Design and Synthesis of Tunable Ligands with 4,4′-Bipyridyl as an Electron-Accepting Unit and Their Rhenium Complexes

Article abstract of DOI:10.1021/acs.organomet.7b00611

We have designed and prepared a series of rhenium complexes with 4,4′-bipyridyl as an electron-accepting unit. Electrochemical studies revealed that oxidation and reduction of these complexes occurred on the rhenium center and the 4,4′-bipyridyl skeleton, respectively. The redox potentials of the rhenium complexes are controllable by tuning the substituents on the 4,4′-bipyridyl skeleton and the coordinating groups to the rhenium center. We have also examined the reactivity of the rhenium complexes in electrochemical and photochemical CO₂ reduction.

Full text of DOI:10.1021/acs.organomet.7b00611

Article
pubs.acs.org/Organometallics
Design and Synthesis of Tunable Ligands with 4,4′-Bipyridyl as an
Electron-Accepting Unit and Their Rhenium Complexes
Takuto Kamatsuka, Hiroshi Shinokubo, and Yoshihiro Miyake*
Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603,
Japan
*
S Supporting Information
ABSTRACT: We have designed and prepared a series of rhenium
complexes with 4,4′-bipyridyl as an electron-accepting unit. Electro-
chemical studies revealed that oxidation and reduction of these
complexes occurred on the rhenium center and the 4,4′-bipyridyl
skeleton, respectively. The redox potentials of the rhenium complexes
are controllable by tuning the substituents on the 4,4′-bipyridyl
skeleton and the coordinating groups to the rhenium center. We have
also examined the reactivity of the rhenium complexes in electro-
chemical and photochemical CO reduction.
2
INTRODUCTION
Scheme 1. Redox Process of (a) Rhenium 2,2′-Bipyridyl
■
Complexes 1, (b) Metalloviologen Bearing a PNP Pincer
Skeleton, and (c) Rhenium 4,4-Bipyridyl Complexes 2
Development of the reduction process of carbon dioxide using
sunlight is of great importance from the viewpoint of shortage
of energy and carbon resources. Since the first report on
photocatalytic reduction of CO2 using rhenium(I) 2,2′-
bipyridyl complex 1a (R = H) by Lehn and co-workers, 1
1
,2
3
has been employed as effective catalysts for the selective
1
reduction of CO to CO. The reduction of 1 is a key step in
2
the catalytic reduction of CO , in which the 2,2′-bipyridyl unit
2
plays dual roles as both an electron acceptor from external
donors and a ligand tuning the electronic nature of the rhenium
atom (Scheme 1a). Consequently, applicable ligands for
photocatalytic systems are limited to 2,2′-bipyridyl derivatives.
To modulate the electrochemical properties of 1, sub-
stituents are often introduced on the 2,2′-bipyridyl ligand.
However, such modification simultaneously alters both the π-
accepting nature of the 2,2′-bipyridyl core and the σ-donating
nature of nitrogen atoms to the metal center. As a result, it is
difficult to control independently these two different electronic
properties of 1 and the analogous metal complexes. Because
both π-accepting and σ-donating natures of ligands are key
factors for promoting CO reduction, it is desirable to create
2
novel ligands with highly tunable electronic properties.
N,N′-disubstituted 4,4′-bipyridinium dications are called
viologens and have attracted considerable attention in various
chemical fields due to their high electron-accepting ability and
reactions (Scheme 1b). We have applied them to photocatalytic
11
4
,5
dihydrogen production. As an extension of our study, we have
synthesized a series of rhenium complexes 2 bearing a 4,4′-
bipyridyl skeleton as novel “metalloviologens” (Scheme 1c). In
order to enhance the tunability of the complexes, we have
designed 2 to separately assign the role as an electron acceptor
to the 4,4′-bipyridyl core and the role as a coordination site to
stability toward redox events.
In addition, significant
attention has been focused on 4,4′-bipyridyls bound to
transition metals, which have been called “metalloviologens”.
Interactions between metallic centers and π-conjugated 4,4′-
bipyridyl systems have been expected to enable intriguing
optical and magnetic properties and to promote unique
6
−10
reactions.
