Synthesis of benzylpalladium complexes through C-O bond cleavage of benzylic carboxylates: Development of a novel palladium-catalyzed benzylation of olefins

Article abstract of DOI:10.1016/j.jorganchem.2007.10.051

Benzylic carboxylates were found to react with Pd(0) complexes bearing tertiary phosphines to give benzylpalladium(II) carboxylate complexes with cleavage of the benzyl-oxygen bond. The benzylpalladium complexes having the trifluoroacetato ligand react with olefins such as ethyl acrylate to give olefin benzylation products. On the basis of these studies a novel palladium-catalyzed benzylation of olefins was developed without using organic halides as the starting materials. The method has another advantage of requiring no base as in the conventional Mizoroki-Heck process using organic halides. The catalytic cycle is proposed to be constituted of elementary processes of (a) oxidative addition of a benzyl carboxylate with C-O bond cleavage to a Pd(0) complex to give a benzylpalladium carboxylate, (b) olefin insertion into the benzylpalladium bond to give an alkylpalladium complex, and (c) β-H abstraction to liberate the benzylated olefin.

Full text of DOI:10.1016/j.jorganchem.2007.10.051

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 283–296
www.elsevier.com/locate/jorganchem
Synthesis of benzylpalladium complexes through C–O bond
cleavage of benzylic carboxylates: Development of a novel
palladium-catalyzed benzylation of olefins
*
*
Hirohisa Narahashi, Isao Shimizu , Akio Yamamoto
Department of Applied Chemistry, Graduate School of Science and Engineering, Advanced Research Institute for Science and Engineering,
Waseda University, 3-4-1, Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan
Received 11 June 2007; received in revised form 25 October 2007; accepted 30 October 2007
Available online 4 November 2007
Abstract
Benzylic carboxylates were found to react with Pd(0) complexes bearing tertiary phosphines to give benzylpalladium(II) carboxylate
complexes with cleavage of the benzyl-oxygen bond. The benzylpalladium complexes having the trifluoroacetato ligand react with olefins
such as ethyl acrylate to give olefin benzylation products. On the basis of these studies a novel palladium-catalyzed benzylation of olefins
was developed without using organic halides as the starting materials. The method has another advantage of requiring no base as in the
conventional Mizoroki–Heck process using organic halides. The catalytic cycle is proposed to be constituted of elementary processes of (a)
oxidative addition of a benzyl carboxylate with C–O bond cleavage to a Pd(0) complex to give a benzylpalladium carboxylate, (b) olefin
insertion into the benzylpalladium bond to give an alkylpalladium complex, and (c) b-H abstraction to liberate the benzylated olefin.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Benzylation; Palladium catalyst; Benzyl-O bond cleavage, Olefin synthesis; Benzylpalladium carboxylate
1. Introduction
coupling of the arylpalladium complexes with other organo-
metallic compounds by transmetallation followed by reduc-
tive elimination produces the cross-coupling products [3].
However, the both processes entail intrinsic problems of
using organic halides as substrates for preparation of prod-
ucts that contain no halogen and addition of a base is
required for performing the Mizoroki–Heck processes with
production of salt wastes. Thus finding a methodology
without using halides to be removed with a base is desirable
for making the process more atom efficient and environ-
mentally benign.
An approach for finding a halogen-free catalytic process
is to utilize an organic compound that is susceptible to cleav-
age of the carbon–hydrogen or carbon–heteroatom bond
for producing organopalladium complexes. We have been
interested in the elementary processes where a carbon–
oxygen bond in an oxygen-containing organic compound
is cleaved on interaction with a low valent transition metal
complex and have found several new palladium-catalyzed
Among various palladium-catalyzed processes to per-
form the C–C bond formation in organic synthesis [1], the
palladium-catalyzed olefin arylation (or vinylation), called
Mizoroki–Heck processes have been extensively utilized as
fundamental tools in organic synthesis [2]. Palladium-cata-
lyzed cross-coupling processes of aryl halides with other
organometallic reagents also rank among the most utilized
processes. Mechanistically, these two types of processes
involve cleavage of the carbon–halogen bond in organic
halides on their interaction with electron-rich Pd(0) com-
plexes to generate reactive organopalladium(II) halide spe-
cies by oxidative addition. In the olefin arylation the
subsequent insertion process to give palladium alkyls fol-
lowed by b-H abstraction yields arylated olefins, whereas
*
Corresponding authors. Tel./fax: +81 332046274.
E-mail address: akioyama@kurenai.waseda.jp (A. Yamamoto).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.10.051

284
H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
processes using the cleavage of the C–O bond in carboxylic
esters and carboxylic anhydrides [4–8].
Pd cat.
H2
RCHO
RCOAr
(MeOCO)2O
In previous studies we have found that carboxylic anhy-
drides readily undergo the oxidative addition on interac-
tion with Pd(0) complexes to afford acylpalladium
carboxylates with cleavage of the acyl-O bond [5]. Aryl
esters such as aryl trifluoroacetates also undergo the oxida-
tive addition involving the acyl-O cleavage to give acylpal-
ladium aryloxide complexes (Scheme 1) [6].
RCOOH
+
or
(tBuCO)2O
Pd cat.
ArB(OH)2
Scheme 2. Synthesis of aldehydes and ketones from carboxylic acids.
Utilizing the reactivity of the acylpalladium complexes
with hydrogen to release aldehydes and carboxylic acids,
we could develop a palladium-catalyzed process to synthe-
size aldehydes from carboxylic anhydrides without using
organic halides (Eq. (1))
carbonates (Tsuji-Trost Process) have been extensively
used in organic synthesis [16]. The catalytic process can
be accounted for by combination of the C–O bond cleavage
of the allyl carboxylate with Pd(0) complex giving an g3-
allylpalladium complex with the subsequent nucleophilic
attack on the allyl ligand. Another type of application
involving the cleavage of the allyl-oxygen bond in allylic
carboxylate is the palladium-catalyzed reduction of allylic
formate to alkenes [17].
[Pd(0)]
ð1Þ
H2
O
O
RCHO + RCOOH
RC OCR
In contrast to these methods, combination of the allyl-O
bond cleaving process with olefin insertion has been mostly
limited to intramolecular synthesis of cyclic compounds,
presumably due to the difficulty of olefin insertion into
the g3-allylpalladium intermediate [18,19]. Recent develop-
ment is the palladium-catalyzed cleavage of allylic alcohols
combined with insertion of olefins to give dienes [20]. Lim-
ited examples for achieving the olefin allylation with benzyl
chloride are known [21].
An approach for accomplishing the palladium-catalyzed
halide-free olefin arylation process has been developed by
de Vries and coworkers [22]. They utilized the concept of
the C–O bond cleavage of carboxylic anhydrides on inter-
action with a Pd(0) complex and combined it with an olefin
insertion process. The process proceeds through oxidative
addition of a carboxylic anhydride to give an aroylpalladi-
um carboxylate followed by decarbonylation to provide an
arylpalladium carboxylate, into which olefin insertion takes
place. Application of a related idea to Rh-catalyzed cou-
pling of an aroyl group in carboxylic anhydride with olefin
insertion and hydrogenation was developed by Miura and
coworkers [23].
Based on a related concept, Gooßen and coworkers
developed a new type of olefination of aryl carboxylate
involving the oxidative addition with the C–O bond cleav-
age, followed by decarbonylation and the olefin insertion
process. [24], They have further expanded the method to
direct conversion of carboxylic acids and olefins into olefin
arylation products in the presence of a dicarbonate [25–27].
In contrast to the extensive application of allylic carbox-
ylates, benzyl esters having allylic nature have attracted
much less attention as the starting material. Fiaud and
Legros reported the benzylic substitution of naphthyl-
methyl carboxylate [28], and Kuwano recently found that
benzyl carboxylates undergo the nucleophilic substitution
at the benzylic group in the presence of palladium catalysts
with nucleophiles such as malonates, amines, and thiols
[29] as well as sulfinates [30]. Further application of the pal-
ladium-catalyzed C–O bond cleavage in benzylic alcohols
As another application of the concept of the C–O bond
cleavage to give acylpalladium complexes, we have devel-
oped a new process to prepare ketones and perfluoroke-
tones by combination of the C–O bond cleavage in
carboxylic anhydride with transmetallation with arylbo-
ronic acids as arylation reagents, providing with further
examples of utility of the process involving the Pd-pro-
moted C–O bond cleavage [9,10].
The concept of the C–O bond cleavage combined with
other elementary processes was further expanded so that
we can use the carboxylic acids themselves without using
the preformed carboxylic anhydrides or carboxylic esters
by using additives such as less reactive carboxylic anhy-
dride or dicarbonates (Scheme 2) [11,12].
Gooßen also reported similar catalytic processes to pro-
duce aldehydes [13] and ketones [14] on the basis of a sim-
ilar concept under somewhat different experimental
conditions. Further example of ketone synthesis utilizing
cleavage of the acyl-O bond cleavage in pyridyl carboxylate
combined with the transmetallation using organoboronic
acids has been also reported [15].
As another type of palladium-catalyzed processes
involving the C–O bond cleavage, palladium-catalyzed
allylation of nucleophiles using allylic carboxylates and
O
F3CC
PMeR2
OAr
Pd
CF3COOAr
(R'CO)2O
R2MeP
R2MeP
Pd
R2MeP
O
Ph
PMeR2
OCOR'
R'C
Pd
R2MeP
Scheme 1. Cleavage of C–O bond in aryl trifluoroacetates and carboxylic
anhydrides.

