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King KE, Franke PR, Pullen GT, Schaefer HF, Douberly GE. Helium Droplet Infrared Spectroscopy of the Butyl Radicals. J Chem Phys 2022; 157:084311. [DOI: 10.1063/5.0102287] [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
Butyl radicals ( n-, s-, i-,} and tert-butyl) are formed from the pyrolysis of stable precursors (1-pentyl nitrite, 2-methyl-1-butyl nitrite, isopentyl nitrite, and azo- tert-butane, respectively). The radicals are doped into a beam of liquid helium droplets and probed with infrared action spectroscopy from 2700-3125 cm-1, allowing for a low temperature measurement of the CH stretching region. The presence of anharmonic resonance polyads in the 2800-3000 cm-1 region complicates its interpretation. To facilitate spectral assignment, the anharmonic resonances are modeled with two model Hamiltonian approaches that explicitly couple CH stretch fundamentals to HCH bend overtones and combinations: a VPT2+K normal mode model based on CCSD(T) quartic force fields and a semi-empirical local mode model. Both of these computational methods provide generally good agreement with the experimental spectra.
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Anila S, Suresh CH, Schaefer HF. Demarcating Noncovalent and Covalent Bond Territories: Imine-CO 2 Complexes and Cooperative CO 2 Capture. J Phys Chem A 2022; 126:4952-4961. [PMID: 35862882 DOI: 10.1021/acs.jpca.2c03221] [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
Chemical bond territory is rich with covalently bonded molecules wherein a strong bond is formed by equal or unequal sharing of a quantum of electrons. The noncovalent version of the bonding scenarios expands the chemical bonding territory to a weak domain wherein the interplay of electrostatic and π-effects, dipole-dipole, dipole-induced dipole, and induced dipole-induced dipole interactions, and hydrophobic effects occur. Here we study both the covalent and noncovalent interactive behavior of cyclic and acyclic imine-based functional molecules (XN) with CO2. All parent XN systems preferred the formation of noncovalent (nc) complex XN···CO2, while more saturated such systems (XN') produced both nc and covalent (c) complexes XN'+-(CO2)-. In all such cases, crossover from an nc to c complex is clearly demarcated with the identification of a transition state (ts). The complexes XN'···CO2 and XN'+-(CO2)- are bond stretch isomers, and they define the weak and strong bonding territories, respectively, while the ts appears as the demarcation point of the two territories. Cluster formation of XN with CO2 reinforces the interaction between them, and all become covalent clusters of general formula (XN+-(CO2)-)n. The positive cooperativity associated with the NH···OC hydrogen bond formation between any two XN'+-(CO2)- units strengthened the N-C coordinate covalent bond and led to massive stabilization of the cluster. For instance, the stabilizing interaction between the XN unit with CO2 is increased from 2-7 kcal/mol range in a monomer complex to 14-31 kcal/mol range for the octamer cluster (XN'+-(CO2)-)8. The cooperativity effect compensates for the large reduction in the entropy of cluster formation. Several imine systems showed the exergonic formation of the cluster and are predicted as potential candidates for CO2 capture and conversion.
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Tran PM, Wang Y, Xie Y, Wei P, Lahm ME, Schaefer HF, Robinson GH. Phosphine-Mediated Cleavage of Sulfur–Sulfur Bonds. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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29
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Goodlett SM, Turney JM, Douberly GE, Schaefer HF. The noncovalent interaction between water and the 3P ground state of the oxygen atom*. Mol Phys 2022. [DOI: 10.1080/00268976.2022.2086934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Wang H, Wang Y, Li H, Hu Y, Fan Q, King RB, Schaefer HF. Adiabatic Electron Detachment Energies, Reaction Barriers, Chemical Balance, and Ligand Effects on the Nucleophilicities of Metal Carbonyl Monoanions. Organometallics 2022. [DOI: 10.1021/acs.organomet.1c00716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Galabov B, Ilieva S, Cheshmedzhieva D, Nikolova V, Popov VA, Hadjieva B, Schaefer HF. Mini-Review on Structure-Reactivity Relationship for Aromatic Molecules: Recent Advances. ACS OMEGA 2022; 7:8199-8208. [PMID: 35309413 PMCID: PMC8928515 DOI: 10.1021/acsomega.1c07176] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 02/22/2022] [Indexed: 06/14/2023]
Abstract
Recent advances in quantifying nucleophilic reactivities in chemical reactions and intermolecular interactions of aromatic molecules are reviewed. This survey covers experimental (IR frequency shifts induced by hydrogen bonding) and theoretical (modeling of potential energy surfaces, atomic charges, molecular electrostatic potential) approaches in characterizing chemical reactivity. Recent advances in software developments assisting the evaluation of the reactive sites for electrophilic aromatic substitution are briefly discussed.
