The reaction of LAl[eta2-(C2(SiMe3)2)] (1; L = HC[(CMe)(NDipp)]2, Dipp = 2,6-iPr2C6H3) with dioxygen leads to the elimination of bis(trimethylsilyl)acetylene and the formation of the corresponding aluminum monohydroxide via the oxidation of one of the CHMe2 groups on the Dipp ring.