Trifluoroselenoacetic acid, CF3C(O)SeH: Preparation and properties

Article abstract of DOI:10.1021/ic101254k

The hitherto unknown trifluoroselenoacetic acid was prepared through the reaction of trifluoroacetic acid with Woollins' reagent. The compound was fully characterized by mass spectrometry, ¹H, ¹⁹F, ⁷⁷Se, and ¹³C NMR, UV-visible, IR and Raman spectroscopy, and the boiling point at 46 °C was estimated from the vapor pressure curve. An IR matrix isolation study revealed the presence of two different syn-anti and anti-syn conformers. The IR spectra of the two stereoisomers have been assigned, aided by DFT, and ab initio calculations. The UV photolysis of Ar matrix isolated CF₃C(O)SeH yielded CO, OCSe, CF₃SeH, and CHF₃. Apart from CF₃SeH, these products were also obtained by vacuum flash-pyrolysis (310 °C) of gaseous CF₃C(O)SeH. Instead of CF₃SeH, CF₂Se, and HF were detected among the pyrolysis products. The different decomposition pathways of CF ₃C(O)SeH are discussed.

Full text of DOI:10.1021/ic101254k

9
972 Inorg. Chem. 2010, 49, 9972–9977
DOI: 10.1021/ic101254k
Trifluoroselenoacetic acid, CF C(O)SeH: Preparation and Properties
3
†
,†
‡
‡
Jovanny A. G ꢀo mez Casta ~n o, Rosana M. Romano,* Helmut Beckers, Helge Willner, and
Carlos O. Della V ꢀe dova
†,§
†
CEQUINOR (UNLP-CONICET ), Departamento de Quı ´m ica, Facultad de Ciencias Exactas,
‡
Universidad Nacional de La Plata, 47 esq. 115, (1900) La Plata, Argentina, Anorganische Chemie,
Bergische Universit a€ t Wuppertal, Gaussstr. 20, D-42097 Wuppertal, Germany, and Laboratorio de Servicios
§
a la Industria y al Sistema Cientı ´f ico (UNLP-CIC-CONICET ), Departamento de Quı ´m ica, Facultad de
Ciencias Exactas, Universidad Nacional de La Plata, Camino Centenario e/505 y 508, (1897) Gonnet, Argentina.
Received June 24, 2010
The hitherto unknown trifluoroselenoacetic acid was prepared through the reaction of trifluoroacetic acid with Woollins’
1
19 77
13
reagent. The compound was fully characterized by mass spectrometry, H, F, Se, and C NMR, UV-visible,
IR and Raman spectroscopy, and the boiling point at 46 °C was estimated from the vapor pressure curve. An IR matrix
isolation study revealed the presence of two different syn-anti and anti-syn conformers. The IR spectra of the two
stereoisomers have been assigned, aided by DFT, and ab initio calculations. The UV photolysis of Ar matrix isolated
CF C(O)SeH yielded CO, OCSe, CF SeH, and CHF . Apart from CF SeH, these products were also obtained by
3
3
3
3
vacuum flash-pyrolysis (310 °C) of gaseous CF C(O)SeH. Instead of CF SeH, CF Se, and HF were detected among
3
3
2
the pyrolysis products. The different decomposition pathways of CF C(O)SeH are discussed.
3
1
19
77
13
Introduction
H, F, Se, and C NMR, UV-visible, IR and Raman
spectroscopy, and its vapor pressure curve. Conformational
properties, the thermal behavior, and the photochemistry of
CF C(O)SeH were studied by means of Ar matrix-isolation
Since the first preparation of trifluoroacetic acid in 1922
from the oxidation of trifluoromethylcyclohexane with nitric
1
3
acid, this compound was the subject of several studies that
FTIR spectroscopy and DFT/ab initio MP2 calculations.
revealed their interesting properties. It is a strong acid (pK =
a
0
.23), a convenient solvent, and an useful reagent in organic
2-4
Experimental Section
and inorganic synthesis.
On the other hand, trifluoro-
thioacetic acid was unknown until 1960, when it was pre-
pared from trifluoroacetic anhydride and hydrogen disulfide
Chemicals. Trifluoroacetic acid (Aldrich) was dried in pres-
ence of 5% of trifluoroacetic anhydride and P
2
O
5
by reflux in an
atmosphere
was performed and further purification was achieved by re-
5
N
2
atmosphere. Fractional distillation under N
2
at 200 °C. This acid was used for obtaining novel compounds,
6
,7
such as CF C(O)SX (X=halogen) molecules. However,
3
peated trap-to-trap condensation in vacuum. Woollins’ reagent,
the seleno-derivative has remained unknown.
