A new family of tunable indolylphosphine ligands by one-pot assembly and their applications in Suzuki-Miyaura coupling of aryl chlorides

Article abstract of DOI:10.1021/jo801544w

(Chemical Equation Presented) This study describes a new class of indolylphosphine ligands, which can be easily accessed by a simple one-pot assembly from commercially available indoles, acid chlorides, and chlorophosphines. A combination of these three starting materials provides a high diversification of the ligand structure. The application of this ligand array in palladium-catalyzed Suzuki-Miyaura coupling reaction of aryl chlorides with arylboronic acids is described. A catalyst loading down to 0.01 mol % of Pd can be achieved.

Full text of DOI:10.1021/jo801544w

reaction of arylboronic acids and aryl halides is useful for the
construction of diversified biaryls, which have numerous ap-
plications in pharmaceutical, material, and agricultural chem-
istry.2
A New Family of Tunable Indolylphosphine
Ligands by One-Pot Assembly and Their
Applications in Suzuki-Miyaura Coupling of
Aryl Chlorides
The structure of the ligand has been recognized to signifi-
cantly influence the efficiency of cross-coupling processes.
Therefore, a strategic ligand modification with appropriate steric
and electronic diversity is crucial in dealing with problematic
and specific substrates in this area. The lore in the field is that
the effective palladium catalysts for C-C bond coupling
processes from aryl chlorides generally contain electron-rich
(enhancement of oxidative addition) and sterically bulky
(improvement of reductive elimination) phosphine ligands.
Novel ligand design was found to be important for a number
of considerable advancements. During the past decade, Beller,3
Buchwald,4 Fu,5 Hartwig,6 and other groups7 have contributed
a huge amount of work to the area of phosphine ligand design
and synthesis. Although significant progress has been made, the
scope of these reactions and ligand syntheses can still be
improved.
Chau Ming So, Chung Chiu Yeung, Chak Po Lau, and
Fuk Yee Kwong*
Open Laboratory of Chirotechnology of the Institute of
Molecular Technology for Drug DiscoVery and Synthesis and
Department of Applied Biology and Chemical Technology,
The Hong Kong Polytechnic UniVersity,
Kowloon, Hong Kong
bcfyk@inet.polyu.edu.hk
ReceiVed July 14, 2008
Phosphine ligands that possess a potential hemilabile coor-
dinating group have been studied in the past decade.8 In 1999,
Guram/Bei et al. reported active benzenoid P,O-type ligands
with an acetyl group for Suzuki-Miyaura cross-coupling
reactions of aryl chloride.9 A simlar ligand using ferrocenyl
(2) (a) King, A. O.; Yasuda, N. In Organometallics in Process Chemistry;
Larsen, R. D., Ed.; Springer-Verlag: Berlin, Heidelberg, 2004; pp 205-245. (b)
Miyaura, N. Top. Curr. Chem. 2002, 219, 11. (c) Suzuki, A. In Modern Arene
Chemistry; Astruc, D., Ed.; Wiley-VCH: Weinheim, 2002; pp 53-106. (d)
Suzuki, A. J. Organomet. Chem. 2002, 653, 54.
(3) For selected references, see: (a) Zapf, A.; Jackstell, R.; Rataboul, F.;
Reirmeier, T.; Monsees, A.; Fuhrmann, C.; Shaikh, N.; Dingerdissen, U.; Beller,
M. Chem. Commun. 2004, 38. (b) Harkal, S.; Rataboul, F.; Zapf, A.; Fuhrmann,
C.; Reirmeier, T.; Monsees, A.; Beller, M. AdV. Synth. Catal. 2004, 346, 1742.
(c) Zapf, A.; Beller, M. Chem. Commun. 2005, 431.
This study describes a new class of indolylphosphine ligands,
which can be easily accessed by a simple one-pot assembly
from commercially available indoles, acid chlorides, and
chlorophosphines. A combination of these three starting
materials provides a high diversification of the ligand
structure. The application of this ligand array in palladium-
catalyzed Suzuki-Miyaura coupling reaction of aryl chlo-
rides with arylboronic acids is described. A catalyst loading
down to 0.01 mol % of Pd can be achieved.
