Synthesis, characterization and X-ray structure of trans-[Pd(COOCH3)(H2O)(PPh3)2] (TsO), a possible intermediate in the catalytic hydroesterification of olefins (TsO = p-toluenesulfonate)

Article abstract of DOI:10.1016/S0020-1693(02)01187-8

The complex trans-[Pd(COOCH₃)(H₂O)(PPh₃)₂] (TsO) (I) has been synthesized by reacting trans-[Pd(COOCH₃)Cl(PPh₃)₂] with AgTsO in methanol. It has been characterized by IR, ¹H and ³¹P NMR spectroscopy. Crystals of trans-[Pd(COOCH₃)(H₂O)(PPh₃)₂] (TsO)·(CH₃OH) (II) have been obtained by re-crystallization of I in methanol. The structure of the complex has been determined by X-ray analysis. It shows a slightly distorted square planar conformation around the central palladium. The coordinated water molecule and the clathrated methanol form a contact with the uncoordinated TsO^- anion, suggesting hydrogen bond interaction. Since I is a possible intermediate in the catalytic hydroesterification of olefins, its catalytic activity in the hydroesterification of ethylene has been tested at 100°C under 45 atm of a 1/1 mixture of ethylene and CO in methanol as solvent, also in the presence of PPh₃ and TsOH. Without addition of PPh₃ and TsOH, I affords to traces of methylpropionate together with Pd(0) complexes and Pd metal. The same results are obtained when complex I is tested in the presence of PPh₃, except that in this case formation of palladium metal is avoided. Using the system I/PPh₃/TsOH=1/6/8, a TOF (mol of ester/mol Pd*h) of 1800 h^-1 is obtained. We propose that the role of the acid TsOH is to favor the formation of a Pd-hydride intermediate and/or to reactivate the Pd(0) species, stabilized by the excess of PPh₃, via an oxidative addition of the acid. Since the acid does not favor the formation of Pd-alkoxy species we suggest that complex I plays only a minor role in catalysis and that this occurs via a Pd-hydride species.

Full text of DOI:10.1016/S0020-1693(02)01187-8

Inorganica Chimica Acta 343 (2003) 183ꢂ188
/
www.elsevier.com/locate/ica
Synthesis, characterization and X-ray structure of trans-
Pd(COOCH )(H O)(PPh ) ](TsO), a possible intermediate in the
[
3
2
3 2
catalytic hydroesterification of olefins (TsOꢀ
/
p-toluenesulfonate)
a
b
b,
Gianni Cavinato , Andrea Vavasori , Luigi Toniolo *, Franco Benetollo
c
a
Department of Inorganic Chemistry (C.I.M.A.), University of Padua, via Marzolo 1, 35131 Padua, Italy
b
Department of Chemistry, University of Venice, Dorsoduro 2137, 30123 Venice, Italy
c
C. I. S. M., C.N.R., Corso Stati Uniti, 35100 Padua, Italy
Received 29 April 2002; accepted 31 May 2002
Abstract
The complex trans-[Pd(COOCH
AgTsO in methanol. It has been characterized by IR,
Pd(COOCH )(H O)(PPh (CH OH) (II) have been obtained by re-crystallization of I in methanol. The structure of the
](TsO)×
3
)(H
2
O)(PPh
3
)
2
](TsO) (I) has been synthesized by reacting trans-[Pd(COOCH
3
)Cl(PPh
3 2
) ] with
1
31
H
and
P
NMR spectroscopy. Crystals of trans-
[
3
2
3
)
2
/
3
complex has been determined by X-ray analysis. It shows a slightly distorted square planar conformation around the central
ꢁ
palladium. The coordinated water molecule and the clathrated methanol form a contact with the uncoordinated TsO anion,
suggesting hydrogen bond interaction. Since I is a possible intermediate in the catalytic hydroesterification of olefins, its catalytic
activity in the hydroesterification of ethylene has been tested at 100 8C under 45 atm of a 1/1 mixture of ethylene and CO in
methanol as solvent, also in the presence of PPh
methylpropionate together with Pd(0) complexes and Pd metal. The same results are obtained when complex I is tested in the
presence of PPh , except that in this case formation of palladium metal is avoided. Using the system I/PPh /TsOHꢀ1/6/8, a TOF
mol of ester/mol Pd+h) of 1800 hꢁ is obtained. We propose that the role of the acid TsOH is to favor the formation of a Pdꢂ
hydride intermediate and/or to reactivate the Pd(0) species, stabilized by the excess of PPh , via an oxidative addition of the acid.
