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Bis(fluorocarbonyl) Peroxide; an Unusual Molecular Structure.

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[7] 1: cubic, space group P43m (No. 215), Z = 1, a = 8.68(1) A, V =
653(1) A', Q ~ = 1.62
~ 2" < 28 <30"; (cu,,,
E.= 1.5418 A,
I( = 76.57 cm-'); T = 2 4 T , 119 reflections, 8/20 scan mode, all 119 reflections had 1 > 6 4 0 and were used to solve (Patterson and direct methods)
and refine (full matrix, least squares) the structure of 1. R = 0.0454,
R, = 0.0569. 9: monoclinic, space group C2/m (No. 12), 2 = 2,
a = 17.36(1),b = 11.97(1),~
=8.52(1)A,p= 113.84(7)"; V = 1620(5)A3,
QcA,cd = 1.340 g ~ m - ~2"
; < 28 < 40"; (Mo,.,
1 = 0.71069 A, I( =
18.78 cm-'); T = 24°C 1440 reflections, 8/28 scan mode, of these 1234
reflections with I > 6 4 4 were used to solve (Patterson and direct methods) and refine (full matrix, least squares) the structure of 9. R = 0.0533,
R, = 0.0668. The Te atom was slightly disordered; however, the structure
was refined successfully by assigning partial occupancies of 0.78 and 0.22
lo the two positions. Futher details of the crystal structure investigations
can be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technischeInformation mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD55575, the names of the authors, and the journal citation.
[8] G. G. Hoffmann, C. Burschka, J. Organomer. Chem. 267 (1984) 229; A.
Boardman, S. E. Feffs, R. W. H. Small, I. J. Worrall, lnorg. Chim. Acta 99
(1985) L39.
191 L. 1. Zakharkin, V. V. Gavrilenko, Iz. Akad. Nauk SSSR Ser. Khim. 1960,
[lo] G. G. Hoffmann, Phosphorus Sulfur Relar. Elem. 28 (1986) 167.
[ll] M. A. Banks, 0. T. Beachley, Jr., H. J. Gysling, H. R. Luss, Organomefallics 9 (1990) 1979.
[12] G. G. Hoffman, C. Burschka, Angew. Chem. 97(1985) 965; Angew. Chem.
l n l . Ed. Engl. 24 (1985) 970.
[13] L. Pauling, The Nature ofthe Chemical Bond, Cornell University Press,
Ithacd, New York 1960; Die Natur der chemischen Bindung, Verlag
Chemie, Weinheim 1976.
Bis(fluorocarbony1) Peroxide; an Unusual
Molecular Structure **
By Hans-Georg Mack, Carlos 0 . Della Mdova,
and Heinz Oberhammer*
Dedicated to Professor Joseph Grobe
The most interesting feature in the structure of peroxides
(X,O,) is the dihedral angle S(XO0X). In the gas phase, this
angle for the parent compound H,O, is 120(5)",t1a1but in
most other peroxides it is larger: 123(4)' in (CF3)202,t1b1
144(6)O in
129(2)O in (SF,),O,,llcI 135(5)' in (CH3)202,[1d1
and 166(3)' in tBu,O, .r1e*21 Two trends are
evident from this rather limited number of experimental results : the dihedral angle increases with increasing steric requirements of the substituents and decreases with their increasing electron-withdrawing properties (cf. (CF,),O, and
(CH,),O,). Unusual structures that do not conform to these
41 The
trends are found in difluoro- and dichlor~peroxide.[~*
dihedral angles for these compounds are smaller than 90
(88.1(4)O in F,O, and 81.03(1)' in C1,0,. Furthermore, the
0-0 bond in F,O, is extremely short (121.9(2) pm) and the
0-F bonds are very long (158.2(2) pm). Usually the qualitative explanation for the gauche orientation of substituents in
peroxides is the interaction between the lone pairs on oxygen
and the anomeric effect.[51The latter describes a stabilizing
overlap between the lone pairs of oxygen and the G* orbitals
of the opposite 0-X bond. The optimal dihedral angle thus
[*I Prof. Dr. H. Oberhammer, Dr. H.-G. Mack
Institut fur Physikalische und Theoretische Chemie der Universitat
Auf der Morgenstelle 8, W-7400 Tubingen (FRG)
Dr. C. 0. Della Vedova
Facultad de Ciencias Exactas
Universidad Nacional de La Plata
Departamento de Quimica, Quimica lnorganica
1900 La Plata (Argentina)
Angeu. Chem. Inr. Ed. Engl. 30 (1991) No. 9
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 must be > 90". From this point
of view the structure of (C(O)F),O, promised to be interesting, since in this molecule a possible conjugation between the
C=O A bonds might lead to a planar COOC framework, or
at least to a pronounced opening of the dihedral angle.
