Chiral bis(oxazoline) ligands. Synthesis of mono- and bi-metallic complexes of nickel and palladium

Article abstract of DOI:10.1039/a807946c

The co-ordination behaviour of the chiral bis(oxazoline) ligands ortho-, meta-, and para-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene (A, B, C, respectively) has been studied. Palladium and nickel complexes were synthesized and characterized in solutio

Full text of DOI:10.1039/a807946c

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Chiral bis(oxazoline) ligands. Synthesis of mono- and bi-metallic
complexes of nickel and palladium
Abdeslam El Hatimi,a Montserrat Gómez,*a Susanna Jansat,a Guillermo Muller,*a
Mercè Font-Bardíab and Xavier Solansb
a Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès, 1-11,
08028 Barcelona, Spain
b Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona,
Martí i Franquès s/n, 08028 Barcelona, Spain
Received 13th October 1998, Accepted 22nd October 1998
The co-ordination behaviour of the chiral bis(oxazoline) ligands ortho-, meta-, and para-bis[(4R)-4-ethyl-3,4-dihydro-
oxazol-2-yl]benzene (A, B, C, respectively) has been studied. Palladium and nickel complexes were synthesized and
characterized in solution and in the solid state. With regard to N,NЈ co-ordination, A gave bidentate monometallic
species, while B and C gave bimetallic compounds, with one or two bridging chiral molecules between two palladium
atoms. Complexes with the C2-symmetrical ligand A showed a loss of symmetry both in solution and in the solid
state, due to the phenyl spacer group between the two oxazoline moieties in the seven-membered ring. The crystal
structure of a monometallic complex has been determined. Palladation with these ligands was also tested. Ligand A
did not give metallated species, but B and C gave mono- and bis-cyclopalladated compounds, respectively.
Caryl–H bond was also investigated. In spite of the electron-
withdrawing oxazoline substituents, ligands B and C afforded
cyclometallated compounds.
Introduction
In last decade bis(oxazolines) have found efficient applications
in several asymmetric organic processes:1 Diels–Alder reactions
catalysed by different metals (Mn, Fe, Co, Ni, Cu, Zn);2 allylic
substitution (Pd);3 hydrosilylation of ketones (Rh);4 cyclo-
2'
2'
O
O
propanation of olefins (Cu);5 etc.
4'
4'
2
1
3'
1
3'
N
1'
5'
The increasing knowledge about metallic precursors has
enabled modifications of nitrogen ligands in order to achieve
better activity and selectivity in asymmetric organic reactions.
For some processes, precursors and intermediate catalytic
species have been isolated. For example, several studies (NMR
spectroscopy and X-ray diffraction) of ionic allylic palladium
complexes with N,NЈ-chelate ligands (precursors and inter-
mediate species in allylic substitutions) have been done,6 and
diaryloxycarbonylruthenium complexes (active species in
cyclopropanation reactions) have been characterized.7 How-
ever, for transformations such as copper-catalysed cyclopropan-
ations of olefins, the precursors and intermediates for the
catalytic cycles are only suggested by indirect evidence. The
postulated active species are carbene complexes, but, to date,
these compounds have not been isolated, due to their easy
decomposition.8
4
3
N
O
3
5'
1'
2
N
*
O
N
B
A
2'
O
4'
1
3'
N
5'
1'
2
N
O
C
In addition, theoretical and computational studies have been
used to obtain more information about organic processes and
precursors in order to correlate experimental data with calcu-
lated parameters.9
In general, the proposed interaction between the metal and
bis(oxazoline) ligand is chelation, giving monometallic N,NЈ-
bound metal precursors. However, for pybox ligands [pybox =
2,6-bis(3,4-dihydrooxazol-2-yl)pyridine],10 the ligand is three-
co-ordinated to the metal by pyridine and oxazoline nitrogen
atoms, and for aryl bis(oxazolines) the ligand may be co-
ordinated by carbon and nitrogen oxazoline atoms, as in the
terdentate palladium complex described recently.11
In this paper we describe the synthesis and characterization
of complexes of NiII and PdII with chiral bis(oxazoline) ligands.