Since the acid does not favor the formation of Pdꢂalkoxy species we suggest that complex I plays only a minor role in catalysis and
that this occurs via a Pdꢂhydride species.
2002 Elsevier Science B.V. All rights reserved.
3 3
and TsOH. Without addition of PPh and TsOH, I affords to traces of
/
3
3
1
(
/
3
/
/
#
Keywords: Synthesis; Catalytic hydroesterification; Olefins
CH ÄCH2
X
CO
[PdꢀCH CH ] X[PdꢀCOꢀCH CH ]
2
1
. Introduction
Pd(II)ꢂphosphine complexes in which the cationic
charge is balanced by weakly coordinating anions, such
ꢃ
ꢃ
ꢃ
[
PdꢀH]
2
3
2
3
ROH
0
/
ꢃ
[PdꢀH] ꢃCH CH COOR
(1)
3
2
CH ÄCH
2
2
ꢁ
ꢃ
ꢃ
as TsO , have been successfully employed as catalyst
[PdꢀCOꢀOR]
CO; ROH
X
[PdꢀCH CH COꢀOR]
2
2
precursor in the carbonylation of olefins [1ꢂ
widely accepted that in such reactions the catalytic cycle
starts from the insertion of the olefin into a Pdꢂhydride
or into a Pdꢂcarboalkoxy species:
/
3]. It is
ꢃ
X
[PdꢀCOꢀOR] ꢃCH CH COOR
(2)
3
2
/
The Pd(II)ꢂ
and a hydrogen source such as an acid, water or
hydrogen, while the Pdꢂcarboalkoxy species forms by
interaction of a Pdꢂcarbonyl species with the alkanol
3ꢂ9]:
/
hydride species forms from the precursor
/
/
/
[
/
[Pd(CO)] ꢃ ꢃCH OHX[Pd(COOCH )] ꢃH
2
ꢃ
ꢃ
(3)
*
517
Corresponding author. Tel.: ꢃ
/
39-041-234 8553; fax: ꢃ
/
39-041-234
3
3
8
0
E-mail address: toniolo@unive.it (L. Toniolo).
In a previous paper we used the preformed
020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 1 8 7 - 8

184
G. Cavinato et al. / Inorganica Chimica Acta 343 (2003) 183ꢂ188
/
[Pd(TsO) (PPh ) ] complex as catalyst precursor for the
hydroesterification of ethylene and the role of the
equipped with a 30 mꢄ
column.
/
0.53 mmꢄ0.1 mm HP 5
/
2
3 2
addition of TsOH and PPh was discussed [3]. Such a
3
precursor was inactive without addition of both PPh3
and TsOH whereas using the [Pd(TsO) (PPh )]/PPh /
2.3. Synthesis of I and of its methanol clathrated II
2
3
3
TsOHꢀ
/
1/6/8 system, under 45 atm of a 1/1 COꢂ
/
AgTsO
is
slowly
added
to
trans-
[Pd(COOCH )Cl(PPh ) ] (0.1 mmol) suspended in 2 ml
ethylene mixture and at 100 8C, a TOF (mol of ester/
3
3 2
ꢁ
1
mol Pd+h) of approximately 1900 h was obtained. In
addition, we found that the catalyst activity was
influenced by the presence of water which can promote
or depress the reaction [3]. Palladium complexes are also
able to catalyze the WGSR via formation of Pd(II)ꢂ
hydride intermediate. In such a reaction coordination of
water to the Pd-center has been proposed [10,11]. On the
basis of these results we proposed that a Pdꢂ
species plays a major role in the catalysis.
