73Ge NMR spectral investigations of singly bonded oligogermanes

Article abstract of DOI:10.1021/om900035r

The synthesis of the two digermanes Bu₃^sGeGePh ₃ and PhMe₂GeGePh₃, as well as the branched tetragermane PhGe(GeBu₃ⁿ)₃, was achieved using the hydrogermolysis reaction.

Full text of DOI:10.1021/om900035r

Organometallics 2009, 28, 3067–3073
3067
73Ge NMR Spectral Investigations of Singly Bonded Oligogermanes
Monika L. Amadoruge,§ Claude H. Yoder,† Julia Hope Conneywerdy,‡ Katie Heroux,
Arnold L. Rheingold, and Charles S. Weinert*,§
Department of Chemistry, Oklahoma State UniVersity, Stillwater, Oklahoma 74078, Department of
Chemistry, Franklin and Marshall College, Lancaster, PennsylVania 17604-3003, Department of Chemistry
and Biochemistry, UniVersity of California, San Diego, La Jolla, California 92093-0332, and Frontier
High School, Red Rock, Oklahoma 74651
ReceiVed January 15, 2009
The synthesis of the two digermanes Bus3GeGePh3 and PhMe2GeGePh3, as well as the branched
tetragermane PhGe(GeBun ) , was achieved using the hydrogermolysis reaction. These species were fully
3 3
characterized by NMR (1H, 13C) spectroscopy and elemental analysis, and the crystal structure of
PhMe2GeGePh3 was determined. These three species, along with 11 other oligogermanes, were also
characterized by 73Ge NMR spectroscopy. Chemical shifts of the 73Ge NMR resonances for these
oligogermanes have been correlated with the substitution pattern at germanium and also with the number
of germanium-germanium bonds at the individual Ge centers. Germanium centers having only one
attached germanium atom result in resonances appearing in the range δ -30 to -65 ppm, while those
having two or three bonded germanium atoms exhibit resonances in the respective ranges δ -100 to
-120 and δ -195 to -210 ppm. Chemical shifts of resonances for germanium centers bearing phenyl
substituents appear upfield from those having alkyl substituents.
data for numerous nonsymmetric compounds. These include the
Introduction
8
vinyl and alkynyl species MexGe(CHdCH2)4-x and MexGe-
The acquisition of meaningful 73Ge NMR data has, until
recently, only been accomplished with difficulty due to a variety
of factors. The highly oblate charge distribution at the 73Ge
nucleus is indicated by its large quadruple moment (q ) -0.2
× 10-28 m2), which typically results in the appearance of broad
resonances upon interaction of the quadruple moment with the
electric field gradient at the nucleus. The line broadening can
be extreme, except in compounds where the germanium atom
is symmetrically substituted, such as GeR4 (R ) Me, Et, Prn,
Bun, OMe),1 GePh4,2 and GeX4 (X ) Cl, Br, I).3 The resonance
frequency at a magnetic field strength of 2.3488 T (1H ) 100
MHz) is 3.488 MHz, and therefore a dedicated low-frequency
probe is required for observation of the 73Ge nucleus. An
additional complication involves acoustic ringing, which arises
from transient responses in the probe resulting from the radio
frequency pulse; however, several pulse sequences have been
developed to suppress this problem.4-7
(Ct CH)4-x,9 the heteroaromatic germanes RxGeMe4-x (R )
2-furyl, 2-thienyl, 4,5-dihydro-2-furyl),10 various Ge-substituted
germacyclohexanes,11 several hypervalent germanium com-
15-17
pounds,12-14 and a number of arylgermanes ArxGeH4-x
.
The 1J(Ge-H) coupling constants for several of these ArxGeH4-x
compounds have recently been determined, including those for
(p-MeOC6H4)GeH3 (97 Hz), (p-H3CC6H4)GeH3 (96 Hz), Mes-
GeH3 (95 Hz), PhGeH3 (98 Hz), Ph2GeH2 (94 Hz), and Ph3GeH
(98 Hz).17 These Ge-H coupling constants are similar to that
observed for GeH4 (97.6 Hz).5 In 1999, the first 73Ge NMR
data for compounds containing Ge-Ge bonds was reported.18
Resonances for Me3GeGeMe3, Ph3GeGePh3, and (Ph3Ge)3GeH
were observed at δ -59, -67, and -314 ppm, where the latter
peak corresponds to the central germanium atom of (Ph3Ge)3-
GeH. A resonance corresponding to the Ph3Ge- atoms was not
observed.
The advent of high-field instruments and advanced software
technology has recently allowed the acquisition of 73Ge NMR
(8) Takeuchi, Y.; Inagaki, H.; Tanaka, K.; Yoshimura, S. Magn. Reson.
Chem. 1989, 27, 72–74.
(9) Liepins, E.; Petrova, M. V.; Bogoradovsky, E. T.; Zavgorodny, V. S.
J. Organomet. Chem. 1991, 410, 287–291.
(10) Liepins, E.; Zicmane, I.; Ignatovich, L. M.; Lukevics, E. J.
Organomet. Chem. 1991, 389, 23–28.
* To whom correspondence should be addressed. E-mail: weinert@
chem.okstate.edu.
§ Oklahoma State University.
† Franklin and Marshall College.
(11) Takeuchi, Y.; Shimoda, M.; Tanaka, K.; Tomoda, S.; Ogawa, K.;
Suzuki, H. J. Chem. Soc., Perkin Trans. 2 1988, 7–13.
