Phenolato and alkoxo promoted change in the ligand coordination mode in a four-membered ortho-metalated ruthenium(II) organometallics

Abstract

The reaction of Ru(κ²C,O-RL)(PPh₃)₂(CO)(Cl) [κ²C,O-RL is C₆H₂O-2-CHNHC₆H₄R(p)-3-Me-5 and R = Me, OMe, Cl] with excess sodium p-methylphenolate (p-MeC₆H₄ONa) or sodium methoxide (MeONa) in dichloromethane–methanol medium afforded the paramagnetic binuclear ruthenium(III) complexes of the type [Ru(µ:κ³C,N,O-RL)(PPh₃)(CO)(OR′)]₂ [κ³C,N,O-RL is C₆H₂O-2-CHNC₆H₄R(p)-3-Me-5] in moderate yield. Three different R and two different R′ groups have been used in this study: R = Me and R′ is p-MeC₆H₄, 2(Me); R = OMe and R′ is p-MeC₆H₄, 2(OMe); R = Cl and R′ is p-MeC₆H₄, 2(Cl); R and R′ = Me, 3. The binding of the phenolato/alkoxo ligand is attended with the cleavage of the RuC(aryl), RuCl and one of the RuP bonds in Ru(κ²C,O-RL)(PPh₃)₂(CO)(Cl) and the RL ligand is now coordinated with one of the metal centers in the complexes via the imine nitrogen and the phenolato oxygen atoms whereas the aryl carbon atom of the RL ligand bridges the other ruthenium center. These are the first examples of structurally characterized binuclear ruthenium(III) complexes in which the RL ligand behaves as a bridging tridentate ligand. These complexes have very similar spectral (UV–vis, IR, EPR) and electrochemical properties which are also reported. Structure determination of [Ru(µ:κ³C,N,O-MeL)(PPh₃)(CO)(OR′)]₂ (R′ = p-MeC₆H₄ and Me) has revealed a distorted octahedral RuC₂O₂NP coordination sphere with the pairs (C, O), (C, N), and (P, O) defining the three trans directions. The Ru⋯Ru distances in the complexes are clearly outside of the range for a RuRu single bond. The magnetic and X-band EPR spectral measurements indicate the absence of any strong magnetic interaction between the two low-spin Ru(III) centers of the complexes.