Transfer hydrogenation of ketones catalyzed by nickel complexes bearing an NHC [CNN] pincer ligand

Abstract

Four NHC [CNN] pincer nickel (II) complexes, [iPrCNN (CH2)4‐Ni‐Br] (5a), [nBuCNN (CH2)4‐Ni‐Br] (5b), [iPrCNN (Me)2‐Ni‐Br] (6a) and [nBuCNN (Me)2‐Ni‐Br] (6b), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl2 in the presence of Et3N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b. With a combination of NaOtBu/iPrOH/80 °C and 2% catalyst loading of 5a, 77–98% yields of aromatic alcohols could be obtained.