Synthetic, structural, and physical investigations of the large linear and branched oligogermanes Ph3GeGePh2GePh2GePh 2H, Ge5Ph12, and (Ph3Ge) 4Ge

Article abstract of DOI:10.1021/om300385n

The syntheses of two linear oligogermanes, Ph₃GeGePh ₂GePh₂GePh₂H and Ge₅Ph₁₂, were achieved using a hydrogermolysis reaction starting with HPh ₂GeGePh₂GePh₂H. The preparation of the hydride-terminated tetragermane indicates that selectivity is possible using the hydrogermolysis reaction, which had not been observed previously. The structures of both of these compounds were determined, and they were also characterized by UV/visible spectroscopy and electrochemical methods (CV and DPV). The pentagermane Ge₅Ph₁₂ exhibits four irreversible oxidation waves in both its CV and DPV, as was observed for other aryl-substituted oligogermanes. The successful synthesis of the neopentane analogue (Ph₃Ge)₄Ge was also achieved by starting from GeH₄ and Ph₃GeCH₂CN. This material was structurally characterized; the structure of (Ph₃Ge)₄Ge is highly sterically congested and contains long Ge-Ge single-bond distances that average 2.497(6) A and exhibits an nearly idealized tetrahedral geometry at the central germanium atom with an average Ge-Ge-Ge bond angle of 109.49(2)°. The UV/visible spectrum of (Ph₃Ge)₄Ge exhibits a broad absorbance maximum centered at 250 nm, and DFT calculations indicate that this compound has a stabilized HOMO at -6.223 eV and a large HOMO-LUMO gap relative to those in other branched oligogermanes.

Full text of DOI:10.1021/om300385n

Article
pubs.acs.org/Organometallics
Synthetic, Structural, and Physical Investigations of the Large Linear
and Branched Oligogermanes Ph3GeGePh2GePh2GePh2H, Ge5Ph12,
and (Ph3Ge)4Ge
Christian R. Samanamu,† Monika L. Amadoruge,† Aaron C. Schrick,† Chao Chen,‡ James A. Golen,‡,§
Arnold L. Rheingold,‡ Nicholas F. Materer,† and Charles S. Weinert*,†
†Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States
‡Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0358, United States
§Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747,
United States
S
* Supporting Information
ABSTRACT: The syntheses of two linear oligogermanes, Ph3GeGePh2GePh2GePh2H and Ge5Ph12, were achieved using a
hydrogermolysis reaction starting with HPh2GeGePh2GePh2H. The preparation of the hydride-terminated tetragermane
indicates that selectivity is possible using the hydrogermolysis reaction, which had not been observed previously. The structures
of both of these compounds were determined, and they were also characterized by UV/visible spectroscopy and electrochemical
methods (CV and DPV). The pentagermane Ge5Ph12 exhibits four irreversible oxidation waves in both its CV and DPV, as was
observed for other aryl-substituted oligogermanes. The successful synthesis of the neopentane analogue (Ph3Ge)4Ge was also
achieved by starting from GeH4 and Ph3GeCH2CN. This material was structurally characterized; the structure of (Ph3Ge)4Ge is
highly sterically congested and contains long Ge−Ge single-bond distances that average 2.497(6) Å and exhibits an nearly
idealized tetrahedral geometry at the central germanium atom with an average Ge−Ge−Ge bond angle of 109.49(2)°. The UV/
visible spectrum of (Ph3Ge)4Ge exhibits a broad absorbance maximum centered at 250 nm, and DFT calculations indicate that
this compound has a stabilized HOMO at −6.223 eV and a large HOMO−LUMO gap relative to those in other branched
oligogermanes.
which occurs via overlap of the relatively large sp3-hybridized
orbitals. In addition, these compounds also absorb in the UV
region and are electrochemically active as a result of their σ
delocalization. The observed UV/visible spectra result from
electronic transitions from the bonding σ orbital to the antibonding
σ* orbital, both of which are localized on the element−element
backbone.
In the case of germanium, the longest discrete linear mole-
cule that has been reported is Ge10H22,46 while the longest
linear molecule that has been crystallographically characterized
is Ge5Ph12.47 Branched oligogermanes are somewhat un-
common, and the first crystallographically characterized
INTRODUCTION
Catenated compounds of the group 14 elements can be regarded
as heavy analogues of simple organic molecules, and both
■
“saturated” species having element−element single bonds and
“unsaturated” species having element−element multiple bonds
have been realized for silicon,1−11 germanium,12−22 and tin.23−42
In addition, various branched and cage-type structures are known
for these elements. However, while long-chain hydrocarbons,
highly branched structures, and polycyclic species are very
common for carbon catenates, these types of materials are less
known for the heavier group 14 elements.
Heavy group 14 singly bonded catenates are of interest since
they possess inherent σ delocalization,43−45 where the bonding
electrons situated in the highest occupied molecular orbital are
delocalized over part or all of the element−element framework
Received: May 7, 2012
Published: May 31, 2012
© 2012 American Chemical Society
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Scheme 1
example of one of these compounds was (Ph3Ge)3GePh, which
was reported in 2008.48 Since then, the structures of (Ph3Ge)3-
GeH,49,50 (Ph3Ge)3GeX (X = Cl, Br, I),49,50 (Me3Ge)3GeGe-
(GeMe3)3,51 (Me3Ge)3GeGeMe2Ge(GeMe3)3,51 and the salt
complex K[(18-crown-6)2][(Me2Ge)2GeGe(GeMe2)2]51 have
been described. We now wish to report the synthesis and char-
acterization of the linear oligogermanes Ph3GeGePh2GePh2GePh2H
(1) and Ge5Ph12 (2), which were obtained by the hydrogermo-
lysis reaction. Compound 1 is a rare example of a structurally
characterized hydride-terminated oligogermane. In addition, we
also have obtained the highly sterically congested (Ph3Ge)4Ge
(7), which is the first structurally characterized example of a
germanium analogue of neopentane. This compound was
thought to be an “impossible molecule” due to the steric environ-
ment at the central germanium atom, and our previous attempts
to synthesize this molecule were not successful.50 In addition,
density functional theory (DFT) calculations on this species
did not converge,52 also leading to our postulating that the
synthesis of 7 might not be possible. The synthesis and full
characterization of 7 are also described herein.
resolved. However, the 13C NMR spectrum of 1 contains the
expected 16 signals for each of the magnetically nonequivalent
carbon atoms present in 1. The UV/visible spectrum of 1 ex-
hibits a broad λmax at 269 nm (ε = 4.5 × 104 M−1 cm−1) that is
blue-shifted in comparison to the λmax value for Ge4Ph10 (3)
reported at 282 nm,55 due to the presence of a terminal
−GePh2H group in 1 versus a −GePh3 group in 3.
