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Reactivity studies on [Cp'Fe(μ-I)]₂: nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation.

ABSTRACT: The iron half-sandwich [Cp'Fe(μ-I)]₂ (Cp' = 1,2,4-(Me₃C)₃C₅H₂, 1) reacts with the pseudohalides NCO^-, SCN^-, SeCN^- and N₃^- to give [Cp'Fe(μ-NCO)]₂ (2), [Cp'Fe(μ-S)]₂ (3), [Cp'Fe(μ-Se₂)]₂ (4) and [Cp'Fe(μ-N)]₂ (5), respectively. Various spectroscopic techniques including X-ray diffraction, solid-state magnetic susceptibility studies and ⁵⁷Fe Mössbauer spectroscopy were employed in the characterization of these species. Mössbauer spectroscopy shows a decreasing isomer shift with increasing formal oxidation state, ranging from Fe(ii) to Fe(iv), in complexes 1 to 5. The sulfido-bridged dimer 3 exhibits strong antiferromagnetic coupling between the Fe(iii) centers. This leads to temperature-independent paramagnetism (TIP) at low temperature, from which the energy gap between the ground and the excited state can be estimated to be 2J = ca. 700 cm^-1. The iron(iv) nitrido complex [Cp'Fe(μ-N)]₂ (5) shows no reactivity towards H₂ (10 atm), but undergoes clean reactions with CO (5 bar) and XylNC (Xyl = 2,6-Me₂C₆H₃) to form the diamagnetic isocyanate and carbodiimide complexes [Cp'Fe(CO)₂(NCO)] (7) and [Cp'Fe(CNXyl)₂(NCNXyl)] (8), respectively. All compounds were fully characterized, and density functional theory (DFT) computations provide useful insights into their formation and the electronic structures of complexes 3 and 5.

SUBMITTER: Reiners M

PROVIDER: S-EPMC6099922 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Reactivity studies on [Cp'Fe(μ-I)]2: nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation.

Reiners Matthias M Maekawa Miyuki M Daniliuc Constantin G CG Freytag Matthias M Jones Peter G PG White Peter S PS Hohenberger Johannes J Sutter Jörg J Meyer Karsten K Maron Laurent L Walter Marc D MD

Chemical science 20170411 5

The iron half-sandwich [Cp'Fe(μ-I)]2 (Cp' = 1,2,4-(Me3C)3C5H2, 1) reacts with the pseudohalides NCO-, SCN-, SeCN- and N3- to give [Cp'Fe(μ-NCO)]2 (2), [Cp'Fe(μ-S)]2 (3), [Cp'Fe(μ-Se2)]2 (4) and [Cp'Fe(μ-N)]2 (5), respectively. Various spectroscopic techniques including X-ray diffraction, solid-state ...[more]

PMID: 30155215

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Project description:Iron(iv)-oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the structural features that govern the catalytic activity of iron(iv)-oxo sites. Heteroleptic μ-nitrido diiron phthalocyanine complexes having an unsubstituted phthalocyanine (Pc1) and a phthalocyanine ligand substituted with electron-withdrawing alkylsulfonyl groups (PcSO2R) were prepared and characterized. A reaction with terminal oxidants gives two isomeric iron(iv)-oxo and iron(iii)-hydroperoxo species with abundances dependent on the equatorial ligand. Cryospray ionization mass spectrometry (CSI-MS) characterized both hydroperoxo and diiron oxo species in the presence of H2O2. When m-CPBA was used as the oxidant, the formation of diiron oxo species (PcSO2R)FeNFe(Pc1)[double bond, length as m-dash]O was also evidenced. Sufficient amounts of these transient species were trapped in the quadrupole region of the mass-spectrometer and underwent a CID-MS/MS fragmentation. Analyses of fragmentation patterns indicated a preferential formation of hydroperoxo and oxo moieties at more electron-rich iron sites of both heteroleptic μ-nitrido complexes. DFT calculations show that both isomers are close in energy. However, the analysis of the iron(iii)-hydroperoxo bond strength reveals major differences for the (Pc1)FeN(PcSO2R)FeIIIOOH system as compared to (PcSO2R)FeN(Pc1)FeIIIOOH system, and, hence binding of a terminal oxidant will be preferentially on more electron-rich sides. Subsequent kinetics studies showed that these oxidants are able to even oxidize methane to formic acid efficiently.

Project description:High valent iron species are very reactive molecules involved in oxidation reactions of relevance to biology and chemical synthesis. Herein we describe iron(iv)-tosylimido complexes [FeIV(NTs)(MePy2tacn)](OTf)2 (1(IV)[double bond, length as m-dash]NTs) and [FeIV(NTs)(Me2(CHPy2)tacn)](OTf)2 (2(IV)[double bond, length as m-dash]NTs), (MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane, and Me2(CHPy2)tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). 1(IV)[double bond, length as m-dash]NTs and 2(IV)[double bond, length as m-dash]NTs are rare examples of octahedral iron(iv)-imido complexes and are isoelectronic analogues of the recently described iron(iv)-oxo complexes [FeIV(O)(L)]2+ (L = MePy2tacn and Me2(CHPy2)tacn, respectively). 1(IV)[double bond, length as m-dash]NTs and 2(IV)[double bond, length as m-dash]NTs are metastable and have been spectroscopically characterized by HR-MS, UV-vis, 1H-NMR, resonance Raman, Mössbauer, and X-ray absorption (XAS) spectroscopy as well as by DFT computational methods. Ferric complexes [FeIII(HNTs)(L)]2+, 1(III)-NHTs (L = MePy2tacn) and 2(III)-NHTs (L = Me2(CHPy2)tacn) have been isolated after the decay of 1(IV)[double bond, length as m-dash]NTs and 2(IV)[double bond, length as m-dash]NTs in solution, spectroscopically characterized, and the molecular structure of [FeIII(HNTs)(MePy2tacn)](SbF6)2 determined by single crystal X-ray diffraction. Reaction of 1(IV)[double bond, length as m-dash]NTs and 2(IV)[double bond, length as m-dash]NTs with different p-substituted thioanisoles results in the transfer of the tosylimido moiety to the sulphur atom producing sulfilimine products. In these reactions, 1(IV)[double bond, length as m-dash]NTs and 2(IV)[double bond, length as m-dash]NTs behave as single electron oxidants and Hammett analyses of reaction rates evidence that tosylimido transfer is more sensitive than oxo transfer to charge effects. In addition, reaction of 1(IV)[double bond, length as m-dash]NTs and 2(IV)[double bond, length as m-dash]NTs with hydrocarbons containing weak C-H bonds results in the formation of 1(III)-NHTs and 2(III)-NHTs respectively, along with the oxidized substrate. Kinetic analyses indicate that reactions proceed via a mechanistically unusual HAT reaction, where an association complex precedes hydrogen abstraction.

Dataset Information

Reactivity studies on [Cp'Fe(μ-I)]₂: nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation.

Publications

Reactivity studies on [Cp'Fe(μ-I)]<sub>2</sub>: nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation.

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