Structural, spectral, and electrochemical investigations of para-tolyl-substituted oligogermanes

Article abstract of DOI:10.1016/j.jorganchem.2010.04.015

The synthesis of four new oligogermanes containing para-tolyl-substituents has been achieved via the hydrogermolysis reaction, including the digermane Tol₃GeGePh₃, the trigermanes Tol₃GeGePh₂GeTol₃ and Tol₃GeGeTol₂GeTol₃, and the tetragermane Tol₃GeGePh₂GePh₂GeTol₃ (Tol?=?p-CH₃C₆H₄). These four oligogermanes have been structurally characterized and their structures have been compared with those of their per-phenyl-substituted analogs. The digermane Tol₃GeGePh₃ exhibits an unusually short Ge-Ge bond distance of 2.408(1)?A?. The four para-tolyl-substituted oligogermanes have also been characterized by UV/visible spectroscopy and cyclic voltammetry. The expected red shift in the absorbance maximum with increasing catenation was observed for this series of compounds. Their cyclic voltammograms each contain n?-?1 irreversible oxidation waves (n?=?the number of Ge atoms), which is atypical since oligogermanes generally exhibit only one irreversible oxidation wave regardless of the degree of catenation.

Full text of DOI:10.1016/j.jorganchem.2010.04.015

Journal of Organometallic Chemistry 695 (2010) 1813e1823
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structural, spectral, and electrochemical investigations of
para-tolyl-substituted oligogermanes
,
Monika L. Amadoruge a, Erin K. Short a, Curtis Moore b, Arnold L. Rheingold b, Charles S. Weinert a
*
a Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA
b Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0303, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of four new oligogermanes containing para-tolyl-substituents has been achieved via the
hydrogermolysis reaction, including the digermane Tol3GeGePh3, the trigermanes Tol3GeGePh2GeTol3
and Tol3GeGeTol2GeTol3, and the tetragermane Tol3GeGePh2GePh2GeTol3 (Tol ¼ p-CH3C6H4). These four
oligogermanes have been structurally characterized and their structures have been compared with those
of their per-phenyl-substituted analogs. The digermane Tol3GeGePh3 exhibits an unusually short GeeGe
bond distance of 2.408(1) Å. The four para-tolyl-substituted oligogermanes have also been characterized
by UV/visible spectroscopy and cyclic voltammetry. The expected red shift in the absorbance maximum
with increasing catenation was observed for this series of compounds. Their cyclic voltammograms each
contain n ꢀ 1 irreversible oxidation waves (n ¼ the number of Ge atoms), which is atypical since oli-
gogermanes generally exhibit only one irreversible oxidation wave regardless of the degree of catenation.
Ó 2010 Elsevier B.V. All rights reserved.
Received 2 February 2010
Received in revised form
14 April 2010
Accepted 16 April 2010
Available online 24 April 2010
Keywords:
Germanium
Oligogermanes
X-ray crystal structures
Cyclic voltammetry
Hydrogermolysis
1. Introduction
that will allow the synthesis of discrete oligogermanes having
a well-defined composition. We have used the hydrogermolysis
The synthesis of catenated compounds of the heavier group 14
elements containing elementeelement single bonds is of signifi-
cant interest since these materials represent the heavy analogs of
hydrocarbons. However, in contrast to their carbon-containing
congeners, catenated compounds of silicon, germanium, and tin
reaction, either alone or in conjunction with a germanium hydride
protection/deprotection strategy, to prepare a library of oligo-
germanium compounds having between two and seven germa-
nium atoms in the GeeGe backbone [41e45]. Our synthetic
methodology can be employed for the systematic variation of not
only the number of germanium atoms in the GeeGe backbone but
also of the organic substituents attached to the germanium atoms
in the chain. This was not possible using other previously reported
synthetic methods, and we have prepared both linear [41,42,44,45]
and branched [43] oligogermane systems using this method. It has
been demonstrated that both the number of catenated germanium
atoms and the electronic attributes of the attached organic
substituents affect the relative energies of the frontier orbitals in
these systems. This has been achieved by characterizing the oli-
gogermane systems using UV/visible spectroscopy and cyclic vol-
tammetry, in conjunction with computational (DFT) studies.[42]
exhibit
s-delocalization, where the constituent electrons of the
elementeelement single bonds are delocalized across the entire
elementeelement backbone [1e8]. This can result in interesting
optical and electronic properties, including thermochromism,
conductivity, and non-linear optical attributes. However, while
silicon- [9e19] and tin-containing [4,5,20e35] catenates have
received considerable attention, an understanding of their germa-
nium-containing analogs is not as well developed. This is due, in
part, to the lack of suitable synthetic methods for the preparation of
catenated germanium compounds, which has until recently
precluded a detailed investigation into the structure/property
relationships in these systems [36e40].
We have shown that the magnitude of the
transition, which corresponds to the promotion of an electron from
the HOMO
-bonding orbital to the LUMO s*-antibonding orbital,
s /
s* electronic
Rather than focusing on polymeric systems that have a distri-
bution of molecular weights and therefore contain mixtures of
products, we have endeavored to develop a synthetic methodology
s
decreases upon increasing the GeeGe chain length and/or by
increasing the number of inductively electron-donating organic
substituents. In general, this effect results from the destabilization
of the HOMO, and these two structural modifications also diminish
the oxidation potential of these systems. The oxidation waves
* Corresponding author. Tel.: þ1 405 744 6543.
E-mail address: weinert@chem.okstate.edu (C.S. Weinert).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.04.015

1814
M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
exhibited in the cyclic voltammograms of all oligogermanes
observed to date are irreversible, indicating that a chemical reac-
tion is occurring after the oxidation event [42,46,47].
based on GeBr4. The 1H NMR spectrum of Tol2GeH2 contains
a singlet at 5.22 ppm corresponding to the two equivalent
hydridic protons, and the IR spectrum of this material contains
a symmetric GeeH stretching band at 2050 cmꢀ1. The amide
reagent Tol3GeNMe2 was prepared from the salt metathesis reac-
tion of Tol3GeCl with LiNMe2 in 76% yield, and the 1H NMR spec-
d
The majority of the oligogermanes we have prepared in our
laboratory, with the exception of several phenyl-substituted
digermanes and the branched tetragermane (Ph3Ge)3GePh, are
either liquids or amorphous solids at room temperature. The
majority of oligogermanes GenR2nþ2 that have been characterized
using X-ray crystallography (n ¼ 2e5) contain phenyl substituents,
although the yields of these products are generally low (0.5e45%)
[20,39,41,44,45,48e51]. Due to our desire to use our oligogermane
systems as precursors for the synthesis of germanium-based
nanomaterials, we were interested in preparing new systems that
could be structurally characterized. The present work focuses on
the preparation of para-tolyl-substituted oligogermanes, where the
para-methyl group of the tolyl substituents can be used for an
initial assessment of the purity of the products using 1H NMR
spectroscopy. We have prepared and structurally characterized four
new tolyl-substituted oligogermanes containing between two and
four germanium atoms in the chain, and these compounds have
been further characterized using NMR, infrared, and UV/visible
spectroscopy, cyclic voltammetry, and elemental analysis. We have
observed, for the first time, multiple irreversible oxidation events
in the cyclic voltammograms of these oligogermanes, and have
postulated the pathway of decomposition after the oxidation event
takes place.
trum of this material exhibits a singlet at
d 2.84 ppm corresponding
to the protons of the amide methyl groups.
