Iron-Catalyzed Transfer Hydrogenation Research Articles

Correction: Room temperature iron catalyzed transfer hydrogenation using n-butanol and poly(methylhydrosiloxane)

Correction for ‘Room temperature iron catalyzed transfer hydrogenation using n-butanol and poly(methylhydrosiloxane)’ by Thomas G. Linford-Wood et al., Green Chem., 2021, 23, 2703–2709, DOI: 10.1039/D0GC04175K.

Direct Synthesis of Pyrrolo[1,2-α]quinoxalines via Iron-Catalyzed Transfer Hydrogenation between 1-(2-Nitrophenyl)pyrroles and Alcohols.

Herein, we describe novel iron-catalyzed transfer hydrogenation between alcohols and 1-(2-nitrophenyl)pyrroles for the synthesis of pyrrolo[1,2-α]quinoxalines. The tricarbonyl (η4-cyclopentadienone) iron complex catalyzed the oxidation of alcohols and the reduction of nitroarenes, and the corresponding aldehydes and aniline were generated in situ. The resulting Pictet-Spengler-type annulation/oxidation completed the quinoxaline structure formation. The protocol tolerated various kinds of functional groups and provided 29 samples of 4-substituted pyrrolo[1,2-α]quinoxalines. The developed method was also applied for the synthesis of additional polyheterocycles.

Iron-Catalyzed Transfer Hydrogenation in Aged N-Methyl-2-pyrrolidone: Reductive Ring-Opening of 3,5-Disubstituted Isoxazoles and Isoxazolines.

3,5-Disubstituted isoxazoles and isoxazolines undergo an iron-catalyzed reductive ring-opening in aged N-methyl-2-pyrrolidone (NMP). 5-Hydroxy-N-methyl-2-pyrrolidone generated in situ via a simple activation of commercial NMP acts as the hydrogen donor in the iron-catalyzed transfer hydrogenation reaction. It is the first example employing a combination of an iron catalyst and 5-hydroxy-N-methyl-2-pyrrolidone as reducing agents in a transfer hydrogenation reaction. The protocol is highly efficient for the synthesis of β-enaminones and 1,3-diketones, providing a versatile route for the preparation of these 1,3-difunctional compounds bearing diversified substitution patterns.

Base‐Free Iron Catalyzed Transfer Hydrogenation of Esters Using EtOH as Hydrogen Source

Herein, we report on the use of the iron pincer complex Iron-MACHO-BH, in the base-free transfer hydrogenation of esters with EtOH as a hydrogen source. More than 20 substrates including aromatic and aliphatic esters and lactones were reduced affording the desired primary alcohols and diols with moderate to excellent isolated yields. It is also possible to reduce polyesters to the diols with this method, enabling a novel way of plastic recycling. Reduction of the renewable substrate methyl levulinate proceeds to form 1,4-pentanediol directly. The yields are largely governed by the equilibrium between the alcohol and the ethyl ester.

Base‐Free Iron Catalyzed Transfer Hydrogenation of Esters Using EtOH as Hydrogen Source

AbstractHerein, we report on the use of the iron pincer complex Iron‐MACHO‐BH, in the base‐free transfer hydrogenation of esters with EtOH as a hydrogen source. More than 20 substrates including aromatic and aliphatic esters and lactones were reduced affording the desired primary alcohols and diols with moderate to excellent isolated yields. It is also possible to reduce polyesters to the diols with this method, enabling a novel way of plastic recycling. Reduction of the renewable substrate methyl levulinate proceeds to form 1,4‐pentanediol directly. The yields are largely governed by the equilibrium between the alcohol and the ethyl ester.

Room Temperature Iron-Catalyzed Transfer Hydrogenation and Regioselective Deuteration of Carbon-Carbon Double Bonds.

