Kinetic Study on the Coupling of CO2 and Epoxides Catalyzed by Co(III) Complex with an Inter- or Intramolecular Nucleophilic Cocatalyst

Abstract

Trivalent cobalt complexes of salicylaldimine in the presence of an inter- or intramolecular nucleophilic cocatalyst have proven to be excellent catalysts for the copolymerization of CO2 and epoxides to selectively afford the corresponding polycarbonates in perfectly alternating nature. Especially, bifunctional cobalt(III)–salen complexes bearing an appended quaternary ammonium salt are more efficient in catalyzing this copolymerization even at high temperatures and extremely low catalyst loading. The present study focuses on comparative kinetics of two different catalyst systems (binary catalyst system of salen(III)X 1/nBu4NX and bifunctional catalyst 2 bearing an appended quaternary ammonium salt, X = 2,4-dinitrophenoxide) for coupling CO2 and epoxides (propylene oxide or cyclohexene oxide) by means of in situ infrared spectroscopy. An induction period was readily found in the binary catalyst system, and its length significantly depends on catalyst loading. Contrarily, no induction period was observed i...