Schiff bases containing ferrocenyl and thienyl units and their utility in the palladium catalyzed allylic alkylation of cinnamyl acetate

Article abstract of DOI:10.1016/j.jorganchem.2007.07.027

The synthesis and characterization of two new ferrocenyl Schiff bases: [Fc-CH{double bond, long}N-(CH₂)_n-(C₄H₃S)] (2) {Fc represents (η⁵-C₅H₅)Fe(η⁵ -C₅H₄)- and n = 1(2a) or 2(2b)} containing the thienyl (C₄H₃S) group are reported. NMR studies indicate that 2 have the anti-(E) conformation in solution and the X-ray crystal structure of 2a confirms that it also adopts the anti-(E) form in the solid state. Ligands 2 have been tested in the palladium catalyzed allylic alkylation of (E)-3-phenyl-2-propen-1-yl (cinnamyl) acetate using sodium diethyl 2-methylmalonate as nucleophile. The reaction of 2 with [Pd(η³-1-Ph-C₃H₄)(μ-Cl)] ₂ in the presence of a slight excess K[PF₆] produced [Pd(η³-1-Ph-C₃H₄){Fc-CH{double bond, long}N-(CH₂)_n-(C₄H₃S)}] [PF₆] {n = 1(5a) or 2(5b)}, which are the intermediates of this catalytic process. NMR studies of 5 reveal the coexistence of several isomers in solution. The stoichiometric reactions of 5 with the nucleophile are also reported. The comparison of the results obtained for 2, [Fc-CH{double bond, long}N-(C₆H₄-2SMe)] (1a) and [(2,4,6-Me₃-C₆H₂)-CH{double bond, long}N-(C₆H₄-2SMe)] (1b) has allowed to establish the importance of the nature of the substituents on the imine group on the regioselectivity of the process.

Full text of DOI:10.1016/j.jorganchem.2007.07.027

Journal of Organometallic Chemistry 692 (2007) 5017–5025
www.elsevier.com/locate/jorganchem
Schiff bases containing ferrocenyl and thienyl units and their utility
in the palladium catalyzed allylic alkylation of cinnamyl acetate
a
a
a
a,
b
*
David Pou , Ana E. Platero-Prats , Sonia P e´ rez , Concepci o´ n L o´ pez , Xavier Solans ,
b
c
c
Merc e` Font-Bard ´ı a , Piet W.N.M. van Leeuwen , Gino P.F. van Strijdonck ,
c
Zoraida Freixa
a
Departament de Qu ı´ mica Inorg a` nica, Facultat de Qu ı´ mica, Universitat de Barcelona, Mart ı´ i Franqu e` s 1-11, 08028 Barcelona, Spain
b
Departament de Cristal Æ lografia, Mineralogia i Dip o` sits Minerals, Facultat de Geologia, Mart ı´ i Franqu e` s s/n, 08028 Barcelona, Spain
Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018-WV Amsterdam, The Netherlands
c
Received 31 May 2007; received in revised form 17 July 2007; accepted 18 July 2007
Available online 27 July 2007
Abstract
5
The synthesis and characterization of two new ferrocenyl Schiff bases: [Fc-CH@N–(CH
5 5 5 4 4 3
2
)
n
–(C
4 3
H S)] (2) {Fc represents (g -
5
C H )Fe(g -C H )– and n = 1(2a) or 2(2b)} containing the thienyl (C H S) group are reported. NMR studies indicate that 2 have
the anti-(E) conformation in solution and the X-ray crystal structure of 2a confirms that it also adopts the anti-(E) form in the solid state.
Ligands 2 have been tested in the palladium catalyzed allylic alkylation of (E)-3-phenyl-2-propen-1-yl (cinnamyl) acetate using sodium
3
diethyl 2-methylmalonate as nucleophile. The reaction of 2 with [Pd(g -1-Ph–C
H
3 4
)(l-Cl)]
2
in the presence of a slight excess K[PF
6
] pro-
3
duced [Pd(g -1-Ph–C H ){Fc-CH@N–(CH ) -(C H S)}][PF ] {n = 1(5a) or 2(5b)}, which are the intermediates of this catalytic process.
3
4
2 n
4
3
6
NMR studies of 5 reveal the coexistence of several isomers in solution. The stoichiometric reactions of 5 with the nucleophile are also
reported. The comparison of the results obtained for 2, [Fc-CH@N–(C –2SMe)] (1a) and [(2,4,6-Me -C )–CH@N–(C –2SMe)]
1b) has allowed to establish the importance of the nature of the substituents on the imine group on the regioselectivity of the process.
2007 Elsevier B.V. All rights reserved.
H
6 4
3
6
H
2
6 4
H
(
ꢀ
Keywords: Ferrocene derivatives; Ferrocenyl-Schiff bases; Allylic alkylation; Palladium(II)-allyl compounds
1
. Introduction
catalyst precursor is a complex containing simultaneously
an allyl moiety and either two mono- or a bidentate ligand.
Due to the importance of this chemical process, many
papers have been focused on studying the influence of the
nature of the donor atoms of bidentate organic ligands
on the enantioselectivity of the reaction. For the catalytic
allylic alkylation process with soft nucleophiles
Ferrocene derivatives and their palladium(II) complexes
have attracted great attention in recent years due to their
applications in a wide variety of fields including organic
and organometallic synthesis and bio-organometallic
chemistry [1–6]. The interest of such compounds as precur-
sors or catalysts in homogeneous catalysis is growing, the
palladium(II) catalyzed allylic alkylation being one of
the most attractive processes [7,8]. This reaction involves
the formation of C–C bonds and it is extremely useful in
organic synthesis [8]. In this type of catalytic process, the
1
2
(Scheme 1), when the substrates used have R = R , the
palladium(II) complex formed in step b has a symmetri-
cally substituted allyl ligand and the attack of the nucleo-
phile in either of the two possible carbons introduces
2
chirality. However, when R = H four different products
could be formed: the two isomers (E and Z) of the non-chi-
*
ral linear product when the attack occurs at the non-substi-
tuted carbon (C ) and the branched derivatives coming
Corresponding author.
