Polyoxoanion-Supported Organometallic Complexes: Carbonyls of Rhenium(I), Iridium(I), and Rhodium(I) That Are Soluble Analogs of Solid-Oxide-Supported M(CO)n+and That Exhibit Novel M(CO)n+Mobility

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Abstract
The Dawson-type P2W15Nb3O629- polyoxoanion-supported Re(CO)3+ complex, [Re(CO)3·P2W15Nb3O62]8- (1), has been synthesized and characterized in two different counter-cation compositions. The [(n-C4H9)4N]88+ complex provides a highly soluble compound which exists as a single isomer in solution. The carbonyl stretching infrared frequencies suggest that the P2W15Nb3O629- ligand serves as a strong electron donor to the Re(CO)3+ fragment. The P2W15Nb3O629- polyoxoanion-supported Ir(CO)2+ complex [Ir(CO)2·P2W15Nb3O62]8- (2) has also been synthesized and characterized as its octakis(tetrabutylammonium), [(n-C4H9)4N]88+, salt. This compound was characterized by NMR and IR, results which demonstrate that 2 also exists as a single isomer in solution. The [Ir(CO)2·P2W15Nb3O62]8- complex is stable in the absence of water, but decomposes quickly in the presence of even 1 equiv of water. Attempted preparation of the analogous P2W15Nb3O629- -supported Rh(CO)2+ complex (3), while monitoring by 31P NMR, revealed that this compound is unstable in solution at room temperature. In addition, we have discovered that added Na+ can induce the formation of non-C3v symmetry isomers of supported Re(CO)3+ and Ir(CO)2+ and, by inference, supported Ir(1,5-COD)+. When Na+ is removed from these systems by addition of Kryptofix[2.2.2], the non-C3v isomers convert back to the single, C3v isomer with heating, thereby providing a model system for the little studied mobility of M(CO)n+ cations across a soluble-oxide surface. When [Rh(CO)2·P2W15Nb3O62]8- is irradiated in the presence of hydrogen and cyclohexene a novel polyoxoanion-stabilized Rh0n nanocluster is formed, results that bear a strong analogy to Yates' work studying atomically-dispersed Rh(CO)2+ on solid Al2O3.10e Yates and co-workers observe that Rh(CO)+·Al2O3 loses a CO upon photolysis, and that the resultant Rh(CO)1+·Al2O3 is reduced under H2 to form Rh(0), which in turn yields Rh0n clusters on Al2O3a process that, intriguingly, is largely reversible if CO is readded. Also briefly discussed is other relevant literature of solid-oxide-supported Re(CO)3+ and M(CO)2+ (M = Ir, Rh), literature that makes apparent the potential significance of these complexes as EXAFS and other spectroscopic models of solid-oxide-supported M(CO)n+.

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