Phosphine free diamino-diol based palladium catalysts and their application in Suzuki-Miyaura cross-coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2009.02.019

Inexpensive air and moisture stable diamino-diol ligands [(2-OH-C₁₀H₆)CH₂(μ-NC₄H₈N)CH₂(C₁₀H₆-2-OH)] (1) and [(5-^tBuC₆H₃-2-OH)CH₂(μ-NC₄H₈N)CH₂(5-^tBuC₆H₃-2-OH)] (2) were synthesized by reacting corresponding alcohols with formaldehyde and piperazine. Treatment of ligands 1 and 2 with Pd(OAc)₂ in 1:1 molar ratio afforded neutral palladium complexes [Pd{(OC₁₀H₆)CH₂(μ-NC₄H₈N)CH₂(C₁₀H₆O)}] (3) and [Pd{(5-^tBuC₆H₃-2-O)CH₂(μ-NC₄H₈N)CH₂(5-^tBuC₆H₃-2-O)}] (4) in good yield. The palladium complexes 3 and 4 are employed in Suzuki-Miyaura cross-coupling reactions between phenylboronic acid and several aryl chlorides or bromides. They are found to be competent homogeneous catalysts for a variety of substrates to afford the coupled products in good to excellent yields. The crystal structures of compounds 2 and 4 are also reported.

Full text of DOI:10.1016/j.jorganchem.2009.02.019

Journal of Organometallic Chemistry 694 (2009) 2114–2121
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Phosphine free diamino-diol based palladium catalysts and their application
in Suzuki–Miyaura cross-coupling reactions
b
Sasmita Mohanty a, D. Suresh a, Maravanji S. Balakrishna a, , Joel T. Mague
*
a Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India
b Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Inexpensive air and moisture stable diamino-diol ligands [(2-OH-C10H6)CH2(l-NC4H8N)CH2(C10H6-2-
OH)] (1) and [(5-tBuC6H3-2-OH)CH2( -NC4H8N)CH2(5-tBuC6H3-2-OH)] (2) were synthesized by reacting
l
Received 26 December 2008
Received in revised form 13 February 2009
Accepted 16 February 2009
Available online 3 March 2009
corresponding alcohols with formaldehyde and piperazine. Treatment of ligands 1 and 2 with Pd(OAc)2
in 1:1 molar ratio afforded neutral palladium complexes [Pd{(OC10H6)CH2( -NC4H8N)CH2(C10H6O)}] (3)
and [Pd{(5-tBuC6H3-2-O)CH2( -NC4H8N)CH2(5-tBuC6H3-2-O)}] (4) in good yield. The palladium com-
l
l
plexes 3 and 4 are employed in Suzuki–Miyaura cross-coupling reactions between phenylboronic acid
and several aryl chlorides or bromides. They are found to be competent homogeneous catalysts for a vari-
ety of substrates to afford the coupled products in good to excellent yields. The crystal structures of com-
pounds 2 and 4 are also reported.
Keywords:
Chelating ligands
Diamino-diols
Palladium(II) complexes
Homogeneous catalysis
Suzuki–Miyaura cross-coupling reaction
X-ray structures
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
often air and moisture sensitive, toxic and require inert atmo-
sphere and mild reaction conditions.
Organometallic catalysis in air and using non-phosphorus cata-
lysts has become an important goal in organic synthesis especially
for the development of industrial process under simple, economi-
cal and environmentally friendly conditions. A broader family of
palladium catalyzed coupling processes is known where a variety
of transmetallating agents such as organomagnesium [1], organo-
tin [2], organosilicon [3] and organozinc [4] reagents are routinely
used. Palladium catalysed Suzuki–Miyaura cross-coupling of aryl
halides with arylboronic acid is among the most powerful C–C
bond forming reactions available to synthetic chemists and its
increasing popularity is due to its broad tolerance of different func-
tional groups and ability to couple sterically demanding substrates
under mild reaction conditions [5]. Further, the process involves
non-toxic easy to handle reagents and also allows scale up produc-
tion in industry [6]. Current technologies demand new catalysts,
which are inexpensive, readily accessible, moisture- and air-stable
and most importantly, highly effective under mild experimental
conditions. To a certain extent this has been achieved by employ-
ing mainly phosphorus-based ligands as co-catalysts in organic
solvents [7]. However, phosphorus-based auxiliary catalysts are
In this context, several non-phosphorus [8] ligands containing
mainly nitrogen donor atoms were designed and employed in var-
ious catalytic reactions with remarkable success. The transition
metal complexes containing heterocyclic carbenes [8b,8c,8e] and
nitrogen donor ligands such as imine and amine [8f,8g], oxime
[8h,8i,8p], diazabutadiene derivatives [8a], imidazole [8d,8k],
oxazoline [9] and bis(pyrimidine) [10] are widely employed in
Suzuki–Miyaura cross-coupling reactions. In a few instances, PdII
species were employed in catalytic reactions which undergo
oxidative addition to give PdIV and revert back to PdII species
[11]. Recently we reported a nitrogen based ligand and studied
the catalytic activity of its in situ generated palladium(II) complex
in carbon–carbon cross-couplings reactions such as Suzuki–Miya-
ura and Mizoraki–Heck coupling reactions [12]. Although, catalytic
efficiency in these reactions was encouraging, we could not isolate
the active palladium species responsible for the coupling reactions.
In view of this, we slightly modified the ligand substituents and
interacted with Pd(acetate)2 and isolated PdII complexes which
are used in catalytic studies. As a part of our interest on transition
metal chemistry and catalytic investigations [13], we herein de-
scribe the synthesis of highly air and moisture stable palladium
complexes containing diamino-diol ligands and their utility in Su-
zuki–Miyaura carbon–carbon cross-coupling reactions for both
aryl bromides and chlorides.
* Corresponding author. Tel.: +91 22 2576 7181; fax: +91 22 2576 7152.
