Coordination behaviors of diphenylketene adsorbed in the nanocages of zeolite NaY and AgY

Article abstract of DOI:10.1246/BCSJ.20200039

We investigated in detail how polar cumulene molecules like diphenylketene were accommodated in faujasite zeolite pores based on ¹³C CP/MAS and DD/MAS NMR analyses as well as quantum chemical calculations after adsorbing the molecule into the zeolite NaY or AgY having “hard” sodium ions or “soft” silver ions. Since the diphenylketene has such a specific structure that a carbonyl group (a hard base) is accumulated by a carbon-carbon double bond (a soft π base), which is conjugated with two benzene rings (soft π bases), it is possible for the diphenylketene to adopt multicoordination modes to different metal ions in the zeolite. Compared with the coordination modes of benzophenone and 1,1-diphenylethene adsorbed in the NaY and AgY, those of diphenylketene were identified, and specific coordination behaviors in the zeolite’s supercages were classified depending on the hard or soft metal characters: The C=O and phenyl coordination modes to Na⁺ in NaY prevail, while the C=C and phenyl coordination to Ag⁺ in AgY is favored. We also unveiled the difference in the molecular mobility depending on the types of cations in the zeolite by comparing the ¹³C CP/MAS and DD/MAS NMR spectra.

Full text of DOI:10.1246/BCSJ.20200039

Document type: Article
Coordination Behaviors of Diphenylketene Adsorbed
in the Nanocages of Zeolite NaY and AgY
Shintaro Shibata,1 Yoichi Masui,1 and Makoto Onaka*2
1Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
2Faculty of Life Sciences, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
E-mail: mo206163@nodai.ac.jp
Received: February 12, 2020; Accepted: March 9, 2020; Web Released: March 14, 2020
Makoto Onaka
Makoto Onaka received his Ph.D. from The University of Tokyo under the supervision of Prof. Teruaki
Mukaiyama in 1980. He joined Prof. Yusuke Izumi’s group at Nagoya University as an assistant professor in
1981. From 1990–1991, he was a postdoc in Professor Jean-Marie Lehn’s group at Université Louis Pasteur
in Strasbourg, France. In 1995, he moved to Graduate School of Arts and Sciences, The University of Tokyo
as an associate professor, and became a full professor and then a professor emeritus in 2018. He is now a
full professor of Tokyo University of Agriculture. His research focuses on catalysis chemistry of nanoporous
inorganic materials such as zeolites, mesoporous silicates/aluminas, clays, and porous carbon nitrides
directed to organic synthesis.
Abstract
tions2 since a molecular cage derived from the self-assembly of
elaborate organic ligands directing their coordination to metal
ions was developed in the 1990s.3 Capsule- or half-bowl-
shaped organic compounds were also well-designed to isolate
labile reaction intermediates such as a carbene,4 highly-strained
cyclobutadiene5 and a hemiaminal,6 observing them live by
NMR for a relatively long period of time even at ambient
temperature. Zeolite is also such an inorganic counterpart with
uniform molecular-sized cavities surrounded by aluminosili-
cate frameworks.
