Amination and Suzuki coupling reactions catalyzed by palladium complexes coordinated by cobalt-containing monodentate phosphine ligands with bis-trifluoromethyl substituents on bridged arylethynyl: Observation of some unusual metal-containing compounds

Article abstract of DOI:10.1016/j.jorganchem.2008.10.005

Two cobalt-containing bulky monodentate phosphines {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂PC{triple bond, long}CAr]} (4cm: Ar = 3-CF₃C₆H₄; 4cmm: A

Full text of DOI:10.1016/j.jorganchem.2008.10.005

Journal of Organometallic Chemistry 694 (2009) 113–121
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Amination and Suzuki coupling reactions catalyzed by palladium complexes
coordinated by cobalt-containing monodentate phosphine ligands with
bis-trifluoromethyl substituents on bridged arylethynyl: Observation of some
unusual metal-containing compounds
*
Po-Cheng Huang, Fung-E. Hong
Department of Chemistry, National Chung Hsing University, 250 Kuo-Kuang Road, Taichung 40227, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Two
(tBu)2PC„CAr]} (4cm: Ar = 3-CF3C6H4; 4cmm: Ar = 3,5-(CF3)2C6H3) were prepared from the reaction of
Co2(CO)6(
-PPh2CH2PPh2) (3) with each corresponding alkynes (tBu)2PC„CAr. Both compounds were
converted to their oxidized forms {[( -PPh2CH2PPh2)Co2(CO)4][(
-(tBu)2P(@O)C„CAr]} (4cmO:
Ar = 3-CF3C6H3; 4cmmO: Ar = 3,5-(CF3)2C6H3) in the presence of oxide. Further reactions of 4cm and
4cmm with Pd(OAc)2 gave palladium complexes {[( -PPh2CH2PPh2)Co2(CO)4][(
-(tBu)2PC„C(Ar)-
C1)]Pd(
-OAc)} 5cm (Ar = 3-CF3C6H3) and 5cmm (Ar = 3,5-(CF3)2C6H2), respectively. By contrast,
reactions of 4cm and 4cmm with Pd(COD)Cl2 gave products, [{ -P,P-PPh2CH2PPh2}Co2(CO)3-
-CO){
-(tBu)2PC„CAr}]-PdCl2] 8cm and 8cmm, respectively, with unique bonding modes. Several
crystallines of [(4cm)2Pd3( -Cl)( -CO)2)( -Cl)]2 (9) were obtained along with crystallines of 8cm during
cobalt-containing
bulky
monodentate
phosphines
{[(l-PPh2CH2PPh2)Co2(CO)4][(l,g-
Received 23 July 2008
Received in revised form 30 September
2008
Accepted 7 October 2008
Available online 14 October 2008
l
l
l,g
l
l,g
j
l
Keywords:
l
Suzuki–Miyaura cross-coupling reaction
Amination reaction
Phosphine ligand
(l
l,g
l
l
l
the crystallization process. The crystal structures of all three compounds, 4cmmO, 8cmm and 9 were
determined by single-crystal X-ray diffraction methods. Fair to excellent efficiencies were observed for
employing 4cmm/palladium salt as catalytic precursor in amination as well as in Suzuki coupling
reactions.
Electron-withdrawing substituent
Palladium–cobalt bond
Palladium cluster
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
ligands’ electronic and steric character by simply varying their
substituents [4–15]. Yet, only a few types of transition metal-
For the past thirty years, the transition metal-catalyzed cou-
pling reactions have experienced the renaissance since the first
discovery of the Ullmann reaction one century ago [1]. The study
on the scope of the ligand assisted transition metal-catalyzed
cross-coupling reaction is prevailing not only in academic re-
search but also industrial interests [2]. With various metals
being employed in coupling reactions, palladium probably is
the most frequently chosen transition metal due mostly to its
excellent catalytic efficiency in this type of reactions. Among
all the factors which might affect the catalytic performance of
the reaction, a well-chosen ligand, beyond doubt, is indispens-
able to the success of a palladium-catalyzed cross-coupling reac-
tion [3]. As a result, numerous efforts have been dedicated to
search for more efficient and versatile ligands which might be
adaptable to various styles of coupling reactions. For a long
while, organic phosphines and their derivatives have been the
most favorite ligands mainly due to the readiness of tuning the
containing phosphine ligands had been prepared and their roles
as ligands had been examined [11–18]. We had reported the
ready preparation of a new class of metal-containing phosphines
{[(l-PPh2CH2PPh2)Co2(CO)4][(l,g
-(tBu)2PC„C(R-C6H4)]} (4b: R =
p-F; 4cp: R = p-CF3; 4cm: R = m-CF3; 4d: R = p-OMe) by the pro-
cedures as shown in Scheme 1. Firstly, alkynyl phosphines,
[(tBu)2PC„C(C6H4R)] (2b: R = p-F; 2cp: R = p-CF3; 2cm: R = m-
CF3; 2d: R = p-OMe)) were prepared by the procedures modified
from literature [19]. Then, the newly prepared 2a–d were al-
lowed to react with (l-PPh2CH2PPh2)Co2(CO)6 (3) to form the
corresponding 4a–d. The rules of abbreviation for the reaction
involved species throughout the article are a, b, c, d for substi-
tuent R = H, F, CF3, OMe, respectively; p, m, o for substituent lo-
cated on para, meta, ortho-position etc. This arrangement
naturally leads this type of phosphines to bulkiness, which is a
character obviously advantageous to the last step of the catalytic
cycle – the reductive elimination process. Their roles as legiti-
mate and active ligands in palladium-catalyzed cross-coupling
reactions have been evaluated and proven to be effective [20–
28]. Fair to excellent performances of these ligands were shown
in various kinds of reactions.
* Corresponding author. Tel.: +886 4 22840411 607; fax: +886 4 22862547.
