Orthometallated palladium trimers in C-C coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2012.03.010

A series of trimeric palladium complexes of the [Pd₃(μ-Cl) ₄(P-C)₂] (P-C = orthometallated aryl phosphite) formula have been prepared and structurally characterized using ³¹P NMR and ESI-MS methods. The structure of [Pd₃(μ₂-Cl) ₄{k²-P,C-P(O-o-CH₃C₆H ₃)(O-o-CH₃C₆H₄)₂} ₂], 1c, was determined by X-ray diffraction. It is compared with the structure of the dimeric complex [Pd₂(μ-Cl)₂{k ²-P,C-P(O-m-CH₃C₆H₃)(O-m-CH ₃C₆H₄)₂}₂], 3b. The trimeric palladium complexes very efficiently catalyzed the Suzuki-Miyaura and Hiyama reactions in ethane-1,2-diol and the Sonogashira cross-coupling in ionic liquids. The mercury test confirmed the homogeneous pathway of the Suzuki-Miyaura reaction, although Pd(0) nanoparticles were observed by TEM in the post-reaction mixture.

Full text of DOI:10.1016/j.jorganchem.2012.03.010

Journal of Organometallic Chemistry 710 (2012) 44e52
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Orthometallated palladium trimers in CeC coupling reactions
Izabela B1aszczyk, Andrzej Gniewek, Anna M. Trzeciak*
Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie, 50-383 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 January 2012
Received in revised form
A series of trimeric palladium complexes of the [Pd3(
m
-Cl) (PeC) ] (PeC ¼ orthometallated aryl
31
4
2
phosphite) formula have been prepared and structurally characterized using P NMR and ESI-
2
MS methods. The structure of [Pd
3 2 4 3 6 3 3 6 4 2 2
(m -Cl) {k -P,CeP(Oeo-CH C H )(Oeo-CH C H ) } ], 1c, was
6
March 2012
determined by X-ray diffraction. It is compared with the structure of the dimeric complex
Accepted 7 March 2012
2
[
2 2 3 6 3 3 6 4 2 2
Pd (m-Cl) {k -P,CeP(Oem-CH C H )(Oem-CH C H ) } ], 3b. The trimeric palladium complexes very
efficiently catalyzed the SuzukieMiyaura and Hiyama reactions in ethane-1,2-diol and the
Sonogashira cross-coupling in ionic liquids. The mercury test confirmed the homogeneous pathway
of the SuzukieMiyaura reaction, although Pd(0) nanoparticles were observed by TEM in the post-
reaction mixture.
Keywords:
Palladium
Palladacycles
Aryl phosphite
CeC coupling reactions
Ionic liquids
Ó 2012 Elsevier B.V. All rights reserved.
Pd(0) nanoparticles
0
0
00
0
0
00
1. Introduction
yl)phosphine) or TRMP (tris(2,2 ,6,6 -tetramethyl[1,1 :3 ,1 -ter-
phenyl]-5 -yl)phosphine) [11,13].
0
The strong ability of palladium compounds to catalyze CeC
bond forming reactions is well documented in the literature
1e9]. Palladium catalysts have found many applications in the
production of pharmaceuticals, new materials, agrochemicals, or
biologically active compounds. In particular, palladium complexes
incorporating phosphorus ligands are the most intensively inves-
tigated due to the fact that their catalytic activity can be effectively
modulated by the electronic and steric properties of the ligands
With triaryl phosphites used instead of phosphine, monomeric
and dimeric palladium complexes have also been formed; however,
in this case orthometallation may proceed, leading to the formation
of palladacycles with PdeC and PdeP bondings [14]. Orthometal-
[
lated palladium complexes were obtained in the reaction of PdCl
with PdCl , and the yield of the reaction increased when HCl,
formed as a byproduct, was removed with a stream of N [14]. For
2
2 2
P
2
t
t
bulkier phosphites, such as P(OC
a more efficient procedure leading to palladacycles consisted in
direct reaction of PdCl with phosphite in 2-methoxyethanol or
6 3 2 3 6 4 3
H -2,4- Bu ) or P(OC H -2- Bu) ,
[
1e9].
Typically, reactions of PdCl
to monomeric, square-planar complexes of the PdCl
2
with tertiary phosphines lead
formula,
2
2
P
2
toluene under reflux [15,16]. The formation of trimers in such
reactions has not been reported till now.
Monomeric and dimeric palladium complexes with phosphito
ligands show excellent catalytic activity in cross-coupling reac-
tions [15,17e21]; therefore, it was interesting to check whether
trimeric complexes can also be successfully applied in these
which form cis or trans isomers depending on the steric
hindrance of the P-ligand [10]. Besides the formation of trans
monomeric compounds, more bulky phosphines form dimeric
species with halide bridges of the [PdX P] type, containing one
2 2
phosphine per palladium atom [11,12]. Trimeric complexes, con-
taining two phosphine ligands per three palladium atoms
reactions. Phosphine-free trimers with
2 3
a (PdX ) fragment
2
have been formed in reaction of PdCl with very bulky phos-
phines, TRIP (tris(2,2 ,6,6 -tetraisopropyl[1,1 :3 ,1 -terphenyl]-5 -
[22e26] have not been tested in catalytic reactions and nothing is
0
0
00
0
0
00
0
known about the catalytic activity of trimeric [(PdX
complexes.
