Oxidative addition versus substitution reactions of group 14 dialkylamino metalylenes with pentafluoropyridine

Article abstract of DOI:10.1021/ic302344a

Dialkylamino compounds of group 14 elements (Si, Ge, Sn) in the +2 oxidation state supported by benzamidinate ligands were synthesized and treated with pentafluoropyridine. Two different modes of reactivity were observed, depending on the metal atom and the basicity of the substituent at the metal. Pentafluoropyridine undergoes oxidative addition reaction at the Si(II) and Ge(II) atoms whereas at the Sn(II) atom substitution of the NMe₂ group by the para fluorine of pentafluoropyridine occurs. The C-F bond activation by the lone pair of germanium is the first report of this kind. The Sn(II) fluoride obtained has an elongated Sn-F bond length and can be used as a good fluorinating agent. The compounds were characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray structural analysis. Single crystal X-ray structural analysis of the tin fluoride shows an asymmetric dimer with weak interactions.

Full text of DOI:10.1021/ic302344a

Article
pubs.acs.org/IC
Oxidative Addition Versus Substitution Reactions of Group 14
Dialkylamino Metalylenes with Pentafluoropyridine
Prinson P. Samuel, Amit Pratap Singh, Sankaranarayana Pillai Sarish, Julia Matussek, Ina Objartel,
Herbert W. Roesky,* and Dietmar Stalke*
Institut fur Anorganische Chemie, Georg-August-Universitat, Tammannstrasse 4, D-37077, Gottingen, Germany
̈
̈
̈
S
* Supporting Information
ABSTRACT: Dialkylamino compounds of group 14 elements
(Si, Ge, Sn) in the +2 oxidation state supported by
benzamidinate ligands were synthesized and treated with
pentafluoropyridine. Two different modes of reactivity were
observed, depending on the metal atom and the basicity of the
substituent at the metal. Pentafluoropyridine undergoes
oxidative addition reaction at the Si(II) and Ge(II) atoms
whereas at the Sn(II) atom substitution of the NMe2 group by
the para fluorine of pentafluoropyridine occurs. The C−F bond activation by the lone pair of germanium is the first report of this
kind. The Sn(II) fluoride obtained has an elongated Sn−F bond length and can be used as a good fluorinating agent. The
compounds were characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray structural
analysis. Single crystal X-ray structural analysis of the tin fluoride shows an asymmetric dimer with weak
interactions.
the lack of convenient synthetic routes and their instability at
room temperature.11 However, very recently we were successful
in synthesizing a lead(II) fluoride in the reaction of a β-
diketiminatolead(II) amine with pentafluoropyridine.12 In this
reaction the NMe2 group at the lead(II) atom was substituted
by the para fluorine atom of pentafluoropyridine affording
L′PbF (L′ = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3). This
encouraged us to follow a similar protocol to investigate the
general applicability of LE(II)(NR2) complexes (L = PhC-
(NtBu)2; E = Si, Ge, Sn; R = Me, iPr) to obtain organo Si(II),
Ge(II), and Sn(II) fluorides. In addition to this, we are
interested to utilize pentafluoropyridine as a fluorinating agent
and as an alternative to the widely used trimethyltin fluoride,
because the byproduct trimethyltin chloride is highly toxic. For
example, studies have proven that trimethyltin chloride could
induce hypokalemia in rats which eventually led to their death
due to respiratory failure.13
In a prior publication we reported the preparation of
dimethylamino silylene, LSi(NMe2) (4), by the reduction of
LSiCl2(NMe2) with potassium.14 However, to explore the
chemistry of dimethylamino silylene in detail, it was essential to
develop a more convenient and high yield based protocol. In
this regard, very recently we reported the synthesis of various
functionalized silylenes (LSiNR2) (L = PhC(NtBu)2; R =
SiMe3, Me, iPr, Cy, Ph) by the treatment of LSiCl with the
corresponding alkali metal amides.14b In a similar way, the
analogous compounds LGeNiPr2 (5) and LSnNMe2 (6) were
INTRODUCTION
■
Heavier carbene analogues of silicon, germanium, and tin are
known as silylenes, germylenes, and stannylenes, respectively.
