Selective aromatic C-F and C-H bond activation with silylenes of different coordinate silicon

Article abstract of DOI:10.1021/ja103988d

Herein we report on the reaction of stable two-coordinate silylene, L ¹Si [L¹ = CH{(C=CH₂)(CMe)(2,6-iPr ₂C₆H₃N)₂}] (1) and three-coordinate silylene (Lewis base stabilized silyle

Full text of DOI:10.1021/ja103988d

Published on Web 07/07/2010
Selective Aromatic C-F and C-H Bond Activation with
Silylenes of Different Coordinate Silicon
Anukul Jana,† Prinson P. Samuel,† Gasˇper Tavcˇar,† Herbert W. Roesky,*,† and
Carola Schulzke‡
Institut fu¨r Anorganische Chemie, UniVersita¨t Go¨ttingen, Tammannstrasse 4, 37077 Go¨ttingen,
Germany, and School of Chemistry, Trinity College Dublin, Dublin 2, Ireland
Received May 10, 2010; E-mail: hroesky@gwdg.de
Abstract: Herein we report on the reaction of stable two-coordinate silylene, L1Si [L1 ) CH{(CdCH2)(CMe)(2,6-
iPr2C6H3N)2}] (1) and three-coordinate silylene (Lewis base stabilized silylene), L2SiCl [L2 ) PhC(NtBu)2]
(2) with aromatic compounds containing C-F and C-H bonds. The reaction of 1 and 2 with hexafluo-
robenzene (C6F6) affords the silicon(IV) fluorides, L1SiF(C6F5) (3) and L2SiFCl(C6F5) (4), respectively. The
reaction proceeds through the unprecedented oxidative addition of one of the C-F bonds to the silicon(II)
center without any additional catalyst. When 1 and 2 are treated with octafluorotoluene (C6F5CF3),
pentafluoropyridine (C5F5N) regioselective C-F bond activation occurs leading to the formation of L1SiF(4-
C6F4CF3) (5), L1SiF(4-C5F4N) (6), L2SiFCl(4-C6F4CF3) (7), and L2SiFCl(4-C5F4N) (8), respectively. More
interestingly, compounds 1 and 2 react with pentafluorobenzene (C6F5H) under formation of silicon(IV)
hydride L1SiH(C6F5) (9) by chemoselective C-H bond activation, in the latter case producing silicon(IV)
fluoride L2SiFCl(4-C6F4H) (10) by chemo- as well as regioselective C-F bond activation. Furthermore, the
reaction of 1 with 1,3,5-trifluorobenzene (1,3,5-C6F3H3) leads to the chemoselective formation of silicon(IV)
hydride L1SiH(1,3,5-C6F3H2) (11). The formation of compounds 9 and 11 occurs via oxidative addition of
the aromatic C-H bond to the silicon(II) center instead of C-F bond activation. All reported reactions
proceed without any additional catalyst. Compounds 3, 4, 5, 6, 7, 8, 9, 10, and 11 were investigated by
microanalysis and multinuclear NMR spectroscopy and compounds 3, 7, 8, and 9 additionally by single
crystal X-ray structural analyses.
Lewis acids and as Lewis bases.7,8 Consequently the silylenes
are electronically and coordinatively unsaturated, and they are
Introduction
Divalent silicon compounds are known as silylenes, and they
represent an indispensable synthon in organosilicon chemistry.1
Since 1994, when West et al.2 isolated the first silylene, it was
known that stable silylenes are generally two-coordinate. In
2006 a three-coordinate base stabilized silylene L2SiCl [L2 )
PhC(NtBu)2] (2),3 was prepared. Following that there were some
reports on the synthesis of three-coordinate stable silylenes,4
including NHC ·SiCl2 and NHC ·SiBr2 [NHC ) C[N(2,6-
iPr2C6H3)CH]2]. Unlike carbenes, silylenes have invariably a
singlet electronic ground state. Therefore they can act both as
capable of a variety of insertion reactions into X-Y bonds
(X-Y: C-H,9 N-H,10 O-H,11 S-H,10c P-P,12 N-Si,13
C-Cl,14 C-Br,14 C-I,14 and Si-Cl14 bonds), to yield silanes
with different substituents. To the best of our knowledge, there
are no reports in literature on the insertion reactions of stable
5
6
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† Universita¨t Go¨ttingen.
‡ Trinity College Dublin.
