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Sundaresan S, Eppelsheimer J, Gera E, Wiener L, Carrella LM, Vignesh KR, Rentschler E. A combined theoretical and experimental approach to determine the right choice of co-ligand to impart spin crossover in Fe(II) complexes based on 1,3,4-oxadiazole ligands. Dalton Trans 2024; 53:10303-10317. [PMID: 38832753 DOI: 10.1039/d4dt01141d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2024]
Abstract
We present the synthesis of two new novel tetradentate ligands based on 1,3,4-oxadiazole, 2-(2-pyridyl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole (LTetraPy-ODA) and 2-(2-phenyl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole (LTetraPh-ODA). The ligands were used to prepare six mononuclear complexes [FeII(LTetraPy-ODA)(NCE)] (C1-C3) and [FeII(LTetraPh-ODA)(NCE)] (C4-C6) where E = S, Se or BH3. In addition, the ligand LTetraPy-ODA was employed in the synthesis of a new di-nuclear complex [FeII2(LTetraPh)](ClO4)4·1 CH3NO2·1.5 H2O (C7). Characterization of all complexes was carried out using single-crystal X-ray crystallography, elemental analysis, and infrared spectroscopy. Magnetic susceptibility measurements, performed in the temperature range of 2-300 K using a SQUID magnetometer, revealed spin crossover behaviour exclusively in the mononuclear complexes C3 and C6, in which two monodentate NCBH3- co-ligands coordinate. The presence of the lattice solvent was found to be crucial to the spin transition property, with complex C3 exhibiting a switching temperature (T1/2) of approximately 165 K and C6 approximately 194 K. The other four mononuclear complexes C1, C2, C4, C5, as well as the dinuclear complex C7 are locked in the high spin state over the measured temperature range. Density Functional Theory (DFT) calculations were performed on complexes C1-C6 to rationalise the observed magnetic behaviour, demonstrating the significant effect of the NCS-, NCSe- and NCBH3- co-ligands ligands on the spin-crossover behaviour of the [FeII(L)(NCE)] complexes.
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Affiliation(s)
- Sriram Sundaresan
- Department Chemie, Johannes-Gutenberg-Universität Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Julian Eppelsheimer
- Department Chemie, Johannes-Gutenberg-Universität Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Esha Gera
- Department of Chemical Scienaces, Indian Institute of Science Education Research (IISER) Mohali, Sector-81, Knowledge City, S.A.S. Nagar, Mohali 140306, Punjab, India.
| | - Lukas Wiener
- Department Chemie, Johannes-Gutenberg-Universität Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Luca M Carrella
- Department Chemie, Johannes-Gutenberg-Universität Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Kuduva R Vignesh
- Department of Chemical Scienaces, Indian Institute of Science Education Research (IISER) Mohali, Sector-81, Knowledge City, S.A.S. Nagar, Mohali 140306, Punjab, India.
