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Kumar M, Gupta MK, Ansari M, Ansari A. C-H bond activation by high-valent iron/cobalt-oxo complexes: a quantum chemical modeling approach. Phys Chem Chem Phys 2024; 26:4349-4362. [PMID: 38235511 DOI: 10.1039/d3cp05866b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
High-valent metal-oxo species serve as key intermediates in the activation of inert C-H bonds. Here, we present a comprehensive DFT analysis of the parameters that have been proposed as influencing factors in modeled high-valent metal-oxo mediated C-H activation reactions. Our approach involves utilizing DFT calculations to explore the electronic structures of modeled FeIVO (species 1) and CoIVO ↔ CoIII-O˙ (species 2), scrutinizing their capacity to predict improved catalytic activity. DFT and DLPNO-CCSD(T) calculations predict that the iron-oxo species possesses a triplet as the ground state, while the cobalt-oxo has a doublet as the ground state. Furthermore, we have investigated the mechanistic pathways for the first C-H bond activation, as well as the desaturation of the alkanes. The mechanism was determined to be a two-step process, wherein the first hydrogen atom abstraction (HAA) represents the rate-limiting step, involving the proton-coupled electron transfer (PCET) process. However, we found that the second HAA step is highly exothermic for both species. Our calculations suggest that the iron-oxo species (Fe-O = 1.672 Å) exhibit relatively sluggish behavior compared to the cobalt-oxo species (Co-O = 1.854 Å) in C-H bond activation, attributed to a weak metal-oxygen bond. MO, NBO, and deformation energy analysis reveal the importance of weakening the M-O bond in the cobalt species, thereby reducing the overall barrier to the reaction. This catalyst was found to have a C-H activation barrier relatively smaller than that previously reported in the literature.
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Affiliation(s)
- Manjeet Kumar
- Department of Chemistry, Central University of Haryana, Mahendergarh-123031, Haryana, India.
| | - Manoj Kumar Gupta
- Department of Chemistry, Central University of Haryana, Mahendergarh-123031, Haryana, India.
| | - Mursaleem Ansari
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
| | - Azaj Ansari
- Department of Chemistry, Central University of Haryana, Mahendergarh-123031, Haryana, India.
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2
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Britto NJ, Sen A, Rajaraman G. Unravelling the Effect of Acid-Driven Electron Transfer in High-Valent Fe IV =O/Mn IV =O Species and Its Implications for Reactivity. Chem Asian J 2023; 18:e202300773. [PMID: 37855305 DOI: 10.1002/asia.202300773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 10/12/2023] [Accepted: 10/16/2023] [Indexed: 10/20/2023]
Abstract
The electron transfer (ET) step is one of the crucial processes in biochemical redox reactions that occur in nature and has been established as a key step in dictating the reactivity of high-valent metal-oxo species. Although metalloenzymes possessing metal-oxo units at their active site are typically associated with outer-sphere electron transfer (OSET) processes, biomimetic models, in contrast, have been found to manifest either an inner-sphere electron transfer (ISET) or OSET mechanism. This distinction is clearly illustrated through the behaviour of [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) complexes, where complex 1 showcases an OSET mechanism, while complex 2 exhibits an ISET mechanism, especially evident in their reactions involving C-H bond activation and oxygen atom transfer reactions in the presence of a Lewis/Bronsted acid. However, the precise reason for this puzzling difference remains elusive. This work unveils the origin of the perplexing inner-sphere vs outer-sphere electron transfer process (ISET vs OSET) in [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) species in the presence of Bronsted acid. The calculations indicate that when the substrate (toluene) approaches both 1 and 2 that is hydrogen bonded with two HOTf molecules (denoted as 1-HOTf and 2-HOTf, respectively), proton transfer from one of the HOTf molecules to the metal-oxo unit is triggered and a simultaneous electron transfer occurs from toluene to the metal centre. Interestingly, the preference for OSET by 1-HOTf is found to originate from the choice of MnIV =O centre to abstract spin-down (β) electron from toluene to its δ(dxy ) orbital. On the other hand, in 2-HOTf, a spin state inversion from triplet to quintet state takes place during the proton (from HOTf) coupled electron transfer (from toluene) preferring a spin-up (α) electron abstraction to its σ* (dz 2 ) orbital mediated by HOTf giving rise to ISET. In addition, 2-HOTf was calculated to possess a larger reorganisation energy, which facilitates the ISET process via the acid. The absence of spin-inversion and smaller reorganisation energy switch the mechanism to OSET for 1-HOTf. Therefore, for the first time, the significance of spin-state and spin-inversion in the electron transfer process has been identified and demonstrated within the realm of high-valent metal-oxo chemistry. This discovery holds implications for the potential involvement of high-valent Mn-oxo species in performing similar transformative processes within Photosystem II.
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Affiliation(s)
| | - Asmita Sen
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400 076, India
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400 076, India
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3
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Singh P, Lee Y, Mayfield JR, Singh R, Denler MC, Jones SD, Day VW, Nordlander E, Jackson TA. Enhanced Understanding of Structure-Function Relationships for Oxomanganese(IV) Complexes. Inorg Chem 2023; 62:18357-18374. [PMID: 37314463 DOI: 10.1021/acs.inorgchem.3c00600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
A series of manganese(II) and oxomanganese(IV) complexes supported by neutral, pentadentate ligands with varied equatorial ligand-field strength (N3pyQ, N2py2I, and N4pyMe2) were synthesized and then characterized using structural and spectroscopic methods. On the basis of electronic absorption spectroscopy, the [MnIV(O)(N4pyMe2)]2+ complex has the weakest equatorial ligand field among a set of similar MnIV-oxo species. In contrast, [MnIV(O)(N2py2I)]2+ shows the strongest equatorial ligand-field strength for this same series. We examined the influence of these changes in electronic structure on the reactivity of the oxomanganese(IV) complexes using hydrocarbons and thioanisole as substrates. The [MnIV(O)(N3pyQ)]2+ complex, which contains one quinoline and three pyridine donors in the equatorial plane, ranks among the fastest MnIV-oxo complexes in C-H bond and thioanisole oxidation. While a weak equatorial ligand field has been associated with high reactivity, the [MnIV(O)(N4pyMe2)]2+ complex is only a modest oxidant. Buried volume plots suggest that steric factors dampen the reactivity of this complex. Trends in reactivity were examined using density functional theory (DFT)-computed bond dissociation free energies (BDFEs) of the MnIIIO-H and MnIV ═ O bonds. We observe an excellent correlation between MnIV═O BDFEs and rates of thioanisole oxidation, but more scatter is observed between hydrocarbon oxidation rates and the MnIIIO-H BDFEs.
