Dehydrogenation Of Primary Alcohols Research Articles

Iridium Nanoparticles on NiO as Heterogeneous Catalysts for Acceptorless Dehydrogenation of Primary Alcohols with Tunable Product Selectivity

Iridium Nanoparticles on NiO as Heterogeneous Catalysts for Acceptorless Dehydrogenation of Primary Alcohols with Tunable Product Selectivity

Oxidative dehydrogenation of alcohols on gold: An experimental and computational study on the role of water and the alcohol chain length

The oxidative dehydrogenation of primary alcohols promoted by gold nanoparticles was investigated from an experimental and computational viewpoint to derive a plausible reaction mechanism and to understand the role of water and alcohol chain length in the elementary steps. The influence of water in reaction kinetics and product distribution was determined in a laboratory-scale microreactor adding water to the reaction mixture in different amounts. DFT calculations revealed that the presence of water on the catalyst surface is beneficial to assist the key step in alcohol oxidation i.e., oxygen activation by protonation. The calculations were performed for primary alcohols ranging from methanol to butanol to understand the role of the alkyl chain length on the catalytic activity and to clarify experimental observations. General conclusions were drawn on the influence of temperature on product distribution when employing a typical support material for gold nanoparticles, Al2O3. The combination of experiments and theory has been useful to improve the knowledge of alcohol oxidation promoted by gold.

Dual Ruthenium-Catalyzed Alkene Isomerization-Hydrogen Auto-Transfer Unlocks Skipped Dienes as Pronucleophiles for Enantioselective Alcohol C-H Allylation.

The first use of 1,4-pentadiene and 1,5-hexadiene as allylmetal pronucleophiles in regio-, anti-diastereo-, and enantioselective carbonyl addition from alcohol proelectrophiles is described. As corroborated by deuterium labeling experiments, primary alcohol dehydrogenation delivers a ruthenium hydride that affects alkene isomerization to furnish a conjugated diene, followed by transfer hydrogenative carbonyl addition. Hydrometalation appears to be assisted by the formation of a fluxional olefin-chelated homoallylic alkylruthenium complex II, which exists in equilibrium with its pentacoordinate η1 form to enable β-hydride elimination. This effect confers remarkable chemoselectivity: while 1,4-pentadiene and 1,5-hexadiene are competent pronucleophiles, higher 1,n-dienes are not, and the olefinic functional groups of the products remain intact under conditions in which the 1,4- and 1,5-dienes isomerize. A survey of halide counterions reveals iodide-bound ruthenium-JOSIPHOS catalysts are uniquely effective in these processes. This method was used to prepare a previously reported C1-C7 substructure of (-)-pironetin in 4 vs 12 steps.

Ni(OH)2 nanoparticles as a recyclable catalyst in acceptorless dehydrogenation of alcohols to acids/acid salts under aerobic conditions

AbstractWe demonstrate herein the catalytic performance of unsupported Ni(OH)2 nanoparticles towards the dehydrogenation of primary alcohols to corresponding acids under aerobic conditions in refluxing toluene. An assortment of aromatic and aliphatic carboxylic acids/acids salts was prepared from corresponding alcohols in moderate to excellent yields. Interestingly, the protocol can also be employed to synthesize carboxylic acids on a gram scale, demonstrating the practical utility of the method. Mechanistic studies suggest that the reaction proceeds through an acceptorless dehydrogenation strategy and follow both Cannizzaro and catalytic dehydrogenative path. Broad substrate scope, operational simplicity, low cost, and reusability are the most interesting features of the current heterogeneous catalytic protocol described herein.

