Coordination of a Si=O subunit to metals: Complexes of donor-stabilized silanone featuring a terminal Si=O→M coordination (M = Zn, Al)

Article abstract of DOI:10.1039/c0dt00148a

The striking reactivity of donor-stabilised silanone LSi(DMAP)O (1) [L = N(Ar)C(CH₂)CHC(Me)N(Ar), Ar = 2,6-iPr₂C₆H ₃, DMAP = p-dimethylaminopyridine] toward Lewis acidic metal substrates Zn(OAc)₂, ZnMe₂, and AlMe₃ is reported. Two unprecedented addition products onto the SiO double bond, [LSi(OAc)(μ-O)Zn(OAc)(DMAP)₂] (2) and [LSi(OAc)(μ-O)] ₂Zn(DMAP) (3), and two terminal complexes LSi(DMAP)O→ZnMe ₂ (4) and LSi(DMAP)O→AlMe₃ (5) were obtained. Compounds 4 and 5 are unique, representing the first isolable and structurally characterised terminal SiO→Zn and SiO→Al complexes. All new compounds were fully characterised by ¹H, ¹³C, and ²⁹Si NMR spectroscopy, EI-MS, elemental analysis and single-crystal X-ray diffraction analyses. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0dt00148a

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PAPER
www.rsc.org/dalton | Dalton Transactions
=
Coordination of a Si O subunit to metals: complexes of donor-stabilized
silanone featuring a terminal Si O→M coordination (M = Zn, Al)†
=
Yun Xiong, Shenglai Yao and Matthias Driess*
Received 16th March 2010, Accepted 28th May 2010
DOI: 10.1039/c0dt00148a
=
The striking reactivity of donor-stabilised silanone LSi(DMAP) O (1) [L =
=
=
N(Ar)C( CH2)CH C(Me)N(Ar), Ar = 2,6-iPr2C6H3, DMAP = p-dimethylaminopyridine] toward
Lewis acidic metal substrates Zn(OAc)2, ZnMe2, and AlMe3 is reported. Two unprecedented addition
=
products onto the Si O double bond, [LSi(OAc)(m-O)Zn(OAc)(DMAP)2] (2) and
=
[LSi(OAc)(m-O)]2Zn(DMAP) (3), and two terminal complexes LSi(DMAP) O→ZnMe2 (4) and
=
LSi(DMAP) O→AlMe3 (5) were obtained. Compounds 4 and 5 are unique, representing the first
=
=
isolable and structurally characterised terminal Si O→Zn and Si O→Al complexes. All new
compounds were fully characterised by 1H, 13C, and 29Si NMR spectroscopy, EI-MS, elemental analysis
and single-crystal X-ray diffraction analyses.
(DMAP = p-dimethylaminopyridine) supported silanone 1.9
Introduction
Among these complexes it turned out that compound 1 is currently
Carbonyl containing species, such as aldehydes, ketones, carbonic
acids and esters, are well known basic building blocks in organic
synthesis. In contrast, related silicon-oxygen double bond species
and even heavier analogues have been long-standing challenges in
=
the best precursor for studying Si O double bond reactivity owing
to the weak and thus transient coordination by the nitrogen donor
from DMAP ligand. Preliminary studies revealed that precursor 1
is suitable for the generation of new functional groups in silicon-
=
=
group 14 chemistry owing to the high polarity of Si O (Ge O,
=
oxygen chemistry. For example, the Si O subunit is capable to
activate N–H bonds of ammonia to furnish an isolable sila-
semiaminal and the first silanoic amide.9 In this context, we were
curious about the reactivity of the Si O group of 1 toward Lewis-
acidic metal centres. Herein we wish to report the striking reactivity
of 1 towards zinc and aluminium complexes which led to the first
=
=
Sn O and Pb O) bonds which result in oligomerization. To date,
such elusive silicon species have been characterized predominantly
by means of spectroscopy in cryogenic matrices at very low
temperature.1–5 By employing the donor–acceptor stabilization
concept we recently synthesized and isolated a b-diketiminato
ligand supported silaformaldehyde complex A6 (Scheme 1)
and silanoic ester B7 as well as the NHC (N-Heterocyclic
Carbene) stabilized cyclic silaureas (silanone) C,8 and DMAP
=
=
isolable metal complexes of a Si O double bond compound.
Results and discussion
It is well known that ketones do not react with zinc acetate
under mild conditions, and acetone can even be used as solvent
in reactions involving zinc acetate as a substrate or catalyst.10
=
In contrast, zinc acetate reacts immediately with Si O precursor
1. Thus, we learned from initial experiments that treatment of
a pale yellow suspension of 1 in toluene with zinc acetate in a
molar ratio of 3 : 2 at ambient temperature leads to a mixture of
colorless compounds 2 and 3 (Scheme 2). Fortunately, compounds
2 and 3 can be separated by fractional recrystallization in toluene.
Compound 2 can be separated at first in 31% yield, and further
work-up of the mother liquor affords 3 in form of colorless crystals
in 51% yield.
