Syntheses and structural analysis of the sterically encumbered germanes (o-ButC6H4)3GeX (X = Br, H, Cl, OH), (o-ButC6H4)2GeBr2, and Mes2GeH2: Distortions arising from the presence of an ortho-tert-butyl substituent

Article abstract of DOI:10.1016/j.jorganchem.2011.05.012

Four new ortho-tert-butylphenyl substituted germanes (o-Bu ^tC₆H₄)₃GeX (X = Br (1), H (2), Cl (3), or OH (4)) have been prepared and structurally characterized. The structures of 1-4 have been obtained and the ortho-tert-butyl substituents were found to be oriented in the same direction as the Ge-X bond in each molecule. The presence of these bulky substituents results in distortions in 1-4 from the ideal tetrahedral geometry, which was assessed by an examination of the C _ipso-Ge-C_ipso-C_ortho torsion angles within these four compounds. The two diaryl-substituted germanes (o-Bu ^tC₆H₄)₂GeBr₂ (5) and Mes₂GeH₂ (6) have also been prepared and structurally characterized, and the absence of a third sterically encumbering aryl group alleviates a significant amount of structural strain in these compounds versus their triaryl-substituted analogues.

Full text of DOI:10.1016/j.jorganchem.2011.05.012

Journal of Organometallic Chemistry 696 (2011) 2993e2999
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses and structural analysis of the sterically encumbered germanes
(o-ButC6H4)3GeX (X ¼ Br, H, Cl, OH), (o-ButC6H4)2GeBr2, and Mes2GeH2:
distortions arising from the presence of an ortho-tert-butyl substituent
,
Christian R. Samanamu a, Courtney R. Anderson a, James A. Golen b c, Curtis E. Moore b,
,
Arnold L. Rheingold b, Charles S. Weinert a
*
a Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA
b Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0358, USA
c Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, USA
a r t i c l e i n f o
a b s t r a c t
Four new ortho-tert-butylphenyl substituted germanes (o-ButC6H4)3GeX (X ¼ Br (1), H (2), Cl (3), or OH
(4)) have been prepared and structurally characterized. The structures of 1e4 have been obtained and
the ortho-tert-butyl substituents were found to be oriented in the same direction as the GeeX bond in
each molecule. The presence of these bulky substituents results in distortions in 1e4 from the ideal
tetrahedral geometry, which was assessed by an examination of the CipsoeGeeCipsoeCortho torsion angles
Article history:
Received 20 April 2011
Received in revised form
19 May 2011
Accepted 20 May 2011
within these four compounds. The two diaryl-substituted germanes (o-ButC6H4)2GeBr2 (5) and Mes2
-
Keywords:
Germanium
Chirality
Structural distortions
X-ray crystal structures
GeH2 (6) have also been prepared and structurally characterized, and the absence of a third sterically
encumbering aryl group alleviates a significant amount of structural strain in these compounds versus
their triaryl-substituted analogues.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
three aryl rings would all be co-planar, and would be lying in
a plane that was disposed slightly beyond the plane defined by the
We have utilized triarylgermanium hydrides and amides for the
construction of germaniumegermanium single bonds via the
hydrogermolysis reaction (Scheme 1) [1e8] and were interested in
the implementation of tri(ortho-tert-butyl)-substituted germanium
halides and hydrides to function as possible chiral synthetic
precursors. Although these systems do not contain an asymmetric
carbon, they do exist as non-superimposable mirror images (Fig. 1)
due to the restricted rotation about the GeeCipso bonds enforced by
the ortho-tert-butyl groups, thus rendering these molecules chiral.
However, compounds of this type having a high degree of steric
encumbrance at the germanium center have been found to exhibit
limited reactivity.
The structures of these tri(ortho-tert-butyl)-substituted germa-
nium compounds are themselves of interest, as the presence of the
bulky ortho-substituents can result in significant distortions of the
ideal positions of the aryl rings relative to unsubstituted phenyl
derivatives. In the ideal geometric case, the six ortho-carbons of the
three ipso carbon atoms. However, this ideal geometry is seldom
realized in triarylgermanium compounds, and even the sterically
unemcumbered species Ph3GeH [9] is distorted from this ideal
geometry and adopts a propeller-like structure by rotation of the
aryl rings about the GeeCipso axis. The degree of steric interactions
between the ortho-substituents of the three aryl rings are depen-
dent on the size of the ortho-substituents present.
We have synthesized the germane (o-ButC6H4)3GeBr (1) and
have converted this species to the three additional sterically
encumbered germanes (o-ButC6H4)3GeX (X ¼ H (2), Cl (3), OH (4)).
We could not convert any of these four species to the desired
amide compound (o-ButC6H4)3GeNMe2 for use in the hydro-
germolysis reaction. However, we have obtained the X-ray crystal
structures of 1e4 and have assessed the degree of structural
distortion in these molecules resulting from the presence of the
three ortho-tert-butyl groups. The structures of 1e4 are also
compared to those of several other related molecules. In addition,
we have obtained the X-ray structures of the two diaryl-
substituted species (o-ButC6H4)2GeBr2 (5) and Mes2GeH2 (6) [10]
which are also compared to the structures of their correspond-
ing triaryl-substituted analogues.
* Corresponding author. Tel.: þ1 405 744 6543.
E-mail address: weinert@chem.okstate.edu (C.S. Weinert).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.05.012

2994
C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 2993e2999
Scheme 1.
2. Results and discussion
Scheme 2.
