The synergistic effect of cobalt on a Pd/Co catalyzed Suzuki-Miyaura cross-coupling in water

Article abstract of DOI:10.1039/C6DT03628G

This work introduces the new trimetallic complex CoPd₂(HBPDC)₂Cl₄·(H₂O)₄(H₂BPDC = 2,2′-bipyridine-4,4′-dicarboxylic acid) as a highly efficient and more cost-effective catalyst for a Suzuki-Miyaura reaction proceeding in water, without additives and under aerobic conditions. Catalytic studies revealed a synergistic Co-Pd cooperativity, fostered by ligation through H₂BPDC, and accounting for the superior performance of the heterobimetallic complex vs. its Co-free counterpart.

Full text of DOI:10.1039/C6DT03628G

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Synergistic effect of cobalt in a Pd/Co catalyzed Suzuki-Miyaura
cross-coupling in water
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a
a
a
Li-Xin You, Hui-Jie Liu, Lan-Xin Cui, Fu Ding, Gang Xiong, Shu-Ju Wang, Bao-Yi Ren, Ileana
b
b
a
Dragutan, Valerian Dragutan* and Ya-Guang Sun*
DOI: 10.1039/x0xx00000x
www.rsc.org/
This work introduces the new trimetallic complex increase in activity of the heterobimetallic Pd catalysts.
CoPd (HBPDC) Cl ·(H O) (H BPDC 2,2’-bipyridine-4,4’- Moreover, the newtransition metal, the organic ligand and Pd
2
2
4
2
4
2
=
dicarboxylic acid) as a highly efficient and more cost-effective may together confer attractive physical-chemical attributes to
catalyst for a Suzuki-Miyaura reaction proceeding in water, the complex like robustness, superior mechanical and thermal
without additives and under aerobic conditions. Catalytic studies stability, and water and air tolerance.
revealed a synergistic Co-Pd cooperativity, fostered by ligation
Cooperativity between different transition metals and
through H BPDC, and accounting for the superior performance of palladium has been clearly demonstrated in cross-couplings
2
4
a,6a
5a,6b,c
the heterobimetallic complex vs. its Co-free counterpart.
with phosphine-free Ni/Pd
and Ln/Pd
Pd (BPDC)
(Ln=Pr,Gd,Tb) and [LnPd(BPDC)5/2(H
catalysts. For
the Ln/Pd catalysts, namely, [Ln
2
3
2
(HBPDC)
O)·4H
2
(μ
O]
2
-
1
The Suzuki-Miyaura reaction is likely the most versatile
6
b
O)Cl
4
(H
2
O)
6
]
n
2
2
n
6
c
protocol for C-C cross-couplings used in production of
pharmaceuticals, agrochemicals, fine chemicals, flavours and
fragrances, advanced materials, etc. This chemical
transformation has been extensively explored with a broad
range of substrates in both homogeneous and heterogeneous
phase employing highly active, chemoselective palladium and
(
Ln = Nd, Sm, Eu, Dy) , our group has shown that interactions
between the electropositive Ln ions and the Pd centres were
facilitated by the 2,2’-bipyridine-4,4’-dicarboxylate ligand. As a
result more robust, easily separable and recyclable
heterobimetallic Pd catalysts were obtained, able to promote
the reaction in aqueous systems (DMF-water), under mild
2
-4
6
b,c
other transition metal catalysts.
conditions.
Herein, we report the convenient, one-pot hydrothermal
Combination of Pd with different transition metals in
newest generations of heterobimetallic Pd complexes in order
to induce synergistic interactions between the active metal
sites has emerged as a fruitful approach in Suzuki-Miyaura
7
-10
synthesis of a new, air-stable trimetallic Pd/Co complex,
Pd Co(HBPDC) Cl4•(H O) ( ), (H BPDC = 2,2’-bipyridine-4,4’-
1
2
2
2
4
2
dicarboxylic acid), its full structural characterization and
superior catalytic performance in Suzuki-Miyaura C-C cross-
coupling in water without any additive. Though cobalt, a non-
precious metal, can save some of the noble metal, it has not
been used, to our knowledge, in conjunction with Pd in
phosphine-free heterobimetallic catalysts for Suzuki-Miyaura.
