Organometallics, vol.28, Issue 7

Chemisorption Pathways and Catalytic Olefin Polymerization Properties of Group 4 Mono- and Binuclear Constrained Geometry Complexes on Highly Acidic Sulfated Alumina

Linda A. Williams and Tobin J. Marks*
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
Organometallics, 2009, 28 (7), pp 2053–2061

Abstract: Mono- and binuclear “constrained-geometry catalyst” (CGC) group 4 hydrocarbyls Me2Si(Me5C5)(tBuN)ZrMe2 [CGCZrMe2, 1], 1-Me2Si(3-ethylindenyl)(tBuN)ZrMe2 [EICGCZrMe2; Zr1, 2], (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si-(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2, Zr2, 3], and (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si-(tBuN)](TiMe2)}2 [EBICGC(TiMe2)2, Ti2, 4] undergo rapid chemisorption on highly Brønsted acidic sulfated alumina (AlS) surfaces. 13C CPMAS NMR spectroscopy of the chemisorbed 13CαH3-enriched complexes EICGCZr13Me2/AlS (2*/AlS) and EBICGC(Zr13Me2)2/AlS (3*/AlS) reveals that chemisorption involves two processes, M−C σ-bond protonolysis at the strong surface Brønsted acid sites and heterolytic M−C scission with methide transfer to strong surface Lewis acid sites, forming similar “cation-like” electrophilic organo-group 4 complexes such as EICGCM13Me+. Relative rates of ethylene homopolymerization mediated by the catalysts prepared via chemisorption on AlS are 4/AlS > 2/AlS > 3/AlS > 1/AlS, for ethylene polymerization at 75 psi ethylene and 25 °C. Ethylene/1-hexene copolymerizations mediated by the same set of catalysts display relative polymerization rates of 4/AlS > 3/AlS > 2/AlS > 1/AlS, for copolymerizations at 75 psi ethylene, 0.8 M 1-hexene, and 25 °C.