Isostructural mesoporous ionic crystals as a tunable platform for acid catalysis

Article abstract of DOI:10.1039/d0dt01202e

Eleven isostructural mesoporous ionic crystals (meso-PICs) are synthesized. The initial activities of the Barbier-Grignard reaction, which is a typical C-C bond formation reaction, catalyzed by the meso-PICs are dependent on the acid dissociation constant

Full text of DOI:10.1039/d0dt01202e

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Douglas W. Stephen et al.
N-Heterocyclic carbene stabilized parent sulfenyl, selenenyl,
and tellurenyl cations (XH , X = S, Se, Te)
+
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DOI: 10.1039/D0DT01202E
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Isostructural Mesoporous Ionic Crystals as a Tunable Platform for
Acid Catalysis
a
a
a
b,c
d
Yuto Shimoyama, Zhewei Weng, Naoki Ogiwara, Takashi Kitao, Yuji Kikukawa and Sayaka
Uchida *a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Eleven isostructural mesoporous ionic crystals (meso-PICs) are resulting in the formation of porous ionic crystals (PICs).7-9
synthesized. Initial activities of Barbier-Grignard reaction, which is Especially, we have been focusing on polyoxometalates
1
0-14
a typical C-C bond formation reaction, catalyzed by meso-PICs are (POMs),
dependent on the acid dissociation constant of the aqua ions of M
which are nano-sized metal-oxide molecular anions
n+
with unique catalytic, electrochemical, magnetic, and
and the types of polyoxometalates, which construct the meso-PICs. luminescent properties, as an ionic component of PICs.
For example, we have previously reported that the
Porous crystalline materials such as zeolites and metal-organic
frameworks (MOFs) have attracted wide attention in materials
sciences due to their well-defined pore structures, composition-
structure-function relationships, and applications in gas
3–
combination of a POM [
α
40
-PW12O ]
with a trinuclear
chromium carboxylate molecular cation with acrylate ligands
+
[
Cr
dimensional micropores with a minimum aperture of 3.3 Å,
which shows shape-selective adsorption of CO and C over
The pore sizes of PICs are generally small and
3 2 6 2 3
O(OOCCHCH ) (H O) ] forms an PIC with stable three-
1
storage/separation, heterogeneous catalysis, etc. Especially,
2
2 2
H
cation-exchange has long been recognized as a synthetic
strategy to fine-tune the functions of porous crystalline
materials systematically.2 For example, lanthanide-ion-
exchanged FAU zeolites show high catalytic activities in Friedel-
Crafts acylation reaction because the large electrostatic
interaction between lanthanide ions and adsorbed water
15
2 4
N and CH .
similar to those of industrially important small inorganic and
hydrocarbon gases, so that ionic crystals are suitable for the
,3
16
storage and separation of these gases. On the other hand, it
would be quite interesting to extend the pore-size of PICs to the
meso-range (defined as 2–50 nm by IUPAC) to incorporate
relatively large organic molecules into the crystal lattice.
We have previously synthesized a mesoporous ionic crystals
4
molecules produce Brønsted acids as catalytically active sites.
A more recent example reports that Brønsted and/or Lewis
acidities of zeolites can be controlled by the types of metal ions
(
meso-PIC) Cr[Cr
Cr ] with Cr , [Cr
building blocks. Compound I-Cr3+ possesses one-dimensional
3
O(OOCCH
O(OOCCH
2
CN)
CN)
6
(H
(H
2
O)
O)
3
]
3
+
[
α
-PW12
O
40
]
2
∙nH
2
O [I-
2+
as counter cations, and Zn -BEA zeolite with high Lewis acidity
exhibits the best performance in Prins reaction.5
3+
3+
3–
3
2
6
2
3
] , and [α-PW12O40] as
Ionic crystals have great potential as functional materials
because of the wide range of choice and combination of anions
and cations. However, ionic crystals normally crystallize in
highly-symmetrical non-porous structures (i.e., NaCl, CsCl)
because of the Coulomb interaction, which works isotropic in a
mesopores with an aperture of 3 nm × 2 nm, and the
mesoporous structure was maintained by hydrogen-bonded
17
3+
water clusters as templates. While I-Cr does not possess
3+
well-defined acid sites, infrared (IR) spectrum of I-Cr treated
with pyridine as a basic probe molecule suggest the existence
6
long-range. We and other research groups have reported that
17
of Brønsted acid sites. The pore structure of PICs can be
the use of molecular ions with appropriate elements, charges,
sizes, and ligands enables the utilization of anisotropic
interactions such as π-π and hydrogen-bonding interactions,
controlled by the ratio of the building blocks, and the PIC with
the highest porosity shows the highest activity in fructose
dehydration to 5-hydroxymethylfurfural, which is a typical
1
8
biomass reaction catalyzed by Brønsted acids.
