Matrix Photochemistry of syn-(Chlorocarbonyl)sulfenyl Bromide, syn-ClC(O)SBr:  Precursor to the Novel Species anti-ClC(O)SBr, syn-BrC(O)SCl, and BrSCl

Abstract

The vapor of (chlorocarbonyl)sulfenyl bromide, ClC(O)SBr, was isolated in solid Ar, Kr, N(2), and Ar doped with 5% CO at 15 K, and the matrix was subsequently irradiated with broad-band UV--visible light (200 < or = lambda < or = 800 nm), the changes being followed by reference to the IR spectrum of the matrix. The initial spectrum showed the vapor of ClC(O)SBr to consist of more than 99% of the syn form (with the C==O bond syn with respect to the S--Br bond) in equilibrium with less than 1% of the anti conformer. Irradiation caused various changes to occur. First, conformational randomization took place, leading to a roughly equimolar mixture of the two rotamers, and so affording the first spectroscopic characterization of an anti-ClC(O)S-containing compound. Simultaneously, the novel constitutional isomer syn-BrC(O)SCl was also formed. Continued photolysis resulted in the decay of all these species while revealing a third reaction channel, leading to the elimination of CO and the formation of the new triatomic sulfur halide BrSCl. The assignment of the IR bands to the different products was made on the basis of the usual criteria, taking account (i) of the effects of the naturally occurring isotopic pairs (35)Cl/(37)Cl and (79)Br/(81)Br, (ii) of the vibrational properties of related molecules, and (iii) of the properties predicted for the relevant molecules by quantum chemical calculations.

Methanesulfenyl Fluoride, CH3SF, a Missing Link in the Family of Sulfenyl Halides: Formation and Characterization through the Matrix Photochemistry of Methyl Thiofluoroformate, FC(O)SCH3

“…[11] The unambiguous identification of IR absorptions due to the less stable anti rotamer allows us to conclude that the vapor is composed of approximately 98 % of the syn form and 2 % of the anti form at ambient temperatures, in good agreement with the forecasts of quantum chemical calculations. Both forms of FC(O)SCH 3 then photodecompose.…”

“…Comparison with the results of theoretical calculations performed with different methods suggests that these absorptions arise not from the syn (A) but from the anti (B) conformer of FC(O)SCH 3 (in which the C=O bond is oriented anti with respect to the SÀCH 3 bond), which has not been identified previously (Scheme 1). The syn-anti randomization of matrix-isolated sulfenyl carbonyl compounds under UV-visible irradiation appears to be a general feature of this family of compounds, as reported previously, for example, for ClC(O)SCl, [9,10] ClC(O)SBr, [11] FC(O)SCl, [12] FC(O)SBr, [4] CH 3 C(O)SH, [13] FC(O)SNSO, [14] and FC(O)SS-C(O)F. [15] For further evidence, we measured the IR spectrum of perdeuteromethyl thiofluoroformate, FC(O)SCD 3 , both as a vapor (see Supporting Information) and isolated in an Ar matrix. The results correlate closely with those for the normal compound and are also well reproduced by the theoretical calculations.…”

“…[19] As with other carbonyl sulfenyl compounds, [9,11] it appears therefore that the elimination of OCS affords a secondary channel for photodecomposition, presumably proceeding in accordance with Equation (2), although no sig- nals attributable to CH 3 F or CD 3 F could be detected, being masked in all probability by stronger absorptions of the largely unchanged thiofluoroformate.…”

“…The most distinctive of these was the cluster of absorptions occurring in the region 2135-2150 cm À1 readily identifiable with the photoelimination of www.chemeurj.org CO. [9,11,17] The sharpest feature, appearing at 2147.9 and 2148.0 cm À1 on photolysis of FC(O)SCH 3 and FC(O)SCD 3 , respectively (see Supporting Information), implies some kind of loose complexation of the CO molecule. While free CO isolated in an Ar matrix absorbs at 2138.2 cm À1 , [17] several loosely bound complexes characterized by a blue shift of the n(CO) fundamental have been reported, for example, 2140.7 cm À1 for OC···Cl 2 , 2148.3 cm À1 for OC···BrCl, 2154.0/ 2157.0 cm À1 for OC···ICl, and 2144.2/2145.6 cm À1 for OC···ClI.…”

“…Following our normal practice in charting the photochemistry of matrix-isolated compounds of this sort, [9,11,19] we grouped the new absorptions into different sets according to their behavior as a function of irradiation time (see Figure 3). Two such sets, identified with distinct products C and D, could thus be recognized: C was an intermediate photoproduct that first accumulated and then decayed on continued photolysis, this decay correlated with the emergence and growth of the final product D.…”