Contrasting with the effect of electropositive Ln ions, we
expect thatinteraction between Co and Pdwill benefit from the
electronegative character of Co acting on the oxidation
potential of Pd via the ligand. The latter, will considerably help
charge transfer between Co and the two Pd atoms (Pd1 and
Pd1A), since they all are connected by the heteroaromatic
4
a,c,5
cross-couplings.
In heteronuclear systems the coordination
environment of Pd can be finely manipulated via the additional
4
a
transition metal. Depending on the electropositivity or
electronegativity of the latter the rates of the distinct steps of
the palladium catalytic cycle (e.g. reductive elimination or
oxidative addition) will be affected. This interaction might be
amplified by the organic linker which, by bridging the different
metal centers, plays the role of a sensitive charge transfer
vector. The anticipated outcome of this cooperation would be
an enhancement of the overall reaction rate, hence an
-
units and their para, conjugated COO groups (Fig. 1). We
a.
The Key Laboratory of Inorganic Molecule-Based Chemistry of Liaoning
anticipate that this synergistic cooperativity will result in
acceleration of the oxidative addition step, the rate
determining step in the Pd catalytic cycle. In the layered
Province,Shenyang University of Chemical Technology,Shenyang, 110142, China.
E-mail: sunyaguang@syuct.edu.cn
Institute of Organic Chemistry,Romanian AcademyBucharest, 060023, Romania.
b.
E-mail: vdragutan@yahoo.com
Electronic Supplementary Informaꢀon (ESI) available: Comprehensive
structure of this Pd /Co complex, the trimetallic configuration
2
†
in which two Pd centres are bridged by the cobaltoligand will
experimentaland analytical information. CCDC 1433103 For ESI and
.
crystallographicdata in CIF or other electronic formatsee increase the concentration and improve the dispersity of the
DOI:10.1039/x0xx00000x
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Pd(II) catalytic sites, enhancing thus the catalyst activity and solvents using K
Journal Name
2
CO
3
as a base showed thatthe yield of cross-
stability in water and air, as compared to conventional coupling product is greater when using neat water as solvent
heterobimetallic Pd complexes. Ultimately, this approach will instead of toluene, DMF or EtOH (Entries 1-4). The base has
lead to cross-coupling with a high efficiency at lower catalyst previously been demonstrated to play a significant role in
1
1
loadings.
Suzuki-Miyaura cross-coupling reactions. The K
in much higher yield than Cs CO , NaOH and t-C
-7), and the reaction cannot be carried out in the absence of
2
CO
3
resulted
2
3
4 9
H OK (Entries
4
the base (Entry 9). In addition, the reaction temperature and
time are essential reaction parameters. We found that the
o
temperature of 70 C and the reaction time of 5 h are the most
effective reaction parameters in providing high yields of cross-
coupling products (Entries 4, 10-13).
Table 1Optimization of reaction conditions in the Suzuki-Miyaura
a
cross-coupling.Table Caption.
Fig. 1View of the coordination environments of Pd(II) and
Pd/Co catalyst, T
Co(II) ions in
1
. Symmetry codes: A1-x, -y, 2-z
I
+
B(OH)
2
solvent, base
o
b
Entry
Solvent
Toluene
EtOH
Base
T/ C
Time/h
Yield (%)
1
2
3
4
5
6
7
8
9
K
K
K
K
2
2
2
2
CO3
70
70
70
70
70
70
70
70
70
50
90
70
70
70
70
70
5
5
5
5
5
5
5
5
5
5
5
3
9
5
5
5
16
82
15
95
83
83
89
CO
CO
CO
3
DMF
3
H O
2
3
H
H
H
2
2
2
O
O
O
Cs
2
CO
3
NaOH
t-C
CO
H
OK
4
9
Fig.2Two-dimensional layer formed by H-bond interactions of
c
1
H O
2
K
2
3
82
Pd
2
Co(HBPDC)
2
Cl
4
•(H
2
O)
4
complex
(
1)
was prepared
H
2
O
None
K2CO3
0
according to the well-established hydrothermal protocol for
synthesis of the Pd coordination complexes, and structurally
characterized by means of single-crystal X-ray diffraction, FT-IR,
powder X-ray diffraction(PXRD), elemental analysis and
thermogravimetric (TG) techniques (see ESI†).
