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13. Unexpected solvation-stabilisation of ions in a protic ionic liquid: insights disclosed by a bond energetic study† †Electronic supplementary information (ESI) available: Detailed pKa measurement procedures, indicators used in this work and their corresponding pKas in the PIL; UV-vis spectra for the representative measurements; and synthesis and characterisation of the PIL and salts. See DOI: 10.1039/c7sc05227h

Author

Wang, Zhen, Gao, Feixiang, Ji, Pengju, and Cheng, Jin-Pei

Subjects
Chemistry
Abstract

Accurate acidity studies of different families of substrates in a pure protic ionic liquid (PIL) show that solute ions in the PIL are free from specific ion associations and the solvation behaviour of PILs is closely related to the number of dissociable protons., Equilibrium acidities (pKas) of 42 organic acids were precisely determined in protic ionic liquid (PIL) [DBUH][OTf]. Surprisingly, the often seen homoassociation complication during the pKa measurement of O–H acids in DMSO was not detected in [DBUH][OTf], implying that the incipient oxanion should be better solvation-stabilized by the PIL, although its “apparent” dielectric constant is much lower than that of the conventional molecular solvent DMSO. Evidence showing that the solute ions in the PIL are also free from other specific ion associations like ion-pairing is further demonstrated by the identical pKas of protic amine salts bearing largely different counter-anions. Correlations between the RO–H, N–H, N+–H and RCOO–H bond acidities in [DBUH][OTf] and in water revealed different slopes and intercepts for each individual series, suggesting far superior properties of the DBUH+-based PIL for differentiating the solvation effect of various species in structural analysis to the well applied EAN that is known for leveling out differential solvation.

Published
2018

20. Is NO (nitric oxide) an electron acceptor or an electrophile? A detailed thermodynamic investigation on the mechanisms of NO-initiated reactions with 3,6-dibromocarbazolide anion and related carbanion

Author

Zhu, Xiao-Qing, Xian, Ming, Wang, Kun, and Cheng, Jin-Pei

Subjects
Thermodynamics -- Research, Nitric oxide -- Research, Electron donor-acceptor complexes -- Research, Biological sciences, Chemistry
Abstract

The first detailed thermodynamic analysis in terms of the driving forces for ach basic step for the nitric oxide (NO)-initiated reaction with 3,6-dibromocarbazolide is presented. It is shown that an electrophilic combination of NO with 3,6-dibromocarbazolide to form the incipient radical anion, followed by electron transfer from the latter to NO, represents the most feasible mechanism. Electron transfer from the electron-rich species to NO may be incorporated when the substrate is a better electron-providing species.

Published
1999

21. Effects of adjacent onium cations and remote substituents on the H-A+ bond equilibrium acidities in dimethyl sulfoxide solution. An extensive ylide thermodynamic stability scale and implication for the importance of resonance effect on ylide stabilities

Author

Cheng, Jin-Pei, Zhao, Yongyu, Liu, Bo, Sun, Yongkai, Zhang, Xian-Man, and Lu, Yun

Subjects
Cations -- Research, Hydrogen bonding -- Research, Dimethyl sulfoxide -- Research, Molecular orbitals -- Research, Stability -- Research, Biological sciences, Chemistry
Abstract

Research was conducted to examine the role of adjacent onium cations and remote substituents on the H-A+ bond equilibrium acidities in dimethyl sulfoxide solution. The study is an extension of previous investigation on ylide thermodynamic stability scale and its implication for the importance of resonance effect on ylide stabilities. Results suggest that part of the stabilization in the phosphonium and sulfonium ylide cases arises from the backbonding stabilization involving the o* and/or 3d orbital participation.

Published
1999

22. Diazaphospholene-Catalyzed Hydrodefluorination of Polyfluoroarenes with Phenylsilane via Concerted Nucleophilic Aromatic Substitution

Author

Zhang, Jingjing, Zhao, Xiao, Yang, Jin-Dong, and Cheng, Jin-Pei

Abstract

The metal-free catalytic C–F bond activation of polyfluoroarenes was achieved with diazaphospholene as the catalyst and phenylsilane as the terminal reductant. Density functional theory calculations suggested a concerted nucleophilic aromatic substitution mechanism.

Published
2022
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23. Homolytic bond dissociation energies of the acidic C-H bonds in alpha-substituted and 10-substituted 9-methylanthracenes and their related radical anions

Author

Zhang, Xian-Man, Bordwell, Frederick G., Bares, Joseph E., Cheng, Jin-Pei, and Petrie, Brian C.

Subjects
Dissociation -- Research, Radicals (Chemistry) -- Research, Oxidation-reduction reaction -- Research, Biological sciences, Chemistry
Abstract

Bond dissociation energies of the acidic C-H bonds in 13 alpha-substituted 9-mehtylanthracenes and 11 10-substituted methylanthracenes. This included equilibium acidity (pKHA), reduction potential Ere(HA), oxidation potential Eox(HA), and oxidation potential of conjugate anions Eox(A-) in dimethyl sulfoxide solution. Equilibrium acidities were linearly correlated with Hammettsigma negative constants. Combinations of equilibrium acidities were used to determine homolytic bond dissociation energies.

