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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.

Qualitatively similar metal coordination as in PQQ-dependent bacterial dehydrogenases was observed for the PQQ triester in the model complex I, although the unusual five-coordinate copper(I) center is smaller and softer than the Ca2+ ion of the native enzymes. The ambidentate PQQ thus prefers coordination through the O(5)/N(6)/O(7‘) atoms even without additional support from the protein scaffold.