Reactivity of 1-allylsilatrane in ruthenium-catalyzed silylative coupling with olefins-mechanistic considerations

Article abstract of DOI:10.1515/hc-2020-0006

We have developed a new effective route for obtaining (E)-vinyl-substituted silatranes via ruthenium-catalyzed silylative coupling of 1-allylsilatrane with olefins. Experimental research allowed us also to propose the mechanism of the process based on sto

Full text of DOI:10.1515/hc-2020-0006

Heterocycl. Commun. 2020; 26: 33–36
Research Article
Open Access
BRoegnaacSzttoivrciht, DyawoidfF1rą-cakolwliyakl,sBiolgadatnrMaanrceinieicn* ruthenium-catalyzed
silylative coupling with olefins – mechanistic
considerations
https://doi.org/10.1515/hc-2020-0006
C=C π-system was discussed [15]. Allylsilatrane was functio-
Received February 13, 2019; accepted October 16, 2019.
nalized in catalytic hydrosilylation and hydrogermylation, as
Abstract: We have developed a new effective route for well as in non-catalytic hydrostannation [16].
obtaining (E)-vinyl-substituted silatranes via ruthenium-
Platinum-catalyzed hydrosilylation of 1 was used in
catalyzed silylative coupling of 1-allylsilatrane with olefins. the preparation of oligosiloxanes with silatrane cages,
Experimental research allowed us also to propose the which may find potential applications in lithium-ion con-
mechanism of the process based on stoichiometric reactions. ductive matrices [17]. There are also reports of reactivity of
1 toward electrophiles and nucleophiles [18,19]and dienes
[20] (in Diels-Alder reactions).
In the last two decades, our group has developed a
catalytic transformation involving vinylmetalloids and
Introduction
Silatranes make a widely studied class of organosilicon olefins, i.e., ruthenium-catalyzed trans-metalation, which
compounds characterized by cage tricyclic structure, leads to functionalized alkenyl-substituted boronates,
pentacoordinate silicon center with donor-acceptor tran- silanes and germanes (Scheme 1) [21].
sannular Si ← N bond, and interesting biological proper-
In our previous study, we have reported the reactivity
ties [1-3]. In the last three decades, research on silatranes of vinylsilatrane in stereoselective trans-silylation with
covered several areas, including organic and organome- styrene derivatives catalyzed by RuHCl(CO)(PCy3)2, which
tallic synthesis [4-6], materials chemistry [7-9] as well as leads to (E)-substituted alkenylsilatranes. We have also
biochemistry and medicine [10-13]
presented a detailed mechanism of this process, suppor-
Given the variety of silatrane derivatives, allylsilatra- ted by studies and DFT calculations [22].
nes are hardly explored, which stands in stark contrast to
In this paper, we describe for the first time the reac-
the wide range of applications of allylsilanes in organic tivity of allylsilatrane in ruthenium-catalyzed trans-
synthesis (e.g., in allylation of carbonyl compounds or silylation with olefins. Experimental examination, such as
olefin metathesis, for review see [14]). 1-Allylsilatrane catalytic tests and stoichiometric reactions, allowed us to
(or allylsilatrane) 1 is the simplest representative of allyl- propose a mechanism for this transformation.
substituted silatranes (Figure 1).
In literature, there are not many reports concerning the
structural aspects of 1 and its reactivity. The crystal structure Results and discussion
of 1 was determined in low temperature, and its correlation
to hyperconjugation between the Si-C σ-electrons and the Synthesis of allylsilatrane
Allylsilatrane 1 was prepared in the transesterification
* Corresponding author: Bogdan Marciniec, Adam Mickiewicz
reaction of allyltrimethoxysilane with triethanolamine in
University in Poznań, Faculty of Chemistry, Uniwersytetu Poznańskiego
8, 61-614 Poznań, Poland; Center for Advanced Technology, Adam
Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 10,
61-614 Poznań, Poland, e-mail: bogdan.marciniec@amu.edu.pl
Bogna Sztorch, Adam Mickiewicz University in Poznań, Center
for Advanced Technology, Uniwersytetu Poznańskiego 10, 61-614
Poznań, Poland, e-mail: bogdan.marciniec@amu.edu.pl
Dawid Frąckowiak, Center for Advanced Technology, Adam
Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 10,
61-614 Poznań, Poland
Figure 1ꢁStructure of 1-allylsilatrane.
Open Access. © 2020 Sztorch et al., published by De Gruyter.ꢀ
Attribution alone 4.0 License.
ꢀThis work is licensed under the Creative Commons

