The formal conversion of SiOH protons into hydrides by germanium(II) species leads to the formation of the germanium(IV) hydride cluster [(RSiO 3GeH)4]

Article abstract of DOI:10.1002/anie.200460849

Germanium cubed: Addition of [Ge{N-(SiMe₃)₂} ₂] to a suspension of RSi(OH)₃ (R = (2,6-iPr ₂C₆H₃)N(SiMe₃)) in hexane/ THF affords the germanium siloxane 1 with terminal Ge-H units in good yield. Compound 1 contains a Ge₄O₁₂Si₄ cubic polyhedron core in which the corners of the cube are alternately occupied by germanium and silicon atoms. Each of the twelve edges of the cube contains one bridging oxygen atom.

Full text of DOI:10.1002/anie.200460849

Angewandte
Chemie
Cluster Compounds
The Formal Conversion of SiOH Protons into
Hydrides by Germanium(ii) Species Leads to the
Formation of the Germanium(iv) Hydride Cluster
[(RSiO3GeH)4]**
Umesh N. Nehete, Vadapalli Chandrasekhar,
Herbert W. Roesky,* and Jꢀrg Magull
Dedicated to Professor Manfred Meisel
on the occasion of his 65th birthday
We have been interested for some time in the synthesis and
characterization of metallosiloxanes containing the Si-O-M
motif[1] (M = main-group or transition-metal atom). Utilizing
the multifunctional N-bonded silanetriol RSi(OH)3 (R = (2,6-
iPr2C6H3)N(SiMe3)) we have successfully assembled
a
number of polyhedral metallosiloxanes with a high metal/
silicon ratio.[1] Many such compounds have been shown to be
structural models for complex, naturally occurring metall-
osilicates or synthetic metal-containing zeolites.[2] Some
compounds, such as [(RSiO3TiOR1)4] (R = (2,6-iPr2C6H3)N-
(SiMe3), R1 = Et, iPr)[3] have been shown to be catalysts for
the epoxidation of olefins.[4] Recently we have been intrigued
by the varied products obtained in the reaction of RSi(OH)3
with tin substrates. Thus, while tin(iv) reagents, such as
PhSnCl3, react with RSi(OH)3 to afford the cubic compound
[(RSiO3SnPh)4] or the bicyclic compound [(RSiO3)2-
(PhSn)3][5] analogous reaction with [Sn{N(SiMe3)2}2] proceeds
in an entirely different manner. The product of this reaction is
a hexatin(ii) assembly [(SnO)6(R2Si2O3)2] which is formed as a
result
of
an
in situ
generated
disiloxanetetrol
[(RSi(OH)2)2O].[6] In view of this unusual reactivity, it was
of interest to probe analogous germanium compounds. It is
also noted that only a handful of structurally characterized
compounds containing the Ge-O-Si linkage are known
[(Ph2Ge)2(Ph2Si)2O4],[7a] [(Me2Ge)2(Ph2Si)2O4],[7a] [(Cl2Ge)2-
(tBuSi)2O4],[7b] [(Et2Ge)2(Ph2Si)2O4],[7c] [(Ph2Ge)2(Ph2Si)2O3],[7d]
[(tBu2Ge)(Ph2Si){[(CH2)3NMe2]2Sn}O3].[7e] Herein, we report
the first polyhedral germanium siloxane [(RSiO3GeH)4] (R =
(2,6-iPr2C6H3)N(SiMe3)). This species also is the first example
of a Ge-O-Si containing compound with terminal functional
À
Ge H units. Although other Group 14 species, such as
[*] U. N. Nehete, Prof. Dr. H. W. Roesky, Prof. Dr. J. Magull
Institut fꢀr Anorganische Chemie
Universitꢁt Gꢂttingen
Tammannstrasse 4, 37077 Gꢂttingen (Germany)
Fax: (+49)551-393-373
E-mail: hroesky@gwdg.de
Prof. Dr. V. Chandrasekhar
Department of Chemistry
IIT-Kanpur, Kanpur-208 016 (India)
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Gꢂttinger Akademie der Wissenschaften. V.C. thanks the
Alexander von Humboldt Foundation, Bonn (Germany), for the
Friedrich Wilhelm Bessel Research Award. R=(2,6-iPr2C6H3)N-
(SiMe3).
Angew. Chem. Int. Ed. 2005, 44, 281 –284
DOI: 10.1002/anie.200460849
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281

