Iron(ii) complexes of ditopic carbanionic carbenes

Abstract

Reaction of dimesityliron(II) (Fe₂(mes)₄) with the N-heterocyclic carbenes 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) and 1,3-bis(2,6-dimethylphenyl)hexahydropyrimidin-2-ylidene (6-Xyl) afforded the novel trigonal planar complexes [Fe(IPr)(mes)₂] (1) and [Fe(6-Xyl)(mes)₂] (2), respectively. Both species were structurally characterized by single crystal X-ray diffraction and display structures and magnetic responses consistent with a quintet ground state (S = 2). Reaction of 1 with KC₈ in THF afforded K⁺ salts of the anionic complex [{:C[N(2,6-ⁱPr₂C₆H₃)]₂(CH)C}₂Fe(mes)]⁻ (3) and the homoleptic organometallic anion [Fe(mes)₃]⁻ (4). By contrast, reduction of 2 resulted in extensive decomposition and intractable product mixtures. Complex 3 is coordinated by two ditopic carbanionic carbenes via the C4/C5 position while the C2 position retains unquenched carbenic character and remains vacant for further coordination. This was corroborated by reacting solutions of 3 with one and two equivalents of triethylaluminium (AlEt₃) which resulted in the formation of [{Et₃Al:C[N(2,6-ⁱPr₂C₆H₃)]₂(CH)C}{:C[N(2,6-ⁱPr₂C₆H₃)]₂(CH)C}Fe(mes)]⁻ (5) and [{Et₃Al:C[N(2,6-ⁱPr₂C₆H₃)]₂(CH)C}₂Fe(mes)]⁻ (6), respectively. Both of these species were structurally characterized as [K(2,2,2-crypt)]⁺ salts.