The composition and constitution of 2 were determined by
mass spectrometry, multinuclear NMR spectroscopy, and ele-
mental (C, H, N) analysis. EI-MS analysis revealed a peak at
m/z 886 (32%) which corresponds to an adduct consisting of
equimolar amounts of 1, Zn(OAc)2, and DMAP. Indeed, addition
of equimolar amounts of 1 to Zn(OAc)2 and DMAP furnishes
compound 2 almost exclusively (see experimental section). The
proton NMR spectrum of 2, exhibiting the expected pattern for
the chelating diamido ligand at silicon, two chemically identical
DMAP molecules and two chemically different acetate groups,
confirms the assumption from EI-mass spectrometry. The 29Si
=
Scheme 1 Several isolable species containing a Si O bond.
Technische Universita¨t Berlin, Institute of Chemistry: Metalorganics and
Inorganic Materials, Sekr. C2, Strasse des 17. Juni 135, D-10623,
Berlin, Germany. E-mail: matthias.driess@tu-berlin.de; Fax: +49(0)30-
314-29732; Tel: +49(0)30-314-29731
† CCDC reference numbers 770199–770201. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00148a
9282 | Dalton Trans., 2010, 39, 9282–9287
This journal is
The Royal Society of Chemistry 2010
©

˚
Table 1 Selected distances (A) for compounds 1–5
Si–Obridge
1.545(2)
1.560(2)
Si–OOAc Si–Nbackbone Si–NDMAP Zn–Obridge Zn–OOAc
1
2
3
4
5
1.743(2)
1.746(2)
1.689(2) 1.726(2)
1.728(2)
1.862(2)
1.910(2)
1.945(2)
1.550(2)
1.553(2)
1.548(1)
1.714(2) 1.721(3)
1.723(2) 1.730(3)
1.730(2)
1.896(2)
1.913(2)
2.023(1)
2.270(2)
2.279(2)
1.848(2)
1.837(3)
1.733(2)
1.717(2)
1.547(2)
1.731(2)
12
˚
observed for ZnMe2(DMAP)2 [2.177(2), 2.169(2) A]. Likewise,
˚
˚
the Zn–Obridge [1.910(2) A] and Zn–OOAc distances [1.945(2) A] in
2 are also similar to those observed in Zn(OAc)2(py)2 [1.941(2)–
1.945(2) A]. The tetrahedral coordinated silicon atom, on the
Scheme 2 Reactivity of 1 toward Zn(OAc)2.
11
˚
other hand, is attached to the bridging oxygen atom, one acetate
group and two nitrogen atoms of the diamido chelate ligand. The
coordination feature reveals two different Si–N bonds [1.726(2),
NMR spectrum of 2 reveals a high-field resonance signal at
d -76.9 ppm, which falls in the range of four coordinate silicon
species.
The molecular structure of 2 has been established by single
crystal X-ray diffraction analysis (Fig. 1). Compound 2 crystallizes
in the monoclinic space group P21/n. The structure indicates that
˚
1.728(2) A] being slightly shorter than those in the precursor
˚
1 [1.743(2), 1.756(2) A] (Table 1). A noteworthy feature is the
˚
significantly short Si–Obridge distance of 1.560(2) A which is
˚
drastically shorter than that of Si–OOAc [1.689(2) A]. The strikingly
=
addition of zinc acetate to the Si O bond is accompanied by
=
short Si–O distance is comparable to the Si O bond in precursor
a migration of the DMAP donor ligand from silicon centre to
the zinc atom. Additionally, a second DMAP molecule is coor-
dinated by zinc to reach a more stable tetrahedral coordination
sphere. Thus, both silicon and zinc feature distorted tetrahedral
coordination environments. Compound 2 consists of a L(OAc)Si-
moiety connected with a Zn(OAc)(DMAP)2 complex fragment
via a bridging oxygen atom (Si–O–Zn angle of 134.8(1)◦). The
Zn–N distances with the DMAP ligands are 2.021(2) and
9
˚
1 [1.545(2) A], probably due to the strong electron donation of
DMAP to zinc which weakens the Zn–O interaction and causes a
larger Si–O bond polarity (electrostatic interaction).
Obviously, 2 is formed by equimolar addition of zinc acetate
=
to the Si O double bond in 1. It can be shown that further
addition of 2 to an equimolar amount of 1 leads to the formation
of 3 along with DMAP (Scheme 2). Alternatively, compound
3 is accessible by treatment of two molar amounts of 1 with
Zn(OAc)2 in toluene (Scheme 2). Complex 3 was characterized
by multinuclear NMR spectroscopy, EI-MS spectrometry, and
elemental analysis. According to 1H NMR and EI-MS spectra, 3
is an adduct with the composition of [LSi(OAc)O]2Zn(DMAP).
The 29Si NMR spectrum of 3 exhibits only one resonance signal
at d -75.7 ppm (vs. -76.9 ppm of 2), indicating two chemically
equivalent Si atoms.
˚
2.024(2) A, which are comparable to those observed for
11
˚
Zn(OAc)2(py)2 [2.021(5)–2.075(2) A], but shorter than those
The structure of 3 could be unequivocally determined by a
single crystal X-ray diffraction analysis. Accordingly, 3 crystallizes
¯
in diethylether in the triclinic space group P1. As expected,
a Zn(DMAP) moiety is connected to two LSi(OAc) fragments
each by a bridging oxygen atom (Fig. 2). Unlike the tetrahedral
coordination geometry around Zn in 2, the Zn atom in 3 is
five-coordinate and features a distorted trigonal bipyramidal
coordination with two OOAc atoms (O3 and O6) in axial positions
and a O3–Zn1–O6 angle of 173.0◦. The Zn–O1 and Zn–O4
˚
distances [1.896(2) and 1.913(2) A] versus those of Zn–O3 and Zn–
˚
˚
O6 [2.279(2) and 2.270(2) A)] differ by about 0.37 A, in line with
a dative bonding interaction between Zn and O3/O6 (Table 1).
