Selective synthesis of tetraarylgermanes and triarylgermanium halides

Article abstract of DOI:10.1016/j.jorganchem.2017.09.027

A series of novel and previously published tetraarylgermanes aryl₄Ge (aryl = m-tolyl, 3,4-xylyl, 3,5-xylyl, 2-naphthyl) and triarylgermanium halides aryl₃GeX (aryl = o-tolyl, 2,4-xylyl, 2,5-xylyl, 2,6-xylyl, 1-naphthyl, 2,4,6-mesityl, X = Cl, Br) were synthesized and characterized. All solids were investigated using single crystal X-ray diffractometry in order to elucidate the molecular structures. Effects of the substitution pattern of the aryl residue employed have been studied in terms of the impact on the product formation.

Full text of DOI:10.1016/j.jorganchem.2017.09.027

Journal of Organometallic Chemistry 851 (2017) 143e149
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Selective synthesis of tetraarylgermanes and triarylgermanium
halides
Melanie Wolf, Astrid Falk, Michaela Flock, Ana Torvisco, Frank Uhlig*
Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9/V, 8010 Graz, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2017
Received in revised form
15 September 2017
Accepted 16 September 2017
Available online 21 September 2017
A series of novel and previously published tetraarylgermanes aryl4Ge (aryl ¼ m-tolyl, 3,4-xylyl, 3,5-xylyl,
2-naphthyl) and triarylgermanium halides aryl3GeX (aryl ¼ o-tolyl, 2,4-xylyl, 2,5-xylyl, 2,6-xylyl, 1-
naphthyl, 2,4,6-mesityl, X ¼ Cl, Br) were synthesized and characterized. All solids were investigated
using single crystal X-ray diffractometry in order to elucidate the molecular structures. Effects of the
substitution pattern of the aryl residue employed have been studied in terms of the impact on the
product formation.
© 2017 Elsevier B.V. All rights reserved.
Keywords:
Tetraarylgermanes
Triarylgermanium halides
Solid state structure
DFT calculations
1. Introduction
atom is bonded to at least one aromatic ligand. The ligands were
chosen carefully concerning their steric bulkiness, bearing either
Despite tetraarylgermanes and organogermanium halides rarely
finding straightforward use in direct applications, they represent
powerful starting materials for the preparation of other organo-
germanium compounds [1e3]. Since the synthesis of organo-
germanium compounds does not follow the usual pattern known
for the silicon and tin derivatives, numerous synthetic pathways
have been studied thus far, including reactions with organometallic
substances such as organolithium or organomagnesium com-
pounds, comproportionation reactions or halogenations starting
from organogermanes [2,4e12]. Thus, there is a multiplicity of
different methods known, but unfortunately until now, no versatile
pathway could be found for the preparation of these compounds, a
problem which has been discussed repeatedly in literature [13e15].
Due to our need for different aryl substituted germanium de-
rivatives and the lack of crystallographic data and reliable synthetic
pathways, it was our aim to study the influence of the aromatic
system on the product formation and behavior of different aryl-
germanium compounds. Therefore, various organogermanium
compounds were synthesized and characterized using NMR, IR,
single crystal X-ray and GCMS methods. In all cases, the germanium
one or two methyl groups in different positions towards the
germanium atom, or include even larger polyaromatic systems
presented in Fig. 1.
2. Experimental
2.1. Materials and methods
All reactions, unless otherwise stated, were carried out using
standard Schlenk line techniques or in a glovebox under nitrogen
atmosphere. All dried and deoxygenated solvents were obtained
from
a solvent drying system (Innovative Technology Inc.).
Germanium tetrachloride was purchased at ABCR and stored under
nitrogen. All other chemicals from commercial sources were uti-
lized without further purification. Elemental analysis was per-
formed on an Elementar vario EL or an Elementar vario MICRO
cube. Melting point measurements were carried out by threefold
determination with a Stuart Scientific SMP 10.
1H (300.2 MHz), 13C (75.5 MHz) NMR spectra were recorded on a
Mercury 300 MHz spectrometer from Varian at 25 ꢀC. Chemicals
shifts are given in parts per million (ppm) relative to TMS
(d
¼ 0 ppm).
GCMS measurements were carried out on an Agilent Technol-
* Corresponding author. 6330 Institute of Inorganic Chemistry, Graz University of
Technology, Stremayrgasse 9/V, 8010 Graz, Austria.
ogies 7890A GC system coupled to an Agilent Technologies 5975C
VLMSD mass spectrometer or MS data were collected on a Waters
E-mail address: frank.uhlig@tugraz.at (F. Uhlig).
http://dx.doi.org/10.1016/j.jorganchem.2017.09.027
0022-328X/© 2017 Elsevier B.V. All rights reserved.

144
M. Wolf et al. / Journal of Organometallic Chemistry 851 (2017) 143e149
Fig. 1. Aromatic residues employed for the preparation of organogermanium compounds.
GCT Premier with EI ionization.
twinned and was refined using the matrix (0 1 0 1 0 0 0 0 -1). The
main contributions of the two twin components refined to a BASF
of 0.03. CCDC 1546216-1546226 contain the supplementary crys-
tallographic data for compounds 1-5, 7-10 respectively. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
Tables containing crystallographic data and details of measure-
ments and refinement for compounds 1-5, 7-10 can be found in
Supplementary Information.
