Synthesis gas transformations with heterogeneous iridium and homogeneous rhodium metal complexes

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Synthesis gas transformations with heterogeneous iridium and homogeneous rhodium metal complexes
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xiv, 179 leaves : ill. ; 28 cm.
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Getty, Cindy S
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Synthesis gas   ( lcsh )
Rhodium catalysts   ( lcsh )
Iridium catalysts   ( lcsh )
Chemistry thesis Ph. D
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bibliography   ( marcgt )
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Thesis:
Thesis (Ph. D.)--University of Florida, 1988.
Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by Cindy S. Getty.
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Typescript.
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Vita.

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SYNTHESIS GAS TRANSFRWMATIOIS WITH HEIEGENEUS
IRIDIUM AND IHMDGEEUS RHIDIEI METAL OCMPIEXES












BY

CINDY S. GETTY


A DISSERTATION PRESETED TO THE GRADUATE
SCHOOL OF 'ME UNIVERSITY OF FIRI3DA IN
PARTIAL FULFILTMENT OF THE REQUIREMENTS F R
THE DEREE OF DOCITR OF PHIIDSOPHY

UNIVERSITY OF FLRIDA

1988


SOF F LIBRARIES






























To My Parents















ACIOlWEDGMEIS


This research and dissertation would not have been possible

without the support, encouragement and guidance of a number of

people. First I would like to thank my mentor, Russell S. Drago and

his wife, Ruth. Had it not been for Doc's ideasr" and skill on the

tennis courts, my stay at the University of Florida would not have

been as well-rounded and fulfilling. He always knew I enjoyed a

good argument. Ruth also deserves a special thanks for making me

feel as if Florida was a second hame.

The entire Drago group has also influenced my graduate studies.

A few members have played a special role. I would like to thank Dr.

Keith Weiss, larry "Chmoo" Chanusco, Jerry "Bear" Grunewald, Thomas

" 1m" Cundari, Ngai "Nagy" Wong and.my brother Alan "Hard Body"

Goldstein. To Mark "Sparticus" Barnes, I owe a special thanks for

his friendship which I will always cherish. Dr. Roy King, of the

Microanalytical laboratories, also deserves a special thanks for all

of his help.

During my undergraduate days at S.U.N.Y. Plattsburgh my studies

in chemistry were greatly influenced by Dr. Gerald F. Kokoszka.

Without his encouragement I might not be pursuing a career as a

chemist.









Finally, for all of their support and love over the years I

would like to thank my entire family and especially my husband and

best friend, Ed. I always imagined graduate school as a time for

total devotion to one's studies and development as a chemist. Ed

has taught me that there is more to life than chemistry. For this I

am forever indebted to him.
















TABLE OF CONTENTS


ACKNOWLEDGEMENTS...........................................

UIST OF TABLES............................................

UST OF FIGURES..........................................

ABSTRACT...................................................

CHAPTER

I. INTR0DUCTIO......................................

II. INVESTIGATION OF SUPPORTED IRIDIUM CARONYL FOR THE
TRANSFCUMATICN OF SYN GAS AND HC1 TO MEIHYL
CHLE DE. o ..... o ................ ... o ................

A. Background ......................................

B. er tal.................................... .

Materials .........................................

Instrumentation ....................................

Fixed Bed Flow Reactor ...........................

Preparation of a Phosphinated Support.............

Preparation of the Supported Triphosphine
Substituted Iridium Car l Clusters. ..........

Preparation of Directly Deposited Tetrairidium
carbcnyl Clusters on the Support. ...............

Preparation of the Aluminum Chloride Tetrairidium
Carb~3 yl Cluster Treated Supports................

Preparation of Other Lewis Acid Deposited
Tetrairidium Carbonyl Clusters ....................

Preparation of Aluminum Chloride Treated
mnaercial Methanol Catalysts ....................

V


iii

ix

x

xiii



1



3

3

18

18

19

20

23


24


24


25


26


26










Reaction of the Supports and the Supported
Metal Ocmplexes with Carbon Manoxide, Hydrogen
HC1(g) ........................................... 27

C. Results and Discussion ............................ 27

Reinvestigation of Earlier Work of the Supported
Thosphine Substituted Tetrairidium Carbonyl
Cluster......................................... 27

Investigation of Directly Deposited Ir4(0)12 ..... 39

Investigation of Supported Ir4 (0) 12 for Catalytic
Activity Upon Reaction with H2, 00 and HC(g) .... 44

Investigation of the Aluminum Chloride Treated
Deposited Iridium Carbonyl Clusters.............. 47

Investigation of the Aluminum Chloride Treated
Supported Iridium Carbonyl Clusters for Catalytic
Activity Upon Reaction with H2, 00 and HCl(g)..... 51

Comparison with the Homgeneous Ir4 (C) 12-Al2C16
System.......................................... 53

Infrared Investigation of Deposited Ir4(C) 12
After Reaction with H2, C0 and HCl(g)............ 55

Infrared Investigation of Supported
Ir4(O0)12-A12Cl6 COmplexes After Reaction with
H2, 00 and HCl(g) ................................ 58

Investigation of Supported IrC1(C0)3 Upon Reaction
with H2, 00 and HC (g) ........................... 63

Investigation of Metallic Iridium Upon Reaction
with H2, CD and HCl(g).......................... 67

Investigation of Other Lewis Acids................ 68

Investigation of A12C16 Treated COamercial 00
Reduction Catalysts ............................. 69

Mechanism Proposed for the Formation of Methyl
loaride ........................................ 71

D. Summary........................................... 75









III. RHODIUM PERFIUn CARBOXYIATE IRIIHENYLP SHINE
COMPLEXES FOR OIEFIN HYDsIFOtMYIATION................. 79

A. Backgrou d........................................ 79

B. Experimental....................................... 88

Reagets ..................................... 88

Instrmentation................... .......... 89

Synthesis of Tetrakis(acetato) Dirhodium(II) ...... 90

Synthesis of Tetrakis(perfluorcbutyrato)
Dirodiu(II).................................... 92

Synthesis of Other Rhodium(II) Carboxylate Dimers. 92

Preparation of Trifluoroacetato
Tris(triphenylphophine) Ihodium(I) ............ 93

Preparation of Trifluoracetato
Tris(triphenylphosphine) Rhodium(I) from Hydrido
Tetrakis(triphenylphosphine) Rhodium(I) .......... 93

Preparation of Trifluoroacetato
Bis(triphenylphosphine) Rhodium(I) Carbonyl...... 94

Preparation of Nafion Supported Rh(O2CF3) (PPh3)3. 94

Hydroformylation of Olefins with the Rhodium
Ocun lexes......................... ............... 95

C. Results and Discussion........................... 95

Investigation of Rhodium(II) Perfluorocarboxylate
cmplexes as Catalysts for Hydroformylation of
1-Hex ne..... ....... ............................. 95

Effect of Added Triphenylphosphine on Catalytic
Activity and Selectityetye........................ 100

COuparative Studies with Other Rhodium Carboxylate
Omplexes.................. o--o ......o ...... 104

Comparative Studies with Rhodium(I) Complexes..... 107

Investigation of the Rhodium Perfluorocarboxylate
Triphenylphosnhine Catalyst System During
Hydroformnylation.................... ........... 108


vii









Visible Investigation on the Effect of Added
Olefin and hosiphine to the Rhodium(II)
Perflurdbutyrate Cmplex ........................ 120

Investigation of the Species Formed Upon Reaction
of rKodium(II) Perfluorocarboxylate Ocmplexes
with TriIpenylphosphine. ................. ..... 121

Investigation of Ph(O2CF3) (PPh3)3 for Catalytic
Hydroformylation of 1-Hexne..................... 133

Investigation of the Rh(02CCF3)(PPh3)3 Systm
During Reaction.................................. 134

Investigation of Trifluoroacetate Carbonyl
Bis(tri enylphopine) Rhodiu(I) ............... 139

Occ~ rative Hydroformylation Studies with Hydrido
Carbonyl Tris(triphenylposphine) Rhodium(I) ..... 140

Prearation of [Ph(PFt3)3]+[(020CF3) ] Exchanged
onto Nafion ...................................... 145

Hydroformylation of 1-Hexene using the Polymer
Supported Rhodium Catalyst ....................... 147

Leaching of the Catalyst from the Resin ......... 150

Hydrofonwylation of Propylene Using
Tris(triphenylphosphine) Rhodium(I) Incorporated
in a Polymeric Membrane Film ..................... 150

Hydroformylation of Other Olefins with
Eh(020CF3) (PI:43)3 ................................. 151
Hydrogenation of 1-Hexene and Other Miscellaneous
Reactions of 00, H2 and Heptaldeyde with
Rh(020CF3) (Ph3)3 ................................ 154
Proposed Mechanism for the Catalytic
Hydroformylation of 1-Hexne with
Ih(020CF3) (PPh3)3 and Added Triphenylpho.phine... 159

D. Sumary.......................... ................. 162

IV. OCM DSION ............................................. 166

REFERENCES................................................... 171

BIOGRAPHICAL SKECH .......................................... 179


viii















LIST OF TABiES


2-1 Ways to Utilize Clusters in Catalysis............ 5

2-2 Advantages of Hmogeneos Versus Hterogeneous
Catalysts ........................................ 8

2-3 Possible Reactions and the thrmodynamic
Feasibility for the Formation of Methyl Chloride. 12

2-4 Major Carbonyl Bands in the Infrared Spectra for
hosphine Substituted Ir4 (C) 12 and Ir4 (0) 12.... 29

2-5 Control Reactions for the Rhosphine Substituted
Supported System............................... 31

2-6 Major Carbonyl Bands in the Infrared Spectra for
iosphine Substituted Ir4(00)12 and I4 (00)12
After Reaction with H2, 00 and HC ............... 57

3-1 Rhospharus NR Data for the Rhodium
Perfluorocarboxylate Ocaplexes.................... 112

3-2 Fluorine NMR Data for the Rhodium
Perfluorocarbrxylate Ocaplexes ................... 115

3-3 Infrared Data for the Rhodium
Perfluorocarboxylate Couplees ................... 118

3-4 Comparison of 1-Hexene Hydrofornylation Activity
for Various Rhodium(I) Catalysts................. 135














LIST OF FIGURES


Figure Pase

2-1 A Proposed Mechanism For the Formation of Methyl
Chloride with the Piosphine Substituted Supported
Iridium Clusters ...................................... 17

2-2 A Diagram of the Fixed Bed Flow Reactor ............. 22

2-3 Structure of the Ethoxy Surface Species Formed
During Functionalization of the Alumina Oxide......... 34

2-4 Schematic Representation of the Decomposition of the
Ethoxy Groups at Elevated Teperatures ................ 37

2-5 Infrared Spectra of Ir4 () Deposited onto Alumina
Before and After Treatment with Al2C6 ................ 41

2-6 Infrared Spectra of Ir4 () 12 Deposited onto Silica
Gel Before and After Treatment with Al2C16............ 42

2-7 A Sample Gas axrcmatograph of the Products Formed
Upon Reaction of H2, C0 and HC over the Supported
Iridium Clusters at 1250C and 1 Atmosphere............ 45

2-8 Activity Curves for the Various Supported Iridium
Carbonyl Clusters for the Formation of Methyl
Chloride........................................... 46

2-9 Infrared Spectra of Ir4(00)12 Deposited onto Alumina
and Silica Gel After Reaction with H2, 0C and HC1 at
1250C .................................... ........... 56

2-10 Infrared Spectrum of Al2o/r4 (CD)12/Al2C After
Reaction with H2, CO and HC1 at 125C................. 60

2-11 Infrared Spectrum of SiO2/Ir4 (C) 12/Al2C6 After
Reaction with H2, 00 and HC1 at 1250C................. 61

2-12 ESCA of Si02/Ir4 (C) 12/A12C16 Before and After Reaction
with H2, CO and HC at 125C .......................... 62

2-13 Infrared Spectra of Al203/IrC (C)3 Before and After
Reaction with H2, CO and HC1 at 1250C ................ 64









Figure Pae

2-14 Infrared Spectra of A1203/IrCl (0 ) 3/A12C16 Before and
After Reaction with H2, 00 and HC1 at 125C ........... 66

2-15 Prposed Mechanism for the Formation of Methyl Chloride
with the Supported Iridium Carbonyl Clusters ......... 72

3-1 A Diagram of the Pressure Bottle Apparatus Used for the
Hydrofonrylation Reactions.......................... 91

3-2 A Sample Gas OCrmnatograph of the Products Forned After
the Hydroformylation of 1-Hexne with the Rhodium(II)
Perfluorocarboxylate Catalyst at 1000C ............... 97

3-3 A Sample Mass Sctra of the Solution After Reaction
Enriched with "Carbon MnKide........................ 99

3-4 Activity Curves for the Formation of Heptaldehyde with
Varying Ratios of Rhodium(II) Perfluorobutyrate to
Triphenylphophine .................................... 101

3-5 Bar Graphs Illustrating the Effect of Added Triphenyl-
phosphine on Isamer Ratio ............................. 103

3-6 OCaparative Activity Curves for the Hydrofnrmylation of
1-Hmexne with IRodium(II) Perfluaorbutyrate and
Rodium(II) Trifluoroacetate with Added hosphine..... 105

3-7 Color Changes Observed During Reaction ................. 109

3-8 31p NR Spectrum of the Reaction Mixture During
Hydroformylation with Rh2 (02C3F7)4 and 5PPh3......... 111

3-9 19F *m Spectrum of the Reaction Mixture During
Hydrofornylation with Rh2 (0CC3F7)4 and 5PMh3......... 114

3-10 Infrared Spectrum of the Reaction Mixture During
Hydrofoamylation with Rh2 (02CC3F7)4 and 5PPh3 ......... 117

3-11 Visible Spectral Overlay Upon Sequential Addition of
1-Hexene to Rhodium(II) Perfluordbutyrate............. 121

3-12 Visible Spectral Overlay Upon Sequential Addition of
Triphenylphosphine to Rhodium(II) Perfluordbutyrate... 123

3-13 Infrared Spectrum of Rh(2CCF3) (PPh3)3 ..... ....... 127

3-14 19F N Spectrum of Rh(O2CF3) (PP3)3 .......... ..... 129

3-15 31p m Spectrum of Rh(O2CF3) (PPh3)3................. 132


xi









Fire Page

3-16 Infrared Spectrum of the Reaction Mixture During
Hydroformylation of 1-Hexne with h (02OCF3) (PPh3)3... 138

3-17 31P NMR Spectrum of the Reaction Mixture During
Hydrofoa ylation of 1-Hexene with h(O2CCF3) (PPh3)3... 142

3-18 Bar Graph -Cparison of the Hydroformylation Activity
of Mh(020CF3) (PPh3)3 Versus RhH(O) (PPh3)3............ 143

3-19 Bar Graph Oc:parison of the Haogenemus Versus the
Heterogeneous Hydroformylation System ................. 149

3-20 A Sample Mass Spectrum of the Reaction Solution After
Hydroformylaticn of Styrene ........................... 153

3-21 A Sample Mass Spectrum of the Reaction Solution After
Hydrofomylation of Ethyl Vinyl Ether................. 156

3-22 Proposed Mechanism for the Hydroformylation of Olefins
with the Tris(triPeny1phosphine) IRodium(I)
Trifluaroaoetate System .............................. 160


xii















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.

