Syntheses, structures, and electrochemistry of polynuclear CuI, AgI, and PtII complexes bearing ferrocenyl group

Abstract

Three polynuclear complexes, [Pt2 II(dppm)2(μ-η1:η 1-HC=CFc)Cl2] (1), [AgI 3(dppm)3(μ3-η1 C≡CFc)]·2CF3SO3 (2·2CF3SO3), and [Cu3 I(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 PtII ions are bridged by two dppm and one ethynylferrocene. Both 2·2CF3SO3 and 3·PF6 are composed of trimetallic Ag3 I and Cu3 I cores 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·PF6 and ferrocenium hexafluo-rophosphate (Cp2FePF6). Cyclic and differential pulse volatmmograms of 3·PF6 show two reversible Fc oxidations separated by 110 ± 14 mV, giving a comproportionation constant Kc of 77 ± 30. The stability of the mixed-valence complex 32+ arises mainly from the reduction of electrostatic repulsion and statistical distribution.