9
2 2 4
Ph P Se , was prepared according to the reported procedure.
As an extension of our recent work on the parent seleno-
8
Vapor Pressure. The vapor pressure of the liquid sample
carboxylic acid, CH C(O)SeH, we report in this paper the pre-
3
was measured in the range from 220-268 K in a small vacuum
line equipped with a calibrated capacitance manometer (MKS
Baratron, AHS-100) and a sample reservoir.
paration of the trifluoroselenoacetic acid, CF C(O)SeH. The
3
compound was fully characterized using mass spectrometry,
3
Mass Spectrometry. CF C(O)SeH (0.2 μL of a 0.6 mM
solution) in chloroform, prepared in a vacuum line, were injected
into a Shimadzu QP-5050 GC-Mass spectrometer equipped with
a chemical-isobutanol ionization source and a FS-OV-1-CB-0.25
column.
*
To whom correspondence should be addressed. E-mail: romano@
quimica.unlp.edu.ar.
(
(
1) Swarts, F. Bull. Cl. Sci., Acad. R. Belg. 1922, 343–370.
2) Peterson, P. E.; Bopp, R. J.; Chevli, D. M.; Curran, E. L.; Dillard,
D. E.; Kamat, R. J. J. Am. Chem. Soc. 1967, 89, 5902–5911.
3) Brown, H. C.; Kawakami, J. H.; Liu, K. J. Am. Chem. Soc. 1970, 92,
536–5538.
4) Reiss, G. J.; Frank, W.; Schneider, J. Main Group Chem. 1995, 18,
87–294.
1
19
13
77
NMR Spectroscopy. For the H, F, C, and Se NMR
measurements, neat samples were held in flame-sealed, thin-
walled 4 mm tubes, which were placed inside 5 mm NMR tubes.
(
5
2
(
CD OD was used as external lock and reference. The spectra
3
(
(
(
(
5) Sheppard, W. A.; Muetterties, E. L. J. Org. Chem. 1960, 25, 180–182.
were recorded with a Bruker Avance 250 spectrometer operating
at 250.13, 235.36, 62.90, and 47.72 MHz for H, F, C, and
6) Rochat, W. V.; Gard, G. L. J. Org. Chem. 1969, 34, 4173–4176.
7) Minkwitz, R.; Sawatzki, J. Z. Anorg. Allg. Chem. 1988, 566, 151–159.
8) G oꢀ mez Casta n~ o, J. A.; Romano, R. M.; Beckers, H.; Willner, H.;
1
19
13
Boese, R.; Della V ꢀe dova, C. O. Angew. Chem., Int. Ed. 2008, 47, 10114–
0118.
(9) Gray, I. P.; Bhattacharyya, P.; Slawin, A. M. Z.; Woollins, J. D.
Chem.;Eur. J. 2005, 11, 6221–6227.
1
pubs.acs.org/IC
Published on Web 09/29/2010
r 2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9973
3
Scheme 1. Chemical Properties of CF C(O)SeH
7
7
Se spectra, respectively. The samples were maintained at
30 °C during the measurements.
68 h, the reaction mixture was separated by repeated trap-to-
trap fractional condensation in vacuum. A pure sample of the
-
UV-visible Spectroscopy. UV-vis spectrum of gaseous CF3-
compound was retained in the -110 °C trap, while CF C-
3
C(O)SeH at 0.7 mbar was recorded using a glass cell (optical
path length 10 cm) equipped with quartz windows and placed
in the sample compartment of a Lambda 900 spectrometer
(
O)OH and a small amount of H Se were found in traps held
2
at -70 and -196 °C, respectively. Starting from about 13
mmol of CF C(O)OH, approximately 0.6 mmol of pure
3
(
Perkin-Elmer, Norwalk, CT). The measurements were carried
CF C(O)SeH were obtained. For the spectroscopical studies,
3
out in the spectral range 200-600 nm.
Vibrational Spectroscopy. The IR spectrum of the vapor was
recorded at a resolution of 2 cm in the range 4000-400 cm
with a Bruker Vector 25 spectrometer. The Raman spectrum
was measured on a liquid sample sealed in 4 mm glass tube using
a Bruker-Equinox 55 FRA 106/S FT-Raman spectrometer and
a 1064 nm Nd:YAG laser (150 mW).
the results of several preparations were collected together.