Synthesis and structural characterization of palladium pincer complexes: Sustainable synthesis of benzothiazoles

An efficient Pd(II)N^N^S pincer type catalysts‐promoted sustainable construction of pharmaceutically important benzothiazole derivatives from primary alcohols and 2‐aminothiophenol via acceptorless dehydrogenative coupling (ADC) method has been described. The newly synthesized ligand L2 and the Pd(II) complexes in addition to L1 and L3 were characterized by analytical and Fourier transform infrared spectroscopy (FT‐IR), UV–visible (UV–vis), and nuclear magnetic resonance (NMR) spectral techniques. Further, the ORTEP views of the complexes 2 and 3 were established by a single crystal XRD study, which evidenced the coordination of the thiosemicarbazone ligands and disclose the square‐planar geometry around the Pd(II) ion. The present homogeneous catalytic system involves synthesizing a range of benzothiazoles via C−S and C−N bond formation with excellent yields up to 93%. The described methodology employs a sustainable, highly abundant, and inexpensive alcohol as starting material using 1 mol% catalyst loading, and water and hydrogen gas are the only by‐products. Furthermore, a plausible mechanism involving in situ aldehyde formation via dehydrogenation of primary alcohols has been proposed. A large‐scale synthesis of 2‐(4‐methoxyphenyl)benzo[d]thiazole illustrates the synthetic utility of the present catalytic protocol.

Asymmetric Ruthenium-Catalyzed Carbonyl Allylations by Gaseous Allene via Hydrogen Auto-Transfer: 1° vs 2° Alcohol Dehydrogenation for Streamlined Polyketide Construction.

Iodide-bound ruthenium-JOSIPHOS complexes catalyze the redox-neutral C-C coupling of primary alcohols 2a-2r with the gaseous allene (propadiene) 1a to form enantiomerically enriched homoallylic alcohols 3a-3r with complete atom-efficiency. Using formic acid as reductant, aldehydes dehydro-2a and dehydro-2c participate in reductive C-C coupling with allene to deliver adducts 3a and 3c with comparable levels of asymmetric induction. Deuterium labeling studies corroborate a mechanism in which alcohol dehydrogenation triggers allene hydroruthenation to form transient allylruthenium-aldehyde pairs that participate in carbonyl addition. Notably, due to a kinetic preference for primary alcohol dehydrogenation, chemoselective C-C coupling of 1°,2°-1,3-diols occurs in the absence of protecting groups. As illustrated by the synthesis of C7-C15 of spirastrellolide B and F (7 vs 17 steps), C3-C10 of cryptocarya diacetate (3 vs 7 or 9 steps), and a fragment common to C8'-C14' of mycolactone F (1 vs 4 steps) and C22-C28 marinomycin A (1 vs 9 steps), this capability streamlines type I polyketide construction.

Acceptorless dehydrogenation of primary alcohols to carboxylic acids by self-supported NHC-Ru single-site catalysts

The acceptorless dehydrogenation of diverse aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished by self-supported NHC-Ru single-site catalysts under mild reaction conditions. Besides broad substrates with excellent activity, selectivity and good tolerance to sensitive functional groups, the solid single-site catalyst could be recovered and reused for more than 20 runs without deactivation. Remarkably, up to 1.8 × 104 turnover numbers could be achieved by this newly developed sustainable protocol in gram scale at low catalyst loading, highlighting its potential in industry.

Insights into the activity and selectivity trends in non-oxidative dehydrogenation of primary and secondary alcohols over the copper catalyst

Density functional theory (DFT) simulations are conducted to understand the differentiation of activity and selectivity trends between primary and secondary alcohols towards the non-oxidative dehydrogenation (NODH) reaction. Propanol and isopropanol are employed as model molecules to explore the NODH on the (111) facets of Cu. The initial dehydrogenation of propanol via the hydroxyl route exhibits a higher barrier (96.8 kJ/mol) as compared to that of isopropanol (61.4 kJ/mol). Furthermore, the second dehydrogenation step resulting in the formation of the carbonyl compound is also calculated to show higher barrier of primary alcohol (83 kJ/mol) than secondary alcohol (51.3 kJ/mol). Overall, for the consecutive dehydrogenation steps, propanol is observed to show higher activation barriers as opposed to that of isopropanol, indicating towards a higher conversion rate for isopropanol, similar to the trend observed experimentally. However, the subsequent dehydrogenation of the carbonyl compound formed shows a barrier of 112.8 kJ/mol for acetone and that of 70.6 kJ/mol for acetaldehyde owing to the higher stability of ketone. The formation of ester from the propionyl produced upon acetaldehyde dehydrogenation is calculated to show the lowest barrier (64.6 kJ/mol) amongst the dehydrogenation steps of primary alcohol dehydrogenation route, suggesting towards lower selectivity in case of NODH of propanol.