2 3 2
) P ]-type
In this paper we present the first example of successful
synthesis of palladium trimers containing orthometallated triar-
ylphosphito ligands and their catalytic activity in SuzukieMiyaura,
Hiyama, and Sonogashira reactions.
*
Corresponding author. Tel.: þ48 71 3757253; fax: þ48 71 3282348.
E-mail address: anna.trzeciak@chem.uni.wroc.pl (A.M. Trzeciak).
0
022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.03.010

I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
45
2
. Results and discussion
To characterize complexes 1ae1d in solution, the ESI-MS
method was used (Table 1). In the spectra of the trimeric
complexes (1ae1d), the most intensive signals were assigned to
3 4 2
2.1. Synthesis of trimeric complexes [Pd (m-Cl) (PeC) ]
þ
þ
(
PeC ¼ orthometallated aryl phosphite)
[Pd
2
Cl(PeC)
2
]
and [Pd
3
Cl
2
(PeC)
3
]
fragments. The spectrum of
the dimeric complex 3a shows a similar bimetallic fragment,
þ
During our studies of synthetic methods leading to orthome-
[Pd
2
Cl(PeC)] . Interestingly, only in the ESI-MS spectra of trimeric
tallated palladium complexes with triphenylphosphito ligands,
a new family of palladium trimers of the [Pd -Cl) (PeC)
PeC ¼ orthometallated aryl phosphite) formula, containing
[Pd -Cl) core and chelating orthometallated phosphito
ligands, was discovered. Trimeric palladium complexes were
obtained under slightly modified conditions in respect to those
used in the preparation of dimeric complexes with orthometallated
complexes there were fragments containing three or four palla-
þ þ
4 4 3
and [Pd Cl (PeC) ] , observed.
3
(m
4
2
]
dium atoms, [Pd
3
Cl
2
(PeC)
2
]
(
a
Although these species can be formed under the ESI-MS conditions,
such a process does not occur for monomeric and dimeric palla-
dium complexes (Table 1). Thus, trimeric complexes show the
strongest tendency to form clusters.
3
(m
4
]
phosphites, [Pd
showed that two different pathways leading to palladium trimers
could be considered, starting from PdCl or PdCl ),
(P ¼ P(OAr)
respectively. Two parameters are the most important for the
2 2 2
(m-Cl) (PeC) ] [14e16] (Scheme 1). Further studies
2
.2. Structural studies of 1c and related palladium complexes with
phosphito ligands
2
P
2 2
3
Single crystals of 1c, 2b, 3b, and 3d were obtained by recrys-
successful synthesis of trimeric complexes: an excess of PdCl
2
2 2
tallization from CH Cl /pentane and characterized structurally by
X-ray diffraction. Selected bond distances and angles are given in
Table 2.
ꢀ
relative to P(OAr)
3
and a reaction temperature of ca. 130 C. In our
experience, the method with the application of PdCl
2 2
P as the
substrate generates a higher yield of the product in shorter time.
The synthesis of trimeric palladium complexes was carried out
with four different triaryl phosphites, and as a result complexes
The structure of the trimeric complex 1c (Fig. 1) consists of two
independent molecules. Each of the molecules is formed by three
Pd atoms linked by bridging chloride ligands with the Pd2 and Pd4
atoms residing at crystallographic inversion centers. The Pd1eCl1
and Pd3eCl3 bond lengths are slightly longer than Pd1eCl2 and
Pd3eCl4, indicating a trans influence of the orthometallated ligand.
There is practically no difference between the Pd2eCl1, Pd2eCl2
and Pd4eCl3, Pd4eCl4 bond lengths, which are close to the
31
1
ae1d were obtained with a 40e50% yield. In the P NMR
spectra of complexes 1ae1d, two signals of different intensity
were observed in the region of 118e126 ppm, indicating the
presence of two isomers. The position of the signals is very close
to that of the signals observed for the dimeric complexes 3
(
Scheme 1), and it is characteristic for the presence of an ortho-
Pde(
bridged trinuclear palladium(II) complexes (2.29e2.31 Å) [11,13,25]
as well as the PdeCl bond of [PdCl (2.31 Å) [27]. The coordination
4
meCl) bond distances in the central PdCl unit of the chloride-
metallated ligand coordinated to palladium [15,16]. However, on
the basis of 31P NMR it is impossible to distinguish trimers (1)
from dimers (3).
2 n
]
geometry of Pd1 and Pd3 is square-planar, substantially distorted
Method I
Method II
R'
OR
O
OR
P
Cl
Cl
2 PdCl2
toluene
Cl
Cl
P(OR)3
2
PdCl2
Cl
Cl
P(OR)3
Pd
Pd
Pd
O
Pd
toluene
P
P(OR)3
o
R'
OR
OR
o
1
30 C, 24h
130 C, 20h
1
2
R = C H
1a: R = C H
b: R = m-MeC H
R' = H
R' = m-Me
R' = o-Me
2a: R = C H
6 5
b: R = m-MeC H
6
5
6
5
R = m-MeC H
6
4
6
4
6
4
t
R = 2,4- Bu C H
c: R = o-MeC H
c: R = o-MeC H
2
6
3
6
4
6
4
t
t
t
d: R = 2,4- Bu C H R' = 2,4- Bu
d: R = 2,4- Bu C H
2 6 3
2
6
3
2
PdCl2
toluene
o
1
10 C, 5h
R'
OR
OR
Pd
P
Cl
Cl
Pd
O
O
P
OR
OR
R'
3
3
a: R = C H
6 5
b: R = m-MeC H
6
4
c: R = o-MeC H
6
4
t
d: R = 2,4- Bu C H
2
6
3
Scheme 1.