a.Department of Basic Science, School of Arts and Sciences, The University of Tokyo,
In order to understand the characteristics of PICs, it is
important to clarify the contribution of each building block to
the catalytic activity and to establish building block-catalytic
3
-8-1 Komaba, Meguro-ku, Tokyo 153-8902 (Japan).
b.
c.
d.
Department of Applied Chemistry, Graduate School of Engineering, The University
of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan).
Department of Advanced Materials Science, Graduate School of Frontier Sciences,
The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan).
Department of Chemistry, Graduate School of Natural Science and Technology,
Kanazawa University, Kakuma-machi, Kanazawa city, Ishikawa 920-1192 (Japan).
activity relationships. In this work, isostructural meso-PICs with
n+
different metal ions or POMs were synthesized:
M
x
H
(3-
3+
n+
nx)[Cr
3
O(OOCCH
2
CN)
6
(H
2
2+
O)
3
]
3
[α-PW12
40
O ]
2
∙yH
2
O
(M = Fe ,
Electronic Supplementary Information (ESI) available: Additional experimental Cr , In , Al , Y , Zn , Ni , Cu , Mg , Ca ) [I-Mn+] and
3+
3+
3+
3+
2+
2+
2+
2+
methods. Fig. S1: SEM-EDX. Fig. S2: IR spectra. Fig. S3: Themogravimetry of II-Cr3+
Fig. S4: H-MASNMR spectrum of II-Cr . Fig. S5: H-NMR of reaction solution. Fig.
.
II-Cr3+].
[
Cr[Cr
3
O(OOCCH
2
CN)
6
(H
2
O)
3
]
3
[α-PMo12
O
40
]
2
∙50H
2
O
1
3+
1
S6: Time courses of the Barbier-Grignard reaction. See DOI: 10.1039/x0xx00000x
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Then, Barbier-Grignard reaction,19 which is a typical carbon-
carbon bond formation reaction catalyzed by acids, was carried
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DOI: 10.1039/D0DT01202E
CN
Mo
P
Cr
n+
3+
out with I-M or II-Cr as heterogeneous catalysts to
investigate the building block-catalytic activity relationships.
Initial catalytic activities were dependent on the acid
dissociation constant (pKa) of the aqua ions of metal ions and
the types of POMs. These findings show that meso-PICs can
serve as a platform for a rational design of heterogeneous acid
catalysts.
(a)
+
O
O
3− [Cr O(OOCCH CN) (H O) ]
+
[α-PMo12O40
]
3
2
6
2
3
2 nm
3
nm
Table 1. Amounts of Mn+ and H in I-M
+
n+ a,b
I-Mn+
I-Fe3+ c
I-In3+
I-Cr3+
I-Al3+
I-Y3+
Mn+
H
I-Mn+
Mn+
H
x
x
(3-nx)
(3-nx)
0.80
0.12
1.1
(b)
a
Fe3+1.26
I-Zn2+
I-Ni2+
I-Cu2+
I-Mg2+
I-Ca2+
Zn2+1.1
H
c
In2+0.88
Cr3+1.0
Al3+0.87
H
Ni2+1.44
Cu2+0.95
Mg2+1.5
Ca2+0.67
H
0.35
H
H
0.39
Y3+0.80
H
H
1.66
0.60
a
Amounts of H was estimated by 3–nx where x is the amounts of Mn+. bAmounts
+
of Cr in I-Mn+ (except for I-Cr3+) were negligible. Amount of Fe (1.26) exceeded
c
1
.0 probably because of the additional exchange with Cr3+ of the macrocation.
(c)
b
a
(d)
b
a
Fig.2 (a) Molecular structures of the POM and macrocation, and the pore-opening of II-
Cr3+. (b) Crystal structure of II-Cr3+ along the c-axis. Red lines and numbers show the
possible dispersion forces and distances, respectively, between the cyano groups. Crystal
structure of II-Cr3+ (ab-plane) represented in (c) polyhedral and (d) space filling models.
