Palladium catalyzed Suzuki coupling reactions using cobalt-containing bulky phosphine ligands

Article abstract of DOI:10.1016/j.tet.2004.01.071

Three bulky mono-dentate alkyne-bridged dicobalt-phosphine complexes [(μ-PPh₂CH₂PPh₂)Co₂(CO) ₄](μ,η-PhC≡CPPh₂) 4a, [(μ-PPh ₂CH₂PPh₂)Co₂(CO)₄

Full text of DOI:10.1016/j.tet.2004.01.071

Tetrahedron 60 (2004) 2639–2645
Palladium catalyzed Suzuki coupling reactions using
cobalt-containing bulky phosphine ligands
*
Fung-E Hong, Yi-Jung Ho, Yu-Chang Chang and Yi-Chun Lai
Department of Chemistry, National Chung-Hsing University, Taichung 40227, Taiwan, ROC
Received 23 October 2003; revised 6 January 2004; accepted 8 January 2004
Abstract—Three bulky mono-dentate alkyne-bridged dicobalt-phosphine complexes [(m-PPh2CH2PPh2)Co2(CO)4](m,h-PhCuCPPh2) 4a,
[(m-PPh2CH2PPh2)Co2(CO)4](m,h-Me3CCuCPPh2) 5a and [(m-PPh2CH2PPh2)Co2(CO)4](m,h-Me3SiCuCPPh2) 6a were prepared from
the reactions of the bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex Co2(CO)6(m-Ph2PCH2PPh2) with PhCuCPPh2 1,
Me3CCuCPPh2 2, and Me3SiCuCPPh2 3, respectively. These three metal-containing compounds 4a, 5a and 6a were employed as ligands,
replacing conventional organic phosphines, in the Suzuki cross-coupling reactions and have been proved to be effective, authentic mono-
dentate phosphine ligands.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
family of bulky phosphines, i.e., cobalt-containing phos-
phine ligands. The electron-donating capacities of the
ligands are expected to be varied after adding cobalt
fragment onto the organic moieties. These mono/bi-dentate
phosphine ligands can be prepared starting from Co2(CO)8
with alkynyl phosphines, having the formula of RCuCPPh2
or Ph2PCuCPPh2.9
Many studies have been focused on Suzuki’s palladium-
catalyzed cross-coupling reaction in recent years because of
its exceptional competence in making sp2–sp2 carbon–
carbon bond.1 After several successful methodologies, still a
great deal of efforts have been made on promoting the
catalytic efficiency with the diversity by the ways of the
modification of phosphine ligands,2 the development of
recyclable catalyst3 and the application to aliphatic electro-
philes.4 It is well known that phosphine ligands play an
important role in metal complexes catalyzed organic
syntheses. Suitable phosphine ligands are always
indispensable for their effective catalytic performance.5 As
established, the mechanism of the palladium-catalyzed
cross-coupling reaction involves both oxidative addition
and reductive elimination processes.6 A phosphine with
either electron-rich or bulky character is presumed to be
able to accelerate the reaction rate and perceived as a
potential candidate for an effectively catalytic perform-
ance.7 Although a variety of organic phosphines have
already been proved to be efficient in palladium-catalyzed
processes, to our best knowledge, only few communications
over metal-containing phosphine ligand were published
lately.8
Palladium-catalyzed Suzuki cross-coupling reactions of aryl
halides with arylboronic acids represent one of the most
powerful transformations in organic synthesis.1b,c,10 In this
work, we report some remarkable results of using new type
of cobalt-containing mono-dentate phosphine ligands in
Suzuki type catalytic coupling reactions. The efficiencies of
these ligands are compared and discussed subsequently.
2. Results and discussion
2.1. Preparations of cobalt-containing phosphine ligands
Treatment of
a dppm-bridged dicobalt compound
[Co2(CO)6(m-P,P–PPh2CH2PPh2)] with one molar
equivalent of alkynyl phosphines R1CuCPPh2 (1: R1¼Ph;
2: R1¼CMe3; 3: R1¼SiMe3) in THF at 45 8C afforded
alkyne-bridged dicobalt compounds [(m-PPh2CH2PPh2)-
Co2(CO)4][m,h-R1CuCPPh2] (4a: R1¼Ph; 5a: R1¼CMe3;
6a: R1¼SiMe3).11 (Scheme 1). In addition, two
oxidized complexes, [(m-PPh2CH2PPh2)Co2(CO)4](m,h-
PhCuCP(uO)Ph2) 4b and [(m-PPh2CH2PPh2)Co2(CO)4]-
(m,h-Me3CCuCP(uO)Ph2) 5b, were also obtained along
with 4a and 5a during the chromatographic processes.
