Reactivity and mechanisms of metalloporphyrin-catalyzed oxidations

Groves, John T.

doi:10.1002/(sici)1099-1409(200006/07)4:4<350::aid-jpp249>3.0.co;2-g

Cited by 88 publications

(5 citation statements)

References 25 publications

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“…Generally, for metalloporphyrin-catalyzed oxidation of substrates, the so-called Groves rebound mechanism is widely accepted. 24 , 25 , 26 A recent investigation on the Mn(V)OP + system performed by Pierloot et al 28 with correlated ab initio methods (CASPT2, RASPT2) provided an accurate description for the spin state energetics, the oxyl character of the complex and for their role in oxygen transfer reactions. Analogously, the Mn(V)OP + singlet ground state was proven to lack the oxyl character and to be kinetically inert.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Reactivity of Mn-Oxo Porphyrins for Substrate Hydroxylation: Theoretical Predictions and Experimental Evidence Reconciled

Ricciarelli

Phung

Belpassi³

et al. 2019

Inorg. Chem.

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The Mn-oxo porphyrin (MnOP) mechanism for substrate hydroxylation is computationally studied with the aim to better understand reactivity in these systems. Theoretical studies suggest Mn(V)OP species as very reactive intermediates with thermally accessible reaction barriers represented by low spin/high spin crossover occurring in the Mn(V)OP oxidant, and kinetics for selected Mn(V)OP species indeed find high reactivity. On the other hand, MnOP complexes lead to low yields in catalytic hydroxylation reactions of several different substrates, suggesting low rate constants and high reaction barriers. The origin of this inconsistency is very important to understand the reactivity of Mn-oxo porphyrins and to improve the catalytic conditions. In this work we use the toluene hydroxylation by Mn(V)OP(H2O) + complex as a case study to gain deep insight into the reaction mechanism and to check that it should indeed have high reactivity. Minimum energy crossing point (MECP) results on H-abstraction process from toluene indicate a first crossover from a singlet to a triplet spin state of the Mn(V)OP(H2O) + species, which represents the rate-determining step with a thermally accessible barrier, followed by a very facile H-abstraction by the triplet complex. Issues concerning i) the validation of the level of the DFT theory employed (BP86) to describe the singlettriplet energy gap in the Mn(V)OP(H2O) + system vs. highly accurate DMRG-CASPT2/CC calculations and ii) the influence of the axial ligand (X = none, Cl -, CH3CN, OHand O 2-) on MnOP reactivity, which models the different experimental conditions, are addressed. The ligand trans 2 influence mainly controls the reactivity through the singlet-triplet energy gap modulation, with the porphyrin ruffling distortion also finely tuning it. Finally, a stepwise model for the H-abstraction process is proposed which allows a direct comparison between the calculated and experimentally measured Gibbs free activation energy barriers (R.

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Section: Introductionmentioning

confidence: 99%

Understanding the Reactivity of Mn-Oxo Porphyrins for Substrate Hydroxylation: Theoretical Predictions and Experimental Evidence Reconciled

Ricciarelli

Phung

Belpassi³

et al. 2019

Inorg. Chem.

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“…13 Complexes of manganese porphyrins are known to catalyse the halogenation of aliphatic substrates, 14 and have shown high reactivity toward alkene epoxidation. 15 Recently, STM imaging of individual manganese porphyrin catalysts at a liquid-solid interface was reported, wherein, the formation of an oxomanganese porphyrin intermediate was visualized prior to the chemical transformation of alkenes into epoxides. 16 Concerning the Cl-MnTPP molecule, the metal-bound Cl ligand maintains the central manganese ion in the stable +3 oxidation state.…”

Section: Introductionmentioning

confidence: 99%

“…The rich coordination chemistry of manganese porphyrins makes them ideal candidates for a wide range of chemically responsive applications [13]. Complexes of manganese porphyrins are known to catalyse the halogenation of aliphatic substrates [14], and have shown high reactivity towards alkene epoxidation [15]. Recently, STM imaging of individual manganese porphyrin catalysts at a liquid-solid interface was reported, wherein, the formation of an oxomanganese porphyrin intermediate was visualized prior to the chemical transformation of alkenes into epoxides [16].…”

