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Communication

Copper-Catalyzed Reaction of N-Monosubstituted Hydrazones with CBr4: Unexpected Fragmentation and Mechanistic Study

by
Valentine G. Nenajdenko
1,
Anna A. Kazakova
2,
Alexander S. Novikov
3,*,
Namig G. Shikhaliyev
4,
Abel M. Maharramov
4,
Ayten M. Qajar
4,
Gulnar T. Atakishiyeva
4,
Aytan A. Niyazova
5,
Victor N. Khrustalev
2,6,
Alexey V. Shastin
7 and
Alexander G. Tskhovrebov
2,*
1
Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1 Bld. 3, 119991 Moscow, Russia
2
Research Institute of Chemistry, Peoples’ Friendship University of Russia, 6 Miklukho-Maklaya Street, 117198 Moscow, Russia
3
Institute of Chemistry, Saint Petersburg State University, Universitetskaya Nab, 7/9, 199034 Saint Petersburg, Russia
4
Department of Organic Chemistry, Baku State University, Z. Xalilov 23, 1148 Baku, Azerbaijan
5
Department of Engineering and Applied Sciences, Azerbaijan State University of Economics, M. Mukhtarov 194, 1001 Baku, Azerbaijan
6
Zelinsky Institute of Organic Chemistry RAS, Leninsky Prosp. 47, 119991 Moscow, Russia
7
Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(8), 1194; https://doi.org/10.3390/catal13081194
Submission received: 27 July 2023 / Revised: 8 August 2023 / Accepted: 8 August 2023 / Published: 9 August 2023
(This article belongs to the Special Issue Free Radicals in Catalysis, Organic Synthesis, and Material Science)
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Abstract

:
The copper catalyzed reaction of N-monosubstituted hydrazones with carbon tetrabromide leads to formation of expected dibromodiazadienes and unexpected dibromostyrenes. The experimental and theoretical study of the reaction revealed a key role of N-centered radicals, which can eliminate aryl radicals to form the corresponding dibromostyrenes. Alternatively, the oxidation of intermediate N-centered radicals by Cu(II) results in the corresponding diazadienes. These two reaction pathways are competitive directions of the reaction. Consequently, the reaction can be useful for the synthesis of both dibromostyrenes and rare dibromodiazadienes.

1. Introduction

Hydrazones are versatile synthons employed in organic chemistry. Recently, Nenajdenko et al. have discovered novel copper-mediated reactions of N-unsubstituted hydrazones with polyhalogenated compounds [1]. As a result, a new general method for the synthesis of various alkenes has been created [2,3,4,5,6]. This approach can be used for the preparation of valuable catalysts [7] or azo dyes [8]. Azo dyes are important organic compounds containing the structural element R–N=N–R’, which exhibits diverse applications in various fields. These applications include their use as sensors, ligands, liquid crystals, optical data storage media, nonlinear optic materials, dye-sensitized solar cells, color-changing substances, molecular switches, and more [9,10,11]. The specific properties of azo dyes mentioned above are significantly influenced by the functional groups attached to the –N=N– structural unit.
Importantly, the N-substitution of hydrazones had a dramatic impact on the reaction outcome. For instance, the copper-mediated reaction of monosubstituted hydrazones 1 with carbon tetrachloride resulted in the formation of the corresponding diazabutadienes 2 (Scheme 1) [1]. The mechanism of this reaction includes participation of short-lived radical species, the reaction path of which has been confirmed using various radical traps.
Excited by this discovery, we decided to systematically investigate the Cu-catalyzed reactions of N-monosubstituted hydrazones with polyhalogenated compounds. Surprisingly, we found that the action of CBr4 on the N-monosubstituted hydrazones results in the formation of the dibromoalkene in addition to the expected dibromodiazabutadienes. This study is devoted to the investigation of the mechanism of the reaction with CBr4. It was studied theoretically by DFT calculations; moreover, some additional experiments revealed the features of the reaction.

