The gas-phase molecular structures of 1,3,2,4-benzodithiadiazine and 5,6,7,8-tetrafluoro-1,3,2,4-benzodithiadiazine have been investigated by ab initio calculations and electron diffraction using the SARACEN method of structural analysis. Important structural parameters for the parent compound were found to be: <r(S=N)> 1.546(3), r(S-N) 1.697(5), r(C-S) 1.784(5), and r(C-N) 1.393(6) Å. For the tetrafluoro derivative, these are: <r(S=N)> 1.552(3), r(S-N) 1.723(8), r(C-S) 1.812(9), and r(C-N) 1.396(7) Å. 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.
Blockhuys, F.; Hinchley, S.L.; Makarov, A.Yu.; Gatilov, Yu.V.; Zibarev, A.V.; Woollins, J.D.; Rankin, D.W.H. Chem. Eur. J. 2001, 7, 3592-3602.
A series of fluorinated 1,3,2,4-benzodithiadiazines has been prepared through both electrophilic and nucleophilic intramolecular ortho-cyclisation reactions, and the former route seems to be more effective. High regioselectivity of the ring-closing procedures is observed in both cases. The compounds have been characterised by X-ray crystallography and multinuclear (H, C, N and F) NMR spectroscopy. In accordance with GIAO calculations, N‹H› experiments and the effects observed on complete substitution of hydrogen by fluorine, the high-field signal in the N NMR spectra can be assigned to N-4 and the low-field signal to N-2. In the crystal, the 5,6,7-trifluoro and 5,6,8-trifluoro derivatives are planar, whereas the 6,8-difluoro derivative 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. One ortho-fluoro-containing starting material cyclises to a fluorinated 2,1,3-benzothiadiazole upon treatment with CsF instead of sulfenyl chloride. For another starting compound 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.
Makarov, A.Yu.; Bagryanskaya, I.Yu.; Blockhuys, F.; Van Alsenoy, C.; Gatilov, Yu.V.; Knyazev, V.V.; Maksimov, A.M.; Mikhalina, T.V.; Platonov, V.E.; Shakirov, M.M.; Zibarev, A.V. Eur. J. Inorg. Chem. 2003, 77-88.
The gas-phase molecular structures of 6,8-difluoro-1,3,2,4-benzodithiadiazine and 5,6,7-trifluoro-1,3,2,4-benzodithiadiazine have been determined using quantum chemical calculations and electron diffraction via the SARACEN method of structural analysis. Of particular interest was the planarity or nonplanarity of the heterocyclic fragments of the molecules. It was shown that the difluoro compound is planar with respect to the heterocyclic fragment [folding angle: 0.0(5)° (figures in parentheses indicated e.s.d.s in the final digits)] and that the trifluoro compound probably deviates from planarity to a small extent [folding angle: 4.0(-30;+3)°; the large uncertainty in the value of this angle is due to the low-frequency, large-amplitude vibrational motion associated with the folding of the heterocyclic fragment]. Pertinent structural parameters from the electron diffraction data of the difluoro compound are av[r(S=N)] = 155.7(7) pm, r(S-N) = 175.8(5) pm, r(C-S) = 176.6(8) pm and r(C-N) = 141.6(2) pm. For the trifluoro compound the equivalent structural parameters are av[r(S=N)] = 155.5(7) pm, r(S-N) = 170.7(6) pm, r(C-S) = 180.6(8) pm and r(C-N) = 140.6(2) pm. The gas-phase electron diffraction structures have been compared with results from ab initio and DFT calculations and also with experimental solid-state structures.
Turner, A.R.; Blockhuys, F.; Van Alsenoy, C.; Robertson, H.E.; Hinchley, S.L.; Zibarev, A.V.; Makarov, A.Yu.; Rankin, D.W.H. Eur. J. Inorg. Chem. 2005, 572-581.
5,6,7,8-Tetrafluoro-3,1,2,4-benzothiaselenadiazine is prepared by an intramolecular nucleophilic cyclization mediated by CsF. According to an X-ray diffraction analysis, its heterocycle is bent along the Se(1)...N(4) line by 6.0(2)° in the crystal. Despite the obvious similarities between this benzothiaselenadiazine and its 1,3-dithia analogue with respect to molecular composition and shape, the crystal packing of the former is substantially different from that of the latter. An interesting consequence of this is the inclusion of atmospheric nitrogen in the crystal lattice of the selenium derivative. The molecular structure and bonding of the benzothiaselenadiazine have been investigated using quantum-chemical calculations at the DFT/B3LYP/6-311+G* level of theory, and the results have been compared to those of the benzodithiadiazine and their hydrocarbon analogues.
Makarov, A.Yu.; Tersago, K.; Nivesanond, K.; Blockhuys, F.; Van Alsenoy, C.; Kovalev, M.K.; Bagryanskaya, I.Yu.; Gatilov, Yu.V.; Shakirov, M.M.; Zibarev, A.V. Inorg. Chem. 2006, 45, 2221-2228.
The molecular structure of 1,3,2,4-benzodithiadiazine has been studied theoretically by a large number of computational methods. The results of calculations using different DFT functionals are compared with those obtained from HF, MP2, MP4(SDQ), QCISD and CCSD calculations. In addition, the influence of a number of basis sets on the calculated geometry was investigated. The results of the post-HF methods show that convergence of the geometrical parameters is already obtained for the relatively small 6-311+G* basis set. Taking the MP4(SDQ)/cc-pVTZ geometry as a reference the DFT/B1B95 functional appears to provide the best description of all the examined functionals.
Tersago, K.; De Dobbelaere, C.; Van Alsenoy, C.; Blockhuys, F. Chem. Phys. Lett. 2007, 434, 200-204.
Our Microreview highlights the most important advances in the heteroatom chemistry of 1,3,2,4-benzodithiadiazines (pi-excessive and formally antiaromatic heterocycles), covering methods for synthesis, nontrivial features of the molecular and pi-electronic structure, spectral properties, and reactivity, in particular the transformations into persistent pi-radicals. The chemistry of 1,3,2,4-benzodithiadiazines is compared to that of related chalcogen-nitrogen compounds, both cyclic and acyclic.
Blockhuys, F.; Gritsan, N.P.; Makarov, A.Yu.; Tersago, K.; Zibarev, A.V. Eur. J. Inorg. Chem. 2008, 655-672.