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Magnesium Cyanide or Isocyanide?
Author(s) -
Ballmann Gerd,
Elsen Holger,
Harder Sjoerd
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201909511
Subject(s) - chemistry , isocyanide , ligand (biochemistry) , isomerization , cyanide , monomer , crystal structure , magnesium , crystallography , stereochemistry , medicinal chemistry , inorganic chemistry , organic chemistry , receptor , catalysis , biochemistry , polymer
Preference for the binding mode of the CN − ligand to Mg (Mg−CN vs. Mg−NC) is investigated. A monomeric Mg complex with a terminal CN ligand was prepared using the dipyrromethene ligand Mes DPM which successfully blocks dimerization. While reaction of ( Mes DPM)MgN(SiMe 3 ) 2 with Me 3 SiCN gave the coordination complex ( Mes DPM)MgN(SiMe 3 ) 2 ⋅NCSiMe 3 , reaction with ( Mes DPM)Mg( n Bu) led to ( Mes DPM)MgNC⋅(THF) 2 . A Mg−NC/Mg−CN ratio of ≈95:5 was established by crystal‐structure determination and DFT calculations. IR studies show absorbances for CN stretching at 2085 cm −1 (Mg−NC) and 2162 cm −1 (Mg−CN) as confirmed by 13 C labeling. In solution and in the solid state, the CN ligand rotates within the pocket. The calculated isomerization barrier is only 12.0 kcal mol −1 and the 13 C NMR signal for CN decoalesces at −85 °C (Mg−NC: 175.9 ppm, Mg−CN: 144.3 ppm). Experiment and theory both indicate that Mg complexes with the CN − ligand should not be named cyanides but are more properly defined as isocyanides.