New ruthenium(II) complexes bearing N-heterocyclic carbenes

N-heterocyclic carbene complexes of ruthenium(II), [CpRu(L*)₂Cl] (2) and [CpRu(CO)(L*)-Cl] (3) (Cp = η⁵-C₅H₅; L* = l,3-dicyclohexyl-imidazolin-2-ylidene), have been obtained in high yields by reaction of [CpRu(PR₂R′)₂Cl] (R = R′ = Ph, la; 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)₂Cl] (1e) with L* gives the pentamethylcyclopentadienyl derivative [Cp*Ru(PPh₃)(L*)Cl] (5) (Cp* = η⁵-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) A). The N-heterocyclic carbene does not undergo substitution by other two-electron ligands.