Like carbon in carbene, they exhibit the +2 oxidation state. The
first stable N-heterocyclic silylene was reported by West et al. in
1994,1 whereas the first N-heterocyclic germylene was isolated
by Veith et al. in 1982.2 The first monomeric stannylene was
synthesized in 1976.3 Since then a number of room
temperature stable silylenes,4a−g germylenes,4h−n and stannyle-
nes4o,p were prepared and structurally characterized. Among
them the chemistry of functionalized silylenes, germylenes, and
stannylenes attracted tremendous attention in the past decade.
The advent of these compounds opened an interesting research
field of group 14 elements with much attention to compounds
containing low valent atoms bearing hydrides, hydroxyl groups,
or halides. In 2006, we successfully prepared the first
heteroleptic chloro silylene (LSiCl (1), L = PhC(NtBu)2)
stabilized by a benzamidinato ligand with tBu substituents on
the nitrogen atoms.5 Later on, we reported the congeners
LGeCl (2)6 and LSnCl (3).7 These compounds were widely
utilized to explore the chemistry of low valent group 14
elements.
In contrast to the ample documentation of chlorides of group
14 elements, reports on fluorides are scarce even if they have
found wide application in the laboratory as well as in industry.8
In the literature, the known group 14 fluoro compounds are
preferentially in the +4 oxidation state. Only a few examples of
organo germanium(II) and tin(II) fluorides are known.9,10 In
contrast to the rich documentation on other silicon halides, the
silicon(II) fluorides are scarcely known in literature, because of
Received: October 26, 2012
Published: January 23, 2013
© 2013 American Chemical Society
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synthesized from 2 and 3, respectively. Herein we report the
synthesis of benzamidinato dialkylamino germylene and
stannylene [LENR2, L = PhC(NtBu)2; E = Ge, R = iPr (5);
and E = Sn, R = Me (6)] and the different modes of reactivity
of 4−6 with pentafluoropyridine. In contrast to the behavior of
LSiNMe2 and LGeNiPr2 toward pentafluoropyridine, where
oxidative addition of one C−F bond occurs at the Si(II) and
Ge(II) atoms, the NMe2 group in LSnNMe2 undergoes
substitution by the para fluorine atom of pentafluoropyridine.
Also we show by some preliminary results that the new Sn(II)F
compound might function as an effective and soluble
fluorinating agent in organometallic chemistry.
But the reaction of LSiNMe2 (4) with pentafluoropyridine
followed a different route, leading to the formation of
LSiF(NMe2)(C5F4N) (7) (Scheme 2). The reaction proceeds
through the oxidative addition of one of the C−F bonds of
C5F5N to the silicon(II) atom. Moreover, the reaction
resembles our previous report in which the para fluorine
atom of the pentafluoropyridine is activated by silylenes.15 The
1H NMR spectrum of compound 7 shows two singlets (δ 0.70,
1.08 ppm) for the tBu protons and one singlet (δ 2.87 ppm)
corresponding to the NMe2 group. The 29Si NMR spectrum
exhibits a doublet (δ −100.25 ppm) with a coupling constant of
J(29Si−19F) = 310.99 Hz. The 19F NMR spectrum of compound
7 shows two doublets (δ −133.29, −93.75 ppm) corresponding
to the fluorine atoms in the C5F4N moiety and a singlet (δ
−84.68 ppm) originating from the fluorine atom bound to the
silicon atom. Compound 7 crystallizes in the space group P1
with one molecule in the asymmetric unit. (Figure 1) The
RESULTS AND DISCUSSION
■
The reaction of LGeCl (2) with LiNiPr2 at room temperature
afforded LGeNiPr2 (5) in good yield. Similarly, the reaction of
LSnCl with LiNMe2 yielded LSnNMe2 (6) (Scheme 1).
