Synthesis and crystal structures of new palladium catalysts for the hydromethoxycarbonylation of alkenes

Article abstract of DOI:10.1016/j.jorganchem.2011.06.008

The preparation and structural characterization of dimeric Pd(I)-Pd(I) complex [Pd₂{(PPh₃)(OSO₂CF₃)} ₂].CH₂Cl₂ (1) and three palladium center [Pd₃{(PPh₃)(OSO₂CF₃)}₂] (2) and [Pd₃(PPh₃)₄](SO3CF₃) ₂ (3) complexes are reported. The complexes exhibit coordination in which the phosphine phenyl ring is used to stabilize Pd(I) centers in (1) and, Pd(I) and Pd(0) centers in (2) and (3) by acting as π electron donors. The complexes were characterized by single crystal X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2011.06.008

Journal of Organometallic Chemistry 696 (2011) 3091e3096
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and crystal structures of new palladium catalysts
for the hydromethoxycarbonylation of alkenes
,
b
b
Bernard Omondi a , Megan L. Shaw , Cedric W. Holzapfel
*
a School of Chemistry, University of KwaZulu-Natal, P.O. Private Bag, X12345, Westville 4000, Durban, South Africa
b Research Center for Synthesis and Catalysis, Department of Chemistry, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
The preparation and structural characterization of dimeric Pd(I)ePd(I) complex [Pd2{(PPh3)(O-
SO2CF3)}2].CH2Cl2 (1) and three palladium center [Pd3{(PPh3)(OSO2CF3)}2] (2) and [Pd3(PPh3)4](SO3CF3)2
(3) complexes are reported. The complexes exhibit coordination in which the phosphine phenyl ring is
Received 8 December 2010
Received in revised form
27 May 2011
used to stabilize Pd(I) centers in (1) and, Pd(I) and Pd(0) centers in (2) and (3) by acting as
p electron
Accepted 9 June 2011
donors. The complexes were characterized by single crystal X-ray crystallography.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Palladium(I)
Palladium(0)
Metalemetal bond
Crystal structure
1. Introduction
ligands [7] or four ligands [8] were displaced resulting in Pd-arene
interactions.
Triphenylphosphine as a ligand and complexes of palladium and
triphenylphosphine have featured prominently in coordination
chemistry [1] and in their applications in organic chemistry and
catalysis [2,3]. One important and well documented reaction in
which palladium phosphine complexes are employed is the alkene
carbonylation reations in which their role hinges on two important
types of complexes; low-coordinate and hemilabile species [4]. In
addition Buchwald has also shown how good tertiary phosphines
are as supporting ligands for most palladium-catalyzed coupling
reactions [5].
A few three-metal-center palladium complexes have also been
reportedand perhaps theclosesttothethree-center-metalstructures
reported here is [Pd3(PPh3)4](BF4)2 [10]. In fact only one structure in
which a three-metal-center is bridged by a P atom and the phenyl
rings of the phosphine ligand are known [10]. They synthesized there
complex via the reduction of a dimeric Pd(II) species in the presence
ofanalcohol (MeOH, iPrOHortBuOH). Howeverthereareexamplesof
related three-metal-center palladium complexes such as
½ðCH3NCÞ8Pd3ꢀ2þðPF6Þ2ꢁ and ½ðCH3NCÞ6fPh3Pg2Pd3ꢀðPF6Þ2 [11].
Wasserman et al. [11], employed a method where complexes with d8
and d10 electronic configurations were reacted resulting in tripalla-
dium complexes. Several examples of similar but bridged complexes
of phosphorus (mainly biphosphines) are also known and can be
found in literature [11 and references therein].
Dinuclear Pd(I)ePd(I) complexes have been shown as precur-
sors in useful catalytic processes [6]. The tuning of the electronic
and steric properties around the metalemetal bonds of these
complexes makes them quite interesting and using ligands like
phosphine in this regard helps since they can also be easily moni-
tored by a number of spectroscopic methods. The phenyl rings in
these Pd(I)ePd(I) dimers have been shown to adopt an unusual
Herein, we report the synthesis and characterization of the
dimeric Pd(I)ePd(I) complex [Pd2{(PPh3)(OSO2CF3)}2].CH2Cl2 (1)
and three palladium center [Pd3{(PPh3)(OSO2CF3)}2] (2) and
[Pd3(PPh3)4](SO3CF3)2 (3).
