Lewis Base Catalyzed Selective Chlorination of Monosilanes

Article abstract of DOI:10.1002/chem.201803921

A preparatively facile, highly selective synthesis of bifunctional monosilanes R₂SiHCl, RSiHCl₂ and RSiH₂Cl is reported. By chlorination of R₂SiH₂ and RSiH₃ with concentrated HCl/ether solutions, the stepwise introduction of Si?Cl bonds is readily controlled by temperature and reaction time for a broad range of substrates. In a combined experimental and computational study, we establish a new mode of Si?H bond activation assisted by Lewis bases such as ethers, amines, phosphines, and chloride ions. Elucidation of the underlying reaction mechanisms shows that alcohol assistance through hydrogen-bond networks is equally efficient and selective. Remarkably, formation of alkoxysilanes or siloxanes is not observed under moderate reaction conditions.

Full text of DOI:10.1002/chem.201803921

A Journal of
Accepted Article
Title: Lewis-Base Catalyzed Selective Chlorination of Monosilanes
Authors: Alexander G Sturm, Julia I Schweizer, Lioba Meyer, Tobias
Santowski, Norbert Auner, and Max C. Holthausen
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To be cited as: Chem. Eur. J. 10.1002/chem.201803921
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10.1002/chem.201803921
Chemistry - A European Journal
Lewis-Base Catalyzed Selective Chlorination of Monosilanes
Alexander G. Sturm, Julia I. Schweizer, Lioba Meyer, Tobias Santowski,
Norbert Auner,* and Max C. Holthausen*
Institut für Anorganische und Analytische Chemie, Goethe-Universität
Max-von-Laue-Straße 7, 60438 Frankfurt/Main (Germany)
Dedicated to Prof. Dr. Robert West on the occasion of his 90th birthday
Abstract: A preparatively facile, highly selective synthesis of bifunctional monosilanes R2SiHCl,
RSiHCl2 and RSiH2Cl is reported. By chlorination of R2SiH2 and RSiH3 with concentrated
HCl/ether solutions the stepwise introduction of Si–Cl bonds is readily controlled by temperature
and reaction time for a broad range of substrates. In a combined experimental and computational
study, we establish a new mode of Si–H bond activation assisted by Lewis bases such as ethers,
amines, phosphines, and chloride ions. Elucidation of the underlying reaction mechanisms shows
that alcohol assistance through hydrogen-bond networks is equally efficient and selective.
Remarkably, formation of alkoxysilanes or siloxanes is not observed under moderate reaction
conditions.
Acknowledgements: Financial Support by Momentive Performance Materials GmbH
(Leverkusen) is acknowledged. Quantum-chemical calculations were performed at the Center for
Scientific Computing (CSC) Frankfurt on the FUCHS and the LOEWE-CSC high-performance
compute clusters.
Bifunctional monosilanes are key compounds in silicone technology for the preparation of
advanced organofunctional siloxane materials.[1] On the one hand, (organo)chlorosilanes are
generally used for the introduction of silyl protecting groups[2] or as Lewis acids in organic
transformations,[3] and as precursor material for siloxanes, silsesquioxanes, and silicones.[4] Their
hydrogenated congeners, on the other hand, emerged as versatile hydrosilylation[1e, 5] and mild
hydrogenation reagents in synthetic chemistry,[6] and various thin-film application are based on
the use of (organo)hydridosilanes.[7] The installation of both Si–H and Si–Cl functionalities at one
silicon center has been the focus of considerable research activities over the last decades but has
8]
proven a synthetic challenge, despite the seeming simplicity of the compounds.[5f, The only
bifunctional silanes available in industrially significant amounts, MeSiHCl2, MeSiH2Cl and
Me2SiHCl, are formed as side products of the MenSiCl4–n synthesis in the Müller-Rochow Direct
Process (0.1–0.5 wt% Me2SiHCl, 1–4 wt% MeSiHCl2, and MeSiH2Cl[9]).[10]
As the nature of organic substituents represents one of the set screws to tune the physical,
chemical and environmental properties of polysiloxane and silicone materials,[1f-h, 11] the design of
efficient preparative routes to well-defined chlorohydridosilanes with flexible choice of R is a
rewarding research goal. Conceivable routes to this end are hydrogenation of chlorosilanes or
chlorination of hydridosilanes but thus far, known synthetic protocols have been unsuitable for
selective partial transformation.[8, 12] Other notorious drawbacks are low yields, use of expensive
or toxic reagents and solvents, formation of waste products in large quantities, long reaction
times, harsh reaction conditions or tedious workup processes.[8, 12] Very recently, Chulsky and
Dobrovetsky reported the selective chlorination of di- and trihydridosilanes with HCl in the
presence of catalytic amounts of B(C6F5)3 or Et2O•B(C6F5)3.[13] In case of B(C6F5)3, the proposed
reaction mechanism involves preactivation of the Si–H bond by the borane, followed by concerted
HCl addition across the Si–H bond in the [Si]–H–B(C6F5)3 intermediate. For Et2O•B(C6F5)3,
transformation into an ethanol borane adduct Et(H)O•B(C6F5)3 as actual catalytically active
species is suggested, which undergoes dehydrocoupling with further silane equivalents to
ethoxysilane intermediates. Subsequent HCl addition across the Si–OEt bond leads to
chlorosilane formation and regeneration of the active catalyst.
