Pseudohalonium ions: [Me3Si-X-SiMe3]+ (X = CN, OCN, SCN, and NNN)

Article abstract of DOI:10.1002/chem.201000289

By utilizing reaction mixtures, such as Me₃Si-XV[Me ₃Si-X-SiMe₃]⁺ (X = CN, OCN, SCN, and NNN), it was possible to prepare the first examples of bissilylated pseudohalonium cations in high yields. The structure and bonding of a whole series of salts containing pseudohalonium cations is discussed on the basis of experimentally observed (X-ray diffraction, Raman, and IR spectroscopy, and mass spectrometry) and theoretically obtained data. Salts containing pseudohalonium cations are only stable in the presence of weakly coordinating anions, such as the well-known tetrakis(pentafluorophenyl)borate, [B(C₆Fs) ₄]^-.

Full text of DOI:10.1002/chem.201000289

DOI: 10.1002/chem.201000289
Pseudohalonium Ions: [Me3Si–X–SiMe3]+ (X=CN, OCN, SCN, and NNN)
Axel Schulz*[a, b] and Alexander Villinger*[a]
Dedicated to Professor Uwe Rosenthal on the occasion of his 60th birthday
Abstract: By utilizing reaction mixtures, such as Me3Si–X/[Me3Si–X–SiMe3]+ (X=
CN, OCN, SCN, and NNN), it was possible to prepare the first examples of bissily-
lated pseudohalonium cations in high yields. The structure and bonding of a whole
series of salts containing pseudohalonium cations is discussed on the basis of ex-
perimentally observed (X-ray diffraction, Raman, and IR spectroscopy, and mass
spectrometry) and theoretically obtained data. Salts containing pseudohalonium
cations are only stable in the presence of weakly coordinating anions, such as the
Keywords: azides
·
main group
chemistry · pseudohalonium ions ·
weakly coordinating anions · X-ray
diffraction
well-known tetrakis(pentafluorophenyl)borate, [BACTHNUTRGNEUNG
(C6F5)4]À.
Introduction
pare salts incorporating the bissilylated pseudohalonium
cation (X=CN, OCN, SCN, and NNN), and to prove and
extend the pseudohalogen concept. To the best of our
knowledge, salts incorporating silylated pseudohalonium
cations have not been reported yet.
The pseudohalogen concept was introduced by Bircken-
bach and Kellermann in 1925 and further developed and
justified in a series of publications in the following years.[6]
Anions such as CNÀ, CNOÀ, NNNÀ, OCNÀ, and SCNÀ can
be regarded as classical linear pseudohalides, as these spe-
cies fulfill the following criteria with respect to halogen-like
chemical behavior:[7,8] A pseudohalogen (X) forms i) a
Similar to a proton, the bulky trimethylsilicenium ion
[Me3Si]+ (“big proton”)[1] is also always solvated and sily-
lates the solvent forming the corresponding cation.[2,3,4] The
full series of salts that contain bissilylated halonium cations
[Me3Si–-X–SiMe3]+ (X=F, Cl, Br, and I) has been generat-
ed and fully characterized in the super Lewis acidic silylat-
ing medium Me3Si–X by using the [Me3Si]+ salt as the sily-
lating reagent in the presence of the chemically robust,
weakly coordinating, anion[5] tetrakis(pentafluorophenyl)bo-
rate, [BACHTUNGTRENNUNG ACHTUNGTRENNUNG
(C6F5)4]À(Scheme 1).[1,2] Here, Me3Si–X is both sol-
C
vent and reactant. Thus it was of great interest to see if, by
means of this synthetic approach, it was also possible to pre-
strongly bound univalent radical (X ), ii) a singly charged
anion (XÀ), iii) a pseudohalogen hydrogen acid of the type
HX, iv) salts of the type M(X)n with silver, lead, and mercu-
ric salts of low solubility, v) a neutral dipseudohalogen com-
pound (X–X), which disproportionates in water and can be
added to double bonds, and vi) interpseudohalogen species
(X–Y).[8,9] In this study, we want to show that this concept
can be extended by the criterion that a pseudohalogen
should also form a pseudohalonium ion, for example, of the
type [Me3Si–X–SiMe3]+. Here we report the first examples
of the synthesis and full characterization of salts that incor-
porate the homoleptic, bissilylated pseudohalonium ions
[Me3Si–CN–SiMe3]+ (1), [Me3Si–OCN–SiMe3]+ (2), [Me3Si–
SCN–SiMe3]+ (3), and the intriguing [(Me3Si)2NNN]+ (4)
(Scheme 1). The trialkylsilylation of a weak base is known
(solvents, arenes, weakly coordinating anions, silanes,
etc.)[2,3,10] and hence we assumed that the lone pairs on both
ends or on one end of an ambidentate pseudohalogen anion
can be silylated. Notably, despite the lack of two sets of lone
Scheme 1. Synthesis of halonium (X=F, Cl, Br, and I) and pseudohaloni-
um salts (X=CN (1), OCN (2), SCN (3), and NNN (4); [A]À =[B-
ACHTUNGTRENNUNG
(C6F5)4]À).