(12) Kupce, E.; Ignatovich, L. M.; Lukevics, E. J. Organomet. Chem.
1989, 372, 189–191.
(13) Kupce, E.; Lukevics, E. J. Magn. Reson. 1988, 79, 325–327.
(14) Yoder, C. H.; Agee, T. M.; Schaeffer, C. D.; Carroll, M. J.; Fleisher,
A. J.; DeToma, A. S. Inorg. Chem. 2008, 47, 10765–10770.
(15) Takeuchi, Y.; Yamamoto, H.; Tanaka, K.; Ogawa, K.; Harada, J.;
Iwamoto, T.; Yuge, H. Tetrahedron 1998, 54, 9811–9822.
(16) Takeuchi, Y.; Tanaka, K.; Aoyagi, S.; Yamamoto, H. Magn. Reson.
Chem. 2002, 40, 241–243.
University of California, San Diego.
‡ Frontier High School.
(1) Kaufmann, J.; Sahm, W.; Schwenk, A. Z. Naturforsch. A 1971, 26A,
1384–1389.
(2) Takeuchi, Y.; Harazono, T.; Kakimoto, N. Inorg. Chem. 1984, 23,
3835–3836.
(3) Kidd, R. G.; Spinney, H. G. J. Am. Chem. Soc. 1973, 95, 88–90.
(4) Belton, P. S.; Cox, I. J.; Harris, R. K. J. Chem. Soc., Faraday Trans.
1985, 81, 63–75.
(5) Mackay, K. M.; Watkinson, P. J.; Wilkins, A. L. J. Chem. Soc.,
Dalton Trans. 1984, 133–139.
(6) Patt, S. L. J. Magn. Reson. 1982, 49, 161–163.
(7) Wilkins, A. L.; Thomson, R. A.; Mackay, K. M. Main Group Met.
Chem. 1990, 13, 219–236.
(17) Riedmiller, F.; Wegner, G. L.; Jockisch, A.; Schmidbaur, H.
Organometallics 1999, 18, 4317–4324.
(18) Thomson, R. A.; Wilkins, A. L.; Mackay, K. M. Phosphorus, Sulfur,
Silicon 1999, 150-151, 319–324.
10.1021/om900035r CCC: $40.75
2009 American Chemical Society
Publication on Web 04/20/2009

3068 Organometallics, Vol. 28, No. 10, 2009
Amadoruge et al.
Scheme 1
We have recently synthesized and characterized a variety of
linear and branched oligogermanes containing Ge-Ge single
bonds via the hydrogermolysis reaction, either alone or coupled
with a germanium hydride protection/deprotection strategy.19-24
We have now characterized a number of these species by 73Ge
NMR spectroscopy, including the digermanes R3GeGePh3 (R3
9.6 Hz). The 13C NMR spectrum of Bus3GeCl in benzene-d6
recorded at 100.6 MHz exhibits only eight resolved resonances
(Vide infra) instead of the predicted 32 peaks since several of
these features overlap (as expected) due to their nearly identical
magnetic environments.
Treatment of Bus3GeCl with LiNMe2 yielded the amide
) Bun3 (1), Bus3 (2), Et3 (3), Pri3 (4), PhMe2 (5), Bun CH2CH2-
Bus3GeNMe2 in 78% yield (Scheme 1). As found for Bus3GeCl,
2
OEt (6)), the trigermanes Ph3GeGeBun GeR2CH2CH2OEt (R )
1
2
three of the four resonances for the sec-butyl groups in the H
Bun (7) or Ph (8)) and EtOCH2CH2R2GeGePh2GeR2CH2CH2OEt
(R ) Bun (9) or Ph (10)), and the branched species Ph-
Ge(GePh3)3 (11), PhGe(GeBun ) (12), PhGe(GeBun CH2CH2-
NMR spectrum of Bus3GeNMe2 appear as multiplets centered
at δ 1.73, 1.34, and 1.12 ppm, while the peak for the γ-methyl
group is a broad triplet at δ 0.89 ppm (J ) 7.2 Hz). Three
separate resonances for the -N(CH3)2 protons of the amide
groups were visible at δ 2.67, 2.66, and 2.65 ppm in an intensity
ratio of 1:1.3:3, and the expected eight individual peaks could
not be resolved at a spectrometer frequency of 600 MHz. The
alkyl region of the 13C NMR spectrum of Bus3GeNMe2
resembles that of Bus3GeCl, having eight resolved peaks, while
two broad features at δ 42.4 and 42.1 ppm correspond to the
carbon atoms of the -N(CH3)2 groups.
3 3
2
OEt)3 (13), and PhGe(GeBun GeBun CH2CH2OEt)3 (14). The
2
2
compounds Bus3GeGePh3 (2), PhMe2GeGePh3 (5), and Ph-
Ge(GeBun ) (12) were newly synthesized for these investiga-
3 3
tions, and the X-ray crystal structure of compound 5 was
obtained.
