Exploring Hydrogen Sources in Catalytic Transfer Hydrogenation: A Review of Unsaturated Compound Reduction

Abstract

Catalytic transfer hydrogenation has emerged as a pivotal chemical process with transformative potential in various industries. This review highlights the significance of catalytic transfer hydrogenation, a reaction that facilitates the transfer of hydrogen from one molecule to another, using a distinct molecule as the hydrogen source in the presence of a catalyst. Unlike conventional direct hydrogenation, catalytic transfer hydrogenation offers numerous advantages, such as enhanced safety, cost-effective hydrogen donors, byproduct recyclability, catalyst accessibility, and the potential for catalytic asymmetric transfer hydrogenation, particularly with chiral ligands. Moreover, the diverse range of hydrogen donor molecules utilized in this reaction have been explored, shedding light on their unique properties and their impact on catalytic systems and the mechanism elucidation of some reactions. Alcohols such as methanol and isopropanol are prominent hydrogen donors, demonstrating remarkable efficacy in various reductions. Formic acid offers irreversible hydrogenation, preventing the occurrence of reverse reactions, and is extensively utilized in chiral compound synthesis. Unconventional donors such as 1,4-cyclohexadiene and glycerol have shown a good efficiency in reducing unsaturated compounds, with glycerol additionally serving as a green solvent in some transformations. The compatibility of these donors with various catalysts, substrates, and reaction conditions were all discussed. Furthermore, this paper outlines future trends which include the utilization of biomass-derived hydrogen donors, the exploration of hydrogen storage materials such as metal-organic frameworks (MOFs), catalyst development for enhanced activity and recyclability, and the utilization of eco-friendly solvents such as glycerol and ionic liquids. Innovative heating methods, diverse base materials, and continued research into catalyst-hydrogen donor interactions are aimed to shape the future of catalytic transfer hydrogenation, enhancing its selectivity and efficiency across various industries and applications.

Keywords: 1,4-cyclohexadiene; alcohol; amine; formic acid; glycerol; hydrogen donor molecules; hydrogen transfer.

Scheme 1

Hydrogen transfer in the MPV reduction via a cyclic transition state (Wang & Astruc, 2015) [8].

Figure 1

Number of publications on transfer hydrogenation reactions (2003–2022, data source: dimensions.ai, accessed on 6 November 2023).

Scheme 2

Transfer hydrogenation of benzaldehyde, with methanol as the hydrogen donor, in the presence of a rhodium catalyst (Aboo et al., 2018) [21].

Scheme 3

Reduction of alkynes catalyzed using manganese pincer complexes in the presence of methanol used as a hydrogen donor (Sklyaruk et al., 2020) [22].

Scheme 4

Reduction of alkenes using a cobalt pincer complex as a catalyst in the presence of isopropanol as a hydrogen donor (Zhang et al., 2016) [34].

Scheme 5

Transfer hydrogenation reaction of unsaturated aldehyde using iridium as a catalyst and isopropanol as a hydrogen donor (Wang et al., 2018) [35].

Scheme 6

Nickel-catalyzed hydrogen transfer of alkenes using isopropanol as a hydrogen donor (Alonso et al., 2009) [37].

Scheme 7

Asymmetric transfer hydrogenation of imines using a rhodium catalyst and isopropanol as a hydrogen donor (Samec & Bäckvall, 2002) [48].

Scheme 8

Transfer hydrogenation of alkenes and alkynes using nickel as a catalyst and water as the hydrogen source (Hu et al., 2019) [70].

Scheme 9

Rhodium-catalyzed hydrogenation of olefins using water as the hydrogen source (Sato et al., 2006) [69].

Scheme 10

Palladium-catalyzed reduction of alkynes (Shirakawa et al., 2005) [71].

Figure 2

Percentage conversion versus reaction time for the asymmetric transfer hydrogenation (ATH) of acetophenone using a Ru catalyst in F-T mixtures with varying initial F/T ratios. (Reprinted with permission from Ref. [80]. Copyright 2012, Elsevier).

Scheme 11

Proposed catalytic cycles for the asymmetric transfer hydrogenation (ATH) of acetophenone under near-neutral conditions (I) and acidic conditions (II) in an F-T solution (Zhou et al., 2012) [80].

Figure 3

Asymmetric transfer hydrogenation of imines in water in F-T mixtures at different initial F/T ratios. (Reprinted with permission from Ref. [84]. Copyright 2015, American Chemical Society).

Scheme 12

Catalytic transfer hydrogenation of diphenyl acetylene using a palladium catalyst and formic acid as the hydrogen source (Chayya et al., 2021) [94].

Scheme 13

Catalytic transfer hydrogenation of an alkyne using an iron catalyst and formic acid as the hydrogen source (Wienhöfer et al., 2012) [95].

Scheme 14

Catalytic cycle of iron-catalyzed transfer hydrogenation of an alkyne using formic acid as the hydrogen source (Wienhöfer et al., 2012) [95].

Scheme 15

Catalytic transfer hydrogenation of nitro compounds using an iron catalyst and formic acid as the hydrogen source (Wienhöfer et al., 2011) [96].

Scheme 16

Catalytic transfer hydrogenation of benzonitrile using a palladium-supported catalyst in the presence of formic acid as a hydrogen donor (Tomar et al., 2020) [98].

Scheme 17

Catalytic transfer hydrogenation of ynamides using a gold catalyst in the presence of ammonium formate as a hydrogen source (Lin et al., 2019) [101].

Scheme 18

Catalytic cycle of the transfer hydrogenation of ynamides using a gold catalyst and ammonium formate as a hydrogen source (Lin et al., 2019) [101].

Scheme 19

Stereoselective hydrogenation of ynamides using palladium as a catalyst and HCOONH₄/EtOH and EtOH as hydrogen sources (Siva Reddy & Kumara Swamy, 2017) [102].

Scheme 20

Catalytic transfer hydrogenation of 4-fluoronitrobenzene using a palladium-supported catalyst in the presence of 1,4-cyclohexadiene as a hydrogen donor (Quinn et al., 2010) [104].

Scheme 21

Catalytic transfer hydrogenation of benzaldehyde, nitrobenzene, and styrene, using glycerol as the hydrogen source (Wolfson et al., 2009) [116].

Scheme 22

Transfer hydrogenation reaction in the presence of an iridium catalyst, using glycerol as a hydrogen donor (Farnetti et al., 2009) [118].