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10.1021/ja103988d  2010 American Chemical Society

C-F and C-H Bond Activation with Silylenes
A R T I C L E S
silylenes into aromatic C-H bonds or into any kind of C-F
bond. Therefore we became interested in studying the reactivity
of stable silylenes, L1Si [L1 ) CH{(CdCH2)(CMe)(2,6-
iPr2C6H3N)2}] (1)15 and L2SiCl (2)3,16 with aromatic compounds
containing C-F and C-H bonds, namely, hexafluorobenzene
(C6F6), octafluorotoluene (C6F5CF3), pentafluoropyridine
(C5F5N), pentafluorobenzene (C6F5H), and 1,3,5-trifluorobenzene
(1,3,5-C6F3H3). These compounds were selected with the
intention to study whether they can form the oxidative addition
products by insertion reactions into the aromatic C-F or C-H
bond. Direct transformations of aromatic C-F and C-H bonds
are a real challenge in chemistry. Specifically the C-F bond is
in most cases thermally, photochemically, electrooxidatively,
and often even chemically stable, so that it is in general not
easy to cleave this bond for chemical modifications of orga-
nofluoro compounds. But still it is potentially useful for synthetic
chemistry to utilize effective C-F bond activation of aryl
fluorides. The organic compounds with fluorine-containing
groups are important in pharmaceutical, agrochemical, and
materials science.17 Polyfluoroarenes are a representative class
of such compounds, and thus the development of a selective
C-F and C-H bond activation method is highly desired. In
the literature one finds mostly reports on transition or lanthanide
metals that are based on catalyzed or stoichiometric activated
C-F and C-H bonds of polyfluoroarene compounds.18-20
Some of these metal complexes are in high oxidation states and
act through an electrophilic σ-metathesis pathway, while others
are in low oxidation states and react by oxidative addition. Braun
and Perutz et al. have reported that Ni(COD)2 [COD ) 1,5-
cyclooctadiene] activates selectively C-F over C-H bonds of
fluoropyridine substrates in the presence of triethylphosphine
(PEt3).21 The reaction of Pt(PCy3)2 [Cy ) cyclohexane] with
pentafluoropyridine and 2,3,5,6-tetrafluoropyridine leads to C-F
and C-H bond activation products, respectively; in the latter
case a preference for C-H over C-F bond activation was
observed.22 Very recently Johnson et al. reported the selective
C-F bond activation of tetrafluorobenzenes by Ni(0) with a
nitrogen donor analogous to N-heterocyclic carbenes.23 In 2008
Ozerov et al. described for the first time aliphatic C-F bond
over aromatic C-F bond activation by using a silylium-
carborane catalyst in the presence of a silicon(IV) hydride.24
In the literature there are reports on C-H bond activation by
compounds with low valent Group 14 elements (carbene,
silylene, germylene, and stannylene)25 and also on the silylene
and germylene mediated C-H bond activation.26 There is,
however, only one report by Kuhn et al. on C-F bond activation
of pentafluoropyridine by compounds with low valent Group
14 elements, namely, 1,3-dimethyl-4,5-dimethyl-2-ylidene and
1,3-diisopropyl-4,5-dimethyl-2-ylidene.27 Very recently we have
described the regioselective hydrodefluorination of carbonyl
compounds containing aromatic C-F bonds including hexafluo-
robenzene by a tin(II) hydride.28 Herein, we report on the
regioselective activation of C-F bonds of fluoroarenes, the
chemoselective activation of a C-H bond of partially fluorinated
arenes using a silylene, L1Si (1), and the regio and chemose-
lective activation of C-F over C-H bonds by three-coordinate
silylene, L2SiCl (2), without any additional catalyst. To the best
of our knowledge this is the first stoichiometric main group
system described that is able to activate the C-F bond of
perfluoroarenes and simultaneously activates the C-H bond over
the C-F bond of polyfluoroarenes. This demonstrates that the
low valent silicon, congener of carbon, mimics transition metal
complexes.29
Results and Discussion
The reaction of L1Si [L1 ) CH{(CdCH2)(CMe)(2,6-
iPr2C6H3N)2}] (1) and L2SiCl [L2 ) PhC(NtBu)2] (2) with
hexafluorobenzene (C6F6) leads to the pentafluorophenyl deriva-
tive of silicon(IV) fluoride, L1SiF(C6F5) (3) and L2SiFCl(C6F5)
(4) (Scheme 1). The reaction proceeds through the unpre-
cedented oxidative addition of one of the C-F bonds of C6F6
to the silicon(II) center.
Compounds 3 and 4 have been well-characterized by spec-
troscopic and analytic measurements, and compound 4 was in
addition characterized by X-ray structural analysis. In the 19F
NMR spectra of 3 and 4 the Si-F resonances arise at δ -131.1
ppm and δ -63.4 ppm, respectively. These two chemical shifts
are very much different due to the different coordination
numbers at the silicon atoms. Compounds 3 and 4 display a
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J. AM. CHEM. SOC. VOL. 132, NO. 29, 2010 10165

A R T I C L E S
Jana et al.
Scheme 1. Preparation of 3 and 4
doublet in the 29Si NMR spectrum (δ -54.3 ppm for 3 and δ
those of NHC ·SiF4 ·NHC (av 1.66(2) Å) (NHC ) C[N(2,6-
iPr2C6H3)CH]2), which are slightly longer.31
2
-91.9 ppm for 4) with a coupling constant of J(29Si-19F) )
2
262.58 Hz and J(29Si-19F) ) 282.89 Hz, respectively. Com-
Furthermore, we were interested in the selectivity of the
oxidative addition of the C-F bond at the silicon(II) center.
Therefore we selected other aromatic perfluoro compounds,
namely, octafluorotoluene (C6F5CF3) and pentafluoropyridine
(C5F5N) (Scheme 2). Compounds 1 and 2 react with octafluoro
toluene and pentafluoro pyridine in toluene at room temperature
to form only one regioisomer with para-C-F bond activation
relative to the CF3 group and the nitrogen atom, respectively.