Compounds 4a, 4b, 5a and 5b were characterized by
In our efforts in searching effective ligands for transition
metal-catalyzed reactions, we are interested in developing a
system that will allow us to straightforward access of a
Keywords: Bulky phosphine; Cobalt-complex; Homogeneous catalysis;
Palladium; Suzuki reaction.
*
Corresponding author. Fax: þ886-4-22862547;
e-mail address: fehong@dragon.nchu.edu.tw
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.01.071

2640
F.-E Hong et al. / Tetrahedron 60 (2004) 2639–2645
Scheme 1. Synthesis of cobalt-containing phosphine ligands.
spectroscopic means as well as by X-ray diffraction methods
(Tables 1 and 2).
Similar observations are perceived for the cases of 4b and
5b. The 31P NMR spectrum of 4b shows two singlets in the
ratio of 2:1 at 35.7 and 28.4 ppm, respectively, for three
phosphorous atoms; while the matching signals are
observed at 35.8 and 28.2 ppm, respectively, for 5b. Large
downfield shifts are observed for the oxidized phosphorous
atoms. In H NMR, a large downfield shift for one of the
methylene protons at 5.94 is observed for 4b, while the
matching signal is observed at 6.05 ppm for 5b.
The 31P NMR spectrum of 4a displays two sets of singlet in
the ratio of 2:1 at the chemical shifts of 37.5 and 6.8 ppm
respectively for three phosphorous atoms. The correspond-
ing signals are 34.7, 26.2 ppm and 34.7, 211.3 ppm for 5a
and 6a, respectively. The upfield and downfield signals are
assigned to the corresponding unbounded and coordinated
phosphorous atoms respectively in all cases. The observed
large discrepancies in chemical shifts of all three
compounds in 31P NMR for the unbounded phosphorous
atoms is attributed to the slight difference in electron-
donating capacities of these phosphorous atoms. In 1H
NMR, there are two distinct chemical shifts 3.32 and
4.25 ppm as well as 3.15 and 4.85 ppm are being observed
for the methylene protons of 5a and 6a, respectively. Yet,
only one set of triplet signal at 3.25 ppm is found for the
matching protons in 4a. It had demonstrated that the signal’s
outward appearance of the bridged dppm is greatly affected
by the degree of its fluxional motion around the dicobalt
1
The selected bond distances and angles for 4a, 4b, 5a and 5b
are displayed in the ORTEP diagrams presented in
Figures 1–4. As presented in the figures, the phenyl rings
of the bridged alkyne in all cases are pointed away from the
center of the molecule to prevent severe steric hindrance.
All of the coordinated carbonyl ligands are situated at the
terminal positions. Interestingly, the coordinated dppm
ligand and the substituent –PPh2 are located on the same
side of molecule in 5a, while they are on the opposite side in
4a. It can be expected due to the result of minimizing the
steric effect among all the bulky groups. In the cases of 4b
and 5b, the coordinated dppm ligand and the substituent
–P(vO)Ph2 are positioned on the same side of molecule.
The structures of 4b and 5b showed the oxygen atom (of the
1
framework.9 Based on the H NMR spectra, we conclude
that the fluxional motion of the bridged dppm is much faster
in 4a than that of 5a and 6a.
