Cyclic silylated onium ions of group 15 elements

Article abstract of DOI:10.1021/ic502968z

Five- and six-membered cyclic silylated onium ions of group 15 elements I were synthesized by intramolecular cyclization of transient silylium ions II. Silylium ions II were prepared by the hydride transfer reaction from silanes III using trityl cation as hydride acceptor. It was found that smaller ring systems could not be obtained by this approach. In these cases tritylphosphonium ions IV were isolated instead. Cations I and IV were isolated in the form of their tetrakispentafluorphenyl borates and characterized by multinuclear NMR spectroscopy and, in two cases, by X-ray diffraction analysis. Cyclic onium ions I showed no reactivity similar to that of isoelectronic intramolecular borane/phosphane frustrated Lewis pairs (FLPs). The results of DFT computations at the M05-2X level suggest that the strength of the newly formed Si-E linkage is the major reason for inertness of I[B(C₆F₅)₄] versus molecular hydrogen.

Full text of DOI:10.1021/ic502968z

Article
pubs.acs.org/IC
Cyclic Silylated Onium Ions of Group 15 Elements
Matti Reißmann,†,‡ Andre Schafer,†,‡ Robin Panisch,† Marc Schmidtmann,† Michael Bolte,§
́
̈
and Thomas Muller*,†
̈
†Institut fur Chemie, Carl von Ossietzky Universitat Oldenburg, Carl von Ossietzky Strasse 9-11, D-26129 Oldenburg, Federal
̈
̈
Republic of Germany
§Institut fur Anorganische und Analytische Chemie, Goethe Universitat Frankfurt, Max von Laue-Strasse 7, D-60438 Frankfurt,
̈
̈
Federal Republic of Germany
S
* Supporting Information
ABSTRACT: Five- and six-membered cyclic silylated onium
ions of group 15 elements I were synthesized by intra-
molecular cyclization of transient silylium ions II. Silylium ions
II were prepared by the hydride transfer reaction from silanes
III using trityl cation as hydride acceptor. It was found that
smaller ring systems could not be obtained by this approach.
In these cases tritylphosphonium ions IV were isolated instead.
Cations I and IV were isolated in the form of their
tetrakispentafluorphenyl borates and characterized by multi-
nuclear NMR spectroscopy and, in two cases, by X-ray diffraction analysis. Cyclic onium ions I showed no reactivity similar to
that of isoelectronic intramolecular borane/phosphane frustrated Lewis pairs (FLPs). The results of DFT computations at the
M05-2X level suggest that the strength of the newly formed Si−E linkage is the major reason for inertness of I[B(C6F5)4] versus
molecular hydrogen.
INTRODUCTION
■
Silyl Lewis acids are potent silylating reagents.1 Particularly
powerful in this respect are silylium-like species such as
perfluorinated tetraarylborates of silylated arenium ions ([R3Si-
(arene)]+, bissilylated hydronium ions ([R3Si−H−SiR3]+), or
their intramolecular variants.2 This was recently demonstrated
by the synthesis and structural characterization of persilylated
haloniums,3 pseudohaloniums,4 chalconiums,5,6 pseudochalco-
niums,7 and pnictoniums8 using these highly electrophilic
species. The most recent landmark in this series of achieve-
ments is the report on the isolation of a tetrasilylammonium
borate by the group of Schulz.9 In the past, ammonium ion
formation in an intramolecular fashion has been utilized to
stabilize Lewis-acidic triorganoboron, -aluminum, -gallium, and
-indium compounds, such as 1.10,11 In these experimental
studies a qualitative relationship between the reactivity of the
intramolecular stabilized species and the ring size and its
flexibility had been drawn.11 An extension of this work to
silicon-based Lewis acids was demonstrated recently by
Oestreich and co-workers.12 They used remote sulfur (as in
cation 2) or nitrogen substituents (3) to stabilize silylium
species by onium ion formation. Interestingly, these studies
revealed a clear dependence of the reactivity of these cations on
the donor atom. While the sulfur stabilized cation 2 showed
significant catalytic activity in Diels−Alder reactions, iminium
ion 3 was found to be inactive under similar conditions.12
A particularly interesting example of an intramolecular
stabilized Lewis acid is the zwitterionic heterocyclic compound
4.13 In solution, it is in equilibrium with its acyclic isomer 5 and
the isomer pair 4/5 represents the prime example for an
intramolecular frustrated Lewis pair (FLP).14,15 Compound 5 is
able to split dihydrogen at mild conditions,13 and it acts as a
catalyst for hydrogenation of polar double bonds.16
On the basis of our recent results on dihydrogen activation
by intermolecular silylium/phosphane Lewis pairs17,18 we
envisaged the use of silyl Lewis acids (6) which are stabilized
Received: December 17, 2014
© XXXX American Chemical Society
A
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
by onium ion formation as possible candidates for intra-
molecular FLPs. The tendency of onium ions 6 to form the
noncyclic isomers 7, which are thought to be the active species
in FLP chemistry, is clearly a function of the strength of the
element silicon bond. The strength of this linkage is controlled
by the nature of the element E, by the ring size, and by the
steric and electronic properties of the substituents R, R1 at the
two heteroatoms. Therefore, we studied the synthesis of
representative examples of cyclic silylated onium ions of group
15 elements 8−11 and their possible use in bond activation
reactions.
metathesis between metalated diphenylpnictogenes and silyl
chloride was also the final step for the synthesis of the
silylpnictogen compounds 21 (overall yields 45% (21a, E = N),
47% (21b, E= P), 42% (21c, E = As), 33% (21d, E = Sb)).
The reaction of silanes 12, 13, 17, and 21 with trityl
tetrakispentafluorophenylborate [Ph3C][B(C6F5)4] was ex-
pected to deliver the corresponding silylium ions as short-
living intermediates according to the standard hydride transfer
protocol.2,22 The intermediate silylium ions would then
undergo consecutive ring closure reactions to give cyclic
silylated onium ions of different ring size (see eq 5, Scheme 2).
Scheme 2. Possible Reactions of Diphenyl(silylalkyl)
a
Phosphanes, 12, 13, and 17 with Trityl Cation
a
The [B(C6F5)4]− anion is omitted.
In contrast to the expectation in the case of the reaction of
silylmethyl- and silylethylphosphanes 12 and 17 with trityl
cation in benzene at room temperature we observed no
formation of triphenylmethane. Instead, the phosphonium
borates 22[B(C6F5)4] and 23[B(C6F5)4] were obtained by
addition of trityl cation to the phosphanyl group (Scheme 2, eq
6). Notably, even after prolonged heating of the reaction
mixture no formation of triphenyl methane was observed. The
NMR spectroscopic results indicated the formation of
phosphonium ions 22 and 23 (see Table 1). 1H NMR
resonances in the typical region for SiH hydrogen atoms with
clearly visible SiH satellites and almost no change of the
position of the 29Si NMR signals upon ionization showed the
presence of an intact SiMe2H functionality. Evidence for the
quarternization of the phosphorus atom was provided by the
significant low-field shift of the 31P NMR resonance to a 31P
NMR chemical shift region that is characteristic for
tetraalkylphosphonium ions.23 The most prominent NMR
feature for the newly formed C−P linkage is the duplet signal
detected for the quarternary carbon atom of the trityl group in
the 13C NMR spectra of compounds 22[B(C6F5)4] and
23[B(C6F5)4] (see Table 1). Similar NMR spectroscopic data
were reported previously for a series of tritylphosphonium
borates.24 In contrast, reaction of [Ph3C][B(C6F5)4] with the
silylpropyl phosphane 13a (E = P) in benzene took the
expected course (Scheme 2, eq 5). In this case, the formation of
triphenyl methane accompanied by the disappearance of the
RESULTS AND DISCUSSION
■
The synthesis of the precursor compounds followed standard
procedures and is summarized in Scheme 1.19−21 The synthesis
Scheme 1. Syntheses of Precursor Compounds19−21
a
a
Conditions: (a) LiAlH4, Et2O; (b) LiPPh2, THF; (c) HPPh2, hν,
neat; Et2O; (d) Me2SiHCl, [H2PtCl6], neat; (e) MEPh2, THF, for E =
P, As, Sb: M = Li; E = N: M = K; (f) i-pr2SiHCl, [H2PtCl6]; (g) Mg,
BrP(C6F5)2, THF.
1
Si−H resonance in the H NMR spectrum demonstrated the
successful hydride transfer reaction. In addition, the low-field
shift of the 29Si signal and the significant splitting due to
coupling with the 31P nuclei of this signal suggested the
formation of the cyclic phosphonium ion 24a via the acylic silyl
cation 25a (Scheme 2, Table 1).
