Transfer reactions involving boron. XX. Disproportionation reactions of alkyl-, alkoxy-, and haloboranes

Article abstract of DOI:10.1021/ic50073a038

The solution redistribution equilibria of borane with alkylboranes, alkoxyboranes, haloboranes, and arylmercaptoboranes have been studied. The results obtained with the various systems are discussed individually and compared with each other and, when available, with gas-phase and other data appearing in the literature. The redistribution of trialkylboranes with borane in tetrahydrofuran produces a mixture of mono-, di-, and trialkylboranes and borane, the first two being the predominant products. Complicating the systems are the presence of five hydrogen-bridged monomer-dimer equilibria. The equilibrium constants for these equilibria have been determined for the n-propyl- and isopropylborane systems. The reaction of 1 or 2 mol of alcohols with 1 mol of borane produces dialkoxyboranes in kinetically controlled reactions. The dialkoxyboranes undergo slow redistribution reactions to give mixtures of borane and di- and trialkoxyboranes. Similarly, trialkyl borates and borane undergo slow disproportionation reactions. The redistribution equilibrium constants are identical, within experimental error, for primary and secondary alkoxyborane systems; however, the t-butoxyborane equilibrium constant is significantly different. The rate of attainment of equilibrium is markedly dependent on the structure of the alkoxy group. Boron trichloride reacts with borane to give either mono- or dichloroborane depending on the stoichiometry of the starting reagents, whereas boron trifiuoride does not react with borane.