Activity In Transfer Hydrogenation Research Articles

Quantifying the modulation of modified ZSM-5 acidity/alkalinity on olefin catalytic pyrolysis to maximize light olefin selectivity

Undesirable side reactions often occur during the catalytic pyrolysis of olefins in FCC gasoline to produce light olefins. We proposed a method to maximize light olefin selectivity by suppressing these side reactions. In this study, P-ZSM-5 and Ce–P-ZSM-5 were prepared by the pore volume impregnation method to investigate the regulatory relationship between their acidity/alkalinity and catalytic pyrolysis. The study found that acid sites could promote the olefin conversion and adjust the cracking pathway. Furthermore, the densities of strong B acid sites and base sites could regulate olefin adsorption, affecting hydrogen transfer activity. Acid strength was crucial in controlling the aromatization reaction. It showed that thermal cracking played a minor role in catalytic pyrolysis, with methane generation mainly resulting from acid sites promoting the cracking of terminal C–C bonds. Loading phosphorus strengthens the acidity of ZSM-5, while loading cerium weakens its acidity and enhances its alkalinity. By optimizing the acidity and alkalinity of ZSM-5, side reactions were suppressed, maximizing the selectivity of light olefins. The results showed that the light olefin selectivity of Ce–P-ZSM-5 increased from 33.2% to over 80%, while the side reaction selectivity decreased from over 60% to below 10%. This work will lay a good foundation for developing catalysts for catalytic pyrolysis of olefins to produce light olefins.

Secondary Amine Catalysis in Enzyme Design: Broadening Protein Template Diversity through Genetic Code Expansion

AbstractSecondary amines, due to their reactivity, can transform protein templates into catalytically active entities, accelerating the development of artificial enzymes. However, existing methods, predominantly reliant on modified ligands or N‐terminal prolines, impose significant limitations on template selection. In this study, genetic code expansion was used to break this boundary, enabling secondary amines to be incorporated into alternative proteins and positions of choice. Pyrrolysine analogues carrying different secondary amines could be incorporated into superfolder green fluorescent protein (sfGFP), multidrug‐binding LmrR and nucleotide‐binding dihydrofolate reductase (DHFR). Notably, the analogue containing a D‐proline moiety demonstrated both proteolytic stability and catalytic activity, conferring LmrR and DHFR with the desired transfer hydrogenation activity. While the LmrR variants were confined to the biomimetic 1‐benzyl‐1,4‐dihydronicotinamide (BNAH) as the hydride source, the optimal DHFR variant favorably used the pro‐R hydride from NADPH for stereoselective reactions (e.r. up to 92 : 8), highlighting that a switch of protein template could broaden the nucleophile option for catalysis. Owing to the cofactor compatibility, the DHFR‐based secondary amine catalysis could be integrated into an enzymatic recycling scheme. This established method shows substantial potential in enzyme design, applicable from studies on enzyme evolution to the development of new biocatalysts.

Secondary Amine Catalysis in Enzyme Design: Broadening Protein Template Diversity through Genetic Code Expansion.

Secondary amines, due to their reactivity, can transform protein templates into catalytically active entities, accelerating the development of artificial enzymes. However, existing methods, predominantly reliant on modified ligands or N-terminal prolines, impose significant limitations on template selection. In this study, genetic code expansion was used to break this boundary, enabling secondary amines to be incorporated into alternative proteins and positions of choice. Pyrrolysine analogues carrying different secondary amines could be incorporated into superfolder green fluorescent protein (sfGFP), multidrug-binding LmrR and nucleotide-binding dihydrofolate reductase (DHFR). Notably, the analogue containing a D-proline moiety demonstrated both proteolytic stability and catalytic activity, conferring LmrR and DHFR with the desired transfer hydrogenation activity. While the LmrR variants were confined to the biomimetic 1-benzyl-1,4-dihydronicotinamide (BNAH) as the hydride source, the optimal DHFR variant favorably used the pro-R hydride from NADPH for stereoselective reactions (e.r. up to 92 : 8), highlighting that a switch of protein template could broaden the nucleophile option for catalysis. Owing to the cofactor compatibility, the DHFR-based secondary amine catalysis could be integrated into an enzymatic recycling scheme. This established method shows substantial potential in enzyme design, applicable from studies on enzyme evolution to the development of new biocatalysts.