H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
285
to cross-coupling reactions to synthesize ketones and diary-
lmethanes were also developed [31]. In another type of
application of benzylic alcohols, production of ethers,
amines and thioethers has been reported [32], while a differ-
ent mechanism from the present examples is proposed.
The application of benzyl halides to the Mizoroki–Heck
olefin arylation has so far received less attention but palla-
dium-catalyzed benzylation of olefins with benzylic chlo-
rides has been reported [33].
On the other hand, the reaction of the PMePh2-coordi-
nated Pd(0) complex, [Pd(styrene)(PMePh2)2] (2b) with
more electronegative benzyl trifluoroacetate took place
smoothly at room temperature to give 3c as pale yellow
crystals (Eq. (2)). In our previous study of the synthesis
of 3c and other related complexes [38], we observed the
formation of two isomers of the benzylpalladium com-
plexes in various solvents as suggested by NMR studies.
We assigned the trans and ‘‘cis’’ configurations to these
isomers observed in solutions, where the trans isomer
dominated
In the first part of the present paper we first examined
the reactions of benzyl carboxylates with Pd(0) complexes
O
Ph2MeP
Ph2MeP
+
Ph
Pd
(Ph2MeP)2Pd
O
F3C
acetone, r. t. , 3 h
ð2Þ
OCOCF3
2b
+
trans-3c
"cis-3c" (minor)
(major)
93 %
to establish the oxidative addition products of benzyl car-
boxylates. The reactivity of the benzylpalladium complexes
with olefins was then examined to see if olefin insertion into
the benzylpalladium bond takes place.
In the second part of the paper, we examine the applica-
tion of the information thus obtained to development of the
catalytic olefin benzylation process with benzyl carboxyl-
ates. On the basis of the fundamental properties of benzyl-
palladium complexes with olefins we propose a reasonable
catalytic cycle for the benzylation of olefins. The present
paper also provides experimental data concerning the results
we reported briefly in the previous communication [34].
The 31P{1H}NMR spectra of the minor isomer showed
two doublets and the H NMR of the benzylic protons
1
exhibited a doublet. The spectroscopic patterns were com-
patible with the configuration of the complex having the
two PMePh2 ligands coordinated with the center metal in
mutually adjacent positions, thus we ascribed the minor
species to the ‘‘cis’’ isomer and studied the equilibrium
between the trans isomer and the other isomer presumed
to have the cis configuration.
However, we later realized that the minor isomer to
which we assigned the ‘‘cis’’ structure may have an ionic
structure with the two PMePh2 ligands in mutually adja-
cent positions and a trifluoroacetato anion, as will be dis-
cussed later.
2. Results
We first determined the molecular structure of the crys-
tals deposited from a THF solution by single crystal X-ray
analysis and found that the g1-benzylpalladium complex
having the PPh2Me ligands, 3c, has the square planar config-
uration with the trans geometry as shown in Fig. 1 [39,40].
Examination of the determined molecular structure of
trans-3c confirms the square planar trans configuration hav-
ing the g1-benzyl ligand at the site trans to the trifluoroace-
tato ligand. Further inspection of the results of the
molecular structure shows that the two mutually trans-situ-
ated PMePh2 ligands are slightly distorted away from the
benzyl ligand in the square planar geometry and are bent
toward the CF3COOꢀ ligand with the P–Pd–P angle of
170.18 degree. The CF3COO–Pd bond is somewhat length-
2.1. Synthesis and characterization of benzyl(carboxylato)-
palladium complexes
The coordinatively unsaturated Pd(0) complex, [Pd(sty-
rene)(PMe3)2] (2a) [35], prepared in situ by thermolysis of
[PdEt2(PMe3)2] (1a) [36] in the presence of styrene, was
found to react readily with benzyl carboxylates with the
benzyl-O bond cleavage to give benzyl(carboxylato)palla-
dium complexes 3a and 3b as shown in Scheme 3.
The PMe3-coordinated trans-benzyl(benzoato)palla-
dium complex 3a and trans-benzyl(nicotinato)palladium
complex 3b were characterized by elemental analysis and
1H, 13C, and 31P NMR spectra. The trans configuration
of 3a and 3b was supported by observation of the methyl
protons in the trans-situated PMe3 ligands as virtual trip-
lets and of the benzyl CH2 protons as a triplet due to cou-
pling with the two mutually trans-situated PMe3 ligands.
The 31P NMR spectra of these complexes showed a singlet,
respectively, in agreement with the trans geometry [37,6].
˚
ened to 2.150(4) A from the usually observed Pd–O dis-
tances in the phosphine-bearing palladium trifluoroacetate
˚
complexes ranging from 2.05 to 2.07 A [37]. The elongation
of the palladium–oxygen bond in the trifluoroacetato ligand
may reflect the trans influence of the benzyl ligand or incli-
nation of the trifluoroacetato ligand to dissociate from the

