Dehydrogenation Of Alcohols Research Articles

Half‐sandwich iridium complexes: Synthesis and catalytic activity in dehydrogenation of alcohols to carboxylic acids

A series of N,N‐chelate half‐sandwich iridium complexes were synthesized by a simple method with good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been successfully achieved by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half‐sandwich iridium catalyst system showed desirable stability and catalytic activity, and the achievement of a high TOF of 372.0 h−1 could be observed with an extremely low catalyst loading of only 0.05 mol%. Furthermore, the sustainable catalyst could be reused for a minimum of five cycles without obviously losing its activity, highlighting its potential application in industry. Structure of N,N‐chelate iridium complexes 1 and 3 were determined by single‐crystal X‐ray analysis.

Iron- and Organo-Catalyzed Borrowing Hydrogen for the Stereoselective Construction of Tetrahydropyrans.

Stereocontrolled oxa-Michael additions are challenging, given the high reversibility of the process, which ultimately leads to racemization of the newly formed stereocenters. When iron-catalyzed borrowing hydrogen from allylic alcohols was combined with a stereocontrolled organocatalytic oxa-Michael addition, a wide array of chiral tetrahydropyrans were efficiently prepared. The reaction could be performed in a diastereoselective manner from pre-existing stereocenters or enantioselectively from achiral substrates. The key to success was the reactivity of the iron complex, which was selective for allylic alcohol dehydrogenation and irreversibly led the reaction to the final product.

Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids.

A series of acylhydrazone-based N,N-chelate half-sandwich iridium complexes have been synthesized through a facile route in good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished catalyzed by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half-sandwich iridium catalyst system exhibited high catalytic activity and stability, and a high TOF of 316.7 h-1 could be achieved with a catalyst loading as low as 0.05 mol %. Furthermore, the sustainable catalyst could be reused at least five times without obviously losing its activity, highlighting its potential application in industry. Molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.

Advancements in biomass conversion: Copper-catalyzed anaerobic dehydrogenation of 5-hydroxymethylfurfural to 2,5-diformylfuran

Developing cost-effective and inherently safe methods for accelerating the sustainable production of value-added chemicals from biomass presents a promising solution to the current energy crisis. This study introduces heterogeneous copper species anchored on a γ-Al2O3 catalyst (Cu/γ-Al2O3) with high dispersibility and small Cu particle size, synthesized via a straightforward incipient-wetness impregnation method. This method facilitates the selective anaerobic dehydrogenation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) in the absence of any oxidant or hydrogen acceptor. An HMF conversion of 69.8 % and a DFF yield of 44.9 % were attained at 130 °C over a 12-h period. Extensive characterizations were conducted to elucidate the correlation between the catalyst’s structure and its dehydrogenation activity. The findings indicated that strong L-acid sites, elevated Cu dispersions, small Cu particle size and an increased number of Cu+ active sites were conducive to enhanced dehydrogenation reactivity. The Cu/γ-Al2O3 catalyst demonstrated superior catalytic efficiency and stability. A possible reaction mechanism is suggested, integrating DFT calculations with experimental observations. This research offers valuable insights into the selective conversion of HMF to DFF and encourages further exploration into the dehydrogenation of biomass alcohols into high-value chemicals under oxidant-free conditions.

Copper-Catalyzed Borrowing Hydrogen Reaction for α-Alkylation of Amides with Alcohols.

We report the first example of copper-catalyzed α-alkylation of acetamides with alcohols via a borrowing hydrogen strategy. Catalyzed by the in situ-generated copper particles, acetamides and various substituted benzyl or alkyl alcohols were transformed into functionalized amides in good yields with excellent selectivity. Compared with previous work, this process is simple using commercially available Cu(OAc)2 as a precatalyst, without an additional ligand or a metal complex, and easier. Mechanistic studies revealed that aldehyde and α,β-unsaturated amides were the intermediates of this reaction and also disclosed the role of copper in alcohol dehydrogenation and C═C bond hydrogenation.

