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, formed 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 (TOF_max) 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.