We have been interested in how unstable organic molecules
are incorporated and stabilized in the nanopores of alumino-
silicate zeolite, such as the small carbonyl molecules of form-
aldehyde,7 acrolein,8 propynal,9 and diazoacetate10 as well as
cyclopentadiene11 having C=C π bonds. In these studies, we
mainly selected the sodium ion-exchanged zeolite Y (desig-
nated as NaY) from the various types of zeolite as the host
vessel for letting the sodium ions interact with the guest
molecules. NaY with a Si/Al ratio of 2.75 has the following
features: (i) it has interconnected supercages of 1.3 nm in
diameter with pore windows of 0.74 nm in diameter,12 which
are large enough to encapsulate various organic compounds;
(ii) it has four sodium ions at site II in the zeolite framework
of NaY that are tetrahedrally located on the surface of the
supercage13 and can interact with polar guest molecules; and
(iii) the guest molecules are then sufficiently activated to react
with subsequently added nucleophilic reagents in the supercage
to induce coupling reactions between them.7-11
We investigated in detail how polar cumulene molecules like
diphenylketene were accommodated in faujasite zeolite pores
based on 13C CP/MAS and DD/MAS NMR analyses as well as
quantum chemical calculations after adsorbing the molecule
into the zeolite NaY or AgY having “hard” sodium ions or
“soft” silver ions. Since the diphenylketene has such a specific
structure that a carbonyl group (a hard base) is accumulated by
a carbon-carbon double bond (a soft π base), which is conju-
gated with two benzene rings (soft π bases), it is possible for
the diphenylketene to adopt multicoordination modes to differ-
ent metal ions in the zeolite. Compared with the coordination
modes of benzophenone and 1,1-diphenylethene adsorbed in
the NaY and AgY, those of diphenylketene were identified, and
specific coordination behaviors in the zeolite’s supercages were
classified depending on the hard or soft metal characters: The
C=O and phenyl coordination modes to Na+ in NaY prevail,
while the C=C and phenyl coordination to Ag+ in AgY is
favored. We also unveiled the difference in the molecular
mobility depending on the types of cations in the zeolite by
comparing the 13C CP/MAS and DD/MAS NMR spectra.
Keywords: Zeolite NaY/AgY
j
Diphenylketene
j
Coordination modes
1. Introduction
A variety of porous organic/inorganic materials having
molecular-sized inner space have attracted much attention in
terms of applications for selective inclusion and separation of
chemicals1 as well as the promotion of specific organic reac-
For example, formaldehyde (HCHO) is so labile that it is
promptly transformed into a cyclic trimer, 1,3,5-trioxane, or a
chain-type polymer, paraformaldehyde. However, we found
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that once the HCHO molecules were adsorbed into a supercage
of NaY, they remained monomeric without oligomerization
even at room temperature.7 Our quantum chemical calculations
revealed that the HCHO was thermodynamically stabilized by
steady coordination with Na+ on the pore surface.14 If the
number of added HCHO molecules per supercage exceeded
three, their trimerization and further oligomerization started.15
In these papers, the carbonyl carbon of HCHO adsorbed on
NaY shows a lower magnetic field shift by 6 ppm in the
13C DD/MAS NMR spectra than that of the unconfined HCHO
in a CDCl3 solution.7 Such a lower magnetic field shift of a
carbonyl carbon is ascribed to the coordination of a carbonyl
oxygen to Na+ on the surface of a supercage, and is similarly
observed for acrolein,8 propynal9 and ethyl diazoacetate.10
Cyclopentadiene also shows lower chemical shifts of the sp2
carbons due to specific π-interactions with Na+.11 In addition,
such low magnetic field shifts were similarly observed when
HCHO and acrolein were adsorbed on Ag+-exchanged Y-type
zeolite (AgY), where the carbonyl oxygens coordinated to the
silver ions.16 Therefore, we can claim that the coordination
modes of an organic molecule having multicoordination sites
to metal ions can be estimated based on the chemical shift
changes in the 13C MAS NMR spectra when the molecule is
adsorbed in the zeolite.
Ketenes are composed of a carbonyl group and an accu-
mulated C-C double bond, and highly reactive toward various
nucleophiles such as water, alcohols, carboxylic acids, amines,
etc. Since the beginning of the 20th century, their synthesis and
chemical behaviors have drawn many chemists’ attention and
been extensively studied in light of organic chemistry, coordi-
nation chemistry, catalysis chemistry and physical chemistry.17
Especially, mononuclear, early to late transition metal com-
plexes18 with ketenes, such as Ti,19 Zr,20 V,21 Nb,22 Cr,23 Mo,24
W,25 Mn,26 Re,27 Fe,28 Os,29 Co,30 Rh,31 Ir,32 Ni33 and Pt,34
have been intensively developed. These ketene complexes
adopt intrinsic coordination modes of η2-C=O or η2-C=C,
depending on the types of metals with different oxophilicities,
ketenes and accompanying ligands. It was also reported that
ketene intermediates were involved in chemical processes
catalyzed by acidic zeolite.35 Ketenes are, therefore, intriguing
adsorbate molecules for zeolite chemistry in light of their com-
plex formations with metals located in the zeolite’s confined
cages: Different coordination modes, such as η2-C=O, η1-C=O
and η2-C=C, can be expected, depending on the types of
metals (Figure 1).