̅
Scheme 1. Preparation of 4, 5, and 6
Compounds 5 and 6 were characterized by NMR spectroscopy,
mass spectrometry, and elemental analysis. The 1H NMR
spectrum of 5 shows a singlet (δ 1.13 ppm) corresponding to
the tBu group and two other singlets (δ 1.31 and 1.61 ppm)
originating from the methyl protons of the NiPr2 group. The
CH protons of the iPr groups resonate at 3.53 and 3.80 ppm
indicating the difference in chemical environment for each of
the iPr groups due to the presence of a lone pair of electrons at
the germanium atom in different proximity. The tBu groups in
6 resonate at δ 0.97 ppm and the NMe2 resonance appears at
3.32 ppm. The 119Sn NMR spectrum of 6 exhibits a singlet (δ
16.57 ppm).
After the successful preparation of the dialkyl amino
functionalized silylene, germylene, and stannylene stabilized
by the benzamidinato ligand, we treated them with
pentafluoropyridine to obtain the corresponding fluorides
LE(II)F (E = Si, Ge, and Sn), inspired by our recent success
in obtaining L′PbF from L′PbNMe2 and pentafluoropyridine.
Figure 1. Molecular structure of 7. The anisotropic displacement
parameters are depicted at the 50% probability level. Selected bond
lengths [Å] and angles [deg]: Si1−F1 1.6563(8), Si1−C1 1.9343(13),
Si1−N1 1.7035(12), Si1−N3 1.9652(11), Si1−N4 1.8115(11); N3−
Si1−N4 69.04(5), N1−Si1−F1 96.80(5), C1−Si1−F1 88.58(5).
coordination polyhedron around the silicon atom features a
distorted trigonal bipyramidal geometry. The Si−F and Si−C
bond lengths are 1.6563(8) Å and 1.9343(13) Å, respectively.
The reaction of LGeNiPr2 (5) with pentafluoropyridine
(C5F5N) in toluene in a 1:1 molar ratio at room temperature
(Scheme 2) leads to the formation of the LGeF(NiPr2)-
(C5F4N) (8) through an oxidative addition pathway in contrast
to our expectation of a metathesis reaction. Such a reaction at
the amino substituted Ge(II) atom is surprising, and this is the
Scheme 2. Preparation of 7, 8, and 9
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first report of a C−F bond activation by a germylene lone pair.
It should be noted that the activity of the lone pair is highly
influenced by the functionalities attached to the germanium
atom. For instance, there is no reaction between LGeCl (2) and
C5F5N. Among the amino functionalized germylenes, LGeN-
(SiMe3)2 (see Supporting Information for preparation) does
not react with C5F5N, even at an elevated temperature of 60
°C, but LGeNMe2 (see Supporting Information for prepara-
tion) reacts very slowly at room temperature. The reaction of
LGeNMe2 with C5F5N proceeds in an uncontrolled protocol,
dimethylaminotetrafluoropyridine. This reaction is comparable
with the synthesis of 4-dimethylaminotetrafluoropyridine from
dimethyl amine or trimethylsilyl-dimethylamine (Me3SiNMe2)
and C5F5N.16a,b The energy required for the cleavage of the C−
F bond is compensated by the formation of the C−N bond. In
addition, the different modes of reactivity shown by Ge(II) and
Sn(II) with pentafluoropyridine are comparable to the oxidative
addition versus arene elimination reaction of Ar2Ge(II) and
Ar2Sn(II) [Ar = C6H3-2,6-(C6H3-2,6-iPr2)2] with ammonia and
hydrogen as reported by Power et al.16c The tBu resonance in
1
1
the H NMR spectrum of compound 9 appears at 1.09 ppm
and we were not able to isolate a clean product. However, H
and the 19F NMR spectrum shows the resonance at δ −98.06
ppm. The 119Sn NMR spectrum exhibits an upfield resonance
(δ −210.92 ppm) when compared with that of the starting
material (δ 16.57 ppm). However, the Sn−F coupling was not
observed in the spectra. The 119Sn NMR spectrum of 9 at a
reduced temperature of −60 °C in toluene-d8 showed a broad
resonance at δ −283.93 ppm.
