Formation of 1-aza-2-silacyclopentanes and unexpected products from the insertion of phenylisocyanate into 2,2-dimethyl-1-(trimethylsilyl)-1-aza-2-silacyclopentane

Article abstract of DOI:10.1515/mgmc-2018-0005

Substances like 3-aminopropyltriethoxysilane are often used as adhesive promoters in various formulations for coatings or to adjust the properties of siloxanes and other polymers. Cyclisation of similar substances is also interesting because of the formation of the Si-N bond. 1-Aza-2-silacyclopentanes were synthesised from 3-aminopropylalkoxysilanes by intramolecular condensation reactions and substitution reactions at the silicon atom. The products tend to undergo ring-opening polymerisation. In contrast to literature reports, they can only be isolated as N-substituted derivatives. Phenylisocyanate inserts into the Si-N bonds of cyclic aminosilanes to form seven-membered heterocycles. Furthermore, phenylisocyanate reacts with N-H bonds in the same molecule. Two insertion products were isolated, and their crystal structures were determined.

Full text of DOI:10.1515/mgmc-2018-0005

Main Group Met. Chem. 2018; 41(1–2): 11–19
Marcus Herbig, Uwe Böhme, Anke Schwarzer and Edwin Kroke*
Formation of 1-aza-2-silacyclopentanes and unexpected products
from the insertion of phenylisocyanate into 2,2-dimethyl-1-
(
trimethylsilyl)-1-aza-2-silacyclopentane
https://doi.org/10.1515/mgmc-2018-0005
Received January 30, 2018; accepted March 23, 2018; previously
published online April 19, 2018
(Salikhov et al., 2014). However, the cyclic products have
never been isolated (Scheme 1).
According to the patent literature, 1-aza-2-silacyclopen-
tanes have been used to modify conjugated diene rubbers
or surface properties similar to 3-aminopropyltriethoxysi-
lane (Arkles et al., 2003; Ziche and Selbertinger, 2006). The
reaction of isocyanates with azasilacyclopentanes has been
used to manufacture thermoplastic rubbers by polymerisa-
tion with polyols (Pepe et al., 1994; Ziche and Selbertinger,
Abstract: Substances like 3-aminopropyltriethoxysilane
are often used as adhesive promoters in various formula-
tions for coatings or to adjust the properties of siloxanes
and other polymers. Cyclisation of similar substances is
also interesting because of the formation of the Si-N bond.
1-Aza-2-silacyclopentanes were synthesised from 3-ami-
2
006; Nyugaku et al., 2011; Tonomura et al., 2011). The Si-N
nopropylalkoxysilanes by intramolecular condensation
reactions and substitution reactions at the silicon atom.
The products tend to undergo ring-opening polymerisa-
tion. In contrast to literature reports, they can only be
isolated as N-substituted derivatives. Phenylisocyanate
inserts into the Si-N bonds of cyclic aminosilanes to form
seven-membered heterocycles. Furthermore, phenylisocy-
anate reacts with N-H bonds in the same molecule. Two
insertion products were isolated, and their crystal struc-
tures were determined.
bonds can react with heterocumulenes like CO and iso-
2
cyanates to form carbamates and ureas (Kraushaar et al.,
2
014). The known reactions of primary N-silylamines are
shown in Scheme 2, but many more insertion reactions are
in principle possible (Scheme S1).
We optimised the condensation reactions to synthe-
sise cyclic N-aminosilanes with an exocyclic trimethyl-
silyl group, reducing the tendency to polymerisation.
Furthermore, we investigated the insertion reaction
with phenylisocyanate (PhNCO). Substitution reactions
Keywords: 3-aminopropylsilanes; aminosilanes; inser- were performed to obtain a variety of cyclic products (2;
tion; isocyanates; silicon heterocycles.
Scheme 3). Having analysed the insertion products, we
present the first molecular structure of a seven-membered
silicon and urea moiety containing heterocycle and a five-
membered cyclic N-aminosilane, which is not a silatrane
or part of other oligocyclic moieties.
Introduction
Substances like 3-aminopropyltriethoxysilane are often
used as adhesive promoters in various formulations for
coatings or to adjust the properties of siloxanes and other Results and discussion
polymers. According to the literature, these substances
undergo intramolecular condensations upon long time
Synthesis of cyclic N-aminosilanes
heating (Speier et al., 1971), which can be accelerated by
the addition of hexamethyldisilazane (HMDS; Kirilin et al.,
All prepared cyclic N-aminosilanes are shown in Table 1.
2
009). The product was reported to be a cyclic N-aminosi-
The starting materials can be heated at reflux and/or
distilled without any evidence of the formation of cyclic
products. Heating with sodium alcoholates (procedure E,
similar to Ziche et al., 1996) is not as efficient as proce-
dure D (see Table 3 in the Experimental section). Accord-
ing to the patent literature, the synthesis and isolation of
unsubstituted cyclic N-aminosilanes is not possible (Pepe
et al., 1994; Arkles et al., 2003). Nevertheless, Kirilin et al.
lane that is highly reactive to ring-opening polymerisation
*
Corresponding author: Edwin Kroke, Institut für Anorganische
Chemie, TU Bergakademie Freiberg, Leipziger Straße 29,
D-09599 Freiberg, Germany, e-mail: kroke@tu-freiberg.de.
http://orcid.org/0000-0002-7934-6439
Marcus Herbig and Uwe Böhme: Institut für Anorganische Chemie,
TU Bergakademie Freiberg, Leipziger Straße 29, D-09599 Freiberg,
Germany
Anke Schwarzer: Institut für Organische Chemie, TU Bergakademie
Freiberg, Leipziger Straße 29, D-09599 Freiberg, Germany
(
2009) reported the isolation of 2,2-diethoxy-1-aza-2-sila-
cyclopentane with procedure B without mentioning the
reaction time.
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1
2ꢀꢀꢀꢀꢁꢀM. Herbig et al.: Cyclosilazanes
Scheme 1:ꢀCyclisation of 3-aminopropyltriethoxysilane by long-time
heating.
The formation of 2,2-diethoxy-1-aza-2-silacyclopentane is dubious.
For the synthesis of the N-aminosilanes 2a–e in
good yields and high purity, only procedure D is suitable.
Heating without ammonium sulfate (procedures A and B)
leaves the reactants mostly unchanged in the given time.
Procedure C yields undefined polymers.
Ammonium sulfate is known as a catalyst for the
transsilylation reaction of amines with HMDS. Therefore,
it might be assumed that ammonium sulfate catalyses the
silylation of the amine moiety. The lower boiling distillate
was characterised to be the corresponding trimethylalkox-
ysilane that is formed by the intramolecular condensa-
tion of the N-trimethylsilylated 3-aminopropylsilane. The
Scheme 3:ꢀSynthesis of all cyclic N-aminosilanes by cyclisation or
4
substitution reactions (R =H or SiMe ).