SYNIESIS GAS TRANSFORMTIONS WrIM HETEGENEOUS
IRIDIIU AND HCMGENEOUS HODIIU METAL COMPLEXES

By

Cindy S. Getty

December 1988

Chairman: Russell S. Drago
Major Department: Chemistry


There has been a great deal of interest in the development of

chemicals from synthesis gas (H2 and 00). Typically, the reactions

are catalyzed by soluble (hamogenecus) metal ccmplexes or supported

(heterogeneous) metal complexes or metal particles. The emphasis of

this work has been on the development of homogeneous and

heterogeneous catalytic systems capable of the indirect

transformation of H2 and CO into chemicals under mild reaction

conditions.

Supported iridium carbonyl and aluminum chloride were

investigated in an attempt to heterogenize an analogous homogeneous

catalyst. The presence of aluminum chloride was found to lead to

cluster interactions resulting in a system capable of selective

reduction of carbon monoxide under mild reaction conditions. When a

gaseous mixture of H2, 00 and HC1 was passed over the supported

cluster at 1250C, methyl chloride, methane, carbon dioxide and water

xiii









were observed as major products. Unlike the hmogeneous analog only

trace C2 products were detected. Infrared spectrosoopy was used to

investigate the preparation of the deposited clusters as well as the

iridium species formed on the support during reaction.

The second study involved the investigation of a rhodium

carboxylate triphenylphosphine complex which was found to be an

active, homogeneous hydroformylation catalyst. The system

selectively produced more of the linear aldehyde than the branched.

The product selectivity was found to depend upon the amount of

phosphine present. Spectroscopic studies supported that a

bis (triphenylphoshine) rhodium (I) trifluoroacetate carbonyl species

was the active catalyst. Ocaparative studies with other rhodium

carboxylate complexes and hydroformylation catalysts showed that the

perfluorocarbOxylate complexes exhibited greater activity.


xiv















I. INIMW CIIlCN


The investigation of fuel sources other than oil has been of

interest since the 1970s. An attractive alternative is coal. The

coubustion of coal results in the formation of a gaseous mixture of

hydrogen and carbon monoxide referred as synthesis gas. Synthesis

gas may be used as a feedstock for the production of chemicals and

fuels.1

A large rnmber of chemicals may be directly or indirectly

produced frma synthesis gas.2 In direct processes, no molecules

other than carbon monoxide and hydrogen are employed as the

reactants. An indirect process would involve the combination of

carbon monoxide and hydrogen with a third reactant molecule. The

reactant molecule may be an olefin, alcohol, HC1, etc.

Transition metal ccnplexes are generally employed as catalysts

for the conversion of synthesis gas into chemicals.3,4 Typically,

the catalysts are soluble (homogeneAus) metal ccuplexes or supported

(heterogeneous) metal ccuplexes or metal particles. Investigation

of the activity and stability of metal ocuplexes that catalyze the

transformation of synthesis gas under mild reaction conditions is of

interest. Reported here are the results of two studies involving

the investigation of transition metal complexes as catalysts for the









2
indirect transformation of synthesis gas into chemicals. The first

study involves the investigation of supported iridium carbonyl

clusters as catalysts for the reaction of H2, CO and HC1 under mild

reaction temperatures and pressures to selectively produce methyl

chloride. The development of a catalytic system for the formation

of methyl chloride based upon synthesis gas would be industrially

attractive. The iridium complexes were studied in an attempt to

heterogenize a homogeneous iridium system reported to produce minor

amounts of methyl chloride during the hydrogenation of carbon

monmide.5,6 Ihis study allows for a direct comparison to be made

on a system employing a metal complex of well-defined composition

and nuclearity. The stability of the metal clusters when supported,

as well as under conditions employed during catalysis, was also

probed. Infrared spectroscopy was used to investigate the

preparation of the deposited clusters and the iridium species formed

during reaction with hydrogen, carbon monoxide, and HC1.

The second study involves the investigation of a homogeneous

rhodium carboxylate system as a catalyst for the hydroformylation of

olefins. mhe ability to vary the carboxylate ligands on the rhodium

complex allows for comparisons to be made of the activities of such

systems during catalysis. The effect of added phosphine on the

distribution of reaction products and the stability of the system

was also studied by a variety of spectroscopic techniques. Finally,

comparative studies with aommonly employed hydroformylation

catalysts allow for investigation of the industrial potential of the

rhodium carboxylate system.














II. INVESTIGATION OF SUPPCR'ED IRIDIUM CARBCNYL FUR THE
TRANS~ NATION OF SYN GAS AND HC1 TO MEIHYL CIIfRIDE




A. Back d



For over a decade there has been a growing interest in the use

of coal as a potential source of chemical feedstocks and fuels.

Such interest was triggered by rising oil prices in the early 1970s

as well as by a growing concern about the eventual depletion of our

oil resources. Unfortunately, coal cannot be directly converted

into fuels. The ccnbustion of coal in the presence of steam results

in the formation of a gaseous mixture of hydrogen and carbon

mnKoxide7 as shown in Equation 2-1. This gaseous mixture



H20(1)

C(coal) > C0 (g) + H2(g) Hrxn = +176 IU/mol (2-1)



is referred to as synthesis gas because synthesis gas and not coal

can be converted into chemical feedstocks and fuels in the presence

of a catalyst. Many articles have focused on the use of synthesis

gas as a raw material for industrial chemicals.2,8-11

One of the best known and oldest processes utilizing synthesis

gas to produce gasoline is the Fischer-Trcpsc Process.12 This

process employs a heterogeneous metal catalyst containing Fe, Ru or

3









4
Co metal dispersed on a support such as alumina or silica gel as

shown in Equation 2-2. Depending upon the catalyst and reaction

conditions the products are hydrocarbons, aoygenates or mixtures

thereof.13 A myriad of products are formed in the Fischer-Topsch


Fe,Ru.,Co Hydrocarbon
n(OD + H2) > and (2-2)
Oxygenated Products

Process. The molecular weight distribution of the products is

characteristic of polymerization reactions. The products follow a

Schulz-Flory distribution function such that the probability of

chain growth is related to the rate of chain propagation and chain

transfer.13

Currently, the only large commercial Fischer-Tropsch facility

for the production of gasoline, gas oil and paraffins from coal is

located in Sasolburg, South Africa, where large deposits of coal

resources exist.14 Typical working conditions are 25 atm. at 220-

2400C employing an extruded iron catalyst. The wide product

distribution and the lack of economically mined coal deposits have

deterred the use of the Fischer-'rcpsch Process elsewhere in the

world.

Research objectives in the area of synthesis gas conversion

have focused on the development of transition metal catalysts

exhibiting high selectivities for the formation of either oxygenated

products15 or low molecular weight unsaturated hydrocarbons.16 Ihe
use of metal carbonyl clusters as catalysts or catalyst precursors

has been the subject of many reviews.17-20 Because of their well-









5
defined composition and nuclearity these clusters may form the basis

for a new generation of highly selective catalysts or catalyst

precursors in reactions such as hydroformylation, hydrogenation,

isomerization, 00 reduction, etc. In clusters, the metal sites are

also subjected to electronic influences of the surrounding ligands

an the metal framework. Analogies between metal carbonyl clusters

and metal surfaces covered with carbon monoxide have been

suggested.18,21,22

There are many advantages for using clusters rather than

monanuclear complexes as catalysts.23,24 The ultinuclear nature of

clusters allows 00 and hydrogen to be bonded in neighboring

positions allowing for interaction between metal atoms. In clusters

there are also a number of metal sites available for the bonding of

carbon monxide. Metal sites in clusters may also be influenced by

electronic changes around the metal framework resulting from

addition of ligands. Shown below in Table 2-1 are the ways of

utilizing clusters in catalysis.17


Table 2-1. Ways to Utilize Clusters in Catalysis.


Homogeneous Heterogenized Heterogenized

Intact Intact Clusters Cluster-Derived
Clusters in -> Anchored or Deposited -> Metal Particles on
Solution an Oxide Supports Oxide Supports


Hmogeneous systems employing metal carbonyl clusters as

catalysts or catalyst precursors exhibit high selectivity for the

formation of oxygenated products such as methanol, ethanol and









6

ethylene glycol and operate under extreme pressure conditions (>1000

atm.). Metal carbrnyl clusters such as Ru3 (C) 12, 25 Rh6 () 1626 and

002 (OD) 827 have been used as catalysts for the homogeneous
hydrogenation of carbon monaxide as shown in Equation 2-3.


Ru, Fh, Co
H2 + D0 200-3 CH3 + C2H50H + (CH2C)2 (2-3)
T= 200-3000C


The product selectivity observed in these homogeneous systems is

dependent upon a number of factors15 including the reaction

temperature and pressure, solvent characteristics, presence of

specific ligands and the use of promoters. The major disadvantage

with homgeneous catalysts involves the difficulty of separating the

catalyst from the product.

Heterogeneous systems using metal carbonyl clusters as

catalysts or catalyst precursors tend to produce hydrocarbon

products such as alkanes and alkenes. The use of metal carbonyl

clusters as catalysts is very attractive in view of recent reports

in the literature indicating that metal particle size has a

significant effect on the selectivity for 00 hydrogenation.28,29 It

is believed that small metal particles lead to the formation of low

molecular weight hydrocarbon products such as ethane and ethylene.

Once aggregation of these metal particles occurs the formation of

higher molecular weight products similar to those observed in

typical Fischer-Tropsch synthesis is observed.30 Understanding the

reactivity of the cluster with the support is essential to









7

controlling metal particle size and determining the chemical

transformations that occur on the way to forming an active catalyst.

When Ru3(00)12 is supported on alumina no oxygenated products

are detected upon reaction with H2 and 00 and the formation of Ru

metal is bserved31 as shown in Equation 2-4. The formation of

oxygenated products was observed when Ru3 (0) 12 supported onto a

basic support such as magnesia as shown in Equation 2-5. After

catalysis the presence of an anionic cluster, [Ru6gC() 16]-2 was

identified. Ihe oxygenated selectivity for ruthenium carbonyl

supported on magnesia was suggested to be a result of the presence

of an intact metal carbonyl cluster on the surface.


Ru3 ()0) 12/A203
H2 + 200-00 2 > C4 + C2-C10 Hydrocarbons (2-4)
200-350C, 21atm.


u3 (00) 12/MO Oxygenates (CH30H + C2H5H)
H2 + O 200-3500 21atm. > CH4 + C-C10 Hydrocarbons (2-5)
200-350Oc, 21atm.


There have been two approaches used for the development of

catalytic materials from metal carbonyl clusters. One involves

supporting the metal complex such that an intact cluster framework

with the ligands still bound to it is maintained. This type of

catalyst resembles a homogeneous catalyst. A second method is to

decompose the cluster to a metal particle where the particle size

distribution can be controlled by the cluster decomposition. The

first approach allows a better understanding of the material because

techniques such as infrared spectroscpy are available for studying











metal carbcnyl complexes. The stability of these intact cluster

catalysts under reaction conditions is often uestined.

A goal of researchers has been to develop heterogenized

hmogeneous catalysts or "hybrid catalysts".32 In the development

of hybrid catalysts the presence of an intact supported metal

complex is desirable. By developing such systems many of the

advantages of both homogenous and heterogeneous catalysts could be

retained. A listing of the advantages of homogeneous and

heterogeneous catalysts is found in Table 2-2. A hybrid catalyst

should exhibit high selectivity and activity as well as exhibit high

thermal stability and ease of product separation.

Heterogenizing metal carbonyl clusters has been the subject of

many reviews.17,33,34 The main routes used to support metal

clusters include: (1) direct surface banding or physisorption with

an inorganic oxide support; (2) anchoring of the cluster on

functionalized inorganic oxides and (3) entrapment in zeolites.


Table 2-2. Advantages of Homgeneous Versus Heterogeneous
Catalysts.


Hmogeneous versus Heterogeneous

1. more active due to 1. separation of catalyst
availability of metal from product

2. reproducible 2. minimizes reactor corrosion

3. electronic and steric 3. high thermal and mechanical
properties can be varied stability

4. more selective









9
The immobilization of metal carbonyl clusters has been achieved

by surface bonding or deposition onto inorganic oxide supports. In

some cases interaction of the cluster with the oxide support has

been established. Ionic and covalent bonding of the cluster with

the support can be employed. Ionic bonding occurs from nucleophilic

attack of a surface hydroxyl group on a 00 ligand of the cluster.

Covalent bonding occurs from oxidative-addition of a surface

hydroxyl group with one of the metal-metal bonds of the cluster.

Physisorption of the cluster onto the inorganic oxide has also been

shown to occur. In these systems intact metal carbonyl clusters

have been shown to be present. The clusters may undergo interaction

with sites present on the support. The type of bonding of a cluster

onto an oxide support is believed to be dependent upon the nature of

the support and its pretreatment.35

The use of a chemically modified support is an alternative

method of anchoring a cluster onto a support. The recent literature

contains many examples of silica and alumina supports that have been

functionalized with reagents of the general formula

(C2H50)3Si(C2) nX where X is a donor group capable of coordinating
to metal ocaplexes.36,37 In general two methods of preparation have

been used to anchor clusters onto oxide supports. The first

involves anchoring the cluster via ligand exchange to a

functionalized support. The other method involves preparing a metal

ccaplex bound to a linking agent followed by coupling to an

inorganic oxide surface. these two methods are depicted below in

Equations 2-6 and 2-7.













t-o-si-aH2aC2X --- > 4-O-Si-iC2CH2CH2MXn (2-6)


(CR) 3-Si-CH2CH2Vi --- > --Si-C2CHHZ Mn-21 (2-7)

In 1981, Muetterties and coworkers5 discovered a novel

homogeneous system that catalyzed the conversion of carbon monoxide

and hydrogen into light hydrocarbons primarilyy ethane) under very

mild reaction conditions as shown in Equation 2-8. The catalyst was

Ir4 (0) 12 in a molten A12C6-NaC medium.

