Hahn FE, García Plumed C, Münder M, Lügger T. Synthesis of BenzannulatedN-Heterocyclic Carbene Ligands by a Template Synthesis from 2-Nitrophenyl Isocyanide.
Chemistry 2004;
10:6285-93. [PMID:
15526316 DOI:
10.1002/chem.200400576]
[Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The reaction of 2-nitrophenyl isocyanide 2 with [M(CO)5(thf)] (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-ylidene 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-hydroxylamine-functionalized phenyl isocyanide [(CO)5M-CN-C6H(4-)-2-N(H)-OH] is postulated and this unstable ligand again undergoes intramolecular cyclization 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.
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