Trip2C6H3SeF: The first isolated selenenyl fluoride

Article abstract of DOI:10.1002/anie.201106708

Joining the stable: The first examples of the highly instable selenenyl fluorides RSeF are prepared from the reaction on the tin selenide RSeSnMe ₃ with XeF₂. Through the use of extremely large protecting groups (m-terphenyl ligands) which stabilizes the RSeF units against disproportionation, the compounds could be isolated and characterized by NMR spectroscopy and single-crystal structure analysis (see structure). Copyright

Full text of DOI:10.1002/anie.201106708

Angewandte
Chemie
DOI: 10.1002/anie.201106708
Selenenyl Fluorides
Trip2C6H3SeF: The First Isolated Selenenyl Fluoride**
Helmut Poleschner,* Stefan Ellrodt, Moritz Malischewski, Jun-ya Nakatsuji, Christian Rohner,
and Konrad Seppelt
In memory of Reiner Radeglia
In spite of intensive research in modern fluorine and selenium
chemistry there are still unknown compounds among these
seemingly simple compounds. The long-sought class of
selenenyl fluorides, RSeF, are clearly very unstable and SeF2
and FSeSeF have only been identified under matrix con-
ditions.[1] The existence of CF3SeF has only been shown
indirectly.[2] But reagents of the type N-phenylselenophthal-
imide/Et3N·3HF,[3] Ph2Se2/XeF2,[4,5] PhSeEMe3/XeF2 (E = Si,
Ge, Sn, Pb),[5a,6] and PhSeOTf/Et3N·3HF[7] function as PhSeF
equivalents and can be used for the addition of PhSeF across
bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]-
phenyl group (Bbt).[13]
The aim of our investigations, starting in 2005, has been to
obtain RSeF and possibly RTeF in pure, crystalline states with
even larger steric protection groups than Mes*. We have
worked with the following ligands: tris(trimethylsilyl)methyl
(Trisyl,
Tsi),
2,6-bis(2,4,6-tri-iso-propylphenyl)phenyl
(Trip2C6H3), and 2,6-bis(mesityl)phenyl (Mes2C6H3).
ꢀ
C C double and triple bonds. The addition to alkynes occurs
with intermediate formation of selenirenium ions.[8] We
identified arylselenium monofluorides, ArSeF, for the first
time by their characteristic NMR spectroscopic signals, when
the compounds are stabilized by steric protection (Ar= 2,4,6-
tri-tert-butylphenyl = supermesityl, Mes*) or by intramolecu-
m-Terphenyl groups in particular have found much use as
steric protection groups[14] and have also been used in
selenium and tellurium chemistry.[15,11]
lar
coordination
with
amino
groups[9]
(Ar= 2-
Me2NCH2C6H4).[10] These experiments showed, supported
by quantum chemical calculations, that non-stabilized RSeF
disproportionate in a reversible equilibrium reaction into
diselenides R2Se2 and organo selenium trifluorides RSeF3,
To obtain the REF (E = Se, Te) compounds, the dichal-
cogenides, R2E2, and the trimethylsilyl and trimethylstannyl
chalcogenides, RESiMe3 and RESnMe3, were to be fluori-
nated with XeF2.[4–6,10] The optimization of the reaction
conditions was usually carried out by low-temperature
NMR spectroscopy.
ꢀ
most likely with the intermediate formation of RSeF2
SeR.[10,11]
Monomeric tellurenyl fluorides, ArTeF, such as 2-
Me2NCH2C6H4TeF, have been identified by NMR spectros-
copy in solution.[12] Recently a report appeared about the
[16]
Tsi2Se2 reacts with XeF2 at ꢀ408C in CFCl3 or CH2Cl2
forming TsiSeF, but its crystallization has been unsuccessful
(Scheme 2, NMR data see Table 1). TsiSeF has the expected
19F resonance of d = ꢀ371.0 ppm for the highly shielded F
atom in combination with the 77Se resonance of d =
ꢀ
dimer BbtTeF2 TeBbt with the sterically demanding 2,6-
1
[*] Dr. H. Poleschner, S. Ellrodt, M. Malischewski, Prof. Dr. K. Seppelt
Institut fꢀr Chemie und Biochemie, Anorganische und Analytische
Chemie, Freie Universitꢁt Berlin
2028.1 ppm, JSe,F = 791.9 Hz; cf. Ref. [10] for the extremely
deshielded Se center.
