Enantiomerically Pure P,N Chelates Based on Phospholene Rings: Palladium Complexes and Catalytic Applications in Allylic Substitution

Article abstract of DOI:10.1002/ejic.200900892

The synthesis of optically pure 2-pyridylphospholene ligands by diastereomeric resolution of Pd^II complexes, bearing the corresponding racemic P,N ligand and (R)-α-methylbenzylamine, by means of fractional, crystallisation is described. A full coordination study of palladium complexes containing 2pyridylphospholene and the corresponding phosphole ligands, both in solution (by means of NMR spectroscopy) and in the solid state (by X-ray diffraction), was carried out. These ligands were evaluated, in Pd-catalysed allylic substitution of racemic substrates (rac-3-acetoxy-l,3- diphenyl-l-propene and rac-3-acetoxy-l-cyclohexene) and (E)-3-acet-oxy-1-phenyl- 1-propene. A modelling study of the palladium allylic intermediates was performed, in order to justify the asymmetric induction observed with the 2-pyridylphospholene ligands.

Full text of DOI:10.1002/ejic.200900892

FULL PAPER
DOI: 10.1002/ejic.200900892
Enantiomerically Pure P,N Chelates Based on Phospholene Rings: Palladium
Complexes and Catalytic Applications in Allylic Substitution
François Leca,[a] Fernando Fernández,[b] Guillermo Muller,[b] Christophe Lescop,[a]
Régis Réau,*[a] and Montserrat Gómez*[b,c]
Keywords: Palladium / Asymmetric catalysis / Chiral resolution / P ligands / Allylic substitutions
The synthesis of optically pure 2-pyridylphospholene ligands
by diastereomeric resolution of PdII complexes, bearing the
corresponding racemic P,N ligand and (R)-α-methylbenzyl-
amine, by means of fractional crystallisation is described. A
full coordination study of palladium complexes containing 2-
pyridylphospholene and the corresponding phosphole li-
gands, both in solution (by means of NMR spectroscopy) and
in the solid state (by X-ray diffraction), was carried out.
These ligands were evaluated in Pd-catalysed allylic substi-
tution of racemic substrates (rac-3-acetoxy-1,3-diphenyl-1-
propene and rac-3-acetoxy-1-cyclohexene) and (E)-3-acet-
oxy-1-phenyl-1-propene. A modelling study of the palladium
allylic intermediates was performed in order to justify the
asymmetric induction observed with the 2-pyridylphos-
pholene ligands.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
gands that contain an additional group, e.g. pyridine, oxaz-
oline or phosphane derivatives, other than the phosphole-
coordinating moiety.[6] However, 2-phospholenes (Figure 1),
an intermediate between phospholanes and phospholes,
have been rarely applied in catalysis probably because of
their minor synthetic development relative to the other two
related P heterocycles.[6b,7]
Introduction
The design of an asymmetric environment around a met-
allic centre in order to accommodate the partners of an
organic transformation allows enantioselectivity induction
in asymmetric catalytic processes.[1,2] A classical approach
to get this goal is the use of enantiomerically pure ligands
containing donor atoms with a defined symmetry, which
combines steric hindrance and electronic effects.[3] The ri-
gidity of the backbone is one of the key aspects to consider
in the structure of chiral ligands. In particular, the coordi-
nating heteroatom placed on a cyclic fragment (like pyr-
idine, thiophene or phosphole derivatives) can play a crucial
role in the asymmetric induction, from both an electronic
and a steric point of view. With regard to P-donor ligands,
the significant contribution of Burk and co-workers in the
early nineties,[4] which describes phospholane ligands (satu-
rated phosphorus-containingcations in several metal-cata-
lysed processes.[5] Phospholes, the related unsaturated het-
erocycles, which exhibits different steric and electronic
properties to those shown by phospholanes, have also been
extensively applied in catalysis, often as hetero-donor li-
Figure 1. Skeletons of the phosphorus-containing five-membered
heterocycles.
With respect to asymmetric catalytic applications of de-
signed chiral ligands, enantioselective palladium-catalysed
substitution of allylic substrates, a powerful synthetic tool
for the enantioselective construction of carbon–carbon or
carbon–heteroatom bonds, has proven to be a useful testing
ground for the evaluation of new optically pure ligands.[8]
For P-heterocycle-containing ligands, phospholes have led
to moderate[9]-to-high (up to 90% ee for the alkylation of
[a] UMR 6226 “Sciences Chimiques de Rennes, Université Rennes 1,3-diphenylprop-2-enylacetate[10]) enantiomeric excesses in
I, Campus de Beaulieu,
Pd-catalysed allylic substitution reactions, in contrast to the
263 Av. du Général Leclerc, 35042 Rennes Cedex, France
excellent enantioselectivities induced by phospholane li-
gands.[11] To the best of our knowledge, there has only been
one report on 2-phospholene ligands in asymmetric allylic
substitution reactions; the results show a 95-% enantio-
meric excess for the allylic amination of cyclopentenyl car-
bonate.[7c] Note that no P,N-chelate-bearing optically pure
2-phospholene moieties are known to date.
Fax: +33-2-23236939
E-mail: regis.reau@univ-rennes1.fr
[b] Departament de Química Inorgànica, Universitat de Barcelona,
Martí i Franquès, 1-11, 08028 Barcelona, Spain
[c] Laboratoire Hétérochimie Fondamentale et Appliquée, UMR
CNRS 5069, Université Paul Sabatier,
118, route de Narbonne, 31120 Toulouse Cedex 9, France
Fax: +33-5-61558204
E-mail: gomez@chimie.ups-tlse.fr
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Scheme 1. Palladium-driven stereoselective synthesis of 2-pyridylphospholenes 4 from 2-pyridylphospholes 1.
On the basis of these precedent research studies, we de-
The first approach designed to obtain enantiomerically
cided to isolate optically pure pyridylphospholene ligands, pure derivatives 4a–4cЈ consisted of the protonation of the
following the previous methodology described by some of basic pyridyl moiety by chiral acids. rac-2-Pyridylphos-
us (Scheme 1),[7b] by means of the resolution of a di- pholene (4c) was selected for this study. Its reaction with
asteromeric mixture of PdII complexes. Application in Pd- one equivalent of a chiral organic acid [(S)-mandelic acid,
catalysed allylic alkylation and amination has been carried (S)-malic acid or (S,S)-dibenzoyl tartaric acid] afforded two
out with the aim to evaluate the catalytic activity, enantio- diastereomeric pyridilium salts [δ(31P) NMR: +26.7 and
selectivity and regioselectivity. Modelling studies of palla- +26.5 ppm]. However, these 2-pyridiliumphospholenes are
dium allyl intermediates have been performed in order to extremely air sensitive, which hinders the separation of the
justify the asymmetric inductions obtained.
diastereomers upon fractional crystallisation. Therefore, an
efficient strategy should prevent oxidation of the rather
electron-rich P centre of derivatives 4.