Fig.1 PXRD patterns of I-Mn+ and II-Cr3+. The group of three numbers in II-Cr3+ show the
Miller indices of each diffraction peaks.
6 6 4
Orange, dark blue, and purple polyhedra in (b)(c) show the [CrO ], [MoO ], and [PO ]
units, respectively. The hexagon in (c) corresponds to that in (a). Blue, dark gray, and red
spheres in (d) are the nitrogen, carbon, and oxygen atoms, respectively, depicted in their
van der Waals radii. Water of crystallization is omitted for the clarity.
We attempted to obtain I-Mn+ by ion-exchange: I-Cr3+ was
dispersed and stirred in water for 2 days at room temperature
(
rt) with 10 molar equivalents of metal salts. However, Mn+ by the addition of metal nitrate or chloride salts instead of
elemental analysis by atomic absorption spectrometry (AAS) chromium nitrate to the synthetic solution. A large variety of
and/or inductivity coupled plasma optical emission trivalent and divalent metal ions were successfully incorporated
n+
n+
spectrometry (ICP-OES) showed that only several metal ions by this method. The amounts of M in I-M were determined
2
+
2+
3+
(
Cu , Mg etc.) could be exchanged with Cr by this method, by AAS and/or ICP-OES, and the results are summarized in Table
+
n+
probably due to the strong electrostatic interaction between 1. Protons (H ) as well as M were probably incorporated into
3
+
n+
3–
Cr and the host crystal. Then, we attempted to synthesize I-
I-M to compensate the anion charge of [α-PW12
O
40
]
since
2
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the synthetic solution is highly acidic (ca. pH 1). Elemental crystallization (see below). While the existence of Cr3+ as a
View Article Online
DOI: 10.1039/D0DT01202E
mappings by scanning electron microscope-energy dispersive X- counter cation was suggested by the charge balance and
3+
3+
ray (SEM-EDX) confirmed that the metal ions are uniformly elemental analysis of II-Cr , Cr sites could not be determined
n+
1
3+
distributed in I-M (Fig. S1).
by SXRD. Solid-state H-MASNMR spectrum of II-Cr showed a
IR spectra of I-Mn+ showed that the molecular structures of broad signal at 5.7 ppm (Fig. S4). Since hydrogen-bonding
+
3–
1
[
Cr
3
O(OOCCH
2
CN)
6
(H
2
O)
3
]
(macrocation) and [α-PW12
O
40
]
causes a low-field shift in the H-NMR signal of water (cf., H
2
O
n+
23
are retained. Powder X-ray diffraction (PXRD) patterns of I-M
are shown in Fig. 1. The PXRD patterns of I-M were analogous network of water molecules is probably formed in the
to that of I-Cr , which shows that I-Mn+ crystallize into the mesopore.
6
in C D
6
0.40 ppm, H
2
O in D
2
O 4.79 ppm), hydrogen-bonding
n+
3+
mesoporous structure. While the mesoporous structure is
In order to investigate the building block-catalytic activity
stable under ambient conditions, the PXRD patterns broadened relationship, Barbier-Grignard reaction (Scheme 1),19 which is
after evacuation at room temperature showing that solvent an environmentally friendly carbon-carbon bond formation
molecules are necessary to maintain the mesoporous reaction catalyzed by acids, was carried out. Our previous study
1
7
3+
structure. These results indicate that the meso-PICs show low has confirmed that I-Cr possesses Brønsted acid sites, which is
3+
porosity and BET surface area based on N
isotherms. However, it is well known that porous host systems according to Scheme 2, and I-Cr catalyzed Barbier-Grignard
filled with appropriate guests also show interesting properties reaction with 91% conversion and 76% yield after 48 h. It is
in guest-exchange, proton conduction, etc.2
2
adsorption probably generated by the hydrolysis of Cr aqua ions
3+
17
0,21
Notably, the well known that the bond strength between the metal ion and
PXRD patterns changed upon the incorporation of monovalent oxygen atoms of the water molecules in metal aqua ions
alkali metal ions, which is probably due to the high affinity increases and decreases with the charge (z) and ionic radius (r),
between the alkali metal ions toward POMs22 These results respectively, of the metal ion (i.e., proportional to z/r).
show that only divalent and trivalent metal ions could be Metal aqua ions are subject to hydrolysis according to Scheme
incorporated into the mesoporous structure, which is a unique 2, and the logarithm of the first hydrolysis constant (logKa = –
24,25
2
4,25
feature of meso-PICs.
pKa) is proportional to z/r for most aqua ions.
