Publications CPC


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Publicaciones CPC – año 2014


A DFT analysis of the participation of zwitterionic TACs in polar (3þ2) cycloaddition reactions.

Luis R. Domingo, Maria J. Aurell, Patricia Pérez (2014): A DFT analysis of the participation of zwitterionic TACs in polar [3þ2] cycloaddition reactions. In: Tetrahedron, (70), pp. 4519–4525, 2014.

Abstract

A set of seven non-substituted tri-atom-components (TACs) participating in [3þ2] cycloaddition (32CA) reactions has been studied using the reactivity indices defined within the conceptual DFT at the B3LYP/6- 31G(d) level of theory. This series of TACs shows a zwitterionic structure and low reactivity towards ethylene. The general characteristic of these TACs is their high nucleophilic and a low electrophilic behaviour. Activation energies computed at the MPWB1K/6-311G(d) level in dichloromethane point to that non-substituted TACs react quickly toward dicyanoethylene showing their ability to react towards electron-deficient ethylenes. However, when the TACs are electrophilically activated by an appropriate substitution there seems to be insufficient activation to react toward electron-rich ethylenes. The electrophilic activation of the TAC moiety for nucleophilic attacks was only determined by the coordination with a Lewis acid. All 32CA reactions studied in this work presented high regioselectivity. The polar character of these 32CA reactions is associated with the global charge transfer found at the TS, which is in agreement with a zwitterionic-type (zw-type) mechanism. According to our results, the present theoretical study suggests that the substitution is required in both, TACs and the ethylene species, in order to experimentally perform these zw-type 32CA reactions under mild conditions.

A quantum chemical topological analysis of the C–C bond formation in organic reactions involving cationic species.

Luis R. Domingo, Patricia Pérez (2014): A quantum chemical topological analysis of the C–C bond formation in organic reactions involving cationic species.. In: Physical Chemistry Chemical Physics, (16), pp. 14108-14115, 2014.

Abstract

ELF topological analysis of the ionic Diels–Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C–C single bond formation. The C–C bond formation begins in the short range of 2.00–1.96 Å via a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P0k Parr functions of the iminium cation, and the nucleophilic Pk_ Parr functions of Cp makes the characterization of the most favourable two-center interaction along the formation of the C–C single bond possible.

Complementarity of reaction force and electron localization function analyses of asynchronicity in bond formation in Diels–Alder reactions.

Diana Yepes, Jane S. Murray, Patricia Pérez, Luis R. Domingo, Peter Politzer, Pablo Jaque (2014): Complementarity of reaction force and electron localization function analyses of asynchronicity in bond formation in Diels–Alder reactions.. In: Physical Chemistry Chemical Physics, (16), pp. 6726-6734, 2014.

Abstract

We have computationally compared three Diels–Alder cycloadditions involving cyclopentadiene and substituted ethylenes; one of the reactions is synchronous, while the others are slightly or highly asynchronous. Synchronicity and weak asynchronicity are characterized by the reaction force constant k(ξ) having just a single minimum in the transition region along the intrinsic reaction coordinate ξ, while for high asynchronicity k(ξ) has a negative maximum with minima on both sides. The electron localization function (ELF) shows that the features of k(ξ) can be directly related to the formation of the new C–C bonds between the diene and the dienophile. There is thus a striking complementarity between k(ξ) and ELF; k(ξ) identifies the key points along ξ and ELF describes what is happening at those points.

DFT Study on the Relative Stabilities of Substituted Ruthenacyclobutane Intermediates Involved in Olefin Cross-Metathesis Reactions and Their Interconversion Pathways.

Katherine Paredes-Gil, Xavier Solans-Monfort, Luis Rodriguez-Santiago, Mariona Sodupe, Pablo Jaque (2014): DFT Study on the Relative Stabilities of Substituted Ruthenacyclobutane Intermediates Involved in Olefin Cross-Metathesis Reactions and Their Interconversion Pathways.. In: Organometallics, (33), pp. 6065−6075, 2014.