2.2. Crystal structure determination
All crystals suitable for single crystal X-ray diffractometry were
removed from a vial or a Schlenk under N2 and immediately
covered with a layer of silicone oil. A single crystal was selected,
mounted on a glass rod on a copper pin, and placed in the cold N2
stream provided by an Oxford Cryosystems cryostream. XRD data
collection was performed on a Bruker APEX II diffractometer with
2.3. Theoretical calculations
use of an Incoatec microfocus sealed tube of Mo K
a radiation
(
l
¼ 0.71073 Å) and a CCD area detector. Empirical absorption
Density functional calculations were performed using the
Gaussian09 program package for all calculations at the
mPW1PW91 hybrid functional level together with 6-311 þ G(d)
basis sets [26,27]. All structures were optimized and verified to be
minima by vibrational frequency calculations.
corrections were applied using SADABS or TWINABS [16,17]. The
structures were solved with use of the intrinsic phasing option in
SHELXT and refined by the full-matrix least-squares procedures in
SHELXL [18e20]. The space group assignments and structural so-
lutions were evaluated using PLATON [21,22]. The solvent of crys-
tallization of toluene for compound 2,4,6-mesityl3GeBr (10) and 1-
naphthyl3GeBr (9) was removed from the refinement by using the
“squeeze” option available in the PLATON program suite [23,24].
Non-hydrogen atoms were refined anisotropically. All other
hydrogen atoms were located in calculated positions corresponding
to standard bond lengths and angles and refined using a riding
model. Disorder was handled by modeling the occupancies of the
individual orientations using free variables to refine the respective
occupancy of the affected fragments (PART) [25]. In some cases, the
similarity SAME restraint, the similar-ADP restraint SIMU and the
rigid-bond restraint DELU, as well as the constraints EXYZ and
EADP were used in modeling disorder to make the ADP values of
the disordered atoms more reasonable. In some cases, the distances
between arbitrary atom pairs were restrained to possess the same
value using the SADI instruction and in some cases distance re-
straints (DFIX) to certain target values were used. In some tough
cases of disorder, anisotropic Uij-values of the atoms were
restrained (ISOR) to behave more isotropically. In compound 3,4-
xylyl4Ge (2), disordered positions for one of the 3,4-xylyl residues
were refined using 50/50 positions. For compound 1-
naphthyl3GeBr ∙ CHCl3 (9b), several restraints and constraints
(FRAG 17, AFIX 66) were used to afford idealized naphthalene ge-
ometry for one of the naphthyl residues. Compound 2,6-xylyl3GeBr
(8) was twinned and was refined using the matrix (-10 0 0 -10 0 0 -
1). The main contributions of the two twin components refined to a
BASF of 0.02. Compound 1-naphthyl3GeBr ∙ naphthyl (9c) was
2.4. Preparation of aryl4Ge
A flask equipped with a dropping funnel and a reflux condenser
was charged with Mg in THF or Et2O. The dropping funnel was
charged with arylbromide in THF or Et2O, about 10% of the solution
was added to the reaction vessel and the solution was heated
carefully or dibromoethane was added to start the reaction. The
arylbromide was subsequently added dropwise. After complete
addition, the reaction was refluxed for 3-12 h. Residual Mg was
filtered off using a filter cannula or a Schlenk-frit charged with
Celite®. Germanium tetrachloride (GeCl4) in toluene was added
slowly to the ethereal Grignard solution at 0 ꢀC. The solution was
placed under vacuum and THF removed. In some cases, additional
toluene was added. The reaction was stirred for 1 h, heated to reflux
for several hours and was subsequently allowed to cool down to
room temperature. After quenching with 10% degassed HCl at 0 ꢀC
under inert atmosphere, the water layer was washed twice with
boiling toluene and the organic layers were dried over Na2SO4. After
removal of solvent under reduced pressure, the product was
washed several times with pentane and purified via
recrystallization.
m-tolyl4Ge (1): 10.0 g (411 mmol, 15.4 eq.) Mg in 100 ml Et2O,
64.3 g (376 mmol, 14.1 eq.) 3-bromotoluene in 50 ml Et2O, 5.70 g
(26.6 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC, refluxed for
12 h. The resulting oil was recrystallized from toluene at room

M. Wolf et al. / Journal of Organometallic Chemistry 851 (2017) 143e149
145
temperature to obtain colorless crystals. Yield: 65%. M.p.: 145 ꢀC.
Elemental analysis (%) for C28H28Ge: C, 76.93; H, 6.46. Found: C,
with pentane and purified via recrystallization or condensation.
o-tolyl3GeX (5): 6.00 g (247 mmol, 12.2 eq.) Mg in 80 ml THF,
38.4 g (224 mmol, 11.1 eq.) 2-bromotoluene in 50 ml THF, 4.32 g
(20.2 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC. The resulting
colorless solid (15-22% o- tolyl3GeCl, 78-85% o-tolyl3GeBr) was
recrystallized from toluene at -30 ꢀC to obtain colorless crystals.
Yield: 85%. Elemental analysis (%) for C21H21GeX: Cl: C, 66.12; H,
5.55. Br: C, 59.22; H, 4.92. Found: C, 60.70; H, 4.92. 1H NMR (CDCl3,
77.68; H, 6.57. 1H NMR (CDCl3, 300 MHz):
d
7.13 (m, 16H, ArH), 2.21
(s, 12H, CH3) ppm. 13C NMR (CDCl3, 75.5 MHz):
d
137.71, 136.34,
136.04, 132.65, 129.93, 128.14, 21.72 (CH3) ppm. GCMS: Method 1:
tR ¼ 24.67 min, m/z: 438.1 (Mþ$), 347.1 (Mþ$ -m-tolyl), 256.0 (Mþ$
-
m-tolyl2), 165.0 (Mþ$ - m-tolyl3) 91.1 (Mþ$ - m-tolyl3Ge).
