Easily Attachable and Detachable ortho-Directing Agent for Arylboronic Acids in Ruthenium-Catalyzed Aromatic C-H Silylation

o-C-H silylation of arylboronic acids has been achieved using 2-pyrazol-5-ylaniline as an ortho-directing agent, which was temporarily attached to the boronyl group via Ru-catalyzed silylation with hydrosilanes. Condensation products of arylboronic acids with 2-pyrazol-5-ylaniline were prepared in situ and subjected to reaction with triorganosilanes in the presence of RuH2(CO)(PPh3)(3) at 135 degrees C. Regioselective silylation at their ortho-positions proceeded in good yields for phenylboronic acids bearing para-substituents such as chloro, fluoro, methyl, methoxy, and trifluoromethyl groups. p-Methoxycarbonyl-substituted phenylboronic acid provided the corresponding silylated product in moderate yield. m-Tolyl- and 2-naphthylboronic acids underwent silylation selectively at the less sterically hindered ortho-positions. The silylated products were utilized in Suzuki-Miyaura coupling, followed either by iodination with ICl or by Tamao oxidation to furnish iodine- or hydroxy-substituted biaryls.