E-mail address: fehong@dragon.nchu.edu.tw (F.-E. Hong).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.10.005

114
P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
1. n-BuLi, -78ºC,1 hr
2. ClPR'2, R' = tBu
H C C
R'2P C C
R
R
THF, r.t., 24 h
2cp: R = p-CF3
2a: R = H
2b: R = p-F
1a: R = H
1b: R = p-F
1cp: R = p-CF3
1cm: R = m-CF3
1d: R = p-OMe
2cm: R = m-CF3
2d: R = p-OMe
O
R
PR'2
C
C
(CO)
3Co
R
(OC)2Co
Ph2P
Co(CO)2
PPh2
(CO)
Co
PPh2
[O]
3
Ph2P
+
4aO: R = H
C
C
PR'2
4cmO: R = m-CF3
4dO: R = p-OMe
H2
H2
3
C
C
THF, 60oC
R'2
(CO)2
Co
(OC)2Co
Ph2P
Co(CO)2
PPh2
P
Ph
2P
O
C
C
C
Pd
C
Me
H2
O
Co
(CO)2
Ph2P
4cp: R = p-CF3
4a: R = H
4b: R = p-F
4cm: R = m-CF3
4d: R = p-OMe
R
5cp: R = p-CF3
5cm: R = m-CF3
5d: R = p-OMe
5a: R = H
5b: R = p-F
Scheme 1. Preparations of cobalt-containing monodentate phosphines 4a–d and palladium complexes 5a–d.
Our previous work also reported the preparation of 4-chelated
palladium complex, 5. An unusual palladium complex {[(
PPh2CH2PPh2)Co2(CO)4][(
-(tBu)2PC„C(p-R-C6H3)- C1)]Pd(
substituted 4cmm and its application in 4cmm-assisted palla-
dium-catalyzed amination and Suzuki cross-coupling reactions
are presented.
l
l-
-
l
,
g
j
OAc)} (5a: R = H) was prepared from the reaction of the cobalt-
containing bulky phosphine 4a with Pd(OAc)2. As disclosed by its
crystal structure, during the formation of 5a a process of orthomet-
allation occurred accompanied by the release of one equivalent of
acetic acid [28–30]. The acetate chelates to the palladium metal in
2. Results and discussion
2.1. Preparation of cobalt-containing phosphine {[(
l-PPh2CH2PPh2)-
Co2(CO)4][(l,g
-(tBu)2PC„C(3,5-(CF3)2C6H3)]} (4cmm)
a
g
2-mode. By the same token, several 5a-related palladium com-
plexes
j
{[(
l-PPh2CH2PPh2)Co2(CO)4][(l,g
-(tBu)2PC„C(R-C6H3)-
A cobalt-containing phosphine 4cmm was prepared from the
reaction of Co2(CO)6(dppm) (3) with (tBu)2PC„C(3,5-(CF3)2C6H3)
by similar procedures as the preparation of 4cm. The reaction
was carried out in THF at 60 °C for 48 h and reddish-brown solid
was yielded in about 40%. Compound 4cmm was characterized
by spectroscopic methods such as 1H and 31P NMR and mass spec-
trum. In the 1H NMR spectrum of 4cmm, one set of multiplets ap-
pears around 3.24 ppm which is corresponding to the methylenic
protons of the coordinated dppm ligand. Two sets of doublets ob-
C1)]Pd(
l-OAc)} (5b: R = p-F; 5cp: R = p-CF3; 5cm: R = m-CF3; 5d:
R = p-OMe) were prepared from the reactions of their correspond-
ing cobalt-containing phosphines (4b: R = p-F; 4cp: R = p-CF3;
4cm: R = m-CF3; 4d: R = p-OMe) with Pd(OAc)2. The charge of the
palladium metal remains +2 in 5. It is generally accepted that the
Pd(II) complex shall be reduced to Pd(0) complex before the oxida-
tive addition process taking place. It was proposed that in Suzuki–
Miyaura reaction the reduction might be proceeded via the attack
of borate, PhBðOHÞꢀ3 , on the palladium center in basic medium [31].
Our previous works had demonstrated that the Suzuki–Miyaura
cross-coupling reaction of aryl halide and organoboronic acid could
be carried out catalytically either by in vitro 4/Pd(OAc)2 or by
isolated and purified 5 [29]. In addition, the latter had also been
employed in the amination reactions of substituted bromobenz-
enes and morpholine. Fair to excellent results were obtained [28].
As revealed in crystal structure of 5cm, orthometallation took
place between palladium and arylethynyl and formed the Pd–Caryl
bond. The bulky substituent, –CF3, stays away from the palladium
metal center thus to prevent the severe steric hindrance [32]. It is
believed that by deliberately placing two –CF3 groups on the two
meta-positions of the arylethynyl group the orthometallation pro-
cess shall be prevented due to its severe steric hindrance. The
bonding mode of the newly-made ligand to palladium moiety shall
be quite different from that in 5 and so as its catalytic performance.
Thereby, we were interested in examining the validity of this
assumption. In this study, the preparation of double –CF3 groups
t
served at 1.26 and 1.23 ppm are assigned to the two Bu groups.
The 31P NMR spectrum displays two singlets at 35.98 and
44.62 ppm. The former signal is assigned to the two equivalent
phosphorus atoms of the coordinated dppm ligand; while the latter
peak is assigned to the free phosphorus site. During the crystalliza-
tion process, the 4cmm was converted to its oxidized form
{[(l-PPh2CH2PPh2)Co2(CO)4][(l,g
-(tBu)2P(@O)C„CAr]} (4cmmO:
Ar = 3,5-(CF3)2C6H3). The molecular structure of 4cmmO was
determined by single-crystal X-ray diffraction methods (Table 1).
