Dirhodium(II) dicarboxylato complexes containing carbonyl and C-bonded methoxycarbonyl ligands

Oxidation of rhodium(I) carbonyl chloride, [Rh(CO)2Cl]2, with copper(II) acetate or isobutyrate in methanol solutions yields binuclear double carboxylato bridged rhodium(II) complexes with RhRh bonds, [Rh(μ-OOCRκO)(COOMeκC)(CO)(MeOH)]2, where R=CH3 or i-C3H7. According to X-ray data, surrounding of each rhodium atom in these complexes is close to octahedral and consists of another rhodium atom, two oxygens of carboxylato ligands, terminal carbonyl group, C-bonded methoxycarbonyl ligand, and axial CH3OH. Methoxycarbonyl ligand is shown to originate from CO group of the parent [Rh(CO)2Cl]2 and OCH3 group of solvent. N- and P-donor ligands L (p-CH3C6H4NH2, P(OPh)3, PPh3, PCy3) readily replace the axial MeOH yielding [Rh(μ-OOCRκO)(COOMeκC)(CO)(L)]2. The X-ray data for the complex with R=i-C3H7, L=PPh3 showed the same molecular outline as with L=MeOH. Electronic effects of axial ligands L on the spectral parameters of terminal carbonyl group are essentially the same as in the known series of rhodium(I) complexes (an increase of δ13C and a decrease of ν(CO) with strengthening of σ-donor and weakening of π-acceptor ability of L).