Copolymerization of CO₂ and Epoxides Catalyzed by Metal Salen Complexes

Abstract

The design of efficient metal catalysts for the selective coupling of epoxides and carbon dioxide to afford completely alternating copolymers has made significant gains over the past decade. Hence, it is becoming increasingly clear that this "greener" route to polycarbonates has the potential to supplement or supplant current processes for the production of these important thermoplastics, which involve the condensation polymerization of diols and phosgene or organic carbonates. On the basis of the experiences in our laboratory, this Account summarizes our efforts at optimizing (salen)CrIIIX catalysts for the selective formation of polycarbonates from alicyclic and aliphatic epoxides with CO2. An iterative catalyst design process is employed in which the salen ligand, initiator, cocatalyst, and reaction conditions are systematically varied, with the reaction rates and product selectivity being monitored by in situ infrared spectroscopy.

Alternating Copolymerization of Carbon Dioxide and Cyclohexene Oxide and Their Terpolymerization with Lactide Catalyzed by Zinc Complexes of N,N Ligands

“…[5] Over the last decade the use of homogeneous catalysts has lead to a drastic increase in catalytic activities. [6][7][8] For the copolymerization of CO 2 and propylene oxide, salen complexes, especially of chromium [9,10] and cobalt [11][12][13] have come into focus. Yet, the highest activities for the alternating copolymerization of CO 2 and cyclohexene oxide so far have been reached by Coates' bdiketiminato (BDI) zinc complexes (see below).…”

Pyrazole Supported Zinc(II) Benzoates as Catalysts for the Ring Opening Copolymerization of Cyclohexene Oxide and Carbon Dioxide

“…In addition to producing PCHC, the copolymerization reactions catalyzed by 1-4 also led to the production of cyclic cyclohexene carbonate (CCHC) as a byproduct. This is generally the result of back-biting of the growing copolymer chain [27].…”

Ionic Liquids in Green Carbonate Synthesis

“…Inoue et al first reported the synthesis of high molecular weight polycarbonates by alternating copolymerization of CO 2 and epoxides using a catalyst derived from diethyl zinc and water [116]. Since then, several excellent reviews [117][118][119][120][121] have appeared on this interesting topic. It is demonstrated that coordination compounds based on zinc, aluminum, cadmium, chromium, manganese, cobalt, and rare-earth metals are promising candidates for highly active catalytic systems for the copolymerization of epoxides with CO 2 .…”