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Mukhopadhyay N, Sengupta A, Vijay AK, Lloret F, Mukherjee R. Ni(II) complexes of a new tetradentate NN'N''O picolinoyl-1,2-phenylenediamide-phenolate redox-active ligand at different redox levels. Dalton Trans 2022; 51:9017-9029. [PMID: 35638812 DOI: 10.1039/d2dt01043g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Three square planar nickel(II) complexes of a new asymmetric tetradentate redox-active ligand H3L2 in its deprotonated form, at three redox levels, open-shell semiquinonate(1-) π radical, quinone(0) and closed-shell dianion of its 2-aminophenolate part, have been synthesized. The coordinated ligand provides N (pyridine) and N' and N'' (carboxamide and 1,2-phenylenediamide, respectively) and O (phenolate) donor sites. Cyclic voltammetry on the parent complex [Ni(L2)] 1 in CH2Cl2 established a three-membered electron-transfer series (oxidative response at E1/2 = 0.57 V and reductive response at -0.32 V vs. SCE) consisting of neutral, monocationic and monoanionic [Ni(L2)]z (z = 0, 1+ and 1-). Oxidation of 1 with AgSbF6 affords [Ni(L2)](SbF6) (2) and reduction of 1 with cobaltocene yields [Co(η5-C5H5)2][Ni(L2)] (3). The molecular structures of 1·CH3CN, 2·0.5CH2Cl2 and 3·C6H6 have been determined by X-ray crystallography at 100 K. Characterization by 1H NMR, X-band EPR (gav = 2.006 (solid); 2.008 (CH2Cl2-C6H5CH3 glass); 80 K) and UV-VIS-NIR spectral properties established that 1, 2 and 3 have [NiII{(L2)˙2-}], [NiII{(L2)-}]+/1+ and [NiII{(L2)3-}]-/1- electronic states, respectively. Thus, the redox processes are ligand-centred. While 1 possesses paramagnetic St (total spin) = 1/2, 2 and 3 possess diamagnetic ground-state St = 0. Interestingly, the variable-temperature (2-300 K) magnetic measurement reveals that 1 with the St = 1/2 ground state attains the antiferromagnetic St = 0 state at a very low temperature, due to weak noncovalent interactions via π-π stacking. Density functional theory (DFT) electronic structural calculations at the B3LYP level of theory rationalized the experimental results. In the UV-VIS-NIR spectra, broad absorptions are recorded for 1 and 2 in the range of 800-1600 nm; however, such an absorption is absent for 3. Time-dependent (TD)-DFT calculations provide a very good fit with the experimental spectra and allow us to identify the observed electronic transitions.
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Affiliation(s)
- Narottam Mukhopadhyay
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal 741 246, India
| | - Arunava Sengupta
- Department of Chemistry, Techno India University, West Bengal, Kolkata 700091, India
| | - Aswin Kottapurath Vijay
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal 741 246, India
| | - Francesc Lloret
- Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMOL), Universitat de València, Polígono de la Coma, s/n, 46980 Paterna, València, Spain
| | - Rabindranath Mukherjee
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India.
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Pashanova KI, Poddel'sky AI, Piskunov AV. Complexes of “late” transition metals of the 3d row based on functionalized o-iminobenzoquinone type ligands: Interrelation of molecular and electronic structure, magnetic behaviour. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2021.214399] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Ranjan R, Kundu BK, Kyarikwal R, Ganguly R, Mukhopadhyay S. Synthesis of Cu(II) complexes by N,O‐donor ligand transformation and their catalytic role in visible‐light‐driven alcohol oxidation. Appl Organomet Chem 2021. [DOI: 10.1002/aoc.6450] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Rishi Ranjan
- Department of Chemistry, School of Basic Sciences Indian Institute of Technology Indore Indore India
| | - Bidyut Kumar Kundu
- Department of Chemistry, School of Applied Science Centurion University of Technology and Management Bhubaneswar India
| | - Reena Kyarikwal
- Department of Chemistry, School of Basic Sciences Indian Institute of Technology Indore Indore India
| | - Rakesh Ganguly
- Department of Chemistry Shiv Nadar University Greater Noida India
| | - Suman Mukhopadhyay
- Department of Chemistry, School of Basic Sciences Indian Institute of Technology Indore Indore India
- Department of Biosciences and Biomedical Engineering, School of Engineering Indian Institute of Technology Indore Indore India
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Chatterjee S, Banerjee S, Jana RD, Bhattacharya S, Chakraborty B, Jannuzzi SAV. Tuning the stereoelectronic factors of iron(II)-2-aminophenolate complexes for the reaction with dioxygen: oxygenolytic C-C bond cleavage vs. oxidation of complex. Dalton Trans 2021; 50:1901-1912. [PMID: 33475662 DOI: 10.1039/d0dt03316b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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 [(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 N3 ligand (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 -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).
