A supramolecular assembly bearing an organic TADF chromophore: synthesis, characterization and light-driven cooperative acceptorless dehydrogenation of secondary amines

Article abstract of DOI:10.1039/c9dt00407f

A noble-metal-free chromophore-catalyst supramolecular assembly, which is composed of an organic thermally activated delayed fluorescence (TADF) chromophore and cobaloximes, has been designed and synthesized for the first time for the efficient acceptorle

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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A supramolecular assembly bearing organic TADF chromophore:
synthesis, characterization and light–driven cooperative
acceptorless dehydrogenation of secondary amines
Received 00th January 20xx,
Accepted 00th January 20xx
Duobin Chao* and Mengying Zhaob
a
DOI: 10.1039/x0xx00000x
www.rsc.org/
A noble–metal–free chromophore–catalyst supramolecular assembly, which is composed of organic thermally activated
delayed fluorescence (TADF) chromophore and cobaloximes, has been designed and synthesized for the first time for
efficient acceptorless dehydrogenation of secondary amines under blue light irradiation at room temperature. The TADF
chromophore has a long lifetime of 17.4 μs with suitable redox potentials for selective acceptorless dehydrogenation of
secondary amines to afford imines and H
supramolecular assembly. high TON of 895 was obtained for acceptorless dehydrogenation of 1,2,3,4–
tetrahydroisoquinoline despite its high oxidation potential (+ 1.38 V vs. SCE).
2
through cooperative catalysis of the chromophore and cobaloximes in the
A
(
Br and I) is strongly required to achieve long–lived excited
Introduction
state to achieve efficient catalysis, resulting in more
complicated synthetic routes and poorer photophysical
properties. Donor–acceptor (D–A) organic chromophores show
intramolecular charge transfer upon light irradiation and may
have long lifetimes such as thermally activated delayed
fluorescence (TADF) compounds with no need of
Chromophore–catalyst supramolecular assemblies have been
employed as considerable photocatalysts in many
homogeneous and heterogeneous light–driven processes such
as hydrogen evolution,1 carbon dioxide reduction, dye–
sensitized photoelectrochemical cells (DSPEC) and organic
transformations6, 7. In general, light–absorbing chromophores
are covalently linked to specific catalysts through a bridging
ligand in supramolecular assemblies and then undergo
cooperative catalysis with adjacent catalysts. The
chromophores play vital roles in light harvesting and electron
transfer processes, and they are commonly composed of
2
12
13
3
‐5
halogenation, which have been investigated in biosensing,
OLEDs,14 solar cells15 and photocatalytic reactions . Moreover,
synthetic routes of D–A type TADF chromophores are well
investigated and their photophysical properties and redox
16
1
7
potentials are tunable as noble metal complexes. In this
context, organic TADF chromophores may be good candidates
to
construct
chromophore–catalyst
supramolecular
III8
II9
assemblies. Chromophore–catalyst supramolecular assemblies
bearing such D–A type TADF chromophores for photocatalytic
reactions have yet to be explored.
Catalytic acceptorless dehydrogenation (CAD) is an
attractive strategy for hydrogen release from liquid organic
hydrogen carriers (LOHCs) that are believed as potential
transition meal complexes such as Ir and Ru complexes.
These transition metal complexes have long excited–state
lifetimes and tunable redox potentials that make them capable
of promoting various photocatalytic reactions. However,
ruthenium and iridium are rare and noble metals. Therefore,
non–precious organic chromophores with long lifetimes are
promising for constructing supramolecular assemblies.
Although several organic chromophores such as BODIPY
materials for hydrogen storage due to reversible
8‐20
hydrogenation
and
dehydrogenation.1
However,
compounds10 and fluorescein11 have been employed to
acceptorless dehydrogenation of LOHCs is rarely conducted
under mild conditions due to high temperature.2
1, 22
Secondary
construct supramolecular photocatalysts, substrates with low
oxidation potentials (e. x. TEA and TEOA) are required as well
as limited turnover numbers (TONs). Moreover, halogenation
amines usually have low melting points and some secondary
amines are liquid at room temperature, which makes
secondary amines as potential nitrogen–containing LOHCs
using reversible conversion between secondary amines and
imines.23 Highly efficient and selective acceptorless
a.