An assessment of the energies of the two competing
reactions shown in Scheme 2 (eqs 5 and 6) at the density
functional M05-2X/6-31G(d) level of theory reveals some
important insights.25,26 The formation of the trityl cation/
phosphane Lewis acid base complex according to eq 6 is for all
of silylalkyl phosphanes 12, 13, and 14 was achieved by
conversion of the silyl chlorides 15 and 16 into the
corresponding silanes followed by simple salt metathesis
(overall yields 31% (12), 10% (13a, E = P), 13% (13b, E =
As)).19,20 For the buildup of the silylethyl derivative 17 a
photohydrophosphanylation20 of vinylchlorosilane 18 followed
by a reduction step was applied (overall yield 32%). The
propylsilyl compounds 16, 19, and 20 were synthesized
according to a standard hydrosilylation protocol.21 Salt
B
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Pertinent NMR Parameters of Cations 22−24a ([B(C6F5)4]− Salts in Benzene-d6)
a
b
b
cation
n
δ1H (SiH); (1JSiH [Hz])
δ29Si (mJSiP [Hz])
Δδ29Si (ΔJSiP [Hz])
δ31P
Δδ31P
δ13C(CPh3) (1JCP [Hz])
22
1
3.55 (205)
3.85 (191)
−12.6 (9, m = 2)
−14.8 (24, m = 3)
23.9 (37, m = 1)
−2.8 (−8)
−3.2 (3)
37.9 (n.d.)
31.6
38.3
−6.2
57.5
48.3
10.6
67.3 (39)
67.2 (36)
23
2
3
c
24a
a
b
Number of methylene groups, see Scheme 2. Calculated as the difference between the NMR parameter of the cation and the precursor compound.
c
JSiP not detected in compound 13a (E = P).
three tested phosphanes exothermic by a nearly constant value
Scheme 4. Competitive Formation of Cyclic Silyl
Phosphonium, 24a, and Trityl Phosphonium, 25, Ions by
Reaction of Silaalkylphosphane 13a with Trityl Cation
of 142−152 kJ mol−1 (Table 2), which corresponds roughly to
Table 2. Calculated DFT Reaction Energies ΔE for Possible
Reactions of Phosphanes 12, 13a, and 17 with Trityl Cation
(Reactions 5 and 6 (Scheme 2), in kJ mol−1, at M05-2X/6-
31G(d))
n
compound
eq 5
eq 6
prevented. This mechanistic proposal should be valid also for
other cases where the hydrogen transfer reaction with trityl
cations competes with onium ion formation and might explain
the observed slow conversion of silanes to silyl cations in the
presence of n-donor substituents.12
1
2
3
12
−37
−118
−187
−149
−152
−142
17
13a
the strength of the newly formed C−P bond. On the other
hand, the reaction energy for the hydride transfer reaction with
subsequent formation of cyclic onium ions (eq 5) strongly
depends on their ring size. The increasing ring strain generated
by the formation of four- and three-membered cyclic ions
results in energies of reaction that are significantly smaller than
those calculated for the formation of the corresponding acyclic
phosphonium ions 22 and 23. Only for the formation of the
five-membered cyclic phosphonium ion 24a is a significantly
larger thermodynamic driving force predicted by the calculation
(Table 2).
Compound 252[B12Cl12] crystallizes as o-dichlorobenzene
solvate in the centrosymmetric space group P21/n (see Figure
1a). The closest contact between cation and closo-borate
dianion was detected between one methyl group of the
dimethylsilyl unit and a chlorine atom (d(Cl···C) = 362 pm).
Despite this clear thermodynamic preference of formation of
the cyclic onium ion 24a, Lewis acid base complex formation is
also an important competitive reaction channel for the reaction
of silane 13a with trityl cation. This became evident from the
following crystallization experiment. When silane 13a was
reacted with 0.5 equiv of trityl closo-borate [Ph3C]2[B12Cl12]27
in o-dichlorobenzene a colorless precipitate was formed
immediately. X-ray diffraction (XRD) analysis of suitable
crystals revealed that the precipitate consists of the
dichlorobenzene solvate of the phosphonium closo-borate
252[B12Cl12] (Scheme 3).
Scheme 3. Formation of Trityl Phosphonium Ion 25 from
Silane 13a
On the basis of these experimental results the following
mechanistic scenario appears to be plausible (Scheme 4).
Alkylation of phosphane 13a to give of trityl phosphonium ion
25 is fast when compared to the hydride transfer reaction that
yields the cyclic silyl phosphonium ion 24a. The trityl adduct
formation is however reversible when [Ph3C][B(C6F5)4] is
applied. Therefore, the thermodynamically more favored cation
24a is the final product. Due to the low solubility of closo-borate
252[B12Cl12] the trityl phosphonium ion formation is practically
irreversible and the hydride transfer reaction is efficiently
Figure 1. (a) Structure of [25]2[B12Cl12] (1,2-Cl2C6H4) in the crystal.
(b) Molecular structure of phosphonium ion 25 as obtained by single-
crystal XRD analysis. Selected bond length P−C 192.76(9) pm
(ellipsoids drawn at 75% probability level; H atoms, except (Si)−H,
omitted for clarity. Color code: gray = C, white = H, bronze = B, green
= Cl, purple = P, pink = Si).
C
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
The most remarkable feature of the molecular structure of
phosphonium ion 25 (Figure 1b) is a very long C−P bond
(d(C−P) = 192.7 pm). It is slightly longer than the P−C bond
in tetra-tert-butyl phosphonium tetrafluoroborate (d(C−P) =
192.5 pm)29 and significantly longer than the C−P bond
determined for the trityl phosphonium borate [Ph3C−PMe3]-
[B(C6F5)4] (d(C−P) = 188.7 pm).24
The formation of cyclic onium ions is also observed in the
case of the reaction of the arsapropyl-substituted silane 13b and
the di-iso-isopropylsilane 14 with [Ph3C][B(C6F5)4] (Scheme
5). This is shown by the disappearance of the Si−H resonance
On the basis of these results it is not surprising that the
reaction of disilanes 21 with trityl borate [Ph3C][B(C6F5)4] in
benzene provides access to the complete series of cyclic
disilylpnictonium ions 27 as colorless to pale yellow micro-
crystalline solids in high yields. The ammonium, phosphonium,
and arsonium borates [27a−c][B(C6F5)4] are stable in arene
solution at room temperature for a period of several days. In
contrast, the stibonium ion 27d quickly decomposes into
several nonidentified products during the NMR measurements
at ambient temperatures. In each case, the equivalence of both
1
SiMe2 groups in H, 13C, and 29Si NMR spectra and only two
13C NMR signals for the propadiyl backbone indicates the
symmetrical structure of the formed cation in solution. In
addition, the low-field shift of the 29Si NMR resonance of the
Si−E group suggests the formation of the bissilylated
pnictonium (see Figure 2 for the 29Si and 31P NMR spectra
of compound 27b[B(C6F5)4]). Remarkably, silylation of the
nitrogen atom to give cation 27a has a shielding effect on the
15N NMR chemical shift compared to the precursor silylamine
(Δδ15N = −6.5).30 Alkylation of trialkylamines results in a low-
field shift for the 15N NMR resonance, for example, Δδ15N =
28.6 for the Me4N+/Me3N couple.31 In the case of the
phosphonium ion 27b the deshielding of the phosphorus nuclei
is only modest (Δδ31P = 5.4)32 compared to that found for the
a
Scheme 5. Formation of Onium Ions 24 and 26
a
(a) Ph3C+, −Ph3CH; [B(C6F5)4]− anion is omitted.
1
[(Me3Si)4P]+/P(SiMe3)3 pair (Δδ31P = 49.9). The JSiP
in the 1H NMR spectra and by a significant low-field shift of the
29Si NMR signal upon ionization (Δδ29Si 45.0 (24b), 44.2
coupling constant of disilylphosphonium ion 27b is surprisingly
small (1JSiP = 11 Hz). It is only one-half of that detected for the
precursor silylphosphane 21b (1JSiP = 22 Hz), which indicates a
weakening of the Si−P linkage upon quarternization. For
1
(26); see Table 3). Compared to cation 24a the JSiP coupling
1
tetrakis(trimethylsilyl)phosphonium an even smaller JSiP
Table 3. Significant NMR Parameters of Onium Ions 24, 26,
coupling constant was reported (1JSiP = 1.4 Hz).8
and 27
a
b
a
b
ion
E
δ29Si (1JSiP [Hz])
Δδ29Si
δE
ΔδE
a
Scheme 6. Formation of Disilylpnictoniums 27
24a
24b
26
P
23.9 (37)
30.9
37.9
45.0
44.2
38.4
6.0
−6.2
−9.4
As
P
50.1 (18)
44.0
−26.9
79
20.1
−6.5
5.4
27a
27b
27c
27d
N
P
8.6 (11)
17.7
−51.3
As
Sb
12.0
15.3
17.5
a
The [B(C6F5)4]− anion is omitted.
a
b
At room temperature in C6D6. Calculated as the difference between
the NMR parameter of the cation and the precursor compound.