With this in mind, a second approach was investigated
based on the resolution of PdII complexes 3 (Scheme 1),
which are stable in air (the P atom is somehow protected
from oxidation by coordination onto the metal centre). Our
strategy involved the introduction of a novel enantiomer-
ically pure ligand [(R)-α-methylbenzylamine] onto the metal
centre in order to form diastereomers. Thus, complex 3a
[δ(31P) NMR: +67.3 ppm] reacted with (R)-α-methylben-
zylamine in the presence of silver hexafluorophosphate
(Scheme 2), which gives the new complex 5a as a mixture
of two diastereomers, 5a1 and 5a2 (89% yield). The 31P{1H}
NMR spectrum of the crude reaction mixture displays two
sharp singlet signals of equal intensity at +73.2 and
+72.5 ppm (Figure 2a). Further, the 1H and 13C NMR
spectra show two sets of signals corresponding to each dia-
stereomer. Although the NMR spectroscopic data could
not help to establish the relative position of the chlorine
and amine ligands with respect to the P and N atoms, this
could be determined by means of an X-ray diffraction study
on diastereoisomer 5a1 (vide infra). A similar behaviour was
observed for complex 3aЈ, which features a P-cyclohexyl
phospholene ligand (Scheme 2). The resulting complex 5aЈ
was isolated as a 1:1 mixture of diastereoisomers [δ(31P)
Results and Discussion
Synthesis of Ligands
We recently described a general and straightforward
route to the first P,N chelates that incorporate phospholene
moieties. This route involves the stereoselective isomeri-
sation of PdII-coordinated 2-pyridylphosphole ligands into
their corresponding 2-pyridyl-2-phospholene isomers in the
presence of pyridine (Scheme 1).[7b] This synthetic approach
is attractive given that (i) the isomerisation process is not
sensitive to the nature of the P substituent and (ii) it is a
highly stereoselective process that only affords isomers in
which the pyridyl and the P substituent are in a mutual
trans configuration (Scheme 1). The free 2-pyridylphos-
pholenes could readily be obtained as a pair of enantiomers
upon addition of 1 equiv. 1,2-(diphenylphosphanyl)ethane
(dppe) to complexes 3a–3cЈ (Scheme 1). Interestingly, no in-
version of the stereogenic P centre occurs below 90 °C,
which reveals that these derivatives are potentially attractive
P-chiral, P,N chelates for homogeneous catalysis. The next
step was thus to investigate the resolution of these readily
available racemic 2-pyridyl-2-phospholene derivatives 4a–
4cЈ.
Scheme 2. Ligand-exchange reactions with 2-pyridylphospholene palladium complexes.
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Palladium Complexes of P,N Chelates Based on Phospholene Rings
1
NMR: +89.2 and +90.2 ppm] in an 85% yield; H and 13C
NMR spectroscopic data confirm the proposed structure.
Quite surprisingly, this ligand-exchange reaction failed for
complexes 3b–3cЈ, which carry either dangling R1 phenyl or
2-thienyl substituents (Scheme 1). It is worth noting that
the overall transformation 1a Ǟ 5a could be performed in
a “one-pot” approach by using (R)-α-methylbenzylamine
both as a base to promote the phosphole–phospholene iso-
merisation (2a Ǟ 3a, Scheme 1) and as a ligand to form 5a
as a mixture of two diastereomers (Scheme 2).
Figure 3. Molecular structure of the monocationic diastereoisomer
5a1. Hydrogen atoms on the phospholene ligand, with the excep-
tion of H(1) and H(3), have been omitted for clarity.
The bond lengths and angles of 5a1 are comparable to
those of related PdII 2-pyridylphospholene complexes.[7]
Note that the two Pd–N bond lengths are essentially equiv-
alent despite the different nature (sp2/sp3) of the N donors
[2.081(3) Å (pyridine) and 2.047(3) Å (benzylamine),
Table 1]. In addition, both the P- and C-stereogenic centres
in ligand 4a1 present an S configuration. The most remark-
able structural feature of this complex, in contrast to what
Figure 2. 31P{1H} NMR spectrum (+70 to +74 ppm window) of
(a) the crude reaction mixture (5a diastereomers), (b) mother solu-
tion and (c) crystals following a single recrystallisation.
Diastereomers of 5a were successfully separated by is expected according to the “trans influence”, is the trans
recrystallisation from a CH2Cl2 solution exposed to pen- arrangement of the two rather “hard” N-donor ligands
tane vapour at room temperature for a week. After a single (Figure 3). The nitrogen atom of the dangling pyridyl group
crystallisation, the mother solution was highly enriched points towards one H atom of the amine ligand (N–H···N
with the diastereoisomer 5a2 (Figure 2b), while the crystals angle, 167.33°), and the short distance between these two
contained pure diastereoisomer 5a1 (Figure 2c). A single- centres (2.059 Å) reveals their interaction. This H-bond
crystal X-ray diffraction study confirms the proposed struc- may be responsible both for (i) the unusual trans arrange-
ture of the optically pure complex 5a1. This compound ment of the two N donors in the square-planar coordina-
crystallises in the noncentrosymmetric space group P21 of tion sphere of the PdII centre and (ii) the fact that the li-
the monoclinic system. As expected, it is a monocationic gand-exchange reaction depicted in Scheme 2 is only suc-
complex in which the PdII metal centre is bound to the P,N cessful with complexes bearing a dangling pyridyl group
chelating ligand 4a1, a chlorido ligand and (R)-α-methyl- since this H-bond helps in stabilising complexes 5a and 5aЈ
benzylamine coordinated by its terminal NH2 group in a (Scheme 2). The free optically pure ligand (SC,SP)-4a1 was
slightly distorted square-planar arrangement (Figure 3).
quantitatively released by addition of 1 equiv. 1,2-(diphenyl-
Table 1. Selected bond lengths and angles for PdII complexes 3a·1.5CH2Cl2,[7b] 5a1, Pd1b and Pd4b.
