Multifunctional Catalytic Surface Design for Concerted Acceleration of One-Pot Hydrosilylation-CO2 Cycloaddition

Article abstract of DOI:10.1021/acs.orglett.9b03602

Silica-supported Rh-ammonium iodide catalyst showed high performance for hydrosilylation-CO₂ cycloaddition reaction sequences. The catalyst was prepared by surface grafting of Rh and the silane-coupling reaction of the ammonium iodide moiety. The acceleration of each catalytic reaction was realized due to the concerted catalysis between Rh species, immobilized organic functions, and surface Si-OH groups. As a result, good to excellent yields of silyl carbonates were obtained from epoxyolefins, hydrosilanes, and CO₂ under mild reaction conditions.

Full text of DOI:10.1021/acs.orglett.9b03602

Letter
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Multifunctional Catalytic Surface Design for Concerted Acceleration
of One-Pot Hydrosilylation−CO Cycloaddition
2
Kei Usui, Kodai Miyashita, Kyogo Maeda, Yuichi Manaka, Wang-Jae Chun, Koji Inazu,‡
†
‡
†
†,§
∥
,
†,⊥
and Ken Motokura*
†Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology,
Yokohama 226-8502, Japan
‡
Department of Chemistry and Biochemistry, National Institute of Technology, Numazu College, Numazu 410-8501, Japan
§
Renewable Energy Research Center, National Institute of Advanced Industrial Science and Technology, Fukushima 963-0298,
Japan
∥
Graduate School of Arts and Sciences, International Christian University, Mitaka, Tokyo 181-8585, Japan
⊥
PRESTO, Japan Science and Technology Agency (JST), Saitama 332-0012, Japan
*
S Supporting Information
ABSTRACT: Silica-supported Rh-ammonium iodide catalyst showed high
performance for hydrosilylation−CO2 cycloaddition reaction sequences. The
catalyst was prepared by surface grafting of Rh and the silane-coupling reaction
of the ammonium iodide moiety. The acceleration of each catalytic reaction was
realized due to the concerted catalysis between Rh species, immobilized organic
functions, and surface Si−OH groups. As a result, good to excellent yields of silyl
carbonates were obtained from epoxyolefins, hydrosilanes, and CO under mild
2
reaction conditions.
ne-pot synthesis of molecules is widely considered to be
Scheme 1. Multifunctional Catalytic Surface for (a) One-Pot
O
an efficient approach for biomaterial, pharmaceutical,
Reaction Sequence, (b) Concerted Catalysis, and (c)
Combined Concept for One-Pot Synthesis Comprising
Accelerated Single Reactions
1
−4
and fine chemical syntheses.
However, conducting multiple
catalytic reactions in a single reactor is typically challenging
due to the deleterious interactions between catalysts and
reagents, which could potentially lead to the formation of
inactive salts. The utilization of solid surfaces with multiple
active sites, based on the site-isolation concept, is a highly
5
,6
efficient approach for addressing this problem (Scheme 1a).
For example, Mizuno and co-workers reported the one-pot
synthesis of flavones using basic Mg−Al layered, double
hydroxide-supported Au nanoparticles via selective dehydro-
6e
genation and C−C bond formation. Shaabani and co-workers
reported the synthesis of pyranopyrazole derivatives using a
cobalt complex immobilized on silica-coated Fe O magnetite
3
4
6
j
catalyst.
Another advantage of the bifunctional catalytic surfaces is
the concerted catalysis-mediated rate acceleration of the
individual reactions (Scheme 1b). Multiple active sites on
the same solid surface can participate in the catalysis of a
reaction, which could significantly improve its productivity.
Silanol activated amine-catalyzed carbon−carbon bond for-
8
functionalities, have been reported. Fernandes and co-workers
reported an immobilized copper complex catalyst which also
7
mation is a well-known concerted surface-catalysis strategy.
Recently, several types of supported metal complexes,
including those with Cu, Pd, and Rh centers with organic
Received: October 11, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b03602
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
comprised imidazole and TEMPO moieties for the accel-
eration of oxidative alcohol dehydrogenation.