and Bases” theory,36 and investigated how ketene molecules
behaved in the supercages of the zeolite by comparing the
spectra of the 13C CP/MAS and DD/MAS NMR with rela-
tively simple quantum chemical calculations in order to exam-
ine which coordination modes are predominant and what trend
of chemical shift changes in the NMR spectra of the ketene
complexes are recognizable.
2. Experimental
2.1 Preparation of Adsorbed Samples and Analysis with
13C CP/MAS NMR, DD/MAS NMR and FTIR. Powder
NaY (Si/Al = 2.75, HSZ-320NAA) was obtained from the
Tosoh Corporation (Japan). AgY was prepared from NaY by
ion-exchange with aq. AgNO3, and its elemental analysis
shows a >99% ion-exchange with Ag+.
MY (M = Na or Ag) was activated in a vacuum at 400 °C,
<0.2 torr for 4 h. In a nitrogen atmosphere, 1,2-13C-labeled
diphenylketene (1), 1-13C-labeled benzophenone (2) or 1,2-13C-
labeled 1,1-diphenylethene (3) was added to MY at room tem-
perature, respectively. Each sample was determined to contain
one molecule of 1, 2 or 3 per supercage of MY. The resulting
adsorbed samples are abbreviated 1@MY, 2@MY, or 3@MY,
respectively. The 13C CP (cross polarization)/MAS (magic
angle spinning) and DD (dipole decoupling)/MAS NMR of 1
to 3@MY were measured. For the IR measurements, 13C-
unlabeled diphenylketene (1¤) was included in each activated
carrier, and applied to ATR (Attenuated Total Reflection)-FTIR
analysis.
2.2 Quantum Chemical Calculation Using MY/5T Clus-
ters. Based on the framework data of NaY from its X-ray
crystal structure analysis,37 the structure around site II of NaY
was cut out, and the terminal silicon atoms of the resulting NaY
cluster model were capped with hydrogens (Figure 2). The
NaY clusters were then optimized at the B3LYP/6-31G(d,p)
level by fixing the positions of silicon, aluminum and oxygen
using Gaussian 16.38 It is also known that AgY has the same
structure as NaY,39 so AgY clusters were created by replacing
Na with Ag with the atoms other than Ag fixed, and optimiza-
tion. For the Ag atom, SDD was used as the basis function of
the effective core potential (ECP) type.40 The clusters are repre-
sented as “MY/5T clusters,” which stand for M = Na or Ag,
and 5T = the total number (5) of silicon and aluminum atoms.
In this study, we selected zeolite Y containing not only
sodium ions as a “hard acid” for NaY, but also silver ions as a
“soft acid” for AgY that are based on the “Hard and Soft Acids
Figure 1. Possible coordination modes of a ketene mole-
cule in a supercage of zeolite Y.
Figure 2. NaY/5T cluster is cut out of the supercage
framework around site II of NaY zeolite.
