This theoretical study reveals the regioselectivity origin of 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 three acrylate monomers (CH2 = CHCOOR: R = H, AA; R = Me, MA; and R = tBu, tBA) insertion 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), the 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 (%Vbur) of the monomer and the NBO charge on the vinyl C1 atom (NBOC1) significantly affect the regioselectivity of monomer insertion. Specifically, the bigger %Vbur tends to 1,2-insertion of PVM, while the higher NBOC1 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 electronic effect plays a secondary role.

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