1
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Ariafard A, Longhurst M, Swiegers GF, Stranger R. Mechanisms of Mn(V)-Oxo to Mn(IV)-Oxyl Conversion: From Closed-Cubane Photosystem II to Mn(V) Catalysts and the Role of the Entering Ligands. Chemistry 2024; 30:e202400396. [PMID: 38659321 DOI: 10.1002/chem.202400396] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 04/02/2024] [Accepted: 04/20/2024] [Indexed: 04/26/2024]
Abstract
The low activation barrier for O-O coupling in the closed-cubane Oxygen-Evolving Centre (OEC) of Photosystem II (PSII) requires water coordination with the Mn4 'dangler' ion in the Mn(V)-oxo fragment. This coordination transforms the Mn(V)-oxo complex into a more reactive Mn4(IV)-oxyl species, enhancing O-O coupling. This study explains the mechanism behind the coordination and indicates that in the most stable form of the OEC, the Mn4 fragment adopts a trigonal bipyramidal geometry but needs to transition to a square pyramidal form to be activated for O-O coupling. This transition stabilizes the Mn4 dxy orbital, enabling electron transfer from the oxo ligand to the dxy orbital, converting the oxo ligand into an oxyl species. The role of the water is to coordinate with the square pyramidal structure, reducing the energy gap between the oxo and oxyl forms, thereby lowering the activation energy for O-O coupling. This mechanism applies not only to the OEC system but also to other Mn(V)-based catalysts. For other catalysts, ligands such as OH- stabilize the Mn(IV)-oxyl species better than water, improving catalyst activation for reactions like C-H bond activation. This study is the first to explain the Mn(V)-oxo to Mn(IV)-oxyl conversion, providing a new foundation for Mn-based catalyst design.
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Affiliation(s)
- Alireza Ariafard
- Research School of Chemistry, Australian National University, Canberra, Australia
| | - Matthew Longhurst
- Intelligent Polymer Research Institute, University of Wollongong, Wollongong, Australia
| | - Gerhard F Swiegers
- Intelligent Polymer Research Institute, University of Wollongong, Wollongong, Australia
| | - Robert Stranger
- Research School of Chemistry, Australian National University, Canberra, Australia
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2
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Keshari K, Santra A, Velasco L, Sauvan M, Kaur S, Ugale AD, Munshi S, Marco JF, Moonshiram D, Paria S. Functional Model of Compound II of Cytochrome P450: Spectroscopic Characterization and Reactivity Studies of a Fe IV-OH Complex. JACS AU 2024; 4:1142-1154. [PMID: 38559734 PMCID: PMC10976569 DOI: 10.1021/jacsau.3c00844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 02/12/2024] [Accepted: 02/26/2024] [Indexed: 04/04/2024]
Abstract
Herein, we show that the reaction of a mononuclear FeIII(OH) complex (1) with N-tosyliminobenzyliodinane (PhINTs) resulted in the formation of a FeIV(OH) species (3). The obtained complex 3 was characterized by an array of spectroscopic techniques and represented a rare example of a synthetic FeIV(OH) complex. The reaction of 1 with the one-electron oxidizing agent was reported to form a ligand-oxidized FeIII(OH) complex (2). 3 revealed a one-electron reduction potential of -0.22 V vs Fc+/Fc at -15 °C, which was 150 mV anodically shifted than 2 (Ered = -0.37 V vs Fc+/Fc at -15 °C), inferring 3 to be more oxidizing than 2. 3 reacted spontaneously with (4-OMe-C6H4)3C• to form (4-OMe-C6H4)3C(OH) through rebound of the OH group and displayed significantly faster reactivity than 2. Further, activation of the hydrocarbon C-H and the phenolic O-H bond by 2 and 3 was compared and showed that 3 is a stronger oxidant than 2. A detailed kinetic study established the occurrence of a concerted proton-electron transfer/hydrogen atom transfer reaction of 3. Studying one-electron reduction of 2 and 3 using decamethylferrocene (Fc*) revealed a higher ket of 3 than 2. The study established that the primary coordination sphere around Fe and the redox state of the metal center is very crucial in controlling the reactivity of high-valent Fe-OH complexes. Further, a FeIII(OMe) complex (4) was synthesized and thoroughly characterized, including X-ray structure determination. The reaction of 4 with PhINTs resulted in the formation of a FeIV(OMe) species (5), revealing the presence of two FeIV species with isomer shifts of -0.11 mm/s and = 0.17 mm/s in the Mössbauer spectrum and showed FeIV/FeIII potential at -0.36 V vs Fc+/Fc couple in acetonitrile at -15 °C. The reactivity studies of 5 were investigated and compared with the FeIV(OH) complex (3).
