The activation of carbon monoxide and carbon dioxide by transition metal carbonyl complexes

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Title:
The activation of carbon monoxide and carbon dioxide by transition metal carbonyl complexes
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xvii, 234 leaves : ill. ; 28 cm.
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English
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Weiss, Keith D
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Subjects / Keywords:
Carbon, Activated   ( lcsh )
Carbon dioxide   ( lcsh )
Carbon monoxide   ( lcsh )
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theses   ( marcgt )
non-fiction   ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1986.
Bibliography:
Includes bibliographical references (leaves 220-233).
Statement of Responsibility:
by Keith D. Weiss.
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Typescript.
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Vita.

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University of Florida
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THE ACTIVATION OF CARBON MONOXIDE AND CARBON
DIOXIDE BY TRANSITION METAL CARBONYL COMPLEXES
















BY

KEITH D. WEISS


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


1986




























To my mother and father















ACKNOWLEDGEMENTS

I am very indebted to Dr. Drago for the guidance he has

given me over the past five years. I would like to thank

him and his wife for making my stay in graduate school both

an enjoyable and a rewarding experience. I must confess

upon departing from Florida that his definition of a "silver

fox" may be correct.

I would like to thank the members of the Drago group

for their support over the past few years. I owe a special

thank you to Jim Miller for his friendship through my stay

at the University of Florida. I would also like to thank

Leigh Ann Files, Cindy Goldstein, Cindy Bailey, Maribel Lisk

and Nancy Miller for giving me over the past several years

many reasons to smile.

The motivation to excel at anything usually stems from

experiences that have happened early in one's life. In this

respect, I would like to acknowledge my high school

chemistry teacher, Mr. Russell Hull, for instilling within

me an interest in chemistry.

The assistance and expertise of several people have

been essential to the research presented in this

dissertation. I would like to acknowledge Tim Koloski for

his contribution as an undergraduate research student to the


iii








chapter on the activation of carbon dioxide. Professor Roy

King and Dr. Tom Gentle are acknowledged for their

help in obtaining, respectively, the GC/MS and ESCA data

presented in this dissertation. It also is acknowledged

that the typing of this dissertation could not have been

completed without the thoughtful diligence of Sharon Decker.

Finally, the devotion and understanding of my parents

have been indispensable during the years I have been in

school. It primarily has been their support that has

enabled me to finish this degree. It was with them in mind

that this dissertation was written.















TABLE OF CONTENTS


ACKNOWLEDGEMENTS. . ....

LIST OF TABLES. . . .

LIST OF FIGURES . . .

ABSTRACT. . . .

CHAPTER

I INTRODUCTION . ...

II ACTIVATION OF CARBON DIOXIDE .

Background . . .

Experimental . .

Reagents . ... *.

Instrumentation. . .

Preparation of Potassium Tetracarbonyl-
cobaltate(l-) . .

Preparation of Potassium Tetracarbonyl-
ferrate(2-) . .

Preparation of Sodium Pentacarbonyl-
manganate(l-) and Sodium Penta-
carbonylrhenate(l-) . .

Preparation of Potassium U-hydridobis-
(pentacarbonyltungsten(O)) ..

Preparation of a Mixture of Rhenium
Carbonyl Hydrides . ..

Reaction of the Transition Metal
Carbonyl Salts with Carbon Dioxide. .


Page

iii

ix

xi

xvi









Reaction of Carbon Dioxide and Hydrogen
with Transition Metal Hydrides in
Alcohol Solvents. . .. 26


Results and Discussion . .

The Binding of Carbon Dioxide by
Transition Metal Carbonyl Anions. .

Formation of Alkyl Formates at Low
Pressures and Temperatures .


Summary. . .

ACTIVATION OF CARBON MONOXIDE. .

Background . .

Experimental . .

Reagents . .

Instrumentation .

Fixed Bed Flow Reactor .

Preparation of Dicarbonylchloro-
(p-toluidine)iridium(I) .


. 57

. 60

. 60

. 76

. 76

. 76

* 78


. 78


Preparation of a Phosphinated Support.

Preparation of Supported Mono- and
Di-phosphine Substituted Tetrairidium
Carbonyl Clusters . .

Preparation of Supported Tri-phosphine
Substituted Tetrairidium Carbonyl
Clusters. . .

Preparation of Other Supported
Phosphine Substituted Metal Carbonyl
Complexes . .

Preparation of Iridium Complexes
Impregnated Onto a Support. .

Reaction of Catalysts with Carbon
Monoxide, Hydrogen and HCl(g) .

Reactions Involving Carbon-13
Isotopically Labelled Gases .

Results and Discussion . .


80



. 81



. 82



. 82


. 83


83


84

85


III


27


27


36









Reproduction of the Previously Reported
Supported Iridium Carbonyl Catalyst
System. . .. 85

Catalyst Deactivation is a Valid
Observation . 91

Investigation of the Methyl Chloride
Formation Observed in the Control
Reactions . 95

Solvent Decomposition Can Explain
Other Reported and Observed Results 101

The Reduction of Carbon Monoxide
Still Occurs. . .. 107

Minor Impurity Routes to Methyl
Chloride. . .. 114

Structural Determination of the
Supported Iridium Clusters by
Infrared Spectroscopy . 121

Examination of the Decomposition of the
Supported Clusters by Infrared
Spectroscopy. . .. 128

Verification That a Discrete Molecular
Complex Exists in the Activated
Iridium Systems. . .. 132

Investigation by Infrared Spectroscopy
of the Discrete Iridium Species Present
in the Activated Systems at 750C. 138

Reevaluation of the Supported Cluster/
AlCI -NaCl System . 150

Proposed Mechanism for the Formation
of Methyl Chloride. . ... 152

Investigation of a Phosphine Substituted
Triosmium Carbonyl System 161

Investigation of Supported Cobalt and
Iron Carbonyl Systems . 165

Investigation of a Phosphine Substituted
Triruthenium Carbonyl System. .. .... 169

Summary. . . .. 188


vii









IV CONCLUSION . . 192

APPENDICES

A Infrared Spectra for Chapter II. ... 194

B Infrared Spectra for Chapter III 211

REFERENCES. . . .. 220

BIOGRAPHICAL SKETCH ................ 234


viii















LIST OF TABLES


Page

2-1 Enthalpy Changes in Reactions Involving
Carbon Dioxide............................. 4

2-2 Modes of Carbon Dioxide Binding for
Complexes with Geometry Determined by
X-ray Crystallography.................... 7

2-3 Acid Dissociation Constants for Metal
Carbonyl Hydrides and the Nucleo-
philicities of the Corresponding Anions.. 10

2-4 A Summary of Catalyst Activity for the
Reduction of Carbon Dioxide to Alkyl
Formates................................ 15

2-5 A Summary of Catalyst Activity for the
Reduction of Carbon Monoxide to Alkyl
Formates................................ 18

2-6 Characterization of Prepared Transition
Metal Carbonyl Anions by Infrared
Spectroscopy.............................. 24

2-7 Color Changes for Reactions Between
Carbon Dioxide and Transition Metal
Carbonyl Anions.......................... 26

2-8 A Summary of Infrared Data Obtained for
Reactions Between Carbon Dioxide and
the Transition Metal Carbonyl Anions.... 29

2-9 A Summary of the Quantitative Data
Obtained for the Reaction Products by
Gas Chromatography....................... 38

2-10 A Summary of Infrared Data Obtained for
the Reaction of Re2(CO) 10 with CO2 and
H2 in Methanol........................... 46

2-11 A Summary of Infrared Data Obtained for
the Reaction of Re (CO) with Carbon
Monoxide in Methan 1.l................... 49









Page


3-1 A Comparison of the Advantages and Dis-
advantages of Using Homogeneous and
Heterogeneous Catalysts................. 63

3-2 A Summary of the Infrared Data Reported
for the Supported Iridium Carbonyl
Catalysts............................... 69

3-3 A Summary of the Reported Activity
for the Supported Iridium Carbonyl
Catalyst System........................... 73

3-4 The Initial Activity of Control
Supports Prepared in 2-methoxyethanol... 95

3-5 Factors That Enhance the Adsorption of
Polar Organic Compounds onto the
Surface of a Hydroxylated Support....... 97

3-6 The Activity of Alumina Supported
Tetrairidium Clusters for Various
Metal Loadings........................... 102

3-7 Thermodynamic Data for Reactions
Involving Synthesis Gas Reduction....... 107

3-8 Thermodynamic Data Concerning the
Decomposition of Toluene................ 117

3-9 A Summary of the Infrared Data Obtained
for the Supported Iridium Carbonyl
Clusters................................ 123

3-10 Infrared Data for Complexes of
Triosmium Carbonyl....................... 163

3-11 Infrared Data for Supported Phosphine
Carbonyl Complexes of Iron.............. 167

3-12 A Summary of Infrared Data Obtained
for the Supported Ruthenium Cluster
System .................................. 179















LIST OF FIGURES


Page

2-1 Modes of Binding for Carbon Dioxide
with a Metal Center....................... 6

2-2 A Proposed Mechanism for the Reduction
of Carbon Dioxide to Alkyl Formates
by Group 6B Metal Carbonyl Hydrides..... 13

2-3 A Proposed Mechanism for the Reduction
of Carbon Monoxide to Methyl Formate
by Tungsten Carbonyl Complexes.......... 19

2-4 Infrared Spectrum of Precipitate
Obtained from Reaction of Carbon Dioxide
and NaMn(CO)5 ........................... 31

2-5 Solution Infrared Spectrum of the
Carbonyl Region for the Reaction Between
Carbon Dioxide and NaMn(CO)5 in
Acetonitrile............................. 32

2-6 Solvent Subtracted Infrared Spectrum
for the Reaction Between Carbon Dioxide
and NaMn(CO)5 in Tetrahydrofuran........ 34

2-7 Mass Intensity Report for Methyl
Formate................................. 39

2-8 Mass Intensity Report for Dimethyl
Ether................................... 40

2-9 Mass Intensity Report for Dimethoxy-
methane................................. 41

2-10 Mass Intensity Report for Hexane........ 42

2-11 Gas Chromatogram of Gas Sample Taken
During Reaction of Re2(CO)10 with CO2
+ H2 in Methanol......................... 43









Page


2-12 Infrared Spectrum of Reaction Products
for CO2/H2 Reaction with Re2(CO)10...... 47

2-13 Infrared Spectrum of Reaction Products
for Rhenium Hydride and CO Reaction
with Re (CO) and Methanol Subtracted
Out......... ............................ 51

2-14 Infrared Spectrum Obtained for the
Reaction of Carbon Monoxide with a
Mixture of [Re2(CO) 6(i-OCH )3] and
[H2Re(CO) 4] in Methanol................ 54

2-15 A Comparison by Gas Chromatography of
Reaction Products in Liquid Samples for
Carbon Monoxide Reactions with Re2(CO) 10,
KH[W(CO) 512 and KOCH3................... 56

3-1 A Proposed Mechanism for the Formation
of Methyl Chloride from Synthesis Gas
and HC1 Over a Supported Iridium
Carbonyl Catalyst System................ 74

3-2 A Diagram of the Fixed Bed Flow Reactor. 79

3-3 A Gas Chromatogram of the Product Gases
(Poropak Q Column, Attenuation = 8,
Column = 1300C) ......................... 87

3-4 Gas Chromatography Separation of
Methanol and Methyl Chloride............ 89

3-5 A Graph of Catalyst Activity Versus
Reaction Temperature.................... 90

3-6 A Graph of Catalyst Activity Versus
Reaction Time. (Residence Time and
HC1(g) Concentration was Observed to
Increase with Time) ...................... 92

3-7 A Graph of Catalyst Activity Versus an
Extended Reaction Time. (Residence
Time and HC1(g) Concentration Held
Constant) ............................... 93

3-8 NMR Spectrum of 2-methoxyethanol That
Condensed at the Top of the Reactor
System .................................. 99


xii









Page


3-9 A Graph of Methyl Chloride Activity
Versus Residence Time for a Reaction
Involving a Control Support............. 104

3-10 A Graph of Initial Methyl Chloride
Activity Versus Time for a Catalyst
Prepared in Toluene..................... 111

3-11 Mass Intensity Report for Acetylene..... 112

3-12 Infrared Spectrum of the C=C Vibrations
in the Phenyl Groups of the Silane
Linkage................................. 119

3-13 Infrared Spectrum of 3-(PPh2)3Ir4(CO)9
Obtained From the Reaction of 3-PPh2
With Ir4(CO) 12.......................... 124

3-14 A Comparison of the Infrared Spectra of
the Mono- and Di-phosphine Substituted
Tetrairidium Carbonyl Clusters Prepared
in 2-methoxyethanol and Toluene......... 127

3-15 Infrared Spectra for the Supported
Clusters After Exposure to the Reactant
Gases at 75C........................... 129

3-16 Infrared Spectra Obtained for the Low
and High Load Iridium Systems at
Various Temperatures.................... 131

3-17 Infrared Spectrum Obtained for Metallic
Iridium/Alumina After Exposure to CO,
H2 and HC1(g) at 200C.................. 136

3-18 X-ray Photoelectron Spectrum for the
Supported Clusters Before and After
Activation.............................. 137

3-19 A Comparison of the Infrared Spectra
Obtained for the Supported Clusters
(Low % Ir) and for IrCl(CO)3 on a
Phosphinated Support.................... 140

3-20 Infrared Spectrum of IrCl(CO)3 + 3-PPh2
at Various Temperatures................. 141


xiii









3-21 A Comparison of the Infrared Spectrum
of IrCl(CO)3/Alumina With the Spectra
Obtained for the Activated Iridium
Clusters at Various Temperatures........ 144

3-22 Infrared Spectrum of IrCl(CO)3/Alumina
at Various Temperatures................. 145

