A (Borylmethyl)silane Bearing Three Hydrolyzable Groups on Silicon: Synthesis via Iridium-Catalyzed C(sp³)-H Borylation and Conversion to Functionalized Siloxanes

An iridium-catalyzed C(sp³)-H borylation of X₃SiMe (X = hydrolyzable group) was established. A trialkoxy(methyl)silane bearing sterically demanding neopentyloxy groups (X = neopentyloxy) underwent C-H borylation at the methyl group on silicon, giving (borylmethyl)tris(neopentyloxy)silane in 70% isolated yield. The choice of the hydrolyzable group X was the key to efficient and chemoselective C-H borylation; trialkoxy(methyl)silanes bearing sterically less demanding alkoxy groups (X = ethoxy, n-butyloxy, and isobutyloxy) suffered from C-H activation at the alkoxy groups, and trichloro(methyl)silane (X = Cl) failed to react. A trimethylsiloxy group could substitute the neopentyloxy groups of the borylated product by the reaction of trimethylsilanol in the presence of tetrabutylammonium fluoride.