3
N-unsubstituted 1-aza-2-silacyclopentasilanes could not be
prepared.
is confirmed by the NMR and infrared spectra, the elemen-
tal analysis (EA) of 2a, the determination of molar mass
of 2a by ebullioscopy in cyclohexane, and the expected
N-unsubstituted cyclic products could not be isolated. All Table 1:ꢀCyclic N-aminosilanes prepared by cyclisation and substi-
attempts using procedure C yielded undefined polymers. tution reactions according to procedures A, B, and D in Table 3.
Without a catalyst (procedure A), only small amounts
Substance no.
Rꢁ
Rꢂ
R5
Yield (%)
have reacted in the given time, and no N-unsubstituted
cyclic product could be found but N-trimethylsilylated ꢂa
OEt
Me
OMe
Me
OEt
OEt
OMe
Me
SiMeꢂ
ꢃꢄ
ꢅꢂ
ꢆꢇ
ꢈꢉ
ꢂb
SiMeꢂ
ones. Also, no distillate is obtained by heating pure N-tri-
ꢂc
SiMeꢂ
SiMeꢂ
Me
SiMeꢂ
SiMeꢂ
SiMeꢂ
methylsilyl-3-aminopropyltrimethoxysilane with ammo-
ꢂd
nium sulfate, but undefined polymers were found in the
a,b
ꢂe
OMe
OEt
OEt
OMe
Et
ꢈꢊ
29
still pot showing similar Si nuclear magnetic resonance
a,b
a,b
a,b
ꢂf
ꢂꢄ
~ꢄꢉꢉ
~ꢄꢉꢉ
n
(
NMR) signals like in experiments using procedure C with ꢂg
Bu
n
n
1
a. Excess of HMDS is needed for the synthesis of cyclic ꢂh
Bu
Bu
N-aminosilanes, which reduces the tendency of polymeri-
a
1
According to H-NMR.
sation, most likely because of steric effects by silylation of
b
1
Products contain impurities, and yields were estimated via H-NMR
the remaining N-H bond. The presence of the SiMe moiety spectra.
3
Scheme 2:ꢀReactions of primary N-silylamines with CO and isocyanates.
2
Both can insert into the Si-N- or the N-H bond, and twofold, threefold, or even fourfold insertion modes are possible (see also Scheme S1,
supporting information).
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M. Herbig et al.: Cyclosilazanesꢋꢁꢀꢀꢀꢋ13
Scheme 4:ꢀSubstitution of the ethoxy group in 2a using EtMgBr-tetrahydrofuran solution.
+
[
Mꢀ+ꢀH] peak in the mass spectrum of 2c. The N-trimethyl- Distillation should be avoided because of possible reac-
silylated products also tend to polymerise, forming high tions at high temperature, i.e., polymerisation catalysed
boiling macromolecules upon reflux but with much by the Grignard reagent or the corresponding ethanolate.
smaller reaction rates. Therefore, in all experiments per-
formed with procedure D polymerisation, products can
be found in the still pot after distillation lowering the Insertion reactions with PhNCO
yield of the pure cyclic product. On long time standing,
the pure N-substituted cyclic N-aminosilane undergoes The reaction of the cyclic N-aminosilanes with PhNCO
polymerisation, too. The polymerisation products can results in a mixture of insertion and oligomerisation
be converted into the starting materials by heating with products of the isocyanate. Only in the reaction mixture
excess of methanol or ethanol, respectively. The stabilisa- obtained from 2d and PhNCO products 3 and 4 are crys-
tion of 1-aza-2-silacyclopentanes by the exocyclic SiMe3 tallised and analysed (Scheme 5). In both molecules, the
moiety is confirmed by heating of N,N-bis(trimethylsilyl)- exocyclic trimethylsilane moiety is absent. There are two
3
-aminopropyltrimethoxysilane with catalytic amounts of possibilities for this observation: (i) there were N-unsub-
ammonium sulfate. In this case, the formation of 2c and stituted products in low concentration in the reaction
trimethylmethoxysilane is observed. N-Methyl-3-amino- mixture, not detected by NMR and having no influence
propyltrimethoxysilane is less reactive and does not form on the other analyses; and (ii) partial hydrolysis took
2
e with a similar yield like the primary amines.
place. The Si-N bond is known to be moisture sensitive
Further derivatives of 2 are accessible starting from (see also section Alcoholysis reactions). Therefore, it is
a. Treatment of 2a with EtMgBr solution in a stoichi- probable that this moiety is more prone to hydrolysis than
2
ometry of 1:1 leads to 2f. A higher amount of EtMgBr per the remaining groups in the cyclic N-aminosilanes 2. In
mole 2a does not react with the N-aminosilane to form the view of 3 and 4, it is likely that the first reaction step is
twofold substituted product (Scheme 4).
the insertion of PhNCO into the exocyclic Si-N bond. The
In contrast to this observation, the reaction with urea moiety activates a second insertion into the endocy-
n
BuLi leads to 2g and 2h depending on the stoichiomet- clic Si-N bond, probably due to steric reasons. The second
ric ratio of the reactants. The removal of the byproducts molecule PhNCO inserts into the five-membered ring to
by filtration and washing with n-pentane is not effective. form a seven-membered one. During this reaction step,
Scheme ꢃ:ꢀReaction of 2d with PhNCO.
Two different products are crystallised from the reaction mixtures.
Unauthenticated
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1
4ꢀꢀꢀꢀꢁꢀM. Herbig et al.: Cyclosilazanes
Scheme 6:ꢀAlcoholysis of 2a with n-pentanol.
The cleavage of both Si-N bonds is preferred.
the endocyclic Si-N bond is weakened and polymerisation Single crystal X-ray diffraction analyses
as side reaction is more likely. Therefore, because of the
evident partial hydrolysis, a mixture of different mole- Compound 3 crystallises in the orthorhombic space group
cular species is obtained. Furthermore, isocyanates can Pbca with one crystallographically independent molecule
undergo oligomerisation reactions, the products of which in the asymmetric unit. Considering the outcome of the
also are present in the final reaction mixture.
reaction leading to 3, one can state that one molecule of
The observed insertion reaction could not be moni- phenylisocyanate is inserted into the azasilacyclopen-
tored by NMR spectroscopy upon melting solutions at tane ring of 2. This leads to a seven-membered ring with
−
25°C of cyclic N-aminosilane and PhNCO in anhydrous a 2,4-diazasilepane structure (Figure 1). Besides, a phe-
nitromethane frozen separately in the NMR tube. Thus, nylcarbamic group replaces the trimethylsilyl group that
after warming the mixture up to −25°C, the reaction was was present in 2. Thus, a second insertion of an isocyanate
completed after seconds.
molecule into the N-H bond has occurred.