3-23 Infrared Spectrum of a Mixture of the
Supported Multinuclear Complex and
IrCl(CO)3 Exposed to Carbon-13 Carbon
Monoxide ................................ 147

3-24 Infrared Spectrum of Vaska's Complex
Supported on Alumina After Exposure to
CO/H2/HC1(g) at Various Temperatures.... 149

3-25 Infrared Spectrum of the Supported
Iridium Clusters in an AlCl 3-NaCI Melt.. 151

3-26 Proposed Mechanism for the Initial
Formation of Methyl Chloride in the
Supported Iridium Cluster System........ 153

3-27 Proposed Mechanism for the Formation of
Methyl Chloride From Synthesis Gas and
HC1(g) .................................. 156

3-28 Overview of Proposed Mechanism for the
Formation of Methyl Chloride in the
Supported Iridium Cluster System........ 162

3-29 Comparison of the Infrared Spectrum
of 3-PPh2Os3(CO)11 Exposed to CO, H2
and HC1(g) with that of Os3(CO)12....... 164

3-30 Infrared Spectrum of 3-PPh2Fe(CO)4 Before
and After Exposure to CO, H2 and HCl(g)
at 75C................................. 168

3-31 Gas Chromatogram of Two Carbon products
Obtained in the Supported Ruthenium
Cluster System.......................... 170

3-32 Mass Intensity Report for Acetaldehyde.. 172

3-33 Mass Intensity Report for Ethyl
Chloride........... .... ................ 173


xiv









3-34 Mass Intensity Report for Ethyl
Formate................................. 174

3-35 Mass Intensity Report for Diethyl
Ether................................... 175

3-36 Mass Intensity Report for 1,1-
Dichloroethane............................ 176

3-37 Mass Intensity Report for Ethyl
Acetate................................. 177

3-38 Infrared Spectrum of a Mixture of the
Supported Ruthenium Clusters Exposed
to Air.................................. 180

3-39 Infrared Spectrum of the Supported
Ruthenium Clusters Exposed to CO, H2
and HC1(g) at 750C...................... 182

3-40 A Comparison of the Infrared Spectrum
of the Supported Ruthenium Clusters
with that of Supported [RuCl2(CO) 32.... 183

3-41 Infrared Spectrum of Supported
[RuCl2(CO)3]2 Before and After Exposure
to CO, H2 and HC1(g) at 75C............ 184

3-42 Fragmentation of Ru3(CO)12 on a Silica
Gel Support............................. 186









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

THE ACTIVATION OF CARBON MONOXIDE AND CARBON
DIOXIDE BY TRANSITION METAL CARBONYL COMPLEXES

By

Keith D. Weiss

August 1986

Chairman: Russell S. Drago
Major Department: Chemistry

The development of new carbon resources to be used

either as fuels or as chemical feedstocks has been of major

concern to the industrial community since the oil shortage

in the early 1970s. In this respect, a lot of activity has

been observed over the past decade concerning the binding

and activation of carbon dioxide and carbon monoxide. The

emphasis in this work has been upon the activation of carbon

dioxide and carbon monoxide by transition metal complexes.

The first study involved the binding of carbon dioxide

to a variety of transition metal carbonyl anions. It was

found that the nucleophilicity of the metal center greatly

affected the coordination of carbon dioxide. This work then

was extended into an investigation of the low pressure

reduction of carbon dioxide to methyl format by a rhenium

carbonyl catalyst. Infrared spectroscopy was used to

characterize the active species and probe the mechanism of

the reaction. It was found that this rhenium carbonyl


xvi








system was more effective towards the reduction of carbon

monoxide than carbon dioxide.

The second study dealt with the conversion of synthesis

gas and HCl(g) to methyl chloride under mild temperatures

and pressures by a supported iridium carbonyl catalyst.

Several different routes to methyl chloride were identified

within the system. Infrared spectroscopy was used to

identify the active species in the reaction and investigate

their various modes of deactivation. It was shown that

discrete iridium carbonyl complexes existed under the

employed reaction conditions. Finally, a mechanism for the

formation of methyl chloride in this system was proposed.

This study concluded with an examination of other supported

metal carbonyl catalysts. It was found that a change in the

composition of the metal catalyst could alter the activity

and selectivity of the reaction. In this respect, a

supported ruthenium carbonyl catalyst was observed to be

active towards the formation of ethyl chloride and various

other two-carbon products.


xvii















CHAPTER I

INTRODUCTION

With the oil shortage in the 1970s, there was great

interest in the development of alternative carbon resources

to be used as fuels and chemical feedstocks. Although the

oil shortage has receded for the time being, the problem has

not been resolved. The reoccurrence of a fuel shortage is

predicted for the economy of the future. One new carbon

resource would involve the gasification of coal into a

mixture of carbon monoxide and hydrogen known as synthesis

gas. Since there is an abundance of coal reserves, the

utilization of synthesis gas as a chemical feedstock or fuel

could hold future economic advantages. Another untapped

carbon reserve is the carbon dioxide released into the

atmosphere as an industrial waste product. Carbon dioxide

has the ability to absorb infrared radiation which is

predicted to give rise to an increase in global temperature

commonly referred to as the "Greenhouse Effect". 2,3

Although other gases can initiate a similar temperature

rise, the most abundant gas in the atmosphere to produce
4
this effect is carbon dioxide. Recycling carbon dioxide

waste by utilizing it as an inexpensive chemical feedstock

would decrease the amount of the gas released into the

atmosphere.






2

There are several methods that can be used to

investigate the activation of carbon monoxide and carbon

dioxide. These methods range from mechanistic studies of

biological or natural systems, such as hemoproteins,

carbonic anhydrase6 and photosynthesis7 to the investigation

of the interaction of carbon monoxide and carbon dioxide

with metal complexes in organometallic reactions. Currently

over 90% of the commercial chemical processes are catalytic

in nature. Since many of these commercial processes employ

either metals (heterogeneous) or metal complexes

(homogeneous) as catalysts, a logical starting point for the

development of carbon monoxide and carbon dioxide as a

chemical feedstock or fuel is a study of their interaction

with transition metal complexes.

Reported here are the results of two studies involving

an evaluation of the feasibility of binding and activating

carbon dioxide and carbon monoxide by transition metal

carbonyl complexes. The first study involves the binding of

carbon dioxide to transition metal carbonyl anions with

varying degrees of nucleophilic metal centers. The results

obtained aid in the understanding of the interaction of

carbon dioxide with transition metal catalysts, as well as

the effect that residual contaminants, such as water, may

have on carbon dioxide activation. This study concludes

with an investigation of the catalytic behavior of the

corresponding transition metal carbonyl hydrides towards

carbon dioxide reduction. Primarily, the low temperature







3

and low pressure reduction of carbon dioxide and hydrogen in

alcohol solvents to alkyl formates was investigated.

The second study involves the low temperature and low

pressure reduction of carbon monoxide by "heterogenized"

homogeneous catalysts. The mechanism of a novel system

employing a supported tetrairidium carbonyl cluster as

catalyst for the conversion of carbon monoxide, hydrogen and

hydrogen chloride to methyl chloride was studied by infrared

spectroscopy. The commercial feasibility of this system was

evaluated through the optimization of the different system

parameters, such as temperature and residence time.














CHAPTER II

ACTIVATION OF CARBON DIOXIDE

Background

The thermodynamic stability of carbon dioxide is the

primary reason it is an "oxygen sink" or waste product in

many commercial chemical processes. However, the two

unsaturated double bonds in carbon dioxide make it

theoretically possible to convert carbon dioxide into

organic products. This is supported by the thermodynamic

feasibility of many reactions involving carbon dioxide as

shown in Table 2-1. Furthermore, carbon dioxide is used as



Table 2-1. Enthalpy Changes in Reactions Involving Carbon
Dioxide


Reaction AHO

CO2(g) + H2(g) CH3OH(1) + H20(1) -31.3

CO2(g) + 4H2(g) CH4(g) + 2H20(l) -60.5

2CO2(g) + 6H2(g) CH3OCH3(g) + 3H20(l) -60.9

CO2(g) + H2(g) + CH3OH(l)---HCO2CH3(1) + H20(l) -7.7

CO2(g) + H2(g) + CH3 OH(l)-- CH3CO2H(1) + H20(1) -33.0

CO2(g) + CH4(g) > CH3CO2H(1) -3.8

CO2(g) + H2(g) + C2H2(g)------C2H5CO2H(1) -40.6



AH0 data given as kcal mole-1







5

a chemical feedstock in the commercial production of

salicylic acid,10,11 urea12,13 and terepthalic acid.14

Unfortunately, the existence of a kinetic barrier in many

reactions involving carbon dioxide prevents these reactions

from spontaneously occurring. These reactions may occur if

the activation energy associated with this kinetic barrier

can be lowered through the binding of carbon dioxide to a

metal catalyst.

There have been a variety of literature review articles

dedicated to the binding and activation of carbon

dioxide.9'15-22 Several possibilities exist for the

interaction of carbon dioxide with a metal center.18,23 One

mode of binding is a donor-acceptor type complex termed

"end-on" formed by electron pair donation from the oxygen's

highest occupied molecular orbital (HOMO) to the

corresponding metal d orbital as shown in Figure 2-1. A

"c-coordination" mode of binding involving a dative

interaction or transfer of two electrons from the metal atom

to the lowest unoccupied molecular orbital (LUMO) of carbon

dioxide also may occur. Finally, a third possible mode of

binding referred to as "side-on" is a combination of the

interaction of the HOMO of carbon dioxide with a vacant

metal d orbital and the simultaneous transfer of metal a

electrons to the vacant LUMO of carbon dioxide. The high

electron affinity of carbon dioxide suggests that the

existence of the "side-on" and "c-coordination" modes of

binding should be more favorable than the "end-on" mode.











"End-on" "C-coordination" "Side-on"



M +-
01

Figure 2-1. Modes of Binding for Carbon Dioxide with a
Metal Center


This is supported by the favorability of "side-on" >

"c-coordination" >> "end-on" reported in several molecular

orbital investigations.2428 These studies point out that

the favorability of "c-coordination" may be enhanced by the

presence of a counter ion which can interact with the

electron density surrounding the oxygen atoms of the bound

carbon dioxide. Further evidence is provided by the limited-

number of x-ray structures that have been obtained for bound

carbon dioxide complexes as shown in Table 2-2. Many other

complexes have been reported to bind carbon dioxide as

suggested by infrared spectroscopy.

Although the "side-on" mode of coordination is the most

favorable, the "c-coordination" mode is very important for

catalysis. Metal-carbon bond formation may lead either to

the growth of carbon-carbon chains through insertion

reactions or to the catalytic formation of format species

through hydrogenolysis. To date there has been only limited

success involving the catalytic reduction of carbon dioxide.

The first example of the catalytic reduction of carbon

dioxide was the conversion of an amine to a formamide









Table 2-2. Modes of Carbon Dioxide Binding for Complexes
with Geometry Determined by X-ray
Crystallography


Bound Carbon Dioxide Complex

(py)Co(salen)K(CO2)

Rh(diars) 2 (CO2)Cl

[HOs3 (CO) 10 (2C)Os6 (CO) 17]

[(OC) 5Re(CO2) Re (CO) 4 2

Ni(CO2) (PCy3) 2

Nb(n-C5H4Me) 2 (CH2SiMe 3) (CO2)

IrCl(C204) (PMe3) 3-0.5.C6H6


Mode of Binding References

c-coordination 29

c-coordination 30

c-coordinationa 31

c-coordination 32

side-on 33

side-on 34

Combination of modes 35


a = Complex not formed directly from carbon dioxide(g).


employing either IrCl(CO)(PPh3)2 or CuCl(PPh3)3 as

catalyst.36 It was proposed that the mechanism for this

reaction proceeded through the insertion of carbon dioxide

into a metal-hydrogen bond.

The interaction of carbon dioxide with a transition

metal hydride may proceed through two different reaction

pathways. Carbon dioxide insertion into a metal-hydrogen

bond will lead to either the formation of a format complex

or to a metallocarboxylic acid derivative as shown in

Equation 2-1. Although the formation of metallocarboxylic

acid complexes has been reported for reactions between

carbon monoxide with a metal hydroxide complex37 and for

hydroxide ion with a metal carbonyl complex, there has

been no direct evidence for the formation of a metallocar-









boxylic acid derivative through the insertion of carbon

dioxide into a metal hydride bond. The isolation of organic

products in several reactions has suggested the possibility



0

M-O-CH or M *CH

CO + M-H

20 (2-1)
II
M-C-OH
43
of a metallocarboxylic acid intermediate. On the other

hand, the formation of format intermediates has been

observed for carbon dioxide reactions with metal hydride

complexes. 44,45

It is possible that metal-carbon bond formation can be

enhanced by altering the nucleophilicity of the metal center

in a transition metal carbonyl hydride complex. It has been

shown by infrared and carbon-13 NMR spectroscopy that alkali

metal salts of transition metal carbonyl hydrides can bind

carbon dioxide through the "c-coordination" mode as shown in

Equation 2-2.46 There are several added advantages for the

interaction of carbon dioxide with a transition metal

0

2Li+ [W(CO) 2- CO2-- Li + (CO) 5W-C Li (2-2)



complex. First, many carbonyl complexes activate hydrogen

under mild conditions to produce metal carbonyl hydride

complexes.47 Since the reduction of carbon dioxide requires







9

a source of hydrogen, the ability to bind carbon dioxide and

activate hydrogen gas by the same transition metal complex

would be advantageous. There also have been recent reports

of transition metal carbonyl complexes reducing carbon

dioxide to carbon monoxide48 and to alkyl formates.49

An evaluation of the feasibility of binding carbon

dioxide through metal-carbon bond formation can be

accomplished by an investigation of the interaction of

carbon dioxide with the alkali metal salts of transition

metal carbonyl hydride complexes whose K values or metal
a
nucleophilicities are known. The Ka and nucleophilicity

data for the complexes to be investigated are summarized in

Table 2-3. The available literature has indicated that

several of these anions do interact with carbon

dioxide.48,50,51 For instance, the formation of iron

pentacarbonyl and sodium carbonate has been reported to

occur for the reaction of carbon dioxide with Na2Fe(CO)48

It also has been reported that carbon dioxide reacts with

NaMn(CO)5 to form sodium bicarbonate and an unidentified

manganese complex.50 More recently, preliminary solution

infrared data were interpreted in a Russian report to

suggest that both NaRe(CO)5 and NaMn(CO)5 stabilize the

formation of a "c-coordination" bound carbon dioxide complex

as shown in Equation 2-3.51 The addition of methyl iodide

to this carbon dioxide bound complex was reported to result

in the formation of [(CO) 3M(CO2CH3)]2 by methyl cation







10

addition to an oxygen of the bound carbon dioxide. After

evaluation of the feasibility of binding carbon dioxide to

transition metal anions, a logical extension of this work



Table 2-3. Acid Dissociation Constants for Metal Carbonyl
Hydrides and the Nucleophilicities of the
Corresponding Anions


Hydride Complex K a(H20)a Anion Nucleophilicity


HCo(CO) 4 <2 Co(CO) 4 1

H2Fe(CO) 4 3.6 x 105 (K1), Fe(CO)4 2
1.0 x 10 (K2)

HMn(CO)5 8 x 10-8 Mn(CO) 5 77

HRe(CO)5 "Very weakly acidic" Re(CO)5 25,000

a = K data obtained from reference 52;
a
b = Nucleophilicity data obtained from reference 53.


would be an investigation into the catalytic behavior of

these complexes towards carbon dioxide reduction.



