Air-Sensitive Photoredox Catalysis Performed under Aerobic Conditions in Gel Networks

Article abstract of DOI:10.1021/acs.joc.8b00797

In this work, we demonstrate that useful C-C bond-forming photoredox catalysis can be performed in air using easily prepared gel networks as reaction media to give similar results as are obtained under inert atmosphere conditions. These reactions are completely inhibited in homogeneous solution in air. However, the supramolecular fibrillar gel networks confine the reactants and block oxygen diffusion, allowing air-sensitive catalytic activity under ambient conditions. We investigate the mechanism of this remarkable protection, focusing on the boundary effect in the self-assembled supramolecular gels that enhances the rates of productive reactions over diffusion-controlled quenching of excited states. Our observations suggest the occurrence of triplet-sensitized chemical reactions in the gel networks within the compartmentalized solvent pools held between the nanofibers. The combination of enhanced viscosity and added interfaces in supramolecular gel media seems to be a key factor in facilitating the reactions under aerobic conditions.

Full text of DOI:10.1021/acs.joc.8b00797

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Article
Air-sensitive Photoredox Catalysis Performed
under Aerobic Conditions in Gel Networks
Marleen Häring, Alex Abramov, Keisuke Okumura, Indrajit Ghosh,
Burkhard König, Nobuhiro Yanai, Nobuo Kimizuka, and David Díaz Díaz
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00797 • Publication Date (Web): 29 May 2018
Downloaded from http://pubs.acs.org on May 29, 2018
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Air-sensitive Photoredox Catalysis Performed under
Aerobic Conditions in Gel Networks
a,‡
a,‡
b
a
a
Marleen Häring, Alex Abramov, Keisuke Okumura, Indrajit Ghosh, Burkhard König,
b
b
,a,c
Nobuhiro Yanai, Nobuo Kimizuka and David Díaz Díaz*
a
Institut für Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg,
Germany
b
Kyushu University, Department of Chemistry and Biochemistry, Graduate School of
Engineering, Center for Molecular Systems (CMS), 744 Motooka, Nishi-Ku, 810-0395 Fukuoka,
Japan
c
IQAC-CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain.
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Table of Contents Graphic and Synopsis
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ABSTRACT: In this work we demonstrate that useful C–C bond forming photoredox catalysis
can be performed in air using easily-prepared gel networks as reaction media to give similar
results as are obtained under inert-atmosphere conditions. These reactions are completely
inhibited in homogeneous solution in air. However, the supramolecular fibrillar gel networks
confine the reactants and block oxygen diffusion allowing air-sensitive catalytic activity under
ambient conditions. We investigate the mechanism of this remarkable protection, focusing on
boundary effect in the self-assembled supramolecular gels that enhance the rates of productive
reactions over diffusion-controlled quenching of excited states. Our observations suggest the
occurrence of triplet sensitized chemical reactions in the gel networks within the
compartmentalized solvent pools held in between the nanofibers. The combination of enhanced
viscosity and added interfaces in supramolecular gel media seems to be a key factor to facilitate
the reactions under aerobic conditions.
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INTRODUCTION
Nature uses confined and compartmentalized environments such as organelles to carry out
chemical reactions under mild conditions with precise control of kinetics and selectivity. Over
the last few decades, this has served as an inspiration to develop artificial nanoreactors based on
directed self-assembly of small molecules through non-covalent interactions.1-3 Within this
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context, photochemistry can benefit from confined spaces, for example when performed in
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mesoporous inorganic materials, microemulsions, micelles, vesicles, polyelectrolyte
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nanoparticles, foams, and gels.
The confinement may improve photochemical processes
by influencing key aspects such as light absorption and the lifetime of redox intermediates.15,16
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Among the above-mentioned confined media, physical or supramolecular gels are typically
made of low-molecular-weight (LMW) compounds, so-called gelators, self-assembled through
non-covalent interactions (e.g., hydrogen-bonding, van der Waals, charge-transfer, dipolar, p-p
stacking), which usually provides reversible gel-to-sol phase transitions as response to external
stimuli. The solid-like appearance and rheological behavior of these materials result from the
immobilization of the liquid (major component) into the interstices of a self-assembled matrix
(minor component) through high surface tension and capillary forces, making the liquid pools
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different from homogeneous solutions. The formation of the 3D-network interconnected
through numerous junction zones results from the entanglement of 1D-strands of gelator
molecules, typically of nm diameters and mm lengths, and can increase the viscosity of the
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medium by factors up to 10 .
18
Along these lines, we recently reported the first photoreduction of aryl halides in air by low-
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energy light irradiation of a proper donor/acceptor pair embedded in a physical gel, which
protected triplet excited states from oxygen deactivation. In this study, we hypothesize that
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compartmentalized low viscosity media provided by self-assembled gels could facilitate even
more challenging air-sensitive photoinduced C–C cross-coupling reactions under aerobic
19
conditions. Boundary effects may enhance the rates of the productive reactions over diffusion
controlled quenching of excited states. In order to demonstrate this we have studied two
important processes involving (1) functionalization of aryl-halides and (2) trifluoromethylation
of arenes.
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RESULTS AND DISCUSSION
The first reaction is the selective functionalization of aryl-halides using rhodamine-6G (Rh-6G)
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as photocatalyst. As previously described, this process is based on the possibility of tuning the
redox potential of Rh-6G over a range of 2.4 V using different colors of visible light.20,21 The
−
strategy involves the generation of the ground-state Rh-6G radical anion in the presence of an

−
electron donor under green-light irradiation, and the excited Rh-6G * radical anion upon blue-
light irradiation. However, due to instability of Rh-6G radical anions in the presence of oxygen,
so far, an oxygen-free environment has been required to carry out these reactions. This limitation
is overcome by simply including a small amount of a low-molecular-weight (LMW) gelator in
the reaction mixture, which transforms the solution into a viscoelastic gel medium.
For the initial proof-of-concept we used 2-bromobenzonitrile (1) as test substrate, N-
methylpyrrole (7) as trapping agent, Rh-6G as photocatalyst, N,N-diisopropylethylamine
(DIPEA) as electron donor, N,N’-bis(octadecyl)-L-Boc-glutamic diamide (G-1) as gelator, and
20
DMSO as solvent (Figure 1). In agreement with previous observations, the dehalogenative
arylation reaction between 1 and 7 was ineffective in aerated DMSO solution at room
temperature (RT) leading to very low yield (5% yield estimated by GC) of the desired coupling
product (Table S1) upon irradiation with blue LED light (λEx = 455 ± 15 nm). In contrast, when
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the same reaction was performed under aerobic conditions within the gel made of G-1 (10 g·L-1),
the GC yield improved drastically to 53% (Table S1). Further experiments gave an improvement
of the yield by increasing the gelator concentration (Table S2) and the amount of DIPEA (Table
-1
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S3), leading to the best result (73%, GC yield) using 15 g·L of G-1 and 2.2 equiv of DIPEA
with respect to 1 (Table S3). Isolated product yields from both solution and gel media were ca.
