First allylpalladium systems containing chiral imidazolylpyridine ligands - Structural studies and catalytic behaviour

Article abstract of DOI:10.1002/ejic.200600682

Palladium/chiral imidazolylpyridine systems were tested in allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene (rac-I) and 3-acetoxy-1-phenyl-1-propene (II), paying particular attention to the influence of the amine nitrogen hybridisation on their catalytic behaviour. Allylpalladium complexes 9-11 containing optically pure imidazolines were synthesised and fully characterised both in solution (NMR) and the solid state (single-crystal X-ray diffraction). NMR studies showed four species in solution for complex 9 containing the unsymmetrical 1-phenylallyl group, while for 10 and 11, involving the symmetrical 1,3-diphenylallyl moiety, two species, endo and exo, were identified. In the solid state, only endo isomers crystallised for each complex. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200600682

FULL PAPER
DOI: 10.1002/ejic.200600682
First Allylpalladium Systems Containing Chiral Imidazolylpyridine Ligands –
Structural Studies and Catalytic Behaviour
Amaia Bastero,[a] Antonio F. Bella,[a] Fernando Fernández,[b] Susanna Jansat,[b]
Carmen Claver,*[a] Montserrat Gómez,*[b,c] Guillermo Muller,[b] Aurora Ruiz,[a]
Mercè Font-Bardía,[d] and Xavier Solans[d]
Keywords: Palladium / Chiral imidazolines / Catalysis / Allylic alkylation / Intermediates / Heterocycles
Palladium/chiral imidazolylpyridine systems were tested in
allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene
(rac-I) and 3-acetoxy-1-phenyl-1-propene (II), paying par-
ticular attention to the influence of the amine nitrogen hy-
bridisation on their catalytic behaviour. Allylpalladium com-
plexes 9–11 containing optically pure imidazolines were syn-
thesised and fully characterised both in solution (NMR) and
the solid state (single-crystal X-ray diffraction). NMR studies
showed four species in solution for complex 9 containing the
unsymmetrical 1-phenylallyl group, while for 10 and 11, in-
volving the symmetrical 1,3-diphenylallyl moiety, two spe-
cies, endo and exo, were identified. In the solid state, only
endo isomers crystallised for each complex.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
workers published their research about Pd-catalysed allylic
alkylation using chiral thioimidazoline ligands, obtaining
moderate activities but excellent enantioselectivities (up to
96% ee),[3] comparable to those obtained with thioether–
oxazolines.[4] Later, chiral phosphanylimidazolines were
tested in Ir-catalysed enantioselective hydrogenation,[5,6]
giving in some cases better asymmetric inductions than
those involving analogous phosphanyloxazolines.[5] This
kind of ligand has also been used in Pd-catalysed asymmet-
ric Heck reactions, yielding better enantioselectivities than
BINAP and phosphanyloxazolines.[7] Besides mono(imida-
zolines), bis(imidazolines) have also been used in catalysis.
Therefore, chiral tridentate 2,6-bis(imidazolinyl)pyridines,
structurally analogous to pybox ligands,[8] have been tested
in Ru-catalysed asymmetric epoxidation reactions.[9] In ad-
dition, C2-symmetric bis(imidazolines) have also been pre-
pared and successfully used in Pd-catalysed allylic alky-
Introduction
In comparison with ligands containing oxazoline
groups,[1] chiral imidazolines have been used less in cataly-
sis, despite the structural analogy between the two heterocy-
cles.[2] For imidazolines, the additional nitrogen atom in
place of oxygen provides a further point for tuning the li-
gand basicity by changing the nature of the R3 group, and
consequently a new modifiable region to be considered in
selective catalytic processes (Figure 1).
Figure 1. Oxazoline and imidazoline heterocycles.
The first enantioselective catalytic application of chiral lation,[10,11] giving asymmetric inductions comparable to
imidazolines appeared in 1997 when Achiwa and co- those obtained with analogous bis(oxazolines).[1d]
Concerning imidazolylpyridines, our investigation on Pd-
[a] Departament de Química Física i Inorgànica, Universitat Ro-
catalysed copolymerisation of carbon monoxide and sty-
rene, which represents the first catalytic work involving this
Marcel.lí Domingo s/n, 43007 Tarragona, Spain
vira i Virgili,
Fax: +34-977559563
E-mail: carmen.claver@urv.net
type of ligand,[12] showed that the electronic nature of the
R3 substituent (Figure 1) could somehow control the ste-
reoregularity of the polyketones obtained,[13,14] in contrast
to the comparable oxazolylpyridine systems, affording in-
variably highly syndiotactic polymers.[15] At the same time,
Davies et al. reported the use of chiral imidazolylpyridines
in Ru-catalysed Diels–Alder reactions and the synthesis and
full characterisation of the first complex containing a chiral
imidazoline group.[16]
[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
[d] Departament de Cristal.lografia, Mineralogia i Dipòsits Min-
erals, Universitat de Barcelona,
Martí i Franquès s/n, 08028 Barcelona, Spain
132
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 132–139

First Allylpalladium Systems Containing Chiral Imidazolylpyridine Ligands
FULL PAPER
With regard to structural studies, few metal complexes ual techniques. IR spectra showed strong signals at 1559–
containing chiral imidazoline moieties have been fully char- 1549 cm–1 corresponding to the C=Nimine moiety and at
acterised.[17] Only our palladium complexes of type about 835 cm–1 assigned to P–F stretching of the PF6
[PdClR(κ2-N,NЈ-L*)] (R = Cl, Me),[13,14] rhodium com- anion. Mass spectra exhibited a peak corresponding to the
pounds, [Rh(cod)(κ2-N,NЈ-L*)]BF4,[14] and Davies’ ruthe- [Pd(η3-1-Ph-3-R-C3Hn)(L)]+ fragment.
nium complexes, [RuCl(1,3,5-trimethylbenzene)(κ2-N,NЈ-
Suitable monocrystals of 9, 10 and 11 for X-ray diffrac-
L*)]SbF6,[16] have been published involving chiral imidazol-
tion measurements were obtained from dichloromethane
ylpyridines.
solutions of the corresponding complexes by slow diffusion
of hexane.
