Computational study of binaphthyl-derived chiral diboranes for stereoselective cyclohexene oxide/CO2 copolymerization across rigid and flexible architectures.

Abstract

Controlling polymer stereochemistry is of significant importance because the tacticity of the polymer backbone directly determines its physical properties. Chiral binaphthyl (NP) based diboranes have proven effective in stereoselective epoxide homopolymerization, whereas spirobiindane (SD) derived analogs exhibit only limited stereoselectivity in cyclohexene oxide (CHO)/CO2 copolymerization. Given the greater intrinsic rigidity of the SD framework relative to NP, this trend is counterintuitive. This observation raises two key questions: can NP diboranes mediate CHO/CO2 copolymerization, and what governs the stereoselectivity in this process? Herein, we report a comprehensive density functional theory (DFT) study on a series of NP chiral organoboron catalysts for the stereoselective copolymerization of CHO with CO2. Owing to the rigid framework, NP1, NP0, and NPe are predicted to deliver excellent enantioselectivity, with calculated ΔΔGS-R values of 7.3, 3.7, and 4.4 kcal mol-1, respectively. Surprisingly, the more flexible NP3 and NP4 also exhibit high enantioselectivity, with calculated ΔΔGS-R values of 5.5 and 5.0 kcal mol-1, respectively. Further distortion interaction analysis (DIAS) reveals that CHO distortion is the primary origin of enantioselectivity, with the shorter diboron distances in the NP catalysts amplifying differences in CHO twisting.