˚
The Zn–N distance of 2.045(3) A is similar to those found in 2
Fig. 1 Molecular structure of 2. Thermal ellipsoids are drawn at 50%
˚
[2.021(2) and 2.024(2) A]. The coordination polyhedron of both
silicon atoms in 3, despite of the dative interaction of the acetate
oxygen atom to zinc, resembles that in 2, showing two significantly
shorter Si–Obridge [1.553(2), 1.550(2) A] distances than those of
Si–OOAc [1.723(2), 1.714(2) A]. Similarly, the two Si–Nbackbone
probability level. H atoms and two toluene molecules are omitted for
◦
˚
clarity. The selected distances (A) and angles ( ): Si1-N2 1.726(2),
Si1-N1 1.728(2), Si1-O1 1.689(2), Si1-O3 1.560(2), Zn1-O3 1.910(2),
Zn1-O4 1.945(2), Zn1-N5 2.021(2), Zn1-N3 2.024(2); N2-Si1-N1 103.8(1),
O3-Si1-O1 105.2(1), Si1-O3-Zn1 134.8(1).
˚
˚
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9282–9287 | 9283
©

˚
˚
those of 1 except the singlet at d -1.47 ppm (CD2Cl2) for the
methyl groups of the ZnMe2 moiety, while the 29Si NMR spectrum
exhibits a similar resonance at d -72.5 ppm (vs -71.1 ppm for 1).
A single-crystal X-ray diffraction analysis revealed that 4 is a ter-
[1.721(3)–1.730(3) A] distances are also shorter than those in 1
[1.743(2), 1.756(2) A] (Table 1).
=
=
minal Lewis acid–base adduct of a Si O bond in LSi(DMAP) O
with ZnMe2 (Fig. 3). In contrast to 2 and 3, the DMAP molecule
in 4 remains coordinated to the Si atom, whereas the Zn centre
adopts a distorted trigonal planar coordination geometry. The
˚
Zn–O distance of [2.023(1) A] is significantly longer than those of
˚
˚
Zn–Obridge in 2 [1.910(2) A] and 3 [1.896(2), 1.913(2) A], indicating
the dative nature of the Si+–O-→Zn interaction in 4 (Table 1);
accordingly, the Si–O→Zn angle is 150.0◦. The Zn–C distances in
˚
4 [1.981(2), 1.984(2) A] are similar to those in Zn[CH2SiMe2OiPr]2
[1.953(7), 1.988(6) A], as a reference compound with similar
13
˚
coordination geometry around zinc. The Si centre adopts a
˚
tetrahedral coordination with a Si–O bond length of 1.548(1) A,
˚
very close to that in 1 [1.545(2) A]. However, the Si–Nbackbone
˚
˚
[1.730(2), 1.733(2) A] and Si–NDMAP distances [1.848(2) A] in 4
are slightly shorter than the corresponding values in 1 [1.743(2),
˚
˚
1.756(2) A for Si–Nbackbone and 1.862(2) A for Si–NDMAP] (Table 1),
presumably caused by the electron donation of the oxygen atom
to zinc.
Fig. 2 Molecular structure of 3. Thermal ellipsoids are drawn at 50%
probability level. H atoms and one diethyl ether molecule are omitted for
◦
˚
clarity. Selected distances (A) and angles ( ): Si1-N2 1.721(3), Si1-N1
1.727(3), Si1-O1 1.553(2), Si1-O2 1.723(2), Si2-O4 1.550(2), Si2-O5
1.714(2), Si2-N3 1.730(3), Si2-N4 1.728(3), Zn1-O1 1.896(2), Zn1-O3
2.279(2), Zn1-O4 1.913(2), Zn1-O6 2.270(2), Zn1-N5 2.045(3); O3-Zn1-O1
89.4(1), O3-Zn1-N5 85.5(1), O3-Zn1-O4 93.1(1), O1-Si1-O2 111.0(1).
The aforementioned reactions indicate preferential addition of
=
salt-like complexes across the Si O bond in 1. In order to learn
whether organometallic zinc complexes behave similarly, dimethyl
zinc was employed as a substrate. Thus, addition of a toluene
solution of dimethyl zinc to an equimolar amount of 1 in toluene
at room temperature furnishes immediately a clear yellow solution.
Indeed, proton NMR spectrum of the reaction solution suggests
quantitative formation of a 1 : 1 complex. From a concentrated
toluene solution, complex 4 could be isolated as yellow crystals in
92% yield (Scheme 3). It is worth mentioning that a 2 : 1 adduct
=
[LSi(DMAP) O]2ZnMe2 cannot be detected through addition of
one equivalent amount of 1 to solutions of 4 in toluene.
