Dramatic Behavioral Differences of the Copolymerization Reactions of 1,4-Cyclohexadiene and 1,3-Cyclohexadiene Oxides with Carbon Dioxide

Abstract

The copolymerization of 1,3-cyclohexadiene oxide (1,2-epoxy-3-cyclohexene) with CO2 in the presence of the binary catalyst (salen)CoX or (salen)CrX and onium salts was shown to selectively afford the completely alternating copolymer poly(1,3-cyclohexadiene carbonate) in good yield. In the process catalyzed by the cobalt(III) system, the reaction was 100% selective for copolymer, whereas employing the higher temperature chromium(III) catalyst, the reaction yielded in addition to copolymer a significant quantity of the cis-1,3-cyclohexadiene carbonate. Importantly, no corresponding trans-1,3-cyclohexadiene carbonate was produced. The reactivity of 1,3-cyclohexadiene oxide in coupling reactions with CO2 was strikingly greater than that of 1,4-cyclohexadiene oxide under either catalytic conditions. Authentic samples of the cis-cyclic carbonate and trans-cyclic carbonate were synthesized from epoxide and CO2 using ZnCl2/PPNI catalyzed and trans-diol/ethyl chloroformate routes, respectively. trans-1,3-Cyclohexa...