Partenaires et organisations internationales
(Anglais)
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AT, BE, BG,CH, CY, CZ, DE, EE, ES, FI, FR, GR, HU, IT, LT, LV, NL, NO, PL, PT, RO, RS, SE, SI, SK, UK
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Résumé des résultats (Abstract)
(Anglais)
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1) We have studied the catalytic activity of the water soluble complexes CpRu(PTA)2Cl (1) and Cp*Ru(PTA)2Cl (2) in the aqueous hydrogenation (up to 100 bar H2 pressure) of CO32-/HCO3-/CO2 into formate as a function of pH over the temperature range 30-80°C. It has been shown that CpRu(PTA)2Cl and Cp*Ru(PTA)2Cl are catalysing the hydrogenation reaction, however (2) has been found to be more active. In general, at higher pH values we have found lower turnover frequencies (TOF) for both (1) and (2). Although the hydride species, generally active in reduction, for (1) and (2) have already been identified (and formed under H2 pressure), in presence of substrate we could not observed the specific signals by 1H NMR. 2) We have investigated the reduction of sodium-bicarbonate in aqueous solutions and in butyl-methyl-imidazolium-tetrafluoro borate ionic liquid, [bmim][BF4]. The hydrogenation of sodium-bicarbonate in a water free system, in pure [bmim][BF4], under 100 bar H2 pressure, using [{RuCl2(mtppms)2}2] catalyst cannot be carried out because of the insolubility of the NaHCO3. Giving 10% D2O to the [bmim][BF4] the sodium-bicarbonate dissolved and as we expected the formation of the formate proceeded (TOF = 3.05 h-1). [{RuCl2(mtppms)2}2] also catalysed the H-D exchange in this system, and 59 % of all formates is present as DCOO-. Being the H/D exchange faster than the reduction, this value stayed constant during the hydrogenation. 3) We have performed high pressure NMR measurements to study hydride formation in Rh(I) - Cl-MeOBIPHEP ligand systems. The complex was synthesized in situ from [(NBD)2Rh]PF6 and Cl-MeOBIPHEP, an atropisomeric diaryl-core diphosphane ligand, and investigated under 50 bar H2 pressure using 1H, 31P spectroscopy, several hydride species were observed. 4) We have compared the kinetics and mechanisms of the reactions of two isomerically related dinucleating hexaaza macrocyclic copper complexes [(metper)Cu2( -OH)2](CF3SO3)2 (1) and [(petper)Cu2(OH)2](CF3SO3)2 (2) with CO2 (from 5 to 55 bar pressures), to afford carbonate complexes, using high pressure FT-IR and UV-visible spectroscopy. The two complexes (1) and (2) have a very different behaviour, when reacting with CO2, although the only difference between them is the binding mode adopted by the two hydroxo ligands. (1), which adopts a bridging OH binding mode, reacts with CO2 following a zero order kinetics, suggesting that the reaction is autocatalytic. (2), having a terminal OH binding mode, reacts following a first order rate law on complex (2) concentration. The results indicate that complex (2) exhibits a nucleophilic behaviour and it is responsible for the attack on CO2. In sharp contrast, complex (1) is not directly active and should undergo some structural modification for the reaction to occur. 5) We have prepared a series of new catalysts via the reaction of RuCl3 with 1-[2-(1,4-cyclohexadiene-1-yl)alkyl]-3-methylimidazolium chloride (alkyl = ethyl, butyl) and 1-[2-(1,4-cyclohexadiene-1-yl)ethyl]-2,3-dimethylimidazolium chloride, resulting the dimeric Ru complexes of the type [RuCl2( 6-arene)]2Cl2. Treatment of these dimeric salts with phosphine ligands leads to the highly water soluble monomeric complexes [RuCl2PR3( 6-arene)]Cl, (PR3 = PPh3, PCy3). Reaction of [RuCl2( 6-1-(2-benzylethyl)-3-butylimidazolium)]Cl with Ag2O gives rise to a 6-arene-carbene chelate complex. The solid-state structures of several of the new imidazolium-functionalized arene complexes including the arene-carbene chelate complex have been determined. The [RuCl2PR3( 6-arene)]Cl complexes (PR3 = PPh3, PCy3), immobilised in water or in ionic liquid, have been used as catalysts in the hydrogenation of styrene, with moderate activity. 6) We have studied the catalytic reduction of CO2/HCO3-/CO32- in aqueous solution under mild experimental conditions using [RuCl2PR3( 6-arene)]Cl complexes as catalysts. The hydrogenation reactions were followed under H2 and CO2 pressure by multinuclear NMR spectroscopy, using high pressure sapphire NMR tubes. The rather low activity of these catalysts (the initial turnover frequencies (TOF) were between 4 and 11 h-1) allowed the direct detection and characterisation of the Ru(H)(PPh3)(HCO3)( 6-arene)]+ intermediate complex, which has been previously proposed, but not identified. Parallel to the reduction, a fast catalytic hydrogen/deuterium exchange between H2/D2O and the formate is observed. 7) We have investigated the catalytic activity of [Cp*Ir(PTA)Cl2] (1) and [Cp*Ir(PTA)2Cl]Cl (2) complexes on the hydrogenation of bicarbonate in aqueous solution. (1) has been found to be inefficient under mild experimental conditions, with very low TOFs. (2), in contrast, showed moderate activity as hydrogenation catalyst. It was revealed that (2) is most active at a pH around 9.
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