Aluminum-Boron Bond Formation by Boron Ester Oxidative Addition at an Alumanyl Anion

The potassium diamidoalumanyl, [K{Al(SiN^Dipp)}]₂ (SiN^Dipp = {CH₂SiMe₂NDipp}₂), reacts with the terminal B-O bonds of pinacolato boron esters, ROBpin (R = Me, i-Pr), and B(OMe)₃ to provide potsassium (alkoxy)borylaluminate derivatives, [K{Al(SiN^Dipp)(OR)(Bpin)}] (R = Me, n = 2; R = i-Pr, n = ∞) and [K{Al(SiN^Dipp)(OMe)(B(OMe)₂)}]_∞, comprising Al-B σ bonds. An initial assay of the reactivity of these species with the heteroallene molecules, N,N'-diisopropylcarbodiimide and CO₂, highlights the kinetic inaccessibility of their Al-B bonds; only decomposition at high temperature is observed with the carbodiimide, whereas CO₂ preferentially inserts into the Al-O bond of [K{Al(SiN^Dipp)(OMe)(Bpin)}]₂ to provide a dimeric methyl carbonate species. Treatment of the acyclic dimethoxyboryl species, however, successfully liberates a terminal alumaboronic ester featuring trigonal N₂Al-BO₂ coordination environments at both boron and aluminum.