1,8-bis(imidazolin-2-yliden-1-yl)carbazolide (bimca): A new CNC pincer-type ligand with strong electron-donating properties. Facile oxidative addition of methyl iodide to Rh(bimca)(CO)

The synthesis of a new CNC pincer-type ligand based on an N-heterocyclic carbene substituted carbazole is presented. The resulting 3,6-di-tert-butyl-1,8-bis(3-methylimidazolin-2-yliden-1-yl)carbazolide (bimca) is a monoanionic, meridionally coordinating tridentate ligand that was generated in situ by deprotonation of the imidazolium salt (bimca)center dot 2HI (3a) or (bimca)center dot 2HBF(4) (3b) and characterized by NMR spectroscopy as the Li complex 4. The successful transmetalation to rhodium upon reaction with [Rh(CO)(2)Cl](2) yielded Rh(bimca)(CO) (5). This complex shows a very small wavenumber in the IR spectrum for the nu(CO) band, thus indicating strong sigma-donor and weak pi-acceptor properties of the bimca ligand. The highly nucleophilic character of the Rh(I) center was proven by the formal oxidative addition of methyl iodide to Rh(bimca)(CO) (5), a reaction that proceeded more quickly than with any other Rh(I) complex reported so far. The complex Rh(bimca)(CH3)I(CO) (6) as well as Rh(bimca)(CO) (5) were characterized by X-ray crystal structure analyses and show a strong distortion of the CO ligand from the Rh(bimca) plane.