Expedient Access to Normal- and Abnormal- N-Heterocyclic Carbene (NHC) Magnesium Compounds from Imidazolium Salts

Treatment of imidazolium salts (IPrH)Cl (1) and (IPrH)I (2) with MeMgI leads to the formation of normal N‐heterocyclic carbene (nNHC) compounds (IPr)MgCl(I) (3) and (IPr)MgI2 (4) [IPr = 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene], respectively. By employing a similar strategy, the first magnesium compound (aIPrPh)MgI2(OEt2) (6) featuring an abnormal‐NHC [aIPrPh = 1,3‐bis(2,6‐diisopropylphenyl)‐2‐phenyl‐imidazol‐4‐ylidene] is prepared by the treatment of a C2‐arylated imidazolium salt (IPrPh)I (5) with MeMgI. While the deprotonation of 1 and 2 can be accomplished at room temperature, an elevated temperature is required to deprotonate 5 with MeMgI. This is most likely due to the higher pKa value of the C4‐H than that of the C2‐H hydrogen atom. Salt metathesis reaction of 6 with KN(SiMe3)2 cleanly leads to the formation of a magnesium amide derivative (aIPrPh)Mg{N(SiMe3)2}2 (7). Compounds 3, 4, 6, and 7 were characterized by elemental analyses and NMR spectroscopic studies. The molecular structures of 3, 4, and 6 were determined by single‐crystal X‐ray diffraction analyses.