Fine Tuning the Redox Potentials of Carbazolic Porous Organic Frameworks for Visible-Light Photoredox Catalytic Degradation of Lignin β-O-4 Models

Article abstract of DOI:10.1021/acscatal.7b01010

We report a facile approach to fine tune the redox potentials of π-conjugated porous organic frameworks (POFs) by copolymerizing carbazolic electron donor (D) and electron acceptor (A) based comonomers at different ratios. The resulting carbazolic copolymers (CzCPs) exhibit a wide range of redox potentials that are comparable to common transition-metal complexes and are used in the stepwise photocatalytic degradation of lignin β-O-4 models. With the strongest oxidative capability, CzCP100 (D:A = 0:100) exhibits the highest efficiency for the oxidation of benzylic β-O-4 alcohols, while the highly reductive CzCP33 (D:A = 66:33) gives the highest yield for the reductive cleavage of β-O-4 ketones. CzCPs also exhibit excellent stability and recyclability and represent a class of promising heterogeneous photocatalysts for the production of fine chemicals from sustainable lignocellulosic biomass.

Full text of DOI:10.1021/acscatal.7b01010

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Article
Fine Tuning the Redox Potentials of Carbazolic Porous Organic Frameworks
for Visible-Light Photoredox Catalytic Degradation of Lignin ##O#4 Models
Jian Luo, Xiang Zhang, Jingzhi Lu, and Jian Zhang
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 21 Jun 2017
Downloaded from http://pubs.acs.org on June 21, 2017
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Fine ꢀTuninge the Redox Potentials of Carbazolic
Porous Organic Frameworks for VisibleꢀLight
Photoredox Catalytic Degradation of Lignin β‐O‐4
Models
Jian Luo, Xiang Zhang, Jingzhi Lu, and Jian Zhang*
Department of Chemistry, University of NebraskaꢀLincoln, Lincoln, Nebraska, 68588ꢀ0304,
United States
*Eꢀmail: jzhang3@unl.edu
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ABSTRACT. We report a facile approach to fineꢀtune the redox potentials of πꢀconjugated
porous organic frameworks (POFs) by copolymerizing carbazolic electron donor (D) and
electron acceptor (A) based comonomers at different ratios. The resulting carbazolic copolymers
0
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(
CzCPs) exhibit a wide range of redox potentials that are comparable to common transitionꢀ
metal complexes and are used in the stepwise photocatalytic degradation of lignin βꢀOꢀ4 models.
With the strongest oxidative capability, CzCP100 (D:A = 0:100) exhibits the highest efficiency
for the oxidation of benzylic βꢀOꢀ4 alcohols, while as highly reductive CzCP33 (D:A = 66:33)
gives the highest yield for the reductive cleavage of βꢀOꢀ4 ketones. CzCPs also exhibit excellent
stability and recyclability, and represent a class of promising heterogeneous photocatalysts for
the production of fine chemicals from sustainable lignocellulosic biomass.
KEYWORDS: visible photocatalysis, carbazole, porous organic frameworks, lignin degradation,
heterogeneous catalysis
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1. INTRODUCTION
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During the past decade, photoredox catalysis has emerged as a powerful synthetic strategy in
1
organic chemistry. Indeed, the simple, mild, and environmentally benign photocatalytic process
driven by visible/solar light is a clean and renewable approach to realize many organic
2
3
transformations that are oftentimes unattainable under conventional thermal conditions. Due to
their large visible light cross sections and tunable photoredox potentials, transitionꢀmetal
2
+
complexes such as [Ru(bpy)
3
]
3
(bpy = 2,2’ꢀbipyridine) and facꢀIr(ppy) (ppy = 2ꢀphenylꢀ
4
pyridine) have been frequently employed as the photoredox catalysts, which unfortunately are
also expensive and potentially toxic. Although organic dyes can address these issues to some
5
extent, the low recyclability and/or difficulty in separation and still limit their ultimate
applications in scaleꢀup synthesis. Recently, metalꢀfree solid materials, such as graphitic carbon
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nitride (gꢀC
3
N
4
), porous organic polymers (POPs), and πꢀconjugated porous organic
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frameworks (POFs or CMPs), have been developed as heterogeneous visible light
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photocatalysts. POFs, in particular, with large surface area and permanent nano/mesosized
1
0
pores, outstanding thermal stability, and chemically tunable photoactive πꢀelectron backbone,
provides an ideal photocatalytic platform for green and economical organic synthesis. In the past
several years, POFs have been used as effective visible light photocatalysts for a variety of
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organic reactions including oxidation of sulfides, amine, and arylboronic acids, reduction of
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15
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halides, CꢀC bond formation, and freeꢀradical or cationic polymerization, among others.
Lignin makes up 15ꢀ25% of the lignocellulosic biomass that is currently mostly treated as a
17
waste product. With the urgent demand of alternative source of energies and fine chemicals
from sustainable sources, degradation of lignin to obtain valueꢀadded energy fuels or small
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molecules has gained increasing attention. One common method of lignin degradation is to
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cleave the CꢀO bond of the βꢀOꢀ4 ethers that consist approximately 50% of the linkage structures
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in lignin. This twoꢀstep approach usually requires the selective oxidation of the benzylic βꢀOꢀ4
alcohol to benzylic βꢀOꢀ4 ketone and a subsequent reductive process that cleaves the CꢀO bond,
2
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which allows the access to complementary fragmentation partners. Recently, photocatalysis has
been considered as an alternative strategy for the degradation of lignin models, and transition
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metal complexes and inorganic semiconductors have been tested as the photocatalysts. We
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questioned the possibilities of using POFs as metalꢀfree heterogeneous photocatalysts in the
degradation of lignin models. The rationale of this approach, aside from the high recyclability, is
the exceptionally high tunability of POFs, which is expected to facilitate the identification of the
optimum photocatalyst with appropriate redox potentials for each of the two step reactions.
Herein, we employ the statistical copolymerization of carbazoleꢀbased donor/acceptor (D/A)
23
comonomers at different ratios as a systematic approach to generate carbazolic POFs (CzCPs)
for visible light mediated degradation of lignin βꢀOꢀ4 models. Nine CzCPs with a D:A ratio
between 100:0 and 0:100 (CzCP0–CzCP100) were constructed and their porosity, photophysical
and electrochemical parameters were characterized. CzCP100 (D:A = 0:100), with the highest
oxidative capability, exhibits the best efficiency for the oxidation of benzylic βꢀOꢀ4 alcohols,
while as CzCP33 (D:A = 66:33) gives the highest yield for the reductive cleavage of βꢀOꢀ4
ketones thanks to its optimized redox potentials. To the best of our knowledge, this study
represents the first report of photocatalytic POFs that catalyze the lignin degradation via the
stepwise oxidation and reduction approach.