Influence of Charge Delocalization on Manganese Catalyzed Transfer Hydrogenation

AbstractHydrogen transfer reactions promoted by Mn(I)‐based catalysts are a recently emerged field of research. Herein, we demonstrate the crucial effect of charge delocalization on the catalytic activity in transfer hydrogenation. Therefore, we synthesized pyridyl‐pyrazole ligands and a pyridyl‐pyridazinone ligand which exhibit resonance structures upon deprotonation with varying capability to transfer charge to the manganese center. The corresponding Mn(I) complexes were characterized and their activity as catalyst in transfer hydrogenation of acetophenone was determined using in‐situ IR techniques. Kinetic data and DFT calculations reveal that the ligands are deprotonated throughout the catalytic cycle and that the catalysts in which resonance structures point towards more negative charge at the metal center are also the more active ones. Thus, we deliver ample evidence that for effective hydrogen transfer the manganese catalyst requires a ligand with a deprotonable moiety allowing efficient delocalization to the metal while geometrical access of the acidic proton to the substrate is not essential. Our findings highlight the importance of an anionic hydrido intermediate, where mesomerism allows an effective charge transfer to the metal. This may support the ongoing development of new manganese‐based catalysts.

BICAAC-Derived Covalent and Cationic Ir(I) Complexes: Application of Ir(BICAAC)Cl(COD) Complexes as Catalysts for Transfer Hydrogenation and Hydrosilylation Reactions.

The ambiphilic bicyclic (alkyl)(amino)carbenes (Me/iPrBICAAC) upon reaction with [IrCl(COD)]2 smoothly afford mononuclear Ir(I) complexes that have been spectroscopically and structurally characterized. These complexes exhibit good catalytic activity for transfer hydrogenation (TH) of 4-chlorobenzaldehyde using isopropyl alcohol (iPrOH), with turnover frequency values ranging between 6269 and 8093 h-1. Choosing the covalent complex Ir(MeBICAAC)Cl(COD) as a catalyst, a wide array of carbonyls and imines functionalized with electron-withdrawing and electron-donating substituents have been surveyed and afforded their reduced products in moderate-to-good yields. No detachment of the BICAAC unit from the Ir center was observed upon prolonged heating of Ir(MeBICAAC)Cl(COD) in toluene-d8 or isopropyl alcohol-d8, which evidenced good thermal stability of the catalyst. Complex Ir(MeBICAAC)Cl(COD) was also found to be catalytically active for the hydrosilylation of a variety of aldehydes using triethylsilane (Et3SiH).

High Selectivity Cofactor NADH Regeneration Organic Iridium Complexes Used for High-Efficiency Chem-Enzyme Cascade Catalytic Hydrogen Transfer.

Our research demonstrated that novel pentamethylcyclopentadienyl (Cp*) iridium pyridine sulfonamide complex PySO2NPh-Ir (7) could highly specifically catalyze nicotinamide adenine dinucleotide (NAD+) into the corresponding reducing cofactor NADH in cell growth media containing various biomolecules. The structures and catalytic mechanism of 7 were studied by single-crystal X-ray, NMR, electrochemical, and kinetic methods, and the formation of iridium hydride species Ir-H was confirmed to be the plausible hydride-transfer intermediate of 7. Moreover, benefiting from its high hydrogen-transfer activity and selectivity for NADH regeneration, 7 was used as an optimal metal catalyst to establish a chem-enzyme cascade catalytic hydrogen-transfer system, which realized the high-efficiency preparation of l-glutamic acid by combining with l-glutamate dehydrogenase (GLDH).

Ru(II) complexes containing NOO donors of tridentate Schiff base ligands: Synthesis, characterization, crystal structure and catalytic activity in transfer hydrogenation of ketones

A new series of pincer type ruthenium(II) Schiff base complexes namely [Ru(CO)(PPh3)2(L1‒6)] (1–6) (where, L1‒6 ​= ​NOO ‒ donors of tri-dentate ligands) have been synthesized from ruthenium precursor such as [RuHCl(CO)(PPh3)3] containing tri-dentate Schiff bases ligands (H2L1‒H2L6). These ruthenium complexes were analyzed by elemental analysis and diverse characterizations such as FT‒IR, UV–Vis and NMR (1H and 31P) spectroscopy studies. The crystal structure of one of the complexes 5 ([Ru(CO)(PPh3)2L5]) was determined by single crystal X‒ray crystallography that revealed pincer type of coordination mode of complexes. Furthermore, complexes 1–6 have been utilized for transfer hydrogenation of aromatic ketones to secondary alcohols in the presence of i‒PrOH/KOH. The catalytic efficiency of complexes showed an efficient for transfer hydrogenation of ketones with alcohol as moderate to high conversions.

