Synthesis and oxidation of bis(triphenylgermyl)zinc

Article abstract of DOI:10.1016/j.jorganchem.2005.02.048

Bis(triphenylgermyl)zinc (Ph₃Ge)₂Zn (1), prepared by the reaction of diethylzinc (Et₂Zn) with two molar amounts of triphenylgermane (Ph₃GeH), was easily reacted by a small amount of oxygen to give tetrameric oxi

Full text of DOI:10.1016/j.jorganchem.2005.02.048

Journal of Organometallic Chemistry 690 (2005) 2952–2955
www.elsevier.com/locate/jorganchem
Synthesis and oxidation of bis(triphenylgermyl)zinc
*
Masato Nanjo , Takashi Oda, Teruhisa Sato, Kunio Mochida
*
Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
Received 15 January 2005; revised 21 February 2005; accepted 22 February 2005
Available online 21 April 2005
Abstract
Bis(triphenylgermyl)zinc (Ph
germane (Ph GeH), was easily reacted by a small amount of oxygen to give tetrameric oxide (Ph
3
Ge)
2
Zn (1), prepared by the reaction of diethylzinc (Et
2
Zn) with two molar amounts of triphenyl-
GeZnO) (2). Four zinc and four
3
3
4
oxygen atoms in 2 are arranged such that a cube is formed as determined by X-ray diffraction analysis. Further oxidation of 2 led to
the formation of digermoxane, (Ph Ge) O as a final product.
3
2
ꢀ
2005 Elsevier B.V. All rights reserved.
Keywords: Germylzinc; X-ray diffraction; Oxidation
1
. Introduction
(1). In the oxidation of 1 we found a novel tetrameric
germylzinc oxide, (Ph GeZnO) (2). Further oxidation
of 2 finally led to the formation of digermoxane,
3
4
Organozinc compounds are useful reagents not only
in organic synthesis but also in organometallic chemistry
1]. The well-known Reformatsky zinc alkylation and
(Ph Ge) O.
3
2
[
the Simons–Smith reaction proceed via organozincs as-
sumed as key intermediates. Despite the large number
of reports on organozinc reagents, far less attention
has been given to silyl- or germyl-substituted zinc com-
pounds [2,3]. Up to now, several bis(silyl)- or bis(ger-
myl)-substituted zinc derivatives {(Ph Si) Zn [2a],
2. Results and discussion
Treatment of diethylzinc (Et Zn) with two molar
2
amounts of triphenylgermane (Ph GeH) in THF at
3
room temperature for 5 days of stirring afforded flam-
mable colorless crystals with a composition of
(Ph Ge) Zn (1) in 26% isolated yield (based on the con-
3
2
(
Me Si) Zn [2b], [(Me Si) Si] Zn [2c], (t-Bu Si) Zn
3
3
2
3
3
2
2
[
Ge] Zn [3c]} and silyl- or germyl-substituted zinc halides
2d], (Ph Ge) Zn [3a], (Et Ge) Zn [3b], and [(Me Si) -
3 2 3 2 3 3
3
2
centration of Et Zn) (Eq. (1)). Unreacted Ph GeH was
2 3
2
{
t-Bu SiZnCl [2d], t-Bu SiZnBr [2d], (Me Si) GeZnX
3
mostly recovered. The bis(germyl)zinc (1) is thermally
stable for prolonged periods in the absence of air at
room temperature.
3
3
3
(X = Cl, Br, I) [3d] have been prepared and a few X-
ray crystal structures of [(Me Si) Si] Zn, (t-Bu Si) Zn,
3
3
2
3
2
t-Bu SiZnBr, [(Me Si) Ge] Zn, and (Me Si) GeZnX
3
3
3
3
2
3
THF
have been determined. However, reports on the reactiv-
ities of silyl- or germyl-zinc derivatives are limited [3c].
We describe herein the first oxidation of bis(germyl)zinc
2Ph
3
GeH þ Et
2
Zn ƒƒƒ! ðPh
3
GeÞ Zn þ2EtH
ð1Þ
2
rt; 5 d
1
1
The bis(germyl)zinc (1) was identified with the H, and
1
3
C NMR spectra. Two THF molecules were included
1 13
for a molecule 1 based on the H and C NMR data.
*
Corresponding authors. Tel.: +81 3 3986 0221; fax: +81 3 5992
029.
E-mail address: kunio.mochida@gakushuin.ac.jp (K. Mochida).
Bychkov et al. [3b] described the formation of (Et3-
1
0
Ge) Zn by treatment of Et Zn with two molar amounts
2
2
022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.048