[a] Prof. Dr. A. Schulz, Dr. A. Villinger
Institut fꢀr Chemie
Albert-Einstein-Strasse 3a, 18059 Rostock (Germany)
[b] Prof. Dr. A. Schulz
Leibniz-Institut fꢀr Katalyse e.V. an der Universitꢁt Rostock
Albert-Einstein-Strasse 29a, 18059 Rostock (Germany)
Fax : (+49)381-4986382
E-mail: axel.schulz@uni-rostock.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000289.
7276
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7276 – 7281

FULL PAPER
pairs, hydride-bridged bissilyl cations of the type [R3Si–H–
SiR3]+, in which the bonding is best described by a two-elec-
tron three-center bond in contrast to the four-electron
three-center bond found in the analogous halonium ions,
have been reported by the groups of Sekiguchi, Mꢀller, and
Reed.[10,11]
causes a significant band shift to higher wavenumbers,[12]
which is also observed upon silylation for 1–4 (DnIR 1: 57, 2:
82, 3: 136, 4: 53 cmÀ1). Hence, both IR and Raman spectros-
copy (DnRaman 1: 56, 2: 77, 3: 120, 4: 52 cmÀ1)[13,14] are partic-
ularly well suited to distinguish between pseudohalonium
ions [Me3Si–X–SiMe3]+ and the free solvents Me3Si–X,
whereas NMR spectroscopy is not suited. Owing to a rapid
exchange process,[15] which has already been described for
Results and Discussion
[R3Si][BACTHNGUTERNNUG
(C6F5)4] and bissilylated halonium ions,[1] no specific
1H, 13C, and 29Si resonances could be detected for the pseu-
dohalonium ions 1–4.
According to Scheme 1, pseudohalonium ions 1–4 are easily
obtained when Me3Si–X (X=CN, OCN, SCN, and NNN
(for 1–4, respectively); 30 to 50 fold molar excess) is added
X-ray quality crystals were obtained from saturated solu-
tions of 1–4 at À258C. Single-crystal X-ray studies revealed
dropwise to neat [Me3Si][B
N
the expected [Me3Si–X–SiMe3][BACTHNGUTERNNU(G C6F5)4] salts (X=pseudo-
ambient temperatures with stirring, which results in a clear
colorless solution (b.p. Me3Si–CN 1148C; Me3Si–NNN
958C; Me3Si–NCO 908C; Me3Si–NCS 1438C; Me3Si–NCSe
758C (175 mm/Hg)). Cooling to À258C over a period of one
hour, results in the deposition of colorless crystals. Removal
of excess trimethylpseudohalogenosilane by decantation and
drying in vacuo gives the corresponding [Me3Si–X–SiMe3]
halogen) without solvent molecules in the cell.[16]
The isoelectronic analogue of bis(trimethylsilyl)acetylene,
+
ꢀ
ꢀ
Me3Si–C C–SiMe3, [Me3Si–C N–SiMe3] crystallizes as the
[BACTHNUTRGNEUNG
(C6F5)4]À salt in the monoclinic space group P21/c with
four units per cell (Table 1). As depicted in Figure 1, the
cation adopts an almost staggered, C3-symmetric conforma-
[BACHTUNGTRENNUNG(C6F5)4] salt (X=CN, OCN, SCN, and NNN), as a color-
less solid in almost quantitative yield (90–95%). It should
be noted that the synthesis of [Me3Si–NCSe–SiMe3][B-
ACHTUNGTRENNUNG(C6F5)4] was also attempted, but only decomposition prod-
ucts were observed on silylation even at very low tempera-
tures.
All salts are extremely air and moisture sensitive, but
stable under an argon atmosphere over a long period, as
solids and in Me3Si–X solutions. Salts of 1–4 are easily pre-
pared in bulk and are stable if stored in a sealed tube and
kept at ambient temperatures. They are even thermally
stable up to 120–1908C (CN 1888C; NNN 1838C; OCN
1648C; SCN 1288C). Although
Figure 1. ORTEP drawing of the molecular structure of 1 in the crystal.
Thermal ellipsoids with 50% probability at 173 K. Selected bond lengths
À
À
À
[ꢃ] and angles [8]: Si2 C1 1.890(2), N C1 1.157(2), Si1 N 1.888(2); C1-
N-Si1 176.8(2), N-C1-Si2 178.5(2).
4[B
G
a
covalently
Table 1. Crystallographic details of 1–4.[30]
bound azide, it is neither heat
nor shock sensitive. Decomposi-
tion starts above 1838C, which
is quite astonishing.
1
2
3
4
formula
Mw [gmolÀ1
color
system
space group
a [ꢀ]
C31H18BF20NSi2
851.45
colorless
monoclinic
P21/c
8.208(4)
17.811(9)
24.084(13)
91.017(14)
3520(3)
4
C31H18BF20NOSi2
867.45
colorless
monoclinic
P2/c
C31H18BF20NSSi2
883.51
colorless
monoclinic
P21/n
C30H18BF20N3Si2
867.46
colorless
orthorhombic
Pbcn
]
Caution: Salts of 1–4 decom-
pose vigorously and appropriate
safety precautions should be
taken when dealing with large
quantities
above 1008C.