2
. RESULTS AND DISCUSSION
2
.1. Design plan. We select two carbazoleꢀbased monomers, DCB (1,4ꢀdi(9Hꢀcarbazolꢀ9ꢀ
24
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yl)ꢀbenzene) and 4CzIPN (1,2,3,5ꢀtetrakis(carbazolꢀ9ꢀyl)ꢀ4,6ꢀdicyanobenzene ) as
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comonomers because the carbazole moieties can undergo a smooth and uniform FeCl
3
ꢀinduced
oxidative polymerization to form carbazoleꢀbased POFs (CzꢀPOFs). The high solubility of both
comonomers in the reaction solvent (e.g. CH Cl ) and the similarly high reactivity of carbazole
unit toward the strong oxidizer (FeCl ) make the statistic copolymerization a likely process. The
statistical nature of this synthesis indicates that the final copolymer is best described as a
random” copolymer. This homo crossꢀcoupling method is also in contrast with the previous
copolymerization approach where three comonomers are needed for the hetero crossꢀcoupling
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(e.g. Sonogashira or Suzuki ). Since DCB is an excellent electron donor and the two cyano
groups in 4CzIPN enables its strong electronꢀaccepting capability, one can predict that a
copolymer with the ratio between DCB and 4CzIPN (D and A) of 100:0 and 0:100 would be
highly reductive and highly oxidative, respectively, and the copolymers would exhibit a range of
average redox potentials that are mainly depending on the D:A ratios (Scheme 1). This is highly
valuable for the optimization of the photocatalysts to promote a specific organic transformation.
Scheme 1. The Schematic Diagram of the Design of Copolymer CzCPs.
2
3
.2. Synthesis and Characterization. CzCPs were prepared using FeCl ꢀinduced, oxidative
2
6
polymerization of DCB and 4CzIPN at nine different ratios (i.e. 100:0, 90:10, 80:20, 66:33,
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55:45, 40:60, 25:75, 10:90, and 0:100). The carbazole groups are oxidized and the resulting
carbon radicals couple with each other and generate 3ꢀD porous networks as fine powders with
high yields (>95%). CzCPs were numbered using the percentage of comonomer 4CzIPN as
shown in Table 1 (e.g. CzCP33 contains 33 mol% 4CzIPN and 67 mol% DCB). Note that CzCP0
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has the same structure of previously reported CPOPꢀ2. All other polymers are reported here for
the first time.
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Figure 1. (a) Solid state CP/MAS C NMR and (b) FTꢀIR spectra of CzCPs. The solution
C
NMR spectra and FTꢀIR spectra of comonomers DCB and 4CzIPN are included for comparison.
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2 2 3
All nine CzCPs are insoluble in common organic solvents, such as CH Cl , CHCl , THF,
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acetone, and DMF, indicating a highlyꢀcrosslinked network structure. Scanning electron
microscopy (SEM) images (Figure S4, Supporting Information) show that all CzCPs are mostly
composed of particles at submicron scale, which become smaller as the percentage of 4CzIPN
increases. Thermal gravimetric analysis (TGA) of CzCPs reveals their excellent thermal stability
(
Figure S5, Supporting Information), with the significant thermal decomposition at a temperature
of 500 ºC. Powder Xꢀray diffraction analysis suggests the amorphous nature of all CzCPs (Figure
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S6, Supporting Information). Solid state CP/MAS C NMR spectra (Figure 1a) reveal five broad
resonance peaks at 139, 136, 124, 119, and 108 ppm are observed for CzCP0, consistent with
2
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CPOPꢀ2 (Figure 1a). Specifically, the peaks at 139 and 136 ppm correspond to the aryl carbons
next to the carbazolic nitrogen atom. The peak at 124 ppm can be attributed to other substituted
aryl carbon and the peaks at 119 and 108 ppm are due to the unsubstituted aryl carbons. As the
molar percentage of 4CzIPN in CzCPs increases, the peak intensity at 136 and 119 ppm
decreases and the resonance peaks at 108 and 124 ppm gradually shift to 110 and 125 ppm,
respectively (Figure 1a). In addition, a characteristic board peak at 145 ppm that can be
attributed to 4CzIPN emerges. FTꢀIR spectra of CzCPs also indicate the successful
−1
copolymerization. For example, the intensity of the peak at 1514 cm (CꢀC stretching in the
phenyl ring in DCB) decreases as the molar percentage of 4CzIPN increases (Figure 1b), which
−1
is also accompanied by the decrease of the intensity of absorption peaks at 726 cm and 767
−1
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cm (CꢀH bending in the bisubstituted phenyl ring) (Figure 1b).
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Table 1. Composition, Apparent Brunauer−Emmett−Teller Surface Areas (SABET), Pore
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Volume, Redox Potentials, and Optical Properties of CzCPs.
SABET
–1
V
(cm³ g
total
–1
V
(cm g
meso
–1
λ
ex
λ
em
oxd
1/2
redd
1/2
ox
red
1/2
e
POFs
DCB%
a
b
3
c
V
meso/Vtotal
E
E
*
E
1/2
*
E
E
0ꢀ0’
(
m² g
992
690
962
)
)
)
(nm)
338
343
340
339,
(nm)
448
428
438
CzCP0
CzCP10
CzCP20
100%
90%
80%
0.70
0.43
0.69
0.44
0.24
0.49
63%
56%
71%
+1.23
+1.27
+1.26
ꢀ1.99
ꢀ1.99
ꢀ1.98
3.22
3.26
3.24
425,
556
CzCP33
CzCP45
CzCP60
67%
55%
40%
1280
1208
1192
0.90
0.91
0.86
0.56
0.66
0.58
62%
73%
67%
+1.47
+1.50
+1.50
ꢀ2.09
ꢀ1.72
ꢀ1.69
+1.20
+1.58
+1.54
ꢀ1.86
ꢀ1.80
ꢀ1.73
3.29
3.30
3.23
4
34
3
4
40,
41
422,
569
3
40,
441,
566
435
434
434
434
CzCP75
CzCP90
CzCP100
25%
10%
1180
1082
1077
0.83
1.10
0.68
0.54
0.95
0.39
65%
86%
57%
561
564
539
+1.72
+1.83
+1.83
ꢀ1.70
ꢀ1.13
ꢀ0.99
+0.84
+1.40
+1.59
ꢀ0.82
ꢀ0.70
ꢀ0.75
2.54
2.53
0%
2.58
a
2
−1
b
3
−1
Surface area (m g ) calculated from the nitrogen adsorption branch based on the BET model. The total pore volume (cm g
)
c
d
calculated at P/P
0
= 0.95. The volume of mesopores with pore width > 2 nm. All potentials are given in volts versus the saturated
e
calomel electrode (SCE). E0ꢀ0’, the zeroꢀzero vibrational state excitation energy, was estimated using the medium wavelengths
between the photoluminescence excitation peak (λex) and emission peak (λem) and was used to calculate *E1/2 (= E1/2 + E0ꢀ0’
and *E1/2 (= E0ꢀ0’ – E1/2 ).
