Visible-light-induced ligand to metal charge transfer excitation enabled phosphorylation of aryl halides

Article abstract of DOI:10.1039/d1cc01858b

We herein described a visible light induced nickel^(II)-catalyzed cross-coupling of secondary phosphine oxides with aryl halides. The Ni^(I)species and chlorine atom radical Cl˙ were generatedviathe ligand to metal charge transfer (LMCT) process of the NiCl₂(PPh₃)₂, which allows nickel^(IV)-phosphorus speciesin situformation, giving various tertiary phosphine oxides under photocatalyst-free conditions.

Full text of DOI:10.1039/d1cc01858b

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Visible-light-induced ligand to metal charge
transfer excitation enabled phosphorylation of
aryl halides†
Cite this: Chem. Commun., 2021,
57, 5702
Received 7th April 2021,
Accepted 5th May 2021
b
Hong Hou,*a Bing Zhou,a Jiawei Wang,a Duhao Sun,a Huaguang Yu,
a
a
Xiaoyun Chen,c Ying Han,a Yaocheng Shi,a Chaoguo Yan
and Shaoqun Zhu
*
DOI: 10.1039/d1cc01858b
rsc.li/chemcomm
We herein described a visible light induced nickel(II)-catalyzed cross- aryl halides have also been proven as a convenient method
coupling of secondary phosphine oxides with aryl halides. The Ni(I) for the preparation of triaryl phosphine oxides.8 The groups of
species and chlorine atom radical Clꢀ were generated via the ligand to Lu & Xiao,9 and Li10 reported the triaryl phosphine oxide
metal charge transfer (LMCT) process of the NiCl2(PPh3)2, which preparation via a combination of nickel and visible-light photo-
allows nickel(IV)-phosphorus species in situ formation, giving various catalysis, respectively. A single electron transfer (SET) or an
tertiary phosphine oxides under photocatalyst-free conditions.
energy transfer step by the excited photosensitizer was accepted
as the generation of Ar–Ni(III)–P(O) species, which then
Tertiary phosphine oxides present an important class of che- furnished the tertiary phosphine oxides by the reductive elimi-
micals, which are widely applied in medicinal, agricultural, and nation process.11
materials chemistry, as well as organic synthesis.1,2 As such, the
The visible-light-induced ligand to metal charge transfer
preparation of triarylphosphine oxides has attracted much (LMCT) excitation of inorganic metals recently has been uti-
attention and numerous efforts, and great developments in lized as a strategy to initiate organic transformation, and the
access to the tri-aryl phosphine oxides have been made and development of a visible-light driven organic transformation
achieved.3
protocol without the use of a photocatalyst has attracted our
The direct arylation of secondary phosphine oxides with aryl great attention.12–14 Recently, we have described a nickel cata-
halides presents one of the most straightforward and efficient lyzed cis-hydrophosphorylation reaction of 1,3-enyne, and the
methods for the C–P(O) bond construction of the tertiary visible-light-induced LMCT process of NiCl2(PPh3)2 was proved
phosphine oxides.4 Compared with the thermal process of to generate a Ni(I) species and chlorine atom radical Clꢀ, which
various transition-metal catalyzed C–P bond formations where in situ generates Ln–Ni(II)–P(O) species in a redox neutral
expensive metals as the catalysts or harsh reaction conditions manner as the key step.15 We envisaged that the use of an aryl
are utilized,5 the visible-light driven C–P bond formation allows electrophile, such as aryl halides, would generate tertiary
a convenient method for the preparation of triaryl phosphine phosphine oxides, and the Ar–LnNi(IV)P(O) species generation
oxides. The Che and Li groups individually demonstrated the and its reductive elimination as the key steps (Scheme 1).