Recently, we have prepared novel PNP pincer
complexes based on N-methyl-4,4′-bipyridinium to obtain
stable complexes toward two-step single-electron-transfer
Received: August 9, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00611
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Organometallics
Article
D, which modifies the electronic nature of the rhenium center.
Herein, we have described the synthesis, structures, electronic
properties, and reactivities of the novel rhenium complexes 2.
The configuration around the Re atom of 2c adopts a typical
octahedral coordination geometry. The chloride ligand on the
Re atom is located cis to the coordinated nitrogen atoms. The
bond distance between the rhenium center and the coordinated
nitrogen of the pyridine ring (Re(1)−N(1) = 2.172(4) Å) is
RESULTS AND DISCUSSION
■
16
similar to those in 1b (R = t-Bu) (2.169(6)−2.175(6) Å).
We prepared rhenium complexes 2 bearing a 4,4′-bipyridyl
The dihedral angle (41.12(9)°) between two pyridine rings
suggests the presence of conjugation over the 4,4′-bipyridyl
unit.
unit. Treatment of ReCl(CO) with 3a in CH CN at 80 °C for
5
3
1
8 h afforded the corresponding rhenium complex 2a in 87%
yield (Scheme 2). The reactions with 3b−e bearing electron-
Figure 2 shows the electronic absorption spectra of 2c and 5
in CH Cl . The absorption band of 2c exhibits a bathochromic
Scheme 2. Synthesis of Rhenium Complexes 2
2
2
Figure 2. Absorption spectra of 2c and 5 (CH Cl ).
2
2
donating and electron-withdrawing groups on the 4,4′-bipyridyl
skeleton in toluene also furnished 2b−2e in good yields. Other
shift in comparison to that of 5, also suggesting effective π
conjugation through the 4,4-bipyridyl unit. To clarify the origin
of the absorption behavior, time-dependent density functional
theory (TD-DFT) calculations were performed at the B3LYP/
coordination sites D such as P-t-Bu and P(O)-t-Bu groups can
2
be also introduced into the rhenium complexes 2f−i. The anion
ligand exchange reaction of 2b from Cl to NCS provided the
6
-31G(d)+SDD level (Figure S1 in the Supporting Informa-
1
2
corresponding complex 4 in 84% yield (Scheme 3). From the
tion). The simulated absorption spectrum was consistent with
the experimental spectrum. On the basis of TD-DFT
calculations, the lowest energy band of 2c was assigned to
the combination of HOMO-1 → LUMO and HOMO →
LUMO transitions. The frontier orbitals of 2c indicate that the
HOMO-1 and HOMO were localized on the rhenium center,
while the LUMO was located mainly on the 4,4-bipyridyl unit
Scheme 3. Synthesis of Rhenium Complex 4
(
Figure 3). These results clearly indicate that the complexes 2
exhibit MLCT transitions.
IR spectrum of 4, the band at 2088 cm− is attributed to the
ν(NC) vibration of the NCS ligand by comparison with the
spectra of transition-metal complexes with N-bonded NCS
1
The cyclic voltammetric analysis of 2 and 4 was performed in
MeCN with 0.1 M Bu NPF as an electrolyte (Table 1). The
complexes 2a−e with a diethylamino group as a coordination
site show similar first oxidation potentials around 1.40 V. In
sharp contrast, the reduction potentials of 2a−e dramatically
4
6
1
2−14
ligands.
Recrystallization of 2c from CH Cl /hexane afforded single
crystals suitable for X-ray diffraction analysis, which unambig-
2
2
15
uously confirmed the molecular structure of 2c (Figure 1).
Figure 1. Molecular structure of 2c (atomic displacement parameters
set at 50% probability; all hydrogen atoms omitted for clarity).
Selected bond lengths (Å) and angles (deg): Re(1)−Cl(1), 2.4907(9);
Re(1)−N(1), 2.172(4); Re(1)−N(3), 2.294(4); C(24)−O(1),
1
.164(5); C(25)−O(2), 1.149(5); C(26)−O(3), 1.152(5); C(4)−
Figure 3. Frontier orbitals of 2c obtained at the B3LYP/6-
31G(d)+SDD level.
C(3)−C(8)−C(9), 41.12(9).
