Mechanism of Potassium tert-Butoxide-Catalyzed Ketones Hydrogenation in the Solution Phase

Double Direct C-H Bond Arylation of Thiophenes with Aryl Chlorides Catalyzed by the N-Heterocyclic Carbene-PdCl2-1-methylimidazole Complex

With the combination of the N-heterocyclic carbene-PdCl2-1-methylimidazole complex and Cu2O, we succeeded in the first example of double direct C-H bond arylation reactions between thiophenes and aryl chlorides, giving the desired 2,5-diarylated thiophenes in moderate to high yields under suitable conditions, consistent with the density functional theory calculations.

Diastereoselective Construction of Tetrahydro-Dispiro[indolinone-3,2'-pyran-5',4″-pyrazolone] Scaffolds via an Oxa-Michael Cascade [4 + 2] Annulation Reaction

A straightforward metal-free oxa-Michael cascade [4 + 2] annulation reaction was established between isatin-derived Morita-Baylis-Hillman (Is-MBH) alcohols with alkylidene pyrazolones to access structural diverse tetrahydro-dispiro[indolinone-3,2'-pyran-5',4″-pyrazolone] scaffolds bearing two tertiary and two quaternary stereocenters. The Is-MBH alcohol was utilized as an oxa-Michael donor for the first time as a new approach in highly atom-economical transformations. This method offered a wide range of bioinspired novel tetrahydro-dispirooxindole-pyran-pyrazolone derivatives in excellent yields (up to 96%) and diastereoselectivities (up to >20:1) in a shorter reaction time (15 min).

On the mechanism of acceptorless dehydrogenation of N-heterocycles catalyzed by tBuOK: a computational study

The catalytic acceptorless dehydrogenation (ADH) of saturated N-heterocycles has recently gained considerable attention as a promising strategy for hydrogen release from liquid organic hydrogen carriers (LOHCs). Recently, a simple ^tBuOK base-promoted ADH of N-heterocycles was developed by Yu et al. (Adv. Synth. Catal. 2019, 361, 3958). However, it is still open as to how the ^tBuOK plays a catalytic role in the ADH process. Herein, our density functional study reveals that the ^tBuOK catalyzes the ADH of 1,2,3,4-tetrahydroquinoline (THQ) through a quasi-metal-ligand bifunctional catalytic channel or a base-catalyzed pathway with close energy barriers. The hydride transfer in the first dehydrogenation process is determined to be the rate determining step, and the second dehydrogenation can proceed directly from 34DHQ regulated by the ^tBuOK. In addition, the computational results show that the cooperation of a suitable alkali metal ion with the ^tBuO^- group is so critical that the ^tBuOLi and the isolated ^tBuO^- are both inferior to ^tBuOK as a dehydrogenation catalyst.

Production of Benzene by the Hydrodemethylation of Toluene with Carbon-Supported Potassium Hydride

The hydrodemethylation (HDM) of toluene to benzene is an industrial process performed at elevated temperatures (≈500 °C and higher). Here, it was reported that heating graphite-supported potassium hydride (KH/C) with toluene under H₂ atmosphere provided benzene already at 125-250 °C. Depending on the H₂ pressure, the reaction was either substoichiometric ( ≤11 bar) or catalytic ( ≥50 bar) with respect to KH, indicating that KH may serve as a radical chain initiator. At 250 °C, the selectivity to benzene was 98 and 63 % when using 6 and 80 bar of H₂ , respectively, owing to the competing formation of cyclohexane and methylcyclohexane at high H₂ pressure. The used KH/C material was amenable to recycling without a notable loss in the yield of benzene.

Performance Analysis of CP2K Code for Ab Initio Molecular Dynamics on CPUs and GPUs

Using a realistic molecular catalyst system, we conduct scaling studies of ab initio molecular dynamics simulations using the popular CP2K code on both Intel Xeon CPU and NVIDIA V100 GPU architectures. Additional performance improvements were gained by finding more optimal process placement and affinity settings. Statistical methods were employed to understand performance changes in spite of the variability in runtime for each molecular dynamics timestep. Ideal conditions for CPU runs were found when running at least four MPI ranks per node, bound evenly across each socket. This study also showed that fully utilizing processing cores, with one OpenMP thread per core, performed better than when reserving cores for the system. The CPU-only simulations scaled at 70% or more of the ideal scaling up to 10 compute nodes, after which the returns began to diminish more quickly. Simulations on a single 40-core node with two NVIDIA V100 GPUs for acceleration achieved over 3.7× speedup compared to the fastest single 36-core node CPU-only version. These same GPU runs showed a 13% speedup over the fastest time achieved across five CPU-only nodes.

Beyond Continuum Solvent Models in Computational Homogeneous Catalysis

In homogeneous catalysis solvent is an inherent part of the catalytic system. As such, it must be considered in the computational modeling. The most common approach to include solvent effects in quantum mechanical calculations is by means of continuum solvent models. When they are properly used, average solvent effects are efficiently captured, mainly those related with solvent polarity. However, neglecting atomistic description of solvent molecules has its limitations, and continuum solvent models all alone cannot be applied to whatever situation. In many cases, inclusion of explicit solvent molecules in the quantum mechanical description of the system is mandatory. The purpose of this article is to highlight through selected examples what are the reasons that urge to go beyond the continuum models to the employment of micro-solvated (cluster-continuum) of fully explicit solvent models, in this way setting the limits of continuum solvent models in computational homogeneous catalysis. These examples showcase that inclusion of solvent molecules in the calculation not only can improve the description of already known mechanisms but can yield new mechanistic views of a reaction. With the aim of systematizing the use of explicit solvent models, after discussing the success and limitations of continuum solvent models, issues related with solvent coordination and solvent dynamics, solvent effects in reactions involving small, charged species, as well as reactions in protic solvents and the role of solvent as reagent itself are successively considered.