2. Results and Discussion

Initially, we aimed to prepare dibromodiazadienes and further explore their reactivity in the analogous fashion as we did for dichloro derivatives [2,7,12,13,14,15]. The starting N-monosubstituted hydrazones were synthesized by the condensation of hydrazines with the corresponding aldehydes. The addition of the excess of CBr4 to hydrazones in the presence of the catalytic amount of CuCl in DMSO resulted in a gradual orange coloration of the mixture and noticeable gas bubbling (presumably N2 exrusion). The analysis of the reaction mixture indicated the formation of expected dibromodiazadienes (Scheme 2). However, in addition to dibromodiazadienes, we observed the formation of unexpected dibromoalkenes in significant yields (Scheme 2, synthetic part). It should be noted that the reaction with CCl4 did not result in the formation of analogous dichloroalkenes in any noticeable amounts. That means that fragmentation takes place in the case of the reaction with carbon tetrabromide and the C–N bond is broken during the reaction.
Previously, we proposed the mechanism of the reaction of N-substituted hydrazones 1 with CCl4 [1]. It includes the addition of the trichloromethyl radical to hydrazone followed by oxidation of the intermediate N-centered radical D. This oxidation leads to the formation of azo-compound E. The subsequent base-induced elimination of HCl gives the final dichlorodiazadiene 2. Having observed unexpected fragmentation in the case of the reaction with carbon tetrabromide, we proposed that the reason for the observed fragmentation is connected with the transformation of intermediate D. Our idea is connected to the elimination of the aryl radical from D to form azene intermediate, which, in turn, is transformed into dibromostyrene (Scheme 3).
First, we performed some model experiments with hydrazones derived from p-cyanophenyl hydrazine and p-bromophenyl hydrazine. GC-MS analyses of the reaction mixtures for 10 and 12 showed the formation of significant amounts of benzonitrile and p-bromobenzonitrile and bromobenzene and p-dibromobenzene, correspondingly. These data indirectly indicated on the generation of the corresponding p-cyanophenyl and p-bromophenyl radicals in the course of the reactions, which abstract either hydrogen or bromine atoms to furnish the final arenes. Most probably, observation of two pathways for transformation of arylradicals can be explained in the frames of their stability and lifetime. It should be noted that relevant chemistries have been observed before [16,17,18].
In order to obtain more insight into the reaction mechanism, we performed DFT calculation of the Cu-mediated reaction between hydrazones and CCl4 or CBr4. The plausible mechanism for catalytic cycle is depicted in Scheme 4.
The results of DFT calculations (in dimethyl sulfoxide continuum solvation model) reveal the following: (a) in the very first step of catalytic cycle, formation of CCl3· is only slightly endergonic (0.1 kcal/mol in terms of Gibbs free energies), whereas formation of CBr3· is much more thermodynamically unfavorable (8.5 kcal/mol in terms of Gibbs free energies); (b) the second step of the catalytic cycle (attack of C=N bond in hydrazone 1 by CX3·, X = Cl, Br) is much more energetically profitable in the case of CBr3· (viz −20.0 kcal/mol in terms