Ni(ii) source as a pre-catalyst for the cross-coupling of benzylic pivalates with arylboronic acids: Facile access to tri- and diarylmethanes

Article abstract of DOI:10.1039/c4ra16452k

A simple and easily-used Ni^II complex, Ni(PPh₃)₂(1-naphthyl)Cl, was employed as a pre-catalyst in the Suzuki-Miyaura cross-coupling of benzylic pivalates with arylboronic acids, affording various tri- or diarylmethanes in good yields under mild conditions. This new protocol provides a cheap, convenient and practical alternative to synthesizing multiaryl methanes. This journal is

Full text of DOI:10.1039/c4ra16452k

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Ni(II) source as a pre-catalyst for the cross-coupling
of benzylic pivalates with arylboronic acids: facile
access to tri- and diarylmethanes†
Cite this: RSC Adv., 2015, 5, 15338
a
a
Qiang Chen,ab Xin-Heng Fan, Li-Peng Zhangab and Lian-Ming Yang
Received 16th December 2014
Accepted 23rd January 2015
*
*
DOI: 10.1039/c4ra16452k
www.rsc.org/advances
A simple and easily-used NiII complex, Ni(PPh3)2(1-naphthyl)Cl, was Suzuki–Miyaura-type cross-couplings.12 Therefore, we
employed as a pre-catalyst in the Suzuki–Miyaura cross-coupling of envisioned that the use of such nickel(II) pre-catalysts would
benzylic pivalates with arylboronic acids, affording various tri- or be feasible in cross-couplings of benzylic pivalates with
diarylmethanes in good yields under mild conditions. This new
protocol provides a cheap, convenient and practical alternative to
synthesizing multiaryl methanes.
The study of methodologies for the construction of multi-aryl
methanes has been attracting strong interest from synthetic
Fig. 1 NiII–(s-aryl) complexes.
chemists because these target molecules are valuable frame-
works in medicinal and materials chemistry, as well as organic
Table 1 Screening of conditions for Ni-catalyzed cross-coupling
synthesis.1 Among the synthetic strategies developed, the
between the pivalate 1 and p-anisylboronic acida
Suzuki–Miyaura reaction of benzylic electrophiles has emerged
as a highly preferred method.2–10 In this regard, successful
examples included cross-couplings of organoboron reagents
with benzylic halides,2 carbonates,3 acetates,4 phosphates5
and sulfones6 (Pd-catalyzed processes), as well as with
benzylic ammonium salts,7 carbamates,8 pivalates9 and
ethers10 (Ni0-catalyzed processes). Despite the impressive
[Ni(II)]
(mol%)
Ligand
(mol%)
Temp.
(ꢀC)
Yieldb
(%)
advances, improvement on the catalyst systems of those
protocols remains urgently needed, since it was recognized
that palladium belongs to precious metals, and the Ni0 species
is difficult to experimentally handle due to its high air-
sensitivity and toxicity.
trans-Haloarylbis(triphenylphosphane)nickel(II) (Fig. 1)
are a special type of nickel(II) compounds, many of which can
be conveniently prepared from cheap, commercially available
starting materials, and display better stability in air and
moisture.11 We previously conrmed that NiII–(s-aryl)
complexes are highly applicable catalyst precursors in
Entry
Base
Solvent
1
2
3
4
5
6
7
8
C-1c (5)
C-1 (5)
C-1 (5)
C-1 (5)
C-1 (5)
C-2d (5)
C-3e (5)
C-4f (5)
C-1 (5)
C-1 (5)
C-1 (5)
C-1 (5)
C-1 (2.5)
C-1 (5)
C-1 (0)
None
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
CsF
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Dioxane
THF
70
70
70
70
70
70
70
70
70
70
70
70
70
50
70
86
41
46
19
27
0
0
0
12
7
9
PPh3 (10)
PCy3 (10)
DPPP (5)
DPPF (5)
None
None
None
None
None
None
None
None
None
9
10
11
12
13
14
15
Trace
39
61
0
Toluene
Toluene
Toluene
aBeijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Green
Printing, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R.
China. E-mail: yanglm@iccas.ac.cn; xinxin9968@iccas.ac.cn; Fax: +86-10-62559373
bUniversity of Chinese Academy of Sciences, Beijing 100049, P. R. China
None
a
Conditions: the pivalate 1 (1.0 mmol), p-anisylboronic acid (1.5 mmol),
base (2.5 mmol), 5.0 mL of solvent, 6 h, N2. Isolated yields. C-1:
Ni(PPh3)2(1-naphthyl)Cl. C-2: NiCl2$6H2O. C-3: Ni(acac)2. C-4:
NiCl2(PPh3)2.
b
c
† Electronic supplementary information (ESI) available: General experimental
procedures, characterization details, 1H and 13C NMR spectra of products. See
DOI: 10.1039/c4ra16452k
d
e
f
15338 | RSC Adv., 2015, 5, 15338–15340
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Table 2 Ni-catalyzed cross-coupling of diarylmethyl pivalates with
arylboronic acids. Herein, we wish to disclose our new
ndings.
arylboronic acidsa
We rst attempted the cross-coupling of a diarylmethyl piv-
alate 1 (belonging to a type of secondary benzylic pivalates) with
p-anisylboronic acid under the NiII–(s-aryl) complex catalysis.