We studied the N,NЈ-co-ordination behaviour of these ligands,
depending on the relative position of the oxazoline moieties
on the phenyl group. Therefore, we obtained mono- (for A)
and bi-metallic (for B and C) species. The activation of the
Results and discussion
Synthesis of bis(oxazoline) ligands
Ligands A, B and C [(R,R)-1,2-(EtOx)2C6H4, (R,R)-1,3-
(EtOx)2C6H4, and (R,R)-1,4-(EtOx)2C6H4, respectively] were
prepared following standard methods with minor modifications
(see Experimental section).12 Reactions between ortho-, meta-,
and para-bis(cyano)benzene and -(-)-2-aminobutanol, in the
presence of a catalytic amount of zinc chloride, produced good
yields of bis(oxazolines). The optical purity was analysed by
gas chromatography (β cyclodex chiral column). For ligands B
and C only one isomer was obtained, but for A a mixture of RR
(80%) and RS (20%) isomers was isolated. This diastereomeric
mixture was treated with nickel perchlorate in ethanol, yielding
an orange solid. This compound was recrystallized from aceto-
nitrile as orange crystals. From these crystals the isomer RS
J. Chem. Soc., Dalton Trans., 1998, 4229–4236
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Table 1 Selected 1H NMR dataa (δ, 500 MHz, CDCl3, 298 K) for complexes containing ligand A
Complex
5Ј
4Ј
3Ј
2Ј
Mesityleneb
1Aa
1.032 (t, 7.5)
1.080 (t, 7.5)
1.83 (dq, 8.5; 7.5)
1.98 (dq, 8.5; 7.5)
2.21 (dm, 7.5; 4.0)
2.62 (dm, 7.5; 4.0)
1.72 (dq, 7.5; 4.0)
2.72 (dm, 7.5; 4.0)
1.63 (m, 2 H)
4.16 (m)
4.77 (m)
4.28 (m)
4.30 (m)
4.68 (dd, 9.5; 9.0)
4.73 (dd, 10.0; 8.5)
4.29 (t, 7.5)
4.73 (dd, 10.0; 9.0)
4.15 (t, 8.5)
4.21 (dd, 8.5; 5.5)
4.61 (dd, 10; 8.5)
4.26 (t, 9.0)
4.37 (t, 8.5)
4.58 (dd, 10.0; 8.5)
n.d.
—
—
—
—
—
—
rac-1Aac
1.037 (t, 7.5)
4.83 (m)
major-2Aa
0.89 (t, 7.5)
1.09 (t, 7.5)
2.60 (m, 1 H)
0.44 (t, 7.5)
1.13 (t, 7.5)
3.50 (m)
4.84 (m)
4.30 (t, 9.0)
3.48 (m)
4.89 (m)
o-Me: 2.15; 2.28
p-Me: 2.89
Aromatic: 6.40; 6.56
o-Me: 2.12; 2.23
p-Me: 2.86
2.40 (m, 1 H)
minor-2Aa
0.73 (m)
1.78 (m)
2.05 (m)
2.52 (m)
1.76 (m, 2 H)
2.24 (m)
3.14 (m)
0.40 (m)
1.62 (m)
1.96 (m)
3.25 (m)
1.74 (m)
1.82 (m)
1.88 (m)
2.00 (m)
Aromatic: 6.36; 6.43
major-2Ab
minor-2Ab
0.88 (t, 7.5)
1.07 (t, 7.5)
4.80 (m, 2 H)
4.92 (m, 2 H)
4.45 (m, 4 H)
o-Me: 2.10; 2.88
p-Me: 3.46
Aromatic: 6.25; 6.42
o-Me: 2.08; 2.81
p-Me: 3.52
1.19 (t, 7.5)
0.38 (t, 7.5)
4.05 (m, 2 H)
4.20 (m, 2 H)
Aromatic: 6.20; 6.34
3Aa
1.05 (t, 7.5)
0.96 (t, 7.5)
4.30 (m)
4.33 (m)
4.52 (dd, 8.5; 7.5)
4.58 (dd, 8.5; 7.5)
5.10 (m, 4 H)
—
—
—
a Multiplicity (d, doublet; t, triplet; m, multiplet) and coupling constants (in Hz) in parentheses. b Multiplicity for mesitylene protons was singlet. c All
signals observed were of complex 1Aa plus rac-1Aa
[PdCl2(cod)]
O
O
Et
M
Et
M
CH2Cl2
Cl
Cl
Br
BrMg(mes)
THF
N
N
N
N
mes
NiCl2.6H2O
ethanol
Et
Et
O
O
M = Pd, 1Aa
M = Ni, 1Ab
M = Pd, 2Aa
M = Ni, 2Ab
O
Et
Et
N
N
2+
Pd(OAc)2
+
O
O
Et
NH4PF6, CH2Cl2
Et
N
N
N
N
O
M = Pd, Y = PF6, 3Aa
M = Ni, Y = ClO4, 3Ab
M
2 Y-
Et
Et
A
Ni(ClO4)2.6H2O
CH2Cl2
O
O
+
O
Et
Pd
Et
N
4Aa
[Pd(µ-Cl)(C3H5)]2
-
PF6
NH4PF6, CH2Cl2
N
O
Scheme 1
was recovered by deco-ordination (treatment with potassium
