Formation of New Halogenothiocarbonylsulfenyl Halides, XC(S)SY, through Photochemical Matrix Reactions Starting from CS2and a Dihalogen Molecule XY (XY = Cl2, Br2, or BrCl)

Preparation of FC(S)SF, FC(S)SeF and FC(Se)SeF through matrix photochemical reactions of F2 with CS2, SCSe, and CSe2

The reactions of F₂ with CS₂, SCSe, and CSe₂, respectively, were analyzed under matrix conditions by co-deposition of the halogen with the triatomic molecules trapped in argon matrices at cryogenic temperatures. In all cases, after co-deposition, the formation of the respective van der Waals complexes is observed. When each mixture is subsequently irradiated by means of broad-band UV-visible light (200 ≤ λ ≤ 800 nm), FC(S)SF, fluorothiocarbonylsulfenyl fluoride, FC(S)SeF, fluorothiocarbonylselenyl fluoride and FC(Se)SeF, fluoroselenocarbonylselenyl fluoride are produced, respectively. All these species exist as two stable planar syn- and anti-conformers (syn- and anti- of the CZ double bond, Y = S, Se, with respect to the S-F or Se-F single bond, respectively). For FC(S)SF, syn- is the rotamer with the lowest energy, while for both FC(S)SeF and FC(Se)SeF the anti-form is the lowest energy conformer. In all cases, other products due to alternative or subsequent photochannels are observed during the photochemical processes carried out in argon matrices at cryogenic temperatures.

Photochemical Reaction of OCSe with ClF in Argon Matrix: A Light-Driven Formation of XC(O)SeY (X, Y = F or Cl) Species

The photochemistry of OCSe with ClF trapped together in argon matrices at cryogenic temperatures has been explored and the first interhalogen representatives of the elusive XC(O)SeY family, namely syn-ClC(O)SeF, anti-ClC(O)SeF, syn-FC(O)SeCl, and anti-FC(O)SeCl, as well as the hitherto triatomic species ClSeF complexed by a CO molecule, were obtained. Both ClC(O)SeF conformers appear to be produced independently by photolysis of the respective precursors; while formation of both FC(O)SeCl structures is ruled by the presence of an angular molecular complex OCSe···Cl-F formed prior to photolysis. This latter photochemical pathway seems to favor the formation of the less stable anti-FC(O)SeCl structure instead of the more stable syn- one. With the aid of quantum chemical calculations, using ab initio, DFT, TDDFT, and CASSCF methods, the mechanism for this photochemical reaction is rationalized both in terms of radical processes as well as a photoinduced electron transfer occurring into the OCSe···Cl-F complex. Also a singlet-triplet conical intersection between anti and syn rotamers of the FC(O)SeCl molecule is theoretically explored.

Conformational and spectroscopic study of xanthogen ethyl formates, ROC(S)SC(O)OCH₂CH₃. Isolation of CH₃CH₂OC(O)SH

ROC(S)SC(O)OCH2CH3, with R=CH3-, (CH3)2CH- and CH3(CH2)2-, were obtained through the reaction between potassium xanthate salts, ROC(S)SK, and ethyl chloroformate, ClC(O)OCH2CH3. The liquid compounds were identified and characterized by (1)H and (13)C NMR and mass spectrometry. The conformations adopted by the molecules were studied by DFT methods. 6 conformers were theoretically predicted for R=CH3- and (CH3)2CH-, while the conformational flexibility of the n-propyl substituent increases the total number of feasible rotamers to 21. For the three molecules, the conformers can be associated in 3 groups, being the most stable the AS forms - the C=S double bond anti (A) with respect to the C-S single bond and the S-C single bond syn (S) with respect to the C=O double bond - followed by AA and SS conformers. The vibrational spectra were interpreted in terms of the predicted conformational equilibrium, presenting the ν(C=O) spectral region signals corresponding to the three groups of conformers. A moderated pre-resonance Raman enhancement of the ν(C=S) vibrational mode of CH3(CH2)2OC(S)SC(O)OCH2CH3 was detected, when the excitation radiation approaches the energy of a n→π∗ electronic transition associated with the C=S chromophore. UV-visible spectra in different solvents were measured and interpreted in terms of TD-DFT calculations. The unknown molecule CH3CH2OC(O)SH was isolated by the UV-visible photolysis of CH3OC(S)SC(O)OCH2CH3 isolated in Ar matrix, and also obtained as a side-product of the reaction between potassium xanthate salts, ROC(S)SK, and ethyl chloroformate, ClC(O)OCH2CH3.

Matrix isolation of the elusive fluorocarbonylsulfenyl fluoride molecule FC(O)SF

The syn and anti conformers of the hitherto unknown fluorocarbonylsulphenyl fluoride FC(O)SF were formed through the photochemical reactions between OCS and F(2), isolated in solid Ar. The reactions were followed by Fourier transform infrared (FTIR) spectroscopy, and the unknown products were proposed by comparison of the observed IR absorptions with their computed IR spectra. The reactions occur through a 1:1 molecular complex between OCS and F(2), forming the anti-FC(O)SF first, which subsequently transforms into the syn form, through a randomization process. At longer times of irradiation, FC(O)SF decomposes by extrusion of a CO molecule with the concomitant formation of SF(2) and the formation of a difluorophosgene molecule, O═CF(2). The migration of fluorine atoms in the matrixes is proposed to explain the formation of SF(4) and SF(6).

Early Barriers in the Matrix Photochemical Formation ofsyn–anti Randomized FC(O)SeF from the OCSe:F2 Complex

The photochemically induced reaction of OCSe and F(2), isolated together in an Ar matrix at about 15 K, leads to formation of the hitherto-unknown fluorocarbonylselenyl fluoride FC(O)SeF. The reaction occurs via a van der Waals complex O=C=Se...F-F that favors very early formation of the anti conformer. The presence and subsequent decay of a band assigned to the F-F vibration correlated with perturbed OCSe bands seems to confirm this hypothesis. Subsequent irradiation of the matrix leads to randomized FC(O)SeF by a photochemically induced conformational equilibrium between syn and anti forms. Another photochemical reaction channel is the formation of CO and SeF(2) molecules, which are produced in the same matrix cage and then form a loose complex. The changes were monitored and the products characterized experimentally by their IR spectra, and the spectra analyzed in the light of the results of theoretical calculations.