Chemistry of ruthenium with some dioxime ligands. Syntheses, structures and reactivities

Abstract

Reaction of two dioxime ligands, viz. dimethylglyoxime (H₂dmg) and diphenylglyoxime (H₂dpg), (abbreviated in general as H₂L, where H stands for the oxime protons) with [Ru(PPh₃)₃Cl₂] in 1¦1 mole ratio affords complexes of type [Ru(PPh₃)₂(H₂L)Cl₂]. Structure of the [Ru(PPh₃)₂(H₂dpg)Cl₂] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N₂P₂Cl₂ with the two PPh₃ ligands in trans and the two chlorides in cis positions. Reaction of the dioxime ligands with [Ru(PPh₃)₃Cl₂] in 2¦1 mole ratio in the presence of a base affords complexes of type [Ru(PPh₃)₂(HL)₂]. Structure of the [Ru(PPh₃)₂(Hdmg)₂] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N₄P₂ with the two PPh₃ ligands in trans positions. Reaction of the [Ru(PPh₃)₂(H₂dpg)Cl₂] complex with a group of bidentate acidic ligands, viz. picolinic acid (Hpic), quinolin-8-ol (Hq) and 1-nitroso-2-naphthol (Hnn), (abbreviated in general as HL′, where H stands for the acidic proton) in the presence of a base affords complexes of type [Ru(PPh₃)₂(H₂dpg)(L′)]⁺ isolated as perchlorate salts. All the complexes are diamagnetic (low-spin d⁶, S=0) and in dichloromethane solution show several intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a reversible ruthenium(II)-ruthenium(III) oxidation within 0.36-0.98 V versus SCE followed by a quasi-reversible ruthenium(III)-ruthenium(IV) oxidation within 0.94-1.60 V versus SCE.