Isolation of chloro-bridged arylpalladium complexes, [Pd2Ar 2(μ-Cl)2(PR3)2], in palladium catalyzed C-C cross coupling reaction of triarylbismuth with arylhalides

Article abstract of DOI:10.1016/j.jorganchem.2011.09.024

The reaction of [Pd₂Cl₂(μ-Cl)₂(PR ₃)₂] with triarylbismuth in dichloromethane at room temperature afforded chloro-bridged arylpalladium complexes, [Pd ₂Ar₂(μ-Cl)₂(PR₃)₂] (Ar = Ph or 4-MeC₆H₄ (tol)) in 85-90% yield as a yellow crystalline powder. These complexes were characterized by elemental analysis and NMR spectroscopy. Molecular structures of [Pd₂tol ₂(μ-Cl)₂(PEt₃)₂] and [Pd ₂Ph₂(μ-Cl)₂(PMePh₂)₂] were established by single crystal X-ray crystallography. These complexes are centrosymmetric dimers with trans configuration. The C-C coupling reaction between triarylbismuth and an arylhalide in the presence of a base is catalyzed by [Pd₂Cl₂(μ-Cl)₂(PR₃) ₂]. The reactions proceed via an arylpalladium complex formed by transmetallation reaction between [Pd₂Cl₂(μ-Cl) ₂(PR₃)₂] and Ar₃Bi. Probable reaction routes for C-C coupling have been discussed.

Full text of DOI:10.1016/j.jorganchem.2011.09.024

Journal of Organometallic Chemistry 698 (2012) 15e21
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Isolation of chloro-bridged arylpalladium complexes, [Pd2Ar2(m-Cl)2(PR3)2],
in palladium catalyzed CeC cross coupling reaction of triarylbismuth with
arylhalides
*
Kamal R. Chaudhari, Amey P. Wadawale, Vimal K. Jain
Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of [Pd2Cl2(
afforded chloro-bridged arylpalladium complexes, [Pd2Ar2(
m
-Cl)2(PR3)2] with triarylbismuth in dichloromethane at room temperature
-Cl)2(PR3)2] (Ar ¼ Ph or 4-MeC6H4 (tol)) in
85e90% yield as a yellow crystalline powder. These complexes were characterized by elemental analysis
and NMR spectroscopy. Molecular structures of [Pd2tol2( -Cl)2(PEt3)2] and [Pd2Ph2( -Cl)2(PMePh2)2]
Received 23 May 2011
Received in revised form
19 September 2011
m
m
m
Accepted 28 September 2011
were established by single crystal X-ray crystallography. These complexes are centrosymmetric dimers
with trans configuration. The CeC coupling reaction between triarylbismuth and an arylhalide in the
presence of a base is catalyzed by [Pd2Cl2(m-Cl)2(PR3)2]. The reactions proceed via an arylpalladium
Keywords:
Palladium
CeC coupling
C coupling
Bismuth
complex formed by transmetallation reaction between [Pd2Cl2(
m
-Cl)2(PR3)2] and Ar3Bi. Probable reaction
routes for CeC coupling have been discussed.
Ó 2011 Elsevier B.V. All rights reserved.
X-ray
Catalysis
1. Introduction
[4], PdCl2(PPh3)2) [8]) have been used as a catalyst and have shown
similar catalytic activity [9]. The formation of an organopalladium
species “ArePdeX” as an intermediate has been envisaged in these
reactions [4,5a,10].
Metal catalyzed cross coupling reaction of organic halides with
organometallic reagents is one of the most important organic
transformations for making CeC bonds [1] and is exploited in
industry for preparing pharmaceuticals, agrochemicals and fine
chemicals [2]. Palladium catalyzed cross coupling reactions are
unparalleled due to their flexibility, and ease of handling and
preparing palladium complexes which show tolerance to a wide
range of functionalities [3]. The well known Suzuki, Negishi, Stille
and Kumada CeC cross coupling reactions employ organoboron,
organozinc, organotin and organomagnesium reagents, respec-
tively [1]. These reactions require organometallic reagents in stoi-
chiometric amounts and suffer from atom economy. In this context,
triarylbismuth compounds are gaining momentum as multi-
coupling organometallic compounds and can react with three
equivalents of electrophilic reagents. Besides this, they are non-
toxic and show high reactivity due to weak BieC bond energy.
Barton [4], Tanaka [5], Rao [6] and others [7], has demonstrated use
of organobismuth compounds in CeC coupling reactions. Both
palladium(0) (e. g., Pd(PPh3)4 [5a]) and palladium(II) (e. g., Pd(OAc)2
Coordinately unsaturated metal complexes are proposed as
catalytically active species in metal catalyzed organic trans-
formations [11], such as hydrogenation, hydroformylation, CeC
coupling reactions, etc. Many palladium-catalyzed reactions are
proposed to involve 14-electron, three coordinate complexes. Such
complexes are generated either by oxidative addition of an aryl-
halide on palladium(0) species or by dissociation of a ligand moiety
from a four coordinate palladium complex. In fact, Hartwig and
coworker [12] have isolated and structurally characterized T-sha-
ped three-coordinate organopalladium complexes. The ease of
formation of three-coordinate palladium(II) species has been
assessed by density functional theory methods [13]. These tri-
coordinated palladium(II) complexes have also been used as
a catalyst for polymerization of norbornenes [14] and reactions of
arylhalides with organometallic species [15] and amines [16].
