Hydrogen-atom and oxygen-atom transfer reactivities of iron(IV)-oxo complexes of quinoline-substituted pentadentate ligands

Sandip Munshi; Arup Sinha; Solomon Yiga; Sridhar Banerjee; Reena Singh; Md Kamal Hossain; Matti Haukka; Andrei Felipe Valiati; Ricardo Dagnoni Huelsmann; Edmar Martendal; Rosely Peralta; Fernando Xavier; Ola F Wendt; Tapan K Paine; Ebbe Nordlander

doi:10.1039/d1dt03381f

Hydrogen-atom and oxygen-atom transfer reactivities of iron(IV)-oxo complexes of quinoline-substituted pentadentate ligands

Dalton Trans. 2022 Jan 17;51(3):870-884. doi: 10.1039/d1dt03381f.

Authors

Sandip Munshi¹, Arup Sinha^{2

3}, Solomon Yiga^{4

5}, Sridhar Banerjee¹, Reena Singh², Md Kamal Hossain², Matti Haukka⁶, Andrei Felipe Valiati⁷, Ricardo Dagnoni Huelsmann⁸, Edmar Martendal⁸, Rosely Peralta⁷, Fernando Xavier⁸, Ola F Wendt⁴, Tapan K Paine¹, Ebbe Nordlander²

Affiliations

¹ School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata, India. ictkp@iacs.res.in.
² Chemical Physics, Department of Chemistry, Lund University, Box 124, SE-221 00 Lund, Sweden. Ebbe.Nordlander@chemphys.lu.se.
³ Department of Chemistry, School of Advanced Science, Vellore Institute of Technology, Vellore, India.
⁴ Center for Analysis and Synthesis, Department of Chemistry, Lund University, Box 124, SE-221 00 Lund, Sweden. Ola.Wendt@chem.lu.se.
⁵ Department of Chemistry, Makerere University, P. O. Box 7062, Kampala, Uganda.
⁶ Department of Chemistry, University of Jyväskylä, Box 35, FI-400 14, Jyväskylä, Finland.
⁷ Department of Chemistry, LABINC, Universidade Federal de Santa Catarina (UFSC), 88040-900 Florianopolis, Santa Catarina, Brazil.
⁸ Department of Chemistry, Center for Technological Sciences, Universidade do Estado de Santa Catarina (UDESC), 89219-710 Joinville, Santa Catarina, Brazil.

PMID: 34994361
DOI: 10.1039/d1dt03381f

Abstract

A series of iron(II) complexes with the general formula [Fe^II(L2-Qn)(L)]ⁿ⁺ (n = 1, L = F^-, Cl^-; n = 2, L = NCMe, H₂O) have been isolated and characterized. The X-ray crystallographic data reveals that metal-ligand bond distances vary with varying ligand field strengths of the sixth ligand. While the complexes with fluoride, chloride and water as axial ligand are high spin, the acetonitrile-coordinated complex is in a mixed spin state. The steric bulk of the quinoline moieties forces the axial ligands to deviate from the Fe-N_axial axis. A higher deviation/tilt is noted for the high spin complexes, while the acetonitrile coordinated complex displays least deviation. This deviation from linearity is slightly less in the analogous low-spin iron(II) complex [Fe^II(L1-Qn)(NCMe)]²⁺ of the related asymmetric ligand L1-Qn due to the presence of only one sterically demanding quinoline moiety. The two iron(II)-acetonitrile complexes [Fe^II(L2-Qn)(NCMe)]²⁺ and [Fe^II(L1-Qn)(NCMe)]²⁺ generate the corresponding iron(IV)-oxo species with higher thermal stability of the species supported by the L1-Qn ligand. The crystallographic and spectroscopic data for [Fe^IV(O)(L1-Qn)](ClO₄)₂ bear resemblance to other crystallographically characterized S = 1 iron(IV)-oxo complexes. The hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reactivities of both the iron(IV)-oxo complexes were investigated, and a Box-Behnken multivariate optimization of the parameters for catalytic oxidation of cyclohexane by [Fe^II(L2-Qn)(NCMe)]²⁺ using hydrogen peroxide as the terminal oxidant is presented. An increase in the average Fe-N bond length in [Fe^II(L1-Qn)(NCMe)]²⁺ is also manifested in higher HAT and OAT rates relative to the other reported complexes of ligands based on the N4Py framework. The results reported here confirm that the steric influence of the ligand environment is of critical importance for the reactivity of iron(IV)-oxo complexes, but additional electronic factors must influence the reactivity of iron-oxo complexes of N4Py derivatives.