Structure/property relationships in branched oligogermanes. Preparation of (Me3Ge)3GePh, (Me2ButGe)3GePh, and (Me2PhGe)3GePh and investigation of their properties by spectroscopi

Article abstract of DOI:10.1016/j.jorganchem.2017.07.021

The three branched oligogermanes (Me₃Ge)₃GePh, (Me₂Bu^tGe)₃GePh, and (Me₂PhGe)₃GePh were synthesized via the hydrogermolysis reaction and were characterized by NMR (¹H,

Full text of DOI:10.1016/j.jorganchem.2017.07.021

Journal of Organometallic Chemistry 848 (2017) 104e113
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structure/property relationships in branched oligogermanes.
Preparation of (Me3Ge)3GePh, (Me2ButGe)3GePh, and (Me2PhGe)3GePh
and investigation of their properties by spectroscopic, spectrometric and
electrochemical methods
Sangeetha P. Komanduri a, F. Alexander Shumaker a, Sydney A. Hallenbeck a,
Cody J. Knight a, Claude H. Yoder b, Beth A. Buckwalter b, Craig P. Dufresne c,
Erico J. Fernandez d, Christopher A. Kaffel d, Ryan E. Nazareno d, Marshall Neu d,
,
*
Geoffrey Reeves d, James T. Rivard d, Lance J. Shackelford d, Charles S. Weinert a
a Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA
b Department of Chemistry, Franklin and Marshall College, Lancaster, PA 17064-3003, USA
c Thermo Fisher Scientific, 1400 Northpoint Parkway Suite 10, West Palm Beach, FL, 33407, USA
d University of Detroit Jesuit High School, 8400 South Cambridge, Detroit, MI 48221, USA
a r t i c l e i n f o
a b s t r a c t
The three branched oligogermanes (Me3Ge)3GePh, (Me2ButGe)3GePh, and (Me2PhGe)3GePh were syn-
thesized via the hydrogermolysis reaction and were characterized by NMR (1H, 13C, and 73Ge) spec-
troscopy. In addition, these three compounds and (Bun3Ge)3GePh were analyzed using high resolution
accurate mass mass spectrometry (HRAM-MS), which represents the first HRAM-MS investigation of
branched oligogermanes. The effects of varying the substituent pattern on the peripheral R3Ge- groups
on the electronic properties of these oligogermanes were investigated using cyclic and differential pulse
voltammetry (CV and DPV), UV/visible spectroscopy, and 73Ge NMR spectroscopy. The CV, DPV, and 73Ge
NMR data were compared to several previously reported branched oligogermanes, including (Bun
Article history:
Received 16 June 2017
Received in revised form
17 July 2017
Accepted 18 July 2017
Available online 20 July 2017
3
-
Ge)3GePh, (Ph3Ge)3GePh, (Ph3Ge)3GeH, and (Me3Ge)4Ge.
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
tin element e element bonds, organic substituents (n-butyl,
methyl, phenyl, etc.) are required.
Oligogermanes are the heavy analogues of hydrocarbons and,
The s-delocalization present in these molecules imparts upon
like their silicon- and tin-containing congeners, exhibit
s
-delocal-
them interesting optical and electronic properties. In the case of
germanium, these systems have been shown to function as optical
and electronic materials and have even recently been suggested to
function as single e molecule molecular wires [12e20]. Various
methods have been used over the years to prepare discrete oligo-
germanes and a number of linear, cyclic, and branched species have
been reported [5,8]. Our work has focused on the use of the
hydrogermolysis reaction between an germanium amide
R3GeNMe2 and a germane R3GeH for formation of germanium e
germanium single bonds. This reaction is carried out in acetonitrile
ization where the electrons comprising the element e element
bonds in these systems are delocalized over the chain rather than
localized between only two atoms [1e11]. This occurs via overlap of
the more diffuse orbitals located on the silicon, germanium, or tin
atoms and in order for effective s-delocalization to occur, the group
14 element atoms must be arranged in a trans-coplanar fashion.
Like their lighter hydrocarbon analogs, linear, cyclic, and branched
structures are known for these systems and in addition to the
oligomeric molecules, polymeric systems are also known. However,
in order to stabilize the substantially weaker silicon, germanium, or
at 85 ꢀC, and involves the in situ formation of an
a-germyl nitrile
R3GeCH2CN that is generated from the amide and the acetonitrile
solvent that is the active species in the germanium e germanium
bond forming process [21,22].
* Corresponding author.
E-mail address: weinert@chem.okstate.edu (C.S. Weinert).
http://dx.doi.org/10.1016/j.jorganchem.2017.07.021
0022-328X/© 2017 Elsevier B.V. All rights reserved.

