Well-Defined ENENES Re and Mn Complexes and Their Application in Catalysis: The Role of Potassium tert-Butoxide

A new family of air-stable Re and Mn complexes bearing bidentate NNS (ENENES) ligands with the general formula E(CH2)2NH(CH)2SR (E = −NC4H8O or −NC5H10, R = Ph or thiophenyl) is introduced. All Re and Mn complexes were catalysts for the hydrogenation of aldehydes. The Mn catalysts were active at milder conditions. A rhenium–hydride complex, featuring cis Re–H and N–H moieties, was isolated to provide an insight into the mechanism for this reaction. DFT (B3PW91-D3) and experimental data suggest that there are two pathways for this system, with and without the presence of the base (t-BuOK). The pathway that included t-BuOK was lower in energy, providing a greater driving force for the overall reaction.