Surface organozirconium electrophiles activated by chemisorption on super acidic sulfated zirconia as hydrogenation and polymerization catalysts. A synthetic, structural, and mechanistic catalytic study

Structural studies including C-13 CPMAS NMR spectroscopy of the C-13(alpha)-enriched model adsorbates Cp'Th-2((CH3)-C-13)(2) (1*) and CpTi((CH3)-C-13)(3) (2*) (Cp = eta(5)-C5H5, Cp' = eta(5)-(CH3)(5)C-5), and organozirconium adsorbates Cp2Zr((CH3)-C-13)(2) (3*), Cp'Zr((CH3)-C-13)(3) (4*), and Zr((13)CH(2)tBu)(4) (6*) chemisorbed on superacidic sulfated zirconia (ZRSx; x = activation temperature) reveal that all adsorbates undergo a new molecular chemisorptive process: protonolytic M-C sigma-bond cleavage at the very strong surface Bronsted acid sites to yield cation-like organometallic electrophiles. A kinetic and mechanistic study is reported for olefin and arene hydrogenation and alpha-olefin homopolymerization meditated by the catalysts formed by chemisorption of Cp2Zr(CH3)(2) (3), Cp'Zr(CH3)(3) (4), Zr(CH2TMS)(4) (5), Zr(CH(2)tBu)(4) (6), and Zr(CH2Ph)(4) (7), onto zirconia (ZR) or ZRSx. At 25 degreesC, 14.7 psi H-2, 1-hexene hydrogenation activity follows the order 4/ZRS400 much greater than 3/ZRS400 greater than or equal to 3/ZRS300 much greater than 3/ZRS720 much greater than 3/ZR similar to 0. Benzene hydrogenation rates (25 degreesC, 14.7 psi H-2) follow the order 4/ZRS400 much greater than 5/ZRS400 > 6/ZRS400 > 7/ZRS400, with N-t = 970 h(-1) for 4/ZRS400 making this the most active benzene hydrogenation catalyst yet discovered. As a function of arene substituent(s), 4/ZRS400 exhibits high chemoselectivity, with hydrogenation rates following the order benzene much greater than toluene much greater than p-xylene similar to 0. For benzene hydrogenation by 6/ZRS400, kinetic data obey the rate law N-t = k(obs)[arene](0)[P-H2](1) with E-a = 10.3(8) kcal mol(-1). Partially hydrogenated products are not detected at partial conversions, with H, delivered pairwise to both faces of C6D6, forming all-cis and cis, cis, trans, cis, trans isotopomers (1:3.1). Protonolytic poisoning experiments reveal that a maximum of similar to68% of Zr sites in 4/ZRS400 are catalytically significant for benzene hydrogenation. Relative homopolymerization rates are 7/ZRS400 > 5/ZRS400 > 6/ZRS400 > 4/ZRS400 for both ethylene (150 Psi C2H4, 60 degreesC) and liquid propylene (20 degreesC).