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

Abstract

Reaction of two dioxime ligands, viz. dimethylglyoxime (H 2dmg) and diphenylglyoxime (H 2dpg), (abbreviated in general as H 2L, where H stands for the oxime protons) with [Ru(PPh 3) 3Cl 2] in 1:1 mole ratio affords complexes of type [Ru(PPh 3) 2(H 2L)Cl 2]. Structure of the [Ru(PPh 3) 2(H 2dpg)Cl 2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N 2P 2Cl 2 with the two PPh 3 ligands in trans and the two chlorides in cis positions. Reaction of the dioxime ligands with [Ru(PPh 3) 3Cl 2] in 2:1 mole ratio in the presence of a base affords complexes of type [Ru(PPh 3) 2(HL) 2]. Structure of the [Ru(PPh 3) 2(Hdmg) 2] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is N 4P 2 with the two PPh 3 ligands in trans positions. Reaction of the [Ru(PPh 3) 2(H 2dpg)Cl 2] 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(PPh 3) 2(H 2dpg)(L′)] + isolated as perchlorate salts. All the complexes are diamagnetic (low-spin d 6, 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.