Insertion aptitudes and insertion regiochemistry of various alkenes (coordinated to cationic (σ-R) (diimine)palladium(II) (R = -CH3, -C6H5).: A theoretical study

The coordination of a range of substituted alkenes (C2H3X; X = H, CH3, t-Bu, CN, CO2-CH3, CF3, OCH3, CHCH2, C6H5, F, Cl, Br) to a cationic methyl- or phenylpalladium(II)-diimine complex and the subsequent migratory insertion into the methyl-palladium and phenyl-palladium bonds are studied using DFT calculations at the B3LYP level of theory. The focus of this investigation is on monitoring the insertion barrier and the regiochemical outcome as a function of alkene properties, with special attention to the functionalized alkene as a potential comonomer in polymerization. In general, electron-rich alkenes coordinate more strongly, whereas electron poor alkenes insert more readily. The barriers of insertion range from 4.7 to 26.5 kcal/mol, and mostly the 2,1-insertion is favored. In all cases the alkenes have a weaker coordination to the phenylpalladium(II)diimine compared to the methylpalladium(II)diimine complex and, as expected, a lower insertion barrier.