catalyst-free, visible-light induced C(sp2)–P(O) bond formation
The protocol development was started by testing the reac-
approach towards the synthesis of tertiary phosphine oxides, tion of diphenylphosphine oxide 1a and 1-iodo-4-
and an excessive amount of strong base, such as NaOtBu or methylbenzene 2a as the substrate, and 10.0 mol% of
KOtBu, was used.6,7 The visible-light photoredox and nickel NiCl2(PPh3)2 as the catalyst, 12.0 mol% of 1,10-phenanthro-
dual-catalyzed cross-coupling of diarylphosphine oxide with line L-1 as the ligand, and 2.0 equiv. of Cs2CO3 as the base were
used. When the reaction was irradiated under visible light
conditions, the reaction solvent screening indicated that MeOH
was the best choice for the current cross-coupling reaction,
giving 3a in 70% isolated yield. Other solvents, such as THF,
toluene, MeCN, DCE or acetone, were tested, and all failed to
give the desired product, and a trace amount of 3a was
observed. Different ligands were tested next, and when 2,
9-dimethyl-1,10-phenanthroline L-2 was used, a trace amount
of 3a was generated, and 4,40-di-tert-butyl-2,20-bipyridine L-3
a School of Chemistry & Chemical Engineering, Yangzhou University,
Yangzhou 225009, China. E-mail: hhou@yzu.edu.cn, shaoqun.zhu@yzu.edu.cn
b Key Laboratory of Optoelectronic Chemical Materials and Devices,
Ministry of Education, School of Chemical and Environmental Engineering,
Jianghan University, Wuhan 430056, China
c School of Environmental and Chemical Engineering, Jiangsu University of Science
and Technology, Zhenjiang 212005, China
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1cc01858b
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Table 1 Optimization of the reaction conditionsa
Yieldb
(%)
Entry Deviation from the standard conditions solvent
1
2
None
70
Trace
THF, Toluene, MeCN, DCE or Acetone instead of
MeOH
3
4
5
6
7
8
L-2 instead of L-1
L-3 instead of L-1
L-4 instead of L-1
No light
No base
In air
Trace
49
26
o5
Trace
Trace
a
1a (0.2 mmol), 2a (0.4 mmol), NiCl2(PPh3)2 (0.02 mmol), L-1
(0.024 mmol), Cs2CO3 (0.4 mmol), MeOH (2.0 mL), for details, see the
b
ESI. Yield of isolated 3a.
Scheme 1 Different strategies for the C(sp2)–P(O) bond formation and
the visible-light driven nickel–phosphorus species in situ generation
enable a cross-coupling reaction of diaryl phosphine oxides with aryl
halides.
gave 3a in 49% yield, and Schiff base containing tri-chelate
ligand L-4 gave 3a in 26% yield. The reaction in the absence of
visible light was tested carefully, and 3a was obtained in very
low yield, and both the reaction without base or in air all led to
a trace amount of 3a formation (Table 1).
The preliminary mechanistic study was carried out by radi-
cal survey experiments, when 1.0 equiv. of TEMPO (2,2,6,
6-tetramethyl-1-piperidinyloxy) as the additive was used, and
3a was not observed (a, Scheme 2). BHT (2,6-di-tert-butyl-4-
methylphenol) as the additive was tested next, and 3a was
obtained in 38% isolated yield; high-resolution mass spectro-
metry (HRMS) analysis indicated that the cross-coupling pro-
duct 4 by BHT with a chlorine atom was detected, and possible
product 5 by the cross-coupling reaction of 1a with BHT was not
detected (b, Scheme 2).16 The above results clearly suggested
that the present cross-coupling reaction underwent a radical
reaction pathway, and the chlorine atom was generated.
Based on the above study, as well as the previous
reports,16,17 a visible-light induced nickel catalyst C–P bond
formation via an Ni(II)/Ni(I)/Ni(III)/Ni(IV)/Ni(II) cycle was proposed
in Scheme 3. The Ni(II) intermediate A was generated by ligand
exchange of Ni(PPh3)2Cl2 with L-1, and the visible light irradia-
tion of complexes A would generate the Ni(I) species B and the
chlorine atom radical Clꢀ via the LMCT process.18 The hydro-
Scheme 2 Radical survey experiments.
gen atom abstraction between 2a and Clꢀ allowed the Scheme 3 Reaction mechanism proposed.