The digermane Tol3GeGePh3 (1) and the trigermanes Tol3Ge-
GePh2GeTol3 (2) and Tol3GeGeTol2GeTol3 (3) were prepared using
the amide Tol3GeNMe2 via the hydrogermolysis reaction in CH3CN
solvent (Scheme 1). As previously described [41e45], the germa-
nium amide reagent Tol3GeNMe2 reacts in situ with the CH3CN
solvent to generate the
a-germyl nitrile Tol3GeCH2CN, which
contains a labile GeeC bond and is the active species in the ger-
maniumegermanium bond forming process. The 1H NMR spectra
of 1 and 2 exhibit similar patterns in the aromatic region that are
consistent with expected chemical shift values. In both compounds
resonances for the ortho-protons of the tolyl rings are shifted
downfield relative to those for the ortho-protons of the phenyl
rings, while resonances for the meta-protons appear upfield rela-
tive to those of the phenyl groups. In addition, resonances for the
ipso-carbons of the tolyl groups in the 13C NMR spectra of 1 and 2
appear downfield relative to those of the phenyl groups. Singlets for
the methyl protons of 1 and 2 were observed at
2.07 ppm, respectively, while the per-tolyl-substituted trigermane
3 exhibits two methyl group resonances at 2.09 and 1.99 ppm,
where the singlet corresponding to the central tolyl substituents
appears upfield at 1.99 ppm.
d 2.02 and
d
2. Results and discussion
d
The crystal structures of 1e3 were determined and an ORTEP
diagram of 1$2C6H6 is shown in Fig. 1 while selected bond distances
and angles are collected in Table 1. Curiously, the GeeGe bond
distance in 1 measures 2.408(1) Å, which is shorter than the
reported GeeGe bond length in the related perphenyl digermane
Ph3GeGePh3$2C6H6 (4$2C6H6) of 2.446(1) Å [48], as well as that in
the unsolvated form of 4 (2.437(2) Å) [52]. A survey of twenty-five
structurally characterized digermanes [41,44,45,48,49,51e67]
reveals that the GeeGe bond distance in 1 is the third shortest
GeeGe bond length to be reported, where only Cl3CCOOPh2GeGe-
Ph2OOCCCl3 (5) [51] and (2,6-Dipp2C6H3)H2GeGeH2(C6H3Dipp2-
2,6) (Dipp ¼ 2,6-diiisopropylphenyl) [58] have shorter bond lengths
of 2.393(2) and 2.402(1) Å, respectively. The short bond length in
the latter compound is not surprising despite the presence of the
bulky aryl groups at each germanium atom, since the other two
2.1. Syntheses and X-ray crystal structures
The germanium starting materials Tol3GeCl and Tol2GeBr2
(Tol ¼ p-H3CC6H4) were prepared by the action of TolMgCl on GeCl4
or TolMgBr on GeBr4 (respectively) under carefully controlled
reaction conditions to prevent the formation of oligogermanes.
While the reaction of GeCl4 with 3 equiv. of TolMgCl yielded
primarily the desired triaryl product Tol3GeCl, the preparation of
the diaryl material Tol2GeBr2 was complicated by the concomitant
formation of Tol3GeBr and TolGeBr3. Separation of the three
components of the product mixture proved difficult, and as a result
the product mixture was treated directly with excess LiAlH4 to yield
a mixture of the corresponding arylgermanium hydrides RnGeH4ꢀn
(n ¼ 1e3). The three hydrides could be readily separated by frac-
tional vacuum distillation and Tol2GeH2 was obtained in 8% yield
Scheme 1. Syntheses of Tol3GeGePh3 (1), Tol3GeGePh2GeTol3 (2), and Tol3GeGeTol2GeTol3 (3).

M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
1815
Fig. 2. ORTEP diagram of Tol3GeGePh2GeTol3$C7H8 (2$C7H8). Thermal ellipsoids are
drawn at 50% probability.
Structurally characterized linear trigermanes are rare, and to our
knowledge the structures of only six other such species have
been previously reported [6,39,69e72]. The average GeeGe bond
distance in 2$C7H8 is 2.4328(5) Å, which is shorter than the
average GeeGe bond length in Ge3Ph8 (6, 2.440(2) Å) [39] but is
similar to the average GeeGe bond distance of 2.429(1) in
Ph3GeGeMe2GePh3 (7) [69]. However, the contraction of the
GeeGe bond lengths in 2$C7H8 compared to those in 6 is not as
pronounced as that observed between 1$2C6H6 and Ph3GeGePh3,
further suggesting that interplay of electronic and steric effects in
the trigermane 2$C7H8 have a combined effect on the GeeGe
bond distance. The GeeGeeGe bond angle at Ge(2) in 2$C7H8
measures 114.80(2)ꢁ, which is more acute that those in both 6
(121.3(1)ꢁ) [39] and 7 (120.3(1)ꢁ) [69] but is similar to those in
the halide-substituted trigermanes XBut2GeGeBut2GeBut2X
(X ¼ Br [72], 113.6(1)ꢁ; X ¼ I [71], 115.4(1)ꢁ). The C(22)eGe(2)eC
(28) bond angle in 2$C7H8 which measures 106.2(1)ꢁ is also more
acute than the corresponding bond angle at the central germa-
nium atom in both 6 (108.7(4)ꢁ) [39] and 7 (109.2(2)ꢁ) [69],
which can be attributed to the steric effects of the six terminal
tolyl groups.
Fig. 1. ORTEP diagram of Tol3GeGePh3$2C6H6 (1$2C6H6). Thermal ellipsoids are drawn
at 50% probability.
substituents are sterically unencumbering hydrogen atoms. The
bond length in 5 is constricted because the carbonyl oxygen atoms
in each of the trichloroacetato ligands are coordinated to the
opposite germanium atom to yield a hypervalent five-coordinate
Ge center in each case [51]. The structure of Ge2Tol6$C6H6 was
recently determined and this compound also has a short GeeGe
distance that measures 2.419(1) Å [68].
The short GeeGe bond distances in 1$2C6H6 and Ge2Tol6$C6H6
can be attributed to electronic effects, since the para-methyl group
of the tolyl substituents presumably renders the germanium atoms
more electron rich via inductive effects relative to a triphenyl-
substituted germanium center. However, the constriction of the
GeeGe bond distance in 1$2C6H6 and Ge2Tol6$C6H6 is drastic
compared to that in Ph3GeGePh3$2C6H6, and similar short GeeGe
bond lengths were not observed in 2$C7H8 or 3$C7H8 (vide infra).
However, steric effects in the trigermanes 2$C7H8 and 3$C7H8 are
greater than those in 1$2C6H6 and Ge2Tol6$C6H6, and this
presumably counteracts the electronic effects of the para-tolyl
groups. Crystal packing effects also could contribute to the con-
tracted GeeGe distances in 1$2C6H6 and Ge2Tol6$C6H6, but it is
unlikely that this solely results in the drastic shortening of the
GeeGe distances in these two digermanes.
The structure of the per-tolyl-substituted trigermane 3$C7H8 is
shown in Fig. 3 and selected bond distances and angles are given in
Table 3. The GeeGe bond distances in 3$C7H8 are longer than those
in 2$C7H8 and 7 due to the additional steric crowding imposed by
the two central tolyl substituents, and the average GeeGe bond
Table 2
The structure of the trigermane 2$C7H8 is shown in Fig. 2 and
selected bond distances and angles are collected in Table 2.
Selected bond distances (Å) and angles (deg) for Tol3GeGePh2GeTol3$C7H8 (2$C7H8).