of summary Gibbs free energies compare with −10.2 kcal/mol in case of CCl3·); (c) the last step of the catalytic cycle resulting in formation of diazene E is endergonic in both cases, but in the case of a reaction system with chlorine-containing species—in a lesser degree compared with the reaction system based on bromine-containing substances; (d) in case of the CBr4-based reaction system, overall thermodynamic favorability of three stages of catalytic cycle (viz. CuX_TMEDA + CX4 → CuX2_TMEDA + CX3·, CX3· + 1 → D·_X, and D·_X + CuX2_TMEDA → CuX_TMEDA + HX + E_X; X = Cl, Br) is −7.7 kcal/mol in terms of Gibbs free energies vs. −2.9 kcal/mol in case of CCl4-based reaction system; and (e) the subsequent TMEDA-assisted elimination of HCl/HBr molecule from E furnishes the reaction product 1,2-diaza-1,3-diene 2, which is highly exergonic in both cases. We also considered some other alternative pathways for the formation of dichaloalkenes, but they all are very energetically unfavorable (Table 1).
As a result, we propose modification of the previous mechanism of the reaction, which can explain the formation of either azadienes or alkenes. The key steps of this radical reaction are the same as those given in Scheme 4. However, one important modification is elimination of aryl radical from the intermediate D to form the corresponding azene F. Finally, base-induced elimination in this case leads to formation of the corresponding dibromo-alkene (Scheme 5).
Compounds 13 and 13a could be recrystallized from CH2Cl2 to produce a single crystal suitable for the X-ray analysis (Figure 1).
Interestingly, 13 featured intermolecular halogen bonding Br···Br (3.435 Å, 94% of Bondi’s vdW radii sum for two bromine atoms [19,20,21], Figure 2) in the solid state, whereas such noncovalent contacts are absent in the X-ray structure of 13a. It should be noted that we demonstrated earlier that highly polarizable dichlorodiazadienes are good sigma-hole donors [12,13,14,15].
To deeper explore these noncovalent interactions in 13, we carried out a theoretical topological analysis of the electron density distribution within the QTAIM approach [22] for model supramolecular associate (appropriate xyz-file with Cartesian atomic coordinates is given in Supplementary Materials). The QTAIM analysis demonstrates the presence of bond critical point (3, −1) (BCP) for halogen bonding Br···Br in the model supramolecular associate under study. The low magnitude of the electron density (0.009 a.u.), positive value of the Laplacian of electron density (0.032 a.u.), and close to zero positive energy density (0.002 a.u.: Lagrangian kinetic energy G(r) = 0.006 a.u. and potential energy density V(r) = −0.004 a.u.) in this BCP, as well as the estimated strength for appropriate contact (1.5 kcal/mol, Eint ≈ 0.58(−V(r)) [23], this empirical correlation was developed exclusively for noncovalent interactions involving bromine atoms) are typical for halogen bonds [21,24,25,26,27,28]. The contour line diagram of the Laplacian of electron-density distribution ∇2ρ(r), bond paths, and selected zero-flux surfaces, visualization of electron localization function (ELF) and reduced-density gradient (RDG) analyses for halogen bonding Br···Br in the model supramolecular associate based on the experimental X-ray structure 13 are shown in Figure 3.