The ring pucker of the seven-membered ring (Si1-C1-
C2-C3-N1-C13-N3) was analysed according to Evans and
Boeyens (1989). The least-squares plane of these seven
atoms in crystal coordinates is given by −8.404xꢀ−ꢀ1.515yꢀ
Alcoholysis reactions
In order to analyse the hydrolysis behaviour of 2a–d, we
+
ꢀ14.142zꢀ=ꢀ3.070. The out-of-plane displacements of the
performed alcoholysis experiments with 1-pentanol and
ring atoms in Å are 0.232 Si1, −0.595 C1, 0.130 C2, 0.602 C3,
2a. The results lead to the conclusion that the hydrolysis
of both Si-N bonds is preferred compared with the hydrol-
ysis of only one of them (Scheme 6). It is assumed that the
first reaction step is the alcoholysis of the exocyclic Si-N
bond, because of the steric hindrance of the endocyclic
bond. Otherwise, the formation of 4 cannot be explained.
The formed N-unsubstituted cyclic N-aminosilane under-
goes ring-opening reaction with the alcohol but does not
form polymers. In all alcoholysis experiments, 3-amino-
propyldiethoxypentoxysilane was formed.
This is similar to the bis-insertion of CO into diami-
2
nosilanes of the type (CH ) Si(NHR) to form bis-carba-
3
2
2
mates of the type (CH ) Si(OCONHR) . Mono-insertion
3
2
2
products can neither be isolated nor detected (Kraushaar
et al., 2012). Similar isocyanate insertions have also been
reported (Schöne et al., 2010). Considering these results,
Figure 1:ꢀMolecular structure of 3 showing the atomic numbering
scheme.
The thermal ellipsoids of the nonhydrogen atoms are drawn at the
50% probability level.
we cannot determine if and when the loss of the SiMe3
moiety took place (via hydrolysis), leading to 3 and 4.
Unauthenticated
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M. Herbig et al.: Cyclosilazanesꢋꢁꢀꢀꢀꢋ1ꢃ
−
0.391 N1, −0.278 C13, and 0.299 N3. These displacements aromatic hydrogen atoms with both aryl moieties are in
lead to the conclusion that the seven-membered ring is in the range of 2.8–2.9ꢀÅ.
a boat conformation.
Compound 4 crystallises in the monoclinic space
Besides, compound 3 contains a biuret unit (carba- group P2 /c with two crystallographically independent
1
mylurea) given by the atoms N2-C6(=ꢀO1)-N1-C13(=ꢀO2)-N3. molecules in the asymmetric unit (Figure 2). The reac-
This unit is composed of two planar urea subunits with tion from 2 to 4 involves replacement of the trimethylsilyl
a dihedral angle between these subunits of 20.463(90)°. group by a phenylcarbamic group. The central urea unit
The phenyl ring C7-C12 is nearly coplanar with the urea of 4 is bound to a phenyl ring via N2 and to the 1,2-azasilo-
subunit N2-C6(=ꢀO1)-N1 with a dihedral angle between lidine via N1. Both crystallographically independent mol-
these planes of 4.576(97)°. In contrast, the phenyl group ecules differ in the conformation of the phenyl ring with
C14-C19 shows a dihedral angle of 71.787(52)° with the urea respect to the central urea unit formed by N1-C6(=ꢀO1)-N2.
subunit N1-C13(=ꢀO2)-N3. The angle between the phenyl The dihedral angle between these planes is in molecule
units is 55.252(48)°. An intramolecular N2-Hꢀ·ꢀ·ꢀ·ꢀO2 inter- A 39.535(82)°, but in molecule B only 18.173(96)°. Intra-
action (1.88ꢀÅ, 142°) stabilises the molecular conformation. molecular C8-H8ꢀ·ꢀ·ꢀ·ꢀO1 distances differ from molecules A
The crystal packing is dominated by C-Hꢀ·ꢀ·ꢀ·ꢀO inter- to B and influences the dihedral angle between the urea
actions in the range of 2.4–2.7ꢀÅ (Table 2). A bifurcated unit and the phenyl moiety (A: 2.45ꢀÅ, 108°; B: 2.25ꢀÅ,
contact at O1 (C15-H15ꢀ·ꢀ·ꢀ·ꢀO1, C5-H5ꢀ·ꢀ·ꢀ·ꢀO1) leads to 121°). Five-membered rings may adopt an envelope or
molecular chains along the crystallographic a axis. These half-chair (twisted) conformation (Fuchs, 1978). Ring
chains are connected via C1-H1Aꢀ·ꢀ·ꢀ·ꢀO2 along the crystallo- puckering analysis of 4 shows that the five-membered
graphic b axis. Further, C-Hꢀ·ꢀ·ꢀ·ꢀπ contacts of aliphatic and ring in molecule A adopts a twisted conformation with the
Table 2:ꢀGeometric parameters of selected intra- and intermolecular hydrogen bonds in 3 and 4.