Following our research in allylic alkylation,[18] we have
carried out a catalytic and structural study with imidazolyl-
pyridines (Figure 1) to compare their behaviour with those
containing analogous oxazoline derivatives (like ligands 7
and 8, see Table 4).[19,20] For this purpose, we have chosen
a short family of imidazolylpyridines coming from 1,2-di-
phenylethylenediamine, by varying the substituent nature
on the amine nitrogen atom (R = H, Me, Bn, Ts, Figure 2).
The influence of heterocycle stereochemistry on catalysis
has also been considered [(R,R)-1, (S,S)-2 and rac-(R,S)-3,
Figure 1]. Allylpalladium intermediates have been synthe-
sised and fully characterised in order to show a relationship
with the catalytic behaviour observed.
In these structures (Figure 3), the palladium atom shows
a distorted square-planar coordination, bonded to two ni-
trogen (N7 and N1) and two terminal allylic carbon atoms
(Table 1), which are nearly coplanar (N1–C12–C14–N7 is
about 4.8° for 9 and 10, and 1.9° for 11). These complexes
crystallised as endo isomers, meaning that the central allylic
carbon atom and the phenyl substituent at 5Ј-position on
the imidazoline ring point in opposite directions.
In a previous study based in neutral and cationic Pd
complexes involving this kind of ligand, it was found that
the C–N bond lengths were sensitive to the R substituents
at 3Ј-position, providing information about the electronic
delocalisation through the amidine fragment.[14] Therefore,
in order to analyse the electronic density involved in the C–
N bonds, Namine (N4) and Nimine (N1) with their common
bonded C atom (C5), we have compared the bond length
difference between C5–N4 and C5–N1. For 9 and 10, the
difference is slightly smaller than for 11 [∆(N1–C5 – N4–
C5) = 0.051 Å for 9; ∆(N1–C5 – N4–C5) = 0.054 Å for 10;
∆(N1–C5 – N4–C5) = 0.069 Å for 11 (Table 1)]. Comparing
these figures with those of related compounds,
[PdClMe(R,R-2)] (∆ = 0.037 Å) and [PdClMe(R,R-5)] (∆ =
0.139 Å),[14] we can state that complexes containing ligands
(R,R)-1 and (S,S)-2 {complexes 9, 10 and [PdClMe(R,R-1)]}
have C–N bonds of a similar nature, with bond lengths in-
termediate between those for single and double bonds;
while for 11, containing (S,S-4), both single and double
bonds are present. In addition, IR spectra for 9–11 exhibit
C=N stretching absorptions (1559–1549 cm–1, see Experi-
mental Section) at lower frequency than those observed for
allylpalladium complexes containing bis(oxazolines)
(1650–1670 cm–1)[22,18a] or oxazolinylpyridines (1630–
1660 cm–1);[19] consequently, weaker C=Nimine bonds for
imidazoline than for oxazoline derivatives are observed.
These structural data point out an electronic delocalisation
between the two nitrogen atoms of the imidazoline hetero-
Figure 2. 2-(4Ј,5Ј-Diphenyl-3Ј-R-imidazolyl)pyridines 1–6 with
numbering scheme.
Results and Discussion
Palladium Complexes
Ionic palladium complexes 9–11 containing 1-phenyl- (9)
and 1,3-diphenylallyl groups (10 and 11) were prepared
from the corresponding palladium precursor and the appro-
priate chiral imidazolylpyridine ligand, (R,R)-1 for 9, (S,S)-
2 for 10 and (S,S)-4 for 11, in the presence of ammonium
hexafluorophosphate (Scheme 1), according to the method-
ology previously described.[19,21]
These compounds were obtained as monometallic com-
plexes of general formula [Pd(η3-1-Ph-3-R-C3Hn)(L)]PF6
[9: R = H, n = 4, L = (R,R)-1; 10: R = Ph, n = 3, L =
(S,S)-2; 11: R = Ph, n = 3, L = (S,S)-4], where L acts as a
κ2-N,NЈ-bidentate ligand affording a five-membered pallad- cycle, mainly when the substituent on the Namine atom is a
acycle. Complexes 9–11 were fully characterised by the us- methyl group [ligands (R,R)-1 and (S,S-2)].
Scheme 1. Allylpalladium complexes 9–11 containing chiral ligands (R,R)-1, (S,S)-2 and (S,S)-4.
Eur. J. Inorg. Chem. 2007, 132–139
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
133

C. Claver, M. Gómez et al.
FULL PAPER
Figure 3. View of the molecular structures of complexes 9 (bottom), 10 (top left) and 11 (top right). Hydrogen atoms and hexafluorophos-
phate anion are omitted for clarity.
Table 1. Selected bond lengths [Å] and bond angles [°] for 9, 10 Pd–C distances in trans position to Nimine, as they are the
and 11 (with esds in parentheses).
same (Pd1–C12 = 2.173 Å for 10 and 11). But the small
increase observed in the Pd–C distances in cis position to
Nimine (Pd1–C14), 2.137 versus 2.163 Å for 10 and 11,
respectively, is probably due to the electronic and also steric
9
10
11
Pd1–N1
Pd1–N7
Pd1–C12
Pd1–C13
Pd1–C14
N1–C5
2.053(4)
2.124(4)
2.168(5)
2.087(5)
2.107(5)
1.289(6)
1.340(6)
77.24(15)
2.096(4)
2.147(5)
2.173(5)
2.122(5)
2.137(5)
1.304(6)
1.358(6)
77.64(15)
67.77(18)
2.109(3)
2.137(3)
2.173(4)
2.145(4)
2.163(4)
1.291(5)
1.360(5)
76.53(12)
68.11(15)
effect of the substituent on Namine
.
1H NMR spectroscopy allowed the determination of the
structure of these complexes in solution.[19,24] For complex
9, four isomers were observed in deuterated chloroform
N4–C5
N1–Pd1–N7
solution at room temperature, with
a relative ratio
C12–Pd1–C14 67.9(2)
46:31:15:8 for 9a/9b/9c/9d. Only for the two major isomers,
9a and 9b, were all carbon and proton atoms assigned. The
isomers detected are formed because of (i) the relative posi-
tion of the central allylic carbon atom and the phenyl sub-
stituent at the 5Ј-position on the imidazoline ring (giving
exo and endo isomers, see above) and (ii) the substitution
on the allyl moiety. 2D NOESY experiments exhibited in-
terconversion between 9a and 9d and between 9b and 9c,
but no π-σ-π allyl isomerisation was observed.