h2
Some structural examples from literature of such complexes
include; Pd2Br2(
-PtBu2Ph)2 [6], [Pd2(PPh3)2(CH3CN)4](PF6)2 [7],
:
h2 bridging mode and high stability on exposure to air [6].
m
2. Material and methods
[Pd2{(PPh2)C20H12-OMe}2](BF4) [8] and [Pd2{PCy2(PhAr)}2](BF4)2
[9]. Different synthetic routes were used in the preparation of these
compounds. These included the reaction of cationic and neutral
palladium complexes [6], the use of cationic species where two
2.1. Synthesis
2.1.1. Preparation of 1 and 2
A solution of PPh3 (525 mg, 2 mmol) in dichloromethane (DCM)
(5 mL) was added to a stirred solution of Pd(OAc)2 (224.5 mg,
* Corresponding author. Tel.: þ27 312607323; fax: þ27 312602819.
E-mail address: owaga@ukzn.ac.za (B. Omondi).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.06.008

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B. Omondi et al. / Journal of Organometallic Chemistry 696 (2011) 3091e3096
1 mmol) in DCM (5 mL). Removal of the solvent in vacuo left
a yellow crystalline solid. The solid was dissolved in 5 mL of DCM
under argon. After cooling to 0 ꢂC, a solution of CF3SO3H (450 mg,
the Apex 2 [12] software utilizing COSMO [12] and were corrected
for Lorentz, polarization and absorption effects using SADABS [12].
The structures were solved by Patterson method using SHELXS97
[13] and refined through full-matrix least-squares cycles using the
SHELX97 [13] software package with S(/Fo/-/Fc/)2 being minimized.
All non-H atoms were refined with anisotropic displacement
parameters.
Aromatic H atoms were placed in geometrically idealized posi-
tions (CeH ¼ 0.95 Å) and constrained to ride on their parent atoms,
with Uiso(H) ¼ 1.2Ueq(C). The deepest residual electron-density
holes (ꢁ0.72, ꢁ0.66 and ꢁ1.71 e.Åꢁ3 for 1, 2 and 3 respectively)
are located 0.78 Å from Pd2 in 1, 0.94 Å from Pd2 in 2 and 0.35 Å
from Pd1 in 3. The highest peaks (0.69, 0.54 and 1.37 e.Åꢁ3 for 1, 2
and 3 respectively) are located 1.07 from Pd2 in 1, 0.86 Å from F1 in
2 and 0.72 Å from Pd2 3. Crystal data and details for data collection
and refinement are given in Table 1.
266 mL, 3 mmol) in 1 mL of DCM was added drop-wise over a period
of 5 min. The resulting dark brown mixture was allowed to warm to
room temperature and in an atmosphere of argon, exposed to
vapors of diethyl ether for 18 h resulting in the slow deposition of
red crystals of 1 (162 mg), m.p. 125 ꢂC (decomp). The supernatant
was removed from the crystals and further exposed to vapors of
diethyl ether at ꢁ5 ꢂC for 12 h. This resulted in the deposition of
brown plates of 2 (85 mg), m.p. 145 ꢂC (decomp).
2.1.2. Preparation of 3
Reaction of PPh3 (525 mg, 2 mmol) and Pd(OAc)2 (224.5 mg,
1 mmol) in 10 mL DCM followed by evaporation of solvent fur-
nished a yellow crystalline solid which was taken up in methanol
(7 mL). The stirred dark yellow solution was cooled to 0 ꢂC in an
All structures were checked for solvent accessible cavities using
PLATON [14] and the graphics performed with DIAMOND [15].
atmosphere of argon, and CF3COOH (450 mg, 266 mL, 3 mmol) was
added slowly from a micro syringe. The solution which first became
bright red and later changed to a dark reddish-brown solution was
exposed to vapors of diethyl ether under argon at 0 ꢂC for 12 h. This
resulted in the deposition of reddish-brown crystals of 3 (144 mg),
m.p. 167 ꢂC (decomp). Additional crystals of 3 (45 mg) were
obtained on leaving the supernatant solution at ꢁ10 ꢂC for 12 h.
2.1.4. NMR spectroscopy
1H, 13C and 31P NMR data was collected using 300 MHz Varian
INOVA spectrometer with 5 mm 4 nucleus probe. Palladium
complexes 1, 2 and 3 are sparingly soluble in most solvents
(including ether, acetone and the alcohols), while in solutions of e.g.
