Ruthenium(ii)-catalyzed selective monoarylation in water and sequential functionalisations of C-H bonds

Article abstract of DOI:10.1039/c2gc36222h

The ruthenium(ii)-phosphine catalyst RuCl₂(PPh ₃)(p-cymene) operating water selectively leads to ortho monoarylation, with arylchlorides and heteroarylhalides, of functional arenes. Further catalytic heteroarylation with Ru(OAc)₂(p-cymene) in water produces mixed bifunctional derivatives.

Full text of DOI:10.1039/c2gc36222h

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Ruthenium(II)-catalyzed selective monoarylation in
water and sequential functionalisations of C–H bonds†
Cite this: Green Chem., 2013, 15, 67
Received 2nd August 2012,
Percia B. Arockiam, Cédric Fischmeister, Christian Bruneau* and Pierre H. Dixneuf*
Accepted 28th September 2012
DOI: 10.1039/c2gc36222h
www.rsc.org/greenchem
The ruthenium(II)-phosphine catalyst RuCl2(PPh3)(p-cymene) ope- preferentially generate monoarylated arenes with rather good
rating water selectively leads to ortho monoarylation, with selectivity.4 The first example of direct arylation with arylbro-
arylchlorides and heteroarylhalides, of functional arenes. Further mides using the ruthenium(II)-PPh3 catalyst was shown by Oi
catalytic heteroarylation with Ru(OAc)2(p-cymene) in water pro- and Inoue and led predominantly to the ortho monoarylation
duces mixed bifunctional derivatives.
of 2-phenylpyridine and arylimines in NMP.4a,b Chanjuan Xi
et al.4c demonstrated a selective monoarylation of 2-phenylpyri-
dine in the presence of a [RuCl2(PPh2(–C(Ph)vCHPh)(arene))]
catalyst precursor. The [RuCl2(L)(p-cymene)]2 complex contain-
ing a bulky monophosphine L ligand was efficient to monoary-
late 2-phenylpyridine and N-phenylpyrazole with arylchlorides
in NMP at 120 °C as reported by Doherty et al.4d In parallel the
carboxylate-ruthenium(II) catalysts when operating in water
were revealed to provide in a rare example a high ratio of
mono(hetero)arylation of functional arene C–H bonds.3c Thus
we have investigated the positive influence of these two
factors: ruthenium(II)-phosphine catalyst and ruthenium cata-
lysis in water in the search for selective monoarylation, thus in
a non-toxic solvent and under greener chemistry conditions.
Several industrial processes are already operating under
aqueous phase organometallic-catalyzed reaction conditions
and there are already some technical solutions such as mem-
brane filtration or phase separation for water recovery.5
Introduction
The direct catalytic functionalisation of C–H bonds is attract-
ing tremendous interest to develop at low cost C–C bond cross-
coupling reactions without the use of a stoichiometric amount
of organometallic reagents, thus via a better atom economy
and greener process.1 However many influencing factors need
to be elucidated and improved such as catalyst efficiency and
cost, compatible non-toxic solvents, and multiple controlled
regioselectivities. Another rising objective consists in the con-
secutive regioselective functionalisations of several C–H bonds
for both synthetic efficiency and green chemistry contribution.
The diarylation with arylhalides and heteroarylhalides of ortho
C–H bonds of functional arenes can now be achieved easily,1
especially with cheap ruthenium(II) catalysts in the presence of
catalytic amounts of carboxylate.2–4 The sequential monoary-
lations with two different functional (hetero)arylhalides of two
identical C–H bonds have not been achieved yet in spite of
their potential to reach new mixed bifunctional polyaryl mol-
ecules of interest for molecular materials and as polymer
precursors.
We now report that Ru(II)-PPh3 catalyst RuCl2(PPh3)(p-cymene)
operating in water, without a carboxylate promoter, constitutes
a good catalytic system for selective monoarylation of func-
tional arenes and that the sequential catalytic functionalisa-
tions in water of two ortho C–H bonds of functional arenes can
be applied to reach unsymmetrical ortho diarylated arenes and
one example of mixed ortho arylated and alkenylated arenes.