The CF3 group of octafluoro toluene is not affected by the
silicon(II) center, when it is reacted with any one of the
mentioned silylenes (1 or 2) contrary to the reported C-F bond
activation of this molecule.24 This was confirmed by 19F NMR
measurement in benzene-d6 solution, showing a triplet for the
CF3 group (δ -56.8 ppm; 3J(19F-19F) ) 21.61 Hz for 5 and δ
pound 3 is soluble in benzene, THF, n-hexane, and n-pentane,
which is in contrast to that of compound 4, which is insoluble
in nonpolar solvents, such as n-hexane and n-pentane, and both
compounds are stable in the solid state as well as in solution
for a long time without any decomposition under an inert
atmosphere. Compound 3 crystallizes in the monoclinic space
group C2/c from a saturated toluene solution at room tempera-
ture after one day, with one molecule in the asymmetric unit.
X-ray crystal structure analysis afforded a monomeric structure
as illustrated in Figure 1.
The coordination polyhedron around the silicon atom features
a distorted tetrahedral geometry. The silicon is attached to two
nitrogen atoms from the backbone of the chelating ligand, the
terminal F atom, and a pentafluoro phenyl group. From the
molecular structure of 3 we can see that the fluorine atom at
silicon (F1) is closer to one of the two ortho fluorine atoms
(F6) of the pentafluoro phenyl group (the distance between F1
and F6 is 2.665(5) Å, and the distance between F1 and F2 is
4.468(4) Å; see Figure 1). The Si1-N1 bond length and
N1-Si1-N2 bond angle are 1.696(1) (Å) and 107.08(6)°,
respectively. These data are comparable with those of related
compounds.30 A noteworthy feature of compound 3 is the
SiF(C6F5) moiety; the Si-F bond length (Si1-F1 1.578(1) Å)
can be compared with those of NHC·SiF4 (av 1.577(2) Å) and
3
1
-56.1 ppm; J(19F-19F) ) 21.75 Hz for 7). The H NMR
spectra exhibit a singlet resonance (δ 5.45 and 5.44 ppm) which
corresponds to the C-H protons of the ligand backbone of the
fluorine substituted silane, L1SiF(4-C6F4CF3) (5) and L1SiF (4-
C5F4N) (6), respectively. It is also worth mentioning that in the
19F NMR spectra of compounds 5, 6, 7, and 8 the Si-F
resonances arise at δ -131.5, -132.2, -63.7, and -64.4 ppm,
respectively, which are almost similar when compared with
those of 3 and 4 (δ -131.1 ppm for 3 and δ -63.4 ppm for 4).
In addition, the Si-F resonances of compounds 3, 5, and 6
exhibit doublets, with almost similar coupling constants (50.03
Hz for 3, 49.71 for 5, and 45.45 for 6), due to coupling with
only one of the ortho fluorines. The 29Si NMR spectra of all
four compounds (5, 6, 7, and 8) show doublets (δ -55.2,
-56.08, -97.2, and -97.9 ppm) with a coupling constant of
J(29Si-19F) ) 263.59, 263.66, 283.65, and 282.72 Hz, respec-
tively. Compounds 5, 6, 7, and 8 exhibit the base peak in the
EI mass spectra at 665 [M+-Me], 598 [M+-Me], 530 [M]+,
and 428 [M+-Cl], respectively.
In addition single crystal X-ray structural analysis was carried
out for compounds 7 and 8, confirming that only the para
fluoride relative to the CF3 group and N atom, respectively, is
activated by the silylene 2. Compounds 7 and 8 both crystallize
j
in the triclinic space group P1, with one monomer in the
asymmetric unit. Compound 8 cocrystallizes with one disordered
toluene molecule. Single crystals of 7 and 8 were obtained from
a saturated toluene solution at room temperature (Table 1). The
coordination polyhedron around the silicon atom features a
distorted trigonal bipyramidal geometry with a terminal Si-F
Figure 1. Molecular structure of 3. Anisotropic displacement parameters
are depicted at the 50% probability level. H atoms are omitted for clarity
reasons except for H on C19 and C23. Selected bond lengths [Å] and angles
[deg]: Si1-F1 1.5780(9), Si1-C1 1.8811(15), Si1-N1 1.6960(14);
N1-Si1-C1 110.97(6), F1-Si1-N1 112.44(6), F1-Si1-C1 103.07(6),
N1-Si1-N2 107.08(6).
(30) (a) Driess, M.; Yao, S.; Brym, M.; van Wu¨llen, C. Angew. Chem.
2006, 118, 6882–6885; Angew. Chem., Int. Ed. 2006, 45, 6730-6733.
(b) Xiong, Y.; Yao, S.; Brym, M.; Driess, M. Angew. Chem. 2007,
119, 4595–4597; Angew. Chem., Int. Ed. 2007, 46, 4511-4513.
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Stalke, D. Organometallics 2009, 28, 6374–6377.
9
10166 J. AM. CHEM. SOC. VOL. 132, NO. 29, 2010

C-F and C-H Bond Activation with Silylenes
Scheme 2. Preparation of 5, 6, 7, and 8
A R T I C L E S
bond (Figure 2 for 7 and Figure 3 for 8). The Si-F bond lengths
are almost similar (1.633(3) Å for 7 and 1.6394(19) Å for 8),
although they are longer compared to that of compound 3
(1.5780(9)Å), due to a different coordination number around
silicon.
the effect of different coordination numbers around the silicon
atoms to the resulting products 9 and 10. In compound 9, silicon
has the coordination number 4, while 10 is 5-fold coordinated.