3a·1.5CH2Cl2
5a1
Pd1b
Pd4b
Pd(1)–P(1)
Pd(1)–N(1)
Pd(1)–N(3)
Pd(1)–Cl(1)
2.2123(10)
2.082(3)
–
2.3665(11)
2.2950(11)
84.64(9)
–
90.48(4)
93.86(9)
–
94.20(17)
–
2.2237(10)
2.081(3)
2.047(3)
2.3493(11)
–
83.00(10)
93.88(10)
–
93.91(10)
89.21(10)
94.1(2)
–
2.293(4)
2.138(10)
–
–
2.2688(12)
2.133(3)
–
–
Pd(1)–Cl(2)
–
–
P(1)–Pd(1)–N(1)
P(1)–Pd(1)–N(3)
P(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(3)
C(1)–P(1)–C(8)
C(100)–Pd(1)–C(102)
82.7(5)
–
–
–
83.97(9)
–
–
–
–
–
91.9(7)
66.9(17)
92.94(16)
67.47(18)
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FULL PAPER
phosphanyl)ethane (dppe) to 5a1 (Scheme 2). Indeed, that two stereoisomers are present in solution (and each of
(SC,SP)-4a1 is the first P,N-chelate-bearing an enantiopure
them is a couple of enantiomers as a result of the chirality
2-phospholene ring. This synthetic approach to P-chiral
mixed phospholene–pyridine chelates failed for the corre-
sponding P-cyclohexyl series.
of the phosphorus atom), and the phenyl ring occupies a
syn position with respect to the central H atom. Single crys-
tals of Pd1b were successfully grown from a CH2Cl2 solu-
tion of the complex exposed to pentane vapours. This com-
pound crystallises in the space group Pna2(1) of the ortho-
rhombic system, and the asymmetric unit contains one
monocationic complex Pd1b and one hexafluorophosphate
counteranion (Figure 4a). The PdII centre possesses a
slightly distorted square-planar geometry around it [P(1)–
Pd(1)–N(1) 82.7° and C(100)–Pd(1)–C(102) 66.9(17),
Table 1], and the maximum deviation from the plane de-
fined by Pd, the N and P donors of the chelating 2-pyridyl-
phosphole ligand and the two terminal allylic C atoms is
0.185 Å. The bond lengths and angles of the coordinated
pyridyl–phosphole ligand are similar to those observed in
PdCl2 complexes.[7b] The bond lengths and angles of the
(η3-C3H5)Pd core are also consistent with known literature
values.[13] A significant difference can be observed in the
distances between Pd and the two terminal allylic carbon
atoms [Pd–C(100) 2.0076(16) Å; Pd–C(102) 2.29(3) Å,
Table 1] owing to the different trans effect of the N- and P-
donor atoms. Finally, it is also noteworthy that (i) the
phenyl substituent of the allylic ligand has a relative cis po-
sition with respect to the less hindered N atom and that (ii)
the phenyl ring occupies a syn position with respect to the
central allylic H atom, as observed in solution (Figure 4a).
Complex Pd4b bearing the phospholene ligand synthe-
sised from 1b, exhibits a singlet at +61.8 ppm in its room
Palladium Allylic Complexes
Pd-catalysed allylic substitution reactions were selected
in order to evaluate the ability of the chiral pyridyl–phos-
pholene and nonchiral pyridyl–phosphole ligands to induce
regio- and enantioselectivity. Cationic (allyl)palladium com-
plexes bearing these new P,N chelates, which are intermedi-
ates in the allylic substitution process, were thus prepared.
Complexes Pd1b and Pd4b were synthesised from the
corresponding dimeric bridged palladium chloride complex
in the presence of a slight excess of the appropriate P,N
ligand, the pyridyl–phosphole 1b and the racemic pyridyl–
phospholene 4b (Scheme 3), by following the methodology
previously described.[12]
Scheme 3. Synthesis of palladium allylic complexes Pd1b and Pd4b.
The room temperature 31P{1H} NMR spectrum of com- temperature 31P{1H} NMR spectrum. This chemical shift
plex Pd1b displays a singlet at +53.5 ppm, and the 1H is shifted lowfield [∆(δ) = +8.3 ppm] relative to that of
NMR spectrum shows broad signals for the allylic ligand. Pd1b, which follows the trend on going from phospholene–
At 253 K, two signals at +53.6 ppm and +53.4 ppm appear to phosphole–pyridine PdII complexes.[7] The structure of
1
in the 31P{1H} NMR spectrum, and the H NMR signals Pd4b in the solid state was established by an X-ray diffrac-
became less broad. Two sets of signals corresponding to tion study (Table 1). Single crystals were obtained from dif-
the allylic ligand are observed [CH2: +3.52 and +3.90 ppm fusion of pentane vapour in a CH2Cl2 solution of Pd4b.
(Hanti); +4.80 and +4.69 (Hsyn); PhCHCH: +7.09 and This derivative crystallises in the C2/c space group of the
+6.71; PhCH: +5.94 and +6.14]. These data clearly show monoclinic system with one monocationic palladium com-
Figure 4. View of the molecular structures of complexes: (a) Pd1b and (b) Pd4b. Hydrogen atoms [with the exception of the allylic, H(1)
and H(3) hydrogen atoms of 4b] and the hexafluorophosphate anion have been omitted for clarity.
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Palladium Complexes of P,N Chelates Based on Phospholene Rings
plex and one hexafluorophosphate counteranion in the
asymmetric unit. This (2-pyridylphospholene) PdII complex
(Figure 4b) shows a structure that is very similar to that of
its phosphole-based analogue Pd1b (Figure 4a). Therefore,
the palladium coordination sphere of Pd4b displays a dis-
torted square-planar geometry, and the phenyl substituent
of the allylic ligand has a cis configuration with respect to
the N atom (Figure 4b). The Pd–N and Pd–P bond lengths,
as well as the Pd–C distances involving the allylic ligand of
the phospholene-containing complex Pd4b, are essentially
comparable with those of its phosphole-based analogue
Pd1b (Table 1).
Scheme 5. Allylic alkylation of rac-11 and rac-12 catalysed by the
Pd/(SC,SP)-4a1 system.
remains low compared to those obtained with other P,N
bidentate ligands, such as oxazolinylphosphane ligands (l/b
= 1:4).[15]
Pd-Catalysed Allylic Substitution
Regioselective Allylic Substitution
Table 2. Pd-catalysed allylic substitution of 6 and 7 by using 2-
pyridylphospholes and 2-pyridylphospholenes ligands.[a]
As stated above, the allylic substitution reaction was se-
lected to test the catalytic ability of palladium complexes
bearing the newly synthesised P,N ligands. In particular, an
interesting aspect of studying Pd-catalysed allylic substitu-
tions is the regioselectivity (branched/linear ratio) for un-
symmetrical substrates such as 3-acetoxy-1-phenyl-1-pro-
pene 6 and 3-acetoxy-1-methyl-1-propene 7 (Scheme 4).