Selective monoarylations are easily achieved only when one
ortho substituent is present or when only one C–H bond is pro-
tected by steric hindrance of a substituent at an arene meta
position. However a few ruthenium(II)-phosphine catalysts Results and discussion
operating in organic solvents have shown the ability to
The activity of an arylation catalyst was often revealed by the
ratio of the diarylation of (hetero)arenes as mono and diaryla-
tions had almost similar rates.3 Thus conditions were searched
to differentiate these two reaction rates. We first investigated
the reaction of a slight excess of 2-phenylpyridine (0.6 mmol)
with chlorobenzene (0.5 mmol) in the presence of various
Centre of Catalysis and Green Chemistry, OMC-Institut Sciences Chimiques de
Rennes, UMR 6226: CNRS-Université de Rennes, Campus de Beaulieu, 35042 Rennes,
France. E-mail: christian.bruneau@univ-rennes1.fr, pierre.dixneuf@univ-rennes1.fr
†Electronic supplementary information (ESI) available: Experimental pro-
cedures, spectroscopic and analytical data. See DOI: 10.1039/c2gc36222h
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Table 1 Catalytic monoarylation of 2-phenylpyridine in watera
60 °C in 16 h (Table 1, entries 11–12). The reaction performed
in NMP at 80 °C for 5 h provided only 45% of conversion
(entry 11). This reveals that water is a more efficient solvent at
lower temperature than NMP for monoarylation.
Time (h)/
Entry
Catalyst
Convb (%)
3a/4ac
1
2
3
4
5
6
7
8
[RuCl2(p-cymene)]2
Ru(OPiv)2(p-cymene)
Ru(OPiv)2(p-cymene) + 2 equiv. PPh3
Ru(OAc)2(p-cymene)
Ru(OAc)2(p-cymene) + 2 equiv. PPh3
RuCl2(PPh3)(p-cymene)
RuCl2(P(CH2Ph)3)(p-cymene)
RuCl2(PCy3)(p-cymene)
RuCl2(Pi-Pr3)(p-cymene)
[RuCl2(p-cymene)]2 + (P(o-Me-C6H4)3)
RuCl2(PPh3)(p-cymene)
24 h – 97
24 h – 98
24 h – 100
24 h – 97
24 h – 89
24 h – 100
24 h – 98
24 h – 94
24 h – 93
24 h – 96
3 h – 81
78/22
78/22
82/12
80/20
94/6
89/11
85/15
89/11
85/15
80/20
96/4
We performed a kinetic study, in order to better observe the
variations of conversion and selectivity as a function of the
reaction time with 5 mol% of the RuCl2(PPh3)(p-cymene) cata-
lyst in water. After 1 h, the conversion was only 71% with 99%
of selectivity towards the monoarylated product. When the
reaction was carried out for 24 h, the selectivity of 3a decreased
from 99% to 89%, which showed that the diarylated product
was formed during the course of the reaction at the expense of
the monoarylated product. We observed that the best for-
mation of monoarylated 2-phenylpyridine 3a was obtained in
3 h (Table S1†). The reaction was performed with various cata-
lysts in 3 h at 100 °C in order to evaluate the influence of
various phosphorous and arene ligands coordinated to ruthe-
nium (Tables S2 and S3†). Hence, after the screening of the
reaction of 2-phenylpyridine with chlorobenzene it could be
concluded that the best conditions to reach the monoarylated
product 3a were to use the RuCl2(PPh3)(p-cymene) catalyst:
(i) at 80 °C, with 5 mol% of the catalyst with a reaction time of
5 h, or (ii) at 100 °C, with 5 mol% of the catalyst with a reac-
tion time of 3 h.
9
10
11d
5 h – 92
95/5
98/2
98/2
5 h – 45e
16 h – 70
12f
RuCl2(PPh3)(p-cymene)
a Reaction conditions: 0.6 mmol of 2-phenylpyridine, 5 mol% of [Ru], 3
equiv. of K2CO3, 10 μL of tetradecane (internal standard) for GC,
0.5 mmol of chlorobenzene in
2 mL of water, 24 h, 100 °C.
b Conversion determined by gas chromatography based on arylhalide.
c 3a/4a ratio determined by gas chromatography. d Reaction at 80 °C.
e Reaction performed in NMP as a solvent. f Reaction at 60 °C.
catalysts in water at 100 °C and in the presence of K2CO3 as a
base, as
Selective monoarylation of 2-phenylpyridine with (hetero)aryl
halides in water
The selective monoarylation with various (hetero)arylhalides
was investigated using 5 mol% of the RuCl2(PPh3)(p-cymene)
catalyst in water at 80 °C (eqn (2), Table 2).
ð1Þ
carbonate also contributes to the C–H bond activation/depro-
tonation6 (eqn (1) and Table 1).
