Photocatalytic hydrogen-evolution dimerization of styrenes to synthesize 1,2-dihydro-1-arylnaphthalene derivatives using Acr+-Mes and cobaloxime catalysts

Article abstract of DOI:10.1016/S1872-2067(18)63095-5

We report a hydrogen-evolution dimerization of styrenes via the synergistic merger of Acr⁺-Mes photocatalyst and cobaloxime proton reduction catalysts. By utilizing this dual catalyst system, 1,2-dihydro-1-arylnaphthalene derivatives can be directly constructed from commercially available styrenes. Our reaction proceeds smoothly under mild conditions without the need for oxidants or hydrogen atom transfer reagents, and the sole byproduct is hydrogen gas. Mechanistic investigation suggests that the reaction is initiated by photoinduced electron transfer under visible-light irradiation.

Full text of DOI:10.1016/S1872-2067(18)63095-5

Chinese Journal of Catalysis 39 (2018) 1194–1201
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Photocatalytic hydrogen‐evolution dimerization of styrenes to
synthesize 1,2‐dihydro‐1‐arylnaphthalene derivatives using
Acr+‐Mes and cobaloxime catalysts
Wenxiao Cao a,b, Chengjuan Wua,Tao Leia, Xiulong Yanga, Bin Chena,b,*,Chenho Tung a,b,
Lizhu Wu a,b,#
a Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences,
Beijing 100190, China
b University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
We report a hydrogen‐evolution dimerization of styrenes via the synergistic merger of Acr+‐Mes
photocatalyst and cobaloxime proton reduction catalysts. By utilizing this dual catalyst system,
1,2‐dihydro‐1‐arylnaphthalene derivatives can be directly constructed from commercially available
styrenes. Our reaction proceeds smoothly under mild conditions without the need for oxidants or
hydrogen atom transfer reagents, and the sole byproduct is hydrogen gas. Mechanistic investigation
suggests that the reaction is initiated by photoinduced electron transfer under visible‐light irradia‐
tion.
Received 20 April 2018
Accepted 27 April 2018
Published 5 July 2018
Keywords:
Hydrogen‐evolution dimerization
Styrenes
1,2‐Dihydro‐1‐arylnaphthalene
derivatives
© 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Photocatalysis
Cobaloxime catalysts
1. Introduction
[9], Heck reaction [10], metal‐catalyzed intramolecular epoxi‐
dation [11], and others [12, 13] have been developed for the
1,2‐Dihydro‐1‐arylnaphthalene derivatives are common
structural units in many biologically active natural products
and pharmaceuticals [1–6]. This skeleton contains an alkene
C=C bond that can be easily derivatized; for example, podo‐
phyllotoxin with high anticancer activity can be constructed by
using this skeleton as a precursor [7, 8]. Over the past decades,
a variety of effective methods such as Friedel‐Crafts reaction
construction of 1,2‐dihydro‐1‐arylnaphthalenes [14–21]. Nev‐
ertheless, these methods often require substrate
pre‐functionalization and high temperatures, and have limited
product regioselectivity. In recent years, visible‐light‐induced
chemical transformations have attracted increasing interest
from organic chemists because of their green and sustainable
features [22–27]. Despite their high oxidation potential, sty‐
* Corresponding author. Tel/Fax: +86‐10‐82543576; E‐mail: chenbin@mail.ipc.ac.cn
# Corresponding author. Tel/Fax: +86‐10‐82543580; E‐mail: lzwu@mail.ipc.ac.cn
This work was supported by the Ministry of Science and Technology of China (2014CB239402, 2017YFA0206903), the National Natural Science
foundation of China (21390404), the Strategic Priority Research Program of the Chinese Academy of Science (XDB17000000), the Key Research Pro‐
gram of Frontier Sciences, the Chinese Academy of Sciences (QYZDY‐SSW‐JSC029).
DOI: 10.1016/S1872‐2067(18)63095‐5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 7, July 2018

Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
1195
renes can undergo dimerization by acridinium‐based organic
dyes in the presence of a stoichiometric oxidant or hydrogen
atom transfer (HAT) reagent [28,29]. 9‐Mesityl‐10‐acridini‐
um‐based organic dye shows a strong absorption band in the
visible region (λ = 430 nm) and high oxidizing ability in the
excited state, and has been successfully employed in the trans‐
formation of a diverse range of alkenes into cation radicals
under irradiation [30–34]. Huang et al. [28] recently reported
using a thermal conductivity detector (TCD) with a 5 Å molec‐
ular sieve column and nitrogen as the carrier gas. Mass spectra
were recorded using a Trio‐2000 GC‐MS spectrometer. Com‐
mercially available reagents and solvents were used without
further purification. Blue LEDs (3 W, λ = 440 ± 10 nm, 145 lm
@700mA) were used as the irradiation light sources.
2.2. General procedure for the preparation of
the
[4+2]
cycloaddition
of
styrenes
by
using
1,2‐dihydro‐1‐arylnaphthalene
9‐mesityl‐10‐phenylacridinium tetrafluoroborate (Ph‐Acr+‐Mes
–
BF4 ) as the photosensitizer and PhSSPh as an HAT reagent for
A 10 mL Pyrex tube equipped with a magnetic stir bar was
charged with styrene (73 L, 0.7 mmol) Acr+‐Mes (8.82 mg,
0.003 mmol), Co(dmgH)2pyCl (19.6 mg, 0.007 mmol), NaH2PO4
(210 mg, 1.75 mmol), and dry MeCN (5 mL). Then, the system
was degassed with a stream of argon for 30 min. The mixture
was irradiated by blue LEDs under an argon atmosphere for 24
h. After removal of the solvent under vacuum, the residue was
purified by silica gel column chromatography using petroleum
ether/ethyl acetate as the eluent to obtain the products.
