Iron(ii) complexes of ditopic carbanionic carbenesElectronic supplementary information (ESI) available: PXRD diffractograms, single crystal X-ray diffraction and magnetic data, computational details and ESI-MS spectra are also available. CCDC 962247-962254. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt52638k

Reaction of dimesityliron( ii ) (Fe 2 (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 KC 8 in THF afforded K + salts of the anionic complex [{:C[N(2,6- i Pr 2 C 6 H 3 )] 2 (CH)C} 2 Fe(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 (AlEt 3 ) which resulted in the formation of [{Et 3 Al:C[N(2,6- i Pr 2 C 6 H 3 )] 2 (CH)C}{:C[N(2,6- i Pr 2 C 6 H 3 )] 2 (CH)C}Fe(mes)] − ( 5 ) and [{Et 3 Al:C[N(2,6- i Pr 2 C 6 H 3 )] 2 (CH)C} 2 Fe(mes)] − ( 6 ), respectively. Both of these species were structurally characterized as [K(2,2,2-crypt)] + salts. The synthesis of the N-heterocyclic carbene complexes [Fe(IPr)(mes) 2 ] ( 1 ) and [Fe(6-Xyl)(mes) 2 ] ( 2 ) is reported. Chemical reduction of 1 using KC 8 affords an anionic trigonal planar complex containing two ditopic carbanionic carbene ligands [{:C[N(2,6- i Pr 2 C 6 H 3 )] 2 (CH)C} 2 Fe(mes)] − ( 3 ).