46
I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
Table 1
The Pd atom of the mononuclear complex 2b (Fig. 4) is four-
coordinated in a square-planar geometry. The molecule adopts
the cis configuration in the solid state. The angles between adjacent
ESI-MS(þ) data for trimeric (1a, 1b, 1c), dimeric (3a) and monomeric (2a, 2b, 2c)
palladium complexes.
ꢀ
Complex
m/z (% rel. int.)
455 (48) [Pd(P
ligands deviate only slightly from the expected value of 90
þ
þ
1a
1b
1c
a
)Cl] , 672 (40), 809 (45) [Pd
3
(P
a
)Cl
5
] , 866 (100)
(Table 2). The Pd1eCl1 and Pd1eCl2 bond distances are within
a range typical for palladium complexes: 2.298e2.354 Å [29]. The
measured PdeP bond lengths, 2.22e2.23 Å, are also commonly
observed in complexes of this kind [30].
þ
þ
[Pd
2
[Pd
4
[Pd
4
(P
a
(P
a
(P
a
eC)
eC)
eC)
2
2
3
Cl] , 1042 (28) [Pd
3
(P
a
eC)
eC)
2
Cl
3
] , 1221 (16)
] , 1493 (12)
þ
þ
þ
Cl
Cl
5
] , 1316 (62) [Pd
]
3
(P
a
3
Cl
2
4
þ
þ
498 (23) [Pd(P
b
)Cl] , 853 (13) [Pd(P
)
b 2
Cl] , 951 (81)
þ
þ
[Pd
2
[Pd
4
[Pd
4
b
(P eC)
b
(P eC)
b
(P eC)
2
2
3
Cl] , 1126 (14) [Pd
(P
3 b
eC)
2
Cl
3
] , 1305 (9)
] , 1620 (8)
þ
þ
þ
Cl
Cl
5
] , 1444 (100) [Pd
] , 1936 (8)
3
(P eC)
b
3
Cl
2
2.3. Catalytic activity of complexes 1ae1d in CeC coupling
reactions
4
þ
þ
þ
498 (4) [Pd(P
Pd (P eC) Cl
c
)Cl] , 951(100) [Pd
2
(P
c
eC)
2
Cl] , 1050 (41); 1128 (7)
þ
[
3
c
2
3
] , 1443 (96) [Pd
3
(P eC)
c
3
Cl ]
2
þ
2
2
2
3
a
b
c
762 (100) [Pd(P
847 (100) [Pd(P
c 2
846 (100) [Pd(P ) Cl]
a 2
) Cl]
Cl] ,984 (62) [Pd(P
þ
þ
þ
b 2
eC)(P )Cl ]
Three cross-coupling reactions, SuzukieMiyaura, Hiyama, and
Sonogashira, were selected for tests of the catalytic activity of the
new trimeric palladium complexes (Scheme 2). We had studied
these model reactions before with the monomeric and dimeric
palladium complexes with triphenylphosphito ligands including
orthometallated derivatives [17,18]. Consequently, the reaction
conditions optimized during the previous studies were applied, and
ethane-1,2-diol was used as a solvent for SuzukieMiyaura and
Hiyama reactions, whereas Sonogashira reactions were carried out
in ionic liquid media.
b
)
2
b
þ
þ
a
415 [Pd(P
a
eC)] (60) 866 [Pd
2
(P
a
eC)
2
Cl] (100)
P
a
¼ P(OC
H
6 5
)
3
; P
b
¼ P(Oem-MeC
6
H
4
)
3
; P
c
¼ P(Oeo-MeC
6 4 3
H ) .
ꢀ
with P1ePd1eC16 and P2ePd3eC46 angles of about 80 and
P1ePd1eCl1, P2ePd3eCl3 approximately 100 . The coordination
plane of Pd1 is inclined at 19.8 to the Pd2 plane. Similarly, the
angle between the Pd3 and Pd4 coordination planes is 10.0 .
ꢀ
ꢀ
ꢀ
The molecular structure of the dimeric complex 3b (Fig. 2)
consists of two Pd atoms linked by bridging chlorides. The bond
lengths and angles in this compound are similar to those found in
other orthopalladated binuclear phosphite complexes [15,16,19].
The square-planar coordination geometry of the palladium atoms is
distorted; however, the distortion of the bond angles is slightly
smaller than in the case of the trimeric complex 1c. Bond distances
are practically the same as in 1c. The coordination plane of Pd1 is
The first screening experiments (Table 3), performed with 1c
as the catalyst precursor, resulted in the selection of the most
suitable bases: Cs CO for the SuzukieMiyaura reaction (wich
had also been found to be an optimal base for this process
during our previous studies [18,31]) and NaOH for the Hiyama
reaction [18].
