Diego Ardura | Universidad internacional de La Rioja (original) (raw)

Papers by Diego Ardura

Research paper thumbnail of ¿Son útiles entornos virtuales de aprendizaje en la enseñanza de las ciencias secundaria? Evaluación de una experiencia en la enseñanza y el aprendizaje de la Relatividad

Revista Eureka Sobre Ensenanza Y Divulgacion De Las Ciencias, 2014

Research paper thumbnail of ¿En qué medida utilizan los estudiantes de Física de Bachillerato sus propios errores para aprender? Una experiencia de autorregulación en el aula de secundaria

Enseñanza de las Ciencias, 2014

Research paper thumbnail of Reactivity of 2-(Diphenylphosphanyl)thiophenol (HSC6H4PPh2) with Ruthenium and Osmium Carbonyl Complexes; Breaking of HSC6H4PPh2 into Sulfide, Phenyl and Diphenylphosphanyl Ligands on a Triruthenium Cluster

Research paper thumbnail of Relative Gibbs Energies in Solution through Continuum Models: Effect of the Loss of Translational Degrees of Freedom in Bimolecular Reactions on Gibbs Energy Barriers

The Journal of Physical Chemistry B, 2005

We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular re... more We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular reactions (or processes of larger molecularity) in which a loss of translational degrees of freedom takes place along the reaction coordinate. With this model, we have studied the Walden inversion processes: Xa- + H3CXb --> XaCH3 + Xb- (X = F, Cl, Br, and I). In these processes, our model yields an increase of about 2.3-3.4 kcal/mol in Gibbs energy in solution corresponding to the loss of the translational degrees of freedom when passing from separate reactants to the TS in good agreement with experimental data. The corresponding value in the gas phase is about 6.7-7.1 kcal/mol. When the difference between these two figures is used to correct the results obtained by the standard UAHF implementation of the continuum model, the theoretical results are brought significantly closer to the experimental ones. This seems to indicate that for these reactions the parametrization used does not adequately introduce the increase in Gibbs energy corresponding to the constriction of the translational motion of the species along the reaction coordinate when passing from the gas phase to solution. Therefore, we believe that continuum models could perform much better if we released the parametrization process from the task of taking into account the constriction in translation motion in solution, which could be more adequately evaluated using the cell model proposed here, thus allowing it to focus on better reproducing all the remaining solvation effects.

Research paper thumbnail of Theoretical Studies on the Ring Opening of �-Lactams: Processes in Solution and in Enzymatic Media

Research paper thumbnail of Three-Carbon Dowd−Beckwith Ring Expansion Reaction versus Intramolecular 1,5-Hydrogen Transfer Reaction: A Theoretical Study

The Journal of Organic Chemistry, Dec 1, 2005

Research paper thumbnail of A Theoretical Study of Rhodium(I) Catalyzed Carbonylative Ring Expansion of Aziridines to β-Lactams: Crucial Activation of the Breaking C−N Bond by Hyperconjugation

J Org Chem, 2006

The regioselectivity and enantiospecificity of the [Rh(CO) 2 Cl] 2 -catalyzed carbonylative ring ... more The regioselectivity and enantiospecificity of the [Rh(CO) 2 Cl] 2 -catalyzed carbonylative ring expansions of N-tert-butyl-2-phenylaziridine to yield 2-azetidinone and the lack of reactivity of N-tert-butyl-2methylaziridine along this process were investigated at the B3LYP/6-31G(d) (LANL2DZ for Rh) theory level taking into account solvent effects. According to our results, the regioselectivity in the ring expansion of N-tert-butyl-2-phenylaziridine and the unreactivity of N-tert-butyl-2-methylaziridine experimentally observed are determined by the different degree of activation of the breaking C-N bond in the initial aziridine-Rh(CO) 2 Cl complex due to its hyperconjugation interaction with the substituent on the carbon atom. When a phenyl substituent is present its hyperconjugation interaction with the C R -N bond facilitates the insertion of the metal atom into this bond. On the other hand, when the substituent is a methyl group, a larger stability of the initial complex along with a lower stabilization through hyperconjugation of the TS for insertion of the Rh atom into the C R -N bond make the ring expansion of N-tert-butyl-2methylaziridine unviable. The enantiospecificity experimentally observed is also reproduced by our calculations given that the stereogenic center is never perturbed to change its configuration.