The colorless liquid revealed a melting point of -145(2) °C.
The vapor pressure in the temperature range 220-268 K,
follows the equation ln p [atm] = 11.88 - 3785/T [K], giving
an extrapolated boiling point of 319 K (Figures S1 and S2 in
the Supporting Information).
-
1
-1
Matrix Measurements. A few milligrams ofpure CF C(O)SeH
3
were transferred to a small U-trap connected to the inlet nozzle of
Stored in a sealed glass vessel at ambient temperatures
the compound decomposed slightly within a few hours, as is
evidenced by the formation of a yellow solid, presumably
CF C(O)SeC(O)CF , and liberation of H Se. In contact
-
1
the matrix apparatus. A stream of Ar (2 mmol h ) was directed
over the sample held at -125 °C, and the resulting gas mixture
was condensed onto the mirror plane of a rhodium plated copper
support held at 15 K. For the pyrolysis experiments, the heated
nozzle (i.d. 4 mm, length 20 mm quartz tube with an end orifice
of 1 mm) was adjusted to 310 °C. Photolysis experiments were
performed with a high-pressure mercury lamp (TQ 150, Heraeus)
using a water-cooled quartz lens optic. Details of the matrix
3
3
2
with air, trifluoroselenoacetic acid is rapidly oxidized to the
corresponding diselenide, CF C(O)Se C(O)CF . Hydrolysis
3
2
3
results in the formation of trifluoroacetic acid and hydrogen
selenide. CF C(O)OH and H Se were identified by their IR
spectrum, while CF C(O)Se C(O)CF was proposed by means
3
2
3
2
3
1
0
13
apparatus are given elsewhere. IR spectra of the Ar matrices
wererecordedinthe reflectance modebymeansofa transfer optic
using the Bruker IFS 66v spectrometer. An MCT-600 detector,
together with a KBr/Ge beam splitter, was used in the region
of its IR and Raman spectra. Scheme 1 summarizes these
reactions.
Mass Spectrometry. The most intense peaks in the
chemical-ionization mass spectrum of CF C(O)SeH are
-
1
3
5
apodized resolutions of 0.5 and 0.15 cm
000-650 cm . 100 scans were added for the spectra with an
þ þ
] and [OCCF] fragments, at m/z
3
-1
arising from the [CF
9 and 59, respectively (see Figure S3 in the Supporting
.
Theoretical Calculations. All quantum chemical calculations
6
8
0
þ
Information). The peaks observed at m/z 130 ([CF Se] ),
2
11
were performed with the Gaussian 03 program package. Second-
order Moller-Plesset (MP2) and density-functional (DFT)
B3LYP methods were employed using the 6-311þþG** basis
set. Geometries were optimized by standard gradient techniques
with simultaneous relaxation of all geometric parameters.
80
þ þ þ
08 ([OC Se] ), 97 ([OCCF ] ), 80 ([ Se] ), 78 ([CF -
3 2
80
1
þ
þ
CO] ), and 50 ([CF ] ) are consistent with the constitu-
2
tion of the molecule (Figure S4, Supporting Information).
NMR Spectroscopy. The H NMR spectrum of neat
1
7
7
CF C(O)SeH shows a singlet at 3.1 ppm but no Se sat-
3
Results and Discussion
ellites because of intermolecular proton-exchange decou-
pling (see Figure S5, Supporting Information). The chem-
ical shift is in the range 2.59-4.74 ppm previously
CF C(O)SeH was prepared by treating CF C(O)OH with
3
3
9,12
an excess of Woollins’ reagent, Ph P Se ,
at 70 °C. After
2
2
4
1
4
reported for related selenocarboxylic acids RC(O)SeH.
1
9
In the F NMR spectrum, a singlet at -78.6 ppm is
observed for the CF group (Figure S6, Supporting
(
10) Schn o€ ckel, H.; Willner, H., Infrared and Raman Spectroscopy,
Methods and Applications; Schrader, B., Ed.; VCH: Weinheim, Germany,
994; p 297.
11) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
3
7
7
1
Information), and a singlet also appeared in the Se
NMR spectrum (Figure S7, Supporting Information) at
(
M. A.; Cheeseman, J. R.; Montgomery Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.;
Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain,
M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski,
J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.04 ed.;
Gaussian, Inc.: Pittsburgh PA, 2003.