B
DOI: 10.1021/acs.organomet.7b00611
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Article
a
Table 1. Redox Potentials of 2 and 4 in CH CN (V vs SCE)
negligible due to both the π-accepting and σ-donating effects of
3
17
the 2,2′-bipyridyl ligand. In our case, we have found that only
complex
Eox1
Ered1
the reduction potentials of 2 affect the electrochemical
2
2
2
2
2
2
2
2
2
4
a
b
c
d
e
f
1.40
1.39
1.38
1.40
1.40
1.39
1.30
1.30
1.30
−1.51
−1.54
−1.61
−1.34
−1.26
−1.55
−1.53
−1.33
−1.26
−1.49
reactivities of 2 under CO , although electrocatalytical reduction
2
of CO by 2 has not been clarified yet at this stage. This result
2
is likely due to the separation of these two electronic effects by
the use of the 4,4′-bipyridyl ligand.
b
b
b
We conducted photochemical CO2 reduction using the
18
rhenium complexes 2a and 4 (Scheme 4). When a solution of
g
h
i
Scheme 4. Photocatalytic CO Reduction Using Rhenium
2
Complexes 2a and 4
b
1.30
a
Measurements were performed in acetonitrile with Bu NPF as an
4
6
electrolyte (0.1 M). A glassy-carbon electrode, a platinum wire, and
Ag/AgClO were used as working, counter, and reference electrodes,
4
b
respectively. Determined by differential pulse voltammetry.
change from −1.26 to −1.61 V depending on the nature of the
1
2
substituents (R and R ) on the 4,4′-bipyridyl unit. On the
1
other hand, the complexes 2b,f,g with the same backbone (R =
2
Me, R = H) exhibit similar reduction potentials (−1.53 to −
1
.55 V), while the oxidation potential of 2g (D = P(O)-t-Bu )
2
was smaller than those of 2b,f (D = NEt , P-t-Bu ). The anion
2
2
ligand exchange on the rhenium atom from Cl to NCS does not
significantly affect the oxidation and reduction potentials. These
results suggest that oxidation and reduction potentials can be
controlled independently by changing the coordination site (D)
1
2
and the substituents (R and R ) on the 4,4′-bipyridyl unit in
2a or 4 (1 mM), [Ir(bpy) (dtbpy)][BF ] (1 mM), and 1,3-
2
4
complex 2.
dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole (BIH; 100
mM) in DMF/TEOA (DMF = N,N-dimethylformamide,
TEOA = triethanolamine) was irradiated by visible light at 25
Furthermore, we investigated electrochemical reactivities of 2
toward CO . The rhenium complex 2b (E
showed a 2.1-fold current increase at the first reduction under
CO in comparison to that under N (Figure 4). Complexes 2d
1
red
= −1.54 V)
2
°C under a CO atmosphere for 2 h, no formation of CO was
2
2
2
observed (TON < 1) with the formation of a small amount of
H . After the reaction with 4, ESI-MS analysis of the resulting
2
solution indicated the formation of dihydrogen adduct 10
without detection of 4 (Figure S15 in the Supporting
Information). The complex 10 may be generated by reduction
and protonation of 4 under photochemical reduction
19
conditions to prevent the reduction of CO2.
CONCLUSION
■
We have described the synthesis and the optical and electronic
properties of a series of novel rhenium complexes 2 with 4,4′-
bipyridyl ligands. The highly tunable electronic properties of
the present 4,4′-bipyridyl ligands has been demonstrated by an
electrochemical analysis. The oxidation and reduction poten-
tials of the rhenium complexes are individually controllable by
the proper choice of coordinating groups to the rhenium center
and substituents on the 4,4′-bipyridyl skeleton. The electro-
chemical and photochemical reactivities of the rhenium
complexes have been investigated, and the reduction potentials
Figure 4. Cyclic voltammograms of 2b in CH CN under N (black
3
2
line) and under CO (green line).
2
1
(
Ered1 = −1.34 V) and 2g (E
= −1.53 V) showed similar
1
red
strongly affect the reduction of CO . On the basis of the
2
current enhancements, while complex 2e (E
= −1.26 V)
red
present findings, we are currently exploring novel complexes for
photocatalytic reduction of CO2.
showed little current increase (Figures S12−S14 in the
Supporting Information). These results suggest that the
reduction potential of 2e is too high to reduce CO2
electrochemically. Unfortunately, we have not confirmed the
formation of CO under electrochmeical reduction conditions
by GC analysis because the amount of the produced CO was
too small.