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Wang Y, Tran PM, Dzikovski B, Xie Y, Wei P, Rains AA, Asadi H, Ramasamy RP, Schaefer HF, Robinson GH. A Cationic Magnesium-Based Dithiolene Radical. Organometallics 2022. [DOI: 10.1021/acs.organomet.1c00607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Jia Z, Li L, Zhang X, Yang K, Li H, Xie Y, Schaefer HF. Acceleration Effect of Bases on Mn Pincer Complex-Catalyzed CO 2 Hydroboration. Inorg Chem 2022; 61:3970-3980. [PMID: 35212516 DOI: 10.1021/acs.inorgchem.1c03614] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Herein, we report a comprehensive study of CO2 hydroboration catalyzed by Mn pincer complexes. The traditional metal-ligand cooperation (MLC) mechanism based on the H-Mn-N-Bpin pincer complex is not viable due to the competing abstraction of the Bpin group from the H-Mn-N-Bpin complex by NaOtBu. Instead, we propose an ionic mechanism based on the H-Mn-N-Na species with a low energy span (22.5 kcal/mol) and unveil the acceleration effect of bases. The X groups in the H-Mn-N-X catalyst models are further modulated, and the steric hindrance and H→B donor-acceptor interactions of the X group increase the energy barrier of the hydride transfer. The hydrogen bond and electrostatic interactions of the X group can accelerate the hydride transfer to HCOOBpin and HCHO molecules except for the nonpolar CO2 molecule. Based on these discoveries, we designed a pyridine-based Mn pincer catalyst system, which could achieve CO2 hydroboration in low-temperature and base-free conditions through a metal-ligand cooperation mechanism.
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Wang Y, Wang H, Li H, Hu Y, Fan Q, King RB, Schaefer HF. Substituent, Solvent, and Dispersion Effects on the Zwitterionic Character and Dimerization Thermochemistry of the Group 6 Fulvene Metal Tricarbonyl Complexes. J Phys Chem A 2022; 126:365-372. [PMID: 35023736 DOI: 10.1021/acs.jpca.1c07276] [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
Dimerizations of fulvene metal tricarbonyl complexes of the type (C5H4CRR')M(CO)3 (R, R' = MeO, Me, H; M = Cr, Mo, W) to form a metal-metal bond and a new carbon-carbon bond, thereby giving binuclear cyclopentadienyl metal carbonyl derivatives, are predicted to be thermochemically favored but to have significant activation energies ranging from ΔE = 19 to 42 kcal/mol. However, the introduction of dimethylamino but not methoxy substituents onto the exocyclic carbon atom changes the situation drastically so that the monomers [C5H4CH(NMe2)]M(CO)3 and [C5H4C(NMe2)2]M(CO)3 become strongly thermochemically favored, lying ΔE = 43 kcal/mol (M = W) to 63 kcal/mol (M = Cr) below their corresponding dimers. In such dimethylamino-substituted (fulvene)M(CO)3 derivatives, the M-C distance to the exocyclic fulvene carbon is lengthened beyond the bonding distance to give a zwitterionic structure with a pentahapto fulvene ligand. Such M-C distances in (fulvene)M(CO)3 complexes, which have preferred zwitterionic structures, increase with increasing solvent polarity (i.e., dielectric constant) until a saturation point is reached.