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Affiliation(s)
- Priya Singh
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Yuri Lee
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Jaycee R Mayfield
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Reena Singh
- Lund University, Chemical Physics, Department of Chemistry, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Melissa C Denler
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Shannon D Jones
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Victor W Day
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Ebbe Nordlander
- Lund University, Chemical Physics, Department of Chemistry, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Timothy A Jackson
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
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Kumar M, Ansari M, Ansari A. Electronic, geometrical and photophysical facets of five coordinated porphyrin N-heterocyclic carbene transition metals complexes: A theoretical study. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 284:121774. [PMID: 36081194 DOI: 10.1016/j.saa.2022.121774] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Revised: 07/21/2022] [Accepted: 08/16/2022] [Indexed: 06/15/2023]
Abstract
In the realm of dye sensitized solar cells (DSSCs), the 3d transition metals as photosensitizers are scarcely studied. In the present work, electronic structures, FMO, MEP surfaces, NBO analysis, energetics and photophysical properties of earth abundant metals (Mn, Fe and Co) based metalloporphyrins coordinated with NHC-carbene have been explored by using DFT and TDDFT calculations. According to formation energies and energy decomposition analysis (EDA), the cobalt based metalloporphyrins species are found to be more stable while in contrast manganese based species are predicted as more reactive among all. Also, from the ligation point of view, the TPP (meso-tetraphenylporphyrin) ligand forms more steady and rigid coordination as compare to the TTP (meso-tetratolylporphyrin) ligand. FMO analysis also support these observations. NBO and SNO results support the electronic configurations as well as unveil the controversial bonding pattern of NHCcarbon and metal atom and found that there is σ-bonding present between the metal and the NHCcarbon by the overlapping of sp-hybridized orbitals of carbenecarbon and sp/d hybrid orbital of the metal atom. TDDFT results show that the highest light harvesting efficiency (LHE) of all the studied species is found under the range of 360 nm - 380 nm (λ) and this may due to the presence of longer π-conjugations. In-depth investigation of this work may help to design new robust energy harvesting systems for high energy conversion efficiency based on earth abundance metals. Our results are in well agreement with the available experimental findings.
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Affiliation(s)
- Manjeet Kumar
- Department of Chemistry, Central University of Haryana, Mahendergarh 123031, India
| | - Mursaleem Ansari
- Department of Chemistry, IIT Bombay, Powai, Mumbai 400076, India
| | - Azaj Ansari
- Department of Chemistry, Central University of Haryana, Mahendergarh 123031, India.
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Ansari M, Rajaraman G. Comparative oxidative ability of mononuclear and dinuclear high-valent iron-oxo species towards the activation of methane: does the axial/bridge atom modulate the reactivity? Dalton Trans 2023; 52:308-325. [PMID: 36504243 DOI: 10.1039/d2dt02559k] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Over the years, mononuclear FeIVO species have been extensively studied, but the presence of dinuclear FeIVO species in soluble methane monooxygenase (sMMO) has inspired the development of biomimic models that could activate inert substrates such as methane. There are some successful attempts; particularly the [(Por)(m-CBA) FeIV(μ-N)FeIV(O)(Por˙+)]- species has been reported to activate methane and yield decent catalytic turnover numbers and therefore regarded as the closest to the sMMO enzyme functional model, as no mononuclear FeIVO analogues could achieve this feat. In this work, we have studied a series of mono and dinuclear models using DFT and ab initio DLPNO-CCSD(T) calculations to probe the importance of nuclearity in enhancing the reactivity. We have probed the catalytic activities of four complexes: [(HO)FeIV(O)(Por)]- (1), [(HO)FeIV(O)(Por˙+)] (2), μ-oxo dinuclear iron species [(Por)(m-CBA)FeIV(μ-O)FeIV(O) (Por˙+)]- (3) and N-bridged dinuclear iron species [(Por)(m-CBA)FeIV(μ-N)FeIV(O)(Por˙+)]- (4) towards the activation of methane. Additionally, calculations were performed on the mononuclear models [(X)FeIV(O)(Por˙+)]n {X = N 4a (n = -2), NH 4b (n = -1) and NH24c (n = 0)} to understand the role of nuclearity in the reactivity. DFT calculations performed on species 1-4 suggest an interesting variation among them, with species 1-3 possessing an intermediate spin (S = 1) as a ground state and species 4 possessing a high-spin (S = 2) as a ground state. Furthermore, the two FeIV centres in species 3 and 4 are antiferromagnetically coupled, yielding a singlet state with a distinct difference in their electronic structure. On the other hand, species 2 exhibits a ferromagnetic coupling between the FeIV and the Por˙+ moiety. Our calculations suggest that the higher barriers for the C-H bond activation of methane and the rebound step for species 1 and 3 are very high in energy, rendering them unreactive towards methane, while species 2 and 4 have lower barriers, suggesting their reactivity towards methane. Studies on the system reveal that model 4a has multiple FeN bonds facilitating greater reactivity, whereas the other two models have longer Fe-N bonds and less radical character with steeper barriers. Strong electronic cooperativity is found to be facilitated by the bridging nitride atom, and this cooperativity is suppressed by substituents such as oxygen, rendering them inactive. Thus, our study unravels that apart from enhancing the nuclearity, bridging atoms that facilitate strong cooperation between the metals are required to activate very inert substrates such as methane, and our results are broadly in agreement with earlier experimental findings.