Concerning relative chemical shifts, the signals of the ter-
minal allyl protons (H3 and H4, Table 2) for the two major
isomers (δ = 2.19–3.33 ppm for 9a and 9b) are upfield-
shielded relative to those of the other two isomers (δ =
3.51–4.25 ppm for 9c and 9d), a fact that can be attributed
to the spatial proximity of the phenyl group at the heterocy-
cle 5Ј-position; similarly, the signal of the H2 proton of 9c
is also upfield-shifted with respect to 9a and 9b [δ = 3.96
(9c) vs. 4.52 and 4.53 ppm for 9a and 9b, respectively,
Table 2]; H5 is also sensitive to the allyl group and for 9c
its signal is more than 1 ppm upfield-shifted because of the
close allylphenyl group [δ = 3.86 (9c) vs. 4.84 and 5.00 ppm
for 9a and 9b, respectively]. Consequently, the two major
isomers could be attributed to exo and endo isomers where
Concerning the planarity around Namine, the angle be-
tween the two planes around this atom has been considered.
The C5–C41–C3–N4 angle is less than 7° for 9 (2.4°) and 10
(6.9°), and 10.2° for 11. Comparing with two other related
complexes, the corresponding angles are 0.6° for
[PdClMe(R,R-1)] and 21.6° for [PdClMe(R,R-5)].[14] Like-
wise, the distance of C41 to N1–C5–N4 is 0.025, 0.133 and
0.365 Å for 9, 10 and 11, respectively. Then a quasi-sp2 hy-
bridisation for [PdClMe(R,R-1)], 9 and 10 can be inferred,
in contrast to an Namine sp3 hybridisation for [PdClMe(R,R-
5)]; for 11, containing the (S,S)-4 ligand, a significant plan-
arity deviation is observed. This prominent feature about
the sp2 character for nitrogen atoms of the imidazoline ring
has been recently stated from the X-ray structural analysis
of a bis(imidazolinyl)pyridine ligand.[23]
The Pd–C distances in trans position to both nitrogen
atoms, Pd1–C12 versus Pd1–C14, point to a higher trans
influence for Nimine than for Npyridine. Therefore, the differ-
ences in the distance between palladium and both terminal
allylic carbon atoms [∆(Pd1–C12 – Pd1–C14)] are 0.036 and
0.010 Å for 10 and 11 respectively. However, the electronic
effect of the R substituent on Namine is not reflected in the the phenylallyl group is located in cis position relative to
134
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 132–139

First Allylpalladium Systems Containing Chiral Imidazolylpyridine Ligands
FULL PAPER
the pyridine nitrogen atom, while 9c corresponds to one of
For complexes 10 and 11, only two isomers were ob-
the minor isomers where the phenylallyl group is located in served in deuterated chloroform solution, with a relative ra-
trans position relative to the pyridine nitrogen atom. These tio of about 6:1. Most of the resonances for minor isomers
data lead us to propose the structures shown in Figure 4.
are overlapped by signals corresponding to those of major
species. 2D NOESY experiments exhibited, in both cases,
interconversion between both isomers and no π-σ-π allyl
isomerisation was detected. Because of the steric hindrance
between both phenyl groups, from the imidazoline ring and
allyl group, the major species for each complex could be
assigned to the endo isomer.
Table 2. Selected 1H NMR (CDCl3, 400 MHz, 298 K) chemical
shifts for 9 (signal multiplicity in parentheses).[a]
9a
9b
9c
9d[b]
H1 (central) 5.76 (td)
5.69 (td)
4.53 (d)
2.72 (d)
2.79 (dd)
5.00 (d)
4.86 (d)
3.29 (s)
5.87–5.95 (m)
3.96 (d)
3.51 (d)
4.25 (d)
3.86 (d)
n.d.
n.d.
n.d.
4.14 (d)
n.d.
n.d.
H2 (anti-Ph) 4.52 (d)
H3 (anti)
H4 (syn)
H5
2.19 (ddd)
3.33 (dd)
4.84 (d)
Pd-Catalysed Allylic Alkylation
H6
4.90 (d)
4.41 (d)
3.21 (s)
H7–9 (CH3) 3.31 (s)
n.d.
Asymmetric allylic alkylation of the racemic substrate
rac-3-acetoxy-1,3-diphenyl-1-propene (rac-I) and 3-acetoxy-
1-phenyl-1-propene (III) with dimethyl malonate under ba-
sic Trost conditions[25] was carried out using a Pd catalytic
systems containing 2-(4Ј,5Ј-diphenyl-5Ј-substituted-imid-
azolyl)pyridines 1–6 (Scheme 2). The results are summa-
rised in Table 3. Catalytic precursors were generated in situ
from [PdCl(C3H5)]2 and the appropriated ligand (Pd/L =
1:1.25).
[a] Proton labels:
guished.
[b] n.d. means not distin-
.
For the allylic alkylation of rac-I, we observed that the
most active palladium systems were those containing a
methyl group in the 5Ј-position of the imidazolyl ring, li-
gands (R,R)-1, (S,S)-2 and rac-(R,S)-3 (Entries 2, 4 and 5,
Table 3). Benzyl and tosyl derivatives [ligands (S,S)-4 and
(R,R)-5, respectively] led to less active catalysts (Entries 7
and 9, Table 3), especially the Pd/(R,R)-5 system, which
showed a very low conversion [36% after 48 h of reaction
(Entry 9, Table 3)].
The activity trend shown by these Pd/L* systems corre-
lates quite well with the Namine hybridisation character. Ac-
tually, methyl derivatives containing sp2-hybridised Namine
(ligands 1, 2 and 3) are more active than benzyl [(S,S)-4],
whose Namine atom exhibits a significant sp3 character and
is clearly more active than the tosyl derivative, which con-
tains an sp3-hybridised Namine atom (Entries 2, 4, 5, 7 and
9, Table 3).