There are see significant results from this hcmgeneous

reaction. The formation of hydrocarbon products was observed with

no oxygenated products detected. Recall that homogeneous systems

containing metal carbonyl clusters as catalysts or catalyst
precursors typically produce oxygenated products from reaction of

carbon monoxide with hydrogen. The reduction of carbon monoxide

also occurred under very mild reaction conditions of 1-2 atmospheres

pressure and temperatures below 2000C. The mild reaction conditions
necessary for the reduction of carbon monoxide in the homogeneous



Ir4 (00) 12/Al2C6-NaC1
H2 + OD > C1-C4 Hydrocarbons (2-8)
1800C, 1 atm. (CH3CI)

system was believed to be due to the strong Lewis acid solvent. In

this medium bifunctional activation of carbon monoxide could occur

in such a manner that the oxygen end of a bound carbonyl group could

interact with the Lewis acid as shown in Equation 2-9. These









11

results were confirmed by Collman et al. and he proposed that the

active catalyst or catalyst precursor in the homogeneous melt system

is IrCl (0)3.6 The presence of methyl chloride was reported as a

product in the work indicating the onsunption of aluminum

M-C0O-->Al2CI6 (2-9)

chloride during the reaction. The methyl chloride was proposed to

be an intermediate formed during the reaction which was involved in

further xomologation and hydrogenation reactions to yield the

observed hydrocarbon products.

Methyl chloride is an important chemical commodity.38 It is

used in the production of organosilioon ca pounds, in the production

of tetramethyl lead and as a solvent in the production of

methylcellulose. As a solvent methyl chloride has come into use in

the last 20 years for the elimination of oils, fats and greases from

surfaces.

The industrial production of methyl chloride is accomplished by

two commercial processes.39 These are the methanol-hydrogen

chloride process and the methane-hlorination process as shown below

in Equations 2-10 and 2-11.



HCl + CH30H > 1CH3C + H20 (2-10)


C14 + c02 > CH3C1 + HC1 (2-11)

The production of methyl chloride from methanol is done usually

in the gas phase over activated alumina at 200-3000C.

Mnochlorination of methane is done in the liquid phase using KC1









12

and COC1 melts. In the formation of methyl chloride,

polychlorinated methanes are also produced. Selectivities of 98-

99% are obtained for the methanol-HCl process.

An attractive alternative method for the direct production of

methyl chloride would be from carbon monoxide, hydrogen and hydrogen

chloride as shown in Equation 2-12.


catalyst
H2 + 00 + HC1 > CH3C1 + H20 (2-12)


Vannice reports the production of methyl chloride from

synthesis gas and HC1 at 2700C and 5 atmospheres pressure on a

catalyst containing supported Group VIII metals on acidic supports

such as alumina.40 Along with methyl chloride, the formation of

multichlorinated methanes, ethane and propane were also reported.

In Table 2-3 is a listing of the possible reactions as well as the

thermodynamic feasibility for the formation of methyl chloride.41



Table 2-3. Possible Reactions and the Thermodynamic Feasibility
(in kcal/mol) for the Formation of Methyl Chloride.


(CH3 C + H -- > C3C1 + H20 AG298 = -7.82 AG400 = -5.98

04 + C02 > CIH3C + HC1 6G298 = -22.89 &G400 = -25.95

2H2 + W0 + HC1 -- > CH3C + H20 G298 = -13.85 AG400 = -6.51

Prior work conducted in this laboratory led to the discovery of

a sported phosphine substituted tetrairidium carbonyl cluster

which was shown to exhibit high activity for the formation of methyl









13
chloride in the presence of H2, CO and .HC 42 The reaction

proceeded under very mild reaction conditions of 25-1000C and 1
atmosphere pressure as shown in Equation 2-13.


0Smi- (CH2) 2-Ph2)xlr4 (00) 12-x
2H2 + 00 + HKI CH3C1 (2-13)
25-1000C, 1 atm.

The coordinated metal carbcnyl cluster was prepared by an

initial functionalization of the support. This was accomplished via

a condensation reaction of the surface hydroxyl groups of an

inorganic oxide support such as alumina or silica with the ethoxy

groups of the silane, (OEt)3SiCHa22Pph2, 43 as show in Equation 2-14.


OH + (OEt)3SiCHCH2C2PE2 -> -(0) x-SiC2C2PP2hh + 3C2H50H

(2-14)

he number of --Si bonds between the support and the silane

linkage is represented as x. The remaining alkapy groups from the
silane are proposed to be hydrolyzed to yield Si-GI and ethanol.43

The phosphine substituted tetrairidium carbonyl cluster was
assembled from the precursor complex as shown in Equation 2-15.


-(0)x-SiCH2C2P P2 + Ir(0O)2C1(H2N-0-CH3)
Zinc, CO
-> (2-15)
2-methoxyethanol

-(0) x-SiCH2CH2PPh2) xIr4 (CD) 12-x









14

The synthesis and characterization of these supported clusters by

infrared spectros opy has been previously reported and shown to

result in the formation of the mmno-phosphine and di-phosphine

substituted clusters.44,45

The catalyst was initially tested in a 3:1 A2CI6-NadC melt

salt under reaction conditions similar to those employed for the

previously reported homogeneous Ir4 (C) 12-Al2C16/NaC system.

Results similar to those previously reported6 were obtained such

that methane, ethane and methyl chloride were detected as products.

The supported phosphine substituted irid um catalyst was shown to

leach the iridium cluster from the support during the reaction

producing the homogeneous Ir4 (00) 12-Al2Cd/NaC system. To

circumvent the problem of catalyst leaching the supported cluster

was tested in the presence of H2, 00 and HC1 and in the absence of

A12Cl /NaM. In all cases the same activity and selectivity
resulted as previously observed. The activity of this system was

shown to be dependent upon a number of factors including the degree

of stirring during catalyst preparation, temperature of the reaction

with synthesis gas and HCM and metal loading.

A later study was conducted to investigate the above effects

with catalyst activity and the cluster stability during reaction.

It was discovered that the previously reported results for the

formation of methyl chloride were clouded by the presence of

adsorbed 2-metha~yethanol which was introduced onto the surface of

the support during preparation of the phosphine supported cluster.46

A number of attempts were investigated to remove adsorbed 2-









15

methoyethanol which were unsuccessful. Investigation of

alternative routes to synthesize the supported phosphine substituted

tetrairidium cluster resulted in the formation of materials which

did not exhibit the high level of activity and selectivity for the

formation of methyl chloride as the supported iridium cluster

prepared in the presence of 2-nethKoyethanol. In these alternative

systems it was proposed that the formation of methyl chloride

resulted from the reduction of carbon monoxide.46 Control

experiments showed that a contribution to the formation of methyl

chloride was due to impurities in the system introduced during

preparation of the catalyst.

Investigation of the material by infrared spectroscopy after

reaction with H2, 00 and HC1 supported the decomposition of the

catalyst to produce ultinuclear complexes and IrCl(C)3. As the

reaction temperature was increased, it was proposed that the

multinuclear iridium complex was converted to IrCl(00)3 or Vaska's

complex on a phosphnated support. It was also proposed that the

stabilized multinuclear complex was active for reduction of carbon

monoxide while IrC (00)3 was inactive. A mechanism was proposed

which accounted far the various routes for the formation of methyl

chloride and other products.46 Figure 2-1 illustrates the proposed

mechanism summarizing the formation of methyl chloride from various

routes. Included in the figure are pathways where by impurities in

the system (such as adsorbed 2-methoxyethanol) may decompose to

methyl chloride as well as a cluster fragmentation pathway believed


































Id
I-I
eq


L








17
I


I A


Z V
* '.


8
S.t



s II






5 ,, |





1 U
aae









I y*


Sr
ftf

6 #


LI
8


I
ja


iil


.4.









18

to yield methyl chloride via reduction of carbon monoxide upon

reaction with H2, 00 and HC1.

Results of the previous studies of the supported iridium

carbonyl cluster suggest that stabilization of a multinuclear

iridium carbonyl complex onto an oxide support could result in the

formation of an active system for the catalytic reduction of carbon

monoxide in the presence of hydrogen and hydrogen chloride to

produce methyl chloride. The formation of methyl chloride from

synthesis gas and HCl(g) under mild reaction carditions would be

extremely attractive from an industrial standpoint. For these

reasons, as well as to get a better understanding of the interaction

of iridium carbonyl clusters with oxide supports and Lewis acids

continued investigation of this system is warranted.




B. EDerimentl


Materials

Iridium carbonyl, IrdC(00)3, and IrC13H20 were purchased from

Strem Chemical Capany. he low Temperature Shift (LTS) methanol

catalyst was supplied by United Catalysts. Aluminum chloride,

anhydrous 99.997%, was purchased from Alfa Products. Iron chloride,

anhydrous, and antimony pentachloride were purchased from Aesar.

Aluminum bromide was purchased from Fischer. All metal ccrplexes

were used as purchased unless otherwise stated. Solvents were dried

by distillation over CaH2 or P205 and stored over 40A molecular

sieves. The 2-methoxyethanol (Kodak, scintillation grade) was used









19

without further purification. The support material was Fisher, acid

Brockman Activity I (80-200 mesh) alumina, or Davison grade no. 62

silica gel purchased from W.R. Grace and Co. This alumina was

determined to have a specific area of 180 m2/g.47 The silica gel

had a specific area of 340 m2/g, a pore diameter of 14m, and a pore

volume of 1.1 c3/g. Ihen used for direct bonding of the cluster,

all powdered oxides were first heated under vacuum at 350C for 15

hours to remove water. When used for functionalization the powdered

oxides were dried at 1400C prior to use.

All silanes where purchased from Petrarch Systems, Inc., and

used without further purification.

Hydrogen was purchased from Airco. Carbon monoxide (CP grade,

99.5%) and hydrogen chloride (isoelectronic grade, 99.99%) were

purchased front Matheson Gas Products. The HCl feed gas was checked

for chlorocarbons which were not detected. All gases were used

without further purification.



Instrumentation

All air sensitive manipulations were performed in an Aldrich

inert atmosphere glove bag. All syntheses were performed under

either a nitrogen or carbon monoxide atmosphere. Infrared spectra

were obtained as Nujol mulls with a Nicolet model 5DXB spectrometer

using NaC1 salt plates. The elemental analyses for iridium were

performed by Galbraith Laboratories, Ehoxville, Tennessee. Gas

chraatographic analyses were performed by using a Model 940 FID

Varian dchraatograph equipped with a 1/8 in. X 8ft. stainless steel









20

Porapak Q column. The column temperature was maintained at 1300C.

Gas dhranatogra-phic mass spectranetry were performed by Dr. Roy King

of the Microanalytical laboratory, University of Florida,

Gainesville, Florida. Samples were run by using a AEI MS 30 mass

spectrometer equipped with a IDIT0S DS55 data station. The system

was equipped with a PYE Unicam 104 gas dhranatograph containing a

1/4 in. X 5ft. Porapak Q column. The system was equipped with a

dual magnesium anode X-ray source and a double pass cylindrical

mirror electron analyzer. Data acquisition was controlled by a

Digital PDP cuputer. All ESCA data were obtained through the

courtesy of Dr. Tam Gentle, Dow Corning Corporation, Midland,

Michigan. ihe samples were run in a Perkin-Elmer Model 551

stainless steel ultra-high vacuum chamber equipped with a dual

magnesium x-ray source and a double pass cylindrical mirror electron

analyzer. Data acquisition was controlled by a Digital PDP

caputer.



Fixed Bed Flow Ractor

A glass flow system as shown in Figure 2-2 was used to test the

catalytic activity of the supported iridium ccaplexes for

hydrogenation of carbon monoxide in the presence of HCl(g). This

system is similar to that previously described by Weiss.46 The

gases were allowed to enter the system and mix via a three stage

bubbler with teflon needle valves to control the individual gas flow

rates. The CO and H2 gases were bubbled through mineral oil while

the HC1 gas was bubbled through sulfuric acid. The catalyst was


























aO
04


e
4J









S)
01 C


T m0O


IlWkC

>ai 3-


m C
0 4' I,


u



r4
C EC
1a >, d



U 1
1-1
u3


'-4
0 U
u









23

placed in a glass tube with a glass frit to hold it in place and the

gases were allowed to flow over the catalyst. Temperatures were

regulated by using a model 123-8 Lindberg thermostated tube furnace.

Sample ports before and after the catalyst allowed for analysis of

the gases. he gases were collected by using a pressure-lok 2ml

syringe purchased fran Precision Sampling Corp. and analyzed by GC.

The addition of a glass spiral trap to the system allowed for

trapping of the gases in a dry ice/acetone slush.


PreMaration of a hosdhinated Support

the phosphinated supports were prepared by a procedure similar

to those previously reported in the literature.33,48 Under a

nitrogen atmosphere 5.0 g of dried support such as alumina or silica

gel was added to a stirred solution of 150ml of toluene or benzene.

The mixture was heated to reflux and 0.45ml (1.25X10-3 moles) of 2-

(diphenylpho~phino)tltethl thxysilane was added by syringe. This

reaction was allowed to continue for 12-15 hours. The

functionalized support was collected by vacuum filtration followed

by successive washing with the toluene or benzene solvent. The

functionalized supports were dried under vacuum at room temperature

for 24 hours prior to use. For the phosphinated supports the

loading of accessible phosphine substituets was 1.25 X 10-3 moles

per gram of support. An analogous synthetic procedure was employed

for functionalization of the supports with 2-

(dipherylphosphino)pr pyltrimethaxysilane. The phosphinated

supports are represented as (S)-PPh2 where S= Al203 and SiO2.









24

Preparation of the Suported Tri hOsphine Substituted Iridium
carbnxvl Clusters

the phosphine substituted iridium carbonyl cluster was prepared

by a procedure similar to that reported by Karel and Norton.49 A

total of 1.3g Ir4(a0)I2 was added to a stirred solution of toluene

or benzene solution containing 5.0g phosphinated support (1.25X10-3

moles of phospine). The reaction was allowed to proceed at reflux

temperature for 24 hours. The brown-yellow resin was collected by

vacum filtration and dried under vacuum at roam temperature for 24

hours. The characterization of this material by infrared

spectroscopy has been previously discussed.46 This material is

represented as (S)-(PPh2)xIr4(C0)12-x where x=1,2 or 3.


