Tuning the stereoelectronic factors of iron(ii)-2-aminophenolate complexes for the reaction with dioxygen: oxygenolytic C–C bond cleavage vs. oxidation of complex. Issue 5 (21st January 2021)

• Record Type: Journal Article
• Authors: Chatterjee, Sayanti; Banerjee, Sridhar; Jana, Rahul Dev; Bhattacharya, Shrabanti; Chakraborty, Biswarup; Jannuzzi, Sergio Augusto Venturinelli
• Is Part Of: Dalton transactions. Volume 50:Issue 5(2020)
• Page Start: 1901
• Page End: 1912
• Publication Date: 2021-01-21
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt03316b
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Modular tuning of stereoelectronic factors of Iron(ii )-2-aminophenolate complexes during the reaction with dioxygen enables to control oxygenolytic C–C bond cleavage vs. metal and/or ligand based oxidation. Abstract : 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 O2 for 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 [(Tp Ph, Me )Fe II (X)], where X = 2-amino-4- tert -butylphenolate (4- t Bu-HAP) (1 ); X = 2-amino-4, 6-di- tert -butylphenolate (4, 6-di- t Bu-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- t Bu-HAP) (4 ) supported by a facial tridentate nitrogen donor ligand (Tp Ph, Me = hydrotris(3-phenyl-5-methylpyrazol-1-yl)borate). Another facial N3 ligand (Tp Ph2 = 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 [(Tp Ph, Me )Fe II (4- t Bu-HAP)] (1 ) and [(Tp Ph, Me )Fe II (4, 6-di- t Bu-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 [(Tp Ph, Me )Fe II (4-NO2 -HAP)] (3 ) displays metal based oxidation to form an iron(iii )-2-amidophenolate complex. Complexes [(Tp Ph, Me )Fe II (NH-Ph-4, 6-di- t Bu-HAP)] (4 ) and [(Tp Ph2 )Fe II (NH-Ph-4, 6-di- t Bu-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 –NH2 group 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 reactivity vs . 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 complexes 1 and 2 that mimic the structure and function of the nonheme enzyme 2-aminophenol-1, 6-dioxygenase (APD).