3 SiCl). Additionally w e are able to add evidence for the intermediacy of an azametallocy c lobutene on route to nitrile expulsion during metal mediated N atom transfer to acid chloride. The piva loylimido intermediate coupled with kinetic investigations suggests the prerequisite for at least one accessible coordination site to complete the N atom transfe r. Research is ongoing to determine the routes to convert the oxo complex to the nitrido complex and also elucidate additional substrat e scope for the rare molybdenum nitride.

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101 Table 3 1. Experimentally determined magnetic moments for the Mo(IV) meta l complexes 3 5 3 6 3 7 and 3 8 Compound B (experimental) [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) 3.06 [ t BuOCO]Mo( Cl )(NHMe 2 ) 2 ( 3 6 ) 2.56 [ t BuOCO]Mo (OTf) (NHMe 2 ) 2 ( 3 7 ) 3.01 [ t BuOCO]Mo (NCO) (NHMe 2 ) 2 ( 3 8 ) 2.96 Table 3 2 Experimentally determined thermodynamic parameters for the equilibration 3 11 SiMe 3 3 13 t Bu and 3 14 Complex (kcal/mol) (kcal/mol) (cal/molK) Coalescence Temperature (C) 3 11 SiMe 3 15.13(2) 15.0(1) 0.6(2) 55 3 14 14.5(3) 13.9(1) 2.5(3) 40 3 13 t Bu 13.8(2) 20.6(1) 24.8(2) 15 Figure 3 1. Comparison of two trianionic pincer ligands (a) [ArNCN]H 3 and (b) [ t BuOCO]H 3 Figure 3 2 Synthesis of [ t BuOCO]Mo(NMe 2 )(NHMe 2 ) 2 ( 3 5 ) and [ t BuOCO]MoCl (NHMe 2 ) 2 ( 3 6 )

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102 Figure 3 3 Four step synthesis of 3,3'' di tert butyl 1,1':3',1'' terphenyl 2,2'' diol [ t BuOCO]H 3 ( 3 4 ) Figure 3 4. Synthesis of [ t BuOCO]Mo (OTf) (NHMe 2 ) 2 ( 3 7 )

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103 Figure 3 5. Solid state molecular structure of [ t BuOCO]Mo (OTf) (NHMe 2 ) 2 ( 3 7 ). The h ydrogen atoms are omitted for clarity. Figure 3 6. Synthesis of [ t BuOCO]Mo (NCO) (NHMe 2 ) 2 ( 3 8 )

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104 Figure 3 7. Solid state molecular structure of [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 ( 3 8 ) The h ydrogen atoms and DME are omitted for clarity. Figure 3 8. Solid state structures of [ t BuOCO]Mo(IV) metal complexes, exhibiting C s and C 2 symmetric structures

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105 Figure 3 9. Attempted synthesis of a trianionic pincer supported molybdenum nitride Figure 3 10. Solid state structure of [ t 2 )(DMF) ( 3 9 ) Figure 3 11. Synthesis of { [ t 2 )Na(DMF)} 2 ( 3 10 )

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106 Figure 3 12. Solid state structure of { [ t 2 ) Na(DMF)} 2 ( 3 10 ) in which the asymmetric unit is displayed. The hydrogen atoms and the DMF molecule are removed for clarity. Figure 3 13. Addition of mild electrophiles to { [ t 2 ) Na(DMF)} 2 ( 3 10 )

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107 Figure 3 14. Synthesis of [ t BuOC H (Cl) (NHMe 2 ) ( 3 12 ) Figure 3 15. Solid state structure of [ t 2 ) ( 3 12 ) Figure 3 16. Addition of acid chlorides to synthesize acylimido complex es 3 13 R

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108 Figure 3 17. Synthesis of [ t BuOCO]Mo=O(NMe 2 ) ( 3 14 ) Figure 3 18. Solid state structure of [ t BuOCO]Mo=NC(O) t Bu (NMe 2 ) (DMF) ( 3 13 t Bu ) The hydrogen atoms are removed of clarity.

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109 Figure 3 19. Eyring plot for the equilibration of N Me 2 resonance in the 1 H NMR spectrum for complex 3 11 SiMe 3 3 14 and 3 13 t Bu Figure 3 20. Mechanism of N tom transfer from 3 13 R to acid chlorides to form nitriles.

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110 Figure 3 21. Selected region of 1 H NMR spectrum featuring conversion of the pivaloyl imido complex 3 13 t Bu to oxo imido complex 3 14 over time at 40C Figure 3 22. Eyring plot for the decay of 3 13 t Bu

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111 Figure 3 23. 1 H NMR spectrum of [ t 2 )(DMF) ( 3 9 ) and mixture of compounds in C 6 D 6

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112 Figure 3 24. 1 H NMR spectrum of [ t 2 ) Na(DMF)} 2 ( 3 10 ) in C 6 D 6

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113 Figure 3 2 5 1 H NMR of [ t BuOCO]Mo=NSiMe 3 (NMe 2 ) ( 3 11 SiMe 3 ) in C 6 D 6

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114 Figure 3 2 6 1 H NMR of [ t BuOCO]Mo=NMe(NMe 2 ) ( 3 11 Me ) in C 6 D 6

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115 Figure 3 2 7 1 H NMR of [ t BuOC H O]Mo N (Cl) (NMe 2 ) ( 3 12 ) in CD Cl 3

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116 Figure 3 2 8 1 H NMR of [ t BuOCO]Mo=NC(O) t Bu(NMe 2 ) ( 3 13 t Bu ) in C 6 D 6

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117 Figure 3 2 9 1 H NMR of [ t BuOCO]Mo=NC(O) Ph (NMe 2 ) ( 3 13 Ph ) in C 6 D 6

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118 CHAPTER 4 UNIQUE PRIMARY CARBO N NITROGEN BOND SCISSI ON ACROSS A W W MULTIPLE BOND AND ME THYL DEHYDROGENATIO N 4 .1 Introduction C hapter 3 described the synthesis and reactivity of a rare molybdenum nitrido anion dimer. Following the discovery of the molybdenum nitride, our group explored the synthesis and reactivity of an analogous chromium oxo complex. Both complexes are capable of promoting atom transfer reactions to organic molecules. In fact, the chromium oxo is the first catalytic system featuring a trianionic pincer for the oxidation of phosphines, where the oxygen is derived from atmospheric oxygen. 147,176 Figure 4 1 illustrates our motivation to make related trianionic pincer complexes of group 6 metal alkylidynes. We envisioned that the constrained geometry imposed by the trianionic pincer ligand would generate a highly reactive W CR fragment. The attachment of the trianionic pincer ligand [OCO] 3 requires the formation of two M O bonds and one M C bond. Figure 4 2 depicts three different endeavours to make a trianionic pincer s upported tungsten alkylidyne. The common aspect for these approaches is a preinstalled W CR fragment in the metal precursors. 177 Starting with (ArO) 2 ( t BuCH 2 )W C t Bu (Ar =2, 6 i PrC 6 H 3 ) and treating with [ t BuOCO]H 3 ( 3 4 ), leads to the formation of the corresponding pincer alkylidene complex [ t BuOCO] W =CH t Bu (O 2,6 i Pr C 6 H 3 ) ( 4 1 ). In contrast, starting with alkoxide free precursor such as ( t BuCH 2 ) 3 W C( t Bu), requires prolonged thermolysis and finally forms an equilibrium mixture of isomers [( t BuOCO)W =CH t Bu ( t BuOCHO)W = CH t Bu ( t BuOCO)] ( 4 2 kin and 4 2 therm ) in a 40:60 ratio. Alternatively, salt metathesis between the dipotassium salt [ t BuOCHO]K 2 (THF) 2 and (DME)Cl 3 W C t Bu provides a

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119 diphenolate complex [ t BuOCHO]W C ( t Bu) Cl ( 4 3 ) along with 4 2 kin and other intractable impurities. The results indicate that starting with a preinstalled W CR fragment typically tends to form the corresponding alkylidene, presumably by the addition of the C ipso H bond across the metal carbon triple bond. 111,178 The problem is amplified by the harsh reaction conditions required. The following section describes a different approach towards our desired metal complex that avoids the use of a preinstalled W CR fragment. 4 2 Original Motivation One of the most convenient ways to access a tungsten alkylidyne species is by the metathesis of methyl butyne is a major driving force for the reaction (Figure 1 1 4). 91 Incorporation of a similar strategy is possible in the synthetic approach toward trianionic pincer supported metal alkylidynes. Figure 4 3, details our plan to make complex 4 5 via 4 4 4 3 Results and Discussion In search of a reactive dinuclear complex of the prototype 4 4 the terphenyl trianionic pincer ligand precursor [ t BuOCO]H 3 ( 3 4 ) is treated with (Me 2 N) 3 2 ) 3 179 Unlike, the form ation of complex 3 5 this reaction occurs at 80 C in C 6 D 6. The reaction progress is periodically monitored by 1 H NMR spectroscopy, which indicates complete consumption of the tungsten precursor prior to complete consumption of the ligand [ t BuOCO]H 3 Initially, the solution remains dark yellow and with the progress of the reaction the solution turn s green Typically, the distinct aliphatic resonances for the t Bu protons of the ligand are followed to monitor the progress of a reaction. Noticeably, several resonances in the aliphatic region appear in this reaction

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120 This indicates the following possibilities: (a) the reaction is multistep where several intermediates overlap; and (b) the reaction forms several low symmetry species. At the end of four days dark green single crystals deposit from the solution The 1 H NMR spectrum of the solution at that point displays a major peak at 2.19 ppm, which is consistent with free HN Me 2 in C 6 D 6 An X ray diffraction experiment performed on the crystals identi fies the solid as the ditungsten complex [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ). T he product form s in 88% yield and are the result of a C N bond scission and double C H bond activation of the coordinated dimethyl amide ligands, with concomitant l oss of both hydrogen atoms as illustrated in Figure 4 4 180 4.3.1 Characterization of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu ] (4 6) Complex 4 6 is sparingly soluble in hydrocarbon solvents; as such, the diagnostic spectroscopic (NMR) features remain undetected in the reaction mixture because the reaction is performed in C 6 D 6 The 1 H NMR spectrum of 4 6 (CDCl 3 ) is consistent wi th a C s symmetric structure. The mirror plane bisects the W W bond and contains all three bridging groups. However, each half of the molecule along the WW axis is distinct, and two sets of in equivalent t Bu protons resonate at 1. 2 2 and 1. 40 ppm The other sharp resonances at 1.65 and 1.93 ppm can be attributed to the diastereotopic NMe 2 groups An NOE difference experiment allows for detailed stereo chemical assignment. The signal at 1.99 ppm ( H 3) correlates to a doublet at 7.32 ppm (H38) The third resonance at 3.99 ppm is due to t he NMe protons which correlates with a doublet at 7.44 ppm identifying the later as H40 (Figure 4 2). Table 4 1 lists the data from 1 H 1 H, 1 H 13 C, one bond and 1 H 13 C long range couplings observed in the gDQC OSY, gHMQC, and gHMBC spectra for this compound which enable absolute assignment of all proton and carbon resonances The conspicuous resonance at 8.27 ppm for two

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121 C ipso H protons indicates that each ligand is bound to the W(V) ion in its diphenolate form The closest complex for comparison is [ t BuOCHO]W C ( t Bu) Cl ( 4 3 ) in which the C ipso H appears even further downfield at 9.75 (C 6 D 6 ). 177 Figure 4 1(a), displays the most interesting feature of the 1 H NMR spectrum, a downfield resonance at 19.11 ppm with a characteristic five line pattern ( J 2 W CH = 21 Hz). This is diagnostic of the proton (H1) residing on a methylidyne carbon that bridges two NMR active 183 W nuclei. HMBC experiments demonstrate that H1 exhibits long range (four bond) correlation with C4, however no three bond coupling is observed. The carbyne carbon could not be lo cated in the 13 C{ 1 H} NMR spectrum, due to low solubility of 4 6 A n HMQC experiment allows for indirect detection of the carbyne carbon (C1) at 349. 9 ppm (Figure 4 1b). This is consistent with the only other example of a methylidyne bridging two tungsten atoms; t Bu 3 SiO) 2 W( CH)( H)( O)W( t Bu 3 SiO) 2 which appears at 319.5 ppm. 181 4.3. 2 Structural D escription of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] (4 6) Figure 4 6 depicts the molecular structure of 4 6 Complex 4 6 crystalizes in a triclinic crystal system with a P space group. Consistent with t he solution state characterization the dinuclear complex is C s symmetric and each W ion adopts distorted square pyramidal coordination geometry. The CH group occupies the apical position with an average W CH bond length of 1.942(2) The basal positions are occupied by a dimethyl amido, methyl imido, and the diphenolate donors from the ligand. E ach carbyne tungsten C ipso axis is close to l inearity wit h C48 W2 C1 = 164.25(1) In addition, the C ipso atoms are located close to the W(V) ions ( W1 C22 = 2.815(2) and W2 C48 = 2.988(2) ), suggesting a W interaction compensates for the open

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122 coordination site. The W(V) ions are bridged by a dimet hyl amid e methyl imido, and methylidyne moiety. The W V W V distance is 2.49879(15) which is consistent with a d 1 d 1 W W single bond. The closest complex for comparison is W 2 (OCH 2 t Bu) 4 ( OCH 2 t Bu)( O)(py) 2 ( C c C 3 H 5 ) which contains three one atom bridges (carbyne, oxo, and alkoxy) and a W W bond length of 2.4456(7) 182 A similar complex [W(OCMe 2 CF 3 ) 2 Cl] 2 ( NAr ) 2 has two one a tom bridges and a significantly longer W W bond length of 2.6296(2) 183 The shortest crystallographically characterized WW distance of 2.155(2) resides in the quad ruply bonded complex W 2 (dmhp) 4 184 Disordered NMe 2 and NMe ligands refine isotropically at half occupancy and, as expected, the average W N bond for the NMe 2 is longer than the NMe by 0.208(9) Supporting our contention that the third bridging atom is a carbon, crystallographic modelling of the atom as either an O or N results in poor refinement statistics and, more importantly, the proton was located in the Difference Fourier map and refined without constraints to give a C1 H3 bond length of 0.88(3) 4.3.3 Confirmation of Methyl Dehydrogenation Event and Fate of Hydrogen Atoms Periodic monitoring of the reaction conducted in a seal ed tube by 1 H NMR spectr o scopy did not reveal the extrusion of H 2 Inspection of the molecular structure of complex 4 6 suggests that each tungsten ion possesses an empty c oordination site trans to the W CH bond. It is possible that W H could form after methyl dehydrogenation 185 which could be below the detection limit for X ray crystallography. In this case, the short W W distance could be a coincidence in which both the metal centers are bridged by three groups. This contradicts our previous assignment of a W V W V bond, and instead the W ions are fully oxidized to +6. To address these concerns we undertook e xhaustive spectroscopic analysis of complex 4 6 The IR

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123 spectrum of 4 6 does not reveal any absorption in the typical range (1600 1800 cm 1 ) for bridging or terminal W H stretching vibrations. 186 The 1 H NMR spectrum (500 MHz) of 4 6 provides excellent resolution of all proton resonances with their corresponding integration, but no hydride s ignal was located. The W hydride in ( t Bu 3 SiO) 2 W( CH)( H)( CH)W( t Bu 3 SiO) 2 appears in the conspicuous location of 11.77 ppm (C 6 D 6 ). 181 A g HMBC experiment did not identify a through bond interaction between the carbyne CH and a W H, and all attempts to locate pro bable hydride ligands via crystallographic methods failed. C onvincing evidence that no hydrides are present, also comes from mass spectroscopic analysis, which reveals the [M+H] parent ion mass of 1199.4116 m/z for C 56 H 67 N 2 O 4 W 2 F inally, a gas chomatrog raph of the headspace of the sealable NMR tube reveals the presence of hydrogen. Figure 4 7, displays the gas chromatograph of the reaction headspace, which indicates presence of hydrogen at a retention time of 2.28 min which matches an authentic sample. 4.3. 4 Synthesis and Characterization of [ t BuOCHO](NMe 2 2 ) 3 (4 7) Such C N and double C H bond activations are relevant to hydrodenitrogenation (HDN) reactions. 187 189 HDN is a part of the crude oil refinement process, 190 192 where nitrogen content is reduced by hydrogenating heterocyclic compounds, ultimately expelling ammonia. This process is crucial, because it produces clean fuel with reduced NO x emissions after combustion and also prevents the poisoning of catalysts which are utilized downstream in the refining process. 193,194 Recent model studies suggest that C=N double bond cleavage of aromatic N heterocycles presents an alternative route which eliminat es an expensive and energy intensiv e hydrogenation step. 195 199 Ultimately, an aliphatic C N bond scission must occur which is related to our current observations when complex 4 6 forms.