Ruthenium Catalyzed Divergent Alkylation and Olefination of Methyl 1,3,5‐Triazines with Alcohols

An efficient ruthenium‐catalyzed divergent alkylation and olefination of methyl 1,3,5‐triazines with alcohols have been developed. The selectivity can be rationally tuned by the judicious choice of ruthenium catalyst, wherein Ru(PPh3)3Cl2 delivers alkylated 1,3,5‐triazines and RuCl3 gives olefinated 1,3,5‐triazines in up to 98 % yield. Following this simple, facile, and high atom economical protocol, a broad range of products was prepared in moderate to good yields and tolerated heterocyclic or benzylic alcohols containing functionalities. The overall transformation operates through dehydrogenation of primary alcohols under the reaction conditions to provide the corresponding aldehydes, which further undergo condensation with methyl 1,3,5‐triazines.

A robust NNP‐type ruthenium (II) complex for alcohols dehydrogenation to esters and pyrroles

A Ru (II) complex bearing pyridyl‐based benzimidazole‐phosphine tridentate NNP ligand was synthesized and structurally characterized by NMR, IR. The complex can efficiently and selectively catalyze the acceptorless dehydrogenation of primary alcohols to esters under relatively mild conditions and the synthesis of pyrroles by means of the reactions of secondary alcohols and β‐amino alcohols through acceptorless deoxygenation condensation.

Ruthenium Catalyzed Dehydrogenation of Alcohols and Mechanistic Study.

We synthesized pyridylamine ligated arene-Ru(II) complexes and employed these complexes for the catalytic acceptorless dehydrogenation of primary alcohols to carboxylic acids. All the synthesized complexes [Ru]-1-[Ru]-10 are characterized using several spectro-analytical techniques, and the structures of complexes [Ru]-1, [Ru]-2, and [Ru]-5 are determined using single crystal X-ray crystallography. Efficient catalytic conversion of primary alcohols to potassium carboxylates or carboxylic acids is achieved in toluene with the quantitative release of hydrogen gas. The studied protocol for carboxylic acid synthesis with hydrogen generation is also employed for a wide range of substrates, including aliphatic alcohols, aromatic alcohols, and heteroaromatic alcohols, to obtain respective carboxylic acids in good yields (up to 86%). The studied arene-Ru catalysts also exhibit superior catalytic activity for the bulk reaction to achieve a turnover number of 1378. Moreover, extensive mass investigations are also performed to elucidate the mechanistic pathway by identifying the crucial catalytic intermediates, including aldehyde and diol coordinated Ru species under the catalytic and controlled reaction conditions.

Dehydrogenation of Alcohols to Carboxylic Acid Catalyzed by in Situ-Generated Facial Ruthenium-CPP Complex.

A selective catalytic system for the dehydrogenation of primary alcohols to carboxylic acids using a facial ruthenium complex generated in situ from the [Ru(COD)Cl2]n and a hybrid N-heterocyclic carbene (NHC)-phosphine-phosphine ligand (CPP) has been first reported. The facial coordination model was unveiled by NMR analysis of the reaction mixture. Such a fac-ruthenium catalyst system exhibited high catalytic activity and stability, and a high turnover number of 20 000 could be achieved with catalyst loading as low as 0.002 mol %. The exceedingly high catalyst stability was tentatively attributed to both the anchoring role of NHC and the hemi-lability of phosphines. The catalytic system also features a wide substrate scope. In particular, the facial coordination of CPP ligands was found to be beneficial for sterically hindered alcohols, and ortho-substituted benzylic alcohols and bulky adamantanyl methanol as well as cholesterol were all found to be viable dehydrogenation substrates.

Zinc Oxide-Catalyzed Dehydrogenation of Primary Alcohols into Carboxylic Acids.

