One-pot Negishi cross-coupling reaction of aryldiazonium salts via Ni catalysis induced by visible-light

Article abstract of DOI:10.1016/j.catcom.2019.105785

Visible-light induced catalysis is of high interest for its mild and environmentally benign properties. Herein, a general Ni catalysis accelerated by visible-light was successfully developed for one-pot Negishi coupling reactions at room temperature in a short reaction time (<2 h), using diazonium salts with Ar₂Zn generated in situ from Grignard reagents and ZnBr₂. This protocol provides a convenient access to C–C bond formation for important biaryl components. It tolerates various functional groups, and Hammett study illuminates the possiblility of Ni(III)/Ni(I) redox catalytic cycle.

Full text of DOI:10.1016/j.catcom.2019.105785

Accepted Manuscript
One-pot Negishi cross-coupling reaction of aryldiazonium salts
via Ni catalysis induced by visible-light
Lianjun Wang, Gao Liu
PII:
S1566-7367(19)30247-X
https://doi.org/10.1016/j.catcom.2019.105785
105785
DOI:
Article Number:
Reference:
CATCOM 105785
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
25 June 2019
22 July 2019
14 August 2019
Please cite this article as: L. Wang and G. Liu, One-pot Negishi cross-coupling reaction of
aryldiazonium salts via Ni catalysis induced by visible-light, Catalysis Communications,
https://doi.org/10.1016/j.catcom.2019.105785
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
One-pot NegishiCross-Coupling Reactionof Aryldiazonium Salts via Ni
Catalysis Induced by Visible-Light
Lianjun Wang*, Gao Liu
College of Chemistry and Chemical Engineering, Hunan Institute of Engineering; Key Laboratory of
Environmental Catalysis and Waste Regeneration, Hunan 411104, P. R. China
*
E-mail: lianjunwang2019@126.com
Abstract
Visible-light induced catalysis is of high interest for its mild and environmentally benign
properties. Herein, a general Ni catalysis accelerated by visible-light was successfully
developed for one-pot Negishi coupling reactions at room temperature in a short reaction
time (< 2 hours), using diazonium salts with Ar2Zn generated in situ from Grignard
reagents and ZnBr2. This protocol provides a convenient access to C-C bond formation
for important biaryl components. It tolerates various functional groups, and Hammett
study illuminates the possiblility of Ni(III)/Ni(I) redox catalytic cycle.
Keywords
Negishi coupling, Visible-light induced Ni-catalysis, Aryldiazonium Salts, Room
temperature
1
. Introduction
The biaryl components are ubiquitous in the structure of natural products, pharmaceutical
agents and functional materials.[1-2] Tremendous efforts have been extended to construct
biaryls. Over the past decade, the aryl-aryl bond formation catalyzed by transition-metal
has been particularly studied, and there has been numerous elegant methodologies
developed in this research area.[3-4] However, despite these progress, the oxidation of
metal catalyst from low valence to high valence in its catalytic process still remains a big
challenge under mild conditions.[5-7] Photocatalysis has emerged as a powerful tool to
accelerate transition-metal catalysis.[8] Notably, in 2011, Sanford group reported visible-
light photocatalysis successfully accelerated the rate of Pd-catalyzed C-H arylation using
aryldiazonium salt as arylation reagent.[9] In 2015, Kobayashi group proved that visible-
light irradiation conspicuously decreased the Cu-catalyzed C-N coupling reaction
temperature.[10] Visible-light as a green energy attracted our attention to facilitate
oxidation of tough transition-metal in its redox-catalytic cycle.[11]
3
2
Ni catalysis induced by visible-light has been well explored for C(sp )-C(sp ) bond
2
2
formation at room temperature.[12-17] However, Ni-catalyzed C(sp )-C(sp ) bond
formation at room temperature was rarely reported to date.[18-20] Negishi coupling as a
C-C bond formation reaction has won its Noble prize. Although Pd-catalyzed Negishi
reaction under mild conditions has been widely reported to construct biaryls,[21] nickel
catalyst has usually been employed in Negishi reaction only with well-designed ligand

