New ruthenium(II) complexes bearing N-heterocyclic carbenes

N-heterocyclic carbene complexes of ruthenium II), [CpRu(L*)(2)Cl] (2) and [CpRu(CO)(L*)Cl] (3) (Cp = eta(5)-C5H5; L* = 1,3-dicyclohexyl-imidazolin-2-ylidene), have been obtained in high yields by reaction of [CpRu(PR2R')(2)Cl] (R = R'= Ph, 1a; R = Ph, R'= 2-MeC6H4, 1b) and [CpRu(CO){PPh2(2-MeC6H4)}Cl] (1c), respectively, with the free carbene L*. The mixed dicarbene complex [CpRu(=CPh2)(L*)Cl] (4) is prepared from [CpRu(=CPh2){PPh2(2-MeC6H4)}Cl] (1d) and an equimolar amount of L*, whereas subsequent reaction of 1d with L* leads to formation of 2, along with tetraphenylethene. The reaction of [Cp*Ru(PPh3)(2)Cl] (1e) with L* gives the pentamethylcyclopentadienyl derivative [Cp*Ru(PPh3)(L*)Cl] (5) (Cp* = eta(5)-C5Me5) by displacement of 1 equiv of PPh3. Complex 5 reacts in toluene with CO, pyridine (Py), and N2CHCO2Et, affording [Cp*Ru(CO)(L*)Cl] (6), [Cp*Ru(Py)(L*)Cl] (7), and the mixed dicarbene [Cp*Ru(=CHCO2Et)(L*)Cl] (8), which were isolated in high yields. The molecular structure of complex 6 has been determined by an X-ray investigation, and the carbene-ruthenium distance clearly indicates a single bond (2.0951(18) Angstrom). The N-heterocyclic carbene does not undergo substitution by other two-electron ligands.