Plumbylenes stability

An interesting plumbylene stabilized by intramolecular Pb- S interactions is obtained by the double insertion of carbon disulfide into Pb S bonds of bis(arylthio) plumbylene according to equation (12). 

This interpretation of the experimental results was corroborated by ab initio calculations on the relative stabilities of a series of double bond compounds, [H2Pb=X] and their plumbylene type isomers, [frans-H-Pb-X-H] and [ciT-H-Pb-X-H] (X = O, S, Se, and Te) (vide supra) 6 The results of the theoretical calculations and experiments for lead-chalcogen double bond species are in sharp contrast to those of the other Group 14 element analogues which do not isomerize to the divalent compounds.14b... 

Although dicyclopentadienyllead(II) compounds, formally called plumbylenes, have been known since 1956, " they are not the congeners of carbenes since they are stabilized by r] -coordination of cyclopentadienyl ligands. In 1974, the first stable diaminoplumbylene [(Me3Si)2N]2Pb (173) was synthesized by Lappert and... 

For E = Pb, neither base-stabilized nor base-free derivatives have been isolated so far. The plumbanethione 123 could be indeed prepared by desulfurization of the respective tetrathiaplumbolane at —78 °C and trapped with several reagents, but has not been isolated to date. Instead, at ambient conditions the plumbylene 124 and the head-to-tail dimer, the 1,3,2,4-dithiadiplumbetane 125, is obtained (equation 16)165. 

In contrast to the heteroatom-substituted plumbylenes, a few plumbylenes bearing only carbon substituents have been reported. Some of them are stabilized by intramolecular coordination of the lone pair of a donor group in the organic substituent, thus giving the lead a coordination number greater than 2 as can be seen in the diarylplumbylene RjPb... 

In order to elucidate the thermal stability of the plumbanethione 174, tetrathiaplum-bolane 171 was desulfurized at higher temperature. Reaction of 171 with 3 equivalents of triphenylphosphine in toluene at 50 °C gave a deep red solution, from which plumbylene 182 was precipitated as pure deep red crystals (Scheme 55)112. Besides 182, 1,3,2,4-dithiadiplumbetane 183 was obtained as another lead-containing major product. It should... 

Further studies on the system showed that the size of the lead substituents is crucial. For example the reaction of the less bulky 2,4,6-triethylphenyl Grignard reagent with PbCb in THF gave an unusual product in which two plumbylenes were stabilized by the weak interactions with Br atoms of a bridging MgBr2 species (Figure 4). 

Figure 5 Plumbylene dimer stabilized by two molecules of MgBr2...

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