Results and Discussion
The digermanes Bus3GeGePh3 (2) and PhMe2GeGePh3 (5)
The hydrogermolysis reaction of Bus3GeNMe2 with Ph3GeH
in CH3CN yielded the digermane Bus3GeGePh3 in 81% yield
via the in situ conversion of Bus3GeNMe2 to the R-germyl nitrile
Bus3GeCH2CN (Scheme 1).19-24 In contrast with most diger-
manes of the general formula R3GeGePh3, compound 2 is a
highly viscous oil at room temperature instead of a solid, which
can be attributed to the presence of multiple diastereomers of 2
due to the chiral nature of the three sec-butyl groups. The
aromatic region of the 1H NMR spectrum of 2 is similar to that
for other digermanes R3GeGePh3, with a triplet and a doublet
at δ 7.68 (J ) 7.2 Hz, p-H) and 7.63 (J ) 7.2 Hz, o-H) ppm
(respectively), and a multiplet centered at δ 7.11 ppm (m-H).
The alkyl region is again complex, with three multiplets centered
at δ 1.75, 1.41, and 1.08 ppm and a broad triplet at δ 0.77 (J
) 7.6 Hz) ppm, and the corresponding region in the 13C NMR
region of 2 exhibits six clearly resolved resonances at δ 28.8,
and the branched tetragermane PhGe(GeBun ) (12) were
3 3
prepared via the hydrogermolysis reaction as shown in Scheme
1. The triakylchlorogermane precursor Bus3GeCl for the diger-
mane 2 was synthesized from GeCl4 and BusMgCl, which
resulted in the formation of a mixture of products BusnGeCl4-n
as well as a polymeric material. Analytically pure Bus3GeCl
was separated from the crude reaction mixture in 27% yield
via fractional distillation at 47 °C (0.25 Torr), which is consistent
with the previously reported boiling point of 93 °C (3 Torr).25
The 1H NMR of Bus3GeCl in benzene-d6 is complex since each
of the three R-carbon atoms of the sec-butyl groups is chiral,
resulting in eight possible diastereomers of this species.
Resonances for the protons of the R-carbon, the methylene
group, and the ꢀ-methyl group appear as multiplets centered at
δ 1.71, 1.35, and 1.11 ppm (respectively), while that for the
γ-methyl group appears as a broad triplet at δ 0.89 ppm (J )
28.6, 26.8, 14.5, 14.4, and 13.8 ppm.
19
The amides PhMe2GeNMe2 and Bun GeNMe2 were pre-
(19) Subashi, E.; Rheingold, A. L.; Weinert, C. S. Organometallics 2006,
25, 3211–3219.
(20) Amadoruge, M. L.; DiPasquale, A. G.; Rheingold, A. L.; Weinert,
C. S. J. Organomet. Chem. 2008, 693, 1771–1778.
(21) Amadoruge, M. L.; Gardinier, J. R.; Weinert, C. S. Organometallics
2008, 27, 3753–3760.
(22) Amadoruge, M. L.; Golen, J. A.; Rheingold, A. L.; Weinert, C. S.
Organometallics 2008, 27, 1979–1984.
(23) Amadoruge, M. L.; Weinert, C. S. Chem. ReV. 2008, 108, 4253–
4294.
(24) Weinert, C. S. Dalton Trans. 2008, Advance Articles, DOI: 10.1039/
b816067h.
(25) Yarosh, O. G.; Voronkov, M. G.; Zhilitskaya, L. V.; Yarosh, N. O.;
Albanov, A. I.; Korotaeva, I. M. Russ. J. Gen. Chem. 2005, 75, 714–718.
3
pared from the corresponding commercially available germa-
nium chlorides and were used for the synthesis of the digermane
5 and the branched tetragermane 12 in yields of 76% and 98%,
respectively (Scheme 1). The branched species 12 is a viscous
colorless oil at room temperature, while 5 is a colorless solid.
The UV/visible spectrum of 12 exhibits an absorption maximum
at 233 nm, which is higher in energy than that of the phenyl-
substituted species (Ph3Ge)3GePh (11), which was observed at
256 nm.22 As shown for linear oligogermanes, the presence of
phenyl versus alkyl substituents stabilizes both the HOMO and

73Ge NMR Spectral InVestigations of Oligogermanes
Organometallics, Vol. 28, No. 10, 2009 3069
Table 2. Previously Determined 73Ge NMR Chemical Shift Data
compound
δ
73Ge (ppm)b
ref
Ge2H6
Ge2D6
Ge3H8
-311.8 (95.5)
-318.0
-298 (94), -310 (90)
-284, -300
-306.2 (90.0)
-209
28
18
28
28
28
28
28
18
28
28
18
30
18
18
18
18
Ge4H10
MeH2GeGeH3
Me2HGeGeMe2H
Me2HGeGeH3
Me2ClGeGeH3
Me3GeGeH3
(MeH2Ge)2GeMeH
Me3GeGeMe3
Et3GeGeEt3
Ph3GeGePh3
(Ph3Ge)3GeH
H3GeGeH2Mn(CO)5
H3GeGeMeHMn(CO)5
-127, -296 (85)
-280.5
-47.7, -295.6 (90.7)
-125, -206.2
-59
-34.7
-67
-314
-291.8
-277.9
a Chemical shifts are relative to GeMe4. b Experimental 1J(Ge-H)
coupling constants are given in parentheses.
amount of information has been accumulated in the last several
years, including chemical shifts, coupling constants, and relax-
ation times for various compounds that do not have a symmetric
environment about the germanium atom. In contrast to simple
germanes, 73Ge NMR data for compounds containing Ge-Ge
single bonds are relatively scarce. Chemical shift data for 16
different compounds is collected in Table 2, and some trends
in these values can be identified. Resonances for germanium
atoms bearing hydride substituents appear upfield relative to
those having methyl or ethyl substituents, while the signal for
the two equivalent germanium atoms of Ph3GeGePh3 (δ -67
ppm) appears upfield from that of Me3GeGeMe3 (δ -59 ppm).
