The kinetics and mechanism of solvolysis of amineboranes

Article abstract of DOI:10.1021/ic50013a027

The rates of solvolysis of substituted phenylamineboranes in aqueous dioxane are described by the expression -d[AB]/dt/ = (k₁ + k₂[H⁺]) where [AB] = concentration of amineborane. The acid-independent solvolysis rate is accelerated and the acid-dependent rate retarded by electron-withdrawing para and meta ring substituents, by increasing N-alkyl substitution and by increasing dioxane content of the solvent. No primary hydrogen isotope effects were observed for either mode of solvolysis. For the acid-independent reaction, the rate of disappearance of amineborane equals the rate of appearance of free amine. This rate is not significantly influenced by the addition of moderate amounts of free amine or neutral salt and is essentially the same in dioxane-D₂O as in dioxane-H2O. The acid-dependent rate is subject to general acid catalysis and k₂ exhibits a slight positive salt effect. Mechanisms for both modes of solvolysis are proposed. Data for the hydrolysis of selected alkyl and heterocyclic amineboranes, including the effect of variations in structure on rate indicate that these substrates hydrolyze by a mechanism similar to that proposed for the acid-dependent solvolysis of arylamineboranes.