Transition-Metal-Catalyzed Direct Arylation of Caged Silsesquioxanes: Substrate Scope and Mechanistic Study

Article abstract of DOI:10.1002/ejic.201900126

Caged silsesquioxane (polyhedral oligomeric silsesquioxane: POSS) is an important class of organic-inorganic hybrid molecules. The electronic properties of POSS have gradually attracted attention from experimental and computational perspectives, while POS

Full text of DOI:10.1002/ejic.201900126

A Journal of
Accepted Article
Title: Transition Metal-Catalyzed Direct Arylation of Caged
Silsesquioxanes: Substrate Scope and Mechanistic Study
Authors: Hiroaki Imoto, Satoshi Wada, Takashi Yumura, and Kensuke
Naka
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10.1002/ejic.201900126
European Journal of Inorganic Chemistry
FULL PAPER
Transition Metal-Catalyzed Direct Arylation of Caged
Silsesquioxanes: Substrate Scope and Mechanistic Study
Hiroaki Imoto,[a] Satoshi Wada,[a] Takashi Yumura,[b] and Kensuke Naka*[a]
Abstract:
Caged
silsesquioxane
(polyhedral
oligomeric
dimensional functional molecules have played important roles in
optoelectronic materials due to their unique morphologies and
intermolecular communications: fullerene, carbon nanotube,
carborane, etc. In the case of POSS, there are a few
experimental and computational studies on the electronic
properties as well. Electron accepting behavior of POSS was
previously observed in the studies on optical properties of
octaaryl-substituted POSSs.[7] Kieffer’s group conducted
calculations to show that the LUMO is located at the POSS core,
and can interact to the aryl groups directly attached to the Si
atoms.[8] Laine’s group developed synthetic methods to
construct octaaryl-substituted POSS derivatives, and the
electron acceptance of the POSS core was shown.[9] In spite of
these pioneering works, there are insufficient experimental
studies on structure-property relationship of aryl-substituted
POSSs. This is because systematic studies are still difficult due
to the lack of synthetic routes towards the aryl-substituted
POSSs.
silsesquioxane: POSS) is an important class of organic-inorganic
hybrid molecules. The electronic properties of POSS have gradually
attracted attention from experimental and computational
perspectives, while POSS is generally utilized for reinforcement of
polymer materials. Practical synthetic routes to access to aryl-
substituted POSS are effective tools for the systematic studies.
Recently, we reported Rh-catalyzed direct arylation of heptaisobutyl-
POSS with electron-rich aryl iodides. Herein substrates for the Rh-
catalyzed direct arylation were widely examined: electron-deficient,
sterically-hindered, and heteroatom-containing aryl halides, and
heptaphenyl-POSS. Pd-catalyzed direct arylation of POSS was
developed as well. Notably, thiophene was introduced by the Pd-
catalyst, whereas the Rh-system did not work for the substrate. In
addition, the reaction mechanism of the Rh-catalyzed reaction was
elucidated by density functional theory calculations.
Introduction
Caged silsesquioxane, denoted as POSS (polyhedral
oligomeric silsesquioxane), is one of the representative building
blocks for inorganic-organic hybrid materials.[1] The siloxane
core of POSS is covered with organic substituents, and hence it
has advantages derived from organic and inorganic materials;
good designability and solubility due to the organic substituents
and excellent materials properties due to the inorganic
components. These characteristic natures are beneficial for
reinforcement of polymer materials, and POSS has been
introduced to polymer matrices as nano-fillers[2] or cross-linking
agents.[3] In addition, polymers containing POSS in the end
groups,[4] side chains,[5] or main chains[6] were synthesized.
