Collect. Czech. Chem. Commun. 2003, 68, 1663-1676

Electrochemical Behaviour of trans-[FeH(CN)(dppe)2] Adducts

Sílvia S. P. R. Almeidaa, M. Fátima C. Guedes Da Silvaa,b and Armando J. L. Pombeiroa,*

a Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
b Universidade Lusófona de Humanidades e Tecnologias, Campo Grande 376, 1749-024 Lisboa, Portugal


Electrochemical behaviour of various metallo cyano adducts of trans-[FeH(CN)(dppe)2], viz. the dinuclear complexes [FeH(dppe)2(μ-CN)PdCl2(PPh3)], [FeH(dppe)2(μ-CN)NiCl2(PCy3)], and trinuclear [{FeH(dppe)2(μ-CN)}2(ReOCl3)], [{FeH(dppe)2(μ-CN)}2PtCl(Ph)] and [{FeX(dppe)2(μ-CN)}2WCl3(OH)] (X = Cl or OH, dppe = 1,2-diphenylphosphinoethane, PCy3 = P(C6H11)3), as well as the benzoylisocyanide mononuclear adduct trans-[FeH(CNCOPh)- (dppe)2], is reported. All of them exhibit FeII/FeIII-based oxidations (which are reversible, except for trans-[FeH(CNCOPh)(dppe)2]). The metallocyanide bridges C≡N-Re-N≡C and C≡N-W-N≡C in [{FeH(dppe)2(μ-CN)}2(ReOCl3)] and [{FeX(dppe)2(μ-CN)}2WCl3(OH)], respectively, allow electronic communication between the iron centres, with possible generation of mixed-valence FeII/FeIII complexes whose comproportionation constant could be estimated in the former case. From the values of the measured oxidation potentials, the electrochemical PL and EL ligand parameters have been estimated for the metallocyanide ligands that were shown to behave as stronger net electron donors than organoisocyanides, although weaker than cyanide itself. Ligand-centred reduction processes were also observed to lead, in the cases of complexes trans-[FeH(CNCOPh)(dppe)2] (CNCOPh-based reduction) and [FeH(dppe)2(μ-CN)PdCl2(PPh3)] (PdII-based reduction in the CNPdCl2(PPh3)- metallocyanide ligand), to the dissociation of the adduct, with regeneration of the parent cyano complex trans-[FeH(CN)(dppe)2], thus reflecting the reductive decrease of the electrophilic (or Lewis acidic) character of the benzoyl and {PdCl2(PPh3)} groups.

Keywords: Bridging cyanide; Heteronuclear complexes; Comproportionation constant; Electrochemistry; Cyclic voltammetry; Redox-potential parameterisation; Iron; Transition metals; Multinuclear complexes.

References: 49 live references.