Photooxidation Reactions of Cyclometalated Palladium(II) and Platinum(II) Complexes

Article abstract of DOI:10.1021/acs.inorgchem.9b01492

New C,N,S-cyclometalated palladium(II) and platinum(II) complexes have been synthesized and their structural, electrochemical, and photochemical properties examined. The blue color of these complexes in solution changed to yellow under visible-light irrad

Full text of DOI:10.1021/acs.inorgchem.9b01492

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Photooxidation Reactions of Cyclometalated Palladium(II) and
Platinum(II) Complexes
Jun Yasuda,† Keisuke Inoue,† Koichi Mizuno,† Shiho Arai,† Koushi Uehara,† Asumi Kikuchi,†
Yin-Nan Yan,† Katsunori Yamanishi,† Yusuke Kataoka,‡ Mai Kato,§ Akio Kawai,†,§
and Tatsuya Kawamoto*,†
†Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka 259-1293, Japan
‡Department of Material Science, Interdisciplinary Graduate School of Science and Engineering, Shimane University, 1060
Nishikawatsu, Matsue 690-8504, Japan
§Department of Chemistry, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
S
* Supporting Information
ABSTRACT: New C,N,S-cyclometalated palladium(II) and platinum(II) complexes have been synthesized and their
structural, electrochemical, and photochemical properties examined. The blue color of these complexes in solution changed to
yellow under visible-light irradiation. By measurement of the absorption spectra for quantifying changes in color, isosbestic
points for each complex clearly indicated the presence of only two species responsible for the change of color. X-ray analysis
revealed that the visible-light-induced yellow species were S-oxygenated sulfinato complexes. Photosensitized generation of
singlet oxygen (1O2) was confirmed by the direct detection of singlet oxygen luminescence at 1275 nm. The present
cyclometalated palladium(II) and platinum(II) complexes are efficient photosensitizers of singlet oxygen, which rapidly reacts
with coordinating sulfur atoms.
2002,19,20 and octahedral iridium(III) complexes21−26 and
INTRODUCTION
■
square-planar platinum(II) complexes26−29 have been reported
Singlet molecular oxygen (1O2) is a reactive oxygen species,
as cyclometalated complexes that can serve as photosensitizers
for singlet oxygen.
In this study, new cyclometalated palladium(II) and
like peroxide, superoxide, etc. Because of the vital role of
singlet oxygen in oxidation reactions with various chemical and
biological molecules,1 its physical and chemical properties have
been well studied.2 Singlet oxygen also has important
platinum(II) complexes were prepared and characterized,
and we found that these complexes, not limited to the
applications in photodynamic cancer therapy and the photo-
oxidation of toxic molecules.3−6 Photosensitized generation by
platinum(II) complex, can readily be converted to the
corresponding sulfinato species under visible-light irradiation.
energy transfer from a photoexcited sensitizer to triplet oxygen
(3O2) is the most common method for singlet molecular
The production of singlet oxygen in the reactions was
confirmed by monitoring the appearance of phosphorescence
centered at 1275 nm under irradiation of the cyclometalated
complex at 355 nm.30 The results of the present study open a
new avenue for the development of efficient photosensitizers of
singlet oxygen.
oxygen generation, and organic dyes, porphyrins, phthalocya-
nine derivatives, and fullerene derivatives have been used as
photosensitizers.7−10 Recently, transition-metal complexes
have been shown to be attractive alternatives as singlet oxygen
producers, separately well-studied organic photosensi-
tizers.11−18 In particular, the cyclometalated complexes have
attracted much attention since the first report of singlet oxygen
generation by a cyclometalated iridium(III) complex in
Received: May 22, 2019
© XXXX American Chemical Society
A
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in other palladium(II) [platinum(II)] thiolate complexes.34,35
This can be explained by the strong trans influence exerted by
the cyclometalated aryl carbon atom.31−33 In contrast, the
typical Pd(Pt)−S distances in the sulfinato species can be
related to the lower trans influence, suggesting that the
oxygenated sulfur atom is a stronger π acceptor than the
coordinated thiolato sulfur atom36 and more competitive with
the cyclometalated aryl carbon atom for electron back-
donation. The SO distances of the sulfinato species were
consistent with other sulfinato metal complexes (Table S2)37
as well as the IR bands for SO2 moieties (Figures S1 and
S2).38,39
RESULTS AND DISCUSSION
■
New cyclometalated palladium(II) and platinum(II) com-
plexes with C,N,S-donor sets were isolated by column
separation of the reaction mixtures obtained by the reactions
of disulfide ligands containing Schiff base moieties with
[Pd(PPh3)4] or [Pt(PPh3)4] and characterized by elemental
analysis, 1H NMR, IR, and UV−vis spectroscopy, single-crystal
X-ray diffraction, and cyclic voltammetry.