CO
NaM(CO) 5(M = Mn, Re) )-[(CO)3M(CO2Na)]2 (2-3)


Recall that the first example of the catalytic

reduction of carbon dioxide was the conversion of an amine

to a formamide.36 It was found that replacement of the

amine with an alcohol produced a formic ester as the primary

product.54 Since then there have been several reports

indicating the formation of metalloformate derivatives

through the interaction of carbon dioxide with group 6B







11

metal carbonyl anions and hydrides.46'50,55-57 The

reduction of carbon dioxide to carbon monoxide by group 6B

metal carbonyl anions, Li2[M(CO)5], has been shown to occur

by the formation of lithium carbonate and the corresponding

group 6B metal hexacarbonyl complex, M(CO)6'. Carbon-13

labeling studies involving the reversible binding of carbon

dioxide to group 6B metal carbonyl hydrides, as shown in

Equation 2-4 (A-B), demonstrate that carbon dioxide is not

reduced to carbon monoxide at atmospheric pressure by these

complexes. A mechanism for the intramolecular conversion

of a metalloformate complex to a metallocarboxylic acid

complex would most likely proceed through the reduction of

the bound carbon dioxide to bound carbon monoxide followed

by the addition of hydroxide-ion to a carbonyl ligand.

Therefore, these carbon-13 labeling studies also suggest





HM( 12CO) 5 + 13CO2 H 13CO2M(12CO) 5 (2-4A)



HM(13CO)5- + CO2-- H12CO2M(13OO) 5 (2-4B)



that the metalloformate complex does not intramolecularly
58
convert to a metallocarboxylic acid species. Although the

formation of metallocarboxylic acid species has not been

reported to occur in reactions between carbon dioxide

and metal hydrides, they have been reported to form as

intermediates in reactions between group 6B metal







12

hexacarbonyls and hydroxide ions en route to the formation

of a metal hydride anion and carbon dioxide. It is

possible that the relative stability of M(COOH), M(O2CH) or

M(OCHO) could be influenced by an alteration in the

nucleophilicity of the metal center.

Equation 2-5 illustrates that at elevated pressures in

alcohol solvents the group 6B metal carbonyl hydrides

catalytically reduce carbon dioxide to alkyl formates and

water.49 The predominate species in solution during

[Catalyst]
CO2 + H2 > HCO2R + H20 (2-5)

(250 psig) (250 psig) ROH



catalysis were determined through the interpretation of

infrared data to be M(CO)6 and HCO2M(CO)5 The existence

of hydrogen bonding between the alcohol solvent and the

metalloformate intermediate also was suggested in the

interpretation of these infrared data. The HCO2M(CO)5

intermediate was proposed to be the catalytically active

species since M(CO)6 was found to be catalytically inactive.

The proposed mechanism49 for this reaction shown in Figure

2-2 suggests that it is actually formic acid which is

produced catalytically. The alcohol solvent then reacts

with this formic acid to form the alkyl format and water.

This mechanism is supported in the identification of formic

acid by gas chromatography in reactions where benzene has

replaced the alcohol as solvent. A decrease in activity was



















'Un
0
Ul


0 -.
U0


| (


0


0e
0


0 0
0 O




CN
0


O)



0


S04
0

0>1
r.

0
-1 .






a)



0














0
41*







14

observed for the formation of ethyl format as compared to

methyl format in the corresponding alcohol solvent. This

effect has been proposed to be due to the increased

coordinating ability of ethanol inhibiting the oxidative

addition of hydrogen by the metalloformate intermediate.

The catalytic activity of systems capable of converting

carbon dioxide into alkyl formates is summarized in Table

2-4. The activity of group 6B metal carbonyl hydrides

compares very closely to the activity for carbon dioxide
59 54
reduction to alkyl formates using ruthenium or iron

carbonyl hydrides as catalysts. Similar activity also has

been established for systems utilizing group VIII metal

phosphine complexes with either BF3 or a tertiary amine as

cocatalyst.60,61 Although HFe3(CO) 11 and HFe(CO)4- have

not been reported to bind carbon dioxide at atmospheric

pressure these species catalyze the formation of methyl

formate.4 The catalytic formation of methyl format in

alcohol solvents was found to follow a general trend of

increasing activity with an increase in temperature,

pressure or reaction time. Infrared spectroscopy was used

to identify the formation of carbonate and iron penta-

carbonyl during the reaction. This reaction was proposed to

be very selective for methyl format formation since no

other low molecular weight products could be identified by
54
gas chromatography. The predominant species present in

reactions involving ruthenium carbonyl hydrides as catalysts

was identified by infrared spectroscopy to be







15

Table 2-4. A Summary of Catalyst Activity for the Reduction
of Carbon Dioxide to Alkyl Formates


Catalyst

u-H [W2 (CO)10]

HCO2W (CO) 5

W(CO) 6

U-H [Cr2 (CO) 10]

HCO2Cr(CO) 5

HRu3 (CO) 11

HCO2Ru3 (CO)10

H3Ru4 (CO) 12

Ru3 (CO) 12

HFe3 (CO) 11

HFe(CO) 4

Pd(Ph2PCH2CH2PPh2 )2

u-H[W2(CO) 10]

HCO2W (CO) 5

HCO2Ru3 (CO) 10


Turnover Numbera

14.7

16.4



14.5

14.6

4.1

5.7

7.3

<0.3

5.2

2.0

23.0b

5.1c

3.8c

4.1c


Reference

49

49

49

49

49

59

59

59

59

54

54

60

49

49

59


Reaction


Conditions


Ref. 49: CO2 (250 psi) + H2 (250 psi) at

Ref. 59: CO2 (250 psi) + H2 (250 psi) at

Ref. 54: CO2 (300 psi) + H2 (300 psi) at

Ref. 60: CO2 (350 psi) + H2 (350 psi) at


125C for 24 hours

1250C for 24 hours

150C for 24 hours

1400C for 21 hours


aTurnover = mole of HCO2CH3/mole of catalyst; b(CH3)3N used

as cocatalyst; cAddition of CO (100 psi) to reactant gases.







16
59
H3Ru4(CO)12 It was suggested that these reactions also

could lead to the formation of carbon monoxide through the

reverse of the water-gas shift reaction as shown in Equation

2-6. It is possible that the observed formation of the

alkyl format may have resulted from the reduction of carbon

monoxide. However, the addition of carbon monoxide to the

carbon dioxide-hydrogen gas mixture in these reactions was



CO + H20- CatalstCO2 + H2 (2-6)



observed to inhibit the formation of alkyl formates. A

similar retarding effect upon carbon monoxide addition was

observed in the activity of the group 6B metal carbonyl

hydrides towards alkyl format formation. It was concluded

that this observed decrease in activity towards the

formation of alkyl formates demonstrated that the reduction

of carbon dioxide in these reactions did not proceed through

the formation of carbon monoxide.49 This was further

substantiated by gas chromatographic detection of less than

0.05% carbon monoxide in the CO2-H2 reaction gas mixture.

This amount was reported to be far below the equilibrium

distribution of carbon monoxide expected for the reverse of

the water-gas shift reaction.

The preceding conclusion is in contradiction to recent

reports which indicate that carbon monoxide will react with

either tungsten carbonyl or ruthenium carbonyl hydrides

in methanol to yield methyl format as shown in Equation







17

2-7. As shown in Table 2-5, the activity for a reaction

utilizing carbon monoxide is vastly increased over the same

reaction using a CO2-H2 mixture. In fact, the addition of

carbon dioxide or hydrogen to the carbon monoxide reactant

gas has been found to inhibit the formation of methyl



CO + ROH- [Catalyst]--HCO2 R (2-7)



format. Tungsten hexacarbonyl was identified by infrared

spectroscopy to be the predominant carbonyl species present

in the reactions involving a tungsten carbonyl hydride and

carbon monoxide.62 Although tungsten hexacarbonyl is

inactive as a catalyst precursor, the addition of potassium

methoxide to this reaction produces methyl format in high

yields. A mechanism consistent with the preceding

observations has been proposed for the reduction of carbon

monoxide to methyl format in a methanol solvent. This

mechanism, shown in Figure 2-3, strongly suggests the

interaction of a methoxide anion with W(CO)6 to produce the

active catalytic species, CH3OW(CO)5 5

The synthesis of methyl format from carbon dioxide or

carbon monoxide is important because methyl format is used

to synthesize several organic chemicals, such as formic

acid, acetic acid, formamide, ethylene glycol and

formaldehyde.63-65 Since most of these are important

commercial commodity chemicals, the formation of methyl

format from carbon monoxide or carbon dioxide could be

















Table 2-5. A Summary of Catalyst Activity for the Reduction
of Carbon Monoxide to Alkyl Formates


Catalyst

U-H [W2 (CO) 10]

HCO2W(CO) 5

CH3W(CO) 5

W(CO) 6

W(CO)6/KOCH3

KOCH3

H3Ru3 (CO) 11

H3Ru3 (CO) 12

H3Ru3 (CO) 11

W(CO) 6/KOCH3


Turnover Numbera

269

185

305



333

50

106

88

40cb
c


Reference

62

62

62

62

62

62

59

59

59

62


Ref. 62:

Ref. 59:


Reaction Conditions

CO (250 psi) at 125C for 24 hours

CO (250 psi) at 1250C for 24 hours


aTurnover
bAddition
cAddition


Number = mole of HCO2H3/mole of catalyst;
of H2 (250 psi) to reactant gas;
of CO2 (25 psi) to reactant gas.

















Q)


Ul I LO 0
+ 0 0


00
o:: 00




00r-






0 U
40






U 4-J U)

0U

0 00
o~~ o >1


UU

- 0 0 O
0 + L >
04
U Lo044J

0 0 a)



0 0'

r4z

U







20

industrially useful. This industrial importance coupled

with a fundamental interest in the activation of CO2 and CO

justifies further research into the formation of alkyl

formates from the reduction of carbon dioxide or carbon

monoxide by metal carbonyl complexes. The final

justification for further careful fundamental work in this

area arises from the contradictory results that have been

reported in the literature.

Experimental

Reagents

All metal complexes were used as purchased unless

otherwise stated. The Re2(CO)10, Mn2(CO) 10, Co2(CO)8 and

W(CO)6 were purchased from Strem Chemical Co. and the

Fe(CO)5 and KOCH3 from Alfa-Thiokol. All solvents were

dried prior to use by distillation over CaH2 or in the case

of alcohols over magnesium metal. The carbon monoxide grade

C. P. 99.5% was purchased from Matheson and the hydrogen and

carbon dioxide were purchased from Strate Welding. The

carbon dioxide was of "bone dry" grade. Even though the

presence of water could not be identified by infrared

spectroscopy or gas chromatography, the carbon dioxide was

dried by passing the gas through two 2 1/2" x 2' glass

columns of 3A molecular sieves prior to use. A trace amount

of carbon monoxide was observed by gas chromatography to be

present in the carbon dioxide.









Instrumentation

All air sensitive manipulations were performed in a

Vacuum Atmosphere Co. model HE-43-2 inert atmosphere box or

in an Aldrich inert atmosphere glovebag. All experiments

were performed under either a nitrogen, carbon dioxide or

carbon monoxide atmosphere. GC analyses were performed on a

model 3700 FID Varian gas chromatograph equipped with a

Hewlett-Packard 3390A integrator and a 1/8" x 8' stainless

steel 5% diethylene glycol adipate on chromosorb P (80/100)

column. GC mass spectrometry was performed by Dr. R. King

of the Microanalytical Laboratory, University of Florida,

Gainesville, Florida. Samples were run on an AEI MS30 mass

spectrometer with a KOITOS DS55 data station. The system

was equipped with a PYE Unicam 104 gas chromatograph

containing a 1/4" x 5' glass 10% diethylene glycol succinate

on chromosorb W-AW (80-100) column. Infrared spectra were

obtained on either a Nicolet 7199/170SX FT spectrometer or a

Nicolet 5DXB FTIR spectrometer. All solution samples were

run using 0.025 mL path length NaCl cells. All solid

samples were run as mulls using KBr salt plates. All

catalytic or high pressure experiments were performed using

a 250 mL Parr pressure bottle equipped with a brass Swagelok

pressure head.66 This reactor system could withstand a

maximum of 120 psig of pressure.

