Trimetallic complexes featuring Group 10 tetracyanometallate dianions as bridging ligands

The trimetallic complexes {Ru(PPh3)2Cp}2{μ-M(CN)4} and {Ru(dppe)Cp*}2{μ-M(CN)4} (M = Ni, Pd, Pt) have been prepared from reactions of RuCl(PPh3)2Cp or RuCl(dppe)Cp* with the appropriate tetracyanometallate salt, and structurally characterised. While a similar reaction of FeCl(dppe)Cp with K2[Pt(CN)4] afforded {Fe(dppe)Cp}2{μ-Pt(CN)4}, the iron cyanide complex Fe(CN)(dppe)Cp was isolated as the only iron containing product from reaction of FeCl(dppe)Cp with K2[Ni(CN)4]. The trimetallic complexes can be oxidised in two sequential one-electron steps. Spectroelectrochemical experiments reveal weak NIR absorption bands in the mono-oxidised complexes which are not present in the binuclear complex K[Ru(dppe)Cp*{Pt(CN)4}], and are therefore attributed to RuII → RuIII charge transfer processes. The coupling parameter, Vab, extracted using Hush-style analysis falls in the range 250 ± 50 cm−1, consistent with the weak interaction between the Group 8 metal centres. The energy of the IVCT process is dominated by reorganisation energy of the Group 8 metal–ligand fragment.

The tetracyanometallate dianions [M(CN)4]2− (M = Ni, Pd, Pt) react readily with RuClL2Cp′ (L = PPh3, Cp′ = Cp; L2 = dppe, Cp′ = Cp*) to give trimetallic complexes. The mixed-valence cations generated by one-electron oxidation of these trimetallic complexes are of the Class II variety, with the reorganisation energy associated with the charge transfer process being a major contribution to the IVCT process.Figure optionsDownload as PowerPoint slide