Characterization of an Oxo(porphyrinato)manganese(<scp>IV</scp>) Complex by X‐ray Absorption Spectroscopy

Charnock, John; Garner, C. David; Trautwein, Alfred X.; Bill, E.; Winkler, H.; Ayougou, Khadija; Mandon, Dominique; Weiss, Raymond

doi:10.1002/anie.199503431

Cited by 58 publications

(10 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Mn-O bond distance (from the major component of the disorder) for the terminal hydroxide ligand in 3 is 1.881(2) Å, which is slightly longer than those reported for the few other Mn IV (OH) n (n = 1, 2) complexes (1.793(2) – 1.830(4) Å), 10, 21–22, 52–53 but much longer than a typical Mn IV (O) distance (1.58 – 1.71 Å). 22, 61–64 The Mn-O distance in 3 is quite close to that seen for Fe IV (OH)(ttppc) (Fe–O = 1.857(3) Å). 20…”

Section: Resultssupporting

confidence: 63%

A Reactive Manganese(IV)–Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds

2018

View full text Add to dashboard Cite

High-valent metal-hydroxide species are invoked as critical intermediates in both catalytic, metal-mediated O activation (e.g., by Fe porphyrin in Cytochrome P450) and O production (e.g., by the Mn cluster in Photosystem II). However, well-characterized mononuclear M(OH) complexes remain a rarity. Herein we describe the synthesis of Mn(OH)(ttppc) (3) (ttppc = tris(2,4,6-triphenylphenyl) corrole), which has been characterized by X-ray diffraction (XRD). The large steric encumbrance of the ttppc ligand allowed for isolation of 3. The complexes Mn(O)(ttppc) (4) and Mn(HO)(ttppc) (1·HO) were also synthesized and structurally characterized, providing a series of Mn complexes related only by the transfer of hydrogen atoms. Both 3 and 4 abstract an H atom from the O-H bond of 2,4-di- tert-butylphenol (2,4-DTBP) to give a radical coupling product in good yield (3 = 90(2)%, 4 = 91(5)%). Complex 3 reacts with 2,4-DTBP with a rate constant of k = 2.73(12) × 10 M s, which is ∼3 orders of magnitude larger than 4 ( k = 17.4(1) M s). Reaction of 3 with a series of para-substituted 2,6-di- tert-butylphenol derivatives (4-X-2,6-DTBP; X = OMe, Me, tBu, H) gives rate constants in the range k = 510(10)-36(1.4) M s and led to Hammett and Marcus plot correlations. Together with kinetic isotope effect measurements, it is concluded that O-H cleavage occurs by a concerted H atom transfer (HAT) mechanism and that the Mn(OH) complex is a much more powerful H atom abstractor than the higher-valent Mn(O) complex, or even some Fe(O) complexes.

show abstract

Section: Resultssupporting

confidence: 63%

A Reactive Manganese(IV)–Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds

2018

View full text Add to dashboard Cite

show abstract

“…This shift is consistent with a lowering of the oxidation state on the metal, and the edge energies match well with other Mn IV complexes. 13,26,27 The intensity of the pre-edge peaks for Mn IV (O-LA)(TBP 8 Cz •+ ) at ~6541.3 eV are significantly lower than the peak seen for Mn V (O)(TBP 8 Cz) at 6541.6 eV. The pre-edge peak arises from a 1s-to-3d transition, and a decrease in intensity for this transition is consistent with a lengthening of the Mn−O bond, as can be expected from the binding of a Lewis acid to the terminal oxo ligand.…”