School of Materials Science and Chemical Engineering, Ningbo University,
2
dehydrogenation of secondary amines along with H release is
Zhejiang 315211, China. Email: chaoduobin@nbu.edu.cn
School of Petroleum and Chemical Engineering, Dalian University of Technology,
b.
poorly investigated in homogeneous catalysis. Most
procedures for oxidative dehydrogenation of secondary
amines in the presence of stoichiometric oxidants could not
Panjin, Liaoning 124221, China.
Electronic Supplementary Information (ESI) available: NMR spectra and HRMS
†
spectra. See DOI: 10.1039/x0xx00000x
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Fig. 1 HOMO and LUMO for chromophore
calculations.
ionization mass spectrometry (HR–ESI–MS). The m/z signal at
1 by DFT
Scheme 1 Dehydrogenation of secondary benzylamine.
.24,
25
2538.4026 (calcd. 2538.4212) in the MS spectrum of 1–Co is
release H
2
Szymczak and co–workers reported solely
+
selective acceptorless dehydrogenation of secondary amines assigned to species [M + Na] (M = 1–Co) (Fig. S1), suggesting
1
II
III moieties. Additionally,
to imines (e.x. secondary benzylamine) using a noble Ru
was successfully tethered to four Co
o
26
catalyst at 110 C after 24 h (Scheme 1). Additionally, the isotopic signals are distributed with an interval of 1 in
+
turnover number (TON) of CAD reactions was relatively low accordance with +1 charge of species [M + Na] (Fig. S2). The
(
~50). It remains a challenge to achieve noble–metal–free cobaloxime Co(dmgH)
2
PyCl is
a
well–known hydrogen
acceptorless dehydrogenation of secondary amines with high evolution catalyst that has been used with various
TON and selectivity at room temperature. On the other hand, photosensitizers.2
7‐29
Thus, we chose it to collaborate with
1
CAD of amines provides an alternative to obtain imines with and examine performance of
high atom economy. As a proof of concept, we herein report photocatalyst 1–Co
1
in the supramolecular
.
the first supramolecular assembly which consists of D–A type
TADF chromophore and Co moieties for CAD of secondary
amines at room temperature under visible light irradiation.
We further found 1 could absorb moderate visible light
III
(Fig. S3). Its emission was structureless and centered at 591
nm with a relative quantum yield of 7.2 % in dichloromethane
2+
3
using [Ru(bpy) ] as the standard (Fig. S3). The broad emission
showed blue shift in solvents with lower polarity such as THF
and toluene (Fig. S4), suggesting intramolecular charge
Results and discussion
The assembly 1–Co, which looks like an android (four CoIII
complexes as the legs and arms and
has been prepared facilely as shown in Scheme 2. 1–Co was
transfer of
D–A nature of
calculation was then carried out to confirm the D–A structure
Fig. 1 and S5). The highest occupied molecular orbital (HOMO)
of is mainly delocalized over the electron–rich carbazolyl
groups as the donor (D) and the lowest unoccupied molecular
orbital (LUMO) of is mainly distributed on the electron–
1. This solvatochromic effect can be ascribed to the
1
. The density functional theory (DFT)
1 as the body and head),
(
first characterized by NMR and high–resolution electrospray
1
1
deficient benzonitrile groups as the acceptor (A). Moreover,
III
similar DFT results were observed when one Co moiety was
tethered to
1 (Fig. S6). A charge transfer (CT) state from
carbazolyl groups to benzonitrile groups can be expected upon
light irradiation.
