Synthesis, characterization and Twin Polymerization of a novel dioxagermine

Article abstract of DOI:10.1016/j.ica.2013.09.052

The synthesis of 6-bromo-2,2-di-tert-butyl-4H-1,3,2-benzo[d]dioxagermine (1) via an alcohol/alkoxide exchange starting from di-tert-butyl-di-ethoxy germane is reported. Characterization of the title compound including single crystal X-ray diffraction and TGA/DSC analysis, mass spectrometry, ¹H NMR, ¹³C{¹H} NMR and IR spectroscopy is reported. DFT-D calculations have been carried out to assign the absorption band maxima of the IR spectrum to the corresponding vibrational modes. The suitability for Twin Polymerization of the novel dioxagermine 1 has been studied by TGA/DSC analysis and mass spectrometry. Proton-assisted Twin Polymerization of 1 results in an organic-inorganic hybrid material composed of a phenolic resin and [ ^tBu₂GeO]_n.

Full text of DOI:10.1016/j.ica.2013.09.052

Inorganica Chimica Acta 409 (2014) 472–478
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization and Twin Polymerization of a novel
dioxagermine
Philipp Kitschke a, Alexander A. Auer b, Andreas Seifert c, Tobias Rüffer d, Heinrich Lang d,
Michael Mehring a,
⇑
a Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Professur Koordinationschemie, 09107 Chemnitz, Germany
b Max-Planck-Institut für Chemische Energiekonversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
c Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Professur Polymerchemie, 09107 Chemnitz, Germany
d Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Professur Anorganische Chemie, 09107 Chemnitz, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2013
Received in revised form 19 September 2013
Accepted 27 September 2013
Available online 9 October 2013
The synthesis of 6-bromo-2,2-di-tert-butyl-4H-1,3,2-benzo[d]dioxagermine (1) via an alcohol/alkoxide
exchange starting from di-tert-butyl-di-ethoxy germane is reported. Characterization of the title com-
pound including single crystal X-ray diffraction and TGA/DSC analysis, mass spectrometry, 1H NMR,
13C{1H} NMR and IR spectroscopy is reported. DFT-D calculations have been carried out to assign the
absorption band maxima of the IR spectrum to the corresponding vibrational modes. The suitability
for Twin Polymerization of the novel dioxagermine 1 has been studied by TGA/DSC analysis and mass
spectrometry. Proton-assisted Twin Polymerization of 1 results in an organic–inorganic hybrid material
composed of a phenolic resin and [tBu2GeO]n.
Keywords:
Twin Polymerization
Germanium
4H-1,3,2-benzo[d]dioxagermine
IR spectroscopy
Ó 2013 Elsevier B.V. All rights reserved.
Mass spectrometry
DFT calculations
1. Introduction
concerted generation of two polymers in one synthetic step starting
from a single monomer. An important aspect of this new type of
Germanium compounds derived from ortho-hydroxybenzyl
alcohol are known in the literature for 50 years now, with the first
report dating back to 1963, when Wieber et al. reported the synthe-
sis of 2,2-dimethyl-4H-1,3,2-benzo[d]dioxagermine [1]. Later on
Gragg et al. described the preparation of 2,2-di-n-butyl-4H-1,3,2-
benzo[d]dioxagermine and 2,2-diphenyl-4H-1,3,2-benzo[d]dioxag-
ermine applying the same synthesis strategy as reported by Wieber
et al. starting from the corresponding dichlorogermane and ortho-
hydroxybenzyl alcohol in the presence of a tertiary amine base.
The latter compounds were characterized by elemental analysis,
boiling point, refractive index and mass spectrometry [2]. Since
then no additional reports appeared in the literature and hence de-
tailed structural studies are still lacking. Here we report a straight-
polymerization is the formation of organic–inorganic hybrid mate-
rials, which exhibit a nanostructured composite of two interpene-
trating networks [3]. Hence further treatment of these hybrid
materials might give access to highly porous materials as was
reported recently by Spange et al. for the Twin Polymerization of
2,2-dimethyl-4H-1,3,2-benzo[d]dioxasiline, which is structurally
related to compound 1 [4,5]. We have chosen the bromo-substi-
tuted salicyl alcoholate rather than the non-substituted one as
ligand, because of the lower reactivity of the alcohol with regard
to Lewis acid promoted polymerization. The polymerization of the
alcohol was identified as major problem in attempts to synthesize
well defined monomers, for example, germanium alcoholates start-
t
ing from different salicyl alcohols [6]. The Bu2Ge-derivative was
forward synthesis and the full characterization of
a
new
identified as a good candidate for Twin Polymerization, because it
is a solid material easy to purify and exhibits solubility and a low
melting point. Its thermal behavior and fragmentation pattern
derived from mass spectrometry were studied in order to probe
suitability for thermally induced Twin Polymerization and proton-
assisted Twin Polymerization, which both were expected to provide
organic–inorganic hybrid materials composed of a phenolic resin
and [tBu2GeO]n.
representative of these cyclic germanium compounds, 6-bromo-
2,2-di-tert-butyl-4H-1,3,2-benzo[d]dioxagermine (1). The latter
compound 1 attracted our interest with regard to a novel synthetic
concept, the so called Twin Polymerization, which is defined as the
⇑
Corresponding author.