3,4-xylyl4Ge (2): 4.94 g (204 mmol, 13.8 eq.) Mg in 100 ml THF,
34.3 g (185 mmol, 12.5 eq.) 4-bromo-o-xylene in 50 ml THF, 3.17 g
(14.8 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC, refluxed for 3 h.
The resulting solid was washed several times with pentane and
recrystallized from toluene at -30 ꢀC to obtain colorless crystals.
Yield: 76%. M.p.: 172 ꢀC. Elemental analysis (%) for C32H36Ge: C,
77.92; H, 7.36. Found: C, 77.95; H, 7.16. 1H NMR (CDCl3, 300 MHz):
300 MHz):
6H, 4,5-H, ArH), 2.35 (s, 9H, CH3) ppm. 13C NMR (CDCl3, 75.5 MHz):
143.89, 135.15, 130.98, 130.84, 126.00, 23.42 (CH3) ppm. GCMS:
d 7.46 (d, 3H, 6-H, ArH), 7.36 (t, 3H, 3-H, ArH), 7.21 (m,
d
Method 2: Cl: tR ¼ 18.25 min, m/z: 382.1 (Mþ$), 347.1 (Mþ$ - Cl),
290.1 (Mþ$ - o-tolyl), 255.1 (Mþ$ - o-tolylCl), 199.0 (Mþ$ - o-tolyl2),
181.1 (Mþ$ -o-tolylGeCl), 165.1 (Mþ$ - o-tolyl2Cl), 91.1 (Mþ$ - o-tol-
yl2GeCl). Br: tR ¼ 18.87 min, m/z: 426.0 (Mþ$), 347.1 (Mþ$ -Br), 334.0
(Mþ$ - o-tolyl), 255.0 (Mþ$ -o-tolylCl), 243.9 (Mþ$ -o-tolyl2), 181.1
(Mþ$ - o-tolylGeCl), 165.1 (Mþ$ - o-tolyl2Br), 91.1 (Mþ$ - o-
tolyl2GeBr).
d
7.25 (d, 8H, 5,6- H, ArH), 7.11 (d, 4H, 2-H, ArH), 2.25 (s, 12H, CH3),
2.20 (s,12H, CH3) ppm. 13C NMR (CDCl3, 75.5 MHz):
d
137.44,136.63,
133.92, 133.26, 129.59, 19.97 (CH3), 19.96 (CH3) ppm. GCMS:
Method 2: tR ¼ 22.90 min, m/z: 494.2 (Mþ$), 389.1 (Mþ$ - 3,4-xylyl),
284.1 (Mþ$ - 3,4-xlyl2), 179.0 (Mþ$ - 3,4-xylyl3), 105.1 (Mþ$ - 3,4-
xylyl3Ge), 77.1 (Mþ$ - 3,4-xylylGe3Me2).
3,5-xylyl4Ge (3): 10.0 g (411 mmol, 12.5 eq.) Mg in 100 ml THF,
60.9 g (329 mmol, 9.97 eq.) 4-bromo-o-xylene in 50 ml THF, 7.04 g
(33.0 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC, refluxed for
4.5 h. The resulting solid was washed several times with pentane
and recrystallized from toluene at -30 ꢀC to obtain colorless crys-
tals. Yield: 70%. M.p.: 195 ꢀC. Elemental analysis (%) for C32H36Ge: C,
76.60; H, 7.12. Found: C, 77.92; H, 7.36. 1H NMR (CDCl3, 300 MHz):
2,4-xylyl3GeX (6): 10.00 g (411 mmol, 11.0 eq.) Mg in 200 ml
THF, 69.2 g (374 mmol, 10.0 eq.) 4-bromo-m-xylene in 100 ml THF,
8.00 g (37.4 mmol,1.00 eq.) GeCl4 in 100 ml toluene at 0 ꢀC. A brown
slurry was obtained (74-80% 2,4-xylyl3GeCl, 26-20% 2,4-
xylyl3GeBr). After several crystallization attempts, 2,4-xylyl3GeCl
was obtained as a colorless liquid. Yield: 72%. Elemental analysis (%)
for C24H27GeCl: Cl: C, 68.06; H, 6.43. Found: C, 67.97; H, 6.35. 1H
NMR (CDCl3, 300 MHz):
ArH), 6.99 (d, 3H, 2-H, ArH), 2.33 (s, 9H, CH3), 2.30 (s, 9H, CH3) ppm.
13C NMR (CDCl3, 75.5 MHz):
143.83, 140.77, 135.02, 131.78, 131.39,
d 7.30 (d, 3H, 6-H, ArH), 7.07 (s, 3H, 3-H,
d
7.12 (s, 8H, 2,6-H, ArH), 7.01 (s, 4H, 4-H, ArH), 2.27 (s, 24H, CH3)
ppm. 13C NMR (CDCl3, 75.5 MHz):
137.50, 136.55, 133.28, 130.88,
21.64 (CH3) ppm. GCMS: Method 1: tR ¼ 25.49 min, m/z: 494.3
(Mþ$), 389.1 (Mþ$ - 3,5-xylyl), 284.1 (Mþ$ - 3,5-xlyl2), 179.0 (Mþ$
d
d
126.70, 23.17 (CH3), 21.59 (CH3) ppm. GCMS: Method 2: Cl:
tR ¼ 20.15 min, m/z: 424.1 (Mþ$), 389.1 (Mþ$ - Cl), 318.1 (Mþ$- 2,4-
xylyl), 281.1 (Mþ$ - 2,4-xylylCl), 209.2 (Mþ$ - 2,4-xylylGeCl), 179.1
(Mþ$ - 2,4-xylyl2Cl), 105.0 (Mþ$ - 2,4-xylyl2GeCl), 77.1 (Mþ$ - 2,4-
xylyl2GeCl(CH3)2).