Zinc oxide has been developed as a catalyst for the dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The reaction is performed in mesitylene solution in the presence of potassium hydroxide, followed by workup with hydrochloric acid. The transformation can be applied to both benzylic and aliphatic primary alcohols and the catalytically active species was shown to be a homogeneous compound by a hot filtration test. Dialkylzinc and strongly basic zinc salts also catalyze the dehydrogenation with similar results. The mechanism is believed to involve the formation of a zinc alkoxide which degrades into the aldehyde and a zinc hydride. The latter reacts with the alcohol to form hydrogen gas and regenerate the zinc alkoxide. The degradation of a zinc alkoxide into the aldehyde upon heating was confirmed experimentally. The aldehyde can then undergo a Cannizzaro reaction or a Tishchenko reaction, which in the presence of hydroxide leads to the carboxylic acid.

Silver‐Catalyzed Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols

A simple silver-catalyzed protocol has been developed for the acceptorless dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The procedure uses 2.5 % Ag2 CO3 and 2.5-3 equiv of KOH in refluxing mesitylene to afford the potassium carboxylate which is then converted into the acid with HCl. The reaction can be applied to a variety of benzylic and aliphatic primary alcohols with alkyl and ether substituents, and in some cases halide, olefin, and ester functionalities are also compatible with the reaction conditions. The dehydrogenation is believed to be catalyzed by silver nanoparticles that are formed in situ under the reaction conditions.

Photocatalytic Dehydrogenation of Primary Alcohols: Selectivity Goes against Adsorptivity.

Solid/liquid heterogeneous photocatalysis was often considered to occur on the active sites of a solid catalyst surface. Herein, we report that the selectivity of photocatalytic dehydrogenative oxidations of aliphatic primary alcohols in acetonitrile solution into corresponding aldehydes exhibits an anomalous relationship with adsorption behavior of the alcohols. By using Pt-loaded TiO2 photocatalyst in an inert atmosphere under UV light illumination, primary short-chain alcohols (SCAs) with strong adsorption were dehydrogenated into aldehydes in very poor selectivity, whereas weak-adsorbable long-chain alcohols (LCAs) were transformed into corresponding aldehydes with much higher selectivity. More than 20 examples of primary LCAs (C4–C10) were successfully transformed into their corresponding aldehydes with satisfactory selectivity and yield. Both solid-state magic-angle-spinning 13C NMR and attenuated total reflectance–Fourier transform infrared spectroscopy studies provided concrete differences in adsorption behaviors on the Pt–TiO2 photocatalyst surface between SCA ethanol and LCA n-octanol. To further uncover the mechanism for different selectivities of SCAs and LCAs in photodehydrogenation, in situ electron paramagnetic resonance (EPR) experiments (at 8 K temperature) were employed to observe the oxidation features of photogenerated hole in the valance band of Pt–TiO2 (hvb+). The EPR experimental studies exhibited that unlike ethanol, either n-octanol or solvent acetonitrile alone all could not scavenge photogenerated hvb+ on Pt–P25 photocatalyst and only n-octanol dissolved in acetonitrile solvent could smoothly react with photoinduced hole. This indicated that selective oxidations of LCAs were achieved by solvent-delivered oxidation rather than directly destructive oxidation of photogenerated hvb+. Our results may open an alternative way in selective dehydrogenative oxidation of various substrates sensitive to both dioxygen and high-temperature treatments.

Synthesis of a series of iridium complexes bearing substituted 2-pyridonates and their catalytic performance for acceptorless dehydrogenation of alcohols under neutral conditions

A series of Cp*Ir complexes bearing 5- and 4,5-substituted 2-pyridonate ligands have been synthesized and their catalytic performance for acceptorless dehydrogenation of alcohols has been investigated under neutral conditions. Electron-withdrawing groups such as methoxycarbonyl, trifluoromethyl, cyano, and nitro groups at the 5-position promoted the acceptorless dehydrogenation of 1-phenylethanol, whereas electron-donating methyl group at the 5-position retarded the reaction. Furthermore, introduction of methyl group at the 4-position improved the catalytic performance. Thus, Cp*Ir(5-trifluoromethyl-4-methyl-2-pyridonate)Cl (2bc) exhibited the highest catalytic performance among the complexes examined, and also showed good catalytic performance for acceptorless dehydrogenation of primary alcohols.