The IR and Raman data of
all considered pseudohalonium
salts show sharp bands in the
21.486(12)
8.078(5)
21.686(13)
112.117(13)
3487(4)
4
11.195(7)
18.966(13)
17.077(11)
104.476(13)
3511(4)
4
18.683(6)
18.366(6)
19.722(7)
90.00
6767(4)
8
b [ꢀ]
c [ꢀ]
b [8]
V [ꢃ3]
Z
temperatures
1calcd [gcmÀ3
]
1.607
0.232
1.652
1.672
1.703
m [mmÀ1
]
0.238
0.293
0.245
lMoKa [ꢃ]
T [K]
measured reflns
independent reflns
I>2s(I)
0.71073
173(2)
38721
10115
6952
0.71073
173(2)
41107
0.71073
173(2)
36363
0.71073
173(2)
23913
expected
n˜ =2000–
2350 cmÀ1, which can be as-
signed to the stretching fre-
quencies nCN (1–3) and nas,NNN
(4), respectively. As previously
shown for neutral R–CN ad-
ducts, the coordination of B-
10157
9278
8533
7131
6925
4803
Rint.
0.0431
1696
0.0434
0.1197
1.077
0.0355
1728
0.0401
1760
0.0482
3456
F
(000)
R1 (R [F2 >2s(F2)])
0.0422
0.1185
1.070
0.0379
0.1069
1.051
0.0439
0.0973
0.928
wR2 (F2)
GoF
parameters
502
531
511
514
ACHTUNGTRENNUNG(C6F5)3 to a NC–R species
Chem. Eur. J. 2010, 16, 7276 – 7281
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7277

A. Schulz and A. Villinger
tion with large C-N-Si and N-C-Si angles of 176.8(3) and
178.5(2)8, in accord with DFT computations (see Table 2).
À
The C N bond length is 1.157(2) ꢃ, which agrees with the
+
À
C N distance of 1.132 ꢃ found in [R–NC–Me] (R=N-
(2,6-dimethylphenyl)).[17] By comparison with typical Si N
À
bond lengths (1.70–1.76 ꢃ),[18] the Si N distance of
À
1.888(2) ꢃ is very long, and similar to those in [iPr3Si+
ACHTUNGTRENNUNG CHTUNGTRENNUGN
(NCCH3)] (1.82(2)[19] or [Me3Si+A(NCtBu)] 1.822(5),[20]
[Me3Si CHTUNGTRENNUNG CHTUNGTNER(NUGN NCCH3)]
+A(NCCH3)] 1.845 (2) ꢃ).[21] [(Bu2MeSi)3Si+A
has also been reported, but without structural data.[22]
Besides the observed 1,2-bissilylated CN cation, [Me3Si–
+
C N–SiMe3] , the N,Nꢁ ([(Me3Si)2NC]+) and, C,Cꢁ
ꢀ
([(Me3Si)2CN]+) silylated constitution isomers are also pos-
sible, but represent high-energy isomers (DE0rel.: 0 ([Me3Si–
CN–SiMe3]+), 38.2 kcalmolÀ1 [(Me3Si)2NC]+), according to
computations at the pbe1pbe/aug-cc-pwCVDZ level of
theory.[23] The N-substituted isomer is often referred to as
the “nitrilium” ion, a term that was adopted by Hantzsch in
1931 for products of the reaction of nitriles with acids.[24] Ni-
trilium ions are assumed to be intermediates in reactions
such as Friedel–Crafts type reactions like the Gatterman
and Houben–Hoesch reactions, as well as the Ritter reac-
tion, or are used in [3+2] cycloadditions of alkyl azides
with nitrilium ions to yield tetrazoles.[25,26] A series of N-sub-
Figure 2. ORTEP drawing of the molecular structure of 2 (top) and 3
(bottom) in the crystal. Thermal ellipsoids with 50% probability at
À
173 K. Selected bond lengths [ꢃ] and angles [8] of 2: C1 N1 1.069(6),
À
À
À
C1 O1 1.282(6), O1 Si2 1.840(6), N1 Si1 1.775(5); N1-C1-O1 176.9(5),
À
À
C1-O1-Si2 128.2(5), C1-N1-Si1 173.9(8). 3: S C1 1.640(2), S Si1
2.296(2), Si2 N 1.816(2), N C1 1.147(2); C1-S-Si1 98.42(6), C1-N-Si2
169.3(2), N-C1-S 177.2(2).
