Unusual reactivities of acridine derivatives in catalytic hydrogenation. A combined experimental and theoretical study

Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69

Contents lists available at SciVerse ScienceDirect

Journal of Molecular Catalysis A: Chemical journal homepage: www.elsevier.com/locate/molcata

Unusual reactivities of acridine derivatives in catalytic hydrogenation. A combined experimental and theoretical study Pierre Mignon a , Martin Tiano b , Philippe Belmont b,c , Alain Favre-Réguillon d , Henry Chermette a , Fabienne Fache e,∗ a Université de Lyon – Université Lyon1, Laboratoire des Sciences Analytiques, UMR5180, Equipe Chimiométrie et Modélisation, 43 boulevard du 11 novembre 1918, Villeurbanne F-69622, France b Université de Lyon – Université Lyon1, Laboratoire de Synthèse et Méthodologie Organiques (LSMO), ICBMS, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, 43 boulevard du 11 novembre 1918, Villeurbanne F-69622, France c Institut Curie et CNRS, UMR 176, Equipe Chimie Organométallique, Hétérocycles et Cibles Biologiques (COHCB), Institut Curie, 26 rue d’Ulm, 75248 Paris cedex 05, France d Laboratoire des Transformations Chimiques et Pharmaceutiques (LTCP), Conservatoire National des Arts et Métiers, 2 rue Conté, 75003 Paris, France e Université de Lyon – Université Lyon1, UMR 5246 CNRS, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Bât. Raulin, 43 boulevard du 11 novembre 1918, Villeurbanne F-69622, France

a r t i c l e

i n f o

Article history: Received 23 October 2012 Received in revised form 8 January 2013 Accepted 19 January 2013 Available online 9 February 2013 Keywords: Aromatic hydrogenation Acridine derivatives Hydrogenation pathway DFT calculations

a b s t r a c t Hydrogenation of acridine derivatives over Rh/Al2 O3 , has been studied. Strong influence of the pyrrolidino-substituent on the reduction pathway and reductions products was found. When, the reaction was performed on the unsubstituted acridine nucleus full conversion was obtained in 8 h. Under the same conditions, when a pyrrolidine substituent was settled on the central ring of acridine (9-position), a pure product was obtained with the two lateral carbocycles reduced whereas the central heterocyclic ring was not reduced. When the pyrrolidine substituent was at the 1-position, pure partially reduced central heterocyclic ring was obtained, but the compound was rapidly re-oxidized by air. In order to clarify such substituent effect, theoretical calculations were performed. Considering the energies and thermodynamic values of each intermediate and product as well as the interaction with the catalyst surface, the selectivity and diversity in the reduced product formation were partially explained and different reaction pathways were drawn according to the substitution pattern on the acridine scaffold. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Acridine derivatives are compounds of interest due to their broad biological activities against bacteria, parasites or tumours [1–7]. Their properties depend mainly on the nature and the position of the substituents on the acridine nucleus [8]. In the course of our studies on hydrogenation of aromatic compounds [9–11], we found of interest to study the reduction of acridine derivatives with the aim of controlling the chemioselectivity of the reaction which should lead to new families of potentially biologically active molecules. In particular, hydrogenation of 9-amino acridine gave access to tacrine (1,2,3,4-tetrahydro-9amino-acridine), a reversible acetylcholine inhibitor, which has been the first drug approved for the treatment of Alzheimer disease [12] in 1993/1994 and new derivatives are still sought after, although tacrine is now out of the market [13–19].