Attempts to obtain the diselenide (Trip2C6H3)2Se2 in pure
form starting with Trip2C6H3I[14a,17] resulted only in mixtures
of diselenide and triselenide (cf. Ref. [18]). Pure
(Trip2C6H3)2Se2, however, can be obtained by nitrosation of
the selenole Trip2C6H3SeH with isoamyl nitrite[15b,d,e,19]
(Scheme 1, structure[20]). It reacts with XeF2 in CH2Cl2 or
CFCl3 within 4 h at ꢀ308C to Trip2C6H3SeF (dF =
ꢀ343.6 ppm) in trace amounts. Besides residual diselenide
mainly the trifluoride Trip2C6H3SeF3 is formed (Scheme 2).
Similarly the synthesis of Trip2C6H3SeSiMe3 is unsuccess-
Fabeckstrasse 34–36, 14195 Berlin (Germany)
E-mail: hpol@chemie.fu-berlin.de
J.-y. Nakatsuji
Department of Chemistry, Graduate School of Science, Hiroshima
University
1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526 (Japan)
C. Rohner
Institut fꢀr Anorganische und Analytische Chemie, Justus-Liebig-
Universitꢁt Gießen
Heinrich-Buff-Ring 58, 35392 Gießen (Germany)
[**] We thank the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie for support of this work. S.E. and C.R.:
synthesis and crystallization of Trip2C6H3SeF; M.M.: synthesis and
crystallization of Trip2C6H3TeF2-TeC6H3Trip2; J.-y.N.: fluorination of
(Mes2C6H3)2Te2. Trip2C6H3 =2,6-bis(2,4,6-tri-iso-propylphenyl)-
phenyl.
ful: Reaction of Trip2C6H3SeLi with Me3SiCl or Me3SiOTf
1
produces largely Trip2C6H3SeH (dSe = 107.8 ppm, JSe,H
=
63.1 Hz, cf. Ref. [15a]). But the analogue reaction with
tBuMe2SiOTf affords Trip2C6H3SeSiMe2tBu (cf. Ref. [21],
Scheme 1, structure[20]). This compound does not react with
XeF2 in CFCl3 in 3 h at ꢀ308C, although PhSeSiMe2tBu is
easily cleaved by XeF2 to [PhSeF] and tBuMe2SiF.[5a] Carrying
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201106708.
Angew. Chem. Int. Ed. 2012, 51, 419 –422
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419

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Table 1: 77Se, 125Te, and 19F NMR data [ppm, Hz] of the Se-F and Te-F compounds, at measurement temperature T [8C].
Compound
Solvent
T
d(77Se) (1JSe,F)jd(125Te) (1JTe,F
)
d(19F) (2JF,F) [1JSe,F]j[1JTe,F
]
TsiSeF
Trip2C6H3SeF
Trip2C6H3SeF3
CFCl3
CFCl3
CD2Cl2
ꢀ80
ꢀ40
RT
2028.1 (d, 791.9)
1784.0 (d, 755.0)
1182.6 (d, t) (794.7, Fe; 110.4, Fa)
ꢀ371.0 [785.8]
ꢀ343.6 [754.0]
Fe: ꢀ73.69 (t, 1F) (83.8) [794.2]
Fa: ꢀ0.37 (d, 2F) (83.8) [110.9]
ꢀ95.9
ꢀ
Mes2C6H3TeF2 TeC6H3Mes2
CH2Cl2
CH2Cl2
CD2Cl2
CD2Cl2
ꢀ80
ꢀ40
RT
1516.6 (t, 1162.0)
1164.9 (s)
1640.2 (d, t) (2286.5, Fe; 261.8, Fa)
Mes2C6H3TeF3
Fe: ꢀ127.0 [2276.6]
Fa: ꢀ62.8
ꢀ
Trip2C6H3TeF2 TeC6H3Trip2
1502.4 (t, 909.2, TeF2-Te)
1285.5 (s, TeF2-Te)
1636.8 (d, t) (2273.6, Fe; 352.2, Fa)
-91.38 (s) [909.6]
Trip2C6H3TeF3
ꢀ20
Fe: ꢀ125.8 (t, 1F) (27.5) [2273.9]
Fa: ꢀ62.9 (d, 2F) (27.2) [373.2]
Figure 1. Molecular structure of Trip2C6H3SeF with thermal ellipsoids
set at 50% probability (DIAMOND[28]). The SeF group is twofold
disordered, only one position is shown. Selected bond lengths [pm]
and angles [8]: Se–F 168.23(5), Se–C1 191.65(4); C1-Se-F 102.84(1),
Se-C1-C2 128.78(1), C2-C1-Se-F ꢀ14.61(2). The dihedral angle between
Scheme 1. Synthesis of the Se and Te starting compounds.
