Ni(NIXANTPHOS)-Catalyzed Mono-Arylation of Toluenes with Aryl Chlorides and Bromides

Article abstract of DOI:10.1021/acs.orglett.9b00294

A nickel-catalyzed cross-coupling of toluene derivatives with both aryl bromides and chlorides using a NIXANTPHOS-ligated nickel(II) complex has been developed. The key factor to success is proposed to be the catalyst activation of toluene by a cation-π complex, enabling methyl arenes (pK_a ≈ 43) to be deprotonated with the relatively mild base NaN(SiMe₃)₂. This method facilitates access to a variety of sterically and electronically diverse hetero- and nonheteroaryl-containing diarylmethanes.

Full text of DOI:10.1021/acs.orglett.9b00294

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Ni(NIXANTPHOS)-Catalyzed Mono-Arylation of Toluenes with Aryl
Chlorides and Bromides
Hui Jiang, Sheng-Chun Sha, Soo A Jeong, Brian C. Manor, and Patrick J. Walsh*
Roy and Diana Vagelos Laboratories, Penn/Merck Laboratory for High-Throughput Experimentation, Department of Chemistry,
University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, United States
S
* Supporting Information
ABSTRACT: A nickel-catalyzed cross-coupling of toluene
derivatives with both aryl bromides and chlorides using a
NIXANTPHOS-ligated nickel(II) complex has been developed.
The key factor to success is proposed to be the catalyst
activation of toluene by a cation−π complex, enabling methyl
arenes (pKa ≈ 43) to be deprotonated with the relatively mild
base NaN(SiMe3)2. This method facilitates access to a variety of sterically and electronically diverse hetero- and nonheteroaryl-
containing diarylmethanes.
romatic hydrocarbons are common starting materials for
toluene, diphenylmethane, benzylic ether, and benzylic amine
Athe preparation of more functionalized and higher value derivatives.9 In the years after our initial work with (η6-R-
C6H5)Cr(CO)3 complexes, we made several observations that
suggested to us that cation−π interactions10 could act as both
directing groups to control selectivity11 and activating groups
to increase the acidity of benzylic C−H bonds.12 Prior
computational work by Periana, Ess, Cundari and their co-
workers implied that cation−π interactions could acidify the
benzylic C−H bonds of toluene.13
small molecules with applications in synthesis, materials
science, and pharmaceutical chemistry. Recent years have
witnessed spectacular advances in transition metal catalyzed
C−H functionalizations,1 and a host of new reactions and
catalysts have been introduced.2 In the realm of toluene
activation at the benzylic position, contributions by Stahl,3
Liu,4 Davies,5 and Kozlowski6 stand out (Scheme 1A−D).
Remarkable progress has also been made on use of
organocatalysts in enantioselective toluene functionalization
reactions.7
We have been interested in the functionalization of weakly
acidic C(sp3)−H bonds by a deprotonative cross-coupling
process (DCCP). In 2010 we demonstrated that activation of
the benzylic C−H bonds by coordination of an arene to the
Cr(CO)3 fragment,8 enabling the arylation of η6-coordinated
Very recently we developed a palladium-catalyzed benzylic
arylation of toluenes with aryl bromides (Scheme 2).12a
Scheme 2. Cation−π Interactions in the Benzylic Arylation
of Toluenes
Scheme 1. Transition-Metal-Catalyzed C(sp3)−H Arylation
Mechanistic and computational studies support acidification of
toluene derivatives by the K+−cation−π interaction. Interest-
ingly, this reaction was only successful with aryl bromides and
not aryl chlorides, despite our prior demonstration that the
Pd(NIXANTPHOS) catalyst can activate aryl chlorides at rt
(in cyclopentyl methyl ether, CPME).14 This observation
inspired us to examine the nickel-based analogue.