In oxygen-rich (C(O)F),O, three conformers are possible,
depending on the orientation of the two carbonyl groups,
regardless of the dihedral angle S(CO0C): syn-syn, syn-anti,
and anti-anti. Structures in which the carbonyl groups are
rotated around the 0-C bond have not been considered. The
C=O vibrational bands in the gas-phase and matrix IR spectra (vas = 1929 and v, = 1902 cm-') show that at room temperature only one conformer is present, and the shape of the
symmetric band suggests a syn-syn structure.@]This interpretation of the spectra is supported by ab initio calculations
(HF/6-31G*). These calculations predict that the syn-anti
conformer is 13.5 and the anti-anti conformer 26.9 kJmol-'
higher in energy. The dihedral angle S(CO0C) and the other
geometric parameters were determined by electron diffraction in the gas phase.
The analysis of the experimental radial distribution function calculated by Fourier transformation of the molecular
scattering intensities (Fig. 1) confirmed the syn-syn configuration suggested by IR spectra and MO calculations. The
Fig. 1. Experimental radial distribution function for (C(O)F),O, and the difference curve. The positions of interatomic distances are indicated by vertical
length of the interatomic distances between the two carbonyl
groups corresponds to a dihedral angle S(CO0C) of ca. 85 '.
In the subsequent least-squares analysis of the scattering
intensities, C, symmetry and nonrotated fluorocarbonyl
groups (i.e., S(0-0-C=O) = 0') were assumed for this molecule. Optimization of the structure allowing for rotated carbony1 groups led to a value of 5 f5 ' for this angle. The C-F
Verlagsgesellschafl mbH. W-6940 Weinheim. 1991
0570-0833jPlj0909-1145 $3.50+.25/0
bond length could not be refined in the least-squares analysis
because of high correlation^.['^ The results of the electron
diffraction study and the calculated parameters are given in
Table 1.
Table 1. Experimental and calculated structural parameters for (C(O)F),O,.
F-C=O [c]
6 (0 -0- c =0)
E.B. [a]
132.0 [b]
83.5( 14)
0.0 [b]
[a] r, distances [pm] and X, angles [“Ifrom electron diffraction studies. Errors
refer to the last digit and are 3a values. [b] Not refined. [c] Dependent parameter.
Some of the calculated values, in particular the 0-0 distance, depend strongly on the basis set (3-21G or 6-31G*). In
general, experimental bond lengths are better reproduced
with the smaller basis set. The agreement in bond angles is
excellent, and the small experimental dihedral angle is confirmed by these ab initio calculations. In other peroxides[*]
the experimental dihedral angle is correctly predicted by calculations only when electron correlation is taken into account. The dihedral angle in bis(fluorocarbony1) peroxide is
extremely small (83.5(14)”), in contrast with the opening of
the angle anticipated for conjugation between C=O n: bonds.
It is comparable with the corresponding angles in F,O, and
CI,O,. These peroxides have strongly electron-withdrawing
substituents and the dihedral angle of less than 90” can only
be described by the above-mentioned model when an attractive interaction between the substituents is postulated. The
overlap populations between the atoms of the fluorocarbonyl groups calculated by Mulliken’s method (HF/6-31 G*)
are indeed slightly positive in some cases (+ 0.002 a.u. for
C I . . C‘, 0.007 a.u. for C ... 02’),and the sum of all interactions (0.014 a.u.) corresponds to attraction between the substituents. This attraction between the C atom of each carbonyl group and the 0 atom of the other is responsible for
the theoretically predicted twisting of the carbonyl groups
about the 0-C bond by 4-6“, which leads to a shortening of
the C .. .02’distances. This slight twisting was not observed
in the electron diffraction study.
[I] a) R. L. Redington, W. B. Olson, P. C. Cross, 1 Chem. Phys. 36 (1962)
1311; b) C. J. Marsden, L. S. Bartell, F. P. Diodati, J. Mol. Struct. 39
(1977) 253; c) P. Zylka, H. Oberhammer, K. Seppelt, ibid. 243 (1991) 41 1:
d) B. Haas, H. Oberhammer, J. Am. Chem. SOC.106 (1984) 6146; e) D.
Kass, H. Oberhammer, D. Brandes, A. Blaschette, J. Mol. Strucf.40(1977)
[2] These dihedral angles are “effective” values as a result of the torsional
vibration. The equilibrium value corresponding to the minimum of the
0-0 torsion potential, 6,, can deviate substantially from them, e.g., 6, =
111.8” in H,O, and 119(4)” in (CH,),O,
[3] L. Hedberg, K. Hedberg, P. G. Eller, R. R. Ryan, Inorg. Chem. 27(1988)
141 M. Birk, R. A. Friedl, E. A. Cohen, H. M. Pickett, S. P. Sander, J. Chem.
Phys. 91 (1989) 6588.
