Rate and mechanism of the reaction of (E)-PhCH=CH-CH(Ph)-OAc with palladium(0) complexes in allylic substitutions

Article abstract of DOI:10.1021/om049420d

The reaction of (E)-1,3-diphenyl-3-acetoxyprop-1-ene, PhCH=CH-CH(Ph)-OAc, with palladium(0) complexes Pd⁰L₂, generated from Pd ⁰(PPh₃)₄ or Pd⁰(dba)₂ + 2L (L = PPh₃ or

Full text of DOI:10.1021/om049420d

Organometallics 2005, 24, 1569-1577
1569
Rate and Mechanism of the Reaction of
(E)-PhCHdCH-CH(Ph)-OAc with Palladium(0) Complexes
in Allylic Substitutions
Christian Amatore,*,† Ali A. Bahsoun,† Anny Jutand,*,† Laure Mensah,†
Gilbert Meyer,† and Louis Ricard‡
De´partement de Chimie, Ecole Normale Supe´rieure, UMR CNRS-ENS-UPMC 8640,
24 Rue Lhomond, F-75231 Paris Cedex 5, France, and Ecole Polytechnique, DCPH,
UMR CNRS 7653, F-91128 Palaiseau, France
Received July 27, 2004
The reaction of (E)-1,3-diphenyl-3-acetoxyprop-1-ene, PhCHdCH-CH(Ph)-OAc, with
palladium(0) complexes Pd0L2, generated from Pd0(PPh3)4 or Pd0(dba)2 + 2L (L ) PPh3 or
L2 ) dppb), gives cationic [(η3-PhCH-CH-CHPh)PdL2]+ complexes with AcO- as the
counteranion in DMF. It is established that this reaction proceeds through two successive
equilibria via neutral intermediate complexes (η2-PhCHdCH-CH(Ph)-OAc)Pd0L2, character-
ized from the kinetics and by UV and 31P NMR spectroscopy. The rate constants and
equilibrium constants of the successive steps have been determined in DMF. They depend
on the ligand and the Pd0 precursor. In all cases, for the concentration range investigated
here, the complexation is considerably faster than the ionization, which is the rate-
determining step of the overall process. Under similar experimental conditions, the formation
of the cationic complex [(η3-PhCH-CH-CHPh)Pd(dppb)]+ is considerably slower than the
formation of the complex [(η3-CH2-CH-CH2)Pd(dppb)]+ in DMF.
Scheme 1
Introduction
The (E)-1,3-diphenyl-3-acetoxyprop-1-ene (1) is often
used as a model molecule in enantioselective palladium-
catalyzed nucleophilic allylic substitutions (eq 1).1
The postulated mechanism involves an oxidative
addition of the racemic substrate 1 to a chiral Pd0
complex, which generates, in the case of a C2-symmetric
chiral ligand, one single cationic complex [(η3-1,3-
diphenylallyl)Pd(L,L)*]+, 2+, due to the symmetry of the
allyl moieties (Scheme 1). The regioselectivity of the
nucleophilic attack is at the origin of the enantioselec-
tivity of the catalytic reaction.1 The introduction of a
functional group on the chiral ligand that can interact
with the nucleophile may generate an enhanced center
* Corresponding authors. Fax: 33
1 44 32 33 25. E-mail:
Anny.Jutand@ens.fr; christian.amatore@ens.fr.
† Ecole Normale Supe´rieure.
‡ Ecole Polytechnique.
(1) (a) Godleski S. A. In Comprehensive Organic Synthesis, Vol. 4;
Trost, B. M., Pflemming, I., Semmelhack, M. F., Eds.; Pergamon:
Oxford, 1991. (b) Frost, C. G.; Howard, J.; Williams, J. M. J.
Tetrahedron Asymmetry 1992, 3, 1089. (c) Tsuji, J. Palladium Reagents
and Catalysts; John Wiley & Sons: Chichester, 1996; p 290. (d) Trost,
B. M.; Van Kanken, D. L. Chem. Rev. 1996, 96, 395. (e) Auburn, P. R.;
Mackenzie, P. B.; Bosnich, B. J. Am. Chem. Soc. 1985, 107, 2033. (f)
Consiglio, G.; Waymouth, R. Chem. Rev. 1989, 89, 257. (g) Hayashi,
T. Pure Appl. Chem. 1988, 60, 7. (h) Hayashi, T.; Yamamoto, A.; Ito,
Y.; Nishioha, E.; Miura, H.; Yanagi, K. J. Am. Chem. Soc. 1989, 111,
6301. (i) Sawamura, M.; Ito, Y. Chem. Rev. 1992, 92, 857. (j) Pfaltz, A.
Acc. Chem. Rev. 1993, 26, 339. (k) Baltzer, N.; Macko, L.; Schaffner,
S.; Zehnder, M. Helv. Chim. Acta 1996, 79, 803. (l) Helmchen, G.;
Pfaltz, A. Acc. Chem. Res. 2000, 33, 336. (m) Markert, C.; Pfaltz, A.
Angew. Chem., Int. Ed. 2004, 43, 2498. (n) Togni, A.; Burckhardt, U.;
Gramlich, V.; Pregosin, P. S.; Salzman, R. J. Am. Chem. Soc. 1996,
118, 1031. (o) Pregosin, P. S.; Salzman, R. Coord. Chem. Rev. 1996,
155, 36. (p) Pregosin, P. S.; Salzman, R. Organometallics 1999, 18,
1207-1215. (q) Barbaro, P.; Pregosin, P. S.; Salzman, R.; Albinati, A.;
Kunz, R. W. Organometallics 1995, 14, 5160. (r) Herrmann, J.;
Pregosin, P. S.; Salzman, R.; Albinati, A. Organometallics 1995, 14,
3311. (s) Burckhardt, U.; Gramlich, V.; Hofmann, P.; Nesper, R.;
Pregosin, P. S.; Salzman, R.; Togni, A. Organometallics 1996, 15, 3496.
(t) Steinhagen, H.; Reggelin, S.; Helmchen, G. Angew. Chem., Int. Ed.
Engl. 1997, 36, 2108.
for the nucleophilic attack on the allylic moieties.1g-i
A
steric repulsion between one phenyl group of the allylic
ligand and the chiral ligand in complex 2+ may result
in a longer Pd-C bond, which favors the nucleophilic
attack at this carbon, as evidenced for chiral N,N-bis-
(oxazoline) ligands.1j Stacking of the phenyl group of the
1,3-diphenylallyl ligand with the phenyl group of chiral
P,P ligands has also been observed.1q
The enantioselectivity may also be related to the
thermodynamic stability of the intermediate (η2-PhCHd
CH-CH(Ph)-Nu)Pd0(L,L)* complexes1j,t generated in the
nucleophilic attack on the cationic complex 2+. In the
case of chiral P,N ligands such as phosphinooxazolines,
one major exo diastereoisomer is formed.1k,m The regio-
10.1021/om049420d CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/25/2005

1570 Organometallics, Vol. 24, No. 7, 2005
Amatore et al.