ꢄ
D-Hꢅ·ꢅ·ꢅ·ꢅA
ꢄ
Symmetry
ꢄ
D-H (Å)
ꢄ Hꢅ·ꢅ·ꢅ·ꢅA (Å)
ꢄ
Dꢅ·ꢅ·ꢅ·ꢅA (Å)
ꢄ D-Hꢅ·ꢅ·ꢅ·ꢅA (°)
ꢆꢌ
Nꢇ-Hꢁ·ꢁ·ꢁ·ꢁOꢇ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
x, y, z
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢉ.ꢆꢊꢃ(ꢄꢈ)
ꢉ.ꢈꢍ
ꢌ ꢄ.ꢆꢅꢈ(ꢄꢆ)
ꢌ ꢇ.ꢍꢈꢆꢂ(ꢄꢍ)
ꢌ ꢂ.ꢂꢆꢈꢄ(ꢄꢆ)
ꢌ ꢂ.ꢃꢊꢊꢇ(ꢄꢆ)
ꢌ ꢂ.ꢊꢃꢍꢄ(ꢄꢅ)
ꢌ ꢂ.ꢆꢄꢄꢅ(ꢄꢅ)
ꢌ ꢂ.ꢃꢃꢉꢅ(ꢄꢍ)
ꢌ ꢂ.ꢃꢆꢈꢈ(ꢄꢍ)
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢄꢊꢄ.ꢈ(ꢄꢅ)
ꢄꢅꢍ.ꢆ
ꢄꢍꢆ.ꢊ
ꢄꢂꢅ.ꢂ
ꢄꢍꢉ
ꢌ
Cꢄꢍ-Hꢄꢍꢁ·ꢁ·ꢁ·ꢁOꢄ
Cꢍ-HꢍCꢁ·ꢁ·ꢁ·ꢁOꢄ
Cꢄ-HꢄAꢁ·ꢁ·ꢁ·ꢁOꢇ
ꢄ/ꢇꢁ+ꢁx, y, ꢄ/ꢇꢁ−ꢁz
ꢄ/ꢇꢁ+ꢁx, y, ꢄ/ꢇꢁ−ꢁz
ꢄ/ꢇꢁ−ꢁx, ꢄ/ꢇꢁ+ꢁy, z
ꢄ/ꢇꢁ−ꢁx, ꢄ/ꢇꢁ+ꢁy, z
x, ꢄ/ꢇꢁ−ꢁy, −ꢄ/ꢇꢁ+ꢁz
−ꢄ/ꢇꢁ+ꢁx, y, ꢄ/ꢇꢁ−ꢁz
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢇ.ꢊꢊ
ꢇ.ꢅꢇ
ꢌ
ꢉ.ꢈꢆ
ꢌ
ꢉ.ꢈꢈ
ꢇ.ꢃꢅ
a
ꢌ
Cꢍ-HꢍBꢁ·ꢁ·ꢁ·ꢁCgꢇ
ꢉ.ꢈꢆ
ꢇ.ꢈꢂ
a
ꢌ
Cꢈ-Hꢈꢁ·ꢁ·ꢁ·ꢁCgꢇ
ꢉ.ꢈꢍ
ꢇ.ꢆꢉ
ꢄꢍꢄ
a
ꢌ
Cꢄꢈ-Hꢄꢈꢁ·ꢁ·ꢁ·ꢁCgꢄ
ꢉ.ꢈꢍ
ꢇ.ꢈꢅ
ꢄꢂꢊ
ꢇꢌ
NꢇA-HꢇNAꢁ·ꢁ·ꢁ·ꢁOꢄB ꢌ
NꢇB-HꢇNBꢁ·ꢁ·ꢁ·ꢁOꢄA ꢌ
CꢄꢇB-HꢄꢇBꢁ·ꢁ·ꢁ·ꢁOꢄAꢌ
−xꢁ+ꢁꢄ, yꢁ+ꢁꢄ/ꢇ, −zꢁ+ꢁꢄ/ꢇꢌ
ꢉ.ꢈꢄ(ꢂ)
ꢉ.ꢈꢉ(ꢂ)
ꢉ.ꢈꢍ
ꢄ.ꢈꢈ(ꢂ)
ꢇ.ꢇꢉ(ꢂ)
ꢇ.ꢊꢆ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢇ.ꢆꢈꢄ(ꢇ)
ꢂ.ꢉꢍꢆ(ꢇ)
ꢂ.ꢂꢉꢄ(ꢂ)
ꢂ.ꢊꢄꢅ(ꢂ)
ꢂ.ꢃꢆꢊ(ꢃ)
ꢂ.ꢃꢍꢍ(ꢂ)
ꢂ.ꢊꢂ(ꢂ)
ꢄꢅꢉ(ꢂ)
ꢄꢍꢈ(ꢇ)
ꢄꢊꢍ.ꢂ
ꢄꢍꢃ.ꢇ
ꢄꢅꢉ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
xꢁ+ꢁꢄ, y, z
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
xꢁ+ꢁꢄ, y, z
CꢂB-HꢂEꢁ·ꢁ·ꢁ·ꢁOꢄA
CꢄB-HꢄCꢁ·ꢁ·ꢁ·ꢁCgꢊ
CꢇA-HꢇBꢁ·ꢁ·ꢁ·ꢁCgꢊ
CꢇC-HꢇEꢁ·ꢁ·ꢁ·ꢁCgꢊ
ꢌ
ꢌ
ꢌ
ꢌ
xꢁ+ꢁꢄ, y, z
ꢉ.ꢈꢈ
ꢇ.ꢊꢈ
−x, ꢄ/ꢇꢁ+ꢁy, ꢄ/ꢇꢁ−ꢁz
−x, ꢄꢁ−ꢁy, −z
−x, ꢄ/ꢇꢁ+ꢁy, ꢄ/ꢇꢁ−ꢁz
ꢉ.ꢈꢈ
ꢇ.ꢅꢄ
ꢉ.ꢈꢈ
ꢇ.ꢅꢄ
ꢄꢍꢈ
ꢄꢊꢃ
ꢉ.ꢈꢈ
ꢇ.ꢍꢃ
aCg is defined as the centroid of the rings (centre of gravity): Cg1: C7-C12; Cg2: C14-C19; Cg4: C7B-C12B.
Figure 2:ꢀMolecular structures of the two crystallographically independent molecules of 4 showing the atomic numbering scheme.
Molecule A is labelled with A, molecule B with B. The thermal ellipsoids of the nonhydrogen atoms are drawn at the 50% probability level.
Molecule B shows a disorder at the five-membered ring with s.o.f. of 0.85.
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6ꢀꢀꢀꢀꢁꢀM. Herbig et al.: Cyclosilazanes
atoms C1A and C2A −0.229 and 0.283ꢀÅ out of the plane derivative 4 and an azasilacyclopentane 3 containing two
of the five-membered ring. The least-squares plane of the and one urea units, respectively.
five atoms in crystal coordinates is given by 9.646xꢀ−ꢀ2.0
7
9yꢀ+ꢀ3.340zꢀ=ꢀ2.250. Molecule B features a disorder at C1
and C2. Both five-membered rings formed by this disor- Experimental
der are in twisted conformation with the atoms C1B/C2B
All starting materials except 1d and N,N-bis(trimethylsilyl)-3-ami-
nopropyl-trimethoxysilane were obtained from Sigma-Aldrich (St.
Louis, MO, USA) and used as received. 1d and N,N-bis(trimethylsilyl)-
(
−0.249/0.299ꢀÅ) and C1C/C2C (0.282/−0.323ꢀÅ) alternating
above and below the plane formed by the five-membered
rings. The least-squares planes of the five-membered rings
in crystal coordinates are given by 1.135xꢀ−ꢀ1.756yꢀ+ꢀ18.192
3-amino-propyl-trimethoxysilane were obtained from ABCR
(
Karlsruhe, Germany) and used without further purification. All reac-
zꢀ=ꢀ6.812 for Si1B-N1B-C1B-C2B-C3B and 2.865xꢀ+ꢀ0.622yꢀ+ꢀ tions were carried out under dry argon atmosphere using standard
17.546zꢀ=ꢀ8.763 for Si1B-N1B-C1C-C2C-C3B.
Schlenk technique.