Herein we report an alternative, preparatively facile protocol for the highly selective partial
chlorination of hydridosilanes. Specifically, reaction of di- and trihydridosilanes with highly
concentrated solutions of HCl in different ethers yields the corresponding chlorohydridosilanes
with concomitant release of H2. The substrate scope of the reaction is broad and the degree of
1
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10.1002/chem.201803921
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chlorination is readily controlled by temperature and reaction time. The results of a quantum-
chemical study on the underlying reaction mechanism are presented.
Table 1. Chlorination of Si–H bonds in concentrated solutions of HCl in different ethers at 60 °C.
H
Cl
Si
+ HCl/ether
– ether, H2
Si
R
R
R
R
H
H
R4-nSiHn
HCl/ether
reagent[a]
t (h)
product yield (%)[b]
Me2SiH2
Et2SiH2
a
a
70.0
30.0
Me2SiHCl (100)
Et2SiHCl (100)
PhMeSiH2
Me2SiH2
Et2SiH2
a
b
b
b
c
c
c
60.0
0.7
1.0
1.7
2.8
2.0
4.5
PhMeSiHCl (95), MeSiH2Cl (5)
Me2SiHCl (100)
Et2SiHCl (100)
PhMeSiH2
Me2SiH2
Et2SiH2
PhMeSiHCl (97), MeSiH2Cl (3)
Me2SiHCl (100)
Et2SiHCl (100)
PhMeSiH2
PhMeSiHCl (88), MeSiH2Cl (12)
[a] HCl concentration in ether: a) 5 M in Et2O, b) 10 M in diglyme, c) 12 M in
1,4-dioxane. [b] Yields were calculated from 1H and 29Si NMR spectroscopy.
In a representative set of experiments we reacted Me2SiH2, Et2SiH2, and PhMeSiH2 with a 5 M
solution of HCl in Et2O at 60 °C (Table 1). Me2SiHCl and Et2SiHCl were quantitatively formed after
70 h and 30 h, respectively; prolonged reaction times at higher temperatures led to ether
cleavage and formation of alkoxysilanes such as Me2ClSiOEt (see Supporting Information).
Chlorination of PhMeSiH2, in turn, afforded a maximum yield of 95% PhMeSiHCl after 60 h at
60 °C. Here, MeSiH2Cl is formed as a side product owing to the well-known lability of the Si–CAr
bond under such reaction conditions.[8b] The same reaction products were observed using
HCl/diglyme (10 M) or HCl/1,4-dioxane (12 M) solutions, yet with significantly increased reaction
rates.
Monitoring of the Et2SiH2 chlorination reaction in 1,4-dioxane by 1H NMR spectroscopy
confirmed a substantial rate acceleration with increasing HCl concentration (Figure 1). In 4.5 M
solution, merely 86% of Et2SiHCl were formed after 160 h at room temperature, while full
conversion was observed after 160 h in 7.5 M and after 36 h in 13.0 M HCl solution. Notably, the
reaction in diglyme proceeds two to four times faster than in 1,4-dioxane, irrespective of the lower
HCl concentration present in the former solution (Table 1). Obviously, the course of the reaction is
influenced by the nature of the ether as well. This effect will be addressed below.
Figure 1. Chlorination of Et2SiH2 in HCl/1,4-dioxane with different HCl concentrations ranging from 4.5 M to 13.0 M at
room temperature (± 0.2 M).
2
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To explore the scope of the reaction, further experiments were conducted with a broad variety
of hydridosilanes RSiH3 and R2SiH2. With R = methyl, ethyl, vinyl, n-propyl, iso-propyl, n-hexyl,
phenyl, and benzyl, essentially quantitative yields of monochlorinated products were obtained,
while side reactions occurred for allyl-, mesityl-, t-butyl-, and p-tolyl-substituted silanes in cases,
dependent on the ether solvent used.[14] Generally, a decrease of the reaction rate is observed
with increasing steric demand of the organic substituents at the silicon atom. With
trihydridosilanes the chlorination selectivity is readily controlled by the reaction temperature.
