Alexander Yu. Makarov

1,2,3-benzodithiazolyl radicals formed by thermolysis and photolysis of 1,3,2,4-benzodithiadiazines

Mild thermolysis (at 110–150°C) of 1,3,2,4-benzodithiadiazine 1 and its carbocyclic substituted derivatives 2–15 in hydrocarbon solvents quantitatively yields stable 1,2,3-benzodithiazolyl π-radicals 1•–15•. Kinetics of this reaction can be described as a first-order process. Arrhenius parameters of the effective rate constant are Ea = 80 ± 8 kJ mol−1, k0 = 106.4 ± 1.1 s−1 for 1 in squalane. Room-temperature photolysis of 1 in hydrocarbon solvents also affords radical 1• in nearly quantitative yield. Quantum yield of photolysis is wavelength dependent and is equal to 0.08 ± 0.01 at 313 nm in benzene. Experimental hyperfine coupling (hfc) constants in the ESR spectra of 1•–15• agree fairly well with those calculated at the B3LYP/CC-pVDZ level of theory. Spin density distribution in 1•–15• is in striking contrast to that of isomeric 1,3,2-benzodithiazolyls but resembles the distribution in correspondingly substituted benzyl radicals. ESR linewidths of radicals 1•-15• display some features likely related to spin-rotational relaxation.

Photochemistry of 1,3,2,4-benzodithiadiazines: formation and oxidation of 1,2,3-benzodithiazolyl radicals

Photolysis of 1,3,2,4-benzodithiadiazine and its derivatives in hydrocarbon solutions yields dinitrogen and stable 1,2,3-benzodithiazolyls (Herz radicals) whose interaction with dioxygen leads finally to O==S==N-substituted diphenyl disulfides via a self termination-like process with an effective second-order rate constant depending linearly on the concentration of dissolved O2.

A polyfluoroaromatic tellurium–nitrogen compound: synthesis and properties of 4,5,6,7-tetrafluoro-2λ4δ2,1,3-benzotelluradiazole

4,5,6,7-Tetrafluoro-2λ4δ2,1,3-benzotelluradiazole compound 2 (and a 15N-enriched sample) is synthesized by treating TeCl4 with the corresponding diamine 4 in the absence of HCl acceptors. Some of its properties, .e.g. high volatility, facile hydrolysis and vibrational frequencies, are experimentally determined.

Interaction of 1,3,2,4-Benzodithiadiazines and Their 1-Se Congeners with Ph3P and Some Properties of the Iminophosphorane Products

Interaction between Ph(3)P and 1,3,2,4-benzodithiadiazine (1); its 6,7-difluoro (2), 5,6,8-trifluoro (3) and 5,6,7,8-tetrafluoro (4) derivatives; and 5,6,8-trifluoro-3,1,2,4-benzothiaselenadiazine (5) proceeded via a 1:1 condensation to give Ph(3)P═N-R iminophosphoranes (1a-5a, R = corresponding 1,2,3-benzodichalcogenazol-2-yls), which are inaccessible by general approaches based on the Staudinger and Kirsanov reactions. In contrast, neither Ph(3)As nor Ph(3)Sb reacted with 1 and 4. Molecular structures of 1a-5a and 5 were confirmed by X-ray diffraction (XRD). The crystals formed by chiral molecules of 2a-5a were racemic, whereas the crystal of 1a was formed by a single enantiomer. In all of the Ph(3)P═N-R derivatives, one of the Ph rings is oriented face-to-face to the hetero ring, R. Upon heating to ∼120 °C in squalane (1a, 3a, 4a) or dissolving in chloroform at ambient temperatures (1a, 2a, 4a), the Ph(3)P═N-R derivatives generated the 1,2,3-benzodithiazolyls (1b-4b, respectively) whose identity was confirmed by electron paramagnetic resonance (EPR). 2,1,3-Benzothiaselenazolyls 5b and 6b were detected by EPR as the main paramagnetic products of solution thermolysis of 5 and its 5,6,7,8-tetrafluoro congener (6), respectively. Passing a chloroform solution of 4a through silica column unexpectedly gave 5-6-6-6 tetracyclic (9) and 6-10-6 tricyclic (10) sulfur-nitrogen compounds, which were characterized by XRD.

Experimental and Computational Study on the Structure and Properties of Herz Cations and Radicals: 1,2,3-Benzodithiazolium, 1,2,3-Benzodithiazolyl, and Their Se Congeners