ACCEPTED MANUSCRIPT
o
and at high temperature (>60 C).[22-25] Inspired by Sanford’s work, we questioned if
visible-light photocatalysis could be used to convert low valence to high valence of
nickel in its catalytic cycle at room temperature.
2
. General procedure for the Ru/Ni catalyzed reaction
Ru(bpy)3(PF6)2 (5.37 mg, 0.00625 mmol, 0.025 equiv), and NiCl2 (6.48 mg, 0.05 mmol,
.20 equiv) were added into a 20 mL Fisherbrand Glass Threaded vial with a stir bar, and
0
then PhN2BF4 (1a, 48.0 mg, 0.25 mmol, 1.0 equiv) and EtOH (3.0 mL) were added. On
the other hand, Ph2Zn was prepared using PhMgBr (1 M in ether, 0.5 mmol, 2.0 equiv),
ZnBr2 (0.25 mmol), LiBr (0.38 mmol) and THF (5 mL) in a 15 mL flask stirring for 30
min at room temperature, after solvent was removed, and then a solution of the residue in
toluene (3 mL) was transferred to light-irradiation vial. The vial was sealed with a Teflon
cap, and placed on a stir plate with two 12 W blue LEDs (one on either side of the vial
about 5 cm away). The reaction mixture was allowed to stir at room temperature for 2 h.
The reaction was then quenched with water (5 mL) and EtOAc (10 mL). The GC yield of
the crude product was determined to be 73% (using hexadecane as the standard). The
reaction mixture was further diluted with additional EtOAc (30 mL) and H2O (20 mL)
and extracted three times with EtOAc (40 mL). Finally, the combined organic layers were
washed with brine (1 x 30 mL), dried over NaSO4, filtered, concentrated, and purified by
flash chromatography column (eluent: 5% - 30% hexanes in ethyl acetate) to get the
product 3a as a white solid (28.2 mg, 73%).
3
. Results and Discussion
We began our initial investigations by examining the Ni-catalyzed C-C bond formation at
room temperature, using phenyldiazonium tetrafluoroborate (1a) and phenylmagnesium
bromide (2a) as substrates, in presence of ZnBr2 and under a Ru-based photocatalysis
(Table 1). Promising results were obtained, when THF was used as solvent and NiCl2 (20
mol%) as catalyst, the reaction gave 14% biphenyl (3a) in open air after 2 hours (entry 1).
Screening of different solvents resulted in highest yield 63%, where toluene was used to
generate organozinc reagent, and then EtOH was added to furnish photocatalyzed cross-
coupling step (entry 7 of entries 1-9). Furthermore, different additives were utilized to
determine the best combination of ZnBr2 (1 equiv.) and LiBr (1.5 equiv.) to provide 73%
yield (entry 12 of 10 - 12). LiBr may lead to a multimetallic synergistic effect in the
reaction. [26-28] The incomplete reaction gave 57% yield after 1 hour (entry 13). Due to
the occurance of side reaction, when the reaction time was extended to 15 h, the 71%
yield was obtained (entry 14). Direct use of Gregnard reagent led to no desired product
(
entry 15). Logically, the control experiments were performed to illustrate that
photoredox catalyst and LED irradiation were all essential for this coupling reaction
entries 16-17). Finally, a reaction under argon was performed to exclude the possibility
(
of oxidization of oxygen (entry 18), and the absence of Ni catalyst caused no target
product (entry 19).
Table 1 Optimization of Ni-catalyzed Negishi Reaction of Phenyldiazonium Tetrafluoroborate (1a) and
.a
Phenylmagnesium Bromide (2a) under LED Irradiation

ACCEPTED MANUSCRIPT
b
Entry
Additive
Solvent
Yield (%)
14
1
2
3
4
5
6
7
8
9
ZnBr
ZnBr
ZnBr
ZnBr
ZnBr
ZnBr
ZnBr
ZnBr
ZnBr
2
2
2
2
2
2
2
2
2
THF
Toluene
21
1,4-dioxane
11
THF+MeOH
6
THF+EtOH
13
Toluene+MeOH
Toluene+EtOH
1,4-dioxane+MeOH
1,4-dioxane+ EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
Toluene + EtOH
26
63
21
58
1
1
1
0
1
2
ZnCl
2
53
ZnCl
ZnBr
ZnBr
ZnBr
2
2
2
2
+LiCl
+LiBr
+LiBr
+LiBr
64
73(73)
57
c
1
3
4
d
1
71
1
5
--
<1
e
1
6
ZnBr
ZnBr
ZnBr
ZnBr
2
2
2
2
+LiBr
<1
f
1
7
+LiBr
+LiBr
+LiBr
<1
g
1
1
8
73
h
9
0
a
Reaction conditions: 1a (0.25 mmol), 2a (0.5 mmol), NiCl2 (0.05 mmol, 20 mol%), Ru(bpy)3(PF6)2 (0.00625 mmol, 2.5 mol%), solvent
b
(
6.0 mL or 3.0 mL/3.0 ml indicated mixture) at room temperature in open air under blue LED irradiation. Yield based on 1a and determined
c
d
by GC analysis using hexadecane as an internal standard, isolated yield in parentheses. Reaction time: 1 hours. Reaction time: 15 hours.
e
f
g
h
Without photoredox Ru catalyst. Without LED irradiation. Under Ar. Without Ni catalyst
As can be deduced from the results listed on Table 2, a wide variety of aryldiazonium
salts were proved to be suitable substrates and provided the desired products in moderate
to good yields (3a-3k). The steric had a negative effect by decreasing the yield to 48%
(3b). When the reactant with electron-donating group was used, the reaction afforded 68%
yield (3c). On the other hand, electron-withdrawing 4-CF3 group had minimal deleterious
effect resulting in 55% yield (3d). Starting compounds containing Cl or Br on the
aromatic ring reacted chemoselectively through diazonium side (entries 5-7): 4-Cl and