(4) For selected references, see: (a) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.;
Yin, J.; Buchwald, S. L. J. Org. Chem. 2000, 65, 1158. (b) Yin, J.; Rainka,
M. P.; Zhang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 1162. (c)
Nguyen, H. N.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2003, 125, 11818.
(d) Walker, S. D.; Barder, T. E.; Martinelli, J. R.; Buchwald, S. L. Angew. Chem.,
Int. Ed. 2004, 43, 1871. (e) Barder, T. E.; Walker, S. D.; Martinelli, J. R.;
Buchwald, S. L. J. Am. Chem. Soc. 2005, 127, 4685. (f) Billingsley, K. L.;
Anderson, K. W.; Buchwald, S. L. Angew. Chem., Int. Ed. 2006, 45, 3484. (g)
Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 3358. (h) Biscoe,
M. R.; Fors, B. P.; Buchwald, S. L. J. Am. Chem. Soc. 2008, 130, 6686.
(5) For selected references, see: (a) Littke, A. F.; Dai, C.; Fu, G. C. J. Am.
Chem. Soc. 2000, 122, 4020. (b) Netherton, M. R.; Dai, C.; Neuschu¨tz, K.; Fu,
G. C. J. Am. Chem. Soc. 2001, 123, 10099. (c) Kirchhoff, J. H.; Netherton,
M. R.; Hills, I. D.; Fu, G. C. J. Am. Chem. Soc. 2002, 124, 13662. (d) Kudo, N.;
Perseghini, M.; Fu, G. C. Angew. Chem., Int. Ed. 2006, 45, 1282.
(6) For selected references, see: (a) Stambuli, J. P.; Kuwano, R.; Hartwig,
J. F. Angew. Chem., Int. Ed. 2002, 41, 4746. (b) Kataoka, N.; Shelby, Q.;
Stambuli, J. P.; Hartwig, J. F. J. Org. Chem. 2002, 67, 5553. (c) Shen, Q.;
Hartwig, J. F. J. Am. Chem. Soc. 2006, 128, 10028. (d) Vo, G. D.; Hartwig,
J. F. Angew. Chem., Int. Ed. 2008, 47, 2127. (e) Shen, Q.; Ogata, T.; Hartwig,
J. F. J. Am. Chem. Soc. 2008, 130, 6586.
Palladium-catalyzed cross-coupling reactions have received
significant attention in the past decades and have become
extremely versatile protocols in organic synthesis for the
connection of electrophilic and organometallic fragments in the
formation of either carbon-carbon or carbon-heteroatom
bonds.1 In particular, the Suzuki-Miyaura cross-coupling
(7) For selected references, see: (a) Nishiyama, M.; Yamamoto, T.; Koie,
Y. Tetrahedron. Lett. 1998, 39, 617. (b) Li, G. Y. Angew. Chem., Int. Ed. 2001,
40, 1513. (c) Urgaonkar, S.; Nagarajan, M.; Verkade, J. G. Org. Lett. 2003, 5,
815. (d) Colacot, T. J.; Shea, H. A. Org. Lett. 2004, 6, 3731. (e) Brenstrum, T.;
Clattenburg, J.; Britten, J.; Zavorine, S.; Dyckx, J.; Robertson, A. J.; McNulty,
J.; Capretta, A. Org. Lett. 2006, 8, 103. (f) Dai, Q.; Gao, W.; Liu, D.; Kapes,
L. M.; Zhang, X. J. Org. Chem. 2006, 71, 3928. (g) Grasa, G. A.; Colacot, T. J.
Org. Lett. 2007, 9, 5489. (h) So, C. M.; Lau, C. P.; Kwong, F. Y. Org. Lett.
2007, 9, 2795. (i) So, C. M.; Zhou, Z.; Lau, C. P.; Kwong, F. Y. Angew. Chem.,
Int. Ed. 2008, 47, 6402.