À
À
forms an almost linear Si-N-C moiety (2: 173.9(8), 3:
169.3(2)8), whereas a fairly small angle is found for the silyl
group attached to the chalcogen atom (2: 128.2(5), 3:
98.42(6)8), in accord with DFT computations, which indicate
smaller angles for the heavier chalcogens (O: 132.1, S:
100.1, Se: 96.88).[23] Within the slightly bent N–C–Y moieties
(2: 176.9(5), 3: 177.2(2); Y=O, S) two significantly different
stituted nitrilium salts was isolated,[27,28] and also the exis-
+
ꢀ
tence of protonated nitrilium salts of the type [R–C NH]
was reported,[29] but so far structural data are only known
for one arylated [R–NC–Me]
phenyl),[17] and one silylated acetonitrile derivative [R–NC–
Me]
[CB9H5Br5] (R=triisopropylsilyl).[19a] The proton ana-
ACHTUNGRTEN[NUNG BF4] (R=N-(2,6-dimethyl-
ACHTUNGTRENNUNG
+
ꢀ
À
logue [HC NH] is known to be a stable ion in the gas
phase[31,32,33] and of substantial interest to astrochemis-
try,[34,35] since it exists in interstellar molecular clouds. In the
condensed phase protonation of hydrogen cyanide was ach-
bonds are experimentally observed: i) A short C N bond of
1.069(6) (2) and 1.147(2) ꢃ (3), respectively, which is close
ꢀ
to a triple bond (ꢀr
(C N)=
À
1.15 ꢃ), and ii) a C O bond of
À
ieved in strong acid systems FSO3H/SbF5/SO2 and studied
1.282(6) and C S 1.640(2) ꢃ,
which corresponds to a typical
+
by NMR spectroscopy,[36] but isolation of [HC NH] salts
ꢀ
have not yet been reported and thus X-ray data are not
available.
C=Y bond (2: ꢀr CHTNUGTREN(NUNG C=O)=
covA
1.23, 3: ꢀr
covACHTUNGTRENN(UNG C=S)=1.61 ꢃ;
Almost nothing is known about bis-alkylated and -ary-
lated OCN and SCN cations of the type [R2NCY]+ or [R–
NCY–R]+ (Y=O, S). The presence of [R2NCO]+ in the
reaction of N,N-dialkyl carbamide acid chloride
(R2NC(Cl)O)[37] with SbCl5 was assumed, but Schmidt and
co-workers showed that, instead of the [R2NCO]+ ion, an
adduct of the type [R2NC(Cl)O–SbCl5] is formed.[38] In
agreement with theory, for 2 and 3, the 1,3-silylated isomer
is experimentally observed (Figure 2). The, N,Nꢄ and the
Y,Yꢄ silylated species (Y=O or S) are energetically un-
Y=O, S).[39]
In contrast to the structures
of 2 and 3, X-ray studies of bis-
silylated azide cation (4),
[(Me3Si)2NNN]+, reveal that
both silyl groups are attached
to one nitrogen atom (Figure 3,
Table 1), in agreement with our
computation. Interestingly, the
Figure 3. ORTEP drawing of
difference between the 1,1- and the molecular structure of one
favored (DE0
:O:
0
[Me3Si–OCN–SiMe3]+, 0.6
1,3-silylated isomer (amino-
diazonium vs. iminodiazenium
independent molecule of 4 in
the crystal. Thermal ellipsoids
with 50% probability at 173 K.
Selected bond lengths [ꢃ] and
rel
[(Me3Si)2NCO]+, 40.2 kcalmolÀ1 [(Me3Si)2OCN]+; S:
0
[Me3Si–SCN–SiMe3]+,
[(Me3Si)2SCN]+; Se:
3.8
0
[(Me3Si)2NCS]+,
[Me3Si–SeCN–SiMe3]+, 6.9
28.8
structure)
(DE0
is
very
small
:
0
[(Me3Si)2NNN]+,
2.4 kcalmolÀ1
[(Me3Si)NNN-
À
angles [8]: Si1 N1 1.876(1),
rel
i
[(Me3Si)2NCSe]+, 27.4 kcalmolÀ1 [(Me3Si)2SeCN]+).[23]
À
À
N1 N2
1.280(3),
À
N1 Si1
(SiMe3)]+).[23] As mentioned in
ACHTUNGTRENNUNG
1.876(1), N2 N3 1.111(3); N2-
N1-Si1i 115.61(7), N2-N1-Si1
115.61(7), Si1i-N1-Si1 128.8(1),
N3-N2-N1 180.000(1). Symme-
[Me3Si–NCO–SiMe3][B
N
[B(C6F5)4] crystallize in the monoclinic space groups P2/c
T
the introduction, the Me3Si
group can be considered as a
and, P21/n, respectively, with four units per cell (Table 1). In
both ions the silyl group attached to the nitrogen atom
“big proton”, and as early as try code: i: Àx, y, Àz+1/2.
7278
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7276 – 7281

Pseudohalonium Ions
FULL PAPER
1966 Schmidt reported the preparation of [H2NNN]
[SbCl6]
closely related to the [(Me3Si)2NNN]+ ion with respect to
the molecular structure.