Crystals suitable for XRD analysis of the borate 27b[B-
(C6F5)4] were obtained from a hexafluorobenzene solution at 6
°C. The crystal structure of 27b[B(C6F5)4] revealed well-
separated anions and cations with the shortest Si···F distance
well above the sum of the corresponding van der Waals radii
(d(SiF) = 377.5 pm, Σ(vdWr(Si,F)) = 357 pm, see Figure
constant of cation 26 is decreased, which suggests a weaker
donor−acceptor interaction for cation 26 (see Table 3). This
assumption is further supported by the stronger deshielding
that is detected for both nuclei involved in the donor−acceptor
interaction in cation 26.
Figure 2. 31P{1H} NMR (left) and 29Si{1H} INEPT NMR (right) spectra of compounds 21b (top) and 27b[B(C6F5)4] (bottom).
D
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3a).33 The molecular structure of phosphonium ion 27b in the
crystal shows a regular chair conformation for the six-
of the three C−Si−C bond angles (Σ(C−Si1−C) = 337° and
Σ(C−Si2−C) = 339.4°.36
Optimization of the molecular structure of cation 27b at the
density functional M05-2X/6-311+G(d,p) level of theory
reveals structural parameters which are very close to the
experiment (see Table 4).25,26 This suggests that this
computational level provides reliable structural data for the
investigated species. According to the results of the calculations
the six-membered cyclic onium ions 27a−c adopt regular chair
conformations, only for stibonium ion 27d a twisted half-chair
conformation is predicted. The five-membered onium ions 24
take up an envelope conformation with the central methylene
group twisted out of the plane of the four remaining ring atoms
(Figure 4a). Finally, for cation 26 the calculations predict a half-
chair conformation (Figure 4b).
Figure 4. Calculated molecular structures (M05-2X/6-311+G(d,p)) of
(a) phosphonium ion 24a and (b) phosphonium ion 26. Selected
bond lengths [pm] 24a, P−Si 231.9; 26, P−Si 242.8 (H atoms omitted
for clarity; aryl substituents presented in wireframe mode. Color code:
light gray = C, green = F, purple = P, pink = Si).
Figure 3. (a) Structure of 27b[B(C6F5)4] in the crystal. (b) Molecular
structure of 27b as obtained by single-crystal X-ray diffraction.
Selected bond lengths [pm] and angles [degrees]: Si1−P 230.76(11);
Si2−P 231.24(11); C1−P 180.92(28); C2−P 182.81(29); Si1−P−Si2
105.025(41); C1−P−C2 106.934(125); (ellipsoids drawn at 50%
probability level; H atoms omitted for clarity. Color code: gray = C,
yellow = B, medium green = F, magenta = P, pink = Si).
The bonding parameters of the Si−E linkage are of particular
interest in view of an application of these cyclic onium ions in
bond activation reactions. Therefore, the following discussion is
concentrated on the properties of the Si−E linkage. In all
investigated cases, the bonds between the silicon acceptor atom
and the tetracoordinated pnictogen donor atom are slightly
elongated compared to standard values (see Table 4).37 Not
surprisingly, the relative elongation Δ(Si−E) is calculated to be
larger for the five-membered onium ions 24 and 26 than for the
six-membered cations 27. Comparison of the bond elongation
data for the disilylpnictoniums 27 reveals no clear trend for the
different group 15 elements.
membered ring (Figure 3b). The most prominent feature of
the molecular structure is an almost symmetric Si−P−Si unit in
which both Si−P bonds are elongated compared to neutral
silylphosphanes (r(Si1P) = 230.8 pm, r(Si2P) = 231.2 (27b) pm
vs r(SiP) = 226.5 pm reported for tricoordinated silylphos-
phanes).34 Similar elongated Si−P bonds in silylated
phosphonium ions were reported recently (r(SiP) = 231.0
pm).35 The innercyclic Si1−P−Si2 bond angle is close to the
ideal tetrahedral angle (Si1−P−Si2 = 105.0°). Both silicon
atoms adopt a tetrahedral coordination as indicated by the sum
More informative are Si−E bond energies, E(Si−E), which
are calculated to a first approximation as the energy differences
Table 4. Calculated Structural Parameters of Onium Ions 24, 26, and 27 and Their Calculated Intramolecular Stabilization
a
Energies ΔEintra
b
c
cation
E
Si−E [pm]
Δ(Si−E) [%]
Si−E−Si(C) [deg]
E(Si−E) [kJ·mol−1
]
24a
24b
26
P
232.9
241.9
237.9
3
95.3
−231
−196
−156
−169
−253
−232
−163
As
P
2
92.9
5
89.4
27a
27b
27c
27d
N
P
194.5; 195.4
4
107.6
231.1; 231.3 (230.8; 231.2)
239.8; 240.5
2 (2)
105.3 (105.0)
104.6
As
Sb
1
2
d
259.9; 260.6
100.6
a
b
M05-2X/6-311+G(d,p), experimental values in parentheses. Elongation of the Si−E bond compared to standard single bond lengths (SiN 187 pm,
c
SiP 227 pm, SiAs 237 pm, SiSb 256 pm). Difference of energies of the cyclic onium ions and the acyclic silylium ions at M05-2X/6-311+G(d,p).
d
The stibonium ion adopts a twisted half-chair conformation.
E
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Lewis pairs that are active in dihydrogen activation, interaction
energies between the phosphane and the silylium ion of −63 kJ
mol−1 (for Lewis pair 34) or less have been predicted by
density functional computations.18 For comparison the strength
of the Si−P bond in the related silylphosphonium ion 35, which
is not active in dihydrogen cleavage, is calculated to be 159 kJ
mol−1, as strong as the Si−P linkage in cation 26.
Consequently, the Si−P linkage in cation 26 is by far too
stable to deliver isomer 29, which is believed to be the active
species in bond activation reactions. Therefore, phosphonium
ion 26 and all other investigated onium ions 24 and 27 are not
active in dihydrogen activation. Test reactions for 27b
supported this conclusion.
between the acyclic silylium ions 28, 29, and 30 and the
corresponding cyclic onium ion 24, 26, and 27. The calculated
Si−E bond energies are substantial, ranging from −156 (for the
pair 26/29) to −253 kJ mol−1 (27b/30b) (Table 4). The
smaller bond energies predicted for the five-membered
silylonium ions 24a,b compared to those of the six-membered
disilylpnictoniums 27b,c indicate the destabilization of the Si−
E linkage due to increased ring strain. In the series of six-
membered disilylpnictoniums 27 the largest bond energy E(Si−
E) is computed for the phosphonium ion 27b. As expected,
E(Si−E) decreases substantially for the arsonium ion 27c and
for the stibonium ion 27d (Table 4). Surprisingly weak is also
the Si−N bond in ammonium ions 27a. This is a consequence
of the small size of the nitrogen atom and the resulting steric
interaction between the substituents of the ammonium ion.9
Steric and electronic factors greatly influence E(Si−E). For
example, the increased steric hindrance produced by the
isopropyl groups at silicon and the decreased donating ability
induced by the fluorine substituents weaken the Si−P linkage in
phosphonium ion 26 by 75 kJ mol−1 compared to the closely
related cation 24a. In fact, the Si−P bond in onium ion 26 is
the weakest of all Si−E bonds in the series of cyclic onium ions
which were investigated. Therefore, we choose phosphonium
ion 26 as a test case for its possible use in bond activation
reactions. According to the results of the calculation the
hydrogenation reaction of cation 26 to give phosphonium ion
31 is thermodynamically slightly disfavored by 21 kJ mol−1.
Also, experimentally, no dihydrogen activation was observed.
Exposition of a benzene solution of 26[B(C6F5)4] to a
dihydrogen atmosphere (0.4 MPa, room temperature, 2 h)
led to no reaction, as no NMR signal due to the phosphonium
ion 31 was detected (Scheme 7 and Figure S60, Supporting
Information).
Si−E bond energies as low as −50 kJ mol−1 and thereby
FLP-like reactivity could be approached simply by further
decreasing the ring size and by simultaneously increasing the
steric bulk around the Si−E linkage. The results of DFT
computations, however, illustrate the limitations of this
approach. In the case of the four-membered cyclic cation 36
a Si−P bond energy is predicted which is reduced to ca. 2/3 of
the bond energy in cation 26 (E(Si−P) (36) = −111 kJ mol−1)
(Scheme 9). This Si−P bond energy is still significantly higher
Scheme 9. Possible Reactions of Silane 39 with Trityl Cation
(anion is omitted)
than the benchmark of −50 kJ mol−1 aimed at. On the other
hand, the results of the computations also indicate that the
formation of the trityl addition product 37 would compete
efficiently with the hydride transfer reaction to give the
phosphonium ion 36 via the silylium ion 38 (Scheme 9). The
computed reaction energies for both reaction channels are
nearly identical (formation of 37 (ER = −48 kJ mol−1);
formation of 36 (ER = −54 kJ mol−1)), which makes this
approach rather unattractive for further experimental inves-
tigations.