Peaks for some of the germanium atoms in the tabulated
compounds were not observed, as found for the branched
germanium hydride (Ph3Ge)3GeH, which exhibits a peak for
the central germanium atom at δ -314 ppm.18 No resonance
was observed for the germanium atoms of the peripheral
Ph3Ge- groups.
Figure 1. ORTEP plot of PhMe2GeGePh3 (5). Thermal ellipsoids
are drawn at 50% probability.
Table 1. Selected Bond Distances (Å) and Bond Angles (deg) for
PhMe2GeGePh3 (5)
Ge(1)-Ge(2)
2.4216(4)
1.965(4)
1.953(3)
1.955(4)
1.959(3)
1.955(4)
1.951(4)
109.5(2)
109.7(1)
106.9(2)
C(19)-Ge(2)-C(25)
C(19)-Ge(2)-C(26)
C(25)-Ge(2)-C(26)
C(1)-Ge(1)-Ge(2)
C(7)-Ge(1)-Ge(2)
C(13)-Ge(1)-Ge(2)
C(19)-Ge(2)-Ge(1)
C(25)-Ge(2)-Ge(1)
C(26)-Ge(2)-Ge(1)
107.6(2)
111.3(2)
108.6(2)
106.7(1)
111.5(9)
112.3(1)
107.1(2)
109.0(1)
113.2(1)
Ge(1)-C(1)
Ge(1)-C(7)
Ge(1)-C(13)
Ge(2)-C(19)
Ge(2)-C(25)
Ge(2)-C(26)
C(1)-Ge(1)-C(7)
C(1)-Ge(1)-C(13)
C(7)-Ge(1)-C(13)
the LUMO, resulting in a lower energy for the σ f σ* electronic
transition.21 Therefore, the λmax for 12 is expected to be blue-
shifted relative to that for 11.
We have obtained 73Ge NMR data for several linear and
branched oligogermanes that we have prepared via the hydrog-
ermolysis reaction. The structures of these species are shown
in Scheme 2, and chemical shifts and half-height linewidths for
these compounds are collected in Table 3. An acquisition time
of 0.01 s, zero-filling, and a line broadening of 20 were used
for all spectra, except for the digermane Bus3GeGePh3 (2), where
an acquisition time of 0.1 s was employed. The lines are broad,
as expected, and this is in part a result of the short acquisition
time. The chemical shifts reported in Table 3 have an associated
error of (3 ppm. Spectra for several samples were run using
longer acquisition times, but this did not allow for the acquisition
of a sufficient number of scans to obtain a reasonable signal-
to-noise ratio. No correction was applied in cases where the
resonances overlap, but the chemical shift data obtained in
spectra where overlapping resonances occur were run several
different times and the data were consistently reproducible.
From the chemical shifts observed for the digermanes 1-6, it
is apparent that triakyl-substituted germanium atoms resonate at
lower field than triphenyl-substituted germanium atoms, and these
findings are consistent with the results of previous 73Ge NMR
spectral investigations of simple alkyl- and aryl-germanes.1,2,5,27-31
The 73Ge NMR spectra obtained for the digermanes 1-3 are shown
in Figure 2. The single 73Ge NMR resonance observed for
compound 2 at δ -52 ppm corresponds to the sec-butyl-
substituted germanium atom, while the single features present
in the 73Ge NMR spectra of 3 at δ -64 ppm correspond to the
triphenyl-substituted germanium atom. Compound 1 exhibits a
Crystals of 5 suitable for X-ray analysis were obtained from
a hot benzene solution, and an ORTEP diagram of 5 is shown
in Figure 1, while selected bond distances and angles are
collected in Table 1. The Ge-Ge bond distance in 5 is 2.4216(4)
Å, which is slightly longer than those in the related compounds
Me3GeGePh3 (2.418(1) Å)26 and Bun GeGePh3 (1) (2.4208(8)
3
Å, average of two independent molecules),19 but shorter than
the Ge-Ge bond distance in Et3GeGePh3 (3) (2.4253(7) Å).19
The ethyl and phenyl substituents in 3 are eclipsed, resulting
in the longer Ge-Ge distance, while the substituents at each of
the germanium atoms in 5, Me3GeGePh3, and 1 are arranged in
a gauche conformation. The presence of a phenyl substituent
at Ge(2) in 5, versus three methyl groups in Me3GeGePh3 or
three n-butyl groups that are attached to germanium via a
methylene group in 1, results in the slightly elongated Ge-Ge
distance in 5. Two of the C-Ge-C bond angles at Ge(1) very
closely match the ideal angle of 109.5°, while the third is slightly
more acute. The C-Ge-C bond angles at Ge(2) are more highly
distorted from the ideal tetrahedral geometry, although the
average bond angle is 109.2°. These distortions result from the
steric interaction of the single phenyl substituent at Ge(2) with
the three phenyl groups attached to Ge(1).
Although observation of the 73Ge nucleus by NMR spectros-
copy is challenging for the reasons described above, a significant
(26) Pa´rka´nyi, L.; Ka´lma´n, A.; Sharma, S.; Nolen, D. M.; Pannell, K. H.