Ge(1)eGe(2)
Ge(2)eGe(3)
Ge(1)eC(1)
Ge(1)eC(8)
Ge(1)eC(15)
Ge(2)eC(22)
Ge(2)eC(28)
Ge(3)eC(34)
Ge(3)eC(41)
Ge(3)eC(48)
2.4318(5)
2.4338(4)
1.958(3)
1.959(3)
1.966(3)
1.958(3)
1.955(3)
1.957(3)
1.945(3)
1.944(3)
C(22)eGe(2)eC(28)
C(34)eGe(3)eC(41)
C(34)eGe(3)eC(48)
C(41)eGe(3)eC(48)
C(1)eGe(1)eGe(2)
C(8)eGe(1)eGe(2)
C(15)eGe(1)eGe(2)
C(22)eGe(2)eGe(1)
C(28)eGe(2)eGe(1)
C(22)eGe(2)eGe(3)
C(28)eGe(2)eGe(3)
C(34)eGe(3)eGe(2)
C(41)eGe(3)eGe(2)
C(48)eGe(3)eGe(2)
106.2(1)
108.7(1)
107.6(1)
109.0(1)
106.7(8)
117.36(9)
108.52(9)
111.50(9)
113.93(8)
105.28(8)
113.93(8)
117.53(8)
106.95(8)
106.81(8)
Table 1
Selected bond distances (Å) and angles (deg) for Tol3GeGePh3$2C6H6 (1$2C6H6).
Ge(1)eGe(2)
Ge(1)eC(1)
Ge(1)eC(8)
Ge(1)eC(15)
Ge(2)eC(22)
Ge(2)eC(28)
Ge(2)eC(34)
2.408(1)
1.942(2)
1.942(2)
1.935(2)
1.941(2)
1.940(2)
1.939(2)
C(8)eGe(1)eC(15)
C(22)eGe(2)eC(28)
C(22)eGe(2)eC(34)
C(28)eGe(2)eC(34)
C(1)eGe(1)eGe(2)
C(8)eGe(1)eGe(2)
C(15)eGe(1)eGe(2)
C(22)eGe(2)eGe(1)
C(28)eGe(2)eGe(1)
C(34)eGe(2)eGe(1)
108.94(9)
109.89(9)
110.32(9)
109.97(8)
108.47(7)
109.72(7)
110.30(7)
109.18(7)
110.47(7)
106.97(7)
Ge(1)eGe(2)eGe(3)
C(1)eGe(1)eC(8)
C(1)eGe(1)eC(15)
C(8)eGe(1)eC(15)
114.80(2)
110.0(1)
108.1(1)
105.8(1)
C(1)eGe(1)eC(8)
C(1)eGe(1)eC(15)
109.64(9)
109.76(9)

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M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
derivative 5 [51], and this was subsequently converted to the 1,2-
dichloride 8 using hydrochloric acid [51]. The synthesis of 8 by the
action of anhydrous HCl on Ph3GeGePh3 under pressure has also
been described, which also lead to the formation of Cl2PhGe-
GePhCl2 (9). [55]. Treatment of 8 with LiAlH4 furnished the 1,2-
dihydride 10 in 79% yield. The 1H NMR spectrum of 10 contains
a singlet for the two equivalent hydridic protons at d 5.58 ppm, and
the GeeH stretching frequency was observed at 2033 cmꢀ1 in the IR
spectrum of 10. The synthesis of 10 has been achieved by other
methods [73e75], including by the hydrolysis of Ph2GeHLi [75] and
also by the catalytic dehydrocoupling of Ph2GeH2 [74], and the
spectral data obtained for 10 agree with the reported values. The
tetragermane 11 was prepared from 10 and two equivalents of
Tol3GeNMe2 in 80% yield via the hydrogermolysis reaction in
CH3CN, which again proceeds via the in situ generation of the
reactive Tol3GeCH2CN intermediate. Similar to what was observed
in the 1H NMR spectra of 1 and 2, resonances for the ortho-protons
of the tolyl substituents of 11 are shifted downfield from those of
the phenyl substituents while those of for the meta-protons are
shifted upfield.
Fig. 3. ORTEP diagram of Tol3GeGeTol2GeTol3$C7H8 (3$C7H8). Thermal ellipsoids are
drawn at 50% probability.
Structurally characterized linear tetragermanes are rare
[39,69e72,76], and compounds that have been characterized by
this method include Ge4Ph10$2C6H6 (12$2C6H6) [39], 1,4-dichloro-
octaphenyltetragermane [70], and 1,4-diiodo-octaphenylte-
tragermane [76]. An ORTEP diagram of the tetragermane 11 is
shown in Fig. 4 and selected bond distances and angles for 11 are
collected in Table 4. Compound 11 crystallizes with two indepen-
dent molecules in the unit cell, where one of the molecules
(molecule 1) is completely ordered and the other (molecule 2) is
disordered. Both molecules of 11 are located on a crystallographic
inversion center, and the germanium atoms of molecule 2 are
disordered over two positions with occupancies of 85.6 and 14.4%.
The bond distances given for molecule 2 are a weighted average of
the two positions. The average GeeGe bond distance in 11 is 2.455
(3) Å which is somewhat shorter to the average GeeGe bond length
in the perphenyl-substituted tetragermane 12$2C6H6 (2.462
(2) Å) [39].
As observed for the digermane 1$2C6H6 and the trigermanes
2$C7H8 and 3$C7H8 versus their perphenyl analogs, the steric and
electronic effects of the tolyl groups in 11 versus the phenyl
groups in 12$2C6H6 have an effect on the structural parameters.
The terminal GeeGe bonds in both molecules of 11 (2.4490(8)
and 2.460(3) Å) are shorter than those in the perphenyl tetra-
germane 12$2C6H6 (2.463(2) Å) [39], and the internal GeeGe
distances in the molecules of 11 (2.457(1) and 2.448(3) Å) are
also shorter than that of 12$2C6H6 (2.461(3) Å) [39]. Further-
more, the GeeGeeGe bond angle in both molecules of 11 (115.53
(3) and 118.9(2)ꢁ) are more acute than that in 12$2C6H6 (121.3
(1)ꢁ) [39].
distance in 3$C7H8 is 2.4404(5) Å. However, this value is nearly
identical to that of trigermane 6 (2.440(2) Å) [39]. The central
GeeGeeGe bond angle in 3$C7H8 of 117.54(1)ꢁ is more acute than
those in both 6 (121.3(1)ꢁ) [39] and 7 (120.3(1)ꢁ) [69], but is more
obtuse than the corresponding angle in 2$C7H8 (114.80(2)ꢁ). The
central C(23)eGe(2)eC(30) angle in 3$C7H8 measures 106.45(9)ꢁ,
which is slightly more obtuse than that in 2$C7H8 (106.2(1)ꢁ), but is
more acute than the corresponding angles in both 6 (108.7(4)ꢁ) [39]
and 7 (109.2(2)ꢁ) [69]. Therefore, the effects resulting from the
presence of tolyl groups versus phenyl groups at the central
germanium atom in the three trigermanes 2$C7H8, 3$C7H8, and 6
depend on the identity of the substituents attached to the terminal
germanium atoms. The trigermane 3$C7H8, which contains eight
tolyl substituents and thus is the most sterically encumbered of
these three molecules, has the longest GeeGe bond distances but
intermediate GeeGeeGe and CeGeeC bond angles at the central
germanium atom. The trigermane 7, which contains sterically
unencumbering methyl substituents at the central germanium
atom, has the shortest GeeGe bond distances among the three
molecules and the most obtuse bond angles at the central germa-
nium atom.
