Transfer hydrogenation

In chemistry, transfer hydrogenation is a chemical reaction involving the addition of hydrogen to a compound from a source other than molecular . It is applied in laboratory and industrial organic synthesis to saturate organic compounds and reduce ketones to alcohols, and imines to amines. It avoids the need for high-pressure molecular used in conventional hydrogenation. Transfer hydrogenation usually occurs at mild temperature and pressure conditions using organic or organometallic catalysts, many of which are chiral, allowing efficient asymmetric synthesis. It uses hydrogen donor compounds such as formic acid, isopropanol or dihydroanthracene, dehydrogenating them to , acetone, or anthracene respectively. Often, the donor molecules also function as solvents for the reaction. A large scale application of transfer hydrogenation is coal liquefaction using "donor solvents" such as tetralin. Organometallic catalysts In the area of organic synthesis, a useful family of hydrog

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Basic organometallic chemistry will be covered in this course.

Structure and bonding in organometallic compounds.
reactivity of organometallic compounds, stoichiometric reactions, catalyzed reactions and reaction mechanisms.

This course on homogeneous catalysis provide a detailed understanding of how these catalysts work at a mechanistic level and give examples of catalyst design for important reactions (hydrogenation, olefin metathesis, cross-coupling).

This lecture presents the development of catalytic asymmetric reactions in organic chemistry, including important current topics of research in the field.

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Hydrogenation

Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is comm

Ruthenium

Ruthenium is a chemical element with the symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum grou

Organic redox reaction

Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. In organic chemistry oxidations and reductions are different from ordin

Basic organometallic chemistry will be covered in this course.

Structure and bonding in organometallic compounds.
reactivity of organometallic compounds, stoichiometric reactions, catalyzed reactions and reaction mechanisms.

This lecture presents the development of catalytic asymmetric reactions in organic chemistry, including important current topics of research in the field.

Highly dispersed cobalt oxides nanoparticles on activated carbon fibres as efficient structured catalysts for the transfer hydrogenation of m-nitrostyrene

Oliver Anthony Beswick, Paul Joseph Dyson, Lioubov Kiwi, Alexander Parastaev

The facile preparation of structured catalysts featuring highly-dispersed non-precious metal (Fe, Ni, Co) oxide nanoparticles stabilized within a super-microporous network of activated carbon fibres (ACF) is described. The catalyst morphology was controlled over multiple levels from the nano-designed active phase up to the macro-structure of the ACF support. A range of physicochemical techniques was used to characterize the catalyst and rationalize the catalytic data during chemoselective transfer hydrogenation of nitroarenes. The challenging reduction of m-nitrostyrene containing an easily reducible vinyl-group was obtained under mild conditions with a near-quantitative yield of m-vinylaniline using hydrazine hydrate as the reducing agent over CoOx/ACF as a structured catalyst. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier Science Bv2017

Iron Complexes for Hydrogen Activation and Catalytic Hydrogenation

Simona Mazza

Inspired by Nature several groups have developed structural and functional iron complexes mimicking the active site of the iron-hydrogenases, which show high reactivity in the H2 cleavage. Usually pendant bases have been incorporated onto families of Fe complexes in order to achieve active systems. In the view of these recent developments, in chapter two, we investigated the possibility of synthesizing novel iron (II) complexes bearing an amine internal base and providing an open site for substrate binding as catalysts for H2 activation. Pentacoordinated Fe(II) low spin complexes [(PhPNP)Fe(CO)(bdt)] (1), [(PhPNP)Fe-(CO)(Nbt)] (4), [(CyPNP)Fe(CO)(Nbt)] (5), [(dppe)Fe(CO)(Nbt)] (6) and the paramagnetic complex [(CyPNP)FeCl2] (10) have been synthesized and fully characterised. Unfortunately, when these complexes were tested as catalysts for hydrogenation reaction of a wide range of unsaturated substrates, no appreciable reactivity was observed. Same behaviour was observed in the case of complexes [(CyPNP)Fe(CO)(Cp)] (11) and [(CyPNP)Fe(CH3CN)(Cp)] (12) where the Cp ligand was installed in order to modulate the electronic and steric properties on the iron center. In chapter three, a new class of well-defined iron pincer complexes is reported. Several Fe(II) complexes supported by a 2,6-bis(phosphinito)pyridine ligand (PONOP) have been synthesized and fully characterised. In particular, the Fe-hydride complexes [(iPrPONOP)-Fe(CO)(H)Br] (14) and (iPrPONOP)Fe(CO)(H)(CH3CN) (15) could activate H2 at room temperature. Moreover, complexes 14 and 15 served as catalysts for the selective hydrogenation of aldehydes at room temperature. In presence of sodium formate as hydrogen donor, 14 and 15 showed an excellent reactivity in hydrogen transfer reaction of aldehydes. The mechanism of hydrogen activation and hydrogenation is discussed based on the observed reactivity of iron complexes. The feature of being chemoselective towards aldehydes and a broad functional-group tolerance make these iron-hydride systems remarkable in the class of the earth-abundant-metal hydrogenation catalysts. Chapter four is dedicated to the tuning of the Fe-PONOP systems reported in chapter three in order to synthesize similar iron(II) complexes exhibiting enhanced reactivity for H2 activation and hydrogenation of unsaturated substrates. As first attempt, complexes [(CyPONOP)Fe(CO)Br2] (22) and the analogous chloride [(CyPONOP)Fe(CO)Cl2] (23) bearing the stronger donor CyPONOP ligand were synthesized and tested as catalysts for hydrogenation reaction, but none of the substrates employed was reduced. As second attempt, the CO ligand was substituted with the better donor ligand tert-butyl isocyanide in presence of iPrPONOP as pincer ligand. Several Fe-PONOP complexes were synthesized and fully characterized. In particular the Fe-hydride complex [(iPrPONOP)Fe(tBuNC)(H)Br] (25) exhibited reactivity towards hydrogenation of aldehydes under the same reaction conditions reported for 14. No reaction was observed in presence of acetophenone, cyclohexene and 1-decene demonstrating that, although spectroscopically different, 25 did not exhibit enhanced reactivity relative to 14.

EPFL2015

Base-Free Transfer Hydrogenation with an Ionic-Liquid-Supported Ruthenium eta(6)-Arene Bis(pyrazolyl)methane Catalyst

Paul Joseph Dyson, Andrew Douglas Phillips, Francisco Sepulveda

Ruthenium complexes of the type [RuCl(eta(6)-arene)-(NN)]X (X = BF4 or BPh4) featuring an eta(6)-arene ligand modified with an imidazolium ring and incorporating the bis(azo) chelating (NN) ligands 2-hydroxyphenylbis(3,5-dimethylpyrazol-1-yl) methane or 2-nitrophenylbis(3,5-dimethylpyrazol-1-yl) methane are reported. The catalytic activities of the complexes were evaluated in the transfer hydrogenation of benzaldehyde to benzyl alcohol with iPrOH as the hydrogen donor in the absence of a base and under biphasic conditions; one of the two phases was iPrOH, and the other was an ionic liquid. The catalysts featuring the imidazolium-modified eta(6)-arene could be recycled and reused with only a minor decrease in substrate conversion after multiple reaction cycles. The reaction rate was strongly influenced by the type of ionic liquid employed in the biphasic system.

Wiley-Blackwell2017