Cadmium dihalides

The wealth of information that has accumulated regarding the UPS of the main group halides is not considered here, since it falls outside the purview of this Chapter. Of the transition metal halides the largest amount of work has been done with the halides of the Group 2B metals and their monomethyl derivatives (28, 33, 63, 108, 112, 129, 233). In these studies it was found that the zinc and cadmium dihalides require significantly higher vaporization temperatures than the mercury compounds hence specialized high-temperature techniques were necessary. A summary of these and related methods may be found in a recent review article by Schweitzer (255). 

Raman spectral studies of the species MX(n" 2) (n = 2—4 M = Zn, Cd, or Hg X = Cl, Br, or I) in anhydrous tributyl phosphate have been reported.24 For the MX2 molecules, sufficient metal dihalide-solvent interaction exists to suggest bent X—M—X species with C2v rather than >ooh symmetry. The effect appears most marked for zinc(n) and least marked for mercury(n), which is in accord with the Lewis acidity sequence ZnX2 > CdX2 > HgX2. A similar analysis of the anionic MX3 complexes formed from a 1 1 mixture of LiX and MX2 again demonstrates solvent interaction, and a tetrahedral C3v species is indicated, rather than the planar structure found in the solid state. Studies involving the halogeno-complexes of zinc, cadmium, and mercury in DMSO and DMF have also been reported.25,26... 

Two interesting anomalies associated with cadmium have been observed. The halides of cadmium are the least volatile dihalides of the group, Moreover, cadmium seems to be the only member of the group that forms a stable peroxide, Cd02. 

Very soon after the reactivity of Cd(CF3)2DME toward main group halides (31) and group 10 dihalides (32) had been established, we set out to determine if the cadmium reagent was effective in trifluoromethylating representative organometallic compounds. One of the first substrates chosen was CpCo(CO)I2, which was selected because the mono-trifluoro-methyl derivative was known, but the disubstituted compound was not. The results of this reaction are (60)... 

In this ketone synthesis, (1) the Grignard reagent reacts with cadmium chloride to yield an organocadmium compound, plus a magnesium dihalide. (2) The organocadmium is then reacted with an acid chloride to yield a ketone plus cadmium chloride. 

The equilibrium structures of the dihalides of the Group 12 metals zinc, cadmium and mercury all appear to be linear or nearly so in no case has an angular structure been proven. The difference between the dihalides of Ca and Zn, between Sr and Cd and between Ba and Hg suggests an explanation of the bent equilibrium stmctures in terms of the vacant valence shell d orbitals of the Group 2 metals. 

A general method of preparation of alkyl phosphonous dihalides is the reaction of phosphorus trihalide with a dialkyl mercury, a dialkyl cadmium or a trialkyl aluminium. 

Lister MW, Sutton LE (1941) The investigation by electron diffraction of some dihalides of cadmium, tin and lead. Trans Faraday Soc 1941 406-409... 

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