Synthesis of Benzannulated N-Heterocyclic Carbene Ligands by a Template Synthesis from 2-Nitrophenyl Isocyanide

摘要

The reaction of 2-nitrophenyl isocyanide 2 with [M(CO)_5(thf)J(M = Cr,Mo,W)yields the isocyanide complexes [M(CO)_5(2)](3:M = Cr;4:M = Mo;5:M = W).Complexes 3-5 react with elemental tin under reduction of the nitro function of the isocyanide ligand to give the complexes with the unstable 2-aminophenyl isocyanide ligand.The coordinated 2-aminophenyl isocyanide ligand in all three complexes reacts spontaneously under intramolecular nucleophilic attack of the primary amine at the isocyanide carbon atom to yield the complexes with the NH,NH-benzimidazol-2-yli-dene ligand(6:M = Cr;7:M = Mo;8:M = W).An incomplete reduction of the nitro group in 3-5 is observed when hydrazine hydrate is used instead of tin.Here the formation of complexes with a coordinated 2-hydroxyl-amine-functionalized phenyl isocyanide [(CO)_5M-CN-C_6H_4.-2-N(H)-OH] is postulated and this unstable ligand again undergoes intramolecular cycliza-tion to give the NH,NOH-stabilized benzimidazol-2-ylidene complexes 9-11.The tungsten derivative 11 can be allylated stepwise by a deprotonation/ alkylation sequence first at the OH and then at the NH position to yield the monoallylated and diallylated species 12 and 13.The molecular structures of 3-5 and 12-13 were established by X-ray crystallography.