Preparation of Potassium Tetracarbonylcobaltate(1-)

The KCo(CO)4 salt was prepared by a procedure similar

to that reported by Edgell and Barbetta. Inside an inert







22

atmosphere box, a total of 4.80 g of powdered KOH was added

to 50 mL of tetrahydrofuran. Another solution containing

2.0 g of Co2(CO)8 in 20 mL of tetrahydrofuran was prepared.

The solutions were mixed together and stirred. After one

hour the red-black solution had turned yellow in color and a

pink precipitate had formed. The solution, which contained

the KCo(CO)4, was filtered away from the precipitate and

used in the carbon dioxide experiments. The KCo(CO)4 salt

was characterized by infrared spectroscopy as shown in Table

2-6.

Preparation of Potassium Tetracarbonylferrate(2-)

The K2Fe(CO)4 salt was prepared by a procedure similar

to that reported by Krumholz and Stettiner. A solution of

0.80 g of KOH and 1.25 g of Ba(OH)2 in 50 mL of distilled

water was degassed with N2 for one hour. Then 1.0 mL of

Fe(CO)5 was syringed into the stirred solution. After one

hour the yellow solution had turned orange in color. After

an additional two hours the solution was red in color and a

white precipitate had formed. Inside a glovebag, the red

solution containing the K2Fe(CO)4 was filtered away from the

precipitate. The red solution was placed onto a vacuum line

and the solvent evaporated to yield a brown solid. The

solid was dried and stored under vacuum until used in the

carbon dioxide experiments. The iron salt was characterized

by infrared spectroscopy as shown in Table 2-6.







23

Preparation of Sodium Pentacarbonylmanganate(1-) and Sodium
Pentacarbonylrhenate(1-)

The NaM(CO)5 salt (M = Mn, Re) was prepared by a

procedure similar to that reported by King and Eisch.

Seven milliliters of mercury was added to a nitrogen purged

reaction flask. A total of 0.50 g of sodium metal was slowly

added to the stirred mercury. Inside an inert nitrogen

glovebag a solution containing either 2.98 g of Mn2(CO) 10 or

1.00 g Re2(CO)10 in 50 mL of acetonitrile or tetrahydrofuran

was prepared. The solution was quickly added to the stirred

amalgam. After 2 1/2 hours the stirring was stopped and the

excess sodium-mercury amalgam was removed from the reaction

flask. The resulting army green NaMn(CO)5 and orange

NaRe(CO)5 solutions were used in the carbon dioxide

experiments. The manganese and rhenium salts were

characterized in solution by infrared spectroscopy as shown

in Table 2-6.

Preparation of Potassium p-Hydridobis(pentacarbonyl-
tungsten(0))

The KH[W(CO) 5]2 was prepared by a procedure similar to

that reported by Grillone and Kedzia. Inside a glovebag a

solution containing 5.63 g of W(CO)6 and 6.3 g KOH in 7.5 mL

water, 30 mL methanol and 70 mL tetrahydrofuran was prepared.

The solution was heated to 45C for five hours and then

continued stirring at room temperature for an additional 14

hours. The reaction solution was filtered and the resulting

filtrate placed onto a vacuum line. The solvent

was removed to yield a yellow paste. A total of 82 mL of

















Table 2-6.


Characterization of Prepared Transition
Metal Carbonyl Anions by Infrared
Spectroscopy


Compound Infrared Data (cm" ) Environment Reference


1890 (vs)

1890(vs), 1857(w)


a(I)

71


K(HFe(CO) 4]

HFe (CO) 4


Fe (CO) 4

H2 Fe(CO) 4



Fe (CO) 5


NaMn (CO)5

KMn (CO) 5


Mn2 (CO) 10


HMn(CO)




NaRe (CO) 5

KRe (CO)


Re 2(CO) 10

HRe (CO)
5


1915(m), 1887(vs) acetonitrile a(II)

2015(w), 1937(sh) water 72
1897(vs)

1786(vs) water 72

2121(w), 2111(vw), hexane 73
2053(m), 2042(s),
2029(vw), 2010(m)

2020(vs) neat 74


1910(vs), 1860(vs) acetonitrile a (Fig. 2-5)

1896(s), 1862(s), THF 71
1830(m)

2045(s), 2009(vs), THF a (III)
1978(s)

2117, 2043, 2015(vs), cyclohexane 75
2008(vs), 1981(vs),
1966


1900(m), 1860(m)

1911(s), 1864(s),
1835(sh)

2008(ms), 1972(s)

2131, 2123, 2053,
2042, 2015(vs),
2005(vs), 1982(vs)


THF

THF


THF

cyclohexane


a (IV)

71


a (IV)

75


KCo(CO)4

KCo(CO)4


a = this work; (I-IV) location of spectrum in appendix A;
vs very strong; s strong; ms medium strong; m = medium;
w weak; vw very weak; sh = shoulder.







25

water was added and the mixture stirred for 24 hours at room

temperature followed by 23 additional hours at 0C in an ice

bath. The mixture was filtered to obtain white crystals

which were dried and stored under vacuum until used in the

carbon dioxide experiments.

Preparation of a Mixture of Rhenium Carbonyl Hydrides

The mixture of rhenium carbonyl hydrides was prepared

by a procedure similar to that reported for the formation of

H3Re3(CO) 12. A solution containing 2.0 g of Re2(CO)10 and

1.6 g of NaBH4 in 50 mL of tetrahydrofuran was refluxed for

4 hours. The solution went through a sequence of color

changes from yellow to orange and finally to red after 4

hours at reflux temperature. The solution was decanted away

from the NaBH4 and the solvent evaporated. The resulting

solid compound was dried under vacuum for several days. A

solution containing 80 mL of cyclohexane and 10 mL of H 3PO4

(deaerated and dried by adding several drops of Na-Hg

amalgam) was added to the solid compound in the reaction

flask. After 6 hours at reflux temperature, the solution

was extracted several times with hot cyclohexane. Cooling

the cyclohexane solution did not precipitate the desired

product as reported. Thus the solvent was evaporated to

yield a brown solid which was characterized by infrared

spectroscopy to be a mixture of H 3Re3(CO) 12, H4Re4(CO)2 and

Re2(CO) 10

Reaction of the Transition Metal Carbonyl Salts with Carbon
Dioxide

Acetonitrile or tetrahydrofuran solutions of the

transition metal carbonyl salts were reacted with carbon







26

dioxide at atmospheric pressure by bubbling the gas through

the solution. Higher pressure experiments were performed by

using a Parr pressure bottle system66 containing the

solution of the transition metal carbonyl salt and carbon

dioxide. The resulting color changes for these reactions

are summarized in Table 2-7. The reaction products were

examined by infrared spectroscopy.



Table 2-7. Color Changes for Reactions Between Carbon
Dioxide and Transition Metal Carbonyl Anions


CO
Anion Initial Solution Color iFinal Solution Color



KCo(CO)4 Yellow Yellow

K2Fe(CO)4 Pink-red Orange

NaMn(CO)5 Army green Orange-red

NaRe(CO)5 Orange Yellow-green





Reaction of Carbon Dioxide and Hydrogen with Transition
Metal Hydrides in Alcohol Solvents

A Parr pressure bottle reactor system containing a
-4
solution of 1.5 x 10 moles of the catalyst in 20 mL of

methanol was charged with either carbon dioxide, hydrogen,

carbon monoxide or some mixture of the three gases in equal

parts while maintaining the total pressure at 20 psig. The

solution was stirred and allowed to react within a

temperature range of 125-1500C. The gaseous reaction







27

products were characterized by gas chromatography, while the

liquid reaction mixture was monitored by both gas

chromatography and infrared spectroscopy.

Results and Discussion

The Binding of Carbon Dioxide by Transition Metal Carbonyl
Anions

Following the increasing trend in the nucleophilicity

(Table 2-3) of the transition metal carbonyl anions, the

alkali metal salt of each anion was prepared and reacted

with "bone dry" carbon dioxide. The reaction products were

characterized by infrared spectroscopy as summarized in

Table 2-8. The reaction of carbon dioxide with K[Co(CO)4]

in tetrahydrofuran at atmospheric and elevated pressures

(<70 psig) substantiated the literature reports of the
50
occurrence of no reaction.

Characterization of the iron salt in acetonitrile by

infrared spectroscopy (Table 2-6) determined the complex to

be K[HFe(CO)4] instead of K2Fe(CO)4. It is a common

procedure to form hydridometal complexes from the

protonation of metal complex anions with water as reported

for several phosphine substituted metal carbonyl

anions.77,78 Although unsubstituted metal carbonyl anions

usually require acidification to form a hydrido complex, it

is reasonable to assume that the trace quantities of water

observed by infrared spectroscopy to be present may be a

strong enough acid in acetonitrile to partially protonate

K2Fe(CO)4 to form K[HFe(CO)4]. The presence of this trace







28

quantity of water is a result of the synthesis of the iron

salt in a water solution, as well as the difficulty in

drying acetonitrile. Upon reaction of this acetonitrile

solution of K[HFe(CO)4] with "bone-dry" carbon dioxide for

several hours at atmospheric pressure, several infrared

absorptions (Table 2-8) indicative of a reduced carbon

dioxide species were observed. These new infrared

absorptions correspond very well with the formation of a
79
small quantity of potassium bicarbonate. During the

protonation of K2Fe(CO)4 by trace quantities of water, the

formation of potassium hydroxide is inevitable as shown in

Equation 2-8. Carbon dioxide can be neutralized by this

potassium hydroxide to form potassium bicarbonate. Carbon



CH3CN

K2Fe(CO)4 + H20 > K[HFe(CO)4] + KOH (2-8)



dioxide also can be hydrated in the presence of water to

form carbonic acid which can dissociate into bicarbonate and

carbonate as shown in Equation 2-9. It previously has been

suggested by the interpretation of solution infrared data

that the reaction of Na2Fe(CO)4 with carbon dioxide yields

iron pentacarbonyl and sodium carbonate.48 The preliminary



CO2 + H20 0 HH2CO 3 0H+ + HCO3 _2H+ + CO3 (2-9)



nature of these reported results has precluded any direct


















Table 2-8. A Summary of Infrared Data Obtained
for Reactions Between Carbon Dioxide
and the Transition Metal Carbonyl Anions


Compound + CO2


KCo(CO) 4


Infrared Data (cm- )


1890 (vs)


Assignment


KCo(CO)4 (V)


Environment


K(HFe(CO) 4]





NaMn (CO) 5








NaMn(CO)5 +
Mn2 (CO) 10


NaRe (CO) +
Re2 (CO) 10


1915(m), 1887(vs) K[HFe(CO) 4 (VI) CH3CN

3600(mw), 3190(mw), 1629(m), KHCO3 (VI) CH3CN
1345(w), 699(m)



2044(m), 2015(s), 1985(s) Mn2(CO) 10 (Fig.2-5) CH3CN

1910(vs), 1860(vs) NaMn(CO)5 (Fig.2-5) CH3CN

1656(s), 1623(vs), 1047(m), NaHCO3 (Fig.2-4) nujol
1033(m) 996(s) 833(s),
703(s)



2045(m), 2010(s), 1975(s) Mn2(CO)10 (Fig.2-6) THF

1895(vs), 1855(vs) NaMn(CO)5 (Fig.2-6) THF

3460(w), 2030(s), 1935(w), "not identified", THF
1667(w) (Fig.2-6)


1985(s)

1880(s)


Re2(CO) 10

NaRe(CO)


(VII)

(VII)


(V-VII) location of spectrum in appendix A;
m medium; mw medium weak; w = weak.


vs very strong; s = strong;







30

comparisons of the reaction conditions and infrared data

with the corresponding conditions and data observed for the

reaction of K[HFe(CO)4] with carbon dioxide. The

determination through infrared spectroscopy (Table 2-8) that

K[HFe(CO)4] was the only iron species present after

completion of the reaction supports the formation of

potassium bicarbonate from the reaction of carbon dioxide

with a reaction contaminant, such as water or potassium

hydroxide.

Characterization of an acetonitrile solution of

NaMn(CO)5 (neucleophilicity = 77) by infrared spectroscopy

(Table 2-6) showed the absence of Mn2(CO) 10, as well as the

absence of any residual water. This solution was reacted

with "dry" carbon dioxide at atmospheric pressure to yield a

solution color change coinciding with the precipitation of a

solid. This solid was identified by infrared spectroscopy

to consist of primarily sodium bicarbonate with possibly the

presence of a trace amount of sodium carbonate as shown in

Figure 2-4. The reaction between carbon dioxide and

NaMn(CO)5 in tetrahydrofuran previously has been reported to

yield sodium bicarbonate and an unidentified manganese

carbonyl complex. Interpretation of the infrared spectrum

of the reaction solution, which is shown in Figure 2-5,

suggests that another manganese carbonyl complex is present

along with NaMn(CO)5. The infrared absorptions (Table 2-8)

assigned to this manganese carbonyl complex correspond to

those of Mn2(CO) 10. An increase in the quantity of












-1
a = 1656 cm 1
b = 1623 cm-
c = 1047 cm-
d = 1033 cm-
e = 996 cm-
f = 833 cm-
Saple spectrg = 703 cm"






O e
b e f 9




3800 2200 1400 800 400

wavenumbers (c -1





Na2p




NaHCO







5000 1500 900 625
-1



Figure 2-4, Infrared Spectrum of Precipitate
Obtained from Reaction of Carbon
Dioxide and NaMn(CO)5















a 24 Hours b 48 ours C c
e C02 CO2

de
dN


d = 1910 amn
e = 1860 on1
f = 2044 an1
g = 2015 cm a
h = 1985 CM


WAVENUMBERS


Figure 2-5.