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Affiliation(s)
- Mursaleem Ansari
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India.
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India.
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6
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Srinivasan P, Madhu DK, Pedugu Sivaraman S, Kuppusamy S, Nagarajan S, Rao CB, Kancharlapalli Chinaraga P, Mohan AM, Deivasigamani P. Chromoionophore decorated renewable solid-state polymer monolithic naked eye sensor for the selective sensing and recovery of ultra-trace toxic cadmium ions in aqueous environment. Colloids Surf A Physicochem Eng Asp 2023. [DOI: 10.1016/j.colsurfa.2022.130377] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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7
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Sen A, Kumar R, Rajaraman G. A theoretical perspective on the reactivity of high-valent Mn-Oxo/nitrene species towards oxidative transformations. Inorganica Chim Acta 2022. [DOI: 10.1016/j.ica.2021.120654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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8
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Sabapathi G, Venuvanalingam P. Oxidative C–C/C–X coupling in organometallic nickel complexes: insights from DFT. NEW J CHEM 2022. [DOI: 10.1039/d2nj02480b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
NiIII and NiIV-center complexes prefer direct reductive elimination than reacting through five-coordinate intermediates. 32+ complex in the presence of Cl− undergoes Cl–Csp2 elimination preferably over Cl–Csp3 and Csp3–Csp2 elimination.
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Affiliation(s)
- Gopal Sabapathi
- Theoretical and Computational Chemistry Laboratory, School of Chemistry, Bharathidasan University, Tiruchirappalli 620024, India
| | - Ponnambalam Venuvanalingam
- Theoretical and Computational Chemistry Laboratory, School of Chemistry, Bharathidasan University, Tiruchirappalli 620024, India
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Kumar R, Pandey B, Singh A, Rajaraman G. Mechanistic Insights into the Oxygen Atom Transfer Reactions by Nonheme Manganese Complex: A Computational Case Study on the Comparative Oxidative Ability of Manganese-Hydroperoxo vs High-Valent Mn IV═O and Mn IV-OH Intermediates. Inorg Chem 2021; 60:12085-12099. [PMID: 34293860 DOI: 10.1021/acs.inorgchem.1c01306] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the comparative oxidative abilities of high-valent metal-oxo/hydroxo/hydroperoxo species holds the key to robust biomimic catalysts that perform desired organic transformations with very high selectivity and efficiency. The comparative oxidative abilities of popular high-valent iron-oxo and manganese-oxo species are often counterintuitive, for example, oxygen atom transfer (OAT) reaction by [(Me2EBC)MnIV-OOH]3+, [(Me2EBC)MnIV-OH]3+, and [(Me2EBC)MnIV═O]2+ (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) shows extremely high reactivity for MnIV-OOH species and no reactivity for MnIV-OH and MnIV═O species toward alkyl/aromatic sulfides. Using a combination of density functional theory (DFT) and ab initio domain-based local pair natural orbital coupled-cluster with single, double, and perturbative triples excitation (DLPNO-CCSD(T)) and complete-active space self-consistent field/N-electron valence perturbation theory second order (CASSCF/NEVPT2) calculations, here, we have explored the electronic structures and sulfoxidation mechanism of these species. Our calculations unveil that MnIV-OOH reacts through distal oxygen atom with the substrate via electron transfer (ET) mechanism with a very small kinetic barrier (16.5 kJ/mol), placing this species at the top among the best-known catalysts for such transformations. The MnIV-OH and MnIV═O species have a much larger barrier. The mechanism has also been found to switch from ET in the former to concerted in the latter, rendering both unreactive under the tested experimental conditions. Intrinsic differences in the electronic structures, such as the presence and absence of the multiconfigurational character coupled with the steric effects, are responsible for such variations observed. This comparative oxidative ability that runs contrary to the popular iron-oxo/hydroperoxo reactivity will have larger mechanistic implications in understanding the reactivity of biomimic catalysts and the underlying mechanisms in PSII.
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Affiliation(s)
- Ravi Kumar
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Bhawana Pandey
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Akta Singh
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
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Chandra A, Ansari M, Monte‐Pérez I, Kundu S, Rajaraman G, Ray K. Ligand‐Constraint‐Induced Peroxide Activation for Electrophilic Reactivity. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202100438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Anirban Chandra
- Department of Chemistry Humboldt-Universität zu Berlin Brook-Taylor-Strasse 2 12489 Berlin Germany
| | - Mursaleem Ansari
- Department of Chemistry Indian Institute of Technology Bombay, Powai Mumbai Maharashtra 400 076 India
| | - Inés Monte‐Pérez
- Department of Chemistry Humboldt-Universität zu Berlin Brook-Taylor-Strasse 2 12489 Berlin Germany
| | - Subrata Kundu
- Department of Chemistry Humboldt-Universität zu Berlin Brook-Taylor-Strasse 2 12489 Berlin Germany
| | - Gopalan Rajaraman
- Department of Chemistry Indian Institute of Technology Bombay, Powai Mumbai Maharashtra 400 076 India
| | - Kallol Ray
- Department of Chemistry Humboldt-Universität zu Berlin Brook-Taylor-Strasse 2 12489 Berlin Germany
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Chandra A, Ansari M, Monte-Pérez I, Kundu S, Rajaraman G, Ray K. Ligand-Constraint-Induced Peroxide Activation for Electrophilic Reactivity. Angew Chem Int Ed Engl 2021; 60:14954-14959. [PMID: 33843113 PMCID: PMC8252416 DOI: 10.1002/anie.202100438] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 03/26/2021] [Indexed: 12/16/2022]
Abstract
μ‐1,2‐peroxo‐bridged diiron(III) intermediates P are proposed as reactive intermediates in various biological oxidation reactions. In sMMO, P acts as an electrophile, and performs hydrogen atom and oxygen atom transfers to electron‐rich substrates. In cyanobacterial ADO, however, P is postulated to react by nucleophilic attack on electrophilic carbon atoms. In biomimetic studies, the ability of μ‐1,2‐peroxo‐bridged dimetal complexes of Fe, Co, Ni and Cu to act as nucleophiles that effect deformylation of aldehydes is documented. By performing reactivity and theoretical studies on an end‐on μ‐1,2‐peroxodicobalt(III) complex 1 involving a non‐heme ligand system, L1, supported on a Sn6O6 stannoxane core, we now show that a peroxo‐bridged dimetal complex can also be a reactive electrophile. The observed electrophilic chemistry, which is induced by the constraints provided by the Sn6O6 core, represents a new domain for metal−peroxide reactivity.