S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
105
Prior to the mid-2000s branched oligogermanes were relatively
rare with only a few examples having been reported in the litera-
(Cl2PhGe)3GePh, which was subsequently treated with MeMgI to
yield 3 that was isolated as a liquid [24]. The previously synthesized
n-butyl substituted oligogermane 4 also is a liquid and did not yield
crystalline material [40].
ture. These included (Ph3Ge)3GeR (R ¼ H, CH3) [23], (Cl2PhGe)3
-
GePh [24], (Me2PhGe)3GePh [24], (PhX2Ge)3GePh (X ¼ OMe, SMe,
Me2N, Et2P) [25], (Me3Ge)3GeCl [26], and (Me3Ge)4Ge [26e28]. The
The appearance of the aryl region in the 1H and 13C NMR spectra
of 1e3 is nearly identical, although the spectrum for 3 has addi-
tional peaks for the three phenyl groups on the peripheral
Me2PhGe- ligands. A peak for the protons of the tert-butyl groups in
first report of a structurally characterized oligogermane (Ph3Ge)3
-
GePh appeared in 2008 [29], and since then a number of struc-
turally characterized branched species have been reported
including (Ph3Ge)3GeX (X ¼ H, Cl, Br, I) [30], the neo-pentyl analogs
(Ph3Ge)4Ge [31], (Me3Ge)3Ge(GePri3) [32], (Me3Ge)3GeSiPri3 [33],
(Me3Ge)3GeGe(GeMe3) [26,33], (Me3Ge)3GeGeMe2Ge(GeMe3)
[32,33], where the latter two compounds can be regarded as mixed
linear/branched species.
It has been shown through experimental and theoretical
methods that both the number of catenated germanium atoms and
the nature of the ancillary organic substituents affects the physical
properties of these oligogermanes [15,28,30,31,34e39]. Increasing
the number of catenated germanium atoms results in a red shift of
the absorbance maximum in the UV/visible spectra of these sys-
tems and the presence of inductively electron donating sub-
stituents also has this effect. Additionally, these two factors affect
the oxidation potential in these systems, which can be measured
using both cyclic (CV) and differential pulse (DPV) voltammetry.
Increasing either the number of catenated germanium atoms or the
inductive electron donating ability of the side groups decreases the
oxidation potential.
In both the UV/visible and electrochemical studies the variation
of the degree of catenation has a more profound effect on the
properties of these molecules than does variation of the organic
side groups. However, variation of the substituents does still result
in measurable changes in the properties of these molecules
[15,34,36]. In order to investigate the substituent effects on the
properties of branched oligogermanes, we have prepared and
characterized the three compounds (Me3Ge)3GePh (1), (Me2But-
Ge)3GePh (2), and (Me2PhGe)3GePh (3) and have compared their
voltammograms and absorbance spectra to the previously syn-
thesized systems (Bun3Ge)3GePh (4) [40] and (Ph3Ge)3GePh (5)
[29]. Additionally, 1e4 were also characterized by high resolution
accurate mass mass spectrometry (HRAM-MS) and 73Ge NMR
spectroscopy.
2 was observed at
d
0.98 in the 1H NMR spectrum of this compound.
All three 1H NMR spectra of 1e3 contain a singlet for the methyl
groups on the peripheral ligands, and these were observed at d 0.37
(1), 0.74 (2), and 0.27 (3) ppm. Similarly, the 13C NMR spectra of 1e3
are very similar in the aryl region except 3 contains four additional
peaks for the three peripheral phenyl groups. A resonance for the
methyl carbons of the tert-butyl substituents in 2 appears at
d
28.3 ppm while the central carbon results in a peak at
Resonances for the methyl groups in these oligogermanes appear at
0.2 (1), e 3.4 (2), and e 0.2 (3) ppm. The resonances for 2 and 3 are
d 26.9 ppm.
d
shifted upfield from that of 1 due to the increase in shielding
resulting from the replacement of a methyl group with a tert-butyl
group or phenyl group, with the tert-butyl group providing the
most shielding.
The cyclic and differential pulse voltammograms of 1e4 were
obtained and are shown as overlaid plots in Fig. 1 (CV) and 2 (DPV)
and values for their oxidation potentials are shown in Table 1. Ex-
periments were carried out in CH2Cl2 solvent using 0.1 M [Bun4N]
[PF6] as the supporting electrolyte and a Ag/AgCl reference elec-
trode. These data indicate that the order of ease of oxidation is 4 < 2
< 3 < 1 and the oligogermanes 1e3 each exhibit only single
oxidation wave, while 4 exhibits two distinct oxidation waves.
The observed oxidation potentials in these systems can be
correlated with the electron donor or acceptor properties of the
substituents on the three peripheral germanium atoms. The
methyl-substituted tetragermane 1 has the most positive oxidation
potential at 1951 (CV) and 1650 (DPV) mV. The three methyl sub-
stituents on the peripheral Me3Ge- groups essentially have no
inductive donating properties, while the single tert-butyl substit-
uent on each Me2ButGe- group in 2 is more electron donating. This
can be quantified by the inductive substituent constants for these
two groups, which are 0.00 for methyl and 0.300 for tert-butyl [41].
