Cooperative catalysis by Ru and Pd for the direct coupling of a chelating aldehyde with iodoarenes or organostannanes

Article abstract of DOI:10.1002/anie.200462006

(Chemical Equation Presented) Two is better than one: The combination of two metallic catalyst systems effects transformations that are difficult to carry out with any single-catafyst systems. This is demonstrated by the coupling of 8-quinolinecarboxaldeh

Full text of DOI:10.1002/anie.200462006

Angewandte
Chemie
Homogeneous Catalysis
Cooperative Catalysis by Ru and Pd for the Direct
Coupling of a Chelating Aldehyde with
Iodoarenes or Organostannanes**
Sangwon Ko, Byungman Kang, and Sukbok Chang*
Dedicated to Professor Yong Hae Kim
Transition-metal catalysts have been designed and utilized
conventionally to mediate single-step transformations.[1] In
addition to the traditional one catalyst/one reaction approach,
however, some recent examples have revealed that the
appropriate combination of suitable and compatible metal
species is able to effect sequential or cooperative catalytic
one-pot transformations that are unprecedented in single-
metal systems.[2] The extensive efforts in this field have borne
fruit recently, and have led to some significant examples in the
area of chemical catalysis.[3] We describe herein a novel
application of cooperative catalysis to the coupling of an
aldehyde with iodoarenes or organostannanes, in which Ru
and Pd collaborate, presumably through catalytic transmeta-
lation pathways. As part of our interest in coordination-
assisted organic transformations,[4] we envisaged the possibil-
ity that aldehydes could be directly coupled with aryl iodides
to afford ketone products in the presence of the appropriate
combination of two catalysts [Eq. (1), X = I].[5] In analogy, we
anticipated that the coupling of aldehydes and organostan-
nanes could also be possible (X = SnR3). The synthetic utility
of these transformations would be extremely high since
multistep processes are generally required for the preparation
of ketones in classical synthetic methods starting from the
same compounds (aldehydes and aryl halides).[6]
We chose 8-quinolinecarboxaldehyde (1) as the coupling
partner since it was initially anticipated that formation of a
five-membered chelate intermediate would effectively sup-
[*] S. Ko, B. Kang, Prof. Dr. S. Chang
Center for Molecular Design and Synthesis (CMDS)
Department of Chemistry and School of Molecular Science (BK 21)
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon 305-701 (Korea)
Fax: (+82)42-869-2810
E-mail: sbchang@kaist.ac.kr
[**] This research was supported by KOSEF (R02-2003-000-10075-0)
through the Basic Research Program.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2005, 44, 455 –457
DOI: 10.1002/anie.200462006
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
455