In this paper we report the synthesis and the
of methanol. The solution is stirred for a few minutes at
15 8C till complete precipitation of AgCl and then
quickly filtered using a micro-filter system. By dropping
directly the solution into 50 ml of cold water (15 8C),
under vigorous stirring, complex I precipitates as a white
solid which is separated by filtration, washed with cold
water, n-pentane and dried under vacuum (yield 80%).
The solid product was separated by filtration, washed
with water/n-pentane and ether and dried under vacuum
(yield higher than 70%). It was identified by elemental
analysis, IR and NMR spectroscopy. By re-crystal-
lization of complex I from methanol/water (4/1, v/v) at
/
/
hydride
characterization of trans-[Pd(COOCH )(H O)(PPh ) ]-
3
2
3 2
(
TsO) (I) complex and the X-ray structure of I with a
clathrated methanol molecule. To our knowledge, Pdꢂ
/
ꢁ10 8C, after several days, crystals of the methanol
/
carboalkoxy species having weakly coordinating anions
have not yet reported in literature and although several
monoaquo cationic transition-metal complexes are
known, there have been very few palladium aquo-
clathrated of complex I, suitable for X-ray diffraction
studies, were obtained.
2.4. Hydroesterification of ethylene in methanol,
employing I as catalyst precursor
complexes reported [12ꢂ
/
15].
In addition, since a Pdꢂ/carboalkoxy species may be
involved in the catalytic cycle we tested the catalytic
activity of I in the hydroesterification of ethylene.
All the experiments were carried out in a stainless steel
autoclave of approximately 250 ml of capacity, provided
with a self-aspirating turbine. In order to prevent
contamination by metallic species, due to corrosion of
the internal surface of the autoclave, the reagents were
added in a approximately 150 ml Pyrex glass beaker
2
. Experimental
2
.1. Materials
placed into the autoclave. Carbon monoxideꢂethylene
/
mixture (1/1) was supplied from a gas reservoir (260 ml)
connected to the autoclave through a constant pressure
regulator. The autoclave was provided with a tempera-
Methanol (purity ꢀ99.5%, 0.05% of water), CD OD
/
3 3
and n-pentane were purchased from Baker; Pd(OAc)2,
TsOH and PPh were Aldrich products. These products
ture control (90.5 8C).
/
3
and the solvents were used without purification. The
complex trans-[Pd(COOCH )Cl(PPh ) ] was prepared
The catalytic activity of complex I was tested as
follows. Complex I (0.1 mmol) was dissolved in 50 ml of
3
3 2
as described in literature [9]. Carbon monoxide and
ethylene were supplied by SIAD Company (‘research
methanol. The autoclave was pressurized (Ptot
B5 atm)
/
at room temperature with a mixture of carbon mon-
oxide and ethylene (1/1). The autoclave was then heated
to the working temperature (100 8C) while stirring. At
this temperature the pressure in the autoclave was
adjusted at 45 atm and maintained constant by a
pressure regulator connected to the gas reservoir
throughout the experiment (2 h). The gas consumption
was monitored by following the pressure drop in the
reservoir. The autoclave was then cooled to room
temperature and vented. The content of the glass bottle
was analyzed by GC analysis. Complex I was tested also
grade’, purity ꢀ
/
99.9%).
2
.2. General procedure
The IR spectra were recorded in nujol mull on a
Nicolet FTIR instruments mod. Nexus.
1
31
H and P NMR spectra were recorded on a Bruker
AMX 300 spectrometer equipped with a BB multi-
nuclear probe operating in the FT mode at 300 and
1
31
1
21.442 MHz for H and P, respectively. All samples
examined were dissolved in deuterated methanol
CD OD) used also as internal reference for the assign-
(i) in combination of PPh and (ii) in combination of
3
(
PPh and TsOH.