In analogy to the bissilylated halonium ions, pseudohalo-
nium ions of the type [Me3Si–X–SiMe3]+ (X=pseudohalo-
gen) can be regarded as solvent complexes between Me3Si–
X and [Me3Si]+. In this context the trimethylsilicenium af-
finity (TMSA), which describes the enthalpy change associ-
ated with the dissociation of the conjugated acid,[1,48] has
been calculated at the pbe1pbe level of theory by utilizing
an aug-cc-pwCVDZ basis set.[23] The largest TMSA value
was found for [Me3Si–CN–SiMe3]+ with 54.4 (34.8 kcalmolÀ1
for X=F), decreasing along the series [Me3Si–NNN–
SiMe3]+ (44.2)>[Me3Si–NCSe–SiMe3]+ (43.3)>[Me3Si–
1
in HF/SbF5, HF/BF3, and HSO3F/SbF5 by means of H and
15N NMR spectroscopy.[41] The experimentally determined
structure of the [H2NNN]+ ion as a [SbF6]À salt was first re-
ported by Christe and co-workers in 1993.[42] Furthermore
aryl- and alkyl-substituted aminodiazonium ions are dis-
cussed as intermediates in a couple of reactions, such as the
Schmidt reaction.[43]
A
ACHTUNGTRENNUNG(C6F5)4] crystallizes in the orthorhombic
A
NCS–SiMe3]+
(41.1)>[Me3Si–NCO–SiMe3]+
(39.3 kcal
molÀ1).[23]
À
G
E
According to NBO analysis all Si X bonds are highly po-
larized, but this polarization decreases considerably if the
heavier atoms S and Se are linked to the Si atom (Table 2),
CTHUNGTRENNUNG
CHTUNGTRENNUNG
[H2NNN]+ ion with
a
pyramidal H2N moiety, the
Table 2. Charge values and selected calculated structural data[a] of
[Me3Si–X–SiMe3]+ ions at the pbe1pbe/aug-cc-pwCVDZ level of
theory.[23]
[(Me3Si)2NNN]+ ion is C2v symmetric and planar with both
silyl groups symmetrically attached to the same nitrogen
(Figure 3). Hence a linear N–N–N group is found (175.38 in
X=
CN
NNN
OCN
SCN
SeCN
+
À
À
[H2NNN] ) with two different N N distances (d
(N1 N2)=
q(X) [e]
À0.34
À0.46
À0.51
À0.28
À0.21
(À0.47)[b] (À0.59)[b] (À0.62)[b] (À0.63)[b] (À0.64)[b]
À
1.280(3) vs. d
N
ogous bond lengths in the [H2NNN]+ ion (1.295(5) vs.
1.101(3) ꢃ).[42] According to natural bond orbital (NBO)
analysis[44] the planarity of 4 (in contrast to [H2NNN]+) may
be partly attributed to hyperconjugation effects, such as the
À
[c]
Dq [e]
QCT [e]
0.13
0.26
54.4
0.13
0.27
44.2
0.11
0.21
39.3
0.35
0.45
41.1
0.43
0.51
43.3
[d]
TMSA
[kcalmolÀ1
YN [ꢃ][e]
]
1.157
180.0
1.123
1.252
115.3
115.3
180.0
1.165
1.166
1.165
intramolecular donor–acceptor interaction between sACTHNUTRGNEUNG(Si
SiNZ [8][f]
176.3
132.1
177.8
176.4
100.1
177.3
177.3
96.8
177.3
À1 [23]
À
N1) and p*ACHTUNGTRENNUNG(N2 N3) bonds (14 kcalmol ) or between the
lone pair at N1 (p-type atomic orbital) and the antibonding
SiYZ [8][g] 180.0
X [8]
–
À1
À
s*
(Si C) bonds (1–3 kcalmol ). As expected, owing to
[a] Only the lowest lying isomers are considered. [b] Values in parenthe-
ses are the partial charges of X in Me3Si X. [c] Dq=q
[d] Charge transfer from Me3Si X to [Me3Si] . [e] Y=N for NNN and C
for all other. [f] Z=N for NNN, C for all other. [g] Y=O, S, Se and Z=
C, for NNN Y=Z=N.
steric repulsion the Si1i-N1-Si1 angle with 128.8(1)8 is signif-
icantly larger than the N2-N1-Si1 angle (115.61(7)8).
À
A
ACHTUNGTRENNUNG(XMe SiX).
3
+
À
Related to the [(Me3Si)2NNN]+ ion are Lewis acid (LA)
adduct azide anions of the type [LA–NNN–LA]À. Two ex-
amples, which contain a N,N-dicoordinated azide anion, are
the borane complex A[45] or the [GaCl3–NNN–GaCl3]À ion
B[46] (structural data are shown in Scheme 2). Lewis acids of
the type ER3 (E=Group 13 element, R=organic or inor-
ganic group) can be considered isolobal to the Me3Si+ ion.
Hence the structural data of A and B are very similar to
those found in 4. There are many examples of N,N-dicoordi-
nated azide compounds in main group chemistry.[47] The
latter compounds are not exactly silylated, but they are still
in accord with the computed partial charges. Interestingly,
all pseudohalonium units composed of second-row elements
display
(Table 2). A significantly larger charge transfer is found for
X=SCN and SeCN with 0.45 and 0.51 e, respectively. In 1,
2, and 4 the pseudohalogen moiety contributes almost half
to the overall charge transfer, whereas the YCN (Y=S, Se)
unit dominates the charge transfer in the [Me3Si–YCN–
SiMe3]+ ions (see Table 2, Dq vs. QCT).
a similar charge transfer between 0.21–0.27 e
As the partial charge (q) at the pseudohalogen unit re-
mains negative even upon bissilylation (Table 2), in accord
with the analogous halonium ions [Me3Si–X–SiMe3]+ (X=F,
Cl, Br; CN, NNN, OCN, SCN and SeCN), but not [Me3Si–I–
SiMe3]+ for which q(I)=0.01 e,[1] we would like to comment
on the name halonium and pseudohalonium, respectively.