E-mail address: conchi.lopez@qi.ub.es (C. L o´ pez).
a
0
022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.027

5018
D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
chelate, we were prompted to prepare and study the cata-
lytic activity of the novel Schiff bases [Fc-CH@N–
CH ) –(C H S)] with n = 1(2a) or 2(2b) (Fig. 1). In both
(
2
n
4
3
ligands, the sulphur atom belongs to the thienyl ring but
they differ in the length of the –(CH ) – chain. This modi-
2
n
fies the size of the chelate formed after the coordination to
the Pd(II) {a five- (for 2a) or a six- (for 2b) membered
ring}, which could affect the regioselectivity of the catalytic
process.
2. Results and discussion
2.1. Synthesis and characterization of the ligands
The ligands [Fc-CH@N–(CH ) –(C H S)] {with
2
n
4
3
Scheme 1. Mechanism for the palladium-catalyzed allylic substitution
0
n = 1(2a) or 2(2b)} were prepared in fairly good yields
(80% and 72%, respectively) using the general method
reported for the synthesis of related ferrocenylaldimines:
reactions using soft nucleophiles, where S represents the solvent, L and L
0
ꢀ
monodentate ligands or (L,L ) bidentate ligand, Nu the nucleophile and
LG is a leaving group.
3
3
Fc-CH@N-R (with R = phenyl, benzyl or naphthyl
group) [14]; but using H N–(CH ) –(C H S) (n = 1 or 2)
c
2
2 n
4
3
from the nucleophilic substitution at C (Scheme 2). Thus,
as starting materials. Elemental analyses and mass spectra
in these cases regiocontrol becomes necessary prior to
enantiocontrol.
of 2 were consistent with the proposed formulae. Com-
1
pounds 2 were also characterized by mono- [ H and
Despite the large amount of articles centered on the
study of ferrocene derivatives and their palladium(II) com-
plexes in enantioselective allylic alkylation [2,9], the effect
of the nature of the donor atoms of the ferrocenyl ligands
on the regioselectivity has not been so deeply studied yet. A
1
3
1
1
1
C{ H}] and two dimensional [{ H– H}-NOESY and
1
13
{
H– C}-HSQC and HMBC] NMR experiments. The
1
1
most relevant feature detected in the { H– H}-NOESY
spectra is the existence of NOE peaks between the signals
due to the imine proton and those of the @N–CH – unit
2
few articles focused on the effects induced by bidentate
0
(Fig. 2) indicating that the ligands 2 adopt the anti-(E) con-
formation in solution.
(
P,E) (E = P , N or S) or (N,O) ligands on the regioselec-
tivity of palladium(II) catalyzed allylic alkylations have
been published [10,11], but related studies involving
Compound 2a was also characterized by X-ray diffrac-
1
tion. Its crystal structure (Fig. 3) consists of molecules
(
N,S) ligands are scarce [12]. We have recently shown that
of [Fc-CH@N–(CH )–(C H S)] separated by van der
2
4
3
the ferrocenylthioimine [Fc-CH@N–(C H –2SMe)] (1a)
6
4
Waals distances.
[
(
13] (Fig. 1) namely its palladium(II) complex [Pd-
˚
3
The C(11)–N bond length [1.263(4) A] is similar to those
reported for related ferrocenylimines [15,16] and the value
of the C(10)–C(11)–N–C(12) torsion angle [179.2ꢁ] is con-
sistent with an anti-(E) conformation of the ligand. The thi-
enyl ring is planar and its main plane forms angles of 84.6ꢁ
and 86.5ꢁ with the substituted pentagonal ring of the ferr-
ocenyl unit and with the imine moiety, respectively.
g -C H ){Fc-CH@N–(C H –2SMe)}][PF ] is an active
3
5
6
4
6
catalysts for the allylic alkylation of (E)-3-phenyl-2-pro-
pen-1-yl (cinnamyl) acetate using sodium diethyl 2-methyl-
malonate as nucleophile [12]. In view of this and in order to
elucidate the influence of the donor properties of the sul-
phur atom and/or the flexibility and size of the ‘‘Pd(N,S)’’
5
5
Bond lengths and angles of the ‘‘(g -C H )Fe(g -
5
5
C H )–’’ unit agree with those reported for most monosub-
5
4
stituted ferrocene derivatives [15]. The two pentagonal
rings are planar, nearly parallel (tilt angle = 2.1ꢁ) and their
conformation deviates by 3.5ꢁ from the ideal eclipsed
conformation.
1
Crystal data for 2a:
16
C H15FeNS, MAR345 diffractometer,
˚
˚
˚
k = 0.71073 A, T = 293(2) K, triclinic, a = 5.872(4) A, b = 9.610(5) A,
c = 12.712(6) A, a = 101.28(3)ꢁ, b = 92.19(4)ꢁ, c = 98.64(4)ꢁ,
V = 693.8(7) A , Z = 2,
˚
˚
3
3
ꢀ1
,
D
calc = 1.480 g/cm , l = 1.212 mm
F(000) = 320, number of reflections collected = 4901, number of unique
reflections 2622 [Rint = 0.0220], number of parameters = 173, goodness-
of-fit = 1.170 and R indices: R = 0.0460 and wR = 0.1253 [for I > 2r(I)]
0
Scheme 2. Allylic alkylation of an asymmetric p-allyl complex {L and L
0
ꢀ
represent monodentate ligands or (L,L ) bidentate ligand and Nu the
nucleophile}.