Solution Infrared Spectrum of the Carbonyl
Region for the Reaction between Carbon
Dioxide and NaMn(CO)5 in Acetonitrile


2000


2000


2000







33

Mn2(CO)10 present in the reaction solution was observed in

these infrared data to coincide with an increase in reaction

time. The reaction of NaMn(CO)5 and carbon dioxide in

tetrahydrofuran instead of acetonitrile produced similar

results. In this case, the presence of a third unidentified

manganese complex along with Mn2(CO)10 and NaMn(CO)5 was

observed by infrared spectroscopy as shown in Figure 2-6.
-l
The infrared absorptions at 2030 and 1935 cm assigned to

this unidentified complex were observed to disappear upon

the replacement of the carbon dioxide atmosphere with

nitrogen. The weak /OH and /C'02 absorptions that were

observed could be due to either a small quantity of

solubilized bicarbonate or to a bound format, bicarbonato,

or metallocarboxylic acid complex of manganese. The

identification of a metallocarboxylic acid derivative,

[(OC)3M(CO2Na)]2 (M = Mn, Re) from solution infrared data

has been reported for the reaction of carbon dioxide with

NaM(CO)5 (M = Mn, Re). Attempts to isolate a bound carbon

dioxide complex have been unsuccessful.

The interaction of carbon dioxide with NaMn(CO)5 could

proceed through a variety of different pathways. First, it

is possible that carbon dioxide directly interacts with

NaMn(CO)5 forming a metallocarboxylic acid derivative as

previously suggested. The observed reaction also could

proceed through the disproportionation of carbon dioxide

into carbon monoxide and carbonate as shown in Equation

2-10. It is possible that the insertion of carbon dioxide



















0Q


0

fa



4->

40




o E-
0o
UU-

LLI
uJ v-
_0 0


z p:


o o
to ro






S C0 0 H



(0
CO)



i -I
Nj'
I I I|8 8







35

into the sodium-manganese bond could form an intermediate

similar to that isolated for IrCl(C204) (PMe3)3-0.5-C6H6 35

The disproportionation of this intermediate into carbonate



2C02 + 2e > CO + CO32- (2-10)



and carbonyl complexes could explain the observed infrared

data. A third alternate way in which a carbonate or

bicarbonate species could be formed is by the interaction of

carbon dioxide with water as shown in Equation 2-9.

However, the absence of any observable O-H absorptions in

the infrared data obtained for the starting solution (Table

2-6) suggests that water is initially not present in the

reaction. It is possible that the reverse of the water-gas

shift reaction as shown in Equation 2-6 could produce the

water necessary to initiate the formation of bicarbonate and

carbonate species. Hydrogen was found to be present in the

reaction as a low level impurity arising from the "dry"

carbon dioxide feed gas. It is impossible to ascertain from

the available data which of these mechanisms is

predominantly responsible for the observed results.

Reaction between carbon dioxide and a mixture of

Re2(CO)10 and NaRe(CO)5 (nucleophilicity = 25,000) in

tetrahydrofuran could not be detected by infrared

spectroscopy. Infrared spectroscopy has been inconclusive

in ascertaining the existence of any rhenium complex besides

Re2(CO)10 or NaRe(CO)5. Attempts to stabilize or isolate







36

any reduced carbon dioxide species has been unsuccessful.

Even though the results concerning the reaction between

carbon dioxide and NaRe(CO)5 have been inconclusive, the

formation of sodium carbonate and an unidentified metal

carbonyl species has been reported50 for the reaction of

carbon dioxide with the more nucleophilic complex,
53
Na[CpNi(CO)] (nucleophilicity = 7,500,000)53

Formation of Alkyl Formates at Low Pressures and
Temperatures

The activation of hydrogen by a transition metal

carbonyl complex is necessary to effectively utilize the

corresponding transition metal carbonyl hydride as a

catalyst for the reduction of carbon dioxide. The

activation of hydrogen by Mn2(CO)10 has been reported to

occur only under extreme conditions of pressure and
80
temperature8. On the other hand, Re2(CO)10 has been

reported to activate hydrogen at atmospheric pressure under

mild temperature conditions to form a mixture of H Re3(CO)12

and H4Re4(CO)12'. Low temperatures and pressures have been

reported to be effective for the activation of hydrogen by
81 49
Ru3(CO) 12 and neutral group 6B metal complexes, such as

W[P(OCH3)3]5H2. However, the current method for the

formation of group 6B metal carbonyl hydrides is the

reduction of the hexacarbonyl metal complex by either

NaBH 82 or two equivalents of KOH in aprotic solvents.57

Dodecacarbonyl dirhenium was tested as a catalyst for the

conversion of carbon dioxide and hydrogen to methyl format







37

in methanol at mild temperatures (125-1500C) and pressures

(20 psig). It should be noted that the major difference

between the reactions conducted in this work and those

previously reported59-61 in the literature is the

utilization of substantially lower pressures in the present

work. The reaction products were monitored by gas

chromatography and infrared spectroscopy.

The quantitative results of the experiments conducted

are summarized in Table 2-9. The formation of methyl

format was observed by gas chromatography and identified by

GC/MS as shown in Figure 2-7. Since only a trace amount of

methyl format was discovered in the reaction of Re2(CO) 10

with carbon dioxide and hydrogen (run 1), no quantitative

data were obtained. A control reaction (run 2) involving

only methanol, carbon dioxide and hydrogen showed no

activity for the formation of methyl format. Analysis by

GC/MS of the reaction mixture (run 1) identified the

existence of several additional low molecular weight

products, such as dimethyl ether, dimethoxymethane and

hexane. The observed mass spectra of these compounds are

shown in Figures 2-8, 2-9 and 2-10. Gas chromatography has

been used to obtain quantitative data for these compounds,

as well as discover the presence of methane and an

unidentified substituent at 1.21 minutes as shown in Figure

2-11. Trace amounts of dimethyl ether and dimethoxymethane

were observed by gas chromatography to be the only products

formed in the control reaction (run 2). The hexane observed





















Table 2-9.


A Summary of the Quantitative Data
Obtained for the Reaction Products
by Gas Chromatography


Run


Run
Number

1


Reaction
Time
(Hrs.)

24


Reaction
in
Methanola

Re2(CO) 10

+ CO2 4 H2


48


2 48 CO2 + H2


3 48 3Re2(CO) 10

+ CO2 + "2


4 48 Re2(CO) 10

+ CO


5 160 Re2(CO)10

+ CO + H2


6 48 Re2(CO)10

+ CO + KOCH3


7 48 Re2(CO)10

+ CO + H2

+ KOCH3


8 48 KOCH3 + CO


9 48 H Re (CO)

+ CO


10 48 KH(W(COl ]2

+ CO


11 48 (H2Re(CO)4]-

+ CO +

- 140 [Re2(CO)6(u-OCH3)3)


ItC3j 20

moles x 10-

15



61


H.2 C(.O.3 12

moles x 10-9

14



41


HCO2CH3

moles x 10"11





weak trace


None


weak trace




Trace




4.0




None




None


160


510


weak trace


1.5




Trace




0.2


19


a In all reactions the catalyst concentration was 7.5 x 10-3 moleal/liter.





















observed spectrum


r'e


0


10 30


reference spectrum83


I


5"0 70 90
m/e


Figure 2-7. Mass Intensity Report for Methyl Formate


















observed spectrum


10 I 20 I
10 20


100
0o J___.


n . .. |- 1,- i I I I I I 1 1 I I I


30
m/e


' S S '


40


reference spectrum83


10 30 50 io
rQ/e


Mass Intensity Report for Dimethyl Ether


100-1


50


I ,


Figure 2-8.















100-i


observed spectrum


29


0A 1 11 11 1 1 1 11 1 111
10 30 50 70 90
n/e


100
dP

10 30 50s


reference spectrun83
1


70 90
n'/e


Figure 2-9. Mass Intensity Report for Dimethoxymethane


1S0
















100-


j observed spectrum


50-
41








20 30 40


.44...............


50


60 70 80 90


n'e


reference spectr83
reference spectrum


i1 i


(I. *.


20 40 60 80 1006
V'e


150


Figure 2-10. Mass Intensity Report for Hexane








43











0





r-- r.4 n CH
I I I I I I



8 | ., | -0 I


m O H r.-4 m m m "

II II I II II II II i






0 J

0
0







u
WN
rT4
en H







rn C
(0 E







44

in the reaction mixture (run 1) is an impurity that arises

from the use of hexane solvent in the commercial

recrystallization of Re2(CO)10.84 Since bulk grade hexane

is used, the unidentified peak at 1.21 minutes can be

assigned as another hydrocarbon impurity. This is supported

by the observed proportional increase in this peak at 1.21

minutes along with the hexane peak as the quantity of

Re2(CO) 10 used in the reaction is increased. Furthermore,

both these peaks remain constant throughout the reaction

period. The dimethyl ether and the dimethoxymethane that is

observed can be considered as reaction products since they

increase in concentration as the reaction time progresses

(run 1). It also is observed that the Re2(CO)10

concentration has no effect upon the quantity of dimethyl

ether or dimethoxymethane produced during the reaction (run

3).

It is possible to speculate that methyl format in this

reaction could be produced through a mechanism similar to

that previously described49 in Figure 2-2. Recently, the

formation and characterization by x-ray crystallography of a

rhenium carbonyl metallocarboxylic acid complex,

Re3(CO)14COOH, was reported. This metallocarboxylic acid

complex of rhenium was formed as a minor product in the

photolysis of Re2(CO)10 in the presence of nitric oxide. It

is possible that an intermediate such as this could

eliminate formic acid within a catalytic cycle. The

interaction of this formic acid with methanol would yield







45

the observed methyl format. The infrared data obtained for

these carbon dioxide reactions are summarized in Table 2-10.

The presence of Re2(CO)10 and other rhenium carbonyl

complexes is suggested by the interpretation of this

infrared data (run 1). The presence of Re2(CO)10 in

solution was confirmed by the infrared characterization of a

white solid that precipitated out of solution upon the

addition of water. Subtraction of the Re2(CO) 10 component

in the infrared spectrum (run 1) as shown in Figure 2-12

allows for accurate determination of the absorptions which

can be assigned to the appearance of new rhenium carbonyl

complexes. The major components in this subtracted infrared
-1
spectrum have strong absorptions at 2009 and 1892 cm It

was noticed that during the reaction a pink film was

observed to form along the glass reactor walls. Partially

dissolving this film in carbon tetrachloride gave an

infrared spectrum similar to the solution data (run 1)
-1
except for the absence of the absorption at 1892 cm .

Since Re2(CO)10 has been reported81 to activate hydrogen

within the reaction conditions employed, the infrared

absorptions observed for this pink film can be assigned to a

mixture of Re2(CO) 10 and a rhenium carbonyl hydride.

Recently it was reported62 that the reduction of carbon

monoxide by tungsten carbonyl hydrides in methanol

catalytically produced methyl format. The moles of methyl

format formed per mole of catalyst used in these

experiments were shown to be approximately two orders of






















0
*4-
.I



0 x


S 0 4 1* --4l

0 rC cc O 0
441 (0
.a "'
S0 II



SC c 1 C C C ->

I -' 0 0 x x x I0 0
Sc o o a
0 C 0 c a CO ( r_ s


4>EJE 3E > > E>E > >1

S0 0 0) )



28 0 .


o -w ~ a 0) u ; co 010 o



4 iCO 0o 0% o 0o0 o0 0 ooN 0 a)
4Q N.4 JM (N (N4N (N N N(c'N ZN 0E


E4 0 3

40 E -> > E
>- (Ni r 'J- .0 o -w1w N 1-4 4c4 mooo n 0
u 44 r- m m en a% Or- in rr r- to O mo a -w a cn
.rtCcu CO M ooa ch oo O% Qon ON OOO O c



-) 0 0 0 4 c4 Qq '. -4 0 0 C

1- o o H o
C(N 4J O 4 'a 14 -4







z >
ui k

E- >

































-l l -4 r-i 1-4



m- C m C14c P) 0m CN 0c
0o 0 01T co
C4 (N r-I H -
II II II II II
i0 U10 0T)


SNOISSISNVU 0

+NOISSIWSvkisl~~*.


*:


0
H --



(o
() 4j


o 0














O
-0 4


0
44C

Q)
(U







rO>




0 M
Hr 0
4-)
U



0 r.



4J M

a)u

0



C!
4-1 N




i(N



(:J
4-0









magnitude greater than those reported for the corresponding

reactions run under carbon dioxide and hydrogen. The small

observed activity in the Re2(CO)10 reactions run using

carbon dioxide and hydrogen can be explained by the

reduction of either the metal bound carbonyl ligands or of

carbon monoxide produced by the reverse of the water-gas

shift reaction as shown in Equation 2-6. This latter case

is possible since both Re2(CO)10 and H3Re3(CO)12 have been

reported to catalyze the water-gas shift reaction under

basic conditions. Although the formation of methyl

format was still too small to quantitate, it was

demonstrated by gas chromatography that more methyl format

was formed under a carbon monoxide atmosphere (run 4). The

yield of-methyl format was found to increase with the use

of a mixture of carbon monoxide and hydrogen over an

extended reaction time (run 5). The catalytic ability of

the Re2 (CO) 10 system at low pressures will not be discussed

since the 2.6 x 10-7 moles of methyl format formed per mole

of Re2(CO)10 used is far below one catalyst turnover

assuming Re2(CO)10 to be the active catalyst.

Infrared spectroscopy was used in an attempt to

determine the active species in the Re2(CO) 10 reaction

systems. All infrared data obtained for reactions using

carbon monoxide are summarized in Table 2-11. The infrared

spectrum of the reaction run under carbon monoxide (run 4)

shows the presence of only one absorption at 1890 cm- that

cannot be assigned to Re2(CO)10. This suggests that the













Table 2-11.