Scheme 2a
Figure 1. X-ray structure of [(η3-PhCH-CH-CHPh)Pd-
a
L,L means either two PPh3 or one bidentate bisphosphine
-
(PPh3)2]+BF4 (5a+BF4-).
ligand: dppb or dppf.
equiv of PPh35 quantitatively generates Pd0(dba)(PPh3)2
as the major but unreactive complex in DMF.6 The
oxidative addition of allylic carboxylates proceeds from
the minor reactive complex SPd0(PPh3)2 and is known
to generate the cationic complex [(η3-allyl)Pd(PPh3)2]+
(Scheme 2).2a The formation of the cationic complex 5a+
in the reaction of 1 with Pd0(dba)(PPh3)2 is therefore
expected (eq 2).
selectivity and consequently the enantioselectivity are
improved since the nucleophilic attack mainly occurs
at the allylic carbon trans to the phosphorus atom. This
specific attack has been observed for a series of chiral
P,N ligands.1m,p,q,s
The formation of the cationic complex in the reaction
of racemic 1 with Pd0 complexes is usually considered
to be fast and irreversible and the nucleophilic attack
slower and turnover limiting.1j,l,m
It has been established that the reaction of allyl
carboxylates2 or carbonates3 to Pd0(L,L) complexes
2a,c,d
ligated by either two monodentate PPh3
or one
bidentate P,P ligand (dppb, dppf)2b-d is reversible and
proceeds in two successive reversible steps (Scheme 2).
However, the existence of the intermediate neutral
Pd0 complexes 4 formed in the complexation step
(Scheme 2) was established from kinetic data only.2b
None of them had been characterized by the usual
spectroscopic techniques (NMR, UV, etc.) due to too
short lifetimes.
We report herein an investigation on the rate and
mechanism of the reaction of (E)-1,3-diphenyl-3-acetoxy-
prop-1-ene (1) to Pd0 complexes ligated by PPh3 (as
representative of monodentate ligands) or dppb (1,4-bis-
(diphenylphosphino)butane, as representative of biden-
tate symmetrical P,P ligands), which establishes that
the overall reaction is reversible and proceeds in two
steps from Pd0L2 complexes. In addition, the existence
of the intermediate complexes (η2-PhCHdCH-CH(Ph)-
OAc)Pd0L2 was confirmed by UV and 31P NMR spec-
troscopy.
This complex 5a+OAc- has indeed been observed by
ESI-MS analysis in the course of a catalytic allylic
substitution performed on 1.7a The complex 5a+BF4
-
was synthesized independently from the dimeric com-
plex7b [(η3-1,3-diphenylallyl)Pd(µ-Cl]2 by addition of
PPh3 (PPh3/Pd ) 2) in the presence of NaBF4 (eq 3).7c
It was characterized by an X-ray structure study (Figure
1, Table 1).
The reaction of complex 5a+BF4- (1 mM) with 1 equiv
of nBu4NOAc and 2 equiv of dba was monitored by 31
P
(4) For the use of conductivity measurements for the determination
of mechanisms see: Jutand, A. Eur. J. Inorg. Chem. 2003, 2017.
(5) (a) For seminal works on the use of Pd(dba)2 with monodentate
phosphine ligands in allylic substitutions, see: Ferroud, D.; Geneˆt, J.
P.; Muzart, J. Tetrahedron Lett. 1984, 25, 4379. (b) For seminal works
on the use of Pd(dba)2 with bidentate phosphine ligands in allylic
substitutions, see: Fiaud, J. C.; Hibon de Gournay, A.; Larcheveˆque,
M.; Kagan, H. B. J. Organomet. Chem. 1978, 154, 175.
(6) (a) Amatore, C.; Jutand, A.; Khalil, F.; M’Barki, M. A.; Mottier,
L. Organometallics 1993, 12, 3168. (b) Amatore, C.; Jutand, A.; Meyer,
G. Inorg. Chim. Acta 1998, 273, 76. (c) Amatore, C.; Jutand, A. Coord.
Chem. Rev. 1998, 178-180, 511.
Results and Discussion
Reaction of (E)-1,3-Diphenyl-3-acetoxyprop-1-
ene (1) with the Pd0 Complex Generated from Pd0-
(dba)2 and 2PPh3. Evidence of the Reversibility of
the Oxidative Addition. Pd0(dba)2 associated with 2
(2) (a) Amatore, C.; Jutand, A.; Meyer, G.; Mottier, L. Chem. Eur.
J. 1999, 5, 466. (b) Amatore, C.; Gamez, S.; Jutand, A. Chem. Eur. J.
2001, 7, 1273. (c) Amatore, C.; Gamez, S.; Jutand, A.; Meyer, G.;
Mottier, L. Electrochim. Acta 2001, 46, 3237. (d) Agenet, N.; Amatore,
C.; Gamez, S.; Ge´rardin, H.; Jutand, A.; Meyer, G.; Orthwein, C.
ARKIVOC 2002, 92. http://www.arkat-usa.org/.
(7) (a) Chevrin, C.; Le Bras, J.; He´nin, F.; Muzart, J. Pla-Quintana,
A.; Roglans, A.; Pleixats, R. Organometallics 2004, 23, 4796-4799. (b)
The dimer [Pd(η3-PhCH-CH-CHPh)(µ-Cl)]2 was synthesized according
to a reported procedure1h but from Na2PdCl4. (b) The cationic complex
-
with BF4 as the counteranion was synthesized as in ref 2a with a
-
(3) Amatore, C.; Gamez, S.; Jutand, A.; Meyer, G.; Moreno-Man˜as,
M.; Morral, L.; Pleixats, R. Chem. Eur. J. 2000, 6, 3372.
procedure similar to that reported for BPh4 as the counteranion:
Powell, J.; Shaw, B. L. J. Chem. Soc. (A) 1968, 774.