1
2
and R = 0.0465 and wR = 0.1257 (for all data).
1
2

D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
5019
Fig. 1. Chemical formulae of the ferrocenylthioimines [Fc-CH@N–(C
palladium(II) catalyzed allylic alkylation of cinnamyl acetate [12] and the ligands [Fc-CH@N–(CH
6
H
4
–2SMe)] (1a) and [(2,4,6-Me
3
-C
–(C
6
H
2
)–CH@N–(C
6
H
4
–2SMe)] (1b) used in the
2
)
n
4 3
H S)] {with n = 1(2a) or 2(2b)} under study
together with the labelling scheme of the atoms.
1
1
3
Fig. 2. { H– H} NOESY spectrum of 2b in CDCl at 298 K. In the chemical formula, the arrows indicate the most relevant NOE contacts.
˚
2 4 3
Fig. 3. ORTEP plot of the crystal structure of [Fc-CH@N–(CH )–(C H S)] (2a). Selected bond lengths (in A) and bond angles (in ꢁ): C(6)–C(10), 1.429(4);
C(9)–C(10), 1.445(4); C(10)–C(11), 1.463(3); C(11)–N, 1.263(4); N–C(12), 1.481(3); C(12)–C(13), 1.495(4); C(13)–C(14), 1.409(4); C(14)–C(15), 1.404(4);
C(15)–C(16), 1.336(5); S–C(13), 1.711(3); S–C(16), 1.691(4); C(6)–C(10)–C(11), 128.2(2); C(9)–C(10)–C(11), 123.2(2); C(10)–C(11)–N, 121.7(2); C(11)–N–
C(12), 116.0(2); N–C(12)–C(13), 111.2(2); C(12)–C(13)–C(14), 127.3(3); C(13)–C(14)–C(15), 111.0(3); C(14)–C(15)–C(16), 114.4(3); C(15)–C(16)–S,
111.8(3) and C(16)–S–C(13), 92.7(17).

5020
D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
2
.2. Catalytic studies
Table 1
Results of the catalytic allylic alkylation of cinnamyl acetate with sodium
a
diethyl 2-methylmalonate
In view of the recent interest of sulphur containing
ligands as precursors for palladium-catalyzed allylic alkyl-
ation [12,17,18], and in order to elucidate the effects
induced by the length of the –(CH ) – chain and the elec-
EtO
2
C
2
CO Et
Ph
OAc
Ph
+
Na
Me
2
n
tronic properties of the heterocyclic sulphur on the viability
of the process, we decided to study the alkylation of cinn-
amyl acetate with sodium diethyl 2-methyl malonate using
Me
2
CO Et
CO Et
2
EtO C
2
[
Pd]
Me
Et
+
3
THF
CO
2
Ph
catalytic amounts of ligands 2 (Fig. 1) and [Pd(g -C H )(l-
3
5
3
4
Cl)] . The results obtained from these studies are presented
2
linear product
trans-(E)
branched product
in Table 1 (entries I–IV). For comparison purposes the
results published for ligands [Fc-CH@N–(C H –2SMe)]
6
4
(
1a) and [(2,4,6-Me –C H )–CH@N–(C H –2SMe)] (1b)
3
6
2
6
4
under identical experimental conditions are also included
b
Entry
L
t (h)
Conversion (%)
Molar ratio (3:4)
(
entries V and VI).
I
II
2a
2a
2b
2b
1a
1b
20
44
20
44
20
20
86.7
95.0
87.3
97.8
100.0
100.0
89:11
88:12
89:11
89:11
96.5:3.5
95.8:4:2
ꢀ3
As shown in Table 1 (entries I–IV), 2a and 2b catalyze
the reaction and the formation of the linear trans-(E)
product (3) is strongly preferred over that of the branched
product (4). The similar regioselectivities obtained when
using 2a (88%) and 2b (89%) suggest that there is no
big influence of the ring size (a five- or a six-membered
ring, for 2a and 2b, respectively) on the catalytic active
species formed when going from five to six membered
rings.
III
IV
c
V
c
VI
a
Experimental conditions: mixtures containing 2.5 · 10 mmol of
H )(l-Cl)] , 5.0 · 10 mmol of 2a (or 2b); 0.5 mmol of cinn-
3 5 2
amyl acetate, 1.0 mmol of sodium diethyl 2-methylmalonate, THF
3
ꢀ3
[
Pd(g -C
(
5.0 mL), and decane (0.258 mmol) at 298 K.
b
Determined by GC.
c
The comparison of the results obtained for 2 and for the
Schiff bases [Fc-CH@N–(C H –2SMe)] (1a) or [2,4,6-
Data from Ref. [12].
6
4
Me C H -CH@N–(C H –2SMe)] (1b) [12], which contain
3
6
2
6
4
H
H
the same heteroatoms (N and S), (entries V and VI of
Table 1) indicate that for ligands 2, both activity and selec-
tivity to linear 3 are lower those reported for the thioimines
H
C
N
SMe
Me
C
N
n
C
N
SMe
S
Fe
Fe
Me
1
a or 1b. Furthermore, comparison of the results obtained
n = 1 (2a) or 2 (2b)
1
a
Me
1
b
for 2a and 1a (which would both generate five-membered
chelate rings) suggest that the replacement of the –C H –
6
4
2
–
SMe moiety (in 1a) by the more flexible backbone
(CH )–(C H S) (in 2a) reduces the regioselectivity of the
3
Treatment of 2a (or 2b) with [Pd(g -1-Ph–C H )(l-Cl)]
2
2
4
3
3
4
catalytic process as well as its rate. Whether this effect is
due to increased ligand flexibility or to the nature of the
S donor atom remains unclear.
