Silica Support-Enhanced Pd-Catalyzed Allylation Using Allylic Alcohols

Article abstract of DOI:10.1002/cctc.201801097

Although allylation using allylic alcohol is an environmentally-friendly method because of water being the sole byproduct in such reactions, allylic alcohol is one of the most difficult allylating agents in Pd-catalyzed allylation of nucleophiles. In this study, we successfully developed a mesoporous silica-supported Pd complex as an efficient catalyst for the allylation of nucleophiles using allylic alcohols as allylating agents. The allylic alcohol is activated by the silanol group on the support surface, which easily undergoes a π-allylpalladium intermediate formation. The catalytic activity of the supported Pd complex was ca. 9 times higher than that of its homogeneous precursor Pd complex. A highest turnover number of 4500 based on Pd was achieved. Various nucleophiles and allylic alcohol derivatives could be used as substrates. Not only the detailed catalyst structure but also the reaction mechanism including the concerted activation of allylic alcohol by the Pd complex and silanol were investigated by several spectroscopic techniques, such as Pd K-edge XAFS, solid-state NMR, and in-situ FT-IR measurements.

Full text of DOI:10.1002/cctc.201801097

Accepted Article
Title: Silica Support-Enhanced Pd-Catalyzed Allylation using Allylic
Alcohols
Authors: Ken Motokura, Marika Ikeda, Minjune Kim, Kiyotaka
Nakajima, Sae Kawashima, Masayuki Nambo, Wang-Jae
Chun, and Shinji Tanaka
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10.1002/cctc.201801097
ChemCatChem
Silica Support-Enhanced Pd-Catalyzed Allylation using Allylic Alcohols
Ken Motokura,*a,b Marika Ikeda,a Minjune Kim,c Kiyotaka Nakajima,c Sae
Kawashima,a Masayuki Nambo,a Wang-Jae Chun,d and Shinji Tanakae
a Dr. K. Motokura, M. Ikeda, S. Kawashima, M. Nambo
Department of Chemical Science and Engineering, School of Materials and Chemical
Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama,
226-8502, Japan. E-mail: motokura.k.ab@m.titech.ac.jp
b Dr. K. Motokura
PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi,
Saitama 332-0012, Japan
c Dr. M. Kim, Dr. K. Nakajima
Institute for Catalysis, Hokkaido University, Kita 20, Nishi 10, Kita-ku, Sapporo
001-0021, Japan
d Prof. Dr. W.-J. Chun
Graduate School of Arts and Sciences, International Christian University, Mitaka, Tokyo,
181-8585, Japan
e Dr. S. Tanaka
Interdisciplinary Research Center for Catalytic Chemistry, National Institute of
Advanced Industrial Science and Technology (AIST), Central 5, Higashi 1-1-1, Tsukuba,
Japan
Table of Contents
Pd-catalyzed allylation with allylic alcohol is accelerated by silanol on support surface.
The catalytic activity of the supported Pd complex was ca. 9 times higher than that of its
homogeneous precursor Pd complex. A highest turnover number of 4500 based on Pd
was achieved.
1
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10.1002/cctc.201801097
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Abstract
Although allylation using allylic alcohol is an environmentally-friendly method because
of water being the sole byproduct in such reactions, allylic alcohol is one of the most
difficult allylating agents in Pd-catalyzed allylation of nucleophiles. In this study, we
successfully developed a mesoporous silica-supported Pd complex as an efficient
catalyst for the allylation of nucleophiles using allylic alcohols as allylating agents. The
allylic alcohol is activated by the silanol group on the support surface, which easily
undergoes a π-allylpalladium intermediate formation. The catalytic activity of the
supported Pd complex was ca. 9 times higher than that of its homogeneous precursor Pd
complex. A highest turnover number of 4500 based on Pd was achieved. Various
nucleophiles and allylic alcohol derivatives could be used as substrates. Not only the
detailed catalyst structure but also the reaction mechanism including the concerted
activation of allylic alcohol by the Pd complex and silanol were investigated by several
spectroscopic techniques, such as Pd K-edge XAFS, solid-state NMR, and in-situ FT-IR
measurements.
2
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Introduction
Allylic alcohol is one of the most readily available sources of allyl groups for organic
synthesis. Usually, activated allylic compounds, such as allyl halides, acetates, and
carbonates, which are generally prepared from allylic alcohol, are used for allylation of
nucleophiles due to their much higher reactivity compared with that of allylic alcohols.
