Browsing by Subject "GAUSSIAN-TYPE BASIS"

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  • Rong, Mark K.; Holtrop, Flip; Bobylev, Eduard O.; Nieger, Martin; Ehlers, Andreas W.; Slootweg, J. Chris; Lammertsma, Koop (2021)
    Novel seven-membered cyclic imine-based 1,3-P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These "cycloiminophosphanes" possess flexible non-isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P-kappa(1)- and P,N-kappa(2)-tungsten(0) carbonyl complexes, by determining the IR frequency of the trans-CO ligands. Complexes with [RhCp*Cl-2](2) demonstrated the hemilability of the ligands, giving a dynamic equilibrium of kappa(1) and kappa(2) species; treatment with AgOTf gives full conversion to the kappa(2) complex. The potential for catalysis was shown in the Ru-II-catalyzed, solvent-free hydration of benzonitrile and the Ru-II- and Ir-I-catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l-menthone, as well as their P,N-kappa(2)-Rh-III and a P-kappa(1)-Ru-II complexes.
  • Boom, Devin H. A.; de Boed, Ewoud J. J.; Nicolas, Emmanuel; Nieger, Martin; Ehlers, Andreas W.; Jupp, Andrew R.; Slootweg, J. Chris (2020)
    The reaction of the intramolecular frustrated Lewis pair (FLP) tBu2PCH2BPh2 with the amine-boranes NH3·BH3 and Me2NH·BH3 leads to the formation of the corresponding FLP-H2 adducts as well as novel five-membered heterocycles that result from capturing the in situ formed amino-borane by a second equivalent of FLP. The sterically more demanding tBu2PCH2BMes2 does not form such a five-membered heterocycle when reacted with Me2NH·BH3 and its H2 adduct liberates dihydrogen at elevated temperatures, promoting the metal-free catalytic dehydrogenation of amine-boranes.
  • Iyer, Siddharth; Reiman, Heidi; Moller, Kristian H.; Rissanen, Matti P.; Kjaergaard, Henrik G.; Kurten, Theo (2018)
    The oxidation of biogenically emitted volatile organic compounds (BVOC) plays an important role in the formation of secondary organic aerosols (SOA) in the atmosphere. Peroxy radicals (RO2) are central intermediates in the BVOC oxidation process. Under clean (low-NOx) conditions, the main bimolecular sink reactions for RO2 are with the hydroperoxy radical (HO2) and with other RO2 radicals. Especially for small RO2, the RO2 + HO2 reaction mainly leads to closed-shell hydroperoxide products. However, there exist other known RO2 + HO2 and RO2 + RO2 reaction channels that can recycle radicals and oxidants in the atmosphere, potentially leading to lower-volatility products and enhancing SOA formation. In this work, we present a thermodynamic overview of two such reactions: (a) RO2 + HO2 -> RO + OH + O-2 and (b) R'O-2 + RO2 -> R'O + RO + O-2 for selected monoterpene + oxidant derived peroxy radicals. The monoterpenes considered are alpha-pinene, beta-pinene, limonene, trans-beta-ocimene, and Delta(3)-carene. The oxidants considered are the hydroxyl radical (OH), the nitrate radical (NO3), and ozone (O-3). The reaction Gibbs energies were calculated at the DLPNO-CCSD(T)/def2-QZVPP//omega B97X-D/aug-cc-pVTZ level of theory. All reactions studied here were found to be exergonic in terms of Gibbs energy. On the basis of a comparison with previous mechanistic studies, we predict that reaction a and reaction b are likely to be most important for first-generation peroxy radicals from O-3 oxidation (especially for beta-pinene), while being less so for most first-generation peroxy radicals from OH and NO3 oxidation. This is because both reactions are comparatively more exergonic for the O-3 oxidized systems than their OH and NO3 oxidized counterparts. Our results indicate that bimolecular reactions of certain complex RO, may contribute to an increase in radical and oxidant recycling under high HO2 conditions in the atmosphere, which can potentially enhance SOA formation.
  • Rong, Mark K.; van Duin, Koen; van Dijk, Tom; de Pater, Jeroen J. M.; Deelman, Berth-Jan; Nieger, Martin; Ehlers, A. W.; Slootweg, J. Chris; Lammertsma, Koop (2017)
    Highly stable iminophosphanes, obtained from alkylating nitriles and reaction of the resulting nitrilium ions with secondary phosphanes, were explored as tunable P-monodentate and 1,3-P,N bidentate ligands in rhodium complexes. X-ray crystal structures are reported for both k1 and k2 complexes with the counterion in one of them being an unusual anionic coordination polymer of silver triflate. The iminophosphane-based ruthenium(II)-catalyzed hydration of benzonitrile in 1,2-dimethoxyethane (180 degrees C, 3 h) and water (100 degrees C, 24 h) and under solvent free conditions (180 degrees C, 3 h) results in all cases in the selective formation of benzamide with yields of up to 96%, thereby outperforming by far the reactions in which the common 2-pyridyldiphenylphosphane is used as the 1,3-P,N ligand.
  • Garcia-Perez, Guillermo; Rossi, Matteo A. C.; Sokolov, Boris; Tacchino, Francesco; Barkoutsos, Panagiotis Kl; Mazzola, Guglielmo; Tavernelli, Ivano; Maniscalco, Sabrina (2021)
    Many prominent quantum computing algorithms with applications in fields such as chemistry and materials science require a large number of measurements, which represents an important roadblock for future real-world use cases. We introduce a novel approach to tackle this problem through an adaptive measurement scheme. We present an algorithm that optimizes informationally complete positive operator-valued measurements (POVMs) on the fly in order to minimize the statistical fluctuations in the estimation of relevant cost functions. We show its advantage by improving the efficiency of the variational quantum eigensolver in calculating ground-state energies of molecular Hamiltonians with extensive numerical simulations. Our results indicate that the proposed method is competitive with state-of-the-art measurement-reduction approaches in terms of efficiency. In addition, the informational completeness of the approach offers a crucial advantage, as the measurement data can be reused to infer other quantities of interest. We demonstrate the feasibility of this prospect by reusing ground-state energy-estimation data to perform high-fidelity reduced state tomography.