According to IUPAC[49] onium ions are cations derived by
addition of a H+ ion to a mononuclear parent hydride of
the nitrogen (H3E, E=element of Group 15), chalcogen
Scheme 2. Structural data of known Lewis-acid (LA) adduct azide anions
A[45] and B[46] (bond lengths in ꢃ; R=C6F5).
Chem. Eur. J. 2010, 16, 7276 – 7281
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7279

A. Schulz and A. Villinger
Chem. Res. 1998, 31, 133–139; c) S. H. Strauss, Chem. Rev. 1993, 93,
927–942, and references therein.
(H2E, E=element of Group 16) and halogen families (HE,
E=element of Group 17) or derivatives formed by substitu-
tion of the parent ions (H4E+, H3E+, H2E+) by univalent
groups. Hence ions of the type [R–E–R]+, for which E is
any halogen or pseudohalogen, are referred to as halonium
ions or pseudohalonium ions, respectively, which may be
open-chain or cyclic.[50,51] This naming does not imply that
the central atom is positively charged, which may be the
case for the heavier group elements, but certainly not for
the electronegative elements, such as N or O, as in the am-
monium (NH4+) or oxonium (H3O+) ions.
[6] a) L. Birckenbach, K. Kellermann, Ber. 1925, 58B, 786–794; b) L.
Birckenbach, K. Kellermann, Ber. 1925, 58B, 2377–2386; c) L.
Birckenbach, K. Huttner, W. Stein, Ber. 1929, 62B, 2065–2075 and
L. Birckenbach, K. Huttner, W. Stein, Ber. 1929, 62B, 2261–2277;
d) L. Birckenbach, M. Linhard, Ber. 1930, 63B, 2528–2544, L. Birck-
enbach, M. Linhard, Ber. 1930, 63B, 2544–258 and L. Birckenbach,
M. Linhard, Ber. 1930, 63B, 2588.
[7] A. M. Golub, H. Kçhler, Chemie der Pseudohalogenide, VEB
Deutscher Verlag der Wissenschaften, Berlin, 1979.
[8] H. Brand, A. Schulz, A. Villinger, Z. Anorg. Allg. Chem. 2007, 633,
22–35.
[9] Not all criteria are always met. Although many linear pseudohalo-
gens (e.g., CN, OCN, CNO, NNN, SCN) are known, often the corre-
sponding pseudohalide acids, dipseudohalogens, and interpseudohal-
ogens are thermodynamically highly unstable (e.g., HNNN, OCN–
NCO, NC–SCN) with respect to N2/CO elimination or polymeri-
zation or indeed, remain unknown (e.g., N3–N3).
Conclusion
In conclusion, we present here a straightforward synthetic
procedure to bissilylated pseudohalonium salts by utilizing
the reaction mixture Me3Si–X/[Me3Si–X–SiMe3]+ (X=pseu-
dohalogen)—a concept which was first applied to halo-
gens.[1] By means of this approach it was possible to prepare
the first bissilylated pseudohalonium cations in high yields,
proving and extending the pseudohalogen concept.[7] Thus it
can be said, that, in analogy to halogen chemistry, a pseudo-
halogen should form pseudohalonium ions of the type [R–
X–R]+ in the presence of a weakly coordinating anion.
[10] a) R. Panisch, M. Bolte, T. Mꢀller, J. Am. Chem. Soc. 2006, 128,
9676–9682; b) T. Mori, S. V. Lindeman, J. K. Kochi, Chem.
Commun. 1998, 927–928; c) R. S. Brown, R. W. Nagorski, A. J.
Bennet, R. E. D. McClung, G. H. M. Aarts, M. Klobukowski, R.
McDonald, B. D. Santarsiero, J. Am. Chem. Soc. 1994, 116, 2448–
2456; d) A. Avelar, F. S. Tham, C. A. Reed, Angew. Chem. 2009,
121, 3543–3545; Angew. Chem. Int. Ed. 2009, 48, 3491–3493; e) M.
Arshadi, D. Johnels, U. Edlund, C.-H. Ottosson, D. Cremer, J. Am.
Chem. Soc. 1996, 118, 5120–5131; f) T. Kꢀppers, E. Bernhardt, R.
Eujen, H. Willner, C. W. Lehmann, Angew. Chem. 2007, 119, 6462–
6465; Angew. Chem. Int. Ed. 2007, 46, 6346–6349; g) M. Kira, T.
Hino, H. Sakurai, J. Am. Chem. Soc. 1992, 114, 6697–6700; h) H. E.
Katz, J. Am. Chem. Soc. 1985, 107, 1420–1421; i) H. E. Katz, J. Org.
Chem. 1985, 50, 5027–5032; j) P. D. Lickiss, P. C. Masangane, W.