Therefore, the oxidation potential for 2 is less positive than that for
1 and was observed at 1782 (CV) and 1575 (DPV) mV, indicating
that 2 is easier to oxidize than 1 and this is consistent with previous
findings. More highly donating substituents destabilize the energy
of the HOMO in these systems, and as the energy of the HOMO is
destabilized the molecule is easier to oxidize [36,37,42].
2. Results and discussion
The three oligogermanes 1e3 were synthesized via the hydro-
germolysis reaction as shown in Scheme 1, where the amides
R3GeNMe2 (R3 ¼ Me3, Me2But, or Me2Ph) were prepared from the
corresponding chlorides and LiNMe2. All three of the oligo-
germanes were pale yellow liquids at room temperature and all
attempts to obtain X-ray quality crystals of these three compounds
were unsuccessful. Compound 3 was previously synthesized via a
different method involving the insertion of the germylene PhGeCl
The oxidation potential of the tetragermane 3 is 1877 (CV) and
1600 (DPV) mV, indicating that is intermediate between the cor-
responding values for 3 and 1. The introduction of a phenyl sub-
stituent in place of a tert-butyl or methyl substituent introduces the
possibility of
of the Ge4 backbone can overlap with the
p
-type interactions, where the
s-bonding framework
p
*-orbitals of the phenyl
into the germanium
e chlorine bonds of PhGeCl3 to give
ring. This has been previously reported for several linear and
branched oligogermanes that show that the phenyl ring acts as
both a
[30,31,34,36,37,42,43]. The inductive
from the phenyl substituent destabilizes the HOMO, while the
acceptor interaction stabilizes the HOMO. Therefore, the -donor
interaction renders 3 easier to oxidize than 1 but the -acceptor
interaction results in 3 being more difficult to oxidize that 2, which
contains a tert-butyl group that is a good -donor.
s-donor and
p-acceptor ligand, and so its effects are twofold
s
-donation of electron density
p
-
s
p
s
The oxidation potential of 4 is 1691 (CV) and 1500 (DPV) mV
indicating that 4 is easier to oxidize than all three branched oli-
gogermanes 1e3. The electron donating ability of the three n-butyl
substituents in 4 results in the most electron rich Ge4 framework
Scheme 1. Synthesis of compounds 1e3.

106
S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
Fig. 1. Overlaid CV plot 1e4 in CH2Cl2 solution with 0.1 M [Bun4N][PF6] as the supporting electrolyte.
Fig. 2. Overlaid DPV plot 1e4 in CH2Cl2 solution with 0.1 M [Bun4N][PF6] as the supporting electrolyte.

S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
107
Table 1
was further confirmed by elemental analysis. If a single Ge e Ge
bond is cleaved after the first oxidation event occurs, this would
result in the formation of either neutral or cationic Bun3Geꢁ that
would then be converted to Bun3GeCl upon abstraction of a chlorine
atom from CCl4. The remaining fragment would then be either
neutral or cationic (Bun3Ge)2GePhꢁ that might then be converted to
(Bun3Ge)2GePhCl. This trigermane fragment could then be the
second species that is oxidized in the second event and then un-
dergoes subsequent decomposition to provide two additional
equivalents of Bun3GeCl (Scheme 2). It is also possible that 1e3 and
5 also decompose in a similar fashion, but the products that are
generated after oxidation either polymerize or undergo rapid
further decomposition.
Electrochemical data for oligogermanes 1e5.
Compound
Eox (CV, mv)a
Eox (DPV, mV)b
(Me3Ge)3GePh (1)
(Me2ButGe)3GePh (2)
(Me2PhGe)3GePh (3)
(Bun3Ge)3GePh (4)
(Ph3Ge)3GePh (5)
1951
1782
1877
1650
1575
1600
1691, 2153
1500, 1950
1435c
1295c
a
Scan rate: 50 mV/s.
Pulse period: 0.5 s, pulse width 0.02 s, sampling time 0.01 s.
Data from Ref. [30].
b
c
among these four compounds, and so it is expected that the
oxidation potential for 4 would be the least positive. In addition, a
second irreversible oxidation wave for 4 was observed at 2153 (CV)
and 1950 (DPV) mV indicating the species generated after the first
oxidation event takes place is stable enough to undergo further
oxidation. Although multiple oxidation waves have been observed
for linear oligogermanes having aryl substituents attached to the
Ge e Ge backbone [31,35,44,45], this is the first example of such a
pattern for a branched system.
Due to the branched configuration of 1e4, it might be expected
that the species generated after the first oxidation event occurs
might be more stable than that generated after oxidation of linear
oligogermanes such that a return reduction wave might be
observed. Therefore, oligogermanes, 1e4 were analyzed using a
microelectrode with scan rates up to 5000 mV/s, but a return
reduction wave was not observed for any of these oligogermanes.