412.8 ppm, which is close to the chemical shift obtained
for 4-CH OC H C(O)SeH (427.5 ppm).
1
5
3
6
4
1
The C NMR spectrum revealed two quartets (Figure
3
S8, Supporting Information). The one attributed to the
= 291.2 Hz),
(C-F)
1
CF group is centered at 115.5 ppm ( J
3
(12) Fitzmaurice, J. C.; Willians, D. J.; Wood, P. T.; Woollins, J. D.
J. Chem. Soc., Chem. Commun. 1988, 741–743. Bhattacharyya, P.; Woollins,
J. D. Tetrahedron Lett. 2001, 42, 5949–5951.
(
13) G oꢀ mez Casta n~ o, J. A. PhD Thesis, University of La Plata, 2009.
(14) Kageyama, H.; Murai, T.; Kanda, T.; Kato, S. J. Am. Chem. Soc.
1994, 116, 2195–2196.
(15) Niyomura, O.; Kato, S. Chalcogenocarboxylic Acids; Springer-Verlag:
Berlin, Germany, 2005; pp 5.

9
974 Inorganic Chemistry, Vol. 49, No. 21, 2010
G ꢀo mez Casta ~n o et al.
Table 1. Experimental and Calculated Vibrational Wavenumbers (in cm- ) of
1
CF
3
C(O)SeH (Relative Intensities Are Given in Parentheses)
experimental
MP2/6-311þþG**
vapor liquid
IR Raman Ar-matrix syn-anti
anti-syn
assignment
2
308.3
2306.0 2536.9 (2)
749.7
2543.0 (3)
ν(Se-H) a-s
ν(Se-H) s-a
2
340
2332
1
1755.3 (96) ν(CdO) a-s
ν(CdO) s-a
1
1
759
277
1738
1276
1748.3 1750.3 (80)
1277.9 1313.5 (35)
ν(C-C) s-a
1
1
274.3
220.0
1310.0 (44) ν(C-C) a-s
1239.7 (68) ν(C-F) a-s
ν(C-F) s-a
1
1
215
188
1213
1172
1210.9 1226.1 (76)
1181.1 1209.4 (100)
ν
as(CF
3
) s-a
) a-s
1
9
169.8
40.8
935.9
79.8
766.3
33.9
728.3
74.9
1180.3 (100) νas(CF
3
969.4 (64)
δ(OCC) a-s
968.6 (48) δ(OCC) s-a
822.2 (12) δ(HSeC) a-s
δ(HSeC) s-a
9
37
935
7
7
68
816.2 (9)
7
739.6 (17)
δ
δ
δ
δ
a
(CF
(CF
oop(CO) a-s
oop(CO) s-a
3
)
)
wag a-s
wag s-a
7
30
732
562
458
735.7 (21)
a
3
6
678.6 (< 1)
6
5
68
60
667.3
562.0
560.1
674.9 (< 1 )
568.9 (6)
δ(CF ) s-a
3
-
1
Figure 1. Gas-phase FTIR spectrum at 3 mbar, 2 cm resolution, and
566.3 (4)
510.3 (1)
δ(CF ) a-s
3
-1
503
52
507.7 (1)
464.6 (1)
344.2 (3)
287.3 (2)
237.1 (< 1)
166.9 (< 1)
δ(CF ) s-a
an optical path length of 20 cm (top) and Raman spectrum of the liquid
at room temperature with excitation at 1064 nm and 150 mW (bottom) of
CF C(O)SeH.
3
3
4
ν(C-Se) s-a
3
2
2
50
94
33
349.6 (< 1) τ(HseCO) s-a
288.4 (1)
209.6 (2)
δ(CCF) s-a
F(CF ) s-a
while the signal assigned to the CdO is centered at 184.7
3
2
160
167.3 (< 1) δ(SeCC) s-a
(
the corresponding values reported for trifluoroacetic acid
J(
=43.4 Hz). These results are consistent with
C-C-F)
1
CF 115.0 ppm, J
vibrational bands it is difficult to verify the presence of
two stereoisomers at ambient temperatures by the IR and
Raman spectra presented in Figure 1. Matrix-isolation
spectroscopy appears thus as an alternative tool to ex-
plore the existence of a conformational equilibrium.