Between 20 °C and 60 °C, monochlorination occurs quantitatively in most cases. With prolonged
reaction times between 80 °C and 120 °C partial dichlorination is feasible but is always
accompanied by formation of side-products (e.g. alkoxysilanes and siloxanes[14]). Full chlorination
of di- and trihydridosilanes was not observed.
Cl
Cl
H
H
H
O
O
H
Cl
O
H
Cl
Cl
Me2O 2 HCl
Me2O (HCl)2
Me2O HCl
4.4
5.3
–0.2
Cl
O
H
Cl
Cl
O
H
O
H
O
Cl
O
H
[(Me2O)2H]Cl
[(Me2O)2H]Cl HCl
[Me2O–H]Cl
12.4
8.7
29.0
Figure 2. Stabilities of potential reactive intermediates formed in HCl/Me2O solutions relative to separated HCl and
Me2O molecules; oxonium ions computed as contact ion pairs (∆G298 in kcal mol–1).
Detailed insights into the chlorination mechanism are provided by a density functional theory
study employing dimethyl ether and Me2SiH2 as molecular models.[15] We searched for potential
reactive intermediates formed in concentrated HCl/ether solutions and identified the Me2OŸHCl
adduct as the only exergonically formed species (Figure 2 and Schemes S4 and S5). Specifically,
we found no evidence for thermodynamically competitive HCl protolysis yielding oxonium ions of
the type [(Me2O)2H][Cl–•n HCl] in line with the absence of corresponding 1H NMR signatures in
our experiments.[16] Clearly, the existence of oxonium ions like [(R2O)2H]+ in solution hinges upon
the presence of weakly coordinating counter ions.[16-17] Thus, the presence of strongly
coordinating Cl– anions renders the existence of di-solvated protons highly unlikely.[18]
Accordingly, a number of studies explicitly reported R2O•HCl adducts instead, that is, complex
formation with non-dissociated HCl.[16-19] In the light of these findings and given molar HCl/ether
ratios between 0.5 and 1.4 in the experiments, we chose the Me2OŸHCl adduct as
thermochemical reference point in the calculations. Concerted H2 elimination by addition of HCl
across the Si–H bond (ts1 in Scheme 1) is connected with a sizeable, kinetically prohibitive
activation barrier of ∆‡G= 37.8 kcal mol–1.[20] A reasonably lower barrier of 28.4 kcal mol–1 is
obtained in the presence of a coordinating ether molecule, which assists Si–H bond cleavage by
stabilization of the developing positive charge at the silicon atom in transition state ts2. The
resulting contact ion pair 1 is, however, thermodynamically unstable and collapses to Me2SiHCl in
an essentially barrierless,[21] strongly exergonic step. Ether-stabilized silylium cations such as 1
are known products from the reaction of hydridosilanes with Brookhart’s acid [(Et2O)2H][BArF4],[16b]
yet the absence of coordinating counter anions is prerequisite for the experimental detection of
these species.[22] In any case, the marked thermodynamic lability in the presence of a chloride
anion renders silylium cation 1 merely a fleeting intermediate under the experimental conditions
applied here. Fully in line with experiment, the second, analogous chlorination step of Me2SiHCl is
prevented by a high kinetic barrier (ts3, ∆‡G= 36.2 kcal mol–1). The concerted H2 release via ts2
thus represents the rate limiting step for the chlorination of Me2SiH2 and we compute a H/D kinetic
isotope effect of 2.0 for the reaction with DCl/Me2O (∆‡G = 28.8 kcal mol–1). For qualitative
validation we conducted a competition experiment employing commercially available 1.0M
HCl/Et2O and DCl/Et2O solutions. At 80 °C, the reaction of Et2SiH2 with HCl/Et2O proceeds twice
as fast as with DCl/Et2O (HCl: 33% Et2SiHCl after 23 h, DCl: 34% Et2SiHCl after 46 h; obtained
1
from integration of the corresponding H and 29Si NMR signals of Et2SiH2 and Et2SiHCl). These
results fully support the computed reaction mechanism.
3
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H
H
Cl
H
H
Cl
Cl
Si
Cl
Si
H
+ Me2O HCl
– Me2O
+ Me2O HCl
Si Cl
O
Si
Si
– H2
– H2
– Me2O
Cl
H
H
∆ G = 36.2
H
Me2SiH2
ts3
Me2SiCl2
ts1
Me2SiHCl
(15.2)
(–40.3)
(37.8)
(–21.0)
(0.0)
NPA charges
barrierless
– Me2O
–0.66
H Cl
1.44
H
–0.18
0.02 0.14 –0.76
–0.21 0.23
–0.19
H
Cl
H
Si
O
H
Cl
H
H
H
Cl
+ Me2O HCl
H
Si
O
H
1.16
Si
1.50
– H2
Si
Si
H
H
O
–0.20
ts1
ts2
(28.4)
1
(5.2)
Me2SiH2
ts2
Scheme 1. Chlorination of Me2SiH2 with (a) HCl and (b) HCl/Me2O (∆G298 in kcal mol–1); atomic charges obtained from
natural population analysis (NPA) in red and blue.