Reaction of (E)-PhCHdCH-CH(Ph)-OAc
Organometallics, Vol. 24, No. 7, 2005 1571
Table 1. Crystal Data for
-
-
[(η3-PhCH-CH-CHPh)Pd(PPh3)]+BF4 (5a+BF4
)
molecular formula
molecular wt
cryst habit
cryst dimens (mm)
cryst syst
space group
a (Å)
C51H43BF4P2Pd
911.00
pale orange block
0.20 × 0.20 × 0.20
orthorhombic
Pbca
19.5620(10)
19.5850(10)
44.0770(10)
90.00
b (Å)
c (Å)
R (deg)
â (deg)
90.00
90.00
γ (deg)
V (Å3)
16886.9(13)
16
Z
d (g cm-3
F000
)
1.433
7456
µ (cm-1
absorp corr
)
0.569
multiple scans; 0.8947 min.,
0.8947 max.
diffractometer
X-ray source
λ (Å)
monochromator
T (K)
scan mode
maximum θ
hkl ranges
no. of reflns measd
unique data
Rint
no. of reflns used
criterion
KappaCCD
Mo KR
0.71069
graphite
150.0(10)
phi and omega scans
Figure 2. (a) UV spectroscopy performed in DMF in a 1
mm length cell at room temperature: (open squares) [(η3-
PhCH-CH-CHPh)Pd(PPh3)2]+BF4- (5a+BF4-) (1 mM); (full
squares) Pd0(dba)(PPh3)2 generated by addition of 10 equiv
23.81
-22 19; -22 22; -49 49
50 716
12 532
-
of nBu4NOAc and 2 equiv of dba to 5a+BF4 (1 mM). (b)
0.0641
Conductivity measurements in DMF versus time of [(η3-
-
9106
PhCH-CH-CHPh)Pd(PPh3)2]+AcO- (5a+AcO-) generated in
the reaction of PhCHdCH-CH(Ph)-OAc (88.6 mM) (+) or
(200 mM) (•) to Pd0(dba)(PPh3)2 (1 mM) formed in situ by
reacting Pd0(dba)2 (1 mM) and PPh3 (2 mM) at 25 °C. κlim
is the theoretical conductivity of 5a+AcO- (1 mM) in DMF
at 25 °C.8a
>2σ(I)
refinement type
hydrogen atoms
no. of params refined
no. of reflns/params
wR2
F2
mixed
1073
8
0.1615
R1
0.0527
weights a, b
GoF
0.1044; 0.0000
1.040
1.293(0.101)/-1.197(0.101)
Scheme 3
diff peak/hole (e/Å-3
)
NMR spectroscopy in DMF containing 10% acetone-d6.
The singlet characterizing 5a+BF4- at 27.8 ppm disap-
peared, whereas two broad signals at 26.7 and 24.8 ppm
corresponding to Pd0(dba)(PPh3)2 appeared. This estab-
lished the reversibility of eq 2, i.e., that the acetate ion
reacts with the cationic complex 5a+ to eventually
generate a Pd0 complex (reverse reaction in eq 4).
The same reaction was monitored by UV spectroscopy
in DMF. The absorption band of the cationic complex
5a+BF4 (1 mM) at λmax ) 350 nm disappeared while
-
the absorption band at λmax ) 395 nm characteristic of
characteristic of the cationic complex 5a+. The magni-
tude of the latter singlet increased with time at the
expenses of that of the two doublets. The cationic
complex 5a+ was never observed alone, even at very long
times (5 days in DMF). Consequently, the reaction of
Pd0(dba)(PPh3)2 with 1 gave the expected cationic
complex 5a+ via an intermediate complex containing
two non magnetically equivalent phosphines as expected
for (η2-PhCHdCH-CH(Ph)-OAc)Pd0(PPh3)2, 6a (Scheme
3). This experiment establishes the existence of two
successive steps, presumably complexation and ioniza-
tion, during the reaction of 1 with SPd0(PPh3)2 (Scheme
3).
Pd0(dba)(PPh3)2 appeared (Figure 2a).
The forward reaction of the equilibrium in eq 4 was
monitored by 31P NMR spectroscopy. To a solution of
Pd0(dba)(PPh3)2 (20 mM), quantitatively formed in situ
from Pd0(dba)2 and 2 equiv of PPh3 in acetone-d6,6a was
added 88 equiv of 1. After 1 h, the two broad singlets of
Pd0(dba)(PPh3)2 at 25.4 and 27.3 ppm were still de-
tected, but two new doublets of equal magnitude had
appeared at 24.97 (d, JPP ) 23 Hz, 1P) and 24.61 ppm
(d, JPP ) 23 Hz, 1P). After one night, Pd0(dba)(PPh3)2
was no longer detected, the two new doublets were still
present together with a minor thin singlet at 27.8 ppm

1572 Organometallics, Vol. 24, No. 7, 2005
Amatore et al.
Under our experimental conditions, the complexation
step was faster than the ionization step. The intermedi-
ate Pd0 complex 6a could thus be accumulated and
characterized. To the best of our knowledge, this is the
first spectroscopic characterization of a Pd0 complex
ligated by the CdC bond of an allylic carboxylate. The
complex 6a could not be characterized by 1H NMR
spectroscopy because it was generated in the presence
of a large amount of 1 (88 equiv with respect to 6a).
The forward reaction of the equilibrium in eq 4 was
monitored by conductivity measurements4 to detect the
formation of the cationic complex 5a+ (Figure 2b). To a
solution of Pd0(dba)(PPh3)2 (1 mM), quantitatively formed
from Pd0(dba)2 (1 mM) and 2 equiv of PPh3 in DMF,
was added the allylic acetate 1 in large excess (200 mM),
i.e., producing conditions in which a fast irreversible
complexation was observed between Pd0(dba)(PPh3)2
and 1 (t1/2 < 1 s). The conductivity slowly increased with
time (Figure 2b). It never stabilized within the time
scale investigated here and never reached the value of
κlim ) 81 µS cm-1 (Figure 2b), which is the theoretical
conductivity of 5a+AcO- (1 mM) in DMF corresponding
to 100% conversion, as determined independently.8a In
DMF, the cationic complex 5a+BF4 (C0 ) 1 mM)
-
partially disappeared in a fast reaction upon addition
of AcO- (C0 ) 1 mM), which implies that k-2[AcO-] >
k2. Consequently, at the concentration of C0 ) 1 mM
used in Figure 2b, one cannot observe the quantitative
formation of 5a+AcO-. What is observed in Figure 2b
is then the slow ionization of the intermediate complex
6a to the cationic complex 5a+ in a reversible step
(Scheme 3) without reaching its equilibrium position.
It is then confirmed that in the presence of a large
excess of 1 (C > 0.03 M) the intermediate neutral
complex 6a was generated in a fast reaction, which is
followed by a slower ionization.
