Inorganic Chemistry
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of heavy atoms to enable access to the photoexcited triplet
state via intersystem crossing for an efficient electron-transfer
process. FC-I also presented long-term stability, and its
heterogeneous nature made it recyclable. Our mechanistic
and the residue was then purified on silica gel over an autocolumn
chromatograph using hexane/ethyl acetate [60:40 (v/v)] as the eluent
1
to afford a white solid of compound 1 (91% yield). H NMR (400
MHz, CDCl ): δ 10.02 (s, 1H, ArCHO), 8.10 (d, J = 8 Hz, 2H, ArH),
3
7
.87 (d, J = 8 Hz, 2H, ArH), 3.88 (s, 3H, ArCOOCH ) ppm.
Synthesis of 4,4-Difluoro-8-[4-(methoxycarbonyl)phenyl]-
3
investigation suggested that the intramolecular oxidative
3
quenching of BDP-I* by the Rh center was a key step in
2
1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-4-bora-s-indacene (2). A
total of 468 mg (2.86 mmol) of 4-formylbenzoate (1) was added to
a 200 mL flame-dried three-necked flask. The compound was
degassed for 30 min before being substituted with argon gas. Then
anhydrous DCM (50 mL) was added to flask, followed by the
dropwise addition of 2,4-dimethylpyrrole (546 mg, 5.74 mmol). Then
II
I
generating the catalytically active Rh Rh -H species. Our
results offer a novel strategy for developing highly ordered
molecule-based heterogeneous systems for visible-light-driven
HER.
2
drops of TFA was added, and the mixture was stirred under an
EXPERIMENTAL SECTION
■
argon atmosphere for 18 h at room temperature. After 1 was totally
consumed, which was monitored by TLC (eluent DCM), 648 mg
(2.85 mmol) of DDQ was added to the reaction mixture, and stirring
was continued for 30 min. The reaction mixture was brought to 0 °C
before absolute TEOA (3.5 mL) was added dropwise. After stirring
Chemicals and Materials. All solvents were purchased from
Wako Pure Chemical Industries, while 4-formylbenzoic acid, 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), a boron trifluoride
ethyl ether complex (BF ·OEt ), and N-iodosuccinimde (NIS) were
3
3
purchased from Tokyo Chemical Industry (TCI). 2,4-Dimethylpyr-
role was acquired from either TCI or Sigma-Aldrich. Triethylamine
was purchased from Wako, dried by reflux over CaH , distilled under
argon, and kept in the dark with KOH pellets. Trifluoroacetic acid
TFA) and o-dichlorobenzene (o-DCB) were also purchased from
was continued for another 15 min, 3.50 mL of BF ·OEt was added.
3 3
The reaction mixture was stirred for the next 2 h, and a gradual
increase of green emission under UV-light irradiation was observed.
After the reaction, the mixture was passed through a silica flash
column chromatograph using DCM as the eluent to remove the
undesired solid. The organic phase with strong green emission was
collected and evaporated by a rotary evaporator. The crude residue
was purified on silica gel over an autocolumn chromatograph using
2
(
23
Wako. Rh (CO CH ) were prepared by a literature method. All
2
2
3 4
syntheses were performed under an atmosphere of dry nitrogen or dry
argon unless otherwise indicated.
Instrumentations. Silica-gel column chromatography was per-
formed on a Biotage (Isolera One) autocolumn chromatograph
DCM as the eluent to afford compound 2 as red crystals (19% yield).
1
H NMR (400 MHz, CDCl ): δ 8.19 (d, J = 8.0 Hz, 2H, ArH), 7.42
3
equipped with SNAP Ultra (ultrahigh-performance silica column with
(d, J = 8.0 Hz, 2H, ArH), 6.00 (s, 2H, pyrrole H), 3.98 (s, 3H,
1
19
25 μm particle size). H NMR spectra were acquired on a JEOL JNM-
COOCH ), 2.57 (s, 6H, pyrrole CH ), 1.37 (s, 6H, pyrrole CH ).
F
3
3
3
LA400 spectrometer, where chemical shifts in MeOD-d or CDCl
NMR (376 MHz, CDCl ): δ −146.08 (d, J = 34.7 Hz), −146.26 (d, J
4
3
3
1
9
were referenced to internal tetramethylsilane. F NMR spectra were
acquired on a JEOL JNM-LA400 spectrometer, where chemical shifts
in MeOD-d4 or CDCl3 were referenced to external standard
trifluorotoluene. Elemental analyses were carried out on a J-SCIENCE
LAB MICRO CORDER JM10 elemental analyzer. UV−vis
absorption and diffuse-reflectance UV−vis spectra were recorded on
a Shimadzu UV-3600 UV−vis−near-IR spectrophotometer. A white
= 28.9 Hz).