EXPERIMENTAL SECTION
■
General Considerations. H NMR (500 MHz), 13C NMR (126
1
31
MHz), and P NMR (202 MHz) spectra were recorded on a Bruker
AVANCE III HD spectrometer. Chemical shifts were reported as the δ
scale in ppm relative to CHCl (δ 7.26 ppm) or acetone-d (δ 2.05
3
6
Kubiak and co-workers reported that the reduction potentials
of 1 have some effects on the catalytic activity in the
1
ppm) for H NMR, CDCl (δ 77.16 ppm) or acetone-d (δ 29.84
3
6
1
3
ppm) for C NMR, and an external standard (H PO in D O: 0 ppm)
3
4
2
electrochemical reduction of CO but other factors are not
for 31P NMR. UV/vis absorption spectra were recorded on a Shimadzu
2
C
DOI: 10.1021/acs.organomet.7b00611
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Article
UV-2550 instrument. FT-IR spectra were recorded on a Bruker
ALPHA instrument using ATR. Mass spectra were recorded on a
Bruker microTOF apparatus using the ESI-TOF or APCI-TOF
154.1, 152.2, 147.9, 147.5, 143.8, 126.8, 123.7, 122.8, 122.0, 64.2, 55.9,
−1
51.3, 11.5, 9.2. IR (ATR): ν(CO)/cm 2015, 1911, 1879. HRMS
(ESI): calcd for C H ClBrN O Re [M − H], 623.9672; found,
18
17
3
3
method for CH CN or i-PrOH solutions. Photoirradiation was carried
623.9675. Anal. Calcd for C H ClBrN O Re: C, 34.54; H, 2.90; N,
3
18 18 3 3
out by a ASAHI SPECTRA MAX-303 (300 W) xenon light source
6.71. Found: C, 34.39; H, 2.91; N, 6.52.
with a UV cutoff filter (>385 nm, light intensity 10%). Evolved H and
Synthesis of 2e. In a 50 mL Schlenk flask were placed 3e (39.4
2
CO were quantified by gas chromatography using a Shimadzu GC-8A
instrument with a TCD detector and a SHINCARBON ST column (6
m × 3 mm). All reactions were carried out under a dry argon or
nitrogen atmosphere. Solvents were dried by the general methods and
degassed before use. Unless otherwise noted, materials obtained from
commercial suppliers were used without further purification.
mg, 0.127 mmol), Re(CO) Cl (46.0 mg, 0.127 mmol), and toluene (5
5
mL), and the mixture was stirred at 100 °C for 2 h. The resulting
mixture was concentrated in vacuo. The residue was purified by
column chromatography on SiO (eluent CH Cl /MeOH 20/1), and
2
2
2
subsequent recrystallization from CH Cl /hexane gave 2e (46.1 mg,
2
2
1
0.0748 mmol, 59% yield) as a pale yellow solid. H NMR (acetone-
d6): δ 9.03 (d, J = 6.0 Hz, 1H), 8.28 (d, J = 1.0 Hz, 1H), 8.01 (m, 3H),
5.04 (d, J = 15.3 Hz, 1H), 4.42 (d, J = 15.3 Hz, 1H), 3.63 (m, 1H),
3.45 (m, 1H), 3.22 (m, 2H), 1.33 (t, J = 7.0 Hz, 3H), 1.23 (t, J = 7.0
Synthesis of 2a. In a 20 mL Schlenk flask were placed 3a (32.1
mg, 0.133 mmol), Re(CO) Cl (48.0 mg, 0.133 mmol), and CH CN
5
3
(
6 mL), and the mixture was stirred at 80 °C for 18 h. The resulting
Hz, 3H). 13C NMR (acetone-d ): δ 199.1, 195.9, 193.8, 162.9, 154.2,
mixture was concentrated in vacuo. Recrystallization from CH Cl /
2
2
6
hexane gave 2a (63.2 mg, 0.116 mmol, 87% yield) as a pale yellow
152.0, 150.7, 146.8, 123.9, 123.0, 122.3, 64.2, 55.9, 51.3, 11.5, 9.2. IR
(ATR): ν(CO)/cm 2015, 1910, 1879. HRMS (ESI): calcd for
1
−1
solid. H NMR (acetone-d ): δ 8.99 (d, J = 6.0 Hz, 1H), 8.79 (dd, J =
6
4
=
.5 and 1.5 Hz, 2H), 8.20 (d, J = 0.5 Hz, 1H), 7.94 (m, 1H), 7.85(dd, J
4.5 and 1.5 Hz, 2H), 5.03 (d, J = 15.3 Hz, 1H), 4.42 (d, J = 15.3 Hz,
C H Cl N O Re [M − H], 613.9789; found, 613.9791. Anal. Calcd
1
8
16
3
3
3
for C H Cl N O Re: C, 35.10; H, 2.78; N, 6.82. Found: C, 35.15; H,
18 17 3 3 3
1
3
1
5
H), 3.63 (m, 1H), 3.44 (m, 1H), 3.21 (m, 2H), 1.33 (t, J = 7.3 Hz,
2.78; N, 6.78.