Concerning the enantioselectivity, only the Pd/(S,S)-4
system gave a significant asymmetric induction, up to 19%
ee (Entry 7, Table 3). The low enantioselectivity observed is
probably due to the higher trans influence of Nimine than
that of Npyridine (see above), directing the nucleophile attack
towards the terminal allylic carbon atom trans to the imine
nitrogen atom. In that position no steric hindrance coming
Figure 4. Proposed structures for the four isomers of 9 observed in
solution (arrows indicate the isomer interconversion observed by
2D NOESY, between 9a and 9d, and 9b and 9c).
Scheme 2. Allylic alkylation of rac-I and III catalysed by Pd/L* systems (L* = 1–6).
Eur. J. Inorg. Chem. 2007, 132–139
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
135

C. Claver, M. Gómez et al.
Table 3. Allylic alkylation of rac-I and III catalysed by palladium systems containing imidazolylpyridines, Pd/L* (L* = 1–6).[a]
FULL PAPER
Entry
L*
Substrate
Time [h]
Conversion [%][b]
ee of II [%][b]
l-IV/b-IV[b]
1
2
3
4
5
6
7
8
9
1
1
2
2
3
4
4
4
5
5
1
2
I
I
5
24
5
41
97
34
100
81
0
46
99
36
94
0
0
0
0
0
–
–
–
–
–
–
–
–
–
–
I
I
24
24
5
24
48
48
96
24
24
I
I
I
19 (S)
15 (S)
0
0
–
–
I
I
10
11
12
I
–
13:1
13:1
III
III
100
100
[a] Results from duplicated experiments. Pd/L*/substrate = 1:1.25:50. See Scheme 2. [b] Conversions based on substrate I or III determined
1
by H NMR spectroscopy; enantiomeric excesses (absolute configuration in parentheses) determined by HPLC and l(inear)/b(ranched)
ratio, by GC.
from the 6-position of the pyridine group exists to discrimi- Table 4. Allylic alkylation of rac-I catalysed by palladium systems
containing imidazolyl- [(R,R)-1, (S,S)-2, (S,S)-4] and oxazolinyl-
nate this attack between both endo and exo isomers. In ad-
dition, the electronic effect due to the Namine substituent
pyridines (7, 8).
Entry
L*
Time [h] Conversion [%][a] ee of II [%][a] Reference
can contribute to this lack of enantioselectivity. An increase
of pyramidal arrangement around the Namine atom means
a decrease of π-electron delocalisation between the amine
and imine nitrogen atom (see above) and consequently
Nimine becomes a better donor Lewis centre, favouring the
stability of cationic intermediate catalytic species responsi-
ble for the enantioselectivity control. The lack of enantio-
selectivity for (R,R)-5 (Entries 9 and 10, Table 3) could be
due to electronic factors.
1
2
3
4
5
1
2
4
7
8
5
5
24
2.5
2
41
34
46
86
84
0
0
this work
this work
19 (S)
55 (R)[b]
25 (S)
this work
[20]
[19]
[a] Conversions based on substrate I determined by 1H NMR spec-
troscopy; enantiomeric excesses (absolute configuration in paren-
theses) determined by HPLC. [b] Determined by 1H NMR spec-
troscopy using Eu(hfc)3 as the chiral shift reagent.
The Pd/(R,R)-6 system was not active, doubtless because
of the NH deprotonation of the imidazoline group under
the basic catalytic conditions used. In this case, the plaus-
ible palladium intermediate containing the anionic imid-
azolylpyridine ligand could induce a less electrophilic char-
acter on the allyl moiety than cationic allylic intermediates
involving bidentate neutral ligands.
The most active catalytic systems [Pd/(R,R)-1 and Pd/
(S,S)-2] were used in the allylic alkylation of 3-acetoxy-1-
phenyl-1-propene (III), under the same conditions de-
scribed above for rac-I, showing a high regioselectivity
towards the linear isomer, l-IV/b-IV ratio = 13:1 (Entries
11 and 12, Table 3).
The higher electronegativity of oxygen with respect to
nitrogen avoids any π-delocalisation between oxygen and
nitrogen atoms in the oxazoline heterocycle. Then the Lewis
base character of the Nimine atom in oxazolines is more im-
portant than that for analogous imidazolines, especially for
those containing an sp2-hybridised amine nitrogen atom.
Therefore, this behaviour becomes crucial to understand the
activity and selectivity diminution of imidazolylpyridines
compared to related oxazolines.
Conclusion
From a structural point of view, the imidazoline ring is
close to the oxazoline heterocycle. When we compare the
catalytic results obtained for rac-I alkylation with (5Ј-
phenyl-oxazolinyl)pyridine and (4Ј,5Ј-disubstituted)oxaz-
olinylpyridine ligands 7 and 8, respectively (Table 4), we ob-
serve that Pd/7 and Pd/8 catalysts are more active and selec-
tive than the most active and selective imidazoline deriva-
tives [ligands (R,R)-1, (S,S)-2 and (S,S)-4, respectively; En-
tries 4 and 5 vs. 1, 2 and 3, Table 4].
We have found the fine-tuning effect of the remote Namine
centre on the Pd-catalysed allylic alkylation reaction. The
delocalisation of the nonbonding electron pair of Namine
causes a basicity diminution in Nimine, which is directly
bonded to the metal atom. This effect seems to be directly
related with the activity and asymmetric induction of Pd/
imidazolylpyridine catalytic systems.