Salts of 1,2,3-benzodithiazolium (1), 2,1,3-benzothiaselenazolium (3), and 1,2,3-benzodiselenazolium (4) (Herz cations), namely, [1][BF4], [1][SbCl6], [3][BF4], [3][GaCl4], [3][SbCl6], and [4][GaCl4], were prepared from the corresponding chlorides and NaBF4, GaCl3, or SbCl5. It was found that [1][SbCl6] and [3][SbCl6] spontaneously transform in MeCN solution to [1]3[SbCl6]2[Cl] and [3]3[SbCl6]2[Cl], respectively. [1][BF4], [1]3[SbCl6]2[Cl], [3][BF4], [3]3[SbCl6]2[Cl], and [4][GaCl4] were structurally characterized by X-ray diffraction (XRD). In solution, these [BF4](-) and [GaCl4](-) salts as well as [1][GaCl4], [2][GaCl4], [3][GaCl4], [3][Cl], and [4][Cl] were characterized by multinuclear nuclear magnetic resonance (NMR). The corresponding Herz radicals 1(•)-4(•) were obtained in toluene and DCM solutions by the reduction of the appropriate salts with Ph3Sb and characterized by EPR. Cations 1-4 and radicals 1(•)-4(•) were investigated computationally at the density functional theory (DFT) and second-order Møller-Plesset (MP2) levels of theory. The B1B95/cc-pVTZ method was found to satisfactorily reproduce the experimental geometries of 1-4; an increase in the basis set size to cc-pVQZ results in only minor changes. For both 1-4 and 1(•)-4(•), the Hirshfeld charges and bond orders, as well as the Hirshfeld spin densities for the radicals, were calculated using the B1B95/cc-pVQZ method. It was found for both the cations and the radicals that replacing S atoms with Se atoms leads to considerable changes in the atomic charges, bond lengths, and bond orders only at the involved and the neighboring sites. According to the calculations, 60% of the positive charge in the cations and 80% of the spin density in the radicals is localized on the heterocycles, with the spin density distributions being very similar for all radicals 1(•)-4(•). For the cations 1-4, the NICS values (B3LYP/cc-pVTZ for B1B95/cc-pVTZ geometries) lie in the narrow range from -5.5 ppm to -6.6 ppm for the carbocycles, and from -14.4 ppm to -15.5 ppm for heterocycles, clearly indicating the aromaticity of the cations. Calculations on radical dimers [1(•)]2-[4(•)]2 revealed, with only one exception, positive dimerization energies, i.e., the dimers are inherently unstable in the gas phase.

HeI photoelectron spectra and π-electronic structure of substituted 1,3,2,4-benzodithiadiazines, formally antiaromatic 12π-electron compounds☆

Abstract The HeI photoelectron spectra of various 5-R-, 6-R- and 7-R-substituted derivatives of 1,3,2,4-benzodithiadiazine (R=F, Cl, CH3, CF3, OCH3), a formally antiaromatic 12π-electron compound, have been measured and assigned in the IE1–IE4 area by Koopmans’ correlation with 6-31G* eigenvalues. Despite a considerable localization (∼70%) of the highest occupied π-MO on the sulfur–nitrogen fragment, IE1 depends upon both position and character of the carbocyclic substituent R.

1,2,4,3,5-benzotrithiadiazepine and its unexpected hydrolysis to unusual 7H,14H-dibenzo[d,i][1,2,6,7,3,8]tetrathiadiazecine.

Previously unknown 1,2,4,3,5-benzotrithiadiazepine 1 was prepared by 1:1 condensation of Ph-N=S=N-SiMe3 with S2Cl2 followed by intramolecular ortho-cyclization of [Ph-N=S=N-S-S-Cl] intermediate, and hydrolyzed in pyridine to unusual macrocyclic 7H,14H-dibenzo[d,i][1,2,6,7,3,8]tetrathiadiazecine 2.

Post-resonance Raman and theoretical studies on 1,3,2,4-benzodithiadiazines, formally anti-aromatic compounds

DFT calculations on 1,3,2,4-benzodithiadiazine (1) and its 5-F (2), 6-Cl (3) and 7-CH3 (4) derivatives showed these compounds to have essentially non-planar molecular conformations. The vibrational (IR and Raman) spectra of 1–4 were measured and assigned on the basis of the results of the theoretical calculations. NSN anti-symmetric and symmetric stretching modes were found at ∽1220–1230 and ∽965–975 cm−1, respectively. Resonance Raman spectra of 1–4 were obtained with the 514.5, 496.5, 488.0, 476.5 and 457.9 nm excitation lines of an Argon laser, and a post-resonance Raman effect was observed. The Raman excitation profiles revealed a weak but definite π-interaction of the carbocyclic and heterocyclic parts of the molecules which became stronger on going from 1 to 2. Comments on the possible existence of antiaromaticity for the title compounds in a planar conformation are given.

Fluorinated 1,3\lambda^{4}\delta^{2},2,4 -benzodithiadiazines : a synthetic, structural and theoretical study

The series of title compounds has been prepared through both electrophilic (C6HnF5−n−N=S=N−SiMe3 + SCl2) and nucleophilic (C6HF4−S−N=S=N−SiMe3 + CsF) intramolecular ortho-cyclisation reactions, and the former route seems to be the more effective. High regioselectivity of the ring-closing procedures is observed in both cases. The compounds were characterised by X-ray crystallography and multinuclear (1H, 13C, 15N and 19F) NMR spectroscopy. In accordance with GIAO calculations, 15N{1H} experiments and the effects observed on complete substitution of hydrogen by fluorine, the high-field signal in the 15N NMR spectra can be assigned to N-4 and the low-field signal to N-2. In the crystal, 5,6,7-trifluoro- (5) and 5,6,8-trifluoro-1,3λ4δ2,2,4-benzodithiadiazine (6) are planar, whereas the 6,8-difluoro derivative 3 is bent along the S1···N4 line by 8.3°. According to NICS calculations the heterocycle moiety in this compound class is antiaromatic while the carbocycle is aromatic. The fluorine substituents increase the aromaticity − and in some cases (especially when a fluorine atom is present in the 8-position) the antiaromaticity − of the corresponding rings. The ortho-fluoro-containing starting material C6HnF5−n−N=S=N−SiMe3 (n = 2: 10) cyclises to the fluorinated 2,1,3-benzothiadiazole 27 upon treatment with CsF instead of SCl2. For starting compound 6-HC6F4−S−N=S=N−SiMe3 (14) the planar (Z,E) configuration features a short intramolecular H···N contact, as evidenced by X-ray diffraction. Both the reaction pathways mentioned are also discussed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)