Silane catecholates: Versatile tools for self-assembled dynamic covalent bond chemistry

Article abstract of DOI:10.1039/c9cc02103e

Shape-persistent macrocycles and 3D nanocages have been prepared in one-pot under MeCN-promoted dynamic covalent bond conditions starting from silane catecholates, whose structures were confirmed by X-ray crystallography. Cation-exchange reactions of macrocycles and nanocages were performed along with the encapsulation of ammonium ions within the cavity of an anionic macrocycle and a tetrahedral nanocage.

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Commun., 2019, DOI: 10.1039/C9CC02103E.
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Silane catecholates: Versatile tools for self-assembled
dynamic covalent bond chemistry
Cite this: DOI: 10.1039/x0xx00000x
Yoshiteru Kawakami,a Tsuyoshi Ogishima,a Tomoki Kawara,a Shota Yamauchi,a
Kazuhiko Okamoto,a Singo Nikaido,a Daiki Souma,b Ren-Hua Jinb and Yoshio
Kabe*a
Received 00th January 2019,
Accepted 00th January 2019
DOI: 10.1039/x0xx00000x
www.rsc.org/
Shape-persistent macrocycles and 3D nanocages have been phenyltriethoxysilane under basic conditions to form a tetraanionic
prepared in one-pot under MeCN-promoted dynamic covalent molecular square.5a Lambert and coworkers described the reaction of
bond conditions starting from silane catecholates, whose biscatechol derivatives linked by a cyclic chain with several types of
structures were confirmed by X-ray crystallography. Cation- trialkoxysilanes under basic conditions to produce macrocycles
exchange reaction of macrocycles and nanocages were performed ranging from monomers to pentermers.5b More recently, Roeser and
along with the encapsulation of ammonium ions within the cavity coworkers were able to produce porous 2D/3D silicate organic
of an anionic macrocycle and tetrahedral nanocage.
frameworks upon reacting biscatechol and triscatechol derivatives
with tetramethoxysilane.5g,h Notably, Robson and coworkers
Dynamic covalent chemistry (DCC)1 is a synthetic strategy that investigated the reaction of
a triscatechol derivative, i.e.,
involves reversible covalent bond formation, thus leading to the cyclotricatechylene (CTC), with phenyltriethoxysilane to produce an
formation of the most thermodynamically stable product. The concept anionic tetrahedral nanocage,6 as an extension of similar previously
of DCC coupled with that of template-directed synthesis has allowed
for the construction of three-dimensional nanostructures from
preorganized simple precursors using one-pot procedures.2-4 While
imine bond formation,1a-c,2a-c,f,4f,g,i boronic acid condensation,2f,3a-e,h,j-l
acetal bond exchange,1f disulfide bond exchange,1h,3f and other
reactions1d,e,g have been largely utilized in DCC, silicon-based
protocols have not been so far explored except for few examples.5a,b,g
In particular, Shea and coworkers reported that racemic biscatechol
derivatives bearing a spirobiindane framework reacted with
HO
HO
OH
OH
2
( ), NR'3
RSi(OMe)3
THF, MeCN, MeOH, reflux
1a
1b
: R = Ph
: R = p-Tolyl
4-
+
R
O
R
O
· 4HNR'3
O
Si O
Si
O
O
O
O
HO
OH
OH
· 0 or 2
HO
a Department of Chemistry, Faculty of Science, Kanagawa University 2946,
Tsuchiya, Hiratsuka 259-1293, Japan. E-mail: kabe@kanagawa-u.ac.jp
FAX: +81-463-58-9684 TEL: +81-463-59-4111
b Department of Material and Life Chemistry, Faculty of Engineering,
Kanagawa University 3-2-7, Rokkakubashi, Kanagawa-ku, Yokohama
221-8686 Japan.
† Electronic supplementary information (ESI) available: Experimental
procedure, spectral for all new compounds, Crystallographic data
4a·4HNEt3, 5a·6Na and 8@4a (CCDC, 1892127, 1892128 and 1892129).
For ESI and crystallographic data in CIF as other electronic format, see DOI:
/ /
O
O Si
O
Si O
O
O
· 0 or 2
· nTHF
O
O
R
R
4a
2
·4HNEt3·2( )·4THF
·4HNEt3
Precipitation with
DMSO-DMF/Et2O
4a
4a
4a
4a
4a
4a
4b
2
·4HNEt2Bn·2( )·4THF
·4HNMe2Bn·2THF
·4HNMe2Bu·2THF
·4TMEDAH·2THF
2
·4HNEt3·2( )·2Anthracene·THF
·4HNEt3·2THF
+
TMEDAH = HNMe2CH2CH2NMe2
Scheme 1 Synthesis of silane catecholate macrocycles 4a,b.