Experimental Section
General Remarks: All compounds were prepared under purified ni-
trogen using standard Schlenk and vacuum-line techniques. The
solvents were purified by standard procedures and distilled under
nitrogen.[26] [Pd(η3-1-phenylallyl)(µ-Cl)][27] and ligands (R,R)-1,[14]
136
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 132–139

First Allylpalladium Systems Containing Chiral Imidazolylpyridine Ligands
FULL PAPER
(S,S)-2,[16] (R,R)-5[14] and (R,R)-6[14] were prepared as described
536.975 for C30H28N3Pd+). H NMR (400 MHz, 298 K): Isomer a
1
previously. NMR spectra were recorded with Varian XL-500 (1H,
(46%): δ = 2.19 (ddd, 1 H, J = 12.4, 1.6, 1.2 Hz), 3.31 (s, 3 H),
standard SiMe4), Varian Gemini (1H, 200 MHz; 13C, 50 MHz; 3.33 (dd, 1 H, J = 7.0, 1.6 Hz), 4.52 (d, 1 H, J = 11.6 Hz), 4.84 (d,
standard SiMe4), Bruker DRX 250 (13C, 62.9 MHz, standard 1 H, J = 10.8 Hz), 4.90 (d, 1 H, J = 10.8 Hz), 5.76 (td, 1 H, J =
SiMe4) and Varian Mercury 400 (1H, 400 MHz; 13C, 100 MHz,
standard SiMe4) spectrometers, using CDCl3 as solvent, unless
stated otherwise. Chemical shifts were reported downfield from
standards. IR spectra were recorded with FTIR Nicolet 520 and
Nicolet 5700 spectrometers. Electron-spray mass spectra were ob-
tained with a Mass ZQ Micromass instrument. High-resolution
mass spectra were obtained with a Waters LCT Premier spectrome-
ter operated in ESI mode. The GC analyses were performed with
a Hewlett-Packard 6890-Network GC system gas chromatograph
[30 m HP5 (5% phenyl)methylpolysiloxane column] with an FID
detector. Enantiomeric excesses were determined by HPLC on a
Chiralcel OD column. Elemental analyses were carried out by the
Serveis Cientifico-Tècnics de la Universitat de Barcelona with an
Eager 1108 microanalyser. Optical rotations were measured with a
JASCO P-1030 polarimeter.
12.1, 7.0 Hz), 6.80–8.35 (aromatic protons, 19 H); Isomer b (31%):
δ = 2.72 (d, 1 H, J = 12.0 Hz), 2.79 (dd, 1 H, J = 7.2, 1.2 Hz), 3.29
(s, 3 H), 4.53 (d, 1 H, J = 11.6 Hz), 4.86 (d, 1 H, J = 10.8 Hz),
5.00 (d, 1 H, J = 11.2 Hz), 5.69 (td, 1 H, J = 12.0, 6.8 Hz), 6.80–
8.35 (aromatic protons, 19 H); Isomer c (15%): δ = 3.21 (s, 3 H),
3.51 (d, 1 H, J = 12.8 Hz), 3.86 (d, 1 H, J = 8.4 Hz), 3.96 (d, 1 H,
J = 11.2 Hz), 4.25 (d, 1 H, J = 7.2 Hz), 4.41 (d, 1 H, J = 8.0 Hz),
5.90 (m, 1 H), 6.80–8.35 (aromatic protons, 19 H) ppm. 13C{1H}
NMR (100.6 MHz): Isomer a (46%): δ = 35.0 (CH3), 55.5 (CH2),
76.9 (CH), 80.2 (CH), 80.3 (CH), 109.4 (CH), 126.0 (CH), 127.0
(CH), 127.8 (CH), 127.9 (CH), 128.3 (CH), 128.8 (CH), 129.1
(CH), 129.2 (CH), 129.5 (CH), 130.0 (CH), 136.4 (C), 137.9 (C),
140.9 (C), 140.9 (CH), 146.6 (C), 149.4 (CH), 165.8 (C=N); Isomer
b (31%): δ = 34.8 (CH3), 55.0 (CH2), 77.0 (CH), 80.2 (CH), 80.9
(CH), 110.2 (CH), 126.1 (CH), 127.2 (CH), 127.7 (CH), 128.0
(CH), 128.4 (CH), 128.8 (CH), 129.0 (CH), 129.1 (CH), 129.5
(CH), 130.0 (CH), 136.2 (C), 137.7 (C), 140.7 (C), 140.9 (CH),
146.5 (C), 149.6 (CH), 165.9 (C=N) ppm.
(4ЈR,5ЈS)-2-(3Ј-Methyl-4Ј,5Ј-diphenyl-2Ј-imidazolyl)pyridine [rac-
(R,S)-3]:
(4ЈR,5ЈS)-2-(4Ј,5Ј-Diphenyl-2Ј-imidazolyl)pyridine[12]
(0.100 g, 0.33 mmol) was dissolved in THF (3 mL) and treated with
NaH (9.5 mg, 0.4 mmol) for 1 h. MeI (22.4 µL, 0.36 mmol) was
then added dropwise at room temperature. After 7 h, the solvent
was removed under reduced pressure, giving a paste, which was
(η3-1,3-Diphenylallyl)[(4ЈS,5ЈS)-2-(3Ј-methyl-4Ј,5Ј-diphenyl-2Ј-imid-
azolyl)pyridine-N,N]palladium(II) Hexafluorophosphate (10): Li-
gand (S,S)-2 (0.075 g, 0.240 mmol) and [Pd(µ-Cl)(η3-1,3-Ph-
C3H3)]2 (0.084 g, 0.13 mmol) were dissolved in dichloromethane
(20 mL) at room temperature under nitrogen overnight. NH4PF6
(0.123 g, 0.760 mmol) was then added and the mixture was stirred
for 24 h. Then the mixture was washed with water (6ϫ15 mL). The
aqueous phase was extracted with dichloromethane (3ϫ10 mL).
All the organic extracts were dried with Na2SO4, filtered and the
solvent was then evaporated to afford a yellow oil. The product
was recrystallised from a mixture of dichloromethane and hexane
purified by column chromatography yielding
a white solid
(77.8 mg, 75%). 1H NMR (200 MHz, CDCl3, 298 K): δ = 8.72–
7.26 (m, 14 H, aromatic), 4.99 (d, 1 H, J = 10.4 Hz), 4.36 (d, 1 H,
J = 10.4 Hz), 2.99 (s, 3 H) ppm. 13C NMR (100.6 MHz, CDCl3,
298 K): δ = 164.6 (C=N), 149.2 (CH), 137.1 (CH), 129.2–127.11
(CH), 125.3 (CH), 124.9 (CH), 79.0 (CH), 77.4 (CH), 34.4 (CH3)
ppm. HRMS-ESI: m/z calcd. for C21H20N3 314.1657; found
314.1647 [M + H]+.
(0.095 g, 52% yield). IR (KBr): ν = 1556 (C=N), 838 (PF ) cm–1.