and 19F NMR spectra clearly indicate the formation of 4-
dimethylaminotetrafluoropyridine (4-NMe2C5F4N), the by-
product of a metathesis reaction. We assume that both
metathesis and oxidative addition occur in parallel in the case
of LGeNMe2. The reaction of 2 with C5F5N is comparatively
faster, and it is unidirectional. From these observations it can be
concluded that the reactivity of the lone pair is tuned by the
basicity of the functional group attached to the germanium
atom. Obviously an increased basic nature results in the higher
activity of the lone pair. The 1H NMR spectrum of 8 shows two
singlets (δ 0.56 and 1.12 ppm) corresponding to the two tBu
groups. The methyl protons of the iPr groups appear as two
close doublets (δ 1.38 and 1.41 ppm) and the CH protons
resonate (δ 3.92 ppm) as a septet. The 19F NMR spectrum
shows two broad signals (δ −130.54 and −92.37 ppm)
originating from the fluorine atoms of the C5F4N unit and a
sharp resonance (δ −91.34 ppm) corresponding to the fluorine
atom bonded to the germanium atom. Compound 8 crystallizes
in the monoclinic space group P21/n and the coordination
environment around the germanium is distorted trigonal
bipyramidal similar to that of compound 7. (Figure 2) The
Ge−F bond length is 1.8009(8) Å, and the Ge−C bond length
shows 1.9944(14) Å.
Storing a saturated solution of 9 in toluene at −4 °C in a
freezer afforded single crystals suitable for X-ray diffraction
investigation. 9 crystallizes in the space group P21/c, and it
exists as a dimer in which two molecules are connected by weak
intermolecular Sn···F bonds (Figure 3). However, Lappert et al.
Figure 3. Molecular structure of 9. The anisotropic displacement
parameters are depicted at the 50% probability level. Selected bond
lengths [Å] and angles [deg]: Sn1−F1 2.0796(11), Sn1−F1′ 2.338,
Sn1−N1 2.1980(14), Sn1−N2 2.254(9); N1−Sn1−N2 59.83(17),
N1−Sn1−F1 97.18(5), N2−Sn1−F1 86.24(15).
reported a compound with Sn(μ-F)2Sn structure where all four
Sn−F bonds are equal each with a bond distance of 2.156 Å.10a
In compound 9 the Sn−F bond lengths are 2.0796(11) and
2.338 Å respectively showing the weak association of the two
molecules. This represents the first example where such an
arrangement of
was observed for a Sn(II)−F
Figure 2. Molecular structure of 8. The anisotropic displacement
parameters are depicted at the 50% probability level. Selected bond
lengths [Å] and angles [deg]: Ge1−F1 1.8009(8), Ge1−N3 =
1.8024(11), Ge1−C16 1.9944(14), Ge1−N1 1.9054(12), Ge1−N2
2.1623(12); N1−Ge1−N2 64.47(5), C16−Ge1−F1 87.74(5), N3−
Ge1−F1 98.56(5).
compound. Each Sn atom adopts a distorted square pyramidal
geometry with the lone pair of electrons in the axial position.
The base of the square pyramid is constituted by two nitrogen
atoms from the amidinate ligand, and the two fluorine atoms of
the Sn−F and Sn···F bonds. The dimeric arrangement of 9 in
solution was confirmed by osmometric molecular mass
determination in toluene. From these observations, it should
be noted that the absence of clear splitting of the 119Sn
resonance may be due to the presence of two chemically
nonequivalent fluorine atoms with respect to the Sn atom. The
Sn−F bond length of 2.0796(11) Å in 9 is of special interest
when compared with those of the monomeric organotin
fluorides containing Sn(IV) atoms. For example, the Sn−F
bond lengths in Me2[(PhMe2Si)3C]SnF,17 Ph2[(TMS)3C]-
SnF,17 and Mes3SnF18 are 1.965, 1.965, and 1.961 Å,
Unlike 4 and 5 the reaction of LSnNMe2 (6) with
pentafluoropyridine affords the anticipated LSnF (9) in a
metathesis reaction (Scheme 2) together with the formation of
4-dimethylaminotetrafluoropyridine (4-NMe2C5F4N). The re-
1
action achieved full conversion within 10 min. The H NMR
spectrum of the crude reaction mixture indicates the complete
disappearance of the resonance for NMe2 (δ 3.31 ppm) of 6,
and the formation of a new resonance (δ 2.54 ppm) for 4-
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Table 1. Crystal and Structure Refinement Parameters for Compounds 7, 8, and (9)2
parameters
CCDC No.