ꢀ
the Se F bond and the plane of the central benzene ring is 14.68.
synthesized Trip2C6H3SeF3 by fluorination of the tin-selenium
compound with two equivalents XeF2. However in attempts
to crystallize this compound Trip2C6H3SeOF was obtained,
clearly by partial hydrolysis (structure[20]).
ꢀ
The Se F bond length in Trip2C6H3SeF is fairly short,
168.23(5) pm and resembles the bond length to the equatorial
Scheme 2. Fluorination of the Se compounds.
F atom in SeF4,[24] 168.2 pm (gas phase) and in the SeOF3
ꢀ
ion,[25] 176.68 pm. Mes2SeF2[26] with 188.87 and 187.76 pm and
out the fluorination by XeF2 in a solution of CH2Cl2 or CHCl3
for 3 h at ꢀ308C yields mainly Trip2C6H3SeF3 and tBuMe2SiF
(dF = ꢀ171.1 ppm, cf. Ref. [22]). However the target,
Trip2C6H3SeF is not even present in traces amounts.
bis(2,2-biphenylen)selenium difluoride[27] with 185.3 pm have
ꢀ
longer Se F bonds. Also the bond angle at the selenium atom,
102.84(1)8 resembles the bond angle between equatorial
fluorine atoms in SeF4,[24] 100.68.
We were finally able to synthesize the tin selenide
Trip2C6H3SeSnMe3 by reaction of Trip2C6H3SeLi and
Me3SnCl, and by the same method, Mes2C6H3SeSnMe3
(Scheme 1, structures[20]). The reaction of Mes2C6H3SeSnMe3
with XeF2 was unsuccessful. Only Trip2C6H3SeSnMe3 reacts
with XeF2 at ꢀ308C within 3 h selectively to the selenenyl
fluoride Trip2C6H3SeF and insoluble Me3SnF without forma-
tion of the selenium trifluoride. The 19F signal appears at d =
ꢀ343.6 ppm and the 77Se resonance at d = 1784.0 ppm with a
coupling constant of 1JSe,F = 755.0 Hz. Single crystals of
Trip2C6H3SeF were obtained from its diethyl ether solution.
Figure 1 shows the main result of this work, the first molecular
structure of a selenenyl fluoride.[23] For comparison we have
In the tellurium system we began with the fluorination of
(Mes2C6H3)2Te2.[11] Reaction with XeF2 in CH2Cl2 at ꢀ308C
gave first indications for
a
mixed-valent difluoride
Mes2C6H3TeF2 TeC6H3Mes2: The 125Te NMR spectrum
ꢀ
shows a triplet at d = 1516.6 ppm and a singlet at d =
1164.9 ppm, but no indication for a monomer Mes2C6H3TeF
[29]
compound. The fluorination of (Trip2C6H3)2Te2
(struc-
ture[20]) with XeF2 in 3 h at ꢀ308C in CFCl3 or CH2Cl2
produces wine-red solutions. From these a similar colored
room-temperature- and air-stable compound can be isolated
after removal of the solvents (Scheme 3). Again no indication
for a monomeric Trip2C6H3TeF exists. The 125Te NMR
spectrum again shows, besides traces of Trip2C6H3TeF3, two
420
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Chemie
product mixtures containing large amounts ditelluride have
been obtained (structure of Mes2C6H3TeSnMe3[20]). The syn-
thesis of pure TripC6H3TeSiMe2tBu was successful, however.
This reacts, in contrast to the analogous selenium compound,
with XeF2 in 3 h at ꢀ308C. But in the wine-red solution no
monomeric Trip2C6H3TeF is found. The main product is the
ꢀ
dimeric difluoride Trip2C6H3TeF2 TeC6H3Trip2 and tBu-
Me2SiF with traces of Trip2C6H3TeF3
(
125Te NMR spec-
trum[20]). This interesting result shows directly the tendency
ꢀ
of RTeF dimerize to RTeF2 TeR, if no donor group is present
to stabilize the monomeric form.[12]
The crystal structure of the ditellurium difluoride has a
Scheme 3. Fluorination of the Te compounds.
