Synthesis and structural diversity of oligosilanylzinc compounds

Article abstract of DOI:10.1039/b910463a

Reactions of potassium oligosilanyls with ZnCl₂ lead to the formation of oligosilanylzinc compounds with zinc's coordination sphere expanded by ligation of TMEDA, an additional oligosilanyl group, or a chloride ion. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b910463a

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Synthesis and structural diversity of oligosilanylzinc compounds†
Walter Gaderbauer, Istvan Balatoni, Harald Wagner, Judith Baumgartner* and Christoph Marschner*
Received 28th May 2009, Accepted 26th October 2009
First published as an Advance Article on the web 10th December 2009
DOI: 10.1039/b910463a
Reactions of potassium oligosilanyls with ZnCl2 lead to the formation of oligosilanylzinc compounds
with zinc’s coordination sphere expanded by ligation of TMEDA, an additional oligosilanyl group, or a
chloride ion.
Several of the obtained oligosilanylmagnesium compounds were
Introduction
characterised by X-ray crystallography. For structural comparison
Organozinc compounds date back almost to the birth of
a study of related divalent zinc compounds therefore was tempting.
organometallic chemistry. Frankland’s reaction of ethyl iodide
It is known that reactions of bulky oligosilanyllithium com-
with zinc can in fact be considered as the starting signal
pounds with one equiv zinc halide lead to the selective formation
for the development of the field.1 Right from the beginning
organozinc compounds were recognised as useful reagents for
synthetic purposes. Although they lost some of their importance to
organomagnesium and later organolithium reagents they always
occupied some space in the toolbox of the synthetic chemist. In
more recent times zincates have become of interest for metalation2
reactions and transmetalations such as in the Negishi coupling.3
The development of silicon congeners of organozinc com-
pounds occurred with some delay.4 Only in 1963 Egon Wiberg
reported the synthesis of triphenylsilylpotassium in liquid am-
monia and its subsequent reaction with zinc chloride to give
bis(triphenylsilyl)zinc.5 In 1979 Ro¨sch described the synthe-
sis of bis(trimethylsilyl)zinc,6 followed by Tilley’s synthesis of
bis[tris(trimethylsilyl)silyl]zinc in 1987.7,8 In the late 1990s, Nils
Wiberg published a number of studies on silylzinc compounds
with very bulky silyl groups.9 Most recently, Mochida10 and
Xue11 continued the organometallic work on silylzinc compounds.
Tilley7 and later Klein et al.12 reported facile adduct formation of
disilylzinc compounds with Lewis bases.
of oligosilanylzinc halides, which are either dimeric10 or ligated
with additional donor ligands12 in the solid state. In the dimeric
structures halide atoms were found to bridge the zinc atoms which
are coordinated by additional THF molecules.10 In the presence of
stronger bases such as trimethylphosphane monomeric structures
were found.12 Zinc atoms in these compounds are tetrahedrally
coordinated.
In the presence of TMEDA, which facilitates formation of
oligosilanyl anions,16 the reaction of equimolar amounts of
tris(trimethylsilyl)silylpotassium (1) and zinc chloride yielded a
TMEDA complexed monomeric oligosilanylzinc chloride (1a)
(Scheme 1).
This short overview only mentioned defined and well char-
acterised organosilylzinc compounds, it did not provide an im-
pression of the huge popularity which organosilylzinc compounds
enjoy as silyl transfer reagents.13 However, most of these reagents
are poorly characterised and usually prepared in situ by reaction
of silyl anions either with zinc halides or organozinc compounds.
The knowledge about structural features of silylzinc compounds
is therefore surprisingly scarce.
Scheme 1 Synthesis of tris(trimethylsilyl)silylzinc chloride·TMEDA (1a).
In analogy to Tilley’s reaction of two equiv tris(trimethylsilyl)-
silyllithium with zinc chloride,7 we found tris(trimethylsilyl)-
silylpotassium reacting in the same way to give the known
bis[tris(trimethylsilyl)silyl]zinc (1b). Compound 1b exhibits a lin-
ear Si–Zn–Si arrangement. To probe whether oligosilanyl anions
larger than the tris(trimethylsilyl)silanide would undergo the same
reaction, zinc chloride was reacted with two equiv of the larger
oligosilanylpotassium compounds 2, 3, and 4. The obtained
compounds 2a, 3a, and 4a all resembled the structure of 1b with
linear Si–Zn–Si arrangements (Scheme 2).