CH2Cl2 and DMSO, rapid deposition of palladium is observed. Due
to their marked instability in solution it was possible to obtain
meaningful NMR spectra NMR spectra only of compound 3 and this
required the use of several fresh samples with CD2Cl2 as solvent.
The 1H, 13C{H} and 31P{H} spectra were analyzed in conjunction
with 1D-TOESY, HSQC and HMBC correlation spectra. It is noted
here that the NMR data for compound 3 were found to agree with
those of [Pd3(PPh3)4](BF4)2 [10].
2.1.3. Crystallography
Crystals of 1, 2 and 3 were grown by diffusion of vapors of
diethyl ether into solutions of the complexes in dichloromethane or
methanol at room temperature. Single crystals X-ray diffraction
data were collected on a Bruker X8 Apex II 4K Kappa CCD diffrac-
tometer using Mo Ka (0.71073 Å) radiation with 4 and u-scans at
100(2) K. The initial unit cell and data collection were achieved by
Table 1
Crystal data and structural refinement for 1, 2 and 3.
1
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C39H32Cl2F6O6P2 Pd2 S2
1120.41
100(2)
0.71073
Monoclinic
P2(1)/c
C38H30F6O6P2Pd3S2
1141.88
100(2)
0.71073
Triclinic
P1
C74H60F6O6P4Pd3S2
1666.44
100(2)
0.71073
Triclinic
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a
b
g
13.6664(9)
13.7718(9)
23.9657(14)
90
111.839(3)
90
4186.9(5)
8.6528(5)
9.0808(5)
13.5872(8)
84.0030(10)
77.3870(10)
70.1960(10)
979.68(10)
9.451(5)
12.709(5)
14.627(5)
80.583(5)
81.045(5)
72.712(5)
1644.2(12)
(ꢂ)
(ꢂ)
(ꢂ)
Volume (Å3)
Z
4
1
1
Dcalc (Mg/m3)
1.777
1.236
2224
1.935
1.625
560
1.683
1.045
836
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
0.19 ꢃ 0.04 ꢃ 0.04
0.31 ꢃ 0.14 ꢃ 0.02
0.17 ꢃ 0.16 ꢃ 0.05
q
range for data collection (ꢂ)
1.61e28.39
2.39e28.46
1.69e28.08
Index ranges
Reflections collected
Independent reflections [Rint
Completeness to
Absorption correction
ꢁ18/18, ꢁ18/18, ꢁ32/32
57832
10469 [0.0644]
99.7%
semi-empirical from equivalents
0.9522 and 0.7991
Full-matrix least-squares on F2
10469/38/532
1.026
ꢁ11/11, ꢁ12/12, ꢁ18/18
23766
4922 [0.0295]
99.2%
semi-empirical from equivalents
0.9682 and 0.6327
Full-matrix least-squares on F2
4922/28/259
1.034
ꢁ12/12, ꢁ16/16, ꢁ19/19
61316
7965 [0.0355]
99.2%
semi-empirical from equivalents
0.9496 and 0.8424
Full-matrix least-squares on F2
7965/0/430
]
q
¼ 28.35ꢂ
Maximum and minimum transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
1.102
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 ¼ 0.0318, wR2 ¼ 0.0597
R1 ¼ 0.0535, wR2 ¼ 0.0664
0.690 and ꢁ0.717
R1 ¼ 0.0190, wR2 ¼ 0.0485
R1 ¼ 0.0210, wR2 ¼ 0.0500
0.530 and ꢁ0.664
R1 ¼ 0.0357, wR2 ¼ 0.0971
R1 ¼ 0.0483, wR2 ¼ 0.1135
1.374 and ꢁ1.708
Largest difference peak and hole (e.Åꢁ3
)

B. Omondi et al. / Journal of Organometallic Chemistry 696 (2011) 3091e3096
3093
3. Results and discussion
Exposure of a solution of (PPh3)2Pd(OCOCH3)2 and 3 mol
equivalents of CF3SO3H in methanol or dichloromethane under
argon to the vapors of diethyl ether for 24 h furnished crystals of
two palladium complexes of compound (1) [(PPh3)2Pd2(OSO2CF3)2]
(red prisms) and compound (2) [(PPh3)2Pd3(OSO2CF3)2] (brown
plates) in the ratio of ca 2:1 and combined yield (based on Pd) of ca
55%. Compound (3) [(PPh3)4Pd3].(SO3CF3)2 was obtained as
reddish-brown prisms (60% yield) directly by treating the 1
Pd(OAc)2: 2 PPh3 complex 2 in MeOH with three equivalents of
CF3SO3H. It appears that the formation of the complexes involves
reduction of the palladium(II) starting material possibly with
methanol and small quantities of water in the case of compound 3
[10,16,17] and with adventitious water and triphenylphosphine as
the reducing agent in the case of compounds 1 and 2 [10]. The
mechanism of the reactions that lead to compounds 1 and 2 is the
subject of further investigation.