286
H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
Me3P
Et
Et
O
Pd
PMe3
Me3P
Ph
Ph
O
Ph
1a
Pd
acetone, 50 oC 4 h
PMe3
PhCOO
-C2H4, -C2H6
Ph
Styrene
59 %
3a
Me3P
Me3P
O
Pd
Ph
O
2a
N
Me3P
Ph
Pd
PMe3
acetone, r. t., 24 h
PyCOO
3b
71 %
Scheme 3. Oxidative addition of benzyl esters with benzyl C–O bond cleavage.
Pd center, particularly in polar solvent. The phenyl ring in
the benzylpalladium complex is oriented to be perpendicu-
lar to the molecular plane. The Pd-benzylic carbon bond
distance of 2.070(6) A is similar to the value of 2.08 A in
trans-[Pd(CH2C6H4-p-Br)Br(PMe3)2] [37].
ligands. The spectroscopic patterns of the ionic complex 4
were thus revealed to be quite similar to those of the minor
isomer of 3c.
˚
˚
We have previously prepared an ionic benzꢀylpalladium
complex having two PPh3 ligands and PF6 anion by
decarbonylation of a phenylacetylpalladium complex hav-
ing two PPh3 ligands [6] and by removing chloride ligand
in trans-PhCH2PdCl(PMe3)2 complex with AgPF4 in ace-
tone [6]. The benzylpalladium complexes having two ter-
tiary phosphine ligands obtained in the present study
showed similar spectroscopic patterns consistent with ionic
struꢀcture having two mutually adjacent PR3 ligands and a
PF6 counter ion.
The NMR spectra of the major isomer observed in solu-
tions are consistent with the trans configuration.
Since isolation of the minor isomer was not feasible, we
prepared an ionic benzylpalladium complex having the PF6
anion, [(PhCH2)(PMePh2)2Pd]PF6 (4), by treatment of the
neutral trans-benzylpalladium chloride complex with
AgPF6 in acetone solution at ꢀ20 ꢁC (Eq. (3)) and com-
pared its NMR spectra with those of the minor isomer
PMePh2
Ph
+ AgPF6,- AgCl
-
[Pd (CH2 Ph) (PMe Ph2 )2 ]+PF6
Pd
ð3Þ
acetone, -20°C
4
Ph2MeP
Cl
1
The H NMR peaks of the methylene protons in the
benzyl group in complex 4 showed a broad doublet. On
the other hand, the 13C{1H} NMR spectrum of 4 showed
the coupling of the benzylic carbon with the two PMePh2
ligands as a doublet of doublets (dd, J = 6.41 and
38.95 Hz). The 31P{1H} NMR showed the two doublets,
consistent with the structure having two adjacent PMePh2
However, for the ionic benzylpalladium complexes hav-
ing two cis PR3 ligands there remains the possibility of exis-
tence of two isomers, a solvent coordinated g1-benzyl
isomer A and g3-benzyl isomer B, as shown in Eq. (4).
These g1 and g3 isomers may be reversibly convertible
and there may be an equilibrium between the two isomers
in solutions
+
+
-
-
O2CCF3
O2CCF3
CH2
PMePh2
PMePh2
CH2
Pd
Pd
ð4Þ
s
Ph2MeP
PMePh2
S
B
A

H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
287
Table 1
Selected bond lengths (A) and angles (ꢁ) for complex 3c
˚
P2–Pd1
O6–Pd1
P2–Pd1–O6
P3–Pd1–O6
C20–Pd1–P2
2.316(2)
2.150(4)
84.1(1)
93.7(1)
94.1(2)
P3–Pd1
C20–Pd1
P2–Pd1–P3
P3–Pd1–C20
C20–Pd1–O6
2.307(2)
2.070(6)
170.18(6)
88.0(2)
178.0(2)
Table 2
Equilibrium ratio of neutral trans-g1- and ‘‘cis’’-ionic benzylpalladium
isomers in chloroform and DMF solutions
neutral trans-g1-complex ¢ trans: ‘‘cis’’-complexa (6)
Solvent
Temperature trans: ‘‘cis’’-
(ꢁC)
Complex
CDCl3
ꢀ20
ꢀ10
0
4.6:1
4.6:1
4.6:1
10
20
ꢀ20
ꢀ10
0
4.6:1
4.6:1
Fig. 1. Perspective view of the trans-[benzyltrifluoroacetatobis(methyldi-
phenylphosphine)Pd(II) complex, trans-3c.
DMF-d7
1: 1.02
1: 1.09
1: 1.23
1: 1.39
1: 1.47
Distinction of the two isomers by NMR is difficult and
unequivocal assignment of the structure was not feasible.
Furthermore, an interconversion process between the sol-
vent-coordinated g1-benzyl isomer A and g3-benzyl isomer
B may be operative. Thus we tentatively assign the cis-like
structure for the ionic benzylpalladium complex without
distinction between A and B.
10
20
Determined by 1H NMR.
a
and the 31P{1H} NMR showed two doublets arising from the
two phosphine ligands in agreement with the structure of 6 in
Eq. (5). The 1H NMR pattern of the benzylic CH2 protons in
6 observed as the doublet of doublets differs from that of the
benzylpalladium 3c observed as a doublet.
1
For gaining further information regarding the H, 13C,
and 31P coupling patterns of the benzylpalladium isomer
of 3c, we prepared a neutral g1-benzylpalladium complex
6 having a ditertiary phosphine ligand, dppe from 5, as
shown in the following equation:
The observation of the minor isomer of 3c in solutions
may now be interpreted by assuming the partial dissocia-
Ph
Ph
Ph2MeP
Cl
Ph
Ph
P
Pd
+
dppe
Pd
P
ð5Þ
Ph
Cl
benzene, r. t., 72 h
PMePh 2
Ph
5
6
82 %
The 1H NMR spectrum of 6 having the Pd-bonded benzyl
ligand adjacent to Cl shows the splitting pattern of the ben-
zylic CH2 protons as a doublet of doublets reflecting the cou-
pling with the two phosphorus atoms, one in trans and the
other in cis positions to the benzyl ligand. The 13C{1H}
NMR of the CH2 carbon in 6 showed a doublet of doublets
tion of the trifluoroacetato ligand in solutions from the
neutral trans-g1-benzyl isomer to give the cationic, sol-
vent-coordinated ‘‘cis’’-g1-benzylpalladium complex (A)
or cationic ‘‘cis’’-g3-benzylpalladium complex (B) (see
Eq. (4)) as shown below (see Table 1)
ionic cis"-[(η1−benzyl)(s)Pd(PMePh2)2]+OCOCF3- (A)
PMePh 2
Ph
or
Pd
ð6Þ
CDCl
ionic "cis"-[η3−(benzyl)Pd(PMePh2)2]+OCOCF3 (B)
-
3
Ph2MeP
OCOCF
3
neutral trans-η1−benzyl form

288
H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
O
The benzylpalladium complex 3c was found to exist
in the trans to ‘‘cis’’ ratio of 4.6:1 in CDCl3 solution with
little change in the isomer ratio between ꢀ20 ꢁC and
20 ꢁC. On the other hand, the NMR spectrum of complex
3c observed in DMF-d7 of larger polarity showed the
increase of the ionic ‘‘cis’’-benzylpalladium isomer, from
1:1.0 at ꢀ20 ꢁC to 1:1.5 at 20 ꢁC as shown in Table 2. On
raising the temperature the signals arising from the trans
isomer in the g1-benzyl form and from the ionic ‘‘cis’’-ben-
zyl form showed broadening. The change of the ratio of the
two forms depending on temperature was reversible and
lowering the temperature restored the original spectro-
scopic pattern.
Determination of the equilibria in Eq. (6) at various
temperatures and performing the Eyring plot of the K val-
ues obtained at various temperatures led to the DH value of
6.0 kJ/mol and DS value of 0.02 kJ/mol K for the
equilibrium.
Ph
OEt
DMF, 100 oC, 24 h
O
(Ph2MeP)2Pd
OCOCF3
OEt
3c
7
25 %
ð7Þ
The higher reactivity of the benzylpalladium trifluoro-
acetate complex 3c in polar solvents that favor the dissoci-
ation of the CF3COOꢀ anion, suggested enhancement of
the reactivity of the benzyl complex by partial dissociation
of the anionic ligand in a polar solvent. In fact the ionic
complex, (g3-benzyl)bis(methyldiphenylphosphine)palla-
dium hexafluorophosphate, 4 smoothly reacted with ethyl
acrylate in CHCl3 at 80 ꢁC to give ethyl (E)-4-phenyl-2-but-
enoate 7 and its isomer (E)-4-phenyl-3-butenoate 8 in a
ratio of 62:13 with the combined yield of 75% at 80 ꢁC.
OEt
5 mol% Pd(OAc)2
20 mol% PPh3
O
OCOCF3
COOEt
+
7
ð8Þ
solvent, temp, 24 h
OEt
O
8
These results suggest that the benzylpalladium complex
tends to dissociate the trifluoroacetato ligand to a greater
degree in solvents of larger polarity, and the dissociation
of the CF3COOꢀ anion in a polar solvent is somewhat
favored at a higher temperature. The dissociation of
the anionic ligand in solution may have implications to
the enhancement of the reactivity of the benzylpalladi-
um complex with olefins in polar solvents as we discuss
later.
The isomer 8 may have been produced by thermal isom-
erization of 7, as was independently verified by heating the
DMF solution of 7 at 130 ꢁC (Eq. (9))
O
OEt
O
8 (83%)
°
DMF, 130 C, 24 h
OEt
O
7
OEt
7 (16%)
2.2. Reactions of benzyl(carboxylato)palladium complexes
with ethyl acrylate
ð9Þ
The occurrence of the olefin insertion into the benzylpalla-
dium bond in 4 followed by b-H elimination to liberate the
benzylated olefin indicated the feasibility of application of
the benzyl-O bond cleavageofbenzylcarboxylates tocatalytic
olefin benzylation processes in the presence of a palladium
catalyst. In fact, we could realize the palladium-catalyzed
olefin benzylation processes with benzyl trifluoroacetates
without using organic halides in the absence of a base.
Having established the structures of the benzylpalladium
complexes derived by oxidative addition of benzyl carboxyl-
ate with the Pd(0) complex and gained some information on
their behavior in solutions, we next examined the reactivity
of the benzylpalladium complexes toward olefins. The trans-
benzyl(benzoato)palladium(II) complex 3a and trans-
benzyl(nicotinato)palladium(II) complex 3b did not react
with ethyl acrylate neither in CDCl3, nor in DMF-d7 under
refluxing conditions of each solution and deposited only
black precipitate. On the other hand, the benzyl(trifluoro-
acetato)palladium complex 3c reacted with ethyl acrylate
in DMF-d7 at the elevated temperature of 100 ꢁC and
yielded ethyl (E)-4-phenyl-2-butenoate 7 in 25% yield,
whereas no reaction proceeded in CDCl3 (Eq. (7))
2.3. Catalytic olefin benzylation with benzyl trifluoroacetates
No catalytic benzylation of ethyl acrylate was observed
in the reaction of benzyl benzoate with various catalysts
such as Pd(OAc)2, Pd(OAc)2 + PPh3, Pd(OAc)2 + 2PBu3,
Pd(PCy3)2, Pd(dba)2 + PPh3, PdCl2, PdCl2 + isoquinoline,