cyanide in ethanol, see Experimental section). Analogously,
from the solution, the isomer RR was isolated.
treatment with Grignard compound (2Aa, 2Ab), see Scheme 1.
The nickel complex 1Ab was paramagnetic; the magnetic
susceptibility value (3.17 µB) at room temperature is consistent
with two unpaired electrons, corresponding to a d8 electronic
configuration in a tetrahedral environment. Other neutral
N,NЈ-Co-ordination chemistry of bis(oxazoline) ligands
1
complexes were diamagnetic and their H NMR spectra were
With regard to N-donor behaviour, ligands A, B, and C differed
in the kind of metallic species that they could stabilize. Ligand
A gave monometallic complexes in which it is bidentate, where-
as B and C gave bimetallic compounds, in which they are
bridging.
studied (see Table 1).
The H NMR spectra for complex 1Aa at variable temper-
atures (313–233 K) showed that the two oxazoline fragments
were non-equivalent in the whole range (see Table 1). For the
C2-symmetrical ligand A the existence of isomers could be due
to the axial chirality. Upon co-ordination, rotation around
single bonds (Caryl–Coxazoline) is restricted by bonding to the two
1
For A, neutral palladium and nickel complexes (1Aa, 1Ab)
were synthesized by substitution of labile ligands, followed by
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Table 2 Selected bond lengths (Å) and bond angles (Њ) for complex
1Aa
Pd–N(1)
Pd–N(2)
Pd–Cl(1)
Pd–Cl(2)
2.010(5)
2.006(5)
2.297(2)
2.289(2)
N(1)–C(1)
N(1)–C(5)
N(2)–C(14)
N(2)–C(12)
1.469(7)
1.277(7)
1.506(8)
1.272(7)
N(1)–Pd–N(2)
N(1)–Pd–Cl(1)
85.8(2)
88.94(2)
N(2)–Pd–Cl(2)
N(2)–Pd–Cl(1) 174.66(13)
94.02(14)
N(1)–Pd–Cl(2) 179.2(2)
nitrogen atoms. So, an efficient bidentate co-ordination towards
a single metal atom in the aRaR or aSaS isomers is not
possible due to the highly strained ring (aR or aS means the
configuration of the chiral axis according to the Cahn–Ingold-
Prelog rules13). Therefore, only the aRaS isomer can stabilize
the non-planar seven-membered ring (see Chart 1, id refers to
equivalent ethyl groups). Thus, the C2-symmetry loss is due
to the bridged phenyl between two oxazoline moieties. The
X-ray diffraction determination of 1Aa (see Fig. 1) showed that
the C2 axis did not exist in the solid state, and showed two
non-equivalent oxazoline moieties and therefore, two non-
equivalent chloro positions. This behaviour contrasts with
other C2-symmetrical bidentate ligands {like CHIRAPHOS
[(2S,3S)-2,3-bis(diphenylphosphino)butane] or Pfaltz bis-
oxazolines} that co-ordinate to the metal center in a C2-
symmetrical fashion in solution, although they may show
asymmetrical distortions in the solid state.15 Complex 1Aa
showed the expected distorted square-planar co-ordination
geometry of the core PdCl2N2 (see Table 2). The Pd–N
distances (2.006–2.010 Å) and the Pd–Cl separations (2.297–
2.289 Å) are consistent with reported values for related com-
pounds.16 The torsion angles between each oxazoline moiety
and the phenyl group are 56.4 and 43.1Њ [N(2)–C(12)–C(11)–
C(6) and N(1)–C(5)–C(6)–C(11), respectively]. Although atrop-
