Access to a Labile Monomeric Magnesium Radical by Ball‐Milling
Dawid Jędrzkiewicz, Jonathan Mai, Jens Langer, Zachary Mathe, Neha Patel, Serena DeBeer, Sjoerd Harder
Abstract
Abstract In order to isolate a monometallic Mg radical, the precursor (Am)MgI⋅(CAAC) ( 1 ) was prepared (Am= t BuC(N‐DIPP) 2 , DIPP=2,6‐diisopropylphenyl, CAAC=cyclic (alkyl)(amino)carbene). Reduction of a solution of 1 in toluene with the reducing agent K/KI led to formation of a deep purple complex that rapidly decomposed. Ball‐milling of 1 with K/KI gave the low‐valent Mg I complex (Am)Mg⋅(CAAC) ( 2 ) which after rapid extraction with pentane and crystallization was isolated in 15 % yield. Although a benzene solution of 2 decomposes rapidly to give Mg(Am) 2 ( 3 ) and unidentified products, the radical is stable in the solid state. Its crystal structure shows planar trigonal coordination at Mg. The extremely short Mg−C distance of 2.056(2) Å indicates strong Mg−CAAC bonding. Calculations and EPR measurements show that most of the spin density is in a π* orbital located at the C−N bond in CAAC, leading to significant C−N bond elongation. This is supported by calculated NPA charges in 2 : Mg +1.73, CAAC −0.82. Similar metal‐to‐CAAC charge transfer was calculated for M 0 (CAAC) 2 and [M I (CAAC) 2 + ] (M=Be, Mg, Ca) complexes in which the metal charges range from +1.50 to +1.70. Although the spin density of the radical is mainly located at the CAAC ligand, complex 2 reacts as a low‐valent Mg I complex: reaction with a I 2 solution in toluene gave (Am)MgI⋅(CAAC) ( 1 ) as the major product.