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Aroeira GJR, Davis MM, Turney JM, Schaefer HF. Fermi.jl: A Modern Design for Quantum Chemistry. J Chem Theory Comput 2022; 18:677-686. [PMID: 34978451 DOI: 10.1021/acs.jctc.1c00719] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Approximating molecular wave functions involves heavy numerical effort; therefore, codes for such tasks are written completely or partially in efficient languages such as C, C++, and Fortran. While these tools are dominant throughout quantum chemistry packages, the efficient development of new methods is often hindered by the complexity associated with code development. In order to ameliorate this scenario, some software packages take a dual approach where a simpler, higher-level language, such as Python, substitutes the traditional ones wherever performance is not critical. Julia is a novel, dynamically typed, programming language that aims to solve this two-language problem. It gained attention because of its modern and intuitive design, while still being highly optimized to compete with "low-level" languages. Recently, some chemistry-related projects have emerged exploring the capabilities of Julia. Herein, we introduce the quantum chemistry package Fermi.jl, which contains the first implementations of post-Hartree-Fock methods written in Julia. Its design makes use of many Julia core features, including multiple dispatch, metaprogramming, and interactive usage. Fermi.jl is a modular package, where new methods and implementations can be easily added to the existing code. Furthermore, it is designed to maximize code reusability by relying on general functions with specialized methods for particular cases. The feasibility of the project is explored through evaluating the performance of popular ab initio methods. It is our hope that this project motivates the usage of Julia within the community and brings new contributions into Fermi.jl.
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Li G, Yao Y, Lin Y, Meng Y, Xie Y, Schaefer HF. The reaction between the bromine atom and the water trimer: high level theoretical studies. Phys Chem Chem Phys 2022; 24:26164-26169. [DOI: 10.1039/d2cp03525a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The Br + (H2O)3 → HBr + (H2O)2OH reaction has been investigated using the CCSD(T) method with the basis sets as large as cc-pVQZ(-PP). The Br + (H2O)3 reaction is also compared with related Br + H2O/(H2O)2 and F/Cl + (H2O)3 reactions.
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Hu Y, Wang H, Ji Y, Li H, Fan Q, King RB, Schaefer HF. Binuclear Alkyne Manganese Carbonyls: Their Rearrangements to Allene, Allyl, and Vinylcarbene Derivatives by Hydrogen Migration from Methyl Substituents. Eur J Inorg Chem 2021. [DOI: 10.1002/ejic.202100375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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38
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Misiewicz JP, Turney JM, Schaefer HF. Cumulants as the variables of density cumulant theory: A path to Hermitian triples. J Chem Phys 2021; 155:244105. [PMID: 34972366 DOI: 10.1063/5.0076888] [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
We study the combination of orbital-optimized density cumulant theory and a new parameterization of reduced density matrices in which the variables are the particle-hole cumulant elements. We call this combination OλDCT. We find that this new Ansatz solves problems identified in the previous unitary coupled cluster Ansatz for density cumulant theory: the theory is now free of near-zero denominators between occupied and virtual blocks, can correctly describe the dissociation of H2, and is rigorously size-extensive. In addition, the new Ansatz has fewer terms than the previous unitary Ansatz, and the optimal orbitals delivered by the exact theory are the natural orbitals. Numerical studies on systems amenable to full configuration interaction show that the amplitudes from the previous ODC-12 method approximate the exact amplitudes predicted by this Ansatz. Studies on equilibrium properties of diatomic molecules show that even with the new Ansatz, it is necessary to include triples to improve the accuracy of the method compared to orbital-optimized linearized coupled cluster doubles. With a simple iterative triples correction, OλDCT outperforms other orbital-optimized methods truncated at comparable levels in the amplitudes, as well as coupled cluster single and doubles with perturbative triples [CCSD(T)]. By adding four more terms to the cumulant parameterization, OλDCT outperforms CCSDT while having the same O(V5O3) scaling.
