Homogeneous Reduction of Carbon Monoxide

In spite of the wealth of information available on organomeiallic model compounds discussed in the previous part, only a few examples of catalytic homogeneous reductions of CO are known. Very often it is difficult to decide whether the reaction is truly homogeneous. Frequently the yields are low, which is indicative of the occurrence of stoichiometric reactions. For the reduction of CO two principal ways can be considered  

Reduciion ofCO with reducing agents other than molecular hydrogen, direct reduction of CO with hydrogen 

REDUCTION 01- CO WITH REDUCING AGENTS OTHER THAN MOUCLLAR HYDROGEN 

Shriver could show that oxyjten proionation of an iron cluster with MjSOsCFs gave methane (Equation (44)) ( 4). 

Isotopic experiments demonstrated that the carbon in CH4 originated from a carbonyl carbon. The yield of methane is sensitive to the acidity thus, no methane is produced with a 1 1 mixture of HS03CFji/H2 0. A possible mecha nism is attack on the oxygen of CO by protons, splitting off uratcr and thus forming a carbide which subsequently is attacked by H to produce methane (Equation (45)). 

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Although most of known homogeneous reductions of carbon monoxide with hydrogen catalyzed by carbonyl complexes produce a mixture of oxygenated products, the iridium carbonyl species Ir4(CO)i2 has proved to catalyze the following homogeneous methanation reaction in toluene solutions. 

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