1,2‐dihydro‐1‐arylnaphthalene (2): colorless oil, yield 60%,
petroleum ether. 1H NMR (400 MHz, CDCl3) δ 7.33 (t, J = 8.0 Hz,
2H), 7.27–7.24 (m, 3H), 7.20 (t, J = 7.6 Hz, 1H), 7.13–7.08(m,
2H), 6.83 (d, J = 7.6 Hz, 1H), 6.56 (d, J = 9.6 Hz, 1H), 6.04–6.00
(m, 1H), 4.16 (t, J = 8.8 Hz ,1H), 2.69–2.64 (m, 2H). 13C NMR
(101 MHz, CDCl3) δ 144.5, 137.9, 134.1, 128.5, 128.4, 128.0,
127.9, 127.3, 127.2, 126.8, 126.5, 126.2, 43.9, 32.0. HRMS (EI)
calcd. for C16H14 [M]: 206.1096, found: 206.1099.
the synthesis of 1,2,3,4‐tetrahydro‐arylnaphthalenes (Scheme
1(a)). Liang and co‐workers [29] took the lead in the oxidative
synthesis of 1,2‐dihydro‐1‐arylnaphthalene derivatives from
styrenes by using 9‐mesityl‐10‐methyl acridinium perchlorate
(Acr+‐Mes
2‐phenylmalononitrile (PMN) and Selectfluor as the oxidants
(Scheme 1(b)). However, the use of an HAT reagent always
leads to the reduced product (tetralins) rather than
1,2‐dihydronaphthalenes. The use of an oxidant, on the other
hand, can result in overoxidized products, naphthalene deriva‐
tives. We contemplated whether we could combine catalytic
amounts of the Acr+‐Mes photosensitizer and cobalt catalyst
[35–37] to synthesize 1,2‐dihydro‐1‐arylnaphthalene deriva‐
tives by a cross‐coupling hydrogen‐evolution (CCHE) reaction
[38–50], which avoids the use of any sacrificial oxidant and
yields hydrogen gas (H2) as the sole byproduct. To our delight,
–
ClO4 )
as
the
photosensitizer,
and
–
the use of Acr+‐Mes ClO4 and cobaloxime catalyst
Co(dmgH)2pyCl helped us execute our idea under visible‐light
irradiation at room temperature.
7‐Methyl‐1‐(p‐tolyl)‐1,2‐dihydronaphthalene (3): colorless
1
oil, yield 66%, petroleum ether. H NMR (400 MHz, CDCl3) δ
7.04–7.00 (m, 4H), 6.94–6.87 (m, 2H), 6.57 (s, 1H), 6.41 (d, J =
9.6 Hz, 1H), 5.84–5.80 (m, 1H), 3.96 (t, J = 7.6 Hz, 1H), 2.54–2.50
(m, 1H), 2.49–2.46 (m, 1H), 2.24 (s, 3H), 2.12 (s, 3H). 13C NMR
(101 MHz, CDCl3) δ 141.6, 137.9, 137.0, 135.9, 131.5, 129.1,
128.6, 128.3, 127.8, 127.3, 126.1, 126.0, 43.5, 32.2, 21.3, 21.0.
HRMS (EI) calcd. for C18H18 [M]: 234.1409, found: 234.1412.
5‐Methyl‐1‐(o‐tolyl)‐1,2‐dihydronaphthalene (4): colorless
2. Experimental
2.1. General methods
1H NMR spectra were recorded using a Bruker Avance DPX
400MHz instrument with tetramethylsilane (TMS) as the in‐
ternal standard. 13C NMR spectra were obtained at 100 MHz
and referenced to the internal solvent signals. Hydrogen gas
was analyzed by gas chromatography (7890‐II, Tianmei, China)
1
oil, yield 71%, petroleum ether. H NMR (400 MHz, CDCl3) δ
7.21 (t, J = 3.2 Hz, 1H), 7.16–7.13 (m, 2H), 7.11 (t, J = 6.4 Hz,
1H), 7.01 (d, J = 7.6 Hz, 1H), 6.95 (t, J = 6.4 Hz, 1H), 6.78 (d, J =
9.6 Hz, 1H), 6.54 (d, J = 7.6 Hz, 1H), 6.10–6.05 (m, 1H),
4.38–4.34 (m, 1H), 2.59–2.54(m, 2H), 2.39 (s, 3H), 2.36 (s, 3H).
13C NMR (101 MHz, CDCl3) δ 142.2, 138.1, 136.2, 133.2, 132.6,
130.4, 128.5, 128.4, 127.6, 126.9, 126.3, 126.1, 125.3, 124.7,
40.1, 30.2, 19.8, 19.3. HRMS (EI) calcd. for C18H18 [M]:
234.1409, found: 234.1409
4‐(2,5‐Dimethylphenyl)‐5,8‐dimethyl‐1,2‐dihydronaphthale
1
ne (5): colorless oil, isolated yield 55%, petroleum ether. H
NMR (400 MHz, CDCl3) δ 7.12 (d, J = 15.2 Hz, 1H), 7.08 (s, 1H),
7.03 (d, J = 8.0 Hz, 1H), 6.94 (d, J = 7.8 Hz, 1H), 6.90 (s, 1H), 6.47
(s, 1H), 5.91–5.71 (m, 1H), 4.39 (d, J = 8.9 Hz, 1H), 2.87 (ddd, J =
11.4, 6.0, 3.2 Hz, 1H), 2.48 (s, 3H), 2.44 (s, 3H), 2.41–2.37 (m,
1H), 2.14 (s, 3H), 2.00 (s, 3H). 13C NMR (101 MHz, CDCl3) δ
141.2, 135.9, 135.1, 133.6, 132.8, 131.8, 131.0, 130.3, 129.3,
128.9, 128.4, 126.8, 125.3, 125.1, 34.6, 29.9, 21.3, 19.5, 18.9,
18.4. HRMS (EI) calcd. for C20H22 [M]: 262.1722, found:
262.1711
Scheme 1. Representative synthesis of 1‐arylnaphthalene derivatives
via photocatalysis.