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Hoobler PR, Villegas-Escobar N, Turney JM, Toro-Labbé A, Schaefer HF. Substituent Effects on Aluminyl Anions and Derived Systems: A High-Level Theory. J Phys Chem A 2021; 125:10379-10391. [PMID: 34812036 DOI: 10.1021/acs.jpca.1c08918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Aluminyl anions are low-valent aluminum species bearing a lone pair of electrons and a negative charge. These systems have drawn recent synthetic interest for their nucleophilic nature, allowing for the activation of σ-bonds, and have been proposed as a pathway to hydrogen energy storage. In this research, we provide high-level ab initio geometries and energies for both the simplest aluminyl anion (AlH2-) and several substituted derivatives. Geometries are reported using the gold-standard CCSD(T)/aug-cc-pV(T+d)Z level of theory. Energies were extrapolated to the complete basis set limit through the focal point approach, utilizing coupled-cluster methods through perturbative quadruples and basis sets up to five-ζ quality. Geometries were rationalized using electrostatic, steric, and orbital donation effects. The donation from substituents to Al is accompanied by back-donation effects, a property traditionally thought of in transition-metal systems. Stereoelectronic effects through the secondary orbital interaction play a fundamental role in stabilizing these low-valent aluminum compounds and would likely also affect the feasibility of their use within several industrial applications. The energetic analysis of the formation of each substituted anion is rationalized as the result of three energetic schemes. The effectiveness of these schemes for determining the relative formation energies is discussed.
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Villegas‐Escobar N, Toro‐Labbé A, Schaefer HF. Cover Feature: Contrasting the Mechanism of H
2
Activation by Monomeric and Potassium‐Stabilized Dimeric Al
I
Complexes: Do Potassium Atoms Exert any Cooperative Effect? (Chem. Eur. J. 69/2021). Chemistry 2021. [DOI: 10.1002/chem.202104120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Li G, Yao Y, Lü S, Xie Y, Douberly GE, Schaefer HF. Potential energy profile for the Cl + (H 2O) 3 → HCl + (H 2O) 2OH reaction. A CCSD(T) study. Phys Chem Chem Phys 2021; 23:26837-26842. [PMID: 34817485 DOI: 10.1039/d1cp04309a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Four different reaction pathways are initially located for the reaction of Cl atom plus water trimer Cl + (H2O)3 → HCl + (H2O)2OH using a standard DFT method. As found for the analogous fluorine reaction, the geometrical and energetic results for the four chlorine pathways are closely related. However, the energetics for the Cl reaction are very different from those for fluorine. In the present paper, we investigate the lowest-energy chlorine pathway using the "gold standard" CCSD(T) method in conjunction with correlation-consistent basis sets up to cc-pVQZ. Structurally, the stationary points for the water trimer reaction Cl + (H2O)3 may be compared to those for the water monomer reaction Cl + H2O and water dimer reaction Cl + (H2O)2. Based on the CCSD(T) energies, the title reaction is endothermic by 19.3 kcal mol-1, with a classical barrier height of 16.7 kcal mol-1 between the reactants and the exit complex. There is no barrier for the reverse reaction. The Cl⋯(H2O)3 entrance complex lies 5.3 kcal mol-1 below the separated reactants. The HCl⋯(H2O)2OH exit complex is bound by 8.6 kcal mol-1 relative to the separated products. The Cl + (H2O)3 reaction is somewhat similar to the analogous Cl + (H2O)2 reaction, but qualitatively different from the Cl + H2O reaction. It is reasonable to expect that the reactions between the chlorine atom and larger water clusters may be similar to the Cl + (H2O)3 reaction. The potential energy profile for the Cl + (H2O)3 reaction is radically different from that for the valence isoelectronic F + (H2O)3 system, which may be related to the different bond energies between HCl and HF.