On the other hand, from the standpoint of environmentally friendly synthesis, direct use
of allylic alcohols realizes minimum waste formation after the reaction with
nucleophiles (Nu-H) as well as a minimum number of synthetic steps (Scheme 1).[1-3]
Scheme 1. Comparison of allylating agents for allylation of nucleophile
Unfortunately, the reactivity of the hydroxyl group as a leaving group is generally
very low. For example, the reactivity of benzyl chloride is much higher than that of
benzyl alcohol in Friedel-Crafts type alkylation. Recently, several effective acid
catalysts, such as Sc(OTf)3,[4] Bi(OTf)3,[5] and montmorillonite,[6] were reported for
the alkylation of nucleophiles with alcohols. In the case of Pd-catalyzed allylation,
acidic activation of allylic alcohol might also be effective for accelerating the formation
of π-allyl palladium, which is a well-known intermediate for Pd-catalyzed allylation.[3]
However, acid sensitivity of the allyl group sometimes cannot allow the use of a strong
acid as an activator. In addition, strong and free acids can possibly prevent the
nucleophilic attack step because anionic nucleophiles would be form in the reaction
with the π-allyl palladium. Due to these difficulties regarding the use of allylic alcohol
for allylation of nucleophiles, increase in the reaction rate and the Pd catalyst turnover
number (TON) remains a challenge.
The solid surface is a unique reaction field due to its multifunctional properties.
Accumulation of active species on the same solid surface realizes concerted activation
of substrate molecules without mutual interactions between different active species,
which sometimes induces deactivation of catalytic sites.[7] Our group recently reported
both silica-supported metal complexes and organic functionalities for efficient organic
reactions based on the concerted activation of substrate molecules.[8] The support,
silica, has a large number of “silanol” (Si-OH) groups on its surface, which can act as
3
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not only functionality-immobilizing sites but also as weak acidic sites, i.e.,
hydrogen-bonding sites. There have been many reports of silanol-assisted catalytic
reactions:[9] for example, the reaction between epoxide and carbon dioxide is promoted
by silanol. The hydrogen-bonding interaction between epoxide and silanol enhances the
ring-opening step of the epoxide, as shown in Scheme 2(A)[9b,c], which is a crucial
step for the overall reaction. These studies encouraged us to examine a silica-supported
Pd complex catalyst for the allylation reaction of nucleophiles with allylic alcohols as
allylating agents.[10] It can be expected that the hydroxyl group of allylic alcohol
interacts with Si-OH (Scheme 2(B)) similar to those of other hydrogen sources reported
in ref [3]. Additionally, strong interaction between the Pd complex and silanol should be
avoided due to immobilization of these two functionalities on solid surface.[11]
Herein, we report a mesoporous silica-supported Pd-bisphosphine complex as an
efficient heterogeneous catalyst for allylation with allylic alcohols. In this study, we
undertook detailed characterization of the catalyst structure by means of several
spectroscopic techniques, investigated the scope of allylation reaction using various
nuleophiles and allylic alcohols, and proposed a plausible reaction mechanism based on
the surface intermediate analysis.
Scheme 2. (A) Silanol-assisted ring-opening of epoxide by Lewis base ([X]-) and (B)
expected allylic alcohol activation by silanol with Pd complex.
Results and Discussion
Preparation and characterization of catalysts: Mesoporous silica (MS) supports were
prepared by modifying a well-known procedure using primary amines, n-octylamine
(C8), and n-dodecylamine (C12) as structure-directing agents.[12] The
Barret-Joyner-Halenda (BJH) pore size distribution curves show homogeneous
distribution of mesopores in a narrow range in both samples (Figure 1), and average
mesopore diameters of MS(C8) and MS(C12) are estimated to be 1.6 and 2.3 nm,
respectively. MS(C8) with small mesopores has larger BET surface area (1865 m2 g-1)
and pore volume (1.5 mL g-1) than MS(C12) with large mesopores (1175 m2 g-1 and 1.0
4
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mL g-1), and no significant change in surface area, pore volume, and pore size was
observed after the calcination of MS(C12) at 813 K for 3 h in air (Table 1). In this study,
nonporous silica (SiO2, Aerosil300) with ca. 300 m2 g-1 of BET surface area was used as
29
a reference support. Solid-state Si dd MAS NMR revealed the presence of 6-7 mmol
g-1 of Si-OH group in the bare MS supports. The amount of Si-OH group for MS(C12)
decreased slightly after the calcination treatment.
