Catalytic activity of k3-X,N,Y-palladium pincer complexes (X, y = O, S) with (thio)phosphoryl-substituted carbamoylmethylphosphine oxide and sulfide ligands in the Suzuki cross-coupling

Article abstract of DOI:10.1016/j.mencom.2013.11.014

Palladium pincer complexes with N-{2-[diphenyl(thio)phosphoryl]phenyl} carbamoylmethylphosphine oxide and sulfide ligands provide moderate activity in the Suzuki cross-coupling.

Full text of DOI:10.1016/j.mencom.2013.11.014

Mendeleev
Communications
Mendeleev Commun., 2013, 23, 344–346
3
Catalytic activity of k -X,N,Y-palladium pincer complexes (X,Y = O, S)
with (thio)phosphoryl-substituted carbamoylmethylphosphine oxide
and sulfide ligands in the Suzuki cross-coupling
a
b
b
b
Andrei A. Vasil’ev, Valentina Yu. Aleksenko, Diana V. Aleksanyan* and Vladimir A. Kozlov
a
b
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 499 135 5328; e-mail: vasiliev@ioc.ac.ru
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 499 135 5085; e-mail: aleksanyan.diana@ineos.ac.ru
DOI: 10.1016/j.mencom.2013.11.014
Palladium pincer complexes with N-{2-[diphenyl(thio)phosphoryl]phenyl}carbamoylmethylphosphine oxide and sulfide ligands
provide moderate activity in the Suzuki cross-coupling.
Functionalized carboxamides have been the objects of intense
research in coordination and organometallic chemistry for many
years. Introduction of ancillary donor centers both into acid and
Table 1 Catalytic activity of amido pincer complexes 1–3 in the Suzuki
cross-coupling between 4-BrC H R and PhB(OH) .
6
4
2
1
Catalyst
loading (mol%)
Entry
R
Catalyst
Product yield (%)
amine parts enables the realization of different coordination
modes, either in N-monoanionic or neutral forms, thus allowing
fine-tuning of physicochemical properties of the resulting com-
plexes. As a rule, the ancillary coordination-active fragments
are nitrogen-, phosphorus- and sulfur-containing groups such as
pyridine, thioether, phosphoryl, and hydroxy groups.2–4 Numerous
palladium complexes are known in which functionalized amides
1
2
3
4
C(O)Me
1
1
100
100
99
0.1
0.01
0.001
8
5
6
7
2
1
87
98
18
5
0.1
0.01
act as mono-, bi- or tridentate ligands. However, to the best of
our knowledge, there is no literature data on catalytic activity of
these complexes in the arylation of haloarenes with arylboronic
acids (the Suzuki cross-coupling), serving as a powerful tool in
8
9
3
1
1
5
6
0.1
6
,7
organic synthesis.
10
11
12
OMe
1
90
76
15
Recently we have shown that P(X)-modified carbamoyl-
methylphosphine oxides and sulfides (X = O, S), derived from
the condensation of o-(thio)phosphorylaniline with (thio)phos-
phorylacetyl chlorides, can serve as monoanionic tridentate
0.1
0.01
1
3
4
2
1
76
61
1
0.1
ii
8
pincer-type ligands for Pd ions (complexes 1–3). Palladium
pincer complexes were actively studied in recent years as (pre)-
catalysts for various chemical processes;9 however, most of
them belong to X,C,Y-type palladacycles (X, Y = P, S, N, etc.)
containing the Pd–C central bond. Taking into account that
S,C,S'- and N,C,S-pincer complexes with organothiophosphorus
,10
Br
[
Pd] cat.
+
PhB(OH)2
DMF, 120 °C,
K PO , 5 h
R
3
4
R
1
1
ligands are efficient (pre)catalysts for the Suzuki cross-coupling,
R = C(O)Me, OMe
it seemed interesting to investigate the catalytic activity of their
amido counterparts 1–3 in model reactions.
Scheme 1
Ph Ph
P
Ph Ph
P
Ph Ph
P
the coupling of 4-bromoacetophenone (Table 1, entries 1, 5),
while their S,N,S'-analogue 3 was completely inactive already
at this catalyst loading (entry 8). This is likely to be attributed to
the hemilabile nature of ligands in 1, 2 bearing the hard oxygen
and soft sulfur donor centers, which is often indicated as a reason
O
S
S
Cl
Cl
Cl
Pd
Pd
Pd
N
S
N
O
N
S
PPh2
PPh2
PPh2
O
O
O
for the better catalytic performance of palladium pincer com-
1
2
3
11(e),13
plexes.
The high level of activity of complexes 1, 2 is
†
In a typical experiment, a solution of 0.25 mmol of bromoarene,
.375 mmol of PhB(OH) , 0.5 mmol of K PO , and the specified amount
All the experiments were carried out under conditions pre-
viously suggested for sulfur-containing palladium pincer com-
0
2
3
4
of the corresponding palladium complex (used as titrated solutions in
DMF) in 1 ml of DMF was heated at 120°C for 5 h. The aliquots of the
reaction mixture were treated with water, extracted with benzene, and
