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Evaluation of Multisite Polypyridyl Ligands as Platforms for the Synthesis of Heterometallic Complexes

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Title:
Evaluation of Multisite Polypyridyl Ligands as Platforms for the Synthesis of Heterometallic Complexes
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Walroth, Richard
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English

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Subjects / Keywords:
Carbon ( jstor )
Chromatography ( jstor )
Crystals ( jstor )
Ethanol ( jstor )
Flasks ( jstor )
Ligands ( jstor )
Oxidation ( jstor )
Purification ( jstor )
Reagents ( jstor )
Solvents ( jstor )
Bipyridine
Ligand binding (Biochemistry)
Ligands
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Undergraduate Honors Thesis

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Abstract:
Ligands containing a bipyridine site and either one or two dipicolylamine sites have been employed in the synthesis of a new class of heterometallic complexes. These ligands have previously been reported to bind zinc selectively at the dipicolylamine site. It was determined that the bipyridine site will selectively bind rhodium, and the dipicolylamine sites will selectively bind copper and palladium. Heterometallic complexes containing rhodium and either palladium or zinc were synthesized. The compounds were characterized using 1H NMR, gHMBC NMR, IR, and ESI-MS. ( en )
General Note:
Awarded Bachelor of Science; Graduated May 8, 2012 magna cum laude. Major: Chemistry
General Note:
Advisor: Lisa McElwee-White
General Note:
College of Liberal Arts and Sciences

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University of Florida
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University of Florida
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Copyright Richard Walroth. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.

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1 EVALUATION OF MULTISITE POLYPYRIDYL LIGANDS AS PLATFORMS FOR THE SYNTHESIS OF HETEROMETALLIC COMPLEXES RICHARD WALROTH THESIS SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS TO GRADUATE WITH HIGH E R HONORS ACCOMPANYING A BACHELOR OF SCIENCE IN CHEMISTRY DEPARTMENT OF CHEMISTRY UNIVERSITY OF FLORIDA 2012

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i Abstract of thesis submitted in partial fulfillment of the requi rements to graduate with highe r honors accompanying a Bachelor of Science in Chemistry. UNIVERSITY OF FLORIDA EVALUATION OF MULTISITE POLYPYRIDYL LIGANDS AS PLATFORMS FOR THE SYNTHESIS OF HETEROMETALLIC CO MPLEXES Richard Walroth Undergraduate Advisor: Dr. Lisa McElwee White Department of Chemistry Ligands containing a bipyridine site and either one or two dipicolylamine sites have been employed in the synthesis of a new class of heterometallic complexes. These ligands have previously been reported to bind zinc selectively at the dipicolylamine site. It was determined that the bipyridine site will selectively bind rhodium, and the dipicolylamine sites will selectively bind copper and palladium. Heterometallic complexes containing rhodium and either palladium or zinc were synthesized. The compounds were characterized using 1 H NMR, g HMBC NMR IR, and ESI MS.

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ii TABLE OF CONTENTS ABSTRACT ................................ ................................ ................................ ................................ ..... i LIST OF FIGURES, SCHEMES, TABLES, AND EQUATIONS ................................ ............... iii ACKNOWLEDGEMENTS ................................ ................................ ................................ ........... iv INTRODUCTION ................................ ................................ ................................ .......................... 1 Heterometallic C omplexes ................................ ................................ ................................ ........ 1 Ligands ................................ ................................ ................................ ................................ ....... 1 Metal Choice ................................ ................................ ................................ .............................. 3 RESULTS AND DISCUSSION ................................ ................................ ................................ ..... 4 Synthesis of Ligands ................................ ................................ ................................ ................. 4 Zn Complexes ................................ ................................ ................................ ............................ 6 Rh Complexes ................................ ................................ ................................ ............................ 6 Pd Complexes ................................ ................................ ................................ ............................ 7 Ru Complexes ................................ ................................ ................................ ............................ 8 Pt Complexes ................................ ................................ ................................ ............................. 9 Cu Complexes ................................ ................................ ................................ ............................ 9 Heterometallic Complexes ................................ ................................ ................................ ...... 11 EXPERIMENTAL ................................ ................................ ................................ ........................ 13 Synthesis of Ligands ................................ ................................ ................................ ............... 13 Zn Complexes ................................ ................................ ................................ .......................... 16 Rh Complexes ................................ ................................ ................................ .......................... 16 Pd Complexes ................................ ................................ ................................ .......................... 17 Cu Complexes ................................ ................................ ................................ .......................... 18 Heterometallic Complexes ................................ ................................ ................................ ...... 19 REFERENCES ................................ ................................ ................................ ............................. 21

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iii LIST OF FIGURES, SCHEMES TABLES, AND EQUATIONS Figure 1 Previous methanol oxidation catalyst de veloped by McElwee White group .......... 1 Scheme 1. Original proposed method for using L1 to pr oduce a heterobimetallic system ....... 2 Scheme 2. Synthesis of L1 ................................ ................................ ................................ ........ 2 Equation 1 Synthesis of L2 ................................ ................................ ................................ ........ 3 Figure 2. Model ligands used to verify binding sit es of metals through IR studies ................ 5 Figure 3. IR spectra of the lig ands be ing studied and their analogues ................................ .... 5 Figure 4. Overlay of 1 H NMR spectra of dpa bpy0 L2 and 3 ................................ ............. 7 Figure 5. 1 H NMR spectrum of 4 ................................ ................................ ............................ 8 Table 1. Attempts to bind Ru to dpa L1 and L2 ................................ ................................ 8 Figure 6. IR spectra of reactions involving the various ligands with Cu(trif) 2 ..................... 10 Table 2. Reactions involving Cu ................................ ................................ .......................... 10 Figure 7 Expanded IR spec tra of Pd, Co, and Cu complexes ................................ .............. 11 Figure 8. 1 H NMR spectrum of 5 ................................ ................................ .......................... 12 Table 3. IR stretches of various Cu( CF 3 SO 3 ) 2 reaction mixtures ................................ ........ 18