ACCEPTED MANUSCRIPT
3
,5-dichloro compounds gave moderate yields (3e: 60% and 3f: 64%), and the yield of 4-
bromo fragment was a bit lower (3g: 41%). To our delight, 4-nitrile substrate was
tolerated, affording 49% yield (3h). Besides, the substrates with labile functional groups
such as aldehyde, ketone or ester (1l-1k) were also compatible in this reaction, giving the
desired coupling products in 33%, 57% and 62% yields, respectively.
a
Table 2 Scope of Aryldiazonium Salts for Ni-catalyzed Negishi Reaction underLED Irradiation.
Isolated
Yield
Entry
1
[Aryl-N2]BF
4
(1)
Product (3)
73
2
3
48
68
4
5
55
60
6
7
64
41
8
9
49
33

ACCEPTED MANUSCRIPT
1
1
0
1
57
62
a
Reaction conditions: 1 (0.25 mmol), 2a (0.5 mmol), NiCl2 (0.05 mmol, 20 mol%), ZnBr2 (0.25 mmol), LiBr (0.38 mmol), Ru(bpy)3(PF6)2
0.00625 mmol, 2.5 mol%), 3.0 mL toluene/3.0 ml ethanol at room temperature in open air under blue LED irradiation.
(
Next, experiments were performed to investigate the scope of Grignard reagents (Table
). The sterically hindered substrate (2b) afforded a bit lower yield (entry 2, 46%). As
expected, both 4-methoxyl and 4-CF3 generated the desired products in good yields
entry 3 and 4). Naphthalene was compatible in this reaction with 66% yield (3l). Notably,
3
(
the compounds containing basic groups such as dimethylamino, pyridinyl and quinolin-8-
yl groups were well tolerant for this protocol, resulting in 45%, 64% and 71% yields,
respectively (entries 6-8). Biphenyl compound gave a good yield, and 4-Cl reagent
afforded the target product in 61% yield (entries 9-10).
a
Table 3 Scope of Grignard Reagent for Ni-catalyzed Negishi Reaction under light Irradiation.
Isolated
Yield
Entry
ArMgBr (2)
Product (3)
1
73
2
3
46
70

ACCEPTED MANUSCRIPT
4
64
5
66
6
7
45
64
8
9
71
70
61
1
0
a
Reaction conditions: 1a (0.25 mmol), 2 (0.5 mmol), NiCl2 (0.05 mmol, 20 mol%), ZnBr2 (0.25 mmol), LiBr (0.38 mmol), Ru(bpy)3(PF6)2
0.00625 mmol, 2.5 mol%), 3.0 mL toluene/3.0 ml ethanol at room temperature in open air under blue LED irradiation.
(
Hammett study was performed to get insight into the mechanism of this photoredox
reaction (Figure 1).[29] Using different-substitutent diazoniums (4-MeO, 4-Cl, 4-COOEt,
4
0
-CF3, -CN vs 4-H), it is showed that this reaction is sensitive to the substituents (ρ =
.75, Figure 1a), indicating that diazonium salts had built up a partial negative charge or
lost a partial positive charge in their transition states, which could be elucidated by one
+
∙
electron trap of ArN2 to form ArN2 radical, and by the low oxidation valence redox
cycle of Ni(III)/Ni(I) instead of Ni(IV)/Ni(II). The Ni(IV)/Ni(II) cycle usually requires a