As revealed in the ORTEP diagram as depicted in Fig. 1, a pseudo-
tetrahedral core Co2C2 was maintained. The phosphorus atom is
oxidized and located in a tetrahedral environment. This substitu-
ent, –P(@O)(tBu)2, is kept away from the dppm thus to prevent
serve steric hindrance. Two –CF3 groups are situated in meta-posi-
tion of the benzene ring. Compound 4cmmO might be prepared
separately by the oxidation of 4cmm. Its 1H and 31P NMR spectra
shows similar patterns as that of 4cmm. One set of multiplets at
3.33 ppm is assigned to the methylenic protons of the coordinated

P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
115
Table 1
Crystal data of 4cmmO, 8cmm and 9.
Compound
Formula
Formula weight
Crystal system
Space group
a (Å)
4cmmO
C47H45Co2F6O5P3
1014.60
Monoclinic
P21/n
12.3394(11)
16.1174(15)
24.095(2)
–
8cmm
9
C47H42Cl2Co2F6O4P3Pd ꢁ 1/2H2O ꢁ CH2Cl2
C72H88Cl4F12O4P4Pd6 ꢁ 0.6CHCl3
1266.81
Monoclinic
P21/n
2221.12
Monoclinic
C2/c
12.8018(8)
25.4586(16)
16.8048(10)
–
35.507(4)
9.0508(9)
31.599(3)
–
b (Å)
c (Å)
a
(°)
b (°)
99.970(2)
–
4719.6(7)
4
103.1870(10)
–
5332.5(6)
4
112.366(2)
–
9390.8(16)
4
c
(°)
V (Å3)
Z
Dc (mg/m3)
1.428
1.578
1.571
k (Mo K
l
a
)
) (Å)
0.71073
0.872
0.71073
1.302
0.71073
1.421
(mmꢀ1
h range (°)
Observed reflections (F > 4
1.53–26.06
9272
1.60–26.02
10462
2.33–26.00
9191
r(F))
No. of refined parameters
586
0.0523
0.1382
1.056
640
496
R1 for significant reflectionsa
wR2 for significant reflectionsb
Goodness-of-fit (GoF)c
0.0459
0.1191
1.009
0.0485
0.1481
1.029
a
R1 = |
R
(|Fo| ꢀ |Fc|)/|
P
RFo||.
P
P
2
2
wR2 ¼ f ½wðF2o ꢀ F2c Þ ꢂ= ½wðF2oÞ ꢂg1=2; w = 0.1000, 0.0690 and 0.1200 for crystal data of 4cmmO, 8cmm and 9, respectively.
b
c
2
1=2
GoF ¼ ½ wðF2o ꢀ Fc2Þ =ðNrflns ꢀ NparamsÞꢂ
.
dppm ligand. Two sets of doublets show up at 1.39 and 1.34 ppm
oxidized phosphorus atom. A significant downfield shift of the oxi-
dized phosphine was observed.
t
are corresponding to the two Bu groups. In 31P NMR spectrum,
two singlets at 35.26 and 59.55 ppm are assigned to the two equiv-
alent phosphorus atoms of the coordinated dppm ligand and the
2.2. Reactions of 4cm and 4cmm with Pd(OAc)2 and Pd(COD)Cl2
Attempts to make 4cmm complexed palladium compounds
were pursued by the reaction of 4cmm with two palladium
sources such as Pd(OAc)2 and Pd(COD)Cl2 (Scheme 2). Interest-
ingly, this newly-made monodentate phosphine ligand 4cmm
shows quite dissimilar reactivities and reaction types towards dif-
ferent palladium salts.
In the case of reacting with Pd(OAc)2, 4cmmO was observed as
the major product accompanied with black precipitates within one
hour. The composition of the latter is believed as the aggregation of
reduced Pd(0). It indicates that 4cmm is a rather efficient reducing
agent toward Pd(II) species. Obviously, the formation of 5cmm is
rather difficult because of the severe steric hindrance between
the two –CF3 groups and the surroundings of the palladium center.
Nevertheless, a rather small quantity of presumably 5cmm was
observed, judging from the spectroscopic data of the product, along
with large quantity of 4cmmO. A process of orthometallation oc-
curred during the formation of 5cmm accompanied by the release
of one equivalent of acetic acid. Another probable product might be
the 4cmm chelated palladium dimer, [(4cmm)2Pd(OAc)]2 6cmm.
In 6cmm, the 4cmm plays the role as a monodentate ligand and
the acetate acts as bridging ligand. Nevertheless, the formation of
6cmm did not observe from the spectroscopic data of the product.
In principle, the reaction of 4cmm with another palladium source
Pd(COD)Cl2 might give a palladium dimmer [4cmmPdCl2]2 7cmm.
In 7cmm, the two chlorides act as the bridging ligands. Compound
8cmm, with a rather unique conformation, was observed as the
major product instead. The identity of 8cmm was confirmed fur-
ther by the X-ray diffraction method. The ORTEP diagram of
8cmm was depicted in Fig. 2. Here, the presumably monodentate
phosphine ligand 4cmm, in fact, acts as a bidentate ligand toward
PdCl2 in a rather unique way. As shown, a direct Pd–Co bond is
formed accompanied with the coordination of a P ? Pd dative
bond (Scheme 2). In 31P NMR spectrum, three sets of signals at
25.74, 31.52 and 64.91 ppm, respectively, for two cobalt atoms
coordinated phosphines and one palladium coordinated phos-
Fig. 1. ORTEP drawing of 4cmmO. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Co(1)–C(2) 1.943(4); Co(1)–C(1) 1.990(5); Co(1)–
P(2) 2.2191(13); P(1)–C(45) 1.840(5); P(1)–Co(2) 2.2419(13); C(1)–C(2) 1.367(6);
C(1)–P(3) 1.792(4); C(1)–Co(2) 1.977(4); Co(2)–C(2) 1.962(4); P(2)–C(45) 1.835(4);
C(2)–C(3) 1.464(6); P(3)–O(5) 1.483(4); P(3)–C(9) 1.864(5); P(3)–C(13) 1.867(5);
C(5)–C(46) 1.511(8); C(7)–C(47) 1.471(9); C(2)–Co(1)–C(1) 40.66(17); C(33)–P(1)–
C(39) 101.1(2); C(2)–C(1)–P(3) 132.1(4); Co(2)–C(1)–Co(1) 77.36(16); C(2)–Co(2)–
C(1) 40.61(17); C(27)–P(2)–C(21) 103.1(2); C(1)–C(2)–C(3) 138.6(4); O(5)–P(3)–C(1)
109.4(2); O(5)–P(3)–C(9) 109.4(2); C(1)–P(3)–C(9) 106.9(2); O(5)–P(3)–C(13)
109.7(2); C(1)–P(3)–C(13) 109.1(2); P(2)–C(45)–P(1) 107.6(2).