The synthesis of the tetragermane Tol3GeGePh2GePh2GeTol3
(11) was achieved in four steps starting from hexaphenyldigermane
(Scheme 2). Using a variation of a published procedure, a single
phenyl group was cleaved from each germanium atom in Ph3Ge-
GePh3 (4) using trichloroacetic acid to yield the 1,2-trichloroacetato
The overall geometry of 11 approximates that of n-butane, and is
also similar to that of the tetragermane 12$2C6H6. Torsion angles
for molecule 1 of 11 about the Ge(1)eGe(2) and Ge(2)eGe(2i) bonds
are collected in Table 5. The two terminal Tol3Ge- groups in mole-
cule 1 are disposed in an anti-conformation about the central Ge
(2)eGe(2i) bond and the dihedral angle is exactly 180ꢁ, and the
environment about the central Ge(2)eGe(20) bond in molecule 1 of
11 is symmetric due to the presence of a crystallographic inversion
center. However, although the phenyl group containing C(8) and Ge
(20) are arranged in an approximate anti-conformation about the Ge
(1)eGe(2) bond, the dihedral angle between C(8) and Ge(20) devi-
ates from the ideal value of 180ꢁ by 13.2ꢁ. The structure of 12$2C6H6
exhibits a similar arrangement along the terminal Ge(1)eGe(2)
bond, but the dihedral angle in 12$2C6H6 is distorted by only 7.4ꢁ,
and the greater distortion in 11 is attributed to the increased steric
bulk of the tolyl substituents.
Table 3
Selected bond distances (Å) and angles (deg) for Tol3GeGeTol2GeTol3$C7H8 (3$C7H8).
Ge(1)eGe(2)
Ge(2)eGe(3)
Ge(1)eC(1)
Ge(1)eC(8)
Ge(1)eC(21)
Ge(2)eC(23)
Ge(2)eC(30)
Ge(3)eC(37)
Ge(3)eC(44)
Ge(3)eC(51)
2.4450(4)
2.4359(5)
1.951(2)
1.951(2)
1.953(2)
1.958(2)
1.960(2)
1.950(2)
1.962(2)
1.949(2)
C(23)eGe(2)eC(30)
C(37)eGe(3)eC(44)
C(37)eGe(3)eC(51)
C(44)eGe(3)eC(51)
C(1)eGe(1)eGe(2)
C(8)eGe(1)eGe(2)
C(21)eGe(1)eGe(2)
C(23)eGe(2)eGe(1)
C(30)eGe(2)eGe(1)
C(23)eGe(2)eGe(3)
C(30)eGe(2)eGe(3)
C(37)eGe(3)eGe(2)
C(44)eGe(3)eGe(2)
C(51)eGe(3)eGe(2)
106.45(9)
107.0(1)
108.8(1)
107.4(1)
114.30(7)
108.32(6)
109.24(6)
106.21(6)
108.76(6)
109.94(7)
107.42(7)
109.16(7)
110.08(7)
114.09(7)
Ge(1)eGe(2)eGe(3)
C(1)eGe(1)eC(8)
C(1)eGe(1)eC(21)
C(8)eGe(1)eC(21)
117.54(1)
108.33(9)
108.02(9)
108.5(1)

M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
1817
Scheme 2. Synthesis of Tol3GeGePh2GePh2GeTol3 (11).
2.2. UV/visible spectra and cyclic voltammetry
for four separate runs and GeeGe bond distance data are collected
in Table 6, and the proposed electrochemical decomposition
pathways for 1e3 and 11 are shown in Scheme 3. The voltammo-
grams for each of these GenAr2nþ2 compounds exhibit a total of
n ꢀ 1 irreversible oxidation waves. This is significant, since oligo-
germanes that have been previously characterized by this method
typically exhibit only one irreversible oxidation wave [42,46,47,77]
due to decomposition of the oligogermane after the oxidation event
occurs. However, the multiple waves observed for 2, 3, and 11
suggest that in the case of these three compounds, the product
generated after oxidation is stable and undergoes either one
(compounds 2 and 3) or two (compound 4) subsequent one-elec-
tron oxidation processes.
The series of four oligogermanes 1e3 and 11 were characterized
using cyclic voltammetry in CH2Cl2 solution with 0.1 M [Bu4N][PF6]
as the supporting electrolyte. Voltammograms for each of the four
species are shown in Fig. 5, average values for the oxidation waves
The oxidation potentials among the three digermanes 1, Ge2Tol6,
and Ge2Ph6 can be correlated with the GeeGe bond distances in
these compounds. The single irreversible oxidation wave for 1 was
observed at 1483 ꢂ 17 mV, and this can be compared to that of
a commercial sample of Ge2Ph6 (1958 ꢂ 19 mV) and a sample of
Ge2Tol6 (1757 ꢂ 18 mV) prepared from Tol3GeH and Tol3GeNMe2.
Compound 1 exhibits the least positive oxidation potential among
these three species and also has the shortest GeeGe bond distance.
The electronic and steric attributes of the substituents both have an
Table 4
Selected bond distances (Å) and angles (deg) for Tol3GeGePh2GePh2GeTol3 (11).
Molecule 1
Molecule 2a
Ge(1)eGe(2)
2.4490(8)
2.457(1)
1.961(4)
1.960(4)
1.964(5)
1.971(4)
1.974(4)
115.53(3)
108.1(1)
107.5(2)
109.4(2)
106.2(2)
116.5(1)
106.2(1)
109.1(1)
103.5(1)
110.7(1)
108.6(1)
111.5(1)
Ge(10)eGe(20)
2.460(3)
2.448(3)
1.953(5)
2.008(5)
1.947(6)
1.980(5)
1.981(5)
118.9(2)
106.6(2)
113.0(2)
106.8(2)
111.2(2)
110.8(1)
114.2(1)
105.5(2)
103.8(2)
108.2(2)
107.8(1)
106.5(2)
i
Ge(2)eGe(2i)
Ge(20)eGe(2’ )
Ge(1)eC(1)
Ge(1)eC(8)
Ge(1)eC(15)
Ge(2)eC(22)
Ge(10)eC(1)
Ge(10)eC(8)
Ge(10)eC(15)
Ge(20)eC(22)
Ge(2)eC(28)
Ge(20)eC(28)
Ge(1)eGe(2)eGe(2i)
C(1)eGe(1)eC(8)
C(1)eGe(1)eC(15)
C(8)eGe(1)eC(15)
C(22)eGe(2)eC(28)
C(1)eGe(1)eGe(2)
C(8)eGe(1)eGe(2)
C(15)eGe(1)eGe(2)
C(22)eGe(2)eGe(1)
C(28)eGe(2)eGe(1)
Ge(10)eGe(20)eGe(2’i)
C(1)eGe(10)eC(8)
C(1)eGe(10)eC(15)
C(8)eGe(10)eC(15)
C(22)eGe(20)eC(28)
C(1)eGe(10)eGe(20)
C(8)eGe(10)eGe(20)
C(15)eGe(10)eGe(20)
C(22)eGe(20)eGe(10)
C(28)eGe(20)eGe(10)
i
i
C(22)eGe(2)eGe(2 )
C(28)eGe(2)eGe(2 )
C(22)eGe(20)eGe(2’ )
C(28)eGe(20)eGe(2’ )
i
i
a
The germanium atoms in Molecule 2 of 11 are disordered over two positions
with occupancies of 85.6 and 14.4%. Distances and angles including Ge(10) and Ge
(20) are a weighted average based on the two occupancies.
Fig. 4. ORTEP diagrams of the two crystallographically independent molecules of
Tol3GeGePh2GePh2GeTol3 (11). Thermal ellipsoids are drawn at 50 % probability.

1818
M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
Table 5
2.4450(4) and 2.4395(5) Å (av. 2.4405(5) Å). The average GeeGe
bond distance in Ge3Ph8 is similar to that of 3 and measures 2.440
(2) Å [39].
Torsion angles (deg) along the Ge(1)eGe(2) and Ge(2)eGe(2i) bond in molecule 1 of
Tol3GeGePh2GePh2GeTol3 (11).