E-mail
addresses:
krishna@chem.iitb.ac.in,
msb_iitb@yahoo.com
(M.S. Balakrishna).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.02.019

S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
2115
ether mixtures (1:1) at room temperature. In the solid state, 2 pos-
sess crystallographically imposed centrosymmetry. The geometry
about the nitrogen atom is distorted pyramidal with the sum of
the bond angles being 330.2°. The N1–C11–C1 bond angle
(112.62(9)°) in ligand 2 is comparable with that of similar ligand
1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-piperazine [14]. In the
crystal there is intramolecular hydrogen bonding between the ter-
tiary nitrogen atom and the hydrogen atom of the phenoxo group
leading to the formation of a six membered ring. The hydrogen
bond distance for O1H1ꢀ ꢀ ꢀN1 is 1.87(2) Å and the O1–H1ꢀ ꢀ ꢀN angle
is 152.4(17)°. In addition, there are weak, complementary C–Hꢀ ꢀ ꢀO
2. Results and discussions
The reactions of piperazine, 40% paraformaldehyde solution and
2-naphthol or 4-tert-butlylphenol under refluxing condition in
methanol for 12 h afforded the colorless [(HOC10H6)CH2(
l
l
-
-
NC4H8N)CH2(C10H6OH)]
(1)
or
[(5-tBuC6H3-2-OH)CH2(
NC4H8N)CH2(5-tBuC6H3-2-OH)] (2) in moderate yield. Treatment
of ligands 1 and 2 with Pd(OAc)2 in equimolar ratio at room tem-
perature afforded [Pd{(OC10H6)CH2(
l-NC4H8N)CH2(C10H6O)}] (3)
and [Pd(5-tBuC6H3-2-O)CH2( -NC4H8N)CH2(5-tBuC6H3-2-O)}] (4),
l
respectively, as shown in Scheme 1.
The 1H NMR spectra of compounds 1 and 2 show sharp singlets
at 4.06 and 3.72 ppm, respectively, for the methylene protons. The
presence of the OH protons was confirmed by a D2O exchange
experiment. The mass spectra of the ligands 1 and 2 show molec-
ular ion peaks at m/z 399.2 and 411.5 [M+H]+, respectively. The
13C{1H} NMR and elemental analyses data are in good agreement
with the proposed molecular structures. The molecular structure
of ligand 2 and palladium complex 4 were confirmed by single
crystal X-ray diffraction studies.
and C–Hꢀ ꢀ ꢀ -ring interactions with the molecule at x, 1.5 ꢁ y,
p
ꢁ0.5 + z (C8–H8bꢀ ꢀ ꢀcenter of gravity of ring C1–C6: 2.86 Å, 161°.
C10–H10bꢀ ꢀ ꢀO2: 2.44 Å, 153°) and a C–Hꢀ ꢀ ꢀO interaction with the
molecule at ꢁx, 2 ꢁ y, ꢁz (C11–H11bꢀ ꢀ ꢀO2: 2.62 Å, 150°).
The complex 4 has a non-centrosymmetric structure with palla-
dium as the central metal atom in a distorted square planar geom-
etry with the corners being occupied by two tertiary nitrogen
atoms (N1 and N2) and two phenolate oxygen atoms (O1 and
O2). The conformation of the piperazine moiety is changed from
chair to boat conformation during complexation. The trans-O2–
Pd1–N1 and trans-O1–Pd1–N2 bond angles are, respectively,
171.01(13)° and 169.89(12)°, whereas the cis angles around the
palladium vary from 74.10(14)° (N1–Pd1–N2) to 97.41(12)° (O2–
Pd1–N2). The N2–C1–C13 bond angle is (115.02(3)°) slightly wider
than that in the free ligand [N1–C11–C1, 112.62(9)°] due to the
complexation. The Pd1–N1 and Pd1–N2 bond distances are
2.017(3) Å and 2.022(3) Å, respectively, whereas the Pd1–O1 and
Pd2–O2 distances are 2.016(2) Å and 2.010(3) Å. As in 2, there
3. Molecular structures of 2 and 4
Perspective views of the molecular structures of 2 and 4 are
shown in Figs. 1 and 2 while selected bond lengths and bond angles
are given as captions to the figures. Crystal data and details of the
structure determinations are given in Table 1.
Single crystals suitable for X-ray diffraction studies were grown
by slow evaporation of solvents from dichloromethane/petroleum
HO
OH
R1
R2
N
NH
N
MeOH
reflux, 10 h
+
aq. HCHO
+
HN
R1
R1
OH
R2
R2
R1-R2 = -(CH)4-
1
R
1 = H; R2 = tBu
2
Pd(OAc)2
CH2Cl2
RT, 5-6 h
R1
R1
N
N
O
R2
R2
Pd
O
R1-R2 = -(CH)4-
1 = H; R2 = tBu
3
4
R
Scheme 1. Synthesis of ligands and their palladium(II) complexes.
Fig. 1. An ORTEP view of molecular structure of 2. Atoms O1i, N1i, etc. are related to O1, N1, etc. by the symmetry operation 2 ꢁ x, 1 ꢁ y, 1 ꢁ z. All hydrogen atoms (except
O1–H1 and O1i–H1i) were omitted for clarity. Thermal ellipsoids are drawn at 50% probability. Selected bond lengths (Å): O1–C2, 1.3673(13); N1–C12, 1.4719(13); N1–C13,
1.4692(14); N1–C11, 1.4747(13). Selected bond angles (°): C2–O1–H1, 104.3(12); C11–N1–C12, 111.70(8); C11–N1–C13, 109.63(8); C12–N1–C13, 108.87(8); C2–C1–C11,
121.04(9); C6–C1–C11, 120.13(10).

2116
S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
Fig. 2. An ORTEP view of molecular structure of 4. All hydrogen atoms were omitted for clarity. Thermal ellipsoids are drawn at 50% probability. Selected bond lengths (Å):
Pd1–O1, 2.016(2); Pd1–O2, 2.010(3); Pd1–N1, 2.017(3); Pd1–N2, 2.022(3); O1–C1, 1.333(4); N1–C7, 1.484(5). Selected bond angles (°): O1–Pd1–O2, 92.70(11); O1–Pd1–N1,
95.80(12); O1–Pd1–N2, 169.89(12); O2–Pd1–N1, 171.01(13); O2–Pd1–N2, 97.41(12); N1–Pd1–N2, 74.10(14); Pd1–O1–C1, 112.8(2); Pd1–N1–C7, 115.0(3).