An iron catalyst has been developed for the transfer hydrogenation of carbon-carbon multiplebonds. Using a well-defined β-diketiminate iron(II) precatalyst, a sacrificial amine and a borane, even simple, unactivated alkenes such as 1-hexene undergo hydrogenation within 1 h at room temperature. Tuning the reagent stoichiometry allows for semi- and complete hydrogenation of terminal alkynes. It is also possible to hydrogenate aminoalkenes and aminoalkynes without poisoning the catalyst through competitive amine ligation. Furthermore, by exploiting the separate protic and hydridic nature of the reagents, it is possible to regioselectively prepare monoisotopically labeled products. DFT calculations define a mechanism for the transfer hydrogenation of propene with nBuNH2 and HBpin that involves the initial formation of an iron(II)-hydride active species, 1,2-insertion of propene, and rate-limiting protonolysis of the resultant alkyl by the amine N-H bond. This mechanism is fully consistent with the selective deuteration studies, although the calculations also highlight alkene hydroboration and amine-borane dehydrocoupling as competitive processes. This was resolved by reassessing the nature of the active transfer hydrogenation agent: experimentally, a gel is observed in catalysis, and calculations suggest this can be formulated as an oligomeric species comprising H-bonded amine-borane adducts. Gel formation serves to reduce the effective concentrations of free HBpin and nBuNH2 and so disfavors both hydroboration and dehydrocoupling while allowing alkene migratory insertion (and hence transfer hydrogenation) to dominate.

High efficient iron-catalyzed transfer hydrogenation of quinolines with Hantzsch ester as hydrogen source under mild conditions

A highly efficient transfer hydrogenation of quinolines with Hantzsch ester as hydrogen source in the presence of 1mol% Fe(OTf)2 under mild conditions has been developed. A series of substituted 1,2,3,4-tetrahydroquinoline derivatives were afforded in excellent yields with good functional group tolerance.

Iron-catalyzed transfer hydrogenation of imines assisted by an iron-based Lewis acid.

An iron-catalyzed transfer hydrogenation of N-aryl and N-alkyl imines using isopropanol as the hydrogen donor is reported for the first time. A combination of two iron complexes serving different roles is the key for the success of this catalytic system. As a result, an environmentally friendly and precious metal-free transfer hydrogenation of imines has been developed. The use of a suitable co-catalyst as an activator not only led to efficient transfer hydrogenation, but also showed potential in enantioselective transformation.

Transfer Hydrogenation of Ethyl Levulinate to γ‐Valerolactone Catalyzed by Iron Complexes

AbstractConversion of biomass‐derived ethyl levulinate to γ‐valerolactone is realized by using homogeneous iron‐catalyzed transfer hydrogenation (CTH). By utilizing Casey's catalyst and cheap isopropanol as hydrogen source, γ‐valerolactone can be generated in 95% yield. Addition of catalytic amount of base is important to achieve good yield.

Selective iron-catalyzed transfer hydrogenation of terminal alkynes

A novel iron-catalyzed transfer hydrogenation of alkynes to the corresponding alkenes applying formic acid as a hydrogen donor is reported. An in situ combination of Fe(BF(4))(2)·6H(2)O and tetraphos allows for highly selective hydrogenation of a broad range of aromatic and aliphatic alkynes tolerating different functional groups.

General and Selective Iron-Catalyzed Transfer Hydrogenation of Nitroarenes without Base

The first well-defined iron-based catalyst system for the reduction of nitroarenes to anilines has been developed applying formic acid as reducing agent. A broad range of substrates including other reducible functional groups were converted to the corresponding anilines in good to excellent yields at mild conditions. Notably, the process constitutes a rare example of base-free transfer hydrogenations.

Iron-Catalyzed Transfer Hydrogenation of Ketones

Several methods exist for the reduction of prochiral ketones to enantiomerically enriched secondary alcohols. These methods include hydrogenation, hydrosilation, and transfer hydrogenation. Typical catalysts include palladium, ruthenium, rhodium, and iridium. Recently, iron has been investigated by several research groups as a less expensive, non-toxic alternative to these precious metals.