1
1
1
0
1
2
H O
2
75
85
67
92
H
2
O
K
K
2
2
CO
3
3
3
3
H O
2
CO
Single crystal X-ray diffraction investigation revealed that
complex
1
crystallizes in the triclinic space group P-1. As 13
H
H
2
2
O
O
K2CO
K2CO
illustrated in Figure 1, the complex consists of two Pd(II) ions,
-
one Co(II)ion, two HBPDC ligands, four chlorine ions, and four
d
14
97
e
coordinated water molecules. Pd1 constructs a square planar 15
coordination mode connecting two nitrogen atoms from one
-
HBPDC ligand and two chlorine atoms in the remaining cis-
2
H O
K2CO3
CO
62
f
16
H O
2
K
2
3
0
positions. Co1 coordinates with six oxygen atoms, two
a
carboxylate oxygen atoms from different H BPDC ligands,
2
Reaction conditions:iodobenzene (1.0 mmol), phenylboronicacid (1.5 mmol), base(2.0
-
3
b
mmol), catalyst (10 mol%Pd),under air. Yields were determined by GC and GC–MS
while the remaining four oxygen atoms are terminal water
molecules. Within the complex, adjacent molecules are
connected to a two-dimensional layer by H-bond interactions
c
-3
analysis. Pd(H
2
BPDC)Cl
2
-3
·H
2
O (10 mol% Pd) was used to replace the Pd/Co catalyst.
d
e
-4
f
Pd/Co catalyst (1.5×10 mol% Pd). Pd/Co catalyst (5×10 mol% Pd). No catalyst
Studies on the influence of the catalyst amount on the
product showed that the reaction affords a satisfactory yield
(
Fig.2). Crystal and structural refinement data for 1 are
displayed in Table S1 while important bond lengths and angles
are listed in Table S2.
-3
(95-97%) with the amount of catalyst of 0.5-1.5×10 mol%
(Entries 4,14). This relatively low catalyst loading is an
With the new Pd /Cocatalyst in hand, we next evaluated its
2
important benefit of our methodology as compared to the
catalytic activity in Suzuki–Miyaura coupling reactions. Initially,
iodobenzene and phenylboronic acid were chosen as the
model substrates to explore the optimal reaction conditions,
and the selected results are shown in Table 1. Screening of
frequently used palladium catalyst loadings (0.1-1 mol%) in
5
Suzuki-Miyaura reactions. Moreover,
a high TON value
5
of1.24×10 could be generated within 5 h with a TOF of
2
| J. Name., 2012, 00, 1-3
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4 −1
.48×10 h when the Pd/Co catalyst loading was decreased to electronegativity values. It was shown that within the Pd
2
-4
5
×10 mol% (Table S3).
It is noteworthy that there is an advantageous cooperation consequences on the oxidative addition step. Indeed, Pd/Ni
between palladium and cobalt, comparing the yields catalyzed catalysts were proved to have higher activities versus
by Pd Co(HBPDC) Cl (H O) ) and Pd(H BPDC)Cl ·H O ( monometallic Pd counterparts as result of the synergism
95% vs 82%, Entry 4 and 8, see also Figure 3). The increase in between Ni and Pd.
the yield of cross-coupling products when Co was incorporated On the other hand, previous investigations carried out with
catalytic cycle the charge transfer from Ni to Pd has beneficial
2
2
4
·
2
4
(
1
2
2
2
2)
1
4a
(
into the Pd complex may be assigned to a substantial bimetallic Pd/Ln catalysts in Suzuki-Miyaura, Heck and
synergistic effect of Co, by its electronegativity pattern (1.84 Sonogashira reactions pointed out to a distinct cooperative
on Allen scale), favoured by the organic linker (2,2′-bipyridine- effect between these two metals, facilitated by the 2,2’-
4,4′-dicarboxylate), a very sensitive charge transfer agent. bipyridine-4,4’-dicarboxylate ligand. Contrasting with the
Noteworthy, Co will consequently affect the oxidation electronegative Co and Ni, the electropositive Ln ions are
potential of Pd, facilitating thus the oxidative addition step, supposed to affect the rate of the reductive elimination step
the rate determining step in the Pd catalytic cycle. That the from the palladium catalytic cycle, resulting in a positive effect
6
b,6c
unique trimetallic structure of our catalyst, consisting of two on the overall reaction rate of the cross-coupling processes
palladium active sites ligated through a Co/organic linker,
improves the catalyst efficiency, is clearly demonstrated by the Table 2 Suzuki-Miyaura cross-coupling reaction of aryl halides and
a
increase attained in the reaction yield (from 82% to 95%). arylboronic acids.