Scheme 3. Preparation of Various Kinds of SiO -Supported
Catalysts
2
8j
These concepts of conducting multiple catalytic reactions
and concerted catalysis-mediated rate acceleration of catalytic
bifunctional surfaces should be combined toward designing
solid surfaces for realizing highly efficient one-pot production
strategies for fine chemical synthesis from simple reaction
substrates under accelerated concerted catalysis (Scheme 1c).
Recently, our group reported a silica-supported Rh complex−
tertiary amine catalyst for hydrosilylation of terminal olefins,
which tolerated the presence of various reactive functional
9
groups such as the epoxy group, on the olefin. Furthermore,
the activity of the Rh complex increased significantly by the
coimmobilization of a tertiary amine. Similarly, we found that
silica-supported quaternary ammonium iodide acts as an
efficient heterogeneous catalyst for cyclic carbonate synthesis
from epoxides and CO by the concerted effect between the
2
10
iodide anion and surface silanols. Having worked on these
two approaches, we envisioned the combination of these two
catalytic systems on the same solid surface, whereby a silica-
supported Rh-ammonium iodide would be prepared, which
could allow the one-pot synthesis of silyl carbonate derivatives
from epoxyolefins, hydrosilanes, and CO . If such a multi-
2
functional catalytic surface is developed, it would not only
facilitate one-pot hydrosilylation−CO cycloaddition reaction
2
sequences but would also confer concerted rate enhancement
of the processes (Scheme 2). The resulting highly function-
Scheme 2. One-Pot Hydrosilylation−CO Cycloaddition
2
+
−
Using SiO /Rh/N I Catalyst
9,10
2
activities.
The elemental analysis results of the prepared
samples are summarized in Table 1. While the presence of
Table 1. Elemental Analysis Results of SiO -Supported Rh
2
Complex-Quaternary Ammonium Salts
element (mmol g−1)
catalyst
C
N
Rh
I
+
−
SiO /Rh/Bu N I
10.7
9.1
9.9
11.4
3.1
0.7
1.4
0.6
0.7
0.5
0.042
0.036
0.040
0.70
0.58
0.65
0.69
0.25
2
3
alized silyl carbonates have been shown to possess unique
physical, chemical, and electrochemical properties and have
+ −
SiO /Rh/PPN I
2
+ −
SiO /Rh-NEt /Bu N I
2
2
3
11
displayed strong potential as synthetic intermediates. For
example, silicon polymers containing the cyclic carbonate
moiety have been synthesized and showed specific properties,
such as high viscosity and large range of dielectric
+ −
SiO /Bu N I
2
3
+ −
SiO /PPN I
2
1
1a,d,g
constant.
In addition, the high reactivity of the silyl
similar nitrogen and iodide amounts was detected in SiO /Rh/
2
+
−
moiety toward the inorganic surface makes the obtained
product a novel surface modification reagent which comprises
a cyclic carbonate skeleton.
Bu N I sample, the nitrogen content was twice higher than
3
+
−
that of iodide in SiO /Rh/PPN I , which indicated the
2
maintenance of the precursor’s quaternary ammonium
The preparation process of the SiO -supported catalysts is
2
1
3
summarized in Scheme 3. Treatment of SiO with [Rh(OH)-
2
9a
cod] afforded the SiO -supported Rh complex (SiO /Rh).