Synthesis of 2f. In a 50 mL Schlenk flask were placed 3f (0.57
mmol), Re(CO) Cl (206.0 mg, 0.570 mmol), and toluene (20 mL),
and the mixture was stirred at 100 °C for 6 h. The resulting mixture
was concentrated in vacuo. The residue was purified by column
H), 1.23 (t, J = 7.3 Hz, 3H). 13C NMR (acetone-d ): δ 199.1, 196.1,
6
93.8, 162.7, 154.0, 151.9, 149.6, 144.2, 123.5, 122.4, 122.3, 64.3, 55.9,
5
1.3, 11.5, 9.2. IR (ATR): ν(CO)/cm−1 2014, 1900, 1879. HRMS
(
5
7
ESI): calcd for C H ClN O Re [M − H], 546.0591; found,
18
18
3
3
46.0592. Anal. Calcd for C H ClN O Re: C, 39.52; H, 3.50; N,
chromatography on SiO (eluent CH Cl /MeOH 20/1), and
2 2 2
18
19
3
3
.68. Found: C, 39.52; H, 3.40; N, 7.59.
Synthesis of 2b. In a 20 mL Schlenk flask were placed 3b (50.4
subsequent recrystallization from MeCN gave 2f (123.5 mg, 0.195
1
mmol, 33% yield in two steps) as a pale yellow solid. H NMR
mg, 0.197 mmol), Re(CO) Cl (72.6 mg, 0.201 mmol), and toluene (5
(acetone-d ): δ 9.10 (d, J = 6.0 Hz, 1H), 8.64 (d, J = 5.0 Hz, 1H), 8.26
6
5
mL), and the mixture was stirred at 80 °C for 30 min. The resulting
(d, J = 1.5 Hz, 1H), 7.76 (dd, J = 6.0 and 2.0 Hz, 1H), 7.72 (s, 1H),
7.62 (dd, J = 5.0 and 1.5 Hz, 1H), 4.19 (m, 1H), 4.04 (m, 1H), 2.59 (s,
mixture was concentrated in vacuo. Recrystallization from CH Cl /
2
2
3
1
1
hexane furnished 2b (63.6 mg, 0.113 mmol, 57% yield) as a pale
3H), 1.48 (d, JPH = 13.5 Hz, 9H), 1.33 (d, JPH = 13.5 Hz, 9H). P{ H}
1
−1
yellow solid. H NMR (acetone-d ): δ 8.97 (d, J = 5.8 Hz, 1H), 8.65
NMR (acetone-d
1876. HRMS (ESI): calcd for C23
found, 633.1073. Anal. Calcd for C23
4.61; N, 4.42. Found: C, 43.54; H, 4.67; N, 4.41.