Published
1993

24. Acidities and hemolytic bond dissociation energies (BDEs) of benzyl-tyoe C-H bonds in sterically congested substrates

Author

Bordwell, F.G., Cheng, Jin-Pei, Satish, A.V., and Twyman, Cary L.

Subjects
Chemical bonds -- Research, Scission (Chemistry) -- Research, Biological sciences, Chemistry
Abstract

Bond dissociation energies and hydronium ion concentrations at equilibrium of benzylic carbon to hydrogen bonds in dimethyl sulfoxide are presented. Nineteen triphenylmethanes, three dihydroanthracenes and nine xanthenes were used in the experiment. The resonance effect due to the solvation of a substituent induced a conformational alteration to allow for conjugative overlap of the anion and the substituents. The effect of substituents far from the carbanion was found to be negligible.

Published
1992

25. Recent progress in reactivity study and synthetic application of N-heterocyclic phosphorus hydrides.

Author

Zhang, Jingjing, Yang, Jin-Dong, and Cheng, Jin-Pei

Subjects
CATALYTIC reduction, HYDRIDES, PHOSPHORUS, HYDROBORATION, UMPOLUNG, PHOSPHINES
Abstract

N-heterocyclic phosphines (NHPs) have recently emerged as a new group of promising catalysts for metal-free reductions, owing to their unique hydridic reactivity. The excellent hydricity of NHPs, which rivals or even exceeds those of many metal-based hydrides, is the result of hyperconjugative interactions between the lone-pair electrons on N atoms and the adjacent σ*(P–H) orbital. Compared with the conventional protic reactivity of phosphines, this umpolung P–H reactivity leads to hydridic selectivity in NHP-mediated reductions. This reactivity has therefore found many applications in the catalytic reduction of polar unsaturated bonds and in the hydroboration of pyridines. This review summarizes recent progress in studies of the reactivity and synthetic applications of these phosphorus-based hydrides, with the aim of providing practical information to enable exploitation of their synthetically useful chemistry. [ABSTRACT FROM AUTHOR]

Published
2021
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31. Origin of Stereoselectivity of the Photoinduced Asymmetric Phase-Transfer-Catalyzed Perfluoroalkylation of β-Ketoesters

Author

Yang, Chen, Zhang, Wei, Li, Yi-He, Xue, Xiao-Song, Li, Xin, and Cheng, Jin-Pei

Abstract

The sources of asymmetric induction in the photoinduced phase-transfer-catalytic perfluoroalkylation of β-ketoesters were interpreted by density functional theory calculations. The calculations indicated that multiple hydrogen-bonding interactions mode rather than π–π stacking interactions model better described the transition structure of the reaction. The quantitative estimation of these noncovalent interactions within the key transition states identified that the O–H···O and specific C–H···O hydrogen bonds play key roles for the stereocontrol.

Published
2024
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32. N-tert-Butyl Sulfinyl Squaramide Receptors for Anion Recognition through Assisted tert-Butyl C–H Hydrogen Bonding

Author

Li, Yao, Yang, Guo-Hui, Shen, Ye-Ye, Xue, Xiao-Song, Li, Xin, and Cheng, Jin-Pei

Abstract

A series of novel N-tert-butyl sulfinyl squaramide receptors have been designed and synthesized. Their interactions with a range of inorganic anions were studied in solution by 1H NMR spectroscopy. This new type of squaramide displayed better anion-binding abilities over conventional diphenyl squaramides. The single crystal analysis and DFT calulations implied the role of the tert-butyl C–H protons in binding Cl–. The energies of C–H···Cl–interactions were estimated to be 1.4–1.6 kcal/mol in solution.

Published
2024
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33. An Acidity Scale of Triazolium-Based NHC Precursors in DMSO

Author

Li, Zhen, Li, Xin, and Cheng, Jin-Pei

Abstract

An acidity scale of triazolium-based N-heterocyclic carbene precursors was established by measuring 25 compounds’ (10a–15b) equilibrium acidities in dimethyl sulfoxide (DMSO) solution using overlapping indicator method. The pKavalues ranged from 12.08 to 15.5, responding not only to the N-aryl motif, but also to the core structure. Excellent correlation was observed between the pKavalues and the Hammett substituent constants (σp).

Published
2024
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35. Establishing the Trifluoromethylthio Radical Donating Abilities of Electrophilic SCF3-Transfer Reagents

Author

Li, Man, Zhou, Biying, Xue, Xiao-Song, and Cheng, Jin-Pei

Abstract

The recent recognition of the novel application of a few traditional electrophilic trifluoromethylthiolating reagents as SCF3radical sources offers a remarkable new opportunity for the development of radical trifluoromethylthiolation reactions. Herein, the first trifluoromethylthio radical donating ability (Tt•DA) scale of electrophilic SCF3-transfer reagents has been developed. This scale is based on Y-SCF3bond dissociation energies, which were obtained by density functional calculations (M06-2X). Single electron transfer is revealed to exhibit a substantial Y-SCF3bond-weakening effect, thus significantly facilitating the SCF3radical (•SCF3) release. The results may aid in future novel radical SCF3-transfer reagent design and new reaction development.

Published
2024
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