Phosphine and palladium-free synthesis of aryl and alkenyl boronates: A nano-catalytic approach

Article abstract of DOI:10.1016/j.catcom.2016.07.014

Superparamagnetic copperferrite nanoparticle is employed as an environmentally benign and efficient catalyst to affect the borylation of aryliodides yielding the corresponding arylboronates at low catalyst loading under mild reaction conditions. This protocol tolerates various substituents present in aryl iodides and also could be extended to beta bromostyrenes in the absence of phosphine and palladium.

Full text of DOI:10.1016/j.catcom.2016.07.014

Catalysis Communications 85 (2016) 61–65
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Catalysis Communications
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Short communication
Phosphine and palladium-free synthesis of aryl and alkenyl boronates: A
nano-catalytic approach
a,b
a
a,
Balaji Mohan , Hyuntae Kang , Kang Hyun Park ⁎
a
Department of Chemistry, Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
Department of Chemistry, Madanapalle Institute of Technology & Science, Madanapalle, Chittoor 517 325, Andhra Pradesh, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Superparamagnetic copperferrite nanoparticle is employed as an environmentally benign and efficient catalyst to
affect the borylation of aryliodides yielding the corresponding arylboronates at low catalyst loading under mild
reaction conditions. This protocol tolerates various substituents present in aryl iodides and also could be extend-
ed to beta bromostyrenes in the absence of phosphine and palladium.
Received 31 March 2016
Received in revised form 8 July 2016
Accepted 19 July 2016
Available online 22 July 2016
©
2016 Elsevier B.V. All rights reserved.
Keywords:
Borylation
Copper
Deuterium
Ligand-free
Nanoparticles
1
. Introduction
Heise et al. successfully prepared the boronate derivatives with the
reaction of glycol borates and Grignard reagents at room temperature
under mild conditions [10]. Chavant et al. described the synthesis of
aryl boronic esters through metal-halogen exchange reaction between
iPrMgCl·LiCl and aryl iodides at 0 °C using cyclic borate esters [11]. Al-
ternate approaches admit transition-metal catalysts for syntheses of
arylboronic acid esters via activation of C\\H and C\\X bonds. Among
those, palladium, nickel, iridium and recently copper complexes or
salts in combination with toxic phosphine ligands was employed for
borylation to take place [12–21]. Notably, Zhang and co-workers were
noticed the borylation of aryl iodides through cesium effect under tran-
sition-metal free conditions [22], followed by Kiatiesevi et al. employed
palladium as catalyst along with copper co-catalyst and
triphenylphosphine to effect borylation take place at C\\I bond of aro-
matics [23].
Arylboronic esters are important class of benchmark reagents
with broad utility in the area of organic synthesis. Because of their
unique chemical properties such as broad functional group availabil-
ity, air stability, and ease of handling, they have been considered as
important building blocks in organic synthesis, and as a conse-
quence, they undergo a wide range of transformations that lead to
the formation of C\\C and C\\X (X = heteroatom) bonds. The
phenylboronic acid skeleton is a privileged structure in medicinal
chemistry for the discovery of pharmaceutical leads. Boron-based
compounds exhibit various important biological activities [1]. Kong
and colleagues utilized boronic acids as antimitotic agents (I and II)
and bortezomib (III), a proteasome inhibitor, has been well known
for anticancer therapy (Fig. 1) [2].
The traditional synthesis of arylboronic acids was accomplished via
the reaction of aromatic organomercury compounds with borane solu-
tion followed by hydrolysis furnish arylboronic acids [3]. Various studies
have reported that direct synthesis of arylboronic acids from aryl ha-
lides employing homogeneous palladium complex [4–9]. Compared to
boronic acids, boronates are environmental friendly, easy to handle,
air and chromatography-stable.
Conversely, there is significant interest in the development of transi-
tion metal nanoparticles for technological applications in various areas
such as chemical sensors, electrocatalysts for fuel cells, and heteroge-
neous catalysts for organic transformations. We wondered if the
nanocatalytic system could be complementary to aforementioned pro-
tocols that involved phosphine and overcome by means of a spinel bi-
metallic nanoparticles as catalysts to effect borylation of haloarenes.
Since the catalytic activities of nanoparticles largely dependent on the
surface design of the support along with the size and shape of the
metal nanoparticles, the quest for more suitable solid supports for cop-
per nanoparticles to provide highly active and selective catalyst is a
challenging problem.
⁎
Corresponding author.
E-mail address: chemistry@pusan.ac.kr (K.H. Park).
http://dx.doi.org/10.1016/j.catcom.2016.07.014
566-7367/© 2016 Elsevier B.V. All rights reserved.
1