ox
red
)
red
ox
2
The porosity parameters of CzCPs were characterized by N adsorption–desorption
measurements at 77 K (Table 1 and Figure S7). A rapid N
0.05) indicates the typical micropores and the gradual increase of the N
.9) is attributed to the mesopores in CzCPs. The hysteresis between adsorption and desorption is
observed for all networks, consistent with the presence of both microꢀ and mesoporosity as well
2
uptake at low relative pressure (P/P
0
<
2
uptake (P/P = 0.05–
0
0
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as the pore network effects. All CzCPs except CzCP10 exhibit a BET surface area (SABET
)
2
−1
over 900 m g ; as the ratio of 4CzIPN increases, the SABET of CzCPs first increases (CzCP10 ~
2
−1
CzCP33, from 690 to 1280 m g ), and then decreases (CzCP45 ~ CzCP100, from 1192 to 1077
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m g ). CzCP33 displays the highest SABET (1280 m g ), which may be attributed to the ideal
stoichiometric ratio (2:1) between numbers of carbazole groups in DCB (two) and 4CzIPN (four)
that likely mitigates the space crowding and crosslinking occurring during the copolymerization.
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Total pore volumes (Vtotal) of CzCPs (calculated from single point N uptake at P/P = 0.95) are
3
−1
ranging between 0.43 to 1.1 cm g , without a clear trend. However, it is gratifying that in all
CzCPs more than 56% of the pore volume is contributed by the mesopores (pore width > 2 nm,
Table 1), in which the organic transformations are expected to occur.
Overall, two broad absorption bands are present in the UVꢀvisible spectra of CzCPs (Figure
S9). As the percentage of 4CzIPN increases, the main absorption band (350ꢀ385 nm) does not
shift significantly while the intensity of the shoulder band (430ꢀ450 nm) increases, which is
consistent with the gradual color change of CzCPs from light grey (CzCP0) to yellow (CzCP100)
(
Figure S9). The enhanced visible light absorbance of CzCPs is an ideal attribute for
photocatalysis. Photoluminescence properties of CzCPs were also characterized. In general, the
emission of CzCP0, CzCP10, and CzCP20, in which the component of 4CzIPN is low (< 20%),
is composed of a single peak between 428 to 438 nm. When the component of 4CzIPN is above
75% as such in CzCP75, CzCP90, and CzCP100, a single emission peak around 539 to 564 nm
appears. Interestingly, these two emission peaks coexist in CzCP33, CzCP45, and CzCP60 with
irregular change of their relative intensity, which can be tentatively attributed to the subtle
3
0
difference in the local distribution of the two comonomers (at the surface, core, or as a shell).
The ground state redox potential of CzCPs was measured by cyclic voltammetry (CV)
(
Figure S14). As shown in Table 1, as the percentage of 4CzIPN increases, the oxidative
ox
potential (E1/2 ) gradually increases from +1.23 V (CzCP0) to +1.83 V (CzCP100) and the
red
31
reductive potential (E1/2 ) gradually decreases from –2.09 V (CzCP33) to –0.99 V (CzCP100).
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This is reasonable since both the HOMO and LUMO energy levels are expected to decrease as
more electronꢀwithdrawing groups (i.e. ꢀCN) are incorporated within CzCPs. The excited state
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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1
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9
0
ox
red
redox potentials (*E1/2 and *E1/2 ) were calculated based on the free energy change (E0−0’
)
between ground state and excited state and a similar general trend was observed: as the
ox
red
percentage of acceptor 4CzIPN increases, *E1/2 (except CzCP75) and *E1/2 gradually become
more positive. Remarkably, the redox potentials of CzCPs almost covers the whole range of the
1
a
ox
redox potentials for the common transitionꢀmetal complexes. For example, *E1/2 = +1.59 V
ox
and E1/2 = +1.83 V for CzCP100, which is comparable with that of highly oxidative
2
+
ox
ox
1a
red
3
[Ru(bpz) ] (bpz: 2,2’ꢀbipyrazine, *E1/2 = +1.45 V, E1/2 = +1.86 V); *E1/2 = –1.86 V and
red
E
1/2 = –2.09 V for CzCP33, which is comparable with that of highly reductive facꢀIr(ppy)
3
red
red
1a
(
*E1/2 = –1.73 V, E1/2 = –2.19 V). More importantly, such high reductive or oxidative
potentials can exist within a single catalyst, such as CzCP33, CzCP45, and CzCP60.
2
.3. Photocatalytic oxidation of benzyl alcohol and
β-O-4 alcohols. The aerobic oxidation of
benzyl alcohol usually requires a highly oxidative photocatalyst. Therefore, we first tested
ox
ox
CzCP100 (*E1/2 = +1.59 V and E1/2 = +1.83 V) for the oxidation of a prototypic benzyl
ox
alcohol, 1ꢀ(4ꢀmethoxyphenyl)ꢀethanꢀ1ꢀol (1, E1/2 = +1.67 V, Figure S15). We conducted this
reaction in a mixture consisting CzCP100 (1.5 mol%, based on monomer 4CzIPN) in acetone
under an O
2
atmosphere and the irradiation from a 26 W white compact fluorescent lamp (CFL),
which gave the corresponding ketone product 2 in 11% yield in 24 h (Table S1, entry 1).