C(1)eGe(1)eGe(2)eGe(2i)
C(1)eGe(1)eGe(2)eC(28)
C(8)eGe(1)eGe(2)eC(28)
C(8)eGe(1)eGe(2)eC(22)
C(15)eGe(1)eGe(2)eC(22)
72.8(1) Ge(1)eGe(2)eGe(2i)eC(22i) 64.3(1)
The data obtained for these digermanes and trigermanes
suggests that decomposition of the oligogermane via germylene
extrusion is occurring in these systems. The loss of :GeR2 fragments
has been detected via trapping with 2,3-dimethyl-1,3-butadiene
from the photolysis of oligo[78] and polygermanes [79], and has also
been postulated to occur in reactions of oligogermanes with tetra-
cyanoethylene [77,80]. It should be noted, however, that homolytic
GeeGe bond cleavage has also been observed as a competing
process. The similarity of the potentials of the second oxidation
waves in 2 and 3 suggests that the same chain contraction product is
being generated from both molecules after the first oxidation event
takes place. We propose that this species is Ge2Tolꢃ6þ, which is
generated by the loss of :GePh2 from 2 and :GeTol2 from 3. The
oxidation potential for the digermane Ge2Tol6 (1) at 1757 ꢂ 18 mV is
also consistent with this statement, since the positively charged
55.1(1) C(28)eGe(2)eGe(2i)eC(22i)
63.3(1)
65.3(1) C(28)eGe(2)eGe(2i)eGe(1i) 52.4(1)
48.2(1) C(22)eGe(2)eGe(2i)eGe(1i) 64.3(1)
69.6(1) C(22)eGe(2)eGe(2i)eC(28i)
63.3(1)
C(15)eGe(1)eGe(2)eGe(2i) 49.0(1) Ge(1)eGe(2)eGe(2i)eC(28i) 52.4(1)
effect on the GeeGe bond length as well as on the relative energies
of the frontier molecular orbitals [42], and since tolyl substituents
are more inductively electron-donating and also more sterically
encumbering than phenyl substituents, the trends in both oxida-
tion potential and GeeGe bond length are as expected.
Compounds 2 and 3 both exhibit two irreversible oxidation
waves in their cyclic voltammograms. The first (least positive)
oxidation wave was observed at 1498 ꢂ 14 mV for 2 and
1542 ꢂ 11 mV for 3, while the second oxidation waves for 2
(1860 ꢂ 15 mV) and 3 (1865 ꢂ 13 mV) were observed at nearly
identical potentials, and two oxidation waves were also observed
for a sample of Ge3Ph8 at 1696 ꢂ 12 mV and 2052 ꢂ 15 mV. As found
for the three digermanes described above, the same correlation of
the potential of the first oxidation wave with bond length was
observed for the trigermanes 2, 3, and Ge3Ph8. The GeeGe bond
distances in 2 are 2.4318(5) and 2.4338(4) Å (av. 2.4328(5) Å) and
are shorter the corresponding distances in 3, which measure
species Ge2Tolꢃ6þ generated from 2 (1860 ꢂ 15 mV) and
3
(1865 ꢂ 13 mV) is expected to have a more positive oxidation
potential than the neutral species 1.
The first oxidation wave for Ge3Ph8 is at a more positive
potential than that of both 2 and 3, which is consistent with the
observations for the three digermanes 1 and Ge2Tol6, and Ge2Ph6
described above. The first oxidation of Ge3Ph8 results in extrusion
of :GePh2 to generate Ge2Phꢃ6þ and this species undergoes an
additional oxidation event at 2052 ꢂ 15 mV, which is more positive
Fig. 5. Cyclic voltammograms for 1 e 3 and 11 in CH2Cl2 with 0.1M [Bu4N][PF6] as the supporting electrolyte.

M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
1819
Table 6
Oxidation potentials, absorbance maxima and GeeGe bond distances for compounds 1e3,11, Ge2Tol6 and GenPh2nþ2 (n ¼ 2e4) in CH2Cl2 solution using 0.1 M [Bu4N][PF6] as the
supporting electrolyte.
Compound
Eox (mV)
lmax (nm)
dGeeGe (Å)
Compound
Eox (mV)
lmax (nm)
dGeeGe (Å)
Tol3GeGePh3 (1)
1483 ꢂ 17
240
2.408(1)
Ge2Tol6
Ge2Ph6 (4)
Ge3Ph8 (6)
1757 ꢂ 18
1958 ꢂ 19
1696 ꢂ 12
2052 ꢂ 15
241
240
238d
2.419(1)b
2.446(1)c
2.440(2)d
Tol3GeGePh2GeTol3 (2)
1498 ꢂ 14
1860 ꢂ 15
1542 ꢂ 11
1865 ꢂ 13
1398 ꢂ 14
1718 ꢂ 11
2242 ꢂ 18
251
253
285
2.4328(5)a
2.4405(5)a
2.455(3)a
Tol3GeGeTol2GeTol3 (3)
Tol3GeGePh2GePh2GeTol3 (11)
Ge4Ph10 (12)
1644 ꢂ 22
2060 ꢂ 17
2450 ꢂ 18
282d
2.462(2)d
a
Average value.
Data taken from ref. [48].
Data taken from ref. [68].
Data taken from ref. [39].
b
c
d
than the oxidation wave for the neutral compound Ge2Ph6 at
1958 ꢂ 19 mV. The second oxidation wave for Ge3Ph8 also occurred
at a more positive potential than that for both 2 and 3, which is
consistent with the oxidation wave of Ge2Ph6 being at a higher
potential than both 1 and Ge2Tol6.
The CV for the tetragermane 11 exhibits three distinct waves at
1398 ꢂ 14, 1718 ꢂ 11, and 2242 ꢂ 18 mV, indicating the sequential
generation of two stable decomposition products. The CV of
Ge4Ph10 also exhibits three oxidation waves that each appear at
more positive potentials (1644 ꢂ 22, 2060 ꢂ 17, and 2450 ꢂ 18 mV)
Scheme 3. Electrochemical decomposition pathways for 1 e 3 and 11.

1820
M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
fragments are released from the GeeGe backbone, since this type of
decomposition has been observed in photolysis studies of oligo-
germanes [77e80]. The first two germylenes resulting from the
sequential oxidations of 11 are most likely :GePh2, since the
internal germanium atoms are phenyl substituted and are more
susceptible to elimination. In the perphenyl-substituted tetra-
germane Ge4Ph10, all three of the germylenes released are: GePh2,
but the third oxidation of 11 results in the generation of the radical
trivalent cation Tol3GeGeTol3ꢃ3þ, and this species then subsequently
decomposes via elimination of the germylene :GeTol2.
The UV/visible spectra of 1e3 and 11 are shown in Fig. 6 and the
lmax values are collected in Table 6. The expected trend among the
di, tri, and tetragermanes was observed, where the position of lmax
is red shifted with increasing catenation. The absorbance maximum
corresponding to the
s /
s* transition in the tetragermane 11 at
285 nm (
3
3.43 ꢄ 104 L molꢀ1 cmꢀ1) is at lower energy than those of
the trigermanes 2 and 3 and the digermane 1. In addition to the
band at 285 nm, three additional features at 274, 268, and 260 nm
are present in the UV/visible spectrum of 11, which are assigned to
electronic transitions between the
p
and p* orbitals of the aryl
p* transitions for compounds 1e3 also are
ligands. Similar
p
/
likely to occur, but the peaks for these transitions were not visible
Fig. 6. UV/visible spectra of 1 e 3 and 11 in CH2Cl2 solution.
due to their overlap with the intense lmax feature resulting from the
s
/
s* electronic transition. The red shift of the lmax for 11 versus
those for 1e3 allows these additional absorbance features to be
than the corresponding waves for 11, which is again consistent with
the results obtained for the phenyl-substituted digermanes and
trigermanes versus their tolyl-containing analogs. The presence of
three oxidation waves for 11 and Ge4Ph10 suggest three germylene
observed in 11. The lmax for Ge4Ph10 was reported at 282 nm (
3
3.98 ꢄ 104 L molꢀ1 cmꢀ1), and a second defined feature was also
observed at 228 nm [39]. The lmax for
2 (251 nm, 3
Table 7
Crystal data and structure refinement details for 1$2C6H6, 2$C7H8, 3$C7H8, and 11.
