Synthesis, Spectroscopy, and Catalytic Properties of Cationic Organozirconium Adsorbates on “Super Acidic” Sulfated Alumina. “Single-Site” Heterogeneous Catalysts with Virtually 100 Active Sites

Abstract

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.

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

“…Complexes B and C were prepared, purified, and chemisorbed on AlS with rigorous exclusion of oxygen and moisture, using techniques described elsewhere (Materials and Methods) (3,17,18). Studies of C/AlS-mediated benzene hydrogenation were carried out as described in SI Materials and Methods, under conditions minimizing mass transport effects (3,17,18).…”

“…Here, H 0 is the standard Hammett acidity function, determined spectroscopically, by reactivity, or by temperature-programmed desorption/reaction (14-16). Remarkably, adsorbate structure C/ AlS is one of the most active arene hydrogenation catalysts yet discovered, and by kinetic poisoning experiments, 97 ± 2% and 87 ± 3% of the Zr centers are catalytically significant for benzene hydrogenation and ethylene polymerization, respectively (17,18). This unusually high percentage of catalytically significant d 0 sites, the relatively clean adsorption/activation chemistry, and the unusual catalytic properties present a unique opportunity to structurally characterize such electrophilic surface catalyst structures in quantitative detail, hence to understand the origin of the unusual catalytic properties.…”

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

“…Other SMOs, including AlS [117,[120][121][122][123], SnS [117], FeS [117], and TiS [117] were analyzed in a similar way and found to yield analogous surface species. In comparing a given series, it is noted that the magnitude of the shift in resonances between the precursor and the adsorbate qualitatively correlates with the electronic unsaturation of the electrophilic species (Table 1).…”

Catalisadores metalocênicos suportados para a produção de poliolefinas: revisão das estratégias de imobilização

“…18,[74][75][76][77][78] Aqui, o suporte também desempenha parcialmente o papel do contra-íon formado pelo MAO, estabilizando o complexo catiônico. Diferentemente, a sílica parcialmente desidroxilada não desempenha esse papel porque não tem um caráter suficientemente ácido, neces-…”

“…Suportes sulfatados tendem a gerar maior número de sítios ativos, devido ao melhor aproveitamento das hidroxilas disponíveis na formação de sítios pela ponte sulfônica. 4,74 Heterogeneização via síntese direta do metaloceno Uma maneira diferenciada de heterogeneizar o metaloceno é sintetizar o próprio complexo de metal de transição diretamente sobre o suporte, em geral um óxido inorgânico. 84 A síntese do complexo ocorre em etapas: a superfície do suporte é tratada quimicamente para padronizar os grupos funcionais da sua superfície; os ligantes requeridos na formação do complexo são enxertados na superfície modificada e, um sal de metal de transição reage com os ligantes previamente inseridos (etapa de metalação), finalizando o metaloceno.…”