Structural and Spectroscopic Characterization of Metastable Thiolate-Ligated Manganese(III)–Alkylperoxo Species

Coggins, Michael K.; Kovacs, Julie A.

doi:10.1021/ja205520u

Cited by 58 publications

(127 citation statements)

References 58 publications

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“…50 The Mn(III)-S bond (2.2747(12) Å) of 3 is 0.096 Å shorter than that of reduced 1 , but comparable to that of oxidized mono-oxo bridged {[Mn III (S Me2 N 4 (6-MeDPEN)] 2 -(μ-O)} 2+ ( 2 ), {[Mn III (S Me2 N 4 (2-QuinoEN)] 2 (μ-O)} 2+ (2.292(1) Å), [Mn III (S Me2 N 4 (6-Me-DPPN))] 2 (μ-O)(BPh 4 ) 2 (2.255(2) Å), and {[Mn III (S Me2 N 4 (6-H-DPEN)] 2 (μ-O)} 2+ (2.2968(15) Å), 50 as well as alkylperoxo-ligated [Mn III (S Me2 N 4 (2-QuinoEN)(OOtBu)] + (2.270(3) Å). 33 The peroxo in 3 is best described as binding in an end-on trans –μ–1,2–O 2 fashion (Figure S-3), as opposed to an asymmetric side-on μ-η 2 : η 2 fashion as shown by the significantly shorter Mn(1)–O(1)(1.832(3) Å) vs Mn(1)•••O(1′) (2.48 Å) distance. Peroxo-bridged 3 represents the first example of a binuclear Mn(III)-peroxo complex , structurally, or otherwise, characterized.…”

Section: Resultsmentioning

confidence: 99%

“…40,44-46 In fact, structurally characterized examples of middle-to-late first-row transition-metal peroxos are, in general, scarce. 1,23,47,48 Of the seven structurally characterized metastable Mn(III)-peroxo compounds, 33,36-39,43 all but one 49 are mononuclear, and five contain the peroxo in a side-on (η 2 ) binding mode. The only structural evidence for an end-on (η 1 ) peroxo binding mode with Mn(III) was reported in 1988, 49 and more recently by our group.…”

Section: Introductionmentioning

confidence: 99%

“…The only structural evidence for an end-on (η 1 ) peroxo binding mode with Mn(III) was reported in 1988, 49 and more recently by our group. 33 There are only two examples of peroxo-bridged Mn-clusters, one binuclear Mn(IV) 2 peroxo compound, 40 and one trinuclear Mn(III) 3 peroxo compound. 49 …”

Section: Introductionmentioning

confidence: 99%

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Characterization of Metastable Intermediates Formed in the Reaction between a Mn(II) Complex and Dioxygen, Including a Crystallographic Structure of a Binuclear Mn(III)–Peroxo Species

et al. 2013

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Transition-metal peroxos have been implicated as key intermediates in a variety of critical biological processes involving O2. Due to their highly reactive nature, very few metal-peroxos have been characterized. The dioxygen chemistry of manganese remains largely unexplored despite the proposed involvement of a binuclear Mn-peroxo, either as a precursor to O2, or derived from O2, in both photosynthetic H2O oxidation and DNA biosynthesis, arguably two of the most fundamental processes of life. Neither of these biological intermediates has been observed. Herein we describe the dioxygen chemistry of coordinatively unsaturated [MnII(SMe2N4(6-MeDPEN))] +(1), and the characterization of intermediates formed en route to a binuclear mono-oxo bridged Mn(III) product {[MnIII(SMe2N4(6-MeDPEN)]2-(μ-O)}2+ (2), the oxo atom of which is derived from 18O2. At low-temperatures, a dioxygen intermediate, [Mn(SMe2N4(6-MeDPEN))(O2)]+ (4), is observed (by stopped-flow) to rapidly and irreversibly form in this reaction (k1(−10 °C)= 3780±180M−1s−1, ΔH1‡ = 26.4±1.7 kJ mol−1, ΔS1‡ = − 75.6±6.8 J mol−1K−1), and then convert more slowly (k2(−10 °C)= 417±3.2 M−1s−1, ΔH2‡ = 47.1±1.4 kJ mol−1, ΔS2‡ = − 15.0±5.7 J mol−1K−1) to a species 3 with isotopically sensitive stretches at νo-o (Δ18O) = 819(47) cm−1, kO–O= 3.02 mdyn/Å, and νMn-O(Δ18O) = 611(25) cm−1 consistent with a peroxo. Intermediate 3 releases approximately 0.5 equiv of H2O2 per Mn ion upon protonation, and the rate of conversion of 4 to 3 is dependent on [Mn(II)] concentration, consistent with the formation of a binuclear Mn-peroxo. This was verified by X-ray crystallography, where the peroxo of {[MnIII(SMe2N4(6-Me-DPEN)]2(trans–μ–1,2–O2)}2+ (3) is shown to be bridging between two Mn(III) ions in an end-on trans-μ-1,2-fashion. This represents the first characterized example of a binuclear Mn(III)-peroxo, and a rare case in which more than one intermediate is observed en route to a binuclear μ–oxo bridged product derived from O2. Vibrational and metrical parameters for binuclear Mn-peroxo 3 are compared with those of related binuclear Fe- and Cu-peroxo compounds.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Characterization of Metastable Intermediates Formed in the Reaction between a Mn(II) Complex and Dioxygen, Including a Crystallographic Structure of a Binuclear Mn(III)–Peroxo Species

