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Bis(fluoroformyl)trioxide FC(O)OOOC(O)F.

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Angewandte
Chemie
Chirality
Bis(fluoroformyl)trioxide, FC(O)OOOC(O)F**
Holger Pernice, Michael Berkei, Gerald Henkel,
Helge Willner,* Gustavo A. Argello,
Michael L. McKee, and Thomas R. Webb
Dedicated to Professor P. J. Aymonino
on the occasion of his 75th birthday
“How long can you make an oxygen chain?” or “How stable
are molecules containing long oxygen chains and what are
their structures?” are frequently asked questions.[1–4] There is
no question that compounds of the type ROxR are less stable
and less known with increasing x. To date there are no
chainlike polyoxides with x > 3 and only a few trioxides are
well characterized. Only for the trioxide CF3OOOCF3, which
is stable at room temperature, is the structure known.[5]
In the family of compounds of the type FC(O)OxC(O)F
with x = 0–3 the species with x = 0[6, 7] and 2[8, 9] have been
isolated and long since studied. After the first IR spectroscopic evidence for FC(O)OOOC(O)F and FC(O)OC(O)F
by photolysis of oxalyl fluoride in the presence of oxygen in a
long-path IR cell,[10] we were able to prepare the more stable
fluoroformic acid anhydride on a preparative scale and to
characterize it comprehensively.[11]
Herein we report the synthesis, characterization, and
structure of bis(fluoroformyl)trioxide, which can be viewed as
the anhydride of the unknown peroxyfluoroformic acid. It is
the second, but most simple example of a chainlike acyl
trioxide after CF3OC(O)OOOC(O)OCF3, whose structure is
still unknown.[12]
We observed the formation of FC(O)OOOC(O)F during
the synthesis of FC(O)OOC(O)F in molar scale by treating
CO with F2 in the presence of O2 according to the literature
method.[13] The gas-phase pyrolysis of FC(O)OOC(O)F
yielded FCO2 radicals and allowed the measurement of
their rotational spectrum.[14]
During vacuum transfer of the crude FC(O)OOC(O)F
product, the formation of oxygen was observed. At the same
time in the IR gas-phase spectra, weak IR bands at 530 and
798 cm1 disappeared while the bands of the other products
remained nearly unchanged. Finally the new compound was
isolated by continuous sublimation of the more volatile
FC(O)OOC(O)F from the product mixture at 95 8C in vacuo.
After fast evaporation of a small sample from the residue
into an evacuated IR-gas cell, a 1.5-fold pressure increase was
observed. Simultaneously at room temperature the IR
spectrum changed with a half-life of 70 s. As the only IRactive compound, pure FC(O)OOC(O)F was left behind as a
decomposition product in the gas cell according to Equation (1).
D
FCðOÞOOOCðOÞF ! FCðOÞOOCðOÞF þ 1=2 O2
ð1Þ
These observations suggest the presence of FC(O)OOOC(O)F. With the aid of a reference spectrum the gas-phase IR
spectrum of pure FC(O)OOOC(O)F was obtained by subtraction of the peroxide contribution to the spectrum
(Figure 1). In Table 1 the observed fundamentals are com-
[*] Dipl.-Chem. H. Pernice, Dr. M. Berkei, Prof. Dr. G. Henkel,++
Prof. Dr. H. Willner+
Fakult4t 4, Anorganische Chemie
Gerhard-Mercator-Universit4t Duisburg, Lotharstrasse 1
47057 Duisburg (Germany)
E-mail: willner@uni-wuppertal.de
Prof. Dr. G. A. Arg=ello
INFIQC, Universidad Nacional de C@rdoba
5000 C@rdoba (Argentina)
Prof. Dr. M. L. McKee, Prof. Dr. T. R. Webb
Department of Chemistry
Auburn University, AL 36849-5312 (USA)
[+] Current address: Fachbereich C, Anorganische Chemie
Bergische Universit4t Wuppertal
42119 Wuppertal (Germany)
Fax: (+ 49) 202-439-2901
[++] Current address: Department Chemie und Chemietechnik
Fakult4t Naturwissenschaften
Universit4t Paderborn
33098 Paderborn (Germany)
[**] Financial support by the Deutsche Forschungsgemeinschaft (H.W.)