Compounds 1, 2 and 3 are remarkably stable in solid state and
remained unchanged on exposure to air for three months. This is
unexpected for compounds containing palladium in the þ1
(compound 1) and 0 and þ1 oxidation states (compound 2 and 3).
Compounds 1, 2 and 3 showed catalytic activity in the hydro-
methoxycarbonylation of alkenes [18]. On reacting the palladium
complex [(PPh3)4Pd(OSO2CF3)2] or [(PPh3)2PdCl2] in the system
normally employed [L2PdX2: L: HX ¼ 1: 6: 6e20; where L ¼ PPh3
and HX ¼ HCl or HOTf; Alkene: MeOH (3:1e1:1), 30-60 Bar CO]
[18], the hydromethoxycarbonylation normally starts at around
90 ꢂC when the temperature of the reaction is ramped from room
temperature to 100 ꢂC at a rate of 4.5 ꢂC per minute. The rate of the
reaction is indicated by the onset in a reduction of reactor pressure.
When the reaction temperature reaches 100 ꢂC there is a period of
5e10 min before steady state uptake of CO2 is attained. When the
above catalysts are replaced by complexes 1, 2 and 3, the reaction
starts at 80 ꢂC and when the temperature reaches 100 ꢂC the steady
state condition is already attained. This difference is tentatively
ascribed to the direct conversion of the complex to the active
palladium hydride complex in the reaction medium without the
reduction normally required (Eqs. (1) and (2)).
Fig. 1. View of 1 with thermal ellipsoids shown at 50% probability level. Hydrogen
atoms have been omitted for clarity.
L2Pd3ðOTfÞ2þ2HOTf þ 2L/2L2PdHðOTfÞ þ L2PdðOTfÞ2
(1)
(2)
L2PdHðOTfÞþCH2 ¼CH2 þCO/L2PdHðCOCH2CH3ÞþCH3OH
L2PdHðOTfÞþCH3CH2COOCH3
However, there is a little difference in the Turnover Frequency
(TOF) of all of the above catalysts when the steady-state condition
at 100 ꢂC is attained. It is of interest to note that related palladium(I)
complexes showed catalytic activity in e.g. the amination of aryl
halides [19].
Fig. 2. View of 2 with thermal ellipsoids shown at 50% probability level. Hydrogen atoms have been omitted for clarity.

3094
B. Omondi et al. / Journal of Organometallic Chemistry 696 (2011) 3091e3096
Fig. 3. View of 3 with thermal ellipsoids shown at 50% probability level. Hydrogen atoms have been omitted for clarity.
3.1. Molecular and crystal analysis
van der Waals radii of Pd and carbon atoms. There is a significant
tilt of the arene rings which is comparable to that of calculated
structure in which the uncoordinated phenyl rings are replaced
with Me groups and the experimentally determined structure
Single crystal X-ray diffraction was used to determine the
absolute structures of complexes 1 to 3. ORTEP diagrams for the
three structures of [(PPh3)2Pd2(OSO2CF3)2] (1), [(PPh3)2Pd3(O-
SO2CF3)2] (2) and [(PPh3)4Pd3](SO3CF3)2 (3) are given in Figs. 1e3
respectively. Selected bond distances and angles are presented in
Tables 2, 3 and 4. In all three complexes the main feature is
a stabilization of Pd(0) and/or Pd(I) center by the phosphine phenyl
rings.
