Siloles and germoles modified by partial hypercoordination through aminoxy substituents

Article abstract of DOI:10.1039/a909547k

l-Dimethylaminoxy-2,3,4,5-tetraphenyl-l-silacyclopentadiene (i); l,2-bis(dimethylaminoxy)-2,3,4,5-tetraphenyl-l-silacyclopentadiene (2) and l,2-bis(dimethylaminoxy)-2,3,4,5-tetraphenyl-l-germacyclopentadiene (3) have been prepared by the reactions of the corresponding chloro-2,3,4,5-tetraphenyl-l-(sila/germa)cyclopentadienes with LiONMe₂. They are yellow crystalline materials, which have been identified by multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁵N, ¹⁷O,²⁹Si), mass spectrometry and elemental analysis. The UV-VIS spectra of 1,2 and 3 show the absorption bands of the silole/germole to be only slightly affected by the Si ... N interaction, which indicates that orbital interactions of the type lp(N)→σ*(SiC) do not play a significant role and thus the Si ... N attraction is better interpreted as a dipole interaction. The crystal structures of 2 and 3 reveal planar C₄Si and C₄Ge rings, with a propeller-like arrangement of the phenyl groups. The SiON and GeON groups contain short Si ... N distances [2.473(3) and 2.503(3) A in 2, and 2.535(7) to 2.608(7) A in 3]. 2 adopts a gauche-gauche conformation for the NOSiON backbone, while in 3, two independent molecules are found in the asymmetric unit, one with an anti-gauche conformation and one with a gauche-gauche conformation. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a909547k

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Siloles and germoles modified by partial hypercoordination through
aminoxy substituents
Udo Losehand and Norbert W. Mitzel*
Anorganisch-chemisches Institut, Technische Universität München, Lichtenbergstraße 4,
85747 Garching, Germany. E-mail: N.Mitzel@lrz.tum.de
Received 3rd December 1999, Accepted 8th February 2000
Published on the Web 7th March 2000
1-Dimethylaminoxy-2,3,4,5-tetraphenyl-1-silacyclopentadiene (1), 1,2-bis(dimethylaminoxy)-2,3,4,5-tetraphenyl-1-
silacyclopentadiene (2) and 1,2-bis(dimethylaminoxy)-2,3,4,5-tetraphenyl-1-germacyclopentadiene (3) have been
prepared by the reactions of the corresponding chloro-2,3,4,5-tetraphenyl-1-(sila/germa)cyclopentadienes with
LiONMe2. They are yellow crystalline materials, which have been identified by multinuclear NMR spectroscopy (1H,
13C, 15N, 17O, 29Si), mass spectrometry and elemental analysis. The UV–VIS spectra of 1, 2 and 3 show the absorption
bands of the silole/germole to be only slightly affected by the Si ؒ ؒ ؒ N interaction, which indicates that orbital
interactions of the type lp(N)→σ*(SiC) do not play a significant role and thus the Si ؒ ؒ ؒ N attraction is better
interpreted as a dipole interaction. The crystal structures of 2 and 3 reveal planar C4Si and C4Ge rings, with a
propeller-like arrangement of the phenyl groups. The SiON and GeON groups contain short Si ؒ ؒ ؒ N distances
[2.473(3) and 2.503(3) Å in 2, and 2.535(7) to 2.608(7) Å in 3]. 2 adopts a gauche-gauche conformation for the
NOSiON backbone, while in 3, two independent molecules are found in the asymmetric unit, one with an anti-gauche
conformation and one with a gauche-gauche conformation.
tronics of the silole and germole rings. The HOMO–LUMO
Introduction
gaps in the siloles and germoles give rise to absorptions in
Silacyclopentadienes, also known as siloles, are the subject of
the visible region of the spectrum, which makes UV–VIS
recent intensive investigations due to their interesting electronic
spectroscopy a valuable tool to evaluate the effect of this substi-
properties, which make them applicable for organic light-
tution and obtain more detailed information about the nature
emitting devices. The first prototypes of such devices, e.g.
