Alkoxide-catalyzed reduction of ketones with pinacolborane.

The reduction of ketones with pinacolborane (4,4,5,5-tetramethyl-1,3,2-dioxaborolane) is catalyzed by 5 mol % NaOt-Bu at ambient temperature. The reaction is high yielding and general, providing complete conversion of aryl and dialkyl ketones. Although spectroscopic studies of the active hydride source in benzene-d(6) were complicated due to poor solubility, the data are consistent with the active hydride source being the trialkoxyborohydride, which is believed to be present in low concentration under the reaction conditions. Performing analogous studies in tetrahydrofuran resulted in a complex equilibrium between several different boron-containing species in which the trialkoxyborohydride compound was the major species.

Synthesis of Ruthenium Boryl Analogues of the Shvo Metal-Ligand Bifunctional Catalyst.

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-Ph(2)-3,4-Tol(2)(η(5)-C(4)COBcat)Ru(CO)(2)Bcat] (Bcat = catecholatoboryl). Addition of bis(catecholato)diboron to complex 1 in the presence of a phenol results in ruthenium boryl complex5 [2,5-Ph(2)-3,4-Tol(2)(η(5)-C(4)COH)Ru(CO)(2)Bcat] 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-Ph(2)-3,4-Tol(2)(η(5)-C(4)COBcat)Ru(CO)(2)Bcat] followed by addition of the phenol, resulting in a 51% yield.