Lewis base mediated autoionization of GeCl2 and SnCl2

Article abstract of DOI:10.1021/ja300563g

Cationic and anionic species of heavier low-valent group 14 elements are intriguing targets in main group chemistry due to their synthetic potential and industrial applications. In the present study, we describe the synthesis of cationic (MCl⁺) and anionic (MCl₃^-) species of heavier low-valent group 14 elements of germanium(II) and tin(II) by using the substituted Schiff base 2,6-diacetylpyridinebis(2,6-diisopropylanil) as Lewis base (LB). Treatment of LB with 2 equiv of GeCl₂·dioxane and SnCl₂ in toluene gives compounds [(LB)Ge^IICl] ⁺[Ge^IICl₃]^- (1) and [(LB)Sn ^IICl]⁺[Sn^IICl₃]^- (2), respectively, which possess each a low-valent cation and an anion. Compounds 1 and 2 are well characterized with various spectroscopic methods and single crystal X-ray structural analysis.

Full text of DOI:10.1021/ja300563g

Article
pubs.acs.org/JACS
Lewis Base Mediated Autoionization of GeCl2 and SnCl2
Amit Pratap Singh,† Herbert W. Roesky,*,† Elena Carl,† Dietmar Stalke,*,† Jean-Philippe Demers,‡
and Adam Lange‡
†Institut fur Anorganische Chemie, Georg-August-Universitat, Tammannstrasse 4, D-37077 Gottingen, Germany
̈
̈
̈
‡Max-Planck-Institut fur Biophysikalische Chemie, Am Faßberg 11, D-37077 Gottingen, Germany
̈
̈
S
* Supporting Information
ABSTRACT: Cationic and anionic species of heavier low-valent group 14 elements are
intriguing targets in main group chemistry due to their synthetic potential and industrial
applications. In the present study, we describe the synthesis of cationic (MCl+) and anionic
−
(MCl3 ) species of heavier low-valent group 14 elements of germanium(II) and tin(II) by
using the substituted Schiff base 2,6-diacetylpyridinebis(2,6-diisopropylanil) as Lewis base
(LB). Treatment of LB with 2 equiv of GeCl2·dioxane and SnCl2 in toluene gives
compounds [(LB)GeIICl]+[GeIICl3]− (1) and [(LB)SnIICl]+[SnIICl3]− (2), respectively,
which possess each a low-valent cation and an anion. Compounds 1 and 2 are well char-
acterized with various spectroscopic methods and single crystal X-ray structural analysis.
cations by cyclopentadienyl-, N-isopropyl-2-(isopropylamino)-
INTRODUCTION
■
troponimine-, or cyclophane-group is possible.10 Notable inves-
tigations on four valence electron species RM:+ with suitable
anions have been documented in the literature. Schmidbaur and
co-workers11 isolated an aluminate of a germanium(II) cation.
Recently, Baines and colleagues12 reported the triflate of a
germanium(II) cation as byproduct in the synthesis of a
cryptand encapsulated germanium dication. Further, Reid and
co-workers13 synthesized and structurally characterized
germanium(II) halide complexes with neutral N-donor ligands.
Alternatively, an unconventional method for the stabilization of
divalent cations of group 14 elements is their coordination
to transition metals,14 which was successfully applied for
the synthesis of trans-[(η1 -Cp*)GeW(MeCN)-
(Ph2PCH2CH2PPh2)2][B(C6F5)4], [L(OTf)Ge][W(CO)5]
(L = NPhC(Me)CHC(Me)NPh) and [(C6H3-2,6-Mes2)SnW-
(Ph2PCH2CH2PPh2)2][PF6], [{2,6-(Me2NCH2)2C6H3}(H2O)-
SnW(CO)5][CB11H12].