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Affiliation(s)
- Sayanti Chatterjee
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
| | - Sridhar Banerjee
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
| | - Rahul Dev Jana
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
| | - Shrabanti Bhattacharya
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
| | - Biswarup Chakraborty
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
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Traore ES, Li J, Chiura T, Geng J, Sachla AJ, Yoshimoto F, Eichenbaum Z, Davis I, Mak PJ, Liu A. Heme Binding to HupZ with a C-Terminal Tag from Group A Streptococcus. Molecules 2021; 26:549. [PMID: 33494451 PMCID: PMC7865249 DOI: 10.3390/molecules26030549] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/14/2021] [Accepted: 01/16/2021] [Indexed: 12/23/2022] Open
Abstract
HupZ is an expected heme degrading enzyme in the heme acquisition and utilization pathway in Group A Streptococcus. The isolated HupZ protein containing a C-terminal V5-His6 tag exhibits a weak heme degradation activity. Here, we revisited and characterized the HupZ-V5-His6 protein via biochemical, mutagenesis, protein quaternary structure, UV-vis, EPR, and resonance Raman spectroscopies. The results show that the ferric heme-protein complex did not display an expected ferric EPR signal and that heme binding to HupZ triggered the formation of higher oligomeric states. We found that heme binding to HupZ was an O2-dependent process. The single histidine residue in the HupZ sequence, His111, did not bind to the ferric heme, nor was it involved with the weak heme-degradation activity. Our results do not favor the heme oxygenase assignment because of the slow binding of heme and the newly discovered association of the weak heme degradation activity with the His6-tag. Altogether, the data suggest that the protein binds heme by its His6-tag, resulting in a heme-induced higher-order oligomeric structure and heme stacking. This work emphasizes the importance of considering exogenous tags when interpreting experimental observations during the study of heme utilization proteins.
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Affiliation(s)
- Ephrahime S. Traore
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249, USA; (E.S.T.); (J.L.); (F.Y.); (I.D.)
| | - Jiasong Li
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249, USA; (E.S.T.); (J.L.); (F.Y.); (I.D.)
| | - Tapiwa Chiura
- Department of Chemistry, Saint Louis University, St. Louis, MO 63103, USA;
| | - Jiafeng Geng
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, USA;
| | - Ankita J. Sachla
- Department of Biology, Georgia State University, Atlanta, GA 30302, USA; (A.J.S.); (Z.E.)
| | - Francis Yoshimoto
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249, USA; (E.S.T.); (J.L.); (F.Y.); (I.D.)
| | - Zehava Eichenbaum
- Department of Biology, Georgia State University, Atlanta, GA 30302, USA; (A.J.S.); (Z.E.)
| | - Ian Davis
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249, USA; (E.S.T.); (J.L.); (F.Y.); (I.D.)
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, USA;
| | - Piotr J. Mak
- Department of Chemistry, Saint Louis University, St. Louis, MO 63103, USA;
| | - Aimin Liu
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249, USA; (E.S.T.); (J.L.); (F.Y.); (I.D.)