Synergistic coupling of photocatalytic H2 evolution and selective oxidation of benzyl alcohol over ZnIn2S4/Ni in aqueous solution

The synergistic coupling of photocatalytic hydrogen evolution and selective organic matter conversion is extremely attractive, as clean fuel and high value–added chemicals can be produced simultaneously with light as the sole energy input. Herein, we developed a dual functional photocatalyst (ZnIn2S4/Ni) for efficient photocatalytic conversion of benzyl alcohol into benzaldehyde with simultaneous hydrogen production. Consequently, ZnIn2S4/Ni displayed a top-level benzaldehyde and H2 evolution rate even in aqueous media. The yield of benzaldehyde reaches 19.3 mmol/g/h, which is 33 times higher than that of naked ZnIn2S4 and even exceeds that of precious metal systems (Pt, Pd, Ru). Here, Ni site not only acted as an effective co–catalyst for charge separation, but also played an important role in accelerating the α–C–H bond cleavage during the dehydrogenation of benzyl alcohol. This work provides a cost-effective and green reference path for the efficient conversion of solar energy to chemical energy.

Dehydrogenation of primary alcohols to carboxylic acids in water catalyzed by PNHN-manganese(I) carbonyl complexes

Three classes of manganese(I) complex cation, [(PNHN)Mn(CO)3]Br (Mn1), [(SNHN)Mn(CO)3]Br (Mn2) and [(NRNHN)Mn(CO)3]Br (Mn3 (NMe), Mn4 (NEt), Mn5 (NiPr)), all incorporating a chelating 5,6,7,8-tetrahydro-8-quinolinamine (NHN) but distinct in their third donor atom, have been assessed as catalysts for the dehydrogenative oxidation of primary alcohols to form their corresponding carboxylic acids. Using water as solvent and NaOH as base, PNHN-containing Mn1 proved the most effective allowing both aromatic and aliphatic alcohols to be converted at 160 °C with excellent functional group tolerance (25 examples disclosed). A possible mechanism for this process, that makes use of an acceptorless dehydrogenation pathway, has been proposed and supported by targeted experimentation. Overall, these catalysts show great promise for applications in atom-economic carboxylic acid synthesis as well as in the development of organic hydride-based hydrogen storage systems.

Effective Proficiency of Manganese Porphyrins as Catalysts in Chemical Transformations: A Review

: Porphyrin ligands are well-known for their promising tendency to produce metal porphyrin complexes of great significance. Out of different metal porphyrins, manganese porphyrins are one of the most valuable metal porphyrins due to effective catalytic performance and potential in many reactions like C-H isocyanation, the cycloaddition of CO2 with epoxides, epoxidation, oxygen reduction reaction, depolymerization reactions, oxidation of aromatic alcohols, selective oxidation of cycloalkenes/ alkanes, aliphatic C-H chlorination, dehydrogenation of alcohols, dye degradation, BSA nitration and others. Hence, in this review, the authors have best tried to present an effective insight overview of these aforementioned applications with the help of some recent studies for signifying the value of manganese porphyrins as a competent catalyst.

Metal-acid synergistic catalysis accelerates the hydrogen borrowing amination of alcohols by confining Ru sites in Beta zeolite

Direct hydrogen transfer amination of alcohols with amines is an environmentally friendly and atom-economical route for the synthesis of N-alkylamines. Noble metal species are highly catalytic active sites, but the exorbitant price makes the urgency to boost the atom efficiency with stable recyclability. Herein, we demonstrated that encapsulation of Ru nanoparticles (NPs) within BEA zeolite through direct hydrothermal approach greatly promoted the catalytic efficiency in the N-alkylation of aromatic alcohols and amines under additive- and solvent-free conditions, resulting in the high yield (∼93 %), maximum turnover number (TON) of 12,822 and turnover frequency (TOF) of 9012 h−1, with stable recyclability and extendable substrate scope. The kinetic studies and in-situ characterizations revealed that the synergy of confined Ru NPs and adjacent acid sites of BEA zeolite significantly promoted the C–H bond activation in the rate-determining step of alcohol dehydrogenation into aldehydes. Besides, the acid sites also accelerated the condensation of aldehyde intermediates and anilines to promote the kinetic equilibrium, while the moderate strength of the Ru–H bond resulting from the confined Ru NPs is advantageous to balance the dehydrogenation and hydrogenation steps to reach the fascinating H-transfer process.

A Phosphine-Oxide Cobalt(II) Complex and Its Catalytic Activity Studies toward Alcohol Dehydrogenation Triggered Direct Synthesis of Imines and Quinolines.