Scheme 7. Attempted Dihydrogen Activation by Silylated
Onium Ion 26 To Give Silaalkyl Phosphonium Ion 31
CONCLUSION
■
The synthesis of borates of five- and six-membered cyclic
silylated onium ions of group 15 elements by intramolecular
addition of transient silylium ions to pnictogenyl groups is
reported. Silylium ions are prepared by the classical hydride
transfer reaction between trityl cation and silanes. Attempts to
synthesize four- and three-membered cyclic silylated phospho-
nium ions using this synthetic approach failed however. In these
cases, Lewis acid−base formation between trityl cation and the
phosphanyl group is energetically more favored than hydride
transfer between silane and trityl cation. Interestingly, we found
that under kinetic control, the formation of the five-membered
cyclic onium ion 24a is prevented and the Lewis acid−base
complex between trityl cation and the phosphanyl substituent,
25, is formed instead. This suggests that the competition
between trityl coordination to the Lewis-basic center and
hydride transfer is a general phenomenon and that it influences
the course of the hydride transfer reaction when donor atoms
are present.12
Scheme 8. Borane/Phosphane and Silylium Phosphane
Lewis Pairs That Are Pertinent to the Discussion
a
a
Pemp: pentamethylphenyl.
Against the background of recent literature reports, this
failure is not unexpected. Isoelectronic zwitterionic borylphos-
phonium systems, 32, show energy differences compared to the
active boraalkylphosphanes isomers 33 of around −50 kJ
mol−1.38 In addition, for intermolecular silylium phosphane
F
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
3JHH = 6 Hz, JSiH = 186 Hz, SiH), 7.09−7.16 (m, 6 H, ArH), 7.46−
We found that the strength of the newly formed bond
between the group 15 element and the silicon atom E(Si−E) in
cyclic onium ions 24, 26, and 27 is substantial (E(Si−E) =
−156 to −253 kJ mol−1). It is predicted to be larger for six-
membered rings, and it depends on the nature of the element.
In general, the Si−P linkages of phosphonium ions are more
stable than the Si−As bond of arsonium ions. In the case of the
bissilylated onium ions 27 it was found that the Si−Sb and Si−
N bonds are of similar strength but weaker than the Si−As
bond in 27c. Steric and electronic substituent effects can be
used to modify the strength of the Si−E linkage to a certain
extent. Increased steric congestion at the silyl group and
decreased Lewis basicity of the phosphanyl substituent result in
a relatively small bond energy for the Si−P linkage (E(Si−P) =
−156 kJ mol−1) in cation 26. Even in cation 26 the Si−P bond
is, however, too strong to allow the formation of the acyclic,
silylium/phosphane isomer 29 in significant concentrations.
Therefore, the perspectives for establishing a FLP-like reactivity
for these compounds are rather low.
7.52 (m, 4 H, ArH). 13C{1H} NMR (125.758 MHz, C6D6, 298 K): δ
2
1
1.20 (CH3), 14.8 (d, JCP = 12.0 Hz, CH2), 21.2 (d, JCP = 15.0 Hz,
CH2), 128.5 (CH), 128.8 (d, 3JCP = 6.5 Hz, CH), 133.1 (d, 2JCP = 18.3
Hz, CH), 139.0 (d, JCP = 15.0 Hz, C). 29Si{1H} NMR (99.362 MHz,
1
C6D6, 298 K): δ −11.6 (d, JSiP = 21 Hz). 31P{1H} NMR (202.456
3
MHz, C6D6, 298 K): δ 3.2. HRMS (CI, isobutane): m/z calcd for
C16H21PSi [M + H]+ 273.1223; found 273.1119. IR (ATR, neat),
ν(SiH): 2108 cm−1
((Dimethylsilyl)methyl)diphenylphosphane 12.20 A solution of
3.43 g of diphenylphosphane (18.41 mmol) in 60 mL of dry THF was
cooled to −80 °C and then treated dropwise with 11.5 mL of a 1.6 M
n-hexane solution of n-BuLi (18.41 mmol). The mixture was stirred at
this temperature for 3 h. Then it was allowed to warm to room
temperature and stirred for 30 min. Subsequently, a solution of 2.00 g
of chlorosilane 15 (18.41 mmol) in 10 mL of dry THF was added
dropwise at −40 °C. The mixture was then stirred overnight at
ambient temperature. The solvent was replaced by 100 mL of dry n-
pentane, and the resulting suspension was filtered using a glass frit
(P4). The residue was washed two times with portions of 10 mL of n-
pentane. The solvent of the combined filtrates was removed under
reduced pressure to yield the desired product in the form of a colorless
oil (yield 3.95 g, 83%). 1H NMR (499.870 MHz, C6D6, 305 K): δ 0.02
EXPERIMENTAL SECTION
3
■
(d, JHH = 3.8 Hz, 6 H, (CH3)2), 1.26−1.27 (m, 2 H, CH2), 4.17
(nonett, 3JHH = 3.7 Hz, SiH), 7.06−7.15 (m, 6 H, ArH), 7.46−7.51 (m,
4 H, ArH). 13C{1H} NMR (125.693 MHz, C6D6, 305 K): δ −4.5 (d,
3JCP = 5.3 Hz, CH3), 11.3 (d, 1JCP = 29.7 Hz, CH2), 131.5 (d, 2JCP = 20
General. All reactions were carried out under inert conditions using
standard Schlenk techniques and 5.0 atm argon unless stated
otherwise. Diethyl ether and tetrahydrofuran were distilled from
sodium/benzophenone. Benzene, toluene, [D6]benzene, [D8]toluene,
pentane, and hexane were distilled from sodium. Chlorosilane was
dried over P4O10 and stored over 4 Å molecular sieves. Starting
materials were purchased from standard commercial suppliers and
used as received. [Ph3C][B(C6F5)4]39 and [Ph3C]2[B12Cl12]27 were
synthesized according to modified literature procedures. NMR spectra
were recorded on Bruker Avance 250 and Avance III 500
spectrometers, if not stated otherwise. 1H NMR spectra were
calibrated using residual protio signals of the solvent (δ1H(CHCl3)
= 7.24, δ1H(C6D5H) = 7.20). 13C NMR spectra were calibrated using
the solvent signals (δ13C(CDCl3) = 77.0, δ13C(C6D6) = 128.0). 29Si
NMR spectra were calibrated using external Me2HSiCl (δ29Si = 11.1 vs
TMS), 31P NMR spectra against external (MeO)3P (δ31P = 141 vs
85% H3PO4(aq)), 19F NMR spectra against external CFCl3 (δ19F-
(CFCl3) = 0.0), 15N NMR spectra against external formamide (δ15N =
112.67 vs NH3), and 11B NMR spectra against BF3·OEt2 (δ11B(BF3
OEt2) = 0.0). 15N NMR chemical shifts were obtained using inverse
detection (1H,15N HMBC). High-resolution mass spectra were
recorded on a Finnigan MAT 95. IR spectra were recorded on a
Bruker Tensor 27. X-ray diffraction analyses were performed on a
Bruker Apex II. Structure solution and refinement was done using the
SHELXS97 and SHELXL97 software.40
Hz, o-CH), 132.9 (d, 3JCP = 16.9 Hz, m-CH), 140.2 (d, 4JCP = 15.4 Hz,
p-CH). 29Si{1H} NMR (99.310 MHz, C6D6, 305 K): δ −15.4, JSiP
=
2
17 Hz. 31P{1H} NMR (202.348 MHz, C6D6, 305 K): δ −21.0. MS (EI,
70 eV): m/z (relative intensity in %): 258 (20), 200 (38), 183 (37),
135 (67), 78 (100). HRMS (CI, isobutane): m/z calcd for C15H20PSi
[M + H]+ 259.1077; found 259.1072. IR (ATR, neat), ν(SiH): 2128
cm−1.
3-((Dimethylsilyl)propyl)diphenylphosphane 13a.20 To a suspen-
sion of 583 mg of freshly prepared lithium turnings (84 mmol) a
solution of 7.34 g of triphenylphosphane (28 mmol) in 100 mL of
THF was added dropwise. The mixture was stirred overnight, resulting
in a dark red suspension. The solution was separated from excess
lithium turnings via a cannula and then treated at 10 °C with 2.59 g of
tert-butyl chloride (28 mmol) and stirred 2 h at room temperature.