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Affiliation(s)
- Anirban Chandra
- Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany
| | - Mursaleem Ansari
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra, 400 076, India
| | - Inés Monte-Pérez
- Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany
| | - Subrata Kundu
- Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra, 400 076, India
| | - Kallol Ray
- Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany
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Ansari M, Senthilnathan D, Rajaraman G. Deciphering the origin of million-fold reactivity observed for the open core diiron [HO-Fe III-O-Fe IV[double bond, length as m-dash]O] 2+ species towards C-H bond activation: role of spin-states, spin-coupling, and spin-cooperation. Chem Sci 2020; 11:10669-10687. [PMID: 33209248 PMCID: PMC7654192 DOI: 10.1039/d0sc02624g] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 06/16/2020] [Indexed: 01/26/2023] Open
Abstract
High-valent metal-oxo species have been characterised as key intermediates in both heme and non-heme enzymes that are found to perform efficient aliphatic hydroxylation, epoxidation, halogenation, and dehydrogenation reactions. Several biomimetic model complexes have been synthesised over the years to mimic both the structure and function of metalloenzymes. The diamond-core [Fe2(μ-O)2] is one of the celebrated models in this context as this has been proposed as the catalytically active species in soluble methane monooxygenase enzymes (sMMO), which perform the challenging chemical conversion of methane to methanol at ease. In this context, a report of open core [HO(L)FeIII-O-FeIV(O)(L)]2+ (1) gains attention as this activates C-H bonds a million-fold faster compared to the diamond-core structure and has the dual catalytic ability to perform hydroxylation as well as desaturation with organic substrates. In this study, we have employed density functional methods to probe the origin of the very high reactivity observed for this complex and also to shed light on how this complex performs efficient hydroxylation and desaturation of alkanes. By modelling fifteen possible spin-states for 1 that could potentially participate in the reaction mechanism, our calculations reveal a doublet ground state for 1 arising from antiferromagnetic coupling between the quartet FeIV centre and the sextet FeIII centre, which regulates the reactivity of this species. The unusual stabilisation of the high-spin ground state for FeIV[double bond, length as m-dash]O is due to the strong overlap of with the orbital, reducing the antibonding interactions via spin-cooperation. The electronic structure features computed for 1 are consistent with experiments offering confidence in the methodology chosen. Further, we have probed various mechanistic pathways for the C-H bond activation as well as -OH rebound/desaturation of alkanes. An extremely small barrier height computed for the first hydrogen atom abstraction by the terminal FeIV[double bond, length as m-dash]O unit was found to be responsible for the million-fold activation observed in the experiments. The barrier height computed for -OH rebound by the FeIII-OH unit is also smaller suggesting a facile hydroxylation of organic substrates by 1. A strong spin-cooperation between the two iron centres also reduces the barrier for second hydrogen atom abstraction, thus making the desaturation pathway competitive. Both the spin-state as well as spin-coupling between the two metal centres play a crucial role in dictating the reactivity for species 1. By exploring various mechanistic pathways, our study unveils the fact that the bridged μ-oxo group is a poor electrophile for both C-H activation as well for -OH rebound. As more and more evidence is gathered in recent years for the open core geometry of sMMO enzymes, the idea of enhancing the reactivity via an open-core motif has far-reaching consequences.
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Affiliation(s)
- Mursaleem Ansari
- Department of Chemistry , Indian Institute of Technology Bombay , Mumbai 400076 , India .
| | - Dhurairajan Senthilnathan
- Center for Computational Chemistry , CRD , PRIST University , Vallam , Thanjavur , Tamilnadu 613403 , India
| | - Gopalan Rajaraman
- Department of Chemistry , Indian Institute of Technology Bombay , Mumbai 400076 , India .
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Sen A, Vyas N, Pandey B, Rajaraman G. Deciphering the mechanism of oxygen atom transfer by non-heme Mn IV-oxo species: an ab initio and DFT exploration. Dalton Trans 2020; 49:10380-10393. [PMID: 32613212 DOI: 10.1039/d0dt01785j] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Oxygen atom transfer (OAT) reactions employing transition metal-oxo species have tremendous significance in homogeneous catalysis for industrial use. Understanding the structural and mechanistic aspects of OAT reactions using high-valent metal-oxo species is of great importance to fine-tune their reactivity. Herein we examine the reactivity of a non-heme high-valent oxo-manganese(iv) complex, [MnIVH3buea(O)]- towards a variety of substrates such as PPh2Me, PPhMe2, PCy3, PPh3, and PMe3 using density functional theory as well as ab initio CASSCF/NEVPT2 methods. We have initially explored the structure and bonding of [MnIVH3buea(O)]- and its congener [MnIVH3buea(S)]-. Our calculations affirm an S = 3/2 ground state of the catalyst with the S = 5/2 and S = 1/2 excited states predicted to be too high lying in energy to participate in the reaction mechanism. Our ab initio CASSCF/NEVPT2 calculations, however, reveal a strong multi-reference character for the ground S = 3/2 state with many low-lying quartets mixing significantly with the ground state. This opens up various reaction channels, and the admixed wave-function evolves during the reaction with the excited triplet dominating the ground state wave-function at the reactant complex. Our calculations predict the following pattern of reactivity, PCy3 < PMe3 < PPh3 < PPhMe2 < PPh2Me for the OAT reaction with the MnIV[double bond, length as m-dash]O species which correlates well with the experimental observations. Detailed electronic structure analysis of the transitions states reveal that these substrates react via an unusual low-energy δ-type pathway where a spin-up electron from the substrate is transferred to the δ*x2-y2 orbital of the MnIV[double bond, length as m-dash]O facilitated by its multi-reference character. The unusual reactivity observed here has implications in understanding the reactivity of [Mn4Ca] species in photosystem II.
