Palladium(I) ? Radicals. Electrochemical Preparation and Study of Their Reaction Pathways

Article abstract of DOI:10.1021/ja00236a018

The reduction of a series of Pd(II) complexes has been studied by electrochemistry and spectroscopy.Neutral Pd(I) radicals may be obtained from the reduction of (η⁵-C5Ph5)Pd(η⁴-diolefin) cations, where diolefin = 1,5-cycloctadiene, norbornadiene, or dibenzocyclooctatetraene.The one-electron processes are diffusion-controlled and highly reversible, yielding the first stable Pd(I) ? radicals.The dibenzocyclooctatetraene derivative is isolable.These complexes undergo radical reaction with water, chlorinated hydrocarbons, and peroxides to give ?,?-Pd(II) complexes identical with those obtained by direct attack of nucleophiles on the starting Pd(II) cationic complexes.Reversible oxidation of (η⁵-C5Ph5)Pd(η⁴-diolefin) cations demonstrates the existence of formal Pd(III) complexes in these systems.The pentaphenylcyclopentadienyl ligand gives kinetic stabilization to both Pd(I) and Pd(III), compared to the unsubstituted cyclopentadienyl analogues.