analyzed by GC. In all cases, the chromatogram contained peaks only for
the starting bromoarenes and cross-coupling products; no homocoupling
or other side products were observed.
1
2
plexes and successfully adopted for C-metallated organothio-
phosphorus systems:1
1(c),(e)
heating in DMF at 120°C for 5 h
using K PO as a base (Scheme 1, Table 1).
†
3
4
The preliminary studies under these conditions showed that
isomeric S,N,O-palladocycles 1, 2 (1 mol%) efficiently promote
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2013 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2013, 23, 344–346
(
a)
100
100
1
2
Hg added at 1 h
8
6
4
2
0
0
0
0
0
80
60
40
20
3
Hg added at 0 h
4 5
0
0
1
2
3
4
5
0
1
2
3
t/h
t/h
(
b)
100
Figure 2 Time dependence of the conversion of 4-bromoacetophenone
catalyzed by complex 1 (catalyst loading 0.1 mol%) in the presence of Hg .
0
8
6
4
2
0
0
0
0
0
and the mechanisms of generation of catalytically active species
may differ.
1
2
A mercury poisoning test, which is used to distinguish between
0
ii
14
heterogeneous Pd and homogeneous Pd catalysts, revealed
0
that the addition of excess Hg to the reaction mixture bearing
complex 1 either at the reaction beginning or in 1 h completely
suppresses the conversion of 4-bromoacetophenone (Figure 2);
0
Hg should have exerted no effect on homogeneous organo-
metallic complexes containing metals in high oxidation states.
0
1
2
3
4
5
t/h
0
This indicates that some Pd species are formed in the course
of the catalytic reaction, which are likely to be true catalysts in
the system involving complex 1 and which are trapped by the
mercury metal. Furthermore, the conversion of 4-bromoaceto-
phenone catalyzed by complex 3 in the presence of 2 mol% of
Figure 1 Plots of yields of the biaryls vs. time for the couplings of
(
(
a) 4-bromoacetophenone and (b) 4-bromoanisole catalyzed by complexes
1) 1, (2) 2 and (3) 3 (catalyst loading 0.1 mol%).
retained also when the catalyst loading is decreased to 0.1 mol%
entries 2, 6). At the same time, the kinetic investigations revealed
Ph P reaches 29% (cf. 5% in the absence of phosphine). In small
3
(
amount, phosphines as well as N-heterocyclic carbenes can
0
that complex 1 was more active than 2, providing the complete
conversion of 4-bromoacetophenone within 3 h vs. 5 h in the case
of complex 2 [Figure 1(a)]. A difference in the activity of 1 and 2
became more apparent when the catalyst loading was diminished
to 0.01 mol%: the yields of the biaryl were 99% and 18%, respec-
tively (entries 3, 7). A further tenfold reduction of the loading of
complex 1 dropped the conversion to only 8% (entry 4). Com-
plexes 1, 2 also catalyzed efficiently the coupling of electronically
deactivated 4-bromoanisole, showing a satisfactory level of activity
even at 0.1 mol% catalyst loading (61–76%, entries 11, 14).
According to the kinetic studies, again complex 1 was more
active than complex 2 [Figure 1(b)]. Note that for an easy-
to-couple substrate, 4-bromoacetophenone, S,N,O-amido pincer
complexes 1, 2 show the same level of activity as the most
active C-palladated pincer complexes with organothiophosphorus
coordinate to Pd particles, preventing their agglomeration and
1
5
precipitation in the form of palladium black. This also sup-
ports the assumption that complexes 1–3 serve as depots for Pd0
catalytically active particles.
In conclusion, although the amido pincer complexes of P(X)-
functionalized carbamoylmethyl(thio)phosphoryl ligands show
1
6
the lower activity than other N-metallated pincer systems,
0
serving only as precatalysts for Pd catalytically active species,
the results presented demonstrate that hemilabile pincer ligands
based on functionalized carboxylic acid amides can be con-
sidered as a novel, promising class of ligands for transition
metal catalysis. The interesting thing is that they are different in
activity, which may give more insight into the pincer complex
properties in general.
1
1(e)
ligands,
but towards 4-bromoanisole, they are considerably
This work was supported by the Russian Foundation for Basic
Research (project no. 12-03-00793-a).
inferior, providing only 15% yield of the biaryl product at
0
.01 mol% concentration vs. 98%.
Although complexes 1–3 are stable upon heating in DMF
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