The HOMO and LUMO are highly isolated and ΔEST of
1 was
found to be 0.13 eV, which are characteristic nature for D
–
A
type TADF compounds.17 It is known that long–lived charge
transfer state is important for transition metal complexes to
mediate electron transfer processes in photocatalytic
reactions. We then found the photoluminescence lifetime of
1
was 17.4 μs in degassed dichloromethane at room
temperature (Fig. S7), which was comparable to lifetimes of
polypyridine ruthenium(II) complexes such as popular
2
+
[
Ru(bpy)
time for
demonstrate chromophore
3
]
(0.87 μs). Such a long lifetime ensures sufficient
to promote photocatalytic reactions. These results
possesses appropriate
1
1
photophysical properties as an efficient photosensitizer in
photoredox catalysis under visible light irradiation.
Redox potentials of
of ground state and excited state were further studied to
confirm thermodynamic feasibility of electron transfer
1 including electrochemical properties
Scheme 2 Synthetic routes of chromophore
1
and assembly 1–
o
o
Co. a) K
c) CH Cl
2
CO
3
, DMF, 70 C and 12 h; b) NaH, THF, 40 C and 16 h;
2
2
/CH
3
OH (v/v = 1:1), NEt
3
, 12 h and room temperature.
between
programs of
1
and Co(dmgH)
1
PyCl. The cyclic voltammetry (CV)
2
showed the oxidation potential E( +
1
/
1) (
1
+
=
2
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oxidized
ARTICLE
1
) was + 1.39 V vs. SCE (Fig. S8). According to the Table 1 Photocatalytic acceptorless dehydrogenation of 2a.a
ground–state oxidation potential and zero−zero excitaꢀon
energy (E0, 0 = 2.10 eV) that was calculated from the emission
+
of
was determined as – 0.71 V vs. SCE (E(
Thus, the oxidative quenching of excited state of
1
at 591 nm, the excited–state oxidation potential E(
1
/
1*
)
+
+
) – E0, 0).30
Entry Variation
conditions
from
the
standard TON
(H
)b
1 /1*) = E(1 /1
1
(
1*) by
vs. SCE) is
0.04 eV). The
fluorescence titration experiments further verified that 1* can
be oxidatively quenched by Co(dmgH) PyCl (Fig. S9).
The assembly 1–Co displayed weaker emission than
chromophore with a quantum yield of 2.9% and the
absorption spectrum is similar to
2
III
II
1
2
3
4
5c
6
none
no visible light
305
0
60
0
53
0
0
Co(dmgH)
2
PyCl (E(Co /Co )
=
–
0.67
V
thermodynamically available (ΔG
=
–
no THF, CH
3
CN as the solvent
2
no 1–Co
no 1–Co, adding
no 1–Co, adding CoIII
no 1–Co, adding
no 1–Co, adding [Ru(bpy)
1
and CoIII
1
1
(Fig. S10). The quenching of
7
8d
1
III
emission was probably due to electron transfer from
1
to Co .
]2+ and CoIII
3
0
III
Energy transfer between
emission of
1
and Co is negligible because the
lies beyond absorption of Co . The emission
aStandard conditions: 2a (0.5 mmol), 1–Co (0.2 μmol) and THF
III
1
(
8 mL) under blue light irradiation for 12 h at room
lifetime of 1–Co decreases a little bit by comparison with
was determined to be 13.8 μs (Fig. S11), indicating Co has
1
and
b
c
2
temperature. TON = n(H )/n(chromophore). 1 (0.2 μmol) and
III
III
d
2+
III
Co (0.8 μmol). [Ru(bpy)
probably due to ligand disassociation in CH
studied by Eisenberg and co workers. A lower TON of 53 was
observed for the multicomponent system including separated
and Co(dmgH) PyCl (Table 1, entry 5). The higher TON for
supramolecular photocatalytic system is probably due to more
feasible electron transfer from 1* to Co(dmgH) PyCl when they
are linked through covalent bond. Additionally, emission of is
3
]
(0.2 μmol) and Co (0.8 μmol).
slight influence on the photophysical properties of
Nevertheless, redox potentials of separated
Co(dmgH) PyCl were observed in the CV spectrum of assembly
–Co (Fig. S12). For instance, the irreversible redox waves at –
1.
and
3
CN that has been
1
–
2
1
0
1
2
III
II
+
.63 V and + 1.38 V vs. SCE are assigned to Co /Co and
1
I
/1,
II
respectively. The reduction potentials of
approximate and overlapped around –1.12 V vs. SCE. These
1
and Co /Co are
2
8
1
results suggest two components
significant electronic interaction at ground state in the
supramolecular assembly 1–Co
Encouraged by feasible electron transfer between 1* and
2
1 and Co(dmgH) PyCl have no
barely quenched by 2a according to titration experiment (Fig.
