Metal carbonyls redox condensation with carbonyl anions

The reaction of metal earbonyl complexes with carbonyl anions is a widely used technique for synthesis of mixed-metal clusters. This reaction is also termed reductive condensation or redox eondensation. The metal carbonyl anion may be generated in situ or may be separately isolated. The mixed-metal product is usually an anion protonation can be used to generate a neutral cluster hydride. 

Redox condensation of an anionic mono or polynuclear carbonyl species with a neutral, cationic, or anionic fragment provides a valuable method for the synthesis of carbonyl metal clusters. 

Related synthetic routes include the redox condensation reaction of carbonylate anions with neutral carbonyls, e.g., Eq. (12) (55), metal exchange reactions between carbonylate anions, e.g., Eq. (13) (56), and direct reductive carbonylation of metal halides, e.g., Eq. (14) (57). The stoichiometry of the products are not rational, and the mechanisms clearly are very complicated, though once again these reactions, under experimental optimization, can provide very useful synthetic routes. 

The reaction of a carbonylmetalate with a neutral metal carbonyl has been labeled a redox condensation by Chini et al. (40, 41) and has been as widely used as a pyrolysis reaction for synthesizing mixed-metal clusters. Carbonylmetalates usually react rapidly with most neutral carbonyls, even under very mild conditions. A large number of mixed-metal hydride clusters have been formed via this type of reaction, primarily because the initial products are anionic clusters that in many cases may be protonated to yield the neutral hydride derivative. 

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