Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex

Yuan Sheng; Chase S Abelson; Jai Prakash; Apparao Draksharapu; Victor G. Young; Lawrence Que

doi:10.1002/anie.202108309

Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex

Yuan Sheng, Chase S Abelson, Jai Prakash, Apparao Draksharapu, Victor G. Young, Lawrence Que

Chemistry (Twin Cities)

Research output: Contribution to journal › Article › peer-review

6 Scopus citations

Abstract

In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [Fe^IV(O_syn)(Bn3MC)]²⁺ (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at −40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major Fe^III−OAr product 3. At the same time, the Fe^II(Bn3MC)²⁺ (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [Fe^IV(O)(L^Ph)]²⁺ (2-syn)→2 [Fe^III(L^OAr)]²⁺ (3)+[Fe^II(L^Ph)]²⁺ (1)+H₂O. This system thus serves as a paradigm for aryl hydroxylation by Fe^IV=O oxidants described thus far. It is also observed that 2-syn can be intercepted by certain hydrocarbon substrates, thereby providing a means to assess the relative energetics of aliphatic and aromatic C−H hydroxylation in this system.

Original language	English (US)
Pages (from-to)	20991-20998
Number of pages	8
Journal	Angewandte Chemie - International Edition
Volume	60
Issue number	38
DOIs	https://doi.org/10.1002/anie.202108309
State	Published - Sep 13 2021

Bibliographical note

Funding Information:
We thank the National Science Foundation for support of this work (CHE1665391 to L.Q.) and Dr. Rahul Banerjee for his insightful comments on the kinetic analyses. XAS data were collected at the Stanford Synchrotron Radiation Lightsource, which is supported by the U.S. DOE under Contract No. DEAC02‐76SF00515. Use of Beamline 9‐3 is supported by the DOE Office of Biological and Environmental Research and the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393).

Publisher Copyright:
© 2021 Wiley-VCH GmbH

Keywords

aromatic hydroxylation
intramolecular vs. intermolecular oxidation
nonheme iron
oxoiron(IV)
reaction mechanism

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10.1002/anie.202108309

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title = "Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex",

abstract = "In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [FeIV(Osyn)(Bn3MC)]2+ (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at −40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major FeIII−OAr product 3. At the same time, the FeII(Bn3MC)2+ (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [FeIV(O)(LPh)]2+ (2-syn)→2 [FeIII(LOAr)]2+ (3)+[FeII(LPh)]2+ (1)+H2O. This system thus serves as a paradigm for aryl hydroxylation by FeIV=O oxidants described thus far. It is also observed that 2-syn can be intercepted by certain hydrocarbon substrates, thereby providing a means to assess the relative energetics of aliphatic and aromatic C−H hydroxylation in this system.",

keywords = "aromatic hydroxylation, intramolecular vs. intermolecular oxidation, nonheme iron, oxoiron(IV), reaction mechanism",

author = "Yuan Sheng and Abelson, {Chase S} and Jai Prakash and Apparao Draksharapu and Young, {Victor G.} and Lawrence Que",

note = "Funding Information: We thank the National Science Foundation for support of this work (CHE1665391 to L.Q.) and Dr. Rahul Banerjee for his insightful comments on the kinetic analyses. XAS data were collected at the Stanford Synchrotron Radiation Lightsource, which is supported by the U.S. DOE under Contract No. DEAC02‐76SF00515. Use of Beamline 9‐3 is supported by the DOE Office of Biological and Environmental Research and the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). Publisher Copyright: {\textcopyright} 2021 Wiley-VCH GmbH",

year = "2021",

month = sep,

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doi = "10.1002/anie.202108309",

language = "English (US)",

volume = "60",

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T1 - Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex

AU - Sheng, Yuan

AU - Abelson, Chase S

AU - Prakash, Jai

AU - Draksharapu, Apparao

AU - Young, Victor G.

AU - Que, Lawrence

N1 - Funding Information: We thank the National Science Foundation for support of this work (CHE1665391 to L.Q.) and Dr. Rahul Banerjee for his insightful comments on the kinetic analyses. XAS data were collected at the Stanford Synchrotron Radiation Lightsource, which is supported by the U.S. DOE under Contract No. DEAC02‐76SF00515. Use of Beamline 9‐3 is supported by the DOE Office of Biological and Environmental Research and the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). Publisher Copyright: © 2021 Wiley-VCH GmbH

PY - 2021/9/13

Y1 - 2021/9/13

N2 - In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [FeIV(Osyn)(Bn3MC)]2+ (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at −40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major FeIII−OAr product 3. At the same time, the FeII(Bn3MC)2+ (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [FeIV(O)(LPh)]2+ (2-syn)→2 [FeIII(LOAr)]2+ (3)+[FeII(LPh)]2+ (1)+H2O. This system thus serves as a paradigm for aryl hydroxylation by FeIV=O oxidants described thus far. It is also observed that 2-syn can be intercepted by certain hydrocarbon substrates, thereby providing a means to assess the relative energetics of aliphatic and aromatic C−H hydroxylation in this system.

AB - In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [FeIV(Osyn)(Bn3MC)]2+ (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at −40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major FeIII−OAr product 3. At the same time, the FeII(Bn3MC)2+ (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [FeIV(O)(LPh)]2+ (2-syn)→2 [FeIII(LOAr)]2+ (3)+[FeII(LPh)]2+ (1)+H2O. This system thus serves as a paradigm for aryl hydroxylation by FeIV=O oxidants described thus far. It is also observed that 2-syn can be intercepted by certain hydrocarbon substrates, thereby providing a means to assess the relative energetics of aliphatic and aromatic C−H hydroxylation in this system.

KW - aromatic hydroxylation

KW - intramolecular vs. intermolecular oxidation

KW - nonheme iron

KW - oxoiron(IV)

KW - reaction mechanism

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DO - 10.1002/anie.202108309

M3 - Article

C2 - 34292639

AN - SCOPUS:85112051609

SN - 1433-7851

VL - 60

SP - 20991

EP - 20998

JO - Angewandte Chemie - International Edition

JF - Angewandte Chemie - International Edition

IS - 38

ER -

Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex

Abstract

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