Hybrid framework compounds including both inorganic and organic moieties have recently developed into an important new class of crystalline porous materials, also known as metal organic frameworks (MOFs) [1]. MOFs contain many metal sites, which might be catalytically active. This implies that MOFs have the potential to replace homogenous catalysts in important industrial applications [2]. Notwithstanding the catalytic activity of some of themit is not always clear what the active sites are and how the reactions are catalyzed. In this contribution, we will focus on certain variations of the UiO-66. Recently, the UiO-66-NH2 has successfully been applied experimentally for the synthesis of Jasminaldehyde from benzaldehyde and heptanal [3]. The presence of the coordinatively unsaturated Lewis acid sites in the material could be increased using a monocarboxylate modulation approach and post synthetic heat treatment [4]. To fully understand the mechanism of Jasminaldehyde condensation on such open active Zr-sites, we applied molecular modeling techniques on extended cluster as well as on periodic models of the UiO-66-X materials. On an extended cluster, the most plausible condensation reaction mechanism was found, showing that benzaldehyde and heptanal are adsorbed and activated on adjacent Zr sites before the coupling reaction. On the UiO66-NH2 model, there should be also an alternative reaction route, where one of the two aldehydes is activated on the amino group, explaining the higher selectivity of the UiO66-NH2 compared to the UiO-66 [3]. Deeper insight into these complex mechanisms allows us to explain the selectivity and activity on the UiO-66 type materials.

Despite various studies on the polymerization of PPV through different precursor routes, detailed mechanistic insight on the level of the individual reactions and intermediates is still incomplete. A recent study was performed to gain insight into the polymerization of PPV via the Gilch route –known to exclusively occur through a radical mechanism– and identify reactions that lead to side products, such as the p-cyclophane system.

The methanol-to-olefin (MTO) process is an important alternative for olefin production as waning oil reserves arouse the use of unconventional carbonaceous feedstocks. H-SAPO-34 and H-ZSM-5 are the archetypal MTO catalysts and shows a high selectivity toward light olefins and branched hydrocarbons, respectively. The generally accepted reaction mechanism for the MTO process is based on a hydrocarbon pool (HP), in which organic molecules – predominantly alkenes and polymethylbenzenes – trapped within the anorganic zeolite framework act as co-catalysts.[1,2] However, to date, no decisive answer exists to the question which mechanism is responsible for olefin production in H-SAPO-34.[3] First-principle DFT calculations can aid the unraveling of the MTO mechanisms and the design of an optimal catalyst. Moreover, this contribution shows an innovative approach wherein static calculations and molecular dynamics simulations complement each other. In the first part of this contribution it is shown that hexamethylbenzene (HMB), the most active HP compound in H-SAPO-34,[4] can subsequently undergo an ipso-methylation, deprotonations and exocylic methylations upon methanol feed. In this fashion side-chains grow, which can be easily split off as ethene or propene. This low-barrier elimination step is in stark contrast with conclusions of earlier studies on this side-chain route.[5,6] Accurate chemical kinetics of all individual reaction steps are presented.[7] In the second part of this contribution the influence of three factors on the chemical kinetics of reactions occurring within the nanoporous host is examined in detail. We distinguish: (1) the confinement imposed by the zeolite, (2) the framework flexibility of the catalyst and (3) the presence of additional solvent molecules. Advanced MD simulations are performed to compute the free energy profile along the reaction coordinates. Methods like metadynamics and thermodynamic integration prove a very useful, yet challenging tool to explore free energy landscapes for chemical reactions.[8] The knowledge of this free energy profile enables the determination of kinetic coefficients which complement experimental catalytic and spectroscopic data.[9] To assess the influence of such a dynamical approach, the methylation of benzene is studied in H-ZSM-5. References 1. Dahl, I. M. and Kolboe, S. Catal. Let. 20, 329 (1993); J. Catal. 149, 304 (1994); J. Catal. 161, 304 (1996) 2. Svelle, S., Joensen, F., Nerlov, J., Olsbye, U., Lillerud, K. P., Kolboe, S. and Bjorgen, M. J. Am. Chem. Soc. 128, 14770 (2006) 3. Haw, J.F. and Marcus, D.M. Top. Catal. 34, 41 (2005) 4. Van Speybroeck, V., Hemelsoet, K., De Wispelaere, K., Qian, Q., Van der Mynsbrugge, J., De Sterck, B., Weckhuysen, B.M. and Waroquier, M. ChemCatChem 5(1), 173 (2013) 5. Lesthaeghe, D., Horre, A., Waroquier, M., Marin, G.B. and Van Speybroeck, V. Chem. Eur. J. 15, 10803 (2009) 6. Wang, C. M., Wang, Y. D., Xie, Z. K. and Liu, Z. P. J. Phys. Chem. C 113, 4584 (2009) 7. Van Speybroeck, V., Van der Mynsbrugge, J., Vandichel, M., Hemelsoet, K., Lesthaeghe, D., Ghysels, A., Marin, G. B. and Waroquier, M. J. Am. Chem. Soc. 133, 888 (2011) 8. Ensing, B., De Vivo, M., Liu, Z. W., Moore, P. and Klein, M. L. Accounts Chem. Res. 39, 73 (2006) 9. Benco, L., Bucko, T. and Hafner, J. J. Catal. 277,104 (2011)