Fig. 3 Molecular structure of 4. Thermal ellipsoids are drawn at
50% probability level. H atoms (except those at C1) and one toluene
˚
molecule are omitted for clarity. The selected distances (A) and
angles (◦): Zn1-C37 1.984(2), Zn1-C38 1.981(2), Zn1-O1 2.023(1),
Si1-O1 1.548(1), Si1-N1 1.730(2), Si1-N3 1.848(2), C1-C2 1.372(3);
Si1-O1-Zn1 150.0(1), N3-Si1-O1 104.8(1), N2-Si1-O1 117.3(1), N1-Si1-O1
119.3(1), N1-Si1-N2 104.2(1), N1-Si1-N3 105.6(1), C37-Zn1-O1 111.5(1),
C38-Zn1-O1 108.4(1), C37-Zn1-C38 140.1(1).
Similarly, the equimolar reaction of 1 with AlMe3 in toluene
at ambient temperature leads to the formation of the new Lewis
=
acid–base adduct 5 with a Si O→Al coordination (Scheme 3).
Compound 5 has a similar solubility as 4 and can be isolated
by crystallization. It was fully characterized by multinuclear
NMR spectroscopy, EI mass spectrometry, elemental analysis, and
Scheme 3 Reactivity of 1 toward ZnMe2 and AlMe3.
1
Compound 4 is soluble in toluene, THF, and dichloromethane,
but insoluble in hexane. The composition of 4 was corroborated by
mass spectrometry and elemental analysis, and the constitution is
consistent with its 1H and 29Si NMR data. The 1H NMR spectrum
shows only slightly different resonance signals compared with
X-ray structural analysis. In the H NMR spectrum a singlet at
-0.68 ppm (C6D6) is observed for the equivalent protons of the
AlMe3 subunit, while the other resonances can be easily assgined
to the chelating diamido and the coordinating DMAP ligand. The
29Si NMR spectrum of 5 shows a singlet at d -74.8 ppm, similar to
9284 | Dalton Trans., 2010, 39, 9282–9287
This journal is
The Royal Society of Chemistry 2010
©

that of 4 (d -72.4 ppm). Since AlMe3 is a more electron-deficient
compound in comparison with ZnMe2, the coordination between
=
Si O and AlMe3 in compound 5 is expected to be stronger than
that in 4. Indeed, the most intensive peak in the EI-mass spectrum
appears at m/z 655, corresponding to the molecular ion [M]+. It is
noteworthy that in the EI-MS of 4 the most intensive peak appears
at m/z 583 for [M-ZnMe2]+, whereas the relative intensity peak for
the molecular ion of 4 is very small (around 2%).
Scheme 4 Resonance structures of 5.
¯
Compound 5 (Fig. 4) crystallizes in the triclinic space group P1,
=
under addition across the Si O subunit and migration of
together with two molecules of toluene in the asymmetric unit.
Both silicon and aluminium centres have a tetrahedral coordina-
tion environment, and the Al–O–Si angle is 166.6(1)◦. Similar to 4,
the DMAP molecule in 5 is still coordinated at the silicon centre.
DMAP to zinc, resulting in two addition products [LSi(OAc)(m-
O)Zn(OAc)(DMAP)2] (2) and [LSi(OAc)(m-O)]2Zn(DMAP) (3),
respectively. On the other hand, reaction of 1 with molecular
dimethyl zinc and trimethyl aluminium furnishes the first ter-
=
As a result of the coordination of Si O subunit to the Al centre, the
=
=
˚
minal Si O→M complexes LSi(DMAP) O→ZnMe2 (4) and
Si–Nbackbone bond lengths [1.717(2), 1.731(2) A] are slightly shorter
=
˚
LSi(DMAP) O→AlMe3 (5). The obviously stronger donor abil-
than those in 1 [1.743(2), 1.756(2) A] and the same is true for the Si–
˚
ity of the terminal oxygen centre in 1 towards metals originates
NDMAP values [1.837(3) vs. 1.862(2) A in 1] (Table 1). However, the
=
˚
from the pronounced ylide-like character of the Si O double bond
Si–O distance of 1.547(2) A in 5 does not vary much in comparison
=
˚
in comparison to the more covalent C O double bond. The novel
with that observed in 1 [1.545(2) A].
Si–O–M compounds represent molecular models for different
chemisorption products from addition of metal compounds on
=
Si O-terminated silicon surfaces and close a knowledge gap in
metal siloxane chemistry.
Experimental section
General considerations
All manipulations were performed under a dry and oxygen-free
atmosphere (N2) by using Schlenk-line and glove-box techniques.
Solvents were purified prior to use by distillation over appropriate
drying agents in a nitrogen atmosphere. The starting material 1 was
prepared according to literature procedure.6b,9 The NMR spectra
were recorded with Bruker spectrometers ARX200, AV400 and
with residual solvent signals as internal reference (1H and 13C{H})
or with an external reference (SiMe4 for 29Si).
Single-crystal X-ray structure determinations
Crystals were each mounted on a glass capillary in per-fluorinated
oil and measured in a cold N2 flow. The data of 2–5 were collected
on an Oxford Diffraction Xcalibur S Sapphire at 150 K (Mo-
Fig. 4 Molecular structure of 5. Thermal ellipsoids are drawn at 50%
probability level. H atoms and two toluene molecules are omitted for
◦
˚
clarity. The selected distances (A) and angles ( ): Al1-O1 1.804(2), Al1-C37
2.001(3), Al1-C38 1.993(3), Si1-O1 1.547(2), Si1-N1 1.717(2), Si1-N2
1.731(2), Si1-N3 1.837(3); Si1-O1-Al1 166.6(1), N3-Si1-O1 105.9(1),
N2-Si1-O1 116.5(1), N1-Si1-O1 118.1(1), N1-Si1-N2 104.7(1), N1-Si1-N3
105.6(1), C37-Al1-O1 105.7(1).