∗ Corresponding author. E-mail address: [email protected] (F. Fache). 1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molcata.2013.01.015

Furthermore, the hydrodenitrogenation reaction (HDN), where nitrogen is removed from the heteroaromatic nitrogen ring of compounds found in fossil fuels, is one of the most important and highly studied reaction [20–22]. HDN is a complex process that involves a variety a chemical sequences and among then, reduction of the aromatic carbocycles [22]. Numerous studies have been published on the acridine as a model of polynuclear heteroaromatic fuel products. The reduction pathway depends on the nature of the metal, on the support and on reaction conditions. Two different competing pathways for the reduction of acridine have been suggested, differing by the fact that the heterocyclic ring of acridine is being reduced first, before the lateral carbocycles, or the inverse [23–28]. In homogeneous catalysis, the reduction catalyzed by ruthenium or boron complexes [29,30] also showed that the pathway can be different depending on the catalysts. The reduction by H2 over metal/oxide surfaces has been the subject of several theoretical works, studying the selectivity brought by the metal nature and/or the oxide support [31–36]. All the calculations indicate that hydrogenation proceeds through dissociated hydrogen (i.e. atomic H·) which attacks the chemisorbed substrate over the surface allowing

64

P. Mignon et al. / Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69

a favourable interaction with the atomic hydrogen bound to the metal In this article, we present our work on the catalytic hydrogenation of pyrrolidine-substituted acridine derivatives, synthesized according to a method published by some of us where pyrrolidine serves as a trigger for a cyclo-isomerization reaction leading to pyrrolidino-aryl moieties [37,38]. However the reactivity of the substrates over Rh/Al2 O3 catalyst was found to be strongly dependent of the substituant position and could not be easily explained. Thus, the hydrogenation of the unsubstituted acridine was carried out, as a model compound, under the same experimental conditions to study the reduction pathway with Rh/Al2 O3 catalyst. Experimental data combined with a theoretical approach based on gas phase calculation of the energies and thermodynamic values of the intermediate products allow us to propose a reaction pathway for the reduction of the acridine derivatives. Thus, most of the unusual reactivity of pyrrolidine-substituted acridines in catalytic hydrogenation over Rh/Al2 O3 catalyst could be explained. 2. Experimental part 2.1. Chemicals All commercially available reagents were used as received. Rh/Al2 O3 (5%) and acridine were purchased from Acros. 2.2. Instrumentation Hydrogenation experiments were performed in a stainless steel autoclave. NMR spectra were recorded with a Bruker AMX 300 spectrometer. Mass data were also acquired on a Shimazu QP2010 GCMS apparatus, with injection on a SLB-5ms column lined with a mass EI detection system.

2.3. General procedure for the hydrogenation under H2 pressure The acridine derivative 1, 3 or 5 (0.046 mmol) and Rh/Al2 O3 (2 mg, 0.0008 mmol) in 0.4 mL of MeOH were put in a stainless steel autoclave. The solution was degased 3 times under hydrogen. The reaction mixture was then stirred at 40 bar H2 and heated at 100 ◦ C, for requested time (the final pressure was 45 bar). The reaction mixture was filtrated through celite, the solvent evaporated and the crude product analyzed by NMR without further purification.

N

H2 40 bar

2.4. Computational details Density Functional Theory calculations were performed with the ADF [39] code using the PBE functional [40] and Triple Zeta plus polarization basis sets. For all given compounds, various stereoisomers were calculated. In each case, frequencies were computed and we always considered the stationary points with the lowest energy. The corresponding electronic energy and zero point energy were used to compute the relative changes in electronic energy, enthalpy and free energy (E, H and G) against the acridine and H2 isolated molecules. The thermodynamic functions, including free energies, were calculated at 298.15 K and 1 atm. 3. Results and discussion 3.1. Reduction of substituted acridine derivatives Hydrogenation of acridine derivatives over Rh/Al2 O3 , has been studied. For the reduction of compound 1, only compound 2 was isolated (Scheme 1). However in the case of product 3, only compound 4 was obtained and underwent a fast re-aromatisation when left in the NMR tube (CDCl3 ). The re-aromatisation of 4 was slower in C6 D6 . These observed selectivities for compounds 1 and 3 are quite surprising and the role of the pyrrolidine substituent uncertain. To clarify the unexpected reactivity of acridine derivatives 1 and 3, the reduction of the unsubstituted acridine 5 was reinvestigated experimentally and theoritically. 3.2. Reduction of unsubstituted acridine 5 Standard conditions were applied to acridine 5 (Rh/Al2 O3 with 40 bar H2 , 100 ◦ C, methanol as solvent). Product distribution as the function of time is given in Fig. 1. After 30 min, the reaction mixture was analyzed by both 1 H NMR and mass spectrometry. The conversion was already high (50%) and the major product was 6, with only the central ring being reduced (compound 7 being the minor product). After 1 h, the conversion was slightly higher (60%), but the distribution of the products was different. The major reduction product was this time 8 with the external rings reduced. After 8 h of reaction, the conversion was total. We obtained a mixture of the fully reduced product 9 (80%) and the partially reduced product 8. From these data, it appears that products 6 and 7 are rapidly formed and that after 1 h they are converted into 8. An accumulation of 8 before the formation of 9 can also be noticed. Finally these results show that the first reduction occurs on the central ring.