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iv ACKNOWLEDGEMENTS I would like to thank Dr. McElwee White for giving me the opportunity to work in her lab; it has been an invaluable experience. She has been a terrific mentor and I have learned a great deal from her. All the members of the McElwee White Group have been ve ry supportive, particularly Marie Correia, who taught me so much as my TA in the Organic Chemistry Teaching lab and introduced me to Dr. McElwee White I would like to acknowledge the Howard Hughes M edical Institute, which prov ided me with a scholarship that allowed me to condu ct research over summer. I would also like to thank Dr. Dunn, who helped me get an internship at the Janelia Farms Research Institute. Finally, I owe a great deal to Sarah Go forth who has taught me more than I thought possible and made me the chemist I am today. Without her I would not know m ost of the techniques that I know, and may have never made the decision to pursue a Ph.D in chemistry.

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1 INTRODUCTION Heterometallic Complexes Metal containing catalysts have become ubiquitous in all forms of synthetic chemistry. Recently, there has been a push to synthesize complexes containing two metal centers as these compounds have been shown to be useful homogeneo us catalysts for a variety of reactions. 1 2 3 Also, it has been found in heterogeneous systems that tw o metal centers can work cooperatively to achieve reactions a single metal center can not 4 However, having two separate metals in the same system poses several challenges synthetically. The McElwee White group has been working with heterobimetallic catalysts for some time 5 and has had some success with phosphine based ligands ( F igure 1 ) The intended purpose of these complexes was as cataly sts in direct alcohol fuel cells through electrochemical oxidation of methanol or ethanol however the catalysts degraded during the oxidation. A large array of catalysts were synthesized by varying several structural moieties including Cp ring substituents halides bridging groups, and metals. Analysis of spent catalyst suggested that catalyst degradation was due to phosphine oxidation so alternative ligands which did not involve the phosphine groups were sought out. F igure 1. Previous met hanol oxidation catalyst developed by McElwee White group Ligands One particular ligand ( L1 ) reported by Zhu et al. stood out as being a promising platform for synthes izing heterometallic catalysts 6 The ligand had a bipyridine ( bpy ) site and a dipicolylamine ( dpa ) site, and it was found that the dpa site preferentially bound Zn. It w as believed that this ligand would selectively bind other metals at one of its sites, allowing for a

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2 heterobimetallic system to be produced. The original plan ( S cheme 1 ) involved using Zn as a protecting group on the dpa site, removing the Zn with a n acid, and binding a second desired metal at the dpa site Deprotection of N bound Zn by HCl has p recedent in porphyrin chemistry 7 Alternatively, a second metal could be incorporated through a transmetalation reaction. S cheme 1. Original proposed method for using L1 to produce a heterobimetallic system. The first step of the synthesis of L1 ( S cheme 2 ) is a radical bromination of bpy0 which always produces two products, bpy1 and bpy2 and it is very difficult to separate bpy1 from the reaction mixture As bpy2 can be much more easily purified, it was used to produce a symmetric analogue of L1 L2 ( Equation 1 ). L2 was then used primarily to test for selectivity as it is easier to produce than L1 S cheme 2. Synthesis of L1

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3 (1) Metal Choice As one of the main projects of the McElwee White group has been the development of direct alcohol fuel cells, the metals Rh, Pd, Ru, Pt, Cu, and Co were chosen because of their applications in such fuel cells. Many heterogeneous direct metha nol fuel cells have used Pt anodes to catalyze the oxidation, however the Pt becomes poisoned by CO and require s high overpotentials 4 Incorporating Ru into the Pt anode allows this problem to be overcome as the Ru is able to deliver another oxygen to the CO, completing the oxidation and regenerating the Pt catalyst 4 In homogeneous systems, the same type of cooperativity between the metal centers should allow the catalysts to completely oxidize methanol. Palladium h as received recent attention in the literature for its ability to aerobically oxidize alcohols 8 Further, there is precedent that both Pd and Pt will be able to bind L1 and L2 at the dpa site 9 R ecently there has been a great deal of interest in using ethanol as a fuel source. It has a high mass energy density, it is bio renewable, it can be easily stored and transported, and it is relatively non toxic 10 However, complete electrochemical oxidation of ethanol would involve cleaving a carbon carbon bond. When the catalysts developed by the McE l wee White group were used in the electrooxidation of ethanol acetaldehyde was observed as one of the products in some cases 5 As Rh has been known to decarbonylate aldehydes 11 it should be a ble to cleave the carbon carbon bond in acetaldehyde and allow for complete oxidation to CO 2 Also, Rh is known to favor a square planar geometry, which means it should preferentially bind the ligands

