An anionic rhodium η4-quinonoid complex as a multifunctional catalyst for the arylation of aldehydes with arylboronic acids

Article abstract of DOI:10.1021/ja0537981

The π-bonded rhodium quinonoid complex, K⁺[(1,4-benzoquinone)Rh(COD)]^-, functions as a good catalyst for the coupling of arylboronic acid and aldehydes to afford diaryl alcohols. The catalysis is heterobimetallic in that both the transition metal and concomitant alkali metal counterion play an integral part in the reaction. In addition, the anionic quinonoid catalyst itself plays a bifunctional role by acting as a ligand to the boronic acid and as a Lewis acid receptor site for the transferring aryl group. Copyright

Full text of DOI:10.1021/ja0537981

Published on Web 08/16/2005
4
An Anionic Rhodium η -Quinonoid Complex as a Multifunctional Catalyst for
the Arylation of Aldehydes with Arylboronic Acids
†
‡
‡
‡
Seung Uk Son, Sang Bok Kim, Jeffrey A. Reingold, Gene B. Carpenter, and
,
‡
Dwight A. Sweigart*
Department of Chemistry, Brown UniVersity, ProVidence, Rhode Island 02912, and Department of Chemistry,
Sungkyunkwan UniVersity, Suwon 440-746, Korea
Received June 9, 2005; E-mail: Dwight_Sweigart@Brown.edu
Complexes containing 1,4-hydroquinone (H
transition metal are rather few in number but of substantial interest
2
Q) π-bonded to a
Scheme 1. Deprotonation and Oxidation of Hydroquinone to
Quinone with the π-Bonded Metal Fragment Acting as an Internal
Electron Acceptor
because of the importance of quinonoid molecules in mediating
1
proton and electron transfer reactions. Hydroquinone has been
6
coordinated in an η -manner to the metal fragments Cr(CO)
3
, Mn-
+
2+
2,3
(
3
CO) , and Cp*M (M ) Rh, Ir). The key chemical property
displayed by these complexes is facile deprotonation of the -OH
groups, which is accompanied by electron transfer to the metal and
3
changes in the hapticity of the quinonoid ring. This is illustrated
6
+
-
4
in Scheme 1 for the new η -H
2
Q complex 1 BF
4
, synthesized in
with AgBF
4
7
4% isolated yield by the reaction of [Rh(COD)Cl]
2
+
-
and H
2
Q. 1 BF
4
cleanly undergoes deprotonation to afford stable
-
neutral semiquinone (2) and anionic quinone (3 ) complexes.
With a catalytically active metal, such as rhodium, it was thought
that the ability to alter the charge on the metal by reversible
deprotonation may constitute a simple way to tune catalytic activity.
Scheme 2. Catalytic Phenylation of Benzaldehydes
4
In addition, the anionic doubly deprotonated η -quinone complex
are the rhodium-catalyzed addition of arylboronic acids to alde-
-
may be able to function as a ligand (“organometalloligand”),5
3
9
10
hydes and the 1,4-addition of arylboronic acids to enones. The
results obtained for arylboronic acid addition to benzaldehydes as
catalyzed by rhodium quinone complexes are given in Table 1.
An inspection of the data in Table 1 shows some remarkable
behavior. From entries 1-6, it is concluded that the cationic
thereby offering the possibility of bifunctional activation with
appropriate substrates. Catalysts able to operate in a bifunctional
6
manner are of considerable current interest. Herein, it is demon-
+
-
strated that the hydroquinone complex 1 BF
4
is a convenient
+
-
precursor to M 3 , which serves as a catalyst for the coupling of
+
-
rhodium hydroquinone complex 1 BF
unless a base (KOH) is present. Addition of the neutral salt K BF
4
has no catalytic activity,
arylboronic acids and benzaldehydes to produce diaryl alcohols
+
-
4
+
-
(
Scheme 2). It is shown that M 3 acts in a multifunctional manner
has no effect (entry 5). It is concluded that the base likely functions
by simultaneously activating both the boronic acid and the aldehyde,
the former by coordination of a quinonoid oxygen in 3 to the boron
and the latter through a Lewis acid interaction among the aldehyde,
the counterion M , and a quinonoid oxygen.
to deprotonate the -quinonoid -OH groups. In agreement with
-
+ -
this, the anionic quinone complex K 3 was found to be a very
effective catalyst, giving high yields at 75 °C or higher temperatures.