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1
0% lower than yields determined by GC. In agreement with previous observations, the
formation of a reduction byproduct was observed in both solution under argon and aerated gel
due to hydrogen atom abstraction of aryl radicals either from the radical cation of DIPEA or
from the solvent molecules. The use of other LMW gelators instead of G-1, such as (S,S)-
dodecyl-3-[2(3-dodecyl-ureido)cyclohexyl]urea (G-2) or N,N’-((1R,2R)-cyclohexane-1,2-
diyl)didodecanamide (G-3), provided comparable results in the photoredox reductive arylation
with slight differences in the yields (Table S2). Remarkably, the use of 1,3:2,4-bis(3,4-
dimethylbenzylidine)-sorbitol (G-4) suppressed the formation of the reduction byproduct. These
results suggest a possible effect of the gel network on different reaction pathways by interactions
with the reactants (see ESI for the structures of G-2, G-3 and G-4).
The scope of the intragel photoredox catalytic arylation in air was established using different
substituted aryl or hetero aryl halides and trapping agents (Figure 1A). Aromatic bromo-
compounds bearing electron-withdrawing substituents (i.e., –CN, –COMe) (1–3) reacted with
pyrrole derivatives (6–8) at RT affording the desired cross-coupling products (10–14) with
modest to good isolated yields and mass balances (> 90%) that were comparable to those
obtained in solution under strict inert conditions and identical reaction times (Figure S13).
Indeed, UV-vis spectroscopy confirmed that the photocatalyst inside the gel shows similar
stability than in solution maintained under nitrogen atmosphere (Figure S12). Interestingly, the
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use of pyrrole (6) as trapping agent gave slightly better results than N-methylpyrrole (7) or N-
phenylpyrrole (8), being the opposite in solution (ESI). Different heterocycles such as 5-
bromopyrimidine (4) and 2-bromobenzo[d]thiazole (5) were also coupled with N-methylpyrrole
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(7) and 3-methylindole (9) providing the expected cross-coupling products in moderate (16) and
good yields (15, 17).
Figure 1. A) Substrate scope of intragel cross-coupling reactions between bromo-compounds
and trapping agents. Reaction conditions: Bromo-compound 15 (0.1 mmol), trapping agent 69
-1
(
518 equiv), Rh-6G (15 mol%), DIPEA (2.2 equiv), G-1 (15 g·L ), DMSO, air, RT, λEx = 455
nm, reaction time: 24-96 h (see Experimental Section for details). Inset picture on the right:
Typical appearance of a gel made of G-1 in DMSO loaded with catalyst, substrate and DIPEA.
B) Chromoselective one or two-fold substitution reactions. C) Sequential substitution reactions.
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All yields correspond to isolated products. See Experimental Section and ESI for yields in
solution under inert conditions.
The selective activation of Rh-6G depending on the irradiation wavelength, previously shown in
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solution under inert atmosphere, was also achieved in gel medium under aerobic conditions
(Figure 1B). Thus, the coupling between 1,4-dibromo-2,5-difluorobenzene (18) and N-
methylpyrrole (7) lead to the corresponding monosubstituted product 20 upon irradiation with
green LED light (λEx = 530 ± 15 nm), which generates the photocatalytic ground state Rh-6G
−
radical anion. The bifunctionalized product 19 was obtained when the same reaction mixture was
irradiated with blue light (λEx = 455 ± 15 nm) due to the enhanced reduction power of Rh-6G

−
through the formation of the excited Rh-6G * radical anion. These results indicate that the
supramolecular gel network enables the generation of air-sensitive radical species and highly
reducing photoredox conditions under aerobic conditions. It should be emphasized that the
photocatalytic reaction selected for this study also present some limitations such as aryl bromide
substrates with several electron-donating groups due to their very high reduction potential.20
Such substrate limitations occurs regardless the reaction media when using the same
photocatalytic system and, therefore, they are not related to the gel medium, which is responsible
for the oxygen-blocking effect.
This chromoselective photocatalytic arylation can also be used to perform sequential reactions
in aerated gel (Figure 1C). Thus, irradiation with green light of ethyl 2-bromo-(4-
bromophenyl)acetate (21), which posses two different carbon–halogen bonds (i.e., benzylic and
aryl), lead to dehalogenation at the benzylic position affording the corresponding product 22 in
modest yield. Isolation of 22 and a new intragel reaction (ESI) in the presence of a trapping agent
such as 1,1-diphenylethylene (23), which posses extremely low reactivity towards nucleophiles
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22
and electrophiles, and irradiation with blue light enabled the activation of the remaining
carbon–bromide bond affording the desired product 24 in 61% yield. Only traces (< 1%) of the
unsaturated product (i.e., [Ph] C=CH-Aryl, see 24b in Experimental Section) were detected in
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the NMR of the crude reaction mixture. In contrast, the saturated:unsaturated ratio was 2.8:1
when the reaction was carried out in solution under nitrogen. Other trapping agents such as N-
methylpyrrole (7) also afforded the expected coupling product with 22 albeit in this case with
lower yield (ESI). It is important to note that the non-covalent nature of the supramolecular
network allows easy separation of the desired products and reutilization of the gelator without
any detriment on its gelation ability (ESI).
The second photoredox reaction investigated in this work yields trifluoromethylated aromatic
products, which constitute structures of relevance in modern medicinal chemistry.23-26 As
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previously reported, the trifluoromethylation of arenes and heteroarenes can be performed
using Ru(phen) Cl as photocatalyst to generate trifluoromethyl radicals (·CF ) via reduction of
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triflyl chloride (TfCl) upon irradiation at suitable wavelengths. The mechanism involves the
formation of a cyclohexadienyl radical from the corresponding arene, which is further oxidized
to form a cyclohexadienyl cation that affords the desired CF
3
arene upon facile deprotonation in
2
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the presence of K
2
HPO
4
. This method also requires strict inert gas atmosphere. We were
delighted to observe that the reactions could be performed in gel medium under aerobic
conditions within identical reaction times and comparable yields to solution reactions under inert
conditions (Figure S13).
Initially, a series of control experiments (Table S4) in both aerated solution and gel media were
performed using G-1 as LMW gelator, MeCN as solvent, N-methylpyrrole (7) as substrate, as
well as Ru(phen)
3
Cl
2
, TfCl and K
2
HPO as above mentioned. The samples were irradiated with
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blue LED light (λEx = 455 ± 15 nm), and the gelator concentration was fixed at 10 g·L , although
this variable was found to have a minor influence in this case (Table S7). The results showed that
no reaction occurred either in aerated solution or in aerated gel in the dark (Table S4).