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4 at the bipyridine site 12 As there is pr ecedent in the literature for Pt and Pd to bind dipicolylamine ligands, Rh should be able to form a heterometallic system with either metal 9 13 One thing that all these metals have in common is that they are scarce and therefore expensive. For this reason more earth abundant transition metals in particular copper and cobalt are being investigated which may be able to do the same reactions Both metals have been reported to be able to oxidize alcohols which means they could potentially replace platinum or palladium 8 Also, both metals have been reported to oxidize carbon monoxide, which could make them viable alternatives to ruthenium 14 Finally, cobalt has been reported to be able to catalytically decarbonylate acetaldehyde, which could allow it to replace rhodium 15 RESULTS AND DISCUSSION Synthesis of Ligands The ligands were synthesized using a modification of the reacti on conditions reported by Zhu et al. and the synthetic route is depicted in S cheme 2 and Equation 1 6 As previously stated, purification of bpy1 was dif ficult. The difficulty lay in its tendency to co elute with bpy2 and multiple silica gel chromatography columns were sometimes required in order to get decent yields. However, bpy2 is much less soluble in dichloromethane (DCM) than bpy1 Therefore, it w as possible to recrystallize bpy2 from hot DCM and obtain similar yields to those obtained for bpy1 Originally, L2 seemed easier to obtain pure and in moderate to high yields as it crystallized out of the reaction mixture upon the addition of hexanes. However, t he crystals had a tan color, and it was realized that this tan color was a NMR silent impurity which had to be

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5 removed by chromatography on alumina It should be noted that no difference in reactivity between the purified off white ligand and t he tan colored impure ligand was ever observed In addition, two model ligands pictured in F igure 2 were synthesized using anal ogous reagents and conditions to those for ligands L1 and L2 Figure 3 shows the IR spectra of the ligands and their analogues. It is evident that there are many similarities between the spectra. Specifically, the stretches around 1590 and 1570 cm 1 seem to be associated with the dpa site and the stretch at 1550 cm 1 seems to correspond to the bpy site. The way the spectra change upon the reaction of the ligands with various metals should reveal information about the preferred binding sites of the various metals. Figure 2. Model ligands used to verify binding sites of metals through IR studies Figure 3. IR spectra of the ligands being studied and their analogues.

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6 Zn Complexes The reactions of L1 with ZnCl 2 followed a literature procedure 6 When L2 was reacted with 2 equivalents of ZnCl 2 the product was completely insoluble in CH 2 Cl 2 THF, benzene, chlorobenzene, benzonitrile, acetone, acetonitrile, DMSO, DMF, and water However, 2 equivalents of Zn(OAc) 2 2H 2 O reacted with L2 to give a single methanol soluble product ( 1 ) When Zn(NO 3 ) 2 6H 2 O was reacted with L2 the product ( 2 ) was solubl e at first, but when 2 is dried extensively it becomes much harder to get it bac k into solution. Evidence for the selective binding at the dpa site of L2 was found in the 1 H NMR spectrum of the product. The methylene peaks associated with the dpa site are normally associated with a singlet, but after L2 is reacted with two equivalen ts of Zn(NO 3 ) 2 6H 2 O this singlet becomes split into two doublets. This means that the hydrogens associated with this site are now diastereotopic, confirming that L2 will also bind Zn selectively at the dpa site. Rh Complexes Both L1 and L2 were found to preferentially bind Rh at the bpy site. The ligands were reacted with 0.5 equivalents of [Rh(COD)Cl] 2 under inert atmosphere using either ethanol or THF as the solvent. The reaction with L2 did not produce a pure product as excess ligand was se en in the 1 H NMR in a 0.44:1 ratio of ligand to product Attempts at purification were unsuccessful and the product would decompose in THF even under inert atmosphere. Still, there was enough evidence in the 1 H NMR to determine the binding site as the peaks corresponding to the different sites are readily distinguished. As shown in F igure 4 the peaks corresponding to bpy0 and those correspo nding to dpa do not shift too far up or downfield in the spectrum of L2 In the spectrum of [(COD)Rh (bpy) ( dpa ) 2 ]Cl ( 3 ) the peaks corresponding to the bpy site shift up and downfield while those corresponding to the dpa site have chemical

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7 shifts very similar to the free ligand In a test reaction between bpy0 and [Rh(COD)Cl] 2 the peaks shifted up a nd down field in the same way. 16 Also, the ratio of bound COD to ligand was approximately 1:1, indicating the COD is bound to Rh, and Cl is on ly serving as a counter ion. Through gHMBC NMR all proton and carbon peaks were identified. Figure 4 Overlay of 1 H NMR sp ectra of dpa bpy0 L2 and 3 Pd Complexes Two equivalents of Pd(COD)Cl 2 were reacted with L2 in THF under argon. A beige precipitate was formed and was th e n purified by additional rinsing with THF. 1 H NMR showed that there was a pure product ( 4 ) and also indicated that the Pd was selectively binding the dpa site. In this case, the shift in pea ks in the aromatic region is not as clear However, the methylene hydrogens associated with the dpa site are again diastereotopic as they were when L2 was reacted with Zn(NO 3 ) 2 6H 2 O indicating t hat Pd is bound at the dpa site ( Figure 5 ) I n addition, ESI MS data confirmed that two Pd atoms are bound to L2 Since 1 H NMR shows a pure product, it can be assumed that the two ions are bound to the dpa site as this is the most likely way a single product can be formed using two metal atoms.