ACCEPTED MANUSCRIPT
haloalkane coupling partner.[30, 31] On the other side, the competition experiments
between different Grignard reactants (4-NMe2, 4-MeO, 4-Ph, 4-Cl, 4-CF3 vs 4-H)
illuminates that these substrates had been building up positive charge (or lost negative
charge) on their intermediates (ρ = -0.45, Figure 1b), [32] this may be due to the more
efficient transmetalation of electron-rich zinc reagent with NiCl2.
Figure 1. (a) Plot of log (kX/kH) vs σ for ArN2BF4 with PhMgBr. (b) Plot of log (kX/kH) vs σ for PhN2BF4 with ArMgBr.
A plausible catalytic cycle of this Ni/Ru photocatalyzed Negishi coupling is shown in
Figure 2. The key steps of Ni catalytic cycle include [31]: (i) generation of Ph2Zn from
ZnBr2 and Grignard reagent PhMgBr; (ii) transmetalation of NiX2 (A) with Ph2Zn to
∙
form PhNi(II)X (B); (iii) one-electron oxidation of PhNi(II)X (B) by Ar radical to
generate PhArNi(III)X (C); (iv) C-C bond formation by reductive elimination to release
3
+
the biaryl product and Ni(I)X (D); (v) one-electron oxidation of Ni(I)X (D) by Ru(bpy)3
to regenerate the initial Ni(II)X2 (A), consistent with Hammett study. The steps on Ru
catalytic cycle are as reported [9] [33]: (i) light-irradiation of the Ru catalyst to generate
2
+
3+
excited Ru(bpy)3 *; (ii) oxidation of the Ru center to Ru(bpy)3 with concomitant
∙
∙
reduction of aryldiazonium salt to ArN2 radical; [34] (iii) N2 releasing of ArN2 to
produce Ar radical; (iv) one-electron reduction of Ru(bpy)3 to regenerate the
photocatalyst.
∙
3+
Figure 2 Plausible Mechanism for Ni/Ru-catalyzed One-pot Negishi-Coupling Reaction