Pd2Br2(
arene rings are only slightly affected with the distances ranging
between 1.405(4) and 1.413(4) Å indicating a fair amount of
electron delocalization on the ring and therefore stabilization of the
system by the arene -electron density and the palladium atoms.
m
-PtBu2Ph)2 [6]. Besides the CipsoeCortho distances of the
p
p
These PdeCortho and PdeCipso bond distances are however notably
Complex 1 crystallizes with two molecules in asymmetric unit,
the complex and a dichloromethane solvent molecule. In the
structure of 1 the phosphine ligands are arranged in a head-to-tail
fashion and coordinated with two palladium atoms through the
phosphorus atoms and a phenyl ring from each of the phosphines,
and in addition to the oxygen atoms of the two triflate anions
(Fig. 1). The coordination of the palladium atoms to the phenyl ring
Table 3
Selected inter-atomic bond distances (Å) and angles (ꢂ) for complexes 2, 3 and for
[Pd3(PPh3)4](BF4)2.
2
3
Kanna et al. [10]
Distances
Pd1ePd2
PdePPh3 [PdeO in 2]
PdePC6H5Ph2
PdeCipso
PdeCortho
PdeCmeta
PdeCpara
could be described as h
2 even though the PdeCortho bond distances
2.57984(16)
[2.2228(13)]
2.2338(4)
2.1962(15)
2.2937(16)
2.3514(17)
2.2665(17)
1.398(3)
2.6622(7)
2.3548(11)
2.2453(12)
2.176(3)
2.283(3)
2.394(3)
2.266(3)
1.428(5)
1.428(5)
2.6587(3)
2. 345(1)
2.255(1)
2.183(4)
2.317(4)
2.397(5)
2.288(4)
1.434(7)
1.437(6)
seem slightly longer 2.542(3) and 2.506(3) Å. The PdeCipso bond
distances are 2.325(2) and 2.381(3) Å and are all close to the sum of
Table 2
Selected bond distances and angles (Å, ꢂ) for complex 1.
C
C
ipsoeCpara
ipsoeCpara
1.419(2)
Distances
Angles
Pd1ePd2
Pd1eP2
Pd2eP1
Pd1eC13ipso
Pd2eC31ipso
Pd1eP2
C31eC36
C13eC18
2.5432(3)
2.2194(7)
2.2210(7)
2.325(2)
2.381(3)
2.2194(7)
1.409(4)
1.406(4)
Pd1eC18ortho
Pd2eC32ortho
Pd1eO1
Pd2eO4
Pd2eP1
2.542(3)
2.506(3)
2.2062(19)
2.1785(19)
2.2210(7)
1.413(4)
PPh3ePde PC6H5Ph2
[PePdeO] in 2
PdePdeCpara
PPh3ePdeCpara
OePdeCpara in 2
PC6H5Ph2ePdePd
[100.65(4)]
102.47(3)
101.35(4)
92.68(5)
92.80(6)
92.26(9)
95.16(9)
e
e
C31eC32
C13eC14
73.834(12)
93.93(4)
86.07(4)
[174.03(3)]
180
70.11(3)
92.55(9)
87.45(9)
172.57(2)
180
71.08(3)
1.405(4)
C
C
ipsoePd1ePd2
ipsoePd1ePd2
Angles
PPh3ePdePd [OePdePd]
PdePdePd
Rms dev. PdePPC
PdePOC in 2
172.27(3)
180
0.0932
O1ePd1ePd2
O1ePd1eC13
P1ePd2ePd1
C18ePd1ePd2
C14eC13eC18
104.22(5)
97.61(8)
71.78(2)
90.95(7)
119.2(2)
O4ePd2ePd1
O4ePd2C31
P2ePd1ePd2
C31ePd2ePd1
C32eC31eC36
104.30(5)
97.95(8)
72.20(2)
85.64(7)
118.8(2)
0.0540
0.1083
Reference
This work
This work
Kannan
et al., 1998 [10]

B. Omondi et al. / Journal of Organometallic Chemistry 696 (2011) 3091e3096
3095
Table 4
of the palladium atoms as Pd(I)ePd(0)ePd(I) [10]. The arene rings
bond to the palladium atoms through four carbon atoms, where the
PdeCipso and PdeCpara bond distances are shorter [2.1962(15) and
2.2665(17) in compound 2, and 2.176(3) and 2.266(3) Å in
compound 3] while the PdeCortho and PdeCmeta are longer
comparatively [2.2937(16) and 2.3514(17) in compound 2, and
2.283(3) and 2.394(3) Å in compound 3]. These distances compare
well with those of [Pd3(PPh3)4](BF4)2 (Table 3) [10].
CeH.O hydrogen bond geometry of compounds 1, 2 and 3.