In general silicon hydrides with high coordinate silicon are less
After the successful reaction of 1 and 2 with perfluoro
aromatic compounds, we turned to partially fluorinated aromatic
compounds, namely, pentafluoro benzene (C6F5H). The reaction
of 1 and 2 with pentafluorobenzene leads to the chemoselective
formation of silicon(IV) hydride L1SiH(C6F5) (9) and silicon(IV)
fluoride L2SiFCl(4-C6F4H) (10), respectively, in good yields
(Scheme 3).
The first reaction occurs via oxidative addition of the aromatic
C-H bond to the silicon(II) center instead of C-F bond
activation. This is most probably due to smaller C-H bond
energy compared to that of the C-F bond. The second reaction
proceeds via oxidative addition of the aromatic C-F bond to
the silicon(II) center instead of C-H bond activation, although
the C-F bond exceeds the C-H bond energy [D(F-C6F5) -
D(H-C6H5) ) 16 kJ mol-1].32 This is possible because the Si-F
bond energy is higher, when compared with that of the Si-H
bond. The ability of compound 2, but not 1, to undergo C-F
bond activation rather than C-H bond activation demonstrates
Figure 2. Molecular structure of 7. Anisotropic displacement parameters
are depicted at the 50% probability level. H atoms are omitted for clarity
reasons. The CF3 group is disordered, and only one of two orientations is
shown. Selected bond lengths [Å] and angles [deg]: Si1-F1 1.633(3),
Si1-Cl1 2.0705(16), Si1-C1 1.913(5), Si1-N1 1.938(3); N1-Si1-C1
91.73(16), F1-Si1-N2 97.92(15), F1-Si1-C1 92.57(16), F1-Si1-Cl1
94.56(11), N1-Si1-N2 69.94(15).
Table 1. Crystallographic Data at T ) 100 [K] for the Structural
Analyses of Compounds 3, 7, 8, and 9
3
7
8·tol
9
empirical
formula
C35H40F6N2Si C22H23ClF8N2Si C27H31ClF5N3Si C35H41F5N2Si
molecular
weight
630.78
530.96
556.09
612.79
T
100 K
770535
100 K
100 K
100 K
706622
monoclinic
P21
9.5252(19)
17.166(3)
10.174(2)
90
93.36(3)
90
1660.7(6)
2
CCDC-No.
crystal system monoclinic
space group
a [Å]
b [Å]
775969
triclinic
775968
triclinic
j
j
C2/c
P1
P1
20.810(4)
9.6243(19)
33.923(7)
90
104.28(3)
90
6584(2)
8
1.273
9.785(2)
9.976(2)
13.842(3)
89.57(3)
82.58(3)
89.18(3)
1339.8(5)
2
9.832(2)
10.142(2)
14.530(3)
88.37(3)
88.69(3)
71.03(3)
1369.4(5)
2
c [Å]
R [deg]
ꢀ [deg]
γ [deg]
V [Å3]
Figure 3. Molecular structure of 8. Anisotropic displacement parameters
are depicted at the 50% probability level. H atoms and cocrystallized toluene
are omitted for clarity reasons. Selected bond lengths [Å] and angles [deg]:
Si1-F1 1.6394(19), Si1-Cl1 2.0756(11), Si1-C1 1.905(3), Si1-N2
1.785(2); N2-Si1-C1 119.96(11), F1-Si1-N2 97.82(10), F1-Si1-C1
92.87(11), F1-Si1-Cl1 93.35(8), N2-Si1-N3 69.77(10).
Z
Fcalc [Mg m-3
]
1.316
0.255
1.349
0.239
1.225
0.125
µ [mm-1
]
0.132
R1 [I > 2σ(I)] 0.0350
wR2 (all data) 0.0818
0.0832
0.2396
0.0550
0.1493
0.0432
0.1087
9
J. AM. CHEM. SOC. VOL. 132, NO. 29, 2010 10167

A R T I C L E S
Jana et al.
Scheme 3. Preparation of 9 and 10
Scheme 4. Preparation of 11
stable than those of the corresponding fluoride analogues. This
is the fundamental reason for the preferred formation of high
coordinate silicon with fluorides and not with hydrides.
Single crystals of 9 were obtained from a saturated n-hexane
solution at -32 °C after two days. Compound 9 crystallizes in
the monoclinic space group P21, with one molecule in the
asymmetric unit. X-ray crystal structural analysis revealed a
monomeric structure as illustrated in Figure 4. The hydrogen
on silicon is not involved in any kind of hydrogen bonding,
whereas intramolecular hydrogen bonds are observed with both
nitrogen atoms and the four CH protons of the iso-propyl groups.
In addition there is an intermolecular hydrogen bond present
between the terminal dCH2 group of the ligand backbone and
the fluorine F3 in para-position to silicon. This type of
intermolecular interaction was also observed in the case of
compound 3. The hydrogen atom on silicon was found and
refined without any restraints. Compound 9 is stable in the solid
state as well as in solution for a long time without any
decomposition under inert atmosphere. The coordination poly-
hedron around the silicon atom features a distorted tetrahedral
geometry like that in compound 3, only that the Si-F moiety
is replaced by Si-H.
tin can rapidly interchange in solution. The 29Si{1H} decoupled
proton spectrum of 9 exhibits a doublet resonance (δ -41.2
ppm) with a coupling constant of 18.28 Hz, due to the silicon
atom (Si1) that couples with one of the ortho fluorine atoms
(F1) of the pentafluoro phenyl group, while the proton coupled
spectrum shows a doublet resonance with a coupling constant
of 2J(29Si-1H) ) 261.63 Hz. In addition the 1H NMR spectrum
exhibits the expected pattern for the ligand with four septets of
the four iso-propyl groups.
