Organocadmium chemistry describes the physical properties, synthesis, reactions, and use oforganocadmium compounds, which areorganometallic compounds containing acarbon tocadmiumchemical bond.[1] Cadmium sharesgroup 12 withzinc andmercury and their corresponding chemistries have much in common. The synthetic utility of organocadmium compounds is limited.
The simplest organocadmium compound isdimethylcadmium. It is a linear molecule with a C-Cdbond length of 213pm.[2] Organocadmium compounds are typically sensitive to air, light, and moisture.
Dimethylcadmium and diethylcadmium were reported in 1917 by Erich Krause. In general, they are prepared bytransmetalation or by an exchange reaction between an alkylating agent and a cadmium salt.[3]
According to one procedure, diethylcadmium is produced by the reaction ofcadmium bromide with two equivalents of theGrignard reagent ethylmagnesium bromide indiethyl ether. Diethylcadmium is a colorless oil withmelting point −21°C. Diphenylcadmium can be prepared by the reaction ofphenyllithium with cadmium bromide. Diphenylcadmium is a solid with a melting point of 174 °C.
Following established trends, perfluorinated alkyl and alkenyl derivatives of cadmium exhibit improved thermal stability. The alkenyl derivatives are generated by the addition ofiodotrifluoroethylene to cadmium metal.[4]
Organocadmium compounds are lessnucleophilic than theorganozincs. This reduced reactivity is demonstrated in the conversion ofacyl chlorides toketones with these reagents.[5] This reaction was reported byHenry Gilman in 1936 and was used until less toxic cuprates were available. The related Grignard reagent would react further, giving to the tertiaryalcohol. Methyl cadmium was used in one of the steps leading tocholesterol total synthesis:[6]
Another synthetic use of an organocadmium is the reaction of diisoamylcadmium with β-carbomethoxypropionyl chloride to methyl 4-keto-7-methyloctanoate without reacting further with theketone group or theester group.[7]
This selectivity is observed provided that the reaction is carried out salt free.[8] When the cadmium reagent is generatedin situ from a cadmium salt, the halide generates a more nucleophilic organocadmium reagent, anate complex. The same salt effect can be observed with organozinc compounds.
Dimethylcadmium has been used to synthesize colloidal nanocrystals of II-VI materials such ascadmium selenide. Its toxic and volatile nature has led researchers to look elsewhere for cadmium precursors such as cadmium oxide.[9]
Cadmium compounds are toxic. Dimethylcadmium is toxic to the kidney, the liver, the central nervous system, and the respiratory organs when inhaled.[10] Cadmium compounds in general are considered to becarcinogen to humans by theIARC.[11]
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