(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 [(η5-Cp*)­Rh­(L)­Cl]­[PF6] (1–3) and [(η5-Cp*)­Ir­(L)­Cl]­[PF6] (4–6) have been prepared by reacting L = L1–L3 (1,2-bis­(phenylthio)­ethane (L1), 1-(phenylseleno)-2-(phenylthio)­ethane (L2) and 1,2-bis­(phenylseleno)­ethane (L3)) with [(η5-Cp*)­RhCl­(μ-Cl)]2 and [(η5-Cp*)­IrCl­(μ-Cl)]2, respectively, at room temperature followed by treatment with NH4PF6. Their HR-MS and 1H, 13C­{1H}, and 77Se­{1H} 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 × 102 and 9.8 × 103, 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.