(η5-Cp*)Rh(III)/Ir(III) Complexes with Bis(chalcogenoethers) (E, E′ Ligands: E = S/Se; E′ = S/Se): Synthesis, Structure, and Applications in Catalytic Oppenauer-Type Oxidation and Transfer Hydrogenation

The air- and moisture-insensitive half-sandwich complexes [(eta(5)-Cp*)Rh(L)Cl][PF6] (1-3) and [(eta(5)-Cp*)Ir(L)Cl][PF6] (4-6) have been prepared by reacting L = L1-L3 (1,2-bis(phenylthio)ethane (L1), 1-(phenyl-seleno)-2-(phenylthio)ethane (L2) and 1,2-bis(phenylseleno)ethane (L3)) with [(eta(5)-Cp*)RhCl(mu-Cl)](2) and [(eta(5)-Cp*)IrCl(mu-Cl)](2), respectively, at room temperature followed by treatment with NH4PF6. Their HR-MS and H-1, C-13{H-1}, and Se-77{H-1} NMR spectra have authenticated them. The single-crystal structures of 1- 6 have been established by X-ray crystallography. Complexes 1-6 have been explored for catalytic Oppenauer-type oxidation of alcohols and transfer hydrogenation of ketones with 2-propanol. 3 and 6 were the most efficient in the two catalytic reactions (TON values up to 9.9 X 10(2) and 9.8 X 10(3), respectively) and were therefore investigated in detail. 3 is the first example of a Rh(III) species explored for Oppenauer-type oxidation. The catalysis appears to be homogeneous. In transfer hydrogenation it appears that one of the catalytic species is without a Cp* ring. DFT calculations indicate higher reactivity for Rh complexes in comparison to Ir complexes. This order has also been found for the two catalytic reactions experimentally. The calculated bond lengths/angles by DFT are generally consistent with the experimental values.