| Popis: |
The cyclization reaction of coordinated β-functional phenyl isocyanides was used to generate coordinated anellated N-heterocyclic carbenes. Coordinated 2-trimethylsiloxyphenyl isocyanide reacts, after SiO bond cleavage, to yield a complex with a coordinated benzoxazol-2-ylidene ligand. The cyclization reaction of coordinated 2-aminophenyl isocyanide, obtained in situ from 2-azidophenyl isocyanide, yields the coordinated benzimidazol-2-ylidene. Both ylidenes can be alkylated at the nitrogen atoms. Attempts to generate four benzimidazol-2-ylidenes at PtII and to bridge them by N-alkylation leading to a crown ether-like ligand with carbene donors are presented here. Free N-heterocyclic carbenes derived from benzimidazole with large N-substituents exist as monomers while they dimerize to dibenzotetraazafulvalenes when substituted with sterically less-demanding substituents at the ring nitrogen atoms. A chemical equilibrium between the monomeric carbene and its dimerized enetetraamine exists for the N,N′-isopropyl substituted derivative. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:540–549, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10099 |