Among the oligogermanes 1e5 the perphenyl-substituted deriva-
tive 5 has the least positive oxidation potential, which is 1435 (CV)
and 1295 (DPV) mV [30]. The low oxidation potential for 5 is due to
The UV/visible spectra of 1e4 were acquired and an overlaid plot
of their spectra is shown in Fig. 3 and the absorbance data is
collected in Table 2. As is typical for the
s / s
* electronic transition
in oligogermanes the extinction coefficients are on the order of
104 Mꢂ1 cmꢂ1. It has been observed with other oligogermanes that
the electronic and steric nature of the organic substituents on the
germanium atoms has a measurable effect on the HOMO/LUMO gap
and therefore on the position of the lmax for these compounds
[30,34,36,42]. Oligogermanes 2 and 4 have the highest energy
absorbance maxima at 223 and 224 nm, respectively, and therefore
these two oligogermanes have the largest HOMO/LUMO gap. The
trimethyl-substituted oligogermane 1 has a lmax at 237 that is red-
shifted relative to those for 2 and 4 indicating that it has a larger
HOMO/LUMO gap than both 2 and 4. Oligogermane 3 has a lmax at
245 nm due to the presence of a phenyl substituent on the three
peripheral germanium atoms, where the
groups are in conjugation with the -bonding system of the Ge4
p
*-orbitals of the phenyl
s
backbone resulting in a decrease of the HOMO/LUMO gap.
the
s-donor capabilities of the nine peripheral phenyl rings.
The three branched oligogermanes 1e3 were characterized by
73Ge NMR spectroscopy (Fig. 4) and their spectroscopic data, along
with those for 4 [40], 5 [40], (Ph3Ge)3GeH (6) [30] and (Me3Ge)4Ge
(7) [28] are collected in Table 3. This nucleus is difficult to measure
since the nuclear spin is 9/2 and the resonance frequency is
17.4 MHz at a magnetic field strength of 11.743 T, resulting in sig-
nificant acoustic ringing in the probe during acquisition [47e52].
However, 73Ge NMR data for a number of oligogermanes have been
reported and the chemical shifts for the germanium atoms have
been shown to be dependent on the substituent pattern present.
Resonances for trisubstituted germanium atoms R3Ge- typically are
Despite the presence of the phenyl substituents, analysis of 5 using
a microelectrode with fast scan rates also did not result in the
observation of a return reduction wave.
A second oxidation wave was not observed for 1e3 nor for 5 as
was seen for 4. Presumably, the significant inductive electron
donating nature of the n-butyl substituents imparts stability to the
product that is formed after 4 undergoes oxidation. It is likely that
both linear and branched oligogermanes break apart by homolytic
scission of the Ge e Ge bonds after the oxidation event takes place,
and we have shown that this is what occurs in these species upon
photolysis [46]. Several attempts to isolate the products being
generated after oxidation failed using bulk electrolysis in the
presence of acetic acid, which should trap any germanium-based
radicals or germylenes that are generated after oxidation.
Bulk electrolysis experiments on 1e5 were conducted in a
three-compartment cell in a 0.1 M solution of [Bun4N][PF6] in
CH2Cl2 in the presence of 10 M equiv. of acetic acid. The working
electrode potential was held at 50 mV higher than the oxidation
potential measured by CV for at least 3 h. After removal of the
solvent from the reaction mixtures, the residual electrolytes were
washed with hexane, the mixtures were filtered, and the hexane
solvent was removed from each sample under vacuum. In each case
an intractable mixture of products resulted that contained no
identifiable products by 1H NMR spectroscopy.
observed between
tuted germanium atoms eR2Ge- range from
and those for monosubstitued germanium atoms RGe- are further
upfield between e 185 to e 235 ppm.
A resonance for the central germanium atoms in 1e5 was
observed in each case, and the chemical shifts range from e 188 to
d
e 30 to e 75 ppm, while those for disubsti-
d
e 110 to e 140 ppm
d
d
e 207 ppm. Peaks for the central germanium atom of the trialkyl-
substituted oligogermanes 1 and 4 appear the furthest downfield,
at
central germanium atom in 2 and 3 appear upfield from those in 1
and 4 at e 207 and e 204 ppm, respectively, and are similar to the
d e 188 and e 195 ppm, respectively. The resonances for the
d
resonance for the central germanium atom of 5 as well [40]. The
presence of aryl and branched alkyl substituents such as tert-butyl
or iso-propyl has been previously shown to impart an upfield shift
on the 73Ge NMR resonances in linear oligogermanes as well
[40,50]. The chemical shifts for the central germanium atom in 1e5
are each further downfield than those for 6 and 7, which were
Alternatively, the use of CCl4 was attempted as a trapping agent
for radicals using the same experimental method. Although the
final product mixture obtained from bulk electrolysis of 1e3 and 5
again contained no identifiable products, that obtained from 4
contained a significant amount of Bun3GeCl that was isolated by
distillation. The 1H and 13C NMR spectra of the distillate were
identical to that of a commercial sample of Bun3GeCl and its identity
observed at
d e 311 and e 339 ppm, respectively [28,30]. The
attachment of a hydrogen or a fourth trialkyl-substituted germa-
nium atom in place of the phenyl substituents in 1e5 has a sig-
nificant shielding effect [50].