M. Nanjo et al. / Journal of Organometallic Chemistry 690 (2005) 2952–2955
2953
of Et GeH in diglyme at 150 ꢁC for 1.5 h. The bis(ger-
myl)zinc (1) was prepared by another method, namely,
the reaction of ZnCl2 with two molar amounts of
Table 1
The selected bond length (A) and bond angles (ꢁ) of (Ph
3
˚
3
2
Ge) Zn (1)
Zn(1)–Ge(1)
Zn(1)–O(1)
2.4315(6) Zn(1)–Ge(2)
2.179(3) Zn(1)–O(2)
2.4346(6)
2.17(3)
triphenylgermylalkali metals (Ph GeM, M = Na, K) in
3
liquid NH [3a].
3
Ge(1)–Zn(1)–Ge(2) 135.24(2)
Ge(1)–Zn(1)–O(2) 105.87(7)
Ge(1)–Zn(1)–O(1) 103.52(7)
O(1)–Zn(1)–O(2) 91.47(11)
The air-sensitive bis(germyl)zinc (1) could be recrys-
tallized from pentane at ꢀ20 ꢁC. The molecular struc-
ture of 1 was unequivocally confirmed by X-ray
diffraction analysis. The molecular structure of 1 is
shown in Fig. 1. The selected bond lengths and bond an-
gles of 1 are summarized in Table 1. Crystallographic
data of 1 are summarized in Section 3. 1 has a bent
structure with Ge–Zn–Ge bond angle of 135.42(2)ꢁ.
Two THF molecules are coordinated to the zinc atom
The signals of 1 completely disappeared after 1 h, result-
ing in the build-up of new signals of an intermediate 2:
1
3
C NMR (d, C D ) 26.0 (THF), 67.9 (THF), 128.2,
6
6
128.7, 136.1, 143.2. which were apparently different
from that found in the starting material 1, together with
digermoxane, (Ph Ge) O. Finally, the signals of
3
2
(Ph Ge) O alone were observed after 10 h.
3 2
˚
with Zn–O bond length of 2.148 A (av). The bond angle
O2
O2
of O–Zn–O is 91.47(11)ꢁ and the Ge–Zn–O bond angles
range from 103.52(7)–105.87(7)ꢁ. The bond lengths of
Ge–Zn (2.4331 A (av)) is almost equal within experi-
1 ! ðPh
3
GeZnOÞ ! ðPh
3
GeÞ O
ð3Þ
4
2
rt
rt
2
˚
Fortunately, the intermediate 2, prepared by the reac-
tion of Ph GeH and Et Zn, could be isolated and recrys-
˚
mental error with the sum (2.47 A) of the covalent radii
[
3
2
7] and is longer than those of (Me Si) GeZnX and
3
tallized from THF at ꢀ20 ꢁC as unstable colorless
3
[
also longer than those of (Me Si) GeZnX and [(Me Si) -
(Me Si) Ge] Zn [3c,3d]. The bond length of Zn–O are
crystals with a composition of (Ph GeZnO) . The ger-
4
3
3
2
3
1
mylzinc oxide (2) was characterized by the H, and
13
C
NMR spectra. The germylzinc oxide (2) is first group
3
3
3
3
Ge] Zn [3c,3d].
2
We have previously reported on a molecular structure
of bis[tris(trimethylsilyl)germyl]zinc, [(Me Si) Ge] Zn
14 element-substituted zinc oxide. Four THF molecules
13
1
were included for a molecule 2 based on the H and
C
3
3
2
[
myl ligands, (Me Si) Ge, were bonded in a linear fash-
ion to the zinc atom and staggered with respect to
each other. The difference of these geometries are con-
sidered to be caused by steric repulsion between the
3c]. In [(Me Si) Ge] Zn, the two tris(trimethylsilyl)ger-
NMR data. The molecular structure of 2 was analyzed
by X-ray diffraction method. The molecular structure
of 2 is shown in Fig. 2. The selected bond lengths and
bond angles of 2 are summarized in Table 2. Crystallo-
graphic data of 2 are also summarized in Section 3.
Interestingly, germylzinc oxide (2) is tetrameric ger-
mylzinc oxide, and four zinc atoms and four oxygen
atoms make a distorted cubic center with Zn–O bond
3
3
2
3
3
bulky Ph Ge groups.
3
Bis(germyl)zinc (1) was easily oxidized in air to give
hexaphenyldigermoxane in high yield (Eq. (2)).
˚
length of 2.054 A (av). The distortion can be described
O2
1
!rt ðPh
3
GeÞ O
ð2Þ
2
in terms of an inward movement of the O atoms along
the threefold axes of the cube, resulting in Zn–O–Zn an-
gles >90ꢁ. The largest deviations from the tetrahedron
values are found for the angles at Zn. The bond angle
of Zn–O–Z and O–Zn–O is 95.69ꢁ (av) and 84.0ꢁ (av),
respectively. The bond length of Zn–O of 2 is larger than
A small amount of oxygen was added to bis(germyl)zinc
1) in C D at room temperature, and the oxidation
(
process of 1 was investigated by C NMR spectra.
6
6
1
3
˚
the 1.97 A obtained from the sum of the tetrahedral
˚
covalent radii and shorter than those (2.089–2.105 A)
of organozinc oxides such as (Me ZnO) [4] and Me -
2
4
14
Zn O [5]. The bond length of 2 is indeed in better agree-
7
8
˚
ment with Zn–O distances (2.04 A) complexes where Zn
is octahedrally coordinated [6]. The bond length of Zn–
˚
Ge is less than the sum (2.47 A) of the covalent radii [7].
This shortening may be explained by invoking hyper-
conjugation between Zn and Ge [4]. The bond length
˚
of Zn–Zn (3.042 A (av)) is also shorter than those of
˚
organozinc oxides (3.068–3.094 A) [4,5]. Four THF mol-
ecules are included in the crystal; however, no interac-
tion between the zinc atom and THF was observed
˚
(Zn–OTHF > 4.0 A). Molecular structures of organozinc
oxides (Me ZnO) and Me Zn O have cubic and dicu-
ban geometries, respectively.
Fig. 1. Molecular structure of 1. Hydrogen atoms are omitted for
clarity.
2
4
14
7
8