et al. 2013

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“…32 This complex is high-spin ( S = 2 ) and intensely blue in color. A lower-resolution structure of an end-on cumenyl peroxo derivative, [Mn III (S Me 2 N 4 (QuinoEN))-(OOCm)](BPh 4 ), was also included.…”

Section: Introductionmentioning

confidence: 99%

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

et al. 2013

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Manganese–peroxos are proposed as key intermediates in a number of important biochemical and synthetic transformations. Our understanding of the structural, spectroscopic, and reactivity properties of these metastable species is limited, however, and correlations between these properties have yet to be established experimentally. Herein we report the crystallographic structures of a series of structurally related metastable Mn(III)–OOR compounds, and examine their spectroscopic and reactivity properties. The four reported Mn(III)–OOR compounds extend the number of known end-on Mn(III)–(η1-peroxos) to six. The ligand backbone is shown to alter the metal–ligand distances and modulate the electronic properties key to bonding and activation of the peroxo. The mechanism of thermal decay of these metastable species is examined via variable-temperature kinetics. Strong correlations between structural (O–O and Mn⋯Npy,quin distances), spectroscopic (E(πv*(O–O) → Mn CT band), νO–O), and kinetic (ΔH‡ and ΔS‡) parameters for these complexes provide compelling evidence for rate-limiting O–O bond cleavage. Products identified in the final reaction mixtures of Mn(III)–OOR decay are consistent with homolytic O–O bond scission. The N-heterocyclic amines and ligand backbone (Et vs Pr) are found to modulate structural and reactivity properties, and O–O bond activation is shown, both experimentally and theoretically, to track with metal ion Lewis acidity. The peroxo O–O bond is shown to gradually become more activated as the N-heterocyclic amines move closer to the metal ion causing a decrease in π-donation from the peroxo πv*(O–O) orbital. The reported work represents one of very few examples of experimentally verified relationships between structure and function.

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“…14–27 Members of this class of compound include side-on peroxomanganese(III) adducts (Mn III -O 2 ) and end-on alkylperoxomanganese(III) adducts (Mn III -OOR). 28,29 …”

Section: Introductionmentioning

confidence: 99%

Geometric and electronic structure of a peroxomanganese(iii) complex supported by a scorpionate ligand

et al. 2014

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A monomeric MnII complex has been prepared with the facially-coordinating TpPh2 ligand, (TpPh2 = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin MnII ion. Treatment of this MnII complex with excess KO2 at room temperature resulted in the formation of a MnIII-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate. The electronic structure of this peroxomanganese(III) adduct was examined by using electronic absorption, electron paramagnetic resonance (EPR), low-temperature magnetic circular dichroism (MCD), and variable-temperature variable-field (VTVH) MCD spectroscopies. Density functional theory (DFT), time-dependent (TD)-DFT, and multireference ab initio CASSCF/NEVPT2 calculations were used to assign the electronic transitions and further investigate the electronic structure of the peroxomanganese(III) species. The lowest ligand-field transition in the electronic absorption spectrum of the MnIII-O2 complex exhibits a blue shift in energy compared to other previously characterized peroxomanganese(III) complexes that results from a large axial bond elongation, reducing the metal-ligand covalency and stabilizing the σ-antibonding Mn dz2 MO that is the donor MO for this transition.

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Structural and Spectroscopic Characterization of Metastable Thiolate-Ligated Manganese(III)–Alkylperoxo Species

Cited by 58 publications

References 58 publications

Characterization of Metastable Intermediates Formed in the Reaction between a Mn(II) Complex and Dioxygen, Including a Crystallographic Structure of a Binuclear Mn(III)–Peroxo Species

Characterization of Metastable Intermediates Formed in the Reaction between a Mn(II) Complex and Dioxygen, Including a Crystallographic Structure of a Binuclear Mn(III)–Peroxo Species

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

Geometric and electronic structure of a peroxomanganese(iii) complex supported by a scorpionate ligand

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