˜
6
(4ЈS,5ЈS)-2-(3Ј-Benzyl-4Ј,5Ј-diphenyl-2Ј-imidazolyl)pyridine [(S,S)-
4]: (4ЈS,5ЈS)-2-(4Ј,5Ј-Diphenyl-2Ј-imidazolyl)pyridine[16] (0.100 g,
0.33 mmol) was dissolved in THF (3 mL) and treated with NaH
(9.5 mg, 0.4 mmol) for 1 h. Benzyl bromide (42.5 µL, 0.36 mmol)
was then added dropwise at room temperature. After 5 h, the sol-
vent was removed under reduced pressure, giving a brown paste,
which was purified by column chromatography yielding a white
solid (96.6 mg, 75%). 1H NMR (400 MHz, CDCl3, 298 K): δ =
8.73–6.97 (m, 19 H, aromatic), 5.67 (d, 1 H, J = 15.6 Hz), 5.03 (d,
1 H, J = 9.2 Hz), 4.45 (d, 1 H, J = 9.2 Hz), 3.96 (d, 1 H, J =
15.6 Hz) ppm. 13C NMR (100.6 MHz, CDCl3, 298 K): δ = 162.8
(C=N), 148.5 (CH), 136.9 (CH), 128.8–126.9 (CH), 125.6 (CH),
122.6 (CH), 77.4 (CH), 73.6 (CH), 49.1 (CH2) ppm. HRMS-ESI:
m/z calcd. for C27H24N3 390.1970; found 390.1980 [M + H]+.
[α]2D0 –4.90 (c = 0.88, CHCl3).
C36H32F6N3PPd·0.2C4H10O·0.5CH2Cl2 (815.29): calcd. C 54.95, H
4.33, N 5.15; found C 55.09, H 4.02, N 5.07. FAB+ MS: m/z = 613.8
[M – PF6]+ (calcd. 613.077 for C36H32N3Pd+). 1H NMR (400 MHz,
298 K): Isomer a (88%): δ = 3.18 (s, 3 H), 3.83 (d, J = 8.4 Hz, 1
H), 4.11 (d, J = 11.2 Hz, 1 H), 4.41 (d, J = 8.4 Hz, 1 H), 4.81 (d,
J = 11.6 Hz, 1 H), 6.23 (t, J = 11.6 Hz, 1 H), 6.86–8.29 (aromatic
protons, 24 H) ppm. 13C{1H} NMR (100.6 MHz): Isomer a (88%):
δ = 34.6 (CH3), 72.4 (CH), 74.6 (CH), 79.2 (CH), 79.4 (CH), 107.6
(CH), 126.0 (CH), 126.0 (CH), 126.8 (CH), 127.7 (CH), 128.0
(CH), 128.1 (CH), 128.2 (CH), 128.4 (CH), 128.9 (CH), 129.1
(CH), 129.3 (CH), 129.4 (CH), 130.2 (CH), 136.4 (C), 137.4 (C),
138.4 (C), 141.0 (C), 141.1 (CH), 145.9 (C), 149.6 (CH), 165.2
(C=N) ppm.
(η3-1,3-Diphenylallyl)[(4ЈS,5ЈS)-2-(3Ј-benzyl-4Ј,5Ј-diphenyl-2Ј-imid-
azolyl)pyridine-N,N]palladium(II) Hexafluorophosphate (11): Li-
gand (S,S)-4 (0.029 g, 0.075 mmol) and [Pd(µ-Cl)(η3-1,3-Ph-
C3H3)]2 (0.025 g, 0.037 mmol) were dissolved in dichloromethane
(η3-1-Phenylallyl)[(4ЈR,5ЈR)-2-(3Ј-methyl-4Ј,5Ј-diphenyl-2Ј-imid-
azolyl)pyridine-N,N]palladium(II) Hexafluorophosphate (9): Ligand
(R,R)-1 (0.050 g, 0.160 mmol) and [Pd(µ-Cl)(η3-1-Ph-C3H4)]2 (10 mL) at room temperature under nitrogen overnight. NH4PF6
(0.043 g, 0.083 mmol) were dissolved in dichloromethane (25 mL)
at room temperature under nitrogen overnight. NH4PF6 (0.156 g,
0.960 mmol) was then added and the mixture was stirred for 3 h.
Then the mixture was washed with water (6ϫ20 mL). The aqueous
phase was extracted with dichloromethane (3ϫ10 mL). All the or-
ganic extracts were dried with Na2SO4, filtered off and the solvent
was then evaporated to afford a yellow solid. The product was
recrystallised from a mixture of dichloromethane and hexane
(0.037 g, 0.220 mmol) was then added and the mixture was stirred
for 72 h. Then the mixture was washed with water (6ϫ15 mL). The
aqueous phase was extracted with dichloromethane (2ϫ10 mL).
All the organic extracts were dried with Na2SO4, filtered and the
solvent was then evaporated to afford a yellow gum. The product
was recrystallised from a mixture of dichloromethane and hexane
(0.021 g, 33% yield). IR (KBr): ν = 1549 (C=N), 832 (P–F) cm–1.
˜
C42H36F6N3PPd (833.01): calcd. C 60.48, H 4.35, N 5.04; found
(0.061 g, 56% yield). IR (KBr): ν = 1559 (C=N), 838 (PF ) cm–1. 6 0 . 9 0 , H 4 . 9 5 , N 5 . 1 6 . E S I M S : m / z = 6 8 8 . 1 [ M –
˜
6
C30H28F6N3PPd (681.94): calcd. C 52.84, H 4.14, N 6.16; found C
PF6]+ (calcd. 688.194 for C42H36N3Pd+). 1H NMR (500 MHz,
53.28, H 4.26, N 6.02. ESI+ MS: m/z = 536.1 [M – PF6]+ (calcd.
298 K): Isomer a (86%): δ = 3.90 (d, J = 6.0 Hz, H), 4.15 (d, J =
Eur. J. Inorg. Chem. 2007, 132–139
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
137

C. Claver, M. Gómez et al.
FULL PAPER
Table 5. Crystal data for 9, 10 and 11.
