C-Pb bond cleavage

Among the C—Pb bond cleavage reactions, thermo- and photo-induced homolytic cleavage is of special theoretical and practical interest. 

The C—Ge bond is less stable toward heterolytic and homolytic cleavage reactions than the C—Si bond, but it is more stable than the C—Sn and C—Pb bonds. This is consistent with the bond energies of these bonds (see Chapter 2). 

Scheme 3 did not require the initial cleavage of the C—Pb bond by A1C13 as well as the intermediate formation of ClR2PbPbR2Cl, which has not yet been identified. 

This result supports the data presented in Section V.A, that of all C—M bonds, the C—Pb bonds can undergo homolytic cleavage, forming carbon-centred free radicals most easily. 

Further disproportionation reaction is important in organolead chemistry. As reported in Section m. C, tetraorganylplumbanes were obtained by reacting PbCl2 with organometal-lic compounds via the intermediates PbR2. The processes were accompanied by cleavage and formation of C—Pb and Pb—Pb bonds as described by equations 22 and 23. 

The thermal and chemical stability of C—M bonds (M = Si, Ge, Sn, Pb), and therefore of all organic compounds of the silicon subgroup elements, decreases, both in homolytic and in heterolytic processes, when the atomic number of the M element increases. For example, the thermal stability of tetraalkyl derivatives R4M diminishes essentially when M is changed consecutively from Si to Pb151 l52. The ease of oxidation of R4M compounds and the ease of cleavage of C—M bonds by halogens, protic and aprotic acids, etc.,... 

Reactions of alkyl- or vinyl-substituted plumbanes with PhjSnH result in Pb — C bond cleavage and formation of Pb—H bonds ... 

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