Synthesis, spectroscopy, and catalytic properties of cationic organozirconium adsorbates on "super acidic" sulfated alumina. "Single-site" heterogeneous catalysts with virtually 100% active sites

Sulfated alumina (AIS), a highly Bronsted acidic sulfated metal oxide, is prepared by the impregnation of gamma-alumina with 1.6 M H2SO4, followed by calcination at 550 degreesC for 3 h. C-13 CPMAS NMR spectroscopy of the chemisorbed C-13(alpha)-enriched organozirconium hydrocarbyl CP'Zr-2((CH3)-C-13)(2) (2*)/AIS (Cp' = eta(5)-(CH3)(5)C-5) reveals that the chemisorption process involves M-C sigma-bond protonolysis at the strong surface Bronsted acid surface sites to yield a "cation-like" highly reactive zirconocenium electrophile, CP'(2)-(ZrCH3+)-C-13. In contrast, chemisorption of 2* on dehydroxylated alumina (DA) yields a similar cation via methide transfer to surface Lewis acid sites, while chemisorption onto dehydroxylated silica yields a mu-oxo CP'(2)-Zr((CH3)-C-13)-OSidrop species. Two complementary active site kinetic assays for benzene hydrogenation show that, unlike typical heterogeneous and supported organometallic catalysts, 97 +/- 2% of all Cp'ZrMe3 (3)/ AIS sites are catalytically significant, demonstrating that the species identified by C-13 CPMAS NMR is indeed the active species. 3/AIS mediates benzene hydrogenation with a turnover frequency of 360 h(-1) at 25 degreesC/1.0 atm H-2. Active site assays were also conducted for ethylene polymerization and reveal that 87 +/- 3% of 3/AIS sites are catalytically active, again demonstrating that nearly all zirconium sites are catalytically significant. Relative rates of ethylene homopolymerization mediated by the catalysts prepared via CP2Zr-(CH3)(2) (1), CP'Zr-2(CH3)(2) (2), Cp'Zr(CH3)(3) (3), Zr(CH2TMS)(4) (4), and Zr(CH2Ph)(4) (5) (CP: = eta(5)-C5H5) chemisorption on AIS are 5/AIS greater than or equal to 4/AIS greater than or equal to 3/AIS > 2/AIS greater than or equal to 1/AIS for ethylene homopolymerization at 150 Psi C2H4, 60 degreesC. Under identical conditions, the polymerization rate for 3/DA is similar to1/10 that for 3/AIS.