2,5-xylyl3GeX (7): 2.74 g (113 mmol, 5.70 eq.) Mg in 100 ml THF,
19.0 g (102 mmol, 5.20 eq.) 2-bromo-p-xylene in 50 ml THF, 4.50 g
(19.7 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC. The resulting
colorless solid (16-50% 2,5- xylyl3GeCl, 50-84% 2,5-xylyl3GeBr) was
recrystallized from toluene at -30 ꢀC to obtain colorless crystals.
Yield: 65-70%. Elemental analysis (%) for C24H27GeX: Cl: C, 68.06; H,
6.43. Br: C, 61.59; H, 5.82. Found: C, 62.97; H, 5.89. 1H NMR (CDCl3,
-
3,5-xylyl3), 105.1 (Mþ$ - 3,5-xylyl3Ge), 77.1 (Mþ$ - 3,5-xylylGe3Me2).
2-naphthyl4Ge (4): 3.23 g (133 mmol, 5.50 eq.) Mg in 100 ml
THF, 25 g (121 mmol, 5.00 eq.) 2-bromonaphthalene in 50 ml THF,
5.17 g (24.1 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC, refluxed
for 3 h. The resulting solid was washed several times with pentane
and recrystallized from toluene at -30 ꢀC to obtain colorless crys-
tals. Yield: 68%. M.p.: 190 ꢀC. Elemental analysis (%) for C40H28Ge: C,
82.65; H, 4.86. Found: C, 82.11; H, 4.82. 1H NMR (CDCl3, 300 MHz):
d
8.12 (s, 4H, 1-H, ArH), 7.87 (d, 4H, 3-H, ArH), 7.85 (d, 4H, 4-H, ArH),
7.74 (t, 8H, 5,8-H, ArH), 7.48 (m, 8H, 6,7-H, ArH) ppm. 13C NMR
300 MHz):
d 7.28 (s, 3H, 6-H, ArH), 7.14 (d, 6H, 3,4-H, ArH), 2.29 (s,
(CDCl3, 75.5 MHz):
d 136.47, 134.01, 133.78, 133.47, 131.80, 128.35,
9H, CH3), 2.25 (s, 9H, CH3) ppm. 13C NMR (CDCl3, 75.5 MHz):
128.02, 127.86, 126.78, 126.26 ppm. DI/MS EI m/z: 582.14 (Mþ$),
455.1 (Mþ$ - 2-naphthyl), 328.1 (Mþ$ -2-naphthyl2), 201.0 (Mþ$ -2-
naphthyl3).
d 140.59, 135.66, 135.28, 134.24, 131.52, 130.80, 22.88 (CH3), 21.27
(CH3) ppm. GCMS: Method 2: Cl: tR ¼ 18.80 min, m/z: 424.1 (Mþ$),
389.1 (Mþ$ - Cl), 318.0 (Mþ$- 2,5-xylyl), 283.1 (Mþ$ - 2,5-xylylCl),
209.1 (Mþ$ - 2,5-xylylGeCl), 179.1 (Mþ$ - 2,5-xylyl2Cl), 105.1 (Mþ$
-
2.5. Preparation of aryl3GeX (X ¼ Cl, Br)
2,5-xylyl2GeCl), 91.1 (Mþ$ - 2,5-xylyl2GeClCH3), 77.1 (Mþ$ - 2,5-
xylyl2GeCl(CH3)2) Br: tR ¼ 19.31 min, m/z: 468.1 (Mþ$), 389.1 (Mþ$
A flask equipped with a dropping funnel and a reflux condenser
was charged with Mg in THF or Et2O. The dropping funnel was
charged with arylbromide in THF, about 10% of the solution was
added to the reaction vessel and the solution was heated carefully
or dibromoethane was added to start the reaction. The arylbromide
was subsequently added dropwise. After complete addition, the
reaction was refluxed for 3-12 h. Residual Mg was filtered off using
a filter cannula or a Schlenk-frit charged with Celite®. Germanium
tetrachloride (GeCl4) in toluene was added slowly to the Grignard
solution at 0 ꢀC. The solution was placed under vacuum and THF
removed. In some cases, additional toluene was added. The reaction
was stirred for 1 h, heated to reflux for several hours and was
subsequently allowed to cool down to room temperature. After
quenching with 10% degassed HCl at 0 ꢀC under inert atmosphere,
the water layer was washed twice with boiling toluene and the
organic layers were dried over Na2SO4. After removal of solvent
under reduced pressure, the product was washed several times
- Br), 362.0 (Mþ$ - 2,5-xylyl), 283.1 (Mþ$ - 2,5-xylylBr), 256.9 (Mþ$
-
2,5-xylyl2), 209.1 (Mþ$ - 2,5-xylylGeBr), 179.1 (Mþ$ - 2,5-xylyl2Br),
105.1 (Mþ$ - 2,5-xylyl2GeBr), 91.1 (Mþ$ - 2,5-xylyl2GeClCH3), 77.1
(Mþ$ - 2,5-xylyl2GeBr(CH3)2).