(in a 2:1 molar ratio) and in the presence of a slight excess
(12%) of K[PF ] in acetone gave orange solids (herein after
6
referred to as 5a and 5b) (Scheme 3). Their elemental anal-
3
yses agreed with those expected for: [Pd(g -1-Ph–C H )-
3
4
2
.3. Palladium allylic intermediates
{Fc-CH@N–(CH ) -(C H S)}][PF ] {with n = 1(5a) or
2
n
4
3
6
2(5b), respectively} and their mass spectra showed a peak
It is well-known that regioselectivity of the allylic alkyl-
at m/z = 532 (for 5a) or at m/z = 546 (for 5b), which is con-
3
ation is dependent on a wide variety of factors including
the number of isomers of the intermediates formed after
the oxidative addition {Scheme 1, step (b)} present in solu-
tion, their relative abundances, their interconversion rates,
the relative arrangement between the non-substituted car-
bon atom of the allyl group and the two donor atoms of
the ligand, the rate of the nucleophilic attack and the posi-
tion where it takes place. For the catalytic process under
sistent with those of the cations [Pd(g -1-Ph–C H ){Fc-
3
4
+
CH@N–(CH ) –(C H S)}] (n = 1 or 2, respectively).
2
n
4
3
Proton NMR spectra of 5 in CDCl or CD Cl at 298 K
3
2
2
showed broad signals (Fig. 4a). This could be indicative of
the existence of dynamic processes between different iso-
meric forms. Several isomers of the cations of 5 could be
expected in principle due to: (a) the conformation adopted
by ligands 2 in the complexes {anti-(E) (Fig. 5) or syn-(Z)};
(b) the conformation of the allyl group {endo- or exo-,
Fig. 5(a–d) or (e–h), respectively}, (c) the relative arrange-
ment between the substituted carbon of the allyl group
3
study these intermediates are the cationic species [Pd(g -
+
1
-Ph–C H ){Fc-CH@N–(CH ) –(C H S)}] . In order to
3
4
2 n
4
3
rationalize the results obtained from the catalytic studies
we decided to prepare and characterize the palladium(II)
complexes containing these cations and to study their
behaviour in solution.
c
(hereafter referred to as C ) and one of the two heteroa-
c
toms (N or S) of the ferrocenyl ligand [i.e. the C and the
sulphur atom could be in a cis- or a trans- arrangement

D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
5021
allyl unit {syn- (Fig. 5a,c,e or g) or anti- (Fig. 5b,d,f or
h)}. Besides that, the non-planar chelates formed by the
binding of the S and N atoms to the palladium(II) may
adopt different conformations. Moreover, if the free rota-
tion around the Cipso–Cimine bond of the ligands is inhib-
ited, different rotameric species could also be present in
solution. This should be especially relevant at low
temperatures.
3
Scheme 3. (i) [Pd(g -1-Ph–C
3
H
4
)(l-Cl)]
2
{in a 2:Pd(II) molar ratio of 1}
1
The resolution of the H NMR spectra of 5 improved
upon cooling (Fig. 4a–c). In particular, the spectrum of
and a slight excess (12%) of K[PF
6
] in acetone at 298 K.
5
a in CD Cl at 273 K showed two sets of resonances of
2 2
relative intensities 10.0:6.3 (Fig. 4b). At 193 K the number
of resonances increased but their width decreased (Fig. 4c)
and the analyses of the sets of signals suggested the coex-
istence of at least seven isomers (here after referred to as
5aI–5aVII) in a relative abundance of 10.0:8.5:7.7:4.9:3.9:
3.4:1.2.
The solution behaviour of 5b was similar to that of 5a,
1
its H NMR spectra at 193 K suggested the coexistence
of six distinguishable isomers (5b –5b ), but in this case
I
VI
their relative ratios were 10.0:5.5:3.9:2.1:1.6:1.4. The
1
1
{
H– H}-NOESY spectra of the major isomers of 5{5a –
I
5
aIII and 5b –5b } showed NOE contacts between the
I II
imine proton and those of the ‘‘@N–CH –’’ moiety; thus,
2
indicating that in these isomers the imine adopted the
anti-(E) conformation. Furthermore, for 5a –5a
and
III
I
3
c
b
5
b –5b , the values of the coupling constant J(H –H )
I II
c
suggest that the proton attached to the C carbon is located
in an anti- position in relation to the central proton of the
b
allyl unit (H ). These findings reduce the number of possi-
ble isomers to four and more specifically to types a,c,e or g
depicted in Fig. 5.
c
The use of molecular models for cations where the C
carbon of the allyl ligand is in a trans- arrangement to
the sulphur (types c and g) reveals that in these isomers, the
phenyl ring would be too close to the C H ring to the ferr-
5
4
ocenyl unit. Consequently, this distribution of the substitu-
ents would introduce significant steric effects. In fact the
1
1
{
H– H}-NOESY and ROESY spectra of 5 {(5a and
I
5
a ) and (5b and 5b )} at 193 K showed NOE peaks be-
II I II
0
5
tween the doublet due to the H proton of the thienyl unit
and one aromatic proton. This is only possible if the het-
erocycle and the phenyl group are proximal, which is indic-
ative of a cis- arrangement between the C carbon and the
sulphur atom. All these findings suggests that the pairs of
c
isomers {(5a and 5a ) and (5b and 5b )} correspond to
I
II
I
II
the types a and e shown in Fig. 5, which differ in the
conformation of the allyl group (endo- and exo-,
respectively).