(
= 282 Hz; CdO: 163.0 ppm,
3
(C-F)
2
J(
16,17
=44 Hz).
C-C-F)
UV-visible Spectroscopy. The vapor-phase UV-visible
spectrum of CF C(O)SeH recorded in the range from 200
to 600 nm exhibits an absorption centered at 251 nm,
3
The IR spectrum of CF C(O)SeH isolated in Ar
3
which is attributed to the lp(π)Se f π*CdO transition
matrix presented in Figure 2 shows a complex pattern
for most of the absorptions. To distinguish between
matrix and conformational splitting, the CF C(O)SeH/
(
Figure S9, Supporting Information). The 20 nm bato-
chromic shift with respect to the corresponding absorp-
8
tion of selenoacetic acid, is attributed to the inductive
3
Ar mixtures were directed through a heated quartz capil-
lary prior to deposition. Increasing the temperature
several weak absorptions observed at ambient tempera-
ture grow simultaneously at the expense of the strong
bands arising from the more stable syn-anti form. This
behavior was used to assign the absorptions to each of the
two conformers in Table 1. Experimental molar ratios of
both the conformers were estimated for different tem-
peratures from integrated intensities of the most intense
absorptions using calculated absorption coefficients
effect of the CF group.
3
Vibrational Spectroscopy. The vapor-phase IR and the
Raman spectra of liquid CF C(O)SeH are presented in
Figure 1. Table 1 compiles observed band positions and
presents a tentative assignment.
The IR absorption at 1759 cm is readily assigned to
3
-
1
the ν(CdO) vibrational mode. This wavenumber is very
-
1
close to the 1758 cm value reported for CF C(O)SH.
18
3
-
1
The band at 1277 cm is associated with the ν(C-C)
mode, which is close to the corresponding mode of tri-
-
1 19
.
(Table 2).
Thermolysis Experiments. The low-pressure thermo-
fluoroacetic acid reported at 1286 cm
appearing in the 1200 cm spectral region are arising
from the CF stretching vibrations. The Raman spectrum
3
The features
-
1
lysis at 310 °C of CF C(O)SeH with subsequent matrix
3
isolation of the products not only increased the features
assigned to the less-stable anti-syn conformer; in addi-
tion new bands appeared at 3962.0, 2138.5, 2009.0,
of liquid CF C(O)SeH is dominated by the strong ν(Se-H)
3
8
band that appears at 2332 cm
-1
.
Although the theoretical calculations presented below
predict an equilibrium between two conformers, how-
ever, because of the predicted small isomeric shift of the
-
1
1
274.1, 1250.6, 1195.7/1195.1, and 1146.3 cm .
-
1
The bands at 2138.5 and 2009.0 cm were readily
associated with CO (2138.0) and OCSe (2009.0), re-
spectively. The presence of OCSe indicates the formation of
CHF , which is confirmed by the appearance of the 1146.3
20
21
(
16) Jacobsen, N. E. NMR Spectroscopy Explained. Simplified Theory,
Applications and Examples for Organic Chemistry and Structural Biology;
3
1
-
-1
22
Wiley: NJ, 2007; p 61.
cm band (Figure 3, reported at 1146.0 cm in solid Ar ).
(
17) Silverstein, R. M; Bassler, G. C.; Morrill, T. C., Spectrometric
Identification of Organic Compounds. 5th ed., Wiley, New York, 1991,
pp 246-247.
(20) Dubost, H. Chem. Phys. 1976, 12, 139–151.
(21) G oꢀ mez Casta n~ o, J. A.; Romano, R. M. Unpublished work.
(22) Kelsall, B. J.; Andrews, L. J. Phys. Chem. 1981, 85, 2938–2941.
(
18) Rochat, W. V.; Gard, G. L. J. Org. Chem. 1969, 34, 4173–4176.
19) Crowder, G. A. Appl. Spectrosc. 1973, 27, 440–443.
(

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9975
3
Figure 2. FTIR spectrum of CF C(O)SeH isolated in solid Ar.
