The chemistry of (cyclopentadienyl)phenyl-lead(IV) compounds

Abstract

The yellow air-stable (cyclopentadienyl)phenyl-lead(IV) compounds, PbPh_4–n(cp)_n[n= 1 or 2, cp = C₅H₅], have been synthesised by the reaction of the corresponding phenyl-lead(IV) chloride and lithium cyclopentadienide in diethyl ether. Crystals of PbPh₃(cp) are monoclinic, space group P2₁/c, with a= 9.5426, b= 12.3843, c= 16.1714 Å, β= 102.3358°, and Z= 4, and comprise discrete non-interacting molecules with a distorted tetrahedral geometry. The Pb–C(cp) bond distance [2.30(2)Å] is significantly longer than the Pb–C(Ph) distances [mean 2.22(2)Å], indicating a substantial weakening of this bond. The endocyclic C–C bonds of the cyclopentadienyl ring (which is planar) are consistent with a concentration of π-electron density over the carbon atoms remote from the lead. Reaction of PbPh₃(cp) with acetic acid, thiophenol, and imidazole proceeds with exclusive Pb–C(cp) bond cleavage affording PbPh₃(O₂CMe), PbPh₃(SPh), and PbPh₃(N₂C₃H₃), respectively. Only PbPh₄ was isolated from the reaction with 4-chlorophenol. The compound PbPh₂(cp)₂ decomposes on attempted sublimation at 60–70 °C and 0.01 mmHg giving Pb(cp)₂, whilst reaction with hydrogen chloride, carboxylic acids, and imidazole yields the corresponding diphenyl-lead(IV) derivative. Cleavage of all four Pb–C bonds occurs on reaction with thiols, when lead(II) thiolates are the products. Reaction with phenols yields products of composition [PbPh₂(O₂CMe)]_n which presumably contain metal–metal bonds. The mechanisms of the reactions are discussed.