K. Kuciński and G. Hreczycho
InorganicaChimicaActa490(2019)261–266
methylallyl reagent (silsesquioxanes are not soluble in acetonitrile),
which was followed by final evaporation under reduced pressure to give
the corresponding compounds 16–19. All compounds are known in
2.3. General procedure for the synthesis of compounds 20–21
To a 25 mL one-necked flask equipped with a stirring bar, 0.015 g of
Amberlyst, alkoxysilane (2.0 equiv., 0.036 mmol), 2-methylallyl re-
agent (1.0 equiv., 0.018 mmol), H2O (1.0 equiv., 0.018 mmol) and
0.5 mL of acetonitrile were added under air atmosphere. Subsequently,
the reaction mixture was stirred at rt for 1 h. After this time, the product
was separated from the catalyst by simple filtration using Pasteur pip-
ette equipped with cotton wool and then the solvent and all volatiles
were evaporated under reduced pressure to give the corresponding
compounds 20–21.
2.4. Gram-scale synthesis of 1,1,1,5,5,5-hexamethyl-3,3-
diphenyltrisiloxane
To a 100 mL one-neck round-bottom flask diphenylsilanediol (2.0 g,
9.2 mmol, 1.0 equiv), 2-methylallyltrimethylsilane (3.54 g, 27.6 mmol,
3.0 equiv), Amberlyst-15 (0.76 g), and acetonitrile (30 mL) were added
under an air atmosphere, and the flask was closed with a stopper.
Subsequently, the reaction mixture was stirred at rt for 0.5 h. After this
time, the product was separated from the catalyst by simple filtration
using glass column equipped with cotton wool and then the solvent and
all volatiles were evaporated under reduced pressure to give
1,1,1,5,5,5-hexamethyl-3,3-diphenyltrisiloxane (11) in 91% (3.03 g).
Fig. 1. The formation of Si-O-E moieties.
samples and are specified in Table 2. Subsequently, the reaction mix-
Pasteur pipette equipped with cotton wool and then the solvent and all
volatiles were evaporated under reduced pressure to give the corre-
sponding compounds 1–15. To our knowledge, all compounds are
known in literature, except for compounds 8 and 9.
3. Results and discussion
Encouraged by our previous works, we decided to examine the
commercially available and stable Amberlyst-15 catalyst (A-cat). This
inexpensive ion exchange resin based on polystyrene has strongly acidic
sulfonic groups. Because of this, A-cat plays an important role as a
reusable catalyst in organic chemistry [12]. To explore the generality
and scope of this catalytic system, we initially performed the O-silyla-
tion of trimethylsilanol with 2-methylallyltris(trimethylsiloxy)silane in
different organic solvents and in the presence of various amounts of the
catalyst (see Table 1). When the reaction was carried out in the absence
35% yield after 1 h (Table 1, entry 1). The best results were observed in
was used in the synthesis of product 3, which is very volatile; see
2.2. General procedure for the synthesis of functionalized silsesquioxanes
16–19
To a 25 mL one-necked flask equipped with a stirring bar, 0.015 g of
Amberlyst, POSS silanol (1 equiv., 0.06 mmol), 2-methylallyl reagent
(3.0 equiv., 0.018 mmol) and 1 mL of toluene were added under air
atmosphere. Subsequently, the reaction mixture was stirred at rt for
20 h. After this time, the product was separated from the catalyst by
simple filtration using Pasteur pipette equipped with cotton wool and
then the solvent and all volatiles were evaporated under reduced
pressure. After that, the product was separated from the remaining
substrate by adding acetonitrile to dissolve the excess of the 2-
The decision about using such a simple silanol stemmed from the
Table 1
Comparison of a catalytic activity of Amberlyst-15 in O-silylation under different conditions.a
Entry
Solvent
Catalyst amount [g]
Time [h]
1
2
3
4
5
6
7
8
–
0.015
0.030
0.015
0.0075
0.015
0.015
0.015
0.015
1
35
99
99
45
99
40
10
70
Acetonitrile
Acetonitrile
Acetonitrile
Dichloromethane
Toluene
0.5
1
1
1
1
Tetrahydrofuran
Hexane
1
1
a
b
rt, air atmosphere, 0.5 mL of solvent, 0.025 g (0.278 mmol) of trimethylsilanol, 0.065 g (0.187 mmol) of 2-methylallyltris(trimethylsiloxy)silane.
Determined by GC chromatography.
262