of the E ؒ ؒ ؒ N secondary interactions. It should be mentioned
illuminated displays, have already been successfully demon-
that the synthesis of a partially hypercoordinate silole contain-
strated to function.1 At the moment, a number of groups are
involved in the development of π-conjugated silole polymers
because unique material properties can be expected, including
small band gaps, electroluminescent, non-linear optic and
ing an 8-dimethylaminonaphthyl substituent has already been
reported by Tamao and co-workers.11
thermochromic behaviour.2,3 The advantage of siloles as com-
pared to conventional π-conjugated polymers based on pyrrole,
furan, thiophene and pyridine units is their large electron affin-
ity caused by the energetically low-lying LUMO.4 The colour
(in general yellow to orange) of the siloles is a result of this
small HOMO–LUMO gap. The low energy level of the LUMO
has been attributed to the interaction between the butadiene π*-
orbital and the exocyclic σ*-orbitals of the silicon centre.2
We intended to modify the electronic properties of siloles and
germoles by binding ONR2 substituents to their group 14
atoms, E = Si and Ge, as compounds with SiON5 and GeON6
(and SnON)7 linkages are known to show attractive inter-
actions between the E and N centres. This has been demon-
strated for a series of compounds, whereby the strength of this
interaction (characterised by the Si ؒ ؒ ؒ N distances and Si–O–N
angles) ranges from predictably weak interactions in Me3-
SiONMe2 [gas; 2.566(8) Å, 107.9(6)Њ],6 H3SiONMe2 [2.453(1)
Å, 102.6(1)Њ]6 and Cl3SiONMe2 [2.437(av.) Å, 103.0(av.)Њ]8
through medium strength interactions in H2Si(ONMe2)2
[2.138(av.) Å, 95.2(av.)Њ]9 to very strong ones in ClH2SiONMe2
[anti conformer in the solid state; 2.028(1) Å, 79.7(1)Њ].9 Models
to rationalise these experimental facts include anomeric inter-
actions of the type lp(N)→σ*(Si–X), which promise to give an
observable effect on the electronic properties of siloles and
germoles if ONR2 substituents are bound to the Si and Ge
atoms. Alternative explanations for the Si ؒ ؒ ؒ N and Ge ؒ ؒ ؒ N
attractions are based on intermolecular dipole interactions,10
which should then lead to less pronounced changes in the elec-
Results
Preparation
The first synthesis of silycyclopentadiene12,13 was described in
1959. We have adapted the preparation methods developed by
Jutzi and Karl14 to generate our starting materials, 1-chloro-
2,3,4,5-tetraphenyl-1-silacyclopentadiene (chlorosilole), 1,1-
dichloro-2,3,4,5-tetraphenyl-1-silacyclopentadiene (dichloro-
silole) and -germacyclopentadiene (dichlorogermole), which
were subsequently reacted with LiONMe2 to give the desired
substituted siloles and germoles 1, 2 and 3 (Scheme 1). These
Scheme 1
DOI: 10.1039/a909547k
J. Chem. Soc., Dalton Trans., 2000, 1049–1052
This journal is © The Royal Society of Chemistry 2000
1049

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Table 1 UV–VIS Absorption maxima of pentane solutions of Ph4C4-
SiH(ONMe2) (1), Ph4C4Si(ONMe2)2 (2), Ph4C4Ge(ONMe2)2 (3) and
Ph4C4SiCl2
Absorption maxima/nm
λ1
λ2
Ph4C4SiH(ONMe2) 1
Ph4C4Si(ONMe2)2
Ph4C4Ge(ONMe2)2 3
Ph4C4SiCl2
375
372
367
378
244
244
234
231
2
Fig. 2 Crystal structure of Ph4C4Si(ONMe2)2 (2). The phenyl rings
are shown as wire models for clarity.
germole 3 (Table 1) with λ1 = 367 nm [λ1(1,1-dimethyltetra-
phenylgermole) = 348 nm, λ1(hexaphenylgermole) = 354 nm].
This is in variance with the small decrease in the π–π*-
transition energy with increasing substituent electronegativity,
as has been found in the siloles Me2(Me3Si)2C4SiX2 with
λ1(X = F) being 13 nm longer than λ1(X = H). It has thus
proven difficult to gauge the influence of the N-donor atom in a
β-position relative to the Si and Ge centres. For comparison,
Tamao’s partially hypercoordinate silole with an 8-dimethyl-
aminonaphthyl group bound to a Ph4C4SiMe silole silicon
atom11 does not show any difference in the position of the
absorption maximum from the corresponding purely four-
coordinate naphthyl compound without the dimethylamino
substituent. Partial hypercoordination at silicon thus seems not
to exert an observable effect on the π-system of siloles. This can
also be understood as an argument against the interpretation of
the Si ؒ ؒ ؒ N attraction in SiON compounds as a remote type of
negative hyperconjugation of the type lp(N)→Σσ*(SiX), as this
should lead to a change in the energetics of the silole π-system.