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Affiliation(s)
- Asmita Sen
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India.
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14
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Sen A, Vyas N, Pandey B, Jaccob M, Rajaraman G. Mechanistic Insights on the Formation of High‐Valent Mn
III/IV
=O Species Using Oxygen as Oxidant: A Theoretical Perspective. Isr J Chem 2020. [DOI: 10.1002/ijch.201900142] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Asmita Sen
- Department of Chemistry Indian Institute of Technology Bombay Mumbai 400076 India
| | - Nidhi Vyas
- Department of Chemistry Indian Institute of Technology Bombay Mumbai 400076 India
- School of Biotechnology Jawaharlal Nehru University New Delhi 110067 India
| | - Bhawana Pandey
- Department of Chemistry Indian Institute of Technology Bombay Mumbai 400076 India
| | - Madhavan Jaccob
- Department of Chemistry Indian Institute of Technology Bombay Mumbai 400076 India
- Department of chemistry Loyola College Chennai 600 034
| | - Gopalan Rajaraman
- Department of Chemistry Indian Institute of Technology Bombay Mumbai 400076 India
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15
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Monika, Ansari A. Mechanistic insights into the allylic oxidation of aliphatic compounds by tetraamido iron( v) species: A C–H vs. O–H bond activation. NEW J CHEM 2020. [DOI: 10.1039/d0nj03095c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This work is based on a deep insight into a comparative study of C–H vs. O–H bond activation of allylic compound by the high valent iron complex. Our theoretical findings can help to design catalysts with better efficiency for catalytic reactions.
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Affiliation(s)
- Monika
- Department of Chemistry
- Central University of Haryana
- Mahendergarh-123031
- India
| | - Azaj Ansari
- Department of Chemistry
- Central University of Haryana
- Mahendergarh-123031
- India
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16
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Panneerselvam M, Jaccob M. Role of Anation on the Mechanism of Proton Reduction Involving a Pentapyridine Cobalt Complex: A Theoretical Study. Inorg Chem 2018; 57:8116-8127. [PMID: 29969023 DOI: 10.1021/acs.inorgchem.8b00286] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Kinetic and thermodynamic aspects of proton reduction involving pentapyridine cobalt(II) complex were investigated with the help of quantum chemical calculations. Free energy profile of all possible mechanistic routes for proton reduction was constructed with the consideration of both anation and solvent bound pathways. The computed free energy profile shows that acetate ion plays a significant role in modulating the kinetic aspects of Co(III)-hydride formation which is found to be the key intermediate for proton reduction. Upon replacing solvent by acetate ion, one electron reduction and protonation of CoI species become more rapid along with slow displacement reaction. Most favorable pathways for hydrogen evolution from Co(III)-hydride species is also investigated. Among the four possible pathways, reduction followed by protonation of Co(III)-hydride (RPP) is found to be the most feasible pathway. On the basis of QTAIM and NBO analyses, the electronic origin of most favorable pathway is explained. The basicity of cobalt center along with thermodynamic stability of putative CoIII/II-H species is essentially a prime factor in deciding the most favorable pathway for hydrogen evolution. Our computed results are in good agreement with experimental observations and also provided adequate information to design cobalt-based molecular electrocatalysts for proton reduction in future.
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Affiliation(s)
- Murugesan Panneerselvam
- Department of Chemistry , Loyola College , Chennai 600 034 , Tamil Nadu , India.,Computational Chemistry Laboratory, Loyola Institute of Frontier Energy (LIFE) , Loyola College , Chennai 600 034 , Tamil Nadu , India
| | - Madhavan Jaccob
- Department of Chemistry , Loyola College , Chennai 600 034 , Tamil Nadu , India.,Computational Chemistry Laboratory, Loyola Institute of Frontier Energy (LIFE) , Loyola College , Chennai 600 034 , Tamil Nadu , India
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17
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Jana K, Bandyopadhyay T, Ganguly B. Stereoselective Metabolism of Omeprazole by Cytochrome P450 2C19 and 3A4: Mechanistic Insights from DFT Study. J Phys Chem B 2018; 122:5765-5775. [PMID: 29741901 DOI: 10.1021/acs.jpcb.8b01179] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The efficacy of S-omeprazole as a proton pump inhibitor compared with that of its enantiomer R-omeprazole is studied using density functional theoretical calculations. The pharmacokinetic studies suggest that the efficacy of S-omeprazole presumably depends on metabolic pathway and excretion from the human body. The density functional theory calculations at SMDwater-B3LYP-D3/6-311+G(d,p)/LANL2DZ//B3LYP/6-31G(d)/LANL2DZ with triradicaloid model active species, [Por•+FeIV(SH)O], of CYP2C19 enzyme with high-spin quartet and low-spin doublet states demonstrate C-H bond activation mechanism through a two-state rebound process for the hydroxylation of R-omeprazole and S-omeprazole. The calculated activation free energy barriers for the hydrogen abstraction are 15.7 and 17.5 kcal/mol for R-omeprazole and S-omeprazole, respectively. The hydroxylation of R-omeprazole and S-omeprazole is thermodynamically favored; however, the hydroxylated intermediate of S-omeprazole further disintegrates to metabolite 5- O-desmethylomeprazole with a higher kinetic barrier. We have examined the sulfoxidation of S-omeprazole to omeprazole sulfone metabolite by CYP3A4, and the observed activation free energy barrier is 9.9 kcal/mol. The computational results reveal that CYP2C19 exclusively metabolizes R-omeprazole to hydroxyomeprazole, which is hydrophilic and can easily excrete, whereas CYP3A4 metabolizes S-omeprazole to lipophilic sulfone; hence, the excretion of this metabolite would be relatively slower from the body. The spin density analysis and molecular orbital analysis performed using biorthogonalization calculations indicate that R-omeprazole favors high-spin pathway for metabolism process whereas S-omeprazole prefers the low-spin pathway.
