The diboration of ketones with the (ICy)CuOt-Bu catalyst was developed to provide access to tertiary α-hydroxyboronate esters. The (ICy)CuOt-Bu catalyst was generated in situ with (ICy)CuCl and NaOt-Bu to afford a more efficient catalyst than the preformed (ICy)CuOt-Bu. These conditions result in the diboration of various ketones in toluene at 50 °C in 2−22 h. Treatment of the resulting products with silica gel affords the corresponding α-hydroxyboronate esters.

Metal boryl complexes have received significant attention in the literature in recent years due to their role as key intermediates in a number of metal-catalyzed borylation reactions. The ligand scaffold is known to have a significant impact on the observed reactivity of these metal boryl complexes. A synthetic strategy to access ruthenium boryl analogues of the Shvo metal−ligand catalysts is described. Heating a precursor to Shvo’s catalyst (1) with bis(catecholato)diboron at 50 °C provided ruthenium boryl complex 3, [2,5-Ph2-3,4-Tol2(η5-C4COBcat)Ru(CO)2Bcat] (Bcat = catecholatoboryl). Addition of bis(catecholato)diboron to complex 1 in the presence of a phenol results in ruthenium boryl complex 5, [2,5-Ph2-3,4-Tol2(η5-C4COH)Ru(CO)2Bcat], at 22 °C in 30% isolated yield. A single-crystal X-ray analysis of complex 5 confirmed the assigned structure. An improved synthesis of ruthenium boryl complex 5 was developed by the in situ formation of complex 3, [2,5-Ph2-3,4-Tol2(η5-C4COBcat)Ru(CO)2Bcat], followed by addition of the phenol, resulting in a 51% yield.

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.