E-mail address: michael.mehring@chemie.tu-chemnitz.de (M. Mehring).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.09.052

P. Kitschke et al. / Inorganica Chimica Acta 409 (2014) 472–478
473
2.2. Synthesis of di-tert-butyl-di-ethoxy germane [8]
2. Material and methods
The compound was prepared according to the literature using a
modified synthetic procedure: Tetraethoxy germane (4.41 mL,
5.02 g, 19.5 mmol) was slowly added to 20.50 mL (39 mmol) of a
stirred solution of 1.9 M tert-butyl lithium in n-pentane at 0 °C.
The mixture was stirred at room temperature for 24 h. The result-
ing precipitate was removed by filtration. Excess of n-pentane was
removed under reduced pressure. The crude product was purified
by distillation at 8 * 10ꢁ2 mbar and 45–50 °C to give di-tert-bu-
tyl-di-ethoxy germane as colorless liquid (5.08 g, 94%); 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): d = 1.19 (s, 18H; CH3–tBu), 1.22
(t, 6H, CH3–OEt, J = 6.9 Hz), 3.88 ppm (q, 4H, CH2–OEt, J = 6.9 Hz);
13C{1H} NMR (125 MHz, CDCl3, 25 °C, TMS): d = 19.3 (CH3–OEt),
28.1 (CH3–tBu), 30.5 (Cq–tBu), 60.4 ppm (CH2–OEt).
All reactions were performed by using Schlenk techniques un-
der argon. Solvents were purified and dried by applying standard
techniques. All reactions were carried out with freshly distilled,
dried solvents. 1H and 13C{1H} NMR spectra were recorded on a
Bruker ‘‘Avance III 500’’ spectrometer at ambient temperature.
ATR-FT-IR spectra were recorded with a BioRad ‘‘FTS-165 spec-
trometer’’. Melting point evaluation was carried out with a ‘‘Melt-
ing Point B-540’’ apparatus from Büchi. Elemental analyses were
determined using a ‘‘vario MICRO’’ from Elementar Analysensys-
teme GmbH. TGA/DSC experiments were determined by using a
Mettler Toledo ‘‘TGA/DSC1 1600 system’’ with an MX1 balance.
The measurement was performed from 40 to 800 °C with a rate
of 10 K/min in Ar atmosphere and a volume flow of 60 mL/min.
GC–MS analysis was performed on a gas chromatograph ‘‘17 A’’
with a quadruple pole mass spectrometer ‘‘QP-5000’’ from Shima-
dzu. A non-polar column, type ‘‘OPTIMA-5’’ from Machery Nagel
consisting of polymethylphenylsiloxane (95% methyl-, 5% phenyl-
groups) was used. The injector temperature was set to 230 °C, a
split of 1:34 and a volume flow of the carrier gas helium of
1.4 mL/min was used. After 5 min at 50 °C the temperature was in-
creased to 320 °C with a rate of 10 K/min and then kept at this tem-
perature for 10 min. A solution of 1 in n-hexane was injected for
GC–MS analysis. The solid state NMR spectrum was collected at
9.4 T on a Bruker Avance 400 spectrometer equipped with double
tuned probes capable of MAS (magic angle spinning). 13C{1H} CP-
MAS NMR spectra were measured at 100.6 MHz in 3.2 mm stan-
dard zirconium oxide rotors (BRUKER) spinning at 20 kHz. Cross
polarization with a contact time of 5 ms was used to enhance sen-
sitivity. The recycle delay was 5 s. The spectrum was referenced
externally to tetramethylsilane (TMS) as well as to adamantane
as secondary standard (38.48 ppm for 13C). The spectra were col-
lected with 1H decoupling using a TPPM pulse sequence.
2.3. Synthesis of 6-bromo-2,2-di-tert-butyl-4H-1,3,2-
benzo[d]dioxagermine (1)
Di-tert-butyl-di-ethoxy germane (1.65 mL, 2.00 g, 7.22 mmol)
was slowly added to a stirred solution of 5-bromo-2-hydroxyben-
zyl alcohol (1.47 g, 7.22 mmol) in xylene (50 mL) under reflux. The
mixture was stirred under reflux for 36 h. After removal of the
xylene under reduced pressure (10ꢁ2 mbar, 90 °C) the crude prod-
uct was dissolved in n-pentane (20 mL). Filtration and evaporation
of n-pentane gave 6-bromo-2,2-di-tert-butyl-4H-1,3,2-benzo[d]
dioxagermine as yellow solid (2.55 g, 91%); mp 59–62 °C; 1H
NMR (500 MHz, C6D6, 25 °C, TMS): d = 1.06 (s, 18H, CH3–tBu),
3
4.67 (s, 2H, CH2), 6.75 (d, H, H /C6H3, Jortho = 8.8 Hz), 6.93 (d, H,
a
4
3
H /C6H3, Jmeta = 2.5 Hz), 7.17 ppm (dd, H, Hb/C6H3, Jortho = 8.8 Hz,
c
4Jmeta = 2.5 Hz); 13C{1H} NMR (125 MHz, C6D6, 25 °C, TMS):
