Organoleads complexes with

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

Analysis by GC of the various organolead species present in gasoline requires special detectors because of the profusion of species with retention times near those of the organometaHic compounds. An old determination method consisted of scrubbing the separated species in iodine solution, foHowed by spectrophotometric determination of the complex with dithizone (2)133,134 (see also Table 2). 

Determination of Pb(II) and organolead compounds in human urine, after LLE of the complexes with 91 and derivatization Et4Pb as internal standard . The aqueous solution is evaporated to dryness, the sohd residue is derivatized and the alkylated Pb was evaporated into an ETAAS instrument the LOD (SNR 2) was 7 ppb . 

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. 

When a mixture of tetrachloromethane and benzaldehyde in DMF was treated, at room temperature, with a catalytic amount of lead(ll) bromide and a shght excess of aluminum as a stoichiometric reductant the coupled product was obtained in good yield (Scheme 13.69) [86]. Subsequent reductive 1,2-elimination of trichloromethyl carbinol by means of the Pb/Al bimetal system could be readily achieved by changing the reaction media. The mechanism of the Pb/Al bimetal redox system presumably involves lead(O) reduction of polyhalomethane to provide an organolead complex which then reacts wifh an aldehyde to give the couphng product. Regenerahon of lead(O) by reduchon of lead(ll) with aluminum metal would complete the catalyhc cycle. 

This phenomenon was attributed to the lower kinetic acidity of nitroalkanes. Dipolar aprotic solvents can be used with aryllead reagents to conduct the arylations, as the deprotonation is accelerated in these solvents. The reactions are preferably performed in DMSO. As DMSO forms strong complexes with organolead compounds, the presence of pyridine or any other complexing base is not required and the reaction proceeded smoothly at 40 C in 30 hours to afford good yields of the a-arylated derivatives. 

Lead enters surface water from atmospheric fallout, run-off, or wastewater. Little lead is transferred from natural minerals or leached from soil. Pb ", the stable ionic species of lead, forms complexes of low solubility with major anions in the natural environment such as the hydroxide, carbonate, sulfide, and sulfate ions, which limit solubility. Organolead complexes are formed with humic materials, which maintain lead in a bound form even at low pH. Lead is effectively removed from the water column to the sediment by adsorption to organic matter and clay minerals, precipitation as insoluble salt (the carbonate, sulfate, or sulfide) and reaction with hydrous iron, aluminum, and manganese oxides. Lead does not appear to bioconcentrate significantly in fish but does in some shellfish such as mussels. When released to the atmosphere, lead will generally occur as particulate matter and will be subject to gravitational settling. Transformation to oxides and carbonates may also occur. 

An organolead chelate complex with lead-nitrogen bonds was recently examined 64). Diphenyllead bis(8-hydroxyquinolate), like the corresponding tin compound, probably has an octahedral structure. 

Determination of organolead metabolites of tetraalkyllead in urine can be carried out after solid-phase enrichment and end analysis using reversed-phase HPLC with chemical reaction detector and by LC-MS (thermospray127). The chemical derivation consists of conversion to the dialky Head form, as shown in reaction 1, followed by complex formation with 4-(2-pyridylazo)resorcinol (11) and spectrophotometic measurement at 515 nm128. 

Organolead compounds containing a lead-transition metal bond are also known. When a lead(II) or lead(IV) compound reacts with Co2(CO)gL2 complexes (L = tert -phosphine, -arsine or a phosphite), the blue, air-stable Pb[Co(CO)3L]4 derivatives are obtained371. 

Metal-catalyzed reactions constitute the second major type of reactions in which organolead compounds act as major partners of the reacting systems. The study of these reactions has considerably increased since COMC (1995) review and they can be divided in two subtypes reactions in which the organolead reactant acts as a stoichiometric partner and reactions in which the organolead is only a catalytic species. In this section, only the reactions with stoichiometric organolead will be reviewed, and these reactions are catalyzed by copper, palladium or rhodium species. The second type is the metathesis reactions where the lead compound acts only as a promoter in a complex catalytic system and is reviewed in Section 9.09.4. 

Divalent organotin and organolead compounds can be divided into two classes, viz, those in which the organic groups are organic groups are 7r-bonded to the metal. We will deal with these two classes separately beginning with the 7r-bonded species. A third section will cover transition metal stannylene and plumbylene complexes from both classes. 

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