Hydrogenation Of Organic Molecules Research Articles

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis.

This review surveys the synthesis and reactivity of low-oxidation state metalate anions of the d-block elements, with an emphasis on contributions reported between 2006 and 2022. Although the field has a long and rich history, the chemistry of transition metalate anions has been greatly enhanced in the last 15 years by the application of advanced concepts in complex synthesis and ligand design. In recent years, the potential of highly reactive metalate complexes in the fields of small molecule activation and homogeneous catalysis has become increasingly evident. Consequently, exciting applications in small molecule activation have been developed, including in catalytic transformations. This article intends to guide the reader through the fascinating world of low-valent transition metalates. The first part of the review describes the synthesis and reactivity of d-block metalates stabilized by an assortment of ligand frameworks, including carbonyls, isocyanides, alkenes and polyarenes, phosphines and phosphorus heterocycles, amides, and redox-active nitrogen-based ligands. Thereby, the reader will be familiarized with the impact of different ligand types on the physical and chemical properties of metalates. In addition, ion-pairing interactions and metal-metal bonding may have a dramatic influence on metalate structures and reactivities. The complex ramifications of these effects are examined in a separate section. The second part of the review is devoted to the reactivity of the metalates toward small inorganic molecules such as H2, N2, CO, CO2, P4 and related species. It is shown that the use of highly electron-rich and reactive metalates in small molecule activation translates into impressive catalytic properties in the hydrogenation of organic molecules and the reduction of N2, CO, and CO2. The results discussed in this review illustrate that the potential of transition metalate anions is increasingly being tapped for challenging catalytic processes with relevance to organic synthesis and energy conversion. Therefore, it is hoped that this review will serve as a useful resource to inspire further developments in this dynamic research field.

Coupling photocatalytic overall water splitting with hydrogenation of organic molecules: a strategy for using water as a hydrogen source and an electron donor to enable hydrogenation

A strategy for using green water as a hydrogen source and electron donor to enable the hydrogenation of aryl bromides is reported.

A comprehensive theoretical study of positron binding and annihilation properties of hydrogen bonded binary molecular clusters.

We studied the positron binding and annihilation of hydrogen bonded binary molecular clusters containing small inorganic molecules such as water, hydrogen fluoride, ammonia, hydrogen sulfide, hydrogen chloride, and phosphine, using first-principles calculation. While unimolecular systems of these species mostly exhibit no or very small positron binding energies (positron affinities), we found that all of their hydrogen bonding clusters have greater positive positron affinities. The permanent dipole moment enhanced by the formation of the intermolecular hydrogen bond acts as a dominant parameter to bind a positron for a given proton donor, whereas it is insufficient for reproducing the dependence of the positron affinity on substitutions of the proton donor. By multiple regression analyses with inherent properties of the clusters, we found a reasonable model with additional effective parameters represented by, particularly, the number of hydrogen atoms free from the hydrogen bond. By density analyses for the single-particle and electron-positron collision probabilities, we revealed that these effective parameters are associated with the electronic structure changes induced by the hydrogen bond and positron binding, which have important roles to enhance the electron-positron contact densities due to the proton-screening effect.

The Effect of Adsorbed Molecule Gas-Phase Deprotonation Enthalpy on Ion Exchange in Sodium Exchanged Zeolites: An In Situ FTIR Investigation

Molecular-level understanding of the interactions between reactants and the surface of solid catalysts is of importance to the rational design of catalysts. Here, in situ transmission Fourier transform infrared spectroscopy is employed to investigate the ion exchange between the acidic hydrogen in organic molecules that have been adsorbed from the gas phase and sodium cations in zeolites. Organic compounds with functional groups common among key biomass-derived compounds are used as probe molecules. We demonstrate that ion exchange between acidic hydrogen in organic molecules and the sodium cations in zeolites with the FAU topology produces Bronsted acid sites and the corresponding adsorbed salt species by identifying signature spectroscopic bands. Furthermore, the gas-phase deprotonation enthalpy (GPDE) of the organic compounds is identified as a key descriptor in determining the feasibility and extent of the exchange process. Molecules with GPDE below 1462 kJ/mol, e.g., m-cresol (1462 kJ/mol), propanoic acid (1454), acetic acid (1457), acrylic acid (1440) and trifluoroacetic acid (1357), show clear vibrational bands for Bronsted acid sites and the corresponding sodium salts, while molecules with higher GPDE, such as trifluoroethanol (1513), ethanol (1586), and water (1622) do not. These data indicate that the degree of dissociation of the acidic hydrogen is a key element in the ion exchange. The generality of this process in zeolites is established by the observation of similar results on zeolites with differing topologies (FAU, MFI, *BEA, and MOR).