Communications
press any destructive decarbonylation pathway by catalytic
(Table 1, entry 8). The fact that a borate group is totally inert
under these reaction conditions shows the highly selective
nature of the present co-catalyst systems (Table 1, entry 9).
The presence of heteroatoms such as nitrogen and sulfur does
not affect the efficiency of the reactions (Table 1, entries 10
and 11). However, the coupling of 1 with vinyl iodides
resulted in low yields (< 10%) with the present system.
Control experiments were performed to verify the pre-
sumed cooperative catalytic pathways. No conversion was
observed when quinoline was treated with iodobenzene under
an atmosphere of CO under otherwise identical conditions
[Eq. (2)]. This result may rule out the possibility that the
reaction of aldehyde 1 and iodoarenes proceeds by Ru-
catalyzed decarbonylation of 1 followed by Pd-catalyzed
arylcarbonylation of iodobenzene.[9] In fact, there are several
precedents for the [Ru3(CO)12]-catalyzed orthometalation of
nitrogen-containing heteroaromatic compounds to provide
ortho-carbonylated adducts.[10] Aldehydes devoid of a coor-
dinating group were not coupled with iodobenzene, which
À
activation of the formyl C H bond. We found that treatment
of iodobenzene with an acylrhodium hydride species,[7]
obtained from the reaction of 1 with an equivalent amount
of [RhCl(PPh3)3], afforded the corresponding diaryl ketone in
60% yield in the presence of a catalytic amount of
[Pd2(dba)3]·CHCl3 (5 mol%; dba = trans,trans-dibenzylidene-
acetone) at 1358C after 5 h. We were further encouraged by
the observation that a direct coupling between aldehyde 1 and
iodobenzene took place even in systems containing both
[RhCl(PPh3)3] and [Pd2(dba)3]·CHCl3 (5 mol% each), albeit
in lower yield (48%, 24 h), under otherwise identical
conditions. The use of various other combinations of Rh
and Pd catalysts proved to be far less efficient (< 5% yields),
and no coupling was observed in the presence of any single-
metal catalyst systems. A greatly improved efficiency was
obtained when a Ru catalyst was employed instead of Rh in
the presence of the Pd co-catalyst. Among all the Ru catalysts
investigated, [Ru3(CO)12] was found to be the most effective
counterpart when combined with [Pd2(dba)3]·CHCl3. This
combination afforded the ketone product in 83% yield
(5 mol% of each catalyst) in the presence of NaHCO3
(1.5 equiv) at 1358C (20 h).
À
implies that activation of a formyl C H bond of 1 is
coordination-directed [Eq. (3)].[11]
Under the optimized conditions, 1 was coupled with
various iodoarenes to afford the corresponding aryl ketones
in good yields (Table 1);[8] no noticeable electronic effects of
the substituents on the iodoarenes were observed (Table 1,
entries 1–5). The fact that a formyl group of the iodoarene
substrate is tolerated suggests that the assumed coordination
of the Ru center to the nitrogen atom of 1 is a driving force for
À
the activation of the formyl C H bond (Table 1, entry 6). An
ester group also turned out to be compatible under these
reaction conditions (Table 1, entry 7). Coupling of 1 with a
bromoarene was much slower than with an iodoarene, as
demonstrated in the reaction with 1-bromo-3-iodobenzene
When 1 was treated with a stoichiometric amount of
[Ru3(CO)12] in 1,2-dichloroethane (1208C, 30 min) the alde-
hydic proton signal disappeared gradually from the 1H NMR
spectrum, to be replaced by a signal for an acylruthenium
hydride (d = À15.9 ppm; singlet in CDCl3).[12] The IR spec-
trum of the isolated adduct shows an absorbance band at
1846 cmÀ1, which is assignable to the stretching band of the
Table 1: Cooperative catalytic coupling of 1 with various iodoarenes.[a]
[13]
À
speculative Ru H bond.
It should be noted that a
stoichiometric activation of 1 has previously been reported
with Na2PdCl4 to afford a chloro-bridged Pd dimer.[14]
However, no conversion was observed upon the treatment
of 1 with aryl iodides in the presence of a range of Pd catalysts
and in the absence of ruthenium co-catalysts. Moreover, the
Entry
Ar
Yield [%][b]
1
2
3
4
5
6
7
8
C6H5
83
66
62
71
76
80
79
73
À
4-Me-C6H4
4-MeO-C6H4
4-Ac-C6H4
4-NO2-C6H4
4-CHO-C6H4
4-EtO2C-C6H4
3-Br-C6H4
C I bond of iodobenzene was inert to the Ru catalyst under
the reaction conditions, even when one equivalent of
[Ru3(CO)12] was used, which strongly suggests that the
activation of iodobenzenes is carried out selectively by Pd
catalysts in the presence of ruthenium species. The above
observation led us to propose a primitive mechanistic
scenario for the cooperative catalysis (Scheme 1). Ruthenium
9
63
89
90
À
may activate a formyl C H bond of the chelating aldehyde 1
to afford a five-membered cycloacylruthenium hydride inter-
mediate,[15] which is subsequently transferred into the Pd
catalytic cycle with iodoarenes and eventually leads to
coupled ketone products after a reductive-elimination step.
The concept of cooperative catalysis by Pd and Ru was
further extended into coupling reactions of 1 with organo-
stannanes [Eq. (4)]. Since it is known that organostannanes
10
11
[a] A mixture of 1 (0.5 mmol), iodoarene (1.0 mmol), [Pd2(dba)3]·CHCl3
