Bridged Complexes Obtained by In-situ Synthesis

A few stable C02 complexes resulting from a formal oxidation of metal carbonyl complex have been described. Although not strictly true C02 complexes, these are important intermediates in the photocatalytic and electrocatalytic reductions of C02 to formate and CO, and also in biologic systems. A few examples of such species are described below. 

In 1998, Gibson et al. reported [69] the synthesis of ruthenium x2-T 2-type C02-bridged complexes from the reaction of ds-Ru(phen)2(CO)(CHO)(PFs) with 02 in dimethyl ether (DME)/H20 (Ru(phen)2(C0)(C02)Ru(phen)2(C0))(PF,s)2, and of the related complex (Ru(phen)2(C0)(C02)Ru(bpy)2(C0))(PF6)2. The latter complex was structurally characterized as having the following values the OCO angle was 122.3° the CO bonds were 1.235 and 1.319 A and the IR bands for the carboxyl bridge were located at 1499 and 1183 cmA 

It is clear that C02 is in an activated state when the bonding involves the central carbon. The activation is evident from structural data such as the bent OCO moiety 

Three types of possible reaction of coordinated C02, illustrated with recent examples of the past decade, are described in the following sections. These include CO bond cleavage and oxygen transfer, reactions with electrophiles, and reactions with nucleophiles. 

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