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124 Figure 4 6 illustrates the one step synthesis of complex 4 6 However, certain questions remain about the actual sequence of events and specifically whether this reaction involves intermediates. Considering that formation of 4 6 requires accommodation of two large diphenolate ligands, it i s reasonable to assume steric pressure initiates the unusual sequences of CN bond cleavage and methyl dehydrogenation. As previously discussed monitoring the reaction peri odically by 1 H NMR spectroscopy reveals the possibility for the build up of intermediate s during the reaction Early in the reaction, metal precursor is consumed before the ligand. With this in mind we decided to attempt a reaction employing the ligand a nd the metal in a 1:1 stoichiometric ratio. According to Figure 4 8, one ligand binds to the metal center as a diphenolate and displaces two equivalents of dimethyl amine to form [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ). This result demonstrates that it is possib le to arrest the reaction prior to the cascade bond activations by using only one equivalent of ligand. Complex 4 7 could be isolated in 97% yield, and the 1 H NMR (C 6 D 6 ) signals are consistent with resonances present early in the reaction during the formation of 4 6 At room temperature the molecule exists as a C s symmetric species in solution, as evidenced from a distinct singlet at 1.46 ppm for 18 t Bu protons from the diphenolate. The mirror plane now contains the W W bond axis, unlike complex 4 6 The conspicuous resonance at 8.82 ppm marks the C ipso H. Other indicative resonances include three sets of broad peaks at 4.09 ppm for one terminal NMe 2 ; at 3.39 ppm for 12 NMe 2 protons residing on opposite side of the mirror plane (Figure 4 9); and finally at 2.39 for the fourth distinct NMe 2 group. Additional confirmation for the structural

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125 assignment comes from a low temperature NMR experiment (toluene d 8 ). Cooling th e NMR probe to 75 C 1 symmetric species. Figure 4 9 displays the results of the variable temperature NMR experiment in which the spectrum at 75 C exhibits two t Bu resonances and eight distin ct NMe resonances. A gHMBC experiment locates correlations between the methyl pairs on each coordinated dimethylamide group. However, the ROESY nOe was poorly resolved and unable to model eight nitrogen nuclei for the absolute stereo chemical assignment in complex 4 7 Addition of a second equivalent of ligand to 4 7 in C 6 D 6 and heating at 80 C for 12 h leads to formation of 4 6 hydrogen and dimethyl amine. 4.3. 5 Synthesis and Characterization of [ t BuOCHO]W( NMe)( NMe 2 )( C H)W(NMe 2 ) 2 (4 8) Isolation of 4 7 indicates that intermediates form during the production of complex 4 6 however details of the bond activation still remain elusive. Heating complex 4 7 in the absence of ligand at 110 C for 15 h leads to a mixture of compounds. Close inspection of the 1 H NMR spectrum of the mixture suggests the formation of a major compound, tentatively assigned as [ t BuOCHO]W( NMe)( NMe 2 )( CH)W(NMe 2 ) 2 ( 4 8 ), which exhibits a characteristic bridging methylidyne proton resonance at 16.40 ppm ( J 2 W C H = 12 Hz ). Formation of the bridging methylidyne suggests the C N bond activation and methyl dehydrogenation event occurs prior to the attachment of the second ligand (Figure 4 10). Complex 4 8 forms along with minor inseparable impurities, which preclude combustion analysis. However, gas chromatography of the reaction head space identifies the liberated H 2 Complex 4 8 would be C 1 symmetric and resonances in

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126 support of th is assignment include : a ) nine protons for each t Bu at 1.75 and 1.91 ppm ; b ) a NMe at 4.96 ppm ; c ) d iastereotopic NMe 2 protons at 3.50 and 4.21 ppm ; and d ) resonances for the terminal NMe 2 protons at 2.29 and 2.50 ppm. Further supporting our justification that 4 8 is indee d an intermediate in the formation of 4 6 addition of one equivalent of ligand to 4 8 results in the formation of 4 6 (80 C, 2h). Monitoring the reaction by 1 H NMR spectroscopy indicates that all the resonances attributable to 4 8 decrease in conjunction with the formation of 4 6 After 2 h consumption of 4 8 is complete and 4 6 precipitates as a cry stalline green solid (Figure 4 11) concomitant with formation of dimethyl amine. 4 4 Experimental S ection 4.4.1 General Considerat ions Unless specified otherwise, all manipulations were performed under an inert atmosphere using standard Schlenk or glovebox techniques. Pentane, hexanes, toluene, diethyl ether, tetrahydrofuran, and 1,2 dimethoxyethane were dried using a GlassContour drying column. C 6 D 6 and toluene d 8 (Cambridge Isotopes) were dried over sodium benzophenone ketyl, distilled or vacuum transferred and stored over molecular sieves. Sublimed WCl 4 and LiNMe 2 were purchased from Sigma Aldrich. W 2 (NMe 2 ) 6 200 and [ t BuOCO]H 3 152 were prepared according to published procedures. The NMR spectra were recorded on a Mercury (300 MHz) Mercurybb (300 MHz) or Varian Inova (500 MHz) instrument. For 1 H and 13 C{ 1 H} NMR spectra, the residual protio solvent peak was used as an internal reference and the temperature was 25 C, unless specified otherwise. The chemical shifts for 15 N were referenced to = 10.1328898, corresponding to 0 for neat ammonia. On the scale the frequency of protons in tetramethylsilane is 100.0 MHz. For

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127 conversion to the neat nitromethane scale, subtract 381.7 ppm. Elemental analyses were performed at Complete Analysis Laboratory Inc., Parsippany, New Jersey. FT IR spectra were recorded on a Thermo scientific instrum ent. Atmospheric pressure chemical ionization (APCI) mass spectra were recorded in an A gilent 6210 TOF with 1200 HPLC and the isotopic distribution of the [M + H] + peak were compared with the corresponding calculated spectrum. 4.4.2 Synthesis of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) A Schlenk tube was charged with (Me 2 N) 3 2 ) 3 (358 mg, 0.57 mmol), [ t BuOCO]H 3 ( 3 5) ( 424 mg, 1.13 mmol), and benzene (8 mL). The solution was heated at 80 C for 4 d and the solution color changed from y ellow to intense dark green in color Cooling the solution to ambient temperature causes deposition of a green crystalline precipitate. The precipitate was filtered, washed with pentane and all volatiles were removed in vacuo to provide 4 6 as a green mi crocrystalline powder (600 mg, 88%). 1 H NMR (300 MHz, CDCl 3 ) : 19.11 (t, J 2 W H = 21 Hz, 1H, W C H1 W ), 8.37 (t, J = 3 Hz, 2H, H22,H48), 7.51 (t, J = 6 Hz, 2H, H13,H39), 7.44 (t, J = 3 Hz, 2H, H14,H40 ), 7.32 (t, J = 3 Hz, 2H, H12,H38 ), 7.21 (t, J = 3 Hz, 2H, H9,H35 ), 7.19 (m, 4H, H7,H33,H21,H47), 7.16 (d, J = 3 Hz, 2H, H19,H45) 6.75 (t, J = 9 Hz, 4H, H8,H34,H20,H46), 3.99 (s, 3H, N(C H 3 ), H4), 1.93 (s, 3H, N(C H 3 ) 2 H3), 1.65 (s, 3H, N(C H 3 ) 2 H2), 1.40 (s, 18H, C(C H 3 ) 3 H24 26,H50 52), 1.22 ( s, 18H, C(C H 3 ) 3 H28 30,H54 56). 13 C { 1 H} NMR (75.36 MHz, CDCl 3 ) : 349.9 (W C1 H W), 161.2 (s, C17,C43), 161.1 (s, C5,C31), 141.5 (s, C15,C41), 140.7 (s, C18,C44), 140.6 (s, C11,C37), 140.3 (s, C6,C32), 131.3 (s, C13,C39), 130.7 (s, C22,C48), 128 .7 (s, C10,C36), 128.2 (s, C16,C42), 126.9 (s, C9,C35), 126.6 (s, C19,C45), 125.9 (s, C12,C38), 125.4 (s, C14,C40), 125.2 (s, C7,C33), 125.1 (s, C21,C47), 120.0 (s,

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128 C20,C46), 119.9 (s, C8,C34), 55.7 (s, N( C H 3 ), C4), 54.7 (s, N( C H 3 ) 2 C3), 51.6 (s, N( C H 3 ) 2 C2), 35.5 (s, C (CH 3 ) 3 C23,C49), 35.1 (s, C (CH 3 ) 3 C27,C53), 30.4 (s, C( C H 3 ) 3 C24 26,C50 52), 30.2 (s, C( C H 3 ) 3 C28 30,C54 56). 15 N NMR (50MHz, CDCl 3 98.1( N1 ), 406.1( N2 ). Selected IR data (neat, cm 1 ): 2957 (w), 2867 (w), 1582 (m), 1423 (m ), 1404 (m), 1380 (m), 1232 (vs), 1191 (s), 1087 (m), 945 (m), 875 (vs), 849 (m), 810 (m), 74 7 (m), and 677 (m). Anal. Calcd For C 56 H 66 N 2 O 4 W 2 : C, 56.11; H, 5.55; N, 2.34. Found: C, 56.04; H, 5.46; N, 2.29. HRMS calculated (found) for C 56 H 67 N 2 O 4 W 2 (M+H) + : 1199.4127 (1199.4116). 4.4.3 Synthesis of [ t BuOCHO]W(NMe 2 )W(NMe 2 ) 3 (4 7) A Schlenk tube was charged with (Me 2 N) 3 2 ) 3 (366 mg, 0.57 mmol), [ t BuOCO]H 3 ( 3 5 ) ( 217 mg, 0.57 mmol), and benzene (5 mL). The solution was heated at 80 C for 75 min and a color change from gold to goldenrod was observed. The solution was cooled, filtered to remove a small amount of black precipitate, and then all volatiles were remov ed in vacuo to provide the product 4 7 as goldenrod colored powder (491mg, 92 %). 1 H NMR (300 MHz, C 6 D 6 25 C ) : 8.82 (s, 1H, H7), 7.34 (d, J = 9 Hz, 4H, H2,H4,H10,H12), 7.30 (t, J = 6 Hz, 1H, H17), 7.25 (d, J = 6 Hz, 2H, H16,H18), 6.91 (t, J = 9 Hz, 2H, H3,H11), 4.09 (bs, 6H, N ( C H 3 ) 2 ), 3.39 (bs, 12H, N ( C H 3 ) 2 ), 2.35 (bs, 6H, N ( C H 3 ) 2 ), 1.46 (s, 18H, C(C H 3 ) 3 ). 1 H NMR (500 MHz, toluene d 8 J = 9 Hz, 2H, H16, H18), 7.32 (d, J = 9 Hz, 2H, H12, H2), 7.27 (t, J = 9 Hz, 1H, H17), 7.22 (d, J = 9 Hz, 1H, H10), 7.16(d, J = 9 Hz, 1H, H4), 6.99 (t, J = 9 Hz, 1H, H11), 6.88 (t, J = 9 Hz, 1H, H3), 4.88 (s, 3H, N ( C H 3 ) 2 ), 4.15 (s, 3H, N ( C H 3 ) 2 ), 4.07 (s, 3H, N ( C H 3 ) 2 ), 3.81 (s, 3H, N ( C H 3 ) 2 ), 2.77 (s, 3H, N ( C H 3 ) 2 ), 2.61 (s, 3H, N ( C H 3 ) 2 ), 1.85 (s, 3H, N ( C H 3 ) 2 ), 1.81(s, 3H, N ( C H 3 ) 2 ), 1.73 (s, 9H, C(C H 3 ) 3, C20), 1.22 (s, 9H, C(C H 3 ) 3 C22). 13 C { 1 H} NMR (125 MHz, toluene d 8 75 C)

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129 C1), 138.7( s, C13), 134.1 (s, C4), 132.3(s, C10), 130.9 (s, C17), 129.4 (s, C7), 129.3 (s, C16, C18), 126.0 (s, C12), 125.9 (s, C2), 120.0 (s, C11), 119.0 (s, C3), 62.1(s, N( C H 3 ) 2 ), 60.8 (s, N( C H 3 ) 2 ), 59.9 (s, N( C H 3 ) 2 ), 58.8 (s, N( C H 3 ) 2 ), 42.4 (s, N( C H 3 ) 2 ), 41.0 (s, N( C H 3 ) 2 ), 40.4 (s, N( C H 3 ) 2 ), 37.8 (s, N( C H 3 ) 2 ), 35.5 (s, C (CH 3 ) 3 C19), 35.0 (s, C (CH 3 ) 3 C21), 30.2 (s, C( C H 3 ) 3 C20), 30.1 (s, C( C H 3 ) 3 C22). Selected IR data (neat, cm 1 ): 2948 (w), 2860 (w), 1579 (m), 1460 (m), 1406 (m), 1230 (vs), 1143 (w), 1090 (m), 1039 (w), 934 (m), 864 (m), 781 (m), 745 (vs), 710 (m). Anal. Calcd f or C 34 H 52 N 2 O 4 W 2 : C, 44.56; H, 5.72; N, 6.11. Found: C, 44.75; H, 5.66; N, 5.99. HRMS calculated (found) for C 34 H 53 N 2 O 4 W 2 (M+H) + : 917.3191 (917.3164). 4.4.4 X ray E xperimental E vidence for [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6) Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined usin g up to 8192 reflections. A full sphere of data (1850 frames) was collected using the scan method (0.3 frame width). The first 50 frames were re measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6, 151 and refined using full matrix leas t squares. The non H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. In addition to the W dimer, there are two half benzene solvent molecules (located on inversion c enters). The two bridging amide and imido groups (

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130 NMe and NMe 2 ) are disordered and were refined with dependent site occupation factors which refined to near 50% and then fixed at 50% in the final refinement cycles. All attempts to locate prob able hydride ligands failed. A total of 628 parameters were refined in the final cycle of refinement using 10621 reflections with I > 2 (I) to yield R 1 and wR 2 of 1.74% and 4.38%, respectively. Refinement was done using F 2 4.5 Conclusion s Although we did not make the desired trianionic pincer supported metal alkylidyne we learned several key lessons from these results. Thermolysis of metal precursors with W CR fragments in the presence of trianionic pincer ligand precursor [ t BuOCO]H 3 predominantly fo rms metal alkylidenes and does not provide the target complex 4 5 This demands metalation approaches under mild reaction conditions. A different approach involves attachment of the trianionic pincer to a M M triple bond and subsequent metathesis with me thyl alkynes. However, complex 4 4 is also not assessible, since the reaction between (Me 2 N) 3 2 ) 3 and [ t BuOCO]H 3 leads to an unprecedented combination of bond activations to provide a rare example of a bridging methylidyne. Such bond activation reactions do not occur when (Me 2 N) 3 2 ) 3 is heated in absence of the ligand. As such, the above result is a testament to the trianionic pincer ligand platform that is capable of making complexes with reactive M M multiple bonds Furthermore, detailed investigation identifies intermediates 4 7 and 4 8 suggesting that these events are not a consequence of the metal attempting to relieve steric congestion.