However, care should be taken to not over-interpret these
findings.
Fig. 1 UV–VIS Spectra of pentane solutions of Ph4C4SiH(ONMe2)
(1), Ph4C4Si(ONMe2)2 (2) and Ph4C4Ge(ONMe2)2 (3).
compounds are obtained as bright yellow crystalline powders,
which can be purified by recrystallisation from benzene–hexane
mixtures.
NMR spectroscopy
1
The identity of the compounds 1, 2 and 3 was proven by H,
13C, 15N, 17O and 29Si NMR spectroscopy, mass spectroscopy
and elemental analyses. The proton NMR spectra show multi-
plets for the phenyl protons and singlets for the methyl protons
of the Me2NO groups. A further singlet for the Si–H proton
is observed in the spectrum of 1. The signals in the aromatic
region of the 13C NMR spectra are similar to those of the
corresponding starting materials, with an additional signal for
the methyl groups of the Me2NO substituents appearing at
about 50 ppm. The 29Si NMR spectrum of 1 shows a doublet at
Crystal structures of Ph4C4Si(ONMe2)2 (2) and Ph4C4Ge-
(ONMe2)2 (3)
Ϫ15.9 ppm, while 2 gives rise to a singlet at Ϫ22.7 ppm. The 17
O
NMR signal of 2 appears at 19 ppm, which is 122 ppm to low
frequency relative to H2Si(ONMe2)2 (141 ppm) and possibly
indicates a dissimilar electronic situation at oxygen in these
two molecules. Despite repeated experiments under a variety of
conditions, we could not observe 17O NMR signals for 1 and 3.
The 15N NMR chemical shifts of both siloles 1 and 2 are found
at Ϫ242.0 ppm, which is in the established range found for
other aminoxysilanes. The resonance of 3 occurs at Ϫ256.8
ppm, which is between that of Cl2Ge(ONMe2)2 (Ϫ231.8 ppm)
and Me3GeONMe2 (Ϫ250.6 ppm).
Molecules of Ph4C4Si(ONMe2)2 (2) (Fig. 2) crystallise as
monomers together with half a formula unit of benzene in the
asymmetric unit. Selected bond lengths and angles for 2 are
listed in Table 2. They adopt an anti-gauche conformation for
their NOSiON skeletons. This conformation is somewhat dis-
torted with respect to an ideal anti-gauche conformation, as one
Me2NO group is positioned with an O–Si–O–N torsional angle
of 61.1(1)Њ, whereas the other adopts a torsion angle of
164.8(2)Њ, which is clearly distinct from the ideal value of 180Њ.
This deformation can be explained by the steric requirements of
the tetraphenylbutadiene part of the molecule, as one H atom
of the anti-Me2NO group is separated by only 2.415 Å from an
H atom of the neighbouring phenyl ring (Σ van der Waals radii
2.40 Å), which prevents a further closing up of these groups,
as would be required to adopt an O–Si–O–N torsional angle
of 180Њ. The related bis(N,N-dimethylaminoxy)silanes X2Si-
(ONMe2)2 (X = F, Cl) without sterically demanding ligands do
not show a corresponding distortion. Despite the different con-
formations of the Me2NOSi groups, the Si–O–N angles are
remarkably similar. By contrast, in ClH2Si–O–NMe2 a small
Si–O–N angle in the anti [87.1(9)Њ] and a larger Si–O–N angle in
the gauche conformer [104.7(11)Њ] was observed in the gas
phase.9 The partial hypercoordination at silicon in 2 is not as
pronounced as in Cl2Si(ONMe2)2 [Si–O–N 102.8(1) and
103.7(1)Њ],16 but stronger than in Me3SiONMe2 [107.9(6)Њ].7
UV–VIS spectra
In order to explore the electronic changes in the silole core,
UV–VIS spectra (Fig. 1) of the new compounds 1, 2 and 3
were recorded in pentane solution. They all show absorption
maxima in similar regions, with the germole 3 absorbing at
the shortest wavelength. For comparison, a spectrum of the
starting material Ph4C4SiCl2 was recorded under the same
conditions.