(1) (a) de Meijere, A., Diederich, F., Eds. Metal-Catalyzed Cross-Coupling
Reactions, 2nd ed.; Wiley-VCH: Weinheim, 2004; Vols. 1 and 2. (b) Beller,
M.; Bolm, C., Transition Metals for Organic Synthesis, Building Blocks and
Fine Chemicals, 2nd ed.; Wiley-VCH: Weinheim, 2004; Vols. 1 and 2. (c)
Nigeshi, E., Ed. Handbook of Organopalladium for Organic Synthesis; Wiley-
Interscience: New York, 2002; Vols. 1 and 2. (d) Tsuji, J. Palladium Reagents
and Catalysts, 2nd ed.; Wiley: Chichester, 2004. (e) Yin, L.; Liebscher, J. Chem.
ReV. 2007, 107, 133. (f) Corbet, J.-P.; Mignani, G. Chem. ReV. 2006, 106, 2651.
(g) Roglans, A.; Pla-Quintana, A.; Moreno-Manas, M. Chem. ReV. 2006, 106,
4622. (h) Molander, G A.; Ellis, N. Acc. Chem. Res. 2007, 40, 275.
(8) For a review, see: (a) Kwong, F. Y.; Chan, A. S. C. Synlett 2008, 1440.
10.1021/jo801544w CCC: $40.75
Published on Web 09/09/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 7803–7806 7803

SCHEME 1. Strategic Design and Exploration of a Simple
and Easily Diversified Phosphine Ligand Family
SCHEME 2. Synthetic Pathways for the Indolyl Phosphine
Ligands
scaffold was also found be effective in coupling processes.10
Moreover, the X-ray crystal structures showed that the ferrocenyl
hemilabile ligands provided both P and O (from either acetyl10
or methoxy group)11 coordination to the palladium center. In
2004, Singer/Tom et al. reported a new sulfone type ligand
containing a hemilabile sulfonyl oxygen and a dialkylphosphino
group.12 Meanwhile, it has been reported that P,O-type ligands
with amido group are highly effective for the Suzuki-Miyaura
coupling of aryl chlorides and amination of aryl halides.13
Although a variety of ligands have been introduced, a rapid
assembly of structurally diverse ligand systems via simple
synthetic methods is still important for the development of
versatile catalysts for widespread applications in coupling
reactions. We speculate that a versatile ligand contains three
components: a main ligand skeleton, a phosphino group, and a
tunable frame. A combination of these three elements would
likely generate multifunctional ligand entities. In addition, the
target ligand will be even more attractive to the industry, if the
ligand synthesis is particularly straightforward. With these
rationales, we herein report our exploration and development
of a new class of indolylphosphine ligand (Scheme 1). The
beneficial features of this ligand family can be highlighted by
their one-pot synthesis and the ease of diversification. Upon
application of this key synthetic pathway, a library of ligands
(by cross-matching between the three principal components)
could be easily prepared by a simple one-pot assembly (Scheme
1).
of the hemilabile property15 of the bottom group should be
applicable toward stabilizing the metal center whenever
needed.16
To fulfill the above criteria, we chose the commercially
available and inexpensive indole as the basic scaffold (Scheme
2). The indole nitrogen was directly deprotonated by NaH, and
the sodium salt was subsequently reacted with different acid
chlorides giving a series of N-substituted indoles. The 2-H on
the indole ring is relatively acidic that could be effectively
abstracted by directed ortho-metalation (DoM)17 using n-BuLi.
Trapping the lithiated intermediate by a variety of ClPR2
generated a series of the corresponding indolylphosphines 2 in
good yields (Scheme 2). Notably, the above cascaded synthetic
steps can be performed as a one-pot procedure. The solid-state
crude product was simply purified by washing with methanol/
ethanol mixture without crystallization or tedious chromato-
graphic purification process. Particularly noteworthy is that this
class of ligand exhibits high air stability in both solid and
solution states.18
To test the effectiveness of the new ligands, the sterically
hindered 2-chloro-m-xylene was used as the benchmark sub-
strate. The indolylphosphine ligands 2a-e bearing the carbam-
oyl group were first examined in the Suzuki-Miyaura reaction
(Table 1). A catalyst loading of 0.05 mol % of Pd(OAc)2 was
initially applied in probing the ligand efficacy (Table 1). The
metal to ligand ratio, metal source and the catalytic activity of
ligand 2a-e were subsequently investigated using toluene as
the solvent and K3PO4 ·H2O as the base. Ligand 2a with a
diphenylphosphino moiety provided no conversion, while the
dicyclohexylphosphino analogue, 2b, gave better catalytic
activity (entries 1 and 2). Ligand 2c bearing a sterically
congested and electron-donating di-tert-butylphosphino moiety
showed a lower catalytic activity toward the coupling reaction.
