Normal to abnormal I t Bu·AlH 3 isomerization in solution and in the solid state.

A complex of an N-heterocyclic carbene (IBu)-Bu-t (1,3-di-tert-butylimidazolin-2-ylidene) and aluminum hydride was observed to isomerize into an abnormal carbene complex aItBu center dot AlH3 (aI(t)Bu = 1,3-ditert-butylimidazolin-4-ylidene) in a polar solvent, and, for the first time, in the solid state. (IBu)-Bu-t center dot AlH3 and aItBu center dot AlH3 were structurally characterized by single crystal X-ray diffraction analysis. NMR studies and DFT computations indicate that the polarity of the solvent promotes the isomerization process. The possible pathways for the isomerization are discussed on the basis of the DFT computational studies.