Mechanism for transfer hydrogenation of ketones to alcohols catalysed by hydridotri-ironundecacarbonylate anion under phase transfer conditions
TL;DR: In this paper, a mechanism for the transfer hydrogenation of ketones to secondary alcohols catalysed by HFe3(CO)11−1 (1) in the presence of Phase Transfer Catalysts (PTC) has been proposed using labelled hydrogen, NMR and IR techniques.
Abstract: A mechanism for the transfer hydrogenation of ketones to secondary alcohols catalysed by HFe3(CO)11−1 (1) in the presence of Phase Transfer Catalysts (PTC) has been proposed using labelled hydrogen, NMR and IR techniques.
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TL;DR: This Focus Review attempts to present a "holistic" overview on the advances in the area, focusing on the achievements recorded around the last three years, including more-efficient and "greener" metal catalysts, catalysts that enable hydrogenation as well as transfer hydrogenation, biomimetic and organocatalysts, and their applications in the reduction of C==O, C==N, and C==C bonds.
Abstract: Asymmetric transfer hydrogenation has become a practically useful tool in reduction chemistry in the last decade or so. This was largely triggered by the seminal work of Noyori and co-workers in the mid-1990s and is driven by its complementing chemistry to hydrogenation employing H2. This Focus Review attempts to present a “holistic” overview on the advances in the area, focusing on the achievements recorded around the last three years. These include more-efficient and “greener” metal catalysts, catalysts that enable hydrogenation as well as transfer hydrogenation, biomimetic and organocatalysts, and their applications in the reduction of CO, CN, and CC bonds. Also highlighted are efforts in the development of environmentally benign and reusable catalytic systems.
385 citations
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TL;DR: It is believed that catalytic hydrosilylations will be used more often in the future in challenging organic syntheses, as the reaction procedures are straightforward, and the reactivity of the silane can be fine-tuned.
Abstract: In the last decade, an increasing number of useful catalytic reductions of carboxylic acid derivatives with hydrosilanes have been developed. Notably, the combination of an appropriate silane and catalyst enables unprecedented chemoselectivity that is not possible with traditional organometallic hydrides or hydrogenation catalysts. For example, amides and esters can be reduced preferentially in the presence of ketones or even aldehydes. We believe that catalytic hydrosilylations will be used more often in the future in challenging organic syntheses, as the reaction procedures are straightforward, and the reactivity of the silane can be fine-tuned. So far, the synthetic potential of these processes has clearly been underestimated. They even hold promise for industrial applications, as inexpensive and readily available silanes, such as polymethylhydrosiloxane, offer useful possibilities on a larger scale.
256 citations
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TL;DR: Evidence of a rare example of asymmetric catalysis with nonprecious metal, zerovalent nanoparticles with iron(0) nanoparticles functionalized with achiral and chiral PNNP-type tetradentate ligands is provided.
Abstract: Investigation into the mechanism of transfer hydrogenation using trans-[Fe(NCMe)CO(PPh2C6H4CH═NCHR—)2][BF4]2, where R = H (1) or R = Ph (2) (from R,R-dpen), has led to strong evidence that the active species in catalysis are iron(0) nanoparticles (Fe NPs) functionalized with achiral (with 1) and chiral (with 2) PNNP-type tetradentate ligands. Support for this proposition is given in terms of in operando techniques such as a kinetic investigation of the induction period during catalysis as well as poisoning experiments using substoichiometric amounts of various poisoning agents. Further support for the presence of Fe(0) NPs includes STEM microscopy imaging with EDX analysis, XPS analysis, and SQUID magnetometry analysis of catalytic solutions. Further evidence of Fe NPs acting as the active catalyst is given in terms of a polymer-supported substrate experiment whereby the NPs are too large to permeate the pores of a functionalized polymer. Final support is given in terms of a combined poisoning/STEM/EDX ex...
190 citations
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TL;DR: The fast development and the recent advances in selective reductions of olefins, alkynes, carbonyl and carboxylic derivatives, imines, and nitro compounds promoted by iron catalysts are summarized.
Abstract: The last two decades have seen an impressive improvement of the use of iron as a fascinating and valuable alternative transition metal in homogeneous catalysis in terms of sustainability and economy. It was efficiently used in catalytic organic synthetic transformations, which in particular include the reduction of unsaturated bonds. This review summarizes the fast development and the recent advances in selective reductions of olefins, alkynes, carbonyl and carboxylic derivatives, imines, and nitro compounds promoted by iron catalysts. The topical hydrogen-borrowing reactions and hydroboration of unsaturated compounds are also reported. It is hoped that this account not only provides an overview of the state of the art in iron catalysis but also stimulates the development of superior greener catalytic systems in the near future.
186 citations
References
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TL;DR: In this paper, the phase transfer agent, phase transfer catalysts, and donors are compared based on the percentage yield of the products, and the efficiencies of phase transfer agents, iron carbonyls and donors.
Abstract: Transfer hydrogenation of ketones to alcohols using iron carbonyls as catalysts in liquid-liquid phase occurs in the presence of phase transfer catalysts (PTC). Based on the percentage yield of the products, the efficiencies of the phase transfer agent, iron carbonyls and the donors are compared. Benzyltriethylammonium chloride and 18-crown-6 are equally effective and better than tricaprylmethylammonium chloride (Aliquat® 336). Among the three iron carbonyls the order of efficiency is Fe3(CO)12 > Fe2(CO)9 > Fe(CO)5. 1-Phenylethanol is a better donor than isopropanol. The relative ease of reducibility of various ketones increases with increasing reduction potential. The stereochemistry of reduction of 4-t-butylcyclohexanone is discussed.
33 citations
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TL;DR: Cyclohexanone has been used as an acceptor for the dehydrogenation of some natural products in the presence of RuCl2(PPh3)3 as mentioned in this paper.
Abstract: Cyclohexanone has been used as an acceptor for the dehydrogenation of some natural products in the presence of RuCl2(PPh3)3. Only menthol undergoes appreciable dehydrogenation when compared to cholesterol and β-citronellol. Menthone, cholest-4-en-3-one and cholest-1,4-diene-3-one and citronellal are the products from these compounds. When carbohydrates are used as donors, in most cases the corresponding lactones are formed. The ratio of acceptor to donor is maintained at 6 in the latter cases to avoid disproportionation of the carbohydrates. Acids, isomer and epimer are formed in certain cases. It is observed that the dehydrogenation of carbohydrates is increased at elevated temperatures. The susceptibility to dehydrogenation of the carbohydrates is in the order sorbitol > mannitol > L-arabinose ≈ D-xylose > D-glucose ≈ sucrose > D-mannose ≈ D-galactose.
13 citations
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TL;DR: In this paper, a homogeneous hydrogen transfer from 1-phenyl-ethanol (D) to cyclohexanone (A) catalyzed by RuCl 2 (PPh 3 ) 3 (C) in diphenyl ether as solvent at 140 °C was observed.
Abstract: In the homogeneous hydrogen transfer from 1-phenyl-ethanol(D) to cyclohexanone(A) catalyzed by RuCl 2 (PPh 3 ) 3 (C) in diphenyl ether as solvent at 140 °C the order of addition of donor, acceptor and catalyst have a pronounced effect on the rate of the reaction. An induction period is observed. The experimental observations correspond to the rate expression: Initial rate = where [C] t is the total concentration of catalyst in the system.
11 citations