title: Exploring electronic and steric effects on the insertion and polymerization reactivity of phosphinesulfonato Pd(II) catalysts.
abstract: Thirteen different symmetric and asymmetric phosphinesulfonato palladium complexes ([{((X)1-Cl)-μ-M}n], M=Na, Li, 1=(X) (P^O)PdMe) were prepared (see Figure 1). The solid-state structures of the corresponding pyridine or lutidine complexes were determined for ((MeO)2)1-py, ((iPrO)2)1-lut, ((MeO,Me2))1-lut, ((MeO)3)1-lut, (CF3) 1-lut, and (Ph)1-lut. The reactivities of the catalysts (X) 1, obtained after chloride abstraction with AgBF4 , toward methyl acrylate (MA) were quantified through determination of the rate constants for the first and the consecutive MA insertion and the analysis of β-H and other decomposition products through NMR spectroscopy. Differences in the homo- and copolymerization of ethylene and MA regarding catalyst activity and stability over time, polymer molecular weight, and polar co-monomer incorporation were investigated. DFT calculations were performed on the main insertion steps for both monomers to rationalize the effect of the ligand substitution patterns on the polymerization behaviors of the complexes. Full analysis of the data revealed that: 1) electron-deficient catalysts polymerize with higher activity, but fast deactivation is also observed; 2) the double ortho-substituted catalysts ((MeO)2)1 and ((MeO)3)1 allow very high degrees of MA incorporation at low MA concentrations in the copolymerization; and 3) steric shielding leads to a pronounced increase in polymer molecular weight in the copolymerization. The catalyst properties induced by a given P-aryl (alkyl) moiety were combined effectively in catalysts with two different non-chelating aryl moieties, such as (cHexO/(MeO)2)1, which led to copolymers with significantly increased molecular weights compared to the prototypical (MeO)1.
authors.affiliation: Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, 78464 Konstanz (Germany), Fax: (+49) 7531-88-5152.
authors.forename: Boris
authors.initials: B
authors.lastname: Neuwald
authors.forename: Laura
authors.initials: L
authors.lastname: Falivene
authors.forename: Lucia
authors.initials: L
authors.lastname: Caporaso
authors.forename: Luigi
authors.initials: L
authors.lastname: Cavallo
authors.forename: Stefan
authors.initials: S
authors.lastname: Mecking
keywords: catalysis; coordination modes; density-functional calculations; kinetics; reaction mechanisms; theoretical chemistry