Redox-active planar complexes. Electrochemical investigations of palladium and platinum bis(dithioacetylacetonate) complexes and their structural analogues

Abstract

Direct- and alternating-current voltammetric investigations in CH₂Cl₂ of 17 variously substituted planar bis(dithio-β-diketonate) complexes [M(S₂C₃RHR′)₂](M = Ni, Pd, or Pt and R,R′= Bu^t,CF₃, Me, or Ph), including many new palladium and platinum complexes, confirm two reversible reductions in each case. The rapid rearrangement reported for [M(S₂C₃MeHMe)₂]^– is largely suppressed in the other derivatives, apparently for steric rather than electronic reasons. The successive one-electron transfers are found to be ligand-centred in [M(S₂C₃RHR)₂], as in the metal ‘dithienes’[M(S₂C₂R₂)₂], despite their difference in topology. An orderly and comparable dependence of reduction potentials on substituent influence (σ*_R) is displayed by all such systems. The isostructural diketonates, [M(O₂C₃RHR′)₂](M = Pd or Pt), show a parallel trend in first reduction potential and are systematically ca. 0.4 V more difficult to reduce than their dithio-analogues.