Cadmium organocadmiums

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 may be prepared by the action of anhydrous cadmium chloride upon the corresponding Grignard reagents, for example ... 

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... 

The most common application of organocadmium compounds has been in the preparation of ketones by reaction with acyl chlorides. A major disadvantage of the use of organocadmium reagents is the toxicity and environmental problems associated with use of cadmium, and this has limited the recent use of organocadmium reagents. 

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... 

The reaction of dabco (l,4-diazobicyclo[2.2.2]octane) with Me2Cd yields a 1 1 adduct 197, which adopts a linear polymeric structure (Figure 34).255 The cadmium atom is coordinated by two dabco units and two methyl carbon atoms giving rise to a distorted tetrahedral environment. Finally, the organocadmium adduct 198 (Figure 35) has been isolated from the reaction of Me2Cd with Cd[(SeP-/-Pr2)2N]2.256 The solid-state structure consists of dimeric units where each methylcadmium unit is coordinated to three selenium atoms. The geometry about the cadmium center is tetrahedral with a Cd-C distance of 2.16 A, which is comparable to that observed in other cadmium alkyl complexes. 

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) ... 

Grignard reagents derived from aryl bromides are readily prepared and may be converted into organocadmium compounds by treatment with cadmium chloride (cf. Section 5.8.4, p. 616). Reaction of an organocadmium with a carboxylic acid chloride constitutes a convenient synthesis of aryl alkyl ketones. 

An unusual cadmium-promoted cyclization to form a pyridine ring, as part of a tricyclic system, was reported (Scheme 7) <95JOC(60)5243>. Zinc and copper (I) salts can replace the cadmium salt. Organocadmium promoters allow room temperature cyclization. 

TL627>. Other metal-catalyzed reactions include the CdC -mediated cyclization of enamines in the presence of a cyano substituent (Scheme 98) <1995JOC5243>. Zinc and copper (i) salts can be used in place of the cadmium however, organocadmium promoters allow room temperature cyclization. A two-step process involving tungsten alkynols, aldehydes, and nitriles in the presence of a Lewis acid yields pyridines (Scheme 99) <1998JA4520>. 

Though the first carbon atoms in LVII and LVIII are asymmetric, only one of the two possible stereoisomers was obtained in each case. It was suggested that the substantial quantities of sirup accompanying the production of these crystalline substances may have contained the other isomer. The authors propose a plausible ionic mechanism for the reaction of organocadmium compounds with tetraacetylglucosyl bromide, leading alternatively to compounds of types IV or LVII. It was reasoned that a carbonium ion was formed at carbon 1 by attack of the cadmium reagent at the bromide function ... 

Cadmium salts and organocadmium reagents also have found applications in cyclization reaction. Cadmium-mediated cyclization of enaminone occurs under mild conditions, whether in presence of a base and a cadmium(ll) salt (60 to 90 °C), or in the presence of dibutylcadmium at room temperature (Equation (181)). 

The most general method of preparation of organocadmium derivatives involves the reactions of RLi, RMgX, or R3 A1 with cadmium salts. For example, Me2Cd is readily prepared by the reaction of Mc3Al with Cd(OAc)2 (equation 1),... 

Grignard reagents react with dry cadmium chloride to yield the corresponding organocadmium compounds, which react with acid chlorides to yield ketones ... 

For the synthesis of some functionalized benzylic organocadmium bromides by using highly reactive cadmium metal powder, see E. R. Burkhardt and R. D. Rieke, J. Org. Chem., 1985, 50, 416. 

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. ... 

Hi) Transfer from Organozincs and -cadmiums. Organozincs are used to prepare organocadmiums ... 

---