2
+
ox
Replacing CzCP100 with other highly oxidative photocatalysts such as [Ru(bpz)
3
]
(E1/2
=
+
ox
+
1.86 V) and Acr ꢀMes (9ꢀmesitylꢀ10ꢀmethylꢀacridinium, E1/2 = +2.06 V) only slightly
increased the yields to 15% and 39%, respectively (Table S1, entries 2ꢀ3), which suggests the
direct photoinduced single electron transfer (SET) from benzyl alcohol to photocatalysts is not
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favorable. It is known that Nꢀhydroxyphthalimide (NHPI) can serve as an effective hydrogen
0
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0
3
2
atom transfer (HAT) catalyst for the oxidation of benzyl alcohol. From a thermodynamic point
ox
of view, it is favorable for CzCP100 to oxidize NHPI (E1/2 = +1.42 V, Figure S15) to generate
the phthalimideꢀNꢀoxyl (PINO) radical for the aerobic oxidation of benzyl alcohol. We thus
conducted the oxidation of 1 in the presence of 15 mol% of NHPI as the cocatalyst. This
CzCP100/NHPI/O
2
photocatalytic system indeed exhibited an excellent activity and selectivity
max = 465 nm, 135
(
99% yield after 24 h, Table 2, entry 1). A blue lightꢀemitting diode (LED) (
λ
mW) was also an effective light source (Table 2, entry 2) although a longer reaction time (36 h)
was required. Control experiments confirmed the essential role of photocatalyst, NHPI, light, and
O
2
(Table 2, entries 3ꢀ6). A reduced loading of NHPI (10 mol%, Table S1, entry 4) gave a lower
yield (70%), while a higher loading (20 mol%) led to a lower selectivity (100% conversion with
81% yield, Table S1, entry 6). The catalytic system also displayed a good tolerance to H O: a 92
yield was obtained in a mixture of acetone:water (9:1, v/v) (Table 2, entry 7). Overall, our
2
%
33
2
CzCP100/NHPI/O catalytic system was comparably efficient as tertꢀbutyl nitrite/DDQ (99%
3
4
2+
35
yield), and more efficient than BQ (59% yield) and [Ru(dtbbpy)
3
] /DIPEA (trace) under the
same condition (Table S1, entries 7ꢀ9).
1
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Table 2. Initial Studies for the Photoinduced Oxidation of Benzylic Alcohol 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
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2
3
4
5
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8
9
0
O
OH
CzCP100
NHPI
acetone, rt.
, light
O
O
O
2
1
2
Conversion
c
Entry
1
Condition
Standard
b
Yield (%)
99
(%)
a
100
Condition
d
2
3
Blue LED
100
0
96
Without light
NR.
Without
CzCP100
4
<5
Trace
5
6
Without NHPI
15
<5
11
Without O
2
Trace
Acetone/H
2
O
7
100
92
9
:1 as solvent
a
Standard condition: CzCP100 (1.5 mol %), 1 (50
mmol), NHPI (7.5 mg, 15 mol %), O (1 atm), 5 mL of
acetone, 26 W CFL, room temperature for 24 h. Measured by
μL, 0.35
2
b
1
c
d
H NMR. Isolated yield. 36 h.
Overall, CzCPs showed good to excellent activities for the aerobic oxidation of benzyl
alcohol 1 (47ꢀ99% yield) with excellent selectivity (the difference between conversion and yield
less than 5%) (Table 3). However, except CzCP90 and CzCP100, most CzCPs were moderately
ox
active, consistent with their inferior oxidative potentials (E1/2 < +1.80 V, Table 1). Since the
ox
E
1/2 of NHPI is +1.42 V, the slow reaction rates associated with CzCP0, CzCP10 and CzCP20
ox
are attributed to the poor thermodynamic driving force (E1/2 ranging from +1.23 V to 1.26 V),
while the poor activities of CzCP33, CzCP45, CzCP60, and CzCP75, despite of favorable
ox
reduction potentials (E1/2 ranging from +1.47 V to +1.72 V), are mostly likely due to an
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unfavorable kinetics. That is, a relatively large overpotential (>0.4 V) is required to efficiently
drive the oxidation step. Indeed, generating PINO radicals from NHPI via the stepꢀwise removal
of an electron and a proton, which often needs to overcome a large kinetic barrier. Although
proton coupled electron transfer (PCET) can be used as an effective strategy to improve the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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6
7
8
9
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1
2
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4
5
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9
0
32b
kinetics, the lack of an effective proton acceptor in CzCPs makes this process unlikely to
occur.
a
Table 3. Optimization of Catalyst for the Photocatalytic Oxidation of Benzylic Alcohol 1.
b
c
Entry
Photocatalyst
CzCP0
Conversion (%)
Yield (%)
1
2
3
4
5
6
7
8
9
55
67
66
72
68
50
55
92
100
52
65
66
69
64
47
53
89
99
CzCP10
CzCP20
CzCP33
CzCP45
CzCP60
CzCP75
CzCP90
CzCP100
a
Reaction condition: 4ꢀmethoxyꢀ
αꢀmethylbenzyl alcohol 46.0 mg (50 µL, 0.3 mmol), NHPI
7.5 mg (0.045 mmol, 15 mol%), photocatalyst 1.5 mol% (based on the monomer), acetone 5
b
1
2
mL with O (1 atm), 26 W white light for 24 h at room temperature. Measured by H NMR.
c
Isolated yield.
Scheme 2 illustrates the proposed reaction mechanism for the oxidation of
βꢀOꢀ4 alcohols
2
by the CzCP100/NHPI/O catalytic system. To generate the highly oxidative ground state
•+
red
red
2
CzCP100 , the photoexcited *CzCP100 (*E1/2 = –0.75 V) first reduces O (E1/2 = –0.82 V)
•
–
to superoxide radical O
2
. This is consistent with the fact that the emission of CzCP100 is
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•
＋
quenched by O
2
(Figure S11). The resulting CzCP100 further oxidizes NHPI and afford the
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2
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9
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2
3
4
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7
8
9
0
PINO radical and a proton, and the ground state CzCP100 is regenerated. Note that PINO can
•–
also be generated through hydrogen abstraction of NHPI by O
benzyl hydrogen atom from the ꢀOꢀ4 alcohol to afford the
during which NHPI is regenerated. This is a thermodynamically favorable step based on the
2
. PINO further abstracts the
β
αꢀhydroxybenzylic radical 3b’,
−1
−1
BDE of C
3b’ is intercepted by O
hydrogen atom from NHPI and releases H
α
−H (75−85 kcal mol ) in
to afford the peroxy radical intermediate 4b’, which abstracts a
and the ꢀOꢀ4 ketone 4b as the product.
βꢀOꢀ4 alcohols and O−H (88 kcal mol ) in NHPI. Radical
2
2
O
2
β
Scheme 2. Proposed Mechanism for the Oxidation of Lignin
β-O-4 Alcohol Models.
