Carbon monoxide homogeneous catalysis

Oxidation of carbon monoxide by metal ions and homogeneous catalysis of the water gas shift reaction and related processes. J. Halpern, Comments Inorg. Chem., 1981,1, 3-15 (42). 

S. Cenini, M. Pizzotti, and C. Crotti, Metal Catalyzed Deoxygenation Reactions by Carbon Monoxide of Nitroso and Nitro Compounds (D. Reidel Publishing), 6, (Aspects of Homogeneous Catalysis A Series of Advances), 97-198 (1988). 

A major advance in homogeneous catalysis was the introduction of a trialkyl-phosphine to supplement the role of carbon monoxide in catalyst stabilization. [3] A ligand modifier such as trialkylphosphine serves three principal roles in a homogeneous catalytic process. It stabilizes the metal, it influences the reaction rate, and it influences process selectivity. 

The reaction between alkenes and synthesis gas (syngas), an equimolar mixture of carbon monoxide and hydrogen, to form aldehydes was discovered in 1938 by Otto Roelen [1,2]. Originally called oxo-reaction , hydroformyla-tion is the term used today. This reflects the formal addition of formaldehyde to the olefinic double bond. Commercially, homogeneous metal complexes based on cobalt and rhodium are used as catalysts. With more than 10 million metric tons of oxo products per year, this reaction represents the most important use of homogeneous catalysis in the chemical industry. 

Insertion of carbon monoxide and alkenes into metal-carbon bonds is one of the most important reaction steps in homogeneous catalysis. It has been found for insertion processes of platinum [16] that the relative positions of the hydrocarbyl group and the unsaturated fragment must be cis in the reacting complex [17], The second issue concerns the stereochemical course of the reaction, insertion versus migration as discussed in Chapter 2.2. 

The prototypical C-C bond forming hydrogenation, hydroformylation combines basic feedstocks (a-olefins, carbon monoxide, and hydrogen) with perfect atom economy and accounts for the production of over 10 million metric tons of aldehyde annually, making it the largest volume application of homogeneous metal catalysis. 

Relatively few hydroformylations using supported cobalt complexes have been reported. Moffat (78, 79) showed that poly-2-vinylpyridine reversibly reacted with both Co2(CO) and HCo(CO)4, the cobalt carbonyl being displaced by excess carbon monoxide. This enabled the polymer to pick up the cobalt carbonyl at the end of the reaction and, thus, allowed it to be separated from the products by filtration. The polymer acted as a catalyst reservoir by rapidly releasing the cobalt carbonyl into solution in the presence of further carbon monoxide, so that the actual catalysis was a homogeneous process. More recently, cobalt carbonyl has been irreversibly bound to a polystyrene resin... 

Chemistry of Hydridoniobium Complexes Approaches to Homogeneous Catalysis of the Carbon Monoxide-Hydrogen Reaction... 

A different homogeneous catalyst system for the carbon monoxide reduc-tition of NO is based on transition metal dinitrosyl complexes and has been investigated by both Johnson and co-workers (184,186, 235), and Ibers and co-workers (185, 236). In 1973 Johnson and Bhaduri (184) reported the separate reactions (116) and (117) which appeared to presage catalysis of NO reduction via (113). Shortly thereafter, Haymore and Ibers (185) showed that Ir(NO)2L2 + and related dinitrosyl... 

If a chemical reaction is operated in a flow reactor under fixed external conditions (temperature, partial pressures, flow rate etc.), usually also a steady-state (i.e., time-independent) rate of reaction will result. Quite frequently, however, a different response may result The rate varies more or less periodically with time. Oscillatory kinetics have been reported for quite different types of reactions, such as with the famous Belousov-Zha-botinsky reaction in homogeneous solutions (/) or with a series of electrochemical reactions (2). In heterogeneous catalysis, phenomena of this type were observed for the first time about 20 years ago by Wicke and coworkers (3, 4) with the oxidation of carbon monoxide at supported platinum catalysts, and have since then been investigated quite extensively with various reactions and catalysts (5-7). Parallel to these experimental studies, a number of mathematical models were also developed these were intended to describe the kinetics of the underlying elementary processes and their solutions revealed indeed quite often oscillatory behavior. In view of the fact that these models usually consist of a set of coupled nonlinear differential equations, this result is, however, by no means surprising, as will become evident later, and in particular it cannot be considered as a proof for the assumed underlying reaction mechanism. 

These experiments strongly indicate that hydrogenations that proceed in the presence of cobalt and a high partial pressure of carbon monoxide very likely proceed by homogeneous catalysis in which either [Co(CO)4]2 or HCo(CO)4 or both function as the catalyst. 

Carbon monoxide and ethylene are common substrates involved in homogeneous catalysis. The bonding of carbon monoxide to a transition metal has been depicted in Fig. 4.4. The bonding of alkenes to transition metals is described by the Chatt-Dewar-Duncanson scheme involving c donation by the filled it orbital of the alkene, and n back donation from the metal into the n orbital of the alkene (see Fig. 4.6). 

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