DeH.A
DeH/Å H.A/Å D.A/Å <DeH.A/ꢂ Symmetry
operator
1
2
3
C16eH16.O2 0.95
C32eH32.O5 0.95
C39eH39.O6 0.95
C4eH4.O3
C8eH8.O1
C18eH18.O2 0.95
C18eH18.O3 0.95
C27eH27.O1 0.95
2.34
2.51
2.57
2.45
2.56
2.54
2.45
2.59
148
3.211(4) 131
3.310(5) 131
3.233(2) 139
3.478(2) 162
3.271(3) 134
3.272(6) 150
3.378(6) 141
ꢁx, ½ þ y, ½ ꢁ z
1 ꢁ x, ½ þ y, ½ ꢁ z
1 ꢁ x, ½ þ y, ½ ꢁ z
ꢁ1 þ x, y, z
0.95
0.95
ꢁ1 þ x, 1 þ y, z
ꢁx, ꢁy, 1 ꢁ z
The Pd1ePd2 bond distance in compound 2 (2.57984(16) Å) is
ꢁ1 þ x, 1 þ y, z
ꢁ1 þ x, y, z
shorter than those in compound
3
(2.6622(7) Å) and
[Pd3(PPh3)4](BF4)2 (2.6587(3) Å). In compound 2 coordination is to
an oxygen atom whereas in 3 and [Pd3(PPh3)4](BF4)2 coordination
is to phosphorus atoms. The distances are however still within the
range of PdePd dimers, PdePdmin 2.4878(7) and PdePdmax
3.1882(6) Å [7]. The PdeO bond distance in 2 (2.2228(13)) is slightly
longer that those in compound 1 [2.2062(19) and 2.1785(19) Å]. In
compound 3, the PdeP bond distances of the phosphine with the
coordinating arene ring and the second phosphine are different.
PdePPh3 is longer (2.3548(11) Å) than PdePC6H5Ph2 (2.2453(12)
Å). The respective distances in and [Pd3(PPh3)4](BF4)2 are 2.345(1)
and 2.255(1) Å [10].
Table 5
CeH.
p
Intermolecular interactions for compounds 1, 2 and 3.
ꢂ
CeH.
p
H.
p/Å <CeH.
p/
C.p
/Å
Symmetry operator
1
2
C3eH3.Cg2
C10eH10.Cg2 2.69
C15eH15.Cg2 2.63
2.99
136
152
152
137
3.732(3) 1 ꢁ x, ½ þ y, ½ ꢁ z
3.553(2) ꢁx, 1ꢁy, ꢁz
3.498(2) 1 þ x, y, z
3
C4eH4.Cg7
2.99
3.748(5) 1 þ x, y, z
In all three complexes, the geometry around each palladium
atom is square planar with a slight deviation from ideal orthogo-
nality. The angles around the palladium atoms range between
70.11(3) in complex 3 to 104.22(5)ꢂ in complex 1 (Tables 2 and 3).
P1ePd2eO4 and P2ePd1eO1 are the wider angles in 1.
P1ePd2eO3 and P1ePd2eP2 are the widest in 2 and 3 respectively.
This is as a result of the arene rings bonding to palladium atoms.
Besides the least-squares plane of atoms coordinated to the palla-
dium centers showed only a small deviation in each complex
(Tables 2 and 3).
In the crystals of the three compounds, molecules are connected
through weak CeH.O hydrogen bond interactions (Table 4). These
interactions involve aromatic ring hydrogen’s and oxygen atoms of
the coordinating triflate anion. In compound 1 these interactions
are between molecules that are related by a screw-axis along the
crystallographic a-axis. In the crystal structures of 2 and 3 hydrogen
bonded molecules are related by translation along the crystallo-
graphic a and b axes. In addition to the weak CeH.O hydrogen
longer than the PdeP bond distances 2.2210(7) and 2.2194(7) Å and
are in good agreement with PdeP separations in similar dicationic
species [20]. The PdeO distances are 2.1785(19) and 2.2062(19) Å.
The PdePd separation distance is 2.5432(3) Å which lies within the
range of PdePd dimers, PdePdmin 2.4878(7) and PdePdmax
3.1882(6) Å [7].