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8 Figure 5 1 H NMR spectrum of 4 Ru Complexes There was some precedent in the literature that Ru should be able to bind the ligands at the dipicolylamine sites. However, many of the more readily available Ru sources were all in the Ru(III) oxidation state, and since Ru(III) is a paramagnetic metal it makes t he use of 1 H NMR impractical Table 1 lists the various attempts by the McElwee White group at coordinating Ru and descriptions of the results. Table 1. Attempts to bind Ru to dpa L1 and L2 Entry Ligand Ru Source Solvent Temperature Result 1 L1 RuCl 3 THF 66 C no reaction 2 dpa RuCl 3 THF 66 C no reaction 3 L1 RuCl 3 EtOH 79 C no reaction 4 dpa RuCl 3 (SMe 2 ) 3 THF RT unidentifiable product 5 dpa RuCl 3 (SMe 2 ) 3 CH 2 Cl 2 RT unidentifiable product 6 dpa RuCl 3 (SMe 2 ) 3 neat RT unidentifiable product 7 dpa Ru 3 (CO) 12 THF RT insoluble brown powder 8 L1 Ru 3 (CO) 12 EtOH 66 C insoluble brown powder 9 dpa cis [Ru(Cl) 2 (dmso) 4 ] EtOH RT low conversion 10 L2 cis [Ru(Cl) 2 (dmso) 4 ] EtOH RT insoluble brown powder

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9 Pt Complexes Based on the reactions of the ligan ds with Pd it was believed that the dpa arms should be able to preferentially bind Pt as well. However, the ligands did not react with Pt(COD)Cl 2 Silver in the form of AgNO 3 and AgPF 6 was added in an attempt to scavenge the chlorine counter ions and drive the reaction. There was evidence of a reaction, but in neither case did the Pt bind the lig and selectively at either site. The 1 H NMR spectra were very messy, and multiple products were evident. Purification attempts were unsuccessful. Cu Complexes In the case of copper it was again not possible to use 1 H NMR to charact erize the products. Though Cu( I) sources are available and labile enough to react, once bound to the ligands the Cu quickly oxidizes even under inert atmosphere to Cu( II) and thus becomes paramagnetic In the past, the McElwee White group has been able to determine the binding site of paramagnetic Co using IR studies. 16 Therefore, IR experiments were conducted with Cu complexes involving L1 and L2 as well as various analogues to show that Cu binds L1 and L2 selectively at the dpa site. Figure 6 shows the IR spectra of the products of the reactions of the various ligands with Cu( CF 3 SO 3 ) 2 Especially in the 1600 to 1560 cm 1 range, the spectra appear most similar when the ratio s of Cu equivalents to dpa sites are the same. The best results were obtained when the ligands were reacted with Cu( CF 3 SO 3 ) 2 W hen reacted with Cu(OAc) 2 the IR spectra were not conclusive. Table 2 lists the different Cu source s used as well as the different ratios and a description of the products

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10 Figure 6. IR spectra of reactions involving the various ligands with Cu(trif) 2 Table 2. Reactions involving Cu. L2 2 L2 Blue green precipitate s 3 Blueish green solid s Blueish green solid bpy0 Bright blue solid L1 Cu(CF 3 SO 3 ) 2 Blue solid s L2 Cu(CF 3 SO 3 ) 2 Blue solid s Cu(CF 3 SO 3 ) 2 Dark green oil s Cu(CF 3 SO 3 ) 2 Blue solid s Cu(CF 3 SO 3 ) 2 Pale green solid All Pd complexes synthesized thus far were found to have Pd bound to the dpa site alone through NMR and ESI MS analysis The fact that they also have IR spectra which are similar to those of the corresponding Co and Cu complexes ( Figure 7 ) is further evidence of the validity of the use of IR in this way for binding site determination.

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11 Figure 7 Expansion of the 1400 to 16 00 cm 1 region of the IR spectra of L1 L2 L1 L2 and L2 bound to either Pd, Co, or Cu. In all spectra the equivalents of metal match the number of dpa sites. Heterometallic Complexes [Rh(COD)Cl] 2 was reacted with 4 to produce heterob imetallic Pd/Rh complex 5 Although the reactions of [Rh(COD)Cl] 2 with L2 never went to completion, the reaction of 4 with [Rh(COD)Cl] 2 seemed to go to completion as no impurity was seen in the 1 H NMR even though no purification steps were performed ( Figure 8 ) Th e bound COD peaks in the 1 H NMR integrate well with the rest of the spectrum, and the methylene peaks are still diastereotopic. In ESI MS the peaks matched the calculated values, and the isotope patterns also confirmed the product. Also, all the proton a nd carbon shifts were identified by g HMBC NMR.

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12 Figure 8 1 H NMR s pectrum of 5 Another heterometallic complex was synthesized by reacting compound 2 with 0.5 equivalents of [Rh(COD)Cl] 2 in THF. The resulting Zn/Rh complex ( 6 ) was isolated as a yellow powder. In the 1 H NMR spectrum, the methylene peaks of the dpa arms are again diastereotopic, and the bound COD peaks integrate well with the rest of the spectrum. Other metals are being explored to produce different heterome tallic complexes. Reacting Cu salts with Co bound L2 did not produce an identifiable product. IR studies, which had proven useful in identifying Cu and Co products in the past, were not conclusive. When Cu bound L2 was reacted with CoCl 2 there did not s eem to be a reaction as there was no color change and the IR spectra did not change significantly When Rh bound L2 was combined with 2 equivalents of [Pt(COD)Cl 2 ] there was a color change which indicated a reaction, though the 1 H NMR data were inconclusi ve. One of the aromatic peaks associated with the bpy site shifted but the rest of the peaks did not shift relative to the original Rh bound complex. In the purified product ( 7 ) t he ratio of Pt bound COD to

