Preparation of an Isocyano-β-diketone via its Metal Complexes, by Use of Metal Ions as Protecting Groups

A ligand containing isocyanide and β-diketone functional groups, 3-(4-isocyanophenyl)-2,4-pentanedione (HacphNC), and several of its metal complexes have been prepared. The free isocyano-β-diketone could not be prepared by dehydration of the analogous formamide, HacphNHCHO, because of the reactivity of its β-diketone moiety. Instead, the metal complexes Al(acphNC)3, Fe(acphNC)3, Cu(acphNC)2, and Zn(acphNC)2 were synthesized by dehydration of the formamido-β-diketonate complexes Al(acphNHCHO)3, Fe(acphNHCHO)3, Cu(acphNHCHO)2, and Zn(acphNHCHO)2. The free isocyano-β-diketone, HacphNC, can be liberated from its Al and Fe complexes by treatment with oxalate (C2O42−) and HC2O4−. In addition to these O-bound complexes, C(N)-bound complexes can be prepared by the reaction of either Al(acphNC)3 or HacphNC with Au(I). X-ray analyses of HacphNC, Al(acphNC)3, (HacphNC)AuCl, Cu(acphNHCHO)2, trans-Zn(acphNHCHO)2(H2O)2, and two other intermediates are also reported.