Structure, UV spectroscopic and electrochemical properties of 2-methyl-8-quinolinolato rhodium (I) complexes, containing carbonyl, triphenylphosphine or triphenylphosphite ligands

The known Rh(2-Me-8-Oxq)(CO)2 complex (1) was prepared through treatment of dicarbonyl(acetylacetonate)rhodium (I) with 2-methyl-8-hydroxyquinoline for the first time. The reactions of 1 with triphenylphosphine and triphenylphosphite result in complexes Rh(2-Me-8-Oxq)(PPh3)(CO) (2) and Rh(2-Me-8-Oxq)[P(OPh)3](CO) (3) that were characterized by IR and NMR spectroscopy. The structures of complexes 2 and 3 were determined by single-crystal X-ray diffraction analysis. The complexes show the 2-methyl-8-quinolinolato ligand in the expected coordination mode with a slightly disordered square planar geometry at the rhodium center. In the crystal, molecules of Rh(2-Ме-8-Oxq)(CO)(PPh3) (2) form centrosymmetric dimers due to π-stacking interactions. No intermolecular contacts are observed in the crystal of 3. The UV spectroscopic and electrochemical properties of complexes 1–3 were studied. Their electronic spectra in CH3CN show three quinoline-centered absorptions. The electrochemical study revealed that the oxidation of the complexes 1–3 is two-electron and leads to the formation of dication Rh (III) species while their reduction gives radical anions, which undergoes rapid decomposition.