Interestingly, the yield drops dramatically when a crown ether is
+
The X-ray structure of [(H
2
Q)Rh(COD)]BF
4
‚Et
2
O established
+ -
added to the reaction mixture or when K(18-C-6) 3 is used as
6
4
+
-
the anticipated η -bonding mode. Deprotonation of 1 BF with
KO Bu in THF occurred readily to afford the semiquinone (2) and
the quinone (K 3 ) analogues (Scheme 1). X-ray quality crystals
of K 3 could not be grown, but the butylammonium salt was
readily obtained by metathesis and its X-ray structure determined
N [(1,4-Q)Rh(COD)] ‚3 Bu
clearly indicated an η -bonding mode, with the quinone Rh-C
distances being ca. 0.2 Å greater for the C(O) carbons in comparison
to that of the other four quinone carbons. Deprotonation of 1 BF
with KO Bu in the presence of 18-crown-6 produced the salt K(18-
C-6) [(1,4-Q)Rh(COD)] ‚K(18-C-6)BF , in which each quinone
4
4
+ -
the catalyst in place of K 3 (entries 13 and 15). In a similar vein,
t
+
-
the activity is reduced by the inclusion of n-Bu
4
N BF
4
(entries
+ -
+
-
1
4 and 16). Likely related to this is the observation that Li 3 is
a more effective catalyst than K 3 , as indicated by entries 10 and
2 compared to 17 and 18. This behavior clearly signals hetero-
+
-
+ -
1
+
-
as Bu
4
4 4
NBF . The Rh-C bond lengths
11,12
bimetallic or dual function catalysis,
in which the alkali metal
4
+
+
Li or K enhances the electrophilic activation of the aldehyde
carbon by interacting with the carbonyl oxygen, thus facilitating
aryl transfer from the rhodium catalyst, as depicted in 4. This
hypothesis is in accord with the reduced reactivity that is found
4
+
-
4
t
+
-
when the alkali metal is chelated with a crown ether or is replaced
oxygen is linked to a crown ether encapsulated potassium ion
+
with the much larger n-Bu
4
N
ion.
(
Scheme 1).7
Entries 7 and 30-33 show that electron-withdrawing para-
The cross-coupling of organoborates and organic electrophiles
substituents on the aryl group in Ar′B(OH)
2
9a
hinder the reaction, as
8
has become an important synthetic tool in organic chemistry. While
palladium is often used as the transition metal in the catalyst for
this reaction, rhodium can also be effective. Especially noteworthy
has been found with other catalyst systems. Table 1 also indicates
that the catalytic conditions are tolerant of a wide range of aryl
substituents in the aldehyde reactant (entries 8 and 24-29).
Suzuki-Miyaura-type coupling reactions involving boronic acids
are usually facilitated by the presence of stoichiometric external
†
Sungkyunkwan University.
Brown University.
‡
12238
9
J. AM. CHEM. SOC. 2005, 127, 12238-12239
10.1021/ja0537981 CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Results of the Rhodium-Catalyzed Arylation of ArCHO
with Ar′B(OH)2 in Water Solvent
In conclusion, we have characterized a π-bonded rhodium
quinonoid complex that functions as a good catalyst for the coupling
of arylboronic acids and aldehydes. The catalysis is heterobimetallic
in that both the transition metal and concomitant alkali metal
counterion play an integral part in the reaction. In addition, the
anionic quinonoid catalyst itself plays a bifunctional role by acting
as a ligand to the boronic acid and as a Lewis acid receptor site for
the aryl group in the requisite transmetalation.
