Iridium-Catalyzed Hydrosilylation of Sulfur-Containing Olefins

Article abstract of DOI:10.1021/acs.orglett.7b02940

Hydrosilylation of various sulfur-containing olefins with (RO)₃SiH has been achieved using iridium catalysts [IrX(cod)]₂ (X = Cl, SPh). The catalysis is applicable to the chemoselective hydrosilylation of thioacetate, which enables the preparation of an industrially important silane coupling agent.

Full text of DOI:10.1021/acs.orglett.7b02940

Letter
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Iridium-Catalyzed Hydrosilylation of Sulfur-Containing Olefins
Venu Srinivas, Yumiko Nakajima,* Kazuhiko Sato, and Shigeru Shimada*
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki
305-8565, Japan
*
S Supporting Information
ABSTRACT: Hydrosilylation of various sulfur-containing
olefins with (RO) SiH has been achieved using iridium
3
catalysts [IrX(cod)] (X = Cl, SPh). The catalysis is applicable
2
to the chemoselective hydrosilylation of thioacetate, which
enables the preparation of an industrially important silane
coupling agent.
8
ydrosilylation of olefins is widely recognized as one of the
most important reactions for the production of various
We thus far developed various hydrosilylation catalysts,
8a
H
some of which exhibit sulfur-functional group tolerance to
give the corresponding hydrosilylation product albeit in low
yields. In this study, hydrosilylation of various sulfur-containing
olefins was successfully achieved using iridium catalysts,
[IrCl(cod)] , 1 (cod = 1,5-cyclooctadiene), [IrCl (η -C H )-
(cod)], 2, and [Ir(μ-SR)(cod)] [3a, R = Ph; 3b, R = 4-
organosilicon compounds and materials, such as silicones and
1
silane coupling agents. Platinum catalysts such as Speier’s and
Karstedt’s catalysts have been used in these reactions for more
than half a century. However, many problems still remain to be
solved, for example, occurrence of side reactions (olefin
hydrogenation, olefin isomerization, dehydrogenative coupling,
etc.) and deactivation of catalysts by reactive and/or
3
2
2
3
5
2
Cl(C H ); 3c, R = 4-MeO(C H ); 3d, R = CH CH Ph]
6
4
6
4
2
2
(Figure 1).
2
coordinating functional groups of the substrates. On the
other hand, organosilicon compounds and materials are
nowadays utilized not only as commodity chemicals but also
as high-performance materials in a wide range of fields due to
their versatile excellent properties. Therefore, there is an
increasing demand for the development of new catalyst systems
that enable the precise synthesis of highly sophisticated
organosilicon materials with a variety of functions. In this
regard, limited functional group compatibility of the conven-
tional Pt catalysts is a crucial issue, and continuous studies have
been made to overcome the drawbacks. As a result, various
catalysts, which exhibit good compatibility toward amino,
epoxy, alkoxy, and carbonyl functional groups, have been
Figure 1. Iridium catalysts 1, 2, and 3a−d.
Catalytic performance of 1 is summarized in Table 1. Allyl
phenyl sulfide 5a was hydrosilylated with (MeO) SiH, 4a, at
3
room temperature in the presence of 2 mol % of 1, leading to
the formation of anti-Markovnikov addition product
trimethoxy(3-(phenylthio)propyl)silane 6a in 85% yield. The
yield was slightly improved to 92% when the reaction was
performed with additional COD (10 mol %) (Table 1, entry 1).
Therefore, hydrosilylation of other olefins was examined under
similar reaction conditions. Allyl phenyl sulfide 5a was also
3
−5
recently reported.
hydrosilylation of sulfur-containing olefins are still scarce. For
On the other hand, examples of selective
6
example, it is reported that [H PtCl ] and [RhCl(PPh ) ]
2
6
3 3
catalyze hydrosilylation of various alkenyl sulfides with a
6
a
moderate selectivity. In particular, when using [RhCl-
(
PPh ) ], the occurrence of the C−S bond cleavage lead to
3
3
hydrosilylated with (EtO) SiH, 4b, and (EtO) MeSiH 4c to
significant decrease in the product yields. Recently, Vranken et
al. reported a hydrosilylation of homoallylic thioethers with
PhMe SiH catalyzed by [H PtCl ], whereas hydrogenation of
3
2
give the corresponding hydrosilylated products 6b and 6c in
0% and 93% yields, respectively (Table 1, entries 2 and 3).
9
2
2
6
6b
Chemoselective hydrosilylation of allyl thioacetate 5b was
achieved to form the corresponding hydrosilylated product S-
the substrates concomitantly proceeded in some cases.
