Nuevos catalizadores para las reacciones de carbonilación e hidrogenación de alquenos en sistemas homogéneos y bifásicos.

Nuevos catalizadores para las reacciones de carbonilación e hidrogenación de alquenos en sistemas homogéneos y bifásicos El trabajo titulado "Nuevos catalizadores para las reacciones de carbonilación e hidrogenación de alquenos en sistemas homogéneos y bifásicos" consta de tres capítulos:Capítulo I: Estudio de las reacciones de hidroformilación e hidrocarboxilación de alquenos en sistemas bifásicos acuosos y perfluorados. En este capítulo se han estudiado en concreto:1) La hidroformilación de vinilarenos en sistemas bifásicos acuosos de rodio/difosfinas sulfonadas. Las difosfinas sulfonadas utilizadas son las difosfinas aquirales 1,3-bis [(di-m-sulfonatofenil)fosfino]propano (dpppts) y 1,4-bis [(di-m-sulfonatofenil)fosfino]butano (dppbts), y las difosfinas sulfonadas quirales (S,S)-2,4-bis [(di-m-sulfonatofenil)fosfino]pentano ((S,S)-BDPPTS) y (R,R)-1,2-[(bis(di-m-sulfonatofenilo)fosfino)metil]ciclobutano ((R,R)-CBDTS). En este estudio se observó que la actividad de los sistemas catalíticos depende del pH del medio, en medio básico estos sistemas son activos debido a la formación de las especies [RhH(CO)2(P-P)], precursoras de las especies activas [RhHCO(P-P)], mientras que en medio neutro no se detectaba la formación de tales especies lo que conduce a una disminución drástica de la actividad.2) La hidroformilación en sistemas bifásicos perfluorados de rodio/P(C6H4-p-OCH2C7F15)3 (L1). Estos sistemas son activos en la hidroformilación de 1-octeno y se obtienen resultados similares a los obtenidos con la trifenilfosfina en sistemas homogéneos, lo que quiere decir que el grupo O-CH2 permite minimizar los efectos electroatractores de la cadena perfluorada sobre el átomo de fósforo del ligando. También la fase catalítica se ha podido reciclar hasta tres veces manteniendo la actividad y la selectividad del sistema. 3) La hidrocarboxilación de estireno y de otros vinilarenos en sistemas bifásicos acuosos de paladio/difosfinas sulfonadas (dpppts, dppbts, (S,S)-BDPPTS y (R,R)-CBDTS). Estos sistemas son activos tanto en medio básico como en medio ácido, sin embargo son mucho más estables en medio ácido lo que permite así el reciclaje de las fases acuosas catalíticas manteniendo la actividad, la regioselectividad y la enantioselectividad en el caso de las difosfinas quirales.4) La hidrocarboxilación de estireno en sistemas bifásicos acuosos de paladio/fosfinas tipo guanidino, trihidrocloruro de tris(3-(N,N- dimetilguanidino)fenil)fosfina (L2) y guanidinopropildifenilfosfina (L3). El sistema Pd/L3 es más activo, mientras que el sistema Pd/L2 es más estable y más selectivo en la formación de los ácidos. Capítulo II: Estudio de la hidroformilación asimétrica de alquenos con sistemas de rodio/ligandos P,N-dadores derivados del esqueleto de la difosfina DIOP.En este capítulo se ha estudiado la hidroformilación asimétrica de estireno y de otros substratos derivados con sistemas de rodio y ligandos P,N-dadores derivados de la DIOP (L4, L5, L6 y L7) (figura 1). Figura 1Estos sistemas son activos en esta reacción, sin embargo los excesos enantioméricos obtenidos son muy bajos debido a la formación de las dos especies [RhH(CO)2(P-N)] y [RhH(CO)2(P-N)2] (donde el ligando actúa como monofosfina) que conducen, por disociación de una molécula de CO, a la formación de dos especies activas. Capítulo III: Síntesis de nuevos ligandos ditioéter relacionados con la difosfina BDPP. Aplicación en la hidrogenación asimétrica con sistemas de iridio. En este capítulo se llevó a cabo la síntesis de los ligandos ditioéter quirales (S,S) BDSP(R) (L8 (R = Ph) y L9 (R = iPr)) (figura 2), y de los complejos catiónicos de iridio(I) correspondientes [Ir((L8) (COD)]BF4 y [Ir((L9) (COD)]BF4, y su aplicación en la hidrogenación del acetamido acrilato de metilo (figura 2). Figura 2En este estudio se observó que los sistemas catalíticos de iridio con los ligandos ditioéter son moderadamente