Preparation and Chemistry of the Active Copper Species Derived from CuI*PBu3, CuI*PPh3, and CuCN*nLiX Complexes

Article abstract of DOI:10.1021/jo00061a023

The preparation of highly reactive copper by the reduction of CuI*PBu3, CuI*PPh3, and CuCN*nLiX copper(I) complexes with the preformed lithium naphthalenide is described.It was found, for all three Cu(I) complexes, that the reduction temperature proved crucial to reactivity of the zerovalent copper species as measured by the ability of the active copper to undergo oxidative addition to carbon-halogen bonds.The lower the reduction temperature the more reactive the zerovalent copper species becomes.The low-temperature reduction allows for the formation of highly reactive copper from CuCN*nLiX complexes.This active copper species undergoes oxidative addition to alkyl and aryl bromides in high yield to form the corresponding organocopper reagent directly without the need for other organometallic precursors.Moreover, the alkyl and aryl bromides can obtain a wide range of functional groups as they are not affected in the oxidative addition step.The functionalized organocopper reagents derived from CuCN*nLiX based active copper are the reagent of choice in the cross-coupling of acid chlorides to produce ketones as well as the 1,4-addition reaction with enones.The lack of phosphines associated with organocopper reagents stemming from CuCN-based active copper makes product isolation more facile.While the functionalized organocopper reagents derived from CuCN*nLiX complexes provide higher isolated yields in the formentioned reactions, they are not nucleophilic enough to undergo inter- or intramolecular epoxide openings.The use of both CuI*PBu3 and CuI*PPh3 Cu(I) complexes in the intramolecular epoxide openings of aryl bromoepoxides is presented.The regiochemistry, endo vs. exo, was shown to be affected by the Cu(I) complex used to generate the active copper species, the solvent, and the pattern of substitution around the epoxide moiety.The active copper species as well as the resulting organocopper reagents derived from both CuI*PBu3 and CuCN*nLiX were investigated using both 31P and 13C NMR.The data from 31P NMR investigation held some evidence for a highly reduced copper(0)-phosphine complex while the 13C studies of the CuCN*nLiX complexes indicated that these species have limited solubility in THF.