Crystals of 1 suitable for X-ray analysis were obtained; an
ORTEP diagram of 1 is shown in Figure 1, and selected bond
RESULTS AND DISCUSSION
■
The hydride-terminated tetragermane Ph3GeGePh2GePh2-
GePh2H (1) was prepared from HGePh2GePh2GePh2H and
Ph3GeNMe2 (Scheme 1). The starting oligogermane HGePh2-
́
GePh2GePh2H was obtained by the method of Satge et al. by
treatment of Ph2GeH2 with ButLi in Et3N solvent with a re-
action time of 9.5 h.53 Curiously, the reaction of HGePh2-
GePh2GePh2H with 1 equiv of Ph3GeNMe2 in CH3CN solvent
produced only the tetragermane 1 in 79% yield, with no
evidence for the formation of the pentagermane Ge5Ph10 (2).
This finding is interesting, since we have not previously
observed a selective reaction of one terminal hydride site in an
oligogermane with an incoming germanium α-germyl nitrile
which is formed via the in situ reaction of a germanium amide
with the CH3CN solvent. The digermane HPh2GeGePh2H
reacts with Ph3GeNMe2 or Tol3GeNMe2 (Tol = p-tolyl) to
provide the tetragermanes Ge4Ph10 (3) and Tol3GeGePh2GePh2-
GeTol3 (4), with no evidence for the formation of the hydride-
Figure 1. ORTEP plot of Ph3GeGePh2GePh2GePh2H (1). Thermal
ellipsoids are drawn at the 50% probability level.
distances and angles are collected in Table 1. Compound 1 is
an unusual example of a catenated germanium compound
having a refined Ge−H distance that measures 1.50(4) Å,
which is similar to reported distances in monomeric germanium
hydride compounds.56−59 The three Ge−Ge distances in 1
average 2.4531(6) Å, and the average Ge−Ge−Ge bond angle
is 114.88(2)°. The bond angle at Ge(2) measuring 110.23(2)°
is substantially more acute than that at Ge(3), which is 119.53(2)°,
due to the presence of the terminal hydrogen atom bound to
Ge(1) versus the third phenyl ring attached to Ge(4). The
structure of 1 can be compared to those of the tetragermanes
Ge4Ph10·2C6H6 (3·2C6H6)55 and Tol3GeGePh2GePh2GeTol3
terminated trigermane Ar3GeGePh2GePh2H.54 The H NMR
1
spectrum of 1 contains a singlet at δ 5.67 ppm corresponding to
the terminal hydrogen atom, and several of the signals assigned
to the aromatic hydrogen atoms of the phenyl rings are not
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Table 1. Selected Bond Distances (Å) and Angles (deg) for
Ph3GeGePh2GePh2GePh2H (1)
Ge(1)−Ge(2)
Ge(2)−Ge(3)
Ge(3)−Ge(4)
Ge(1)−H(1)
Ge(1)−C(1)
2.4466(5)
2.4577(6)
2.4551(5)
1.50(4)
Ge(2)−C(49)
Ge(3)−C(37)
Ge(3)−C(43)
Ge(4)−C(19)
Ge(4)−C(25)
Ge(4)−C(31)
1.962(3)
1.964(3)
1.969(3)
1.957(3)
1.961(3)
1.967(4)
1.956(3)
1.962(4)
1.969(3)
110.23(2)
107(1)
Ge(1)−C(7)
Ge(2)−C(13)
Ge(1)−Ge(2)−Ge(3)
Ge(2)−Ge(1)−H(1)
Ge(2)−Ge(3)−Ge(4)
C(1)−Ge(1)−C(7)
C(1)−Ge(1)−H(1)
C(7)−Ge(1)−H(1)
C(13)−Ge(2)−C(49)
C(37)−Ge(3)−C(43)
C(19)−Ge(4)−C(25)
C(19)−Ge(4)−C(31)
C(25)−Ge(4)−C(31)
108.2(1)
110.1(2)
107.3(1)
106.3(2)
107.5(1)
119.53(2)
106.0(1)
104(1)
108(1)
Figure 2. ORTEP plot of Ge5Ph12 (2). Thermal ellipsoids are drawn at
the 50% probability level.
(4; Tol = p-CH3C6H4),60 which are both C2 symmetric.
3·2C6H6 has an average Ge−Ge bond distance of 2.462(3) Å
and a Ge−Ge−Ge bond angle of 117.8(1)°, while in 4
the corresponding values are 2.454(4) Å and 117.2(2)°.
The terminal Ge(1)−Ge(2) bond in 1 is shorter than the
corresponding distance in 3·2C6H655 by 0.016 Å, and the Ge−
Ge−Ge bond angle centered at Ge(2) in 1 is more acute than the
corresponding angle in 3·2C6H6 by 7.8°. The average Ge−Ge
bond length in 460 is only slightly shorter than that in 1, while
the average Ge−Ge−Ge bond angle in 1 is more acute than the
average angle in 4 by 3.0°. The shorter Ge−Ge bond distances
and more acute Ge−Ge−Ge bond angles in 1 result from the the
presence of a terminal hydrogen atom in 1, which lowers the overall
steric congestion in the molecule and therefore results in the
different metric parameters in 1 versus those in 3·2C6H6 and 4.
The reaction of 1 with another 1 equiv of Ph3GeNMe2 yielded
the pentagermane Ge5Ph12 (2) in 83% yield, and compound 2
could also be obtained directly from HPh2GeGePh2GePh2H
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Ph3GeGePh2GePh2GePh2GePh3 (2)
Ge(1)−Ge(2)
Ge(2)−Ge(3)
Ge(3)−Ge(4)
Ge(4)−Ge(5)
Ge(1)−C(55)
Ge(1)−C(61)
Ge(1)−C(67)
Ge(2)−C(43)
Ge(1)−Ge(2)−Ge(3)
Ge(2)−Ge(3)−Ge(4)
Ge(3)−Ge(4)−Ge(5)
C(55)−Ge(1)−C(61)
C(55)−Ge(1)−C(67)
C(61)−Ge(1)−C(67)
2.4359(6)
2.4701(6)
2.4549(6)
2.4397(6)
1.941(4)
1.964(4)
1.957(4)
1.960(4)
116.70(2)
114.25(2)
115.61(2)
106.8(2)
110.5(2)
107.9(2)
Ge(2)−C(49)
Ge(3)−C(1)
Ge(3)−C(37)
Ge(4)−C(25)
Ge(4)−C(31)
Ge(5)−C(7)
Ge(5)−C(13)
Ge(5)−C(19)
C(43)−Ge(2)−C(49)
C(1)−Ge(3)−C(37)
C(25)−Ge(4)−C(31)
C(7)−Ge(5)−C(13)
C(7)−Ge(5)−C(19)
C(13)−Ge(5)−C(19)
1.946(4)
1.964(4)
1.962(4)
1.982(4)
1.963(4)
1.965(4)
1.953(4)
1.957(4)
106.2(2)
107.1(2)
107.2(2)
105.5(2)
109.2(2)
110.0(2)
1
using 2 equiv of Ph3GeNMe2 in 85% yield. The H and 13C
NMR data for 2 agree with the data previously reported in the
literature,47 where 12 resonances were observed in the 13C
NMR spectrum of 2. The UV/visible spectrum of 2 exhibits
λmax at 295 nm (ε = 4.5 × 104 M−1 cm−1), which is close to the
previously reported value of 293 nm.47 As expected, the
absorbance maximum of 2 is red-shifted relative to that for 1,
due to the increase in catenation in the pentagermane.
