Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes
dc.contributor.author
dc.date.accessioned
2021-05-13T08:14:32Z
dc.date.available
2021-05-13T08:14:32Z
dc.date.issued
2021-08-03
dc.identifier.issn
1615-4150
dc.identifier.uri
dc.description.abstract
The oxidation of aromatic substrates to phenols with H2O2 as a benign oxidant remains an ongoing challenge in synthetic chemistry. Herein, we successfully achieved to catalyze aromatic C−H bond oxidations using a series of biologically inspired manganese catalysts in fluorinated alcohol solvents. While introduction of bulky substituents into the ligand structure of the catalyst favors aromatic C−H oxidations in alkylbenzenes, oxidation occurs at the benzylic position with ligands bearing electron‐rich substituents. Therefore, the nature of the ligand is key in controlling the chemoselectivity of these Mn‐catalyzed C−H oxidations. We show that introduction of bulky groups into the ligand prevents catalyst inhibition through phenolate‐binding, consequently providing higher catalytic turnover numbers for phenol formation. Furthermore, employing halogenated carboxylic acids in the presence of bulky catalysts provides enhanced catalytic activities, which can be attributed to their low pKa values that reduces catalyst inhibition by phenolate protonation as well as to their electron‐withdrawing character that makes the manganese oxo species a more electrophilic oxidant. Moreover, to the best of our knowledge, the new system can accomplish the oxidation of alkylbenzenes with the highest yields so far reported for homogeneous arene hydroxylation catalysts. Overall our data provide a proof‐of‐concept of how Mn(II)/H2O2/RCO2H oxidation systems are easily tunable by means of the solvent, carboxylic acid additive, and steric demand of the ligand. The chemo‐ and site‐selectivity patterns of the current system, a negligible KIE, the observation of an NIH‐shift, and the effectiveness of using tBuOOH as oxidant overall suggest that hydroxylation of aromatic C−H bonds proceeds through a metal‐based mechanism, with no significant involvement of hydroxyl radicals, and via an arene oxide intermediate
dc.description.sponsorship
The European Commission is acknowledged
for financial support through the NoNoMeCat project (675020-
MSCA-ITN-2015-ETN). We also thank Utrecht University.
Support by the Spanish Ministry of Science (PGC2018-101737-
B-I00 to M.C. and PhD grant to M.B. BES-2016-076349), and
Generalitat de Catalunya (ICREA Academia Award to M.C. and
2017 SGR 00264) is acknowledged
dc.format.mimetype
application/pdf
dc.language.iso
eng
dc.publisher
Wiley
dc.relation
info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020/PGC2018-101737-B-I00/ES/CATALISIS DE OXIDACION BIOINSPIRADA MEDIANTE DISEÑO RACIONAL DE CATALIZADORES/
dc.relation.isformatof
Reproducció digital del document publicat a: https://doi.org/10.1002/adsc.202001590
dc.relation.ispartof
Advanced Synthesis and Catalysis, 2021, vol. 363, núm. 15, p. 3783-3795
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Articles publicats (D-Q)
dc.rights
Attribution-NonCommercial 4.0 International
dc.rights.uri
dc.title
Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes
dc.type
info:eu-repo/semantics/article
dc.rights.accessRights
info:eu-repo/semantics/openAccess
dc.relation.projectID
info:eu-repo/grantAgreement/EC/H2020/675020/EU/Non-Noble Metal Catalysis/NoNoMeCat
dc.type.version
info:eu-repo/semantics/publishedVersion
dc.identifier.doi
dc.contributor.funder
dc.type.peerreviewed
peer-reviewed
dc.relation.FundingProgramme
dc.relation.ProjectAcronym
dc.identifier.eissn
1615-4169