Incorporation of POSS gives high thermal stability to organic
polymers without diminishing intrinsic transparency of the
polymers. In these traditional researches, electronic properties
of POSS tend to be ignored. On the other hand, three-
[a]
Dr. H. Imoto, S. Wada, Prof. Dr. K. Naka*
Faculty of Molecular Chemistry and Engineering, Graduate School
of Science and Technology
Kyoto Institute of Technology
Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
E-mail: kenaka@kit.ac.jp
Homepage: http://www.cis.kit.ac.jp/~kenaka/index_eng.html
Prof. Dr. T. Yumura
[b]
Faculty of Material Science and Technology, Graduate School of
Science and Technology
Kyoto Institute of Technology
Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
Scheme 1. Syntheses of aryl-POSSs: (a) condensation, (b) cross coupling
reactions, (c) Heck or metathesis reactions, and (d) direct arylation (this work).
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.201900126
European Journal of Inorganic Chemistry
FULL PAPER
Conventionally,
aryl-substituted
POSSs
have
been
Table 1. Scope of substrates for Rh-catalyzed direct arylation.a
synthesized via condensation of an incompletely-condensed
POSS with a silane-coupling agent having an aryl group
(Scheme 1a), though silane-coupling agents are typically
unstable under ambient condition due to theirs moisture-
sensitivity. Cross coupling or metathesis reactions (Schemes 1b
and 1c) are effective for this end, but phenylene or vinylene
linkers should be inserted between POSS and the aryl
moieties.[9,10] Recently, we have developed Rh-catalyzed direct
arylation of monohydro-POSS by using aryl halides (Scheme
1d).[11] This reaction is a promising tool for the systematic
investigation of the aryl-substituted POSSs. In that previous
paper, only limited substrates are examined for proof of concept;
the substituents of the POSS core are isobutyl group, and the
aryl halides possess electron-donating groups.
Herein, we have examined Pd catalysts for the direct arylation
of POSSs besides the Rh catalyst. Furthermore, the scope of
the substrates has been widened; heptaisobutyl- and
heptaphenyl-POSSs were reacted with electron-donating,
electron-withdrawing, sterically hindered, or heteroatom-
containing aryl halides. In addition, the reaction mechanism of
the Rh-catalyzed direct arylation was computationally studied.
Yieldb
Run
1c
POSS
Ar−X
Product
4a
[%]
1
1
1
87 (78)
2c
4b
87 (62)
81 (74)
78 (71)
76 (43)
3c
4c
4c
5
1
1
1
4d
4e
4f
Results and Discussion
6
81 (79)
Rh-catalyzed direct arylation
7c
8
1
1
4g
4h
n.d.
Heptaisobutyl- and heptaphenyl-POSSs (1 and 2,
respectively) were prepared as the reaction substrates. In the
previous paper, we have optimized the reaction condition of the
Rh-catalyzed direct arylation of 1 with aryl halides.[11] We firstly
focused on scope of the substrates for the Rh-catalyzed direct
arylation. POSS derivatives 1 and 2 were reacted with aryl
halides including electron-rich, electron-deficient, sterically
hindered, heteroatom-containing aryl halides. Yields of aryl-
POSSs 4a-k and 5a-f under the optimized reaction condition in
hand are summarized in Table 1. The NMR yields were
81 (79)
9
1
4i
69 (53)
10
11
1
1
4j
n.d.
4k
60 (52)
1
evaluated by the H-NMR spectra, and isolation was carried out
12
13
14
15
16
17
2
2
2
2
2
2
3a
3b
3c
3d
3e
3f
5a
5b
5c
5d
5e
5f
75 (20)
(11)
with column chromatography over silica gel or high performance
liquid chromatography (HPLC).
Yields of the reaction with heptaisobutyl-POSS 1 (run 1-11)
were moderate except for run 7 and 10. The present reaction
can be applied to electron-rich (3a,b,d), electron-deficient (3e,f),
sterically hindered (3d,i), reactive (3h) and heteroatom-
containing (3k) aryl halides. In run 7 and 10, no reaction
proceeded with 3g and 3j probably because the nitrogen and
sulfur atoms worked as a catalytic poison through coordination
to the metal center.
In the case of heptaphenyl-POSS 2 (run 12-17), the NMR
yields were hard to be evaluated because the crude products
contained complicating mixtures of oligomeric silsesquioxanes.