S13). Then we can conclude that the catalytic cycle begins with
.
oxidative quenching of 1* by Co(dmgH)
covalent linkage is positively helpful for oxidative quenching of
by Co(dmgH) PyCl, resulting in higher efficiency when
2
PyCl. That is to say,
Co(dmgH)
Co(dmgH)
2
PyCl, we next employed assembly 1–Co
PyCl (abbreviated as Co ) in photocatalytic CAD of
,
1
and
1
*
2
III
2
assembly 1–Co was used. We further found imine 3a was
generated by H NMR, indicating successful acceptorless
dehydrogenation of 2a with H release. Control experiments
2
showed that visible light and two components were all
required to achieve efficient acceptorless dehydrogenation,
indicating the catalytic cycle is light–driven cooperative
catalysis process. We examined performance of [Ru(bpy)
for CAD of 2a. However, unlike CAD of 2–MeTHQ (THQ =
secondary amines. Initially, secondary benzylamine 2a was
used as the substrate to examine generation of imine and H in
dry THF. Dry THF was used here to ensure 2a as the only
hydrogen source of H . As shown in Fig. 2, efficient H release
1
2
2
2
was observed in degassed dry THF solution containing 1–Co
and 2a upon light irradiation with blue LEDs at room
temperature. A TON of 305 was obtained after 12 h of
irradiation (Table 1, entry 1). However, 1–Co displayed much
lower TON when CH3CN was used as the solvent, which is
2+
3
]
2
+31
tetrahydroquinoline) with [Ru(bpy)
found (Table 1, entry 8). This is probably due to high oxidation
3
]
2
, no detectable H was
+
•
potential of 2a (EOx
which is higher than Ru(bpy)
It is worth mentioning that light–driven CAD of secondary
amine 2a for H release is significantly different from H
evolution from water using tertiary amines such as TEA
Eo (TEA) = + 0.69 V vs. SCE) as substrate, because tertiary
(2a /2a) = + 1.37 V vs. SCE) (Fig. S15),
2+
III/II
3
(E(Ru ) = + 1.29 V vs. SCE).
2
2
(
x
amines have much lower oxidation potentials than 2a. When
III
tertiary amines were used, photosensitizers (e. x. Ir
complexes) are commonly reductively quenched by TEA.
Additionally, tertiary amines are decomposed along with
generation of complicated by–products that could not undergo
release from 2a (0.5 mmol) with reversible dehydrogenation–hydrogenation process.32
Acceptorless dehydrogenation of other secondary amines
2c and 2d was also investigated (Table 2). A
Fig. 2 Time–dependent H
assembly 1–Co (0.2 μmol) and separated system containing
0.2 μmol) and Co(dmgH)
PyCl (0.8 μmol) in THF (8 mL) at including 2b,
2
1
(
2
room temperature under blue light irradiation.
higher TON of 360 was obtained for the substrate with low
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Table
2 Photocatalytic acceptorless dehydrogenation of
a
various secondary amines.
Entry Substrate
1
Product
Sel. (%) TON (H
2
)b
99
99
99
360
301
50
2
3
4
96
96
98
895
538
604
5c
6d
Fig. 4 Plausible mechanism for CAD of 2e using 1–Co
.
aStandard conditions: substrate (0.5 mmol), 1–Co (0.2 μmol)
of 2a upon light irradiation. As can be seen from Fig. 3, at t = 0
min, no obvious absorption peak was observed from 400 to
500 nm. After the solution was irradiated for 4 min, the
absorption increased and a shoulder peak appeared in the
range of 400 to 500 nm. The enhancement was ascribed to
and THF (8 mL) under blue light irradiation for 12 h at room
b
c
temperature. TON = n(H
2
)/n(1–Co). 1–Co (0.4 μmol), 2e (0.25
mmol). 2f (0.25 mmol), 1–Co (0.4 μmol).
oxidation potential such as 2b (EOx
2b+•
SCE)(Fig. S16), while 2d (EOx
2d+•/2d) = + 1.49 V vs. SCE) (Fig.
