An electron spin resonance study of the photolysis of some cyclopentadienyl-lead compounds: the comparison with tin

Abstract

Photolysis of a hydrocarbon solution of cyclopentadienyltrimethyl-lead, cyclopentadienyltriphenyl-lead, or dicyclopentadienyldiphenyl-lead with u.v. light shows the e.s.r. spectrum of the cyclopentadienyl radical. Under the same conditions, cyclopentadienyltriethyl-lead shows the spectrum of only the cyclopentadienyl radical above –50 °C, and of only the ethyl radical below –100 °C. These reactions provide a convenient source of the corresponding organo lead radicals. The lead radicals have properties parallel to those of the corresponding tin CpPbR₃ [graphic omitted] Cp˙+˙PbR₃ radicals, though they are less reactive towards alkyl bromides and alkenes. The radicals Me₃Pb˙, Et₃Pb˙, and Ph₃Pb˙ add to biacetyl to give pairs of radicals which are identified as the fluxional cis- and trans- monodentate adducts; CpPh₂Pb˙ gives what is believed to be the cis-adduct which is non-fluxional on the e.s.r. time scale. Similarly Me₃Pb˙ and Ph₃Pb˙ form an adduct with 3,6-di-t-butyl-1,2-benzoquinone which is rapidly fluxional, whereas CpPh₂Pb˙ gives an adduct which is slowly fluxional. All four lead radicals are trapped by 2-methyl-2-nitropropane to give the persistent nitroxyl radicals Me₃C(R₃PbO)NO˙.