3. Materials and Methods

General remarks: Unless stated otherwise, all the reagents used in this study were obtained from commercial sources (Aldrich, TCI-Europe, Strem, ABCR). NMR spectra were recorded on a L. Krause.
Avance 300 (1H: 300 MHz, Karlsruhe, Germany); and chemical shifts (δ) are given in ppm relative to TMS, coupling constants (J) in Hz. Solvents were purified by distillation over the indicated drying agents and were transferred under Ar: Et2O (Mg/anthracene), CH2Cl2 (CaH2), and hexane (Na/K). Flash chromatography: Merck Geduran® Si 60 (Darmstadt, Germany) (40–63 μm).
Computational details: The full geometry optimization of all model structures and single point calculations based on the experimental X-ray geometry of 13 were carried out at the DFT level of theory using the dispersion-corrected hybrid functional ωB97XD [29] with the help of the Gaussian-09 program package [30]. The standard 6-31+G* basis sets were used. No symmetry restrictions were applied during the geometry optimizations. The solvent effects were taken into account using the SMD (Solvation Model based on Density) continuum solvation model suggested by Truhlar and coworkers [31] for dimethyl sulfoxide. The Hessian matrices were calculated analytically for all optimized model structures to prove the location of the correct minimum on the potential energy surface (no imaginary frequencies were found in all cases) and to estimate thermodynamic parameters at 25 °C and 1 atm. The topological analysis of the electron density distribution has been performed by using the Multiwfn program (version 3.7) [32]. The Cartesian atomic coordinates for all model structures are presented in xyz-files (Supplementary Materials).
Schiff bases 1–6 were synthesized according to the following method (similar procedures for the synthesis of hydrazones were reported earlier) [13,14,15,33,34,35,36,37,38,39]. A mixture of a corresponding hydrazine (10.2 mmol), CH3COONa (0.82 g) and p-bromobenzaldehyde (10 mmol) were refluxed with stirring in ethanol (50 mL) for 2 h. The reaction mixture was cooled to room temperature and water (50 mL) was added to give a precipitate of crude product, which was filtered off, washed with diluted ethanol (1:1 with water) and dried in vacuo.
1. (E)-1-(4-methylbenzylidene)-2-phenylhydrazine. white solid (82%), mp 175 °C. 1H NMR (300 MHz, DMSO-d6) δ 10.27 (s, 1H, –NH), 7.84 (s, 1H, –CH), 7.54 (d, J = 7.4 Hz, 2H, arom), 7.20 (d, J = 7.2 Hz, 4H, arom), 7.07 (d, J = 7.5 Hz, 2H, arom), 6.73 (t, J = 7.4 Hz, 1H, arom), 2.31 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 145.8, 137.8, 137.0, 133.5, 129.7, 129.5, 126.05, 118.9, 112.3, 21.3.