ꢀ
ꢀ
disorder of the TeF2 Te part of the molecule. The Te F bonds
have lengths similar to those of the axial tellurium fluorine
bonds in TeF4·2THF,[31] 196.6(2) and 194.1(2) pm, or in
signals, a triplet at d = 1502.4 ppm and a singlet at d =
1285.5 ppm. The 19F NMR signal appears at d =
ꢀ91.38 ppm. The red compound can be recrystallized from
pentane and the crystal-structure determination[23] shows the
TripC6H3TeF3,[20] 198.57(11) and 192.82(11) pm. The Te Te
distance in the difluoride is almost the same as in the
ditelluride,[20] 273.05(5) pm. But the already large C-Te-Te-C
dihedral angle in the ditelluride[20] of 146.97(1)8 increases
ꢀ
ꢀ
mixed-valent Trip2C6H3TeF2 TeC6H3Trip2 (Figure 2). This
[13]
ꢀ
result corresponds to the structure of BbtTeF2 TeBbt:
further to 159.11(8)8 in the difluoride. The structure is quite
[13]
ꢀ
ꢀ
Sterically protected tellurenyl fluorides are stable in the
dimerized molecular form RTeF2 TeR. This structure type
similar to the TeF2 Te core of BbtTeF2 TeBbt.
ꢀ
We have calculated the reaction energies of the dimeriza-
was first described for tellurenyl chlorides and bromides,[11,30a]
but in the meantime has also been found for iodides.[30b]
The trifluoride Trip2C6H3TeF3 is obtained from the
ditelluride and 3 equivalents XeF2 and is structurally charac-
terized as well.[20]
tion 2REF!REF2 ER and the disproportionation 3REF!
ꢀ
REF3 +R2E2 for E = Se and Te. Geometry optimization
reproduced the structures of all the compounds without
imaginary frequencies, particularly the bi-axial EF2 geometry
ꢀ
of REF2 ER, cf. Ref. [10,11]. The results are shown in
To find out if starting compounds with a single tellurium
atom might give monomeric ArTeF we tried to prepare
Mes2C6H3TeSnMe3 and Trip2C6H3TeSnMe3. But inevitably
Table 2. The Se and Te compounds with Me and Ph groups are
thermodynamically unstable against dimerization and dispro-
portionation: the tellurium compounds about 5 kcalmolꢀ1
more exothermic than the selenium compounds (see also
Ref. [11]). With the bulky Tsi ligand both processes are
reduced by 8–12 kcalmolꢀ1, so that the reaction energies for
the selenium compound (TsiSeF) are close to zero, while
those of the tellurium compound (TsiTeF) remain exother-
mic. This result is in accord with TsiSeF being observable
experimentally. Even the reaction 2BbtTeF!BbtTeF2-TeBbt
remains exothermic by 8.5 kcalmolꢀ1.[13] On the other hand
for the bulky Bbt ligand the dimerizations of the chlorides,
bromides, and iodides BbtTeX (X = Cl, Br, I) are endother-
mic, they exist as monomers.[32] The 2-Me2NCH2C6H4 ligand
reduces the tendency to dimerize: Dimerization of the
selenium compound becomes endothermic and of the tellu-
rium compound with ꢀ2 kcalmolꢀ1 close to zero. In line with
this situation, monomeric RSeF and RTeF compounds with
this donor ligand have been shown to exist.[10,12]
Table 2: Zero point energy corrected reaction energies per chalcogen
atom calculated with B3PW91/6-311+G(d,p) (Se and Te basis set: SDB-
aug-cc-pVTZ) for the dimerization, DE1, 2REF!REF2-ER+2DE1 and the
disproportionation, DE2, 3REF!REF3 +R2E2 +3DE2, values in kcal
molꢀ1
R
.
ꢀ
Figure 2. Molecular structure of Trip2C6H3TeF2 TeC6H3Trip2, hydrogen
atoms and solvent molecules omitted, thermal ellipsoids set at 50%
probability (DIAMOND[28]). The TeF2-Te group is twofold disordered,
only one orientation is shown. Selected bond lengths [pm] and angles
[8]: Te1–C1 214.10(23), Te2–C11 216.27(21), Te1–Te2 272.81(33), Te1–
F1 200.82(22), Te1–F2 196.18(23); Te2-Te1-C1 107.878(62), Te1-Te2-
C11 95.072(60), F1-Te1-F2 167.861(74), C1-Te1-Te2-C11 ꢀ159.109(75).
