J. Phys. Chem. A 2004, 108, 7179-7187
7179
Matrix Photochemistry of the Chlorocarbonyl Sulfenyl Compounds ClC(O)SY, with Y ) Cl or CH3 Rosana M. Romano,*,† Carlos O. Della Ve´ dova,†,‡ and Anthony J. Downs§ CEQUINOR (CONICET) and Laboratorio de SerVicios a la Industria y al Sistema Cientı´fico (UNLP-CIC-CONICET), Departamento de Quı´mica, Facultad de Ciencias Exactas, UniVersidad Nacional de La Plata, 47 esq. 115, (1900) La Plata, Argentina, and Inorganic Chemistry Laboratory, UniVersity of Oxford, South Parks Road, Oxford, OX1 3QR, U.K. ReceiVed: March 19, 2004; In Final Form: June 7, 2004
The photochemistries of the molecules ClC(O)SCl and ClC(O)SCH3 (in both their normal and perdeuterated forms) isolated in solid Ar or N2 matrixes at 15 K have been investigated. On the basis of evidence of the IR spectra of the matrixes, the products of irradiation with broad-band UV-visible light (200 e λ e 800 nm) were identified, thereby revealing quite different photochemical behaviors for the two molecules. ClC(O)SCl is subject to multichannel changes that include interconversion of the syn and anti rotamers, photodecomposition to give CO and SCl2, formation of the hitherto unknown radical ClC(O)S•, and subsequent decomposition of this radical to give either the ClCO• radical or the OCS molecule. By contrast, ClC(O)SCH3 decomposes in two steps, the first consisting of fragmentation to CO and ClSCH3, and the second entailing detachment of a hydrogen atom from the methyl group of ClSCH3 with the formation of the molecular complex H2CdS‚‚‚HCl. The IR spectra of both the ClC(O)S• radical and H2CdS‚‚‚HCl have been interpreted with reference to the spectra predicted by ab initio and density functional theory methods.
Introduction The La Plata research group has been interested in recent years in the structural, and particularly the conformational, properties of carbonyl sulfenyl derivatives of the type XC(O)SY and in gaining a detailed understanding of the photochemical behaviors of these compounds when isolated in solid inert matrixes at cryogenic temperatures. Three aspects of the rich matrix photochemistry that has thus come to light are noteworthy: (i) The studies reveal photochemical interconversion between the more stable syn conformer and the anti conformer. This has been observed for several members of the sulfenyl carbonyl family, for example, FC(O)SCl,1 FC(O)SBr,2 FC(O)SNSO,3 FC(O)SSC(O)F,4 ClC(O)SBr,5 CH3C(O)SH,6 and FC(O)SCH3.7 (ii) The isolation, identification, and characterization of a variety of novel molecules have been achieved through photodecomposition of sulfenyl carbonyl compounds, including for example, sulfur (II) halides, such as BrSF2 and BrSCl,5 as well as isomers of the parent molecules, for example, BrC(O)SCl (from ClC(O)SBr)5 and ClC(O)SF (from FC(O)SCl).8 (iii) Interpretation of the photochemistry, made possible by identification of all the photoproducts and detailed studies of their behavior as a function of irradiation time, has led to the development of new routes for the preparation of novel compounds by photochemical reactions brought about in matrix conditions. The first reported example was the isolation of BrC(O)SBr9 by photolysis of a mixture of Br2 and OCS in an †
CEQUINOR, Universidad Nacional de La Plata. Laboratorio de Servicios a la Industria y al Sistema Cientı´fico, Universidad Nacional de La Plata. § University of Oxford. ‡
SCHEME 1: Photochemical Interconversion between the Syn and Anti Forms of XC(O)SY Compounds in Matrix Conditions.
Ar matrix, a method suggested by detailed analysis of the matrix photochemistry of ClC(O)SBr.5 It is in this general context and as a second stage of our studies of the structural and vibrational properties of (chlorocarbonyl)sulfenyl chloride, ClC(O)SCl, and methyl thiochloroformate, ClC(O)SCH3,10 that we report here on the matrix photochemistry of these two molecules. To assist with the identification of the products formed on photolysis of ClC(O)SCH3, we have also studied the matrix photochemistry of the perdeuterated compound. In addition, attribution to new species of some of the IR bands appearing on photolysis has been supported by ab initio and density functional theory (DFT) calculations. Experimental and Computational Procedures Experimental Methods. ClC(O)SCl and ClC(O)SCH3 were purchased from Aldrich and subsequently purified by repeated trap-to-trap distillation in vacuo. ClC(O)SCD3 was prepared for the first time by the reaction of ClC(O)OCCl3 with CD3SH (both ex-Aldrich) at ambient temperature, and subsequently purified by repeated trap-to-trap distillation. The matrix gases Ar and N2 were used as supplied (both BOC, research grade). Gas mixtures of ClC(O)SCl, ClC(O)SCH3, or ClC(O)SCD3, each taken severally with Ar or N2 in the proportions ∼1:1000, were prepared by standard manometric methods. Such a mixture
10.1021/jp048756y CCC: $27.50 © 2004 American Chemical Society Published on Web 08/03/2004
7180 J. Phys. Chem. A, Vol. 108, No. 35, 2004
Romano et al. TABLE 1: Wavenumbers and Assignments of the IR Absorptions Appearing after Broad-Band UV-Visible Photolysis of ClC(O)SCl Isolated in an Ar or N2 Matrix Ar matrix N2 matrix ν (cm-1) ν (cm-1)
Figure 1. IR spectra of an Ar matrix containing ClC(O)SCl (A) following deposition and (B) after 120 min of broad-band UV-visible photolysis.