1H, 19F, and 29Si NMR spectroscopy confirmed that 10 has a
SiF(4-C6F4H) moiety. The C-H proton shows a resonance at
δ 6.48 ppm, and there is no indication for the formation of a
Si-H bond. In the 19F NMR, there is a Si-F resonance present
at δ 59.2 ppm, which is attributed to 29Si satellites with a
1
The H, 19F, and 29Si NMR spectra revealed that 9 has a
SiH(C6F5) moiety. The Si-H proton shows a resonance at δ
5.46 ppm. The fluorine NMR displays five different resonances,
which are similar to those of compound 3, but different when
compared to those of LSnC6F5 [L ) CH{(CMe)2(2,6-
iPr2C6H3N)2}].28 The reason is probably that compound 9 exists
in solution in the same form as in the solid state, while in case
of LSnC6F5 the pentafluoro phenyl group and the lone pair at
2
coupling constant of J(29Si-19F) ) 288.84 Hz. This is finally
documented by measuring the 29Si NMR, which exhibits a
doublet (δ -96.03 ppm) with the same coupling constant. In
the EI mass spectrum compounds 9 and 10 are showing the
base peak at 597 [M+-Me] and 427 [M+-Cl], respectively.
Moreover, we reacted compound 1 with 1,3,5-trifluoro
benzene (1,3,5-C6F3H3) for checking whether the C-H or C-F
bond activation has occurred. The reaction of 1 with 1,3,5-
trifluoro benzene leads also to the chemoselective formation of
silicon(IV) hydride L1SiH(1,3,5-C6F3H2) (11) in good yield
(Scheme 4). The reaction occurs at 80 °C oil bath temperature,
which is in contrast to the formation of compound 9, which
occurs at room temperature.
In the case of compound 11 the Si-H resonance appears at
5.42 ppm in the 1H NMR spectrum, and the three fluorine atoms
are displaying three different resonances in the 19F NMR
spectrum (δ -90.4 (o-F), -99.6 (o-F), and -103.9 (p-F) ppm).
The 29Si NMR spectrum exhibits a doublet of doublets (δ -40.1
ppm) with a coupling constant of 1J(29Si-1H) ) 256.3 Hz and
3J(29Si-19F) ) 18.73 Hz. In the EI mass spectrum compound
11 shows the base peak at 576 [M]+ as the molecular ion.
Conclusion
Figure 4. Molecular structure of 9. Anisotropic displacement parameters
are depicted at the 50% probability level. H atoms are omitted for clarity
reasons except for H on silicon, which was found and refined freely, and H
on C19 and C23. Selected bond lengths [Å] and angles [deg]: Si1-N1
1.7203(17), Si1-C1 1.890(2); N1-Si1-C1 113.01(9), N1-Si1-N2
105.79(9).
In summary we have shown that aromatic C-F bond
activation is possible with both silylenes L1Si (1) and L2SiCl
(2), when they are reacted with perfluoroaromatic compounds
in the absence of any additional catalyst. But the behavior of
the two silylenes is very distinct when they are reacted with
9
10168 J. AM. CHEM. SOC. VOL. 132, NO. 29, 2010

C-F and C-H Bond Activation with Silylenes
A R T I C L E S
Synthesis of [CH(CdCH2)(CMe)(2,6-iPr2C6H3N)2]SiF(4-C6F4-
CF3) (5). A solution of octafluorotoluene (0.23 g, 1.00 mmol in 5
mL of toluene) was added by cannula to a solution of 1 (0.44 g,
1.00 mmol in toluene 25 mL) at room temperature. After 12 h all
volatiles were removed in vacuo, and the remaining residue was
extracted with n-hexane (25 mL) to yield compound 5. Yield 0.52 g
(80%). Mp 61 °C. 1H NMR (200 MHz, C6D6, 25 °C): δ 6.89-7.17
(m, 6H, ArH), 5.46 (s, 1H; CH), 4.03 (s, 1H, CH2), 3.72 (sept, 2H,
CH(CH3)2), 3.47 (s, 1H, CH2), 3.22 (sept, 1H, CH(CH3)2), 2.98
(sept, 1H, CH(CH3)2), 0.90-1.47 (m, 21H; CH3 and CH(CH3)2),
0.38 (d, 6H, CH (CH3)2) ppm. 19F NMR (188.29 MHz, C6D6): δ
-56.8 (t, 3F, CF3), -122.4 (br, 1F, o-F), -123.6 (d, 1F, o-F),
-131.4 (d, 1F, Si-F), -138.3 (br, 1F, m-F), -141.0 (br, 1F, m-F)
ppm. 29Si NMR (99.36 MHz, C6D6, 25 °C): δ -55.2 (2J(29Si-19F)
) 263.59 Hz) ppm. EI-MS (70 eV; m/z (%)): 665 (100) [M-Me]+.
