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111.
Mantica P Van Eester D Garbet X Imbeaux F Laborde L Mantsinen M Marinoni A Mazon D Moreau D Hawkes N Joffrin E Kiptily V Pinches S Salmi A Sharapov S Thyagaraja A Voitsekhovitch I de Vries P Zastrow KD 《Physical review letters》2006,96(9):095002
The first electron temperature modulation experiments in plasmas characterized by strong and long-lasting electron and ion internal transport barriers (ITB) have been performed in JET using ion cyclotron resonance heating in mode conversion scheme. The ITB is shown to be a well localized narrow layer with low heat diffusivity, characterized by subcritical transport and loss of stiffness. In addition, results from cold pulse propagation experiments suggest a second order transition process for ITB formation. 相似文献
112.
113.
Baber A de Vries JG Orpen AG Pringle PG von der Luehe K 《Dalton transactions (Cambridge, England : 2003)》2006,(40):4821-4828
The new unsymmetrical, optically active ligands 1,2-C(2)H(4)(PPh(2))(2'R,5'R-2',5'-dimethylphospholanyl) (L(a)) and 1,3-C(3)H(6)(PPh(2))(2'R,5'R-2',5'-dimethylphospholanyl) (L(b)) form complexes of the type [Rh(L)(cyclooctadiene)][BF(4)] where L = L(a) (1a) or L(b) (1b), [PtCl(2)(L)] where L = L(a) (2a) or L(b) (2b) and [PdCl(2)(L)] where L = L(a) (3a) or Lb (3b). The crystal structures of 2a and 2b show the chelate ligand backbones adopt delta-twist and flattened chair conformations respectively. Asymmetric hydrogenation of enamides and dehydroaminoesters using 1a and 1b as catalysts show that the ethylene-backboned diphosphine L(a) gives a more efficient catalyst in terms of asymmetric induction than the propylene-backboned analogue L(b). The greatest enantioselectivities were obtained with 1a and enamide substrates with ees up to 91%. Substrate-induced conformational changes in the Rh-diphosphine chelates are proposed to explain some of the ees observed in the hydrogenation of enamides. 相似文献
114.
de Vries JG 《Dalton transactions (Cambridge, England : 2003)》2006,(3):421-429
The Heck reaction has been the subject of intense investigation in the past decade. Many new types of catalysts have been developed in addition to the existing palladium/phosphine complexes. Prominent among these are palladacycles, pincers, several types of heterogeneous palladium catalysts, colloids and ligand-free palladium, usually in the form of Pd(OAc)2. Most of the newer types function only at higher temperatures, typically between 120 and 160 degrees C. It has been shown that irrespective of the catalyst precursor, none of these catalysts are stable at these high temperatures. They all have a tendency to form soluble palladium(0) colloids or nanoparticles, certainly with less reactive substrates such as aryl bromides or chlorides. The Heck reaction takes place by attack of the arylating agent on the palladium atoms in the outer rim of the nanoparticles. This leads to formation of monomeric or dimeric anionic palladium complexes that undergo the usual steps of the Heck mechanism as described by Amatore and Jutand. 相似文献
115.
T. de Vries W. J. H. Moll und H. C. Burger 《Fresenius' Journal of Analytical Chemistry》1931,86(7-8):306-307
Ohne Zusammenfassung 相似文献
116.
Nataša Mršić Thomas Jerphagnon Adriaan J. Minnaard Ben L. Feringa Johannes G. de Vries 《Tetrahedron: Asymmetry》2010,21(1):7-10
The rhodium-catalyzed asymmetric hydrogenation of 2-substituted N-protected-indoles using monodentate phosphoramidites as ligands was examined. Full conversion and 74% ee, were obtained with a catalyst based on PipPhos. The use of a catalytic amount of base is necessary for activity; best results were obtained with Cs2CO3. 相似文献
117.
Peña D Minnaard AJ Boogers JA de Vries AH de Vries JG Feringa BL 《Organic & biomolecular chemistry》2003,1(7):1087-1089
The combination of monodentate ligands in the rhodium-catalysed enantioselective hydrogenation enables a new approach when searching for the optimal activity and enantioselectivity in catalysis. 相似文献
118.
Jiang XB Minnaard AJ Hessen B Feringa BL Duchateau AL Andrien JG Boogers JA de Vries JG 《Organic letters》2003,5(9):1503-1506
Secondary phosphine oxides were prepared from R(1)PCl(2) and R(2)MgBr, followed by hydrolysis. They were obtained in an enantiopure form by preparative chiral HPLC. These new monodentate ligands were tested in the iridium-catalyzed hydrogenation of imines at 25 bar. Enantioselectivities up to 76% were obtained at L/Ir = 2. Addition of pyridine (Pyr/Ir = 1:2) raised the ee to 83%. Using pyridine as an additive allowed reduction of the L/Ir ratio to 1 without reduction of ee. [reaction: see text] 相似文献
119.
[reaction: see text] Bidentate chiral phosphines are no longer essential for achieving a fast and highly enantioselective hydrogenation of alpha- or beta-dehydroamino acid derivatives. In particular, a readily accessible and stable monodentate phosphoramidite can be highly effective in these asymmetric hydrogenations. 相似文献
120.
Caira MR de Vries EJ Nassimbeni LR 《Chemical communications (Cambridge, England)》2003,(16):2058-2059
The isolation and structural elucidation by single crystal X-ray diffraction of triclinic and monoclinic modifications of an inclusion complex of beta-cyclodextrin with the same guest, methylparaben, are reported. 相似文献