A Boron-Substituted Analogue of the Shvo Hydrogenation Catalyst: Catalytic Hydroboration of Aldehydes, Imines, and Ketones

The boron-substituted hydroxycycylopentadienyl ruthenium hydride [2,5-Ph 2 -3,4-Tol 2 (η 5 -C 4 COBpin)Ru(CO) 2 H] (Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) 5 was synthesized by the addition of pinacolborane to ruthenium dimer [2,5-Ph 2 -3,4-Tol 2 (η 5 -C 4 CO)Ru(CO) 2 ] 2 4 . Complex 5 reacts with aldehydes both stoichiometrically and catalytically, providing hydroboration products under mild reaction conditions. A Hammett correlation plot of para-substituted benzaldehydes provided a ρ value of +0.91. Catalytic hydroboration of aryl imines provided high yields of the corresponding amines. The hydroboration of aryl ketones, however, required strongly electron-withdrawing substituents to induce hydroboration in reasonable reaction times.