116
P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
(tBu)2
(CO)2
P
Co
P
O
C
C
Ph2
+ [Pd(0)]
R1
P
Co
(CO)2
R1
Ph2
4cmO
4cmmO
C
C
P(tBu)2
R2
2cm: R1=CF3, R2=H
2cmm: R1=CF3, R2=CF3
R2
t
( Bu)
P
2
(CO)
Co
2
P
Ph
O
C
C
2
Pd
C CH
3
+ Pd(OAc)2
O
P
Co
R1
Ph
2
(CO)
(CO)
(CO)
Co
C
Co
PPh
3
2
3
5cm
5cmm
Ph P
2
+
2
R2
H
2
3
CH3
C
O
O
O
C
P
(tBu)2
P
Pd
Pd
(CO)2
Co
C
P
P
O
C
Ph2
C
6cm (Not detected)
6cmm (Not detected)
C
CH3
Cl
P
Co
R1
4cm
Ph2
(CO)2
L
Cl
R2
Pd
Pd
L: 4cmm
4cmm
Cl
L
Cl
7cm (Not detected)
7cmm (Not detected)
(tBu)2
P
CF3
(CO)2
Co
(tBu)2
P
C
C
P
Ph2
F3C
P
+ Pd(COD)Cl2
C
C
Cl
Cl
P
O
Co
Pd
C
R1
Ph2
C
(CO)2
(OC)2Co
Ph2P
Co
C
O
PPh2
R2
8cm (Not detected)
8cmm
O
C
L
Cl
Pd
Pd
Cl
L: 2cm
Pd
L
C
2
O
9
Scheme 2. Reactions of 4cm and 4cmm with Pd(OAc)2 and Pd(COD)Cl2.
phine. The significant downfield shift of the last signal indicates
that it is a palladium coordinated phosphine. Similar result was
small amount of red crystallines were observed during the crystal-
lization process. The structure of this unusual compound 9 was
determined by the X-ray diffraction method and its ORTEP plot
was depicted in Fig. 3. As shown from the drawing, the compound
can be regarded with a bow tie structure which is consisted of two
triangular palladium moieties bridging by two chlorides. There are
also four bridging carbonyls as well as two more chlorides are
found. The bridging carbonyls shall come from the fragmented
dicobalt carbonyls moiety. Unexpectedly, four phosphines,
(tBu)2PC„C(3,5-(CF3)2C6H3), are observed as terminal ligands.
These phosphines most likely are from the unreacted starting
material or even the cleavage of alkynyl bridging ligand from
dicobalt fragment of 4cm. The structure of a 9-related compound,
obtained from our previous work in which a reaction of [{
PPh2CH2PPh2}Co2(CO)4{ -PPh2C„CP(@O)Ph2}] (10) with one mo-
lar equivalent of (COD)PdCl2 gave a red-brown colored product,
[{ -P,P-PPh2CH2PPh2}Co2(CO)3( -CO){ -PPh2C„CP(@O)Ph2}]PdCl2]
l-P,P-
l
l
l
l
(11) [25]. As expected, the orthometallation did not take place
between palladium and arylethynyl. The bulky substituents, –CF3,
prevent the approach of the substituted phenyl toward the metal
center.
By similar procedures, the reaction of 4cm with Pd(COD)Cl2
give 8cm by judging from the spectroscopic data. Unfortunately,
attempts to grow crystal for 8cm resulted in failure. Interestingly,

P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
117
was stirred at either 60 °C or 80 °C for 4 h. Normally, an induction
period is needed for the reduction of Pd(II) to Pd(0) before the reac-
tion reaches reasonable speed.
First, the reactions using 4cmm as a ligand, NaOtBu/toluene and
various palladium sources were carried out (Table 3). The ratio of
ligand to number of palladium atom is 1:1. As shown, the best per-
formance was obtained while using [(
dium source (Entry 1).
g
3-C3H5)PdCl]2 as the palla-
The amination reaction which was carried out in toluene in the
presence of NaOtBu under various [( 3-C3H5)PdCl]2/4cmm ratios
helped to determine the preferred one (Table 4). The optimum
yield was achieved with [(
3-C3H5)PdCl]2/4cmm = 1/1 (Entry 5).
g
g
It indicates that 4cmm most likely acts as a bidentate ligand and
the conformation of the active species in this reaction might with
a similar geometry as that of 8cmm. As shown, the yields dropped
significantly while the ratio of ligand/palladium salt close to 2. The
excess amount of the bulky phosphine 4cmm might force the for-
mation of the palladium complex in a trans-form, trans-Pd(L)2(Cl)2.
Thereby, the reaction rate was greatly retarded by catalyst in this
conformation.
Reaction temperature is another factor critical for amination
reaction. In general, amination reaction requires much high
reaction temperature than that of Suzuki reaction. As shown in
Table 5, a poor performance was observed when the reaction
temperature was below 60 °C (Entry 1). However, good efficiency
was reached when the reaction temperature was higher than
60 °C (Entries 2 and 3).
