Paramagnetic organolead complexes. EPR investigation of their formation and structures

Article abstract of DOI:10.1016/0022-328X(91)86097-A

Various triaryllead hydroxides or chlorides have been shown to react with catechols or o-benzoquinones to give paramagnetic complexes, whose structures have been investigated by EPR and ENDOR spectroscopy.The spectra indicate that the formation of these complexes involves either the cleavage of a C-Pb bond or the loss of the inorganic group.The hyperfine splittings for the organometallic radicals were interpreted in terms of a permutation equilibrium between two paramagnetic species.Investigation of the temperature dependence of the EPR-signals has given the kineticparameters for some typical compounds.In general, complexes consisting of the semiquinone and the triaryllead moiety at room temperature undergo a rapid interconversion on the EPR time scale, but replacement of an aryl by OH or Cl group leads to lower rates and so to the co-existence of two isomeric species at ambient temperature.From the results a cation migration mechanism seems very unlikely and so a permutation isomerisation is proposed.Semiquinone-triphenyllead complexes can undergo a secondary reaction with photolytically generated alkoxy radicals to give products formed by substitution of one phenyl group by the alkoxy group.These paramagnetic compounds show slow permutation rates.