A Summary of Infrared Data Obtained for
the Reaction of Re2(CO)10 with Carbon
Monoxide in Methanol


Reaction
or
Run Complex

4 Re2(CO)10 + CO


6 Re2 (CO)10 +


Infrared Data,
YCO, (cm-1)

2071(s), 2013(vs),
1971(s), 1891(m)


CO + KOCH3


2071(m),
1972(m),
1732(w),
1605(vs)


2013(s) ,
1888(s),
1717 (w),


Environment


Reference


methanol a (XII)


methanol a (XIII)


7 Re2(CO)10 + CO + H2 +

KOCH3


8 KOCH3 + CO


9 H xRe (CO)z + CO


Subtract
out
Re2(CO) 10


2071(w), 2013(s),
2000(s), 1971(w),
1888(vs),1606(vs)

1735(m), 1718(m),
1605(vs)

2072(m), 2031(s) ,
2010(vs),1971(m),
1927(vs),1891(vs)

2031(s), 2008(s) ,
1928(vs),1892(vs)


methanol


a (XIV)


methanol a (XV)


methanol


a (XVI)


a (Fig. 2-13)


[(CO)3Re(u-OCH3)3Re(CO)3]

1990(s), 1875(vs)


[- H2Re(CO)4]J


- [Re(CO)30OCH3]4


2020(vw),1995(w),
1930(vs),1895(s)

2036, 1935


dichloromethane 88

dichloromethane 88


- (Re3 -H) 3(u-OCH3) (CO)10)

2096(w), 2020(m)
2000(vs),1985(sh),
1957(vs),1935(vs),
1888(s)


dichloromethane 90


a = This work; (XII-XVI) Location of spectrum in appendix A;
vs = very strong; s strong; sh shoulder; m medium; w = weak;
vw = very weak.







50
-i
observed absorptions at 2031 and 1927 cm-1 in reactions run

in the presence of hydrogen can be assigned to the formation

of a rhenium carbonyl hydride complex such as H3Re3(CO) 12.

Since methyl format formation was enhanced in the presence

of hydrogen over an extended reaction time (run 5), it is

proposed that the active species in the reaction is a

rhenium carbonyl hydride. This proposal is further

supported by the enhanced formation of methyl format in the

reaction of carbon monoxide with a mixture of rhenium

carbonyl hydrides (run 9). The resulting infrared spectrum

for this reaction, which is shown in Figure 2-13, resembles

those obtained for reactions between Re2(CO) 10 with hydrogen

and either carbon dioxide (run 1) or carbon monoxide (run

5).

Recall that in the previously proposed mechanism62

shown in Figure 2-4 for the carbonylation of methanol to

methyl format by tungsten carbonyl hydrides, the active

catalytic species was suggested to be a methoxy tungsten

carbonyl complex. Recently the bridging methoxy compound

[(CO) 3Re(P-OCH3)3Re(CO)3] [N(C2H5)41 was reported to be
88
formed by the addition of methanolic KOH to Re2(CO)10.88

Along with the hexacarbonyl tri-p-methoxydirhenate(1-) the

reaction was found to form [H2Re(CO)4) as a coproduct. The

complete conversion of this rhenium hydride to the isolated

bridging methoxy compound [(CO)6Re2(P-OCH3)3] was observed

to occur at elevated temperatures. The formation of other

alkoxide rhenium carbonyl complexes, such as





















a) 41-


o :
0 Io I

04J


-4-4 -4 -4 .,-q 4J



r44




0 C N
(0 (0(




o- oo o








C)W
(ID-







Cw> 0-,4


0.)



0 0Z


V- H o
C*4



H
OD (0
a)

.-.I







52
89 90
[Re(CO)3OCH3]4, [Re3(u-H) 3(p-OCH3) (CO)10] ,

[(CO)6Re2(u-OC2H5)2(u-OCH3)]- 91 and [Re3H3(v3-OC2H5)-

(CO) ]- 92 also have been reported. The preparation of

these alkoxy rhenium carbonyl hydride complexes was

reported92 to proceed through a reaction of a rhenium

carbonyl hydride with the corresponding alcohol. The

similarities between the infrared spectra for these

complexes and the infrared data obtained for the Re2 (CO) 10
-1
reactions (Table 2-11) suggests that the 1890 cm-

absorption can be assigned to the formation of a methoxy

rhenium carbonyl complex such as [(CO) 6Re2(u-OCH3)3] This

is further supported in that no new infrared adsorptions are

observed for the addition of several equivalents of KOCH3 to

the Re2(CO)10 reactions run under either carbon monoxide

(run 6) or carbon monoxide and hydrogen (run 7). Since gas

chromatography could not identify the formation of any

methyl format in these reactions (runs 6, 7), the methoxy

rhenium carbonyl complex is most likely catalytically

inactive. The infrared spectrum of the reaction performed

under carbon monoxide and hydrogen (run 7) was observed not

to exhibit any absorptions that could be assigned to a

rhenium carbonyl hydride. This suggests that deactivation

of the active rhenium carbonyl hydride results in the

formation of an inactive methoxy rhenium carbonyl complex.

Attempts to isolate this methoxy rhenium carbonyl complex

have been unsuccessful.









A mixture of [(CO) 3Re(u-OCH3 ) 3Re(CO) ] and H2Re(CO)4

in methanol was prepared by the previously reported
88
procedure and identified by infrared spectroscopy as shown

in Figure 2-14. The formation of methyl format was

observed to occur for the reaction (run 11) of carbon

monoxide with this mixture of rhenium complexes. The

activity observed for the formation of methyl format was

found to decrease with an increase in reaction time. The

resulting solution was observed by infrared spectroscopy to

contain only the [Re2(CO) 6(p-OCH3)3] complex as shown in

Figure 2-14. It is proposed that a mixture of rhenium

carbonyl hydrides, such as H3Re3(CO) 12 and H2Re(CO)4 are

the active species responsible for the formation of methyl

format from carbon monoxide and methanol. These hydride

species can be converted under the employed reaction

conditions to the resulting inactive rhenium alkoxy carbonyl

complex [Re2(CO) 6(v-OCH3) 3]. The only infrared absorption

in Figure 2-14 that cannot be assigned to either a rhenium

carbonyl hydride or alkoxy complex is the medium strength

band at 1605 cm 1. It has been observed by infrared

spectroscopy that a similar absorption results from the

addition of KOCH3 to methanol (run 8).

At elevated pressures the carbonylation of methanol to

methyl format has been reported to occur using sodium

methoxide as catalyst.93'94 A comparison of the low

pressure formation of methyl format by this reaction (run

















CO
A B


A
S tartng
solution


B
Product
solution


2301


2019 1788
wavenumbers (an )


Figure 2-14.


Infrared Spectrum Obtained for the Reaction
of Carbon Monoxide With a Mixture of
[Re2(CO) 6(j-OCH3)3]- and [H2Re(CO)4]- in
Methanol


2038
2009
1992
1971
1926
1880
1605


-1
an1
an_
-1
ani
_-1
an
-1
n-1


1557







55

8) with the Re2(CO)10 (run 4) and KH[W(CO) 5]2 (run 10)

systems was done. The results as shown in Figure 2-15

indicate that Re2(CO) 10 > KH[W(CO)5]2 > KOCH3 in activity

for the carbonylation of methanol at low pressures to form

methyl format. This sequence of activity at low pressures

parallels a recent report which indicates that KH[W(CO) 5]2

is more active than KOCH3 for the carbonylation of methanol

to methyl format at elevated pressures. An investigation

of the activity of the Re2(CO) 10 system at elevated

pressures was not done because of the lack of a high

pressure reactor.

The utilization of low pressures in the Re2(CO)10

system has allowed the identification of dimethyl ether and

dimethoxymethane which may be key intermediates in the

formation of methyl format. A discussion concerning the

mechanism for the formation of methyl format in the

Re2(CO) 10/CH3OH/CO system would be speculative and premature

at this time. However, it should be noted that formaldehyde

has been reported to form dimethoxymethane in methanol95 and

methyl format in the presence of a nickel catalyst

Although a rhenium carbonyl bound formaldehyde complex has

not been observed, both its precursor, a formyl complex,

such as [Re2(CO) 9(CHO)]- 97,98 and its product, an

alkoxymethyl complex, such as Re(CO)5CH20CH3 have been

reported. Another way in which dimethoxymethane,100

dimethyl ether100 and methyl formate01',102,103 have been

reported to be formed is through the direct oxidation of




























4-i


Time


Re2 (CO)10 + CO


Timeo


K[HW2 (CO)10] + CO


I0CH3 + 00


a = 0.77 minutes dimethyl ether
b = 1.95 minutes methyl format
c = 1.23 minutes unidentified


Figure 2-15.


A Comparison by Gas Chromatography of
Reaction Products in Liquid Samples for
Carbon Monoxide Reactions with Re2(CO)10
KH[W(CO)5]2 and KOCH3









methanol over a variety of different catalyst substrates.

Carbon-13 carbon monoxide was reacted with Re2(CO) 10 in

methanol to ascertain if the methyl format was being formed

by the carbonylation of methanol or by methanol oxidation.

GC/MS results so far have been inconclusive in obtaining the

extent of carbon-13 incorporation in dimethyl ether,

dimethoxymethane or methyl format because of the relatively

small amounts of products observed. It is proposed that the

methyl format observed in the Re 2(CO)10 systems is from the

carbonylation of methanol as reported for the analogous

KH[W(CO) 62 and KOCH393,94 This proposal is

based upon the differences observed in reactions (runs 1-3)

performed under carbon dioxide and those reactions (runs 4,

5) performed under carbon monoxide. If the formation of

methyl format was governed by the oxidation of the methanol

solvent, there should have been no differences in the

observed results.

Summary

The main goal of this investigation was to evaluate the

feasibility of binding and activating carbon dioxide by

transition metal carbonyl complexes. The first study dealt

with the interaction of carbon dioxide with a variety of

transition metal carbonyl anions that differed in the

nucleophilicity of the metal center. Although no reaction

with carbon dioxide was observed to occur for KCo(CO)4, the

formation of potassium bicarbonate was observed in the

K[HFe(CO)4] system. This result was clouded by the reaction







58

of carbon dioxide with residual contaminants of water and

potassium hydroxide. Interaction of carbon dioxide with

NaMn(CO)5 was found to form sodium bicarbonate, Mn2(CO)10

and an unidentified manganese carbonyl complex. The

occurrence of a reaction between carbon dioxide and

NaRe(CO)5 was not observed. These results suggest that it

is possible to bind carbon dioxide to a transition metal

carbonyl anion. Although no conclusion concerning the

preferred coordination mode of binding can be made, it does

seem that the interaction of carbon dioxide with transition

metal carbonyl anions is affected by the nucleophilicity of

the metal center.

The second study dealt with an investigation of the

activity of Re2(CO)10 with respect to the reduction of

carbon dioxide in methanol to form methyl format at low

pressures. Reactions performed under carbon dioxide and

hydrogen produced trace quantities of dimethyl ether,

dimethoxymethane and methyl format as identified by GC and

GC/MS. Although these products could be formed directly

from carbon dioxide, it is more likely that the reduction of

carbon monoxide produced from the reverse of the water-gas

shift reaction has occurred. This contention is supported

by the increased activity for the formation of all products

in reactions run under carbon monoxide.

Infrared spectroscopy was used to investigate the

active species in these reactions. It has been proposed

through an interpretation of this data that the active







59

species is a mixture of rhenium carbonyl hydrides, such as

H3Re3(CO)12 and [H2Re(CO)4] These hydride complexes

slowly decompose during the course of the reaction to form

the inactive methoxy rhenium carbonyl complex,

[Re2(CO)6(u-OCH3)3] Since an accurate measurement of the

amount of the active species present during the reaction

could not be obtained, a discussion of the Re2(CO) 10

system's catalytic ability was not undertaken. The

formation of dimethoxymethane and dimethyl ether was

observed during the course of the reaction. A comparison at

low pressures of the Re2(CO)10 system with systems, such as

K[HW2(CO)10] and KOCH3, that are known to carbonylate

methanol and form methyl format was done. The results

indicate that the activity of Re2(CO) 10 > K[HW2(CO)10] >

KOCH3 in the carbonylation of methanol to form methyl

format. The possibility of increasing the activity of the

Re2(CO) 10 system at high pressures similar to that

previously shown for KH[W(CO) 5 2 and KOCH3 may allow for a

more thorough investigation of the reaction mechanism.
















CHAPTER III

ACTIVATION OF CARBON MONOXIDE

Background

The conversion of synthesis gas (CO + H2) into organic

substrates has been an active field of research since the

initial work of Sabatier and Sendrens in the early
104
1900's. Many articles have reviewed various processes

that activate carbon monoxide, such as the water-gas shift
105-111
and Fischer-Tropsch reactions. The latter has

evolved for the hydrogenation of carbon monoxide and is

described in Equation 3-1. The Fischer-Tropsch synthesis112

usually employs a heterogeneous catalyst consisting of



Catalyst
CO + H2 > Hydrocarbons + Oxygenates (3-1)
(Fe,Co,Ru)



either Fe, Co or Ru metal. This reaction takes place over a

wide range of temperatures and pressures. Moderate

temperatures and high pressures seem to favor the formation

of oxygenated products while milder pressure conditions

increase the ratio of hydrocarbon products. In both

cases the ratio of products obtained follows a simple

polymerization model (Schulz-Flory distribution) as







61

described by Equations 3-2 and 3-3.114-116 In Schulz-Flory


2 n-i
W = n (1-a) a (3-2)



Q = r + r = 1 (3-3)

rt 1-a



kinetics the weight fraction, Wn of carbon number, n, is

related to the probability of chain growth, a, which is

defined in terms of the average degree of polymerization, Q.