The MS-supported Pd-bisphosphine complex (MS/PP-Pd) was prepared by a simple
silane-coupling reaction (Scheme 3) using bare and calcined MS samples. A
Pd-bisphosphine complex with triethoxysilyl group (PP-Pd) was prepared beforehand,
followed by a reaction between the MS surface and PP-Pd that afforded MS/PP-Pd.
Elemental analysis of MS/PP-Pd indicated 0.3, 0.4, and 0.4 mmol g-1 of Pd, N, and Cl
contents, respectively, suggesting that the PP-Pd structure was maintained.[10]
Scheme 3. Preparation of MS(Cn)/PP-Pd
Dispersion and immobilization of PP-Pd inside the mesopores were confirmed by
SEM-EDX analysis. The SEM images along with the line analysis of elements are
shown in Figure 2. In the SEM images, MS particles with the average size of approx.
0.5 μm were observed for both MS(C8)/PP-Pd and MS(C12)/PP-Pd. The line analysis
results also represented similar location profiles for P, Cl, and Pd elements relative to
two main components (Si and O) of the MS support, in the cases of both C8 and C12.
These results clearly indicate that the PP-Pd functionalities are homogeneously
dispersed inside the mesopores of MS.
The chemical structure of PP-Pd was determined by solid-state NMR analysis. Figure
3 shows the 13C and 31P NMR results for MS(C12)/PP-Pd along with that of its
homogeneous precursor. The main carbon skeleton was maintained, as determined by
13C CP/MAS NMR: clear signals assigned to carbon next to Si (10 ppm), next to
nitrogen (55 ppm), and belonging to a phenyl group (120-140 ppm) were observed. A
31
single strong signal at around 0 ppm in P MAS NMR also indicated coordination of
PP-Pd. For detailed analysis of the local coordination structure of PP-Pd on MS, Pd
5
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K-edge XAFS measurements were conducted. Figure 4 shows the Pd K-edge XANES
spectra and FT of k3-weighted Pd K-edge EXAFS spectra of MS/PP-Pd and the
reference samples. The XANES spectral features of MS/PP-Pd were similar to those of
the reference Pd complex (PdCl2(PPh3)2) but differed from those of PdO and Pd foil,
indicating the complex structure of Pd species on the MS surface. EXAFS oscillation
spectra of MS(C8)/PP-Pd and MS(C12)/PP-Pd are shown in Figure 5. These two spectra
were almost identical, indicating the same coordination environment of the Pd complex
in these two samples. Fourier transform of k3-weighted Pd K-edge EXAFS indicated
strong signals at 1.8 Å in MS/PP-Pd samples (Figure 4). This signal position is close to
that of PdCl2(PPh3)2[13] but different from that for Pd-O and Pd-Pd. This suggests that
the Pd complex on MS/PP-Pd involved Pd-P and Pd-Cl bonds (denoted as Pd-P/Cl).
Curve-fitting analysis of the signal at 1.8 Å using Pd-P/Cl shell parameters is
summarized in Table 2. In the case of MS/PP-Pd, the coordination number (N) and bond
distance (r) were around 3 and 2.28 Å, respectively, indicating the coordination
environment of the PP-Pd precursor being maintained. Conclusively, the structure of
prepared MS/PP-Pd is shown in Scheme 3.
Allylation of nucleophiles with allylic alcohols: Allylation of ethyl acetoacetate with
allylic alcohol was examined using supported and homogeneous Pd catalysts. The
results are summarized in Table 3. MS(C12)/PP-Pd showed good catalytic performance
to afford allylation products in 50% yield with a TON of 87 (entry 1). Similar product
yield and slightly higher selectivity were observed with MS(C8)/PP-Pd (entry 2).
Decrease in amount of surface silanol by calcination and capping using Si(OMe)3Me
induced decrease in the catalytic activity (entries 3 and 4). Product yield obtained with
the homogeneous precursor PP-Pd was very low (entry 6) compared with that offered
by the supported catalysts. The reaction using Pd complex with
1,3-bis(diphenylphosphino)propane ligand (dppp-Pd) also showed lower activity (yield
of mono-allylated product: 16%) than immobilized catalysts with silanol.[14] Results
shown in Table 3 suggest that the presence of surface silanol is effective for allylation
with allylic alcohols. On the other hand, the reaction with allyl methyl carbonate was
not accelerated by the presence of the SiO2 support: homogeneous PP-Pd and
SiO2/PP-Pd showed similar catalytic performance for the allylation of ethyl acetoacetate
with it.[8d] The interaction between the surface silanol and the hydroxyl group of allylic
alcohol is a key factor for the acceleration. Additionally, MS(C12)/PP-Pd showed much
higher activity than that of SiO2/PP-Pd, nonporous support (entry 5). Our group
previously reported the positive effect of mesoporous structure of support on
6
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cooperativity between Pd complex and tertiary amine.[10] Similar phenomena might be
observed in this Pd complex-silanol pairing. The catalytic reaction completely stopped
by hot filtration of solid catalyst during the reaction, indicating that the reaction occurs
at the Pd species anchored on MS support. This fact also supports the acceleration effect
of silica surface.
