Comprehensive Basicity Scales for N‐Heterocyclic Carbenes in DMSO: Implications on the Stabilities of N‐Heterocyclic Carbene and CO2 Adducts. Issue 1 (12th December 2019)

• Record Type: Journal Article
• Authors: Wang, Zhen; Xue, Xiao‐Song; Fu, Yanhua; Ji, Pengju
• Is Part Of: Chemistry, an Asian journal. Volume 15:Issue 1(2020)
• Page Start: 169
• Page End: 181
• Publication Date: 2019-12-12
• Subjects: Acidity Scale -- Gibbs Reaction Energy -- Linear Correlation -- NHC-CO2 Stability -- N-Heterocyclic Carbenes; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201901418
• Languages: English
• ISSNs: 1861-4728

Abstract

Abstract: A very broad acidity scale (≈40 p K 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 (Δ G r s) for the reactions between the corresponding NHCs and CO2 were also calculated. There is a good linear correlation between the p K a s of most NHCPs and Δ G r 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 Δ G r values. Abstract : The basicities of nearly 400 N‐heterocyclic carbenes (NHCs) and their corresponding Gibbs energies for the reaction of NHC and CO2 (Δ G r ) were calculated in DMSO. A good linear correlation exists between the p K a s of most NHCPs and Δ G r values, suggesting that a stronger basicity leads to a more stable NHC‐CO2 adduct.