Received: January 23, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b00294
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
The replacement of the precious metal palladium (Scheme
2) with the first-row, abundant metal nickel for catalytic
synthesis of diarylmethanes could significantly reduce the cost
of this process. Additionally, due to the high reactivity of nickel
toward oxidative addition,15 nickel catalysts often show
enhanced catalytic efficiency relative to palladium analogues
with substrates that are difficult to oxidatively add, including
aryl chlorides16 and fluorides.17 In several cases, nickel
precatalysts16c,d,18 have been shown to exhibit significantly
enhanced catalytic activity in comparison to Ni(COD)2 and
the corresponding phosphine ligand. This observation may be
due to the absence of COD, which is known to hinder catalysis
in some instances.18e Based on our success with the
Ni(COD)2/NIXANTPHOS catalyst system19 and these
precedents, we sought to develop an air-stable, highly active
NIXANTPHOS-ligated Ni(II) precatalyst for C(sp3)−H
arylation of methyl arenes.
approach using van Leeuwen’s NIXANTPHOS.20 Thus, the
synthesis of the precatalyst was accomplished by exchange of
the triphenylphosphine ligands on (Ph3P)2Ni(2-tolyl)Cl (P1)
with NIXANTPHOS in THF at room temperature, resulting in
P2 in 78% yield (Scheme 3; see SI for details). The structure
of P2 is shown in Figure 1 (see SI for details).
Scheme 3. Synthesis of (NIXANTPHOS)Ni(ο-tolyl)Cl (P2)
We initiated our research into the arylation of toluene with
1-bromo-4-tert-butylbenzene, NaN(SiMe3)2, 10 mol % Ni-
(COD)2, and 15 mol % NIXANTPHOS with toluene as the
solvent for 12 h at 110 °C, rendering 3a in 76% assay yield
1
(AY, determined by H NMR integration against an internal
standard, Table 1, entry 1) (for examination of other nickel
precursors, see the Supporting Information (SI)).
Figure 1. X-ray crystal structure of (NIXANTPHOS)Ni(2-tolyl)Cl
(P2) (from two different angles). Hydrogen atoms are omitted for
clarity.
Table 1. Optimization of Ni-Catalyzed Arylation of
a
Toluene
Performing the toluene arylation using 5 mol % of P2 as the
catalyst with NaN(SiMe3)2 as the base in toluene for 12 h at
110 °C resulted in a 77% AY (Table 1, entry 2). LiN(SiMe3)2
and KN(SiMe3)2 as the base led to reduced reactivity, giving
the coupled product 3a in 8% and 26% AY, respectively (Table
1, entries 3−4). Increasing the precatalyst loading of P2
resulted in an increase in the yield of coupling product 3a to
89% AY with an 84% isolated yield (Table 1, entry 5).
Increasing the catalyst loading to 10 mol % had little impact on
the AY (90%, Table 1, entry 6). Addition of an extra 7.5 mol %
ligand led to a slight decrease in AY (84%, Table 1, entry 7).
Attempts to decrease the equivalents of NaN(SiMe3)2,
temperature, or reaction concentration led to a diminished
AY of 3a (Table 1, entries 8, 10, and 13). When the dosage of
NaN(SiMe3)2 was increased from 4 to 4.5 equiv, we obtained
the same AY (entry 5 vs 9). Increasing the reaction
concentration from 0.033 to 0.1 M decreased the AY of 3a
from 89% to 65% (Table 1, entry 5 vs 11−12).
Under the optimized conditions, the scope of the direct
arylation of toluene with selected aryl bromides was
investigated (Scheme 4). Diphenylmethane (3b) was isolated
using 1a and bromobenzene (2b) in 83% yield. Sterically
hindered 1-bromonaphthalene (2h) was well tolerated,
affording 3h in 85% yield, respectively. The yields with these
aryl bromides were 5−9% lower than when the Pd-
(NIXANTPHOS)-based catalyst was used with KN(SiMe3)2
at the same 110 °C.
ligand
b
entry
1
base
[Ni] (mol %)
(mol %)
concn
0.033
AY (%)
76
NaN(SiMe3)2 Ni(COD)2
(10)
NaN(SiMe3)2 P2 (5)
LiN(SiMe3)2
KN(SiMe3)2
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (10)
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (7.5)
NaN(SiMe3)2 P2 (7.5)
15
2
3
4
5
6
7
−
−
−
−
−
7.5
−
−
−
−
−
−
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.1
77
8
P2 (5)
P2 (5)
26
c
89(84 )
90
84
78
89
18
65
66
72
d
8
e
9
f
10
g
11
h
12
0.05
0.025
i
13
a
Reactions conducted on a 0.10 mmol scale of 2a with 3 mL toluene
b
at 110 °C for 12 h. Assay yield (AY) determined by 1H NMR
c
spectroscopy of the crude reaction mixtures. Isolated yield after
d
e
chromatographic purification. 3 equiv of NaN(SiMe3)2. 4.5 equiv of
f
g
h
i
NaN(SiMe3)2. 80 °C. 1 mL of toluene. 2 mL of toluene. 4 mL of
toluene.
