Regioselective Diboration and Silaboration of Allenes Catalyzed by Au Nanoparticles

Under catalysis by commercially available supported Au nanoparticles on TiO2 (1 mol %), terminal allenes undergo diboration and silaboration exclusively on the terminal double bond, in high yields and stereoselectivity. In silaboration, the boron moiety (Bpin) is attached on the terminal carbon and the silyl group on the sp-C, a regioselectivity pattern that is unusual. No ligands or additives are required, while the catalyst is recyclable and reusable. The selectivity is rationalized in terms of a pi-allyl type or an eta-1 complex intermediate with an apparent allylic carbocationic character, as revealed through the use of allenes cyclopropyl as sensitive probes.