1
The complexity of the H and the two dimensional
1
3
1
1
1
1
1
13
Fig. 4. H NMR spectra (500 MHz) of [Pd(g -1-Ph–C
(
(
7
3
H
4
){Fc-CH@N–
[
{ H– H}-NOESY, { H– H}-ROESY and { H– C}-
HSQC] NMR spectra of 5 at 193 K together with
the low abundance of 5a –5a and 5b –5b and
CH
c), together with an expansion of the spectrum at 193 K in the range
.55 ppm < d < 8.52 ppm (d).
2 4 3 6 2 2
)-(C H S)}][PF ] (5a) in CD Cl at 298 K (a), 273 K (b) and 193 K
IV
VII
III
VI
the partial overlapping of the resonances due to these
isomers and those of the major components did not
allow us to assign the resonances due these minor
isomers.
{
Fig. 5(a–b, e–f) or (c–d, g–h), respectively}] and (d) the
c
position occupied by phenyl group attached to C in rela-
tion to the hydrogen bound to the central carbon of the

5022
D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
3
Fig. 5. Schematic view of some of the isomeric forms expected for the cations of compounds [Pd(g -1-Ph–C
{
3
H
4
){Fc-CH@N–(CH
2
)
n
–(C
4 3 6
H S)}][PF ]
5
n = 1(5a) or 2(5b)}, in which the ligand adopts the anti-(E) conformation (see text). The wavy lines indicate that the ‘‘Fe(g -C
5
H
5
)’’ moieties may be
situated in an upper (or in a lower) plane in reference to that of the C
5
H
4
ring of the ferrocenyl unit. An additional set of isomers could also be formed if
the ligand exhibits the syn-(Z) conformation.
2
.4. Stoichiometric reactions
the results obtained for 2 and those reported recently for
[
Fc-CH@N–(C H –2SMe)] (1a), has allowed us to estab-
6
4
We also studied the reactions between compounds 5 and
an excess of sodium diethyl 2-methylmalonate in THF at
98 K (stoichiometric reaction). The reaction gave after
work up a mixture of the linear trans-(E) derivative (3)
and the branched product (4) in molar ratios 3:4 of
lish the relevancy of the electronic properties of the sulphur
atom and the flexibility of the chain connecting these two
donor atoms on the regioselectivity and rate of the catalytic
process. The presence of the thienyl unit (in 2a and 2b)
slows down the reaction and produces a significant
decrease (ca. 9%) in the regioselectivity towards the linear
product (3) in comparison with data obtained for 1a, where
the sulphur belongs to a thioether group. Besides that, data
presented in Table 1 also indicate that this factor has
greater influence on the regioselectivity of the catalytic pro-
cess than that due to the length of the –(CH ) – chain. Sev-
2
9
4.1:5.9 (for 5a) and 93.0:7.0 (for 5b).
The study of the solution behaviour of 5 (described
above) showed that in the two major isomers of 5a(5aI
and 5a ) and 5b (5b and 5b ) differ in the conformation
II
I
II
of the ‘‘(1-Ph–C H )’’, but in all cases: (a) the ligand adopts
3
4
the anti-(E) conformation, (b) the phenyl ring is located on
the syn-position and (c) the substituted carbon of the allyl
2
n
eral factors such as the different trans-influence of the
sulphur atom and the lability of the Pd–S bond in the inter-
mediate species formed in the catalytic process, may also be
important to determine the number of isomers present in
c
group (C ) is in a cis-arrangement to the sulphur of the thi-
enyl unit.
In addition, the results obtained from the stoichiometric
and catalytic studies indicate that the formation of the lin-
ear product 3 is preferred over that of the branched prod-
uct 4. This could be due to several factors such as the
3
solution {i.e. four in [Pd(g -1-Ph–C H )(1a)] [12] or seven
3
4
(in 5a) at 193 K}, their interconversion rates or the prefer-
ential position for the nucleophilic attack in each one of the
isomeric species. Further experimental work on this field is
required to clarify the relative weight of each one of these
factors.
smaller steric hindrance on the non-substituted carbon
a
(
C ) or its higher electrophilic character when compared
c
with that of the C carbon atom.
2
.5. Conclusions
3. Experimental
The results presented here have shown the potential util-
3.1. Materials and methods
ity of ligands [Fc-CH@N–(CH ) –(C H S)] (2), that con-
2
n
4
3
tain two different donor atoms (N and S), in the
palladium catalyzed allylic alkylation of cinnamyl acetate
under mild experimental conditions. The comparison of
Ferrocenecarboxaldehyde and the amines H N–(CH ) –
2
2 n
(C H S) (with n = 1 or 2) were purchased from Aldrich and
4
3
3
used as received. Compound [Pd(g -1-Ph–C H )(l-Cl)]
2
3
4

D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
5023
0
5
13
1
was prepared as described previously [19]. Sodium diethyl
H ). C{ H} NMR-data [21]: d = 163.3(–CH@N–), 69.2
1
2
5
3
4
2
2
-methylmalonate (0.5 M) was synthesized from diethyl
-methyl malonate and NaH in THF at 273 K. Solvents
(C H ), 79.3 (C ), 69.0 (C and C ), 71.4 (C and C ),
5 5
0 0 0
58.3 (@N–CH –), 141.2 (C ), 125.7 (C ), 127.1 (C ) and
125.3(C ). For 2b: Anal. Calc. for C H NFeS: C,
2
3
4
2
0
5
(
except benzene) were distilled and dried before use [20].
1
7
17
Some of the preparations described below require the use
of highly hazardous reagents (such as benzene) that should
be handled with Caution.
63.17; H, 5.30; N, 4.33; S, 9.92 Found: C, 63.3; H, 5.5;
N, 4.4; S, 10.2%. MS (FAB ): m/z = 323, [M] . IR-data:
+
+
ꢀ
1
1
1645 cm
{m(˜C@N–)}. H NMR data [21]: d = 8.05
Elemental analyses were carried out at the Serveis de
Recursos Cientifics i T e` cnics (Universitat Rovira i Virgili).
