Chiral SalenCr and SalanCr complexes with bulky substituents for asymmetric alternating copolymerization of cyclohexene oxide with carbon dioxide or phthalic anhydride

Abstract

A series of new chiral salenCr and salanCr complexes bearing (R,R)-1,2-diaminocyclohexane backbone with bulky substituents (cumyl, 1,1-diphenylethyl and trityl) at the ortho-position of the aryloxide moieties were synthesized and investigated as catalysts in the asymmetric copolymerization of cyclohexene oxide (CHO) with CO2 or phthalic anhydride (PA). The substituents of the Cr complexes affect the catalytic activity as well as stereoselectivity greatly toward the copolymerizations. The different salen/salan backbones of the Cr complexes also play an important role on catalytic performance. Poly(cyclohexene carbonate)s (PCHCs) with number-average molecular weight (Mn) of 4.8-9.1 kg·mol−1 and 19.0-19.4% enantiomeric excess (ee) value of the 1,2-cyclohexanediol unit were prepared by using salenCr with 1,1-diphenylethyl groups and salanCr with cumyl or 1,1-diphenylethyl groups as catalyst, respectively. Poly(cyclohexene phthalate)s (PCHPs) with Mn of 1.6 kg·mol−1 and ee value of 7.1-8.7% were obtained by using salenCr with cumyl or 1,1-diphenylethyl groups as catalyst, respectively. While, the salanCr complexes resulted in atactic PCHPs.