7‐Methyl‐4‐(m‐tolyl)‐1,2‐dihydronaphthalene
(6)
and

1196
Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
5‐methyl‐4‐(m‐tolyl)‐1,2‐dihydro‐naphthalene (6’): colorless
oil, isolated yield 76%, petroleum ether. H NMR (400 MHz,
4.06–3.98 (m, 1H), 2.89–2.74 (m, 1H), 2.59–2.49 (m, 1H). 13C
NMR (101 MHz, CDCl3) δ 142.1, 139.2, 132.7, 132.6, 132.5,
129.7, 129.2, 128.8, 128.7, 128.0, 127.9, 127.4, 127.3, 127.2,
127.1, 43.2, 31.6. HRMS (EI) calcd. for C16H12Cl2 [M]: 274.0316,
found: 274.0353
5‐Chloro‐1‐(o‐chlorophenyl)‐1,2‐dihydronaphthalene (12):
colorless oil, isolated yield 50%, petroleum ether/ethyl acetate
= 100/1. 1H NMR (400 MHz, CDCl3) δ 7.40 (dd, J = 7.4, 2.0 Hz,
1H), 7.25–7.20 (m, 2H), 7.17–7.16 (m, 1H), 7.15‐7.13(m, 1H),
7.03–7.01 (m, 1H), 7.01–6.98 (m,1H), 6.72 (d, J = 7.4 Hz, 1H),
1
CDCl3) δ 7.86–7.74 (m, 2H), 7.46 (m, 1H), 7.41–7.32 (m, 2H),
7.30 (m, 3H), 6.98–6.91 (m, 3H), 6.87 (m, 1H), 6.78 (m, 1H),
6.70 (m, 1H), 6.50 (t, 2H), 6.03–5.95 (m, 1H), 5.80–5.70 (m, 1H),
4.20 (t, J = 8.4 Hz, 1H), 4.05 (t, J = 8.9 Hz, 1H), 2.91 (m, 2H),
2.62–2.57 (m, 2H), 2.32 (s, 3H), 2.30 (s, 3H), 2.26 (s, 3H), 2.09
(s, 3H). 13C NMR (101 MHz, CDCl3) δ 144.7 , 137.9, 137.6, 137.0,
136.2, 136.1, 135.5, 134.1, 134.0, 130.8, 130.4, 129.6, 129.2,
128.5, 128.3, 128.0, 127.8,127.7,127.3, 127.2, 126.9, 126.7 ,
125.5, 125.1, 124.9, 124.5, 124.3, 43.4, 38.4, 32.4, 32.2, 21.6,
21.0. HRMS (EI) calcd. for C18H18 [M]: 234.1409, found:
234.1409
6.10–6.05 (m, 1H), 4.69 (t, J = 8.0 Hz, 1H), 2.68‐2.63 (m, 2H). 13
C
NMR (101 MHz, CDCl3) δ 140.8, 138.8, 133.7, 131.9, 131.5,
129.9, 129.7, 128.7, 128.1, 127.9, 127.8, 126.9, 126.5, 125.2,
124.0, 39.9, 29.7. HRMS (EI) calcd. for C16H12Cl2 [M]: 274.0316,
found: 274.0266
6‐Methoxy‐4‐(4‐methoxyphenyl)‐1,2‐dihydronaphthalene
1
(7): colorless oil, yield 47%, petroleum ether. H NMR (400
MHz, CDCl3) δ 7.14 (m, 3H), 7.02 (s, 1H), 6.84 (d, J = 1.8 Hz, 2H),
6.70 (m, 1H), 6.39 (m, 1H), 5.94–5.73 (m, 1H), 4.14–3.97 (m,
1H), 3.78 (s, 3H), 3.69 (s, 3H), 2.27 (d, J = 3.3 Hz, 1H), 2.06 (d, J =
4.8 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 159.1, 157.9, 140.0,
137.0, 129.3, 127.5, 127.4, 127.2, 124.7, 114.5, 113.9, 113.7,
111.3, 111.0, 55.4, 54.9, 48.0, 26.0. HRMS (EI) calcd. for
C18H18O2 [M]: 266.1307, found: 266.1309
6‐Ethoxy‐4‐(4‐ethoxyphenyl)‐1,2‐dihydronaphthalene (8):
colorless oil, isolated yield 41%, petroleum ether. 1H NMR (400
MHz, CDCl3) δ 7.13 (s, 1H), 7.11 (s, 1H), 7.01 (d, J = 8.2 Hz, 1H),
6.80 (s, 1H), 6.68 (m, 1H), 6.48 (d, J = 9.6 Hz, 1H), 6.39 (d, J = 2.4
Hz, 1H), 5.94–5.78 (m, 1H), 4.01 (m, 2H), 3.90 (m, 2H), 3.44 (m,
1H), 2.58–2.53 (m, 1H), 2.27–2.25 (m, 1H), 2.07 (t, J = 5.0 Hz,
1H), 1.39 (s, 3H), 1.32 (t, J = 7.0 Hz, 3H). 13C NMR (101 MHz,
CDCl3) δ 158.2, 157.6, 157.4, 140.2, 136.4, 136.2, 129.5, 127.6,
127.0, 124.6, 115.0, 114.8, 114.3, 111.7, 63.3, 63.0, 43.5, 26.0,
15.0, 14.8. HRMS (EI) calcd. for C20H22O2 [M]: 294.1620, found:
294.1620
6‐(tert‐Butyl)‐4‐[4‐(tert‐butyl)phenyl]‐1,2‐dihydronaphthal
ene (9): white solid, isolated yield 62%, petroleum ether. 1H
NMR (400 MHz, CDCl3) δ 7.32 (d, J = 8.3 Hz, 2H), 7.26–7.23 (m,
1H), 7.14 (m, 2H), 7.07 (d, J = 8.0 Hz, 1H), 6.96 (s, 1H), 6.53 (d, J
= 9.6 Hz 1H), 5.99–5.91 (m, 1H), 4.12 (t, J = 7.8 Hz, 1H),
2.75–2.69 (m, 1H), 2.66–2.61 (m, 1H), 1.34 (s, 9H), 1.25 (s, 9H).
13C NMR (101 MHz, CDCl3) δ 150.2, 149.0, 141.6, 137.4, 131.6,
127.8, 127.7, 126.3, 125.7, 125.3, 125.1, 123.5, 43.3, 34.6, 34.4,
31.4, 31,3. HRMS (EI) calcd. for C24H30 [M]: 318.2348, found:
318.2350
6‐Fluoro‐4‐(4‐fluorophenyl)‐1,2‐dihydronaphthalene (10):
colorless oil, yield 67%, petroleum ether/ethyl acetate = 100/1.
