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–).