and for a travel grant (PROALAR) by the Deutscher Akademischer
Austauschdienst (DAAD) and the Agencia National de Promoci@n
Cientifica y Tecnologica (H.P., H.W. and G.A.A.) is gratefully
acknowledged.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2004, 43, 2843 –2846
Figure 1. Top: IR gas spectrum of FC(O)OOOC(O)F in absorbance
(p = 67 Pa, T = 25 8C, optical path length 195 mm, 0.5 mm Si wafer as
windows). Bottom: low-temperature (196 8C) Raman spectrum of the
solid compound.
pared with the calculated (DFT) band positions and intensities. Of the 21 possible fundamentals 18 could be assigned.
The bands at around 800 and 900 cm1 are characteristic of
the O-O-O stretching vibrations. The excellent agreement
between observed and calculated band positions is further
evidence for the existence of FC(O)OOOC(O)F. In addition
it was possible to produce pure trioxide along with OCF2 and
CO2 by treating CO/O2 mixtures with O2F2 at 120 8C.
DOI: 10.1002/anie.200353369
2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2843
Communications
Table 1: Vibrational wavenumbers [cm1] for the fundamentals of the lowest-energy rotamer of
FC(O)OOOC(O)F (C2) and their assignments.
IR (Gas, 25 8C) I[a]
Calcd[b] I[b]
Raman (solid, 196 8C) Assignment Approximate
description
1921.7
43.9
1207.1
1167.1
1139sh
969sh
944.9
918.5
797.2
761.8
755sh
18.3
100[c]
4.3
2.1
11.4
2.4
5.9
4.4
1954
1960
1196
1155
89.7
5.8
21.8
100[d]
1915 m
1890 s
1243 w
1166 vw
992
948
936
818
752
747
671
670
600
527
380
376
218
158
69
63
50
0
17.8
0.2
14.2
5.0
1.9
0
0.8
0
4.1
0
0.2
0.1
0
0
0.2
0.1
974 s
926 m
909 vs
798 s
678.0
0.5
530.6
3.0
748 w
680 m
670 s
604 m
537 m
391 vs
387 s
241 vs
177 w
B, n12
A, n1
A, n2
B, n13
n13
A, n3
B, n14
A, n4
B, n15
A, n5
B, n16
A, n6
B, n17
A, n7
B, n18
A, n8
B, n19
A, n9
B, n20
A, n10
B, n21
A, n11
nas(C=O)
ns(C=O)
ns(C-F)
nas(C-F)
nas(13C-F)
nas(C-O)
ns(O-O-O)
nas(O-O-O)
gs(oop, ip, FC(O)O)
gas(oop, op, FC(O)O)
ds(COO, OC(O), OOO)
das(COO, OC(O))
ds(OOO)
das(C(O)F)
das(COO)
ds(COO)
t
t(C-O)
t
t(O-O)
[a] Relative intensities. [b] B3 LYP basis set 6-31+G(d). [c] Absorption cross sections at 1167.1 cm1:
685 H 1020 cm2/molecule. [d] Corresponds to 852 km mol1.
For the formation of the trioxide the following reaction
sequence is assumed, taking into account the kinetic measurements of the CO reaction with O2/F2 mixtures[15] (M = third
body collision partner):
In the mixture CO/O2/F2, the rate-determining step in the
starting reaction is given by Equation (2), and, if CO/O2 is
treated with O2F2 the rate-determining step is given by
Equation (3).
COþF2 ! FCOþF
ð2Þ
COþO2 F2 ! FCOþFOO
ð3Þ
The subsequent reactions [Eq. (4)–(7)] proceed very fast.
FCOþO2 þM ! FCðOÞOOþM
ð4Þ
2 FCðOÞOO ! 2 FCO2 þO2
ð5Þ
FCðOÞOOþFCO2 þM ! FCðOÞOOOCðOÞFþM
ð6Þ
2 FCO2 þM ! FCðOÞOOCðOÞFþM
ð7Þ
The ratio of the products trioxide [Eq. (6)] to peroxide
[Eq. (7)] is strongly dependent on the temperature, with an
increasing yield of trioxide with decreasing temperature.
