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Solvate Complexes (solvate + complex)
Selected AbstractsAsymmetric Hydrogenation with Highly Active IndolPhos,Rh Catalysts: Kinetics and Reaction MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2010Jeroen Wassenaar Abstract The mechanism of the IndolPhos,Rh-catalyzed asymmetric hydrogenation of prochiral olefins has been investigated by means of X-ray crystal structure determination, kinetic measurements, high-pressure NMR spectroscopy, and DFT calculations. The mechanistic study indicates that the reaction follows an unsaturate/dihydride mechanism according to Michaelis,Menten kinetics. A large value of KM (KM=5.01±0.16,M) is obtained, which indicates that the Rh,solvate complex is the catalyst resting state, which has been observed by high-pressure NMR spectroscopy. DFT calculations on the substrate,catalyst complexes, which are undetectable by experimental means, suggest that the major substrate,catalyst complex leads to the product. Such a mechanism is in accordance with previous studies on the mechanism of asymmetric hydrogenation reactions with C1 -symmetric heteroditopic and monodentate ligands. [source] Asymmetric Ring Opening of Benzo-7-oxabicyclo[2.2.1]heptadienes with Cationic Rhodium ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Angelika Preetz Abstract The efficient design of stereochemically challenging ring systems by ring opening of heterobicyclic alkenes has become a very important reaction in the chemistry of CC and CX bond formation. By using the hitherto applied in situ technique for the generation of the ,2 -bridged, dimeric neutral rhodium complexes, however, the catalytically active species and its concentration remained unidentified. Furthermore, the reaction temperature is at least 80,°C. The application of cationic rhodium(I) solvate complexes (that no longer contain blocking diolefins) shows that a much greater activity and enantioselectivity for the synthesis of 1,2-dihydro-1-naphthols can be reached than was described so far, even at ambient temperature. NMR spectroscopy and X-ray analysis show that a product inhibition during the ring opening reaction takes place that is independent of the nucleophile. [source] Unusual Deactivation in the Asymmetric Hydrogenation of Itaconic AcidADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2009Thomas Schmidt Abstract During the asymmetric hydrogenation of itaconic acid with rhodium solvate complexes of the type [Rh(PP)(MeOH)2] BF4 (PP=DIPAMP, Me-DuPHOS) a deactivation with increasing substrate concentration is observed. It is shown that this inhibition phenomenon is due to the in situ formation of an inactive rhodium(III)-alkyl complex. Two crystal structures of single crystals of the responsible complexes (1) and (2) support the deactivation pathway. [source] Trinuclear Rhodium Complexes and Their Relevance for Asymmetric HydrogenationCHEMISTRY - AN ASIAN JOURNAL, Issue 11 2008Angelika Preetz Abstract Various trinuclear rhodium complexes of the type [Rh3(PP)3(,3 -OH)x(,3 -OMe)2,x]BF4 (where PP=Me-DuPhos, dipamp, dppp, dppe; different ligands and , -bridging anions) are presented, which are formed upon addition of bases such as NEt3 to solvate complexes [Rh(PP)(solvent)2]BF4. They were extensively characterized by X-ray diffraction and NMR spectroscopy (103Rh, 31P, 13C, 1H). Their in,situ formation resulting from basic additives (NEt3) or basic prochiral olefins (without addition of another base) can cause deactivation of the asymmetric hydrogenation. This effect can be reversed by means of acidic additives. [source] | ||||||||||