The chemistry of the heavier group 14 elements has been driven
by their industrial applications especially for electronic materials.1
During the past two decades, chemists have been largely moti-
vated to study the reactivity of compounds with low-valent
germanium and tin due to their higher stability when compared
with the carbon and silicon analogues.2,3 Tin dichloride is a very
common reducing agent,4 usually applied for the precipitation of
metals such as silver and mercury and for the reduction of Fe3+
to Fe2+. The first step of the autoionization might be the forma-
tion of the SnCl3− anion, which attacks the positively charged
metal cation. Already in 1972 G. W. Parshall showed that molten
alkyl ammonium salts of R4N+SnCl3 could be used for
−
hydrogenation reaction of olefins.5 Cationic species of low-
valent heavier group 14 elements with the composition of RM:+
(R = halide, organic group) are intriguing to image the reactivity,
which combines the ambiphilic nature of a Lewis base and high
electrophilicity of a cation.6 In organic chemistry, carbenes and
N-heterocyclic carbenes are well-known.7 However, to the best
of our knowledge, dissociation of a carbene of composition R2C:
to the ionic species RC:+ and R3C:− has so far not been observed.
These cationic and anionic species of heavier group 14 elements
can be prepared by adding a Lewis acid (LA) and a chloride base,
respectively, to the neutral MCl2 species (Scheme 1).8
Herein, we report the Lewis base mediated autoionization of
MCl2 to cationic (MCl+) and anionic (MCl3−) species, where M is
germanium or tin. Two novel compounds [(LB)GeIICl]+[GeIICl3]−
(1) and [(LB)SnIICl]+[SnIICl3]− (2) have been synthesized by
reacting the substituted Schiff base 2,6-diacetylpyridinebis(2,6-
diisopropylanil) (LB) with the corresponding metal dichloride.
Compounds 1 and 2 have both the cationic [(LB)MIICl]+ as
well as the anionic [MIICl3]− species of their respective low-
valent group 14 elements.
Scheme 1. Preparation of Cations and Anions
RESULTS AND DISCUSSION
■
Synthesis. The ligand (LB) was treated separately with
GeCl2·dioxane and SnCl2 in a ratio of 1:2 in toluene at room tem-
perature under a nitrogen atmosphere to afford the compounds
Moreover, covalently bound substituents on cationic centers of
heavier group 14 elements are required to provide steric and
electronic stabilization to protect the positively charged species
from reactions with solvent and counteranions.9 It is evident from
the pioneering work that the stabilization of RGe:+ or RSn:+
Received: January 18, 2012
Published: February 13, 2012
© 2012 American Chemical Society
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[(LB)GeIICl]+[GeIICl3]− (1) and [(LB)SnIICl]+[SnIICl3]− (2),
respectively (Scheme 2). Compounds 1 and 2 are highly soluble
around the tin center of the SnCl3− anion occurs at low temperature
in the absence of a solvent is thus invalidated; the shifts observed in
solution-state NMR are rather related to a solvent effect.
Crystal Structure Analysis. To establish unambiguously
the structural feature of compounds 1 and 2, single crystal
X-ray structural analysis was carried out. Suitable single crystals
of 1 and 2 were obtained from saturated toluene solutions at
room temperature. Both compounds 1 and 2 are isostructural
and crystallize in the triclinic crystal system with space group
Scheme 2. Synthesis of Compounds 1 and 2
P1 (Table 1). The molecular structures of 1 and 2 reveal that
̅
one cation [(LB)MIICl]+ and one anion [MIICl3]− are present
in the same crystal lattice where M = Ge for 1 (Figure 1 ) and
M = Sn for 2 (Supporting Information Figure S2). In the cation
[(LB)MIICl]+, the metal center is connected to three nitrogen
atoms of the ligand (LB) and one chlorine atom. Three
nitrogen atoms N1, N2, and N3 of the ligand along with the
metal atom M1 form a basal plane. The metal center in the
cation [(LB)MIICl]+ adopts a distorted square pyramidal
geometry if the electron lone pair of M1 is considered at
fourth position of the basal plane. The chlorine atom occupies
the top of the square pyramid. This arrangement of ligand (LB)
gives rise to two five-membered chelating rings. The
coordination bond formed by the nitrogen atom N1 and M1
is acting as a bridge between these two rings. In case of