Synthesis of 2g. In a 50 mL Schlenk flask were placed 3g (75.1
mg, 0.218 mmol), Re(CO) Cl (79.7 mg, 0.220 mmol), and toluene (6
mL), and the mixture was stirred at 80 °C for 30 min. The resulting
mixture was concentrated in vacuo. Recrystallization from CH Cl
hexane gave 2g (80.2 mg, 0.123 mmol, 58% yield) as a pale yellow
6
): δ 61.4 (s). IR (ATR): ν(CO)/cm 2008, 1908,
PRe [M − H], 633.1081;
PRe: C, 43.56; H,
6
(
d, J = 5.0 Hz, 1H), 8.17 (d, J = 1.5 Hz, 1H), 7.91 (dd, J = 5.8 and 1.5
H
28ClN
29ClN O
2 3
2 3
O
Hz, 1H), 7.72 (s, 1H), 7.62 (dd, J = 5.0 and 1.5 Hz, 1H), 5.02 (d, J =
H
1
3
5.3 Hz, 1H), 4.40 (d, J = 15.3 Hz, 1H), 3.63 (m, 1H), 3.44 (m, 1H),
.22 (m, 2H), 2.60 (s, 3H), 1.33 (t, J = 7.0 Hz, 3H), 1.22 (t, J = 7.0
13
Hz, 3H). C NMR (acetone-d ): δ 199.1, 196.1, 193.8, 162.6, 160.7,
5
6
1
2
53.9, 151.2, 149.8, 144.4, 123.4, 122.4, 121.5, 119.3, 64.3, 55.9, 51.2,
4.6, 11.5, 9.2. IR (ATR): ν (CO)/cm−1 2016, 1901, 1875. HR-MS
/
2
2
(
5
ESI): calcd for C H ClN O Re [M − H], 560.0748; found,
1
9
20
3
3
1
60.0736. Anal. Calcd for C H ClN O Re: C, 40.68; H, 3.77; N,
solid. H NMR (acetone-d ): δ 9.16 (d, J = 6.5 Hz, 1H), 8.66 (d, J =
6
19
21
3
3
7
.49. Found: C, 40.66; H, 3.71; N, 7.48.
Synthesis of 2c. In a 50 mL Schlenk flask with a J. Young valve
5.4 Hz, 1H), 8.31 (d, J = 1.5 Hz, 1H), 7.97 (m, 1H), 7.73 (s, 1H), 7.64
(dd, J = 5.4 Hz, 1H), 4.42 (m, 1H), 4.10 (m, 1H), 2.60 (s, 3H), 1.48
3
1
1
were placed 3c (226.4 mg, 0.640 mmol), Re(CO) Cl (231.7 mg, 0.641
(d, JPH = 14.8 Hz, 9H), 1.16 (d, JPH = 14.8 Hz, 9H). P{ H} NMR
5
−1
mmol), and toluene (10 mL), and the mixture was stirred at 110 °C
for 4 h. The resulting mixture was concentrated in vacuo.
Recrystallization from CH Cl /hexane gave 2c (400.4 mg, 0.608
mmol, 95% yield) as a white solid. H NMR (acetone-d ): δ 8.94 (d, J
=
(acetone-d
HRMS (ESI): calcd for C23
found, 649.1012. Anal. Calcd for C23
4.50; N, 4.31. Found: C, 42.37; H, 4.49; N, 4.16.
Synthesis of 2h. In a 50 mL Schlenk flask were placed 3h (14.1
mg, 0.0344 mmol), Re(CO) Cl (12.4 mg, 0.0343 mmol), and toluene
(5 mL), and the mixture was stirred at 90 °C for 11 h. The resulting
mixture was concentrated in vacuo. Recrystallization from CH Cl
hexane gave 2h (10.7 mg, 0.0150 mmol, 44% yield) as a pale yellow
6
): δ 74.4 (s). IR (ATR): ν(CO)/cm 2015, 1895, 1880.
PRe [M − H], 649.1030;
PRe: C, 42.49; H,
H
28ClN O
2 4
H
29ClN O
2 4
2
2
1
6
5.5 Hz, 1H), 8.19 (d, J = 0.5 Hz, 1H), 7.94 (dd, J = 5.5 and 1.5 Hz,
H), 7.65 (s, 2H), 5.02 (d, J = 15.3 Hz, 1H), 4.39 (d, J = 15.3 Hz),
1
3
7
1
6
1
6
4
5
.64 (m, 1H), 3.44, (m, 1H), 3.21 (m, 2H), 1.42 (s, 18H), 1.33 (t, J =
.0 Hz, 3H), 1.22 (t, J = 7.0 Hz, 3H). 13C NMR (acetone-d ): δ 199.2,
/
2
6
2
96.2, 193.9, 169.8, 162.5, 153.7, 151.2, 145.3, 123.8, 122.7, 114.8,
4.3, 55.9, 51.3, 38.6, 30.4, 11.6, 9.1. IR (ATR): ν(CO)/cm 2017,
900, 1876. HRMS (ESI): calcd for C H ClN O Re [M − H],
−1
1
solid. H NMR (acetone-d ): δ 9.19 (d, J = 6.3 Hz, 1H), 8.60 (dd, J =
6
5.0 and 0.5 Hz, 1H), 8.37 (d, J = 2.0 Hz, 1H), 8.10 (d, J = 1.3 Hz, 1H),
8.02 (dd, J = 6.3 and 2.0 Hz, 1H), 7.92 (dd, J = 5.0 and 1.3 Hz, 1H).