Reaction of zinc chloride with the sterically less encumbered
trisilanylpotassium compound 5 showed the formation of the
tris(oligosilanyl)zincate 5a (Scheme 3).17 Interestingly, the for-
mation of 5a occurred regardless of the stoichiometry of the
reaction. A similar structural motif was observed previously by
Xue and co-workers in their reaction of an oligosilanyl dianion
with zinc chloride.11 This result indicates that the formation of
threefold silylated zincates is not connected to the bidentate nature
of the involved silyl groups. The formation of 5a right from
Results and discussion
Synthesis
As part of our studies concerning the chemistry of oligosilanyl
anions14 we recently reported reactions of oligosilanylpotassium
compounds with magnesium halides and Grignard reagents.15
Institut fu¨r Anorganische Chemie, Technische Universita¨t Graz, Stremayr-
gasse 16, 8010, Graz, Austria. E-mail: baumgartner@tugraz.at, christoph.
marschner@tugraz.at; Fax: 0043 316 873 8701; Tel: 0043 316 873 8209
† Electronic supplementary information (ESI) available: CCDC reference
numbers 645719–645723. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b910463a
1598 | Dalton Trans., 2010, 39, 1598–1603
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Scheme 2 Synthesis of bis(oligosilanyl)zinc compounds.
Scheme 5 Dimeric structure of 7a with bridging chloride ion.
Scheme 3 Tris(2-heptamethyltrisilanyl)zincate formation.
Scheme 6 Formation of chloride bridged dimeric structure 8a (major
isomer drawn).
the beginning of the reaction implies that silylzinc species with
reasonably small (smaller than (Me3Si)3Si and Ph3Si) silyl groups,
and in the absence of strong donor molecules exist preferentially
as zincates.18 Considering the fact that even tetrasilylated zinc
compounds are known this is not completely unexpected.19
To avoid the linear Si–Zn–Si arrangement we considered
reactions of zinc chloride with various oligosilanyl dianions in
order to obtain cyclic compounds. Xue’s reaction of an alkylene
bridged dianion11 and our recently reported reaction of a 1,1¢-
bis(trisilanylpotassium)ferrocene with zinc chloride giving a disi-
lylzinc etherate20 seemed to support this assumption. Accordingly,
we found the conversion of the dipotassium polysilane 6,21 with
zinc chloride to give zincate 6a (Scheme 4) featuring a five-
membered ring containing a zinc atom coordinated by a chloride
ion.22
X-ray crystallography
A number of known silylzinc compounds were structurally
characterised. Donor-free bis-silylated zinc compounds fre-
quently show a linear coordination geometry as was found
for bis(tri-tert-butylsilyl)-,9e bis[bis(tri-tert-butylsilyl)silyl]-,9b and
bis[tris(trimethylsilyl)silyl]zinc.7 If donors such as bipy are present,
the geometry around zinc changes to tetrahedral. In cases of
monosilylated zinc halides the halide usually serves as a Lewis base
donor to a neighbouring molecule. In the presence of additional
donors such as THF, dimeric structures can be formed.10a In
the absence of other donors tetramerisation to a cubane type
structure was observed.9e A single example of a trisilylated trigonal
coordinated zincate was reported.11
Compound 1a (Fig. 1) crystallised with an additional molecule
of toluene in the asymmetric unit. Its Si–Zn bond length is
˚
˚
2.3671(13) A, only slightly longer than the 2.3537(9) A observed
10
for [(Me3Si)3SiZnCl]2·(THF)2 and comparable to the distance
Scheme 4 Formation of the cyclic zincate 6a.
The expectation that the 1,3-dipotassium compound 721 would
yield an analogous four-membered ring, similar to that observed
with group 4 metallocene dichlorides,21,23 was not met. Instead
a dimeric structure with an eight-membered ring bridged by a
chloride ion (7a), which coordinates to the two zinc atoms, was
formed (Scheme 5).17 This structural motif allows the zinc to avoid
the acute Si–Zn–Si angle of about 90◦.
Reaction of the novel cyclic dianion 8 with zinc chloride led
to a structure (8a) related to 7a (Scheme 6). However, for the
formation of 8a there are a number of different isomers possible.