N

Rh/Al2O3 MeOH, 100°C, 8h

N

1

N

N 3

MeOH, 100°C, 8h

N

N

H2 40 bar Rh/Al2O3

2 100%

N

r.t. N H

p.atm 4

t1/2= 4h

conv. 70% selectivity 100% Scheme 1. Reduction outcome of 9- or 1-pyrrolidino-acridine derivatives (1 or 3).

N 3

P. Mignon et al. / Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69

65

Table 1 Energies and thermodynamic values of reduction products of compound 5 (kcal/mol).

Fig. 1. Product distribution as the function of time for the reduction of acridine by Rh/Al2 O3 with H2 .

This confirms one of the two suggested mechanisms that were proposed in earlier works [23,27] for catalysis on Pd, Pt or Rh supported materials. 3.3. Theoretical calculations In order to understand the reduction mechanism of compounds 1 and 3 we have performed DFT calculations from the simplest model, the unsubstituted acridine 5 (Fig. 2). For each intermediate, different isomers can be formed through the hydrogenation/adsorption process. For the observed compounds 5–9, all possible structures were computed. In the present work we have considered that the dominant role of the surface, as discussed below, consists in a geometrical constraint towards the hydrogenation mechanism by hydrogenation on the same side of the aromatic

From compound 5

E

H

G

6 7 8 9

−23.1 −44.2 −84.7 −122.8

−16.7 −31.8 −60.0 −79.3

−8.4 −14.9 −25.9 −18.2

ring. The reduction by H2 over metal/oxide surfaces has been the subject of several theoretical works, studying the selectivity brought by the metal nature and/or the oxide support [31–36]. All the calculations indicate that hydrogenation proceeds through dissociated hydrogen (i.e. atomic H·) which attacks the chemisorbed substrate over the surface allowing a favourable interaction with the atomic hydrogen bound to the metal. As a result for compound 9, hydrogen atoms were added in the cis position on the central ring. The corresponding electronic energies and thermodynamic values are given in Table 1 and free energy changes are shown in Fig. 2. From 5 to 9, the hydrogenation of aromatic molecules leads to more and more stable compounds (see E and H values, Table 1). From G values one can see that the formation of each intermediate is favourable, except for the final product 9. Indeed from 5 to 8, the change in free energy is negative in the range of −6 to −10 kcal/mol for each step. From 8, the positive change in free energy (+7.7 kcal/mol) shows that the formation of 9 is not favoured, although it is observed experimentally. According to the experimental conditions, H2 is present at high pressure (40 bar) which can influence drastically the equilibrium towards 9. Moreover the positive change in free energy suggests that the reduction from 8 to 9 is less easy than the previous ones. This may explain why the reaction is delayed and why accumulation of 8 (54% after 1 h, see Fig. 1) is observed before the formation of 9.

Fig. 2. Gas-phase reaction profiles of the reduction of unsubstituted acridine 5. (Gibbs free energies, in kcal/mol) and distances, in Å, of axial hydrogen and pyrrolidine hydrogen atoms above/below the plane of the aromatic ring.