Considering the importance of sulfur-containing organosilicon
compounds (RO) Si(CH ) (S) (CH ) Si(OR) (R = Me or
(
3-(trimethoxysilyl)propyl) thioacetate (6d, 94%) (Table 1,
3
2 3
n
2 3
3
entry 4). The reaction of allyl methyl sulfide 5c, homoallyl
methyl sulfide 5d, and methyl pent-4-en-1-yl sulfide 5e with
Et, n = 2−8) and (RO) Si(CH ) SH as useful silane coupling
3
2 3
7
agents in the tire production process, development of new
hydrosilylation catalysts that attain direct synthesis of these
(
MeO) SiH, 4a, resulted in the moderate to good product
3
compounds starting from (RO) SiH and sulfur-containing
3
olefins is one of the most challenging topics in the
Received: September 28, 2017
hydrosilylation chemistry.
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b02940
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 1. Hydrosilylation Reactions of Sulfur-Containing
Olefins Catalyzed by 1
It was confirmed that conventional Karstedt’s catalyst and
[RhCl(PPh ) ] were not efficient for the hydrosilylation of allyl
a
3 3
phenyl sulfide with 4a, resulting in the recovery of unreacted
starting materials with no or 33% of the hydrosilylated product.
The reaction was also performed using other iridium catalyst
candidates. Either [Ir(OMe)(cod)] or [IrCl(coe) ] (coe =
2
2 2
cyclooctene) did not exhibit catalytic activity for the hydro-
silylation reaction of allyl phenyl sulfide with (MeO) SiH, 4a.
3
In contrast, complex 2 exhibited a similar catalytic activity to
that of 1. Thus, the hydrosilylation of allyl phenyl sulfide 5a
with (MeO) SiH, 4a, was catalyzed by 2 to form the
3
hydrosilylated product 6a in 86% yield at the catalyst loading
of 4 mol % (Table 2, entry 1). Since 2 is easily converted to 1
Table 2. Hydrosilylation Reactions of Sulfur-Containing
a
Olefins Catalyzed by 2 and 3a−d
a
Reaction conditions: 1 (4 μmol), COD (0.02 mmol), silane (0.24
mmol for entries 1−7, 0.48 mmol for entries 8−10), olefin (0.20
b
mmol) in CD Cl (0.5 mL) at rt. NMR yield determined using
2
2
c
mesitylene (0.10 mmol) as an internal standard (isolated yield). 5c
d
(
(
(
30%) was recovered, and Me(CH ) SMe (18%) was also formed. 5d
2 2
e
18%) was recovered, and Me(CH ) SMe (10%) was also formed. 5e
2
3
6%) was recovered, and Me(CH2) SMe (4%) was also formed.
4
yields, trimethoxy(3-(methylthio)propyl)silane 6e (42%),
trimethoxy(4-(methylthio)butyl)silane 6f (70%), and
trimethoxy(5-(methylthio)pentyl)silane 6g (77%), respectively
a
Reaction conditions: cat. (4 μmol), COD (0.02 mmol), olefin (0.20
mmol), (MeO) SiH (0.24 mmol for entries 1−8, 0.48 mmol for
3
b
entries 9−11) in CD Cl (0.5 mL) at rt. NMR yield determined using
2
2
c
(
Table 1, entries 5−7). This is probably due to the higher
mesitylene (0.10 mmol) as an internal standard (isolated yield). 4 mol
d e
coordination ability of the SMe group compared to SPh and
SAc groups. In these reactions, hydrogenation of the starting
olefins concomitantly proceeded to give the corresponding
hydrogenated products in 18%, 10%, and 4% yields,
respectively. Disulfides also underwent hydrosilylation without
the occurrence of S−S bond cleavage. Thus, both diallyl
disulfide 5f and dihomoallyl disulfide 5g smoothly reacted with
% of 2 (8 μmol) was used. Starting materials were recovered. 5c
f
(31%) was recovered, and Me(CH ) SMe (30%) was also formed. 5d
2 2
(21%) was recovered, and Me(CH ) SMe (11%) was also formed.
2
3
9
on the treatment of (MeO) SiH, 4a, hydrosilylation reactions
catalyzed either 1 or 2 are likely to proceed following the same
reaction mechanism.
3
2
equiv of (MeO) SiH, 4a, at room temperature to form the
Sulfide-bridged dinuclear iridium complex 3a also showed
catalytic activity similar to those of 1 and 2 for the
3
corresponding bis-hydrosilylated products 6h and 6i in good
yields (Table 1, entries 8 and 9). In a similar manner, the 1,2-
di(hex-5-en-1-yl) disulfide 5h was also reacted with
hydrosilylation of allyl phenyl sulfide 5a with (MeO) SiH, 4a,
3
giving the hydrosilylated product 6a in 91% yield (Table 2,
entry 2). To investigate the substituent effect of the bridging
sulfide ligand, complexes 3b−d with different sulfide ligands
(
(
MeO) SiH, 4a, to afford the product 6j in excellent yields
Table 1, entry 10).