S18) with high oxidation potential showed poor TON of 50.
Nevertheless, 2a release one H (~1.0 wt%). We then tested 1–
Co in the photocatalytic CAD of another kind of secondary
amines such as N–heterocyclic compound 2e 2e also released
one H but with 1.5 wt%. Additionally, 3e was generated with a
d
(
/2b) = + 1.25 V vs.
(
II
formation of Co species, indicating an electron transfer from
III
II 27
1
*
to Co along with generation of Co . We also observed
2
slight enhancement of absorption in the range of 550 to 700
I
27
nm, which can be assigned to Co species.
.
On the basis of the above results, we proposed a plausible
2
mechanism for hydrogen release from 2e (Fig. 4). Initially, 1–
TON of 895 when the amount of 1–Co was 0.2 μmol (Table 2,
entry 4). The apparent quantum yield (AQY) at 450 nm was
estimated to be 2.1% when 1–Co was 0.4 μmol and the yield of
III
Co achieves the excited state 1*–Co under blue light
irradiation along with subsequent electron transfer from 1* to
III
+
Co . The resulting
1 then oxidize 2e to generate radical cation
3
e
was 86%. 2f was dehydrogenated to 3f in 96% yield (TON =
33
4
.
The deprotonation of
4
would produce strongly reducing
604) when more 1–Co was used (Table 2, entry 6). The yield
II
radical
Deprotonation of
Meanwhile, Co is reduced to Co . It is worth noting that Co
5
that is further oxidized to iminium ion
6
by Co .
was calculated with isolated 3f after careful column
chromatography. Although released hydrogen content of
these amines and yields of imines are still relatively low, these
results are helpful for developing noble–metal–free
photocatalytic acceptorless dehydrogenation of secondary
amines as well as other nitrogen–containing LOHCs.
3
4
6 affords dehydrogenation product 3e.
II
I
II
could not be reduced by excited state 1*, because higher
+
II
I
potential of E(1 /1*) (–0.71 V) than E(Co /Co ) (–1.12 V).
I
III
III
Further protonation of Co leads to Co –H. Co –H is then
protonated to release H
catalytic cycle. Other pathway such as homolysis of Co –H to
2
generate H and Co is not ruled out.
III
2
along with generation of Co for next
To know better about the catalytic cycle, we monitored
changes of UV–vis absorption spectra of 1–Co in the presence
III
II
28
Conclusions
In summary, we developed a unique supramolecular assembly
for highly efficient CAD of secondary amines under blue light
irradiation at room temperature. The supramolecular
assembly is composed of an organic TADF chromophore as
III
light–harvesting unit and Co complexes as catalytic center. An
III
electron transfer from the chromophore to Co center occurs
upon light irradiation and they further undergo cooperative
catalysis for enhaced acceptorless dehydrogenation of
secondary amines. Secondary amines were selectively
converted to corresponding imines despite their high oxidation
potentials. The highest TON of 895 was achieved. Our results
show a promising noble–metal–free strategy for CAD reactions
through cooperative photocatalysis. Organic D–A type TADF
chromophores are developed increasingly, which indicates
Fig. 3 Time–dependent absorption spectra of
presence of 2a (50 mM) in degassed dry THF (3 mL) upon blue
light irradiation at room temperature.
1 (25 μM) in the
4
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that more efficient CAD of secondary amines may be Chromophore 1. 4–(pyridin–4–ylmethoxy)–9H–carbazole (230
established by using more suitable. We expect organic TADF mg, 0.84 mmol) was dissolved in THF (20 mL). NaH (35 mg, 1.4
chromophores will be applied in light–driven acceptorless mmol) was added and stirred for 30 min at room temperature
2
dehydrogenation of more organic substrates at room under N atmosphere. Then 3,4,5,6–tetrafluorophthalonitrile
temperature.