Preparation of Directly Deposited 'etrairidium Carbonvl Clusters on
the support

The method used to support Ir4(C0)12 was to adsorb the carbonyl

cluster from solution onto an inorganic oxide support such as

alumina or silica gel. A total of 0.5g Ir4 (0)12 was added to a

stirred or benzene solution of 5.0g support. The reaction was

allowed to proceed at reflux temperature for 15 hours. The yellow

resin was collected by vacuum filtration and washed with solvent

benzene. The cluster deposited supports were dried under vacuum for

24 hours prior to use. The characterization of these materials by

infrared spectroscopy is discussed in the results section. This

material is represented as s/Ir4(0c)12 where = A1203 and SiO2.











Preparation of the Aluminum chloride Tetrairidium C rtnyl Cluster
Treated Suports

A total of 0.33g A12C16 was added to a stirred carbon

tetrachloride solution containing 1.0g of tetrairidium carbonyl

cluster on alumina or silica gel which had been deposited on the

support as previously described. The reaction was allowed to

proceed for 12 hours at 500C. Ihe lewis acid treated materials were

collected by vacuum filtration and washed with carbon tetrachloride

solvent. The materials were dried under vacuum at roam temperature

for 24 hours prior to use.

Another procedure was also employed to prepare the supported

aluminum chloride tetrairidium carbonyl oumplexes. This reaction

was conducted under a nitrogen atmosphere. A total of 0.5g A12C16

was added to a stirred solution of 1.0g support in carbon

tetrachloride solvent. The reaction was allowed to proceed for 12

hours at 500C. The aluminum chloride treated support was then

collected by vacuum filtration, washed with carbon tetrachloride

solvent and dried under vacuum for 12 hours. The aluminum chloride

treated supports were then reacted with tetrairidium carbonyl

clusters where a total of 0.1g Ir4(C0)12 was added to a stirred

solution of 1.0g aluminum chloride treated support in carbon

tetrachloride solvent. The reaction was allowed to proceed for 12

hours under nitrogen. The solids were collected by vacuum

filtration and dried under vacuum at roam temperature for 24 hours

prior to use. The lewis acid treated deposited materials are

represented as S/Ir4 (0) 12/A12C16. he characterization of these

materials is discussed in the results section.









26

Preparation of Other Lewis Acid Treated Deposited Tetrairidiu
Carbawl Custers

All other Lewis acids such as SbC15, FeC3 and AlBr3 were

reacted with the deposited tetrairidium carbonyl cluster in an

analogous procedure employed for the reaction with aluminum

chloride. Appropriate amounts of the Lewis acid were added to a

stirred solution of deposited Ir4(00)12. The reactions were allowed

to proceed for 12 hours and the solids were collected by vacuum

filtration then dried under vacum at room temperature for 24 hours

prior to use.


Preparation of Aluminm Chloride Treated Ocmrercial Methanol
catalysts

The A12C16 treated camnercial methanol catalysts were prepared

by using an analogous procedure employed for reaction of deposited

iridium carbonyl with aluminum chloride. The catalyst employed had

the cunposition CuO/ZnO/Al203 (42:47:10). A total of 2.0g of United

Catalysts Low Teaperature Shift (LTS) Catalyst was added to a

stirred mixture of 0.66g aluminum chloride in 50ml of c014. The

reaction was allowed to proceed for '15 hours under nitrogen. The

solid resin was collected by filtration, washed with carbon

tetrachloride solvent and dried under vacuum at roam temperature for

24 hours prior to use.









27

Reaction of the SuMports and the SuaMorted Metal Cmplexes with
Cazbon Mcno=ide. Hvdroen and HCl (c

A total of 1.0g of solid material was placed into the glass

fritted reactor tube. The reactor tube was placed into the fixed

bed flow reactor system previously described in Figure 2-2. A

typical reaction was run at 125C with the individual H2:C0:HC1 gas

flaws at a ratio of 2:1:0.5 combining to give an overall flow rate

of 2ml/30-60 seconds. The reactant and product gases wre monitored

by gas chromatography. Investigation of the active species for

carbon monaide reduction by infrared spectroscopy is discussed in

the results section.




C. Results and Discussin


Reinvestigation of Earlier Work of the Supported Thosuhine
Subtituted Tetraiidiui Carbonvl Cluster

The supported phosphine substituted tetrairidium clusters were

prepared as described by Weiss.46 An inoranic oxide such as

alumina or silica gel was functionalized via a simple condensation

reaction of the alkoxy groups of silane and the hydroxyl groups of

the surface of the support as shown in Equation 2-16. Then the

tetrairidium carbonyl cluster was reacted with the phosphino groups

of the functionalized support as shown in Equation 2-17. These

materials wre characterized by infrared spectroscopy and shown to

contain mostly the tri-phosphine substituted cluster as well as same

mono-phosphine and di-phosphine substituted tetrairidium carbonyl









28
clusters as previously described.46 he major V o bands for the

supported hosphine substituted iridium clusters are listed in

Table 2-4.


(OEt) 3SiCH2C2PPh2 4 i2C h2 (2-16)
S---------S2(2-16)
I
Ir4 (0) 12
I > 2-Si o H2CH2Ph2) xIr4 (C) 12-x (2-17)


Ihe supported phosphine substituted clusters were investigated

for catalytic activity in the presence of 00, H2 and HCl(g) at 750C

in the fixed bed flow reactor previously described in Figure 2-2.
Results similar to those previously reported46 were observed upn

reaction of the phosphine substituted cluster with the reactant

gases as detected by chrcmatography using a Porapak Q column at

1300C. Ihe major product observed in these systems is ethyl

chloride which was previously unreported. Other products observed

by dchrnatography include methane, methyl chloride, ethane and
acetaldehyde. Water and carbon dioxide were also confirmed by

GC/MS. It was found that if the amount of HCl(g) present in the

system was reduced, the identification of ethanol by gas
chromatography was possible.

As described earlier, when the supported phosphine substituted

tetrairidium carbonyl cluster was prepared in the presence of 2-

methoxyethanol solvent from the reaction of the functionalized

support with the iridium precursor complex IrC1(00)2 p.toluidine,

methyl chloride was found to be the major product detected upon
reaction of the supported cluster with the gases.42 An in depth









29

Table 2-4. Major V (a) Bands in the Infrared Spectra for
bosphiine Substituted Ir4(00)12 and Ir4(00)12.


Mound on )


Mixture of
Al203- (P2) 1,2Ir4 (00) 11, 10a

A1203-(Ph2) 3Ir4 (00) 9b

Ir4(00) 12

Ir4 (co) 12

Al203/r4 (00) 12

SiO2/Ir4 (00)12


Al203/Ir4 (00) 12/A12CI6

Si02/Ir4 (00) 12/A12C16

Al203/Irl (00)3

Al203/IrC (00) 3/A12CI6


2083(w), 2070(w), 2053(s)
2030(s), 2020(s), 2000(s)
1845(w), 1825(m), 1795(w)

2045(s), 1995(vs), 1791(m)
1774(w)

2073(sh), 2059(s), 2020(m)
2000(w)

2075(w), 2058(s), 2020(m)
2003 (vw), 1994 (w)

2075(w), 2062(s), 2022(m)
1996(w)

2075sh), 2063(s), 2023 (m)
1996 (w)

2127 (w), 2105 (w), 2062(s)
2022 (m), 1996 (w)

2111(w), 2075(sh), 2063(s)
2041(w), 2023(m), 1996(w)

2082(s)

2071(s)


a= cluster formed by reduction of IrC (00)2(p toludine)

b= cluster formed by substitution of carbonyl ligands in Ir4 (00)12

c= Crawford, et. al. J. Catal., (1983), 83, 454.
* s=strcng, m=moderate, w=weak, sh=shoulder


Ref.


42,46

46

C









30
investigation of that system revealed that the methyl chloride

product resulted from cracking of residual 2-metha ethanol adsorbed
onto the surface of the oxide support during preparation of

phosphine substituted cluster.46 A series of control reactions were

conducted on the system containing the supported phosphine

substituted iridium cluster5 prepared frCo reaction of the

phosphino groups of the functionalized support with the carbonyl

groups of the tetrairidium carbonyl cluster as shown in Equations 2-
16 and 2-17. These experiments were conducted in order to determine

if carbon monoxide was being reduced catalytically.

A series of control reactions were conducted on the system

containing the supported phosphine substituted iridium cluster50

prepared from reaction of the hosphino groups of the functionalized

support with the carbonyl groups of the tetrairidium carbonyl

cluster as shown in Equations 2-16 and 2-17. These experiments were

conducted in order to determine if carbon monroide was being reduced

catalytically. The necessity for investigation of all the possible

routes for the formation of methyl chloride is obvious in view of

the activity of the previously described activity reported by

Miller.42 The production of methyl chloride in these systems could

result from adventitiaus carbon sources introduced into the system

during preparation of the catalyst. The reactions conditions

employed are those expected to lead to reduction of CO in a
catalytic system.

The results of these experiments are found in Table 2-5.

Contained in Table 2-5 for comparison are the previously described




T t' -


Sa


NO
I I
00
I I










Umtt
-I

9a






N


C

I


0











0
^s




it

8
*-4




U
i

=
a



0
1


I
0


b


A Q
f"
m













32








S 0 0 0 0 -0 0 0 0 0 0
01 1 a 1 1 1 10





o 0 0 00 0 0


q qu S-
i 0 1i a g5





8 8 8 i!
8 8 m




s s& a *f
5 U S U
0 4
















sI;
oPN m m m
N &







o 1 1 1 1- 1


. :r.,V









33

results from cracking of 2-methaxyethanol solvent over the inorganic

oxide support. The results of the control experiments involving the

cracking of 2-methxyethanol by HCI to produce methyl chloride are

shown in experiments 1-3. As shown in the Table, '10-10 mol CH3C1/

sec/g material was observed even in absence of the iridium cluster.

As previously described the amount of observed CH3Cl in these

systems was dependent upon a number of factors including the degree

of stirring during preparation, loading of the phosphino silane, and

the amount of C1l present in the reactant gas. The results of these

control experiments indicate that the formation of methyl chloride

is a result of the cracking of 2-methaxyethanol solvent used to

prepare the supported phosphine substituted cluster.

In Table 2-5, experiments 4 and 5 were conducted in an attempt

to investigate the possibility that alkoxy groups from the

functionalizing agent could lead to the formation of alkyl chloride.

Alumina was functionalized with (130) 3SiC3H6P(C6H5)2 and

(C2H50)3SiC2H4P(C6H5)2 in toluene and benzene solvent (experiments

4-6). In both instances the alcohol corresponding to the alkoxy

group was detected when H2 and 0 were passed over the

functionalized support at 600C. The alkyl chloride was observed

when the gas mixture of H2/OD/HC1 was passed over the same support.

These observations are interesting in view of the reaction reported
by Waddell et al.43 and by Studer and Schrader.44 In these

articles, the alknxy groups in (alky) 3Si(C2)xPPh2 are reported to

be hydrolyzed off of the silicon in the course of functionalization

producing the alcohol and forming hydroxyl groups bound to the
























H-C-H
I

H --C --H
I
-Si-0OCH2CH3
I HO


HH
II
O-C-C-H OH
H H


Figure 2-3.


Structure of the Ethoxy Surface Species Formed
During Functionalization of the Alumina Oxida


/////////~I-////~I'I//117/////'









35

inorganic oxide. If this hydrolysis occurs, the alumina surface

retains the alcohol or alkoxy groups as shown in Figure 2-3. The

alcohol products corresponding to the alkoxy groups from the silane

are obtained upon reaction with H2 and 00 and upon addition of HCl

to the reactant gases the corresponding alkyl halides are formed

(experiments 4-6).

When a gas mixture of H2/OO/HC1 was passed over the support

functionalized with (C2H50) 3SiC2H5P(CH5)2 in toluene (experiment 5)

at 1000C, methyl chloride was observed. This product was not

detected when benzene was used instead of toluene as a solvent

during the functionalization procedure. The formation of methyl

chloride in addition to ethyl chloride was detected in the benzene

preparation when H2 and HC1 were passed over the solid at

temperatures greater than 1500C. Although at temperatures of 1000C

the formation of methyl chloride is detected from the toluene

preparation (experiment 5), the same preparation in benzene

(experiment 6) did not result in the detection of methyl chloride at

this temperature. In the benzene preparation, methyl chloride

production was observed only at temperatures above 150C. It is

possible that the methyl chloride is produced from the cracking of

toluene in experiment 5. The detection of CH3Cl above 1500C in

experiment 5 is believed to occur from decnrposition of the ethoxy

groups present on the phosphino silane, or on the alumina surface

and cracking of benzene does not appear to occur.

As discussed previously46 the cracking of toluene to produce

methane (and benzene) is thermodynamically possible. This type of









36

reaction could result in the formation of methyl fragments on the

surface of the support which then react with HC1(g) present to

produce methyl chloride. As shown in Table 2-4, the quantity of

methyl chloride formed in the experiments conducted in the absence

of 2-methoayethanol is low.

A reaction scheme corresponding to the decomposition of the

ethoxy groups from the phosphinosilane to form CH3Cl is represented

in Figure 2-4. In this scheme, reaction of the adsorbed ethoxy

groups would lead to ethanol production. Dehydration of coordinated

ethanol or ethaoy groups would result in the formation of ethylene

while dehydrogenation of ethanol produces acetaldehyde.

Acetaldehyde is detected in the early phases of the experiments by

GC and GC/M. Ethylene/ethane is detected throughout the experiment

as a minor byproduct. As shown in Figure 2-4, ethylene may then

react with HCl to produce ethyl chloride which is the major product

from the reaction of ethanol or ethoxy groups with HC1. Ethylene

may be cracked over the alumina surface producing carbon species.

Reaction of the carbon species with hydrogen and HC1 would account

for the methane and methyl chloride observed in the experiments with

the ethoxy silane. All of these reactions are further complicated

by reactions involving the intermediate species. Evidence for such

a scheme is supported by reports in the literature. Several reports

indicate that ethanol can be converted over inorganic oxides to

ethylene,51-53 ethane,51 and acetaldehyde54,55 all of which were

observed as minor products in the reactions. It is generally

recognized that olefins are an important source of carbon formation


TT ---i























HO OCH2CH3
T>150'C
///////


+ CH3CH2OH


CH3CHO
-H CH
-HO CH= CH.


