Synthesis of a CCC‐NHC pincer Re complex: An air stable catalyst for coupling ketones with primary alcohols via borrowing hydrogen

Abstract

To date, no CCC‐NHC pincer complexes of Re have been reported in the literature. The first CCC‐NHC pincer complex of Re is reported. It was fully characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy, elemental analysis, and X‐ray crystallographic methods to determine the molecular structure. It was synthesized via transmetallation from an isolated Zr precursor and was found to be air stable. The catalytic activity of the CCC‐NHC Re(I) pincer complex was demonstrated for the borrowing hydrogen coupling reaction between benzylic ketones and primary alcohols to generate a new C–C bond in an environmentally friendly catalysis requiring no activating groups for the alcohol functionality. This borrowing hydrogen coupling reaction produced a stoichiometric amount of water as the only by‐product and did not require the conversion of the primary alcohol to a leaving group. A broad range of substrates was examined, and isolated yields from 53% to 92% were obtained. A catalytic cycle for the CCC‐NHC Re(I) pincer complex catalyzed borrowing hydrogen coupling reaction is proposed.