| | - Eva Rentschler
- Department Chemie, Johannes-Gutenberg-Universität Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
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Muthuramalingam S, Velusamy M, Singh Rajput S, Alam M, Mayilmurugan R. Nickel(II) Complexes of Tripodal Ligands as Catalysts for Fixation of Atmospheric CO 2 as Organic Carbonates. Chem Asian J 2023; 18:e202201204. [PMID: 36734191 DOI: 10.1002/asia.202201204] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 01/26/2023] [Accepted: 01/27/2023] [Indexed: 02/04/2023]
Abstract
The fixation of atmospheric CO2 into value-added products is a promising methodology. A series of novel nickel(II) complexes of the type [Ni(L)(CH3 CN)2 ](BPh4 )2 1-5, where L=N,N-bis(2-pyridylmethyl)-N', N'-dimethylpropane-1,3-diamine (L1), N,N-dimethyl-N'-(2-(pyridin-2-yl)ethyl)-N'-(pyridin-2-ylmethyl) propane-1,3-diamine (L2), N,N-bis((4-methoxy-3,5-dimethylpyridin-2-ylmethyl)-N',N'-dimethylpropane-1,3-diamine (L3), N-(2-(dimethylamino) benzyl)-N',N'-dimethyl-N-(pyridin-2-ylmethyl) propane-1,3-diamine (L4) and N,N-bis(2-(dimethylamino)benzyl)-N', N'-dimethylpropane-1,3-diamine (L5) have been synthesized and characterized as the catalysts for the conversion of atmospheric CO2 into organic cyclic carbonates. The single-crystal X-ray structure of 2 was determined and exhibited distorted octahedral coordination geometry with cis-α configuration. The complexes have been used as a catalyst for converting CO2 and epoxides into five-membered cyclic carbonates under 1 atmospheric (atm) pressure at room temperature in the presence of Bu4 NBr. The catalyst containing electron-releasing -Me and -OMe groups afforded the maximum yield of cyclic carbonates, 34% (TON, 680) under 1 atm air. It was drastically enhanced to 89% (TON, 1780) under pure CO2 gas at 1 atm. It is the highest catalytic efficiency known for CO2 fixation using nickel-based catalysts at room temperature and 1 atm pressure. The electronic and steric factors of the ligands strongly influence the catalytic efficiency. Furthermore, all the catalysts can convert a wide range of epoxides (ten examples) into corresponding cyclic carbonate with excellent selectivity (>99%) under this mild condition.
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Affiliation(s)
- Sethuraman Muthuramalingam
- Department of Chemistry, Indian Institute of Technology Bhilai, Raipur, 492015 Chattisgarh, India.,Institut de Química Computacional i Catalisì (IQCC) and Departament de Química, Universitat de Girona, Girona, E-17003 Catalonia, Spain
| | - Marappan Velusamy
- Department of Chemistry, North Eastern Hill University, Shillong, 793022, India
| | - Swati Singh Rajput
- Department of Chemistry, Indian Institute of Technology Bhilai, Raipur, 492015 Chattisgarh, India
| | - Mehboob Alam
- Department of Chemistry, Indian Institute of Technology Bhilai, Raipur, 492015 Chattisgarh, India
| | - Ramasamy Mayilmurugan
- Department of Chemistry, Indian Institute of Technology Bhilai, Raipur, 492015 Chattisgarh, India
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Addison AW, Jaworski SJ, Jasinski JP, Turnbull MM, Xiao F, Zeller M, O'Connor MA, Brayman EA. Chlorocobalt complexes with pyridylethyl-derived diazacycloalkanes. Acta Crystallogr E Crystallogr Commun 2022; 78:235-243. [PMID: 35371556 PMCID: PMC8900507 DOI: 10.1107/s2056989022001220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 02/01/2022] [Indexed: 11/24/2022]
Abstract
With cobalt(II) chloride, some piperazine- and homo-piperazine-derived ligands yield tetra- or pentacoordinate complexes. Observed variations in coordination number are ascribed as being related to chloride solvophobicity. Optical spectra are presented, while magnetism measurements indicate governance of the magnetism by zero-field splitting of the cobalt ion. Syntheses are described for the blue/purple complexes of cobalt(II) chloride with the tetradentate ligands 1,4-bis[2-(pyridin-2-yl)ethyl]piperazine (Ppz), 1,4-bis[2-(pyridin-2-yl)ethyl]homopiperazine (Phpz), trans-2,5-dimethyl-1,4-bis[2-(pyridin-2-yl)ethyl]piperazine (Pdmpz) and tridentate 4-methyl-1-[2-(pyridin-2-yl)ethyl]homopiperazine (Pmhpz). The CoCl2 complexes with Ppz, namely, {μ-1,4-bis[2-(pyridin-2-yl)ethyl]piperazine}bis[dichloridocobalt(II)], [Co2Cl4(C18H24N4)] or