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Abstract

The organonitrile or carbonyl complexes cis-[ReCl(RCN)(dppe)₂] (1) (R = 4-Et₂NC₆H₄ (1a), 4-MeOC₆H₄ (1b), 4-MeC₆H₄ (1c), C₆H₅ (1d), 4-FC₆H₄ (1e), 4-ClC₆H₄ (1f), 4-O₂NC₆H₄ (1g), 4-ClC₆H₄CH₂ (1h), t-Bu (1i); dppe = Ph₂PCH₂CH₂PPh₂), or cis-[ReCl(CO)(dppe)₂] (2), as well as trans-[FeBr(RCN)(depe)₂]BF₄ (3) (R = 4-MeOC₆H₄ (3a), 4-MeC₆H₄ (3b), C₆H₅ (3c), 4-FC₆H₄ (3d), 4-O₂NC₆H₄ (3e), Me (3f), Et (3g), 4-MeOC₆H₄CH₂ (3h); depe = Et₂PCH₂CH₂PEt₂), novel trans-[FeBr(CO)(depe)₂]BF₄ (4) and trans-[FeBr₂(depe)₂] (5) undergo, as revealed by cyclic voltammetry at a Pt-electrode and in aprotic non-aqueous medium, two consecutive reversible or partly reversible one-electron oxidations assigned as Re^I → Re^II → Re^III or Fe^II → Fe^III → Fe^IV. The corresponding values of the oxidation potentials ^IE_1/2^ox and ^IIE_1/2^ox (waves I and II, respectively) correlate with the Pickett's and Lever's electrochemical ligand and metal site parameters. This allows to estimate these parameters for the various nitrile ligands, depe and binding sites (for the first time for a Fe^III/IV couple). The electrochemical ligand parameter show dependence on the "electron-richness" of the metal centre. The values of ^IE_1/2^ox for the Re^I complexes provide some supporting for a curved overall relationship with the sum of Lever's electrochemical ligand parameter. The Pickett parametrization for closed-shell complexes is extended now also to 17-electron complexes, i.e. with the 15-electron Re^II and Fe^III centres in cis-{[ReCl(dppe)₂]}⁺ and trans-{FeBr(depe)₂}²⁺, respectively.

Keywords: Electrochemistry; Redox potential; Nitrile complexes; Carbonyl complexes; Rhenium; Iron; Cyclic voltammetry.

References: 41 live references.