Then 3.85 g of silane 1641 (28 mmol) was added dropwise, and the
mixture was stirred for 1 h at room temperature. All volatiles were
removed in vacuo, and the residue was suspended in n-hexane and
filtered using a glass frit (P4). The filtrate was concentrated in vacuo.
The crude product was fractionally distilled at 135−137 °C and 0.1
1
mbar to afford a colorless oil (yield 4.01 g, 50%). H NMR (499.870
MHz, C6D6, 305 K): δ −0.02 (d, 3JHH = 4.0 Hz, 6 H, Si(CH3)2), 0.70−
2-((Dimethylsilyl)ethyl)diphenylphosphane 17.20 In a photo-
reactor 2.28 g of dimethylvinylchlorosilane 18 (18.8 mmol) and 3.50
g of diphenylphosphane (18.8 mmol) were combined and irradiated
(Mercury-Medium-Pressure Lamp, TQ-150, 150 W, 200−280 nm,
distance ca. 5 cm) for 5 h at room temperature while stirring
vigorously. The resulting highly viscous, colorless oil was suspended in
5 mL of benzene. The clear solution was separated from the
precipitate by decanting. The solvent was then removed under reduced
pressure to yield 2-((dimethylchlorosilyl)ethyl)diphenylphosphane in
high purity (almost quantitative yield). The chlorosilane (5.77 g, 18.8
mmol) was dissolved in 20 mL of dry diethyl ether. This solution was
then dropped slowly to a suspension of 471 mg of lithium
aluminumhydride (12.42 mmol) in 50 mL of dry diethyl ether. The
mixture was stirred at room temperature for 3 h. The solvent was
removed under reduced pressure. The residue was suspended in 80
mL of dry n-pentane. The suspension was filtered using a P4 glass frit.
The filtrate was evaporated to give an oily, colorless residue. The raw
product was fractionally distilled (100 °C, 1 × 10−3 mbar) to yield the
desired product as a colorless oil (yield 1.65 g, 32%). 1H NMR
(500.130 MHz, C6D6, 298 K): δ 0.17 (d, 6 H, 3JHH = 6 Hz, Si(CH3)2),
0.85−0.92 (m, 2 H, CH2), 2.14−2.19 (m, 2 H, CH2), 4.12 (sept, 1 H,
0.74 (m,
2 H, SiCH2CH2CH2P), 1.56−1.65 (m, 2 H,
SiCH2CH2CH2P), 2.07−2.10 (m, 2 H, SiCH2CH2CH2P), 4.11
3
1
(nonett, JHH = 4.0 Hz, JSiH = 182.0 Hz, SiH), 7.09−7.16 (m, 6 H),
7.48−7.51 (m, 4 H). 13C{1H} NMR (125.692 MHz, C6D6, 305 K): δ
3
−4.5 (Si(CH3)2), 16.3 (d, JPC = 12.0 Hz, SiCH2CH2CH2P), 21.5 (d,
2JPC = 18.0 Hz, SiCH2CH2CH2P), 32.3 (d, JPC = 13.0 Hz,
1
SiCH2CH2CH2P), 128.6, 128.7 (d, JPC = 6.0 Hz), 133.1 (d, JPC
=
18.0 Hz), 139.9 (d, JPC = 15 Hz). 29Si{1H} NMR (99.310 MHz, C6D6,
305 K): δ −14.0. 31P{1H} NMR (202.351 MHz, C6D6, 305 K): δ
−16.8. IR (ATR, neat), ν(SiH): 2106 cm−1.
3-((Dimethylsilyl)propyl)diphenylarsane 13b. The arsane 13b was
prepared in a similar fashion described above for the phosphane 13b
using 8.57 g of triphenylarsane (28 mmol) instead of triphenylphos-
phane. Fractioning distillation of the crude product at 145−150 °C
1
and 0.1 mbar afforded a colorless oil (yield 5.83 g, 63%). H NMR
(499.870 MHz, C6D6, 305 K): δ −0.03−0.01 (m, 6 H, Si(CH3)2),
0.67−0.73 (m, 2 H, SiCH2CH2CH2P), 1.60−1.67 (m, 2 H,
SiCH2CH2CH2P), 2.05−2.08 (m, 2 H, SiCH2CH2CH2P), 4.01−4.10
(m, 1JSiH = 176.0 Hz, SiH), 7.10−7.16 (m, 6 H), 7.43−7.50 (m, 4 H).
13C{1H} NMR (125.710 MHz, C6D6, 305 K): δ −4.4 (Si(CH3)2), 16.9
(SiCH2CH2CH2P), 22.0 (SiCH2CH2CH2P), 32.2 (SiCH2CH2CH2P),
G
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
128.4, 128.8, 133.4, 141.4. 29Si{1H} NMR (99.310 MHz, C6D6, 305
K): δ −14.1. IR (ATR, neat), ν(SiH): 2106 cm−1.
(d, 3JCP = 4.4 Hz, CH2), 19.5 (d, 2JCP = 11.1 Hz, CH2), 127.4, 128.3 (d,
3JCP = 6.7 Hz), 133.8 (d, 2JCP = 17.1 Hz), 135.7 (d, 1JCP = 14.8 Hz, Cq).
29Si{1H} NMR (49.695 MHz, CDCl3, 305 K): δ −14.4 (SiH), 2.5 (d,
1JSiP = 21.7 Hz, SiP). 31P{1H} NMR (161.951 MHz, CDCl3, 305 K): δ
−56.7.
3-Di-isopropylsilyl)propyl-bispentafluorophenylphosphane 14. A
solution of 615 mg of chloropropylsilane 20 (4.5 mmol) in 50 mL of
THF was added dropwise to 120 mg of magnesium turnings (4.96
mmol). The resulting suspension was heated to reflux for 3 h. Excess
magnesium was filtered off. Then a solution of 2.00 g of BrP(C6F5)2
(4.5 mmol) in 20 mL of THF was slowly added at 0 °C. After
complete addition, the reaction mixture was warmed to room
temperature and stirred for an additional hour. The solvent THF
was removed under reduced pressure, and 50 mL of n-hexane was
added. The resulting suspension was filtered, and from the filtrate the
solvent was removed under reduced pressure. The remaining oily
residue was distilled to give a highly viscous oil (bp 190 °C, 30 mbar;
Diphenylarsanylsilane 21c. To 0.14 g of freshly grated lithium
turnings (20 mmol) in 20 mL of dry THF 3.06 g of triphenylarsane
(10 mmol) was added under stirring. The mixture was stirred for 2 h at
room temperature; excessive lithium turnings were separated. The red
brown solution was treated with 0.9 g of tert-butyl chloride (10 mmol)
at 10 °C and stirred for 30 min while slowly warming to room
temperature. At 10 °C 1.94 g of chlorosilane 2 (10 mmol) was added
dropwise. The solution lost its color, and a colorless precipitate was
formed. After 20 min of stirring at room temperature the solvent was
replaced by 30 mL of n-pentane and the lithium salts were filtered off
using a glass frit (P 4). The n-pentane was removed under reduced
pressure. The crude product was purified by fractioning distillation at
195−200 °C and 0.2 mbar to yield a colorless oil (yield 2.2 g, 57%).
1
yield 1.17g, 59%). H NMR (499.870 MHz, CDCl3, 305 K): δ 0.75−
0.81 (m, 2 H, CH2), 0.95−1.02 (m, 14 H, (CH(CH3)2)2), 1.46−1.57
(m, 2 H, CH2), 2.50−2.58 (m, 2 H, CH2), 3.36−3.40 (m, 1 H, SiH).
3
13C{1H} NMR (125.692 MHz, CDCl3, 305 K): δ 10.1 (d, JCP = 14
Hz, CH2), 10.5 (CH), 18.6 (CH3), 18.9 (CH3), 22.5 (d, 2JCP = 20 Hz,
3
1H NMR (250.131 MHz, CDCl3, 300 K): δ −0.03 (d, JHH = 3.3 Hz,
1
CH2), 27.2−27.5 (m, CH2), 109.1 (br s, C), 137.6 (d, JCF = 257 Hz,
SiMe2H, 6 H), 0.15 (SiMe2), 0.52−0.60 (m, CH2, 2 H), 0.72−0.79 (m,
C), 142.3 (d, 1JCF = 257 Hz, C), 147.8 (d, 1JCF = 257 Hz, C). 19F{1H}
NMR (470.348 MHz, CDCl3, 305 K): δ −160.41 to −160.26 (m, 4F),
−150.16 to −150.04 (t, 3JFF = 20 Hz, 2 F), −130.19 to −130.03 (m, 4
F). 29Si{1H} NMR (99.310 MHz, CDCl3, 305 K): δ 5.89. 31P{1H}
NMR (202.351 MHz, CDCl3, 305 K): δ −47.03 (p, 3JPF = 25 Hz). MS
(CI, isobutane): m/z (relative intensity, %) 522 (1), 479 (100), 365
(12), 296 (8), 217 (5), 129 (8), 69 (17), 43 (41). HRMS (CI,
isobutane): m/z C17H14F10SiP [M + H]+: 523.1069; found:523.1055.