orientation must occur in a 50/50 left/right distribution but the
other molecule differing from the one shown in Figure 2 was
not found, indicating that the two individual species must
spontaneously resolve.
We have shown that aryl-substituted linear oligogermanes
GenAr2n+2 (Ar = Ph, p-CH3C6H4) typically exhibit n − 1
irreversible oxidation waves in their cyclic voltammograms,60
and the same number of features is also typically observed in
their differential pulse voltammograms (DPV). The CV of 1
exhibits two waves at 1690 and 1946 mV, but the expected
third oxidation wave was not observed. Only two waves were
observed in the DPV of 1 at 1710 and 1960 mV as well, despite
the higher resolution of this method versus that of CV (Figure 3).
Presumably the product present after the second oxidation event
is unstable and decomposes rapidly, which could be due to the
presence of the hydride at the terminal germanium atom. Com-
pound 1 is slightly more difficult to oxidize than Ge4Ph10 (3), as
the first oxidation wave for 3 was observed at 1644 mV.60
In contrast to 1, the CV and DPV for compound 2 follow the
expected trend and are shown in Figure 4. The CV exhibits four
waves at 1385, 1605, 1772, and 1998 mV, and the first
oxidation wave is at a lower potential than the corresponding
first oxidation for Ge4Ph10 (1644 mV),60 which is expected with
an increase in catenation of one −GePh2− unit in 2. The DPV
for 2 also exhibits four oxidation waves at 1290, 1510, 1680,
and 1890 mV that are slightly shifted to potentials lower than
Crystals of 2 suitable for X-ray analysis were obtained via
slow cooling of a refluxing benzene solution, and an ORTEP
diagram of 2 is shown in Figure 2, while selected bond dis-
tances and angles are collected in Table 2. The structure of 2
was previously determined at room temperature,47 while the
present data for 2 were collected at 100 K. Therefore, the bond
distances and angles shown in Table 2 differ from the
previously reported values. The average Ge−Ge bond distance
in 2 is 2.4502(6) Å, and the average Ge−Ge−Ge bond angle is
115.52(2)°, which are nearly identical with those of the
previously reported structure.47 An interesting aspect of the
structure of 2 that was mentioned previously but described in a
different fashion is the fact that the four atoms Ge(2)−Ge(3)−
Ge(4)−Ge(5) are coplanar, while the fifth germanium atom
Ge(1) is canted out of the plane, as shown in Figure 2.
The P212121 space group is noncentrosymmetric, and the
disposition of the Ge(1) atom in 2 clearly implies that the
molecule as pictured in Figure 2 must be present, along with a
second species that has the out-of-plane germanium atom
canted in the opposite direction. Furthermore, this out-of-plane
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Figure 3. Differential pulse voltammogram of Ph3GeGePh2GePh2GePh2H (1) (pulse period 0.1 s, pulse width 0.05 s, sample time 0.02 s). Note that
the weak features at ca. 1250 and 1350 mV are due to background noise.
those found in the CV due to the suppression of the charging
current using this technique. As we postulated for other aryl-
substituted oligogermanes,60 the pentagermane 2 likely under-
goes four consecutive germylene extrusions to yield cationic
tetra-, tri-, and digermane species during the course of the sweep.
In addition to the preparation of linear oligogermanes, we
have employed the hydrogermolysis reaction for the successful
preparation and structural characterization of several branched
oligogermanes, including (Ph3Ge)3GePh (5),48 (Ph3Ge)3-
GeH (6),49,50 and (Ph3Ge)3GeX (X = Cl, Br, I).49,50 We were
interested in the preparation of the germanium neopentyl analogue
(Ph3Ge)4Ge (7) and initially attempted its synthesis via
treatment of GeH4 with 4 equiv of Ph3GeNMe2 in CH3CN
solvent. However, this method yielded only the compound 6.
We then attempted to prepare 7 by the two methods illustrated
in Scheme 2, but neither of these methods were successful.49,50
The route starting from 6 only furnished unreacted 6 and
Ph3GeCH2CN even if a prolonged reaction time (ca. 5 days) or
excess Ph3GeNMe2 was used in the reaction. The branched
amide (Ph3Ge)3GeNMe2 was obtained in two steps from 6,49,50
but the reaction of (Ph3Ge)3GeNMe2 with Ph3GeH also did
not provide 7. Instead, we isolated 3-aminocrotononitrile and
2,6-dimethylpyrimidine, which are oligomers of acetonitrile,
and identified Ph3GeGePh3 as a product of the reaction.49,50
Several other unidentified germanium-containing products
were also generated, suggesting that (Ph3Ge)3GeNMe2 had
decomposed during the course of the reaction. We sub-
sequently demonstrated that that Ph3GeCH2CN could be
converted to Ph3Ge[NHC(CH3)CHCN] and 2,6-dimethyl-4-
(triphenylgermylamino)pyrimidine upon prolonged heating of
Ph3GeCH2CN in CH3CN in the presence of HNMe2,61 which
explains how the aforementioned products were formed.
The methyl-substituted neopentane analogue (Me3Ge)4Ge
(8) was prepared in 40% yield by Marschner et al.51 and also
had been reported earlier by Glockling et al.62,63 However, the
four −GeMe3 groups attached to the central germanium atom
in this species are significantly less sterically encumbering than
four −GePh3 groups. In addition, the tin analogue of 7
(Ph3Sn)4Sn (9) had been prepared and structurally charac-
terized,64 but in this case the larger covalent radius of tin (1.40 Å)
versus that of germanium (1.22 Å) also allows the more facile
accommodation of four triphenyl-substituted peripheral groups.
