Two- and three-coordinate formal iron(i) compounds featuring monodentate aminocarbene ligands

Abstract

Bulky monodentate aminocarbene ligands, IMes and Me2-cAAC (IMes: 1,3-bis(2′,4′,6′-trimethylphenyl)imidazol-2-ylidene; Me2-cAAC: 3,3,5,5-tetramethyl-1-(2′,6′-diisopropylphenyl)pyrrolidine-2-ylidene), have been shown to be effective in supporting formal 13- and 11-electron iron(i) species. From the reactions of ferrous precursors and one equivalent of a reducing agent, three-coordinate complexes of the type [L2FeCl] (L = IMes or Me2-cAAC) have been synthesized in good yields. A mixed-ligand complex [(IMes)(Me2-cAAC)FeCl] was prepared from the ligand substitution reaction of [(IMes)2FeCl] with Me2-cAAC. All of the three-coordinate iron complexes can react with Na[BArF]4, from which a two-coordinate species [(Me2-cAAC)2Fe][BArF4] has been isolated. Single-crystal X-ray diffraction studies established their molecular structures to be the first examples of two- and three-coordinate formal iron(i) species supported by carbene ligands. The large solution magnetic moments, differentiated Fe-C(carbene) distances and 57Fe Mössbauer isomer shifts are indicative of their rich electronic properties.