A Stable Homoleptic Organometallic Iron(IV) Complex

Abstract

A homoleptic organometallic FeIV complex that is stable in both solution and in the solid state at ambient conditions has been synthesized and isolated as [Fe(phtmeimb)2](PF6)2 (phtmeimb=[phenyl(tris(3-methylimidazolin-2-ylidene))borate]−). This FeIV N-heterocyclic carbene (NHC) complex was characterized by 1H NMR, HR-MS, elemental analysis, scXRD analysis, electrochemistry, Mößbauer spectroscopy, and magnetic susceptibility. The two latter techniques unequivocally demonstrate that [Fe(phtmeimb)2](PF6)2 is a triplet FeIV low-spin S=1 complex in the ground state, in agreement with quantum chemical calculations. The electronic absorption spectrum of [Fe(phtmeimb)2](PF6)2 in acetonitrile shows an intense absorption band in the red and near IR, due to LMCT (ligand-to-metal charge transfer) excitation. For the first time the excited state dynamics of a FeIV complex was studied and revealed a ≈0.8 ps lifetime of the 3LMCT excited state of [Fe(phtmeimb)2](PF6)2 in acetonitrile.