Abstract
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(nBu) 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.