3
3
ment of the chemical shifts.
Products of the hydroesterification reaction were
analyzed by GC on a HP 5890 series II apparatus
All experiments were carried out in the presence of
800 ppm of water in order to compare the reactivity of I
with the reactivity of [Pd(TsO) (PPh ) ] [3].
2
3 2

G. Cavinato et al. / Inorganica Chimica Acta 343 (2003) 183ꢂ
/188
185
ꢁ
1
absorptions at 1230, 1035 and 1013 cm are character-
2
.5. Crystal data for II
M ꢀ
ꢁ
ꢁ
istic the ꢀ
/
SO3 group of the TsO anion [19ꢂ25].
/
3
The P NMR spectrum in CD OD shows singlets at
1
¯
/
911.27, triclinic, space group P1, aꢀ
/
9.224(2),
r
3
˚
bꢀ
1
Dcalc
/
11.004(3), cꢀ
/
11.583(3) A, aꢀ
/
74.84(3)8, bꢀ
1096.8(5) A , Zꢀ
/
16.51 ppm indicating a trans position of the two
1
triphenylphosphine ligands [9]. The H NMR analysis
3
˚
04.55(3)8, gꢀ90.85(2)8, Vꢀ
/
/
/
1,
ꢁ
3
˚
ꢀ
/
1.38 Mg m , l(Mo Ka)ꢀ
/
0.71073 A, m(Mo
shows singlets at 2.58 ppm due to the CH protons of
3
ꢁ
1
Ka)ꢀ
A prismatic colorless crystal of dimension 0.22ꢄ
.26ꢄ0.30 mm was centered on a four-circle Philips
PW1100 diffractometer operating in u ꢂ2u scan mode
/
5.92 cm , Tꢀ
/293(2) K.
the alcohoxy group and at 2.36 ppm due to the CH
ꢁ
3
/
protons of the TsO anion. On the basis of elemental
0
/
analysis, IR and NMR spectra, the complex I can be
formulated as trans-[Pd(COOCH )(H O)(PPh ) ](TsO).
/
3
2
3 2
with graphite-monochromated Mo Ka radiation, fol-
lowing standard procedures. There were no significant
fluctuations of intensities other than those expected
from Poisson statistics. The intensity data were cor-
rected for Lorentz-polarization effects and for absorp-
tion, as described by North et al. [16]. No correction was
made for extinction. The structure was solved by heavy
The X-ray structure of methanol clathrated complex
II is shown in Fig. 1 together with the atom labeling.
The most relevant structural parameters are reported in
Table 2.
It consists of monomeric palladium cations and TsOꢁ
anions, together with clathrated methanol molecule in
the ratio 1:1:1. The complex shows a slightly distorted
square planar conformation around the central palla-
dium with deviations of the atoms from the P(1), P(2),
atom method. Refinement was carried out by full-matrix
2
least-squares; the function minimized was Sw(F ꢁ
/
o
2
2
2
2
F ) , with weighting scheme wꢀ
/
1/[s (F )ꢃ
/
1.41P],
O(1), C(37) best mean plane ꢁ
/
0.033(4); ꢁ0.035(4);
/
c
o
2
2
˚
where Pꢀ
/
max(F ꢃ
/
2F )/3. All non-hydrogen atoms
0.031(4); 0.036(4) A, respectively.
The triphenyl phosphine groups in trans position
display a staggered conformation with respect to the Pꢂ
P axis. The PdꢀP bond lengths of 2.359(2) and 2.350(3)
A are slightly larger than those reported for the neutral
[Pd(OCOCH )(COOCH )(PPh ) ] [26] (2.338(1),
o
c
were refined with anisotropic thermal parameters.