7
8
(9)2
899944
899945
899946
empirical formula
formula weight
crystal system
C22H29F5N4Si
472.58
C26H37F5GeN4
573.18
C30H46F2N4Sn2
738.09
triclinic
monoclinic
monoclinic
space group
P1
̅
P21/n
P21/c
unit cell dimensions
a = 9.2560(10) Å
b = 10.2020(10) Å
c = 13.9106(10) Å
α = 93.480(10)°
β = 92.283(10)°
γ = 115.677(10)°
1178.48(19) Å3, 2
1.332 Mg/m3
a = 15.1223(8) Å
b = 19.2483(10) Å
c = 19.8868(10) Å
β = 112.045(2)°
a = 10.149(3) Å
b = 9.614(2) Å
c = 16.921(2) Å
β = 99.62(2)°
volume, Z
5365.4(5) Å3, 8
1.419 Mg/m3
1.198 mm−1
1627.8(6) Å3, 2
1.506 Mg/m3
1.570 mm−1
density (calcd)
absorption coefficient
F (000)
0.156 mm−1
496
2384
744
crystal size/mm
θ range for data collection
limiting indices
0.1 × 0.1 × 0.08
1.471 to 27.894°.
−12 ≤ h ≤ 12
−13 ≤ k ≤ 13
−18 ≤ l ≤ 18
0.15 × 0.1 × 0.05
1.458 to 27.523°.
−19 ≤ h ≤ 19
−25 ≤ k ≤ 23
−25 ≤ l ≤ 25
0.325 × 0.290 × 0.277
2.035 to 26.788°
−12 ≤ h ≤ 12
−12 ≤ k ≤ 12
−21 ≤ l ≤ 21
40528
reflections collected
31603
98347
independent reflections
completeness to θ
5626 (Rint = 0.0332)
99.9% (θ = 25.242°)
full-matrix least-squares on F2
5626/0/297
12312 (Rint = 0.0364)
100.0% (θ = 25.242°)
full-matrix least-squares on F2
12312/0/669
3475 (Rint = 0.0284)
100.0% (θ = 25.242°)
refinement method
full-matrix least-squares on F2
3475/107/209
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.008
1.033
1.087
R1 = 0.0358, wR2 = 0.0872
R1 = 0.0433, wR2 = 0.0909
0.332 and −0.269 e Å−3
R1 = 0.0247, wR2 = 0.0576
R1 = 0.0299, wR2 = 0.0593
0.375 and −0.273 e Å−3
R1 = 0.0180, wR2 = 0.0409
R1 = 0.0205, wR2 = 0.0422
0.511 and −0.392 e Å−3
largest diff. peak and hole
respectively. The extended Sn−F bond length of 9 is an
interesting feature which is due to the larger ionic radius of
Sn(II) compared to that of Sn(IV). This increases the reactivity
in the case of Sn(II) fluorides when compared with those of
Sn(IV) fluorides. Interestingly, the Sn−F bond length in 9 is
still larger than that in L′SnF (1.988 Å) [L′ = HC(CMeNAr)2,
Ar = 2,6-iPr2C6H3] which we reported previously.10b
Subsequently compound 9 is presumed to have a large
synthetic utility as an effective fluorinating agent that does
not cause hazardous byproducts like Me3SnCl. To investigate
the fluorinating ability of 9 we treated this compound with
organic and inorganic substrates. The preliminary results from
our laboratory show the clean conversion of Me3SiCl, PhCOCl,
and CH(SiMe3)2PCl2 to Me3SiF, PhCOF, and CH(SiMe3)2PF2
respectively, and the formations of products were confirmed
from the corresponding resonances in the 19F NMR spectra.