3
B
DOI: 10.1021/acs.orglett.7b02940
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
1
0
were prepared by a similar procedure for 3a. Thus, the
The insertion of the double bond into the Ir−H bond and
reaction of [Ir(OMe)(cod)] with RSH afforded 3b−d in good
subsequent intramolecular coordination of the S atom to the Ir
2
atom provides intermediate C. Oxidative addition of (RO) SiH
yields (Scheme 1).
3
on C gives Ir(III) species D, from which the reductive
elimination of the product regenerate A. The mechanistic
details (for example, interaction of the Ir atom with the sulfide
moiety, etc.) are not clear at this moment, and further detailed
mechanistic studies will be performed in due course.
Scheme 1. Preparation of Iridium Complexes 3b−d
With the effective catalyst 1 in hand, the utility of the system
for the synthesis of an industrially important silane coupling
13
agent 3-(trimethoxysilyl)propane-1-thiol (7) is demonstrated.
Reaction of allyl thioacetate (5b, 1.0 g) and (MeO) SiH (4a,
3
1
.26 g) catalyzed by 1 gave S-(3-(trimethoxysilyl)propyl)
ethanethioate 6d in 88% isolated yield, and subsequent
Next, hydrosilylation of allyl phenyl sulfide 5a with
hydrolysis of the product with NaOMe (1.2 equiv) in
(
3
MeO) SiH, 4a, was examined in the presence of 2 mol % of
3
14
MeOH afforded the desired silane coupling agent 3-
b−d. The use of 3b and 3c, which have Cl- or MeO-
(
trimethoxysilyl)propane-1-thiol (7, 1.31 g, 88% isolated
substituted phenyl sulfides, required a longer reaction time than
that with 3a and resulted in the formation of the desired
product 6a in 66% and 45% yields, respectively, after 24 h
yield) (Scheme 3).
Scheme 3. Preparation of Silane Coupling Agent 7
(
Table 2, entries 3 and 4). Complex 3d bearing phenethyl
sulfides exhibited further suppressed activity to produce the
product 6a in 20% yield (Table 2, entry 5). Hydrosilylation
reactions of allyl thioacetate 5b and disulfides 5e−g were also
examined using the most active 3a (2 mol %) to give the
corresponding hydrosilylated products 6d and 6h−j in 88−92%
yields (Table 2, entries 6, 9−11), whereas hydrosilylation of
allyl methyl sulfide 5c and homoallyl methyl sulfide 5d resulted
in the formation of the desired products 6e and 6f in moderate
yields (Table 2, entries 7 and 8). These results indicated the
comparable catalytic activity of 3a to that of 1.
In summary, hydrosilylation of various sulfur-containing
olefins was achieved using iridium catalysts 1−3. To the best of
our knowledge, this is the first example of the efficient
hydrosilylation of various sulfur-containing olefins with
trialkoxysilanes that are industrially important.
The utility of 1 as a hydrosilylation catalyst is already
11
reported in the alkyne hydrosilylation reactions. DFT studies
in the paper supported that the reaction is initiated with the
formation of active [Ir(H)(cod)] via reaction of 1 with
1
2
(
MeO) SiH, 4a. Considering this report, one possible
3
mechanism is proposed in Scheme 2. Complex 1 initially
ASSOCIATED CONTENT
■
reacts with (RO) SiH to form the hydride species A with the
3
*
S
Supporting Information
formula of [Ir(H)(cod)] and (RO) SiCl. In the reaction
3
mixture, the coordinatively unsaturated A might exist as an
adduct with additional coordinated ligands such as solvents,
silanes, or other Ir species. Then the coordination of the
olefinic part of allyl phenyl sulfide to A affords intermediate B.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.7b02940.
Experimental procedures and compound characterization
data for products (PDF)
Scheme 2. Plausible Mechanism for the Formation of
Hydrosilylated Products
AUTHOR INFORMATION
■
Corresponding Authors
*
*
E-mail: yumiko-nakajima@aist.go.jp
E-mail: s-shimada@aist.go.jp
ORCID
Yumiko Nakajima: 0000-0001-6813-8733
Shigeru Shimada: 0000-0001-7081-6759
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the “Development of Innovative
Catalytic Processes for Organosilicon Functional Materials”
project (PL: K.S.) from the New Energy and Industrial
Technology Development Organization (NEDO).
C
DOI: 10.1021/acs.orglett.7b02940
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(
11) Song, L.-J.; Ding, S.; Wang, Y.; Zhang, X.; Wu, Y.-D.; Sun, J. J.
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DOI: 10.1021/acs.orglett.7b02940
Org. Lett. XXXX, XXX, XXX−XXX