2
2
2
The SiO -supported Rh-ammonium iodides (SiO /Rh/
2
2
+
−
+ −
Bu N I and SiO /Rh/PPN I ) were prepared by the reaction
3
2
of the SiO /Rh and the corresponding quaternary ammonium
2
salts via silane-coupling reaction. The catalysts bearing
+
−
+ −
ammonium iodide alone (SiO /Bu N I and SiO /PPN I )
2
3
2
10
were also prepared from the parent SiO2. The SiO with both
2
the Rh complex and tertiary amine (SiO /Rh-NEt ) was
2
2
9a
prepared from a mixed solution of both precursors, followed
by ammonium iodide immobilization to afford SiO /Rh-NEt /
the reaction of 1,2-epoxy-5-hexene (1a, R = CH ), the catalyst
2
2
2
+
−
+ −
Bu N I (Supporting Information). During the preparation,
with both Rh and ammonium iodide (SiO /Rh/PPN I )
3
2
we used an iodide loading, which was greater than 10 times the
Rh loading, to account for the differences in their catalytic
showed good performance for the direct synthesis of the silyl
carbonate (5aa) (entry 1). While the reaction with SiO /Rh
2
B
DOI: 10.1021/acs.orglett.9b03602
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
afforded the hydrosilylation product 3aa (entry 2) only, the
formation of the cyclic carbonate 4aa alone was detected with
could be reused at least twice with maintenance of high
+
−
product yield (total TON: 900 (Rh), 57 (N I )). The used
catalyst could be recoverable from the reaction mixture, and
the recovered catalyst also showed good catalytic activity. A
part of alkylammonoum group is possibly detached from the
+
−
SiO /PPN I (entry 3). These results clearly indicate that
2
hydrosilylation and cyclic carbonate synthesis are promoted by
the Rh and quaternary ammonium iodide sites, respectively.
+
−
10
Notably, the bifunctional catalyst SiO /Rh/Bu N I furnished
silica surface under the reaction conditions; however, the
2
3
+
−
+ −
a higher yield of 5aa than that of SiO /Rh/PPN I (entry 4).
good recoverability and reusability of SiO /Rh/Bu N I
2
2
3
This result was comparable with that obtained with the
catalyst as well as much lower activity of homogeneous
+
−
+ −
physical mixture of SiO /Rh and SiO /Bu N I (entry 5),
Bu N I for the cycloaddition reaction (Table 2, entry 6)
2
2
3
4
whereas only 10% yield of the final product 5aa was obtained
+
−
when homogeneous Bu N I was used instead of SiO2/
Table 2. Hydrosilylation−CO Cycloaddition Sequences
4
2
+
−
Bu N I (entry 6). It should be mentioned that the concerted
effect between the iodides and surface Si−OH groups is
necessary for the promotion of CO cycloaddition.
Catalyzed by SiO -Supported Rh Complex and Ammonium
3
2
a
Salt
10
2
Next, allyl glycidyl ether (1b) was examined, and SiO /Rh/
2
+
−
Bu N I showed good activity for production of 5ba, and
3
delivered the product in 53% yield (entry 7). Due to the lower
reactivity of 1b than 1a, tertiary amine was coimmobilized on
9
a
SiO /Rh surface. The product selectivity improved with the
2
+
−
use of the SiO /Rh-NEt /Bu N I catalyst bearing the tertiary
2
2
3
amine functionality (entry 8). The physical mixture of SiO /
2
+
−
Rh and SiO /Bu N I also afforded final product 5ba, albeit in
2
3
a much lower yield than that obtained with both bifunctional
catalysts (entry 11). Interestingly, the total hydrosilylation
yield (%)
1
a (R = −CH −)
yield (3ba + 5ba) with the bifunctional catalysts, SiO /Rh/
2
2
+
−
+ −
Bu N I (57%) and SiO /Rh-NEt /Bu N I (61%), was
entry
1
catalyst
3aa
4aa
5aa
3
2
2
3
higher than that obtained with the physical mixture of the
supported Rh and ammonium iodide (SiO /Rh + SiO /
+ −
SiO /Rh/PPN I
11
80
0
3
10
90
22
0
83
23
15
0
61
0
0
74
74
10
2
b
2
2
2
3
SiO
SiO
2
2
/Rh
+
−
b
+ −
Bu N I : 46%) catalysts, which indicates that ammonium
3
/PPN I
SiO /Rh/Bu N I
+
−
iodide has a positive effect on the hydrosilylation reaction
under one-pot reaction conditions. Co-immobilization of
organic functionality is effective for the reaction of 1b, which
showed relatively low hydrosilylation selectivity.
