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Non-heme FeIV=O complexes supported by four new pentadentate ligands : reactivity towards H- and O-atom transfer processes

Li, Yong LU ; Singh, Reena LU ; Sinha, Arup LU ; Lisensky, George C. ; Haukka, Matti ; Nilsson, Justin ; Yiga, Solomon LU ; Demeshko, Serhiy ; Gross, Sophie Jana and Dechert, Sebastian , et al. (2023) In Inorganic Chemistry 62(45). p.18338-18356
Abstract
Four new pentadentate N5-donor ligands, [N-(1-methyl-2-imidazolyl)methyl-N-(2-pyridyl)-methyl-N-(bis-2-pyridylmethyl)-amine] (L1), [N-bis(1-methyl-2-imidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), (N-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L3) and N,N-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (L4), have been synthesized based on the N4Py ligand framework, where one or two pyridyl arms of the N4Py parent are replaced by (N-methyl)imidazolyl or N-(isoquinolin-3-ylmethyl) moieties. Using these four pentadentate ligands, the mononuclear complexes [FeII(CH3CN)(L1)]2+ (1a), [FeII(CH3CN)(L2)]2+ (2a), [FeII(CH3CN)(L3)]2+ (3a) and [FeII(CH3CN)(L4)]2+ (4a) have been synthesized and... (More)
Four new pentadentate N5-donor ligands, [N-(1-methyl-2-imidazolyl)methyl-N-(2-pyridyl)-methyl-N-(bis-2-pyridylmethyl)-amine] (L1), [N-bis(1-methyl-2-imidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), (N-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L3) and N,N-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (L4), have been synthesized based on the N4Py ligand framework, where one or two pyridyl arms of the N4Py parent are replaced by (N-methyl)imidazolyl or N-(isoquinolin-3-ylmethyl) moieties. Using these four pentadentate ligands, the mononuclear complexes [FeII(CH3CN)(L1)]2+ (1a), [FeII(CH3CN)(L2)]2+ (2a), [FeII(CH3CN)(L3)]2+ (3a) and [FeII(CH3CN)(L4)]2+ (4a) have been synthesized and characterized. The half-wave potentials (E1/2) of the complexes become more positive in the order: 2a < 1a < 4a  3a  [Fe(N4Py)(CH3CN)]2+. The order of oxidation potentials correlates well with the Fe-Namine distances observed by crystallography, which are 2a  1a  4a  3a  [Fe(N4Py)(CH3CN)]2+. The corresponding ferryl complexes [FeIV(O)(L1)]2+ (1b), [FeIV(O)(L2)]2+ (2b), [FeIV(O)(L3)]2+ (3b), and [FeIV(O)(L4)]2+ (4b) could be prepared by reaction of the ferrous complexes with isopropyl 2-iodoxybenzoate (IBX ester) in acetonitrile. The greenish complexes 3b and 4b could also be isolated in the solid state by reaction of the ferrous complexes in CH3CN with ceric ammonium nitrate in water. Mössbauer spectroscopy and magnetic measurements (SQUID) show that the four complexes 1b, 2b, 3b and 4b are low-spin (S = 1) FeIV=O complexes. UV/Vis spectra of the four FeIV=O complexes in acetonitrile show typical long wavelength absorptions around 700 nm, which are expected for FeIV=O complexes with N4Py-type ligands. The wavelengths of these absorptions decrease in the following order: 721 nm (2b) > 706 nm (1b) > 696 nm (4b) > 695 nm (3b) = 695 nm ([FeIV(O) (N4Py)]2+), indicating that the replacement of pyridyl arms with (N-methyl) imidazolyl moieties makes L1 and L2 exert weaker ligand fields than the parent N4Py ligand, while the ligand field strengths of L3 and L4 are similar to the N4Py parent despite the replacement of pyridyl arms with N-(isoquinolin-3-ylmethyl) moieties. Consequently, complexes 1b and 2b tend to be less stable than the parent [FeIV(O)(N4Py)]2+ complex: the half-life sequence at room temperature is 1.67 h (2b) < 16 h (1b) < 45 h (4b) < 63 h (3b) ≈ 60 h ([FeIV(O)(N4Py)]2+). Compared to the parent complex, 1b and 2b exhibit enhanced reactivity in both oxidation of thioanisole by oxygen atom transfer (OAT) reaction and oxygenation of C-H bonds of aromatic and aliphatic substrates, presumed to occur via an oxygen rebound process. Furthermore, second-order rate constants for hydrogen atom transfer (HAT) reactions affected by the ferryl complexes can be directly related to the C-H bond dissociation energies of a range of substrates that have been studied. Using either IBX ester or H2O2 as oxidant, all four new FeII complexes display good performance in catalytic reactions involving both HAT and OAT reactions. (Less)
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Inorganic Chemistry
volume
62
issue
45
article number
3c02526
pages
19 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:37913548
  • scopus:85176990046
ISSN
1520-510X
DOI
10.1021/acs.inorgchem.3c02526
language
English
LU publication?