Section: Introductionmentioning

confidence: 99%

Control of the axial coordination of a surface-confined manganese(III) porphyrin complex

Beggan¹,

Krasnikov²,

Sergeeva³

et al. 2012

Nanotechnology

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The organization and thermal lability of chloro(5,10,15,20-tetraphenyl porphyrinato)manganese(III) (Cl-MnTPP) molecules on the Ag(111) surface have been investigated under ultra-high vacuum conditions, using scanning tunnelling microscopy, low energy electron diffraction and x-ray photoelectron spectroscopy. The findings reveal the epitaxial nature of the molecule-substrate interface, and moreover, offer a valuable insight into the latent coordination properties of surface-confined metalloporphyrins. The Cl-MnTPP molecules are found to self-assemble on the Ag(111) surface at room temperature, forming an ordered molecular overlayer described by a square unit cell. In accordance with the threefold symmetry of the Ag(111) surface, three rotationally equivalent domains of the molecular overlayer are observed. The primitive lattice vectors of the Cl-MnTPP overlayer show an azimuthal rotation of ±15° relative to those of the Ag(111) surface, while the principal molecular axes of the individual molecules are found to be aligned with the substrate (0(-)11) and ((-)211) crystallographic directions. The axial chloride (Cl) ligand is found to be orientated away from the Ag(111) surface, whereby the average plane of the porphyrin macrocycle lies parallel to that of the substrate. When adsorbed on the Ag(111) surface, the Cl-MnTPP molecules display a latent thermal lability resulting in the dissociation of the axial Cl ligand at ~423 K. The thermally induced dissociation of the Cl ligand leaves the porphyrin complex otherwise intact, giving rise to the coordinatively unsaturated Mn(III) derivative. Consistent with the surface conformation of the Cl-MnTPP precursor, the resulting (5,10,15,20-tetraphenyl porphyrinato)manganese(III) (MnTPP) molecules display the same lattice structure and registry with the Ag(111) surface.

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“…These processes are of vital importance in biosystems, where the enzyme participates in detoxification and in biosyntheses [1]. Since the activation of inert C–H bonds is one of the holy grails of chemistry [9], the facility to carry out this process makes the P450 enzyme superfamily a model for creative mimetic chemistry [10] designed to generate novel catalysts that can perform C–H activation.…”

Section: Introductionmentioning

confidence: 99%

Coupling and uncoupling mechanisms in the methoxythreonine mutant of cytochrome P450cam: a quantum mechanical/molecular mechanical study

et al. 2009

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The Thr252 residue plays a vital role in the catalytic cycle of cytochrome P450cam during the formation of the active species (Compound I) from its precursor (Compound 0). We investigate the effect of replacing Thr252 by methoxythreonine (MeO-Thr) on this protonation reaction (coupling) and on the competing formation of the ferric resting state and H2O2 (uncoupling) by combined quantum mechanical/molecular mechanical (QM/MM) methods. For each reaction, two possible mechanisms are studied, and for each of these the residues Asp251 and Glu366 are considered as proton sources. The computed QM/MM barriers indicate that uncoupling is unfavorable in the case of the Thr252MeO-Thr mutant, whereas there are two energetically feasible proton transfer pathways for coupling. The corresponding rate-limiting barriers for the formation of Compound I are higher in the mutant than in the wild-type enzyme. These findings are consistent with the experimental observations that the Thr252MeO-Thr mutant forms the alcohol product exclusively (via Compound I), but at lower reaction rates compared with the wild-type enzyme.Electronic supplementary materialThe online version of this article (doi:10.1007/s00775-009-0608-3) contains supplementary material, which is available to authorized users.

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Reactivity and mechanisms of metalloporphyrin-catalyzed oxidations

Cited by 88 publications

References 25 publications

Understanding the Reactivity of Mn-Oxo Porphyrins for Substrate Hydroxylation: Theoretical Predictions and Experimental Evidence Reconciled

Understanding the Reactivity of Mn-Oxo Porphyrins for Substrate Hydroxylation: Theoretical Predictions and Experimental Evidence Reconciled

Control of the axial coordination of a surface-confined manganese(III) porphyrin complex

Coupling and uncoupling mechanisms in the methoxythreonine mutant of cytochrome P450cam: a quantum mechanical/molecular mechanical study

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