Figure 3. (a) UV spectroscopy performed in DMF in a 1
mm length cell at 25 °C of Pd0(dba)(PPh3)2 (1 mM) (formed
in situ by reacting Pd0(dba)2 (1 mM) and PPh3 (2 mM)) after
successive additions of PhCHdCH-CH(Ph)-OAc (1) (n is the
total number of equivalents of 1 added to Pd0(dba)(PPh3)2).
app
(b) Kinetics of the overall complexation step (see k1
in
Scheme 3) as monitored by UV spectroscopy in DMF at 25
°C. Determination of the reaction order in PhCHdCH-CH-
(Ph)-OAc: plot of kexp versus PhCHdCH-CH(Ph)-OAc
concentration. kexp ) K0k1[1]/C0, k1
) 4.5 M-1 s-1, and
app
Complexation Step: Kinetic and Thermody-
namic Data. In DMF at 25 °C, the absorbance6b of Pd0-
(dba)(PPh3)2 (C0 ) 1 mM) partly decreased in a fast
reaction (occurring during mixing) and stabilized in the
presence of various amounts of 1 (nC0) added succes-
sively (Figure 3a). This attests that Pd0(dba)(PPh3)2 and
the allylic acetate 1 were involved in an equilibrium
with the intermediate complex 6a since the latter
accumulated due to its very slow ionization to 5a+ (as
evidenced above by conductivity measurements). The
equilibrium constant K0K1 ) [6a][dba]/[1][Pd0(dba)-
(PPh3)2] of the overall complexation step (Scheme 4) was
then determined (Table 2, entry 2, Figure S1a in the
Supporting Information) using the UV data shown in
Figure 3a, by neglecting the very slow ionization of 6a
within the experiment time.
K0k1 ) 4.5 × 10-3 s-1 (DMF, 25 °C).
Scheme 4. Overall Complexation Step
ible complexation step. Taking into account the varia-
tion of the dba concentration during the reaction, the
kinetic law is given in eq 5 (x is the molar fraction of
Pd0(dba)(PPh3)2 that has not reacted: x ) (Dn - D∞)/
(D0 - D∞) (D0: initial absorbance of Pd0(dba)(PPh3)2;
Dn: absorbance of Pd0(dba)(PPh3)2 at t in the presence
of n ) 30 equiv of 1; D∞: residual absorbance at the
end of the complexation step).
app
The kinetics of the overall complexation step (see k1
in Scheme 3) was monitored by UV spectroscopy by
recording the decrease of the absorbance of Pd0(dba)-
(PPh3)2 (C0 ) 0.99 mM) versus time in the presence of
large amounts of 1 (nC0 > 0.03 M). Such conditions were
designed to allow the observation of an overall irrevers-
2 ln x - x + 1 ) -K0k1[1]t/C0 ) - kexpt ) -k1app[1]t
(5)
The plot of 2 ln x - x + 1 versus time was linear (Figure
S1b in the Supporting Information) and the experimen-
tal rate constant kexp determined from the slope. The
plot of kexp versus the concentration of 1 was linear
(Figure 3b) and went through zero, which demonstrates
a first-order reaction in 1 (eq 5). The value of k1app was
calculated from the slope in Figure 3b as well as the
value of K0k1 (Table 2, entry 2). The value of k-1
(8) (a) The theoretical conductivity κ of 5a+AcO- (1 mM) in DMF
was calculated from the measured conductivity κ1 ) 66.7 µS cm-1 of
nBu4N+AcO- (1 mM), the conductivity κ2 ) 102 µS cm-1 of 5a+BF4
-
(1 mM), and the conductivity κ3 ) 78 µS cm-1 of nBu4N+BF4- (1 mM)
in DMF: κ ) κ2 + κ1 - κ3 ) 81 µS cm-1 (κlim in Figure 2a). (b) The
theoretical conductivity of 5a+AcO- (1 mM) in acetonitrile (κlim in
Figure S2a in Supporting Information) was independently calculated
as in ref 8a.

Reaction of (E)-PhCHdCH-CH(Ph)-OAc
Organometallics, Vol. 24, No. 7, 2005 1573
Table 2. Equilibrium and Rate Constants for the Reaction of PhCHdCH-CH(Ph)-OAc with Pd0 Complexes
(C0 ) 1 mM) in DMF at 25 °C Excepta at 30 °C (comparison with CH2dCH-CH2-OAc is given in entry 52b
)
Pd0 precursor
K ) K0K1K2 (M)
K0K1
K0k1 (s-1
)
k1app (M-1 s-1
)
k-1 (s-1
)
k2 (s-1
)
k-2 (M-1 s-1
)
b
1
2
3
4
5
Pd0(PPh3)4
nd
nd
8.7
2.3 × 10-2
23
5 × 10-3
1 × 10-5
5.3 × 10-4 d
3 × 10-4 a
2.5 × 10-2
.10-2
c
c
Pd0(dba)2 + 2 PPh3
Pd0(dba)2 + 2 PPh3
0.19
4.5 × 10-3
4.5
5 × 10-3
1 × 10-5
.10-2
Pd0(dba)2 + 1 dppbe
Pd0(dba)2 + 1 dppbf
0.021
0.018
nd
nd
5.3 × 10-4
5.8 × 10-2
0.53
58
nd
nd
<3× 10-7 a
nd
a 30 °C. b See Scheme 6 with K0 ) K′0. c See Scheme 3. d In acetonitrile. e See Scheme 9. f Reaction with CH2dCH-CH2-OAc.2b
Scheme 5. Ionization Step
Scheme 6
(Scheme 3) could then be deduced from the value of K0K1
determined above (Table 2, entry 2).
Ionization Step: Kinetic Data. As evidenced above
(Figure 2a), the ionization step is reversible in DMF
(Scheme 5). The rate of formation of the cationic complex
5a+ could be monitored by conductivity measurements
versus time (Figure 2b), after addition of a large excess
of 1 (88.6 or 200 mM) to Pd0(dba)(PPh3)2 (C0 ) 1 mM)
in DMF. Under these conditions, the formation of the
intermediate complex 6a was considerably faster than
the ionization step and the slow equilibration of the
ionization step was then observed in Figure 2b, though
without completely reaching its final equilibrium posi-
tion within the time scale investigated here. In the very
first time of the ionization step, k-2[AcO-] could be
neglected in front of k2 because of the low AcO-
concentration (,1 mM). The value of k2 was then
calculated from the initial slope of the curve in Figure
2b (Table 2, entry 2) taking into account the value of
the theoretical final conductivity κlim determined above
(Figure 2b).8a The initial slope did not depend on the
concentration of 1 within the investigated concentration
range, confirming a zero-order reaction in 1 for the
ionization step. The value of k-2 could not be determined
monitored by 31P NMR spectroscopy in DMF containing
10% acetone-d6. The broad signal characteristic of the
fast equilibrium involving Pd0(PPh3)3, SPd0(PPh3)2, and
PPh3 at 10.6 ppm6a was not detected, but the two
doublets of the intermediate Pd0 complex 6a were
observed at 24.97 and 24.61 ppm, as when the reaction
was performed from Pd0(dba)(PPh3)2 (vide supra). The
singlet of the cationic complex 5a+ appeared after 1 day.