9
10
11
Empirical formula
Formula mass
Crystal size [mm]
Temperature [K]
Crystal system
C31H30Cl2F6N3PPd
766.85
0.30ϫ0.27ϫ0.05
120(2)
monoclinic
P21/c
C37H34Cl2F6N3PPd
842.94
0.2ϫ0.18ϫ0.02
120(2)
monoclinic
C2/c
C42H36F6N3OPPd·H2O
852.12
0.2ϫ0.1ϫ0.1
293(2)
monoclinic
P21/c
Space group
a [Å]
b [Å]
18.781(5)
9.728(3)
39.157(8)
10.708(2)
10.113(6)
26.731(11)
c [Å]
17.523(5)
92.297(4)
3199.0(16)
4
17.471(4)
103.537(4)
7122(3)
8
15.026(6)
107.46(2)
3875(3)
4
β [°]
Volume [Å3]
Z
Density (calculated) [Mg/m3]
Absorption coefficient [mm–1]
θ range for data collection [°]
Reflections collected [I Ն 2σ(I)]
Independent reflections
Final R indices [I Ͼ 2σ(I)][a]
R indices (all data)[a]
Gof on F2
1.592
0.859
1.572
0.780
1.98–26.73
7569
7569 [R(int) = 0.0000]
R1 = 0.0530, wR2 = 0.1237
R1 = 0.0928, wR2 = 0.1370
1.051
1.461
0.586
2.60–30.00
8370
8489 [R(int) = 0.0000]
R1 = 0.0608, wR2 = 0.1043
R1 = 0.0612, wR2 = 0.1044
1.423
2.17–26.02
6272
6272 [R(int) = 0.0000]
R1 = 0.0492, wR2 = 0.1332
R1 = 0.0791, wR2 = 0.1480
1.120
Largest diff. peak/hole [e/Å3]
1.308/–0.696
0.762/–1.401
0.424/–0.382
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo| and wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
8.8 Hz, H), 4.41 (d, J = 14.4 Hz, H), 4.50 (d, J = 6.4 Hz, H), 4.83
φ-ω scan method. Absorption corrections were applied using the
(d, J = 9.6 Hz, H), 5.05 (d, J = 14.4 Hz, H), 6.31 (t, J = 9.2 Hz, SADABS program.[28] The structures were solved by direct meth-
H), 6.87–7.97 (aromatic protons, 29 H) ppm. 13C{1H} NMR ods using the SHELXS-97 computer program[29] for crystal struc-
(100.6 MHz): Isomer a (86 %): δ = 49.6 (CH2), 72.3 (CH), 74.4 ture determination and refined by full-matrix least-squares method
(CH), 76.9 (CH), 79.6 (CH), 107.8 (CH), 126.0 (CH), 126.0 (CH), on F2, with the SHELXL-97 computer program.[30] The weighting
2
126.8 (CH), 127.7 (CH), 128.0 (CH), 128.1 (CH), 128.2 (CH), 128.4 schemes employed were w = 1/[σ2{Fo + (0.08259P)}2 + 0.0000P]
(CH), 128.9 (CH), 129.1 (CH), 129.3 (CH), 129.4 (CH), 130.2 for 9, w = 1/[σ2{Fo + (0.0678P)}2 + 0.0000P] for 10 and w =
2
(CH), 136.4 (C), 137.4 (C), 138.4 (C), 141.0 (C), 141.1 (CH), 145.9 1/[σ2{Fo + (0.0079P)}2 + 4.7017P] for 11, where P = (|Fo|2
(C), 149.6 (CH), 165.6 (C=N) ppm.
+
2
2|Fc|2)/3. Hydrogen atoms were included in calculated positions and
refined in riding mode. CCDC-291543 (for 9), -614143 (for 10)
and -613925 (for 11) contain the supplementary crystallographic
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.
Palladium-Catalysed Allylic Alkylation of rac-3-Acetoxy-1,3-di-
phenyl-1-propene (I): The catalytic precursor was generated in situ
from [Pd(η3-C3H5)(µ-Cl)]2 and the appropriate ligand (0.02 mmol
of Pd source and 0.025 mmol of chiral ligand) in CH2Cl2 (2 mL)
for 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 diethyl 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, filtered and the solvent was removed under reduced
pressure. The product was purified by column chromatography
(SiO2; ethyl acetate). The enantiomeric excesses were determined
by HPLC on a Chiralcel OD column, using hexane/2-propanol,
99:1, as eluent in a flow of 0.3 mL/min.
Acknowledgments
The authors wish to thank the Ministerio de Educación y Ciencia
(CTQ2004-01546/BQU) and the Generalitat de Catalunya for fin-
ancial support. The authors also thank the Unidade de RaiosX
of the Universidade de Santiago de Compostela for their X-ray
crystallographic contribution.
[1] General references about oxazolines and their catalytic applica-
tions: a) I. Ojima (Ed.), Catalytic Asymmetric Synthesis, 2nd
ed., Wiley, New York, 2000; b) G. Helmchen, A. Pfaltz, Acc.
Chem. Res. 2000, 33, 336–345; c) P. G. Cozzi, N. Zimmermann,
R. Hilgraf, S. Schaffner, A. Pfaltz, Adv. Synth. Catal. 2001,
343, 450–454; d) A. Ghosh, P. Mathivanan, J. Cappiello, Tetra-
hedron: Asymmetry 1998, 9, 1–45; e) M. Gómez, G. Muller, M.
Rocamora, Coord. Chem. Rev. 1999, 193–195, 769–835.
[2] P. J. Guiry, C. P. Saunders, Adv. Synth. Catal. 2004, 346, 497–
537.
Palladium-Catalysed Allylic Alkylation of (E)-3-Acetoxy-1-phenyl-
1-propene (III): The procedure was analogous to the one described
for rac-3-acetoxy-1,3-diphenyl-1-propene (I). The product was
purified by column chromatography (SiO2; ethyl acetate). Regiose-
lectivity was determined by GC.
X-ray Crystallographic Study: Yellow crystals of 9, 10 and 11 were
selected and mounted on a Bruker SMART-CCD-1000 area detec-
tor single crystal diffractometer with graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å). Crystal data are summarised in
Table 5. Preliminary unit cell constants were calculated with a set
of 45 narrow-frame (0.3° in ω) scans. Data were collected using the
[3] T. Morimoto, K. Tachibana, K. Achiwa, Synlett 1997, 783–
785.
