C-H bond functionalization in water catalyzed by carboxylato ruthenium(II) systems

Article abstract of DOI:10.1002/anie.201002870

In water it's better: In-situ-generated [Ru(O2CR)2(arene)] catalysts efficiently perform the direct ortho-arylation of functional arenes with chloroarenes or chloroheterocycles in water (see scheme; KOPiv=potassium pivalate), without the need for a surfactant. The activity of these catalysts is higher in water than in organic solvents.

Full text of DOI:10.1002/anie.201002870

Angewandte
Chemie
DOI: 10.1002/anie.201002870
Catalysis in Water
À
C H Bond Functionalization in Water Catalyzed by Carboxylato
Ruthenium(II) Systems**
Percia B. Arockiam, Cꢀdric Fischmeister, Christian Bruneau, and Pierre H. Dixneuf*
À
Direct metal-catalyzed C H bond activation/functionaliza-
tion reactions have become a topic of tremendous interest[1]
owing to their potential to replace the classical catalytic cross-
coupling reactions, without the intermediate formation of
organometallic C–M species (M = metal center). Significant
achievements in this field have already been reached using
À
palladium[2,3] and rhodium[4] catalysts. Ruthenium(0)[5,6] and
recently ruthenium(II)[7–11] systems have contributed to the
This intramolecular C H bond deprotonation mecha-
nism, rather than an electrophilic substitution, suggests that
such a process could take place in water with ruthenium(II)
catalytic systems, as some ruthenium(II) catalysts have
already been shown to be stable for several catalytic trans-
formations in water.[16] Catalysis in water is developing not
only to avoid the use of organic solvents as reaction medium
but also to reach better catalytic activity and regioselectiv-
ity.[17,18]
À
functionalization of C H bonds through two different pro-
cesses. In parallel, the contribution of various metal catalysts
À
for the functionalization of C H bonds has also been
reported.[12]
À
For the formation of C C bonds directly from aromatic
2
À
sp C H bonds, initial studies suggested an electrophilic
substitution reaction of the arene by PdII or RuIV species
that are generated in situ from aryl bromide or aryl iodide
oxidative addition to the Pd0 and RuII catalysts. Significant
recent contributions by Fagnou and co-workers[3a–d] and
Echavarren, Maseras, and co-workers[13] based on both
experimental studies with Pd0 catalysts and density functional
theory (DFT) calculations, support a concerted metalation–
deprotonation mechanism. With ruthenium(II) catalysts, the
influence of coordinated carbonate, as supported by DFT
À
A few examples of palladium-catalyzed C H bond
functionalization in water have just been shown,[18,19] includ-
À
ing the ortho C H bond functionalization by Lipshutz and co-
workers for the coupling of arylureas with aryl iodide and for
the alkenylation of phenylamides in the presence of a
surfactant.[19]
We now report that [Ru(O2CR)2(arene)] catalysts 1) can
efficiently perform the direct ortho arylation of functional
arenes with aryl chlorides in water, without the need for
surfactant, 2) when they operate in water these catalysts can
lead to a better catalyst activity than in an organic solvent
(N-methylpyrrolidone (NMP)), and 3) they allow selective
calculations, indicates a mechanism based on the cooperative
II
À
actions of both the Ru site and the carbonate ligand for C H
bond deprotonation. This step generates a cyclometalated
species before the oxidative addition of arylhalides.[9]
[Eq. (1); X = halide, carboxylate; Y= OH, Me]. This result
revealed the tremendous positive influence of coordinated
À
C C bond formation leading to a variety of functional arenes
and polyheterocycles including potential polydentate ligands
À
carboxylate ligands, assisted by ruthenium(II), for C H bond
[Eq. (2); KOPiv = potassium pivalate].
functionalization.[10] The beneficial influence of a carboxylate
ligand coordinated to PdII[3] and RuII centers[8d] has also been
demonstrated.
À
The concerted intramolecular deprotonation of inert C H
bonds with the assistance of a coordinated ligand appears to
be a general phenomenon.[14,15]
[*] P. B. Arockiam, Dr. C. Fischmeister, Dr. C. Bruneau,
Prof. P. H. Dixneuf
Our preliminary study showed that the direct arylation of
2-phenylpyridine 1 in water preferentially takes place accord-
ing to the sequence of arylhalides PhCl > PhBr> PhI, a result
of decreasing arylhalide solubility, and bases K2CO3 >
KHCO3 > Me4NOH (see Tables S1 and S2 in the Supporting
Information). 2-Phenylpyridine 1 (0.5 mmol) was treated with
phenylchloride (1.25 mmol) in the presence of 5 mol% of
various ruthenium(II) catalysts in the presence of 2 equiv-
alents of KO2CR ligand precursor in distilled water (2 mL),
with 3 equivalents of K2CO3 as a base at 1008C for 2 h. The
results displayed in Table 1 show that ruthenium(II) catalysts
Catalyse et Organomꢀtalliques
Institut Sciences Chimiques de Rennes
UMR 6226-CNRS-Universitꢀ de Rennes
Av. gꢀnꢀral Leclerc, 35042 Rennes (France)
E-mail: pierre.dixneuf@univ-rennes1.fr
[**] We are grateful to the CNRS, the French Ministry for Research, the
Institut Universitaire de France for membership (P.H.D.), the ANR
“RuCHCat” program 09-Blanc-0101-01, and to the European Net-
work IDECAT (2005-011730) for support.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201002870.
Angew. Chem. Int. Ed. 2010, 49, 6629 –6632
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6629