The absorption maxima (Table 1) of the two siloles 1 and 2 at
375 and 372 nm are assigned to the HOMO–LUMO transition
(π–π*) and appear at longer wavelengths than those of the
less electronegatively substituted compounds 1,1-dimethyltetra-
phenylsilole (λ1 = 351 nm)15 and hexaphenylsilole (λ1 = 365
nm13 or 360 nm15). This red-shift is also observed for the
1050
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Table 2 Selected geometry parameter values, as determined by low-temperature X-ray diffraction of Ph4C4Si(ONMe2)2 (2) and Ph4C4Ge(ONMe2)2
(3) single crystals. The values are listed in different columns to represent the different ONMe2 groups
Ph4C4Ge(ONMe2)2 (3)
Ph4C4Si(ONMe2)2 (2)
Molecule 1 (gauche-gauche)
Molecule 2 (anti-gauche)
Bond lengths (Å)
and angles (Њ)
O(1)N(1)Me2
O(2)N(2)Me2
O(1)N(1)Me2
O(2)N(2)Me2
O(1)N(1)Me2
O(2)N(2)Me2
E–O
E ؒ ؒ ؒ N
O–N
N–C1
N–C(2)
EON
O–N–C(1)
O–N–C(2)
O–E–C(40)
O–E–C(10)
τO–E–O–N
1.651(2)
2.473(3)
1.478(3)
1.457(3)
1.445(4)
104.3(1)
105.2(1)
105.4(1)
109.1(1)
113.6(1)
61.1(1)
1.654(2)
2.503(3)
1.481(2)
1.452(4)
1.452(4)
105.8(1)
104.8(1)
105.8(1)
115.0(1)
118.5(1)
164.8(2)
1.802(5)
2.568(7)
1.460(8)
1.448(11)
1.449(12)
103.4(4)
106.7(7)
105.0(7)
116.9(3)
114.5(3)
78.8(7)
1.776(5)
2.596(7)
1.472(7)
1.437(10)
1.475(10)
1.785(5)
2.535(7)
1.480(7)
1.455(8)
1.457(9)
101.5(4)
105.5(5)
103.7(5)
117.8(2)
115.2(2)
172.5(7)
1.789(5)
2.608(7)
1.468(8)
1.444(10)
1.457(9)
105.8(4)
105.5(4)
104.9(6)
104.1(6)
110.7(3)
115.0(2)
71.4(7)
105.1(6)
103.9(7)
108.9(2)
120.4(2)
57.6(7)
E–C(40)
E–C(10)
C(10)–C(20)
C(20)–C(30)
C(30)–C(40)
1.853(2)
1.858(3)
1.362(3)
1.512(4)
1.358(3)
1.928(7)
1.921(7)
1.932(7)
1.360(9)
1.543(8)
1.330(9)
1.926(7)
1.353(10)
1.518(9)
1.355(9)
O(1)–E–O(2)
C(40)–E–C(10)
106.3(1)
94.0(1)
107.6(2)
91.8(3)
102.7(2)
92.4(3)
Fig. 4 The C4Ge(ONC2)2 skeletons of the two independent molecules
in the asymmetric unit of the Ph4C4Ge(ONMe2)2 (3) crystal. The view
is along the local C2 axis of the germole ring.
Fig. 3 Crystal structure of one molecule of Ph4C4Ge(ONMe2)2 (3) in
the asymmetric unit. The phenyl rings are shown as wire models for
clarity.
On the basis of the presented results and earlier investi-
gations on hypercoordinate siloles we conclude that (partial)
hypercoordination of the Si and Ge atoms in siloles and
germoles does not affect the electronic structure of the silole
or germole rings significantly.
The geometry of the silole ring is very similar to that of
Tamao’s hypercoordinate silole11 and the bis-methylated silole
Ph4C4SiMe2.17 All these compounds show a propeller-like
arrangement of the phenyl groups.
Ph4C4Ge(ONMe2)2 (3) (Fig. 3) crystallises from hexane with
two independent molecules in the asymmetric unit. The geom-
etry of the germole ring and the orientation of the phenyl
groups is similar in both molecules, but the conformations of
the Ge(ONMe2)2 units are completely different (Fig. 4). One
molecule adopts an anti-gauche conformation, similar to that of
the silole 2, whereas the other features an almost C2 symmetric
gauche-gauche conformation. The distortion of the anti-gauche
conformer by repulsive H ؒ ؒ ؒ H contacts is less pronounced
than in the silole 2. Selected bond lengths and angles for 3 are
listed in Table 2. The GeON angle of the anti-Me2NOGe unit in
the germole 3 [anti-gauche conformer, 101.5(4)Њ] is smaller than
the respective Si–O–N angle in silole 2. All the other E–O–N
angles fall over a range of about 3Њ. The Ge–O–N angles in 3
are similar to those in the compound Cl2Ge(ONMe2)2 [Ge–O–
N 102.0(1), 102.0(1)Њ],16 but slightly smaller than in Me3-
GeONMe2 [108.9(7)Њ].6 The Si ؒ ؒ ؒ N and Ge ؒ ؒ ؒ N distances in
both compounds 2 and 3 are smaller than the sum of the
Bartell’s one-angle-radii18,19 for Si/Ge and N (2.69 and 2.72 Å),
which justifies the classification of these compounds as (4 ϩ 2)
coordinate.