According to
The meso-PIC with [α-PMo12
O
40]3– was obtained as yellow- these ideas, we reached an idea that the amounts of Brønsted
green crystals at the interface between aqueous solutions of acid sites and catalytic activity of I-M would depend on the
). IR types of M . The initial product yields (1 h) together with the
spectrum of II-Cr3+ showed that that the molecular structures of pKa of first hydrolysis constant of M are summarized in Table
n+
n+
3
H [α-PMo12
O40]∙nH
2
O and [Cr
3
O(OOCCH
2
CN)
6
(H
2
O)
3
](NO
3
n+
3+
POM and macrocation are retained (Fig. S2). Elemental analysis 2: I-Fe with a small pKa (i.e., high acidity) showed high activity
2+
2+
2+
and thermogravimetry (TG) (Fig. S3) showed that the (entry 1, yield 11.9%), while I-Cu
composition of II-Cr3+ is Cr[Cr
O(OOCCH CN) (H O) [α- pKa (i.e., low acidity) showed lower activities (entry 8–10, yield
∙50H
, I-Mg , and I-Ca with large
3
2
6
2
3 3
]
40
PMo12O ]
2
2
O. Elemental mapping by SEM-EDX confirmed 9.1–9.7%). The product yields increased with the decrease in
that the metal ions are uniformly distributed in II-Cr3+ (Fig. S1). the pKa, and a significant correlation was observed as shown in
The PXRD pattern of II-Cr3+ fairly agreed with that of I-Cr
3+
,
Fig. 3. A similar phenomenon has been observed in the
which shows that II-Cr3+ crystallizes into the mesoporous hydrolysis of cellulose by metal salts of [α-PW12
3–
O
40
]
as
structure (Fig. 1). Notably, Meso-PICs could not be obtained by homogeneous catalysts, and the reaction rate increases with
2
–
4–
26
the use of [α-SMo12
O
40
]
or [α-SiW12
40] (M = W, Mo) so that the negative charge of the POM
–3) is an important parameter to obtain the mesoporous
structure.
The crystal structure of II-Cr3+ was further analyzed with
single crystal X-ray diffraction analysis (SXRD). As shown in Fig.
a, POMs and macrocations were arranged alternately in the
O
40
]
instead of [α- the Lewis acidity of the metal ion, which is proportional to z/r.
3–
PM12O
Table 2. Yield of 1-phenyl-3-buten-1-ol in Barbier-Grignard reaction catalyzed by
various Meso-PICs (Scheme 1), and pKa of the hydrolysis of metal aqua ions
(
(
Scheme 2)
Mn+
Entry
Yield [%]
11.9
11.5
11.2
10.3
10.1
10.6
9.8
pK
a
2
1
2
3
4
5
6
7
8
9
Fe3+
In3+
Cr3+
Al3+
Y3+
Zn2+
Ni2+
Cu2+
Mg2+
Ca2+
2.2
4
ab-plane, and formed a one-dimensional ring and a mesopore
with an opening of ca. 3 nm × 2 nm. The distances between
adjacent ions in the ring were in the range of 3.280–3.368 Å
4
(
C(H)-O), showing weak hydrogen-bonding between POMs and
5
macrocations. POMs and macrocations lined up along the c-
axis, and cyano groups of adjacent macrocations were aligned
parallel to each other with distances of 3.561 and 3.976 Å,
suggesting that weak dispersion forces existed between the
cyano groups (Fig. 2b). These anisotropic interactions may
contribute to the formation of mesopores. Figs. 2c and 2d show
the polyhedral and space filling representation of the
mesoporous structure of II-Cr3+. Polar cyano groups and aqua
ligands of macrocations pointed toward the center of the
mesopore, and probably interacted with the water of
7.7
9
9.9
11.3
11.4
12.8
9.2
9.7
1
0
9.1
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In order to show that the observed catalysis is truly
Journal Name
Investigating the interaction of small polar molecules such
View Article Online
3+
DOI: 10.1039/D0DT01202E
heterogeneous, the catalyst (I-Cr ) was removed from the as methanol with meso-PICs may help to understand the nature
reaction solution at
≤ 1 h (product yield 8.3%). The product of the heterogeneous catalysis. Notably, IR spectroscopic study
yields at 3 and 5 h were 8.7 and 10.0%, respectively. AAS of the of porous materials such as zeolites treated with methanol has
31
reaction solutions showed that a little amount of chromium has been an active area of research in materials chemistry. Fig. 4
3+
3+
leached from the catalysts after 1 h (about 1% of chromium in shows the IR spectra of (a) I-Cr and (b) II-Cr before and after
the catalysts). These results show that slight leaching of the the treatment with methanol. A broad band appeared around
1
–1
catalysts has almost no effect on the catalysis. H-NMR of the 1050 cm , which is due to the
reaction solution is shown in Fig. S5. The signals of the reaction of the broad band around 1600 cm , which can be assigned to
product (1-phenyl-3-buten-1-ol) were clearly observed. Note the (HOH) of water, decreased by the treatment with
that the product yields of the following metal nitrates Fe(NO methanol suggesting that water molecules in the mesopores
Cr(NO , Cu(NO , and Y(NO as catalysts were 1.5–3.7% at 1 have exchanged with methanol molecules.