oisomers may exist, due to the two chiral axes Pd–N, only one
isomer is observed (aRaS) in the solid state and in solution, as
discussed previously. The phenyl bridge between two oxazoline
fragments in the seven-membered ring breaks the C2 symmetry.
Fig. 1 An ORTEP view of the structure of complex 1Aa [PdCl2-
{(R,R)-1, 2-(EtOx)2C6H4}] showing the atom labelling scheme. Hydro-
gen atoms have been omitted for clarity.
co-ordination positions are equivalent, with only one type of
oxazoline group (see Table 1).
Ionic nickel and palladium complexes were also synthesized
from metallic salts (3Aa and 3Ab) and from neutral dimeric
species [{Pd(η3-C3H5)(µ-Cl)}2] (4Aa). Palladium ionic com-
plexes with bidentate ligands of formula [Pd(N–N)2]Y2 (where
N–N is phenanthroline or bipyridine derivative ligands) have
been known for a long time,17 due to their application in cata-
lytic processes. Van Leeuwen and co-workers18 have recently
described another synthetic route from [PdCl2(C6H5CN)2] in
two reaction steps, isolating neutral monosubstituted [PdCl2-
(N–N)] compounds as intermediates. In our study, a high yield
of [Pd(A)2][PF6]2 was obtained in one reaction step, starting
from palladium acetate and ammonium hexafluorophosphate.
During the course of this study, Milani et al.19 have also pub-
lished a one-pot synthesis method for preparing this kind of
ionic complex, using protonated bipyridine and phenanthrol-
ine ligands.
a
c
N
O
O
O
O
N
N
N
aSaR
aSaS
id
b
1
c
The H NMR study of these complexes showed that the
N
N
N
O
nickel complex 3Ab was very labile in solution. The ligand was
substituted by the solvent, either in co-ordinating (acetone,
acetonitrile) or non-co-ordinating solvents (chloroform,
dichloromethane) even at a low temperature. At variable tem-
peratures (223–298 K), in deuteriated chloroform solution, the
‘free’ ligand spectrum was observed over the whole range. How-
ever, the analogous palladium complex, 3Aa, was less labile,
exhibiting only partial deco-ordination, of A after 24 h in
chloroform or dichloromethane solutions. This complex is
expected to be a mixture of two isomers, syn and anti, depend-
ing on the position of the bridge phenyl relative to the co-
ordination sphere. However, the syn complex is less stable due
to steric interactions, as shown by molecular mechanics calcu-
O
O
N
O
aRaR
aRaS
Chart 1
The 1H NMR spectra for complexes 2Aa and 2Ab confirmed
the non-equivalence of the two co-ordination positions trans-
to N atoms due to the formation of two isomers, in a relative
proportion of 2:1, depending on the halogen position substi-
tuted by the organic group. This non-statistical ratio reflects the
larger steric hindrance between ethyloxazoline and mesitylene
groups in the minor isomer. So, mesitylene exhibited two pairs
of singlets in its aromatic region (δ 6–6.6) and two groups of
three singlets in its methyl zone of the two different mesityl-
ene groups (δ 2–3). In addition, four oxazoline moieties were
distinguished (see Table 1). For 2Aa the major isomer was
separated by recrystallization.
