Selenirenium and tellurirenium ions

Article abstract of DOI:10.1002/anie.200801691

Canted chalcogens: Relatively stable selenirenium salts (R¹ ₂C₂SeR)⁺X^- (R¹=tert- alkyl) are prepared by reaction of RSe⁺X^- with acetylenes; the bond angle at selenium is only 38°. Highly unstable tellurirenium salts (R¹₂C₂TePh)⁺X^- from PhTe⁺X^- and di-tert-alkylacetylenes have a bond angle at tellurium of 34° (see picture). These three-membered-ring cations were experimentally and theoretically investigated. (Chemical Equation Presented).

Full text of DOI:10.1002/anie.200801691

Angewandte
Chemie
DOI: 10.1002/anie.200801691
Selenium and Tellurium
Selenirenium and Tellurirenium Ions**
Helmut Poleschner* and Konrad Seppelt
Table 1: Reactions of RSe+XÀ reagents with acetylenes, and detection of
Reactive compounds with three-membered rings, such as
borirenes,[1] phosphirenes,[2] or the silicon and germanium
analogues of the cyclopropenylium ion,[3] are particularly
challenging to synthesize. Apart from thiirenium salts,[4]
seleniranium ions which play a key role in the asymmetric
synthesis with chiral diselenides have also been investigated.[5]
Selenirenium ions have been postulated as principal inter-
mediates in addition reactions of selenium-containing elec-
trophiles to acetylenes, although they have never been
identified.[6] The early 13C NMR spectroscopic identification
by Schmid and Garratt[7] is incorrect, and possible decom-
position products may have been detected instead. Tellurire-
nium ions have not been mentioned in the literature at all.
We found a strong indication for the existence of
selenirenium ions in the distinct steric influence of the
group R on the addition of PhSeF[8] to BuC ꢀ CR.[9] We
expected that these three-membered ring ions should have
low stability, and therefore initial detection experiments used
low-temperature NMR spectroscopy.
the selenirenium ions by 77Se and 13C NMR spectroscopy.[a]
RSe+XÀ
Reagent
Acetylene
T
d(77Se)
d(13CRing
)
[8C][b]
Ph2Se2/XeF2/
2SbF5
Ph2Se2/Br2/
2AgSbF6
Ph2Se2/
2NOSbF6
(PhSeO)2O/
2Ph2Se2/3Tf2O
PhSeCl/SbCl5
PhSeCl/SbCl5
PhSeCl/SbCl5
PhSeCl/SbCl5
PhSeCl/SbCl5
PhSeCl/SbCl5
tBuCꢀCtBu
tBuCꢀCtBu
tBuCꢀCtBu
tBuCꢀCtBu
À40
À40
À40
À40
À40
À88.0 112.5
À86.5 112.9
À86.8 112.8
À82.9 112.8
À83.7 113.3
tBuCꢀCtBu
AdCꢀCAd[d]
PhCꢀCtBu
BuCꢀCtBu
iPrCꢀCiPr
BuCꢀCBu
À40 À105.3 111.0
À40
À40
À40
À40
À80
À78.7 101.9, 114.4
À81.4 107.0, 117.3
À87.5 112.9
[c]
–
–
À95.3 109.8
The following PhSe+XÀ equivalents are used for the
addition to alkynes: Ph2Se2/XeF2/2SbF5, Ph2Se2/Br2/
PhSeCl/SbCl5
PhSeCl/SbCl5
À80
À82.8[e] 110.3[e]
2AgSbF6,[5,10]
Ph2Se2/2NOSbF6,[11]
(PhSeO)2O/2Ph2Se2/
3Tf2O (Tf2O = trifluoromethanesulfonic acid anhydride),[12]
and PhSeCl/SbCl5.[4] (MeSe)3 SbCl6
is used as a MeSe+
+
À[13]
À80
À95.6[e] 110.4
source. The reaction of the RSe+XÀ reagents with acetylenes
in CH2Cl2 between À40 and À808C produces the selenire-
nium ions, which are detected by 77Se NMR spectroscopy
(Scheme 1, Table 1). Signals are substantially upfield
(betweenÀ79 and À105 ppm (R = Ph) and À169 and
+
(MeSÀe)3
tBuCꢀCtBu
AdCꢀCAd
À40 À169.0 112.7
À40 À185.0 109.3
SbCl6
+
(MeSÀe)3
SbCl6
[a] d values in ppm. [b] Temperature of reaction and NMR measurement.