There is only one structure from literature, [Pd3(PPh3)4](BF4)2,
that is similar to compounds 2 and 3 [10]. In fact the reported
structure is very similar to compound 3 with the only difference
being the counterions used. The centrosymetric Pd3 cation struc-
tures of complexes 2 and 3 are given in Figs. 2 and 3. Each of the
structures consists of a linear chain described by OePdePdePdeO
in 2 and PePdePdePdeP in 3 and coordinated to Ph2PeC6H6
groups, in a head-to-tail fashion. In compound 2 the coordination of
Pd1 is to an O atom from the triflate anion, to a P atom of the tri-
phenylphosphine ligand with Pd2 being stabilized by an arene ring
of the triphenylphosphine whereas in compound 3 the coordina-
tion of Pd1 is to two triphenylphosphine ligands with the stabili-
zation of Pd2 done by an arene ring of one of the
triphenylphosphine ligands, and with the counterion (the triflate)
kicked out of the coordination sphere. There might also be some
interaction between the P atoms holding the arene rings and the
central Pd atom [P1ePd ¼ 2.9045(4) and 2.8391(12) Å in 2 and 3
respectively]. The bridging of the two Pd atoms in the chain was
bonds’, packing in the three compounds is also aided by CeH.
intermolecular interactions (Table 5). Packing is further stabilized
by heteroatom. intermolecular interactions in the compounds 2
and 3 (and not in 1). In 2 there are two SeO. intermolecular
p
p
p
interactions [O1.Cg4 and O1.Cg5 ¼ 3.512(2) Å; S1-O1.Cg4 and
S1-O1.Cg5 ¼ 144.7(9)ꢂ; symmetry operators, 1 ꢁ x, ꢁy, 1 ꢁ z and
1 þ x, ꢁ1 þ y, z respectively]. In compound 3, there CeF.
p
described as m-h:
2h2-diene (Figs. 1 and 2) with the oxidation states
intermolecular interactions that connect molecules along the
Fig. 4. 31P NMR spectrum of complex 3.

3096
B. Omondi et al. / Journal of Organometallic Chemistry 696 (2011) 3091e3096
crystallographic
b
axis [F1.Cg5
¼
3.989(4) Å, C37-
3.601(4) Å, C37-
stabilize the Pd(I) centers in complex (1) and Pd(I) and Pd(0)
centers in complexes (2) and (3).
F1.Cg5
¼
160.6(3)ꢂ and F3.Cg
¼
F3.Cg7 ¼ 127(2)ꢂ.
Acknowledgments
4. NMR spectroscopy analysis
We would like to acknowledge the University for Johannesburg
for financial assistance.
Solutions of compound 3 in CD2Cl2 showed rapid depositions of
palladium and as such several fresh samples of the solution had to
be used to obtain any meaningful data. The 31P NMR spectrum of
compound 3 showed the resonances of P atoms in two different
environments as in the case of the solid state. The two resonances
occur at 42.65 and 9.18 ppm. The spectrum is completely
symmetrical around the midpoint consistent with an AA’BB’ type
system in which each phosphorus gives rise to a symmetrical 10-
line pattern (see Fig. 4 and inset). This is agreement with what
was observed for the compound [Pd3(PPh3)4](BF4)2 [10]. The
singlets at 37.72 and 23.29 ppm, arise from decomposition almost
immediately after dissolution and continues to grow rapidly.
As in the case of related palladium complexes [20] where an
arene ring is coordinated to a Pd, the 1H and 13C signals are shifted
to higher field compared to corresponding non-coordinated arenes.
The coordinated phenyl ring of 3 shows three 1H resonances at 7.05
(multiplet), 6.04 (broad triplet, J z 7.4 Hz) and 4.87 (broad triplet,
J z 7.42 Hz) in the ratio 1:2:2. The corresponding 13C resonances
appear at 88.09, 117.05 and 107.36 ppm respectively. The remaining
proton signals appear in the region 7.20e7.55 ppm. The aromatic
CH carbons resonante at 135.72, 133.75, 131.62, 131.49, 129.65 and
129.60 ppm, while their ipso-carbons, resonate at 132.87, 128.90
and 125.08 ppm.
Appendix A. Supplementary material
CCDC 803811; 803812; 803813 contains the supplementary
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.
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In summary we have presented the synthesis structures of three
palladium complexes as characterized by single crystal X-ray
crystallography and for compound 3, NMR spectroscopy. The
structures have provided us with an insight as to why they are
active as catalysts for hydromethoxycarbonylation of alkenes. The
three complexes reported here use a phosphine phenyl ring to