and [Ru3(CO)12] (5 mol% each), and NaHCO3 (0.75 mmol) in benzene
(1.0 mL) was stirred at 1358C for 20 h. [b] Yield of isolated product.
456
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Angewandte
Chemie
[2] a) E. K. van den Beuken, B. L. Feringa, Tetrahedron 1998, 54,
12985; b) E. Y.-X. Chen, T. J. Marks, Chem. Rev. 2000, 100, 1391.
[3] J. M. Lee, Y. Na, H. Han, S. Chang, Chem. Soc. Rev. 2004, 33,
302.
[4] a) S. Ko, Y. Na, S. Chang, J. Am. Chem. Soc. 2002, 124, 750; b) S.
Ko, C. Lee, M.-G. Choi, Y. Na, S. Chang, J. Org. Chem. 2003, 68,
1607; c) S. Ko, H. Han, S. Chang, Org. Lett. 2003, 5, 2687; d) Y.
Na, S. Ko, L. K. Hwang, S. Chang, Tetrahedron Lett. 2003, 44,
4475.
[5] a) G. Dyker, Angew. Chem. 1999, 111, 1808; Angew. Chem. Int.
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Scheme 1. Proposed pathway for the Ru/Pd co-catalytic coupling of
aldehyde 1 with iodobenzenes.
[6] For the metal-mediated synthesis of ketones from the reaction of
aryl iodides with aldimines or aldehydes, albeit taking place by
distinctively different mechanistic pathways compared to this
study, see: a) T. Satoh, T. Itaya, M. Miura, M. Nomura, Chem.
Lett. 1996, 823; b) T. Ishiyama, J. Hartwig, J. Am. Chem. Soc.
2000, 122, 12043; c) Y.-C. Huang, K. K. Majumdar, C.-H. Cheng,
J. Org. Chem. 2002, 67, 1682.
are readily activated by certain Pd complexes,[16] their
coupling with 1 was initially investigated in the presence of
Ru and Pd co-catalysts. We were pleased to find that the
corresponding ketone products were generated in acceptable
yields from the reactions with a range of tin compounds
(1.5 equiv relative to 1). The reaction proceeds most effec-
tively in 1,2-dichloroethane at 1208C when [PdCl2(PPh3)2]
and [Ru3(CO)12] (5 mol% each) are used simultaneously.
Various functional groups, including cyano, formyl, and
heteroatoms, are tolerated under the present conditions. As
anticipated, tributyltin hydride was generated as a side-
product from the reactions (yields of over 60%). It should be
mentioned that, to the best of our knowledge, this represents
the first example of a direct coupling between an aldehyde
and organotin compounds.[17] As in the above coupling
reactions between 1 and iodoarenes, the use of any single-
catalyst systems of Ru, Pd, or Rh gave none of the desired
products.
[7] J. W. Suggs, J. Am. Chem. Soc. 1978, 100, 640.
[8] All new compounds were fully characterized by 1H NMR,
13C NMR, and IR spectroscopy, as well as HRMS. See the
Supporting Information for the spectral data.
[9] For the Pd-catalyzed alkoxycarbonylation of haloarenes, see: M.
Mori, in Handbook of Organopalladium Chemistry for Organic
Synthesis, Vol. 2 (Ed.: E. Negishi), Wiley-Interscience, New
York, 2002, p. 2313.
[10] See, for example: N. Chatani, T. Fukuyama, F. Kakiuchi, S.
Murai, J. Am. Chem. Soc. 1996, 118, 493.
À
[11] For selected examples of efficient C C bond formation by
À
catalytic C H formyl activation, see: a) R. C. Larock, M. J.
Dorty, S. Cacchi, J. Org. Chem. 1993, 58, 4579; b) K. Tanaka,
G. C. Fu, J. Am. Chem. Soc. 2001, 123, 11492; c) M. C. Willis, S. J.
McNally, P. J. Beswick, Angew. Chem. 2004, 116, 344; Angew.
Chem. Int. Ed. 2004, 43, 340.
[12] a) J. A. Ayllon, S. F. Sayers, S. Sabo-Etienne, B. Donnadieu, B.
Chaudret, E. Clot, Organometallics 1999, 18, 3981; b) S. G. Bott,
H. Shen, R. A. Senter, M. G. Richmond, Organometallics 2003,
22, 1953; c) G. Albertin, S. Antoniutti, A. Bacchi, C. DꢀEste, G.
Pelizzi, Inorg. Chem. 2004, 43, 1336.
[13] a) K. Abdur-Rashid, M. Faatz, A. J. Lough, R. H. Morris, J. Am.
Chem. Soc. 2001, 123, 7473; b) S. Ogo, K. Uehara, T. Abura, Y.
Watanabe, S. Fukuzumi, Organometallics 2004, 23, 3047.
[14] The catalytic activity of the thus-generated binuclear Pd com-
plex was not reported: C. G. Anklin, P. S. Pregosin, J. Organo-
met. Chem. 1983, 243, 101.
[15] For a discussion of the preparation and characterization of a
related acylplatinum hydride of 1, see: J. J. Koh, W.-H. Lee, P. G.
Williard, W. M. Risen, Jr., J. Organomet. Chem. 1985, 284, 409.
[16] E. Shirakawa, H. Yoshida, T. Kurahashi, Y. Nakao, T. Hiyama, J.
Am. Chem. Soc. 1998, 120, 2975.
[17] It has been reported that Pd catalyzes the addition of organotin
reagents to aldehydes to give alcohols rather than ketones: H.
Nakamura, H. Iwama, Y. Yamamoto, J. Am. Chem. Soc. 1996,
118, 6641.
In summary, we have demonstrated that the appropriate
combination of two suitable and compatible metallic catalyst
systems provides a new possibility for the development of
novel synthetic methodologies that are difficult to carry out
with any single-catalyst systems. More detailed mechanistic
studies and further application of this cooperative catalysis
are now in progress.
Received: September 16, 2004
À
Keywords: C H activation · cooperative phenomena ·
homogeneous catalysis · palladium · ruthenium
.
[1] a) Transition Metals for Organic Synthesis (Eds.: M. Beller, C.
Bolm), Wiley-VCH, Weinheim, 1998; b) Applied Homogeneous
Catalysis with Organometallic Compounds (Eds.: B. Cornils,
W. A. Herrmann), Wiley-VCH, Weinheim, 2002.
Angew. Chem. Int. Ed. 2005, 44, 455 –457
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