1H NMR (400 MHz, CDCl3) δ 7.19–7.15 (m, 2H), 7.06 (m, 1H),
7.04–6.98 (m, 2H), 6.88–6.84 (m, 1H), 6.52–6.48 (m, 2H),
5.98–5.93 (m, 1H), 4.10–4.07 (m, 1H), 2.64–2.58 (m, 1H),
2.57–2.49 (m, 1H). 13C NMR (101 MHz, CDCl3) δ 163.0, 160.5,
140.3, 139.3, 130.3, 129.8, 127.6, 127.1, 126.2, 115.5, 115.0,
113.5, 43.3, 31.6. HRMS (EI) calcd. for C16H12F2 [M]: 242.0907,
found: 242.0909
6‐Bromo‐4‐(4‐bromophenyl)‐1,2‐dihydronaphthalene (13):
colorless oil, isolated yield 62%, petroleum ether/ethyl acetate
= 100/1. H NMR (400 MHz, CDCl3) δ 7.43 (d, J = 8.0 Hz, 2H),
1
7.31 (d, J = 10.0 Hz, 1H), 7.21 (dd, J = 8.4, 8.8 Hz, 1H),7.07 (d, J =
8.4 Hz, 2H), 6.97(d, J = 4.0 Hz, 1H ), 6.48 (d, J = 9.6 Hz, 1H),
6.02–5.99 (m, 1H), 4.08–4.03 (m, 1H), 2.63–2.60 (m, 1H),
2.57–2.53 (m, 1H). 13C NMR (101 MHz, CDCl3) δ 142.6, 139.3,
132.9, 131.7, 131.6, 130.7, 130.0, 127.6, 127.8, 127.4, 127.2,
120.6, 43.1, 31.6. HRMS (EI) calcd. for C16H12Br2 [M]: 361.9306,
found: 361.9251
5‐Bromo‐1‐(o‐bromophenyl)‐1,2‐dihydronaphthalene (14):
colorless oil, isolated yield 48%, petroleum ether/ethyl acetate
= 100/1. 1H NMR (400 MHz, CDCl3) δ 7.59 (dd, J = 7.9, 1.1 Hz,
1H), 7.42 (dd, J = 12.6, 4.7 Hz, 2H), 7.35–7.27 (m, 1H), 7.22–7.12
(m, 1H), 7.06 (dd, J = 7.7, 1.9 Hz, 1H), 6.97–6.90 (m, 1H), 6.75
(d, J = 7.8 Hz, 1H), 6.14–5.91 (m, 1H), 4.66 (t, J = 8.1 Hz, 1H),
2.85 (d, J = 6.2 Hz, 1H), 2.63 (m, 1H). 13C NMR (101 MHz, CDCl3)
δ 144.1, 142.4, 136.4, 133.0, 131.9, 130.1, 129.4, 128.4, 127.7,
127.0, 126.9, 126.6, 126.0, 123.6, 42.4, 30.0. HRMS (EI) calcd.
for C16H12Br2 [M]: 361.9306, found: 361.9183.
6‐Ethoxy‐4‐(4‐ethoxyphenyl)‐1,2‐dihydronaphthalene (15):
colorless oil, yield 53%, petroleum ether/ethyl acetate = 100/1.
1H NMR (400 MHz, CDCl3) δ 7.21 (d, J = 8.5 Hz, 2H), 7.15–7.03
(m, 2H), 7.01 (dd, J = 13.7, 8.4 Hz, 2H), 6.90 (dd, J = 8.1, 2.2 Hz,
1H), 6.51 (d, J = 11.4 Hz, 1H), 6.06–5.91 (m, 1H), 4.08 (dt, J =
50.1, 25.2 Hz, 1H), 2.58 (s, 1H), 2.56 (s, 1H), 2.31–2.24 (m, 3H),
2.18 (d, J = 6.8 Hz, 3H). 13C NMR (101 MHz, CDCl3) δ 169.5,
169.5, 149.6, 149.4, 141.3, 139.2, 131.9, 129.4, 127.2, 126.9,
121.6, 121.0, 119.9, 43.5, 31.8, 21.2. HRMS (EI) calcd. for
C18H18O4 [M]: 322.1205, found: 322.1205
6‐Benzyl‐4‐(4‐benzylphenyl)‐1,2‐dihydronaphthalene (16):
colorless oil, isolated yield 60%,petroleum ether/ethyl acetate
= 100/1. 1H NMR (400 MHz, CDCl3) δ 7.50 (s, 1H), 7.44 (d, J =
8.1 Hz, 3H), 7.39 (d, J = 7.6 Hz, 2H), 7.33 (d, J = 7.4 Hz, 3H), 7.25
(d, J = 8.1 Hz, 3H), 7.23–7.17 (m, 3H), 7.13–7.05 (m, 2H), 6.51
(d, J = 9.6 Hz, 1H), 6.05–5.84 (m, 1H), 4.14 (t, J = 8.2 Hz, 1H),
2.71–2.56 (m, 1H), 2.05 (s, 1H). 13C NMR (101 MHz, CDCl3) δ
143.7, 143.6, 141.0, 141.1, 140.2, 139.4, 138.2, 133.4, 129.3,
128.9, 127.8, 128. 7, 127.8, 127.3, 127.2, 127.1, 127.1, 127.1,
127.0, 126.9, 126.7, 125.7, 43.8, 32.1. HRMS (EI) calcd. for
C28H22 [M]: 358.1722, found: 358.1722
6‐Chloro‐4‐(4‐chlorophenyl)‐1,2‐dihydronaphthalene (11):
colorless oil, isolated yield 62%, petroleum ether/ethyl acetate
1
= 100/1. H NMR (400 MHz, CDCl3) δ 7.26 (d, J = 2.5 Hz, 2H),
7.12 (dd, J = 6.9, 4.9 Hz, 2H), 7.00 (dd, J = 10.1, 8.3 Hz, 2H),
6.80–6.74 (m, 1H), 6.49 (d, J = 9.6 Hz, 1H), 6.10–5.79 (m, 1H),
1‐(Naphthalen‐1‐yl)‐1,2‐dihydronaphthalene (17): white

Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
1197
solid, isolated yield 58%, petroleum ether/ethyl acetate =
100/1. H NMR (400 MHz, CDCl3) δ 8.21 (dd, J = 15.5, 8.6 Hz,
to a decrease in the product yield (Table 1, entry 4). Then, sev‐
eral cobaloxime catalysts were evaluated (Table 1, entries 3,
5–7), and Co(dmgH)2pyCl was found to be the best (Table 1,
entry 3), indicating that the structure of the cobalt complex has
a greater impact on the reaction. In order to further optimize
the yield, we added additives, including Na2CO3, NaHCO3,
NaH2PO4, DMAP, and K2CO3, to the system and found that 2.5
equiv. NaH2PO4 could increase the yield of the desired product
2 to 72% (Table 1, entry 8), where NaH2PO4 might aid in pro‐
ton transfer. Other photocatalysts such as rose bengal, rhoda‐
mine B, [Ir(dtbbpy)(ppy)2][PF6], eosin Y, and Ru(bpy)3Cl2 did
not afford the desired product at all. In the control experiments,
no desired product was observed without the photosensitizer
Acr+‐Mes, cobalt catalyst, or visible light, indicating that
Acr+‐Mes and cobalt catalysts are essential for this transfor‐
mation (Table 1, entries 9–11).
