C–C Bond Formation at an Aluminacyclopropane

The reactivity of the aluminacyclopropane compound K[Al(NON)(η2-C2H4)] (NON = κN,N’-[O(SiMe2NDipp)2]2–; Dipp = 2,6-iPr2C6H3) toward isocyanides R–NC (R = Cy, Ad, tBu; Cy = cyclohexyl, Ad = 1-adamantyl) and benzophenone is described. All reactions proceed via insertion of the substrate into an Al–C bond of the aluminacycle, with C–C bond formation leading to ring-expanded products. With isocyanide substrates, either monoinsertion (R = Cy, Ad, tBu) to afford the four-membered aluminacyclobuta-1-imine ring, or double insertion (R = tBu) to form an aluminacyclopenta-1,2-diimine ring is observed. The reaction with benzophenone affords the corresponding insertion product that incorporates the C═O functionality to form an expanded five-membered AlOC3 ’alumina-tetrahydrofuran’ ring. The NON-ligand of this product undergoes a thermally induced, intramolecular 1,3-silyl retro-Brook rearrangement to afford the corresponding “Al(NNO)” product ([NNO]2– = κN,O-[N(Dipp)SiMe2N(Dipp)SiMe2O]2–).