Application In Transfer Hydrogenation Research Articles

Bidentate Donor-Functionalized N-Heterocyclic Carbenes: Valuable Ligands for Ruthenium-Catalyzed Transfer Hydrogenation

Ruthenium complexes are by far the most studied compounds that catalyze hydrogen transfer reactions. In this review, we describe the use in this field of ruthenium complexes bearing bidentate donor-functionalized N-heterocyclic carbene ligands. The review specifically covers the application in transfer hydrogenations of (κ2-CNHC,Y)-ruthenacyclic compounds where the Y donor atom is a N, P, O, or S atom, and where the N-heterocyclic carbene ligand is a classical imidazol-2-ylidene, a benzimidazol-2-ylidene, a mesoionic 1,2,3-triazolylidene, or an imidazol-4-ylidene ligand. Tridentate donor-functionalized N-heterocyclic carbene complexes thus fall outside the scope of the review. Applications in (asymmetric) transfer hydrogenation of ketones, aldehydes, imines, alkenes, and nitrobenzene are discussed.

Carboxymethyl cellulose nanocolloids anchored Pd(0) nanoparticles (CMC@Pd NPs): synthesis, characterization, and catalytic application in transfer hydrogenation.

Herein, we report on the preparation of novel colloidal system based on carboxymethyl cellulose (CMC) and Pd nanoparticles (CMC@Pd NPs) via an ecofriendly auto-reduction process under mild conditions. In the first step, the follow-up of reduction and preparation of CMC anchored palladium nanoparticles (Pd NPs) in aqueous solution was carried out using UV-Vis spectroscopy. Thereafter, the monodispersed colloids were fully characterized by advanced analytical, structural, and morphological techniques. Based on Scherrer equation, the as-synthesized CMC@Pd NPs crystallite size was about 10.88nm. Accordingly, the detailed microscopic study revealed CMC nanocolloids anchored uniform distribution of Pd NPs and the presence of CMC nanofilm as protective monolayer. To the best of our knowledge, the observed nanoscale properties are reported for the first time for CMC-M system. The performance of the as-synthesized CMC@Pd nanocolloids was first investigated in the reduction of 4-nitrophenol, as a model substrate, to 4-aminophenol using NaBH4 as a hydrogen source. Moreover, the catalytic reduction of various nitroarenes bearing electron withdrawing or donating substituents was carried out and monitored by UV-Vis spectroscopy. The chemo- and regioselectivity of the catalytic reduction in presence of CMC@Pd NPs were also studied. Consequently, the prepared CMC@Pd nanocolloids exhibit remarkable activity, good heterogeneity, and higher reusability and stability for the catalytic reduction reaction under mild conditions.

Abnormal NHC ruthenium catalysts: mechanistic investigations of their preparation and steric influence on catalytic performance

Preparation of bis-aNHC Ru catalysts, identification of formation intermediates and application in transfer hydrogenation and Oppenauer-type oxidation, observing an inversion in activity appearing to be dependent on steric hindrance.

Achiral and chiral NNN-pincer nickel complexes with oxazolinyl backbones: application in transfer hydrogenation of ketones

NNN-based achiral and chiral (oxazolinyl)amido-pincer nickel complexes are developed and employed for the catalytic transfer hydrogenation of ketones.

Synthesis and characterization of a ruthenium complex with bis(diphenylphosphino)propane and thioether containing ONS donor ligand: Application in transfer hydrogenation of ketones

The synthesis and characterization of a mixed ligand Ru(II) complex, [Ru(dppp)(L)Cl] (1) (where, dppp=bis(diphenylphosphino) propane) is reported. The distorted octahedral geometry of the complex is confirmed by X-ray diffraction method. Cyclic voltammogram in CH3CN exhibits Ru(II)/Ru(III) quasireversible oxidation couple along with reversible azo-bond reductions peaks with reference to Ag/AgCl electrode. The efficiency of the complex towards the transfer hydrogenation of ketones in i-PrOH is examined and an excellent catalytic conversion (90–98%) is observed. The electronic structure and redox properties are well corroborated with the DFT calculations.

Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones

A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η6-arene)Ru(μ-Cl)Cl]2 with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η6-arene)RuCl(C5H4N-2-CH=N-R)]PF6, with arene = C6H6, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by 1H NMR and 13C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.

Ruthenium (II) complexes of NO ligands: Synthesis, characterization and application in transfer hydrogenation of carbonyl compounds

New Schiff base ligands including azo group such as (4-((E)-(4-ethylphenyl)diazenyl)-2-((E)-(phenylimino)methyl)phenol 2, 4-((E)-(4-ethylphenyl)diazenyl)-2-((E)-(naphthalen-1-ylimino)methyl)phenol 3, 2-((E)-(benzylimino)methyl)-4-((E)-(4-ethylphenyl)diazenyl)phenol 4 and azo group-free ligand (E)-2-((benzylimino)methyl)phenol 8 and their ruthenium complexes 5–7 and 9 with [RuCl2(p-cymene)] were synthesized and characterized by spectroscopic techniques including 1H and 13C NMR, FT-IR and UV–Vis. According to the UV–visible, IR and NMR data, the Ru (II) complexes 5–7 and 9 are formed by the coordination of N, O atoms of the ligands. Molecular structures of the complex 7 and complex 9 were determined by single crystal X-ray diffraction studies. These Ruthenium (II) complexes 5–7 and 9 were used as catalysts for the transfer hydrogenation of a series of ketones and benzaldehyde in 2-propanol. Following the comparison of complex 9 with the other three azo containing complexes 5–7, it was observed that azo group has got remarkable increasing effect on the catalytic activity. The results showed that the complex 5 is efficient than the other Ru (II) complexes.