[c] No selenirenium ion detectable. [d] Ad=1-adamantyl. [e] Broad.
calculations[15] of 77Se and 13C NMR shifts of model com-
pounds agree well with the experimental data and confirm the
structure (Scheme 2). Strong magnetic shielding in three-
membered rings as compared to larger rings is a common
phenomenon, for example, in cycloalkanes and cycloalkenes
(13C), in cyclic ethers (17O), thioethers (33S), amines (15N) and
phosphines (31P).[16]
Scheme 1. Preparation of the selenirenium ions.
À185 ppm (R = Me); cf. Me3Se+ 254 ppm[14]). The 13C signal
also showed upfield shifts for the ring carbon atoms that are
similar to those found for thiirenium ions.[4] GIAO-MP2
With di-tert-butylacetylene, all the PhSe+XÀ equivalents
produce the expected three-membered rings. Acetylenes
[*] Dr. H. Poleschner, Prof. Dr. K. Seppelt
Institut für Chemie und Biochemie
Anorganische und Analytische Chemie
Freie Universität Berlin
Fabeckstrasse 34-36, 14195 Berlin (Germany)
Fax: (+49)30-8385-3310
E-mail: hpol@chemie.fu-berlin.de
Scheme 2. GIAO-MP2/6-311+G(d,p) calculations on the 77Se, 125Te,
and 13C NMR chemical shifts of selenirenium and tellurirenium ions
(Cs symmetry) relative to Me2Se, Me2Te, and TMS; d value in ppm
(optimization with MP2/6-311+G(d,p), Te basis: SDB-cc-pVTZ, Te
basis for GIAO: IGLO II-type[15]).
[**] We thank the Deutsche Forschungsgemeinschaft (DFG) and the
Fonds der Chemischen Industrie for support of this work.
Supportinginformation for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200801691.
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having the substituents Ad/Ad, Ph/tBu, nBu/tBu and iPr/iPr
also react with PhSeCl/SbCl5 to give selenirenium ions at
À408C. Products formed with 5-decyne, cycloundecyne, and
cyclododecyne decompose at À408C, and selenirenium ions
are observed only at below À808C. Cyclododecyne and 2-
butyne do not form selenirenium ions with PhSeCl/SbCl5,
even at À808C, and 2-butyne also fails to react with Ph2Se2/
Br2/2AgSbF6 at À808C.
Schmid and Garratt worked with 2-butyne and p-tolyl-
SeCl/AgPF6 at room temperature. The 13C NMR signal at
136 ppm, which they assigned to the three-membered ring,
can only come from decomposition products.[7] The MeSe+
+
À
source (MeSe)3 SbCl6 reacts with di-tert-butylacetylene or
diadamantylacetylene to form methylselenirenium ions.
Selenirenium ions can also be formed by elimination of a
halide ion from vicinal (E)-halogen(phenylseleno)olefins.
Fluoro[9] and chloro[15] olefins are however too stable, and
fluoride ion abstraction by Tf2NSiMe3 or chloride ion
abstraction by AgSbF6 does not take place. Only the
bromoolefins[15] react with AgSbF6 with a configuration
change from (E) to (Z) with formation of the three-
membered ring (Scheme 3).
Figure 1. Molecular structure of the cation of
(Ad2C2SePh)+SbCl6À·CH2Cl2. Ellipsoids are set at 50% probability.
Selected bond lengths [pm] and angles [8]: Se–C1 191.4(8), Se–C7
197.1(8), Se–C8 198.6(9), C7–C8 128.5(12) C7–C9 147.9(12), C8–C19
147.9(12); C7-Se-C8 37.9(3), C1-Se-C7 105.6(4), C1-Se-C8 106.5(4), C7-
C8-C19 155.7(9), C8-C7-C9 156.0(9).