Hydrogen atoms were located in calculated positions
and refined as riding, including free torsion of the
methyl groups, with fixed isotropic thermal parameters
/
/
˚
(
1.2 Ueq of the parent carbon atom). For a total of 521
3
3
3 2
2
2 2
2 2 1/2
˚
2.339(1) A). The almost planar methoxycabonyl group,
forms a dihedral angle of 80.4(4)8 with the coordination
parameters, wR?ꢀ
Sꢀ1.21, and conventional Rꢀ
values of 4358 reflections having F ꢀ
/
[Sw(F ꢁ
/
F ) /Sw(F ) ]
ꢀ
/
0.079,
o
c
o
/
/
0.034, based on the F
2
2
2s(F ). Struc-
/
plane.
The Pdꢀ
comparable with the value found in the complex cation
o
o
˚
O(1)(water) bond distance of 2.160(7) A is
ture refinement and final geometrical calculations were
carried out with SHELXL-97 program [17]; drawings were
produced using ORTEP II [18].
/
˚
[Pd(TsO)(H O)(dppp)](TsO) [14] (2.138(4) A). The co-
2
ordinated water molecule forms
a contact with
O(1)Á Á ÁO(6) of the uncoordinated TsO group of
˚
.698(7) A and the O(7) of the clathrated methanol is
2
3
. Results and discussion
ꢁ
in contact with O(5) of the TsO anion (O(7)Á Á ÁO(5)
˚
˚
O(5) 1.84(9) A) with an angle of
2
1
.62(1) A ((O(7)ꢀ
/
H×
/
72.6(8)8 suggesting hydrogen bond interaction (the
3.1. Synthesis and characterization of complex I and
complex II
water protons were not detected).
The synthesis of complex I was carried out by reacting
trans-[Pd(COOCH )Cl(PPh ) ] with AgTsO in metha-
3
3 2
3.2. Catalytic tests of complex I
nol:
Pd(COOCH )Cl(PPh ) ]ꢃAgTsOꢃH O
[
The catalytic activity of complex I in the hydroester-
ification of ethylene has been checked as described in
Section 2.
3
3 2
2
0
[Pd(COOCH )(H O)(PPh ) ](TsO)ꢃAgCl
(4)
3
2
I)
3 2
(
CH ÄCH ꢃCO
By dropping the pale yellow solution in water at 15 8C
complex I precipitates as a white solid.
2
2
complex I
0
ꢃCH OH
CH CH COOCH
3
(5)
3
3
2
The elemental analysis and the characterizing IR and
NMR data are reported in Table 1. The IR spectrum
Table 3 shows the results obtained carrying out the
hydroesterification of ethylene using I as catalyst pre-
ꢁ
1
shows two broad absorptions at 3489 and 3412 cm
which are attributed to n (OꢀH) and n (OꢀH), respec-
tively, of a water molecule coordinated to the metal [12ꢂ
,
/
/
cursor in the presence of different amounts of PPh and
3
as
s
/
TsOH.
By reacting complex I in methanol without adding
PPh and TsOH, methylpropionate forms in less than
ꢁ
1
1
5,19] and a strong absorption at 1684 cm assigned to
the n (CÄO) of the carboalkoxy ligand [9]. The
/
3

186
G. Cavinato et al. / Inorganica Chimica Acta 343 (2003) 183ꢂ
/188
Table 1
Elemental analysis, selected IR, H and P NMR data of I
1
31
1
31
Analysis
%)
IR
H NMR
P NMR
1
a
(
C
H
S
cmꢁ
d (ppm)
d
(ppm)
Found
Calc.
61.92
4.51 3.64 1684 (s, CO)
3
4.81 3.65 1230, 1035, 1013 (s, SO
2.36 s (CH
2.58 s (CH
3
3
, 3H, TsO)
3
, 3H, OCH )
3
16.51 s (PPh )
489, 3412 (m, OH)
61.47
3
)
7.20ꢂ
/
7.71 m (C
6
H
5
, 34H, PPh
3
and TsO)
Abbreviations: sꢀsinglet, mꢀmultiplet.
a
31
3 4
d ( P) values in ppm from external 85% H PO , downfield shifts being taken as positive.