(s, 1H, –CH@N–), 4.07 (s, 5H, C H ), 4.33 (t, 2H,
J = 1.5, H and H ), 4.58 (t, 2H, J = 1.5, H and H ),
5
3 4 3 2 5
5
3
+
3
3
FAB mass spectra were performed at the Servei d’Espec-
3.73 (t, 2H, J = 6.0, @N–CH –), 3.18 (t, 2H, J = 6.0,
0
3 3
2
trometria de Masses (Universitat de Barcelona) with a VG-
Quatro Fissions instrument and using 3-nitrobenzylalcohol
–CH –), 6.84 (br., 1H, H ), 6.92 (dd, 1H, J = 5.0 and
2
0 0
4
4
3
5
13
1
J = 3.0, H ) and 7.12 (d, 1H, J = 5.0, H ). C{ H}
(
NBA) as matrix. IR spectra were obtained with a Nicolet
NMR-data [21]: d = 161.9 (–CH@N–), 69.1 (C H ), 80.4
5
5
1
1
2
5
3
4
4
00-FTIR instrument using KBr pellets. Routine H and
(C ), 70.6 (C and C ), 68.6 (C and C ), 63.1 (@N–
0 0 0
2 3 4
1
3
1
C{ H} NMR spectra were recorded with a Gemini-
CH –), 31.5 (–CH –), 142.7 (C ), 125.0 (C ), 126.8 (C )
2 2
0
5
2
00 MHz or a Mercury-400 MHz instruments, respectively.
and 123.5 (C ).
1
High resolution H NMR spectra and the two-dimensional
1
1
1
13
3
[
{ H– H}-NOESY and ROESY and { H– C}-HSQC and
3.2.2. Synthesis of [Pd(g -1-Ph–C H ){Fc-CH@N–
3
4
HMBC] NMR experiments were registered with a Varian
VRX-500 or a Bruker Avance DMX-500 MHz instruments
at 298 K. The latter equipment was also used to perform
the variable temperature (VT) NMR experiments. The
chemical shifts (d) are given in ppm and the coupling
constants (J) in Hz. Except where quoted, the NMR spec-
(CH ) –(C H S)}][PF ] {n = 1(5a) or 2(5b)}
4
2
n
4
3
6
ꢀ
3
A 0.150 g (2.89 · 10 mol) amount of [Pd(g -1-Ph–
ꢀ
4
C H )(l-Cl)] and 5.78 · 10 mol of the corresponding
3
4
2
ligand [Fc-CH@N–(CH ) –(C H S)] {n = 1(2a) or 2(2b)}
2
n
4
3
were dissolved in 20 ml of acetone. Then, 0.123 g (6.68 ·
ꢀ4
10
mol) of K[PF ] was added. The reaction mixture
6
tra were recorded using CDCl (99.9%) as solvent and
was stirred at 298 K for 1.5 h and then filtered. The filtrate
was concentrated to dryness on rotatory evaporator. The
orange residue was treated with the minimum amount of
CH Cl and the undissolved materials were removed by fil-
3
SiMe as internal reference.
4
The product distribution of alkylation experiments was
measured on a Trace-DQS instrument equipped with a
HP-5 column, length 25 m, inner diameter 0.2 mm, film
thickness 0.5 lm, and an electron impact mass detector.
2
2
tration and discarded. The addition of Et O to the filtrate
2
produced the formation of an orange solid, which was col-
lected by filtration and dried in vacuum for 24 h. [Yield:
0.150 g, (38%) for 5a and 0.209 g, (52%) for 5b]. Character-
ization data for 5a: Anal. Calc. for C H F FeNPPdS: C,
3
.2. Preparation of the compounds
2
5
24 6
3
[
.2.1. Synthesis of [Fc-CH@N–(CH ) –(C H S)]
44.31; H, 3.57; N, 2.07; S, 4.73. Found: C, 44.5; H, 3.7; N,
2
n
4
3
+
+
n = 1(2a) or 2(2b)]
Ferrocenecarboxaldehyde (1.00 g, 4.67 · 10 mol) was
2.15; S, 4.95%. MS (FAB ): m/z = 532, {Mꢀ[PF ]} .