Research paper thumbnail of The Dowd�Beckwith ring expansion: a theoretical study

Tetrahedron Letters, Nov 15, 2004

UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the eff... more UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the effect of benzene solvent through the PCM-UAHF method render a concerted mechanism without fragmentation as the most favourable one for the Dowd-Beckwith radical ring expansion of the bromomethyl adduct of methyl cyclopentanone-2-carboxylate to yield methyl cyclohexanone-3-carboxylate. The corresponding concerted TS is a bicyclic alcoxy radical.

Research paper thumbnail of A Theoretical Investigation of the Co(CO) 4 - -Catalyzed Carbonylative Ring Expansion of N -Benzoyl-2-methylaziridine to β-Lactams: Reaction Mechanism and Effect of Substituent at the Aziridine C α Atom

J Org Chem, 2007

The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2met... more The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2methylaziridine to afford N-benzoyl-4-methyl-2-azetidinone and N-benzoyl-3-methyl-2-azetidinone was investigated by using the B3LYP density functional theory methodology in conjunction with the conductor polarizable continuum model/united atom Kohm-Sham method to take into account solvent effects. Computations predict that the most favorable reaction mechanism differs from the experimental proposals except for the nucleophilic ring-opening step, which is the rate-determining one. The regioselectivity and stereospecificity experimentally observed is explained in terms of the located reaction mechanism. The substitution of the methyl group at the carbon R of aziridine by the phenyl one gives rise to the obtaining of an only product that corresponds to the CO insertion into the C(substituted)-N bond in accordance with experimental findings. When the ethyl group replaces the methyl one the CO insertion occurs into the two C-N bonds, but the regioselectivity of the process is higher than that of the methyl substituent.

Research paper thumbnail of Protonation of triruthenium carbonyl cluster complexes containing a bridging 1-azavinylidene ligand. Experimental results and EHMO calculations

J Organomet Chem, 1998

The η1-1-azavinylidene cluster complex [Ru3(μ-H)(μ-NCPh2)(CO)10] (1) cannot be protonated with t... more The η1-1-azavinylidene cluster complex [Ru3(μ-H)(μ-NCPh2)(CO)10] (1) cannot be protonated with tetrafluoroboric acid in dichlorometane solvent. However, under analogous conditions, the phosphine-substituted derivatives [Ru3(μ-H)(μ-NCPh2)(μ-dppm)(CO)8] (2), [Ru3(μ-H)(μ-NCPh2)(PPh3)(CO)9] (3) and [Ru3(μ-H)(μ-NCPh2)(PPh3)2(CO)8] (4) undergo protonation at the metal atoms to give the cationic dihydrido derivatives [Ru3(μ-H)2(μ-NCPh2)(μ-dppm)(CO)8][BF4] (5), [Ru3(μ-H)2(μ-NCPh2)(PPh3)(CO)9][BF4] (6) and [Ru3(μ-H)2(μ-NCPh2)(PPh3)2(CO)8][BF4] (7), respectively. EHMO calculations on complex 1 and on the phosphine-substituted model compound [Ru3(μ-H)(μ-NCPh2)(PH3)2(CO)8] (8) have shown that the protonation is expected to take place on the metal atoms (the highest ten occupied MOs of 1 and 8 are fundamentally of metallic character) and that the ruthenium atoms of 8 are electron richer, and therefore more basic, than those of 1, suggesting that phosphine-substituted derivatives of 1 are more liable to undergo protonation than complex 1.

Research paper thumbnail of Self-Association of Naphthalene at the Air−Ice Interface †

The Journal of Physical Chemistry A, 2009

We present a molecular dynamics study of the interactions between two molecules of naphthalene pr... more We present a molecular dynamics study of the interactions between two molecules of naphthalene present at air-water versus air-ice interfaces. In agreement with the inference from our previous experimental work [Kahan, T. F.; Donaldson, D. J. J. Phys. Chem. A 2007, 111, 1277], the results suggest that self-association of the molecules is more likely to take place on the ice surface than on the water surface. A shorter average distance between the two naphthalene molecules, in conjunction with a stronger interaction energy and free energy of association, point to a stronger tendency to self-associate on ice than on water. The distinct behavior at the two interfaces appears be due to more favorable interactions between naphthalene molecules on liquid water surfaces than on ice surfaces.

