Intermediates Formed in the Reactions of Organocuprates with α,β‐Unsaturated Nitriles

Abstract

Conjugate additions of organocuprates are of outstanding importance for organic synthesis. To improve our mechanistic understanding of these reactions, we have used electrospray ionization mass spectrometry for the identification of the ionic intermediates formed upon the treatment of LiCuR2 ⋅LiCN (R=Me, Bu, Ph) with a series of α,β-unsaturated nitriles. Acrylonitrile, the weakest Michael acceptor included, did not afford any detectable intermediates. Fumaronitrile (FN) yielded adducts of the type Lin-1 Cun R2n (FN)n (-) , n=1-3. When subjected to fragmentation in the gas phase, these adducts were not converted into the conjugate addition products, but re-dissociated into the reactants. In contrast, the reaction with 1,1-dicyanoethylene furnished the products of the conjugate addition without any observable intermediates. Tri- and tetracyanoethylene proved to be quite reactive as well. The presence of several cyano groups in these substrates opened up reaction pathways different from simple conjugate additions, however, and led to dimerization and substitution reactions. Moreover, the gas-phase fragmentation behavior of the species formed from these substrates indicated the occurrence of single-electron transfer processes. Additional quantum-chemical calculations provided insight into the structures and stabilities of the observed intermediates and their consecutive reactions.

Electrospray Ionization Tandem Mass Spectrometry and DFT Survey of Copper(I) Ate Complexes Containing Coordinated Borohydride Anions

“… Given that it has been established from organocopper chemistry that one way of stabilizing a neutral organocopper complex, RCu (R = alkyl or aryl) is the addition of an organolithium, RLi, to form a lithium ate complex, Li + [CuR 2 ] − , it is surprising that there are no reported attempts at preparing the related borohydride ate complexes Li + [Cu­(BH 4 ) 2 ] − . Inspired by the extensive studies of Koszinowski that have demonstrated the power of using negative-ion electrospray ionization to probe organocuprates, − here we survey the formation of copper ate complexes containing coordinated borohydride. We use electrospray ionization tandem mass spectrometry ((−)­ESI-MS) in an ion-trap mass spectrometer , to establish the stoichiometry (types of ligand and nuclearity) of such complexes, and we study their gas-phase fragmentation reactions under collision-induced dissociation (CID) conditions.…”