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Smith DGA, Lolinco AT, Glick ZL, Lee J, Alenaizan A, Barnes TA, Borca CH, Di Remigio R, Dotson DL, Ehlert S, Heide AG, Herbst MF, Hermann J, Hicks CB, Horton JT, Hurtado AG, Kraus P, Kruse H, Lee SJR, Misiewicz JP, Naden LN, Ramezanghorbani F, Scheurer M, Schriber JB, Simmonett AC, Steinmetzer J, Wagner JR, Ward L, Welborn M, Altarawy D, Anwar J, Chodera JD, Dreuw A, Kulik HJ, Liu F, Martínez TJ, Matthews DA, Schaefer HF, Šponer J, Turney JM, Wang LP, De Silva N, King RA, Stanton JF, Gordon MS, Windus TL, Sherrill CD, Burns LA. Quantum Chemistry Common Driver and Databases (QCDB) and Quantum Chemistry Engine (QCEngine): Automation and interoperability among computational chemistry programs. J Chem Phys 2021; 155:204801. [PMID: 34852489 DOI: 10.1063/5.0059356] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Community efforts in the computational molecular sciences (CMS) are evolving toward modular, open, and interoperable interfaces that work with existing community codes to provide more functionality and composability than could be achieved with a single program. The Quantum Chemistry Common Driver and Databases (QCDB) project provides such capability through an application programming interface (API) that facilitates interoperability across multiple quantum chemistry software packages. In tandem with the Molecular Sciences Software Institute and their Quantum Chemistry Archive ecosystem, the unique functionalities of several CMS programs are integrated, including CFOUR, GAMESS, NWChem, OpenMM, Psi4, Qcore, TeraChem, and Turbomole, to provide common computational functions, i.e., energy, gradient, and Hessian computations as well as molecular properties such as atomic charges and vibrational frequency analysis. Both standard users and power users benefit from adopting these APIs as they lower the language barrier of input styles and enable a standard layout of variables and data. These designs allow end-to-end interoperable programming of complex computations and provide best practices options by default.
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Abstract
The utility of high energy density materials (HEDMs) comes from their thermodynamic properties which arise from specific structural features that contribute to energy storage. Studies of such structural features seek to increase our understanding of these energy storage mechanisms in order to further enhance their properties. High-nitrogen-containing HEDMs are of particular interest because they are less toxic than traditional HEDMs. Pentazole is the largest of the nitrogen rings which has been synthesized and considered for an HEDM; however, few experimental studies exist due to the difficulty involved in the synthesis, and most previous theoretical studies employed composite methods where lower level geometries were used with higher level methods. Here, the decomposition reaction of pentazole is studied. Geometries, fundamental frequencies, and energies for each of the stationary points of the decomposition pathway are computed using ab initio methods up to CCSDT(Q). Decomposition rates are calculated over a range of temperatures using canonical transition state theory in order to determine the kinetic stability of pentazole. Based on the present results, it would be difficult for pentazole to act as an HEDM, requiring temperatures close to 200 K to achieve a suitable level of stability.
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Mitchell EC, Wolf ME, Turney JM, Schaefer HF. Group 15 and 16 Nitrene-Like Pnictinidenes. Chemistry 2021; 27:14461-14471. [PMID: 34327737 DOI: 10.1002/chem.202101832] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Indexed: 11/09/2022]
Abstract
Pnictinidenes are an increasingly relevant species in main group chemistry and generally exhibit proclivity for the triplet electronic ground state. However, the elusive singlet electronic states are often desired for chemical applications. We predict the singlet-triplet energy differences (ΔEST =ESinglet -ETriplet ) of simple group 15 and 16 substituted pnictinidenes (Pn-R; Pn=P, As, Sb, or Bi) with highly reliable focal-point analyses targeting the CCSDTQ/CBS level of theory. The only cases we predict to have favorable singlet states are P-PH2 (-3.2 kcal mol-1 ) and P-NH2 (-0.2 kcal mol-1 ). ΔEST trends are discussed in light of the geometric predictions as well as qualitative natural bond order analysis to elucidate some of the important electronic structure features. Our work provides a rigorous benchmark for the ΔEST of fundamental Pn-R moieties and provides a firm foundation for the continued study of heavier pnictinidenes.
