| Abstrakt: |
The title ligands were prepared by Oacylation of 2diphenylphosphanyl4methylphenol 1 or directly by double lithiation of 2bromo4methylphenol and stepwise coupling with ClPPh2and ClPOPh2or RCOCl R = Me, tBu, Ph, 4MeOC6H4 to afford diphenylphosphinate 2and carboxylic esters 3a–d. Xray crystal structure analyses of 3b–dshow conformations in which the Pphenyl substituents are rotated away from the ester group and the COO π planes are nearly perpendicular to the phenol ring π plane. OAcylated phosphanylphenols 2and 3a–dform highly active catalysts with Ni1,5cod2as does 1 for polymerization of ethylene, whereas phosphanylphenyl ethers do not give catalysts under the same conditions. The reason is the cleavage of the Oacyl bond upon heating with nickel0 precursor compounds in the presence of ethylene. The precursors are Pcoordinated Ni0complexes, which are formed at room temperature, such as 4dobtained from 3dand Nicod2in a 2:1 molar ratio, and characterized by multinuclear NMR spectroscopy. Upon heating in the presence of ethylene, the precatalysts are activated. Catalysts 2Niand 3a–dNiconvert ethylene nearly quantitatively, 2Nislowly, and 3a–dNirapidly, into linear polyethylene with vinyl and methyl end groups, and in the latter case, COR end groups are also detectable. This proves insertion of Ni0into the O–COR bond of 3a–dligands for formation of the primary catalyst. Termination of the first chain growing cycle by βhydride elimination changes the mechanism to the phosphanylphenolate–NiH initiated polymerization providing the main body of the polymer. A small retardation in the ethylene consumption rate with 3a–dNicatalysts relative to that observed for 1Niand stabilization of the catalyst, which gives rise to reproducibly high ethylene conversion, is observed. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009 |
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