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

摘要

Mono- and binuclear "constrained-geometry catalyst" (CGC) group 4 hydrocarbyls Me2Si(Me5C5)-((BuN)-Bu-t)ZrMe2 [CGCZrMe(2),1], 1-Me2Si(3- ethylindenyl)((BuN)-Bu-t)ZrMe2 [EICGCZrMe(2); Zr-1,Zr- 2], (mu-CH2CH2-3,3'){(eta(5)- indenyl)[1-Me2Si-((BuN)-Bu-t)](ZrMe2)}(2) [EBICGC(ZrMe2)(2), Zr-2, 3], and (mu- CH2CH2-3,3'){(eta(5)-indenyl)[1-Me2Si-((BuN)-Bu-t)](TiMe2)}(2) [EBICGCTiMe(2))(2), Ti-2, 4] undergo rapid chemisorption on highly Bronsted acidic sulfated alumina (AlS) surfaces. C-13 CPMAS NMR spectroscopy of the chemisorbed (C alpha H3)-C-13-enriched complexes EICGCZr(13)Me(2)/AlS (2*/AlS) and EBICGC((ZrMe2)-Me-13)(2)/AlS (3*/AlS) reveals that chemisorption involves two processes, M-C sigma-bond protonolysis at the strong surface Bronsted 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 EICGCM(13)Me(+). 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 degrees 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 degrees C.