66

P. Mignon et al. / Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69

Table 2 Energies and thermodynamic values of reduction products of compound 1 (kcal/mol). From compound 1

E

H

G

10 11 2 12

−23.5 −43.5 −84.0 −111.5

−16.9 −31.5 −59.1 −67.9

−8.3 −13.0 −24.8 −7.3

3.4. Reduction of 1-pyrrolidino substituted acridine 1: theoretical calculation The same reduction pathway was considered for the substituted product 1 even if only intermediates 11 and 2 have been detected by NMR (Scheme 2). The reduction reactions are still favourable and lead to stable compound 11, up to molecule 2. From 2, the formation of 12 is not favourable at all, the difference between the free energy values being of +17.5 kcal/mol. This value is 10 kcal/mol higher than the difference between 8 and 9. Moreover, the electronic energy and enthalpy values of 12 are about 10 kcal/mol less than those of 9 (see Tables 1 and 2). Furthermore, steric interactions between the pyrrolidine substituent and the external cycles could prevent the adsorption of

N

N

N

N H

1

the intermediate 2 on the catalyst surface and thus prevent the hydrogenation of the central ring to give product 12 (Fig. 3). 3.5. Reduction of substituted acridine derivative 3 For compound 3 (Scheme 3) two routes were computed for the reduction of 4, the only detected intermediate. We distinguish the formation of 13 and 14, depending on whether the reduction occurs on the substituted aromatic cycle or not. Energies and thermodynamic values show that after the formation of compound 4 the reduction would rather lead to 13 than to 14. Thus, the reduction is easier when it occurs on an unsubstituted aromatic cycle. From 13, the formation of 15 would be favoured, if we considered the G (6.5 kcal/mol), but the difference is rather low compared to the G for 7–8 (11 kcal/mol) and 11–2 (11.8 kcal/mol) (see Tables). Nevertheless, these data could not explain why products 15 or 16 were not formed. In previous theoretical studies on the hydrogenation of aromatic molecules the loss of aromaticity or resonance energy, measured as the change in enthalpy upon addition of H2 on double bonds, was found to be a measure of the reactivity of the substrate [41,42]. In the present work the loss in aromaticity, going from one intermediate to the following one, is quite similar

10

N

N

N

N 11

N

2

N H

12

Scheme 2. Reduction of compound 1.

Fig. 3. Gas-phase reaction profiles of the reduction of 9-pyrrolidino substituted acridine 1. (Gibbs free energies, in kcal/mol) and distances, in Å, of axial hydrogen and pyrrolidine hydrogen atoms above/below the plane of the aromatic ring.

P. Mignon et al. / Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69

N

N 3

N

N H

N

N

4

N

N

13

15

67

N

N H 16

N

N

14

Scheme 3. Reduction of compound 3.

for the unsubstituted acridine or the substituted ones, except for reduction of 2–12. In that case, the resonance energy is only 8.8 kcal/mol (H, Table 2), as compared to the other molecules (about 20 kcal/mol; 8–9 and 15–16). Thus molecule 2 is less aromatic and less reactive, which can explain why the reduction of 2 into 12 is not observed (Scheme 2). Numerous previous theoretical studies on the hydrogenation of unsaturated cyclic and non-cyclic molecules on metal surfaces have been investigated [31–36]. In all cases on Pt, Pd, Ru–Zn and Ni surfaces the cyclic molecule is adsorbed on the surface before the hydrogen is being transferred to the aromatic carbon. Although calculations are performed at the DFT/GGA level, without a specific exchange-correlation functional to better describe dispersion forces, it is well established that the aromatic molecules chemisorb the surface metal atoms via several carbon atoms. According to the reported mechanisms, the aromatic molecule is more or less coplanar to the surface and carbon atoms bind to surface metal atoms before the dissociated hydrogen is being transferred to the aromatic carbon via cis addition through the same side of the aromatic ring. The effect of the surface on the hydrogenation mechanism was respected in our molecular structure searches. Thus, the unfavourable free energy change for the hydrogenation from 2 to 12 could be explained by steric interaction between pyrrolidine and the external cycles (Fig. 3). It

