Syntheses, structures, and electrochemistry of polynuclear Cu^I, Ag^I, and Pt^IIcomplexes bearing ferrocenyl group

Three polynuclear complexes, [Pt2II(dppm)2(μ-η1:η1-HC=CFc)Cl2] (1), [AgI3(dppm)3(μ3-η1C≡CFc)]·2CF3SO3(2·2CF3SO3), and [Cu3I(dppm)3(μ3-η1-C≡CFc)2]·PF6(3·PF6), were synthesized and characterized using single-crystal X-ray diffraction, UV-vis spectroscopy, and voltammetry (dppm = bis(diphenylphosphino)methane; Fc = ferrocenyl). Compound 1 is an A-frame complex in which two PtIIions are bridged by two dppm and one ethynylferrocene. Both 2·2CF3SO3and 3·PF6are composed of trimetallic Ag3Iand Cu3Icores bridged by three dppm and capped with one and two ferrocenylacetylides, respectively. All complexes exhibit reversible Fc oxidation in their cyclic voltammograms (CV), ranging from -48 ± 10 to 235 ± 10 mV vs Ag/AgNO3(0.1 M). The reduction potential difference between silver and copper complexes is mostly due to intramoleuclar. electrostatic interactions. A weak intervalence charge-transfer transition at 1250 nm arising from the mixed-valence 32+is observed in the solution near-infrared absorption spectrum of a mixture of 3·PF6and ferrocenium hexafluo-rophosphate (Cp2FePF6). Cyclic and differential pulse volatmmograms of 3·PF6show two reversible Fc oxidations separated by 110 ± 14 mV, giving a comproportionation constant Kcof 77 ± 30. The stability of the mixed-valence complex 32+arises mainly from the reduction of electrostatic repulsion and statistical distribution.