Structural Characterization, Olefin Polymerization, and Arene Hydrogenation Properties of Group 4 Complexes Supported on Highly Acidic Sulfated Aluminas.

摘要

Mono- and binuclear "constrained-geometry catalyst" (CGC) group 4 hydrocarbyls supported on sulfated alumina were investigated as olefin polymerization catalysts. Chemisorption of complexes; Me2Si(Me 5C5)(tBuN)ZrMe2 [CGCZrMe 2], 1-Me2Si(3-ethylindenyl)(tBuN)ZrMe 2 [Zr1], (&mgr;-CH2CH2-3,3'){(&eegr; 5-indenyl)[1-Me2Si-(tBuN)](ZrMe2)}2 [Zr2], and (&mgr;-CH2CH2-3,3'){(&eegr; 5-indenyl)[1-Me2Si-(tBuN)](TiMe2)} 2 [Ti2] on sulfated alumina was studied by 13C CPMAS NMR spectroscopy. It was revealed that chemisorption occurs through both M-C sigma-bond protonolysis at the strong surface Bronsted acid sites, as well as heterolytic M-C scission with methide transfer to strong surface Lewis acid sites, forming similar "cation-like" electrophilic organo-group 4 complexes. Relative rates of ethylene homopolymerization mediated by the supported catalysts was found to be Ti2/AlS > Zr1/AlS > Zr2/AlS > CGCZrMe2/AlS.;Sulfated alumina nanoparticles (n-AlS) are introduced as a high surface area support/activator for organozirconium catalysts. The large external surface area allows chemisorption of 3x more organozirconium catalyst/nm 2 than previously possible on bulk sulfated alumina. It is found that Cp*ZrMe2/n-AlS (Cp* = &eegr;5-(CH3) 5C5, Me = CH3) and ZrBz3/n-AlS (Bz = CH2C6H5) are active catalysts for arene hydrogenation as well as for olefin polymerizations. The less sterically encumbered ZrBz3/n-AlS exhibits, greater arene hydrogenation turnover frequency, greater substrate tolerance, higher polymerization activity, and increased 1-hexene incorporation in ethylene/1-hexene copolymerizations, than the slightly more encumbered Cp*ZrMe2/n-AlS.;Density functional theory (DFT) analysis in conjunction with Zr K-edge X-ray absorption fine structure spectroscopic (XAFS) characterization of Cp 2ZrH2 (Cp = &eegr;5-C 5H5), Cp2Zr(CH3)2, Cp&feet;2ZrH 2 (Cp&feet; = &eegr;5-(CH3) 5C5), and Cp&feet;ZrMe3 and as well as the AlS-supported product catalysts are used to quantify the metrical nature of the Zr˙˙˙AlS interaction. Analysis of the XAFS data indicates the supported organozirconium centers have electrostatic interactions with the surface sulfate O atoms at average (long) Zr˙˙˙O distances of 2.25 -- 2.36 A, and the result is confirmed by DFT analysis of the chemisorption process. EXAFS analysis of benzene dosing experiments with the arene hydrogenation catalyst Cp'ZrMe2/AlS reveals that benzene is captured by essentially all of the Zr centers and is bound in an &eegr;6 fashion, with an average Zr-C bond distance of 2.27 A. These results are in excellent agreement with experimental catalytic mechanistic data and the computational results.