Mechanistic insights and comparative analysis of Ru(ii)–NNC pincer complexes with anionic-, protic-, and classical-NHCs for transfer hydrogenation of ketones

A series of Ru(ii)–NNC pincer-type complexes bearing anionic-, protic- and classical-NHC ligands are reported. Comparative analysis of catalytic activity in transfer hydrogenation of ketones is investigated both experimentally and computationally.

Recent advances of Cp*Ir complexes for transfer hydrogenation: focus on formic acid/formate as hydrogen donors.

Transfer hydrogenation reactions offer synthetically powerful strategies to deliver various hydrogenated compounds with the advantages of efficiency, atom economy, and practicability. On one hand, formic acid/formate function as promising hydrogen sources owing to their readily obtainable, inexpensive, and easy to handle nature. On the other hand, Cp*Ir complexes show high activities in transfer hydrogenation. This review highlights progress achieved for transfer hydrogenation of CO, CC, and CN bonds of a variety of unsaturated substrates, as well as amides focusing on Cp*Ir complexes as catalysts and formic acid/formate as hydrogen sources.

Reaction characteristics of maximizing light olefins and decreasing methane in C5 hydrocarbons catalytic pyrolysis

When converting C5 hydrocarbons to light olefins by catalytic pyrolysis, the generation of low value-added methane will affect the atomic utilization efficiency of C5 hydrocarbons. To improve the atomic utilization efficiency, different generation pathways of light olefins and methane in the catalytic pyrolysis of C5 hydrocarbons were analyzed, and the effects of reaction conditions and zeolite types were investigated. Results showed that light olefins were mainly formed by breaking the C2–C3 bond in the middle position, while methane was formed by breaking the C1–C2 bond at the end. Meanwhile, it was discovered that the hydrogen transfer reaction could be reduced by about 90% by selecting MTT zeolite with 1D topology and FER zeolite with 2D topology under high weight hourly space velocity (WHSV) and high temperature operations, thus leading to the improvement of the light olefins selectivity for the catalytic pyrolysis of n-pentane and 1-pentene to 55.12% and 74.60%, respectively. Moreover, the fraction ratio of terminal C1–C2 bond cleavage was reduced, which would reduce the selectivity of methane to 6.63% and 1.83%. Therefore, zeolite with low hydrogen transfer activity and catalytic pyrolysis process with high WHSV will be conducive to maximize light olefins and to decrease methane.

Mo2N as a high-efficiency catalyst for transfer hydrogenation of nitrobenzene using stoichiometric hydrazine hydrate

A straightforward and commonly-used approach of direct pyrolysis for the preparation of molybdenum nitride (Mo2N) is conducted via reduction of MoO3 under ammonia atmosphere. The as-synthesized Mo2N catalyst demonstrated high activity for transfer hydrogenation of nitrobenzene, giving a 99% aniline yield at near-room temperature of 30 °C within only 50 min. More significantly, the amount of the hydrogen donor hydrazine monohydrate (N2H4·H2O) can be limited to stoichiometric molar ratio (-NO2: N2H4·H2O = 1: 1.5), preventing the possible generation of hazardous NH3, which is seldom reported in previous protocols. Through various characterizations and control experiments, conclusively, the remarkable catalytic performance of Mo2N catalyst should be credited to the large quantity of Lewis-acidic Mo sites. This research might provide a practical approach to aromatic amines production.

Chemoenzymatic catalysis of tert-butyl 6-cyano-(3R,5R)-dihydroxyhexanoate by aldo-keto reductase coupled with composite Fe3O4 nanozyme scaffold

Cofactor NADPH is widely used in enzymatic redox reactions, however, its regeneration by glucose dehydrogenase (GDH) suffers from massive glucose consumption, costly wastewater treatment, and low atom efficiency. Herein, Fe3O4 nanoparticles supported on helical multi-walled carbon nanotubes (Fe3O4@HMWCNTs) was prepared and displayed comparable transfer hydrogenation activity to Exiguobacterium sibiricum GDH (EsGDH). We developed a chemoenzymatic catalysis based on a combination of an aldo–keto reductase KmAKR with Fe3O4@HMWCNTs scaffold, which asymmetrically synthesized optically pure tert-butyl 6-cyano-(3R,5R)-dihydroxyhexanoate ((3R,5R)-2, > 99.5 % dep). Under the optimized conditions, 10 mM NADP+ was converted to NADPH by 5.0 mg Fe3O4@HMWCNTs, in a yield of > 80.0 %. The combination of Fe3O4@HMWCNTs with KmAKRM7 completely reduced 10 mM tert-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate ((5R)-1) to (3R,5R)-2, in a conversion of > 99.0 % and dep > 99.5 %. Contrast to the previous developed biocatalytic approach with KmAKR and EsGDH, this efficient and compatible nanozyme-enzyme process required neither glucose/alcohols as co-substrate nor a glucose dehydrogenase/alcohol dehydrogenase for NADPH regeneration.

