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Structural Characterization of a Series of N5-Ligated Mn^IV -Oxo Species.

ABSTRACT: Analysis of extended X-ray absorption fine structure (EXAFS) data for the Mn^IV -oxo complexes [Mn^IV (O)(^DMM N4py)]²⁺ , [Mn^IV (O)(2pyN2B)]²⁺ , and [Mn^IV (O)(2pyN2Q)]²⁺ (^DMM N4py=N,N-bis(4-methoxy-3,5-dimethyl-2-pyridylmethyl)-N-bis(2-pyridyl)methylamine; 2pyN2B=(N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine, and 2pyN2Q=N,N-bis(2-pyridyl)-N,N-bis(2-quinolylmethyl)methanamine) afforded Mn=O and Mn-N bond lengths. The Mn=O distances for [Mn^IV (O)(^DMM N4py)]²⁺ and [Mn^IV (O)(2pyN2B)]²⁺ are 1.72 and 1.70?Å, respectively. In contrast, the Mn=O distance for [Mn^IV (O)(2pyN2Q)]²⁺ was significantly longer (1.76?Å). We attribute this long distance to sample heterogeneity, which is reasonable given the reduced stability of [Mn^IV (O)(2pyN2Q)]²⁺ . The Mn=O distances for [Mn^IV (O)(^DMM N4py)]²⁺ and [Mn^IV (O)(2pyN2B)]²⁺ could only be well-reproduced using DFT-derived models that included strong hydrogen-bonds between second-sphere solvent 2,2,2-trifluoroethanol molecules and the oxo ligand. These results suggest an important role for the 2,2,2-trifluoroethanol solvent in stabilizing Mn^IV -oxo adducts. The DFT methods were extended to investigate the structure of the putative [Mn^IV (O)(N4py)]²⁺ ?(HOTf)₂ adduct. These computations suggest that a Mn^IV -hydroxo species is most consistent with the available experimental data.

SUBMITTER: Massie AA

PROVIDER: S-EPMC7388070 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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Project description:The oxo- and catecholate-bridged UIV/UIV Pacman complex [{(py)UIVOUIV(μ-O2C6H4)(py)}(LA)] A (LA = a macrocyclic "Pacman" ligand; anthracenylene hinge between N4-donor pockets, ethyl substituents on meso-carbon atom of each N4-donor pocket) featuring a bent UIV-O-UIV oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. Complex A reacts with H2O or MeOH to afford [{(py)UIV(μ-OH)2UIV(μ-O2C6H4)(py)}(LA)] (1) and [{(py)UIV(μ-OH)(μ-OMe)UIV(μ-O2C6H4)(py)}(LA)] (2), respectively, in which the bridging oxo ligand in A is substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively, A reacts with either 0.5 equiv. of S8 or 4 equiv. of Se to provide [{(py)UIV(μ-η2:η2-E2)UIV(μ-O2C6H4)(py)}(LA)] (E = S (3), Se (4)) respectively, in which the [E2]2- ion bridges the two UIV centres. To the best of our knowledge, complex A is the first example of either a d- or f-block bimetallic μ-oxo complex that activates elemental chalcogens. Complex A also reacts with XeF2 or 2 equiv. of Me3SiCl to provide [{(py)UIV(μ-X)2UIV(μ-O2C6H4)(py)}(LA)] (X = F (5), Cl (6)), in which the oxo ligand has been substituted for two bridging halido ligands. Reacting A with either XeF2 or Me3SiCl in the presence of O(Bcat)2 at room temperature forms [{(py)UIV(μ-X)(μ-OBcat)UIV(μ-O2C6H4)(py)}(LA)] (X = F (5A), Cl (6A)), which upon heating to 80 °C is converted to 5 and 6, respectively. In order to probe the importance of the bent UIV-O-UIV motif in A on the observed reactivity, the bis(boroxido)-UIV/UIV complex, [{(py)(pinBO)UIVOUIV(OBpin)(py)}(LA)] (B), featuring a linear UIV-O-UIV bond angle was treated with H2O and Me3SiCl. Complex B reacts with two equiv. of either H2O or Me3SiCl to provide [{(py)HOUIVOUIVOH(py)}(LA)] (7) and [{(py)ClUIVOUIVCl(py)}(LA)] (8), respectively, in which reactions occur preferentially at the boroxido ligands, with the μ-oxo ligand unchanged. The formal UIV oxidation state is retained in all of the products 1-8, and selective reactions at the bridging oxo ligand in A is facilitated by: (1) its highly nucleophilic character which is a result of a non-linear UIV-O-UIV bond angle causing an increase in U-O bond covalency and localisation of the lone pairs of electrons on the μ-oxo group, and (2) the presence of the bridging catecholate ligand, which destabilises a linear oxo-bridging geometry and stabilises the resulting products.

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Structural Characterization of a Series of N5-Ligated Mn^IV -Oxo Species.

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Dataset Information

Structural Characterization of a Series of N5-Ligated MnIV -Oxo Species.

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OmicsDI is part of the ELIXIR infrastructure

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Structural Characterization of a Series of N5-Ligated Mn^IV -Oxo Species.