activos en la hidrogenación de acetamido acrilato de metilo, sin embargo se obtienen excesos enantioméricos nulos debido a la ausencia de rigidez en el anillo formado por el metal y los ligandos L8 y L9.New catalysts for the carbonylation and hydrogenation of alkenes in homogeneous biphasic systemsThe work entitled "New catalysts for the carbonylation and hydrogenation of alkenes in homogeneous and biphasic systems" consists of three chapters:Chapter I: This chapter studies the hydroformylation and hydrocarboxylation of alkenes in aqueous and perfluorinated biphasic systems. In particular:1) The hydroformylation of vinylarenes in aqueous biphasic systems with rhodium complexes and sulfonated diphosphines. The sulfonated diphosphines used are the achiral diphosphines 1,3-bis [(di-m-sulfonatophenyl)phosphino]propane (dpppts) and 1,4-bis [(di-m-sulfonatophenyl)phosphino]butane (dppbts), and the chiral sulfonated diphosphines (S,S)-2,4-bis [di(m-sulfonatophenyl)phosphino]pentane ((S,S)-BDPPTS) and (R,R)-1,2-bis [di (m-sulfonatophenyl)phosphinomethyl]cyclobutane ((R,R)-CBDTS). In this study it was observed that the activity of the catalytic systems depends on the pH of the medium. In basic medium, these systems are active because [RhH(CO)2(P-P)] species are formed, which are precursors of the active species [RhHCO(P-P)]. In neutral medium, however, these species are not formed, which leads to a drastic decrease in activity.2) The hydroformylation in perfluorinated biphasic systems with rhodium /P(C6H4-p-OCH2C7F15)3 (L1). Those systems are active in the hydroformylation of 1-octene and the results are similar to those obtained with triphenylphosphine in homogeneous systems, which means that the group O-CH2 minimizes the electroattractive effects of the perfluorinated chain on the phosphorus atom of the ligand. The catalytic phase was recycled up to three times with the same activity and selectivity of the system. 3) The hydrocarboxylation of styrene and other vinyl arenes in aqueous biphasic systems with palladium complexes and sulfonated diphosphines (dpppts, dppbts, (S,S)-BDPPTS and (R,R)-CBDTS). These systems are active both in basic and acidic medium. They are, however, much more stable in acidic medium, which makes the catalytic aqueous phases possible to be recycled and the activity, regioselectivity and enantioselectivity in the case of the chiral diphosphines to be maintained.4) The hydrocarboxylation of styrene in aqueous biphasic systems with palladium complexes and the guanidine phosphines tris(3-(N,N-dimethylguanidino)phenyl) phosphine tri-hydrochloride (L2) and 3-guanidinopropyldiphenylphosphine (L3). The system Pd/L3 is more active, while the Pd/L2 system is more stable and more selective in the formation of acids. Chapter II: The chapter studies how rhodium systems and P,N donor ligands derived from DIOP (L4, L5, L6 and L7) can be used in the asymmetric hydroformylation of styrene and other related substrates (figure 1). Figure 1Those systems are active in this reaction however, the enantiomeric excesses obtained are very low because two species are formed ([RhH(CO)2(P-N)] and [RhH(CO)2(P-N)2] in which the ligand acts as a monophosphine) by reaction of Rh and the ligand under H2/CO pressure. Because of the disassociation of a CO molecule, those two species lead to the formation of two active species. Chapter III: This chapter describes the synthesis of chiral bis-(thio)ether ligands (S,S) BDSP(R) (L8 (R = Ph) and L9 (R = iPr)) (figure 2), and the corresponding cationic iridium complexes [Ir((L8) (COD)]BF4 and [Ir((L9) (COD)]BF4. It also describes their application in the hydrogenation of methyl-2- acetamidoacrylate. Figure 2 In this study it has been observed that iridium catalytic systems with bis-(thio)ethers ligands are moderately active in the hydrogenation of methyl-2-acetamido acrylate. The enantiomeric excesses obtained, however, are virtually nonexistent, probably, because the ring formed by the metal and the ligands L8 and L9 is not rigid