Experimental
General
The syntheses were carried out using a standard Schlenk line
under a purified nitrogen gas atmosphere. All NMR spectra
were recorded at 21 ЊC on a Jeol JNM-LA400 spectrometer
in C6D6 solvent dried over K–Na alloy. 1,4-Dilithio-1,2,3,4-
tetraphenylbutadiene,20
1-chloro-2,3,4,5-tetraphenyl-1-sila-
cyclopentadiene, 1,1-dichloro-2,3,4,5-tetraphenyl-1-silacyclo-
pentadiene and 1,1-dichloro-2,3,4,5-tetraphenyl-1-germacyclo-
pentadiene were prepared according to or by adapting literature
procedures.14
1-(N,N-Dimethylaminoxy)-2,3,4,5-tetraphenyl-1-silacyclo-
pentadiene (1)
n-Butyllithium (0.2 g, 2.5 mmol, 1.7 M solution in hexane) was
added dropwise to a solution of N,N-dimethylhydroxylamine
(0.5 ml, 7 mmol) in pentane (25 ml) at Ϫ20 ЊC. The reaction
mixture was allowed to warm to ambient temperature and was
J. Chem. Soc., Dalton Trans., 2000, 1049–1052
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Table 3 Crystallographic data for compounds 2 and 3
ml, 14 mmol) in 25 ml pentane, 1,1-dichloro-2,3,4,5-tetra-
phenyl-1-germacyclopentadiene (1.49 g, 3 mmol) dissolved in
30 ml THF. Yield 60% (1.98 g, 3.6 mmol), yellow, hexagonally-
shaped crystals. 1H NMR: δ 2.54 (s, H3C), 6.84–7.58 (m, Ph-H).
13C{1H} NMR: δ 50.9 (CH3), 152.0, 139.2, 138.9, 132.7, 130.1,
129.9, 127.8, 127.7, 127.5, 126.5 (Ph-C/1-germacyclopenta-
diene-C). 15N{1H} NMR: δ Ϫ256.8 (s). MS(CI): m/z = 550
[Mϩ], 490 [Mϩ Ϫ ONMe2], 356 [C4Ph4ϩ], 178 [C2Ph2ϩ]. Analysis
for C32H32O2N2Ge (M = 549.2): calcd. C 69.98, H 5.87, N 5.10,
found C 66.82, H 6.40, N 4.66%.
Compound
2
3
Formula
Molecular mass
Crystal system
Space group
a/Å
b/Å
c/Å
C32H32N2O2Siؒ0.5C6H6 C32H32N2O2Ge
543.74
monoclinic
P21/n
12.547(2)
9.905(2)
549.19
triclinic
P1
12.399(4)
12.543(3)
19.955(3)
81.16(2),
84.37(2), 66.05(2)
2780.2(12)
4
1.133
143(2)
10945
10945
¯
24.461(4)
90, 96.91(1), 90
α, β, γ/Њ
Crystal structure determinations
V/Å3
Z
3017.9(9)
4
0.71073
158(2)
6509
Single crystals of 2 and 3 were mounted under inert perfluoro-
polyether on the goniometer of a CAD4 diffractometer. Details
of the data collection and refinement are listed in Table 3. The
structure solution was performed by direct methods, the
refinement based on F2 and carried out with the SHELXTL
5.01 program.21
µ(Mo-Kα)/mmϪ1
Temperature/K
Measured reflections
Independent reflections 6509
R1/wR2 0.0500, 0.1389
0.0659, 0.1825
CCDC reference number 186/1848.