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HO OH
groups of reactant 2. It was assumed that all catechol groups were
transformed
3
( ), NEt3 or NaOH
HO
HO
OH
OH
ArH
1a
/THF
2
+
a)
SiPh
m, p-CH
RSi(OMe)3
OH
DMF or DMF-MeCN, 60-100 ºC
1a-f
o-CH
NH+
a: R = Ph, b: R = p-Tolyl, c: R = Me
d: R = Vinyl, e: R = (CH2)3SH, f : R = (CH2)3NMe2
4a
(ArH)
1a
2
b)
+
9-
2
(OH)
Ph
4a
(SiPh)
m, p-CH
Ph
Ph
/THF/MeOH
/MeCN
O
O
O
R
O
O
2
(ArH)
Si
6-
Si
O
O
O
Si
O
O
O
O
O
O
Si
O
o-CH
O
+
O
Si
O
R
O
4a
R
(NH )
O
O
O
Si
O
O
O
O
O
O
Si
Ph
O
+
· 6M+
· 9HNEt3
O
O
+
Ph
5a
Si
O PhO
(ArH)
Si
O
O
Si
O
O
Si
O
1a
/DMF
3
+
c)
d)
O
O
O
O
O
5a 6a
,
(SiPh)
O
DMF
R
R
O
O
O
O
o-CH
Si
R
6a
(ArH)
O
O
m, p-CH
O
+
O
Si
Ph
Si
5a 6a
,
(NH )
O
O
O
O
O
O
Si
*
O
*
*
5a
5b
5c
5d
5e
5f
: R = Ph, M = HNEt3 or Na
: R = p-Tolyl, M = HNEt3
: R = Me, M = HNEt3 or Na
: R = Vinyl, M = HNEt3
: R = (CH2)3SH, M = HNEt3
: R = (CH2)3NMe2, M = Na
O
Ph
Ph
5a
(ArH)
6a
1a
3
+
5a
(SiPh)
/DMF/MeCN
m, p-CH
o-CH
DMF
+
5a
(NH )
Scheme 2 Synthesis of silane catecholate nanocages 5a-f and 6a.
Fig. 1 1H NMR spectra of the reaction mixtures of PhSi(OMe)3
(1a)with biscatechol (2) and triscatechol (3) in the presence of Et3N
(a) in THF, (b) in THF/MeCN/MeOH, (c) in DMF, and (d) in
DMF/MeCN. *SiPh groups located inside the nanocage of 6a.
reported transition metal bridged tetrahedral cages [M6(CTC)4]12- (M
= Cu, V=O).7 These independent studies prompted us to publish our
results, which are DCC feature of silane catecholate as well as their
host-guest chemistries.8
However, based on the above precedents, it was not evident how
to select suitable DCC conditions and tailor the structure of silane
catecholates in order to promote the formation of the desired
molecular architectures. Herein, we demonstrate that the addition of
MeCN as co-solvent allowed to rapidly reach a dynamic equilibrium
under DCC conditions for silane catecholate bond formation. As a
result, we accomplished the preparation of shape-persistent silane
catecholate macrocycles (4a,b) as well as nanocages (5a-d, 6a) by
reacting two polycatechol building blocks, such as 2,3,6,7-
tetrahydroxy-9,10-dimethyl-9,10-ethano-9,10-dihydroanthracene
(EAT) (2) and cyclotricatechylene (CTC) (3), with various
trimethoxysilanes (1a-f), as shown in Scheme 1 and 2. Both
macrocycles (4a,b) and nanocages (5a-d, 6a) exhibited a molecular
recognition behavior via amine-cation attractions, which was
confirmed by solid-state X-ray crystallography and solution NMR
spectroscopy upon counter cation exchange.
