Iridium-promoted conversion of chlorosilanes to alkynyl derivatives in a one-pot reaction sequence

Article abstract of DOI:10.1021/om500320t

By making use of the catalytic potential of the iridium system [{Ir(μ-Cl)(CO)₂}₂]/NEt(i-Pr)₂ in the synthesis of silyl-functionalized alkynes via silylative coupling of terminal alkynes/diynes with iodosilanes, we propose

Full text of DOI:10.1021/om500320t

Article
pubs.acs.org/Organometallics
Iridium-Promoted Conversion of Chlorosilanes to Alkynyl Derivatives
in a One-Pot Reaction Sequence
Ireneusz Kownacki,*,† Bartosz Orwat,† and Bogdan Marciniec*,†,‡
†Faculty of Chemistry, Adam Mickiewicz University in Poznan
́ ́
, Umultowska 89b, 61-614 Poznan
‡Center of Advanced Technology, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan
́
S
* Supporting Information
ABSTRACT: By making use of the catalytic potential of the
iridium system [{Ir(μ-Cl)(CO)2}2]/NEt(i-Pr)2 in the synthesis
of silyl-functionalized alkynes via silylative coupling of terminal
alkynes/diynes with iodosilanes, we propose a new protocol
allowing employment of various mono- and dichlorosilanes as reagents. The process is based on a sequence of two reactions
occurring simultaneously: i.e., conversion of initial chlorosilane (SiR1 Cl4−n) to the appropriate iodosilane via Cl/I nucleophilic
n
substitution and its further conversion to a silylalkyne derivative ((SiR1 (CCR2)4−n) via iridium-catalyzed silylative coupling
n
with terminal alkyne. Under optimum conditions, the method has proved to be effective and versatile in the conversion of a wide
range of chlorosilanes to a rich portfolio of various corresponding alkynyl-functionalized silicon derivatives. Additionally, NMR
studies of the equimolar reaction of a well-defined iridium(I) alkynyl precursor with Me3Si−I revealed that Si−I bond
activation in iodosilane molecules occurred via oxidative addition to the iridium center.
CH)12 and triorganosilylacetylides ([M(CCSiR3)n]: M =
INTRODUCTION
■
MgX, n = 1; M = In, n = 3; M = ZnCl, n = 1)13 with halogeno-
functionalized organic compounds, or similar nickel-catalyzed
reactions14 yielding silylethynyl-functionalized aryl derivatives.
Our group has also contributed to the development of new
catalytic methods for the synthesis of silyl-functionalized
terminal alkynes particularly through Si−Csp bond for-
mation, with employment of vinylsilanes as silylation agents.15
Since 2006, a series of papers have been published, devoted to
the synthesis of silylalkynes via the ruthenium- or rhodium-
catalyzed coupling of terminal aliphatic or silyl alkynes (RC
CH) with various vinylsilanes (R3SiCHCH2).15 Recently, we
have also reported a new and efficient catalytic route for the
silylation of terminal alkynes/diynes by trisubstituted iodosi-
lanes, promoted by an iridium(I) carbonyl precursor in the
presence of a tertiary amine (Scheme 1).16,17
Efficient synthesis of silyl-functionalized alkynes is of great
interest in organic and material chemistry because currently
derivatives of this type are increasingly being used as stable and
convenient synthons of alkynyl carboanions. The latter can be
successfully applied as essential components for preparation of
organic and natural products,1 as well as conjugated oligomers
and polymers for the construction of electronic or optoelec-
tronic materials containing a linear carbon−carbon triple bond
in their structure, liquid crystals, nonlinear materials, molecular
wires, and other engineering materials.2
The known methods, commonly used in the preparation of
various alkynylsilanes, are based on two different pathways:
namely, silyl functionalization of terminal alkynes via Si−Csp
bond formation or incorporation of a whole silylethynyl
function (−CCSiR3) with C−C bond creation. The first
group includes methods employing the equimolar reactions of
various chlorosilanes (SiClnR4−n),3 alkoxysilanes,4 or amino-
silanes5 with organometallic species of the type MCCR′ (M
= Li, MgX, where X = Cl, Br), as well as those that rely on zinc
or zinc salt promoted coupling of terminal alkynes with
aminosilanes,6a chlorosilanes,6b−d Me3SiOTf6e (OTf =
−O3SCF3) or trisubstituted silanes (SiR3H),6f and comprise
also transition-metal-mediated reactions such as terminal alkyne
dehydrogenative silylation with hydrosilanes,7 ruthenium-
promoted coupling with chlorosilanes,8 palladium-catalyzed
coupling with SiMe3CF3,9 or SiMe3OTf.10
Scheme 1. Iridium-Promoted Silylative Coupling of
Terminal Alkynes with Trisubstituted Iodosilanes
It has been shown that the iridium(I) catalytic system works
perfectly only if a Si−I bond is present in the organosilicon
reagent. Unfortunately, iodosilanes are less common and less
stable than other halosilanes. A number of methods are
available for the synthesis of such derivatives; some of them are
based on PdCl2-catalyzed H/I exchange18 in hydrosilanes or
On the other hand, the second group comprises methods
that use the equimolar reactions of lithium triorganosilylace-
tylides (Li+−CCSiR3) with a wide range of ketones that lead
to the formation of appropriate hydroxyl-functionalized
aliphatic silylalkynes,11 catalytic processes such as palladium-
promoted cross-coupling of various silylalkynes (R3SiC
Received: March 24, 2014
© XXXX American Chemical Society
A
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nucleophilic substitution of the chlorine atom in chlorosilanes
with iodide anions in a polar solvent system.19
Table 1. Coupling of Trichloro-Substituted Silanes with
Phenylacetylene
a
In view of the literature devoted to the synthesis of
iodosilanes, we are extraordinarily interested in the method
consisting of substitution of a chlorine atom in the initial
chlorosilane by an iodide anion19 with employment of
inorganic salts (alkali-metal iodides). In organic chemistry,
this type of process is known as the Finkelstein reaction,20 and
it is commonly used for the preparation of organic iodo
derivatives by reaction of alkyl chlorides or bromides with NaI
in acetone solution.