H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
289
Table 3
Effects of solvents and reaction temperatures on palladium-catalyzed benzylation of ethyl acrylate using benzyl trifluoroacetate
OEt
5mol% Pd(OAc)2
20mol% PPh3
O
O
OCOCF3
7
8
COOEt
+
solvent, temp, 24 h
OEt
Run
Solvent
Temperature (ꢁC)
Yield (%)a (7:8 ratio)
1
2
3
4
5
6
7
8
a
THF
Reflux
80
80
80
80
100
120
140
N.R.
N.R.
Trace
24
31
61 (20:1)b
68 (1:1)
46 (1:5)
Toluene
NMP
DMSO
DMF
DMF
DMF
DMF
Isolated yield.
b
Ratio of 7–8 was determined by 1H NMR.
PdCl2 + LiCl in polar solvents such as DMF or NMP at
elevated temperatures of 100 ꢁC or even at temperatures
as high as 160 ꢁC.
trifluoroacetate with ethyl acrylate at 100 ꢁC in DMF
was examined and the results are summarized in Table 4.
Among various palladium catalysts examined in DMF,
combination of Pd(OAc)2 with 4 equiv. of PPh3 gave the
olefin benzylation product 7 in good yields at 100 ꢁC (runs
5 and 6). Employment of ditertiary phosphines such as
dppe and dppp was not suitable for the catalysis, and addi-
tion of bulky tri-o-methylphenylphosphine had an inhibi-
tion effect (run 7).
Use of Pd(OAc)2 alone as the catalyst was not effective
and addition of a tertiary phosphine such as PPh3 was nec-
essary to maintain the catalytic activity. Since Pd(0) com-
plexes such as Pd(PCy3)2 and Pd(PPh3)4 served as
catalysts, it is clear that Pd(0) species plays an important
role as catalyst [1]. However, use of the preformed Pd(0)
complexes is not necessary and combination of Pd(OAc)2
with tertiary phosphines can be conveniently used as cata-
lyst, probably because Pd(OAc)2 is reduced into Pd(0) in
the presence of PPh3 ligands accompanied by oxidation
of PPh3 to OPPh3 [42,43].
Benzyl trifluoroacetate, the more electronegative car-
boxylate, was found to be more reactive than benzyl benzo-
ate in the catalytic process as observed in the reactions of
the isolated benzylpalladium trifluoroacetate with olefins.
Table 3 shows the results of reactions of benzyl trifluoro-
acetate with ethyl acrylate performed in the presence of
5 mol% of Pd(OAc)2 and 20 mol% of PPh3 in various sol-
vents. The results show that benzyl trifluoroacetate can
be catalytically converted into its olefination products
under suitable experimental conditions as described below.
2.3.1. Effect of solvent and temperature
In THF, toluene, or NMP (N-methylpyrrolidinone) no
reaction took place by heating the mixture of benzyl tri-
fluoroacetate and ethyl acrylate at elevated temperatures
in the presence of the palladium catalyst. For carrying
out the benzylation of ethyl acrylate successfully, employ-
ment of polar solvents such as DMSO and DMF was nec-
essary. Dimethyl formamide proved to be most suitable
among the solvents examined giving ethyl (E)-4-phenyl-2-
butenoate 7 in a good yield at 100 ꢁC accompanied by for-
mation of a small amount of its isomerization product,
ethyl (E)-4-phenyl-3-butenoate, 8. Carrying out the same
reaction in DMF at higher temperature of 120 ꢁC gave a
somewhat higher yield of 7 accompanied by formation of
a considerable amount of 8. The reaction at still higher
temperature of 140 ꢁC caused decrease in the yield of 7 with
extensive isomerization to 8 (Table 3).
2.3.3. Scope of the catalytic process
We chose the combination of Pd(OAc)2 and 4 equiv. of
PPh3 as a standard catalyst mixture and examined the
applicability of the present method to the reactions of var-
ious substituted and unsubstituted phenylmethyl trifluoro-
acetates with various olefins by carrying out the
experiments under the standardized procedure. The results
summarized in Table 5 demonstrate that the present pro-
cess is applicable to a broad variety of substrates affording
benzylation products of various olefins. Benzyl trifluoroac-
etates having an electron-withdrawing substituent such as
chloride or fluoride at the para position of the phenyl
group in the benzyl moiety could be catalytically converted
into the corresponding compounds in good yields (Entries
2.3.2. Examination of catalytic systems
The catalytic activities of various palladium complexes
with tertiary phosphine ligands in the reaction of benzyl

