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A magnesium benzenehexolate complex

A magnesium benzenehexolate complex
25 September 2020 - Chemical Zoo

CameronJonesMagnesiumComplexAngewandte2020.PNGJustus Liebig would have turned in his grave had he learned of L6Mg6C6O6, shorthand for a novel compound recently investigated by Cameron Jones group. In their publication in The Angewandte (DOI) they describe a synthesis of this magnesium benzenehexolate complex by reaction of a beta-diketiminate-stabilized magnesium dimer with molybdenum hexacarbonyl and carbon monoxide in benzene at 80 degrees for 14 hours. The new compound is a hexahydroxybenzene with all oxygen atoms bridged by magnesium and each magnesium linked to an anionic ligand.

The magnesium dimer (LMg-MgL) is unusual in itself. Magnesium compounds tend to have a +2 oxidation state but already in 2007 the Jones group managed to synthesize this first ever Mg(I) compound by reducing the methylmagnesium iodide adduct of a nacnac compound with potassium metal (DOI).

The dimer is the reducing agent in the reaction with CO. Molybdenum hexacarbonyl alone can provide all the CO required but acts mainly as a catalyst. Bulky substituents on the nacnac ligand are also key. The reaction product is stable but prone to oxidation.

And the connection to Liebig? The authors point out that Liebig in 1834 (DOI) had been pioneering the field by reacting carbon monoxide with molten potassium with "die sonderbarsten und merkw├╝rdigen resultaten". He named the reaction product potassium carbonyl but had to leave it at that because back in 1834 laboratories obviously were really crappy with barely any of the fancy equipment or chemicals we know today. It also did not help that Liebig was a committed radical theory believer.