Organocadmium compound

An organocadmium compound is a organometallic compound containing a carbon to cadmium chemical bond. Organocadmium chemistry describes physical properties, synthesis, reactions and use of these compounds. Cadmium shares group 12 with zinc and mercury and their corresponding chemistries have much in common.

Dimethylcadmium is a linear molecule with C-Cd bond lengths of 211.2 pm. All organocadmiums are sensitive to air, light and moisture.

Synthesis
The first organocadmium compounds, dimethylcadmium, CH3-Cd-CH3 and diethylcadmium CH3CH2-Cd-CH2CH3 were prepared in 1917 by Krause. In general they are prepared by transmetalation or by an exchange reaction between an organometallic reagent and a cadmium salt.

One procedure for synthesis diethylcadmium is by reaction of cadmium bromide with two equivalents of the Grignard reagent ethylmagnesium bromide in diethyl ether. A byproduct is magnesium bromide. Diethylcadmium is a colorless oil with melting point −21 °C.

Diphenylcadmium can be prepared by reaction of phenyllithium with the same salt. This solid has a melting point of 174 °C

Reactions
The synthetic utility of organocadmiums is limited. The alkyl groups in them are less nucleophilic than the organozincs due to the general increase in electronegativity going down group 12. this reduced reactivity is demonstrated in the conversion of acid chlorides to ketones with these reagents. With other organometallic reagents such reaction would continue to the corresponding alcohol.

An example of the synthetic use of an organocadmium is the reaction of diisoamylcadmium with β-carbomethoxypropionyl chloride to methyl 4-keto-7-methyloctanoate without reacting further with the ketone group or the ester group.

This selectivity exists provided that the reaction is carried out salt free. When the cadmium reagent is generated in situ from a cadmium salt, the presence of a halide salt makes the reagent much more reactive, even to ketones. the same salt effect can be observed in organozinc compounds.