Yuya Hu

Direct and inexpensive: A palladium‐catalyzed highly stereoselective sulfonylation of vinylethylene carbonates for the precise synthesis of structurally diverse (Z)‐allylic sulfones was achieved with excellent regioselectivity and stereoselectivity (Z/E ratio, up to 99 : 1).

Abstract

A palladium‐catalyzed highly stereoselective sulfonylation of vinylethylene carbonates for the precise synthesis of structurally diverse (Z)‐allylic sulfones was achieved with excellent regioselectivity and stereoselectivity (Z/E ratio, up to 99 : 1). This protocol used inexpensive sodium sulfinates as sulfonyl sources to construct valuable (Z)‐allylic sulfones in good to excellent yields. The controlling experiment suggested that the hydroxyl proton came from the α‐hydrogen of sulfone group through 1, 5‐H shift.

State of N ‐pendants: A series of dimeric aluminum compounds containing heterocyclic pendant groups attached to the nitrogen catalyze the coupling of CO₂ with epoxides under ambient conditions. In a comparison of their catalytic activities with those of aluminum complexes without pendant groups or with non‐heterocyclic groups at N, the complexes containing heterocycles, in show higher catalytic activities for the synthesis of cyclic carbonates.

Abstract

A series of dimeric aluminum compounds [Al(OCMe₂CH₂N(R)CH₂X)]₂ [X=pyridin‐2‐yl, R=H (Pyr^H ); X= pyridin‐2‐yl, R=Me (Pyr^Me ); X=furan‐2‐yl, R=H (Fur^H ); X= furan‐2‐yl, R=Me (Fur^Me ); X=thiophen‐2‐yl, R=H (Thio^H ); X= thiophen‐2‐yl, R=Me (Thio^Me )] containing heterocyclic pendant group attached to the nitrogen catalyze the coupling of CO₂ with epoxides under ambient conditions. In a comparison of their catalytic activities with those of aluminum complexes without pendant groups at N [X=H, R=H (H^H ); X=H, R=Me (H^Me )] or with non‐heterocyclic pendant groups [X=CH₂CH₂OMe, R=H (OMe^H ); X=CH₂CH₂NMe₂, R=H (NMe2^H ); X=CH₂CH₂NMe₂, R=Me (NMe2^Me )], complexes containing heterocycles, in conjunction with (nBu)₄NBr as a cocatalyst, show higher catalytic activities for the synthesis of cyclic carbonates under the same ambient conditions. The best catalyst system for this reaction is Pyr^H/(nBu)₄NBr system, which gives a turnover number of 99 and a turnover frequency of 4.1 h⁻¹, making it 14‐ and 20‐times more effective than H^H/(nBu)₄NBr and H^Me/(nBu)₄NBr, respectively. Although there are no direct interactions between the aluminum and the heteroatoms in the heterocyclic pendants, electronic effects combined with the increased local concentration of CO₂ around the active centers influences the catalytic activity in the coupling of CO₂ with epoxides. In addition, Pyr^H/(nBu)₄NBr shows broad epoxide substrate scope and seven terminal epoxides and two internal epoxides undergo the designed reaction.

Fine‐tuning energy levels: A three‐dimensional porous fluorographdiyne network on carbon cloth serves as an active metal‐free catalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as overall water splitting (OWS) under acidic as well as alkaline conditions. The strong F−C bonding modifies the local p–p coupling, which affects the filling of the electronic orbitals.

Abstract

A highly efficient bifunctional metal‐free catalyst was prepared by growth of three‐dimensional porous fluorographdiyne networks on carbon cloth (p‐FGDY/CC). Our experiments and density functional theory (DFT) calculations show the 3D p‐FGDY/CC network is highly active and it is a high potential metal‐free catalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as overall water splitting (OWS) under both acidic and alkaline conditions. The experimental and theoretical results show very good consistency; for example, in the HER process, p‐FGDY/CC exhibits small overpotentials of 82 and 92 mV to achieve 10 mA cm⁻² under alkaline and acidic conditions, respectively. This ensures an even higher selectivity for the adsorption/desorption of various O/H intermediate species. The essential key promotion accomplishes a bifunctional H₂O redox performance application under pH‐universal electrochemical conditions.

Biomimetic heterogeneous catalysts: Multifunctional metalloporphyrin covalent ionic frameworks with a highly porous structure for cooperative catalysis by Lewis acidic metal sites and nucleophilic Br⁻ ions showed efficient catalytic activity in CO₂ cycloaddition to epoxides (see figure), and the catalytic performance could be further enhanced by altering the functional groups and the BET surface area.