Inorg. Chem. 1994, 33, 180–182.

3070 Organometallics, Vol. 28, No. 10, 2009
Amadoruge et al.
Scheme 2
Table 3. 73Ge NMR Dataa for Various Oligogermanes (L )
has been demonstrated that there is not a linear correlation
between inductive effects and 73Ge NMR chemical shift
values.28-30 For example, the tetraalkyl germanes GeR4 exhibit
chemical shifts of δ 0.0 (R ) Me), 17.8 (R ) Et), 2.4 (R )
Prn), and 6.0 (R ) Bun) ppm.1 However, among the digermanes
1-4, the observed chemical shift values exhibit a consistent
upfield shift as the calculated inductive (σI) and polar (σ*)
substituent constants32 of the alkyl groups become more
negative, and the relationship between δ(73Ge) for the R3Ge-
groups and each of these constants is nearly linear (Figure 3).
Germanium-73 NMR spectra for the two linear compounds
Ph3GeGeBun CH2CH2OEt (6) and Ph3GeGeBun GePh2CH2CH2-
CH2CH2OEt)
compound
δ (ppm)
∆ν1/2 (Hz)
assignment
1
-58
-65
-52
-64
-56
-65
-65
-57
-64
-57
-63
-54
-65
-111
-121
-202
-33
-195
-43
-203
-38
-209
100
340
30b
270
80
240
90
90
330
310
310
120
390
180
170
290
100
240
90
Bun GeGePh3
3
Bun GeGePh3
3
2
3
4
Bus3GeGePh3
Et3GeGePh3
Pri3GeGePh3
Pri3GeGePh3
PhMe2GeGePh3
5
6
Ph3GeGeBun L
2
Ph3GeGeBun L
2
7
8
Ph3GeGeBun GeBun L
2
2
2
2
Ph3GeGeBun GeBun L
2
2
OEt (8) and the branched oligomers PhGe(GeBun CH2-
Ph3GeGeBun GePh2L
2
2
CH2OEt)3 (13) and PhGe(GeBun GeBun CH2CH2OEt)3 (14) are
Ph3GeGeBun GePh2L
2
2
2
9
LGeBun GePh2GeBun L
2
2
shown in Figures 4 and 5, respectively. The digermane 6 exhibits
two resonances in its 73Ge NMR spectrum at δ -57 and -64
ppm, where the former resonance corresponds to the alkyl-
substituted germanium atom and the latter corresponds to the
triphenyl-substituted germanium atom. The spectrum of 8
exhibits a resonance for two of the three germanium atoms,
with a feature for the terminal Ph3Ge- atom at δ -65 ppm
and a resonance at δ -54 ppm that corresponds to the
-GePh2CH2CH2OEt atom. This resonance is shifted upfield
relative to triphenyl-substituted germanium atoms due to the
presence of the ethoxyethyl substituent.
10
11
12
LGePh2GePh2GePh2L
PhGe(GePh3)3
PhGe(GeBun )3
3
PhGe(GeBun )3
3
13
14
PhGe(GeBun L)3
2
380
110
320
PhGe(GeBun L)3
2
PhGe(GeBun GeBun L)3
2
2
PhGe(GeBun GeBun L)3
2
2
a Chemical shifts are relative to external GeMe4 by substitution.
Chemical shift values are (3 ppm, and ∆ν1/2 are (10%. No correction
for overlapping peaks was applied. Acquisition time
) 0.01 s.
b Acquisition time ) 0.1 s.
peak for each type of germanium atom, and the resonance for
the tri-n-butyl-substituted germanium atom appears at δ -58
ppm, while that for the triphenyl-substituted germanium atom
appears upfield at δ -65 ppm. The spectrum of the digermane
5 exhibits a single peak for the Ph3Ge- atom at δ -65 ppm,
while that for 4 contains two resonances corresponding to each
type of germanium atom.
(27) Zicmane, I.; Liepins, E.; Lukevics, E.; Gar, T. K. Zh. Obsch. Khim.
1982, 52, 896–899.
(28) Wilkins, A. L.; Watkinson, P. J.; Mackay, K. M. J. Chem. Soc.,
Dalton Trans. 1987, 2365–2372.
(29) Mackay, K. M.; Thomson, R. A. Main Group Met. Chem. 1987,
10, 83–108.
(30) Liepins, E.; Zicmane, I.; Lukevics, E. J. Organomet. Chem. 1988,
341, 315–333.
(31) Takeuchi, Y.; Takayama, T. Annu. Rep. NMR Spectrosc. 2005, 54,
155–200.
(32) Hanson, P. J. Chem. Soc., Perkin Trans. 2 1984, 101–108.
Although chemical shifts observed in 73Ge NMR spectroscopy
are highly sensitive to the substitution pattern at germanium, it

73Ge NMR Spectral InVestigations of Oligogermanes
Organometallics, Vol. 28, No. 10, 2009 3071
Figure 3. Plots of the 73Ge NMR chemical shift (in ppm) of 1-4
versus the calculated inductive substituent constant (top) and polar
substituent constant (bottom).
two germanium atoms. This effect is more evident in the data
collected for the branched oligogermanes 11-14, where the
central germanium atoms in these species are substantially more
shielded due to their being connected to three other germanium
atoms. Resonances for these atoms are shifted upfield and range
from δ -195 to -209 ppm, and a similar chemical shift was
reported for the central germanium atom of (Ph3Ge)3GeH at δ
-314 ppm.18
Figure 2. 73Ge NMR spectra of R3GeGePh3 (R ) Bun (1), Bus (2),
or Et (3)).