2. (E)-1-(4-methylbenzylidene)-2-(p-tolyl)hydrazine. white solid (87%), mp 152 °C. 1H NMR (300 MHz, DMSO-d6) δ 10.15 (s, 1H, –NH), 7.80 (s, 1H, –CH), 7.52 (d, J = 7.4 Hz, 2H, arom), 7.18 (d, J = 7.4 Hz, 2H, arom), 7.00 (q, J = 7.8 Hz, 4H, arom), 2.30 (s, 3H, –CH3), 2.21 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 143.6, 137.6, 136.3, 133.6, 129.9, 129.6, 127.4, 125.9, 112.3, 21.3, 20.7.
3. (E)-1-(4-CHlorophenyl)-2-(4-methylbenzylidene)hydrazine. Yellow solid (70%), mp 155 °C. 1H NMR (300 MHz, DMSO-d6) δ 10.42 (s, 1H, –NH), 7.88 (s, 1H, –CH), 7.55 (s, 2H, arom), 7.41–6.95 (m, 6H, arom), 2.29 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 144.8, 138.0, 137.9, 133.35, 129.6, 129.3, 126.1, 122.3, 113.7, 21.3.
4. (E)-4-(2-(4-methylbenzylidene)hydrazinyl)benzonitrile. White solid (67%), mp 178 °C. 1H NMR (300 MHz, DMSO-d6) δ 10.89 (s, 1H, –NH), 7.94 (s, 1H, –CH), 7.68–7.50 (m, 5H, arom), 7.18 (dd, J = 26.3, 7.6 Hz, 5H, arom), 2.32 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 140.6, 138.9, 134.1, 132.7, 132.2, 129.8, 126.6, 120.6, 116.5, 112.4, 21.4.
5. (E)-1-(4-methylbenzylidene)-2-(4-nitrophenyl)hydrazine. red solid (79%), mp 168 °C. 1H NMR (300 MHz, DMSO-d6) δ 11.24 (s, 1H, –NH), 8.12 (d, J = 8.9 Hz, 2H, arom), 8.01 (s, 1H, –CH), 7.62 (d, J = 7.8 Hz, 2H, arom), 7.24 (d, J = 7.8 Hz, 2H, arom), 7.15 (d, J = 8.5 Hz, 2H, arom), 2.32 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 150.0, 141.4, 138.4, 137.6, 131.4, 128.8, 125.9, 125.6, 110.5, 20.4.
6. (E)-1-(4-bromophenyl)-2-(4-methylbenzylidene)hydrazine white solid (72%), mp 181 °C. 1H NMR (300 MHz, DMSO-d6) δ 10.40 (s, 1H, –NH), 7.84 (s, 1H, –CH), 7.54 (d, J = 8.0 Hz, 2H, arom), 7.35 (d, J = 8.8 Hz, 2H, arom), 7.20 (d, J = 7.9 Hz, 2H, arom), 7.01 (d, J = 8.8 Hz, 2H, arom), 2.31 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 145.1, 138.1, 138.0, 133.2, 132.1, 129.72, 126.2, 114.2, 109.7, 21.3.
Synthesis of dibromodiazadiens.
A 20 mL screw neck vial was charged with DMSO (10 mL), 1–7 (1 mmol), tetramethylethylenediamine (TMEDA) (295 mg, 2.5 mmol), CuCl (2 mg, 0.02 mmol) and CBr4 (1 mmol). After 1–3 h (until TLC analysis showed complete consumption of corresponding Schiff base), the reaction mixture was poured into ~0.01 M solution of HCl (100 mL, ~pH = 2), and extracted with dichloromethane (3 × 20 mL). The combined organic phase was washed with water (3 × 50 mL), brine (30 mL), dried over anhydrous Na2SO4 and concentrated in vacuo. The residue was purified by column chromatography on silica gel using appropriate mixtures of hexane and dichloromethane (3/1–1/1).
7. (E)-1-(2,2-dibromo-1-(p-tolyl)vinyl)-2-phenyldiazene. Red solid (52%), mp 125 °C. 1H NMR (300 MHz, Chloroform-d) δ 7.85–7.77 (m, 2H, arom), 7.46 (d, J = 5.2 Hz, 3H, arom), 7.25 (s, 1H, arom), 7.09 (d, J = 7.9 Hz, 2H, arom), 2.43 (s, 3H, –CH3). 13C NMR (75 MHz, CDCl3) δ 156.4, 152.9, 138.5, 131.5, 131.2, 129.6, 129.0, 128.9, 123.3, 21.5.
