Hydroxycarbonyl complexes as key intermediates in the base-assisted reduction of ruthenium carbonyls

Abstract

Since the recognition of metal-hydroxycarbonyl (or, metallacarboxylic acid) as a key intermediate in water gas shift (WGS) catalysis, numerous metal complexes incorporating hydroxycarbonyl ligands have been synthesized. In this Perspective, a brief account on the chemistry of metallacarboxylic acid and metallacarboxylate is presented. Special emphasis is placed on the hydroxycarbonyl-bridged dinuclear compounds. The relevance of hydroxycarbonyl complexes in the base-assisted reduction of ruthenium carbonyls is investigated. In particular, Lavigne's synthesis of Roper's catalyst Ru(CO)₂(PPh₃)₃, triruthenium dodecacarbonyl Ru₃(CO)₁₂, and Bera's mechanistic investigation on the preparation of the metal–metal singly bonded diruthenim(I) complex [Ru₂(CO)₄(CH₃CN)₆]²⁺ are described in detail. These reactions involve the decarboxylation of a “[Ru_m(COOH)_n]” species, followed by the reductive elimination of HX (X = H, Cl or OH), steps akin to WGS catalysis. The prospect of hydroxycarbonyl chemistry in the development of bimetallic catalysis is examined.