compound 1, the Ge−N1, Ge−N2, and Ge−N3 bond distances
are 2.071(2), 2.255(2), and 2.267(2) Å. Other structurally
characterized Ge(II) species with N-donor ligands are mostly
dicationic, for example, [Ge(Me4-cyclam)]2+ and [Ge(Me3-
tacn)]2+ for which the average Ge−N distance is 2.250 and
2.140 Å.16 However, the M−N bond distances of heavier group
14 elements would be influenced by the metal oxidation state
and its coordination number. In compound 2, the Sn1−N1
bond distance (2.286 Å) is significantly shorter than that of
Sn1−N2 (2.403 Å) and Sn1−N3 (2.411 Å). A similar trend is
also observed in compound 1, although the average Sn1−N
bond distance (2.366 Å) of 2 is comparatively longer than the
average Ge1−N bond length (2.197 Å) of 1. The angles
delaminated at the M1 metal center, within the five-membered
chelate rings N1−M1−N2 and N1−M1−N3, are 73.52(7) and
73.28(7)° for 1, and 68.71(7) and 68.79(7)° for 2. In the cation
[(LB)MIICl]+ of 1 and 2, the chlorine atom attached to the
metal center is oriented nearly perpendicular to the basal plane
constituted by the nitrogen atoms N1, N2, and N3 of the ligand
with M1−Cl1 bond distance of 2.2433(9) and of 2.4359(10) Å,
respectively. The average N−M1−Cl1 bond angle is 89.84° and
86.69° for compounds 1 and 2, respectively. In the anion
[MIICl3]− of 1 and 2, three chlorine atoms (Cl2, Cl3, and Cl4)
are attached to the metal ion M2, resulting in a trigonal
pyramidal shape of the anion. The average M2−Cl bond length
for 1 and 2 is 2.316 and 2.495 Å, while the average Cl−M2−Cl′
bond angle is 96.37 and 94.32°, respectively. Small differences
in the bond lengths and bond angles of 1 and 2 can be
explained by the different radii of Sn and Ge. The superposition
plot of both the compounds 1 and 2 is depicted in Figure S3.
Selected bond distances and bond angles for both compounds
are summarized in Table 2.
in polar solvents like tetrahydrofuran (THF) but sparingly soluble
in nonpolar solvents indicating the ionic nature of these com-
pounds. Highly saturated solutions of compounds 1 and 2 give
crystalline products in an excellent yield (80−85%). Furthermore,
they are stable both in solution and in the solid state for a long
period of time without any decomposition under an inert gas
atmosphere. These compounds have been fully characterized by
elemental analysis, solution- as well as solid-state 119Sn NMR
1
spectroscopy, and single crystal X-ray structural analysis. The H
NMR resonances were assigned by integration and comparison
with the signals of the free ligand. In compound 1 especially, aro-
matic protons resonate downfield (δ 8.99, 8.88, and 7.15 ppm) in
comparison to the free ligand (δ 8.52, 8.04, and 7.05 ppm), which
clearly indicates the coordination of the germanium with the
binding sites of the ligand, whereas in compound 2, the corre-
sponding results have been reciprocated with tin. Another inter-
esting observation in the 1H NMR spectrum are the CH3 protons
of the NC−CH3 groups, which exhibit two different res-
onances (2.64, 2.22 and 2.70, 2.30 ppm for compounds 1 and 2)
in comparison to the free ligand (CH3 protons of the NC−CH3
groups resonate at 2.31 ppm). We assume that this is probably due
to the coordination of the metal ion to the ligand binding sites
which result in a different electronic environment for the N
C−CH3 protons. Accordingly, the CH3 carbons of the N
C−CH3 groups in the 13C NMR spectrum resonate at two
different positions (29.12, 28.16 ppm for 1 and 24.21, 23.21 ppm
for 2), whereas in the free ligand, the resonances are observed at
28.32 ppm. To investigate the electronic environment around
the tin centers in compound 2, the solution- and solid-state 119Sn
NMR spectra were recorded at variable temperatures. The room
temperature solution-state 119Sn NMR spectrum consists of two
singlets at −60.2 and −435.0 ppm (Supporting Information
Figure S1). These two singlets correspond to two differently
coordinated tin(II) atoms present in compound 2. The
available literature data15 suggest that the broad signal at
−
−60.2 ppm corresponds to the SnCl3 anion, while the
remaining singlet at −435.0 ppm could be assigned to the
[(LB)SnCl]+ cation. The 119Sn NMR spectrum of compound 2
at low temperature varying in a range of 298−173 K indicates
that the tin center in the [(LB)SnCl]+ cation is intact.