Research paper thumbnail of Mechanism of Aqueous-Phase Ozonation of S(IV)

The Journal of Physical Chemistry A, 2010

The ozonation of dissolved sulfur dioxide is an important route for sulfate formation, especially... more The ozonation of dissolved sulfur dioxide is an important route for sulfate formation, especially in fog and cloud droplets of high pH. However, little is known about the detailed chemical mechanism of this process. We have mapped out the fate of aqueous SO(2) in the presence of ozone by use of density functional theory (DFT) calculations in solution (via the polarized continuum model, PCM), including up to two explicit water molecules. The calculations predict that the hydrolysis of SO(2).H(2)O, although possessing a barrier, is still more energetically favorable than its ozonation. The ozonation of HOSO(2)(-) and SO(3)(2)(-) proceeds without barriers and gives S(VI) products that are more stable than the reagents by 77.1 and 88.6 kcal/mol, respectively. By comparing our calculated pH dependence of the ozonation kinetics to those determined experimentally, we conclude that, despite a high calculated energy barrier to the ozonation of sulfonate (HSO(3)(-)), it is the dominant form of S(IV) in solutions of neutral pH and is the species through which ozonation occurs.

Research paper thumbnail of The Dowd–Beckwith ring expansion: a theoretical study

Tetrahedron Letters, 2004

UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the eff... more UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the effect of benzene solvent through the PCM-UAHF method render a concerted mechanism without fragmentation as the most favourable one for the Dowd-Beckwith radical ring expansion of the bromomethyl adduct of methyl cyclopentanone-2-carboxylate to yield methyl cyclohexanone-3-carboxylate. The corresponding concerted TS is a bicyclic alcoxy radical.

Research paper thumbnail of Relative Gibbs Energies in Solution through Continuum Models:  Effect of the Loss of Translational Degrees of Freedom in Bimolecular Reactions on Gibbs Energy Barriers

The Journal of Physical Chemistry B, 2005

We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular re... more We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular reactions (or processes of larger molecularity) in which a loss of translational degrees of freedom takes place along the reaction coordinate. With this model, we have studied the Walden inversion processes: Xa- + H3CXb --> XaCH3 + Xb- (X = F, Cl, Br, and I). In these processes, our model yields an increase of about 2.3-3.4 kcal/mol in Gibbs energy in solution corresponding to the loss of the translational degrees of freedom when passing from separate reactants to the TS in good agreement with experimental data. The corresponding value in the gas phase is about 6.7-7.1 kcal/mol. When the difference between these two figures is used to correct the results obtained by the standard UAHF implementation of the continuum model, the theoretical results are brought significantly closer to the experimental ones. This seems to indicate that for these reactions the parametrization used does not adequately introduce the increase in Gibbs energy corresponding to the constriction of the translational motion of the species along the reaction coordinate when passing from the gas phase to solution. Therefore, we believe that continuum models could perform much better if we released the parametrization process from the task of taking into account the constriction in translation motion in solution, which could be more adequately evaluated using the cell model proposed here, thus allowing it to focus on better reproducing all the remaining solvation effects.

Research paper thumbnail of Theoretical Study of the Fragmentation of the β-Lactam Ring:  Ozonolysis of 3-Methoxy-4-methyl- N -(ethylideneamino)-2-azetidinone

The Journal of Physical Chemistry A, 2003

... Diego Ardura and Tomás L. Sordo*. Departamento de Química ... B3LYP/6-31+G* intrinsic reactio... more ... Diego Ardura and Tomás L. Sordo*. Departamento de Química ... B3LYP/6-31+G* intrinsic reaction coordinate (IRC) calculations starting at each saddle point verified the two minima connected by that TS using the Gonzalez and Schlegel method 13 implemented in Gaussian 98. ...

Research paper thumbnail of Where does acid hydrolysis take place?

Physical Chemistry Chemical Physics, 2009

We present the results of computations on the dissociation of HCl and HNO(3) at the air-water int... more We present the results of computations on the dissociation of HCl and HNO(3) at the air-water interface. Molecular dynamics simulations of the acid molecule and 200 water molecules were propagated for several nanoseconds, and the resulting structures were used as input to QM/MM geometry optimization runs. Approximately 20-30 water molecules were included along with the acid in the QM portion of the calculation, which was carried out at the B3LYP/6-31+G(d) level. Whereas dissociation to ions is always spontaneous in the bulk, we find that acid molecules confined to the water surface dissociate only with the participation of two additional water molecules, forming a "critical cluster" about the solute. Thus acid dissociation may occur in the near-surface zone at a dynamic air-water interface, in agreement with our earlier experimental conclusions [Clifford et al., Phys. Chem. Chem. Phys.. 2007, 9, 1362].