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Wang Y, Tran PM, Xie Y, Wei P, Glushka JN, Schaefer HF, Robinson GH. Carbene‐Stabilized Dithiolene (L
0
) Zwitterions. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202108498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Wang Y, Tran PM, Xie Y, Wei P, Glushka JN, Schaefer HF, Robinson GH. Carbene-Stabilized Dithiolene (L 0 ) Zwitterions. Angew Chem Int Ed Engl 2021; 60:22706-22710. [PMID: 34314562 DOI: 10.1002/anie.202108498] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 07/23/2021] [Indexed: 11/06/2022]
Abstract
A series of reactions between Lewis bases and an imidazole-based dithione dimer (1) has been investigated. Both cyclic(alkyl)(amino)carbene (CAAC) (2) and N-heterocyclic carbene (NHC) (4), in addition to N-heterocyclic silylene (NHSi) (6), demonstrate the capability to cleave the sulphur-sulphur bonds in 1, giving carbene-stabilized dithiolene (L0 ) zwitterions (3 and 5) and a spirocyclic silicon-dithiolene compound (7), respectively. The bonding nature of 3, 5, and 7 are probed by both experimental and theoretical methods.
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Villegas-Escobar N, Toro-Labbé A, Schaefer HF. Contrasting the Mechanism of H 2 Activation by Monomeric and Potassium-Stabilized Dimeric Al I Complexes: Do Potassium Atoms Exert any Cooperative Effect? Chemistry 2021; 27:17369-17378. [PMID: 34613646 DOI: 10.1002/chem.202103082] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Indexed: 11/06/2022]
Abstract
Aluminyl anions are low-valent, anionic, and carbenoid aluminum species commonly found stabilized with potassium cations from the reaction of Al-halogen precursors and alkali compounds. These systems are very reactive toward the activation of σ-bonds and in reactions with electrophiles. Various research groups have detected that the potassium atoms play a stabilization role via electrostatic and cation ⋯ π interactions with nearby (aromatic)-carbocyclic rings from both the ligand and from the reaction with unsaturated substrates. Since stabilizing K⋯H bonds are witnessed in the activation of this class of molecules, we aim to unveil the role of these metals in the activation of the smaller and less polarizable H2 molecule, together with a comprehensive characterization of the reaction mechanism. In this work, the activation of H2 utilizing a NON-xanthene-Al dimer, [K{Al(NON)}]2 (D) and monomeric, [Al(NON)]- (M) complexes are studied using density functional theory and high-level coupled-cluster theory to reveal the potential role of K+ atoms during the activation of this gas. Furthermore, we aim to reveal whether D is more reactive than M (or vice versa), or if complicity between the two monomer units exits within the D complex toward the activation of H2 . The results suggest that activation energies using the dimeric and monomeric complexes were found to be very close (around 33 kcal mol-1 ). However, a partition of activation energies unveiled that the nature of the energy barriers for the monomeric and dimeric complexes are inherently different. The former is dominated by a more substantial distortion of the reactants (and increased interaction energies between them). Interestingly, during the oxidative addition, the distortion of the Al complex is minimal, while H2 distorts the most, usually over 0.77 Δ E d i s t ≠ . Overall, it is found here that electrostatic and induction energies between the complexes and H2 are the main stabilizing components up to the respective transition states. The results suggest that the K+ atoms act as stabilizers of the dimeric structure, and their cooperative role on the reaction mechanism may be negligible, acting as mere spectators in the activation of H2 . Cooperation between the two monomers in D is lacking, and therefore the subsequent activation of H2 is wholly disengaged.
