Gold-Nanoparticle-Catalyzed Mild Diboration and Indirect Silaboration of Alkynes without the Use of Silylboranes

Commercially available Au nanoparticles supported on TiO2 were used to catalyze the cis diboration of terminal and internal alkynes with bis(pinacolato)diboron. The products were obtained in excellent yields by using milder conditions, shorter reaction times, and lower catalyst loadings than those required for a heterogeneous Au nanopore catalyst. The catalytic system could be recovered and reused for five consecutive runs without any loss of activity. The combination of bis(pinacolato)-diboron with the 1,2-disilane in the presence of Au/TiO2 allowed for the sigma-bond metathesis to take place and the in situ formation of the Au nanoparticle-tethered silylborane. Given that the Au-catalyzed silaboration of alkynes is faster than the rates of the corresponding disilylation and diboration pathways, we were able to achieve the indirect silaboration of alkynes with good chemoselectivities (65-85 %) without the direct use of silylboranes, which are expensive and difficult to synthesize.