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A High-Valent Non-Heme ?-Oxo Manganese(IV) Dimer Generated from a Thiolate-Bound Manganese(II) Complex and Dioxygen.

ABSTRACT: This study deals with the unprecedented reactivity of dinuclear non-heme MnII -thiolate complexes with O2 , which dependent on the protonation state of the initial MnII dimer selectively generates either a di-?-oxo or ?-oxo-?-hydroxo MnIV complex. Both dimers have been characterized by different techniques including single-crystal X-ray diffraction and mass spectrometry. Oxygenation reactions carried out with labeled 18 O2 unambiguously show that the oxygen atoms present in the MnIV dimers originate from O2 . Based on experimental observations and DFT calculations, evidence is provided that these MnIV species comproportionate with a MnII precursor to yield ?-oxo and/or ?-hydroxo MnIII dimers. Our work highlights the delicate balance of reaction conditions to control the synthesis of non-heme high-valent ?-oxo and ?-hydroxo Mn species from MnII precursors and O2 .

SUBMITTER: Brazzolotto D

PROVIDER: S-EPMC5531755 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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A High-Valent Non-Heme μ-Oxo Manganese(IV) Dimer Generated from a Thiolate-Bound Manganese(II) Complex and Dioxygen.

Brazzolotto Deborah D Cantú Reinhard Fabián G FG Smith-Jones Julian J Retegan Marius M Amidani Lucia L Faponle Abayomi S AS Ray Kallol K Philouze Christian C de Visser Sam P SP Gennari Marcello M Duboc Carole C

Angewandte Chemie (International ed. in English) 20170609 28

This study deals with the unprecedented reactivity of dinuclear non-heme MnII -thiolate complexes with O2 , which dependent on the protonation state of the initial MnII dimer selectively generates either a di-μ-oxo or μ-oxo-μ-hydroxo MnIV complex. Both dimers have been characterized by different techniques including single-crystal X-ray diffraction and mass spectrometry. Oxygenation reactions carried out with labeled 18 O2 unambig ...[more]

PMID: 28544340

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Project description:The reactivity between a thiolate-ligated five-coordinate complex [FeII(SMe2N4(tren))]+ (1) and dioxygen is examined in order to determine if O2 activation, resembling that of the metalloenzyme cytochrome P450, can be promoted even when O2 binds cis, as opposed to trans, to a thiolate. Previous work in our group showed that [FeII(SMe2N4(tren))]+ (1) reacts readily with superoxide (O2-) in the presence of a proton source to afford H2O2 via an Fe(III)-OOH intermediate, thus providing a biomimetic model for the metalloenzyme superoxide reductase (SOR). Addition of O2 to 1 affords binuclear mu-oxo-bridged [FeIII(SMe2N4(tren))]2(mu2-O)(PF6)2.3MeCN (3). At low temperatures, in protic solvents, an intermediate is detected, the details of which will be the subject of a separate paper. Although the thiolate ligand does not appear to perturb the metrical parameters of the unsupported mu-oxo bridge (Fe-O= 1.807(8) A, and Fe-O-Fe= 155.3(5) degrees fall in the usual range), it decreases the magnetic coupling between the irons (J=-28 cm(-1)) and creates a rather basic oxo site. Protonation of this oxo using strong (HBF4, HCl) or weak (HOAc, NH4PF6, LutNHCl) acids results in bridge cleavage to cleanly afford the corresponding monomeric anion-ligated (OAc- (6), or Cl- (7)) or solvent-ligated (MeCN (4)) derivatives. Addition of OH- converts [FeIII(SMe2N4(tren))(MeCN2+ (4) back to mu-oxo 3. Thus, mu-oxo bridge cleavage is reversible. The protonated mu-hydroxo-bridged intermediate is not observed. In an attempt to prevent mu-oxo dimer formation, and facilitate the observation of O2-bound intermediates, a bulkier tertiary amine ligand, tren-Et4= N-(2-amino-ethyl)-N-(2-diethylamino-ethyl)-N',N'-diethyl-ethane-1,2-diamine, and the corresponding [FeII(SMe2N4(tren-Et4))]+ (5) complex was synthesized and structurally characterized. Steric repulsive interactions create unusually long FeII-N(3,4) amine bonds in 5 (mean distance=2.219(1) A). The [(tren-Et4)N4SMe2]1- ligand is unable to accommodate iron in the +3 oxidation state, and consequently, in contrast to most thiolate-ligated Fe(II) complexes, [FeII(SMe2N4(tren-Et4))]+ (5) does not readily react with O2. Oxidation of 5 is irreversible, and the potential (Epa=+410 mV (vs SCE)) is anodically shifted relative to 1 (E1/2=-100 mV (vs SCE)).

Dataset Information

A High-Valent Non-Heme ?-Oxo Manganese(IV) Dimer Generated from a Thiolate-Bound Manganese(II) Complex and Dioxygen.

Publications

A High-Valent Non-Heme μ-Oxo Manganese(IV) Dimer Generated from a Thiolate-Bound Manganese(II) Complex and Dioxygen.

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