The stabilizing role of ether in ts2 is mechanistically intriguing, as it reveals the possibility to
assist the chlorination reaction by intermediate coordination of a Lewis base as an alternative to
Lewis-acid catalysis exploited by Chulsky and Dobrovetsky.[13] This hypothesis was validated by
further experiments employing additional amounts of Lewis bases (Table 2). The reference
reaction, i.e. chlorination of Et2SiH2 to Et2SiHCl in 5 M HCl/Et2O solution, required 30 h at 60 °C to
complete. Addition of 5 mol% nBu3P or nBu3N, in turn, both led to significant rate enhancements
and quantitative product formation was observed after 2 or 2.5 h, respectively. Also the
chlorination of MeSiH3 in 12 M HCl/1,4-dioxane was much faster in the presence of 5 mol%
nBu3P. Already after 6 h the doubly chlorinated product MeSiHCl2 was formed in 91% whereas
95% of the singly chlorinated product MeSiH2Cl were observed after 6 h in the reference reaction
without additional base.
Quite clearly, phosphines or amines form their corresponding hydrochlorides within the
reaction mixture, which immediately suggests Lewis basic chloride ions as active species[23] under
the reaction conditions. This tallies well with an essentially identical rate enhancement observed
for the chlorination of Et2SiH2 upon addition of 5 mol% [nBu4P]Cl in a control experiment (Table 2)
and the fact that nBu3P was formed almost quantitatively in a stoichiometric reaction of
[nBu3PH]Cl with Et2SiH2 in Et2O or benzene.[14] Correspondingly, the 31P NMR spectrum of nBu3P
in 5 M HCl/Et2O or 12 M HCl/1,4-dioxane features a doublet at 12.2 ppm (1JPH: 484.9 Hz),
indicating the formation of [nBu3PH]Cl.[24] These experimental observations are confirmed by DFT
calculations using PMe3 as a molecular model: Formation of the phosphonium chloride ion-pair
[Me3PH]+Cl– is thermodynamically clearly preferred over formation of the hydrogen-bonded
HCl•PMe3 adduct (∆RG = –4.3 and –0.9 kcal mol–1, respectively, relative to separated PMe3 and
HCl).
Table 2. Chlorination of Si–H bonds with HCl/ether solutions and different catalysts at 60 °C.
R4-nSiHn
catalyst
(mol%)[a]
HCl/ether
reagent[b]
t (h)
product yield (%)[c]
Et2SiH2
Et2SiH2
Et2SiH2
Et2SiH2
MeSiH3
MeSiH3
–
a
a
a
a
c
c
30
2.0
2.5
2.7
6.0
6.0
Et2SiHCl (100)
Et2SiHCl (100)
Et2SiHCl (100)
Et2SiHCl (100)
nBu3P (5.0)
nBu3N (5.0)
nBu4PCl (5.0)
–
MeSiH2Cl (94.7)
MeSiHCl2 (5.3)
MeSiHCl2 (91.4)
MeSiCl3 (6.0)
nBu3P (5.0)
MeSiH2Cl (2.6)
[a] Based on the amount of silane. [b] a: HCl/Et2O (5M); c: HCl/1,4-dioxane
(12M). [c] Yields were calculated from 1H and 29Si NMR spectroscopy.
4
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Considering both PMe3 and the chloride ion in [Me3PH]Cl as potential Lewis bases, we
investigated a variety of plausible chlorination pathways for Me2SiH2,[14] among which the
chloride-assisted formation of Me2SiHCl is energetically most favorable (Table 3). The activation
barrier for this route is 1.4 kcal mol–1 lower than for the ether-catalyzed chlorination reaction via
ts2 and without exception, lower barriers result in all cases investigated computationally. In
pleasing agreement with experiment, the activation barrier for the second chlorination of MeSiH3
is significantly decreased in contrast to the reaction in HCl/Me2O. These findings provide a
consistent explanation for the experimentally observed increase in reaction rate in the presence of
phosphine, amine and phosphonium chloride.
Table 3. Comparison of computed activation barrier heights for the chlorination of monosilanes with Me2O•HCl and
[Me3PH]Cl.