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H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
Table 4
Effects of palladium catalysts on benzylation of ethyl acrylate with benzyl trifluoroacetate
OEt
5 mol% Pd cat.
DMF, 100 oC, 24 h
OCOCF3
COOEt
+
O
7
Run
Pd cat.
Yield (%)a
1
Pd(OAc)2
0
2
3
4
5
6b
7
8
9
10
11
12
13
14
15
a
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(PCy3)2
Pd(PPh3)4
1 PPh3
34
45
46
61
75
0
55
Trace
0
23
23
60
23
49
2 PPh3
3 PPh3
4 PPh3
4PPh3
4 P(o-MeC6H4)3
4 PnBu3
dppe
dppp
2 PPh3
3 PPh3
4 PPh3
Isolated yield.
Reaction time was 39.5 h.
b
Table 5
The palladium-catalyzed benzylation of olefins with benzyl trifluoroacetates
5 mol% Pd(OAc)2
20 mol% PPh3
DMF, 100 oC, 39 h
R
Ar
R
+
OCOCF3
Ar
R'
R'
Entry
Ar
Ph
R
R0
Yield (%)
1
2
3
4
5
6
7
8
9
COOEt
COOEt
H
H
H
H
H
H
H
Ph
H
H
H
75
59
65
42
81
80
27
21
56
69
56
p-MeOC6H4
Ph
p-MeOC6H4
p-ClC6H4
p-FC6H4
Ph
p-MeOC6H4
p-MeOC6H4
2,4,6-trimethyphenyl
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
2-pryridine
Ph
p-ClC6H4
p-MeC6H4
p-MeC6H4
10
11
3,5,6-trimethoxyphenyl
5–6). p-Chlorophenylmethyl trifluoroacetate was trans-
formed selectively into corresponding compounds without
undergoing the C–Cl bond cleavage.
Substitution at the para position of the benzyl group
with the MeO group caused some decrease in the yield of
the benzylated olefins as shown in Entries 2, 4, 8, and 9.
The process was also applicable to benzylic trifluoroace-
tates having multiply substituted phenyl groups (Entries
10–11).
The palladium-catalyzed benzylation can be also per-
formed with olefins such as 2-vinylpyridine, 4-methylsty-
rene, 4-chlorostyrene, and 1,1-diphenylstyrene, whereas
acrylonitrile did not react with benzyl trifluoroacetate.
3. Discussion
3.1. Proposed mechanism for the palladium-catalyzed
benzylation of olefins
On the basis of fundamental studies described above on
the reaction of Pd(0) complexes with benzyl carboxylates
and on the reactions of the benzylpalladium complexes
toward olefins, we propose a catalytic cycle to account
for the mechanism of the present palladium-catalyzed ben-
zylation of olefins as shown in Scheme 4.
Since the Pd(0) complexes in combination with tertiary
phosphines act as the catalysts for the benzylation reaction,

H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
291
CF3COOH
+
L
Pd
n
OCOCF3
R
(A)
+
R
OCOCF3
+
LnPd
Pd
Ln
OCOCF3
OCOCF3
PdLn
H
(B)
(η3−benzyl)
(η1−benzyl)
(D)
R
+
PdLn
OCOCF3
(C)
R
Scheme 4. Proposed mechanism for palladium-catalyzed olefin benzylation.
it is reasonable to assume the Pd(0) species (A in Scheme 4) at
the start of the catalytic cycle [43]. As was established in the
studies on the oxidative addition of benzyl carboxylates with
Pd(0) complexes, the C–O bond in benzyl carboxylate is
cleaved on interaction with a Pd(0) complex to give benzyl-
palladium carboxylate (B). The oxidative addition of the
electron-rich Pd(0) complexes to give benzylpalladium inter-
mediate seems to occur more readily in the reaction with
more electronegative benzyl carboxylates. The model studies
revealed that the benzylpalladium trifluoroacetate species is
in an equilibrium between the neutral and ionic forms, which
may have solvent-coordinated g1- or g3-benzylic forms.
The olefin will approach and coordinate to the benzyl-
palladium species B giving C which undergoes insertion
of the coordinated olefin into the benzylpalladium bond
to give the alkylpalladium complex D. The experimental
results that the olefin insertion takes place more readily
with the benzyl trifluoroacetate than with benzoate or nic-
otinate suggest the involvement of dissociation of the
CF3COOꢀ ligand to provide a coordination site for the
incoming olefin.
After the usual syn b-H abstraction to liberate the ben-
zylated olefin and a Pd hydride species, CF3COOH will be
released into the solution with regeneration of the Pd(0)
species A to carry the further catalytic cycle. A solvent like
DMF may be serving to make the liberation of CF3COOH
easier by having an interaction with the acid. The ready
release of the carboxylic acid may help driving the catalytic
OH
3.0 eq. (CF3CO)2O
MeO
5 mol% Pd(OAc)2
1.0 eq.
20 mol% PPh3
DMF, 100 oC, 39 h
+
MeO
42%
1.2 eq.
Ph
Ph
3.0 eq. (CF3CO)2O
5 mol% Pd(OAc)2
20 mol% PPh3
DMF, 100 oC, 39 h
Ph
OH
+
Ph
56%
1.2 eq.
Scheme 5. Direct benzylation of p-methylstyrene with benzylic alcohols.

292
H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
cycle by hindering the re-insertion of the produced olefin
into the Pd–H bond formed in the b-H abstraction. An
alternative route to the b-H elimination by palladium is
the direct hydrogen abstraction by the CF3COOꢀ anion.
(c) insertion of the coordinated olefin into the benzylpalla-
dium bond, and (d) b-H elimination to liberate the benzy-
lated olefin. Utility of the present palladium-catalyzed
benzylation method for synthesis of various useful organic
compounds has been demonstrated.
3.2. Development of catalytic processes using benzylic
alcohols in the presence of anhydride
5. Experimental
As we described earlier in Scheme 2, the direct conver-
sion of carboxylic acids into aldehydes or ketones could
be accomplished in the presence of an external anhydride
or dicarbonate such as pivalic anhydride or dimethyl dicar-
bonate without preparing the anhydride of the carboxylic
acid.
By application of the similar concept, we examined if
benzylic alcohols could be utilized directly for benzylation
of olefins without using the preformed benzylic esters.
Treatment of p-methoxybenzyl alcohol with p-methylsty-
rene at 100 ꢁC in DMF in the presence of trifluoroacetic
anhydride (3 equiv.) and a palladium catalyst for 24 h gave
the benzylation product of p-methylstyrene. Similarly, sub-
stitution of p-methylstyrene with diphenylmethanol could
be achieved (Scheme 5).
All manipulations were carried out under argon using
Schlenk tube techniques. Solvents were purified by the usual
methods under argon. Benzylic trifluoroacetates were syn-
thesized by the reaction of trifluoroacetic anhydride with
corresponding benzyl alcohols in the presence of triethyl-
amine. The palladium complexes, [Pd(PPh3)4] [44] [Pd-
(PCy3)2] [45], [Pd(dba)2] [46], trans-[Pd(CH2Ph)Cl(PMe3)2]
[47], [Pd(CH2Ph)(OCOCF3)(PMePh2)] [6], and [Pd(CH2Ph)-
OCOCF3(PMe3)2] [6] were prepared by the reported proce-
dures. NMR spectra were recorded on JEOL Lambda 500
or 400 spectrometers for 1H (referenced to SiMe4 via resid-
ual solvent protons), 13C{1H} (referenced to SiMe4 via the
solvent resonance) and 31P{1H} (referenced to 85% H3PO4
as an external standard). Coupling patterns are expressed
by d (doublet), t (triplet), vt (virtual triplet), q (quartet),
sep (septet), and m (multiplet). Low-resolution mass spectra
were obtained with a JEOL JMS-Automass 150 that is
coupled with a gas chromatograph. FAB mass analysis
and elemental analysis were performed by the Material
Characterization Central Laboratory of Waseda Univer-
sity. Assignment of the NMR signals of benzyl palladium
complexes was made by comparison with the related ben-
zylic palladium complexes [48].
These results indicate the possibility of further expan-
sion of the present methodology to olefination of various
benzylic alcohols without prior preparation of benzylic
carboxylates.
4. Conclusion
We have developed a novel and practical method for
accomplishing catalytic substitution of olefins with ben-
zylic groups affording arylalkyl-2-alkenes by using palla-
dium catalysts. The method has been developed on the
basis of fundamental studies on cleavage of C–O bond
in benzylic esters on their interaction with a Pd(0) complex
to give benzyl(carboxylato)palladium complexes. The
method does not require the use of organic halides nor
of a base, thus providing an advantage over the conven-
tional Mizoroki–Heck process where organic halides are
used in combination with bases producing byproducts as
waste.
Examination of properties of the isolated benzyl palla-
dium trifluoroacetate complexes that are assumed as the
reaction intermediate in the catalytic cycle revealed that
the benzylpalladium trifluoroacetate exists as an equilib-
rium mixture of neutral g1- and ionic g3-benzylpalladium
complexes and the ionic g3-form is favored in polar media.
It was established that the benzylpalladium trifluoroacetate
reacted with ethyl acrylate to afford the Mizoroki–Heck
product by insertion of the olefin into the benzylpalladium
bond followed by b-H abstraction.
5.1. Preparation of trans-[Pd(CH2Ph)(OCOPh)(PMe3)2]
(3a)
Styrene (0.31 ml, 2.01 mmol) was added to a mixture of
acetone (5 ml) and trans-[PdEt2(PMe3)2] (1a, 424.0 mg,
1.33 mmol) at ꢀ20 ꢁC. The mixture was stirred at 50 ꢁC
for 2 h to give a homogeneous yellow solution. After cooling
the solution at room temperature, benzyl benzoate (0.27 ml,
1.41 mmol) was added to this solution and the solution was
stirred at 50 ꢁC for 4 h. On concentrating the solution, hex-
ane was added to the solution to yield a white precipitate,
which was filtered and collected. Subsequent washing with
hexane and drying in vacuo gave a pale white powder of
trans-[Pd(CH2Ph)(OCOPh)(PMe3)2] (390.0 mg, 0.83 mmol,
1
59% yield, based on benzyl benzoate). H NMR (CDCl3,
500 MHz, 293 K) d 8.12–7.14 (m, 10H, aromatic H), 2.63
(t, J = 7 Hz, 2H, CH2Ph), 1.3 (vt, J = 3 Hz, 18H, PMe3).
13C NMR (CDCl3, 125 MHz, 293 K) d 171.6 (s, PhCOO),
147.7 (s), 147.6 (s), 137.4 (s), 129.8 (s), 129.5 (m), 127.7 (s),
127.5 (s), 124.0 (s, aromatic C), 13.2 (m CH2Ph), 13.1 (vt,
J = 14 Hz, 18H, PMe3). 31P NMR (CDCl3, 202 MHz) d
ꢀ13.3 (s, PMe3). FAB-MS. Found: 470.08 (M), Calc. for
C20H30O2P2Pd: 470.08 (M). Anal. Calc. for C20H30O2P2Pd:
C, 51.02; H, 6.42. Found: C, 51.10; H, 6.31%.
These results support the proposed mechanistic cycle in
Scheme 4, which is constituted of elementary processes
comprising (1) oxidative addition of a benzylic ester to a
Pd(0) complex to give a benzylpalladium carboxylate, (b)
coordination of an olefin to the benzylpalladium species,

