Nonheme FeIV═O Complexes Supported by Four Pentadentate Ligands: Reactivity toward H- and O- Atom Transfer Processes.
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SUBMITTER: Li Y
PROVIDER: S-EPMC10647104 | biostudies-literature | 2023 Nov
REPOSITORIES: biostudies-literature
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Nonheme Fe<sup>IV</sup>═O Complexes Supported by Four Pentadentate Ligands: Reactivity toward H- and O- Atom Transfer Processes.
Li Yong Y Singh Reena R Sinha Arup A Lisensky George C GC Haukka Matti M Nilsson Justin J Yiga Solomon S Demeshko Serhiy S Gross Sophie Jana SJ Dechert Sebastian S Gonzalez Ana A Farias Giliandro G Wendt Ola F OF Meyer Franc F Nordlander Ebbe E
Inorganic chemistry 20231101 45
Four new pentadentate N5-donor ligands, [<i>N</i>-(1-methyl-2-imidazolyl)methyl-<i>N</i>-(2-pyridyl)-methyl-<i>N</i>-(bis-2-pyridylmethyl)-amine] (<b>L</b><sup><b>1</b></sup>), [<i>N</i>-bis(1-methyl-2-imidazolyl)methyl-<i>N</i>-(bis-2-pyridylmethyl)amine] (<b>L</b><sup><b>2</b></sup>), (<i>N</i>-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-<i>N</i>-(pyridin-2-ylmethyl)methanamine (<b>L</b><sup><b>3</b></sup>), and <i>N</i>,<i>N</i>-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (< ...[more]
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Project description:The reactions of the tetrasiloxide U(iii) complexes [U(OSi(O t Bu)3)4K] and [U(OSi(O t Bu)3)4][K18c6] with 0.5 equiv. of triphenylphosphine sulfide led to reductive S-transfer reactions, affording the U(iv) sulfide complexes [SU(OSi(O t Bu)3)4K2]2, 1, and [{SU(OSi(O t Bu)3)4K2}2(μ-18c6)], 2, with concomitant formation of the U(iv) complex [U(OSi(O t Bu)3)4]. Addition of 1 equiv. of 2.2.2-cryptand to complex 1 resulted in the isolation of a terminal sulfide complex, [SU(OSi(O t Bu)3)4K][Kcryptand], 3. The crucial role of the K+ Lewis acid in these reductive sulfur transfer reactions was confirmed, since the formation of complex 3 from the reaction of the U(iii) complex [U(OSi(O t Bu)3)4][Kcryptand] and 0.5 equiv. of PPh3S was not possible. Reactivity studies of the U(iv) sulfide complexes showed that the sulfide is easily transferred to CO2 and CS2 to afford S-functionalized products. Moreover, we have found that the sulfide provides a convenient precursor for the synthesis of the corresponding U(iv) hydrosulfide, {[(SH)U(OSi(O t Bu)3)4][K18c6]}, 5, after protonation with PyHCl. Finally, DFT calculations were performed to investigate the nature of the U-S bond in complexes 1, 3 and 5. Based on various analyses, triple-bond character was suggested for the U-S bond in complexes 1 and 3, while double-bond character was determined for the U-SH bond in complex 5.
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Project description:High-valent Fe-OH species are often invoked as key intermediates but have only been observed in Compound II of cytochrome P450s. To further address the properties of non-heme FeIV-OH complexes, we demonstrate the reversible protonation of a synthetic FeIV-oxo species containing a tris-urea tripodal ligand. The same protonated FeIV-oxo species can be prepared via oxidation, suggesting that a putative FeV-oxo species was initially generated. Computational, Mössbauer, XAS, and NRVS studies indicate that protonation of the FeIV-oxo complex most likely occurs on the tripodal ligand, which undergoes a structural change that results in the formation of a new intramolecular H-bond with the oxido ligand that aids in stabilizing the protonated adduct. We suggest that similar protonated high-valent Fe-oxo species may occur in the active sites of proteins. This finding further argues for caution when assigning unverified high-valent Fe-OH species to mechanisms.
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Project description:A dianionic tetrapodal pentadentate diborate ligand is introduced. This ligand forms a high spin neutral iron(ii) complex that reacts with a variety of organoazides to yield transient Fe(iii) imido radicals that are extremely potent hydrogen atom abstractors. The nature of these species is supported by full characterization of the Fe(iii) amido products, kinetic studies, density functional computations and Mössbauer spectroscopy on the -C6H4-p- t Bu substituted derivative.
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Project description:The spin states (S = 1 and S = 2) of nonheme FeIVO intermediates are believed to play an important role in determining their chemical properties in enzymatic and biomimetic reactions. However, it is almost impossible to investigate the spin state effect of nonheme FeIVO species experimentally, since FeIVO models having the S = 1 and S = 2 spin states at the same time neither exist nor can be synthesized. However, recent synthesis of an FeIVO complex with an S = 1 spin state (triplet), [(Me3NTB)FeIVO]2+ (1), and a structurally similar FeIVO complex but with an S = 2 spin state (quintet), [(TQA)FeIVO]2+ (2), has allowed us to compare their reactivities at 233 K. In the present study, we show that structural variants control the spin-state selectivity and reactivity of nonheme FeIVO complexes. While 1 and 2 were proposed to be in an octahedral geometry based on DFT calculations and spectroscopic characterization done at 4 K, further DFT calculations show that these species may well assume a trigonal bipyramidal structure by losing one coordinated solvent ligand at 233 K. Thus, the present study demonstrates that the structure and spin state of nonheme FeIVO complexes can be different at different temperatures; therefore, the structural and/or spin state information obtained at 4 K should be carefully used at a higher temperature (e.g., 233 K). In addition to 1 and 2, [(TPA)FeIVO]2+ (3) with an S = 1 spin state, whose spin state was determined spectroscopically and theoretically at 233 K, is included in this study to compare the chemical properties of S = 1 and S = 2 FeIVO complexes. The present results add another dimension to the discussion of the reactivites of nonheme FeIVO species, in which the structural preference and spin state of nonheme FeIVO species can vary depending on temperature.
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