Hydroxycarbonyl-metal complexes, decarboxylation

Scheme 1. Decarboxylation from hydroxycarbonyl- and C02-metal complexes.

In this context we postulated that the shift reaction might proceed catalytically according to a hypothetical cycle such as Scheme I. There are four key steps in Scheme I a) nucleophilic attack of hydroxide or water on coordinated CO to give a hydroxycarbonyl complex, b) decarboxylation to give the metal hydride, c) reductive elimination of H2 from the hydride and d) coordination of new CO. In addition, there are several potentially crucial protonation/deprotonation equilibria involving metal hydrides or the hydroxycarbonyl. The mechanistic details have been worked out (but only incompletely) for a couple of the alkaline solution WGSR homogeneous catalysts. In these cases,... 

Formation of Bonds between Hydrogen and Transition Metals 1.10.9 by Decarboxylation of Hydroxycarbonyl or Formate Complexes. 

The hydroxycarbonyl complex generated by the attack of OH on the coordinated CO (Scheme 1.34a) is susceptible to decarboxylation affording a metal hydride, which may react with a proton to produce H2. The process is considered to be involved in catalytic conversion of CO and H2O into CO2 and H2 (the water gas shift reaction) as shown in Eq. 1.17. 

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