However, a little broadening observed at 173 K is probably due
to inherent freezing properties of the THF-d8 solvent which
was used for the experiment. In addition, the downfield
−
resonance at −60.2 ppm for the SnCl3 anion shows a very
Solid-State 119Sn NMR Spectroscopy. Three tin sites
(A, B, and B′) are detected in solid-state 119Sn NMR, in con-
trast to the two tin resonances detected in solution-state NMR.
The isotropic chemical shifts (−77.4 ppm (A), −415.4 ppm
(B), and −431.5 ppm (B′)) indicated by red arrows in Figure 2,
are identified by recording the spectra at two different magic-
angle spinning rates (11.0 and 11.8 kHz). The chemical shift
irregular change in the position at low temperature. This
irregular change can be due to coordination of THF-d8 solvent
−
molecules to the SnCl3 anion leading to different geometrical
species. To test this hypothesis, solid-state 119Sn NMR was
recorded for compound 2. The spectra obtained in the range of
282−305 K were virtually unchanged at three different tem-
peratures. The possibility that a rearrangement of the geometry
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Table 1. Crystal and Structure Refinement Parameters for Compounds 1 and 2
parameters
1·1.5 toluene
C43.50H55Cl4N3Ge2
2·1.5 toluene
C43.50H55Cl4N3Sn2
Empirical formula
Formula Weight
CCDC no.
906.89
862039
triclinic
999.09
862038
triclinic
Crystal system
Space group
P1
̅
P1
̅
Unit cell dimensions
a = 10.330 (3) Å
b = 13.013 (3) Å
c = 16.873(7) Å
α = 93.66 (1)°
β = 97.33 (1)°
γ = 103.26 (1)°
2179.4 (12) Å3
a = 10.438 (2) Å
b = 13.174 (2) Å
c = 16.908(4) Å
α = 90.68 (1)°
β = 99.080 (1)°
γ = 103.21 (1)°
2226.8 (8) Å3
2
Volume
Z
2
Density (calcd)
1.382 g/cm3
1.490 g/cm3
Absorption coefficient
F (000)
1.658 mm−1
0.738 mm−1
938
1010
Crystal size
0.1 × 0.05 × 0.05 mm
1.22−26.94°
−12≤ h ≤ 13, −14≤k ≤ 16, −14≤ l ≤ 21
31860
0.1× 0.05 × 0.05 mm
0.97−20.60°
−13≤ h ≤ 13, −16≤k ≤ 16, −21≤ l ≤ 21
53144
θ range for data collection
Limiting indices
Reflections collected
Independent reflections
Completeness to θ
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ (I)]
R indices (all data)
Largest diff. peak and hole
64933 (Rint = 0.0398)
98.2% (θ = 26.83)
Full-matrix least-squares on F2
9181/30/518
9045 (Rint = 0.0628)
98.1% (θ = 26.60)
Full-matrix least-squares on F2
9044/96/513
1.045
1.030
R1 = 0.0253, wR2 = 0.0550
R1 = 0.0332, wR2 = 0.0569
R1 = 0.0306, wR2 = 0.0638
R1 = 0.0457, wR2 = 0.0684
0.939 and −1.124 eÅ−3
−3
0.387 and −0.291 eÅ
Figure 1. Molecular structure of [(LB)GeIICl]+[GeIICl3]− (1). Anisotropic displacement parameters are depicted at the 50% probability level.