This experiment shows that the ionization step was
much slower than the complexation step. The interme-
diate complex (η2-PhCHdCH-CH(Ph)-OAc)Pd0(PPh3)2,
6a, accumulated and could then be characterized by 31
P
-
because of a too fast reaction between 5a+BF4 and
NMR spectroscopy. The mechanism of the reaction may
then be described as in Scheme 6 since the reversibility
of the ionization and complexation steps has already
been established in the reaction of 1 with Pd0(dba)-
(PPh3)2 (Scheme 3).
The reaction of 1 with Pd0(PPh3)4 (1 mM) was
monitored by UV spectroscopy in DMF. The absorbance
of Pd0(PPh3)3 at λmax ) 320 nm6b decreased and stabi-
lized upon successive addition of 1 up to 16 equiv
(Figure 4a), attesting that Pd0(PPh3)3 and 1 were
involved in an equilibrium.
However, the absorbance of Pd0(PPh3)3 at 320 nm
never reached a residual value as observed for Pd0(dba)-
(PPh3)2 (vide supra, Figure 2a) because a new band
developed at ca. 340 nm (Figure 4a).10 This band was
assigned to the intermediate Pd0 complex 6a which
accumulated, due to its very slow ionization to the
cationic complex 5a+. This was further confirmed by the
following experiment. The cationic complex 5a+BF4- (1
AcO- even at low acetate concentrations (1 mM each).
Therefore, in DMF, the reaction of 1 with the Pd0
complex generated from Pd0(dba)2 and 2PPh3 is revers-
ible and proceeds in two successive equilibria (Scheme
3) after the initial formation of SPd0(PPh3)2. A fast
overall complexation step is followed by a slower ioniza-
tion step: k1app[1] > k2 as soon as [1] > 0.2 mM.
In contrast to what was observed in DMF, the
ionization went to completion in acetonitrile, since the
final value of the conductivity κlim was equal to the
expected one, as determined independently.8b The rate
constant k2 of the ionization step was then determined
(Table 2, entry 3, Figure S2 in Supporting Information).
The ionization was faster in acetonitrile than in DMF.
Reaction of (E)-1,3-Diphenyl-3-acetoxyprop-1-
ene (1) with Pd0(PPh3)4. Further Evidence of the
Formation of the Neutral Intermediate Complex
(η2-PhCHdCH-CH(Ph)-OAc)Pd0(PPh3)2, 6a. It is
known that Pd0(PPh3)4 dissociates in DMF to give Pd0-
(PPh3)3 as the major complex, whereas the minor
complex SPd0(PPh3)2 is the active species in oxidative
additions.9 The reaction of Pd0(PPh3)4 (20 mM) with (E)-
1,3-diphenyl-3-acetoxyprop-1-ene (1) (22 equiv) was
(9) Fauvarque, J. F.; Pflu¨ger, F.; Troupel, M. J. Organomet. Chem.
1981, 208, 419.
(10) It is only when PhI was added that all the Pd0(PPh3)3 disap-
peared (Figure 4a) due to a faster reaction of PhI with the Pd0 involved
in the equilibrium with 1.

1574 Organometallics, Vol. 24, No. 7, 2005
Amatore et al.
Scheme 7. Overall Complexation Step
Comparison to the value of K0K1 determined for Pd0-
(dba)(PPh3)2 (Table 2, entry 2) allows the determination
of the ratio K′0/K0 ) 9.6 (DMF, 25° C). This shows that
the SPd0(PPh3)2 concentration in the equilibrium with
Pd0(PPh3)3 is ca. 10 times higher than that formed in
the equilibrium with Pd0(dba)(PPh3)2 at identical initial
Pd0 concentrations. This result is fully coherent with
that already established during our previous investiga-
tion of the kinetics of the oxidative addition with PhI
for which K′0/K0 ) 8.6 (DMF, 20 °C) was found.6a This
confirms that dba is a much better ligand for the moiety
Pd0(PPh3)2 than PPh3.
The kinetics of the overall complexation step (see
app
k′1 in Scheme 6) was monitored by UV spectroscopy
by recording the decrease of the absorbance of Pd0-
(PPh3)3 (C0 ) 1 mM) at 320 nm versus time in the
presence of large amounts of 1 (nC0 > 0.015 M), i.e.,
upon conditions of an overall irreversible step. The
kinetic law is given in eq 6 similar to eq 5.
2 ln x - x + 1 ) -K′0k1[1]t/C0 ) - kexpt ) k′1app[1]t
Figure 4. UV spectroscopy performed in DMF in a 1 mm
length cell at 25 °C. (a) Pd0(PPh3)4 (1 mM) after successive
additions of PhCHdCH-CH(Ph)-OAc (as indicated by the
arrows, n is the total number of equivalents added). PhI
(50 equiv) was added at the end of the reaction as indicated
by the arrow to observe the total disappearance of the
initial Pd0(PPh3)4 complex. (b) [(η3-PhCH-CH-CHPh)Pd-
(PPh3)2]+BF4- (5a+BF4-) (1 mM); [(η2-PhCHdCH-CH(Ph)-
OAc)Pd0(PPh3)2, 6a, generated by addition of nBu4NOAc
(1 mM) to 5a+BF4-. Pd0(PPh3)3 generated after addition of
PPh3 (2 mM) to the previous solution.
(6)
app
The values of k′1
and K′0k1 were determined (Table
2, entry 1) using the same procedure as above for Pd-
(dba)2 associated to 2PPh3 (Figure S3b in the Supporting
Information).
Ionization Step. This step (Scheme 5) is common to
both systems whatever the Pd0 precursor, Pd0(PPh3)4
or Pd0(dba)2, and 2PPh3 with k2 already determined
above (Table 2, entry 2). It was found to be slower than
the overall complexation step: k′1app[1] > k2 as soon as
[1] > 4 µM.