Aluminum‐Ligand Cooperative O−H Bond Activation Initiates Catalytic Transfer Hydrogenation

AbstractMolecular design ultimately furnishes improvements in performance over time, and this has been the case for Rh‐ and Ir‐based molecular catalysts currently used in transfer hydrogenation (TH) reactions for fine chemical synthesis. In this report, we describe a molecular pincer ligand Al catalyst for TH, (I2P2−)Al(THF)Cl (I2P=diiminopyridine; THF=tetrahydrofuran). The mechanism for TH is initiated by two successive Al‐ligand cooperative bond activations of the O−H bonds in two molecules of isopropanol (iPrOH) to afford six‐coordinate (H2I2P)Al(OiPr)2Cl. Stoichiometric chemical reactions and kinetic experiments suggest an ordered transition state, supported by polar solvents, for concerted hydride transfer from iPrO− to substrate. Metal‐ligand cooperative hydrogen bonding in a cyclic transition state is a likely support for the concerted hydride transfer event. The available data does not support involvement of an intermediate Al‐hydride in the TH. Proof‐of‐principle reactions including the conversion of isopropanol and benzophenone to acetone and diphenylmethanol with 90 % conversion in 1 h are described. The analogous hydride compound, (I2P2−)Al(THF)H, also cleaves the O−H bond in iPrOH to afford (HI2P−)Al(OiPr)H and (HI2P−)Al(OiPr)2, but no activity for catalytic TH was observed.

Effect of cysteine thiols on the catalytic and anticancer activity of Ru(II) sulfonyl-ethylenediamine complexes.

We have synthesized a series of novel substituted sulfonyl ethylenediamine (en) RuII arene complexes 1-8 of [(η6-arene)Ru(R1-SO2-EnBz)X], where the arene is benzene, HO(CH2)2O-phenyl or biphenyl (biph), X = Cl or I, and R1 is phenyl, 4-Me-phenyl, 4-NO2-phenyl or dansyl. The 'piano-stool' structure of complex 3, [(η6-biph)Ru(4-Me-phenyl-SO2-EnBz)I], was confirmed by X-ray crystallography. The values of their aqua adducts were determined to be high (9.1 to 9.7). Complexes 1-8 have antiproliferative activity against human A2780 ovarian, and A549 lung cancer cells with IC50 values ranging from 4.1 to >50 μM, although, remarkably, complex 7 [(η6-biph)Ru(phenyl-SO2-EnBz)Cl] was inactive towards A2780 cells, but as potent as the clinical drug cisplatin towards A549 cells. All these complexes also showed catalytic activity in transfer hydrogenation (TH) of NAD+ to NADH with sodium formate as hydride donor, with TOFs in the range of 2.5-9.7 h-1. The complexes reacted rapidly with the thiols glutathione (GSH) and N-acetyl-L-cysteine (NAC), forming dinuclear bridged complexes [(η6-biph)2Ru2(GS)3]2- or [(η6-biph)2Ru2(NAC-H)3]2-, with the liberation of the diamine ligand which was detected by LC-MS. In addition, the switching on of fluorescence for complex 8 in aqueous solution confirmed release of the chelated DsEnBz ligand in reactions with these thiols. Reactions with GSH hampered the catalytic TH of NAD+ to NADH due to the decomposition of the complexes. Co-administration to cells of complex 2 [(η6-biph)Ru(4-Me-phenyl-SO2-EnBz)Cl] with L-buthionine sulfoximine (L-BSO), an inhibitor of GSH synthesis, partially restored the anticancer activity towards A2780 ovarian cancer cells. Complex 2 caused a concentration-dependent G1 phase cell cycle arrest, and induced a significant level of reactive oxygen species (ROS) in A2780 human ovarian cancer cells. The amount of induced ROS decreased with increase in GSH concentration, perhaps due to the formation of the dinuclear Ru-SG complex.

Ru(Ii) Complexes Containing Noo Donors of Tridentate Schiff Base Ligands: Synthesis, Characterization, Crystal Structure and Catalytic Activity in Transfer Hydrogenation of Ketones

Ru(Ii) Complexes Containing Noo Donors of Tridentate Schiff Base Ligands: Synthesis, Characterization, Crystal Structure and Catalytic Activity in Transfer Hydrogenation of Ketones

A Cyclometalated NHC Iridium Complex Bearing a Cationic (η5 -Cyclopentadienyl)(η6 -phenyl)iron Backbone*.