Thus, we assumed that the synthesis of compound 7 might not be
possible due to steric effects. The progress of the hydrogermolysis
reaction has been shown to be hampered by sterically demanding
substituents, as the digermane But3GeGePh3 could not prepared
by this method, and only But3Ge[NHC(CH3)CHCN] was
isolated.54 However, it now appears that this assumption was some-
what premature, since we have now prepared 7 via a hydro-
germolysis reaction and have obtained its X-ray crystal structure.
The first suggestion that the preparation of 7 was in fact
possible was indicated by the outcome of the reaction of
GeH4 with a large excess (ca. 20 equiv) of Ph3GeNMe2 in
CH3CN. The major product isolated from this reaction was
(Ph3Ge)3GeH (6) in 73% yield, and a significant amount of
Ph3GeCH2CN (10) was also left over, which could be removed
via distillation using a Kugelrohr oven. Compound 10 cry-
stallized in the receiving flask, and an X-ray crystal structure of
this material was obtained. An ORTEP diagram of 10 is shown
in Figure 5, and selected bond distances and angles are
collected in Table 3. The Ge−C distance in the bond to the
α-carbon is 1.982(4) Å and is similar to those in two other
crystallographically characterized α-germyl nitriles, [Mes*PC]-
GeBut(Tip)CH2CN (11)65 and [(Me3Si)2CH]2Ge(H)CH2CN
(12),66 which measure 2.004(2) and 1.911(9) Å, respectively.
The −CH2CN ligand is nearly linear, as shown by the C(19)−
C(20)−N(1) bond angle, which is 178.9(5)°, and the Ge(1)−
C(19)−C(20) bond angle is 116.6(3)°, which is similar to the
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Figure 4. Cyclic voltammogram (bottom; scan rate 100 mV/s) and differential pulse voltammogram (top; pulse period 0.1 s, pulse width 0.05 s,
sample time 0.02 s) for Ge5Ph12 (2).
disposition of the −CH2CN ligand in the germanium complexes
11 and 12. In these compounds, the C−C−N bond angles are
179.4(2)° (11) and 117(1)° (12), while the Ge−C−C bond
angles are 113.5(1)° (11) and 115.2(7)° (12).
The mixture of 6 and 10 also was contaminated with a
trace amount of a second phenyl-containing product that
we suspected was (Ph3Ge)4Ge (7). The presence of a large
excess of Ph3GeNMe2 in the aforementioned reaction prompted
us to attempt the synthesis of 7 as shown in Scheme 3. The key
feature of the successful preparation of 7 is the use of 10
itself as the reactant rather than Ph3GeNMe2. We have shown
that Ph3GeNMe2 is completely converted to 10 within ca. 6 h
in CH3CN solvent,54 and therefore a large excess of 10 would
be present relative to GeH4 if ca. 20 equiv of Ph3GeNMe2 was
employed as described above. However, the reaction shown
in Scheme 3 is still very sluggish, and a prolonged reaction
time of 5 days was necessary for 7 to be formed in an
appreciable amount (32% yield). Curiously, the reaction of 6
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Scheme 2
respectively, while the 13C NMR of this compound has four
features at δ 139.8, 137.3, 128.5, and 127.8 ppm corresponding
to the ipso, ortho, para, and meta carbon atoms of the phenyl
rings, respectively. The 13C NMR data match very well with the
chemical shift values predicted by Drager et al. in 1987.67
̈
Crystals of 7 suitable for X-ray analysis were obtained from a
benzene/hexane solution; an ORTEP diagram of compound 7
is shown in Figure 6, and selected bond distances and angles
are collected in Table 4. Compound 7 crystallizes with two
independent molecules in the unit cell, which also incorporates
a molecule of hexane that is disordered. The average Ge−Ge
bond distance among the two molecules of 7 is 2.497(6) Å,
which is longer than those in (Ph3Ge)3GeH (6) and
(Ph3Ge)3GePh (5) that measure 2.4310(5) and 2.469(4) Å,
respectively. This is expected, given the steric congestion at the
central germanium atom in 7 resulting from the attachment of a
fourth Ph3Ge− group to the central germanium atom. In fact,
three of the Ge−Ge bond distances among the two molecules
of 7 are longer than 2.50 Å. The Ge(1)−Ge(3) and Ge(1)−
Ge(4) bonds in molecule 1 measure 2.5042(6) and 2.5136(6)
Å, respectively, while the Ge(6)−Ge(7) and Ge(6)−Ge(7)
bonds both measure 2.5136(6) Å. These bond distances are
shorter than those found in the congested cyclotrigermanes
Mes6Ge3 and But6Ge3, which average 2.537(2)68 and 2.563(1)
Å,69 respectively.
Figure 5. ORTEP diagram of Ph3GeCH2CN (9). Thermal ellipsoids
are drawn at the 50% probability level.
The Ge−Ge−Ge bond angles in 7 have an overall average
value of 109.49(2)°, which matches the idealized tetrahedral
bond angle exactly. It is likely that this is a necessary geometric
requirement for the formation of the four Ge−Ge bonds
that incorporate four −GePh3 moieties around the central
germanium atom. This differs from the average bond angles
about the central germanium atom in 6 and 5, which are
115.50(2)49,50 and 112.72(1)°,48 respectively. The most obtuse
angle averaged between the two molecules of 8 is 113.28(2)°,
while in 5 the most obtuse angle measures 115.70(1)° and in 6
it is 117.89(2)°. The degree of steric congestion in 7 can be
seen in the space-filling diagram shown in Figure 7. The Ge5
framework in 7 is almost completely encapsulated by the
peripheral phenyl rings, and the rings are oriented such that
they adopt a twisted conformation.
Table 3. Selected Bond Distances (Å) and Angles (deg) for
Ph3GeCH2CN (10)
Ge(1)−C(1)
Ge(1)−C(7)
Ge(1)−C(13)
C(1)−Ge(1)−C(7)
C(1)−Ge(1)−C(13)
C(7)−Ge(1)−C(13)
C(1)−Ge(1)−C(19)
1.940(4)
1.929(4)
1.944(4)
110.5(2)
111.9(2)
111.5(2)
102.4(2)
Ge(1)−C(19)
C(19)−C(20)
C(20)−N(1)
C(7)−Ge(1)−C(19)
C(13)−Ge(1)−C(19)
Ge(1)−C(19)−C(20)
C(19)−C(20)−N(1)
1.982(4)
1.450(6)
1.149(5)
108.9(2)
111.3(2)
116.6(3)
178.9(5)
with either a stoichiometric amount or an excess of 10 lead
only to the recovery of 6 without formation of any detectable
amount of 7, even when a 5 day reaction time was employed.