ChemInform Abstract: Synthesis and Characterization of Rhodium(I) Complexes with P—N Donor Ligands and Their Catalytic Application in Transfer Hydrogenation of Carbonyl Group.

Three rhodium(I) complexes of the types [Rh(COE)Cl(η2-L)] (1a,1b) and [RhCl(η2-L) (η1-L)] (1c), where L = P~N donor ligands 2-[2-(diphenylphosphino) ethyl]pyridine, (PPh2Etpy) (a), 2-(diphenylphosphino)pyridine (PPh2py) (b), and 3-(diphenylphosphino)-1-propylamine (PPh2(CH2)3NH2) (c), have been synthesized by reacting [Rh(coe)2Cl]2 with the respective ligands in 1:2 molar ratio for 1a, 1b and 1:4 molar ratio for 1c in DCM under refluxing condition. The complexes were characterized using different analytical techniques such as FT-IR, ESI(+) mass spectrometry, 1H and 31P{ 1H} NMR spectrometry, conductivity measurements, and melting point determination. The synthesized complexes were found to exhibit good catalytic activity for the transfer hydrogenation of carbonyl compounds to corresponding alcohols with high conversion rate.

Synthesis and Characterization of Rhodium(I) Complexes with P–N Donor Ligands and Their Catalytic Application in Transfer Hydrogenation of Carbonyl Group

Three rhodium(I) complexes of the types [Rh(COE)Cl(η2‐L)] (1a,1b) and [RhCl(η2‐L) (η1‐L)] (1c), where L = P~N donor ligands 2‐[2‐(diphenylphosphino) ethyl]pyridine, (PPh2Etpy) (a), 2‐(diphenylphosphino)pyridine (PPh2py) (b), and 3‐(diphenylphosphino)‐1‐propylamine (PPh2(CH2)3NH2) (c), have been synthesized by reacting [Rh(coe)2Cl]2 with the respective ligands in 1:2 molar ratio for 1a, 1b and 1:4 molar ratio for 1c in DCM under refluxing condition. The complexes were characterized using different analytical techniques such as FT‐IR, ESI(+) mass spectrometry, 1H and 31P{ 1H} NMR spectrometry, conductivity measurements, and melting point determination. The synthesized complexes were found to exhibit good catalytic activity for the transfer hydrogenation of carbonyl compounds to corresponding alcohols with high conversion rate.

A ruthenium(II) bipyridine complex containing a 4,5-diazafluorene moiety: Synthesis, characterization and its applications in transfer hydrogenation of ketones and dye sensitized solar cells

The ruthenium(II) complex [Ru(bpy)2L](PF6)2, where bpy is 2,2′-bipyridine and L is 1,5-dihydro-2-H-cyclopenta[1,2-b:5,4-b′]dipyridine-2-one, was synthesized from the reaction of cis-Ru(bpy)2Cl2·2H2O with L, and isolated as the hexafluorophosphate salt. The structure of L was unequivocally elucidated by single-crystal X-ray diffraction analysis. The new ruthenium(II) complex was thoroughly characterized by 1H and 13C NMR spectroscopy, along with FTIR, UV–Vis and LC MS/MS Triple Quadrupole Mass spectroscopy and elemental analysis. The catalytic activity of [Ru(bpy)2L](PF6)2 was tested in the transfer hydrogenation of various ketones in 2-propanol as both the solvent and hydrogen donor. The usage of [Ru(bpy)2L](PF6)2 for the formation of a dye sensitized solar cell is also presented.

Synthesis of ruthenium (II) complexes containing a dihydroperimidine-derived phosphine ligand and their application in transfer hydrogenation of ketones

The new ruthenium (II) phosphine complexes (η6-C6H6)RuCl2[μ- (PPh2CH2N)2CH2(C10H6)]RuCl2(η6-C6H6) (1) and RuCl2(PPh3)[(PPh2CH2N)2CH2(C10H6)] (2) were synthesized and characterized by 1H NMR, 31P {1H} NMR and elemental analysis. Moreover, the structure of ruthenium (II) phosphine complex 1 was confirmed by X-ray crystallography. With complex 1 as the catalyst, the transfer hydrogenation of ketones reacted well, affording the corresponding alcohols in good yields under mild conditions.