The solvent effect is summarized in Table 4. The reaction proceeded well with
toluene (entry 2) among the solvents examined; however, the most effective reaction
condition was without solvent: the highest TON of 199 was achieved under neat
conditions (entry 1). Polar solvents, such as ethanol, 1,4-dioxane, and acetonitrile did
not provide good results (entries 3-7). Moderate results achieved using n-hexane (entry
8) indicated that nonpolar reaction conditions are better for this MS/PP-Pd-catalyzed
allylation. These solvent effects also suggest that hydrogen bonding between silanol and
allylic alcohol is necessary to promote the reaction.
In this PP-Pd-catalyzed reaction system, addition of a catalytic amount of base is
necessary for the activation of the PP-Pd structure: formation of an active Pd(0)
complex by abstraction of Cl and the η-allyl group from the Pd metal center is promoted
by the base.[8d] Table 5 summarizes the effect of base additives on the catalytic
performance. Among the inorganic bases, K2CO3 was found to be most effective (entry
1). Organic amines were also examined as additives. Only DBU showed specific
performance toward the allylation reaction among the other amines (entry 6). Based on
these screening results, K2CO3 or DBU were selected for the following allylation
experiments.
The substrate scope of nucleophiles is shown in Table 6. The reactions were
examined in the presence of 2.0 mmol of nucleophile, 2.5 equivalents of allylic alcohol,
and 6.0 μmol of Pd in the MS(C8)/PP-Pd catalyst under solvent-free conditions. Acyclic,
cyclic, and aromatic ketoesters and diketones reacted with allylic alcohol smoothly to
give the corresponding allylation product in 71-95% yield (entries 1-8). For example,
the reaction of ethyl 2-oxocyclopentanecarboxylate afforded the allylation product in
95% yields with a TON of 340 (entry 1). Nitriles were also found to be good substrates
for the allylation with allylic alcohols (entries 9 and 10).
The scope of allylic alcohols is summarized in Table 7. Reaction with 3-buten-2-ol
afforded three isomers, (E)-linear, (Z)-linear, and branched products, in a 63:11:26 ratio,
with total yield of 72% (entry 2). Crotyl alcohol also acted as an allylating agent to give
same three isomers in a 72:12:16 ratio in 43% total yield (entry 3). The similar isomer
ratios produced by the two starting allylic alcohols indicate the formation of a
π-allylpalladium intermediate.[15] The much higher selectivity for the linear isomer
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suggested an outer sphere allylation mechanism. The majority of E–product indicated
the preferred formation of a syn-configured π-allylpalladium intermediate.[15]
Large-scale allylation using allylic alcohols was examined using MS/PP-Pd catalysts,
as shown in Scheme 4. The reaction using 17.5 mmol of ethyl acetoacetate successfully
proceeded with 6.0 μmol of Pd in MS(C12)/PP-Pd in the presence of 0.5 mmol of DBU:
a product yield of 74% with a TON of 4500 was achieved in 72 h. This TON value is
significantly higher than that previously reported in Pd[2,3]- and Ni[16]-catalyzed
allylation using allylic alochols (e.g. Pd(OAc)2: TON=190;[2c] Pd(0)/AdCOOH:
TON=150;[3b] Pd(0)/phosphoramidite ligand/phosphoric acid: TON=50;[3i]
Ni(0)/dppb:
TON=200[16]).
The
TON
of
the
reaction
of
ethyl
2-oxocyclopentanecarboxylate also reached up to 2040 using the MS(C8)/PP-Pd
catalyst.
