Closed Shell Iron(IV) Oxo Complex with an Fe–O Triple Bond: Computational Design, Synthesis, and Reactivity

Abstract

Iron(IV)-oxo intermediates in nature contain two unpaired electrons in the Fe-O antibonding orbitals,which are thought to contribute to their high reactivity.T ochallenge this hypothesis,w ed esigned and synthesized closed-shell singlet iron(IV) oxo complex [(quinisox)Fe(O)] + (1 + ; quinisox-H = (N-(2-(2-isoxazoline-3-yl)phenyl)quinoline-8-carboxamide). We identified the quinisoxl igand by DFT computational screening out of over 450 candidates.After the ligand synthesis, we detected 1 + in the gas phase and confirmed its spin state by visible and infrared photodissociation spectroscopy(IRPD). The Fe-O stretching frequency in 1 + is 960.5 cm À1 ,c onsistent with an Fe-O triple bond, which was also confirmed by multireference calculations.T he unprecedented bond strength is accompanied by high gas-phase reactivity of 1 + in oxygen atom transfer (OAT)a nd in proton-coupled electron transfer reactions.T his challenges the current view of the spin-state driven reactivity of the Fe-O complexes.

A Pseudotetrahedral Terminal Oxoiron(IV) Complex: Mechanistic Promiscuity in C−H Bond Oxidation Reactions

“…The computational and experimental analyses are consistent with the presence of an S =2 Fe IV =O core in 2 . Complex 2 represents the only example of a high‐spin complex with metal‐ligand multiple bond character in a pseudotetrahedral geometry; notably, a pseudotetrahedral oxoiron(IV) complex has been very recently demonstrated to possess an S =0 state in the gas‐phase [19] . The absorption spectrum, Mössbauer Δ E Q , Fe K‐edge energy, and the ν(Fe=O) mode of 2 (Table 1) bear very close resemblance to the corresponding spectroscopic properties of TauD‐ J .…”

“…Research Articles ited a signal at m/z = 518.7, consistent with its formulation as [Fe IV (O)( t Bu 3 tacn)(OTf)] + (m/z calc = 518.2). However, the 19 F-NMR spectrum ( Figure S5) of 2 displayed a single resonance at À77.0 ppm, which confirmed that the triflate (OTf) anion is not bound to the Fe-centre in 2. This observation together with the same UV-vis spectrum ( Figure S6) of 2 in both coordinating (PrCN) and non-coordinating (CH 2 Cl 2 ) solvents corroborates the absence of any exogeneous ligands binding to the iron centre.…”

A Pseudotetrahedral Terminal Oxoiron(IV) Complex: Mechanistic Promiscuity in C−H Bond Oxidation Reactions

“…Complex 2 represents the only example of a high-spin complex with metal-ligand multiple bond character in a pseudotetrahedral geometry; notably, a pseudotetrahedral oxoiron(IV) complex has been very recently demonstrated to possess an S = 0 state in the gas-phase. [19] The absorption spectrum, Mçssbauer DE Q , Fe K-edge energy, and the n(Fe=O) mode of 2 (Table 1) bear very close resemblance to the corresponding spectroscopic properties of TauD-J. 2 also exhibits the distinct high-reactivity features known from the strongly oxidizing iron-oxo cores in biology and accordingly possesses one of the most reactive oxoiron(IV) cores that have been synthesized to date.…”

“…Forschungsartikel ited a signal at m/z = 518.7, consistent with its formulation as [Fe IV (O)( t Bu 3 tacn)(OTf)] + (m/z calc = 518.2). However, the 19 F-NMR spectrum ( Figure S5) of 2 displayed a single resonance at À77.0 ppm, which confirmed that the triflate (OTf) anion is not bound to the Fe-centre in 2. This observation together with the same UV-vis spectrum ( Figure S6) of 2 in both coordinating (PrCN) and non-coordinating (CH 2 Cl 2 ) solvents corroborates the absence of any exogeneous ligands binding to the iron centre.…”

Cationic Gold(II) Complexes: Experimental and Theoretical Study**

“…The helium complexes then served for the spectroscopic experiments. The complexes were irradiated with the OPO/OPA system from LaserVision pumped by Nd:YAG laser Surelite EX from Continuum (tuning range 700–4700 cm −1 , FWHM $${\sim }$$ 1.5 cm −1 , 10 ns pulse length) or with supercontinuum laser NKT Photonics SuperK Extreme (430–700 nm range using acusto‐optic tuneable filter SuperK Select) [84] . The spectra are constructed as (1‐ N i / N i0 ), where N i and N i0 are numbers of helium complexes with and without laser irradiation [85,86] …”