Next, the scope of the arylation of toluene with various aryl
chlorides was investigated (Scheme 4). With the nickel
precatalyst, toluene coupled with chlorobenzene (2b′) to
give the parent diphenylmethane (3b) in 86% yield under the
same conditions used with aryl bromides. Aryl chlorides
bearing electron-donating groups at the 4-position, such as tert-
butyl, methyl, and methoxy, generated the corresponding
diarylmethanes 3a, 3c−3d in good yields (65−87%). Aryl
chlorides bearing 3-Me (2e′) and 3-NMe2 (2f′) were also used
To facilitate the reaction optimization and substrate studies,
we desired to prepare a nickel precatalyst bearing the
NIXANTPHOS ligand. Nickel(II) aryl halide complexes
have been known to be relatively air stable since the work of
Chatt and Shaw.18b Inspired by advances from Buchwald’s18g
and Jamison’s18d,e laboratories, who successfully developed
nickel precatalyst derived from substitution of phosphine
ligands on (Ph3P)2Ni(2-tolyl)Cl, we adopted a similar
B
DOI: 10.1021/acs.orglett.9b00294
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 4. Substrate Scope of Aryl Bromides and Chlorides
in Ni-Catalyzed Arylation of Toluene
Scheme 5. Substrate Scope in Ni-Catalyzed Direct Arylation
of Toluene Derivatives
a
a b
,
a
Reactions conducted on a 0.10 mmol scale of 2b′, ArCH3 (0.5 mL)
b
and cyclohexane (0.5 mL). Isolated yield after chromatographic
c
purification. 3 mL of toluene derivatives without cycloheaxance.
d
1
Yield determined by H NMR spectroscopy of the crude reaction
a
mixtures.
Reactions conducted on a 0.10 mmol scale of 2 and 2′; for aryl
bromides, 4 equiv of NaN(SiMe3)2; for aryl chlorides, 4.5 equiv of
NaN(SiMe3)2.
Although product derived exclusively from arylation at the
methyl group was observed, the isolated yield was 45%. 3-
Methyl anisole underwent the coupling reaction and afforded
the product 3n in 57% yield. Ethylbenzene was a challenging
substrate, with an isolated yield of only 17%. In most cases,
these reactions worked better in the methylarene/cyclohexane
solvent mixtures. A limitation of this system is that it does not
work with electron-withdrawing groups on the toluene
derivatives, such as 4-CF3, 4-CN, and 4-F. The reason for
this finding is not clear at this time, but consistent with the
Pd(NIXANTPHOS)-catalyzed process.
Next, we desired to probe cooperativity between the Ni and
NIXANTPHOS ligand in this nickel-catalyzed arylation of
toluene. Despite the outward similarity of NIXANTPHOS, its
N-benzylated analogue (N-Bn-NIXANTPHOS), and the
parent XANTPHOS ligand scaffolds (Scheme 6, eq 1),
catalysts bearing these ligands showed very different reactivity
in the toluene arylation. Using Ni(COD)2 as a precursor, the
Ni(NIXANTPHOS)-based catalyst promoted the coupling of
as coupling partners, affording 3e and 3f in 92−95% yield.
Sterically hindered 2-chloroanisole (2g′) and 1-chloronaph-
thalene (2h′) gave desired products 3g and 3h in 54% and
92% yield, respectively. Heterocycle-containing diarylmethanes
are valuable targets because of their use in pharmaceuticals. To
our delight, under the optimized conditions, 6-chloroindole 2i′
afforded products 3i in 62% yield. To demonstrate the
scalability of this approach, we performed the coupling of 6-
chloroindole (2i′) (1 mmol) with toluene (30 mL) to generate
3i in 53% isolated yield. We were also able to produce a
pyrrole-containing diarylmethane 3j from the corresponding
aryl chloride, albeit with reduced yield (35%).
