Copper(I) Chloride1

CuCl

[7758-89-6]  · ClCu  · Copper(I) Chloride  · (MW 99.00)

(catalyst for diazo and diazonium chemistry; for use with Grignard reagents1)

Alternate Name: cuprous chloride.

Physical Data: mp 430 °C; d 4.140 g cm-3.

Solubility: insol H2O and most organic solvents; partially sol dimethyl sulfide (DMS).

Form Supplied in: light green-tinged white solid; 99.99% grade available commercially.

Handling, Storage, and Precautions: maintenance of a dry N2 or Ar atmosphere is recommended.

General Discussion.

Copper(I) chloride is the most popular CuI salt for use in many of the classic name reactions of organic chemistry.1a Examples include the Sandmeyer reaction,1b the CuCl induced decomposition of arenediazonium salts to afford aryl chlorides,2 and the related Bart reaction1c of arenediazonium salts with sodium metaarsenite to yield arylarsonic acids,3 which is also catalyzed by CuCl. Kochi has elucidated the mechanisms of the Sandmeyer reaction and the Meerwein reaction1d of arenediazonium salts with alkenes and established that they proceed via a common radical intermediate which could be generated from other precursors.4 Nagashima et al. took advantage of this fact when they cyclized an N-allyltrichloroacetamide derivative with CuCl,5 in what is a significant extension and generalization of the Meerwein reaction (eq 1).

a-Diazo ketones with aryl substituents in the b- or g-positions are decomposed by CuCl to give cyclized products. For example, Scott has reported an azulene synthesis starting from 3-phenylpropanoic acid,6 and Iwata et al. have developed a spiroannulation method for phenolic a-diazo ketones,7,8 as illustrated in eq 2 by the synthesis of a-chamigrene.7 Many other examples1e of intramolecular reactions of diazo carbonyl compounds are known in an area that was pioneered by Stork,9 who used Copper Bronze. CuCl has also been used to catalyze cyclopropanations with Diazomethane,10 and with diazoacetic esters.1f It should be noted that CuI, CuBr, and CuCN have also been used to catalyze the reactions of diazo compounds, as have Cu0 and CuII.1e,f,9

The Gattermann-Koch synthesis of aromatic aldehydes involves a Friedel-Crafts formylation by ClCHO in the presence of Aluminum Chloride and CuCl catalysts.1g,11 The reaction proceeds without Cu, but at much higher pressures.1g

The Glazer reaction couples terminal alkynes by using dioxygen and CuCl, usually in the presence of ammonia or another amine (pyridine, EtNH2).1h Many examples are known; eq 3 shows an example in the overlapping areas of medium-sized ring formation and annulene chemistry.12 A related reaction mixture which uses pyridine instead of ammonia oxidatively cleaves 1,2-diaminobenzene to cis,cis-mucononitrile,13a and phenanthrenequinone to 2,2-biphenyldicarboxylic acid.14a It also oxidizes the bishydrazones of a-diketones to alkynes and the monohydrazones to a-diazo ketones.13b 1,10-Phenanthroline has been used in conjunction with CuCl and dioxygen to oxidize alcohols to ketones or aldehydes.14b

Marino has reported that cyclic a,b-unsaturated epoxides react with Cu carboxylates, generated in situ from Na carboxylates and CuCl, to give syn-1,4-diol derivatives.15a Goering has shown that allyl pivalates give a-alkylation with inversion of configuration with Grignard reagents catalyzed by CuCl, but (anti) g-alkylation with Copper(I) Cyanide as catalyst.15b

Kharasch discovered that CuCl catalyzes the coupling of aryl Grignard reagents with aryl halides,16a and also the 1,4-addition of Grignard reagents to a,b-unsaturated ketones.16b While the former has been called the Kharasch reaction,1i today the latter is much more important synthetically,1i-k and it should be named for its inventor, who was one of the true pioneers in the synthetic applications of transition metals. One way to avoid confusion would be to call the reagent prepared from a Grignard reagent and a CuI salt a (catalytic or stoichiometric) Kharasch Reagent by analogy with the commonly used Gilman Reagent, which is synonymous with cuprate prepared from 2 equiv of lithium reagent and a CuI salt.

While Copper(I) Iodide, CuBr.DMS (see Copper(I) Bromide), and CuCN are now used more commonly than CuCl in the preparation of organocopper reagents, there are still interesting examples which utilize CuCl. For example, the addition of BuMgBr to sorbate esters gives a mixture of 1,2- and 1,4-addition products; however, upon the addition of CuCl, 1,6-addition predominates.17 This example also illustrates one of the problems commonly encountered when trying to interpret the results of experiments using the Kharasch reagent. Experimenters frequently mix a Grignard reagent containing one halide with a CuI salt containing another. CuBr.DMS has also been shown to dramatically favor 1,6-addition of Grignard reagents (see Copper(I) Bromide).