Abstract

DFT (M06-L) calculations have been used to determine the relative stabilities of the metallacyclobutane intermediates arising from the cross-metathesis reactions of terminal olefins as well as to get insights into the origin of the nondetection of the α,β-substituted species. For that, we discuss the structures, NMR signatures, stabilities with respect to separated reactants, and experimentally proposed interconversion pathways of all potential metallacyclobutane intermediates arising from propene and styrene homocoupling. For the case of propene, the unsubstituted and mono- and disubstituted metallacycles are lower in Gibbs energy than the separated reactants under the NMR experimental conditions. Moreover, for the same number of substituents, regardless of their nature, the metallacycles presenting substituents at the Cα carbons are always lower in energy than those presenting substituents at Cβ, the energy difference being between 1.7 and 8.8 kcal mol–1. The computed energy barriers associated with the olefin and carbene rotation processes, two of the experimentally proposed pathways for the metallacycle interconversion, are low and are in excellent agreement with the values previously determined through NMR studies. Cycloaddition and cycloreversion energy barriers are also low, and in fact, there is not a significant difference between the barrier heights of the processes leading to observed or nonobserved intermediates. Therefore, the nondetection of metallacyclobutane intermediates with substituents in Cβ seems to arise from their lower stability in comparison with the isomers with substituents in Cα, which makes their detection not feasible under thermodynamic equilibrium conditions. That is, for cross-metathesis processes involving small terminal alkenes and activated carbenes, the nature of the observed metallacycles is based on thermodynamic control. The preference of having the substituents in Cα is attributed to the formation of stronger M–C and C–C bonds during the cycloaddition when the substituents are in an α position due to higher charge transfer from the original alkene fragment to the metal carbene.

Driving and retarding forces in a chemical reaction.

Peter Politzer, Jane S. Murray, Diana Yepes, Pablo Jaque (2014): Driving and retarding forces in a chemical reaction.. In: Journal of Molecular Modeling, (20), pp. 2351-2356, 2014.

Abstract

The reaction force F(ξ) is the negative gradient of the potential energy of a chemical process along the intrinsic reaction coordinate ξ. We extend the rigorous concept of F(ξ) to the "activation strain model" of Bickelhaupt et al., to formulate the "strain" force Fstr(ξ) that retards a reaction and the "interaction" force Fint(ξ) that drives it. These are investigated for a group of Diels-Alder cycloadditions. The results fully support the interpretation of the minimum of F(ξ) as defining the beginning of the transition from deformed reactants to eventual products.

Initiation stage of alkene metathesis: Insights from natural bondorbital and charge decomposition analyses.

Katherine Paredes-Gil, Pablo Jaque (2014): Initiation stage of alkene metathesis: Insights from natural bondorbital and charge decomposition analyses.. In: Chemical Physics Letters, (618), pp. 174-181, 2014.

Abstract

The RuPR3 bonds of 1–2(a-b)-PC, RuCHPh bonds of 1a-b, 2-Inact/Act and 1a-b,2-RCB were analyzed by charge decomposition (CDA) and natural bond orbital (NBO). We have found that the dissociation step of the RuPR3 bond is driven by charge transfer, while the RCB by polarization effects. Furthermore, the π(Cipso)–π*(RuC) interaction was associated with delocalization effects in the benzylidene ring. Likewise, the nature of the rotameric changes in the carbene was studied through the resonance stabilization energy (ENLW). 2 presented a lower ΔENLW (Inactive → Active) than 1a-b, which confirms that the delocalization effects are related to a low carbene rotameric energy.


Publicaciones CPC – año 2015


Atomic decomposition of conceptual DFT descriptors: The example of proton transfer reactions.

Ricardo Inostroza-Rivera, Meziane Yahia-Ouahmed, Vincent Tognetti, Laurent Joubert, Bárbara Herrera, Alejandro Toro-Labbé (2015): Atomic decomposition of conceptual DFT descriptors: The example of proton transfer reactions.. In: Physical Chemistry Chemical Physics, (17), pp. 17797, 2015.

Abstract

In this study, we present an atomic decomposition, in principle exact, at any point on a given reaction path, of the molecular energy, reaction force and reaction flux, which is based on Bader’s atoms-inmolecules theory and on Penda´s’ interacting quantum atoms scheme. This decomposition enables the assessment of the importance and the contribution of each atom or molecular group to these global properties, and may cast the light on the physical factors governing bond formation or bond breaking. The potential use of this partition is finally illustrated by proton transfers in model biological systems.

A Computational and Conceptual DFT Study on the Mechanism of Hydrogen Activation by Novel Frustrated Lewis Pairs.

Patricia Pérez, Diana Yepes, Pablo Jaque, Eduardo Chamorro, Luis R. Domingo, René S. Rojas, Alejandro Toro-Labbé (2015): A Computational and Conceptual DFT Study on the Mechanism of Hydrogen Activation by Novel Frustrated Lewis Pairs.. In: Physical Chemistry Chemical Physics, (17), pp. 10715-10725, 2015.