26
36
3
3
58.1843; found, 658.1820. Anal. Calcd for C H ClN O Re: C,
26
35
3
3
31
1
−1
7.37; H, 5.35; N, 6.37. Found: C, 47.35; H, 5.29; N, 6.33.
Synthesis of 2d. In a 50 mL Schlenk flask were placed 3d (45.5
P{ H} NMR (acetone-d
6
): δ 73.4 (s). IR: ν(CO)/cm 2015, 1897,
1860. HRMS (ESI): calcd for C H BrClN O PRe [M − H],
22
25
2
4
mg, 0.142 mmol), Re(CO) Cl (51.7 mg, 0.143 mmol), and toluene (5
712.9954; found, 712.9964. Anal. Calcd for C H BrClN O PRe: C,
5
22 26 2 4
mL), and the mixture was stirred at 100 °C for 2 h. The resulting
mixture was concentrated in vacuo. The residue was purified by
column chromatography on SiO (eluent CH Cl /MeOH 20/1), and
36.96; H, 3.67; N, 3.92. Found: C, 36.55; H, 3.67; N, 3.72.
Synthesis of 2i. In a 50 mL two-neck round-bottom flask were
placed 3i (14.4 mg, 0.0361 mmol), Re(CO) Cl (13.2 mg, 0.0365
2
2
2
5
subsequent recrystallization from CH Cl /hexane gave 2d (64.4 mg,
mmol), and toluene (3 mL), and the mixture was stirred at 100 °C for
2 h. The resulting mixture was concentrated in vacuo. Recrystallization
from CH Cl /hexane gave 2i (18.1 mg, 0.0257 mmol, 71% yield) as a
2
2
1
0
.103 mmol, 73% yield) as a pale yellow solid. H NMR (acetone-d ):
6
δ 9.01, (d, J = 6.0 Hz, 1H), 8.59 (dd, J = 5.0 and 0.5 Hz, 1H), 8.23 (d,
J = 0.5 Hz, 1H), 8.10 (m, 1H), 7.97 (m, 1H), 7.91 (dd, J = 5.0 and 1.5
Hz, 1H), 5.04 (d, J = 15 Hz, 1H), 4.42 (d, J = 15 Hz, 1H), 3.63
2
2
1
pale yellow solid. H NMR (acetone-d ): δ 9.21 (d, J = 6.5 Hz, 1H),
6
8.41 (d, J = 1.5 Hz, 1H), 8.06 (m, 1H), 8.00 (s, 2H), 4.41 (m, 1H),
(
m,1H), 3.44 (m, 1H), 3.23 (m, 2H), 1.33 (t, J = 7.3 Hz, 3H), 1.23 (t,
4.11 (m, 1H), 1.49 (d, J = 14.8 Hz, 9H), 1.16 (d, JPH = 14.8 Hz,
PH
13
31
1
−1
J = 7.3 Hz, 3H). C NMR (acetone-d ): δ 199.1, 196.0, 193.8, 162.8,
9H). P{ H} NMR (acetone-d ): δ 73.4 (s). IR (ATR): ν(CO)/cm
6
6
D
DOI: 10.1021/acs.organomet.7b00611
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2
016, 1896, 1869. HRMS (ESI): calcd for C H Cl N O PRe [M −
22
24
3
2
4
ACKNOWLEDGMENTS
■
(
H], 703.0071; found, 703.0073. Anal. Calcd for C H Cl N O PRe:
C, 37.48; H, 3.57; N, 3.97. Found: C, 37.12; H, 3.50; N, 3.80.