Solution and gas phase deuterium derivatization reactions for gas chromatography/microwave emission detection

Deuterium is monitored and quantitated in the presence of hydrogen in organic molecules with the helium microwave emission detector (MED). Various functional groups are tagged utilizing deuterated reagents which also serve to modify the components' Chromatographic characteristics. Lithium aluminum deuteride (LAD) will reduce aldehydes, carboxylic acids, esters, amides and acid halides to non-exchangeable CD 2-tagged alcohols which can be further derivatized with multi-element reagents such as chlorodifluoroacetic anhydride. Other reagents include D 9-BSA (N, O-bistrimethylsilylacetamide) for silylation, Deuter-8 TM for esterifications, D 3-acetylchloride for acetylation, and D 2-diazomethane for generalized N and O alkylations. Gas phase derivatization utilizes an on-line deuteration reactor in series with the GC injection port. The reactor contains catalysts such as nickel, platinum, or palladium coated on a suitable substrate in a deuterium atmosphere. This technique is used to tag olefins, alkanes, aromatics, nitriles and other functionalities subject to D-H exchange, reduction, isomerization, and a variety of cleavage reactions. The element-selective MED provides qualitative and quantitative information for a variety of compounds in which deuterium is incorporated.

NMR determination of absolute site-specific natural isotope ratios of hydrogen in organic molecules. Analytical and mechanistic applications

It has been shown that the “internal” isotope distribution within a given molecular species at the natural abundance level is accessible by a new method, SNIF-NMR, which is based on deuterium NMR. Relative internal factors, R i/j,have been defined which enable the isotope content of a given site, i, to be compared to that of another molecular site, j, taken as the reference. Several referencing methods intended to provide direct access to relative externals , T i , and absolute , (D/H) i , site-specific parameters, are now discussed from both the theoretical and the experimental points of view. In the intramolecular referencing method , which involves a time-consuming chemical transformation of the sample, the risk exists of more or leas systematic errors resulting from discriminating fractionation effects. However this technique offers, conversely, an interesting way of investigating kinetic isotope effects without the need for specific labelling. In spite of its lower spectral precision the external referencing method has the advantage of being fast and less sensitive to systematic errois and may be used for direct rough routine determinations of the site-specific isotope contents. More precise results can be obtained, at the price of contaminating the sample, when an intermolecular reference is added and signal heights are used, remembering however that the intensity parameters then have no strict physical meaning in terms of absolute isotope contents. The site-specific parameters, T i and (D/H) i thus accessible, provide new information on the mechanisms of the fractionation effects occurring in natural conditions and examples are considered.

Field-Ionization Mass Spectra of Some Hydrocarbons and Monochloro-Substituted Derivatives

Field-ionization mass spectra have been obtained for about 30 straight-chain and branched hydrocarbons, together with the corresponding monochloro derivatives. Electric fields of about 1 × 107V cm−1 were produced with a 2.5-μ Pt wire. Mass-analyzed ion currents of about 10−14–10−16 A were detected for applied anodecathode voltages of 10–11 kV. Along with the most intense parent ion currents there were detected fragment ions with lifetimes of 10−8–10−13 sec resulting from decomposition of field-excited parent ions. Also present in the spectra were ions arising from long-lived metastable parent ions with lifetimes of 10−5–10−7 sec. Correlation of the observed mass and intensity of fragment and parent ions with the parent molecular structures yielded conclusions related to the various decomposition processes. Increased branching of isomeric structures resulted in increased fragmentation. The presence of a double bond in a molecule greatly reduced fragmentation compared with molecules of similar structure with no double bond. The substitution of chlorine for hydrogen in organic molecules increased fragmentation.