Pd, Ni, Fe and Cu complexes containing a novel SNS-pincer ligand bearing pyridine: Synthesis and catalytic application to form cyclic carbonates

Abstract

A new SNS pincer type ligand, 2,6-bis[[(4-bromophenyl)thio]carbonyl]pyridine (L) and its metal complexes (L-Pd, L-Ni, L-Fe, L-Cu) were synthesized and characterized by using X-ray (for ligand), NMR (for ligand), UV-Vis, FT-IR, mass, elemental analysis techniques. The products of reaction with L were new bidentate pincer complex [Pd(κ2-L)(OAc)2] and three tridentate pincer complexes [M(κ3-L)(OAc)2] (M = Fe, Ni, Cu). The molecular structure of ligand (L) was characterized by X-ray single crystal structure determination. The molecular structures of Fe, Cu, and Ni complexes exhibit a five-coordinate distorted trigonal bipyramidal geometry around their metal centers, while the Pd complex exhibits a four-coordinated square plane structure. Moreover, the compounds were used to obtain cyclic carbonates from the reaction of epoxide and CO2 as catalysts. The best performance was obtained in the presence of L-Pd catalyst and DMAP as co-catalyst, with a 93.9% yield and 98.9% selectivity.