The structures of these complexes (1a and 2a) were
determined by single-crystal X-ray diffraction (Table S1) and
are depicted in Figure 1. The blue eluates in column
The absorption spectra of the cyclometalated palladium(II)
and platinum(II) complexes showed the diagnostic peaks
responsible for their blue color at around 600 nm (Figures S3
and S4). Although this spectral feature was similar to those of
[Pt(dbbpy)(edt)] (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine
and edt = 1,2-ethanedithiolate)11 and [Pt(bpy)(bdt)] (bdt =
1,2-benzenedithiolate)12 reported by Schanze and Gray and
co-workers, respectively, which convert to sulfinato species
when irradiated with visible light in the presence of oxygen, the
long-wavelength bands of the present complexes with cyclo-
metalated tridentate ligands arise from a highest occupied
molecular orbital (HOMO)-to-lowest unoccupied molecular
orbital (LUMO) transition (Figure S5), as supported by time-
dependent density functional theory (DFT) calculations
(Table S3 and Figure S6) and are assigned as an intraligand
charge-transfer (ILCT) transition with a minor metal-to-ligand
charge-transfer (MLCT) contribution instead of a platinum/
sulfur → diimine charge transfer (MMLL′CT) observed for
[Pt(diimine)(dithiolate)] complexes composed of two biden-
tate ligands.12,40 The color changes from blue to yellow
corresponded with the disappearance of absorption bands
dominated primarily by ILCT transitions at ca. 600 nm and the
appearance of ILCT bands mixed with MLCT transitions
(HOMO−1 → LUMO) at ca. 400 nm with extinction
coefficients between 2000 and 5000 M−1 cm−1. Under aerobic
conditions, the absorption bands of 1a and 2a changed with
the photoirradiation time, and the presence of several
isosbestic points was observed (Figure 3), confirming a color
change between two clearly defined structures of the
cyclometalated complexes and the corresponding sulfinato
species (Figures S7 and S8).
Figure 1. Molecular structures of 1a and 2a with ellipsoids drawn at
the 50% probability levels. Hydrogen atoms and solvents were
omitted for clarity.
chromatography contained the cyclometalated palladium(II)
and platinum(II) complexes, and their CH2Cl2 solutions
changed color to yellow under visible-light irradiation. The
yellow solutions were also crystallized by slow evaporation (1b
and 2b), and the single-crystal X-ray diffraction data
demonstrated them to be sulfinato species in which two
oxygen atoms were bonded to the same sulfur-donor atoms in
cyclometalated ligands (Figure 2). The palladium and platinum
To explore the photosensitized formation of singlet oxygen,
we performed photooxidation of anthracene with 1a and 2a
under visible-light irradiation. However, a dichloromethane
solution of anthracene containing 1a and 2a showed no
definite change in the UV−vis spectroscopy (Figure S9). We
then tried to determine the rate constants for the quenching of
singlet oxygen by 1a and 2a for comparison because
anthracene has a known rate constant (8.5 × 105 M−1 s−1)
for the quenching of singlet oxygen in toluene.41 The
quenching rate constants were determined by a time-resolved
phosphorescence quenching method. Decay traces of singlet
oxygen phosphorescence at 1275 nm (Figure S10) were
recorded at different 1a or 2a concentrations, and the
quenching rate constants [kq = 1.10 ( 0.05) × 108 M−1 s−1
for 1a and 1.32 ( 0.02) × 107 M−1 s−1 for 2a] were evaluated
from the slopes of the Stern−Volmer plots (Figure S11).