1
2H), 8.01–7.92 (m, 1H), 7.93–7.89 (m, 1H), 7.83–7.70 (m, 3H),
7.57–7.49 (m, 4H), 7.41–7.37 (m, 1H), 7.29 (d, J = 3.5 Hz, 1H),
7.04 (d, J = 6.4 Hz, 1H), 6.20–6.07 (m, 1H), 5.13 (t, J = 8.0 Hz,
1H), 3.05–2.78 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 139.3,
135.0, 134.4, 133.0, 131.4, 129.6, 129.2, 128.6, 127.8, 127.5,
127.2, 126.8, 126.2, 125.9, 125.6, 125.5, 125.4, 125.3, 123.1,
122.8, 39.8, 37.8. HRMS (EI) calcd. for C24H18 [M]:306.1409,
found: 306.1407
3. Results and discussion
Initially, styrene was chosen as the standard substrate for
the desired product. As shown in Table 1, when using Acr+‐Mes
–
ClO4 (3 mol%) as the photocatalyst and Co(dmgH)2pyCl (7
mol%) as the proton reduction catalyst, 35% yield of the de‐
sired product 2 was obtained after 24 h of irradiation (Table 1,
entry 1). The produced hydrogen gas was also detected by
GC–TCD. No other product was detected, except for a very small
amount of tetralin derivative. We hypothesized that the gener‐
ated hydrogen and the target product were further hydrogen‐
ated to give a hydrogenated compound. To enhance the reac‐
tion efficiency, various concentrations of 1 were screened (Ta‐
ble 1, entries 1–4). At a high concentration, the yield of product
2 was increased to 56% (Table 1, entry 3) due to the bimolecu‐
lar reaction character. Further increasing the concentration led
With the optimal conditions in hand, we attempted to ex‐
plore
the
scope
of
the
visible‐light
catalytic
1,2‐dihydro‐1‐arylnaphthalene formation. As summarized in
Scheme 2, most of the styrenes containing elec‐
3 mol% Acr+-Mes
R
7 mol% Co(dmgH)2pyCl
R
2.5 equiv. NaH2PO4, MeCN
440 nm LEDs, Ar, r.t., 24 h
+
H2
R
Me
Me
Me
Table 1
Me
Me
Optimization of reaction conditions a.
Me
Me
5, 55%
Me
3, 66%
2, 60%
4, 71%
Me
EtO
MeO
Me
Entry
1
2
3
4
1 (mmol)
0.3
Co catalyst
Co(dmgH)2pyCl
Co(dmgH)2pyCl
Co(dmgH)2pyCl
Co(dmgH)2pyCl
Co(dmgH)(dmgH2)Cl2
Co(dmgH)2(4‐CO2Mepy)Cl
Co(dmgBF2)2(MeCN)2
Co(dmgH)2pyCl
Co(dmgH)2pyCl
─
Yieldb (%)
35
Me
Me
OEt
8, 41%
OMe
7, 47%
0.5
0.7
1.0
0.7
46
56
36
10
6:6'=1:1.4 , 76%
Cl
Cl
F
t-Bu
5
6
0.7
28
Cl
7
0.7
0.7
0.7
0.7
0.7
38
72
n.d.
n.d.
n.d.
n.d.
Cl
8c
9 d
10
11 e
12f
F
t-Bu
9, 62%
12, 50%
10, 67%
11, 62%
Br
Co(dmgH)2pyCl
Co(dmgH)2pyCl
MeO2C
Br
Ph
0.7
Br
CO2Me
Br
13, 62%
Ph
15, 60%
16, 53%
14
, 48%
N
O2N
NC
–
a Reaction conditions: corresponding 1, Acr+‐Mes ClO4 (3 mol%), Co
catalyst (7 mol%) in 5 mL of dry MeCN under argon atmosphere, irra‐
diation with blue LEDs (λ = 440 nm), at room temperature for 24 h;
N
NO2
CN
b Yields detected by 1H NMR, using diphenylacetonitrile as the internal
20, n.d.
–
17, 58%
18, n.d.
19, n.d.
standard; c 2.5 equiv. NaH2PO4; d Without Acr+‐Mes ClO4 ; e In the dark;
f In air.
Scheme 2. Substrate scope for the dimerization of styrenes.

1198
Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
tron‐withdrawing groups or electron‐donating groups could
afford the corresponding 1,2‐dihydro‐1‐arylnaphthalenes in
moderate yields under standard conditions. Meanwhile, sty‐
renes with halo group substitution at the ortho or para‐position
were
also
smoothly
converted
into
the
1,2‐dihydro‐1‐arylnaphthalene products in moderate yields,
which have the potential for further transformation. When a
meta‐methyl styrene derivative was employed in the reaction,
two region‐isomers 6 and 6’ were obtained. The presence of a
methoxy group or ethyloxy group at the para‐position of sty‐
rene afforded 1,2‐dihydro‐1‐arylnaphthalene (7,8) in only 47%
and 41% yields because of the formation of some unidentified
byproducts. Styrene with a tertiary butyl substituent at the
para‐position also gave the desired product 9 in 62% yield.
Interestingly, 2‐vinyl‐naphthalene also worked well for this
protocol and afforded the product 17 in 58% yield. However,
the electron‐deficient 2‐pyridylethylene failed to afford the
corresponding annulation product, similar to the results ob‐
served for 4‐nitrostyrene and 4‐cyanogroup. A large gram‐scale
reaction (10 mmol 1 in 50 mL dry CH3CN) was performed to
obtain 1,2‐dihydro‐1‐arylnaphthalene 2 in 55% yield after 48 h
of irradiation.
Scheme 4. Free radical capture experiment.
107 (mol/L)–1 s–1, which is two orders of magnitude smaller
than that of 1. The concentration of styrene was also much
higher than that of Co(dmgH)2pyCl. Thus, we considered that
the excited Acr+‐Mes preferentially reacted with styrene than
with Co(dmgH)2pyCl (Fig. 1(a)). Furthermore, upon irradiation,
the absorption spectrum (Fig. 1(b)) of the system containing
styrene, Acr+‐Mes, and Co(dmgH)2pyCl in degassed dry MeCN
immediately exhibited absorption bands at 440–500 nm and
550–650 nm, which indicated the formation of CoII and CoI spe‐
cies, respectively, based on reports in the literature [49].