The germane (o-ButC6H4)3GeBr (1) was synthesized starting
from o-ButC6H4NH2, which was converted to the aryl bromide o-
ButC6H4Br via the Sandmeyer reaction and then to the corre-
sponding Grignard reagent (o-ButC6H4)MgBr. The Grignard reagent
was then added to GeBr4 in a 3:1 stoichiomeric ratio to furnish 1
(Scheme 2). Germanium(IV) bromide was used in lieu of the less
expensive GeCl4 to avoid obtaining mixed halide products, and the
Grignard reagent was used instead of the organolithium reagent
o-ButC6H4Li since we have found that use of the latter type of
alkylating agents results in the generation of a significant amount
of polymeric material. Compound 1 has been characterized by NMR
(1H and 13C) spectroscopy and elemental analysis. The protons of
ORTEP diagrams are shown in Figs. 2e5 (respectively) while metric
parameters are collected in Table 1. Compound 1 adopts a C3-
symmetric structure in the solid state (Fig. 2), with a GeeC bond
ꢀ
ꢀ
length of 1.997(2) A and a GeeBr bond distance of 2.362(1) A
(Table 1). The GeeBr bond length compares to those in other
related triaryl-susbstituted compounds, including Ph3GeBr (7) [12],
(o-(MeOCH2)C6H4)3GeBr (8) [13], and (o-(ButO)2C6H3)3GeBr (9)
[14], and relevant metric parameters for these three compounds are
shown in Table 2. It also matches with the sum of the covalent radii
ꢀ
of germanium and bromine of 2.35 A [15]. The GeeC distance in 1 is
ꢀ
elongated from that of the typical GeeCipso bond length of 1.95 A
and also from the sum of the covalent radii of germanium and
the ortho-tert-butyl group give rise to a singlet at d 1.53 ppm in the
1H NMR of 1 and resonances for the four aromatic protons were
observed as the expected pattern of two doublets and two triplets.
We attempted to prepare the amide (o-ButC6H4)3GeNMe2 from
1 by the metathesis reaction of 1 and LiNMe2 in benzene or THF
solvent, but both reactions were unsuccessful. However, 1 could be
converted to the hydride species (o-ButC6H4)3GeH (2) upon treat-
ment with lithium aluminum hydride in 93% yield (Scheme 3). The
ꢀ
carbon (1.96 A) [15] due to the presence of the bulky ortho-tert-
butyl groups. The GeeC bond distances in 1 are also elongated
relative to the average GeeC bond lengths in 7, 8, and 9, due the
steric effects of the ortho-tert-butyl groups. Compound 9 also
contains a tert-butyl group, but the oxygen atom located between
the tertiary carbon of the tert-butyl group and the ortho-carbon of
the aryl ring diminishes the steric impact of the But-group.
1H NMR spectrum of 2 exhibits a peak at
to the GeeH proton as well as a peak at
d
5.95 ppm corresponding
1.56 ppm for the protons
The aryl rings in 1 are oriented such that each of the tert-butyl
groups are pointed in the same direction as the GeeBr bond. The
orientation of the three aryl rings and the resulting disposition of
the substituents limits access to the bromine in 1. Despite the steric
congestion, however, the bond angles about the central germanium
atom do not differ significantly from the idealized tetrahedral angle
of 109.5ꢁ. The CipsoeGeeCipso bond angle in 1 is 108.26(6)ꢁ while the
BreGeeCipso bond is 110.66(6)ꢁ. This contrasts with the structures
of 8 [13] and 9 [14], where the corresponding bond angles are
distorted from the idealized tetrahedral geometry (Table 2).
The structure of 2 was obtained and is partially disordered with
a molecule of the bromide 1 that occupies essentially the same
volume as the hydride species and is present approximately 6% of
the time. Additionally, there are two independent molecules of the
hydride 2 in the unit cell, and the ORTEP diagram shown in Fig. 3
shows one of the two molecules. We made several attempts to
obtain X-ray quality crystals of 2 that were not disordered in this
fashion but were unsuccessful. Overall, the structure of 2 resembles
that of the bromo-substituted derivative 1. The average GeeC bond
d
of the tert-butyl group, and the IR spectrum of 2 contains a sharp
band at 2083 cmꢀ1 resulting from the stretching of the GeeH bond.
The attempted reaction of 2 with Ph3GeNMe2 in CH3CN solvent at
85 ꢁC was unsuccessful, as the hydride resonance for 2 remained
present even after a reaction time of 96 h. Compound 2 was con-
verted to the corresponding chloride compound (o-ButC6H4)3GeCl
(3) by reluxing the hydride in benzene in the presence of CuCl2
(Scheme 3) [11], and 3 was characterized by 1H NMR spectroscopy
and elemental analysis. The 1H NMR spectrum of 3 is nearly iden-
tical to that of 1 and 2, with a resonance at
d 1.52 ppm corre-
sponding to the o-But group and four aromatic resonances for the
protons attached to the phenyl rings. Although the salt metathesis
reaction between 1 and LiNMe2 was not successful, the reaction of 1
with KOH in refluxing absolute ethanol yielded the germanol (o-
ButC6H4)3GeOH (4) in 77% yield (Scheme 3). The 1H NMR spectrum
of 4 contains a singlet at d 1.51 ppm corresponding to the protons of
the tert-butyl group as well as a broad singlet at
assigned to the single proton of the eOH group.
d 4.05 ppm that is
ꢀ
length in 2 among the two independent molecules is 1.985(2) A and
the average CipsoeGeeCipso angle is 108.05(8)ꢁ, both of which are
also very similar to the corresponding values in 1 (Table 1). The
hydrogen bound to germanium was refined, and the GeeH bond
In order to assess the steric environment about the central
germanium atom, the X-ray structures of 1e4 were obtained, and
ꢀ
distance is 1.37(2) A.
Fig. 1. Non-superimposable mirror images of ortho-tert-butylphenyl substituted
germanes.