As a result, the isolated yields were significantly lowered from
those of 1. In particular, 5c and 5d failed to be isolated due to
large amounts of oligomeric products. These results suggests
that heptapheyl-POSS is sensitive to the present reaction
condition; in general, the substituents affect hydrolysis behavior
of POSS.[12] In our previous paper, even heptaisobutyl-POSS
n.d.
n.d.
(28)
(32)
a[POSS] = 0.15 M, [aryl halide] = 0.225 M, [Rh] = 7.5 mM, [iPr2EtN]
= 1.15 M. bNMR yield (bare) and isolated yield (in a parenthesis).
cCited from reference 11.
were partially decomposed by using strongly nucleophilic
amines as well.[11]
Then, we measured the UV-vis absorption spectrum of
octaphenyl-POSS 5c to examine the electronic effect of the
POSS core, though we failed to synthesize 5c by the present
reaction (5c is commercially available). However, the three
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10.1002/ejic.201900126
European Journal of Inorganic Chemistry
FULL PAPER
dimensional unoccupied orbital of the POSS did not contributed
to the LUMO of 5c as we have already reported the same
phenomenon in the case of 4c. For the detail, see supporting
information (Figure S31).
Table 3. Scope of substrates for Pd-catalyzed direct arylation.
Pd-catalyzed direct arylation
Masuda and coworkers reported Pd(0)-catalyzed silylation of
aryl halides with triethoxysilane.[13] Inspired by this closely
related report, plladium was chosen in order to expand the
scope of applicable metals for the direct arylation. The reaction
condition of 1 with p-iodoanisole was firstly optimized (Table 2).
In run 1, P(o-tol)3 iPr2EtN, and DMF were selected as ligand,
base, and solvent, respectively in reference to the Masuda’s
paper[13] and our previous paper on the Rh-catalyzed direct
arylation.[11] DMF, NMP, toluene, and THF were examined in run
1-4, and DMF and NMP were suitable for the reaction (78%).
Reaction temperature was changed from 50 °C to 120 °C (run 1,
5, and 6), and the reaction at 80 °C offered the highest yield.
Amines were investigated in run 6 and 7. Et3N (62%, run 7) and
iPr2HN (65%, run 8) gave lower yields than iPr2EtN (78%, run 1).
Finally we investigated phosphine ligands. DeShong and
coworkers employed biphenyl-di-tert-butylphosphine (JohnPhos)
for improvement of the Pd-catalyzed silylation.[14] Here, we
examined Cy JohnPhos (run 9) and PPh3 (run 10), but the yields
were lower than that of run 1. Hence, we have concluded that
the reaction condition of run 1 is the best for the present reaction.
Under the reaction condition optimized above, several kinds of
substrates were examined (Table 3). The yields of 4a-e of the
Yield
Run
1
Ar−X
Product
4a
[%]
78
2
4b
52
41
3
4c
4
5
6
4d
4e
4j
n.d.
18
73 (61)
aReaction condition of run 1 in Table 2. bNMR yield (bare) and
isolated yield (in a parenthesis).
3d did not proceed. On the other hand, it is worth noting that the
thienyl group was introduced in moderate yield by utilizing the
Pd catalyst (run 6), whereas the Rh catalyst did not work for 3j
(Run 11 in Table 1). This result corresponds to the case of
arylation of triethoxysilane,[15] though the reason remains to be
clear. It has been demonstrated that adequate selection from the
present Rh and Pd catalysts can expand the scope of applicable
substrates.