d = 27.8 (CH3–tBu), 32.5 (Cq–tBu), 66.5 (CH2), 112.3 (C6H3), 121.9
(C6H3), 130.7 (C6H3), 132.4 (C6H3), 132.6 (C6H3), 158.0 ppm
(C6H3); m/z: 390, 388, 386 and 384 [M+Å]; ATR-FT-IR: 3079 w
(Caryl–H), 2934 m (CH3), 2857 m (CH2), 1472 s (CH2), 1260 s (O–Caryl),
1183 s (CH2–Caryl), 812 s (C–CH3), 791 s (C6H3), 675 s (Ge–OCaryl),
615 cmꢁ1 s (Ge–OCH2); Anal. Calc. for C15H23BrGeO2: C, 46.45; H,
5.98. Found: C, 46.29; H, 5.91%.
Tetraethoxy germane (98%), 5-bromo-2-hydroxybenzaldehyde
and 1.9 M tert-butyllithium in n-pentane were purchased from
ABCR GmbH & Co. KG, Merck Schuchardt OHG and Acros Organics,
respectively. All starting materials were used without further
purification.
2.4. Polymerization of compound 1
Trifluoromethanesulfonic acid (0.042 mL, 0.480 mmol) was
added to a stirred solution of 6-bromo-2,2-di-tert-butyl-4H-1,3,2-
benzo[d]dioxagermine (1.862 g, 4.800 mmol) in dichloromethane
(50 mL) at 0 °C. The mixture was stirred at room temperature for
4 days. The resulting precipitate was filtered off and washed with
n-hexane (10 mL) and diethyl ether (10 mL) three times, respec-
tively. Removal of residual solvent in air at 60 °C gave an
amorphous brown powder. Yield based on 1 (0.71 g, 38%); 13C{1H}
CP-MAS NMR (100.6 MHz, 25 °C, TMS, adamantane): d = 27 (CH3–
tBu), 33 (CH2), 114 (C6H3), 130 (C6H3), 149 ppm (C6H3); ATR-
FT-IR: 3210 b (OH), 2940 m (CH3), 2863 m (CH2), 1466 s, 1449 s,
2.1. Synthesis of 5-bromo-2-hydroxybenzyl alcohol [7]
The compound was prepared according to the literature using a
modified synthetic procedure: 5-bromo-2-hydroxybenzaldehyde
(10.1 g, 50 mmol) was dissolved in 250 mL of ethanol at 0 °C.
NaBH4 (1.88 g, 50 mmol) was added in portions (ꢀ0.3 g) to the stir-
red solution. The mixture was stirred at room temperature for 18 h.
After removal of ethanol under reduced pressure (10ꢁ2 mbar) the
resulting pale yellow solid was dissolved in 200 mL of a saturated,
aqueous NH4Cl solution. The crude product was extracted with
diethyl ether (three times 80 mL). The organic phase was washed
with brine (three times 20 mL) and dried with MgSO4 for 2 h. After
removal of MgSO4 by filtration and excess solvent under reduced
pressure (10ꢁ2 mbar) the product was purified by flash chromatog-
raphy with silica (eluent: n-hexane/ethyl acetate – volume ratio of
8/2) to give a colorless solid after evaporation of the solvent
(8.52 g, 84%); mp 104–107 °C; 1H NMR (500 MHz, CDCl3, 25 °C,
TMS): d = 2.21 (s, H; OH(CH2OH)), 4.84 (s, 2H, CH2), 6.77 (d, H,
1207 s, 1175 s, 1026 s, 862 s, 633 s (Ge–O), 513 s (Ge–C) cmꢁ1
.
2.5. X-ray diffraction analysis of compound 1
Single crystals suitable for X-ray structural analysis were grown
from a saturated solution in n-hexane at room temperature. X-ray
crystallographic data were collected on an Oxford diffractometer
of the type Gemini S using Cu Ka-radiation (k = 1.54 Å) at 100 K
3
4
H /C6H3, Jortho = 8.6 Hz), 7.16 (d, H, H /C6H3, Jmeta = 2.4 Hz), 7.30
a
c
using oil-coated shock-cooled crystals [9–11]. The structure was
solved by direct methods using SIR-92 and refined by full matrix
least-square procedures on F2 using SHELXL-97 [12,13]. All non-
hydrogen atoms were refined anisotropically and a riding model
3
(s, H, OH(C6H3)), 7.30 ppm (dd, H, Hb/C6H3, Jortho = 8.6 Hz,
4Jmeta = 2.4 Hz); 13C{1H} NMR (125 MHz, CDCl3, 25 °C, TMS):
d = 64.2 (CH2), 111.9 (C6H3), 118.5 (C6H3), 126.4 (C6H3), 130.3
(C6H3), 132.2 (C6H3), 155.3 ppm (C6H3).