Accordingly, the 29Si NMR spectrum of the reaction solution
indicated a mixture of one major and two minor by-products from
which the main product could be isolated by crystallisation.
Fig. 1 Crystal structure of tris(trimethylsilyl)silylzinc chloride·TMEDA
1a.
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Fig. 2 Crystal structure of 2a.
Fig. 3 Crystal structure of 3a.
Fig. 4 Polymeric chain-like arrangement of 6a in the solid state.
of 2.3652(12) A found for [(Me3Si)2PhSiZnCl]2·(THF)2.10 In these
and 3a (2.387(2), 2.388(2) A) reflect the higher steric demand
˚
˚
˚
dimeric complexes, however, the Zn–Cl bond lengths are substan-
of the larger oligosilanyl groups compared to 2.342(4) A for
[(Me3Si)3Si]2Zn.7 Also Si–Si bond lengths are increased (from
2.34/2.35 A for 1b to 2.35–2.37 A for 3a and 2.37–2.38 A
for 2a).
Compound 6a (Fig. 4 and 5) crystallises with an additional
molecule of 18-crown-6 in the asymmetric unit. The presence of
this crown ether possibly facilitates the ion pair separation of 6a as
[K·18-crown-6][ClZn{Si(SiMe3)2SiMe2}2]. The compound can be
interpreted as the KCl adduct of the neutral zincacyclopentasilane
where the chloride ion serves as a donor to the zinc. The Zn–Cl
˚
˚
tially longer (2.36–2.40 A) than in compound 1a (2.2769(11) A).
Such elongation is frequently found for bridging halides.
The compounds in this study belonging to the structure type
(R3Si)2Zn follow the outlined trend to display linear coordination
geometry.
Crystal structure analyses of 2a (Fig. 2) and 3a (Fig. 3) show
nearly linear Si–Zn–Si arrangements. Si–Zn bond lengths of
2a (with two crystallographically independent molecules in the
7
˚
˚
˚
˚
asymmetric unit: 2.4028(15), 2.4066(15), 2.4060(15), 2.4058(15) A)
1600 | Dalton Trans., 2010, 39, 1598–1603
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Table 1 29Si-NMR shifts (in ppm) of reported and some related
compounds
Compound
SiZn
ZnSiSiMe3 SiMe2 and other Si
1a
-156.8
-123.9
-150.8
-149.9
-125.8
-122.3
-122.9
-8.0
-7.2
-6.6
-7.7
-7.7
-8.5
-7.4
7
1bRef.
1b·bpyRef.
7
1a Br·2THF
2a
3a
4a
-129.3
-9.8; -25.7; -103.4;
-9.8; -24.4; -34.7;
-129.8
5a
-97.4
-10.8
Zn2{[(Me3Si)2SiCH2]2}3
Ref. 11
[K·18-crown-6]2
-85.2/-87.3 -10.0
{Fe[CpSi(SiMe3)2]2}Zn· -92.2
-11.0
Et2ORef.
20
6a
7a
8a
-152.1
-123.2
-125.0
-6.3
-7.4
-5.6
-26.6
-26.6
Fig. 5 Anionic part of the crystal structure of 6a.
-21.5/-25.6
˚
˚
bond is rather short (2.2701(11) A) and in the range of a covalent
While the Zn–Cl distances of 8a (2.4686(19) and 2.454(2) A)
˚
Zn–Cl bond such as in 1a (2.2769(11) A). The environment around
are substantially longer compared to 6a, the Si–Zn bond lengths
are slightly reduced (2.3783(19), 2.3881(19), 2.3871(19), and
Zn is distorted trigonal with the sum of angles around Zn being
357.64(4)◦. Si–Zn bond lengths are slightly elongated [2.3995(10)
˚
2.4075(19) A).
In contrast to 6a where the Si–Zn–Si angle of 115.58(4)◦ is close
to the expected 120◦ for trigonal geometry, the angles for 8a are
154.92(7)◦ and 149.37(7)◦ resulting from distortion of the linear
arrangement by the coordination of the chloride ion.
