Magnesium Complexes with Isomeric Pyrazol‐4‐ylidene and Imidazol‐2‐ylidene Ligands

Dimagnesium(I) complexes [{( Ar nacnac)Mg} 2 ], where Ar nacnac=HC(MeCNAr) 2 , Ar=Dip=2,6‐ i Pr 2 −C 6 H 3 , Ar=Dep=2,6‐Et 2 −C 6 H 3 , Ar=Mes=2,4,6‐Me 3 −C 6 H 2 , react with iodoarenes in oxidative addition reactions. With iodobenzene, magnesium phenyl and magnesium iodide complex fragments were obtained, and from a reaction with 4‐iodo‐1,2,3,5‐tetramethylpyrazolium iodide, [ Me PZI]I, the pyrazol‐4‐ylidene complex [( Dip nacnac)MgI( Me PZ)] was structurally characterised, alongside other products. The isomeric imidazol‐2‐ylidene complex [( Dip nacnac)MgI( Me NHC)], where Me NHC is 1,3,4,5‐tetramethylimidazol‐2‐ylidene, was prepared and characterised. X‐ray crystal structure determinations and DFT computational studies have been carried out to compare the related complexes. The results show that the Me PZ ligand is higher in energy and more nucleophilic than its more common isomeric Me NHC carbene.