Novel chromium (III) complexes with N4-donor ligands as catalysts for the coupling of CO2 and epoxides in supercritical CO2

10.1016/j.molcata.2013.10.021New neutral and cationic chromium(III) complexes with N4 Schiff base ligands have been prepared and characterized. These complexes are active catalysts for the cycloaddition of CO2 and styrene oxide in CH2Cl2 solutions, affording epoxide conversions in a 39¿92% range, with encouraging cyclic carbonate yields (up to 63%). It is to notice that the cationic species were significantly more active than their neutral analogs. Addition of tetrabutylammonium halides improved the selectivity toward styrene carbonate (87% yield). Dichloromethane could be avoided using solvent free or supercritical carbon dioxide as a solvent (scCO2) and, moreover, this improved the catalytic activity of the cationic complexes (TOF up to 652 h-1). Using scCO2, these chromium catalysts afforded the rapid and selective formation of cyclic carbonates from the coupling of CO2 to various linear terminal epoxides, such as epichlorydrin, propylene oxide and long chain terminal oxiranes. Coupling of cyclohexene oxide and carbon dioxide led to mixtures of poly(cyclohexene) carbonate and cyclic carbonate depending on the conditions (pressure and co-catalyst/catalyst ratio). Poly(cyclohexene) carbonate was isolated with a productivity 388 g/g Cr. Selective formation of the cyclic cyclohexene carbonate was obtained working under scCO2 conditions

Chemical profile and in vitro antibacterial potential of essential oils and hydrolat extracts from aerial parts of three wild species of Moroccan Thymus

The present study aims to determine and compare the chemical composition of essential oils (EO) and hydrolat extracts (HE), isolated from three wild varieties of Moroccan thyme (T. satureioides Coss., T. willdenowii Boiss. and T. zygis L.) and to assess their antibacterial activity against four bacterial strains: Gram- (E. coli, Pr. Mirabilis) and Gram+ (B. subtilis, S. aureus). The findings showed that carvacrol (44.95%) and its biogenetic precursor p-cymene (23.36%) were the most dominant compounds of T. zygis L EO. The major volatile compounds in T. willdenowii Boiss EO were found to be thymol (42.38%), carvacrol (16.49%), and p-cymene (13.29%). Thus, T. satureioides Coss EO consists mainly of carvacrol (27.57%) and borneol (21.56%). On the other hand, carvacrol (72.33%) and thymol (10.70%) were the most prominent constituents in T. zygis L HE. T. willdenowii Boiss was dominated by thymol (65.01%) and carvacrol (21.74%). Furthermore, T. satureioides Coss HE was characterized by a high percentage of carvacrol (47.45%), borneol (25.04%), and γ-terpineol (19.34%). All investigated extracts exercised a strong antibacterial power against both tested Gram-positive and Gram-negative strains. However, the weakest activity was observed with T. satureioides Coss. EO and HE. The biological potential of HEs was found much higher than that of the corresponding EOs, which may give hydrolats a great value in aromatherapy to the detriment of essential oils

Rhodium-sulfonated diphosphine catalysts in aqueous hydroformylation of vinyl arenes: high-pressure NMR and IR studies

Hydroformylation of vinyl arenes (p-metboxystyrene and p-fluorostyrene) was performed in aqueous solutions using as catalyst precursor [Rh(mu-OMe)(cod)](2) (cod = 1,5-cyclooctadiene) associated with the sulfonated 1,3-diarylphosphines (tetra-sulfonated 1,3-bis(diphenylphosphino)propane (dpppts)) and the chiral (S,S)-bdppts (2,4-bis(diphenylphosphino)pentane). The influence of pH on the reaction rate was studied. After 24 h conversion was practically total with the achiral system in basic medium for the substituted styrene substrates. Selectivities in aldehydes were >85%. At neutral pH, the asymmetric hydroforrnylation of p-substituted styrenes using the rhodium-bdppts systems provides low conversion but the enantioselectivities were as high as 66%, the highest reported so far for this kind of substrates in aqueous systems. Comparison experiments using rhodium precursors with the non-sulfonated bdpp in organic solvents indicated that the enantioselectivity was higher in aqueous solutions for the p-methoxystyrene derivative and slightly lower for p-fluorostyrene. However, in both the cases the conversions in aqueous systems were low. High-pressure NMR and IR experiments in water/methanol indicate that [RhH(CO)(2)(sulfonated diphosphine)] species form under catalytic conditions in basic medium. At neutral pH, the main species observed in the case of the bdppts ligand is [Rh(bdppts)(2)](+) which may account for the low conversion in this medium. (C) 2002 Elsevier Science B.V. All rights reserved