These values are 2 or 3 orders of magnitude higher than that
for anthracene, and this is the reason why 1a and 2a were not
activatable photosensitizers for the photooxidation of anthra-
cene. Thus, 1a and 2a undergo self-sensitized photooxidation
Figure 2. Molecular structures of 1b and 2b with ellipsoids drawn at
the 50% probability levels. Hydrogen atoms and solvents were
omitted for clarity.
atoms in the cyclometalated complexes adopted a distorted
square-planar coordination geometry with S−Pd(Pt)−C angles
much smaller than 180° (Table S2).
The Pd(Pt)−N and Pd(Pt)−C distances were comparable
to those found in other Schiff base palladium(II) [platinum-
(II)] complexes,31−33 while the Pd(Pt)−S distances in the
cyclometalated complexes, except for the corresponding
sulfinato species, were significantly longer than those found
B
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features were also consistent with the results of DFT
calculations (Figure S5).
In order to better understand the mechanism of sulfinato
formation, the reactions of cyclometalated complexes with
singlet oxygen generated by the thermolysis of naphthalene
endoperoxides were carried out in the dark. The formation of
sulfinato species could be followed by monitoring of the
reduction of the absorption intensities of 1a and 2a. In fact, the
intensities of the absorption peaks at ca. 600 nm decrease
through the reactions with naphthalene endoperoxides at room
temperature in the dark (Figure S15). This result indicates that
the singlet oxygen generated via energy transfer from excited
3
1a or 2a to ground-state O2 attacks the highly electron-rich
sulfur atom of the ground-state cyclometalated complex, as
shown by DFT calculations (Figure S5), resulting in
conversion of the cyclometalated complexes to the correspond-
ing sulfinato species. DFT was also used to investigate the
nature of the intermediate in this sulfinato formation reaction,
and it established the structures of the intermediates imposed
by partial charge transfer between the electrophilic singlet
oxygen and sulfur atoms of 1a and 2a (Figure S16).11,12
A
possible mechanism for photooxidation of the cyclometalated
complex, which involves the formation of a reactive oxygen
species (1O2) and yields a very stable sulfinato species, was
thereby proposed, as shown in Scheme 1.
Scheme 1. Proposed Reaction Mechanism for the
Photooxidation of 1a and 2a
Figure 3. Time-dependent UV−vis absorption spectra of 1a (3.02 ×
10−5 M) and 2a (3.16 × 10−5 M) in dichloromethane under
photoirradiation (λ > 400 nm).
analogous to that of [Pt(diimine)(dithiolate)] complexes
reported by Schanze and Gray,11−13 leading to the formation
of only sulfinato products.
In order to prove the production of singlet oxygen by energy
transfer from the triplet excited states of 1a and 2a to the
ground state of molecular oxygen, we studied the luminescence
properties of these complexes (Figures S12 and S13). The very
weak luminescence bands overlapped with the low-energy
absorption bands (ca. 575 nm for 1a and ca. 655 nm for 2a)
were observed in the 600−750 nm region for 1a and at longer
wavelengths beyond 650 nm for 2a with lifetimes on the order
of 10−8 and 10−6 s in degassed CH2Cl2 at 77 K, respectively.
The difference of the lifetimes of 1a and 2a can be related to a
stronger singlet oxygen phosphorescence signal (Figure S10)
detected directly for 2a with longer lifetime, enabling efficient
triplet energy transfer to molecular oxygen.
