Dialkylcadmium compounds

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

Dialkylcadmium compounds are also reactive towards H2S. For example, (Me3SiCH2)2Cd reacts immediately with H2S to give CdS (equation 19). Other organocadmium compounds with Cd S bonds include the thiocyanate derivatives RCdSCN that are obtained by the reaction of R2Cd with (SCN)2 (equation 20). ... 

In contrast to dialkylcadmium compounds, allylcadmium derivatives react readily with aldehydes and ketones in the absence of metal salts (equation 31). Substituted allylic derivatives undergo rearrangement upon addition (equation 32). 

Other related alkylating reagents which have been used are dimethylzinc, tetraethyl-lead, trimethylaluminium and dialkylcadmium compounds (see pp. 238-239, 254-255). 

Figure 16 Suppression of the prereaction between dialkylcadmium/zinc compounds and hydrogen sulfide/...

Mixed alkyl halide compounds result from the reaction of dialkylcadmium with cadmium halides. 

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) ... 

The first perfluoroalkykadmium compounds were prepared via metathesis between bis(trifluaromethyl)mercury and dialkylcadmiums [12d] An equilibrium mixture of all possible cadmium and mercury compounds was formed, the equilibrium could be shifted toward the bis(tnfluoromethyl)cadmium by using excess bis(tnflu-oromethyl)mercury When the reaction was earned out in glyme, a stable bis(tnflu-oromethyl)cadmium gly ine complex was isolated [124, 125 126] (equation 96) Other analogues were synthesized and isolated in essentially quantitative yield via direct reaction of primary and secondary perfluoroalkyl iodides with di-alkylcadmiums in basic Lewis solvents [127 128] (equaUon 97)... 

When alkyl halides react with metallic cadmium96,151 the primary product is probably the compound of type RCdX, as with the other elements of Group II, but so far such compounds have been obtained pure only by the action of anhydrous cadmium salts on dialkylcadmiums in anhydrous ether.152... 

Dialkylcadmiums can be isolated by cautious distillation from a water-bath or oil-bath under diminished pressure and diphenylcadmium can be purified by sublimation in a high vacuum.148 In many cases, however, the organocadmium compound is not isolated, the solution obtained by reaction as above being used directly for further reaction. 

Recent investigations have shown that the reactivity of organocadmium compounds is increased by the presence of magnesium salts if prepared in solution from a Grignard reagent and a cadmium halide, dialkylcadmiums — the members most studied — are appreciably more reactive than pure dialkylcadmiums in ether.158... 

Dialkylcadmium derivatives readily partake in exchange reactions with other metal compounds. NMR studies on the... 

Catalytic action of oxygen was observed with various organometallic compounds. One example is dialkylzinc that probably forms an active peroxide. The same is also true of dialkylcadmium and of triethylaluminum. Peroxide formation is believed to be an important step in all these initiations. Initiating radicals, however, do not appear to be produced from mere decompositions of these peroxides. 

Use of strongly anionic nucleophiles such as alkylmagnesium halides and lithium alkyls leads to reductive dimerization or displacement of the olefin. It is quite possible however that alkylation of olefin-iron cations (IX) would be feasible with alkyl derivatives of zinc, cadmium, or tin reagents. Alkylation of dienyliron cations with dialkylzinc and dialkylcadmium reagents has recently been demonstrated (Section III,A,4). Alkylation of olefin-iron cations can be achieved under mild conditions with cr-bonded allyliron compounds [Eqs. (9) and (10), (Rosan et ai, 1973)]. 

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