Scheme 3.

C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 2993e2999
2995
Fig. 2. ORTEP diagram of (o-ButC6H4)3GeBr (1). Thermal ellipsoids are drawn at 50%
probability.
The structure of 2 can be compared to the arylgermanium
hydride species Ph3GeH (10) [9], (o-CH3C6H4)3GeH (11) [16], and
Mes3GeH (12) (Table 2) [17]. The average GeeC bond distance in 2 is
elongated relative to the average GeeC bonds in both 10 [9], and 11
[16] but are shorter than that in 12 [17]. The GeeH bond distance in
Fig. 4. ORTEP diagram of (o-ButC6H4)3GeCl (3). Thermal ellipsoids are drawn at 50%
probability.
ꢀ
2 is similar to that in 10 (1.48(3) A) [9] but shorter than the corre-
and more electronegative chlorine atom in 3 versus the bromine
atom in 1, and the aryl rings in both molecules of 3 are again
oriented such that the ortho-tert-butyl substituents are disposed in
the same direction as the GeeCl bonds. The geometry at the central
germanium atom is nearly idealized tetrahedral in 3, which has an
average CipsoeGeeCipso bond angle of 108.8(2)ꢁ and an average
ꢀ
sponding distance in 11 (1.712(1) A) [16]. The average Cipsoe
GeeCipso angle in 2 is more acute than that in 10 but is more obtuse
than that in 11 and nearly identical to that in 12. The structures of 2,
10, 11, and 12 are only slightly distorted from the ideal tetrahedral
geometry, but the steric effects of two ortho-methyl groups in the
mesityl-substituted compound 12 have a more significant impact
on the GeeC bond lengths than do the single ortho-But or ortho-Me
groups in 2 and 11.
C
ipsoeGeeCl bond angle of 110.1(1)ꢁ. The geometry at germanium
in 3 differs from those of the related species Ph3GeCl (13) [18,19],
(o-(MeOCH2)C6H4)3GeCl (14) [13], (o-EtOC6H4)3GeCl (15) [20]
(Table 2), where two different structures of 13 having different
bond distances and angles have been reported. A comparison of
these data indicates that among these four compounds, the struc-
ture of 3 most closely resembles the ideal tetrahedral structure
expected for a germanium(IV) center.
The structure of 3 is disordered, and all of the carbon atoms
except C(10) occupy one of two sites with 50% occupancy, and the
ORTEP diagram shown in Fig. 4 shows one orientation of the
aromatic rings. Taking into account the dirsorder, the average
ꢀ
ꢀ
GeeCipso bond is 1.990(4) A and the GeeCl bond length 2.198(1) A
(Table 1), and the latter matches exactly with the sum of the
ꢀ
covalent radii for germanium and chlorine (2.20 A) [15]. The GeeC
distances in 1 and 3 are similar despite the presence of the smaller
Fig. 3. ORTEP diagram of one molecule (molecule 1) of (o-ButC6H4)3GeH (2). Thermal
Fig. 5. ORTEP diagram of (o-ButC6H4)3GeOH (4). Thermal ellipsoids are drawn at 50%
ellipsoids are drawn at 50% probability.
probability.

2996
C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 2993e2999
Table 1
bond lengths in 4 are longer than the corresponding distances in 16
and 17, while the average CipsoeGeeCipso bond angle in 4 is the most
acute and also the least distorted from the idealized tetrahedral
bond angle. The CipsoeGeeO bond angle is more obtuse in 4 than in
16 or 17, with the bond angle in 17 being the most acute. The
hydroxide moiety in 17 is hydrogen bonded to the oxygen atom in
Mes3GeNCO, but no evidence for hydrogen bonding is present in
the crystal structure of 4. However, the infrared spectrum of 4
exhibits a broad band at 3356 cmꢀ1, indicating that some hydrogen
bonding is present in the bulk material in nujoll mull.
ꢁ
ꢀ
Selected bond distances (A) and angles ( ) for 1e4.
(o-ButC6H4)3GeBr (1)
Ge(1)eBr(1)
Ge(1)eC(1)
2.362(1)
1.997(2)
C(1)eGe(1)eBr(1)
C(1)eGe(1)eC(10)
110.66(6)
108.26(6)
(o-ButC6H4)3GeH (2)
Molecule 1
Ge(1)eC(1)
Ge(1)eC(11)
Ge(1)eC(21)
Ge(1)eH(1)
1.979(2)
1.985(2)
1.987(2)
1.37(2)
C(1)eGe(1)eC(11)
C(1)eGe(1)eC(21)
C(11)eGe(1)eC(21)
C(1)eGe(1)eH(1)
C(11)eGe(1)eH(1)
C(21)eGe(1)eH(1)
108.61(8)
106.85(8)
108.85(8)
111(1)
112(1)
110(1)
The presence of the ortho-tert-butyl groups in 1e4 result in
a distortion of the relative orientations of the aryl rings from the
ideal geometry. In an ideal tetrahedral geometry, the dihedral angle
between the plane of one aryl ring and that of each of the others
would be 30ꢁ. These angles correspond to the angles between the
GeeCipso axis of one aryl ring and the CipsoeCortho axis of the other
aryl two rings, and therefore this corresponds to the Cipsoe
GeeCipsoeCortho torsion angles within the molecule. In order to
accommodate the three ortho-tert-butyl groups, the aryl rings are
Molecule 2
Ge(10)eC(10)
Ge(10)eC(110)
Ge(10)eC(210)
Ge(10)eH(10)
1.990(2)
1.982(2)
1.984(2)
1.37(2)
C(10)eGe(10)eC(110)
C(10)eGe(10)eC(210)
C(110)eGe(10)eC(210)
C(10)eGe(10)eH(10)
C(110)eGe(10)eH(10)
C(210)eGe(10)eH(10)
107.54(8)
108.53(8)
107.91(8)
110(1)
109(1)
114(1)
rotated such that one angle becomes more acute than 30ꢁ
one becomes more obtuse than 30ꢁ
) as shown in Fig. 6 [17,23].
