Comprehensive Basicity Scales for N-Heterocyclic Carbenes in DMSO: Implications on the Stabilities of N-Heterocyclic Carbene and CO2 Adducts.,Chemistry - An Asian Journal

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Comprehensive Basicity Scales for N-Heterocyclic Carbenes in DMSO: Implications on the Stabilities of N-Heterocyclic Carbene and CO2 Adducts.
Chemistry - An Asian Journal ( IF 3.5 ) Pub Date : 2019-11-27 , DOI: 10.1002/asia.201901418
Zhen Wang ₁ , Xiao-Song Xue _{1,

2} , Yanhua Fu ₁ , Pengju Ji ₃

Affiliation

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 (ΔGr s) for the reactions between the corresponding NHCs and CO2 were also calculated. There is a good linear correlation between the pKa s of most NHCPs and ΔGr s, 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.

中文翻译：

DMSO中N-杂环卡宾的综合碱度标度：对N-杂环卡宾和CO2加合物稳定性的影响。

具有约400个具有各种主链和电子特征的N-杂环卡宾前体（NHCP）的非常宽的酸度标度（约40 pK单位），包括咪唑基亚烷基，1,2,4-三唑基亚烷基，环二氨基卡宾（CDAC），二酰胺基卡宾（DAC） DMSO中，通过充分研究的计算方法建立了噻唑烷，环状（烷基）（氨基）卡宾（CAAC）和中离子碳烯（MIC）。取决于取代基的性质和数量，改变主链结构或侧接的N-取代基可具有不同程度的酸化作用。还计算了相应的NHC与CO2之间反应的吉布斯能量（ΔGrs）。大多数NHCP的pKa s与ΔGrs之间具有良好的线性相关性，这表明NHC的碱度越高，NHC-CO2加合物的稳定性就越高。有趣的是，

更新日期：2019-12-13

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