Research paper thumbnail of Binuclear Iron(I), Ruthenium(I), and Osmium(I) Hexacarbonyl Complexes Containing a Bridging Benzene-1,2-dithiolate Ligand. Synthesis, X-ray Structures, Protonation Reactions, and EHMO Calculations †

Organometallics, 1998

The dithiolate-bridged complexes [M 2 (µ-bdt)(CO) 6 ] (M ) Fe (1), Ru (2), Os (3); bdt ) benzene-... more The dithiolate-bridged complexes [M 2 (µ-bdt)(CO) 6 ] (M ) Fe (1), Ru (2), Os (3); bdt ) benzene-1,2-dithiolate) have been prepared. X-ray diffraction studies have revealed that although the three compounds have analogous molecular structures their crystal structures are different as a result of different molecular packings. Complex 1 does not react with tetrafluoroboric acid in 1,2-dichloroethane, while compounds 2 and 3, under the same conditions, undergo protonation at the metal atoms to give the cationic hydrido derivatives [M 2 (µ-H)(µ-bdt)(CO) 6 ][BF 4 ] (M ) Ru, Os). EHMO calculations have been used to rationalize the results of the protonation reactions. a R(F) ) ∑||Fo| -|Fc||/∑|Fo|. b Rw(F 2 ) ) [∑w(Fo 2 -Fc 2 ) 2 / ∑w(Fo 2 ) 2 ] 1/2 . c Goodness of fit (GOF) ) [∑w(Fo 2 -Fc 2 ) 2 /(N -P)] 1/2 .

Research paper thumbnail of Triosmium carbonyl complexes containing bridging ligands derived from ortho-functionalized anilines

Journal of Organometallic Chemistry, 1996

The trinuclear carbonyl clusters [Os3)(μ-H(μ,η2-o-HNC6H2Me2NH2)(CO)9] (1) (o-H2NC6H2Me2NH2 = 1,2-... more The trinuclear carbonyl clusters [Os3)(μ-H(μ,η2-o-HNC6H2Me2NH2)(CO)9] (1) (o-H2NC6H2Me2NH2 = 1,2-diamino-4,5-dimethylbenzene), [Os3(μ-H)(μ,η2-o-OC6H4NH2)(CO)9] (2) (o-HOC6H4NH2 = 2-aminophenol) and [Os3(μ-H)(μ,η1-o-SC6H4NH2)(CO)10] (3) (o-HSC6H4NH2 = 2-aminothiophenol) have been prepared by reacting [Os3(CO)10(MeCN)2] with the appropriate ortho-functionalized aniline in THF solvent. Compounds 1 and 2 are isostructural, having an Os-Os edge spanned by a hydride ligand and by the amido (1) or alkoxy (2) fragment of the

Research paper thumbnail of Protonation of triruthenium carbonyl cluster complexes containing a bridging 1-azavinylidene ligand. Experimental results and EHMO calculations

Journal of Organometallic Chemistry, 1998

Research paper thumbnail of A Theoretical Investigation of the Co(CO) 4 - -Catalyzed Carbonylative Ring Expansion of N -Benzoyl-2-methylaziridine to β-Lactams:  Reaction Mechanism and Effect of Substituent at the Aziridine C α Atom

The Journal of Organic Chemistry, 2007

The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2met... more The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2methylaziridine to afford N-benzoyl-4-methyl-2-azetidinone and N-benzoyl-3-methyl-2-azetidinone was investigated by using the B3LYP density functional theory methodology in conjunction with the conductor polarizable continuum model/united atom Kohm-Sham method to take into account solvent effects. Computations predict that the most favorable reaction mechanism differs from the experimental proposals except for the nucleophilic ring-opening step, which is the rate-determining one. The regioselectivity and stereospecificity experimentally observed is explained in terms of the located reaction mechanism. The substitution of the methyl group at the carbon R of aziridine by the phenyl one gives rise to the obtaining of an only product that corresponds to the CO insertion into the C(substituted)-N bond in accordance with experimental findings. When the ethyl group replaces the methyl one the CO insertion occurs into the two C-N bonds, but the regioselectivity of the process is higher than that of the methyl substituent.