Table 1. Crystal data of 4a, 4b, 5a and 5b
Compound
4a
4b
5a
5b
Formula
C49H37Co2O4P3·CH2Cl2
985.48
C49H37Co2O5P3
916.56
C47H41Co2O4P3·CHCl3
998.93
C47H41Co2O6P3
912.57
Triclinic
P-1
11.2292(10)
12.1443(10)
17.4801(16)
96.014(2)
96.402(2)
112.343(2)
2162.8(3)
2
1.401
0.71073
0.926
1.84 to 26.02
1753
531
0.0574
0.1081
0.853
Formula weight
Crystal system
Space group
Monoclinic
P2(1)/c
13.0444(14)
19.232(2)
18.983(2)
90(3)
101.294(2)
90(2)
4670.0(9)
4
1.402
0.71073
0.971
1.52 to 26.05
1437
550
0.0592
0.1149
0.828
Monoclinic
P2(1)/n
18.431(3)
11.5373(17)
21.411(3)
90
111.955(2)
90
4222.7(10)
4
1.442
0.71073
0.947
2.04 to 25.99
4760
540
0.0319
0.0826
0.518
Monoclinic
P2(1)/n
23.425(3)
9.3966(13)
23.702(3)
90
118.080(3)
90
4603.0(11)
4
1.441
0.71073
1.402
1.68 to 26.02
2984
541
0.0735
0.2001
0.895
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
V (A )
Z
Dc (Mg/m3)
l (Mo Ka), A
˚
m (mm21
u range (8)
)
Observed reflections (F.4s(F))
No. of refined parameters
R1 for significant reflectionsa
wR2 significant reflectionsb
GoFc
P
P
a
b
c
R1 ¼ l ðlFol 2 lFclÞ=l Foll:
P
P
wR2 ¼ { ½wðFo2 2 Fc2Þ = ½wðFo2Þ }}1=2; w ¼ 0:0588; 0.1009, 0.1508 and 0.0509 for 4a, 4b, 5a and 5b, respectively.
2
2
P
GoF ¼ ½ wðFo2 2 Fc2Þ =ðNrflns 2 NparamsÞꢀ
:
2
1=2

F.-E Hong et al. / Tetrahedron 60 (2004) 2639–2645
Table 2. Comparison of selected structural parameters of 4a, 4b, 5a and 5b
Compound
2641
4a
4b
˚
Bond lengths (A)
Co(1)–C(2)
Co(1)–C(1)
Co(1)–P(2)
Co(1)–Co(2)
Co(2)–C(1)
Co(2)–C(2)
Co(2)–P(3)
P(1)–O(1)
P(1)–C(1)
P(2)–C(49)
P(3)–C(49)
C(1)–C(2)
C(2)–C(3)
1.945(8)
1.996(8)
2.242(3)
2.4711(16)
1.945(8)
1.961(8)
2.225(2)
1.966(2)
1.974(2)
2.2358(8)
2.4851(5)
1.952(2)
1.968(2)
2.2524(7)
1.5022(19)
1.774(2)
1.843(3)
1.841(2)
1.361(3)
1.474(3)
1.770(8)
1.855(7)
1.810(8)
1.371(10)
1.485(10)
Bond angles (8)
C(2)–Co(1)–C(1)
P(2)–Co(1)–Co(2)
C(1)–Co(2)–C(2)
P(3)–Co(2)–Co(1)
C(49)–P(2)–Co(1)
C(49)–P(3)–Co(2)
C(2)–C(1)–P(1)
Co(2)–C(1)–Co(1)
C(1)–C(2)–C(3)
Co(1)–C(2)–Co(2)
P(3)–C(49)–P(2)
40.7(3)
94.05(7)
41.1(3)
100.44(8)
111.8(3)
109.8(3)
140.8(6)
77.6(3)
40.42(10)
96.81(2)
40.62(10)
96.79(2)
110.00(9)
109.86(9)
139.1(2)
78.54(9)
142.4(2)
78.36(9)
109.94(12)
137.1(7)
78.5(3)
112.2(4)
Figure 1. ORTEP drawing of 4a. Hydrogen atoms are omitted for clarity.
effect of the intramolecular hydrogen bonding plays a
crucial role in the arrangement of two bulky groups, dppm
and –P(vO)Ph2, in 4b and 5b ligands. The bond lengths of
the bridged alkynes are 1.371(10), 1.361(3), 1.340(10) and
5a
5b
˚
Bond lengths (A)
Co(1)–C(2)
Co(1)–C(1)
Co(1)–P(2)
Co(1)–Co(2)
Co(2)–C(1)
Co(2)–C(2)
Co(2)–P(3)
P(1)–O(1)
P(1)–C(1)
P(2)–C(47)
P(3)–C(47)
C(1)–C(2)
C(2)–C(3)
1.965(7)
2.006(7)
2.235(2)
2.4621(15)
1.994(8)
1.991(8)
2.240(2)
1.984(5)
1.967(5)
2.2533(16)
2.4715(11)
1.998(5)
1.966(6)
2.2328(16)
1.489(4)
1.772(5)
1.817(6)
1.814(5)
1.357(7)
1.511(7)
˚
1.357(7) A for 4a, 4b, 5a and 5b, respectively, which are
close to the regular double bond range. The bond length
values between two cobalt atoms are very close in all the
ligands. They are 2.4711(16), 2.4851(5), 2.4621(15) and
˚
2.4715(11) A for 4a, 4b, 5a and 5b, respectively.