was then deposited on a CsI window cooled to ∼15 K by means of a Displex closed-cycle refrigerator (Air Products, model CS202) using the pulsed deposition technique.11,12 IR spectra of the matrix samples were recorded at a resolution of 0.5 cm-1, with 256 scans and an accuracy of (0.1 cm-1, using a Nicolet Magna-IR 560 FTIR instrument equipped with either an MCTB or a DTGS detector (for the range 4000-400 or 600-250 cm-1, respectively). Following deposition and IR analysis of the resulting matrix, the sample was exposed to broad-band UVvisible radiation (200 e λ e 800 nm) from a Spectral Energy Hg-Xe arc lamp operating at 800 W. The output from the lamp was limited by a water filter to absorb IR radiation and so minimize any heating effects. The IR spectrum of the matrix was then recorded at different times of irradiation in order to monitor closely the decay and growth of the various absorptions. Experiments were also performed with a filter cutting out visible light and so confining the photolyzing radiation to wavelengths in the range 200-400 nm. Computational Details. MP2 and DFT (B3LYP) calculations with a 6-31+G* basis set were performed using the Gaussian 98 program package13 under the Linda parallel execution environment using two coupled personal computers.
wavenumber reported previously
2140.4
2145.7 2144.6
OC‚‚‚Cl2
νCdO
2140.7a
2137.9 2137.2
2139.6 2137.2
CO
νCdO
2138.2a
2050.7 2049.6 2046.9 2043.1
2057.9 2056.0 2054.2 2053.5 2052.4
OCS
νCdO
2049.3b
1998.0 1994.3
2005.2 2003.1 2000.9 1999.5
O13CS
νCdO
2000b
1892.5 1888.8 1876.7
1896.3 1894.0
ClCO•
νCdO
1876.7c
1774.8 1773.7
1762.6 1760.4
ClCOS•
νCdO
1714.3 1707.1
1712.7 1711.3
anti-ClC(O)SCl νCdO
1046.8 1045.2
1046.5 1044.1
OCS
913.5 908.9
919.9 918.5 917.8 915.6 914.1
ClCOS•
886.5 885.4 883.9 881.9 879.3
895.4 894.7 892.7 888.9 886.7 884.8
anti-ClC(O)SCl νasCl-C-S
859.5 857.3 839.5
848.8 843.7 835.0
OCS
νCdS
858b
520.2
526.5 524.5
SCl2
νs35ClS35Cl
524.2d
517.5
521.6 520.9
SCl2
νas35ClS35Cl
520.2d
515.2
519.5 518.5
SCl2
νs35ClS37Cl
512.8
515.6 514.6
SCl2
νas35ClS37Cl
a
Results and Discussion Photolysis of ClC(O)SCl. Exposure of an Ar or N2 matrix doped with roughly 0.1% ClC(O)SCl to broad-band UV-visible light (200 e λ e 800 nm) resulted in the decay of the bands due to ClC(O)SCl (as its syn conformer)10 and the appearance and growth of new bands belonging to several different products. Attempts to achieve some photoselectivity were unavailing. Thus, UV light restricted to the range λ ) 200-400 nm had the same effect as broad-band UV-visible light, but the reduced flux of photoactive radiation in the filtered beam meant that the rate of change was appreciably slower. Figure 1 illustrates the difference between the IR spectrum of an Ar matrix after broad-band irradiation for 2 h and the spectrum recorded immediately after deposition, revealing the absorptions that develop as a result of the photolysis. As reported previously,10
assignment vibrational mode molecule
2 δ(OCS)
1045b
Ref 18. b Ref 14. c Ref 17. d Ref 16.
some of the new bands can be assigned to the less stable anti conformer of ClC(O)SCl. These absorptions, which occur at 1701 and 870 cm-1 for an Ar matrix, are already present as extremely weak features in the original spectrum, with intensities suggesting that the anti form makes up