2954
M. Nanjo et al. / Journal of Organometallic Chemistry 690 (2005) 2952–2955
Fig. 2. Molecular structure of 2. Hydrogen atoms are omitted for clarity.
Table 2
The selected bond length (A) and bond angles (ꢁ) of (Ph
˚
3 4
GeOZn) (2)
Zn(1)–Ge(1)
Zn(1)–O*(1)
2.3759(7)
2.054(3)
Zn(1)–O(1)
Zn(1)–O**(1)
2.049(3)
2.059(3)
Ge(1)–Zn(1)–O(1)
129.10(9)
Ge(1)–Zn(1)–O*(1)
O(1)–Zn(1)–O*(1)
O*(1)–Zn(1)–O**(1)
Zn(1)–O(1)–Zn***(1)
128.03(9)
84.47(13)
83.70(12)
96.06(12)
Ge(1)–Zn(1)–O**(1)
O(1)–Zn(1)–O**(1)
Zn(1)–O(1)–Zn*(1)
Zn*(1)–O(1)–Zn***(1)
131.06(9)
83.85(13)
95.12(13)
95.88(13)
Addition of oxygen at room temperature for 10 h led
to complete decomposition of 2 with the formation of
by a SILICON graphics O with MAXUS. THF, diethyl ether
2
and other solvents were purified and dried as reported in
the literature.
(
Ph Ge) O quantitatively.
3 2
3
.2. Materials
3
. Experimental
Ph GeH [8], Et Zn [3c], and (Ph Ge) O [9] were pre-
3
2
3
2
3
.1. General methods
pared as reported in the literature.
The NMR spectra were obtained on a Varian Unity
3.3. Structural studies
Inova 400 MHz spectrometer. The GC-MS spectra were
measured on a JEOL JMS-DX 303 mass spectrometer.
Gas chromatography was performed on a Shimadzu
GC8A with a 1 m 20% SE30 column. X-ray crystallo-
graphic data and diffraction intensities were collected
on a MacScience DIP2030 diffractometer utilizing
Bis(germyl)zinc (1) and germylzinc oxide (2) could be
obtained in the form of crystals suitable for X-ray dif-
fraction studies. A single crystal was sealed in a capillary
glass tube for the collection. Diffraction data were col-
lected at 200 K on a MacScience DIP2030 image plate
diffraction employing graphite-monochromated Mo
˚
graphite-monochromated Mo Ka(k = 0.71073 A) radia-
tion. The structures were solved by direct methods using
the program system SIR-92. Refinement was performed
˚
Ka radiation (k = 0.71073 A). Crystallographic data
for 1 and 2 are listed in Table 3.