Based on the above results, we proposed a plausible mecha‐
nism for this reaction (Scheme 5). Photosensitizer Acr+‐Mes is
A cross‐dimerization reaction using two styrenes with dif‐
ferent substituents on the phenyl ring (e.g., a 1:1 mixture of
4‐methylstyrene and 4‐fluorostyrene) was also conducted
(Scheme 3). The corresponding homodimerized and
cross‐dimerized products were obtained as a mixture (3:21:10
= 2.2:2.1:1.0) in 57% total isolated yield, which further broad‐
ened the scope of our substrates.
Acr+-Mes
(a)
Acr+-Mes + Co(dmgH)2pyCl
Acr+-Mes+ styrene
Acr+-Mes + Co(dmgH)2pyCl + styrene
Mechanistic studies were conducted to gain insights into the
aforementioned
transformation.
When
2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) was used as the
radical scavenger, no desired products were formed (Scheme
4), implying that radicals are involved in our reaction process.
To shed more light on the process of the reaction, we examined
the interaction between styrene 1 and the excited Acr+‐Mes.
The luminescence of the excited Acr+‐Mes could be significantly
quenched by 1 with a rate constant of 9.6 × 108 (mol/L)–1 s–1.
On the other hand, Co(dmgH)2pyCl could also quench the lu‐
minescence of Acr+‐Mes with a quenching rate constant of 1.6 ×
450
500
550
600
650
700
750
Wavelength (nm)
0.5
irradiation time 1 min
irradiation time 0 min
(b)
0.4
0.3
0.2
0.1
0.0
R1
3 mol% Acr+-Mes
R1
CoII
7 mol% Co(dmgH)2pyCl
2.5 equiv. NaH2PO4, MeCN
440 nm LEDs, Ar, r.t., 24 h
H2
+
CoI
R2
R2
400
450
500
550
600
650
700
F
Me
Me
Wavelength (nm)
Fig. 1. (a) Emission spectra of Acr+‐Mes (0.03 mmol/L) in the absence
and respective presence of Co(dmgH)2pyCl (0.07 mmol/L) (dash line)
and styrene 1 (1.0 mmol/L, short dash line) in degassed dry CH3CN, and
Acr+‐Mes (0.03 mmol/L) in the presence of Co(dmgH)2pyCl (0.07
mmol/L), and styrene 1 (1.0 mmol/L) in degassed dry CH3CN (dot line).
(b) UV‐vis absorption spectra of a mixture of Acr+‐Mes (0.03 mmol/L),
Co(dmgH)2pyCl (0.07 mmol/L) and styrene 1 (1.0 mmol/L) in degassed
dry MeCN before and after irradiation under blue LEDs.
F
F
Me
10
21
3
(3:21:10
)
57%
=2.2:2.1:1.0
Scheme 3. Cross‐over reaction between 4‐methylstyrene and
4‐fluorostyrene.

Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
1199
be transformed into the desired products in moderate to good
yields, and H2 is the only byproduct. As opposed to previous
methods, this reaction proceeds smoothly under extremely
mild conditions, and no oxidized products (naphthalene deriv‐
atives) are produced. We believe that this methodology would
be significant for application to a series of organic reactions.
References
[1] C. Canel, R. M. Moraes, F. E. Dayan, D. Ferreira, Phytochemistry,
2000, 54, 115–120.
[2] H. M. L. Davies, X. Dai, M. S. Long, J. Am. Chem. Soc., 2006, 128,
2485–2490.
[3] L. F. Silva. Jr, F. A. Siqueira, E. C. Pedrozo, F. Y. M. Vieira, A. C.
Doriguetto, Org. Lett., 2007, 9, 1433–1436.
Scheme 5. Possible mechanism.
[4] S. O. De Silva, C. St. Denis, R. Rodrigo, J. Chem. Soc. Chem. Comm.,
1980, 995–997.
[5] V. Nair, V. Sheeba, S. B. Panicker, T.G. George, R. Rajan, L.
Balagopal, M. Vairamani, S. Prabhakar, Tetrahedron, 2000, 56,
2461–2467.
[6] B. L. Yvon, P. K. Datta, T.N. Le, J. L. Charlton, Synthesis, 2001,
1556–1560.
[7] T. Linker, F. Rebien, G. Toth, A. Simon, J. Kraus, G. Bringmann,
Chem. Eur. J., 1998, 4, 1944–1951.
[8] J. C. T. Reddel, K. E. Lutz, A. B. Diagne, R. J. Thomson, Angew. Chem.
Int. Ed., 2014, 53, 1395–1398.
[9] R. R. Malladi, N. S. Li, D. Tejedor, G. W. Kabalka, Synth. Commun.,
2000, 30, 3613–3616.
[10] K. Maeda, E. J. Farrington, E. Galardon, B. D. John, J. M. Brown, Adv.
Synth. Catal., 2002, 344, 104–109.
[11] C. K. Chan, N. C. Hsueh, Y. L. Tsai, M. Y. Chang, J. Org. Chem., 2017,
82, 7077–7084.
irradiated by visible light to reach its excited state Acr•‐Mes•+
(E1/2 = + 2.06 V vs. SCE) [30–34], which undergoes sin‐
red
gle‐electron transfer (SET) with styrene to generate styrene
radical cation 1+• and Acr•‐Mes radical anion. Electrophilic
trapping of intermediate 1+• by a neutral alkene molecule gives
distal 1,4‐radical cation A, which readily undergoes
Friedel–Crafts annulation to form intermediate B via deproto‐
nation and aromatization. The generated Acr•‐Mes radical ani‐
on donates an electron to Co(dmgH)2pyCl (CoIII) to produce CoII
species and regenerate the photosensitizer Acr+‐Mes. The car‐
bon‐ centered radical B is further oxidized by CoII to afford CoI
species and product 2. Protonation of the CoI species provides
CoIII‐H [52,53], which can react with a proton to release H2
eventually and regenerate the generate CoIII catalyst.
[12] K. R. Kopecky, M. C. Hall, Can. J. Chem., 1981, 59, 3095–3104.
[13] M. Y. Chang, Y. C. Cheng, Org. Lett., 2016, 18, 1682–1685.
[14] J. J. M. Lamberts, T. J. H. M. Cuppen, W. H. Laarhoven, J. Chem. Soc.
Perkin Trans., 1985, 1819–1827.
