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Organolead compounds are chemical compounds containing a chemical bond between carbon and lead. Organolead chemistry is the corresponding science. The first organolead compound was hexaethyldilead (Pb2(C2H5)6), first synthesized in 1858.〔''Main Group Metals in Organic Synthesis'' Yamamoto, Hisashi / Oshima, Koichiro (eds.) 2004 ISBN 3-527-30508-4〕 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 222 pm long with a dissociation energy of 49 kcal/mol (204 kJ/mol). For comparison the C–Sn bond in tetramethyltin is 214 pm long with dissociation energy 71 kcal/mol (297 kJ/mol). The dominance of Pb(IV) in organolead chemistry is remarkable because inorganic lead compounds tend to have Pb(II) centers. The reason is that with inorganic lead compounds elements such as nitrogen, oxygen and the halides have a much higher electronegativity than lead itself and the partial positive charge on lead then leads to a stronger contraction of the 6s orbital than the 6p orbital making the 6s orbital inert; this is called the inert pair effect.〔''Synthesis of Organometallic Compounds: A Practical Guide'' Sanshiro Komiya Ed. 1997〕 By far the most important organolead compound is tetraethyllead, formerly used as an 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 the toxicity is only 10% of that of 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 g/cm³. Reaction of a lead(II) source with sodium cyclopentadienide gives the lead metallocene, plumbocene. Certain arene compounds react directly with lead tetraacetate to aryl lead compounds in an electrophilic aromatic substitution. For instance anisole with lead tetraacetate forms 'p-methoxyphenyllead triacetate in chloroform and dichloroacetic acid: : Other compounds of lead are organolead halides of the type RnPbX(4-n), organolead sulfinates (RnPb(OSOR)(4−n)) and organolead hydroxides (RnPb(OH)(4−n)). Typical reactions are:〔Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7〕 : + HCl → R3PbCl + RH : + SO2 → R3PbO(SO)R :R3PbCl + 1/2Ag2O (aq) → R3PbOH + AgCl :R2PbCl2 + 2 OH− → + 2 Cl− compounds are amphoteric. At pH lower than 8 they form R2Pb2+ ions and with pH higher than 10, R2Pb(OH)3− ions. Derived from the hydroxides are the plumboxanes: :2 R3PbOH + Na → (R3Pb)2O + NaOH + 1/2 H2 which give access to polymeric alkoxides: :(R3Pb)2O + R'OH → 1/n (R3PbOR')n - n H2O 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Organolead compound」の詳細全文を読む スポンサード リンク
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