The methanol-to-olefin (MTO) process is an important alternative for olefin production as waning oil reserves arouse the use of unconventional carbonaceous feedstocks. The archetypal MTO catalyst is H-SAPO-34, exhibiting a high selectivity towards light olefins due to its chabazite topology. It is generally accepted that the MTO process is based on a hydrocarbon pool (HP) with highly methylated benzene compounds as the most active species in H-SAPO-34.[1] Despite the numerous experimental and theoretical studies performed during the last decades, no decisive information exists on the reaction mechanism(s) responsible for olefin production in H-SAPO-34.

The methanol-to-olefin (MTO) process is a very promising alternative for olefin production as waning oil reserves and an increasing demand for base chemicals arouse the use of alternative feedstocks. Methanol conversion occurs in acidic zeotype catalyst materials such as H-ZSM-5 and H-SAPO-34. The latter exhibits a particularly high selectivity towards light olefins due to its chabazite topology.[1] The generally accepted reaction mechanism for the MTO process is based on a hydrocarbon pool (HP) in which organic molecules (predominantly polymethylbenzenes) trapped within the anorganic zeolite framework co-catalyze the reactions.[2] To date, no decisive and detailed information exists on the dominant reaction mechanisms responsible for olefin production during methanol conversion in H-SAPO-34.

Structure prediction and determination of thermoelastic properties of planetary inner cores is a problem of great interest to both planetology and material science. Much work has been done through seismography and high-pressure experiments, wherein both communities have aided each other in refining and verifying their knowledge. Ab-initio calculations can help in obtaining reliable and accurate data. Density functional theory combined with phonon calculations can provide detailed information on material properties at conditions of high temperature and high pressure.

In this contribution we present calculated band gaps for a set of ca. 200 semiconductors for which experimental band gaps are available in standard tabulations [1]. Calculations were performed with the LAPW method implemented in the WIEN2k code [2], using the PBE and modified Becke-Johnson (mBJ) functionals. Correlations between the two sets of calculations and experiment will be presented and discussed, as well as correlations between the two sets of calculations themselves. It will be shown to which extent such an approach can be used to identify ‘suspicious’ entries in tabulated experimental data.

N-spiro bis-aziridinium ions are highly strained spiro-intermediates activated towards nucleophile-induced ring opening. Although their existence has been postulated in order to explain the outcome of certain reactions [1], their formation seems kinetically and thermodynamically too unfavorable to yield viable intermediates. DFT calculations were carried out to evaluate these claims. The intramolecular nucleophilic subsitution of chloride by the aziridine nitrogen atom in 1(2-chloroalkyl)aziridines results in the formation of N-spiro bis-aziridinium ions. This formation reaction is the rate-determining step in any reaction sequence involving these types of intermediates and seems to be promoted by polar solvent interactions and intramolecular hydrogen bonding between chloride and the hydroxyl group. To account for the solvent influence, optimizations and energy refinements were performed using either no solvation, a polarizable continuum model (PCM), a supermolecule model with explicit solvent molecules or a combination of the last two. An extensive set of functionals (B3LYP, CAM-B3LYP, ωB97X-D, MPW1B95, BMK, M06-2X) was considered in these calculations. Intramolecular hydrogen bonding is a key factor in the stability of the N-spiro bisaziridinium intermediates considered and eliminates the need for solvation with explicit solvent molecules. Selecting PCM geometry optimizations as the method of choice, chloride was replaced by more or less potent leaving groups to reveal that in the case of good leaving groups the formation reaction is kinetically and thermodynamically viable.

Aziridines are useful synthetic intermediates for the preparation of a variety of ring-opened and ring-expanded amines. The key element in the design of a strategy based on the use of aziridium intermediates is the control of regioand stereoselectivity in ring opening, which is dependent on the substrate, the type of nucleophile and the solvent environment. All three factors have been studied by means of DFT-based computational studies. The difference in reactivity between activated and non-activated aziridines with respect to sodium methoxide in methanol was analyzed. Since nucleophilic substitution reactions are known to be influenced by reaction conditions, the pathways were modeled with a proper solvent environment. As explicit solvent interactions are present, discrete solvent molecules were placed around the chemically active species to form a so-called “supermolecule” structure. Furthermore, the energetics that arise from this explicit solvent approach were critically evaluated. It was found that for the chemical problems at hand, where the solvent is able to make explicit hydrogen bonds with the reacting substrate, the supermolecule approach gives a fair representation of the molecular environment. On the other hand, explicit accounting for the methanol environment was found to be essential to acquire an adequate representation of the free energy surface and the competition between the possible pathways.