Ni(PPh3)2(1-naphthyl)Cl (C-1) was preferably selected as pre-
catalyst, as previously in our laboratory.12 Aer some experi-
mentation, the reaction was found to proceeded smoothly with a
high isolated yield of 86% (entry 1), and over-loading ligands was
virtually unfavourable for the reaction (entries 2–5). As expected,
other types of nickel(II) sources, such as NiCl2$6H2O, Ni(acac)2
and Ni(Ph3P)2Cl2, were ineffective for the desired C–C coupling
(entries 6–8). This may be because common NiII precursors are
unable to produce the catalytically active Ni0 species in the
reaction system.12a The type of bases is also important (entry 1 vs.
entries 9 and 10). Toluene appeared to be the solvent of choice
for the reaction and far superior to ethereal solvents such as
dioxane (entry 11) and THF (entry 12). In addition, reducing the
catalyst loading (entry 13) or lowering the reaction temperature
(entry 14) would cause a dramatic decrease in yields. Finally, the
role of the NiII complex in the reaction was demonstrated clearly
in a control experiment (entry 15) (Table 1).
Next, the scope and limitations of this NiII-catalyzed benzyl–
aryl coupling reactions were investigated. Under the optimized
conditions we carried out the reaction of diarylmethyl pivalates
(Table 2) and of primary benzylic pivalates (Table 3), respec-
tively, with arylboronic acids.
Regarding the boronic acid component, both electron-rich (2–
4, 11, 13, and 15) and -neutral (5, 9, 10, 12, 14, 16, and 18) aryl-
boronic acids showed excellent reactivity, providing desired
products in high yields. Electron-decient p-uorophenylboronic
acid (8) performed poorly under the standard conditions, but the
outcome was improved by increasing its amounts (8). The reason
may be that electron-decient boronic acids are less nucleophilic
and undergo a slower transmetallation as compared to electron-
rich and -neutral ones. This coupling reaction is also very sensi-
tive to the steric effects of arylboronic acids: 1-naphthyl boronic
acid gave a lower yield (6, 17, and 20); the ortho-substituted
substrate completely retarded the reaction (7). With respect to
diarylmethyl pivalates, at least one aryl should belong to fused
aromatic rings such as naphthyl group,13 or else the reaction does
not occur (comparing 25 and 26 with other cases in Table 2). For
the second aryl group, the limitation is relatively less: whether
electron-neutral (2–5), -rich (9, 11, and 12), or -poor (10 and 13)
ones can offer good yields of the desired products, with the
exception of heteroaryls (23 and 24). Dinaphthyl-substituted
substrates appeared more favorable for the reaction (14–20),
since even sterically congested coupling reactions (17, 19, and 20)
proceeded smoothly under the slightly modied conditions.
To our delight, the optimized conditions can be extended
with no difficulty to the Suzuki–Miyaura cross-coupling of
primary benzylic pivalates for diarylmethane synthesis (Table
3). A wider array of arylboronic acids, including electron-rich
(27–29, and 34–37), -neutral (30 and 31), -decient (32) and
even heteroaryl (33) boronic acid, can be utilized in the reaction
with good to excellent yields. Similarly, only benzylic pivalate
a
Conditions: diarylmethyl pivalate (1.0 mmol), arylboronic acid (1.5
mmol), C-1 (0.05 mmol), K3PO4 (2.5 mmol), toluene (5.0 mL), 70 ꢀC, 6
b
h, N2. 2.5 mmol of p-uorophenyl boronic acid, 4.0 mmol of K3PO4,
70 ꢀC. c 2.5 mmol of arylboronic acid, 4.0 mmol of K3PO4, 120 ꢀC.
outcome (27–37).13 Benzylic pivalates with no naphthyl group
were not coupled under our standard conditions, but a sluggish
conversion was achieved upon the use of DPPF as an additional
containing the naphthyl substructure gave
a satisfactory
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Table 3 Ni-catalyzed cross-coupling of primary benzylic pivalates
S. C. Mathew and K. G. Abhilash, Tetrahedron, 2006, 62,
6731; (c) M. S. Shchepinov and V. A. Korshun, Chem. Soc.
Rev., 2003, 32, 170; (d) D. F. Duxbury, Chem. Rev., 1993, 93,
381.
with arylboronic acidsa
2 (a) S. Chowdhury and P. E. Georghiou, Tetrahedron Lett.,
´
1999, 40, 7599; (b) L. Botella and C. Najera, Angew. Chem.,
Int. Ed., 2002, 41, 179; (c) S. Langle, M. Abarbri and
ˆ
A. Duchene, Tetrahedron Lett., 2003, 44, 9255; (d)
B. P. Bandgar, S. V. Bettigeri and J. Phopase, Tetrahedron
Lett., 2004, 45, 6959; (e) S. M. Nobre and A. L. Monteiro,
Tetrahedron Lett., 2004, 45, 8225; (f) G. A. Molander and
M. D. Elia, J. Org. Chem., 2004, 69, 3447; (g) N. Henry,
C. Enguehard-Gueiffier, I. Thery and A. Gueiffier, Eur. J.
´
Org. Chem., 2008, 4824; (h) B. Ines, I. Moreno,
´
R. SanMartin and E. Domınguez, J. Org. Chem., 2008, 73,
8448; (i) D. Srimani and A. Sarkar, Tetrahedron Lett., 2008,
49, 6304; (j) A. Yu, X. Li, D. Peng, Y. Wu and J. Chang,
Appl. Organomet. Chem., 2012, 26, 301.