(a) and
(o-ButC6H4)3GeCl (3)
Ge(1)eCl(1)
Ge(1)eC(1)
Ge(1)eC(11)
Ge(1)eC(21)
2.198(1)
1.975(4)
2.015(4)
1.979(4)
C(1)eGe(1)eC(11)
C(1)eGe(1)eC(21)
C(11)eGe(1)eC(21)
C(1)eGe(1)eCl(1)
C(11)eGe(1)eCl(1)
C(21)eGe(1)eCl(1)
108.2(2)
110.3(2)
107.9(2)
109.6(1)
110.1(1)
110.6(1)
(b
With the exception of the C3-symmetric 1, these angles each occur
three times in each molecule, and the values shown in Table 3 are
the average of these three values for each molecule. This type of
distortion is also observed in substituted aryl germanes where the
ortho-substituents all point in the same direction, or in compounds
(o-ButC6H4)3GeOH (4)
Ge(1)eO(1)
Ge(1)eC(1)
Ge(1)eC(11)
Ge(1)eC(21)
that have two ortho-substituents, and so is also observed in Mes3
-
1.885(3)
1.991(3)
1.983(3)
1.976(4)
C(1)eGe(1)eC(11)
C(1)eGe(1)eC(21)
C(11)eGe(1)eC(21)
C(1)eGe(1)eO(1)
C(11)eGe(1)eO(1)
C(21)eGe(1)eO(1)
107.2(1)
108.0(1)
109.8(1)
113.5(1)
107.4(1)
110.9(1)
GeH (12) [17] and Mes3GeOH (17) [23]. The value of
4 can then be
used to describe the rotation of the rings in these species, where
4
¼ 1/2[(
a
þ 30ꢁ) þ (
b
ꢀ 30ꢁ)].
The data shown in Table 3 indicate that 1e4 and 12 all have
approximately the same amount of distortion from the idealized
structure. The hydride species 2 is the most distorted among these
molecules, with a
significantly distorted with a
4
value of 49.3ꢁ, and the hydroxide 4 also is
4
value of 48.0ꢁ. The fourth substit-
The structure of 4 (Fig. 5) again resembles those of 1e3, where
the ortho-tert-butyl groups are disposed in the same direction as
uent at germanium in 2 and 4 are the smallest among the four
compounds 1e4 and these two species have the shortest GeeC
bond lengths. These data also indicate that the steric effects of one
ortho-tert-butyl group are comparable to those of two ortho-methyl
groups as the distortions of the five species 1e4 and 12 are similar.
The ortho-tolyl substituted compound 11, which has only one
methyl group in the ortho-position, is significantly less distorted
than the more sterically encumbered species 1e4 and 12. Similarly,
the di(ortho-tert-butoxy) substituted compound 9 is also less dis-
torted than these five molecules since the oxygen atom in this
species results in the six tert-butyl groups being disposed farther
from one another than in 1e4.
ꢀ
the GeeO bond and the average GeeC bond length is 1.983(3) A.
The CipsoeGeeCipso angle in 4 is 108.3(1)ꢁ and the CipsoeGeeO angle
ꢁ
ꢀ
is 110.6(1) . The GeeO bond distance is 1.885(3) A, which is elon-
gated relative to typical germaniumeoxygen bonds that range from
ꢀ
1.76 to 1.84 A in linear compopunds [21]. The structure of 4 can be
compared to the unsubstituted derivative Ph3GeOH [22] (16) as
well as the sterically congested species Mes3GeOH [23] (17)
(Table 2). Compound 16 contains eight independent molecules in
the unit cell [22], while 17 was obtained as a hydrogen bonded pair
with Mes3GeNCO. Among the three structures, the GeeC and GeeO
Table 2
Structural parameters for compounds 7e17.
Compound
GeeX bond
length (A)
Avg.
GeeCipso
bond length (A)
Avg. CipsoeGeeCipso
bond angle (ꢁ)
Avg. CipsoeGeeX
bond angle (ꢁ)
Ref.
ꢀ
ꢀ
Ph3GeBr (7)
2.3188(7)
2.3617(5)
2.3791(6)
1.48(3)
1.712(1)
n/a
2.187(2)
2.161(2)
2.213(1)
2.2287(8)
1.791(8)
1.805(3)
1.934(1)
1.951(4)
1.965(2)
1.945(5)
1.981(1)
2.037(9)
1.937(6)
1.933(5)
1.951(2)
1.941(3)
1.93(2)
112.44(1)
114.7(2)
115.55(9)
110.2(1)
106.3(1)
108.9(4)
112.5(2)
112.7(2)
115.3(1)
112.6(1)
111.8(4)
114.7(2)
106.31(1)
103.6(1)
102.38(6)
109(2)
112.69(1)
n/a
106.2(2)
106.0(1)
102.81(9)
106.1(1)
107.1(4)
103.6(2)
[12]
[13]
[14]
[9]
[16]
[17]
[18]
[19]
[13]
[20]
[22]
[23]
(o-(MeOCH2)C6H4)3GeBr (8)
(o-(ButO)2C6H3)3GeBr (9)
Ph3GeH (10)a
(o-CH3C6H4)3GeH (11)
Mes3GeH (12)
Ph3GeCl (13)
Ph3GeCl (13)
(o-(MeOCH2)C6H4)3GeCl (14)
(o-EtOC6H4)3GeCl (15)
Ph3GeOH (16)
Mes3GeOH (17)
1.972(5)
a
Values are for the average of two different morphologies.