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Affiliation(s)
- Kritika Keshari
- Department
of Chemistry, Indian Institute of Technology
Delhi, Hauz Khas, New Delhi 110016, India
| | - Aakash Santra
- Department
of Chemistry, Indian Institute of Technology
Delhi, Hauz Khas, New Delhi 110016, India
| | - Lucía Velasco
- Instituto
de Ciencia de Materiales de Madrid, Consejo
Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Maxime Sauvan
- Instituto
de Ciencia de Materiales de Madrid, Consejo
Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Simarjeet Kaur
- Department
of Chemistry, Indian Institute of Technology
Delhi, Hauz Khas, New Delhi 110016, India
| | - Ashok D. Ugale
- Instituto
de Ciencia de Materiales de Madrid, Consejo
Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Sandip Munshi
- School
of Chemical Science, Indian Association
for the Cultivation of Science, Raja S C Mulliick Road, Kolkata 700032, India
| | - J. F. Marco
- Instituto
de Quimica Fisica Blas Cabrera, Consejo
Superior de Investigaciones Científicas, C. de Serrano, 119, Serrano, Madrid 28006, Spain
| | - Dooshaye Moonshiram
- Instituto
de Ciencia de Materiales de Madrid, Consejo
Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Sayantan Paria
- Department
of Chemistry, Indian Institute of Technology
Delhi, Hauz Khas, New Delhi 110016, India
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3
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Bera M, Kaur S, Keshari K, Santra A, Moonshiram D, Paria S. Structural and Spectroscopic Characterization of Copper(III) Complexes and Subsequent One-Electron Oxidation Reaction and Reactivity Studies. Inorg Chem 2023; 62:5387-5399. [PMID: 36972560 DOI: 10.1021/acs.inorgchem.2c04168] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
Abstract
The formation of Cu(III) species are often invoked as the key intermediate in Cu-catalyzed organic transformation reactions. In this study, we synthesized Cu(II) (1) and Cu(III) (3) complexes supported by a bisamidate-bisalkoxide ligand consisting of an ortho-phenylenediamine (o-PDA) scaffold and characterized them through an array of spectroscopic techniques, including UV-visible, electron paramagnetic resonance, X-ray crystallography, and 1H nuclear magnetic resonance (NMR) and X-ray absorption spectroscopy. The Cu-N/O bond distances in 3 are ∼0.1 Å reduced compared to 1, implying a significant increase in 3's overall effective nuclear charge. Further, a Cu(III) complex (4) of a bisamidate-bisalkoxide ligand containing a trans-cyclohexane-1,2-diamine moiety exhibits nearly identical Cu-N/O bond distances to that of 3, inferring that the redox-active o-PDA backbone is not oxidized upon one-electron oxidation of the Cu(II) complex (1). In addition, a considerable difference in the 1s → 4p and 1s → 3d transition energy was observed in the X-ray absorption near-edge structure data of 3 vs 1, which is typical for the metal-centered oxidation process. Electrochemical measurements of the Cu(II) complex (1) in acetonitrile exhibited two consecutive redox couples at -0.9 and 0.4 V vs the Fc+/Fc reference electrode. One-electron oxidation reaction of 3 further resulted in the formation of a ligand-oxidized Cu complex (3a), which was characterized in depth. Reactivity studies of species 3 and 3a were explored toward the activation of the C-H/O-H bonds. A bond dissociation free energy (BDFE) value of ∼69 kcal/mol was estimated for the O-H bond of the Cu(II) complex formed upon transfer of hydrogen atom to 3. The study represents a thorough spectroscopic characterization of high-valent Cu complexes and sheds light on the PCET reactivity studies of Cu(III) complexes.