Table 1
Table 2
Crystallographic data for the compounds 2 and 4
Effect of base and solvent on the Suzuki–Miyaura coupling reaction.a
O
O
2
4
Cat., RT
+
Br
B(OH)2
Solvent
H3C
Formula
C26H38N2O2
410.58
Triclinic
P1 (No. 2)
6.4837(5)
8.2885(6)
11.0749(8)
88.528(1)
75.360(1)
77.175(1)
561.19(7)
1
C26H36N2O2Pd
514.97
H3C
base, solvent
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Entry
Base
Yield (%)b
Yield (%)c
Monoclinic
P21/c (No. 14)
17.987(3)
12.503(2)
10.542(1)
90
92.111(2)
90
2369.2(6)
4
ꢀ
1
2
3
4
5
6
7
8
9
10
K3PO4
K2CO3
Na2CO3
Cs2CO3
Et3N
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
MeOH
MeOH
MeOH
MeOH
MeOH
DMF
Toluene
Dioxane
DCM
100
100
100
100
83
98
81
68
53
100
100
100
99
80
82
60
15
40
32
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (g cmꢁ3
)
1.215
0.076
224
1.444
0.808
1072
THF
38
l
(Mo K
a
) (mmꢁ1
)
a
Reaction conditions: 4-Bromoacetophenone (0.5 mmol), phenylboronic acid
(0.75 mmol), catalyst (0.5 mol%), base (1 mmol) and solvent (5 mL). Conversion to
the coupled product determined by GC based on 4-bromoacetophenone; average of
two runs.
F(000)
Crystal size (mm3)
T (K)
0.16 ꢂ 0.19 ꢂ 0.30
0.06 ꢂ 0.20 ꢂ 0.26
100
100
2h range (°)
Total no. of reflections
2.5, 28.3
9891
2745 (0.023)
0.0392
2.0, 28.4
20133
5615 (0.046)
0.0564
b
Using catalyst 1/(Pd(OAc)2.
Catalyst 2/(Pd(OAc)2.
c
No. of independent reflections (Rint
)
a
R1
wR2
b
0.1094
0.1615
GOF (F2)
1.065
1.0437
The solvents play an important role in the cross-coupling reactions.
In the present study non-polar solvent like toluene gave moderate
yield of the coupled product whereas polar solvents such as meth-
anol or DMF are found to be more efficient (Table 2).
a
R =
R
||Fo| ꢁ |Fc||/
R|Fo|.
P
P
wR2 ¼ f½ wðFo2 ꢁ Fc2Þ= wðF2oÞ ꢃg1=2w ¼ 1=½r2ðFo2Þ þ ðxPÞ ꢃ where P ¼ ðFo2þ
2
2
b
2F2c Þ=3.
Under the optimized reaction conditions the Suzuki–Miyaura
cross-coupling reactions were carried out for various aryl bromides
(0.5 mmol) with phenylboronic acid (0.75 mmol) using K2CO3
(1 mmol) and 5–7 ml methanol at room temperature with the
catalyst loading of 0.5–1 mol%. The reaction time has not been
optimized. The results are displayed in Table 3. Electron-poor bro-
mides such as 4-bromoacetophenone and 4-bromobenzonitrile
were coupled with phenylboronic acid efficiently (entries 1, 2) in
presence of Pd(OAc)2/1 or 2 catalyst mixture. The coupling reac-
tions of some bromo heterocycles were also carried out with phen-
ylboronic acid. Use of 2-bromopyridine and 2-bromothiophene
produced excellent yield. The electron-poor 4-bromobenzaldehyde
coupled with phenylboronic acid in presence of ligand 1 with low
catalyst loading afforded good conversion whereas in the presence
of ligand 2 the yields were moderate (entry 5). The electronically
neutral bromobenzene (entry 6) produced good amount of desired
product when coupled with phenylboronic acid. The electron rich
or deactivated 4-bromoanisole and 2-bromo-6-methoxynaphtha-
lene also afforded good conversion (entry 7, 9) in the presence of
ligand 1 or 2. Under the same standard conditions, 3-bromobenz-
aldehyde furnished the desired biaryls in good yield (entry 8).
The high efficiency of these catalysts at room temperature
makes them valuable. To our knowledge, only few catalysts are
known for Suzuki–Miyaura cross-coupling reactions which are
effective at room temperature [22a–i]. The comparison data
are complementary C–Hꢀ ꢀ ꢀ
p-ring interactions with the molecule at
1 ꢁ x, 2 ꢁ y, 1 ꢁ z (C11–H11aꢀ ꢀ ꢀcenter of gravity of ring C1–C6:
2.79 Å, 161°) and a weak C–Hꢀ ꢀ ꢀO interaction with the molecule
at 1 + x, y, z (C12–H12bꢀ ꢀ ꢀO1: 2.65 Å, 156°).
4. Suzuki–Miyaura cross-coupling reactions for aryl bromides
The room temperature Suzuki–Miyaura coupling reactions of
aryl bromides with phenylboronic acid were carried out by
employing the in situ generated palladium complexes of 1 or 2 with
Pd(OAc)2 in a 1:1 molar ratio. Both the systems are found to be
highly active catalysts for the Suzuki–Miyaura cross-coupling reac-
tions under mild reaction conditions. To optimize the reaction con-
ditions, a series of reactions were carried out at room temperature
with 4-bromoacetophenone and phenylboronic acid as a model
reaction.
The effect of base on the coupling reaction was evaluated by
taking 4-bromoacetophenone (0.5 mmol) with phenylboronic acid
(0.75 mmol) in methanol at room temperature in presence of
0.5 mol% of the in situ generated catalyst with various bases
(1 mmol). The results revealed that the inorganic bases used were
more effective than Et3N (Table 2) and hence the economically
cheaper K2CO3 was chosen as base for the coupling reactions.

S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
2117
Table 3
Suzuki–Miyaura cross-coupling of aryl bromides with phenylboronic acid.a
R1
R1
Cat., K2CO3
MeOH, RT
B(OH)2
X
+
Entry
1
Aryl halides
Product
Ref.
Ligand (mol%)
Yield (%)b
O
O
1(0.5)
2(0.5)
100c
100c
Br
[15]
H3C
NC
H3C
NC
2
3
4
[16]
[17]
[18]
1 (0.5)
2 (1)
100c
100c
Br
Br
N
N
1 (1)
2 (1)
100
100
1 (1)
2 (1)
94
100
S
Br
S
O
H
O
H
5
6
7
8
Br
[19]
[18]
[18]
[20]
1 (0.5)
2 (0.5)
97c
72c
1 (1)
2 (1)
96
92
Br
1 (0.5)
2 (1)
90
96
Br
MeO
OHC
MeO
OHC
1 (1)
2 (1)
85
93
Br
MeO
MeO
9
[21]
1 (1)
2 (1)
79
100
Br
a
Reaction conditions: Aryl bromide (0.5 mmol), phenylboronic acid (0.75 mmol), K2CO3 (1 mmol), MeOH (5 mL).