As can be concluded from the data presented in Table 3,
complexes 1ae1c exhibit high catalytic activity (94e98% yield) in
the SuzukieMiyaura cross-coupling. Only 1d provided a slightly
lower yield of 2-methylbiphenyl (82%). Even better results were
obtained in the Hiyama reaction, with yields reaching 93e98%,
which is higher than with other palladium triphenylphosphito
complexes.
2
3
ꢀ
inclined at 57.8 to the Pd2 plane.
2 2
A molecule of 3d (Fig. 3) contains a dimetallacyclic Pd Cl core
with a crystallographic center of inversion at the mid-point of the
i
Pd1$$$Pd1 line [symmetry code: (i) 1ꢁx, 1ꢁy, 1ꢁz]. As a result of
i
i
the presence of the inversion center, the Pd1/Cl1/Pd1 /Cl1 ring is
strictly planar. Surprisingly, the Pd1eCl1 and Pd1eCl1i bond
lengths are almost identical: 2.4064(7) and 2.4052(9) Å, respec-
tively, indicating that in this complex the trans effect of the phos-
phorus ligand is not observed. However, the structure of this
complex already reported in the literature also showed a very weak
trans effect: the difference between the PdeCl bond lengths was
merely about 0.01 Å [28]. All other bond distances and angles in 3d
are similar to those in 3b.
Further experiments showed that complexes 1ae1d also effi-
ciently catalyze the Sonogashira reaction in ionic liquid media.
Typically, a yield of ca. 80% was obtained in the first run in all
reactions (Fig. 5). Interestingly, comparable results were obtained
in three different ionic liquids containing imidazolium cations,
[bmim]PF , [bmim]BF , and [emim][EtSO ], whereas in previous
6
4
4
studies a remarkably lower productivity of palladium phosphito
complexes was observed in [bmim]BF4.
Table 2
ꢀ
Selected bond lengths (Å) and angles ( ) for 1c, 2b, 3b and 3d.
1c (first molecule)
1c (second molecule)
2b
3b
3d
Pd1eP1
2.1504(17)
2.011(4)
Pd3eP2
2.1619(16)
Pd1eP1
Pd1eP2
2.2268(12)
2.2297(7)
Pd1eP1
Pd2eP2
Pd1eC16
2.1535(13)
2.1589(12)
2.003(4)
Pd1eP1
2.1603(8)
Pd1eC16
Pd3eC46
2.007(5)
Pd1eC16
2.0076(16)
Pd2eC46
2.006(4)
Pd1eCl1
Pd1eCl2
Pd2eCl1
Pd2eCl2
2.4203(14)
2.4089(16)
2.3009(16)
2.2999(13)
79.44(14)
Pd3eCl3
Pd3eCl4
Pd4eCl3
Pd4eCl4
2.4314(14)
2.3928(16)
2.3082(15)
2.2808(14)
78.69(14)
Pd1eCl1
Pd1eCl2
2.3372(8)
2.3288(12)
Pd1eCl1
Pd2eCl1
Pd1eCl2
Pd2eCl2
P1ePd1eC16
P2ePd2eC46
P1ePd1eCl1
P2ePd2eCl2
C16ePd1eCl2
C46ePd2eCl1
Cl1ePd1eCl2
Cl1ePd2eCl2
2.4267(12)
2.3943(12)
2.3991(14)
2.4372(13)
80.68(11)
81.42(11)
96.39(5)
Pd1eCl1
Pd1eCl1
2.4064(7)
2.4052(9)
i
P1ePd1eC16
P2ePd3eC46
P1ePd1eP2
P1ePd1eCl1
P2ePd1eCl2
Cl1ePd1eCl2
92.45(3)
87.60(3)
88.31(3)
91.64(3)
P1ePd1eC16
P1ePd1eCl1
C16ePd1eCl1i
Cl1ePd1eCl1i
80.70(5)
98.48(2)
95.71(5)
85.15(2)
P1ePd1eCl1
C16ePd1eCl2
Cl1ePd1eCl2
Cl1ePd2eCl2
99.72(5)
97.78(13)
82.88(5)
P2ePd3eCl3
C46ePd3eCl4
Cl3ePd3eCl4
Cl3ePd4eCl4
103.69(5)
94.42(14)
83.01(5)
95.80(4)
96.81(11)
96.75(11)
86.17(4)
86.04(4)
88.01(5)
91.99(5)
88.32(5)
91.68(5)
i
ii
Cl1ePd2eCl2
Cl3ePd4eCl4
Symmetry codes: (i) 1ꢁx, 1ꢁy, 1ꢁz; (ii) 1ꢁx, 1ꢁy, ꢁz.

I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
47
Fig. 1. Molecular structure and atom numbering scheme of 1c. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary
radii. Unlabeled atoms are symmetrically dependent via inversion centers [symmetry codes: (i) 1ꢁx, 1ꢁy, 1ꢁz; (ii) 1ꢁx, 1ꢁy, ꢁz].
When considering the activity of complexes 1ae1d, complex 1b
could be pointed out as the most productive one in all three ionic
liquids. It also provided the best results in the second run, espe-
cially in an [emim][EtSO ] medium, where 80% and 81% of the
4
product was formed in the first and the second run, respectively.
under the SuzukieMiyaura reaction conditions for complexes 1a,
2a, and 3a showed a similar profile in all three cases (Fig. 6). Only
the initial step of the reaction with the trimer 1a was slightly
slower, but already after 5 min ca. 90% of the product had been
formed. This may indicate that the trimeric complex is more diffi-
cult to reduce to Pd(0).