yes
id
2b6dd6a6-09d0-4623-95c2-7116b7add897
date added to LUP
2023-12-11 10:31:09
date last changed
2023-12-12 15:49:48
@article{2b6dd6a6-09d0-4623-95c2-7116b7add897,
  abstract     = {{Four new pentadentate N5-donor ligands, [N-(1-methyl-2-imidazolyl)methyl-N-(2-pyridyl)-methyl-N-(bis-2-pyridylmethyl)-amine] (L1), [N-bis(1-methyl-2-imidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), (N-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L3) and N,N-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (L4), have been synthesized based on the N4Py ligand framework, where one or two pyridyl arms of the N4Py parent are replaced by (N-methyl)imidazolyl or N-(isoquinolin-3-ylmethyl) moieties. Using these four pentadentate ligands, the mononuclear complexes [FeII(CH3CN)(L1)]2+ (1a), [FeII(CH3CN)(L2)]2+ (2a), [FeII(CH3CN)(L3)]2+ (3a) and [FeII(CH3CN)(L4)]2+ (4a) have been synthesized and characterized. The half-wave potentials (E1/2) of the complexes become more positive in the order: 2a &lt; 1a &lt; 4a  3a  [Fe(N4Py)(CH3CN)]2+. The order of oxidation potentials correlates well with the Fe-Namine distances observed by crystallography, which are 2a  1a  4a  3a  [Fe(N4Py)(CH3CN)]2+. The corresponding ferryl complexes [FeIV(O)(L1)]2+ (1b), [FeIV(O)(L2)]2+ (2b), [FeIV(O)(L3)]2+ (3b), and [FeIV(O)(L4)]2+ (4b) could be prepared by reaction of the ferrous complexes with isopropyl 2-iodoxybenzoate (IBX ester) in acetonitrile. The greenish complexes 3b and 4b could also be isolated in the solid state by reaction of the ferrous complexes in CH3CN with ceric ammonium nitrate in water. Mössbauer spectroscopy and magnetic measurements (SQUID) show that the four complexes 1b, 2b, 3b and 4b are low-spin (S = 1) FeIV=O complexes. UV/Vis spectra of the four FeIV=O complexes in acetonitrile show typical long wavelength absorptions around 700 nm, which are expected for FeIV=O complexes with N4Py-type ligands. The wavelengths of these absorptions decrease in the following order: 721 nm (2b) &gt; 706 nm (1b) &gt; 696 nm (4b) &gt; 695 nm (3b) = 695 nm ([FeIV(O) (N4Py)]2+), indicating that the replacement of pyridyl arms with (N-methyl) imidazolyl moieties makes L1 and L2 exert weaker ligand fields than the parent N4Py ligand, while the ligand field strengths of L3 and L4 are similar to the N4Py parent despite the replacement of pyridyl arms with N-(isoquinolin-3-ylmethyl) moieties. Consequently, complexes 1b and 2b tend to be less stable than the parent [FeIV(O)(N4Py)]2+ complex: the half-life sequence at room temperature is 1.67 h (2b) &lt; 16 h (1b) &lt; 45 h (4b) &lt; 63 h (3b) ≈ 60 h ([FeIV(O)(N4Py)]2+). Compared to the parent complex, 1b and 2b exhibit enhanced reactivity in both oxidation of thioanisole by oxygen atom transfer (OAT) reaction and oxygenation of C-H bonds of aromatic and aliphatic substrates, presumed to occur via an oxygen rebound process. Furthermore, second-order rate constants for hydrogen atom transfer (HAT) reactions affected by the ferryl complexes can be directly related to the C-H bond dissociation energies of a range of substrates that have been studied. Using either IBX ester or H2O2 as oxidant, all four new FeII complexes display good performance in catalytic reactions involving both HAT and OAT reactions.}},
  author       = {{Li, Yong and Singh, Reena and Sinha, Arup and Lisensky, George C. and Haukka, Matti and Nilsson, Justin and Yiga, Solomon and Demeshko, Serhiy and Gross, Sophie Jana and Dechert, Sebastian and Gonzalez, Ana and Farias, Giliandro and Wendt, Ola and Meyer, Franc and Nordlander, Ebbe}},
  issn         = {{1520-510X}},
  language     = {{eng}},
  month        = {{11}},
  number       = {{45}},
  pages        = {{18338--18356}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Inorganic Chemistry}},
  title        = {{Non-heme FeIV=O complexes supported by four new pentadentate ligands : reactivity towards H- and O-atom transfer processes}},
  url          = {{http://dx.doi.org/10.1021/acs.inorgchem.3c02526}},
  doi          = {{10.1021/acs.inorgchem.3c02526}},
  volume       = {{62}},
  year         = {{2023}},
}