Conversion to the coupled product determined by GC based on aryl bromide.
Isolated yield.
b
c
presented in Table 4 show the efficiency of these new catalysts to-
wards the coupling reactions.
7600 and 66000 TONS were achieved for catalyst loading of 0.0125
and 0.0005 mol%, respectively (entries 5, 6), indicating the effi-
ciency of the catalyst systems.
It is important to evaluate the catalytic activity in the Suzuki–
Miyaura coupling reactions at lower concentrations. We therefore
examined the effect of catalyst loading in the reaction between 4-
bromobenzonitrile and 4-bromoacetophenone with phenylboronic
acid (Table 5). The results are encouraging with the catalysts show-
ing good activity at room temperature. In order to asses the effec-
tiveness of the ligands, blank reaction containing only the metal
precursor, Pd(OAC)2 was tested which showed 16.6% conversion
with relatively low TON of 1326 (entry 1). The ligand supported
catalysts showed around 8000 TON (entry 2) with ligand 2. Very
high turnover number was observed at 0.00005 mol% catalyst con-
centration (entry 4). Similarly when we carried out the coupling
reactions by taking 4-bromoacetophenone and phenylboronic acid,
5. Suzuki–Miyaura cross-coupling reactions for aryl chlorides
Optimized conditions for the Suzuki–Miyaura coupling of aryl
chlorides with phenylboronic acid in the presence of Pd(OAc)2/1
or 2 mixture catalyst (1–4 mol%) were found to be combination
of aryl chloride (0.5 mmol) with phenylboronic acid (0.753 mmol)
using 4 mol% in situ catalyst systems Pd(OAc)2/1 or 2 in DMF with
K2CO3 (1.0 mmol) as base at 110 °C under aerobic condition. The
reaction time has not been optimized. Various aryl chlorides were
utilized for the coupling reaction under the optimized reaction
conditions and the results obtained were tabulated in Table 6. In

2118
S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
Table 4
Comparison with other catalytic systems.
Entry
Ar–Br
[Pd] (mol%)
Base
Solvent
Conditions
Yield (%)
Ref.
1
2
3
4-MeCOPhBr
4-MeCOPhBr
4-MeCOPhBr
[PdCl2(dppf)], 1 mol%
K2CO3
Cs2CO3
K2CO3
Toluene
Dioxane
Toluene
70 °C, 2 h
80 °C, 1 h
70 °C, 1 h
94
98
92
[23]
[8a]
[24]
Pd(OAc)2/diazobutadiene, 3 mol%
Bis(oxazolinyl)-pyrrole dimeric palladium
complex, 0.01 mol%
4
4-MeCOPhBr
Palladium(II) metallamacrocycle
supported by an amino-functionalised
ferrocene complex, 0.5 mol%
Pd(OAc)2/2-aryl-2-oxazolines, 2 mol%
Oxime-derived palladacycle, 0.001 mol%
Oxime-derived palladacycles, 0.01 mol%
C17H21Cl2N3OPd ꢀ 2CHCl3, 0.2 mol%
Pd(OAc)2/2, 0.0125 mol%
K2CO3
Methanol
RT, 1 h
99
[25]
5
6
7
8
4-MeOPhBr
4-MeCOPhBr
4-MeCOPhBr
4-MeCOPhBr
4-MeCOPhBr
4-MeCOPhBr
4-MeCOPhBr
4-MeOPhBr
Cs2CO3
K2CO3
KOH
Cs2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Dioxane
Toluene
80 °C, 4 h
110 °C, 0.5–1 h
RT, 5 h–4 days
80 °C, 1.5 h
RT, 1 h
RT, 1 h
RT, 0.5 h
60 °C, 3 h
61–96
77–99
94–100
98
95
100
[10]
[26]
[8i]
[27]
This work
This work
This work
This work
MeOH/H2O
Dioxane
Methanol
Methanol
Methanol
Methanol
9
10
11
12
Pd(OAc)2/2, 0.5 mol%
Pd(OAc)2/2, 0.0005 mol%
Pd(OAc)2/2, 0.5 mol%
33.0
96
Table 5
Effect of low catalyst loading on the coupling reactions.a
R
R
Cat., K2CO3
B(OH)2
Br
+
MeOH, RT, 1hr
Entry
–R
Catalyst
Amount of catalyst (mol%)
Yield (%)b
TONc
1
2
3
4
5
6
–CN
–CN
–CN
–CN
–COCH3
–COCH3
Pd(OAc)2
0.0125
0.0125
0.0005
0.00005
0.0125
0.0005
16.6
1328
7634
69380
548400
7600
Pd(OAc)2/2
Pd(OAc)2/2
Pd(OAc)2/2
Pd(OAc)2/2
Pd(OAc)2/2
95.43
34.69
27.42
95.00
33.00
66000
a
Reaction conditions: Aryl bromide (0.5 mmol), phenylboronic acid (0.75 mmol), K2CO3 (1 mmol), MeOH (5 mL).
Conversion to the coupled product determined by GC based on aryl bromide.
In units of (mol of product)/(mol of Pd).
b
c
Table 6
Suzuki–Miyaura cross-coupling of aryl chlorides with phenylboronic acid.a
R1
R1
Cat., K2CO3
DMF,110oC
B(OH)2
+
Cl
+
7
6a-d
5a-d
Entry
1
Aryl halides
Product
Ref.
Ligand
Yield (%)b
6
Yieldb (%) 7
H
H
1
2
74
92
18
7
O
O
6a [28]
Cl
Cl
2
3
6b [29]
6c [16]
6d [18]
1
2
87
58
8
37
NO2
NO2
1
2
49
72
51
21
Cl
NC
NC
4
1
2
45
50
54
50
Cl
O2N
O2N
a
Reaction conditions: Aryl chloride (0.5 mmol), phenylboronic acid (0.75 mmol), K2CO3 (1 mmol), 4 mol% catalyst (1:1), DMF (5 mL).
Conversion to the coupled product determined by GC, average of two runs.
b

S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
2119
all the cases, along with the expected coupled products, small
quantities of biphenyl were also obtained as a result of homocou-
pling of phenylboronic acid. Under the standardized reaction con-
ditions, the electron-poor o-chlorobenzaldehyde and o-
chloronitrobenzene plus phenylboronic acid gave coupled product
in excellent yields with less homocoupled product (entries 1, 2).
