Synthesis and Characterization of an Unsolvated Dimeric Diarylmagnesium Compound and Its Magnesium Iodide Byproducts

The Grignard reagent 2,6-Et2C6H3MgI(THF)n, 1, undergoes rapid aryl exchange in THF solution at room
temperature to afford the diorganomagnesium compound (2,6-Et2C6H3)2Mg(THF)n, 2, and the sparingly soluble
salt Mg(THF)6I2, 5. Removal of the coordinated THF in 2 under reduced pressure and elevated temperature affords
the unique diorganomagnesium species [2,6-Et2C6H3Mg(μ-C6H3Et2-2,6)]2, 3, which features three-coordinate
magnesium. Compound 3 is fluxional in benzene or toluene solution at room temperature and dissociates into
monomeric (2,6-Et2C6H3)2Mg around 115 °C. Recrystallization of crude 5 from benzene solution gave large
well-shaped crystals of MgI2(THF)3, 4, and 5. Benzene solutions of 4 and 5 are remarkably easily oxidized by
laboratory air to MgI(THF)5I3, 6. Coumpound 3 has been characterized by variable-temperature 1H NMR
spectroscopy and X-ray crystallography, and compounds 4−6 have been characterized by X-ray crystallography.