should be noticed that the free energy change is also the highest observed in our examples (17.5 kcal/mol, Table 2) On the other hand, the selectivity observed for compound 2 cannot be simply explained by energy calculations. Thus, we have to focus on the steric hindrance induced by the pyrrolidine and how this substituent could modify the chemisorption of the substrates (Fig. 3). During the reduction of the unsubtituted acridine 5, hydrogen atoms lie by about 1.08–1.18 A˚ above the aromatic plane (Fig. 2). On the contrary, for substituted acridines, the pyrrolidine brings an important steric hindrance, which prohibits the binding of the aromatic carbon atoms to the surface and thus the hydrogenation of the ring. This appears to be clear for compound 1. The pyrrolidine prevents the hydrogenation of the central ring and the external rings of 1 can chemisorb on the surface, leading to 11 and 2 (Fig. 3). Steric hindrance rather than energy explains that 2 is not reduced into 12. The same behaviour may be observed for compound 3. The opposite external ring can be reduced but not the ring carrying the pyrrolidine. Thus in the case of compound 3 the reaction was stopped to 13 the first intermediate being compound 4 with the reduced central ring, as expected from Gibbs energy calculations (Table 3; Fig. 4). From these remarks one may re-examine the reduction mechanism for compounds 1 and 3.

Fig. 4. Gas-phase reaction profiles of the reduction of 1-pyrrolidino substituted acridine 3. (Gibbs free energies, in kcal/mol) and distances, in Å, of axial hydrogen and pyrrolidine hydrogen atoms above/below the plane of the aromatic ring.

68

P. Mignon et al. / Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69

Table 3 Energies and thermodynamic values of reduction products of compound 3 (kcal/mol). From compound 3

E

H

G

4 14 13 15 16

−21.7 −37.2 −42.7 −78.3 −119.6

−15.3 −25.1 −30.4 −54.0 −76.4

−7.3 −8.5 −13.7 −20.2 −14.4

For compound 1, the reduction of the central ring is excluded because of the presence of pyrrolidine substituent. As such, compound 10 should not be formed. In that case the hydrogenation mechanism occurs directly and only on the external rings, following the pathway described in Scheme 2. For compound 3, only compound 4 is observed experimentally while 13 is not. However 4 is observed to be rapidly re-oxidized to 3 at normal conditions. This shows that 4 is not stable under atmospheric conditions although it is showed theoretically to be stable and its formation favourable. For 13, as compared to 4 it is an external ring which is hydrogenated. Although it is more stable and thermodynamically favourable, one might imagine that 13 is also rapidly rearranged to 4 under atmospheric conditions and then back to 3. However these hypotheses cannot be answered rigorously from the present results. Additional work would be necessary in order to assess whether short-living 13 is formed or not, and in that case if it is very rapidly re-oxidized to 3.

4. Conclusion This study combining experimental and theoretical techniques aimed to understand the hydrogenation reduction pathway of acridine derivatives over an Rh/Al2 O3 catalyst. In our conditions, the unsubstituted acridine is totally reduced. As a function of time, two intermediates have been identified. Reduction pathway can be explained by energy calculations and steric hindrance. In comparison, for substituted acridines, the reduction is stopped before the hydrogenation of the aromatic cycle carrying the pyrrolidine substituent. For the acridine molecule substituted at the central ring, the energetics indicate that the last hydrogenation of the central ring is less favourable than for the free acridine, showing that the reaction is much more difficult. This is in line with the experimental observations. For the acridine substituted at a lateral ring the energetics, however, do not explain the experimental observations. From previous theoretical studies it is assumed that the hydrogenation takes place when the aromatic ring is chemisorbed on the metal surface. In that sense we expect a probable hindrance due to the pyrrolidine substituent. For the acridine substituted at the central ring, it clearly appears that the pyrrolidine prevents the aromatic carbon of the central ring to bind the surface. This confirms the experimental observations and shows that the reduction pathway is somehow different from that of the free acridine, lateral rings being hydrogenated while the central ring is not. For the acridine substituted at the lateral ring, the hindrance due to pyrrolidine substituent only prevents the hydrogenation of this ring. This however does not explain the experimental observation. One could argue that the molecule formed is rapidly re-oxydized at standard conditions, as it is observed for molecule 4, but further studies are needed to conclude on that point. Finally, the combination of an experimental and theoretical approach of the present study allowed us to understand the reduction mechanism of acridine 5 and to show that the mechanism is different for derivative 1.