(42 mg, 0.21 mmol) was added into the solution. The mixture
o
was further stirred at 40 C for 16 h under N
2
atmoshpere.
After the solution was cooled to room temperature, water was
added to quench excess NaH. Then THF was removed under
reduced pressure and water was added to the residue. The
Conflicts of interest
There are no conflicts to declare.
2 2
aqueous solution was extracted with CH Cl three times. The
organic layer was collected and CH Cl was further removed
2
2
Experimental section
Materials and instruments
under rotary evaporator to give brown powder. The brown
powder was then purified to give yellow powder by silica gel
1
column chromatography (CH
NMR (500 MHz, DMSO–d
2
Cl
2
/CH
3
OH = 50:1). Yield: 85%. H
All starting materials were purchased from commercial
suppliers and used as received. Dry THF (water < 50 ppm) was
6
), δ (ppm): 8.60 (t, 4H, J = 6.5 Hz),
.46–8.50 (m, 4H), 7.92–7.95 (m, 2H), 7.70–7.76 (m, 2H), 7.37–
.50 (m, 10H), 7.07–7.22 (m, 12H), 6.74–6.82 (m, 4H), 6.54–
.64 (m, 4H), 6.38 (t, 2H, J = 7.5 Hz), 5.31–5.33 (m, 4H), 5.07 (t,
8
7
6
4
1
1
1
1
1
1
3
5
35
used. Co(dmgH)(dmgH
2
)Cl
2
and Co(dmgH)
2
PyCl
were
1
synthesized as reported. H NMR spectra were carried out
using
a
Bruker Avance 500 MHz instrument with
13
6
H, J = 10.0 Hz). C NMR (125 MHz, DMSO–d ), δ (ppm):
tetramethysilane (TMS) as an internal standard. HRMS (ESI)
spectra were recorded using a Thermofisher Q–Exactive
instrument. Emission spectra were measured by Lengguang
Tech. Instruments (F97PRO) with Xe lamp as the light source.
UV–vis absorption spectra were obtained on a PerkinElmer
Lambda 950 spectrophotometer. Cyclic voltammetry (CV) was
carried out on CHI660E in a one–compartment cell equipped
with a glassy carbon working electrode, a saturated calomel
electrode reference electrode, and a platinum plate counter
electrode at a scan rate of 0.1 V s–1 at room temperature. The
potentials were referenced to SCE through an internal
standard oxidation of ferrocene. GC analysis was carried out
54.01, 153.20, 150.31, 150.08, 146.48, 146.32, 142.25,
41.79, 140.90, 140.84, 139.69, 138.81, 138.75, 138.68,
37.56, 126.85, 125.64, 124.91, 123.88, 122.65, 122.29,
21.91, 121.34, 119.96, 113.75, 112.60, 112.34, 111.42,
05.20, 104.33, 103.87, 68.26, 67.84. HR–ESI–MS (m/z): found
+
+
217.4146 for [M + H] (calcd. 1217.4246, C80
)Cl (36 mg, 0.1 mmol) was
added to a reaction flask and then CH OH (15 mL) was added
to afford a suspension. NEt (20 μL) was added to the
suspension and stirred for 30 min to form a brown solution. A
solution of 1 (27 mg, 0.022 mmol) in CH Cl was added slowly
through a dropping funnel. The mixed solution was stirred for
h at room temperature under air atmosphere. CH OH was
added to afford yellow precipitate. The precipitate was
collected through filtration and washed with CH OH to afford
–Co after drying under vacuo. Yield: 92%. H NMR (500 MHz,
DMSO–d ), δ (ppm): 8.58–8.61 (m, 1H), 8.45–8.49 (m, 1H),
.07 (s, 3H), 7.97 (s, 3H), 7.88–7.97 (m, 2H), 7.68–7.73 (m, 2H),
53 10 4
H N O ).