These good results correspond well with the high activity of the
dimer 3b with the same P(Oem-MeC
.4. Comparative analysis of catalytic activity
Having in hand monomeric, dimeric, and trimeric palladium
6
H
4
)
3
ligand.
Further reactions were performed at different concentrations
of palladium complexes in the range [bromotoluene]:
[Pd] ¼ 100e10000. It is worth noting that after 15 min a high
yield of cross-coupling product was obtained in all reactions
(Table 4). As can be concluded from the data presented in Table 4,
2
ꢁ
1
complexes with triphenylphosphito ligands, it was interesting to
compare their catalytic activity. A kinetic experiment performed
high TOF values, 25,000e30,000 h , were obtained in all the
systems studied, regardless of the structure of the catalyst
Fig. 2. Molecular structure and atom numbering scheme of 3b. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary
radii.

48
I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
Fig. 3. Molecular structure and atom numbering scheme of 3d. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary
radii. Solvent molecules (toluene) have been omitted for clarity. Unlabeled atoms are symmetrically dependent via an inversion center [symmetry code: (i) 1ꢁx, 1ꢁy, 1ꢁz].
precursor. The high catalytic activity of the studied complexes is in
agreement with reports of Bedford who also found an extremely
active catalyst formed in reaction of orthometallated palladium
On the other hand the stability and, in particular, recyclability of
palladacycles formed from phosphito ligands have so far not been
tested. Therefore, attempts were undertaken to recover the catalyst
and to use it in a second run. Two series of experiments were
3
dimer with PCy [15].
2
conducted, in air atmosphere and under N , with complexes 1a, 2a,
3a and 4a (Table 5). The experiment was quite successful, although
the cross-coupling product was formed with a lower yield than in
the first run, 62e82%, with one exception (40%) for 1a in air.
Interestingly, better results in the second run were obtained under
2
an N atmosphere than in air.
According to the literature, palladacycles undergo ring-opening
process in SuzukieMiyaura conditions to generate catalytically
active “underligated” Pd(0) complexes [6]. However in the absence
of stabilizing agents, as it is in our conditions, transformation
of Pd(0) complexes to Pd(0) nanoparticles seems to be possible.
In order to estimate
a role of Pd(0) nanoparticles in the
SuzukieMiyaura reaction with phosphito palladium catalysts, the
Hg(0) test was performed, using a 200-fold excess of Hg(0) relative
to palladium. According to the literature, an inhibiting effect of
Hg(0) is expected when Pd(0) nanoparticles or “naked” Pd(0)
species catalyze the reaction [3]. It is clear from the data collected in
Table 5 that in the first run Hg(0) had no effect and in all reactions
the product was formed in high yield (90e100%). Thus, homoge-
neous reaction pathway was confirmed. For the analysis of the
2
second run the results obtained under N can be considered more
representative because decomposition of phosphorus ligands is less
plausible under these conditions. In particular, the activity of
complex 2a in the second reaction was practically not affected by
Hg(0) (69% vs. 68%), indicating the presence of a soluble palladium
catalyst. A similar feature we observed earlier for palladium
Fig. 4. Molecular structure and atom numbering scheme of 2b. Displacement ellip-
soids are drawn at the 30% probability level and H atoms are shown as small spheres of
arbitrary radii.

I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
49
CH3
H C
3
CH3
OH
B
Br
Si(OEt)3
Br
1
a - 1d
1a - 1d
OH
+
+
ethane-1,2-diol
ethane-1,2-diol
o
o
Cs CO , 80 C, 2h
NaOH, 80 C, 2h
2
3
Suzuki-Miyaura reaction
Hiyama reaction
1a - 1d
I
+
H
IL, NEt3
o
8
0 C, 1h
Sonogashira reaction
Scheme 2.
complexes with imidazole ligands [31]. An inhibiting effect of Hg(0)
was, however, clearly seen in reactions catalyzed by the orthome-
tallated monomer 4a. Similarly, a decrease of 2-methylbiphenyl
yields was noted when Hg(0) was added to the recovered palla-
dium catalysts 3a (dimer) and 1a (trimer).
Thus, it can be concluded that at the end of the catalytic reaction
catalyzed by soluble palladium complexes originated from palla-
dacycles, some Pd(0) nanoparticles were formed. However, based
on the results of catalytic reactions performed without Hg(0), these
nanoparticles can participate in the SuzukieMiyaura reaction as
catalysts or as a source of soluble catalytically active forms [32].
To confirm the presence of Pd(0) nanoparticles, TEM measure-
ments were performed for post-reaction mixtures with 1a as
catalyst. Agglomerates of Pd(0) nanoparticles, from 40 to several
hundred nanometers in diameter, were observed together with
a few nanoparticles of 6e7 nm (Fig. 7).