M. Nanjo et al. / Journal of Organometallic Chemistry 690 (2005) 2952–2955
2955
Table 3
Crystallographic data for 1 and 2
orless crystals were filtered off, and shown to be
Ph GeZnO) (4THF) (0.17 g, 0.09 mmol) in 18% yield
(
3
4
1
1
2
(based on the concentration of Et Zn). H NMR (d,
2
Formula
Molecular weight
C
817.41
44
H
46Ge
2
ZnO
2
C
457.36
22
H
23Ge
2
ZnO
2
C D ) 1.34–1.41 (m, 16H, THF), 3.48–3.56 (m, 16H,
6
6
1
3
THF), 7.31–7.39 (m, 24H), 7.62–7.68 (m, 24H);
C
3
Crystal size (mm )
Crystal system
Space group
0.35 · 0.30 · 0.25
Monoclinic
0.30 · 0.30 · 0.35
Tetragonal
NMR (d, C D ) 26.0 (THF), 67.9 (THF), 128.2, 128.7,
6
6
136.1, 143.2.
P2
1
/n
1
P-42 c
Unit cell dimensions
˚
3
.6. Reaction of bis(germyl)zinc oxide (1) with oxygen
a (A)
˚
10.0687(6)
19.408(1)
19.871(1)
101.408(3)
3806.5(4)
4
15.7770(5)
16.7830(2)
b (A)
˚
c (A)
A C D (0.6 ml) solution of bis(germyl)zinc (1) (0.08
6
6
b (ꢁ)
V (A )
mmol) was bubbled with a small amount of oxygen in an
NMR tube. After 10 h, the solvent was removed under
vaccum. Crude colorless crystals of (Ph Ge) O were ob-
˚
3
4177.5(1)
8
Z
3
2
˚
Radiation Mo Ka (k/A)
Temperature (K)
0.71070
200
1.426
0.71070
200
1.454
tained quantitatively.
ꢀ3
Dcalc (g cm
)
Unique reflections
Goodness-of-fit
R(I > 2r(I))
4964
0.926
2940
1.078
Acknowledgment
0.0300
0.0400
0.0435
0.1271 (all data)
wR
2
This work was supported by a Grant-in-aid for Scien-
tific Research (No. 11740344) from Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan.
3
.4. Preparation of bis(triphenylgermyl)zinc (Ph Ge) Zn
3 2
(
1)
Et Zn (0.5 ml, 0.5 mmol) in hexane reacted with two
2
References
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3
[
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6
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7
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3
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6
6
[
(
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(
(
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3
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4
(
(
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2
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3
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the solvent under vaccum, pentane (3 ml) was added
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