Compound
Empirical formula
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
1$2C6H6
C51H48Ge2
150(2)
0.71073
Triclinic
2$C7H8
C61H60Ge3
120(2)
0.71073
Monoclinic
P21/n
13.7610(5)
26.044(1)
14.1583(5)
90
92.437(2)
90
5069.6(3)
4,0
1.324
3$C7H8
C63H64Ge3
150(2)
0.71073
Triclinic
11
C66H62Ge4
150(2)
0.71073
Triclinic
P ꢀ 1
P ꢀ 1
P ꢀ 1
8.884(5)
11.563(2)
13.825(2)
17.739(3)
86.381(2)
88.798(2)
72.552(2)
2702.3(8)
2,0
11.582(4)
13.114(4)
19.527(6)
83.531(5)
79.175(4)
72.021(4)
2766(1)
2,0
b (Å)
c (Å)
10.428(6)
21.52(1)
89.200(8)
79.094(8)
81.806(8)
1937(2)
2,0
1.315
1.584
794
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
Volume (Å3)
Z, Z0
Calculated density (g/cm3)
Absorption coefficient (mmꢀ1
F(000)
1.277
1.695
1076
1.375
2.192
1172
)
2.374
2088
Crystal size (mm)
Crystal size and shape
0.25 ꢄ 0.18 ꢄ 0.12
Colorless block
1.93e28.31
ꢀ11 ꢅ h ꢅ 11
ꢀ13 ꢅ k ꢅ 13
ꢀ28 ꢅ l ꢅ 28
42 366
0.15 ꢄ 0.10 ꢄ 0.10
Colorless block
3.39e66.11
ꢀ15 ꢅ h ꢅ 13
ꢀ28 ꢅ k ꢅ 29
ꢀ14 ꢅ l ꢅ 16
26 445
0.35 ꢄ 0.15 ꢄ 0.08
Colorless block
1.55e28.20
ꢀ15 ꢅ h ꢅ 15
ꢀ17 ꢅ k ꢅ 18
ꢀ23 ꢅ l ꢅ 23
69 956
0.25 ꢄ 0.21 ꢄ 0.11
Colorless block
1.64e27.51
ꢀ12 ꢅ h ꢅ 14
ꢀ12 ꢅ k ꢅ 16
ꢀ25 ꢅ l ꢅ 24
15 530
q
range for data collection (o)
Index ranges
Reflections collected
Independent reflections
9055 (Rint ¼ 0.0456)
25.00 (99.9%)
Multi-scan
0.8327 and 0.6929
8224 (Rint ¼ 0.0502)
60.00 (99.4%)
Multi-scan
0.7972 and 0.7171
12 152 (Rint ¼ 0.0431)
25.00 (99.8%)
Multi-scan
0.8763 and 0.5884
9778 (Rint ¼ 0.0335)
25.00 (83.2%)
Multi-scan
Completeness to
q
Absorption correction
Maximum and minimum transmission
Refinement method
0.7945 and 0.6102
Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2
Data/restraints/parameters
9055/0/454
1.053
8224/0/520
1.032
12152/0/540
1.075
9778/0/656
1.026
Goodness of fit on F2
Final R indices (I > 2s(I))
R1
wR2
0.0320
0.0701
0.0367
0.0773
0.0374
0.0915
0.0499
0.1110
Final R indices (all data)
R1
wR2
0.0534
0.0750
0.0544
0.0813
0.591 and ꢀ0.347
0.0448
0.0968
1.070 and ꢀ0.666
0.0691
0.1237
0.808 and ꢀ0.487
Largest difference in peak and hole (e Åꢀ3) 0.433 and ꢀ0.295

M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
1821
3.17 ꢄ 104 L molꢀ1 cmꢀ1) and 3 (253 nm,
3
2.55 ꢄ 104 L molꢀ1 cmꢀ1
)
mixture was refluxed for 2 h, was allowed to cool, and then was
added to a solution of GeCl4 (8.43 g, 39.3 mmol) in THF (50 mL). The
reaction mixture was refluxed for 90 min, was allowed to cool, and
then was carefully poured over a 20% aqueous HCl solution at 0 ꢁC.
The THF layer was separated and the aqueous layer was extracted
with ether (3 ꢄ 50 mL). The combined THF layer and ethereal
extracts were dried over anhydrous MgSO4. The suspension was
filtered and the volatiles were removed in vacuo to yield a viscous
oil. The crude product was distilled in vacuo (125 ꢁC, 0.05 torr) to
remove impurities to yield Tol3GeCl (12.425 g, 83%) as a white solid.
appear at nearly the same wavelength, and are red shifted relative
to that of 1 but are blue shifted relative to that of 11. Both absor-
bance maxima are red shifted relative to the reported lmax for
Ge3Ph8 at 238 nm (
lmax for 1 and Ge2Ph6[36] were both observed at 240 nm.
3
3.16 ꢄ 104 L molꢀ1 cmꢀ1) [39]; however, the
3. Conclusions
The series of para-tolyl-substituted oligogermanes Tol3GeGePh3
(1), Tol3GeGePh2GeTol3 (2), Tol3GeGeTol2GeTol3 (3), and Tol3Ge-
GePh2GePh2GeTol3 (11) can be prepared via the hydrogermolysis
reaction using Tol3GeNMe2 and Tol2GeH2 as synthetic building
blocks. The structures of these four compounds differ from their
per-phenyl-substituted analogs, in both the GeeGe bond distances
and, in the case of 2, 3 and 11, in the GeeGeeGe bond angles, due to
the different steric and electronic effects of the tolyl substituents. In
general, the GeeGe bond distances are shorter and the GeeGeeGe
bond angles are more acute when tolyl substituents are introduced
along the GeeGe backbone in place of phenyl substituents.
The incorporation of tolyl substituents also has an effect on the
oxidation potential and UV/visible absorbance maxima in these
compounds. Oligogermanes 1e3 and 11, which have the general
formula GenAr2nþ2 (Ar ¼ p-CH3C6H4 or Ph), exhibit n ꢀ 1 oxidation
waves in their cyclic voltammograms. This has not been observed
previously, as oligogermanes typically exhibit only one irreversible
oxidation wave regardless of the degree of catenation. We suggest
that the first oxidation event for 1e3 results in extrusion of the
germylene :GeTol2, and the resulting electrochemical by-products
for 2 and 3 are stable and undergo a second oxidation event with
concomitant extrusion of a second germylene fragment.
1H NMR
m-H3CC6H4), 2.06 (s, 9H, H3CC6H4) ppm. 13C NMR
d
7.66 (d, J ¼ 7.8 Hz, 6H, o-H3CC6H4), 7.00 (d, J ¼ 7.8 Hz, 6H,
d
140.6 (ipso-
H3CC6H4), 134.6 (o-H3CC6H4), 130.0 (p-H3CC6H5), 129.8 (m-
H3CC6H4), 21.4 (p-H3CC6H4) ppm. Anal. Calcd. for C21H21ClGe: C,
66.10; H, 5.55. Found: C, 66.25; H, 5.61.