H
Si
O
H
Cl
Cl
+ Me2O HCl
R
R
R
– Me2O
– H2
Cl
Si
H
Si
R
R
R
R
H
H
+ 2 [Me3PH]Cl
– PMe3
Si
R
– [Me3PH]Cl
– H2
H
Cl
P
R = H, Me, Cl
reactant
product
∆‡G Me2O•HCl
∆‡G [Me3PH]Cl
(kcal mol–1
28.4 (ts2)
36.2
)
(kcal mol–1
)
Me2SiH2
Me2SiHCl
MeSiH3
Me2SiHCl
Me2SiCl2
MeSiH2Cl
MeSiHCl2
MeSiCl3
27.0
30.5
28.0
26.7
MeSiH2Cl
MeSiHCl2
31.5
28.8
42.5
34.5
Turning to the influence of different ethers on the reaction rate, we note that in previous work
Et2O cleavage was observed only upon heating of a 5 M HCl/Et2O solution above 100 °C resulting
in formation of EtCl, EtOH, and H2O.[4a] Accordingly, in our experiments alkoxysilane and siloxane
formation set in only at temperatures of 100 °C and above. Under the reaction conditions applied
1,4-dioxane remained resistant against cleavage, whereas MeCl formation indicated cleavage of
diglyme already at room temperature. This suggests that the high chlorination reactivity in diglyme
is related to concomitant alcohol formation. For further scrutiny we performed experiments in
12 M HCl/1,4-dioxane with its cleavage product 2-(2-chloroethoxy)ethanol added: No significant
rate enhancement was observed upon addition of 7 mol% alcohol while the amount of product
formed tripled in the presence of stoichiometric amounts of alcohol (Table 4). Formation of
alkoxysilanes or siloxanes was not observed in any of the experiments.
Table 4. Chlorination reaction of Et2SiH2 in a 12 M HCl/1,4-dioxane solution and 2-(2-chloroethoxy)ethanol.
R–OH (mol%)[a]
T (°C) t (h) product yield (%)[b] remaining reactant (%)
–
60
60
60
0.5 Et2SiHCl (34)
0.5 Et2SiHCl (38)
0.5 Et2SiHCl (95)
(66)
(62)
(5)
7
100
[a] based on the molar amount of Et2SiH2. [b] Yields were calculated by 1H
and 29Si NMR spectroscopy.
5
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In concert with experiment, the quantum-chemical evaluation[14] reveals exceedingly large
barriers for the cleavage of Me2O and 1,4-dioxane whereas diglyme cleavage competes
kinetically (∆‡G = 28.8 kcal mol–1) with the chlorination of Me2SiH2 via ts2 (Scheme 2). All three
reactions proceed through classical SN2 transition states located late along the reaction
coordinates. Additional intramolecular oxygen coordination in ts9, possible only in the case of
diglyme, lowers the activation barrier by 6 kcal mol–1 compared to the unassisted step ts8. For
both of the other ethers, the same stabilizing effect is attainable through intermolecular cluster
formation (ts5, ts7), yet the associated entropic penalty retains barriers high enough to preclude
cleavage at moderate temperatures.
(a)
Cl
C
Cl
H
H
H
H
H
O
ts4
(37.2)
2
MeOH + MeCl
(–3.4)
O
H
Cl
– HCl
– Me2O
Cl
O
H
H
H
H
Me2O HCl
(0.0)
H
C
O
H
Cl
ts5
(32.8)
(b)
Cl
Cl
C
H
H
H
H
O
O
ts6
(39.0)
O
H
O
2
O
HO
Cl
– HCl
– C4H8O2
Cl
2
(0.0)
3
(1.0)
Cl
O
H
H
H
H
H
C
O
Cl
O
ts7
(33.5)
Cl
C
H
Cl
(c)
H
H
H
O
H
(H2C)2
O
Cl
(H2C)2
O
H
O
O
O
O
2
H
O
+ MeCl
O
– HCl
– C6H14O3
ts8
(34.7)
5
(–5.9)
4
(0.0)
Cl
C
H
H
Cl
H
H
O
O
H
O
ts9
(28.8)
Scheme 2. Computed reaction pathways for the cleavage of Me2O, 1,4-dioxane, and diglyme (∆G298 in kcal mol–1).
For an assessment of potential alternative reaction routes in the presence of alcohol we used
MeOH as computational model (Scheme 3). Acting as a Lewis base it assists the chlorination akin
to Me2O with identical barrier lowering (cf. tsS33 in the Supporting Information vs. ts2). However,
MeOH efficiently enables proton-shuttling through hydrogen-bond networks and participation of
two alcohol moieties in ts10 opens a kinetically favored chlorination pathway for Me2SiH2: With
26.4 kcal mol–1 the cluster-assisted direct chlorination (ts10) is preferred over sequential
methoxylation and chlorination via ts11 and ts12, respectively. Interestingly, the formation of
6
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10.1002/chem.201803921
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Me2SiCl2 via ts13 and ts14 is kinetically irrelevant, despite reasonably low barriers, because the
marginal barrier of ts12 provides an energetically unrivaled shortcut to Me2SiHCl. From here, both
pathways leading to Me2SiCl2 are kinetically hindered (ts15, ts16). The mechanistic picture put
forth above consistently explains diglyme cleavage, the associated rate enhancement in the
presence of (added) alcohol as well as the exclusive formation of the experimentally observed
product.