Hydrogen atoms are omitted for clarity.
anisotropy δaniso = δzz − δiso is quite large for all three sites
(−617.5 ppm (A), −750 ppm (B), and −744.7 ppm (B′)) while
the asymmetry of the chemical shift anisotropy (CSA) tensor
ηasym = (δyy − δxx)/(δaniso) is close to 0 for all sites. Values of
the asymmetry such as 0.03 for sites A, B′, and 0.0 for site B
indicate an axially symmetric CSA tensor. The observed large
anisotropies are a distinctive feature of tin(II) species.17
By similarity to the solution-state 119Sn isotropic chemical shift,
site A is assigned to Sn2 in the SnCl3− anion (See Supporting
information Figure S1). The two latter sites (B and B′) share
similar values for isotropic and anisotropy chemical shift which
can be assigned to Sn1 in the [(LB)SnCl]+ cation. The
occurrence of two 119Sn resonances for Sn1 could arise because
of polymorphism in the sample, with site B′ as a minor
component. Indeed, the ratio of summed sideband
intensities (A/B/B′ 4:3:1) suggests a stoichiometry of 1:1
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a MBraun MB 150-GI glovebox maintained at or below 1 ppm of O2
and H2O. All solvents were dried by a MBraun solvent purifying
system prior to use. Substituted Schiff base ligand (LB) was prepared
using modified reported procedure. Other chemicals were purchased
Table 2. Selected bond lengths [Å] and angles [°]
Parameters for Compounds 1 and 2
bond lengths and angles
1
2
1
commercially and used as received. Solution-state H, 13C, and 119Sn
M(1)−N(1)
M(1)−N(2)
M(1)−N(3)
M(1)−Cl(1)
M(2)−Cl(2)
M(2)−Cl(3)
M(2)−Cl(4)
N(1)−M(1)−N(2)
N(1)−M(1)−N(3)
N(2)−M(1)−N(3)
N(1)−M(1)−Cl(1)
N(2)−M(1)−Cl(1)
N(3)−M(1)−Cl(1)
Cl(2)−M(2)−Cl(3)
Cl(2)−M(2)−Cl(4)
Cl(3)−M(2)−Cl(4)
2.071(2)
2.255(2)
2.267(2)
2.2433(9)
2.3100(8)
2.3246(9)
2.3128(9)
73.52(7)
73.28(7)
145.99(7)
94.25(6)
87.18(5)
88.09(5)
97.18(3)
97.17(3)
94.75(3)
2.286(2)
2.403(2)
2.411(2)
2.4359(10)
2.4801 (8)
2.5190(9)
2.4870(8)
68.71(7)
68.79(7)
136.87(7)
88.31(6)
86.18(6)
85.59(6)
93.03(3)
94.24(3)
95.69(3)
NMR spectra were recorded on a Bruker Avance DRX instrument
(300 or 500 MHz). The chemical shifts δ are given in ppm with
tetramethylsilane (1H and 13C) and Me4Sn (119Sn) as external
standards. Elemental analyses were performed by the Analytisches
Labor des Instituts fur Anorganische Chemie der Universitat
̈
̈
Gottingen. EI-MS were measured on a Finnigan Mat 8230 or a
̈
Varian MAT CH5 instrument.
Solid-State NMR. Compound 2 was loaded under an inert atmo-
sphere into a 4.0 mm MAS rotor. All spectra were recorded on a wide-
1
bore 9.4 T instrument (400 MHz, H Larmor frequency) at magic-
angle spinning rates of 11 or 11.8 kHz. 119Sn chemical shifts are given
in reference to Me4Sn, using the sharp resonance of tetracyclohexyltin
as external calibration. A cross-polarization contact time of 3.5 ms was
employed, with an effective acquisition time of 4 ms and a recycling
delay of 1 s. The full sideband pattern was acquired by the variable
offset cumulative spectrum technique,18 recording 9 subspectra span-
ning each a 75.2 kHz spectral window, and each time moving the 119Sn
rf carrier frequency by 37.6 kHz. The number of scans ranges from
50 176 to 71680 per subspectrum, for a total measurement time
ranging from 5 to 8 days per spectrum. The temperature was calibrated
between Sn2 and Sn1 sites which is in agreement with the
crystal structure of 2.
19
1
externally using the H chemical shift of nickelocene.