C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 2993e2999
2997
Fig. 6. Newman projections of ortho-tert-butylphenyl substituted germanes showing
the idealized geometry (left) and distorted geometry (right).
The diaryl-substituted derivatives (o-ButC6H4)2GeBr2 (5) and
Mes2GeH2 (6) were also prepared and structurally characterized.
Compound 5 was prepared in a similar manner to the method used
for 1 using a 2:1 stoichiometric ratio of Grignard reagent to GeBr4,
while 6 was prepared according to the literature procedure [10].
The 1H NMR of 5 is again similar to those of 1e4, with a resonance
at
aromatic resonances. The 1H NMR of 6 matches that in the litera-
ture [10], with a resonance at 5.27 ppm corresponding to the
d 1.54 ppm for the ortho-tert-butyl protons and four distinct
d
Fig. 7. ORTEP diagram of one molecule (molecule 1) of (o-ButC6H4)2GeBr2 (5). Thermal
hydrogen attached to the central germanium atom.
ellipsoids are drawn at 50% probability.
The ORTEP diagrams for 5 and 6 are shown in Figs. 7 and 8, and
structural parameters are collected in Table 4. Compound 5 crys-
tallizes with two independent molecules in the unit cell, and in
both molecules the ortho-tert-butyl groups are directed away from
the two GeeBr bonds. The average GeeC bond length among the
structures of 1e4 have been obtained and the ortho-tert-butyl
substituents are oriented in the same direction as the GeeX bond in
each molecule. The presence of these substituents results in
distortions in 1e4 from the ideal tetrahedral geometry. An assess-
ment of the torsion angles within these four compounds indicates
that the distortion is more significant in the hydride 2 and the
hydroxide 4, which contain the least sterically encumbering fourth
substituent at germanium. The two diaryl-substituted germanes (o-
ButC6H4)2GeBr2 (5) and Mes2GeH2 (6) have also been prepared and
structurally characterized, and a comparison of the structures of
these two compounds versus their corresponding triaryl-
substituted analogues (o-ButC6H4)3GeBr (1) and Mes3GeH (12)
indicate that the absence of a third sterically encumbering aryl
group alleviates a significant amount of structural strain leading to
shorter GeeCipso bond distances in 5 and 6.
ꢀ
two independent molecules is 1.965(6) A while the average GeeBr
ꢀ
bond distance is 2.345(9) A. Both of these distances are shorter than
those in the corresponding triaryl species 1 due to an alleviation of
the steric crowding at the germanium center in 5 since only two
ortho-substituted aryl substituents are present. The average
BreGeeBr,
CipsoeGeeCipso, and BreGeeCipso angles in 5 are
97.61(3), 130.4(3), and 106.1(2)ꢁ (respectively). The CeGeeC bond
angle at the central germanium atom in 5 is substantially more
obtuse than that in 1, and the absence of a third aryl substituent
allows the two sterically encumbered aryl groups in 5 to be
disposed farther away from one another.
The structure of 6 is C2-symmetric, with a GeeC bond distance
of 1.965(2) A and a CipsoeGeeCipso bond angle of 113.2(1)ꢁ. The
ꢀ
hydrogen atoms attached to germanium were found and refined,
ꢀ
and the GeeH bond distance is 1.43(3) A, and the two CipsoeGe(1)e
3. Experimental
H(1) bond angles are 111(1) and 107(1)ꢁ. As expected, the absence
of a third mesityl group in 6 versus the three mesityl groups present
in 12 alleviates a significant amount of steric strain. The GeeC bond
length in 6 is shorter than the average distance in 12 (2.05(1) A) by
0.08 A and the CipsoeGeeCipso bond angle in 6 is more obtuse than
3.1. General considerations
ꢀ
All manipulations were carried out using standard Schlenk,
syringe, and glovebox techniques [24]. The starting material
o-ButC6H4NH2 was purchased from Aldrich and was distilled prior
to use, and was converted to o-ButC6H4Br via a literature method
[25]. Germanium(IV) bromide was purchased from Gelest and
anhydrous CuCl2 was purchased from Fluka, and these reagents
ꢀ
that in 12 (109.0(3)ꢁ) by 4.1ꢁ.
In conclusion, the four new ortho-tert-butylphenyl substituted
germanes (o-ButC6H4)3GeX (X ¼ Br (1), H (2), Cl (3), or OH (4)) have
been prepared and structurally characterized. For the halide
substituted species 1 and 3, limited reactivity at the central GeeX
bond was observed, and these compounds could not be used to
prepare the desired amide (o-ButC6H4)3GeNMe2 for use in the
hydrogermolysis reaction. Compound 2 was also found to be
unreactive in the hydrogermolysis reaction with Ph3GeNMe2. The
Table 3
Torsion angles and structural parameters for 1e4, 9, 11, and 12.
Compound
a
(ꢁ)
b
(ꢁ)
f
(ꢁ)
(o-ButC6H4)3GeBr (1)
14.8
18.0
15.8
17.5
14.0
2.7
74.3
80.6
75.7
78.5
59.2
66.1
81.8
44.5
49.3
45.8
48.0
36.6
34.4
42.4
(o-ButC6H4)3GeH (2)
(o-ButC6H4)3GeCl (3)
(o-ButC6H4)3GeOH (4)
(o-(ButO)2C6H3)3GeBr (9) [14]
(o-CH3C6H4)3GeH (11) [16]
Mes3GeH (12) [17]
Fig. 8. ORTEP diagram of Mes2GeH2 (6). Thermal ellipsoids are drawn at 50%
probability.
