Biomimetic transfer hydrogenation of ketones with iron porphyrin catalysts

μ-Oxo-bridged iron(iii) complexes for the selective reduction of aromatic ketones catalyzed through base promoted in situ nanoparticle formation

Selective TH of aromatic ketones catalyzed by μ-oxo-diiron complexes and in situ NP formation in the presence of a base gave excellent yields (∼99–100%).

Fe/N co-doped mesoporous carbon derived from cellulose-based ionic liquid as an efficient heterogeneous catalyst toward nitro aromatic compound reduction reaction

Iron and nitrogen-doped carbon substances with abundant active sites that related to dispersion of heteroatom species (Fe and N) on the surface of carbonous structure, are promising choice for eco-friendly catalytic reactions. Herein, cellulose-based ionic liquid (IL) derivative not only employed as the both nitrogen and iron heteroatom precursors, but also has been used as the green and biodegradable substrate. The non-noble Fe-NC@550, was successfully fabricated by convenient carbonization of cellulose-based IL. Further, the FeCl₄^- anion was used as the iron precursor and also it has been applied to elevate the SSA (specific surface area) of catalyst (from 40.96 to 160.42 m²/g) due to the presence of chlorine. On the basis of several pertinent physicochemical and experimental outcomes, the structure of the catalyst was successfully proved in different synthetic steps. As expected, the Fe-NC@550 exhibited the substantial efficiency toward hydrogenation of nitroarenes with high TOF value and also remarkable reusability.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

An iron variant of the Noyori hydrogenation catalyst for the asymmetric transfer hydrogenation of ketones

We report the design of a new iron catalyst for the asymmetric transfer hydrogenation of ketones. This type of iron catalyst combines the structural characteristics of the Noyori hydrogenation catalyst (an axially chiral 2,2'-bis(phosphino)-1,1'-binaphthyl fragment and the metal-ligand bifunctional motif) and an ene(amido) group that can activate the iron center. After activation by 8 equivalents of potassium tert-butoxide, (S_A,R_P,SS)-7a and (S_A,R_P,SS)-7b are active but nonenantioselective catalysts for the transfer hydrogenation of acetophenone and α,β-unsaturated aldehydes at room temperature in isopropanol. A maximum turnover number of 14480 was observed for (S_A,R_P,SS)-7a in the reduction of acetophenone. The right combination of the stereochemistry of the axially chiral 2,2'-bis(phosphino)-1,1'-binaphthyl group and the carbon-centered chiral amine-imine moiety in (S_A,R_P,RR)-7b' afforded an enantioselective catalyst for the preparation of chiral alcohols with moderate to good yields and a broad functional group tolerance.

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 multiple bonds. 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.

Cobalt(ii)-catalysed transfer hydrogenation of olefins

Catalytic transfer hydrogenation of olefins is achieved by an earth-abundant metal cobalt catalyst. A range of alkene substrates including those with functional groups have been hydrogenated in high yields.

Nickel-catalyzed transfer hydrogenation of ketones using ethanol as a solvent and a hydrogen donor

We report a nickel(0)-catalyzed direct transfer hydrogenation (TH) of a variety of alkyl–aryl, diaryl, and aliphatic ketones with ethanol.

Transfer hydrogenation of unsaturated bonds in the absence of base additives catalyzed by a cobalt-based heterogeneous catalyst

A novel non-noble Co@C–N system for catalytic transfer hydrogenation reactions is developed. The heterogeneous Co@C–N catalysts are highly active and selective in the hydrogenation of a variety of unsaturated bonds with isopropanol in the absence of base additives.

Syntheses and catalytic application of hydrido iron(ii) complexes with [P,S]-chelating ligands in hydrosilylation of aldehydes and ketones

Four hydrido iron(ii) complexes (1–4) with [P,S]-chelating ligands were synthesized by the reactions of (2-diphenylphosphanyl)thiophenols, C₆H₃(1-SH) (2-PPh₂) (4-R₁) (6-R₂), abbreviated as (P^SH), with Fe(PMe₃)₄.

The mechanism of efficient asymmetric transfer hydrogenation of acetophenone using an iron(II) complex containing an (S,S)-Ph2PCH2CH═NCHPhCHPhN═CHCH2PPh2 ligand: partial ligand reduction is the key

On the basis of a kinetic study and other evidence, we propose a mechanism of activation and operation of a highly active system generated from the precatalyst trans-[Fe(CO)(Br)(Ph(2)PCH(2)CH═N-((S,S)-C(Ph)H-C(Ph)H)-N═CHCH(2)PPh(2))][BPh(4)] (2) for the asymmetric transfer hydrogenation of acetophenone in basic isopropanol. An induction period for catalyst activation is observed before the catalytic production of 1-phenethanol. The activation step is proposed to involve a rapid reaction of 2 with excess base to give an ene-amido complex [Fe(CO)(Ph(2)PCH(2)CH═N-((S,S)-C(Ph)H-C(Ph)H)-NCH═CHPPh(2))](+) (Fe(p)) and a bis(enamido) complex Fe(CO)(Ph(2)PCH═CH-N-(S,S-CH(Ph)CH(Ph))-N-CH═CHPPh(2)) (5); 5 was partially characterized. The slow step in the catalyst activation is thought to be the reaction of Fe(p) with isopropoxide to give the catalytically active amido-(ene-amido) complex Fe(a) with a half-reduced, deprotonated PNNP ligand. This can be trapped by reaction with HCl in ether to give, after isolation with NaBPh(4), [Fe(CO)(Cl)(Ph(2)PCH(2)CH(2)N(H)-((S,S)-CH(Ph)CH(Ph))-N═CHCH(2)PPh(2))][BPh(4)] (7) which was characterized using multinuclear NMR and high-resolution mass spectrometry. When compound 7 is treated with base, it directly enters the catalytic cycle with no induction period. A precatalyst with the fully reduced P-NH-NH-P ligand was prepared and characterized by single crystal X-ray diffraction. It was found to be much less active than 2 or 7. Reaction profiles obtained by varying the initial concentrations of acetophenone, precatalyst, base, and acetone and by varying the temperature were fit to the kinetic model corresponding to the proposed mechanism by numerical simulation to obtain a unique set of rate constants and thermodynamic parameters.

Iron-catalyzed intramolecular allylic C-H amination

A highly selective C-H amination reaction under iron catalysis has been developed. This novel system, which employs an inexpensive, nontoxic [Fe(III)Pc] catalyst (typically used as an industrial ink additive), displays a strong preference for allylic C-H amination over aziridination and all other C-H bond types (i.e., allylic > benzylic > ethereal > 3° > 2° ≫ 1°). Moreover, in polyolefinic substrates, the site selectivity can be controlled by the electronic and steric character of the allylic C-H bond. Although this reaction is shown to proceed via a stepwise mechanism, the stereoretentive nature of C-H amination for 3° aliphatic C-H bonds suggests a very rapid radical rebound step.