SuzukieMiyaura reaction were similar to those with the applica-
tion of dimeric and monomeric palladium complexes with triar-
ylphosphito ligands. This may be explained by the presence of the
same catalytically active palladium forms in all systems. Based on
the results of the Hg(0) test, the homogeneous mechanism domi-
nated. Palladium exhibited a strong tendency to form polymetallic
species, as was also seen in ESI-MS spectra, which finally led to
Pd(0) nanoparticles at the end of the catalytic process. Under
catalytic reaction conditions, Pd(0) nanoparticles can be solubilized
and form catalytically active species.
4. Experimental
The palladium complexes 2aec [14,17], 2d [15], 3aec [14],
and 3d [15] were obtained according to literature methods.
2
0
3
. Conclusions
4.1. Trimeric complexes [Pd
1ae1d)
3 2 4 2 2
(m -Cl) {k -P,CeP(OR )(OR) } ]
(
Trimeric palladium complexes with orthometallated triar-
ylphosphito ligands were synthesized for the first time in reaction
of PdCl with a phosphite or with PdCl
Method I. PdCl
appropriate phosphite P(OR)
reaction mixture was stirred for 24 h at 130 C. Next, the solvent
was evaporated in vacuo and the product was precipitated by the
addition of pentane and recrystallized from the CH
mixture.
Method II. PdCl
appropriate complex PdCl
2
(1 mmol) was added to the solution of an
P
2
(P ¼ aryl phosphite)
3
(0.5 mmol) in toluene (5 mL). The
2
2
ꢀ
compounds. These synthetic procedures enabled us to obtain
trimeric palladium complexes regardless of the steric hindrance of
the aryl phosphite.
2 2
Cl /pentane
2
The trimeric compound [Pd
Oeo-CH
3
(m
-Cl)
4
{k -P,CeP(Oeo-CH
3
C
6
H
3
)
-
(
Cl)
3
C
6
H
4
)
2
}
2
] and the analogous dimeric complex [Pd
2
(m
2
(1 mmol) was added to the solution of an
2
{k -P,CeP(Oem-CH )(Oem-CH
3
C
6
H
3
3
C
6
H
4
)
2
}
2
] were obtained
2
[P(OR)
3
]
2
(0.5 mmol) in toluene (5 mL).
2
ꢀ
as single crystals suitable for X-ray diffraction analysis. Both
structures are characterized by similar geometric parameters. On
The reaction mixture was stirred for 20 h at 130 C. Next, the
solvent was evaporated in vacuo and the product was precipitated
2
the other hand, the structure of another dimeric complex, [Pd (m-
2
t
t
Cl)
2
{k -P,CeP(2,4- Bu
2
C
6
H
2
)(2,4- Bu
2
C
H
6 3
)
2
}
2
],
revealed
that
a slight modification of the phosphorus ligand may influence the
PdeCl bond lengths in the metallacyclic core.
Trimeric palladium complexes exhibited high catalytic activity
in CeC bond forming reactions, and the results obtained in the
Table 3
Results of the SuzukieMiyaura and Hiyama reactions catalyzed by complexes
1a e 1d.
Catalyst
SuzukieMiyaura
Hiyama
Base
Base
Yield (%)
Yield (%)
1
1
1
a
b
c
Cs
Cs
Cs
2
2
2
CO
CO
CO
3
3
3
94
96
98
96
95
97
82
NaOH
NaOH
95
98
81
80
35
93
96
Cs
2
CO
PO
3
K
3
PO
4
K
3
4
NaHCO
NaOH
Cs CO
2 3
3
NaHCO
NaOH
NaOH
3
Fig. 5. Results of the Sonogashira reaction catalyzed by the complexes 1ae1d in ionic
liquids.
1
d

50
I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
Table 5
100
Results of recycling and Hg(0) test in the SuzukieMiyaura reaction catalyzed by
complexes 1a, 2a, 3a and 4a.
80
60
40
20
0
Catalyst/yield %
1a
2a
3a
4a
In air
st cycle
2nd cycle
1a
a
a
a
a
1
98 (97 )
95 (89 )
62 (2 )
96 (96 )
71 (23 )
93 (95 )
60 (15 )
a
a
a
a
2
3
a
a
40 (9 )
In N2
a
a
a
a
1st cycle
98 (95 )
92 (89 )
69 (68 )
98 (97 )
75 (32 )
100 (100 )
65 (19 )
a
a
a
a
2nd cycle
82 (38 )
0
1
2
3
4
5
10 15 20 30 45 60
Reaction conditions: [Pd] 1 mol%, [PhB(OH)
2
3
] 1.5 mmol, [2-bromotoluene] 1 mmol,
ꢀ
[
Cs
2
CO
3
] 2 mmol, [ethane-1,2-diol] 2.5 cm , 80 C, 1 h.
Time [min]
a
Yield of product obtained at the presence of Hg(0), [Hg]:[Pd] ¼ 200.
Fig. 6. Kinetic profile of SuzukieMiyaura reaction catalyzed by 1a, 2a and 3a at
.1 mol%.
0
2
4
.1.4. [Pd
3
(
m
-Cl)
4
{k -P,CeP(O-2,4-tBu
2
C
6
H
3
)(O-2,4-tBu
2 6 4 2 2
C H ) } ], 1d
1
Yield: 0.45 g, 51%; H NMR (300.1 MHz, CDCl
3
): (major isomer)
3
4
by the addition of pentane and recrystallized from the CH
pentane mixture.