In this paper we present the results of our studies focused on
the design of a catalytic system, based on the discovered
iridium-promoted coupling reaction,16,17 enabling conversion
of chlorosilanes to a wide variety of appropriate alkynylsilanes.
Furthermore, mechanistic considerations based on the results
of spectroscopic studies of the equimolar reaction of a well-
defined iridium(I) complex with SiMe3I are also presented.
a
Reaction conditions: [R3SiCl]:[PhCCH]:[M+I−]:[NEt(i-Pr)2]:[Ir]
= 1:1.2:1.2:1.6:10−2, 80 °C, 24 h. The conversion and yield were
determined by GC analysis and calculated using decane as a internal
standard.
RESULTS AND DISCUSSION
■
As mentioned above, only iodosilanes can be used as silylation
agents because chlorosilanes as well as bromosilanes appeared
unreactive in this process. Therefore, in our study, we applied
the Finkelstein method for the creation of a system that would
allow combining a sequence of two reactions in a one-pot
protocol: i.e., in situ transformation of chlorosilane (SiRnCl4‑n)
to a corresponding iodosilane and its further conversion to
silylalkyne derivative ((SiRn(CCR′)4−n) via iridium-catalyzed
silylative coupling with terminal alkyne. However, to find the
best inorganic reagent/solvent system allowing the reaction
sequence, i.e. conversion of the initial chlorosilane to the
appropriate iodosilane via Cl/I exchange and iridium-promoted
silylative coupling of the iodosilane formed with terminal
alkyne, as well as to recognize the efficiency of the iridium
catalytic system in the alkyne silylation process in a one-pot
protocol, a series of silylative coupling tests was performed
(Scheme 2). The tests were aimed at optimizing the reaction
chlorosilanes (SiR3Cl) significant amounts of undesirable
byproducts formed such as R3SiCH2CN, (R3Si)2CHCN, and
[CH3CN+SiR3]I−.19a Similarly, as noted for MeCN, the use
of other polar solvents such DMF and NMP also led to the
formation of unwanted side products.
The results compiled in Table 1 demonstrate that under
a
typical reaction conditions (see footnote ) the presence of the
inorganic salt has no deactivating effect on the efficiency of the
iridium catalyst used (for comparison see refs 16 and 17).
It should also be noted that Cl/I nucleophilic substitution is
an equilibrium reaction, which can be driven to completion by
the differential solubility of halide salts or by use of a large
excess of the halide salt.21 In the case of our one-pot process, it
is not necessary to use a large excess of iodide salts because the
concentration of iodosilane formed is decreasing continuously
during the consecutive catalytic process, i.e. iridium-catalyzed
silylation of the alkynyl moiety; therefore, formally the
equilibrium is continuously shifted toward the formation of
iodosilane.
Scheme 2. Silylation of Phenylacetylene by SiR3Cl in a One-
Pot Reaction Sequence
Therefore, for further studies on the iridium-promoted
conversion of various chlorosilanes to the corresponding
alkynyl functionalized silicon derivatives, the system based on
LiI/α,α,α-trifluorotoluene was chosen.
The results compiled in Tables 2−4 demonstrate the
versatility of the one-pot protocol in the conversion of a wide
range of chlorosilanes to a rich portfolio of the corresponding
alkynyl-functionalized silicon derivatives, according to Scheme
3:
conditions under which various trisubstituted chlorosilanes
(SiR3Cl) in situ were converted to the appropriate iodosilanes
(SiR3I) by reaction with two selected iodide salts (NaI and LiI)
in different polar solvents as the reaction medium.
Scheme 3. Coupling of Mono- and Dichlorosilanes with
Terminal Alkynes
The results of screening for selected trisubstituted chlor-
osilanes and polar solvents, compiled in Table 1, have
confirmed that the initial chlorosilane only in combination
with the group 1 metal iodides (NaI, LiI) can react with
terminal alkyne in the presence of iridium(I) precatalyst. The
highest yield of silylated phenylacetylene was possible to obtain
only with three reagent systems: i.e., SiMe3Cl/NaI in MeCN
(entry 2) and SiMe3Cl/LiI and SiMe2PhCl/LiI in α,α,α-
trifluorotoluene (entries 6 and 8, respectively). The use of
MeCN as a reaction medium allowed obtaining the silylation
product in high yield only when SiMe3Cl was employed as a
silylation agent. Unfortunately, in the case of other
a
Under the optimum conditions (see Table 2, footnote ) this
protocol was successfully applied to the coupling of vinyl-
functionalized monochlorosilanes with PhCCH and
Me3SiCCH, giving desirable products in a quantitative
manner (entries 1−4).
B
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Considering the results shown in Tables 1 and 2, the
proposed method seems to be general and can be efficient also
for the alkynylation of dichloro-substituted silicon derivatives
having also two chloro substituents at one silicon atom (gem
position) (Table 3, entries 1−13). The examples presented in
Table 3 show that iridium-promoted silylative coupling via a
sequence of two reactions under one-pot conditions can be
successfully used for the preparation of a wide range of bis-
alkynyl silicon compounds, with employment of various
dichlorosilanes, even those containing a reactive vinyl group
at silicon (entries 9−11), as well as in combination with a
terminal alkyne containing a reactive functional group such as
−B(OCMe2CMe2O) in its structure (entries 7, 8, and 11 in
Table 3). For most of the dichloro silicon reagents presented in
Table 3, except for ClMe2SiOSiMe2Cl (entries 12 and 13), the
bis-alkynylation process with the use of selected terminal
alkynes (PhCCH, Me3SiCCH, (OCMe2CMe2O)-
Table 2. Coupling of Selected Vinyl-Substituted
Monochlorosilanes with Exemplary Terminal Alkynes
a
a
Reaction conditions: [SiR3Cl]:[R1CCH]:[LiI]:[NEt(i-Pr)2]:[Ir] =
1:1.4:1.2:1.6:10−2, C6H5CF3, 90 °C, argon, 24 h. The conversion and
yield were determined by GC analysis and calculated using the solvent
b
as a standard. Yield of isolated product in parentheses.
