Ambi-Valence Taken Literally: Ruthenium vs Iron Oxidation in (1,1′-Diphosphinoferrocene)ruthenium(II) Hydride and Chloride Complexes as Deduced from Spectroelectrochemistry of the Heterodimetallic “Mixed-Valent” Intermediates

Combining two different redox-active organometallic moieties, we prepared the compounds [(Cym)RuCl(dpf)](PF6), with Cym = p-cymene = 1-isopropyl-4-methylbenzene, and the diphosphinoferrocenes (dpf) 1,1′-bis(diphenylphosphino)ferrocene (dppf; complex 3), 1,1′-bis(diisopropylphosphino)ferrocene (dippf; complex 4), and 1,1′-bis(diethylphosphino)ferrocene (depf; complex 5) as well as the structurally characterized hydride complex [(C5Me5)RuH(dippf)] (2). In contrast to the case for 2, with an approximately staggered ferrocene conformation, the chloride complexes 3−5 exhibit a syn-periplanar ferrocene arrangement due to a Cl···H(C5H4) interaction in the solid and in solution. The related new compounds [(Cym)RuH(dppf)](PF6) (6) and trinuclear (μ-dpf)[(Cym)RuCl2)]2 (7−9) were also obtained and identified by 1H and 31P NMR spectroscopy. The redox behavior of 2−6 and of the known [(C5Me5)RuH(dppf)] (1) was investigated using cyclic voltammetry, spectroelectrochemistry in the UV/vis/near-IR and IR regions, and, in part, by EPR. The first oxidation of the areneruthenium compounds 3−6 occurs reversibly at the ferrocene site, while the reduction proceeds via an ECE two-electron pattern under chloride dissociation. These results are compared to those obtained for the pentamethylcyclopentadienide/hydride complexes 1 and 2, which demonstrate unambiguously the ruthenium center as the site of the first electron loss. The different results for the two kinds of heterodimetallic d5/d6 mixed-valent intermediates, FeIIRuIII for 1+ and 2+ and FeIIIRuII for 3+−6+, are discussed with respect to the possible uses of such heterodinuclear systems in H2 conversion catalysis.

我们将两种不同的氧化还原活性有机金属片段（redox-active organometallic moieties）相结合，合成了化合物[(Cym)RuCl(dpf)](PF6)，其中Cym为对异丙基甲苯（p-cymene，即1-异丙基-4-甲基苯），而二膦二茂铁（diphosphinoferrocenes, dpf）包括1,1'-双(二苯基膦基)二茂铁（1,1′-bis(diphenylphosphino)ferrocene, dppf；配合物3）、1,1'-双(二异丙基膦基)二茂铁（1,1′-bis(diisopropylphosphino)ferrocene, dippf；配合物4）以及1,1'-双(二乙基膦基)二茂铁（1,1′-bis(diethylphosphino)ferrocene, depf；配合物5），同时还得到了经结构表征的氢化物配合物[(C5Me5)RuH(dippf)]（2）。与配合物2近似交错式的二茂铁构象不同，固态及溶液中的氯化物配合物3~5因存在Cl…H(环戊二烯基)（Cl···H(C5H4)）相互作用，呈现出顺式平面型（syn-periplanar）的二茂铁排布。我们还得到了新型相关化合物[(Cym)RuH(dppf)](PF6)（6）以及三核配合物(μ-dpf)[(Cym)RuCl2)]2（7~9），并通过1H和31P核磁共振（NMR）光谱对其进行了表征鉴定。采用循环伏安法（cyclic voltammetry）、紫外-可见-近红外（UV/vis/near-IR）及红外（IR）区域的光谱电化学（spectroelectrochemistry），并部分结合电子顺磁共振（EPR）技术，我们研究了配合物2~6以及已知配合物[(C5Me5)RuH(dppf)]（1）的氧化还原行为。芳烃钌配合物3~6的首次氧化发生在二茂铁位点，且为可逆过程；而还原过程则遵循ECE双电子路径，伴随氯离子解离。将上述结果与五甲基环戊二烯基/氢化物配合物1和2的相关结果进行对比后可明确，这两类配合物的首次电子失位位点均为钌中心。我们还针对两种不同的异双金属d5/d6混合价中间体——配合物1+和2+为FeIIRuIII型，而3+~6+为FeIIIRuII型——的差异结果展开了讨论，并探讨了此类异双核体系在氢气转化催化中的潜在应用价值。