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131 Table 4 1. 1 H and 13 C chemical shifts assignments for [ t BuOCHO]W( NMe )( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) Position (ppm) Protons which display a cross peak in the gHMBC spectrum to the carbon in this position Protons which display an nOe with the proton in this position 1 349.9 19.11 H4 H24 H26, H50 H52, H28 H30, H54 H56 2 51.6 1.65 H3, H4 H3 3 54.7 1.93 H2 H2, H12, H38 4 55.7 3.99 H1 H14, H40 5, 31 161.1 H7 H9, H33 H35 6, 32 140.3 H8, H34, H25 H27, H50 H52 7, 33 125.2 7.19 H9, H35 H24 H26, H50 H52 8, 34 119.9 6.75 9, 35 126.9 7.21 H7, H33 10, 36 128.7 H8, H34, H12, H38 11, 37 140.6 H9, H35, H13, H39 12, 38 125.9 7.32 H14, H40, H22, H48 H3 13, 39 131.3 7.51 14, 40 125.4 7.44 H12, H38, H22, H48 H4, H21, H47 15, 41 141.5 H13, H39, H21, H47 16, 42 128.2 H14, H40, H20, H46 17, 43 161.2 H19 H21, H45 H47 18, 44 140.7 H20, H46, H28 H30, H54 56 19, 45 126.6 7.16 H21, H47 H28 H30, H54 H56 20, 46 120.0 6.75 21, 47 125.1 7.19 H19, H45 H14, H40 22, 48 130.7 8.37 H12, H38, H14, H40 H24 H26, H50 H52, H28 H30, H54 H56 23, 49 35.5 H7, H33, H24 H26, H50 H52 24 26, 50 52 30.4 1.40 H24 H26, H50 H52 H1, H7, H33 27, 53 35.1 H19, H28 H30, H45, H54 H56 28 30, 54 56 30.2 1.22 H28 H30, H54 H56 H1, H19, H45 N1 98.1 a H2, H3 N2 406.1 a H4 a 15 N chemical shifts, on the neat ammonia scale.

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132 Table 4 2. 1 H and 13 C chemical shifts assignments for [ t BuOCHO]W(NMe 2 )W(NMe 2 ) 3 ( 4 7 ). Positions 20 30.2 1.73 22 30.1 1.22 21 35.0 19 35.5 7 129.4 9.03 17 130.9 7.27 6,8 141.5 5,9 139.0 14 160.9 15 160.4 13 138.7 1 138.8 11 120.0 6.99 3 119.0 6.88 12 126.0 7.32 2 125.9 7.32 10 132.3 7.22 4 134.1 7.16 16,18 129.3 7.40 NMe 2 a 62.1 4.88 42.4 2.77 NMe 2 a 60.8 4.15 41.0 2.61 NMe 2 a 58.8 4.07 37.8 1.81 NMe 2 a 59.9 3.81 40.4 1.85 a The p airs of methyl groups that are attached to the same nitrogen atom are grouped together.

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133 Figure 4 1. Motivation for making group 6 metal alkylidyne supported by trianionic pincer ligand

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134 Figure 4 2. Synthesis of (a) [ t BuOCO]W= CH t Bu(O 2,6 i PrC 6 H 3 ) ( 4 1 ), (b) [( t BuOCO) W =CH t Bu ( t BuOCHO)W = CH t Bu ( t BuOCO)] ( 4 2 kin and 4 2 therm ) and, (c) [ t BuOCHO] W C ( t Bu) Cl ( 4 3 )

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135 Figure 4 3. Synthetic strategy towards [ t BuOCO]W CR(S) ( 4 5 ) Figure 4 4. Synthesis of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) Figure 4 5. (a) Selected region of 1 H NMR spectrum of complex 4 6 (CDCl 3 500 MHz) (b) Selected region of an HMQC spectrum of complex 4 6

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136 Figure 4 6 Molecular structure of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ). Hydrogen atoms (except H1), a benzene molecule, and disordered NMe groups are removed for clarity. Figure 4 7. Gas chromatograph of the reaction headspace

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137 Figure 4 8. Synthesis of [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ) Figure 4 9. Variable temperature 1 H NMR spectra of [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ) (toluene d 8 ).

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138 Figure 4 10. Formation of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W(NMe 2 ) 2 ( 4 8 ) Figure 4 11. Overall sequence of reactions that contribute to the formation of 4 6 via 4 7 and 4 8

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139 Figure 4 12. Position numbering in compound 4 6 for 2D NMR assignment Figure 4 13. Position numbering in compound 4 7 for 2D NMR assignment

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140 Figure 4 1 4 1 H NMR spectrum of [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) in CDCl 3

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141 Figure 4 15. 1 H NMR spectra of [ t BuOCHO](NMe 2 2 ) 3 ( 4 7 ) in C 6 D 6 at 25 C

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142 CHAPTER 5 SYNTHESIS AND REACTI VITY OF AN OCO 3 TRIANIONIC PINCER TUNGSTEN ALKYLIDYNE 5.1 Introduction Chapter 1 details several methodologies for making high oxidation state metal alkylidynes and their principal use as alkyne metathesis catalysts. The alkyne metathesis reaction typically occurs via formation of a metallacyclobutadiene ring, followed by a retro [2+2 ] cycloaddition to reform a n ew alkylidyne complex and a new alkyne. However, in certain cases a side reaction competes with the catalytic metathesis. The most common side reaction is polymerization of non sterically hindered alkyne monomers (2 butyne an d terminal acetylenes) to produce polyacetylenes. 201 203 Polyacetylenes (PA) are an important class of functional materials 204 208 that have unique properties including electrical conductivity, 209 213 paramagnetic susceptibility, 214,215 optical nonlinearity, 216 218 photoconductivity, 219,220 gas permeability, 221 224 liquid crys tallinity 225,226 and chain helicity. 227 230 Early catalysts monomers. 231 233 Masuda and coworkers later reported that commercially available WCl 6 and MoCl 5 in the presence of cocatalysts such as R 4 Sn ( R = Ph, n Bu), to produce phenylacetylene derived polymers, with molecular weights of approximately 10 4 g mol 1 234 Other catalysts were developed, such as M(CO) 6 4 ( M = Mo, W), in which the a verage molecular weight of polymers were as high as 2x10 6 g mol 1 235 Katz et al. verified the active species in these systems were metal alkylidenes, which polymerize alkynes via a metathesis pathway. 236,237 Polymerization of alkynes using early transition metal c atalysts typically requires dry, anaerobic reaction conditions; polar functional

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143 groups in the substrate poison the catalysts. Several l ate transition metal catalysts based on Rh and Pd are known and, unlike the early transition metal systems, they posses s high tolerance towards air, water and an array of functional groups. 204,208,238 240 Depending on the type of catalyst used for acetylene polymerization, two reaction mechanisms can operate. Multi component systems involving metal halides and well defined transition metal alkylidenes operate via a metathesis mechanism. 236,241 243 Systems that are capable of living polymerization of acetylenes are known. 244 250 Alternatively, catalysts that contain a m etal alkyl operate via an insertion mechanism. 251 253 There are few reports featuring metal alkylidynes as catalysts for polyacetylene production, 254 256 except the cases in which a side reaction of 2 butyne polymerization occurs during alkyne metathesis reactions. Schrock et al. outlined a ring expansion mechanism for acetylene polymerization by metal alkylidynes (Figure 5 1). 257 The first step involves the formation of a metallacyclobutadiene intermediate. A second acetylene molecule then coordinates to the metal center, preceding the key regioselective metathesis between the M=C bond and the C C bond. 258 Subsequent steps involve ring expansion to generate larger MC x rings (x is odd) with alternating single and double bonds. 93,255 Methods to impede the polymerization side reaction during alkyne metathesis are known. One such method involves blocking the vacant site that pe rmits additional alkyne coordination upon forming the metallacyclobutadiene intermediate. Zang et al. utilize a multidentate ligand, 259 while Moore et al. employ bulky polyhedral oligomeric silsesquioxane (POSS) ligands. 260,261 Another option is to use sterically bulky monomers that thwart coordination of addition al alkynes to the metallacyclobutadiene

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144 intermediate. 93 The design of ligands capable of generating open or labile coordination sites in the metallacyclobutadiene intermediate allows the exploration of the alkyne polymerization, mediated by metal alkylidynes. Trianionic pincer ligand s 111, 136,152 constrain three anionic donors in a meridional plane 262,263 and are capable of supporting high oxidation state metal complexes 167,264 bearing vacant coordination sites. 147 As such coordination of additional alkynes to a metallacyclobutadiene supported by a trianionic pincer should be feasible Herein we report the synthesis of the first group 6 idyne supported by an OCO 3 trianionic pincer ligand and its application towards polyalkyne synthesis. 5.2 Results and Discussion 5.2.1 Synthesis and C haracterization of [ t BuOCHO] 3 ) 3 (O t Bu) (THF) (5 1 ) A straightforward approach to making a trianionic pincer alkylidyne complex is to first synthesize the corresponding dianionic diphenolate alkylidyne with a suitable leaving group on the metal center. Judicious choice of base permits deprotonat ion of the backbone to pincer bond leaving the alkylidyne fragment intact. Alcoholysis between 1 equiv. of the commercially available ( t BuO) 3 t Bu ( 1 10 ) with terphenyl diol [ t BuOCO]H 3 ( 3 4 ) in THF results in the formation of [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) as a yellow crystalline s olid in 72% yield ( Figure 5 2 ). A distinct singlet in the 1 H NMR spectrum at 1.67 ppm for the eighteen t Bu protons of the OCO ligand suggests a C s t Bu protons of the alkylidyne fragment resonate at 0.86 ppm, and the t Bu protons of the alkoxide ligand appear as a broad signal at 1.49 ppm. Consistent with documented ex amples of metal

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145 complexes bearing a diphenolate, the C ipso H appears downfield at 8.74 ppm d 8 149,180 The protons of the coordinated THF appear at 3.17 and 0.99 ppm as broad resonances. The most salient feature in the 13 C{ 1 H} NMR spectrum is the resonance at 291.7 ppm for the alkylidyne carbon, which does not correlate to any protons in a gHMQC experiment. 5.2.2 Structural Description of [ t BuOCHO] 3 ) 3 (O t Bu) (THF) (5 1 ) Cooling a pentane solution of 5 1 at provides single crystals. Figure 5 3 depicts the results of a single crystal X ray diffraction experiment, in which complex 5 1 crystallizes in a P space group. The pincer ligand binds to the metal ion as a diphenolate. The complex is C s mmetric in the solid state and the 5 coordinate W(VI) = 0.85. 265 The pincer ligand chelates through the phenolate donors which comprises the equatorial sites with a bite angle of 135.65(9). A t BuO ligand completes the the equatorial plane. The THF molecule and the alkylidyne fragment occupy the axial sites with a near is longer than typical W(VI) CR fragments. 266,267 To the best of our knowledge the W(VI) ion; suc h bond elongation is attributable to the trans influence of the tungsten W 2 ( 2 2 CAr) 4 (THF) 2 (where Ar = p (OMe)C 6 H 4 ), 268

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146 imparts an even stronger trans Isolation of 5 1 is key to the realization of trianionic pincer sup ported metal alkylidynes. The reaction occurs at ambient temperature providing analytically pure product in 72% yield. This is a noteworthy improvement over our previous approach to attach the [ t BuOCO]H 3 ligand to (ArO) 2 ( t BuCH 2 t Bu and ( t BuCH 2 ) 3 t Bu. 177 The previous reactions were performed on an NMR scale, and high temperatures w ere required to drive the low yielding reaction. The most interesting achievement, however, is that 5 1 represents the first structurally characterized compound in which we have our ligand attached to the metal center in a dianionic form, with the W CR fr agment still intact. This is in stark contrast to our previous attempts, in which the alkylidyne functionality was lost upon metalation by forming alkylidenes. 5.2.3 Synthesis and Characterization of { [ t BuOCO] 3 ) 3 (O t Bu) }{PPh 3 CH 3 } (5 2 ) Schrock et al demonstrated the deprotonation of an alkylidene proton using triphenylphosphorane (PPh 3 =CH 2 ) as a mild base to generate anionic metal alkylidynes. 269 Our group utilized the same base to depronate the C ipso terphenyl diphenolate complex [ t BuOCHO]Mo(NAr)CHCMe 2 Ph to form { [ t BuOCO]Mo(NAr)(CHCMe 2 Ph)}{Ph 3 PCH 3 } as the corresponding trianionic pi ncer alkylidene s alt. 270 Similarly, treatment of 5 1 with 1 equiv. of triphenylphosphorane in Et 2 O at room temperat ure precipitates the corresponding trianionic pincer alkylidyne salt { [ t BuOCO] 3 ) 3 (O t Bu)}{PPh 3 CH 3 } ( 5 2 ) as a canary colored solid in 83% yield (Figure 5 4). Attempts to obtain single crystals of complex 5 2 have been unsuccessful. However a combination of 1 H, 13 C, 31 P, and correlation experiments using NMR

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14 7 spectroscopy and combustion analysis allows for its unambiguous identification. Two distinct resonances in the 13 C{ 1 H} NMR spectrum at 305.3 and 205.3 p pm identify the W C t pincer carbon, respectively. Complex 5 2 is the first trianionic pincer supported metal alkylidyne. A distinct singlet at 1.97 ppm for the eighteen t Bu protons of the OCO ligand suggests a C s symmetric species in solution. pincer t Bu, and W C t Bu bonds. The t Bu protons of the alkylidyne fragment appear upfield at 0.91 ppm, while the t Bu protons of the alkoxide ligand appear as a bro ad signal at 2.03 ppm. A doublet at 1.83 ppm ( J 1 P H = 12.8 Hz), which corresponds to the methyl group protons in the phosphonium cation, is another diagnostic feature. The 31 P{ 1 H} NMR spectrum reveals a singlet at 21.6 ppm which is consistent with documented examples such as { [ t BuOCO]Mo(NAr)(CHCMe 2 Ph)}{Ph 3 PCH 3 } 270 and {Mo(NAr)(CCMe 3 )( OCMe(CF 3 ) 2 ) 2 }{Ph 3 P CH 3 } 269 5.2.4 Synthesis and Characterization of [ t BuOC O] 3 ) 3 (Et 2 O) (5 3 ) Literature precedent demonstrates that strong electrophiles, such as alkyl triflate or alkyl tetrafluoroborate, react with anionic metal complexes bearing both imido and alkylidyne ligands to give neutral N alkylated complexes with the metal alkylidyne fragment intact. 269 In an analogous fashion, compound 5 3 reacts with 1 equiv. of methyl triflate in diethylether to form [ t 3 ) 3 (Et 2 O) ( 5 3 ) as an orange solid, concomitant with the formation of phosphonium triflate and tert butylmethyl ether. The 1 H NMR spectrum of the bulk material of 5 3 suggests the presence of excess phosphonium triflate, evident from the signature doublet for the methy l group of the phosphonium cation at 1.85 ppm ( J 1 P H = 12.8 Hz). Detailed inspection of the 1 H NMR spectrum reveals diagnostic resonances at 0.67 and 1.95 ppm, attributable to the