a
Table 3. Coupling of Dichlorosilicon Derivatives with Selected Terminal Alkynes under One-Pot Reaction Conditions
a
Reaction conditions (unless stated otherwise): [SiR2Cl2]:[R1CCH]:[LiI]:[NEt(i-Pr)2]:[Ir] = 1:2.8:2.4:3.2:2 × 10−2, C6H5CF3, 90 °C, argon, 24
b
h. the The conversion and yield were determined by GC analysis and calculated using the solvent as a standard. Reaction conditions: [SiR2Cl2]:
c
[R1CCH]:[LiI]:[NEt(i-Pr)2]:[Ir] = 1:2.06:2.4:3.2:2 × 10−2, C6H5CF3, 90 °C, argon, 24 h. Yield of isolated product in parentheses.
C
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BC6H4CCH) led to complete conversion of the dichloro-
substituted silane, giving the desired products in very high yield.
Considering the results shown in Tables 2 and 3, it can be
concluded that the presence of a vinyl group in the
chlorosilicon reagent, most likely due to its electronic
properties, promotes the Cl/I exchange process as well as the
coupling of iodosilane formed with terminal alkynes. On the
other hand, as demonstrated by entries 12 and 13 in Table 3,
the presence of siloxane moieties, presumably due to the dπ−
pπ interaction between the oxygen atom and the silicon atoms,
makes the latter less reactive in nucleophilic substitution by
iodide anions, as well as in the Si−I bond activation process
(a result of these effects), which is reflected in significantly
lower yields of the expected products.
equiv of SiMe2Cl2 or 1 equiv of SiPh2Cl2 leads to selective
formation of coupling products in a good yield (Table 4). The
products contain in their structure the remaining one chloro
substituent, in addition to the alkyne functional group, as
shown in Scheme 4.
Table 4. Selective Monocoupling of Dichloro-Substituted
a
Silanes with Selected Terminal Alkynes
Generally, the literature data concerning the synthesis of
alkynyl- and bis-alkyl-functionalized vinylsilanes are very scarce,
including those on silicon derivatives containing in their
structures other functional groups, such as −B-
(OCMe2CMe2O).
Very recently we have reported the preparation of mono- and
bis-alkynylsilanes via iridium-catalyzed coupling of terminal
alkynes with various iodo- and diiodosilanes,17b which were
prepared in a catalytic manner.18 This method proved to be
very efficient for simple iodosilanes; however, for the
preparation of vinyl-functionalized mono- and diiodosilanes it
seems to be problematic, because the synthesis of appropriate
vinyl-functionalized iodo- and diiodosilanes requires several
steps, including the preparation of Si−H derivatives (H2C
CHSiHnR3−n) by reduction of the corresponding chlorosilanes
a
Reaction conditions (unless stated otherwise): [SiR1 Cl2]:[R2C
2
CH]:[LiI]:[NEt(i-Pr)2]:[Ir] = 3:1:1:1.6:2 × 10−2, 90 °C, argon, 48 h.
The conversion and yield were determined by GC analysis and
b
calculated using the solvent as a standard. Reaction conditions:
[SiR1 Cl2]:[R2CCH]:[LiI]:[NEt(i-Pr)2]:[Ir] = 1:1:1:1.6:2 × 10−2.
2
c
Yield of isolated product in parentheses.
Scheme 4. Synthesis of Chloro- and Alkynyl-Substituted
Silanes
22
(H2CCHSiClnR3−n or HCCHSiClnR3−n) with LiAlH4
and then palladium-catalyzed H/I substitution.18 However, as
palladium compounds are also well-known as hydrosilylation
catalysts,23 the use of PdCl2 as an H/I exchange catalyst in
H2CCHSiHnR3−n also could lead to the formation of
undesirable polyhydrosilylation products.
The synthesis of mono- and bis-alkynyl silanes, according to
the previously used method,17b would require two additional
steps, i.e. Cl/H substitution and Pd-catalyzed H/I exchange,
and it would not guarantee a high yield of the expected
products. The one-pot protocol proposed has significant
advantages over the previously used method,17b because it
allows the direct application of chlorosilanes in the generation
of the corresponding iodosilicon derivatives without any
additional steps and simultaneous coupling with terminal
alkynes in a single batch.
It seems that in all aspects, especially the availability of
chlorosilanes, the method that allows direct application of
chlorosilanes in the generation of the corresponding iodo
derivatives seems to be the most convenient, practical, and
atom economical.
We think that, in comparison with other methods, our one-
pot system is more convenient also for the synthesis of alkynyl
silanes, particularly those containing in their structure one or
more −B(OCMe2CMe2O) functional groups, because all of the
substrates are commercially available (SiRnCl4−n, Si(CH
CH2)RnCl3−n, (OCMe2CMe2O)BC6H4CCH) unlike the
reagents necessary for carrying out the multistep synthesis via
Sonogashira protocol in combination with conventional
synthetic pathways:24 e.g., B(OCMe2CMe2O)(O-i-Pr)-
SiR2(CCH)2, BrC6H4B(OCMe2CMe2O), BrC6H4B4C
CSiMe3, etc.
Thus, the developed one-pot method allows the selective
conversion of dichloro silicon compounds not only to bis-
alkynyl derivatives but also to alkynyl-functionalized chlor-
osilanes in one step.
It should be noted that the synthesis of such silicon
derivatives may not be difficult but may be very time-
consuming because it requires to carry out several noncatalytic
steps with isolation and purification of all intermediates.25
All of the mono- and bis(alkynyl)-functionalized silicon
derivatives presented in Tables 2−4 were isolated and
characterized by spectroscopic methods (see the Supporting
Information), to show the scope of this new versatile and
efficient synthetic method.