IR (neat): 2109 cm−1.
CH2, 2 H), 1.16−1.42 (m, CH2, 2 H), 3.77 (sept, 3JHH =3.3 Hz, 1JSiH
=
180 Hz, SiMe2H, 1 H), 7.19−7.25 (m, ArH, 6 H), 7.38−7.47 (m, ArH,
4 H). 13C{1H} NMR (62.902 MHz, CDCl3, 300 K): δ −4.3 (SiMe2H),
−2.6 (SiMe2), 18.5 (CH2), 19.2 (CH2), 20.0 (CH2), 127.2, 128.5,
134.3, 137.2 (Cq). 29Si{1H} NMR (49.695 MHz, CDCl3, 300 K): δ
−14.4 (Si−H), 5.7 (Si−As).
Diphenylstibanylsilane 21d. To a suspension of 0.14 g of freshly
grated lithium turnings (20 mmol) in 20 mL of dry THF 3.53 g of
triphenylstibane (10 mmol) was added. The mixture was stirred for 2
h at room temperature. A deep red solution is decanted from the
excessive lithium turnings. At 0 °C 0.90 g of tert-butyl chloride (10
mmol) was added. After the mixture was stirred for 30 min, 1.94 g of
chlorosilane 2 (10 mmol) was added. A black suspension was formed.
After 20 min the solvent was replaced by 50 mL of n-pentane. The
salts were removed using a glass frit (P 4). The solvent of the filtrate
was removed under reduced pressure. The crude product was
fractionally distilled at 160 °C and 0.2 mbar to yield the desired
Diphenylaminosilane 21a. A 1.56 g amount of diphenylamine (9.2
mmol) was dissolved in 75 mL of dry THF. At −50 °C 5.8 mL of 1.6
M methyllithium solution in diethyl ether (9.3 mmol) was added
dropwise over a period of 30 min. The mixture was warmed to −10 °C
and stirred for 30 min before it was cooled to −40 °C. At this
temperature 1.80 g of chlorosilane 1942 (9.2 mmol) was added
dropwise. The mixture was stirred at room temperature overnight. The
ether was removed under reduced pressure, and 20 mL of n-pentane
was added. The lithium salts were filtered off using a glass frit (P4).
The solvent of the filtrate was removed under reduced pressure. The
raw product was fractionally distilled at 145 °C and 0.2 mbar to yield
1
product in the form of a yellow liquid (yield 1.90 g, 44%). H NMR
3
(250.131 MHz, CDCl3, 300 K): δ 0.00 (d, JHH = 3.7 Hz, SiMe2H, 6
H), 0.23 (SiMe2), 0.55−0.62 (m, CH2, 2 H), 0.80−0.87 (m, CH2,
1
the desired product as a viscous, colorless oil (yield 1.81 g, 58%). H
3
2H), 1.31−1.45 (m, CH2, 2 H), 3.78 (sept, JHH = 3.7 Hz, SiMe2H, 1
3
NMR (500.133 MHz, CDCl3, 300 K): δ 0.00 (d, JHH = 3.3 Hz,
H), 7.22−7.25 (m, ArH, 6 H), 7.47−7.51 (m, ArH, 4 H). 13C{1H}
NMR (62.902 MHz, CDCl3, 300 K): δ −4.4 (SiMe2H), −1.6 (SiMe2),
18.6 (CH2), 19.8 (CH2), 21.1 (CH2), 127.6, 128.7, 132.1 (Cq), 137.4.
29Si{1H} NMR (49.695 MHz, CDCl3, 300 K): δ −14.4 (SiH), 2.3
(SiSb).
Si(CH3)2, 6 H), 0.18 (s, Si(CH3)2, 6 H), 0.55−0.59 (m, CH2, 2 H),
0.88−0.91 (m, CH2, 2 H), 1.41−1.46 (m, CH2, 2 H), 3.79 (sept, 3JHH
= 3.3 Hz, 1JSiH = 179.8 Hz, SiH, 1 H), 6.86−6.89 (m, ArH, 2 H), 6.91−
6.93 (m, ArH, 4 H), 7.08−7.12 (m, ArH, 4 H). 13C{1H} NMR (62.902
MHz, CDCl3, 300 K): δ −4.3 (Si(CH3)2), −0.3 (Si(CH3)2), 18.6
(CH2), 18.8 (CH2), 21.3 (CH2), 122.1, 124.5, 129.2, 148.6 (Cq). 15N
NMR (50.680 MHz, C6D6, 300 K): δ 85.5. 29Si{1H} NMR (49.695
MHz, C6D6, 300 K): δ −14.4 (Me2SiH), 5.6 (SiMe2).
General Procedure for Hydride Transfer Reactions. In a typical
reaction 500 mg of [Ph3C][B(C6F5)4] (0.54 mmol) was evacuated
over 1 h in a Schlenk tube. Then, 2 mL of dry benzene, toluene, or
chlorobenzene was condensed onto the solid, resulting in a typical
two-phase solution. The corresponding silane 13 or 21 (0.54 mmol)
was added via a syringe. The mixture was stirred for 30−60 min until
the color of the upper, nonionic layer changed from orange to light
brown or even colorless. After that, stirring was stopped and the
phases were allowed to separate. The upper layer, which mostly
contained triphenylmethane, was discarded. The lower, ionic layer was
washed three times with portions of 5 mL of dry n-pentane. The
volatiles were evaporated, resulting in a colorless to light brown foam.
The residue was dissolved in the respective deuterated solvent for
NMR spectroscopy.
Diphenylphosphanylsilane 21b. A 375 mg amount of lithium
turnings (54 mmol) was suspended in 40 mL of dry THF. A solution
of 2.02 g of triphenylphosphane (7.7 mmol) in 20 mL of THF was
added. The mixture was stirred at room temperature for 4 h. The dark
red solution was then decanted from the excessive lithium turnings. At
10 °C 713 mg of tert-butyl chloride (7.7 mmol) was added slowly. The
mixture was stirred for 1 h while slowly warming to room temperature.
At 10 °C 1.50 g of chlorosilane 1942 (7.7 mmol) was added dropwise.
The solution became colorless and was stirred for 1 h at room
temperature. The solvent was then replaced by 50 mL of dry n-
pentane. The lithium salts were removed using a glass frit (P 4). The
solvent was subsequently removed under reduced pressure. The crude
product was fractionally distilled at 170 °C and 0.1 mbar to obtain
desired product as a colorless oil (yield 2.17 g, 82%). 1H NMR
(250.131 MHz, CDCl3, 305 K): δ 0.00 (d, 3JHH = 3.6 Hz, Si(CH3)2H,
6 H), 0.15 (d, 3JHP = 4.8 Hz, Si(CH3)2P, 6 H), 0.55−0.62 (m, CH2, 2
H), 0.71−0.79 (m, CH2, 2 H), 1.35−1.43 (m, CH2, 2 H), 3.79 (sept,
3JHH = 3.6 Hz, 1JSiH = 180.5 Hz, SiH, 1 H), 7.23−7.31 (m, ArH), 7.38−
7.45 (m, ArH). 13C{1H} NMR (62.902 MHz, CDCl3, 305 K): δ −4.5
NMR Data for the [B(C6F5)4]− Anion. [B(C6F5)4]−. 11B{1H} NMR
(160.378 MHz, C6D6, 305 K): δ −16.6. 13C{1H} NMR (125.692
1
MHz, C6D6, 305 K): δ 124.6 (br s, i-C), 136.7 (dm, JCF = 246 Hz),
1
1
138.6 (dm, JCF = 246 Hz), 148.7 (d, JCF = 241 Hz). 19F{1H} NMR
(470.348 MHz, C6D6, 305 K): δ −166.9 (t, 3JFF = 18 Hz), −163.3 (tm,
3JFF = 20 Hz), −132.4 (dm, JFF = 7 Hz).