into the corresponding silane catecholates to produce macrocyclic
structures. Silane biscatecholates of phenylsilane are pentacoordinate
structures, which might undergo a more facile bond exchange and
pseudo-rotation upon addition of MeCN to the silicon center (Section
4, ESI†).9 When 1a was reacted with 2, the replacement of the solvent,
such as THF/MeOH/MeCN by DMF/MeCN, led to a homogeneous
oligomeric mixture rather than the precipitation of macrocycle 4a. It
can be suggested that the reaction in THF/MeOH/MeCN is driven by
the insolubility of macrocycles 4a,b and their molecular complexes
with/without templates. Ditopic catechol 2 itself and anthracene
played the role of templates, as they were removable by
reprecipitation from DMSO/DMF/CH2Cl2/Et2O (Scheme 1 and
Section 1.2, ESI†). Since the molecular complex induced the
predominant formation of tetrameric macrocycle 4a, which then
produced tubular aggregates as described later, it precipitated from the
reaction mixture during the condensation reaction. The white
precipitates were collected by suction filtration to give 4a,b and their
molecular complexes with different ammonium cations in 54.2-
88.6% yields, as shown in Scheme 1. Further replacement of the
phenyl and p-tolyl substituents on the silicon atoms of RSi(OMe)3
(1a,b) with methyl and octyl groups increased the solubility of the
resulting products, preventing the precipitation-driven reaction to
yield oligomeric mixtures.
The reaction of phenyltrimethoxysilane (1a) with ditopic catechol
2 (ETA) and triethylamine in a 1:1:3 or 3:2:6 molar ratio (Scheme 1)
was performed in THF under reflux. Aliquots of the reaction mixture
were periodically withdrawn and monitored by 1H NMR
spectroscopy. Several hours after the initial mixing, complex
equilibria involving various oligomeric intermediates were reached
(Fig. 1a), which did not further change even after several hours.
However, the addition of MeCN as co-solvent initiated the conversion
into a highly symmetrical and monodisperse compound as the only
detectable product after 1-2 days (Fig. 1b). The 1H NMR analysis of
the reaction mixture revealed a reduction of the polycatechol end
In contrast to the reaction of 1a,b with 2, the reaction of 1a with
tritopic catechol 3 and triethylamine in a 3:2:9 molar ratio in DMF at
100 ºC afforded a homogeneous solution, whose product consisted of
1
a mixture of nanocages 5a and 6a, based on H NMR spectroscopy
(Fig. 1c). Nanocages 5a and 6a were separated by reprecipitation from
2 |Chem.Commun., 2019, 00, 1-4
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DMF/THF (Section 1.10, ESI†). Once the addition of MeCN induced Fig.2 ESI-MS spectra of (a) 5a, (b) 5b, and (c) scrambling products
from the reaction mixture of 5a and 5b in a 1:1 molecular ratio in
DMF/MeCN at 100 °C for 2 days (MeOH).
the conversion of 6a to 5a (Fig. 1d), 5a was obtained in 94.6% yield
after redissolution in THF/MeCN and precipitation with Et2O. When
the condensation of 1a with 3 was conducted at a temperature lower
than 100 ºC, 6a was also produced together with 5a, e.g., 77.4 and
15.2% of 5a and 6a at 80 ºC, and 55.8 and 41.1% of 5a and 6a at 60
ºC in DMF/MeCN respectively (Section 4, ESI†). This dependence on
MeCN and the temperature demonstrates that the formation of 6a is
kinetically rather than thermodynamically controlled. The non-
precipitation driven reaction of 1a with 3 allowed the phenyl group of
RSi(OMe)3 to be replaced with a variety of substituents at the silicon
atoms such as p-tolyl, methyl, vinyl, and (CH2)3SH to afford 5b (R =
p-tolyl, 99.6%), 5c (R = Me, 99.4%), 5d (R = vinyl, 94.6%), and 5e
(R = (CH2)3SH, 98.0%), respectively, as shown in Scheme 2. The
replacement of triethylamine with NaOH also resulted in the
formation of 5a, 5c and 5f with a Na+ counter cation in 85.8, 97.6 and
91.8% yields. Using derivatives of tetrahedral cages 5a and 5b, a
scrambling experiment was conducted in DMF/MeCN at 100 ºC and
followed by ESI mass analysis (Fig. 2). A series of scrambled
nanocage compounds having different combinations of phenyl and p-
tolyl substituted side chains were observed, demonstrating the
reversibility of the MeCN-promoted condensation reaction.
a)
b)
c)
d)
Fig.
3
X-ray molecular and crystal structures of (a)
4a·4HNEt3·8MeOH, (b) 4a·4HNEt3·8MeOH as viewed along the c-
axis, (c) 5a·6Na·7THF·2DMF·2C6H6·23H2O, and (d) 8@4a
·14DMSO·5H2O showing 30% probability ellipsoids. All hydrogen
All isolated silane catecholate macrocycles 4a,b and nanocages
5a-f, 6a with different counter cations were fully characterized by 1H, atoms and solvent molecules were omitted for clarity.
13C, and 29Si NMR as well as ESI mass spectroscopy (Section 1 and
being appropriate for 5a·6Na·7THF·2DMF·2C6H6·23H2O (R = 9.65).