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Affiliation(s)
- Moumita Bera
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Simarjeet Kaur
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Kritika Keshari
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Aakash Santra
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Dooshaye Moonshiram
- Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
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4
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Bera M, Kaur S, Keshari K, Moonshiram D, Paria S. Characterization of Reaction Intermediates Involved in the Water Oxidation Reaction of a Molecular Cobalt Complex. Inorg Chem 2022; 61:21035-21046. [PMID: 36517453 DOI: 10.1021/acs.inorgchem.2c03559] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Molecular cobalt(III) complexes of bis-amidate-bis-alkoxide ligands, (Me4N)[CoIII(L1)] (1) and (Me4N)[CoIII(L2)] (2), are synthesized and assessed through a range of characterization techniques. Electrocatalytic water oxidation activity of the Co complexes in a 0.1 M phosphate buffer solution revealed a ligand-centered 2e-/1H+ transfer event at 0.99 V followed by catalytic water oxidation (WO) at an onset overpotential of 450 mV. By contrast, 2 reveals a ligand-based oxidation event at 0.9 V and a WO onset overpotential of 430 mV. Constant potential electrolysis study and rinse test experiments confirm the homogeneous nature of the Co complexes during WO. The mechanistic investigation further shows a pH-dependent change in the reaction pathway. On the one hand, below pH 7.5, two consecutive ligand-based oxidation events result in the formation of a CoIII(L2-)(OH) species, which, followed by a proton-coupled electron transfer reaction, generates a CoIV(L2-)(O) species that undergoes water nucleophilic attack to form the O-O bond. On the other hand, at higher pH, two ligand-based oxidation processes merge together and result in the formation of a CoIII(L2-)(OH) complex, which reacts with OH- to yield the O-O bond. The ligand-coordinated reaction intermediates involved in the WO reaction are thoroughly studied through an array of spectroscopic techniques, including UV-vis absorption spectroscopy, electron paramagnetic resonance, and X-ray absorption spectroscopy. A mononuclear CoIII(OH) complex supported by the one-electron oxidized ligand, [CoIII(L3-)(OH)]-, a formal CoIV(OH) complex, has been characterized, and the compound was shown to participate in the hydroxide rebound reaction, which is a functional mimic of Compound II of Cytochrome P450.
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Affiliation(s)
- Moumita Bera
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi110016, India
| | - Simarjeet Kaur
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi110016, India
| | - Kritika Keshari
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi110016, India
| | - Dooshaye Moonshiram
- Consejo Superior de Investigaciones Científicas, Instituto de Ciencia de Materiales de Madrid, Sor Juana Inés de la Cruz, 3, 28049Madrid, Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi110016, India
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5
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Hong YH, Lee YM, Nam W, Fukuzumi S. Reaction Intermediates in Artificial Photosynthesis with Molecular Catalysts. ACS Catal 2022. [DOI: 10.1021/acscatal.2c05033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Young Hyun Hong
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul03760, Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul03760, Korea
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul03760, Korea
| | - Shunichi Fukuzumi
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul03760, Korea
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6
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Zhang J, Lee YM, Seo MS, Nilajakar M, Fukuzumi S, Nam W. A Contrasting Effect of Acid in Electron Transfer, Oxygen Atom Transfer, and Hydrogen Atom Transfer Reactions of a Nickel(III) Complex. Inorg Chem 2022; 61:19735-19747. [PMID: 36445726 DOI: 10.1021/acs.inorgchem.2c02504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
There have been many examples of the accelerating effects of acids in electron transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. Herein, we report a contrasting effect of acids in the ET, OAT, and HAT reactions of a nickel(III) complex, [NiIII(PaPy3*)]2+ (1) in acetone/CH3CN (v/v 19:1). 1 was synthesized by reacting [NiII(PaPy3*)]+ (2) with magic blue or iodosylbenzene in the absence or presence of triflic acid (HOTf), respectively. Sulfoxidation of thioanisole by 1 and H2O occurred in the presence of HOTf, and the reaction rate increased proportionally with increasing concentration of HOTf ([HOTf]). The rate of ET from diacetylferrocene to 1 also increased linearly with increasing [HOTf]. In contrast, HAT from 9,10-dihydroanthracene (DHA) to 1 slowed down with increasing [HOTf], exhibiting an inversely proportional relation to [HOTf]. The accelerating effect of HOTf in the ET and OAT reactions was ascribed to the binding of H+ to the PaPy3* ligand of 2; the one-electron reduction potential (Ered) of 1 was positively shifted with increasing [HOTf]. Such a positive shift in the Ered value resulted in accelerating the ET and OAT reactions that proceeded via the rate-determining ET step. On the other hand, the decelerating effect of HOTf on HAT from DHA to 1 resulted from the inhibition of proton transfer from DHA•+ to 2 due to the binding of H+ to the PaPy3* ligand of 2. The ET reactions of 1 in the absence and presence of HOTf were well analyzed in light of the Marcus theory of ET in comparison with the HAT reactions.
