1H and 13C NMR spectra of phenylcoppermagnesium and methylcoppermagnesium reagents

Abstract

The 1H and 13C NMR spectra of the phenylcoppermagnesium reagent, prepared from 2 PhMgBr + CuI, show that the reagent contains several organocopper species in a THF- d 8toluene- d 8Me 2S ( A) or Et 2Otoluene- d 8Me 2S ( B) solvent system over a temperature range of 0 to −60°C. However, if a 15% excess of CuI is employed in the preparation, only one major species is present in Et 2Otoluene- d 8 ( D) solution. This dominant species coordinates with ether and remains as a single species between 0 to −80°C. The coordinated ether exchanges wih free ether with an activation energy of 53 kJ mol −1 at 0−C; this provides the first spectroscopic evidence for the existence of such an exchange process. The methylcoppermagnesium, on the other hand, when prepared from 2 MeMgl + CuI, gives a single NMR signal for the methyl protons and a single 13C signal for the methyl carbon in either B or D solvent system over the range 0 to −80°C, indicating that only one organocopper species is formed (provided there is no fast exchange of methyl groups).