Hydrogen-bridged digermyl and germylsilyl cations

Article abstract of DOI:10.1021/om500154n

The synthesis of the digermyl and germylsilyl hydronium borates 7[B(C ₆F₅)₄] and 8[B(C₆F₅) ₄] is reported. Spectroscopic (IR, NMR) and structural data supported by the results of density functional calculations indicate in both cases a symmetric or almost symmetric E-H-E′ three-center-two-electron linkage (7, E = E′ = Ge; 8, E = Si, E′ = Ge). The [B(C₆F ₅)₄]^- and the [HCB₁₁H ₅Br₆]^- salts of both cations are active in catalytic hydrodefluorination reactions of alkyl and benzyl fluorides. No significant effect of the element atom E on the determined turnover numbers was found.

Full text of DOI:10.1021/om500154n

Article
pubs.acs.org/Organometallics
Hydrogen-Bridged Digermyl and Germylsilyl Cations
Natalie Kordts, Corinna Borner, Robin Panisch, Wolfgang Saak, and Thomas Muller*
̈
Institut fu
Federal Republic of Germany
̈
̈
r Chemie, Carl von Ossietzky Universitat Oldenburg, Carl von Ossietzky-Strasse 9-11, D-26129 Oldenburg,
*
S Supporting Information
ABSTRACT: The synthesis of the digermyl and germylsilyl hydronium borates
[B(C F ) ] and 8[B(C F ) ] is reported. Spectroscopic (IR, NMR) and structural
7
6
5 4
6 5 4
data supported by the results of density functional calculations indicate in both cases a
symmetric or almost symmetric E−H−E′ three-center−two-electron linkage (7, E =
−
−
E′ = Ge; 8, E = Si, E′ = Ge). The [B(C F ) ] and the [HCB H Br ] salts of both
6
5 4
11
5
6
cations are active in catalytic hydrodefluorination reactions of alkyl and benzyl fluorides. No
significant effect of the element atom E on the determined turnover numbers was found.
INTRODUCTION
silyl cations. It was shown that the widely applied silylium
borate formed by reaction of triethylsilane and trityl borate
■
The organic chemistry of group 14 elements is dominated by
electronically saturated compounds. The octet rule provides the
basis to understand their structures and much of their reactivity.
In low-coordinated compounds of group 14 elements multiple-
center bonding is operative to account for the electron defi-
[
Ph C][B(C F ) ] in excess silane is in fact the hydronium
3 6 5 4
species [(Et Si) H][B(C F ) ], and not the alleged silylium
3
2
6 5 4
8
borate [(Et Si)][B(C F ) ]. These results are important for
3
6 5 4
the interpretation of the course of silylium ion catalyzed
hydrodefluorination (HDF) reactions of alkyl fluorides,
especially in those cases where the reactions are carried out
1
ciency. Prominent examples can be found in carbocation and
2
−6
silyl cation chemistry.
An important structural motif in the
9
with an excess of the silanes as the hydrogen source. Pre-
chemistry of alkyl-substituted silyl cations is the Si−H−Si two-
electron−three-center linkage. This structural feature was first
verified in its intramolecular version in well-defined molecular
viously, we found that also bis-silylhydronium ion 2 is an active
2
b,10
catalyst in HDF chemistry.
We expected that the
2
−4
replacement of the silicon atoms in cation 2 by atoms of its
homologue germanium to have a marked influence on the
structure and reactivity of the resulting cations. Therefore, we
studied the synthesis and characterization of bis-germyl
hydronium borate 7[B(C F ) ] and silylgermyl hydronium
environments, as provided in cations 1−4.
6
5 4
borate 8[B(C F ) ] and their use as catalyst in HDF reactions.
6
5 4
This research is directed toward the modification of the HDF
catalyst to allow the activation of specific C−F bonds and the
synthesis of fluorinated compounds with a specific substitution
9d
pattern.
Reed and co-workers established the existence of simple bis-
silylated hydronium ions 5 and of the germanium analogue 6
under extremely weakly coordinating conditions (i.e., using the
RESULTS AND DISCUSSION
−
■
corresponding silanes and germanes as solvents and [HCB Cl ] ,
1
1
11
2−
−
5,6
The precursors, digermane 10, naphthyl silane 11 and
silylnaphthylgermane 12, were prepared in satisfactory yields
from 1,8-dihalonaphthalenes 9 by standard lithiation and salt
metathesis reactions (Schemes 1 and 2). Hydronium ions 7 and
were obtained as tetrakis(pentafluorophenyl)borate salts by
reaction of the corresponding precursors with 1 equiv of trityl
[
B X ] (X = Cl, Br), and [B(C F ) ] as counteranions).
12 12 6 5 4
Quite recently hydrogen-bridged silyl cations were also detected in
7
the gas phase by IR spectroscopic methods. Interestingly, both
inter- and intramolecular versions of the SiHSi linkage do not show
8
a linear structure (α(SiHSi) = 160° (5, R = Me) and α(SiHSi) =
2b,5a
131° (2)).
The cyclic structure of cation 2 enforces the smaller
Si···Si distance and the stronger bending of the SiHSi bridge. (2)).
Recent results by the Reed group highlighted the importance of
these hydrogen-bridged species in chemical reactions involving
Received: February 12, 2014
Published: March 10, 2014
©
2014 American Chemical Society
1492
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Article
a
1H-coupled 29Si INEPT spectrum into a doublet of multiplets
Scheme 1. Synthesis of Borate 7[B(C F ) ]
6
5 4
1
with a small J(SiH) coupling constant of 58 Hz (see Figure
1
S14, Supporting Information). This J(SiH) coupling was also
1
1
detected in the H NMR spectra. Similar small J(SiH) coupl-
ing constants are reported for three-center−two-electron SiHSi
1
2−4
bonds in silyl cations 1−4 ( J(SiH) = 26−46 Hz).