The number of germanium-germanium bonds to each
germanium atom can have a pronounced effect on the 73Ge
chemical shift in these compounds. Both of the germanium
atoms in the digermanes 1-6, as well as the terminal germanium
atoms in the higher oligomers 7-14, are bound to only one
other germanium atom. Resonances for these germanium atoms
range from δ -33 ppm in 12 to δ -65 ppm in 8, which compare
with the previously determined values of δ -35, -59, and -67
ppm for the compounds R3GeGePh3 (R ) Et,30 Me,18 Ph,18
respectively). Trends for the resonances corresponding to the
terminal germanium centers in 7-14 are similar to those
observed for the digermanes 1-6, in that phenyl substituents
result in an upfield shift of the observed 73Ge NMR resonances.
The trigermanes 7-10 and the branched species 14 each contain
a germanium atom that is attached to two other germanium
atoms, and for compounds 9 and 10 resonances corresponding
to the central phenyl-substituted germanium atoms were ob-
served at δ -111 and -121 ppm (respectively). Resonances
for the germanium atoms bound to two other germanium centers
in compounds 7, 8, and 14 were not observed. The upfield shift
for these peaks in 9 and 10 versus those observed for germanium
centers bound to only one germanium atom (Vide supra) is a
result of the increased shielding resulting from attachment to
Conclusions
The 73Ge NMR resonances for oligogermanes can be cor-
related with the substitution pattern at germanium and also with
the connectivity of the germanium centers. Germanium centers
bound to only one additional germanium atom give rise to peaks
in the approximate range δ -30 to -65 ppm, while the more
shielded germanium centers which are connected to two or three
additional germanium atoms exhibit resonances in the respective
ranges of δ -100 to -120 and δ -195 to -210 ppm. In all
cases, resonances for alkyl-substituted germanium atoms appear
downfield from their phenyl-substituted analogues, which is
consistent with previous findings for related systems. Due to
the limitation that some substitution patterns do not allow an
observable 73Ge NMR resonance, 73Ge NMR spectroscopy is
not as versatile a technique as that for the corresponding group
14 elements carbon, silicon, tin, and lead. However, these
investigations described here indicate that structural information

3072 Organometallics, Vol. 28, No. 10, 2009
Amadoruge et al.
Figure 4. 73Ge NMR spectra of Ph3GeGeBun CH2CH2OEt (6) and
2
Ph3GeGeBun GePh2CH2CH2OEt (8).
2
Figure 5. 73Ge NMR spectra of PhGe(GeBun CH2CH2OEt)3 (13)
2
and PhGe(GeBun Gen CH2CH2OEt)3 (14).
2
2
can be obtained using this method, and the compilation of a
database of 73Ge NMR spectral data is a worthwhile endeavor.
Table 4. Crystallographic Data for 5
formula
C26H26Ge2
483.65
fw (g mol-1
)
Experimental Section
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
0.07 × 0.07 × 0.02
All manipulations were carried out using standard Schlenk,
syringe, and glovebox techniques.33 The reagents BusMgCl (2.0
M in Et2O solution), LiNMe2, and Ph3GeH were purchased from
Aldrich, while GeCl4 and PhMe2GeCl were purchased from Gelest,
and were used as received. Solvents were purified using a Glass
Contour solvent purification system. 1H (400 MHz) and 13C (100.5
MHz) NMR spectra were recorded on a Varian INOVA 400 MHz
spectrometer and were referenced to the benzene-d6 solvent.
Germanium-73 NMR spectra of the products (50 mg/mL in
benzene-d6) were recorded on a Varian INOVA 500 MHz spec-
trometer using a 10 mm low gamma broadband probe at 17.43 MHz
with the Carr-Purcell-Maiboom-Gill (CPMG) pulse sequence34,35
to reduce baseline roll. The following parameters were used with
proton decoupling during acquisition: spectral width ) 100 000 Hz,
acquisition time ) 0.01 s (except for compound 2), delay time )
0 s, line broadening factor ) 20, number of transients ) 1 × 106
to 1 × 107. This pulse sequence was found to give peak widths
within ca. 5% of those obtained using the standard pulse sequence
up to peak widths of ca. 800 Hz. Based on multiple runs of the
same sample, the error in the chemical shifts is estimated to be (3
ppm. The error in helf-height linewidths is ca. 10%. No correction
was applied to the measurement of overlapping peaks. The spectra
were referenced to external GeMe4 by substitution. Elemental
analyses were obtained from Midwest Microlab, LLC (Indianapolis,
IN).