Recently binuclear chloro-bridged complexes, [Pd2Cl2(m-Cl)2(PR3)2]
have been used as a catalyst in Heck [17] and SuzukieMiyaura [18]
cross coupling reactions. In SuzukieMiyaura cross coupling, the
reaction between p-bromoanisole and ArB(OH)2 (Ar ¼ Ph or 4-
MeC6H4) in the presence of [Pd2Cl2(m-Cl)2(PPh3)2] gives 32 and
* Corresponding author. Tel.: þ91 22 25595095; fax: þ91 22 25505151/25519613.
E-mail address: jainvk@barc.gov.in (V.K. Jain).
46% yields, respectively of the crossed-coupled product [18].
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.09.024

16
K.R. Chaudhari et al. / Journal of Organometallic Chemistry 698 (2012) 15e21
With the above perspective we have examined catalytic activity
of chloro-bridged binuclear palladium complexes, Pd2Cl2(
Cl)2(PR3)2 in the reactions of arylhalides with triarylbismuth. It
was anticipated that three coordinate palladium complex
“PdArCl(PR3)” would form as an intermediate by transmetallation
reaction. Indeed we could isolate binuclear arylpalladium
9-iodo-m-carborane [22], and (ii) oxidative addition of arylhalides
m-
(halide ¼ Br or I) on a two coordinate palladium(0) species, [Pd{P(o-
tol)3}2] [23]. Interestingly the corresponding methylpalladium
a
complexes, [Pd2Me2(
transmetallation reaction of [Pd2Cl2(
AlMe3 [24] or Me4Sn [25e27]. In an alternative method for the
synthesis of [Pd2Me2( -Cl)2(PR3)2] complexes, [CODPdMeCl] is
m-Cl)2(PR3)2] are obtained in excellent yield by
m
-Cl)2(PR3)2] with either
complexes, [Pd2Ar2(m-Cl)2(PR3)2] from these reactions. Results of
m
this work are described herein.
treated with one equivalent of tertiary phosphine in an appropriate
solvent [14,28e31].
Â
Ã
Â
Ã
Pd2Cl2ð
m
ꢀ ClÞ2ðPR3Þ2 þ Ar3Bi/ Pd2Ar2ð
m
ꢀ ClÞ2ðPR3Þ2 þ ArBiCl2
(1)
2. Results and discussion
(where PR3 ¼ PEt3, PMe2Ph, PMePh2, PPh3; Ar ¼ Ph or 4-MeC6H4
(tol))
Halide- bridged palladium complexes, [Pd2Y2(
m
-X)2L2]
To assess the utility of chloro-bridged derivatives for the
(X ¼ halide, L ¼ neutral donor ligand) are versatile synthons
synthesis of other binuclear complexes, reaction of [Pd2Ph2(
Cl)2(PMe2Ph)2] with Pb(EPh)2 were carried out and complexes of
m-
employed for the preparation of a myriad coordination and
organometallic complexes [19]. The reaction of [Pd2Cl2(
Cl)2(PR3)2] with Ar3Bi in dichloromethane proceeds smoothly
affording chloro-bridged arylpalladium complexes, [Pd2Ar2(
Cl)2(PR3)2] (Ar ¼ Ph or 4-MeC6H4 (tol)) (eq. (1)) as a pale yellow
powder in 85e90% yield. Although as prepared complexes were
spectroscopically pure for further reactions, they could be recrys-
tallized from dichlormethane-hexane mixture as pale yellow
crystals in 42e59% yield. It is noteworthy that the method is
a convenient synthetic approach for the isolation of arylpalladium
m
-
the type [Pd2Ph2(
isolated.
m
-EPh)2(PMe2Ph)2] (E ¼ S or Se) (eq. (2)) were
m-
Â
Ã
Pd2Ph2ð
m
ꢀ ClÞ2ðPMe2PhÞ2
Â
Ã
þ PbðEPhÞ2/ Pd2Ph2ð
m
ꢀ EPhÞ2ðPMe2PhÞ2
(2)
The 1H NMR spectra (Table 1) of chloro-bridged complexes
exhibited expected resonances. The 31P{1H} NMR spectra displayed
a single resonance indicating the presence of one isomeric form.
complexes, [Pd2Ar2(
son [20] for the preparation of such complexes involved a reaction
between [Pd2Cl2( -Cl)2(PR3)2] and diorganomercurials, Ar2Hg. The
m-Cl)2(PR3)2]. The method reported by Ander-
The analogous platinum complexes, [Pt2Ar2(m-Cl)2(PR3)2], exists in
m
a mixture of cis and trans isomers in solution [19]. The palladium
complexes are known to undergo rapid cis # trans isomerization
in solution [19,25], consequently resulting in the observation of
a single 31P NMR resonance. Unlike chloro-bridged complexes, the
31P{1H} NMR spectra of phenyl dichalcogenolato bridged
products were isolated in moderate yields due to difficulties in
removing RHgCl. Other synthetic methods involve (i) decomposi-
tion of a formate-bridged complex, [Pd2Ph2(m-O2CH)2(PPh3)2],
either in iodobenzene [21] or in the presence of iodobenzene and
Table 1
Physical, analytical and NMR (1H and 31P) spectral data of organopalladium complexes.