1.780(8)
1.815(8)
1.831(7)
1.340(10)
1.534(10)
2.2. Suzuki reaction using cobalt-containing phosphine
ligands 4a, 5a and 6a with Pd complexes
Suzuki type coupling reactions for arylbromide and
phenylboronic acid were carried out by employing the
newly made cobalt-containing phosphine ligands 4a, 5a and
6a. The catalytic reaction is performed according to Wolfe’s
procedures.7d Table 3 summarizes the reaction conditions
and results.
Bond angles (8)
C(2)–Co(1)–C(1)
P(2)–Co(1)–Co(2)
C(1)–Co(2)–C(2)
P(3)–Co(2)–Co(1)
C(47)–P(2)–Co(1)
C(47)–P(3)–Co(2)
C(2)–C(1)–P(1)
Co(2)–C(1)–Co(1)
C(1)–C(2)–C(3)
Co(1)–C(2)–Co(2)
P(3)–C(47)–P(2)
39.4(3)
95.41(7)
39.3(3)
98.65(7)
111.8(2)
110.1(2)
154.7(6)
76.0(3)
40.15(19)
97.68(5)
40.0(2)
95.59(5)
109.32(19)
109.8(2)
144.6(4)
77.10(18)
144.0(5)
77.45(19)
111.4(3)
The cross-coupling reaction of phenylboronic acid with
2-bromothiophene was carried out by employing 1 mol% Pd
catalyst (Pd/ligand¼1/2) at the reaction temperature of
50 8C for 19 h. The yields are 33 and 42% using 4a and 5a as
ligands, respectively (entries 1 and 2). These yields are
improved to 63 and 75% by raising the temperature to 80 8C
and reacting for 16 h (entries 3 and 4). The highest yields 86
and 91% are obtained for 4a and 5a ligands, when these
reactions were carried out at 100 8C and for 16 h in toluene
as solvent (entries 5 and 6). Under similar conditions, the
yield is 87% using 6a as phosphine ligand (entry 7). The
results show that these cobalt-containing mono-dentate
phosphines are efficient ligands for the Suzuki reactions.
Similarly, the cross-coupling reaction was carried out for a
less reactive substrate, aryl bromide, under the identical
reaction conditions. Initially, the yield was poor (#29%) in
146.6(7)
77.0(3)
111.6(4)
oxidized phosphorus) points down toward the adjacent
proton of the methylene. The distances between the oxygen
˚
and hydrogen atoms are 2.464 and 2.215 A for 4b and 5b,
respectively, which are within the normal range of hydrogen
bonding.12 The shorter bond distance in 5b than 4b is caused
by the stronger repulsive force arose from the much bulkier
–tBu group from the back. The presumption of an
intramolecular hydrogen bonding between the oxide and
the adjacent methylene proton is also evidenced by the
1
observation of a large downfield shift in H NMR at 5.94
and 6.05 ppm for 4b and 5b, respectively. Consequently, the

2642
F.-E Hong et al. / Tetrahedron 60 (2004) 2639–2645
Figure 2. ORTEP drawing of 4b. Some carbon and hydrogen atoms are omitted for clarity.
the absence of any phosphine ligand (entry 8). On the other
hand, much better yields ($91%) were observed when 4a,
5a and 6a were employed as ligands (entries 9–11). These
results are comparable to the data reported by Gladysz et al.