7a. 1-(2,2-dibromovinyl)-4-methylbenzene. mp 115 °C, (22%). 1H NMR (300 MHz, DMSO-d6) δ 7.68 (s, 1H, -vinyl H), 7.48 (d, J = 8.0 Hz, 2H, arom), 7.19 (d, J = 7.9 Hz, 2H, arom), 2.28 (s, 3H, –CH3). 13C NMR (75 MHz, DMSO) δ 138.8, 137.2, 132.5, 129.4, 128.6, 88.5, 21.4. The spectra of a given compound overlaps with those of the literature [40].
1H NMR (400 MHz, CDCl3) δ = 7.44 (s,1H), 7.43 (d, J = 6.7 Hz, 2H), 7.17 (d, J = 7.5 Hz, 2H), 2.34 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 138.8, 136.9, 132.6, 129.2, 128.5, 88.7, 21.5.
8. (E)-1-(2,2-dibromo-1-(p-tolyl)vinyl)-2-(p-tolyl)diazene. red solid (60%), mp 117 °C. 1H NMR (300 MHz, Chloroform-d) δ 7.82–7.73 (m, 2H, arom), 7.33–7.25 (m, 4H, arom), 7.13 (d, J = 8.0 Hz, 2H, arom), 2.45 (d, J = 7.5 Hz, 6H, –CH3). 13C NMR (75 MHz, CDCl3) δ 131.4, 130.9, 129.8, 129.7, 129.3, 129.2, 128.9, 128.4, 123.4, 122.9, 21.7, 21.0.
7a. (Twenty-one percent)
9. (E)-1-(4-chlorophenyl)-2-(2,2-dibromo-1-(p-tolyl)vinyl) diazene. red solid (51%), mp 132 °C. 1H NMR (300 MHz, Chloroform-d) δ 7.75 (d, J = 8.2 Hz, 2H, arom), 7.41 (d, J = 8.4 Hz, 2H, arom), 7.25 (d, J = 8.1 Hz, 2H, arom), 7.05 (d, J = 7.6 Hz, 2H, arom), 2.42 (s, 3H, –CH3). 13C NMR (75 MHz, CDCl3) δ 135.3, 135.0, 134.6, 131.3, 131.1, 129.5, 129.3, 128.9, 125.4, 124.5, 30.99
7a. (Seventeen percent)
10. (E)-4-((2,2-dibromo-1-(p-tolyl)vinyl)diazenyl)benzonit-rile. yellow solid (56%), mp 142 °C. 1H NMR (300 MHz, Chloroform-d) δ 7.70–7.62 (m, 4H, arom), 7.54 (d, J = 8.6 Hz, 4H, arom), 1.27 (s, 3H, –CH3). 13C NMR (75 MHz, CDCl3) δ 142.9, 138.5, 136.8, 133.4, 132.6, 128.0, 123.8, 118.0, 113.0, 111.2, 100.5, 29.7.
7a. (Twenty-one percent)
11. (E)-1-(2,2-dibromo-1-(p-tolyl)vinyl)-2-(4-nitrophenyl) diazene. red solid (48%), mp 184 °C. 1H NMR (300 MHz, Chloroform-d) δ 8.41 (s, 1H, arom), 8.23 (d, J = 7.4 Hz, 2H, arom), 7.92–7.73 (m, 2H, arom), 7.27–7.21 (m, 3H, arom), 2.43 (s, 3H, –CH3). 13C NMR (75 MHz, CDCl3) δ 129.7, 129.3, 128.0, 126.8, 126.1, 124.6, 123.4, 114.5, 112.8, 112.6, 21.3.
7a. (Twenty-four percent)
12. (E)-1-(4-bromophenyl)-2-(2,2-dibromo-1-(p-tolyl)vinyl) diazene. red solid (56%), mp 110 °C. 1H NMR (300 MHz, Chloroform-d) δ 7.67 (d, J = 8.7 Hz, 2H, arom), 7.57 (d, J = 8.8 Hz, 2H, arom), 7.24 (d, J = 8.0 Hz, 2H, arom), 7.05 (d, J = 8.0 Hz, 2H, arom), 2.41 (s, 3H, –CH3). 13C NMR (75 MHz, CDCl3) δ 151.6, 138.7, 132.3, 131.3, 130.9, 129.5, 128.9, 126.1, 124.7, 111.1, 21.4.
7a. (Twenty percent)
13. Orange solid (10%). 1H NMR (700 MHz, DMSO-d6) δ 6.90–6.84 (m, 6H, H3, H6 and H7), 6.71–6.65 (m, 3H, H13 and H14), 6.62 (t, J = 7.7 Hz, 2H, H2), 6.53 (t, J = 7.4 Hz, 1H, H1), 6.43 (d, J = 8.3 Hz, 2H, H12); 13C NMR (176 MHz, DMSO-d6) δ 156.3, 152.7, 140.8, 139.9, 133.6, 132.7, 130.8, 130.1, 129.5, 128.3, 127.2, 127.0, 123.3, 112.2.
13a. 4-(2,2-dibromovinyl)-1,1’-biphenyl. Colorless solid (56%). Analytical data were in accord with the literature [41].