[4] J. V. Allen, G. J. Dawson, C. G. Frost, I. M. J. Williams, Tetra-
hedron 1994, 50, 799–808.
[5] F. Menges, M. Neuburger, A. Pfaltz, Org. Lett. 2002, 4, 4713–
4716.
138
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 132–139

First Allylpalladium Systems Containing Chiral Imidazolylpyridine Ligands
FULL PAPER
[6]
[7]
Ferran, M. Gómez, F. Jiménez, G. Muller, M. Rocamora,
Chem. Eur. J. 2002, 8, 4164–4178; c) D. Franco, M. Gómez, F.
Jiménez, G. Muller, M. Rocamora, M. A. Maestro, J. Mahía,
Organometallics 2004, 23, 3197–3209.
E. Guiu, C. Claver, J. Benet-Buchholz, S. Castillón, Tetrahe-
dron: Asymmetry 2004, 15, 3365–3373.
a) C. A. Busacca, D. Grossbach, R. C. So, E. M. O’Brien,
E. M. Spinelli, Org. Lett. 2003, 5, 595–598; b) C. A. Busacca,
D. Grossbach, S. J. Campbell, Y. Dong, M. C. Ericsson, R. E.
Harris, P.-J. Jones, J.-Y. Kim, J. C. Lorenz, K. B. McKellop,
E. M. O’Brien, F. Qiu, R. D. Simpson, L. Smith, R. C. So,
E. M. Spinelli, J. Vitous, C. Zavattaro, J. Org. Chem. 2004, 69,
5187–5195.
[19] J. M. Canal, M. Gómez, F. Jiménez, M. Rocamora, G. Muller,
E. Dunach, D. Franco, A. Jiménez, F. H. Cano, Organometal-
lics 2000, 19, 966–978.
[20] G. Chelucci, S. Medici, A. Saba, Tetrahedron: Asymmetry 1997,
8, 3183–3184.
[21] P. von Matt, G. C. Lloyd-Jones, A. B. E. Minidis, A. Pfaltz, L.
Macko, M. Neuburger, M. Zehnder, H. Rüegger, P. S. Pregosin,
Helv. Chim. Acta 1995, 78, 265–284.
[22] M. Gómez, S. Jansat, G. Muller, M. A. Maestro, J. Mahia, M.
Font-Bardia, X. Solans, J. Chem. Soc., Dalton Trans. 2001,
1432–1439.
[8]
[9]
H. Nishiyama, Adv. Catal. Processes 1997, 2, 153–188.
S. Bhor, G. Anilkumar, M. K. Tse, M. Klawonn, C. Döbler, B.
Bitterlich, A. Grotevendt, M. Beller, Org. Lett. 2005, 7, 3393–
3396.
N. A. Boland, M. Casey, S. J. Hynes, J. W. Matthews, H.
Müller-Bunz, P. Wilkes, Org. Biomol. Chem. 2004, 2, 1995–
2002.
J. Dupont, G. Ebeling, M. R. Delgado, C. S. Consorte, R. Bur-
row, D. H. Farrar, A. J. Lough, Inorg. Chem. Commun. 2001,
4, 471–474.
[10]
[11]
[23] K. Ma, L. Cheng, H. Mou Gau, J. You, Acta Crystallogr., Sect.
E: Struct. Rep. Online 2006, 62, o1595–o1597.
[24] a) P. S. Pregosin, H. Rüegger, R. Salzmann, A. Albinati, F. Li-
anza, R. W. Kunz, Organometallics 1994, 13, 83–90; b) P. S.
Pregosin, R. Salzmann, Coord. Chem. Rev. 1996, 155, 35–68.
[25] B. M. Trost, D. J. Murphy, Organometallics 1985, 4, 1143–1145.
[26] W. L. F. Armarego, D. D. Perrin, Purification of Laboratory
Chemicals, 4th ed., Butterworth-Heinemann, Oxford, UK,
1996.
[12] A. Bastero, A. Ruiz, C. Claver, S. Castillón, Eur. J. Inorg. Chem.
2001, 3009–3011.
[13] A. Bastero, A. Ruiz, C. Claver, B. Milani, E. Zangrando, Orga-
nometallics 2002, 21, 5820–5829.
[14] A. Bastero, C. Claver, A. Ruiz, S. Castillón, E. Daura, C. Bo,
E. Zangrando, Chem. Eur. J. 2004, 10, 3747–3760.
[15] M. Brookhart, M. I. Wagner, G. G. A. Balavoine, H. A. Had-
dou, J. Am. Chem. Soc. 1994, 116, 3641–3642.
[16] A. J. Davenport, D. L. Davies, J. Fawcett, D. R. Russell, J.
Chem. Soc., Perkin Trans. 1 2001, 1500–1503.
[27] Y. Tatsuno, T. Yoshida, S. Otsuka, Inorg. Synth. 1990, 28, 342.
[28] G. M. Sheldrick, SADABS, A Program for Empirical Absorp-
tion Correction of Area Detector Data, University of Göttingen,
Germany, 1996. Based on the method of Robert Blessing:
R. H. Blessing, Acta Crystallogr., Sect. A: Found. Crystallogr.
1995, 51, 33.
[17] For complexes containing chiral imidazolylphosphane ligands,
see refs.[6,7b]; for a palladium complex containing a chiral bis(i-
midazoline)ligand, see ref.[11]
[18] For recent contributions, see: a) M. Gómez, S. Jansat, G.
Muller, M. A. Maestro, J. Mahia, Organometallics 2002, 21,
1077–1087; b) M. A. Pericàs, C. Puigjaner, A. Riera, A. Vidal-
[29] G. M. Sheldrick, SHELXS 97, a computer program for crystal
structure determination, University of Göttingen, 1997.
[30] G. M. Sheldrick, SHELXL 97, a computer program for crystal
structure refinement, University of Göttingen, 1997.
Received: July 21, 2006
Published Online: November 14, 2006
Eur. J. Inorg. Chem. 2007, 132–139
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
139