Note that the conversion of CH(Me3Si)2PCl2 to CH(Me3Si)2)-
PF2 was completed in a few minutes at room temperature in
the presence of 2 equiv of 9 whereas the same conversion using
Me3SnF will take more than 6 h toward completeness at an
elevated temperature of 60 °C.
example of the C−F bond activation at a Ge(II) atom. Unlike 4
and 5, compound 6 undergoes the expected metathesis reaction
with pentafluoropyridine affording LSnF (9) with an elongated
Sn−F bond. Preliminary experiments show that compound 9 is
a promising mild fluorinating agent. Application of 9 for
synthesizing organometallic fluoride compounds are under
progress in our laboratory, and such results will be reported in
due course.
EXPERIMENTAL SECTION
■
Syntheses were carried out under an inert gas atmosphere of
dinitrogen in oven-dried glassware using standard Schlenk techniques.
Other manipulations were accomplished in a dinitrogen filled
glovebox. Solvents were purified by MBRAUN solvent purification
system MB SPS-800. All chemicals were purchased from Aldrich and
used without further purification. Compounds 1,5b 2,6 3,7 and 414b
were prepared as reported in the literature. H, 13C, and 29Si NMR
1
spectra were recorded with a Bruker Avance DPX 200 or a Bruker
Avance DRX 300 spectrometer, using C6D6 as solvent. Chemical shifts
δ are given relative to SiMe4. EI-MS spectra were obtained using a
Finnigan MAT 8230 instrument. Elemental analyses were carried out
in the Analytischen Labor der Anorganischen Chemie der Universitat
̈
Gottingen. Molecular mass determination was performed with a
KNAUER vapor pressure osmometer.
̈
CONCLUSION
■
Synthesis of 5. Toluene (50 mL) was added to a Schlenk flask
(100 mL) containing 2 (2 g, 5.88 mmol) and LiNiPr2 (0.62 g, 5.88
mmol). The reaction mixture was stirred at room temperature for 6 h.
The solution was filtered, and the solvent was reduced in vacuo to
about 10 mL and stored at −32 °C in a freezer for two days to obtain
5 as a white crystalline product. (1.92 g, 81%). Elemental analysis (%)
calcd for C21H37GeN3 (405.22): C, 62.40; H, 9.23; N, 10.40; Found:
C, 62.74; H, 9.10; N, 10.89. 1H NMR (200 MHz, C6D6, 25 °C): δ 1.13
Dialkylamino functionalized group 14 metalylenes LSiNMe2
(4), LGeNiPr2 (5), and LSnNMe2 (6) were synthesized, and
the reaction of these compounds with pentafluoropyridine was
probed. C−F bond activation of pentafluoropyridine occurred
at the Si(II) and the Ge(II) atoms of 4 and 5 followed by the
oxidative addition to yield LSiF(NMe2)(C5F4N) (7) and
LGeF(NiPr2)(C5F4N) (8). The formation of 8 is the first
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(s, 18 H, C(CH3)3), 1.31 (s, 6 H, CH(CH3)2), 1.61 (s, 6H,
CH(CH3)2), 3.53 (br, 1H, CH(CH3)2), 3.80 (br, 1H, CH(CH3)2),
6.95−7.22 (m, 5H, Ph) ppm. EI-MS: m/z 405 [M+].
squares methods against F2 (SHELXL-97)23b,c within the SHELXLE
GUI.23d All non-hydrogen atoms were refined with anisotropic
displacement parameters. The hydrogen atoms were refined isotropi-
cally on calculated positions using a riding model with their Uiso values
constrained to equal 1.5 times the Ueq of their pivot atoms for terminal
sp3 carbon atoms and 1.2 times for all other carbon atoms. Disordered
moieties were refined using bond length and angle restraints and
anisotropic displacement parameter restraints. Crystallographic data
(excluding structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre. The CCDC numbers, crystal data and experimental details for
the X-ray measurements are listed in Table 1.
Synthesis of 6. To a Schlenk flask (100 mL) containing 3 (2 g,
5.19 mmol) and LiNMe2 (0.26 g, 5.19 mmol) was added toluene (50
mL) at −60 °C. The reaction mixture was allowed to warm to room
temperature and stirring was continued for 6 h. The solution was
filtered, and concentrated in vacuo to about 10 mL and stored at −32
°C in a freezer for two days to obtain 6 as a white crystalline product.
