Andrey V. Zibarev

Breathing Some New Life into an Old Topic: Chalcogen-Nitrogen π-Heterocycles as Electron Acceptors

Recent progress in the design, synthesis and characterization of chalcogen-nitrogen π-heterocycles, mostly 1,2,5-chalcogenadiazoles (chalcogen: S, Se and Te) and their fused derivatives, possessing positive electron affinity is discussed together with their use in preparation of charge-transfer complexes and radical-anion salts—candidate building blocks of molecule-based electrical and magnetic functional materials.

Cyclic aryleneazachalcogenenes. Part III [1] synthesis of polyfluorinated 2,1,3-benzothia-(selena) diazoles

Abstract 1-(4-X-Tetrafluorophenyl)-3-trimethylsilyl-1,3-diaza-2- thiaallenes (X = H, CH 3 , Br, F, CF 3 ) treated with CsF in acetonitrile or THF cyclized to 6-X-4,5,7-trifluoro-2,1,3-benzothiadiazoles whose reduction led to the corresponding 1,2-diamino- benzenes. Cyclization of the latter with SeCl 4 gave 6-X-4,5,7- trifluoro-2,1,3-benzoselenadiazoles.

Cyclic aryleneazachalcogenenes—VI. Synthesis, crystal and molecular structure of 5,6,7,8-tetrafluoro-1,3,2,4-benzodithiadiazine, a formally antiaromatic stable compound

Abstract 1-Pentafluorophenyl-4-trimethylsilyl-2,4-diaza-1,3-dithia-2,3-butadiene is cyclized by CsF in acetonitrile to 5,6,7,8-tetrafluoro-1,3,2,4-benzodithiadiazine (54% yield), a thermodynamically stable formally antiaromatic 12Π-electron compound having an almost planar molecular geometry, as shown by the X-ray structure analysis data. The crystal and molecular structure of the polyfluorinated derivative appreciably differ from those of its hydrocarbon analogue, 1,3,2,4-benzodithiadiazine.

Interaction of 1,2,5-Chalcogenadiazole Derivatives with Thiophenolate: Hypercoordination with Formation of Interchalcogen Bond versus Reduction to Radical Anion

According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 Å) is ca. 0.5 Å longer than the sum of the covalent radii of these atoms but ca. 1 Å shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9.

Heterospin π-Heterocyclic Radical-Anion Salt: Synthesis, Structure, and Magnetic Properties of Decamethylchromocenium [1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl

Decamethylchromocene, Cr(II)(eta(5)-C(5)(CH(3))(5))(2) (2), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) in a tetrahydrofuran solvent at ambient temperature with the formation of radical-anion salt [2](+)[1](-) (3) isolated in 97% yield. The heterospin salt 3 ([2](+), S = 3/2; [1](-), S = 1/2) was characterized by single-crystal X-ray diffraction as well as magnetic susceptibility measurements in the temperature range 2-300 K. The experimental data together with theoretical analysis of the salts magnetic structure within the CASSCF and spin-unrestricted broken-symmetry (BS) density functional theory (DFT) approaches revealed antiferromagnetic (AF) interactions in the crystalline 3: significant between anions [1](-), weak between cations [2](+), and very weak between [1](-) and [2](+). Experimental temperature dependences of the magnetic susceptibility and the effective magnetic moment of 3 were very well reproduced in the assumption of the AF-coupled [1](-)...[1](-) (J(1) = -40 +/- 9 cm(-1)) and [2](+)...[2](+) (J(2) = -0.58 +/- 0.03 cm(-1)) pairs. The experimental J(1) value is in reasonable agreement with the value calculated using BS UB3LYP/6-31+G(d) (-61 cm(-1)) and CASSCF(10,10)/6-31+G(d) (-15.3 cm(-1)) approaches. The experimental J(2) value is also in agreement with that calculated using the BS DFT approach (-0.33 cm(-1)).

Planar 1,3λ4δ2,2,4‐Benzodithiadiazine and Its Nonplanar 5,6,7,8‐Tetrafluoro Derivative: Gas‐Phase Structures Studied by Electron Diffraction and Ab Initio Calculations

The gas-phase molecular structures of 1,3lambda4delta2,2,4-benzodithiadiazine and 5,6,7,8-tetrafluoro-1,3lambda4delta2,2,4-benzodithiadiazine have been investigated by ab initio calculations and electron diffraction using the SARACEN method of structural analysis. Important structural parameters (r(h1) structure) for the parent compound were found to be: 1.546(3), r(S-N) 1.697(5), r(C-S) 1.784(5), and r(C-N) 1.393(6) A. For the tetrafluoro derivative, these are (r(h1) structure): 1.552(3), r(S-N) 1.723(8), r(C-S) 1.812(9), and r(C-N) 1.396(7) A. Furthermore, the GED experiment (Gas Electron Diffraction) quite convincingly demonstrates the nonplanarity of the former and the planarity of the latter in agreement with DFT calculations; but the results contradict calculations at the MP2 level. The effect of the fluorine atoms on the conformations of the molecules is discussed.

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.

Bis(toluene)chromium(I) [1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl and [1,2,5]Thiadiazolo[3,4-b]pyrazinidyl: New Heterospin (S1 = S2 = 1/2) Radical-Ion Salts

Bis(toluene)chromium(0), Cr(0)(η(6)-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formation of heterospin, S1 = S2 = ½, radical-ion salts [3](+)[1](-) (4) and [3](+)[2](-) (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffraction (XRD), solution and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2-300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anions were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functional theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactions were revealed. The experimental χT temperature dependences of the salts were simulated using the Van Vleck formula and a diagonalization of the matrix of the Heisenberg spin Hamiltonian for the clusters of 12 paramagnetic species with periodic boundary conditions. According to the calculations and χT temperature dependence simulation, a simplified magnetic model can be suggested for the salt 4 with AF interactions between the anions ([1](-)···[1](-), J1 = -5.77 cm(-1)) and anions and cations ([1](-)···[3](+), J2 = -0.84 cm(-1)). The magnetic structure of the salt 5 is much more complex and can be characterized by AF interactions between the anions, [2](-)···[2](-), and by both AF and ferromagnetic (FM) interactions between the anions and cations, [2](-)···[3](+). The contribution from FM interactions to the magnetic properties of the salt 5 is in qualitative agreement with the positive value of the Weiss constant Θ (0.4 K), whereas for salt 4, the constant is negative (-7.1 K).

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.

Molecular complexes of octafluoronaphthalene with acyclic and heterocyclic sulfur–nitrogen compounds

Abstract Mismatched molecular 1:1 complexes were prepared from C10F8 and sulfur diimides ArNSNAr 1 and ArNSN–SiMe3 2, 3 (1, 2: Ar=2,6–dimethylphenyl; 3: Ar=phenyl). In the case of 2, the complexation is accompanied by the unexpected cyclization of 2 into 7-methyl-2,1-benzisothiazole 4. The X-ray molecular structures of C10F8·1, C10F8·3 and C10F8 are presented; in C10F8·4 the 7-methyl-2,1-benzisothiazole 4 is highly disordered. The complexes provide very rare examples of markedly bent (C10F8·1), polyheteroatom (C10F8·3) and heterocyclic (C10F8·4) molecules involved in non-covalent arene-polyfluoroarene π-stacking interactions.