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, USA;
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Paul GC, Sarkar P, Sarmah A, Shaw P, Maity S, Mukherjee C. A combined experimental and theoretical study on a single, unsupported oxo-bridged Mn(III,III) dimer coordinated to two iminobenzosemiquinone π-radical anions. Dalton Trans 2021; 50:8768-8775. [PMID: 34085670 DOI: 10.1039/d1dt00489a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ligand H2LAP comprises a non-innocent 2-aminophenol unit and an innocent bis(pyridin-2-ylmethyl)amine unit. The ligand, upon reaction with an equivalent amount of Mn(ClO4)2·6H2O in the presence of Et3N under air in MeOH, provided a mono(oxo)-bridged dinuclear Mn2 complex ({[(LISQ)MnIII-O-MnIII(LISQ)][(ClO4)]2}; 1). X-ray crystal structure analysis of complex 1 revealed that in the dicationic unit, the physical oxidation state of each Mn ion was +III and the 2-aminophenol unit of ligand H2LAP was in its one-electron oxidized iminobenzosemiquinone form. 1H-NMR measurement of complex 1 confirmed that the complex acquired a diamagnetic ground state (St = 0). Thus, antiferromagnetic couplings among the paramagnetic centers were realized. The UV-Vis-NIR spectrum of complex 1 was consisted of ligand-to-metal charge-transfer transitions in the visible region, while ligand-to-metal and metal-to-ligand charge-transfer transitions were noticed in the near-infrared region due to the presence of iminobenzosemiquinone radical units. The cyclic voltammogram of the complex showed three one-electron oxidation waves and two one-electron reduction waves. While the first two oxidation processes were metal-based, the two successive reductions were ligand-centered. DFT-based theoretical studies confirmed the assignment.
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Affiliation(s)
- Ganesh Chandra Paul
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India. and Department of Chemistry, ICFAI Science School, ICFAI University Tripura, Agartala, 799210, Tripura(W), India
| | - Prasenjit Sarkar
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.
| | - Amrit Sarmah
- Department of Molecular Modelling, Institute of Organic Chemistry and Biochemistry ASCR, v.v.i. Flemingovo nám. 2, CZ-166 10 Prague 6, Czech Republic and Regional Centre of Advanced Technologies and Materials, Faculty of Science, Palacký University Olomouc, 78371 Olomouc, Czech Republic
| | - Prantick Shaw
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.
| | - Suvendu Maity
- Department of Chemistry, R. K. Mission Residential College, Narendrapur, Kolkata, 700103, India
| | - Chandan Mukherjee
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.
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Ershova IV, Piskunov AV. Complexes of Group III Metals based on o-Iminoquinone Ligands. RUSS J COORD CHEM+ 2020. [DOI: 10.1134/s1070328420030021] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Credendino L, Sproules S. Modulating Iron Spin States with Radical Ligands: A Density Functional Theoretical Study. ASIAN J ORG CHEM 2020. [DOI: 10.1002/ajoc.201900626] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Stephen Sproules
- WestCHEM School of ChemistryUniversity of Glasgow Glasgow G12 8QQ UK
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Fujita D, Kaga A, Sugimoto H, Morimoto Y, Itoh S. Controlling Coordination Number of Rhodium(III) Complex by Ligand-Based Redox for Catalytic C–H Amination. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2020. [DOI: 10.1246/bcsj.20190291] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Daiki Fujita
- Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Akira Kaga
- Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hideki Sugimoto
- Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Yuma Morimoto
- Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Shinobu Itoh
- Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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Rajput A, Saha A, Barman SK, Lloret F, Mukherjee R. [Cu II{(L ISQ)˙ -} 2] (H 2L: thioether-appended o-aminophenol ligand) monocation triggers change in donor site from N 2O 2 to N 2O (2)S and valence-tautomerism. Dalton Trans 2019; 48:1795-1813. [PMID: 30644480 DOI: 10.1039/c8dt03778g] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Using a potentially tridentate o-aminophenol-based redox-active ligand H2L1 (2-[2-(benzylthio)phenylamino]-4,6-di-tert-butylphenol) in its deprotonated form, [Cu(L1)2] has been synthesized and crystallized as [CuII(L1)2]·CH2Cl2 (1·CH2Cl2). A cyclic voltammetry experiment (in CH2Cl2; V vs. SCE (saturated calomel electrode)) on 1·CH2Cl2 exhibits two oxidative (E = 0.20 V (peak-to-peak separation, ΔEp = 100 mV) and E = 0.90 V (ΔEp = 140 mV)) and two reductive (E = -0.52 V (ΔEp = 110 mV) and E = -0.92 V (ΔEp = 120 mV)) responses. Upon oxidation using a stoichiometric amount of [FeIII(η5-C5H5)2](PF6), 1·CH2Cl2 yielded [Cu(L1)2](PF6) (2). Structural analysis (100 K) reveals that 1·CH2Cl2 is a four-coordinate bis(iminosemiquinonato)copper(ii) complex (CuN2O2 coordination), and that the thioethers remain uncoordinated. The twisted geometry of 1 (distorted tetrahedral) results in considerable changes in the electronic