Compound
Re-crystallization solvent (% yield)
m.p (ꢁC)
% Analysis
Found (calc.)
NMR data
C
H
31P{1H}
27.0
1H
[Pd2Ph2(
m
-Cl)2(PEt3)2]
Dichloromethaneehexane (48)
Dichloromethaneehexane (52)
Dichloromethaneehexane (59)
Dichloromethane-hexane (52)
Dichloromethane-hexane (51)
Dichloromethane-hexane (55)
120
120
135
145
140
110
43.01
6.08
1.15 (d, t, 6H, CH3CH2P); 1.49e1.55 (m, 4H, CH2P);
6.95 (m, 6H, 3, 4, 5 C6H5Pd); 7.31e7.34 (m,
4H, 2, 6 C6H5Pd), 7.60 (d, 8 Hz)
1.18e1.21 (m, 6H, CH3CH2P); 1.51 (q, 4H, CH2P);
2.20 (s, 6H, CH3eC6H4Pd); 6.81 (br, 4H, C6H4);
7.18 (br, 4H, C6H4)
1.43 (d, 11 Hz, Me2P), 6.85 (br, 6H, 3, 4, 5 C6H5Pd);
7.07 (br, 4H, 2, 6 C6H5Pd); 7.35e7.47 (m, 6H,
3, 4, 5 C6H5P); 7.60 (d, 4H, 2, 6 C6H5P)
1.43 (d, 11 Hz, Me2P); 2.17 (s, 6H, H3C-C6H5Pd);
6.71 (br, C6H4); 6.94 (br, C6H4); 7.42 (m, 6H,
3, 4, 5 C6H5P); 7.63 (br, 4H, 2, 6 C6H5P)
1.49 (d, 10.5 Hz, CH3P), 6.75 (m, 6H, 3, 4, 5 C6H5Pd);
7.07 (m, 4H, 2, 6 C6H5Pd); 7.33 (m, 6H, 3, 4, 5 C6H5P);
7.59 (m, 4H, 2, 6 C6H5P)
(42.75)
(5.98)
[Pd2tol2(
m
-Cl)2(PEt3)2]
45.02
(44.49)
6.37
(6.32)
27.2
3.7
[Pd2Ph2(
m
-Cl)2(PMe2Ph)2]
47.10
(47.08)
4.44
(4.51)
[Pd2tol2(
m
-Cl)2(PMe2Ph)2]
48.63
(48.54)
4.94
(4.89)
3.9
[Pd2Ph2(
m
-Cl)2(PMePh2)2]
53.98
(54.43)
4.34
(4.32)
16.8
16.6
[Pd2tol2(
m
-Cl)2(PMePh2)2]
55.45
(55.44)
4.84
(4.65)
1.49 (d, 10.5 Hz, CH3P); 2.11 (s, 6H, H3C-C6H5Pd);
6.62 (d, C6H4); 6.90 (dd, C6H4); 7.42 (m, 6H,
3, 4, 5 C6H5P); 7.60 (m, 4H, 2, 6 C6H5P)
6.60 (br, 6H, 3,4,5 C6H5Pd); 6.96 (br);
[Pd2Ph2(
m
-Cl)2(PPh3)2]
Dichloromethane-hexane (42)
Dichloromethane-hexane (45)
Benzeneehexane (51)
170
150
125
125
59.44
(59.89)
58.71
(60.62)
55.47
(55.75)
50.6
3.86
(4.19)
4.39
(4.47)
4.85
(4.91)
4.51
31.6
31.3
7.23e7.62 (m, Ph)
[Pd2tol2(
m
-Cl)2(PPh3)2]
2.40 (s, 6H, H3C-C6H5Pd); 6.60 (m, 6H, 3, 4, 5 C6H5Pd);
6.96 (m, 4H, 2, 6 C6H5Pd); 7.23e7.79 (m, Ph)
1.14 (d, 9.3 Hz, Me2P); 1.23 (d, 9.6 Hz);
1.75 (d, 13.2 Hz); 6.66e6.95 (m); 7.42e7.76 (m)(Ph)
1.16 (d, 6H, Me2P); 6.61e7.59(m,Ph).
[Pd2Ph2(
m
-SPh)2(PMe2Ph)2]
-SePh)2(PMe2Ph)2]a
ꢀ2.9,
ꢀ3.4
ꢀ5.8,
ꢀ6.5
[Pd2Ph2(
m
Benzeneehexane (40)
(50.28)
(4.43)
a
77Se{1H} NMR, cis isomer: 66.8 (t, 2J(77See31P) ¼ 138 Hz); ꢀ201.2 (s). trans isomer; ꢀ110.4 (d, 2J(77Se e 31P) ¼ 134 Hz).

K.R. Chaudhari et al. / Journal of Organometallic Chemistry 698 (2012) 15e21
17
derivatives exhibited two resonances attributable to cis and trans
isomers. The analogous hydroxo-bridged complex, [Pd2Ph2(
m-
OH)2(PPh3)2], has been shown to exist as a 1:4 mixture of cis and
trans isomers in solution [32].