The cyclic voltammograms of 1a and 2a showed quasi-
reversible redox waves in the anodic regions (Figure S14), but
sulfinato species 1b and 2b showed irreversible oxidation peaks
in the more positive potential region. These results were
related to the energies of HOMO obtained from DFT
calculations for 1a, 1b, 2a, and 2b (Figure S5) and indicate
that 1b and 2b formed by the oxidation of 1a and 2a are much
more difficult to oxidize further. Although the energies of
LUMO are not affected much by oxidation to the sulfinato
species, because the orbitals are largely localized in cyclo-
metalated ligands except for coordinated sulfur atoms, the
oxidation products 1b and 2b showed irreversible reduction
peaks at potentials slightly more positive than those for 1a and
2a in the cathodic regions (Figure S14 and Table S4). These
CONCLUSIONS AND OUTLOOK
■
In summary, the cyclometalated palladium(II) and platinum-
(II) complexes, which were prepared by the reactions of
disulfide ligands containing Schiff base moieties with [Pd-
(PPh3)4] or [Pt(PPh3)4], have potential as singlet oxygen
photosensitizers and undergo photooxidation reaction to afford
the corresponding sulfinato species. Further work will involve
the preparation of some related cyclometalated complexes. We
are working toward correlating the physicochemical properties
of palladium(II) and platinum(II) complexes to their chemical
reactivity.
EXPERIMENTAL SECTION
■
General Information. The reagents and solvents were purchased
from commercial sources (Tokyo Chemical Industry, Wako Pure
Chemical Industries, Sigma-Aldrich Japan, Kishida Chemical, Tanaka
Kikinzoku Kogyo, or Strem Chemicals) and used without further
purification. NMR spectra were recorded on a JEOL ECA-400 NMR
spectrometer with tetramethylsilane as an internal standard. IR
spectra were recorded on a Jasco FT/IR-4100 spectrometer using KBr
pellets. UV−vis absorption spectra were recorded on a Jasco V-570
spectrometer. Cyclic voltammetry was carried out with a Bas CV-
620A instrument using a three-electrode cell with a glassy carbon
C
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working electrode, a platinum wire counter electrode, and a saturated
calomel reference electrode. Elemental analyses were obtained using a
PerkinElmer 2400II CHN analyzer. Crystallographic data were
collected by a Rigaku CCD Saturn 724 system using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). Luminescence
was measured by a homemade time-resolved spectroscopic apparatus
composed of an excitation light source (Nd3+ YAG laser, Continuum
Surelite, 532 nm), a monochromator (Nikon P250), and a
photomultiplier tube (Hamamatsu Photonics R928). The sample
solution was placed in a fused-silica dewar tube, and its temperature
was kept at 77 K by liquid N2.
Preparation of the Ligand and Complexes. Ligand.
Benzaldehyde (302 mg, 2.83 mmol) was added to a solution of
2,2′-dithiodianiline (353 mg, 2.84 mmol) in 20 mL of ethanol under a
nitrogen atmosphere in a Schlenk tube. The mixture was heated under
reflux for 1 h. The resulting solution was allowed to cool to room
temperature. The solution was concentrated to half, and the
suspension was filtered. The resulting light-yellow powder (ligand)
was washed with hexane and dried in vacuo. Yield: 213 mg, 17.7%. 1H
NMR (400 MHz, chloroform-d): δ 7.07 (dd, J = 7.3 and 1.4 Hz, 2H),
7.17 (tdd, J = 14.2, 6.8, and 1.5 Hz, 4H), 7.47−7.52 (m, 6H), 7.67
(dd, J = 7.8 and 1.4 Hz, 2H), 7.96−8.00 (m, 4H), 8.50 (s, 2H). Elem
anal. Calcd for C26H20N2S2 (424.58): C, 73.55; H, 4.75; N, 6.60.
