Reaction pathway of the conjugate addition of lithium organocuprate clusters to acrolein

The reaction pathway of transfer of a methyl group of a cuprate cluster (Me2CuLi)(2) to acrolein (conjugate addition of the methyl group) has been studied with the hybrid density functional B3LYP method. All intermediates and transition structures (TSs) on the potential surface of the reaction as well as the structures on the intrinsic reaction coordinate near the C-C bond forming stage of the reaction have been determined. In addition to two previously proposed species, a lithium/carbonyl coordination complex (CPli) and a copper/olefin complex retaining a closed cuprate structure (CPcl), a new copper/olefin complex with an open cuprate structure (CPop) was characterized and proven to be an intermediate directly leading to the conjugate addition product (PD) via a TS of C-C bond formation (TS). The overall pathway of the reaction can be viewed, in one way, as C-C bond formation via reductive elimination of a Cu(III) species and, in another, as a 1,4-addition of MeLi assisted by copper. The present studies revealed that the large cluster framework of (Me2CuLi)(2) allows intricate cooperation of two lithium atoms and a copper atom. A small cluster such as Me2CuLi cannot achieve such cooperative action of different metal atoms as smoothly as larger clusters such as (Me2CuLi)(2) and Me2CuLi . LiCl. Mechanistic relationships between conjugate addition, carbocupration, and alkylation reactions of cuprate are discussed. A close similarity has been found between the conjugate addition and the carbocupration of acetylene for the cooperative action of metal and the involvement of a Cu(III) species.