H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
293
5.2. Preparation of trans-(benzyl)(nicotinato)bis(trimethyl-
phosphine)palladium (3b)
immediately a white suspension. The suspension was stirred
for 2 h at ꢀ20 ꢁC. Removal of AgCl by filtration gave a clear
yellow solution. After its concentration followed by addi-
tion of ether, a yellow precipitate was formed. Filtration
of the precipitate and the subsequent washing with ether
and hexane and drying in vacuo gave a pale yellow
powder of (g3-benzyl)bis(methyldiphenylphosphine)palla-
dium hexafluorophosphate (515 mg, 0.69 mmol, 85% yield).
1H NMR (CDCl3, 500 MHz, 253 K) d 7.36–6.67 (m, 25H,
aromatic H), 3.01 (d, J = 9 Hz, 2H, CH2), 1.97 (d, J =
10 Hz, 3H, PMePh2), 1.23 (d, J = 8 Hz, 3H, PMePh2).
13C{1H} NMR (CDCl3, 125 MHz, 293 K) d 133.3, 132.2,
(m), 132.9, 131.8, 131.7 (m), 131.5.31.3, 131.1 (m), 130.5
(m) 130.4 (m), 129.0 (m), 128.8 (m), 120.5 (m), 117.3 (m),
59.4 (dd), J = 6.41, 38.95 Hz, 14.5, (d, J = 30.12 Hz),
10.89 (d, J = 29.4 Hz), 10.89 (d, J = 24.4 Hz). 31P NMR
(CDCl3, 202 MHz, 253 K) d 16.5 (d, J = 44 Hz, PMePh2),
6.22 (d, J = 44 Hz, PMePh2), ꢀ142.9 (sept., J = 710 Hz,
PF6ꢀ). Anal. Calc. for C33H33F6P3Pd: C, 53.35; H, 4.48.
Found: C, 53.28; H, 4.56%.
Styrene (0.47 ml, 4.11 mmol) was added to a mixture of
acetone (5 ml) and trans-[PdEt2(PMe3)2] (642.0 mg,
2.03 mmol), at ꢀ20 ꢁC. On stirring the mixture at 50 ꢁC for
2 h, the mixture became homogeneous. After cooling this
yellow solution at room temperature, benzyl nicotinate
(0.42 ml, 2.34 mmol) was added to this solution and the solu-
tion was stirred at room temperature for 24 h. On concen-
trating the solution, hexane was added to the solution to
yield a white precipitate, which was filtrated and collected.
Subsequent washing with hexane and drying in vacuo gave
a white powder of trans-(benzyl)(nicotinato)bis(trimethyl-
phosphine)palladium (777.0 mg, 1.65 mmol, 71% yield
based on benzyl nicotinate). 1H NMR (CD2Cl2, 500 MHz)
d = 9.20 (d, J = 1 Hz, 1H, nicotinate H), 8.64 (dd, J = 1,
5 Hz, 1H, nicotinate H), 8.29 (dt, J = 1, 1, 8 Hz, 1H, nicotin-
ate H), 7.53 (d, J = 8 Hz, 2H, phenyl H), 7.35 (dd, J = 5,
8 Hz, 1H, nicotinate H), 7.27 (t, 8 Hz, 2H, phenyl H), 7.15
(t, J = 8 Hz, 1H, phenyl H), 2.66 (t, J = 7 Hz, 2H, CH2Ph),
1.28 (vt, J = 3 Hz, 18H, PMe3). 13C NMR (CDCl3,
125 MHz, 293 K) d 169.8 (s), 151.3 (s), 150.7 (s), 147.5 (s),
136.9 (s), 132.7 (s), 129.6 (m), 127.9 (s), 124.3 (s), 122.9
(s, phenyl and nicotinate C), 13.5 (m, CH2Ph) 13.2 (t,
J = 4 Hz, PMe3). 31P NMR (CDCl3, 202 MHz) d ꢀ13.0 (s,
PMe3). FAB-MS. Found: 471.07 (M), Calc. for C19H29-
NO2P2Pd: 471.07 (M). Anal. Calc. for C19H29NO2P2Pd: C,
48.37; H, 6.20; N, 2.97. Found: C, 47.58; H, 6.36; N, 2.79%.
5.5. Preparation of [Pd(CH2Ph)Cl(dppe)] (6)
To a mixture of benzene (20 ml) and trans-[Pd(CH2Ph)-
Cl(PMePh2)2] 4 (656.0 mg, 1.04 mmol), dppe (413.3 mg,
1.04 mmol) was added at room temperature. On standing
the mixture at room temperature for 3 days, a yellow precip-
itate was formed from the solution. The precipitate was fil-
tered, washed with ether (5 ml · 5) and dried in vacuo to
give a yellow powder (536.0 mg, 0.85 mmol, 82% yield).
1H NMR (CDCl3, 500 MHz) d 7.82–6.80 (m, 25H, aromatic
H), 3.2 (dd, J = 4, 11 Hz, 2H, PhCH2), 2.42–2.32, 2.02–1.92
(m, 4H, PC2H4P). 13C{1H} (CDCl3, 125 MHz, 293 K) d
147.4, 147.3, 133.8, 133.2, 132.6, 132.0, 131.0, 128.5, 128.4,
128.0, 127.0, 122.5, 34.25 (dd, J = 3.14, 94.11 Hz), 31.46
(dd, J = 23.87, 33.48 Hz), 23.21 (dd, J = 10.38, 24.91 Hz).
31P NMR (CDCl3, 202 MHz) d 55.64, 33.14 (d, J = 40,
PC2H4P). Anal. Calc. for C33H31ClP2Pd: C, 62.77; H,
4.95. Found: C, 62.09; H, 4.85%.
5.3. Preparation of trans-[Pd(CH2Ph)Cl(PMePh2)2] (5)
To a mixture of benzene (10 ml) and trans-[PdEt2(P-
MePh2)2] (2.20 g, 3.89 mmol), styrene (1.40 ml, 12.21 mmol)
was added at ꢀ20 ꢁC. On stirring at 50 ꢁC for 2 h, the mix-
ture became a homogeneous yellow solution. After cooling
the solution at room temperature, benzyl chloride (9.90 ml,
86.03 mmol) was added and the solution obtained was stir-
red at room temperature for 10 h. On concentrating the solu-
tion in vacuo, hexane was added to the solution to yield a
white precipitate, which was filtered and collected. Subse-
quent washing with hexane and drying in vacuo gave a pale
white powder of trans-[Pd(CH2Ph)Cl(PMePh2)2] (2.01 g,
3.31 mmol, 85% yield). 1H NMR (CDCl3, 500 MHz) d
7.51–7.35 (m, 20H, aromatic H), 6.83–6.36 (m, 5H, aromatic
H), 2.47 (m, 2H, CH2Ph), 1.3 (m, 6H, PMePh2). 31P{1H}
NMR (CDCl3, 202 MHz, 293 K) d 12.4 (s, PMePh2).
FAB-MS. Found: 632.08 (M), Calc. for C33H33ClP2Pd:
632.08 (M). Anal. Calc. for C33H33ClP2Pd: C, 62.57; H,
5.25. Found: C, 62.02; H, 5.12%.
5.6. Reaction of (benzyl)(trifluoroacetato)bis(methyldi-
phenylphosphine)palladium (3) with ethyl acrylate
To a DMF solution (3 ml) of (benzyl)(trifluoroacetato)-
bis(methyldiphenylphosphine)palladium 3 (66.6 mg, 0.094
mmol) was added ethyl acrylate (0.0121 ml, 0.133 mmol).
The mixture was stirred for 24 h at 80 ꢁC. After the mixture
was cooled to room temperature, the solvent was evapo-
rated in vacuo. The yield of ethyl (E)-4-phenyl-2-butenoate
(7) was determined as 25% by 1H NMR using C2H2Cl2 as an
internal standard. Characterization of 7 was made by
5.4. Preparation of (g3-benzyl)bis(methyldiphenyl-
phosphine)palladium hexafluorophosphate (4)
GC–MS and NMR. H NMR (CDCl3, 400 MHz): d 7.22–
1
7.11 (m, 5H, aromatic H), 6.91 (dt, J = 6, 15 Hz, 1H,
CH2CHCH), 4.00 (q, J = 7 Hz, 2H, OCH2CH3), 3.45 (d,
J = 6 Hz, 2H, CH2CHCH), 1.08 (t, J = 7 Hz, 3H,
OCH2CH3). GC-MS m/z (rel intensity) 190 (47), 145 (38),
117 (100), 91 (77), 77 (9).
To an acetone solution (20 ml) of trans-[Pd(CH2Ph)-
Cl(PMePh2)2] (518.0 mg, 0.82 mmol), AgPF6 (206.9 mg,
0.82 mmol) in 2 ml of acetone was added at ꢀ20 ꢁC to give