Scheme 4. High TON allylation using allylic alcohol
Reaction mechanism: Our group previously reported
a
silica-supported
Pd-bisphosphine complex (SiO2/PP-Pd) as a catalyst for allylation with allyl methyl
carbonate.[8d] In this case, the reaction between η-allylpalladium and a base (K2CO3)
affords a Pd(0) complex, which immediately reacts with allyl methyl carbonate to give a
π-allylpalladium(II) intermediate.[8d] In the case of allylic alcohol, the formation of a
π-allylpalladium is also strongly supported by the observed similar product selectivity
obtained with 3-buten-2-ol and crotyl alcohol (Table 7). In order to investigate in detail
the active Pd complex structure, the solid catalyst was separated during the allylation
reaction (TON~20), and Pd K-edge XAFS measurements were conducted. The
separated sample is denoted as “used” catalyst. Figure 6 shows the XANES spectra of
8
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fresh and used MS(C12)/PP-Pd catalyst with references. Edge positions of both fresh
and used MS(C12)/PP-Pd were close to that of Pd(II)Cl2(PPh3)2 but much higher than
that of Pd(0) foil. This result indicates that the valence of Pd(II) complex was
maintained after the reaction, which is agreement with the π-allylpalladium(II)
formation. Figure 7 represents the EXAFS oscillation and FT of k3-weighted Pd K-edge
EXAFS of fresh and used MS(C12)/PP-Pd. The EXAFS oscillation phase patterns of
the two samples were different, suggesting different Pd local coordination structures.
The FT EXAFS spectra suggest shortened bond distances and lowered coordination
number (N) after the catalytic reaction. The curve-fitting analysis of used
MS(C12)/PP-Pd is shown in Table 2. After the reaction, N decreased from 2.6±0.4 to
2.0±0.3. The decreased value of N noted for Pd-P/Cl is in agreement with the formation
of π-allylpalladium with two phosphine ligands after Cl species removal from the Pd
center.[8d]
After the formation of the Pd(0) species, the next step is the reaction between the
Pd(0) complex and allylic alcohol, forming π-allylpalladium(II). Interaction between
allylic alcohol and surface silanol group was determined by 13C MAS NMR and in situ
13
FT-IR measurements. Preliminary investigation using C NMR analysis of the allylic
alcohol adsorbed on the MS(C12) surface showed sharp and broad signals, assigned to
physisorbed and chemisorbed allylic alcohol, respectively.[10] The board signals shifted
to downfield for the carbon next to the OH group (64 to 66 ppm), and shifted upfield for
the terminal carbon (138 to 137 ppm).[10] These shifts were similar to those exhibited
by allylic alcohol adsorbed on H-ZSM-5 zeolite.[17] FT-IR analysis was also performed
for the adsorbed allylic alcohol on MS(C12)/PP-Pd at room temperature. Figure 8
represents the differential FT-IR spectra of MS(C12)/PP-Pd after adsorption of allylic
alcohol. With the increase in the gas-phase pressure of allylic alcohol, the intensity of a
negative peak at around 3700 cm-1, assigned to SiO-H stretching vibrations, also
increased. This decrease is derived from the adsorption of allylic alcohol on the Si-OH
group of the MS surface. After adsorption of allylic alcohol, several positive bands
appeared at around 3200-3300 cm-1, 2900-3100 cm-1, 1370 cm-1, and 1425 cm-1. The
band at 3200-3300 cm-1 was assigned to O-H stretching vibration of SiOH interacting
with allylic alcohol. The adsorbed allylic alcohol species gave several C-H stretching
vibration bands in 2900-3100 cm-1 and two C-H deformation vibration bands at 1370
and 1425 cm-1, respectively.[18] Theses results from in-situ FT-IR measurement indicate
that the Si-OH group on MS interacts strongly with allylic alcohol (Scheme 5(i)-(ii)). In
order to evaluate the reactivity of the adsorbed allylic alcohol, after evacuation of the
allylic alcohol-adsorbed MS/PP-Pd, ethyl acetoacetate and triethylamine as a
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nucleophile and base, respectively, were introduced to the IR sample, and then the
o
sample was heated to 80 C to promote the reaction. The solid sample was collected
from the IR cell and washed with toluene to recover the products. GC-MS analysis of
the extracted solvent revealed the formation of the allylation product. Therefore, allylic
alcohol activated with SiOH groups is available as an active allylating reagent for the
Pd-catalyzed allylation reaction in the presence of a base additive (Scheme 5(ii)-(iv)).
Additionally, this in-situ FT-IR analysis implies that the simple interaction between one
allylic alcohol molecule and Si-OH group was enough for the promotion of the reaction
step shown in Scheme 5(iii)-(iv), because gas phase adsorption of the isolated allylic
alcohol occurred onto the MS surface in IR cell.
Scheme 5. Adsorption of allylic alcohol onto MS surface and proposed catalytic
pathway through the adsorbed allylic alcohol.