This
suggests a related bonding situation for the Si−H−Ge linkage
in cation 8. For cation 7 a symmetric structure in solution is
indicated by H and C NMR spectroscopy. The broad re-
a
Legend: (a) n-BuLi (2 equiv), Et O, T = −60 °C; (b) n-Bu GeHCl
2
2
1
13
(2 equiv), Et O, T = −60 °C to room temperature; (c) [Ph C][B(C F ) ]
2
3
6 5 4
1
(1 equiv), benzene, room temperature.
sonance of the bridging hydrogen atom (δ H 1.91; Δw = 7
1/2
Hz) is characteristic for the GeHGe linkage and is significantly
a
1
H
Scheme 2. Synthesis of Borate 8[B(C F ) ]
shielded in comparison to the precursor digermane 10 (Δδ
3.43). The structure of cation 7 was derived from the analysis
of the H/ C HMBC and the H/ H COSY spectra. The
correlation of the H NMR resonance of the bridging hydrogen
=
6
5 4
−
1
13
1
1
1
atom to the methylene groups in positions α to the germanium
1
13
atoms (δ H 1.35−1.43, relative intensity 8H, δ 19.5) was
C
found in both spectra (see Figures S10 and S11, Supporting
Information). IR spectra of borates 7[B(C F ) ] and
6
5 4
8
[B(C F ) ] show very broad bands for the Si−H−Ge and
6
5 4
Ge−H−Ge stretching vibrations, which are significantly
bathochromically shifted in comparison to the precursor
a
Legend: (a) n-BuLi (1 equiv), Et O, T = −60 °C; (b) Me SiHCl
2
2
−1
−1 11
(
1 equiv), Et O, T = −60 °C to room temperature; (c) BuLi (1 equiv),
2
compounds (7, ν 1630 cm , Δw = 100 cm , Δν =
1/2
Et O, T = −60 °C; (d) n-Bu GeHCl (1 equiv), Et O, T = −60 °C to
−1
−1
2
2
2
−421 cm vs digermylnaphthene 10; 8, ν 1736 cm , Δw
=
1
/2
room temperature; (e) [Ph C][B(C F ) ] (1 equiv), benzene, room
−1
−1
−1
3
6 5 4
1
80 cm , Δν = −427 cm vs SiH and Δν = −319 cm vs
GeH in silylgermylnaphthene 12; see Table 1 and Figure S2
Supporting Information)). The position, signature, and shift
temperature.
(
borate [Ph C][B(C F ) ] in benzene at room temperature. The
3
6 5 4
versus the neutral precursor material of this IR band agree well
borates 7[B(C F ) ] and 8[B(C F ) ] were isolated as pale
6
5 4
6 5 4
with literature data for cation 2 and related silylated and
brown solids in high yields.
Cation 8 was identified by its characteristic H and Si NMR
6−8,11,12
germylated hydronium ions.
1
29
Despite considerable efforts using different arene solvents
and crystallization conditions, no single crystals suitable for
X-ray diffraction (XRD) of the borate 8[B(C F ) ] were
spectroscopic data, which closely resemble those reported pre-
1
viously for cation 2 (see Table 1). The broad H NMR signal
6
5 4
obtained. In contrast, colorless needles suitable for XRD were
Table 1. Selected Spectroscopic Parameters of Cations 2, 7,
and 8
isolated by recrystallization of 7[B(C F ) ] from hexafluoro-
a
6 5 4
benzene at +3 °C. The solid-state structure of the salt reveals
|1
J(SiH)|
ν(EHE′)
−1
c
an asymmetric unit that contains only the cation 7 and the
b
b
b
−
2
9
1
compd
δ
δ (EHE′)
(Hz])
(cm
)
[B(C F ) ] anion (see Figure 1). The cation is well separated
Si
H
6
5 4
7
8
2
, E = E′ = Ge
1.91
2.49
3.34
1630
d
1
641
, E = Ge, E′ = Si 40.5
58.0
1736
e
f
d
4
0.3
47.7
1746
g
, E = E′ = Si
54.4
45.7
1834
e
f
d
5
7.2
38.1
1860
a
b
Computed values are given in italics for comparison. In C D at
6
6
c
d
3
05 K. Neat, ATR. IR wavenumbers were calculated at the B3LYP/
cc-pvtz level and scaled by a factor of 0.9606 to account for
e
anharmonicity effects. NMR chemical shifts δ were calculated at the
f
GIAO/M06L/6-311G(2d,p)//B3LYP/cc-pvtz level. Coupling con-
stants J were calculated using the M06L functional and a modified
6
-311G(2d,p) basis set; see the Supporting Information for further
g
Figure 1. (a) Ellipsoid presentation of the asymmetric unit of
[B(C F ) ] in the crystal. Relevant distance (pm): Ctr−Ctr 395.4 pm.
details. Data from refs 2b and 12.
7
6
5 4
(b) Molecular structure of digermyl hydronium ion 7 in the crystal (all H
1
1,12
1
atoms but the bridging H atom omitted). Relevant distances (pm) and
for the SiHGe group in cation 8 (δ 2.49, Δw = 9 Hz)
is
=
H
1/2
1
2
1
2
1
1
H
angles (deg): Ge −H, 148(3); Ge −H, 178(3); Ge −Ge , 304.77(3);
1 1 2 7 1 2
shifted unusually to high field (Δδ = −2.87 (SiH) and Δδ
H
Ge −C , 193.15(28); Ge −C , 192.57(26); Ge −H−Ge , 137(2).
