Metal-Template-Controlled Stabilization of β-Functionalized Isocyanides

Reaction of 2-azidoethyl isocyanide 1, 2-azidophenyl isocyanide 2, or 2-nitrophenyl isocyanide 3 with complexes [Mo(CO)3(dppe)(py)] [4] or [W(CO)3(dppe)(N≡CCH3)] [5] yields the isocyanide complexes [Mo(CO)3(dppe)(C≡NR)] ([6]: C≡NR = 1; [12]: C≡NR = 2; [13]: C≡NR = 3) and [W(CO)3(dppe)(C≡NR)] ([7]: C≡NR = 1; [14]: C≡NR = 2; [15]: C≡NR = 3). Reduction of the nitro or azido groups attached to the isocyanide ligands by Zn/NH4Cl (azidoethyl or azidophenyl isocyanides) or Raney-nickel/hydrazine hydrate (nitrophenyl isocyanide) yields exclusively the complexes bearing the 2-amino-functionalized isocyanides. The normally unstable 2-amino-functionalized isocyanides are stabilized by M→C≡NR back-bonding, which deactivates the isocyanide carbon atom for an intramolecular nucleophilic attack by the primary amine.