Found: C, 73.39; H, 4.71; N, 6.61.
chloroform-d): δ 6.56 (dd, J = 7.3 and 4.2 Hz, 1H), 6.78 (td, J = 7.6
and 1.5 Hz, 1H), 7.06 (td, J = 7.5 and 1.1 Hz, 1H), 7.47−7.34 (m,
8H), 7.50 (tt, J = 5.6 and 1.8 Hz, 3H), 7.58 (dd, J = 7.7 and 1.4 Hz,
1H), 7.72 (td, J = 4.8 and 3.0 Hz, 1H), 7.84−7.74 (m, 6H), 7.90 (td, J
= 5.0 and 2.4 Hz, 1H), 8.93 (d, J = 8.2 Hz, 1H). IR (KBr, cm−1):
1481, 1438, 1239, 1178 (νSO), 1098, 1064, 1038 (νSO). UV−vis
[dichloromethane; λmax, nm (ε, M−1 cm−1)]: 305 (15100), 345
(6910), 395 (4510). Elem anal. Calcd for C31H24NO2PPdS·
0.75CH2Cl2 (675.69): C, 56.44; H, 3.80; N, 2.07. Found: C, 56.36;
H, 3.83; N, 2.16.
Complex 2b. Complex 2a (20.5 mg, 30.6 μmol) in dichloro-
methane was irradiated with a xenon lamp (λ > 400 nm), and the
color of the solution changed from blue to yellow. The yellow
solution was concentrated to dryness and dissolved in a mixed solvent
of dichloromethane and methanol (19:1). The solution was poured
onto a silica gel column and eluted with the same mixed solvent. The
second yellow band (2b) was collected and concentrated to dryness.
Yield: 14.6 mg, 67.8%. 1H NMR (400 MHz, chloroform-d): δ 6.64 (d,
J = 7.3 Hz, 1H), 6.85 (dd, J = 7.6 and 6.2 Hz, 1H), 7.09 (t, J = 7.1 Hz,
1H), 7.55−7.34 (m, 12H), 7.60 (d, J = 6.4 Hz, 1H), 7.85−7.71 (m,
6H), 7.85−7.90 (m, 1H), 9.21 (d, J = 9.6 Hz, 1H). IR (KBr, cm−1):
1484, 1438, 1187 (νSO), 1099, 1069, 1038 (νSO). UV−vis
[dichloromethane; λmax, nm (ε, M−1 cm−1)]: 351 (9390), 445
(2180). Elem anal. Calcd for C31H24NO2PPtS·0.8CH2Cl2 (768.60):
C, 49.69; H, 3.36; N, 1.82. Found: C, 49.37; H, 3.36; N, 1.91.
Detection of Singlet Oxygen Generated by 1a and 2a. The
singlet oxygen quenching rate constants by 1a and 2a were
determined by means of time-resolved luminescence measurements
in the near-IR (NIR) wavelength region. A Nd3+:YAG laser
(Continuum, Surelight, 355 nm, 1 Hz operation) was utilized as
the light source. O2(1Δg) NIR phosphorescence from the sample
solutions was dispersed with a monochromator (SolarTII, MS3504)
and detected by a NIR-sensitive photomultiplier tube (Hamamatsu
Photonics, H10330-45). Unwanted scattering light was excluded by
an optical filter with a cutoff wavelength of 1100 nm. The output
signals from the detecter were recorded by an oscilloscope
(Tektronix, TDS 2022C). To determine the lifetime of O2(1Δg),
the emission at 1275 nm was monitored. This emission was generated
by photosensitization reactions of 1a or 2a with dissolved O2. Stern−
Volmer analysis in Figure S11 was done by plotting the lifetime of
O2(1Δg) under a variety of different 1a or 2a concentrations. To
obtain the dispersed spectrum of O2(1Δg) shown in Figure S10, the
phosphorescence decays at various wavenumbers were measured and
the time-integrated signal intensities at each decay were plotted
against a wavelength of around 1275 nm. There were no differences in
the O2(1Δg) phosphorescence spectra obtained by photosensitizers 1a
and 2a in dichloromethane.
A mixture of 1a (0.106 mg, 0.182 μmol) and anthracene (3.04 mg,
17.1 μmol) in 10 mL of dichloromethane was irradiated with a xenon
lamp (λ > 400 nm), and the spectral changes were monitored by UV−
vis spectroscopy. A mixture of 2a (0.118 mg, 0.176 μmol) and
anthracene (3.16 mg, 17.6 μmol) in 10 mL of dichloromethane was
irradiated with a xenon lamp (λ > 400 nm), and the spectral changes
were monitored by UV−vis spectroscopy.