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Interestingly, the use of K
2
HPO also suppressed any gel-to-sol transition during the reaction
4
caused for example by the generation of reaction products or uncontrolled thermal effects
(Tables S4S5). In addition, no or negligible background reaction occurred with different
substrates in aerated gel in the absence of the photocatalyst (Tables S4 and S6).
Several electron-rich 5-membered heteroarenes (7, 25–28) were converted into the desired
products in moderate yields (Figure 2). In general, obtained yields and mass balances (> 90%)
were comparable to those obtained in solution under rigorous inert conditions. Unless otherwise
stated, the reported yields correspond in this case to values obtained directly from NMR analyses
of the corresponding reaction crudes in the presence of a proper internal standard (ESI). Other
substrates such as 6-membered unactivated arenes (29–31) yielded, regardless the reaction
media, mainly the monosubstituted product (43–45) mixed sometimes with a disubstituted
derivative as minor product. The amount of disubstituted product increased with the electronic
density of the aromatic system in the starting material (31 > 30 > 29) and the amount of TfCl
(
ESI). Various electron-deficient 6-membered heteroarenes (32–34) as well as some natural
compounds (35, 36) were also tested affording the desired products (46–48 and 49, 50,
respectively) with modest to good yields, which were in general comparable to those obtained in
solution under inert atmosphere. The reactions proceed equally well using LED irradiation or a
household light bulb; a comparative study between both methods for some examples is given in
the ESI (Tables S10S11). Interestingly, although G-1 and G-3 gave similar results, the use of
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Fmoc-Lys(Fmoc)-OH as LMW gelator resulted in much lower selectivity (Table S12),
suggesting again the possibility of further optimization based on the nature of the gel network.
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Figure 2. Substrate scope of intragel trifluoromethylation of 5- and 6-membered (hetero)arenes
with TfCl. Reaction conditions: (hetero)arene 7, 25–36 (0.25 mmol), TfCl (2–4 equiv),
photocatalyst (Ru(phen)
3
Cl
2
(for 5-membered rings) or Ir(Fppy)
3
(for 6-membered rings)
(catalyst loading: 1 mol% for 5-membered heteroarenes and 6-membered arenes; 2 mol% for 6-
-1
membered heteroarenes), K
2
HPO
4
(3 equiv), G-1 (10 g·L ), 2.5 mL MeCN, air, RT, λEx = 455 ±
15 nm (for (Ru(phen) Cl ) or 365 nm ± 15 nm (for Ir(Fppy)
3
2
3
), reaction time: 24–48 h: Yields
1
9
were determined in this case by F-NMR using hexafluorobenzene (1 equiv) as internal
standard. Isolation of representative products showed ca. 10% decreased yields with respect to
NMR yields. *The minor disubstituted position is labelled with the respective carbon atom
number. Picture on the right: Typical appearance of a gel made of G-1 in MeCN loaded with
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Ru(phen)
3
Cl
2
, substrate and K
2
HPO . See Experimental Section and ESI for yields in solution
4
under inert conditions.
It is also worth mentioning that the preservation of the gel state (i.e., storage modulus G' > loss
modulus G'') during the reactions discussed in this paper was demonstrated for representative
examples by oscillatory rheological measurements (i.e., dynamic frequency, strain and time
sweeps (DFS, DSS and DTS, respectively) and determination of the gel-to-sol transition
temperature (Tgel) before and after irradiation (Figures S6 and S9). In all cases, G' was
approximately one order of magnitude higher than G'' within the linear viscoelastic regime (i.e.,
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.1% strain and 1 Hz frequency). These values were also stable over time as determined by DTS
experiments. Additionally, DFS and DSS measurements showed a reduction of the elastic
response (G') of the materials by one order of magnitude after the reactions. However, both the
dissipation factor (tan G''/G') and the sol-to-gel transition temperature (Tgel) of the gels
remained practically constant before and after irradiation within the experimental error, and did
not show significant differences with the corresponding undoped gels. These results suggest
some morphological changes of the gels, but without a major detriment of their damping
properties and thermal stability. Interestingly, comparative field-emission scanning electron
microscopy (FE-SEM) images of undoped gels, gels loaded with the corresponding
photocatalyst, and gels loaded with the photocatalyst and substrates, before and after irradiation,
indicated that the incorporation of the substrates caused apparently a higher impact on the
fibrillar morphology of the xerogel network than the photocatalysts alone (Figure 3). Visible
fragmentation of some fibers was observed after the reactions, albeit the gel phase was retained.
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Figure 3. Representative scanning electron microscopy images of xerogels prepared by freeze-
drying the corresponding gels. Gel compositions, photoredox catalytic arylation: 1 (0.1 mmol), 7
-1
(
1.8 mmol), Rh-6G (10 mol%), DIPEA (2.2 mmol), G-1 = 15 g L , DMSO (1.5 mL);
trifluoromethylation: 2-Methylfuran (18 µL, 0.25 mmol), Ru(phen)
3
Cl
2
(1.8 mg, 0.01 mmol),
-1
TfCl (53 L, 0.5 mmol), G-1 = 10 g L , K
2
HPO
4
(131 mg, 0.75 mmol), MeCN (2.5 mL).
Product yield = 55%.
At this point, additional experiments were carried out in order to get insights into the
mechanism by which the gel network facilitate the photocatalytic processes in air. Remarkably,
both Rh-6G and Ru-catalyzed reactions were also achieved in aerated solution and in the
presence of gelator G-1 at a concentration slightly below the critical gelation concentration
(CGC). In this situation, the gel network is not yet fully developed despite the formation of
1
7
molecular aggregates, which also increase the viscosity of the medium. Although the product
yields were ca. 1015% lower than those obtained in gel phase, the results suggest potential
intermolecular interactions within some domains of the gel network and/or a beneficial effect of
the enhanced viscosity reducing the oxygen diffusion. The latter was also supported by the
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formation of the reaction product in aerated frozen solution, albeit in ca. half yield compared to
that observed in gel at RT (Figure S11).
Furthermore, we performed a series of spectroscopic studies under different conditions.
Kimizuka and co-workers have previously demonstrated that platinum(II) octaethylporphyrin
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(PtOEP, sensitizer) and 9,10-diphenylanthracene (DPA, emitter) were solvophobically
2
8
incorporated inside the gel nanofibers formed from G-1 in DMF. In that example, the
supramolecular gel showed efficient triplet-triplet annihilation (TTA)-based photon
upconversion (UC) even under aerated conditions, because the triplet excited states of PtOEP
and DPA were protected from the quenching by dissolved molecular oxygen. Importantly, the
solvophobic accumulation of sensitizers and emitters in gel nanofibers is essential, since these
excited triplets were quenched in the G-1 gel formed in less polar carbon tetrachloride. This
1
8
observation enabled us to perform intragel photoreduction of aryl halides in air. In the present
study, we initially expected that a similar oxygen blocking effect might also occur during C–C
bond-forming photoredox catalysis, assuming that the photocatalysts are accumulated in the gel
nanofibers. However, such oxygen barrier effect was not observed in phosphorescence lifetime
-1
measurements conducted for Ru(phen)
3
Cl
2
(1 mM) in acetonitrile with/without G-1 (10 g·L ).