Molecular structures of [Pd2tol2(m-Cl)2(PEt3)2] and [Pd2Ph2(m-
Cl)2(PMe2Ph)2] were established unequivocally by single crystal
X-ray diffraction analyses. ORTEP drawings with crystallographic
numbering scheme are shown in Figs. 1 and 2, and the selected
interatomic parameters are given in Table 2. The complexes are
centrosymmetric sym trans dimers with the inversion center in
the planar Pd2Cl2 rhombus. The coordination environment around
each distorted square planar palladium atom is defined by two
cis-bridging chloride ligands, phosphorus atom of tertiary phos-
phine and the Cs carbon atom of the aryl group. The PdeCl
distances (w2.41 and w2.45 Å) differ significantly. The PdeCl
bond trans to the aryl group is longer than the one trans to the
phosphine ligand, and is consistent with the aryl group exerting
greater trans influence than the phosphine ligand. These
distances are in accord with the binuclear organopalladium
complexes [19,26,31]. The PdeC distances (2.00 Å) are signifi-
cantly shorter than the binuclear chloro-bridged methylpalladium
Fig. 2. Molecular structure of [Pd2tol2(
probability).
m
-Cl)2(PEt3)] (ORTEP diagram with 50%
complexes, [Pd2Me2(
m
-Cl)2(L)2] (L ¼ PR3, AsPri3) (2.029e2.100 Å)
[14,26,29e31] but are comparable to halo-bridged complexes,
and homo-coupled products in the reactions of Ph3Bi with iodo-
benzene (entry no. 1) and tol3Bi with p-tolylhalides (entry nos.
15e17) could not be ascertained as in these reactions only one
product is expected (PhePh in the former and toletol in the latter).
[Pd2Ph2(
p)2(
m
-I)2(PPh3)2] (Pd-C ¼ 1.993(1)Å) [22] and [Pd2(C6H4Bun-
m
-Br)2(P-o-tol3)2] (Pd-C ¼ 2.02(1)Å) [23]. The ClePdeCl angles
are within the range (w85ꢁ) reported for chloro-bridged binu-
clear palladium complexes [22,25,28,32].
Pd Cl ð ꢀClÞ ðPR Þ Base
m
½
2ꢂ=
2
2
3
2
Ar3Bi þ 3Ar0X
3 ꢀ n Ar ꢀ Ar0 þ n Ar ꢀ Ar
(3)
Dioxane; 100ꢁC
2.1. CeC coupling reactions
As is evident from Table 3, cross coupling reaction with arylio-
dides, as expected, is better than the corresponding arylbromides.
The arylbromides containing electron releasing groups (e.g. Me)
gave better yields than those containing electron withdrawing
groups in para position (e.g. OMe) (entries 2 and 8). An increase in
yield of biaryls was observed with tetrabutylammonium hydroxide
as a base in comparison with K2CO3 (entries, 5, 6; 10, 11 and 12, 14).
However, in some cases a reverse trend was noticed (entries 3, 4).
The CeC cross coupling reactions (eq. (3)) between triar-
ylbismuth and a variety of arylhalides in the presence of base and
a chloro-bridged palladium complex [Pd2Cl2(
or Ph) as a catalyst in refluxing dioxane gave cross-coupled biaryls
in addition to homo-coupled products (Table 3). The relative ratio
of cross-coupled product and homo-coupled product in each
reaction was evaluated by 1H NMR integration. The cross-coupled
m
-Cl)2(PR3)2] (R ¼ Et
The PPh3 complex, [Pd2Cl2(
better catalytic activity than the one containing more basic phos-
phine, [Pd2Cl2( -Cl)2(PEt3)2] (entries 4, 15).
m-Cl)2(PPh3)2] (entries 6, 16) showed
m
The CeC cross coupling reactions are often accompanied with
a homo-coupled product. Considering the formation of both homo-
and cross-coupled products, one can conceive a number of
Table 2
Selected bond lengths (Å) and angles (O) for [Pd2tol2(
Cl)2(PMe2Ph)2].
m-Cl)2(PEt3)2] and [Pd2Ph2(m-
[Pd2tol2(
m
-Cl)2(PEt3)2]
[Pd2Ph2(m-Cl)2(PMe2Ph)2]
Pd1eCl1
2.4102(16)
2.4573(18)
2.2187(16)
2.002(6)
3.538
2.402(2)
2.459(2)
2.216(2)
2.004(8)
3.564
Pd1eCl1i
Pd1eP1
Pd1eC1
Pd1.Pd1i
Cl1ePd1eCl1i
Cl1ePd1eC1
Cl1ePd1eP1
Cl1iePd1eC1
Cl1iePd1eP1
C1ePd1eP1
Pd1eCl1ePd1i
86.74(6)
92.33(17)
178.13(5)
178.97(5)
91.59(6)
89.34(17)
93.26(6)
85.70(8)
92.4(2)
177.17(9)
177.0(2)
96.76(8)
85.2(2)
Fig. 1. Molecular structure of [Pd2Ph2(m-Cl)2(PMePh2)] (ORTEP diagram with 50%
probability).