3.0

2998
C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 2993e2999
The NMR spectra (1H and 13C) were recorded using a Gemini 2000
NMR spectrometer and were referenced to residual protio solvent,
and IR spectra were obtained using a Hewlett-Packard IR spec-
trometer. Elemental analyses were obtained by Midwest Microlabs
(Indianapolis, IN) or Galbraith Laboratories (Knoxville, TN).
Table 4
ꢁ
ꢀ
Selected bond distances (A) and angles ( ) for 5 and 6.
(o-ButC6H4)2GeBr2 (5)
Molecule 1
Ge(1)eBr(1)
Ge(1)eBr(2)
Ge(1)eC(1)
Ge(1)eC(11)
2.3497(9)
2.3404(9)
1.958(6)
1.967(6)
Br(1)eGe(1)eBr(2)
Br(1)eGe(1)eC(1)
Br(1)eGe(1)eC(11)
Br(2)eGe(1)eC(1)
Br(2)eGe(1)eC(11)
C(1)eGe(1)eC(11)
96.14(3)
103.7(2)
110.1(2)
109.1(2)
104.9(2)
128.4(3)
3.1.1. Synthesis of (o-ButC6H4)3GeBr (1)
A 15 mL aliquot of solution of o-ButC6H4Br (10.60 g, 49.76 mmol)
in THF (100 mL) was added to Mg metal (1.77 g, 72.8 mol) in
a
three-necked round bottom flask equipped with a reflux
Molecule 2
Ge(10)eBr(10)
Ge(10)eBr(20)
Ge(10)eC(10)
Ge(10)eC(110)
2.3486(9)
2.341(1)
1.969(6)
1.967(6)
Br(10)eGe(10)eBr(20)
Br(10)eGe(10)eC(10)
Br(10) eGe(10)eC(110)
Br(20)eGe(10)eC(10)
Br(20)eGe(10)eC(110)
C(10)eGe(10)eC(110)
99.08(4)
108.9(2)
101.3(2)
101.7(2)
109.1(2)
132.3(3)
condenser and addition funnel and the reaction was initiated with
a single crystal of I2. The remaining solution was added dropwise to
the flask and was subsequently refluxed for 90 min. After cooling to
room temperature, the resulting solution was added to GeBr4
(6.50 g, 16.6 mmol) in THF (50 mL) via cannula. The solution was
refluxed under N2 for 60 min, was cooled to room temperature, and
was poured over 100 mL of aqueous HBr solution in an ice bath. The
mixture was extracted with benzene (5 ꢂ 50 mL) in air, the organic
phase was dried over MgSO4, and the volatiles were removed in
vacuo after gravity filtration to yield 3.7 g (40%) of 1 as a white solid.
Mes2GeH2 (6)
Ge(1)eC(1)
Ge(1)eH(1)
1.965(2)
1.43(3)
C(1)eGe(1)eC(10)
C(1)eGe(1)eH(1)
C(10)eGe(1)eH(1)
113.2(1)
111(1)
107(1)
1H NMR (C6D6, 25 ꢁC)
d
7.64 (d, J ¼ 7.2 Hz, 3H, o-C6H4), 7.53 (d,
were used without further purification. Compound 6 (Mes2GeH2)
was prepared according to a literature procedure [10]. All solvents
were purified using a Glass Contour solvent purification system.
J ¼ 7.5 Hz, 3H, m-C6H4), 7.08 (t, J ¼ 7.2 Hz, 3H, m-C6H4), 6.74 (t,
J ¼ 7.5 Hz, 3H, p-C6H4), 1.53 (s, 27H, eC(CH3)3) ppm. 13C NMR (C6D6,
25 ꢁC)
d
156.6 (GeeCipso), 139.1 (o-CH), 137.0 (o-CBut), 130.8 (m-C),
Table 5
Crystallographic data for compounds 1e6.
Compound
1
2
3
4
5
6
Empirical formula
Formula weight
Temperature (K)
C30H39BrGe
552.11
100(2)
0.71073
Rhombohedral
R3
11.247(3)
11.247(3)
38.28(2)
90
90
120
4193(2)
6
1.312
C30H40Br0.03Ge
475.61
100(2)
1.54184
Triclinic
P-1
10.7792(6)
15.0437(8)
17.435(1)
69.111(3)
88.715(3)
76.374(3)
2561.1(2)
4
C30H39ClGe
507.65
100(2)
0.71073
Triclinic
P-1
10.712(4)
10.766(4)
14.495(6)
111.577(4)
91.723(5)
116.183(4)
1357.4(9)
2
C30H40GeO
489.21
200(2)
0.71073
Monoclinic
P21/c
13.584(2)
17.852(2)
10.8475(2)
90
91.425(5)
90
2629.8(7)
4
1.236
1.184
C20H26Br2Ge
498.82
150(2)
0.71073
Triclinic
P-1
9.527(1)
13.997(2)
15.749(2)
105.350(2)
92.389(2)
98.993(2)
1992.7(5)
4
C18H24Ge
312.96
100(2)
0.71073
Monoclinic
C2/c
13.298(3)
9.040(2)
