Organic Zinc
1. Oxidative addition. Diethylzinc, which was discovered by Frankland, is prepared in this way: Ethyl iodide and monomeric zinc are added under the “protection” of hydrogen (also known as Frankland synthesis). The activity of the zinc metal is enhanced by the reagent Rieke zinc, which is obtained by the reduction of potassium metal and zinc chloride.
2RI + 2Zn → ZnR2 + ZnI2
2. Zinc halide exchange. The method is divided into two main types: for zinc iodide exchange and zinc boron exchange. The second reaction (right to left) step is the borohydride of olefins.
3. Metal transfer (Transmetalation). In a typical metal transfer reaction, diphenylmercury and zinc monomers are reacted in ether to give diphenylzinc and metallic mercury, which is a very slow reaction that takes up to two weeks.
4. Organozinc compounds can also be obtained directly from zinc metal. In this method, the zinc is activated by 1,2-dibromoethane and trimethylchlorosilane (the preparation of Grignard’s reagent can also be activated in this way). The key reagent is lithium chloride, which rapidly forms soluble adducts with the organic zinc compounds and thus removes the zinc reagent from the metal surface.
Organozinc compounds are organic compounds that contain carbon-zinc bonds. Organozinc chemistry is the study of the physical and chemical properties, synthesis and reactions of organic zinc compounds.
Many organic zinc compounds are flammable and difficult to handle. Most organic zinc compounds are easily oxidized and decompose when dissolved in protonated solvents. In many reactions, organozinc reagents need to be made ready to use and cannot be isolated and purified or stored for long periods of time. All reactions using organozinc reagents need to be carried out under the protection of an inert gas, such as nitrogen or argon.
The common oxidation state of organozinc compounds is +2 valence. It can be categorized into three types: organozinc halogen compounds (R-Zn-X, where X represents a halogen atom); dihydrocarbon-based zinc compounds (R-Zn-R, where R represents an alkyl or aryl group); and lithium zincate or magnesium zincate salts (M+R3Zn-, where M represents lithium or magnesium).
Organozinc reagents were among the first organometallic reagents to be discovered. The relatively low reactivity of organozinc reagents gives them the advantages of good functional group compatibility, high chemical, regioselectivity and stereoselectivity. In addition, organozinc reagents can react with many transition metal salts or complexes in metal exchange reactions to obtain highly active organotransition metal reagents, and can react with a variety of electrophilic reagents. What do I need to pay attention to when preparing organozinc reagents?