Anal. Calcd for C36H40F8N2Si (680.28): C, 63.51; H, 5.92; N, 4.11.
Found: C, 62.97; H, 6.02; N, 3.89.
Synthesis of [CH(CdCH2)(CMe)(2,6-iPr2C6H3N)2]SiF(4-C5F4N)
(6). A solution of pentafluoropyridine (0.17 g, 1.00 mmol in 5 mL
of toluene) was added by cannula to a solution of 1 (0.42 g, 1.00
mmol in toluene 25 mL) at room temperature. After 12 h all the
volatiles were removed in vacuo, and the remaining residue was
extracted with n-hexane (20 mL) to yield compound 6. Yield 0.54 g
(88%). Mp 166 °C. 1H NMR (200 MHz, C6D6, 25 °C): δ 6.85-7.17
(m, 6H, ArH), 5.44 (s, 1H; CH), 4.04 (s, 1H, CH2), 3.73 (sept, 2H,
CH(CH3)2), 3.48 (s, 1H, CH2), 3.26 (sept, 1H, CH(CH3)2), 2.96
(sept, 1H, CH(CH3)2), 0.90-1.45 (m, 21H; CH3 and CH(CH3)2),
0.35 (d, 6H, CH (CH3)2) ppm. 19F NMR (188.29 MHz, C6D6): δ
-90.0 (br, 1F, o-F), -92.7 (d, 1F, o-F), -126.8 (br, 1F, m-F),
-128.9 (br, 1F, m-F), -132.2 (d, 1F, Si-F) ppm. 29Si NMR (99.36
MHz, C6D6, 25 °C): δ -56.08 (2J(29Si-19F) ) 263.66 Hz) ppm.
EI-MS (70 eV; m/z (%)): 598 (100) [M+-Me]. Anal. Calcd for
C34H40F5N3Si (613.29): C, 66.53; H, 6.57; N, 6.85. Found: C, 66.62;
H, 6.64; N, 6.88.
partially fluorinated aromatic compounds. The two coordinate
silylene of L1Si (1) reacts via C-H bond activation, while the
three-coordinate silylene of L2SiCl (2) reacts via C-F bond
activation. This is the first time that aromatic C-F bond
activation has proved to be a useful tool for the preparation of
silicon fluorine compounds. The stability of compounds 3-11
at room temperature favors their further functionalization.
Currently, we are engaged in investigating other main-group
reagents for selective C-F bond activation.
Experimental Section
All manipulations were performed under a dry and oxygen free
atmosphere (N2) using standard Schlenk techniques or inside a
MBraun MB 150-GI glovebox maintained at or below 1 ppm of
O2 and H2O. All solvents were distilled from Na/benzophenone
prior to use. The starting materials 115 and 216 were prepared using
literature procedures. Other chemicals were purchased commercially
and used as received. 1H, 19F, and 29Si NMR spectra were recorded
on a Bruker Avance DRX instrument and referenced to the SiMe4
1
in the case of the H and 29Si NMR and CFCl3 for the 19F NMR
spectra, respectively. Elemental analyses were performed by the
Analytisches Labor des Instituts fu¨r Anorganische Chemie der
Universita¨t Go¨ttingen. EI-MS were measured on a Finnigan Mat
8230 or a Varian MAT CH5 instrument. Melting points were
measured in sealed glass tubes with a Bu¨chi melting point B 540
instrument.
Synthesis of [CH(CdCH2)(CMe)(2,6-iPr2C6H3N)2]SiF(C6F5) (3).
An NMR tube was loaded with hexafluorobenzene (0.048 g, 0.25
mmol) and 1 (0.11 g, 0.25 mmol) at room temperature. After that
toluene-d8 (0.6 mL) was added, and the sealed NMR tube was kept
in a hot oil bath at 120-130 °C. After 12 h the 1H NMR spectrum
was recorded and showed the formation of compound 3. The
solution from the NMR tube was transferred into a Schlenk flask,
the solvent evaporated, and the residue extracted with toluene (2
mL). Storing this solution overnight at room temperature afforded
colorless crystals, which were suitable for X-ray diffraction analysis.
Synthesis of [PhC(NtBu)2]SiFCl(4-C6F4CF3) (7). A solution of
octafluorotoluene (0.23 g, 1.00 mmol in 5 mL toluene) was added
by cannula to a solution of 2 (0.29 g, 1.00 mmol in 25 mL of
toluene) at room temperature. After 12 h all volatiles were removed
in vacuo, and the remaining residue was extracted with toluene
(20 mL), concentrated to about 5 mL and kept at room temperature.
Colorless crystals of 7 suitable for X-ray diffraction analysis are
1
Yield 0.13 g (85%). Mp 156 °C. H NMR (200 MHz, C6D6, 25
°C): δ 6.90-7.12 (m, 6H, ArH), 5.46 (s, 1H, CH), 4.02 (s, 1H,
CH2), 3.77 (sept, 2H, CH(CH3)2), 3.46 (s, 1H, CH2), 3.24 (sept,
1H, CH(CH3)2), 3.03 (sept, 1H, CH(CH3)2), 1.02-1.47 (m, 21H;
CH3 and CH(CH3)2), 0.40 (d, 6H, CH (CH3)2) ppm. 19F NMR
(188.29 MHz, C6D6): δ -123.92 (br, 1F, o-F), -125.41 (d, 1F,
o-F), -131.13 (d, 1F, Si-F), -148.90 (t, 1F, p-F), -159.53 (br,
1F, m-F), -162.79 (br, 1F, m-F) ppm. 29Si NMR (99.36 MHz, C7D8,
25 °C): δ -54.37 (2J(29Si-19F) ) 262.58 Hz) ppm. EI-MS (70
eV; m/z (%)): 630 (100) [M]+. Anal. Calcd for C35H40F6N2Si
(630.29): C, 66.64; H, 6.39; N, 4.44. Found: C, 66.00; H, 6.51; N,
4.30.
