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Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions

Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L1) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [FeII(CH3CN)(L)]2+ (L = L1 (1); L2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [FeIV(O)(L)]2+ (L = L1 (3); L2 (4)), which were characterized by UV鈥搗is spectroscopy, high resolution mass spectrometry, and M枚ssbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L1) and 2.5 h (L = L2). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([FeIV(O)(N4Py)]2+), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [FeIV(O)(L2)]2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C鈥揌 bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state

This research has been carried out within the framework of the International Research Training Group Metal Sites in Biomolecules: Structures, Regulation and Mechanisms (www.biometals.eu) and has also been supported by COST Action CM1003. M.M. thanks the European Union for an Erasmus Mundus fellowship. M.G.R. thanks the Robert A. Welch Foundation (Grant B-1093) and the Wenner鈭扜ren Foundation for financial support and acknowledges computational resources through UNT鈥檚 High Performance Computing Services funded by NSF (CHE-0741936)

漏 Inorganic Chemistry, 2015, vol. 54, n煤m. 15, p. 7152-7164

American Chemical Society (ACS)

Author: Mitra, Mainak
Nimir, Hassan
Demeshko, Serhiy
Bhat, Satish S.
Malinkin, Sergey O.
Haukka, Matti
Lloret Fillol, Julio
Lisensky, George C.
Meyer, Franc
Shteinman, Albert A.
Browne, Wesley R.
Hrovat, David A.
Hrovat, David A.
Richmond, Michael G.
Costas Salgueiro, Miquel
Nordlander, Ebbe
Date: 2015
Abstract: Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L1) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [FeII(CH3CN)(L)]2+ (L = L1 (1); L2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [FeIV(O)(L)]2+ (L = L1 (3); L2 (4)), which were characterized by UV鈥搗is spectroscopy, high resolution mass spectrometry, and M枚ssbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L1) and 2.5 h (L = L2). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([FeIV(O)(N4Py)]2+), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [FeIV(O)(L2)]2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C鈥揌 bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state
This research has been carried out within the framework of the International Research Training Group Metal Sites in Biomolecules: Structures, Regulation and Mechanisms (www.biometals.eu) and has also been supported by COST Action CM1003. M.M. thanks the European Union for an Erasmus Mundus fellowship. M.G.R. thanks the Robert A. Welch Foundation (Grant B-1093) and the Wenner鈭扜ren Foundation for financial support and acknowledges computational resources through UNT鈥檚 High Performance Computing Services funded by NSF (CHE-0741936)
Format: application/pdf
ISSN: 0020-1669 (versi贸 paper)
1520-510X (versi贸 electr貌nica)
Document access: http://hdl.handle.net/10256/12270
Language: eng
Publisher: American Chemical Society (ACS)
Collection: Reproducci贸 digital del document publicat a: http://dx.doi.org/10.1021/ic5029564
Articles publicats (D-Q)
info:eu-repo/grantAgreement/EC/FP7/239910
Is part of: 漏 Inorganic Chemistry, 2015, vol. 54, n煤m. 15, p. 7152-7164
Rights: Tots els drets reservats
Subject: Reaccions qu铆miques
Chemical reactions
Ferro -- Compostos
Iron compounds
Title: Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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