Figure 2. Molecular structure of the cation of
Scheme 3. Attempts to obtain selenirenium ions by halide abstraction
from (E)-halogen(phenylseleno)olefins.
(tBu2C2SeMe)+SbCl6À·0.5CH2Cl2. Ellipsoids are set at 50% probability.
Selected bond lengths [pm] and angles [8]: Se1–C1 195.2(4), Se1–C2
198.4(3), Se1–C3 198.5(3), C2–C3 127.9(5), C3–C4 150.1(5), C2–C8
150.5(5); C2-Se1-C3 37.60(14), C1-Se1-C2 102.51(16), C1-Se1-C3
102.02(16), C2-C3-C4 156.2(3), C3-C2-C8 157.3(3).
The structure of 1-phenyl-2,3-di-tert-butyl-, 1-phenyl-2,3-
diadamantyl-, and 1-methyl-2,3-di-tert butylselenirenium salts
have been determined by single-crystal X-ray diffraction
(Figures 1 and 2).[15,17] Se C bonds within the three-mem-
the salts (tBu2C2SePh)+SbCl6
,
(A 2CdSePh)+SbCl6
,
À
À
À
2
(tBu2C2SeMe)+SbCl6À, and (Ad2C2SeMe)+ SbCl6 was possi-
ble. The colorless or slightly yellow compounds can be kept
under argon for a few hours at room temperature, but
decompose within one week to a significant extent. These
salts have an intense peak in the FAB mass spectrum for the
molecular cation.
À
bered rings are markedly longer (197.1–198.6 pm) than those
between selenium and the phenyl or methyl groups (191.4 and
195.2 pm). The latter are similar to those in normal seleno-
nium ions, such as PhMeEtSe+ (Se Ph 193.0 pm, Se Me
192.6 pm).[18] The bond angles at the selenium atom are small
(388) and are thus even smaller than in the thiirenium ion
À
À
(40.858).[4] The C C bond lengths (127.9 and 128.5 pm, sulfur
To obtain tellurirenium ions, the PhTe+XÀ reagents
=
analogues 127.8 pm[4]) are remarkable short, and are inter-
Ph2Te2/XeF2/2SbF5, Ph2Te2/Br2/2AgSbF6,[20] and Ph2Te2/
[11]
=
mediate between
a
double bond ((Z)-tBuCH CHtBu
2NOSbF6 were reacted exclusively with di-tert-alkylacety-
134.3 pm) and a triple bond (tBuC ꢀ CtBu 120.2 pm).[19]
lenes at À408C in CH2Cl2 (Scheme 4, Table 2). Tellurirenium
ions could be clearly identified under the chosen conditions,
with 125Te NMR signals at À380 to À426 ppm. Relative to
Me3Te+ (408 ppm),[14] the 125Te signals are extremely upfield.
The 13C d values are often detectable only at very low
temperatures, and are similar to those of the selenium
compounds. GIAO-MP2 calculations confirm the high mag-
netic shielding of the tellurium and carbon ring atoms that is
observed (Scheme 2). No reagent exists for methyltellurire-
There is a linear correlation between the Raman C–C
[15]
À
=
vibrational frequency and C C bond lengths.
The C C
=
distance and the C C-C angle of about 1568 are indicative of a
sp1.5 hybridization of the carbon ring atoms. The natural bond
orbital (NBO) analysis[15] of the trimethylselenirenium ion
results in sp1.35 hybridization for the C C bond.
=
The compounds that were determined crystallographi-
cally are stable to the extent that isolation of
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À
than the Te Ph bond (213.7 pm). The latter value is similar to
those in telluronium ions such as PhMeEtTe+ (211.7 pm).[18]
=
The C C bond length (128.8 pm) is as was found in the
selenium compounds, but the C-Te-C angle (34.18) is even
À
smaller. Ring strain, and the Te C bond, which is weaker than
Scheme 4. Preparation of tellurirenium ions.
À
a Se C bond, and in this case even more elongated, explain
the low stability of these compounds.