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H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
5.7. Reaction of (g3-benzyl)bis(methyldiphenylphosphine)-
palladium hexafluorophosphate (4) with ethyl acrylate
(s), 126.0 (s), 39.2 (s), 21.1 (s). FAB-MS. Found: 208.13
(M), Calc. for C19H22O3: 208.13 (M). Anal. Calc. for
C19H22O3: C, 92.26; H, 7.74. Found: C, 92.09; H, 7.32%.
To a CHCl3 solution (5 ml) of (g3-benzyl)bis(diphenylm-
ethylphosphine)palladium hexafluorophosphate (226.0 mg,
0.304 mmol) was added ethyl acrylate (0.040 ml, 0.372
mmol). The mixture was stirred for 24 h at 80 ꢁC. After
the mixture was cooled to room temperature, the solvent
was evaporated in vacuo. The yields of ethyl (E)-4-phenyl-
2-butenoate (7) and of ethyl (E)-4-phenyl-3-butenoate (8)
were determined by 1H NMR using C2H2Cl2 as an internal
standard (the sum of the yields of 7 and 8 was 62%).
5.8.4. Entry 4 of Table 5
Colorless oil (42%); 1H NMR (CDCl3, 400 MHz) d
7.24–7.13 (d, J = 8 Hz, 2H, aromatic H), 7.14 (d,
J = 9 Hz, 2H, aromatic H), 7.08 (d, J = 8 Hz, 2H, aromatic
H), 6.85 (d, J = 9 Hz, 2H, aromatic H), 6.39 (d, J = 16 Hz,
1H, CH2CHCH), 6.27 (dt, J = 7, 16 Hz, 1H, CH2CHCH),
3.78 (s, 3H, OMe), 3.47 (d, J = 7 Hz, 2H, CH2CHCH),
2.31 (s, 3H, CH3). 13C NMR (CDCl3, 125 MHz) d 158.1
(s), 136.8 (s), 134.8 (s), 132.4 (s), 130.6 (s), 129.6 (s),
129.2 (s), 128.6 (s), 126.0 (s), 113.9m (s), 55.3 (s), 38.4 (s),
21.1 (s). FAB-MS. Found: 238.14 (M), Calc. for
C17H18O: 238.14 (M). Anal. Calc. for C20H30O2P2Pd: C,
85.67; H, 7.61. Found: C, 85.18; H, 7.28%.
5.8. Palladium-catalyzed olefin benzylation with benzyl
trifluoroacetate
The general procedure for the reaction is shown below.
A DMF solution (5 ml) containing benzyl trifluoroacetate
(1.00 mmol), olefin (1.20 mmol), Pd(OAc)2 (0.05 mmol)
and PPh3 (0.20 mmol) was placed in a 25 ml Schlenk tube.
The solution was stirred at 100 ꢁC for 39 h. On cooling the
mixture, ethyl acetate and water were added and the aque-
ous layer was extracted with ethyl acetate. The organic
layer was dried over MgSO4 and the solvent was evapo-
rated in vacuo. Purification of the residue on column chro-
matography (hexane/ethyl acetate as the elute) gave the
benzylation compound.
5.8.5. Entry 5 of Table 5
Colorless oil (81%); 1H NMR (CDCl3, 400 MHz) d7.29–
7.24 (m, 2H, aromatic H), 7.17–7.16 (m, 2H, aromatic H),
7.12–7.10 (m, 2H, aromatic H), 7.19–7.17 (m, 2H, aromatic
H), 6.43–6.39 (d, J = 16 Hz, 1H, CH2CHCH), 6.28–6.21
(dt, J = 7, 16 Hz, 1H, CH2CHCH), 3.50 (d, J = 7 Hz,
2H, CH2CHCH), 2.34 (s, 3H, CH3). 13C NMR (CDCl3,
125 MHz) d138.8 (s), 137.0 (s), 134.5 (s), 131.9 (s), 130.0
(s), 129.2 (s), 128.6 (s), 127.5 (s), 38.6 (s), 21.1 (s). FAB-
MS. Found: 242.09 (M), Calc. for C16H15Cl: 242.09, Anal.
Calc. for C16H15Cl: C, 79.17; H, 6.23. Found: C, 79.31; H,
6.02%.
5.8.1. Entry 1 of Table 5
Colorless oil (75%); 1H NMR (CDCl3, 400 MHz) d
7.22–7.11 (m, 5H, aromatic H), 6.91 (dt,J = 6, 15 Hz, 1H,
CH2CHCH), 4.00 (q, J = 7 Hz, 2H, OCH2CH3), 3.45 (d,
J = 6 Hz, 2H, CH2CHCH), 1.08 (t, J = 7 Hz, 3H,
OCH2CH3). GC–MS m/z (rel intensity) 190 (47), 145
(38), 117 (100), 91 (77), 77 (9). Anal. Calc. for C19H22O3:
C, 75.76; H, 7.42. Found: C, 75.30; H, 7.37%.
5.8.6. Entry 6 of Table 5
Colorless oil (80%); 1H NMR (CDCl3, 400 MHz) d
7.02–6.96 (m, 2H, aromatic H), 7.13–7.09 (m, 2H, aromatic
H), 7.19–7.16 (m, 2H, aromatic H), 7.25–7.23 (m, 2H, aro-
matic H), 2.32 (m, 3H, CH3), 3.50–3.48 (d, J = 6.71 Hz,
2H, F(C6H4)CH2CH), 6.31–6.22 (m, J = 7 Hz, J = 14 Hz,
1H, CH2CHCH(C6H4)CH3), 6.43–6.38 (m,J = 14 Hz, 1H,
5.8.2. Entry 2 of Table 5
Colorless oil (59%); 1H NMR (CDCl3, 400 MHz) d
7.11–7.05 (m, 3H, aromatic H and CH2CHCH), 6.85 (d,
J = 8 Hz, 2H, aromatic H), 5.78 (d, J = 16 Hz, 1H,
CH2CHCH), 4.17 (q, J = 7 Hz, 2H, COOCH2CH3), 3.79
(s, 3H, OMe), 3.46 (d, J = 7 Hz, 2H, CH2CHCH), 1.27
(t, J = 7 Hz, 3H, COOCH2CH3). 13C NMR (CDCl3,
125 MHz) d 166.5 (s), 158.4 (s), 147.7 (s), 129.8 (s), 129.7
(s), 122.1 (s), 114.1 (s), 60.2 (s), 55.3 (s), 37.6 (s), 14.2 (s).
FAB-MS. Found: 220.11(M), Calc. for C19H22O3: 220.11
(M). Anal. Calc. for C19H22O3: C, 70.89; H, 7.32. Found:
C, 70.12; H, 7.38%.
CH2CHCH(C6H4)CH3).
13C{1H}NMR
(CDCl3,
125 MHz) d 160.5 (s), 137.0 (s), 135.9 (s), 134.6 (s), 131.1
(s), 130.0 (s), 129.2 (s), 127.9 (s), 126.0 (s), 115.1 (s), 38.5
(s), 21.1 (s). FAB-MS. Found: 226.12 (M) Calc. for
C16H15F: 226.12. Anal. Calc. for C16H15F: C, 84.92; H,
6.68. Found: C, 84.69; H, 6.46%.
5.8.7. Entry 7 of Table 5
Colorless oil (27%); 1H NMR (CDCl3, 400 MHz, 303 K)
d 8.51 (d, J = 4 Hz, 1H, 2-pyridine H), 7.53 (m, 1H, 2-pyr-
idine H), 7.25–7.12(m, 6H, 2-pyridine H + Ph H), 7.02 (m,
1H, 2-pyridine H), 6.80 (dt, J = 7, 16 Hz, 1H, CH2CHCH),
6.45 (d, J = 16 Hz, 1H, CH2CHCH), 3.53 (d, J = 7 Hz, 2H,
CH2CHCH). 13C NMR (CDCl3, 125 MHz) d 155.9 (s),
149.5 (s), 139.6 (s), 136.3 (s), 134.2 (s), 131.3 (s), 128.8
(s), 128.6 (s), 126.3 (s), 121.8 (s), 121.1 (s), 39.2 (s). GC–
MS m/z (rel intensity) 78 (25), 93 (100), 118 (58), 167
(12), 180 (10), 195 (87). FAB-MS. Found: 196.11
(M + H), Calc. for C19H22O3: 195.10(M).
5.8.3. Entry 3 of Table 5
Colorless oil (65%); 1H NMR (CDCl3, 400 MHz) d
7.24–7.13 (m, 9H, aromatic H), 6.41 (d, J = 16 Hz, 1H,
CH2CHCH), 6.28 (dt, J = 7, 16 Hz, 1H, CH2CHCH),
3.51 (d, J = 7 Hz, 2H, CH2CHCH), 2.30 (s, 3H, Me). 13C
NMR (CDCl3, 125 MHz) d 140.3 (s), 136.8 (s), 134.7 (s),
130.9 (s), 129.2 (s), 128.6 (s), 128.4 (s), 128.2 (s), 126.2