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148 alkylidyne and the t Bu protons of the ligand, respectively. This suggests a C s symmetric species in solution. Signals for the coordinated diethyl ether appear at 1.12 and 3.27 ppm, and the nine aromatic protons appear at 7.72, 7.67, 7.51, 7.05 and 6.69 ppm. 5.2.5 Structural Description of [ t BuOC O] 3 ) 3 (Et 2 O) (5 3 ) Single crystals amenable for X ray diffraction interrogation deposit from a concentrated Et 2 O solution of 5 3 6 represents the solid state molecular structure of complex 5 3 which crystallizes in the monoclinic space group P2(1)/n The solid state structural investigation reveals that the trianionic pincer ligand binds to the W(VI) ion in a terdentate meridional fashion. The complex is C s symmetric and the W(VI) ion is in a square pyramid al geometry, with a calculated Addison parameter ( ) of 0.14. 265 The basal plane contains the trianionic pincer and a coordina ted ether molecule. The bond angles in the basal plane comprise of The W(VI) ion resides 0.486 above the basal plane containing the O1 O3 O12 C12 atoms. The 2 O is rather weakly bound to the ond length of 2.185(2) The closest complex to compare is W(OAr) 4 Cl(Et 2 O), 271 (Ar = 2,6 Cl 2 C 6 H 3 ), in which the W(V) OEt 2 bond length is 2.104(13) 5.2.6 Synthesis and Characterization of [ t BuOC O] 3 ) 3 (THF) 2 (5 4 )

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149 Access to a phosphonium triflate free tungsten alkylidyne complex 5 4 is possible via a modified route illustrated in Figure 5 7. Addition of 0.1 mL THF to ether containing crude mixture of 5 4 allows for selective dissolution of the tungsten complex over the phosphonium salt. Excess phosphonium triflate is removed by fil tration, and cooling of the filtrate overnight provides analytically pure [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) as a dark red crystalline material. A combination of 1 H and 13 C NMR spectroscopy along with combustion analysis allows for unambiguous identification o f 5 4 Broad signals in the 1 H NMR spectrum at 4.07, 3.40, 1.45 and 1.16 ppm, each integrating to four protons, indicate that two symmetrically different THF molecules coordinate to the W(VI) metal ion. Distinct resonances for the t Bu and alkylidyne protons appear at 1.65 and 0.61 ppm, respectively, suggesting a C s in the 13 C { 1 H} NMR spectrum represents the W C t Bu carbon, and a resonance at pi ncer suggesting the formation of a trianionic pincer supported metal alkylidyne complex. 5.2.7 Structural Description of [ t BuOCO] 3 ) 3 (THF) 2 (5 4) Complex 5 4 crystallizes from an ether solution at 35 C in the Pna2 1 space group. Unlike 5 3 the tungsten center now holds two coordinated THF molecules with bond lengths W1 O4 = 2.473(2) and W1 O3 = 2.177(2) This suggests that the alkylidyne ligand imparts a stronger trans influence than the aryl M C bond. The pincer ligand is bound in it s trianionic form and the phenoxide donors span a bite angle (O1 W1 O2) of 153.47(10) and the W1 C pincer bond length is 2.132(3) To coordinate in a meridional fashion considerable strain is imparted to the pincer backbone. As such, the central ring i s twisted away from planarity of the terphenyl motif

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150 creating dihedral angles of C5 C6 C7 C8 = 39.56(5) and C3 C2 C17 C22 = 22.12(5) t Bu bond length of 1.759(4) is cons istent with a documented example such as (ArO) 2 ( t BuCH 2 t Bu, in which the t Bu bond length is 1.755(2) 88 5.2.8 Polymerization of A lkynes using [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) Figure 5 9 illustrates a route to synthesize poly(phenylacetylenes) (PPA). A typical polymerization reaction involves addition of the catalyst 5 4 to a stirring solution of monomer in toluene. After stirring for 30 min at 25 C, the reaction is quenched with methanol forming a deep orange solid. Filtering the solution through a medium porosity includes 1 H and 13 C NMR, and FTIR. Table 5 1 summarizes the polymeriza tion results. Typically, the monomers absorb infrared radiation at approximately 3300 and 2100 cm 1 attributable to the stretching vibrations of C bonds, respectively. These IR bands decrease beyond detection as the reaction progresses and a new band appears at approximately 1595 cm 1 223 The 1 H NMR spectra of the polymers in CDCl 3 reveals broad resonances centered at 6.7 and 5.8 ppm, indicating the presence of ( C H =C Ph ) n units. 272 5.3 Experimental Section 5.3.1 General Considerat ions Unless specified otherwise, all manipulations were performed under an inert atmosphere using glove box techniques. Tetrahydrofuran (THF), pentane, diethyl ether (Et 2 O), and toluene were dried using a GlassContour drying column. C 6 D 6 (Cambridge Isoto pes) was dried over sodium benzophenone ketyl, distilled or vacuum transferred

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151 and stored over 4 molecular sieves. CDCl 3 (Cambridge Isotopes) was dried over anhydrous CaCl 2 vacuum transferred, and stored over 4 molecular sieves. ( t BuO) 3 3 ) 3 wa s purchased from Strem Chemicals Inc. and used as received or synthesized according to literature procedures. 91 Methyl triflate (MeOTf) was purchased from TCI Chemicals and used as received. [ t BuOCO]H 3 and Ph 3 P=CH 2 w ere p repared according to literature procedures. 152,269 Phenyl acetylene 4 methoxyphenyl acetylene, and 4 f luorophenylacetylene were purchased from Sigma Aldrich, degassed, dried over activated 4 molecular sieves, and filtered through a basic alumina column prior to use. NMR spectra were obtained on Varian Mercury 300 MHz, Varian Mercury Broad Band 300 MHz, (ppm). For 1 H and 13 C NMR spectra, the residual solvent peak s were used as an internal reference. FT IR spectra were recorded on a Thermo scientific instrument. 5.3. 2 Synthesis of [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) In a nitrogen filled glove box a glass vial was charged with [ t BuOCO]H 3 ( 3 4 ) (140 mg, 0.37 mmol) in THF(1 ( t BuO) 3 3 ) 3 ( 1 10 ) (200 mg, 0.42 mmol) was dissolved in THF (1 mL) and added dropwise to the first solution while stirring. As the solution warmed to room temperature a gradual color change from brown to dark yellow was observed and the stirring was continued for 30 min at room temperature. A dark yellow tacky m aterial was obtained after removing all volatiles. As cold pentane (4 mL) was added, a bright yellow material precipitated from a brown suspension. Product 5 1 was filtered immediately and washed with additional cold pentane. Single crystals were obtain ed by h ; y ield (206 mg, 72%). 1 H NMR (300 MHz, C 6 D 6 (ppm) ) : 8.94 (s, tol d 8 65 C, C ipso H ), 7.46 (d, J = 7.8 Hz, 4H, Ar H ),

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152 7.33 7.27 (m, 4H, Ar H ), 6.96 (t, J = 8 .0 Hz, 2H, Ar H ), 3.43(m, 4H, OCH 2 C H 2 / THF ), 1.67 (s, 18H, C(C H 3 ) 3 ), 1.49 (bs, 9H, OC(C H 3 ) 3 ), 1.29 (m, 4H, OC H 2 CH 2 / THF ), 0.86 (s, 9H, H 3 ) 3 ). 13 C{ 1 H} NMR (75.36 M Hz, C 6 D 6 ) : 297.1 (s, C C(CH 3 ) 3 ), 165.2 (s C aromatic), 144.8 (s C aromatic) 138.0 (s C aromatic) 130.5 (s C aromatic) 127.5 (s C aromatic) 126.9 (s C aromatic) 121.7 (s C aromatic), 80.7 (s, O C (CH 3 ) 3 C (CH 3 ) 3 ), 35.7 (s, C (CH 3 ) 3 ), 32.9 (s, C H 3 ) 3 ), 32.2 (s, OC( C H 3 ) 3 ), 31.3 (s, C( C H 3 ) 3 ). Anal. Calcd for C 35 H 46 O 3 W: C, 60.18; H, 6.64. Found: C, 59.76, H, 6.74. 5.3. 3 Synthesis of {[ t BuOCO] 3 ) 3 (O t Bu)}{Ph 3 PCH 3 } ( 5 2 ) A glass vial was charged with [ t BuOCHO] 3 ) 3 (O t Bu)(THF) ( 5 1 ) (206 mg, 0.267 mmol) and Et 2 O (1 mL) and then frozen ( 35 C). Ph 3 P=CH 2 (74 mg, 0.267 mmol) was dissolved in Et 2 O (0.5 mL) and was then added to the cold solution of 5 2 The resulting mixture was warmed to 2 5 C and the solution color changed from dark yellow to canary yellow. As the solution was stirred for 45 min at room temperature the product 5 2 precipitated as a yellow solid. The product was collected by filtration, and the crude compound was washed with pentanes (3 x 1 mL) ; y ield (216 mg, 83%). 1 H NMR (500 MHz, C 6 D 6 (ppm) ) : 7.77 (d, J = 7.2 Hz, 2H, Ar H ), 7.52 (t, J = 7.2 Hz, 4H, Ar H ), 7 .04 (d, J = 7.3 Hz, 2H, Ar H ), 6.96(t, J = 7.9 Hz, 3H, Ar H ), 6.84 (dt, J = 2.5 Hz, J = 7.7 Hz, 6H, Ar H ), 6.78 (t, J = 7.3 Hz, 1H, Ar H ), 6.58(d, J = 7.9 Hz, 3H, Ar H ), 6.55(d, J = 7.7 Hz, 3H, Ar H ), 2.03 (s, 9H, OC(C H 3 ) 3 ), 1.97 (s, 18H, C(C H 3 ) 3 ), 1.83 (d, J PH = 12.8 Hz, 3H, P C H 3 ), 0.91 (s, 9H, H 3 ) 3 ). 13 C{ 1 H} NMR ( 126 M Hz, C 6 D 6 (ppm) ) C C(CH 3 ) 3 ), 205.3 ( s, W C ipso ), 164.8 (s C aromatic) 143.1 (s C aromatic) 137.2, 135.2 (d, J CP = 2.7 Hz C aromatic ), 133.1 (d, J CP = 10.1 Hz C aromatic ), 130.7 (d, J CP = 12.8 Hz C aromatic ), 127.9 (s C aromatic) 124.7 (s C

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153 aromatic) 124.4 (s C aromatic) 124.0 (s C aromatic) 119.6 (s C aromatic) 118.5 ( d, J CP = 7.3 Hz, C aromatic ), 76.2 (s, O C (CH 3 ) 3 ), 50.2 C (CH 3 ) 3 ), 36.5 (s, C (CH 3 ) 3 ), 34.9 ( OC( C H 3 ) 3 C H 3 ) 3 ), 31.8 (s, C( C H 3 ) 3 ), 9.1 ( d, J CP = 6.7 Hz) 31 P{ 1 H} NMR (121M Hz, C 6 D 6 ) : 21.6. Anal. Calcd for C 54 H 63 O 3 PW: C, 66.53; H, 6.51. Found: C, 66.57, H, 6.51. 5.3. 4 Synthesis of [ t BuOCO] 3 ) 3 (Et 2 O) (5 3) A glass vial was charged with {[ t BuOCO] 3 ) 3 (O t Bu)}{Ph 3 PCH 3 } ( 5 2 ) (118 mg, 0.121 mmol) and Et 2 O (1 mL) and then frozen ( 35 C). MeOTf 0.121 mmol ) was dissolved in Et 2 O (0.5 mL) and was then added dropwise to the cold suspension of 5 2 The resulting mixture was warmed to 2 5 C, and stirred until the solution color changed from canary yellow to dark orange. After stirring the solution for 1 h phosphonium triflate prec ipitates as a white solid which was removed via filtration. All volatiles were removed from the solution and the resulting orange solid was triturated with pentane. Single crystals were obtained by cooling a dilute diethyl ether solution at d ; y ield (56 mg, 66%). 1 H NMR (300 MHz, C 6 D 6 (ppm) ) : 7.72 (d, J = 6 .0 Hz, 2H, Ar H ), 7.67 (d, J = 6 .0 Hz, 2H, Ar H ), 7.51 (d, J = 6 .0 Hz, 2H, Ar H ), 7.05 (t, J = 6 .0 Hz, 1H, Ar H ), 6.69 (t, J = 6 .0 Hz, 2H, Ar H ), 3.27 (q, J = 6 .0 Hz, 4H, OC H 2 CH 3 /Et 2 O ), 1.95 (s, 18H, C(C H 3 ) 3 1.12 (t, J = 6 Hz, 6H, OCH 2 C H 3 /Et 2 O ), 0.67 (s, 9H, H 3 ) 3 ). 5.3.5 Synthesis of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) A glass vial was charged with [ t BuOCO] 3 ) 3 (Et 2 O) ( 5 3 ) (115 mg, 0.164 mmol) and in Et 2 O (5 mL) to provide an orange suspension. THF (0.1 mL) was added to precipitate phosphoniumtriflate as a white solid. The solution was filtered and

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154 compound 5 4 as a d ark red crystalline material; yield ( 100 mg, 78 %). 1 H NMR (500 MHz, C 6 D 6 (ppm) ) : 8.00 (d, J = 7. 4 Hz, 2H, Ar H ), 7. 84 ( d J = 8.5 Hz, 2 H, Ar H ), 7. 46 (d, J = 7.9 Hz, 2H, Ar H ), 7.35 (t, J = 8.5 Hz, 1 H, Ar H ), 7.05 ( t J = 7. 5 Hz, 2 H, Ar H ), 4.07 ( br 4 H, OC H 2 CH 2 /THF ), 3.40 ( br 4 H, C H 2 CH 2 /THF ) 1. 65 (s, 18H, C(C H 3 ) 3 ), 1.45(br 4 H, OC H 2 C H 2 /THF ) 1.16( br 4 H, OC H 2 C H 2 /THF ) 0. 6 1 (s, 9H, H 3 ) 3 ). 13 C{ 1 H} NMR ( 126 M Hz, C 6 D 6 ) : 320.7 ( s C C(CH 3 ) 3 ), 193.5 ( s, W C ipso ) 163.1 (s C aromatic) 139.2 (s C aromatic), 135.4 (s C aromatic) 134.5 (s C aromatic) 128.0 (s C aromatic) 126.4 (s C aromatic) 125.3 (s C aromatic) 124.3 (s C aromatic) 119.9 (s C aromatic) 76.8 (s O C H 2 C H 2 /THF ) 67.3 (s O C H 2 C H 2 /THF ) 48.6 C (CH 3 ) 3 ) 35.3 (s, C (CH 3 ) 3 ) 32.5 C H 3 ) 3 ) 30.6 (s, C( C H 3 ) 3 ) 25.6 (s O C H 2 C H 2 /THF ) 24.9 (s O C H 2 C H 2 /THF). Anal. Calcd for C 39 H 52 O 4 : C, 60.94 ; H, 6. 82 Found: C, 60.88 H, 6. 87 5.3. 6 General Procedure for Polymerization Reactions In a nitrogen filled glove box a stock solution of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) ( 0.2 mol ) in toluene (50 L) was added to a dried phenyl acetylene monomer ( 1000 mol ) The mixture was allowed to stir at room temperature for 30 min The reaction mixture was removed from the glove box and quenched with methanol (20 mL). The polymeric material was collected by filtration and dried under vacuum at 80 C for 2 h prior to weighing to obtain the yield 5.3. 7 X Ray E xperimental Details for [ t 3 ) 3 (O t Bu)(THF) (5 1) X Ray Intensity data were collected at 100 K on a Bruker SMART diffractometer using MoK radiation ( = 0.71073 ) and an APEXII CCD area detector. Raw data frames were analyzed by program SAINT and integrated using 3D profiling algorith ms. Reducing t he resulting data produced the hkl reflections and their corresponding