We then turned our attention to the scope of toluene
derivatives using chlorobenzene as the coupling partner
(Scheme 5). First, six commonly used solvents [THF, DME
(dimethoxyethane), dioxane, 2-MeTHF, cyclohexane, and
CPME] were screened with the goal of decreasing the quantity
of the toluene derivatives employed (see Supporting
Information for details). Cyclohexane was the leading hit in
this screen. Next, we examined arylation of toluene derivatives
with chlorobenzene under the optimized conditions (see Table
S3 for details). As expected, the different xylene isomers
exhibited different reactivity under the reaction conditions. For
example, para-xylene (1c) underwent arylation in 70% yield
with a para-xylene/cyclohexane 1:1. Use of para-xylene alone
gave a similar yield (67%). ortho-Xylene (1b) reacted with
chlorobenzene to form the desired product 3k in 72% yield.
Interestingly, meta-xylene proved to be the best of the xylenes,
providing the arylation product in 93% yield. In contrast, ortho-
xylene provided the arylation product in 72% yield with an
ortho-xylene/cyclohexane ratio of 1:1, but jumped to 90% yield
in pure ortho-xylene.
Scheme 6. Control Experiments of Ni-Catalyzed Arylation
of Toluene
Mesitylene (1e) proved to be an excellent coupling partner
generating the corresponding product 3l in 95% yield. To test
the selectivity of the arylation, we examined 4-ethyltoluene.
C
DOI: 10.1021/acs.orglett.9b00294
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(c) Johansson, C. C. C.; Colacot, T. J. Angew. Chem., Int. Ed. 2010,
49, 676.
(2) For reviews, see: (a) Lyons, T. W.; Sanford, M. S. Chem. Rev.
2010, 110, 1147. (b) Davies, H. M. L.; Du Bois, J.; Yu, J.-Q. Chem.
Soc. Rev. 2011, 40, 1855.
(3) Vasilopoulos, A.; Zultanski, S. L.; Stahl, S. S. J. Am. Chem. Soc.
2017, 139, 7705.
(4) Zhang, W.; Chen, P.; Liu, G. J. Am. Chem. Soc. 2017, 139, 7709.
(5) Qin, C.; Davies, H. M. L. J. Am. Chem. Soc. 2014, 136, 9792.
(6) Curto, J. M.; Kozlowski, M. C. J. Am. Chem. Soc. 2015, 137, 18.
(7) Mazzarella, D.; Crisenza, G. E. M.; Melchiorre, P. J. Am. Chem.
Soc. 2018, 140, 8439.
1-bromo-4-tert-butylbenzene with toluene to afford the
diarylmethane product in 78% AY. In contrast, under identical
reaction conditions, the N-Bn-NIXANTPHOS- and the parent
XANTPHOS-based catalysts exhibited 15% and 0% AY,
respectively. These results indicate the importance of the
deprotonated NIXANTPHOS ligand for efficient arylation of
toluene.
We then decided to investigate the cation effect in the
presence of additives (Scheme 6, eq 2). Addition of 4 equiv of
15-crown-5 to the arylation of toluene caused a dramatic drop
in the reactivity, furnishing only a 7% yield of the arylation
product, compared to 78% in the absence of crown ether
(Scheme 6, eq 1). Addition of 8 equiv of 15-crown-5 shut
down the reaction. These results provide circumstantial
evidence for cooperativity between the main group metals
Na and K with the Ni or Pd centers, respectively, in these
heterobimetallic catalysts.
In summary, we have developed a versatile nickel-catalyzed
C−H functionalization of toluene and its derivatives with aryl
bromides and chlorides to generate diarylmethanes. The
difference between the Pd(NIXANTPHOS)- and Ni-
(NIXANTPHOS)-based catalysts is that the nickel catalysts
introduced herein function with aryl chlorides, whereas the
palladium catalysts do not. Furthermore, the optimal main
group element for nickel is sodium, whereas potassium forms a
more active heterobimetallic with the palladium derivative.
