Room-Temperature Ni(0)-Catalyzed Cross-Coupling Reactions of Aryl Arenesulfonates with Arylboronic Acids

Article abstract of DOI:10.1021/ja038752r

Room-temperature Ni(0)-catalyzed cross-coupling reactions of aryl arenesulfonates with arylboronic acids are described. The Ni(0) catalyst, derived from Ni(COD)₂ and PCy₃, proved to be a general one for the Suzuki?Miyaura cross-coupling of a variety of aryl arenesulfonates. The mild reaction condition, the readily availability of the catalyst, and excellent coupling yields make aryl arenesulfonates potentially useful substrates in organic synthesis. Copyright

Full text of DOI:10.1021/ja038752r

Published on Web 02/21/2004
Room-Temperature Ni(0)-Catalyzed Cross-Coupling Reactions of Aryl
Arenesulfonates with Arylboronic Acids
Zhen-Yu Tang and Qiao-Sheng Hu*
Department of Chemistry, College of Staten Island and the Graduate Center of the City UniVersity of New York,
Staten Island, New York 10314
Received September 26, 2003; E-mail: qiaohu@postbox.csi.cuny.edu
Table 1. Room-Temperature Pd(0) and Ni(0)-Catalyzed
The Suzuki-Miyaura coupling reactions of aryl halides/triflates
with arylboronic acids are among the most powerful transformations
Cross-Couplings of p-Tolyl Tosylate with Phenylboronic Acida
in organic synthesis.1 Although remarkable progress has been made
in employing very inert, widely available aryl chlorides as coupling
partners in Suzuki-Miyaura coupling reactions including conduct-
ing the reactions at room temperature during the past years,2,3 very
limited success has been realized for widely available aryl arene-
sulfonates,4-9 a large family of synthetic materials that are readily
accessible from phenols and cheap arenesulfonyl chlorides. To date,
only few reports have appeared, and the reported systems have re-
quired either the use of lithium arylborates4 or elevated reaction
temperature (80 or 130 °C).5-7 To our knowledge, aryl arenesulfo-
nates have not been established as synthetically useful substrates
for the Suzuki-Miyaura couplings under mild conditions. In view
of their easier preparation, increased stability, and less expense
relative to aryl triflates, it is of great interest to develop general
protocols to employ aryl arenesulfonates as coupling partners for
Pd(0)- and Ni(0)-catalyzed Suzuki-Miyaura cross-coupling reac-
tions under mild reaction conditions. Herein, we disclose the room-
temperature Ni(0)-catalyzed cross-coupling reactions of aryl are-
nesulfonates with arylboronic acids.
At the outset of our research, we recognized that aryl arene-
sulfonates are structurally different from aryl halides: they contain
C-O bonds that undergo oxidative addition as compared to C-Cl
bonds for aryl chlorides. This structural difference implies that cat-
alyst systems that work well for the room-temperature cross-
couplings of aryl chlorides may not work for the room-temperature
Suzuki-Miyaura couplings of aryl arenesulfonates. Our initial ex-
periments unsurprisingly showed that catalysts derived from
Pd(0) and monophosphines including Buchwald’s arylphosphines10
were ineffective for the coupling of p-tolyl tosylate with phenyl-
a Reaction conditions: tolyl tosylate (1.0 equiv), phenylboronic acid (1.5
boronic acid at room temperature (Table 1, entries 1-3). It has
been established that the Ni(0) species, in situ generated from
Ni(PCy3)2Cl2, underwent oxidative addition with aryl tosylates at
130 °C.5 Our study on the room-temperature cross-coupling of
p-tolyl tosylate with phenylboronic acid suggested that Ni(PCy3)2Cl2
and Ni(PCy3)2Cl2/Zn were inefficient catalysts likely because of
their ineffectiveness to generate catalytically active Ni(0) species
under the reaction conditions (Table 1, entries 4, 5). We have thus
focused on using Ni(COD)2 as catalyst precursor for the develop-
ment of general catalysts that can effect the room-temperature
Suzuki-Miyaura couplings of aryl arenesulfonates. A number of
phosphines have been screened, and the results are summarized in
Table 1. As shown in Table 1, less electron-rich triarylphosphines
(PPh3, P(o-tolyl)3) and bidentate DPPF and DPPE were poor