Research paper thumbnail of ¿Son útiles entornos virtuales de aprendizaje en la enseñanza de las ciencias secundaria? Evaluación de una experiencia en la enseñanza y el aprendizaje de la Relatividad

Revista Eureka Sobre Ensenanza Y Divulgacion De Las Ciencias, 2014

Research paper thumbnail of ¿En qué medida utilizan los estudiantes de Física de Bachillerato sus propios errores para aprender? Una experiencia de autorregulación en el aula de secundaria

Enseñanza de las Ciencias, 2014

Research paper thumbnail of Reactivity of 2-(Diphenylphosphanyl)thiophenol (HSC6H4PPh2) with Ruthenium and Osmium Carbonyl Complexes; Breaking of HSC6H4PPh2 into Sulfide, Phenyl and Diphenylphosphanyl Ligands on a Triruthenium Cluster

Research paper thumbnail of Relative Gibbs Energies in Solution through Continuum Models: Effect of the Loss of Translational Degrees of Freedom in Bimolecular Reactions on Gibbs Energy Barriers

The Journal of Physical Chemistry B, 2005

We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular re... more We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular reactions (or processes of larger molecularity) in which a loss of translational degrees of freedom takes place along the reaction coordinate. With this model, we have studied the Walden inversion processes: Xa- + H3CXb --> XaCH3 + Xb- (X = F, Cl, Br, and I). In these processes, our model yields an increase of about 2.3-3.4 kcal/mol in Gibbs energy in solution corresponding to the loss of the translational degrees of freedom when passing from separate reactants to the TS in good agreement with experimental data. The corresponding value in the gas phase is about 6.7-7.1 kcal/mol. When the difference between these two figures is used to correct the results obtained by the standard UAHF implementation of the continuum model, the theoretical results are brought significantly closer to the experimental ones. This seems to indicate that for these reactions the parametrization used does not adequately introduce the increase in Gibbs energy corresponding to the constriction of the translational motion of the species along the reaction coordinate when passing from the gas phase to solution. Therefore, we believe that continuum models could perform much better if we released the parametrization process from the task of taking into account the constriction in translation motion in solution, which could be more adequately evaluated using the cell model proposed here, thus allowing it to focus on better reproducing all the remaining solvation effects.

Research paper thumbnail of Theoretical Studies on the Ring Opening of �-Lactams: Processes in Solution and in Enzymatic Media

Research paper thumbnail of Three-Carbon Dowd−Beckwith Ring Expansion Reaction versus Intramolecular 1,5-Hydrogen Transfer Reaction: A Theoretical Study

The Journal of Organic Chemistry, Dec 1, 2005

Research paper thumbnail of A Theoretical Study of Rhodium(I) Catalyzed Carbonylative Ring Expansion of Aziridines to β-Lactams: Crucial Activation of the Breaking C−N Bond by Hyperconjugation

J Org Chem, 2006

The regioselectivity and enantiospecificity of the [Rh(CO) 2 Cl] 2 -catalyzed carbonylative ring ... more The regioselectivity and enantiospecificity of the [Rh(CO) 2 Cl] 2 -catalyzed carbonylative ring expansions of N-tert-butyl-2-phenylaziridine to yield 2-azetidinone and the lack of reactivity of N-tert-butyl-2methylaziridine along this process were investigated at the B3LYP/6-31G(d) (LANL2DZ for Rh) theory level taking into account solvent effects. According to our results, the regioselectivity in the ring expansion of N-tert-butyl-2-phenylaziridine and the unreactivity of N-tert-butyl-2-methylaziridine experimentally observed are determined by the different degree of activation of the breaking C-N bond in the initial aziridine-Rh(CO) 2 Cl complex due to its hyperconjugation interaction with the substituent on the carbon atom. When a phenyl substituent is present its hyperconjugation interaction with the C R -N bond facilitates the insertion of the metal atom into this bond. On the other hand, when the substituent is a methyl group, a larger stability of the initial complex along with a lower stabilization through hyperconjugation of the TS for insertion of the Rh atom into the C R -N bond make the ring expansion of N-tert-butyl-2methylaziridine unviable. The enantiospecificity experimentally observed is also reproduced by our calculations given that the stereogenic center is never perturbed to change its configuration.