Table 2: Reactions of PhTe+SbF6 reagents with acetylenes, and detec-
À
Calculations of the nucleus-independent chemical shifts
(NICS)[23,24] for the chalcogenirenium ions give negative
values: (H2C2SH)+ NICS(1) À7.82 ppm, (H2C2SeH)+
NICS(1) À10.34 ppm, (H2C2TeH)+ NICS(1) À12.32 ppm.[15]
These three-membered rings should therefore have a dia-
magnetic ring current as a result of aromatic electron
delocalisation (cf. NICS of silicon- and germanium-containing
aromatic three-membered rings[3]). However, according to
CCSD(T)/aug-cc-pVTZ calculations, the ions (Me2C2EMe)+
tion of the tellurirenium ions by 125Te and 13C NMR spectroscopy at
À408C.[a]
PhTe+SbF6 Reagent
Acetylene
d(125Te)
d(13Cring
)
À
[b]
Ph2Te2/XeF2/2SbF5
Ph2Te2/Br2/2AgSbF6
Ph2Te2/2NOSbF6
Ph2Te2/2NOSbF6
Ph2Te2/Br2/2AgSbF6
Ph2Te2/2NOSbF6
tBuCꢀCtBu
tBuCꢀCtBu
tBuCꢀCtBu
AdCꢀCAd
AdCꢀCtBu
AdCꢀCtBu
À381.0
À383.5
À380.5
À426.3
À407.1
À402.1
–
112.2
110.7[b,c]
108.8[b,c]
[b]
–
109.9, 109.5[b,c]
have only small aromatic stabilization energies:[23,25] E S
=
[a] d values in ppm. [b] No signal at À408C. [c] Broad signal at À908C.
À2.72 kcalmolÀ1, E Se À2.79 kcalmolÀ1, and E Te
À4.72 kcalmolÀ1 (E = chalcogen).[15] Thus the question of
aromaticity remains unclear. Further experimental investiga-
tions into the reactivity of these compounds with nucleo-
philes, and theoretical calculations to clarify the bonding
situation are planned.
=
=
nium ions: Me2Te2/2NOSbF6/tBuC ꢀ CtBu forms only
decomposition products, and (Me2TeTeMe)+BF4
and
À[15,21]
the novel (Me2SeSeMe)+BF4À[15] do not react with acetylenes.
+
Attempts to prepare (MeTe)3 salts as in reference [13]
resulted in the formation of the new four-membered ring
(R4Te4)2+.[22]
Experimental Section
For the preparation of the PhSe+, PhTe+, and MeSe+ reagents, NMR
spectroscopic detection of the selenirenium and tellurirenium ions,
and ab initio calculations, see the Supporting Information.
Preparation of the selenirenium salts: Di-tert-butylacetylene
(420 mg, 3 mmol) or diadamantylacetylene (884 mg, 3 mmol, dis-
solved in 5 mL CH2Cl2) is added dropwise to a 3 mmol solution of the
Crystallization of the tellurirenium ions has been very
difficult, even with the asymmetric acetylene AdC ꢀ CtBu.
Only decomposition and a black coloration is usually
observed. However, the reaction of tBuC ꢀ CtBu with
Ph2Te2/Br2/2AgSbF6 yields 1-phenyl-2,3-di-tert-butyltellurire-
niumhexafluoroantimonate (Figure 3).[17]
reagent PhSe+SbCl6 or (MeSe)3+SbCl6 in CH2Cl2 (20 mL) at
À408C, followed by stirring at this temperature for 30 min, cooling
to À788C, and addition of pentane (50 mL). After filtration, the
crystals are washed three times with pentane (30 mL) and then dried
in vacuum. Recrystallization is carried out with CH2Cl2/pentane at
À788C.
À
À
À
In a similar fashion to the selenium compounds, the Te C
bonds within the heterocycle (219.0 and 220.1 pm) are longer
(tBu2C2SePh)+SbCl6À: Yield 1,19 g (63%), mp. 111–111.58C
(decomp). FAB-MS: m/z 295 (100, M+ for 80Se). 77Se NMR
(CD2Cl2): d = À70.6 ppm. 13C NMR (CD2Cl2) d = 115.64 (C C),
=
33.77 (CMe3), 29.40 (CMe3); Ph: 126.04 (i), 131.60 (o), 129.10 (m),
132.90 ppm (p).
