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

THESIS
Structural Characterization, Olefin Polymerization, and Arene Hydrogenation Properties of Group 4 Complexes Supported on Highly Acidic Sulfated Aluminas 
by Williams, Linda Ann, Ph.D., NORTHWESTERN UNIVERSITY, 2011
Abstract:
Mono- and binuclear "constrained-geometry catalyst" (CGC) group 4 hydrocarbyls supported on sulfated alumina were investigated as olefin polymerization catalysts. Chemisorption of complexes; Me2 Si(Me 5 C5 )(t BuN)ZrMe2 [CGCZrMe 2 ], 1-Me2 Si(3-ethylindenyl)(t BuN)ZrMe 2 [Zr1 ], (-CH2 CH2 -3,3'){( 5 -indenyl)[1-Me2 Si-(t BuN)](ZrMe2 )}2 [Zr2 ], and (-CH2 CH2 -3,3'){( 5 -indenyl)[1-Me2 Si-(t BuN)](TiMe2 )} 2 [Ti2 ] on sulfated alumina was studied by 13 C CPMAS NMR spectroscopy. It was revealed that chemisorption occurs through both M-C -bond protonolysis at the strong surface Brnsted 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* = 5 -(CH3 ) 5 C5 , Me = CH3 ) and ZrBz3 /n-AlS (Bz = CH2 C6 H5 ) 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 2 ZrH2 (Cp = 5 -C 5 H5 ), Cp2 Zr(CH3 )2, Cp feet2 ZrH 2 (Cp feet = 5 -(CH3 ) 5 C5 ), and Cp feetZrMe3 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 , 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 6 fashion, with an average Zr-C bond distance of 2.27 . These results are in excellent agreement with experimental catalytic mechanistic data and the computational results.
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