CONCLUDING REMARKS
Synthesis of 2,6-Diacetylpyridinebis(2,6-diisopropylanil)
(LB). The ligand (LB) was synthesized by a modified reported pro-
cedure.20 The 2,6-diisopropylaniline (7.34 mL, 38.61 mmol) was
added to the absolute ethanol (50 mL) solution of 2,6-diacetylpyridine
(3.00 g, 18.38 mmol). After the addition of a few drops of glacial acetic
acid, the solution was refluxed for 6 h. Volatiles were removed under
reduced pressure to afford a yellow colored solid product. The product
was crystallized from ethanol at low temperature which gives a white
colored crystalline compound (yield 7.34 g, 83%). 1H NMR
(500 MHz, THF-d8, TMS, 25 °C): δ 8.52 (d, 2H, Py−Hm), 8.04
(t,1H, Py−Hp), 7.05 (m, 6H, Ar−H), 2.83 (sept, 4H, Ar−CH(CH3)2),
2.31(s, 6H, NCCH3), 1.18 (m, 24 H, CHCH3) ppm. 13C NMR
(500 MHz, THF-d8, TMS, 25 °C): δ 167.04 (NC), 155.25 (Py−Co),
146.25 (Ar−Cip), 135.69 (Ar−Co), 123.75 (Ar−Cp), 123.02 (Py−Cp),
122.57 (Py−Cm), 122.30 (Ar−Cm), 28.32 (NC−CH3), 23.21
(CH(CH3)2), 17.15 (CH(CH3)2) ppm.
■
The carbenium ion RC:+ and carbanion R3C− analogues of
heavier low-valent group 14 elements with the composition of
RM:+ and R3M− have potential application in synthesis and
industrial processes. In the present study, we have demon-
strated a completely new approach to the synthesis of such low-
valent cationic and anionic species for heavier group 14 metals
by using a Lewis base (LB). Two novel compounds
[(LB)GeIICl]+[GeIICl3]− (1) and [(LB)SnIICl]+[SnIICl3]− (2)
have been synthesized and well characterized with various
spectroscopic techniques and single crystal X-ray structural
analysis. Crystal structure analysis reveals that compounds 1
and 2 are isostructural to each other.
Synthesis of [(LB)GeCl]+[GeCl3]− (1). The solution of ligand LB
(500 mg, 1.03 mmol) in toluene (50 mL) was added to solid
GeCl2·dioxane (480 mg, 2.07 mmol) at room temperature (25 °C).
EXPERIMENTAL SECTION
All manipulations were performed in a dry and oxygen free
atmosphere (N2) using standard Schlenk-line techniques and inside
■
Figure 2. Solid-state 119Sn NMR cross-polarization spectra of compound 2 at 11.0 kHz (a and c) and 11.8 kHz (b and d). Experimental (a and b)
and simulated (c and d) spectra, as obtained from the fitting of spinning sideband intensities.
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The reaction mixture was stirred for 12 h at this temperature. Then, all
volatiles were removed under vacuum. The residue was washed with n-
hexane (50 mL) to afford a red colored solid. The crude compound
was again dissolved in a minimum amount of toluene and filtered
through the pad of Celite in a medium porosity frit. The filtrate was
stored 3 days at room temperature to give a red crystalline compound
suitable for single crystal analysis (yield 654 mg, 82%). Elemental
analysis (%) calcd for C47H51Cl4N3Ge2 (953.08): C, 59.23; H, 6.24; N,
4.41. Found: C, 59.76; H, 6.34; N, 4.89. 1H NMR (500 MHz, THF-d8,
TMS, 25 °C): δ 8.99 (t, 1H, Py−Hp), 8.88 (d, 2H, Py−Hm), 7.15 (m,
6H, Ar−H), 2.83 (sept, 4H, CH(CH3)2), 2.64 (s, 3H, NC−CH3),
2.22 (s, 3H, NC−CH3), 1.15 (m, 24H, CH(CH3)2) ppm. 13C NMR
(500 MHz, THF-d8, TMS, 25 °C): δ 150.14 (NC), 139.25 (Py−
Co), 138.21 (Ar−Cip), 137.23 (Ar−Co), 134.55 (Ar−Cp), 127.02 (Py−
Cp), 124.57 (Py−Cm), 123.30 (Ar−Cm), 29.12 (NC−CH3), 28.16
(NC−CH3′), 25.29 (CH(CH3)2), 24.31(CH′(CH3)2), 19.35
(CHCH3), 18.65 (CHCH3′) ppm. EI-MS: m/z (%) 590 (100)
[(LB)GeCl]+, 178 (100) [GeCl3]+.