22
25
3
2
4
This work was supported by JSPS KAKENHI Grant Number
16H01013) in Grant-in-Aids for Scientific Research on
Innovative Area “Precisely Designed Catalysts with Customized
Scaffolding” from the Japanese Ministry of Education, Culture,
Sports, Science & Technology (MEXT).
Synthesis of 4. In a 100 mL two-neck round-bottom flask were
placed 2b (53.7 mg, 0.0920 mmol), NaSCN (779.0 mg, 9.61 mmol),
EtOH (15 mL), and H O (15 mL), and the mixture was refluxed for
2
18 h. The resulting mixture was extracted with CH Cl (50 mL × 3).
2 2
Each organic layer was washed with H O, and the combined organic
2
layers were dried with anhydrous Na SO and concentrated in vacuo.
2
4
REFERENCES
■
Reprecipitation from CH Cl /hexane afforded 4 (47.1 mg, 0.0807
2
2
1
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6
2
(
d, J = 5.8 Hz, 1H), 8.66 (d, J = 5.3 Hz, 1H), 8.28 (d, J = 1.5 Hz, 1H),
7
1
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(
2
1
3
C NMR (acetone-d ): δ 197.1, 195.6, 194.1, 162.3, 160.8, 154.3,
6
1
1
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HR-MS (ESI): calcd for C H N O ReS [M − H], 583.0807; found,
20
20
4
3
5
83.0795. Anal. Calcd for C H N O ReS: C, 41.16; H, 3.63; N, 9.60.
20 21 4 3
Found: C, 41.05; H, 3.75; N, 9.29.
Electrochemical Measurement. Electrochemical measurements
were recorded on an ALS 612C electrochemical analyzer. Measure-
ments of the rhenium complexes (0.5 mM) were performed in
acetonitrile with nBu NPF as an electrolyte (0.1 M). A glassy-carbon
2
(
4
6
electrode, a platinum wire, and Ag/AgClO were used as working,
4
counter, and reference electrodes, respectively. The scan rate was 100
−1
mV s . The measurements were performed after bubbling of nitrogen
gas or carbon dioxide gas for 5 min. All potentials are referenced to the
potential of the ferrocene/ferrocenium cation couple and converted
(
1
1
(
20
into the values vs SCE.
Photocatalytic Reduction of CO Using 4. In a 18 mL test tube
2
were placed BIH (44.9 mg, 0.20 mmol), [Ir(ppy) (dtbpy)][BF ] (2.0
2
4
μmol), the rhenium complex 4 (2.0 μmol), and DMF/TEOA (5/1 v/
(
v, 2 mL). The mixture was saturated with CO by bubbling the gas for
2
30 min. The resulting reaction mixture was stirred and irradiated by
(
(
visible light (λ >385 nm) for 3 h. The amounts of produced CO and
H were quantified by gas chromatography analysis of 500 μL samples
2
of the headspace.
ASSOCIATED CONTENT
■
*
S
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00611.
Experimental procedures, spectroscopic data, and X-ray
data (PDF)
1
2
25, 5610. (m) Liard, D. J.; Kleverlaan, C. J.; Vlce
003, 42, 7995. (n) Coe, B. J.; Foxon, S. P.; Harper, E. C.; Helliwell,
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Soc. 2010, 132, 1706. (o) Kuchison, A. M.; Wolf, M. O.; Patrick, B. O.
Dalton Trans. 2011, 40, 6912.
CCDC 1544312 contains the supplementary crystallographic
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
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AUTHOR INFORMATION
■
*
Corresponding Author
E-mail for Y.M.: miyake@chembio.nagoya-u.ac.jp.
ORCID
2
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Hiroshi Shinokubo: 0000-0002-5321-2205
Yoshihiro Miyake: 0000-0003-0247-531X
2
Notes
(
́
ez, J. P.; Dong, W.-F.
The authors declare no competing financial interest.
Chem. Commun. 2005, 2119. (b) Arm, K. J.; Leslie, W.; Williams, J. A.
E
DOI: 10.1021/acs.organomet.7b00611
Organometallics XXXX, XXX, XXX−XXX

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27 37
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7
1
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DOI: 10.1021/acs.organomet.7b00611
Organometallics XXXX, XXX, XXX−XXX