4. Conclusions
In summary, we have developed a hydrogen‐evolution di‐
[15] J. Yun, S. L. Buchwald, J. Org. Chem., 2000, 65, 767–774.
[16] T. Kudoh, T. Mori, M. Shirahama, M. Yamada, T. Ishikawa, S. Saito,
H. Kobayashi, J. Am. Chem. Soc., 2007, 129, 4939–4947.
[17] Z. Yu, W. Dan, H. Jie, Z. Li, Med. Chem. Res., 2009, 19, 71–76.
[18] M. L. N. Rao, D. N. Jadhav, V. Venkatesh, Eur. J. Org. Chem., 2009,
2009, 4300–4306.
merization
methodology
for
the
synthesis
of
1,2‐dihydro‐1‐arylnaphthalenes by combining photocatalysis
and proton reduction catalysis under visible‐light irradiation.
By using the dual catalyst system of photosensitizer Acr+‐Mes
and cobaloxime catalyst Co(dmgH)2pyCl, various styrenes can
Graphical Abstract
Chin. J. Catal., 2018, 39: 1194–1201 doi: 10.1016/S1872‐2067(18)63095‐5
Photocatalytic hydrogen‐evolution dimerization of styrenes to
synthesize 1,2‐dihydro‐1‐arylnaphthalene derivatives using
Acr+‐Mes and cobaloxime catalysts
Wenxiao Cao, Chengjuan Wu, Tao Lei, Xiulong Yang, Bin Chen *,
Chenho Tung, Lizhu Wu *
Technical Institute of Physics and Chemistry,
Chinese Academy of Sciences;
University of Chinese Academy of Sciences
By combining Acr+‐Mes and cobaloxime catalysts, hydrogen‐evolution
dimerization of styrenes has been achieved without the use of oxidants
or HAT reagents. This reaction proceeds smoothly under mild condi‐
tions, and the sole byproduct is hydrogen gas.

1200
Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
[19] V. Gudla, R. Balamurugan, Chem. Asian J., 2013, 8, 414–428.
[20] K. Wang, L. G. Meng, Q. Zhang, L. Wang, Green Chem., 2016, 18,
2864–2870.
[21] Y. L. Liu, M. F. Zhang, C. H. Tung, Y. F. Wang, Acs Catal., 2016, 6,
8389–8394.
[22] E. P. Farney, T. P. Yoon, Angew. Chem. Int. Ed., 2014, 53, 793–797.
[23] J. Liu, Q. Liu, H. Yi, C. Qin, R. P. Bai, X. T. Qi, Y. Lan, A. W. Lei. Angew.
Chem. Int. Ed., 2014, 53, 502–506.
[37] P. W. Du, R. Eisenberg, Energy Environ. Sci., 2012, 5, 6012–6021.
[38] Q. Y. Meng, J. J. Zhong, Q. Liu, X. W. Gao, H. H. Zhang, T. Lei, Z. J. Li, K.
Feng, B. Chen, C. H. Tung, L. Z. Wu, J. Am. Chem. Soc., 2013, 135,
19052–19055.
[39] J. J. Zhong, Q. Y. Meng, B. Liu, X. B. Li, X. W. Gao, T. Lei, C. J. Wu, Z. J.
Li, C. H. Tung, L. Z. Wu, Org. Lett., 2014, 16, 1988–1991.
[40] X. W. Gao, Q. Y. Meng, J. X. Li, J. J. Zhong, T. Lei, X. B. Li, C. H. Tung, L.
Z. Wu, ACS Catal., 2015, 5, 2391–2396.
[24] S. M. Stevenson, M. P. Shores, E. M. Ferreira, Angew. Chem. Int. Ed.,
2015, 54, 6506–6510.
[25] C. J. Wu, W. X. Cao, T. Lei, Z. H. Li, Q. Y. Meng, X. L. Yang, B. Chen, V.
Ramamurthy, C. H. Tung, L. Z. Wu, Chem. Commun., 2017, 53,
8320–8323.
[26] P. K. Pei, F. Zhang, H. Yi, A. W. Lei, Acta Chim. Sin., 2017, 75, 15‐21
[27] X. Y. Yu, F. Zhou, J. R. Chen, W. J. Xiao, Acta Chim. Sin., 2017, 75,
86–91.
[28] L. F. Wang, F. J. Wu, J. A. Chen, D. A. Nicewicz, Y. Huang, Angew.
Chem. Int. Ed., 2017, 56, 6896–6900.
[41] M. Xiang, Q. Y. Meng, J. X. Li, Y. W. Zheng, C. Ye, Z. J. Li, B. Chen, C. H.
Tung, L. Z. Wu, Chem. Eur. J., 2015, 21, 18080–18084.
[42] G. T. Zhang, C. Liu, H. Yi, Q. Y. Meng, C. L. Bian, H. Chen, J. X. Jian, L.
Z. Wu, A. W. Lei, J. Am. Chem. Soc., 2015, 137, 9273–9280.
[43] C. J. Wu, Q. Y. Meng, T. Lei, J. J. Zhong, W. Q. Liu, L. M. Zhao, Z. J. Li, B.
Chen, C. H. Tung, L. Z. Wu, ACS Catal., 2016, 6, 4635–4639.
[44] Y. W. Zheng, B. Chen, P. Ye, K. Feng, W. G. Wang, Q. Y. Meng, L. Z.
Wu, C. H. Tung, J. Am. Chem. Soc., 2016, 138, 10080–10083.
[45] G. T. Zhang, X. Hu, C. W. Chiang, H. Yi, P. K. Pei, A. K. Singh, A. W.
Lei, J. Am. Chem. Soc., 2016, 138, 12037–12040.
[29] D. L. Wei, Y. R. Li and F. S. Liang, Adv. Synth. Catal., 2016, 358,
3887–3896.
[46] G. T. Zhang, L. L. Zhang, H. Yi, Y. Luo, X. T. Qi, C. H. Tung, L. Z. Wu, A.
W. Lei, Chem. Commun., 2016, 52, 10407–10410.
[30] S. Fukuzumi, H. Kotani, K. Ohkubo, S. Ogo, N. V. Tkachenko, H.
Lemmetyinen. J. Am. Chem. Soc., 2004, 126, 1600–1601.
[31] H. Kotani, K. Ohkubo, S. Fukuzumi, J. Am. Chem. Soc., 2004, 126,
15999–16006.
[47] L. B. Niu, H. Yi, S. C. Wang, T. Y. Liu, J. M. Liu, A. W. Lei, Nat. Com‐
mun., 2017, 8, 14226–16223.
