Oxidation and Deprotonation of a Ruthenium(II) Complex with Quinoline-2-carbaldehyde (Pyridine-2-carbonyl)hydrazone and Formation of Hydrazonato-Bridged Heterodimetallic Complexes

Abstract Reactions of a ruthenium(II) complex containing quinoline-2-carbaldehyde (pyridine-2-carbonyl)hydrazone (HL), trans(P,P)-[RuCl2(PPh3)2(HL)] (1), and 3d-metal(II) chlorides resulted in heterodimetallic complexes, [RuCl2(PPh3)2(µ-L)MCl2] (2M, M = Mn, Fe, Co, Ni, Cu, and Zn), in which the deprotonated hydrazonate (L−) bridged two metal ions in the µ-1(Ru)κ2N,O:2(M)κ3N′,N′′,N′′′ mode. The coordination bond lengths around the Ru and M centers suggested that the oxidation states in the complexes 2M could be assigned as RuIII and MII; this was also supported by magnetic, electrochemical, and spectroscopic measurements. In addition, oxidation of complex 1 by (NH4)2[Ce(NO3)6] gave the corresponding mononuclear RuIII complex with the deprotonated hydrazonate, trans(P,P)-[RuCl2(PPh3)2(L)] (3). It is suggested that oxidation of the Ru center lead to the concerted deprotonation from the hydrazone ligand. Addition of excess HClO4 to complex 3 gave a doubly protonated RuIII complex, 4(ClO4)2; in this complex the hydrazonate moiety was not protonated, but both the quinolyl and pyridyl N atoms were protonated. Complexes 3 and 42+ could be interconverted by the addition of acid or base without changing the oxidation state of the Ru center.