Heteroleptic, two-coordinate [M(NHC){N(SiMe3)2}] (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(SiMe3)(2)}] (IPr = 1,3-bis(diisopropylphenyl)- imidazol-2-ylidene), formally M-I complexes (M = Co, 3; Fe, 4) were obtained by the reduction of [M(IPr)Cl{N(SiMe3) (2)}] with KC8, or [Co(IPr){N(SiMe3)(2)}(2)] with mes(star)PH(2), mes(star) = 2,4,6-tBu(3)C(6)H(2). The magnetism of 3 and 4 implies Co-II and FeII 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(SiMe3)(2)}] with excess KC8 in toluene gave the heteronuclear 'inverse-sandwich' Fe-K complex 7, featuring eta(6)-toluene sandwiched between one Fe-0 and one K+ centre.