Mechanistic Considerations. Our previous publication
gave the results and discussion of a preliminary study on the
reactivity of the initial iridium(I) precursor ([{Ir(μ-Cl)-
(CO)2}2]) in sequential reactions with each of the substrates
in the equimolar systems, in addition to catalytic data
concerning silylation of terminal alkynes/diynes by SiMe3I.17a
The outcomes presented in the cited paper have unambigu-
ously proven that the activation of the Csp−H bond in a
terminal alkyne by an iridium(I) metallic center and formation
of [Ir(H)(CCR)] species is the key step of this new coupling
reaction. On the basis of these studies, we have proposed a
possible mechanism for this process, in which the first catalytic
run involves the transformation of the initial precursor [{Ir(μ-
Cl)(CO)2}2] (I) to the four-coordinated complex [Ir(Cl)-
(CO)(NR′3)2] (II) in the presence of a tertiary amine. In a
Surprisingly, it was also found that, for dichloro-substituted
silanes, the use of a ratio of 1 equiv of terminal alkyne to 3
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Scheme 5. Transformation of Iridium Precursor I to Alkynyl Species IV via a Csp−H Bond Activation Step
Scheme 6. Equimolar Reaction of IVa with Iodotrimethylsilane
further step, this iridium species reacts with terminal alkyne via
oxidative addition of the C−H bond, giving the six-
coordinated alkynyl−hydride iridium(III) complex III (struc-
ture determined by X-ray analysis when pyridine was used as
NR′3),17a which in the presence of a tertiary amine is
transformed to four-coordinated iridium(I) alkynyl derivatives
IV with evolution of ammonium chloride, as shown in Scheme
5. In this mechanism, on the basis of sequential reactions, we
have postulated that the activation of the Si−I bond in the
silicon reagent molecules also plays an important role in the
silylation process, but we did not have evidence regarding the
mechanism of Si−I activation. It may take place by two
possible mechanisms: namely, σ-bond metathesis or oxidative
addition of the Si−I bond to the iridium center with
formation of the iridium(III) species IV with iodide and silyl
ligands bonded to the metallic center. In order to confirm one
of the aforementioned theses, the equimolar reaction of the
well-defined iridium(I) alkynyl complex [Ir(cod)(PCy3)(C
CPh)]26 (IVa) with SiMe3I was performed and monitored by
1H, 13C, and 31P NMR techniques. In the 1H NMR spectrum of
the initial complex IVa, the resonances at 7.42 (d), 7.16 (t), and
6.97 (t) ppm were assigned to phenyl group protons of alkynyl
ligand. The signals located at 5.26 and 3.75 ppm and the
multiplet at 2.41 ppm were assigned to a cyclooctadiene ligand
bonded to the iridium center. In the 13C NMR spectrum the
resonances at 131.20, 129.84, 125.17, and 121.61 ppm were
assigned to a phenyl substituent bonded to the alkynyl moiety
that gave two doublets located at 126.42 ppm (2JC−P = 13.5 Hz)
and 83.23 ppm (3JC−P = 12.6 Hz). The line at 67.30 ppm was
assigned to olefinic carbon atoms of the cyclooctadiene ligand.
In the 31P NMR spectrum a resonance at 19.53 ppm was
detected. The reaction of complex IVa with model iodosilane
(SiMe3I) (Scheme 6) enabled us to identify the six-coordinate
iridium(III) complex Va. Adding 1 equiv of SiMe3I to a
solution of complex IVa and conducting the reaction at room
temperature for 24 h did not result in visible changes in the
spectroscopic picture of the resulting reaction mixture. Only in
the 1H NMR and 13C NMR spectra was the appearance of new
singlets at 0.50 and 5.35 ppm, respectively, coming from
SiMe3I, observed. Heating the reaction mixture at 50 °C for 24
1
h resulted in a number of significant changes in the H, 13C,
and 31P NMR spectra, confirming the transformations of the
initial iridium(I) complex. After this time, the 1H NMR
spectrum was found to reveal new resonance lines located in
the area of chemical shifts characteristic of aromatic protons (in
the ranges 7.47−7.44 and 7.00−6.94 ppm) and alkenyl protons
of the cod ligand (multiplets at 5.58 and 5.42 ppm) as well as a
multiplet at 3.28 ppm for protons of cod-allyl positions.
Additionally, a new singlet was detected at 0.13 ppm, which was
assigned to the Me3Si− moiety bonded to the iridium center. In
the 13C NMR spectrum, two doublets at 128.76 ppm (2JC−P
=
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12.1 Hz) and 87.96 ppm (3JC−P = 13.09 Hz) coming from the
ethynylene moiety and three singlets at 132.25, 128.53, and
123.81 ppm assigned to the phenyl ring of the phenyl-
ethynylene ligand in the new complex formed were found
(compare with data for the initial complex IVa). In addition, a
singlet at 53.96 ppm assigned to the alkenyl carbons of the cod
ligand in the new complex formed as well as a singlet at 2.22
ppm coming from the Me3Si− ligand were found. In the 31P
NMR spectrum, in addition to the resonance line derived from
the initial complex (19.57 ppm), an additional line at 14.72
ppm was observed and assigned to the PCy3 ligand bonded to
the iridium(III) center in the new six-coordinated complex. It
should also be noted that in the 13C NMR spectrum, apart from
the signals characteristic of the six-coordinated complex, the
appearance of singlets at 106.04 and 94.33 ppm, typical of the
ethynylene moiety present in the coupling product formed
(PhCCSiMe3), was also observed (see Scheme 6).
further is transformed to compound VI with the release of
silylalkyne. The next stage of the cycle involves the C−H
bond activation process, which occurs during the reaction of
terminal alkyne with the four-coordinated complex VI. It leads
to the formation of alkynyl−hydride species VII, which in the
presence of tertiary amine is converted to the initial iridium
alkynyl complex IV with evolution of ammonium salt according
to a dehydrohalogenation process.27
CONCLUSIONS
■
The catalytic protocol created on the basis of the one-pot two-
reaction sequence, namely in situ generation of the
corresponding iodosilane from the initial chlorosilane
(SiRnCl4−n) and its coupling with terminal alkyne in the
presence of iridium catalyst, appeared to be very efficient and
versatile in the conversion of a wide range of chlorosilanes to
the appropriate alkynyl-functionalized silicon compounds.
