Substituted epoxy alcohols and amines allow substrate‐controlled conversion of CO2 into a wide range of heterocyclic structures through different mechanistic manifolds. This new approach results in an unusual scope of CO2‐derived products by initial activation of CO2 through either the amine or alcohol unit, thus providing nucleophiles for intramolecular epoxy ring opening under mild reaction conditions. Control experiments support the crucial role of the amine/alcohol fragment in this process with the nucleophile‐assisted ring‐opening step following an SNi pathway, and a 5‐exo‐tet cyclization, thus leading to heterocyclic scaffolds. 相似文献
Discovery of the mechanisms for selective transformations of CO2 into organic compounds is a challenge. Herein, we describe the reaction of low‐coordinate Fe silylamide complexes with CO2 to give trimethylsilyl isocyanate and the corresponding Fe siloxide complex. Kinetic studies show that this is a two‐stage reaction, and the presence of a single equivalent of THF influences the rates of both steps. Isolation of a thermally unstable intermediate provides mechanistic insight that explains both the effect of THF in this reaction, and the way in which the reaction achieves high selectivity for isocyanate formation. 相似文献
Activate and reduce : Carbon dioxide was reduced with silane using a stable N‐heterocyclic carbene organocatalyst to provide methanol under very mild conditions. Dry air can serve as the feedstock, and the organocatalyst is much more efficient than transition‐metal catalysts for this reaction. This approach offers a very promising protocol for chemical CO2 activation and fixation.
We carried out a principle study on the reaction mechanism of rhodium‐catalyzed intramolecular aziridination and aziridine ring opening at a sugar template. A sulfamate ester group was introduced at different positions of glycal to act as a nitrene source and, moreover, to allow the study of the relative reactivity of the nitrene transfer from different sites of the glycal molecule. The structural optimization of each intermediate along the reaction pathway was extensively done by using BPW91 functional. The crucial step in the reaction is the Rh‐catalyzed nitrene transfer to the double bond of the glycal. We found that the reaction could proceed in a stepwise manner, whereby the N atom initially induced a single‐bond formation with C1 on the triplet surface or in a single step through intersystem crossing (ISC) of the triplet excited state of the rhodium–nitrene transition state to the singlet ground state of the aziridine complexes. The relative reactivity for the conversion of the nitrene species to the aziridine obtained from the computed potential energy surface (PES) agrees well with the reaction time gained from experimental observation. The aziridine ring opening is a spontaneous process because the energy barrier for the formation of the transition state is very small and disappears in the solution calculations. The regio‐ and stereoselectivity of the reaction product is controlled by the electronic property of the anomeric carbon as well as the facial preference for the nitrene insertion, and the nucleophilic addition. 相似文献
A one‐step conversion of CO2 into heteroaromatic esters is presented under metal‐free conditions. Using fluoride anions as promoters for the C?Si bond activation, pyridyl, furanyl, and thienyl organosilanes are successfully carboxylated with CO2 in the presence of an electrophile. The mechanism of this unprecedented reaction has been elucidated based on experimental and computational results, which show a unique catalytic influence of CO2 in the C?Si bond activation of pyridylsilanes. The methodology is applied to 18 different esters, and it has enabled the incorporation of CO2 into a polyester material for the first time. 相似文献
The synthesis of N‐arylimidazoles substituted at the sterically encumbered 5‐position is a challenge for modern synthetic approaches. A new family of imidazolyl aryliodonium salts is reported, which serve as a stepping stone on the way to selective formation of N1‐aryl‐5‐iodoimidazoles. Iodine acts as a “universal” placeholder poised for replacement by aryl substituents. These new λ3‐iodanes are produced by treating the NH‐imidazole with ArI(OAc)2, and are converted to N1‐aryl‐5‐iodoimidazoles by a selective copper‐catalyzed aryl migration. The method tolerates a variety of aryl fragments and is also applicable to substituted imidazoles. 相似文献
