Magnesium complexes with isomeric pyrazol-4-ylidene and imidazol-2-ylidene ligands

Abstract

Dimagnesium(I) complexes [{(Arnacnac)Mg}2], where Arnacnac = HC(MeCNAr)2, Ar = Dip = 2,6-iPr2-C6H3, Ar = Dep = 2,6-Et2-C6H3, Ar = Mes = 2,4,6-Me3-C6H2, 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, [MePZI]I, the pyrazol-4-ylidene complex [(Dipnacnac)MgI(MePZ)] was structurally characterised, alongside other products. The isomeric imidazol-2-ylidene complex [(Dipnacnac)MgI(MeNHC)], where MeNHC 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 MePZ ligand is higher in energy and more nucleophilic than its more common isomeric MeNHC carbene.