675877-56-2

Upstream product

• 124-38-9 carbon dioxide 
• 141556-42-5 [1,3-bis(2,4,6-trimethylphenyl)imidazol]-2-ylidene 
• 141556-45-8 1,3-bis(mesityl)imidazolium chloride 

Relevant academic research and scientific papers

Reversible carboxylation of N-heterocyclic carbenes

Spectroscopic analysis, thermogravimetric analysis, and cross-over experiments performed on a series of imidazolium carboxylates revealed carboxylation was reversible with N-aryl substituted adducts.

Synthesis of mono- and bis-N-heterocyclic carbene copper(I) complexes via decarboxylative generation of carbenes

Zwitterionic carboxylates can be thermally decarboxylated in the presence of copper salts to form NHC-copper complexes. The selective formation of either mono- or bis-NHC complexes is possible through simple control of the molar equivalents of the copper

N-Heterocyclic Carbene Based Tri-organyl-Zn–Alkyl Cations: Synthesis, Structures, and Use in CO2 Functionalization

Tri-organyl and tricoordinate N-heterocyclic carbene (NHC) Zn–NHC alkyl cations [(nNHC)2Zn-Me]+ (nNHC=C2-bonded-IMes/-IDipp; 3+ and 4+; IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were first synthesized and structurally characterized by ionization of the corresponding neutral precursors [(nNHC)ZnMe2] with [Ph3C][B(C6F5)4] in the presence of one equivalent of free NHC. Whereas cation [(nIMes)2Zn-Me]+ (3+) is stable, its sterically congested analogue [(nIDipp)2Zn-Me]+ (4+) readily undergoes an nNHC-to-aNHC isomerization in the presence of THF or IDipp to afford the more thermodynamically stable [(aIDipp)(nIDipp)Zn-Me]+ (aIDipp=C4-bonded IDipp, 5+), reflecting the adaptable-to-sterics coordination chemistry of these cations for improved stability. Cations 3+–5+ are the first Zn cations of the type Zn(C)(C′)(C′′)+ (C, C′, C′′=σ-donor carbyl ligand). Kinetic studies combined with DFT calculations agree with an nNHC-to-aNHC process proceeding through the initial deprotonation of 4+ (at a Zn-bonded C4-IDipp moiety) by IDipp. Unlike 3+ and 4+, the rearranged cation 5+ reacts with CO2 through insertion into the Zn–Me bond yielding the corresponding Zn(κ2-OAc)+ cation 6+. Both cations 5+ and 6+ were successfully used in CO2 hydrosilylation catalysis for silylformate formation.

Highly Modular Piano-Stool N-Heterocyclic Carbene Iron Complexes: Impact of Ligand Variation on Hydrosilylation Activity

The piano-stool configuration combined with N-heterocyclic carbene (NHC) ligation constitutes an attractive scaffold for employing iron in catalysis. Here, we have expanded this scaffold by installing a pentamethyl cyclopentadienyl (Cp*) ligand as a strong electron donor compared to the traditionally used unsubstituted cyclopentadiene (Cp). Moreover, decarboxylation is introduced as a method to prepare these iron(II) NHC complexes, which avoids the isolation of air-sensitive free carbenes. In addition to the Cp/Cp? variation, the complexes have been systematically modulated at the NHC scaffold, the NHC wingtip groups, and the ancillary ligands in order to identify critical factors that govern the catalytic activity of the iron center in the hydrosilylation of aldehydes. These modulations reveal the importance of steric tailoring and optimization of electron density for high catalytic performance. The data demonstrate a critical role of the NHC scaffold with triazolylidenes imparting consistently higher activity than imidazolylidenes and a correlation between catalytic activity and steric rather than electronic factors. Moreover, the implementation of steric bulk is strongly dependent on the nature of the NHC and severely limited by the Cp? iron precursor. The best performing catalytic systems reach turnover frequencies, TOFmax's, of up to 360 h-1 at 60 °C. Mechanistic investigations by 1H NMR and in situ IR spectroscopies indicate a catalyst activation that involves CO release and aldehyde coordination to the [Fe(Cp)(NHC)I] fragment.

Efficient conversion of CO2into cyclic carbonates at room temperature catalyzed by Al-salen and imidazolium hydrogen carbonate ionic liquids

A novel process for the efficient synthesis of cyclic carbonates from CO2 and epoxides at room temperature in the absence of a solvent has been achieved by using Al-salen complexes as catalysts and imidazolium hydrogen carbonate ionic liquids ([CnCmIm][HCO3]) as cocatalysts. As a halide ion-free cocatalyst, [CnCmIm][HCO3] showed higher catalytic reactivity compared to traditional halogen-containing quaternary ammonium salts (such as (nBu)4NBr) and organic bases. The catalytic system can be used for the cycloaddition of a series of substrates with good to excellent yields at room temperature in the absence of a solvent. Besides, the catalytic system can be easily recycled at least four times without significant loss of catalytic activity. A possible mechanism was proposed, in which Al-salen and carbene activate the epoxides and CO2 respectively.

