Plumbyl anions

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

Nucleophilic cleavage of hexaphenyldiplumbane by potassium tert-butoxide results in the formation of the plumbyl anion K+PbPh3, which is principally characterized by the high field shift of the C-l nuclei to 191.11 ppm in the NMR spectrum hexaphenyldigermane and hexaphenyldistanne behave analogously.30... 

Lead(IV) trifluoroacetate in TFAH is a very reactive electrophile that is capable of plumbylating less electron-rich arenes. Nonetheless, the use of trifluoroacetate anions in the plumbylation reactions should be avoided, because aryllead(IV) tri-fluoroacetates are unstable compounds that readily decompose to the corresponding aryl trifluoroacetates and biaryls [34—37, 40, 41]. It has been reported [41] that 4-FC6H4ArPb(TFA)3 is reasonably stable and can be isolated from the reaction of Pb(TFA)4/TFAH with fluorobenzene. A mechanistic study [41] indicated an electrophilic substitution path for the plumbylation reaction, which seemed to be substantially more para-selective than mercuration and thallation. For example, the plumbylation of toluene with Pb(OAc)4 in dichloroacetic acid has been reported [41] to occur with >90 % para-selectivity. 

Nucleophilic cleavage of the lead-lead bond is one of the few ways to form plumbyl anions (equations 30, 37 and 38)45,51,52, but in the case of a sterically hindered and thus weak lead-lead bond, a metal-metal cleavage is required (equation 39)45,51-53. 

Cyclic pentacoordinate plumbyl anions were synthesized by the oxidative addition of tetraalkylammonium halides to a dithiolatoplumbole (equation 63)79. An X-ray structure analysis of the adduct revealed a monocyclic anionic geometry. 

Similarly, at low-T the borane anion [BjHg] also yields a plumbyl-bridged cluster, although the product is thermally unstable at RT ... 

Few new examples became available for compounds with Pb-B bonds (see Fig. 4), and triorganoplumbyl lithium compounds in solution (e.g. Bu3Pb-Li in THF at -30°C 5 Pb = +1573.8 ) were studied. Since scalar O Pb- Li coupling was not observed in the cases of R3pb-Li (R = Me, Et, Bu), the lithium cation must be solvated by THF, and the 5 o Pb value of Bu3Pb-Li corresponds to the free plumbyl anion. 

Scheme 24 Fonnation of silanylated plumbyl anions and radicals...

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