Nucleophilic substitution of [(η5‐cyclopentadienyl)(η6‐chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η5‐1,2,3,4,5‐pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]+ substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X‐ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]+ unit at the NHC ligand.

Hg(II) and Ru(II) complexes of mono- and dichalcogenides of bis(diphenylphosphino)amine chelating ligands: Synthesis, characterization and catalytic activity in transfer hydrogenation of acetophenone derivatives

Reactions of C10H7-1-N(PPh2)2 (1) and C10H7-1-N(P(Se)Ph2)2 (2) ligands with mercury(II)iodide in equimolar ratio gave cis-[HgI2{1-κ2 P,P}] (3) and cis-[HgI2{2-κ2 Se,Se}] (4). Also, refluxing of monooxidized thioyl and selenoyl bis(phosphino)amine ligands C10H7-1-N(P(E)Ph2)(PPh2) (E = S (5), Se (6)) with [Ru(CO)3Cl2]2 dimer afforded cis-[Ru(CO)2Cl2{5-κ2 P,S}] (7) and cis-[Ru(CO)2Cl2{6-κ2 P,Se}] (8). Complexes 3, 4, 7 and 8 were identified and characterized by multinuclear NMR (1H, 13C, 31P and 77Se NMR) and IR spectroscopy. The molecular structure of 5 was determined by single X-ray crystallography. 5 is the first structurally characterized example of this kind of κ2 P,S -bidentate ligand. The novel ruthenium(II) complexes 7 and 8 show high catalytic activity in the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source.

Cationic ruthenium(II)–NHC pincer complexes: Synthesis, characterisation and catalytic activity for transfer hydrogenation of ketones

Cationic ruthenium pincer complexes, [Ru(CNC)(CO)(PPh3)Cl]X (CNC = 2,6‐bis(1‐methylimidazol‐2‐ylidene)‐pyridine, X = Cl− [1a], PF6− [1b]), [Ru(CNC)(PPh3)2Cl]X (X = Cl− [2a], PF6− [2b]) and [Ru(CNC)(PPh3)2(H)]X (X = Cl− [3a], PF6− [3b]) with triphenylphosphine, CO and halides as coligands have been synthesised and characterised by 1H, 13C, 31P NMR, mass and single‐crystal X‐ray crystallography. The application of Ru complexes in the transfer hydrogenation of a wide range of ketones with 2‐propanol as the hydrogen source is explored. The in situ transformations observed during the synthesis help understand and suggest a plausible mechanism via the hydride complex 3b. All complexes appear to be efficient catalyst precursors for transfer hydrogenation of ketones.

Synthesis and Structural Characterization of Half-Sandwich Arene–Ruthenium(II) Complexes with Bis(imidazol-1-yl)methane, Imidazole and Benzimidazole

Mono- and binuclear arene–ruthenium(II) complexes with imidazole-containing ligands were prepared by the reaction of the ligands (L1 = bis(imidazole-1-yl)methane; ImH = 1H-Imidazole; BImH = 1H-Benzimidazole) with [(p-cym)Ru(µ-Cl)2]2 dimers. When bis(imidazole-1-yl)methane reacted with [(p-cym)Ru(µ-Cl)2]2 in methanol, a binuclear complex of the type [Ru2(L1)2(p-cym)2Cl2]Cl2 (2) with cyclic structure was synthesized, whereas by using acetonitrile as a solvent under the same reaction conditions, an unexpected C–N bond cleavage was observed, and a complex of formula [Ru(ImH)2(p-cym)Cl]Cl (1) with coordinated imidazole molecules was obtained. Another type of arene–ruthenium complex [Ru(BImH)(p-cym)Cl2] (3) was obtained by the reaction of benzimidazole and [(p-cym)Ru(µ-Cl)2]2. All compounds were characterized by spectral (FT-IR, NMR 1H, 13C) and single-crystal X-ray diffraction methods; their catalytic activity in transfer hydrogenation and the cytotoxicity against MCF-7 and HepG2 cells were evaluated.

Synthesis of New Secondary Amines and Their In Situ Catalytic Activity in Transfer Hydrogenation of Ketones and Antioxidant Properties

Synthesis of New Secondary Amines and Their In Situ Catalytic Activity in Transfer Hydrogenation of Ketones and Antioxidant Properties