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155 intensities and estimated standard deviations. The data were corrected for Lorentz and polarization effects and numerical absorption corrections were applied based on in dexed and measured faces. The structure was solved and refined in SHELXTL6.1, 151 using full matrix least square refinement s The non H atoms were refined with anisotropic thermal parameters and all of t he H atoms were calculated in idealized positions and refined riding on their parent atoms. A small electron density peak near the C23 t Bu group could not be attributed to any reasonable disorder. In the final cycle of refinement, 8054 reflections (of wh ich 7347 are observed with I > 2 (I)) were used to refine 409 parameters and the resulting R 1 wR 2 and S (goodness of fit) were 2.54 %, 5.37 % and 1.060 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 wa s calculated to provide a reference to the conventional R value but its function wa s not minimized. 5.3. 8 X ray E xperimental Details for [ t BuOCO] 3 ) 3 (Et 2 O) (5 3) X Ray Intensity data were collected at 100 K on a Bruker DU O diffractometer using MoK radiation ( = 0.71073 ) and an APEXII CCD area detector. Raw data frames were analyzed by program SAINT and was integrated using 3D profiling algorithms. Reducing t he resulting data produced the hkl reflections and their corresponding intensities and estimated standard deviations. The data were corrected for Lorentz and polarization effects and numerical absorption corrections were applied based on indexed and measured faces. The structure was solved and refined in SHEL XTL6.1, 151 using full matrix least squares refinement. The non H atoms were refined with anisotropic thermal

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156 parameters and all of the H atoms were calculated in idealized positions and refined riding on their parent atoms. There are two disordered regions in the complex. In one, the three methyl groups on C28 were refined in two parts. The other part includes the disordered coordinated ether ligand. In each case, the site occupation factors of related parts were dependently refined. In the final cycle of refinement, 7070 reflections (of which 5138 are observed with I > 2 (I)) were used to refine 349 parameters and the resulting R 1 wR 2 and S (goodness of fit) were 2.62 %, 4.94 % and 0.912 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 was calculated to provide a reference to the conventional R value but its function was not minimized. 5.3. 9 X ray E xperimental Details for [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) X Ray Intensity data were collected at 100 K on a Bruker DUO diffractometer using MoK radiation ( = 0.71073 ) and an APEXII CCD area detector. Raw data frames were analyzed by the program SAINT and integrated using 3D profiling algorithms. Reducing t he resulting data produced the hkl reflections and their corresponding intensities and estimated standard deviations The data were corrected for Lorentz and polarization effects and numerical absorption corrections were applied based on index ed and measured faces. The structure was solved and refined in SHELXTL6.1, 151 using the full matrix least square refinements. The non H atoms were refined with anisotropic thermal parameters and all of the H atoms were calculated in idealized positions and refined riding on their parent atoms. In the final cycle of refinement, 8159 reflections (of which 7035 are observed with I > 2 (I)) were used to refine 406 parameters and the resulting

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157 R 1 wR 2 and S (goodness of fit) were 2.18 %, 4.69 % and 0.952 respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 was calculated to provide a reference to the conventional R value but its function was not minimized. 5.4 Conclusions For the first time, we provide the blue print to synthesize a trianionic pincer supported metal alkylidyne. The multistep synthetic scheme initiates with successful attachment of the pincer liga nd precursor to the metal center, while keeping the alkylidyne fragment intact to form [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) In the following step a mild base such as triphenylphosphorane, deprotonates the C ipso proton to generate the anionic pincer sup ported alkylidyne { [ t BuOCO] 3 ) 3 (O t Bu)}{PPh 3 CH 3 } ( 5 2 ). Addition of methyltriflate to 5 2 in Et 2 O provides the corresponding neutral complex [ t BuOCO] 3 ) 3 (Et 2 O) ( 5 3 ) as part of an interactable mixture containing phosphonium triflate. However, addition of THF displaces the Et 2 O ligand in 5 3 thus subtly changing the solubiity and allowing isolation of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) in high yield and purity. Complex [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) is a highly active catalyst for polymerization of phenyl acetylenes. Compared to other literature precedence of metal alkylidyne catalyzed polymerization of acetylenes, 5 4 is the best to date, with activity as high as 1,050 ,000 g(mol cat) 1 This result is a proof of concept, to utilize a constrained geometry metal alkylidyne to improve alkyne polymerization. In addition, the tridentate trianionic pincer ligand renders stability to the catalyst, and is reflected in a high turn over number (TON)>4,000. Future studies require exploration of the polymerization reaction with: ( a) disubstituted acetylenes; and ( b) monomers containing functional

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158 groups such as OH, NO 2 CO 2 H, and N 3 which could allow post synthetic modificatio n of the polymers. 273,274 Table 5 1. Polymerization of alkynes using [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) Substrate Substrate :Catalyst Yield (%) Activity (g PPA(mol cat) 1 ) TON Phenyl acetylene 5000 66 670,000 3,280 4 Fluorophenyl acetylene 5000 87 1,050,000 4,371 4 Methoxyphenyl acetylene 5000 47 620,000 2,346 Figure 5 1. Ring expansion mechanism for poly acetylene formation using metal alkylidynes Figure 5 2. Synthesis of [ t 3 ) 3 (O t Bu)(THF) ( 5 1 )

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159 Figure 5 3. Solid state molecular structure of [ t BuOCHO] 3 ) 3 (O t Bu)(THF) ( 5 1 ). The hydrogen atoms except H 12a, are omitted for clarity. Figure 5 4. Synthesis of { [ t BuOCO] 3 ) 3 (O t Bu)}{PPh 3 CH 3 } ( 5 2 ) Figure 5 5. Synthesis of [ t 3 ) 3 (Et 2 O) ( 5 3 )

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160 Figure 5 6. Solid state molecular structure of [ t 3 ) 3 (Et 2 O) ( 5 3 ) The hydrogen atoms are omitted for clarity. Figure 5 7. Synthesis of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 )

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161 Figure 5 8. Solid state molecular structure of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) The hydrogen atoms are omitted for clarity. Figure 5 9. General polymerization reaction with [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 )

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162 Figure 5 10. 1 H NMR spectrum of [ t 3 ) 3 (O t Bu)(THF) ( 5 1 ) in C 6 D 6

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163 Figure 5 11. 1 H NMR spectrum of {[ t BuOCO] 3 ) 3 (O t Bu)}{Ph 3 PCH 3 } ( 5 2 )

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164 Figure 5 12. 1 H NMR spectrum of crude [ t BuOCO] 3 ) 3 (Et 2 O) ( 5 3 ) and {PPh 3 CH 3 }{OTf}

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165 Figure 5 13. 1 H NMR spectrum of [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) in C 6 D 6

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166 APPENDIX CRYSTAL DATA AND REF INEMENT PARAMETER Table A 1. Data and refinement for {3,5 Me 2 NCHNLi 2 (THF) 2 } 2 ( 2 14 ) I dentification code ss04 empirical formula C 64 H 84 Li 4 N 4 O 4 formula weight 1001.11 T (K) 173(2) 0.71073 crystal system Tetragonal space group I a () 14.6408(12) b () 14.6408(12) c () 13.991(2) (deg) 90 (deg) 90 (deg) 90 V ( 3 ) 2999.1(6) Z 2 calcd (Mg mm 3 ) 1.109 crystal size (mm 3 ) 0.24 x 0.22 x 0.17 abs coeff (mm 1 ) 0.067 F (000) 1080 range for data collection 1.97 to 27.48 limiting indices h k no. of reflns collcd 5847 no. of ind reflns ( R int ) 3104 (0.0473) completeness to = 27.50 94.8 % absorption corr Analytical refinement method Full matrix least squares on F 2 data / restraints / parameters 3104/ 0 / 166 R 1, a wR 2 b 0.0555, 0.1362[1848] R 1, a wR 2 b (all data) 0.0988, 0.1531 GOF c on F 2 0.903 largest diff. peak and hole 0.154 and 0.151 e 3

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167 Table A 2. Data and refinement for [3,5 MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 2 15 ) I dentification code ss05 empirical formula C 72 H 110 Li 6 N 4 O 12 formula weight 1265.28 T (K) 173(2) 0.71073 crystal system Tetragonal space group P 2 1 c a () 15.3065(5) b () 15.3065(5) c () 16.118(1) (deg) 90 (deg) 90 (deg) 90 V ( 3 ) 3776.3(3) Z 2 calcd (Mg mm 3 ) 1.113 crystal size (mm 3 ) 0.34 x 0.20 x 0.11 abs coeff (mm 1 ) 0.073 F (000) 1368 range for data collection 1.83 to 27.50 limiting indices h k no. of reflns collcd 24967 no. of ind reflns ( R int ) 4331 (0.0853) completeness to = 27.50 100.0 % absorption corr None refinement method Full matrix least squares on F 2 data / restraints / parameters 4331/ 0 / 277 R 1, a wR 2 b 0.0493, 0.1221 R 1, a wR 2 b (all data) 0.0860, 0.1384 GOF c on F 2 0.943 largest diff. peak and hole 0.154 and 0.151 e 3

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168 Table A 3. Data and refinement for [(3,5 MeNCN) 2 Hf][Li 2 (DME) 2 ] ( 2 16 ) I dentification code ss06 empirical formula C 56 H 70 HfLi 2 N 4 O 4 formula weight 1055.53 T (K) 173(2) 0.71073 crystal system Monoclinic space group P2(1)/m a () 39.443(4) b () 16.5027(17) c () 16.2419(17) (deg) 90 (deg) 98.916(2) (deg) 90 V ( 3 ) 10444.5(19) Z 8 calcd (Mg mm 3 ) 1.343 crystal size (mm 3 ) 0.20 x 0.17 x 0.08 abs coeff (mm 1 ) 2.045 F (000) 4352 range for data collection 1.34 to 27.50 limiting indices h k no. of reflns collcd 66794 no. of ind reflns ( R int ) 23838 (0.0736) completeness to = 27.50 99.4 % absorption corr Integration refinement method Full matrix least squares on F 2 data / restraints / parameters 23838/ 0 / 1207 R 1, a wR 2 b [I > 0.0422, 0.0660 R 1, a wR 2 b (all data) 0.0933, 0.0736 GOF c on F 2 0.868 largest diff. peak and hole 1.575 and 1.308 e 3

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169 Table A 4. Data and refinement for [2,6 i PrNCHN]Zr(NMe 2 ) 2 ( 2 18 ) identification code ss46 empirical formula C 36 H 54 N 4 Zr formula weight 634.05 T (K) 173(2) 0.71073 crystal system Triclinic space group P a () 8.2682(14) b () 12.2632(16) c () 18.800(4) (deg) 107.72(2) (deg) 91.20(2) (deg) 108.229(19) V ( 3 ) 1710.4(5) Z 2 calcd (Mg mm 3 ) 1.231 crystal size (mm 3 ) 0.258 x 0.247 x 0.092 abs coeff (mm 1 ) 0.350 F (000) 676 range for data collection 1.15 to 27.50 limiting indices h k l no. of reflns collcd 12504 no. of ind reflns ( R int ) 7445(0.1286) completeness to = 27.50 94.9 % absorption corr None refinement method Full matrix least squares on F 2 data / restraints / parameters 7445 / 0 / 374 R 1, a wR 2 b 0.0337, 0.0950[7081] R 1, a wR 2 b (all data) 0.0353, 0.0966 GOF c on F 2 1.043 largest diff. peak and hole 0.768 and 0.732 e. 3

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170 Table A i PrNCNHfMe 2 ][Li(DME) 2 ] ( 2 20 ) I dentification code ss50 empirical formula C 46 H 77 HfLiN 2 O 6 formula weight 939.53 T (K) 100(2) 0.71073 crystal system Monoclinic space group P2(1)/n a () 11.2841(13) b () 20.515(2) c () 20.880(2) (deg) 90 (deg) 90.893(2) (deg) 90 V ( 3 ) 4833(1) Z 4 calcd (Mg mm 3 ) 1.291 crystal size (mm 3 ) 0.30 x 0.17 x 0.13 abs coeff (mm 1 ) 2.203 F (000) 1960 range for data collection 1.95 to 27.50 limiting indices h k l no. of reflns collcd 68129 no. of ind reflns ( R int ) 11108(0.0223) completeness to = 27.50 100.0% absorption corr Numerical refinement method Full matrix least squares on F 2 data / restraints / parameters 11108 / 0 / 521 R 1, a wR 2 b 0.0182, 0.0443[10208] R 1, a wR 2 b (all data) 0.0211, 0.0464 GOF c on F 2 1.027 largest diff. peak and hole 1.116 and 0.763 e. 3

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171 Table A 6. Data and refinement for [ t BuOCO]Mo(OTf)(NHMe 2 ) 2 ( 3 7 ) I dentification code ss64 empirical formula C 31 H 41 F 3 MoN 2 O 5 S formula weight 706.66 T (K) 100 (2) 0.71073 crystal system Triclinic space group P a () 1 3 393(3) b () 14. 476(3) c () 18 732(4) (deg) 105.484(4) (deg) 108.430(4) (deg) 92.442(4) V ( 3 ) 3288.2(12) Z 4 calcd (Mg mm 3 ) 1.427 crystal size (mm 3 ) 0.1 2 x 0.1 1 x 0. 09 abs coeff (mm 1 ) 0.519 F (000) 1464 range for data collection 1.60 to 27.50 limiting indices 1 7 h 7 1 8 k 8 24 24 no. of reflns collcd 57398 no. of ind reflns ( R int ) 15094 (0.03 3 7) completeness to = 27.50 99.8 % absorption corr Numerical refinement method Full matrix least squares on F 2 data / restraints / parameters 15094 / 0 / 811 R 1, a wR 2 b [I > 0.02 66 0.0 562 [ 11452 ] R 1, a wR 2 b (all data) 0.0 436 0.0 592 GOF c on F 2 0.925 largest diff. peak and hole 0. 716 and 0. 525 e 3

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172 Table A 7 Data and refinement for [ t BuOCO]Mo(NCO)(NHMe 2 ) 2 ( 3 8 ) I dentification code ss63 empirical formula C 35 H 51 MoN 3 O 5 S formula weight 693.73 T (K) 100 (2) 0.71073 crystal system Triclinic space group P a () 8.9635(9) b () 17.7147(18) c () 23.171(2) (deg) 70.470(2) (deg) 89.980(2) (deg) 82.557(2) V ( 3 ) 3434.7(6) Z 4 calcd (Mg mm 3 ) 1.342 crystal size (mm 3 ) 0.1 5 x 0.1 0 x 0. 05 abs coeff (mm 1 ) 0.427 F (000) 1464 range for data collection 1.78 to 27.50 limiting indices 1 1 h 1 22 k 22 30 30 no. of reflns collcd 48464 no. of ind reflns ( R int ) 15770 (0.0 592 ) completeness to = 27.50 99.2 % absorption corr Numerical refinement method Full matrix least squares on F 2 data / restraints / parameters 15770 / 0 / 832 R 1, a wR 2 b 0.0 415 0.0 925 [ 8974 ] R 1, a wR 2 b (all data) 0.0 859 0. 1010 GOF c on F 2 0.845 largest diff. peak and hole 0. 806 and 0. 865 e 3

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173 Table A 8 Data and refinement for [ t 2 )(DMF) ( 3 9 ) I dentification code ac12 empirical formula C 42 H 5 3 MoN 2 O 2 Cl formula weight 749.25 T (K) 173 (2) 0.71073 crystal system Orthorhombic space group P bcn a () 10.4875(8) b () 17.2088(13) c () 21.1554(15) (deg) 90 (deg) 90 (deg) 90 V ( 3 ) 38818(5) Z 4 calcd (Mg mm 3 ) 1.303 crystal size (mm 3 ) 0.1 5 x 0. 08 x 0. 08 abs coeff (mm 1 ) 0.450 F (000) 1576 range for data collection 1.93 to 27.50 limiting indices 1 3 h 0 22 k 21 27 25 no. of reflns collcd 24328 no. of ind reflns ( R int ) 4392 (0.0 493 ) completeness to = 27.50 99.9 % absorption corr Integration refinement method Full matrix least squares on F 2 data / restraints / parameters 4392 / 0 / 223 R 1, a wR 2 b 0.0 263 0.0 771 [ 3320 ] R 1, a wR 2 b (all data) 0.0 386 0. 0804 GOF c on F 2 1.241 largest diff. peak and hole 0. 331 and 0. 380 e 3