2,6-xylyl3GeX (8): 10.00 g (411 mmol, 6.85 eq.) Mg in 100 ml
THF, 69.2 g (374 mmol, 6.00 eq.) 2-bromo-m-xylene in 150 ml THF,
12.85 g (60.0 mmol, 1.00 eq.) GeCl4 in 60 ml toluene at 0 ꢀC. The
resulting solid was recrystallized from toluene at -30 ꢀC to obtain
colorless crystals (17-21% 2,6-xylyl3GeCl, 79-83% 2,6-xylyl3GeBr).
Yield: 55-70%. Elemental analysis (%) for C24H27GeX: Cl: C, 68.06; H,
6.43. Br: C, 61.59; H, 5.82. Found: C, 62.17; H, 5.95. 1H NMR (CDCl3,
300 MHz):
d
7.19 (t, 3H, 4-H, ArH), 7.00 (d, 6H, 3,5-H, ArH), 2.31 (s,
143.60, 140.32,
18H, CH3) ppm. 13C NMR (CDCl3, 75.5 MHz):
d
129.89, 129.10, 25.19 (CH3) ppm. GCMS: Method 2: Cl:
tR ¼ 19.92 min, m/z: 424.1 (Mþ$), 389.1 (Mþ$ - Cl), 283.1 (Mþ$ - 2,6-
xylylCl), 209.1 (Mþ$ - 2,6-xylylGeCl),179.1 (Mþ$ - 2,6-xylyl2Cl),105.1
(Mþ$ - 2,6-xylyl2GeCl), 77.1 (Mþ$ - 2,6-xylyl2GeCl(CH3)2). Br:

146
M. Wolf et al. / Journal of Organometallic Chemistry 851 (2017) 143e149
tR ¼ 20.57 min, m/z: 468.1 (Mþ$), 389.1 (Mþ$ - Br), 362.0 (Mþ$ - 2,6-
xylyl), 283.1 (Mþ$ - 2,6-xylylBr), 256.9 (Mþ$ - 2,6-xylyl2), 209.1 (Mþ$
- 2,6-xylylGeBr), 179.1 (Mþ$ - 2,6-xylyl2Br), 105.1 (Mþ$ -2,6-
xylyl2GeBr), 77.1 (Mþ$ - 2,6-xylyl2GeBr(CH3)2).
Fig. 2. Grignard route for the preparation of aryl4Ge and aryl3GeX for R ¼ o-tolyl (5),
m-tolyl (1), 2,4-xylyl (6), 2,5-xylyl (7), 2,6-xylyl (8), 3,4-xylyl (2), 3,5-xylyl (3), 1-
naphthyl (9) and 2-naphthyl (4).
1-naphthyl3GeX (9): 8.00 g (329 mmol, 6.85 eq.) Mg in 70 ml
THF, 61.9 g (299 mmol, 6.23 eq.) 1-bromonaphthalene in 200 ml
THF, filtered hot over Celite® using a Schlenk frit. 10.3 g (48.0 mmol,
1.00 eq.) GeCl4 in 60 ml toluene at RT. The resulting solid (10-35% 1-
naphthyl3GeCl, 65-90% 1- naphthyl3GeBr) was washed several
times with pentane and toluene and recrystallized from toluene,
chloroform and THF at -30 ꢀC to obtain colorless crystals of 1-
naphthyl3GeCl or 1- naphthyl3GeBr, which were used for further
analysis. Yield: 50-65%. Elemental analysis (%) for C30H21GeX: Br: C,
67.47; 3.96 H, 4.32. Found: C, 68.07; H, 3.96. 1H NMR (CDCl3,
reaction and removed via filtration before further reaction with
GeCl4, in order to avoid the formation of digermanes as described
by Glockling et al. [29]. GeCl4 in toluene was then added to the
Grignard solution. When necessary, the reaction mixture was
refluxed for at least 1 h, or stirred overnight at room temperature.
After the reaction was complete, the mixture was quenched under
acidic conditions and the organic layers were worked up. After
removal of solvents and purification steps, products were crystal-
lized from toluene either at lower temperatures or via evaporation
techniques.
300 MHz):
3H, 4-H, ArH), 7.73 (d, 3H, 5-H, ArH), 7.47 (t, 3H, 7-H, ArH), 7.36 (m,
6H, 3,6-H, ArH) ppm. 13C NMR (CDCl3, 75.5 MHz):
136.06, 135.45,
d 8.28 (d, 3H, 8-H, ArH), 7.98 (d, 3H, 2-H, ArH), 7.90 (d,
d
For the synthesis of all presented tetraarylgermanes and triar-
ylgermanium halides, varying excesses of Grignard reagent were
employed. In some cases, very large excesses of Grignard reagent
were used (14e10 equivalents of Grignard reagent to germanium
halide) and were thought to be necessary in order to provide the
tetraarylgermanes in high yields. However, we determined that
ratios as low as 5:1 Grignard reagent to germanium halide were
sufficient to provide acceptable yields. Following this pathway for
3,4-xylyl (2), 3,5-xylyl (3) and 2-naphthyl (4) residues, the tet-
raarylgermanes were obtained as has been reported for phenyl, m-
tolyl (1) and p-tolyl moieties (Fig. 3). However, expanding these
experiments to o-tolyl (5), did not result in formation of tetraar-
ylgermanes, but rather the triarylgermanium halides, as was re-
ported by Simons et al. [7]. Takeuchi et al. claimed to prepare o-
tolyl4Ge using the Grignard route, however this could not be
reproduced within the course of this work [30]. It should be
mentioned that it is possible to prepare o-tolyl4Ge over other
preparation pathways, i.e. by reacting the Grignard reagent with
zinc chloride, forming the arylzinc, which can be further reacted
with GeCl4, although the formation of mixtures is observed [2].