Research paper thumbnail of The Dowd�Beckwith ring expansion: a theoretical study

Tetrahedron Letters, Nov 15, 2004

UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the eff... more UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the effect of benzene solvent through the PCM-UAHF method render a concerted mechanism without fragmentation as the most favourable one for the Dowd-Beckwith radical ring expansion of the bromomethyl adduct of methyl cyclopentanone-2-carboxylate to yield methyl cyclohexanone-3-carboxylate. The corresponding concerted TS is a bicyclic alcoxy radical.

Research paper thumbnail of A Theoretical Investigation of the Co(CO) 4 - -Catalyzed Carbonylative Ring Expansion of N -Benzoyl-2-methylaziridine to β-Lactams: Reaction Mechanism and Effect of Substituent at the Aziridine C α Atom

J Org Chem, 2007

The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2met... more The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2methylaziridine to afford N-benzoyl-4-methyl-2-azetidinone and N-benzoyl-3-methyl-2-azetidinone was investigated by using the B3LYP density functional theory methodology in conjunction with the conductor polarizable continuum model/united atom Kohm-Sham method to take into account solvent effects. Computations predict that the most favorable reaction mechanism differs from the experimental proposals except for the nucleophilic ring-opening step, which is the rate-determining one. The regioselectivity and stereospecificity experimentally observed is explained in terms of the located reaction mechanism. The substitution of the methyl group at the carbon R of aziridine by the phenyl one gives rise to the obtaining of an only product that corresponds to the CO insertion into the C(substituted)-N bond in accordance with experimental findings. When the ethyl group replaces the methyl one the CO insertion occurs into the two C-N bonds, but the regioselectivity of the process is higher than that of the methyl substituent.

Research paper thumbnail of Protonation of triruthenium carbonyl cluster complexes containing a bridging 1-azavinylidene ligand. Experimental results and EHMO calculations

J Organomet Chem, 1998

The η1-1-azavinylidene cluster complex [Ru3(μ-H)(μ-NCPh2)(CO)10] (1) cannot be protonated with t... more The η1-1-azavinylidene cluster complex [Ru3(μ-H)(μ-NCPh2)(CO)10] (1) cannot be protonated with tetrafluoroboric acid in dichlorometane solvent. However, under analogous conditions, the phosphine-substituted derivatives [Ru3(μ-H)(μ-NCPh2)(μ-dppm)(CO)8] (2), [Ru3(μ-H)(μ-NCPh2)(PPh3)(CO)9] (3) and [Ru3(μ-H)(μ-NCPh2)(PPh3)2(CO)8] (4) undergo protonation at the metal atoms to give the cationic dihydrido derivatives [Ru3(μ-H)2(μ-NCPh2)(μ-dppm)(CO)8][BF4] (5), [Ru3(μ-H)2(μ-NCPh2)(PPh3)(CO)9][BF4] (6) and [Ru3(μ-H)2(μ-NCPh2)(PPh3)2(CO)8][BF4] (7), respectively. EHMO calculations on complex 1 and on the phosphine-substituted model compound [Ru3(μ-H)(μ-NCPh2)(PH3)2(CO)8] (8) have shown that the protonation is expected to take place on the metal atoms (the highest ten occupied MOs of 1 and 8 are fundamentally of metallic character) and that the ruthenium atoms of 8 are electron richer, and therefore more basic, than those of 1, suggesting that phosphine-substituted derivatives of 1 are more liable to undergo protonation than complex 1.

Research paper thumbnail of Self-Association of Naphthalene at the Air−Ice Interface †

The Journal of Physical Chemistry A, 2009

We present a molecular dynamics study of the interactions between two molecules of naphthalene pr... more We present a molecular dynamics study of the interactions between two molecules of naphthalene present at air-water versus air-ice interfaces. In agreement with the inference from our previous experimental work [Kahan, T. F.; Donaldson, D. J. J. Phys. Chem. A 2007, 111, 1277], the results suggest that self-association of the molecules is more likely to take place on the ice surface than on the water surface. A shorter average distance between the two naphthalene molecules, in conjunction with a stronger interaction energy and free energy of association, point to a stronger tendency to self-associate on ice than on water. The distinct behavior at the two interfaces appears be due to more favorable interactions between naphthalene molecules on liquid water surfaces than on ice surfaces.