The activated p-chlorobenzonitrile plus phenylboronic acid in the
presence of 1 and 2 gave moderate yields of coupling product (en-
try 3). p-Substituted chlorides such as p-chloronitrobenzene affor-
ded moderate amounts of coupled product under similar reaction
conditions (entry 4).
These results suggested that these catalysts are quite effective
in promoting C–C coupling under mild conditions for both bromo
and chloro derivatives. All the catalytic runs generate palladium
black due to the partial catalytic decomposition and the experi-
mental data including the TEM analysis has confirmed that the pal-
ladium black is not the active catalyst [30] as there was no change
in the particle size. Further, the homogeneous nature of the catal-
ysis was checked by classical mercury test [31]. Addition of a drop
of mercury to the reaction mixture did not affect the conversion of
the reaction which suggests that the catalysis is homogeneous in
nature, since heterogeneous catalysts would form an amalgam,
there by poisoning it.
trometry experiments were carried out using Waters Q-Tof mi-
cro-YA-105. Infrared spectra were recorded on a Nicolet Impact
400 FT-IR instrument as a KBr disk or in Nujol mull. Melting points
were observed in capillary tubes and are uncorrected.
7.1. Synthesis of [(2-HOC10H6)CH2(l-NC4H8N)CH2(C10H6-2-OH)] (1)
A mixture of piperazine (1.49 g, 17.3 mmol) and 40% aqueous
formaldehyde solution (3.9 mL, 52 mmol) were dissolved in meth-
anol (40 mL) and heated to reflux for 2 h to give a clear solution.
The solution was cooled to room temperature and 2-naphthol
(5.0 g, 34.7 mmol) in methanol (60 mL) was added. The resulting
reaction mixture was refluxed for a further 12 h and then cooled
to room temperature. The colorless crystalline solid 1 was filtered
off and dried in vacuum. M.p.: >250 °C. Anal. Calc. for C26H26N2O2:
C, 78.36; H, 6.57; N, 7.02. Found: C, 78.24; H, 6.49; N, 7.10%. FT-IR
(KBr disc): m .
OH = 3445 (br) cmꢁ1 1H NMR (400 MHz, DMSO-d6): d
8.19 (s, naphthyl, H), d 7.91 (d, JHH = 8.4 Hz, naphthyl, H), d 7.72
(d, JHH = 7.6 Hz, naphthyl, H), d 7.64 (d, JHH = 8.8 Hz, naphthyl, H),
d 7.41–7.21 (m, naphthyl, H), d 7.03 (d, JHH = 8.8 Hz, naphthyl, H),
4.06 (s, CH2, 4H), d 3.18 (br s, NCH2, 8H). MS (EI): m/z 399.2 [M+H]+.
7.2. Synthesis of [(5-tBuC6H3-2-OH)CH2( -NC4H8N)CH2(5-tBuC6H3-2-
l
OH)] (2)
6. Conclusions
This was synthesized by a procedure similar to that of 1, using
(7.51 g, 50 mmol) 4-tert-butyl phenol, piperazine (2.2 g, 25 mmol)
and 40% aqueous formaldehyde solution (5.3 mL, 75.36 mmol).
Yield: 65% (6.68 g, 16.3 mmol). Anal. Calc. for C26H38N2O2: C,
76.05; H, 9.32; N, 6.82. Found: C, 76.18; H, 9.43; N, 6.88%. FT-IR
In summary, palladium complexes of diamino-diol ligands are
very efficient catalysts for the Suzuki–Miyaura cross-coupling
reactions under mild reaction conditions. Very good conversions
of the coupled product were obtained using methanol as solvent
in aerobic conditions for the aryl bromides at room temperature,
whereas the aryl chlorides show good conversion rate under ele-
vated temperature in DMF. The present system is highly air and
moisture stable and the ligands can be synthesized readily from
inexpensive and commercially available starting materials. Utiliza-
tion of these catalysts in various other organic transformations
such as Heck coupling, amination and dehalogenation reactions
are in progress. Presently we do not have any experimental sup-
port to propose a mechanism for the catalytic pathway. In a typical
Suzuki–Miyaura cross-coupling reaction, PdII species is reduced to
Pd0 species prior to the oxidative addition. In the present case, sim-
ilar speculation may lead to a Pd0 species containing only nitrogen
donors which is less likely as nitrogen donor ligands can not stabi-
lize Pd0 complexes. An alternative reaction path may involve a PdII
species which can be oxidized to PdIV during the oxidative addition
and is eventually reduced to the PdII species. However, further
investigations are needed to substantiate one of these aspects
and the work is in progress in this direction.
(KBr disc):
m .
OH = 3444 (br) cmꢁ1 1H NMR (400 MHz, CDCl3): d
10.45 (br, OH, 2H), d 7.19 (d, JHH = 6.8 Hz, phenyl, 2H), d 6.96 (s, phe-
nyl, 2H), d 6.75 (d, JHH = 8.4 Hz, phenyl, 2H), 3.72 (s, CH2, 4H), d 2.93
(s, NCH2, 4H), d 2.37 (s, NCH2, 4H) d 1.27 (s, tBu, 18H). 13C {1H} NMR
(100 MHz, CDCl3, d): 155.2 (s, phenyl), 142.2 (s, phenyl), 125.8 (s,
phenyl), 125.7 (s, phenyl), 120.2 (s, phenyl), 115.6 (s, phenyl), 61.8
(s, CH2), 52.6 (s, NCH2), 34.1 (s, C(Me)3), 31.7 (s, CH3). MS (EI): m/
z 411.6 [M+H]+.
7.3. Synthesis of [(2-OC10H6)CH2(l-NC4H8N)CH2(C10H6-2-O)Pd] (3)
A solution of [Pd(OAc)2] (0.028 g, 0.127 mmol) in dichlorometh-
ane (5 mL) was added dropwise to 1 (0.051 g, 0.127 mmol) also in
dichloromethane (5 mL) at room temperature. The reaction mix-
ture was stirred for 6 h. The pale yellow precipitate formed was
collected by filtration and washed with diethyl ether to give ana-
lytically pure product of 3 as a yellow crystalline solid. Yield:
77% (0.049 g, 0.098 mmol). M.p.: 236–240 °C (dec.). Anal. Calc. for
C26H24N2O2Pd: C, 62.09; H, 4.81; N, 5.57. Found: C, 62.02; H,
4.90; N, 5.48%. 1H NMR (400 MHz, DMSO-d6): d 8.23–7.12 (m, naph-
thyl protons), 4.0 (s, CH2, 4H), d 3.14 (br s, NCH2, 8H). MS (EI): m/z
503.4 [M+H]+.