ts10
(26.4)
ts15
(33.0)
H
Cl
Si
Cl
Si
Si
H
H
Cl
Me2SiH2
Me2SiHCl
Me2SiCl2
(–21.0)
(–40.3)
(0.0)
ts16
(32.7)
ts12
(14.3)
ts11
(27.7)
OMe
Si
OMe
Si
ts14
(22.7)
H
ts13
(24.9)
Cl
Me2Si(OMe)H
(–16.1)
Me2Si(OMe)Cl
(–39.7)
Cl
H
O
H
H
H
H
H
Si
Cl
Si
Cl
O
Cl
H
X
H
H
H
H
O
O
ts10
X = Cl: ts15 (33.0)
(26.4)
X = OMe: ts13 (24.9)
Cl
H
Cl
H
H
O
H
H
Si
O
O
O
Si
Cl
X
X
H
H
H
H
Cl
Cl
X = H: ts11 (27.7)
X = Cl: ts16 (32.7)
X = H: ts12 (14.3)
X = OMe: ts14 (22.7)
Scheme 3. Computed reaction pathways for competing alcohol mediated chlorination of Me2SiH2 (∆G298 in kcal mol–1).
In conclusion, we have established access to fundamentally important bifunctional silanes by
means of a preparatively efficient protocol. The substrate scope of the selective chlorination of
hydridomonosilanes R2SiH2 and RSiH3 in different HCl/ether solutions is broad and the degree of
chlorination is readily controlled by temperature and reaction time. The theoretical assessment
provides detailed rationalizations of the experimental findings and establishes a new mode of
Si–H bond activation assisted by Lewis bases such as ethers, amines, phosphines and chloride
ions as an alternative to Lewis acid assistance reported in earlier work.[13] Furthermore, we have
shown that alcohol assistance through hydrogen-bond networks is equally efficient and selective,
effectively bypassing side reactions like siloxane formation.
[1]
a) M. N. Missaghi, C. M. Downing, M. C. Kung, H. H. Kung, Organometallics 2008, 27, 6364-6366; b) W. Xue,
M. C. Kung, H. H. Kung, Chem. Commun. 2005, 2164-2166; c) H. Uchida, Y. Kabe, K. Yoshino, A. Kawamata,
T. Tsumuraya, S. Masamune, J. Am. Chem. Soc. 1990, 112, 7077-7079; d) B. Arkles, in Kirk-Othmer
Encyclopedia of Chemical Technology, John Wiley & Sons, Inc., 2000; e) B. Marciniec, Hydrosilylation: a
comprehensive review on recent advances, Vol. 1, Springer Science & Business Media, 2008; f) D. Brand, H. H.
Moretto, M. Schulze, D. Wrobel, Adv. Synth. Catal. 1994, 336, 218-224; g) J. Sejpka, F. Wimmer,
DE19536176C2, 1995; h) T. Ebbrecht, G. Feldmann-Krane, S. Silber, S. Stadtmüller, EP0845488B1, 1999.
M. A. Brook, Silicon in Organic, Organometallic, and Polymer Chemistry, Wiley, 1999.
[2]
[3]
[4]
A. D. Dilman, S. L. Ioffe, Chem. Rev. 2003, 103, 733-772.
a) F. Neumeyer, N. Auner, Chem. Eur. J. 2016, 22, 17165-17168; b) D. Gnanasekaran, K. Madhavan, B.
Reddy, J. Sci. Ind. Res. 2009, 68, 437-464; c) R. H. Baney, M. Itoh, A. Sakakibara, T. Suzuki, Chem. Rev.
7
This article is protected by copyright. All rights reserved.

10.1002/chem.201803921
Chemistry - A European Journal
1995, 95, 1409-1430; d) D. B. Cordes, P. D. Lickiss, F. Rataboul, Chem. Rev. 2010, 110, 2081-2173; e) A. M.
Muzafarov, Silicon polymers, Vol. 235, Springer Science & Business Media, 2010.
[5]
a) M. C. Lipke, A. L. Liberman-Martin, T. D. Tilley, Angew. Chem. Int. Ed. 2017, 56, 2260-2294; b) M. Oestreich,
J. Hermeke, J. Mohr, Chem. Soc. Rev. 2015, 44, 2202-2220; c) Y. Nakajima, S. Shimada, RCS Adv. 2015, 5,
20603-20616; d) S. Díez-González, S. P. Nolan, Acc. Chem. Res. 2008, 41, 349-358; e) B. Marciniec, Coord.
Chem. Rev. 2005, 249, 2374-2390; f) S. Kyushin, in Efficient Methods for Preparing Silicon Compounds (Ed.: H.