a
additives
(equiv)
T
time yield
b
entry
aldehyde
catalyst
(
°C) (h)
(%)
+
-
NRc
NR
NR
97
1
2
C
C
C
C
C
C
C
C
C
C
C
C
C
C
6
6
6
6
6
6
6
6
6
6
6
6
6
6
H
H
H
H
H
H
H
H
H
H
H
H
H
H
5
5
5
5
5
5
5
5
5
5
5
5
5
5
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
1 BF
4
none
none
none
95
95
75
3
3
3
3
3
d
+
-
-
-
-
-
1 BF
4
4
4
4
4
+
3
4
5
6
7
8
9
0
1
2
3
4
1 BF
+
1 BF
KOH (1.2)
75
+
+
-
4
1 BF
K BF
(1.2) 75
NR
+
1 BF
none
none
none
none
none
none
none
50 16 NR
+
-
K 3
95
75
60
50
3
3
3
3
96
93(90)
81
Acknowledgment. We are grateful to the donors of the
Petroleum Research Fund, administered by the American Chemical
Society, and to the National Science Foundation (CHE-0308640)
for support of this research.
+
-
-
-
-
-
-
-
K 3
+
K 3
+
1
1
1
1
1
K 3
48
+
K 3
50 16 84
25 16 19
+
K 3
+
K 3
18-C-6 (0.075) 75
3
3
14
24
Supporting Information Available: Experimental details, char-
acterization and crystallographic (CIF) data, which have also been
deposited with the Cambridge Crystallographic Data Center as registry
number CCDC 274874-274875. This material is available free of
charge via the Internet at http://pubs.acs.org.
+
+
-
4
K 3
n-Bu
4
N BF
75
(0.075)
+
-
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
C
6
C
6
C
6
C
6
C
6
C
6
C
6
C
6
C
6
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
K (18-C-6)3
none
none
none
none
none
none
75
75
50
3
3
3
13
2
96(91)
+
-
n-Bu
4
-
N 3
+
Li 3
+
-
Li 3
25 16 40
75
75
[Rh(COD)Cl]
[Rh(COD)] BF
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
NR
NR
1
99
References
+
-
4
+
-
[Rh(COD)
[Rh(COD)
none
2
] BF
4
4
KOH (0.025) 75
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Ebadi, M.; Lever, A. B. P. Inorg. Chem. 1999, 38, 467. (c) Coenzyme Q:
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+
-
2
] BF
KOH (1.2)
KOH (1.2)
none
none
none
none
none
none
none
75
75
75
75
75
75
75
75
75
75
75
75
NR
+
-
-
-
-
-
-
-
-
-
-
4-MeOC
2,4,6-Me
4-MeC
4-ClC
4-PhC
4-O NC
6
H
4
CHO
K 3
81(78)
69(68)
99(97)
99(97)
98(93)
99(92)
96(91)
94(90)
20
(
2) (a) Huang, Y.-S.; Sabo-Etienne, S.; He, X.-D.; Chaudret, B. Organome-
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+
3
C
H
6 2
CHO K 3
+
6
H
4
CHO
CHO
CHO
CHO
K 3
+
6
H
4
K 3
+
6
H
4
K 3
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+
2
6
H
4
K 3
e
f
+
C
C
C
C
6
6
6
6
H
5
5
5
5
CHO
CHO
CHO
CHO
K 3
+
H
H
H
K 3
none
none
none
g
h
+
K 3
(
e) Fairhurst, G.; White, C. J. Chem. Soc., Dalton Trans. 1979, 1531.
+
K 3
2
(
4) See Supporting Information for details.
(
5) The ability of a quinone complex to function as an organometalloligand
a
has been demonstrated in the case of (η -benzoquinone)Mn(CO) . See:
4
-
Conditions: 2 mL of water, 0.025 mmol of catalyst, 1.0 mmol of
3
Oh, M.; Carpenter, G. B.; Sweigart, D. A. Acc. Chem. Res. 2004, 37, 1.
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b
d
c
(6) (a) Casey, C. P.; Johnson, J. B.; Singer, S. W.; Cui, Q. J. Am. Chem. Soc.