Co2(Ppz)Cl4, and Pdmpz (structure not reported as X-ray quality crystals were not obtained), are shown to be dinuclear, with the ligands bridging the two tetrahedrally coordinated CoCl2 units. Co2(Ppz)Cl4 and {dichlorido{4-methyl-1-[2-(pyridin-2-yl)ethyl]-1,4-diazacycloheptane}cobalt(II) [CoCl2(C13H21N3)] or Co(Pmhpz)Cl2, crystallize in the monoclinic space group P21/n, while crystals of the pentacoordinate monochloro chelate 1,4-bis[2-(pyridin-2-yl)ethyl]piperazine}chloridocobalt(II) perchlorate, [CoCl(C18H24N4)]ClO4 or [Co(Ppz)Cl]ClO4, are also monoclinic (P21). The complex {1,4-bis[2-(pyridin-2-yl)ethyl]-1,4-diazacycloheptane}dichloridocobalt(II) [CoCl2(C19H26N4)] or Co(Phpz)Cl2 (P) is mononuclear, with a pentacoordinated CoII ion, and entails a Phpz ligand acting in a tridentate fashion, with one of the pyridyl moieties dangling and non-coordinated; its displacement by Cl− is attributed to the solvophobicity of Cl− toward MeOH. The pentacoordinate Co atoms in Co(Phpz)Cl2, [Co(Ppz)Cl]+ and Co(Pmhpz)Cl2 have substantial trigonal–bipyramidal character in their stereochemistry. Visible- and near-infrared-region electronic spectra are used to differentiate the two types of coordination spheres. TDDFT calculations suggest that the visible/NIR region transitions contain contributions from MLCT and LMCT character, as well as their expected d–d nature. For Co(Pmhpz)Cl2 and Co(Phpz)Cl2, variable-temperature magnetic susceptibility data were obtained, and the observed decreases in moment with decreasing temperature were modelled with a zero-field-splitting approach, the D values being +28 and +39 cm−1, respectively, with the S = 1/2 state at lower energy.
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Muthuramalingam S, Velusamy M, Mayilmurugan R. Fixation of atmospheric CO 2 as C1-feedstock by nickel(ii) complexes. Dalton Trans 2021; 50:7984-7994. [PMID: 34018501 DOI: 10.1039/d0dt03887c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The development of molecular catalysts for the activation and conversion of atmospheric carbon dioxide (CO2) into a value-added product is a great challenge. A series of nickel(ii) complexes, [Ni(L)(CH3CN)3](BPh4)2, 1-4 of diazepane based ligands, 4-methyl-1-[(pyridin-2-yl-methyl)]-1,4-diazepane (L1), 4-methyl-1-[2-(pyridine-2-yl)ethyl]-1,4-diazepane (L2), 4-methyl-1-[(quinoline-2-yl)-methyl]-1,4-diazepane (L3) and 1-[(4-methoxy-3,5-dimethyl-pyridin-2-yl)methyl]-4-methyl-1,4-diazepane (L4), have been synthesized and characterized as catalysts for the activation of atmospheric CO2. The single-crystal X-ray structure of 1 shows a distorted octahedral geometry with a cis-β configuration around the NiN6 coordination sphere. All the complexes are used as catalysts for the conversion of atmospheric CO2 and epoxides into cyclic carbonates at 1 atmosphere (atm) pressure and in the presence of Et3N. Catalyst 4 was found to be the most efficient catalyst and showed a 31% formation of cyclic carbonates with a TON of 620 under 1 atm air as the CO2 source. This yield was enhanced to 94% with a TON of 1880 under 1 atm pure CO2 gas and it is the highest catalytic efficiency known for nickel(ii)-based catalysts. Catalyst 4 enabled the transformation of a wide range of epoxides (eight examples) into corresponding cyclic carbonates with excellent selectivity (>99%) and yields of 59-94% and 11-31% under pure CO2 and atmospheric CO2, respectively. The catalytic efficiency is strongly influenced by the electronic nature of the complexes. The CO2 fixation reactions without an epoxide substrate led to the formation of the carbonate bridged dinuclear nickel(ii) complexes [(LNiII)2CO3](BPh4)21a-4a, which are speculated as catalytically active intermediates. The formation of these species was accompanied by the formation of new absorption bands around 592-681 nm and was further confirmed by the ESI-MS and IR spectral studies. The molecular structures of these carbonate-bridged key intermediates were determined by X-ray analysis. The structures contain two Ni2+-centers bridged via a carbonate ion that originated from CO2. Distorted square pyramidal geometries are adopted around each Ni(ii) center. All these results support that CO2 fixation reactions occur via CO2-bound nickel key intermediates.