(8) Hartwig, J. F. Organotransition Metal Chemistry; University
Science Books: Sausalito, CA, 2010.
(9) (a) McGrew, G. I.; Temaismithi, J.; Carroll, P. J.; Walsh, P. J.
Angew. Chem., Int. Ed. 2010, 49, 5541. (b) Zhang, J.; Stanciu, C.;
Wang, B.; Hussain, M. M.; Da, C.-S.; Carroll, P. J.; Dreher, S. D.;
Walsh, P. J. J. Am. Chem. Soc. 2011, 133, 20552. (c) Mao, J.; Zhang, J.;
Jiang, H.; Bellomo, A.; Zhang, M.; Gao, Z.; Dreher, S. D.; Walsh, P. J.
Angew. Chem., Int. Ed. 2016, 55, 2526.
(10) For a review, see: Kennedy, C. R.; Lin, S.; Jacobsen, E. N.
Angew. Chem., Int. Ed. 2016, 55, 12596.
(11) (a) Li, M.; Gonzalez-Esguevillas, M.; Berritt, S.; Yang, X.;
Bellomo, A.; Walsh, P. J. Angew. Chem., Int. Ed. 2016, 55, 2825.
(b) Zhang, J.; Sha, S.-C.; Bellomo, A.; Trongsiriwat, N.; Gao, F.;
Tomson, N. C.; Walsh, P. J. J. Am. Chem. Soc. 2016, 138, 4260.
(12) (a) Sha, S.-C.; Tcyrulnikov, S.; Li, M.; Hu, B.; Fu, Y.;
Kozlowski, M. C.; Walsh, P. J. J. Am. Chem. Soc. 2018, 140, 12415.
(b) Wang, Z.; Zheng, Z.; Xu, X.; Mao, J.; Walsh, P. Nat. Commun.
2018, 9, 1.
(13) Pardue, D. B.; Gustafson, S. J.; Periana, R. A.; Ess, D. H.;
Cundari, T. R. Comput. Theor. Chem. 2013, 1019, 85.
(14) (a) Zhang, J.; Bellomo, A.; Creamer, A. D.; Dreher, S. D.;
Walsh, P. J. J. Am. Chem. Soc. 2012, 134, 13765. (b) Zhang, J.;
Bellomo, A.; Trongsiriwat, N.; Jia, T.; Carroll, P. J.; Dreher, S. D.;
Tudge, M. T.; Yin, H.; Robinson, J. R.; Schelter, E. J.; Walsh, P. J. J.
Am. Chem. Soc. 2014, 136, 6276.
(15) For reviews, see: (a) Tasker, S. Z.; Standley, E. A.; Jamison, T.
F. Nature 2014, 509, 299. (b) Rosen, B. M.; Quasdorf, K. W.; Wilson,
D. A.; Zhang, N.; Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev.
2011, 111, 1346. (c) Henrion, M.; Ritleng, V.; Chetcuti, M. J. ACS
Catal. 2015, 5, 1283. (d) Glorius, F. Angew. Chem., Int. Ed. 2008, 47,
8347. (e) Cornella, J.; Zarate, C.; Martin, R. Chem. Soc. Rev. 2014, 43,
8081. (f) Balcells, D.; Nova, A. ACS Catal. 2018, 8, 3499. For
selected examples, see: (g) Wu, K.; Doyle, A. G. Nat. Chem. 2017, 9,
779. (h) Shimasaki, T.; Tobisu, M.; Chatani, N. Angew. Chem., Int. Ed.
2010, 49, 2929. (i) Ramgren, S. D.; Silberstein, A. L.; Yang, Y.; Garg,
N. K. Angew. Chem., Int. Ed. 2011, 50, 2171.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b00294.
Procedures, characterization data for all new compounds
(PDF)
Accession Codes
CCDC 1890453 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(16) For selected examples, see: (a) Zultanski, S. L.; Fu, G. C. J. Am.
Chem. Soc. 2011, 133, 15362. (b) Lavoie, C. M.; MacQueen, P. M.;
Rotta-Loria, N. L.; Sawatzky, R. S.; Borzenko, A.; Chisholm, A. J.;
Hargreaves, B. K. V.; McDonald, R.; Ferguson, M. J.; Stradiotto, M.
