Synthesis and characterization of an unsolvated dimeric diarylmagnesium compound and its magnesium iodide byproducts

The Grignard reagent 2,6-Et(2)C(6)H(3)MgI(THF)(n), 1, undergoes rapid aryl exchange in THF solution at room temperature to afford the diorganomagnesium compound (2,6-Et(2)C(6)H(3))(2)Mg(THF)(n), 2, and the sparingly soluble salt Mg(THF)(6)I(2), 5. Removal of the coordinated THF in 2 under reduced pressure and elevated temperature affords the unique diorganomagnesium species [2,6-Et(2)C(6)H(3)Mg(mu-C(6)H(3)Et(2)-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-Et(2)C(6)H(3))(2)Mg around 115 degrees C. Recrystallization of crude 5 from benzene solution gave large well-shaped crystals of MgI(2)(THF)(3), 4, and 5. Benzene solutions of 4 and 5 are remarkably easily oxidized by laboratory air to MgI(THF)(5)I(3), 6. Compound 3 has been characterized by variable-temperature (1)H NMR spectroscopy and X-ray crystallography, and compounds 4-6 have been characterized by X-ray crystallography.