SC2 CH C A CARBON SPECIES
CH3CHC2C
CHaCH2CI


Figure 2-4.


H2, HCI CHCI
H-- CH
CH4


Schaatic Representation of the Desccposition
of the Ethaxy Groups at Elevated Temperatures


.'**-' "









38

involved in catalytic cracking.56 Reports indicate that over a

metal surface ethylene may decompose to carbon atoms via an

acetylene intenediate.57,58 It is proposed that similar chemistry

is occurring whereby decomposition of ethoxy groups eventually lead

to the formation of methyl chloride.

In order to determine if the methyl chloride or other products

detected are being produced from the catalytic reduction of carbon

monoxide with H2 and HCl it is necessary to remove the organic

residues from the surface of the supported iridium clusters. An

initial method of investigation in this work involved passing a

gaseous mixture of H2 and HC over the phosphine functionalized

support at 1500C until ethyl chloride or other products were no

longer detected in the exit gas. Reaction of the HCl treated

material with Ir4 (C)12 in refluxing resulted in supporting the

intact cluster. Upon passing a gaseous mixture of H2, 00 and HCl

over the supported cluster at 700C, no products corresponding to

those expected froC the reduction of carbon monoxide or from organic

resides introduced during synthesis were detected.

These results of the reinvestigation of the earlier work42,46

on the phosphine supported iridium cluster indicate that any

reduction of 00 by the system is masked by the presence of organic

residues absorbed onto the surface of the oxide support. These

residues were shown to be introduced into the system during

preparation of the material. The support functionalization
procedure was shown to cause the most misleading results in the

previously reported study. It was shown that through a series of









39
control experiments0 (see Table 2-5) that the decomposition of the

alkoxy groups present on the phosphinosilane linking agent led to

the formation of significant amounts of halogenated products.

Attempts to remove these residues by treating the supports with H2

and HCl(g) resulted in the formation of inactive materials for

reduction of carbon monoxide.

Another approach was undertaken to support the iridium cluster.

The objective of this study was to prepare the supported iridium

carbonyl cluster in the absence of any organic residues as well as

to optimize conditions for the bifunctional activation of carbon

monoxide. he main approach was to prepare a heterogeneous analog

to the reported Ir4 (C0)12/Al2Cl6-Nac system previously reported by

Muetterties et al.5 and Collman et al.6 his was originally the

goal of the previously described systems however the difficulties

encountered (which were described above) caused the original

objective to be unattainable.



Investigation of Directly Deposited Ir4 (C)12

In order to eliminate adventitious carbon sources in the

system, Ir4 (CO)12 was directly deposited onto an inorganic oxide

support such as alumina or silica gel. First the oxide support was

heated under vacuum at 3000C to remove any water or organic residues

which may be present and then the tetrairidium carbonyl cluster was

adsorbed from benzene solution onto the surface of the oxide support

as shown in Equations 2-18 and 2-19.


-~-. -~-t-












-H20
A 203 > A1203 (2-18)

A1203 + Ir4 (00) 12 > A203/Ir4 (0) 12 (2-19)

The directly deposited iridium cluster was characterized by

infrared spectroscopy. The infrared spectrum of Ir4(C0)12 adsorbed

onto alumina is shown in Figure 2-5A and the major V co bands are

listed in Table 2-4. A similar infrared spectrum was obtained for

reaction of Ir4 (C0)12 with silica gel (see Figure 2-6A). The four

band pattern present in Figures 2-5A and 2-6A are indicative of

iridium carbonyl both in the solid state and in solution. It is

proposed that aggregates of Ir4(00)12 exist an the support. The

broad absorption in the 2100-2200 cm-1 region probably involve

molecules on the surface of the aggregate interacting with acid

sites on the support.

Assignments of the metal carbonyl stretching modes for

Ir4(00)12 have been reported by Abel and cowarkers.59 As noted

previously,60 the spectrum of Ir4(00)12 in the solid state closely
resembles supported Ir4(00)12 although improved resolution in this

and previous work has revealed some differences in the relative

intensities of the bands compared to those previously reported by

Abel.59 The 2062 and 2022 cm-1 bands of Ir4(00)12 in the solid

state and on alumina and silica supports are assigned to the two T2

infrared-active carbonyl stretching modes. Abel attributed the 1995

am-1 band to the T1 mode which is infrared inactive in exact Td

symetry, Ibt which becomes active on a slight distortion towards


__









































2100


2000


WAVENUMBERS (CM-')


Figure 2-5.


Infrared Spectra of Ir4 (C)12 Deposited onto Alumina
(A) Before and (B) After Treatment with A12C16.


1996
2022
2062
2075
2105
2127


2200


cm-I
cm-
cm-'
cmt
cm-I
cm-1


1900


___




















z





cr
0-


2200








2200


Figure 2-6.


Infrared Spectra of Ir4 (c0)12 Deposited onto Silica
Gel (A) Before and (B) After Treatment with Al2Cl


2100 2000 1900
WAVENUMBERS (CM -')









43

D- symmetry. This band is observed in the solid but not in
solution.59 We observe the 1995 ca-1 band and also observe one at

2075 c-1 for r4 (00)12 on alumina and silica. The appearance of

the 2075 cmn1 band observed in our complexes could be due to further

splitting of the T2 mode (which contains the E mode of the M(CO)3

unit) by distortion toward lower symmetry.

The spectra of iridium carbonyl deposited onto alumina and

silica gel exhibit strong 2062 and 2022 cm-1 absorbances

respectively indicating that most of the material present on the

support is Ir4(0o)12.


Investiaation of Suorted Ir4 (CO 12 for Catalytic Activity Upon
Reaction With H2, 00 and H()

The deposited iridium carbonyl clusters were investigated for

catalytic activity for reaction with H2, 0C and Hl(g) using the

fixed bed flow reactor previously described and shown in Figure 2-2.

Upon passing a gaseous mixture of H2, CO and HC over the supported

Ir4 (C0)12 cluster the formation of methane, ethane, methyl chloride,
aoetaldehyde, ethyl chloride and minor amounts of dichlorcmethane

were detected by using gas chromatography as shown in Figure 2-7.

GC/MS of the product gas stream also confirmed the formation of

carbon dioxide and water. The major product formed in this system

is methyl chloride. The activity of the Al203/Ir4 ()12 system for

the formation of methyl chloride is between 10-11 to 10-12 mol

CH3Cl/g/sec. A plot of the formation of methyl chloride versus time

is shown in Figure 2-8. The observed activity of the system is

similar to that previously reported for the phosphine



























methane
ethane/ethylene
methyl chloride
acetaldehyde
ethyl chloride
methylene chloride







e f


0 2.0 4.0


6.0 8.0


Time (minutes)


Figure 2-7.


A Sample Gas ChrtCatograph of the Products Formed
Upon action of H2, CO and HC1(g) ver the Suported
Iridium Clusters at 1250C and 1 Amospher.


am
b-
Cu
cc
c df
es
f=


10.0






































TIME (HOURS)


Figure 2-8.


Activity Curves for the Various Supported
Iridium Carbonyl Clusters for the
Formation of Methyl Chloride.
(A) Al203/Ir4 (O) 12/A12C16
(B) SiO2/Ir4 (C) 12/A12Cl6 (C) Al203/Ir4 (O) 12


LU

16-1
LU
.J
0




U
LI
-o
0
LU


10"6



10-7



10-8


I0-O


40









46

substituted supported iridium carbonyl clusters prepared with the

ethory silanes.44 In the previously reported system organic

residues present on the support were shown to contribute to the

CH3C formed.
In the directly deposited system the absence of these organic

residues confirms the reduction of carbon monoxide either from the

reactant gas or frm the carbonyl groups directly bound to the

original cluster. MWile a ccplete mass balance was not conducted

the total moles of detected product in this system is significantly

less than the number of moles of 00 from the original supported

cluster. These results suggest that the observed products are

primarily from derbpoition of the cluster.

Adsorbed metal carbonyl clusters will react with the surface

hydroxyl groups present on inorganic oxide supports.6061 This type

of interaction has been reported to occur for absorbed iridium

carbonyl on alumina supports. Iridium carbonyl, Ir4(C0)12, may

undergo a decarbinylation reaction with surface hydroxyl groups at

temperatures above 100C60 as shown in Equation 2-20. The carbon



Ir4(0O)12 + XSCH > Ir4(00)12-x(SCH)x + X) (2-20)


monaoide evolved is then proposed to undergo reduction in the

presence of H2 and HC to produce the observed products.

The thermal deocCposition of supported iridium carbonyl on

inorganic oxides such as alumina or silica has been previously

investigated.62-64 Studies in flowing H2 of Ir4(C0)12 an A1203









47

resulted in the evolution of 00 and 0H4 as well as small amounts of

C2H4, C2H6 and 002. It was reported that Ir4(C0)12 does not lose
its 00 groups until 1250C. The initial deomposition of the metal

carbonyl cluster was believed to occur through both the interaction

of the cluster with the surface hydroxyl groups of the support as

well as direct hydrogenation of the carbonyl ligands. There have

not been any reports of the stability of metal carbonyl clusters in

the presence of H2, 00 and HC1. In order to get a better

understanding of the stability of Ir4 (C)12 under reaction

conditions an infrared study was conducted. These results are

discussed in a later section.


Investigation of the Aluminum Clloride Treated Deosited Iridium
Carbonyl Clusters
The aluminum chloride treated Ir4(00)12 cluster materials were

prepared by reaction of the oxide deposited cluster with aluminum

chloride as shown in Equation 2-21.



Al203/4 (0) 12 + A12C16 -> A120/I4 (C) 12/Al2C6 (2-21)


The hydrayl groups of a support have been shown to react with

Al2C6 according to the following scheme as shown below in Equation

2-22.65 This reaction could minimize decarbonylation of Ir4 (O)12

through reaction with surface hydroxyl groups and reduce the

possibility of the reaction in Equation 2-20 occurring with the

Al2C16 treated solids. Further attempts to minimize the occurrence
of a decarbonylation reaction was provided by a second sample









48

preparation method. In this case, the support materials were first

reacted with A12C16 followed by reaction with Ir4 (OD)12. his



S-O-H -s

2 0 + A12Cl6 > 2 0 + 2HCI (2-22)

-S O-H -S

O-AlC12


method of preparation should minimize the presence of any remaining

hydroxy groups which were not converted to AlC2 groups and prevent

decarbonylation by reaction of hydroxyl groups on the support

surface with carbonyl groups of Ir4 (0) 12 during the A 62Cg

treatment used earlier.

The aluminum chloride treatment could (i) increase the

stability of the cluster by minimizing cluster interactions with

surface hydroxyl groups upon conversion of the hydroxyl groups to

aluminum chlaro groups; (ii) lead to bifunctional activation of

carbon mamidde by forming a Lewis acid adduct with a bound carbonyl

group of the iridium cluster as shown below. The overall result

Ir-C33 -> A1C13

of this treatment should produce a material which exhibits greater

stability and activity for the reduction of carbon monmoide. The

results of reaction of these materials with H2, 00 and HC1 are found

in a later section.

These materials were investigated by infrared spectroscopy.

Ihe infrared spectrum of iridium carbonyl deposited onto alumina and









49

silica and then treated with aluminum chloride are shown in Figures
2-5B and 2-6B respectively. The major V (C0) bands in the infrared
are listed in Table 2-4. The infrared spectrum of the silica

supported cluster is essentially unchanged by reaction with Al2C6
except for the appearance of very weak peaks at 2111 and 2041 cm-1.

Mare prconaced changes o ur in the infrared spectrum when

Ir4 (a )12 supported on A1203 reacts with A2C16 as shown in Figure
2-5B. The spectrum has a high frequency peak of weak intensity at

2127 cm-1 and one of moderate intensity at 2105 m-1. These peaks
have replaced the broad absorption in Figure 2-5A. They are
attributed to the surface molecules of the r4 ()12 aggregate

udergoing discrete interaction with bound AC12 species instead of

a variety of surface acid sites. The infrared spectra of the
alumirmm chloride treated supports that were subs ently reacted

with Ir4 (CO)12 did not show any differences in co region from the

materials in which the support was first reacted with Ir4 (00)12

followed by reaction with A2C16. Ihe 2105 cm-1 peak in the A1203

supported material is presumed due to a discrete species formed by

reaction of sme Ir4 (D) 12 surface molecules with AlC2. These high
frequency peaks are not seen for Ir4 (0) 12 in solution or the solid

state. These findings indicate chemical reactivity of at least sone
of the iridium carbonyl clusters when treated with A2C6g.
Interaction of the AC102 group shown in equation 2-22 with

metal carbtnyls would lead to shifts in the infrared.66 Possible
acid-base interaction include: (1) interaction of the oxygen of a
carbnyl group with the Lewis acid resulting in a decrease in V co








50

of that group and a smaller increase in V co of the remaining

uncoordinated (terminal) carbonyls of the cluster or (2) direct

interaction between a metal atom and the Lewis acid resulting in an

increase in the V o for all carbonyl ligands. The interaction of

the oxygen of a carbonyl group with the lewis acid has been shown to

result in terminal-to-bridging 00 shifts as reported by Shriver and

cowarkers for Ru3 (00)12 interacting with A1Br367 as shown in

Equation 2-23.



=k-M- + ACID > *M- M (2-23)



A third possibility for an increased carbonyl frequency would

involve oxidation of the iridium cluster.

Correa et al.68 has demonstrated that the Lewis acid sites of

alumina can promote 00 insertion. Upon impregnating alumina with

Me(OD)5(CH3) the presence of an acetyl species with a cyclic
structure as shown in Equation 2-24 was detected by infrared

spectroscopy.


CH3
A1203
Mn (Co)5 (C3) 4(OC)M -C;r.O (2-24)
rapid 250C I I
-Al10 Al

The AlC12 molecules in contact with the surface of an Ir4 (0)12

aggregate probably give rise to the 2105 cm-1 peak for

A1203/Ir4(0C)12 (see Figure 2-5B) and the 2041 and 2111 cm-1 peaks









51

for SiO2/Ir4 (C)12 (see Figure 2-6B). These peaks could be the high

frequency crxepant of an Ir4 (00)12 cluster coordinated to Al2C16

coordinating to a metal center or a carbanyl group with the low

frequency cumpo.nnt being too weak to be detected. Oxidation of an

iridium center in sane of the surface clusters to a higher oxidation

state can also cause the frequency of coordinated 00 to increase.

