Theoretical studies on the regioselectivity of polar vinyl monomer insertion catalyzed by an α-diimine Pd(ii) complex

Abstract

This theoretical study reveals the origin of regioselectivity of a polar vinyl monomer (PVM) in the copolymerization of different PVMs with ethylene by the DBB–Ipty α-diimine Pd(II) complex with a bulky dibenzobarrelene (DBB) backbone and bulky axial pentiptycenyl (Ipty) substituents. DFT calculations were employed to investigate the regioselectivity of the insertion of three acrylate monomers (CH₂CHCOOR: R = H, AA; R = Me, MA; and R = ^tBu, ^tBA) catalyzed by the DBB–Ipty Pd(II) complex. The results indicate that with the increase of the size of the monomer substituents (AA < MA < ^tBA), greater repulsion occurs between the monomer and the catalyst, leading to a gradual preference for 1,2-insertion. By stepwise regression analysis, a multivariate linear regression (MLR) model on the factors affecting regioselectivity was constructed. Coefficient analysis of the MLR equation reveals that the buried volume (%V_bur) of the monomer and the NBO charge on the vinyl C₁ atom (NBO_C1) significantly affect the regioselectivity of monomer insertion. Specifically, the bigger %V_bur tends to 1,2-insertion of the PVM, while the higher NBO_C1 is apt to 2,1-insertion. Through the contribution values of the coefficients in the equation, we can derive that steric hindrance is the primary factor of regioselectivity, while the electronic effect plays a secondary role.