As it is well known in the wildly accepted reaction mechanism,
the deprotonation of the coordinated amine, which requires base,
is essential in amination reaction. Thereby, a well-chosen base is
crucial to the success of the reaction [34–37]. The influence of
the base used in this reaction was examined (Table 6). As shown,
the best performance was observed with NaOtBu (Entry 1). Unex-
pectedly, the yield was noticeably low when a strong base such
as KOtBu was employed (Entry 2).
Fig. 2. ORTEP drawing of 8cmm. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (°): Pd(1)–P(3) 2.2236(14); Pd(1)–Cl(2) 2.3209(15);
Pd(1)–Cl(1) 2.4022(15); Pd(1)–C(20) 2.466(6); Pd(1)–Co(1) 2.6777(7); C(1)–C(2)
1.354(6); C(1)–P(3) 1.779(5); C(1)–Co(2) 1.924(4); C(1)–Co(1) 2.025(5); P(1)–C(45)
1.832(5); P(1)–Co(2) 2.2443(14); Co(1)–C(2) 1.978(5); Co(1)–P(2) 2.2487(14); P(2)–
C(45) 1.825(5); C(2)–C(3) 1.482(7); C(2)–Co(2) 1.955(5); Cl(2)–Pd(1)–Cl(1)
90.72(6); P(3)–Pd(1)–Co(1) 78.64(4); C(20)–Pd(1)–Co(1) 40.44(14); C(2)–C(1)–
P(3) 140.3(4); C(20)–Co(1)–Pd(1) 63.39(17); C(2)–Co(1)–Pd(1) 104.92(13);
C(1)–Co(1)–Pd(1) 76.46(13); P(2)–Co(1)–Pd(1) 149.48(4); C(1)–C(2)–C(3)
141.1(4); C(9)–P(3)–C(13) 113.7(2); C(1)–P(3)–Pd(1) 94.49(16); P(2)–C(45)–P(1)
109.6(2); P(3)–C(1)–Co(1) 110.3(2).
The solubility of the reactants and catalyst in the solvent is
important to the success of the coupling reaction. The concentra-
tion of the reaction is also crucial. Subsequently, the impacts of
various solvents on the reactions were evaluated. As shown in
Table 7, the reaction is greatly affected by the nature of the solvent
used. For instance, the coupling reaction in toluene was rather
effective (Entries 4–7). However, the performance was not accept-
able for the rest of solvents. The effect of the concentration of the
reaction is also demonstrated. The efficiency is better for more con-
centrated solution (Entry 1).
It has been a common observation that in a palladium-catalyzed
Suzuki coupling reaction a better conversion is achieved with aryl
halides bearing an electron-withdrawing rather than an electron-
donating substituent [11]. In fact, it is valid for the reaction with
the oxidative addition process as the rate-determining-step
(r.d.s.). Nevertheless, it may not be true for other reactions where
the r.d.s. might be anything but the oxidative addition process such
as Heck reaction [38–41]. As shown in Table 8, compatible perfor-
mances were observed for substances with electron-donating
groups (Entries 2–3). Nevertheless, steric effect plays the most crit-
ical role here (Entries 3–6).
12, was reported and was prepared from a rather different reaction
pathway [33] (see Diagram 1).
2.3. Structural comparison of 8cmm and 11
The structures of 8cmm and 11 reveal that each molecule is
consisted of a Pd–Co bond and P ? Pd dative bond. The structural
comparison of 8cmm and 11 are listed in Table 2. As shown, the
corresponding bond lengths are similar, yet, the bond angles are
varied considerably within the tetragon which is consisted of four
atoms: Pd, Co(1), C(1) and P. It indicates that the shapes of these
two tetragons are not quite the same. The 8cmm is with two bridg-
ing carbonyls; only one bridging carbonyl is observed in 11 (see
Diagram 2).
2.4. Applications of 4cmm/Pd(OAc)2 in amination reactions
As known, the performance of a successful metal-catalyzed
cross-coupling reaction is governed by a number of factors [2].
By finding an optimized condition of the reaction, the effects of
various bases, palladium sources, temperatures, solvents and reac-
tion hours on the amination process employing 4cmm/palladium
salt were surveyed. Amination reactions of bromobenzene by mor-
pholine were carried out by employing the cobalt-containing phos-
phine ligand 4cmm-chelated palladium complexes as the catalyst
precursors (Scheme 3). The general procedures for the catalytic
reactions under investigation are shown as the follows. A suitable
Schlenk tube was first charged with 1.0 mmol of arylbromide,
1.2 equivalent of morpholine, 1.4 equivalent of base, 1 ml solvent,
and 1 mol% of 4cmm/palladium salt; then, the reaction mixture
For comparison, the catalytic efficiencies of amination reactions
employing in situ-prepared or isolated catalytic precursors were
examined. As revealed in Table 9, compatible performances were
observed for all systems.
2.5. Applications of 4cmm/Pd(OAc)2 in Suzuki reactions
Suzuki coupling reactions were carried out in situ by employing
the newly-made cobalt-containing phosphine ligand 4cmm
modified palladium complexes. The reaction was proceeded with

118
P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
Fig. 3. ORTEP drawing of 9. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Pd(1)–C(36) 2.052(5); Pd(1)–C(36) 2.074(5); Pd(1)–Cl(1)
2.4734(14); Pd(1)–Cl(1)#1 2.4833(14); Pd(1)–Pd(3) 2.7398(6); Pd(1)–Pd(2) 2.7543(6); O(1)–C(36) 1.138(6); P(1)–C(9) 1.766(6); P(1)–C(1) 1.871(6); P(1)–C(5) 1.893(7); P(1)–
Pd(2) 2.3242(13); Pd(2)–C(36) 1.916(5); Pd(2)–Cl(2) 2.4122(15); Pd(2)–Pd(3) 2.7115(6); P(2)–Pd(3) 2.3148(13); O(2)–C(35) 1.149(6); Cl(2)–Pd(3) 2.4133(15); Pd(3)–C(35)
1.913(5); C(9)–C(10) 1.199(8); C(35)–Pd(1)–C(36) 96.3(2); Cl(1)–Pd(1)–Cl(1)#1 86.20(4); Pd(3)–Pd(1)–Pd(2) 59.145(14); Pd(1)–Cl(1)–Pd(1)#1 93.80(4); C(9)–P(1)–C(1)
103.7(3); C(9)–P(1)–C(5) 101.7(3); C(1)–P(1)–C(5) 114.2(3); C(9)–P(1)–Pd(2) 111.1(2); C(1)–P(1)–Pd(2) 110.6(2); C(5)–P(1)–Pd(2) 114.5(2); Pd(3)–Pd(2)–Pd(1) 60.161(14);
Pd(2)–Cl(2)–Pd(3) 68.38(4); Pd(2)–Pd(3)–Pd(1) 60.693(15); C(10)–C(9)–P(1) 171.0(6); C(9)–C(10)–C(11) 177.2(7); Pd(3)–C(35)–Pd(1) 87.3(2); Pd(2)–C(36)–Pd(1) 87.2(2).
