Rhodium bis(quinolinyl)benzene complexes for methane activation and functionalization

A series of rhodium(III) bis(quinolinyl)benzene (bisq^x) complexes was studied as candidates for the homogeneous partial oxidation of methane. Density functional theory (DFT) (M06 with Poisson continuum solvation) was used to investigate a variety of (bisq^x) ligand candidates involving different functional groups to determine the impact on Rh^III(bisq^x)-catalyzed methane functionalization. The free energy activation barriers for methane C-H activation and Rh-methyl functionalization at 298 K and 498 K were determined. DFT studies predict that the best candidate for catalytic methane functionalization is Rh^III coordinated to unsubstituted bis(quinolinyl)benzene (bisq). Support is also found for the prediction that the η²-benzene coordination mode of (bisq^x) ligands on Rh encourages methyl group functionalization by serving as an effective leaving group for S_N2 and S_R2 attack.