Nat. Commun. 2016, 7, 11073. (c) Ge, S.; Hartwig, J. F. J. Am. Chem.
Soc. 2011, 133, 16330. (d) Ge, S.; Green, R. A.; Hartwig, J. F. J. Am.
Chem. Soc. 2014, 136, 1617.
(17) For reviews, see: (a) Clot, E.; Eisenstein, O.; Jasim, N.;
MacGregor, S. A.; McGrady, J. E.; Perutz, R. N. Acc. Chem. Res. 2011,
44, 333. (b) Braun, T.; Perutz, R. N. Chem. Commun. 2002, 2749.
For selected examples, see: (c) Johnson, S. A.; Huff, C. W.; Mustafa,
F.; Saliba, M. J. Am. Chem. Soc. 2008, 130, 17278. (d) Bohm, V. P. W.;
Gstottmayr, C. W. K.; Weskamp, T.; Herrmann, W. A. Angew. Chem.,
Int. Ed. 2001, 40, 3387.
(18) For reviews, see: (a) Standley, E. A.; Tasker, S. Z.; Jensen, K.
L.; Jamison, T. F. Acc. Chem. Res. 2015, 48, 1503. For a pioneering
work, see: (b) Chatt, J.; Shaw, B. L. J. Chem. Soc. 1960, 1718. For
selected examples, see: (c) Zhang, N.; Hoffman, D. J.; Gutsche, N.;
Gupta, J.; Percec, V. J. Org. Chem. 2012, 77, 5956. (d) Standley, E. A.;
Smith, S. J.; Muller, P.; Jamison, T. F. Organometallics 2014, 33, 2012.
(e) Standley, E. A.; Jamison, T. F. J. Am. Chem. Soc. 2013, 135, 1585.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: pwalsh@sas.upenn.edu.
ORCID
Hui Jiang: 0000-0001-6431-3004
Patrick J. Walsh: 0000-0001-8392-4150
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
P.J.W. thanks the National Science Foundation [CHE-
1464744], and H.J. thanks the China Scholarship Council
[201406350156] for financial support.
REFERENCES
■
(1) For reviews, see: (a) Culkin, D. A.; Hartwig, J. F. Acc. Chem. Res.
2003, 36, 234. (b) Bellina, F.; Rossi, R. Chem. Rev. 2010, 110, 1082.
D
DOI: 10.1021/acs.orglett.9b00294
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(f) Shields, J. D.; Gray, E. E.; Doyle, A. G. Org. Lett. 2015, 17, 2166.
(g) Park, N. H.; Teverovskiy, G.; Buchwald, S. L. Org. Lett. 2014, 16,
220. (h) Miyakoshi, R.; Yokoyama, A.; Yokozawa, T. J. Am. Chem. Soc.
2005, 127, 17542. (i) Leowanawat, P.; Zhang, N.; Safi, M.; Hoffman,
D. J.; Fryberger, M. C.; George, A.; Percec, V. J. Org. Chem. 2012, 77,
2885. (j) Lanni, E. L.; McNeil, A. J. J. Am. Chem. Soc. 2009, 131,
16573. (k) Ge, S.; Hartwig, J. F. Angew. Chem., Int. Ed. 2012, 51,
12837. (l) Bronstein, H. A.; Luscombe, C. K. J. Am. Chem. Soc. 2009,
131, 12894.
(19) Cao, X.; Sha, S.-C.; Li, M.; Kim, B.-S.; Morgan, C.; Huang, R.;
Yang, X.; Walsh, P. J. Chem. Sci. 2016, 7, 611.
(20) (a) van Leeuwen, P. W. N. M.; Kamer, P. C. J. Catal. Sci.
Technol. 2018, 8, 26. (b) Van der Veen, L. A.; Keeven, P. H.;
Schoemaker, G. C.; Reek, J. N. H.; Kamer, P. C. J.; Van Leeuwen, P.
W. N. M.; Lutz, M.; Spek, A. L. Organometallics 2000, 19, 872.
E
DOI: 10.1021/acs.orglett.9b00294
Org. Lett. XXXX, XXX, XXX−XXX