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Each molecule of 1 to 3 was placed on the MY/5T cluster,
and the structure optimization and frequency calculation were
carried out at the B3LYP/6-31+G(d,p) level.41 For Ag, SDD
was used. In order to maintain the rigid pore framework of the
zeolite, the structure optimization and frequency calculation
were performed by fixing the positions of the atoms other than
an Na or Ag atom and an adsorbate. The single point energy
and NMR calculations were performed at the B3LYP/6-
311+G(2d,p) level. For Ag, SDD was used. In the single point
energy calculations, the basis set superposition error (BSSE)
was corrected using the counterpoise method.42 The differences
in the Gibbs free energy (¦G) and chemical shift (δ) between a
coordinated mode and an uncoordinated substrate were then
determined. The adsorption energy of Eads is given as follows:
200 and 202 ppm with lower chemical shifts by 3 and 5 ppm
than that for (a), respectively (Figures 3(b)-(e)). It is reason-
ably considered that 2 can adopt CO coord and/or Ph coord
modes to M+ in the zeolite. Table 1 shows the Gibbs free
energy (¦G), the adsorption energy (Eads) and the chemical
shift (δ) for each of the most stable coordinated configurations
based on the MY/5T cluster model. Comparing the CO coord
modes for 2@MY, the η1-coordination of a carbonyl oxygen to
a metal (C=O£M+) was preferred over the corresponding η2-
C=O complex. When comparing ¦G at 2@AgY/5T, CO coord
was more stable than Ph coord by +6.02 kcal/mol. For
2@NaY/5T, CO coord was much more stable by +10.96 kcal/
mol. Concerning the chemical shift of each species, the
calculated δ values of the C1 for CO coord in 2@AgY/5T and
2@NaY/5T are 212.9 ppm and 212.1 ppm, respectively, which
are lower than that of 203.6 ppm for the uncoordinated benzo-
phenone. In contrast, the δs of Ph coord for 2@MY/5T are
E
ads = E1 to 3@MY/5T ¹ (E1 to 3 + EMY/5T).
3. Results and Discussion
3.1 Synthesis 1,2-13C-Labeled Diphenylketene, 1-13C-
Labeled Benzophenone and 1,2-13C-Labeled 1,1-Diphenyl-
ethene.
We first adsorbed non-substituted ketene, H2C=
C=O, that had been prepared from diketene, in NaY, and ana-
lyzed the sample by 13C MAS NMR. Unfortunately, we could
not detect any decisive 13C signals of the ketene adsorbed on
NaY since the 13C content was only 1% in the unlabeled ketene
molecule. We then changed our strategy to employ the rela-
tively stable 143 as an adsorbate, synthesized it starting from
bromobenzene and Ba13CO3 according to Scheme 1 (see the
Supporting Information for details),44 and investigated how 1
coordinated to a sodium or silver ion in the zeolite. We expect-
ed that 1 would have three coordination modes to the Na+ or
Ag+: (1) a carbonyl group coordination (designated as “CO
coord”), (2) a carbon-carbon double bond coordination (“CC
coord”) and (3) a benzene ring coordination (“Ph coord”). We
also prepared 2, which has a carbonyl and two phenyl groups,
and 3, which has a C-C double bond and two phenyl groups,
and compared their 13C NMR spectra with the spectra of 1.
3.2 Analysis of Coordination Modes for 1-13C-Labeled
Benzophenone. Figure 3 shows the 13C NMR spectrum in
CDCl3 of 2 and 13C CP/MAS and DD/MAS NMR spectra of
2@MY. The carbonyl carbon C1 of 2 appears at 196.9 ppm in
CDCl3 (Figure 3(a)). For 2@AgY and 2@NaY, where one
supercage includes one molecule of 2, the C1 carbon appears at
Figure 3. 13C NMR spectrum of 2 in CDCl3 (a), and
MAS NMR spectra for CP of 2@AgY (b), DD of
2@AgY (c), CP of 2@NaY (d) and DD of 2@NaY (e).
O
O
Br
1) n-BuLi, THF, -78 o
C
1) SOCl2, reflux
C
*
C
*
OH
2) AlCl3, benzene, 50 o
92%
C
2) 13CO2, -78 oC to r.t.
71%
2
Table 1. Differences in calculated Gibbs free energy
(¦G), adsorption energy (Eads) and chemical shifts (δ)
for uncoordinated and coordinated modes of 2.