474
P. Kitschke et al. / Inorganica Chimica Acta 409 (2014) 472–478
Table 1
Selected bond lengths (Å) and bond angles (°) for compound 1 determined by single crystal X-ray diffraction analysis and by DFT-D calculations (B3LYP-D3/def2-TZVPP level of
theory), respectively.
Measured (Å)
Calculated (Å)
Measured (°)
Calculated (°)
Ge1–O1
Ge1–O2
Ge1–C8
Ge1–C12
O1–C1
1.8168(17)
1.7846(18)
1.963(3)
1.959(3)
1.362(3)
1.436(3)
1.8299
1.7984
1.988
1.988
1.360
1.429
O1–Ge1–O2
O1–Ge1–C8
O1–Ge1–C12
O2–Ge1–C8
O2–Ge1–C12
C8–Ge1–C12
C1–O1–Ge1
C7–O2–Ge1
101.24(8)
109.84(11)
104.81(10)
105.24(11)
111.25(9)
122.51(12)
119.41(15)
115.98(15)
101.10
109.77
103.87
105.92
112.12
122.09
118.72
116.36
O2–C7
C–C distance (tBu): 1.508(5)–1.531(4) Å (calculated: 1.533–1.535 Å).
C–C–C angle (tBu): 108.5(3)–111.3(3)° (calculated: 109.8–110.6°).
was employed in the refinement of hydrogen atom positions. Crys-
tal data: C15H23BrGeO2, M = 387.83 g molꢁ1, crystal size 0.36 ꢂ
0.18 ꢂ 0.12 mm3, monoclinic, space group P21/c, Z = 4, a =
spectroscopy in d6-benzene, which are assigned to the CH3 groups
of the tert-butyl substituents and the methylene protons of the
benzyl group, respectively. The aromatic protons were observed
at d 6.75, 6.93 and 7.17 ppm with expected multiplicity. 13C{1H}
NMR spectroscopy revealed nine signals, six in the aromatic and
three in the aliphatic region including a characteristic signal at d
66.5 ppm for the CH2 group.
8.9041(6) Å, b = 8.8890(9) Å, c = 21.6996(14) Å,
a
= 90°, b =
99.065(6)°,
c
= 90°,
V = 1696.0(2) Å3,
Dc = 1.519 g cmꢁ3
,
F(000) = 784, T = 100 K, 4.13° < 2h < 63.17°, completeness to 2h:
97.8%, maximum/minimum residual electron density: 1.021/
ꢁ0.414 e Åꢁ3. A total of 4590 reflections was collected, 2694 reflec-
tions were independent (Rint = 0.0177). Final R1 = 0.0332 (I > 2
r(I))
3.1. Single crystal X-ray diffraction analysis
and wR2 = 0.0927 (all data).
Suitable single crystals for X-ray diffraction studies were ob-
tained from a solution of the germine 1 in n-hexane by evaporation
of n-hexane at ambient temperature. Compound 1 crystallizes in
the monoclinic space group P21/c as orange needles with the cell
dimensions a = 8.9041(6) Å, b = 8.8890(9) Å, c = 21.6996(14) Å,
b = 99.065(6)° and a volume of 1696.0(2) Å3. The molecular struc-
ture of 1 is given in Fig. 1, a selection of measured and calculated
(obtained at the B3LYP-D3/def2-TZVPP level of theory) bond
lengths and bond angles is presented in Table 1.
Compound 1 is monomeric in the solid state and shows a distorted
tetrahedral coordination at the germanium atom. The O1–Ge1–O2
and C8–Ge1–C12 angles are 101.24(8)° and 122.51(12)°, respectively,
which both differ from the ideal tetrahedral angle and hence a
strained heterocyclic GeO2C3-ring is observed. The Ge(1)–O(2)
(1.7846(18) Å) distance involving the benzylic oxygen atom is
slightly shorter than the Ge(1)–O(1) (1.8168(17) Å) distance involv-
ing the phenolic oxygen atom. This hints at a higher ionic character
of theformerbond. The germanium oxygenbondlengthsareinagree-
ment with phenolic oxygen germanium bond lengths, for example,
ranging from 1.782(2) to 1.800(2) Å for LGe(OiPr)ꢃ(HOiPr)
(L = 6,60,600-(nitrilotris(methylene))tris(2,4-dimethylphenolate)) and
with alkoxide oxygen germanium bond lengths, for example, ranging
from 1.749(3) to 1.751(3) Å for GeL2 (L = [1,10-bi(cyclohexane)]-1,10-
bis(olate)) as reported elsewhere [23,24]. The relatively large angle
2.6. Computational details
The quantum chemical calculations to simulate the IR spectrum
of compound 1 have been carried out at the DFT-D (B3LYP-D3
using the def2-TZVPP basis set) level of theory using the TURBO-
MOLE program package [14–21]. We obtained the IR spectrum
after relaxing the structure of compound 1 (X-ray diffraction data)
to a minimum. A selection of calculated bond lengths and bond an-
gles is provided in Table 1. The calculated frequencies were cor-
rected by a factor of 0.965 [22].