˚
and 2.4166(11) A] as was also observed previously for Xue’s
trisilylated Zn.11 The packing plot of compound 6a (Fig. 4) reveals
that the additional crown ether molecule bridges two K·18-crown-
6 units in a way that it provides additional coordination sites for
both potassium atoms. Additional interactions of the potassium
ions can be observed with C–H bonds of trimethylsilyl groups.
Considering these interactions compound 6a forms a coordination
polymer in the solid state (Fig. 4).
NMR spectroscopy
29Si-NMR spectra of the oligosilanylzinc compounds are quite
significant (see Table 1). The effect of Lewis bases coordinating
to the Zn atoms is profound. The chemical shifts of compounds
of the type [(R3Si)3Si]2Zn (1b, 2a, 3a, 4a) are typically around
-124 ppm, a region also typical for tetrasilylated silanes. The
addition of a donor such as bipy, THF, or TMEDA effects a change
of geometry around Zn, resulting in upfield shifts of about 30 ppm.
This shift is similar but less pronounced to what is observed
for trisilylated silyl magnesium compounds.15 Considering this
picture, compound 6a with the strong upfield shift behaves rather
like a donor adduct (d = -152.1 ppm), while 7a (-123.2 ppm) and
8a (-125.0 ppm), displaying a more linear Si–Zn–Si geometry,
exhibit NMR properties resembling donor free compounds. The
trisilylated compounds 5a and Zn2{[(Me3Si)2SiCH2]2}3·[K·18-
The structure of 8a (Fig. 6) shows again a zincate but the
position of the donor chloride ion is different. From the mixtures
of isomers observed by NMR spectroscopy only one type of crystal
was obtained. The isomer in this crystal features both bridging
dimethylsilylene groups on the same side of the molecule with the
chloride ion acting as a bridging donor to both Zn atoms on the
opposite side.
crown-6]2 as well as {Fe[CpSi(SiMe3)2]2}Zn·Et2O20 also follow
11
the outlined trend.
Conclusions
A number of oligosilanylzinc compound were prepared by reac-
tions of oligosilanyl mono- and dipotassium compounds with zinc
chloride. Using larger oligosilanyl residues a preference for the
formation of disilylated zinc with a linear coordination geometry
was observed. The use of oligosilanyl dianions prevented the
formation of linear Si–Zn–Si arrangements. The more accessible
Zn atoms therefore showed a tendency to accommodate a chloride
ion in their coordination sphere. In order to avoid very acute Si–
Zn–Si angles a dimerisation of bis-silylated zinc compounds was
observed, which leads to a distorted linear Si–Zn–Si arrangement
with chloride ions serving both Zn atoms as a Lewis base.
Fig. 6 Anionic part of the crystal structure of 8a.
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Similar compounds having two tin, aluminium, or gallium
atoms were studied recently as chelating Lewis acids with promis-
ing properties as phase transfer catalysts, anion receptors and
other applications.24 Similar potentiality of compounds like 7a
and 8a with respect to this remains to be studied.
General procedure A for the synthesis of oligosilanylzinc
compounds
To a solution of the respective polysilane in THF was added potas-
sium tert-butoxide (1 equiv). The reaction solution usually turned
yellow immediately and was stirred at room temperature until
complete conversion monitored by 29Si-NMR spectroscopy was
achieved. An equivalent amount of ZnCl2 (previously dissolved in
THF) was added slowly and after stirring for 30 min the precipitate
was removed by filtration and the solvent removed in vacuum.
Crystallisation was achieved from toluene at low temperature
(-35 ◦C).
Experimental
General remarks
All reactions involving air-sensitive compounds were carried
out under an atmosphere of dry nitrogen or argon using ei-
ther Schlenk techniques or a glove box. All solvents besides
CDCl3 were dried over sodium/potassium alloy under nitro-
gen and were freshly distilled prior to use. Potassium tert-
butanolate was purchased from Merck. All other chemicals were
bought from different suppliers and were used without further
purification.
1H (300 MHz), 13C (75.4 MHz), and 29Si (59.3 MHz) NMR
spectra were recorded on a Varian INOVA 300 spectrometer.