Table 2. Optimization of reaction condition for Pd-catalyzed direct
arylation.a
Reaction mechanism
Xu and coworkers reported mechanism of the Pd-catalyzed
silylation of aryl iodides with hydrosilanes by density functional
theory (DFT) calculations,[16] whereas that of the Rh-catalyzed
reaction is still unclear. In addition, mechanistic studies on
catalytic reactions for POSS substrates have never been
performed despite their recent progress. Therefore, we decided
to conduct DFT calculations for understanding of the mechanism
of the Rh-catalyzed direct arylation. A relevant previous study of
Murata group indicates that a RhI complex is formed prior to
starting the direct arylation.[13] Following the previous paper, a
plausible reaction mechanism is given in Scheme 2. A Si−H
bond in a POSS is clearly indicated by H−Si(POSS). The
reaction is initiated by insertion of the RhI complex into a
Temp.
[°C]
Yieldb
[%]
Run
Ligand
Amine
Solvent
1
2
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
P(o-tol)3
Cy JohnPhos
PPh3
iPr2EtN
iPr2EtN
iPr2EtN
iPr2EtN
iPr2EtN
iPr2EtN
Et3N
DMF
NMP
toluene
THF
80
80
78
78
63
66
67
66
62
65
64
50
3
reflux
80
4
5
DMF
DMF
DMF
DMF
DMF
DMF
50
6
120
80
7
8
iPr2HN
iPr2EtN
iPr2EtN
80
9
80
H−Si(POSS) bond to form
a
silyl hydride species,
10
80
(H−RhI−Si(POSS)) by the H(POSS) atom migration to the Rh
atom (Path A). From the resultant silyl hydride species, H and X
atoms are removed by triethylamine NEt3 to form a silyl rhodium
complex (Rh−Si(POSS)) together with I·HNEt3 (Path B). After
that event, the resultant Rh−Si(POSS) complex reacts with an
a[POSS] = 0.15 M, [p-iodoanisole] = 0.225 M, [Pd] = 7.5 mM, [ligand]
= 30 mM, [amine] = 1.15 M. bNMR yield.
Pd-catalyzed reaction were lower than those of the Rh-catalyzed
one. In particular, the reaction with sterically-hindered substrate
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10.1002/ejic.201900126
European Journal of Inorganic Chemistry
FULL PAPER
aryl halide (ArI) leads to an arylrhodium intermediate
(Ar−RhI−Si(POSS)) via a transition state for I-atom migration
from ArI to the Rh atom (Path C). In the arylrhodium
intermediate, a C atom of the Ar group is bound to the Si(POSS)
atom to form a Si−C bond. The Si−C bond formation results in
an Ar−POSS species bound by RhI. After that, the product
complex dissociates into an Ar−Si(POSS) species and RhI.
The resultant RhI complex serves a species reacting with POSS,
and thus the reaction continuously proceeds in the same
pathway along Scheme 2.
hindered, heteroatom-containing aryl halides were applicable.
The Rh-catalyzed direct arylation was computationally studied,
and the energetically preferable reaction mechanisms, obtained
from the DFT calculations, can support the above experimental
findings. Though the effect of the three dimensional unoccupied
molecular orbital located in the POSS core has not been
observed yet, further investigation will open a way to creation of
POSS-based electronic materials. We are now trying to optimize
the substituents of POSS, and to introduce various conjugated
systems. These results will be reported in future publications.
Experimental Section
1. Materials
Bis(1,5-cyclooctadiene)rhodium(I)
tetrafluoroborate
([Rh(cod)(MeCN)2]BF4) and (2-biphenyl)dicyclohexylphosphine (Cy
JohnPhos) were purchased from Sigma Aldrich. Toluene, hexane, ethyl
acetate
(EtOAc),
methanol
(MeOH),
triethylamine
(Et3N),
diisopropylethylamine (iPr2EtN), iodobenzene, and triphenylphosphine
(PPh3) were purchased from Nacalai Tesque, Inc. Tetrahydrofuran (THF,
super dehydrated grade), N,N-dimethylformamide (DMF, super
dehydrated grade), 1-methyl-2-pyrrolidone (NMP, super dehydrated
grade), and toluene (super dehydrated grade) were purchased from
Wako Pure Chemical Industry, Ltd. Trichlorosilane, 4-iodotoluene, 4-
iodoanisole, 2-iodoanisole, 4-iodoacetophenone, 3-iodobenzotrifluoride,
4-iodobenzonitrile,
4-diiodobenzene,
4-bromoiodobenzene,
4-
hydoroxyiodobenzene, 4-iodophenol, 2-iodobiphenyl, 2-iosoyhiophene,
3-bromopylidine, tris(dibanzylideneacetone)dipalladium(0) (Pd2(dba)3)
and tris(2-metylphenyl)phosphine (P(o-tol)3) were purchased from Tokyo
Chemical Industry Co., Ltd. Heptaisobutyl-trisilanol-POSS and
heptaphenyl-trisilanol-POSS were purchased from Hybrid Plastics.
