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Androutsopoulos A, Sader S, Miliordos E. Potential of Molecular Catalysts with Electron-Rich Transition Metal Centers for Addressing Long-Standing Chemistry Enigmas. J Phys Chem A 2024; 128:4401-4411. [PMID: 38797970 DOI: 10.1021/acs.jpca.4c01800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
Molecular complexes with electron-rich metal centers are highlighted as potential catalysts for the following five important chemical transformations: selective conversion of methane to methanol, capture and utilization of carbon dioxide, fixation of molecular nitrogen, water splitting, and recycling of perfluorochemicals. Our initial focus lies on negatively charged metal centers and ligands that can stabilize anionic metal atoms. Catalysts with electron-rich metal atoms (CERMAs) can sustain catalytic cycles with a "ping-pong" mechanism, where one or more electrons are transferred from the metal center to the substrate and back. The donated electrons can activate the chemical bonds of the substrate by populating its antibonding orbitals. At the last step of the catalytic cycle, the electrons return to the metal and the product interacts only weakly with the formed anion, which enables the solvent molecules to remove the product fast from the catalytic cycle and prevent subsequent unfavorable reactions. This process resembles electrocatalysis, but the metal serves as both an anode and a cathode (molecular electrocatalysis). We also analyze the usage of CERMAs as the base of Frustrated Lewis pairs proposing a new type of bimetallic catalysts. This Featured Article aspires to initiate systematic experimental and theoretical studies on CERMAs and their reactivity, the potential of which has probably been underestimated in the literature.
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Affiliation(s)
| | - Safaa Sader
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
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Miliordos E, Moore JL, Obisesan SV, Oppelt J, Ivanović-Burmazović I, Goldsmith CR. Computational Analysis of the Superoxide Dismutase Mimicry Exhibited by a Zinc(II) Complex with a Redox-Active Organic Ligand. J Phys Chem A 2024; 128:1491-1500. [PMID: 38354404 DOI: 10.1021/acs.jpca.3c07403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2024]
Abstract
Previously, we found that a Zn(II) complex with the redox-active ligand N-(2,5-dihydroxybenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (H2qp1) was able to act as a functional mimic of superoxide dismutase, despite its lack of a redox-active transition metal. As the complex catalyzes the dismutation of superoxide to form O2 and H2O2, the quinol in the ligand is believed to cycle between three oxidation states: quinol, quinoxyl radical, and para-quinone. Although the metal is not the redox partner, it nonetheless is essential to the reactivity since the free ligand by itself is inactive as a catalyst. In the present work, we primarily use calculations to probe the mechanism. The calculations support the inner-sphere decomposition of superoxide, suggest that the quinol/quinoxyl radical couple accounts for most of the catalysis, and elucidate the many roles that proton transfer between the zinc complexes and buffer has in the reactivity. Acid/base reactions involving the nonmetal-coordinating hydroxyl group on the quinol are predicted to be key to lowering the energy of the intermediates. We prepared a Zn(II) complex with N-(2-hydroxybenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hpp1) that lacks this functional group and found that it could not catalyze the dismutation of superoxide; this confirms the importance of the second, distal hydroxyl group of the quinol.
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Affiliation(s)
- Evangelos Miliordos
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
| | - Jamonica L Moore
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
| | - Segun V Obisesan
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
| | - Julian Oppelt
- Department of Chemistry, Ludwig-Maximilians-Universität München, 81377 München, Germany
| | | | - Christian R Goldsmith
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
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He N, Nakatani N, Hada M. How does multi-reference computation change the catalysis chemistry? DFT and CASPT2 studies of the Cu-catalysed coupling reactions between aryl iodides and β-diketones. Phys Chem Chem Phys 2023; 25:28871-28884. [PMID: 37853798 DOI: 10.1039/d3cp03418f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2023]
Abstract
The molecular mechanism of a Cu-catalysed coupling reaction was theoretically studied using density functional theory (DFT) and the complete active space self-consistent field method followed by the second-order perturbation theory (CASSCF/CASPT2) to investigate the effects of the strong electron correlation of the Cu centre on the reaction profile. Both DFT and CASSCF/CASPT2 calculations showed that the catalytic cycle proceeds via an oxidative addition (OA) reaction, followed by a reductive elimination (RE) reaction, where OA is the rate-determining step. Although the DFT-calculated activation energies of the OA and RE steps are highly dependent on the choice of functionals, the CASSCF/CASPT2 results are less affected by the choice of DFT-optimised geometries. Therefore, with a careful assessment based on the CASSCF/CASPT2 single-point energy evaluation, an optimal choice of the DFT geometry is of good qualitative use for energetics at the CASPT2 level of theory. Based on the changes in the electron populations of the 3d orbitals during the OA and RE steps, the characteristic features of the DFT-calculated electronic structure were qualitatively consistent with those calculated using the CASSCF method. Further electronic structure analysis by the natural orbital occupancy of the CASSCF wavefunction showed that the ground state is almost single-reference in this system and the strong electron correlation effect of the Cu centre can be dealt with using the MP2 or CCSD method, too. However, the slightly smaller occupation numbers of the 3dπ orbital in the course of reactions suggested that the electron correlation effect of the Cu(III) centre appears through the interaction between the 3dπ orbital and the C-I antibonding σ* orbital in the OA step, and between the 3dπ orbital and the Cu-C antibonding σ* orbital in the RE step.