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Affiliation(s)
- Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai-625021, India.
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5
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Muthuramalingam S, Anandababu K, Velusamy M, Mayilmurugan R. Benzene Hydroxylation by Bioinspired Copper(II) Complexes: Coordination Geometry versus Reactivity. Inorg Chem 2020; 59:5918-5928. [DOI: 10.1021/acs.inorgchem.9b03676] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
| | - Karunanithi Anandababu
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
| | - Marappan Velusamy
- Department of Chemistry, North Eastern Hill University, Shillong 793022, India
| | - Ramasamy Mayilmurugan
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
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Anandababu K, Muthuramalingam S, Velusamy M, Mayilmurugan R. Single-step benzene hydroxylation by cobalt(ii) catalysts via a cobalt(iii)-hydroperoxo intermediate. Catal Sci Technol 2020. [DOI: 10.1039/c9cy02601k] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cobalt(ii) complexes reported as efficient and selective catalysts for single-step phenol formation from benzene using H2O2. The catalysis proceeds likely via cobalt(iii)-hydroperoxo species.
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Affiliation(s)
- Karunanithi Anandababu
- Bioinorganic Chemistry Laboratory/Physical Chemistry
- School of Chemistry
- Madurai Kamaraj University
- Madurai-625021
- India
| | - Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry
- School of Chemistry
- Madurai Kamaraj University
- Madurai-625021
- India
| | - Marappan Velusamy
- Department of Chemistry
- North Eastern Hill University
- Shillong-793022
- India
| | - Ramasamy Mayilmurugan
- Bioinorganic Chemistry Laboratory/Physical Chemistry
- School of Chemistry
- Madurai Kamaraj University
- Madurai-625021
- India
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7
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Muthuramalingam S, Sankaralingam M, Velusamy M, Mayilmurugan R. Catalytic Conversion of Atmospheric CO2 into Organic Carbonates by Nickel(II) Complexes of Diazepane-Based N4 Ligands. Inorg Chem 2019; 58:12975-12985. [DOI: 10.1021/acs.inorgchem.9b01908] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
| | - Muniyandi Sankaralingam
- Department of Chemistry, National Institute of Technology Calicut, Kozhikode, Kerala 673601, India
| | - Marappan Velusamy
- Department of Chemistry, North Eastern Hill University, Shillong 793022, India
| | - Ramasamy Mayilmurugan
- Bioinorganic Chemistry Laboratory/Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
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8
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Muthuramalingam S, Maheshwaran D, Velusamy M, Mayilmurugan R. Regioselective oxidative carbon-oxygen bond cleavage catalysed by copper(II) complexes: A relevant model study for lytic polysaccharides monooxygenases activity. J Catal 2019. [DOI: 10.1016/j.jcat.2019.03.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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9
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Alexandropoulos DI, Vignesh KR, Stamatatos TC, Dunbar KR. Rare "Janus"-faced single-molecule magnet exhibiting intramolecular ferromagnetic interactions. Chem Sci 2019; 10:1626-1633. [PMID: 30842825 PMCID: PMC6368239 DOI: 10.1039/c8sc04384a] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Accepted: 11/03/2018] [Indexed: 11/21/2022] Open
Abstract
The unusual ferromagnetically coupled compound was prepared by the use of Me3SiN3 with the metal ions being exclusively bridged by end-on N3–. Th cationic molecule is a rare example of a 3d-metal cluster exhibiting a “Janus”-faced SMM behavior for the dried and wet forms.