Heptaisobutyl-POSS (1)[18] and heptaphenyl-POSS (2)[19] were prepared
according to the literature procedures.
Scheme 2. Plausible mechanism of Rh-catalyzed direct arylation of POSS.
Following reaction mechanisms in Scheme 2, we obtained
local minima and transition states. Detailed discussion on the
energetics of the Rh-catalyzed direct arylation of POSS is
described in Supporting Information (SI), including Figures S33-
S35. Briefly, the DFT calculations found that all local minima and
transition states are energetically stable relative to the initial
state (POSS, RhI, ArI, and NEt3). The results indicated that the
Rh-catalyzed direct arylation of POSS easily proceeds in an
exothermic manner. Importantly, the rate-determining step of the
overall reaction is removal of I·HNEt3 from the Rh center in Path
B (Ea = 23.2 kcal/mol), while the reductive elimination in Path C
needs similar activation energy (Ea = 21.3 kcal/mol). The
electron donating or accepting groups on the aryl halides
modulate the activation energy in the reductive elimination;
electron withdrawing groups slightly raise the activation
energy,[17] resulting in slightly lower yields in the experimental
study summarized in Table 1.
2. Instruments
1H- (400 MHz), 13C- (100 MHz), and 29Si- (80 MHz) NMR spectra were
recorded on
a Bruker DPX-400 spectrometer. The samples were
analyzed in CDCl3 using Me4Si as an internal standard. The following
abbreviations are used; s: singlet, d: doublet, dd: doubledoublet, dt:
doublet of triplets, t: triplet, qd: quartet of doublets, m: multiplet.
Preparative high-performance liquid chromatography (HPLC) for
purification was performed on LC-6AD (SHIMADZU) with a Shodex KF-
2001 column (SHOWADENKO, Tokyo, Japan) using CHCl3 as an eluent.
3. Synthetic procedure and characterization data
General Procedure A: A DMF solution (2 mL) of 1 (245 mg, 0.3 mmol),
aryl halide (0.45 mmol), [Rh(cod)(MeCN)2]BF4 (6 mg, 0.015 mmol), and
iPr2EtN (2.3 mmol) was stirred for 1.5 h under nitrogen atmosphere. After
the reaction, toluene (75 mL) was added to the reaction mixture, and the
organic layer was washed with water. The volatiles were removed under
reduced pressure, and the residue was subjected to short column
chromatography over silica gel (eluent: hexane/EtOAc = 9/1). The
product including small amounts of impurities was recrystallized from
CH2Cl2, EtOAc, and MeOH to obtain colorless crystals.
Conclusions
In summary, we have investigated scope of substrates for our
previously reported Rh-catalyzed direct arylation of POSS, and
newly developed Pd-catalyzed one. Wide variety of aryl groups
can be introduced to the POSS backbones with isobutyl or
phenyl groups; electron-rich, electron-deficient, sterically
4a-d: The characterization data are shown in the previous paper.[11]
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10.1002/ejic.201900126
European Journal of Inorganic Chemistry
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1
4e: H-NMR (CDCl3, 400 MHz) δ 7.95 (d, 2H, J = 8.0 Hz), 7.77 (d, 2H, J
29Si-NMR (CDCl3, 80 MHz) δ -78.1 -78.2 -79.2 ppm. HR-FAB-MS (m/z):
= 8.4 Hz), 2.62 (s, 3H), 1.93-1.81 (m, 7H), 0.99-0.94 (m, 42H), 0.67-0.60
(m, 14H) ppm; 13C-NMR (CDCl3, 100 MHz) δ 198.4 138.3 137.8 127.2
26.7 25.7 25.7 23.9 23.8 22.5 22.4 ppm; 29Si-NMR (CDCl3, 80 MHz) δ -
67.0 -67.7 -81.4 ppm. HR-FAB-MS (m/z): calcd for C36H70O13Si8 [M+H]+,
935.3049; obs, 935.3041.