Tandem organocuprate b-addition to a,b-unsaturated carbonyl compounds followed by a-alkylation, acylation or other functionalization of the regiospecifically generated a-enolate has become an important methodology.1j,k In what has been described as the first one-pot, three-component tandem vicinal difunctionalization reaction,1j Stork used CuCl to catalyze the 1,4-addition of m-methoxyphenylmagnesium bromide to 5,5-dimethylcyclohex-2-en-1-one, followed by a-alkylation with allyl bromide,18 which was the seminal step in the synthesis of lycopodine. Bunce and Harris have recently combined b-addition with intramolecular a-acylation in a tandem conjugate addition-Dieckmann condensation reaction, which was used to prepare six-membered rings (eq 4).19 It is interesting to note that the Stork conditions (RMgBr/CuCl) gave better results than the Gilman reagents prepared from 2 equiv of the corresponding Li reagent and either CuI or CuCN.19

CuCl has been directly compared with CuBr, CuBr.DMS, CuI, CuCN, and Copper(I) Trifluoromethanesulfonate as a precursor for Gilman reagents,20 and it appears to be inferior to the usual CuI salts for this important class of compounds. It was found early on that CuII salts catalyze many of the same organic reactions as the corresponding CuI salts,1 e.g. a popular catalyst for coupling reactions with Grignard reagents is Dilithium Tetrachlorocuprate(II) = CuCl2 + 2LiCl.1i-l It is generally assumed that the CuII salt is reduced to CuI under the reaction conditions; however, in most cases this has not been proven.

Along with CuBr and CuBr.DMS, CuCl continues to be a favored precursor for structural work and the preparation of new organocopper derivatives. For example, p-complexes between nonconjugated dienes and CuCl or CuBr have been characterized by X-ray crystallography.21 Chaudret et al. have shown that (C5Me5)Ru(PCy3)H3 reacts smoothly with CuCl to give (C5Me5)Ru(PCy3)H3CuCl,22 which was of interest in relation to the proposal that trihydrogen ligands might exist. In these two cases the product still contains the Cl atom. Many interesting examples exist where it does not (see below). A study illustrating both Cl-containing and Cl-free products is provided by Zybill and Müller, who reacted hexaphenylcarbodiphosphorane with CuCl to form a 1:1 adduct, which they reacted further with [C5Me5]- to yield (C5Me5)CuC(PPh3)2.23

Both dinuclear and tetranuclear Cu alkyl complexes have been prepared from CuCl and 2-substituted pyridines containing bis(trimethylsilyl)methyl and trimethylsilylmethyl substituents, respectively.24 MeCu(PPh3)3 has been prepared and studied by NMR and X-ray crystallography;25 such phosphine-complexed organocopper reagents have proven useful for organic synthesis. Several copper(I) cupracarboranes have been synthesized, including an interesting trimer.26 (Trimers are much less common than tetramers in CuI chemistry.27) In a most incredible communication, Fenske et al. characterize the brobdingnagian product of the reaction 146 CuCl + 73 Se(SiMe3)2 + 30 PPh3 -> Cu146Se73(PPh3)30 + 146 ClSiMe3.28

One of the most interesting arylcopper(I) compounds is mesitylcopper(I),29 which is a pentamer in the solid state and a tetramer in the presence of S-ligands.30 It has recently been shown to split dioxygen,31 and is highlighted here because it is prepared from CuCl. Hexafluoroacetylacetonatocopper(I)-alkyne complexes (prepared from CuCl) have been shown to be useful in the chemical vapor deposition of Cu metal.32 (E)-1-Trimethylsilyl-1-alkenes have been prepared in high yields by the CuCl-catalyzed decomposition of a-trimethylsilyldiazoalkanes.33 Finally, Indian chemists have shown that 1,2-diketones are produced in good yield when Na(RCO)Fe(CO)4 is treated with CuCl.34

Related Reagents.

Copper(II) Chloride; Copper(II) Chloride-Copper(II) Oxide; Iodine-Copper(II) Chloride; Copper(I) Chloride-Oxygen; copper(I) chloride-tetrabutylammonium chloride Copper(I) Chloride-Sulfur Dioxide; Iodine-Aluminum(III) Chloride-Copper(II) Chloride; Iodine-Copper(I) Chloride-Copper(II) Chloride; Methylmagnesium Iodide-Copper(I) Chloride; Palladium(II) Chloride-Copper(I) Chloride; Palladium(II) Chloride-Copper(II) Chloride; Phenyl Selenocyanate-Copper(II) Chloride; Vinylmagnesium Chloride-Copper(I) Chloride; Zinc-Copper(I) Chloride.


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Steven H. Bertz & Edward H. Fairchild

LONZA, Annandale, NJ, USA



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