Oxygenation and carbonylation studies of some ruthenium(III) Schiff base complexes containing nitrogen and oxygen as donor atoms. II

Abstract

Synthesis and characterization of a series of ruthenium(III) Schiff base complexes of the type [Ru^IIILXY] where L=Schiff base viz. bis(naphthaldehyde)-o-phenylenediimine (naphoph), bis(naphthaldehyde)ethylenediimine (naphen), bis(naphthaldehyde)propylenediimine (naphprop) and bis(naphthaldehyde)diethylenetriimine (naphdien); X=Cl and Y=Cl imidazole (Im) or 2-methylimidazole (2-MeIm) are reported. Elemental analysis, conductivity and IR studies of the complexes suggest an octahedral geometry around ruthenium. Magnetic moments of the complexes indicate a single unpaired electron in a low spin d⁵ configuration. Oxygenation studies in DMF or THF solutions suggest the reversible binding of molecular oxygen to the ruthenium(III) complexes. EPR studies at liquid nitrogen temperature and UV---Vis measurements at room temperature support the formation of a Ru(IV) superoxo species [Ru^IVL(O₂)⁻Y]. The EPR spectrum of the Ru(IV) superoxo complex at 77 K (g₁=2.063, g₂=2.047, g₃=2.023) is consistent with the odd electron occupying a highly localized antibonding π^∗ orbital of molecular oxygen. The reversible binding of O₂ and CO has been carried out in DMF at 10, 25 and 40°C. The complexes show discrimination against the binding of CO over O₂ as evinced by values of K_O2 and K_CO in the complexes. The thermodynamic paramegers ΔH°, ΔG° and ΔS° for oxygenation and carbonylation reactions are evaluated.