108
S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
Scheme 2. Proposed electrochemical decomposition pathway of 4.
Fig. 3. Overlaid UV/visible plot for oligogermanes 1e4 in CH2Cl2 solution.
Table 2
molecules. However, this also can occur in oligogermanes having
germanium atoms that have three identical organic substituents, as
was observed for 5. Defined resonances for the peripheral germa-
UV/visible data for oligogermanes 1e4 in CH2Cl2 solution.
Compound
lmax (nm)
ε (Mꢂ1 cmꢂ1
)
nium atoms in 1 and 4 were observed, where the peak at
d e
(Me3Ge)3GePh (1)
(Me2ButGe)3GePh (2)
(Me2PhGe)3GePh (3)
(Bun3Ge)3GePh (4)
237
223
245
224
2.0 ꢃ 104
5.2 ꢃ 104
5.5 ꢃ 104
7.4 ꢃ 104
45 ppm in 1 is similar to that for the Me3Ge- groups in 7. The
resonance for the Bun3Ge- groups in 4 is also in the usual region for
trialkyl-substituted germanium atoms [40].
The High Resolution Accurate Mass mass spectra for compounds
1e4 were acquired, and to our knowledge these data are the first
HRAM-MS studies conducted on branched oligogermanes. There
are five non-radioactive isotopes of germanium and the three most
abundant isotopes (74Ge, 72Ge, and 70Ge) result in a distinct pattern
in their mass spectra. The HRAM-MS data for 1e4 are collected in
Table 4 and several mass spectra are shown in Fig. 5. As we have
previously observed using this method [46], the parent compounds
Resonances were observed for the peripheral germanium atoms
only in 1 and 4. The presence of a symmetric environment about
germanium is typically required in order to observe 73Ge NMR
resonances that are sharp enough to observe. An asymmetric
environment often results in the broadening of the resonances into
the baseline. Peaks for the peripheral germanium atoms in 2 and 3
were not observed due to the substituent pattern in these two

S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
109
Fig. 4. 73Ge NMR spectra of 1 (top), 2 (middle), and 3 (bottom) in benzene-d6 solution. Note: The sharp line in the middle of the spectrum of 1 is an artifact.

110
S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
Table 3
73Ge NMR data for oligogermanes 1e5.a
Compound
d
eGeperipheral (ppm)
D1/2 eGeperipheral (Hz)
d
eGecentral (ppm)
D1/2 eGecentral (Hz)
(Me3Ge)3GePh (1)
(Me2ButGe)3GePh (2)
(Me2PhGe)3GePh (3)
(Bun3Ge)3GePh (4)
(Ph3Ge)3GePh (5)
(Ph3Ge)3GeH (6)
e 45
n/o
n/o
e 33
n/o
e 56
e 38
296
n/o
n/o
240
n/o
35
e 188
e 207
e 204
e 195
e 202
e 311
e 339
157
296
104
100
290
n/ob
9
(Me3Ge)4Ge (7)
164
a
n/o ¼ not observed.
b
The resonance at e 311 ppm is a doublet.
Table 4
HRAM-MS data for oligogermanes 1e4.
Compound
m/z
Assignment
Calcd. m/z
Error (ppm)
1
595.9871
425.9714
309.9878
160.0173
670.0970
551.0922
510.0656
352.0331
243.0907
202.0641
161.0377
782.0344
377.0171
222.0328
181.0063
922.3793
678.2539
528.2840
286.1579
245.1315
(Me3Ge)2(Me3GeO)GePh(CH3CN)(H2O)2 þ Hþ
(Me3Ge)2GePh(CH3CN)þ
(Me3Ge)GePh(CH3CN) þ Hþ
Me3Ge(CH3CN)þ
595.9890
425.9713
309.9866
160.0176
670.1138
551.0918
510.0652
352.0336
243.0911
202.0646
161.0380
782.0359
377.0176
222.0333
181.0067
922.3955
678.2530
528.2840
286.1585
245.1319
3.2
0.2
3.9
1.9
25.0
0.7
7.8
1.4
1.6
2.5
1.9
1.9
1.3
2.3
2.2
17.6
1.3
0.1
2.1
1.6
2
(Me2ButGe)3GePh(CH3CN) þ Hþ
(Me2ButGe)2GePh(CH3CN)þ2
(Me2ButGe)2GePh(CH3CN)þ
(Me2ButGe)GePh(CH3CN) þ Hþ
(Me2ButGe)(CH3CN)þ2
(Me2ButGe)(CH3CN)þ
(Me2ButGe)þ
3
4
(Me2PhGe)2(Me2PhGeO)GePh(CH3CN)(H2O)2 þ Hþ
(Me2PhGe)2O þ Hþ
Me2PhGe(þCH3CN)þ
Me2PhGe
(Bun3Ge)3GePh(CH3CN) þ Hþ
(Bun3Ge)2GePh(CH3CN)þ
(Bun3Ge)2(CH3CN)þ
Bun3Ge(CH3CN)þ
Bun3Geþ
are typically observed as adducts with acetonitrile, which is the
solvent used in the measurements, and/or water that is present in
trace amounts in the acetonitrile. Germoxanes are also often
observed that result from the insertion of an oxygen atom into one
of the Ge e Ge bonds in the oligogermane.