These alkylations were carried out using bis(trimethysilyl)
acetamide (BSA) and a catalytic amount of potassium ace-
tate as base[14] (Scheme 5). When optically pure ligands are
involved, the branched isomer is desired since it contains a
stereogenic C atom. This reaction was investigated by using
two types of nucleophiles, namely dimethyl malonate
(DMM) and benzylamine (BnNH2). Furthermore, 2-pyr-
idylphospholes and 2-pyridylphospholenes were used as li-
gands in order to compare the two families of related P,N
chelates. The catalytic precursors were generated in situ
from [PdCl(C3H5)]2 and the appropriate ligand (Pd/L =
1:1.25).
Entry
L
Sub-
strate
NuH[b] Time
[h]
Conversion
[%][c]
l/b[d]
1
2
3
4
5
6
7
8
1a
6
6
6
6
6
6
6
DMM
DMM
DMM
DMM
DMM
DMM
DMM
DMM
BnNH2
BnNH2
BnNH2
DMM
DMM
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
7
7
7
0.25
0.25
90
100
91
100
99
63
99
34
45
99
46:1
7:1
1aЈ
1b
100:0[e]
100:0[e]
23:1
4:1
1bЈ
1c
rac-4a
rac-4b
4:1
3:1
rac-4bЈ 6
1aЈ
1b
rac-4b
1b
rac-4b
9
6
6
6
7
7
20:1
20:1
9:1
10
11
12
13
96
95
100
1.4:1[f]
2.2:1[g]
[a] Results from duplicated experiments; Pd/L/substrate
=
1:1.25:50; see Scheme 4. [b] NuH = dimethylmalonate (DMM) with
BSA and a catalytic amount of KOAc as a base; NuH = benzyla-
mine (BnNH2). [c] Conversions based on the substrate 6 or 7 deter-
mined by GC. [d] Linear/branched ratio (l/b) determined by GC.
[e] Branched isomer not detected by GC. [f] ltrans/lcis = 7:1. [g] ltrans
lcis = 9:1.
/
With the phosphole-based ligands, high conversions were
obtained for substrate 6 after a reaction time of 15 min (En-
tries 1–5, Table 2). The linear/branched ratio depends on
In the allylic amination with benzylamine as a nucleo-
the substitution pattern of the phosphole, and the highest phile, high conversions were reached after 7 h (Entries 9–
selectivity in the branched derivative (l/b = 7:1) was reached 11, Table 2). However, the major product was the linear re-
with the (2-pyridyl)-capped P-cyclohexyl ligand 1aЈ (Entry gioisomer l-10 (l/bՆ9). The highest selectivity in the
2, Table 2). In contrast, with phospholene-based P,N li- branched product b-9 was observed for the allylic alkylation
gands, complete conversion was only achieved with 2-(2- of 3-acetoxy-1-methyl-1-propene 7 with both kinds of li-
pyridyl)-5-phenylphospholene 4b (Entries 6–8, Table 2). gands – the phosphole derivative gave the best results (l/b
Interestingly, the selectivity towards the branched re- = 1.4:1, Entry 12, Table 2). In both cases, high activity was
gioisomer b-8 (l/b = 4:1) increases markedly relative to that observed with complete conversion within 15 min (Entries
observed with the phosphole analogues. However, this ratio 12 and 13, Table 2).
Scheme 4. Allylic substitution of 6 and 7 catalysed by Pd/L systems (L = 2-pyridylphosphole and 2-pyridylphospholene ligands).
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Figure 5. Modelled structures [PM3(tm)] for cationic allyl palladium complexes containing the 2-pyridylphospholene ligand 4a1: (top)
1,3-diphenylallyl isomers (Pd4a1-Ph); (bottom) cyclohexenylallyl isomers (Pd4a1-Cy). In parenthesis, relative energies calculated by DFT
(in kcal/mol) are given. Hydrogen atoms are omitted for clarity.
Enantioselective Allylic Alkylation
mer is more stable than the endo isomer (Figure 5). The fact
that the energy difference between the two cyclohexenylallyl
isomers (2.3 kcal/mol) is higher than that for the corre-
sponding 1,3-diphenylallyl isomers (0.33 kcal/mol) agrees
with the higher enantiomeric excess obtained when 3-acet-
oxy-1-cyclohexene is used as the substrate. In addition, the
absolute configuration observed for the major alkylated
products, (R)-13 and (S)-14 is in agreement with the ex-
pected nucleophilic attack at the more electrophilic terminal
allylic carbon atom placed in a position trans to the phos-
phorus atom (see calculated Pd–Cterm-allyl bond lengths in
Figure 5).
Having one of our target enantiomerically pure 2-pyr-
idylphospholene ligands in hand, we also investigated its
use in Pd-catalysed asymmetric allylic alkylation. These al-
kylations were carried out with racemic 3-acetoxy-1,3-di-
phenyl-1-propene (rac-11) and 3-acetoxy-1-cyclohexene
(rac-12) as substrates under the same basic conditions as
those used for substrates 6 and 7 (Scheme 5). Catalytic pre-
cursors were generated in situ from [PdCl(C3H5)]2 and the
optically pure (SC,SP)-4a1 ligand (Pd/L = 1:1.25). For both
substrates, the catalytic system was found to be very active
at room temperature, which gave rise to an almost complete
conversion within 15 min for rac-11 and 3 h for rac-12.
However, the enantiomeric excesses remain very low for this
type of catalytic reaction. Note that the highest asymmetric
induction (ee = 31%) was achieved with the less-hindered
cyclic cyclohexenyl substrate.