H2
C
*
O
Pd/C, HCO2NH4
1) n-BuLi, THF, -78 o
C
*
HC
C
*
AcOH, 110 o
95%
C
2) 13CO2, -78 oC to r.t.
85%
OH
4
O
SOCl2
Et3N
*
*
C O
*
C
HC
C
*
Et2O, 0 o
77%
C
benzene, reflux
86%
Cl
1
overall 35%
Scheme 1. Synthesis of 1,2-13C-labeled diphenylketene (1)
from bromobenzene.
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Table 2. Differences in calculated Gibbs free energy
(¦G), adsorption energy (Eads), and chemical shifts (δ)
for uncoordinated and coordinated modes of 3.
Next, the calculated δs at the C1 and C2 of each coordination
mode were compared with the δs of 164.1 ppm for C1 and 118.7
ppm for C2 of the uncoordinated molecule. The C1 and C2 of
3 in the CC coord for 3@AgY/5T were shifted to the lower
magnetic field of 175.0 ppm and the higher one of 83.2 ppm,
respectively, whereas the C1 and C2 in the Ph coord were
shifted to the higher magnetic field of 158.7 ppm and the lower
one of 127.9 ppm, respectively. Therefore, it can be estimated
that the two peaks at 106 and 153 ppm ( ) belong to the CC
coord mode and the peaks at 121 and 146 ppm ( ) are related
to the Ph coord mode.
For 3@NaY/5T, almost no difference was found between
¦G of the CC and Ph coord (¦GPh ¹ ¦GCC = ¹0.85
kcal/mol). In addition, compared to the calculated δ values
for the uncoordinated molecule 3 (C1: 164.1 ppm, C2: 118.7
ppm), the same trend of the upper or lower magnetic field shift
for C1 and C2 was calculated for CC coord (C1: 162.8 ppm, C2:
123.1 ppm) and Ph coord (C1: 157.2 ppm, C2: 136.2 ppm).
Given the above experimental and calculated results as well as
the discussion in Section 3.5, the peaks at 149 and 119 ppm in
Figures 4(d) and (e) would be derived from the coalescence of
the CC coord mode ( ) and Ph coord mode ( ).
3.4 Analysis of Coordination Modes for 1,2-13C-Labeled
Diphenylketene. Not only NaY but also AgY preferentially
coordinated to the carbonyl oxygens of α,β-unsaturated car-
bonyls like acrolein as described above. Our next concern is
to disclose whether the accumulated carbonyl molecule of
diphenylketene prefers the C=O or C=C coordination.16
Figure 5 shows the 13C NMR spectrum in CDCl3 of 1 and
the 13C CP/MAS and DD/MAS NMR spectra of 1@MY. For
the 1@MY spectra of CP and DD in Figures 5(b)-(e), the
peaks at 176 and 58 ppm were assigned to diphenylacetic acid
4 ( ) which was a side-product by the hydrolysis of 1. The
peaks at 167 to 170 ppm and 58 ppm probably corresponded
to diphenylacetic anhydride 5 ( ) formed by reacting 1 with
4, or the corresponding silanol ester formed by reacting 1 with
a silanol on the zeolite. Indeed, the direct assignment of these
Figure 4. 13C NMR spectrum of 3 in CDCl3 (a), and
MAS NMR spectra for CP of 3@AgY (b), DD of
3@AgY (c), CP of 3@NaY (d) and DD of 3@NaY (e).
almost the same as the δ of the uncoordinated benzophenone. It
can be concluded from Figures 3(b)-(e) and Table 1 that only
the CO coord mode ( or ) is predominant for both 2@AgY
and 2@NaY with the carbonyl carbon shifted to a lower mag-
netic field, which was a phenomenon similar to that of HCHO
adsorbed in NaY.7
3.3 Analysis of Coordination Modes for 1,2-13C-Labeled
1,1-Diphenylethene. The coordination modes of 3 to M+
should be CC coord and/or Ph coord. Figure 4 shows the
13C NMR spectrum in CDCl3 of 3 and the 13C CP/MAS and
DD/MAS NMR spectra of 3@MY. Carbons C1 and C2 appeared
at 150.2 and 114.5 ppm in CDCl3, respectively (Figure 4(a)).
