The X-ray crystal structure of a cuprate-carbonyl π-complex.

Complexes between copper reagents and double-bonds have been proposed as intermediates in a number of synthetically important reactions. Many h-complexes between organocuprates and carbon–carbon double-bonds, which are intermediates in 1,4-addition reactions of a,b-unsaturated carbonyl compounds, have been observed by using NMR spectroscopy. Moreover, h-O,C-complexes between organocopper compounds and carbon–oxygen double-bonds have been proposed as intermediates in 1,2-additions to carbonyl compounds, for example, copper-catalyzed asymmetric induction reactions. Carbophilic additions to thiocarbonyl compounds, mediated by organocuprates, have been explained in terms of h-S,C-complexes of carbon–sulfur double-bonds. However, there has been no report of an X-ray structure for any of these p-complexes. Therefore, we applied our rapid-injection techniques, which were previously used to prepare several important intermediates, to screen a number of typical aldehydes and ketones for complex formation with Me2CuLi, [9] and we discovered such a species with unusual stability, which has allowed us to prepare it on a larger scale and grow highquality crystals (see the Supporting Information). We now report the first X-ray crystal structure of a cuprate– carbonyl p-complex, 1 (Scheme 1 and Figure 1).