Complexes of Gilman reagents with C-S and C-N double bonds: δ or π bonding?

Article abstract of DOI:10.1021/ja103068h

Upon rapid injection, a variety of thiocarbonyl compounds react with the Gilman reagent Me₂CuLi at -100 °C inside the probe of an NMR spectrometer to give high yields of complexes. Typical examples of substrates include carbon disulfide, methyl dithioacetate, methyl dithiobenzoate, thiobenzophenone, ethylene trithiocarbonate, and phenyl isothiocyanate. Evidence suggesting the formal oxidation state of copper in these complexes to be Cu^III is presented. The last example was particularly interesting, since it involved a transient intermediate that was identified as a complex with a C-N double bond. Methyl isothiocyanate gave a stable C-N double-bond complex.