An iron(ii) hydride complex of a ligand with two adjacent β-diketiminate binding sites and its reactivity

Abstract

After lithiation of PYR-H₂ (PYR = [(NC(Me)C(H)C(Me)NC₆H₃(iPr)₂)₂(C₅H₃N)]²⁻) – the precursor of an expanded β-diketiminato ligand system with two binding pockets – with KN(TMS)₂ the reaction of the resulting potassium salt with FeBr₂ led to a dinuclear iron(II) bromide complex [(PYR)Fe(μ-Br)₂Fe] (1). Through treatment with KHBEt₃ the bromide ligands could be replaced by hydrides to yield [PYR)Fe₂(μ-H)₂] (2), a distorted analogue of known β-diketiminato iron hydride complexes, as evidenced by NMR, Mößbauer and X-ray absorption spectroscopy, as well as by its reactivity: for instance, 2 reacts with the proton source lutidinium triflate via protonation of the hydride ligands to form an iron(II) product [(PYR)Fe₂(OTf)₂] (4), while CO₂ inserts into the Fe–H bonds generating the formate complex [(PYR)Fe₂(μ-HCOO)₂] (5); in the presence of traces of water partial hydrolysis occurs so that [(PYR)Fe₂(μ-OH)(μ-HCOO)] (6) is isolated. Altogether, the iron(II) chemistry supported by the PYR²⁻ ligand is distinctly different from the one of nickel(II), where both, the arrangement of the two binding pockets and the additional pyridyl donor led to diverging features as compared with the corresponding system based on the parent β-diketiminato ligand.