6
ꢀ
3
ꢀ1
ꢀ
1
IR-data: 1645 {m(˜C@N–)} and 839 cm {[PF ] }. H
NMR data in CD Cl at 273 K: two isomeric forms (5a
I
6
dissolved in 20 mL of benzene. The reaction mixture was
stirred at 298 K for 10 min and then filtered out. The undis-
solved materials were discarded, the filtrate was transferred
to an erlenmeyer flask and then equimolar amount (4.80 ·
2
2
and 5a ) coexisted in a molar ratio 5a :5a 10.0:6.3. For
II
I
II
5a [22,23]: 7.82 (s, 1H, –CH@N–), 4.33 (s, 5H, C H ),
I
5
5
2
5
3
4
4.54 (s, 2H, H and H ), 4.39 (s, 2H, H and H ), 5.29
and 4.63 (m, 2H, @N–CH –), 5.71 (br s, 1H, H ), 3.97
(br s, 1H, H ) and 3.03 (br s, 1H, H ). For 5a [22,23]:
ꢀ
3
b
1
0
mol) of the corresponding amine {H N–(CH ) –
2
2 n
2
a
a
(
C H S) (n = 1 or 2)} was added. The flask was introduced
4
3
s
a
II
in an ethyleneglycol bath and it was connected to a
Dean-Stark apparatus and to a condenser. The reaction
mixture was refluxed until ca. 10 mL had condensed on
the Dean-Stark apparatus. The hot reaction mixture was
filtered out and the deep-red filtrate was concentrated to
dryness on a rotary evaporator. The solids formed were
collected and dried. [Yield: 1.17 g (80%) and 1.08 g (72%)
for 2a and 2b, respectively]. Characterization data for 2a:
Anal. Calc. for C H NFeS: C, 62.15; H, 4.89; N, 4.53;
8.38 (s, 1H, –CH@N–), 4.28 (s, 5H, C H ), 4.73 and 4.48
b
5
5
(br s, 2H, @N–CH –), 5.84 (br s, 1H, H ), 3.83 (br s, 1H,
2
a
s
a
a
c
a
H ) and 2.80 (br s, 1H, H ). The resonances of the H
protons (for 5a and 5a ) were overlapped by the signals
I
II
due to the @N–CH – and C H – protons of the two
2
5
4
species. At 193 K: 5a –5a
coexisted in a ratio
I
VII
10.0:8.5:7.7:4.9:3.9:3.4 and 1.2. Due to the low abundance
of 5a –5a only the assignment of the signals due to 5aI–
IV
VII
5aIII was possible. For 5a [22,23]: 7.83 (s, 1H, –CH@N–),
1
6
15
I
2
5
3
S, 10.37. Found: C, 62.1; H, 5.0; N, 4.6; S, 11.3%. MS
4.31 (s, 5H, C H ), 4.51 (s, 2H, H and H ), 4.35 (s, 2H, H
5 5
+
+
ꢀ1
4
(
@
4
4
7
FAB ): m/z = 309, [M] . IR-data: 1629 cm
{m(˜C
and H ), 5.21 and 4.53 (m, 2H, @N–CH –), 7.23 (br s, 1H,
0 0 0
3 4 3 5
2
1
N–)}. H NMR data [21]: d = 8.21 (s, 1H, –CH@N–),
.20 (s, 5H, C H ), 4.46 (t, 2H, J = 1.5, H and H ),
.77 (t, 2H, J = 1.5, H and H ), 4.83 (s, 2H, @N–CH –),
.02 (br s, 2H, H and H ) and 7.26 (d, 1H, J = 4.0,
H ), 6.94 (br s, 1H, H ), 6.52 (d, 1H, J = 7, H ), 3.41(d,
3
3
4
3
c
3
b
1H, J = 11.5, H ), 5.67 (m, 1H, J = 11.5 and 6.5, H ),
a
5
5
3
2
5
3
a
s
3
3.79 (d, 1H, J = 6.5, H ) and 2.76 (d, 1H, J = 11.5,
2
0
0
3
4
3
a
a
H ). For 5a [22–24]: 7.77 (s, 1H, –CH@N–), 4.18 (s, 5H,
II

5024
D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
C H ), 4.71 and 4.35 (m, 2H, @N–CH –), 4.13 (d, 1H,
3.3.2. Stoichiometric reaction
5
5
2
3
c
3
b
J = 12.0, H ), 5.86 (m, 1H, J = 12.0 and 6.5, H ), 3.81
The stoichiometric alkylation of 5 was performed
under nitrogen atmosphere at 298 K by adding an excess
of sodium diethyl 2-methylmalonate (0.7 mL of a 0.5 M
solution in THF) to a solution containing 70 mg,
a
3
a
3
a
(
d, 1H, J = 6.5, H ) and 2.93 (d, 1H, J = 12.0, H ). For
s a
5
5
aIII [22–24]: 8.39 (s, 1H, –CH@N–), 4.25 (s, 5H, C H ),
5
5
3
.05 and 4.61(m, 2H, @N–CH –), 4.38 (d, 1H, J = 12.0,
2
c
a
3
b
ꢀ4
ꢀ4
H ), 5.16(m, 1H, J = 12.0 and 6.0, H ), 2.84 (d, 1H,
(1.03 · 10 mol) of 5a (or 1.01 · 10 mol of 5b). The
3
a
3
a
13
J = 6.0, H ) and 2.56 (d, 1H, J = 12.0, H ). C NMR
reaction was instantaneous and H O was added after
s
a
2
data [25] in CD Cl at 193 K, for 5a [22,23]: 164.6
10 min. The reaction mixture was filtered over Celite.
2
2
I
5
2
3
(
–CH@N–), 70.3 (C H ), 72.5 (C and C ), 72.6 (C and
The filtrate was then treated with Et O (ꢁ15 mL) and
5
5
2
4
c
b
a
C ), 60.2 (@N–CH –), 72.9 (C ), 107.4 (C ), 56.0 (C ),
the organic layer was washed three times with water.
The organic layer was then dried over Na SO and the
2
0
0
0
5
3
4
1
29.7 (C ), 127.5 (C ) and 127.0 (C ). For 5a [22,23]:
II
2
4
1
64.7(–CH@N–), 70.0 (C H ), 58.4 (@N–CH –), 79.4
filtrate was concentrated to dryness on a rotary evapora-
tor. The residue was dissolved in the minimum amount
5
5
a
2
c
b
(
C ), 107.1 (C ) and 55.3 (C ). For 5b [22,23]: 166.7
III
c
(
–CH@N–), 70.2 (C H ), 61.4 (@N–CH –), 76.5 (C ),
of Et O and passed through a short SiO2 column
5
5
2
2
b
a
1
07.1 (C ) and 56.8 (C ). For 5b: Anal. Calc. for
(4.0 cm · 0.6 cm). The band released was collected and
C H F FeNPPdS: C, 45.14; H, 3.79; N, 2.02; S, 4.63.