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Affiliation(s)
| | - Tusar Bandyopadhyay
- Theoretical Chemistry Section, Chemistry Group MOD LAB , Bhabha Atomic Research Centre , Trombay , Mumbai 400085 , India
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18
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Ramesh M, Kumar MD, Jaccob M, Therrien B, Venkatachalam G. Cyclometalated ruthenium(II) carbonyl complexes containing 2-(biphenylazo)phenolate ligands: Synthesis, structure, DFT study and catalytic activity towards oxidation and transfer hydrogenation. Inorganica Chim Acta 2018. [DOI: 10.1016/j.ica.2018.02.023] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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19
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Kumar R, Ansari A, Rajaraman G. Axial vs. Equatorial Ligand Rivalry in Controlling the Reactivity of Iron(IV)-Oxo Species: Single-State vs. Two-State Reactivity. Chemistry 2018; 24:6818-6827. [DOI: 10.1002/chem.201800380] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Indexed: 11/08/2022]
Affiliation(s)
- Ravi Kumar
- Department of Chemistry; Indian Institute of Technology Bombay; Powai, Mumbai 400076 India
| | - Azaj Ansari
- Department of Chemistry; Central University of Haryana; Haryana 123031 India
| | - Gopalan Rajaraman
- Department of Chemistry; Indian Institute of Technology Bombay; Powai, Mumbai 400076 India
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20
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Ansari A, Ansari M, Singha A, Rajaraman G. Interplay of Electronic Cooperativity and Exchange Coupling in Regulating the Reactivity of Diiron(IV)-oxo Complexes towards C−H and O−H Bond Activation. Chemistry 2017; 23:10110-10125. [DOI: 10.1002/chem.201701059] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Indexed: 11/08/2022]
Affiliation(s)
- Azaj Ansari
- Department of Chemistry; CUH Haryana; Haryana 123031 India
| | | | - Asmita Singha
- Department of Chemistry; IIT Bombay; Mumbai 400076 India
| | - Gopalan Rajaraman
- Department of Chemistry; Indian Institute of Technology Bombay, Powai; Mumbai, Maharashtra 400076 India
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21
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Vaddypally S, Kondaveeti SK, Karki S, Van Vliet MM, Levis RJ, Zdilla MJ. Reactive Pendant Mn═O in a Synthetic Structural Model of a Proposed S4 State in the Photosynthetic Oxygen Evolving Complex. J Am Chem Soc 2017; 139:4675-4681. [DOI: 10.1021/jacs.6b05906] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Shivaiah Vaddypally
- Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
| | - Sandeep K. Kondaveeti
- Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
| | - Santosh Karki
- Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
| | - Megan M. Van Vliet
- Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
| | - Robert J. Levis
- Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
| | - Michael J. Zdilla
- Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
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22
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Shul’pin GB, Nesterov DS, Shul’pina LS, Pombeiro AJ. A hydroperoxo-rebound mechanism of alkane oxidation with hydrogen peroxide catalyzed by binuclear manganese(IV) complex in the presence of an acid with involvement of atmospheric dioxygen. Inorganica Chim Acta 2017. [DOI: 10.1016/j.ica.2016.04.035] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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23
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Huang XC, Wang HF, Lang JP. Theoretical view on a linear end-on manganese–dioxygen complex bearing a calix[4]arene ligand. RSC Adv 2016. [DOI: 10.1039/c6ra11199h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Mn–O–O angle of mononuclear manganese(iii)-superoxo complexes supported by zwitterionic calix[4]arene ligands can be modulated via solvent polarity perturbations and/or ligand size adjustment as indicated by DFT calculations.
