TY - JOUR
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 - 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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U2 - 10.1002/anie.202108309
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 -