13.426(3)
90
102.752(4)
90
1574.1(7)
4
1.321
1.932
ꢀ
Wavelength (A)
Crystal system
Space group
ꢀ
a, A
ꢀ
b, A
ꢀ
c, A
ꢁ
ꢁ
ꢁ
a
,
b
,
g
,
3
ꢀ
V, A
Z
r
(g cmꢀ1
)
1.233
1.710
1012
1.242
1.242
536
1.663
5.546
992
Absorption coefficient (mmꢀ1
F(000)
)
2.540
1716
1040
656
Crystal size (mm3)
0.26 ꢂ 0.25 ꢂ 0.20
0.35 ꢂ 0.17 ꢂ 0.15
0.30 ꢂ 0.20 ꢂ 0.10
0.29 ꢂ 0.28 ꢂ 0.28
0.25 ꢂ 0.25 ꢂ 0.15
0.24 ꢂ 0.20 ꢂ 0.18
Theta range for data collection
1.60e28.03ꢁ
4.23e65.60ꢁ
1.55e28.65ꢁ
2.63e25.06ꢁ
1.35e25.43ꢁ
2.75e27.91ꢁ
Index ranges
ꢀ14 ꢃ h ꢃ 14
ꢀ14 ꢃ k ꢃ 10
ꢀ46 ꢃ l ꢃ 49
ꢀ10 ꢃ h ꢃ 12
ꢀ17 ꢃ k ꢃ 17
ꢀ20 ꢃ l ꢃ 20
ꢀ14 ꢃ h ꢃ 14
ꢀ14 ꢃ k ꢃ 14
ꢀ18 ꢃ l ꢃ 18
ꢀ16 ꢃ h ꢃ 16
ꢀ20 ꢃ k ꢃ 21
ꢀ12 ꢃ l ꢃ 12
ꢀ11 ꢃ h ꢃ 11
ꢀ16 ꢃ k ꢃ 16
ꢀ18 ꢃ l ꢃ 18
ꢀ17 ꢃ h ꢃ 17
ꢀ11 ꢃ k ꢃ 11
ꢀ16 ꢃ l ꢃ 17
Reflections collected
10,332
21,818
21,182
25,659
29,446
7069
Independent reflections
2150 (Rint ¼ 0.0445) 8330 (Rint ¼ 0.0340) 6121 (Rint ¼ 0.0439) 4643 (Rint ¼ 0.0576) 7270 (Rint ¼ 0.0439) 1800 (Rint ¼ 0.0371)
Completeness to
q
q
¼ 25.00 (100.0%)
q
¼ 60.00 (99.2%)
q
¼ 25.00 (98.1%)
q
¼ 25.00 (99.9%)
q
¼ 25.00 (99.3%)
q
¼ 25.00 (100.0%)
Absorption correction
Multi-scan/sadabs
Semi-empirical from None
equivalents
Multi-scan/sadabs
Multi-scan
Multi-scan/sadabs
Max. and min. transmission
Refinement method
0.6306 and 0.5581
Full-matrix
0.7782 and 0.5779
Full-matrix
0.8859 and 0.7070
Full-matrix
0.7328 and 0.7253
Full-matrix
0.4901 and 0.3378
Full-matrix
0.7224 and 0.6542
Full-matrix
least-squares on F2 least-squares on F2
least-squares on F2 least-squares on F2 least-squares on F2 least-squares on F2
Data/restraints/parameters
2150/0/100
1.014
8330/0/631
1.028
6121/0/566
1.043
4643/12/1293
1.044
7270/0/427
1.076
1800/0/94
1.077
Goodness-of-fit on F2
Final R indices (I < 2s(I))
R1
wR2
0.0283
0.0659
0.0323
0.0806
0.0374
0.0842
0.0435
0.1083
0.0527
0.1555
0.0290
0.0779
Final R indices (all data)
R1
wR2
0.0371
0.0699
0.0384
0.0855
0.0486
0.0911
0.0736
0.1207
0.0647
0.1630
0.0306
0.0792
ꢀꢀ3
Largest diff. peak and hole (e A
CCDC deposition number
)
0.414 and ꢀ0.745
0.567 and ꢀ0.390
0.808 and ꢀ0.587
0.669 and ꢀ0.416
3.080 and ꢀ1.136
1.085 and ꢀ0.640
822221
822223
822222
822437
822220
822224

C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 2993e2999
2999
129.2 (m-C), 125.1 (p-C), 38.4 (-C(CH3)3), 33.8 (-C(CH3)3) ppm. Anal.
Calcd. for C30H39BrGe: C, 65.24; H, 7.12. Found: C, 65.11; H, 7.25.
solid. 1H NMR (C6D6, 25 ꢁC)
d
7.64 (d, J ¼ 7.2 Hz, 2H, o-C6H4), 7.54 (d,
J ¼ 7.8 Hz, 2H, m-C6H4), 7.09 (t, J ¼ 7.8 Hz, 2H, m-C6H4), 6.74 (t,
J ¼ 7.2 Hz, 2H, p-C6H4), 1.54 (s, 18H, -C(CH3)3) ppm. 13C NMR (C6D6,
3.1.2. Synthesis of (o-ButC6H4)3GeH (2)
25 ꢁC) 156.6 (GeeCipso), 139.1 (o-CH), 137.0 (o-CBut), 130.4 (m-C),
d
To a solution of 1 (1.00 g, 1.81 mmol) in Et2O (40 mL) was added
a suspension of LiAlH4 (0.23 g, 6.1 mmol) in Et2O (20 mL) via
cannula at 0ꢁC. The reaction mixture was stirred for 3 h at room
temperature and then was quenched with deoxygenated deionized
water. The organic phase was separated and dried over anhydrous
MgSO4. The suspension was filtered and the volatiles were removed
in vacuo to yield 0.80 g (93%) of 2 as a white solid. 1H NMR (C6D6,
129.2 (m-C), 125.0 (p-C), 38.4 (-C(CH3)3), 33.8 (-C(CH3)3) ppm. Anal.
Calcd. for C20H26Br2Ge: C, 48.13; H, 5.25. Found: C, 47.92; H, 5.13.