ν(C-O) of methanol. The intensity
–
1
δ
3 3
) ,
3
)
3
3
)
2
3 3
)
h and much lower than those of the meso-PICs.
ν (W-Oc-W)
(
a)
8
15
ν (W-Oe-W)
Scheme 1
ν (W=O)
ν (C-O)
Abs.
0.2
OH
O
n+
ν (P-O)
I-M 0.66 mol%
SnBu3
H+
Toluene 1.0 ml
8
01
353 K, 1 h
Scheme 2
M(H O) ] + H O
n+
[M(H
O)m-1(OH)](n-1)+ + H O+
2 3
[
2
m
2
δ (HOH)
1
800
1500
1000
500
Wavenumber [cm-1]
ν (Mo-Oc-Mo)
(b)
803
ν (Mo-Oe-Mo)
ν (Mo=O)
Abs.
.2
0
ν (C-O)
ν (P-O)
784
Fig.3 Correlation between the pKa of the hydrolysis of metal aqua ions in I-Mn+ and the
product (1-phenyl-3-buten-1-ol) yields in Barbier-Grignard reaction catalyzed by I-Mn+
.
The error bars show the minimum and maximum yields of each plot.
δ (HOH)
Next, to reveal the contribution of POM to the catalytic
3+
activity, Barbier-Grignard reaction was carried out with II-Cr
as a catalyst. The product yield after 1 h was 4.5% and much
3+
1800
1500
1000
500
lower than that of I-Cr (yield 11.2%). The time course of the
Wavenumber [cm-1]
3+
reaction is shown in Fig. S6. These results indicate that I-Cr
possess higher acidity than II-Cr3+, which is probably due to the
Fig.4 IR spectra of (a) I-Cr3+ and (b) II-Cr3+ before (bottom) and after (top) the treatment
with methanol by ATR method.
3–
3–
difference in the POMs: [α-PW12O40] vs. [α-PMo12O40] . It has
been reported that the order of acid strengths of acidic salts of
POMs (heteropolyacids), as determined by microcalorimetry
40]3– possesses four skeletal
(M-Oc-M) and (M-Oe-
Highly symmetrical [α-PM12
vibration bands, i.e., (P-O), (M=O),
O), where Oc and Oe stand for the corner and edge sharing
oxygen of [MO ], respectively. It has been well known that the
bridging oxygens (M-O-M) are more basic than the terminal
O
ν
ν
ν
ν
and temperature programmed desorption of ammonia, is H
3
[α-
32
2
7-29
3
PW12O40] > H [α-PMo12O40].
In addition, polarizability or
6
softness of acids/bases plays an important role in stabilizing
reaction intermediates, and the order of softness as bases
determined by the reaction of silver salts of POMs with NaI in
33
oxygens (M=O), and water molecules in the mesopores of I-
Cr and II-Cr are probably hydrogen-bonded to the bridging
3+
3+
3–
3– 30
aqueous solutions is [α-PW12
40
O ]
> [α-PMo12O40] . Our
oxygens of the POMs. As shown in Fig. 4, by the treatment with
results on Barbier-Grignard reaction with I-Cr3+ or II-Cr3+ as
heterogeneous catalysts are in agreement with these
observations.
