Sulfated alumina (AlS), a highly Brønsted acidic sulfated metal oxide, is prepared by the impregnation of gamma-alumina with 1.6 M H(2)SO(4), followed by calcination at 550 degrees C for 3 h. (13)C CPMAS NMR spectroscopy of the chemisorbed (13)C(alpha)-enriched organozirconium hydrocarbyl Cp'(2)Zr((13)CH(3))(2) (2)/AlS (Cp' = eta(5)-(CH(3))(5)C(5)) reveals that the chemisorption process involves M[bond]C sigma-bond protonolysis at the strong surface Brønsted acid surface sites to yield a "cation-like" highly reactive zirconocenium electrophile, Cp'(2)Zr(13)CH(3)(+). 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((13)CH(3))-OSi[triple bond] species. Two complementary active site kinetic assays for benzene hydrogenation show that, unlike typical heterogeneous and supported organometallic catalysts, 97 +/- 2% of all Cp'ZrMe(3) (3)/AlS sites are catalytically significant, demonstrating that the species identified by (13)C CPMAS NMR is indeed the active species. 3/AlS mediates benzene hydrogenation with a turnover frequency of 360 h(-1) at 25 degrees C/1.0 atm H(2). Active site assays were also conducted for ethylene polymerization and reveal that 87 +/- 3% of 3/AlS 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 Cp(2)Zr(CH(3))(2) (1), Cp'(2)Zr(CH(3))(2) (2), Cp'Zr(CH(3))(3) (3), Zr(CH(2)TMS)(4) (4), and Zr(CH(2)Ph)(4) (5) (Cp = eta(5)-C(5)H(5)) chemisorption on AlS are 5/AlS > or = 4/AlS > or = 3/AlS > 2/AlS > or = 1/AlS for ethylene homopolymerization at 150 psi C(2)H(4), 60 degrees C. Under identical conditions, the polymerization rate for 3/DA is approximately 1/10th that for 3/AlS.

Organozirconium complexes are chemisorbed on Brønsted acidic sulfated ZrO2 (ZrS), sulfated Al2O3 (AlS), and ZrO2-WO3 (ZrW). Under mild conditions (25 °C, 1 atm H2), the supported Cp*ZrMe3, Cp*ZrBz3, and Cp*ZrPh3 catalysts are very active for benzene hydrogenation with activities declining with decreasing acidity, ZrS ≫ AlS ≈ ZrW, arguing that more Brønsted acidic oxides (those having weaker corresponding conjugate bases) yield stronger surface organometallic electrophiles and for this reason have higher benzene hydrogenation activity. Benzene selective hydrogenation, a potential approach for carcinogenic benzene removal from gasoline, is probed using benzene/toluene mixtures, and selectivities for benzene hydrogenation vary with catalyst as ZrBz3(+)/ZrS(-), 83% > Cp*ZrMe2(+)/ZrS(-), 80% > Cp*ZrBz2(+)/ZrS(-), 67% > Cp*ZrPh2(+)/ZrS(-), 57%. For Cp*ZrBz2(+)/ZrS(-), which displays the highest benzene hydrogenation activity with moderate selectivity in benzene/toluene mixtures. Other benzene/arene mixtures are examined, and benzene selectivities vary with arene as mesitylene, 99%, > ethylbenzene, 86% > toluene, 67%. Structural and computational studies by solid-state NMR spectroscopy, XAS, and periodic DFT methods applied to supported Cp*ZrMe3 and Cp*ZrBz3 indicate that larger Zr···surface distances are present in more sterically encumbered Cp*ZrBz2(+)/AlS(-) vs Cp*ZrMe2(+)/AlS(-). The combined XAS, solid state NMR, and DFT data argue that the bulky catalyst benzyl groups expand the "cationic" metal center-anionic sulfated oxide surface distances, and this separation/weakened ion-pairing enables the activation/insertion of more sterically encumbered arenes and influences hydrogenation rates and selectivity patterns.

A well-defined, silica-supported tungsten oxo alkyl species prepared by the surface organometallic chemistry approach displays high and sustained activity in propene metathesis. Remarkably, its catalytic performances outpace those of the parent imido derivative, underlining the importance of the oxo ligand in the design of robust catalysts.

The grafting of an oxo chloro trisalkyl tungsten derivative on silica dehydroxylated at 700 °C was studied by several techniques that showed reaction via W-Cl cleavage, to afford a well-defined precatalyst for alkene metathesis. This was further confirmed by DFT calculations on the grafting process. (17)O labeling of the oxo moiety of a series of related molecular and supported tungsten oxo derivatives was achieved, and the corresponding (17)O MAS NMR spectra were recorded. Combined experimental and theoretical NMR studies yielded information on the local structure of the surface species. Assessment of the (17)O NMR parameters also confirmed the nature of the grafting pathway by ruling out other possible grafting schemes, thanks to highly characteristic anisotropic features arising from the quadrupolar and chemical shift interactions.

A solid understanding of the molecular-level mechanisms responsible for zeolite crystallization remains one of the most challenging issues in modern zeolite science. Here we investigated the formation pathway for high-silica LTA zeolite crystals in the simultaneous presence of tetraethylammonium (TEA(+)), tetramethylammonium (TMA(+)), and Na(+) ions as structure-directing agents (SDAs) with the goal of better understanding the charge density mismatch synthesis approach, which was designed to foster cooperation between two or more different SDAs. Nucleation was found to begin with the formation of lta-cages rather than the notably smaller sod and d4r-cages, with concomitant incorporation of TMA(+) and Na(+) into a very small amount of the solid phase with a low Si/Al ratio (ca. 2.5). The overall characterization results of our work demonstrate that sod-cages are first built around the preorganized lta-cages and that d4r-cages are in turn constructed by the progressive addition of low-molecular-weight (alumino)silicate species, which promotes the formation and growth of embryonic LTA zeolite crystals. We also show that the crystal growth may take place by a similar process in which TEA(+) is also incorporated, forming a single LTA zeolite phase with a higher Si/Al ratio (ca. 3.3).

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