Research paper thumbnail of Mechanism of Aqueous-Phase Ozonation of S(IV)

The Journal of Physical Chemistry A, 2010

The ozonation of dissolved sulfur dioxide is an important route for sulfate formation, especially... more The ozonation of dissolved sulfur dioxide is an important route for sulfate formation, especially in fog and cloud droplets of high pH. However, little is known about the detailed chemical mechanism of this process. We have mapped out the fate of aqueous SO(2) in the presence of ozone by use of density functional theory (DFT) calculations in solution (via the polarized continuum model, PCM), including up to two explicit water molecules. The calculations predict that the hydrolysis of SO(2).H(2)O, although possessing a barrier, is still more energetically favorable than its ozonation. The ozonation of HOSO(2)(-) and SO(3)(2)(-) proceeds without barriers and gives S(VI) products that are more stable than the reagents by 77.1 and 88.6 kcal/mol, respectively. By comparing our calculated pH dependence of the ozonation kinetics to those determined experimentally, we conclude that, despite a high calculated energy barrier to the ozonation of sulfonate (HSO(3)(-)), it is the dominant form of S(IV) in solutions of neutral pH and is the species through which ozonation occurs.

Research paper thumbnail of The Dowd–Beckwith ring expansion: a theoretical study

Tetrahedron Letters, 2004

UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the eff... more UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the effect of benzene solvent through the PCM-UAHF method render a concerted mechanism without fragmentation as the most favourable one for the Dowd-Beckwith radical ring expansion of the bromomethyl adduct of methyl cyclopentanone-2-carboxylate to yield methyl cyclohexanone-3-carboxylate. The corresponding concerted TS is a bicyclic alcoxy radical.

Research paper thumbnail of Relative Gibbs Energies in Solution through Continuum Models:  Effect of the Loss of Translational Degrees of Freedom in Bimolecular Reactions on Gibbs Energy Barriers

The Journal of Physical Chemistry B, 2005

We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular re... more We present here a cell model for evaluating Gibbs energy barriers corresponding to bimolecular reactions (or processes of larger molecularity) in which a loss of translational degrees of freedom takes place along the reaction coordinate. With this model, we have studied the Walden inversion processes: Xa- + H3CXb --> XaCH3 + Xb- (X = F, Cl, Br, and I). In these processes, our model yields an increase of about 2.3-3.4 kcal/mol in Gibbs energy in solution corresponding to the loss of the translational degrees of freedom when passing from separate reactants to the TS in good agreement with experimental data. The corresponding value in the gas phase is about 6.7-7.1 kcal/mol. When the difference between these two figures is used to correct the results obtained by the standard UAHF implementation of the continuum model, the theoretical results are brought significantly closer to the experimental ones. This seems to indicate that for these reactions the parametrization used does not adequately introduce the increase in Gibbs energy corresponding to the constriction of the translational motion of the species along the reaction coordinate when passing from the gas phase to solution. Therefore, we believe that continuum models could perform much better if we released the parametrization process from the task of taking into account the constriction in translation motion in solution, which could be more adequately evaluated using the cell model proposed here, thus allowing it to focus on better reproducing all the remaining solvation effects.

Research paper thumbnail of Theoretical Study of the Fragmentation of the β-Lactam Ring:  Ozonolysis of 3-Methoxy-4-methyl- N -(ethylideneamino)-2-azetidinone

The Journal of Physical Chemistry A, 2003

... Diego Ardura and Tomás L. Sordo*. Departamento de Química ... B3LYP/6-31+G* intrinsic reactio... more ... Diego Ardura and Tomás L. Sordo*. Departamento de Química ... B3LYP/6-31+G* intrinsic reaction coordinate (IRC) calculations starting at each saddle point verified the two minima connected by that TS using the Gonzalez and Schlegel method 13 implemented in Gaussian 98. ...

Research paper thumbnail of Where does acid hydrolysis take place?

Physical Chemistry Chemical Physics, 2009

We present the results of computations on the dissociation of HCl and HNO(3) at the air-water int... more We present the results of computations on the dissociation of HCl and HNO(3) at the air-water interface. Molecular dynamics simulations of the acid molecule and 200 water molecules were propagated for several nanoseconds, and the resulting structures were used as input to QM/MM geometry optimization runs. Approximately 20-30 water molecules were included along with the acid in the QM portion of the calculation, which was carried out at the B3LYP/6-31+G(d) level. Whereas dissociation to ions is always spontaneous in the bulk, we find that acid molecules confined to the water surface dissociate only with the participation of two additional water molecules, forming a "critical cluster" about the solute. Thus acid dissociation may occur in the near-surface zone at a dynamic air-water interface, in agreement with our earlier experimental conclusions [Clifford et al., Phys. Chem. Chem. Phys.. 2007, 9, 1362].

