TY - JOUR

T1 - Aromatic C[sbnd]H oxidation by non-heme iron(V)-oxo intermediates bearing aminopyridine ligands

AU - Zima, Alexandra M.

AU - Lyakin, Oleg Y.

AU - Lubov, Dmitry P.

AU - Bryliakov, Konstantin P.

AU - Talsi, Evgenii P.

PY - 2020/3

Y1 - 2020/3

N2 - Direct data on the reactivity of the nonheme iron(V)-oxo intermediates toward substituted benzenes at −70 °C have been obtained. The intermediates are generated in the catalyst systems 1/CH3CO3H/RCOOH (1 = [(PDP*)2FeIII 2(μ-OH)2](OTf)4, PDP* = N,N′-bis(3,5-dimethyl-4-methoxypyridyl-2-methyl)-(S,S)-2,2′-bipyrrolidine) and 2/CH3CO3H/RCOOH (2 = [(TPA*)2FeIII 2(μ-OH)2](OTf)4, TPA* = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine), RCOOH are various linear and branched carboxylic acids). It has been found that only one type of iron(V)-oxo intermediates 1aRCOOH with the proposed structure [(PDP*)FeV=O(OC(O)R)]2+ (g1 = 2.071–2.072, g2 = 2.007, g3 = 1.959–1.960) can be observed in the systems 1/CH3CO3H/RCOOH, whereas in the systems 2/CH3CO3H/RCOOH, two types of iron(V)-oxo intermediates 2aRCOOH (g1 = 2.070–2.071, g2 = 2.004, g3 = 1.960–1.962) and 2a (g1 = 2.075, g2 = 2.011, g3 = 1.964) are formed, with the proposed structures [(TPA*)FeV=O(OC(O)R)]2+ and [(TPA*)FeV=O(OH)]2+, respectively. For linear carboxylic acids, intermediate 2a strongly predominates in the reaction solution just after the reaction onset. When RCOOH is branched carboxylic acid, the concentration of 2aRCOOH can be higher than the concentration of 2a just after the reaction onset at −70 °C; then, 2aRCOOH converts into 2a within 5-10 min at this temperature. The reactivity of the iron-oxo species toward substituted benzenes is higher for more electron-rich substrates, varying in the following order acetophenone < chlorobenzene < benzene < toluene, which is consistent with the electrophilic aromatic substitution mechanism. In agreement with this, the highest turnover numbers in aromatic oxidation (up to 25) were obtained for toluene. The second-order rate constants for the reaction of intermediates 1aRCOOH and 2a with acetophenone and chlorobenzene have been evaluated. The aromatic hydroxylation reactivities of the observed intermediates vary in the following order 2aRCOOH < 2a < 1aRCOOH.

AB - Direct data on the reactivity of the nonheme iron(V)-oxo intermediates toward substituted benzenes at −70 °C have been obtained. The intermediates are generated in the catalyst systems 1/CH3CO3H/RCOOH (1 = [(PDP*)2FeIII 2(μ-OH)2](OTf)4, PDP* = N,N′-bis(3,5-dimethyl-4-methoxypyridyl-2-methyl)-(S,S)-2,2′-bipyrrolidine) and 2/CH3CO3H/RCOOH (2 = [(TPA*)2FeIII 2(μ-OH)2](OTf)4, TPA* = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine), RCOOH are various linear and branched carboxylic acids). It has been found that only one type of iron(V)-oxo intermediates 1aRCOOH with the proposed structure [(PDP*)FeV=O(OC(O)R)]2+ (g1 = 2.071–2.072, g2 = 2.007, g3 = 1.959–1.960) can be observed in the systems 1/CH3CO3H/RCOOH, whereas in the systems 2/CH3CO3H/RCOOH, two types of iron(V)-oxo intermediates 2aRCOOH (g1 = 2.070–2.071, g2 = 2.004, g3 = 1.960–1.962) and 2a (g1 = 2.075, g2 = 2.011, g3 = 1.964) are formed, with the proposed structures [(TPA*)FeV=O(OC(O)R)]2+ and [(TPA*)FeV=O(OH)]2+, respectively. For linear carboxylic acids, intermediate 2a strongly predominates in the reaction solution just after the reaction onset. When RCOOH is branched carboxylic acid, the concentration of 2aRCOOH can be higher than the concentration of 2a just after the reaction onset at −70 °C; then, 2aRCOOH converts into 2a within 5-10 min at this temperature. The reactivity of the iron-oxo species toward substituted benzenes is higher for more electron-rich substrates, varying in the following order acetophenone < chlorobenzene < benzene < toluene, which is consistent with the electrophilic aromatic substitution mechanism. In agreement with this, the highest turnover numbers in aromatic oxidation (up to 25) were obtained for toluene. The second-order rate constants for the reaction of intermediates 1aRCOOH and 2a with acetophenone and chlorobenzene have been evaluated. The aromatic hydroxylation reactivities of the observed intermediates vary in the following order 2aRCOOH < 2a < 1aRCOOH.

KW - aromatic C[sbnd]H

KW - bioinspired catalysis

KW - EPR

KW - iron-oxo

KW - mechanism

KW - oxidation

KW - ACTIVATION

KW - MECHANISM

KW - HYDROXYLATION

KW - COMPLEXES

KW - REACTIVITY

KW - aromatic C-H

KW - COMPOUND I

KW - FUNCTIONALIZATION

KW - ENZYMES

KW - BONDS

KW - ELECTRONIC-STRUCTURE

UR - http://www.scopus.com/inward/record.url?scp=85075442403&partnerID=8YFLogxK

U2 - 10.1016/j.mcat.2019.110708

DO - 10.1016/j.mcat.2019.110708

M3 - Article

AN - SCOPUS:85075442403

VL - 483

JO - Molecular Catalysis

JF - Molecular Catalysis

SN - 2468-8231

M1 - 110708

ER -