NMR spectra were measured with a Bruker DPX400 (Bruker,
In contrast to 3, the crystal packing of 4 is domi-
1
13
Karlsruhe, Germany, frequencies: H, 400.13ꢀMHz; C, 100.61ꢀMHz;
nated by C-Hꢀ·ꢀ·ꢀ·ꢀπ interactions (Nishio, 2004) in the range
of 2.56 to 2.71ꢀÅ. However, the π-system of molecule A is
not involved in C-Hꢀ·ꢀ·ꢀ·ꢀπ contacts. Instead, the oxygen O1
29
Si, 79.49ꢀMHz; all substitution reaction products) or a Bruker
Avance III 500ꢀMHz (Bruker, Karlsruhe, Germany, frequencies:
1
13
29
H, 500.13ꢀMHz; C, 125.76ꢀMHz; Si, 99.36ꢀMHz; all condensation
atom interacts with the NH and two CH groups in strong and insertion products) spectrometer in CDCl (Armar Chemicals,
3
Ahmedabad, Gujarat, India, purified by distillation from CaH ) with
N-Hꢀ·ꢀ·ꢀ·ꢀO [2.20ꢀÅ, 159(2)°] and weak C-Hꢀ·ꢀ·ꢀ·ꢀO hydrogen
bonding (2.5ꢀÅ). These interactions occur in the same
direction as a possible C-Hꢀ·ꢀ·ꢀ·ꢀπ can be localised (C3B-
H3Dꢀ·ꢀ·ꢀ·ꢀCg3, with Cg3 as the centre of gravity of C7A-C12A)
2
tetramethylsilane as internal standard.
Raman spectra were measured with Bruker Fourier Transform
Raman Spectrometer RFS100/S (Bruker, Karlsruhe, Germany). The
device works with an air-cooled Nd:YAG laser with a wavelength of
and form intermolecular dimers with molecule B. Further- 1064ꢀnm and a nitrogen-cooled detector. The samples were filled in
more, via N-Hꢀ·ꢀ·ꢀ·ꢀO (Table 2) bridges of molecule B, the glass tubes and sealed with PTFE-paste Triboflon MYN 503 (Spezials-
crystal packing is stabilised.
chmierstoffe Anja Heibach, Odenthal, Germany).
The EAs were conducted using a vario Micro cube (Elementar
Analysensysteme GmbH, Hanau, Germany) with about 2ꢀmg samples
in a tin capsule.
Conclusions
The ebullioscopic molecular mass determination was done with
cyclohexane (VWR International GmbH, Darmstadt, Germany, puri-
fied by distillation from Na/benzophenone) as solvent and a four-
Intramolecular cyclisation reactions of 3-aminopropy-
wired Pt100 resistance thermometer.
lalkoxysilanes to form 1-aza-2-silacyclopentane appear
The mass spectrum was measured with an Advion expression
obvious and have been reported in literature. However, the
CMS mass spectrometer (Advion, Ithaca, NY, USA).
corresponding five-membered cyclic condensation products
have neither been isolated nor structurally analysed. Only
Synthesis of 2a–e by cyclisation reactions
in the presence of excess HMDS and (NH ) SO as a catalyst
4
2
4
it is possible that 1-aza-2-silacyclopentanes are formed and
The 3-aminopropylsilanes 1a–e were refluxed for 2 h with the reac-
tants listed in Table 3. The reaction mixture was distilled under
reduced pressure to isolate 2a–e. The catalyst and the amount of
HMDS were varied in order to find optimised reaction conditions.
stabilised bearing SiMe -substituents at the N atom.
3
Via this route, we obtained the derivatives 2a–2e
in yields between 61% and 94%. Unsubstituted 1-aza-
2
-silacyclopentanes with N-H group are not obtainable.
1
2
,2-Diethoxy-1-trimethylsilyl-1-aza-2-silacyclopentane (2a) 2,2-Diethoxy-1-trimethylsilyl-1-aza-2-silacyclopentane (2a):ꢁ H-
3
can be treated with Grignard or alkyllithium reagents to NMR: δ [ppm]ꢀ=ꢀ3.68 (q, 4H, CH CH O-, J ꢀ=ꢀ7.0ꢀHz), 2.85 (t, 2H, CH -
3
2
H,H
2
3
3
N, J ꢀ=ꢀ5.9ꢀHz), 1.72 (qu, 2H, CH -CH -CH , J ꢀ=ꢀ6.8ꢀHz), 1.14 (t, 6H,
form the monoalkylated or dialkylated products 2f–2g.
All 1-aza-2-silacyclopentanes tend to undergo ring-
opening polymerisation reactions upon long-term standing
at room temperature. Besides, hydrolysis and alcoholysis
of the Si-N bond in 2a–2g can take place easily.
During our studies on PhNCO insertion reactions into
the Si-N bonds of 2d, we isolated the partial hydrolysis and
double-insertionproduct3andthemono-insertionproduct
H,H
2
2
2
H,H
3
3
CH CH O-, J ꢀ=ꢀ7.0ꢀHz), 0.50 (t, 2H, Si-CH -CH -, JH,Hꢀ=ꢀ7.6ꢀHz), 0.33
3
2
H,H
2
2
1
3
(
HMDS), 0.01 (s, 9H, Si(CH ) ); C-NMR: δ [ppm]ꢀ=ꢀ58.3 (CH CH O-),
3
3
3
2
4
5.4 (CH -N), 25.4 (CH -CH -CH ), 18.3 (CH CH O-), 5.9 (Si-CH -CH -),
2
2
2
2
3
2
2
2
29
1
−
0.4 (Si(CH ) ); Si-NMR: δ [ppm]ꢀ=ꢀ2.6 (Si(CH ) ), −16.9 (Si ); see also
3
3
3 3
−1
Tsai and Marshall (1969); Raman ν [cm ]ꢀ=ꢀ2958, 2927, 2900, 2839,
763, 2715, 2671, 2620, 2485, 1478, 1452, 1409, 1290, 1247, 1193, 1144,
2
1
1
089, 1020, 947, 888, 854, 771, 750, 679, 628, 573, 503, 416, 379, 194,
06; EA: calc for C H NO Si : C: 48.53%, H: 10.18%, N: 5.66%; found
1
0
25
2
2
C: 48.23%, H: 10.29%, N: 5.47%; yieldꢀ=ꢀ6.82 g (61%, procedure D); M
calc. for C H NO Si 247.5 g/mol, found Mꢀ=ꢀ(246ꢀ±ꢀ17) g/mol (ebullio-
4
. The single crystal X-ray diffraction analyses indicate
1
0
25
2
2
the unexpected formation of 2,4-diaza-1-silacycloheptane scopically measured in cyclohexane).
Unauthenticated
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M. Herbig et al.: Cyclosilazanesꢋꢁꢀꢀꢀꢋ17
Table 3:ꢀParameters of different synthesis procedures.