structure, compared to well-known square-planar analogues. Crystallographic analysis of 2 both at 100 K and at 293 K reveals that it is effectively a four-coordinate complex with a CuN2OS coordination; however, a substantial interaction with the other phenolate O is observed. The metal-ligand bond distances and metric parameters associated with the o-aminophenolate rings indicate a valence-tautomeric (VT) equilibrium involving monocationic (iminosemiquinonato)(iminoquinone)copper(ii) and bis(iminoquinone)copper(i). Complex 1·CH2Cl2 is a three-spin system and a magnetic study (4-300 K) established that it has a S = 1/2 ground-state, owing to the strong antiferromagnetic coupling between the unpaired spin of the copper(ii) and the iminosemiquinonate(1-) π-radical anion. Electron paramagnetic resonance (EPR) spectral studies corroborate this result. Complex 2 is diamagnetic and the existence of VT in 2 was probed using variable-temperature (248-328 K) 1H NMR and EPR (100-298 K) spectral measurements and X-ray photoelectron spectroscopic studies at 298 K. Remarkably, modification of the well-studied 2-anilino-4,6-di-tert-butylphenol by incorporation of a benzylthioether arm leads to the occurrence of VT in 2. The electronic structure of 1·CH2Cl2 and 2 has been assigned using density functional theory (DFT) calculations at the B3LYP-D3 level of theory. Time-dependent (TD)-DFT calculations have been performed to elucidate the origin of the observed UV-VIS-NIR absorptions.
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Affiliation(s)
- Amit Rajput
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India. and Department of Basic and Applied Sciences, School of Engineering, G. D. Goenka University, Sohna Road, Gurugram 122 103, Haryana, India
| | - Anannya Saha
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 246, India
| | - Suman K Barman
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India.
| | - Francesc Lloret
- Departament de Quımíca, Inorgànica/Instituto de Ciencia Molecular (ICMOL), Universitat de Valeńcia, Polígono de la Coma, s/n, 46980-Paterna, València, Spain
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Paul GC, Sarkar P, Mukherjee C. Effect of H-bond and molecular geometry towards innocent and non-innocent behavior of 3,5-di-tert-butyl-2-aminophenol units attached to a piperazine backbone: Co(III) and Cu(II) complexes. Inorganica Chim Acta 2019. [DOI: 10.1016/j.ica.2018.10.048] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Rajput A, Sharma AK, Barman SK, Lloret F, Mukherjee R. Six-coordinate [Co III(L) 2] z (z = 1-, 0, 1+) complexes of an azo-appended o-aminophenolate in amidate(2-) and iminosemiquinonate π-radical (1-) redox-levels: the existence of valence-tautomerism. Dalton Trans 2018; 47:17086-17101. [PMID: 30465680 DOI: 10.1039/c8dt03257b] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Aerobic reaction of the ligand H2L1, 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol, CoCl2·6H2O and Et3N in MeOH under refluxing conditions produces, after work-up and recrystallization, black crystals of [Co(L1)2] (1). When examined by cyclic voltammetry, 1 displays in CH2Cl2 three one-electron redox responses: two oxidative, E11/2 = 0.30 V (peak-to-peak separation, ΔEp = 100 mV) and E21/2 = 1.04 V (ΔEp = 120 mV), and one reductive E1/2 = -0.27 V (ΔEp = 120 mV) vs. SCE. Consequently, 1 is chemically oxidized by 1 equiv. of [FeIII(η5-C5H5)2][PF6], affording the isolation of deep purple crystals of [Co(L1)2][PF6]·2CH2Cl2 (2), and one-electron reduction with [CoII(η5-C5H5)2] yielded bluish-black crystals of [CoIII(η5-C5H5)2][Co(L1)2]·MeCN (3). A solid sample of 1 exhibits temperature-independent (50-300 K) magnetism, revealing the presence of a free radical (S = 1/2), which exhibits an isotropic EPR signal (g = 2.003) at 298 K and at 77 K an eight-line feature characteristic of hyperfine-interaction of the radical with the Co (I = 7/2) nucleus. Based on X-ray structural parameters of 1-3 at 100 K, magnetic and EPR spectral behaviour of 1, and variable-temperature (233-313 K) 1H NMR spectral features of 1-3 and 13C NMR spectra at 298 K of 2 and 3 in CDCl3 point to the electronic structure of the complexes as either [CoIII{(LAP)2-}{(LISQ)}˙-] or [CoIII{(L1)2}˙3-] (delocalized nature favours the latter description) (1), [CoIII{(LISQ)˙-}2][PF6]·2CH2Cl2 (2) and [CoIII(η5-C5H5)2][CoIII{(LAP)2-}2]·MeCN (3) [(LAP)2- and (LISQ)˙- represent the redox-level of coordinated ligands o-amidophenolate(2-) ion and o-iminobenzosemiquinonate(1-) π-radical ion, respectively]. Notably, all the observed redox processes are ligand-centred. To the best of our knowledge, this is the first time that six-coordinate complexes of a common tridentate o-aminophenolate-based ligand have been structurally characterized for the parent 1, its monocation 2 and the monoanion 3 counterparts. Temperature-dependent 1H NMR spectra reveal the existence of valence-tautomeric equilibria in 1-3. Density Functional Theory (DFT) calculations at the B3LYP-level of theory corroborate the electronic structural assignment of 1-3 from experimental data. The origins of the observed UV-VIS-NIR absorptions for 1-3 have been assigned, based on time-dependent (TD)-DFT calculations.
