Inorg. Chem. 2003, 42, 3079−3085
Perfluoromethyl Fluorocarbonyl Peroxide, CF3OOC(O)F: Structure, Conformations, and Vibrational Spectra Studied by Experimental and Theoretical Methods Frank Trautner,† Khodayar Gholivand,‡,§ Pla´cido Garcı´a,‡ Helge Willner,*,‡ Mauricio F. Erben,| Carlos O. Della Ve´dova,*,|,⊥ and Heinz Oberhammer*,† Institut fu¨ r Physikalische und Theoretische Chemie, UniVersita¨ t Tu¨ bingen, D-72076 Tu¨ bingen, Germany, Fakulta¨ t 4, Anorganische Chemie, Gehard-Mercator-UniVersita¨ t Duisburg, Lotharstr. 1 D-47048 Duisburg, Germany, CEQUINOR (CONICET-UNLP), Departamento de Quı´mica, Facultad de Ciencias Exactas, UniVersidad Nacional de La Plata, 47 esq. 115 (1900) La Plata, Repu´ blica Argentina, and Laboratorio de SerVicios a la Industria y al Sistema Cientı´fico (UNLP-CIC-CONICET), Camino Centenario, Gonnet, Buenos Aires, Repu´ blica Argentina Received December 11, 2002
The conformational properties and the geometric structure of perfluoromethyl fluorocarbonyl peroxide, CF3OOC(O)F, have been studied by matrix IR spectroscopy, gas electron diffraction, and quantum chemical calculations (HF, B3LYP, and MP2 methods with 6-311G* basis sets). Matrix IR spectra imply a mixture of syn and anti conformers (orientation of the CdO bond relative to the OsO bond) with ∆H° ) Hanti° − Hsyn° ) 2.16(22) kcal/mol. At room temperature, the contribution of the anti rotamer is about 3.0%. The OsO bond (1.422(15) Å) is within the experimental uncertainties equal to those in related symmetrically substituted peroxides CF3OOCF3 and FC(O)OOC(O)F (1.419(20) and 1.419(9) Å, respectively), and the dihedral angle δ(COOC) (111(5)°) is intermediate between the values in these two compounds (123(4)° and 83.5(14)°, respectively).
Introduction The most interesting structural feature of peroxides X2O2 is the dihedral angle δ(XOOX). For the parent compound H2O2, an effective dihedral angle (vibrationally averaged value) of 120.0(5)° was derived from rotational constants.1 The estimated experimental equilibrium value, which corresponds to the minimum of the torsional potential, is 112(1)°.2 In many other peroxides, this value is larger: 123(4)° in CF3OOCF3,3 129(2)° in SF5OOSF5,4 135(5)° in CH3OOCH3,5 * Authors to whom correspondence should be addressed. E-mail:
[email protected] (C.O.D.V.);
[email protected] (H.O.). ‡ Gehard-Mercator-Universita ¨ t Duisburg. § Permanent address: Tarbiat Modarres University, P. O. Box 141554838, Teheran, Iran. | Universidad Nacional de La Plata. ⊥ Laboratorio de Servicios a la Industria y al Sistema Cientı´fico (UNLP-CIC-CONICET). † Universita ¨ t Tu¨bingen. (1) Redington, R. L.; Olson, W. B.; Cross, P. C. J. Chem. Phys. 1962, 36, 1311. (2) Koput, J. Chem. Phys. Lett. 1995, 236, 512. (3) Marsden, C. J.; Bartell, L. S.; Diodati, F. P. J. Mol. Struct. 1977, 39, 253. (4) Zylka, P.; Oberhammer, H.; Seppelt, K. J. Mol. Struct. 1991, 243, 411.