Procedureꢄ Catalyst ꢄ Remarks
ꢄ
ꢄ
Yield (%)
ꢂa
ꢄ ꢂb
ꢄ ꢂc
ꢄ ꢂd
ꢄ ꢂe
a
a
a
b
A
B
C
D
E
ꢌ
ꢌ
ꢌ
ꢌ
ꢌ
—
—
ꢌ
ꢌ
Stoichiometry HMDS:silaneꢁ=ꢁꢄ:ꢄꢌ
Excess HMDS
Stoichiometry HMDS:silaneꢁ=ꢁꢄ:ꢄꢌ
ꢈ
ꢌ ꢍ
ꢌ ꢇ
ꢌ ꢉ
ꢌ
ꢌ
ꢌ
—
a
a
a
a
a
ꢌ
ꢊ
ꢌ ꢈ
ꢌ ꢍ
ꢌ ꢃ
ꢉ
c
ꢌ ꢉc
ꢌ ꢅꢂ
ꢌ ꢉc
ꢌ ꢆꢇ
ꢌ ꢉc
ꢌ ꢈꢉ
c
(NH ) SO ꢌ
ꢉ
ꢉ
ꢊ
ꢇ
ꢊ
a
(NH ) SO ꢌ
NaOMe
Excess HMDS
Without HMDS
ꢌ
ꢌ
ꢃꢄ
ꢌ ꢈꢊ
ꢊ
ꢇ
ꢊ
a
a
a
a
a
ꢌ
ꢉ
ꢌ ꢉ
ꢌ ꢉ
ꢌ ꢉ
ꢌ ꢉ
a
According to 29Si-NMR, refer to 1a–e.
b
Many impurities, not determined.
Undefined polymer.
c
2
-Ethoxy-2-methyl-1-trimethylsilyl-1-aza-2-silacyclopentane (2b):ꢁ n-butyllithium (2.5 ꢂ in hexane) is added dropwise. After warming
1
H-NMR: δ [ppm]ꢀ=ꢀ3.61 (m, 2H, CH CH O-), 2.97 and 2.81 (m, each 1H, to room temperature, volatiles are removed in vacuo, and the residue
3
2
3
CH -N), 1.70 (m, 2H, CH -CH -CH ), 1.14 (t, 3H, CH CH O-, J ꢀ=ꢀ7.0ꢀHz), is suspended in n-pentane. The suspension is filtered via a G4 frit,
2
2
2
2
3
2
H,H
1
0
.68 and 0.41 (m, each 1H, Si-CH -CH -), 0.14 (s, 3H, CH Si ), 0.04 and the solvent is removed in vacuo. Some residues and byproducts
2
2
3
1
3
3
(
s, 9H, Si(CH ) ); C-NMR: δ [ppm]ꢀ=ꢀ57.6 (CH CH O-), 47.1 (C ), 25.9 remain in the liquid.
3
3
3
2
(
CH -CH -CH ), 18.2 (CH CH O-), 10.6 (Si-CH -CH -), 2.4 (HMDS), −0.3
2
2
2
3
29
2
2
2
1
1
(
Si(CH ) ), −1 (CH Si ); Si-NMR: δ [ppm]ꢀ=ꢀ2.5 (Si(CH ) ), 11.1 (Si );
1
3
3
3
3
3
2-Ethoxy-2-ethyl-1-trimethylsilyl-1-aza-2-silacyclopentane (2f):ꢁ H-
−1
Raman ν [cm ]ꢀ=ꢀ2956, 2925, 2899, 2834, 2714, 2669, 2618, 2487, 1477,
452, 1409, 1287, 1246, 1137, 1106, 1061, 1013, 964, 890, 856, 750, 709,
NMR: δ [ppm]ꢀ=ꢀ3.67 (m, 2H, CH CH O-), 3.02 and 2.85 (m, each 1H,
3
2
1
3
CH -N), 1.75 (m, 2H, CH -CH -CH ), 1.18 (t, 3H, J ꢀ=ꢀ7.0 Hz) and 0.94
2
2
2
2
H,H
6
84, 656, 626, 563, 485, 412, 232, 192; EA: calc for C H NOSi : C:
9.71%, H: 10.66%, N: 6.44%; found C: 48.73%, H: 10.70%, N: 6.57%;
1
9
23
2
(m, 3H, CH CH O- and CH CH Si -), 0.63 (m, 4H, Si-CH -CH - and
2 2
1 13
3
3
2
2
4
CH CH Si -), 0.09 (s, 9H, Si(CH ) ); C-NMR: δ [ppm]ꢀ=ꢀ57.9 (CH CH O-),
3
2
3
3
3
2
yieldꢀ=ꢀ8.5 g (73%, procedure D).
1
4
(
7.6 ( CH -N), 26.4 (CH -CH -CH ), 18.5 (CH CH O-), 8.1 (CH CH Si -), 7.2
2 2
1 29
2
2
2
2
3
3
CH CH Si -), 7.1 (Si-CH -CH -), −0.2 (Si(CH ) ); Si-NMR: δ [ppm]ꢀ=ꢀ12.9
2
1
3
2
2
3 3
1
2
,2-Dimethoxy-1-trimethylsilyl-1-aza-2-silacyclopentane (2c):ꢁ H- (Si ), 2.2 (Si(CH ) ); yieldꢀ=ꢀ0.52 g (56%).
3
3
3
NMR: δ [ppm]ꢀ=ꢀ3.39 (m, 6H, CH O-), 2.82 (q, 2H, CH -N, J ꢀ=ꢀ6.2ꢀHz),
3
2
H,H
3
1
.69 (m, 2H, CH -CH -CH ), 0.47 (q, 2H, Si-CH -CH -, JH,Hꢀ=ꢀ7.6ꢀHz),
2
2
2
2
2
2-n-Butyl-2-ethoxy-1-trimethylsilyl-1-aza-2-silacyclopentane (2g):ꢁ
1
13
0
.00 (m, 9H, Si(CH ) ); C-NMR: δ [ppm]ꢀ=ꢀ50.1 (CH O-), 45.2 (CH -
3
3
3
2
H-NMR: δ [ppm]ꢀ=ꢀ3.69 (m, 2H, CH CH O-), 3.03 and 2.85 (m, each
2
3
29
N), 25.4 (CH -CH -CH ), 4.5 (Si-CH -CH -), −0.7 (Si(CH ) ); Si-NMR: δ
n
2
2
2
2
2
3
3
1H, CH -N), 1.77 (m, 2H, CH -CH -CH ), 1.44 (m, 6H, CH of Bu); 1.22
3 4 n
2
2
2
2
2
1
[
ppm]ꢀ=ꢀ2.9 (Si(CH ) ), −13.7 (Si ); see also Salikhov et al. (2014); Raman
3
3
(t, 3H, CH CH O-, J ꢀ=ꢀ7.0ꢀHz) and 0.98 (t, 3H, H and CH of Bu),
2
13
3
H,H
3
−
1
ν [cm ]ꢀ=ꢀ2957, 2900, 2837, 2671, 2620, 2485, 1477, 1453, 1408, 1346, 1247,
0
[
.75 and 0.60 (m, 2H, Si-CH -CH -), 0.24 (s, 9H, Si(CH ) ); C-NMR: δ
2
2
3 3
1
4
146, 1098, 1061, 1021, 987, 961, 888, 858, 784, 749, 676, 628, 565, 490,
ppm]ꢀ=ꢀ57.4 (CH CH O-), 47.2 (CH -N), 26.4 and 26.3 and 26.0 (CH -CH -
2
n n
3
2
2
2
+
12, 370, 219, 195, 108; yieldꢀ=ꢀ2.49 g (82%, procedure D); MS: [Mꢀ+ꢀH]
CH and CH of Bu), 18.3 (CH CH O-), 15.4 (CH of Bu); 13.8 (CH of
2
2
3
2
2
3
m/z calc. for C H NO Si : 220 g/mol, found 220 g/mol.