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13 Rh bound COD was 2 to 1, but the methylene hydrogens of the dpa arms were not diast ereot opic. The presence of the desired Pt/Rh complex could not be confirmed through mass spectrometry. EXPERIMENTAL Unless otherwise stated, all reactions were conducted under inert atmosphere using standard Schl enk line or glove box techniques. All anhydrous solvents were stored over 3 molecular sieves. Dichloromethane ( DCM), hexane, and toluene were p assed through a n M Braun MB SP solvent purification system prior to use. Tetrahydrofuran (THF) was distilled from sodium/benzophenone, and ethanol was di s tilled from magnesium turnings and I 2 Most reagents were ob tained from commercial vendors. Ligand analogues L1 and L2 16 RuCl 3 (SMe 2 ) 3 17 and cis [Ru(Cl) 2 (dmso) 4 ] 18 were previously prepared by the McElwee White group. 1 H NMR spectra were obtained using either a 300 MHz Mercury or a 300 MHz Gemini instrument. 2D GHMBC was performed using a n INOVA 500 MHz instrument. High resolution mass spectrometry (HRMS) data were recorded on an electrospray ionization, time of flight (ESI TOF) mass spectrometer. Infrared spectra were measured on a Perkin Elmer 1600 FTIR either as pure solid or as neat oil. Synthesis of Ligands 5 (bromomethyl) 5 methyl 2,2' bipyridine (bpy1). N bromosuccinimide (0 .964 g, 5. 43 mmol) dimethyl b ipyridine ( bpy0 ) ( 1.00 g, 5.43 m mol) and a catalytic amount of AIBN were combined with 20 mL CCl 4 The resultant yellow mixture was refluxed for 19 hours. The insoluble succinimide was filtered out of the reaction mixture a nd solvent was pulled off the remaining products under reduced pressure A small amount of DCM was added

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14 to the crude product and a small amount of white powder was removed by filtration The solution was purified via silica gel chromatography using 0 50 % EtOAc in DCM to give 0.410 g (29% ) of bpy1 as a white powder 1 H NMR (300 MHz CDCl 3 ) = 8.66 (d, J = 2.3 Hz, 1 H), 8.50 (dd, J = 0.7, 1.5 Hz, 1 H), 8.36 (d, J = 8.2 Hz, 1 H), 8.28 (d, J = 8.2 Hz, 1 H), 7.84 (dd, J = 2.3, 8.2 Hz, 1 H), 7.63 (ddd, J = 0.7, 2.3, 8.1 Hz, 1 H), 4.53 (s, 2 H), 2.40 (s, 3 H) L1. A 50 mL Schlenk flask was charged with bpy1 (0.410 g, 1.56 mmol) K 2 CO 3 (0.863 g, 6.24 mmol) and a catalytic amount of Bu 4 NI. To this was added 12.5 mL of THF, followed by dpa and a second addition of 12.5 mL of THF. The resultant yellow mixture was stirred at room temperature ov ernight. An off white solid was removed by filtration and the yellow soluti on was purified via chromatography on alumina with EtOAc as the eluent to afford L1 as an off white solid ( 0.459 g 77%) 1 H NMR (300 MHz, CDCl 3 ) = 8.70 (d, J = 2.0 Hz, 1H), 8.54 (d, J = 5.5 Hz, 2H), 8.50 (d, J = 2.2 Hz, 1H), 8.30 (d, J = 8.2 Hz, 1H), 8.25 (d, J = 8.2 Hz), 7.84 (dd, J = 2.2, 8.2 Hz, 1H), 7.68 (td, J = 1.7, 7.7 Hz, 2H), 7.62 (dd, J = 2.0, 8.4 Hz, 1H), 7.57 (d, J = 8.0 Hz, 2H), 7.17 (ddd, J = 1.1, 5.0, 7.2 Hz, 2H), 3.86 (s, 4H), 3.76 (s, 2H), 2.40 (s, 3H). IR (neat, cm 1 ): 3007 (w), 2921 (w), 2823 (w), 1590 (s), 1570 (m), 1554 (m), 1466 (s), 1433 (s), 1365 (m), 1301 (w), 1241 (w) 1220 (w), 1148 (w), 1127 (m), 1089 (w), 1048 (w), 1029 (w), 994 (m), 830 (m), 763 (s), 742 (m). 5,5' bis(bromomethyl) 2,2' bipyridine (bpy2). A mixture of bpy0 ( 0.381 g, 2.07 mmol), N bromosuccinimide (0.772 g, 4.34 mmol), and a catalytic amount of AIB N was refluxed for 19 hours in CCl 4 The reaction mixture was filtered w hile still hot and solvent was removed under vacuum. The off white crude product was washed with a small amount of DCM, and the remaining solid was recrystallized from hot DCM. White needle like crystals formed