10.1021/ic0262583 CCC: $25.00 Published on Web 04/01/2003
© 2003 American Chemical Society
144(6)° in Me3SiOOSiMe3,6 and 166(3)° in ButOOBut.6 Two trends are evident from this rather limited number of examples: the dihedral angle increases with increasing steric requirements of the substituents and decreases with their increasing electron-withdrawing properties (cf. CF3OOCF3 and CH3OOCH3). Interaction between the lone pairs7 of the two oxygen atoms and anomeric effects8 are usually the qualitative explanation for the gauche orientation of substituents in peroxides. The latter describes a stabilizing overlap between the lone pair of oxygen and the σ* orbital of the opposite O-X bond. Thus, the dihedral angle depends on the form of the lone pairs, the size of the anomeric effect, and the steric demands of the substituents. According to this model, the angle should be g90°. However, unusual structures that do not obey this model are found in FOOF9 and (5) Hass, B.; Oberhammer, H. J. Am. Chem. Soc. 1984, 106, 6146. (6) Ka¨ss, D.; Oberhammer, H.; Brandes, D.; Blaschette, A. J. Mol. Struct. 1977, 40, 65. (7) Alleres, D. R.; Cooper, D. L.; Cunningham, T. P., Gerratt, J.; Karadakov, P. B.; Raimondi, M. J. Chem. Soc., Faraday Trans. 1995, 91, 3357. (8) Kirby, J. The Anomeric Effect and Related Stereochemical Effects at Oxygen; Springer: Berlin, 1983.
Inorganic Chemistry, Vol. 42, No. 9, 2003
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with dihedral angles of 88.1(4)° and 81.03(1)°, respectively. Similarly, in a series of peroxides, such as FC(O)OOC(O)F,11 CF3C(O)OOC(O)CF3,12 FC(O)OONO2,13 CH3C(O)OONO2, and CF3C(O)OONO2,14 the dihedral angle around the O-O bond is also smaller than 90°. Hence, dihedral angles smaller than 90° are observed in peroxides with two sp2-hybridized substituents (RC(O) or NO2), and if both substituents are sp3-hybridized, the dihedral angle is larger than 120°. An intermediate angle has been observed in CF3OONO2 (105.1(16) °),15 which contains one sp3- and one sp2-hybridized substituent. In order to continue the studies on peroxide structures, we report in this paper the characterization of CF3OOC(O)F, which contains sp3and sp2-hybridized carbon atoms, using vibrational spectroscopy, gas electron diffraction (GED), and quantum chemical calculations. Another aspect of this work is an improved preparation of CF3OOC(O)F. The title compound was synthesized for the first time in 1967 by Cauble and Cady by photochemical reaction of FC(O)OOC(O)F with fluorine16 with a yield of about 5% based upon the quantity of peroxide consumed. Talbot17 and Aymonino18 reported new photochemical reactions involving the formation of this peroxide. Anderson and Fox19 and DesMarteau20 synthesized CF3OOC(O)F using the reaction between CF2(OF)2 and COF2 catalyzed by CsF. Experimental Section Caution! CF3OOC(O)F is potentially explosiVe, especially in the presence of oxidizable materials. It is important to take safety precautions when this compound is handled in the liquid or solid state. Reactions inVolVing this species should be carried out only in millimolar quantities. General Procedure and Reagents. Volatile materials were manipulated in a glass vacuum line equipped with two capacitance pressure gauges (221 AHS-1000 and 221 AHS-10, MKS Baratron, Burlington, MA) and three U-traps and glass valves with PTFE systems (Young, London, U.K.). The vacuum line was connected to an IR cell (optical path length 200 mm, Si windows 0.5 mm thick) contained in the sample compartment of an FTIR instrument (Nicolet Impact 400D, Madison, WI). This arrangement allowed us to observe the purification processes and to follow the course of the reactions. Solid materials were handled in a drybox (Braun, Unilab) filled with nitrogen containing less than 1 ppm H2O and O2. The pure products were stored in flame-sealed glass ampules (9) Hedberg, L.; Hedberg, K.; Eller, P. G.; Ryan, R. R. Inorg. Chem. 1988, 27, 232. (10) Birk, M.; Friedl, R. A.; Cohen, E. A.; Pickett, H. M.; Sander, S. P. J. Chem. Phys. 1989, 91, 6588. (11) Mack, H.-G.; Della Ve´dova, C. O.; Oberhammer, H. Angew. Chem., Int. Ed. Engl. 1991, 30, 1145. (12) Kopitzky, R.; Willner, H.; Hermann, A.; Oberhammer, H. Inorg. Chem. 2001, 40, 2693. (13) Scheffler, D.; Schaper, J.; Willner, H.; Mack, H.-G.; Oberhammer, H. Inorg. Chem. 1997, 36, 339. (14) Hermann, A.; Niemeyer, J.; Mack, H.-G.; Kopitzky, R.; Beuleke, M.; Willner, H.; Christen, D.; Scha¨fer, M.; Bauder, A.; Oberhammer, H. Inorg. Chem. 2001, 40, 1672. (15) Kopitzky, R.; Willner, H.; Mack, H.-G.; Pfeiffer, A.; Oberhammer, H. Inorg. Chem. 1998, 37, 6208. (16) Cauble, R.; Cady, G. H. J. Am. Chem. Soc. 1967, 89, 5161. (17) Talbott, R. L. J. Org. Chem. 1968, 33, 2095. (18) Aymonino, P. J.; Blesa, M. A. An. Asoc. Quı´m. Argent. 1970, 58, 27. (19) Anderson, L. R.; Fox, W. B. Inorg. Chem. 1970, 9, 2182. (20) DesMarteau, D. D. Inorg. Chem. 1970, 9, 2179.
