Aryl plumbylene

Note also the reactivity of the heteroleptic plumbylene 174 toward carbon disulfide. Treatment of 174 with excess amount of carbon disulfide resulted in a formation of unexpected product, lead(II) bis(aryl trithiocarbonate) (192), as a yellow, air- and moisture-stable solid (Scheme 14.85). The reaction must involve not only the insertion of carbon disulfide into the Pb—S bond, but also the formal insertion of a sulfur atom into the Pb C(Tbt) bond and subsequent insertion of another... 

The successful synthesis of a cyclic oligoplumbane was not reported until 2003. The outcome of reactions of lead(II) halides with aryl Grignard reagents ArMgBr depends on both the steric requirements of the ligand and the reaction conditions. When Ar = 2- Bu-4,5,6-Me3C6H a monomeric plumbylene... 

Finally, we shall briefly discuss the compounds of the silicon subgroup elements in their divalent state (germylenes, stannylenes and plumbylenes) R2M (R = alkyl, aryl). The chemical bonds in R2M are formed by the px and py orbitals of M. The pz orbital is unoccupied and there is an unshared electron pair in an s-orbital of M. Therefore, the R2M compounds have both electrophilic and nucleophilic properties. The valence angle R—M—R diminishes as the atomic number of M increases. The distances of M—R bonds in R2M are less than in the corresponding tetracoordinate R4M derivatives87. The spatial structure of R2M compounds, the shielding of the reaction centre (M ) as well as the possibility for R2M molecules to transit from a singlet state into a triplet state depend on the steric bulk of the R substituents. If the R substituents are bulky, some R2M ... 

Surprisingly, in compound 31 two relatively short Pb Si contacts to adjacent Me3Si groups are observed49 which are only about 20% longer than the covalent Pb(II)—Si bonds in heteroleptic aryl(silyl)plumbylenes. 

In 1974 the first stable diaminoplumbylene (76) was synthesized by Lappert and coworkers68 and since then many other stable plumbylenes with heteroatom substituents have been reported. Recently, the synthesis and characterization of a stable aryl(arylthio)-plumbylene (77), which is one of the rare examples of heteroleptic plumbylenes, have also been reported (Scheme 29)69. 

The reaction of less hindered diarylplumbylenes with elemental sulfur, Sg, gives three different types of Pb-S heterocycles, whereas the reaction of highly crowded diaryl plumbylenes gives only the aryl substituted polysulfides (Scheme 2). 

Scheme 2 Reactions of diaryl plumbylenes with Sg showing the formation of plumbathione hetrocycles and aryl polysulfides...

Other synthetic methods are less known. For example, an aryl (arylthio)plumbylene has been obtained by unusual 1,2-aryl migration from cyclic five-membered tetrathiaplumbane by desulfurization with a triphenylphosphine along with other products at high temperature according to equation (3). Presumably, the reaction occurs through the plumbathione Ar2Pb=S intermediate. 

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