ACCEPTED MANUSCRIPT
4
. Conclusion and Future Directions
In sum, we reported a mild one-pot approach for nickel-catalyzed Negishi reaction, being
accelerated by photocatalysis. These reactions proceeded smoothly at room temperature
and were compatible with a range of functional groups. This protocol successfully
utilized visible-light photoredox to facilitate Ni redox catalysis. We anticipate that this
new approach will benefit other Ni-catalyzed synthetic transformations.
Acknowledgements
We gratefully acknowledge the funding support received for Talent Engineering Project
(09001003/17RC002) from Hunan Institute of Engineering.
References and notes
1
2
3
.
.
.
J. Hassan, M. Sevignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev. 102 (2002) 1359-1470.
G. Bringmann, T. Gulder, M. Breuning, Chem. Rev. 111 (2010) 563-639.
A. Fihri, M. Bouhrara, B. Nekoueishahraki, J. Basset, V. Polshettiwar, Chem. Soc. Rev. 40 (2011) 5181-
5203.
4
5
6
7
8
9
1
1
1
1
.
.
.
.
.
.
F. Han, Chem. Soc. Rev. 42 (2013) 5270-5298.
M. Hopkinson, A. Tlahuext-Aca, F. Glorius. Acc. Chem. Res. 49 (2016) 2261−2272.
X. Zhang, D. W. C. MacMillan, J. Am. Chem. Soc. 139 (2017), 11353−11356.
E. B. McLean, A. Lee, Tetrahedron, 74 (2018) 4881-4902.
C. K. Prier, D. A. Rankic, D. W. C. MacMillan Chem. Rev. 113 (2013) 5322-5363.
D. Kalyani, K. McMurtrey, S. Neufeldt, M. Sanford, J. Am. Chem. Soc. 133 (2011) 18566-18569.
0. W. Yoo, T. Tsukamoto, S. Kobayashi, Angew. Chem. Int. Ed. 54 (2015) 6587-6590.
1. M. Hopkinson, A. Tlahuext-Aca, F. Glorius, Acc. Chem. Res. 49 (2016) 2261 - 2272.
2. J. Twilton, C. Le, P. Zhang, M. H. Shaw, R.W. Evans, D. W. C. MacMillan, Nat. Rev. Chem. 1 (2017) 1-18.
3. R. T. Smith, X. -H Zhang, J. A. Rincꢀn, ꢁ. Agejas, C. Mateos, M. Barberis, S. García-Cerrada, O. Frutos, D.
W. C. MacMillan J. Am. Chem. Soc. 140 (2018) 17433−17438.
1
1
4. V. Bacauanu, S. Cardinal, M. Yamauchi, M. Kondo, D. F. Fernández, R. Remy, D. W. C. MacMillan
Angew. Chem. Int. Ed. 57 (2018) 12543 –12548.
5. I. B. Perry, T. F. Brewer, P. J. Sarver, D. M. Schultz, D. A. DiRocco, D. W. C. MacMillan Nature 560
(
2018) 70-75.
1
1
6. I. Abdiaj, A. Fontana, M. V. Gomez, A. Hoz, J. Alcázar, Angew. Chem.Int. Ed. 57 (2018) 8473 –8477.
7. G. Lise-Lotte in Targets in Heterocyclic Systems, Vol. 14 (Eds.: O. Attanasi, D. Spinelli), Wiley-VCH,
Weinheim, 2008, pp. 85-119.
1
1
8. S. Z. Tasker1, E. A. Standley, T. F. Jamison Nature 509 (2014) 299-309.
9. A. Fihri, M. Bouhrara, B. Nekoueishahraki, J. Basset, V. Polshettiwar, Chem. Soc. Rev. 40 (2011) 5181-
5203.
2
2
2
2
2
2
2
2
0. F. Han, Chem. Soc. Rev. 42 (2013) 5270-5298.
1. F. -X. Felpin, S. Sengupta, Chem. Soc. Rev. 48 (2019), 1150—1193.
2. V. Phapale, D. Cárdenas, Chem. Soc. Rev. 38 (2009) 1598–1607.
3. K. Yamamoto, S. Otsuka, K. Nogi, H. Yorimitsu, ACS Catal. 7 (2017) 7623−7628.
4. R. Gerber, C. Frech, Chem. Eur. J. 17 (2011) 11893 – 11904.
5. J. M. Bhojane, S. A. Sarode, J. M. Nagarkar New J. Chem. 40 (2016) 1564—1570.
6. J.-L. Tao, B. Yang, Z.-X. Wang, ꢁ. Org. Chem. 80 (2015) 12627−12634.
7. D. R. Armstrong, W. Clegg, P. García-Álvarez, A. R. Kennedy, M. D. McCall, L. Russo, E. Hevia, Chem.
Eur. J. 17 (2011) 8333 – 8341.
2
2
3
8. L. C. McCann, H. N. Hunter, J. A. C. Clyburne, M. G. Organ, Angew. Chem. Int. Ed. 51 (2012) 7024 –7027.
9. L. Hammett, J. Am. Chem. Soc. 59 (1937) 96–103.
0. Y. –Z. Li, L. –F. Zou, R. -P Bai, Y. Lan, Org. Chem. Front. 5 (2018) 615–622.

ACCEPTED MANUSCRIPT
3
1. V. B. Phapale, M. Guisán‐Ceinos, E. Buñuel, D. J. Cárdenas, Chem. Eur. J. 15 (2009) 12681 – 12688.
3
3
3
2. A. Stein, M. Tencer, E. Moffatt, R. Dawe, J. Sweet, J. Org. Chem. 45 (1980) 3539–3540.
3. H. Cano-Yelo, A. Deronzier, J. Chem. Soc., Faraday Trans. 1. 80 (1984) 3011-3019.
4. The addition of 1.0 equivalent TEMPO completely quenched the reaction, no desired product was obtained.
This reaction procedure: Ru(bpy)
mmol, 0.20 equiv) were added into a 20 mL Fisherbrand Glass Threaded vial with a stir bar, and then
PhN BF (1a, 48.0 mg, 0.25 mmol, 1.0 equiv), TEMPO (39 mg, 0.25 mmol, 1.0 equiv.) and EtOH (3.0 mL)
were added, and then followed thegeneral procedure for therest of operation.
3 6 2 2
(PF ) (5.37 mg, 0.00625 mmol, 0.025 equiv), and NiCl (6.48 mg, 0.05
2
4

ACCEPTED MANUSCRIPT
Highlights
2
2





A Negishi reaction forC(sp )-C(sp ) bond formation was achieved.
This room-temperature transformation completed in 2 hours.
Visible-lightinduced this Ni-catalyzed cross-couplingreaction.
Aryldiazonium salts were used as couplingpartners with Ar
The labile functionalgroups were tolerated.
2
Zn.