Divalent lead compounds

Whereas GeCl2 and SnCl2 are strong reducing agents, many divalent lead compounds, such as the halides and the diacetate, are perfectly stable, thanks to the inert pair effect. Like... 

Among group IV elements it is the most electropositive, and has the most stable divalent state. The coordination number for divalent lead compounds ranges from 2 to 7, and for tetravalent ones from 4 to 8. The stereochemistry is usually octahedral or tetrahedral. 

Several different chemical classes of additives are used for thermal stabilization of PVC. These include divalent lead compounds, tin and antimony based chemicals, and mixed compounds of cadmium/ barium, calcium/zinc, and many others. In general, the lead based thermal stabilizers are used in electrical applications, the tin based ones are used for external uses in siding and other extruded shapes, and mixed compounds are used in plastisols and injection molded parts. 

Chalcogenation of a divalent germanium compound with styrene sulfide has been examined as an alternative route to the first free germanethione Tbt(Tip)Ge = S 165142 (Scheme 32) and later on allowed the synthesis of new base-stabilized germanethiones 187 and 188156 [Eq. (37)]. Phenyl isocyanate also may serve as a sulfur source leading to 165, which was evidenced by electronic spectroscopy and underwent a subsequent [2 + 2] cycloaddition with phenyl isocyanate157 (Scheme 36). 

The M(C=C—CHs) ion is the base peak except for the lead compound (base peak = Pb+ ) and the phosphine [base peak = (P—CH3) "]. For Group V divalent metal species are of lower abundance than either mono-or trivalent ions. As expected, metal-containing ions carry the bulk of the ion current. Rearrangements were also observed corresponding simply to loss of a neutral metalloid atom. 

Lead forms amphoteric compounds in +2 and +4 valence states, forming plumbous and plumbic salts, such as PbCL and PbCL, as well as plumbites and plumbates, such as Na4Pb03 and Ca2Pb04,. Over a thousand compounds of lead are known which include divalent and tetravalent salts, complexes, and organometaUics. Divalent compounds of lead are far more numerous than the tetravalent compounds. Most compounds, however, result from the reactions involving other lead compounds, rather than elemental lead. Only the reactions involving elemental lead are outlined briefly below. 

A unique type of R2Pb compound is the cyclopentadienyl derivative of divalent lead. Only two such compounds are known, bis(cyclopenta-dienyl)lead and bis(methylcyclopentadienyl)lead. From dipole moments and infrared and NMR spectra, these compounds are postulated to possess a sandwich-type configuration, similar to that of ferrocene and the other metallocenes, but one in which the cyclopentadienyl rings are located angularly about the lead atom. This type of structure is the first... 

While the inorganic chemistry of divalent tin and lead is well established, there are few well-characterized divalent organotin and organo-lead compounds. The R2Sn formulation seen in the older literature has proved to be an empirical formula, the formally divalent stannylene actually being an oligomeric linear or cyclic organostannane. Neumann has commented on this point several times (1-3). 

---