Palladium complexes with rac-A were also prepared: rac-1Aa
and rac-2Aa. The spectra of these complexes exhibited the sum
of two diastereoisomers: RaRaSR (equivalent to SaRaSS) and
RaRaSS (SaRaSR). The resonances of the former isomer have
been analysed above. In the meso form, for rac-1Aa, both chloro
1
lations. The H NMR spectrum showed one isomer, with two
inequivalent oxazoline moieties (see Table 1).
The 1H NMR spectra for the allylic palladium complex 4Aa
showed a dynamic behaviour and broad signals were observed
in the temperature range studied (223–323 K).
For ligands B and C, bimetallic species with one and two
bridging ligands were prepared (see Scheme 2). The reaction
between B or C and starting palladium complexes [PdCl-
(X)(cod)], where X = chloride or methyl group, afforded bis-
J. Chem. Soc., Dalton Trans., 1998, 4229–4236
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Table 3 Selected 1H NMR dataa (δ, 500 MHz, CDCl3, 298 K) for complexes with ligands B and C
Complex
5Ba
5Ј
4Ј
3Ј
2Ј
Other
b
1.15 (m)
1.55 (m)
1.75 (m)
1.60 (m)
1.80 (m)
2.05 (m)
2.15 (m)
2.42 (m)
3.38 (m)
3.94 (m)
4.35 (m)
aromatic: 7.45 to 9.91 (m)
8Bac
0.93 (t, 7.5)
0.95 (t, 7.5)
4.50 (m)
4.43 (m)
4.10 (m)
4.70 (m)
allyl: Hcentral 5.40 (h); Hanti 2.73, 2.83, 2.95, 2.99
(d, 12); Hsyn 4.30 (m), 3.60, 4.0 (d, 6)
9Ba
1.31 (t, 7.5)
1.32 (t, 7.2)
1.91 (t, 7.7)
1.95 (t, 6.5)
0.99 (m)
0.88 (t); 0.91 (t);
1.13 (t); 1.14 (t)
(7.5)
4.49 (m)
4.50 (m)
4.7 (m)
4.82 (m)
4.63 (m)
4.21; 4.28;
4.65; 4.70 (m)
aromatic: 8.01 (pdd, 7.7, 1.7)
7.53 (m)
10Ba
6Ca
1.50 (m)
1.30; 1.44;
2.10; 2.96 (m)
4.65 (m)
4.60 (m)
aromatic: 6.9–7.7 (m)
aromatic: 7.50; 7.68 (m); 9.2–9.0 (m)
7Ca
1.01 (t, 7.7)
1.27 (m)
2.60 (m)
2.15 (m)
2.95 (m)
2.16 (m)
2.98 (m)
4.60 (m)
4.14 (m)
4.57 (m)
4.30 (pt, 8.4)
4.67 (pt, 8.6)
4.32 (t, 7.9)
4.70
aromatic: 8.71–9.25
aromatic: 8.89–9.22
11Ca
12Ca
1.15 (t, 7)
1.16 (t, 6)
1.17 (t, 7.5)
4.57 (m)
4.69 (m)
4.60 (m)
aromatic: 9.01 (s)
7.71 (m)
(dd, 7.9, 9.8)
7.42 (m)
δ(31P) 29.6
a Multiplicity (d, doublet; h, heptuplet; p. pseudo; t, triplet; m, multiplet) and coupling constants (in Hz) in parentheses. b Overlapped signal.
c Measured at 223 K.