Psaro et al.69 reported a 30-40 cm-1 increase in the

frequencies of the infrared bands for [Os3(aC)11]2- ionicly bound to

the surface of MgO. They proposed that the increase in the carbonyl

frequencies was caused by the interaction of the cluster with a

Lewis acid center, probably a magnesium ion surface species. A

similar kind of specific bonding was reported for iron carbonyls

interacting with a proton or with carbocations.67 The fact that the

principle bands at 2062 and 2022 cm-1 do not shift for

Ir4 (O) 2/SiO2, Ir4 (D) 12/A1203 or in A12CI6 treated analogues

suggests that most of the material exists as aggregated clusters on

the surface of the support. A summary of all the infrared

abeorbances in the carbcryl region for the iridium complexes is

found in Table 2-4.


Investiation of the Aluminum Chloride Treated Suported Iridium
Carbonl Clusters for Catalytic Activity Ubon MM action with H2- 0
and HC (a)

The aluminum chloride treated deposited Ir4(00)12 clusters were

investigated for catalytic activity upon reaction with H2, 00 and

HCI(g) using the fixed bed flow reactor previously described and
shown in Figure 2-2. These materials are proposed to represent the









52

heterogeneous analog of the previously reported Ir4 (0) 12-A12C6

hmoeneos system.5,6

Upon reaction of the supported Ir4 (O) 12-A12C16 materials with

H2, 00 and HC1 at 1250C high selectivity for the formation of

methyl chloride was observed. 'he formation of methane, trace C2

products and didclorcmethane was also detected by gas dhromatography

similar to that shown for the Al203/Ir4 ()12 system in Figure 2-7.

Carbon dioxide and water were also detected by GC/MS. A comparison

of the activity for the different supported iridium materials is

shown in Figure 2-8.

The lewis acid treated materials exhibit reactivity of

approximately two orders of magnitude greater than the deposited

clusters which were not treated. In the deposited iridium carbonyl

clusters which were not treated with aluminum chloride the

reactivity of those material is proposed to represent primarily a

stoichiometric decamposition of the cluster to the observed

products. This activity is believed to be initiated by interaction

of the carbonyl groups of the original cluster with the surface

hydroxyl groups of the support as previously daribed60 and shown

in Equation 2-20. The Lewis acid treated solids described here also

exhibit approximately two orders of magnitude greater reactivity

than the previously reported phosphine substituted supported iridium

clusters.46 In those systems it was shown that organic residues

present on the surface of the oxide support made a contribution to

the observed products.


__I









53

With time the activity of the supported Ir4 () 12 materials

decreases and eventually reduction of carbon maoxide is no longer

observed to occur as indicated by the absence of products detected

by gas chroatography. These resulting inactive materials were

investigated by infrared spectroscopy in an attempt to determine the

nature of the iridium species formed. A discussion of these results

is found in a later section.



Owaprison with the HomoIeneous Ir4 (00) A12 S6ytm
In the previously reported hcmogeneous Ir4(00)12-Al2Cl6 system

the major product observed upon reaction with H2 and C0 was

ethane.5,6 No ouyqenated products were detected in the hcageneous

iridium system unlike typical homogeneous 0 hydrogenation systems

employing metal carbonyl clusters as catalysts. Other products

detected in that system include methane, methyl chloride and

propane. Oollmn et al.6 proposed that the methyl chloride produced

was an intermediate species in the molten system which undergoes

further hcanlogation and hydrogenation reactions leading to the

formation of higher hydrocarbon products. However, in the supported

iridium carbcnyl system investigated in this study methyl chloride

was observed to be the major product in the reaction of the

supported iridium clusters with H2, C0 and HC1. This increase in

product selectivity may result from two factors. One would involve

the HCl present in the reactant gases whic would convert C1

intermediates to methyl chloride. The short contact time between


F











CH3C1 and A12C16 would also minimize subequent reaction of H03C1
leading to hmologation.6

The catalytic synthesis of hydrocarbos frm H2 and 00 over

supported iridium metal on alumina has been previously investigated

and shown to produce methane as the major product as well as minor

amounts of ethane, ethylene and methyl chloride.40 The formation of

methyl chloride in the Ir/Al20 system was found to be due to the

presence of chloride ions on the alumina surface after impregnation

of the metal halide.70

Iamb and Gates71 have reported that magnesia supported

H20s(00)4 is active for the catalytic hydrogenation of carbon
monoxide to yield C1 to C4 alkanes. The rate of formation of

methane was reported to be 4.2 x 10-4 mol hydrocarbcr/mol Os/s at

275C and 10 atm. The rate of formation of the C2-C4 products was

reported to be 5 x 10-5 to 7 x 10-7 mol hydrocarboimol Os/s. The

supported iridium carbonyl systems reported here are less active

(810-5 to 9xL-6 mol methyl chloride/mol Ir4 () 12) but more

selective.

In this iridium system it is proposed that the methyl chloride

is being formed by the catalytic reduction of carbon monoxide or

from a stoichiometric decrposition reaction involving the original

cluster. Under the conditions, the curve in Figure 2-8 would have

to be investigated for over 1000 hours at the activity level seen at

forty hours in order to exhaust all of the 00 originally present in

the cluster. Even from the data reported for similar systems71,5 it

is difficult to differentiate between the occurrence of catalytic 00


1









55

reduction and cluster deccuposition. Experiments with labelled 00

have been shown not to be definitive46 for exchange of C0 with the

clusters and intermediates formed in their dec~rposition could occur

and lead to labelled carbon products. A discussion of the proposed

mechanism for reduction of 00 in the supported iridium systems

reported here is found in a latter section.


Infrared Investigation of DeMosited Ir4 (00)12 After Reaction with
2". 00 and HCIta)
Infrared spectroscopy was used to investigate the alumina and

silica supported tetrairidium carbonyl clusters after reaction with

H2, 00 and HCl at 1250C. Ihe infrared spectrum of A1203/Ir4 (C) 12

and SiO2/Ir4 (D)12 after exposure to the reactant gases is shown in

Figure 2-9 and the major V co bands are listed in Table 2-6. A

comparison with the original spectrum shown in Figure 2-5 indicates

that significant changes in the carbonyl region have occurred. The

decrease in intensity of the 2062 and 2022 ca-1 peaks of Ir4 (00)12

attributable to the tetrairidium carbonyl cluster indicates that

most of the Ir4(00)12 cluster has decmposed. As can be seen in

Figure 2-9 two strong absorbances at 2140 and 2080 cmI1 appear.

This spectrum is attributed to deccposition of Ir4(OD)12 to lower

nulearity iridium chlorocarbonyl species.

Deonrrosition of Al203/Ir4 (00)12 is believed to be initiated by

reaction at catalytic conditions of the support surface hydroxyl

groups with the carbonyl groups of Ir4 (C)12 as reported by Tanaka

et al.60 and shown in Equation 2-20. In their infrared study of the
adecr~neition of Ir4 (00)12 on A1203 no absorbenes at wavenumbers





































a= 1987 cm"'
b 1995 cm-1
c= 2022 cm'"
d 2068 cm-"
e= 2075 cm"i


2000


WAVENUMBERS (CM -)


Figure 2-9.


Infrared Spectra of Deposited Ir4 () 12
on (A) Silica Gel and (B) Alumina After
Reaction with H2, 0D and HCl(g) at 1250C.


f 2082
g= 21 18
ha 2140
i 21 II
ka 2137


cm-1
cm'-
cm-'
cm'i
cm I


2100


1900


1800













Table 2-6.




compound


Major V (co) Bands in the Infrared Spectra
for Fhompie Substitutd Ir4 (OD) 12 and Ir4 (D) 12
After Reaction with H2, D0 and HC1.


V co*
(ca-1) Ref.


Al203-(PPh2) 1,2,3Ir4 (C0) 11,10,9
after reaction at
a) 750C


b) 1250C


2150 (m), 2102(sh), 2069(s)
2026(w), 1734(w), 1719(w)


2137 (m),
1990(m),


2069 (s), 2026(w)
1734(w), 1719 (w)


C) 20000


Al203/Ir4 (00) 12 after
reaction at 1250C


A1203/Ir4 (00) 12/A12C16
after reaction at 125;k


A1203/IrC1 (D)3 after
reaction at 1250C


Al203/ICl (00) 3/A12 6
after reaction at 125%


Ir4 (00) 12/Al2C6-NaCl


2055(s)


2140(s), 2118(w), 2082(s)
2022 (w), 1997 (w)


2140(m),
2062(s),


2118(m),
2022(m),


2075(sh)
1997 (m)


2118(m), 2075(w), 2062(s)
2022(m), 1997 (w)


2113(m), 2080(w), 2060(m)


2190(s), 2160(s), 2125(s)
2112 (m), 1630(m)


* s=stzrc, m moderate, wjweak, sh=dhoulder









58

greater than 2080 cma1 were observed, even after reduction of the

cluster to metallic iridium and subsequent expoue to carbon

uancwdde. The appearance of absorptions at waverumbers greater than

2080 cm-1 in our results (Figure 2-9) suggests the formation of

discrete chloro carbonyl iridium amplexes.


Infrared Investigatin of Suxorted Ir4 (00)12 2Al 6 OColexes After
Reaction with .H2, X and HCl( )

As previously discrujsse and shown in Figure 2-9 supported

Ir4(o0)12 on alumina or silica gel supports decoaposes to produce

lower rclearity iridium chlorocarbonyl species ehibiting an

infrared spectrum which is different from the starting material.

hmis deocyposition was proposed to be initiated by interaction of

the carbonyl groups of the cluster with the surface hydroxyl groups.

lhe possibility of cluster dermposition by interaction with

hydroxyl groups was investigated by reacting the support material

with aluminum chloride. In this case, interactions between the

surface hydroyl groups and the carbonyl groups of the cluster

should have been greatly reduced as shown in Equation 2-22. If the

major decmprsition mechanism of the supported clusters involves the

displace~ nt of carbWyl ligands by surface hydroxyl groups, the

conversion of these hydroxyl to aluminum chloride groups65 should

not only increase the acidity of the support material, but should

also lead to an increased stability of the supported Ir4(00)12.

Ihe infrared spectrum of alumina supported Ir4 (0) 12 treated

with Al2C16 after exposure to H2, C0 and HC at 1250C is shown in

Figure 2-10 (see Table 2-6 for a listing of the major co bands).









59

The infrared spectnru of silica supported Ir4 (D) 12/A12C6 is found

in Figure 2-11. The 2062 an-1 and 2022 c-1 peaks indicate that

sae of the original Ir4 (0)12 cluster is still present. The high

frequency peaks and oeplexity of the spectrum indicate that the

clusters have undergne transformations to produce stabilized

multiruclear iridium chlorocarbonyl species. The possibility of

minor amounts of small metal particles undetectable by infrared

spectrosoopy cannot be ruled out.

In the I homage usI Ir4 (C) 12-A12C6 previously reported,5

infrared spectroscopy was used to investigate the material after

reaction with H2 and 0D. A nultiband spectrum in the 2100 cm-1

region (see Table 2-6) was found as well as a peak at 1630 m-1. It

was previously proposed that the low frequency peak was

characteristic for M -D-Iewis acid banding. In the heterogeneous

Ir4(C) 12/Al2Cl6 system studies here, no bands in the 1900-1600 m-1

region were observed. It is possible that absorbances corresponding

to bridging carbnyl groups are present but are either too weak or

masked by ahbsrba nes from the support. Alumina does exhibit a

strong absorbance at 1630 c-1.

Final evidence suggesting the existence of several iridium

chlorocarbaonyl complexes was provided by photoelectron spectroscopy

(ESCA). The materials were investigated before and after reaction

with the gases. The results are shown in Figure 2-12. At best the

results are qualitative. The data obtained from samples of the

supported clusters after exposure to the reactant gases at 1250C

suggested the presence of at least two different oxidation states in



























a= 1996 cm'"
b = 2022 cm-
c 2862 cm-
d 2075 cm-
e 8 2116 cm-"
f 2140 cm-'


2100 2000

WAVENUMBERS (C.M )


1900


Figure 2-10.


Infrared Spectrum of A20/Ir4 (00) 12/A2C6
After Reaction with H2, 00 and H1 (g) at 1250C.






























a a 1996 cm-
b = 2023 cm-
c = 2063 cm-
d a 2075 cm-'
e 2 2142 cm-


2100 2000


1900


WAVENUMBERS (CM )


Figure 2-11.


Infrared Spectum of SiO2/Ir4 () 12/A216
After Reaction with H2, 00 and HCl(g) at 125-C.











































-76 -74 -72 -47 -6S -4 -64 -a2 -4 -56 -"
IIKNDIW MC EV


Figure 2-12.


ESCA of SiO2/Ir4 (C) 2/A12C6
(A) Before and (B) After action
with H2, 00 and H (g) at 1250C.









63
the resulting iridium ocaplexes as indicated by a minor shift to

higher binding energy.


Investigation of Suported IrC(O)C Ubn IRaction with H. 0 and

Oollman et al.6 reported that the manIrclear complex,

IrC(OD)3, was either the active catalyst or catalytic precursor

for 00 conversion in the hcmogeneous Ir4 () 12/A2CI6-NadC melt

system. In order to gain further insight into what transformations

occurred in the supported iridium systems and the nature of the

inactive iridium species which may have been formed during reaction

with H2, CO and HC1, an investigation of supported IrC1(CD)3 was

undertaken. IrCl(00)3 was deposited onto A1203 (see Figure 2-13A).

Upon exposure of Al203/IrC(00)3 to H2, CO and HCI at 1250C only

minor amounts of methyl chloride were formed. The infrared spectrum

of deposited IrCl(CD)3 after exposure to H2, 00 and HC1 at 1250C is

shown in Figure 13B and the major bands are listed in Table 2-6.

The four band pattern present in supported Ir4(CO)12 (see Figures 2-

5 and 2-6) and Al203/Ir4 (C) 12/Al2C6 after exposure to H2, CD and

HC1 (Figure 2-10) is also present in A1203/IrC1(00)3 after exposure

to the gases.

Physisorbed Rhg6(O0)16 is easily formed on the surface of a

support by reaction of Rh(I) surface species with CD in the presence

of a partial pressure of water.72 Clini and Mrtineng73 also
0
reported that 6 (CD)16 was easily synthesized by reaction of

[Rh(OD)2C]2 with CD in the presence of water under slightly basic


__


































2100 2000 1900 1800


WAVENUMBERS (CM-')


Figure 2-13.