Abstract

A computational and conceptual density functional theory (DFT) study on the mechanism of the molecular hydrogen activation by a set of three frustrated Lewis pairs (FLPs) was performed at the ωB97X-D/6-311G(d,p) level of theory. A reduced model and other two prototypes derived from experimental data, based on the donor nitrogen and acceptor boron atoms, were used. Analysis grounded on the energy results, geometries and the global electron density transfer at the TSs made it possible to obtain some interesting conclusions: i) despite the well-known very low reactivity of molecular hydrogen, the catalytic effectiveness of the three FLPs produces reactions with almost unappreciable activation energies; ii) the reactions, being exothermic, follow a one-step mechanism via polarised TSs; iii) there are neither substituent effects on the kinetics nor on the thermodynamics of these reactions; iv) the activation of molecular hydrogen seems to be attained when the N–B distance in the FLP derivatives is around 2.74 A; and v) the proposed FLP model is consistent with the behaviour of the experimental prototypes. Finally, the ability of the three FLPs as efficient catalysts was evaluated studying the hydrogenation of acetylene to yield ethylene.

A DFT Study of the Ionic (2+2) Cycloaddition Reactions of Keteniminium Cations with Terminal Acetylenes.

Luis R. Domingo, Mar Ríos-Gutiérrez, Patricia Pérez (2015): A DFT Study of the Ionic [2+2] Cycloaddition Reactions of Keteniminium Cations with Terminal Acetylenes. In: Tetrahedron, (71), pp. 2421-2427, 2015.

Abstract

The molecular mechanism of the ionic [2+2] cycloaddition (I-22CA) reactions of a keteniminium cation (KC) with acetylene and propyne has been investigated using DFT methods at the MPWB1K/6-311G(d,p) level. These I-22CA reactions take place via a two-step mechanism. The first step is the nucleophilic attack of these alkynes on the central carbon of KC, yielding cyclopropene intermediates, while the second step corresponds to the conversion of these intermediates into more stable cyclobuteniminium cations (CCs). The first step is the rate-determining step, while the second step is responsible for the formation of the two regioisomeric CCs experimentally observed in the reaction with propyne. Analysis of the DFT reactivity indices indicates that the strong electrophilic character of KC accounts for the feasibility of these I-22CA reactions. An ELF topological analysis of the changes of the electron density along the IRCs of the two reaction steps allows the molecular mechanism of these I-22CA reactions to be established.

A mechanistic study of the participation of azomethine ylides and carbonylylides in (3+2) cycloaddition reactions.

Luis R. Domingo, Maria J. Aurell, Patricia Pérez (2015): A mechanistic study of the participation of azomethine ylides and carbonylylides in (3+2) cycloaddition reactions. In: Tetrahedron, (71), pp. 1050-1057, 2015.

Abstract

The participation of azomethine ylides (AYs) and carbonyl ylides (CYs) in [3+2] cycloaddition (32CA) reactions has been analysed at the DFT B3LYP/6 31G(d) level. The asymmetric substitution breaks the pseudodiradical character of the simplest three-atom-components (TACs), modifying their electrophilic and nucleophilic behaviours. These TACs react quickly towards electrophilic nitroethylene. However, while the reaction with AY takes place via a zw-type mechanism, the reaction with CY appears to take place via a pr-type mechanism. A different behaviour is found in the reactivity towards the nucleophilic methyl vinyl ether. While AY presents a high activation energy, CY presents a high reactivity via a pr-type mechanism. These reactions are completely regioselective, displaying exo stereoselectivity. The present study makes it possible to establish that the substitution provokes a different reactivity pattern in these TACs; while in CYs does not substantially modify their pr-type reactivity, AYs only participate in zw-type 32CA reactions towards electrophilic ethylenes.

Charge separation and isolation in strong water droplet impacts.

F. Wiederschein, E. Vöhringer-Martinez, A. Beinsen, F. Postberg, J. Schmidt, R. Srama, F. Stolz, H. Grubmüllera, B. Abelcg (2015): Charge separation and isolation in strong water droplet impacts.. In: Physical Chemistry Chemical Physics, (17), pp. 6858-6864, 2015.

Abstract

Charge separation in condensed matter after strong impacts is a general and intriguing phenomenon in nature, which is often identified and described but not necessarily well understood in terms of a quantitative mechanistic picture. Here we show that charge separation naturally occurs if water droplets/ clusters or ice particles with embedded charge carriers, e.g., ions, encounter a high energy impact with subsequent dispersion – even if the involved kinetic energy is significantly below the molecular ionization energy. We find that for low charge carrier concentrations (c o 0.01 mol L_1) a simple statistical Poisson model describes the charge distribution in the resulting molecular ‘‘fragments’’ or aggregates. At higher concentrations Coulomb interactions between the charge carriers become relevant, which we describe by a Monte Carlo approach. Our models are compared to experimental data for strong (laser) impacts on liquid micro beams and discussed for the charge generation in cluster-impact mass spectrometry on cosmic dust detectors where particle kinetic energies are below the plasma threshold. Taken together, a simple and intuitive but quantitative microscopic model is obtained, which may contribute to the understanding of a larger range of phenomena related to charge generation and separation in nature.

