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[[(2′,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 CoCl<inf>2</inf>, FeCl<inf>2</inf>·4H<inf>2</inf>O, CuCl<inf>2</inf>·2H<inf>2</inf>O metal salts. The products of reaction with SNS-1 were three new tridentate pincer complexes [M(κ3-SNS-1)Cl<inf>2</inf>] (M = Fe, Co, Cu). The reactions of ligand SNS-2 yielded analogous complexes, [M(κ3-SNS-2)Cl<inf>2</inf>], for FeCl<inf>2</inf> and CoCl<inf>2</inf> but in the case of the reaction with CuCl<inf>2</inf> the product was an unanticipated Cu(I) complex [Cu(κ2-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 CO<inf>2</inf> and epoxides was investigated and the less sterically hindered Co(II) complex, [Co(κ3-SNS-1)Cl<inf>2</inf>] showed superior activity. The effects of variation in time, temperature, CO<inf>2</inf> pressure, and epoxide identity were investigated. © 2017