Synthesis of 4,4-Difluoro-8-(4-carboxyphenyl)-1,3,5,7-tetra-
methyl-4-bora-3a,4a-diaza-4-bora-s-indacene Acid (BDP-H). The
synthesis of BDP-H was performed using the modified method
25
reported in the literature. Compound 2 (650 mg, 1.70 mmol) was
dissolved in MeOH (150 mL), and then 10 mL of 0.2 N NaOH was
added dropwise. The mixture was refluxed at 80 °C for 4 h. The
reaction completion was monitored by TLC (eluent 80:20 ethyl
acetate/hexane). Then the reaction mixture was evaporated and
acidified by 2 N HCl. The aqueous phase was extracted with ethyl
acetate until the green emission was diminished. The organic layers
were combined, dried over anhydrous Na SO , filtered, and
standard of BaSO was used as the reference for diffuse-reflectance
4
spectroscopic measurements. The photocatalytic studies were
performed by using a xenon lamp (λ > 420 nm, 300 W) equipped
with a CM-1 cold mirror. Gas analysis for H was performed using a
2
Shimadzu GC-2014 gas chromatograph equipped with a thermal
conductivity detector and fitted with a molecular sieve 5A column
2
4
evaporated. The crude was purified by silica gel autocolumn
(
argon carrier gas), calibrated with standard H (4990 ppm of H in
chromatography using chloroform/MeOH [95:5 (v/v)] as the eluent
2
2
1
argon). Electrospray ionization time-of-flight mass spectrometry (ESI-
TOF-MS) spectra were recorded on a JEOL JMS-T100LP mass
spectrometer. All of the ESI-TOF-MS measurements were recorded in
the positive-ion mode at a cone voltage of 20 V. Cyclic
voltammograms were measured at room temperature on a BAS
ALS model 650DKMP electrochemical analyzer. Measurements in
solution were performed in THF (sample = 0.5 mM; 0.1 M tetra-n-
to afford BDP-H as red-to-purple crystals (82% yield). H NMR (400
MHz, MeOD-d ): δ 8.20 (d, J = 8.0 Hz, 2H, ArH), 7.48 (d, J = 8.0
4
Hz, 2H, ArH), 6.09 (s, 2H, pyrrole H), 2.50 (s, 6H, pyrrole CH ),
3
1
9
1.41 (s, 6H, pyrrole CH3). F NMR (376 MHz, MeOD-d ): δ
4
−146.98 (d, J = 32.2 Hz), −147.16 (d, J = 33.3 Hz). Elem anal. Calcd
for C H N O BF (BDP-H·0.25H O): C, 64.45; H, 5.20; N,
2
0
19.5
2
2.25
2
2
7.61. Found: C, 64.18; H, 5.21; N, 7.38. Crystals of BDP-H suitable
butylammonium perchlorate as an electrolyte). A glassy carbon disk, a
for single-crystal X-ray structural determination were obtained by the
+
platinum wire, and Ag/Ag (Ag/0.01 M AgNO ) were used as the
vapor diffusion of Et O into a chloroform solution of BDP-H.
3
2
working, auxiliary, and reference electrodes, respectively. The
potentials in THF were corrected by employing a ferrocene/
Synthesis of 4,4-Difluoro-8-(4-carboxyphenyl)-2,6-diiodo-
1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-4-bora-s-indacene Acid
(BDP-I). The synthesis of BDP-I was performed using the modified
+
ferrocenium (Fc/Fc ) couple as the internal standard. Measurements
26
in the solid state were performed in an acetate buffer, and a glassy
carbon disk or glassy carbon plate, a platinum wire, and a saturated
calomel electrode were used as the working, auxiliary, and reference
electrodes, respectively.
method reported in the literature. BDP-H (3.0 g, 8.15 mmol) and
NIS (7.43 g, 33.0 mmol) were dissolved in 50 mL of DCM. After the
mixture was stirred for 12 h, it was quenched with aqueous NaHCO
The aqueous phase was extracted with DCM (50 mL × 3). The
combined organic phase was dried over anhydrous Na SO , filtered,
.
3
2
4
Synthesis. Synthesis of Methyl 4-Formylbenzoate (1). To 4-
2
4
formylbenzoic acid (1.00 g, 7.24 mmol) in superdehydrated MeOH
and concentrated in vacuo to afford a crude solid. The crude was
purified by silica gel autocolumn chromatography using chloroform/
(
200 mL) was added dropwise at 0 °C thionyl chloride (SOCl ; 6.00
2
mL, 7.24 mmol) until all compound dissolved. The reaction was
slowly brought to room temperature and then stirred for another 2 h.
The reaction was monitored by thin-layer chromatography (TLC;
eluent 60:40 hexane/ethyl acetate). After all of the starting compound
was consumed, the solvent was then removed in vacuo by
coevaporation with DCM (3 × 50 mL) to remove excess SOCl2,
MeOH [97:3 (v/v)] as the eluent to afford BDP-I as deep-red
1
crystals (80% yield). H NMR (400 MHz, THF-d ): δ 11.64 (b, 1H,
8
COOH), 8.24 (d, J = 8.0 Hz, 2H, ArH), 7.50 (d, J = 8.0 Hz, 2H,
1
9
ArH), 2.60 (s, 6H, pyrrole CH ), 1.40 (s, 6H, pyrrole CH ). F NMR
3
3
(376 MHz, THF-d ): δ −150.92 (d, J = 32.2 Hz). Elem anal. Calcd
8
for C H I N O BF : C, 38.75; H, 2.76; N, 4.52. Found: C, 39.00; H,
20
17 2
2
2
2
G
Inorg. Chem. XXXX, XXX, XXX−XXX