E
DE1
DE2
E
DE1
DE2
Me
Ph
Tsi
Se ꢀ12.30 ꢀ11.74
Se ꢀ10.91 ꢀ10.89
Te ꢀ17.03 ꢀ16.36
Te ꢀ15.97 ꢀ15.79
Se
ꢀ0.28
ꢀ2.65
ꢀ1.23
Te
Te
ꢀ5.64
ꢀ1.95
ꢀ7.33
ꢀ5.19
2-Me2NCH2C6H4 Se
2.03
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421

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[13] K. Sugamata, T. Sasamori, N. Tokitoh, Chem. Asian J. 2011, 6,
2301 – 2303.
Experimental Section
The Se or Te starting compound (0.5 mmol) is given into 12 mm PFA
tube[33] and in vacuum dry CFCl3 or CH2Cl2 (5 mL) are condensed in
at ꢀ1968C. At ꢀ408C (Tsi2Se2), in all other cases at ꢀ308C, XeF2
(0.5 mmol, 85 mg) is added and the mixture is stirred for 3 h at this
temperature. Clear solutions are reduced in volume to ca. 1 mL under
further cooling at ꢀ408C. Cloudy solutions, particularly when
Me3SnF has formed, are filtered through a precooled syringe filter
and given under argon into another precooled 12 mm PFA tube. The
solution is likewise reduced in volume to ca. 1 mL. A trace of CD2Cl2
for the NMR lock is added. This solution is transferred with argon
pressure at ꢀ408C through a 1 mm teflon tube or by a cooled syringe
into a 4 mm PFA tube. This tube is sealed and fitted into a 5 mm NMR
tube.
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ꢀ
The isolation of Trip2C6H3SeF, Trip2C6H3SeF3, Trip2C6H3TeF2
TeC6H3Trip2, and Trip2C6H3TeF3 is performed similarly with the same
amounts, except that the clear solutions are evaporated to dryness at
the end.
The trifluorides Trip2C6H3SeF3 (from Trip2C6H3SeSnMe3) 1 mmol
XeF2 is required, and Trip2C6H3TeF3 (from (Trip2C6H3)2Te2) requires
1.5 mmol XeF2 for the reaction. NMR data are shown in Table 1. M.p.
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ꢀ
Trip2C6H3TeF2 TeC6H3Trip2: 235–2368C (decomp. under blue colo-
ration). IR spectrum: Bands at 471 cmꢀ1 (Te F) and 205 cm (Te
ꢀ1
ꢀ
ꢀ
Te).
[20] See the Supporting Information.
Single crystals of Trip2C6H3SeF are obtained by slow cooling of a
CFCl3 solution from ꢀ40 to ꢀ808C. These crystals contain disordered
CFCl3 solvent molecules. Solvent-free crystals are obtained after
completely removing all CFCl3 in vacuum and recrystallization from
diethyl ether by slow cooling from ꢀ40 to ꢀ808C.
[21] M. R. Detty, M. D. Seidler, J. Org. Chem. 1981, 46, 1283 – 1292.
[22] B. Ray, T. G. Neyroud, M. Kapon, Y. Eichen, M. S. Eisen,
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[23] a) Crystal data for Trip2C6H3SeF (C36H49FSe): Mr = 579.72, a =
805.8(3), b = 2540.6(8), c = 1591.7(5) pm, V= 3.258(2) nm3, Z =
4, Pnma, 3286 independent reflections, 190 parameters, R1 =
ꢀ
Single crystals of Trip2C6H3TeF2 TeC6H3Trip2 are obtained by
slow cooling of a solution in pentane from room temperature to
ꢀ808C.
ꢀ
0.0491, wR2 = 0.1422; b) Crystal data for Trip2C6H3TeF2
TeC6H3Trip2·2pentane (C82H122F2Te2): Mr = 1401.00, a =
1526(2), b = 1240(2), c = 2031(2) pm, b = 91.27(6), V=
3.843(8) nm3, Z = 2, P2/n, 11513 independent reflections, 420
Received: September 21, 2011
Published online: November 30, 2011
parameters,
R1 = 0.0615,
wR2 = 0.1498.
CCDC 828793
ꢀ
(Trip2C6H3SeF)
and
828799
(Trip2C6H3TeF2
Keywords: ab initio calculations · fluorine · selenium ·
structure elucidation · tellurium
TeC6H3Trip2·2pentane) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
.
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