CzCP100
O
OH
H
O
O
N OH
NHPI
O
O
3b
Photocatalytic
*CzCP100
SET
Cycle
HAT
OH
O
-
H
O
SET
2 2
PINO + H O
2
N O
PINO
CzCP100
O
O
3b'
2
NHPI + O
2
O
2
PINO
+
2 2
H O
NHPI
OH
O
O
O
O
O
O
O
O
O
4
b
4b'
With the optimized reaction condition in hand, the CzCP100/NHPI/O
2
photoredox catalytic
system was applied to lignin ꢀOꢀ4 models. A series of ꢀOꢀ4 alcohols, including several with
β
β
a hydroxymethyl fragment that is often featured in lignin, were employed to evaluate the scope
of substrates (Figure 2). Excellent activity and selectivity were observed, for instance, for the
benzylic carbonyl compounds 4aꢀ4j (83ꢀ99% yield). Aliphatic alcohols (3c, 3g and 3i) and
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phenols (3h, 3i) were well tolerated under the oxidation condition. More importantly, the
separation of the polymer catalyst can be conducted by simple filtration or centrifugation and
there was almost no byproduct or impurities in the reaction mixture (Figure S2).
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Lignin
Lignin oxide
Ketone
Phenol
O
24 h
89%
O
Figure 2. Photoredox catalyzed oxidation and degradation of lignin models.
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2.4. Photocatalytic cleavage of
β
-O-4 ketones. The initial oxidation of the benzylic alcohol
0
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2
3
4
5
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8
9
0
1
2
3
4
5
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7
8
9
0
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2
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5
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8
9
0
1
2
3
4
5
6
7
8
9
0
3
6
decreases the CꢀO bond energy in the
βꢀOꢀ4 linkage from ~69.2 to ~55.9 kcal/mol, which
allows for an easier subsequent reductive bond cleavage to access highꢀvalue aromatic products.
Nevertheless, such bond cleavage step still requires a highly reductive photocatalyst. For
red
example, the E1/2 of the lignin oxide 4b was determined as –1.84 V. Using acid additives such
as Brønsted acid (e.g. AcOH) or Lewis acid (e.g. LiBF
4
) can further reduce this potential to –
1
.53 V (Figure S16), which is still considerably high for many common photocatalysts.
Therefore, we first chose CzCP33 as the initial photocatalyst (2.0 mol% based on comonomers)
red
for the cleavage of the lignin
βꢀOꢀ4 ketones due to its strong reduction capability (*E1/2 = –
red
1
.86 V, E1/2 = –2.09 V).
In the presence of a Brønsted acid (HCOOH, 5.0 eq.), a sacrificial electron donor (DIPEA, N,
Nꢀdiisopropylethylamine, 5.0 eq.), and light irradiation from a 26 W white CFL at room
temperature, lignin oxide 4b was efficiently converted to acetophenone (5a, 89% yield) and
phenol (6b, 86% yield) (Table 4, entry 1). Control experiments confirmed that the photocatalyst,
formic acid, DIPEA, and light are all essential for this reaction (Table 4, entries 2ꢀ5). Lewis acid
LiBF
significantly retarded in the presence of a weaker Brønsted acid (i.e. acetic acid) or a weaker
hydrogen donor (i.e. Et N and MeOH) (Table 4, entries 7ꢀ9).
4
also promotes this reaction (Table 4, entry 6). It is noteworthy that the reaction is
3
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5
5
5
5
5
5
5
6
Table 4. Initial Studies for the Photocatalytic Cleavage of Lignin
βꢀOꢀ4 Ketones.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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5
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9
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1
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0
1
2
3
4
5
6
7
8
9
0
b
c
Entry
Reaction Condition
Conversion (%)
Yield (%)
a
d
1
2
3
4
5
6
7
8
Standard condition
100
0
89
Without light
Without photocatalyst
Without DIPEA
N.R.
N.R.
0
<5
<5
100
74
17
Trace
Trace
Without HCOOH
e
LiBF
Et
LiBF
4
replaces HCOOH
91
3
N replaces DIPEA
60
15
4
replaces HCOOH and
MeOH replaces DIPEA
9
AcOH replaces HCOOH and
28
23
3
Et N replaces DIPEA
a
Standard condition: 4b 54 mg (0.2 mmol), DIPEA 174 µL (1.0 mmol), HCOOH 38 µL (1.0
mmol), CzCP33 2.0 mol% (based on comonomer), MeCN 4 mL under Ar, 26 W CFL for 24
b
1
c
h at room temperature. Measured by H NMR. Isolated yield, based on acetophenone.
8
d
e
6% yield of phenol was also obtained. 18 h.
Compared to CzCP33, other CzCPs are less active under the same reaction conditions (21ꢀ
1% yield, Table 5). We first attempted to correlate such result to the energetics of the two SET
8
processes involved in this reaction, namely, the reduction of the lignin oxide and oxidation of
ox
DIPEA (vide infra). Since the oxidation of DIPEA (E1/2 = +0.81 V) is a relatively favorable
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process for most CzCPs, the reduction of the lignin oxide is likely the rateꢀdetermining step. The
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9
0
highest reaction yield of CzCP33 seems to be consistent with its largest reductive capability
red
(
E
1/2 = –2.09 V). However, it is of interest that CzCP0, CzCP10, and CzCP20 gave sluggish
red
reaction yields (< 40%) despite their large *E1/2 (~ –2 V), which is best attributed to the
unfavorable reduction kinetics at their excited state. Thus, it is likely that this reduction reaction
is promoted more favorably by the reduced photocatalyst at its longerꢀlived ground state.
Therefore, the appropriate D:A ratio in CzCP33 ensures its good oxidative capability at the
ox
red
excited state (*E1/2 = 1.20 V) and excellent reductive capability at the ground state (E1/2 = –
2.09 V), and results in the highest reaction activity among the CzCPs. It should be noted that
although others characteristics of POFs such as surface area and pore volume could also affect
the photocatalytic performance, they are generally considered to have a less significant
2
3a
contribution.
a
Table 5. Optimization of Catalyst for the Photocatalytic Reduction of Lignin
βꢀOꢀ4 Ketone 4b.
b
c
Entry
Photocatalyst
CzCP0
Conversion (%)
Yield (%)
1
2
3
4
5
6
7
8
9
35
47
52
100
75
91
50
31
72
30
41
44
89
68
82
41
21
63
CzCP10
CzCP20
CzCP33
CzCP45
CzCP60
CzCP75
CzCP90
CzCP100
a
Reaction condition: 4b 54 mg (0.2 mmol), DIPEA 174 µL (1.0 mmol),
HCOOH 38 µL (1.0 mmol), CzCP33 2.0 mol% (based on comonomer),
MeCN 4 mL under Ar, 26 W CFL for 24 h at room temperature.