using CpRu(PEt3)2PPh2 as catalyst.8c It clearly shows that
all these three compounds are competent phosphine ligands
with fairly good activity in Suzuki reaction. Almost
complete conversions were obtained using 4-bromo-
benzaldehyde as substrate, which is in consistence with
the common observation for an aryl halide with an electron-
withdrawing substituent8g (entries 12–14). The results
observed in Table 2 echoes the observations of Buchwald
and Fu stating that a phosphine ligand with a bulky –tBu as
substituent is more efficient than with a less bulky –Ph.2,7d
3. Summary
We have demonstrated the preparations and reactivity
studies of three new organometallic phosphine ligands 4a,
5a and 6a designed for the palladium-catalyzed Suzuki
cross-coupling reaction. Compound 5a exhibited the highest
catalytic efficiency among ligands 4a, 5a and 6a for the
cross-coupling reaction of aryl bromides with phenyl-
boronic acid.
4. Experimental
4.1. General
All operations were performed in a nitrogen-flushed glove
box or in a vacuum system. Freshly distilled solvents were
used. All processes of separations of the products were
performed by Centrifugal Thin Layer Chromatography
(CTLC, Chromatotron, Harrison model 8924) or column
chromatography. 1H NMR spectra were recorded on
300 MHz Varian VXR-300S spectrometer. The chemical
shifts are reported in ppm relative to internal standard
CHCl3 or CH2Cl2. 31P and 13C NMR spectra were recorded
at 121.44 and 75.46 MHz, respectively. Some other routine
1H NMR spectra were recorded over Gemini-200 spec-
trometer at 200.00 MHz or Varian-400 spectrometer at
400.00 MHz. IR spectra of samples using KBr were
Figure 3. ORTEP drawing of 5a. Hydrogen atoms are omitted for clarity.

F.-E Hong et al. / Tetrahedron 60 (2004) 2639–2645
2643
Figure 4. ORTEP drawing of 5b. Some carbon and hydrogen atoms are omitted for clarity.
Table 3. Suzuki coupling reactions using cobalt-containing phosphine ligandsa
Entry
Aryl halide
Product
Ligand
Time (h)
Yield (%)
1
2
3
4
5
6
7
4a
5a
4a
5a
4a
5a
6a
19
19
16
16
16
16
16
33b
42b
63c
75c
86
91
87
8
9
10
11
None
4a
5a
16
16
16
16
29
93
95
91
6a
12
13
14
4a
5a
6a
16
16
16
98
99
97
a
Reaction conditions: 1.0 equiv. aryl bromide, 1.5 equiv. boronic acid, 2.0 equiv. K3PO4, 1 mol% Pd(OAc)2, 2 mol% cat. ligand, toluene (1 mL/mmol aryl
bromide), 100 8C; reaction times have not been minimized. Yields in the table are represented in isolated yields (average of two or more experiments) of
1
compounds are estimated to be $95% pure as determined by H NMR.
b
c
The reaction was conducted at 50 8C using THF (1 mL/mmol aryl bromide) and KF (3.0 equiv.) in place of toluene and K3PO4.
The reaction was conducted at 80 8C.
recorded on a Hitachi 270-30 spectrometer. Mass spectra
cyclohexane) dissolved in dimethylether (5 mL). The
n-butyllithium solution is slowly added to the above mixture
under stirring at 278 8C. The resultant mixture is continued
to stir at 278 8C for more than 1 h, then one molar
equivalent of diphenylchlorophosphine (2.206 g,
10.0 mmol) dissolved in 5 mL dimethylether (5 mL) was
slowly added to it. The reaction mixture was then allowed to
warm up to room temperature and then stirred for another
1 h. The solvent was removed under reduced pressure and
toluene was added to precipitate the lithium chloride. After
filtration, the resulted solution was further purified by
chromatography. The solid obtained in white needles was
identified as 1.The isolated yield obtained in the reaction is
were recorded on JOEL JMS-SX/SX 102A GC/MS/MS
spectrometer. Elemental analyses were recorded on Heraeus
CHN-O-S-Rapid.