Infrared Spectrum of A120/IrC (0)3
(A) Before and (B) After Reaction
with H2, 00 and HC(g) at 1250C.


2200









65
conditions. Recently, ruthenium and osmium carbonyl clusters have

been prepared by the conversion of supported moannuclear halide

complexes (RuCI3 and H2OsC6 respectively) under conditions of
catalytic hydrogenation of carbon monoxide.74 It is believed that

similar chemistry could occur with the supported IrC1(CO)3 system.
The monnuclear coplex could interact with surface hydroxyl groups

of the alumina support under the conditions of 00 hydrogenation

employed resulting in the formation of a higher nuclearity iridium
carbonyl complex. This type of reaction could result in the
formation of an iridium carbonyl cluster exhibiting an infrared
spectrum similar to Ir4 (00)12 (see Figures 2-5 and 2-6).

Deposited IrC1(00)3 was also reacted with A12C16 (see Figure 2-

14A) and investigated as a catalyst or catalyst precursor. The
2071 cm-1 peak has replaced the broad absorption in Figure 2-13A

and is attributed to surface molecules of IrdC(00)3 undergoing a
discrete interaction with bound A1C2 species instead of a variety

of surface acid sites. Upo exposure of Al203/IrC (C) 3/12C16 to

H2, C0 and HMI at 1250C only minor amounts of methyl chloride were

formed similar to A1203/rCl (00)3. The infrared spectrum of

A1203/IrCl(0) 3/Al2Cl6 after exposure to H2, 00 and HC (shown in
Figure 14B) and the major V co bands listed in Table 2-6) contains
high frequency absorptions at 2113 and 2060 aa-1 similar to

A1203/IrC1(00)3 after exposure to the gases (see Figure 2-13B) but
does not contain any substantial absorptions below 2060 cm-1. They
could be present but are obscured by broad absorptions. The

differences in reactivity for 00 reduction of the supported






































2100 2000 1900

WAVENUMBERS (CM-I)


Figure 2-14.


Infrared Spectrum of Al203/IC (00) 3/Al2Cl6
(A) Before and (B) After Reaction
with 2H, CD and Hc(g) at 1250C.


z

0
V)


z

F-
00






2200


1800









67

n wmxlear iridium chloro carbonyl cacplexes compared to their

harogeneous analog suggest that their chemical reactivities have

been greatly altered upon heterogenizing then.


Investiation of Metallic Iridium U=on Rbaction with H2, 00 and
HC1(g)

Either Ir4(00)12 or IrCl3 3H20 was physically adsorbed onto

alumina. Each sample was retreated by calcination at 2500C under

hydrogen for five hours. The resulting gray supports were

investigated for catalytic activity upon reaction with H2, CO and

HCl and were observed to produce only a trace amount of methyl

chloride at 125C under H2, 00 and HC1 in a stagnant reactor. An

increase in activity to approximately 2.5 x 10-7 mol CH3C1/ mol Ir/

s was observed for these metallic iridium systems upon raising the

reaction taperature to 2000C. The catalytic formation of

halogenated hydrocarmbns from synthesis gas and HCl(g) over

inorganic xide supported iridium metal between 200 10000C has

previously been reported.40

The infrared spectra observed for the metallic iridium systems

exposed to H2, 00 and HCl was observed to contain one broad weak

absorption whose location was dependent upon the extent of metal

loading. Ihe spectra resembled the spectrum of th decmposed

phosphine supported cluster resulting frcm exposure to the reactant
gases at 2000C as previously reported.46 The predmint infrared

absarptions assigned for carbon monoxide absorption onto an iridium

metal surface has been reported to range from 2010 cm-1 at low metal

coverage to 2093 an-1 at metal saturation.75-77 It was previously









68

concluded from the similarities in the infrared spectra of metallic

iridium and the demorposed phosphine supported clusters that

metallic iridium is formed above 2000C under a H2, 00 and HC1

atmosphere (see Table 2-6). However, below 2000C the stabilization

of discrete iridium complexes is indicated by the complexity of the

infrared spectra.46 The results of this infrared study conducted

with the supported Ir4 (0) 12-A2C16 materials after reaction with

H2, 00 and HCl suggest that discrete iridium ccuplexes have also

been stabilized on the support. A variety of iridium chlorocarbonyl

caplexes have been reported to be formed by the reaction of

powdered iridium metal with C0 and Cl- icns.78 The possible role of

these stabilized iridium complexes in the reduction of carbon

mnaxide is discussed in the mechanism for 00 reduction found in a

later section.



Investigation of Other Lewis Acids

Other Lewis acids were investigated for the preparation of an

Ir4 (CD)12-ewis acid solid material capable of catalytically

hydrogenating carbon monoxide with HCl to methyl chloride. The

acids investigated were FeC33, ABr3 and SbCl5. he activity

observed whn the other Lewis acids were investigated was less than

that observed for the aluminum chloride treated material. For the

material treated with iron chloride the conversion of the iron

chloride to iron carbonyl is believed to occur in the presence of

the carbon mmoxide reactant gas. This is followed by loss of the

iron carbonyl from the system as indicated from a noticeable yellow


--i-


I









69

coloration of a post bubbler in the flow system. This type of

reaction is not unreasonable considering the volatility of iron

pentacarbonyl. In the case of the aluminum bromide treated iridium

clusters the conversion of the bromide complex to the chloride

complex is believed to occur in the presence of HC1. Even in

these systems the activity for the formation of methyl chloride was

less than the analogous solids prepared form aluminum chloride. The

antimony pentachloride treated materials exhibited the highest

activity for the formation of methyl chloride of the three

alternative acids employed. During the course of the reaction with

H2, CO and HCl the formation of metal was observed to occur. This

was evident fron plating out of a black mirrored ring above the

solid material in the reactor tube. Attempts to increase the

activity and stability of these systems (by varying the reaction

temperature and amount of added HC1) for the reduction of carbon

monoxide were unsuccessful.


Invesiatitin of Al2C6 Treated Ocmnercial 0 IReduction Catalysts

A copper methanol catalyst was investigated for catalytic

activity in the reduction of carbon monoxide with hydrogen and

hydrogen chloride to produce methyl chloride. The Low Temperature

Shift catalyst (United Catalyst) did not exhibit any activity for

the reduction of carbon monoxide under the reaction conditions

employed even at temperatures of 200C. These result are not

surprising because the materials are reported to exhibit activity at

220-270C and 50-100 atmosphere pressure.79









70

Upon treatment with aluminum chloride these materials did

exhibit activity for the formation of methyl chloride. The activity

of these catalysts was -10-10 mol CH3C1/s/g catalyst which is

similar to that observed for the previously described supported

Ir4 (D) 12-Al2C16 system. The observed activity for the reduction

of carbon monaride under mild conditions with the methanol catalysts

is attributed to the bifunctional activation of carbon monoxide

occurring upon treatment with aluminum chloride.

7he lifetime of the treated methanol catalysts was observed to

be appraxmately 8-15 hours depending upon the amount of HCl

reactant gas and the flow rates. A color change in these materials

from brown-black to dark green is accpanied by a decrease in

activity. It is suspected that the decrease in activity is a result

of the formation of copper chloride. These methanol catalyst have

been reported to be sensitive to poisoning by IHC leading to the

formation of copper chloride79 as shown in Equation 2-25.


CO-O-Zn + HC. > QC1l + HDZn (2-25)


Accompanying this change is the accunulaticn of water in the reactor

tube which leads to the conversion of aluminum chloride to aluminum

hydrox2de decreasing any Lewis acid interactions. Several

eperime, ts were comxucted to try to increase the stability and
activity of these systems for the formation of methyl chloride

including varying the amount of EHC present as a reactant and

taperature. In all cases the activity of the system would decrease









71

a;icpanying a color change in the catalysts. It is proposed that

the activity displayed by these systems is due to the Lewis acid

treatment leading to mild reduction of carbon monoxide via a

bifunctional activation mechanism.


Mehanism Pra=xsed far the Formation of Methyl Chloride

A schematic representation summarizing the reaction of H2, 00

and HCI with all the various supported iridium carbonyl complexes is

shown in Figure 2-15. A series of control reactions completed in

this work support the formation of methyl chloride from organic

residues introduced onto the supported phosphine substituted iridium

ccuplexes during preparation. An infrared study previously

conducted by Weiss46 of these materials before and after reaction

established that decc position of the phosphine substituted clusters

to lower nuclearity iridium species occurred during the formation of

methyl chloride.

In this work, tetrairidium carbonyl clusters were deposited

onto inorganic oxide supports. These materials were then treated

with aluminum chloride and shown to undergo interactions with Lewis

acid sites present on the surface of the support. Evidence for

these interactions was provided by the presence of new absorbances

in the carbonyl region as indicated by infrared spectrosoopy. The

deposited Ir4(O0)12 clusters were found to react with H2, CO and HC

to produce methyl chloride as the major product detected in the post

gas stream. The formation of methane, trace C2 products, water and

carbon dioxide was also detected. The aluminum chloride treated














PPh I




(PPh2), I r4(CO)12-, Ir


H2/CO/HCI
750C



CH4 + CH3CI + C02
+ H20


r4(CO),


2
2 +Al2Ci6




2 AICI2-I r4(CO),2
INTERACTION
OBSERVED J


H2/CO/HCI
125C



H4 + CH3CI + CO2
+ H20


LOWER NUCLEARITY
COMPLEXES
Ir, Cly (CO)z


H2/CO/HCI
200C


METALUC IRIDIUM
(Ir)n- CO


Figure 2-15.


Proposed Mechanism for the Forantion
of Methyl Chloride with the Supported
Iridium Carbonyl Clusters.


--~f-


h -


--


-7


L ,


4(CO)l
I









73

materials were found to be aproximately two orders of magnitude

more active for the formation of methyl chloride than the analogous

materials which were not treated with the Lewis acid.

Studies of the deposited iridium clusters after exposure to the

reactant gases indicate that demcaposition of the iridium clusters

has occurred during the course of reaction. Infrared spectroscopy

supports the adecrposition of the clusters to lower nuclearity

iridium chloro carbonyl species and not to metallic iridium. These

resulting iridium species which are formed during reaction are

eventually inactive for the reduction of carbon monoxide. At

elevated temperatures (>2000C) further decomposition to metallic

iridium is observed. The supported metallic iridium materials

exhibit minor activity upon reaction with H2, 00 and HCI for the

formation of CI-C3 hydrocarbons and methyl chloride. The formation

of methyl chloride at temperatures above 2000C can be explained by a

Fiscer-Tropsch mechanism as previously described by Vannice.40

It is proposed that the formation of methyl chloride at

temperatures below 2000C may result from a pathway involving the

reduction of carbon monoxide. For the deposited Ir4 (C)12 materials

in the absence of the aluminum chloride treatment it is proposed

that the formation of methyl chloride results from deccmposition of

carbonyl groups present on the original cluster. This reduction is

proposed to be initiated via a decarbanylation mechanism from

interaction of the carbonyl groups of the cluster with the hydroxyl

groups of the support (as shown in Equation 2-26)













Ir4(0) 12 + XSCH > Ir4(0) 12-x(SH )x + X0 (2-26)


followed by subsequent reduction of carbon monoxide to the observed

products. The resulting materials exhibit strong absorbances at

2082 and 2140 cmI1 indicative of monrnuclear ccuplexes. The

investigation of supported monuclear IrC1(00)3 for activity for

reduction of carbon monoxide in this work resulted in the formation

of only trace amounts of methyl chloride.

The formation of methyl chloride in the aluminum chloride

treated materials is proposed to be initiated by a bifunctional

activation of carbon monoxide via interaction of the oxygen end of a

bound iridium carbonyl species with aluminum chloride. Subsequent

reaction with H2 and HC1 would lead to the formation of the observed

products. he resulting material after reaction supports the

presence of iridium species which are not monauclear as indicated

by the complexity of the infrared data. It cannot be ruled out that

deoc Xosition of the supported Ir4 (00) 12-A12C6 materials is not

initiated by interaction of the carbonyl groups of the iridium with

the aluminum chloro present on the surface of the support. It is

proposed that the increased activity for the formation of methyl
chloride for the Lewis acid treated materials is due to the

stabilization of imltinuclear iridium species. The stabilization of

multirclear iridium species in the supported phosphine substituted

iridium complexes were believed to be active for the formation of

methyl chloride in that system.









75

7he activity of the deposited iridium carbonyl clusters were

shown to be greater for the formation of methyl chloride than any of

the previously investigated supported iridium systems. Even with

the systems described in this study high levels of activity were not

achieved such that commercial production of methyl chloride based

upon synthesis gas would be attractive.




D. Summer



Tme investigation of supported phosphine substituted iridium

carbonyl clusters resulted in the identification of organic residues

on the surface of the inorganic oxide support which were

incorporated during preparation. The presence of these residues was

shown to result in the formation of alkyl halides (CCH32C and

CH3Cl) upon reaction with H2, 00 and HC1. The results of control

experiments suggest that the previously reported activity for the

formation of methyl chloride frEm reduction of CD with H2 and HCl by

these systems were clouded by the presence of carbon sources

introduced during the support functionalization procedure.50

A study was undertaken whereby Ir4 (C)12 was deposited on to

inorganic oxide supports such as alumina and silica gel and also

treated with aluminum chloride. The characterization of these

supported clusters was conducted by infrared spectroscopy. The data

obtained suggest that Ir4 (D) 12 remains intact upon deposition onto

the oxide supports and exhibit spectral features cannon to Ir4 (C0)12









76

in the solid state and in solution. Upon reaction of the deposited

iridium clusters with aluminum chloride the appearance of high

frequency bands in the infrared spectra of these materials was

observed. These data suggest that the supported iridium carbonyl

clusters have undergone interactions with strong Iais acid sites

present on the surface of the support.

7he supported iridium carbonyl clusters were investigated for

catalytic activity for reaction with H2, CO and HCI to produce

methyl chloride. Precedence for this reaction is provided from a

report of a homogeneous CD hydrogenation system where methyl

chloride was produced though ethane was the major product reported.

