Catalytic Hydrosilylation of Imines by Aluminum Hydride Cations

Abstract

AbstractIn this work, the catalytic activity of electronically unsaturated three coordinated aluminum hydride cations [LAlH]+[HB(C6F5)3]− (1) and [LAlH]+[B(C6F5)4]− (2) in hydrosilylation of imines has been disclosed (L={(2,6‐iPr2C6H3N)P(Ph2)}2N). A variety of organo‐silanes such as Et3SiH, MePhSiH2, PhSiH3, TMDSO, and PHMS are screened in this endeavour. The amines as products of catalysis were obtained in good to excellent yields after the hydrolysis of silylamine intermediates. Further, a series of controlled experiments systematically designed to investigate the underlying mechanistic pathway through multinuclear NMR analysis showed Lewis adduct formation between cationic aluminum centre and the imine nitrogen, which subsequently undergoes reaction with silane to afford the product. The hydrosilylation of imine performed with Et3SiH using catalyst 1 with a loading of 2 mol % at 60 °C occurs smoothly. Whereas 2 led to the product formation with Et3SiH only when used in stoichiometric quantity. Further, to investigate this unique behaviour of 1 NMR investigations were performed and revealed that the anion in 1 competes for hydride delivery and in‐situ generates B(C6F5)3 that cooperatively reinforces the catalytic activity of 1.