4.2. Synthesis of PhCuCPPh2 1 and Me3CCuCPPh2 2
The preparative procedure for the formation of 1 or 2 was
modified to the method reported in literature.13 Phenyl-
acetylene (1.021 g, 10.000 mmol) and dimethylether
(10 mL) were taken in a 100 mL round bottomed flask
charged with magnetic stirrer. In a separate round bottomed
flask, one molar equivalent of n-butyllithium (2.0 M in

2644
F.-E Hong et al. / Tetrahedron 60 (2004) 2639–2645
75.0% (2.147 g, 7.500 mmol). The same procedure was
followed for the preparation of 2.The reaction is started with
3,3-dimethyl-1-butyne (0.822 g, 10.000 mmol) as the
alkyne source. The white colored compound obtained was
identified as 2.The isolated yield obtained in the reaction is
78.0% (2.077 g, 7.800 mmol).
(CvO). MS (FAB): m/z 918 (Mþþ1). Anal. Calcd for
C49H37Co2O5P3: C, 64.21; H, 4.07. Found: C, 61.50; H, 3.59.
1
4.3.3. Complex 5a. H NMR (CDCl3, ppm): 7.46–7.00
(30H, arene), 4.33–4.19 (m, 1H, CH2), 3.39–3.28 (m, 1H,
CH2), 1.29 (s, 9H, C(CH3)3). 13C NMR (CDCl3, ppm):
207.8, 203.1 (s, 2C, CO), 138.5–127.4 (36C, arene), 37.6 (s,
1C, CH2), 33.2 (s, 3C, C(CH3)3). 31P NMR (CDCl3, ppm):
34.7 (s, 2P, dppm), 26.2 (s, 1P, PPh2). IR (KBr, cm21):
2009 (s), 1984 (s), 1962 (s) (CvO). MS (ESI): m/z 880
(Mþ). Anal. Calcd for C47H41Co2O4P3: C, 64.10; H, 4.69.
Found: C, 63.92; H, 5.07.
1
4.2.1. Compound 1. H NMR (CDCl3, ppm): 7.70–7.22
(15H, arene). 31P NMR (CDCl3, ppm): 232.7 (s, 1P,
CuCP). IR (KBr, cm21): 2170 (s) (CuC). MS (FAB): m/z
286 (Mþ).
1
4.2.2. Compound 2. H NMR (CDCl3, ppm): 7.71–7.36
(10H, arene), 1.42 (s, 9H, CMe3). 31P NMR (CDCl3, ppm):
233.6 (s, 1P, CuCP). IR (KBr, cm21): 2171 (s), 2220 (s)
(CuC). MS (FAB): m/z 266 (Mþ).
4.3.4. Complex 5b. H NMR (CDCl3, ppm): 7.82–7.00
1
(30H, arene), 6.05 (brd, 1H, CH2), 3.29 (brd, 1H, CH2), 1.26
(s, 9H, C(CH3)3). 13C NMR (CDCl3, ppm): 209.6, 208.0 (s,
2C, CO), 138.5–125.1 (36C, arene), 38.0 (s, 1C, C(CH3)3),
4.3. Synthesis of [(m-PPh2CH2PPh2)Co2(CO)4](m,h-
PhCuCPPh2) 4a, [(m-PPh2CH2PPh2)Co2(CO)4](m,h-
PhCuCP(vO)Ph2) 4b, [(m-PPh2CH2PPh2)Co2(CO)4]-
(m,h-Me3CCuCPPh2) 5a and [(m-PPh2CH2PPh2)-
Co2(CO)4](m,h-Me3CCuCP(vO)Ph2) 5b
35.4 (t, JP–C¼76.4 Hz, 1C, CH2), 33.2 (s, 3C, C(CH3)3). 31
P
NMR (CDCl3, ppm): 35.8 (s, 2P, dppm), 28.2 (s, 1P, PPh2).
IR (KBr, cm21): 2016 (s), 1991 (s), 1960 (s) (CvO). MS
(FAB): m/z 896 (Mþ). Anal. Calcd for C47H41Co2O5P3: C,
62.96; H, 4.61. Found: C, 63.83; H, 4.91.