Found: C, 45.2; H, 3.6; N, 2.1; S, 4.8%. MS (FAB ):
m/z = 546 {M-[PF ]} . IR-data: 1629 {m(˜C@N–)} and
8
concentrated to dryness. The oily residue contained
2
6
26 6
+
1
{according to H NMR (500 MHz) and GC} 3 and 4
+
in a molar ratios 3:4 = 94.1:5.9 (for 5a) and 93.0:7.0
(for 5b).
6
1
ꢀ
1
ꢀ
40 cm {[PF ] }. H NMR data in CD Cl at 193 K:
6 2 2
six isomeric forms (5b –5b ) coexisted in solution in molar
I
VI
ratios 10.0:5.5: 3.9:2.1:1.6:1.4. Due to the low abundance
3.4. Crystallography
of 5b –5b only the assignment of the signals due to 5bI
III
VI
and 5b was possible. For 5b [22]: 7.78 (s, 1H, –CH@N–),
A prismatic crystal of 2a (0.1 mm · 0.1 mm · 0.2 mm)
was selected and mounted on a MAR345 diffractometer
with a image plate detector. Unit-cell parameters were
determined from 250 reflections in the range 3ꢁ < H < 31ꢁ
and refined by least-squares method. Intensities were
collected with a graphite monochromatized Mo Ka radia-
tion. The number of reflections measured in the range
3.52ꢁ 6 H 6 29.32ꢁ was 4901 of which 2622 were non-
II
I
2
5
4
.14 (s, 5H, C H ), 4.61 (s, 2H, H and H ), 4.52 (s, 2H,
5 5
3
4
H and H ), 3.96 and 3.00 (m, 2H, @N–CH –), 3.26 (m,
2
H ), 6.84 (br s, 1H, H ), 4.31 (d, 1H, J = 12.0, H ),
2
0
3
3
H, –CH –), 7.54 (br s, 1H, H ), 6.91 (t, 1H, J = 8.0,
2
0 0
4
5
3
c
a
3
b
6
.02 (m, 1H, J = 12.0 and 6.5, H ), 3.90 (d, 1H,
3
a
3
a
J = 6.5, H ) and 3.04 (d, 1H, J = 12.0, H ). For 5b
II
s
a
[
(
1
22,23]: 7.50 (s, 1H, –CH@N–), 4.03 (s, 5H, C H ), 4.74
s, 1H, H ), 4.37 (s, 1H, H ), 4.49 (s, 1H, H ), 4.57 (s,
5
5
2 3 4
equivalent by symmetry {R (on I) = 0.022} and 2542
int
5
H, H ), 3.75 (br s, 2H, @N–CH –), 3.21 and 2.48 (m,
reflections were assumed as observed applying the condi-
tion I > 2r(I). Lorentz-polarization corrections were made
but absorption corrections were not. The structure was
solved by Direct methods using SHELXS computer program
[26] and refined by full-matrix least-squares method with
the SHELX97 computer program [27] using 4910 reflections.
2
3
c
2
H, –CH –), 4.26 (d, 1H, J = 11.5, H ), 5.77 (m, 1H,
2 a
J = 11.5 and 7.0, H ), 3.84 (d, 1H, J = 7.0, H ) and
.90 (d, 1H, J = 11.5, H ). The resonances due to the
a
0 0 0
3
b
3
a
s
3
a
2
3
4
5
protons H , H and H were partially masked by those
due to the aromatic protons of the phenyl ring.
NMR data [25] in CD Cl at 193 K, for 5b [22,23]: 171.8
1
3
C
2
2 2
The function minimized was RwjjF j ꢀ jF j j , where
2
2
I
o
c
2
5
3
2
2
ꢀ1
2
(
–CH@N–), 75.2 (C H ), 77.8 (C and C ), 77.7 (C and
w = [r (I) + (0.0710P) + 0.3514P]
and P = (jF j +
5
5
o
0
4
3
2
0
00
C ), 65.6 (@N–CH –), 36.4 (–CH –), 133.1 (C ), 132.7
(
For 5b [22,23]: 171.7 (–CH@N–), 75.1 (C H ), 77.8 (C ),
7
2jF j )/3; f, f and f were obtained from the literature
2
2
c
0
0
4
5
c
b
a
C ), 132.4 (C ), 83.2 (C ), 111.9 (C ) and 61.8 (C ).
[28]. All hydrogen atoms were computed and refined using
a riding model with an isotropic temperature factor equal
to 1.2 times the equivalent temperature factor of the atoms
linked to it.
2
II
3
5
5
4
5
7.3 (C ), 77.9 (C ), 78.1 (C ), 70.5 (@N–CH –), 35.3
c b a
2
(
–CH –), 84.3 (C ), 111.8 (C ) and 61.5 (C ).
2
3
3
.3. Allylic alkylation reactions
Appendix A. Supplementary material
.3.1. Catalytic reactions
These reactions were performed under nitrogen at 298 K
CCDC 648588 contains the supplementary crystallo-
graphic data for 2a. These data can be obtained free of
ꢀ
3
3
in THF (5 mL), using 2.5 · 10 mmol of [Pd(g -C H )-
3
5
ꢀ
3
(
l-Cl)] , 5.0 · 10 mmol of 2a or 2b, 0.5 mmol of
charge
via
http://www.ccdc.cam.ac.uk/conts/retriev-
2
cinnamyl acetate and 1.0 mmol of sodium diethyl 2-methyl-
malonate. The reaction was monitored by taking samples
from the reaction mixture. Each aliquot was diluted with
Et O, washed with water, and dried over Na SO . Aliquots
then were analyzed by GC using decane (0.258 mmol) as
the internal standard.
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2007.07.027.
2
2
4

D. Pou et al. / Journal of Organometallic Chemistry 692 (2007) 5017–5025
5025
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(
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(
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[
5
(
(
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[
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