For 3@AgY, where one molecule of 3 per supercage was
adsorbed, the four major peaks derived from C1 and C2 were
observed at 106, 121, 146 and 153 ppm in both the CP and DD
spectra of Figures 4(b) and (c). Since only 3 was detected in
the extracts from the sample of 3@AgY with methanol,
Figures 4(b) and (c) indicated the inclusion of two sets of
different coordinated species. On the other hand, carbons C1 and
C2 of 3@NaY gave peaks at 149 and 119 ppm, respectively,
in both the CP and DD spectra of Figures 4(d) and (e).
We then calculated ¦G, Eads and δ for each of the most
stable coordinated configurations by using the MY/5T cluster
model as shown in Table 2. When comparing ¦G for 3@AgY/
5T, CC coord was more stable than Ph coord by +3.79
kcal/mol. For 3@NaY/5T, Ph coord was also preferred by
¹0.85 kcal/mol.
peaks to
4 and 5 was performed by measuring the
13C MAS NMR of the separately synthesized, unlabeled diphen-
ylacetic acid (4¤) and diphenylacetic anhydride (5¤) adsorbed in
MY.45 Furthermore, a small peak near 125 ppm for the DD
measurements of 1@MY was assigned to 13CO2, which was
probably generated by the reaction of 1 with oxygen together
with 2 (Figures 5(c) and (e)).46
666 | Bull. Chem. Soc. Jpn. 2020, 93, 663–670 | doi:10.1246/bcsj.20200039
© 2020 The Chemical Society of Japan

Table 3. Differences in calculated Gibbs free energy
(¦G), adsorption energy (Eads), and chemical shifts (δ)
for uncoordinated and coordinated modes of 1.
Figure 6. Observed coordination modes for diphenylketene
adsorbed in AgY or NaY.
Figure 5. 13C NMR spectrum of 1 in CDCl3 (a), and
MAS NMR spectra for CP of 1@AgY (b), DD of
1@AgY (c), CP of 1@NaY (d) and DD of 1@NaY (e).
C1 in both CC coord and Ph coord was shifted to the higher
magnetic fields at 191.8 and 203.2 ppm, respectively, and the
C2 in CC coord and Ph coord was also shifted to the higher
magnetic fields at 38.8 and 52.3 ppm, respectively. Compared
to the Ph coord, the CC coord tends to give lower chemical
shifts. Thus, in the spectra of Figures 5(b) and (c), it can be
concluded that the peaks ( ) at 43 and 195 ppm belong to the
CC coord, and the peaks ( ) at 48 and 200 ppm are assigned to
the Ph coord as shown in Figure 6.
On the other hand, concerning ¦G for 1@NaY/5T, the order
of stability became CO > Ph coord by +0.22 kcal/mol, and the
CC coord for 1@NaY/5T was not optimized as a ground state
in the calculation. Compared with the δs of C1 = 212.9 and
C2 = 53.8 ppm for the uncoordinated 1, the calculated δs of
both the C1 and C2 for CO coord were shifted to the lower
magnetic fields at 235.5 and 57.0 ppm, respectively, whereas
the C1 and C2 for Ph coord were conversely shifted to the
higher magnetic field of 203.2 ppm and 51.7 ppm, respectively.
Consequently, in the spectrum of Figure 5(d), the two peaks
( ) at 49 and 208 ppm belong to CO coord, and the peaks ( )
at 49 and 202 ppm are attributed to Ph coord, where the peak of
49 ppm is shared by the CO coord and Ph coord as shown in
Figure 6.