[S] A. J. Kirby: The Anomeric Effect and Related Stereoelectronic Ejfects at
Oxygen, Springer, Berlin 1983.
[6] C. 0. Della Vkdova, Disserlation, Universitat Bochum 1990.
(71 The C-F distance was set equal to the value calculated by the HF/3-21G
method, which gives very good agreement with experimental C-F distances in FC(0)SCI (H.-G. Mack, H. Oberhammer, c. 0. Della Vedova, J.
Phys. Chem., 95 (1991) 4238) and (C(O)F),S, (unpublished).
[8] a) H.-G. Mack, D. Christen, H. Oberhammer, Tetrahedron 44 (1988) 7363;
b) D. Cremer, J. Chem. Phys. 69 (1978) 4440.
[9] R. L. Talbott, J. Org. Chem. 33 (1968) 2095.
[lo] H. Oberhammer: Molecular Slructure by Dffraction Methods, Vol. 4, The
Chemical Society, London 1976, p. 24.
[Ill H. Oberhammer, W. Gombler, H. Willner, J. Mol. Struct. 70 (1981) 273.
[I21 J. Haase, Z . Nulurforsch. A25 (1970) 936.
[13] M. J. Frisch, J. S. Binkley, H. B. Schlegel, K. Raghavachari, C. F. Melius,
R. L. Martin, J. J. P. Stewart, F. W. Bobrowicz, C. M. Rohlfing, L. R.
Kahn, D. F. DeFrees, R. Seeger, R. A. Whiteside, D. J. Fox, E. M. Fleuder. J. A. Pople, GAUSSIAN 86, Carnegie-Mellon Quantum Chemistry
Publishing Unit, Pittsburgh 1984.
On the Origin of n-Facial Diastereoselectivity
in Addition Reactions of Cyclohexane-Based
Systems **
By Gernot Frenking,* Klaus E Kohler, and Manfred 7: Reetz
The failure of the Felkin-Anh[’] model to explain the observed diastereoselectivity in nucleophilic additions to substituted cyclohexanones and related systems and the alternative rationale based on the “Cieplak model”[’I are currently
topics of lively discussion in stereochemistry.[’, 31 The most
detailed experimental study pertinent to the subject has been
carried out by Cieplak, who could show that in 3-substituted
cyclohexanones the relative proportion of axial attack of the
nucleophile increases when the substituent becomes more
electronegative.[2b1The same trend was also found for the
addition of electrophiles to 3-substituted methylenecyclohexanes (Scheme
Experimental Procedure
(C(O)F),O, has been known for more than 20 years and was prepared here by
the same method [9]. The scattering intensities were recorded with a Balzers Gas
Diffractograph KD-G2 [lo] using two camara distances (25 and 50 cm) and an
accelerating voltage of ca. 60 kV. The electron wavelength was calibrated with
ZnO powder. The temperature of the sample was - 4 5 T , of the inlet nozzle
10°C. Two photographic plates for each camera distance were evaluated by
standard methods [Ill and the scattering intensities in the s ranges of 20180 nm-’ and 80-350 nm-’ were used for the structure analysis. Molecular
scattering intensities were modified by a diagonal weighting matrix and known
values [I21 were used for the scattering amplitudes and phases. The ab initio
calculations were performed using the GAUSSIAN 86 program [13] and 3-21‘3
and 6-31G’ basis sets on a Convex-C22O computer (ZDVAM, University of
Received: March 13, 1991 [Z4494 IE]
German version: Angew. Chem. 103 (1991) 1166
CAS Registry number:
(C(O)F),O,, 692-74-0.
1146 0 VCH
Verlugsgesellschafi mbH, W-6940 Weinheim, 1991
Scheme 1. Attack of a nucleophile CH,M, for example CH,Li, on a cyclohexanone.
The explanation given by Cieplak for the observed trend is
based on a rather paradoxical assumption : Stereoelectronic
control in cyclohexane-based systems is attributed to electron donation from the occupied orbitals of the cyclohexane
Prof. Dr. G. Frenking, Dip1.-Chem. K. F. Kohler, Prof. Dr. M. T. Reetz
Fachbereich Chemie der Universitat
Hans-Meerwein-Strasse, W-3550 Marburg (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, and the computer companies Silicon
Graphics and Convex.
0570-0833/91/0909-1146$3.50+ ,2510
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 9
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peroxide, structure, fluorocarbon, molecular, unusual, bis
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