Ruthenium Induced C−N Bond Activation of an N-Heterocyclic Carbene:  Isolation of C- and N-Bound Tautomers

C−N bond activation of the N-heterocyclic carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene occurs with Ru(PPh3)3(CO)HCl to give the C-2 bound 1-isopropyl-4,5-dimethylimidazol-2-ylidene complex Ru(C−IiPrHMe2)(PPh3)2(CO)HCl via loss of propene. In the presence of free carbene, this undergoes tautomerism to the corresponding imidazole compound Ru(N−IiPrHMe2)(PPh3)2(CO)HCl.