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 2 , FeCl 2 ·4H 2 O, CuCl 2 ·2H 2 O metal salts. The products of reaction with SNS-1 were three new tridentate pincer complexes [M(κ 3 - SNS-1 )Cl 2 ] (M = Fe, Co, Cu). The reactions of ligand SNS-2 yielded analogous complexes, [M(κ 3 - SNS-2 )Cl 2 ], for FeCl 2 and CoCl 2 but in the case of the reaction with CuCl 2 the product was an unanticipated Cu(I) complex [Cu(κ 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 CO 2 and epoxides was investigated and the less sterically hindered Co(II) complex, [Co(κ 3 - SNS-1 )Cl 2 ] showed superior activity. The effects of variation in time, temperature, CO 2 pressure, and epoxide identity were investigated.