Ni(ii)–N′NN′ pincer complexes catalyzed dehydrogenation of primary alcohols to carboxylic acids and H2accompanied by alcohol etherification

Ni(L)catalyzed acceptorless dehydrogenation of alcohol/alkoxide to carboxylate with H2liberation.

Ru(II) complexes bearing 2,6-bis(benzimidazole-2-yl)pyridine ligands: A new class of catalysts for efficient dehydrogenation of primary alcohols to carboxylic acids and H2 in the alcohol/CsOH system

Mono-cationic Ru(II)-complexes [Ru(L)X(CH3CN)2]⋅X 1∼4 (1, L = 2,6-bis(benzimidazol-2-yl) pyridine (L1), X = Cl; 2, L = L1, X = OTf; 3, L = 2-(N-benzyl-benzimidazole-2-yl)-6-(benzimidazole-2-yl)pyridine (L2), X = Cl; 4, L = 2,6-bis(N-benzyl-benzimidazole-2-yl)pyridine (L3), X = Cl) were prepared and fully characterized. The two acetonitrile ligands of each complex are coordinated to the metal center cis to each other. Complex 2 was also structurally characterized by X-ray crystallography. It was found that complexes 1∼4 can catalyze the acceptorless dehydrogenation of primary alcohols to corresponding carboxylic acids and H2 in the basic aqueous solution, and the reactivity follows the order 1 = 2 > 4 >3. Furthermore, complexes 1 or 2 can efficiently catalyze the conversion of various primary alcohols to carboxylic acid in good yields (72%–98%) and high selectivity in an alcohol/CsOH system (1/1, mol/mol). Using an excess amount of alcohol to CsOH results in the formation of the carboxylic acid in higher yield (up to 100%, based on CsOH) and higher turnover numbers (TON ∼ 10000) accompanied by the H2 evolution. Complexes 1 and 2 can act as a new class of phosphine- and N-heterocycle carbene free Ru(II) complexes for efficient conversion of primary alcohols to carboxylic acids and H2 in a homogeneous system.

ChemInform Abstract: Enantioselective Alcohol C—H Functionalization for Polyketide Construction: Unlocking Redox‐Economy and Site‐Selectivity for Ideal Chemical Synthesis

AbstractReview: [75 refs.

Catalytic oxidation of primary aromatic alcohols using half sandwich Ir(III), Rh(III) and Ru(II) complexes: A practical and theoretical study

The complexes [Cp*IrCl(N-(pyridin-2-ylmethylene)aniline)]PF6 (1), [Cp*RhCl(N-(pyridin-2-ylmethylene)aniline)]PF6 (2), (where Cp*=1,2,3,4,5-pentamethylcyclopentadiene) and [η6-areneRuCl(N-(pyridin-2-ylmethylene)aniline)]PF6 (3) have been synthesized and the structure and purity of these were confirmed by single crystal XRD and elemental analyses. Iridium and rhodium complexes exhibit the P21/n space group, the ruthenium complex the P21/c space group and all three complexes show the expected pseudo octahedral “piano-stool” geometry. The catalytic performance of these complexes for the dehydrogenation of primary alcohols to their respective aldehydes with different bases and solvents was investigated. The complexes of iridium and ruthenium give good conversions in different alkaline solutions. Density functional theory was applied to determine the respective MO energy levels, bond lengths, bond angles and binding energies of all the metal complexes. It was also used to study the activity, stability and intermediates of the complexes. A Gibbs free energy (ΔG) DFT calculation was carried out to help understand the reaction mechanism/catalytic cycle of the Rh complex (2). The energy barrier for oxidation of aromatic alcohols by the rhodium hydride complex is much lower (10.32kcal/mol) than the barrier for hydride transfer of the corresponding Rh benzyloxo species (15.19kcal/mol), in agreement with mechanisms proposed for related systems.