Thermal ellipsoids are given at the 50% probability level; alkyl groups
at the Ge atoms are displayed in the wire frame mode. Color code: red,
Ge; green, F; gray, C; orange, B; white, H.
−
2.82 (GeH) in comparison to germylsilylnaphthene 12) and
indicates its hydrogen-bridged structure.
1
1
The assignment was made by analyzing the 2D H/ H
correlation NMR spectrum. Cross signals of the bridging
hydrogen atom and the methylene protons in positions α to
the germanium atom and to the protons of the silylmethyl
groups are visible (see Figure S15, Supporting Information).
from the anion. The closest contact between a fluorine atom of
the anion and a germanium atom is 390.4 pm, clearly beyond
In addition, the 29Si NMR resonance at δ 40.5 splits in the
the sum of the van der Waals radii of both elements (358 pm).
13
29
Si
1
493
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The nearly parallel orientation of the naphthyl rings and one of
the aryl substituents of the anion (interplanar angle 9.1°)
and the relatively short distance between both ring centroids
hydronium ion 8 also the 29Si NMR spectroscopic parameter
can be used to gauge the quality of the calculated molecular
structure (see Table 1). The good accordance between
experimental spectroscopic values and theoretical predictions
(Table 1) indicates the structure optimization to be well suited
for a comparative structural discussion of cations 7 and 8. In
order to complete the picture, the discussion is extended to the
structure of hydronium ion 2 with a SiHSi bridge. For all three
cations 2, 7, and 8, the results of the computations predict a
three-center−two-electron E−H−E bridge (E = Si, Ge) with a
dicoordinated hydrogen atom. The cyclic structure of all three
cations enforces a bending of the three-center bond (α(E−H−E) =
131.6−136.6°; see Figure 2) in contrast to acyclic cations such
as 5 (R = Me), which features an almost linear Si−H−Si link-
age (XRD, α(E−H−E) = 160(1)°; calculated, α(E−H−E) =
(
395.4 pm) suggest a π-stacking interaction between the cation
14
and anion (Figure 1a). The two germanium atoms in cation 7
are tetracoordinated. The relatively small sum of the bonding
angles α involving germanium and its carbon neighbors for
both germyl groups, ∑α, indicates considerable deviations
toward planarity (∑α = 345.9 and 348.4°). Larger ∑α values
were only reported for the ion pair [Et Ge][CHB H Br ]
3
11
5
6
6
(
3
∑α = 351.9°) and for the germylium ions 13−15 (∑α =
1
5−17
60°).
The germanium atom Ge(2) is observably bent out
2
7 6 1
of the plane defined by the naphthyl ring (ϑ(Ge C C C ) =
0.9°). Both germanium atoms form a six-membered ring in a
1
distorted-half-chair conformation with the bridging hydrogen
atom.
5a
179.1°). The individual E−H bonds are all significantly elongated
in comparison to the corresponding bonds in the model
tetranes PhMe E−H (E = Si (16), Ge (17)) (see Table 2). In
2
detail, the Ge−H bonds in cation 7 are 10% longer and the Si−
H bonds in 2 are 8% longer than the corresponding bonds of
the model compounds. Interestingly, the Ge−H distance in the
unsymmetrical cation 8 is even larger than in the symmetrical
cation 7 (Ge−H: 173.4 pm (8) vs 170.4 pm (7)), and the
Si−H bond is shorter than of disilyl cation 2 (Si−H: 160.5 (8)
vs 162.4 pm (2)). Consequently, a natural bond orbital (NBO)
Although the position of the bridging hydrogen atom in
cation 7 was detected in the differential Fourier analysis and
the coordinates of the hydrogen atoms were refined, the exact
bonding parameters of the GeHGe linkage in cation 7 are
20
analysis predicts that the E−H bonds of cations 7 and 2 have
21
Wiberg bond indices (WBIs) which are approximately 50% of
the E−H WBIs of the model compounds 16 and 17 (Table 2).
In comparison to the situation in cation 2, a higher WBI is
predicted for the Si−H bond of cation 8, while the WBI of the
Ge−H bond of cation 8 is the smallest of all three cations.
According to the NBO analysis the calculated negative charge
at the bridging hydrogen atom is higher in the cations 2, 7, and
8 than at the terminal hydrogen atoms of the tetranes 16 and
17. These results point to a relevant contribution of the Lewis
representation B to the bonding situation in cations having an
E−H−E structural motif, such as 2, 7, and 8 (Scheme 3), and
it is in agreement with the interpretation of the previous
molecular orbital analysis of cation 1.
18
subject to appreciable errors. Therefore, the bonding situation
of the GeHGe linkage will not be discussed on the basis of the
experimental structural data. On the other hand, the heavy-
atom distances in the molecular structure of cation 7 are well-
defined and can be used to gauge the quality of structures
predicted by quantum mechanical calculations. Density func-
tional calculations at the B3LYP/cc-pvtz level of theory predict
a molecular structure of cation 7 that is very close to that
1
8,19
determined by XRD (see Figures 1b and 2a).
