Hydrogenation, catalytic transformation

Jessop and co-workers studied asymmetric hydrogenation reactions with the catalyst complex Ru(OAc)2(tolBINAP) dissolved in [BMIM][PFg]. In both reactions under investigation - the hydrogenation of tiglic acid (Scheme 5.2.10) and the hydrogenation of the precursor of the anti-inflammatory dmg ibuprofen (Scheme 5.2.11) - no CO2 was present during the catalytic transformation. However, SCCO2 was used in both cases to extract the reaction products from the reaction mixture when the reaction was complete. 

The total hydrogenation of benzene derivatives represents an important industrial catalytic transformation, in particular with the conversion of benzene into cyclohexane, a key intermediate in adipic acid synthesis, which is used in the production of Nylon-6,6 (Scheme 1). This reaction is still the most important industrial hydrogenation reaction of monocyclic arenes [1]. 

The ability of transition-metal complexes to activate substrates such as alkenes and dihydrogen with respect to low-barrier bond rearrangements underlies a large number of important catalytic transformations, such as hydrogenation and hydroformy-lation of alkenes. However, activation alone is insufficient if it is indiscriminate. In this section we examine a particularly important class of alkene-polymerization catalysts that exhibit exquisite control of reaction stereoselectivity and regioselec-tivity as well as extraordinary catalytic power, the foundation for modern industries based on inexpensive tailored polymers. 

The etherified starch was further transformed by hydrogenation of the double bonds to yield the corresponding linear octyl groups using [RhCl(TPPTS)3] catalyst soluble in EtOH-H20 mixtures. Complete hydrogenation was obtained at 40 °C under 30 bar of H2 after 12 h using 0.8-wt.% Rh-catalyst [84]. Other catalytic transformations such as double bond oxidation and olefin metathesis could possibly be used to prepare other modified starches for various applications. 

Proton transfer to negatively charged hydrogen atoms has attracted the attention of many chemists over the last two decades. This process plays an important role in many chemical and biochemical phenomena that occnr in the gas phase, in solution, and in the solid state [1-3], For example, direct proton attack on hydride ligands generates transition metal dihydrogen complexes which are then involved in various catalytic transformations [4] ... 

In view of the historical perspective and future requirements, it is important to reduce the amount of reductants for the coupling reactions. In the future, molecular hydrogen or electricity should be used in lieu of zinc in stoichiometric amounts for the reductive coupling reactions. In addition, catalytic transformations should be developed that may include oxidation of the resulting reductive coupling products so as to adjust the oxidation state. 

The reaction of hydrogen peroxide with copper(I) salts produces a Fenton-like hydroxylating system involving reactive hydroxyl radical intermediates (equation 265).486,491 Hydroxylation of benzene to phenol can be achieved by air in the presence of copper(I) salts in an acidic aqueous solution.592 593 This reaction is not catalytic (phenol yields are ca. 8% based on copper(I) salts) and stops when all copper(I) has been oxidized to copper(II). A catalytic transformation of benzene to phenol can occur when copper(II) is electrolytically reduced to copper(I) (equation 266).594,595... 

In addition to hydrogenation reactions, modular phospholane ligands are being applied in a growing rank of other useful asymmetric catalytic transformations. For instance, Jiang and Sen reported the discovery of a dicationic Me-DuPhos-Pd catalyst for the alternating copolymerization of aliphatic a-olefins and carbon monoxide (Scheme 13.21).67... 

The activation of propargylic ethers also provides the generation of ruthenium allenylidene species with elimination of alcohols (Eq. 13). This reaction has been used in the catalytic transformation of benzyl propargyl ethers into 1,3-dienes via dealkoxylation, addition of benzyl alcohol to the a-carbon atom of the allenylidene intermediate and hydrogen-transfer reactions according to Scheme 21 [89]. 

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