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15 which were found to be pure bpy2 ( 0 .298 g 42 % yield ). 1 H NMR (300 MHz CDCl 3 ), 8.68 (d, J = 2.04 Hz, 2 H) 8.40 (d, J = 8.33 Hz, 2 H) 7.86 (dd, J = 8.18, 2.34 Hz, 2 H) 4.54 (s, 4 H) L2 A 50 mL Schlenk flask was charged with dpa (0.521 g, 2.62 m mol) bpy 2 (0.2983 g, 0.8 72 mmol), and K 2 CO 3 (1.0393 g, 7.52 m mol) The reagents were dissolved in 17 mL anhydrous THF, and the reaction mixture was stirred at room temperature for 22 hours. An off white solid was removed by filtration and 51 mL of hexane was added to the filtrate. Solids sank to the bottom, and the solution was decanted into a 100 mL Schle nk at which point tan crystals began to form. The crystals were a llowed to grow under Ar atmosphere for 3 days and then collected by vacuum filtration to afford L2 ( 0.3188 g 63 % ). It was later found that the tan color of the crystals was due to a 1 H NMR silent impurity. In subsequent syntheses of L2 the crysta ls were purified by chromatography on alumina using EtOAc as the eluent or by recrystallization in to afford pure L2 in 30 45% yields 1 H NMR (300 MHz CDCl 3 ) = 8.70 (d, J = 1.5 Hz, 2 H), 8.53 (ddd, J = 1.0, 1.9, 4.9 Hz, 4 H), 8.31 (d, J = 8.5 Hz, 2 H), 7.84 (dd, J = 2.2, 8.0 Hz, 2 H), 7.67 (td, J = 1.8, 7.6 Hz, 4 H), 7.56 (d, J = 7.9 Hz, 4 H), 7.16 (ddd, J = 1.2, 4.9, 7.4 Hz, 4 H), 3.85 (s, 8 H), 3.76 (s, 4 H) IR (neat, cm 1 ): 3011 (w), 2956 (w), 2920 (w), 2852 (w), 2812 (w), 1590 (s), 1568 (m), 1554 (w), 1473 (m), 1458 (m), 1434 (s), 1388 (w), 1363 (m), 1311 (w), 1242 (w), 1154 (w), 1124 (m), 1089 (w), 1049 (w), 1021 (w), 989 (m), 973 (m), 960 (m), 929 (w), 898 (w), 836 (m), 816 (m), 769 (s ), 759 (s), 742 (m), 734 (m). Dibenzylamine (0.126 g, 0.614 mmol), bpy2 (0.0998 g, 0.292 mmol), K 2 CO 3 (0.342 g, 2.47 mmol), and a catalytic amount of Bu 4 NI were combined with THF in a Schlenk flask. The reaction mixtu re was allowed to stir for 22 ho urs at room temperature, then an off w hite solid was removed by filtration and the remaining solution was pur ified by column chromatography using silica gel and 0 25% EtOAc in DCM to give 0.107 g (64%) of an

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16 off white powder 1 H NMR (300 MHz, CDCl 3 ) = 8.68 (d, J = 1.6 Hz, 2 H), 8.31 (d, J = 8.0 Hz, 2 H), 7.82 (dd, J = 2.2, 8.2 Hz, 2 H), 7.44 7.37 (m, 8 H), 7.37 7.28 (m, 9 H), 7.25 7.18 (m, 2 H), 3.61 (s, 4 H), 3.58 (s, 8 H). IR (neat, cm 1 ): 3926 (m), 2790 (m), 2713 (w), 2578 (w), 2333 (w), 172 5 (w), 1548 (m), 1496 (m), 1458 (m), 1449 (m), 1419 (m), 1285 (w), 1210 (m), 1117 (w), 1089 (w), 1030 (m), 1007 (w), 976 (m), 933 (w), 920 (w), 846 (w), 8001 (m), 757 (m), 745 (s), 699 (s). Zn Complexes [(bpy) (dpa) 2 (Zn(OAc) 2 ] ( 1 ). A solution of Zn(OAc) 2 2H 2 O (0.0124 g, 0.0565 mmol) in methanol was added to a solution of L2 (0.0186 g, 0.0321 mmol) in methanol open to air. The solvent was removed under reduced pressure to afford (0.0163 g, 61%) as a pale yellow solid. 1 H NMR (300 MHz CD 3 OD ) = 8.78 ( d, J = 4.2 Hz, 4 H), 8.55 (br s 2 H), 8.36 (d, J = 7.6 Hz, 2 H), 8.06 (t, J = 7.5 Hz, 4 H), 7.94 (br s 2 H), 7.61 (t, J = 6.3 Hz, 4 H), 7.56 (d, J = 8.0 Hz, 4 H), 4.18 (br d, J = 40.0 Hz, 8 H), 3.90 (br s 4 H) [(bpy) ( dpa ) 2 (Zn (NO 3 ) 2 ] ( 2 ) L2 (0.0168 g 0.0290 mmol) and Zn(NO 3 ) 2 6H 2 O (0.0170 g, 0.0571 mmol) were both added to a 25 mL round bottom flask and dissolved in methanol under ambient atmosphere As soon as all reagents had gone in to solution the solvent was removed under reduced pressure to afford ( 0.0146 g 5 2.5%) of a pale yellow solid 1 H NMR ( 300 MHz CD 3 OD ) = 7.60 (d, J = 5.1 Hz, 4 H), 7.43 (d, J = 1.7 Hz, 2 H), 7.31 (d, J = 7.4 Hz, 2 H), 7.06 (td, J = 1.3, 7.3 Hz, 4 H), 6.76 (dd, J = 2.0, 7.6 Hz, 2 H), 6.66 6.54 (m, 8 H), 3.27 (d, J = 15.0 Hz, 4 H), 2.87 (d, J = 16.4 Hz, 4 H), 2.71 (s, 4 H) Rh Complexes [(COD)Rh (bpy) ( dpa ) 2 ]Cl ( 3 ) [Rh(COD)Cl] 2 (0.149 g, 0.0302 m mol) was added along with L 2 ( 0.362 g, 0.0302 mmol ) to a 10 mL Schlenk. The reagents were dissolved in 8 mL of

