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Hydrogen Transfer Reaction (hydrogen + transfer_reaction)
Selected AbstractsSelective Reduction of C=O in ,,,-Unsaturated Carbonyls Through Catalytic Hydrogen Transfer Reaction over Mixed Metal Oxides.CHEMINFORM, Issue 20 2004Sachin U. Sonavane Abstract For Abstract see ChemInform Abstract in Full Text. [source] Hydrido-Osmium(II), -Osmium(IV) and-Osmium(VI) Complexes with Functionalized Phosphanes as Ligands,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Birgit Richter Abstract Reaction of five-coordinate [OsHCl(CO)(PiPr3)2] (1) with the chelating phosphane iPr2PCH2CO2Me gave six-coordinate [OsHCl(CO)(PiPr3){,2(P,O)- iPr2PCH2C(=O)OMe}] (2), which upon treatment with CO and O2 afforded the 1:1 adducts [OsHCl(CO)(L)(PiPr3){,(P)- iPr2PCH2CO2Me}] (3, 4) by partial opening of the chelate ring. The vinyl complex [OsCl(CH=CHPh)(CO)(PiPr3){,2(P,O)- iPr2PCH2C(=O)OMe}] (5) was obtained from 2 and PhC,CH by insertion of the alkyne into the Os,H bond. Reaction of 2 with sodium acetate led to metathesis of the anionic ligands and formation of [OsH(,2 -O2CCH3)(CO)(PiPr3){,(P)- iPr2PCH2CO2Me}] (6). Osmium(VI) compounds [OsH6(PiPr2R)2] with R = CH2CH2OMe (12), CH2CO2Me (13) and CH2CO2Et (14), and [OsH6(PiPr3){,(P)- iPr2PCH2CH2NMe2}] (16) were prepared from osmium(IV) precursors and shown to rapidly react with O2 and primary alcohols. Exploratory studies revealed that the catalytic activity of the hexahydrido complexes in the hydrogen transfer reaction from 2-propanol to cyclohexanone and acetophenone depends on the type of the functionalized phosphane and is best for R = CH2CH2OMe. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Mechanistic Insights into Acetophenone Transfer Hydrogenation Catalyzed by Half-Sandwich Ruthenium(II) Complexes Containing 2-(Diphenylphosphanyl)aniline , A Combined Experimental and Theoretical StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2008Alessia Bacchi Abstract Several new half-sandwich ruthenium(II) complexes containing 2-(diphenyphosphanyl)aniline (PNH2) of formula {Ru[(,2P,N)PNH2](p -cymene)Cl}Y [Y = Cl (1a), PF6 (1b), BF4 (1c), BPh4 (1d), TfO (1e)] were synthesized and fully characterized both in solution (1H NMR and 31P{1H} NMR spectroscopy) and in the solid state (FTIR, X-ray analysis on single crystal). Complexes 1a and 1b are active precatalysts in the hydrogen transfer reaction of acetophenone, leading to tof values up to 4440 h,1. In comparison, the {Ru[(,2P,N)PNMe2](p -cymene)Cl}Cl complex leads to a tof value of 100 h,1 under the same catalytic conditions. The mechanism through which the precatalysts operate was deeply explored by high-resolution MS (ESI) and DFT/PCM studies. The results reveal that the complexes containing PNH2 operate through a bifunctional mechanism analogous to that proposed for diamines and amino alcohol ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Polymer-Supported, Carbon Dioxide-Protected N-Heterocyclic Carbenes: Synthesis and Application in Organo- and Organometallic CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010Gajanan Manohar Pawar Abstract The synthesis of a resin-supported, carbon dioxide-protected N-heterocyclic carbene (NHC) and its use in organocatalysis and organometallic catalysis are described. The resin-bound carbon dioxide-protected NHC-based catalyst was prepared via ring-opening metathesis copolymerization of 1,4,4a,5,8,8a-hexahydro-1,4,5,8- exo,endo -dimethanonaphthalene (DMNH6) with 3-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-1-(2-propyl)-3,4,5,6-tetrahydropyrimidin-1-ium-2-carboxylate (M1), using the well-defined Schrock catalyst Mo[N -2,6-(2-Pr)2 -C6H3](CHCMe2Ph)(OCMe3)2 and was used for a series of organocatalytic reactions, i.e., for the trimerization reaction of isocyanates, as well as for the cyanosilylation of carbonyl compounds. In the latter reaction, turn-over numbers (TON) up to 5000 were achieved. In addition, the polymer-supported, carbon dioxide-protected N-heterocyclic carbene served as an excellent progenitor for various polymer-supported metal complexes. It