3. Results and discussion
The
synthesis
of
6-bromo-2,2-di-tert-butyl-4H-1,3,2-
benzo[d]dioxagermine (1) was carried out by an alcohol/alkoxide
exchange reaction of 5-bromo-2-hydroxybenzyl alcohol with di-
tert-butyl-di-ethoxy germane. The latter was synthesized accord-
ing to a modified procedure described by von Schnering et al. [8].
The title compound was prepared by stirring the germane and
the alcohol in xylene at reflux for several hours. The crude product
was purified by crystallization from n-hexane to give orange nee-
dles with 91 % yield (Eq. (1)).
ð1Þ
Compound 1 was characterized by 1H NMR and 13C{1H} NMR
spectroscopy, single crystal X-ray diffraction analysis, IR spectros-
copy, mass spectrometry and TGA/DSC analysis. Two singlets at d
1.06 and d 4.67 ppm in a 9:1 ratio were observed by 1H NMR
between the two carbon atoms of the tert-butyl groups (C8–Ge1–
C12 = 122.506(3)°), which results from steric hindrance, is close to
that of other di-tert-butyl germanium compounds studied by single
crystal X-ray diffraction analysis [25–27].

P. Kitschke et al. / Inorganica Chimica Acta 409 (2014) 472–478
475
date. To provide such data we measured the IR spectrum and
simulated it by DFT-D calculations (B3LYP-D3/def2-TZVPP) in or-
der to assign the observed absorption bands. The measured IR
spectrum and the calculated one of the germine 1 are shown in
Fig. 2. Table 2 provides a selection of vibrational modes, their cal-
culated frequencies and relative intensities as well as the as-
signed absorption band maxima with their absorbance of the
measured IR spectrum.
The data listed in Table 2 represent the strong absorption band
maxima of the IR spectrum. The assignment of the vibrational
modes is based on a comparison of the relative intensities of the
calculated frequencies that are close to the absorption band max-
ima. There are in some cases groups of different vibrational modes,
which result in similar frequencies assigned to a specific absorp-
tion band, but show much lower calculated relative intensity. In
addition the calculated relative intensities can deviate from mea-
sured absorption band intensities of the assigned vibrational
modes within the error of the applied level of theory and due to
non-ideal gas phase environment of the real system. Table 2 lists
vibrational modes for which measured absorption band maxima
for the single alkyl groups as well as the aryl group of 1 are in
excellent agreement with literature data [28]. For Ge–O vibrational
modes only limited data were published to date. For example,
Schwab et al. reported for the Ge–O(H) stretching vibration of
Fig. 1. ORTEP diagram including the atom numbering scheme of 6-bromo-2,2-di-
tert-butyl-4H-1,3,2-benzo[d]dioxagermine (1) (ellipsoids drawn with 50% proba-
bility). H atoms are omitted for clarity.
the di-tert-butyl-di-hydroxy germane dimer a value of 650 cmꢁ1
,
which is close to the absorption band maxima at 615 and
675 cmꢁ1 as well as the calculated frequencies at 602 and
664 cmꢁ1 for the Ge–OCH2 and Ge—OCC
stretching vibrational
6H3
modes, repectively, of germine 1 [25]. Calculated and consecutive
assigned frequencies for the symmetric Ge–C streching vibrations
(measured 546 cmꢁ1/calculated 510 cmꢁ1) as well as for the asym-
metric Ge–C stretching vibration (measured 567 cmꢁ1/calculated
539 cmꢁ1) of compound 1 are in agreement with data given in
the literature for the symmetric Ge–C streching vibrations at 558
and 532 cmꢁ1 as well as for the asymmetric Ge–C stretching vibra-
tions at 602 and 572 cmꢁ1 for tetramethyl germane and tetraethyl
germane, respectively [29]. In addition, reported frequencies for
Fig. 2. ATR-FT-IR spectrum (black line) and relative intensities of the calculated
frequencies of the vibrational modes (DFT-D calculations) (red lines) of compound
1. (For interpretation of the references to color in this figure legend, the reader is
referred to the web version of this article.)
C
Aryl–Br stretching vibrations at 1071 and 1088 cmꢁ1 for 4-bromo-
phenol and 5-bromo-2-nitropyridine, respectively, aꢁre1 in accor-
3.2. IR spectroscopy
dance with the calculated frequency at 1058 cm
and the
assigned absorption band maximum at 1077 cmꢁ1 for the
There are no data of vibrational frequencies for di-substituted
4H-1,3,2-benzo[d]dioxagermines reported in the literature to
CC —Br stretching vibration [30,31].
6H3
Table 2
Selected calculated frequencies and intensities (DFT-D calculations) as well as measured absorption band maxima of vibrational modes with their absorbance of compound 1.