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Affiliation(s)
- Amit Rajput
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India.
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Mondal S, Bera S, Maity S, Ghosh P. Cobalt Ion Promoted Redox Cascade: A Route to Spiro Oxazine-Oxazepine Derivatives and a Dinuclear Cobalt(III) Complex of an N-(1,4-Naphthoquinone)-o-aminophenol Derivative. Inorg Chem 2017; 56:13194-13204. [PMID: 29035522 DOI: 10.1021/acs.inorgchem.7b01961] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The study discloses that the redox activity of N-(1,4-naphthoquinone)-o-aminophenol derivatives (LRH2) containing a (phenol)-NH-(1,4-naphthoquinone) fragment is notably different from that of a (phenol)-NH-(phenol) precursor. The former is a platform for a redox cascade. LRH2 is redox noninnocent and exists in Cat-N-(1,4-naphthoquinone)(2-) (LR 2-) and SQ-N-(1,4-naphthoquinone) (LR •-) states in the complexes. Reactions of LRH2 with cobalt(II) salts in MeOH in air promote a cascade affording spiro oxazine-oxazepine derivatives (OXLR) in good yields, when R = H, Me, tBu. Spiro oxazine-oxazepine derivatives are bioactive, and such a molecule has so far not been isolated by a schematic route. In this context this cascade is significant. Dimerization of LRH2 → OXLR in MeOH is a (6H+ + 6e) oxidation reaction and is composed of formations of four covalent bonds and 6-exo-trig and 7-endo-trig cyclization based on C-O coupling reactions, where MeOH is the source of a proton and the ester function. It was established that the active cascade precursor is [(LMe •-)CoIIICl2] (A). Notably, formation of a spiro derivative was not detected in CH3CN and the reaction ends up furnishing A. The route of the reaction is tunable by R, when R = NO2, it is a (2e + 4H+) oxidation reaction affording a dinuclear LR 2- complex of cobalt(III) of the type [(LNO2 2-)2CoIII2(OMe)2(H2O)2] (1) in good yields. No cascade occurs with zinc(II) ion even in MeOH and produces a LMe •- complex of type [(LMe •-)ZnIICl2] (2). The intermediate A and 2 exhibit strong EPR signals at g = 2.008 and 1.999, confrming the existence of LMe •- coordinated to low-spin cobalt(III) and zinc(II) ions. The intermediates of LRH2 → OXLR conversion were analyzed by ESI mass spectrometry. The molecular geometries of OXLR and 1 were confirmed by X-ray crystallography, and the spectral features were elucidated by TD DFT calculations.
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Affiliation(s)
- Sandip Mondal
- Department of Chemistry, R. K. Mission Residential College, Narendrapur , Kolkata 103, West Bengal, India
| | - Sachinath Bera
- Department of Chemistry, R. K. Mission Residential College, Narendrapur , Kolkata 103, West Bengal, India
| | - Suvendu Maity
- Department of Chemistry, R. K. Mission Residential College, Narendrapur , Kolkata 103, West Bengal, India
| | - Prasanta Ghosh
- Department of Chemistry, R. K. Mission Residential College, Narendrapur , Kolkata 103, West Bengal, India
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