Reaction of (E)-1,3-Diphenyl-3-acetoxyprop-1-
ene (1) with the Pd0 Complex Generated from Pd0-
(dba)2 and dppb. As previously reported, the complex
Pd0(dba)(dppb) is generated quantitatively in DMF from
Pd0(dba)2 (1 mM) and 1 equiv of dppb after a slow
reaction (45 min) because of the formation of the
intermediate complex Pd0(dppb)2 (Scheme 8).11
mM) in DMF exhibited an absorption band at λmax
)
350 nm (Figure 4b). After addition of 1 equiv of nBu4-
NOAc, the absorption band of 5a+BF4 immediately
-
disappeared and a new band appeared at λmax ) 330
nm (Figure 4b). After further addition of PPh3, the
absorption band at λmax ) 320 nm characteristic of Pd0-
(PPh3)3 was restored (Figure 4b). This shows that the
reaction of AcO- with the cationic complex 5a+ resulted
in the fast formation of the intermediate Pd0 complex
6a absorbing at λmax ) 330 nm, whose allylic acetate
ligand 1 was then displaced by further addition of excess
PPh3. The intermediate Pd0 complex 6a could not be
detected by UV spectroscopy starting from Pd0(dba)-
(PPh3)2 due to overlapping with the absorbance of dba
(Figure 2a). When starting from Pd0(PPh3)4, the inter-
mediate complex (η2-PhCHdCH-CH(Ph)-OAc)Pd0(PPh3)2,
6a, could then be characterized by UV spectroscopy in
addition to 31P NMR.
Complexation Step: Kinetic and Thermody-
namic Data. Since the ionization step is much slower
than the complexation step within the concentration
range of 1 investigated here, it can be neglected and
the equilibrium constant K′0K1 ) [6a][PPh3]/[1][Pd0-
(PPh3)3] of the overall complexation step (Scheme 7) was
determined using the UV data presented in Figure 4a
(Table 2, entry 1, see Figure S3a in the Supporting
Information).
Scheme 8. Mechanism of the Formation of
Pd0(dba)(dppb)
This reaction was investigated by 31P NMR spectros-
copy performed in DMF containing acetone-d6. The
singlet of Pd(dppb)2 at 28.91 ppm progressively disap-
peared to give two broad singlets at 20.6 and 17.7 ppm
characteristic of Pd0(dba)(dppb).11 When 69 equiv of (E)-
1,3-diphenyl-3-acetoxypropene, 1, was added, two close
singlets appeared at 20.66 and 20.44 ppm as well as
one singlet at 23.14 ppm. The latter characterizes the
cationic complex 5b+(η3-PhCH-CH-CHPh)Pd(dppb)+,
(11) Amatore, C.; Broeker, G.; Jutand, A.; Khalil, F. J. Am. Chem.
Soc. 1997, 119, 5176.

Reaction of (E)-PhCHdCH-CH(Ph)-OAc
Organometallics, Vol. 24, No. 7, 2005 1575
Scheme 9
Scheme 10
equiv) in the course of the reaction. Consequently, the
kinetics of formation of 5b+AcO- did not depend on the
concentration of 1 (zero-order reaction), which means
that whatever the concentration of 1 investigated here
(>24 mM), the ionization step was always slower than
the overall complexation step and was closely kinetically
irreversible.
The reversibility of the ionization step could never-
theless be established upon addition of successive ali-
quots of dba (n′ equiv) after the almost quantitative
formation of 5b+ (Figure 5, t > 20 000 s). This resulted
in successive decreases of the conductivity, reflecting
the corresponding decrease of the concentration of the
ionic species. Since the reversibility was induced by
addition of dba, the overall equilibrium constant K )
K0K1K2 ) [5b+][AcO-][dba]/[Pd0(dba)(dppb)][1] (Scheme
10) could be determined (Table 2, entry 4, Figure S4a
in the Supporting Information) using the conductivity
data shown at t > 20 000 s in Figure 5.
which was independently synthesized by reacting dppb
with [(η3-PhCH-CH-CHPh)Pd(µ-Cl)]2 (dppb/Pd ) 1) in
the presence of NaBF4, in a reaction similar to that
described in eq 3. The two close singlets generated in
the very first step of the reaction were assigned to the
intermediate Pd0 complex: (η2-PhCHdCH-CH(Ph)-OAc)-
Pd0(dppb), 6b (Scheme 9). Complex 6b should be
characterized by two doublets, but since they were very
close, only two close singlets were then observed.
Evidence of the Reversibility of the Oxidative
Addition. The formation of the cationic complex 5b+
was monitored by conductivity measurements in DMF
after addition of n ) 32.1 equiv of 1 to Pd0(dba)(dppb)
(C0 )1 mM), quantitatively generated from Pd0(dba)2
(1 mM) and dppb (1 mM). The conductivity increased
with time (Figure 5, 3000 < t < 20 000 s) to reach a
limiting value that was close to that expected for
5b+AcO- (1 mM) (κlim ) 65 µS cm-1, vide infra). What
was observed in Figure 5 is then the nearly irreversible
formation of the cationic complex 5b+ from complex 6b.
In another experiment involving n ) 24 equiv of 1, it
was observed that the conductivity was not modified by
the successive addition of 1 (10.4 equiv and then 6.4
Complexation Step: Kinetic Data. The kinetics of
the reaction of Pd0(dba)(dppb) (C0 ) 1 mM) with 1 (n
equiv) was monitored by UV spectroscopy in DMF by
recording the decrease of its absorbance at λmax ) 385
nm under conditions where the overall complexation
step was irreversible (n > 10), as performed above for
Pd0(dba)(PPh3)2 (vide supra). The values of K0k1 and
app
k1
(Scheme 9) were determined (Table 2, entry 4,
Figure S5 in the Supporting Information).
Ionization Step: Kinetic Data. As explained above,
the increase of the conductivity with time (3000 < t <
20 000 s in Figure 5) gives the kinetics of the ionization
of the intermediate complex 6b to the cationic complex
5b+AcO- in DMF. Since the experiment was stopped
slightly before the ionization was over, the kinetics was
treated using the Guggenheim method (Figure S4b in
the Supporting Information), which allowed the deter-
mination of k2 (Table 2, entry 4).12,13 As expected, k2 does
not depend on the concentration of 1, which confirms
the mechanism of Scheme 9 with an overall complex-
ation step faster than the ionization step, which is the
rate-determining step of the overall process: k1app[1] >
k2 as soon as [1] > 1 mM.
The values of all the equilibrium and rate constants
determined in this work are gathered in Table 2 (entries
1-4) for the different precursors of Pd0 complexes
investigated here. Once more, we observe that not only
the ligand of the Pd0 complex but also the precursor of
the Pd0 complex affect the overall thermodynamics and
kinetics of the reactions.
