Efficient Catalysis of Transfer Hydrogenation of Ketones and Oxidation of Alcohols with Newly Designed Half-Sandwich Rhodium(III) and Iridium(III) Complexes of Half-Pincer Chalcogenated Pyridines

The in situ generated ArE- (E = S or Se) reacts with (2-chloromethyl)pyridine in N-2 atmosphere, resulting in half-pincer (N, S/Se) ligands (2-arylchalcogenomethyl)pyridine (L1-L3; aryl = Ph/2-pyridyl for S, Ph for Se). Half-sandwich complexes [(eta(5)-Cp*)Rh(L)Cl][PF6] (1, 2), [(eta(5)-Cp*)Rh(L2)CH3CN]PF6](2) (3), and [(eta(5)-Cp*)Ir(L)Cl][PF6] (4-6), where L = L1-L3, have been synthesized by reacting L with [(eta(5)-Cp*)RhCl(mu-Cl)](2) and [(eta(5)-Cp*)IrCl(mu-Cl)](2) respectively. The ligands and complexes have been characterized by IR, HR-MS, and H-1, C-13{H-1}, and Se-77{H-1} NMR spectra. The single-crystal structures of all the complexes (1-6) have been determined with X-ray crystallography [Rh-S, Rh-Se, Ir-S, Ir-Se bond distances: 2.383(2)12.353(2), 2,4867(9), 2.343(2)/2.341(3), 2.453(1) angstrom, respectively]. Each metal has pseudo-octahedral half-sandwich piano-stool geometry. The PF6- ions in crystals are packed between half-sandwich complex molecules, resulting in various H center dot center dot center dot F secondary interactions. Complexes 1-6 have been explored for catalysis of oxidation of secondary alcohols with N-methylmorpholine-N-oxide and transfer hydrogenation reaction of ketones with 2-propanol and found very efficient, as revealed by TON values, which are up to 9.6 X 10(3) and 9.8 X 10(3) respectively for the two catalytic reactions. The formation of the M H bond has been noticed in the intermediates of both the catalytic reactions. DFT calculations indicate a reactivity order for the complexes of Rh > Ir, which is also found for the two catalytic reactions experimentally. The calculated (DFT) and observed bond distances and angles of 1-6 are reasonably close.