Acknowledgements H.C. and P.M. thank the Centre Informatique National de l’Enseignement Supérieur (CINES) and Grand Equipement National de Calcul Intensif (GENCI) for computer resources allocation, project: cpt2130. M.T. thanks the Ministère Franc¸ais de l’Enseignement Supérieur et de la Recherche and P.B. thanks, the “Association pour la Recherche sur le Cancer” and the “Cluster de Recherche Chimie de la Région Rhône-Alpes.” Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.molcata.2013.01.015. References [1] P. Belmont, I. Dorange, Expert Opin. Ther. Pat. 18 (2008) 1211. [2] P. Belmont, J. Bosson, T. Godet, M. Tiano, Anticancer Agents Med. Chem. 7 (2007) 139. [3] L.R. Kelland, Eur. J. Cancer 41 (2005) 971. [4] R. Martinez, L. Chacon-Garcia, Curr. Med. Chem. 12 (2005) 127. [5] M.D. Pujol, M. Romero, I. Sanchez, Curr. Med. Chem. – Anticancer Agents 5 (2005) 215. [6] M. Demeunynck, Expert Opin. Ther. Pat. 14 (2004) 55. [7] W.A. Denny, Curr. Med. Chem. 9 (2002) 1655. [8] J. Chiron, J.P. Galy, Synthesis (2004) 313. [9] F. Fache, Synlett (2004) 2827. [10] F. Fache, S. Lehuede, M. Lemaire, Tetrahedron Lett. 36 (1995) 885. [11] (a) F. Fache, O. Piva, Synlett (2004) 1294; (b) D. Clarisse, B. Fenet, F. Fache, Org. Biomol. Chem. 10 (2012) 6587. [12] F. Rouhart, Rev. Med. Interne 16 (1995) 860. [13] T. Darreh-Shori, H. Soininen, Curr. Alzheimer Res. 7 (2010) 67. [14] M. Ouberai, K. Brannstrom, M. Vestling, A. Olofsson, P. Dumy, S. Chierici, J. Garcia, Org. Biomol. Chem. 9 (2011) 1140. [15] J. Patocka, D. Jun, K. Kuca, Curr. Drug Metab. 9 (2008) 332. [16] C. Ronco, L. Jean, H. Outaabout, P.Y. Renard, Eur. J. Org. Chem. (2011) 302. [17] H. Sugimoto, Chem. Biol. Interact. 175 (2008) 204. [18] V. Tumiatti, A. Minarini, M.L. Bolognesi, A. Milelli, M. Rosini, C. Melchiorre, Curr. Med. Chem. 17 (2010) 1825. [19] W. Luo, Y.-P. Li, Y. He, S.-L. Huang, J.-H. Tan, T.-M. Ou, D. Li, L.-Q. Gu, Z.-S. Huang, Bioorg. Med. Chem. 19 (2011) 763. [20] T. Kabe, A. Ishihara, W. Qian, Hydrodesulfurization and Hydrodenitrogenation: Chemistry and Engineering, Wiley-VCH, Weinheim, 1999. [21] M. Macaud, M. Sevignon, A. Favre-Reguillon, M. Lemaire, E. Schulz, M. Vrinat, Ind. Eng. Chem. Res. 43 (2004) 7843. [22] C. Bianchini, A. Meli, F. Vizza, Eur. J. Inorg. Chem. (2001) 43. [23] K.Y. Sakanishi, M.S. Ohira, I. Mochida, H. Okazaki, M.H. Soeda, Bull. Chem. Soc. Jpn. 62 (1989) 3994. [24] G. Radivoy, F. Alonso, M. Yus, Tetrahedron 55 (1999) 14479. [25] K. Sakanishi, I. Mochida, H. Okazaki, M. Soeda, Chem. Lett. (1990) 319. [26] K. Kamata, Y. Tominaga, A. Tori-i, T. Thiemann, K. Takahashi, S. Mataka, Heterocycles 57 (2002) 1683. [27] K. Sakanishi, M. Ohira, I. Mochida, H. Okaaki, M. Soeda, J. Chem. Soc. Perkin Trans. 2 (1988) 1769. [28] C. Bianchini, V. Dal Santo, A. Meli, S. Moneti, M. Moreno, W. Oberhauser, R. Psaro, L. Sordelli, F. Vizza, J. Catal. 213 (2003) 47. [29] A.F. Borowski, S. Sabo-Etienne, B. Donnadieu, B. Chaudret, Organometallics 22 (2003) 1630. [30] S.J. Geier, P.A. Chase, D.W. Stephan, Chem. Commun. 46 (2010) 4884. [31] P.Q. Yuan, B.Q. Wang, Y.M. Ma, H.M. He, Z.M. Cheng, W.K. Yuan, J. Mol. Catal. A: Chem. 301 (2009) 140. [32] P.Q. Yuan, B.Q. Wang, Y.M. Ma, H.M. He, Z.M. Cheng, W.K. Yuan, J. Mol. Catal. A: Chem. 309 (2009) 124. [33] C. Morin, D. Simon, P. Sautet, Surf. Sci. 600 (2006) 1339. [34] F. Mittendorfer, C. Thomazeau, P. Raybaud, H. Toulhoat, J. Phys. Chem. B 107 (2003) 12287. [35] M. Saeys, M.F. Reyniers, M. Neurock, G.B. Marin, J. Phys. Chem. B 107 (2003) 3844. [36] F. Mittendorfer, J. Hafner, J. Phys. Chem. B 106 (2002) 13299. [37] P. Belmont, T. Belhadj, Org. Lett. 7 (2005) 1793. [38] M. Tiano, P. Belmont, J. Org. Chem. 73 (2008) 4101. [39] E.J. Baerends, J.A., D. Bashford, A. Bérces, F.M. Bickelhaupt, C. Bo, P.M. Boerrigter, L. Cavallo, D.P. Chong, L. Deng, R.M. Dickson, D.E. Ellis, M. van Faassen, L. Fan, T.H. Fischer, C. Fonseca Guerra, A. Ghysels, A. Giammona, S.J.A. van Gisbergen, A.W. Götz, J.A. Groeneveld, O.V. Gritsenko, M. Grüning, F.E. Harris, P. van den Hoek,