Vibration mode
Calculated frequencies (cmꢁ1
)
Calculated relative intensities (%) Measured absorption band maxima (cmꢁ1
)
Measured absorbance (%)
ms – Ge–C(CH3)3
mas – Ge–C(CH3)3
511
539
602
664
728
775
780
995
1010
1.0
6.6
18.2
29.6
9.6
21.8
4.4
8.8
17.9
9.7
28.8
100
50.2
8.2
546
567
615
675
733
44.4
45.0
79.0
78.1
42.0
71.8
65.6
59.8
58.8
43.1
53.1
76.1
62.8
17.7
35.4
26.5
33.5
11.3
12.9
m
m
d
– Ge–OCH2
– Ge–OCaryl
– C6H3
c
db – CH2–C@C (C6H3)
ms – C–(CH3)3
dp – CH3
791
812
1013
1028
1077
1183
1260
1472
1594
2857
2892
2934
3054
3079
d
m
m
m
– CH3
x
– Caryl–Br (backbone) 1058
– CH2–Caryl
– O–Caryl
1159
1237
1457
1574
2873
2904
2957
3075
3092
db – CH2
mas – C@C (C6H3)
mas – CH2
ms – CH3
mas – CH3
16.1
45.6
14.7
0.9
mas – Caryl–H
ms – Caryl–H
0.9
m
– stretching vibration, mas – asymmetric stretching vibration, ms – symmetric stretching vibration, d – deformation vibration, d – out of plane deformation vibration, d – out
c x
of plane wagging deformation vibration, db – in plane bending deformation vibration.

476
P. Kitschke et al. / Inorganica Chimica Acta 409 (2014) 472–478
and B gives the cation C. Note that the latter cannot be assigned
to one specified fragment, because different tautomers might be
formed as illustrated in Fig. 4. Additionally, the mass peaks of the
cations B and C overlap. Taking into account the isotopic pattern
of germanium and bromine formation of species B seems to be
slightly favored. The ion peaks with mass to charge ratios of m/z
187 and m/z 185 indicate the formation of the ortho quinone met-
hide D, which results from fragmentation of species A, B and C.
Note that the ion peak with a mass to charge ratio of m/z 187 could
also be explained by the 73Ge(tBu)2 radical ion. However, its for-
+Å
mation seems to be unlikely here as no other evidence for its for-
mation is found. Additionally, the relative intensities of the ion
peaks with the mass to charge ratio of m/z 185 and m/z 187 are al-
most identical as is expected for species with 81Br/79Br isotopes.
+
Further fragmentation of the organic molecular ions gave C7H7
,
C7H5+, C6H6+, C6H5 and C4H3
In contrast to compound 1 the base peaks for 2,2-di-n-butyl-
4H-1,3,2-benzo[d]dioxagermine and 2,2-diphenyl-4H-1,3,2-
.
+
+
Fig. 3. Mass spectrum of 6-bromo-2,2-di-tert-butyl-4H-1,3,2-benzo[d]dioxager-
mine (1); (M) – molecular peaks, red line – base peak; the embedded table lists
relative intensities of the most intense ion peaks and associated less intense ion
peaks with respect to the isotopic pattern. (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
benzo[d]dioxagermine were reported to be the molecular ions,
formed upon removal of a hydrogen atom after ionization (MꢁH
– base peaks). Additionally the molecular peaks (M) were also
found to give high relative intensities (both >85%).[2] Formation
of the MꢁH species was not found for germine 1 and the molecular
peaks (M) were observed with low intensities (<2%) in the mass
spectrum, which might be a consequence of the preferred fragmen-
tation leading to ionic tert-butyl and 6-bromo-4H-1,3,2-
benzo[d]dioxagermine systems. Thus, we conclude that the ability
to form MꢁH and M species for this type of compounds depends on
the nature of the organic substituents at germanium. However, it is
noteworthy, that formation of ortho quinone methide like frag-
ments was also observed for 2,2-di-n-butyl-4H-1,3,2-
benzo[d]dioxagermine and 2,2-diphenyl-4H-1,3,2-benzo[d]dioxag-
ermine as part of their fragmentation cascades [2].
3.3. Mass spectrum
The mass spectrum of compound 1 was recorded by GC–MS
analysis starting from a n-hexane solution (Fig. 3). The table
embedded in Fig. 3 lists the relative intensities of the most intense
ion peaks. The proposed fragmentation scheme derived from the
mass spectrum of germine 1 is shown in Fig. 4.
Germine 1 mainly liberates tert-butyl cations (m/z 57 – base
peak) as major fragmentation step. The presence of species A in
the mass spectrum can be explained by a cleavage process of the
tert-butyl groups following a b-H elimination reaction starting
from the radical cation M. The ionic 6-bromo-4H-1,3,2-
benzo[d]dioxagermine species B can be formed directly from M
and/or consecutively from A. Further fragmentation of species A
3.4. DSC/TGA analysis
The thermograms of the DSC/TGA analysis of compound 1 are
given in Fig. 5.
Fig. 4. Fragmentation scheme of 6-bromo-2,2-di-tert-butyl-4H-1,3,2-benzo[d]dioxagermine (1) as obtained by mass spectrometry.