For cation 7
these calculations predict a molecular structure of approximate
C2 molecular symmetry and consequently an almost symmetric
GeHGe bridge with long Ge−H distances of 170.2 and 170.6
pm. The computed molecular structure is further validated by
the good agreement of the computed energy of the asymmetric
In the framework of the quantum theory of atoms in mole-
22
cules (QTAIM) the E−H bonds in all investigated com-
pounds have high ionic contributions, as indicated by relatively
small electron densities ρ(r) and by the significant positive
as
stretching vibration ν (GeHGe) with the experimental data
as
−1
−1
2
(
ν (GeHGe) 1641 cm (computed) vs 1630 cm (exper-
Laplacian ∇ ρ(r) at the bond critical points (see Figure 3 and
imental); see Table 1). In the case of the silylgermyl-substituted
Table 2). Imposed by the symmetry of the molecules, the
Figure 2. Computed molecular structures (B3LYP/cc-pvtz) of hydronium ions (a) 7, (b) 8, and (c) 2. Alkyl groups at the Ge and Si atoms are
displayed in the wire frame mode. Color code: red, Ge; violet, Si; gray, C; white, H. Relevant distances (pm) and angles (deg) are as follows. Cation
1
2
1
2
1
1
2
7
1
2
7
: Ge −H, 170.6; Ge −H, 170.2; Ge −Ge , 310.8(3); Ge −C , 194.9; Ge −C , 195.4; Ge −H−Ge , 131.6. Cation 8: Ge−H, 173.5; Si−H, 160.5;
1 7 1 1 2 1 1 1 2
Ge−Si, 306.1; Ge−C , 194.5; Si−C , 186.5; Ge−H−Si, 132.8. Cation 2: Si −H, 162.4; Si −Si , 301.9; Si −C , 185.7; Si −H−Si , 136.6.
1
494
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Table 2. Properties of the Computed Electron Density at the Bond Critical Points of E−H Bonds in Cations 2, 7, and 8 and
Model Compounds According to QTAIM Analysis (See also Figure 3)
2
bond type
compd
atomic distance (pm)
WBI
charge at H (au)
ρ(r) (au)
∇ ρ (au)
Si−H
PhMe Si−H, 16
149.1
160.6
0.91
0.48
−0.21
−0.27
−0.31
−0.16
−0.24
−0.27
0.1191
0.0817
+0.1894
+0.1189
2
8
2
162.4
0.42
0.0756
+0.1164
Ge−H
PhMe Ge−H, 17
154.7
0.92
0.1330
+0.0229
2
7
170.2; 170.6
173.4
0.44; 0.44
0.38
0.0843; 0.0836
0.0766
+0.0754; +0.0751
+0.0827
8
Scheme 3. Lewis Description of the Bonding in Bistetryl
Hydronium Ions
Scheme 4. Lewis Description of the Bonding in Cation 8
prepared in o-dichlorobenzene. The pale brown solutions
were diluted with excess triethylsilane. After hexafluorobenzene
was added as internal standard, either trifluorotoluene or
fluorodecane was added as substrate. The influence of the
counteranion on the catalysis was tested using the trityl
2
calculated Laplacian of the electron density ∇ ρ(r) in the
plane of the E−H−E bond in cations 7 and 2 is symmetric with
charge accumulations around the bridging hydrogen bond
Figures 3a,c). In contrast, the contour plot of ∇ ρ(r) for
9
b,25
2
carborate [Ph C][HCB11H Br ] for the cation synthesis.
3 5 6
(
1
9
The strongly exothermic reactions were followed by F NMR
spectroscopy (see Scheme 5 and Table 3). After 8 h the relative
cation 8 clearly indicates unequal charge distribution around
the bridging hydrogen (Figure 3b). The contour map is remi-
niscent of that of phenyldimethylsilane 16 (Figure 3d), with the
modification that the presence of the germyl cation leads to
strong polarization of the electron density toward the
germanium atom. Therefore, the QTAIM analysis suggests in
agreement with the NBO analysis and structural arguments that
the Ge−H−Si bond in cation 8 is a three-center−two-electron
bond. To understand the details of the electronic situation in
cation 8, contributions from the germylium ion like resonance
form 8A are more important than those from the cor-
responding silylium ion structure 8C (Scheme 4). This is also
in accord with the results of isodesmic reactions, which predict
that germylium ions are more stable than silylium ions if
identically substituted. For example, trimethylgermylium,
Scheme 5. Catalytic Hydrodefluorination Reaction of Alkyl
and Benzyl Fluorides
concentrations of decyl fluoride and Et SiF were determined
3
via 19F NMR spectroscopy. The turnover number (TON) cal-
culated from these data clearly indicated a catalytic reaction in
each case (Table 3). The data summarized in Table 3 reveal
that the variation of the cation has only an insignificant influence
on the catalyst’s activity, as expressed in the determined TONs
(see for example entries 1, 3, and 5). This suggests only a minor
influence of the group 14 element on the activity of the C−F
activation catalyst as long as only TONs are compared. In all
tested cases the use of the more robust brominated carborate as
anion led to a slightly higher TON, which is in agreement with
+
−1
Me Ge , is 36 kJ mol more stable than trimethylsilylium,
3
+
23
Me Si .
3
Digermyl and germylsilyl hydronium ions 7 and 8 were
tested for their activity as catalysts in hydrodefluorination
2
,9,24
(
HDF) reactions.
