DFT Studies on Substituent Effects in Palladium-Catalyzed Olefin Polymerization

Abstract

Gradient-corrected density functional theory has been used to study substituents effects on the cationic N∧N−Pd(II) diimine catalyst in ethene and propene polymerization. Here N∧N = −C(R)−N(Ar)−N(Ar)−C(R)− with R = H, −CH3, −An and Ar = H, C6H5, −2,6-C6H3(Me)2, −2,6-C6H3(iPr)2. Calculations have been performed on the [N∧N-Pd(II)−P]+ (P = n-propyl and isopropyl) alkyl complexes (1) and the corresponding [N∧N-Pd(II)−P(η2-CH2CHRo)]+ π-complexes of ethene (Ro = H) and propene (Ro = CH3), as well as the ethene and propene (1,2- and 2,1-) insertion transition states. The results show that an increase in the size of the substituents on the Pd(II) catalyst enhances the preference of 1 for the isomer with the branched isopropyl alkyl group P, while for the olefin complexes [N∧N-Pd(II)−P(η2-CH2CHRo)]+ the isomer with the linear n-propyl group P becomes preferred. Further, an increase in the size of the substituents affects the relative binding of ethene and propene. Thus, the electronic preference of propene comple...