The value of Q, determined from the rate of polymerization,

r and the rate of chain termination, rt, is influenced by

the characteristics of the metal catalyst and the reaction

conditions, such as temperature and pressure. The inherent

lack of selectivity as demonstrated by Schulz-Flory kinetics

is the major disadvantage to a Fischer-Tropsch type

conversion of synthesis gas.

In order to deviate from this Schulz-Flory product

distribution, thereby increasing the selectivity of the

Fischer-Tropsch synthesis, research efforts have

concentrated on new loading techniques and the use of

shape selective supports. 18,119 There is considerable

evidence that the probability of polymerization in the

Fischer-Tropsch synthesis is influenced by the size of the

metal crystallites.116'120'121 A variety of reasons for

this particle size effect ranging from differences in the

electronic band structure of small particles as compared to







62

that of the bulk metal to a stronger support interaction and

higher degree of unsaturation with small particles have been

suggested.122 The final outcome has been the development of

new methods for the preparation of small metal particles,

such as the solvated metal atom dispersed catalyst method123

and the thermal decomposition of metal carbonyl clustersl4

onto inorganic oxide supports. The utilization of these

techniques has led in several instances to catalysts that

exhibit higher activities and selectivities for synthesis

gas conversion to C2 C5 hydrocarbons as compared to
125
conventionally prepared catalysts. These dispersed metal

catalysts deposited on high surface area supports are

considered a new class of catalysts that lie between the

boundaries of traditional heterogenous and homogeneous

catalysts.

As shown in Table 3-1 there are several advantages and

disadvantages associated with using either homogeneous or

heterogeneous catalysts. 126 The major disadvantage of

heterogeneous catalysts besides their non-selective nature

has been the lack of physical techniques to adequately

characterize these systems. Recent advances in surface

techniques, such as ESCA, SEM, XPS, Auger, etc. are

beginning to aid in understanding and characterizing these

catalyst systems. Homogeneous catalysts, on the other hand,

are usually well characterized and reproducible. The major

industrial concern for these catalysts is the additional









Table 3-1.


63

A Comparison of the Advantages and Disadvantages
of Using Homogeneous and Heterogeneous
Catalysts


Advantages


Disadvantages


Homogeneous Catalysts


1. Relatively resistant to 1. Necessary process
catalyst poisoning step for catalyst
separation
2. High activity
2. Temperature
3. No mass-transfer problems sensitive

4. High selectivity

5. Characterization, reproducible

Heterogeneous Catalysts


1. Catalyst easily separated
from substrate

2. Insensitive to high
temperatures


1. Sensitive to
catalyst poisoning

2. Mass transfer
problems

3. Characterization


process step that is necessary to separate the reactant/

product/catalyst mixture.

Another method to obtain a more selective process

focuses around the utilization of homogeneous catalysts for

the hydrogenation of carbon monoxide. A vast body of

literature has developed for the conversion of synthesis gas

to oxygenated products by solubilized catalysts.127131

These systems usually operate under extreme pressure

conditions (>1000 atm.). Recently there have been several

reports of anionic ruthenium carbonyl complexes being







64

effective in the homogeneous reduction of carbon monoxide to

ethylene glycol at moderate temperatures and

pressures.132-133 Moderate temperatures and pressures have

also been reported for the conversion of synthesis gas to

methanol using a neutral metal complex, Ru(CO)5, as
134
catalyst. The addition of carboxylic acids to this

reaction promoted the formation of glycol esters. Most of

the homogeneous systems reported have formed oxygenated

products from the hydrogenation of carbon monoxide.

Although several non-catalytic systems have been

reported that reduce a carbonyl ligand to hydrocarbon

products,135-137 there have been very few reports concerning

the homogeneous catalytic reduction of synthesis gas to

hydrocarbons. The first report, in 1976, employed selected

metal carbonyl cluster catalysts, such as Os3(CO)12 and
138
Ir4(CO) 12. Substitution of several of the carbonyl

groups in Ir4(CO)12 by triphenylphosphine was found to

increase the hydrocarbon production rate. This rate was

further enhanced by dissolving the Ir4(CO)12 in an
139,140
A1Cl3-NaCl melt solvent as shown in Equation 3-4.39

This reduction of carbon monoxide was done under very mild

conditions, 125-2100C and one atmosphere of pressure.

Ir4(CO)12 1 atm.
CO + H2 4 12 1 C1-C4 alkanes (3-4)
AlCl -NaCl 1250-210C


The introduction of metallic aluminum to this system was
21
found to increase the yield of hydrocarbon products. It







65

was proposed that the addition of this aluminum metal

enhanced the formation of HAIX2 which bifunctionally induced

the reduction of carbon monoxide.

A kinetic investigation of the Ir4(CO) 12 melt salt

system at 175C discovered the formation of a sustained low

level concentration of methyl chloride which was proposed to

be an intermediate in the formation of the hydrocarbon
141
products. This kinetic study proposed that the active

catalytic species was a chlorocarbonyl iridium complex, such

as IrCl(CO)3. A similar system using Os3(CO)12 in a BBr3

melt to convert synthesis gas to hydrocarbon products has
142
been reported. In this case, the formation of a low

level concentration of methyl bromide was detected. It was

suggested that Os2(CO)6Br4 was the active catalytic species

in the reaction. The most significant contribution of these

reports was to demonstrate the importance of a Lewis acid

adduct with a metal carbonyl ligand. This bifunctional



M-CO .-AIlClI



activation leads to a weakening of the carbon-oxygen bond

which allows the carbonyl group to be reduced under very

mild conditions.

The functionalization of reactive supports with

discrete molecular catalyst systems also could utilize this

concept of bimetallic synergism by exploiting the support as

cocatalyst. These supported catalysts may stabilize and







66

increase the concentration of the catalytic active species

which would allow the reduction of carbon monoxide to occur

under milder conditions.143 The immobilization of

homogeneous transition metal catalysts on various polymer

supports is currently a very active field in catalysis

research. The techniques for the covalent or ionic

attachment of discrete metal complexes to various types of

supports are well documented.144,145 These supported

catalysts can be considered as "hybrid" catalysts which

offer the advantages, such as high activity and selectivity,

of homogeneous catalysts as well 6s the ease of

product/catalyst separation associated with heterogeneous

catalysts. Several reports have indicated an increase in

activity and selectivity using a polymer bound catalyst as

compared to its molecular analog. For instance, the

polymer bound analog of Vaska's complex, ()-(PPh2) 2IrCl(CO),

catalyzes the hydrogenation of 1,5-cyclooctadiene at a

faster rate than observed for the homogeneous reaction as

shown in Equation 3-5.147



/ \ IrCl(CO)(PPh3)2 + / \ (3-5)

H 2 1700C



Prior work done concerning the catalytic behavior of

supported complexes in Dr. Drago's research group led to the

discovery of a unique system for the selective catalytic

conversion of synthesis gas and HC1 to methyl chloride by a








67

supported tetrairidium cluster under very mild temperature
148
(250-1000C) and pressure (1 atm.) conditions as shown in

Equation 3-6. The support of choice was an inorganic oxide



3-OSiC2H4PPh2Ir4(CO)11
2H2 + CO + HC1 ->24 ( 1- H20 + CH Cl (3-6)
25 100C, 1 atm.




(alumina or silica gel) because of its high thermal

stability and the availability of Lewis acid sites to

promote a bifunctional interaction with carbon monoxide.

The support was functionalized through a condensation

reaction involving the hydroxyl groups of the support and

the ethoxy substituents of the phosphinated silane linkage,

(C2H50)3SiC2H4PPh2 as shown in Equation 3-7. The letter

y represents the number of support 3-0-Si bonds between


(OH)3-y
3-OH + (C2H50) 3Si(CH2)2PPh2 benzene/p-dioxane 3(-0-) Si(CH2)2PPh2 + 3C2H50H


(3-7)



the support surface and the silane linkage. Evidence

indicates that this number is dependent upon the

concentration of the organosilane used.150 The remaining

ethoxy groups have been reported to be hydrolyzed by the

solvent to yield ethanol and Si-OH functionalities. The

tetrairidium carbonyl cluster was immobilized on the support













through covalent attachment to the phosphine of the silane

linkage as previously reported.151'152 The major difficulty

in this synthesis, as shown in Equation 3-8, was to maintain

(OH) 3y
340* Si(CH2)2PPh2 (OH)
CO, Zn, H20 | 3-Y
+ 34 (O* Si(CH2)2PPh2] Ir4(CO) (3-8)
CH3 0C2H4OH (z = 1, 2; x = 11, 10)
Ir(CO) 2C1(H2N-O -CH3)



adequate stirring during the reaction. A poorly active

catalyst was reported in cases where complete mixing was not

obtained. An infrared investigation of the supported

tetrairidium cluster, as summarized in Table 3-2, was

reported to result in the identification of a mixture of

mono-phosphine and di-phosphine substituted clusters,

3-OSi(CH2)2PPh2Ir4(CO)11 and 3-[OSi(CH2)2PPh2 2Ir4(CO) 10,

respectively.

The catalyst was initially tested in a 3:1 AlCI -NaCl

melt salt under similar conditions as reported by

Meutterties et al.140 and Collman et al.141 for the

Ir4(CO) 12/AlCl3-NaCl system. A typical catalyst run

consisted of using 0.7 g of the supported iridium catalyst,

8 g of A1Cl3 and 1.8 g of NaCI in a glass fixed bed reactor

system. The catalyst was exposed to a 3:1 mixture of H2:CO

at 1450C. The major products were identified by gas

chromatography to be methane, ethane, and chloromethane

which are similar to those previously reported










69















u





0
o 4J






0-i1 0 0 0 u,) u I
40 UJ I a) -
-a 0 .c .C 0) 0) 0 "- 0E-
u>1 > u 44 44 u kW44 u U








o -4 -o
(a4J 1 -









oo
a) rn u) >-r E tn E I E > E > v) E>


mo c 0 c U U ) ,
4-4 >( rr, .4 :3
0C '-4
.0 0.0 00

co C rr- r->u or-,u-L -m n c ) it -
44.4 = a) i 4 O ilw ID ai 0 Oe(N'- :
4JI r U a cO OCr- C0 co 0 c c00 0 --l E E
f14 r4( c4 N -.NC (NN-4 (Cc4.-. ( (N CN Cr4f f 4N I0 E



>4 c) c I.-c
g C i


4o -4 2C



44 4 w 0)

0 Ia 0 04







70

for the homogeneous system.139-141 When the supported

tetrairidium catalyst was filtered from the molten salt and

the AlCl3-NaCl retested, there was no decrease in activity

observed. It was proposed that the supported tetrairidium

catalyst leached off the support to give the homogeneous

Ir4(CO) 12/AlCl3-NaCl system. However, it was observed that

prior to melting of the AlCl3-NaCl, methyl chloride was

produced. The production of methyl chloride at 25C was

seen to decrease with time. This decrease in production was

assumed to be caused by the depletion of the AlCl -NaCl.

The addition of anhydrous HCl(g) to the reactant gas stream

rejuvenated the activity of the system for chloromethane

formation. The cycling between the addition of HC1(g) and

the absence of HCl(g) was done several times with no

detrimental effects to the catalyst. It was reported that

exposure of the activated catalyst to oxygen caused

permanent deactivation of the system.

The presence of HC1(g) in the reactant stream should

initiate an interaction with the remaining hydroxyl groups

of the support making either Al-Cl or Si-Cl bonds and water.

If this is the case, then the presence of AlCl -NaCl may not

be necessary for the reaction to occur. Both silica gel and

alumina supported clusters were tested in the presence of

HC1(g) and the absence of A1C1 3-NaCl. In both cases after a

15-20 minute incubation period methyl chloride was observed

at 250C with the same activity and selectivity as seen

previously. This induction period was suggested to be due







71

to the interaction of HC1 with the support hydroxyl groups.

These Al-Cl or Si-Cl groups are believed to behave in a

similar manner as that of A1C1 Gas chromatography and

GC/MS identified trace quantities of methane, ethylene,

methyl chloride, ethyl chloride, acetaldehyde and methyl

format as reaction products. No difference was noticed

H H
0 0 Cl Cl
i I + 2HC1 > + 2H20


between the aluimina and silica gel bound systems in regards

to activity or selectivity.

The activities of the silica gel and alumina catalyst

systems were shown to be dependent upon temperature. The

activity of both systems increased with increasing tempera-

ture. A slight deactivation of the catalyst was observed to

occur at 1000C over a period of time. At temperatures below

100C the catalyst was observed to be stable for several

days. The activity also was found to be affected by the

concentration of HCl(g) in the reactant gas stream. The

concentration of HC1(g) had to be kept at a minimum to

insure catalyst stability. The comparison of metal loadings

(% wt.) at various temperatures demonstrated that the

catalyst activity increased with higher concentrations of

iridium in the catalyst. It was noted that other factors

besides the metal loading, such as support interactions,

deactivation process and phosphine concentration, may

influence this observed increase in activity.









Although a complete material balance wasn't obtained, a

calculation using the amount of chloromethane produced

relative to the other products at 100C showed the reaction

to be at least 99% selective for chloromethane. This wasn't

considering a polar product that condensed along with water

at the top of the reactor tube. Even though the existence

of this compound was discovered using gas chromatography,

the identity of the complex was not reported.

All control reactions run with or without AlCl -NaCI

showed either little or no activity for chloromethane

production as summarized in Table 3-3. A conclusion drawn

from these control experiments was that the tetrairidium

cluster had to be supported through a phosphine linkage for

catalytic methyl chloride production to occur. It was shown

that Vaskas' complex bound to a support, 3-v(PPh2)2IrCl(CO),

was slightly active for methyl chloride in the temperature

range 25-100C. This activity was far below that observed

for the supported tetrairidium cluster.