The HRAM-MS of 1 contains four main peaks. The parent com-
pound is observed as a germoxane complexed with one CH3CN
molecule and two water molecules. This ion is protonated and the
added proton could be attached to either a water or acetonitrile
molecule, or to the oxygen atom of the germoxane. As previously
observed with other oligogermanes, 1 undergoes fragmentation
under the experimental conditions resulting in the observation of
the (Me3Ge)2GePh(CH3CN)þ ion due to loss of the Me3GeO- group,
the protonated (Me3Ge)GePh(CH3CN)Hþ ion resulting from the loss
of a Me3Ge- group, and the Me3Ge(CH3CN)þ ion from fragmenta-
tion of all three of the peripheral Me3Ge- groups.
molecular ion was observed as the protonated acetonitrile solvate
(Bun3Ge)3GePh(CH3CN)Hþ, and this species fragments via loss of a
Bun3Ge- group to yield the (Bun3Ge)2GePh(CH3CN)þ ion. Formation of
the solvated digermane ion (Bun3Ge)2(CH3CN)þ was also observed
and the peripheraltri-n-butyl germane groups result in the formation
of the (Bun3Ge)(CH3CN)þ and Bun3Geþ ions.
In summary, the three branched oligogermanes (Me3Ge)3GePh
(1), (Me2ButGe)3GePh (2), and (Me2PhGe)3GePh (3) were synthe-
sized using the hydrogermolysis reaction and along with (Bun
3-
Ge)3GePh (4) were characterized by cyclic and differential pulse
voltammetry as well as UV/visible spectroscopy. These studies
indicate that variation of the substituents on the three peripheral
germanium atoms imparts measurable changes in both their
oxidation potentials and their absorbance spectra. Among these
four oligogermanes, 4 is unique in that it exhibits two irreversible
oxidation waves in both its CV and DPV while 1e3 only exhibit a
single wave. Furthermore, bulk electrolysis of 4 in the presence of
CCl4 resulted in the isolation of Bun3GeCl indicating that these
oligogermanes decompose by homolytic scission of the Ge e Ge
bonds to generate radical species.
Compound 2 does not undergo oxygen insertion into a Ge e Ge
bond and the parent compound was found as the protonated aceto-
nitrile adduct (Me2ButGe)3GePh(CH3CN)Hþ. Fragmentation of 2 also
occurredandlossofoneMe2ButGe- group resulted intheformation of
the (Me2ButGe)2GePh(CH3CN)þn ions (n ¼ 1 or 2), while loss of a sec-
ond Me2ButGe- groupgenerated the(Me2ButGe)GePh(CH3CN)Hþ ion.
The fragmentation of the three peripheral Me2ButGe- groups lead to
the observation of the Me2ButGe(CH3CN)nþ ions (n ¼ 1e3).
Oligogermanes 1e3 were characterized by 73Ge NMR spectros-
copy, and only in the case of 1 were resonances observed for both
the peripheral and central germanium atoms, since 1 has a sym-
metric substitution pattern at the peripheral Ge atoms. The four
oligogermanes 1e4 were also characterized by HRAM-MS and their
mass spectra each show an ion corresponding to the parent com-
pound that was observed as either an adduct with the acetonitrile
solvent and/or a germoxane that results from insertion of an
The molecular ion of 3 in its HRAM-MS was found as the proton-
ated germoxane (Me2PhGe)2(Me2PhGeO)GePh(CH3CN)(H2O)2Hþ,
and thisfragmentsintotheprotonateddigermoxane (Me2PhGe)2OHþ
as well as the Me2PhGe(CH3CN)þ and Me2PhGeþ ions. For 4, the

S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
111

112
S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
oxygen atom into the Ge e Ge bonds of these species. The parent
ions undergo fragmentation resulting in the observation of several
daughter ions. These studies represent the first use of HRAM-MS
investigations on branched oligogermanes.