Samples were either dissolved in a deuterated solvent, or measured
with a D2O capillary in order to provide an external lock frequency
signal. To compensate for the low isotopic abundance of 29Si
the INEPT pulse sequence was used for amplification of the
signal.25
General procedure B for the synthesis of oligosilanylzinc
compounds in the presence of 18-crown-6
To a solution of the respective silane in THF–benzene (1 : 1)
potassium tert-butoxide (2.1 equiv) and 18-crown-6 (2.1 equiv)
was added. The reaction was stirred at room temperature until
complete conversion, monitored by 29Si-NMR spectroscopy, was
achieved. An equivalent amount of ZnCl2 was added and after
stirring for 30 min the precipitate was removed by filtration and
the solvent removed in vacuum. Crystallisation was achieved from
mixtures of toluene and a minimum of THF at -35 ◦C.
NMR spectroscopic data
Bis[1,1,1,2,2-pentakis(trimethylsilyl)disilanyl]zinc (2a) (method
A). 29Si-NMR (D2O-capillary, d ppm): -7.7; -9.7; -125.8; -
X-Ray structure determination
1
-129.3. 13C (C6D6, d ppm): 5.9; 4.0. H (C6D6, d ppm): 0.56 (s,
For X-ray structure analyses the crystals were mounted onto
the tip of glass fibres, and data collection was performed
with a Bruker-AXS SMART APEX CCD diffractometer using
18H); 0.50 (s, 27H).
Bis[1,1,1,3,3-pentakis(trimethylsilyl)-2,2-dimethyltrisilanyl]zinc
(3a) (method A). 29Si-NMR (D2O-capillary, d ppm): -8.5; -9.8;
-25.7; -103.4; -122.3. 13C (D2O-capillary, d ppm): 8.6; 5.5; 3.7. 1H
(D2O-capillary, d ppm): 0.70 (s, 6H); 0.38 (s, 18H); 0.24 (s, 27H).
˚
graphite-monochromated Mo-Ka radiation (0.71073 A). The
2
data were reduced to Fo and corrected for absorption effects
with SAINT26 and SADABS,27 respectively. The structures were
solved by direct methods and refined by a full-matrix least-squares
method (SHELXL97).28 If not noted otherwise all non-hydrogen
atoms were refined with anisotropic displacement parameters. All
hydrogen atoms were located at calculated positions to correspond
to standard bond lengths and angles. All diagrams were drawn with
30% probability thermal ellipsoids and all hydrogen atoms were
omitted for clarity. Unfortunately the obtained crystal quality of
some substances was poor. This fact is reflected by quite high R
and low theta values.
Bis[1,1,1,4,4-pentakis(trimethylsilyl)-2,2,3,3-tetramethyltetra-
silanyl]zinc (4a) (method A). 29Si-NMR (D2O-capillary, d ppm):
-7.4; -9.8; -24.4; -34.7; -122.9; -129.8. 13C (C6D6, d ppm): 5.2;
3.4; 2.7; 2.5. 1H (C6D6, d ppm): 0.50 (s, 6H); 0.48 (s, 6H); 0.33 (s,
18H); 0.22 (s, 27H).
Tris[methylbis(trimethylsilyl)silyl]zincat·K·(THF)4 (5a) (method
A). 29Si-NMR (D2O-capillary, d ppm): -10.8; -97.4. 13C (D2O-
capillary, d ppm): 68.1, 25.6, 0.7; -12.3. 1H (D2O-capillary, d ppm):
3.69 (m, 16H), 1.81 (m, 16H), 0.11 (s, 18H); 0.09 (s, 3H).
Chloro-2,2,5,5-tetrakis(trimethylsilyl)-3,3,4,4,-tetramethylcy-
clopentasilanylzincat·K·(18-crown-6)1.5 (6a) (method B). 29Si-
NMR (C6D6, d ppm): -6.3; -26.6; -152.1. 13C (C6D6, d ppm):
70.8; 5.4; -0.4. H (C6D6, d ppm): 3.45 (s, 36H); 0.73 (m, 12H);
0.55 (s, 36H).
