TY - JOUR
T1 - Tuning the stereoelectronic factors of iron(ii)-2-aminophenolate complexes for the reaction with dioxygen
T2 - oxygenolytic C-C bond cleavagevs. oxidation of complex
AU - Chatterjee, Sayanti
AU - Banerjee, Sridhar
AU - Jana, Rahul Dev
AU - Bhattacharya, Shrabanti
AU - Chakraborty, Biswarup
AU - Jannuzzi, Sergio Augusto Venturinelli
N1 - Funding Information:
The authors acknowledge the School of Chemical Sciences, Indian Association for the Cultivation of Science, India. R. D. J thanks the Council of Scientific and Industrial Research (CSIR), India for a research fellowship. Special thanks to Prof. Tapan Kanti Paine for sharing his laboratory space, chemicals and analytical equipment and also for the insightful suggestions and critical proofreading of the manuscript.
Publisher Copyright:
© The Royal Society of Chemistry 2021.
PY - 2021/2/7
Y1 - 2021/2/7
N2 - Oxidative C-C bond cleavage of 2-aminophenols mediated by transition metals and dioxygen is a topic of great interest. While the oxygenolytic C-C bond cleavage reaction relies on the inherent redox non-innocent property of 2-aminophenols, the metal complexes of 2-aminophenolates often undergo 1e−/2e−oxidation events (metal or ligand oxidation), instead of the direct addition of O2for subsequent C-C bond cleavage. In this work, we report the isolation, characterization and dioxygen reactivity of a series of ternary iron(ii)-2-aminophenolate complexes [(TpPh,Me)FeII(X)], where X = 2-amino-4-tert-butylphenolate (4-tBu-HAP) (1); X = 2-amino-4,6-di-tert-butylphenolate (4,6-di-tBu-HAP) (2); X = 2-amino-4-nitrophenolate (4-NO2-HAP)(3); and X = 2-anilino-4,6-di-tert-butylphenolate (NH-Ph-4,6-di-tBu-HAP) (4) supported by a facial tridentate nitrogen donor ligand (TpPh,Me= hydrotris(3-phenyl-5-methylpyrazol-1-yl)borate). Another facial N3ligand (TpPh2= hydrotris(3,5-diphenyl-pyrazol-1-yl)borate) has been used to isolate an iron(ii)-2-anilino-4,6-di-tert-butylphenolate complex (5) for comparison. Both [(TpPh,Me)FeII(4-tBu-HAP)] (1) and [(TpPh,Me)FeII(4,6-di-tBu-HAP)] (2) undergo regioselective oxidative aromatic ring fission reaction of the coordinated 2-aminophenols to the corresponding 2-picolinic acids in the reaction with dioxygen. In contrast, complex [(TpPh,Me)FeII(4-NO2-HAP)] (3) displays metal based oxidation to form an iron(iii)-2-amidophenolate complex. Complexes [(TpPh,Me)FeII(NH-Ph-4,6-di-tBu-HAP)] (4) and [(TpPh2)FeII(NH-Ph-4,6-di-tBu-HAP)] (5) react with dioxygen to undergo 2e−oxidation with the formation of the corresponding iron(iii)-2-iminobenzosemiquinonato radical species implicating the importance of the -NH2group in directing the C-C bond cleavage reactivity of 2-aminophenols. The systematic study presented in this work unravels the effect of the electronic and structural properties of the redox non-innocent 2-aminophenolate ring and the supporting ligand on the C-C bond cleavage reactivityvs. the metal/ligand oxidation of the complexes. The study further reveals that proper modulation of the stereoelectronic factors enables us to design a well synchronised proton transfer (PT) and dioxygen binding events for complexes1and2that mimic the structure and function of the nonheme enzyme 2-aminophenol-1,6-dioxygenase (APD).
AB - Oxidative C-C bond cleavage of 2-aminophenols mediated by transition metals and dioxygen is a topic of great interest. While the oxygenolytic C-C bond cleavage reaction relies on the inherent redox non-innocent property of 2-aminophenols, the metal complexes of 2-aminophenolates often undergo 1e−/2e−oxidation events (metal or ligand oxidation), instead of the direct addition of O2for subsequent C-C bond cleavage. In this work, we report the isolation, characterization and dioxygen reactivity of a series of ternary iron(ii)-2-aminophenolate complexes [(TpPh,Me)FeII(X)], where X = 2-amino-4-tert-butylphenolate (4-tBu-HAP) (1); X = 2-amino-4,6-di-tert-butylphenolate (4,6-di-tBu-HAP) (2); X = 2-amino-4-nitrophenolate (4-NO2-HAP)(3); and X = 2-anilino-4,6-di-tert-butylphenolate (NH-Ph-4,6-di-tBu-HAP) (4) supported by a facial tridentate nitrogen donor ligand (TpPh,Me= hydrotris(3-phenyl-5-methylpyrazol-1-yl)borate). Another facial N3ligand (TpPh2= hydrotris(3,5-diphenyl-pyrazol-1-yl)borate) has been used to isolate an iron(ii)-2-anilino-4,6-di-tert-butylphenolate complex (5) for comparison. Both [(TpPh,Me)FeII(4-tBu-HAP)] (1) and [(TpPh,Me)FeII(4,6-di-tBu-HAP)] (2) undergo regioselective oxidative aromatic ring fission reaction of the coordinated 2-aminophenols to the corresponding 2-picolinic acids in the reaction with dioxygen. In contrast, complex [(TpPh,Me)FeII(4-NO2-HAP)] (3) displays metal based oxidation to form an iron(iii)-2-amidophenolate complex. Complexes [(TpPh,Me)FeII(NH-Ph-4,6-di-tBu-HAP)] (4) and [(TpPh2)FeII(NH-Ph-4,6-di-tBu-HAP)] (5) react with dioxygen to undergo 2e−oxidation with the formation of the corresponding iron(iii)-2-iminobenzosemiquinonato radical species implicating the importance of the -NH2group in directing the C-C bond cleavage reactivity of 2-aminophenols. The systematic study presented in this work unravels the effect of the electronic and structural properties of the redox non-innocent 2-aminophenolate ring and the supporting ligand on the C-C bond cleavage reactivityvs. the metal/ligand oxidation of the complexes. The study further reveals that proper modulation of the stereoelectronic factors enables us to design a well synchronised proton transfer (PT) and dioxygen binding events for complexes1and2that mimic the structure and function of the nonheme enzyme 2-aminophenol-1,6-dioxygenase (APD).
UR - http://www.scopus.com/inward/record.url?scp=85100749825&partnerID=8YFLogxK
U2 - 10.1039/d0dt03316b
DO - 10.1039/d0dt03316b
M3 - Article
C2 - 33475662
AN - SCOPUS:85100749825
VL - 50
SP - 1901
EP - 1912
JO - Dalton Transactions
JF - Dalton Transactions
SN - 1477-9226
IS - 5
ER -