Communications
[(HSiO3)4], are known,[8] the corresponding germanium or
germanium siloxane analogues have not been reported. The
synthesis of [(RSiO3GeH)4] also involves an unprecedented
be possible that first an oxidative addition of RSi(OH)3 to
[Ge{N(SiMe3)2}2] occurs with an elimination of H[N(SiMe3)2]
resulting in the formation of 1. Although oxidative addition
reactions are common in organometallic chemistry, we have
found no precedence for an oxidative addition reaction
involving the SiOH group. Moreover, during the course of this
reaction the proton of the SiOH group is formally converted
into a hydride.
À
oxidative addition of an SiO H bond to a germanium(ii)
center, which leads to the formal conversion of the OH proton
into a hydride. The oxidative addition of an alcohol to an
alkylgermanium(ii) compound is known.[9]
The reaction of the germanium(ii) amide[10] [Ge{N-
[11]
(SiMe3)2}2] with RSi(OH)3 in a 1:1 molar ratio afforded
Compound 1 crystallizes in the monoclinic space group
C2/c (Figure 1and Figure 2).
[(RSiO3GeH)4] (1) in about 64% yield (Scheme 1). The
The structure of 1 can be described as a polyhedral cubic
cage where the alternate corners of the cube are occupied by
germanium and silicon atoms. The edges of the cube contain
Scheme 1. Synthesis of compound 1.
Figure 1. Molecular structure of 1.
colorless crystals of 1 were obtained at room temperature
from its saturated solution in hexane. Compound 1 is soluble
in a large number of common organic solvents including
hydrocarbons such as hexane and pentane. Compound 1 has
been characterized by analytical, spectroscopic, and X-ray
crystallographic techniques (see Figures 1 and 2).[12] Com-
pound 1 is thermally quite stable and is also stable under the
conditions of the EI mass spectrometry. The EI-mass
spectrum of 1 shows the molecular ion peak at 1592.5
(100%) [M+].
À
The presence of the Ge H motif is also detected in the
1H NMR spectrum as a singlet at d = 5.83 ppm.[13] The 29Si
NMR spectrum shows a single resonance (d = À87.4 ppm) for
the core of 1 indicating the equivalence of the silicon atoms,
À
while the IR spectrum exhibits the characteristic Ge H
stretching frequency (n˜ = 2211, 2184 cmÀ1).[13] The formation
of 1 involves the oxidation of germanium(ii) to germani-
um(iv). We assume that the first step of the reaction involves
the intermediate [{RSi(OH)O2Ge}2] (1a; Scheme 1) which
can result from a condensation of the germanium amide with
the silanetriol. The next step is the fusion of two molecules of
1a through an intermolecular oxidative addition reaction of
Figure 2. Core structure of 1. The substituents on the silicon atoms
have been omitted for clarity. Selected bond lengths [ꢃ] and angles [8]:
Ge(1)-O(5A) 1.737(1), Ge(2)-O(6A) 1.738(1), Ge(1)-O(1) 1.740(1),
Ge(2)-O(2) 1.745(1), Ge(1)-O(4) 1.741(1), Ge(2)-O(3) 1.742(1), Ge(1)-
H(1) 1.40(2), Ge(2)-H(2) 1.38(2), Si(2)-O(6) 1.623(1), Si(2)-O(4)
1.623(2), Si(2)-O(3) 1.628(1), Si(1)-O(2) 1.620(2), Si(1)-O(5) 1.628(2),
Si(1)-O(1) 1.628(1); Si(2)-O(4)-Ge(1) 142.78(9), Si(1)-O(5)-Ge(1A)
142.55(10), Si(1)-O(1)-Ge(1) 140.74(9), Si(1)-O(2)-Ge(2) 142.52(9),
Si(2)-O(3)-Ge(2) 140.05(9), Si(2)-O(6)-Ge(2A) 142.55(9).
À
SiO H with germanium(ii) centers. Such a process leads to a
concomitant Ge-O-Si bond formation. Alternatively it may
282
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Angew. Chem. Int. Ed. 2005, 44, 281 –284

