Photophysical properties of arylcarbonitrile derivatives: Synthesis, absorption and emission spectra, and quantum chemical studies

Tetracyanoethylene is an archetypal electron acceptor and in the presence of aromatic amines forms charge transfer π-complexes, which subsequently leads to the formation of a tricyanovinylation product by the electrophilic aromatic substitution at para position of tertiary amine ring. Factors as amine concentration and solvent polarity influence both the rate and extension of reaction. In contrast to the aromatic amines containing only one phenyl ring, in the case of N-methyldiphenylamine, the rate of reaction is much slower in particular conditions allowing the spectroscopic characterization (ultraviolet-visible and Raman) of all the species involved, including the neutral adduct and zwitterionic intermediate species. The stabilities of such intermediate species in solution can be controlled by both the concentration of amine and solvent polarity. The results illustrate the dual role played by the amine as a reactant and as a catalyst in the proton abstraction, the rate determining step. The comparison of the reactions in dichloromethane and acetonitrile shows that the neutral adduct and zwitterionic intermediate species are stabilized in nonpolar medium, revealing the role played by the solvent in defining the mechanistic pathways of this model charge transfer initiated reaction. Quantum chemical calculations based on density functional theory and time-dependent density functional theory were used to obtain the theoretical vibrational and electronic spectra and showed fair agreement with experimental data. Figure 6. (a) Raman spectra of the solutions at 1NMPA : 1TCNE proportion in CH 2 Cl 2 and CH 3 CN excited at λ 0 = 364 nm; (b) theoretical Raman spectra of neutral adduct considering CH 2 Cl 2 and CH 3 CN as solvent [solvation model based on density (SMD)].

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“…The reaction between TCNE and N‐methyldiphenylamine (NMPA) follows the proposed tricyanovinylation mechanism showed in Figure …”

Section: Introductionmentioning

confidence: 93%

Resonance Raman and UV–VIS spectroscopic investigation of the reaction of tetracyanoethylene and N‐methyldiphenylamine

Monezi

Ando

2017

J Raman Spectroscopy

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“…The formal reaction of the ketenimine adduct 1 b ⋅ 2 B (formed upon treatment of 1 a with B(C 6 F 6 ) 3 ) with aromatic solvents such as benzene or toluene affording amino‐malononitrile‐substituted arenes (Scheme 3 bottom) corresponds to a classical electrophilic aromatic substitution (EAS) reaction: The classic S E Ar mechanism starts with the fast formation of π‐complex and the attack of an electrophile E + on the aromatic system, forming a σ‐(Wheland)‐complex stabilized by mesomerism. A deprotonation‐protonation reaction step results in the restoration of the aromatic system (Scheme 3 top) [19–32] . The S E Ar mechanism has been intensively studied recently and is used to explain halogenations, nitration, sulfonation, Friedel‐Crafts substitutions, and others mechanistically [19–33] .…”

Section: Resultsmentioning

confidence: 99%

“…A deprotonation‐protonation reaction step results in the restoration of the aromatic system (Scheme 3 top). [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ] The S E Ar mechanism has been intensively studied recently and is used to explain halogenations, nitration, sulfonation, Friedel‐Crafts substitutions, and others mechanistically. [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ] Often a catalyst (Lewis acid) is needed to form the electrophile.…”

Section: Resultsmentioning

confidence: 99%

A Lewis Acid Stabilized Ketenimine in an Unusual Variant of the Electrophilic Aromatic Substitution

Surkau

Bläsing

Bresien

et al. 2022

Chemistry A European J

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Electrophilic aromatic substitution (EAS) can provide a straightforward approach to the efficient synthesis of functionalized complex aromatic molecules. In general, Lewis acids serve as a beneficial stimulus for the formation of a Wheland complex, the intermediate in the classical SEAr mechanism of EAS, which is responsible for H/E (E=electrophile) substitution under formal H+ elimination. Herein, we report an unusual variant of EAS, in which a complex molecule such as the tricyanomethane, HC(CN)3, is activated with a strong Lewis acid (B(C6F5)3) to the point where it can finally be used in an EAS. However, the Lewis acid here causes the isomerization of the tricyanomethane to the ketenimine, HN=C=C(CN)2, which in turn directly attacks the aromatic species in the EAS, with simultaneous proton migration of the aromatic proton to the imino group, so that no elimination occurs that is otherwise observed in the SEAr mechanism. By this method, it is possible to build up amino‐malononitrile‐substituted aromatic compounds in one step.

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“…It should be noted that a very few examples have been reported for the substitution of cyano-group by reaction of amines under solvent-free conditions in some other heterocycles, for instance, in pyrazines, 46 4H-imidazole, 47 1-arylethene-1,2,2-tricarbonitriles, 48 quinazolinone (in an aqueous media), 49 and benzonitrile. 50 In addition, the intermolecular cyclization reaction of tetrazine followed by the ipso-substitution of cyanogroup has been reported.…”

Section: Resultsmentioning

confidence: 99%

Solvent-free synthesis of 5-(aryl/alkyl)amino-1,2,4-triazines and α-arylamino-2,2′-bipyridines with greener prospects

et al. 2017

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Photophysical properties of arylcarbonitrile derivatives: Synthesis, absorption and emission spectra, and quantum chemical studies

Cited by 7 publications

References 18 publications

Resonance Raman and UV–VIS spectroscopic investigation of the reaction of tetracyanoethylene and N‐methyldiphenylamine

Resonance Raman and UV–VIS spectroscopic investigation of the reaction of tetracyanoethylene and N‐methyldiphenylamine

A Lewis Acid Stabilized Ketenimine in an Unusual Variant of the Electrophilic Aromatic Substitution

Solvent-free synthesis of 5-(aryl/alkyl)amino-1,2,4-triazines and α-arylamino-2,2′-bipyridines with greener prospects

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