Moreover, pure water as the solvent provides an ideal reaction
medium for the mass transfer of all ionic species involved in
the palladium catalytic cycle with a beneficial effect on the
reaction yield. The general reaction conditions for the C-C
coupling protocol have been optimized as follows: a mixture of
iodobenzene (1.0 mmol), phenylboronic (1.5 mmol), K CO (2.0
Pd/Co catalyst, 70 o
C
R
1
X +
R
2
B(OH)
2
R1
R2
H
2
O, K
2
CO
3
b
Entry
R
1
CH
CH
H
R
2
X
Yield (%)
1
2
3
4
5
6
7
8
9
a
3
3
H
I
I
90
2
3
mmol), water (6.0 ml), 5 h reaction time and Pd/Co complex
o
CO
CO
H
98
-3
(
1
) (10 mol% Pd), was stirred at 70 C in air, under normal
H
Br
Br
Br
Br
Br
Cl
70
conditions.
To further examine the scope of our trimetallic Pd /Co
2
CH3
H
64
catalyst, the optimized conditions (Table 1, entry 4) were
CH
H
3
H
75
employed for reactions between various aryl halides and
arylboronic acids in water under air. Selected results are given
in Table 2 and illustrated in Fig.3. Higher yields are achieved
for aryl halides endowed with electron-withdrawing
substituents, as evidenced by the reactions of phenylboronic
acid and substituted aryl iodides or bromides at the para
position (Entries 1-2 and 3-5). Substituted arylboronic acids
were also tested to furnish the corresponding biaryl products
CH
CH
H
3
3
71
H
CO
67
H
trace
24
CH
3
CO
H
Cl
Reaction conditions:iodobenzene (1.0 mmol), phenylboronic acid (1.5 mmol),
o
(Entries 6-7) and a better activity was observed for electron-
-
3
b
K
2
CO
3 2
(2.0 mmol), H O (6.0 mL), catalyst (10 mol% Pd), 70 C, 5h. Yields were
rich arylboronic acid. As expected, aryl chlorides were less
reactive than aryl bromides and iodides owing to the much
determined by GC and GC–MS analysis.
1
2
higher C-Cl bond strength (vs. C-Br and C-I) (Entries 8-9).
The proposed mechanism for the Pd/Co-catalyzed process,
as shown in Scheme S1†, assumes that the palladium catalyꢀc
cycle involves, in a first step, the oxidative addition of Pd(0) to
the aryl halide to form arylpalladium(II) species which, after
complexation with base, undergoes transmetalation with aryl
boronic acid. Finally, the reductive elimination step leading to
the biaryl product and re-establishment of the Pd (0)/Co
complex end the palladium catalytic cycle. The oxidative
addition step, which is the rate determining step of the Pd
catalytic cycle, appears to be substantially facilitated by charge
transfer from Co to Pd, through the organic linker (2,2’-
bipyridine-4,4’-dicarboxylate), thus enhancing the rate of the
1
00
95
90
8
8
7
7
5
0
5
0
1
3
overall process.
Studies effected by others
(
a)
(b)
(c)
(d)
(e)
(f)
4
a,6a,14
on cross-couplings with
Reaction conditions
Pd/Ni catalysts revealed a similar influence of Ni, as we have
observed for Co, due to the fact that Ni and Co have close
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Fig.3 Increase in catalyst activity in Suzuki-Miyaura of aryliodide
3
(a) T. J. Colacot, Ed., New Trends in Cross-Coupling: Theory
and Applications, RSC Catalysis Series No. 21, Cambridge, UK,
2015; (b) P. G. Alsaber and M. Stradiotto, Angew. Chem. Int.