Disilyl cation 2 was included in this study
to enable a comparison of the catalytic activities of the different
cations. For this purpose, small quantities (0.01 mmol) of the
borates 7[B(C F ) ], 8[B(C F ) ], and 2[B(C F ) ] were
9b
previous results of the Ozerov group. In all cases, however, the
determined TONs are markedly smaller than those reported
6
5 4
6
5 4
6 5 4
2
Figure 3. Contour plots of the calculated Laplacian of the electron density, ∇ ρ(r), in the E−H−E′ plane of hydronium ions (a) 7, (b) 8, (c) 2 and
ipso
(
d) in the C −Si−H plane of model silane 16. Relevant parts of the molecular graphs of the cations are projected onto the respective contour plot.
The bond paths which follow the line of maximum electron density between bonded atoms are shown by solid black lines, and the corresponding
bcps are shown as green circles. Red contours indicate regions of local charge accumulation (∇ ρ(r) < 0); blue contours indicate regions of local
charge depletion ((∇ ρ(r) > 0).
2
2
1
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Article
were dried over P O and stored over molecular sieves 4 Å.
Table 3. HDF Reactions of Alkyl Fluorides Catalyzed by
Ditetrylhydronium Ions 2, 7, and 8
4
10
Fluorodecane was freshly distilled from P O , and hexafluorobenzene
4
10
and trifluorotoluene were dried over P O , distilled, and stored over
4
10
amt,
molecular sieves 4 Å. n-Butyllithium in hexane (1.6 M) was purchased
28
entry
catalyst
RF
RH
mol %
TON
from Acros Organics and used as received. [Ph C][B(C F ) ] and
3
6 5 4
2
9
1
2
3
4
5
6
7
8
9
7[B(C F ) ]
n-C H −F
n-C H
1.25
1.25
1.25
1.25
1.25
1.25
0.42
0.19
0.42
0.18
0.17
0.17
51
80
[Ph C][HCB H Br ] were synthesized according to modified
3 11 5 6
6
5
4
10 21
10 22
literature procedures. Di-n-butylchlorogermane was synthesized in a
7[CB H Br ]
n-C H −F
n-C H
10 22
11
6
6
10 21
30
two-step reaction starting from di-n-butyldichlorogermane. 1,8-
8[B(C F ) ]
n-C H −F
n-C H
10 22
49
6
5
4
10 21
Dibromonaphthalene and 1,8-Diiodonaphthalene were prepared by a
8[CB H Br ]
n-C H −F
n-C H
80
11
6
6
10 21
10 22
31
standard diazotization reaction of 1,8-diaminonaphthalene. 1-Bromo-
2[B(C F ) ]
n-C H −F
n-C H
10 22
65
6
5
4
10 21
8
-dimethylsilylnaphthalene (11) was synthesized as described pre-
2[CB H Br ]
n-C H −F
n-C H
10 22
105
30
27
11
6
6
10 21
viously. NMR spectra were recorded on Bruker Avance 500 and
Avance III 500 spectrometers at 305 K, if not stated otherwise. H NMR
7[B(C F ) ]
Ph−CF3
Ph−CF3
Ph−CH3
Ph−CH3
1
6
5 4
7[CB H Br ]
269
114
169
221
600
11
6
6
spectra were calibrated using residual protio signals of the solvent
1
3
8[B(C F ) ]
Ph−CF3
Ph−CH3
(δ (CHCl ) 7.24, δ (C D H) 7.20). C NMR spectra were
H 3 H 6 5
13 13
1
1
6
5
4
1
1
1
0
1
2
8[CB H Br ]
Ph−CF3
Ph−CF3
Ph−CH3
Ph−CH3
calibrated using the solvent signals (δ (CDCl ) 77.0, δ (C D )
C 3 C 6 6
11
6
6
29
2[CB H Br ]
128.0). Si NMR spectra were calibrated against external Me HSiCl
2
29
11
6
6
1
9
a
(
δ (Me SiHCl) 11.1), F NMR spectra against external CFCl
Si 2 3
9 11
Et Si[CB H Cl ]
n-C H −F
n-C H
3
11
6
6
10 21
10 22
11
1
a
(δ (CFCl ) 0.0), and B NMR spectra against BF ·OEt (δ (BF ·
F 3 3 2 B 3
Data from ref 9c.
OEt ) 0.0). IR spectra were recorded on a Bruker Tensor 27 instrument.
2
X-ray diffraction analyses were performed on a Bruker Apex II
instrument. Structure solution and refinement was done using the
SHELXS97 and SHELXL97 software.
9
c
using [Et Si][CB H Cl ] as the actual catalyst. These results
3
11
6
6
3
2
suggest that the germanium- and silicon-based cations 7 and 8
are the active catalysts in the investigated HDF reactions
1,8-Bis(di-n-butylgermyl)naphthalene (10). A 1.53 mL amount
of n-butyllithium (1.6 M in hexane, 2.45 mmol) was added to a solution
of 0.464 g of 1,8-diiodonaphthalene (1.22 mmol) in diethyl ether at
(
Scheme 6), which is in agreement with a similar proposal for
2b,10,26
HDF reactions catalyzed by cation 2.
−
60 °C, and the mixture was stirred for 90 min at this temperature.
After 0.547 g of di-n-butylchlorogermane (2.45 mmol) was added via
syringe, the mixture was warmed to room temperature. The solvent was
removed under reduced pressure, and hexane was added to the residue.