2
Cl
2
/
d
7.66 (d, J
¼ 8.5 Hz, 4H; H6 free ring), 7.53 (d, J
¼ 8.49 Hz,
HeH
HeH
4
2H; H5, orthometallated ring), 7.37 (d, J
HeH
8.49 ¼ Hz, 4H; H3 free
ring), 7.33 (br s, 2H; H3, orthometallated ring), 6.89 (dd,
HeH
2.5 Hz, 4H; H5 free ring), 1.38 (s, 36H; tBu free
ring), 1.33 (s, 18H; tBu orthometallated ring), 1.23 (s, 18H; tBu
3
4
4
.1.1. [Pd3(
Yield: 0.20 g, 37%; H NMR (300.1 MHz, CDCl
orthopalladated ring), 7.3 (t, 10H, H2, JHeH ¼ 8.2 Hz), 7.2 (d, 10H, H1,
m
-Cl)4{k2-P,CeP(OC6H4)(OC6H5)2}2], 1a
JHeH ¼ 8.5 Hz, J
1
3
):
d
7.8 (d, 2H, H5,
orthometallated ring), 1.19 (s, 36H; tBu free ring); (minor isomer)
3
1
4
J
(
HeH ¼ 8.2 Hz), 7.1 (t, 6H, H3, JHeH ¼ 7.4 Hz);
P NMR
d
7.48 (d, J
HeH
¼ 8.49 Hz, 2H; H5, orthometallated ring); 7.04 (br s,
202.5 MHz, CDCl
3
): 125.4 (major isomer), 124.5 (minor isomer);
2H; H3, orthometallated ring); 6.95e7.14 (m, 12H, Ph, free ring);
1.21 (s, 36H; tBu free ring), 1.18 (s, 36H; tBu free ring), 1.14 (s, 36H;
tBu orthometallated ring); P NMR (202.5 MHz, CDCl ): 119.27
3
þ
ESI-MS(m/z): 1044 (M ꢁ Cl) ; found: C 44.08, H 2.87; calcd for
31
C
43
H
36Cl
4
O
6
P
2
Pd
3
C: 44.08, H 3.10%.
(
major isomer), 118.75 (minor isomer); found: C 56.63, H 7.26; calcd
2
4
.1.2. [Pd
3
(
m
-Cl)
4
{k -P,CeP(Oem-CH
3
C
6
H
3
)(Oem-CH
):
; minor isomer), 2.01 (s, 3H, CH
3
3
C
6
H
4
)
2
}
2
], 1b
6.63e7.34 (m,
; major
for C42H40Cl O P Pd : C 57.56, H 7.13%.
4
6
2
3
1
Yield: 0.25 g, 43%; H NMR (300.1 MHz, CDCl
4H, Ph), 2.27 (s, 3H, CH
isomer); P NMR (202.5 MHz, CDCl
3
d
4
3
4
.2. Crystallographic data collection and structure determination
31
3
): 125.01 (major isomer),
þ
1
4
22.13 (minor isomer); ESI-MS(m/z): 1128 (M ꢁ Cl) ; found: C
Single crystals of 1c, 2b, 3b and 3d suitable for X-ray
3.06, H 3.61, Pd 27.4; calcd for C42
4 6 2 3
H40Cl O P Pd : C 43.35, H 3.46,
measurements were mounted on glass fibers in silicone grease,
cooled to 100 K in a nitrogen gas stream, and the diffraction data
were collected on a KUMA KM-4 CCD diffractometer with
graphite monochromated Mo-K
structures were subsequently solved using direct methods and
Pd 27.9%.
2
4
.1.3. [Pd
3
(m
-Cl)
4
{k -P,CeP(Oeo-CH
3
C
6
H
3
)(Oeo-CH
):
3
C
d
6
H
4
)
2
}
2
], 1c
6.70e7.40 (m,
; minor
a
radiation (
l
¼ 0.71073 Å). The
1
Yield: 0.19 g, 32%; H NMR (300.1 MHz, CDCl
4H, Ph), 2.30 (s, 3H, CH
isomer) ppm; P NMR (202.5 MHz, CDCl
3
4
3
; major isomer), 2.25 (s, 3H, CH
3
2
developed by full least-squares refinement on F . Structural
31
3
): 121.95 (major isomer),
þ
1
22.89 (minor isomer); ESI-MS(m/z): 1128 (M ꢁ Cl) ; found: C 43.51,
H 3.49, Pd 27.9; calcd for C42
4 6 2 3
H40Cl O P Pd : C 43.35, H 3.46, Pd
2
8.3%.
Table 4
Effect of catalyst concentration in the SuzukieMiyaura reaction catalyzed by
complexes 1a, 2a and 3a.
ꢁ
Catalyst
[2-bromotoluene]/[Pd]
100
Yield [%]
TON
96
950
1760
6400
TOF [h 1
]
1a
2a
3a
96
95
88
64
384
3800
7040
1
2
000
000
1
1
1
0000
25600
100
100
89
83
100
890
1660
6900
400
3560
6640
1
2
000
000
0000
69
27600
100
100
86
86
100
860
1720
7700
400
3440
6880
1
2
000
000
0000
77
30800
Reaction conditions: [PhB(OH)
2
] 7.5 mmol, [2-bromotoluene] 5 mmol, [Cs
2
CO
3
]
Fig. 7. TEM micrograph of the post-reaction mixture after SuzukieMiyaura reaction
with 1a.
