Yanqun Wang

Chemodivergent transfer hydrogenation of unsaturated esters is achieved using a manganese complex with ammonia borane. CC reduction furnishes saturated esters in dioxane, whereas full reduction delivers primary alcohols in MTBE.

We report a solvent-switchable chemoselective transfer hydrogenation of α,β-unsaturated esters, employing an earth-abundant manganese complex as catalyst and ammonia borane as hydrogen donor. Diverse unsaturated esters are efficiently converted to saturated esters in dioxane and primary alcohols in MTBE. Mechanistic investigations demonstrate that manganese hydride species formed in MTBE exhibit superior reactivity to those in dioxane, establishing a practical protocol for this chemoselective reduction. Gram-scale transfer hydrogenation of ethyl cinnamate validates the methodology, affording the saturated ester in 91.2% yield and the primary alcohol in 80% yield under the respective conditions.

To explore the catalytic cracking mechanism of CuO on oil shale and the catalytic activity of surface modifications of CuO on oil shale, dimethyl sulfoxide (C₂H₆OS) is used as a model molecule representative of organic sulfur compounds in oil shale, and the adsorption and dissociation behaviors of C₂H₆OS molecules on pure and OH pre-adsorbed CuO(111) surfaces were investigated by density functional theory calculations. The results indicate that C₂H₆OS selectively adsorbs at the Cu_sub sites via the S atom and decomposes through cleavage of the C–H bond prior to the breaking of the C-S bond on both surfaces. The presence of OH on the CuO(111) surface promoted the dissociation of C₂H₆OS. The energy barriers of dehydrogenation and desulfurization of C₂H₆OS on the OH pre-adsorbed CuO(111) surface were 20.0 and 19.3 kcal/mol, respectively, which are 41% and 49% lower than those on pure surfaces. The present results provide crucial guidance for the synthesis and improvement of high-performance pyrolysis catalysts specifically designed for oil shale applications. Additionally, they also present important data regarding to the thermal stability of C₂H₆OS in the presence of incompatible substances.

The interaction mechanism between oil shale and catalyst is very important for the design and synthesis of related catalysis. In this work, dimethyl sulfoxide (DMSO) serves as a model molecule for organic sulfur compounds in oil shale to explore the catalytic effect and mechanism of the pure and transition metal Cu−doped SBA−15 molecular sieves regarding the decomposition of organic sulfur compounds in oil shale using the density functional theory (DFT) method. It is found that DMSO adsorption on both surfaces is primarily attributed to hydrogen bonding or the interaction between the S and O moieties within the molecule and the surface Cu atoms. The adsorption energies on both surfaces are indistinguishable; however, the Cu−doped SBA−15 shows enhanced catalytic activity in dissociation reactions. The Gibbs free energy changes for both possible reaction pathways of DMSO breaking C−S bonds on the pure SBA−15 surface are positive, and the activation energy barriers are as high as ~75 kcal/mol, indicating that the dissociation of C−S bonds in DMSO is unlikely to occur on this surface. In contrast, the Gibbs free energy change for the same reaction on the Cu−doped SBA−15 surface is negative, and the energy barrier is reduced by ~40 kcal/mol compared to that on the pure SBA−15 surface. Furthermore, the resulting methyl group is more likely to bond with the bridging oxygen atom. In addition, our research proposes that the dissociation of the C−H and C−S bonds of DMSO on the Cu−doped SBA−15 surface was competitive. These findings provide theoretical guidance for the development of highly efficient catalysts intended for the pyrolysis of oil shale under appropriate conditions.

The stability of aluminum hydride (AlH3) based high-energy propellants is important for its large-scale application. In this work, to explore the stability mechanism of systems composed of AlH3 and a binder containing C–O–C or –N3 groups, molecular dynamics simulations were carried out to explore the thermal expansion properties of AlH3, and density functional theory calculations were employed to study the micro-interaction between molecules containing C–O–C or –N3 groups and AlH3. More specifically, CH3OC2H5 and CH3N3 were used to model polyethylene glycol and glycidyl azide polyether, respectively. It is found that AlH3 is more sensitive to temperature changes than its oxide layer. Upon contact between the alumina layer and CH3OC2H5 or CH3N3, these compounds exist stably on the α-Al2O3(0001) and γ-Al2O3(110) surfaces. Upon direct contact with the α-AlH3(010) surface, CH3OC2H5 is relatively stable, while CH3N3 can trigger the surface hydrogen transfer reaction due to the low energy barrier (5.0 kcal/mol). The current work provides a theoretical basis for understanding the sensitivity of AlH3 and binders containing C–O–C or –N3 groups, and is useful in the research and development of superior composite energetic propellants.