˚
Ka-radiation, l = 0.71073 A). The structures were solved by
direct methods and refined on F2 with the SHELX-9717 software
package. The positions of the H atoms were calculated and
considered isotropically according to a riding model.
2: Monoclinic, space group P21/n, a = 14.5359(4), b =
◦
3
˚
˚
˚
The Al–O bond distance [1.804(2) A] is significantly
21.7258(5), c = 17.8232(4) A, b = 90.067(2) , V = 5628(2) A ,
Z = 4, rc = 1.212 Mg m-3, m(Mo-Ka) = 0.509 mm-1, 48804
collected reflections, 9881 crystallographically independent reflec-
tions [Rint = 0.0715], 6671 reflections with I > 2s(l), qmax = 25.00◦,
R(Fo) = 0.0485 (I > 2s(l)), wR(Fo2) = 0.1144 (all data), 684 refined
parameters.
shorter than the corresponding values observed in
t
14
˚
=
=
(PhO)2C O→Al( Bu)3 [2.070(3) A], Ph2C O→Al(Me)(BHT)2
15
˚
˚
(BHT
=
2,6-tBu2-4-Me-Phenol) [1.903(6) A],
and Me3-
16
=
=
AlN(Me) C(Ph)C(Ph) O→AlMe3 [1.983(2) A], indicating a
stronger interaction between the Al and O atom in 5 due to the
¯
=
high ylide-like character of the Si O subunit and the push-pull
3: Triclinic, space group P1, a = 12.5933(3), b = 13.2139(4),
◦
˚
effect by the N-donor DMAP (Scheme 4).
c = 23.3919(6) A, a = 104.044(2), b = 95.106(2), g = 101.459(2) ,
3
-3
˚
V = 3662.2(2) A , Z = 2, rc = 1.180 Mg m , m(Mo-Ka) =
0.422 mm-1, 34027 collected reflections, 12847 crystallographically
independent reflections [Rint = 0.0496], 9629 reflections with I >
2s(l), qmax = 25◦, R(Fo) = 0.0604 (I > 2s(l)), wR(Fo2) = 0.1435
(all data), 826 refined parameters.
Conclusions
In contrast to ketones, the silanone-like (silaurea) adduct
LSi(DMAP) O (1) reacts easily with salt-like zinc acetate
=
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9282–9287 | 9285
©

4: Monoclinic, space group P21/c, a = 15.8193(4), b =
MeCO2), 28.0, 28.3, 28.6, 29.0 (CHMe2), 38.0 (NMe2), 84.2
(NCCH2), 105.4 (g-C), 106.4 (DMAP), 123.6, 123.9, 124.0, 124.5,
126.7, 126.8, 139.2, 139.5, 141.2, 142.0, 142.8, 149.3, 149.6, 150.0,
151.4, 154.6, 170.1 ppm (NCMe, NCCH2, 2,6-iPr2C6H3, DMAP,
◦
3
˚
˚
22.5525(5), c = 12.4294(3) A, b = 101.727(2) , V = 4341.8(2) A ,
Z = 4, rc = 1.179 Mg m-3, m(Mo-Ka) = 0.630 mm-1, 30879
collected reflections, 7634 crystallographically independent reflec-
tions [Rint = 0.0371], 5747 reflections with I > 2s(l), qmax = 25◦,
R(Fo) = 0.0350 (I > 2s(l)), wR(Fo2) = 0.0786 (all data), 483
refined parameters.
◦
MeCO2); 29Si{ H} NMR (79.49 MHz, [D6]benzene, 25 C): d =
-76.9 ppm (s); EI-MS: m/z (%): 886 (32) [M]+, 327 (100) [M–
OZn(OAc)(DMAP)2-Me-iPr2C6H3]+; elemental analysis calcd (%)
for C47H66N6SiO5Zn·C7H8 : C 66.14, H 7.61, N 8.57; found: C
66.35, H 7.42, N 8.57.
1
¯
5: Triclinic, space group P1, a = 11.3598(3), b = 14.2375(6), c =
◦
˚
17.6960(9) A, a = 108.081/4), b = 98.036(3), g = 90.780(3) , V =
2689.1(2) A , Z = 2, rc = 1.036 Mg m , m(Mo-Ka) = 0.097 mm ,
3: M.p.178 ◦◦C (decomposed); 1H NMR (200.13 MHz,
3
-3
-1
˚
21383 collected reflections, 9449 crystallographically independent
[D6]benzene, 25 C): d = 0.33 (d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2),
3
3
reflections [Rint = 0.0464], 6432 reflections with I > 2s(l), qmax
=
0.63 (d, J (H,H) = 7.0 Hz, 6 H; CHMe2), 1.30 (d, J (H,H) =
7.0 Hz, 6 H; CHMe2), 1.31 (d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2),
1.37 (d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2), 1.39 (s, 6 H, DMAP),
1.66 (s, 6 H, NCMe), 1.52 (d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2), 1.54
(d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2), 1.69 (d, 3J (H,H) = 7.0 Hz,
6 H; CHMe2), 2.31 (s, br., 6 H; CH3CO2), 2.99 (s, 2 H; NCCH2),
3.32–3.47 (m, 4 H; CHMe2), 3.80 (s, 2 H; NCCH2), 3.87–4.13 (m,
4 H; CHMe2), 5.39 (s, 2 H; g-CH), 5.64 (br., 2 H; DMAP), 6.63
25◦, R(Fo) = 0.0704 (I > 2s(l)), wR(Fo2) = 0.1762 (all data), 683
refined parameters.