1
The H NMR of 7 exhibits resonances at δ 7.65, 7.11, and
Compound 7 was further characterized using UV/visible
spectroscopy and cyclic and differential pulse voltammetry, and
7.04 ppm corresponding to the ortho, para, and meta protons,
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Scheme 3
Figure 6. ORTEP diagram of the two crystallographically independent molecules of (Ph3Ge)4Ge·C6H14 (7·C6H14). Thermal ellipsoids are drawn at
the 50% probability level.
its structure was computed using density functional theory
(DFT) calculations. The calculated structure of 7 resembles the
crystallograhically determined structure, having an encapsulated
central germanium atom and a twisted disposition of the phenyl
substituents. The structure is more symmetrical than the closely
packed crystal structure and has significant interaction between
the phenyl rings, which are rotationally staggered around
each of the four peripheral germanium atoms. The peripheral
germanium atoms are essentially neutral, and there is a positive
charge on the central germanium atom. The Ge−C bond
distances are identical with those in the X-ray structure.
However, the calculated Ge−Ge bond distances are shorter
than those in the X-ray structure of 7 by an average of 0.06 Å
and measure 2.44 Å. Figures depicting the HOMO and LUMO
of 7 are shown in Figure 8. The HOMO in 7 is composed
primarily of the p orbital on the central germanium atom, while
the LUMO contains p orbital density on the four peripheral
germanium atoms as well as a contribution from the 4s orbital
on the central germanium atom. The HOMO of 7 lies at
−6.220 eV, and the LUMO is at −0.571 eV; thus, the HOMO−
LUMO gap is 5.653 eV (220 nm). The energy values for the
frontier orbitals of 7, as well as those calculated for (Ph3Ge)3GePh
(5),50 (Ph3Ge)3GeH (6),50 and (Me3Ge)4Ge (8),70 are collected
in Table 5.
HOMO among the phenyl-substituted species 5−7, resulting
from the effective increase in catenation relative to that in the
tetragermanes 5 and 6. This results in a larger HOMO−LUMO
gap for 7 compared to those in 5 and 6, and thus the calculated
energy of 220 nm for 7 is blue-shifted relative to the
corresponding energies for 5 and 6. Time-dependent DFT
calculations reveal the presence of three primary transitions in
the UV region from the HOMO, HOMO- 1, and HOMO-2 to
the LUMO, where the three HOMO levels are approximately
degenerate in energy and each contains a different p orbital on
the central germanium atom. The calculated λmax with the
highest oscillator strength in 7 is 245 nm, and the observed
UV/visible absorbance maximum for 7 is a broad band centered
at 250 nm (ε = 1.59 × 10 4 M−1 cm−1) that tails to ca. 325 nm.
The CV of 7 exhibits a single irreversible oxidation wave at
1954
11 mV, while the DPV of 7 contains a single wave
at 1923 7 mV. Therefore, 7 is more difficult to oxidize than
the other phenyl-substituted tetragermanes 5 and 6 but is easier
to oxidize than the methyl-substituted species 8. These data are
consistent with the calculated HOMO energies of these species,
as the HOMO of 7 is stabilized relative to those of 5 and
6 but destabilized relative to the HOMO of 8. Therefore,
the experimental and theoretical data for 7 are in excellent
agreement.
The methyl-substituted compound 8 has the lowest-lying
HOMO and the most destabilized LUMO among these four
oligogermanes. Compound 7 has the most highly stabilized
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Table 4. Selected Bond Distances (Å) and Angles (deg) for (Ph3Ge)4Ge·C6H14 (7·C6H14)
molecule 1
molecule 2
molecule 1
molecule 2
average
average
Ge(1)−Ge(2)
2.4948(6) Ge(6)−Ge(7)
2.5136(6) 2.5042(6)
2.4842(6) 2.4894(6)
2.4957(6) 2.4910(6)
2.4977(6) 2.5057(6)
1.966(4) 1.968(4)
1.959(4) 1.960(4)
1.968(4) 1.969(4)
1.978(4) 1.967(4)
1.956(4) 1.953(4)
1.954(4) 1.955(4)
1.965(4) 1.960(4)
1.953(4) 1.960(4)
1.971(4) 1.967(4)
1.961(4) 1.962(4)
1.961(4) 1.968(4)
1.963(4) 1.963(4)
106.04(2) 107.19(2)
112.65(2) 113.28(2)
C(7)−Ge(2)−C(13) 107.4(2) C(79)−Ge(7)−C(85)