Scheme 6. Suggested Cycle for the HDF Reaction Catalyzed
by Ditetrylhydronium Ions 7 (R E = R′ E′ = n-Bu Ge) and 8
2
2
2
(
R E = SiMe ; R′ E′ = n-Bu Ge) (Anion Omitted)
2
2
2
2
After aqueous workup with NH Cl solution, the crude product was
4
purified by column chromatography on silica gel using hexane as eluent:
1
R = 0.52. Yield: 0.589 g, 1.17 mmol, light yellow oil, 96%. H NMR
f
3
(
(
499.87 MHz, C D ): δ 0.89 (t, 12H, J = 7.4 Hz, CH ), 1.21−1.57
6
6
HH
3
3
m, 24H, CH ), 5.34 (p, 2H, J = 2.6 Hz, Ge−H), 7.30−7.34 (m, 2H,
2
HH
1
3
arom), 7.64−7.70 (m, 2H, arom), 7.71−7.74 (m, 2H, arom). C NMR
(
(
1
3
125.77 MHz, C D ): δ 13.9 (CH ), 16.1 (CH ), 26.5 (CH ), 28.9
6 6 3 2 2
q
q
CH ), 124.6 (CH), 130.9 (CH), 135.1 (C ), 135.8 (CH), 139.9 (C ),
2
q
+
42.9 (C ). GC/MS (m/z (%)): 502.1 [M − 2H] (2), 445.1 (10),
89.0 (13), 333.0 (16), 272.9 (100), 201.0 (53). IR: ν
2051 cm−
1
Ge−H
(
film). Anal. Found/calcd: C, 62.91/62.22; H, 9.10/8.84.
1-Dibutylgermyl-8-dimethylsilylnaphthalene (12). A 0.925
mL amount of n-butyllithium (1.6 M in hexane, 1.48 mmol) was added
to a solution of 0.393 g (1.48 mmol) of 1-bromo-8-(dimethylsilyl)-
naphthalene (11) in diethyl ether at −60 °C, and the mixture was
stirred for an additional 90 min at this temperature. Then 0.330 g of
di-n-butylchlorogermane (1.48 mmol) was added via syringe, and
the reaction mixture was warmed to room temperature. The solvent
was removed under reduced pressure, and hexane was added to
CONCLUSION
■
Cations 7 and 8 with intramolecular Ge−H−Ge and Si−H−Ge
structural motifs have been synthesized and characterized by
IR and NMR spectroscopy, supported by the results of DFT
calculations. Although compounds with an intermolecular
6
Ge−H−Ge linkage were described previously, cation 7 is the
the residue. After aqueous workup with NH Cl solution, the crude
4
first structurally characterized example of this class of electron-
deficient germanium compound. These cations features sym-
metrical (cation 7) or almost symmetrical (cation 8) electron-
deficient two-electron−three-center E−H−E bonds, similar to
the situation found in the case of the bis-silyl cation 2. The
theoretical analysis suggests that cations such as 2, 7, and 8 are
best described as bis-tetrylhydronium ions. Similar to bis-
silylhydronium ion 2, cations 7 and 8 are active catalysts in
hydrodefluorination reactions. Interestingly, there is no
significant influence of the nature of the tetryl atom of the
catalyst on its activity in HDF reactions.
product was purified by column chromatography on silica gel using
hexane as eluent: R = 0.65. Yield: 0.549 g, 1.47 mmol, colorless oil,
f
9
9%. Minor amounts of the byproduct 1-dimethylsilylnaphthalene
could not be separated from the product (see Figures S5−S7 in the
1
Supporting Information). H NMR (499.87 MHz, C D ): δ 0.45 (d,
6
6
3
3
6H, CH
(
5
, JHH = 3.5 Hz), 0.87 (t, 6H, CH
, JHH = 7.2 Hz), 1.21−1.30
3
3
m, 4H, CH ), 1.30−1.43 (m, 4H, CH ), 1.44−1.58 (m, 4H, CH ),
2
2
2
3
3
.31 (p, 1H, Ge−H, J = 2.5 Hz), 5.36 (sept, 1H, Si−H, J = 3.4
HH
HH
13
Hz), 7.25−7.37 (m, 2H, arom), 7.65−7.78 (m, 4H, arom). C NMR
(
(
(
1
125.77 MHz, C D ): δ −0.7 (CH ), 13.9 (CH ), 16.1 (CH ), 26.4
6
6
3
3
2
CH ), 28.8 (CH ), 124.6 (CH), 124.7 (CH), 130.8 (CH), 131.6
2
2
q
q
q
CH), 134.7 (CH), 135.9 (CH), 136.0 (C ), 138.4 (C ), 139.8 (C ),
q
29
42.5 (C ). Si NMR (99.30 MHz, C D ): δ −20.4. GC/MS (m/z
6
6
EXPERIMENTAL SECTION
+
■
(%)): 373 [M − H] (1), 359 (1), 317 (100), 259 (45), 201 (30), 185
−1 −1
General Considerations. All reactions were carried out under
inert conditions, using standard Schlenk techniques and an
atmosphere of argon (99.999%), unless stated otherwise. Diethyl
ether and tetrahydrofuran were distilled from sodium/benzophenone.
Benzene, toluene, [D ]benzene, [D ]toluene, pentane, and hexane
(59), 169 (64), 59 (37). IR: ν
2055 cm , ν
2163 cm (film);
Si−H
Ge−H
Anal. Found/calcd: C, 63.50/64.37; H, 9.00/8.64.
Cation Preparation: General Procedure. The stirred biphasic
solution of 258 mg of [Ph C][B(C F ) ] (0.28 mmol) in 1 mL of
3
6 5 4
benzene was added dropwise via a flexible Teflon tube to a well-stirred
6
8
were distilled from sodium. Dimethylchlorosilane and triethylsilane
solution of 0.28 mmol of the precursor compound in 1 mL of benzene
1
496
dx.doi.org/10.1021/om500154n | Organometallics 2014, 33, 1492−1498

Organometallics
Article
at room temperature. The mixture was stirred for an additional 30 min.