It was found that other halide sources, such as C12,

HBr(g) and HCl(aq) could be substituted for the HC1(g) with

no decrease in initial activity or selectivity. In the case

of HCl(aq) the activity was observed to decrease with time.

It also was found that chloromethane production could be

changed to methyl bromide by substitution of HBr(g) for

HC1(g) in an active system. However, the reformation of

methyl chloride by the reverse substitution of HCl(g) for

HBr(g) was observed not to occur.








73

Table 3-3. A Summary of the Reported Activity for the
Supported Iridium Carbonyl Catalyst System


Catalyst


Activity


Ir4(CO)12 + ACl 3-NaCl


SG + AlCl3-NaCl

SG ^PPH2 + AlCl 3-NaCl

(C2H50) 3Si A^PPh2Ir4(CO)11 +

AlCl3

(C2H50) 3Si~PPh2] 2Ir4 (CO) 10

Ir4(CO) 11PPh3 + AlCI3

Ir4 (CO) 12 + Al + HC1

Ir4(CO)11PPh3 + Al + HCI

Ir(CO)Cl(PPh3)2 + Al + HCI

Al "^PPh2Ir(CO)PPh3


25C

N.A.


N.A.

N.A.


1000C


145C

CH C2 H6
CH4C1

N.A.

N.A.


Trace CH 3Cl



- N.A.

- N.A.

- N.A.

- N.A.

- Trace CH3C1


N.A. = no activity; SG = silica gel; Al = alumina.





A speculative mechanism for this reaction was proposed

as shown in Figure 3-1. Presumably oxidative addition of

hydrogen by the supported catalyst would generate a

dihydride species. Interaction of the Al-Cl or Si-Cl groups

with a bound carbonyl ligand of the iridium dihydride

species could induce rapid hydride migration to form a

formyl complex. This is similar to the alkyl migration onto

a bound carbonyl group in a (CH3)Mn(CO)5/AlBr3 system as

shown in Equation 3-9.153'154 The reaction then could





























I..

0







4/


o o
I I
I. -----I-O


00

n\

,.,. < .


Ij


4


Is, ~
Is


I





/


I
o-6
/
~ 4
-~.. I.... -
0.0


I

2a.


04
.1"

+


4-)
01
0 r-l
44 4-
(U
Q) U

ro
-r- r-i
r4 >1
0 rC










r- 0 (
SQ)


S-.4 *,




O 'O U
0 H 4-4
4J 14 0






00
On(U
0) (U1
0 .
r- 4-
Ue U-H
-H





U O



(L ) E

O< UU)


* .4-
(a
4


f-







75

proceed through the formation of a Lewis acid stabilized

formaldehyde complex or a hydroxymethyl type intermediate.

Finally, the formation of support 3-OCH3 groups or support

3-(CH3OH) groups in the presence of HC1(g) would produce the

observed methyl chloride.



,.CH3 ,CH3
(CO) 4Mn + AlBr3 (CO) 4Mn-C (3-9)
CO I "*\
Br *0
BAl
Br 'Br



The possibility of a methanol intermediate parallels

the fact that the current industrial process for methyl

chloride production involves the chlorination of methanol by

HC1 as shown in Equation 3-10.155 Methyl chloride is a

major commodity chemical with consumption in the range of



CH3 OH + HC1 2800C CH 3C + H20 (3-10)
Alumina



hundreds of thousands of metric tons annually. The major

uses of chloromethane include the production of methyl

chlorosilanes, tetramethyl lead and butyl rubbers.155 The

formation of methyl chloride from synthesis gas and HC1

under extremely mild conditions may be industrially useful.

For this reason, a further in-depth investigation into the

mechanism, as well as the optimization of this unique system

is warranted.







76

Experimental

Reagents

All metal complexes were used as purchased unless

otherwise stated. The IrCI3*3H20 and all the metal carbonyl

complexes were purchased from Strem Chemical Company. All

solvents, except 2-methoxyethanol and 2-ethoxyethanol, were

dried prior to use by distillation over CaH2. All solvents

were degassed with N2 prior to use. The alumina, acid

Brockman Activity I (80-200 mesh) and the mossy zinc metal

were purchased from Fisher Scientific Company. The alumina

was dried at 140C prior to use. This alumina was determin-

ed to have a specific area of 180 m 1/g.56 The silica gel,

Davison grade #62, purchased from W. R. Grace, was dried

under vacuum at 3000C prior to use. It had a specific area

of 340 m 2/g, a pore diameter of 14 mm and a pore volume of

1.1 cm3/g. The zeolite, LZY-82, was purchased from Alfa-

Thiokol. All silanes were purchased from Petrarch Chemical

Company and used without purification. The carbon monoxide

C. P. grade 99.5% and the hydrogen chloride technical grade

99.0% or semiconductor grade 99.995% were purchased from

Matheson Gas Products. The hydrogen was obtained from

Strate Welding. All carbon-13 isotopically labelled gases

were purchased from Merk, Sharp and Dohme Isotopes.

Instrumentation

All air sensitive manipulations were performed in a

Vacuum Atmosphere Co. model HE-43-2 inert atmosphere box or

in an Aldrich inert atmosphere glovebag. All syntheses were







77

performed under either a nitrogen or carbon monoxide

atmosphere. GC analyses were performed on either a model

3700 FID Varian gas chromatograph equipped with a Hewlett-

Packard 3390A integrator and a 1/8 inch x 8 foot stainless

steel 5% diethylene glycol adipate on chromosorb P (80/100)

column or on a model 940 FID Varian gas chromatograph

equipped with a 1/8 inch x 8 foot stainless steel poropak Q

(100/120) column. GC mass spectrometry was performed by Dr.

R. King of the Microanalytical Laboratory, University of

Florida, Gainesville, Florida. Samples were run on an AEI

MS 30 mass spectrometer with a KOITOS DS55 data station.

The system was equipped with a PYE Unicam 104 gas chromato-

graph containing a 1/4 inch x 5 foot poropak Q column.

Nuclear Magnetic Resonance spectra were obtained on a Varian

EM360L NMR spectrometer. Infrared spectra were obtained as

mulls on a Nicolet 5DXB FTIR spectrometer using KBr salt

plates. All elemental analyses for carbon, phosphorous and

iridium were performed by Galbraith Laboratories, Knoxville,

Tennessee. All ESCA data was obtained through the courtesy

of Dr. Tom Gentle, Dow Corning Corporation, Midland,

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

stainless steel ultra-high vacuum chamber 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 computer. All high pressure

experiments were performed using a 50 mL Parr pressure







78

bottle equipped with a brass or stainless steel Swagelok

pressure head.66

Fixed Bed Flow Reactor

A glass flow system as shown in Figure 3-2 was

assembled. This was modified from the previously described

system148 to allow the entire gas mixture to flow through

the catalyst. The individual gas flow rates were controlled

by three teflon needle valves (A, B and C). The CO and H2

were bubbled through mineral oil while the HC1 bubbler

contained sulfuric acid. The gases were allowed to flow

over the catalyst which was supported on a glass frit and

held in place with glass wool. The overall flow rate of the

gas mixture was monitored by a bubble flowmeter. The

temperature was regulated by a model 123-8 Lindberg thermo-

stated tube furnace that surrounded the reactor tube. Gas

samples for GC analyses could be obtained through two sample

ports, one prior to and one after the catalyst. Gas samples

were collected using a pressure-lok 2 mL syringe purchased

from Precision Sampling Corporation. Gases could be trapped

out through the addition of a glass spiral trap to the glass

reactor system. The spiral trap allowed for maximum contact

of the gas flow with the dry ice/acetone slush.

Preparation of Dicarbonylchloro(p-toluidine)iridium(I)

The IrCl(CO)2(p-toluidine) was prepared by a procedure

similar to that reported by Klabunde.157 Inside an inert

atmosphere glovebag a pressure bottle system containing 1.0 g

of IrCl 3*3H20, 0.30 g of lithium chloride and 50 mL of






















I cflO
4r1 L
U) 0
(a i-4
3: r&


0



1>


I>


o
I-)
Cfl >1 W
-~ >
'~ 0
4~i
C-)


.-4
0
01

i02-
*-4
O
(n
Cn







80

degassed 2-methoxyethanol was assembled. The pressure

bottle was charged with 45 psig of carbon monoxide and

allowed to react for several hours at 1300C. When the

initial black color had changed to yellow, the pressure

bottle system was cooled to room temperature. The pressure

bottle was dismantled under a nitrogen atmosphere and 0.35 g

of p-toluidine added. After several minutes of stirring,

the yellow solution was poured into a beaker containing 250

mL of distilled water. A purple precipitate was formed

immediately upon the mixing of the two solutions. The

precipitate was collected by vacuum filtration and dried

under vacuum for 24 hours. The purple solid was dissolved

in a minimum amount of benzene. Then a small amount of

anhydrous sodium sulfate was added to the stirred brown

solution. After several hours the solution was filtered.

The solvent was evaporated from the filtrate to give a

purple compound which was characterized by infrared spectro-

scopy to be IrCl(CO)2(p-toluidine). A typical yield was

approximately 85% based on the initial IrCl *3H2 0 complex.

Preparation of a Phosphinated Support

The phosphinated supports were prepared by a procedure

similar to that previously reported in the literature.144,145

Under a nitrogen atmosphere a total of 5.0 g of a dried

support, such as alumina, silica gel, or a zeolite was added

to a stirred solution of 150 mL of toluene. The mixture was

heated to reflux temperature prior to addition of 0.45 mL of







81

2-(diphenylphosphino)ethyltriethoxysilane,

(C2H50)3SiC2H4PPh2, by a syringe method. This reaction was

allowed to continue for 12 hours prior to collecting the

functionalized resin by vacuum filtration. The

functionalized support was dried under vacuum at room

temperature for 24 hours before use. This reaction gave a

phosphinated support containing 1.25 x 10-3 moles of

accessible phosphine substituents. Supports with different

phosphine concentrations were prepared in an analogous

manner. In experiments where the rest of the surface was

silanated with dichlorodiphenylsilane, an appropriate amount

of the silane was added by syringe 6 hours after the

2-(diphenylphosphino)ethyltriethoxysilane had been added.

Preparation of Supported Mono- and Di-phosphine Substituted
Tetrairidium Carbonyl Clusters

The phosphine substituted tetrairidium carbonyl cluster

was supported by a procedure similar to that reported by

Struder et al.151 and Castrillo et al..152'158 This

procedure was adopted from one reported by Stuntz and
159
Shapley for the formation of Ir4(CO) 11PPh3. Inside a

glovebag a total of 130 mL of 2-methoxyethanol and 5 mL of

water was added to a pressure bottle containing 5.0 g of a

phosphinated support (1.25 x 10-3 moles of phosphine) and

0.057 g of dicarbonylchloro(p-toluidine)iridium(I). The

amount of IrCl(CO)2(p-toluidine) used changed according to

the concentration of phosphine on the support that was used.

The 15.0 g of mossy zinc metal was placed into a teflon







82

basket suspended in the solution above the cylindrical 1/2

inch long stirbar. The pressure bottle was charged with 45

psig of carbon monoxide and heated to 950C. The reaction

was allowed to proceed for 12 hours. The slightly yellow

resin was collected by vacuum filtration, washed with

approximately 75 mL of toluene and dried under vacuum for 24

hours. The catalyst prepared in other solvents, such as

2-ethoxyethanol or toluene was done in an analogous manner.

The characterization of each catalyst by infrared

spectroscopy is discussed in the results section.

Preparation of Supported Tri-phosphine Substituted
Tetrairidium Carbonyl Clusters

The tri-phosphine substituted tetrairidium carbonyl

cluster was supported by a procedure similar to that report-

ed by Karel and Norton.160 A total of 1.3 g of Ir4(CO)12

was added to a stirred toluene solution containing 5.0 g of

a phosphinated support (1.25 x 10-3 moles of phosphine).

The reaction was allowed to proceed at reflux temperature

for 24 hours. The yellow resin was collected by vacuum

filtration and dried under vacuum for 24 hours. The

characterization of the catalyst by infrared spectroscopy is

discussed in the results section.

Preparation of Other Supported Phosphine Substituted Metal
Carbonyl Complexes

All other metal carbonyl complexes, such as Ru3(CO)12,

Os3(CO)12, Rh6(CO)16, Mn2(CO)10, Re2(CO)10, Co2(CO)8,

Fe(CO)5, IrCl(CO)3 and IrCl(CO)(PPh3)2 were supported in an

analogous manner to the preparation of the supported tri-







83

phosphine substituted tetrairidium cluster. Appropriate

amounts of the metal carbonyl complexes were added to

stirred toluene solutions containing 5.0 g of a phosphinated

support. The reaction was allowed to proceed at reflux

temperature for 24 hours. The resins were collected by

vacuum filtration and dried under vacuum for 24 hours. The

characterization of each catalyst by infrared spectroscopy

is discussed in the results section.

Preparation of Iridium Complexes Impregnated Onto a Support

The iridium complexes were impregnated onto a support

through the incipient wetness impregnation of the support

with a solution containing the metal complex. An

appropriate amount of an iridium complex, such as Ir4(CO) 12,

Ir(CO)3Cl or IrCl 3*3H20 was added to a stirred cyclohexane

solution containing 5.0 g of the support. The amount of

metal complex added was dependent upon the concentration of

iridium desired on the support. The mixture was allowed to

stir at room temperature for several hours. The supported

complexes were collected by vacuum filtration and dried

under vacuum for 24 hours. The characterization of each

catalyst by infrared spectroscopy is discussed in the

results section.

Reaction of Catalysts with Carbon Monoxide, Hydrogen and
HC1(g)

Prior to running the catalyst experiments, the blank

reactor tube was tested for any residual activity towards

methyl chloride formation. Then a total of 1.0 g of a