Research paper thumbnail of Binuclear Iron(I), Ruthenium(I), and Osmium(I) Hexacarbonyl Complexes Containing a Bridging Benzene-1,2-dithiolate Ligand. Synthesis, X-ray Structures, Protonation Reactions, and EHMO Calculations †

Organometallics, 1998

The dithiolate-bridged complexes [M 2 (µ-bdt)(CO) 6 ] (M ) Fe (1), Ru (2), Os (3); bdt ) benzene-... more The dithiolate-bridged complexes [M 2 (µ-bdt)(CO) 6 ] (M ) Fe (1), Ru (2), Os (3); bdt ) benzene-1,2-dithiolate) have been prepared. X-ray diffraction studies have revealed that although the three compounds have analogous molecular structures their crystal structures are different as a result of different molecular packings. Complex 1 does not react with tetrafluoroboric acid in 1,2-dichloroethane, while compounds 2 and 3, under the same conditions, undergo protonation at the metal atoms to give the cationic hydrido derivatives [M 2 (µ-H)(µ-bdt)(CO) 6 ][BF 4 ] (M ) Ru, Os). EHMO calculations have been used to rationalize the results of the protonation reactions. a R(F) ) ∑||Fo| -|Fc||/∑|Fo|. b Rw(F 2 ) ) [∑w(Fo 2 -Fc 2 ) 2 / ∑w(Fo 2 ) 2 ] 1/2 . c Goodness of fit (GOF) ) [∑w(Fo 2 -Fc 2 ) 2 /(N -P)] 1/2 .

Research paper thumbnail of Triosmium carbonyl complexes containing bridging ligands derived from ortho-functionalized anilines

Journal of Organometallic Chemistry, 1996

The trinuclear carbonyl clusters [Os3)(μ-H(μ,η2-o-HNC6H2Me2NH2)(CO)9] (1) (o-H2NC6H2Me2NH2 = 1,2-... more The trinuclear carbonyl clusters [Os3)(μ-H(μ,η2-o-HNC6H2Me2NH2)(CO)9] (1) (o-H2NC6H2Me2NH2 = 1,2-diamino-4,5-dimethylbenzene), [Os3(μ-H)(μ,η2-o-OC6H4NH2)(CO)9] (2) (o-HOC6H4NH2 = 2-aminophenol) and [Os3(μ-H)(μ,η1-o-SC6H4NH2)(CO)10] (3) (o-HSC6H4NH2 = 2-aminothiophenol) have been prepared by reacting [Os3(CO)10(MeCN)2] with the appropriate ortho-functionalized aniline in THF solvent. Compounds 1 and 2 are isostructural, having an Os-Os edge spanned by a hydride ligand and by the amido (1) or alkoxy (2) fragment of the

Research paper thumbnail of Protonation of triruthenium carbonyl cluster complexes containing a bridging 1-azavinylidene ligand. Experimental results and EHMO calculations

Journal of Organometallic Chemistry, 1998

Research paper thumbnail of A Theoretical Investigation of the Co(CO) 4 - -Catalyzed Carbonylative Ring Expansion of N -Benzoyl-2-methylaziridine to β-Lactams:  Reaction Mechanism and Effect of Substituent at the Aziridine C α Atom

The Journal of Organic Chemistry, 2007

The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2met... more The reaction mechanism of the Co(CO) 4 --catalyzed carbonylative ring expansion of N-benzoyl-2methylaziridine to afford N-benzoyl-4-methyl-2-azetidinone and N-benzoyl-3-methyl-2-azetidinone was investigated by using the B3LYP density functional theory methodology in conjunction with the conductor polarizable continuum model/united atom Kohm-Sham method to take into account solvent effects. Computations predict that the most favorable reaction mechanism differs from the experimental proposals except for the nucleophilic ring-opening step, which is the rate-determining one. The regioselectivity and stereospecificity experimentally observed is explained in terms of the located reaction mechanism. The substitution of the methyl group at the carbon R of aziridine by the phenyl one gives rise to the obtaining of an only product that corresponds to the CO insertion into the C(substituted)-N bond in accordance with experimental findings. When the ethyl group replaces the methyl one the CO insertion occurs into the two C-N bonds, but the regioselectivity of the process is higher than that of the methyl substituent.