Syntheses
Synthesis of 2 and 3.
Reaction of 1 with Zn(OAc)2 in a molar ratio of 3:2. Zn(OAc)2
(0.052 g, 0.29 mmol) was added to a suspension of 1 (0.25 g, 0.43
mmol) in toluene (15 mL) at room temperature. After one hour
stirring the reaction was completed. By cooling the concentrated
solution (8 mL) at -20 ◦C compound 2 (0.12 g, 0.13 mmol, 31%)
crystallized at first, the subsequent work-up of the rest solution
afforded 3 as colorless crystals (0.14 g, 0.11 mmol, 51%) (based on
the amount of 1).
Reaction of 1 with a mixture of Zn(OAc)2 and DMAP.
Zn(OAc)2 (0.10 g, 0.55 mmol) and DMAP (0.067 g, 0.55 mmol)
were mixed in toluene (8 mL) at room temperature. After one hour
stirring compound 1 (0.32 g, 0.55 mmol) was added to the reaction
mixture. One hour later the reaction was completed. The 1H
NMR spectrum (200.13 MHz, [D6]benzene, 25 ◦C) of the solution
displays only signals for compound 2.
Reaction of two equiv. of 1 with Zn(OAc)2. Zn(OAc)2 (0.052 g,
0.28 mmol) was added to a suspension of 1 (0.33 g, 0.56 mmol) in
toluene (20 mL) at room temperature under stirring. The reaction
was completed within one hour and the suspension became clear.
The solvent was changed to diethylether (8 mL) and the resulting
solution was cooled at -4 ◦C. The by-product DMAP remains in
the solution, whereas product 3 crystallized as colorless crystals.
Yield: 0.27 g (0.21 mmol, 75%);
1
(br, 2 H, DMAP), 6.73–7.38 ppm (m, 12 H; iPrC6H3); 13C{ H}
NMR (100.61 MHz, [D6]benzene, 25 ◦C): d = 21.9, 23.5, 23.9,
24.4, 24.6, 24.7, 25.1, 25.3, 25.9, 26.3 (NCMe, CHMe2, MeCO2),
27.7, 28.3, 28.8, 29.0 (CHMe2), 38.3 (NMe2), 84.1 (NCCH2), 106.8
(g-C), 107.2 (DMAP), 123.9, 124.2, 124.9, 125.3, 127.0, 127.2,
138.2, 138.5, 142.3, 147.8, 148.6, 148.8, 149.7, 150.6, 173.6 ppm
1
(NCMe, NCCH2, 2,6-iPr2C6H3, DMAP, MeCO2); 29Si{ H} NMR
(79.49 MHz, [D6]benzene, 25 ◦C): d = -75.7 ppm (s); EI-MS: m/z
(%): 1225 (4) [M]+, 1103 (100) [M-DMAP]+; elemental analysis
calcd (%) for C69H96N6Si2O6Zn: C 67.54, H 7.89, N 6.85; found: C
67.74, H 7.95, N 6.63.
Synthesis of 4. To a suspension of 1 (0.49 g, 0.84 mmol) in
toluene (15 mL) was added at room temperature ZnMe2 (0.70 ml,
0.84 mmol, 1.2 mol L-1 in toluene). The reaction mixture became
clear immediately. At room temperature compound 4 crystallized
from toluene as yellow prism. The◦ collected crystals amounts
1
0.52 g (0.77 mmol, 92%). m.p. 193 C (decomposed); H NMR
(400.13 MHz, [D6]benzene, 25 ◦C): d = -0.62 (s, 6 H; ZnMe2), 0.37
(d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2), 0.59 (d, 3J (H,H) = 7.0 Hz,
3 H; CHMe2), 1.06 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.29 (d,
3J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.40 (d, 3J (H,H) = 7.0 Hz, 3
H; CHMe2), 1.53 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.60 (s, 3
H; NCMe), 1.78 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.79 (d, 3J
(H,H) = 7.0 Hz, 3 H; CHMe2), 1.82 (s, 6 H; DMAP), 2.63–2.75 (m,
2 H; CHMe2), 3.47 (s, 1 H; NCCH2), 4.05 (s, 1 H; NCCH2), 4.15
(sept., 3J (H,H) = 7.0 Hz, 1 H; CHMe2), 4.30 (sept., 3J (H,H) =
7.0 Hz, 1 H; CHMe2), 5.50 (s, 1 H; g-CH), 5.51–5.53 (m, 2 H;
DMAP), 7.00–7.40 (m, br, 6 H; 2,6-iPr2C6H3), 8.57–8.58 ppm◦(m,
Reaction of 2 with 1. Compound 1 (0.18 g, 0.20 mmol) was
added to a solution of 2 (0.12 g, 0.20 mmol) in toluene (8 mL)
at room temperature under stirring. After one hour stirring the
reaction was completed. The 1H NMR spectrum displayed signals
for 3 and for DMAP.