Highly regio- And stereoselective synthesis of cyclic carbonates from biomass-derived polyols: Via organocatalytic cascade reaction

The cascade reaction of CO2, vicinal diols, and propargylic alcohol, was firstly achieved by dual Lewis base (LB) organocatalytic systems involving LB-CO2 adducts and commercially available organic amines. This methodology could overcome the chemical inertness of CO2, providing an alternative route to various functionalized five-membered cyclic carbonates in moderate to high yields under mild reaction conditions (25 °C, 1.0 atm of CO2). More importantly, this method could also be applied for facile and efficient synthesis of chiral polycyclic carbonates from biomass-derived polyols with complete configuration retention of chiral centers. This study provides an environment-friendly, scalable and cost effective protocol to construct value-added cyclic carbonates with multi-functional groups and chiral centers.

Imidazolium hydrogen carbonates versus imidazolium carboxylates as organic precatalysts for N-heterocyclic carbene catalyzed reactions

Imidazolium-2-carboxylates (NHC-CO2 adducts, 3) and (benz)imidazolium hydrogen carbonates ([NHC(H)][HCO3], 4) were independently employed as organic precatalysts for various molecular N-heterocyclic carbene (NHC) catalyzed reactions. NHC-CO2 adducts were obtained by carboxylation in THF of related free NHCs (2), while the synthesis of [NHC(H)][HCO3] precursors was directly achieved by anion metathesis of imidazolium halides (1) using potassium hydrogen carbonate (KHCO3) in methanolic solution, without the need for the prior preparation of free carbenes. Thermogravimetric analysis (TGA) and TGA coupled with mass spectrometry (TGA-MS) of most [NHC(H)][HCO3] precursors 4 showed a degradation profile in stages, with either a concomitant or a stepwise release of H2O and CO2, between 108 and 280 °C, depending on the nature of the azolium and substituents. In solution, NHC generation from both [NHC(H)][HCO3] salts and NHC-CO2 adducts could be achieved at room temperature, most likely by a simple solvation effect. Both types of precursors proved efficient for organocatalyzed molecular reactions, including cyanosilylation, benzoin condensation, and transesterification reactions. The catalytic efficiencies of NHC-CO2 adducts 3 were found to be approximately 3 times higher than those of their [NHC(H)][HCO3] counterparts 4.

Imidazol(in)ium-2-carboxylates as efficient precursors to N-heterocyclic carbene complexes of copper and silver

Copper and silver N-heterocyclic carbene (NHC) complexes were prepared through a simple, base-free protocol involving the decomposition of corresponding imidazol(in)ium-2-carboxylates under thermolytic conditions and a subsequent reaction of the in situ g

A systematic investigation of factors influencing the decarboxylation of imidazolium carboxylates

(Chemical Equation Presented) A series of 1,3-disubstituted-2-imidazolium carboxylates, an adduct of CO2 and N-heterocyclic carbenes, were synthesized and characterized using single crystal X-ray, thermogravimetric, IR, and NMR analysis. The TG

Imidazol(in)ium-2-carboxylates as N-heterocyclic carbene precursors in ruthenium-arene catalysts for olefin metathesis and cyclopropanation

Five imidazol(in)ium-2-carboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon dioxide. They were characterized by IR and NMR spectroscopies, and by TGA. Their ability to act as NHC precursors for in situ catalytic applications was probed in ruthenium-promoted olefin metathesis and cyclopropanation reactions. When visible light induced ring-opening metathesis polymerization of cyclooctene or cyclopropanation of styrene with ethyl diazoacetate were carried out at 60 °C in the presence of [RuCl2(p-cymene)]2, the NHC · CO2 adducts and their NHC · HX counterparts (X = Cl, BF4) displayed similar activities. When metathesis polymerizations were performed at room temperature, the carboxylates proved far superior to the corresponding imidazol(in)ium acid salts. They displayed the same level of activity as the preformed RuCl2(p-cymene)(IMes) complex, whereas the combination of NHC · HX and KO-t-Bu were almost totally inactive. Results obtained for cyclopropanation reactions at room temperature did not show such a large discrepancy of behavior between the two types of adducts.