The reactions produced only 3a and 4a derivatives without
side products such as homocoupling products. With [RuCl2(p-
cymene)]2 as the catalyst precursor in the absence of a carboxy-
late ligand a conversion of 97% was reached in 24 h with a 3a/
ð2Þ
The reaction of 2-phenylpyridine with various electron
4a ratio of 78/22 (Table 1, entry 1). The reaction performed in donating and electron withdrawing heteroarenes was per-
the presence of Ru(OPiv)2(p-cymene) and Ru(OAc)2(p-cymene), formed. The monophenylated 2-phenylpyridine 3a was
which were previously shown to be efficient catalysts for diary- obtained by the reaction with phenylchloride in 5 h with 76%
lation in water,3c,7 led to 97% conversion, with a moderate 3a/ isolated yield (Table 2, entry 1). The reaction with arylhalides
4a ratio (Table 1, entries 2, 4). Addition of 2 equiv. of PPh3 to containing the para substituted electron donating groups,
the ruthenium carboxylate catalysts showed only a slight –OMe, –NMe2, gave 69% and 72% yield, respectively in 8–13 h
improvement in the selectivity towards 3a (Table 1, entries 3, 5 (Table 2, entries 2–3). With the electron withdrawing para CF3-
vs. 2, 4).
substituted phenylchloride 99% of conversion was obtained in
Better conversion and selectivity towards the monoarylated 13 h leading to 80% of monoarylated product 3h (Table 2,
product were obtained after 24 h with 5 mol% of RuCl2(PPh3)- entry 4). With 4-methyl chlorobenzoate 2j and 4-chloroaceto-
(p-cymene) (Table 1, entry 6). The replacement of PPh3 by phenone 2k the reactions were completed in shorter reaction
bulkier and more electron donating phosphines such as times (3–10 h), providing 83% and 77% of monoarylated
P(CH2Ph)3, PCy3, Pi-Pr3 or P(o-Me-C6H4)3 did not improve the products 3j and 3k, respectively (Table 2, entries 6–7). With
selectivity of the formation of 3a (Table 1, entries 7–10). o-methylchlorobenzene 2l only 30% of product 3l was isolated
Neither steric nor electronic property of the phosphine ligand after 24 h (Table 2, entry 8).
had a significant positive effect on the selective formation of
The reaction with heterocyclic halides such as 2-chlorothio-
3a with respect to PPh3 in water. Noteworthily, the selective phene, 5-methyl-2-chlorothiophene, 6-bromo-2-methylpyridine
formation of 3a could be achieved at 80 °C in 5 h, and even at was performed successfully with short reaction times (Table 2,
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Table 2 Selective monoarylation of 2-phenylpyridine with various aryl and
heteroarylhalidesa
Table 3 Selective monoarylation of N-phenylpyrazole with various aryl and
heteroarylhalidesa
Entry
1
Het-X
T (h)
Convb (%)
98
M/Dc
94/6
Yieldd (%)
Entry Het-X
T (h)
Convb (%) M/Dc
Yd (%)
5
1a
1b
7
97
90/10
93/7
14 (65 °C) 62
2a
2b
5
96
89/11
90/10
2
3
4
8
10
88
89
96/4
96/4
20 (65 °C) 98
3a
3b
5
7
80
84
78/22
75/25
74/26
13
14
90
92
90/10
90/10
20 (65 °C) 98
4a
4b
8
78
84/16
75/25
6
13
78
99
96/4
90/10
24 (65 °C) 91
a Reaction conditions: 0.6 mmol of phenylpyrazole,
5 mol% of
5
6
6
10
—
RuCl2(PPh3)(p-cymene), 3 equiv. of K2CO3, 10 μL of tetradecane
(internal standard) for GC, 0.5 mmol of Het-X in 2 mL of water, 80 °C.
b Conversion determined by gas chromatography. c M/D ratio
determined by gas chromatography. d Isolated yield.
3
4
96
97
96/4
95/5
whereas with 2d, only 81% conversion of 2-phenylpyridine was
obtained in 3 h, but the complete conversion was obtained in
6 h leading only to 52% of isolated 3d (Table 2, entry 11).
7
8
6
10
90
96
90/10
88/12
Selective monoarylation of N-phenylpyrazole with (hetero)aryl
halides
8
24
50
60
88/12
80/20
The reaction of N-phenylpyrazole 1b with 4-chloromethoxy-
benzene and 4-methyl chlorobenzoate was performed in the
presence of RuCl2(PPh3)(p-cymene) and 3 equiv. of K2CO3 in
water at 80 °C, affording the monoarylated products 5f and 5j
in a moderate yield of 52–53% (eqn (3), Table 3, entries 1a–2a).
Bidentate ligands 5c and 5d were isolated in moderate yields
from the reaction of N-phenylpyrazole with 5-methyl-2-chloro-
thiophene and 6-bromo-2-methylpyridine (Table 3, entries
3a–4a). It is noteworthy that the efficient catalytic system
allowed us to carry out the reaction in water at 65 °C in reason-
able reaction times (14–24 h), with good conversion and selec-
tivity (Table 3, entries 1b–4b).
