The Relation between Ion Pair Structures and Reactivities of Lithium Cuprates

✍ Scribed by Michael John; Carsten Auel; Christoph Behrens; Michael Marsch; Klaus Harms; Ferdinand Bosold; Ruth M. Gschwind; Pattuparambil R. Rajamohanan; Gernot Boche

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 323 KB
• Volume: 6
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20000818)6:16<3060::aid-chem3060>3.0.co;2-m

✦ Synopsis

From Li well-solvating solvents or complex ligands such as THF, [12]crown-4, amines etc., lithium cuprates R 2 CuLi( . LiX) crystallise in a solvent-separated ion pair (SSIP) structural type (e.g. 10). In contrast, solvents with little donor qualities for Li such as diethyl ether or dimethyl sulfide lead to solid-state structures of the contact ion pair (CIP) type (e.g. 11). 1 H, 6 Li HOESY NMR investigations in solutions of R 2 CuLi( . LiX) (15, 16) are in agreement with these findings: in THF the SSIP 18 is strongly favoured in the equilibrium with the CIP 17, and in diethyl ether one observes essentially only the CIP 17. Salts LiX (X CN, Cl, Br, I, SPh) have only a minor effect on the ion pair equilibrium. These structural investigations correspond perfectly with Bertzs logarithmic reactivity profiles (LRPs) of reactions of R 2 CuLi with enones in diethyl ether and THF: the faster reaction in diethyl ether is due to the predominance of the CIP 17 in this solvent, which is the reacting species; in THF only little CIP 17 is present in a fast equilibrium with the SSIP 18. A kinetic analysis of the LRPs quantifies these findings. Recent quantum-chemical studies are also in agreement with the CIP 17 being the reacting species. Thus a uniform picture of structure and reactivity of lithium cuprates emerges.