Thermally, the trioxide decomposes unimolecularly according
to the reverse of Equation (6) as shown by matrix isolation
experiments.[16] Pure trioxide reacts with equimolar amounts
of NO2 at low temperature (slow thawing) to form the known
FC(O)OONO2.[17]
For further characterization of the trioxide, NMR, UV,
and mass spectra were recorded, and an X-ray diffraction
2844
2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Table 2:
study was performed. The NMR spectroscopic data fit very well with the data of the
related compounds FC(O)OxC(O)F, x = 0–3
(Table 2). The couplings in the AA’XX’ spin
system decrease between the FC(O) groups
with increasing Ox-chain length and the
signals of the trioxide appear as an AX spin
system. The UV spectrum is very similar to
that of FC(O)OOC(O)F[18] but with somewhat higher absorption cross sections overall. The 70 eV mass spectrum with the
fragments F2CO+(3), FCO2+(4), FCO+(59),
CO2+(100), O2+(32), CO+(28) is also consistent with FC(O)OOOC(O)F.
On storage of the trioxide in evacuated
glass ampoules on dry ice, over several
months single crystals of mm size were
formed. On further cooling to 196 8C the
crystals shatter as the result of a phase
transition. Therefore for the structure determination small crystals were collected in a
85 8C nitrogen gas stream on a copper
trough under a microscope.[19] Suitable crystals were wedged in glass capillaries, flame
sealed, transferred to a diffractometer and
measured at 123 8C.
19
F and 13C NMR data of FC(O)Ox(O)F, x = 0–3.
[a]
FC(O)C(O)F
FC(O)OC(O)F[a]
FC(O)OOC(O)F[a]
FC(O)OOOC(O)F[b]
d (19F) d (13C)
1
+ 23.8
10.6
34.1
30.6
366.3 50.6
293.8 34.6
301.1 3.8
308.6 –
+ 143.2
+ 136.0
+ 142.3
+ 143.8
J(CF)
j (x+3)J(FF) j
(x+2)
J(CF)
+ 102.8
+ 12.6
–
–
[a] Ref. [11]. [b] In CD2Cl2 at 243 K. Chemical shifts in ppm relative to
internal CFCl3 (19F) and CD2Cl2 at 53.7 ppm (13C), coupling constants in
Hz.
In the crystal (unit cell see Figure 2) the fragment
FC(O)OO0.5 forms the asymmetric unit and the molecule is
present in the most stable conformer with C2 symmetry. In the
studied crystal only one of the two possible (left- and righthand thread) of the trans-syn-syn conformers (the CO bonds
trans and both C=O bonds syn with respect to the O3 plane) is
present and it belongs to the chiral space group P43212.
However, similar compounds, such as CF3OOOCF3,[5]
CF3SxCF3,[20] x = 2, 3, and CCl3S7CCl3[21] crystallize as racemic
mixtures of left- and right-hand threads in nonchiral space
groups. The observed bond lengths and bond angles are
generally in good agreement with the calculated data
(Table 3). Only the COOO dihedral angle is clearly wider
than calculated, presumably caused by packing effects in the
crystal. In Figure 3 and the Supporting Information the chiral
left-handed C-O-O-O-C chain can be seen. In this case as well
as in the structure of CF3OOOCF3 the theoretically postulated helical structure of the oxygen framework is found.[3]
Sulfur chains with similar features are present in the
compounds CF3SxCF3, x = 2, 3, and CCl3S7CCl3.[20, 21]
www.angewandte.org
Angew. Chem. Int. Ed. 2004, 43, 2843 –2846
Angewandte
Chemie
indications for the presence of more than one rotamer in the
IR matrix spectrum and the low-temperature Raman spectrum.
Experimental Section
Figure 2. X-ray structure of FC(O)OOOC(O)F at low temperature. View
of the unit cell along [100].
Table 3: FC(O)OOOC(O)F,
angles [8].
Bond
Crystal
CF
C=O
CO
OO
FC=O
O-C-O
F-C-O
O=C-O-O
C-O-O-O
O-O-O
trans-syn-syn:
bond
FC(O)OOOC(O)F
Calculated[a]
1.314(2)
1.162(2)
1.364(2)
1.440(1)
125.8(1)
130.1(1)
104.1(1)
2.1(1)
99.0(1)
104.0(1)
1.334
1.181
1.376
1.430
126.2
129.9
103.9
2.9
90.7
106.4
lengths [M]
and
F3COOOCF3
Crystal[b]
1.315(2)
1.389(2)
1.437(2)
95.9(8)
106.4(1)
[a] B3 LYP basis set 6-31 + G(d). [b] Ref. [5].