9
3
4
100
100
86/14
85/15
10
11
3
4
100
100
89/11
87/13
3
4
6
81
83
100
81/19
80/20
73/22
a Reaction conditions: 0.6 mmol of 2-phenylpyridine, 5 mol% of
RuCl2(PPh3)(p-cymene), 3 equiv. of K2CO3, 10 μL of tetradecane
(internal standard) for GC, 0.5 mmol of Het-X in 2 mL of water, 80 °C.
b Conversion determined by gas chromatography based on (hetero)
arylhalide. c M/D ratio determined by gas chromatography. d Isolated
yield.
ð3Þ
Similar conditions for selective catalytic monoarylation
were used to produce new monoarylated products in water
entries 9–11). With 2b and 2c, the reaction went to completion from functional arenes containing already one ortho substitu-
within 3 h affording 3b and 3c in 76–79% isolated yields, ent. As there is no risk to get parasite ortho diarylation the
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phosphine can be replaced by the carboxylate ligand. Thus the performed in the presence of RuCl2(PPh3)(p-cymene) in water
[RuCl2(p-cymene)]2–4 KOPiv catalytic system was applied for for 20 h to give only 70% of conversion. Then the same reac-
the monoarylation of the ortho C–H bond of 2-o-tolylpyridine 1c. tion in the presence of Ru(OAc)2(p-cymene) or Ru(OPiv)2-
Thus the ortho (hetero)arylated derivatives 4e (71%), 4f (60%), 4g (p-cymene)7 was carried out at 120 °C and provided the mixed
(63%), 4h (58%) were obtained by direct arylation with chloro- diarylated product with 99% conversion in 20 h and afforded
benzene, and the heterocyclic halides 2b, 2c and 2d (Scheme 1).
77% isolated yield of 7 (Scheme 2). For comparison, when the
same reaction with 3j was performed in NMP as a solvent, only
20% conversion was obtained after 20 h. The advantage of
using water as a solvent medium was obvious as water not only
acts as a solvent but also enhances the rate of the reaction for
the formation of unsymmetrical or mixed diarylated products.
The transformation in water of 3j with 4-chloroacetophe-
none provided the mixed ketone carboxylate product 8 isolated
in 71% yield after 24 h. Similarly, the monoarylated pyrazole 5j
was reacted in water with 2-chlorothiophene and 4-chloroace-
tophenone. After 24 h the unsymmetrical diarylated products 9
and 10 were isolated in 72 and 83% yields.
Successive monoarylations in water
One major aim of the selective monoarylation reaction is to
utilize the remaining available ortho C–H bond, as a functional
group, for further functionalisation in order to prepare unsym-
metrical bifunctional arenes.
The monoheteroarylated derivative 3j was first obtained
from the monoarylation of phenylpyridine with 4-chlorobenzo-
ate in water in the presence of RuCl2(PPh3)(p-cymene)
(Table 2). The reaction of 3j with 2-chlorothiophene was then
Successive alkenylation of monoarylated heteroarene
The ruthenium(II)-catalyzed alkenylation of monoarylated hetero-
arenes was then investigated. The reaction of monoarylated
2-phenylpyridine and phenylpyrazole derivatives 3j and 5j with
n-butyl acrylate was attempted in the presence of a [RuCl2-
(p-cymene)]2/AgSbF6 catalyst8 with Cu(OAc)2·H2O as an oxidant
which was shown to be an efficient catalytic system for the
alkenylation of arenes containing weakly coordinating
directing groups.8 Unfortunately, this catalytic system did not
provide any conversion of 3j and 5j.
Scheme 1 Selective monoarylation of 2-o-tolylpyridine with (hetero)arylha-
lides in water. (a) Reaction conditions: 0.5 mmol of 2-o-tolylpyridine, 5 mol% of
[RuCl2(p-cymene)]2, 20 mol% of KOPiv, 3 equiv. of K2CO3, 10 μL of tetradecane
(internal standard) for GC, 1.25 mmol of aryl(hetero)halide in 2 mL of water. (b)
Conversion determined by gas chromatography. (c) Isolated yield.
ð4Þ
Scheme 2 Successive arylations in water and preparation of difunctional unsymmetrical diarylated arenes. Reaction conditions: 0.25 mmol of monoarylated het-
eroarenes, 5 mol% of Ru(OAc)2(p-cymene), 3 equiv. of K2CO3, 10 μL of tetradecane (internal standard) for GC, 0.5 mmol of Het-X in 1.5 mL of water. (a) Conversion
determined by gas chromatography. (b) Isolated yield.