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B. Sztorch et al.: Reactivity of 1-allylsilatrane in ruthenium-catalyzed silylative coupling with olefins
Scheme 1ꢁRuthenium catalyzed trans-metalation of olefins with vinylmetalloids.
Scheme 2ꢁRuthenium-catalyzed silylation of olefins with triethoxyallylsilane.
boiling xylene in 82% yield, which is a slightly modified pro- Table 1ꢁallylsilatrane 100 mg (0.46 mmol), olefin (1-3) 0.92 mmol,
olefin (4) 0.46 mmol, 2 mol% RuHCl(CO)(PCy3)2, 110oC, toluene
(3 mL), open system, 24 h
cedure based on the work of Corriu et al. [19] 1 Was isolated
as white, powdery flakes stable in air and toward moisture.
Olefin
Product
Isolated yield [%]
1
87
Reactivity of allylsilatrane in trans-silylation with olefins
In 1999, Murai et al. presented an alternative protocol for
the silylation of olefins by using allylsilanes as silylating
agents [23]. The process was then dubbed as dehydroge-
native silylation, even though it is a different variant of
the silylative coupling reaction which proceeds with the
evolution of propene instead of ethylene. The authors
studied the reactions of allyltrimethyl- and allyltriethoxy-
silane with selected styrenes in the presence of RuHCl(CO)
(PPh3)3 and isolated several (E)-triethoxystyrylsilanes.
We were able to use 1 as a silylating reagent for the
catalytic synthesis of (E)-styrylsilatranes with selected
styrenes in the presence of 2 mol% RuHCl(CO)(PCy3)2,
which is the most efficient catalyst for the silylative coup-
2
90
92
93
3
4
ling reaction (Table 1, Scheme 3).
tube) proved that the gas product of the reaction was
1
1
Examination of the H 13C 29Si NMR spectra, showed propene (Scheme 5), which was confirmed by H NMR
1
full conversion of 1 and confirmed that the reaction was analysis. However, the H NMR spectrum also showed
(E)-selective. The same products could also be obtained that the Ru–H proton signal did not entirely disap-
when 1-vinylsilatrane acted as a silylating reagent, which pear, which was explained as a result of the regene-
was previously mentioned [22]. However, contrary to Murai’s ration of the complex during the initial stage of the
report, the product of dimerization of 1 was not observed.
Nevertheless, the homocoupling of catalyzed
mol% of RuHCl(CO)(PCy3)2 gave 1-silatranyl-2- mediate in the coupling reaction of vinylsilatrane with
catalytic cycle.
1
As the Ru-silatranyl complex is also the same inter-
by
2
(silatranylmethyl)ethene in 90% yield as a mixture of E/Z olefins, we added styrene to the equimolar reaction
isomers (Scheme 4).
system, which after 12 h was fully converted to (E)-styryl-
silatrane 5 (Scheme 6).
Based on our experimental evidence and Murai’s
work, as well as our previous study on silylative coupling
of vinylsilatrane, we proposed a general mechanism for
Mechanistic implications
The equimolar reaction of 1 with RuHCl(CO)(PCy3)2 in the first part of the catalytic cycle of ruthenium-catalyzed
toluene-d8 carried out in a closed system (Young NMR silylative coupling of 1 with olefins (Scheme 7).

B. Sztorch et al.: Reactivity of 1-allylsilatrane in ruthenium-catalyzed silylative coupling with olefinsꢂ
ꢂ35
Scheme 3ꢁTrans-silylation of 1 with styrenes catalyzed by RuHCl(CO)(PCy3)2.
Scheme 4ꢁHomocoupling of allylsilatrane.
Scheme 5ꢁThe equimolar reaction of 1 with RuHCl(CO)(PCy3)2.
Scheme 6ꢁThe equimolar reaction of 1 with RuHCl(CO)(PCy3)2.
Scheme 7ꢁProposed mechanism for the first half of the catalytic cycle of silylative coupling of 1-allylsilatrane with olefins.
Allylsilatrane 1 undergoes a 1,2-migratory inser- Conclusions
tion into the Ru–H bond of the ruthenium complex and
forms intermediate A, which subsequently converts to We have developed catalytic trans-silylation of allyl-
more stable conformer B due to coordination of ruthe- silatrane with olefins leading to (E)-vinyl-substituted
nium center to the oxygen atom of silatrane frame- silatranes - the same products as those coming with
work. The ruthenium-silatranyl complex C is formed via vinylsilatrane as the substrate in very good yields. The
β-elimination of propene molecule. The second part of the mechanism for the coupling reaction of allylsilatrane
catalytic cycle is identical to the one present in coupling with styrenes was studied by catalytic and stoichiometric
reaction of vinylsilatrane with olefins, which we previ- reactions — the evolution of propene and formation of
ously mentioned [22].
ruthenium-silatranyl species was confirmed. We also

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B. Sztorch et al.: Reactivity of 1-allylsilatrane in ruthenium-catalyzed silylative coupling with olefins
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The authors declare no conflict of interest.
Acknowledgements
The authors gratefully acknowledge the financial support
from the National Science Centre (OPUS project UMO-
2017/27/B/ST5/00149). This research was supported in part
by PL-Grid Infrastructure.
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