Iridium-carbon dioxide complex, coordination

The other carbon dioxide complex characterized by x-ray crystallography contains two linked C02 molecules in the coordination sphere (116). This complex, [IrCl(C204)(PMe3)3], was prepared by the interaction of C02 with chloro(cyclooctene)[tris(trimethylphosphine)]iridium(I), [IrCl(C8 H j 4)-(PMe3)3], in benzene solution. The structure, (25), shows essentially octahedral coordination about the iridium center, with one metal-carbon bond and a five-membered chelate ring formed with the second C02 molecule. 

In recent years, interest has intensified in the chemistry of carbon dioxide, stimulated by the current concern about alternate petrochemical feedstocks. One area under active exploration involves C02 activation via coordination to a transition metal complex.1 Several adducts of C02 have been claimed, and two monometallic complexes, with x-ray structures which have been published, are shown below schematically (1 and 2).2,3 We report here two examples of the preparation of 1 1 C02 adducts of a series of rhodium and iridium complexes and, relatedly, methods for preparing the 2 1 C02 lr complex 2. 

The combination of hard oxophilic early transition metals and soft nucleophilic late transition metals with opposite functionalities, provided they do not inhibit one another, is a priori ideal for promoting cooperative effect. A proof of concept can be found in the stoichiometric reactivity of early—late heterobimetallic complexes featuring a metal-metal bond [76]. It has been shown that such complexes are good candidates to realize the heterolytic cleavage of a bond in polar and apolar substrates. An illustrative example by Bergman et al. is the reaction of the Zr-lr complex 20 with carbon dioxide which leads to the rupture of the metal—metal bond (Scheme 18) [77]. The CO2 insertion occurs in the expected fashion with the CO2 bridging the two metals, the carbon atom coordinated to iridium, and the oxygen atom on the zirconium center. 

The iridium compound [IrCl(C8H,4)(PMe3)3] reacts with carbon dioxide to afford the complex (13.226). " Coordinated CO2 undergoes migratory insertion to the... 

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