94.30(8)

18
K.R. Chaudhari et al. / Journal of Organometallic Chemistry 698 (2012) 15e21
Table 3
Cross coupling reaction of triarylbismuth with arylhalide.
Entry No.
Reactant
Ar3Bi
Catalyst
Base
Reaction time
% yielda
Product(% of cross-coupled product)
ArBr
1
Bi
Bi
Bi
Bi
Bi
Bi
Bi
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
m
-Cl)2(PEt3)2
-Cl)2(PEt3)2
-Cl)2(PEt3)2
-Cl)2(PEt3)2
-Cl)2(PPh3)2
-Cl)2(PPh3)2
-Cl)2(PEt3)2
Bu4NOH
K2CO3
4 h
4 h
5h
98
34
75
35
51
58
71
(98)
I
3
3
3
3
3
3
3
2
3
4
5
6
7
m
m
m
m
m
m
Me (93)
Me (85)
Me (66)
Me (97)
Me (79)
Br
Br
Br
Br
Me
Me
Me
Me
Me
K2CO3
Bu4NOH
K2CO3
6 h
10 h
6 h
4 h
Br
Br
Bu4NOH
K2CO3
MeO
(96)
OMe
Bi
Bi
Bi
8
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
m
m
m
-Cl)2(PEt3)2
-Cl)2(PPh3)2
-Cl)2(PEt3)2
K2CO3
K2CO3
K2CO3
4 h
4 h
4 h
18
50
78
MeO
MeO
(96)
(98)
(95)
Br
OMe
3
3
3
9
Br
OMe
CH
Br
H C
H C
CH
CH
10
H C
H C
H C
Br
H C
CH
Bi
11
Pd2Cl2(
m
-Cl)2(PEt3)2
Bu4NOH
4 h
90
(97)
3
H C
H C
Bi
Bi
Bi
12
13
14
15
16
17
18
Me
Me
Me
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
Pd2Cl2(
m
m
m
m
m
m
m
-Cl)2(PEt3)2
-Cl)2(PEt3)2
-Cl)2(PEt3)2
-Cl)2(PEt3)2
-Cl)2(PPh3)2
-Cl)2(PEt3)2
-Cl)2(PEt3)2
K2CO3
4 h
3 h
4 h
3 h
2 h
3 h
4 h
66
84
90
46
65
72
16
Me (30)
Me (58)
Me (73)
I
I
3
3
3
Bu4NOH
Bu4NOH
Bu4NOH
Bu4NOH
Bu4NOH
K2CO3
I
Bi
Bi
Bi
Bi
Me
Me
Me
Me
Me
Me
Me (100)
Br
Br
Me
Me
3
3
3
3
Me (100)
Me (100)
(5)
Me
I
Me
Br
MeO
Me
OMe
Br
Br
MeO
MeO
Bi
Bi
19
20
Me
Me
Pd2Cl2(
m
m
-Cl)2(PPh3)2
-Cl)2(PPh3)2
K2CO3
K2CO3
6 h
9 h
45
72
(51)
(18)
Me
Me
3
3
OMe
OMe
Pd2Cl2(

K.R. Chaudhari et al. / Journal of Organometallic Chemistry 698 (2012) 15e21
19
Table 3 (continued )
Entry No. Reactant
Catalyst
Base
Reaction time
% yielda
Product(% of cross-coupled product)
Ar3Bi
ArBr
Bi
Bi
21
Me
Me
Pd2Cl2(
m
-Cl)2(PEt3)2
-Cl)2(PPh3)2
K2CO3
K2CO3
4 h
4 h
44
75
MeO
MeO
Me (5)
Br
Br
OMe
OMe
3
3
22
Pd2Cl2(
m
Me (45)
a
Corresponds to cross-coupled and homo-coupled product.
pathways for the reaction between triarylbismuth with arylhalides
catalyzed by [Pd2Cl2( -Cl)2(PR3)2] (Scheme 1). Initially trans-
metallation reaction between [Pd2Cl2( -Cl)2(PR3)2] and Ar3Bi yields
coordinate palladium(IV) intermediate, ‘[PdArAr’ClXL]’ which on
reductive elimination of a cross-coupled product (AreAr’) gener-
ates ‘PdClXL’. In a control experiment, reactions between p-tolyl-
m
m
a three-coordinate arylpalladium complex “PdClArL” (L ¼ PR3)
which undergoes second transmetallation, when excess of Ar3Bi is
present, to give “Ar2PdL”. In the absence of excess of triarylbismuth,
bromide and isolated [Pd2Ph2(
m
-Cl)2(PR3)2] (PR3
¼
PEt3 and
PMe2Ph) in 2: 1 stoichiometry in refluxing dioxane in the presence
of Bu4NOH, though sluggish, gave a crossed-coupled product
(tolePh) indicating the formation of a ‘[PdArAr’ClXL]’ species. The
latter after transmetallation by arylbismuth compounds (it may be
as during the synthesis of [Pd2Ar2(m-Cl)2(PR3)2], dimerization of
“PdClArL” [13] takes place to afford isolable chloro-bridged
arylpalldium complexes. The diarylpalladium species “Ar2PdL”
undergoes reductive elimination of biaryl (a homo-coupled
product) with concomitant formation of a palladium(0) (PdL)
species. In a control experiment a reaction between tol3Bi and
noted that the transmetallation of [Pd2Cl2(
m-Cl)2(PEt3)2] by Ph2BiCl
affording [Pd2Ph2( -Cl)2(PEt3)2] was equally facile) yield the parent
m
three-coordinate palladium complex, ‘[PdClArL]’. The oxidative
addition of an organic halide on palladium(II) to give organo-
palladium(IV) complexes and reductive elimination of a CeC
coupled product from the latter is well documented in literature
[34,35].