These specimens were prepared in air or Ar-filled glove box ([O
2
] < 0.1 ppm). The deaerated
solution and deaerated gel samples prepared under Ar atmosphere showed phosphorescence
lifetimes of 377 ns and 325 ns, respectively (Figure 4). On the other hand, both aerated solution
and aerated gel samples showed much shorter lifetimes (i.e., 105 ns and 139 ns, respectively)
than those observed for the corresponding deaerated samples. This result indicates that the Ru
complex is not effectively shielded inside gel nanofibers from dissolved oxygen.
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Figure 4. Photoluminescence decay at 605 nm of Ru(phen)
3
Cl in aerated/deaerated acetonitrile
2
in the absence/presence of G-1 under pulsed excitation at 405 nm.
To investigate the possibility of local oxygen consumption under continuous light exposure,
phosphorescence lifetime of aerated gel samples was measured after a prolonged
photoirradiation. The samples were irradiated by a xenon lamp through a 450 nm band-pass
filter, which condition is similar to that of the photocatalytic reaction using LED irradiation at
3
4
45 nm. Oxygen quenches the excited metal-to-ligand charge transfer ( MLCT) state. Transfer of
triplet energy to oxygen converts it into the excited singlet state. The singlet oxygen has a long
lifetime and is a highly reactive species, which serves as a powerful oxidant in photosensitized
oxidation processes. We expected that such single oxygen formed in the system (i.e., gel
prepared in air) would show some deteriorative actions to the gelator molecules and therefore the
3
quenching of the MLCT states by oxygen would result in the consumption of local molecular
oxygen concentration in the gel. If this is the case, the photo-illumination over long periods may
lead to the recovery of phosphorescence lifetime of the Ru complex. However, no significant
difference was observed in the phosphorescence decays after photoirradiation for 8 h, 15 h and
24 h (Figure S14). The local consumption of oxygen during photoirradiation may take place, but
its effect is too small to be detected by the change in phosphorescene decay curves. Furthermore,
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kinetic studies did not show an induction period for the reaction in aerated gel vs. solution under
nitrogen (Figure S15). We further investigated the effect of other additives and reactants in the
reaction such as K
2
HPO , TfCl and 7 at the same concentrations than those in the reaction.
4
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Elongation of phosphorescence decay was neither observed for these specimens (Figure S15).
These results indicate that the Ru complex undergo oxygen quenching as it is dissolved in the
MeCN solution phase trapped in between the gel nanofibers.
Taking together all the experimental evidences, and considering that photoinduced electron
3
transfer (ET) is unlikely to be faster than the quenching of the MLCT states by dissolved
molecular oxygen, the occurrence of triplet sensitized chemical reactions in the organogel could
take place within the confined solvent pools held in between the nanofibers. There, the
volume/surface ratio and viscosity changes dramatically compared to homogeneous solution.
This is in agreement with earlier kinetics studies of some photoinduced ET-based reactions in gel
14
media compared to homogeneous and micellar solutions. In contrast to our previous
observations based on TTA-UC,18,28 the photocatalytic species here are not incorporated into the
gel fibers. Moreover, the gel slows down significantly the diffusion of external oxygen through
the gel-air interface (Figure S11), thus preventing a fast deactivation of excited species generated
−
after the initial photoexcitation of the catalysts (e.g., Rh-6G *, Figure S12). In contrast to free
diffusion in solution, the oxygen initially trapped in the gel –which was proven to be still
reactive (Figure S11)– should go through numerous entangled fibers to quench active species
compartmentalized in other solvent pools. Thus, even a non-fully meshed network may offer
some interfaces to protect against oxygen deactivation compared to homogeneous solution. This
was supported by the observation of product in aerated solution in the presence of the gelator
slightly below its CGC. Although the combination of high viscosity and liquid interfaces in
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supramolecular gel media seems to be a key factor to facilitate the reactions, other effects such as
increased local substrate concentration or affinity of substrates and active catalytic species to the
surface of the fibers can not be excluded at this point.29,30
0
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CONCLUSION
In conclusion, air-sensitive C–C bond-forming photoredox catalysis can be performed under
aerobic conditions using supramolecular gels, which are very easy to make and remove, as
confined reaction media. The desired products are obtained in similar yields compared to
reactions in homogeneous solutions under strict inert conditions. A judicious hydrophobic-
hydrophilic balance of the photocatalysts, the nature of the solvent and type of gel network are
parameters that can be used to optimize intragel reactivity. Due to its facile operation, this
method may expedite high-throughput screening of photocatalysts, automatization of
photoinduced processes, and facilitate the way photochemistry and photocatalysis are
traditionally carried out in research laboratories.
EXPERIMENTAL SECTION
Materials and methods
Unless otherwise stated, all chemicals were used as received without further purification and
were purchased from ABCR, Acros, Sigma-Aldrich, TCI Europe or Merk. Rhodamine 6G (Rh-
6
G, Sigma-Aldrich, catalog number R4127); dichlorotris(1,10-phenanthroline)ruthenium(II)
hydrate (Ru(phen)
3
Cl
2
, Sigma-Aldrich, catalog number 343714); tris[2-(4,6-
2
difluorophenyl)pyridinato-C ,N]iridium(III) (Ir(Fdppy)
3
, Sigma-Aldrich, catalog number
6
82594). Photocatalysts were stored under protective nitrogen atmosphere.
Trifluoromethanesulfonyl chloride (TfCl, Sigma-Aldrich, catalog number 164798) was
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transferred into a Schlenk tube right after purchase and stored in a freezer under nitrogen
atmosphere.
Photochemical reactions were performed using a custom made set-up (Figure S1) with an array
of suitable LEDs (3.5 V, 700 mA), i.e. ex = 365 ± 15 nm, ex = 455 ± 15 nm, ex = 530 ± 15 nm.
The yields reported are referred to the isolated compounds unless otherwise stated. Oxygen- and
moisture-free reactions were carried out with dry and degassed solvents, as well as glassware
subjected to several evacuation (vacuum)/refill (nitrogen) cycles.
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Column chromatography was performed using either silica gel (63 – 200 m) or flash silica gel
(40 – 63 m).
Thin-layer chromatography was performed using Merck pre-coated TLC aluminum sheets
silica gel ALUGRAM® Xtra SIL G/UV254. Visualization was accomplished with short
wavelength (254 nm) and near UV (366 nm) lights.
