Organolead chemistry
Organolead compounds are chemical compounds containing a chemical bond between carbon and lead. Organolead chemistry is the corresponding science. the first organolead was hexaethyldilead synthesised in 1858 [1]. Sharing the same group with carbon, lead is tetravalent.
Going down the carbon group the C-X (X = C, Si. Ge, Sn, Pb) bond becomes weaker and the bond length larger. The C-Pb bond in tetramethyllead is 2224 pm long with a dissociation energy of 204 Kcal/mole. For comparison the C-Sn bond in tetramethyltin is 214 pm long with dissociation energy 297 Kcal/mole.
By far the most important organolead compound is tetraethyl lead used as a anti-knocking agent. The most important lead reagents for introducing lead are lead tetraacetate and lead chloride.
The use of organoleads is limited partly due to their toxicity although it is remarked [1] that the toxicity is only 10% of that palladium compounds.
Synthesis
Organolead compounds can be derived from Grignard reagents and lead chloride. For example methylmagnesium chloride reacts with lead chloride to tetramethyllead, a water-clear liquid with boiling point 110°C and density 1.995.
reaction of lead chloride with the lithium salt of pentamethylcyclopentadiene gives the lead metallocene.
Reactions
The C-Pb bond is weak and for this reason homolytic cleavage of organolead compounds to free radicals is easy. In its anti-knocking capacity, its purpose is that of a radical initiator. Organoleads find some use in coupling reactions between arene compounds. They are more reactive than the likewise organotins and can therefore be used to synthesise sterically crowded biaryls.
See also
- Compounds of carbon with other group 14 elements: organosilicon compounds, organogermanium compounds, organotin compounds, organolead compounds.