4.3. Synthesis of Tol3GeNMe2
To a solution of Tol3GeCl (1.951 g, 5.117 mmol) in benzene
(20 mL) was added a suspension of LiNMe2 (0.280 g, 5.49 mmol) in
benzene (10 mL). The reaction mixture was stirred for 18 h and then
filtered through Celite. The volatiles were removed in vacuo to yield
Tol3GeNMe2 (1.51 g, 76%) as a thick colorless oil. 1H NMR
d
7.71 (d,
J ¼ 7.8 Hz, 6H, o-H3CC6H4), 7.09 (d, J ¼ 7.8 Hz, 6H, m-H3CC6H4), 2.84
(s, 6H, N(CH3)2), 2.11 (s, 9H, H3CC6H4) ppm. 13C NMR
139.1 (ipso-
d
H3CC6H4), 135.5 (o-H3CC6H4), 129.4 (p-H3CC6H5), 129.4 (m-
H3CC6H4), 41.7 (N(CH3)2), 21.4 (p-H3CC6H4) ppm. Anal. Calcd. for
C23H27GeN: C, 70.80; H, 6.98. Found: C, 71.21; H, 7.08.
4.4. Synthesis of Tol2GeBr2 [82] and Tol2GeH2 [83]
To a solution of GeBr4 (5.00 g,12.7 mmol) at 0 ꢁC in ether (70 mL)
was added a solution of TolMgBr in THF (1.0 M, 25.5 mL) dropwise
via syringe. The resulting reaction mixture was refluxed for 3 h, was
allowed to cool, and was carefully poured over a 0.1 M aqueous HBr
solution. The aqueous layer was separated and extracted with ether
(3 ꢄ 25 mL). The organic layer and the combined ether extracts
were dried over anhydrous MgSO4. The volatiles were removed in
vacuo after filtration to yield a viscous liquid. The crude reaction
mixture (1.852 g) in ether (30 mL) was treated with a suspension of
LiAlH4 (0.340 g, 8.94 mmol) in ether (30 mL) at 0 ꢁC. The reaction
mixture was subsequently refluxed for 3 h and then was quenched
with 1 M aqueous HCl at ꢀ78 ꢁC. The temperature was raised to
25 ꢁC and the reaction mixture was stirred for 30 min. The solution
was cooled to ꢀ78 ꢁC and the ether layer was cannulated into
a separate flask. The remaining aqueous layer was extracted with
ether (2 ꢄ 15 mL) and the combined ether solutions were dried over
anhydrous MgSO4. The volatiles were removed in vacuo to yield
a colorless liquid that was distilled in vacuo (65 ꢁC, 0.10 torr) to yield
4. Experimental section
4.1. General considerations
All manipulations were performed under an atmosphere of
nitrogen using standard Schlenk, syringe, and glovebox techniques
[81]. The reagents p-CH3C6H4Cl, elemental Mg, TolMgBr (1.0 M
solution in THF), Ph3GeH, LiNMe2, trichloroacetic acid, and LiAlH4
were purchased from Aldrich. The compounds GeBr4, GeCl4, and
Ge2Ph6 were purchased from Gelest, Inc. Solvents were purified
using a Glass Contour Solvent Purification System. NMR spectra
were recorded in C6D6 at room temperature using a Varian Gemini
2000 spectrometer operating at 300 MHz (1H) or 75.5 MHz (13C)
and were referenced to the C6D6 solvent. Cyclic voltammograms
were obtained using a Bioanalytical Systems Epsilon Electro-
chemical Workstation with a glassy-carbon working electrode,
a platinum wire counter electrode, and an Ag/AgCl reference elec-
trode using 1.0 M [Bu4N][PF6] as the supporting electrolyte. UV/
visible spectra were obtained using a HewlettePackard Agilent UV/
visible spectroscopy system. IR spectra were recorded using
a HewlettePackard Infrared Spectrometer. Elemental analyses
were obtained by Midwest Microlabs or Galbraith Laboratories.
Tol2GeH2 (0.250 g, 8% based on GeBr4). 1H NMR
4H, o-H3CC6H4), 6.99 (d, J ¼ 7.5 Hz, 4H, m-H3CC6H4), 5.22 (s, 2H,
GeH), 2.07 (s, 6H, H3CC6H4) ppm. 13C NMR
139.8 (ipso-H3CC6H4),
d
7.43 (d, J ¼ 7.5 Hz,
d
136.5 (o-H3CC6H4), 131.7 (p-H3CC6H4), 130.6 (m-H3CC6H4), 22.4 (p-
H3CC6H4) ppm. Anal. Calcd. for C14H16Ge: C, 65.43; H, 6.28. Found:
C, 65.22; H, 6.37.
4.2. Synthesis of Tol3GeCl
4.5. Synthesis of Tol3GeGePh3 (1)
A flame-dried 3-necked flask equipped with a reflux condenser
was charged with magnesium metal (4.30 g, 177 mmol). A solution
of p-CH3C6H4Cl (14.92 g, 117.9 mmol) in THF (100 mL) was placed in
a dropping funnel. The magnesium metal was coated with approx.
15 mL of the p-CH3C6H4Cl solution and a crystal of iodine was
added to the flask. The mixture was gently heated with a heat gun
until the iodine color had faded, and the remaining p-CH3C6H4Cl
solution was added dropwise over 45 min. The resulting reaction
To a solution of Ph3GeH (0.380 g, 1.25 mmol) in CH3CN (10 mL)
was added a solution of Tol3GeNMe2 (0.484 g, 1.24 mmol) in CH3CN
(10 mL). The reaction mixture was sealed in a Schlenk tube and
stirred for 48 h at 90 ꢁC. The volatiles were removed in vacuo to
yield an off-white solid. Distillation in a Kugelrohr oven (125 ꢁC,
0.050 torr) to remove excess Ph3GeH yielded a white solid that was
recrystallized from a hot benzene (5 mL) solution to yield 1 as

1822
M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
colorless crystals (0.684 g, 85%). 1H NMR
d
7.68e7.64 (m, 9H, m-
(0.382 g, 54%) as needle-shaped colorless crystals. 1H NMR
7.77e7.73 (m, 8H, o-C6H5), 7.03e7.01 (m, 12H, m-C6H5 and p-C6H5)
ppm. 13C NMR
136.0 (ipso-C6H5), 134.1 (o-C6H5), 130.8 (p-C6H5),
C6H5 and p-C6H5), 7.57 (d, J ¼ 7.5 Hz, 6H, o-H3CC6H4), 7.10 (m, 6H, o-
d
C6H5), 6.93 (d, J ¼ 7.5 Hz, 6H, m-H3CC6H4), 2.02 (s, 9H, H3CC6H4)
d
ppm. 13C NMR
d
138.8 (ipso-H3CC6H4), 136.2 (o-H3CC6H4), 136.0 (o-
129.1 (m-C6H5) ppm.
C6H5), 133.6 (ipso-C6H5), 129.7 (p-C6H5), 129.2 (p-H3CC6H4), 128.8
(m-H3CC6H4), 127.7 (m-C6H5), 21.4 (p-H3CC6H4) ppm. Anal. Calcd.
for C51H48Ge2 (1$2C6H6): C, 75.96; H, 6.00. Found: C, 75.81; H, 6.11.
4.10. Synthesis of HPh2GeGePh2H (10)
To a solution of 8 (0.110 g, 0.209 mmol) in THF (10 mL) was
added a suspension of LiAlH4 (0.016 g, 0.416 mmol) in THF (10 mL).
The resulting mixture was stirred for 18 h under N2. The solvent
was removed in vacuo yielding a white solid that was washed with
benzene (2 ꢄ 3 mL). The product was dried in vacuo to yield 10
4.6. Synthesis of Tol3GeGePh2GeTol3 (2)
To a solution of Ph2GeH2 (0.100 g, 0.437 mmol) in acetonitrile
(10 mL) in a Schlenk tube was added a solution of Tol3GeNMe2
(0.340 g, 0.874 mmol) in acetonitrile (10 mL). The tube was sealed
and the reaction mixture was stirred in an oil bath at 90 ꢁC for 48 h.