62
B. Mohan et al. / Catalysis Communications 85 (2016) 61–65
Fig. 1. Some biologically active organoboron compounds.
In the course of a program devoted to the discovery in designing a
new nanoparticle catalysts for efficient organic transformations [24–
1], we were interested in the synthesis of arylboronates using cost-
effective, readily available and magnetically recoverable copper ferrite
nanoparticles is used as a catalyst to prepare arylboronates from aryl io-
dides under mild conditions. Of particular importance, we discovered
3
Table 1
Optimization of reaction conditions.
Entry
Cat. (mol%)
Solvent
Base
Yield (%)a
1
2
3
4
5
6
7
8
9
–
2.5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
dmf
dmf
dmf
dmf
dmf
dmf
dmpu
dmso
thf
Acetonitrile
Toluene
dma
nmp
dmf
dmf
dmf
dmf
dmf
(CH
(CH
(CH
(CH
(CH
3
)
)
)
)
)
3
3
3
3
3
COK
COK
COK
COLi
CONa
NR
77
90
57
44
80
Trace
2
3
3
3
3
MeOLi
(CH
(CH
(CH
(CH
(CH
(CH
(CH
(CH
(CH
(CH
(CH
(CH
(CH
3
3
3
3
3
3
3
3
3
3
3
3
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
)
3
COK
COK
COK
COK
COK
COK
COK
COK
COK
COK
COK
COK
COK
3
2
1
1
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
53
20
8
13
48
55
41
ND
b
c
d
e
f
g
dmf
a
b
c
d
e
f
Determined by GC–MS.
Reaction with micro copper powder catalyst.
CuO nanopowder.
CuO hollow spheres.
2
Cu O nanocubes.
Copper nanoparticles.
Iron oxide nanoparticles.
g

B. Mohan et al. / Catalysis Communications 85 (2016) 61–65
63
Table 2
Evaluation of substrate scope.
Entry
1
Arylhalide
Product
Yield (%)a
71
2
3
72
89
4
5
77
62
6
7
40
45
8
9
42
81
59
1
0
1
1
32
12
13
14
15
16
17
68
58
81
Traceb
Tracec
ND
a
b
c
Yield was determined by GC–MS includes ArH side products.
-Iodoanisole (1 mmol), HBPin (1.5 mmol), NaH (1.5 mmol), CuFe
Bis(neopentyl glycolato)diboron was used as borylating agent under Table 1 conditions.
4
2 4
O (5 mol%), THF (5 mL), RT for 12 h under argon with magnetic stirring.
the beneficial synergistic effect of CuFe
efficiency. In this letter, we only show the CuFe
borylation of iodoarenes in the combination of an inexpensive, environ-
mentally benign boron source B Pin in air under ligand-free conditions.
2
O
4
nanoparticles on the reaction
2. Experimental
2 4
O
NPs catalyzed
2.1. General description
2
2
In addition, all reagents used in this paper are commercially available
and bench stable, eliminating the use of glove box.
Reagents were purchased from Aldrich Chemical Co., TCI and Strem
Chemical Co. and used as received. CuFe nanoparticles were
2 4
O

