Template synthesis of benzannulated N-heterocyclic carbene ligands

The reaction of 2-azidophenyl isocyanide (7) with [M(CO)(5)(thf)] (M = Cr, W) yields the isocyanide complexes [M(CO)5(7)] (M = Cr 8, M = W 9). Complexes 8 and 9 react with tertiary phosphines such as triphenylphosphane at the azido function of the isocyanide ligand to give the 2-triphenylphosphiniminophenyl isocyanide complexes 10 (M = Cr) and 11 (M = W). The polar triphenylphosphiniminophenyl function in complexes 10 and 11 can be hydrolyzed with H2O/HBr to afford triphenyl-phosphane oxide and the complexes containing the unstable 2-aminophenyl isocyanide ligand. This ligand spontaneously cyclizes by intramolecular nucleophilic attack of the primary amine at the isocyanide carbon atom to yield the 2,3-dihydro-1H-benzimidazol-2-ylidene complexes 12 (M = Cr) and 13 (M = W). Double deprotonation. of the cyclic NH,NH-carbene ligands in 12 and 13 with KOtBu and reaction with two equivalents of allyl bromide yields the N,N'-dialkylated benzarmulated N-heterocyclic carbene complexes 14 (M Cr) and 15 (M = W). The molecular structures of complexes 9 and 11-15 were confirmed by X-ray diffraction studies.