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174 Table A 9 Data and refinement for {[ t 2 )Na(DMF)} 2 ( 3 10 ) I dentification code ss12 empirical formula C 31 H 40 MoN 3 O 3 Na formula weight 621.59 T (K) 173(2) 0.71073 crystal system Monoclinic space group P2(1)/n a () 14.1177(10) b () 14.6884(10) c () 15.0127(10) (deg) 90 (deg) 100.867(1) (deg) 90 V ( 3 ) 3057.3(4) Z 4 calcd (Mg mm 3 ) 1.350 crystal size (mm 3 ) 0.14 x 0.12 x 0.12 abs coeff (mm 1 ) 0.478 F (000) 1296 range for data collection 1.82 to 27.50 limiting indices h k no. of reflns collcd 20387 no. of ind reflns ( R int ) 7017 (0.0317) completeness to = 27.50 100.0 % absorption corr Integration refinement method Full matrix least squares on F 2 data / restraints / parameters 7017/ 0 / 354 R 1, a wR 2 b [I > 0.0270, 0.0662 [5783] R 1, a wR 2 b (all data) 0.0377, 0.0695 GOF c on F 2 1.029 largest diff. peak and hole 0.419 and 0.308 e 3

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175 Table A 10 Data and refinement for [ t 2 ) ( 3 12 ) I dentification code ss 33 empirical formula C 62 H 76 Mo 2 N 4 O 4 Cl 2 formula weight 1204.05 T (K) 173(2) 0.71073 crystal system Monoclinic space group P2(1) /c a () 14. 2293 (1 5 ) b () 15.8373(17) c () 26.137(3) (deg) 90 (deg) 94.965(2) (deg) 90 V ( 3 ) 5868.0(11) Z 4 calcd (Mg mm 3 ) 1.363 crystal size (mm 3 ) 0. 25 x 0. 11 x 0.0 2 abs coeff (mm 1 ) 0. 567 F (000) 2504 range for data collection 1.44 to 27.50 limiting indices 1 4 h 8 20 k 20 3 33 no. of reflns collcd 37536 no. of ind reflns ( R int ) 13435 (0. 0699 ) completeness to = 27.50 99.6% absorption corr Integration refinement method Full matrix least squares on F 2 data / restraints / parameters 13435 / 0 / 683 R 1, a wR 2 b 0.0 392 0. 0784 [ 9996 ] R 1, a wR 2 b (all data) 0. 0633 0. 0858 GOF c on F 2 0. 975 largest diff. peak and hole 0. 528 and 0.715 e 3

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176 Table A 11 Data and refinement for [ t BuOCO]Mo=NC(O) t Bu(NMe 2 )(DMF) ( 3 13 t Bu ) I dentification code ss45 empirical formula C 76 H 108 Mo 2 N 6 O 9 formula weight 1441.56 T (K) 173(2) 0.71073 crystal system Orthorhombic space group Pca2(1) a () 14.3169(17) b () 29.023(3) c () 18.438(2) (deg) 90 (deg) 90 (deg) 90 V ( 3 ) 7661.6(15) Z 4 calcd (Mg mm 3 ) 1.250 crystal size (mm 3 ) 0.26 x 0.18 x 0.01 abs coeff (mm 1 ) 0.384 F (000) 3048 range for data collection 0.70 to 25.00 limiting indices h k no. of reflns collcd 41691 no. of ind reflns ( R int ) 12108 (0.1632) completeness to = 27.50 99.4 % absorption corr Integration refinement method Full matrix least squares on F 2 data / restraints / parameters 12108/ 2 / 804 R 1, a wR 2 b 0.0710, 0.1666 [5483] R 1, a wR 2 b (all data) 0.1412, 0.1949 GOF c on F 2 0.866 largest diff. peak and hole 0.826 and 2.545 e 3

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177 Table A 12 Data for [ t BuOCHO]W( NMe)( NMe 2 )( CH)W[OCHO t Bu] ( 4 6 ) I dentification code adam empirical formula C 56 H 68 N 2 O 4 W 2 formula weight 1276.92 T (K) 100(2) 0.71073 crystal system Triclinic space group P a () 12.6185(7) b () 12.6932(6) c () 18.1297(9) (deg) 102.523(1) (deg) 96.866(1) (deg) 105.512(1) V ( 3 ) 2682.4(2) Z 2 calcd (Mg mm 3 ) 1.581 crystal size (mm 3 ) 0.19 x 0.09 x 0.08 abs coeff (mm 1 ) 4.334 F (000) 1276 range for data collection 1.72 to 27.50 limiting indices h k l no. of reflns collcd 24345 no. of ind reflns ( R int ) 11424 (0.0179) completeness to = 27.50 92.5 % absorption corr Analytical refinement method Full matrix least squares on F 2 data / restraints / parameters 11424 / 0 / 628 R 1, a wR 2 b 0.0174, 0.0438 [10621] R 1, a wR 2 b (all data) 0.0194, 0.0447 GOF c on F 2 1.037 largest diff. peak and hole 0.913 and 0.742 e. 3

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178 Table A 13 Data and refinement for [ t BuOCHO] 3 ) 3 (O t Bu)(THF) ( 5 1 ) I dentification code ss72 empirical formula C 39 H 54 O 4 W formula weight 770.67 T (K) 100(2) 0.71073 crystal system Triclinic space group P a () 10.2871(2) b () 11.2440(2) c () 17.2488(3) (deg) 79.010(1) (deg) 84.608(1) (deg) 63.709(1) V ( 3 ) 1755.84(6) Z 2 calcd (Mg mm 3 ) 1.458 crystal size (mm 3 ) 0.29 x 0.05 x 0.02 abs coeff (mm 1 ) 3.783 F (000) 788 range for data collection 2.05 to 27.50 limiting indices no. of reflns collcd 29784 no. of ind reflns ( R int ) 8054 [R(int) = 0.0491] completeness to = 27.50 100.0 % absorption corr Numerical refinement method Full matrix least squares on F 2 data / restraints / parameters 8054 / 0 / 409 R 1, a wR 2 b R1 = 0.0254, wR2 = 0.0537 [7347] R 1, a wR 2 b (all data) R1 = 0.0300, wR2 = 0.0547 GOF c on F 2 1.060 largest diff. peak and hole 1.395 and 1.602

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179 Table A 14 Data and refinement for [ t 3 ) 3 (Et 2 O) ( 5 3 ) I dentification code ss73 empirical formula C 35 H 46 O 3 W formula weight 698.57 T (K) 100(2) 0.71073 crystal system Monoclinic space group P2(1)/n a () 11.2257(12) b () 18.630(2) c () 14.8896(16) (deg) 90 (deg) 98.466(2) (deg) 90 V ( 3 ) 3079.9(6) Z 4 calcd (Mg mm 3 ) 1.507 crystal size (mm 3 ) 0.14 x 0.09 x 0.03 abs coeff (mm 1 ) 3.783 F (000) 1416 range for data collection 1.76 to 27.50 limiting indices no. of reflns collcd 41874 no. of ind reflns ( R int ) 7070 [R(int) = 0.0598] completeness to = 27.50 100.0% absorption corr Numerical refinement method Full matrix least squares on F 2 data / restraints / parameters 7070 / 0 / 349 R 1, a wR 2 b R1 = 0.0262, wR2 = 0.0494 [5138] R 1, a wR 2 b (all data) R1 = 0.0491, wR2 = 0.0532 GOF c on F 2 0.912 largest diff. peak and hole 1.572 and 0.787

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180 Table A 15 Data and refinement for [ t BuOCO] 3 ) 3 (THF) 2 ( 5 4 ) I dentification code ss7 7 empirical formula C 3 9 H 52 O 4 W formula weight 768.66 T (K) 100(2) 0.71073 crystal system Orthorhombic space group Pna2 1 a () 1 6.6415(8) b () 11.6477(5) c () 18.3227(9) (deg) 90 (deg) 90 (deg) 90 V ( 3 ) 3551.6(3) Z 4 calcd (Mg mm 3 ) 1. 438 crystal size (mm 3 ) 0. 18 x 0. 14 x 0.0 2 abs coeff (mm 1 ) 3.783 F (000) 1568 range for data collection 2.07 to 27.50 limiting indices 21 20 15 15 23 23 no. of reflns collcd 53295 no. of ind reflns ( R int ) 8159 [R(int) = 0.05 50 ] completeness to = 27.50 100.0% absorption corr Numerical refinement method Full matrix least squares on F 2 data / restraints / parameters 8159 / 1 / 406 R 1, a wR 2 b [I > R1 = 0.02 18 wR2 = 0.04 69 [ 7035 ] R 1, a wR 2 b (all data) R1 = 0.0 282 wR2 = 0.0 485 GOF c on F 2 0.9 52 largest diff. peak and hole 1.572 and 0.787 For all tables: a R 1 = || F o | F c ||/ | F o |. b w R 2 = ( ( w ( F o 2 F c 2 ) 2 )/ ( w ( F o 2 ) 2 )) 1/2 c GOF = ( w ( F o 2 F c 2 ) 2 /( n p )) 1/2 where n is the number of data and p is the number of parameters refined.

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181 LIST OF REFERENCES (1) Hemminger, J. New Science for a Secure and Sustainable Energy Future U.S. Department of Energy, 2008. (2) Lewis, N. S.; Nocera, D. G. Proc. Natl. Acad. Sci. 2007 104 20142 20142. (3) Lippard, S. J. Chem. Eng. News 2000 78 64 65 (4) Smaglik, P. Nature 2000 406 807 808. (5) Centi, G.; Perathoner, S. Top. Catal. 2009 52 948 961. (6) Vlachos, D. G.; Caratzoulas, S. Chem. Eng. Sci. 2010 65 18 29. (7) Laplaza, C. E.; Johnson, A. R.; Cummins, C. C. J. Am. Chem. Soc. 1996 118 709 710. (8) Leigh, G. J. Science 1995 268 827 828. (9) Wigley, D. E. Prog. Inorg. Chem. 1994 42 239 482. (10) Nugent, W. A.; Mayer, J. M. Metal Ligand Multiple Bonds ; Wiley Interscience: New York, 1988. (11) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005 38 839 849. (12) Odom, A. L. Dalton Trans. 2011 40 2689 2695. (13) Eikey, R. A.; Abu Omar, M. M. Coord. Chem. Rev. 2003 243 83 124. (14) McDonough, J. E.; Mendiratta, A.; Curley, J. J.; Fortman, G. C.; Fantasia, S.; Rybak Akimova, E. V.; Nolan, S. P.; Hoff, C. D.; Cummins, C. C. Inorg. Chem. 2008 47 2133 2141. (15) Brudvig, G. W.; McEvoy, J. P. Chem. Rev. 2006 106 4455 4483. (16) Shilov, A. E. Metal Complexes in Biomimetic Chemical Reactions ; CRC Press: Boca Raton, 1996. (17) Winter, C. H.; Sheridan, P. H.; Lewkebandara, T. S.; Heeg, M. J.; Proscia, J. W. J. Am. Chem. Soc. 1992 114 1095 1097. (18) Carmalt, C. J.; Newport, A.; Parkin, I. P.; Mountford, P.; Sealey, A. J.; Dubberley, S. R. J. Mater. Chem. 2003 13 84 87. (19) S chrock, R. R. Science 1983 219 13 18.

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182 (20) Feldman, J.; Schrock, R. R. Prog. Inorg. Chem. 1991 39 1 74. (21) Grubbs, R. H. Handbook of Metathesis ; Willey Interscience: Weinheim, 2008. (22) Tolman, W. B. Activation of Small Molecules: Organometallic and Bioinorganic Perspectives ; Willey Interscience, 2007. (23) Cummins, C. C. Chem. Commun. 1998 1777 1786. (24) Fout, A. R.; Scott, J.; Miller, D. L.; Bailey, B. C.; Pink, M.; Mindiola, D. J. Organometallics 2009 28 331 347. (25) Woo, L. K. Chem. Rev. 199 3 93 1125 1136. (26) Silvia, J. S.; Cummins, C. C. J. Am. Chem. Soc. 2010 132 2169 2171. (27) Tofan, D.; Cummins, C. C. Angew. Chem. Int. Ed. 2010 49 7516 7518. (28) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements ; Oxford: Butterworth Heinem an, 2000. (29) Smil, V. Enriching the Earth ; The MIT Press: Boston, 2001. (30) Alberty, R. A. J. Biol. Chem. 1994 269 7099 7102. (31) Haber, F. The Synthesis of Ammonia from Its Elements ; Nobel Lecture: Stockholm, 1920. (32) Bosch, C. The Development of the Chemical High Pressure Method During the Establishment of the New Ammonia Industry ; Nobel Lecture: Stockholm, 1932. (33) Schlogl, R. Angew. Chem. Int. Ed. 2003 42 2004 2008. (34) Smith, B. E.; Richards, R. L.; Newton, W. E. Catalysis for Nitrogen Fix ation ; Kluwer Academic: Boston, 2004. (35) Richards, R. L. Biology and Biochemistry of Nitrogen Fixation ; Elsevier: Amsterdam, 1991. (36) Burgess, B. K.; Lowe, D. J. Chem. Rev. 1996 96 2983 3011. (37) Einsle, O.; Tezcan, F. A.; Andrade, S. L. A.; Schmid, B.; Yoshida, M.; Howard, J. B.; Rees, D. C. Science 2002 297 1696 1700. (38) Barriere, F. Coord. Chem. Rev. 2003 236 71 89. (39) Kozak, C. M.; Mountford, P. Angew. Chem. Int. Ed. 2004 43 1186 1189. (40) Hidai, M.; Mizobe, Y. Chem. Rev. 1995 95 1115 1133.

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183 (41) Fryzuk, M. D.; Johnson, S. A. Coord. Chem. Rev. 2000 200 379 409. (42) Gambarotta, S. J. Organomet. Chem. 1995 500 117 126. (43) Gambarotta, S.; Scott, J. Angew. Chem. Int. Ed. 2004 43 5298 5308. (44) Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. Rev. 1978 78 589 625. (45) Hidai, M. Coord. Chem. Rev. 1999 185 6 99 108. (46) Yandulov, D. V.; Schrock, R. R. Science 2003 301 76 78. (47) Yandulov, D. V.; Schrock, R. R.; R heingold, A. L.; Ceccarelli, C.; Davis, W. M. Inorg. Chem. 2003 42 796 813. (48) Schrock, R. R. Acc. Chem. Res. 2005 38 955 962. (49) Schrock, R. R. Angew. Chem. Int. Ed. 2008 47 5512 5522. (50) Arashiba, K.; Miyake, Y.; Nishibayashi, Y. Nat. Chem. 2 010 3 120 125. (51) Laplaza, C. E.; Cummins, C. C. Science 1995 268 861 863. (52) Laplaza, C. E.; Johnson, M. J. A.; Peters, J. C.; Odom, A. L.; Kim, E.; Cummins, C. C.; George, G. N.; Pickering, I. J. J. Am. Chem. Soc. 1996 118 8623 8638. (53) Cui, Q.; Musaev, D. G.; Svensson, M.; Sieber, S.; Morokuma, K. J. Am. Chem. Soc. 1995 117 12366 12367. (54) Laplaza, C. E.; Odom, A. L.; Davis, W. M.; Cummins, C. C.; Protasiewicz, J. D. J. Am. Chem. Soc. 1995 117 4999 5000. (55) Leigh, G. J. Acc. Chem. Res. 1992 25 177 181. (56) Dehnicke, K.; Strahle, J. Angew. Chem. Int. Ed. 1992 31 955 978. (57) Mori, M. J. Organomet. Chem. 2004 689 4210 4227. (58) Van Tamalen, E. E.; Rudler, H. J. Am. Chem. Soc. 1970 92 5253 5254. (59) Van Tamalen, E. E.; Seel ey, D.; Schnelle.S; Rudler, H.; Cretney, W. J. Am. Chem. Soc. 1970 92 5251 5252. (60) Pool, J. A.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2003 125 2241 2251. (61) Pool, J. A.; Lobkovsky, E.; Chirik, P. J. Nature 2004 427 527 530. (62) Knobloc h, D. J.; Lobkovsky, E.; Chirik, P. J. Nat. Chem. 2010 2 30 35.