Oxidation of 1a and 2a by Endoperoxide (4-Methyl-1,4-
etheno-2,3-benzodioxin-1(4H)-propanoic Acid). Complex 1a
(0.878 mg, 1.51 μmol) was added to a solution of endoperoxide (3.79
mg, 15.0 μmol) in 20 mL of chloroform under a nitrogen atmosphere
in a Schlenk tube. The mixture was warmed for 1 h at room
temperature under dark conditions. The resulting light-purple
solution was characterized by UV−vis spectroscopy. Complex 2a
(1.01 mg, 1.51 μmol) was added to a solution of endoperoxide (3.74
mg, 14.9 μmol) in 20 mL of chloroform under a nitrogen atmosphere
in a Schlenk tube. The mixture was warmed for 1 h at room
temperature under dark conditions. The resulting light-green solution
was characterized by UV−vis spectroscopy.
Complex 1a. Tetrakis(triphenylphosphine)palladium(0) (233 mg,
0.201 mmol) was added to a solution of the ligand (85.3 mg, 0.201
mmol) in 20 mL of toluene under a nitrogen atmosphere in a Schlenk
tube. The mixture was heated under reflux for 2 h. The resulting dark-
brown solution was cooled to room temperature and concentrated to
oil. The brown oil was dissolved in a mixed solvent of dichloro-
methane and hexane (3:2). The solution was poured onto a silica gel
column and eluted with the same mixed solvent. The purple band was
collected and concentrated to dryness. Crystals of 1a suitable for X-
ray crystal structure analysis were grown by the slow evaporation of a
dichloromethane solution. Yield: 32.4 mg, 27.8%. 1H NMR (400
MHz, chloroform-d): δ 6.29 (dd, J = 7.3 and 4.2 Hz, 1H), 6.57 (t, J =
7.6 Hz, 1H), 6.74 (t, J = 7.1 Hz, 1H), 6.91−6.78 (m, 2H), 7.18−7.06
(m, 2H), 7.27 (d, J = 1.4 Hz, 1H), 7.50−7.32 (m, 9H), 7.74−7.64 (m,
6H), 8.37 (d, J = 8.7 Hz, 1H). IR (KBr, cm−1): 1481, 1462, 1437,
1236, 1188, 1156, 1101. UV−vis [dichloromethane; λmax, nm (ε,
M
−1cm−1)]: 355 (6480), 577 (924). Elem anal. Calcd for
C31H24NPPdS (579.99): C, 64.20; H, 4.17; N, 2.42. Found: C,
64.15; H, 4.10; N, 2.40.
Complex 2a. Tetrakis(triphenylphosphine)platinum(0) (250 mg,
0.201 mmol) was added to a solution of the ligand (85.4 mg, 0.201
mmol) in 20 mL of toluene under a nitrogen atmosphere in a Schlenk
tube. The mixture was heated under reflux for 2 h. The resulting dark-
brown solution was cooled to room temperature and concentrated to
oil. The brown oil was dissolved in a mixed solvent of dichloro-
methane and hexane (3:2). The solution was poured onto a silica gel
column and eluted with the same mixed solvent. The blue band was
collected and concentrated to dryness. Crystals of 2a suitable for X-
ray crystal structure analysis were grown by the slow evaporation of a
dichloromethane solution. Yield: 19.1 mg, 14.2%. 1H NMR (400
MHz, chloroform-d): δ 6.32 (d, J = 7.8 Hz, 1H), 6.52 (td, J = 7.4 and
1.5 Hz, 1H), 6.67−6.58 (m, 1H), 6.87−6.72 (m, 2H), 7.09−6.95 (m,
2H), 7.14 (dd, J = 7.3 and 1.4 Hz, 1H), 7.47−7.34 (m, 9H), 7.80−
7.58 (m, 6H), 8.23 (d, J = 9.6 Hz, 1H). IR (KBr, cm−1): 1482, 1464,
1437, 1235, 1189, 1158, 1100. UV−vis [dichloromethane; λmax, nm
(ε, M−1 cm−1)]: 311 (18200), 321 (18400), 355 (7420), 656 (350).