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Affiliation(s)
- Nan He
- Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397, Japan.
| | - Naoki Nakatani
- Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397, Japan.
| | - Masahiko Hada
- Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397, Japan.
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Depastas T, Androutsopoulos A, Tzeli D. Analysis of chemical bonding of the ground and low-lying states of Mo 2 and of Mo 2Cl x complexes, x = 2 - 10. J Chem Phys 2022; 157:054302. [DOI: 10.1063/5.0091907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
In the present study, we perform accurate calculations via multireference configuration interaction and coupled cluster methodologies on the dimolybdenum molecule in conjunction with complete series of correlation and weighted core correlation consistent basis sets up to quintuple size. The bonding, dissociation energies, and spectroscopic parameters of the seven states that correlate to the ground state products are calculated. The ground state has a sextuple chemical bond and each of the calculated excited state has one less bond than the previous one. The calculated values for the ground(X1Σg+ ) state of Mo2 have been extrapolated to the complete basis set limits. Our final values, re=1.9324 Å and De(D0)=4.502{plus minus}0.007(4.471{plus minus}0.009) eV, are in excellent agreement with the experimental values of re=1.929, 1.938(9) Å and D0=4.476(10) eV. The Mo2 in 13Σg+ state is a weakly bound dimer, forming 5s...5pz bonds, with De=0.120 eV at re=3.53 Å. All calculated excited states (except 13Σg+) have a highly multireference character (C0=0.25-0.55). The ordering of the molecular bonding orbitals changes as the spin is increased from quintet to septet state. The quite low bond dissociation energy of the ground state is due to the splitting of the molecular bonding orbitals in two groups differing in energy by ~3 eV. Finally, the bond breaking of Mo2, as the multiplicity of spin is increased, is analyzed in parallel with the Mo-Mo bond breaking in a series of Mo2Clx complexes when x is increased. Physical insight into the nature of the sextuple bond and its low dissociation energy is provided.
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Affiliation(s)
| | | | - Demeter Tzeli
- Department of Chemistry, National and Kapodistrian University of Athens Department of Chemistry, Greece
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Zhang NX, Wang C, Wu Q, Lan J, Chai Z, Shi W. Highly stable actinide(III) complexes supported by doubly aromatic ligands. Phys Chem Chem Phys 2022; 24:5921-5928. [DOI: 10.1039/d1cp05058c] [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
Owing to the electron-deficient nature of boron atom, the structures and properties of boron clusters can be enriched by doping various metal atoms, including lanthanide metal atoms. Nevertheless, the viability...
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Khan SN, Miliordos E. Electronic Structure of RhO 2+, Its Ammoniated Complexes (NH 3) 1-5RhO 2+, and Mechanistic Exploration of CH 4 Activation by Them. Inorg Chem 2021; 60:16111-16119. [PMID: 34637614 DOI: 10.1021/acs.inorgchem.1c01447] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
High-level electronic structure calculations are initially performed to investigate the electronic structure of RhO2+. The construction of potential energy curves for the ground and low-lying excited states allowed the calculation of spectroscopic constants, including harmonic and anharmonic vibrational frequencies, bond lengths, spin-orbit constants, and excitation energies. The equilibrium electronic configurations were used for the interpretation of the chemical bonding. We further monitored how the Rh-O bonding scheme changes with the gradual addition of ammonia ligands. The nature of this bond remains unaffected up to four ammonia ligands but adopts a different electronic configuration in the pseudo-octahedral geometry of (NH3)5RhO2+. This has consequences in the activation mechanism of the C-H bond of methane by these complexes, especially (NH3)4RhO2+. We show that the [2 + 2] mechanism in the (NH3)4RhO2+ case has a very low energy barrier comparable to that of a radical mechanism. We also demonstrate that methane can coordinate to the metal in a similar fashion to ammonia and that knowledge of the electronic structure of the pure ammonia complexes provides qualitative insights into the optimal reaction mechanism.
