Nickel complexes of primary amido-functionalized N-heterocyclic carbene ligands: Synthesis, characterization, and base-free transfer hydrogenation

Three new nickel complexes featuring primary amido-functionalized N-heterocyclic carbene ligands have been synthesized and characterized using NMR spectroscopy, combustion analysis, and, in one case, single crystal x-ray diffraction. Each complex serves as a pre-catalyst for base-free transfer hydrogenation of aryl ketones in air using 2-propanol or 2-butanol as the solvent and hydrogen donor. Furthermore, in methanol-d(4) solutions of the nickel complexes, hydrogen-deuterium exchange is observed on the ligands at moderate temperatures. These nickel complexes represent rare examples of transfer hydrogenation catalysts that operate under base-free and aerobic conditions. (C) 2018 Elsevier B.V. All rights reserved.