W. Roesky), Academic Press, 2016, pp. 455-498.
[6]
[7]
a) Y. Nagai, Org. Prep. Proced. Int. 1980, 12, 13-48; b) R. J. Rahaim, R. E. Maleczka, Org. Lett. 2005, 7, 5087-
5090; c) J. Pesti, G. L. Larson, Org. Process Res. Dev. 2016, 20, 1164-1181; d) S. Fountoulaki, V. Daikopoulou,
P. L. Gkizis, I. Tamiolakis, G. S. Armatas, I. N. Lykakis, ACS Catal. 2014, 4, 3504-3511.
a) T. Shimoda, Y. Matsuki, M. Furusawa, T. Aoki, I. Yudasaka, H. Tanaka, H. Iwasawa, D. Wang, M. Miyasaka,
Y. Takeuchi, Nature 2006, 440, 783-786; b) M. Haas, V. Christopoulos, J. Radebner, M. Holthausen, T. Lainer,
L. Schuh, H. Fitzek, G. Kothleitner, A. Torvisco, R. Fischer, O. Wunnicke, H. Stueger, Angew. Chem. 2017, 129,
14259-14262; c) S. H. Zaferani, Renewable Sustainable Energy Rev. 2017, 71, 359-364; d) R. Yoneyama, T.
Sato, K. Imato, T. Kosuge, T. Ohishi, Y. Higaki, A. Takahara, H. Otsuka, Chem. Lett. 2016, 45, 36-38; e) S.
Guruvenket, J. M. Hoey, K. J. Anderson, M. T. Frohlich, R. A. Sailer, P. Boudjouk, Thin Solid Films 2015, 589,
465-471.
[8]
a) F. Whitmore, E. Pietrusza, L. Sommer, J. Am. Chem. Soc. 1947, 69, 2108-2110; b) J. Zech, H. Schmidbaur,
Chem. Ber. 1990, 123, 2087-2091; c) R. Savela, W. Zawartka, R. Leino, Organometallics 2012, 31, 3199-3206;
d) S. Mawaziny, J. Chem. Soc. 1970, 1641-1642; e) A. Kunai, T. Kawakami, E. Toyoda, M. Ishikawa,
Organometallics 1992, 11, 2708-2711; f) A. Kunai, T. Sakurai, E. Toyoda, M. Ishikawa, Organometallics 1996,
15, 2478-2482; g) M. Ishikawa, E. Toyoda, M. Ishii, A. Kunai, Y. Yamamoto, M. Yamamoto, Organometallics
1994, 13, 808-812; h) W. Wang, Y. Tan, Z. Xie, Z. Zhang, J. Organomet. Chem. 2014, 769, 29-33; i) A. Kunai,
J. Ohshita, J. Organomet. Chem. 2003, 686, 3-15; j) L. D. Balashova, A. B. Bruker, L. Z. Soborovskiim, Zh.
Obshch. Khim. 1962, 32, 2982-2983; k) K. M. Lewis, R. A. Cameron, J. M. Larnerd, B. Kanner, US4973725,
1990.
[9]
Accessible from tetraalkylammonium salt catalyzed redistribution reactions of MeSiHCl2: K. Moedtritzer, J. R.
van Wazer, J. Organomet. Chem. 1968, 12, 69–77.
[10] a) E. G. Rochow, J. Am. Chem. Soc. 1945, 67, 963-965; b) D. Seyferth, Organometallics 2001, 20, 4978-4992;
c) B. R. Yoo, I. N. Jung, Adv. Organomet. Chem. 2004, 50, 145-177; d) E. G. Rochow, E. G. Rochow, An
Introduction to the Chemistry of the Silicones, Vol. 12, Wiley New York, 1951; e) L. Rösch, P. John, R.
Reitmeier, in Ullmann's Encyclopedia of Industrial Chemistry, 2000.
[11] a) M. J. Owen, in Silicon-Based Polymer Science, Vol. 224, Am. Chem. Soc., 1989, pp. 705-739; b) C. Rücker,
K. Kümmerer, Chem. Rev. 2015, 115, 466-524.
[12] a) M. Ishikawa, H. Sakamoto, T. Tabuchi, Organometallics 1991, 10, 3173-3176; b) T. Kusukawa, Y. Kabe, B.
Nestler, W. Ando, Organometallics 1995, 14, 2556-2564; c) A. Naka, Y. Matsumoto, T. Itano, K. Hasegawa, T.
Shimamura, J. Ohshita, A. Kunai, T. Takeuchi, M. Ishikawa, J. Organomet. Chem. 2009, 694, 346-352; d) V.
Pongkittiphan, E. A. Theodorakis, W. Chavasiri, Tetrahedron Lett. 2009, 50, 5080-5082; e) L. H. Sommer, J. D.