7. Experimental
Most of the bromo and chloro compounds, phenylboronic acid,
naphthol and 4-tert-butyl phenol were purchased from Aldrich.
Anhydrous K3PO4, and K2CO3 were purchased from SIGMA chemi-
cals and SDFINE chemicals, respectively, and used as such received
without further purification. Technical grade methanol and DMF
were used for all catalytic reactions. All other reagents were used
as received. Gas chromatographic analyses were performed on a
Perkin–Elmer Clarus 500 GC and Hewlett Packard G 1800A GCD
Systems equipped with a packed column. The 1H and 13C{1H}
NMR (d in ppm) spectra were obtained on a Varian VXR 400 spec-
trometer operating at an appropriate frequencies of using TMS as
standard. Positive shifts lie downfield of the standard in all the
cases. Microanalyses were carried out on a Carlo Erba Model
1106 elemental analyzer. Electro-spray ionization (EI) mass spec-
7.4. Synthesis of [(2-O-5-tBuC6H3)CH2( -NC4H8N)CH2(5-tBuC6H3-2-
l
O)Pd] (4)
This was synthesized by a procedure similar to that of 3 by
reacting [(5-tBuC6H3-2-OH)CH2( -NC4H8N)CH2(5-tBuC6H3-2-OH)]
l
(0.029 g, 0.072 mmol) and [Pd(OAc)2] (0.016 g, 0.072 mmol) at
room temperature. Yield: 85% (0.032 g, 0.061 mmol). M.p.: 140–
142 °C (dec.). Anal. Calc. for C26H36N2O2Pd: C, 60.63; H, 7.05; N,
5.44. Found: C, 60.67; H, 7.17; N, 5.55%. 1H NMR (400 MHz, CDCl3):
d 7.12 (d, JHH = 7.22 Hz, phenyl, 2H), d 6.98 (s, phenyl, 2H), d 6.82 (d,
JHH = 8.4 Hz, phenyl, 2H), 3.62 (s, CH2, 4H), d 2.91 (s, NCH2, 4H), d
t
2.32 (s, NCH2, 4H) d 1.26 (s, Bu, 18H).

2120
S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
7.5. X-ray crystallography
C13H9N: C, 87.12; H, 5.06; N, 7.81. Found: C, 86.22; H, 5.03; N,
7.70%. MS (EI): m/z 179.0 [M]+.
Crystals of 2 and 4 were mounted in a CryoloopTM with a drop of
Paratone oil and placed in the cold nitrogen stream of the Kryo-
flexTM attachment of the Bruker APEX CCD diffractometer. A full
8.3. 4-Phenylbenzaldehyde [19]
sphere of data was collected for 2 using 606 scans in
x
(0.3° per
Yellow liquid. 1H NMR (400 MHz, CDCl3): d7.98–7.25 (m, phenyl,
9H), 10.04 (s, CHO, 1H). 13C{1H} NMR (100 MHz, CDCl3): d 192.1
(C@O), 147.3 (s, phenyl), 139.8 (s, phenyl), 135.3 (s, phenyl), 130.4
(s, phenyl), 130.2 (s, phenyl), 129.2 (s, phenyl), 128.9 (s, phenyl),
128.6 (s, phenyl), 128.4 (s, phenyl), 127.8 (s, phenyl), 127.5 (s, phe-
nyl). MS (EI): m/z 182.0 [M]+.
scan) at / = 0, 120 and 240° using the SMART software package
[32a] while for 4 three sets of 400 frames, each of width 0.5° in
omega, collected at / = 0.00, 90.00 and 180.00° and 2 sets of 800
frames, each of width 0.45° in /, collected at
x
= ꢁ30.00 and
210.00° employing the APEX2 [32b] program suite were used. The
raw data were reduced to F2 values using the SAINT+ software [33]
and a global refinements of unit cell parameters using 3595 (for
2) or 9962 (for 4) reflections chosen from the full data set were
performed. Multiple measurements of equivalent reflections pro-
vided the basis for an empirical absorption correction as well as
a correction for any crystal deterioration during the data collection
Acknowledgements
We are grateful to the Department of Science and Technology
(DST), New Delhi for financial support of this work through grant
SR/S1/IC-02/2007. We thank SAIF IIT Bombay, for LC-MS data.
S.M. thanks CSIR for Research Associate (RA) Fellowship and DS
is thankful to IIT Bombay for JRF and SRF.
(SADABS) [34]. The structures were solved by direct methods and re-
fined by full-matrix least-squares procedures using the SHELXTL pro-
gram package [35]. Hydrogen atoms were placed in calculated
positions and included as riding contributions with isotropic dis-
placement parameters tied to those of the attached non-hydrogen
atoms.
Appendix A. Supplementary material
CCDC 690771 and 690772 contain the supplementary crystallo-
graphic data for 2 and 4. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2009.02.019.
8. Typical procedure for Suzuki–Miyaura cross-coupling
reactions
In a two-necked round bottom flask the appropriate amount of
ligand, metal precursors and 5 mL of solvent were placed with a
magnetic stir bar. After stirring for 5 min the aryl halide
(0.5 mmol), aryl boronic acid (0.75 mmol) and base (1 mmol) were
added to the reaction flask. The reaction mixture was heated to the
appropriate temperature for the required time (the course of reac-
tion was monitored by GC analysis) and then the solvent was re-
moved under reduced pressure. The resultant residual mixture
was diluted with H2O (8 mL) and Et2O (8 mL), followed by extrac-
tion twice (2 ꢂ 6 mL) with Et2O. The organic fraction was dried
(MgSO4), filtered, stripped of the solvent under vacuum and the
residue was redissolved in 5 mL of dichloromethane. An aliquot
was taken with a syringe and subjected to GC/GCMS analysis.
Yields were calculated against consumption of the aryl halides.
The crude material was purified by silica column chromatography
using hexane-ethyl acetate as an eluent to give the desired biaryls.
For experiments with low catalyst loading and for comparison of
other Pd(II) sources, stock solution of appropriate concentration
was prepared by dissolving 1.0 mg of the palladium catalyst in
appropriate amount of DCM and used for each independent run.
References
[1] (a) K. Tamao, K. Sumitani, M. Kumada, J. Am. Chem. Soc. 94 (1972) 4374;
(b) M. Yamamura, I. Moritani, S. Murahashi, J. Organomet. Chem. 91 (1975)
C39;
(c) A. Sekiya, N. Ishikawa, J. Organomet. Chem. 118 (1976) 349.