Sohal, G. L. Veneziani, in Organosilicon Chemistry V (Eds.: N.
Auner, J. Weis), Wiley-VCH, Weinheim, 2003, p. 45.
Experimental Section
Synthesis of 1–4: To neat [Me3Si][BACHTNUGRTNEUNG
(C6F5)4] (0.752 g, 1.0 mmol),[1,2]
[11] a) T. Mꢀller, Angew. Chem. 2001, 113, 3123–3126; Angew. Chem.
Int. Ed. 2001, 40, 3033–3036; b) T. Mꢀller in Organosilicon Chemis-
try V (Eds.: N. Auner, J. Weis), Wiley-VCH, Weinheim, 2003, p. 34;
c) A. Sekiguchi, A. Muratami, N. Fukaya, Y. Kabe, Chem. Lett.
2004, 33, 530–531; d) S. P. Hoffmann, T. Kato, F. S. Tham, C. A.
Reed, Chem. Commun. 2006, 767–769.
Me3Si–X (30 to 40 fold molar excess) was added dropwise at ambient
temperatures with stirring, followed by gently heating to 608C. This re-
sulted in a clear colorless solution. Cooling to À258C over a period of
one hour resulted in the deposition of colorless crystals. In the case of 3
the solution was concentrated to promote crystallization prior to cooling.
À
Removal of excess Me3Si X by decantation and drying in vacuo gave the
[12] H. Jacobsen, H. Berke, S. Doering, G. Kehr, G. Erker, R. Froehlich,
O. Meyer, Organometallics 1999, 18, 1724–1735.
corresponding [Me3Si–X–SiMe3] [B
G
salt as a colorless solid in almost quantitative yield (90–95%).[52]
[13] Owing to the presence of two independent [(Me3Si)2NNN]+ ions in
the unit cell, the antisymmetric stretching mode is split (Raman: n˜ =
2190/2177 and IR: n˜ =2189/2175 cmÀ1).
[14] A. Bernsdorf, H. Brand, R. Hellmann, M. Kçckerling, A. Schulz, A.
Villinger, K. Voss, J. Am. Chem. Soc. 2009, 131, 8958–8970.
[15] H. Wang, C. E. Webster, L. M. Perez, M. B. Hall, F. P. Gabbaꢅ, J.
Am. Chem. Soc. 2004, 126, 8189–8196.
Acknowledgements
[16] Crystals of 1 contain one equivalent of the solvent (Me3SiCN),
which can be removed by recrystallization from benzene.
[17] A. K. Gjøystdal, C. Romming, Acta Chem. Scandinavica 1977, 31b,
56–62.
We are indebted to Mathias Lehmann (University of Rostock) for the
NMR study and Johannes Thomas (University of Rostock) for measuring
the Raman spectra. We thank both reviewers for most valuable com-
ments.
[18] W. S. Sheldrick in The Chemistry of Organic Silicon Compounds,
(Eds.: S. Patai, Z. Rappoport), Wiley, New York, 1989, p. 227.
[19] a) Z. Xie, D. J. Liston, T. Jelꢆnek, V. Mitro, R. Bau, C. A. Reed, J.
Chem. Soc. Chem. Commun. 1993, 384–386; b) S. Bahr, P. Boud-
jouk, J. Am. Chem. Soc. 1993, 115, 4514–4519.
[20] M. Ichinohe, H. Fukui, A. Sekiguchi, Chem. Lett. 2000, 29, 600–601.
[21] Synthesis and structural data of this compound is given in the Sup-
porting Information (compound 5).
[22] M. Nakamoto, T. Fukawa, A. Sekiguchi, Chem. Lett. 2004, 33, 38–
39.
[23] See the Supporting Information for the computational details, E0,
H298 and, G298 values, relative energies, structural data, frequencies,
and details of the NBO analysis.
[1] M. Lehmann, A. Schulz, A. Villinger, Angew. Chem. 2009, 121,
7580–7583; Angew. Chem. Int. Ed. 2009, 48, 7444–7447.
[2] a) J. B. Lambert, S. Zhang, S. M. Ciro, Organometallics 1994, 13,
2430–2443; b) J. B. Lambert, S. Zhang, J. Chem. Soc. Chem.
Commun. 1993, 383–384.
[3] C. A. Reed, Z. Xie, R. Bau, A. Benesi, Science 1993, 262, 402–404.
[4] a) G. K. S. Prakash, S. Keyaniyan, R. Aniszfeld, L. Heiliger, G. A.
Olah, R. C. Stevens, H.-K. Choi, R. Bau, J. Am. Chem. Soc. 1987,
109, 5123–5126; b) J. B. Lambert, W. J. Schulz, J. A. McConnell, W.
Schilf, J. Am. Chem. Soc. 1988, 110, 2201–2210.
[5] Reviews: a) I. Krossing, I. Raabe, Angew. Chem. 2004, 116, 2116–
2142; Angew. Chem. Int. Ed. 2004, 43, 2066–2090; b) C. Reed, Acc.
[24] A. Hantzsch, Chem. Ber. 1931, 64, 667–678.