Table 2. Experimental and Calculated Molar Ratios and Relative Energies of the
syn-anti and anti-syn Rotamers of CF C(O)SeH
3
2
98 K
583 K
a
a
ΔE
ΔG°
sa % as % sa % as [kJ/mol] [kJ/mol]
%
b
Ar-matrix
MP2/6-311þþG**
82.5 17.5 74.0 26.0
83.1 16.9 69.3 30.7
2.47
2.47
3.93
1.97
B3LYP/6-311þþG** 69.0 31.0 60.1 39.9
a
Figure 3. Section of the FTIR spectra in the range from 1230 to 1140 cm-1
of a solid deposit obtained at 15 K from Ar/CF C(O)SeH mixtures with the
Relative energy of the anti-syn rotamers with respect to the most
stable syn-anti. Experimental values are obtained from integrated in-
b
3
tensities of the ν(CdO) absorptions in the Ar-matrix IR spectra cor-
lr ee vc et el .d by calculated absorption coefficients at the B3LYP/6-311þþG**
spray-on nozzle held at room temperature (bottom) and at 310 °C (top).
Although the elimination of CO from CF C(O)SeH sug-
3
gests the concomitant formation of CF SeH, no features
3
could be assigned to this species. Instead, bands at 1274.1
and 1195.7/1195.1 cm (Figures 3 and 4) were attributed
-
1
-
1 23
to CF dSe (1275.0 [ν ] and 1196.0 [ν ] cm ) while the
2
1
4
-
1
962.0 cm band is associated with the formation of HF
3
-
1 24
3953.8 cm ). The presence of the CF radical is con-
(
firmed by an absorption at 1250.6 cm (Figure 4) by com-
3
-
1
-
1
parison with the 1250 cm value reported for the most
25
intense absorption of this radical isolated in Ar matrix.
The experimental results indicates two different ther-
mal decomposition pathways of CF C(O)SeH, which are
3
presented in Scheme 2. Although the CF SeH molecule
3
was not detected in the spectrum, it is reasonable to
assume that CF dSe and HF were formed from a thermo-
2
labile CF SeH intermediate. The CF radical is assumed
3
3
to be involved in both decomposition routes.
Photochemistry of Matrix-Isolated CF C(O)SeH.
3
CF C(O)SeH displayed a rich photochemistry when it
3
was subjected to light in the wavelengths range 200 e λ e
8
00 nm of a high pressure mercury lamp. After 8 min of
photolysis, the compound was completely decomposed,
while several new absorption appeared, which are listed in
Table 3 and depicted in Figures 5, S10, and S11.
(
23) Haas, A.; Willner, H.; B u€ rger, H.; Pawelke, G Spectrochim. Acta
977, 33A, 937–945.
24) Andrews, L.; Johnson, G. L. J. Phys. Chem. 1984, 88, 425–432.
25) Milligan, D. E.; Jacox, M. E.; Comeford, J. J. J. Chem. Phys. 1966,
4, 4058–4059.
Figure 4. Section of the FTIR spectra in the range from 1282 to
1248 cm of solid deposits obtained at 15 K from Ar/CF C(O)SeH mix-
3
tures with the spray-on nozzle held at room temperature (bottom) and at
310 °C (top).
1
-1
(
(
4

9
976 Inorganic Chemistry, Vol. 49, No. 21, 2010
G ꢀo mez Casta ~n o et al.
Scheme 2. Proposed Low-Pressure Pyrolysis Mechanisms for
CF C(O)SeH
3
3
Figure 5. Section of the FTIR spectra of CF C(O)SeH isolated in solid
-1
Ar in the 1300-1050 cm region prior (bottom) and after 5 and 8 min of
photolysis.
3
Scheme 3. Proposed Photolysis Mechanisms for CF C(O)SeH
Isolated in Solid Ar
Table 3. Band Positions (in cm-1) and Assignments of the IR Absorptions
Appearing after Photolysis of CF C(O)SeH Isolated in Solid Ar
3
vibrational
mode
wavenumber
reported prerviously
Ar-matrix
molecule
a
2
2
1
1
1
1
1
1
1
1
147.8
009.0
279.5
247.2
171.3
146.3
137.2
112.0
085.8
076.6
CO
OCSe
ν(CdO)
2138.0
2009.0
b
ν
1
ν
2
ν
3
ν
4
/ν(CdO)
c
CF
CF
CF
3
3
3
SeH
þ ν
5
1270
1250
d
/ν
/ν
a
(CF
(CF
3
)
)
c
SeH
a
3
1170
1146
e
CHF
CHF
3
e
3
1134c
1125
CF
CF
CF
CF
CF
3
3
3
3
3
SeH
ν
1
ν
1
ν
2
ν
8
ν
2
/ν
/ν
s
(CF
(CF
3
)
)
d
s
3
1084
1080
c
SeH
SeH
SeH
þ ν
3
c
7
7
85.3
46.4
/δ(CSeH)
785
748
c
/δ
a
(CF
3
)
a
b
Reference 20. Reference 21. Reference 28. Reference 25.
c
d
e
Reference 22.
