Reduction of Carbene Complexes

Reduction of carbene complexes of group 6 metals leads to their decomposition, or does not proceed at all because of unfavorable changes in oxidation states. Nevertheless, reduction reactions are known for carbene complexes of group 8 elements. 

In these compounds, the carbene carbon atom is prochiral. However, during reduction, no asymmetric induction was observed enantiomers are formed in equal quantities (the Fe atom may also be asymmetric). 

The following iridium carbene complex may be reduced by hydrogen as recently described  

The reductive removal of carbene ligands by means of lithium aluminum hydride does not proceed in a satisfactory manner good results may be obtained by hydrogen reduction. 

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