C6H5), 0.2 (-CH3) ppm. Anal. Calcd. for C15H32Ge4: C, 35.80; H, 6.41.
Found: C, 35.91; H, 6.38.
3.3. Synthesis of (Me2ButGe)3GePh (2)
In a Schlenk tube, a solution of Me2ButGeNMe2 (1.60 g, 7.85 mmol)
in 11 mL of CH3CN was added to PhGeH3 (0.390 g, 2.55 mmol). The
tube was sealed with a Teflon plug and the reaction mixture was
heated in an oil bath at 95 ꢀC for 72 h. The solutionwas transferred via
cannula to a Schenk flask and the volatiles were removed in vacuo to
yield a pale yellow oil. Byproducts were removed from the crude
product by distillation ina Kugelrohroven (120ꢀC, 0.03torr) toyield 2
3. Experimental section
3.1. General remarks
All manipulations were carried out under a nitrogen atmo-
sphere using standard Schlenk, syringe, and glovebox techniques.
Solvents were dried using a GlassCountour solvent purification
system. The reagents Me3GeNMe2 [53,54], Me2ButGeNMe2 [36],
and Me2PhGeNMe2 [40] were prepared using literature procedures
and PhGeH3 was purchased from Gelest and used without further
purification. NMR spectra were acquired using a Bruker Inova
spectrometer operating at 400.00 MHz (1H) or 100.57 MHz (13C).
Germanium-73 NMR spectra of the products (50 mg/mL in ben-
zene-d6) were recorded on a Varian INOVA 500 MHz spectrometer
using a 10-mm low gamma broadband probe at 17.43 MHz with the
Carr-Purcell-Maiboom-Gill (CPMG) pulse sequence [55,56] to
reduce baseline roll. The following parameters were used with
proton decoupling during acquisition: spectral width ¼ 100,000 Hz,
acquisition time ¼ 0.01 s (except for compound 2) that used 0.50 s,
delay time ¼ 0 s, line broadening factor ¼ 20, number of
transients ¼ 1 ꢃ 106 to 1 ꢃ 107. This pulse sequence was found to
give peak widths within ca. 5% of those obtained using the standard
pulse sequence up to peak widths of ca. 800 Hz. Based on multiple
runs of the same sample, the error in the chemical shifts is esti-
mated to be 3 ppm. The error in helf-height linewidths is ca. 10%.
No correction was applied to the measurement of overlapping
peaks. The spectra were referenced to an external GeMe4 sample.
UV/visible spectra were obtained using an Ocean Optics Red Tide
USB650UV spectrometer. Electrochemical data (CV, DPV, BE) were
obtained using a DigiIvy DY2312 potentiostat using a glassy carbon
working electrode, a platinum wire counter electrode, and a Ag/
AgCl reference electrode in CH2Cl2 solution using 0.1 M [Bu4N][PF6]
as the supporting electrolyte. HRAM-MS data were collected using
a Thermo Fisher Q Exactive™ Hybride Quadrupole-Orbitrap™ Mass
Spectrometer. Elemental analyses were conducted by Galbraith
Laboratories.
(1.38 g, 86%) as a pale yellow oil. 1H NMR (C6D6, 25 ꢀC)
d 7.51 (d,
J ¼ 8.0 Hz, 2H, o-C6H5), 7.17e7.03 (m, 3H, m-C6H5 and p-C6H5), 0.98 (s,
27H, -C(CH3)3), 0.74 (s, 9H, -CH3) ppm. 13C{1H} NMR (C6D6, 25 ꢀC)
d
138.8 (ipso-C6H5), 136.0 (o-C6H5), 128.4 (m-C6H5), 127.8 (p-C6H5),
28.3 (-C(CH3)3), 26.9 (-C(CH3)3), ꢂ3.4 (s, -CH3) ppm. Anal. Calcd. for
24H50Ge4: C, 45.79; H, 8.01. Found: C, 45.66; H, 8.06.
C
3.4. Synthesis of (Me2PhGe)3GePh (3)
In Schlenk tube, solution of Me2PhGeNMe2 (1.37 g,
a
a
6.12 mmol) in 12 mL of CH3CN was added to PhGeH3 (0.30 g,
1.97 mmol). The tube was sealed with a teflon plug and the reaction
mixture was heated in an oil bath at 95 ꢀC for 72 h. The reaction
mixture was transferred via cannula to a Schlenk flask and the
volatiles were removed in vacuo to yield yellow oil. Byproducts
were removed from the crude product by distillation in a Kugelrohr
oven (130 ꢀC, 0.02 torr) to yield 3 (1.11 g, 82%) as a pale yellow oil. 1H
NMR (C6D6, 25 ꢀC)
d 7.31e7.25 (m, 8H, o-C6H5Ge and o-C6H5Me2Ge),
7.12e7.05 (m, 4H, p-C6H5Ge and p-C6H5Me2Ge), 6.92e6.80 (m, 8H,
m-C6H5Ge and m-C6H5Me2Ge), 0.27 (s, 18H, -CH3) ppm. 13C{1H}
NMR (C6D6, 25 ꢀC)
d 141.7 (ipso-C6H5Ge), 138.8 (ipso-C6H5Me2Ge),
136.6 (o-C6H5Ge), 134.0 (o-C6H5Me2Ge), 128.4 (m-C6H5Ge), 123.3
(m-C6H5Me2Ge), 127.9 (p-C6H5Ge), 127.8 (p-C6H5Me2Ge), - 0.2 (s,
-CH3) ppm. Anal. Calcd. for C30H38Ge4: C, 52.26; H, 5.56. Found: C,
52.15; H, 5.49.