C(19)−Ge(3)−C(25) 106.9(2) C(91)−Ge(8)−C(97)
106.0(2) 106.7(2)
106.5(2) 106.7(2)
Ge(1)−Ge(3)
Ge(1)−Ge(4)
Ge(1)−Ge(5)
Ge(2)−C(1)
Ge(2)−C(7)
Ge(2)−C(13)
Ge(3)−C(19)
Ge(3)−C(25)
Ge(3)−C(31)
Ge(4)−C(37)
Ge(4)−C(43)
Ge(4)−C(49)
Ge(5)−C(55)
Ge(5)−C(61)
Ge(5)−C(67)
2.4945(6) Ge(6)−Ge(8)
2.5042(6) Ge(6)−Ge(9)
2.5136(6) Ge(6)−Ge(10)
1.972(4) Ge(7)−C(73)
1.961(4) Ge(7)−C(79)
1.970(4) Ge(7)−C(85)
1.956(4) Ge(8)−C(91)
1.950(4) Ge(8)−C(97)
1.956(4) Ge(8)−C(103)
1.954(4) Ge(9)−C(109)
1.967(4) Ge(9)−C(115)
1.962(4) Ge(9)−C(121)
1.963(4) Ge(10)−C(127)
1.974(4) Ge(10)−C(133)
1.962(4) Ge(10)−C(139)
C(19)−Ge(3)−C(31) 108.6(2) C(91)−Ge(8)−C(103) 104.9(2) 106.8(2)
C(25)−Ge(3)−C(31) 106.3(2) C(97)−Ge(8)−C(103) 107.9(2) 107.1(2)
C(37)−Ge(4)−C(43) 106.9(2) C(109)−Ge(9)−C(115) 106.0(2) 106.5(2)
C(37)−Ge(4)−C(49) 107.3(2) C(109)−Ge(9)−C(121) 106.0(2) 106.7(2)
C(43)−Ge(4)−C(49) 105.4(2) C(115)−Ge(9)−C(121) 104.7(2) 105.1(2)
C(55)−Ge(5)−C(61) 105.6(2) C(127)−Ge(10)−C(133) 105.0(2) 105.3(2)
C(55)−Ge(5)−C(67) 101.2(2) C(127)−Ge(10)−C(139) 105.5(2) 103.4(2)
C(61)−Ge(5)−C(67) 108.2(2) C(133)−Ge(10)−C(139) 106.7(2) 107.5(2)
C(1)−Ge(2)−Ge(1) 111.1(1) C(73)−Ge(7)−Ge(6)
C(7)−Ge(2)−Ge(1) 110.2(1) C(79)−Ge(7)−Ge(6)
C(13)−Ge(2)−Ge(1) 117.3(1) C(85)−Ge(7)−Ge(6)
C(19)−Ge(3)−Ge(1) 113.6(1) C(91)−Ge(8)−Ge(6)
C(25)−Ge(3)−Ge(1) 113.7(1) C(97)−Ge(8)−Ge(6)
114.0(1) 112.6(1)
110.8(1) 110.5(1)
112.5(1) 114.9(1)
116.7(1) 115.2(1)
108.0(1) 110.9(1)
Ge(2)−Ge(1)−Ge(3) 108.34(2) Ge(7)−Ge(6)−Ge(8)
Ge(2)−Ge(1)−Ge(4) 113.90(2) Ge(7)−Ge(6)−Ge(9)
Ge(2)−Ge(1)−Ge(5) 105.08(2) Ge(7)−Ge(6)−Ge(10) 111.69(2) 108.39(2)
Ge(3)−Ge(1)−Ge(4) 105.16(2) Ge(8)−Ge(6)−Ge(9) 111.88(2) 108.52(2)
Ge(3)−Ge(1)−Ge(5) 113.50(2) Ge(8)−Ge(6)−Ge(10) 108.74(2) 111.12(2)
Ge(4)−Ge(1)−Ge(5) 111.04(2) Ge(9)−Ge(6)−Ge(10) 105.87(2) 108.46(2)
C(31)−Ge(3)−Ge(1) 107.4(1) C(103)−Ge(8)−Ge(6) 112.5(1) 110.0(1)
C(37)−Ge(4)−Ge(1) 108.9(1) C(109)−Ge(9)−Ge(6) 112.2(1) 110.6(1)
C(43)−Ge(4)−Ge(1) 116.1(1) C(115)−Ge(9)−Ge(6) 115.4(1) 115.8(1)
C(49)−Ge(4)−Ge(1) 111.8 (1) C(121)−Ge(9)−Ge(6) 111.8(1) 111.8(1)
C(55)−Ge(5)−Ge(1) 116.3(1) C(127)−Ge(10)−Ge(6) 114.6(1) 115.5(1)
C(61)−Ge(5)−Ge(1) 111.9(1) C(133)−Ge(10)−Ge(6) 109.6(1) 110.8(1)
C(67)−Ge(5)−Ge(1) 112.8(1) C(139)−Ge(10)−Ge(6) 114.7(1) 113.8(1)
C(1)−Ge(2)−C(7) 107.6(2) C(73)−Ge(7)−C(79)
C(1)−Ge(2)−C(13) 102.7(2) C(73)−Ge(7)−C(85)
109.6(2) 108.6(2)
103.4(2) 103.1(2)
Figure 8. Calculated HOMO and LUMO molecular orbitals for 7.
Four of the five germanium atoms in 2 are coplanar, while the
fifth atom is canted out of the plane. Since 2 crystallizes in a
noncentrosymmetric space group, the experimentally deter-
mined structure for 2 contains a single conformation of 2 that is
present via spontaneous resolution with the second conformation
that must also be present. The CV and DPV of 2 exhibit the ex-
pected pattern for aryl-substituted oligogermanes, each having
Figure 7. Space-filling diagram of (Ph3Ge)4Ge·C6H14 (7·C6H14).
CONCLUSIONS
■
The hydride-terminated tetragermane Ph3GeGePh2GePh2-
GePh2H (1) was prepared via the selective reaction of 1
equiv of Ph3GeNMe2 with HPh2GeGePh2GePh2H and was
converted to the pentagermane Ge5Ph12 (2) by reaction with a
another 1 equiv of Ph3GeNMe2. Compound 2 could also be ob-
tained by treatment of HPh2GeGePh2GePh2H with 2 equiv of
Ph3GeNMe2. The crystal structures of 1 and 2 have been deter-
mined, and the Ge−H bond distance in 1 measures 1.50(4) Å.
The Ge−Ge bond distance between the −GePh2H group and
its neighboring germanium atom was found to be shorter than
that in the perphenyl-substituted tetragermane Ge4Ph10 (3),
and the Ge−Ge−Ge bond angle at the germanium atom
adjacent to the −GePh2H moiety in 1 is also more acute than
that in 3.
four irreversible oxidation waves that correspond to the expec-
60
ted n − 1 pattern for oligogermanes of the formula GenAr2n+2
.
However, the CV and DPV for 1 exhibit only two waves rather
than the expected three, suggesting that the terminal hydride in
1 imparts instability to the species generated after the second
oxidation event takes place.