Tris[(trimethylsilyl)silyl]zinc chloride·TMEDA (1a)
To a solution of the tetrakis(trimethylsilyl)silane in toluene (5 mL)
potassium tert-butoxide (1.02 equiv) and tetramethylethylenedi-
amine (3 equiv) were added. The solution was stirred for 5 d
and turned yellow. Completeness of conversion was controlled by
NMR before the solvent was removed in vacuum. The residue
was dissolved in toluene and ZnCl2 (0.51 equiv) was added. After
stirring for 60 min the precipitate was removed by filtration and
the solvent removed in vacuum. C◦rystallisation was achieved by
cooling a pentane solution to -70 C. 29Si-NMR (D2O-capillary,
d ppm): -8.0; -156.8. 13C (D2O-capillary, d ppm): 58.5; 46.2;
1
Compound 7a (method B). 29Si-NMR (D2O-capillary, d ppm):
-7.4; -26.6; -123.2. 13C (D2O-capillary, d ppm): 70.8; 7.0; 5.5. 1H
(pentane, D2O-capillary, d ppm): 3.67 (s, 36H); 0.64 (s, 6H); 0.36
(s, 36H).
1,3-Dipotassium-1,3-bis(trimethylsilyl)hexamethylcyclopenta-
silane·(18-crown-6)2 (8). 29Si-NMR (C6D6, d ppm): -3.8; -5.4;
1
1
4.7. H (D2O-capillary, d ppm): 2.60 (s, 4H); 2.44 (s, 9H); 0.55
-11.3; -178.4. 13C (C6D6, d ppm): 70.6; 14.2; 9.0; 4.6. H (C6D6,
(s, 27H).
d ppm): 3.34 (s, 48H); 0.99 (s, 6H); 0.87 (s, 12H); 0.75 (s, 18H).
1602 | Dalton Trans., 2010, 39, 1598–1603
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Compound 8a (method B). 29Si-NMR (C6H6, D2O-capillary,
d ppm): -5.6; -21.5; -25.6; -125.0. 1H (toluene-d8, THF, d ppm):
3.50 (s, 36H); 0.89 (s, 12H); 0.78 (s, 6H); 0.76 (s, 6H); 071 (s, 12H);
0.67 (s, 36H).
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1986, 119, 1581; (t) Y. Morizawa, H. Oda, K. Oshima and H. Nozaki,
Tetrahedron Lett., 1984, 25, 1163.
100 K; R1 = 0.064 and 0.085, (wR2 = 0.165 and 0.176) for 5225
unique measured reflections. CCDC 645719.
C60H180Si28Zn2 2a: monoclinic, P21/c (no. 14), a = 38.527(8), b =
◦
3
˚
˚
15.157(3), c = 19.744(4) A, b = 91.62(3) , V = 11525(4) A , Z =
4, Dc = 1.049 g cm-3, m = 0.736 mm-1 (Mo-Ka, l = 0.71073 A),
˚
T = 100 K; R1 = 0.075 and 0.089, (wR2 = 0.145 and 0.151) for
19158 unique measured reflections. CCDC 645722.
C34H102Si16Zn 3a: monoclinic, P21/n (no. 14), a = 16.261(3), b =
◦
3
˚
˚
9.6806(19), c = 41.968(8) A, b = 100.33(3) , V = 6499(2) A , Z =
4, Dc = 1.048 g cm-3, m = 0.694 mm-1 (Mo-Ka, l = 0.71073 A),
˚
T = 100 K; R1 = 0.096 and 0.107, (wR2 = 0.184 and 0.189) for
8501 unique measured reflections. CCDC 645723.
C34H84ClKO9Si8Zn 6a: monoclinic, P21/c (no. 14), a =
◦
˚
17.580(4), b = 9.934(2), c = 32.951(7) A, b = 92.20(3) , V =
3
-3
-1
˚
5750(2) A , Z = 4, Dc = 1.157 g cm , m = 0.753 mm (Mo-Ka,
˚
l = 0.71073 A), T = 100 K; R1 = 0.055 and 0.083, (wR2 = 0.147
and 0.157) for 11733 unique measured reflections. CCDC 645720.
¯
Zn2ClKSi14O12C51H123 8a: triclinic, P1 (no. 2), a = 12.652(3),
˚
3
b = 16.971(3), c = 21.022(4) A, a = 98.67(3), b = 105.65(3),
◦
-3
˚
g = 100.28(3) , V = 4181(2) A , Z = 2, Dc = 1.213 g cm , m =
0.901 mm-1 (Mo-Ka, l = 0.71073 A), T = 100 K; R1 = 0.071
˚
14 For a recent overview on the polysilyl anion chemistry from our
laboratory see: C. Marschner, Organometallics, 2006, 25, 2110.
