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Lithium Dichloro(2,2,6,6‐tetramethylpiperidinato)‐zincate

Thomas Klatt, P. Knochel, M. Mosrin
Published 2015 · Chemistry

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[1145881-09-9] C9H18Cl2LiNZn (MW 283.47) InChI = 1S/C9H18N.2ClH.Li.Zn/c1-8(2)6-5-7-9(3,4)10-8;;;;/h5-7H2,1-4H3;2*1H;;/q-1;;;+1;+2/p-2 InChIKey = VSOHSDUAQKXCAF-UHFFFAOYSA-L (reagent used in the preparation of various alkyl, vinyl, acetylenyl, benzyl, aryl, and heteroaryl zinc compounds via metalation reactions) Alternate Name: 2,2,6,6-tetramethylpiperidinozinc chloride–lithium chloride complex. Physical Data: solution in THF, similar to the solvent. Solubility: solution in THF miscible with majority of organic solvents, neat compound insoluble in alkanes, soluble in coordinating solvents (ethers, amines, etc.) Form Supplied in: THF solution (0.7–1.4 M). Purification: not considered. Handling, Storage, and Precautions: solution of the reagent decomposes in air, should be stored and handled under inert atmosphere. Reacts vigorously with water and aqueous solutions. Due to strong dehydrating ability, spills may cause serious damage to skin and eyes. Commercial solution in THF is a flammable liquid. Analysis of Reagent Purity: the commercially supplied 2,2,6,6-tetramethylpiperidinatozinc chloride–lithium chloride solution (TMPZnCl·LiCl) in THF (usually 0.7 M) is stable at ambient temperature, but readily reacts with moisture. Care should be taken in handling open bottles to prevent the entrance of air into the bottle. The reagent solution can be prepared starting from n-BuLi and dry 2,2,6,6-tetramethylpiperidine in THF, followed by the addition of a ZnCl2 solution in THF. Evaporation of the solvents affords a yellowish solid, which can be dissolved in THF to afford TMPZnCl·LiCl (usually 1.4 M).1 An alternative route starts from zinc dust, lithium chloride, and 1-chloro-2,2,6,6-tetramethylpiperidine (TMPCl) that is readily prepared by chlorination of 2,2,6,6-tetramethylpiperidine with an aqueous bleach solution (13% aqueous NaOCl).2 It is recommended to determine the actual concentration of the reagent in a newly opened bottle, and if the reagent was stored in an opened bottle for more than 1–2 months. A convenient titration method uses benzoic acid in the presence of 4-phenylazodiphenylamine as indicator.
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