The synthesis of the germanium neopentane analogue
(Ph3Ge)4Ge (7) was also achieved via a hydrogermolysis re-
action starting with GeH4 and the α-germyl nitrile Ph3GeCH2-
CN (10). The successful preparation of 7 seemed unlikely,
since we had previously shown that 7 could be synthesized
neither by the reaction of (Ph3Ge)3GeH (6) with Ph3GeNMe2
nor via reaction of (Ph3Ge)3GeNMe2 with Ph3GeH.49,50 Further-
more, treatment of GeH4 with 4 equiv of Ph3GeNMe2 yielded
The structure of 2 was also determined and found to be
similar to the previously reported structure by Drager et al.47
̈
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Table 5. Theoretical and Experimental Data for Compounds 5−8
compd
HOMO (eV) LUMO (eV) HOMO−LUMO gap (eV) HOMO−LUMO gap (nm) λmax(calcd) (nm) λmax (nm)
Eox (mV)
(Ph3Ge)3GePh (5)
(Ph3Ge)3GeH (6)
(Ph3Ge)4Ge (7)
(Me3Ge)4Ge (8)
−5.907
−6.003
−6.223
−6.529
−0.593
−0.576
−0.570
−0.527
5.314
5.427
5.653
6.002
233
228
220
207
262
253
245
206
256
251
250
212
1435 14
1921
1954 11
2090
8
2
Table 6. Crystallographic Data for Compounds 1, 2, 7·C6H14, and 10
1
2
7
10
empirical formula
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
a, Å
C54H46Ge4
985.27
123(2)
0.71073
monoclinic
P21/c
C72H60Ge5
1288.15
100(2)
0.71073
orthorhombic
P212121
14.303(1)
19.159(2)
21.398(2)
90
C150H134Ge10
2662.47
100(2)
0.71073
monoclinic
P21/n
C20H17GeN
343.96
100(2)
0.71073
triclinic
P1
̅
13.193(1)
17.557(2)
19.868(2)
90
13.3210(6)
49.968(2)
18.4106(8)
90
9.412(2)
9.440(2)
9.779(2)
92.021(3)
108.696(3)
98.341(3)
811.2(3)
2
b, Å
c, Å
α, deg
β, deg
105.178(1)
90
90
90.028(2)
90
γ, deg
V, Å3
90
4441.6(8)
4
5863.5(9)
4
12254(1)
4
Z
ρ (g cm−3
)
1.473
1.459
1.443
1.408
abs coeff (mm−1
)
2.717
2.576
2.468
1.844
F(000)
1992
2608
5416
352
cryst size (mm3)
0.24 × 0.23 × 0.20
θ range for data collection (deg) 1.57−25.38
index ranges
0.32 × 0.30 × 0.28
3.19−25.42
−17 ≤ h ≤ 16
−23 ≤ k ≤ 16
−25 ≤ l ≤ 25
35 345
0.15 × 0.10 × 0.10
2.25−26.83
−16 ≤ h ≤ 14
−63 ≤ k ≤ 63
−23 ≤ l ≤ 23
153 538
0.18 × 0.15 × 0.10
2.19−28.36
−12 ≤ h ≤ 12
−12 ≤ k ≤ 12
−12 ≤ l ≤ 12
9828
−15 ≤ h ≤ 15
−20 ≤ k ≤ 21
−23 ≤ l ≤ 23
36 823
no. of rflns collected
no. of indep rflns (Rint)
8125 (0.0585)
10 770 (0.0441)
99.5
25 464 (0.0918)
98.7
3695 (0.0862)
99.8
completeness to θ = 25.00° (%) 100.0
abs cor
multiscan
multiscan
multilayer/SADABS
0.7904 and 0.7085
semiempirical from equivalents
max and min transmission
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I < 2σ(I))
R1
0.6795 and 0.5654
0.762 and 0.683
0.8340 and 0.7280
full-matrix least squares on F2 full-matrix least squares on F2 full-matrix least squares on F2 full-matrix least squares on F2
8125/0/527
1.002
10 770/0/694
1.060
25 464/10/1425
1.033
3695/0/199
1.000
0.0340
0.0748
0.0320
0.0847
0.0482
0.1068
0.0545
0.1102
wR2
final R indices (all data)
R1
0.0540
0.0350
0.0801
0.0831
wR2
0.0841
0.0861
0.1256
0.1249
largest diff peak and hole (e Å−3
)
0.486 and −0.630
1.522 and −0.557
1.225 and −0.803
0.971 and −0.879
only the hydride 6.49,50 However, the key to the successful
preparation of 7 is the use of the α-germyl nitrile 10 directly
with a longer (5 days) reaction time. The X-ray crystal structure
of 7 was obtained and represents the first structurally
characterized example of a germanium neopentane analogue.
The molecular structure of 7 indicates that this species is highly
congested at the central germanium atom, and this was also
confirmed by DFT computations. The Ge−Ge distances in 7
are on average longer than those typically found in other linear
and branched oligogermanes, and the central germanium atom
in 7 is in a nearly idealized tetrahedral environment. We also
obtained the X-ray crystal structure of 10, which contains a
tetrahedral germanium atom, a linear −CH2CN ligand, and a
Ge−Cα bond distance of 1.982(4) Å.
The UV/visible spectrum of 7 exhibits λmax at 250 nm, and a
single oxidation wave was observed for 7 at 1923 mV in its CV;
these are consistent with the energies of the HOMO and LUMO
in 7 computed by DFT calculations. These data indicate that
the HOMO in 7 is slightly lower in energy than those of the
other phenyl-substituted oligogermanes (Ph3Ge)3GePh (5) and
(Ph3Ge)3GeH (6) by an average of −0.283 eV but is higher
in energy than the methyl-substituted neopentane analogue
(Me3Ge)4Ge (8) by 0.340 eV. As a result, 7 is also more difficult
to oxidize than 5 and 6 but is easier to oxidize than 5.
The findings reported here represent some significant
advances in the synthesis of oligogermanes via the hydro-
germolysis reaction. The selectivity observed in the reaction of
Ph3GeNMe2 with HPh2GeGePh2GePh2H to yield 1 might
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vacuo to yield 3 (1.37 g, 32%). 1H NMR (C6D6, 25 °C): δ 7.65 (d, J =
7.6 Hz, 24H, o-H), 7.11 (t, J = 7.5 Hz, 12H, p-H), and 7.04 (t, J =
7.8 Hz, 24H, m-H). ppm. 13C NMR (C6D6, 25 °C): δ 139.8 (ipso-C),
137.3 (o-C), 128.5 (p-C), and 127.8 (m-C) ppm. UV/visible (CH2Cl2):
250 nm (ε = 1.59 × 104 M−1 cm−1). Anal. Calcd for C72H60Ge5: C,
67.10; H, 4.70. Found: C, 67.05; H, 4.74.
open new pathways for the preparation of higher oligomers.
Furthermore, the successful preparation of 7 using Ph3GeCH2-
CN directly also suggests that the synthesis of additional highly
sterically congested branched oligogermanes, possibly including
dendridic structures, might also be possible.
Computational Details. Gaussian 03 was utilized for all
computations.72 The total electronic energy and frequency calculations
were performed using the hybrid density functional method, including
Becke’s three-parameter nonlocal exchange functional73 with the
correction functional of Lee−Yang−Parr B3LYP.74 The 6-31G* basis
set was employed for all atoms.75 All atomic positions were optimized
without geometry constraints to a minimum in the total force. The
frequency calculation was performed at a lower level due to the size of
the system. Once the optimized structure had been found, time-
dependent density functional calculations as implemented by Gaussian
03 were utilized to explore the excited state manifold and compute the
possible electronic transitions and oscillator strengths. GaussSum was
used to compute the UV/visible spectra.76
X-ray Crystal Structure Determinations. Diffraction intensity
data were collected with a Siemens P4/CCD diffractometer.
Crystallographic data for the X-ray analysis of 1, 2, 7·C6H14, and 10
are collected in Table 6. The crystal-to-detector distance was 60 mm,
and the exposure time was 20 s per frmae using a scan width of 0.5°.
The data were integrated using the Bruker SAINT software program.