Under optimum reaction conditions, the one-pot method
proposed allowed the synthesis of various mono-alkynyl-
functionalized (R3SiCCR1) and bis-alkynyl-functionalized
silicon derivatives ([Si](CCR1)2) as well as monoalkynyl
The presence of trimethylsilylphenylacetylene in the reaction
mixture is direct evidence of the next step in the proposed
mechanism, involving the conversion of the six-coordinate
complex Va, shown in Scheme 6, to the four-coordinated iodide
complex VIa with the release of the coupling product. The 1H,
13C, and 31P NMR spectra, recorded 48 h after introduction of
an additional 2 equiv of Me3Si−I to the reaction mixture,
showed a substantial increase in the intensity of the
aforementioned resonance lines. These spectra confirmed a
significant shift of the equilibrium toward the six-coordinate
complex, which is the product of oxidative addition of
iodosilane to the initial complex IVa (see the Supporting
Information).
chloro silanes (R1 SiCl(CCR2)) in high yield. Most of the
3
obtained compounds were isolated and characterized by
spectroscopic methods. Moreover, an NMR study of the
equimolar reaction between a well-defined iridium(I) alkynyl
complex and SiMe3I gave evidence of Si−I bond activation in
the iodosilanes via oxidative addition to the iridium center. This
has enabled us to propose a plausible mechanism of alkyne
silylative coupling with iodosilanes derived from chlorosilanes.
EXPERIMENTAL SECTION
In summary, the stoichiometric studies described above
prompted us to propose the coupling reaction mechanism
shown in Scheme 7, in which we assume that the IrI alkynyl
species IV, generated according to Scheme 5, is a real catalyst
that initiates the reaction between iodosilanes and alkynes.
Considering the above, we assume that in the first step complex
IV reacts with SiR″3I via Si−I two-electron oxidative
addition, which results in the formation of complex V, which
■
All synthesis and manipulations were carried out under argon using
standard Schlenk-line and vacuum techniques. The chemicals were
obtained from the following sources: IrCl3·3H2O from Pressure
Chemicals, cod, C6D6, CDCl3, DMF, THF, decane, NEt(i-Pr)2,
Me3SiI, NaI, LiI, MeCN, C6H5CF3, PhCCH, and (OCMe2CMe2O)-
BC6H4CCH from Aldrich, SiEt3Cl, SiMe2PhCl, SiMe2Cl2, SiPh2Cl2,
H2CCHSiMe2Cl, H2CCHSiPh2Cl, and H2CCHSiMeCl2 from
ABCR, CO (class 4.7) from Linde Gas. The complexes [{Ir(μ-
Cl)(cod)}2]28 and [{Ir(μ-Cl)(CO)2}2]29 were synthesized according
to the published methods. All solvents and liquid reagents were dried
and distilled under argon prior to use.
Scheme 7. Proposed Mechanism of Terminal Alkyne
Silylative Coupling with in situ Generated Iodosilanes
The NMR spectra in the liquid phase were recorded in CDCl3 or
benzene-d6 using 300 and 600 MHz spectrometers and referenced to
the residual protonated solvent peaks (1H δH 7.26 ppm and 13C, δC
77.16 ppm for CDCl3 and 1H δH 7.16 ppm and 13C δC 128.05 ppm for
benzene-d6) or external Si(CH3)4. The compound purity was
determined by elemental analysis. The GC analyses were performed
on gas chromatography apparatus equipped with a TCD detector and
capillary column VF-5 (30 m × 0.53 mm). Products were identified by
GC/MS equipped with a VF-5 column (30 m × 0.25 mm) and ion
trap mass detector.
General Procedure for Catalytic Tests. A thick-walled vacuum
glass Schlenk reactor (25 mL) equipped with a magnetic stirring bar
was evacuated and flushed with argon. Then, the calculated amount of
M+I− (M = Na, Li) (6 mmol) and 10 mL of solvent were placed in the
reactor. Then, to the mixture obtained were successively added SiR3Cl
(5 mmol), NEt(i-Pr)2 (8 mmol), PhCCH (6 mmol), decane (10%
of initial liquid substrates volume), and the complex [{Ir(μ-
Cl)(CO)2}2] (0.025 mmol) under a flow of argon. The reactor was
placed in an oil bath, and the reaction was conduced at a given
temperature. The reaction mixture was analyzed by GC and GC/MS
at the beginning and after 24 h. The conversion and yield were
calculated using the internal standard calculation method.
General Procedure for Silylative Coupling of Terminal
Alkynes with Chlorosilanes. A thick-walled vacuum glass Schlenk
F
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Organometallics
Article
reactor (50 mL) equipped with a magnetic stirring bar was evacuated
and flushed with argon. Then, the calculated amount of Li+I− and 20
mL of anhydrous and deoxidized C6H5CF3 were placed in the reactor.
300 K): δ (ppm) 136.87, 135.17, 133.45, 132.92, 132.19, 129.88,
128.99, 128.25, 127.98, 122.67 (Ph and SiCHCH2), 109.33 (
SiCC), 88.46 (SiCC). 29Si NMR (119.23 MHz, C6D6, 300 K):
δ (ppm) −31.86.
Then to the mixture obtained were successively added SiRnCl4−n
,
NEt(i-Pr)2, RCCH, and the complex [{Ir(μ-Cl)(CO)2}2] under a
flow of argon. The reactor was placed in an oil bath, and the reaction
was conduced at a given temperature. The reaction mixture was
analyzed by GC and GC/MS prior to the reaction and after 24 or 48 h.
The conversion and yield were calculated using the internal standard
calculation method using the solvent as a standard (for detailed
procedures see the Supporting Information).
