I. Kownacki et al. / Tetrahedron Letters 55 (2014) 548–550
549
Table 2
catalytic system for the efficient synthesis of bis(arylethynyl-
Coupling of selected diiodo-disubstituted silanes with phenylacetylenea
ene)silanes via coupling of terminal alkynes with exemplary gem-
inal diiodo-disubstituted silanes.16
Entry
R2
Product
Yieldb (%)
Employing the most efficient iridium catalytic system, reported
in a previous paper,17 that is [{Ir(
l-Cl)(CO)2}2]/NEt(i-Pr)2, a series
1
Et3
99
of trial coupling experiments using terminal arylalkynes with se-
lected iodo-trisubstituted and diiodo-disubstituted silanes were
performed.16 Under the optimized conditions the coupling process
occurred smoothly and led to the formation of the desired silyla-
tion products in high yields, according to the following scheme:
2
3
Me2Ph
Ph2
99 (96)
99 (95)c
Reaction conditions: [alkyne]: [R2SiI2]: [NEt(i-Pr)2]: [Ir] = 2.6: 1: 2.8: 2 ꢁ 10ꢀ2
,
a
90 °C, argon, 48 h. Conversion and yield were determined by GC analysis and cal-
culated using the solvent as a standard.
b
Yield of isolated product in parentheses.
Reaction at 100 °C.
c
R3 = Me3, Et3, Me2Ph
R2 = Et2 , Meph, Ph2
promoted silylative coupling can be successfully used for the
preparation of a wide range of terminal alkyne silyl derivatives,
even those containing reactive functional groups such as
AB(OCMe2CMe2O), AN(SiMe3)2 (entries 9–13) in their structures.16
In the case of the H2N-functionalized alkyne (entry 13), it was
also possible to prepare the final product via a ‘one-pot’ protocol,
where both non-catalytic N-silylation and catalytic C-silylation
processes occurred.16
The results compiled in Table 1 show that the iridium(I) pre-catalyst
successfully catalyzed the silylation of terminal alkynes with differ-
ent trisubstituted iodosilanes. Under the optimum conditions (see
Table 1, footnote a) and irrespective of the alkyne applied, the cou-
pling occurred efficiently for Me3SiI and Me2PhSiI particularly, giv-
ing the respective
Csp-silyl-functionalized alkynes, exclusively
In order to demonstrate the synthetic potential of this reaction,
the iridium-based catalytic system was also successfully used for
the preparation of selected bis(alkynyl)disubstituted silanes via
coupling of phenylacetylene (as a model reagent) with appropriate
diiodo-disubstituted silanes (see Table 2, entries 1–3). Generally, for
diiodosilanes used as reagents, under the optimum reaction condi-
tions (see Table 2, footnote a), the complete transformation of the
initial dihalosilanes, and almost quantitative formation of bis(phen-
ylethynylene)disubstituted silicon derivatives were observed after
48 hours. The high activity of the iridium-based catalytic system
in the coupling of diiodosilanes (R2SiI2) with phenylacetylene
clearly illustrates the high potential of this reaction, not only in
the synthesis of various molecular bis(arylethynyl)silanes, but also
ethynylene-silylene or arylene-ethynylene-silylene oligomers, if in-
stead of terminal alkynes, organic or silicon diethynyl derivatives
are used. Several silyl-functionalized alkynes and bis(phenylethyn-
ylene) disubstituted silicon derivatives were isolated and character-
ized by spectroscopic methods (see Supplementary data), to show
the scope of this new and efficient catalytic reaction.
(entries 2, 3, 5, 6, 8, 9, 11 and 12). Lower yields of the products were
observed when Et3SiI was used as the silylation agent.
It is presumably an effect of the steric hindrance, resulting from
the presence of three ethyl groups at the silicon atom, which signif-
icantly hampers the activation of the „SiAI bond by the iridium
center, and which is also an important process in the proposed
catalytic cycle17 of this coupling reaction.
Considering the results shown in Table 1, the developed method
seems to be general and can be utilized efficiently for the silylation
of various terminal alkynes, and not only non-functionalized
examples. The examples presented in Table 1 show that iridium-
Table 1
Coupling of various terminal alkynes with trisubstituted iodosilanesa
Entry R3
Alkyne
Product
Yieldb (%)
1
2
Et3
Me2Ph
70
100 (98)
3
4
5
Me3
100 (96)
75
Et3
In conclusion, we have presented the application of a novel,
iridium-promoted silylative coupling of terminal alkynes with
iodosilanes (ISiR3) for the synthesis of various arylethynylene
functionalized silicon derivatives. The iridium-based catalytic
Me2Ph
98
6
7
8
Me3
100 (97)
73
system, [{Ir(l
-Cl)(CO)2}2]/NEtiPr2, under optimum conditions,
catalyzed efficiently the transformation of a wide range of various
terminal alkynes, even those containing reactive functional groups
such as ANH2, AB(OCMe2CMe2O), to give the desired silylated
product. Various (arylethynyl)trisubstituted silanes were isolated
and characterized by spectroscopic methods. Moreover, we found
that the iridium catalytic system could be used in the double
alkynylation of diiodosilanes. Using reaction conditions similar to
those employed for the reactions with monoiodosilanes, bis(pheny-
lethynylene)silanes were yielded almost quantitatively. Selected
compounds were also isolated and characterized by spectroscopic
methods.
Et3
Me2Ph
99
9
Me3
99 (96)
69
10
11
Et3
Me2Ph
98
99
(96)
12
13
Me3
General procedure
98 (92)
A glass Schlenk reactor (10 mL) equipped with a magnetic stir
bar was evacuated and flushed with argon. The calculated amount
a
Reaction conditions: [alkyne]: [R3SiI]: [NEt(i-Pr)2]: [Ir] = 1: 1.6: 1.8: 10ꢀ2, 80 °C,
argon, 24 h. Conversion and yield were determined by GC analysis and calculated
using the solvent as a standard.
of [{Ir(
l-Cl)(CO)2}2] complex (0.005 or 0.0025 mmol) was placed in
b
Yield of isolated product in parentheses.
the reactor under the flow of argon, then 3 mL of solvent and amine