1
formed after two days. Yield 0.37 g (70%). Mp 72 °C. H NMR
(200 MHz, C6D6, 25 °C): δ 6.94-7.08 (m, 5H, ArH), 0.98 (s, 18H,
C (CH3)3) ppm. 19F NMR (188.29 MHz, C6D6): δ -56.1 (t,
4J(19F-19F) ) 21.75 Hz, 3F, CF3), -63.7 (s, 1F, Si-F), -128.9
(br, 2F, o-F), -140.2 (br, 2F, m-F) ppm. 29Si NMR (99.36 MHz,
C6D6, 25 °C): δ -97.2 (1J(29Si-19F) ) 283.65 Hz) ppm. EI-MS
(70 eV; m/z (%)): 530 (100) [M]+. Anal. Calcd for C22H23ClF8N2Si
(530.96): C, 49.77; H, 4.37; N, 5.28. Found: C, 50.77; H, 5.37; N,
5.92.
Synthesis of [PhC(NtBu)2]SiFCl(C6F5) (4). An NMR tube was
loaded with hexafluorobenzene (0.048 g, 0.25 mmol) and 2 (0.07
g, 0.25 mmol) at room temperature. Then toluene-d8 (0.6 mL) was
added, and the sealed NMR tube was kept in a hot oil bath at
120-130 °C. After 24 h the 1H NMR spectrum was recorded and
showed the formation of only compound 4. The solution from the
NMR tube was transferred into a Schlenk flask; after evaporation
of the solvent compound 4 remained. Yield 0.09 g (76%). Mp 132
°C. 1H NMR (200 MHz, C6D6, 25 °C): δ 6.81-7.04 (m, 5H, ArH),
0.97 (s, 18H, C (CH3)3) ppm. 19F NMR (188.29 MHz, C6D6): δ
-63.4 (s, 1F, Si-F), -130.7 (br, 2F, o-F), -153.4 (t, 3J(19F-19F)
) 20.20 Hz, 1F, p-F), -161.3 (br, 2F, m-F) ppm. 29Si NMR (99.36
MHz, C7D8, 25 °C): δ -91.9 (1J(29Si-19F) ) 282.89 Hz) ppm.
EI-MS (70 eV; m/z (%)): 480 (25) [M]+, 445 (100) [M+-Cl]. Anal.
Calcd for C21H23ClF6N2Si (480.95): C, 52.44; H, 4.82; N, 5.82.
Found: C, 53.04; H, 5.31; N, 6.18.
Synthesis of [PhC(NtBu)2]SiFCl(4-C5F4N) (8). A solution of
pentafluoropyridine (0.17 g, 1.00 mmol in 5 mL of toluene) was
added by cannula to a solution of 2 (0.29 g, 1.00 mmol in 25 mL
of toluene) at room temperature. After 12 h all volatiles were
removed in vacuo, and the remaining residue was extracted with
toluene (20 mL), concentrated to about 10 mL, and stored at room
temperature. Colorless crystals of 8 suitable for X-ray diffraction
analysis are formed after one day. Yield 0.38 g (82%). Mp 137
°C. 1H NMR (200 MHz, C6D6, 25 °C): δ 7.02-7.09 (m, 5H, ArH),
0.96 (s, 18H, C (CH3)3) ppm. 19F NMR (188.29 MHz, C6D6): δ
-64.4 (s, 1F, Si-F), -92.1 (br, 2F, o-F), -133.2 (br, 2F, m-F)
ppm. 29Si NMR (99.36 MHz, C6D6, 25 °C): δ -97.9 (1J(29Si-19F)
) 282.72 Hz) ppm. EI-MS (70 eV; m/z (%)): 463 (35) [M]+, 428
(100) [M+-Cl]. Anal. Calcd for C20H23ClF5N3Si (463.95): C, 51.78;
H, 5.00; N, 9.06. Found: C, 51.96; H, 5.29; N, 8.97.
Synthesis of [CH(CdCH2)(CMe)(2,6-iPr2C6H3N)2]SiH(C6F5) (9).
A solution of pentafluorobenzene (0.17 g, 1.00 mmol in 5 mL of
toluene) was added by cannula to a solution of 1 (0.490 g, 1.00
mmol in 25 mL of toluene) at room temperature. After 12 h all the
(32) Weast, R. C. CRC Handbook of Chemistry and Physics, 67th ed.; CRC
Press, FL, 1986, pp F186-F187.