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Affiliation(s)
- Jisheng Zhang
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Mi Sook Seo
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Madhuri Nilajakar
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Shunichi Fukuzumi
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
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7
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Kaur S, Bera M, Santra A, Munshi S, Sterbinsky GE, Wu T, Moonshiram D, Paria S. Effect of Redox-Inactive Metal Ion-Nickel(III) Interactions on the Redox Properties and Proton-Coupled Electron Transfer Reactivity. Inorg Chem 2022; 61:14252-14266. [PMID: 36041064 DOI: 10.1021/acs.inorgchem.2c01472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mononuclear nickel(II) and nickel(III) complexes of a bisamidate-bisalkoxide ligand, (NMe4)2[NiII(HMPAB)] (1) and (NMe4)[NiIII(HMPAB)] (2), respectively, have been synthesized and characterized by various spectroscopic techniques including X-ray crystallography. The reaction of redox-inactive metal ions (Mn+ = Ca2+, Mg2+, Zn2+, Y3+, and Sc3+) with 2 resulted in 2-Mn+ adducts, which was assessed by an array of spectroscopic techniques including X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and reactivity studies. The X-ray structure of Ca2+ coordinated to Ni(III) complexes, 2-Ca2+T, was determined and exhibited an average Ni-Ca distance of 3.1253 Å, close to the metal ions' covalent radius. XAS analysis of 2-Ca2+ and 2-Y3+ in solution further revealed an additional coordination to Ca and Y in the 2-Mn+ adducts with shortened Ni-M distances of 2.15 and 2.11 Å, respectively, implying direct bonding interactions between Ni and Lewis acids (LAs). Such a short interatomic distance between Ni(III) and M is unprecedented and was not observed before. EPR analysis of 2 and 2-Mn+ species, moreover, displayed rhombic signals with gav > 2.12 for all complexes, supporting the +III oxidation state of Ni. The NiIII/NiII redox potential of 2 and 2-Mn+ species was determined, and a plot of E1/2 of 2-Mn+ versus pKa of [M(H2O)n]m+ exhibited a linear relationship, implying that the NiIII/NiII potential of 2 can be tuned with different redox-inactive metal ions. Reactivity studies of 2 and 2-Mn+ with different 4-X-2,6-ditert-butylphenol (4-X-DTBP) and other phenol derivatives were performed, and based on kinetic studies, we propose the involvement of a proton-coupled electron transfer (PCET) pathway. Analysis of the reaction products after the reaction of 2 with 4-OMe-DTBP showed the formation of a Ni(II) complex (1a) where one of the alkoxide arms of the ligand is protonated. A pKa value of 24.2 was estimated for 1a. The reaction of 2-Mn+ species was examined with 4-OMe-DTBP, and it was observed that the k2 values of 2-Mn+ species increase by increasing the Lewis acidity of redox-inactive metal ions. However, the obtained k2 values for 2-Mn+ species are much lower compared to the k2 value for 2. Such a variation of PCET reactivity between 2 and 2-Mn+ species may be attributed to the interactions between Ni(III) and LAs. Our findings show the significance of the secondary coordination sphere effect on the PCET reactivity of Ni(III) complexes and furnish important insights into the reaction mechanism involving high-valent nickel species, which are frequently invoked as key intermediates in Ni-mediated enzymatic reactions, solar-fuel catalysis, and biomimetic/synthetic transformation reactions.
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Affiliation(s)
- Simarjeet Kaur
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Moumita Bera
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Aakash Santra
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Sandip Munshi
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
| | - George E Sterbinsky
- X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
| | - Tianpin Wu
- X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
| | - Dooshaye Moonshiram
- Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
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