Photoinduced Generation of (Boryl)Silyl and (Chloro)Silyl Radicals: Access to Trisubstituted Silylboranes and Chlorosilanes

Trisubstituted silylboranes and chlorosilanes are in high demand for the precise synthesis of tetrasubstituted organosilicons. However, conventional synthetic methods often require harsh conditions and exhibit low functional-group tolerance, limiting their chemical diversity. In this study, we present a versatile photoinduced hydro(boryl)silylation and hydro(chloro)silylation of alkenes to construct trisubstituted silylboranes and chlorosilanes. This method employs the in situ generation of novel silyl radicals, such as (boryl)silyl radicals (R₂(pinB)Si•) or (chloro)silyl radicals (R₂ClSi•), from hydroborylsilanes or hydrochlorosilanes through highly selective hydrogen-atom transfer. The unprecedented silylboranes and chlorosilanes obtained using this method enable the direct synthesis of highly complex tetrasubstituted organosilicons. Mechanistic studies reveal a photoactivation pathway in which a sulfur radical generated from a combination of (^tBuO)₂ and ⁱPr₃SiSH directly facilitates Si─H bond cleavage without inducing any redox events at the Si─B/Si─Cl bonds, enabling radical hydrosilylation with a broad scope of alkenes.