Synthesis of heteroleptic copper(I) complexes with phosphine-functionalized thiosemicarbazones: An efficient catalyst for regioselective N-alkylation reactions

Abstract

Three new heteroleptic copper(I) complexes [Cu(PPh3)(PNS-H)] (1) (PNS-H=2-(2-(diphenylphosphino)benzylidene) thiosemicarbazone), [Cu(PPh3)(PNS-Me)] (2) (PNS-Me=2-(2-(diphenylphosphino)benzylidene)-4-methyl-3-thiosemicarbazone) and [Cu(PPh3)(PNS-Et)] (3) (PNS-Et=2-(2-(diphenylphosphino)benzylidene)-4-ethyl-3-thiosemicarbazone) have been synthesized and characterized by various spectral and analytical technique. The single-crystal X-ray diffraction study of complexes 2 and 3 confirmed the formation of complexes with Cu(I) ion, coordinated through P,N,S-donor atoms from the phosphino-thiosemicarbazone ligands. All the copper(I) complexes have been demonstrated as highly efficient catalysts for the synthesis of N-alkylated heterocyclic amine by the coupling of primary amines with alcohols at low catalyst loading, and the maximum yield was obtained up to 99%. The N-alkylation reactions were readily carried out under moderate conditions, and release of water was the only by-product. In addition, the effects of substituent’s on the ligand, solvents, base and catalyst loading on the catalytic activity of the complexes have also been investigated. Advantageously, only one equivalent of the alcohol was consumed in the process.