Tetraorganolead compounds

The tetraorganolead molecules have a tetrahedral configuration around the central lead atom, and therefore the lead electrons can be considered to be sp hybridized. The lead-to-carbon bond has a high degree of covalent character. 

Symmetrical tetraaryllead compounds are solids, which are usually colorless, having melting points in the range of about 120 to 250 C. They are soluble in chloroform, acetone, and aromatic hydrocarbons they are much less or largely insoluble in ethers, alcohols, and aliphatic hydrocarbons. They generally are thermally more stable than the tetraalkyllead compounds. Often decomposition occurs only at, or slightly above, the melting point. 

PbR4-type compounds usually are not sensitive to air, insoluble in water, and very stable to hydrolysis. However, prolonged contact with air causes slow degradation, especially in the presence of light. They react readily with halogens, hydrogen halides, nonmetal halides, a series of salts (mainly metal halides), and with aqueous solutions of strong acids. They are much less sensitive to bases. 

---

Me3PbH (mp —106°, decomp above —30°) and Et3PbH (mp —145°, decomp above —20°) readily add to alkenes and alkynes (hydroplumbation) to give stable tetraorganolead compounds. 

Hand in hand with the declining ecological significance of tetraorganolead compounds, the interest in such molecules is also decreasing, and comprises now mostly purely academic aspects. Most results in this field have been summarized in COMC(1982) and COMC(1995), as well as the five volumes of the Gmelin series Organoelement Compounds that appeared between 1987 and 1996.14 18... 

The tetraorganolead compounds are the best characterized of all the different types of organolead compounds, and tend to be the most stable and least reactive. Generally, they are formed as the major product in the synthesis reactions employed for organolead compounds and they serve as the starting material in the synthesis of other types of organolead compounds. 

From the electronic structure of the lead atom, one would expect the tetraorganolead compounds to form via an spz hybridization of the two s and two p electrons in the outer shell of the lead atom, with the carbon atoms arranged in a tetrahedral configuration around the lead atom. All... 

The physical properties of the various types of organolead compounds have not been investigated as systematically as those of the other metals. Most of the physical properties measurements have been devoted to the tetraorganolead compounds, although in the past few years some interest has been generated in the organolead halides and carboxylates. A detailed discussion of the physical properties is beyond the scope of this article. This subject has been reviewed recently by Shapiro and Frey 289>. 

Tetraorganolead compounds are also useful in the preparation of RBXj and RjBX. However, there are side reactions (e.g., formation of RX) and mixtures of RBX2, R2BX and R3B are obtained. ... 

The influence of various substituents on tJ Pb of tetracoordinate lead(IV) compounds has been shown in previous reviews.3 4 The slowly growing dataset available today for tetraorganolead compounds confirms the trends outlined previously. This holds for various trimethylplumbyl-substituted methanes,65 for alkenylplumbanes,66-73 tetraarylplumbanes,74 75 and also for 207Pb NMR data of a number of tri(ter -butyl)lead derivatives 33-38 with selected data given below 76... 

The metal cleavage reaction is an important synthetic approach to the reactive R3PbM derivatives. In turn, these latter compounds are useful intermediates for the preparation of unsymmetrical tetraorganolead compounds. 

All coupling constants y(2 Pb, 3C) in tetraorganolead compounds are positive except for 7(2 Pb, - Cs) in many l-alkynyl(triorgano)lead derivatives, where a negative sign was proposed originally because of the solvent dependence," and later on this was confirmed by 2D C/ H HETCOR experiments (Fig. 9)." ... 

Vinyl substituents on lead are cleaved by sodium in liquid ammonia (111) with greater difficulty than alkyl substituents. Tetravinyllead can also be used as an alkenylating agent in the same way as the tetraorganolead compounds. Thus boron trichloride at — 78° C with Vi4Pb yields, almost quantitatively, trivinylboron (113). 

The reaction of Pb(CH3)4 and of other tetraorganolead compounds with HCl proceeds in two steps ... 

Pb(CH3)4 can be applied to extract aluminium and alkylaluminium alkoxide impurities from organoaluminium complexes used in the electrolytic preparation of tetraorganolead compounds [177]. Pb(CH3)4 was claimed to prevent corrosion of graphite by CO2 used as fluid coolant in nuclear reactors [178], and to stabilize halogenated aryl compounds, employed as dielectric, insulating, or cooling agents [179]. 

Listing of symmetric unsubstituted tetraorganolead compounds concludes in Table 270. 

Other unsaturated symmetric tetraorganolead compounds are listed in Table 271. 

Several new functionally substituted tetraorganolead compounds are listed in this chapter. The derivatives stmraarlzed in Table 271 are prepared by methods from the following scheme. 

The nonfunctional unsyinmetric tetraorganolead compounds listed in Table 272 are prepared by the following methods. 

---