Magnesium Cyanide or Isocyanide?

摘要

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 (DPM)-D-Mes which successfully blocks dimerization. While reaction of ((DPM)-D-Mes)MgN(SiMe3)(2) with Me3SiCN gave the coordination complex ((DPM)-D-Mes)MgN(SiMe3)(2).NCSiMe3, reaction with ((DPM)-D-Mes)Mg(nBu) led to ((DPM)-D-Mes)MgNC.(THF)(2). A Mg-NC/Mg-CN ratio of approximate to 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 C-13 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 C-13 NMR signal for CN decoalesces at -85 degrees 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.