Conclusions
We could obtain the optically pure 2-pyridylphospholene
(SC,SP)-4a1 by resolution of a diastereomeric mixture of
In order to justify the different selectivities between both PdII complexes, {PdCl(κ2-P, N -4a)[κ1-N-(R)-methylbenzyl-
racemic substrates rac-11 and rac-12, we calculated the amine]}PF6 (5a), by means of fractional crystallisation fol-
equilibrium geometry and the corresponding energies for lowed by reaction with 1,2-(diphenylphosphanyl)ethane,
the Pd4a1 cationic intermediates containing 1,3-diphenylal- which prevents the oxidation of the ligand. Unfortunately,
lyl (Pd4a1-Ph) or cyclohexenylallyl (Pd4a1-Cy) groups. In an analogous protocol applied to 5aЈ, which features the
both cases, two isomers are possible because of the relative corresponding P-cyclohexylphosphole ligand, did not work.
position of the central allylic carbon atom and the phenyl P,N-2-Pyridylphosphole and P,N-2-pyridylphospholene li-
group bonded to the phosphorus atom: the exo isomer, if gands were tested in Pd-catalysed allylic substitutions. The
both groups point in the same direction as observed in the nonchiral phospholes (1a, 1aЈ, 1b, 1bЈ and 1c) and racemic
solid state (Figure 4), and the endo isomer, if one group 2-phospholenes (rac-4b and rac-4bЈ) were used in the alky-
points away from the other group (Figure 5). Structures of lation and amination of 3-acetoxy-1-phenyl-1-propene (6)
these isomers were optimised at the semiempirical PM3(tm) and 3-acetoxy-1-methyl-1-propene (7), in order to evaluate
level, and their energies calculated by density functional their influence on regioselectivity. With rac-4b and rac-4bЈ
methods with 6-31G* polarisation basis sets and pseudopo- phospholenes, a trend to favour the branched-substituted
tentials. For both types of PdII allyl complexes, the exo iso- product was observed relative to the corresponding phos-
5588
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5583–5591

Palladium Complexes of P,N Chelates Based on Phospholene Rings
3
25.4 (s, C=CCH2), 25.6 (s, C=CCH2), 27.7 (d, JP-C = 10.5 Hz,
pholes using 3-acetoxy-1-phenyl-1-propene as substrate;
however, the linear isomer was in any case the major prod-
uct. With respect to the asymmetric induction, (SC,SP)-4a1
was employed in the allylic alkylation of racemic model
substrates 11 and 12, which gives up to 31% enantiomeric
excess for the less-sterically hindered substrate rac-3-ace-
toxy-1-cyclohexene (12). This trend could be rationalised by
a modelling study of the PdII allyl intermediates responsible
for the asymmetric induction.
3
C=CCH2), 27.9 (d, JP-C = 10.3 Hz, C=CCH2), 55.2 (s, CH3CH),
1
1
55.9 (s, CH3CH), 56.5 (d, JP-C = 38.5 Hz, P–CH), 56.6 (d, JP-C
=
38.4 Hz, P–CH), 123.4 (s, C5 Py), 123.6 (s, C5 Py), 124.9 (d, JP-C
= 7.4 Hz, C3 Py), 125.0 (s, C5 Py), 125.1 (d, 3JP-C = 7.1 Hz, C3 Py),
3
125.2 (s, C5 Py), 125.8 (d, JP-C = 13.7 Hz, C3 Py), 125.9 (d, JP-C
3
3
= 9.4 Hz, C3 Py), 126.4 (s, m-C PhCHNH2), 126.8 (s, m-C
1
1
PhCHNH2), 127.6 (d, JP-C = 57.8 Hz, ipso-C Ph), 128.6 (d, JP-
= 56.4 Hz, ipso-C Ph), 128.7 (s, p-C PhCHNH2), 128.8 (s, o-C
C
3
PhCHNH2), 128.9 (s, p-C PhCHNH2), 129.6 (d, JP-C = 11.5 Hz,
3
m-C Ph), 129.6 (s, o-C PhCHNH2), 129.8 (d, JP-C = 11.3 Hz, m-
C Ph), 132.5 (d, 2JP-C = 12.9 Hz, o-C Ph), 132.6 (d, 2JP-C = 13.0 Hz,
o-C Ph), 133.5 (d, 4JP-C = 3.1 Hz, p-C Ph), 133.6 (d, 4JP-C = 3.1 Hz,
p-C Ph), 135.7 (d, 3JP-C = 6.5 Hz, C=CH), 136.0 (d, 3JP-C = 6.6 Hz,
Experimental Section
2
2
C=CH), 136.4 (d, JP-C = 11.7 Hz, PC=Cβ), 136.7 (d, JP-C
=
General Remarks: All compounds were prepared under a purified
nitrogen atmosphere by using standard Schlenk and vacuum-line
techniques. The solvents were purified by standard procedures and
distilled under nitrogen.[16] [Pd(η3-1-phenylallyl)(µ-Cl)][17] and li-
gands 1a–1cЈ[7b] were prepared as described previously. NMR spec-
tra were recorded on Varian XL-500 (1H, standard SiMe4), Varian
Gemini (1H, 200 MHz; 13C, 50 MHz; standard SiMe4), Bruker
DRX 250 (13C, 62.9 MHz, standard SiMe4) and Varian Mercury
400 (1H, 400 MHz; 13C, 100 MHz, standard SiMe4) spectrometers,
with CDCl3 as solvent, unless stated otherwise. Chemical shifts are
reported downfield from those of the standards. IR spectra were
recorded on FTIR Nicolet 520 and Nicolet 5700 spectrometers.
Electron-spray mass chromatograms were obtained on a Mass ZQ
Micromass instrument. High-resolution mass chromatograms were
obtained on a Waters LCT Premier spectrometer operated in ESI
mode. The GC analyses were performed on a Hewlett–Packard
6890-Network GC system gas chromatograph [30 m HP5 (5%
phenyl)methylpolysiloxane column] with a FID detector. Enantio-
meric excess was determined by HPLC on a Hewlett-Packard 1050
Series chromatograph (Chiralcel-OD chiral column) with a UV de-
tector and by GC on a Hewlett–Packard 5890 Series II gas chroma-
tograph [25-m FS-cyclodex-β-I/P column: heptakis(2,3,6-tri-O-
methyl)-β-cyclodextrin/polysiloxan] with a FID detector. Elemental
analyses were carried out by the Serveis Cientifico-Tècnics de la
Universitat de Barcelona in an Eager 1108 microanalyzer. Model-
ling studies have been carried out by using the following software:
SPARTANЈ06 for Windows and Linux.[18]
11.3 Hz, PC=Cβ), 138.6 (s, C4 Py), 138.7 (s, C4 Py), 140.8 (s, C4
Py), 140.9 (s, C4 Py), 141.3 (s, ipso-C PhCHNH2), 142.0 (s, ipso-C
PhCHNH2), 148.8 (s, C6 Py), 149.0 (s, C6 Py), 150.9 (d, JP-C
=
2
9.4 Hz, C2 Py), 151.1 (d, JP-C = 9.1 Hz, C2 Py), 154.4 (s, C6 Py),
2
154.5 (s, C6 Py), 156.2 (d, JP-C = 12.9 Hz, PC=Cβ), 157.0 (d,
2
2JP-C = 12.9 Hz, PC=Cβ), 161.4 (d, JP-C = 6.8 Hz, C2 Py), 161.6
2
(d, JP-C = 6.0 Hz, C2 Py) ppm; the signal for PCα=C is not ob-
2
served. 31P{1H} NMR: δ = +72.5, +73.2 and –144.3 (sept, JP-F
=
1
709 Hz) ppm. C32H32ClF6N3P2Pd (776.41): calcd. C 81.72, H 6.04,
N 3.81; found C 81.65, H 6.08, N 3.75.
