| Abstract
| - Substituent effects in the polymerization of ethene and propene catalyzed by N∧N-Pd(II) have been studied by DFT with 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. The influence of catalyst substiuents on relative stabilities of isomeric alkyl complexes (n- and isopropyl) and the different olefin π-complexes with n- and isopropyl alkyl, as well as the insertion barriers for ethene and propene insertion, is discussed.
- Gradient-corrected density functional theory has been used to study substituents effectson the cationic N∧N−Pd(II) diimine catalyst in ethene and propene polymerization. HereN∧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 andpropene (1,2- and 2,1-) insertion transition states. The results show that an increase in thesize of the substituents on the Pd(II) catalyst enhances the preference of 1 for the isomerwith 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, anincrease in the size of the substituents affects the relative binding of ethene and propene.Thus, the electronic preference of propene complexes is overridden by steric factors in thecase of the largest substituents. The regioselectivity of propene insertion is strongly affectedas well: an increase in steric demand decreases the 2,1-:1,2-insertion ratio, with 1,2-insertion becoming favored for the sterically most congested catalyst [R = −CH3, Ar = −2,6-C6H3(iPr)2].
|