Stirring was stopped, and the two phases were allowed to separate.
The upper phase was removed. The remaining brown salt was purified
by washing twice with 2 mL portions of benzene. Residual benzene
all computational details, including absolute energies and
Cartesian coordinates of relevant molecular structures. This
material is available free of charge via the Internet at http://
pubs.acs.org.
was evaporated, and [D ]benzene was added to regain a biphasic
6
solution. The lower phase was transferred into a NMR tube and
investigated by NMR spectroscopy. Recrystallization of the brown oil
from fluorobenzene at +3 °C gave crystals suitable for XRD analysis.
Analytical Data for 7[B(C F ) ]. Pale brown solid, 178 mg (0.151
AUTHOR INFORMATION
Corresponding Author
*E-mail for T. M.: thomas.mueller@uni-oldenburg.de.
Notes
■
6
5 4
1
mmol, 77%). H NMR (499.87 MHz, C D ): δ 0.79 (t, 12H, CH ,
6
6
3
3
JHH = 7.2 Hz), 1.12−1.20 (m, 8H, CH ), 1.21−1.34 (m, 8H, CH ),
2
2
The authors declare no competing financial interest.
1
H
(
1
.35−1.43 (m, 8H, CH ), 1.91 (s, 1H, GeHGe), 7.15−7.18 (m, 2H,
2
2
/7
3/6
4/5
1
), 7.32−7.36 (m, 2H, H ), 7.69−7.73 (m, 2H, H ). H NMR
3
ACKNOWLEDGMENTS
250.131 MHz, C D ): δ 0.68 (t, 12H, CH , J = 6.9 Hz), 1.04−
■
7
8
3
HH
2
/7
.37 (m, 24H, CH ), 1.87 (s, 1H, GeHGe), 7.10−7.12 (m, 2H, H ),
This study was supported by the CvO University Oldenburg
and by 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.
2
3
/6
4/5 13
7
.23−7.26 (m, 2H, H ), 7.59−7.62 (m, 2H, H ). C NMR (125.77
MHz, C D ): δ 13.0 (CH ), 19.3 (CH ), 25.5 (CH ), 26.9 (CH ),
6
6
3
2
2
2
3
/6
q
10
2/7
1
[
26.4 (CH, C ), 131.5 (C , C ), 132.4 (CH, C ), 125.2 (b,
4
/5
q
1/8
1
B(C F ) ]), 133.4 (CH, C ), 134.9 (C , C ), 136.1 (t, J = 12.7
6
5
4
C
F
1
q
Hz, [B(C F ) ]), 137.9 (d, J = 12.7 Hz, [B(C F ) ]), 138.5 (C ,
C ), 139.9 (t, J = 12.7 Hz, [B(C F ) ]), 149.1 (d, J = 243.4 Hz,
6
5
4
CF
6 5 4
REFERENCES
9
1
1
■
CF
6
5
4
CF
1
3
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[
(
B(C F ) ]). C NMR (62.902 MHz, C D ): δ 13.1 (CH ), 19.5
6 5 4 7 8 3
3/6
q
10
CH ), 25.7 (CH ), 27.1 (CH ), 126.5 (CH, C ), 131.6 (C , C ),
32.6 (CH, C ), 133.6 (CH, C ), 135.1 (C , C ), 138.7 (C , C ).
2
2
2
2
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(
Analytical Data for 8[B(C F ) ]. Pale brown solid, 262 mg (0.249
6
5 4
1
mmol, 99%). H NMR (499.87 MHz, C D ): δ 0.40 (s, 6H, CH ),
6
6
3
3
(4) Khalimon, A. Y.; Lin, Z. H.; Siminonescu, R.; Vyboishchikov, S.
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0
(
.76 (t, 6H, CH , J = 7.2 Hz), 1.07−1.16 (m, 4H, CH ), 1.16−1.24
3
HH
2
1
m, 4H, CH ), 1.31−1.46 (m, 4H, CH ), 2.49 (s, 1H, J = 58.0 Hz,
2
2
HSi
(
GeHSi), 7.12−7.15 (m, 1H, arom), 7.24−7.28 (m, 1H, arom), 7.32−
1
3
7
.38 (m, 2H, arom), 7.72−7.76 (m, 2H, arom). C NMR (125.77
1 1 2
M. Organometallics 2013, 32, 7478.
MHz, C D ): δ −2.1 (CH C ′), 12.9 (CH C ″), 19.6 (CH C ″),
6
6
3,
3,
2,
1
3
(
6) Wright, J. H., II; Mueck, G. W.; Tham, F. S.; Reed, C. A.
Organometallics 2010, 29, 4066.
7) (a) Savoca, M.; Langer, J.; Dopfer, O. Angew. Chem., Int. Ed.
2013, 52, 1568. (b) George, M. A.R.; Savoca, M.; Dopfer, O. Chem.