5a1: Crystallisation of complex 5a with dichloromethane/pentane
solution afforded enantiomerically pure complex 5a1 as orange
crystals. 1H NMR (200 MHz, CD2Cl2): δ = 1.52 (d, 3JH-H = 6.4 Hz,
3 H, CH3), 1.95–2.12 (m, 2 H, =CCH2CH2), 2.26–2.54 (m, 2 H,
=CCH2), 2.83–3.16 (m, 2 H, =CCH2), 4.65 (d, JP-H = 13.4 Hz, 1
H, P-CH), 4.88 (m, 2 H, CH3CH and NH2), 5.79 (br. s, 1 H, NH2),
6.18 (m, 1 H, C=CH), 7.03–7.24 (m, 5 H, Harom), 7.38–7.68 (m, 8
2
3
H, Harom), 7.82–8.21 (m, 4 H, Harom), 9.81 (d, JH-H = 5.5 Hz, 1
H, H6 Py) ppm. 13C{1H} NMR (75.467 MHz, CD2Cl2): δ = 21.3
3
(s, C=CCH2CH2), 21.7 (s, CH3), 25.4 (s, C=CCH2), 27.6 (d, JP-C
1
= 10.8 Hz, C=CCH2), 55.2 (s, CH3CH), 56.5 (d, JP-C = 38.1 Hz,
P-CH), 123.5 (s, C5 Py), 124.8 (d, JP-C = 7.5 Hz, C3 Py), 125.1 (s,
3
C5 Py), 125.8 (d, JP-C = 13.1 Hz, C3 Py), 126.8 (s, m-C
3
1
PhCHNH2), 127.6 (d, JP-C = 57.8 Hz, ipso-C Ph), 128.7 (s, p-C
3
PhCHNH2), 128.8 (s, o-C PhCHNH2), 129.6 (d, JP-C = 11.2 Hz,
2
4
m-C Ph), 132.5 (d, JP-C = 12.9 Hz, o-C Ph), 133.5 (d, JP-C
=
3
1
3.1 Hz, p-C Ph), 135.7 (d, JP-C = 6.6 Hz, C=CH), 135.8 (d, JP-C
5a: To a solution of [1-phenyl-2,5-(2-pyridyl)phosphol-2-ene]PdCl2
(3a, 0.45 g, 0.82 mmol) in dichloromethane (5 mL), was added (+)-
(R)-methylbenzylamine (1.5 equiv., 156 µL, 1.23 mmol). The mix-
ture was stirred for 1 h, and dichloromethane was removed. The
product was then washed with diethyl ether and dried under vac-
uum. Dichloromethane (5 mL) was added followed by AgPF6
(1 equiv., 0.206 g, 0.82 mmol). After 4 h of stirring, the solution
was filtered with Celite, and the solvent was removed to afford
complex 5a as an orange solid. Yield: 0.56 g (0.73 mmol, 89%). 1H
= 6.6 Hz, PCα=C), 136.4 (d, JP-C = 11.7 Hz, PC=Cβ), 138.5 (s, C4
2
Py), 140.9 (s, C4 Py), 141.2 (s, ipso-C PhCHNH2), 148.8 (s, C6 Py),
150.9 (d, JP-C = 9.6 Hz, C2 Py), 154.5 (s, C6 Py), 156.2 (d, JP-C
=
2
2
12.9 Hz, PC=Cβ), 161.4 (d, JP-C = 6.4 Hz, C2 Py) ppm. 31P{1H}
2
1
NMR: δ = +72.5, and –143.8 (sept, JP-F = 713 Hz) ppm.