3.5. Bulk electrolysis of (BunGe3)3GePh (4)
To a 1.0 M solution of [Bun4N][PF6] in CH2Cl2 (150 mL) was added
4 (0.400 g, 0.454 mmol) and CCl4 (2.50 g, 16.3 mmol). Under a
stream of nitrogen, the mixture was transferred to a three
compartment cell having a reticulated vitreous carbon electrode, a
platinum wire counter electrode, and a Ag/AgCl reference elec-
trode. The sample was electrolyzed at a potential of 2200 mV for 3 h
under a stream of nitrogen. The reaction mixture was transferred to
a Schlenk flask and the volatiles were removed in vacuo. The
resulting residue was washed with hexane (2 ꢃ 25 mL), the mixture
was filtered, and the volatiles were removed from the filtrate in
vacuo to yield a colorless oil. The crude product mixture was
distilled (275 C, 760 torr) to yield Bun3GeCl (0.20 g, 52%) as a
colorless oil. The 1H and 13C NMR spectra matched that of a com-
mercial sample (Gelest). Anal. Calcd. for C12H27ClGe: C, 51.56; H,
9.74. Found: C, 51.51; H, 9.76.
3.2. Synthesis of (Me3Ge)3GePh (1)
In a Schlenk tube, a solution of Me3GeNMe2 (0.810 g, 5.01 mmol)
in 15 mL of CH3CN was added to PhGeH3 (0.255 g, 1.67 mmol). The
tube was sealed with a Teflon plug and the reaction mixture was
heated in an oil bath at 85 ꢀC for 72 h. The solution was transferred
via cannula to a Schenk flask and the volatiles were removed in
vacuo to yield a pale yellow/orange oil. Byproducts were removed
from the crude product by distillation in a Kugelrohr oven (125 ꢀC,
0.04 torr), which yielded 1 (0.60 g, 72%) as a pale yellow oil. 1H NMR
(C6D6, 25 ꢀC)
C6H5 and p-C6H5), 0.37 (s, 27H, -CH3) ppm. 13C{1H} NMR (C6D6,
25 ꢀC)
137.2 (ipso-C6H5), 135.8 (o-C6H5), 128.5 (m-C6H5), 127.8 (p-
d
7.52 (d, J ¼ 7.6 Hz, 2H, o-C6H5), 7.19e7.05 (m, 3H, m-
d
Fig. 5. HRAM-MS spectra for 1e4.
a). HRAM-MS spectrum of (Me3Ge)2(Me3GeO)GePh(CH3CN)(H2O)2 þ Hþ
.
b). HRAM-MS spectrum of Me3Ge(CH3CN)þ
.
c). HRAM-MS spectrum of (Me2ButGe)3GePh(CH3CN) þ Hþ
.
d). HRAM-MS spectrum of (Me2ButGe)(CH3CN)þ
.
e). HRAM-MS spectrum of (Me2PhGe)2(Me2PhGeO)GePh(CH3CN)(H2O)2 þ Hþ
.
þ
f). HRAM-MS spectrum of Me2PhGe
.
g). HRAM-MS spectrum of (Bun3Ge)3GePh(CH3CN) þ Hþ
.
h). HRAM-MS spectrum of Bun3Geþ
.

S.P. Komanduri et al. / Journal of Organometallic Chemistry 848 (2017) 104e113
113
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(2008) 1979e1984.
Acknowledgements
[30] C.R. Samanamu, M.L. Amadoruge, C.H. Yoder, J.A. Golen, C.E. Moore,
A.L. Rheingold, N.F. Materer, C.S. Weinert, Organometallics 30 (2011)
1046e1058.
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A.L. Rheingold, N.F. Materer, C.S. Weinert, Organometallics 31 (2012)
4374e4385.
This work was supported by a research grant from the National
Science Foundation (NSF), USA (Grant Number CHE-1464462) and
is gratefully acknowledged.
[32] J. Hlina, R. Zitz, H. Wagner, F. Stella, J. Baumgartner, C. Marschner, Inorg. Chim.
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