Organozincs disproportionation

A number of compounds having a direct zinc transition metal bond are known for long time, that is, zinc-bis(transition metal) such as Zn[Co(C04)]2 and transition metal zinc halides such as (CO)4Fe(ZnCl)2. However, organozinc-transition metal compounds RZn-TM are comparatively more recent. They can be prepared by hydrocarbon elimination between a diorganozinc derivative and a transition metal hydride (see Hydrides) (equation 35), but dialkyl- and diarylzinc compounds usually fail to react or react very slowly. Furthermore, when they do react they give unstable products that show a very strong tendency to disproportionate and cannot be isolated (equation 36). 

In contrast to organomagnesium see Beryllium Magnesium Organometallic Chemistry) componnds, dialkylzinc derivatives do not disproportionate in coordinated zincate anions and organozinc cations under addition of cryptand... 

At the T used for these reactions, disproportionation of the first-formed products, RZnI, to R2Zn and Znij may result, but at lower T, e.g., 85-90°C with EtI and Zn dust, the organozinc iodides can be isolated". As R Zn compounds can inflame in air, an inert atmosphere, e.g., COj, should be provided. Dialkyl sulfates also react with.Zn metal with... 

These reactions are reminiscent of those used in the preparation of Grignard reagents and of Frankland s synthesis of organozinc halides. The products, RMX and R2MX2, are often extremely reactive and disproportionate readily. They can be stabilized, however, by complex formation with other ligands... 

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