N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

The annelated N-heterocyclic carbene 1 was obtained by Na/K reduction of the corresponding thione. Compound 1 exhibits the topology of an "unsaturated" carbene, yet, on the basis of 13C NMR spectroscopy and X-ray structure analysis, it behaves like a carbene with a saturated N-heterocyclic five-membered ring. The pentacarbonyl tungsten complex (2) of the sterically demanding substituted 1 contains a nonplanar carbene ligand.