Synthesis of [(Trimethylsilyl)ethynyl]diphenylvinylsilane,
SiPh2(CCSiMe3)(CHCH2) (4; Table 2). Following the procedure
used for preparation of compound 1 (Table 2), a reaction was carried
out with 1.93 g (14.4 mmol) of LiI, 2.94 g (12 mmol) of Si(H2C
CH)Ph2Cl, 1.65 g (16.8 mmol) of Me3SiCCH, and 2.48 g (19.2
mmol) of NEt(i-Pr)2 in the presence of 34.04 mg (0.06 mmol) of the
complex [{Ir(μ-Cl)(CO)2}2]. A 3.53 g amount of [(trimethylsilyl)-
ethynyl]diphenylvinylsilane was obtained (yield 96%). Anal. Calcd for
C19H22Si2: C, 74.44; H, 7.23. Found: C, 74.50; H, 7.26. 1H NMR (300
MHz, CDCl3, 300 K): δ (ppm) 7.70 (m, 4H, m-Ph); 7.43 (m, 6H, o,p-
Ph); 6.48 (dd, 1H, SiCHCH2); 6.30 (dd, 1H, SiCHCH2); 6.03
(dd, 1H, CH2); 0.29 (s, 9H, SiMe3). 13C NMR (74.46 MHz, C6D6,
300 K): δ (ppm) 136.98, 135.27, 133.45, 132.97, 129.98, 128.08, (Ph
and SiCHCH2), 119.46 (SiCC), 107.47 (SiCC), −0.01
(SiMe3). 29Si NMR (119.23 MHz, C6D6, 300 K): δ (ppm) −17.97
(SiMe3), −33.23 (SiPh2).
Synthesis of Dimethyl(phenylethynyl)vinylsilane, SiMe2(C
CPh)(CHCH2) (1; Table 2). A thick-walled vacuum glass Schlenk
reactor (50 mL) equipped with a magnetic stirrer was charged, under
an argon atmosphere, with 1.93 g (14.4 mmol) of anhydrous lithium
iodide (LiI) and 20 mL of anhydrous and deoxidized C6H5CF3. Then,
to the mixture obtained were successively added 1.45 g of Si(H2C
CH)Me2Cl (12 mmol), 2,48 g of NEt(i-Pr)2 (19.2 mmol), 1.71 g of
PhCCH (16.8 mmol), and 34.04 mg of the complex [{Ir(μ-
Cl)(CO)2}2] (0.06 mmol) under a flow of argon. The reactor was
placed in an oil bath, and the reaction was conducted at 90 °C with
vigorous stirring. The reaction was carried out until complete
conversion of the silicon reagent, typically 24 h. The reaction mixture
was analyzed by GC and GC/MS at the beginning and after 24 h. The
conversion and yield were calculated using the internal standard
calculation method (the solvent pick was used as an internal standard).
After completion of the reaction, in order to remove the catalyst and
ammonium salt from the reaction mixture, the solvent and unreacted
substrates were evaporated at a reduced pressure and then 30 mL of
pentane was added. The resulting suspension was filtered off, and the
resulting deposit was rinsed with two portions of pentane. The solvent
was initially evaporated from the filtrate, and the residual product was
distilled by means of the trap to trap technique at reduced pressure,
giving 2.17 g of the final product. Dimethyl(phenylethynyl)vinylsilane
was obtained in a yield of 97%. Anal. Calcd for C12H14Si: C, 77.35; H,
7.57. Found: C, 77.39; H, 7.59. 1H NMR (300 MHz, CDCl3, 300 K):
δ (ppm) 7.52 (m, 2H, m-Ph); 7.33 (m, 3H, o,p-Ph); 6.26 (dd, 1H,
SiCHCH2); 6.10 (dd, 1H, SiCHCH2); 5.97 (dd, 1H, =CH2);
0.37 (s, 6H, SiMe2). 13C NMR (75.46 MHz, C6D6, 300 K): δ (ppm)
136.63, 133.27, 132.13, 128.73, 128.32, 123.11 (Ph and SiCH
CH2); 106.35 (CC-SiMe2); 92.09 (CCSiMe2), −1.32 (SiMe2).
29Si NMR (119.23 MHz, C6D6, 300 K): δ (ppm) −24.67.