The carbons C1 and C2 of 1 appeared at 201.1 and 47.0 ppm
in CDCl3, respectively (Figure 5(a)). 1 could have three coor-
dination modes of CO, CC and Ph to M+ in the zeolite. In fact,
for 1@AgY, where one supercage included one molecule of 1,
four peaks derived from the C1 and C2 appeared at 43, 48, 195
and 200 (as a shoulder) ppm in both the CP and DD spectra of
Figures 5(b) and (c). Similarly, 1@NaY gave three 13C peaks
at 49, 202 and 208 ppm in Figure 5(d) and two peaks at 49 and
208 ppm were observed in Figure 5(e).
We also calculated ¦G, Eads and δ for each of the most stable
coordinated configurations by using the MY/5T cluster as
shown in Table 3. In our calculation, when 1 has the CO coord,
the type of η1-C=O£M+ would be energetically preferred over
that of η2-C=O similar to the coordination of 2. Also, with
respect to Ph cood, η6-Ph for NaY/5T and η2-Ph for AgY/5T
are stable structure (η2-Ph for 1@NaY/5T and η6-Ph for
1@AgY/5T was not optimized as a ground state in the
calculation.).
First, the ¦G in 1@AgY/5T decreased in the order of CO >
CC º Ph coord, indicating the thermodynamic stability order
of Ph º CC > CO. The calculated δs of the C1 and C2 for each
coordinated structure were compared to those of C1 = 212.9
and C2 = 53.9 ppm for the uncoordinated 1. For 1@AgY/5T,
the C1 and C2 for CO coord were both shifted to the lower mag-
netic fields of 238.7 and 58.6 ppm, respectively. In contrast, the
3.5 Adsorption State and Mobility of Adsorbates on AgY
and NaY. The differences in Eads between the CO and Ph
coord for 2 in Table 1 definitely indicate that 2 is strongly
adsorbed on MY only by the CO coord mode. Generally, when
Bull. Chem. Soc. Jpn. 2020, 93, 663–670 | doi:10.1246/bcsj.20200039
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Figure 7. Energy diagrams for the relocation of Na+
positions between the coordination to 1 and 3 (kcal/mol).
Figure 8. Time-course of the carbonyl peaks of 1¤@Q-10
(a), 1¤@AgY (b) and 1¤@NaY (c) in the air at 34% relative
humidity at 25 °C using ATR-FTIR.
a probe molecule is restricted in motion on the solid surface,
the enhanced 13C signals are observed in the CP measurement
due to magnetization transfers through the dipolar interaction
that of 3. As the energy barrier for the coordination-site
exchange of 3 is relatively low with a faster exchange rate than
the NMR time scale, the sensitivity of the DD measurement for
3@NaY increases, and the peaks corresponding to CC and Ph
coord of 3 could be averaged to be one set of peaks as shown in
Figures 4(d) and (e).
On top of the higher barrier for the relocation of Na+ at the
Ph and CO coord sites of 1, the restricted rotation around Na+
of an η6-phenyl ring would enhance the sensitivity of the CP
spectrum in Figure 5(d) compared to the DD spectrum in
Figure 5(e).
1
between the H and 13C nuclei.47 Comparing the CP and DD
spectra of 2@AgY in Figure 3, the CP spectrum has a stronger
sensitivity than the DD one. On the contrary, for 2@NaY, the
DD spectrum is more sensitive than the CP one. Based on
the differences in sensitivity of the CP/MAS and DD/MAS
measurements and the calculated Eads, it is obvious that 2 is
adsorbed more tightly on AgY than on NaY. This is because 2
can be fixed on AgY through the stronger bonding.
Tables 3 and 2 clearly show that the Eads of 1 on AgY and 3
on AgY is negatively far greater than those on NaY. It is also
found in Figures 5 and 4 that the CP spectra of 1@AgY and
3@AgY have higher sensitivities than the corresponding DD
spectra, which is a situation similar to the spectra of 2. This is
probably because 1 and 3 are more strongly fixed on AgY than
on NaY by the interaction48 between the 4d orbital of Ag+ and
the π*C=C orbitals of 1 and 3. In Figures 4(b)-(e), therefore, it
is reasonable to conclude that the motion of 3 on AgY is more
hindered than that on NaY, so that the two sets of peaks corre-
sponding to the CC coord and Ph coord are separately
observed.