3+
3+
methanol, the
ν (M-Oc-M) bands of I-Cr and II-Cr shifted to
–1
the higher wavenumber from 801 to 815 cm and 784 to 803
–1
cm , respectively, which suggest that the exchange of water
with methanol weakens the hydrogen bonds. Moreover, the
4
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shift of the Mo-Oc-Mo band (+19 cm ) is larger than that of the
COMMUNICATION
–
1
SHELXL-2018 package through the Olex2 interfacVeie.w AArltliclae tOonmlines
were refined anisotropically. Hydrogen at
–
1
oms of the m0Dethy12lene
DOI: 10.1039/D T0 02E
W-Oc-W band (+14 cm ). All these results suggest that the
groups and aqua ligands were placed geometrically. The PLATON
SQUEEZE tool was used in the refinement to mask the water of
3
+
interaction of water molecules with POMs is larger in II-Cr
3+
than I-Cr and that the strong interaction may have inhibited
3+
crystallization and Cr as a counter cation in the mesopore.
the catalytic reaction. It has been reported that the mobility of PLATON/SQUEEZE have found 3523 electrons (881 electrons for Z
1) in the void. A water molecule has 10 electrons, which would
=
protons and water molecules is highly related to the acidity of
–
–
3
4
amount to 881 e / 10 e
TG suggests the existence of 50 H
8 H O. The compound easily loses the water of crystallization,
and the X-ray diffraction data was collected under low
≃
88 H
2
O in the void. On the other hand,
POM-based solid compounds. These observations are further
supported by the broader H-MASNMR signal for II-Cr (Fig. S4)
suggesting that the mobility of water
molecules in II-Cr3+ is much lower than that of I-Cr probably temperature (163 K) while TG was carried out under ambient
2
O, which is much smaller than
1
3+
8
2
3+ 17
than that of I-Cr
,
3+
conditions. Therefore, it is quite natural that the compound
stored under ambient conditions contains less water in the void.
Crystal data for II-Cr3+: monoclinic, C2/c (#15), a = 57.570(16), b =
because of the rigid hydrogen-bonding network.
In summary, eleven isostructural meso-PICs were
synthesized and characterized. Initial activities of Barbier-
2
=
4.215(7), c = 18.769(12), β = 103.351(3), V = 25459(12), Z = 4, R
0.0665, wR = 0.1775, GOF = 1.071. CCDC-1991929 contains the
1
Grignard reaction catalyzed by meso-PICs were dependent on
2
n+
the acid dissociation constant of the aqua ions of M and the crystallographic data.
§
Characterization: Combustion analysis (Elementar, vario MICRO
cube) was used for the quantitative analysis of C, H, and N.
types of POMs, which construct the meso-PICs. These findings
show that meso-PICs can serve as a platform for a rational
design of heterogeneous acid catalysts.
Inductively coupled plasma optical emission spectrometry (ICP
OES) (Agilent Technologies, ICP OES720) or atomic absorption
‐
‐
spectrometry (AAS) (Hitachi, ZA3000) was used for the
quantitative analysis of the metals and phosphorous. Prior to the
ICP-OES or AAS measurements, nitric acid (1 mL) was added to ca.
Conflicts of interest
There are no conflicts to declare.
n+
3+
1
0 mg (accurately weighed) of I-M or II-Cr to dissolve the solid
completely into water (50 mL). Scanning electron microscopy-
energy dispersive X-ray (SEM-EDX) measurements were
conducted using a HORIBA EMAX Evolution EX-370 attached to a
HITACHI S-3000N operated at an accelerating voltage of 20 kV.
Samples were placed on a conducting carbon tape attached by
the SEM grid and then coated with platinum. FT-IR spectra were
Acknowledgements
This work was supported by Grant-in-Aids for Scientific Research on
Innovative Area JP19H04564 (Coordination Asymmetry) and measured by the KBr pellet method with a JASCO FT/IR 4100
spectrometer (JASCO) equipped with a TGS detector. The samples
treated with methanol were measured by attenuated total
reflection (ATR) method with a ZnSe prism with JASCO FT/IR 4200
spectrometer (JASCO) equipped with a TGS detector, and a
JP19H04686 (Mixed Anion), and JSPS Core-to-Core program on
International Network on Polyoxometalate Science for Advanced
Functional Energy Materials. Prof. Motoyuki Matsuo, Dr. Katsumi
3+
3+
Shozugawa, Dr. S. Takizawa (Univ. of Tokyo) are acknowledged for mixture of the powder of I-Cr or II-Cr and a drop of methanol
was prepared on the prism. Thermogravimetry (TG) was
conducted with a Thermo Plus 2 thermogravimetric analyzer
providing access to the ICP instrument. Prof. Takashi Uemura (Univ.
of Tokyo) is acknowledged for providing access to the SEM-EDX
instrument.