1.0 mol% of 4cmm/Pd(OAc)2 or 4cmm/PdCl2 under 60 °C for desig-
nated times (Scheme 4).
O
O
L
L
C
C
Cl
Cl
Pd
Pd
Pd
Pd
The general procedures for the catalytic reactions under inves-
tigation are shown as the follows. A suitable Schlenk tube was first
charged with 1.0 mmol of bromobenzene, 1.2 equivalent of mor-
pholine, 1.4 equivalent of NaOtBu, 1.0 ml toluene, and 1 mol% of
4cmm/Pd(OAc)2; then, the reaction mixture was stirred at either
40 °C (or 60 °C) for 3 (or 4) h depending on the reactions executed.
As shown in Table 10, it requires only 40 °C for 3 h to reach
excellent efficiency for most of the cases. The reaction condition
is milder than that in amination reaction.
Pd
Pd
Cl
Cl
C
C
O
O
L
L
Diagram 1. Generalized structure for 9 (L: 2cm) and 12 (L: PPh3).
Table 2
Comparison for selected structural parameters of 8cmm and 11.
8cmm
11
3. Summary
Bond length (Å)
Two cobalt-containing monodentate phosphine ligands, 4cm
and 4cmm, were prepared. These ligands have been proven to be
fairly efficient in the ligands assisted palladium-catalyzed amina-
tion and Suzuki reactions. In addition, some palladium complexes
with rather unique conformation were observed and characterized
while reacting with various palladium sources.
Pd–Co(1)
Pd–P
C(1)–P
C(1)–Co(1)
Pd–Cl(1)
Pd–Cl(2)
2.6777(7)
2.2236(14)
1.779(5)
2.025(5)
2.3209(15)
2.4022(15)
2.6171(5)
2.2050(9)
1.766(3)
2.049(3)
2.3282(9)
2.3997(9)
Bond angle (°)
P–Pd–Co(1)
Pd–Co(1)–C(1)
Co(1)–C(1)–P
C(1)–P–Pd
78.64(4)
76.46(13)
110.3(2)
94.49(16)
90.72(6)
75.90(2)
81.07(8)
102.65(14)
100.36(10)
94.58(4)
4. Experimental
4.1. Synthesis of 4cmm or 4cmmO
Cl(1)–Pd–Cl(2)
Into a 100 mL round-bottom flask, charged with a magnetic stir-
rer, was placed dicobalt octacarbonyl Co2(CO)8 (2.00 mmol,
0.684 g), dppm (2.00 mmol, 0.769 g) and 15 mL of THF. The
solution was stirred at 60 °C for 6 h and gave a yellow compound
one molar equivalent of 2-bromothiophene, 1.5-fold phenylbo-
ronic acid, and 3-fold of base in 1.0 mL solvent, and with

P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
119
CF3
O
(tBu)2
P
(1)
Ph2
Ph2P
P
F3C
(1)
C
C
Cl(1)
(2)
C
C
(1)
Cl
O
Pd
O
Pd
C
C
Cl
(2)
Cl
(OC)2Co
Ph2P
Co
(OC)2Co
Ph2P
Co
C
(1)
(1)
C
O
O
PPh2
PPh2
11
8cmm
Diagram 2. Generalized structure for 8cmm and 11.
L/[Pd]
Br +
HN
O
N
O
L = 4cmm
Table 6
R
R
Amination reactions employing [(
g
3-C3H5)PdCl]2/4cmm and various bases.a
Scheme 3. 4cmm-assisted palladium complex catalyzed amination reaction of
bromobenzene and morpholine.
Entry
Base
Yield (%)b
1
2
3
4
NaOtBu
KOtBu
NaOH
KF
82.2
1.4
Trace
Trace
Table 3
Dependence of the amination reaction yield on the Pd sources.a
a
Entry
Palladium source
[(
3-C3H5)PdCl]2
Pd(COD)Cl2
Pd(OAc)2
PdCl2(CH3CN)2
Pd2(dba)3
PdCl2
Yield (%)b
With the exception of base, reaction conditions same as in the footnote of
Table 3.
1
2
3
4
5
6
g
82.2
71.2
71.0
62.0
34.8
6.0
b
Determined by 1H NMR, Average of two runs.
Table 7
Dependence of the amination reaction yield on solvent.a
a
Reaction conditions: 1.0 mmol of bromobenzene, 1.2 mmol morpholine,
1.4 mmol of NaOtBu, 2.0 mL toluene, 4 h, 60 °C, and [Pd]/4cmm = 1:1.
Entry
Solvent
Yield (%)b
b
Determined by 1H NMR, average of two runs.