Angewandte
Chemie
Magull, Organometallics 2004, 23, 2251 – 2256; e) U. N. Nehete,
oxygen atoms which act as bridging atoms between germa-
nium and silicon. Each of the six-faces of the cube is made up
of a puckered eight-membered Ge2O4Si2 ring. The average
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Jancik, H. W. Roesky, R. Herbst-Irmer, Organometallics 2004,
23, 5372 – 5374.
À
À
À
bond lengths in 1 are Ge O 1.7405 ꢀ, Si O 1.625 ꢀ, and Ge
H (1.39 ꢀ). The Ge-O-Si bond angle (av. 141.868) indicates
the bent nature of this bond. In the eight-membered rings
[(Me2Ge)2(Ph2Si)2O4],[7a]
[(Cl2Ge)2(tBuSi)2O4],[7b]
and
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1.77(6) and 1.60(7), 1.69(4) and 1.63(4), 1.75(5) and
1.61(6) ꢀ, respectively. The Ge-O-Si bond angles observed
for these compounds are 136.9(3), 158.8(2), and 142.0(3)8.
These parameters compare well with those observed for 1.
À
À
À
The Ge H bond length in 1 (1.39(2) ꢀ) is similar to that in p-
anisylgermane (1.40 ꢀ).[13a]
In conclusion, we have prepared the first cubic polyhedral
cage compound that contains Ge-O-Si linkages. The forma-
tion of this compound occurs by an unprecedented oxidative
addition reaction involving the SiOH unit to a germanium(ii)
center.
Experimental Section
1: [Ge{N(SiMe3)2}2] (1.2 g, 3.06 mmol) was slowly added to a stirred
suspension of the silanetriol (1.0 g, 3.06 mmol) in hexane (20 mL) and
THF (3 mL). During the addition the milky suspension of silanetriol
changes to a colorless clear solution. This clear solution was stirred for
12 h at room temperature. The volatile components were removed
in vacuo to obtain a white product. To this hexane (9 mL) was added.
Colorless crystals of 1 were obtained from the concentrated solution
after two days at room temperature. Yield: 0.78 g (64%), m.p. 2518C
(decomp), 1H NMR (300 MHz, C6D6, TMS): d = 0.19 (s, 36H,
Si(CH3)3), 1.22, 1.24 (d, J = 6.85 Hz, 48H, CH(CH3)2), 3.55 (sept,
J = 6.85 Hz, 8H, CH(CH3)2), 5.83 (s, 4H, GeH), 7.04 ppm (s, 12H,
aromatic); 29Si NMR (99 MHz, C6D6, TMS): d = 6.55 (SiMe3),
À87.4 ppm (SiO3); IR (Nujol, KBr): n˜ = 2211 (m), 2184 (m, GeH),
1439 (m), 1318 (m), 1248 (s), 1183 (m), 1079 (s), 1045 (s), 1022 (s), 976
(s), 904 (s), 878 (m), 840 (s), 799 (s), 752 (s), 738 (s), 685 (w), 611 (m),
545 (m) cmÀ1; EIMS (70 eV): m/z (%) 1592.5 (100) [M+]; Elemental
analysis (%) calcd for C60H108Ge4N4O12Si8 (1592.58) C 45.25, H 6.84,
N 3.52; found: C 44.80, H 6.94, N 4.05.
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[12] Crystal data for compound 1 C60H108Ge4N4O12Si8, Mr = 1592.58,
monoclinic, space group C2/c, a = 26.4229(12), b = 12.5692(6),
c = 26.1702(12) ꢀ, a = 90, b = 112.945(4)8, V= 8003.8(6) ꢀ3, Z =
4, 1calcd = 1.322 mgmÀ3, F(000) = 3328, T= 133(2) K, m(MoKa) =
1.660 mmÀ1. The data was collected using the w scan mode in the
range of À31 ꢀ h ꢀ 31, À14 ꢀ k ꢀ 14, À30 ꢀ l ꢀ 30. Of 41571
reflections collected, 6890 were unique. Final R1 (I > 2s(I)) =
0.0252; wR2 (all data) = 0.0622. Maximum and minimum heights
Received: June 2, 2004
Keywords: cluster compounds · germanium · hydrides ·
.
oxidative addition · silicon
in the final Fourier difference map were 0.296 and À0.380 eAÀ3
.
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model with Uiso tied to the Uiso of the parent atoms. CCDC-
236577 (1) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB21EZ, UK; fax: (+ 44)1223-336-033; or deposit@
ccdc.cam.ac.uk).
Angew. Chem. Int. Ed. 2005, 44, 281 –284
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Communications
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Angew. Chem. Int. Ed. 2005, 44, 281 –284