Aluminum organoleads

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. 

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. 

In general it can be said that aluminum organic reducing agents in organolead chemistry do not as yet show the same advantages which have been observed with organotin compounds. 

Radical formers as catalysts were of no help they mostly accelerated the decomposition of Bu3PbH. Also catalysis by aluminum alkyls 189,201), used for the addition of organotin hydrides to olefins, is not useful because the transfer of an alkyl group to RjPbH depends upon the necessary addition of R2AIH to the olefin 189, 284) at 20° C (which is the limit for the stability of the organolead compounds used) and this does not take place. 

Organolead hydrides. Dimethyl ether condensed in vacuo on a liq. Ng-cooled mixture of trimethyllead chloride and a slight excess of lithium aluminum hydride, the reaction initiated by warming to —78°, and the product isolated after a few min. at that temp. trimethyllead hydride. Y 95%. F. e. in lower yield s. W. E. Becker and S. E. Gox, Am. Soc. 82, 6264 (1960). 

Organoaluminum compounds are used as polymerization catalysts of butene, isoprene and butadiene besides ethylene and propylene, dimerization catalysts of linear higher a-olefins, linear higher-a-alcohols and olefins, productions of organo-metallic compounds such as organotin compounds and organolead compounds, productions of high purity alumina and aluminum thin film. 

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