was loaded with a series of rhodium(I), iridium(I), and palladium(II) precursors and the resulting Rh-, Ir-, and Pd-loaded resins were successfully used in the polymerization of phenylacetylene, in the hydrogen transfer reaction to benzaldehyde, as well as in Heck-type coupling reactions. In the latter reaction, TONs up to 100,000 were achieved. M1, as a non-supported analogue of poly-M1- b -DMNH6, as well as the complexes PdCl2[1,3-bis(2-Pr)tetrahydropyrimidin-2-ylidene]2 (Pd-1) and IrBr[1-(norborn-5-ene-2-ylmethyl)-3-(2-Pr)-3,4,5,6-tetrahydropyrimidin-2-ylidine](COD) (Ir-1) were used as homogeneous analogues and their reactivity in the above-mentioned reactions was compared with that of the supported catalytic systems. In all reactions investigated, the TONs achieved with the supported systems were very similar to the ones obtained with the unsupported, homogeneous ones, the turn-over frequencies (TOFs), however, were lower by up to a factor of three. [source] Enzymatic Redox Cofactor Regeneration in Organic Media: Functionalization and Application of Glycerol Dehydrogenase and Soluble Transhydrogenase in Reverse MicellesBIOTECHNOLOGY PROGRESS, Issue 4 2005Hirofumi Ichinose An enzymatic system for the regeneration of redox cofactors NADH and NADPH was investigated in nanostructural reverse micelles using bacterial glycerol dehydrogenase (GLD) and soluble transhydrogenase (STH). Catalytic conversion of NAD+ to NADH was realized in the sodium dioctylsulfosuccinate (AOT)/isooctane reverse micellar system harboring GLD and a sacrificial substrate, glycerol. The initial rate of NADH regeneration was enhanced by exogenous addition of ammonium sulfate into the reverse micelles, suggesting that NH4+ acts as a monovalent cationic activator. STH was successfully entrapped in the AOT/isooctane reverse micelles as well as GLD and was revealed to be capable of catalyzing the stoichiometric hydrogen transfer reaction between NADP+ and NADPH in reverse micelles. These results indicate that GLD and STH have potential for use in redox cofactor recycling in reverse micelles, which allows the use of catalytic quantities of NAD(P)H in organic media. [source] Heavy atom motions and tunneling in hydrogen transfer reactions: the importance of the pre-tunneling stateJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2010Hans-Heinrich Limbach Abstract Arrhenius curves of selected hydrogen transfer reactions in organic molecules and enzymes are reviewed with the focus on systems exhibiting temperature-independent kinetic isotope effects. The latter can be rationalized in terms of a ,pre-tunneling state' which is formed from the reactants by heavy atom motions and which represents a suitable molecular configuration for tunneling to occur. Within the Bell,Limbach tunneling model, formation of the pre-tunneling state dominates the Arrhenius curves of the H and the D transfer even at higher temperatures if a large energy Em is required to reach the pre-tunneling state. Tunneling from higher vibrational levels and the over-barrier reaction via the transition state which lead to temperature-dependent kinetic isotope effects dominate the Arrhenius curves only if Em is small compared to the energy of the transition state. Using published data on several hydrogen transfer systems, the type of motions leading to the pre-tunneling state is explored. Among the phenomena which lead to large energies of the pre-tunneling state are (i) cleavage of hydrogen bonds or coordination bonds of the donor or acceptor atoms to molecules or molecular groups in order to allow the formation of the pre-tunneling state, (ii) the occurrence of an energetic intermediate on the reaction pathway within which tunneling takes place, and (iii) major reorganization of a molecular skeleton, requiring the excitation of specific vibrations in order to reach the pre-tunneling state. This model suggests a solution to the puzzle of Kwart's findings of temperature-independent kinetic isotope effects for hydrogen transfer in small organic molecules. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||