1
13
19
NMR spectra were recorded on Bruker Avance 400 ( H: 400 MHz, C: 101 MHz, F: 376
1
13
19
MHz) and Bruker Avance 300 ( H: 300 MHz, C: 75 MHz, F: 282 MHz) spectrometers.
1
Chemical shifts for H NMR were reported as δ, parts per million (ppm), relative to the signal of
13
CHCl
3
at 7.26 ppm or of DMSO at 2.50 ppm. Chemical shifts for C NMR were reported as δ,
ppm, relative to the signal of CDCl
3
at 77 ppm or of DMSO at 39.5 ppm. Coupling constants J
are given in Hertz (Hz). The following notations indicate the multiplicity of the signals: s =
singlet, brs = broad singlet, d = doublet, t = triplet, q = quartet, dd = doublet of doublets, td =
triplet of doublets, m = multiplet.
Gas chromatography (GC) analyses were performed using a capillary column (length: 30 m;
diam. 0.25 mm; film: 0.25 µm) using He gas as carrier and FID detector.
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UV-Vis measurements were performed on an Ocean Optics DH-2000-BAL UV-VIS-NIR
spectrophotometer. Measurements under different conditions were carried out as following: (1)
Solution under nitrogen: A screw-capped cuvette with septum was equipped with a small stirring
bar and charged with 3 mL of a 16.7 μM rhodamine-6G solution in DMSO and subsequently
0
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evacuated and backfilled with N
2
(3). DIPEA (50 μL) was added and another vacuum-N cycle
2
was applied. The stirred reaction mixture was irradiated with 455 nm LED and UV-Vis spectra
were recorded every 10 min. (2) Solution in air: A cuvette was equipped with a small stirring bar
and charged with 3 mL of a 16.7 μM rhodamine-6G solution in DMSO and DIPEA (50 μL). The
stirred reaction mixture was irradiated in air (without cap) with 455 nm LED and UV-Vis spectra
were recorded every 10 min. (3) Gel under nitrogen: A screw-capped vial septum was charged
-1
with 10 mg L gelator, 3 mL of a 16.7 μM rhodamine-6G solution in DMSO and subsequently
evacuated and backfilled with N
2
(3). DIPEA (50 μL) was added and another vacuum-N cycle
2
was applied. The reaction mixture was heated until everything was dissolved and the hot solution
was transferred into a screw-capped cuvette, which was previously evacuated and backfilled with
N
2
(3). The mixture was subsequently allowed to cool to RT leading to gelation. The gel was
then irradiated with 455 nm LED and UV-Vis spectra were recorded every 10 min. (4) Gel in
-1
air: A 5 mL vial was charged with 10 mg L gelator, 3 mL of a 16.7 μM rhodamine-6G solution
in DMSO and DIPEA (50 μL). The reaction mixture was heated until everything was dissolved
and the hot solution was transferred into a cuvette. The mixture was allowed to cool to RT
leading to gelation. The gel was then irradiated in air (without cap) with 455 nm LED and UV-
Vis spectra were recorded every 10 min.
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High-resolution mass spectra (HRMS) were obtained from the central analytic mass
spectrometry facilities of the Faculty of Chemistry and Pharmacy (University of Regensburg)
and are reported according to the IUPAC recommendations 2013.
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Oscillatory rheology was performed with an AR 2000 Advanced rheometer (TA Instruments)
equipped with a Julabo C cooling system. A 500 or 1000 µm gap setting and a torque setting of
4
0,000 dynes/cm² at 25 °C were used for the measurements in a plain-plate (40 mm, stainless
steel). The following experiments were performed using 1.5 – 2.5 mL total gel volume: (1)
Dynamic frequency sweep (DFS): variation of G' and G'' with frequency (from 0.1 to 10 Hz at
0
.1% strain); (2) dynamic strain sweep (DSS): variation of G' and G'' with strain (from 0.01 to
100%); (3) dynamic time sweep (DTS): variation of G' and G'' with time, keeping the strain and
frequency constant and within the linear viscoelastic regime as determined by DSS and DFS
measurements (strain = 0.1%; frequency = 1 Hz).
Gel-to-sol transition temperatures (Tgel) were determined using a custom made set-up where a
sealed vial was placed into a mold of an alumina block and heated up at 2 °C/5 min using an
electric heating plate equipped with a temperature control couple (Figure S2). The temperature at
which the gel started to collapse was defined as Tgel. The values obtained by this method have
been previously verified with different supramolecular gels by means of DSC measurements as
well as the inverse flow method. Moreover, verification of the independence of the position
1
4
inside the custom made apparatus has also been carried out. Herein, the temperature at which
the gel started to break was defined as Tgel with an estimated error of ± 2 °C after several heating-
cooling cycles.
Field Emission Scanning Electron Microscopy (FESEM) images of the bulk xerogels were
obtained with a Zeiss Merlin, Field Emission Scanning Electron Microscope operated at an
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accelerating voltage of 10 kV. For visualization, samples were prepared by the freeze-drying
(FD) method as following: A 4 mL glass vial containing the corresponding gel (total volume = 1
mL) was frozen in liquid nitrogen and the solvent was immediately evaporated under reduced
pressure (0.6 mmHg) overnight at RT. The obtained fibrous solid was placed on top of a tin plate
and shielded with Pt (40 mA during 30 – 60 s; film thickness = 5 – 10 nm). Images were taken at
the University of Zaragoza (Servicio General de Apoyo a la Investigación-SAI).
0
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9
0
Time-resolved photoluminescence measurements were carried out by using a time-correlated
single photon counting lifetime spectroscopy system, Hamamatsu Quantaurus-Tau C11367-02.
Photoirradiation were conducted with a xenon lamp (MAX-303, Asahi Spectra), in which 450
nm band-pass filter was employed. Sample preparation for phosphorescence lifetime
measurements: (a) Solution samples: Ru(phen)
transferred to a glass cell; (b) gel samples: Gelator (G-1) was directly weighed in a glass cell and
MeCN solution of Ru(phen) Cl was added to the cell. The mixture was heated with a heat gun
3
Cl
2
was dissolved in MeCN in a vial, then
3
2
until it turns to clear yellow solution. The sample was left at room temperature (RT) for the
gelation. Deaerated samples were prepared under Ar atmosphere in an Ar-filled glove box by
using a glass cell with a sealing cap. Aerated samples were prepared under ambient conditions.
The concentrations of Ru(phen)
3
Cl
2
(1 mM), G-1 (10 g/L), K
2
HPO (300 mM), TfCl (200 mM),
4
7
(100 mM) were identical to those for the photocatalytic reaction.
Synthesis and characterization of compounds
Low molecular weight gelators
31
32
33
LMW gelators G-1, G-2 and G-3 were synthesized according to literature procedures with
slight modifications. G-4 was purchased from CHEMOS GmbH & Co. KG (catalog number
187667).