A rare disk-like single-molecule magnet (SMM) exclusively bridged by end-on azides with a spin ground state of S = 14 was prepared by the reaction of a divalent FeII precursor with Me3SiN3 under basic conditions. AC magnetic susceptibility studies revealed unusual, “Janus”-faced SMM behavior for the dried and pristine forms of the compound attributed to solvation/de-solvation effects of the coordinated MeCN ligands which leads to alterations in the crystal field and symmetry of the metal ions. DFT calculations confirmed the ferromagnetic nature of the interactions between the FeII spin carriers with the zero-field splitting parameters D = –0.2323 cm–1 and E/D = 0.027. The results have important implications for the future study of single-molecule magnets incorporating volatile solvent molecules in the first coordination sphere of the metal ions and their effect on the relaxation dynamics.
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Affiliation(s)
| | - Kuduva R Vignesh
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , USA .
| | - Theocharis C Stamatatos
- Department of Chemistry , Brock University , 1812 Sir Isaac Brock Way , L2S 3A1 St. Catharines , Ontario , Canada .
| | - Kim R Dunbar
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , USA .
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Muthuramalingam S, Anandababu K, Velusamy M, Mayilmurugan R. One step phenol synthesis from benzene catalysed by nickel(ii) complexes. Catal Sci Technol 2019. [DOI: 10.1039/c9cy01471c] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Nickel(ii)complexes of N4-ligands are reported as efficient catalysts for direct benzene hydroxylation via bis(μ-oxo)dinickel(iii) intermediate species. The exclusive phenol formation is achieved with a yield of 41%.
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Affiliation(s)
- Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry
- School of Chemistry
- Madurai Kamaraj University
- Madurai-625021
- India
| | - Karunanithi Anandababu
- Bioinorganic Chemistry Laboratory/Physical Chemistry
- School of Chemistry
- Madurai Kamaraj University
- Madurai-625021
- India
| | - Marappan Velusamy
- Department of Chemistry
- North Eastern Hill University
- Shillong-793022
- India
| | - Ramasamy Mayilmurugan
- Bioinorganic Chemistry Laboratory/Physical Chemistry
- School of Chemistry
- Madurai Kamaraj University
- Madurai-625021
- India
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Phonsri W, Macedo DS, Vignesh KR, Rajaraman G, Davies CG, Jameson GNL, Moubaraki B, Ward JS, Kruger PE, Chastanet G, Murray KS. Halogen Substitution Effects on N
2
O Schiff Base Ligands in Unprecedented Abrupt Fe
II
Spin Crossover Complexes. Chemistry 2017; 23:7052-7065. [DOI: 10.1002/chem.201700232] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Wasinee Phonsri
- School of Chemistry, Building 23 Monash University Clayton Victoria 3800 Australia
| | - David S. Macedo
- School of Chemistry, Building 23 Monash University Clayton Victoria 3800 Australia
| | | | - Gopalan Rajaraman
- Department of Chemistry Indian Institute of Technology Mumbai 400076 India
| | - Casey G. Davies
- Department of Chemistry MacDiarmid Institute for Advanced, Materials and Nanotechnology University of Otago Dunedin 9054 New Zealand
| | - Guy N. L. Jameson
- Department of Chemistry MacDiarmid Institute for Advanced, Materials and Nanotechnology University of Otago Dunedin 9054 New Zealand
| | - Boujemaa Moubaraki
- School of Chemistry, Building 23 Monash University Clayton Victoria 3800 Australia
| | - Jas S. Ward
- Department of Chemistry MacDiarmid Institute for Advanced, Materials and Nanotechnology University of Canterbury Private Bag 4800 Christchurch 8041 New Zealand
| | - Paul E. Kruger
- Department of Chemistry MacDiarmid Institute for Advanced, Materials and Nanotechnology University of Canterbury Private Bag 4800 Christchurch 8041 New Zealand
| | - Guillaume Chastanet
- CNRS Université de Bordeaux, ICMCB 87 avenue du Dr. A. Schweitzer Pessac 33608 France
| | - Keith S. Murray