Ihe reported catalyst was Ir4 (00)12 in a molten A12C6-NaC1

medium.5,6 The mild reaction conditions (1-2 atmosphere pressure

and teperatures below 2000C) necessary for the reduction of carbon

monoxide in the haogeneous system were believed to be due to the

strong lewis acid solvent where bifunctional activation of carbon

manadde could ocur. The supported iridium carbanyl clusters

treated with aluminum chloride are this researcher's version of the

homogenous Ir4 (O) 12-Al2Cl6 system. These materials were

investigated for the reduction of carbon monoxide with H2 and HC1 at

1 atmosphere pressure and 1250C. The supported iridium carbonyl

clusters were found to result in the formation of methyl chloride as

the major product which was quantified, unlike the hanogeneous

system where ethane was the major product reported. The formation

of methane, ethane/ethylene, acetaldehyde, ethyl chloride, methylene

chloride, carbon dioxide, and water were also detected in the









77

supported Ir4(00)12-Al2C 6 system. The lewis acid treated materials
were found to edxibit approximately two order of magnitude greater

activity than the iridium clusters deposited on alumina. The high

selectivity for the formation of methyl chloride in the supported

system is attributed to the presence of the HC1 in the reactant

gases which would convert C1 intermediates to methyl chloride prior

to hbmologation and hydrogenation.

In the oogeneous system IrCl(CD)3 was also proposed to be an

active catalyst or catalyst precursor.6 Investigation of this

supported monarulear complex both in the absence and presence of

aluminum chloride resulted in the formation of only minor amounts of

methyl chloride upon reaction with H2, CD and HCI. The formation of

methyl chloride has also been previously reported from the reaction

of H2, 0D and HC over supported metallic iridium.40 Ihe

investigation of metallic iridium as a catalyst for the reduction of

carbon monrxide to methyl chloride resulted in only trace amounts of

methyl chloride below 2000C in a stagnant reactor while above 2000C

the activity was observed to increase. It is proposed that metallic

iridium is not responsible for the observed formation of methyl

chloride in the supported Ir4(00)12-Al2Cl6 system and that

stabilization of a discrete iridium complex active for methyl

chloride formation occurs.

The supported iridium clusters were investigated by infrared

spectroscopy after reaction with H2, CO and HC1. The materials

investigated were no longer active for reduction of carbon monoxide.

Iridium carbonyl on alumina or silica gel is proposed to decampose









78

to mnumrclear iridium chlorocarbonyl complexes as indicated by

infrared data. A decarbonylation reaction whereby interaction of

the bound carb yl groups of the cluster may interact with hydroxyl

groups n the surface of the support is believed to result in

decmposition of the cluster. Infrared investigation of the

aluminum chloride treated iridium clusters after reaction revealed

complex spectra which are attributed to the presence of stabilized

miltimrlear and not metallic iridium. Similar complex infrared

data was stained in the previously studied46 phosphne substituted

clusters which were proposed to be multinuclear iridium

dilorcarbonyl species. The decomposition of supported Ir4 (00) 12-

Al2C16 via interaction with surface AlCl2 grops formed upon
treatment with aluminum chloride and the presence of small amounts

of iridium metal undetected by infrared spectroscopy cannot be ruled

out.

In the phosphine substituted and the aluminum chloride treated

iridium carbnyl systems data suggest that catalytic reduction of

carbon monoxide is not the major pathway which would account for the

formation of methyl chloride. Discarding the presence of organic

residues in the supported systems the major route for the formation

of methyl chloride appears to be one comprising of the deocaposition

of the carb nyl groups originally present on the Ir4 (O) 12 clusters.

Ihe inability to form and stabilize an active heterogeneous analog

of the ogeneous Ir4 (CO) 1-Al2Cl6 system from Ir4 (C0) 1 or

IrCl(CO)3 suggests that alterations of the active environment have
occurred in the heterogenized system during catalysis.















III. RHODIUM PEWRF1I XCARBKXYLATE
IRIPHENYLEIHOSPHNE OCMPIEXES FOR
OIEFIN HYERDIORMYIATICN


A. Badlao



Metal carboxylate dimers have been the subject of many

reviews.80-82 The investigation of these coaplexes is of interest

since they can act as model compounds for the study of metal

synergism. These dinuclear ccuplexes contain metal-metal bonds and

four bridging carboxylate ligands resulting in a "lantern

structure." Rhodium(II) carboxylates of the general formula

I412 (02CR)4, possess a rhodium-rhodium single bond and readily form
adducts, in which the axial positions are occupied by solvents or

ligands.

The reactivity of rhodium(II) carbaKylates with a variety of

donor ligands has been widely investigated.83-89 ago and

coworkers have measured equilibrium constants and enthalpy of

coordination for various axial ligands.83,86 Ihe formation of 1:1

and 2:1 ligand to dimer complexes has been observed. Once the 1:1

adduct has been formed, the second axial ligand is less strongly

bound at the second rhodium center.84 Studies have established that

electron withdrawal from rhodium(II) perfluorocarboxylate complexes

enhances the Lewis acidity of the axial coordination sites. Fully

fluorinated rhodium(II) tetrakis(heptafluordutyrate) has greater

79









80

covalent and electrostatic sigma acceptor properties than the

corresponding butyrate complex. Research has also focused on the

influence of base coordination at one rhodium center on the

stretching frequency of coordinated 00 at the second metal center.85

The coordination chemistry of rhodium(II) carboxylates has also

been extended to include olefins. Spectrosoopic studies conducted

by Doyle et al. yielded the first demonstration of olefin

coordination with rhodium(II) perfluorocarboxylate complexes.87

Equilibrium constants were reported for the 1:1 adducts of

Rh2(02CCF3)4 with a series of alkenes. No spectroscopic evidence
for the binding of alkenes by rhodium(II) acetate in solution was

obtained in Doyle's study. These results are in contrast to those

reported by Schurig where equilibrium constants for olefin-

rhodium(II) acetate adducts have been determined from retention data

by ocaplexation gas chrmnatography rather than from spectroscopic

studies.88

The olefin coordination chemistry of rhodium(II)

perfluorocarboxylates in solution has been extended by Doyle et al.

to include rhodium(II) tetrakis (heptafluorbutyrate).89 Equilibrium

constants for 1:1 complexes between rhodium(II) perfluorobutyrate

are approximately three times greater than those determined for

thodium(II) trifluoroacetate. The increased ability of the

flurinated rhodium(II) carboxylates to coordinate molecules is

attributed to the increased Lewis acidity of the rhodium center due

to the electron-withdrawing properties of the fluorinated

carboxylate ligands. Based upon these findings, rhodium









81

carboxylates would be expected to exhibit activity in catalytic

reactions involving the binding and subsequent activation of

molecules such as olefins, carbon monoxide, etc.

Modium(II) acetate has been reported to be an active catalyst

for the hoogeneous hydrogenation of olefins in a wide variety of

solvents.90,91 A mechanism has been proposed which involves the

intact diuer and heterolytic cleavage of dihydrogen92 as shown below

in Equation 3-1. Terminal olefins have been shown to undergo 15-20%



+H2 +L
h2 (OAc) 4 > H(Ac) ( )3 >

HIAc (3-1)
(HL) (QAc) 3h > H2L + &2(O ) 4

isamnrization while the catalyst is less active or inactive for

internal olefins.

The cycloprpanation of diazoesters to alkenes to yield

cyclopropanes has also been reported to most effectively be

catalyzed by rhodium(II) carboxylates93,94 as shown in Equation

3-2. The cyclcprqpane carboxylic acid ester products have use as



R1 R3 R1 R3
\ / Ih2 (02R)4 \
C=C + N2= CH-00R -> C-C (3-2)
/ \ /\/\
R2 R R2 C R4
H 0OCR









82

insecticides. Mecanistically, a h2 (O2CR)4-carbene complex is

proposed which then transfers the carbene to the substrate.95 In

the presence of rhodium(II) carboxylates and vanadium or molybdenum

compounds cyclohexene can be oxidized to give 1,2 epoxycyclohexene-

3-ol.96 The reaction takes place at 55C under 1 atm. of oxygen and

proceeds via a cyclohexyl hydroperoxide intermediate. The best
results have been reported for fluorinated carboxylate ligands such

as trifluoroacetate.97 Rhodium(II) carboxylates react in methanolic

HBF4 in the presence of triphenylposphiqne and lithium carboxylate

to produce Rh(02CR) (Ph3)3.98 These complexes have been reported to

catalyze the homogeneous hydrogenation of alkenes and alkynes.

Rhodium(II) carboxylates have received attention as second

generation platinum metal anticancer compounds. The use of these

cnplexes was first reported by Bear in 1972.99 Investigation into

the chemical properties and biological effects of rhodium(II)

carboxylates in relationship to their ability to bind unprotonated

amino and sulphydryl groups have been conducted. Invivo studies

have shown that rhodium carboxylates are able to inhibit certain

biological processes in particular the cellular synthesis of ENA

While these complexes have been studied as catalysts for sane

reactions as dias ssed above, the fluorinated diners have not been

extensively investigated. The reported increased ability of the

fluorinated rhodium carboxylates to bind molecules such as olefins

and 0D would be expected to render these complexes active catalysts

for reactions such as hydroformylations.









83

The hydroformylation reaction was discovered by 0. Roelen in

1938 while studying the effect of added olefins in the Fischer-

Trpech Process.100 later studies concluded that the presence of

cobalt in the heterogeneous Fischer Trcpsch catalyst was catalyzing

the hydrofornylation reaction and that the actual catalyst was

homogeneous.101 'he hydroformylation or oxo" reaction is the

reaction of synthesis gas with an olefin102 as shown in Equation

3-3. In the absence of a catalyst the reaction does not proceed.


catalyst
H2 + 00 + 1CH C2 > RPCHCHZCH + {CH(CHO)CH3

(3-3)


The products from the hydrofonrylation reaction are aldehydes. Both

the linear and branched aldehyde may be formed. Linear aldehydes

have the greatest chemical utility. The addition of bulky phosphine

ligands to hydroformylation catalysts results in an increase in the

selectivity for the formation of the linear aldehyde. Byproducts

camomnly formed during hydroformylations include alkanes and

alcohols.

The production of butyraldehyde from the reaction of H2, CO and

propylene is the largest camercial application of the

hydroformylation process.103 Apprximately 6 billion pounds of

butyraldehyde are produced annually. The ondesation and

hydrogenation of the aldehydes ultimately yields alcohols which are

used as ccunpnents of plasticizers. An additional 2-6 billion

pounds of other aldehydes are also produced annually by the

hydrofonmylation process. The ultimate products are long chain









84

alcohols which have application in the production of biodegradable

soaps, detergents, and as components of plasticizers.

Two aspects of the hydroformylation reaction are of industrial

importance. One involves the formation of undesirable byproducts

which should be minimized during reaction. The other aspect

concerns the development of processes which avoid expensive

operating conditions which occur when high pressures and

temperatures are employed to carry out the reaction. Commercial

processes have been developed based upon both cobalt and rhodium

catalysts with each having their own advantages and

disadvantages.104

Cobalt hydroformylation processes typically employ dicobalt

octacarbnyl, Oo (00) 8, as the catalyst precursor.105 The active

catalyst is 30o (0) 4 which is a volatile, unstable complex that is

difficult to separate from the reaction products and recycle into

the system. Processes based upon hydrido cobalt catalysts typically

operate under severe reaction conditions. Reaction pressures of

200-350 atmospheres and temperatures between 150-2000C are generally

employed. The product isomer ratio obtained with hydrido cobalt

catalysts is approximately 3 or 4:1 (mol linear : mol branched

aldeyde product). The high reaction pressures and temperatures

used to stabilize these complexes promote the formation of

byproducts.

Phosphine modified hydrido cobalt catalysts have also been

developed for the hydroformylation of olefins.106 These systems

usually result in the complete reduction of the aldehyde to the









85
alcohol. The phosphine used is tributylphosphine and the active

catalytic species is proposed to be HO (C))3(PBu3). The Phosphine

modified system is less active for hydroformylation but much more

active for hydrogenation and generally results in a linear :

branded alcohol ratio of 7:1. This catalyst is more stable than

the unmodified catalysts resulting in lower reaction pressures of

100 atmospheres.

Omnercial hydroformylation processes have recently been

developed based upon rodium.107 Much milder reaction conditions

are used with the rhodium systems compared to any of the cobalt

systems and rhodium has an activity 104 times greater than that of

cobalt. Reaction pressures of 10-25 atmospheres and temperatures

around 100C are generally employed. Rhoshine modified hydrido

rhodium complexes, such RhH(OC) (PRh3)3,108,109 are used as

catalysts. Excess trihenylphosphine is added to increase the

product selectivity for the formation of the linear aldehyde while

decreasing the rate of hydroformylation. The reaction has even been

conducted in molten triphenylhos e.110 Despite the high

activity and selectivity and milder reaction conditions employed

with modified rhodium catalysts, the high cost of rhodium and

recovery problems has limited their use. The development of

hcamgeneous rhodium systems or heterogeneus systems which exhibit

greater activity and selectivity than those currently employed and

operate under milder reaction conditions may offset same of the

disadvantages associated with current rhodium systems.









86
The proposed mechanism for the hydroformylation of olefins with

prosphine modified rhodium catalysts is similar to that proposed
with cobalt catalysts.111 The mechanism of the hydroformylation

reaction catalyzed by phospine modified rhodium systems has been

the subject of many review articles.102,112,113 In the modified

rhodium systems, the immediate catalyst precursor is RhH(0)) (PPh3)3.

To create a vacant coordination site on the rhodium center,

phosphine dissociation is proposed to occur as shown in Equation 3-

4. The decrease in activity encountered upon addition of excess

triphenylphosphine to hydrido rhodium hydroformylation


BHh(CO) (Pah3)3 < > HRh(O) (Ph3)2 + PP3 (3-4)

catalysts is believed to be a result of driving the equilibrium in

Equation 3-4 toward the side of the tris(phosphine) complex. Other

investigators have proposed that the addition of phosphine inhibits

a similar dissociation reaction114,115 as shown in Equation 3-5.

Either of the coordinatively unsaturated rhodium hydrido complexes

in Equations 3-4 and 3-5 may then coordinate olefin.


Hh(CD)2(PPh3)2 < > HRh(00)2(PPh3) + PPh3 (3-5)

The mode of olefin coordination across the rhodium-hydride bond

ultimately determines the product selectivity for the formation of

linear or branched aldehydes. Markovnikov addition of the olefin

across the Rh-H bond results in the formation of a branched alkyl

intermediate and eventually the branched aldehyde. Anti-markovnikov

addition of the olefin across the Rh-H bond leads to the formation