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3
1
N,N’-Bis(octadecyl)-L-Boc-glutamic diamide (G-1): Boc-glutamic acid (0.01 mol, 1.0 equiv)
and octadecylamine (0.02 mol, 2.0 equiv) in dichloromethane (200 mL) were mixed. Then 1-
ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC∙HCl) (0.022 mol, 2.2 equiv
was added to the mixture, and stirred at RT for 72 h. The obtained white solid was isolated by
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
filtration and washed three times with dichloromethane. The crude product was dissolved in THF
1
and precipitated by water. A fine white solid was obtained (80%). H NMR (300 MHz CDCl
3
) δ
6
.69 (brs, 1H), 6.32 (brs, 1H), 5.77 (brs, 1H), 4.08 (brs, 1H), 3.26 – 3.22 (m, 4H), 2.41 – 2.27 (m,
H), 2.06 – 1.93 (m, 2H), 1.58 – 1.46 (m, 4H), 1.43 (s, 9H), 1.25 (s, 60H), 0.87 (t, 6H) ppm.
2
3
2
(S,S)-Dodecyl-3-[2(3-dodecyl-ureido)cyclohexyl]urea (G-2): A solution of
dodecylisocyanate (15 mmol, 2.0 equiv) in toluene (20 mL) was slowly added to a solution of
S,S)-1,2-cyclohexyldiamine (7 mmol, 1.0 equiv) in toluene (100 mL). The reaction mixture was
(
stirred for 16 h at RT and 2 h at 100 °C. After cooling to RT, the gel-like reaction mixture was
filtered to give a white waxy solid. The waxy solid was further stirred for 16 h with
dichloromethane (50 mL) and collected by filtration. This procedure was repeated with diethyl
1
ether. After drying, a white solid was obtained (70%). H NMR (300 MHz, CDCl
3
) δ 5.18 (brs,
2
H), 4.67 (brs, 2H), 3.42 (m, 2H), 3.08 (m, 4H), 2.03 (d, 2H), 1.72 (m, 6H), 1.45 (m, 4H), 1.25
s, 36H), 0.87 (t, 6H) ppm.
N,N’-((1R,2R)-Cyclohexane-1,2-diyl)didodecanamide (G-3): The compound was prepared
(
3
3
following the general procedure with modifications. To a stirred solution of (1R,2R)-(+)-N,N’-
dimethyl-1,2-cyclohexanediamine (1.00 mmol, 1.0 equiv) in THF (18 mL), lauroyl chloride
(
2.00 mmol, 2.0 equiv) and triethylamine (3.33 mmol, 3.3 equiv) were added dropwise. The
mixture was refluxed for 5 h and allowed to cool to RT. The precipitated triethylammonium
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1
1
1
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
chloride was filtered off and the solvent of the remaining filtrate removed under reduced
pressure. The obtained residue was washed with aqueous 1 M HCl (4  5 mL) and water (4  5
1
mL), dried and recrystallized from acetone affording G-3 as white solid in 39% yield. H NMR
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
300 MHz, CDCl ) δ 5.86 (d, 2H), 3.65 (m, 2H), 2.15 – 1.96 (m, 6H), 1.79 – 1.67 (m, 2H), 1.57
3
(s, 8H), 1.25 (s, 33H), 0.88 (s, 6H) ppm.
1,3:2,4-Bis(3,4-dimethylbenzylidine)-sorbitol (G-4): The compound was purchased from
CHEMOS GmbH & Co. KG and it was used without further purification.
Photoredox catalytic arylation using Rh-6G
General procedure for the arylation in gel medium and air: A 5-mL snap vial was charged with
the respective aryl halide (0.1 mmol, 1.0 equiv), trapping reagent (1.8 mmol, 18 equiv), DIPEA
-1
(
0.22 mmol, 2.2 equiv), Rh-6G (15 mol%), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a
cap. The reaction mixture was gently heated with a heat gun at 80 °C during 1 min until an
isotropic solution was obtained. The corresponding gel was obtained upon cooling the mixture to
RT. The snap vial was then equipped with two needles to ensure a constant air atmosphere
(Figure S3A). The reaction was irradiated through the plane bottom side of the snap vial using a
455 (± 15) nm LED at 25 °C. The reaction progress was monitored by GC-FID. After completion
of the reaction as judged by GC-FID, the reaction mixture of three reactions (performed in
parallel) were combined and transferred into a separating funnel and adequate amount of distilled
water and brine were added. The mixture was extracted with ethyl acetate (3  15 mL). The
combined organic layers were dried over MgSO , filtered, and concentrated under reduced
4
pressure. Purification of the crude product was achieved by flash silica gel column
chromatography using hexanes/ethyl acetate as eluents. Note: The gelator can be easily separated
and reused in subsequent experiments without any detriment of its gelation properties.
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20
2
-(1H-Pyrrol-2-yl)benzonitrile (10): The compound was prepared according to the general
procedure. A 5-mL snap vial was charged with 2-bromobenzonitrile (1) (0.1 mmol, 1.0 equiv),
Rh-6G (0.015 mmol, 0.15 equiv), pyrrole (6) (1.8 mmol, 18 equiv), DIPEA (0.22 mmol, 2.2
-1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
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1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction mixture was gently
heated with a heat gun at 80 °C during 1 min until an isotropic solution was obtained. The
corresponding gel was obtained upon cooling the mixture to RT. The snap vial, equipped with
two needles to ensure a constant air atmosphere was irradiated through the plane bottom side of
the snap vial using a 455 (± 15) nm LED at 25 °C for 48 h. Three reactions were run in parallel,
and the combined reaction mixture was subjected to the work-up procedure outlined in the
general procedure. The crude product was purified by flash column chromatography on silica gel
using a mixture of ethyl acetate (20%) and hexanes as eluent (R
f
= 0.3) affording the title
) δ 11.52 (brs, 1H), 7.87 – 7.78
1
compound in 71% yield (36 mg). H NMR (300 MHz, DMSO-d
6
(m, 1H), 7.76 – 7.65 (m, 2H), 7.41 – 7.30 (m, 1H), 7.05 – 6.98 (m, 1H), 6.88 – 6.80 (m, 1H),
1
3
6
1
.27 – 6.18 (m, 1H) ppm; C NMR (75 MHz, DMSO-d ) δ 135.5, 134.3, 133.3, 127.2, 126.3,
6
26.0, 121.2, 119.4, 109.5, 109.4, 106.3 ppm.