Section: Resultsmentioning

confidence: 99%

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

et al. 2016

View full text Add to dashboard Cite

The addition of Lewis or Brönsted acids (LA = Zn(OTf)2, B(C6F5)3, HBArF, TFA) to the high-valent manganese—oxo complex MnV(O)(TBP8Cz) results in the stabilization of a valence tautomer MnIV(O-LA)(TBP8Cz•+). The ZnII and B(C6F5)3 complexes were characterized by manganese K-edge X-ray absorption spectroscopy (XAS). The position of the edge energies and the intensities of the pre-edge (1s to 3d) peaks confirm that the Mn ion is in the +4 oxidation state. Fitting of the extended X-ray absorption fine structure (EXAFS) region reveals 4 N/O ligands at Mn−Nave = 1.89 Å and a fifth N/O ligand at 1.61 Å, corresponding to the terminal oxo ligand. This Mn−O bond length is elongated compared to the MnV(O) starting material (Mn−O = 1.55 Å). The reactivity of MnIV(O-LA)(TBP8Cz−+) toward C−H substrates was examined, and it was found that H• abstraction from C−H bonds occurs in a 1:1 stoichiometry, giving a MnIV complex and the dehydrogenated organic product. The rates of C−H cleavage are accelerated for the MnIV(O-LA)(TBP8Cz•+) valence tautomer as compared to the MnV(O) valence tautomer when LA = ZnII, B(C6F5)3, and HBArF, whereas for LA = TFA, the C−H cleavage rate is slightly slower than when compared to MnV(O). A large, nonclassical kinetic isotope effect of kH/kD = 25–27 was observed for LA = B(C6F5)3 and HBArF, indicating that H-atom transfer (HAT) is the rate-limiting step in the C−H cleavage reaction and implicating a potential tunneling mechanism for HAT. The reactivity of MnIV(O-LA)(TBP8Cz•+) toward C−H bonds depends on the strength of the Lewis acid. The HAT reactivity is compared with the analogous corrole complex MnIV(O−H)(tpfc•+) recently reported.

show abstract

“…Although the Mn IV ‐oxo species supported by N4py derivatives and Bn‐TPEN require the use of TFE as a solvent for formation, the analogous Fe complexes can be formed in either protic TFE or aprotic MeCN . Thus, TFE is not the privileged solvent for Fe IV ‐oxo complexes as it is for Mn IV ‐oxo analogues.…”

Section: Discussionmentioning

confidence: 99%

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

Massie

Denler

Singh

et al. 2019

Chemistry A European J

View full text Add to dashboard Cite

Analysis of extendedX -ray absorption fine structure (EXAFS) data for the Mn IV -oxo complexes [Mn IV (O)( DMM N4py)] 2+ + ,[ Mn IV (O)(2pyN2B)] 2+ + ,a nd [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-2pyridylmethyl)amine, and 2pyN2Q = N,N-bis(2-pyridyl)-N,Nbis(2-quinolylmethyl)methanamine) afforded Mn=Oa nd MnÀNb ond lengths.T he Mn=Od istances for [Mn IV (O)( DMM N4py)] 2+ + and [Mn IV (O)(2pyN2B)] 2+ + are 1.72 and 1.70 ,r espectively.I nc ontrast, the Mn=Od istance for [Mn IV (O)(2pyN2Q)] 2+ + was significantly longer( 1.76 ). We attribute this long distance to sample heterogeneity, which is reasonable given the reduced stability of [Mn IV (O)(2pyN2Q)] 2+ + .T he Mn=Od istances for [Mn IV (O)( DMM N4py)] 2+ + and [Mn IV (O)(2pyN2B)] 2+ + could only be well-reproduced using DFT-derived modelst hat included strong hydrogen-bonds between second-sphere solvent 2,2,2-trifluoroethanol molecules and the oxo ligand. These results suggesta ni mportantr olef or 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 aM n IV -hydroxos pecies is most consistentw ith the availablee xperimental data.[a] Dr.

show abstract

Characterization of an Oxo(porphyrinato)manganese(IV) Complex by X‐ray Absorption Spectroscopy

Cited by 58 publications

References 20 publications

A Reactive Manganese(IV)–Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds

A Reactive Manganese(IV)–Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

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

Contact Info

Product

Resources

About

Characterization of an Oxo(porphyrinato)manganese(IV) Complex by X‐ray Absorption Spectroscopy

Cited by 58 publications

References 20 publications

A Reactive Manganese(IV)–Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds

A Reactive Manganese(IV)–Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

Structural Characterization of a Series of N5‐Ligated MnIV‐Oxo Species

Contact Info

Product

Resources

About

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