ligands, and low conversions of p-tolyl tosylate were observed
(<20%). Electron-rich tri-tert-butylphosphine and Buchwald’s
arylphosphines were also ineffective ligands. Electron-rich but less
sterically hindered tri-n-butylphosphine and tri-i-butylphosphine
were more efficient ligands, and moderate conversions were
observed. Tricyclohexylphosphine was found to be an excellent
equiv), K3PO4 (3 equiv), THF (2 mL). b Reaction time: 6 h.
ligand for this coupling, suggesting that both the electron-richness
and the size of the phosphine ligand play important roles in the
catalyst system. Further study established that catalysts generated
from a 1:3 to 1:4 ratio of Ni(COD)2 and PCy3 were the most
efficient, and the reaction went to completion in 6 h. Among the
solvents and bases screened, THF was the best solvent, and K3PO4
and K2CO3 were the best choice of bases (Table 2).
A variety of aryl arenesulfonates and arylboronic acids have thus
been examined for the room-temperature Ni(0)-catalyzed cross-
coupling reactions using the optimized catalyst system, and the
results are summarized in Table 3. As shown in Table 3, the Ni-
(0)/PCy3 system proved to be a general catalyst for both activated
and deactivated aryl arenesulfonates, including those with ortho-,
meta-, and para-substituents. Complete conversion and excellent
isolated yields were observed for all aryl arenesulfonates employed.
p-Methoxyphenyl benzenesulfonate was slightly less reactive than
aryl tosylates, and reactions involving it as coupling partner required
12 h to go to completion (Table 3, entries 14, 16).
9
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10.1021/ja038752r CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
Table 2. Solvent and Base Effects in Room-Temperature
Ni(0)-Catalyzed Suzuki-Miyaura Cross-Couplings of p-Tolyl
Tosylatea
mediate suggested that the oxidative addition should not be slower
than the transmetalation/reductive elimination steps. Why the oxida-
tive addition occurred faster in the presence of PhB(OH)2 and base
remains unclear at present11 and is worthy of further investigation.
In summary, we have demonstrated for the first time that readily
available aryl arenesulfonates can be employed as coupling partners
for room-temperature Suzuki-Miyaura cross-couplings in general.
The catalyst system, derived from Ni(COD)2 and PCy3, represents
the first general palladium or nickel catalyst system that can catalyze
the Suzuki-Miyaura couplings of aryl arenesulfonates at room
temperature. Because several other cross-coupling reactions such
as the Kumada coupling and the Negeshi coupling are believed to
furnish the products via the same oxidative addition intermediate
as the Suzuki-Miyaura couplings,12 aryl arenesulfonates may also
be suitable coupling partners for these cross-couplings at room
temperature. Efforts toward this direction are underway.
entry
solvent
base
conv (%) entry solvent
base
conv (%)
1
2
3
4
5
benzene-d6 K3PO4
46
30
32
72
54
6
7
8
9
THF K2CO3
THF Na2CO3
THF KOH
61
27
0
dioxane
toluene
THF
K3PO4
K3PO4
K3PO4
KF
THF Cs2CO3
9
THF
a Reaction conditions: tolyl tosylate (1.0 equiv), phenylboronic acid (1.5
equiv), base (3 equiv), solvent (2 mL), room temperature.
Table 3. Room-Temperature Ni(0)-Catalyzed Cross-Couplings of
Aryl Arenesulfonates with Arylboronic Acidsa
Acknowledgment. This work was supported by the Department
of Chemistry, College of Staten Island-CUNY. Partial support from
PSC-CUNY Research Award Programs is gratefully acknowledged.
Supporting Information Available: Experimental procedure and
data for Ni(COD)2/PCy3-catalyzed cross-coupling of aryl arene-
sulfonates (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
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addition intermediate with 67% conversion of the tosylate within
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diate completely converted to the cross-coupling product in 1 h
when mixed with PhB(OH)2 and K3PO4. Interestingly, when
p-MeOPhOTs, Ni(COD)2 (1 equiv), PCy3 (4 equiv), PhB(OH)2 (1.5
equiv), and K3PO4 (3 equiv) were mixed in THF-d8 at room tem-
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