P. Kitschke et al. / Inorganica Chimica Acta 409 (2014) 472–478
477
Fig. 5. Thermal gravimetric analysis (blue curve) and differential scanning
calorimetry (black curve) of compound 1; heat rate 10 K/min, Ar atmosphere, Ar
volume flow of 60 mL/min. (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
Fig. 6. Differential scanning calorimetry of compound 1 with addition of CCl3COOH
– n =nCCl
¼ 3:2 (red curve) and without addition CCl3COOH (black curve);
ð1Þ
3 COOH
heat rate 10 K/min, N2 atmosphere, N2 volume flow of 50 mL/min. (For interpre-
tation of the references to color in this figure legend, the reader is referred to the
web version of this article.)
Compound 1 does not show any weight loss up to 170 °C. The
DSC curve indicates an endothermic process with an onset temper-
ature of 56 °C, which is assigned to the melting point. Three single
mass loss processes with different thermodynamic behavior are ob-
served above 170 °C: (i) an endothermic mass loss of 80.7% in a first
step with an onset temperature of 254 °C. The weight loss is as-
signed mainly to partial vaporization; (ii) an endothermic decom-
position step starting with an onset temperature of 375 °C and a
mass loss of 5.6%; (iii) an exothermic decomposition step with an
onset temperature of 434 °C that results in a mass loss of 5.1%.
The exothermic character of the last decomposition step as well
as the appearance of the resulting material, which was a black car-
bon like solid, indicate a carbonization reaction of the residue of the
previous decomposition steps. However, vaporization starting with
an onset temperature of 254 °C counteracts against the suitability
for thermally induced Twin Polymerization. Thus, we decided to
probe germine 1 for its suitability for proton induced Twin Polymer-
ization. DSC measurements of compound 1 with addition of CCl3-
COOH as a catalyst up to 400 °C were carried out (Fig. 6).
Trifluoromethanesulfonic acid was chosen as initiating reagent
because of its higher reactivity as compared with weaker acids
such as trichloroacetic acid or methanesulfonic acid. The 13C{1H}
CP-MAS NMR and ATR-FT-IR spectra of the obtained hybrid mate-
rial in comparison with compound 1 are shown in Fig. 7.
The 13C{1H} CP-MAS NMR spectrum of the hybrid material dis-
plays typical signals for a phenolic resin [33] and an intense signal
at 27 ppm, which is assigned to the tert-butyl groups at germa-
nium. No resonance signal for benzylic CH2O groups (signal G in
the 13C{1H} NMR spectrum for germine 1) was observed for the hy-
brid material indicating completeness of the polymerization pro-
cess. An absorption band maximum at 3210 cmꢁ1, which is
assigned to O–H stretching vibrations of the phenolic resin, is ob-
served by IR spectroscopy of the hybrid material. Absorption band
maxima at 633 and 513 cmꢁ1 are assigned to Ge–O and Ge–C
stretching vibrations (see Section 3.2 IR spectroscopy). Elemental
analysis reveals a carbon content of 40.75% and a hydrogen content
of 3.46% of the hybrid material, which deviates from the calculated
values (C: 46.45%, H: 5.98%) for complete conversion of germine 1.
This might be explained by the formation of soluble by-products,
that were removed in the work up procedure, as was previously re-
ported for 2,2-dimethyl-4H-1,3,2-benzo[d]dioxasiline [4].
Addition of CCl3COOH results in an onset temperature of 50 °C
for the endothermic melting process of a mixture of compound 1
and CCl3COOH (melting point at 59 °C [32]). In contrast to pure
germine 1 two exothermic processes are observed by DSC analysis
of the mixture with a molar ratio of n =nCCl
¼ 3:2. The onset
ð1Þ
3COOH
temperatures are 217 and 300 °C. The exothermic character as well
as the formation of a brown phenolic resin indicate suitability for
proton induced Twin Polymerization of the title compound 1.
4. Conclusions
3.5. Polymerization
A
novel dioxagermine, 6-bromo-2,2-di-tert-butyl-4H-1,3,2-
Proton-assisted Twin Polymerization of germine 1 dissolved in
dichloromethane was carried out by addition of 10 mol.% trifluoro-
methanesulfonic acid at 0 °C. Stirring the mixture at room temper-
ature for 4 days gave a yield of 38% hybrid material (Eq. (2)).
benzo[d]dioxagermine (1), was synthesized by an alcohol/alkoxide
exchange starting from di-tert-butyl-di-ethoxy germane and was
fully characterized. IR-vibrational modes have been assigned to
the experimental absorption band maxima by applying DFT-D
ð2Þ

478
P. Kitschke et al. / Inorganica Chimica Acta 409 (2014) 472–478
Acknowledgments
We gratefully acknowledge financial support by the DFG For-
schergruppe 1497 ‘‘organic and inorganic nanocomposites through
twin polymerization’’, Prof. Dr. S. Spange for helpful discussions
and the Fonds der Chemischen Industrie for a fellowship (P. Kitsch-
ke). We also thank C. Georgi for the TGA/DSC measurement of com-
pound 1.
Appendix A. Supplementary material
CCDC 946928 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2013.09.052.
References
[1] M. Wieber, M. Schmidt, J. Organomet. Chem. 1 (1963) 93.
[2] R.H. Cragg, M. Nazery, J. Organomet. Chem. 71 (1974) 225.
[3] S. Spange, P. Kempe, A. Seifert, A.A. Auer, P. Ecorchard, H. Lang, M. Falke, M.
