Highly Efficient Conversion of Propargylic Amines and CO 2 Catalyzed by Noble‐Metal‐Free [Zn 116 ] Nanocages

Biomass-Based N-Rich Porous Carbon Materials for CO2 Capture and in-situ Conversion

Capturing CO₂ and subsequently converting into valuable chemicals has attracted extensive attention. Herein, a series of biomass-based N-rich porous carbon materials with high specific surface area and pore volume were prepared using biomass waste soybean dregs as precursors. The nitrogen content was up to 4 % with different forms in the carbon skeleton such as pyridine-N, pyrrole-N. The synergistic effect of ultra-micropore (pore size <0.7 nm) and N-containing groups endowed the materials with a high CO₂ adsorption capacity, reaching 6.3 and 3.6 mmol g^-1 at 0 and 25 °C under atmospheric pressure, respectively. In addition, the sufficient interaction between N-containing groups and CO₂ was demonstrated by solid-state nuclear magnetic resonance spectroscopy, and the captured CO₂ was possibly activated in the form of carbamate, which is conducive to subsequent conversion. Therefore, the supported catalyst with the as-synthetic porous carbon material as the carrier and Zn^II as catalytic sites was prepared and successfully applied for carboxylative cyclization of propargylic amine with CO₂ to afford the 3-benzyl-5-methyleneoxazolidin-2-one. The results showed that CO₂ capture and in-situ conversion work effectively to produce highly value-added chemicals. In this process, the captured CO₂ could be activated and fixed into chemicals in mild conditions. More importantly, the energy consumption in CO₂ desorption and adsorbent regeneration could be avoided. The valorization of both solid waste and CO₂ to valuable chemicals provides an elegant strategy of killing three birds with one stone.

Highly Efficient Conversion of Propargylic Alcohols and Propargylic Amines with CO2 Activated by Noble-Metal-Free Catalyst Cu2 O@ZIF-8

The cyclization reactions of propargylic alcohols and propargylic amines with CO₂ are important in industrial applications, but it was a great challenge that non-noble-metal catalysts catalyzed both reactions under mild conditions. Herein, the catalyst Cu₂ O@ZIF-8 was prepared by encapsulating Cu₂ O nanoparticles into robust ZIF-8, and it can effectively catalyze the cyclization of both propargylic alcohols and propargylic amines with CO₂ into valuable α-alkylidene cyclic carbonates and oxazolidinones with turnover numbers (TONs) of 12.1 and 19.6, which can be recycled at least five times. The mechanisms were further uncovered by NMR, FTIR, ¹³ C isotope-labeling experiments and DFT calculations, in which Cu₂ O and DBU can synergistically activate the C≡C bond and the hydroxy/amino group of substrates. Importantly, it is the first example of a noble-metal-free catalyst that can catalyze both propargylic alcohols and propargylic amines with CO₂ simultaneously.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal-Organic Frameworks

Cyclization of propargylamines with CO₂ to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique Cu^I /Cu^II mixed valence copper-based framework {[(Cu^I ₆ I₅ )Cu₃ ^II L₆ (DMA)₃ ](NO₃ )⋅9DMA}_n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO₂ , and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h^-1 , which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO₂ without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between Cu^I /Cu^II and uncoordinated amino groups promotes highly efficient and green conversion of CO₂ . Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO₂ source.

Expanded Ring NHC Silver Carboxylate Complexes as Efficient and Reusable Catalysts for the Carboxylative Cyclization of Unsubstituted Propargylic Derivatives

Stabilized by a bulky N-heterocyclic carbene [^BP DPr, 1,3-bis(2,6-diisopropylphenyl)-1,3-diazonine-2-ylidene] ligand, new silver carboxylate complexes of the form ^BP DPrAgO₂ C-R (R=Me, Ph) have been synthesized and fully characterized in solution and in the solid state and implemented as sole catalysts (base-, additive-, and, in some cases, solvent-free) in the challenging fixation of carbon dioxide to unsubstituted propargylic derivatives for the synthesis of oxazolidinones and α-methylene cyclic carbonates. Derived from X-ray diffraction studies, the molecular geometry and the concept of buried volume were employed to describe the structural and steric features of these silver complexes. Their stability and efficiency as catalysts have been demonstrated by the synthesis of 29 carboxylation products (72-98 % yield) at low catalyst loadings (0.01-1.5 mol%). Characteristics are high turnover numbers (up to 9400), catalyst recyclability (up to 96 % yield after the 7th cycle with no decomposition of the silver complex), and the possibility to scale-up the reaction.

Construction of Hybrid Bimetallic Uranyl Compounds Based on a Preassembled Terpyridine Metalloligand

Six hybrid uranyl-transition metal compounds [UO₂ Ni(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (1), [UO₂ Ni(cptpy)₂ (BTPA)₂ ] (2), [UO₂ Fe(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (3), [UO₂ Fe(cptpy)₂ (BTPA)₂ ] (4), [UO₂ Co(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (5), and [UO₂ Co(cptpy)₂ (BTPA)₂ ] (6), based on bifunctional ligand 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine (Hcptpy) are reported (H₂ BTPA = 4,4'-biphenyldicarboxylic acid). Single-crystal XRD revealed that all six compounds feature similar metalloligands, which consist of two cptpy^- anions and one transition metal cation. The metalloligand M(cptpy)₂ can be considered to be an extended linear dicarboxylic ligand with length of 22.12 Å. Compounds 1, 3, and 5 are isomers, and all of them feature 1D chain structures. The adjacent 1D chains are connected together by hydrogen bonds and π-π interactions to form a 3D porous structure, which is filled with solvent molecules and can be exchanged with I₂ . Compounds 2, 4, and 6 are also isomers, and all of them feature 2D honeycomb (6,3) networks with hexagonal units of dimensions 41.91×26.89 Å, which are the largest among uranyl compounds with honeycomb networks. The large aperture allows two sets of equivalent networks to be entangled together to result in a 2D+2D→3D polycatenated framework. Remarkably, these uranyl compounds exhibit high catalytic activity for cycloaddition of carbon dioxide. Moreover, the geometric and electronic structures of compounds 1 and 2 are systematically discussed on the basis of DFT calculations.