- School of Chemistry, Building 23 Monash University Clayton Victoria 3800 Australia
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Muthuramalingam S, Subramaniyan S, Khamrang T, Velusamy M, Mayilmurugan R. Copper(II)-Bioinspired Models for Copper Amine Oxidases: Oxidative Half-Reaction in Water. ChemistrySelect 2017. [DOI: 10.1002/slct.201601786] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Sethuraman Muthuramalingam
- Bioinorganic Chemistry Laboratory/Physical Chemistry; School of Chemistry; Madurai Kamaraj University; Madurai 625 021, Tamil Nadu India
| | - Shanmugam Subramaniyan
- Bioinorganic Chemistry Laboratory/Physical Chemistry; School of Chemistry; Madurai Kamaraj University; Madurai 625 021, Tamil Nadu India
| | - Themmila Khamrang
- Department of Chemistry; North Eastern Hill Universuty; Shillong- 793022 India
| | - Marappan Velusamy
- Department of Chemistry; North Eastern Hill Universuty; Shillong- 793022 India
| | - Ramasamy Mayilmurugan
- Bioinorganic Chemistry Laboratory/Physical Chemistry; School of Chemistry; Madurai Kamaraj University; Madurai 625 021, Tamil Nadu India
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Kroll N, Theilacker K, Schoknecht M, Baabe D, Wiedemann D, Kaupp M, Grohmann A, Hörner G. Controlled ligand distortion and its consequences for structure, symmetry, conformation and spin-state preferences of iron(II) complexes. Dalton Trans 2015; 44:19232-47. [PMID: 26488906 DOI: 10.1039/c5dt02502h] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The ligand-field strength in metal complexes of polydentate ligands depends critically on how the ligand backbone places the donor atoms in three-dimensional space. Distortions from regular coordination geometries are often observed. In this work, we study the isolated effect of ligand-sphere distortion by means of two structurally related pentadentate ligands of identical donor set, in the solid state (X-ray diffraction, (57)Fe-Mössbauer spectroscopy), in solution (NMR spectroscopy, UV/Vis spectroscopy, conductometry), and with quantum-chemical methods. Crystal structures of hexacoordinate iron(II) and nickel(II) complexes derived from the cyclic ligand L(1) (6-methyl-6-(pyridin-2-yl)-1,4-bis(pyridin-2-ylmethyl)-1,4-diazepane) and its open-chain congener L(2) (N(1),N(3),2-trimethyl-2-(pyridine-2-yl)-N(1),N(3)-bis(pyridine-2-ylmethyl) propane-1,3-diamine) reveal distinctly different donor set distortions reflecting the differences in ligand topology. Distortion from regular octahedral geometry is minor for complexes of ligand L(2), but becomes significant in the complexes of the cyclic ligand L(1), where trans elongation of Fe-N bonds cannot be compensated by the rigid ligand backbone. This provokes trigonal twisting of the ligand field. This distortion causes the metal ion in complexes of L(1) to experience a significantly weaker ligand field than in the complexes of L(2), which are more regular. The reduced ligand-field strength in complexes of L(1) translates into a marked preference for the electronic high-spin state, the emergence of conformational isomers, and massively enhanced lability with respect to ligand exchange and oxidation of the central ion. Accordingly, oxoiron(IV) species derived from L(1) and L(2) differ in their spectroscopic properties and their chemical reactivity.
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Affiliation(s)
- Nicole Kroll
- Technische Universität Berlin, Institut für Chemie, Sekr. C2, Straße des 17. Juni 135, 10623 Berlin, Germany.
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14
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Synthesis, selected coordination chemistry and extraction behavior of a (phosphinoylmethyl)pyridyl N-oxide-functionalized ligand based upon a 1,4-diazepane platform. Polyhedron 2015. [DOI: 10.1016/j.poly.2015.05.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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15
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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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