Selective coupling of carbon dioxide and epoxystyrene via salicylaldimine-, thiophenaldimine-, and quinolinaldimine-iron(II), iron(III), chromium(III), and cobalt(III)/Lewis base catalysts

Abstract

A series of chromium(III)-, cobalt(III)-, and iron(III)-based complexes of the general formula [(N∩O)2MCl] (1–7) (N∩O: N-salicylidene(R)amine, R = 1-naphthyl or cyclohexyl) have been applied as catalysts for the coupling reaction of carbon dioxide and epoxystyrene (styrene oxide) in the presence of tetrabutylammonium bromide (Bu4NBr) as a cocatalyst. The reactions were carried out under relatively low pressure and solvent-free conditions. In addition, iron complexes (8–10) containing the ligands, N′-(thiophene-2-methylene)benzene-1,2-diamine, (8), N′-(quinoline-2-methylene)benzene-1,2-diamine (9), and sodium N-(4-sulfonato-salicylidene)-1,2-phenylenediamine (10) were also utilized for the catalytic reaction. The influence of metal center, ligand, temperature, and reaction time on the coupling reaction was investigated. The catalyst systems proved to be selective in the coupling reaction of CO2 and styrene oxide, resulting in cyclic styrene carbonate. In general, the iron(III)- and cobalt(III)-based catalysts bearing the aromatic 1-naphthyl terminal groups showed the highest catalytic activity under similar reaction conditions.