calcd for C50H42O13Si8 [M+H]+, 1078.0858; obs, 1075.0853.
5f: 1H-NMR (CDCl3, 400 MHz) δ 8.06 (s, 1H), 7.92 (d, 1H, J = 7.6 Hz),
7.77-7.68 (m, 14H), 7.68 (d, 1H), 7.45 (d, 1H, J = 7.6 Hz), 7.46-7.43 (m,
7H), 7.38-7.35 (m, 14H) ppm; 13C-NMR (CDCl3, 100 MHz) δ 137.5 134.3
134.2 131.6 131.0 130.9 130.4 130.1 130.0 129.9 128.4 128.0 128.0
127.5 127.5 125.5 122.8 ppm; 29Si-NMR (CDCl3, 80 MHz) δ -78.0 -78.2
ppm. HR-FAB-MS (m/z): calcd for C49H39F3O12Si8 [M+H]+, 1101.0626;
obs, 1101.0637.
4f: 1H-NMR (CDCl3, 400 MHz) δ 7.93 (s, 1H), 7.84 (d, 1H, J = 7.6 Hz),
7.68 (d, 1H, J = 8.0 Hz), 7.48 (t, 1H, J = 7.8 Hz), 1.94-1.82 (m, 7H), 0.99-
0.94 (m, 42H), 0.68-0.60(m, 14H) ppm; 13C-NMR (CDCl3, 100 MHz) δ
137.2 133.1 130.8 130.8 127.9 126.9 126.9 25.7 25.6 23.9 22.5 22.4
ppm; 29Si-NMR (CDCl3, 80 MHz) δ -66.9 -67.7 -67.8 -81.5 ppm. HR-FAB-
MS (m/z): calcd for C35H67F3O12Si8 [M+H]+, 961.2817; obs, 961.2820.
General Procedure C: A DMF solution (2 mL) of 1 (245 mg, 0.3 mmol),
aryl halide (0.45 mmol), Pd2(dba)3 (14 mg, 0.015 mmol), P(o-tol)3 (18 mg,
0.06 mmol) and iPr2EtN (2.3 mmol) was stirred for 1.5 h under nitrogen
atmosphere. After the reaction, toluene (75 mL) was added to the
reaction mixture, and the organic layer was washed with water. The
volatiles were removed under reduced pressure, and the residue was
subjected to flash column chromatography over silica gel (eluent:
hexane/EtOAc = 9/1). The product was purified by preparative HPLC
using CHCl3 as an eluent.
4h: 1H-NMR (CDCl3, 400 MHz) δ 7.51 (s, 4H), 1.91-1.82 (m, 7H), 0.98-
0.93 (m, 42H), 0.65-0.62 (m, 14H) ppm; 13C-NMR (CDCl3, 100 MHz)
δ135.6 130.9 130.7 125.2 25.7 23.9 22.5 22.4 ppm; 29Si-NMR (CDCl3, 80
MHz)
δ -67.1 -67.8 -67.9 -80.6 ppm. nano-ESI (m/z): calcd for
C34H67BrO12Si8Na [M+Na]+: 993.2; obs, 993.1.