Herein, a new pincer-like amino phosphine donor ligand, H2L1, and its phosphine-oxide analog, H2L2, were synthesized. Subsequently, cobalt(II) complexes 1 and 2 were synthesized by the reaction of anhydrous Co(II)Cl2 with ligands H2L1 and H2L2, respectively. The ligands and complexes were fully characterized by various physicochemical and spectroscopic characterization techniques. Finally, the identity of the complexes 1 and 2 was confirmed by single crystal X-ray structure determination. The phosphine ligand containing complex 1 was converted to the phosphine oxide ligand containing complex 2 in air in acetonitrile solution. Both complexes 1 and 2 were investigated as precatalysts for alcohol dehydrogenation-triggered synthesis of imines in air. The phosphine-oxide complex 2 was more efficient than the phosphine complex 1. A wide array of alcohols and amines were successfully reacted in a mild condition to result in imines in good to excellent yields. Precatalyst 2 was also highly efficient for the synthesis of varieties of quinolines in air. As H2L2 in 2 has side arms that can be deprotonated, we investigated complex 2 for its base (KOtBu) promoted deprotonation events by various spectroscopic studies and DFT calculations. These studies have shown that mono deprotonation of the amine side arm attached to the pyridine is quite feasible, and deprotonation of complex 2 leads to a dearomatized pyridyl ring containing complex 2a. The mechanistic investigations of the catalytic reaction, by a combination of experimental and computational studies, have suggested that the dearomatized complex, 2a acted as an active catalyst. The reaction proceeded through the hydride transfer pathway. The activation barrier of this step was calculated to be 26.5 kcal/mol, which is quite consistent with the experimental reaction temperature under aerobic conditions. Although various pincer-like complexes are explored for such reactions, phosphine oxide ligand-containing complexes are still unexplored.

Ambiphilic Alcohol Dehydrogenation by BICAAC Mimicking Metal–Ligand Cooperativity

Ambiphilic Alcohol Dehydrogenation by BICAAC Mimicking Metal–Ligand Cooperativity

Selective amination of furfuryl alcohol to furfurylamine over nickel catalysts promoted by alumina encapsulation

Direct amination of bio-based furfuryl alcohol over metal catalysts provides an alternative route to produce furfurylamine without consuming expensive reducing reagents. The harsh and reductive condition of furfuryl alcohol amination, however, requires high durability and excellent resistance to side furan-ring hydrogenation for efficient catalysts, which is still substantially challenging to non-noble metals. We show here that alumina-encapsulated Ni catalysts prepared via a sol–gel method exhibited an outstanding and stable performance in selective amination of furfuryl alcohol to furfurylamine under mild NH3 and H2 partial pressures. Structural characterization unveiled that the alumina framework with appropriate mesopores effectively restrained the agglomeration of Ni nanoparticles and the side furan-ring hydrogenation. A volcano-type dependance of the intrinsic activity of Ni nanoparticles on their sizes was established with the maximum attained at about 5 nm, which correlated well with the redox ability of surface Ni sites. Kinetic assessments further indicated the kinetic relevance of furfural formation from furfuryl alcohol dehydrogenation, evidenced by quasi-zero and negative reaction orders on NH3 and H2 pressures, respectively. Combined with infrared spectroscopy, furfuryl alcohol was identified as the predominant adsorbed species with a nearly saturated coverage under reaction condition, consistent with the high susceptibility of furan-ring hydrogenations to H2 pressure. As a consequence, a slight amount of inert Ag (0.05 wt%) was introduced onto the alumina-encapsulated Ni catalysts to weaken the adsorption of furfuryl alcohol and its derivatives, which suppressed the side over-hydrogenation reactions to an extremely low level without sacrificing catalytic activity significantly.

Significant augmentation of hydrogen and benzaldehyde production through mediator-free in-situ synthesis of CuNi/CN photocatalysts for benzyl alcohol splitting

Amidst growing concerns surrounding global warming and energy scarcity, there is an urgent demand for more efficient and environmentally friendly methods of hydrogen production. In response, we introduce a novel mediator-free in-situ approach for synthesizing CuNi/CN composite photocatalysts. This method entails the synthesis of copper and nickel complexes to fabricate bimetallic Cu and Ni nanoparticles on carbon nitride (CN). These catalysts are deployed for the photocatalytic dehydrogenation of benzyl alcohol, resulting in the generation of hydrogen and benzaldehyde. The CuNi bimetal-loaded CN structure provides ample active sites and demonstrates a low hydrogen reduction overpotential, thereby enhancing both charge separation and surface hydrogen reduction processes. In comparison to pure CN, the composite photocatalyst exhibits significantly improved photocatalytic activity. Notably, the composite 2 % Cu1Ni1/CN photocatalyst achieves a record-high hydrogen production rate of about 80 μmol g-1h−1, representing an impressive increase of approximately 533 times compared to pristine CN. Moreover, the catalyst offers cost-effectiveness, ease of preparation, and reusability, ensuring stable hydrogen production efficiency over multiple cycles. This precious metal-free composite photocatalyst not only facilitates the synthesis of valuable compounds but also promotes sustainable advancements in efficient hydrogen energy generation.