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Langstieh DR, Lyngdoh RHD, King RB, Schaefer HF. Lantern-Type Divanadium Complexes with Bridging Ligands: Short Metal-Metal Bonds with High Multiple Bond Orders. Chemphyschem 2021; 22:2014-2024. [PMID: 34036735 DOI: 10.1002/cphc.202100121] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 05/16/2021] [Indexed: 11/08/2022]
Abstract
Vanadium forms binuclear complexes with a variety of ligands often containing V≡V triple bonds. Many tetragonal divanadium paddlewheel complexes with bridging bidentate ligands have been experimentally characterized. This research exhaustively treats model tetragonal, trigonal, and digonal paddlewheel-type divanadium complexes V2 Lx (L=formamidinate, guanidinate, and carboxylate; x=2, 3, 4), each in the three lowest-energy spin states. The V-V formal bond orders are obtained from metal-metal MO diagrams for representative structures. A number of short V-V multiple bonds of order 3, 3.5, and 4 are found in these model complexes. The short V≡V triple bonds and singlet ground state predicted here for the model tetragonal complexes correspond well with the limited experimental results for the series of known tetragonal paddlewheels. Digonal divanadium lanterns with very short V-V quadruple bonds are predicted as interesting synthetic targets. The V-V bond distances are categorized into distinct ranges according to the formal bond order values from 0.5 to 4. These bond length ranges are compared with the ranges compiled for other divanadium complexes including carbonyl complexes.
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Wolf ME, Vandezande JE, Schaefer HF. Catalyzed reaction of isocyanates (RNCO) with water. Phys Chem Chem Phys 2021; 23:18535-18546. [PMID: 34612391 DOI: 10.1039/d1cp03302f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The reactions between substituted isocyanates (RNCO) and other small molecules (e.g. water, alcohols, and amines) are of significant industrial importance, particularly for the development of novel polyurethanes and other useful polymers. We present very high-level ab initio computations on the HNCO + H2O reaction, with results targeting the CCSDT(Q)/CBS//CCSD(T)/cc-pVQZ level of theory. Our results affirm that hydrolysis can occur across both the N[double bond, length as m-dash]C and C[double bond, length as m-dash]O bonds of HNCO via concerted mechanisms to form carbamate or imidic acid with ΔH0K barrier heights of 38.5 and 47.5 kcal mol-1. A total of 24 substituted RNCO + H2O reactions were studied. Geometries obtained with a composite method and refined with CCSD(T)/CBS single point energies determine that substituted RNCO species have a significant influence on these barrier heights, with an extreme case like fluorine lowering both barriers by close to 15 kcal mol-1 and most common alkyl substituents lowering both by approximately 3 kcal mol-1. Natural Bond Orbital (NBO) analysis provides evidence that the predicted barrier heights are strongly associated with the occupation of the in-plane C-O* orbital of the RNCO reactant. Key autocatalytic mechanisms are considered in the presence of excess water and RNCO species. Additional waters (one or two) are predicted to lower both barriers significantly at the CCSD(T)/aug-cc-pV(T+d)Z level of theory with strongly electron withdrawing RNCO substituents also increasing these effects, similar to the uncatalyzed case. The 298 K Gibbs energies are only marginally lowered by a second catalyst water molecule, indicating that the decreasing ΔH0K barriers are offset by loss of translational entropy with more than one catalyst water. Two-step 2RNCO + H2O mechanisms are characterized for the formation of carbamate and imidic acid. The second step of these two pathways exhibits the largest barrier and presents no clear pattern with respect to substituent choice. Our results indicate that an additional RNCO molecule might catalyze imidic acid formation but have less influence on the efficiency of carbamate formation. We expect that these results lay a firm foundation for the experimental study of substituted isocyanates and their relationship to the energetic pathways of related systems.
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Wu Z, Li L, Li W, Lu X, Xie Y, Schaefer HF. Carbonylic-Carbon-Centered Mechanism for Catalytic α-Methylation. Organometallics 2021. [DOI: 10.1021/acs.organomet.1c00150] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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