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Affiliation(s)
- Xiang-Cui Huang
- College of Chemistry
- Chemical Engineering and Materials Science
- Soochow University
- Suzhou 215123
- People's Republic of China
| | - Hui-Fang Wang
- College of Chemistry
- Chemical Engineering and Materials Science
- Soochow University
- Suzhou 215123
- People's Republic of China
| | - Jian-Ping Lang
- College of Chemistry
- Chemical Engineering and Materials Science
- Soochow University
- Suzhou 215123
- People's Republic of China
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24
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Ansari A, Rajaraman G. ortho-Hydroxylation of aromatic acids by a non-heme Fe(V)=O species: how important is the ligand design? Phys Chem Chem Phys 2015; 16:14601-13. [PMID: 24812659 DOI: 10.1039/c3cp55430a] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
There is a growing interest in probing the mechanism of catalytic transformations effected by non-heme iron-oxo complexes as these reactions set a platform for understanding the relevant enzymatic reactions. The ortho-hydroxylation of aromatic compounds is one such reaction catalysed by iron-oxo complexes. Experimentally [Fe(II)(BPMEN)(CH3CN)2](2+) (1) and [Fe(II)(TPA)(CH3CN)2](2+) (2) (where TPA = tris(2-pyridylmethyl)amine and BPMEN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) complexes containing amino pyridine ligands along with H2O2 are employed to carry out these transformations where complex 1 is found to be more reactive than complex 2. Herein, using density functional methods employing B3LYP and dispersion corrected B3LYP (B3LYP-D) functionals, we have explored the mechanism of this reaction to reason out the importance of ligand design in fine-tuning the reactivity of such catalytic transformations. Dispersion corrected B3LYP is found to be superior to B3LYP in predicting the correct ground state of these species and also yields lower barrier heights than the B3LYP functional. Starting the reaction from the Fe(III)–OOH species, both homolytic and heterolytic cleavage of the O···O bond is explored leading to the formation of the transient Fe(IV)=O and Fe(V)=O species. For both the ligand systems, heterolytic cleavage was energetically preferable and our calculations suggest that both the reactions are catalyzed by an elusive high-valent Fe(V)=O species. The Fe(V)=O species undergoes the reaction via an electrophilic attack of the benzene ring to effect the ortho-hydroxylation reaction. The reactivity pattern observed for 1 and 2 are reflected in the computed barrier heights for the ortho-hydroxylation reaction. Electronic structure analysis reveals that the difference in reactivity between the ligand architectures described in complex 1 and 2 arise due to orientation of the pyridine ring(s) parallel or perpendicular to the Fe(V)=O bond. The parallel orientation of the pyridine ring is found to mix with the (πFe(dyz)–O(py))* orbital of the Fe-oxo bond leading to a reduction in the electrophilicity of the ferryl oxygen atom. Our calculations highlight the importance of ligand design in this chemistry and suggest that this concept can be used to (i) stabilize high-valent intermediates which can be trapped and thoroughly characterized (ii) enhance the reactivity and efficiency of the oxidants by increasing the electrophilicity of the ferryl oxygen containing FeVO species. Our computed results are in general agreement with the experimental results.
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Affiliation(s)
- Azaj Ansari
- Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai, India.
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25
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Structures, bonding and reactivity of iron and manganese high-valent metal-oxo complexes: A computational investigation. J CHEM SCI 2015. [DOI: 10.1007/s12039-015-0770-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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26
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Boaz NC, Bell SR, Groves JT. Ferryl protonation in oxoiron(IV) porphyrins and its role in oxygen transfer. J Am Chem Soc 2015; 137:2875-85. [PMID: 25651467 PMCID: PMC4363944 DOI: 10.1021/ja508759t] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Ferryl porphyrins, P-Fe(IV)═O, are central reactive intermediates in the catalytic cycles of numerous heme proteins and a variety of model systems. There has been considerable interest in elucidating factors, such as terminal oxo basicity, that may control ferryl reactivity. Here, the sulfonated, water-soluble ferryl porphyrin complexes tetramesitylporphyrin, oxoFe(IV)TMPS (FeTMPS-II), its 2,6-dichlorophenyl analogue, oxoFe(IV)TDClPS (FeTDClPS-II), and two other analogues are shown to be protonated under turnover conditions to produce the corresponding bis-aqua-iron(III) porphyrin cation radicals. The results reveal a novel internal electromeric equilibrium, P-Fe(IV)═O ⇆ P(+)-Fe(III)(OH2)2. Reversible pKa values in the range of 4-6.3 have been measured for this process by pH-jump, UV-vis spectroscopy. Ferryl protonation has important ramifications for C-H bond cleavage reactions mediated by oxoiron(IV) porphyrin cation radicals in protic media. Both solvent O-H and substrate C-H deuterium kinetic isotope effects are observed for these reactions, indicating that hydrocarbon oxidation by these oxoiron(IV) porphyrin cation radicals occurs via a solvent proton-coupled hydrogen atom transfer from the substrate that has not been previously described. The effective FeO-H bond dissociation energies for FeTMPS-II and FeTDClPS-II were estimated from similar kinetic reactivities of the corresponding oxoFe(IV)TMPS(+) and oxoFe(IV)TDClPS(+) species to be ∼92-94 kcal/mol. Similar values were calculated from the two-proton P(+)-Fe(III)(OH2)2 pKa(obs) and the porphyrin oxidation potentials, despite a 230 mV range for the iron porphyrins examined. Thus, the iron porphyrin with the lower ring oxidation potential has a compensating higher basicity of the ferryl oxygen. The solvent-derived proton adds significantly to the driving force for C-H bond scission.
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Affiliation(s)
- Nicholas C. Boaz
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Seth R. Bell
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - John T. Groves
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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27
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Kotani H, Kaida S, Ishizuka T, Sakaguchi M, Ogura T, Shiota Y, Yoshizawa K, Kojima T. Formation and characterization of a reactive chromium(v)-oxo complex: mechanistic insight into hydrogen-atom transfer reactions. Chem Sci 2015; 6:945-955. [PMID: 29560181 PMCID: PMC5811151 DOI: 10.1039/c4sc02285h] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 10/17/2014] [Indexed: 12/27/2022] Open
Abstract
A mononuclear Cr(v)-oxo complex, [CrV(O)(6-COO--tpa)](BF4)2 (1; 6-COO--tpa = N,N-bis(2-pyridylmethyl)-N-(6-carboxylato-2-pyridylmethyl)amine) was prepared through the reaction of a Cr(iii) precursor complex with iodosylbenzene as an oxidant. Characterization of 1 was achieved using ESI-MS spectrometry, electron paramagnetic resonance, UV-vis, and resonance Raman spectroscopies. The reduction potential (Ered) of 1 was determined to be 1.23 V vs. SCE in acetonitrile based on analysis of the electron-transfer (ET) equilibrium between 1 and a one-electron donor, [RuII(bpy)3]2+ (bpy = 2,2'-bipyridine). The reorganization energy (λ) of 1 was also determined to be 1.03 eV in ET reactions from phenol derivatives to 1 on the basis of the Marcus theory of ET. The smaller λ value in comparison with that of an Fe(iv)-oxo complex (2.37 eV) is caused by the small structural change during ET due to the dπ character of the electron-accepting LUMO of 1. When benzyl alcohol derivatives (R-BA) with different oxidation potentials were employed as substrates, corresponding aldehydes were obtained as the 2e--oxidized products in moderate yields as determined from 1H NMR and GC-MS measurements. One-step UV-vis spectral changes were observed in the course of the oxidation reactions of BA derivatives by 1 and a kinetic isotope effect (KIE) was observed in the oxidation reactions for deuterated BA derivatives at the benzylic position as substrates. These results indicate that the rate-limiting step is a concerted proton-coupled electron transfer (PCET) from substrate to 1. In sharp contrast, in the oxidation of trimethoxy-BA (Eox = 1.22 V) by 1, trimethoxy-BA radical cation was observed by UV-vis spectroscopy. Thus, it was revealed that the mechanism of the oxidation reaction changed from one-step PCET to stepwise ET-proton transfer (ET/PT), depending on the redox potentials of R-BA.
