A dinuclear bis(bipyridine)ruthenium(ii) complex, [(bpy)2RuII{L2–}RuII(bpy)2]2+, incorporating an unusual non-innocent bridging ligand containing a p-benzoquinonediimine fragment: synthesis, structure, redox, and UV/VIS/NIR and EPR spectroelectrochemical properties
作者:Soma Chakraborty、Rebecca H. Laye、Rowena L. Paul、Rajesh G. Gonnade、Vedavati G. Puranik、Michael D. Ward、Goutam Kumar Lahiri
DOI:10.1039/b107307a
日期:2002.3.8
The reaction of [Ru(bpy)2(EtOH)2]2+ (bpy = 2,2â²-bipyridine) with the symmetrical binucleating phenolatodiimine ligand HOC6H4NCHC6H4CHNC6H4OH (H2L1) in ethanol under dinitrogen results in the unexpected formation of the diruthenium complex [(bpy)2RuIIOC6H4NC6H3(NH)O}RuII(bpy)2](ClO4)21. In this complex, the bridging ligand (Lsq,sq)2â contains two inequivalent o-iminophenolate N,O-chelating binding sites, each formally at the semiquinone oxidation level, linked such that there is a p-benzoquinonediimine bridge between the two Ru centres. The crystal structures of H2L1 and of 1 have been determined. Complex 1 is electrochemically active and undergoes two reversible oxidations and two reversible reductions which, on the basis of UV/VIS/NIR and EPR spectroelectrochemical evidence, comparison with related systems and consideration of the redox potentials, we assign as centred on the bridging ligand. The two oxidations (at +0.12 and + 0.35 V versus SCE) result in formation of a neutral, fully quinonoidal bridging ligand Lq,q; in the âmixed-valenceâ mono-oxidised state, a near-IR transition (1570 nm) is ascribed to an intra-ligand charge transfer from the non-oxidised (semiquinone-like) to the oxidised (quinone-like) terminus. The two reductions (at â0.98 and â1.38 V versus SCE) are localised on the central p-benzoquinonediimine unit of the bridging ligand, affording the p-benzosemiquinone radical and then
a p-diamide unit. In addition, at more extreme potentials, two oxidations at +1.49 and +1.70 V versus SCE are ascribed to Ru(II)/Ru(III) couples, and the reduction at â1.81 V versus SCE is bpy-based.
Ru(bpy)2(EtOH)2]2+ (bpy = 2、2â²-联吡啶)与对称双核酚二亚胺配体 HOC6H4NCHC6H4CHNC6H4OH (H2L1) 在二氮条件下于乙醇中反应,意外地形成了二钌配合物 [(bpy)2RuIIOC6H4NC6H3(NH)O}RuII(bpy)2](ClO4)21 。在该复合物中,桥接配体 (Lsq,sq)2â 包含两个不等价的邻亚氨基苯酚 N,O 螯合结合位点,每个位点形式上都处于半醌氧化水平,并连接在一起,这样在两个 Ru 中心之间就形成了一个对苯醌二亚胺桥。H2L1 和 1 的晶体结构已经确定。根据 UV/VIS/NIR 和 EPR 光谱电化学证据、与相关系统的比较以及对氧化还原电位的考虑,我们认为复合物 1 具有电化学活性,会发生两次可逆氧化和两次可逆还原。两次氧化(+0.12 和 + 0.35 V 相对于 SCE)形成了中性、全醌状桥接配体 Lq,q;在 "混价 "单氧化状态下,一个近红外转变(1570 nm)可归因于配体内电荷从非氧化(半醌状)向氧化(醌状)末端的转移。两次还原(相对于 SCE 的电压分别为 0.98 和 1.38 V)发生在桥接配体的中心对苯醌二亚胺单元上,产生对苯二醌自由基,然后是对二酰胺单元。此外,在更极端的电位下,Ru(II)/Ru(III)偶联物在+1.49 V和+1.70 V与SCE发生了两次氧化反应,而在â1.81 V与SCE发生的还原反应则是基于铋。