Structural studies of organometallic compounds in solution: III. A large angle scattering (LAXS) study of organomagnesium iodides in diethyl ether

Abstract

Structures of methyl-, ethyl- and phenyl-magnesium iodides have been determined in diethyl ether solution by the large angle X-ray scattering (LAXS) technique. Solutions in the concentration range 0.9–2.7 M have been studied. The Grignard reagents are present as solvated monomeric and dimeric species. Magnesium coordinates an iodide ion, an alkyl or aryl group, and four diethyl ether molecules octahedrally in the monomeric complex. In the dimeric complex each magnesium is octahedrally coordinated by two bridging iodide ions, an alkyl or aryl group, and three solvent molecules. The distribution of monomeric and dimeric species in the different solutions is given by a dimerisation constant, K di = [(RMgX) 2][RMgX] −2, which is in the range 0.2–0.8 M −1. The MgI bond distance is between 2.74 and 2.81 Å.