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However it was recently established that arenes containing
a nitrogen directing group were successfully alkenylated with a
carboxylate-ruthenium(II) catalyst but in acetic acid.9 The
alkenylation of monoarylated product 5j with n-butyl acrylate
(o) V. Ritleng, C. Sirlin and M. Pfeffer, Chem. Rev., 2002, 102,
1731; (p) J. A. Labinger and J. E. Bercaw, Nature, 2002, 417,
507; (q) C. Jia, T. Kitamura and Y. Fujiwara, Acc. Chem. Res.,
2001, 34, 633; (r) A. Sen, Acc. Chem. Res., 1998, 31, 550.
was attempted using these conditions in the presence of 2 (a) L. Ackermann, P. Novak, R. Vicente and N. Hofmann,
Ru(OAc)2(p-cymene) as a catalyst with Cu(OAc)2·H2O as an
oxidant in AcOH at 100 °C during 24 h. The difunctional
mixed aryl alkenylheteroarene 11 was thus successfully iso-
lated in 43% yield (eqn (4)).
Angew. Chem., Int. Ed., 2009, 48, 6045; (b) L. Ackermann and
P. Novak, Org. Lett., 2009, 11, 4966; (c) L. Ackermann,
P. Novak, R. Vicente, V. Pirovano and H. K. Potukuchi, Syn-
thesis, 2010, 2245; (d) L. Ackermann, R. Vicente,
H. K. Potukuchi and V. Pirovano, Org. Lett., 2010, 12, 5032;
(e) L. Ackermann and A. V. Lygin, Org. Lett., 2011, 13, 3332;
(f) L. Ackermann, N. Hofmann and R. Vicente, Org. Lett.,
2011, 13, 1875; (g) L. Ackermann, J. Pospech and
H. K. Potukuchi, Org. Lett., 2012, 14, 2146.
3 (a) P. Arockiam, V. Poirier, C. Fischmeister, C. Bruneau and
P. H. Dixneuf, Green Chem., 2009, 11, 1871; (b) F. Pozgan
and P. H. Dixneuf, Adv. Synth. Catal., 2009, 351, 1737;
(c) P. B. Arockiam, C. Fischmeister, C. Bruneau and
P. H. Dixneuf, Angew. Chem., Int. Ed., 2010, 49, 6629;
(d) W. B. Li, P. B. Arockiam, C. Fischmeister, C. Bruneau and
P. H. Dixneuf, Green Chem., 2011, 13, 2315; (e) B. Li,
C. B. Bheeter, C. Darcel and P. H. Dixneuf, ACS Catal., 2011,
1, 1221; (f) B. Li, K. Devaraj, C. Darcel and P. H. Dixneuf,
Tetrahedron, 2012, 68, 5179.
4 (a) S. Oi, S. Fukita, N. Hirata, N. Watanuki, S. Miyano and
Y. Inoue, Org. Lett., 2001, 3, 2579; (b) S. Oi, Y. Ogino,
S. Fukita and Y. Inoue, Org. Lett., 2002, 4, 1783; (c) B. R. Yu,
X. Y. Yan, S. Wang, N. Tang and C. J. Xi, Organometallics,
2010, 29, 3222; (d) S. Doherty, J. G. Knight, C. R. Addyman,
C. H. Smyth, N. A. B. Ward and R. W. Harrington, Organome-
tallics, 2011, 30, 6010.
5 (a) A. Behr, “Technical solutions”, in “Aqueous-phase Organo-
metallic Catalysis – Concepts and Applications”, ed. B. Cornils
and W. A. Herrmann, Wiley, Weinheim, 1998, pp. 163–180;
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Conclusion
The above results show the selective ortho monoarylation of
functional arenes directed by N-containing heterocyclic
directing groups. It is selectively obtained using the
RuCl2(PPh3)(p-cymene) catalyst operating in water, for which
both phosphine PPh3 linked to ruthenium(II) and water
medium are cooperative to the monoarylation catalyst activity.
The profit of this selective mono(hetero)arylation is shown in
the sequential preparations of bifunctional polyaryl deriva-
tives. One example of synthesis of mixed ortho aryl alkenyl
benzene is shown and mixed ortho diarylated arenes are pro-
duced using the Ru(O2CMe)2(p-cymene) catalyst in water for
the second monoarylation step.
Acknowledgements
The authors are grateful to the CNRS, the French Ministry for
Research, the Institut Universitaire de France (P. H. D.), and
the ANR program 09-Blanc-0101-01 for support and for a PhD
grant to P. B. A.
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