Table 2
Selected bond distances (A), bond angles (8) for II
and [Pd (CO) (PPh ) ], and palladium metal (entry 1)
3 3 3 3
˚
[27,28].
The same results are obtained when complex I is
tested in the presence of PPh (entry 2). In this case the
PdꢀP(1)
2.359(2)
1.976(9)
PdꢀP(2)
PdꢀO(1)
2.350(3)
2.160(6)
1.182(11)
1.439(7)
1.452(5)
3
PdꢀC(37)
C(37)ꢀO(2)
O(2)ꢀC(38)
O(5)ꢀS
1.315(10) C(37)ꢀO(3)
formation of palladium metal is avoided and the
precursor is reduced to [Pd(CO)(PPh ) ].
1.461(9)
1.439(7)
1.775(9)
O(4)ꢀS
O(6)ꢀS
3
3
Reduction can take place through the reaction
scheme:
SꢀC(39)
C(37)ꢀPdꢀO(1)
P(2)ꢀPdꢀC(37)
P(1)ꢀPdꢀC(37)
PdꢀC(37)ꢀO(3)
O(2)ꢀC(37)ꢀO(3)
O(5)ꢀSꢀO(6)
174.6(3)
87.9(3)
88.2(3)
P(2)ꢀPdꢀO(1)
P(1)ꢀPdꢀO(1)
P(1)ꢀPdꢀP(2)
PdꢀC(37)ꢀO(2)
C(37)ꢀO(2)ꢀC(38)
O(4)ꢀSꢀO(6)
87.7(2)
96.3(2)
[Pd(COOCH )(H O)(PPh ) (TsO)
3
2
3 2
176.04(8)
111.4(6)
116.7(7)
113.8(4)
X[Pd(OCH )(H O)(PPh ) ](TsO)ꢃCO
(6)
(7)
3
2
3 2
124.5(8)
124.1(8)
110.6(4)
113.4(5)
[
[
Pd(OCH )(H O)(PPh ) (TsO)
3 2 3 2
X[Pd(H)(H O)(PPh ) ](TsO)ꢃHCHO
O(4)ꢀSꢀO(5)
2
3 2
Pd(H)(H O)(PPh ) (TsO)ꢃCOꢃPPh
3
2
3 2
X[Pd(CO)(PPh ) ] (or [Pd(CO)(PPh ) or Pdmet)
stoichiometric amount with respect to complex I, which
3 3
3 3
decomposes to Pd(0) species, such as [Pd(CO)(PPh ) ]
3
ꢃH OꢃTsOH
(8)
3
2
Fig. 1. ORTEP plot of [Pd(COOCH
3 2 3 2
)(H O)(PPh ) ](TsO). The non-hydrogen atoms are represented at 30% probability thermal ellipsoids. The
hydrogen atoms have been omitted for clarity.

G. Cavinato et al. / Inorganica Chimica Acta 343 (2003) 183ꢂ
/188
187
Table 3
Reactivity of I in the hydroesterification of ethylene
Entry no
PPh
3
/I molar ratio
TsOH/I molar ratio
TOF mol/mol Pd/h
Pd metal
1
2
3
4
0
6
0
6
0
0
8
8
traces
traces
traces
1800
yes
no
yes
no
Run conditions: Iꢀ0.1 mmol, methanolꢀ50 ml, H
timeꢀ2 h.
2
Oꢀ800 ppm, Tꢀ100 8C, Pꢀ45 atm (CO/ethyleneꢀ1/1), stirrer speedꢀ700 rpm, reaction
Complex I may be in equilibrium with the Pdꢂ
/
4. Supplementary material
methoxy species trans-[Pd(OCH )(H O)(PPh ) ](TsO)
3
2
3 2
(
Reaction (6)), which forms a Pdꢂ
Reaction (7) [29]. Under the reaction conditions, the
Pdꢂhydride species is unstable and decomposes to a
/
hydride species via
Tables of additional material, including atomic co-
ordinates, full listing of bond lengths/angles and aniso-
tropic thermal parameters are available from the
Cambridge Crystallographic Data Centre, CCDC No.