Citron, J. Org. Chem. 1967, 32, 2470-2472; f) J. W. Jenkins, H. W. Post, J. Org. Chem. 1950, 15, 556-559; g) L.
Sommer, C. Frye, G. Parker, K. Michael, J. Am. Chem. Soc. 1964, 86, 3271-3276; h) S. Varaprath, D. H. Stutts,
J. Organomet. Chem. 2007, 692, 1892-1897; i) R. F. Cunico, E. M. Dexheimer, Syn. React. Inorg. Metal-Org.
Chem. 1974, 4, 23-26; j) J. Curtice, H. Gilman, G. S. Hammond, J. Am. Chem. Soc. 1957, 79, 4754-4759; k) H.
Sakurai, M. Murakami, M. Kumada, J. Am. Chem. Soc. 1969, 91, 519-520; l) Y. Nagai, K. Yamazaki, I.
Shiojima, N. Kobori, M. Hayashi, J. Organomet. Chem. 1967, 9, 21-24.
[13] K. Chulsky, R. Dobrovetsky, Angew. Chem. Int. Ed. 2017, 56, 4744-4748.
[14] See Supporting Information for further details.
[15] Geometry optimizations were performed at the SMD-M06-2X-D3/6-31+G(d,p) level of theory. Me2O was used
as molecular model throughout; essentially identical results were obtained with Et2O and 1,4-dioxane. See
Section D1 in the Supporting Information for full computational details and benchmark data to validate the use
of the DFT method chosen.
[16] a) P. Jutzi, C. Muller, A. Stammler, H. G. Stammler, Organometallics 2000, 19, 1442-1444; b) M. Brookhart, B.
Grant, A. F. Volpe, Organometallics 1992, 11, 3920-3922.
[17] a) L. D. Henderson, W. E. Piers, G. J. Irvine, R. McDonald, Organometallics 2002, 21, 340-345; b) S. Kliem, U.
Klingebiel, M. Noltemeyer, Z. Anorg. Allg. Chem. 2005, 631, 99-104.
[18] C. A. Reed, Acc. Chem. Res. 2013, 46, 2567-2575.
8
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10.1002/chem.201803921
Chemistry - A European Journal
[19] a) V. Buch, F. Mohamed, M. Krack, J. Sadlej, J. Devlin, M. Parrinello, J. Chem. Phys. 2004, 121, 12135-12138;
b) R. A. Burdham, C. J. Ludman, R. J. Lynch, T. C. Waddington, J. Magn. Reson. 1979, 34, 223-231; c) I.
Giebels, M. van den Broek, M. Kropman, H. Bakker, J. Chem. Phys. 2000, 112, 5127-5132; d) A. Hinchliffe,
Adv. Mol. Relax. Interact. Processes 1979, 14, 225-233; e) G. J. Janz, S. S. Danyluk, Chem. Rev. 1960, 60,
209-234; f) R. T. Myers, Inorg. Chem. 1977, 16, 2671-2674; g) A. Pankov, V. Y. Borovkov, V. Kazanskii, J. Appl.
Spectrosc. 1982, 37, 953-957; h) S. R. Perumalla, C. C. Sun, Chem. Eur. J. 2012, 18, 6462-6464.
[20] An even higher barrier is obtained for the chlorination of Me2SiH2 with the [Me2O-H-OMe2]Cl ion pair (∆‡G = 46
kcal mol–1), clearly rendering the oxonium acid also kinetically irrelevant as reactive species in our experiments
(see Scheme S16 in the Supporting Information).
[21] Coordination of a second ether molecule stabilizes the silyl cation to some extent (–1.6 kcal mol–1 with reference
to the reactants, see Supporting Information). While this result indicates the possible intermediacy of a
siliconium ion in the course of the reaction, no supporting evidence was found in corresponding NMR
spectroscopic investigations.
[22] a) M. Kira, T. Hino, H. Sakurai, J. Am. Chem. Soc. 1992, 114, 6697-6700; b) A. Simonneau, T. Biberger, M.
Oestreich, Organometallics 2015, 34, 3927-3929; c) Q. A. Chen, H. F. Klare, M. Oestreich, J. Am. Chem. Soc.
2016, 138, 7868-7871.
[23] J. Tillmann, L. Meyer, J. I. Schweizer, M. Bolte, H.-W. Lerner, M. Wagner, M. C. Holthausen, Chem. Eur. J.
2014, 20, 9234-9239.
[24] Essentially identical 1H, 13C and 31P NMR characteristics were reported for [nBu3PH]BF4 and [nBu3PH]Br: M. R.
Netherton, G. C. Fu, Org. Lett. 2001, 3, 4295-4298; P. Das, J. McNulty, Eur. J. Org. Chem. 2010, 66, 3587-
3591.
9
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