3
ꢀ
10 mmol, [ethane-1,2-diol] 10 cm , 80 C, 15 min.

I. Błaszczyk et al. / Journal of Organometallic Chemistry 710 (2012) 44e52
51
Table 6
Crystallographic data for 1c, 2b, 3b and 3d.
1c
2b
3b
3d
Chemical formula
Formula Mass
Crystal system
a/Å
C
42
H
40Cl
4
O
6
P
2
Pd
3
C
42
H
42Cl
2
O
6
P
2
Pd
C
42
H
40Cl
2
O
6
P
2
Pd
2
C
84
H
124Cl
2
O
6
P
Pd
2 2
ꢂ3C
7 8
H
1163.68
Triclinic
882.00
Triclinic
986.38
Triclinic
9.464(3)
1851.87
Monoclinic
12.062(4)
26.575(8)
15.828(5)
90
96.92(3)
90
5037(3)
100(2)
11.965(4)
12.362(4)
17.058(5)
70.48(3)
69.62(3)
77.70(3)
2215.8(12)
100(2)
Pe1
12.282(4)
12.585(4)
15.003(5)
77.86(3)
74.21(3)
61.95(3)
1960.1(13)
100(2)
Pe1
b/Å
12.294(4)
18.036(6)
89.88(3)
81.02(3)
80.52(3)
2043.9(12)
100(2)
Pe1
c/Å
ꢀ
ꢀ
a
/
b
/
ꢀ
g
/
3
Unit cell volume/Å
Temperature/K
Space group
P2
1
/n
No. of formula units per unit cell, Z
2
2
2
2
ꢁ
1
Absorption coefficient,
m
/mm
1.563
20161
10048
523
0.739
24800
8960
1.135
25542
9378
0.492
No. of reflections measured
No. of independent reflections
No. of parameters
48229
11548
564
484
493
R
int
0.0489
0.0442
0.0831
0.0855
0.0905
1.037
0.0261
0.0243
0.0644
0.0326
0.0662
1.092
0.0415
0.0358
0.0880
0.0523
0.0923
1.083
0.0310
0.0277
0.0701
0.0361
0.0722
1.038
Final R
Final wR(F ) values (I > 2
Final R values (all data)
1
values (I > 2s(I))
2
s(I))
1
2
Final wR(F ) values (all data)
Goodness of fit on F2
solution and refinement was carried out using SHELX suite of
programs [33]. Analytical absorption corrections were performed
with CrysAlis RED [34]. C, O, P, Cl, and Pd atoms were refined
anisotropically. The carbon-bonded H atoms were positioned
geometrically and refined isotropically using a riding model with
a common fixed isotropic thermal parameter. The molecular
structure plots were prepared using ORTEP-3 program [35].
Crystal data and selected details of structure determination are
summarized in Table 6.
4.3.3. Sonogashira reaction
Sonogashira reactions were carried out in a Schlenk tube with
magnetic stirring. Reagents: iodobenzene (0.11 mL, 1 mmol), phe-
3
nylacetylene (0.11 mL, 1 mmol), Et N (0.26 mL, 1.9 mmol), ionic
liquid (1.5 mL) and palladium precatalyst (1 mol%) were introduced
directly to the Schlenk tube. Next, the Schlenk tube was sealed with
a rubber stopper and introduced into an oil bath pre-heated to
ꢀ
ꢀ
80 C. The reaction was carried out at 80 C for 1 h, and after that
time the Schlenk tube was cooled down. The organic products were
separated by extraction with hexane (4 mL, 3 mL and 3 mL). The
extracts (10 mL) were GC-FID analyzed (Hewlett Packard 5890)
with 0.05 mL of mesitylene as an internal standard. The products
were identified by GCeMS (Hewlett Packard 5971A).
4
4
.3. Catalytic reactions
.3.1. SuzukieMiyaura reaction
SuzukieMiyaura reactions were carried out in a Schlenk tube
Acknowledgment
with magnetic stirring. Reagents: phenylboronic acid (0.183 g,
.5 mmol), 2-bromotoluene (0.118 mL, 1 mmol), Cs CO (2 mmol),
1
2
3
Financial support of the Polish Ministry of Science and
Higher Education (N164/COST/2008) and COST D40 are gratefully
acknowledged.
ethane-1,2-diol (2.5 mL) and palladium precatalysts (1 mol%) were
introduced directly to the Schlenk tube. Next, the Schlenk tube was
sealed with a rubber stopper and introduced into an oil bath pre-
ꢀ
ꢀ
heated to 80 C. The reaction was carried out at 80 C for 2 h and
after that time cooled down. The organic products were separated
by extraction with hexane (4 mL, 3 mL and 3 mL). The extracts
Appendix A. Supplementary material
CCDC 820370, 820371, 820372 and 820373 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
(
0
10 mL) were GC-FID analyzed (Hewlett Packard 5890) with
.076 mL of dodecane as an internal standard. The products were
identified by GCeMS (Hewlett Packard 5971A).
4
.3.2. Hiyama reaction
Hiyama reactions were carried out in a Schlenk tube with
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