A Mononuclear Nonheme Iron(IV)-Oxo Complex of a Substituted N4Py Ligand : Effect of Ligand Field on Oxygen Atom Transfer and C-H Bond Cleavage Reactivity
(2019) In Inorganic Chemistry 58(3). p.1862-1876- Abstract
A mononuclear iron(II) complex [FeII(N4PyMe2)(OTf)](OTf)(1), supported by a new pentadentate ligand, bis(6-methylpyridin-2-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (N4PyMe2), has been isolated and characterized. Introduction of methyl groups in the 6-position of two pyridine rings makes the N4PyMe2 a weaker field ligand compared to the parent N4Py ligand. Complex 1 is high-spin in the solid state and converts to [FeII(N4PyMe2)(CH3CN)](OTf)2 (1a) in acetonitrile solution. The iron(II) complex in acetonitrile displays temperature-dependent spin-crossover behavior over a wide range of temperature. In its reaction with m-CPBA or oxone in acetonitrile... (More)
A mononuclear iron(II) complex [FeII(N4PyMe2)(OTf)](OTf)(1), supported by a new pentadentate ligand, bis(6-methylpyridin-2-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (N4PyMe2), has been isolated and characterized. Introduction of methyl groups in the 6-position of two pyridine rings makes the N4PyMe2 a weaker field ligand compared to the parent N4Py ligand. Complex 1 is high-spin in the solid state and converts to [FeII(N4PyMe2)(CH3CN)](OTf)2 (1a) in acetonitrile solution. The iron(II) complex in acetonitrile displays temperature-dependent spin-crossover behavior over a wide range of temperature. In its reaction with m-CPBA or oxone in acetonitrile at -10 °C, the iron(II) complex converts to an iron(IV)-oxo species, [FeIV(O)(N4PyMe2)]2+ (2). Complex 2 exhibits the Mössbauer parameters δ = 0.05 mm/s and ΔEQ = 0.62 mm/s, typical of N-ligated S = 1 iron(IV)-oxo species. The iron(IV)-oxo complex has a half-life of only 14 min at 25 °C and is reactive toward oxygen-atom-transfer and hydrogen-atom-transfer (HAT) reactions. Compared to the parent complex [FeIV(O)(N4Py)]2+, 2 is more reactive in oxidizing thioanisole and oxygenates the C-H bonds of aliphatic substrates including that of cyclohexane. The enhanced reactivity of 2 toward cyclohexane results from the involvement of the S = 2 transition state in the HAT pathway and a lower triplet-quintet splitting compared to [FeIV(O)(N4Py)]2+, as supported by DFT calculations. The second-order rate constants for HAT by 2 is well correlated with the C-H bond dissociation energies of aliphatic substrates. Surprisingly, the slope of this correlation is different from that of [FeIV(O)(N4Py)]2+, and 2 is more reactive only in the case of strong C-H bonds (>86 kcal/mol), but less reactive in the case of weaker C-H bonds. Using oxone as the oxidant, the iron(II) complex displays catalytic oxidations of substrates with low activity but with good selectivity.
(Less)
- author
- Singh, Reena LU ; Ganguly, Gaurab ; Malinkin, Sergey O. LU ; Demeshko, Serhiy ; Meyer, Franc ; Nordlander, Ebbe LU and Paine, Tapan Kanti
- organization
- publishing date
- 2019-01-15
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Inorganic Chemistry
- volume
- 58
- issue
- 3
- pages
- 1862 - 1876
- publisher
- The American Chemical Society (ACS)
- external identifiers
-
- pmid:30644733
- scopus:85060245763
- ISSN
- 0020-1669
- DOI
- 10.1021/acs.inorgchem.8b02577
- language
- English
- LU publication?
- yes
- id
- 9911d050-d671-4067-9eb7-5888b2eaa06b
- date added to LUP
- 2019-02-01 12:29:31
- date last changed
- 2024-10-01 15:58:14
@article{9911d050-d671-4067-9eb7-5888b2eaa06b, abstract = {{<p>A mononuclear iron(II) complex [Fe<sup>II</sup>(N4Py<sup>Me2</sup>)(OTf)](OTf)(1), supported by a new pentadentate ligand, bis(6-methylpyridin-2-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (N4Py<sup>Me2</sup>), has been isolated and characterized. Introduction of methyl groups in the 6-position of two pyridine rings makes the N4Py<sup>Me2</sup> a weaker field ligand compared to the parent N4Py ligand. Complex 1 is high-spin in the solid state and converts to [Fe<sup>II</sup>(N4Py<sup>Me2</sup>)(CH<sub>3</sub>CN)](OTf)<sub>2</sub> (1a) in acetonitrile solution. The iron(II) complex in acetonitrile displays temperature-dependent spin-crossover behavior over a wide range of temperature. In its reaction with m-CPBA or oxone in acetonitrile at -10 °C, the iron(II) complex converts to an iron(IV)-oxo species, [Fe<sup>IV</sup>(O)(N4Py<sup>Me2</sup>)]<sup>2+</sup> (2). Complex 2 exhibits the Mössbauer parameters δ = 0.05 mm/s and ΔE<sub>Q</sub> = 0.62 mm/s, typical of N-ligated S = 1 iron(IV)-oxo species. The iron(IV)-oxo complex has a half-life of only 14 min at 25 °C and is reactive toward oxygen-atom-transfer and hydrogen-atom-transfer (HAT) reactions. Compared to the parent complex [Fe<sup>IV</sup>(O)(N4Py)]<sup>2+</sup>, 2 is more reactive in oxidizing thioanisole and oxygenates the C-H bonds of aliphatic substrates including that of cyclohexane. The enhanced reactivity of 2 toward cyclohexane results from the involvement of the S = 2 transition state in the HAT pathway and a lower triplet-quintet splitting compared to [Fe<sup>IV</sup>(O)(N4Py)]<sup>2+</sup>, as supported by DFT calculations. The second-order rate constants for HAT by 2 is well correlated with the C-H bond dissociation energies of aliphatic substrates. Surprisingly, the slope of this correlation is different from that of [Fe<sup>IV</sup>(O)(N4Py)]<sup>2+</sup>, and 2 is more reactive only in the case of strong C-H bonds (>86 kcal/mol), but less reactive in the case of weaker C-H bonds. Using oxone as the oxidant, the iron(II) complex displays catalytic oxidations of substrates with low activity but with good selectivity.</p>}}, author = {{Singh, Reena and Ganguly, Gaurab and Malinkin, Sergey O. and Demeshko, Serhiy and Meyer, Franc and Nordlander, Ebbe and Paine, Tapan Kanti}}, issn = {{0020-1669}}, language = {{eng}}, month = {{01}}, number = {{3}}, pages = {{1862--1876}}, publisher = {{The American Chemical Society (ACS)}}, series = {{Inorganic Chemistry}}, title = {{A Mononuclear Nonheme Iron(IV)-Oxo Complex of a Substituted N4Py Ligand : Effect of Ligand Field on Oxygen Atom Transfer and C-H Bond Cleavage Reactivity}}, url = {{http://dx.doi.org/10.1021/acs.inorgchem.8b02577}}, doi = {{10.1021/acs.inorgchem.8b02577}}, volume = {{58}}, year = {{2019}}, }