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b
1
c
Measured by H NMR. Isolated yield, based on acetophenone.
0
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8
9
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Since the fluorescence of CzCP33 is strongly quenched by the DIPEA (Figure S12) but is not
quenched by the ꢀOꢀ4 ketone 4b (Figure S13), a reductive quenching process is likely
involved in the reduction of ꢀOꢀ4 ketones, and the proposed reaction mechanism is illustrated
In the CzCP33/DIPEA/formic acid catalytic system, CzCP33 acts as
photocatalyst, formic acid is the Brønsted acid cocatalyst, and DIPEA provides the proton and
β
β
2
1a,37
in Scheme 3.
ox
ox
electron. The photoexcited *CzCP33 (*E1/2 = 1.20 V) first oxidize DIPEA (E1/2 = +0.81 V) to
•
－
red
generate the highly reductive CzCP33 (E1/2 = –2.09 V), which then further reduces the
βꢀOꢀ
red
4 ketone 4b in the presence of formic acid (FA) (E1/2 = –1.53 V for 4b-FA complex) and
•–
regenerates the ground state photocatalyst CzCP33. The anion radical 4b-FA is further
rearranged and decomposed into a formate, phenol product 6b, and radical 5a’. The 5a’ radical
abstracts a hydrogen atom from the oxidized DIPEA to afford the ketone product 5a.
Scheme 3. Proposed Mechanism for Reduction of Lignin
β
-O-4 Ketone.
H
O
O
H
O
O
O
O
CzCP33
O
O
HCOOH
O
O
O
4b-FA
4
b
*
CzCP33 Photocatalytic
H
H
Cycle
SET
O
O
O
O
H
N
SET
H
O
O
O
CzCP33-
O
O
O
O
N
b-FA-
4
N
O
O
HAT
O
+
HCOO-
+
HO
O
O
5
a
N
a
5 '
6b
2
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The CzCP33/formic acid/DIPEA photocatalytic system was next applied to a wide scope of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
β
ꢀOꢀ4 ketones, 4a~4j. As shown in Figure 2, good to excellent yields were obtained after
visible light irradiation for 16ꢀ24 h (69ꢀ91% yield for the ketone products 5aꢀg, 74ꢀ86% yield for
the phenol products 6aꢀc). An excellent selectivity was also observed: no ꢀCꢀC cleavage
The aliphatic alcohols 4c, 4g, and 4i were tolerated
α, β
3
4,38
product or elimination product generated.
under this reaction condition. However, the phenol group slightly reduced the yield of benzylic
carbonyl compounds (78% yield of 5h from 4h, 69% yield of 5i from 4i). This is likely because
phenol can act as the proton or electron donor and decompose during the reaction. This can also
explain why the yields of phenol products 6 were always lower than those of their corresponding
benzylic ketone products 5. As a heterogeneous catalytic system, the photocatalyst can be easily
separated by filtration or centrifugation, and besides the formic acid and DIPEA, no byproducts
or impurities appeared in the reaction mixture (Figure S3).
2
.6. Stability and Recyclability. Besides the excellent photocatalytic activity and wide
substrate scope, the stability and recyclability of CzCPs as the heterogeneous catalysts were
noteworthy. All CzCPs can easily be separated from the reaction mixtures through centrifugation
or filtration. CzCP100 and CzCP33 were reused five times in the oxidation of benzyl alcohol 1
and reductive cleavage of
βꢀOꢀ4 ketone 4b, respectively. For the oxidation of benzyl alcohol 1
(
Figure 3a), after five times of reuse, the reaction rate slightly decreased from 98% to 82% (24
h). A higher reaction yield (95%) was obtained when the reaction time was increased to 36 h.
This mainly due to the 30% loss of the photocatalyst CzCP100 during the separation process
after five times of recycled use. However, chemical stability of CzCP100 is excellent: after five
times of reuse, all the IR peaks of CzCP100 remained unchanged (Figure S17). In the reductive
cleavage of
βꢀOꢀ4 ketone 4b, the reaction rate remained relatively stable, especially after the
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2
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2
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2
2
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first three times of recycles. After five times of reuse, 75% yield and 84% yield were obtained
after 24 h and 32 h reaction, respectively. Partial loss of the photocatalyst CzCP33 was also
observed during the recovery process. Again, the FTꢀIR spectra of recovered photocatalyst did
not show s significant difference from the original sample (Figure S18).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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5
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9
0
1
2
3
4
5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. Recycle of (a) CzCP100 for the oxidation of benzylic alcohol 1 and (b) CzCP33 for the
reductive cleavage of
βꢀOꢀ4 ketone 4b. The gray bars are the reaction yields after 24 h reaction,
1
determined by H NMR. The ketone product 5a was used to determine the yield of the
degradation of 4b.
3
. CONCLUSIONS
In summary, we have demonstrated that the copolymerization of carbazoleꢀbased electron
Formatted: Justified, Indent: First line: 0.14"
donor and electron acceptor based comonomers is an effective strategy to fineꢀtune the
photoredox potentials of the resulting πꢀconjugated CzCPs. Using different ratios of D/A
comonomers, a wide range of redox potentials comparable to common transitionꢀmetal
2
−1
complexes were obtained. Together with their high BET surface area (690ꢀ1280 m g ) and
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−
1
9
1
1
1
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1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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5
5
5
5
5
5
5
6
large pore volume (0.43ꢀ1.10 mL g ), these CzCPs can used as excellent heterogeneous
photocatalysts for degradation of the lignin ꢀOꢀ4 models. CzCPs exhibit high efficiency and
selectivity for the aerobic oxidation of ꢀOꢀ4 alcohols and reductive cleavage of ꢀOꢀ4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
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8
9
0
1
2
3
4
5
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8
9
0
1
2
3
4
5
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8
9
0
1
2
3
4
5
6
7
8
9
0
β
β
β
ketones. CzCPs are highly stable and can be recycled multiple times without a significant loss of
the catalytic activity. To the best of our knowledge, our work represents the first report of POFs
that promote the photocatalytic lignin degradation via the stepwise oxidation and reduction
approach.Our work represents the first report of POFs that promote the photocatalytic lignin
degradation via the stepwise oxidation and reduction approach. The copolymerization via homo
crossꢀcoupling is a straightforward approach that can be adapted toward a wider scope of other
organic transformations.
ASSOCIATED CONTENT
Supporting Information.
The Supporting Information is available free of charge on the ACS Publications website.