2
0
2
-(1-Methyl-1H-pyrrol-2-yl)benzonitrile (11): The compound was prepared according to the
general procedure. A 5-mL snap vial was charged with 2-bromobenzonitrile (1) (0.1 mmol, 1.0
equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole (7) (1.8 mmol, 18 equiv), DIPEA
-1
(
0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction
mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was
obtained. The corresponding gel was obtained upon cooling the mixture to RT. The snap vial,
equipped with two needles to ensure a constant air atmosphere was irradiated through the plane
bottom side of the snap vial using a 455 (± 15) nm LED at 25 °C for 24 h. Three reactions were
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1
1
1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
run in parallel, and the combined reaction mixture was subjected to the work-up procedure
outlined in the general procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (15%) and hexanes as eluent (R =
f
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0
.4) affording the title compound in 59% yield (32 mg). H NMR (300 MHz, CDCl
3
) δ 7.89 (dd,
1
H), 7.73 (dt, 1H), 7.59 – 7.48 (m, 2H), 6.94 (t, 1H), 6.29 (dd, 1H), 6.13 (dd, 1H), 3.55 (s, 3H)
13
ppm; C NMR (75 MHz, DMSO-d
6
) δ 136.1, 133.8, 133.0, 130.7, 129.2, 127.9, 125.3, 118.7,
1
11.4, 111.0, 107.7, 34.5 ppm.
20
2
-(1-Phenyl-1H-pyrrol-2-yl)benzonitrile (12): The compound was prepared according to the
general procedure. A 5-mL snap vial was charged with 2-bromobenzonitrile (1) (0.1 mmol, 1.0
equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-phenylpyrrole (8) (1.8 mmol, 18 equiv), DIPEA
-1
(
0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction
mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was
obtained. The corresponding gel was obtained upon cooling the mixture to RT. The snap vial,
equipped with two needles to ensure a constant air atmosphere was irradiated through the plane
bottom side of the snap vial using a 455 (± 15) nm LED at 25 °C for 48 h. Three reactions were
run in parallel, and the combined reaction mixture was subjected to the work-up procedure
outlined in the general procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (5%) and hexanes as eluent (R =
f
1
0
.3) affording the title compound in 41% yield (30 mg). H NMR (300 MHz, DMSO-d
6
) δ 7.81
– 7.72 (m, 1H), 7.56 – 7.45 (m, 1H), 7.45 – 7.17 (m, 6H), 7.16 – 7.00 (m, 3H), 6.56 (dd, 1H),
13
6
1
.39 (t, 1H) ppm; C NMR (75 MHz, DMSO-d
6
) δ 139.1, 135.8, 133.4, 132.6, 130.7, 129.2,
28.4, 127.6, 126.7, 125.4, 125.0, 118.2, 113.3, 111.1, 109.5 ppm.
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20
4
-(1-Methyl-1H-pyrrol-2-yl)benzonitrile (13): The compound was prepared according to the
general procedure. A 5-mL snap vial was charged with 4-bromobenzonitrile (2) (0.1 mmol, 1.0
equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole (7) (1.8 mmol, 18 equiv), DIPEA
-1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction
mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was
obtained. The corresponding gel was obtained upon cooling the mixture to RT. The snap vial,
equipped with two needles to ensure a constant air atmosphere was irradiated through the plane
bottom side of the snap vial using a 455 (± 15) nm LED at 25 °C for 24 h. Three reactions were
run in parallel, and the combined reaction mixture was subjected to the work-up procedure
outlined in the general procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (15%) and hexanes as eluent (R =
f
1
0
.2) affording the title compound in 69% yield (37 mg). H NMR (300 MHz, CDCl
3
) δ 7.66 –
7.60 (m, 2H), 7.49 – 7.42 (m, 2H), 6.77 – 6.71 (m, 1H), 6.30 (dd, 1H), 6.19 (dd, 1H), 3.67 (s,
1
3
3
1
H) ppm; C NMR (75 MHz, DMSO-d ) δ 137.3, 132.3, 131.5, 127.7, 126.5, 119.0, 110.6,
6
08.1, 107.9, 35.2 ppm.
2
0
1
-(4-(1-Methyl-1H-pyrrol-2-yl)phenyl)ethan-1-one (14): The compound was prepared
according to the general procedure. A 5-mL snap vial was charged with 4’-bromoacetophenone
3) (0.1 mmol, 1.0 equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole (7) (1.8 mmol, 18
(
-1
equiv), DIPEA (0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap.
The reaction mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic
solution was obtained. The corresponding gel was obtained upon cooling the mixture to RT. The
snap vial, equipped with two needles to ensure a constant air atmosphere was irradiated through
the plane bottom side of the snap vial using a 455 (± 15) nm LED at 25 °C for 70 h. Three
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
reactions were run in parallel, and the combined reaction mixture was subjected to the work-up
procedure outlined in the general procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (15%) and hexanes as eluent (R =
f
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0
7
3
1
.3) affording the title compound in 50% yield (30 mg). H NMR (300 MHz, CDCl
3
) δ 8.03 –
.95 (m, 2H), 7.54 – 7.46 (m, 2H), 6.81 – 6.74 (m, 1H), 6.35 (dd, 1H), 6.23 (dd, 1H), 3.72 (s,
1
3
H) ppm; C NMR (75 MHz, DMSO-d
6
) δ 197.2, 137.3, 134.2, 132.2, 128.5, 127.2, 126.0,
10.0, 107.8, 35.2, 26.5 ppm.
34
5
-(1-Methyl-1H-pyrrol-2-yl)pyrimidine (15): The compound was prepared according to the
general procedure. A 5-mL snap vial was charged with 5-bromopyrimidine (4) (0.1 mmol, 1.0
equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole (7) (1.8 mmol, 18 equiv), DIPEA
-1
(
0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction
mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was
obtained. The corresponding gel was obtained upon cooling the mixture to RT. The snap vial,
equipped with two needles to ensure a constant air atmosphere was irradiated through the plane
bottom side of the snap vial using a 455 (± 15) nm LED at 25 °C for 72 h. Three reactions were
run in parallel, and the combined reaction mixture was subjected to the work-up procedure
outlined in the general procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (50%) and hexanes as eluent (R =
f
1
0
.3) affording the title compound in 79% yield (38 mg). H NMR (300 MHz, CDCl
3
) δ 9.12 (s,
1
3
1H), 8.8 (s, 2H), 6.86 – 6.79 (m, 1H), 6.37 (dd, 1H), 6.25 (dd, 1H), 3.71 (s, 3H) ppm; C NMR
75 MHz, CDCl ) δ 156.5, 155.4, 127.6, 127.0, 126.0, 110.9, 108.8, 35.2 ppm.
-Methyl-2-(pyrimidin-5-yl)-1H-indole (16): The compound was prepared according to the
(
3
3
4
3
general procedure. A 5-mL snap vial was charged with 5-bromopyrimidine (4) (0.1 mmol, 1.0
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7
8
9
equiv), Rh-6G (0.015 mmol, 0.15 equiv), 3-methylindole (9) (1.8 mmol, 18 equiv), DIPEA (0.22
-1
mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction mixture
was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was obtained.