ACKNOWLEDGMENTS
■
H.W.R. thanks the Deutsche Forschungsgemeinschaft for support
(DFG RO 224/55-3). D.S. is grateful for funding from the DFG
Priority Programme 1178, the DNRF funded Center for Materials
Crystallography (CMC) for support, and the Land Niedersachsen
for providing a fellowship in the Catalysis for Sustainable
Synthesis (CaSuS) Ph.D. program. J.-P.D. thanks NSERC of
Canada for a Postgraduate Scholarship. A.L. thanks the Deutsche
Forschungsgemeinschaft for an Emmy Noether Fellowship. This
paper is dedicated to Professor R. Adams on the occasion of his
65th birthday.
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Synthesis of [(LB)SnCl]+[SnCl3]− (2). Compound 2 was syn-
thesized by a similar procedure as compound 1 using SnCl2 (394 mg,
2.07 mmol) instead of GeCl2·dioxane. A saturated toluene solution of
compound 2 gives yellow colored crystals suitable for structural
analysis (yield 759 mg, 85%). Elemental analysis (%) calcd for
C47H51Cl4N3Sn2 (1045.22): C, 54.01; H, 5.69; N, 4.02. Found: C,
54.56; H, 5.34; N, 4.39. 1H NMR (500 MHz, THF-d8, 25 °C, TMS): δ
9.01 (t, 1H, Py−Hp), 8.89 (d, 2H, Py−Hm), 7.17 (m, 6H, Ar−H), 3.05
(sept, 4H, CH(CH3)2), 2.70 (s, 3H, NC−CH3), 2.30 (s, 3H, N
C−CH3′), 1.16 (m, 24H, CH(CH3)2) ppm. 13C NMR (500 MHz,
THF-d8, TMS, 25 °C): δ 147.04 (NC), 138.25 (Py−Co), 136.25
(Ar−Cip), 135.69 (Ar−Co), 133.75 (Ar−Cp), 125.02 (Py−Cp), 122.57
(Py−Cm), 122.30 (Ar−Cm), 28.32 (NC−CH3), 27.36 (NC−
CH3′), 24.21 (CH(CH3)2), 23.21(CH′(CH3)2), 18.15 (CHCH3),
17.35 (CHCH3′) ppm. 119Sn NMR (500 MHz, THF-d8, Me4Sn, 25
°C): δ −60.27 and −435.07 ppm. EI-MS: m/z (%) 636 (100)
[(LB)SnCl]+, 224 (100) [SnCl3]+.
Crystal Structure Determination. Suitable single crystals for
X-ray structural analysis of compounds 1 and 2 were mounted at low
temperature under nitrogen atmosphere by applying the X-TEMP-2
device.21 The diffraction data for compound 1 were collected at 100 K
on Bruker TXS-Mo rotating anode with Helios mirror optics and an
APEX II detector with D8 goniometer. Data for 2 were collected at
100 K on SMART APEX Quazar with INCOATEC Ag microsource
with mirror optics (λ = 0.56086 Å). The data were integrated with
SAINT22 and an empirical absorption correction with TWINABS23 for
1 and SADABS24 for 2 was applied. The structures were solved by
direct methods (SHELXS-97) and refined against all data by full-
matrix least-squares methods on F2 (SHELXLE v 0.477).25 All non-
hydrogen-atoms were refined with anisotropic displacement parame-
ters. The hydrogen atoms were refined isotropically on calculated posi-
tions using a riding model with their Uiso values constrained to 1.5 Ueq
of their pivot atoms for terminal sp3 carbon atoms and 1.2 times for all
other carbon atoms (Table 1).
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ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files for 1 and 2, solution-state 119Sn NMR, and molecular
structure of 2. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
hroesky@gwdg.de; dstalke@chemie.uni-goettingen.de
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M. R.; Ragogna, P. J.; Macdonald, C. L. B.; Baines, K. M. Angew.
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Notes
The authors declare no competing financial interest.
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