Copper ate complexes

Ryu, I. Nakahira, H. Ikebe, M. Sonoda, N. Yamato, S.-Y. Komatsu, M. Chelation-aided generation of ketone a,/1-dianions and their use as copper ate complexes. Unprecedented enolate intervention in the conjugate addition to enones./. Am. Chem. Soc. 2000, 122,1219-1220. 

A remarkably stable organocopper compound was obtained on treatment of Me3P=CH2 with CuCl (see Scheme 1.10) [54, 55). Formally, this product should be regarded as an ate complex, with positive charges on the phosphorus atoms and negative charges on the copper atoms. 

In 1952 Gilman and co-workers reported that the yellow, ether-insoluble methylcopper dissolved to give a clear colorless solution on addition of a further equivalent of methyllithium 119). The new copper compound, of composition LiCu(CH3)2, is an ate complex now usually known as lithium dimethylcuprate. Mixed cuprates can be prepared from a preformed organocopper compound, RCu, and a lithium reagent 147, 259, 298, 301). 

The nature of organocopper reagents appears to be dependent on the method of preparation and the stoichiometry. Specific examples are methylcopper (76, 310), phenylcopper 73), and pentafluorophenyl-copper 34, 37, 147). The best method of preparing pentafluorophenyl-copper of composition CeFsCu appears to be via the addition of copper(I) bromide to pentafluorophenylmagnesium bromide 34, 37), since the lithium reagent and copper iodide gives an ate complex 147). An ate complex was also obtained from pentafluorophenyllithium and silver chloride in equimolar proportions 265). As shown in Table III, many of the isolated copper compounds gave somewhat incorrect or irreproducible analyses, and others contain metal halide and solvent molecules. 

The reaction of 2,2 -dilithiobiphenyl, or the analogous Grignard reagent, with excess copper(II) chloride gave a mixture of products from which biphenylene and o-tetraphenylene were isolated 235, 304). Other products were tetra- and octaphenyls. The reaction was explained in terms of the formation of a copper(II) ate complex (IX) which, under the influence of further Cu " " ions, oxidatively couples to give a 60%... 

Although there are numerous examples of dimerizations of organo-metallic reagents by copper(II) salts, one particularly interesting example concerns 2,2 -dilithiobiphenyl 304). Wittig and Klar have proposed several transient copper(II) ate complexes and a stable copper(I) complex to account for the high yields of biphenylene and o-tetraphenyl-ene. Diarylcopper(II) compounds were supposedly isolated, and characterized by elemental analysis, from diarylmercury compounds and copper at 120°C 11, 197) an unlikely reaction. 

The ate-complexes (34) also react with benzylic halides aroyl chlorides allyl halides and proj r l halides to afford the (x>rr ponding products, respectively (Eq. 75). (E)-a,P-Unsaturated carboxylic esters can also be obtains by the reaction of such borate complexes with ethyl propiolate The same type of reaction between copper(I) methyltrialkylborates and l-(l-pyrrolidinyl)-6-chloro--1-cyclohexene gives the corresponding alkylation products which are readily hydrolyzed to 2-alkylcyclohexanone... 

The reaction of organolithiums or organomagnesium halide reagents with gold halides proceeds similarly to the copper halides in a 1 1 ratio. Their phosphine complexes can be isolated and characterized. In a 2 1 ratio, the transmetallation reaction is followed by ate complexation to form organoaurate complexes ... 

Besides the well-known Grignard compounds, other magnesium, aluminium, lithium, and copper-lithium organometaliic compounds have been used as reagents — most recently, ate complexes of aluminium have been introduced. 

Suzuki reported that copper borates (RsMeB Cu ) exhibit predominant Sn2 reactivity toward allylic halides. A similar ate complex (RFaB Cu ) is also proposed to be the reactive intermediate in the RCu BFa system developed about the same time by Yamamoto and coworkers. This latter reagent exhibits remarkable Sn2 regiospecificity in reactions with a variety of allylic substrates, including halides. 

The difficulties of direct oxidative insertion with metals other than Mg or Li mean that o-complexes are often made from organo-lithium or Grignard reagents by metal exchange. This reaction amounts to a nucleophilic substitution at the metal without a change of oxidation state so the metal is used in whatever oxidation state is finally needed. Attack of methyl lithium on a Cu(I) halide gives methyl copper 50, a o-complex of Me- and Cu(I). If an excess of MeLi is present an ate complex is formed, lithium dimethylcuprate 51. This is formally a compound of a copper anion 51a, just as BF4 is a borate. The term ate complex refers to such formally anionic complex in which the metal has one extra anionic ligand. Its true structure is dimeric 51b and it exists as an equilibrium with 52 in solution.20... 

Treatment of vinyl Sn, B, or Al compounds with BuLi results in effective addition of Bu to the metal to form a hypervalent anion such as 154. These are often referred to as ate complexes. The analogy is with the names of anions such as sulfate or carbonate. You are already familiar with the copper analogues, usually called cuprates. Lithium now replaces tin at the vinyl group 155 to form a vinyl-lithium derivative -156. The reaction is an electrophilic substitution at carbon - the lithium atom attacks the C-Sn bond and does so with retention of configuration. 

Oxidative coupling. Organolithium and organomagnesium compounds react with the complex in THF or dimethoxyethane at —78° to give copper(l) ate complexes, which in the presence of atmospheric oxygen undergo coupling.2 The reaction of it-butyllithium is typical ... 

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