PAGE 184

184 (63) Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997 275 1445 1447. (64) Nugent, W. A.; Mckinney, R. J.; Kasowski, R. V.; Vancatledge, F. A. Inorg. Chim. Acta Lett. 1982 65 L91 L93. (65) Bennett, B. K.; Crevier, T. J.; DuMez, D. D.; Matano, Y.; McNeil, W. S.; Mayer, J. M. J. Organomet. Chem. 1999 591 96 103. (66) Groves, J. T.; Takahashi, T. J. Am. Chem. Soc. 1983 105 2073 2074. (67) DuBois, J.; Tomooka, C. S.; Hong, J.; Carreira, E. M. Acc. Chem. Res. 1997 30 364 372. (68) Gdula, R. L.; Johnson, M. J. A. J. Am. Chem. Soc. 2006 128 9614 9615. (69) Gdula, R. L.; Ockwig, N. W.; Johnson, M. J. A. Inorg. Chem. 2005 44 9140 9142. (70) Geyer, A. M.; Gdula, R. L.; Wiedner, E. S.; Johnson, M. J. A. J. Am. Chem. Soc. 2007 129 3800 3801. (71) Chisholm, M. H.; Delbridge, E. E.; Kidwell, A. R.; Quinlan, K. B. Chem. Commun. 2003 126 127. (72) Geyer, A. M.; Wiedner, E. S.; Gary, J. B.; Gdula, R. L.; Kuhlmann, N. C.; Dunietz, B. D.; Kampf, J. W.; Johnson, M. J. A. J. Am. Chem. Soc. 2008 130 8984 8999. (73) Finke, A. D.; Moore, J. S. Chem. Commun. 2010 46 7939 7941. (74) Mendiratta, A.; Cummins, C. C.; Kryatova, O. P.; Rybak Akimova, E. V.; McDonough, J. E.; Hoff, C. D. Inorg. Chem. 2003 42 8621 8623. (75) Clough, C. R.; Greco, J. B.; Figueroa, J. S.; Diaconescu, P. L.; Davis, W. M.; Cummins, C. C. J. Am. Chem. Soc. 2004 126 7742 7743. (76) Clough, C. R.; Muller, P.; Cummins, C. C. Dalton Trans. 2008 4458 4463. (77) Curley, J. J.; Sceats, E. L.; Cummins, C. C. J. Am. Chem. Soc. 2006 128 14036 14037. (78) Zhang, W.; Moore, J. S. Angew. Chem. Int. Ed. 2006 45 4416 4439. (79) Zhang, W.; Moore, J. S. Adv. Synth. Catal. 2007 349 93 120. (80) Schrock, R. R.; Czekelius, C. Adv. Synth. Catal. 2007 349 55 77. (81) Bunz, U. H. F.; Kloppenburg, L. Angew. Chem. Int. Ed. 1999 38 478 481.

PAGE 185

185 (82) Furstner, A.; Muller, C. Chem. Commun. 2005 5583 5585. (83) Furstner, A.; Heppekausen, J.; Stade, R. ; Goddard, R. J. Am. Chem. Soc. 2010 132 11045 11057. (84) Bunz, U. H. F. Chem. Rev. 2000 100 1605 1644. (85) Schrock, R. R. Chem. Rev. 2002 102 145 179. (86) Mclain, S. J.; Wood, C. D.; Messerle, L. W.; Schrock, R. R.; Hollander, F. J.; Youngs, W. J.; Churchill, M. R. J. Am. Chem. Soc. 1978 100 5962 5964. (87) Schrock, R. R.; Sancho, J.; Pederson, S. F.; Virgil, S. C.; Grubbs, R. H. Inorg. Synth. 1989 26 44 51. (88) Tonzetich, Z. J.; Lam, Y. C.; Mller, P.; Schrock, R. R. Organometallics 2007 26 475 477. (89) Bailey, B. C.; Fan, H. J.; Baum, E. W.; Huffman, J. C.; Baik, M. H.; Mindiola, D. J. J. Am. Chem. Soc. 2005 127 16016 16017. (90) Mayr, A.; Mcdermo tt, G. A. J. Am. Chem. Soc. 1986 108 548 549. (91) Listemann, M. L.; Schrock, R. R. Organometallics 1985 4 74 83. (92) Bindl, M.; Stade, R.; Heilmann, E. K.; Picot, A.; Goddard, R.; Furstner, A. J. Am. Chem. Soc. 2009 131 9468 9470. (93) Zhang, W.; Kraft, S.; Moore, J. S. J. Am. Chem. Soc. 2004 126 329 335. (94) Zhang, W.; Kraft, S.; Moore, J. S. Chem. Commun. 2003 832 833. (95) Furstner, A.; Mathes, C.; Lehmann, C. W. Chem. Eur. J. 2001 7 5299 5317. (96) Furstner, A.; Mathes, C.; Leh mann, C. W. J. Am. Chem. Soc. 1999 121 9453 9454. (97) Schrock, R. R.; Pedersen, S. F.; Churchill, M. R.; Ziller, J. W. Organometallics 1984 3 1574 1583. (98) Katz, T. J.; Mcginnis, J. J. Am. Chem. Soc. 1975 97 1592 1594. (99) Churchill, M. R.; Zille r, J. W.; Freudenberger, J. H.; Schrock, R. R. Organometallics 1984 3 1554 1562. (100) Freudenberger, J. H.; Schrock, R. R.; Churchill, M. R.; Rheingold, A. L.; Ziller, J. W. Organometallics 1984 3 1563 1573.

PAGE 186

186 (101) Schrock, R. R.; Murdzek, J. S.; Freudenberger, J. H.; Churchill, M. R.; Ziller, J. W. Organometallics 1986 5 25 33. (102) Schrock, R. R. Acc. Chem. Res. 1986 19 342 348. (103) Woo, T.; Folga, E.; Ziegler, T. Organometallics 1993 12 1289 1298. (104) F reudenberger, J. H.; Schrock, R. R. Organometallics 1986 5 398 400. (105) Engel, P. F.; Pfeffer, M. Chem. Rev. 1995 95 2281 2309. (106) Goller, R.; Schubert, U.; Weiss, K. J. Organomet. Chem. 1993 459 229 232. (107) Fout, A. R.; Bailey, B. C.; Tomasz ewski, J.; Mindiola, D. J. J. Am. Chem. Soc. 2007 129 12640 12641. (108) Bailey, B. C.; Fout, A. R.; Fan, H. J.; Tomaszewski, J.; Huffman, J. C.; Gary, J. B.; Johnson, M. J. A.; Mindiola, D. J. J. Am. Chem. Soc. 2007 129 2234 2235. (109) Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2007 129 5302 5303. (110) Koller, J.; Sarkar, S.; Abboud, K. A.; Veige, A. S. Organometallics 2007 26 5438 5441. (111) Agapie, T.; Bercaw, J. E. Organometallics 2007 26 2957 2959. (112) Frisch, M. J. T., G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; S tratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuc k, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al Laham, M. A.; Peng, C. Y.; Nanayak kara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.; Gaussian 03, Revision B.04 ed.; Gaussian Inc.: Wallingford, CT, 2004 (113) Becke, A. D. J. Chem. Phys. 1993 98 5648 5652. (114) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988 37 785 789.

PAGE 187

187 (115) Yoon, T. P.; Jacobsen, E. N. Science 2003 299 1691 1693. (116) van Koten, G.; Gebbink, R. J. M. K. Dalton Trans. 2011 40 8731 8732. (117) Singleton, J. T. Tetrahedron 2003 59 1837 1857. (118) Albrecht, M.; Kocks, B. M.; Spek, A. L.; van Koten, G. J. Organomet. Chem. 2001 624 271 286. (119) Albrecht, M.; Gossage, R. A.; Lutz, M.; Spek, A. L.; van Koten, G. Chem. Eur. J. 2000 6 1431 1445. (120) Vanderploeg, A. F. M. J.; Vankoten, G.; Brevard, C. Inorg. Chem. 1982 21 2878 2881. (121) Loeb, S. J.; Shimizu, G. K. H.; Wisner, J. A. Organometallics 1998 17 2324 2327. (122) Hall, J. R.; Loeb, S. J.; Shimizu, G. K. H.; Yap, G. P. A. Angew. Chem. Int Ed. 1998 37 121 123. (123) Morales, D. M.; Jensen, C. M. The Chemistry of Pincer Compounds ; Elsevier: Amsterdam, 2007. (124) Albrecht, M.; van Koten, G. Angew. Chem. Int. Ed. 2001 40 3750 3781. (125) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003 103 1759 1792. (126) Leis, W.; Mayer, H. A.; Kaska, W. C. Coord. Chem. Rev. 2008 252 1787 1797. (127) Choi, J.; MacArthur, A. H. R.; Brookhart, M.; Goldman, A. S. Chem. Rev. 2011 111 1761 1779. (128) Szabo, K. J.; Selander, N. Chem. Rev. 2011 111 2 048 2076. (129) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976 1020 1024. (130) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1976 365 366. (131) van Koten, G. Pure and Appl. Chem. 1989 61 1681 1694. (132) Errington, J.; Mcdon ald, W. S.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1980 2312 2314. (133) Daniele, S.; Hitchcock, P. B.; Lappert, M. F.; Nile, T. A.; Zdanski, C. M. J. Chem. Soc., Dalton Trans. 2002 3980 3984. (134) Estler, F.; Eickerling, G.; Herdtweck, E.; Anwander, R. Organometallics 2003 22 1212 1222.

PAGE 188

188 (135) Carlson, A. R., M.S. Thesis University of Florida, 2007 (136) Sarkar, S.; McGowan, K. P.; Culver, J. A.; Carlson, A. R.; Koller, J.; Peloquin, A. J.; Veige, M. K.; Abboud, K. A.; Veige, A. S. Inorg. Chem. 2010 49 5143 5156. (137) Kuppuswamy, S.; Veige, A. S. unpublised results (138) Turculet, L.; Tilley, T. D. Organometallics 2002 21 3961 3972. (139) Greco, G. E.; Schrock, R. R. Inorg. Chem. 2001 40 3850 3860. (140) Weng, W.; Guo, C. Y.; Celenligil C etin, R.; Foxman, B. M.; Ozerov, O. V. Chem. Commun. 2006 197 199. (141) Fan, L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2004 23 326 328. (142) Kilgore, U. J.; Yang, X. F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. Inorg. Chem. 2006 45 10 712 10721. (143) DeMott, J. C.; Basuli, F.; Kilgore, U. J.; Foxman, B. M.; Huffman, J. C.; Ozerov, O. V.; Mindiola, D. J. Inorg. Chem. 2007 46 6271 6276. (144) Contel, M.; Stol, M.; Casado, M. A.; van Klink, G. P. M.; Ellis, D. D.; Spek, A. L.; van Koten G. Organometallics 2002 21 4556 4559. (145) Steenwinkel, P.; James, S. L.; Grove, D. M.; Veldman, N.; Spek, A. L.; vanKoten, G. Chem. Eur. J. 1996 2 1440 1445. (146) Chuchuryukin, A. V.; Huang, R. B.; Lutz, M.; Chadwick, J. C.; Spek, A. L.; van Koten G. Organometallics 2011 30 2819 2830. (147) O'Reilly, M.; Falkowski, J. M.; Ramachandran, V.; Pati, M.; Abboud, K. A.; Dalal, N. S.; Gray, T. G.; Veige, A. S. Inorg. Chem. 2009 48 10901 10903. (148) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allg. Chem. 1995 621 2021 2024. (149) Kuppuswamy, S.; Ghiviriga, I.; Abboud, K. A.; Veige, A. S. Organometallics 2010 29 6711 6722. (150) Scollard, J. D.; McConville, D. H.; Vittal, J. J.; Payne, N. C. J. Mol. Catal. A: Chem. 1998 128 201 214. (151) SHELXT L6; Bruker, AXS: Madison, WI, 2000 (152) Sarkar, S.; Carlson, A. R.; Veige, M. K.; Falkowski, J. M.; Abboud, K. A.; Veige, A. S. J. Am. Chem. Soc. 2008 130 1116 1117. (153) Agapie, T.; Day, M. W.; Bercaw, J. E. Organometallics 2008 27 6123 6142.

PAGE 189

189 (154) Kays, D. L. Organomet. Chem. 2010 36 56 76. (155) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.; Power, P. P. Science 2005 310 844 847. (156) Golisz, S. R.; Bercaw, J. E. Macromolecules 2009 42 8751 8762. (157) Kerschner, J. L .; Yu, J. S.; Fanwick, P. E.; Rothwell, I. P.; Huffman, J. C. Organometallics 1989 8 1414 1418. (158) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J. Am. Chem. Soc. 1994 116 4382 4390. (159) Zhang, Y. T.; Wang, J. H.; Mu, Y.; Shi, Z.; Lu, C. S.; Zh ang, Y. R.; Qiao, L. J.; Feng, S. H. Organometallics 2003 22 3877 3883. (160) Yoshida, T.; Adachi, T.; Yabunouchi, N.; Ueda, T.; Okamoto, S. J. Chem. Soc., Chem. Commun. 1994 151 152. (161) Dilworth, J. R.; Gibson, V. C.; Davies, N.; Redshaw, C.; White, A. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1999 2695 2699. (162) Leoni, P.; Pasquali, M.; Braga, D.; Sabatino, P. J. Chem. Soc., Dalton Trans. 1989 959 963. (163) Evans, D. F. J. Chem. Soc. 1959 2003 2005. (164) Tonks, I. A.; Henling, L. M.; D ay, M. W.; Bercaw, J. E. Inorg. Chem. 2009 48 5096 5105. (165) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds ; Wiley VCH, 2009. (166) Brandts, J. A. M.; Gossage, R. A.; Boersma, J.; Spek, A. L.; van Koten, G. Organometall ics 1999 18 2642 2648. (167) Sarkar, S.; Abboud, K. A.; Veige, A. S. J. Am. Chem. Soc. 2008 130 16128 16129. (168) Song, J. I.; Gambarotta, S. Chem. Eur. J. 1996 2 1258 1263. (169) Zarkesh, R. A.; Ziller, J. W.; Heyduk, A. F. Angew. Chem. Int. Ed. 20 08 47 4715 4718. (170) Sarkar, S.; Veige, A. S. U.S. Pat. Appl. Publ. 2009 20090281343 20020091112. (171) Figueroa, J. S.; Piro, N. A.; Clough, C. R.; Cummins, C. C. J. Am. Chem. Soc. 2006 128 940 950.