5aЈ: By following the procedure described for compound 5a, reac-
tion of complex 3aЈ (0.47 g, 0.85 mmol) and (+)-(R)-methylbenz-
ylamine (156 µL, 1.23 mmol) afforded compound 5aЈ as an orange
solid. Yield: 0.56 g (0.72 mmol, 85%). 1H NMR (300 MHz,
NMR (300 MHz, CD2Cl2): δ = 1.42 (d, 3JH-H = 6.5 Hz, 3 H, CH3),
3
3
3
1.48 (d, JH-H
=
6.9 Hz,
3
H, CH3), 2.01–2.12 (m,
4
H,
CD2Cl2): δ = 1.58 (d, JH-H = 6.0 Hz, 3 H, CH3), 1.67 (d, JH-H =
=CCH2CH2), 2.26–2.58 (m, 4 H, =CCH2), 2.83–3.24 (m, 4 H,
6.1 Hz, 3 H, CH3), 1.64–1.78 (m, 4 H, CH2), 1.82–2.36 (m, 18 H,
=CCH2CH2 and CH2), 2.57–2.93 (m, 8 H, =CCH2 and CH2), 2.98–
3.27 (m, 4 H, =CCH2, CH), 4.15 (br. s, 2 H, P-CH), 4.75 (m, 4 H,
2
2
=CCH2), 4.62 (d, JP-H = 13.4 Hz, 1 H, P–CH), 4.75 (d, JP-H
=
12.6 Hz, 1 H, P–CH), 4.92 (m, 4 H, CH3CH and NH2), 5.85 (br.
s, 1 H, NH2), 6.13 (br. s, 1 H, NH2), 6.20 (m, 1 H, C=CH), 6.27 CH3CH and NH2), 6.05 (m, 4 H, C=CH, NH2), 7.14–7.53 (m, 20
3
3
(m, 1 H, C=CH), 7.14 (dd, JH-H = 6.3, JH-H = 6.8 Hz, 1 H, H5 H, Harom), 7.92 (dd, 3JH-H = 5.8, 3JH-H = 6.8 Hz, 1 H, H4 Py), 8.05
Py), 7.13–7.36 (m, 13 H, Harom), 7.41–7.79 (m, 18 H, Harom), 7.96 (dd, JH-H = 7.3, JH-H = 7.3 Hz, 1 H, H4 Py), 8.37 (d, JH-H
=
3
3
3
(dd, JH-H = 6.8, JH-H = 6.1 Hz, 1 H, H4 Py), 8.13 (dd, JH-H
=
4.5 Hz, 1 H, H6 Py), 8.53 (dd, JH-H = 4.5, JH-H = 6.5 Hz, 1 H,
3
3
3
3
3
6.3, JH-H = 6.5 Hz, 1 H, H4 Py), 8.25 (m, 2 H, H6 Py), 9.77 (d, H6 Py), 9.50 (d, JH-H = 5.7 Hz, 1 H, H6 Py), 9.58 (d, JH-H
=
3
3
3
3JH-H = 7.03 Hz, 1 H, H6 Py), 9.79 (d, 3JH-H = 6.8 Hz, 1 H, H6 Py) 5.9 Hz, 1 H, H6 Py) ppm. 13C{1H} NMR (50.322 MHz, CD2Cl2):
ppm. 13C{1H} NMR (75.467 MHz, CD2Cl2):
21.2 (s, δ = 21.5 (s, C=CCH2CH2), 23.1 (s, CH3), 23.4 (s, CH3), 23.7 (s,
C=CCH2CH2), 21.4 (s, C=CCH2CH2), 21.7 (s, CH3), 22.9 (s, CH3), CH2), 24.4 (s, CH2), 25.0 (s, C=CCH2), 25.3 (s, C=CCH2), 25.8 (d,
δ
=
Eur. J. Inorg. Chem. 2009, 5583–5591
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5589

F. Leca, F. Fernández, G. Muller, C. Lescop, R. Réau, M. Gómez
JP-C = 7.4 Hz, CH2), 26.2 (m, CH2), 26.5 (d, JP-C = 9.8 Hz, CH2), 2.85 (br. s, 1 H), 2.88 (br. s, 1 H), 3.23 (br. s, 1 H), 3.25 (br. s, 1
FULL PAPER
26.7 (d, JP-C = 10.2 Hz, CH2), 27.7 (s, CH2), 27.9 (s, C=CCH2),
H), 3.52 (br. s, 1 H), 4.80 (br. s, 1 H), 5.94 (br. s, 1 H), 7.09 (br. s,
1 H), 6.98–8.06 (aromatic protons, 19 H) ppm; Isomer b (47%): δ
= 1.83 (br. s, 2 H), 1.97 (br. s, 2 H), 2.73 (br. s, 2 H), 3.42 (br. s, 2
H), 3.90 (br. s, 1 H), 4.69 (br. s, 1 H), 6.14 (br. s, 1 H), 6.71 (br.
s, 1 H), 6.98–8.06 (aromatic protons, 19 H) ppm. 31P{1H} NMR
(101 MHz, [D6]acetone, 253 K): δ = –144.5 (hp, JP-F = 706.0 Hz),
1
1
28.5 (s, C=CCH2), 35.2 (d, JP-C = 20.1 Hz, CH), 35.6 (d, JP-C
=
=
1
23.5 Hz, CH), 54.8 (s, CH3CH), 55.0 (s, CH3CH), 54.8 (d, JP-C
1
59.1 Hz, P-CH), 55.8 (d, JP-C = 56.2 Hz, P-CH), 124.0 (s, C5 Py),
3
124.2 (s, C5 Py), 124.7 (br. d, JP-C = 7.3 Hz, C3 Py), 125.1 (s, C5
3
Py), 125.2 (s, C5 Py), 126.2 (br. d, JP-C = 12.2 Hz, C3 Py), 126.8
(s, m-C PhCHNH2), 127.4 (s, m-C PhCHNH2), 129.0 (s, p-C 53.4 (s), 53.5 (s) ppm. MALDI MS: m/z = 591.7 [M – PF6]+ (calcd.
PhCHNH2), 129.1 (s, p-C PhCHNH2), 129.4 (s, o-C PhCHNH2),
for [C34H31NPPd]+ 590.999).
3
129.7 (s, o-C PhCHNH2), 135.5 (d, JP-C = 6.1 Hz, C=CH), 135.7
Palladium-Catalysed Allylic Alkylation of rac-3-Acetoxy-1,3-di-
phenyl-1-propene (rac-11): The catalytic precursor was generated in
situ from [Pd(η3-C3H5)(µ-Cl)]2 and the appropriate ligand
(0.02 mmol of Pd and 0.025 mmol of the chiral ligand) in CH2Cl2
(2 mL) over 30 min before adding the substrate. rac-3-Acetoxy-1,3-
diphenyl-1-propene (0.252 g, 1 mmol), dissolved in CH2Cl2 (2 mL),
was added followed by dimethyl malonate (0.396 g, 3 mmol), BSA
(0.610 mg, 3 mmol) and a catalytic amount of KOAc. The mixture
was stirred at room temperature until total conversion of the sub-
strate (monitored by TLC, unless stated otherwise). The solution
was then diluted with ethyl ether, filtered through Celite and
washed with saturated ammonium chloride solution (4ϫ10 mL)
and water (4ϫ10 mL). The organic phase was dried with anhy-
drous Na2SO4 and filtered off, and the solvent was removed under
reduced pressure. The product was purified by column chromatog-
raphy (SiO2; ethyl acetate). The enantiomeric excess was deter-
mined by HPLC on a Chiralcel OD column, by using hexane/2-
propanol (99:1) as eluent with a flow rate of 0.3 mL/min.
3
2
(d, JP-C = 6.3 Hz, C=CH), 137.1 (d, JP-C = 10.7 Hz, PC=Cβ),
137.2 (d, JP-C = 10.7 Hz, PC=Cβ), 138.9 (s, C4 Py), 139.2 (s, C4
2
Py), 141.3 (s, ipso-C PhCHNH2), 142.1 (s, ipso-C PhCHNH2),
142.6 (s, C4 Py), 142.7 (s, C4 Py), 149.5 (s, C6 Py), 149.7 (s, C6 Py),
2
151.7 (d, 2JP-C = 9.8 Hz, C2 Py), 151.9 (d, JP-C = 10.0 Hz, C2 Py),
2
154.3 (s, C6 Py), 154.4 (s, C6 Py), 154.9 (d, JP-C = 10.5 Hz,
2
2
PC=Cβ), 155.6 (d, JP-C = 10.8 Hz, PC=Cβ), 162.4 (d, JP-C
=
5.7 Hz, C2 Py), 162.6 (d, 2JP,C = 5.6 Hz, C2 Py), PCα=C ppm is not
observed. 31P{1H} NMR: δ = +89.2, +90.2 and –142.9 (sept, JP-F
1
= 712 Hz) ppm.