A Detailed Analysis of the Mechanism of a Carbocationic Triple Shift Rearrangement.

Daniela E. Ortega, Soledad Gutiérrez-Oliva, Dean J. Tantillo, Alejandro Toro-Labbé (2015): A Detailed Analysis of the Mechanism of a Carbocationic Triple Shift Rearrangement.. In: Physical Chemistry Chemical Physics, (17), pp. 9771-9779, 2015.

Abstract

The mechanism of carbocationic triple shift rearrangement is analyzed within the conceptual framework of the reaction force. All systems were characterized computationally using DFT through B3LYP/6-31+G(d,p) methodology. A complete description of the electronic activity taking place during the reaction emerged through the use of the reaction electronic flux that, together with NBO Wiberg bond order, produces a detailed picture of the reaction mechanism in terms of chemical events that drive the reaction during the different stages of the process. It is found that carbocation triple shift occurs asynchronously although in a concerted way.

Insights into Some Diels-Alder Cycloadditions Via the Electrostatic Potential and the Reaction Force Constant.

Jane S. Murray, Diana Yepes, Pablo Jaque, Peter Politzer (2015): Insights into Some Diels-Alder Cycloadditions Via the Electrostatic Potential and the Reaction Force Constant.. In: Computational and Theoretical Chemistry, (1053), pp. 270-280, 2015.

Abstract

We have investigated computationally a series of 18 Diels–Alder cycloadditions, involving four dienes (butadiene, 2-hydroxybutadiene, cyclopentadiene and cyclohexadiene) and variously-substituted ethylenes and acetylenes as dienophiles. It is demonstrated that the respective molecular electrostatic potentials can be used to provide insight into the initial modes of interaction of the dienes and dienophiles, focusing particularly upon the synchronicities and nonsynchronicities of the processes. This is shown to complement predictions based upon the profiles of the reaction force constantsκ(ξ) in the transition regions along the intrinsic reaction coordinates ξ: one κ(ξ) minimum ∼ synchronicity, a minimum and a shoulder ∼ moderate nonsynchronicity, two minima ∼ strong nonsynchronicity. Temporal aspects of the reactions can also be examined through κ(ξ).

Synthesis and structures of N-arylcyano-β-diketiminate zinc complexes and adducts and their application in ring‐opening polymerization of L-lactide.

Oleksandra S. Trofymchuk, Constantin G. Daniliuc, Gerald Kehr, Gerhard Erker, Rene S. Rojas (2015): Synthesis and structures of N-arylcyano-β-diketiminate zinc complexes and adducts and their application in ring‐opening polymerization of L-lactide.. In: RSC Advances, (5), pp. 21054-21065, 2015.

Abstract

Zinc amide complexes ZnL1N(SiMe3)2, ZnL2N(SiMe3)2 (1 and 2), their tris(pentafluorophenyl)borane adducts ZnL1N(SiMe3)2·B(C6F5)3 (3), ZnL2N(SiMe3)2·2B(C6F5)3(4), pentafluorophenyl zinc complex ZnL1C6F5 (5) and its adduct ZnL1C6F5·B(C6F5) (6) supported by N-arylcyano-β-diketiminate ligands, as well as bis-ligated Zn(L2)2 (7) were synthesized and characterized by NMR, IR, elemental analysis and X-ray diffraction. Zinc crystal structures of 1, 4, and 7 showed mononuclear complexes, while 2 and 5 were dimmers. ROP ofL-lactide with zinc complexes and their B(C6F5)3 adducts leads to generation of poly(L-LA) with high molecular weight and relatively narrow molecular weight distribution. The monomer conversion reached completion in 40 min only for zinc amide complex 1, while for other compounds it was necessary to use at least 5 hours to achieve significant polymerization yields. Coordination of the B(C6F5)3 molecule close to the metal center blocks L-lactide insertion and thus decreases the activity of respective adducts in comparison with borane-free zinc complexes.

Understanding the thermal dehydroclorination reaction of 1-chlorohexane. Revealing the driving bonding pattern at the planar catalytic reaction center.