1
2
3
4
5
6
7
THF (2.0 mL)
1,4-Dioxene (2.0 mL)
DMF (2.0 mL)
Toluene (1.0 mL)
Toluene (1.5 mL)
Toluene (2.0 mL)
Toluene (3.0 mL)
21.1
13.6
10.4
>99.0
85.1
82.2
76.0
Table 4
Dependence of the amination reaction yield on the [(
g
3-C3H5)PdCl]2/4cmm ratio.a
Entry
Pd:L (mol%)
Conversion (%)b
1
2
3
4
5
6
0.5:1
1:0.5
1:1
1:2
2:1
20.1
64.1
82.2
6.8
74.0
2.0
a
With the exception of solvent, reaction conditions same as in the footnote of
Table 3.
b
Determined by 1H NMR, average of two runs.
1:0
with CH2Cl2/ethyl acetate (1:1) was identified as {[(
l-PPh2CH2-
a
Reaction conditions are the same as in footnote of Table 3 except for the pal-
ladium source employed.
PPh2)Co2(CO)4(
l,g
-(tBu)2P(@O)C„C(3,5-(CF3)2C6H3)]} (4cmmO)
b
Determined by 1H NMR, average of two runs.
in 10% (0.200 mmol, 0.103 g).
4.1.1. Selected spectroscopic data for 4cmm
1H NMR (CD2Cl2, d/ppm): 7.03–7.60 (23H, arene), 3.24 (m, 2H,
dppm), 1.26, 1.23 (d, JP–H = 11.2 Hz, 18H, tBu); 31P NMR (CDCl3,
d/ppm): 35.98 (s, 2P, dppm), 44.62 (s, 1P, P(tBu)2); elemental anal-
ysis: Anal. Calc.: C, 56.64; H, 4.35. Found: C, 56.48; H, 4.68%. MS
(FAB): m/z = 998.0 [M]+.
Table 5
Dependence of the amination reaction yield on temperature.a
Entry
T (°C)
Yield (%)b
1
2
3
25
60
80
Trace
82.2
85.2
4.1.2. Selected spectroscopic data for 4cmmO
a
With the exception of temperature, reaction conditions same as in the footnote
1H NMR (CD2Cl2, d/ppm): 7.02–8.04 (23H, arene), 3.33 (m, 2H,
of Table 3.
t
dppm), 1.39, 1.34 (d, JP–H = 18.4 Hz, 18H, Bu); 31P NMR (CDCl3, d/
b
Determined by 1H NMR, Average of two runs.
ppm): 35.26 (s, 2P, dppm), 59.55 (s, 1P, P(tBu)2); 13C NMR (CD2Cl2,
d/ppm): 122.03–147.75 (30C, arene), 28.31, (d, 6C, –C(CH3)3), 38.40
(d, 2C, JP–C = 25.11 Hz, –C(CH3)3, 33.70 (t, 1C, JP–C = 17.0 Hz, –CH2–);
elemental analysis: Anal. Calc.: C, 56.59; H, 4.51. Found: C, 55.89;
H, 4.64%. MS (FAB): m/z = 1013.0 [M]+.
[Co2(CO)6(l-P,P-dppm)] (3). Without further separation, the reac-
tion flask was charged again with one equivalent of
[(tBu)2PC„C(3,5-(CF3)2C6H3)] (0.696 g) in THF (15 mL). Subse-
quently, the solution was stirred at 60 °C for another 48 h before
the solvent was removed under reduced pressure. The residue
was further separated by CTLC. A reddish-brown band eluted with
4.2. Synthesis of 8cmm
A 100 mL round-bottom flask equipped with a magnetic stirrer
was charged with 1.00 mmol of 4cmm (0.998 g), one molar
equivalent of PdCl2 (1.0 mmol, 0.285 g) and 15 mL THF. The solu-
CH2Cl2/ethyl acetate (1:10) was identified as {[(
Co2(CO)4(
-(tBu)2PC„C(3,5-(CF3)2C6H3)]} (4cmm) in 40% yield
(0.80 mmol, 0.799 g). Another reddish-brown band eluted
l-PPh2CH2PPh2)-
l,g

120
P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
Table 8
Table 10
Dependence of the yield of the amination reaction using 4cmm/[(
g
3-C3H5)PdCl]2 on
Dependence of the yield of the Suzuki reaction using various catalytic precursors.a
substrate.a
Entry
Catalyst
Yield (%)b
Entry
Substrate
Product
Yield (%)b
>99.0
1
2
3
4
5
4cm/Pd(OAc)2
91.2
5cm
4cmm/[(
>99.0
>99.0
1
g
3-C3H5)PdCl]2
Br
N
O
4cmm/Pd(COD)Cl2
6cmm
60.0(>99.0c)
70.0(>99.0c)
2
3
90.1
a
N
Me
Me
Br
Me
Me
O
Reaction conditions: 1.0 mmol of 2-bromothiophene, 1.5 mmol phenylboronic
acid, and 3.0 mmol of NaOH, 1.0 ml toluene, 40 °C, 3 h, 1.0 mol% of L/[Pd] = 1:1.
b
Average of two runs; isolated yield.
60 °C, 4 h.
c
18.4
Br
N
O
m/z = 1118 [Mꢀ2CO]+; elemental analysis: Anal. Calc.: C, 48.09;
4
5
98.9
95.2
MeO
MeO
Br MeO
MeO
N
O
H, 3.69. Found: C, 46.41; H, 4.63%.
4.3. General procedure for coupling reactions
Br
N
O
For amination reaction, the following procedures were fol-
lowed. An oven-dried Schlenk tube was charged with 4cmm
(0.01 mmol, 0.998 mg), palladium salt (0.01 mmol) and a base
(1.4 mmol). The tube was evacuated and backfilled with nitrogen
and followed by the addition of aryl bromide (1.0 mmol, 0.156 g),
morpholine (1.2 mmol, 0.103 g) and toluene (1.0 mL). The tube
was sealed with a Teflon screw cap, and the mixture was stirred
at 60 °C for 3 h. After all starting materials had been consumed;
the mixture was allowed to cool down to room temperature and
then diluted with ether (30 mL). The resulting suspension was
transferred into a separatory funnel and washed with water
(10 mL). The organic layer was separated, dried with anhydrous
MgSO4 and concentrated under reduced pressure. The crude resi-
due was purified by CTLC with hexane/ethyl acetate as a mobile
phase. The solvent was removed under reduced pressure, and the
yield of the eluted product was determined.