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Affiliation(s)
- Shahriar N Khan
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
| | - Evangelos Miliordos
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
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Lam CS, Lau KC. High-Level ab Initio Predictions for the Ionization Energies, Bond Dissociation Energies, and Heats of Formation of Vanadium Methylidene, Vanadium Methyl Species, and Their Cations (VCH 2/VCH 2+, VCH 3/VCH 3+). J Phys Chem A 2021; 125:4957-4966. [PMID: 34076442 DOI: 10.1021/acs.jpca.1c01381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ionization energies of VCH2 and VCH3, the various 0 K bond dissociation energies (D0s) in their neutrals and cations, and their respective heats of formation at 0 and 298 K are computed by the single-reference, wave function-based CCSDTQ/CBS procedure. The core of the composite method is the approximation to the complete basis set (CBS) limit at the coupled cluster (CC) level which includes up to full quadruple excitations. The zero-point vibrational energy, core-valence correlation, spin-orbit coupling, and scalar relativistic effects have their contributions incorporated in an additive manner. For the species in the current study, this protocol requires geometry optimizations and harmonic frequency calculations practically no higher than the CCSD(T)/aug-cc-pwCVTZ and CCSD(T)/aug-cc-pVTZ levels, respectively. The present calculations successfully predict D0(V+-CH3) = 2.126 eV and D0(V+-CH2) = 3.298 eV in remarkable agreement with the data recently measured by a spin-orbit state selected V+ + CH4 collision experiment (Phys. Chem. Chem. Phys. 2021, 23, 273-286). The good accord encourages the use of CCSDTQ/CBS protocol in thermochemical predictions of various feasible product channels identified in methane activation by transition metal species.
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Affiliation(s)
- Chow-Shing Lam
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong
| | - Kai-Chung Lau
- Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong
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White MV, Kirkland JK, Vogiatzis KD. Redox states of dinitrogen coordinated to a molybdenum atom. J Chem Phys 2021; 154:224308. [PMID: 34241210 DOI: 10.1063/5.0050596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Chemical structures bearing a molybdenum atom have been suggested for the catalytic reduction of N2 at ambient conditions. Previous computational studies on gas-phase MoN and MoN2 species have focused only on neutral structures. Here, an ab initio electronic structure study on the redox states of small clusters composed of nitrogen and molybdenum is presented. The complete-active space self-consistent field method and its extension via second-order perturbative complement have been applied on [MoN]n and [MoN2]n species (n = 0, 1±, 2±). Three different coordination modes (end-on, side-on, and linear NMoN) have been considered for the triatomic [MoN2]n. Our results demonstrate that the reduced states of such systems lead to a greater degree of N2 activation, which can be the starting point of different reaction channels.
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Affiliation(s)
- Maria V White
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996-1600, USA
| | - Justin K Kirkland
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996-1600, USA
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Sader S, Miliordos E. Methane to Methanol Conversion Facilitated by Anionic Transition Metal Centers: The Case of Fe, Ni, Pd, and Pt. J Phys Chem A 2021; 125:2364-2373. [PMID: 33710883 DOI: 10.1021/acs.jpca.0c10577] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Density functional theory and high-level ab initio electronic structure calculations are performed to study the mechanism of the partial oxidation of methane to methanol facilitated by the titled anionic transition metal atoms. The energy landscape for the overall reaction M- + N2O + CH4 → M- + N2 + CH3OH (M = Fe, Ni, Pd, Pt) is constructed for different reaction pathways for all four metals. The comparison with earlier experimental and theoretical results for cationic centers demonstrates the better performance of the metal anions. The main advantage is that anionic centers interact weakly with the produced methanol. This fact facilitates the fast removal of methanol from the catalytic center and prevents the overoxidation of methane. Moreover, a moderate or high energy barrier for the M- + CH4 → HMCH3- reaction step is observed, which protects the metal center from deactivation. Future work should focus on the identification of proper ligands, which stabilize the negative charge on the metal (electronic factors) and prevent the formation of the global CH3MOH- minimum (steric factors). Finally, a composite electronic structure method (combining size extensive coupled clusters approaches and accurate multireference configuration interaction) is proposed for computationally demanding systems and is applied to Fe-.