183064. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
/
Pd(0) species (Reaction (8)), which is inactive in the
carbonylation of ethylene.
In addition, complex I may decompose to Pd(0) also
via interaction of H O and CO on the metal center:
Cambridge CB2 1EZ, UK (fax: ꢃ44-1223-336-033;
/
2
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
ꢃ
ꢀH
ꢀCO2
2
ꢃ
ꢃ
ꢃ
[
PdꢀH O] ꢃCO X [PdꢀCOOH] X [PdꢀH]
2
ꢃ
0
Pd(0)ꢃH
(9)
References
The alternative pathway to reduce the complex I to a
Pd(0) complex with formation of dimethyl carbonate
Reaction (10)) [30,31] can be excluded because the
carbonate has not been detected by the GC analysis.
[1] E. Drent, P.H.M. Budzelaar, J. Organomet. Chem. 593 (2000) 211
(
and references cited therein).
(
[
[
2] A. Seayad, A.A. Kelkar, L. Toniolo, R.V. Chaudhari, J. Mol.
Cat. 151 (2000) 47.
3] A. Vavasori, G. Cavinato, L. Toniolo, J. Mol. Cat. 176 (2001) 11.
3
IꢃCH OHꢃCOꢃPPh3
[4] J. Knifton, J. Org. Chem. 41 (1976) 793.
[
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X[Pd(CO)(PPh ) ]ꢃCH OCOOCH ꢃH O
ꢃTsOH
3
3
3
3
2
Acta 35 (1979) L345.
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(10)
[
[
[
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No significant catalytic activity is observed when
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8
10] R.M. Laine, E.J. Crawford, J. Mol. Cat. 44 (1988) 357.
4 (1993) 165.
Pdꢀ
Instead, when complex I is used in the presence of
both PPh and TsOH [(I)/PPh /TsOHꢀ1/6/8], a TOF of
800 h is achieved (entry 4), which is comparable with
the TOF obtained using the precursor
Pd(TsO) (PPh ) ], under the same experimental condi-
/
8/1: entry 3).
[
[11] V.N. Zudin, V.D. Chinakov, V.M. Nekipelov, V.A. Rogov, V.A.
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/
3
3
ꢁ
1
1
[
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[
2
3 2
ꢁ
[14] F. Benetollo, R. Bertani, G. Bombieri, L. Toniolo, Inorg. Chim.
Acta 233 (1995) 5.
1
tions (ca. 1900 h ) [3]. The acid prevents the reduction
to unactive Pd(0) species or reoxidized these species:
[
[
[
[
[
15] P.J. Stang, D.H. Cao, G.T. Poulter, A.M. Arif, Organometallics
4 (1995) 1110.
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1968) 902.
1
ꢃ
ꢃ
Pd(0)ꢃH X[PdꢀH]
(11)
(
17] G.M. Sheldrick, SHELX-97, University of G o¨ ttingen, G o¨ ttingen,
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Moreover, it is known [9] that in the presence of an
18] C.K. Johnson, ORTEP II Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
acid the formation of Pdꢂ/alkoxy species is not favored:
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Kiss, C.D. Hoff, Organometallics 11 (1992) 3390.
ꢃ
ꢃ
2ꢃ
[
Pd(COOMe)] ꢃH X[Pd(CO)] ꢃMeOH
(12)
[
[
20] S. Baker, H.A. Strobel, J. Phys. Chem. 83 (1979) 732.
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These results suggest that complex I plays only a
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PdꢂH species according to the reaction scheme (1).
2971.
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[
/
69.

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[
[
[
[
[
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