Conclusion
A mesoporous silica-supported Pd bisphosphine complex (MS/PP-Pd) was found to be
an excellent catalyst for the allylation of nucleophiles using allylic alcohols. The
structure of the prepared supported catalyst was characterized by solid-state NMR, SEM,
and Pd K-edge XAFS. The catalytic activity of the supported catalyst increased on
increasing the amount of surface silanol: as a result, the MS/PP-Pd showed a 9 times
higher activity than that of its homogeneous precursor (PP-Pd). Various nucleophiles,
10
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including ketoesters, diketones, and nitriles, could be used as good substrates. A highest
TON of 4500 with simple allylic alcohol was achieved in this MS/PP-Pd-catalyzed
reaction system, which is significantly higher than those of reported for Pd catalysts for
allylation of carbonucleophiles using allylic alcohol. The reaction mechanism, including
activation of allylic alcohol on the silanol group, was evaluated by 13C NMR and in situ
FT-IR measurements. The proposed concerted activation procedure, involving
assistance of the surface silanol for the metal-catalyzed reaction, might be a novel
technique for efficient organic synthesis.
Acknowledgements
XAFS measurements were conducted under the approval of the Photon Factory
Advisory Committee (Proposal no. 2016G025 and 2018G042). This study was
supported by Cooperative Research Program of the Institute for Catalysis, Hokkaido
University (Grant #17A1002) and JSPS Grant-in-Aid for Scientific Research on
Innovative Areas (Grant no. 18H04242 and 26105003). We would like to thank Dr.
Yohei Uemura (Institute for Molecular Science) for his support with XAFS analysis.
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D. Voort and G. B. Marin, ChemCatChem, 2014, 6, 255; (f) K. C. Kim, E. G.
Moschetta, C. W. Jones and S. S. Jang, J. Am. Chem. Soc., 2016, 138, 7664.
10 For preliminary results on silica-supported Pd complex for allylation with allylic
alcohol, see: K. Motokura, M. Ikeda, M. Nambo, W.-J. Chun, K. Nakajima and S.
Tanaka, ChemCatChem, 2017, 9, 2924.
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13 R. S. Corrêa, A. E. Graminha, J. Ellena, A. A. Batista, Acta Cryst., 2011, C67, m304.
14 Mixed use of dppp-Pd and MS(C12) did not enhance catalytic performance (yield:
15%). Immobilization of catalytic functionalities on surface (active-site accumulation)
may be necessary for the cooperative catalysis between Pd complex and silanol.
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Lang, T. M. Locascio and J. A. Tunge, Org. Lett., 2014, 16, 4308.
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Eur. J. Org. Chem. 2016, 1194.
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Zibrowius, Catal. Lett., 1995, 31, 377.
13
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ChemCatChem
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
Pore Diameter / nm
Figure 1. BJH pore size distribution of MS(C8) (1.6 nm, red), MS(C12) (2.3 nm, green),
and MS(C12,cal) (2.3 nm, blue).
14
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10.1002/cctc.201801097
ChemCatChem
O
Si
A
1 μm
Pd
P
Cl
O
Si
B
1 μm
Pd
P
Cl
Figure 2. SEM image of (A) MS(C8)/PP-Pd and (B) MS(C12)/PP-Pd and their line
analysis results for elements O, Si, P, Cl, and Pd elements.
15
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10.1002/cctc.201801097
ChemCatChem
13C
31P
Ph
OEt
OEt
f
b
e
c
d
a
(B)
(B)
OEt
Ph
OEt
*
f
*
c
b
e
d
(A)
(A)
60
40
20
0
-20
-40
140
120
100
80
60
40
20
0
31P Chemical Shift / ppm
13C Chemical Shift / ppm
13
31
Figure 3. C and P NMR spectra of (A) MS(C12)/PP-Pd and (B) PP-Pd precursor.
13C CP/MAS and 31P MAS NMR spectra are shown for (A).
16
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10.1002/cctc.201801097
ChemCatChem
5
4
3
2
1
0
40
30
20
10
0
×0.2
×0.5
(E)
(D)
(E)
(D)
(C)
(B)
(A)
(C)
(B)
(A)
24.30 24.32 24.34 24.36 24.38 24.40
0
1
2
3
4
5
6
Photon Energy / 10 keV
r / Å
Figure 4. Pd K-edge XANES (left) spectra and Fourier transform of k3-weighted Pd
K-edge EXAFS spectra (right) of (A) MS(C8)/PP-Pd, (B) MS(C12)/PP-Pd, (C)
PdCl2(PPh3)2, (D) PdO, and (E) Pd0 foil. The k range for FT was k=2.8-12 Å-1.