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under liquid nitrogen in a long-term Dewar vessel. The ampules were opened and resealed with an ampule key21 on the vacuum line, an appropriate amount was taken out for the experiments, and then, they were flame-sealed again. For Raman measurements, the sample was transferred into a 4 mm glass capillary. NMR measurements were carried out on samples in 3 mm o.d. flamesealed capillaries, which were centered inside 5 mm NMR tubes containing CDCl3 (Merck) and CFCl3 (Merck) as lock and reference. Details of the matrix-isolation apparatus have been given elsewhere.22 FC(O)OOC(O)F was prepared in a flow system according to the procedure described in the literature by reacting CO, F2, and O2.23 For the synthesis of CF2(OF)2, an 80 mL metal reactor was charged with 4 g of fine grounded CsF (p.a. Fluka) inside the drybox. The reactor was filled with a mixture of 20 mmol of CO2 and 80 mmol of F2. After a reaction time of 3 days at room temperature, the bulb was cooled to -196 °C, and the excess of F2 was pumped off. The product was passed in a vacuum through a series of traps held at -70, -120, and -196 °C, and pure CF2(OF)2 was collected in the -120 °C trap.24,25 CO (95.5%, Linde, Munich, Germany), F2 (Solvay), and O2 (99.999% Linde, Munich, Germany) were obtained from commercial sources and used without further purification. Synthesis of CF3OOC(O)F. To ensure the quality of the final product, we have synthesized CF3OOC(O)F by two different routes: (i) in a modified synthesis described by Cauble and Cady16 and (ii) by reaction of CF2(OF)2 with COF2 in the presence of CsF, according to the literature procedure.19 (i) In a typical run, a 1 L quartz bulb was charged with 50 mbar of FC(O)OOC(O)F, 50 mbar COF2, and 100 mbar F2. After the bulb was immersed in a water bath at 20 °C, the content was irradiated with a low-pressure mercury lamp (40 W) for 3 h. The excess of F2 was pumped off at -196 °C, and the products of several batches were separated in a series of traps held at -100, -140, and -196 °C. After repeated trap-to-trap distillation, pure CF3OOC(O)F was obtained in the -140 °C trap. (ii) The method reported by Anderson and Fox19 and DesMarteau20 was also used, by mixing in a metal reactor 50 mmol COF2 and 20 mmol CF2(OF)2 over treated CsF (CsOCF3). After a reaction time of 18 h at -20 °C, the mixture was passed in a vacuum through a series of traps held at -100, -140, and -196 °C, and pure CF3OOC(O)F was collected in the -140 °C trap. The purity of the products was checked by 19F and 13C NMR spectroscopy at -70 °C because of the high volatility of the compound and for safety reasons: δF(CF3) ) -69.2 ppm (doublet), δF(COF) ) -32.6 ppm (quartet), δc(CF3) ) 123.2 ppm (quartet), δc(COF) ) 142.7 ppm (doublet), 1JCF(CF3) ) 269.2 Hz, 1JCF(COF) ) 298.1 Hz. The data are in accordance with previous reported values.26 Preparation of Matrixes. Small amounts (
