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

The boron-substituted hydroxycycylopentadienyl ruthenium hydride [2,5-Ph2-3,4-Tol2(η5-C4COBpin)Ru(CO)2H] (Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) 5 was synthesized by the addition of pinacolborane to ruthenium dimer [2,5-Ph2-3,4-Tol2(η5-C4CO)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.