3
1
24a[B(C6F5)4]. H NMR (499.870 MHz, C6D6, 305 K) δ −0.05 (d,
3JPH = 7.8 Hz, 6 H, PSi(CH3)2), 0.61−0.68 (m, 2 H,
SiCH2CH2CH2P), 1.44−1.56 (m, 2 H, SiCH2CH2CH2P), 1.77−1.86
2
(Si(CH3)2H), −2.9 (d, JCP = 12.6 Hz, Si(CH3)2P), 18.6 (CH2), 19.0
H
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2
2
(m, 2 H, SiCH2CH2CH2P), 6.81−6.88 (m, 4 H, ArH), 7.14−7.19 (m,
4 H, ArH), 7.23−7.27 (m, 2 H, ArH). 13C{1H} NMR (125.692 MHz,
C6D6, 305 K): δ 7.5 (d, JCP = 26.7 Hz, CH2), 12.5 (d, JCP = 8.7 Hz,
CH), 16.3 (d, 3JCP = 3.5 Hz, CH3), 17.0 (d, 3JCP = 2.1 Hz, CH3), 21.0
3
1
2
(d, JCP = 11.0 Hz, CH2), 27.5 (d, JCP = 32.7 Hz, CH2), 128.2 (C),
130.0 (C), 141.9 (C), 142.9 (C). 19F{1H} NMR (470.35 MHz, C6D6,
305 K): δ −167.85 to −167.64 (m, 8 F), −163.65 to −163.40 (m, 4
F), −154.75 to −154.53 (m, 4 F), −136.75 to −136.50 (m, 2 F),
−133.10 to −132.60 (m, 8 F), −127.15 to −126.90 (m, 4 F). 29Si{1H}
NMR (99.31 MHz, C6D6, 305 K): δ 50.09 (d, 1JSiP = 17 Hz). 31P{1H}
NMR (202.35 MHz, C6D6, 305 K): δ −26.88.
C6D6, 305 K): δ −4.4 (d, JPC = 9.3 Hz, Si(CH3)2), 15.4 (CH2), 21.5
(CH2), 26.4 (CH2), 118.3 (d, JCP = 62 Hz, Cq), 130.5 (d, JCP = 12
Hz, CH), 132.1 (d, JCP = 11 Hz, CH), 134.1 (d, JCP = 3 Hz, CH).
29Si{1H} NMR (99.310 MHz, C6D6, 305 K): δ 23.9 (d, 1JSiP = 37 Hz).
31P{1H} NMR (202.348 MHz, C6D6, 305 K): δ −6.2.
1
24b[B(C6F5)4]. H (499.87 MHz; C6D6, 305 K): δ = 0.05 (s, 6H,
Si(CH3)2), 0.65 (t, 2H, 3JHH = 7 Hz, 2H, SiCH2CH2CH2As), 1.51 (p,
3
3
2H, JHH = 7 Hz, 2H, SiCH2CH2CH2As), 1.90 (t, 2H, JHH = 7 Hz,
2H, SiCH2CH2CH2As), 6.83 (d, 3JHH = 8 Hz 4H, o-H), 7.17 (t, 3JHH
=
ASSOCIATED CONTENT
* Supporting Information
■
8 Hz 4H, m-H), 7.25 (t, JHH = 7 Hz 2H, p-H). 13C{1H} (125.69
MHz; C6D6, 305 K): δ = −4.42 (Si(CH3)2), 17.0 (SiCH2CH2CH2As),
22.0 (SiCH2CH2CH2As), 28.5 (SiCH2CH2−CH2As), 122.2 (Cq),
130.8 (CH), 131.8 (CH), 133.2 (CH). 29Si{1H} (99.31 MHz; C6D6,
305 K): δ = 30.9.
3
S
Relevant NMR spectra, cif files, additional X-ray crystallo-
graphic information for compounds 252[B12Cl12] and 27b[B-
(C6F5)4], and all computational details including a table of
absolute energies and Cartesian coordinates of relevant
molecular structures. This material is available free of charge
via the Internet at http://pubs.acs.org.
27a[B(C6F5)4]. 1H NMR (499.870 MHz, C6D6, 305 K): δ 0.02 (s, 12
H, Si(CH3)2), 0.70−0.77 (m, 4 H, CH2), 1.58−1.67 (m, 2 H, CH2),
6.71−6.75 (m, 4 H, ArH), 6.99−7.07 (m, 6 H, ArH). 13C{1H} NMR
(125.692 MHz, C6D6, 305 K): δ 0.4 (CH3), 15.8 (CH2), 18.5 (CH2),
125.5 (CH), 128.5 (CH), 130.1 (CH), 143.1 (C). 15N{1H} NMR
(50.651 MHz, C6D6, 305 K): δ 79.0. 29Si{1H} INEPT NMR (99.310
MHz, C6D6, 305 K): δ 44.0.
AUTHOR INFORMATION
Corresponding Author
*E-mail: thomas.mueller@uni-oldenburg.de.
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
■
27b[B(C6F5)4]. 1H NMR (250.131 MHz, C7D8, 300 K): δ −0.05 (d,
3JPH = 7.0 Hz, 12 H, SiMe2), 0.57−0.66 (m, 4 H, CH2), 1.47−1.55 (m,
2 H, CH2), 6.86−7.16 (m, ArH). 13C{1H} NMR (62.902 MHz, C7D8,
2
2
300 K): δ −4.4 (d, JPC = 8.1 Hz, SiMe2), 16.3 (d, JPC = 11.3 Hz,
CH2), 16.9 (CH2), 118.9 (d, 1JPC = 47.7 Hz, C), 130.9 (d, 3JPC = 11.1
2
Hz, CH), 133.5 (d, JCP = 8.0 Hz, CH), 133.5 (CH). 29Si{1H} NMR
Author Contributions
(49.695 MHz, C7D8, 300 K): δ 8.6 (d, JSiP = 11.3 Hz, SiP). 31P{1H}
1
‡These authors contributed equally.
NMR (161.951 MHz, C7D8, 300 K): δ −51.3.
27c[B(C6F5)4]. 1H NMR (250.131 MHz, C7D8, 300 K): δ 0.01 (s, 12
H, Si(CH3)2), 0.59−0.63 (m, 4 H, CH2), 1.47−1.53 (m, 2 H, CH2),
6.89−6.92 (m, ArH), 7.08−7.19 (m, ArH). 13C{1H} NMR (62.902
MHz, C7D8, 300 K): δ −4.0 (Si(CH3)2), 16.5 (CH2), 17.0 (CH2),
122.1 (C), 131.1 (CH), 132.3 (CH), 133.0 (CH). 29Si{1H} NMR
(99.367 MHz, C6D6, 300 K): 17.7.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This study was supported by the CvO University Oldenburg
and the DFG (Mu-1440/6-1 and 7-1). The High End
Computing Resource Oldenburg (HERO) at the CvO
University is thanked for computer time.
27d[B(C6F5)4]. 1H NMR (250.131 MHz, C7D8, 283 K): δ 0.10 (s, 12
H, Si(CH3)2), 0.57−0.61 (m, 4 H, CH2), 1.43−1.52, (m, 2 H, CH2),
6.89−7.14 (m, 10 H, ArH). 13C{1H} NMR (62.902 MHz, C7D8, 263
K): δ −2.8 (Si(CH3)2), 16.9 (CH2), 18.5 (CH2), 118.7 (C), 131.2
(CH), 136.2 (CH) (the missing CH signal could not be identified due
to overlapping signals). 29Si{1H} NMR (49.695 MHz, C7D8, 263 K): δ
17.5.
REFERENCES
■
(1) Dilmann, A. D.; Ioffe, S. L. Chem. Rev. 2003, 103, 733−772.
(2) Muller, T. In Structure and Bonding (Berlin); Scheschkewitz, D.,
̈
1
22[B(C6F5)4]. H NMR (499.87 MHz, 305 K, C6D6): δ −0.27 (d,
Ed.; Springer: Berlin, 2014; Vol. 155, pp 107−162. (b) Muller, T. In
̈
3JHH = 3.6 Hz, 6 H, Si(CH3)2), 2.12−2.22 (m, 2 H, CH2), 3.50−3.59
(m, 1 H, 1JSiH = 205.1 Hz, SiH), 6.75−6.82 (m, 4 H, ArH), 7.00−7.09
(m, 7 H, ArH), 7.09−7.17 (m, 7 H, ArH), 7.21−7.31 (m, 7 H, ArH).
13C{1H} NMR (125.69 MHz, 305 K, C6D6): δ −3.6 (d, 3JCP = 3.4 Hz,
Science of Synthesis: Knowledge Updates 2013/3; Oestreich, M., Ed.;
Thieme: Stuttgart, Germany, 2013; pp 1−42.
(3) Lehmann, M.; Schulz, A.; Villinger, A. Angew. Chem., Int. Ed.
2009, 48, 7444−7447.