Hietschold, A. Pohlers, W. Hoyer, G. Cox, E. Kockrick, S. Kaskel, Angew. Chem.,
Int. Ed. 48 (2009) 8254.
[4] T. Löschner, A. Mehner, S. Grund, A. Seifert, A. Pohlers, A. Lange, G. Cox, H.J.
Hähnle, S. Spange, Angew. Chem., Int. Ed. 51 (2012) 3258.
[5] P. Kempe, T. Löschner, D. Adner, S. Spange, New J. Chem. 35 (2011) 2735.
[6] P. Kitschke, Diplomarbeit, Technische Universität Chemnitz, 2011.
[7] B. Zeynizadeh, T. Behyar, Z. Naturforsch. B 60 (2005) 453.
[8] M. Weidenbruch, A. Ritschl, K. Peters, H.G. von Schnering, J. Organomet. Chem.
437 (1992) C25.
[9] T. Kottke, D. Stalke, J. Appl. Crystallogr. 26 (1993) 615.
[10] T. Kottke, R.J. Lagow, D. Stalke, J. Appl. Crystallogr. 29 (1996) 465.
[11] D. Stalke, Chem. Soc. Rev. 27 (1998) 171.
[12] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26
(1993) 343.
[13] G.M. Sheldrick, SHELXL-97 Crystal Structure Refinement program, University of
Göttingen, Göttingen, Germany, 1997.
[14] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
Fig. 7. (a) 13C{1H} CP-MAS NMR spectrum of the hybrid material (black line) and
13C{1H} NMR spectrum of compound 1 in CDCl3 (red line), assignment of the signals
are given by numbers as well as capital letters for the hybrid material and for
compound 1, respectively; (b) ATR-FT-IR spectra of the hybrid material (black line)
and of compound 1 (red line). (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
[15] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[16] R. Ahlrichs, M. Bär, M. Häser, H. Horn, C. Kölmel, Chem. Phys. Lett. 162 (1989)
165.
[17] R. Ahlrichs, O. Treutler, J. Chem. Phys. 102 (1995) 346.
[18] M.V. Arnim, R. Ahlrichs, J. Comput. Chem. 19 (1998) 1746.
[19] F. Weigend, M. Häser, H. Patzelt, R. Ahlrichs, Chem. Phys. Lett. 294 (1998) 143.
[20] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 7 (2005) 3297.
[21] S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem. Phys. 132 (2010) 154104.
[22] <http://cccbdb.nist.gov/vibscalejust.asp>, 2013 (accessed 14.01.13).
[23] P. Klüfers, C. Vogler, Z. Anorg. Allg. Chem. 633 (2007) 908.
[24] A.J. Chmura, C.J. Chuck, M.G. Davidson, M.D. Jones, M.D. Lunn, S.D. Bull, M.F.
Mahon, Angew. Chem., Int. Ed. 46 (2007) 2280.
[25] H. Puff, S. Franken, W. Schuh, W. Schwab, J. Organomet. Chem. 254 (1983) 33.
[26] H. Puff, S. Franken, W. Schuh, W. Schwab, J. Organomet. Chem. 244 (1983) C41.
[27] J. Beckmann, K. Jurkschat, M. Schürmann, Eur. J. Inorg. Chem. (2000) 939.
[28] H. Günzel, H.M. Heise, IR-Spektroskopie, third ed., VCH, Weinheim, 1996.
[29] W.R. Cullen, G.B. Deacon, J.H.S. Green, Can. J. Chem. 43 (1965) 3193.
[30] N. Sundaraganesan, S. Ilakiamani, H.S. Aleem, P.M. Wojciechowski, D.
Michalska, Spectrochim. Acta, Part A 62 (2005) 753.
calculations. Mass spectra of germine 1 reveal a different fragmen-
tation behavior as given in the literature for this class of com-
pounds. Most importantly for the process of Twin Polymerization,
ortho quinone methide formation was observed for the germines
as part of the induced fragmentation cascades. This result is of sig-
nificant importance, because formation of ortho quinone methides
is suggested to be one of the key steps in Twin Polymerization of
precursors based on benzyl alcoholates. Noteworthy, they are also
reported to be intermediate products in the synthesis of phenolic
resins [34]. However, the title compound 1 is not suitable for ther-
mally induced Twin Polymerization as a result of its high vapor
pressure, but the proton-assisted Twin Polymerization of germine
1 to give a hybrid material consisting of a phenolic resin and [tBu2-
GeO]n is quite promising.
[31] W. Zierkiewicz, D. Michalska, T. Zeegers-Huyskens, J. Phys. Chem. A 104 (2000)
11685.
[32] R.A. McDonald, S.A. Shrader, D.R. Stull, J. Chem. Eng. Data 4 (1959) 311.
[33] R.L. Bryson, G.R. Hatfield, T.A. Early, A.R. Palmer, G.E. Maciel, Macromolecules
16 (1983) 1669.
[34] M.P. Stevens, Polymer Chemistry: An introduction, third ed., Oxford Univ.
Press, New York, 1999.