The corresponding gel was obtained upon cooling the mixture to RT. The snap vial, equipped
with two needles to ensure a constant air atmosphere was irradiated through the plane bottom
side of the snap vial using a 455 (± 15) nm LED at 25 °C for 48 h. Three reactions were run in
parallel, and the combined reaction mixture was subjected to the work-up procedure outlined in
the general procedure. The crude product was purified by flash column chromatography on silica
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
gel using a mixture of ethyl acetate (15 – 40%) and hexanes as eluent (R = 0.1 at 30% ethyl
f
1
acetate in hexanes) afording the title compound in 32% yield (20 mg). H NMR (300 MHz,
CDCl
H), 2.49 (s, 3H) ppm.
2-(1-Methyl-1H-pyrrol-2-yl)benzo[d]thiazole (17): The compound was prepared according
3
) δ 9.12 (s, 1H), 9.01 (s, 2H), 7.66 – 7.51 (m, 1H), 7.45 – 7.36 (m, 1H), 7.31 – 7.09 (m,
3
3
4
to the general procedure. A 5-mL snap vial was charged with 2-bromobenzo[d]thiazole (5) (0.1
mmol, 1.0 equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole (7) (1.8 mmol, 18 equiv),
-1
DIPEA (0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The
reaction mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic
solution was obtained. The corresponding gel was obtained upon cooling the mixture to RT. The
snap vial, equipped with two needles to ensure a constant air atmosphere was irradiated through
the plane bottom side of the snap vial using a 455 (± 15) nm LED at 25 °C for 72 h. Three
reactions were run in parallel, and the combined reaction mixture was subjected to the work-up
procedure outlined in the general procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (5 – 40%) and hexanes as eluent
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2
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
(
R
f
= 0.2 at 15% ethyl acetate in hexanes) affording the title compound in 78% yield (50 mg). H
NMR (300 MHz, CDCl ) δ 7.99 – 7.91 (m, 1H), 7.85 – 7.79 (m, 1H), 7.43 (dt, 1H), 7.31 (dt,
1H), 6.87 – 6.79 (m, 2H), 6.21 (q, 1H), 4.15 (s, 3H) ppm; C NMR (75 MHz, DMSO-d
59.8, 153.6, 132.9, 128.9, 126.2, 125.3, 124.6, 121.9, 121.6, 114.9, 108.7, 36.6 ppm.
3
1
3
6
) δ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
0
2
,2'-(2,5-Difluoro-1,4-phenylene)bis(1-methyl-1H-pyrrole) (19): The compound was
prepared according to the general procedure but with double amount of N-methylpyrrole (7). A
-mL snap vial was charged with 1,4-dibromo-2,5-difluorobenzene (18) (0.1 mmol, 1.0 equiv),
Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole (7) (2.6 mmol, 26 equiv), DIPEA (0.22
5
-1
mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction mixture
was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was obtained.
The corresponding gel was obtained upon cooling the mixture to RT. The snap vial, equipped
with two needles to ensure a constant air atmosphere was irradiated through the plane bottom
side of the snap vial using a 455 (± 15) nm LED at 25 °C for 96 h. Three reactions were run in
parallel, and the combined reaction mixture was subjected to the work-up procedure outlined in
the general procedure. The crude product was purified by flash column chromatography on silica
gel using a mixture of ethyl acetate (5%) and hexanes as eluent (R
f
= 0.4) affording the title
1
compound in 41% yield (33 mg). H NMR (300 MHz, DMSO-d
6
) δ 7.38 (t, 2H), 7.00 – 7.25 (m,
13
2
H), 6.31 – 6.21 (m, 2H), 6.18 – 6.09 (m, 2H), 3.60 (s, 6H) ppm; C NMR (75 MHz, DMSO-d )
6
δ 156.3 (dd), 153.1 (dd), 125.4, 124.7, 120.9, 120.7 (dd), 120.5, 118.0, 117.8 (dd), 117.6, 110.8,
107.6, 34.4 ppm.
20
2
-(4-Bromo-2,5-difluorophenyl)-1-methyl-1H-pyrrole (20): The compound was prepared
according to the general procedure. A 5-mL snap vial was charged with 1,4-dibromo-2,5-
difluorobenzene (18) (0.1 mmol, 1.0 equiv), Rh-6G (0.015 mmol, 0.15 equiv), N-methylpyrrole
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7
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9
-1
(
7) (1.8 mmol, 18 equiv), DIPEA (0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and
sealed with a cap. The reaction mixture was gently heated with a heat gun at 80 °C during 1 min
until an isotropic solution was obtained. The corresponding gel was obtained upon cooling the
mixture to RT. The snap vial, equipped with two needles to ensure a constant air atmosphere
was irradiated through the plane bottom side of the snap vial using a 530 (± 15) nm LED at 25
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
°
C for 96 h. Three reactions were run in parallel, and the combined reaction mixture was
subjected to the work-up procedure. The crude product was purified by flash column
chromatography on silica gel using a mixture of ethyl acetate (5%) and hexanes as eluent (R =
f
1
0
.5) affording the title compound in 40% yield (33 mg). H NMR (300 MHz, DMSO-d
6
) δ 7.81
(q, 1H), 7.49 (q, 1H), 6.97 – 6.91 (m, 1H), 6.26 – 6.20 (m, 1H), 6.12 (q, 1H), 3.56 (s, 3H) ppm;
13C NMR (75 MHz, DMSO-d
6
) δ 125.0, 124.7, 121.9 – 121.3 (m), 120.7, 120.3, 118.3 (dd),
1
17.9 (dd), 111.0, 107.6 (dd), 34.4 (dd) ppm.
2
0
Ethyl 2-(4-bromophenyl)acetate (22): A 5-mL snap vial was charged with ethyl 2-bromo-2-
4-bromophenyl)acetate (21) (0.1 mmol, 1.0 equiv), Rh-6G (0.015 mmol, 0.15 equiv), DIPEA
(
(
-1
0.22 mmol, 2.2 equiv), G-1 (15 g L ), DMSO (1.5 mL) and sealed with a cap. The reaction
mixture was gently heated with a heat gun at 80 °C during 1 min until an isotropic solution was
obtained. The corresponding gel was obtained upon cooling the mixture to RT. The snap vial,
equipped with two needles to ensure a constant air atmosphere was irradiated through the plane
bottom side of the snap vial using a 530 (± 15) nm LED at 25 °C for 24 h. The yield was
determined by GC-FID with biphenyl as internal standard (35% yield).
20
Ethyl 2-(4-(2,2-diphenylethyl)phenyl)acetate (24): The compound was prepared according to
the general procedure. A 5-mL snap vial was charged with ethyl 2-(4-bromophenyl)acetate (22)
(0.1 mmol, 1.0 equiv), Rh-6G (0.015 mmol, 0.15 equiv), 1,1-diphenylethylene (23) (1.8 mmol,
29
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