1
1
Si(CH3)2), 8.8 (d, JPC = 37.3 Hz, CH2), 67.3 (d, JCP = 39.3 Hz,
PCPh3), 119.7 (d, 1JCP = 76.8 Hz, ipso-ArC), 129.2 (s, ArC), 129.7 (d,
12.6 Hz, ArC), 129.9 (s, ArC), 131.6 (d, 6.2 Hz, ArC), 134.0 (d, 7.3
Hz, ArC), 135.1 (d, 2.1 Hz, ArC). 29Si{1H} NMR (99.31 MHz, 305 K,
C6D6): δ −12.6 (d, 2JSiP = 9.0 Hz). 31P{1H} NMR (202.35 MHz, 305
K, C6D6): δ 31.6 (s).
(4) Schulz, A.; Villinger, A. Chem.Eur. J. 2010, 16, 7276−7281.
(5) Olah, G. A.; Li, X.-Y.; Wang, Q.; Rasul, G.; Prakash, G. K. S. J.
Am. Chem. Soc. 1995, 117, 8962−8966.
(6) Prakash, G.; Bae, C.; Wang, Q.; Rasul, G.; Olah, G. A. J. Org.
Chem. 2000, 65, 7646−7649.
(7) Ibad, M. F.; Langer, P.; Reiß, F.; Schulz, A.; Villinger, A. J. Am.
Chem. Soc. 2012, 134, 17757−17768.
23[B(C6F5)4]. 1H NMR (500.13 MHz, 298 K, C7D8): δ −0.06 (6 H,
3JHH = 3.7 Hz, Si(CH3)2), 0.40−0.49 (m, 2 H, CH2), 2.91−3.00 (m, 2
H, CH2), 3.82−3.88 (m, 1 H, 1JSiH = 190.7 Hz, SiH), 6.77−6.83 (4 H,
ArH), 6.97−7.13 (br m, 18 H, ArH), 7.22−7.28 (m, 3 H, ArH).
13C{1H} NMR (125.76 MHz, 298 K, C7D8): δ −5.7 (s, CH3), 8.5 (d,
(8) Driess, M.; Barmeyer, R.; Monse, C.; Merz, K. Angew. Chem., Int.
Ed. 2001, 40, 2308−2310.
(9) Labbow, R.; Reiß, F.; Schulz, A.; Villinger, A. Organometallics
2014, 33, 3223−3226.
1
2JCP = 9.5 Hz, CH2), 20.6 (d, JPC = 37.0 Hz, CH2), 67.2 (1JPC = 35.7
(10) Schumann, H.; Hartmann, U.; Dietrich, A.; Pickhardt, J. Angew.
Chem. Int. Ed. 1988, 27, 1077−1078.
Hz, PCPh3), 118.3 (1JCP = 73.3 Hz, ipso-C), 129.3 (s, ArCH), 129.9 (d,
11.7 Hz, CH), 130.1 (s, ArCH), 131.6 (d, 5.3 Hz, ArCH), 134.7 (d, 7.2
Hz, ArCH), 135.2 (d, 3.1 Hz, ArCH). 29Si{1H} NMR (99.31 MHz,
(11) Schumann, H.; Hartmann, U.; Wassermann, W.; Dietrich, A.;
Gorlitz, F. H.; Pohl, L.; Hostalek, M. Chem. Ber. 1990, 123, 2093−
̈
3
298 K, C7D8): δ −14.8 (d, JSiP = 23.6 Hz). 31P{1H} NMR (202.46
2099.
MHz, 298 K, C7D8): δ 38.3 (s).
(12) Rohde, V. H. G.; Pommerening, P.; Klare, H. F. T.; Oestreich,
M. Organometallics 2014, 33, 3618−3628.
(13) Spies, P.; Erker, G.; Kehr, G. H.; Bergander, K.; Frohlich, R.;
1
26[B(C6F5)4]. H NMR (499.87 MHz, C6D6, 305 K): δ 0.66−0.84
(m, 14 H, (CH(CH3)2)2), 1.14−1.24 (m, 2 H, CH2), 1.75−1.90 (m, 2
̈
H, CH2), 2.46−2.55 (m, 2 H, CH2). 13C{1H} NMR (125.692 MHz,
Grimme, S.; Stephan, D. W. Chem. Commun. 2007, 5072−5074.
I
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(14) Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2010, 49, 46−
(39) (a) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 245−
250. (b) Chien, J. C. W.; Tsai, W.-M.; Rausch, M. D. J. Am. Chem. Soc.
1991, 113, 8570−8571.
76.
(15) (a) Erker, G.; Stephan, D. W. Top. Curr. Chem. 2013, 332, 1−
347. (b) Erker, G.; Stephan, D. W. Top. Curr. Chem. 2013, 334, 1−
313.
(40) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122.
(41) Jarvie, A. W. P.; Rowley, R. J. J. Organomet. Chem. 1972, 57,
261−268.
(16) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.;
̈
(42) Muller, T. Angew. Chem., Int. Ed. 2001, 40, 3033−3036.
̈
Erker, G. Angew. Chem. Int. Ed. 2008, 47, 7543−7546.
(17) Schafer, A.; Reißmann, M.; Schafer, A.; Saak, W.; Haase, D.;
̈
̈
Muller, T. Angew. Chem., Int. Ed. 2011, 50, 12636−12638.
̈
(18) Reißmann, M.; Schafer, A.; Jung, S.; Muller, T. Organometallics
̈
̈
2013, 32, 6736−6744.
(19) Doak, G. O.; Freedman, L. D. Synthesis 1974, 328−338.
(20) Holmes-Smith, R. D.; Osei, R. D.; Stobart, S. R. J. Chem. Soc.,
Perkin Trans. 1 1983, 861−866.
(21) Ryan, J. W.; Menzie, G. K.; Speier, J. L. J. Am. Chem. Soc. 1960,
82, 3601−3604.
(22) (a) Bartlett, P. D.; Condon, F. E.; Schneider, A. J. Am. Chem.
Soc. 1944, 66, 1531−1539. (b) Corey, J. Y. J. Am. Chem. Soc. 1975, 97,
3237−3238.
(23) Berger, S.; Braun, S. Kalinowski, H.-O. NMR Spektroskopie von
Nichtmetallen; Thieme: Stuttgart Verlag, 1993; Vol. 3 (31P NMR
Spektroskopie).
(24) Cabrera, L.; Welch, G. C.; Masuda, J. D.; Wei, P.; Stephan, D.
W. Inorg. Chim. Acta 2006, 359, 3066−3071.
(25) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, P. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.;
Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
̈
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Ortiz, J.
V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision B.01 ; Gaussian,
Inc.: Wallingford, CT, 2010.
(26) See the Supporting Information for further details.
(27) (a) Kessler, M.; Knapp, C.; Sagawe, V.; Scherer, H.; Uzun, R.
Inorg. Chem. 2010, 49, 5223−5230. (b) Schafer, A.; Reißmann, M.;
̈
Jung, S.; Schafer, A.; Saak, W.; Brendler, E.; Muller, T. Organometallics
2013, 32, 4713−4722.
̈
̈
(28) Heating of a solution of 252[B12Cl12] in acetonitrile leads to
triphenyl methane formation accompanied however with substantial
decomposition of the formed cation.
(29) Schmidbaur, H.; Blaschke, G.; Zimmer-Gasser, B.; Schubert, U.
Chem. Ber. 1980, 113, 1612−1622.
(30) Calculated as Δδ15N = δ15N(ammonium) − δ15N(amine).
(31) Berger, S.; Braun, S. Kalinowski, H.-O. NMR Spektroskopie von
Nichtmetallen; Thieme: Stuttgart Verlag, 1993; Vol. 2 (15N NMR
Spektroskopie).
(32) Calculated as Δδ31P = δ31P(phosphonium) − δ31P(phosphane).
(33) vdWr(Si) = 210 pm; vdWr(F) = 147 pm, according to Mantina,
M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G. J. Phys.
Chem. A 2009, 113, 5806−5812.
(34) Kaftory, M.; Kapon, M.; Botashansky, M. In The chemistry of
organosilicon compounds Vol. 2, Rappoport, Z., Apeloig, Y., Eds.; Wiley:
Chichester, 1998; Chapter 5, pp 181−265.
(35) Nie, W.; Klare, H. T. F.; Oestreich, M.; Frohlich, R.; Kehr, G.;
̈
Erker, G. J. Chem. Sci. 2012, 67b, 987−994.
(36) Ideal values: 360° (trigonal planar); 328.5° (tetrahedral).
(37) The following covalent radii have been used: Si 116 pm, N 71
pm, P 111 pm, As 121 pm, Sb 140 pm. See: Pyykko, P.; Atsumi, M.
̈
Chem.Eur. J. 2009, 15, 186−197.
(38) Momming, C. M.; Otten, E.; Kehr, G.; Frohlich, R.; Grimme, S.;
Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2009, 48, 6643−6646.
̈
̈
J
DOI: 10.1021/ic502968z
Inorg. Chem. XXXX, XXX, XXX−XXX