Abstract

The development of multifunctional heterogeneous catalysts with high porosity and remarkable catalytic activity still remains a challenge. Herein, four highly porous metalloporphyrin covalent ionic frameworks (CIFs) were synthesized by coupling 5,10,15,20‐tetrakis(4‐nitrophenyl)porphyrin (TNPP) with 3,8‐diamino‐6‐phenylphenanithridine (NPPN) or 5,5′‐diamino‐2,2′‐bipyridine (NBPy) followed by ionization with bromoethane (C₂H₅Br) or dibromoethane (C₂H₄Br₂) and then metalization with Zn or Co. The resulting CIFs showed high efficiency in catalyzing the cycloaddition of propylene oxide (PO) with CO₂ to form propylene carbonate (PC). All of the Zn‐containing CIF catalysts were able to catalyze the cycloaddition reaction with a PC yield greater than 97 %. The TNPP/NBPy (CIF2) catalyst ionized with C₂H₄Br₂ and metalized with Zn (Zn‐CIF2‐C₂H₄) exhibited the highest catalytic activity among the synthesized catalysts. The high catalytic performance of Zn‐CIF2‐C₂H₄ is related to its high porosity (577 m² g⁻¹), high Br:metal ratio (1:3.89), and excellent synergistic action between the Lewis acidic Zn sites and the nucleophilic Br⁻ ions. Zn‐CIF2‐C₂H₄ is sufficiently stable that greater than 94 % PC yield could be obtained even after six cycles. In addition, Zn‐CIF2‐C₂H₄ could catalyze the cycloaddition of several other epoxides with CO₂. These highly porous materials are promising multifunctional and efficient catalysts for industrially relevant reactions.

Multi‐task catalysts: Unique self‐assembled macrocyclic multinuclear Zn^II and Ni^II complexes with binaphthyl–bipyridyl ligands (L) were synthesized. These complexes consisted of an outer ring (Zn₃L₃ or Ni₃L₃) and an inner core (Zn₂ or Ni). These complexes acted as multitask catalysts for CO₂ fixations.

Abstract

Unique self‐assembled macrocyclic multinuclear Zn^II and Ni^II complexes with binaphthyl‐bipyridyl ligands (L) were synthesized. X‐ray analysis revealed that these complexes consisted of an outer ring (Zn₃L₃ or Ni₃L₃) and an inner core (Zn₂ or Ni). In the Zn^II complex, the inner Zn₂ part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO₂ fixations: synthesis of cyclic carbonates from epoxides and CO₂ and temperature‐switched N‐formylation/N‐methylation of amines with CO₂ and hydrosilane.

Just add water: Water acts as a hydrogen bond donor under very mild reaction conditions [25–45 °C, p(CO₂)=10 bar], boosting the performance of organic iodides in catalyzing the fixation of CO₂ into cyclic carbonates. The efficiency of water in promoting the activity of the organic halide is compared with three state‐of‐the‐art hydrogen bond donors (i.e., phenol, gallic acid and ascorbic acid).

Abstract

The role of water as highly effective hydrogen‐bond donor (HBD) for promoting the coupling reaction of CO₂ with a variety of epoxides was demonstrated under very mild conditions (25–60 °C, 2–10 bar CO₂). Water led to a dramatic increase in the cyclic carbonate yield when employed in combination with tetrabutylammonium iodide (Bu₄NI) whereas it had a detrimental effect with the corresponding bromide and chloride salts. The efficiency of water in promoting the activity of the organic halide was compared with three state‐of‐the‐art hydrogen bond donors, that is, phenol, gallic acid and ascorbic acid. Although water required higher molar loadings compared to these organic hydrogen‐bond donors to achieve a similar degree of conversion of CO₂ and styrene oxide into the corresponding cyclic carbonate under the same, mild reaction conditions, its environmental friendliness and much lower cost make it a very attractive alternative as hydrogen‐bond donor. The effect of different parameters such as the amount of water, CO₂ pressure, reaction temperature, and nature of the organic halide used as catalyst was investigated by using a high‐throughput reactor unit. The highest catalytic activity was achieved with either Bu₄NI or bis(triphenylphosphine)iminium iodide (PPNI): with both systems, the cyclic carbonate yield at 45 °C with different epoxide substrates could be increased by a factor of two or more by adding water as a promoter, retaining high selectivity. Water was an effective hydrogen‐bond donor even at room temperature, allowing to reach 85 % conversion of propylene oxide with full selectivity towards propylene carbonate in combination with Bu₄NI (3 mol %). For the conversion of epoxides in which PPNI is poorly soluble, the addition of a cyclic carbonate as solvent allowed the formation of a homogeneous solution, leading to enhanced product yield.

Oxazolidinone synthesis by the coupling of carbon dioxide and aziridines is catalysed by an aluminium(salphen) complex at 50‐100 oC and 1‐10 bar pressure under solvent‐free conditions. The process is applicable to a variety of substituted aziridines, giving products with high regioselectivity. It involves the use of a sustainable and reusable aluminium‐based catalyst, uses carbon dioxide as a C‐1 source and provides access to pharmaceutically important oxazolidinones as illustrated by a total synthesis of toloxatone. This protocol is scalable and the catalyst can be recovered and reused. A catalytic cycle is proposed based on stereochemical, kinetic and Hammett studies.

Herein, we report a modular synthetic route to linear and branched homoallylic amines that operates via a sequential one‐pot Lewis base/transition metal catalyzed allylic alkylation/Hofmann rearrangement strategy. This protocol is operationally trivial, proceeds from simple and easily prepared substrates and catalysts, and enables all aspects of regio‐ and stereoselectivity to be controlled via a conserved experimental protocol. Overall, the high levels of enantio‐, regio‐ and diastereoselectivity obtained, in concert with the ability to access orthogonally‐protected or free amines, render this a straightforward and effective approach for the preparation of useful enantioenriched homoallylic amines. We have also demonstrated the utility of the products in the context pharmaceutical synthesis.