In order to determine whether the formation of the product is
determined by the size of the ligand or the substitution pattern of
the aryl residue, two naphthyl moieties, distinguishable concerning
their substitution pattern, were employed. Interestingly, while the
2-naphthyl moiety led to the formation of the tetraarylgermane (4),
the 1-naphthyl residue once again lead to the formation of the
triarylgermanium halide (9), thus indicating, that the substitution
pattern and thus the orientation of the substituent plays a more
important role on the number of residues that can accommodate
around the germanium metal as compared to the size of the ligand.
While other preparation pathways were conducted for the prepa-
ration of 1-naphthyl3GeX (X ¼ Cl, Br), the results were inconclusive
[31]. In 1952, West reported that all attempts to synthesize 1-
naphthyl4Ge over organolithium or Grignard reagents were un-
successful, agreeing with the results of this work. Interestingly,
reaction of 1-naphthylLi with 1-naphthyl3GeBr gave small amounts
of 1-naphthyl4Ge [32]. Preparation became very difficult upon
employment of the 1-naphthyl residue due to solubility reasons
and thus proved to be a time intensive preparation. Higher amounts
of solvents had to be used to prevent solidification of the Grignard
reagent. Moreover, the Grignard reagent was never allowed to cool
to room temperature before reaction with germanium tetrahalide,
thus cannulated hot or filtered off using a hot Schlenk frit. Work up
procedures were rather challenging due to the fact that free
naphthalene was present in most cases, which could not be
removed upon sublimation due to the instability of the desired
product. Nevertheless, extraction using a mixture of solvents
including toluene and pentane was helpful for removal of side
134.19, 133.30, 131.79, 129.10, 128.98, 126.58, 126.32, 125.48 ppm.
GCMS: Method 2: Cl: tR ¼ 29.02 min, m/z: 490.1 (Mþ$), 455.1 (Mþ$
-
Cl), 363.0 (Mþ$ - 1-naphthyl), 252.1 (Mþ$ - 1-naphthylGeCl), 127.1
(Mþ$ - 1-naphthyl2GeCl), 77.1 (Mþ$ - 1-naphthyl2GeCl(C4H4)). Br:
tR ¼ 30.55 min, m/z: 534.0 (Mþ$), 455.1 (Mþ$ - Br), 406.9 (Mþ$ -1-
naphthyl), 327.0 (Mþ$ -1-naphthylBr), 252.1 (Mþ$
-
1-
naphthylGeBr), 201.0 (Mþ$ -1-naphthyl2Br), 127.1 (Mþ$ -1-
naphthyl2GeBr), 77.1 (Mþ$ - 1-naphthyl2GeBr(C4H4)).
2,4,6-mesityl3GeX (10): 7.50 g (309 mmol, 8.80 eq.) Mg in 70 ml
THF, 55.9 g (281 mmol, 8.00 eq.) 2-bromo-1,3,5-trimethylbenzene
in 300 ml THF, 7.52 g (35.1 mmol, 1.00 eq.) GeCl4 in 100 ml
toluene at RT. The resulting solid (25-40% 2,4,6-mesityl3GeCl, 60-
75% 2,4,6-mesityl3GeBr) recrystallized from toluene at -30 ꢀC to
obtain colorless crystals of 2,4,6-mesityl3GeBr. Yield: 55-65%.
Elemental analysis (%) for C30H21GeX: Cl: C, 69.65; H, 7.14. Br: C,
63.58; H, 6.52. Found: C, 67.56; H, 6.97. 1H NMR (CDCl3, 300 MHz):
d
6.78 (s, 6H, 3,5-H ArH), 2.24 (s, 9H, CH3), 2.13 (s, 18H, CH3) ppm.
13C NMR (CDCl3, 75.5 MHz):
d 143.78, 138.32, 135.0, 128.89, 23.72,
21.20 ppm. GCMS: Method 2: Cl: tR ¼ 29.02 min, m/z: 466.1 (Mþ$),
431.1 (Mþ$ - Cl), 346.10 (Mþ$ - 2,4,6-mesityl), 237.2 (Mþ$ - 2,4,6-
mesitylGeCl), 228.0 (Mþ$ - 12,4,6-mesityl2), 119.1 (Mþ$ - 2,4,6-
mesityl2GeCl). Br: tR ¼ 21.84 min, m/z: 510.1 (Mþ$), 431.2 (Mþ$
-
Br), 390.1 (Mþ$ - 2,4,6-mesityl), 311.1 (Mþ$ - 2,4,6-mesitylBr), 270.9
(Mþ$ - 2,4,6-mesityl2), 237.2 (Mþ$ - 2,4,6-mesitylGeBr), 119.1 (Mþ$
2,4,6-mesityl2GeBr).
-
3. Results and discussion
3.1. Synthesis and theoretical calculations
As previously mentioned, the most commonly used methods for
the introduction of an aryl residue onto a metal center is the
employment of Grignard or organolithium reagents [2,9e11]. In a
typical Grignard reaction, excess of magnesium is reacted with an
arylhalide in order to yield the corresponding Grignard reagent,
which can be further reacted with a proportion of metal halide to
yield the desired product. This is valid to some extent for other
group 14 elements and smaller ligands [28]. However, in the case of
organogermanium compounds bearing larger substituents, this
route entails various disadvantages independent of the stoichi-
ometry used [4e8,28]. These drawbacks include the formation of
mixtures, from which the desired product is very difficult or in
some cases impossible to separate, long and challenging work-up
procedures and low yields, and as a consequence, cost intensive
preparation over a number of steps [11].