The reaction of pyranoside 2-uloses with DAST revised. Synthesis of 1-fluoro-ketofuranosyl fluorides and their reactivity with alcohols

We have reinvestigated the reaction of α-pyranosides-2-uloses 13, 14, 19 and 24 with DAST and shown that the 1,2-difluorinated compounds 17, 18 and 25 are produced by a ring-contraction reaction. The reaction of 18 with benzyl alcohol gives the tri-benzyl derivative 26 or compound 27, depending on the reaction conditions. Treating 17 with 2-naphthol produced the spiranic compounds 29–31. The reaction of 17 with bis(trimethylsilyl)uracil produced the mononucleoside 28, which preserves the fluorine atom in the more substituted carbon.Peer reviewe

Chromium complexes with tridentate NN'O Schiff base ligands as catalysts for the coupling of CO2 and epoxides

10.1016/j.molcata.2013.11.026New Cr(III) hexacoordinated complexes with tridentate NN'O-donor Schiff base ligands, M(NN'O)2Cl, have been prepared. They form active catalytic systems for the coupling of epoxides and carbon dioxide in the presence of co-catalysts. Best results were obtained with the complex with N-(2-pyridylmethyl)-3,5-di-tert-butyl-salicylaldimine (1) ligand and a co-catalyst. Cyclohexene oxide reacts with carbon dioxide in the presence of these catalysts to form mixtures of polycarbonate (PC) (productivity up to ca. 900 g PC/g Cr) and cyclic carbonate depending on the co-catalyst and conditions employed. Cyclopentene, styrene and propylene oxides form selectively the cyclic carbonates at the conditions studied (epoxide conversion up to 97%). Although some of the co-catalysts are also active for the cycloaddition, the presence of both complex and co-catalyst has proved to be beneficial

Chiral S,S-donor ligands in palladium-catalysed allylic alkylation

Chiral dithioether ligands have been tested in the model Pd-catalysed allylic alkylation reaction of (+/-)-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate. giving high enantioselectivity (up to 81% e.e.) for the first time in this type of system. Pd(Il)-allylic intermediates, [Pd(eta (3)-1,3-Ph-2-C3H3)(dithioether)]PF6 were prepared and characterised both in solution by NMR spectroscopy and solid state. The X-ray structure for [Pd(eta (3)-1,3-Ph-2-C3H3)(L)]PF6 (L=(R,R)-7,8-O-isopropylidene-1,5-dithiacyclononane) was determined. (C) 2001 Elsevier Science Ltd. All rights reserved

Allylic alkylations catalyzed by palladium systems containing modular chiral dithioethers. A structural study of the allylic intermediates

Palladium allylic systems containing modular chiral dithioether ligands were chosen as catalysts for a systematic study of homodonor ligands in allylic alkylation reactions. For this purpose, new type-DMPS (4-6) and -DEGUS (8, 9) ligands were synthesized. Dithioethers 4-6 afforded high activities and excellent selectivities in all Pd-catalyzed allylic reactions. Particularly the Pd/6 catalytic system provided b-VIII with an ee > 99% and a regioselectivity 1/b (VIII) = 1/1.6. A family of intermediate complexes containing several allyl groups (symmetrical, 13-16 and 20, and nonsymmetrical, 17-19, moieties) and dithioether ligands (4-6, 8, 9, 11, and 12) is described. The complexes were fully characterized both in solution and in the solid state. X-ray structures of four of these complexes (16-18 and 20) were determined. The diastereomers present in solution were studied by NMR spectroscopy, and in some cases it was possible to establish a relationship between the diastereomeric excesses and the selectivities found in the catalytic process