PAGE 190

190 (172) Figueroa, J. S.; Cummins, C. C. Dalton Trans. 2006 2161 2168. (173) Kegley, S. E.; Pinhas, A. R. Problems and solutions in organometallic chemistry ; University Science Books: Mill Valley, CA, 1986. (174) Bradley, D. C.; Chisholm, M. H. J. Chem. Soc. A: Inorg. Phys. Theor. 1971 2741 2744. (175) Vandersluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990 46 194 201. (176) O'Reilly, M. E.; Del Castillo, T. J.; Falkowski, J. M.; Ramachandran, V.; Pati, M.; Correia, M. C.; Abboud, K. A.; Dalal, N. S.; Richardson, D. E.; Veige, A. S. J. Am. C hem. Soc. 2011 133 13661 13673. (177) Kuppuswamy, S.; Peloquin, A. J.; Ghiviriga, I.; Abboud, K. A.; Veige, A. S. Organometallics 2010 29 4227 4233. (178) Lefebvre, F.; Leconte, M.; Pagano, S.; Mutch, A.; Basset, J. M. Polyhedron 1995 14 3209 3226. ( 179) Chisholm, M. H.; Parkin, I. P.; Folting, K.; Lubkovsky, E. B.; Streib, W. E. J. Chem. Soc., Chem. Commun. 1991 1673 1675. (180) Sarkar, S.; Culver, J. A.; Peloquin, A. J.; Ghiviriga, I.; Abboud, K. A.; Veige, A. S. Angew. Chem. Int. Ed. 2010 49 971 1 9714. (181) Miller, R. L.; Wolczanski, P. T.; Rheingold, A. L. J. Am. Chem. Soc. 1993 115 10422 10423. (182) Chisholm, M. H.; Folting, K.; Glasgow, K. C.; Lucas, E.; Streib, W. E. Organometallics 2000 19 884 892. (183) Lopez, L. P. H.; Muller, P.; Sc hrock, R. R. Organometallics 2008 27 3857 3865. (184) Cotton, F. A.; Niswander, R. H.; Sekutowski, J. C. Inorg. Chem. 1979 18 1152 1159. (185) Cabeza, J. A.; del Rio, I.; Miguel, D.; Sanchez Vega, M. G. Angew. Chem. Int. Ed. 2008 47 1920 1922. (186) Miller, R. L.; Lawler, K. A.; Bennett, J. L.; Wolczanski, P. T. Inorg. Chem. 1996 35 3242 3253. (187) Bianchini, C.; Meli, A.; Vizza, F. Eur. J. Inorg. Chem. 2001 43 68. (188) Weller, K. J.; Fox, P. A.; Gray, S. D.; Wigley, D. E. Polyhedron 1997 16 3139 3163. (189) Angelici, R. J. Polyhedron 1997 16 3073 3088.

PAGE 191

191 (190) Ancheyta, J.; Rana, M. S.; Furimsky, E. Catal. Today 2005 109 3 15. (191) Furimsky, E. Catal. Rev. Sci. Eng. 2005 47 297 489. (192) Ho, T. C. Catal. Rev. Sci. Eng. 1988 30 117 160 (193) Kabe, T.; Ishihara, A.; Qian, W. Hydrodesulfurization and Hydrodenitrogenation ; Wiley VCH: Tokyo, 1999. (194) Furimsky, E.; Massoth, F. E. Catal. Today 1999 52 381 495. (195) Diaconescu, P. L. Curr. Org. Chem. 2008 12 1388 1405. (196) Bonanno, J. B.; Veige, A. S.; Wolczanski, P. T.; Lobkovsky, E. B. Inorg. Chim. Acta 2003 345 173 184. (197) Kleckley, T. S.; Bennett, J. L.; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem. Soc. 1997 119 247 248. (198) Pool, J. A.; Scott, B. L.; Kiplinger, J. L Chem. Commun. 2005 2591 2593. (199) Miller, K. L.; Williams, B. N.; Benitez, D.; Carver, C. T.; Ogilby, K. R.; Tkatchouk, E.; Goddard, W. A.; Diaconescu, P. L. J. Am. Chem. Soc. 2010 132 342 355. (200) Chisholm, M. H.; Cotton, F. A.; Extine, M.; Stult s, B. R. J. Am. Chem. Soc. 1976 98 4477 4485. (201) Jyothish, K.; Zhang, W. Angew. Chem. Int. Ed. 2011 50 8478 8480. (202) Wengrovius, J. H.; Sancho, J.; Schrock, R. R. J. Am. Chem. Soc. 1981 103 3932 3934. (203) Mccullough, L. G.; Listemann, M. L.; Schrock, R. R.; Churchill, M. R.; Ziller, J. W. J. Am. Chem. Soc. 1983 105 6729 6730. (204) Shiotsuki, M.; Sanda, F.; Masuda, T. Polym. Chem. 2011 2 1044 1058. (205) Liu, J. Z.; Lam, J. W. Y.; Tang, B. Z. Chem. Rev. 2009 109 5799 5867. (206) Lam, J. W. Y.; Tang, B. Z. Acc. Chem. Res. 2005 38 745 754. (207) Masuda, T. J. Polym. Sci., Part A: Polym. Chem. 2007 45 165 180. (208) Masuda, T.; Sanda, F. In Handbook of Metathesis ; Grubbs, R. H., Ed.; Wiley VCH: Wheinh eim, 2003, p 375 406. (209) Chiang, C. K.; Fincher, C. R.; Park, Y. W.; Heeger, A. J.; Shirakawa, H.; Louis, E. J.; Gau, S. C.; MacDiarmid, A. G. Phys. Rev. Lett. 1977 39 1098 1101.

PAGE 192

192 (210) Shirakawa, H.; Louis, E. J.; Macdiarmid, A. G.; Chiang, C. K.; Hee ger, A. J. J. Chem. Soc., Chem. Commun. 1977 578 580. (211) Shirakawa, H. Angew. Chem. Int. Ed. 2001 40 2575 2580. (212) Heeger, A. J. Angew. Chem. Int. Ed. 2001 40 2591 2611. (213) MacDiarmid, A. G. Angew. Chem. Int. Ed. 2001 40 2581 2590. (214) Mo raes, F.; Davidov, D.; Kobayashi, M.; Chung, T. C.; Chen, J.; Heeger, A. J.; Wudl, F. Synth. Met. 1985 10 169 179. (215) Chen, J.; Chung, T. C.; Moraes, F.; Heeger, A. J. Solid State Commun. 1985 53 757 763. (216) Samuel, I. D. W.; Ledoux, I.; Dhenaut, C.; Zyss, J.; Fox, H. H.; Schrock, R. R.; Silbey, R. J. Science 1994 265 1070 1072. (217) Yin, S. C.; Xu, H. Y.; Shi, W. F.; Gao, Y. C.; Song, Y. L.; Wing, J.; Lam, Y.; Tang, B. Z. Polymer 2005 46 7670 7677. (218) San Jose, B. A.; Matsushita, S.; Moro ishi, Y.; Akagi, K. Macromolecules 2011 44 6288 6302. (219) Tang, B. Z.; Chen, H. Z.; Xu, R. S.; Lam, J. W. Y.; Cheuk, K. K. L.; Wong, H. N. C.; Wang, M. Chem. Mater. 2000 12 213 221. (220) Tang, B. Z.; Xu, H. Y.; Lam, J. W. Y.; Lee, P. P. S.; Xu, K. T .; Sun, Q. H.; Cheuk, K. K. L. Chem. Mater. 2000 12 1446 1455. (221) Hu, Y.; Shiotsuki, M.; Sanda, F.; Freeman, B. D.; Masuda, T. Macromolecules 2008 41 8525 8532. (222) Hu, Y. M.; Shiotsuki, M.; Sanda, F.; Masuda, T. Chem. Commun. 2007 4269 4270. (223) Nagai, K.; Masuda, T.; Nakagawa, T.; Freeman, B. D.; Pinnau, I. Prog. Polym. Sci. 2001 26 721 798. (224) Raharjo, R. D.; Lee, H. J.; Freeman, B. D.; Sakaguchi, T.; Masuda, T. Polymer 2005 46 6316 6324. (225) Lam, J. W. Y.; Kong, X. X.; Dong, Y. P .; Cheuk, K. K. L.; Xu, K. T.; Tang, B. Z. Macromolecules 2000 33 5027 5040. (226) Choi, S. K.; Lee, J. H.; Kang, S. J.; Jin, S. H. Prog. Polym. Sci. 1997 22 693 734. (227) Goto, H.; Zhang, H. Q.; Yashima, E. J. Am. Chem. Soc. 2003 125 2516 2523.

PAGE 193

193 (22 8) Moore, J. S.; Gorman, C. B.; Grubbs, R. H. J. Am. Chem. Soc. 1991 113 1704 1712. (229) Kwak, G.; Minakuchi, M.; Sakaguchi, T.; Masuda, T.; Fujiki, M. Chem. Mater. 2007 19 3654 3661. (230) Aoki, T.; Kokai, M.; Shinohara, K.; Oikawa, E. Chem. Lett. 19 93 2009 2012. (231) Natta, G.; Giorgio, M.; Paolo, C. Atti, Accad. Naz. Lincei, Rend. Classe Sci. Fis. Mat. Nut. 1958 25 3 12. (232) Ehrlich, P.; Kern, R. J.; Pierron, E. D.; Provder, T. J. Polym. Sci., Part B: Polym. Lett. 1967 5 911 915. (233) Simionescu, C. I.; Percec, V.; Dumitrescu, S. J. Polym. Sci., Part A: Polym. Chem. 1977 15 2497 2509. (234) Masuda, T.; Hasegawa, K. I.; Higashim.T Macromolecules 1974 7 728 731. (235) Xu, K. T.; Peng, H.; Lam, J. W. Y.; Poon, T. W. H.; Dong, Y. P.; Xu H. Y.; Sun, Q. H.; Cheuk, K. K. L.; Salhi, F.; Lee, P. P. S.; Tang, B. Z. Macromolecules 2000 33 6918 6924. (236) Katz, T. J.; Lee, S. J. J. Am. Chem. Soc. 1980 102 422 424. (237) Masuda, T.; Sasaki, N.; Higashimura, T. Macromolecules 1975 8 717 721. (238) Shiotsuki, M.; Onishi, N.; Sanda, F.; Masuda, T. Polym. J. 2011 43 51 57. (239) Furlani, A.; Napoletano, C.; Russo, M. V.; Camus, A.; Marsich, N. J. Polym. Sci., Part A: Polym. Chem. 1989 27 75 86. (240) Gorman, C. B.; Vest, R. W.; Palov ich, T. U.; Serron, S. Macromolecules 1999 32 4157 4165. (241) Sheng, Y. H.; Wu, Y. D. J. Am. Chem. Soc. 2001 123 6662 6668. (242) Choi, S. K.; Gal, Y. S.; Jin, S. H.; Kim, H. K. Chem. Rev. 2000 100 1645 1681. (243) Katz, T. J.; Hacker, S. M.; Kendri ck, R. D.; Yannoni, C. S. J. Am. Chem. Soc. 1985 107 2182 2183. (244) Mayershofer, M. G.; Nuyken, O. J. Polym. Sci., Part A: Polym. Chem. 2005 43 5723 5747. (245) Hayano, S.; Itoh, T.; Masuda, T. Polymer 1999 40 4071 4075. (246) Fox, H. H.; Wolf, M. O.; Odell, R.; Lin, B. L.; Schrock, R. R.; Wrighton, M. S. J. Am. Chem. Soc. 1994 116 2827 2843.

PAGE 194

194 (247) Kaneshiro, H.; Hayano, S.; Masuda, T. Polym. J. 1999 31 348 352. (248) Wallace, K. C.; Liu, A. H.; Davis, W. M.; Schrock, R. R. Organometallics 1989 8 644 654. (249) Schrock, R. R.; Luo, S. F.; Lee, J. C.; Zanetti, N. C.; Davis, W. M. J. Am. Chem. Soc. 1996 118 3883 3895. (250) Schrock, R. R.; Luo, S. F.; Zanetti, N. C.; Fox, H. H. Organometallics 1994 13 3396 3398. (251) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1994 116 12131 12132. (252) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Kainosho, M.; Ono, A.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1999 121 12035 12044. (253) Miyake, M.; Misumi, Y.; Masuda, T. Macromolecules 2000 33 6636 6639. (254) Katz, T. J.; Ho, T. H.; Shih, N. Y.; Ying, Y. C.; Stuart, V. I. W. J. Am. Chem. Soc. 1984 106 2659 2668. (255) Weiss, K.; Goller, R.; Loessel, G. J. Mol. Catal. 1988 46 267 27 5. (256) Mortreux, A.; Petit, F.; Petit, M.; Szymanskabuzar, T. J. Mol. Catal. A: Chem. 1995 96 95 105. (257) Strutz, H.; Dewan, J. C.; Schrock, R. R. J. Am. Chem. Soc. 1985 107 5999 6005. (258) Dotz, K. H.; Kreiter, C. G. J. Organomet. Chem. 1975 99 309 314. (259) Jyothish, K.; Zhang, W. Angew. Chem. Int. Ed. 2011 50 3435 3438. (260) Cho, H. M.; Weissman, H.; Wilson, S. R.; Moore, J. S. J. Am. Chem. Soc. 2006 128 14742 14743. (261) Weissman, H.; Plunkett, K. N.; Moore, J. S. Angew. Chem. Int. Ed. 2006 45 585 588. (262) Nguyen, A. I.; Blackmore, K. J.; Carter, S. M.; Zarkesh, R. A.; Heyduk, A. F. J. Am. Chem. Soc. 2009 131 3307 3316. (263) Schrock, R. R.; Lee, J.; Liang, L. C.; Davis, W. M. Inorg. Chim. Acta 1998 270 353 362. (264) McGowan, K P.; Abboud, K. A.; Veige, A. S. Organometallics 2011 30 4949 4957.

PAGE 195

195 (265) Addison, A. W.; Rao, T. N.; Reedijk, J.; Vanrijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984 1349 1356. (266) on Cambridge Structural Database information. (267) Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci 2002 58 380 388. (268) Cotton, F. A.; Wang, W. Inorg. Chem. 1984 23 1604 1610. (269) Tonzetich, Z. J.; Schrock, R. R.; Muller, P. Organometallics 2006 25 4301 4306. (270) Jan, M. T.; Sarkar, S.; Kuppuswamy, S.; Ghiviriga, I.; Abboud, K. A.; Veige, A. S. J. Organomet. Chem. In Press (271) Kolodziej, R. M.; Schrock, R. R.; Dewan, J. C. Inorg. Chem. 1989 28 1243 1248. (272) Zhang, X. A.; Chen, M. R.; Zhao, H.; Gao, Y.; Wei, Q.; Zhang, S.; Qin, A. J.; Sun, J. Z.; Tang, B. Z. Macromolecules 2011 44 6724 6737. (273) Yuan, W. Z.; Tang, L.; Zhao, H.; Jin, J. K.; Sun, J. Z.; Qin, A. J.; Xu, H. P.; Liu, J. H.; Yang, F.; Zheng, Q.; Chen, E. Q.; Tang, B. Z. Macromolecules 2009 42 52 61. (274) Zeng, Q.; Li, Z.; Li, Z.; Ye, C.; Qin, J.; Tang, B. Z. Macromolecules 2007 40 5634 5637.

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196 BIOGRAPHICAL SKETCH Soumya Sarkar was born in Kolkata, India, 1983. He spent his initial days at Tribeni fo llowing which his family permanently moved to Kalyani. He attended Kalyani Central Model School for his education and graduated with H igh S chool degree from there as a science major. He then registered as an undergraduate with chemistry major at Ramakris hna Krishna Mission Vivekananda Centenary College at Rahara. He discovered his zeal and passion for chemistry and thereafter decided to travel to west coast of India to do his masters in IIT Bombay. In 2006, he completed his Masters of Science degree, co ntinued his journey towards west, and joined University of Florida as a PhD candidate in the Che mistry Department. He led the project for making reactive metal complexes with trianionic pincer ligands under the supervision of Dr. Adam S. Veige. He receiv ed his PhD from the University of Florida in the fall of 2011.