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Yield determined by NMR; isolated yields in parentheses. No reaction.
e
f
Solvent was p-dioxane (2 mL). Ar′ ) 4-MeOC6H4B(OH)2. Ar′ )
-MeC6H4B(OH)2. Ar′ ) 4-ClC6H4B(OH)2. Ar′ ) 4-O2NC6H4B(OH)2.
3
0, 97. (c) Josephsohn, N. S.; Kuntz, K. W.; Snapper, M. L.; Hoveyda,
g
h
4
A. H. J. Am. Chem. Soc. 2001, 123, 11594. (d) Mermerian, A. H.; Fu, G.
C. J. Am. Chem. Soc. 2003, 125, 4050.
base (e.g., compare entries 20 and 22).8-10 It has been debated
(7) X-ray data for this salt were (to date) of only moderate quality, but
nevertheless sufficient to establish the connectivity shown.
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boron to the transition metal catalyst by binding to the former or
by binding to the latter. Recent theoretical studies suggest that the
(
8) (a) Suzuki, A. Acc. Chem. Res. 1982, 15, 178. (b) Miyaura, N.; Suzuki,
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3
279. (b) Ueda, M.; Miyaura, N. J. Org. Chem. 2000, 65, 4450. (c)
-
hard base OH functions by binding to the electrophilic boron, and
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Darses, S.; Genet, J.-P. J. Am. Chem. Soc. 2004, 126, 15356.
13
that this increases the rate of subsequent transmetalation. The data
(
10) (a) Takaya, Y.; Ogasawara, M.; Hayashi, T. J. Am. Chem. Soc. 1998,
+
-
+ -
in Table 1 show that K 3 and Li 3 are effective catalysts without
120, 5579. (b) Batey, R. A.; Thadani, A. N.; Smil, D. V. Org. Lett. 1999,
1, 1683. (c) Ramnauth, J.; Poulin, O.; Bratovanov, S. S.; Rakhit, S.;
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J.; Feringa, B. L. J. Org. Chem. 2004, 69, 8045.
-
that the 3 complex itself functions as the base by binding to the
14
boron via the quinonoid oxygens, possibly as depicted in 5. The
ability of the quinone ring system to undergo facile hapticity
4
5
-
changes (η f η , etc.) may play a role in the ability of 3 to
function as an organometalloligand in this manner. We conclude
-
(11) Sammis, G. M.; Danjo, H.; Jacobsen, E. N. J. Am. Chem. Soc. 2004, 126,
that catalyst 3 is able to act in a bifunctional (and cooperative)
9
928.
manner as has recently been suggested for other types of catalytic
(
12) (a) Shibasaki, M.; Yoshikawa, N. Chem. ReV. 2002, 102, 2187. (b)
6
-
Yamagiwa, N.; Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc. 2003,
reactions. In the present case, the binding of 3 to the boronic
acid assists the transmetalation step by decreasing the electrophi-
licity of the boron and by placing the transition metal in the vicinity
of the transferring group (Ar′).15
1
25, 16178. (c) Li, C.; Eidjaja, E.; Garland, M. J. Am. Chem. Soc. 2003,
25, 5540. (d) Guo, N.; Li, L.; Marks, T. J. J. Am. Chem. Soc. 2004, 126,
1
6542. (e) Comte, V.; Le Gendre, P.; Richard, P.; Mo ¨ı se, C. Organome-
tallics 2005, 24, 1439.
(
(
(
13) Braga, A. A. C.; Morgon, N. H.; Ujaque, G.; Maseras, F. J. Am. Chem.
Soc. 2005, 127, ASAP.
14) 1H NMR spectra of PhB(OH)
in D
indicate that an interaction occurs.
O with and without K+3- present
2
2
15) It should be noted that some Rh-catalyzed Suzuki-Miyaura couplings
with suitable phosphine ligands do not require stoichiometric external
9
a,b
base.
JA0537981
J. AM. CHEM. SOC.
9
VOL. 127, NO. 35, 2005 12239