Solution by direct methods (SIR-2004) produced a complete heavy-
atom phasing model consistent with the proposed structures. All non-
hydrogen atoms were refined anisotropically by full-matrix least
squares (SHELXL-97). Aside from the germanium-bound hydrogen in
1, all hydrogen atoms were placed using a riding model. Their
positions were constrained relative to their parent atom using the
appropriate HFIX command in SHELXL-97.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried out using
standard Schlenk, syringe, and glovebox techniques. Germane was
purchased from Gelest, and Ph3GeNMe2,71 Ph3GeCH2CN,54 and
HPh2GeGePh2GePh2H53 were prepared by literature methods. 1H and
13C NMR spectra were recorded at 300 and 75.46 mHz using an
INOVA Gemini 2000 spectrometer. IR spectra were obtained using a
Perkin-Elmer 1720 infrared spectrometer, and UV/visible spectra were
recorded using a Hewlett-Packard 8453 diode array spectrometer. CV
and DPV data were obtained using a DigiIvy DY2300 potentiostat
with a glassy-carbon working electrode, a platinum-wire counter
electrode, and an Ag/AgCl reference electrode using 0.1 M
[Bu4N][PF6] as the supporting electrolyte. Elemental analyses were
conducted by Gailbraith Laboratories.
Synthesis of Ph3GeGePh2GePh2GePh2H (1). To a solution of
HPh2GeGePh2GePh2H (0.100 g, 0.147 mmol) in acetonitrile (10 mL)
was added a solution of Ph3GeNMe2 (0.051 g, 0.147 mmol) in
acetonitrile (10 mL). The reaction mixture was sealed in a Schlenk
tube and was heated at 85 °C for 48 h, after which time the volatiles
1
were removed in vacuo to yield 1 (0.114 g, 79%) as a white solid. H
NMR (C6D6, 25 °C): δ 7.62 (d, J = 7.8 Hz, 6H, o-C6H5), 7.52 (t, J =
8.1 Hz, 6H, m-C6H5), 7.40 (d, J = 6.6 Hz, 4H, o-C6H5), 7.31 (d, J = 7.2
Hz, 4H, o-C6H5), 7.16−7.06 (m, 25H, m-C6H5 and p-C6H5), 5.67 (s,
1H, −GePh2H) ppm. 13C NMR (C6D6, 25 °C): δ 138.3 (ipso-C
Ph3Ge), 138.1 (ipso-C Ph2Ge), 138.0 (ipso-C Ph2Ge), 137.0 (ipso-C
HPh2Ge), 136.9 (o-C Ph3Ge), 136.7 (o-C Ph2Ge), 136.1 (o-C Ph2Ge),
136.0 (o-C HPh2Ge), 129.0 (m-C Ph3Ge), 128.8 (m-C Ph2Ge), 128.7
(m-C Ph2Ge), 128.6 (m-C HPh2Ge), 128.5 (p-C Ph3Ge), 128.4 (p-C
Ph2Ge), 128.3 (p-C Ph2Ge), 128.1 (p-C HPh2Ge) ppm. IR (Nujol
mull): 2009 cm−1 (νGe−H). UV/visible (CH2Cl2): λmax 269 nm (ε = 4.5
× 104 M−1 cm−1). Anal. Calcd for C54H46Ge4: C, 65.79; H, 4.71.
Found: C, 65.91; H, 4.62.
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystallographic data for 1, 2, 7·C6H14, and 10.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Synthesis of Ge5Ph12 (2). To a solution of 1 (0.114 g, 0.116
mmol) in acetonitrile (10 mL) was added a solution of Ph3GeNMe2
(0.040 g, 0.116 mmol) in acetonitrile (5 mL). The reaction mixture
was sealed in a Schlenk tube and was heated at 85 °C for 48 h, after
which time the volatiles were removed in vacuo to yield 2 (0.124 g,
83%) as a white solid. 1H NMR (C6D6, 25 °C): δ 7.71 (d, J = 6.0 Hz,
6H, o-C6H5), 7.60 (d, J = 6.6 Hz, 4H, o-C6H5), 7.51(t, J = 7.5 Hz, 6H,
m-C6H5), 7.48 (d, J = 6.6 Hz, 4H, o-C6H5), 7.32−7.03 (m, 40H, m-
C6H5 and p-C6H5) ppm. 13C NMR (C6D6, 25 °C): δ 138.5 (ipso-C
(Ph3Ge)2), 138.3 (ipso-C (Ph2Ge)2), 137.2 (ipso-C (Ph2Ge)), 137.0
(o-C (Ph2Ge)2), 136.2 (o-C (Ph3Ge)2), 128.7 (m-C (Ph3Ge)2), 128.5
(p-C (Ph3Ge)2), 128.4 (p-C (Ph2Ge)2), 128.3 (p-C (Ph2Ge)), 127.8
(m-C (Ph2Ge)), 127.7 (m-C (Ph2Ge)2), 126.7 (o-C (Ph2Ge)) ppm.
UV/visible (CH2Cl2): λmax 295 nm (ε = 4.5 × 104 M−1 cm−1). Anal.
Calcd for C72H60Ge5: C, 67.10; H, 4.70. Found: C, 66.91; H, 4.84.
Alternate Synthesis of Ge5Ph12 (2). To a solution of HPh2-
GeGePh2GePh2H (0.288 g, 0.293 mmol) in acetonitrile (10 mL) was
added a solution of Ph3GeNMe2 (0.203 g, 0.584 mmol) in acetonitrile
(10 mL). The reaction mixture was sealed in a Schlenk tube and was
heated at 85 °C for 48 h, after which time the volatiles were removed
in vacuo to yield 2 (0.316 g, 84%) as a white solid.
Synthesis of (Ph3Ge)4Ge (7). Germane gas (GeH4, 0.256 g, 3.34
mmol) was condensed into an evacuated Schlenk tube at 77 K. A
nitrogen atmosphere was established, and subsequently a solution of
Ph3GeCH2CN (9.20 g, 26.7 mmol) in acetonitrile was transferred via
cannula to the Schlenk tube and a nitrogen atmosphere was established.
The reaction mixture was allowed to come to room temper-
ature and then was heated in an oil bath at 85 °C for 5 days. The
volatiles were removed in vacuo, and the resulting solid was distilled
using a Kugelrohr oven (175 °C, 0.01 Torr) to remove unreacted
Ph3GeCH2CN. The resulting solid was washed with hexane and dried in
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: weinert@chem.okstate.edu.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Funding for this work was provided by a CAREER grant from
the National Science Foundation (No. CHE-0844758) and is
gratefully acknowledged.
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