Template Synthesis of Benzannulated N-Heterocyclic Carbene Ligands

✍ Scribed by F. Ekkehardt Hahn; Volker Langenhahn; Nicole Meier; Thomas Lügger; Wolf Peter Fehlhammer

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 285 KB
• Volume: 9
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200390079

✦ Synopsis

Abstract

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 H~2~O/HBr to afford triphenylphosphane 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‐1__H__‐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 KO__t__Bu and reaction with two equivalents of allyl bromide yields the N,N′‐dialkylated benzannulated 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.