2: M.p. 135◦ ◦C (decomposed); 1H NMR (200.13 MHz,
[D6]benzene, 25 C): d = 1.39 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2),
2 H; DMAP); 13C{ H} NMR (100.61 MHz, [D6] benzene, 25 C):
1
3
3
1.40 (d, J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.42 (d, J (H,H) =
d = -7.78 (ZnMe2), 21.4 (NCMe), 24.1, 24.2, 24.5, 25.1, 25.2,
25.4, 25.7, 26.4 (CHMe2), 28.8, 29.4, 29.5 (CHMe2), 38.5 (NMe2),
86.8 (NCCH2), 104.9 (g-C), 106.0 (DMAP), 123.6, 124.3, 125.0,
125.3, 136.5, 137.3, 143.9, 146.9, 147.0, 149.7, 150.0, 156.4 ppm
(NCMe, NCCH2, 2,6-iPr2C6H3, DMAP); 29Si NMR (79.49 MHz,
[D6]benzene, 25 ◦C): d = -72.4 (s); 1H NMR (400.13 MHz,
[D2]dichloromethane, 25 ◦C): d = -1.47 (s, 6 H; ZnMe2), 0.37 (d,
3J (H,H) = 7.0 Hz, 3 H; CHMe2), 0.55 (d, 3J (H,H) = 7.0 Hz, 3
7.0 Hz, 3 H; CHMe2), 1.43 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2),
3
3
1.46 (d, J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.60 (d, J (H,H) =
7.0 Hz, 3 H; CHMe2), 1.59 (d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2),
1.67 (s, 3 H; NCMe), 2.07 (s, br. 12 H; DMAP), 2.09 (s, 3 H;
CH3CO2), 2.20 (s, br., 3 H; CH3CO2), 3.33 (s, 1 H; NCCH2), 3.91–
4.02 (m, 2 H; CHMe2), 4.02 (s, 1 H; NCCH2), 4.24–4.35 (m, 2 H;
CHMe2), 5.58 (s, 1 H; g-CH), 5.82–5.84 (m, 4 H; DMAP), 6.97–
7.32 (m, 6 H; iPr2C6H3), 8.17 ppm (br., 4 H; DMAP); 13C{ H}
H; CHMe2), 1.05 (d, J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.06 (d,
1
3
NMR (100.61 MHz, [D6]benzene, 25 ◦C): d = 21.4, 23.4, 23.9,
24.4, 24.5, 25.0, 25.1, 25.3, 25.9, 26.3, 26.4 (NCMe, CHMe2,
3J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.18 (d, 3J (H,H) = 7.0 Hz, 3
H; CHMe2), 1.20 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.36 (d, 3J
9286 | Dalton Trans., 2010, 39, 9282–9287
This journal is
The Royal Society of Chemistry 2010
©

(H,H) = 7.0 Hz, 3 H; CHMe2), 1.42 (d, 3J (H,H) = 7.0 Hz, 3 H;
CHMe2), 1.59 (s, 3 H; NCMe), 2.46–2.63 (m, 2 H; CHMe2), 2.97
(s, 1 H; NCCH2), 3.19 (s, 6 H; DMAP), 3.75 (s, 1 H; NCCH2),
3.71–3.85 (m, 2 H; CHMe2), 5.41 (s, 1 H; g-CH), 6.67–6.69 (br., 2
H; DMAP), 7.01–7.27 (m, br, 6 H; 2,6-iPr2C6H3), 8.65 ppm (br.,
[M+-AlMe3]; elemental analysis calcd (%) for C39H59N4SiOAl :
C 71.52, H 9.08, N 8.55; found: C 71.81, H 9.22, N 8.37.
Acknowledgements
1
2 H; DMAP); 13C{ H} NMR (100.61 MHz, [D2]dichloromethane,
Financial support by the Deutsche Forschungsgemeinschaft and
Fonds der Chemischen Industrie is gratefully acknowledged.
25 ◦C): d = -9.11 (ZnMe2), 21.5, 24.0, 24.1, 24.2, 24.8, 24.9,
25.3, 25.4, 25.9 (NCMe, CHMe2), 28.9, 29.1, 29.2 (CHMe2), 40.2
(NMe2), 86.0 (NCCH2), 104.3 (g-C), 106.8 (DMAP), 123.9, 124.5,
124.6, 124.7, 127.4, 127.5, 136.4, 137.1, 144.3, 147.7, 148.0, 149.0,
149.4, 149.9, 157.3 ppm (NCMe, NCCH2, 2,6-iPr2C6H3, DMAP);
29Si NMR (79.49 MHz, [D2]dichloromethane, 25 ◦C): d = -72.5 (s);
EI-MS: m/z (%): 676 (2) [M]+, 583 (100) [M-ZnMe2]+; elemental
analysis calcd (%) for C38H56N4SiOZn·0.5C7H8 : C 68.80, H 8.34,
N 7.74; found: C 69.01, H 8.48, N 7.85.
References
1 Y. Apeloig, Theoretical aspects of organosilicon compounds, in The
Chemistry of Organic Silicon Compounds ed. S. Patai and Z. Rappoport,
Wiley, New York, 1989, Vol. 1, Chapt. 2, p. 57 and references cited
therein.
2 M. S. Gordon and C. George, J. Am. Chem. Soc., 1984, 106, 609.
3 J. Kapp, M. Remko and P. v. R. Schleyer, J. Am. Chem. Soc., 1996, 118,
5745.