Materials, general procedures, synthesis, physical measurements, fluorescence spectra, and
catalyst recycle study.
AUTHOR INFORMATION
Corresponding Author
*Eꢀmail for J.Z.: jzhang3@unl.edu
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENT
0
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J.Z. acknowledges a National Science Foundation CAREER Award (DMRꢀ1554918) for
support of this research.
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REFERENCES
0
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2
3
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5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
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9
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2
3
4
5
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0
1
2
3
4
5
6
7
8
9
0
(
(
1)
2)
(a) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. Chem. Rev. 2013, 113, 5322ꢀ5363; (b)
Schultz, D. M.; Yoon, T. P. Science 2014, 343, 1239176.
(a) Ischay, M. A.; Anzovino, M. E.; Du, J.; Yoon, T. P. J. Am. Chem. Soc. 2008, 130,
1
2886ꢀ12887; (b) Nicewicz, D. A.; MacMillan, D. W. C. Science 2008, 322, 77ꢀ80; (c)
Narayanam, J. M.; Tucker, J. W.; Stephenson, C. R. J. Am. Chem. Soc. 2009, 131, 8756ꢀ
757.
(a) Karkas, M. D.; Porco, J. A., Jr.; Stephenson, C. R. Chem. Rev. 2016, 116, 9683ꢀ9747;
b) Ravelli, D.; Protti, S.; Fagnoni, M. Chem. Rev. 2016, 116, 9850ꢀ9913; (c) Arora, A.;
8
(
3)
(
Weaver, J. D. Acc. Chem. Res. 2016, 49, 2273ꢀ2283; (d) Morris, S. A.; Wang, J.; Zheng,
N. Acc. Chem. Res. 2016, 49, 1957ꢀ1968; (e) Chen, J. R.; Hu, X. Q.; Lu, L. Q.; Xiao, W.
J. Chem. Soc. Rev. 2016, 45, 2044ꢀ2056.
AriasꢀRotondo, D. M.; McCusker, J. K. Chem. Soc. Rev. 2016, 45, 5803ꢀ5820.
(a) Ghosh, I.; Ghosh, T.; Bardagi, J. I.; König, B. Science 2014, 346, 725ꢀ728; (b)
Romero, N. A.; Nicewicz, D. A. Chem. Rev. 2016, 116, 10075ꢀ10166; (c) Theriot, J. C.;
Lim, C. H.; Yang, H.; Ryan, M. D.; Musgrave, C. B.; Miyake, G. M. Science 2016, 352,
1082ꢀ1086; (d) Majek, M.; Jacobi von Wangelin, A. Acc. Chem. Res. 2016, 49, 2316ꢀ
2327; (e) Pitre, S. P.; McTiernan, C. D.; Scaiano, J. C. Acc. Chem. Res. 2016, 49, 1320ꢀ
(
(5)
4)
1330.
(
(
(
6)
7)
8)
9)
Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.;
Antonietti, M. Nat. Mater. 2009, 8, 76ꢀ80.
Li, R.; Wang, Z. J.; Wang, L.; Ma, B. C.; Ghasimi, S.; Lu, H.; Landfester, K.; Zhang, K.
A. I. ACS Catal. 2016, 1113ꢀ1121.
Zhang, K.; Kopetzki, D.; Seeberger, P. H.; Antonietti, M.; Vilela, F. Angew. Chem., Int.
Ed. 2013, 52, 1432ꢀ1436.
Wong, Y. L.; Tobin, J. M.; Xu, Z.; Vilela, F. J. Mater. Chem. A 2016, 4, 18677ꢀ18686.
(
(
10) (a) Jiang, J. X.; Su, F.; Trewin, A.; Wood, C. D.; Campbell, N. L.; Niu, H.; Dickinson,
C.; Ganin, A. Y.; Rosseinsky, M. J.; Khimyak, Y. Z.; Cooper, A. I. Angew. Chem., Int.
Ed. 2007, 46, 8574ꢀ8578; (b) Kaur, P.; Hupp, J. T.; Nguyen, S. T. ACS Catal. 2011, 1,
819ꢀ835; (c) Wu, D.; Xu, F.; Sun, B.; Fu, R.; He, H.; Matyjaszewski, K. Chem. Rev.
2012, 112, 3959ꢀ4015; (d) Zou, X.; Ren, H.; Zhu, G. Chem. Commun. 2013, 49, 3925ꢀ
3936; (e) Zhu, Y.; Yang, H.; Jin, Y.; Zhang, W. Chem. Mater. 2013, 25, 3718ꢀ3723; (f)
Das, S.; Heasman, P.; Ben, T.; Qiu, S. Chem. Rev. 2017, 117, 1515ꢀ1563.
(11) (a) Wang, Z. J.; Ghasimi, S.; Landfester, K.; Zhang, K. A. Chem. Commun. 2014, 50,
8177ꢀ8180; (b) Su, C.; Tandiana, R.; Tian, B.; Sengupta, A.; Tang, W.; Su, J.; Loh, K. P.
ACS Catal. 2016, 3594ꢀ3599; (c) Liras, M.; Iglesias, M.; Sánchez, F. Macromolecules
2
016, 49, 1666ꢀ1673.
12) Wang, Z. J.; Ghasimi, S.; Landfester, K.; Zhang, K. A. Adv. Mater. (Weinheim, Ger.)
015, 27, 6265ꢀ6270.
13) Luo, J.; Zhang, X.; Zhang, J. ACS Catal. 2015, 5, 2250ꢀ2254.
14) Wang, Z. J.; Ghasimi, S.; Landfester, K.; Zhang, K. A. I. J. Mater. Chem. A 2014, 2,
8720ꢀ18724.
15) Wang, Z. J.; Ghasimi, S.; Landfester, K.; Zhang, K. A. I. Adv. Synth. Catal. 2016, 358,
576ꢀ2582.
(
2
(
(
1
(
2
2
5
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Page 26 of 28
1
2
3
4
5
6
7
8
9
1
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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
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5
5
5
5
5
5
5
5
5
5
6
(16) DadashiꢀSilab, S.; Bildirir, H.; Dawson, R.; Thomas, A.; Yagci, Y. Macromolecules
2014, 47, 4607ꢀ4614.
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
(
(
17) Graglia, M.; Kanna, N.; Esposito, D. ChemBioEng Rev. 2015, 2, 377ꢀ392.
18) Ragauskas, A. J.; Beckham, G. T.; Biddy, M. J.; Chandra, R.; Chen, F.; Davis, M. F.;
Davison, B. H.; Dixon, R. A.; Gilna, P.; Keller, M.; Langan, P.; Naskar, A. K.; Saddler, J.