The volatiles were removed in vacuo to yield a white solid that was
distilled in a Kugelrohr oven (125 ꢁC, 0.05 torr). The material
remaining in the distillation flask was recrystallized from hot
toluene to yield 2 (0.283 g, 71%) as colorless crystals. 1H NMR
(0.075 g, 79%) as a white solid. 1H NMR
d 7.54e7.50 (m, 8H, o-C6H5),
7.08e7.04 (m, 12H, m-C6H5 and p-C6H5), 5.58 (s, 2H, GeH) ppm. 13
NMR 136.0 (ipso-C6H5), 135.7 (o-C6H5), 129.1 (p-C6H5), 128.7 (m-
C6H5) ppm. IR (Nujol mull): 2033 cmꢀ1
C
d
.
d
7.78e7.74 (m, 6H, m-C6H5 and p-C6H5), 7.46 (d, J ¼ 7.5 Hz, 12H, o-
H3CC6H4), 7.05e7.03 (m, 4H, o-C6H5), 6.91 (d, J ¼ 7.5 Hz, 12H, m-
H3CC6H4), 2.07 (s, 18H, H3CC6H4) ppm. 13C NMR
139.1 (ipso-
4.11. Synthesis of Tol3GeGePh2GePh2GeTol3 (11)
d
To a solution of 10 (0.075 g, 0.165 mmol) in acetonitrile (5 mL) in
a Schlenk tube was added a solution of Tol3GeNMe2 (0.128 g,
0.330 mmol) in CH3CN (5 mL). The tube was sealed and the reaction
mixture was stirred in an oil bath at 90 ꢁC for 48 h. The volatiles
were removed in vacuo to yield a pale yellow solid that was
recrystallized from a hot benzene/hexane mixture (1:1, 10 mL) to
H3CC6H4), 137.0 (o-H3CC6H4), 136.2 (o-C6H5), 134.9 (ipso-C6H5),
129.4 (p-C6H5), 128.6 (p-H3CC6H4), 128.3 (m-H3CC6H4), 127.9 (m-
C6H5), 21.3 (p-H3CC6H4) ppm. Anal. Calcd. for C61H60Ge3 (2$C7H8):
C, 72.45; H, 5.98. Found: C, 72.39; H, 6.01.
yield 11 (0.150 g, 80%) as colorless crystals. 1H NMR
d 7.55 (d,
4.7. Synthesis of Tol3GeGeTol2GeTol3 (3)
J ¼ 7.5 Hz, 12H, o-C6H4CH3), 7.31 (d, J ¼ 7.2 Hz, 8H, o-C6H5), 7.11 (t,
J ¼ 7.2 Hz, 4H, p-C6H5), 6.97 (t, J ¼ 7.2 Hz, 8H, m-C6H5), 6.85 (d,
J ¼ 7.5 Hz, 12H, m-C6H4CH3), 2.02 (s, 18H, C6H4CH3) ppm. 13C NMR
To a solution of Tol2GeH2 (0.175 g, 0.681 mmol) in acetonitrile
(10 mL) in a Schlenk tube was added a solution of Tol3GeNMe2
(0.531 g, 1.36 mmol) in acetonitrile (10 mL). The tube was sealed
and the reaction mixture was stirred in an oil bath at 90 ꢁC for 48 h.
The volatiles were removed in vacuo to yield a pale yellow solid that
was recrystallized from a hot benzene/hexane mixture (1:1, 10 mL)
d
138.4 (ipso-H3CC6H4), 137.2 (o-C6H5), 136.2 (o-CH3C6H4), 135.1
(ipso-C6H5), 129.5 (p-C6H5), 129.4 (p-H3CC6H4), 128.4 (m-H3CC6H4),
127.9 (m-C6H5), 21.3 (p-H3CC6H4) ppm. Anal. Calcd. for C80H78Ge4
(7$2C7H8): C, 72.23; H, 5.91. Found: C, 72.38; H, 6.05.
to yield 3 (0.458 g, 71%) as colorless crystals. 1H NMR
d 7.69 (d,
J ¼ 7.8 Hz, 4H, o-Ge(C6H4CH3)2), 7.49 (d, J ¼ 7.8 Hz, 12H, o-Ge
(C6H4CH3)3), 6.93 (d, J ¼ 7.8 Hz, 12H, m-Ge(C6H4CH3)3), 6.87 (d,
J ¼ 7.8 Hz, 4H, m-Ge(C6H4CH3)2), 2.09 (s, 18H, Ge(C6H4CH3)3), 1.99
4.12. X-ray crystal structure of compounds 1e3 and 11
(s, 6H, Ge(C6H4CH3)2) ppm. 13C NMR
d 138.3 (ipso-Ge(C6H4CH3)3),
Diffraction intensity data were collected with a Siemens P4/CCD
diffractometer. Crystallographic data and details are shown in Table
7. Absorption corrections were applied for all data using SADABS.
The structures were solved using direct methods, completed by
difference Fourier syntheses, and refined on full-matrix least-
squares procedures on F2. All ordered non-hydrogen atoms were
refined with anisotroptic displacement coefficients and hydrogen
atoms were treated as idealized contributions. Solvent molecules
were removed using SQUEEZE for compounds 2 and 3. All software
and sources of scattering factors are contained in the SHEXTL (5.10)
program package (G. Sheldrick, Bruker XRD, Madison, WI). ORTEP
diagrams were drawn using the ORTEP3 program (L.J. Farrugia,
Glasgow).
138.2 (ipso-Ge(C6H4CH3)2), 137.0 (o-Ge(C6H4CH3)2), 136.4 (o-Ge
(C6H4CH3)3),135.4 (p-Ge(C6H4CH3)2),135.2 (p-Ge(C6H4CH3)3),129.4
(m-Ge(C6H4CH3)3), 129.3 (m-Ge(C6H4CH3)2), 21.4 (Ge(C6H4CH3)3),
21.3 (Ge(C6H4CH3)2) ppm. Anal. Calcd. for C56H56Ge3 (3): C, 71.01;
H, 5.96. Found: C, 70.91; H, 5.96.
4.8. Synthesis of Cl3(O)COPh2GeGePh2OC(O)CCl3 (5) [51]
To a solution of Ph3GeGePh3 (2.000 g, 3.392 mmol) in toluene
(3.6 mL) was added a solution of Cl3CC(O)OH (2.34 g, 14.32 mmol)
in toluene (3.0 mL). The reaction mixture sealed in a Schlenk tube
and was heated at 110 ꢁC for 72 h in an oil bath. The resulting
solution was cooled to room temperature and layered with hexane
to yield a white precipitate which was filtered and washed with
a mixture of hexane and toluene (1:1) to yield 5 (2.006 g, 76%) as
Acknowledgment
a white solid. IR (Nujol mull): 1644.8 cmꢀ1
(nco).
Funding for this work by a CAREER award from the National
Science Foundation (Grant CHE-0844758) is gratefully
acknowledged.
4.9. Synthesis of ClPh2GeGePh2Cl (8) [51]
To a solution of 5 (1.050 g, 1.349 mmol) in acetone (8.75 mL) was
added 3 ml of concentrated hydrochloric acid. The reaction mixture
was stirred under N2 at 50 ꢁC for 18 h in an oil bath. The resulting
dark red solution was cooled to ꢀ28 ꢁC using a dry ice/ortho-xylene
mixture to yield ochre-colored crystals which were washed with
a mixture of hexane and acetone (1:1). Recrystallization of the
crude product with a mixture of E2O and hexane (2:1) yielded 8
Appendix A. Supplementary material
CCDC 763304 (1), 763305 (2), 763306 (3), 763308 (11) contain
supplementary crystallographic data. These data can be obtained
free of charge from the Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.

M.L. Amadoruge et al. / Journal of Organometallic Chemistry 695 (2010) 1813e1823
1823
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