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[BAr^F]₄, from which a two-coordinate species [(Me₂-cAAC)₂Fe][BAr^F₄] 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.