Ed., 2013, 52, 7242; (c) J. Schranck, A. Tlili, H. Neumann, P. G.
with phenylboronic acid, in water and air, induced by
Pd
2 2 4 2 4 2 2 2
Co(HBPDC) Cl ·(H O) (1) as compared to Pd(H BPDC)Cl ·H O
-3
(2);(a) iodobenzene, catalyst 2 (10 mol% Pd) 5h;(b) iodobenzene,
Alsabeh, M. Stradiotto and M. Beller,Chem. Eur. J., 2012, 18
15592.
,
-3
-3
catalyst 1 (10 mol% Pd) 5h; (c) iodobenzene, catalyst 1 (1.5×10
-3
mol% Pd); 5h (d) iodobenzene, catalyst 1 (10 mol% Pd), 9h; (e)
4
5
6
(a)F. Liao, T. W. B. Lo and S. C. E Tsang, ChemCatChem, 2015,
7, 1998; (b) J. Malineni, R. L. Jezorek, N. Zhang and V. Percec,
Synthesis,2016, 48, 2795; (c)Sh. C. Van Wyk, M. O. Onani and
E. Nordlander, Chem. Papers, 2016, 70, 1003.
(a) S.-L. Huang, A.-Q. Jia and G.-X. Jin, Chem. Commun., 2013,
49, 2403; (b) L. Wang, W. Yang, F.-Y. Yi, H. Wang, Z. Xie, J.
Tang and Z.-M. Sun, Chem. Commun., 2013, 49, 7911; (c) J.
Feng and H. Zhang, Chem. Soc. Rev., 2013, 42, 387.
(a) Y. Wu, D.-S. Wang, P. Zhao, Z.-Q. Niu, Q. Peng, and Y.-D.
Li, Inorg. Chem. 2011, 50, 2046; (b) L.-X. You, W.-H. Zong, G.
Xiong, F. Ding, S.-J. Wang, B.-Y. Ren, I. Dragutan, V. Dragutan,
and Y.-G. Sun, Appl. Catal. A Gen., 2016, 511, 1; (c) L.-X. You,
W.-L. Zhu, S.-J. Wang, G. Xiong, F. Ding, B.-Y. Ren, I.
-3
3
Substrate CH COArI, catalyst 1 (10 mol% Pd) 5h; (f) Substrate
-3
CH
3
ArI, catalyst 1 (10 mol% Pd) 5h.
In summary, a new trimetallic Pd /Co complex, involving
2
the 2,2’-bipyridine-4,4’-dicarboxylate heteroleptic ligand,
enabled high-yielding Suzuki-Miyaura cross-couplings in neat
water and air and at low catalyst loadings. This robust and
cost-effective catalyst led to environmentally friendly
application with a variety of reagents. The synergistic
cooperation between Co and Pd within this complex, mediated
by the ligand acting as an effective charge transfer vector, has
been for the first time clearly evidenced in a Suzuki-Miyaura
process. Our results will be valuable for design of further
potent Pd/Co catalysts suitable for diverse C-C cross-couplings.
This work was supported by the Natural Science Foundation
of China (21671139, 21071100 and 21201123) and the
Distinguished Professor Project of Liaoning province
Dragutan, V. Dragutan and Y.-G. Sun, Polyhedron, 2016, 115
4
,
7.
7
(a) H. Wang, J. Xu, D.-S. Zhang, Q. Chen, R.-M. Wen, Z. Chang
and X.-H. Bu, Angew. Chem. Int. Ed., 2015, 54, 5966; (b)Y.-N.
Sun, G. Xiong, V. Dragutan, I. Dragutan, F. Ding, and Y.-G.
Sun, Inorg. Chem. Commun., 2015, 62 103; (c) Y.-G. Sun, J. Li,
J. You, Y. Guo, G. Xiong, B.-Y. Ren, L.-X. You, F. Ding, S.-J.
Wang, F. Verpoort, I. Dragutan, and V. Dragutan, J. Coord.
Chem., 2015, 68, 1199; (d) J. Huang, W. Wang and H. Li, ACS
Catal., 2013,
ChemCatChem., 2016, 8
3, 1526; (e) R. Sun, B. Liu, B.-G. Li and S. Jie,
, 3261.