In addition the photolysis of matrix-isolated CF C(O)-
3
-
1
The set of absorptions that appeared near 2140 cm
21
SeH yield OCSe, CHF3, and CF radicals. As with
22
25
3
was attributed to CO, probably perturbed by other photo-
products formed in the same matrix cage. The possible
formation of perfluoroketene, F CdCdO, which also
exhibits absorptions in this spectral region, was discarded
on the basis of the ν( CdO) band, that was shown to be
useful to distinguish between CO and the ketene and,
also due to the absence of other bands attributable to this
species. In contrast to the results of the thermolysis
experiments, CF SeH was identified as the main photo-
3
product by comparison of its absorptions with the values
reported for gaseous CF SeH.
the thermal decomposition, the photolysis products also
suggest two different photodecomposition pathways of
CF C(O)SeH, which are outlined in Scheme 3.
2
3
Theoretical Calculations. The conformational proper-
ties of CF C(O)SeH were explored using the DFT/
1
3
3
2
6
B3LYP and the ab initio MP2 methods in combination
with the 6-311þþG** basis set. Two stable structures,
syn-anti and anti-syn depicted in Figure 6, were found
on the potential energy surface. The geometrical param-
eters are compiled in Table S1. In the most stable syn-
anti form the Se-H single bond is syn with respect to the
CdO double bond while one of the C-F single bonds is
anti with respect to the CdO double bond. Computed
relative energies and standard Gibbs free energy differ-
ences for the two conformers are listed in Table 2, to-
gether with the Boltzmann distribution at two different
2
7
2
8
3
(
26) Romano, R. M.; Della V ꢀe dova, C. O.; Downs, A. J. J. Phys. Chem. A
002, 106, 7235–7244.
27) K o€ tting, C.; Sander, W.; Senzlober, M.; B u€ rger, H. Chem.;Eur. J.
998, 4, 1611–1615.
28) Marsden, C. J. J. Fluorine. Chem. 1975, 5, 401–422.
2
1
(
(

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9977
with the MP2/6-311þG* approximation are placed as
Supporting Information (Table S2).
Acknowledgment. C.O.D.V. and R.M.R. thank the
Consejo Nacional de Investigaciones Cientı
CONICET) (PIP 4695), the Agencia Nacional de
Promoci oꢀ n Cientıfica y Tecnol oꢀ gica (ANPCyT), the
Comisi oꢀ n de Investigaciones Cientı
ficas de la Provincia de
´
ficas y T ꢀe cnicas
(
´
´
Buenos Aires (CIC), and the Facultad de Ciencias Exactas,
UNLP for financial support. J.A.G. acknowledges an
award from the Deutsche Akademische Austauschdienst
Figure 6. B3LYP/6-311þþG** molecular models for the syn-anti
(
3
left) and anti-syn (right) conformers of CF C(O)SeH.
(
DAAD). C.O.D.V. especially acknowledges the DAAD,
temperatures. The syn-syn and anti-anti forms corre-
spond to transition states.
which generously support the DAAD Regional Program
of Chemistry of the Republic Argentina that encourages
Latin-American students to realize their PhD work in
La Plata.
The assignment of the spectra obtained from matrix-
isolation experiments were guided by computed vibrational
spectra of the two stable conformers. The calculated wave-
numbers for the syn-anti and anti-syn conformers are
listed in Table 1.
Supporting Information Available: Tables of selected geomet-
rical parameters, energies, enthalpies, and Gibbs free energies
and figures showing vapor pressure, Claussis-Clapeyron plot,
GC/chemical-ionization mass spectrum, proposed mass frag-
mentationpattern, H, F, Se, and C NMR spectra, gas-phase
UV-vis spectra, and FTIR spectra. This material is available free
of charge via the Internet at http://pubs.acs.org.
Theoretical calculations predict the following trend for
the gas phase acidity: CF C(O)SeH > CF C(O)SH >
CF C(O)OH. The energies, enthalpies, and Gibbs free
3
3
1
19 77
13
3
energies at 298 K of deprotonation of syn trifluorochalco-
genoacetic acids CF C(O)EH (E=O, S and Se) calculated
3