SalenCo（Ⅲ）X Complexes Mediated CO₂/Phenyl Glycidyl Ether Alternating Copolymerization

Chemical fixation of CO2into useful organic compounds has received intense scrutiny over the past decade. This is a consequence of CO2being an inexpensive, abundant, nontoxic, and biorenewable resource. The development of suitable routes for the utilization of CO2has been the subject of multinational research laboratories. One of the most promising methodologies in this area is the alternating copolymerization of CO2and epoxides to afford polycarbonates, which have potential applications as ceramic binders, adhesives, and packaging materials, as well as in the synthesis of engineering thermoplastics and resins. As for this transformation, significant advances have been made for the design of efficient catalysts from multinational research programs. However, the scope of epoxides used in the copolymerization is very narrow, mostly propylene oxide and cyclohexene oxide and their derivatives. So, extending the scope of epoxides to prepare polycarbonates possessing a variety of properties is another important goal in this area.Trivalent Cobalt-based catalyst systems have proven to be efficient for catalyzing the coupling of CO2and epoxides. Particularly, the single-component SalenCo(III)X complexes with an intramolecular cocatalyst exhibit excellent activity and selectivity for the formation of polycarbonates from various epoxides including those with electron-withdrawing groups even at high temperatures and very low catalyst loading. Herein, we report the synthesis of the CO2copolymer with perfectly alternating nature from the copolymerization of CO2and phenyl glycidyl ether employing a single-component SalenCo(Ⅲ)X complex with an intramolecular cocatalyst,1,5,7-triabicyclo[4.4.0] dec-5-ene (designated as TBD). We performed the asymmertric, regio-and stereoselective copolymerization of CO2and racemic phenyl glycidyl ether using the chiral Co(Ⅲ)-based catalysts, and the results indicated that the SalenCo(III)X catalyst systems containing an inter-and intramolecular cocatalyst display an opposite chiral induction mechanism. The optically active polycarbonate with perfect head-to-tail linkage of more than99%was obtained from the enantiopure phenyl glycidyl ether. Importantly, the completely isotactic copolymer is a typical semicrystalline thermoplastic, which possesses a melting point of75℃.