Synthesis of complexes Fe, Co and Cu supported by "SNS" pincer ligands and their ability to catalytically form cyclic carbonates

Abstract

Two pincer ligands, 2,6-bis[[(2'-methylphenyl)thio]methyl]pyridine (SNS-1) and 2,6-bis[[(20,6'-dimethylphenyl) thio]methyl]pyridine (SNS-2), each possessing a central pyridyl N-donor flanked by two thioether S-Ar functionalities were prepared and metallated with CoCl2, FeCl2 center dot 4H(2)O, CuCl2 center dot 2H(2)O metal salts. The products of reaction with SNS-1 were three new tridentate pincer complexes [M(kappa(3)-SNS-1)Cl-2] (M = Fe, Co, Cu). The reactions of ligand SNS-2 yielded analogous complexes, [M(kappa(3)-SNS-2)Cl-2], for FeCl2 and CoCl2 but in the case of the reaction with CuCl2 the product was an unanticipated Cu(I) complex [Cu(kappa(2)-SNS-2)Cl]. Single crystal X-ray diffraction analysis revealed that this Cu(I) complex displayed a bidentate S,N ligand and a pseudo-trigonal planar geometry for the Cu center. The ability of these metal complexes to catalyze the formation of cyclic carbonates from CO2 and epoxides was investigated and the less sterically hindered Co(II) complex, [Co(kappa(3)-SNS-1)Cl-2] showed superior activity. The effects of variation in time, temperature, CO2 pressure, and epoxide identity were investigated. Crown Copyright (C) 2017 Published by Elsevier B.V. All rights reserved.