Synthesis of 5. To a suspension of 1 (0.33 g, 0.57 mmol) in
toluene (15 mL) was added at room temperature AlMe3 (0.28 ml,
2.0 mol L-1 in toluene). The solution became clear immediately.
From the concentrated toluene solution compound 5 crystallized
as pale yellow needles. Yield: 0.50 g (0.76 mmol, 88%). m.p. 158 ◦C
(decomposed); 1H NMR (200.13 MHz, [D6]benzene, 25 ◦C): d =
-0.68 (s, 9 H; AlMe3), 0.53 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2),
4 M. Kimura and S. Nagase, Chem. Lett., 2001, 1098.
5 (a) T. Akasaka, S. Nagase, A. Yabe and W. Ando, J. Am. Chem. Soc.,
1988, 110, 6270; (b) M. Remko and B. M. Rode, THEOCHEM, 2000,
505, 269.
6 (a) S. Yao, M. Brym, C. van Wu¨llen and M. Driess, Angew. Chem., Int.
Ed., 2007, 46, 4159; (b) M. Driess, S. Yao, M. Brym, C. van Wu¨llen and
D. Lentz, J. Am. Chem. Soc., 2006, 128, 9628.
7 (a) M. Driess, S. Yao, M. Brym and C. van Wu¨llen, Angew. Chem.,
Int. Ed., 2006, 45, 6730; (b) S. Yao, Y. Xiong, M. Brym and M. Driess,
J. Am. Chem. Soc., 2007, 129, 7268.
8 Y. Xiong, S. Yao and M. Driess, J. Am. Chem. Soc., 2009, 131, 7562.
9 Y. Xiong, S. Yao, R. Mu¨ller, M. Kaupp and M. Driess, J. Am. Chem.
Soc., 2010, 132, 6912.
10 see for example: D. Max. Roundhill, Inorg. Chem., 1980, 19, 557.
11 B. Singh, J. R. Long, F. F. de Biani, D. Gatteschi and P. Stavropoulos,
J. Am. Chem. Soc., 1997, 119, 7030.
12 F. Thomas, S. Schulz and M. Nieger, Angew. Chem., Int. Ed., 2005, 44,
5668.
13 H.-J. Gais, G. Bu¨low and G. Raabe, J. Am. Chem. Soc., 1993, 115, 7215.
14 C. S. Branch, L. C. van Poppel, S. G. Bott and A. R. Barron, J. Chem.
Crystallogr., 1999, 29, 993 and references cited therein.
15 M. B. Power, S. C. Bott, J. L. Atwood and A. R. Barron, J. Am. Chem.
Soc., 1990, 112, 3446.
16 M. R. P. van Vliet, G. van Koten, M. A. Rotteveel, M. Schrap, K. Vrieze,
B. Kojic-Prodic, A. L. Spek and A. J. M. Duisenberg, Organometallics,
1986, 5, 1389.
3
3
0.72 (d, J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.02 (d, J (H,H) =
7.0 Hz, 3 H; CHMe2), 1.21 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2),
3
3
1,35 (d, J (H,H) = 7.0 Hz, 3 H; CHMe2), 1.51 (d, J (H,H) =
7.0 Hz, 3 H; CHMe2), 1.56 (s, 3 H; NCMe), 1.80 (d, 3J (H,H) =
7.0 Hz, 3 H; CHMe2), 1.83 (d, 3J (H,H) = 7.0 Hz, 3 H; CHMe2),
1.85 (s, 6 H; DMAP), 2.50 (sept., 3J (H,H) = 7.0 Hz, 2 H; CHMe2),
3.51 (s, 1 H; NCCH2), 4.03 (sept., 3J (H,H) = 7.0 Hz, 2 H; CHMe2),
4.08 (s, 1 H; NCCH2), 5.42 (s, 1 H; g-CH), 5.48 (br., 1 H; DMAP),
5.90 (br., 1 H; DMAP), 6.98–7.45 (m, br, 6 H; 2,6-iPr2C6H3), 8.40
1
(br., 1 H; DMAP), 9.00 ppm (br., 1 H; DMAP); 13C{ H} NMR
(100.61 MHz, [D6]benzene, 25 ◦C): d = -4.78 (AlMe3), 22.0, 24.5,
24.7, 24.9, 25.2, 25.7, 25.8, 26.1 (CHMe2, NCMe), 28.9, 29.1,
29.5, 29.6 (CHMe2), 38.8 (NMe2), 88.6 (NCCH2), 104.4 (g-C),
106.7 (DMAP), 124.3, 124.4, 125.0, 125.5, 135.7, 136.1, 144.1,
147.0, 147.3, 148.7, 149.2, 149.4, 156.4 ppm (NCMe, NCCH2,
2,6-iPr2C6H3, DMAP); 29Si NMR (79.49 MHz, [D6]benzene,
17 G. M. Sheldrick, SHELXS-97, Program for solution of crystal struc-
tures, University of Go¨ttingen, Germany, 1997; G. M. Sheldrick,
SHELXL-97, Program for refinement of crystal structures, University
of Go¨ttingen, Germany, 1997.
◦
25 C): d = -74.8 (s); EI-MS: m/z (%): 655 (100) [M+], 583 (17)
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9282–9287 | 9287
©