Synthesis of Dimethyl[bis{(4-(4,4,5,5-tetramethyl-1,3,2-diox-
oboran-2-yl)phenyl)ethynyl}]silane, SiMe2[CCC6H4B-
(OCMe2CMe2O)]2 (7; Table 3). Following the methodology used
for preparation of compound 1 (Table 2), a reaction was carried out in
10 mL of C6H5CF3 with 0.96 g (7.2 mmol) of LiI, 0.39 g (3 mmol) of
SiMe2Cl2, 1.41 g (6.18 mmol) of (OCMe2CMe2O)BC6H4CCH,
and 1.24 g (9.6 mmol) of NEt(i-Pr)2 in the presence of 17.02 mg (0.03
mmol) of the complex [{Ir(μ-Cl)(CO)2}2]. After completion of the
reaction, in order to remove the catalyst and ammonium salt from the
reaction mixture, the solvent and unreacted substrates were evaporated
at reduced pressure and then 30 mL of Et2O was added. The resulting
suspension was filtered off, and the resulting deposit was rinsed with
two additional portions of Et2O. The solvent was initially evaporated
from the filtrate. The residual product was sublimated under vacuum,
and 1.38 g of dimethyl[bis{4-(4,4,5,5-tetramethyl-1,3,2-dioxoboran-2-
yl)phenylethynyl)]silane was obtained (yield of 90%). Anal. Calcd for
C30H38B2O4Si;: C, 70.33; H, 7.48. Found: C, 87.52; H, 5.29. 1H NMR
3
(300 MHz, CDCl3, 300 K): δ (ppm) 7.74 (d, JH−H = 8.1 Hz, 4H,
3
C6H4); 7.50 (d, JH−H = 8.1 Hz, 4H, C6H4); 1.34 (s, 24H,
B(OCMe2CMe2O)); 0.48 (s, 6H, SiMe2). 13C NMR (74.46 MHz,
C6D6, 300 K): δ (ppm) 134.58; 131.42; 125.41; 106.14 (CC-
SiMe3); 92.04 (CCSiMe3); 84.13 (B(OCMe2CMe2O)); 25.04
(B(OCMe2CMe2O)); 0.59 (SiMe2). 29Si NMR (119.23 MHz, C6D6,
300 K): δ (ppm) −39.22.
Synthesis of Methylphenyl(phenylethynyl)vinylsilane,
SiMePh(CCPh)(CHCH2) (2; Table 2). Following the procedure
used for preparation of compound 1 (Table 2), a reaction was carried
out with 1.93 g (14.4 mmol) of LiI, 2.19 g (12 mmol) of Si(H2C
CH)(Me)(Ph)Cl, 1.71 g (16.8 mmol) of PhCCH, and 2.48 g (19.2
mmol) of NEt(i-Pr)2 in the presence of 34.04 mg (0.06 mmol) of the
complex [{Ir(μ-Cl)(CO)2}2]. A 2.86 g amount of methylphenyl-
(phenylethynyl)vinylsilane was obtained (yield 96%). Anal. Calcd for
C17H16Si;: C, 82.20; H, 6.49. Found: C, 82.30; H, 6.53. 1H NMR (300
MHz, CDCl3, 300 K): δ (ppm) 7.76 (m, 2H, m-Ph); 7.58 (m, 2H, m-
Ph); 7.46 (m, 3H, o,p-Ph); 7.37 (m, 3H, o,p-Ph); 6.38 (dd, 1H,
SiCHCH2); 6.22 (dd, 1H, SiCHCH2); 6.06 (dd, 1H, CH2);
0.63 (s, 3H, SiCH3). 13C NMR (74.46 MHz, C6D6, 300 K): δ (ppm)
135.14, 134.83, 134.76, 134.24, 132.08, 129.62, 128.80, 128.21, 127.92,
122.78 (Ph and SiCHCH2), 107.84 (SiCC), 89.99 (
SiCC), −2.54 (SiMe).
Synthesis of Diphenyl[bis{(4-(4,4,5,5-tetramethyl-1,3,2-diox-
oboran-2-yl)phenyl)ethynyl)]silane, SiPh2[CCC6H4B-
(OCMe2CMe2O)]2 (8; Table 3). Following the methodology used
for preparation of compound 1 (Table 2), a reaction was carried out in
10 mL of C6H5CF3 with 0.96 g (7.2 mmol) of LiI, 0.76 g (3 mmol) of
SiPh2Cl2, 1.41 g (6.18 mmol) of (OCMe2CMe2O)BC6H4CCH, and
1.24 g (9.6 mmol) of NEt(i-Pr)2 in the presence of 17.02 mg (0.03
mmol) of the complex [{Ir(μ-Cl)(CO)2}2] After completion of the
reaction, in order to remove the catalyst and ammonium salt from the
reaction mixture, the solvent and unreacted substrates were evaporated
at reduced pressure and then 30 mL of Et2O was added. The resulting
suspension was filtered off, and the resulting deposit was rinsed with
two additional portions of Et2O. The solvent was initially evaporated
from the filtrate. The residual product was purified by a flash column
filled with silica using hexane/Et2O (93/7%) as the mobile phase.
After purification 1.66 g of diphenyl[bis{4-(4,4,5,5-tetramethyl-1,3,2-
dioxoboran-2-yl)phenylethynyl)]silane was obtained (yield 87%).
Anal. Calcd for C40H42B2O4Si: C, 75.48; H, 6.65. Found: C, 75.57;
Synthesis of Diphenyl(phenylethynyl)vinylsilane, SiPh2(C
CPh)(CHCH2) (3; Table 2). Following the procedure used for
preparation of compound 1 (Table 2), a reaction was carried out with
1.93 g (14.4 mmol) of LiI, 2.94 g (12 mmol) of Si(H2CCH)Ph2Cl,
1.71 g (16.8 mmol) of PhCCH, and 2.48 g (19.2 mmol) of NEt(i-
Pr)2 in the presence of 34.04 mg (0.06 mmol) of the complex [{Ir(μ-
Cl)(CO)2}2]. A 3.65 g amount of diphenyl(phenylethynyl)vinylsilane
was obtained (yield 98%). Anal. Calcd for C22H18Si: C, 85.11; H, 5.84.
1
H, 6.70. H NMR (300 MHz, CDCl3, 300 K): δ (ppm) 7.85 (m, 4H,
3
3
m-Ph); 7.76 (d, JH−H = 8.1 Hz, 4H, C6H4); 7.57 (d, JH−H = 8.1 Hz,
4H, C6H4-); 7.43 (m, 6H, o,p-Ph); 1.34 (s, 24H, Me). 13C NMR
(74.46 MHz, C6D6, 300 K): δ (ppm) 135.09; 134.61; 132.97; 131.61;
130.43; 128.26; 125.13 (Ph, C6H4); 108.94 (CCSiPh2); 89.04 (C
CSiPh2); 84.18 (B(OCMe2CMe2O)); 25.03 (B(OCMe2CMe2O)).
Synthesis of Methyl[bis(phenylethynyl)]vinylsilane, SiMe-
(CCPh)2(CHCH2) (9; Table 3). Following the procedure used for
1
Found: C, 85.14; H, 5.86. H NMR (300 MHz, CDCl3, 300 K): δ
(ppm) 7.82 (m, 4H, m-Ph); 7.66 (m, 2H, m-Ph); 7.51 (m, 6H, o,p-
Ph); 7.43 (m, 3H, o,p-Ph); 6.66 (dd, 1H, SiCHCH2); 6.40 (dd, 1H,
SiCHCH2); 6.15 (dd, 1H, CH2). 13C NMR (74.46 MHz, C6D6,
G
dx.doi.org/10.1021/om500320t | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
preparation of compound 1, a reaction was carried out with 1.93 g
(14.4 mmol) of LiI, 0.85 g (6 mmol) of Si(Me)(H2CCH)Cl2, 1.71 g
(16.8 mmol) of PhCCH, and 2.48 g (19.2 mmol) of NEt(i-Pr)2 in
the presence of 34.04 mg (0.06 mmol) of the complex [{Ir(μ-
Cl)(CO)2}2]. A 1.57 g amount of methylbis(phenylethynyl)vinylsilane
was obtained (yield 96%). Anal. Calcd for C19H16Si: C, 83.77; H, 5.92.