Synthesis of 2‐aminomethylpiperidine ruthenium(II) phosphine complexes and their applications in transfer hydrogenation of aryl ketones

The complex trans,cis‐[RuCl2(PPh3)2(ampi)] (2) was prepared by reaction of RuCl2(PPh3)3 with 2‐aminomethylpiperidine(ampi) (1). [RuCl2(PPh2(CH2)nPPh2)(ampi) (n = 3, 4, 5)] (3–5) were synthesized by displacement of two PPh3 with chelating phosphine ligands. All complexes (2–5) were characterized by 1 H, 13C, 31P NMR, IR and UV‐visible spectroscopy and elemental analysis. They were found to be efficient catalysts for transfer hydrogen reactions. Copyright © 2012 John Wiley & Sons, Ltd.

Synthesis and characterization of ruthenium(II) complexes based on diphenyl-2-pyridylphosphine and their applications in transfer hydrogenation of ketones

Synthesis and characterization of the ruthenium complexes [RuH(CO)Cl(κ1-P-PPh2Py)2(PPh3)] (1) and [Ru(CO)Cl2(κ1-P-PPh2Py)(κ2-P–N-PPh2Py)] (2) containing diphenyl-2-pyridylphosphine (PPh2Py) are described. Spectral and structural data suggested linkage of the PPh2Py in κ1-P bonding mode in 1 and both the κ1-P and κ2-P–N bonding modes in 2. The complex 1 reacted with N,N-donor bases viz., ethylenediamine (en), N,N′-dimethyl-(ethylenediamine) (dimen), 1,3-diaminopropane (diap), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and di-2-pyridylaminomethylbenzene (dpa) to afford cationic complexes of formulation [RuH(CO)(κ1-P-PPh2Py)2(N-N)]+ (3–8) [N-N=en, 3; dimen, 4; diap, 5; bipy, 6; phen, 7; and dpa, 8], which have been isolated as their tetrafluoroborate salts. The complexes under investigation have been characterized by elemental analyses, spectroscopic and electrochemical studies. Molecular structures of 2, 3, 6, and 8 have been determined by single crystal X-ray diffraction analyses. Further, the complexes 1–8 act as effective precursor catalyst in transfer hydrogenation of acetophenone/ketones in basic 2-propanol.

ChemInform Abstract: Chlorocarbonyl Ruthenium(II) Complexes of Tripodal Triphos {MeC(CH2PPh2)3}: Synthesis, Characterization and Catalytic Applications in Transfer Hydrogenation of Carbonyl Compounds.

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Chlorocarbonyl ruthenium(II) complexes of tripodal triphos {MeC(CH 2PPh 2) 3}: Synthesis, characterization and catalytic applications in transfer hydrogenation of carbonyl compounds

The complex [Ru(CO) 2(triphos-κ 2P)Cl 2] ( 1) underwent decarbonylation in dichloromethane solution under air over a period of about two weeks to afford the chelated monocarbonyl complex [Ru(CO)(triphos-κ 3P)Cl 2] ( 2). The Single Crystal X-ray structure of 2 showed a slightly distorted metal centred complex. The catalytic activity of one of the complexes [Ru(CO)(triphos-κ 3P)Cl 2] ( 2) was examined in the transfer hydrogenation of aromatic carbonyl compounds and was found to be efficient with conversion up to 100% in the presence of isopropanol/NaOH.

Octahedral ruthenium(II) complexes cis, cis-[RuX 2(CNR)(CO)(P ∧P)] and cis, cis, cis-[RuX 2(CO) 2(P ∧P)] (X = Cl, Br; P ∧P = 1,1′-bis(diphenylphosphino)ferrocene, 1,1′-bis(diisopropylphosphino)ferrocene): Synthesis and catalytic applications in transfer hydrogenation of acetophenone and cycloisomerization of ( Z)-3-methylpent-2-en-4-yn-1-ol

Carbonyl–isocyanide-ruthenium(II) complexes cis, cis-[RuX 2(CNR)(CO)(P ∧P)] (P ∧P = dppf, dippf; X = Cl, Br; R = Bn, Cy, t Bu, 2,6-C 6H 3Me 2, ( S)-(−)-C(H)MePh) ( 3– 6a– e) have been prepared in high yields by treatment of the dimeric derivatives [{RuX(μ-X)(CO)(P ∧P)} 2] (P ∧P = dppf, dippf; X = Cl, Br) ( 1– 2a– b) with isocyanides. Dimers 1– 2a– b also react with carbon monoxide to afford the dicarbonyl species cis, cis, cis-[RuX 2(CO) 2(P ∧P)] ( 7– 8a– b). The catalytic activity of these compounds in transfer hydrogenation of acetophenone by propan-2-ol as well as in cycloisomerization of ( Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran has been studied.

Development of New Camphor‐Based N,S Chiral Ligands and Their Application in Transfer Hydrogenation

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Development of new camphor based N,S chiral ligands and their application in transfer hydrogenation.

A new class of N,S-containing chiral compounds based on the camphor scaffold have been synthesised and evaluated as chiral catalysts in the transfer hydrogenation of acetophenone. The best results were achieved using compound 6a as the ligand and [Ir(COD)Cl](2) as the metal precursor.