n
29
1
8
21
2
2
Bu); 8.6 (Si-CH -CH -), −0.3 (Si(CH ) ); Si-NMR: δ [ppm]ꢀ=ꢀ11.2 (Si ),
2
2
3 3
−1
2
.2 (Si(CH ) ); Raman ν [cm ]ꢀ=ꢀ2956, 2923, 2897, 2874, 2834, 2760, 2711,
3
3
1
2
,2-Dimethyl-1-trimethylsilyl-1-aza-2-silacyclopentane (2d):ꢁ H- 2668, 2618, 2485, 1476, 1449, 1409, 1344, 1289, 1245, 1191, 1137, 1106,
3
NMR: δ [ppm]ꢀ=ꢀ2.91 (t, 2H, CH -N, J ꢀ=ꢀ6.0ꢀHz), 1.73 (m, 2H, CH -CH - 1062, 1011, 963, 889, 852, 749, 683, 646, 629, 567, 499, 414, 224, 192,
2
3
H,H
2
2
1
CH ), 0.63 (t, 2H, Si-CH -CH -, J ꢀ=ꢀ7.4ꢀHz), 0.31 (HMDS), 0.11 (s, 6H, 108; yieldꢀ=ꢀ100% according to H-NMR, LiOEt not removed.
CH Si ), 0.05 (s, 9H, Si(CH ) ); C-NMR: δ [ppm]ꢀ=ꢀ48.3 (CH -N), 26.6
2
2
2
H,H
13
1
3
3
3
2
1
29
(
CH -CH -CH ), 13.23 (Si-CH -CH -), 1.6 (CH Si ), 0.2 (Si(CH ) ); Si-
1
2
2
2
2
2
3
3
3
2,2-Di-n-butyl-1-trimethylsilyl-1-aza-2-silacyclopentane (2h):ꢁ H-
1
NMR: δ [ppm]ꢀ=ꢀ22.8 (impurity), 18.2 (Si ), 2.1 (Si(CH ) ); Raman ν
3
3
3
NMR: δ [ppm]ꢀ=ꢀ3.92 (m, 2H, LiOEt), 2.88 (t, 2H, CH -N, J ꢀ=ꢀ6.1 Hz),
2
H,H
−
1
[
cm ]ꢀ=ꢀ2954, 2898, 2831, 2666, 2617, 2483, 1474, 1450, 1410, 1344, 1245,
132, 1059, 1007, 889, 862, 832, 785, 746, 682, 645, 621, 554, 475, 368,
12, 213, 184, 109; yieldꢀ=ꢀ4.25 g (90%, procedure D).
3
n
1
.69 (qu, 2H, CH -CH -CH , J ꢀ=ꢀ6.8 Hz), 1.33 (m, 12H, CH of Bu); 0.91
2
n
2
2
H,H
2
1
3
(
m, 6H, CH of Bu), 0.65 (m, 2H, Si-CH -CH -), 0.60 (m, 3H, LiOEt);
3
2
2
13
0
.12 (s, 9H, Si(CH ) ); C-NMR: δ [ppm]ꢀ=ꢀ58.0 (LiOEt), 48.6 (CH -N),
3
3
2
n
2
6.9 and 26.6 and 26.2 (CH -CH -CH and CH of Bu), 22.8 (LiOEt), 16.6
2
2
2
2
29
n
n
2
9
2
,2-Dimethoxy-1-methyl-1-aza-2-silacyclopentane (2e):ꢁ Si-NMR: (CH of Bu); 13.7 (CH of Bu); 9.5 (Si-CH -CH -), −0.4 (Si(CH ) ); Si-
2
3
2
2
3 3
1
1
−
1
δ [ppm]ꢀ=ꢀ−20.8 (Si ), 2.4 (HMDS), −41.6 (N-methyl-3-aminopropyltri- NMR: δ [ppm]ꢀ=ꢀ21.2 (Si ), 1.8 (Si(CH ) ); Raman ν [cm ]ꢀ=ꢀ2955, 2934,
3
3
methoxysilane). Because of impurities, no Raman spectrum was meas- 2898, 2874, 2859, 2734, 2705, 2668, 2616, 1447, 1410, 1343, 1289, 1245,
ured. Yieldꢀ=ꢀ94 mol% (according to Si-NMR, refer to 1e, procedure D). 1188, 1133, 1052, 1006, 962, 888, 850, 747, 682, 639, 605, 564, 495, 417,
29
1
2
30, 188, 136; yieldꢀ=ꢀ100% according to H-NMR, LiOEt not removed.
Substitutions reactions with 2a
Insertion reaction of PhNCO with 2d
A solution of 2a and about 20 mL of n-pentane is cooled to −78°C by
stirring in a bath of dry ice and isopropanol. Stoichiometric amounts The cyclic N-aminosilane 2d (one part) in n-pentane is cooled to 0°C,
of a solution of ethylmagnesiumbromide (1 ꢂ in tetrahydrofuran) or the stoichiometric amount (two parts) of PhNCO is carefully added
Unauthenticated
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1
8ꢀꢀꢀꢀꢁꢀM. Herbig et al.: Cyclosilazanes
Table 4:ꢀCrystal data and structure refinement for 3 and 4.