(Ad2C2SePh)+SbCl6
: Yield 1.96 g (83%), mp. 105–1068C
À
(decomp). FAB-MS: m/z 451 (55, M+ for 80Se), 293 (19,
M+ÀPhSeH), 135 (100, C10H15+). Raman: n = 1856 cmÀ1 (C C). 77Se
=
13
=
NMR (CD2Cl2): d = À93.5 ppm. C NMR (CD2Cl2): d = 113.55 (C
C); Ad: 35.27 (C1), 41.36 (C2), 28.10 (C3), 35.67 (C4); Ph: 126.60 (i),
131.46 (o), 128.88 (m), 132.64 ppm (p).
(tBu2C2SeMe)+SbCl6À: Yield 1.37 g (81%), mp. 1308C (decomp).
FAB-MS: m/z 233 (100, m+ for 80Se). 77Se NMR (CD2Cl2): d =
13
=
À161.4 ppm. C NMR (CD2Cl2): d = 114.09 (C C), 33.36 (CMe3),
28.78 (CMe3), 22.10 ppm (MeSe).
(Ad2C2SeMe)+SbCl6À
: Yield 1.96 g (90%), mp. 140–1418C
(decomp). FAB-MS: m/z 389 (55, m+ for 80Se), 293 (47,
M+ÀMeSeH), 135 (100, C10H15+). 77Se NMR (CD2Cl2): d =
13
=
À184.0 ppm. C NMR (CD2Cl2): d = 112.54 (C C); Ad: 34.75 (C1),
40.95 (C2), 28.01 (C3), 35.77 (C4); 23.27 ppm (MeSe).
Figure 3. Molecular structure of the cation of
(tBu2C2TePh)+SbF6À·1.5CCl4. Ellipsoids are set at 50% probability.
Selected bond lengths [pm] and angles [8]: Te–C1 213.7(10), Te–C7
220.1(9), Te–C8 219.0(9), C7–C8 128.8(14), C7–C13 149.7(15); C8–C9
149.9(14); C7-Te-C8 34.1(4), C1-Te-C7 99.3(4), C1-Te-C8 99.3(4), C7-C8-
C9 155.5(10), C8-C7-C13 157.6(9).
Received: April 10, 2008
Keywords: Ab initio calculations · NMR spectroscopy ·
.
selenium · tellurium · X-ray diffraction
Angew. Chem. Int. Ed. 2008, 47, 6461 –6464
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www.angewandte.org 6463

Communications
[17] a) Crystal data for (Ad2C2SePh)+SbCl6À·CH2Cl2 (C28H35Cl6SbSe·
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1021.6(2), c = 1980.1(5) pm, b = 115.2(0)8, V= 3434.5(14) ”
106 pm3, Z = 4, 23895 measured and 4807 independent reflec-
tions, 364 parameters, GooF = 1.009, R1 = 0.0441, wR2 = 0.1222.
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data
for
(tBu2C2SeMe)+SbCl6À·0.5CH2Cl2
(C11H21Cl6SbSe·0.5CH2Cl2): Mr = 609.15, orthorhombic, Cmc21,
a = 1491.73(16), b = 3618.4(4), c = 1670.6(3) pm, V= 9017(2) ”
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reflections, 538 parameters, GooF = 1.003, R1 = 0.0278, wR2 =
0.0679. c) Crystal data for (tBu2C2TePh)+SbF6À·1.5CCl4
(C16H23F6SbTe·1.5CCl4): Mr = 809.41, monoclinic, P2/c, a =
1649.0(7), b = 935.3(4), c = 1954.1(8) pm, b = 110.01(1)8, V=
2832(2) ” 106 pm3, Z = 4, 34549 measured and 6845 independent
reflections, 336 parameters, GooF = 1.092, R1 = 0.0737, wR2 =
0.1941. CCDC-638635 ((Ad2C2SePh)+SbCl6À·CH2Cl2), CCDC-
683631 ((tBu2C2SeMe)+SbCl6À·0.5CH2Cl2), and CCDC-683634
((tBu2C2TePh)+SbF6À·1.5CCl4) contain the supplementary crys-
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