Molecular Addition Compounds. 12. Borane Adducts of Trialkylamines with Isopropyl and Isobutyl Groups of Intermediate Steric Requirements for Hydroboration

Abstract

Borane adducts of selected trialkylamines with isopropyl and isobutyl groups of intermediate steric requirements have been prepared and examined as hydroborating agents. Their reactivity toward 1-octene follows the order i-Pr2NEt·BH3 < i-Bu3N·BH3 < i-PrNBui2·BH3 < i-Pr2NCH2CH2OMe·BH3 < i-Pr2NBui·BH3 < i-Pr3N·BH3 < i-Pr2NBus·BH3. Borane adducts with i-Pr2NBui, i-Pr3N, and i-Pr2NBus are highly reactive, hydroborating 1-octene in THF at room temperature in less than 1 h. The adduct i-Pr2NBui·BH3 is a liquid above 0 °C, 4.6 M in BH3, stable over long periods, and soluble in diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, dichloromethane, and n-pentane. The adduct i-Pr3N·BH3 is a solid, while i-Pr2NBus·BH3 is a liquid, unstable, slowly evolving diborane at room temperature.