Redox potential and substituent effects in ferrocene derivatives: II |
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Authors: | M Emí lia NPRA Silva Armando J L Pombeiro and Jo o J R Fraú sto da Silva Rudolf Herrmann and Norbert Deus Richard EBozak |
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Institution: | Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Avenida Rovisco Pais, 1096 Lisboa Codex, Portugal Organisch-Chemisches Institut, Technische Universität München, Lichtenbergstrasse 4, D-8046 Garching, Germany Department of Chemistry, California State University, Hayward, CA 94542, USA |
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Abstract: | The anodic behavior of 31 ferrocene derivatives (FcX) (four of which have been prepared for the first time) of the types shown below has been investigated by cyclic voltammetry (and, in some cases, also by controlled-potential electrolysis and differential pulse polarography) at a Pt electrode, in an aprotic solvent: Fc---C(Y)=Z (class A; Y = R (hydrogen, alkyl or unsaturated-carbon moiety) or Cl; Z = CRR′, derived functionalized groups or {W(CO)5}); Fc---C(Y)=O (class B; Y --- R or OH); other types (class C, including azide, other unsaturated N moieties, acyloxy or phosphino); disubstituted ferrocenes (class D, with alkyl, aminoalkyl, phosphino, B(OH)2 or −HGCl substituents, or the S---S---S bridge). All these substituted ferrocenes exhibit a one-electron reversible oxidation centered at iron and the effect of the substituents on the half-wave oxidation potential is discussed in terms of electronic properties. Using the accepted linear correlations between the half-wave oxidation potential and the Hammett constant σp of the substituent, σp was estimated for the first time for 29 of the substituents in the ferrocenes listed above. The anomalous behavior of complexes with a hydroxy or a carbonyl group is discussed. No correlation was observed between the oxidation potential and either the energy of the electronic absorption bands or the 1H NMR chemical shift of the unsubstituted cyclopentadienyl ring, although there are rough correlations for class A compounds. This behaviour is compared with those of Fc-CHYZ]. kw]Iron; Redox potentials; Ferrocenes; Electrochemistry; Substituent effects |
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