15 W. Gaderbauer, M. Zirngast, J. Baumgartner, C. Marschner and T. D.
Tilley, Organometallics, 2006, 25, 2599.
and 0.171, (wR2 = 0.139 and 0.170) for 16748 unique measured
reflections. CCDC 645721.
16 D. Frank, J. Baumgartner and C. Marschner, Chem. Commun., 2002,
1190.
Acknowledgements
17 Structural assignments of 5a and 7a are based on low quality crystal
structures and multinuclear NMR spectroscopy.
18 The only known compound of the type (R3Si)2Zn with rather small
silyl ligands and no additional donors is (Me3Si)2Zn (cf. Ref. 6). As
the compound was prepared by the reaction of LiAl(SiMe3)4 it can be
imagined that the silyl transfer reagent is not basic enough to allow for
a third addition to the zinc compound.
This study was supported by the Austrian Fonds zur Fo¨rderung
der Wissenschaften (FWF) via the projects Y-120, P-18538 and
P-19338.
19 S. Nakamura, M. Uchiyama and T. Ohwada, J. Am. Chem. Soc., 2004,
Notes and references
126, 11146.
1 For an exciting account on the early days of organometallic chemistry
see: Dietmar Seyferth’s most enjoyable essay: Dietmar Seyferth,
Organometallics, 2001, 20, 2940–2955.
2 For a recent review on contemporary ate chemistry including zincates
see: R. E. Mulvey, Organometallics, 2006, 25, 1060.
3 A. O. King, N. Okukado and E.-i Negishi, J. Chem. Soc., Chem.
Commun., 1977, 683.
20 H. Wagner, J. Baumgartner and C. Marschner, Organometallics, 2007,
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21 (a) C. Kayser, G. Kickelbick and C. Marschner, Angew. Chem.,
2002, 114, 1031; C. Kayser, G. Kickelbick and C. Marschner, Angew.
Chem., Int. Ed., 2002, 41, 989; (b) R. Fischer, D. Frank, W. Gader-
bauer, C. Kayser, C. Mechtler, J. Baumgartner and C. Marschner,
Organometallics, 2003, 22, 3723.
4 Silyl derivatives of group 1, 2, 11 and 12 elements were reviewed
recently: H.-W. Lerner, Coord. Chem. Rev., 2005, 249, 781.
5 E. Wiberg, O. Stecher, H. J. Andrascheck, L. Kreuzbichler and E.
Staude, Angew. Chem., 1963, 75, 516.
22 For related structures of cyclopentasilanindate and -gallate complexes
see: W. Uhl, B. Jasper, A. Lawerenz, C. Marschner and J. Fischer,
Z. Anorg. Allg. Chem., 2007, 633, 2321.
23 M. Zirngast, U. Flo¨rke, J. Baumgartner and C. Marschner, Chem.
Commun., 2009, 5538.
24 W. Uhl, M. Claesener and A. Hepp, Organometallics, 2008, 27, 2118.
25 (a) G. A. Morris and R. Freeman, J. Am. Chem. Soc., 1979, 101, 760;
(b) B. J. Helmer and R. West, Organometallics, 1982, 1, 877.
26 SAINTPLUS: Software Reference Manual, Version 6.45, Bruker-AXS,
Madison, WI, 1997–2003.
6 L. Ro¨usch and G. Altnau, Angew. Chem., 1979, 91, 62.
7 J. Arnold, T. D. Tilley, A. L. Rheingold and S. J. Geib, Inorg. Chem.,
1987, 26, 2106.
8 For
more
spectroscopic
and
structural
studies
of
bis[tris(trimethylsilyl)silyl]zinc see: K. W. Klinkhammer and J.
Weidlein, Z. Anorg. Allg. Chem., 1996, 622, 1209. For ist conversion
to alkali tris(trimethylsilyl)silanides see: K. W. Klinkhammer,
Chem.–Eur. J., 1997, 3, 1418.
27 R. H. Blessing, Acta Crystallogr., Sect. A: Found. Crystallogr., 1995,
51, 33: SADABS: Version 2.1 Bruker AXS 1998.
9 (a) N. Wiberg, A. Wo¨rner, H.-W. Lerner and K. Karaghiosoff,
Z. Naturforsch. B, 2002, 57, 1027; (b) N. Wiberg, W. Niedermayer,
28 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
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