Surface Protected Organozirconium Catalyzes C─H Alumination of Saturated Hydrocarbons

C─H alumination of saturated aliphatic hydrocarbons is catalyzed by surface-grafted organozirconium species, with high selectivity for the least-hindered, terminal position, enabled by selective silylation of a small number of residual silanols in the catalyst. Exclusive mono-alumination of methane is accomplished with more than 70 turnovers.

Abstract

Surface grafted organozirconium catalyzes C─H/Et─Al exchange reactions, involving saturated hydrocarbons and AlEt₃, to afford organoaluminum compounds and ethane. The Zr(O ^t Bu)₃@SiO₂-Al₂O_3–700 (1) catalyst contains monopodal ≡SiO─Zr(O ^t Bu)₃ and only a few residual silanols (<5%). Nonetheless, these silanols are the Achille's heel of 1, providing a pathway for surface and catalyst degradation during catalysis, limiting the alkylaluminum yield and catalyst turnover. Support degradation, involving the cleavage of Si─O bonds by activated surface organometallics, is inhibited by capping silanols with ─SiMe₃. Residual silanols in 1 react with allyltrimethylsilane, as determined by solid-state ¹³C and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and reaction stoichiometry, to form Zr(O ^t Bu)₃/SiMe₃@SiO₂-Al₂O_3–700 (2), which is resistant to degradation by AlEt₃. C─H alumination of dodecane catalyzed by 2 produces higher yields of the 1-dodecylaluminum product in comparison to 1, and in >95% selectivity. Additionally, methane undergoes 2-catalyzed C─H alumination, providing a route to AlMe₃.

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