Frustrated Lewis pairs (FLP), a couple comprising a sterically encumbered Lewis acid and Lewis base, can offer latent reactivity for activating inert gas molecules. However, their use as a platform for fabricating gas‐responsive materials has not yet developed. Merging the FLP concept with polymers, we report a new generation CO2‐responsive system, differing from the first‐generation ones based on an acid–base equilibrium mechanism. Two complementary Lewis acidic and basic block copolymers, installing bulky borane‐ and phosphine‐containing blocks, were built as the macromolecular FLP. They can bind CO2 to drive micellar formation, in which CO2 as a cross‐linker bridges the block chains. This dative bonding endows the assembly with ultrafast response (<20 s), thermal reversibility, and excellent reproducibility. Moreover, such micelles bound highly active CO2 can function as nanocatalysts for recyclable C1 catalysis, opening a new direction of sustainable CO2 conversion. 相似文献
A very broad acidity scale (≈40 pK units) for about 400 N‐heterocyclic carbene precursors (NHCPs) with various backbones and electronic features, including imidazolylidenes, 1,2,4‐triazolylidenes, cyclic diaminocarbenes (CDACs), diamidocarbenes (DACs), thiazolylidenes, cyclic (alkyl)(amino)carbenes (CAACs) and mesoionic carbenes (MICs), was established in DMSO by a well examined computational method. Varying the backbone structure or flanking N‐substituents can have different extent of acidifying effects, depending on both the nature and number of substituent(s). The Gibbs energies (ΔGrs) for the reactions between the corresponding NHCs and CO2 were also calculated. There is a good linear correlation between the pKas of most NHCPs and ΔGrs, suggesting that a greater basicity of NHC leads to a more stable NHC‐CO2 adduct. Interestingly, the nearby asymmetric environment has virtually no differential effect on the acidities of the chiral NHCP enantiomers, but has a pronounced effect on the ΔGr values. 相似文献
Getting a fix : N‐heterocyclic carbenes (NHCs) and NHC–CO2 adducts serve as potent organocatalysts for carbonate synthesis by the addition of a CO2 unit to propargylic alcohols or epoxides under mild and solvent‐free reaction conditions (see scheme). The enhanced Lewis basicity of imidazol‐2‐ylidenes bearing electron‐donating alkyl groups on the nitrogen atoms leads to utilizing CO2 as a nucleophilic fragment in the chemical fixation processes.
The purpose of this research idea is to develop a method to electrochemically convert carbon dioxide into higher alcohol chains such as ethanol to be used as fuel. Electrochemical CO2 reduction has low yields and poor product selectivity, being able to improve this reaction would have an impact in the energy and food market. We propose the use of a modified nanofluidic transistor to block reaction steps that are thermodynamically favored by constraining the kinetics of the reaction when the reaction takes place in a geometrically restricted environment with different double layer properties to those found in conventional planar electrosynthesis. 相似文献
Gold nanoparticles in metallic or plasmonic state have been widely used to catalyze homogeneous and heterogeneous reactions. However, the catalytic behavior of gold catalysts in non‐metallic or excitonic state remain elusive. Atomically precise Aun clusters (n=number of gold atoms) bridge the gap between non‐metallic and metallic catalysts and offer new opportunities for unveiling the hidden properties of gold catalysts in the metallic, transition regime, and non‐metallic states. Here, we report the controllable conversion of CO2 over three non‐metallic Aun clusters, including Au9, Au11, and Au36, towards different target products: methane produced on Au9, ethanol on Au11, and formic acid on Au36. Structural information encoded in the non‐metallic clusters permits a precise correlation of atomic structure with catalytic properties and hence, provides molecular‐level insight into distinct reaction channels of CO2 hydrogenation over the three non‐metallic Au catalysts. 相似文献
The oriented conversion of CO2 into target high-value chemicals is an effective way to reduce carbon emissions, but still presents a challenge. In this communication, we report the oriented conversion of CO2 into value-added aromatics, especially para-xylene, in a single pass by combining core–shell structured Zn-doped H-ZSM-5 (Zn-ZSM-5@SiO2) and a Cr2O3 component. Through precise regulation of the acidity of Zn-ZSM-5@SiO2, high para-xylene selectivity (38.7 % in the total products) at a CO2 conversion of 22.1 % was achieved. Furthermore, a CO2-assisted effect in the synthesis of aromatics during the tandem process has been clarified through a control experiment. The CO2 reactant can act as a hydrogen acceptor to accelerate the dehydrogenation of alkenes, intermediates in the synthesis of aromatics, thereby increasing the driving force towards aromatics in the tandem reaction process. 相似文献