Borenium Ion Equivalents Stabilized by BICAAC and Their Implementation as Catalysts in Hydrosilylation of Carbonyls

Hydride abstraction from the borane adduct, (BICAAC)‧BH3 afforded the hydride bridged dinuclear borenium ion equivalent complexes 1 and 2 that have been characterized by various spectroscopic and spectrometric techniques followed by the assessment of Lewis acidity using the Gutmann-Beckett method. The single crystal X-ray structure of complex 2 revealed the presence of discrete ions in the solid state. The complex (BICAAC)‧BH2(OTf) (3), obtained from the reaction of (BICAAC)‧BH3 with MeOTf, forms the corresponding boronium cations [(BICAAC)‧BH2(L)]+(OTf)- on reaction with Lewis bases (L = pyridine (4) and DMAP (5)). Complexes 1 and 2 demonstrated notable catalytic activity in the hydrosilylation of a diverse array of carbonyls using 1.0 mol% catalyst loading (achieving the highest turnover frequency (TOFmax) of up to 1200 h-1 with benzaldehyde. A broad substrate scope has been presented for aldehydes and ketones decorated with various electron-donating and withdrawing substituents along with this the hydrosilylation of a few para-quinone methides has also been presented.