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Higgins, S. J. Dalton Trans. 2013, 42, 338−341.
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Grimsdale, A. C.; Weil, T.; Enkelmann, V.; Muellen, K.; Meghdadi, F.;
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1
Found: C, 83.83; H, 5.97. H NMR (300 MHz, CDCl3, 300 K): δ
(ppm) 7.53 (m, 4H, m-Ph); 7.33 (m, 6H, o,p-Ph); 6.21 (m, 3H,
SiCHCH2); 0.55 (s, 3H, Si(CH3)). 13C NMR (74.46 MHz,
C6D6, 300 K): δ (ppm) 135.30, 133.69, 132.35, 129.13, 128.37, 122.71,
(Ph and SiCHCH2), 107.10 (SiCC), 88.90 (SiCC),
−0.55 (Si(CH3)). 29Si NMR (119.23 MHz, C6D6, 300 K): δ (ppm)
−46.30.
Synthesis of Methyl[bis{(4-(4,4,5,5-tetramethyl-1,3,2-dioxo-
boran-2-yl)phenyl)ethynyl)]vinylsilane, SiMe[CCC6H4B-
(OCMe2CMe2O)]2(CHCH2) (11; Table 3). Following the proce-
dure used for preparation of compound 1, a reaction was carried out in
10 mL of C6H5CF3 with 0.96 g (7.2 mmol) of LiI, 0.42 g (3 mmol) of
Si(Me)(H2CCH)Cl2, 1.41 g (6.18 mmol) of (OCMe2CMe2O)-
BC6H4CCH, and 1.24 g (9.6 mmol) of NEt(i-Pr)2 in the presence
of 17.02 mg (0.03 mmol) of the complex [{Ir(μ-Cl)(CO)2}2]. The
residual product was purified by a flash column filled with silica. After
purification 1.38 g of methyl[bis{4-(4,4,5,5-tetramethyl-1,3,2-dioxo-
boran-2-yl)phenylethynyl)]vinylsilane was obtained (yield 88%). Anal.
Calcd for C31H38B2O4Si: C, 71.01; H, 7.31. Found: C, 71.10; H, 7.36.
3
1H NMR (300 MHz, CDCl3, 300 K): δ (ppm) 7.75 (d, JH−H = 8.1
3
Hz, 4H, C6H4); 7.52 (d, JH−H = 8.1 Hz, 4H, C6H4); 6.19 (m, 3H,
CHCH2); 1.34 (s, 24H, Me); 0.55 (s, 3H, SiMe). 13C NMR
(74.46 MHz, C6D6, 300 K): δ (ppm) 133.43; 134.59; 133.51; 129.18;
125.26 (C6H4, CHCH2); 107.17 (CCSiMe3); 90.16 (C
CSiMe3); 84.14 -OC(Me)2); 25.03 (Me); −0.63 (SiMe). 29Si
NMR (119.23 MHz, C6D6, 300 K): δ (ppm) −46.24.
Stoichiometric Reaction of [Ir(cod)(PCy3)(CCPh)] (IVa) with
Me3SiI. An 85 mg amount (0.125 mmol) of [Ir(cod)(PCy3)(C
CPh)] (IVa) and 0.6 mL of benzene-d6 were placed in a J. Young
1
NMR tube under an argon atmosphere, and H, 13C, and 31P NMR
spectra were recorded. After NMR analysis, 25 mg (0.125 mmol) of
Me3Si−I was added to the solution of IVa and the reaction was
1
conducted for 24 h at room temperature. After this time H, 13C, and
31P NMR spectra were also recorded, and then the reaction was carried
out for 24 h at 50 °C. After NMR analysis, an additional 2 equiv of
Me3Si−I was introduced into the NMR tube and the reaction was
continued for the next 48 h.
ASSOCIATED CONTENT
* Supporting Information
■
S
Text and figures giving experimental procedures and NMR data
of synthesized compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*E-mail for I.K.: Ireneusz.Kownacki@amu.edu.pl.
*E-mail for B.M.: Bogdan.Marciniec@amu.edu.pl.
■
Notes
The authors declare no competing financial interest.
(12) (a) Lu, P.; Lam, J. W. Y.; Liu, J.; Jim, C. K. W.; Yuan, W.; Chan,
C. Y. K.; Xie, N.; Hu, Q.; Tang, B. Z.; Cheuk, K. K. L. Macromolecules
2011, 44, 5977−5986. (b) Neenan, T. X.; Whitesides, G. M. J. Org.
Chem. 1988, 53, 2489−2496. (c) Gelman, D.; Tsvelikhovsky, D.;
Molander, G. A.; Blum, J. J. Org. Chem. 2002, 67, 6287−6290.
(d) Arcadi, A.; Cacchi, S.; Marinelli, F. Tetrahedron Lett. 1986, 27,
6397−6400. (e) Erdelyi, M.; Gogoll, A. J. Org. Chem. 2001, 66, 4165−
4169. (f) Zhou, N.; Wang, L.; Thompson, D. W.; Zhao, Y. Tetrahedron
2011, 67, 125−143. (g) Hill, L. L.; Smith, J. M.; Brown, W. S.; Moore,
L. R.; Guevera, P.; Pair, E. S.; Porter, J.; Chou, J.; Wolterman, C. J.;
Craciun, R.; Dixon, D. A.; Shaughnessy, K. H. Tetrahedron 2008, 64,
6920−6934. (h) Fudickar, W.; Linker, T. Chem. Eur. J. 2011, 17,
ACKNOWLEDGMENTS
This work was financially supported by the National Science
Centre (Grant No. N N 204 443840).
■
REFERENCES
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