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2005, 127, 2852. (b) Douvris, C.; Ozerov, O. V. Science 2008, 321,
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Ozerov, O. V. J. Am. Chem. Soc. 2010, 132, 4946. (d) Meier, G.; Braun,
T. Angew. Chem., Int. Ed. 2009, 48, 1546.
2
5.4 (CH C ″), 26.6 (CH C ″), 125.2 (b, [B(C F ) ]), 126.4 (CH,
2
,
2,
6 5 4
3 4 3 4 q 1 q 9
C /C ), 126.6 (CH, C /C ), 129.9 (C , C ), 130.7 (C , C ), 131.9
2
5
6
q
10
7
(
(
(
1
CH, C ), 133.6 (CH, C /C ), 134.1 (C , C ), 134.1 (CH, C ), 134.2
CH, C /C ), 136.1 (t, J = 12.7 Hz, [B(C F ) ]), 137.9 (d, J
2.7 Hz, [B(C F ) ]), 138.1 (C , C ), 139.9 (t, JCF = 12.7 Hz,
B(C F ) ]), 149.1 (d, J = 243.4 Hz, [B(C F ) ]). Si NMR (99.30
5
6
1
1
=
CF
6
5
4
CF
q
8
1
6
5 4
1
29
[
6
5
4
CF
6 5 4
1
2
MHz, C D ): δ 40.5 (dsept, J = 58.0 Hz, J = 6.8 Hz). IR:
6
6
SiH
SiH
−
1
νGe−H−Si 1736 cm (film).
9
HDF Catalysis Experiments (see Scheme 3 and Table 3).
HDF reactions may be very rapid, self-accelerating reactions and may
produce significant amounts of heat. Preliminary testing of safe
reaction condition is necessary for performing the HDF reactions in
closed vessels. In a glovebox a round-necked NMR tube was loaded
with either trityl borate [Ph C][B(C F ) ] or with trityl carborate
(10) Lu
2010, 24, 533.
(11) (a) Δw1/2 denotes the full width at half maximum. (b) Δδ
̈
hmann, N.; Panisch, R.; Mu
̈
ller, T. Appl. Organomet. Chem.
1
H
=
3
6 5 4
1
H
1
[
Ph C][CB H Br ] (0.010 mmol). The trityl salt was dissolved in
δ
(cation) − δ
(12) Luhmann, N. Ph.D. Thesis, Carl von Ossietzky Universitat
Oldenburg, 2011.
H
(precursor).
3
11
6
6
o-dichlorobenzene (0.3 mL), and C F (10 μL) was added as internal
̈
̈
6
6
standard. Then the cation precursor compound (0.015 mmol) was
added. The mixture was shaken well until the disappearance of the
orange color indicated the formation of the corresponding hydronium
(13) Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.;
Truhlar, D. G. J. Phys. Chem. 2009, 113, 5806.
ion. After an additional 10 min Et SiH (0.5 mL) was added and the
(14) For C H ·C F cocrystals plane−plane distances of about 340
3
6
6
6 6
tube was shaken once again. Finally, the alkyl fluoride (0.8 mmol) was
added and the tube was shaken. The reaction mixture was allowed to
stand for 1 h in the glovebox. The tube was closed and taken out of the
glovebox for 19F NMR spectroscopy measurements. In the case of the
HDF reactions between carborates and C H CF it was advisable to
pm and centroid−centroid distances of 370 pm were reported. For a
review see: Meyer, E. A.; Castellano, R. K.; Diederich, F. Angew. Chem.
2003, 115, 1244.
(15) Sekiguchi, A.; Tsukamoto, M.; Ichinohe, M. Science 1997, 275,
60.
6
5
3
prepare the catalyst in a press-on glass lid in the glovebox and to add
the fluoride in small amounts until the reaction ceased. Then the
reaction mixture was cooled to room temperature and was transferred
(16) Sekiguchi, A.; Fukawa, T.; Lee, V. Ya.; Nakamoto, M.; Ichinohe,
M. Angew. Chem., Int. Ed. 2003, 42, 1143.
(17) Schenk, C.; Drost, C.; Schnepf, A. Dalton Trans 2009, 773.
(18) See the Supporting Information for further details.
(19) The Gaussian 09, Rev B.01 program was used.
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programs was applied for the NBO analysis: Reed, A. E.; Weinstock, R.
B.; Weinhold, F. J. Chem. Phys. 1985, 83, 735.
19
to a NMR tube. The progress of the reaction was followed by
F
19
NMR spectroscopy. The product Et SiF was detected by F NMR
3
19
spectroscopy. Et SiF: F NMR (235.33 MHz, C D ) δ −175.8 (s,
3
6
6
1
JSiF = 288.7 Hz).
(
(
21) Wiberg, K. B. Tetrahedron 1968, 24, 1083.
22) (a) Bader, R. F. W. Atoms in Molecules: A Quantum Theory;
ASSOCIATED CONTENT
■
* Supporting Information
Text, tables, figures, and a CIF file giving relevant NMR spectra,
X-ray crystallographic data for compound 7[B(C F ) ], and
S
Clarendon Press: Oxford, U.K., 1990. (b) The QTAIM analysis was
performed with the AIMALL program: Keith, T. A. AIMAll (Version
11.05.16), 2011.
6
5 4
1
497
dx.doi.org/10.1021/om500154n | Organometallics 2014, 33, 1492−1498

Organometallics
Article
(
(
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̈
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(
(
25) Reed, C. A. Acc. Chem. Res. 1998, 31, 133.
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E′ = Ge), adopts according to the results of DFT calculations at the
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pm, α(GeFGe) = 123°). Therefore, this species closely resembles the
corresponding silicon compound in all structural and electronic
features; see refs 2b and 27 for an extensive discussion on structure
and bonding in disilylfluoronium ions.
(
2
(
27) Lu
011, 30, 4087.
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̈ ̈
hmann, N.; Hirao, H.; Shaik, S.; Muller, T. Organometallics
(
1
(
991, 113, 8570.
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8
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(
6
(
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498
dx.doi.org/10.1021/om500154n | Organometallics 2014, 33, 1492−1498