3.2. X-ray structure analysis
X-ray crystallographic measurements for 1e4 and 6 were made
using a Bruker APEX CCD system under a stream of nitrogen gas.
Data were corrected for absorption using SADABS and the struc-
tures were solved using direct methods (SIR-2004). All non-
hydrogen atoms were refined anisotropically by full-matrix least
squares (SHELXL-97). The structure of 5 was acquired using
a Bruker SMART X2S benchtop crystallographic system, using
APEX2 software for the unit cell determination. Data were cor-
rected from absorption using SADABS and all non-hydrogen atoms
were refined using full-matrix least squares (SHELXL-2008). Crys-
tallographic data for 1e6 are collected in Table 5.
25 ꢁC):
d
7.66 (d, J ¼ 7.8 Hz, 3H, o-C6H4), 7.56 (d, J ¼ 7.8 Hz, 3H, m-
C6H4), 7.12 (t, J ¼ 7.8 Hz, 3H, m-C6H4), 6.76 (t, J ¼ 7.2 Hz, 3H, p-C6H4),
5.95 (s, 1H, GeeH), 1.56 (s, 27H, -C(CH3)3) ppm. 13C NMR (C6D6,
25 ꢁC):
d
156.4 (GeeCipso), 138.8 (o-CH), 136.7 (o-CBut), 130.1 (m-C),
128.9 (m-C), 124.7 (p-C), 38.1 (-C(CH3)3), 33.5 (-C(CH3)3) ppm. IR
(nujol mull): 2083 cmꢀ1
(nGeeH). Anal. Calcd. for C30H40Ge: C, 76.12;
H, 8.52. Found: C, 75.93; H, 8.44.
3.1.3. Synthesis of (o-ButC6H4)3GeCl (3)
To a solution of 2 (1.00 g, 2.11 mmol) in benzene (40 mL) was
added CuCl2 (0.57 g, 4.2 mmol) and a crystal of CuI. The reaction
mixture was refluxed under N2 for 24 h, was allowed to cool, and
was filtered through Celite. The volatiles were removed in vacuo to
Appendix A. Supplementary material
CCDC 822220e822224 and 822437 contains the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
yield 3 (0.600 g, 56%) as a white solid. 1H NMR (C6D6, 25 ꢁC):
d 7.53
(d, J ¼ 7.2 Hz, 3H, o-C6H4), 7.50 (d, J ¼ 7.2 Hz, 3H, m-C6H4), 7.08 (t,
J ¼ 7.2 Hz, 3H, m-C6H4), 6.73 (t, J ¼ 7.2 Hz, 3H, p-C6H4), 1.52 (s, 27H,
-C(CH3)3) ppm. 13C NMR (C6D6, 25 ꢁC):
d 156.7 (GeeCipso), 138.8 (o-
CH), 138.3 (o-CBut), 130.4 (m-C), 128.9 (m-C), 125.1 (p-C), 38.2
(-C(CH3)3), 33.3 (-C(CH3)3) ppm. Anal. Calcd. for C30H39ClGe: C,
70.95. H, 7.75. Found: C, 70.79; H, 7.71.
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3.1.4. Synthesis of (o-ButC6H4)3GeOH (4)
A solution of 1 (0.776 g, 1.41 mmol) in absolute ethanol (40 mL)
was added to a solution of KOH (0.125 g, 2.23 mmol) in absolute
ethanol (50 mL) under N2. The reaction mixture was refluxed under
N2 for 24 h and the volatiles were removed in vacuo. Benzene
(25 mL) was added to the resulting solid material and the mixture
was agitated and subsequently filtered through Celite. The volatiles
were removed in vacuo to yield 4 (0.478 g, 69%) as a white solid. 1H
NMR (C6D6, 25 ꢁC):
d
7.63 (d, J ¼ 7.2 Hz, 3H, o-C6H4), 7.52 (d,
J ¼ 7.2 Hz, 3H, m-C6H4), 7.11 (t, J ¼ 7.2 Hz, 3H, m-C6H4), 6.82 (t,
J ¼ 7.2 Hz, 3H, p-C6H4), 4.05 (br s, 1H, -OH), 1.51 (s, 27H, -C(CH3)3)
ppm. 13C NMR (C6D6, 25 ꢁC):
d 156.9 (GeeCipso), 139.1 (o-CH), 138.6
(o-CBut), 130.2 (m-C), 129.3 (m-C), 125.4 (p-C), 38.3 (-C(CH3)3), 33.7
(-C(CH3)3) ppm. IR (nujol mull): 3356 cmꢀ1 (br, nOeH). Anal. Calcd.
for C30H40GeO: C, 73.63; H, 8.24. Found: C, 73.48; H, 8.18.
3.1.5. Synthesis of (o-ButC6H4)2GeBr2 (5)
A 15 mL aliquot of solution of o-ButC6H4Br (7.73 g, 36.3 mmol) in
THF (60 mL) was added was to Mg metal (1.32 g, 54.3 mol) in
a
three-necked round bottom flask equipped with a reflux
condenser and addition funnel and the reaction was initiated with
a single crystal of I2. The remaining solution was added dropwise to
the flask and was subsequently refluxed for 90 min. After cooling to
room temperature, the resulting solution was added to GeBr4
(7.12 g, 18.1 mmol) in THF (40 mL) via cannula. The solution was
refluxed under N2 for 90 min, was cooled to room temperature, and
was poured over 100 mL of aqueous HBr solution in an ice bath. The
mixture was extracted with benzene (5 ꢂ 50 mL) in air, the organic
phase was dried over MgSO4, and the volatiles were removed in
vacuo after gravity filtration to yield 6.30 g (70%) of 5 as a white