Communications
Table 1: Direct arylation of 2-phenylpyridine with PhCl in water.[a]
Table 2: Ligand influence on reaction of 2-phenylpyridine (1) with phenyl
chloride in water with ruthenium catalyst A.[a]
Entry
Catalyst
Conv. [%]/t [h]
2/3
Entry
Solvent
KO2CR
T [8C]
T [h]
Conv [%]
2/3
1
2
3
4
5
6
7
8
9
RuCl3·3H2O
–
68/2
100/2
100/2
–
100/2
100/4
100/6
99/1
–
[RuCl(dppb)(p-cymene)]Cl
RuCl2{P(OMe)3}(p-cymene)]
[RuCl2(PPh3)(p-cymene)]
[RuCl2(PPh3)3]
75/25
58/42
74/26
–
9/91
0/100
9/91
6/96
0/100
1
2
3
4
5
6
7
8
9
water
water
water
water
water
NMP
DEC
water
water
water
KOAc
KOPiv
–
100
100
100
100
100
100
100
80
2
2
2
2
2
2
2
4
24
62
100
100
97
92
62
100
100
100
100
100
26/74
0/100
21/79
77/23
93/7
25/75
45/55
0/100
9/91
KOAc[b]
KOPiv[c]
KOPiv
KOPiv
KOPiv
KOPiv
KOPiv
[{RuCl2(p-cymene)}2] (A)[b]
[{RuCl2(p-cymene)}2] (A)[b]
[{RuCl2(p-cymene)}2] (A)[c]
[Ru(O2CtBu)2(p-cymene)] (B)[d]
[Ru(O2CtBu)2(p-cymene)] (B)[d]
10
100/2
60
25
10
17/83
[a] 2-phenylpyridine (0.5 mmol), ruthenium catalyst (5 mol%), K2CO3
(3 equiv), tetradecane (10 mL as GC internal standard), potassium
pivalate (20 mol%), chlorobenzenze (1.25 mmol), and distilled water
(2 mL). [b] 2.5 mol% of A. [c] 1 mol% of A. [d] 10 mol% of isolated B.[20]
[a] 1 (0.5 mmol), A (5 mol%), KO2CR (20 mol%), K2CO3 (3 equiv), PhCl
(1.25 mmol), 2 mL of water or other solvent. [b] No K2CO3 but
3 equivalents of KOAc. [c] No K2CO3 but 3 equivalents of KOPiv.
Table 3: Functionalization of heteroarylbenzene derivatives.[a]
are operative in water, even with
the least-reactive arylchloride. As
an attempt to reach diarylation, the
best system appears to be the in-
situ-generated
catalyst
from
Entry
1
T [8C]
Solvent
T [8C]
Conv [%]
Product
m/d(yield)[b]
[{RuCl2(p-cymene)}2] (A) with
2 equivalents of potassium pivalate
(KO2CtBu) per ruthenium atom,
which was shown to give the com-
H2O
NMP
10
10
100
99
1/99 (89)
2/98
100
plex
[Ru(O2CtBu)2(p-cymene)]
(B).[20] Complete diarylation can
be reached with this catalyst at
1008C for 4 h with only 2.5 mol%
H2O
NMP
10
10
100
99
1/99 (92)
3/97
2
3
4
100
100
of
A
and without surfactant
(Table 1; entry 7). The use of well-
defined (that is, isolated) B led to
only slightly better results than the
in-situ-prepared catalyst B from
A[20] (Table 1; entries 7 vs. 10) and
thus justifies the use of the more
convenient in situ preparation of
catalysts from ruthenium precursor
and potassium carboxylates.
H2O
NMP
20
20
100
70
0/100 (41)
38/62
100
40
H2O
H2O
2
62
100
100
0/100 (94)
3/97 (90)
It is noteworthy that phosphine
complexes (Table 1; entry 4), while
promoting good conversion, favor
monoarylation over diarylation.
Based on the highest efficiency of
the catalyst precursor A, the influ-
ence of carboxylate ligands in water
on arylation of 1 with phenylchlo-
ride [Eq. (2)] has been investigated
(Table 2). In water with A, the
pivalate ligand is more efficient
that the acetate one (Table 2;
entries 1 and 2). Without K2CO3,
3 equivalents of KOAc per Ru
atom, as the only base and ligand
precursor, is not as efficient as the
combination of 20mol% KOAc
5
6
100
100
H2O
10
100
4/96 (90)
H2O
NMP
100
95
100
95
3/97 (95)
64/36
H2O
NMP
100
95
100
95
3/97 (48)
17/83
7
8
100
100
H2O
100
100
– (83)
(2 equivalents
atom) and 3 equivalents of K2CO3
(Table 2; entries 1 and 4). Similar see text for the identity of Het-X in each entry), 2 mL of water. [b] Yield of isolated product in parenthesis.
per
ruthenium
[a] Heteroarylbenzene (0.5 mmol), A (5 mol%) KOPiv (20 mol%), K2CO3 (3 equiv). Het-X (1.25 mmol;
6630 www.angewandte.org
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Angewandte
Chemie
behavior is observed for pivalate with and without K2CO3
(Table 2; entries 2 and 5). K2CO3 alone without KO2CR
ligand is efficient at promoting the ruthenium(II) catalyst
activity in water, but not as much as with the pivalate ligand
(Table 2; entries 2 and 3). However, this result is an indication
of the coordination of carbonate, as it also took place in other
solvents.[9,21]
À
More importantly the C H bond activation with ruth-