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Affiliation(s)
- Safaa Sader
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
| | - Evangelos Miliordos
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
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Khan SN, Miliordos E. Scandium in Neutral and Positively Charged Ammonia Complexes: Balancing between Sc2+ and Sc3+. J Phys Chem A 2020; 124:4400-4412. [DOI: 10.1021/acs.jpca.0c00693] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Shahriar N. Khan
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
| | - Evangelos Miliordos
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States
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Jackson BA, Miliordos E. Weak-field ligands enable inert early transition metal oxides to convert methane to methanol: the case of ZrO. Phys Chem Chem Phys 2020; 22:6606-6618. [PMID: 32159167 DOI: 10.1039/c9cp06050b] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Zirconium monoxide, ZrO, was studied by multi-reference configuration interaction (MRCI) and coupled cluster methods using large basis sets in conjunction with effective core potentials. Complete potential energy curves were constructed and bonding patterns are proposed for several electronic states. Numerical results include accurate equilibrium bond lengths, harmonic vibrational frequencies, anharmonicities, excitation energies, dipole moments, and binding energies for both ground and excited states. The application of a ZrO unit as the catalytic center for methane activation is explored through the reaction ZrO + CH4→ Zr + CH3OH. Optimal density functional structures combined with single-point MRCI energy calculations are obtained for the complete reaction pathway. It is found that the lower energy singlet and triplet multiplicities (oxo states) favor the [2+2] mechanism and the higher energy quintets (oxyl states) favor the radical mechanism, which is overall more efficient in producing methanol. We finally suggest proper ligands that stabilize the oxyl states. These include halogens or other weak-field ligands, which finally convert the inert early transition metal oxide units to efficient methane-to-methanol catalysts.
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Affiliation(s)
- Benjamin A Jackson
- Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36849-5312, USA.
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Almeida NMS, Ariyarathna IR, Miliordos E. O-H and C-H Bond Activations of Water and Methane by RuO 2+ and (NH 3)RuO 2+: Ground and Excited States. J Phys Chem A 2019; 123:9336-9344. [PMID: 31580075 DOI: 10.1021/acs.jpca.9b05910] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Investigation of the ground and excited states of RuO2+ is carried out using multireference quantum chemical methodologies. The electronic structure is explored in detail, and accurate spectroscopic constants for 12 states are reported. Although ruthenium belongs to the same group as iron, the ground state of RuO2+ is 1Σ+ with a strong oxo character as opposed to the 3Δ of FeO2+ with primarily oxyl character. To see the effect of the different electronic structure of RuO2+ on the O-H and C-H bond activation processes, we studied its reaction with one water or methane molecule. Reaction energies and activation barriers are given for six low-lying electronic states of singlet, triplet, and quintet spin multiplicities. It is found that the higher-energy quintet state (5Σ+) provides the lowest activation energies and is the same state responsible for the C-H activation for FeO2+ complexes. The reason is attributed to its weaker metal-oxygen bond (longer bond length), which is "prepared" to be activated at the same time with the O-H and C-H bonds. The effect of an ammonia ligand in the chemical activity is also discussed.
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Affiliation(s)
- Nuno M S Almeida
- Department of Chemistry and Biochemistry , Auburn University , Auburn , Alabama 36849-5312 , United States
| | - Isuru R Ariyarathna
- Department of Chemistry and Biochemistry , Auburn University , Auburn , Alabama 36849-5312 , United States
| | - Evangelos Miliordos
- Department of Chemistry and Biochemistry , Auburn University , Auburn , Alabama 36849-5312 , United States
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Claveau EE, Miliordos E. Quantum chemical calculations on NbO and its reaction with methane: ground and excited electronic states. Phys Chem Chem Phys 2019; 21:26324-26332. [DOI: 10.1039/c9cp05408a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Our high-level calculations show that high-spin NbO electronic states facilitate the methane to methanol transformation via a very efficient radical mechanism, as opposed to the [2+2] mechanism observed for the rest of the low-lying states.
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Affiliation(s)
- Emily E. Claveau
- Department of Chemistry and Biochemistry
- Auburn University
- Auburn
- USA
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