The calculations at NaY/5T in Tables 2 and 3 indicate
almost no differences in ¦G and Eads. Figure 5 shows that the
CP measurement for 1@NaY has a higher sensitivity than the
DD one. In contrast, in Figure 4, the sensitivity of the DD
measurement for 3@NaY is higher than that of the CP one.
This incompatibility would be derived from the difference in
the exchange rates between the coordination modes for 1 and 3.
Since the mutual distance between the Ph and CO coordination
sites of 1 to Na+ is longer than that between the Ph and CC
coordination sites of 3 to Na+, it can be easily estimated that
the rapid relocation of Na+ at the two coordination sites of 1 is
less energetically favored than that of 3. As shown in Figure 7,
calculating the ¦G values of the transition states (TS) between
each coordination mode revealed that the ¦G of the TS
between CO coord and Ph coord in 1@NaY/5T was +7.02
kcal/mol, and that the ¦G of the TS between CC coord and Ph
coord in 3@NaY/5T was +2.08 kcal/mol, resulting in a slower
exchange for 1 than 3 and a longer sojourn of 1 on Na+ than
3.6 Retardation of Hydrolysis for Diphenylketene in NaY
and AgY Zeolite. In order to realize how the diphenylketene
adsorbed in the zeolite cages behaves, we compared the rates of
the hydrolysis for the samples of 13C-unlabeled diphenylketene
(1¤)@NaY, 1¤@AgY and 1¤@porous silica Q-10 which were
exposed in air at 34% relative humidity at 25 °C, observing the
changes in the carbonyl absorption by ATR-FTIR (attenuated
total reflection) spectrometry (Figure 8). In this study a certain
amount of 1¤ was mixed with each carrier and placed on the
ATR apparatus to show almost the same absorbance area for
the carbonyl peak at the beginning. Q-10 is a commercially-
available, pure silica having around 10 nm-sized pores and was
used as a control carrier. We also measured the rates of the
adsorption of water into each porous carrier: Each dried carrier
was placed in a desiccator maintained at 33% relative humidity
in the presence of a saturated, aqueous MgCl2 solution at 25 °C,
and the changes in the weight of the carrier were recorded at
regular intervals, signifying that NaY and AgY zeolite had
much higher water adsorption efficiency than silica Q-10
(Figure 9).
Neat 1¤ showed a carbonyl absorption at 2,189 cm¹1, and
was simultaneously and quantitatively hydrolyzed to diphenyl-
acetic acid at RT when contacted with water.49 On the other
hand, 1¤ included in the porous carrier was gradually hydro-
lyzed depending on the carrier. Judging from the time taken for
the complete disappearance of the carbonyl peak of 1¤ (50 min
for 1¤@NaY; 30 min for 1¤@AgY and 9 min for 1¤@ Q-10), it
can be said that NaY and AgY can retard the hydrolysis of 1¤
668 | Bull. Chem. Soc. Jpn. 2020, 93, 663–670 | doi:10.1246/bcsj.20200039
© 2020 The Chemical Society of Japan

Supporting Information
The Supporting Information contains the experimental and
calculation details, the supplementary MAS NMR data and the
spectral data of 1H/13C NMR, IR and MS for the organic com-
pounds. This material is available on https://doi.org/10.1246/
bcsj.20200039.
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The present study was partially supported by JSPS
KAKENHI Grant Number JP16H04562.
We are grateful to Professor Shuichi Hiraoka of The Univer-
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670 | Bull. Chem. Soc. Jpn. 2020, 93, 663–670 | doi:10.1246/bcsj.20200039
© 2020 The Chemical Society of Japan