Ionic aggregates of lithium organocuprates.

We have used a combination of electrospray ionization mass spectrometry and electrical conductivity measurements to analyze solutions of the Gilman cuprates LiCuR2·LiX, with R=Ph, Bu and X=Cl, Br, I, in tetrahydrofuran and have compared our findings with previous results on cyanocuprates LiCuR2·LiCN. Among the various polynuclear organocuprate ions observed, Li2Cu3Ph6(-), LiCu4Ph6(-), and Cu5Ph6(-) are of particular interest because aggregates of the same composition are known from X-ray crystal structures. Control experiments have indicated that the polynuclear organocuprate anions detected in solution are indeed identical to those formed in the solid state. As abundant ions of the type Li2Cu3R6(-) are found in solutions of Gilman cuprates and cyanocuprates alike, their possible involvement in organocuprate reactions should be considered. For comparison, we have also included solutions of LiCu(R)I, LiCuX2·LiX, LiCuX2, and CuCN·2LiX in the present study.