(
2013204). F.D. acknowledges Chinese Scholarship Council
[2012]5031) for the financial support. I.D. and V.D. gratefully
(
8
9
(a) Y.-G. Sun, D. Sun, W. Yu, M.-C. Zhu, F. Ding, Y.-N. Liu, E.-J.
Gao, S.-J. Wang, G. Xiong, I. Dragutan, and V. Dragutan,
Dalton Trans., 2013, 42, 3957; (b) Y.-G. Sun, Y. Guo, D. Sun,
M.-C. Zhu, F. Ding, Y.-N. Liu, E.-J. Gao, S.-J. Wang, G. Xiong, I.
acknowledge the support from Romanian Academy, Institute
of Organic Chemistry, Bucharest.
Dragutan, and V. Dragutan, Eur. J. Inorg. Chem., 2014, 33
5
,
741.
Notes and references
(a) Y.-G. Sun, B. Jiang, T.-F. Cui, G. Xiong, P. F. Smet, F. Ding,
E.-J. Gao, T.-Y. Lv, K. V. D. Eeckhout, D. Poelmanb, and F.
Verpoort, Dalton Trans., 2011, 40, 11581; (b) L.-X. You, S.-J.
Wang, G. Xiong, F. Ding, K.W Meert, D. Poelman, P. F. Smet,
‡
Synthesis of Pd
mmol), Co(NO
mol·L-1 NaOH (1 mL) was sealed in a Teflon-lined stainless steel vessel (23 mL),
2
Co(HBPDC)
2
Cl
4
·(H
2
O)
4 2 4
(1): A mixture containing K PdCl (0.2
3
)
3
·6H O (0.1 mmol), H
2
2
BPDC (0.2 mmol), water (8mL) and 0.01
B.-Y. Ren, Y.-W. Tian and Y.-G. Sun, Dalton Trans., 2014, 43
7385.
0 S.-J. Wang, Y.-W. Tian, L.-X. You, F. Ding, K. W Meert, D.
,
which was heated at 95
Yellow thin crystals of
o
C for 96 hr and then cooled to room temperature.
were obtained and were picked out, washed with
1
1
1
1
distilled water and dried in air (Yield: 40.6% based on Pd ). Elemental analysis
Calcd (%) for C24 Co ( ): C 30.63; H 2.34; N 5.95. Found: C 31.01;
H 2.51; N 6.23. IR(KBr,cm–1): 3448w, 1719m, 1638s, 1550s, 1356s, 1258w,
235w, 767m.
Crystal data for
.301(11) Å, = 12.470(3) Å,
1.30(3)°, = 792.8(3) Å = 1,
Poelman, P. F. Smet, B.-Y. Ren and Y.-G. Sun, Dalton Trans.,
014, 43, 3462.
H
22Cl
4
N
4
O
12Pd
2
1
2
1 (a) S. M. Islam, N. Salam, P. Mondal and A. S. Roy, J. Mol.
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1
§
1
Pd
2
Co(HBPDC)
=12.610(3) Å,
= 273 K,
2
Cl
4
·(H
2
O)
4
: Triclinic, space group
= 76.80(3)° = 79.55(3)°, γ
(MoK ) =2.043 mm
p
-1,
a
=
=
=
5
8
2
b
c
α
, β
−
V
3
,
Z
T
μ
α
1
, D
calc
1
1
1
.036mg cm−3, 8006 reflections measured, 3591 unique (Rint = 0.0696) which
were used in all calculations. The final
R
1
was 0.0756 ( > 2 )) and w was
I
σ
(
I
R
2
0.2171 (all data)
1
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(
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8
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4
| J. Name., 2012, 00, 1-3
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Dalton Transactions
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DOI: 10.1039/C6DT03628G
Graphical Abstract
We report on the first Suzuki-Miyaura reaction promoted by a phosphine-free trimetallic Co/Pd catalyst
2
proceeding in water, under aerobic conditions. Results reveal a synergistic Co-Pd cooperation, fostered by
the metals ligated through 2,2′-bipyridine-4,4′-dicarboxylate.