Elem anal. Calcd for C31H24NPPtS (668.66): C, 55.68; H, 3.62; N,
2.09. Found: C, 55.76; H, 3.62; N, 2.05.
Complex 1b. Complex 1a (50.0 mg, 86.2 μmol) in dichloro-
methane was irradiated with a xenon lamp (λ > 400 nm), and the
color of the solution changed from blue to yellow. The yellow
solution was concentrated to dryness, and the residue was dissolved in
a mixed solvent of dichloromethane and methanol (19:1). The
solution was poured onto a silica gel column and eluted with the same
mixed solvent. The second yellow band (1b) was collected and
concentrated to dryness. Yield: 49.7 mg, 94.3%. 1H NMR (400 MHz,
D
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b01492.
■
S
Crystallographic data and experimental and calculated
data (PDF)
Accession Codes
CCDC 1911429−1911432 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(16) O’Donnell, R. M.; Grusenmeyer, T. A.; Stewart, D. J.; Ensley,
T. R.; Shensky, W. M.; Haley, J. E.; Shi, J. Photodriven Oxygen
Removal via Chromophore-Mediated Singlet Oxygen Sensitization
and Chemical Capture. Inorg. Chem. 2017, 56, 9273−9280.
(17) Pushpanandan, P.; Maurya, Y. K.; Omagari, T.; Hirosawa, R.;
Ishida, M.; Mori, S.; Yasutake, Y.; Fukatsu, S.; Mack, J.; Nyokong, T.;
Furuta, H. Singly and Doubly N-Confused Calix[4]phyrin
Organoplatinum(II) Complexes as Near-IR Triplet Sensitizers.
Inorg. Chem. 2017, 56, 12572−12580.
AUTHOR INFORMATION
Corresponding Author
*E-mail: kaw@kanagawa-u.ac.jp.
ORCID
Katsunori Yamanishi: 0000-0002-3141-1991
Yusuke Kataoka: 0000-0002-3587-3974
Akio Kawai: 0000-0002-7804-202X
Tatsuya Kawamoto: 0000-0002-3572-1225
■
(18) Potocny, A. M.; Pistner, A. J.; Yap, G. P. A.; Rosenthal, J.
1
Electrochemical, Spectroscopic, and O2 Sensitization Characteristics
Notes
of Synthetically Accessible Linear Tetrapyrrole Complexes of
Palladium and Platinum. Inorg. Chem. 2017, 56, 12703−12711.
(19) Gao, R.; Ho, D. G.; Hernandez, B.; Selke, M.; Murphy, D.;
Djurovich, P. I.; Thompson, M. E. Bis-cyclometalated Ir(III)
Complexes as Efficient Singlet Oxygen Sensitizers. J. Am. Chem. Soc.
2002, 124, 14828−14829.
(20) Ashen-Garry, D.; Selke, M. Singlet Oxygen Generation by
Cyclometalated Complexes and Applications. Photochem. Photobiol.
2014, 90, 257−274.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by JSPS KAKENHI Grant 25620145
and also by the Strategic Research Base Development Program
for Private Universities of the Ministry of Education, Culture,
Sports, Science and Technology of Japan.
(21) Sun, J.; Zhao, J.; Guo, H.; Wu, W. Visible-light harvesting
iridium complexes as singlet oxygen sensitizers for photooxidation of
1,5-dihydroxynaphthalene. Chem. Commun. 2012, 48, 4169−4171.
(22) Kando, A.; Hisamatsu, Y.; Ohwada, H.; Itoh, T.; Moromizato,
S.; Kohno, M.; Aoki, S. Photochemical Properties of Red-Emitting
Tris(cyclometalated) Iridium(III) Complexes Having Basic and Nitro
Groups and Application to pH Sensing and Photoinduced Cell Death.
Inorg. Chem. 2015, 54, 5342−5357.
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