4. Conclusions

In this work, we demonstrated that the Cu-catalyzed reaction between CBr4 and the N-monosubstituted hydrazones results in the formation of corresponding mixtures of dibromodiazabutadienes and dibromoalkenes. The mechanism was investigated, and the results indicated on the generation of aryl radicals over the course of the hydrazone fragmentation. Overall, the reaction can be useful for the synthesis of both dibromosyrenes and rare dibromodiazadienes.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal13081194/s1, Table S1: Calculated total electronic energies (E, in Hartree), enthalpies (H, in Hartree), Gibbs free energies (G, in Hartree), and entropies (S, cal/mol·K) for optimized equilibrium model structures; Table S2: Crystal data and structure refinement for the compounds studied [42,43,44].

Author Contributions

Conceptualization, V.G.N. and A.G.T.; investigation, A.A.K., N.G.S., G.T.A., A.A.N., V.N.K., A.S.N., A.M.M., A.M.Q., G.T.A. and A.V.S., writing—original draft preparation, V.G.N., A.G.T. and A.S.N.; writing—review and editing, V.G.N., A.G.T. and A.S.N. All authors have read and agreed to the published version of the manuscript.

Funding

This paper has been supported by the RUDN University Strategic Academic Leadership Program (award no. 025238-2-174, recipient: Tskhovrebov A.G.).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 13 01194 sch001
Scheme 1. Synthesis of dichlorodiazadienes.
Scheme 1. Synthesis of dichlorodiazadienes.
Catalysts 13 01194 sch001
Catalysts 13 01194 sch002
Scheme 2. Cu-mediated reaction between hydrazones and CBr4.
Scheme 2. Cu-mediated reaction between hydrazones and CBr4.
Catalysts 13 01194 sch002
Catalysts 13 01194 sch003
Scheme 3. Plausible route to dibromostyrene via aryl radical elimination.
Scheme 3. Plausible route to dibromostyrene via aryl radical elimination.
Catalysts 13 01194 sch003
Catalysts 13 01194 sch004
Scheme 4. Schematic representation of elementary steps for theoretically studied plausible model catalytic cycle involving reaction system with chlorine-containing species (in case of CBr4-based reaction system all transformations are the same).
Scheme 4. Schematic representation of elementary steps for theoretically studied plausible model catalytic cycle involving reaction system with chlorine-containing species (in case of CBr4-based reaction system all transformations are the same).
Catalysts 13 01194 sch004
Catalysts 13 01194 sch005
Scheme 5. Proposed mechanism for all observed transformations in the studied reaction system.
Scheme 5. Proposed mechanism for all observed transformations in the studied reaction system.
Catalysts 13 01194 sch005
Catalysts 13 01194 g001
Figure 1. Molecular structures of 13 (top) and 13a (bottom) in the crystal. Thermal ellipsoids are at 50% probability. Blue, brown, gray and light gray ellipsoids represent nitrogen, bromine, carbon and hydrogen atoms, respectively.
Figure 1. Molecular structures of 13 (top) and 13a (bottom) in the crystal. Thermal ellipsoids are at 50% probability. Blue, brown, gray and light gray ellipsoids represent nitrogen, bromine, carbon and hydrogen atoms, respectively.
Catalysts 13 01194 g001
Catalysts 13 01194 g002
Figure 2. Intermolecular halogen bonding Br···Br in the crystal structure of 13.
Figure 2. Intermolecular halogen bonding Br···Br in the crystal structure of 13.
Catalysts 13 01194 g002
Catalysts 13 01194 g003
Figure 3. Contour line diagram of the Laplacian of electron density distribution ∇2ρ(r), bond paths, and selected zero-flux surfaces (top panel), visualization of electron localization function (ELF, center panel) and reduced density gradient (RDG, bottom panel) analyses for halogen bonding Br···Br in the model supramolecular associate based on the experimental X-ray structure 13. Bond critical points (3, −1) are shown in blue, nuclear critical points (3, −3)—in pale brown, bond paths are shown as pale brown lines, length units—Å, and the color scale for the ELF and RDG maps is presented in a.u.
