- Activation of carbon monoxide by (Me3tpa)Rh and (Me3tpa)Ir
- Volume | Issue number
- 28 | 6
- Pages (from-to)
- Document type
- Faculty of Science (FNWI)
- Van 't Hoff Institute for Molecular Sciences (HIMS)
Cationic iridium and rhodium carbonyl complexes supported with the tetradentate N-donor ligand Me(3)tpa (Me(3)tPa = N,N,N-tri(6-methyl-2-pyridylmethyl)amine) were synthesized. Their structures were investigated using X-ray diffraction, NMR, and IR, and their redox properties were probed using cyclic voltammetry and EPR spectroscopy. Iridium forms a trigonal bipyramidal 18 VE biscarbonyl complex, while rhodium forms a square-planar 16 VE monocarbonyl species. In both compounds the Me3tpa ligand coordinates in a kappa(3) rather than the expected kappa(4) mode and is fluxional on the NMR time scale. Complex [Ir(kappa(3)-Me(3)tpa)(CO)(2)]PF6 (2(+)) reacts at room temperature with methanol and water to form the methoxycarbonyl iridium compound [Ir(kappa(3)-Me(3)tpa)(CO)(H)(COOMe)]PF6 (4(+)) and the hydroxycarbonyl iridium compound [Ir(kappa(3)-Me(3)tpa)(CO)(H)(COOH)]PF6 (5(+)), respectively. The hydroxycarbonyl iridium complex 5(+) is not stable and decomposes to bis-hydride iridium complex [Ir(kappa(3)-Me(3)tpa)(CO)(H)(2)]PF6 (6(+)), thus illustrating subsequent steps of the water gas shift reaction. Complex 2(+) is converted to [Ir(kappa(4)-Me(3)tpa)(CO)(H)](PF6)(2) (7(+)) upon one-electron oxidation with AgPF6. Rhodium complex [Rh(kappa(3)-Me(3)tpa)(CO)]PF6 (3(+)) is selectively oxygenated by 02 in the presence of water to form the carbonato rhodium complex [Rh(kappa(3)-Me(3)tpa)(CO3)]PF6 (8(+)). This represents a rare example of formation of a stable rhodium carbonate complex via oxygenation of a coordinated CO molecule.
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