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17 THF and stirred at room temperature for 45 minutes The solvent was removed under reduced pressure, leaving 3 as a shiny red solid which adhered strongly to the sides of the flask Purification was attempted by recrystallization from CH 2 Cl 2 with hexanes and also from CH 2 Cl 2 with toluene. 1 H NMR ( 300 MHz CDCl 3 ) = 9.37 (d, J = 8.2 Hz, 2 H), 8.53 (d, J = 4.2 Hz, 4 H), 8.26 (d, J = 7.9 Hz, 2 H), 7.86 (br. s., 2 H), 7.70 (t, J = 8.0 Hz, 4 H), 7.47 (d, J = 7.9 Hz, 3 H), 7.24 7.08 (m, 5 H), 4.59 (br. s., 4 H), 3.82 (s, 6 H), 3.73 (br. s., 8 H), 2.74 2.50 (m, 4 H), 2.19 (q, J = 7.6 Hz, 4 H) Note that in the 1 H NMR data listed here, only the peaks corresponding to product are listed. The L2 starting material was al so present in a 0.44 : 1.0 ratio of L2 : 3 HRMS (ESI TOF ): calcd. [M Cl] + 789.2895 found 789.2914. Pd Complexes [(bpy) ( dpa ) 2 (PdCl) 2 ]Cl 2 ( 4 ). A 100 mL Schlenk flask was charged with Pd(COD)Cl 2 (0.0990 g, 0.347 mmol) and L2 (0.100 g, 0.173 mmol). The reagents were combined with 60 mL THF, though not everything was observed to go into solution. The reaction mixture was stirred for 24 h at which point a beige preci pitate had formed. The supernatant was removed and the solid was rinse d with THF, after which the solid was dried under reduced pressure yielding 4 as a beige powder (0.150 g, 93%) 1 H NMR ( 300 MHz CD 3 OD ) = 9.08 (d, J = 1.7 Hz, 2 H), 8.58 (dd, J = 1.0, 5.8 Hz, 4 H), 8.45 (dd, J = 2.3, 8.2 Hz, 2 H), 8.01 (td, J = 1.5, 7.8 Hz, 2 H), 7.97 (d, J = 8.8 Hz, 4 H), 7.60 (d, J = 7.9 Hz, 4 H), 7.41 (ddd, J = 1.0, 5.7, 7.2 Hz, 4 H), 5.53 (d, J = 16.1 Hz, 4 H), 4.73 (d, J = 15.5 Hz, 4 H), 4.42 (s, 4 H) HRMS (ESI TOF): calcd. [M 2 Cl] 2+ 431.0175 found 431.0165; calcd. [M Cl] + 897.0039 found 897.0040; calcd. [M HCl 2 ] + 861.0277 found 861.0270. IR (neat, cm 1 ): 3384 (m), 3035 (w), 1609 (m), 1572 (w), 1558 (w), 1474 (m), 1448 (m), 1391 (w), 1373 (w), 1285 (m), 1235 (w), 1160 (w), 1111 (w), 1080 (w), 1056 (m), 1037 (w), 998 (w), 935 (w), 860 (m), 817 (m), 772 (s), 722 (m), 663 (m).

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18 Cu Complexes The reactions of t he various ligands involving Cu were conducted in ambient atmosphere. Different ratios of Cu( CF 3 SO 3 ) 2 to the ligand were used in order to be able to compare their IR spectra for p atterns which would indicate the site the metal was binding In each case C u( CF 3 SO 3 ) 2 and the ligand were dissolved in separate solutions in methanol and the Cu solution was then added dropwise to the stirring ligand solution. The solvent was then pulled off under reduced pressure and an IR spectr um of the product was obtained. The IR stretches of all the products are collected in Table 3 Table 3. IR stretches of products of the various Cu( CF 3 SO 3 ) 2 reactions Ligand Ratio (L:M) IR Stretches ( neat, cm 1 ) L1 1:0.5 1609 (m) 1590 (m) 1570 (m) 1475 (m) 1434 (m) 1249 (s) 1222 (s) 1149 (s) 1052 (w) 1028 (s) 994 (m) 833 (m) 764 (m) 731 (m) L2 1:1 1608 (m) 1591 (m) 1570 (m) 1475 (m) 1434 (m) 1361 (w) 1246 (s) 1223 (s) 1150 (s) 1053 (w) 1028 (s) 995 (w) 828 (m) 764 (s) L1 1:0.5 3473 (w) 3031 (w) 2937 (w) 2832 (w) 2016 (w) 1980 (w) 1697 (w) 1609 (m) 1572 (w) 1521 (w) 1487 (m) 1448 (m) 1411 (w) 1370 (w) 1251 (s) 1223 (s) 1151 (s) 1100 (w) 1077 (w) 1055 (w) 1028 (s) 1008 (m) 841 (m) 819 (m) 763 (s) 745 (m) 698 (s) L2 1:1 1611 (m) 1573 (w) 1498 (w) 1482 (w) 1449 (m) 1367 (w) 1246 (s) 1224 (s) 1158 (s) 1099 (w) 1058 (w) 1028 (s) 1006, 979, 840 (w) 800 (m) 762 (s) 724 (w) L1 1:1 1609 (m) 1573 (w) 1482 (m) 1450 (w) 1244 (s) 1223 (s) 1155 (s) 1055 (w) 1027 (s) 83 5 (w) 814 (w) 766 (m) 734 (w) L2 1:2 1613 (m) 1573 (w) 1483 (m) 1452 (w) 1276 (s) 1252 (s) 1226 (s) 1164 (s) 1029 (s) 771 (m) L1 1:1 1613 (m), 1575 (w) 1488 (m) 1450 (m) 1286 (s) 1242 (s) 1226 (s) 1168 (s) 1029 (s) 819 (w) 767 (m) 700 (w) L2 1:2 1612 (m) 1575 (w) 1486 (w) 1450 (m) 1371 (w) 1277 (s) 1238 (s) 1222 (s) 1157 (s) 1098 (w) 1058 (w) 1025, 853 (w) 800 (m) 765 (m) 724 (w) L2 1:1 3032 (w) 2800 (w) 1606 (w) 1495 (w) 1479 (m) 1454 (m) 1418 (w) 1369 (w) 1277 (s) 1236 (s) 1223 (s) 1162 (s) 1073 (w) 1052 (w) 1028 (s) 973 (m) 913 (m) 821 (m) 750 (s) 698 (s) 679 (w) 660 (w)