Despite these issues, the structures of tetrameric macrocycle 4a and
tetrahedral cage 5a were clearly and unambiguously defined, as
shown in Fig. 3a and c. Especially, the structure of tetrahedral cage 5a
was nearly consistent with that reported by Robson and coworkers.6
The X-ray packing structure of 4a·4HNEt3 showed an anionic
macrocycle stacked on top of another and cemented by electrostatic
2, ESI†). Furthermore, the structures of tetraanion (4a) and hexaanion
(5a) derivatives were unequivocally determined by X-ray
crystallographic analysis (Section 3, ESI†). Recrystallization of
4a·4HNEt3 and 5a·6Na from MeOH/MeCN over molecular sieves
and THF/benzene, respectively, generated solvated crystals. Due to
the size of the molecules, lack of heavy atoms, and presence of large
amounts of disordered solvent molecules, the quality of the X-ray
diffraction data was poor for 4a·4HNEt3·8MeOH (R = 17.51), while
+
attractions and hydrogen bonding of the HNEt3 ion to produce a
tubular aggregate structure (Fig. 3b).5c,d
p-Tolyl
Ph
A cation exchange reaction between 5a·6HNEt3 and a variety of
6-
6-
O
O
O
O
O
O
O
O
Si
Si
+
+
+
NR4 X- salts took place yielding 5a·6NR4, NMe4 (70.3%), NEt4
O
Si
O
Si
O
Si
O
p-Tolyl
Ph
Ph
O
O
p-Tolyl
O
O
O
O
Si
Scrambling
O
O
O
O
(59.9%), N-MePy+ (80.8%), and N-BuPy+ (74.1%), respectively
(Section 1.18, ESI†). During the 1H NMR titration upon cation
exchange, an upfield shift of the signals corresponding to the
encapsulated guest cations into the cage of 5a was observed, which
varied depending on the structure of the ammonium cation.
Specifically, the N-butylpyridinium cation produced the largest shift
in the 1H NMR spectrum (Section 5, ESI†). According to this
observation, we tried to employ Stoddart’s blue box (8·4PF6) as well
as its synthetic precursor (7·2PF6) as exchangeable guest cations, as
shown in Scheme 3. Pleasingly, the 1H NMR titration of both
4a·4TMEDAH and 5a·6HNEt3 with 72+ or 84+ could be monitored in
DMSO-d6 (Section 5.5 to 5.8, ESI†). The proton signals of 72+ were
shifted when 72+ and 4a4- as well as 72+ and 5a6- were mixed in
DMSO-d6, indicating that the incorporation of 72+ in their cavity
occurred to give 7@4a and 7@5a, respectively. In terms of proton
signals of 84+, it was assumed that 84+ could be included in 4a4-
O
O
O
O
[(SiPh)n(SiTolyl)6-n
(CTC)4·6HNEt3]
(n = 0-6)
+
O
O
O
O
O
O
O
O
Si
O
Si
O
O
Si
O
Si
O
O
Ph
p-Tolyl
Ph
p-Tolyl
O
O
O
O
O
O
O
O
Si
Si
Ph
p-Tolyl
+
+
· 6HNEt3
· 6HNEt3
5a
5b
2-
5a
[M+4HNEt3
]
a)
m/z = 1239.4
2-
5b
[M+4HNEt3
]
b)
c)
m/z = 1281.5
Ph3
(Tolyl)3
Ph2
(Tolyl)4
Ph2
(Tolyl)4
Ph5
(Tolyl)1
Ph1
(Tolyl)5
Ph6
(Tolyl)6
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(8@4a), while 84+ was too large to be included in 5a6- (5a·8), as
illustrated in Scheme 3, and Section 5.7 and 5.8, ESI†. On one
occasion, pure crystals were successfully grown from a residue of the
1H NMR titration experiment, and the structure of 8@4a was resolved
by X-ray analysis (Fig. 3d). The inclusive association afforded a
supramolecular ring@ring structure.5f Despite the presence of empty
cavities in 5a·8 as well as 5a·6Na due to the fact that the blue box (8)
and Nan(H2O)m cluster were too large to be encapsulated, they were
not available for gas adsorption so far (Section 6, ESI†).
