Engineering of Yolk/Core-Shell Structured Nanoreactors for Thermal Hydrogenations

Heterogeneous hydrogenation reactions are of great importance for chemical upgrading and synthesis, but still face the challenges of controlling selectivity and long-term stability. To improve the catalytic performance, many hydrogenation reactions utilize special yolk/core-shell nanoreactors (YCSNs) with unique architectures and advantageous properties. This work presents the developmental and technological challenges in the preparation of YCSNs that are potentially useful for hydrogenation reactions, and provides a summary of the properties of these materials. The work also addresses the scientific challenges in applications of these YCSNs in various gas and liquid-phase hydrogenation reactions. The catalyst structures, catalytic performance, structure-performance relationships, reaction mechanisms, and unsolved problems are discussed too. Also, a brief outlook and opportunities for future research in this field are presented. This work on the advancements in YCSNs might inspire the creation of new materials with desired structures for achieving maximal hydrogenation performances.

Enzyme-Inspired Assembly: Incorporating Multivariate Interactions to Optimize the Host-Guest Configuration for High-Speed Enantioselective Catalysis

To achieve a rapid asymmetry conversion, the substrate objects suffer from accelerated kinetic velocity and random rotation at the cost of selectivity. Inspired by natural enzymes, optimizing the host-guest configuration will realize the high-performance enantioselective conversion of chemical reactions. Herein, multivariate binding interactions were introduced into the 1D channel of a chiral catalyst to simulate the enzymatic action. An imidazolium group was used to electrophilically activate the C═O unit of a ketone substrate, and the counterion binds the hydrogen donor isopropanol. This binding effect around the catalytic center produces strong stereo-induction, resulting in high conversion (99.5% yield) and enantioselectivity (99.5% ee) for the asymmetric hydrogenation of biomass-derived acetophenone. In addition, the turnover frequency of the resulting catalyst (5160 h^-1 TOF) is more than 58 times that of a homogeneous Ru-TsDPEN catalyst (88 h^-1 TOF) under the same condition, which corresponds to the best performance reported till date among all existing catalysts for the considered reaction.

Porous Organic Frameworks Featured by Distinct Confining Fields for the Selective Hydrogenation of Biomass-Derived Ketones

The asymmetric hydrogenation of biomass-derived molecules for the preparation of single enantiomer compounds is an effective method to reduce the rapid consumption of fossil resources. Porous organic frameworks (POFs) with pure organic surfaces may provide unusual confinement effects for organic substrates in chiral catalysis. Here, a series of POF catalysts are designed with chiral active centers decorated into sharply defined one-dimensional channels with diameters in the range of 1.2-2.9 nm. Due to the synergistic effect originating from the conjugated inner wall, the POF material (aperture size 2.4 nm) concentrates over 90% of aromatic species into the porous architecture, and its affinity is one or two orders of magnitude higher than those of classical porous solids. As determined by PBE+D3 calculation, the phenyl fragment reveals strong π-π interaction for steric hindrance around the metal active site to achieve stronger asymmetric induction. Therefore, this POF catalyst achieves high conversion (>99% yield) and enantioselectivity (>99% ee) for various substrates. The advantages of using the POF platform as a chiral catalyst can provide new perspectives on POF-based solid-state host-guest chemistry and asymmetric heterogeneous catalysis.

Fine Regulation of Porous Architectures of Core-Shell Silica Nanocomposites Offers Robust Nanoprobes with Accelerated Responsiveness

Probes bearing good aqueous solubility and biocompatibility as well as fast response can serve as ideal tools for evaluating the underlying molecular mechanism of endogenous production of H₂S caused by drugs; however, they are still lacking but highly desirable. Here, we demonstrate a novel strategy for constructing highly efficient H₂S nanoprobes through locking Förster resonance energy transfer borondipyrromethene (BODIPY) pairs in water-dispersible core-shell silica nanoparticles. Importantly, these nanocomposites can effectively confine complementary guests within the same cores due to the existence of a shield, thus guaranteeing efficient Förster resonance energy transfer. Interestingly, the interior microenvironment of such nanoparticles could be tuned by silylation agents. In this way, an ideal probe for rapid and ratiometric detection of H₂S within 15 s is established by optimizing the amount of silylation agent with a polar organic group. Obviously, the silylation agents are explored to serve as a platform not only for establishment of robust structures but also for optimizing the microenvironment of the interior to afford an ideal probe. These silica nanocomposites have also been successfully employed in disclosing the endogenous production of H₂S induced by estrogen in cardiomyocytes.

Photoacoustic probes for real-time tracking of endogenous H2S in living mice

H₂S is a key chemical mediator that exerts a vital role in diverse physiological and pathological processes. However, in vivo tracking of endogenous H₂S generation still remains difficult due to the lack of reliable analytical methods. Herein, we present the first example of activatable photoacoustic probes for real-time imaging of H₂S in living mice through the full utilization of the superiority of photoacoustic imaging modality at fine spatial resolution during deep tissue penetration. The designed probe can generate high NIR absorption at 780 nm in the presence of H₂S, thus producing a strong photoacoustic signal output in the NIR region. Furthermore, this probe exhibits extremely fast and highly selective responsiveness, good water-solubility and excellent biocompatibility. In light of these outstanding features, this probe realizes the direct photoacoustic trapping of endogenous H₂S generation in a HCT116 tumor-bearing mouse model. These preliminary imaging studies show that HCT116 colon tumors exhibit CBS upregulation activity, resulting in an increased rate of H₂S generation.

Asymmetric Transfer Hydrogenation of Imines in Water by Varying the Ratio of Formic Acid to Triethylamine

Asymmetric transfer hydrogenation (ATH) of imines has been performed with variation in formic acid (F) and triethylamine (T) molar ratios in water. The F/T ratio is shown to affect both the reduction rate and enantioselectivity, with the optimum ratio being 1.1 in the ATH of imines with the Rh-(1S,2S)-TsDPEN catalyst. Use of methanol as a cosolvent enhanced reduction activity. A variety of imine substrates have been reduced, affording high yields (94-98%) and good to excellent enantioselectivities (89-98%). In comparison with the common azeotropic F-T system, the reduction with 1.1/1 F/T is faster.

Asymmetric hydrogenation by RuCl2(R-Binap)(dmf)n encapsulated in silica-based nanoreactors

RuCl₂-(R-Binap)(dmf)_n encapsulated in silica-based nanoreactors: a solid catalyst as a whole, but a homogeneous catalyst on the nanoscale.

High-turnover supramolecular catalysis by a protected ruthenium(II) complex in aqueous solution

The design of a supramolecular catalyst capable of high-turnover catalysis is reported. A ruthenium(II) catalyst is incorporated into a water-soluble supramolecular assembly, imparting the ability to catalyze allyl alcohol isomerization. The catalyst is protected from decomposition by sequestration inside the host but retains its catalytic activity with scope governed by confinement within the host. This host-guest complex is a uniquely active supramolecular catalyst, capable of >1000 turnovers.