4i: 1H-NMR (CDCl3, 400 MHz) δ 7.89 (d, 1H, J = 7.2 Hz), 7.49-7.24 (m,
8H), 1.86-1.74 (m, 7H), 0.96-0.90 (m, 42H), 0.63-0.43 (m, 14H) ppm; 13C-
NMR (CDCl3, 100 MHz) δ 148.9 143.8 136.1 130.4 130.3 129.9 129.2
127.8 127.0 126.0 25.8 25.8 25.7 23.9 23.9 23.8 22.6 22.6 22.4 22.3
ppm; 29Si-NMR (CDCl3, 80 MHz) δ -66.8 -67.7 -67.9 -67.9 -87.1 ppm.
HR-FAB-MS (m/z): calcd for C40H72O12Si8 [M+H]+, 969.3257; obs,
969.3253.
4j: 1H-NMR (CDCl3, 400 MHz) δ 7.62 (d, 1H, J = 4.8 Hz), 7.64 (d, 1H, J =
2.4 Hz), 7.18 (dd, 1H, J = 4.8 and 3.6 Hz), 1.91-1.84 (m, 7H), 0.97-0.94
(m, 42H), 0.66-0.60 (m, 14H) ppm; 13C-NMR (CDCl3, 100 MHz) δ 136.5
131.5 130.3 127.8 25.7 25.7 23.9 22.5 22.4 ppm; 29Si-NMR (CDCl3, 80
MHz) δ -67.2 -67.5 -67.8 -83.7 ppm. HR-FAB-MS (m/z): calcd for
C32H66O12SSi8 [M+H]+, 899.2508; obs, 899.2507.
4k: 1H-NMR (CDCl3, 400 MHz) δ 8.81 (dd, 1H, J = 1.6 and 1.2 Hz), 8.64
(dd, 1H, J = 4.8 and 1.6 Hz), 7.92 (dt, 1H, J = 7.6 and 1.6 Hz), 7.28 (qd,
1H, J = 4.8 and 0.8 Hz), 1.90-1.80 (m, 7H), 0.98-0.94 (m, 42H), 0.65-0.60
(m, 14H) ppm; 13C-NMR (CDCl3, 100 MHz) δ 154.4 151.1 141.7 127.2
123.0 25.7 25.7 23.9 22.5 22.3 ppm; 29Si-NMR (CDCl3, 80 MHz) δ -66.8 -
67.0 -67.7 -81.1 ppm. HR-FAB-MS (m/z): calcd for C33H67NO12Si8 [M+H]+,
894.2896; obs, 894.2886.
Acknowledgments
This work was supported by JSPS KAKENHI Grant Number
JP18K19114. H. I. acknowledges Grant-in-Aid for Young
Scientists (B) (JSPS KAKENHI Grant Number JP17K14530).
General Procedure B: A DMF solution (2 mL) of 1 (245 mg, 0.3 mmol),
aryl halide (0.45 mmol), [Rh(cod)(MeCN)2]BF4 (6 mg, 0.015 mmol), and
iPr2EtN (2.3 mmol) was stirred for 1.5 h under nitrogen atmosphere. After
the reaction, toluene (75 mL) was added to the reaction mixture, and the
organic layer was washed with water. The volatiles were removed under
reduced pressure, and the residue was subjected to flash column
chromatography over silica gel (eluent: hexane/EtOAc = 1/1). The
product was purified by preparative HPLC using CHCl3 as an eluent.
Keywords: Arylation • Silsesquioxane • Pd catalyst • Rh catalyst
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European Journal of Inorganic Chemistry
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Entry for the Table of Contents
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Functional cage
H. Imoto, S. Wada, T. Yumura, K. Naka*
Page No. – Page No.
Transition Metal-Catalyzed Direct
Arylation of Caged Silsesquioxanes:
Substrate Scope and Mechanistic
Study
Functional cages: Pd- or Rh-catalyzed direct arylation of cage-silsesquioxane has
been attained. Phenyl- and isobutyl-substituted cage-silsesquioxanes were
applicable for the arylation with electron-donating, electron-withdrawing,
heteroatom-containing, and reactive substrates. The reaction mechanism of the Rh-
catalyzed direct arylation has been computationally studied in detail.
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