9
J. AM. CHEM. SOC. VOL. 132, NO. 29, 2010 10169

A R T I C L E S
Jana et al.
volatiles were removed in vacuo, and the remaining residue was
extracted with n-hexane (15 mL), concentrated to about 5 mL, and
stored in a freezer at -30 °C. Colorless crystals of 9 suitable for
X-ray diffraction analysis are formed after one day. Yield 0.54 g
(90%). Mp 152 °C. 1H NMR (200 MHz, C6D6, 25 °C): δ 6.77-7.15
(m, 6H, ArH), 5.46 (br, 2H; CH and SiH), 4.02 (s, 1H, CH2), 3.74
(sept, 1H, CH(CH3)2), 3.63 (sept, 1H, CH(CH3)2), 3.45 (s, 1H, CH2),
3.24 (sept, 1H, CH(CH3)2), 3.10 (sept, 1H, CH(CH3)2), 1.01-1.67
(m, 21H; CH3 and CH(CH3)2), 0.41 (d, 6H, CH (CH3)2) ppm. 19F
NMR (188.29 MHz, C6D6): δ -122.8 (d, 1F, o-F), -131.8 (d, 1F,
o-F), -149.6 (t, 1F, p-F), -160.2 (t, 1F, m-F), -161.7 (t, 1F, m-F)
ppm. 29Si NMR (99.36 MHz, C7D8, 25 °C): δ -41.2 (J(29Si-1H)
) 261.63 Hz) ppm. EI-MS (70 eV; m/z (%)): 597 (100) [M+-Me].
Synthesis of [PhC(NtBu)2]SiFCl(4-C6F4H) (10). A solution of
pentafluorobenzene (0.17 g, 1.00 mmol in 5 mL of toluene) was
added by cannula to a solution of 2 (0.29 g, 1.00 mmol in 25 mL
of toluene) at room temperature. After 12 h all the volatiles were
removed in vacuo, and the remaining residue was extracted with
toluene (15 mL) to yield compound 10. Yield 0.34 g (75%). Mp
solution to yield compound 11. Yield 0.120 g (82%). Mp 208 °C.
1H NMR (200 MHz, C6D6, 25 °C): δ 7.03-7.15 (m, 6H, ArH),
6.33 (m, 1H, Ar-H), 5.85 (m, 1H, Ar-H), 5.54 (s, 1H, CH), 5.42
(br, 1H, SiH), 3.99 (s, 1H, CH2), 3.84 (sept, 1H, CH(CH3)2), 3.67
(sept, 1H, CH(CH3)2), 3.36 (br, 2H, CH2 and CH(CH3)2), 3.16 (sept,
1H, CH(CH3)2), 3.10 (sept, 1H, CH(CH3)2), 1.62 (s, 3H, CH3),
1.14-1.43 (m, 18H, CH(CH3)2), 0.49 (d, 6H, CH (CH3)2) ppm.
19F NMR (188.29 MHz, C6D6): δ -90.4 (br, 1F, o-F), -99.6 (br,
1F, o-F), -103.9 (m, 1F, p-F). 29Si NMR (99.36 MHz, C6D6, 25
°C): δ -40.1 (J(29Si-1H) ) 256.3 Hz) ppm. EI-MS (70 eV; m/z
(%)): 576 (100) [M]+.
Crystallographic Details for Compounds 3, 7, 8, and 9. Suitable
crystals of 3, 7, 8, and 9 were mounted on a glass fiber, and data
was collected on an IPDS II Stoe image-plate diffractometer
(graphite monochromated Mo KR radiation, λ ) 0.71073 Å) at
133(2) K. The data was integrated with X-area. The structures were
solved by Direct Methods (SHELXS-97)33 and refined by full-
matrix least-squares methods against F2 (SHELXL-97).33 All non-
hydrogen atoms were refined with anisotropic displacement pa-
rameters. The hydrogen atoms were refined isotropically on
calculated positions using a riding model except hydrogen bound
to silicon, which was found and refined freely.
1
126 °C. H NMR (200 MHz, C6D6, 25 °C): δ 6.97-7.05 (m, 5H,
ArH), 6.48 (m, CH), 0.99 (s, 18H, C (CH3)3) ppm. 19F NMR (188.29
MHz, C6D6): δ -59.2 (s, 1F, Si-F), -126.3 (br, 2F, o-F), -133.4
(br, 2F, m-F) ppm. 29Si NMR (99.36 MHz, C6D6, 25 °C): δ -96.0
(1J(29Si-19F) ) 288.84 Hz) ppm. EI-MS (70 eV; m/z (%)): 462
(20) [M]+, 427 (100) [M+-Cl].
Acknowledgment. This work was supported by the Deutsche
Forschungsgemeinschaft.
Synthesis of [CH(CdCH2)(CMe)(2,6-iPr2C6H3N)2]SiH(1,3,5-
C6F3H3) (11). An NMR tube was loaded with 1,3,5-trifluorobenzene
(0.033 g, 0.25 mmol) and 1 (0.11 g, 0.25 mmol) at room
temperature. After that benzene-d6 (0.6 mL) was added, and the
sealed NMR tube was kept in an oil bath at 60-70 °C. After 12 h
Supporting Information Available: X-ray data for 3, 7, 8,
and 9 (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
JA103988D
1
the H NMR spectrum was recorded showing the formation of
compound 11. The solution from the NMR tube was transferred
into a Schlenk flask; after that all volatiles were removed from the
(33) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.
9
10170 J. AM. CHEM. SOC. VOL. 132, NO. 29, 2010