Assembly 1–Co. Co(dmgH)(dmgH
2
2
3
3
2
2
2
on Scion 436/456 (TCD detector, N carrier gas, 5 Å molecular
6
3
sieve column). Transient PL spectrum was carried out with
Edinburgh Instruments FLS980 Spectrometer at room
temperature. Incident photons were measured on a solar
power meter from Shenzhen Sanpo Instrument Co., Ltd.
3
1
1
6
8
7
7
Synthesis and characterization
.54–7.63 (m, 4H), 7.37–7.45 (m, 6H), 7.25–7.30 (m, 4H), 7.04–
.20 (m, 8H), 6.71–6.81 (m, 4H), 6.50–6.63 (m, 4H), 6.35–6.38
4
–(pyridin–4–ylmethoxy)–9H–carbazole.
180 mg, 1 mmol) and 4–(bromomethyl)pyridine (171 mg, 1
mmol) were dissolved in DMF (15 mL). Then K CO (270 mg, 2
mmol) was added into the solution. The mixture was stirred at
9H–carbazol–4–ol
(
m, 2H), 5.33–5.37 (m, 4H), 5.10–5.16 (m, 4H), 2.31–2.34 (m,
4H), 2.26–2.28 (m, 24H). 13C NMR (125 MHz, DMSO–d
), δ
ppm): 153.69, 153.64, 153.01, 152.72, 151.17, 151.05, 150.61,
150.40, 142.04, 141.67, 140.79, 139.56, 137.40, 124.08,
(
2
6
2
3
(
o
7
0 C for 12 h. Then DMF was removed under reduced
1
1
23.88, 123.85, 123.80, 113.67, 112.47, 111.39, 111.33,
pressure. The resulting precipitate was dissolved in water and
filtered to collect filter cake. The filter cake was further
purified to obtain brown solid by silica gel column
11.23, 105.47, 105.40, 67.32, 66.86, 13.15, 13.09. HR–ESI–MS
+
(
m/z): found 2538.4026 for [M + H] (calcd. 2538.4212,
+
1
C
112
H
108Cl
4
Co
4
N
26NaO20 ).
chromatography (CH
2
Cl
), δ (ppm): 11.33 (s, 1H), 8.64 (d, 2H, J =
.0 Hz), 8.19 (d, 1H, J = 5.0 Hz), 7.57 (d, 2H, J = 5.5 Hz), 7.47 (d,
2 3
/CH OH = 100:1). Yield: 40%. H NMR
(
500 MHz, DMSO–d
6
2
General procedure for photocatalytic H release
5
1
7
8
1
1
1
H, J = 8.0 Hz), 7.36 (t, 1H, J = 7.5 Hz), 7.30 (t, 1H, J = 8.0 Hz),
.17 (t, 1H, J =7.5 Hz), 7.11 (d, 1H, J = 8.0 Hz), 6.76 (d, 1H, J =
The THF solution (8 mL) containing catalyst (1–Co, 1 and CoIII)
and substrates was added to a tube equipped with a small stir
.0 Hz), 5.45 (s, 2H). 13C NMR (125 MHz, DMSO–d
), δ (ppm):
6
bar. Then the tube was degassed by N
with 16 blue LEDs (450 ± 10 nm, 3W) at room temperature.
The reaction was monitored through H generation. H was
2
and then irradiated
54.57, 150.34, 146.97, 141.70, 139.49, 126.91, 125.21,
22.62, 122.25, 122.00, 119.29, 112.02, 111.04, 104.91,
01.46, 68.41. HR–ESI–MS (m/z): found 275.1215 for [M + H]
2
2
+
determined by GC. The headspace was analyzed by
periodically sampling 100 μL with a sample lock syringe. When
+
(
calcd. 275.1179, C18
H
15
N
2
O ).
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J. Name., 2013, 00, 1‐3 | 5
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DOI: 10.1039/C9DT00407F
ARTICLE
increased no more, the reaction was stopped and solvent 16.
was removed in vacuum. Then crude products were collected 17.
and further purified by column chromatography over silica for
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