1T/2H MoSe2 modified ZnIn2S4 with modulating internal electric field to boost efficient performance of photocatalytic H2 evolution and epoxide alcoholysis

Herein, the extended layer spacing 1T MoSe2 coupled with ZnIn2S4 nanosheets through in-situ growth, and ultimately obtained 1T /2H MoSe2/ZnIn2S4 photocatalysts with S-scheme heterojunction. This rational structure enables photogenerated carriers to rapidly transfer to MoSe2 via Mo-S bond. In order to further address the problem of wasted oxidative half-reaction, we rely on the dehydrogenation of benzyl alcohol as a carrier for hole depletion. Notably, optimized 1T/2H MoSe2/ZnIn2S4 has superior H2 evolution ability, reaching up to 11.271 mmol·g−1·h−1 and the apparent quantum efficiency at 420 nm is 10.3 %. Meanwhile, the conversion rate of benzyl alcohol to high value-added benzaldehyde is 60.60 %. In addition, the Zn acidic sites can achieve polarization of epoxides and precise cleavage C-O bond. Thus, it also has the ability to high selectivity and efficient photocatalytic epoxide alcoholysis. This work proposes a new insight for enhancing photocatalytic properties via regulating IEF to fabricate S-scheme heterostructure.

Pincer Nickel-Catalyzed Olefination of Alcohols with Benzylphosphine Oxides.

N,N,P-Pincer nickel complexes effectively catalyze reaction of alcohols with benzylphosphine oxides to form alkenes in good yields. The protocol suits for a wide scope of substrates and generates only E-configurated alkenes. The method also shows good compatibility of functional groups. Methoxy, methylthio, trifluoromethyl, ketal, fluoro, chloro, bromo, thienyl, and furyl groups are tolerated. The mechanism studies support that the reaction proceeds through catalytic dehydrogenation of alcohols to aldehydes or ketones followed by condensation with benzyldiphenylphosphine oxides in the presence of KOtBu.

A DFT study on the formation mechanism of side product 1,2-propanediol in the hydrogenation of dimethyl oxalate over copper catalyst

The costly separation of 1,2-propanediol (1,2-PDO), an unavoidable byproduct in the hydrogenation of dimethyl oxalate (DMO), significantly hampers the economic viability of coal-to-ethylene glycol (EG) technology. To address this challenge, the formation mechanism of the side product 1,2-PDO on the Cu(111) and Cu2O(111) surfaces during DMO hydrogenation was investigated, which focused on the active sites of copper catalyst and the dominant pathway through density functional theory calculation. The thermodynamics of each elementary step and the adsorption behavior of various species involved in the reaction network along with the local density of states and charge density difference were systematically analyzed. The results indicate that 1,2-PDO is generated more favorably on the Cu2O(111) surface than that on the Cu(111) surface, owing to the Lewis acid-base pairs, i.e. Cu+ us and O– suf sites, present on the Cu2O(111) surface, which strengthens the binding of reactants, products, and reaction intermediates to the substrate. EG reacts primarily with methanol (MeOH) to form 1,2-PDO through Guerbet alcohol condensation reaction through three consecutive steps: alcohol dehydrogenation, aldol condensation, and unsaturated aldehyde hydrogenation. The O– suf sites promote the dehydrogenation of alcohols into aldehydes, the generation of enolates during aldol condensation and the hydrogenation of unsaturated aldehydes, while the Cu+ us sites are responsible for the C–C coupling reaction. These findings may shed light on the mechanism of 1,2-PDO formation over Cu catalyst and provide fundamental knowledge for the development of more efficient catalysts and process optimization.