See http://www.rsc.org/suppdata/dt/a9/a909547k/ for crystal-
lographic files in .cif format.
stirred for 1 h. The solvents were removed under reduced pres-
sure. The LiONMe2 formed was suspended in THF (20 ml) and
cooled to Ϫ196 ЊC. 1-Chloro-2,3,4,5-tetraphenyl-1-silacyclo-
pentadiene (1.2 g, 2.4 mmol) dissolved in THF (30 ml) was
added and the mixture allowed to warm to Ϫ96 ЊC (toluene–
liquid N2 slush). The mixture was stirred for 1 h and then slowly
warmed to ambient temperature. The THF was removed under
reduced pressure from the resulting yellow solution. The resi-
due was extracted with benzene and the solution filtered. The
benzene was removed by evaporation and a yellow powder
remained, which was further purified by recrystallisation from
benzene to yield 0.94 g (1.9 mmol, 78%) of 1. 1H NMR: δ 7.5–
6.5 (m, Ph-H), 5.78 (s, SiH) 2.48 (s, H3C). 13C{1H} NMR:
δ 155.0, 139.2, 138.9, 132.7, 130.1, 129.9, 127.8, 127.7, 127.5,
126.5 (Ph-C/1-silacyclopentadiene-C), 50.7 (CH3). 15N{1H}
Acknowledgements
This work was supported by the Bayerisches Staats-
ministerium für Wissenschaft, Forschung und Kunst
(Bayerischer Habilitationsförderpreis 1996 for N. W. M.), the
Deutsche Forschungsgemeinschaft, the Fonds der Chemischen
Industrie, the Leonhard-Lorenz-Stiftung and by Bayer AG
through a donation of N,N-dimethylhydroxylamine hydro-
chloride. We thank Dr G. Raudaschl-Sieber for measurement
of the UV–VIS spectra. Generous support from Prof. H.
Schmidbaur (Garching) is gratefully acknowledged.
1
NMR: δ Ϫ242 (s). 29Si{1H} NMR: δ Ϫ15.9 (d, JSiH = 226.4
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Madison, WI, 1995.
1,1-Bis(N,N-dimethylaminoxy)-2,3,4,5-tetraphenyl-1-silacyclo-
pentadiene (2)
n-Butyllithium (0.9 g, 14 mmol, 1.7 M in hexane) was added
dropwise to a solution of N,N-dimethylhydroxylamine (1.0 ml,
14 mmol, 0.86 g) in pentane (25 ml) at Ϫ20 ЊC. The mixture was
warmed to ambient temperature, stirred for 1 h and the solvents
were removed under reduced pressure to yield LiONMe2. This
solid was suspended in THF (20 ml) and cooled to Ϫ196 ЊC.
1,1-Dichloro-2,3,4,5-tetraphenyl-1-silacyclopentadiene (3.16 g,
6.9 mmol) dissolved in THF (50 ml) was added, the resulting
mixture stirred for 1 h at Ϫ96 ЊC (toluene–liquid N2 slush) and
the THF removed under vacuum. The product was extracted
with benzene, the resulting yellow solution filtered and the
benzene removed in vacuo to yield microcrystalline 2, which
was further purified by recrystallisation from benzene–hexane
(50:50) to yield 2.9 g of pure 2ؒ0.5C6H6 (5.7 mmol, 83%) as
bright yellow, hexagonally-shaped crystals. 1H NMR: δ 7.5–6.5
(m, Ph-H), 2.48 (s, H3C). 13C{1H} NMR: δ 155.0, 139.2, 138.9,
132.7, 130.1, 129.9, 127.8, 127.7, 127.5, 126.5 (Ph-C/1-silacyclo-
pentadiene-C), 50.7 (CH3). 15N{1H} NMR: δ Ϫ242.0 (s). 17O
NMR: δ 19 (s). 29Si{1H} NMR: δ Ϫ22.7. MS(CI): m/z = 504
[Mϩ], 461 [Mϩ Ϫ NMe2], 444 [Mϩ Ϫ ONMe2], 418 [Mϩ Ϫ
2NMe2], 356 [C4Ph4ϩ], 266 [C3Ph3ϩ], 178 [C2Ph2ϩ]. Analysis for
C32H32O2N2Siؒ0.5C6H6 (M = 543.74): calcd. C 77.31, H 6.49, N
5.15: found C 75.57, H 6.58, N 4.55%.
1,1-Bis(N,N-dimethylaminoxy)-2,3,4,5-tetraphenyl-1-germa-
cyclopentadiene (3)
The procedure is analogous to the preparation of 2, with the
following quantities of reagents employed: n-butyllithium (0.4
g, 6 mmol, 1.7 M in hexane), N,N-dimethylhydroxylamine (1.0
Paper a909547k
1052
J. Chem. Soc., Dalton Trans., 2000, 1049–1052