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3
For reviews and selected papers on the template-driven synthesis of
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2+
N
N
N
N
N
Ph
Ph
O
Ph
O
O
O
O
Si
O
O
Si
Si
O
N
O
O
O
O
O
O
Si
Ph
Ph
·2PF6
4
O
O
O
N
N
Si
O
O
7
·2PF6
O
O
N
N
or
O
O
O
O
N
N
Si
O
Si
O
O
Si
O
O
O
O
Ph
Ph
O
O
O
O
O
Si
O
O
O
Si
Ph
Ph
Ph
4a
·4TMEDAH
or
7
4a
@
7
5a
@
4+
5a
·6HNEt3
N
N
N
Ph
Ph
O
Ph
N
O
O
O
O
O
Si
O
O
Si
N
N
Si
O
O
O
O
O
Si
O
Ph
·4PF6
Ph
O
O
N
O
N
N
N
Si
O
O
8
·4PF6
O
O
N
or
O
O
O
O
N
Si
O
Si
O
O
Si
O
O
O
O
Ph
Ph
O
O
O
O
O
Si
O
O
O
Si
Ph
Ph
Ph
8
4a
@
5a 8
·
Scheme 3 Polypyridinium cation inclusion of 4a and 5a.
In conclusion, we demonstrated that ditopic and tritopic silane
catecholates can successfully be employed for the synthesis of
macrocycles as well as 3D nanocages in a predicted manner. In order
to achieve dynamic covalent bonding conditions, MeCN was used as
co-solvent. The macrocyclic products were formed by precipitation-
driven reactions with the aid of templates such as reactants,
anthracene, and ammonium cation linkers, while nanocage products
were the result of thermodynamic and kinetic equilibria. An anionic
macrocycle and tetrahedral cage were exchanged and encapsulated in
solution using several ammonium cations. Aiming to attain gas
adsorption, the design and synthesis of stackable macrocycles and
larger cages using different types of polycatechol building blocks are
currently underway in our laboratory.
5
6
7
J. L. Holmes, B. F. Abrahams, A. Ahveninen, B. A. Boughton, T. A.
Hudson, R. Robson, D. Thinagaran, Chem. Commun, 2018, 54, 11877–
11880.
For studies on CTC derived coordination cages, see: (a) B.ꢀF. Abrahams,
N.ꢀJ. FitzGerald, R. Robson, Angew. Chem. Int. Ed., 2010, 49, 2896–2899;
(b) B. F. Abrahams, B. A. Boughton, N. J. FitzGerald, J. L. Holmes, R.
Robson, Chem. Commun, 2011, 47, 7404–7406.
Our results were presented at the 20th and 21th symposium of the Society
of Silicon Chemistry Japan, October 7-8, 2016 (Abstract P18) and October
27-28, 2017 (Abstract P24) as well as the annual meeting of the Chemical
Society of Japan, March 16, 2018 (Abstract 1PA-116).
D. Kost, I. Kalikhman “Hypervalent Silicon Compounds” in the
Chemistry of Organic Silicon Compounds, Volume 2, Part 2, edited by Z.
Rappoport, Y. Apeloig, John Wiley & Sons, 1998, Chap. 23, pp. 1339–
1445.
This work was supported by the MEXT-Supporting Program for the
Strategic Research Foundation at Private Universities. The authors are
grateful to Colcoat Co., Ltd. for financial support.
Notes and references
8
9
1
For reviews on dynamic covalent chemistry (DCC), see: (a) S. J. Rowan,
S. J. Cantrill, G. R. L. Cousins, J. K. M. Sanders, J. F. Stoddart, Angew.
Chem. Int. Ed., 2002, 41, 898–952; (b) C. D. Meyer, C. S. Joiner, J. F.
Stoddart, Chem. Soc. Rev., 2007, 36, 1705–1723; (c) M. E. Belowich, J.
F. Stoddart, Chem. Soc. Rev., 2012, 41, 2003–2024; (d) Y. Jin, C. Yu, R.
J. Denman, W. Zhang, Chem. Soc. Rev., 2013, 42, 6634–6654; (e) W.
Zhang, J. S. Moore, Angew. Chem. Int. Ed., 2006, 45, 4416–4439; (f) R.-
C. Brachvogel, M. von Delius, Eur. J. Org. Chem., 2016, 3662–3670; (g)
H. Kudo, R. Hayashi, K. Mitani, T. Yokozawa, N. C. Kasuga, T.
Nishikubo, Angew. Chem. Int. Ed., 2006, 45, 7948–7952; (h) S. P. Black,
J. K. M. Sanders, A. R. Stefankiewicz, Chem. Soc. Rev., 2014, 43, 1861–
1872.
2
For reviews and selected papers on the template-directed synthesis of
cavitand and carcerand, see: (a) M. L. C. Quan, D. J. Cram, J. Am. Chem.
4 |Chem.Commun., 2019, 00, 1-4
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