In all cases, for the preparation of desired aryl substituted
germanium compounds, the same Grignard method was employed
(Fig. 2). A slight excess of magnesium was used for the Grignard

M. Wolf et al. / Journal of Organometallic Chemistry 851 (2017) 143e149
147
Fig. 3. Influence of substituent position on the aryl residue on product formation using the Grignard route for aryl ¼ phenyl [9,10,38], o-tolyl (5) [2], m-tolyl (1) [2], p-tolyl [2], 2,4-
xylyl (6), 2,5-xylyl (7) [35,36], 2,6-xylyl (8) [34], 3,4-xylyl (2), 3,5-xylyl (3), 1-naphthyl (9a-c) [31], 2-naphthyl (4), 2,4,6-mesityl (10) [34].
Table 1
products.
DFT calculated reaction enthalpy
DH values in kJ/mol for
the preparation of aryl4Ge in dependence of the aryl
substituent.
Expanding this research to subsequently higher substituted
residues such as 2,4-xylyl, 2,5-xylyl, 2,6-xylyl, the effect of the
substitution pattern becomes even more apparent. While 3,4-xylyl
(2) and 3,5-xylyl (3) exclusively yielded the tetraarylgermane, the
2,4-xylyl (6), 2,5-xylyl (7), 2,6-xylyl (8) residues lead to the for-
mation of the triarylgermanium halide without any side products
present [33e36]. Therefore, it can be concluded that the number of
residues around the germanium central atom is controlled by the
position of the substituents on the aryl residue used [37]. A steri-
cally demanding substituent, i.e. the methyl group, on at least one
ortho position results in preferred formation of triarylgermanium
halides rather than the tetraarylgermane derivatives. Dumler et al.
observed similar results for the preparation of 2,5-xylyl3GeBr [35].
This is also supported by the fact, that in both cases, the 2,6-xylyl
(8) and also the previously reported larger 2,4,6-mesityl (10) res-
idue the expected triarylgermanium halide was obtained
[33,34,37].
aryl
DH (kJ/mol)
2-naphthyl
phenyl
m-tolyl
ꢁ103.5
ꢁ102.9
ꢁ102.4
ꢁ102.3
ꢁ101.4
ꢁ90.5
ꢁ85.5
ꢁ68.0
ꢁ54.1
ꢁ41.5
ꢁ36.0
3,5-xylyl
3,4-xylyl
2,5-xylyl
1-naphthyl
o-tolyl
2,4-xylyl
2,4,6-mesityl
2,6-xylyl
with increasing steric demand around the metal center, the reac-
tion enthalpy decreases noticeably, showing the lowest value for
the crowded 2,6-xylyl4Ge.
Compulsory approximations, namely DFT calculations, were
conducted and compared to the results by direct means confirming
that the outcome of the reaction indeed depends on the steric bulk
of the ligand used. The reaction mechanism was investigated and
In the case of the triarylgermanium halides, occurrence of
halogen-metal exchange presents another complication, a problem
that was reported for other group 14 elements as well [1e3].
Nevertheless, it must be mentioned that separation and charac-
terization of aryl3GeX (X ¼ Cl, Br) proves to be very difficult using
standard techniques. While this might be problematic, this issue
could be neglected since halide mixtures of aryl3GeX (X ¼ Cl, Br)
could be used as educts for subsequent reactions.
the
reaction
enthalpies
DH
were
calculated
(
D
H ¼ H(aryl4Ge) þ H(MgBr2) e H(aryl3GeBr) e H(arylMgBr))
(Fig. 4, Table 1).
It can be observed in Table 1 that the reaction enthalpy varies in
value depending on the functional group introduced. It was
possible to isolate and even recrystallize all systems showing a
reaction enthalpy higher than -100 kJ/mol over the Grignard route.
3.2. X-ray crystallography
In contrast, all reactions showing lower values (DH < -100 kJ/mol)
seemed to stop at the trisubstituted stage and the triar-
ylgermanium halide was formed. Therefore, DFT calculations sup-
port the observation that formation of tetraarylgermanes is highly
dependent on the substituent position of the residue used, since
All solid compounds were characterized using single X-ray
crystallography. Crystallization from toluene at low temperatures
or via evaporation techniques worked best in most cases, with the
exception of 2,4-xylyl3GeX (6) (X ¼ Cl, Br) which was a brown oil
from which it was not possible to obtain a crystal structure and 1-
naphthyl3GeBr (9a-c) which cocrystallizes with various recrystal-
lization solvents.
Compounds m-tolyl4Ge (1), 3,4-xylyl4Ge (2), 3,5-xylyl4Ge (3)
and 2-naphthyl4Ge (4) (Fig. 5) are comparable to previously
Fig. 4. Base reaction for the calculation of the enthalpies DH, in dependence of the aryl
substituents.