orthorhombic
Pna2
24.7570(3)
7.7560(5)
11.701(1)
90
90
90
2246.8(3)
Z
4
Fcalc (g cm-3
)
1.430
2.684
984
absorp coeff (mm-1
F(000)
)
θ range (deg)
index ranges
1.65 to 28.20
-30 e h e 31, -10 e k e 10,
-15 e l e 15
29 898
5198 (Rint ) 0.0567)
100.0%
semiempirical from equivalents
0.9483 and 0.8344
full-matrix least-squares on F2
5198/1/255
1.048
100(2)
reflns collected
indep reflns
completeness to θ ) 25.00°
absorp corr
max. and min. transmn
refinement method
data/restraints/params
goodness-of-fit on F2
temperature (K)
radiation
Mo KR
0.71073
0.0332
0.0655
wavelength (Å)
R
Rw
Preparation of Bus3GeCl. A solution of BusMgCl (44.0 mL,
2.0 M in Et2O, 88.0 mmol) was added to a solution of GeCl4 (6.25
g, 29.1 mmol) in Et2O (140 mL) at 0 °C over 30 min. The reaction
largest peak and hole (e Å-3
)
0.952 and -0.324
mixture was stirred at 0 °C for 1 h, and the volatiles were removed
in Vacuo. The resulting material was dissolved in hexane (100 mL)
and treated with 50 mL of 1.0 M HCl. The organic layer was
separated and the aqueous layer was extracted with hexane (3 ×
15 mL). The combined organic layer and extracts were dried over
(33) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air SensitiVe
Compounds, 2nd ed.; John Wiley and Sons: New York, 1986.
(34) Carr, H. Y.; Purcell, E. M. Phys. ReV. 1954, 94, 630–638.
(35) Meiboom, S.; Gill, D. ReV. Sci. Instrum. 1958, 29, 688–691.

73Ge NMR Spectral InVestigations of Oligogermanes
Organometallics, Vol. 28, No. 10, 2009 3073
anhydrous MgSO4 and filtered, and the volatiles were removed in
Vacuo to yield a colorless oil. Vacuum distillation (47 °C, 0.25
a solution of Ph3GeH (0.302 g, 0.990 mmol) in acetonitrile (10
mL). The reaction mixture was stirred at 85 °C for 96 h, and the
volatiles were removed in Vacuo to yield a yellow viscous oil. The
crude product was vacuum distilled (120 °C, 0.05 Torr) to yield 5
1
Torr) yielded Bus3GeCl (2.20 g, 27%) as a colorless oil. H NMR
(C6D6, 25 °C): δ 1.77-1.66 (m, 3H, CH3CHCH2CH3), 1.38 - 1.31
(m, 6H, CH3CHCH2CH3), 1.12-1.07 (m, 9H, CH3CHCH2CH3),
0.89 (t, J ) 9.6 Hz, 9H, CH3CHCH2CH3) ppm. 13C NMR (C6D6,
25 °C): δ 27.00, 26.97, 26.94 (CH3CHCH2CH3), 25.95, 25.32
(CH3CHCH2CH3), 15.01, 14.96 (CH3CHCH2CH3), 13.4 (CH3CH-
CH2CH3) ppm. Anal. Calcd for C12H27ClGe: C, 51.59; H, 9.74.
Found: C, 51.69; H, 9.50.
1
(0.360 g, 76%) as a colorless solid. H NMR (C6D6, 25 °C): δ
7.58-7.55 (m, 6H, m-(C6H5)3), 7.44-7.41 (m, 2H, m-C6H5),
7.17-7.14 (m, 9H, o-(C6H5)3 and p-(C6H5)3), 7.12-7.09 (m, 3H,
o-C6H5 and p-C6H5), 0.64 (s, 6H, -CH3) ppm. 13C NMR (C6D6,
25 °C): δ 135.80 (ipso-C), 134.19 (ipso-C), 129.00 (ortho-C),
128.72 (ortho-C), 128.39 (meta-C), 128.22 (meta-C), 128.76 (para-
C), 128.68 (para-C), 1.94 (-CH3) ppm. Anal. Calcd for C26H26Ge2:
C, 64.57; H, 5.42. Found: C, 64.28; H, 5.64.
Preparation of Bus3GeNMe2. A flask was charged with 0.274
g (0.981 mmol) of Bus3GeCl dissolved in benzene (10 mL). To
this was added LiNMe2 (0.057 g, 1.12 mmol) in benzene (10 mL).
The resulting suspension was stirred 36 h and then filtered through
Celite to yield a clear solution. The volatiles were removed in Vacuo
to yield Bus3GeNMe2 (0.221 g, 78%) as a slightly turbid colorless
oil. 1H NMR (C6D6, 25 °C): δ 2.67, 2.66, 2.65 (s, 6H, -N(CH3)2),
1.78-1.70 (m, 3H, CH3CHCH2CH3), 1.36-1.30 (m, 6H,
CH3CHCH2CH3), 1.16-1.11 (m, 9H, CH3CHCH2CH3), 0.89 (t, J
) 7.2 Hz, 9H, CH3CHCH2CH3) ppm. 13C NMR (C6D6, 25 °C): δ
42.44, 42.11 (-N(CH3)2), 27.03, 26.98 (CH3CHCH2CH3), 25.93
(CH3CHCH2CH3), 15.04, 14.86 (CH3CHCH2CH3), 13.61, 13.44,
13.27 (CH3CHCH2CH3) ppm. Anal. Calcd for C14H33GeN: C, 58.38;
H, 11.55. Found: C, 58.32; H, 11.24.
