Ruthenium(II) complexes containing phosphino hydrazone/thiosemicarbazone ligand: An efficient catalyst for regioselective N-alkylation of amine via borrowing hydrogen methodology

Abstract

In the aspect of more effective ruthenium based catalyst design, three new ruthenium(II) phosphino-hydrazone/thiosemicarbazone complexes (1–3) have been synthesized by the reactions of cis-[RuCl2(dmso)4] or [RuHCl(CO)(AsPh3)3] with deprotonated 2-(2-(diphenylphosphino)benzylidene)-2-thiophenecarboxylic acid hydrazone (PNO-Thy) or 2-(2-(diphenylphosphino)benzylidene)-4-phenyl-3-thiosemicarbazone (PNS-Ph). The structures of the complexes (2 and 3) were established by X-ray crystallography and spectroscopic methods including elemental analysis, FT-IR and NMR (1H, 13C & 31P). Single crystal XRD upshots of complexes (2 and 3) revealed a distorted octahedral geometry around the ruthenium ion with hydrazone/thiosemicarbazone acts as a monoanionic tridentate PNO/PNS donor fashion. The catalytic study of complexes 1–3 towards regioselective N-alkylation reactions of amines was completed, showing that all catalysts are active toward catalytic transformations. Notably, complex 3 was found to be very efficient catalysts toward N-alkylation of a wide range of heterocyclic amines with alcohols. This catalysis provides a clean, convenient and practical route for the direct N-alkyl amine synthesis. © 2018 Elsevier B.V.