Heteroleptic, two-coordinate [M(NHC){N(SiMe)}] (M = Co, Fe) complexes: synthesis, reactivity and magnetism rationalized by an unexpected metal oxidation state.

The linear, two-coordinate and isostructural heteroleptic [M(IPr){N(SiMe)}] (IPr = 1,3-bis(diisopropylphenyl)-imidazol-2-ylidene), formally M complexes (M = Co, 3; Fe, 4) were obtained by the reduction of [M(IPr)Cl{N(SiMe)}] with KC, or [Co(IPr){N(SiMe)}] with mesPH, mes = 2,4,6-tBuCH. The magnetism of 3 and 4 implies Co and Fe centres coupled to one ligand-delocalized electron, in line with XPS and XANES data; the ac susceptibility of 4 detected a pronounced frequency dependence due to slow magnetization relaxation. Reduction of [Fe(IPr)Cl{N(SiMe)}] with excess KC in toluene gave the heteronuclear 'inverse-sandwich' Fe-K complex 7, featuring η-toluene sandwiched between one Fe and one K centre.