CPCM model
To test the performance of CPCM solvation model in such copolymerization systems, single-point solvation calculations have been performed at the level of PBE0/6-31+G(d), which was shown to be suitable for CPCM model.34 As shown in Table 3, in the case of ethylene insertion, all the tested functionals underestimated the reaction energy barrier, among which the hybrid M06-HF performs the worst with an error of 2.3 kcal/mol. For MA insertion, all the functionals shown in Table 3 perform well. In the case of VB insertion, like the case of SMD model, GGA andmeta -GGA functionals underestimated the reaction energy barrier with errors of larger than 1.0 kcal/mol. The hybrid functional LC-ωPBE with D3 dispersion correction overestimated the barrier (17.9 vs15.9±0.1 kcal/mol). This can be ascribed to that the functional LC-ωPBE itself considered the long-range interaction, and further D3 dispersion correction may lead to overcorrection. The hybrid functional BHandH also overestimated the energy barrier (17.3 kcal/mol). When larger basis set 6-31+G(d,p) was used for the non-metal atoms, similar results was obtained (Table S1). Therefore, with the CPCM solvent model, the lower theoretical level of 6-31+G(d) for single-point calculation is sufficient to obtain accurate energy barriers in such copolymerization system. It is noteworthy that, although some functionals produced errors of > 1.0 kcal/mol, the errors are not so large (< 3 kcal/mol), suggesting a wide range of functionals suitable for dealing with such (α-diimine)Pd-catalyzed copolymerizations.