[2] (a) J.K. Stille, Angew. Chem., Int. Ed. Engl. 25 (1986) 508;
(b) T.N. Mitchell, F. Diederich, P.J. Stang (Eds.), Metal Catalysed Cross-coupling
Reactions, Willey-VCH, Weinhem, 1998, p. 167;
(c) S.T. Handy, X. Zhang, Org. Lett. 3 (2001) 233.
[3] Y. Hatanaka, T. Hiyama, Synlett (1991) 845.
[4] E. Erdik, Tetrahedron 48 (1992) 9577.
[5] (a) D. Alberico, M.E. Scott, M. Lautens, Chem. Rev. 107 (2007) 174;
(b) J.P. Corbet, G. Mignani, Chem. Rev. 106 (2006) 2651;
(c) F. Alonso, I.P. Beletskaya, M. Yus, Tetrahedron 64 (2008) 3047;
(d) S. Kotha, K. Lahiri, D. Kashinath, Tetrahedron 58 (2002) 9633;
(e) N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457;
(f) A. Suzuki, J. Organomet. Chem. 576 (1999) 147;
(g) M. Beller, C. Bolm, Transition Metals for Organic Synthesis, vols. 1–2,
Wiley-VCH, Weinheim, 1998;
(h) B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis with
Organometallic Coumpounds, Wiley-VCH, Weinheim, 1996;
(i) A. Huth, I. Beetz, I. Schumann, Tetrahedron 45 (1989) 6619;
(j) D.S. Ennis, J. McManus, W. Wood-Kaczmar, J. Richardson, G.E. Smith, A.
Carstairs, Org. Proc. Res. Dev. 3 (1999) 248.
8.1. 4-Acetylbiphenyl
[6] S. Haber, H.J. Kleiner, DE 19527118, 1997.
[7] (a) M.G. Andreu, A. Zapf, M. Beller, Chem. Commun. (2000) 2475;
(b) A. Zapf, A. Ehrentraut, M. Beller, Angew. Chem., Int. Ed. 39 (2000) 4153;
(c) X. Bei, H.W. Turner, W.H. Weinberg, A.S. Guram, J.L. Petersen, J. Org. Chem.
64 (1999) 6797;
(d) X. Bei, T. Crevier, A.S. Guram, B. Jandeleit, T.S. Powers, H.W. Turner, T. Uno,
W.H. Weinberg, Tetrahedron Lett. 40 (1999) 3855;
(e) A.F. Littke, G.C. Fu, Angew. Chem., Int. Ed. 37 (1998) 3387.
[8] (a) G.A. Grasa, A.C. Hillier, S.P. Nolan, Org. Lett. 3 (2001) 1077;
(b) T. Weskamp, V.P.W. Bohm, W.A. Herrmann, J. Organomet. Chem. 585
(1999) 348;
White powder. M.p.: 126–128 °C, (lit. [15] 123 °C) Anal. Calc. for
C14H12O: C, 85.68; H, 6.16. Found: C, 86.20; H, 6.49%. 1H NMR
(400 MHz, CDCl3): d 8.05–7.26 (m, phenyl, 9H), 2.65 (s, CH3, 3H).
13C{1H} NMR (100 MHz, CDCl3): d 198.0 (C@O), 146.0 (s, phenyl),
140.1 (s, phenyl), 136.0 (s, phenyl), 129.1 (s, phenyl), 129.6 (s, phe-
nyl), 128.4 (s, phenyl), 127.5 (s, phenyl), 127.4 (s, phenyl), 26.7
(CH3). MS (EI): m/z 196.0 [M]+.
(c) C. Zhang, J. Huang, M.L. Trudell, S.P. Nolan, J. Org. Chem. 64 (1999) 3804;
(d) C. Zhang, M.L. Trudell, Tetrahedron Lett. 41 (2000) 595;
(e) V.P.W. Bohm, C.W.K. Gstottmayr, T. Weskamp, W.A. Herrmann, J.
Organomet. Chem. 595 (2000) 186;
8.2. [1,10-Biphenyl]-4-carbonitrile
(f) H. Weissman, D. Milstein, Chem. Commun. (1999) 1901;
(g) R.B. Bedford, C.S.J. Cazin, Chem. Commun. (2001) 1540;
(h) D.A. Alonso, C. Najera, M.C. Pacheco, Org. Lett. 2 (2000) 1823;
(i) L. Botella, C. Najera, Angew. Chem., Int. Ed. 41 (2002) 179;
(j) D. Yang, Y.C. Chen, N.Y. Zhu, Org. Lett. 6 (2004) 1577;
(k) G.A. Grasa, M.S. Viciu, J. Huang, C. Zhang, M.L. Trudell, S.P. Nolan,
Organometallics 21 (2002) 2866;
White powder. M.p.: 83–85 °C., (lit. [16] 85–86 °C) 1H NMR
(400 MHz, CDCl3): d 7.77–7.26 (m, phenyl, 9H). 13C{1H} NMR
(100 MHz, CDCl3): d 145.9 (s, phenyl), 139.4 (s, phenyl), 132.8 (s,
phenyl), 129.3 (s, phenyl), 128.8 (s, phenyl), 127.9 (s, phenyl),
127.4 (s, phenyl), 119.1 (C„N), 111.1 (C–C„N). Anal. Calc. for

S. Mohanty et al. / Journal of Organometallic Chemistry 694 (2009) 2114–2121
2121
(l) C.R. LeBlond, A.T. Andrews, Y. Sun, J.R. Sowa, Org. Lett. 3 (2001) 1555;
(m) H. Sakurai, T. Tsukuda, T. Hirao, J. Org. Chem. 67 (2002) 2721;
(n) G.W. Kabalka, V. Namboodiri, L. Wang, Chem. Commun. (2001) 775;
(o) N.E. Leadbeater, M. Marco, Org. Lett. 4 (2002) 2973;
(p) L. Botella, C. Najera, J. Organomet. Chem. 663 (2002) 46.
[9] B. Tao, D.W. Boykin, Tetrahedron Lett. 43 (2002) 4955.
[10] M.R. Buchmeiser, T. Schareina, R. Kempe, K. Wurst, J. Organomet. Chem. 634
(2001) 39.