Increasing the bulkiness of 2b and 2c (giving 2d and 2e,
respectively) by the addition of a methyl group to the indole
3-position decreased the catalytic activity of the ligands. Since
2b provided the highest catalytic activity in the coupling
reaction, it was selected to further optimize the reaction
We propose designing this new class of ligand based on
several strategic points: (1) the ligand synthetic route should
be straightforward; (2) the starting materials should be inex-
pensive and readily available; (3) the ligand synthesis should
eliminate the metal/halogen exchange (from either ArBr or ArI)
to have a better scope of atom economy;14 (4) the ligand
diversity and tuning should be easily accessible; (5) the potential
(9) (a) Bei, X. H.; Crevier, T.; Guram, A. S.; Jandeleit, B.; Powers, T. S.;
Turner, H. W.; Uno, T.; Weinberg, W. H. Tetrahedron Lett. 1999, 40, 3855. (b)
Bei, X.; Turner, H. W.; Weinberg, W. H.; Guram, A. S.; Peterson, J. L. J. Org.
Chem. 1999, 64, 6797.
(10) Teo, S.; Weng, Z.; Hor, T. S. A. Organometallics 2006, 25, 1199.
(11) Atkinson, R. C. J.; Gibson, V. C.; Long, N. J.; White, A. J. P.; Williams,
D. J. Organometallics 2004, 23, 2744.
(12) Singer, R. A.; Tom, N. J.; Frost, H. N.; Simon, W. M. Tetrahedron
Lett. 2004, 45, 4715.
(13) For benzamide derived phosphine ligands, see: (a) Kwong, F. Y.; Lam,
W. H.; Yeung, C. H.; Chan, K. S.; Chan, A. S. C. Chem. Commun. 2004, 1922.
(b) Chen, G. S.; Lam, W. H.; Fok, W. S.; Lee, H. W.; Kwong, F. Y Chem.
Asian J. 2007, 2, 306. For independent reports on a similar type ligand, see: (c)
Dai, W. M.; Li, Y. N.; Zhang, Y.; Lai, K. W.; Wu, J. L. Tetrahedron Lett. 2004,
45, 1999. (d) Dai, W. M.; Zhang, Y. Tetrahedron Lett. 2005, 46, 1377.
(14) For initial descriptions on atom economy, see: (a) Trost, B. M. Science
1991, 254, 1471. (b) Trost, B. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 259.
(15) For amide-type P,O-coordination to Pd center, see: Butts, C. P.; Crosby,
J.; Lloyd-Jones, G. C.; Stephen, S. C. Chem. Commun. 1999, 1707.
(16) Amatore, A.; Fuxa, A.; Jutand, A. Chem.sEur. J. 2000, 6, 1474.
(17) For reviews of DoM, see: (a) Whisler, M. C.; MacNeil, S.; Snieckus,
V.; Beak, P. Angew. Chem., Int. Ed. 2004, 43, 2206. (b) Snieckus, V. Chem.
ReV. 1990, 90, 879. (c) Clayden, J. Tetrahedron Organic Chemistry Series, Vol.
23, Orgranolithiums: SelectiVity for Synthesis; Pergamon: Oxford, 2002.
(18) There were no detectable phosphine oxide signal of this class of
indolylphosphine ligands from 31P NMR when the solid form ligand was stored
under air for a month or in a solution for at least 7 days. In contrast, P-t-Bu3 has
been shown to be oxidized in air within 2 h; see ref 4a.
