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Transition metal-catalyzed hydrogenation
Published in Ilya D. Gridnev, Pavel A. Dub, Enantioselection in Asymmetric Catalysis, 2016
Ketones are among the most common unsaturated substrates containing a C=O group.63 Homogeneous transition metal-catalyzed asymmetric hydrogenation (AH) and transfer hydrogenation (ATH) of prochiral ketones is one of the most powerful and efficient methods for the preparation of optically active alcohols.63–86 The hydrogenation process uses cheap molecular hydrogen (H2), the most abundant molecule in the universe and the most atom-efficient reducing chemical agent, and produces enantioenriched alcohols without forming any waste and with minimal workup involved.87 If a hydrogen donor is different from H2 (e.g., propan-2-ol, a HCO2H/NEt3 mixture, HCO2Na/water etc.), the process is known as transfer hydrogenation.64,82,88–90 The selectivity in terms of stereo-, chemo-, and regioselectivity could be different from AH systems; therefore, ATH may complement the latter. When hydrogenation is carried out in alcohols, these two processes may be concurrent, although hydrogenation is usually the dominant process. Beginning with a moderate enantiomeric excess (ee) of 82% reported by Markó et al. in 1985 (BDPP–RhI complex),91 the optical yields in the asymmetric hydrogenation of aromatic ketones in particular, have rapidly grown and achieved >99% ee. The most significant progress was made in the mid-1990s, when Noyori, Ikariya, and coworkers discovered the novel and very practical (pre)catalysts, trans-[RuCl2{(S)-binap}{(S, S)-dpen}]86,92–1 and (S)-RuCl[(R, R)-XCH(Ph)CH(Ph)NH2](η6-arene) [X = NTs,100–102 O103] 2 as shown in Chart 1.1, for the enantioselective hydrogenation and transfer hydrogenation of aromatic ketones, respectively.
Ketone transfer hydrogenation reactions catalyzed by catalysts based on a phosphinite ligand
Published in Journal of Coordination Chemistry, 2022
Duygu Elma Karakaş, Khadichakhan Rafikova, Akin Baysal, Nermin Meriç, Alexey Zazybin, Cezmi Kayan, Uğur Işik, Islam Sholpan Saparbaykyzy, Feyyaz Durap, Murat Aydemir
The need for more selective chemical processes producing minimal waste (i.e. green chemistry) has increased continuously due to environmental concerns. Transfer hydrogen reactions are mild methods to reduce ketones and oxidize alcohols. In these reactions, hydrogen is transferred by a catalyst selective for a specific substrate between the substrate and a hydrogen donor or acceptor [1–3]. The reduction of carbon-oxygen double bonds to corresponding alcohols is a key stage in the synthesis of fine chemicals, both in pharmaceutical and agricultural chemistry [4]. Hydrogenation reactions generally involve molecular hydrogen, metal hydride, or transfer hydrogenation [5]. When transfer hydrogenation is compared to molecular hydrogen or hydrides, it has advantages such as more convenient chemical sources of hydrogen, commonly isopropanol or formic acid/formate, low catalyst loading, safe manipulations, and simple equipment [6, 7]. Since transfer hydrogenation of ketones is operationally simpler and reductants are easily available, this reaction has become an alternative way for hydrogenation to obtain alcohols [8].
One-pot domino conversion of biomass-derived furfural to γ-valerolactone with an in-situ formed bifunctional catalyst
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Xialing Lin, Mingrui Li, Yumei Jian, Jinshu Huang, Song Yang, Hu Li
In summary, without the need of complex catalyst preparation procedures, Brønsted acid (HCl) and Lewis acid/base (ZrO(OH)n·xH2O) species could be in situ derived from cheap and commercially available ZrCl4 by hydrolysis, which synergistically and efficiently catalyze FF being converted to GVL in one pot. After reacting at 180°C for 6 h, GVL in a high yield of 56.5% was obtained. The use of the transfer hydrogenation strategy not only reduces the risk of the reaction but also benefits the green and sustainable application prospects. Moreover, the residual solid ZrO(OH)n·xH2O after reaction could be used as a precursor to prepare ZrO2-(C) by calcination. The humin attached to the ZrO(OH)n·xH2O is used as a hardwood agent for calcination, which is conducive to obtaining a more porous structure. With more active sites presented, ZrO2-(C) exhibited predominant catalytic performance in the upgrading of FF to FAOL with 80.0% yield at 150°C for 5 h. It is worth mentioning that the in-situ generated bifunctional catalysis strategy opens new avenue for integrated conversion of biomass derivatives in a single step or a more facile way.
Synthesis and characterization of new ruthenium(III) complexes derived from fluoreneamine-based Schiff base ligands and their catalytic activity in transfer hydrogenation of ketones
Published in Journal of Coordination Chemistry, 2020
Veerasamy Nagalakshmi, Raja Nandhini, Galmari Venkatachalam, Kasturi Balasubramani
Catalytic transfer hydrogenation is being increasingly used in industry because of its selectivity, efficiency, scope, simplicity, economic viability and also the growing awareness of the need for green chemistry. In general, recent aims have been to improve catalyst turnover and selectivity, either through more active catalysts or ones that can be recycled, to enable lower costs and higher purity products, as well as more productive, less wasteful processes. Ruthenium complexes catalyzed transfer hydrogenation reactions require the Ru-H an intermediate species and hence complexes with Ru-H bond or with potential for the in-situ formation of such a bond are suitable candidates for these catalytic reactions. Given the propensity toward in situ formation of ruthenium-hydrido species in the present family of complexes, we wish to explore their catalytic activity in transfer hydrogenation of ketones. In order to optimize the reaction conditions, the effect of solvents, bases, time, temperature and catalyst:substrate ratios were studied.