Preparation of PhMe2GeNMe2. To a solution of PhMe2GeCl
(1.000 g, 4.646 mmol) in Et2O (15 mL) was added a solution of
LiNMe2 (0.249 g, 4.88 mmol) in Et2O (10 mL). The reaction
mixture was stirred for 18 h, and the ether was removed to yield a
yellow oil, which was dissolved in hexane and filtered through
Celite. The volatiles were removed from the filtrate to yield
PhMe2GeNMe2 (0.775 g, 75%) as a colorless oil. 1H NMR (C6D6,
25 °C): δ 7.61 (d, J ) 6.4 Hz, 2H, m-H), 7.37-7.32 (m, 3H, o-H
and p-H), 2.64 (s, 6H, -N(CH3)2), 0.49 (s, 6H, -CH3) ppm. 13C
NMR (C6D6, 25 °C): δ 133.79 (ipso-C), 129.20 (ortho-C), 128.40
(meta-C), 128.08 (para-C), 40.94 (-N(CH3)2), - 4.33 (-CH3) ppm.
Anal. Calcd for C10H17GeN: C, 53.66; H, 7.65. Found: C, 53.36;
H, 7.41.
Synthesis of PhGe(GeBun ) (12). To a solution of Bun GeNMe2
3 3
3
(0.819 g, 2.84 mmol) in acetonitrile (15 mL) was added a solution
of PhGeH3 (0.132 g, 0.864 mmol) in acetonitrile (5 mL). The
reaction mixture was stirred at 85 °C for 72 h, and the volatiles
were removed in Vacuo to yield a colorless oil. The crude product
mixture was vacuum distilled at 140 °C (0.01 Torr) to yield 0.747
1
g (89%) of 12 as a colorless oil. H NMR (C6D6, 25 °C): δ 7.77
(d, 1H, J ) 7.8 Hz, para-H), 7.68 (d, 2H, J ) 7.8 Hz, ortho-H),
7.08 (t, 2H, J ) 7.5 Hz, meta-H), 1.54-1.24 (m, 36H,
-CH2CH2CH2CH3), 1.11-1.06 (m, 18H, -CH2CH2CH2CH3),
0.97-0.82 (m, 27H, -CH2CH2CH2CH3) ppm. 13C NMR (C6D6,
25 °C): δ 136.22 (ipso-C), 128.41 (ortho-C), 128.19 (meta-C),
127.38 (para-C), 28.92 (-CH2CH2CH2CH3), 27.00 (-CH2CH2CH2-
CH3), 15.31 (-CH2CH2CH2CH3), 13.94 (-CH2CH2CH2CH3) ppm.
UV/vis (hexane): λmax 233 nm (ε 1.8 × 195 L mol-1 cm-1). Anal.
Calcd for C42H86Ge4: C, 57.23; H, 9.83. Found: C, 56.77; H, 9.44.
X-ray Crystal Structure of PhMe2GeGePh3 (5). Diffraction
intensity data were collected with a Siemens P4/CCD diffractometer.
Crystallographic data for the X-ray analysis of 5 are collected in
Table 4. Crystal-to-detector distance was 60 mm and exposure time
was 20 s per frame using a scan width of 0.5°. Data collection was
100.0% complete to 25.00° in θ. The data were integrated using
the Bruker SAINT software program and scaled using the SADABS
software program. Solution by direct methods (SIR-2004) produced
a complete heavy-atom phasing model consistent with the proposed
structure. All non-hydrogen atoms were refined anisotropically by
full-matrix least-squares (SHELXL-97). 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.
Preparation of Bus3GeGePh3 (2). To a solution of Bus3GeNMe2
(0.201 g, 0.698 mmol) in acetonitrile (5 mL) was added a solution
of Ph3GeH (0.220 g, 0.721 mmol) in acetonitrile (10 mL). The
reaction mixture was sealed in a Schlenk tube and heated at 90 °C
for 72 h. The volatiles were removed in Vacuo to yield a viscous
yellow oil, which was Kugelrohr distilled (135 °C, 0.05 Torr) to
1
yield Bus3GeGePh3 (0.308 g, 81%) as a colorless oil. H NMR
(C6D6, 25 °C): δ 7.68 (t, J ) 7.2 Hz, 3H, para-H), 7.63 (d, J ) 7.2
Hz, 6H, ortho-H), 7.13-7.08 (m, 6H, meta-H), 1.78-1.73 (m, 3H,
CH3CHCH2CH3), 1.46-1.23 (m, 6H, CH3CHCH2CH3), 1.13-1.04
(m, 9H, CH3CHCH2CH3), 0.77 (t, J ) 7.6 Hz, 9H, CH3CHCH2CH3)
ppm. 13C NMR (C6D6, 25 °C): δ 138.91 (ipso-C), 135.33 (ortho-
C), 128.83 (meta-C), 128.44 (para-C), 28.80, 28.64 (CH3CHCH2-
CH3), 26.83 (CH3CHCH2CH3), 14.49, 14.46 (CH3CHCH2CH3),
13.78 (CH3CHCH2CH3) ppm. Anal. Calcd for C30H42Ge2: C, 65.77;
H, 7.73. Found: C, 65.72; H, 7.88.
Acknowledgment. Funding for this work by the Depart-
ment of Chemistry at Oklahoma State University and a
CAREER grant from the National Science Foundation (CHE-
0844758) is gratefully acknowledged.
Supporting Information Available: Crystallographic data for
5 in.cif format and 73Ge NMR spectra for compounds 4, 5, 7, and
9-12. This material is available free of charge via the Internet at
http://pubs.acs.org.
Synthesis of PhMe2GeGePh3 (5). To a solution of PhMe2-
GeNMe2 (0.220 g, 0.983 mmol) in acetonitrile (10 mL) was added
OM900035R