7280
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7276 – 7281

Pseudohalonium Ions
FULL PAPER
[25] E. Vilsmaier, R. Schneider, J. Schiitz, Liebigs Ann. Chem. 1980,
1064–1074.
[26] H. Quast, L. Bieber, G. Meichsner, Liebigs Ann. Chem. 1987, 469–
475.
[27] H. Meerwein, P. Laasch, R. Mersch, J. Spille, Chem. Ber. 1956, 89,
209–224.
[28] F. Klages, W. Grill, Liebigs Ann. Chem. 1955, 594, 21–32.
[29] F. Klages, R. Ruhnau, W. Hauser, Liebigs Ann. Chem. 1959, 626,
60–70.
[30] CCDC-764307 (1), CCDC-764310 (2), CCDC-764311 (3), and
CCDC-764309 (4) contain the supplementary crystallographic 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.
[31] R. S. Altman, M. W. Crofton, T. Oka, J. Chem. Phys. 1984, 80, 3911–
3912.
[32] M. Kajita, K. Kawaguchi, E. Hirota, J. Mol. Spectrosc. 1988, 127,
275–276.
[44] a) E. D. Glendening, A. E. Reed, J. E. Carpenter, F. Weinhold, NBO
Version 3.1; b) J. E. Carpenter, F. Weinhold, THEOCHEM 1988,
169, 41–62; c) F. Weinhold, J. E. Carpenter, The Structure of Small
Molecules and Ions, Plenum Press, 1988, 227; d) F. Weinhold, C.
Landis, Valency and Bonding. A Natural Bond Orbital Donor–Ac-
ceptor Perspective, Cambridge University Press, Cambridge, 2005,
and references therein.
[45] J. Chai, S. P. Lewis, S. Collins, T. J. J. Sciarone, L. D. Henderson,
P. A. Chase, G. J. Irvine, W. E. Piers, M. R. J. Elsegood, W. Clegg,
Organometallics 2007, 26, 5667–5679.
[46] D. Michalik, A. Schulz, A. Villinger, N. Weding, Angew. Chem.
2008, 120, 6565–6568; Angew. Chem. Int. Ed. 2008, 47, 6465–6468.
[47] For example: a) M. Veith, A. Rammo, Z. Anorg. Allg. Chem. 2001,
627, 662–668; b) T. M. Klapçtke, H. Nçth, T. Schmitt, M. Warch-
hold, Angew. Chem. 2000, 112, 2197–2199; Angew. Chem. 2000, 112,
2197–2199; Angew. Chem. Int. Ed. 2000, 39, 2108–2109; c) R.
Haiges, A. Vij, J. A. Boatz, S. Schneider, T. Schroer, M. Gerken,
K. O. Christe, Chem. Eur. J. 2004, 10, 508–517.
[33] T. Amano, K. Hashimoto, T. Hirao, J. Mol. Struct. 2006, 795, 190–
193.
[48] M. Swart, E. Rçsler, M. Bickelhaupt, J. Comput. Chem. 2006, 27,
1486–1493.
[34] M. Araki, H. Ozeki, S. Saito, Astrophys. J. Lett. 1998, 496, L53–L55.
[35] L. M. Ziurys, B. E. Turner, Astrophys. J. Lett. 1986, 302, L31–L36.
[36] G. A. Olah, T. E. Kiovsky, J. Am. Chem. Soc. 1968, 90, 4666–4672.
[37] F. Klages, G. Lucasczyk, Chem. Ber. 1963, 96, 2066–2069.
[38] D. Beierl, A. Schmidt, Chem. Ber. 1973, 106, 1637–1642.
[39] Holleman Wiberg—Lehrbuch der Anorganischen Chemie, 102. Ed.:
Walter de Gruyter, Berlin, 2007.
[40] A. Schmidt, Chem. Ber. 1966, 99, 2976–2983.
[41] A. Mertens, K. Lammertsma, M. Arvanaghi, G. A. Olah, J. Am.
Chem. Soc. 1983, 105. 5657–5660.
[49] Compendium of Chemical Terminology, 2nd ed. (Eds.: A. D.
McNaught, A. Wilkinson), Blackwell Science, New York, 1997.
[50] G. A. Olah, Halonium Ions, Wiley-Interscience, New York, 1975.
[51] A. Olah, G. K. S. Prakash, J. Sommer, Superacids, Wiley, New York,
1985.
[52] Synthesis and characterization of starting materials including the X-
ꢀ
ray data of [Me–C N–SiMe3][BACHTNUGTRNE(UGN C6F5)4] and detailed analytical data
of all products are given in the Supporting Information.
[42] K. O. Christe, W. W. Wilson, D. A. Dixon, S. I. Khan, R. Bau, T.
Metzenthin, R. Lu, J. Am. Chem. Soc. 1993, 115, 1836–1842.
[43] W. H. Pearson, R. Walavalkar, J. M. Schkeryantz, W. Fang, J. D.
Blickensdorf, J. Am. Chem. Soc. 1993, 115, 10183–10194.
Received: February 2, 2010
Revised: March 22, 2010
Published online: May 12, 2010
Chem. Eur. J. 2010, 16, 7276 – 7281
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7281