148
M. Wolf et al. / Journal of Organometallic Chemistry 851 (2017) 143e149
GeꢁC bond lengths (Table 3). As compared to phenyl3GeBr
(1.934(1) Å) [44], a slight increase in the average GeꢁC bond
lengths is seen for o-tolyl3GeBr (5) (1.947(2) Å) and 2,5-xylyl3GeBr
(7) (1.948(2) Å) due to the presence of substituents on the ortho
position of the aryl residue.However, with the increase of steric
bulk around the germanium center due to methyl groups at both
the 2- and 6 positions of the aryl residue, this bond elongation
becomes more pronounced, with averaged GeꢁC distances of
1.977(3)
Å in 2,6-xylyl3GeBr (8) and 1.971(6) Å in 2,4,6-
t
mesityl3GeBr (10). Finally, as expected, the larger butyl substitu-
ent on the ortho position of the aryl residue in 2-tbutylphenylGe3Br
causes the longest GeꢁC bond length of 1.997(2) Å [45]. Conse-
quently, 2-tbutylphenylGe3Br displays a wider CꢁGeꢁBr angle of
110.66(6)ꢀ and narrower CꢁGeꢁC angle of 108.26(6)ꢀ, whereas all
other molecules display wider CꢁGeꢁC angles than CꢁGeꢁBr an-
gles, highlighting the steric strain from the tbutyl substituent of the
aryl residue on the central germanium atom environment [45]. This
increased steric bulk around the germanium center is also man-
ifested by an increased GeꢁBr bond in 2-tbutylphenylGe3Br
(2.362(1) Å) and 2,4,6-mesityl3GeBr (10) (2.364(4) Å) as compared
to phenyl3GeBr (2.318(7) Å) [44,45].
Curiously, all three trinaphthylgermanium bromides crystallize
in the presence of either a solvent of crystallization as seen for 1-
naphthyl3GeBr $ toluene (9a), 1-naphthyl3GeBr $ CHCl3 (9b), or
with a naphthyl molecule as seen in 1-naphthyl3GeBr $ naphtha-
lene (9c) (Fig. 6) This highlights the inherent difficulties with
isolating naphthyl derivatives of germanium. Both GeꢁC and
GeꢁBr bond lengths do not seem to be affected by the solvent of
crystallization or cocrystallized naphthyl molecule, and compare
well to other triarylgermanium bromides with aryl residues
substituted at the ortho position.
Fig. 5. Crystal structure of 2-naphthyl4Ge (4). All non-carbon atoms shown as 50%
shaded ellipsoids. Hydrogen atoms removed for clarity.
reported tetraaryl substituted germanes (Table 2). Each molecule is
in a near tetrahedral environment with average CꢁGeꢁC angles of
109ꢀ. With respect to averaged GeꢁC bond lengths, these fall within
a narrow range of 1.94e1.96 Å and are not affected by the degree of
bulkiness afforded by the organic substituent onto the germanium
atom.
4. Conclusion
3.3. Triarylgermanium bromides or aryl3GeBr
Tetraarylgermanes and triarylgermanium halides were pre-
pared and fully characterized to gather new information on this
challenging compound class. Aryl residues with different steric
demands were applied, having ortho, meta or para substitution on
the phenyl ring, as is the case for o-tolyl, m-tolyl, 2,4-xylyl, 2,5-
In contrast to the tetraarylgermanes, the substituent position on
the residue around the central germanium atom in the triar-
ylgermanium derivatives does seem to have an effect on averaged
Table 2
List of selected bond lengths and angles for selected tetraaryl substituted germanes.
Space
Group
GeꢁC
CꢁGeꢁC
(Å) (avg.)
(ꢀ) (avg.)
phenyl4Ge [39e41]
o-tolyl4Ge [2,42]
m-tolyl4Ge [2]
p-tolyl4Ge [43]
3,4-xylyl4Ge
P-421c
P-1
I41/a
Pc
P21/c
P2/c
P21/n
1.960(2)
1.954(4)
1.956(3)
1.949(5)
1.943(7)
1.953(2)
1.953(2)
109.5(2)
109.5(2)
109.47(9)
109.5(2)
109.45(9)
109.48(9)
109.47(6)
1
2
3
4
3,5-xylyl4Ge
2-naphthyl4Ge
Table 3
List of selected bond lengths and angles for selected triaryl substituted germanium bromides.
Space Group
GeꢁC
GeꢁBr
CꢁGeꢁC
CꢁGeꢁBr
(Å) (avg.)
(Å)
(ꢀ) (avg.)
(ꢀ) (avg.)
phenyl3GeBr [44]
o-tolyl3GeBr
2,5-xylyl3GeBr
2,6-xylyl3GeBr
P21/c
P21/c
P21/c
P-1
R-3
P-1
R-3
P-1
R-3
1.934(1)
1.947(2)
1.948(2)
1.977(3)
1.946(5)
1.945(6)
1.946(3)
1.971(6)
1.997(2)
2.318(7)
2.339(3)
2.357(4)
2.345(5)
2.346(4)
2.346(8)
2.357(5)
2.364(4)
2.362(1)
112.4(4)
106.3(4)
5
7
8
9a
9b
9c
10
111.79(8)
113.11(10)
115.01(14)
110.84(7)
111.67(19)
111.03(13)
115.28(2)
108.26(6)
107.05(5)
105.50(7)
103.12(10)
108.07(7)
107.18(17)
107.86(9)
102.77(4)
110.66(6)
1-naphthyl3GeBr $ toluene
1-naphthyl3GeBr $ CHCl3
1-naphthyl3GeBr $ naphthalene
2,4,6-mesityl3GeBr
2-tbutylphenylGe3Br [45]

M. Wolf et al. / Journal of Organometallic Chemistry 851 (2017) 143e149
149
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Supplementary data related to this article can be found at
https://doi.org/10.1016/j.jorganchem.2017.09.027.
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