H. Narahashi et al. / Journal of Organometallic Chemistry 693 (2008) 283–296
295
5.8.8. Entry 8 of Table 5
(3.00 mmol). olefin (1.20 mmol), Pd(OAc)2 (0.05 mmol)
and PPh3 (0.20 mmol) was placed in a 25 ml Schlenk tube.
The solution was stirred at 100 ꢁC for 39 h. On cooling
the mixture, ethyl acetate and water were added and the
aqueous layer was extracted with ethyl acetate. The organic
layer was dried over MgSO4 and the solvent was evaporated
in vacuo. Purification of the residue by column chromatog-
raphy (hexane/ethyl acetate) gave benzylation compound.
Colorless oil (21%); 1H NMR (CDCl3, 400 MHz) d
7.23–6.75 (m, 14H, aromatic H), 6.17 (t, J = 8 Hz, 1H,
CH2CH), 3.71 (s, 3H, OMe), 3.33 (d, J = 8 Hz, 2H,
CH2CH). 13C NMR (CDCl3, 125 MHz) d 158.0 (s), 142.5
(s), 142.2 (s), 139.9 (s), 133.0 (s), 130.0 (s), 129.3 (s),
128.3 (s), 128.2 (s), 128.1 (s), 127.3 (s), 127.1 (s), 114.0
(s), 55.3 (s), 35.0 (s). FAB-MS. Found: 300.15 (M), Calc.
for C17H18O: 300.15 (M). Anal. Calc. for C20H30O2P2Pd:
C, 87.96; H, 6.71. Found: C, 88.05; H, 6.76%.
Acknowledgements
5.8.9. Entry 9 of Table 5
The study was supported by Nippon Zeon Company
and by the Ministration of Education, Science, Sports,
and Culture. We gratefully acknowledge their support.
1
Colorless crystal (58%); H NMR (CDCl3, 400 MHz) d
7.15–7.13 (m, 2H, aromatic H), 6.86–6.84 (m, 2H, aromatic
H), 7.23–7.22 (m, 2H aromatic H), 7.21 (m, 2H aromatic
H), 3.73 (s, 3H, OCH3), 3.46–3.45 (d, J = 6 Hz, 2H,
Appendix A. Supplementary data
CH3O(C6H4)CH2CH),
6.37–6.27
(m,
2H,
CH2CHCH(C6H4)Cl). 13C NMR (CDCl3, 125 MHz)
d158.2 (s), 136.0 (s), 132.6 (s), 131.8 (s), 130.5 (s), 129.5
(s), 128.6 (s), 127.3 (s), 114.0 (s), 55.2 (s, CH3O(C6H4)),
38.4 (s, CH3O(C6H4)CH2CHCH). FAB-MS. Found:
258.08 (M), Calc. for C16H15ClO: 258.08 (M). Anal. Calc.
for C16H15ClO: C, 74.27; H, 5.84. Found: C, 74.39; H,
5.68%.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.jorganchem.2007.10.051.
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1
Colorless oil (56%); H NMR (CDCl3, 400 MHz, r.t.) d
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space
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P21/n(#14);
˚
˚
˚
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