[Pd2Ph2(
m-Cl)2(PMe2Ph)2] in the presence of Bu4NOH in refluxing
dioxane gave
a
cross-coupled product (Ph-tol) suggesting
the formation of “PhtolPd” species which reductively eliminates
the biaryl. Alper et.al, has shown the formation of ‘[PdL]’ as a cata-
lytically active species involved in palladium catalyzed carbonyla-
tion reactions [21,33]. The stability of this species is dependent on
the nature of the L [33]. The ‘[PdL]’ undergoes oxidative addition
reactions with various substrates (Ar’X, Ar3Bi, Ar2BiX, etc.) to
generate palladium(II) derivatives which on transmetallation fol-
lowed by reductive elimination of biaryls regenerates “PdL”
(Scheme 1). An alternative pathway can also be considered. This
route may involve oxidative addition of an arylhalide on a three-
3. Experimental
3.1. Material and methods
The compounds [Pd2Cl2(
m-Cl)2(PR3)2] (PR3 ¼ PEt3, PMe2Ph,
PMePh2, PPh3) [36] and Ar3Bi (Ar ¼ Ph, 4-MeC6H4 (tol)) [37] were
prepared according to literature methods. All reactions were
carried out under an argon atmosphere in dry and distilled
solvents. Microanalyses were carried out on a Thermo Fischer EA
1110eCHNS instrument. IR spectra were recorded as Nujol mulls
between CsI plates on a Bomem MB-102 FT IR spectrometer. The 1H,
31P{1H} and 77Se{1H} NMR spectra were recorded in CDCl3 on
a Bruker Avance-II 300 MHz NMR spectrometer operating at
300.13, 121.49 and 57.24 MHz, respectively. Chemical shifts are
relative to internal CHCl3 for 1H and external 85% H3PO4 for 31P and
coordinate palladium(II) species, [PdClArL], to give
a five
Me2Se for 77Se NMR (secondary reference Ph2Se2,
d 463 ppm)
3.2. Syntheses
3.2.1. Synthesis of [Pd2Ph2(m-Cl)2(PEt3)2]
To a dichloromethane (20 ml) solution of [Pd2Cl2(m-Cl)2(PEt3)2]
(163 mg, 0.275 mmol), a benzene solution of Ph3Bi (122 mg,
0.277 mmol) was added with stirring under a nitrogen atmosphere.
The reactants were stirred for 3 h and then filtered through a G-3
filtering unit. The filtrate was evaporated under vacuum to give
a pale yellow solid (164 mg, 88%) which was recrystallized from
dichloromethaneehexane mixture in 48% yield. Pertinent data are
given in Table 3. Similarly, other chloro-bridged complexes have
been isolated.
3.2.2. Synthesis of [Pd2Ph2(m-SPh)2(PMe2Ph)2]
To dichloromethane (20 ml) solution of [Pd2Ph2(m-Cl)2
a
(PMe2Ph)2] (58 mg, 0.081 mmol) solid Pb(SPh)2 (39 mg,
0.091 mmol) was added with stirring which continued for 3 h. The
solution was filtered through a celite column and the filterate was
Scheme 1. Proposed catalytic cycle.

20
K.R. Chaudhari et al. / Journal of Organometallic Chemistry 698 (2012) 15e21
Table 4
Acknowledgments
Crystallographic and structural refinement data for [Pd2tol2(
[Pd2Ph2( -Cl)2(PMe2Ph)2].
m-Cl)2(PEt3)2] and
m
Authors thank Drs T. Mukherjee and D. Das for encouragement
of this work.
Complex
[Pd2tol2(
(PEt3)2]
m
-Cl)2
[Pd2Ph2(m-Cl)2
(PMePh2)2]0.2(CH2Cl2)
Chemical formula
Formula weight
Crystal size (mm3)
Crystal system
Space group
Unit cell dimensions
a(Å)
C
26H44Cl2P2Pd2
C38H36Cl2P2Pd2 2(CH2Cl2)
1008.16
Appendix A. Supplementary material
702.25
0.15 ꢃ 0.15 ꢃ 0.30 0.1 ꢃ 0.1 ꢃ 0.2
monoclinic
P21/n
Triclinic
P-1
CCDC 823413 and 823414 contain the supplementary crystal-
lographic data for [Pd2Ph2(m-Cl)2(PMe2Ph)2] and [Pd2tol2(m-
Cl)2(PEt3)2], respectively for this paper. These data can be obtained
free of charge atwww.ccdc.cam.ac.uk/conts/retrieving.htmlor from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, UK (Fax: þ44 1223 336033; E-mail : deposit@
ccdc.cam.ac.uk).