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Affiliation(s)
- Hiroaki Kotani
- Department of Chemistry , Faculty of Pure and Applied Sciences , University of Tsukuba , 1-1-1 Tennoudai , Tsukuba , Ibaraki 305-8571 , Japan . ;
| | - Suzue Kaida
- Department of Chemistry , Faculty of Pure and Applied Sciences , University of Tsukuba , 1-1-1 Tennoudai , Tsukuba , Ibaraki 305-8571 , Japan . ;
| | - Tomoya Ishizuka
- Department of Chemistry , Faculty of Pure and Applied Sciences , University of Tsukuba , 1-1-1 Tennoudai , Tsukuba , Ibaraki 305-8571 , Japan . ;
| | - Miyuki Sakaguchi
- Graduate School of Life Science , University of Hyogo , Kouto , Hyogo 678-1297 , Japan
| | - Takashi Ogura
- Graduate School of Life Science , University of Hyogo , Kouto , Hyogo 678-1297 , Japan
| | - Yoshihito Shiota
- Institute for Materials Chemistry and Engineering , Kyushu University , Motooka , Nishi-Ku , Fukuoka 819-0395 , Japan
| | - Kazunari Yoshizawa
- Institute for Materials Chemistry and Engineering , Kyushu University , Motooka , Nishi-Ku , Fukuoka 819-0395 , Japan
- Elements Strategy Initiative for Catalysts & Batteries , Kyoto University , Nishikyo-ku , Kyoto 615-8520 , Japan
| | - Takahiko Kojima
- Department of Chemistry , Faculty of Pure and Applied Sciences , University of Tsukuba , 1-1-1 Tennoudai , Tsukuba , Ibaraki 305-8571 , Japan . ;
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Ansari M, Vyas N, Ansari A, Rajaraman G. Oxidation of methane by an N-bridged high-valent diiron–oxo species: electronic structure implications on the reactivity. Dalton Trans 2015; 44:15232-43. [DOI: 10.1039/c5dt01060h] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Methane activation by dinuclear high-valent iron–oxo species: do we need two metals to activate such inert bonds? Our theoretical study using DFT methods where electronic structure details and mechanistic aspects are established answers this intriguing question.
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Affiliation(s)
- Mursaleem Ansari
- Department of Chemistry
- Indian Institute of Technology Bombay
- Mumbai-400076
- India
| | - Nidhi Vyas
- Department of Chemistry
- Indian Institute of Technology Bombay
- Mumbai-400076
- India
| | - Azaj Ansari
- Department of Chemistry
- Indian Institute of Technology Bombay
- Mumbai-400076
- India
| | - Gopalan Rajaraman
- Department of Chemistry
- Indian Institute of Technology Bombay
- Mumbai-400076
- India
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29
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Ansari A, Jayapal P, Rajaraman G. CH Bond Activation by Metal-Superoxo Species: Magnetic Coupling Correlated to High Reactivity in Metal-Superoxo species. Angew Chem Int Ed Engl 2014; 54:564-8. [DOI: 10.1002/anie.201409844] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Indexed: 11/12/2022]
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30
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Ansari A, Jayapal P, Rajaraman G. CH Bond Activation by Metal-Superoxo Species: What Drives High Reactivity? Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201409844] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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31
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Geng C, Ye S, Neese F. Does a higher metal oxidation state necessarily imply higher reactivity toward H-atom transfer? A computational study of C-H bond oxidation by high-valent iron-oxo and -nitrido complexes. Dalton Trans 2014; 43:6079-86. [PMID: 24492533 DOI: 10.1039/c3dt53051e] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
In this work, the reactions of C-H bond activation by two series of iron-oxo ( (Fe(IV)), (Fe(V)), (Fe(VI))) and -nitrido model complexes ( (Fe(IV)), (Fe(V)), (Fe(VI))) with a nearly identical coordination geometry but varying iron oxidation states ranging from iv to vi were comprehensively investigated using density functional theory. We found that in a distorted octahedral coordination environment, the iron-oxo species and their isoelectronic nitrido analogues feature totally different intrinsic reactivities toward C-H bond cleavage. In the case of the iron-oxo complexes, the reaction barrier monotonically decreases as the iron oxidation state increases, consistent with the gradually enhanced electrophilicity across the series. The iron-nitrido complex is less reactive than its isoelectronic iron-oxo species, and more interestingly, a counterintuitive reactivity pattern was observed, i.e. the activation barriers essentially remain constant independent of the iron oxidation states. The detailed analysis using the Polanyi principle demonstrates that the different reactivities between these two series originate from the distinct thermodynamic driving forces, more specifically, the bond dissociation energies (BDEE-Hs, E = O, N) of the nascent E-H bonds in the FeE-H products. Further decomposition of the BDEE-Hs into the electron and proton affinity components shed light on how the oxidation states modulate the BDEE-Hs of the two series.
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Affiliation(s)
- Caiyun Geng
- Max-Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany.
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