17
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10.1002/cctc.201801097
ChemCatChem
4
2
0
-2
-4
0
2
4
6
8
10
12
14
k / Å-1
Figure 5. k3-weighted EXAFS spectra of MS(C8)/PP-Pd (red) and MS(C12)/PP-Pd
(black).
18
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10.1002/cctc.201801097
ChemCatChem
Photon Energy / keV
Figure 6. XANES spectra for MS(C12)/PP-Pd (black), MS(C12)/PP-Pd-used (red), Pd
foil (dotted line), PdO (blue), and PdCl2(PPh3)2 (green).
19
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10.1002/cctc.201801097
ChemCatChem
10
8
4
2
6
0
4
2
-2
-4
0
0
2
4
6
8
10
12
14
0
1
2
3
4
5
6
k / Å-1
r / Å
Figure 7. EXAFS spectra (left) and FT of k3-weighted Pd K-edge EXAFS spectra
(right) of MS(C12)/PP-Pd (black) and MS(C12)/PP-Pd-used (red)
20
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10.1002/cctc.201801097
ChemCatChem
ν(O–H)
ν(C–H)
0.02
0.05
ν(C–H)
4000
3600
3200
2800
1600 1550 1500 1450 1400 1350 1300
wavenumber / cm-1
wavenumber / cm-1
Figure 8. Differential FT-IR spectra for allylic alcohol adsorbed MS(C12)/PP-Pd at
o
room temperature. Prior to allylic alcohol adsorption, the sample was heated at 80 C
for 1 h under vacuum. Gas phase allylic alcohol pressure: (red) 0.48, (yellow) 0.64,
(green) 0.88, (blue) 1.1, and (purple) 1.3 kPa.
21
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10.1002/cctc.201801097
ChemCatChem
Table 1. Physicochemical properties of synthesized MS supports
MS Support
Surface area
[m2g-1] a
1865
Pore size
[nm] b
1.6
Pore vol.
[ml g-1] b
1.5
Si-OH
[mmol g-1] c
MS(C8)
5.9
7.4
6.3
MS(C12)
1175
2.3
1.0
MS(C12,cal)
Nonporous SiO2
(Aerosil300)
1215
2.3
0.98
300±30
-
-
6.7
a Determined by N2 adsorption-desorption isotherm measurement.
b Determined by BJH method.
c Determined by 29Si dd/MAS NMR measurement.
22
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10.1002/cctc.201801097
ChemCatChem
Table 2. Curve-fitting analysis of EXAFS spectra for MS(Cn)/PP-Pd catalysts a
Sample
Shell
N b
r c
∆σ2 d
[Å2×10–3] [eV]
∆E e
Rf f
[Å]
[%]
2.6
±0.4
2.6
±0.4
2.0
±0.3
3.0
(fix)
2
2.27
±0.01
2.27
±0.01
2.21
±0.01
2.29
±0.01
2.34 j
2.30 j
2.80
–11.2
±2.1
–10.8
±2.1
–15.8
±2.3
–5.9
MS(C8)/PP-Pd
MS(C12)/PP-Pd
Pd-P/Cl
Pd-P/Cl
Pd-P/Cl
Pd-P/Cl
1.9
±0.29
2.80
1.9
2.3
1.3
±0.29
2.03
MS(C12)/PP-Pd
(used)
±0.32
2.64
PP-Pd
(THF solution) g
±0.03
±1.9
(Pd-P)
i
Pd(II)Cl2(PPh3)2
(Pd-Cl)
2
a Fourier transform and Fourier-filtering regions were limited, where ∆k = 2.8 ~ 12 Å-1.
and ∆r = 1.1 ~ 2.4 Å, respectively. Curve-fitting analysis was performed for the Pd-P/Cl
shell. b Coordination number. c Bond distance between absorber and backscatter atoms. d
e
The Debye-Waller factor (DW). The inner potential correction accounts for the
f
difference in the inner potential between the sample and reference. The goodness of
g
i
j
curve fit. Homogeneous THF solution of the PP-Pd complex. Data from ref.[12]
Average value was reported.
23
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10.1002/cctc.201801097
ChemCatChem
Table 3. Effect of support on allylation of ketoester using allylic alcohola
Entry Catalyst
Si-OH of Conversi Yield
TON
support
[mmol g-1]
7.4
on [%]
(mono/di)
[%]
1
2
3
4
MS(C12)/PP-Pd
MS(C8)/PP-Pd
MS(C12,cal)/PP-Pd
MS(C12)/PP-Pd
treated by Si(OMe)3Me
SiO2/PP-Pd
58
42
43
20
47 / 3
41 / 1
38 / 1
19 / 0
87
72
68
31
5.9
6.3
N.D.
