Organoleads structure

See introductory remarks in Section I.A.2 of Chapter 7. Table 4 summarizes examples published in the recent literature, with brief comments about structural features of organolead compounds. 

TABLE 3. Structural determination of organolead compounds by NMR spectroscopy... 

Organolead compounds comprise the broad class of structures that are characterized by at least one carbon atom bonded directly to a lead atom. 

Catena-[(p2-acetoxy)-acetoxydiphenyllead(IV)] (19) is among the few structurally characterized hypervalent hexacoordinate organolead acetates. The latter forms a polymer via intermolecular O —y Pb interactions152. 

TABLE 45. Selected structural parameters for pentacoordinated triorganotin and organolead complexes with PrN and related moieties... 

CHART 1. The structures of organotin and organolead complexes of the type 387 containing monoanionic X,D-chelating ligands (X, D = N, O, S)... 

Hexacoordinate cationic organogermanium and organolead complexes, for which structures were established by X-ray crystallography, have not been reported so far. 

Early examples of structurally characterised organolead coordination polymers with Pb—N interactions are trimethyllead cyanide, Me3PbCN335, dimethyllead dicyanide, Me2Pb(CN)2337, and trimethyllead azide, Me3PbN3 (179)467,468. The latter compound forms a linear chain polymer with a /X2-N atom symmetrically bridging the pentacoordinated lead centres [Pb—N 2.54(1) A], The N—Pb—N angle [178.6(5)°] deviates only slightly from the ideal value of 180°. 

In an approach toward the synthesis of the marine natural product cytotoxin Diazonamide A, the arylation of a lactonic /3-diester 20 with a tyrosinyllead triacetate was realized and afforded 21 as a mixture of diastereomers in 85% overall yield from 3-iodotyrosine (Scheme 5).36 It later appeared that the first suggested structure of Diazonamide A37 was in fact erroneous38, a and that the organolead-based approach could not be used for the total synthesis of this natural product. 

The organolead complexes contain few examples of monomeric neutral adducts (Table 30). The structure of Ph3PbBr(OPPh3) shows that the OPPh3 molecule (O Pb = 2.556 A) and the bromine atom (Pb—Br = 2.754 A) are both at the axial positions displaying hypervalent bonding for the lead atom. The other adducts have the same five-coordinate structure with the three equatorial phenyl groups. 

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