Pd1b: Ligand 1b (0.0844 g, 0.230 mmol) and [Pd(µ-Cl)(η3-1-Ph-
C3H4)]2 (0.0592 g, 0.114 mmol) were dissolved in dichloromethane
(20 mL) at room temperature under nitrogen overnight. NH4PF6
(0.122 g, 0.747 mmol) was then added, and the mixture was stirred
for 24 h. After this time, the mixture was washed with degassed
water (6ϫ10 mL). The aqueous phase was extracted with dichloro-
methane (3ϫ10 mL). All the organic extracts were dried with
Na2SO4 and filtered off, and the solvent was then evaporated to
afford an orange solid. The product was recrystallised from a mix-
Palladium-Catalysed Allylic Alkylation of rac-3-Acetoxy-1-cyclo-
ture of dichloromethane and hexane (1:2). Yield: 0.100 g (65%). hexene (rac-12): This procedure was analogous to the one described
C34H31F6NPPd (735.97): calcd. C 55.49, H 4.24, N 1.90; found C
55.00, H 4.40, N 1.95. IR (KBr): ν = 3053, 2961, 1596, 1461, 1434,
for rac-3-acetoxy-1,3-diphenyl-1-propene. Purification of the prod-
uct was performed by column chromatography (SiO2; ethyl ace-
˜
1260, 1099, 838 (PF6) cm–1. 1H NMR (50 MHz, [D6]acetone, tate). The enantiomeric excess was determined by GC on a FS-
273 K): Isomer a (53%), δ = 1.65–1.70 (m, 2 H), 1.97 (br. s, 2 H),
cyclodex-β-I/P column.
Table 3. Structure determination data of complexes 5a1, Pd1b and Pd4b.
5a1
Pd1b
Pd4b
Formula
Formula mass
T [K]
C32H32ClF6N3P2Pd
776.40
100(2)
C34H31F6NP2Pd
735.94
298(2)
C32H31F6NP2Pd
735.94
120(2)
Crystal size [mm]
Crystal system
Space group
a [Å]
0.15ϫ0.10ϫ0.05
monoclinic
P21
9.4880(2)
0.12ϫ0.05ϫ0.05
orthorhombic
Pna2(1)
17.3602(18)
0.20ϫ0.05ϫ0.05
monoclinic
C2/c
25.907(5)
b [Å]
18.1207(4)
12.9213(13)
14.068(5)
c [Å]
α [°]
9.8438(2)
90
14.3200(15)
90
17.584(5)
90
β [°]
106.4610(10)
90
1623.07(6)
90
90
3212.2(6)
98.221(5)
90
6343(3)
γ [°]
V [Å3]
Z
2
4
4
ρcalcd. [Mgm–3]
F(000)
1.589
784
0.815
1.522
1488
0.737
1.541
2976
0.747
µ [mm–1]
θ limit [°]
3.12–27.52
6859
6859
6257
6859/1/407
1.109
2.12–28.37
19845
5966
5966
5966/1/398
0.977
2.96–27.48
14204
7252
5339
7252/0/414
1.028
Reflections collected
Independent reflections
Reflections [IϾ2σ(I)]
Data/restraints/parameters
GoF on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
Absolute structure parameter
R1 = 0.0403, wR2 = 0.1022
R1 = 0.0466, wR2 = 0.1072
0.00
R1 = 0.0689, wR2 = 0.1552
R1 = 0.2272, wR2 = 0.2351
–0.04(8)
R1 = 0.0514, wR2 = 0.1407
R1 = 0.0717, wR2 = 0.1594
–
Largest diff. peak and hole [eÅ–3] 1.065 and –0.479
1.102 and –0.603
0.907 and –1.009
5590
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5583–5591

Palladium Complexes of P,N Chelates Based on Phospholene Rings
2001; c) K. M. Pietrusiewicz, M. Zablocka, Chem. Rev. 1994,
94, 1375–1411.
Palladium-Catalysed Allylic Alkylation of (E)-3-Acetoxy-1-phenyl-
1-propene (6) and (E)-3-Acetoxy-1-methyl-1-propene (7): This pro-
cedure was analogous to the one described for rac-3-acetoxy-1,3-
diphenyl-1-propene. The product was purified by column
chromatography (SiO2; ethyl acetate). Regioselectivity was deter-
mined by GC.
[7] a) F. Leca, M. Sauthier, B. le Guennic, C. Lescop, L. Toupet,
J.-F. Halet, R. Réau, Chem. Commun. 2003, 1774–1775; b) F.
Leca, C. Lescop, L. Toupet, R. Réau, Organometallics 2004,
23, 6191–6201; c) Z. Pakulski, O. M. Demchuk, J. Frelek, R.
Luboradzki, K. M. Pietrusiewicz, Eur. J. Org. Chem. 2004,
3913–3918; d) Z. Pakulski, R. Kwiatosz, K. M. Pietrusiewicz,
Tetrahedron 2005, 61, 1481–1492.
[8] For a key contribution, see: B. M. Trost, C. Lee in Catalytic
Asymmetric Synthesis (Ed.: I. Ojima), 2nd ed., Wiley-VCH,
New York, 2000.
[9] a) J. Hydrio, M. Gouygou, F. Dallemer, J.-C. Daran, G. G. A.
Balavoine, Tetrahedron: Asymmetry 2002, 13, 1097–1102; b)
J. G. Lopez Cortes, O. Ramon, S. Vincendeau, D. Serra, F.
Lamy, J.-C. Daran, E. Gouygou, Eur. J. Inorg. Chem. 2006,
5148–5157.
[10] J. Wassenaar, S. van Zutphen, G. Mora, P. Le Floch, M. A. Si-
egler, A. L. Spek, J. N. H. Reek, Organometallics 2009, 28,
2724–2734.
[11] Selected contributions: a) P. Dierkes, S. Ramdeehul, L. Barloy,
A. De Cian, J. Fischer, P. C. J. Kamer, P. W. N. M.
van Leeuwen, J. A. Osborn, Angew. Chem. Int. Ed. 1998, 37,
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X-ray Crystallographic Study: Crystals of 5a1, Pd1b and Pd4b were
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isotropic displacement parameters. CCDC-746795 (for 5a1), 746796
(for Pd1b) and -746797 (for Pd4b) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
The authors wish to thank Prof. Agusti Lledós for fruitful dis-
cussions on modelling palladium complexes and the Ministerio de
Educación y Ciencia (CTQ2007–61058/BQU), the Generalitat de
Catalunya and CNRS for financial support.
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Received: September 8, 2009
Published Online: November 11, 2009
Eur. J. Inorg. Chem. 2009, 5583–5591
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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