4
5
6
2
3
+
−
SiO /Rh + SiO /Bu N I
2
2
3
+
−
SiO /Rh + Bu N I
2
4
yield (%)
+
−
Time-course analysis of the SiO /Rh/Bu N I -catalyzed
2
3
1
b (R = −O(CH )−)
2
one-pot reaction clearly indicated that the main reaction
pathway was hydrosilylation−cycloaddition (Figure S5). The
initial hydrosilylation rate is much higher than that for the
formation of cyclic carbonate. Notably, a small amount of the
olefin bearing the cyclic carbonate moiety (4) remained after
prolonged reaction time, indicating the low reactivity of 4
toward hydrosilylation. To increase the desired silyl carbonate
selectivity, stepwise synthesis was examined (Scheme 4), and a
quantitative yield of the silyl carbonate was achieved by
hydrosilylation under inert atmosphere followed by cyclic
carbonate formation. The addition of new substrates after the
completion of the catalytic reaction revealed that the catalyst
entry
catalyst
3ba
4ba
5ba
+
−
7
8
9
SiO /Rh/Bu N I
4
0
55
0
14
12
0
80
18
53
61
0
0
38
2
3
+
−
SiO /Rh-NEt /Bu N I
2
2
3
SiO /Rh-NEt
SiO /Bu N I
2
2
−
+
1
1
0
1
2
3
+
−
SiO /Rh + SiO /Bu N I
8
2
2
3
a
Reaction conditions: 1 (1.0 mmol), 2a (1.5 mmol), CO
balloon), catalyst (Rh: 3.25 μmol, ammonium iodide: 50 μmol), neat,
0 °C, 24 h. Yields were determined by GC and H NMR using
(1 atm,
2
1
8
internal standard. A part of the terminal CC bond of 4 was
b
isomerized in the presence of Rh. 2a (1.0 mmol).
Scheme 4. Stepwise Hydrosilylation−CO Cycloaddition
suggest that the catalytic reaction mainly occurs on the silica
support surface. To further increase the TONs, we examined
the reaction using a much lower catalyst amount, and the
2
and Reuse Experiment
+
−
TONs increased to 7600 (Rh) and 130 (N I ), with the
retention of the 85% yield of the final product (Scheme 5).
The scope of the silanes which were compatible with the
+
−
SiO /Rh/Bu N I -catalyzed reaction is summarized in Scheme
2
3
6
. The reaction performed the stepwise method: hydro-
silylation under Ar followed by addition of CO to the reactor
2
for cycloaddition. The silanes bearing phenyl groups, such as
methyldiphenylsilane and dimethylphenylsilane, were found to
be good substrates for the reaction. However, the product yield
decreased slightly when triphenylsilane was used as the silane
substrate. Alkylsilanes and alkoxysilane also reacted smoothly
to afford the corresponding silyl carbonates in high yields.
Scheme 6 also summarizes the scope of the epoxy olefins for
a
Seventeen hours for hydrosilylation.
C
DOI: 10.1021/acs.orglett.9b03602
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 5. High TON One-Pot Synthesis of Organosilicon
ASSOCIATED CONTENT
Supporting Information
■
+
−
Carbonate Catalyzed by SiO /Rh/Bu N I
2
3
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b03602.
Experimental conditions of catalytic preparation and
catalytic reactions, catalyst characterization spectra, and
product characterization data (PDF)
AUTHOR INFORMATION
Corresponding Author
■
+
−
*
E-mail: motokura.k.ab@m.titech.ac.jp.
Scheme 6. Substrate Scope for the SiO /Rh/Bu N I -
2
3
Catalyzed One-Pot Synthesis of the Organosilicon
Carbonate
ORCID
a
Wang-Jae Chun: 0000-0003-4084-3603
Ken Motokura: 0000-0002-0066-5139
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This study was supported by a JSPS Grant-in-Aid for Scientific
Research on Innovative Areas (Grant no. 18H04242),
Innovative Research Initiative project in Tokyo Tech, and
the AIST-Tokyo Tech cross-appointment system.
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DOI: 10.1021/acs.orglett.9b03602
Org. Lett. XXXX, XXX, XXX−XXX