Lina López, Pablo Ruiz, Manuela Castro, Jairo Quijano, Mario Duque-Noreña, Patricia Pérez, Eduardo Chamorro (2015): Understanding the thermal dehydroclorination reaction of 1-chlorohexane. Revealing the driving bonding pattern at the planar catalytic reaction center.. In: RSC Advances, (5), pp. 62946-62956, 2015.

Abstract

The nature of bonding along the gas-phase thermal decomposition of 1-chlorohexane to produce 1-hexene and hydrogen chloride has been examined at the DFT M05-2X/6-311+G(d,p) level of theory. Based on results both from energetical and topological analysis of the electron localization function (ELF), we propose to rationalize the experimental available results not in terms of a decomposition via a four-membered cyclic transition structure (TS), but properly as atwo stage one step reaction mechanism featuring a slightly asynchronous process associated to the catalytic planar reaction center at the TS. In this context, the first electronic stage corresponds to the Cδ+⋯Clδ− bond cleavage, which take place on the activation path earlier the transition structure be reached. There is no evidence of a Cl–C bond at the TS configuration. The second stage, associated to the top of the energy barrier, includes the TS and extends beyond on the deactivation pathway towards the products. The existence of both bonding and nonbonding non covalent interactions (NCI) are also revealed for the first time for the TS configuration.

Understanding the Highly Varying pKa of Arylamines. A Perspective from the Average Local Ionization Condensed-to-Atom Framework.

Eduardo Chamorro, Mario Duque-Noreña (2015): Understanding the Highly Varying pKa of Arylamines. A Perspective from the Average Local Ionization Condensed-to-Atom Framework.. In: The Journal of Physical Chemistry A, (119), pp. 8156-8162, 2015.

Abstract

The highly varying experimental pKa values for 36 arylamines spanning 7 orders of magnitude is carefully examined. Within this framework, a valence condensed-to-atom model for the average ionization energy is introduced and tested. The theoretical approach is connected to orbital Fukui functions directly mapped into semilocal or regional site-specific responses. It is revealed that the average local ionization energies associated with the amino nitrogen atom is linearly correlated to the basicity of the substituted arylamines, properly reproducing the experimental ordering of basicity. The condensed-to-atom descriptor exhibits a high predictive power, providing a new direct reactivity evaluation of significant value.

On the intrinsic reactivity index for electrophilicity/nucleophilicity responses.

Eduardo Chamorro, Junia Melin (2015): On the intrinsic reactivity index for electrophilicity/nucleophilicity responses.. In: Journal of Molecular Modeling, (21), pp. 53, 2015.

Abstract

We present a critical discussion related to the recent definition of the intrinsic reactivity index, IRI, (Tetrahedron Lett. 2013, 54, 339-342; Tetrahedron 2013, 69, 4247-4258) formulated to describe both, electrophilicity (charge acceptance) and nucleophilicity (charge donation) reactivities. We here stress that such an IRI model, based on the quantity μ/η, should be properly related to theoretical approximations associated to the change in the global electronic energy of a given chemical system under interaction with a suitable electron bath (Gazquez JL et al. J Phys Chem A 2007, 111, 1966-1970). Further, the limitations of the IRI model are presented by emphasizing that the intrinsic relative scales of electrophilicity and nucleophilicity within a second-order perturbation approach must account for the further stabilization of the two interacting species (Chamorro E et al. J Phys Chem A 2013, 117, 2636-2643).

Insights into the chemical meanings of the reaction electronic flux.

Christophe Morell, Vincent Tognetti, Emmanuelle Bignon, Elise Dumont, Noemi Hernandez‑Haro, Barbara Herrera, André Grand, Soledad Gutiérrez‑Oliva, Laurent Joubert, Alejandro Toro‑Labbé, Henry Chermette (2015): Insights into the chemical meanings of the reaction electronic flux.. In: Theoretical Chemistry Accounts, pp. 133-134, 2015.

Abstract

The negative derivative of the chemical potential with respect to the reaction coordinate is called reaction electronic flux and has recently focused a wide interest to better understand chemical reactions at molecular level. After much consideration, it is now well accepted that positive REF values are associated with spontaneous processes, while negative REF ones translate unspontaneous phenomena. These characteristics of the REF are based on a thermodynamic analogy and have been shown right through computational results. In this paper, we develop two analytical expressions of the REF in both the canonical and the grand canonical ensembles. The connection between both equations is established. They are then analyzed, and some arguments are put forward to support the alleged characteristic of the REF and its ability to properly discriminate spontaneous from unspontaneous phenomena.