As far as the complexation step is concerned, the
reactivity order is the following:
Figure 5. Conductivity measurements in DMF versus
time of [(η3-PhCH-CH-CHPh)Pd(dppb)]+AcO- (5b+AcO-)
generated in the reaction of PhCHdCH-CH(Ph)-OAc (32.1
mM) with Pd0(dba)(dppb) (1 mM) formed in situ by reacting
Pd0(dba)2 (1 mM) and dppb (1 mM) at 30 °C. Once the
reaction was almost over (t ) 20 000 s), dba was succes-
sively added (n′ is the total number of equivalents of added
dba). κlim is the conductivity of 5b+AcO- (1 mM) in DMF
at 25 °C, as determined from the kinetics of the ionization
step.13
(12) Guggenheim, E. A. Philos. Mag. 1936, 22, 322
(13) Using this value of k2, one can evaluate that t1/2 ) 2340 s with
κ1/2 ) 30.7 µS cm-1. The theoretical conductivity of 5b+AcO- (1 mM in
DMF at 30 °C) is then 61.4 µS cm-1. Taking into account the residual
conductivity κ0 ) 4 µS cm-1, one predicts a final experimental
conductivity of 65.4 µS cm-1 (κlim in Figure 5), for a total displacement
of the equilibrium. This shows a posteriori that the ionization reaction
(Figure 5) was indeed almost complete at t ) 20 000 s, before the
addition of dba.

1576 Organometallics, Vol. 24, No. 7, 2005
Amatore et al.
acetate ion on [(η3-PhCH-CH-CHPh)Pd(dppb)]+, must
be considerably lower than that on [(η3-CH2-CH-CH2)-
Pd(dppb)]+, due also to steric hindrance.
For k1app: Pd0(PPh3)4 > Pd0(dba)2 + 2 PPh3 >
Pd0(dba)2 + 1 dppb
This reactivity order is very reminiscent of that observed
for the oxidative addition of PhI.6a,c,11 Even if a com-
plexation of a CdC bond strongly differs from an
oxidative addition, similar arguments may explain the
difference of reactivity. That is to say (i) the higher Pd0-
(PPh3)2 concentration in its equilibrium with Pd0(PPh3)3
Conclusion
In DMF, the reaction of (E)-PhCHdCH-CH(Ph)-OAc
with Pd0L2 complexes (L ) PPh3 or L2 ) dppb) is
reversible and proceeds in two steps: complexation
followed by ionization leading to cationic complexes [(η3-
PhCH-CH-CHPh)PdL2]+AcO-. The intermediate Pd0
complexes, (η2-PhCHdCH-CH(Ph)-OAc)Pd0L2, have been
characterized for the first time in DMF. The overall
complexation step starting from Pd0(PPh3)3, Pd0(dba)-
(PPh3)2, or Pd0(dba)(dppb) is faster than the ionization
step, which is rate-determining. The rate of the com-
plexation step depends both on the ligand and on the
Pd0 precursor. In DMF, for the precursor Pd(dba)2, the
ionization step is faster considering dppb compared to
PPh3. Considering the same dppb ligand and the same
precursor Pd(dba)2, with identical concentrations of the
reagents, the formation of the cationic complex from
PhCHdCH-CH(Ph)-OAc is considerably slower than
with the simple allyl acetate CH2dCH-CH2-OAc.
Work is in progress to compare the rate of formation
of the cationic complexes with the rate of the nucleo-
philic attack. Some preliminary results on the kinetics
of the nucleophilic attack14 of morpholine on the cationic
complex 5a+ indicate that for identical concentrations
of 1 and morpholine the nucleophilic attack is consider-
ably faster than the overall formation of the cationic
complex 5a+, which is then turnover limiting.
6a
than in its equilibrium with Pd0(dba)(PPh3)2 and (ii)
the higher Pd0(PPh3)2 concentration in its equilibrium
with Pd0(dba)(PPh3)2 than the Pd0(dppb) concentration
in its equilibrium with Pd0(dba)(dppb).11 Moreover, dppb
is more electron rich than PPh3. This disfavors the
complexation of the CdC bond of 1 to the Pd0 moiety.
As far as the ionization step from the neutral com-
plexes 6a or 6b is concerned, only the effect of the ligand
has to be taken into consideration with the following
reactivity order (Table 2):
For k2: dppb > PPh3
In all cases investigated here, the ionization was found
to be slower than the complexation step, and a complete
ionization reaction was observed only for the dppb
ligand under comparable experimental conditions in
DMF, which suggests that the reverse reaction, i.e., the
attack of the acetate ion on the cationic complex, follows
the reverse reactivity order (Table 2):
For k-2: PPh3 > dppb
The ionization step may be considered as an oxidative
addition, which should be favored by the more electron-
rich dppb ligand, whereas the reverse reaction, nucleo-
philic attack of the acetate ion onto the cationic complex,
will be favored for the more electron-poor PPh3.
Experimental Section
General Procedures. 31P NMR spectra were recorded in
acetone-d6 or in DMF containing 10% acetone-d6 on a Bruker
spectrometer (101 MHz) with H3PO4 as an external reference.
UV spectra were recorded on a mc2 Safas Monaco spectrom-
eter. Conductivity measurements were performed on a Tacus-
sel CDM210 conductivity meter (cell constant ) 1 cm-1). All
experiments were performed under argon atmosphere.
Chemicals. DMF was distilled from calcium hydride under
vacuum and kept under argon. dba, PPh3, and dppb were
commercial. Pd0(dba)2,15 (E)-1,3-diphenyl-3-acetoxyprop-1-ene
The values of the equilibrium and rate constants of
the reaction of PhCHdCH-CH(Ph)-OAc with Pd0(dba)-
(dppp) generated from Pd(dba)2 and 1 dppp (Table 2,
entry 4) in DMF can be compared to those obtained for
CH2dCH-CH2-OAc reported in a previous work2b (Table
2, entry 5). The overall equilibrium constants K are very
similar. However, for similar concentrations of the
reagents, the overall complexation is slower for PhCHd
CH-CH(Ph)-OAc than for CH2dCH-CH2-OAc (compare
K0k1 in entries 4 and 5). The ionization step is also
slower (compare k2 in entries 4 and 5). This is due to
steric hindrance induced by the two phenyl groups,
which disfavors both the complexation of the CdC bond
and the release of the acetate ion as in an SN2 substitu-
tion. Since the overall equilibrium constant K is similar
for both allylic acetates, this means that the overall
backward reaction is also slower for PhCHdCH-CH(Ph)-
OAc than for CH2dCH-CH2-OAc. The value of k-1k-2
can be calculated from the known values of K and K0k1k2
since K ) K0k1k2/k-1k-2. One obtains k-1k-2 ) 7.5 ×
7b
(1),16 and [Pd(η3-Ph-CH-CH-CH-Ph)(µ-Cl)]2 were prepared
according to described procedures.