3 (a) R. Kuwano and M. Yokogi, Org. Lett., 2005, 7, 945; (b)
J.-Y. Yu and R. Kuwano, Org. Lett., 2008, 10, 973.
4 R. Kuwano and M. Yokogi, Comm. Commun., 2005, 5899.
5 M. McLaughlin, Org. Lett., 2005, 7, 4875.
6 M. Nambo and C. M. Crudden, Angew. Chem., Int. Ed., 2014,
53, 742.
7 P. Maity, D. M. Shacklady-McAtee, G. P. A. Yap, E. R. Sirianni
and M. P. Watson, J. Am. Chem. Soc., 2013, 135, 280.
8 M. R. Harris, L. E. Hanna, M. A. Greene, C. E. Moore and
E. R. Jarvo, J. Am. Chem. Soc., 2013, 135, 3303.
a
Conditions: benzylic pivalate (1.0 mmol), arylboronic acid (1.5 mmol),
C-1 (0.05 mmol), K3PO4 (2.5 mmol), toluene (5.0 mL), 70 ꢀC, 6 h, N2. b 2.5
c
mmol of p-uorophenylboronic acid, 4.0 mmol of K3PO4, 70 ꢀC. 0.1
mmol of C-1, 0.1 mmol of DPPF, 120 ꢀC, 24 h.
9 Q. Zhou, H. D. Srinivas, S. Dasgupta and M. P. Watson, J. Am.
Chem. Soc., 2013, 135, 3307.
10 M. Tobisu, A. Yasutome, H. Kinuta, K. Nakamura and
N. Chatani, Org. Lett., 2014, 16, 5572.
11 For the preparation of trans-haloarylbis(triphenylphosphane)
nickel(II), see: (a) J. van Soolingen, H. D. Verkruijsse,
M. A. Keegstra and L. Brandsma, Synth. Commun., 1990, 20,
3153; (b) L. Brandsma, S. F. Vasilevsky and
H. D. Verkruijsse, in Application of Transition Metal
Catalysts in Organic Synthesis, Springer, New York, 1998, pp.
3–4.
ligand in the NiII catalyst system (38–41). Notably, a high yield of
diarylethane 37 was obtained without b-hydride elimination.
The mechanism of the reaction is believed to be almost the
same as that of the well-established nickel-catalyzed Suzuki–
Miyaura cross-coupling reaction: that is a typical catalytic cycle
of the Ni0–NiII shuttle involving sequential oxidative addition of
the Ni0 (in situ generated from the Ni(PPh3)2(1-naphthyl)Cl
precursor12) into benzylic C–O bond, transmetallation, and
reductive elimination.
12 (a) C. Chen and L.-M. Yang, Tetrahedron Lett., 2007, 48, 2427;
(b) X.-H. Fan and L.-M. Yang, Eur. J. Org. Chem., 2010, 2457;
(c) X.-H. Fan and L.-M. Yang, Eur. J. Org. Chem., 2011, 1467;
(d) Q. Chen, X.-H. Fan, L.-P. Zhang and L.-M. Yang, RSC Adv.,
2014, 4, 53885.
13 Generally, benzylic electrophiles without a fused aromatic
show less reactive in Ni-catalyzed cross-couplings as well
as in some Pd-catalyzed cross-couplings: (a) M. A. Greene,
I. M. Yonova, F. J. Williams and E. R. Jarvo, Org. Lett.,
2012, 14, 4293; (b) S. Tabuchi, K. Hirano, T. Satoh and
M. Miura, J. Org. Chem., 2014, 79, 5401 and references
cited therein; (c) Also see: ref. 8–10.
In summary, we have demonstrated a facile route to tri- and
diarylmethanes by a nickel-catalyzed Suzuki–Miyaura cross-coupling
reaction of benzylic pivalates. This new protocol is characteristic of
no using nickel(0) sources and special ligands in Ni-based catalyst
systems. Further work to expand the scope of substrates and eluci-
date the mechanistic details is currently underway in our lab.
Acknowledgements
We thank National Natural Science Foundation of China
(Project nos 20872142 and 21102150) for nancial support of
this work.
Notes and references
1 (a) A very recent comprehensive review: S. Mondal and
G. Panda, RSC Adv., 2014, 4, 28317; (b) V. Nair, S. Thomas,
15340 | RSC Adv., 2015, 5, 15338–15340
This journal is © The Royal Society of Chemistry 2015