Figure 3. Contour line diagram of the Laplacian of electron density distribution ∇2ρ(r), bond paths, and selected zero-flux surfaces (top panel), visualization of electron localization function (ELF, center panel) and reduced density gradient (RDG, bottom panel) analyses for halogen bonding Br···Br in the model supramolecular associate based on the experimental X-ray structure 13. Bond critical points (3, −1) are shown in blue, nuclear critical points (3, −3)—in pale brown, bond paths are shown as pale brown lines, length units—Å, and the color scale for the ELF and RDG maps is presented in a.u.
Catalysts 13 01194 g003
Table 1. Calculated values of total electronic energies, enthalpies, and Gibbs free energies of reaction (ΔE, ΔH, and ΔG in kcal/mol) for elementary steps of model catalytic cycle.
Table 1. Calculated values of total electronic energies, enthalpies, and Gibbs free energies of reaction (ΔE, ΔH, and ΔG in kcal/mol) for elementary steps of model catalytic cycle.
Catalysts 13 01194 i001
Elementary StepΔEΔHΔG
CCl4-based reaction system
CuCl_TMEDA + CCl4 → CuCl2_TMEDA + CCl3· (1)1.41.90.1
CCl3· + 1 → D·_Cl (2)−27.0−24.7−10.3
D·_Cl + CuCl2_TMEDA → CuCl_TMEDA + HCl + E_Cl (3)22.318.57.3
E_Cl + TMEDA → H-TMEDA+ + Cl– + 2_Cl (4)−20.2−18.1−27.6
2_Cl + HCl → Cl2C=CHPh + Cl– + PhN=N+ (5a)17.819.08.8
2_Cl + HCl → Cl2C=CHPh + PhN=N+···Cl– (5b)12.914.39.8
2_Cl + H-TMEDA+ → Cl2C=CHPh + TMEDA + PhN=N+ (5c)48.744.232.1
F_Cl_cis → F_Cl_trans−3.4−3.1−3.2
D·_Cl → F_Cl_trans + Ph· (6)63.761.247.9
F_Cl_trans → HCl + N2 + Cl2C=CHPh (7)−31.8−37.0−58.8
CBr4-based reaction system
CuBr_TMEDA + CBr4 → CuBr2_TMEDA + CBr3· (1)8.89.68.5
CBr3· + 1 → D·_Br (2)−45.6−43.1−28.5
D·_Br + CuBr2_TMEDA → CuBr_TMEDA + HBr + E_Br (3)28.223.412.3
E_Br + TMEDA → H-TMEDA+ + Br– + 2_Br (4)−3.9−0.9−8.5
cis-PhN=N–Br → trans-PhN=N–Br2.52.72.9
2_Br + HBr → Br2C=CHPh + cis-PhN=N–Br (5a)13.914.711.1
2_Br + HBr → Br2C=CHPh + Br– + PhN=N+ (5a’)29.030.018.3
2_Br + HBr → Br2C=CHPh + PhN=N+···Br– (5b)14.616.812.0
2_Br + H-TMEDA+ → Br2C=CHPh + TMEDA + PhN=N+ (5c)56.251.137.4
F_Br_cis → F_Br_trans−3.5−3.4−3.5
D·_Br → F_Br_trans + Ph· (6)66.463.850.7
F_Br_trans → HBr + N2 + Br2C=CHPh (7)−14.9−20.5−43.3
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Nenajdenko, V.G.; Kazakova, A.A.; Novikov, A.S.; Shikhaliyev, N.G.; Maharramov, A.M.; Qajar, A.M.; Atakishiyeva, G.T.; Niyazova, A.A.; Khrustalev, V.N.; Shastin, A.V.; et al. Copper-Catalyzed Reaction of N-Monosubstituted Hydrazones with CBr4: Unexpected Fragmentation and Mechanistic Study. Catalysts 2023, 13, 1194. https://doi.org/10.3390/catal13081194

AMA Style

Nenajdenko VG, Kazakova AA, Novikov AS, Shikhaliyev NG, Maharramov AM, Qajar AM, Atakishiyeva GT, Niyazova AA, Khrustalev VN, Shastin AV, et al. Copper-Catalyzed Reaction of N-Monosubstituted Hydrazones with CBr4: Unexpected Fragmentation and Mechanistic Study. Catalysts. 2023; 13(8):1194. https://doi.org/10.3390/catal13081194

Chicago/Turabian Style

Nenajdenko, Valentine G., Anna A. Kazakova, Alexander S. Novikov, Namig G. Shikhaliyev, Abel M. Maharramov, Ayten M. Qajar, Gulnar T. Atakishiyeva, Aytan A. Niyazova, Victor N. Khrustalev, Alexey V. Shastin, and et al. 2023. "Copper-Catalyzed Reaction of N-Monosubstituted Hydrazones with CBr4: Unexpected Fragmentation and Mechanistic Study" Catalysts 13, no. 8: 1194. https://doi.org/10.3390/catal13081194

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