[22] (a) J.P. Wolfe, R.A. Singer, B.H. Yang, S.L. Buchwald, J. Am. Chem. Soc. 121
(1999) 9550;
(b) X. Cuia, Y. Zhoua, N. Wanga, L. Liu, Q. Guo, Tetrahedron Lett. 48 (2007) 163;
(c) N. Marion, O. Navarro, J. Mei, E.D. Stevens, N.M. Scott, S.P. Nolan, J. Am.
Chem. Soc. 128 (2006) 4101;
(d) O. Navarro, N. Marion, J. Mei, S.P. Nolan, Chem. Eur. J. 12 (2006) 5142;
(e) J.C. Anderson, H. Namli, C.A. Roberts, Tetrahedron 53 (1997) 15123;
(f) S.A. Frank, H. Chen, R.K. Kunz, M.J. Schnaderbeck, W.R. Roush, Org. Lett. 2
(2000) 2691;
[11] (a) D. Morales-Morales, R. Redon, C. Yung, C.M. Jensen, Chem. Commun.
(2000) 1619;
(g) N. Kataoka, Q. Shelby, J.P. Stambuli, J.F. Hartwig, J. Org. Chem. 67 (2002)
5553;
(b) M. Ohff, A. Ohff, M.E. van der Boom, D. Milstein, J. Am. Chem. Soc. 119
(1997) 11687;
(c) Q. Yao, E.P. Kinney, Z. Yand, J. Org. Chem. 68 (2003) 7528;
(d) B.L. Shaw, New J. Chem. (1998) 77.
(h) A. Kamatani, L.E. Overman, J. Org. Chem. 64 (1999) 8743;
(i) Y. Uozumi, H. Danjo, T. Hayashi, J. Org. Chem. 64 (1999) 3384;
(j) T.J. Colacot, E.S. Gore, A. Kuber, Organometallics 21 (2002) 3301;
(k) D. Zim, A.S. Gruber, G. Ebeling, J. Dupont, A.L. Monteiro, Org. Lett. 2 (2000)
2881;
[12] S. Mohanty, D. Suresh, M.S. Balakrishna, J.T. Mague, Tetrahedron 64 (2008)
240.
[13] (a) B. Punji, C. Ganesamoorthy, M.S. Balakrishna, J. Mol. Catal. A 259 (2006) 78;
(b) P. Chandrasekaran, J.T. Mague, M.S. Balakrishna, Organometallics 24
(2005) 3780;
(l) J.C. Bussolari, D.C. Rehborn, Org. Lett. 1 (1999) 965.
[23] T.J. Colacot, H. Qian, R. Cea-Olivares, S. Hernandez-Ortega, J. Organomet. Chem.
637–639 (2001) 691.
(c) C. Ganesamoorthy, M.S. Balakrishna, P.P. George, J.T. Mague, Inorg. Chem.
46 (2007) 848;
(d) M.S. Balakrishna, D. Suresh, P.P. George, J.T. Mague, Polyhedron 25 (2006)
3215;
(e) R. Venkateswaran, J.T. Mague, M.S. Balakrishna, Inorg. Chem. 46 (2007)
809;
(f) S. Mohanty, B. Punji, M.S. Balakrishna, Polyhedron 25 (2006) 815;
(g) B. Kaboudin, M.S. Balakrishna, Synth. Commun. 31 (2001) 2773–2776;
(h) S. Priya, M.S. Balakrishna, J.T. Mague, Inorg. Chem. Commun. 4 (2001) 437–
440.
[24] C. Mazet, L.H. Gade, Organometallics 20 (2001) 4144.
[25] Z. Weng, S. Teo, L.L. Koh, T.S.A. Hor, Organometallics 23 (2004) 3603.
[26] D.A. Alonso, C. Najera, M.C. Pacheco, J. Org. Chem. 67 (2002) 5588.
[27] V. Cesar, S.B. Laponnaz, L.H. Gade, Organometallics 21 (2002) 5204.
[28] C. Stroh, M. Mayor, C.V. Hänisch, Eur. J. Org. Chem. (2005) 3697.
[29] L. Wang, Y. Zhang, L. Liu, Y. Wang, J. Org. Chem. 71 (2006) 1284.
[30] (a) J.G. de vries, Dalton Trans. (2006) 421;
(b) A.H.M. de vries, J.M.C.A. Mulders, J.H.M. Momers, H.J.W. Henderickx, J.G. de
vries, Org. Lett. 5 (2003) 3285.
[31] (a) K. Inamoto, J. Kuroda, K. Hiroya, Y. Noda, M. Watanabe, T. Sakamoto,
Organometallics 25 (2006) 3095;
(b) J.A. Widegren, R.G. Finke, J. Mol. Catal. A 198 (2003) 317;
(c) E. Peris, J.A. Loch, J. Mata, R.H. Crabtree, Chem. Commun. (2001) 201.
[32] (a) Bruker-AXS, SMART, Version 5.625, Madison, WI, 2000.;
(b) Bruker-AXS, APEX2, Version 2.1-0, Madison, WI, 2006.
[33] Bruker-AXS, SAINT+, Version 6.35A, Madison, WI, 2002.
[34] G.M. Sheldrick, SADABS, Version 2.05, University of Gottingen, Germany, 2002.
[35] (a) Bruker-AXS, SHELXTL, Version 6.10, Madison, WI, 2000;
(b) G.M. Sheldrick, SHELXS97 and SHELXL97, University of Göttingen, Germany,
1997.
[14] S. Mukhopadhyay, D. Mandal, P.B. Chatterjee, C. Desplanches, J.P. Sutter, R.J.
Butcher, M. Chaudhury, Inorg. Chem. 43 (2004) 8501.
[15] C. Dupuis, K. Adiey, L. Charruault, V. Michelet, M. Savignac, J. Gene,
Tetrahedron Lett. 42 (2001) 6523.
[16] C. Najera, J. Gil-Molto, S. Karlstrom, L.R. Falvello, Org. Lett. 5 (2003) 1451.
[17] Y. Kobayashi, A.D. William, R. Mizojiri, J. Organomet. Chem. 653 (2002) 91.
[18] L. Liang, P. Chien, M. Huang, Organometallics 24 (2005) 353.
[19] J. Ma, X. Cui, B. Zhang, M. Song, Y. Wu, Tetrahedron 63 (2007) 5529.
[20] B. Tao, D.W. Boykin, J. Org. Chem. 69 (2004) 4330.
[21] D. Badone, M. Baroni, R. Cardamone, A. Ielmini, U. Guzzi, J. Org. Chem. 62
(1997) 7170.