64
B. Mohan et al. / Catalysis Communications 85 (2016) 61–65
procured from Aldrich; Catalog No. 641723. All compounds reported
have been well known and their mass splitting pattern consistent
with existing literature. Reaction products were analyzed by GC–MS
catalyst (not shown). Further optimization, by variation of the base,
showed that lithium and sodium tertiary butoxide were produced less
satisfactory results (Table 1, entries 4 and 5). Moderate yield was
achieved with lithium methoxide (Table 1, entry 6). Solvents such as
N,N′-dimethyl-N,N′-trimethylene urea (dmpu), dimethyl sulfoxide
(dmso), tetrahydrofuran (thf), acetonitrile and toluene completely
shut down the borylation and returned only unreacted starting material
(Table 1, entries 7–11). Dimethylacetamide (dma) and N-methyl
pyrrolidinone (nmp) were detrimental (Table 1, entries 12 and 13).
Among the various sources of copper nanocatalysts examined such as
micro-copper powder, commercially available CuO nanopowder [32],
(
Shimadzu-QP2010 SE).
2
.2. General procedure for borylation of iodoarenes
4
-Iodo anisole (0.813 mmol, 200 mg), bis(pinacolato) diboron
(
1.219 mmol, 309 mg) were dissolved in 3 mL of dmf followed by cop-
per ferrite nanoparticles (5 mol% with respect to 4-iodo anisole) and po-
tassium tert-butoxide (1.219 mmol, 137 mg) were added to a 10 mL
capped vial and stirred at RT for time indicated. After stirring, the mix-
ture was diluted with diethyl ether and filtered through celite bed.
The filtrate was extracted with water (3 times) and the organic phase
2
CuO hollow spheres, Cu O nanocubes and Cu nanoparticles [24,33,34]
were compared in order to prove superior catalytic activity and syner-
gistic effect at the interface between copper and iron oxide nanoparti-
cles (Table 1, entries 14–18) while borylation was ineffective with sole
iron oxide nanoparticles catalyst (Table 1, entry 19).
4
was dried over anhydrous MgSO . The crude product was subjected to
analyze by GC–MS. The conversion yield is accurately measured based
on the consumption of 4-iodo anisole and the side product formed
due to protodeiodination.
As can be seen from Table 1, the reactivity of copper ferrite NPs is 1 to
9 times higher than copper oxide nanoparticles and clearly underlines
the effectiveness of the synergistic catalysis. We hypothesize that the
high efficacy of the bimetallic catalyst can also be attributed to the pres-
ence of iron may play a crucial role in activation of C\\I bond and as a
consequence, conversion is better than sole copper catalysts. Recently,
despite the synergistic effect and other parameters, Ranu and co-
workers demonstrated the role of iron present in copper ferrite NPs in
the synthesis of unsymmetrical 1,3-diynes. The Lewis acidity of the
3
. Results and discussion
3
.1. Catalytic activity
We began a careful optimization study with the arylation of 4-
iodoanisole (1 mmol) with bis(pinacolato)diboron (1.5 mmol) and
base (1.5 mmol). No reaction was observed in the absence of copper cat-
III
Fe center significantly contributed to the enhanced activation of the
alyst (Table 1, entry 1). However, the use of 2.5 mol% of CuFe
proved to be satisfactory, with moderate conversion being achieved
Table 1, entry 2). Slight increase to 5 mol% proved to be optimal, with
good conversion (Table 1, entry 3). The use of a 10 mol% of catalyst
gave a comparable yield to that of the 5 mol% of the copper ferrite NPs
O
2 4
NPs
C\\Br bond, whereas the same reaction with CuO NPs was ineffective.
It is noteworthy that the distinct role of iron is paramount important
in the reaction specified [35]. Similarly, in our case the iron would
have possibly involved synergistic catalysis with copper in enhancing
the oxidative addition of C\\I bond, which led to higher conversion.
(
Table 3
a
CuFe
2
O
4
NPs catalyzed borylation of β-bromostyrene .
Entry
1
β-bromostyrene
Product
Yield (%)b,c
29d
2
3
4
5
61e
62f
74g
60
6
7
75
83
a
2 2
Reaction conditions: β-bromostyrene (1 mmol), B Pin (1.5 mmol), catalyst (5 mol% respect to β-bromostyrene), Base (1.5 mmol), dmf (3 mL), RT, 24 h.
Determined by GC–MS includes side products from protodebromination.
See the Supporting Information for selectivity.
b
c
d
e
f
3
Me COK used as base.
LiOMe base was employed.
10 mol% of catalyst was used.
g
β-Bromostyrene was synthesized from known literature.

B. Mohan et al. / Catalysis Communications 85 (2016) 61–65
65
To the best of our knowledge, the use of a nanoparticles based het-
erogeneous catalyst has never been described for the borylation of
aryl iodides with B Pin under ligand-free conditions. After evaluation
2 2
available, inexpensive copper ferrite nanoparticles at low catalyst load-
ing under ligand free conditions. The role of Iron in the catalyst was ex-
emplified in terms of higher yield of products.
of numerous reaction parameters, we identified that arylboronate (3a)
could be generated in 90% yield (GC–MS) by treatment of 4-iodoanisole
Acknowledgements
2 2 2 4
(1a) and B Pin (2a) in the presence of 5 mol% CuFe O NPs and 3 mL
dmf solvent at room temperature (RT) for 12 h. We believe this work
will be useful to gain some insights into nanomaterials catalyzed
borylation of aryliodides, although the substrate scope was not enough
at this stage. Despite, several points regarding our optimized reaction
conditions are noteworthy: 1) the reaction operates well under mild
conditions (30 °C); 2) short reaction time (12 h); 3) use of low copper
loading; 4) ligand free.
This work was supported by a 2-year Research Grant of Pusan Na-
tional University.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2016.07.014.
With an optimized set of conditions in hand, we explored further the
scope and limitations of this process. As it can be seen from Table 2, our
protocol tolerated wide variety of substituents including electron-with-
drawing and donating groups present in the aromatic ring and afforded
corresponding boronates in moderate to good yields (entries 1–14,
Table 2). Reactions with other boron sources such as pinacolborane
and bis(neopentyl glycolato)diboron were unsuccessful (entries 15
and 16, Table 2). Shifting of the haloarene to 4-bromoanisole was not re-
active under identical conditions (entry 17, Table 2). The yield denoted
in Table 2 includes the side product stem from protodeiodination of
starting precursor that usually observed during borylation reaction.
To further evaluate the versatility of our catalytic system, we shifted
our attention to the viability of β-bromostyrenes. We were delighted to
found that phenylvinyl boronates could be obtained in good yields
with high regioselectivity. The reaction of β-bromostyrene with
bis(pinacolato diboron) underwent smoothly affording borylated prod-
uct with enhanced trans-selectivity from the starting precursor under
mild conditions. In fact, β-bromostyrenes are less reactive with copper
catalysts rather than palladium in borylation reactions and to the best
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