Figure 3. Structure of FC(O)OOOC(O)F (Thermal ellipsoids set at
25 % probability). The left-handed chiral thread can be recognized.
According to DFT calculations[22] FC(O)OOOC(O)F
should be present at room temperature in a mixture of the
trans-syn-syn rotamer with C2 symmetry (see Figure 3) and
the 4 kJ mol1 energetic higher trans-syn-anti rotamer of C1
symmetry (see Supporting Information). Indeed there are
Angew. Chem. Int. Ed. 2004, 43, 2843 –2846
Caution: The mixture of reagents for the synthesis of FC(O)OOC(O)F and FC(O)OOOC(O)F and the peroxide and trioxide are
potentially explosive, especially in the presence of oxidizable
materials. They must be handled with appropriate safety precautions.
Similar to the described method,[13] an oxygen (80 cm3 min1) and
a fluorine gas stream (25 cm3 min1) were mixed in a stainless steel Tjoint piece (Swagelok). In a following stainless steel T-joint piece a
stream of CO (10 to 15 cm3 min1) was introduced into the O2/F2
mixture. Subsequently the reaction mixture passed through a 500-mL
glass reactor at 25 8C followed by two cold traps held at 78 8C (dry
ice) and 183 8C (liquid oxygen). Residual O2, CO, and F2 were
released in the hood through a bubbler filled with perfluorinated oil.
The contents of both traps were separated by trap-to-trap condensation in vacuum in traps held at 78, 110, and 196 8C. FC(O)OOC(O)F and FC(O)OOOC(O)F were retained in the trap at 110 8C.
The temperature was raised to 95 8C and under continuous pumping
(ca. 103 mbar) the more volatile FC(O)OOC(O)F is transferred to
another trap until pure FC(O)OOOC(O)F is left behind at 95 8C.
After work up of approximately 70 g FC(O)OOC(O)F about 3 g
FC(O)OOOC(O)F were obtained (yield 4 % relative to the peroxide
and 1 % relative to CO).
The samples were flame sealed in glass ampoules and stored
under liquid nitrogen. By using a special device[23] ampoules can be
opened at the vacuum apparatus, the desired amount can be taken
out, and the ampoule flame sealed again.
19
F- or 13C NMR: Bruker Avance 300, 282.40 MHz or 75.47 MHz,
30 8C, CFCl3 and CD2Cl2 as internal standard and lock. Vibrational
spectra: Bruker FTIR 66v, FT Raman FRA 106.
Crystal structure analysis: Siemens P4RA 4-cycle diffractometer,
rotating anode, MoKa radiation (l = 0.71073 I) with graphite monochromator scintillation counter, T = 150 K, empiric absorption correction (Y-scan), direct methods, least-square refinements (full
matrix) on F2, all atoms anisotropic, one extinction parameter, one
scaling factor. C2F2O5, Mr = 142.02 g mol1, tetragonal, a = 6.108(2),
c = 12.295(5) I, V = 458.7 I3, space group P43212, Z = 4, 1 =
2.057 Mg m3, l(MoKa) = 0.252 mm1, transmission range 0.763–
0.731, 2Vmax = 488, w-scan, crystal size ca. 0.60 mm J 0.35 mm J
0.22 mm, 501 symmetry independent reflections, R1 (wR2) = 0.0285
(0.0577) for 447 reflections with I > 2s(I), 42 variables. CCDC 224327
(C2F2O5) contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+ 44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
Six conformers of FC(O)OOOC(O)F were found at the B3LYP631+G(D)+ZPC level (including thermal corrections)[22] with the
trans-syn-syn species at lowest energy (see Supporting Information).
The calculated (B3LYP6-31+G(D)) IR band positions and intensities
supported the assignment of the observed spectra.
Received: November 20, 2003 [Z53369]
.
Keywords: chirality · crystal structure · density functional
calculations · IR spectroscopy · oxygen · radical reaction
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2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2845
Communications
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