[48] H. Yi, L. B. Niu, C. L. Song, Y. Y. Li, B. W. Dou, A. K. Singh, A. W. Lei,
Angew. Chem. Int. Ed., 2017, 56, 1120–1124.
[32] K. Ohkubo, K. Mizushima, R. Iwata, K. Souma, N. Suzuki, S.
Fukuzumi, Chem. Commun., 2010, 46, 601–603.
[33] D. A. Nicewicz, T. Nguyen, ACS Catal., 2014, 4, 355–360.
[34] N. A. Romero, D. A. Nicewicz, Chem. Rev., 2016, 116,
10075–10166.
[35] J. L. Dempsey, B. S. Brunschwig, J. R. Winkler, H. B. Gray, Acc. Chem.
Res., 2009, 42, 1995–2004.
[36] A. Bhattacharjee, M. Chavarot‐Kerlidou, E. S. Andreiadis, M.
Fontecave, M. J. Field, V. Artero, Inorg. Chem, 2012, 51,
7087–7093.
[49] X. Hu, G. T. Zhang, F. X. Bu, X. Luo, K. B. Yi, H. Zhang, A. W. Lei,
Chem. Sci., 2018, 9, 1521–1526.
[50] X. Hu, G. T. Zhang, F. X. Bu, A. W. Lei, Angew. Chem. Int. Ed., 2018,
57, 1286–1290.
[51] P. W. Du, K. Knowles, R. Eisenberg, J. Am. Chem. Soc., 2008, 130,
12576–12577.
[52] N. A. Romero, D. A. Nicewicz, J. Am. Chem. Soc., 2014, 136,
17024–17035.
[53] P. A. Jacques, V. Artero, J. Pecaut, M. Fontecave, Proc. Natl. Acad.
Sci. USA, 2009, 106, 20627–20632.
吖啶和钴肟配合物协同光催化苯乙烯放氢二聚反应构筑 1,2-二氢-1-芳基萘
曹文晓 a,b, 吴成娟 a, 雷 涛 a, 杨修龙 a, 陈 彬 a,b,*, 佟振合 a,b, 吴骊珠 a,b,#
a中国科学院理化技术研究所, 光化学转换与功能材料重点实验室, 北京 100190
b中国科学院大学, 北京 100049
摘要: 芳基二氢萘类衍生物是许多生物活性的天然产物以及药物的常见结构单元, 其合成一直都受到化学家们的关注. 传
统的 1,2-二氢-1-芳基萘骨架化合物的构筑大都需要进行底物的预官能团化, 在高温条件下进行, 且产物的选择性较差, 因
此发展一种简单温和的制备方法很有必要. 最近兴起的可见光催化因具有条件温和、环境友好等特点而成为了合成化学
家的研究热点. 近期研究发现, 在可见光作用下利用吖啶光敏剂的强氧化能力, 可以实现苯乙烯的加成. 但此类反应需要
当量的氧化剂或氢原子转移试剂, 容易导致苯乙烯的二聚环合产物的进一步氧化或还原. 我们在前期发展的“放氢交叉偶
联”反应的基础上, 利用吖啶光催化和钴肟催化的协同作用, 实现了苯乙烯的放氢二聚反应, 在室温下高效构筑了 1,2-二氢
-1-芳基萘骨架, 反应条件温和, 底物脱除的电子和质子在钴肟催化剂作用下以氢气的形式释放, 反应具有中等及以上的收
率.
本文以苯乙烯为模型底物, 吖啶为光敏剂, 钴肟配合物为质子还原催化剂, 在乙腈溶剂中, 蓝色 LED 灯下光照 24 h 可
以获得 56% 的产率, 对于其它的光敏剂如 fac-Ir(ppy)3 等则不能催化该反应. 通过催化剂种类及用量筛选表明, 7 mol% 的
Co(dmgH2)pyCl 配合物具有最好的反应效果, 可以获得 72% 的收率. 控制实验表明, 光敏剂、钴肟催化剂和光照都是必须
的. 通过底物拓展我们发现, 烷基、卤素等不同取代基的苯乙烯类化合物均可以获得较好的收率, 不同苯乙烯之间也可以
发生交叉反应.
随后, 我们进一步通过光谱和中间体捕获实验对反应机理进行了研究. 自由基捕获实验说明反应过程可能涉及自由
基历 程; 光谱淬 灭实 验 表明 苯乙 烯 和 Co(dmgH2)pyCl 均可淬 灭吖 啶的 发 光, 但苯乙 烯 淬灭吖 啶的 程度远 大于

Wenxiao Cao et al. / Chinese Journal of Catalysis 39 (2018) 1194–1201
1201
Co(dmgH2)pyCl 淬灭吖啶的程度. 在反应时苯乙烯的浓度远大于催化剂的溶度, 因此, 我们认为激发态吖啶首先与苯乙烯
发生反应; 可见光照射反应体系 1 min 后在 440–500 和 550–650 nm 处观察到明显的 CoII 和 CoI 的吸收峰. 基于以上实验
结果, 我们提出了可能的催化循环: 吖啶受光激发到达激发态后, 首先与底物苯乙烯发生单电子转移生成苯乙烯正离子自
由基和吖啶阴离子自由基 Acr•-Mes, Acr•-Mes 还原 Co(dmgH2)pyCl 生成 CoII 中间体, 从而回到基态完成光催化循环. 苯乙
烯正离子自由基与另一分子苯乙烯加成环合, 进而通过芳构化生成自由基中间体, 再与 CoII 作用生成目标产物 1,2-二氢-1-
芳基萘和 CoI, CoI 通过结合体系中的质子进而释放出氢气回到 CoIII 从而完成钴肟催化循环.
关键词: 放氢二聚; 苯乙烯; 1,2-二氢-1-芳基萘; 光催化; 钴肟催化剂
收稿日期: 2018-04-20. 接受日期: 2018-04-27. 出版日期: 2018-07-05.
*通讯联系人. 电话/传真: (010)82543576; 电子信箱: chenbin@mail.ipc.ac.cn
#通讯联系人. 电话/传真: (010)82543580; 电子信箱: lzwu@mail.ipc.ac.cn
基金来源: 中国科技部 (2014CB239402, 2017YFA0206903); 国家自然科学基金 (21390404); 中科院战略性先导科技专项（B类）
项目 (XDB17000000); 中科院前沿科学重点研究计划项目 (QYZDY-SSW-JSC029).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).