OMe
OMe
6
7.4
Br
N
O
O
N
N
7
56.7
Br
N
a
Reaction conditions are the same as in footnote of Table 3 except for the sub-
strate employed.
Determined by 1H NMR, average of two runs.
b
Table 9
Dependence of the yield of the amination reaction using various catalytic precursorsa
Entry
Catalyst
Yield (%)b
Similar procedures were taken for Suzuki reaction except the
reactants and conditions were varied. A Schlenk tube was first
charged with 1.0 mmol of bromobenzene, 1.2 equivalent of mor-
pholine, 1.4 equivalent of NaOtBu, 1.0 ml toluene, and 1 mol% of
4cmm/Pd(OAc)2; then, the reaction mixture was stirred at either
40 °C (or 60 °C) for 3 (or 4) h depending on the reactions executed.
1
2
3
4
5
4cm/Pd(OAc)2
>99.0
>99.0
>99.0
90.2
5cm
4cmm/[(g
3-C3H5)PdCl]2
4cmm/Pd(COD)Cl2
6cmm
94.2
a
Reaction conditions are the same as in footnote of Table 3 except for the cat-
alytic precursor employed.
Determined by 1H NMR, average of two runs.
b
4.4. X-ray crystallographic studies
tion was stirred at 25 °C for 1 h before the solvent was removed
under reduced pressure. The residue was further separated by CTLC.
A reddish-brown band eluted with CH2Cl2/ethyl acetate (5:1)
Suitable crystals of 4cmmO, 8cmm and 9 were sealed in thin-
walled glass capillaries under nitrogen atmosphere and mounted
on a Bruker AXS SMART 1000 diffractometer. Intensity data were
was identified as {[(
l
-PPh2CH2PPh2)Co2(CO)4][(
l,g
-(tBu)2PC„
collected in 1350 frames with increasing x (width of 0.3° per
C(3,5-(CF3)2C6H3))]PdCl2} (8cmm) in the yield of 42% (0.42 mmol,
0.494 g).
frame). The absorption correction was based on the symmetry
equivalent reflections using SADABS program. The space group deter-
mination was based on a check of the Laue symmetry and system-
atic absences, and was confirmed using the structure solution. The
structure was solved by direct methods using a SHELXTL package
[42]. All non-H atoms were located from successive Fourier maps
and hydrogen atoms were refined using a riding model. Aniso-
tropic thermal parameters were used for all non-H atoms, and
fixed isotropic parameters were used for H atoms [43]. Crystallo-
graphic data for compounds 4cmmO, 8cmm and 9 are summarized
in Table 1.
4.2.1. Selected spectroscopic data for 8cmm
1H NMR (CD2Cl2, d/ppm): 6.71–7.91 (23H, arene), 3.63 (t, JP–H
=
=
=
t
22.8 Hz, 2H, CH2), 1.18 (d, JP–H = 16.4 Hz, 9H, Bu), 1.85 (d, JP–H
t
16.4 Hz, 9H, Bu); 31P NMR (CD2Cl2, d/ppm): 25.40–26.07 (d, JP–P
26.8 Hz, 1P, dppm), 31.18–31.85 (d, JP–P = 26.8 Hz, 1P, dppm),
64.91 (s, 1P, P(tBu)2); 13C NMR (CD2Cl2, d/ppm): 122.03–143.75
(30C, arene), 27.93, (d, 6C, –C(CH3)3), 30.63 (d, 2C, JP–C = 25.11 Hz,
–C(CH3)3, 31.41 (t, 1C, JP–C = 17.0 Hz, –CH2–); MS (FAB):
S
S
Br
+
1 mol % 4cmm/[Pd]
B(OH)2
1.5
3 equiv. base, 1 mL solvent
Scheme 4. 4cmm-assisted palladium complex catalyzed Suzuki–Miyaura cross-coupling reaction of 2-bromothiophene and phenylboronic acid.

P.-C. Huang, F.-E. Hong / Journal of Organometallic Chemistry 694 (2009) 113–121
[16] O. Delacroix, J.A. Gladysz, Chem. Commun. (2003) 665–675.
121
Acknowledgment
[17] A. Salzer, Coord. Chem. Rev. 242 (2003) 59–72.
[18] J.F. Jesen, M. Johannsen, Org. Lett. 5 (2003) 3025–3028.
[19] T.J. O’Connor, H.A. Patel, Can. J. Chem. 49 (1971) 2706–2711.
[20] F.-E. Hong, Y.-J. Ho, Y.-C. Chang, Y.-L. Huang, J. Organomet. Chem. 690 (2005)
1249–1257.
We thank the National Science Council of the ROC (Grant NSC
95-2113-M-005-015-MY3) for financial support.
[21] C.-P. Chang, Y.-L. Huang, F.-E. Hong, Tetrahedron 61 (2005) 3835–3839.
[22] Y.-C. Chang, F.-E. Hong, Organometallics 24 (2005) 5686–5695.
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[24] F.-E. Hong, Y.-J. Ho, Y.-C. Chang, Y.-C. Lai, Tetrahedron 60 (2004) 2639–2645.
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Appendix A. Supplementary material
CCDC 692970, 692971 and 692972 contain the supplementary
crystallographic data for 4cmmO, 8cmm and 9. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.jorganchem.2008.10.005.
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(2002) 961–967.
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[31] R.B. Bedford, S.L. Hazelwood, P.N. Horton, M.B. Hursthouse, Dalton Trans.
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[43] The hydrogen atoms were ride on carbons or oxygens in their idealized
positions and held fixed with the C–H distances of 0.96 Å.