6.893(3)
17.315(4)
12.744(6)
e
6.860(4)
b(Å)
c(Å)
13.000(5)
13.469(4)
68.30(2)
77.74(4)
76.59(4)
1074.9(8)
1.557
1
1.311/504
ꢀ8 ꢅ h ꢅ 4
ꢀ16 ꢅ h ꢅ 16
ꢀ17 ꢅ h ꢅ 17
2.74 to 27.51
4909/2470
4909/0/227
0.0622/0.1441
0.1684/0.1830
0.985
a
b
g
(ꢁ)
(ꢁ )
(ꢁ )
94.46(4)
e
Volume (Å3)
1516.5(11)
1.538
2
1.480/712
ꢀ8 ꢅ h ꢅ 8
ꢀ22 ꢅ k ꢅ 0
ꢀ9 ꢅ l ꢅ 16
r
Z
m
calcd. (g cmꢀ3
)
References
(mmꢀ1)/F(000)
[1] (a) F. Diederich, P.J. Staug (Eds.), Metal Catalyzed Cross-Coupling Reactions,
Wiley VCH, 1998;
(b) L. Yin, J. Liebscher, Chem. Rev. 107 (2007) 133e173.
[2] C. Torborg, M. Beller, Adv. Synth. Catal. 351 (2009) 3027e3043.
[3] L.S. Hegedus, in: M. Schlosser (Ed.), Organometallics in Synthesis e A Manual,
John Wiley & Sons Ltd., 1994.
[4] D.H.R. Barton, N. Ozbalik, M. Ramesh, Tetrahedron 44 (1988) 5661e5668.
[5] (a) M.L.N. Rao, S. Shimada, O. Yamazaki, M. Tanaka, J. Organomet. Chem. 659
(2002) 117e120;
Limiting indices
q
range of data collection (ꢁ ) 2.85 to 27.48
Reflections collected/unique
Data/restraints/parameters
3467/2227
3467/0/149
0.0482/0.1146
0.0987/0.1351
1.021
Final R1,
R1, R2 (all data)
Goodness of fit on F2
uR2 indices
u
(b) M.L.N. Rao, O. Yamazaki, S. Shimada, T. Tanaka, Y. Suzuki, M. Tanaka, Org.
Lett. 3 (2001) 4103e4105.
[6] (a) M.L.N. Rao, S. Banerjee, D.N. Jadhav, Tetrahedron Lett. 48 (2007)
6644e6647;
(b) M.L.N. Rao, S. Banerjee, D.N. Jadhav, Tetrahedron Lett. 48 (2007)
2707e2711;
(c) M.L.N. Rao, D.N. Jadhav, S. Banerjee, Tetrahedron 64 (2008) 5762e5772;
(d) M.L.N. Rao, D. Banerjee, R.J. Dhanorkar, Tetrahedron Letters 51 (2010)
6101;
dried in vacuo to give an orange solid (62 mg, 90%). Similarly
[Pd2Ph2( -SePh)2(PMe2Ph)2] was prepared employing [Pb(SePh)2].
m
(e) M.L.N. Rao, D. Banerjee, S. Giri, J. Organomet. Chem. 695 (2010) 1518;
(f) M.L.N. Rao, V. Venkatesh, D.N. Jadhav, Eur. J. Inorg. Chem. (2010) 3945.
[7] H. Suzuki, Y. Matano (Eds.), Organobismuth Chemistry, Elsevier, 2001.
[8] (a) M.L.N. Rao, V. Venkatesh, D.N. Jadhav, Tetrahedron Lett. 47(2006) 6975e6978;
(b) M.L.N. Rao, D.N. Jadhav, V. Venkatesh, Eur. J. Org. Chem. (2009) 4300e4306.
[9] M.L.N. Rao, V. Venkatesh, D. Banerjee, Tetrahedron 63 (2007) 12917e12926.
[10] M.L.N. Rao, S. Shimada, M. Tanaka, Org. Lett. 1 (1999) 1271e1273.
[11] R.H. Crabtree, The Organometallic Chemistry of the Transition Metals, third
ed. John Wiley & Sons, New York, 2000.
[12] J.P. Stambuli, C.D. Incarvito, M. Bühl, J.F. Hartwig, J. Am. Chem. Soc. 126 (2004)
1184e1194.
[13] S. Moncho, G. Ujaque, A. Lledos, P. Espinet, Chem. Eur. J. 14 (2008)
8986e8994.
[14] M. Yamashita, I. Takamiya, K. Jin, K. Nozaki, Organometallics 25 (2006)
4588e4595.
[15] (a) J.P. Stambuli, M. Bühl, J.F. Hartwig, J. Am. Chem. Soc. 124 (2002)
9346e9347;
(b) T.E. Barder, S.D. Walker, J.R. Martinelli, S.L. Butchwald, J. Am. Chem. Soc.
127 (2005) 4685.
[16] M. Yamashita, J.F. Hartwig, J. Am. Chem. Soc. 126 (2004) 5344e5345.
[17] A. Skarzynska, A.M. Trzeciak, M. Siczek, Inorg. Chim. Acta 365 (2011)
204e210.
