Nature of Organocopper Reagents

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. 

Little attention has been paid to the elucidation of the structures of organocopper compounds until recently. The structures of some copper compounds have been determined either by X-ray crystallography or by a combination of NMR and mass spectroscopic data, and the degree of association. Aggregation states have been determined mostly by cry-oscopy, but occasionally by vapor pressure osmometry and ebulliometry where permitted by the stability of the organocopper compound 36, 37, 281f). 

Although methylcopper and phenylcopper are generally considered to be polymeric because of their insolubility in organic solvents, no evidence exists to support this belief. The tolylcopper and o-anisylcopper compounds are reported to have low aggregation states which increase in size with time for various solutions 40) they are also ether-insoluble. 

Ethynylcopper compounds are known to be polymeric. X-ray diffraction analysis indicated that they are composed of infinite zigzag chains of copper atoms, each bound to three ethynyl group by a- and 7r-bonds 

Indenyl-CuIf-CiHaNOa- CgHs + C1I2O + 3/-C4H9NC 247 

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