1.0 mmol of dicobalt octacarbonyl, Co2(CO)8 (0.342 g),
1.0 mmol of dppm (0.385 g) and 10 mL of THF were taken
in a 100 mL round bottomed flask charged with magnetic
stirrer. The solution was stirred at 65 8C for 6 h, a yellow-
colored compound, Co2(CO)6(m-P,P–PPh2CH2PPh2), was
yielded. Without separation, the reaction flask was further
charged with one molar equivalent of 1 (0.286 g) in 5 mL of
THF and then the solution was allowed to stir at 45 8C for
8 h. The solvent was removed under reduced pressure and
the resulted dark red-colored residue was separated by
CTLC. A purple band was eluted out by mixed solvent
(CH2Cl2–hexane¼1:1) and the compound was identified as
4a with the yield of 55.0% (0.495 g, 0.550 mmol). A small
red band, followed by 4a during the chromatographic
process, was eluted out and the red-colored compound was
identified as 4b with the yield of 9.3% (0.085 g,
0.093 mmol). The similar procedure was followed for the
preparations of 5a and 5b started with Co2(CO)8 (0.342 g,
1.000 mmol), dppm (0.385 g, 1.000 mmol) and 2 (0.266 g,
1.000 mmol). The first separated red-colored compound,
which was eluted out by mixed solvent (CH2Cl2 –
hexane¼1:1), was identified as 5a with the yield of 60.0%
(0.480 g, 0.600 mmol). The second red-colored compound
was identified as 5b with the yield of 6.1% (0.055 g,
0.061 mmol).
4.4. General procedure for the Suzuki coupling reactions
Suzuki coupling reaction was performed according to
Wolfe’s procedure.7d The four reactants, Pd(OAc)2
(2.200 mg, 0.010 mmol), phosphine ligand 4a (or 5a, 6a)
(L/Pd(OAc)2¼2/1), the boronic acid (0.183 g, 1.500 mmol)
and K3PO4 (0.425 g, 2.000 mmol) were taken into a suitable
oven-dried Schlenk flask. The flask was evacuated and
backfilled with nitrogen before adding toluene (1 mL) and
the aryl halide (1.000 mmol) through a rubber septum. The
aryl halides being solids at room temperature were added
prior to the evacuation/backfill cycle. The flask was sealed
with Teflon screw cap and the solution was stirred at the
required temperature for designated hours. Then, the
reaction mixture was diluted with ether (30 mL) and poured
into a separatory funnel. The mixture was washed with
aqueous NaOH (1 M, 20 mL) and the aqueous layer was
extracted with ether (20 mL). The combined organic layer
were washed with brine (20 mL) and dried with anhydrous
magnesium sulfate. The dried organic layer was concen-
trated in vacuo. The crude material was further purified by
flash chromatography on silica gel.
4.4.1. 2-Phenylthiophene. 1H NMR (CDCl3, ppm): 7.69 (d,
J¼7.2 Hz, 2H), 7.44 (dd, J¼7.8, 7.2 Hz, 2H), 7.44 (t,
J¼7.8 Hz, 1H), 7.37 (d, J¼3.8 Hz, 1H), 7.33 (d, J¼5.0 Hz,
1H), 7.13 (dd, J¼5.0, 3.8 Hz, 1H).
4.4.2. Biphenyl. 1H NMR (CDCl3, ppm): 7.59 (t,
J¼11.2 Hz, 2H), 7.44 (m, J¼46.8 Hz, 4H), 7.35 (d,
J¼8 Hz, 4H).
1
4.3.1. Complex 4a. H NMR (CDCl3, ppm): 7.54–6.92
(35H, arene), 3.30 (t, JP–H¼10.2 Hz, 2H, CH2). 13C NMR
(CDCl3, ppm): 132.3–127.8 (42C, arene), 36.6 (s, 1C,
CH2). 31P NMR (CDCl3, ppm): 37.5 (s, 2P, dppm), 6.8 (s,
1P, PPh2). IR (KBr, cm21): 2020 (s), 1994 (s), 1967 (s)
(CvO). MS (ESI): m/z 902 (Mþþ1). Anal. Calcd for
C49H37Co2O4P3: C, 65.35; H, 4.14. Found: C, 62.56; H, 3.86.
1
4.4.3. 4-Biphenylcarbaldehyde. H NMR (CDCl3, ppm):
10.01 (s, 1H, COH), 7.73 (d, J¼8.2 Hz, 2H), 7.52 (d,
J¼8.2 Hz, 2H), 7.40 (d, J¼8.4 Hz, 2H), 7.30–7.19 (m,
J¼23.4 Hz, 3H).