enium(II) catalysis performed in water appears to be more
efficient than in organic solvents, such as N-methylpyrroli-
done (NMP) or diethyl carbonate (DEC) (Table 2; compare
entries 6, 7, and 2). It is noteworthy that in water, the
temperature of the reaction can be decreased to 608C and
even to room temperature but extended reaction times are
necessary to reach complete conversion and high diarylation
À
ratio (Table 2; entries 8–10). No efficient C H bond func-
tionalization could take place with RuII systems at these low
temperatures in organic solvents.[8a,10b]
The best conditions (Table 2, entry 2) were used for the
introduction of two heterocyclic groups in the ortho positions
of heteroarylbenzene derivatives [Eq. (3) in Table 3). The
formation of the disubstituted (d) product rather than the
monosubstituted (m) one was attempted. Thus from 2-phe-
The above results show that it is now possible to perform
2
À
ruthenium(II) catalyzed sp C H bond functionalization of
functional arenes in water without surfactant on reaction even
with aryl and heteroaryl chlorides. The preferential influence
of [Ru(O2CtBu)2(p-cymene)] (B) is shown in the presence of
K2CO3. The activity of these catalyst systems in water is
À
nylpyridine 1 the C C coupling of two thiophenyl groups and
two 2-(6-methyl)(pyridyl) can be achieved in water with
2-chlorothiophene (4), 5-methyl-2-chlorothiophene (5;
Table 3; entries 1, 2) and 6-bromo-2-picoline (6; Table 3;
entry 3) leading, respectively, to the tridentate ligand 1,2,3-
trisheteroaryl benzenes 7, 8 and 9 which could be isolated in
good yields. Note that the formation of these compounds in
water was easier than in NMP (Table 3; entries 1–3).
À
compatible with concerted C H bond deprotonation process
and appears to be higher than in organic solvent (NMP)
allowing transformation at low temperature, including room
temperature. Thus the reaction allows the grafting of two aryl
or heteroaryl groups at the ortho positions of the arene
functionality (pyridines, pyrazole) and trisheteroaryl benzene
compounds can be directly produced from simple chloro-
heterocycles. The nature of the ruthenium catalyst operating
in water from these precursors, with the non-innocent
carbonate base, needs to be elucidated.
N-phenyl pyrazole was employed and its ortho-diphenyl
derivative 10 was isolated in 94% yield (1008C, 2 h) (Table 3;
entry 4). The two bis-(ortho-2-thienyl) derivatives 11 and 12
were quantitatively formed and obtained in 90% and 95%
yield upon reaction with 2-chlorothiophene (4), 5-methyl-2-
chlorothiophene (5), respectively (Table 3; entries 5, 6). From
N-phenyl pyrazole and 6-bromo-2-picoline (6) the bis
2-pyridyl derivative 13 was formed and identified by GC/
MS but decomposed during separation on silica (Table 3;
entry 7). The monoarylation of 7,8-benzoquinoline with
phenylchloride performed in water produced the derivative
14 in 83% yield (Table 3; entry 8). The same transformation
in DEC led only to 53% conversion after 24 h at 1208C.
Polydentate ligands containing pyridyl coordinating
groups are receiving interest for their use in catalysis,[22] but
now more importantly for molecular material for optics.[23]
Their importance thus requires that new methods of direct
preparation are found. The easy direct arylation with
arylchlorides in water led us to extend this reaction to the
arylation of 2-(2-pyridyl)toluene (15) with 1,3,5-trichloroben-
zene for the production of the tridentate ligand 16. The
reaction in water under reflux for 36 h led to the isolation of
the 1,3,5-trispyridylbenzene (16) in 77% yield, [Eq. (4)]
whereas in NMP at 1508C for 24 h only 45% of 16 were
formed. The reaction of benzoquinoline (17) with 1,3,5-
trichlorobenzene in refluxing water for 36 h led to the
isolation of trisbenzoquinoline (18) in 45% yield [Eq. (5)]
whereas 40% were obtained in NMP after 24 h at 1508C.
Received: May 12, 2010
Published online: July 27, 2010
À
Keywords: C H activation · carboxylates · polydentate ligands ·
.
ruthenium · water chemistry
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