ꢆ
ꢇ
Empirical formula
C H N O Si
C H N OSi
ꢄꢈ ꢇꢂ
ꢂꢍꢂ.ꢊꢈ
ꢂ
ꢇ
ꢄꢇ ꢄꢆ
ꢇꢂꢊ.ꢂꢅ
ꢇ
Formula weight
Temperature (K)
Crystal system, space group
ꢄꢈꢂ(ꢇ)
ꢄꢍꢂ(ꢇ)
Orthorhombic, Pbca
Monoclinic, Pꢇ /c
ꢄ
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
ꢄꢉ.ꢇꢃꢅꢈ(ꢂ)
aꢁ=ꢁꢈ.ꢈꢆꢂꢊ(ꢊ)
ꢄꢊ.ꢊꢍꢊꢍ(ꢍ)
bꢁ=ꢁꢄꢊ.ꢂꢊꢍꢉ(ꢍ)
ꢇꢍ.ꢉꢂꢂꢇ(ꢅ)
cꢁ=ꢁꢄꢆ.ꢍꢂꢊꢍ(ꢈ)
ꢈꢉ
ꢈꢉ
ꢈꢉ
ꢈꢄ.ꢈꢊꢅ(ꢊ)
ꢈꢉ
ꢈꢉ
ꢂ
Volume (Å )
ꢂꢅꢄꢍ.ꢊ(ꢇ)
ꢇꢃꢍꢇ.ꢆꢂ(ꢄꢈ)
Z
ꢆ
ꢆ
ρηοcalc (g/cmꢂ)
ꢄ.ꢇꢃꢊ
ꢄ.ꢄꢅꢊ
−ꢄ
Absorption coefficient (mm )
F(ꢉꢉꢉ)
Crystal size (mm)
Reflections collected/unique
Data/restraints/parameters
Final R indices [Iꢁ>ꢁꢇσ(I)]
R indices (all data)
ꢉ.ꢄꢊꢊ
ꢉ.ꢄꢃꢉ
ꢄꢍꢉꢊ
ꢄꢉꢉꢆ
ꢉ.ꢍꢉꢉꢁ×ꢁꢉ.ꢍꢉꢉꢁ×ꢁꢉ.ꢇꢍꢉ
ꢂꢈ ꢃꢅꢆ/ꢂꢃꢂꢆ [R(int)ꢁ=ꢁꢉ.ꢉꢅꢅꢈ]
ꢂꢃꢂꢆ/ꢉ/ꢇꢂꢇ
ꢉ.ꢊꢈꢉꢁ×ꢁꢉ.ꢊꢍꢉꢁ×ꢁꢉ.ꢄꢆꢉ
ꢂꢍ ꢈꢅꢇ/ꢍꢃꢈꢅ [R(int)ꢁ=ꢁꢉ.ꢉꢊꢍꢉ]
ꢍꢃꢈꢅ/ꢂ/ꢂꢇꢉ
R ꢁ=ꢁꢉ.ꢉꢂꢂꢇ, wR ꢁ=ꢁꢉ.ꢉꢆꢃꢍ
R ꢁ=ꢁꢉ.ꢉꢍꢍꢊ, wR ꢁ=ꢁꢉ.ꢄꢇꢇꢅ
ꢄ
ꢇ
ꢄ
ꢇ
R ꢁ=ꢁꢉ.ꢉꢂꢃꢃ, wR ꢁ=ꢁꢉ.ꢉꢆꢈꢅ
R ꢁ=ꢁꢉ.ꢉꢅꢇꢇ, wR ꢁ=ꢁꢉ.ꢄꢂꢊꢂ
ꢄ ꢇ
ꢄ
ꢇ
via syringe, and the solution is stirred overnight. In the first experi- equipped with a low-temperature device with Mo-Kα radiation
ment, 3 crystallised from this mixture overnight. In the second exper- (λꢀ=ꢀ0.71073 Å) using ω and ϕ scans. Software for data collection:
iment, the solvent is removed in vacuo and replaced with dry CDCl . X-AREA, cell refinement: X-AREA and data reduction: X-RED (Stoe
3
After a few weeks, 4 crystallised from this solution.
and Cie, 2009). Preliminary structure models were derived by direct
methods (Sheldrick, 2008), and the structures were refined by full-
2
1
matrix least-squares calculations based on F for all reflections using
3
:ꢁ H-NMR: δ [ppm]ꢀ=ꢀ10.85 (s, 1H, NH), 7.50–7.15 (m, 10H, Ar), 4.05
3
3
SHELXL (Sheldrick, 2015). The hydrogen atoms at the amine nitro-
(
t, 2H, CH -N, J ꢀ=ꢀ6.0ꢀHz), 2.15 (qu, 2H, CH -CH CH , J ꢀ=ꢀ7.0ꢀHz),
2
H,H
2
2-
2
H,H
13
3
gen atoms N in both structures were localised from the differences
1
.08 (t, 2H, CH -Si, J ꢀ=ꢀ7.2ꢀHz), 0.18 (s, 6H, CH -Si ); C-NMR: δ
2
2
H,H
3
in the Fourier maps and refined without restraints. All other hydro-
gen atoms were included in the models in calculated positions and
were refined as constrained to the bonding atoms. Further crystallo-
graphic and structure refinement data are listed in Table 4.
[
ppm]ꢀ=ꢀ163.0, 153.5 (Cꢀ=ꢀO), 139.8, 138.4 (C
), 130.1–.2 (Ar), 48.7
quart)
(
2
9
(
CH -N), 21.1 (CH -CH CH ), 11.5 (CH -Si), −0.7 (CH -Si); Si-NMR:
2
2
2-
2
2
3
δ [ppm]ꢀ=ꢀ12.9.
4
:ꢁCrystallised from a CDCl solution after standing several weeks.
3
NMR analysis of this solution showed that a mixture of insertion and Acknowledgements: The authors gratefully acknowledge
oligomerisation products of phenylisocanate was formed. Therefore,
help from Beate Kutzner (NMR), Regina Moßig (Raman),
1
13
unambiguous assignment of H- and C-NMR data of 4 is not possible
Konstantin Kraushaar (MS), and Ute Groß (EA). The
German Research Foundation, DFG, is acknowledged for
financial support. Part of this work was performed within
the research group “Chemical utilization of carbon dioxide
in this case.
Alcoholysis of 2a
with aminosilanes (CO -Sil)” that is financially supported
2
by the European Union (European Regional Development
Fund), the Ministry of Science and Art of Saxony (SMWK)
Stoichiometric as well as sub-stoichiometric amounts of dry 1-pen-
tanol were added dropwise to a solution of 2a in n-pentane in an ice
2
9
bath. The Si-NMR spectrum shows signals of 2a (δꢀ=ꢀ2.7, −17.0 ppm) and the Sächsische Aufbaubank (SAB).
n
and of the alcoholysis products (δꢀ=ꢀ16.7ꢀppm (Me SiO Pent) and
3
−
45.4 ppm (3-aminopropyldiethoxypenthoxysilane)).
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