(
Rigaku) with α-Al
2
O
3
as a reference under a dry N
2
flow (100
−1
mLꢀmin ) in the temperature range of 298–773 K and an
−
1
increasing rate of 10 Kꢀmin . Powder XRD (PXRD) patterns were
measured with a D8 advance X-ray diffractometer (Bruker) by
using Cu Kα radiation (λ = 1.54056 Å, 40 kV-40 mA) at 1.8
Notes and references
−
1 1
degꢀmin . H-NMR spectrum was recorded with a Bruker AVANCE
III 500 MHz spectrometer (Bruker). Solid state magic angle
spinning (MAS) NMR spectrum (MAS rate = 10 kHz) was recorded
with an AVANCE 400WB spectrometer (Bruker), and adamantane
‡
n+
Synthesis: I-M was synthesized as follows: [Cr
O) ](NO ) (594 mg, 0.75 mmol) and metal cation source (e.g.
Cr(NO 9H O (0.30 g, 0.75 mmol)) were dissolved in 75 mL of
water followed by filtration. H nH O (1.5 g, 1.7
mmol) was dissolved in a minimum amount of water and added
3 2 6
O(OOCCH CN)
(
H
2
3
3
3
)
3
⋅
2
3
[
α
-PW12
O
40
]
⋅
2
(
1.91 ppm) was used as an external standard for the calibration of
chemical shifts.
slowly to the filtrate. Green crystals of I-M were obtained after §§
n+
40
Catalytic Reaction: Reaction was carried out in a glass reactor
equipped with a magnetic stirrer. In a typical run of Barbier-
Grignard reaction, a mixture of benzaldehyde (53.1 mg, 0.50
mmol), allyltributyltin (331.6 mg, 1.0 mmol), 1,2-
dimethoxybenzene (69.1 mg, 0.50 mmol, internal standard), and
2
4 h (1.2 g, yield 62ꢀ% based on H
3
[
α
-PW12
O
]
⋅
nH
similar manner using
nH O. Elemental
O(OOCCH CN) (H O) [α-
O [II-Cr ]: C 9.55, H 2.29, N 3.71, Cr 7.66, P 0.91,
2
O). Compound
3+
II-Cr was synthesized in
nH instead of
analysis (%) calcd for Cr[Cr
a
3
H [α-
PMo12
O
40
]
⋅
2
O
H
3
[
α
-PW12
3
O
40
]
⋅
2
2
6
2
3 3
]
3+
PMo12
O
40
]
2
∙50H
2
n+
3+
−3
catalyst (30 mg of I-M or 24 mg of II-Cr , 3.3 × 10 mmol) in
toluene (1.0 mL) was stirred under air at 353 K. The amounts of
products (1-phenyl-3-buten-1-ol) were followed by gas
chromatography using a GC-2014 (Shimadzu) fitted with a TC-
WAX (GL Sciences) and a flame ionization detector. The reaction
solution (with the solid catalyst) was sampled periodically and
injected directly into the GC system.
Mo 33.9; found: C 9.98, H 2.05, N 3.83, Cr 8.11, P 0.92, Mo 33.3.
If Cr3+ as a counter cation is omitted from the chemical formula,
3+
the difference between the calculated (with Cr : 7.66wt%,
3
+
without Cr : 6.95wt%) and the experimental (8.11wt%) weights
of Cr would be larger.
‡
‡
Single-Crystal X-ray Diffraction (SXRD) Analysis: X-ray diffraction
data of II-Cr3+ was collected at 163 K with a CCD 2-D detector by
using
Rigaku
Saturn
diffractometer
with
graphite
1
J. Liang, Z. Liang, R, Zou and Y. Zhao, Adv. Mater., 2017, 29
7011139.
,
monochromated Mo Kα radiation. Structures were solved by
1
direct methods (SHELXS-97), expanded using Fourier techniques,
2
3
J. B. Rivest and P. K. Jain, Chem. Soc. Rev., 2013, 42, 89-96.
S. Uchida, Chem. Sci., 2019, 10, 7670-7679.
2
and refined by full-matrix least squares against F with the
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