N.; Tschaplinski, T. J.; Tuskan, G. A.; Wyman, C. E. Science 2014, 344, 1246843.
19) Boerjan, W.; Ralph, J.; Baucher, M. Annu. Rev. Plant Biol. 2003, 54, 519ꢀ546.
20) (a) Rahimi, A.; Azarpira, A.; Kim, H.; Ralph, J.; Stahl, S. S. J. Am. Chem. Soc. 2013,
(
(
135, 6415ꢀ6418; (b) Lancefield, C. S.; Ojo, O. S.; Tran, F.; Westwood, N. J. Angew.
Chem., Int. Ed. 2015, 54, 258ꢀ262; (c) Wang, M.; Lu, J.; Zhang, X.; Li, L.; Li, H.; Luo,
N.; Wang, F. ACS Catal. 2016, 6, 6086ꢀ6090; (d) Zhang, C.; Li, H.; Lu, J.; Zhang, X.;
MacArthur, K. E.; Heggen, M.; Wang, F. ACS Catal. 2017, 3419ꢀ3429.
(
21) (a) Nguyen, J. D.; Matsuura, B. S.; Stephenson, C. R. J. Am. Chem. Soc. 2014, 136,
1218ꢀ1221; (b) Karkas, M. D.; Bosque, I.; Matsuura, B. S.; Stephenson, C. R. Org. Lett.
2016, 18, 5166ꢀ5169.
(22) Luo, N.; Wang, M.; Li, H.; Zhang, J.; Liu, H.; Wang, F. ACS Catal. 2016, 6, 7716ꢀ7721.
(23) (a) Sprick, R. S.; Jiang, J. X.; Bonillo, B.; Ren, S.; Ratvijitvech, T.; Guiglion, P.;
Zwijnenburg, M. A.; Adams, D. J.; Cooper, A. I. J. Am. Chem. Soc. 2015, 137, 3265ꢀ
3270; (b) Li, L.; Cai, Z.; Wu, Q.; Lo, W. Y.; Zhang, N.; Chen, L. X.; Yu, L. J. Am. Chem.
Soc. 2016, 138, 7681ꢀ7686; (c) Yang, C.; Ma, B. C.; Zhang, L.; Lin, S.; Ghasimi, S.;
Landfester, K.; Zhang, K. A.; Wang, X. Angew. Chem., Int. Ed. 2016, 55, 9202ꢀ9206.
(
(
24) Koene, B. E.; Loy, D. E.; Thompson, M. E. Chem. Mater. 1998, 10, 2235ꢀ2250.
25) (a) Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Nature 2012, 492, 234ꢀ
238; (b) Luo, J.; Zhang, J. ACS Catal. 2016, 873ꢀ877; (c) Vara, B. A.; Jouffroy, M.;
Molander, G. A. Chem. Sci. 2017, 8, 530ꢀ535.
(
26) (a) Chen, Q.; Luo, M.; Hammershoj, P.; Zhou, D.; Han, Y.; Laursen, B. W.; Yan, C. G.;
Han, B. H. J. Am. Chem. Soc. 2012, 134, 6084ꢀ6087; (b) Zhang, X.; Lu, J. Z.; Zhang, J.
Chem. Mater. 2014, 26, 4023ꢀ4029.
(
(
27) Chen, Q.; Liu, D. P.; Luo, M.; Feng, L. J.; Zhao, Y. C.; Han, B. H. Small 2014, 10, 308ꢀ
315.
28) (a) Gu, C.; Chen, Y.; Zhang, Z.; Xue, S.; Sun, S.; Zhang, K.; Zhong, C.; Zhang, H.; Pan,
Y.; Lv, Y.; Yang, Y.; Li, F.; Zhang, S.; Huang, F.; Ma, Y. Adv. Mater. (Weinheim, Ger.)
2013, 25, 3443ꢀ3448; (b) Gu, C.; Huang, N.; Gao, J.; Xu, F.; Xu, Y.; Jiang, D. Angew.
Chem., Int. Ed. 2014, 53, 4850ꢀ4855.
(29) Budd, P. M.; Elabas, E. S.; Ghanem, B. S.; Makhseed, S.; McKeown, N. B.; Msayib, K.
J.; Tattershall, C. E.; Wang, D. Adv. Mater. (Weinheim, Ger.) 2004, 16, 456ꢀ459.
(30) Bonillo, B.; Sprick, R. S.; Cooper, A. I. Chem. Mater. 2016, 28, 3469ꢀ3480.
(
(
31) Note: the reduction potentials of CzCP0, ꢀ10 and ꢀ20 were not detectable.
32) (a) Galli, C.; Gentili, P.; Lanzalunga, O. Angew. Chem., Int. Ed. 2008, 47, 4790ꢀ4796; (b)
Luo, J.; Zhang, J. J. Org. Chem. 2016, 81, 9131ꢀ9137.
(
(
(
33) Walsh, K.; Sneddon, H. F.; Moody, C. J. Org. Lett. 2014, 16, 5224ꢀ5227.
34) Mitchell, L. J.; Moody, C. J. J. Org. Chem. 2014, 79, 11091ꢀ11100.
35) Rueping, M.; Vila, C.; Szadkowska, A.; Koenigs, R. M.; Fronert, J. ACS Catal. 2012, 2,
2810ꢀ2815.
(
36) Kim, S.; Chmely, S. C.; Nimlos, M. R.; Bomble, Y. J.; Foust, T. D.; Paton, R. S.;
Beckham, G. T. J. Phys. Chem. Lett. 2011, 2, 2846ꢀ2852.
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(37) (a) Hasegawa, E.; Takizawa, S.; Seida, T.; Yamaguchi, A.; Yamaguchi, N.; Chiba, N.;
Takahashi, T.; Ikeda, H.; Akiyama, K. Tetrahedron 2006, 62, 6581ꢀ6588; (b) Larraufie,
M. H.; Pellet, R.; Fensterbank, L.; Goddard, J. P.; Lacote, E.; Malacria, M.; Ollivier, C.
Angew. Chem., Int. Ed. 2011, 50, 4463ꢀ4466.
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38) (a) Rahimi, A.; Ulbrich, A.; Coon, J. J.; Stahl, S. S. Nature 2014, 515, 249ꢀ252; (b) Gazi,
S.; Hung Ng, W. K.; Ganguly, R.; Putra Moeljadi, A. M.; Hirao, H.; Soo, H. S. Chem.
Sci. 2015, 6, 7130ꢀ7142.
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