Exploring Electronic and Steric Effects on the Insertion and Polymerization Reactivity of Phosphinesulfonato Pd super(II) Catalysts

• Published in: Chemistry : a European journal 2013-12, Vol.19 (52), p.17773-17788
• Main Authors: Neuwald, Boris, Falivene, Laura, Caporaso, Lucia, Cavallo, Luigi, Mecking, Stefan
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Copolymerization; Decomposition reactions; Electronics; Insertion; Molecular weight; Polymerization
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201301365

Thirteen different symmetric and asymmetric phosphinesulfonato palladium complexes ([{( super(X)1-Cl)- mu -M} sub(n)], M=Na, Li, 1= super(X)(P omicron )PdMe) were prepared (see Figure1). The solid-state structures of the corresponding pyridine or lutidine complexes were determined for super((MeO)2)1-py, super(()irO)2-lut, super((MeO,Me2))1-lut , super((MeO)3)1-lut, super(CF3)1-lut, and super(Ph)1-lut. The reactivities of the catalysts super(X)1, obtained after chloride abstraction with AgBF sub(4), toward methyl acrylate (MA) were quantified through determination of the rate constants for the first and the consecutive MA insertion and the analysis of [beta]-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 super((MeO)2)1 and super((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 super()cexO/(MeO)2, which led to copolymers with significantly increased molecular weights compared to the prototypical super(MeO)1. Catalyst control: The influence of steric and electronic effects on the reactivity of phosphinesulfonato Pd super(II) catalysts in polymerization and copolymerization is explored through experimental and DFT methods. A comparison of thirteen different super(X)(PO)PdMe catalysts ((PO)=[kappa] super(2)- P,O-R super(1)R super(2)PC sub(6)H sub(4)SO sub(2)O; see figure) reveals insights into the catalyst reactivity toward methyl acrylate and ethylene, their influence on the polymer microstructure, and the decomposition pathways. The unraveling of these relations provides guidelines for a directed choice of catalysts.