5
6
6.7
-
18
6
14 / 0
6 / 0
24
10
PP-Pd
aReaction conditions: Pd catalyst (6.0 μmol), ethyl acetoacetate (1.0 mmol), allylic
o
alcohol (2.5 mmol), K2CO3 (0.50 mmol), toluene (4.0 mL), 70 C, 1 h. N.D.=not
determined.
24
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10.1002/cctc.201801097
ChemCatChem
Table 4. Effect of solvent on catalytic activity for allylation reaction using allylic
alcohol a
Entry
Solvent
Yield (mono/di) / %
TON
199
72
1
2
3
4
5
6
7
8
Neat
53 / 29
41 / 1
8 / 0
Toluene
Ethanol (65 oC)
THF (55 oC)
1,4-dioxane
Acetonitrile
CPME
14
9 / 0
15
13 / 0
13 / 1
6 / 0
22
24
10
n-Hexane
23 / 1
44
a Reaction conditions: MS(C8)/PP-Pd (6.0 μmol), ethyl acetoacetate (1.0 mmol), allylic
alcohol (2.5 mmol), K2CO3 (0.50 mmol), solvent (4.0 mL), 70 oC, 1 h.
25
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10.1002/cctc.201801097
ChemCatChem
Table 5. Effect of base additives on catalytic activity for allylation reaction using allylic
alcohol a
Entry
Base
Time
Yield (mono/di) / %
53 / 29
19 / 15
45 / 2
TON
199
80
89
85
4
1
K2CO3
1
1
1
1
6
2
4
4
6
4
1
2
KOH
3
Na2CO3
tBuOK
4
30 / 3
5
Ammonia
DBU
3 / 0
6
24 / 15
12 / 0
114
28
3
7
Tributylamine
Aniline
8
1 / 0
9
4-dimethylaminopyridine
Pyrrolidine
None
22 / 1
39
14
-
10
11
7 / 0
trace
a Reaction conditions: MS(C8)/PP-Pd (6.0 μmol), ethyl acetoacetate (1.0 mmol), allylic
alcohol (2.5 mmol), base (0.50 mmol), neat, 70 oC.
26
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10.1002/cctc.201801097
ChemCatChem
Table 6. Scope of nucleophiles for MS/PP-Pd-catalyzed allylation reaction a
Entry
Nu-H
Yield (mono / di) [%]
95
TON [Pd-1]
340
1
2 b
87
730
250
3
71 (64 / 7)
4
5
76 (8 / 68)
94
470
310
6
7
79 (48 / 31)
79
260
280
8 c
9 d
77 (77 / 0)
78
160
31
10 e
94
38
a
Reaction conditions: MS(C8)/PP-Pd (6.0 μmol), nucleophile (2.0 mmol), allylic
alcohol (5.0 mmol), K2CO3 (0.50 mmol), neat, 70 oC, 17 h.
b MS(C8)/PP-Pd (6.0 μmol), nucleophile (5.1 mmol), allylic alcohol (12 mmol), K2CO3
(0.50 mmol), neat, 70 oC, 24 h.
c MS(C8)/PP-Pd (6.0 μmol), nucleophile (1.3 mmol), allylic alcohol (5.2 mmol), K2CO3
(0.50 mmol), neat, 70 oC, 17 h.
d
MS(C12)/PP-Pd (12.5 μmol), nucleophile (0.50 mmol), allylic alcohol (1.3 mmol),
K2CO3 (0.25 mmol), DMSO (2.0 mL), 70 oC, 20 h.
e
MS(C12)/PP-Pd (12.5 μmol), nucleophile (0.50 mmol), allylic alcohol (1.3 mmol),
K2CO3 (0.25 mmol), toluene (2.0 mL), 80 oC, 18 h.
27
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10.1002/cctc.201801097
ChemCatChem
Table 7. Scope of allylic alcohols for MS/PP-Pd-catalyzed Allylation Reaction a
Total yield
[%] b
Entry Allylic alcohol
1
Product
Isomer ratio TON [Pd-1]
95
-
340
239
2
72
63
11
26
3c
43
72
136
12
16
4
77
-
282
a
Reaction conditions: MS(C8)/PP-Pd (6.0 μmol), ketoester (2.0 mmol), allylic alcohol
(5.0 mmol), K2CO3 (0.50 mmol), neat, 70 oC, 17 h.
b Yield was determined by 1H NMR and GC using internal standard.
c 80 oC.
28
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