7804 J. Org. Chem. Vol. 73, No. 19, 2008

TABLE 1. Optimization of the Reaction Conditions Using an
Array of Indolyl Phosphine Ligand 2a
TABLE 2. Palladium-Catalyzed Suzuki-Miyaura Coupling of
ArCla
entry
Pd:L
ligand
base
solvent
% yieldb
1
2
3
4
5
1:2
1:2
1:2
1:2
1:2
1:2
1:3
1:4
1:3
1:3
1:3
1:3
1:3
1:3
1:3
1:3
1:3
1:3
2a
2b
2c
2d
2e
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2f
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4
Cs2CO3
Na2CO3
CsF
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
K3PO4 ·H2O
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
THF
7
55
11
5
0
6c
26
80
76
51
39
2
82
>99
1
7
8
9
10
11
12
13
14
15
16
17
18
dioxane
DMF
THF
THF
THF
1
82
10
14
2g
2h
a Reaction conditions: Pd(OAc)2 (0.05 mmol, 0.05 mol %), ligand 2
(as indicated), ArCl (1.0 mmol), PhB(OH)2 (1.5 mmol), base (3.0
mmol), and solvent (3.0 mL) were stirred for 24 h at 100 °C under
nitrogen. b Calibrated GC yields were reported using dodecane as the
internal standard. c Pd2(dba)3 as the Pd source.
conditions. Upon investigating the metal/ligand ratio from 1:2
to 1:4, the ratio of 1:3 provided the highest yield. Several bases
were examined in the presence of ligand 2b. K3PO4 ·H2O and
CsF were found to be the best base of choice in this catalytic
system. K3PO4 ·H2O was finally chosen as the base for further
study of the coupling reaction due to economical aspect. Among
the commonly used organic solvents examined, THF gave the
best result.
To further expand the scope of these indolylphosphine
ligands, we additionally synthesized 2f and 2g by reacting the
sodium salt of indole with phenyl tert-butyl carbonate and
benzenesulfonyl chloride, respectively. The catalytic activity of
Pd-2f is comparable to that of Pd-2b in the coupling reaction,
whereas that of Pd-2g is significantly lower compared with
Pd-2b. On the other hand, by comparing the ligands 2b, 2d,
and 2h, either increasing the steric bulkiness through the addition
of methyl group at the indole 3-position or decreasing the steric
bulkiness through the replacement of the carbamoyl group by
methyl group would also decrease the catalytic activity of
Pd-2b. The highest catalytic activity of Pd-2b may be
explained by the optimum steric effect provided by the ligand
skeleton to the Pd metal center during the course of the coupling
reaction.
a Reaction conditions: ArCl (1.0 mmol), Ar′B(OH)2 (1.5 mmol),
K3PO4 ·H2O (3.0 mmol), Pd(OAc)2/L ) 1:3, and THF (3.0 mL) were
stirred for 24 h at 100 °C under nitrogen. b Isolated yields (two or more
runs).
A range of aryl chlorides were examined under the prelimi-
nary optimized reaction conditions (Table 2). Sterically hindered
aryl chlorides were coupled with arylboronic acid and vice versa
in excellent yields (entries 1 and 2). Although 0.05 mol % of
Pd was generally applicable for our catalysis, additional efforts
were placed to further optimize each entry. Functional groups
such as keto, aldehyde, ester, and nitriles were compatible under
these reaction conditions, and the catalyst loading ranged from
0.01-0.04 mol % of Pd were achieved (Table 2, entries 4-8,
10, and 11). Deactivated aryl chloride was coupled with boronic
acid in excellent yield (Table 2, entry 9).
Apart from functionalized aryl chlorides, the coupling of
heteroaryl chloride was also studied. Under low catalyst loading
conditions, 4 equiv of ligand was required to compete with the
nitrogen binding to the metal. The results show that the
heteroarylchloridesarealsoeffectivesubstrateforSuzuki-Miyaura
coupling (Table 3). In addition, preliminary study on the
coupling of alkylboronic acid with aryl chloride was successful
(Table 3, entry 8).