(1.53 g, 75%). Elemental analysis (%) calcd for C17H29N3Sn (395.14):
1
C, 51.80; H, 7.42; N, 10.66; Found: C, 52.05; H, 7.26; N, 10.78. H
NMR (300 MHz, C6D6, 25 °C): δ 0.98 (s, 18 H, C(CH3)3), 3.32 (s, 6
H, N(CH3)2), 6.96−7.10 (m, 5H, Ph) ppm. 119Sn NMR (111 MHz,
C6D6): δ 16.57 ppm. EI-MS: m/z 395 [M+].
ASSOCIATED CONTENT
■
Synthesis of 7. To a toluene solution (30 mL) of 4 (1 g, 3.30
mmol) in a Schlenk flask (100 mL) pentafluoropyridine (0.58 g, 3.46
mmol) dissolved in toluene (10 mL) was added slowly at −60 °C. The
reaction mixture was allowed to warm to room temperature and
stirring was continued for 6 h. The solution was concentrated to
dryness, redissolved in toluene (20 mL), and stored at −4 °C in a
freezer for three days to obtain 7 as single crystals suitable for X-ray
diffraction. (1.21 g, 78%). Elemental analysis (%) calcd for
C22H29F5N4Si (472.21): C, 55.91; H, 6.19; N, 11.86; Found: C,
S
* Supporting Information
Preparation of LGeNMe2 and LGeN(SiMe3)2 and CIF files for
compounds 7−9. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
1
55.42; H, 6.29; N, 11.55. H NMR (300 MHz, C6D6, 25 °C): δ 0.70
*E-mail: hroesky@gwdg.de (H.W.R.), dstalke@chemie.uni-
goettingen.de (D.S.).
(s, 9 H, C(CH3)3), 1.08 (s, 9 H, C(CH3)3), 2.87 (s, 6 H, N(CH3)2),
6.87−6.98 (m, 5H, Ph) ppm. 29Si NMR (99.36 MHz, C6D6, 25 °C): δ
−100.25 (J(29Si−19F) = 310.99 Hz) ppm; 19F NMR (188.29 MHz,
C6D6): δ −84.68 (s, 1F, Si-F), −93.75 (d, 2F, o-F), −133.29 (d, 2F, m-
F) ppm. EI-MS: m/z 428 [M+−NMe2].
Notes
The authors declare no competing financial interest.
Synthesis of 8. To a toluene solution (30 mL) of 5 (1 g, 2.46
mmol) in a Schlenk flask (100 mL) pentafluoropyridine (0.43 g, 2.59
mmol) dissolved in toluene (10 mL) was added slowly at room
temperature and stirred for 4 h. The solution was concentrated to
dryness, the solid residue was redissolved in toluene (20 mL), and
stored at −4 °C in a freezer for a day to obtain single crystals of 8.
(1.04 g, 74%). Elemental analysis (%) calcd for C26H37F5GeN4
(574.22): C, 54.48; H, 6.51; N, 9.77; Found: C, 55.06; H, 6.23; N,
ACKNOWLEDGMENTS
■
We are thankful to the Deutsche Forschungsgemeinschaft and
Prohama, Ludwigshafen, for supporting this work. D.S. is
grateful to the DNRF funded Center for Materials Crystallog-
raphy (CMC) for support and Land Niedersachsen for
providing a fellowship in the Catalysis of Sustainable Synthesis
(CaSuS) Ph.D. program.
1
9.89. H NMR (200 MHz, C6D6, 25 °C): δ 0.56 (s, 9 H, C(CH3)3),
1.12 (s, 9 H, C(CH3)3), 1.37 (d, 6 H, CH(CH3)2), 1.40 (d, 6 H,
CH(CH3)2), 3.85−3.98 (sept, 2H, CH(CH3)2), 6.74−7.04 (m, 5H,
Ph) ppm. 19F NMR (188.29 MHz, C6D6): δ −91.34 (s, 1F, Ge-F),
−92.37 (br, 2F, o-F), −130.54 (br, 2F, m-F) ppm.
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