3.3. CeC cross coupling reaction between an arylhalide and
organobismuth compound
To a dioxane (3 ml) solution of 2-bromomesitylene (110 mg,
0.55 mmol) and Ph3Bi (72.9 mg, 0.17 mmol) was added
powdered K2CO3 (92.4 mg, 0.67 mmol) and [Pd2Cl2(m-Cl)2(PEt3)2]
(10 mg, 0.017 mmol). (A lower concentration of the catalyst
ArX:Pd (35:1) also gave similar results). The whole was heated at
100 ꢁC in an oil bath with stirring for 4 h. The contents were
cooled to room temperature and acidified with dilute HCl
(10 ml) and extracted with ethylacetate (15 ml
ꢃ
3). The
combined extracts were washed with water (2 ꢃ 15 ml) and
brine (15 ml) and dried over anhydrous Na2SO4. This was filtered
and dried under vacuum to give colorless oil (75 mg, 78% yield)
and was characterized as Mes-Phenyl by 1H NMR spectroscopy.
Similarly, other CeC coupling reactions were carried out and
yields were calculated based on aryl groups of Ar3Bi consumed
in the reactions.
[18] H. Wang, R. Zhong, X.Q. Guo, X.Y. Feng, X.F. Hou, Eur. J. Inorg. Chem. (2010)
174.
[19] V.K. Jain, L. Jain, Coord. Chem. Rev. 249 (2005) 3075.
[20] G.K. Anderson, Organometallics 2 (1983) 665.
[21] V.V. Grushin, C. Bensimon, H. Alper, Organometallics 14 (1995) 3259e3263.
[22] W.J. Marshall, R.J. Young Jr., V.V. Grushin, Organometallic 20 (2001) 523e533.
[23] F. Paul, J. Patt, J.J. Hartwig, Organometallics 14 (1995) 3030e3039.
[24] Y. Hayashi, K. Isobe, Y. Nakamura, S. Okeya, J. Organomet. Chem. 310 (1986)
127.
[25] A. Singhal, V.K. Jain, J. Chem. Soc. Dalton Trans. (1993) 1515e1517.
[26] P.P. Phadnis, V.K. Jain, A. Knoedler, W. Kaim, Z. Anorg. Allg. Chem. 628 (2002)
1332.
[27] H. Mahalakshmi, V.K. Jain, E.R.T. Tiekink, Polyhedron 22 (2003) 549.
[28] F.T. Ladipo, G.K. Anderson, Organometallics 13 (1994) 303e306.
[29] J.S. Kim, A. Sen, I.A. Guzei, L.M. Liable-Sands, A. Rheingold, J. Chem. Soc. Dalton
Trans. (2002) 4726e4731.
[30] H.P. Chen, Y.H. Liu, S.M. Peng, S.T. Liu, Dalton Trans. (2003) 1419e1424.
[31] M. Yamashita, I. Takamiya, K. Jin, K. Nozaki, J. Organomet. Chem. 691 (2006)
3189e3195.
3.4. Crystallography
Intensity data for [Pd2tol2(
Cl)2(PMe2Ph)2] were collected at room temperature (298 ꢄ 2 K) on
a Rigaku AFC 7S diffractometer fitted with Mo-K -0.71069 Ǻ)
m-Cl)2(PEt3)2] and [Pd2Ph2(m-
a (l
radiation so that qmax ¼ 27.5ꢁ. The intensity data were corrected for
Lorenz, polarization and absorption effects with an empirical
procedure [38,39]. The structures were solved by direct methods
[40] and refinement was on F2 [41]. The non-hydrogen atoms were
modeled with anisotropic displacement parameters while the
hydrogen atoms were fixed in their calculated positions. Molecular
structures were drawn using ORTEP [42]. Crystal data and refine-
ment details are given in Table 4.
[32] S.J. Geib, A.L. Rheingold, Acta Cryst. C43 (1987) 1427.
[33] V.V. Grushin, H. Alper, Organometallics 12 (1993) 1890e1901.
[34] V.P.W. Böhn, W.A. Herrmann, Chem. Eur. J. 7 (2001) 4191e4197.

K.R. Chaudhari et al. / Journal of Organometallic Chemistry 698 (2012) 15e21
21
[35] A.J. Canty (Chapter 5), in: , Comprehensive Organometallic Chemistry-II, vol. 9,
Pergamon Press, 1995.
[39] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr. Sect. A 24 (1968)
351e359.
[36] H.C. Clark, G. Ferguson, V.K. Jain, M. Parvez, Inorg. Chem. 24 (1985) 1477.
[37] (a) Z.M. Manulkm, A.N. Tatarenk, Zh. Obchch. Khim 21 (1951) 93;
(b) Chem. Abstr. 45 (1951) 7038.
[38] T. Higashi, ABSCOR, Empirical Absorption Correction Based on Fourier Series
Approximation. Rigaku Corporation, 3-9-12 Matsubara, Akishima, Japan,
1995.
[40] A. Altomase, G. Cascarano, C. Gracovazzo, A. Guagliardi, J. Appl. Crystallogr. 26
(1993) 343e350.
[41] G.M. Sheldrick, SHELX97, Programs for the Solution of Crystal Structure.
University of Göttingen, Germany, 1997.
[42] C.K. Johnson, ORTP-III, Report ORNL-5136. Oak Ridge National Laboratory, Oak
Ridge, TN, 1976.