P. Mignon et al. / Journal of Molecular Catalysis A: Chemical 371 (2013) 63–69 C.R. Jacob, H. Jacobsen, L. Jensen, G. van Kessel, F. Kootstra, M.V. Krykunov, E. van Lenthe, D.A. McCormack, A. Michalak, M. Mitoraj, J. Neugebauer, V.P. Nicu, L. Noodleman, V.P. Osinga, S. Patchkovskii, P.H.T. Philipsen, D. Post, C.C. Pye, W. Ravenek, J.I. Rodríguez, P. Ros, P.R.T. Schipper, G. Schreckenbach, M. Seth, J.G. Snijders, M. Solà, M. Swart, D. Swerhone, G. te Velde, P. Vernooijs, L. Versluis, L. Visscher, O. Visser, F. Wang, T.A. Wesolowski, E.M. van Wezenbeek, G. Wiesenekker, S.K. Wolff, T.K. Woo, A.L. Yakovlev, T. Ziegler. ADF2009.01,

69

SCM, Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands, http://www.scm.com, 2009. [40] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. [41] D.R. Hou, M.S. Wang, M.W. Chung, Y.D. Hsieh, H.H.G. Tsai, J. Org. Chem. 72 (2007) 9231. [42] H.H.G. Tsai, M.W. Chung, Y.K. Chou, D.R. Hou, J. Phys. Chem. A 112 (2008) 5278.