Cadmium organozincs

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

In this edition, one of the most obvious changes is the separation of the organometallic chemistry of zinc from that of cadmium. This change was made necessary by the ever-increasing number of publications for both elements and the need to keep the amount of material manageable. Even with this focus on only one element the current chapter cannot be an all-inclusive coverage of organozinc chemistry. 

Whereas organomercury compounds do not add to aldehydes and ketones, cadmium organometallics show a useful reactivity. As in the case of organozinc derivatives, allylic cadmium compounds... 

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. ... 

Organozincs and -cadmiums are reactive towards O2, e.g., the alkylzincs inflame in air. Hence, care must be taken to exclude air and to provide an inert atmosphere, such as CO2 or N2, during the preparations. The reactivity of organozincs and -cadmiums toward proton sources makes it essential also to avoid contact with H2O. 

Transfer from Organoalumlnum Compounds. Organoaluminums are used to prepare organozinc, -cadmium and -mercury compounds e.g., trimethylaluminum reacts with Zn(OAc)2 or Znij to give MejZn. Diethylzinc can be prepared from [Et A Na (92% yield) or Et2AlCl (10%) with zinc halides. Another example is ... 

The acylation of organozinc reagents derived from dialkyl 1-bromo-1,1-difluoromethylphosphonates with acyl chlorides proceeds smoothly at room temperature to afford the desired products in moderate to good yields (60-77%, Scheme 3.75). Esters, lactones, and triflates did not react at all, even at Although these zinc and cadmium reagents appear to have similar reactivities,... 

Organozinc compounds are historically important39 since they were the first organometallic compounds to be prepared their discovery by Frank-land in 1849 played a decisive part in the development of modern ideas of chemical bonding. The zinc and cadmium compounds are also of interest since their mild reactivities toward certain organic functional groups give them unique synthetic potentialities. 

Reaction of the organozinc reagent with P,y-unsaturated ketones gives the relevant furan as shown in the case of lipid (30). The authors examined the reaction using both cadmium and copper in place of the zinc and found that whilst zinc gave the highest yield for cyclopropanation adjacent to a carbonyl group, it was surpassed by copper in the case of the equivalent allylic alcohol (Scheme 59). 

Of the metals, mercury and lead enter into this type of reaction most readily. There are data on the formation of organometallic compounds durii electrolysis of ketones at cadmium [12] and germanium [13] electrodes. The vigorous disint ration of a zinc cathode observed durii electrochemical reduction of acetone is also attributed to the formation of an unstable organozinc compound [14]. 

On the other hand, the consumable anode process does not allow access to less-reactive organometallic compounds such as zinc species. Indeed, the metallic ion generated by the oxidation of the anode has to be reduced at more negative potential than the halide. The use of a zinc anode indeed produces 7.n ions, which are in most cases more easily reduced than organic halides. Consequently, organozinc species can only be obtained by this method from easily reduced halides. The same remarks apply to other metals such as cadmium or copper. For example, the preparation of cadmium, zinc [5], and copper compounds [6] can be performed from CF3Br, which is easily reduced. (Scheme 15.2). 

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