1
4.3.2. Complex 4b. H NMR (CDCl3, ppm): 7.78–7.04
(35H, arene), 6.02–5.94 (m, 1H, CH2), 3.40–3.33 (m, 1H,
CH2). 13C NMR (CDCl3, ppm): 206.5, 200.8 (s, 2C, CO),
138.2–126.4 (42C, arene), 36.7 (t, JP–C¼78.0 Hz, 1C,
CH2). 31P NMR (CDCl3, ppm): 35.7 (s, 2P, dppm), 28.4 (s,
1P, PPh2). IR (KBr, cm21): 2021 (s), 1995 (s), 1974 (s)
4.5. X-ray crystallographic studies
Suitable crystals of 4a, 4b, 5a, and 5b were sealed in

F.-E Hong et al. / Tetrahedron 60 (2004) 2639–2645
2645
Wiley: New York, 1994. (b) Applied homogeneous catalysis
with organometallic compounds; Cornils, B., Herrmann,
W. A., Eds.; VCH: New York, 1996; Vols. 1 and 2.
(c) Kagan, H. B. Comprehensive organometallic chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon:
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S. D. Homogeneous catalysis; 2nd ed. Wiley: New York,
1992; Chapter 8.
thin-walled glass capillaries under nitrogen atmosphere and
mounted on a Bruker AXS SMART 1000 diffractometer.
Intensity data were collected in 1350 frames with increasing
v (width of 0.38 per frame). The absorption correction was
based on the symmetry equivalent reflections using
SADABS program. The space group determination was
based on a check of the Laue symmetry and systematic
absences, and was confirmed using the structure solution.
The structure was solved by direct methods using a
SHELXTL package.14 All non-H atoms were located from
successive Fourier maps and the hydrogen atoms were
refined using a riding model. Anisotropic thermal par-
ameters were used for all non-H atoms and fixed isotropic
parameters were used for H atoms.15 Crystallographic data
of 4a, 4b, 5a, and 5b are summarized in Table 1.
6. Crabtree, R. H. The organomatalic chemistry of the transition
metals; 2nd ed. Wiley: New York, 1994; Chapter 6.
7. (a) Chemler, S. R.; Trauner, D.; Danishefsky, S. J. Angew.
Chem. Int. Ed. 2001, 40, 4544–4568. (b) Wolfe, J. P.;
Buchwald, S. L. Angew. Chem. Int. Ed. 1999, 38, 2413–2416.
(c) Littke, A. F.; Fu, G. C. Angew. Chem. Int. Ed. 1998, 37,
3387–3388. (d) Wolfe, J. P.; Singer, R. A.; Yang, B. H.;
Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 9550–9561.
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S. L. J. Org. Chem. 2000, 65, 1158–1174. (f) Bei, X.; Crevier,
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5. Supplementary information
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Center, CCDC no. 216404-216407 for compounds 4a, 4b,
5a, and 5b, respectively. Copies of this information may be
obtained free of charge from the Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: þ44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
8. (a) Salzer, A. Coord. Chem. Rev. 2003, 242, 59–72.
(b) Delacroix, O.; Gladysz, J. A. Chem. Comm. 2003,
665–675. (c) Planas, J. G.; Gladysz, J. A. Inorg. Chem.
2002, 41, 6947–6949. (d) Hu, Q.-S.; Lu, Y.; Tang, Z.-Y.; Yu,
H.-B. J. Am. Chem. Soc. 2003, 125, 2856–2857. (e) Mann, G.;
Hartwig, G. F. J. Am. Chem. Soc. 1996, 118, 13109–13110.
(f) Pickett, T. E.; Roca, F. X.; Richards, C. J. J. Org. Chem.
2003, 68, 2592–2599. (g) Kataoka, N.; Shelby, Q.; Stambuli,
J. P.; Hartwig, J. F. J. Org. Chem. 2002, 67, 5553–5566.
(h) Tang, Z.-Y.; Lu, Y.; Hu, Q.-S. Org. Lett. 2003, 5,
297–300.
Acknowledgements
We are grateful to the National Science Council of the ROC.
(Grant NSC 92-2113-M-005-015) for financially supporting
this research.
9. Hong, F.-E; Chang, Y.-C.; Chang, R.-E.; Chen, S.-C.; Ko,
B.-T. Organometallics 2002, 21, 961–967.
10. Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. Rev. 2002, 102, 1359–1470.
References and notes
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