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Table 2 Reaction scope for the cross-coupling reactiona
phosphorus atom radical formation, and the generated Ni(I) species
underwent an oxidative addition with aryl halide 2a giving a Ni(III)
species C, then re-bonded with the phosphorus atom radical to
afford the Ni(IV) intermediate D, and then reductive elimination led
to the desired product 3a formation.19
Under the above best reaction conditions established, different
diaryl phosphine oxides 1 and aryl halides 2 were subjected to the
reaction conditions and all the tested reactions were successful,
and the corresponding products 3a–3w were obtained in general
satisfactory isolated yields (40–75%, Table 2).
Entry Product
3
Yieldb [%]
1
2
3
4
5
6
7
8
3a R = Me
3b R = H
3c R = OMe
3d R = Et
3e R = F
3f R = CF3
3g R = Me
3h R = CF3
70
75c
43c
62c
44c
61
Various aryl bromides and aryl iodines were tested to react
with diphenylphosphine oxide 1a, and all the reactions success-
fully furnished the desired products, and the corresponding
triaryl phosphine oxides 3a–3k were obtained in good yields.
Different aryl iodines, such as 1-iodo-4-methylbenzene 2a and
1-iodo-4-(trifluoromethyl)benzene 2f were tested to react with
1a, and the desired products 3a and 3f were obtained in 70%
and 61% yields, respectively (entries 1 and 6, Table 2). Different
aryl bromides, including bromobenzene 2b, 1-bromo-4-
methoxybenzene 2c, 1-bromo-4-ethylbenzene 2d and 1-bromo-
4-fluorobenzene 2e were subjected to the reaction next, to our
great delight, the desired products 3b–3e were obtained in good
yields (43–75%, entries 2–5, Table 2).
40c
52c
9
3i
3j
40c
41c
10
In order to explore the present photochemical phosphoryla-
tion approach accessing various tertiary phosphine oxides, we
next turned our attention to different di-aryl phosphine oxides
scope investigation. Various diarylphosphine oxides 1l–1o,
derived from the same aryl groups, were tested to react with
2a or 2b, and all the tested reactions were successful, giving the
desired tri-aryl phosphine oxides 3l–3o in good yields. Various
different aryl group desired diarylphosphine oxides were sub-
jected to the reaction conditions next, and all were proved to be
compatible; the tested reactions were successful, and various
different aryl groups containing triarylphosphine oxides 3p–3u
were obtained in good yields (41–74% yields, entries 16–21,
Table 2).
11
12
3k
3l
42c
53c
13
14
15
3m Ar = 4-ClC6H4
3n Ar = 4-PhC6H4
3o Ar = 3-CF3C6H4
42
56
47
The amino acid derived aryl iodines were tested next under
the best reaction conditions, and the desired tri-aryl phosphine
oxides 3v and 3w were obtained in 46% and 41% isolated yields,
respectively (entries 22 and 23, Table 2). It should be mentioned
that aryl chloride and dialkyl phosphites as the substrates were
tested and no reactions were observed.
16
3p
45c/74
17
18
19
20
21
3q Ar = 4-FC6H4
3r Ar = 4-CF3C6H4
3s Ar = 3-OMeC6H4 45
3t Ar = 4-PhC6H4 51
3u Ar = 4-OMeC6H4 47c/70
41c/65
61
In conclusion, we have developed a visible-light induced
nickel catalyst cross-coupling reaction of diarylphosphine
oxides with aryl halide, and various tri-aryl phosphine oxides
were obtained in good yields. The use of the present
strategy for other organic transformations is ongoing in our
laboratory.
We gratefully acknowledge the National Natural Science
Foundation of China (21602085 and 21702179); the Priority
Academic Program Development of Jiangsu Higher Education
Institutions, Project supported by the Natural Science Founda-
22
3v
46
41
23
3w
a
1 (0.2 mmol), aryl iodines 2 (0.4 mmol), NiCl2(PPh3)2 (0.02 mmol), L-1 tion of the Jiangsu Higher Education Institutions of China
(0.024 mmol), Cs2CO3 (0.4 mmol), MeOH (2.0 mL), for details, see the
ESI. Yield of isolated 3. Aryl bromides were used instead of aryl
iodines.
(17KJB150042), and Lvyangjinfeng Talent Program of Yangzhou
for the financial support. We also thank the Testing Centre of
Yangzhou University for the sample analysis.
b
c
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Conflicts of interest
There are no conflicts to declare.
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