Salt‐melt synthesis of poly(heptazine imide) in binary alkali metal bromides for enhanced visible‐light photocatalytic hydrogen production

AbstractPoly(heptazine imide) (PHI), a semicrystalline version of carbon nitride photocatalyst based on heptazine units, has gained significant attention for solar H2 production benefiting from its advantages including molecular synthetic versatility, excellent physicochemical stability and suitable energy band structure to capture visible photons. Typically, PHI is obtained in salt‐melt synthesis in the presence of alkali metal chlorides. Herein, we examined the role of binary alkali metal bromides (LiBr/NaBr) with diverse compositions and melting points to rationally modulate the polymerization process, structure, and properties of PHI. Solid characterizations revealed that semicrystalline PHI with a condensed π‐conjugated system and rapid charge separation rates were obtained in the presence of LiBr/NaBr. Accordingly, the apparent quantum yield of hydrogen using the optimized PHI reaches up to 62.3% at 420 nm. The density functional theory calculation shows that the dehydrogenation of the ethylene glycol has a lower energy barrier than the dehydrogenation of the other alcohols from the thermodynamic point of view. This study holds great promise for rational modulation of the structure and properties of conjugated polymeric materials.

Boosting photocatalytic hydrogen peroxide evolution through aerobic oxidative dehydrogenation of benzyl alcohol over amino acid hyper-cross-linked polymer in two-phase system

The fusion of photocatalytic hydrogen peroxide (H2O2) production with the generation of high-value organic compounds carries the potential to optimize the utilization of solar energy. The efficient generation and separation of products constitute indispensable elements in constructing a proficient reaction system. Herein, the photocatalytic production of H2O2 via the aerobic oxidative dehydrogenation of benzyl alcohol (BA) was realized through the application of an amino acid hyper-cross-linked polymer (H6P-HCPs) in two-phase system. The outcomes unveiled that the H6P-HCPs with 1:6 M ratio of L-phenylalanine (L-Phe) and hexaphenylbenzene (HPB) achieves the highest generation rate of H2O2 (29.26 mmol∙gcat-1∙h-1), stoichiometric amount of benzyl alcohol oxidation products were obtained as 96% benzaldehyde (23.94 mmol∙gcat-1∙h-1) and 4% benzoic acid (5.56 mmol∙gcat-1∙h-1). Time-dependent density functional theory (TDDFT) calculations illuminated that the presence of L-Phe monomers of H6P-HCPs not only facilitated electron transfer from L-Phe to HPB, capitalizing on electronegativity differentials, but also instigated the formation of O2•- while concurrently adjusting its hydrophobic nature. These factors, in concert, were instrumental in the accomplishment of this highly efficient photocatalytic process.

Acceptorless Dehydrogenation of Primary and Secondary Alcohols Catalysed by Phosphine‐free C, C Chelated Ir (III) NHC Complexes

AbstractHerein, an efficient, atom‐economic, environmentally benign catalytic protocol has been developed for synthesising ketones and aldehydes by acceptorless dehydrogenation of alcohols. The protocol employs C, C chelated Ir (III) NHC complexes to promote acceptorless dehydrogenation of both secondary and primary alcohols. Notably, oxidation of primary alcohol selectively yields the corresponding aldehyde where forming ester byproducts is possible. Using C, C chelated Ir (III) NHC complexes (0.1 mol%), and a catalytic amount of base tBuONa (5 mol%), several aliphatic and aromatic aldehydes and ketones including more challenging carbonyl compounds bearing heterocyclic rings were obtained in moderate to high yields. Moreover, the protocol is also efficient for synthesising industrially important molecules like heliotropin and 3,4,5‐trimethoxy acetophenone in moderate yields. Remarkably, the catalytic system allows the straightforward synthesis of the potentially bio‐active compound cholest‐4‐en‐3‐one through acceptorless dehydrogenation followed by double bond isomerisation under the reaction conditions. Low catalyst loading, mild reaction conditions, high selectivity, short reaction time, and broad‐substrate scopes are a few interesting characteristics of the catalytic protocol described herein.

KOtBu Mediated Alcohol Dehydrogenation Strategy: Synthesis of 2‐Aryl Quinazolinones

AbstractHerein we report an atom‐economical, transition metal‐free method for synthesizing 2‐aryl quinazolinones through a cascade annulation of 2‐amino benzamide and benzyl alcohol. The reaction proceeds via KOtBu‐mediated acceptorless alcohol dehydrogenation pathways. The procedure tolerates a wide variety of functional groups and provides a convenient method for the synthesis of 2‐aryl quinazolinones. Mechanistic insights by experiments and DFT calculations lead to unveil the reaction mechanism.