Typical Procedure for UV Experiments. From a mother
solution of 10 mL of DMF containing 8.6 mg (30 µmol) of Pd0-
(dba)2 and 15.7 mg (60 µmol) of PPh3, a 300 µL aliquot was
transferred under argon to the thermostated UV cell (1 mm
length) and UV was performed. It was followed by the addition
of known amounts of (E)-1,3-diphenyl-3-acetoxyprop-1-ene
from a mother solution (see Figure 3a). The UV was performed
immediately after hand-shaking the cell. When necessary, the
dilution was taken into account.
(14) (a) Amatore, C.; Jutand, A.; Mensah, L. 2004, unpublished
results. For the investigation of the kinetics of the nucleophilic attack
on cationic (η3-allyl)palladium complexes see also: (b) Antonaroli, S.;
Crociani, B. J. Organomet. Chem. 1998, 560, 137. (c) Kuhn, O.; Mayr,
H. Angew. Chem., Int. Ed. 1999, 38, 343. (d) Canovese, L.; Visentin,
F.; Chessa, G.; Niero, G.; Uguagliati, P. Inorg. Chim. Acta 1999, 293,
44. (e) Crociani, B.; Antonaroli, S.; Canovese, L.; Visentin, F.; Ugua-
gliati, P. Inorg. Chim. Acta 2001, 315, 172. (f) Cantat, T.; Ge´nin, E.;
Giroud, C.; Meyer, G.; Jutand, A. J. Organomet. Chem. 2003, 687, 365.
(15) Takahashi, Y.; Ito, Ts.; Ishii, Y. J. Chem. Soc., Chem. Commun.
1970, 1065.
10-6 M-1 s-2 for PhCHdCH-CH(Ph)-OAc and k-1k-2
)
8 × 10-2 M-1 s-2 for CH2dCH-CH2-OAc. One would
expect a faster decomplexation step from (η2-PhCHd
CH-CH(Ph)-OAc)Pd0(dppb) than from (η2-CH2dCH-
CH2-OAc)Pd0(dppb) due to steric decompression; that
is, one expects k-1 to be higher for PhCHdCH-CH(Ph)-
OAc than for CH2dCH-CH2-OAc. This suggests that the
value of k-2, i.e., the rate constant of the attack of the
(16) Leung, W.; Cosway, S.; Jones, R. H. V.; McCann, H.; Wills, M.
J. Chem. Soc., Perkins Trans. 1 2001, 2288.

Reaction of (E)-PhCHdCH-CH(Ph)-OAc
Organometallics, Vol. 24, No. 7, 2005 1577
In another experiment (see Figure 2a), from a mother
solution of 2 mL of DMF containing 2.8 mg (2 µmol, 1 mM) of
5a+BF4-, a 300 µL aliquot was transferred under argon to the
thermostated UV cell (1 mm length) and UV was performed.
It was followed by the addition of 10 equiv of nBu4NOAc (20
µL from a mother solution containing 105.5 mg of nBu4NOAc
in 2 mL of DMF). UV was performed. Two equivalents of dba
(10 µL from a mother solution containing 32.8 mg of dba in 2
mL of DMF) was then added and UV was performed.
NMR (101 MHz, DMF + acetone-d6 10%): δ 28.2 (s); (101 MHz,
CDCl3); δ 23.36 (s). FAB-MS (MB 001): m/z ) 823 [M]+, 630
[M - (Ph-CH-CH-CH-Ph)], 561 [M - PPh3].
Synthesis of [(η3-Ph-CH-CH-CH-Ph)Pd(dppb)]+BF4-.
The procedure was the same as that used above for PPh3. [(η3-
Ph-CH-CH-CH-Ph)Pd(dppb)]+BF4 (260 mg, 90%) was col-
-
lected. 1H NMR (250 MHz, CDCl3, TMS): δ 1.60-12.1 (m, 4H,
CH2-CH2 of dppb), 2.45 (dm, JPH ) 6.7 Hz, 4H, CH2-P), 5.35
(ddd, 2H, JHH ) 12 Hz, JPH ) 6 Hz, JPH ) 6 Hz, Hanti), 6.33 (t,
1H, JHH ) 12 Hz, central H), 6.75-6.9 (m, 6H, Ph), 6.9-7.1
(m, 4H, Ph), 7.2-7.5 (m, 20 H, Ph of PPh3). 31P NMR NMR
(101 MHz, DMF + acetone-d6 10%): δ 23.16 (s); (101 MHz,
CDCl3) δ 21.35 (s). FAB-MS (MB 001): m/z ) 725 [M]+, 532
[M - (Ph-CH-CH-CH-Ph)].
Typical Procedure for Conductivity Measurements.
In a thermostated cell containing a solution of 17.2 mg (30
µmol) of Pd0(dba)2 and 15.7 mg (60 µmol) of PPh3 in 10 mL of
DMF was added known amounts of (E)-1,3-diphenyl-3-acetoxy-
prop-1-ene. The conductivity was recorded with time using a
computerized homemade program.4
- 7c
Synthesis of [(η3-Ph-CH-CH-CH-Ph)Pd(PPh3)2]+BF4
.
Acknowledgment. This work has been supported
in part by the Centre National de la Recherche Scien-
tifique (UMR CNRS-ENS-UPMC 8640) and the Minis-
te`re de la Recherche (Ecole Normale Supe´rieure). We
thank Johnson Matthey for a generous loan of sodium
tetrachloropalladate.
A solution of 763 mg (2.91 mmol) of PPh3 in 10 mL of acetone
was added to a solution of 384 mg (0.728 mmol) of [Pd[(η3-Ph-
CH-CH-CH-Ph)(µ-Cl)]2 in 13 mL of acetone, followed by a
solution of 799 mg (7.3 mmol) of NaBF4 in 13 mL of water. A
yellow precipitate appeared. After filtration, the solid was
washed with water and diethyl ether and dried under vacuum.
[(η3-Ph-CH-CH-CH-Ph)Pd(PPh3)2]+BF4 (798 mg, 60%) was
-
collected. The product was crystallized from dichloromethane
and pentane as a cosolvent. Monocrystals were formed (see
Figure 1 for the X-ray structure). 1H NMR (250 MHz, CDCl3,
TMS): δ 5.72 (ddd, JHH ) 11 Hz, JPH ) 6 Hz, JPH ) 6 Hz, 2H,
CHanti), 6.35 (t, JHH ) 14 Hz, 1H, central H), 6.78 (m, 10H,
Ph), 7.05 (m, 18H, Ph of PPh3), 7.2 (m, 12H, Ph of PPh3). 31P
Supporting Information Available: Graphs for the
determination of equilibrium constants, rate constants, and
X-ray data. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM049420D