Organocadmium halides

A series of adducts of organocadmium halides with neutral bidentate ligands RCdX L (L = dioxane, bipy or phen) have been prepared by electrochemical oxidation of the metal in the presence of L and the alkyl halide. In the additional presence of [N(n-propyl)4]X, salts of the [RCdX2] anion may be isolated.1064... 

Little information is available about the structure of organocadmium halides. They are poorly soluble in organic solvents, suggesting supramolecular association in the solid state. Some organocadmium halides with bulky substituents were found... 

Habeeb, J.J., Osman, A. and Tuck, D.G. (1976) The direct electrochemical synthesis of neutral and anionic organocadmium halides , Chem. Comm., 379-380. 

Solvent plays a significant role in these reactions In contrast to the formation of organocadmium compounds in the duect reaction of perfluoroalkyl iodides and cadmium powder in DMF [729], dimerization of the perfluoroalkyl halide was observed in acetonitrile [777] (equation 100)... 

Organocadmium compounds can be prepared from Grignard reagents or organo-lithium compounds by reaction with Cd(II) salts.180 They can also be prepared directly from alkyl, benzyl, and aryl halides by reaction with highly reactive cadmium metal generated by reduction of Cd(II) salts.181... 

Efforts to improve the efficient synthesis of organocadmium complexes by reaction of elemental cadmium with alkyl halides have been reported. Recent studies show that the presence of catalytic amounts of Cul and BuMgl in the reaction of alkyliodides with cadmium metal allows for the formation of 172a-c in high yield and high purity (Equation (58)).241... 

Many organocadmium compounds are known but few have been of commercial importance. Wanklyn first isolated diethyl cadmium in 1856. The properties of this and other dialkylcadmiums are listed in Table 4. In general, these materials are prepared by reaction of an anhydrous cadmium halide with a Grignard or alkyUithium reagent followed by distillation of the volatile material in an inert atmosphere or in vacuo. Only the liquid dimethyl compound is reasonably stable and then only when stored in a sealed tube. Dimethylcadmium is mildly pyrophoric in air and produces dense clouds of white, then brown, cadmium oxide smoke, which is highly toxic if breathed (45). When dropped into water, the liquid sinks in large droplets that decompose with a series of small explosive jerks and pops. For this reason, and particularly because of the low thermal stability, most dialkylcadmium materials are prepared and used in situ without separation, eg, in the conversion of acid chlorides to speciality ketones (qv) ... 

While most of the chemistry discussed in this chapter has been developed in the past decade, several important methods have withstood the test of time and have made important contributions in areas such as natural product synthesis. Methods such as cuprate acylation and the addition of organolithiums to carboxylic acids have continued to enjoy widespread use in organic synthesis, whereas older methods including the reaction of organocadmium reagents with acid halides, once virtually the only method available for acylation, has not seen extensive utilization recently. In the following discussion, we shall be interested in cases where selective monoacylation of nonstabilized carbanion equivalents has been achieved. Especially of concern here are carbanion equivalents or more properly organometallics which possess no source of resonance stabilization other than the covalent carbon-metal bond. Other sources of carbanions that are intrinsically stabilized, such as enolates, will be covered in Chapter 3.6, Volume 2. 

A donor such as hexamethylphosphoramide (HMPA) , dioxane or bipy , also can be added toward the end of the transmetallation to enable easier separation of the organometallic product from the metal halides present. This is particularly useful for organozinc and -cadmium preparations, because the reaction media cannot be treated with HjO to separate the metal halides, e.g., addition of HMPA to an EtjO solution containing an organocadmium product and Mg salts, MgXj, results in precipitation of MgX2 2 HMPA, thereby leaving R Cd in solution free of Mg halides, e.g. ... 

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