In summary, we have developed a new series of efficient
phosphine ligand 2. These ligands are easily accessible and could
J. Org. Chem. Vol. 73, No. 19, 2008 7805

TABLE 3. Palladium-Catalyzed Suzuki-Miyaura Coupling of
Experimental Section
Heteroaryl Chlorides with Aryl or Alkylboronic Acida
One-Pot, Two-Step Synthesis of Indolylphosphine Ligand
2b. Indole (585 mg, 5.0 mmol) was dissolved in anhydrous THF
(10 mL) and transferred dropwise to the THF (50 mL) solution
containing 1.1 equiv of NaH (60% in mineral oil, 220 mg, 5.5
mmol) at 0 °C. (Note: NaH was prewashed with dry hexane under
N2.) The mixture was stirred for 20 min at rt. After the mixture
was recooled to 0 °C, 1.1 equiv of N,N-diisopropylcarbamoyl
chloride (0.896 g, 5.5 mmol) in THF (10 mL) was added dropwise,
and the mixture was stirred at rt for 2 h. After the completion of
the reaction as confirmed by GC-MS analysis, the solution was
cooled to -78 °C in dry ice/acetone bath. Titrated n-BuLi (5.5
mmol) was added dropwise by a syringe. The reaction mixture was
further stirred for 1 h at -78 °C and chlorodicyclohexylphosphine
(1.32 mL, 6.0 mmol) was then added dropwise by a syringe. The
reaction was allowed to reach rt and stirred overnight. EtOH (∼10
mL) was added slowly to quench the reaction. Solvent was removed
under reduced pressure. Dichloromethane (∼200 mL) and water
(∼100 mL) were added to the mixture, and the organic phase was
separated. The aqueous phase was further extracted with dichlo-
romethane (∼100 mL × 2). The combined organic phases was
washed with brine, dried over MgSO4, and concentrated. After the
solvent was removed under vacuum, the product was successively
washed with cold ethanol. The product was then dried under
vacuum. The product 2b was isolated as a white solid (1.54 g, 70%):
mp192.1-193.8 °C; 1H NMR (400 MHz, CDCl3) δ 1.25-1.92 (m,
34H), 3.43 (m, 2H), 6.74 (s, 1H), 7.12-7.22 (m, 2H), 7.31 (d, J )
7.9 Hz, 1H), 7.62 (d, J ) 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3)
δ 20.5, 26.2, 27.2, 29.9, 30.0, 33.8, 109.7, 109.8, 110.3, 120.2,
120.4, 122.4, 127.9, 134.6, 134.8, 136.8, 136.9, 151.6 (unresolved
C-P couplings were observed); 31P NMR (162 MHz, CDCl3) δ
-22.08; IR (cm-1) 2992, 2922, 2848, 1685, 1492, 1431, 1368, 1327,
1206, 1155, 1119, 1060, 1027, 1000, 914, 884, 848, 824, 790, 751,
737, 669, 631, 610, 583, 538, 515, 482, 429; MS (EI) m/z (relative
intensity) 440 (M+, 6), 397 (53), 357 (100), 315 (32), 275 (11),
242 (35), 227 (40), 191 (23), 148 (76); HRMS calcd for
C27H41N2OPH+ 441.3035, found 441.3041.
a Reaction conditions: Het-ArCl (1.0 mmol), Ar′B(OH)2 (1.5 mmol),
K3PO4 ·H2O (3.0 mmol), Pd(OAc)2/L ) 1:4, and THF (3.0 mL) were
stirred for 24 h at 100 °C under nitrogen. b Isolated yields (two or more
runs). c Reaction conditions: ArCl (1.0 mmol), n-BuB(OH)2 (2.0 mmol),
K3PO4 ·H2O (3.0 mmol), Pd(OAc)2/L ) 1:3, and toluene (3.0 mL) were
stirred for 24 h at 100 °C under nitrogen.
Acknowledgment. We thank the Research Grants Council
of Hong Kong (CERG: PolyU5006/05P), PolyU (A-PG13), and
the University Grants Committee Areas of Excellence Scheme
(AoE/P-10/01) for financial support. Special thanks goes to Prof.
Albert S. C. Chan’s research group (HK PolyU) for sharing of
GC instruments.
be readily fine-tuned by cross-matching of the three components
via simple one-pot assembly of the commercially available
starting materials. Palladium complexes derived from these
ligands provide highly active catalysts for Suzuki-Miyaura
coupling of aryl chlorides. In view of the simplicity of the ligand
synthesis as well as the high ability in modifying the ligand
skeleton, we anticipate that further enhancements in reactivity
and versatility of the ligand series will be attainable.
Supporting Information Available: Detailed experimental
procedures, initial screening results, compound characterization
1
data, and copies of H NMR, 13C NMR, 31P NMR, and MS
spectra. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO801544W
7806 J. Org. Chem. Vol. 73, No. 19, 2008