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19 Heterometallic Complexes [(COD)Rh (bpy) ( dpa ) 2 (PdCl) 2 ]Cl 3 ( 5 ) A 50 mL Schlenk was charged with [Rh(COD)Cl] 2 (0.0106 g, 0.0215 mmol) and 4 (0.0400 g, 0.0429 mmol). The reagents were suspended in 20 mL of ethanol. After 40 min all reagents had dissolved into a pink solution. Solvent was removed under reduced pressure giving 5 as a brown product (0.0375 g, 79%) 1 H NMR ( 300 MHz CD 3 OD ) = 8.84 (s, 2 H), 8.63 (d, J = 5.4 Hz, 4 H), 8.45 (dd, J = 1.1, 8.3 H z, 2 H), 8.05 (d, J = 2.3 Hz, 2 H), 8.07 (td, J = 1.5, 7. 8 Hz, 4 H), 7.66 (d, J = 7.6 Hz, 2 H), 7.49 (t, J = 6.5 Hz, 4 H), 5.56 (d, J = 16.4 Hz, 4 H), 5.06 (br s., 4 H), 4.83 (d, J = 16.4 Hz, 4 H), 4.53 (s, 4 H), 2.79 (br. s., 4 H), 2.35 (d, J = 8.5 Hz, 4 H) HRMS (ESI TOF): calcd. [M Cl] + 1144.9714 found 1144.9680 ; calcd. [M 2Cl] 2+ 554.0015 found 554.0021. [(COD)Rh (bpy) ( dpa ) 2 (ZnNO 3 ) 2 ]Cl 3 ( 6 ). A solution of L2 (0.0160 g, 0.0276 mmol) in 5 mL methanol was prepared in a 25 mL round bottom flask open to air. To this was added a solution of Zn(NO 3 ) 2 6H 2 O (0.0162 g, 0.0544 mmol) also dissolved in methanol. The solvent was removed under reduced pr essure, and the round bottom flask was charged with argon. Anhydrous T HF was added to the flask but not all solids dissolved. The white suspension was can n ula transferred to a Schlenk flask containing an orange solution of [Rh(COD)Cl] 2 (0.0068 g, 0.014 mmol) in THF. The reaction mixture turned yell ow but not everything went into solution Solvent was removed under reduced pressure, yielding 6 as a tan solid (0.0201 g, 61%) 1 H NMR (300MHz, CD 3 OD) = 8.76 (ddd, J = 0.7, 1.3, 5.2 Hz, 4 H), 8.32 (d, J = 8.2 Hz, 2 H), 8.28 (dd, J = 1.3, 8.5 Hz, 2 H), 8.14 (td, J = 1.6, 7.6 Hz, 4 H), 7.90 (s, 2 H), 7.74 (ddd, J = 0.9, 5.0, 8.0 Hz, 4 H), 7.63 (d, J = 7.9 Hz, 4 H), 4.68 (br. s., 4 H), 4.40 (d, J = 16.1 Hz, 4 H), 4.13 (s, 4 H), 4.14 (d, J = 15.0 Hz, 4 H), 2.7 0 (br. s., 4 H), 2.27 (d, J = 9.3 Hz, 4 H).

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20 7 A Schlenk flask was charged with [Rh(COD)Cl] 2 (0.0107 g, 0.0217 mmol) and L2 (0.0255 g, 0.0441 mmol). The reagents were dissolved in THF and stirred at room temperature for 30 min Solvent was removed under reduced pressure yielding an orange solid. Pt(COD)Cl 2 (0.0324 g, 0.0866 mmol) was added to the Schlenk in a glove box, followed by a solution of AgPF 6 (0.0218 g, 0.0862 mmol) in 4 mL THF. The solids all went into solution who se color then changed to a brighter orange and solids began to precipitate Solvent was removed under reduced pressure, and the solids were redissolved in acetonitrile. Ether was added, precipitating a white solid. The solid was removed by filtration and the solvent of the filtrate was removed to give orange impure product 7 1 H NMR (300 MHz CDCl 3 ) = 8.56 (d, J = 4.4 Hz, 4 H), 8.26 (d, J = 8.3 Hz, 2 H), 8.18 (d, J = 8.5 Hz, 2 H), 7.92 (s, 2 H), 7.73 (td, J = 1.0, 7.7 Hz, 4 H), 7.47 (d, J = 7.7 Hz, 4 H), 7.22 (ddd, J = 0.6, 4.8, 7.2 Hz, 4 H), 5.76 5.43 (m, 8 H), 4.64 (br s 4 H), 3.85 (s 8 H), 3.78 (s, 4 H), 2.69 (br s 12 H), 2.31 2.11 (m, 12 H)

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