*
N
N
N^N = B, X = X' = Cl, 5Ba
N^N = C, X = X' = Br, 6Ca
N^N = C, X = Cl, X' = Me, 7Ca
[PdClX(cod)]
CH2Cl2
X
X
Pd
N
Pd
N
O
O
X'
X'
N
N
Et
Et
*
B
+
O
Et
O
N
*
O
Et
Pd
Et
N
8Ba
[Pd(η3-C3H5)(µ-Br)]2
Br
N
N
Pd
CH2Cl2
O
Et
*
C
Br
Scheme 2
(oxazoline)bispalladium compounds (5Ba, 6Ca and 7Ca). The
differentiated, with two non-equivalent anti and syn protons for
each. The aromatic zone was more complicated, with different
configurations at low temperatures due to the slow rotation, on
the NMR timescale, around single Caryl–Coxazoline bonds. Any
contribution of the π–σ–π allyl movement was not detected.
complexes were characterized by NMR spectroscopy (see Table
1
3). The H NMR spectrum for 6Ca showed eight signals of
the same intensity in the aromatic region, showing the non-
equivalence of the two bridging ligands.
Starting from the allylic palladium complex [{PdBr(η3-C3H5)-
(µ-Br)}2] a bimetallic compound with B was also obtained, but
with only one bridging ligand, 8Ba, even with an excess of lig-
and. Proton NMR studies were carried out at different temper-
atures (323–223 K). For the allyl group, Hcentral exhibited one
signal at δ 5.5 in the whole temperature range, with a narrow
pseudo heptuplet at 323 K. Above room temperature, Hanti and
Hsyn of the allyl system showed one broad signal each (δ 3.0
and 4.0, respectively). At room temperature, Hsyn split into two
broad signals and at 273 K both protons showed two broad
signals, being sharper and more defined at 223 K: Hanti showed
four doublets at δ 2.80 (12 Hz) and Hsyn showed two doublets
and a multiplet at δ 3.80 (6.0 Hz) and 4.40, respectively. Coales-
cence between Hanti and Hsyn was not observed in the range of
temperatures studied. Therefore, allylic rotation around the Pd–
π–allyl group was slow enough on the NMR timescale for
distinguishing allylic protons. At 223 K two allyl groups are
Palladation chemistry of bis(oxazoline) ligands
It is well known that the cyclopalladation reaction proceeds by
an electrophilic attack by the metal on the aryl group,20 this
being favoured when electron donating ligands are bonded, in
ortho and para positions, to the metallated carbon. However, in
the literature, there are several examples of the activation of
C–H with electron-withdrawing substituents.21 Also, for the
oxazoline group, which is a strong electron-withdrawing sub-
stituent, cyclometallated compounds have been described with
one oxazoline moiety on the aromatic system.22 However,
metallation may be less favoured with two oxazoline substitu-
ents on the phenyl group. Moreover, steric factors may be very
important, impeding the process if the substituent ortho to the
metallation is not co-ordinating. For B and C the positions to
be activated are indicated by an arrow in Scheme 3.
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J. Chem. Soc., Dalton Trans., 1998, 4229–4236

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1
For B, two different cases are possible: mono- and bis-
metallation, depending on the activated Caryl–H bond. If
position 3 were activated, bis-cyclometallated compounds
would be isolated. Meanwhile, if activation was in position 2,
monopalladation would be observed. When 1 equivalent of B
reacted with 2 equivalents of Na2PdCl4 only co-ordination
products were obtained. However, when 1 equivalent of B
reacted with 1 equivalent of Pd(O2CMe)2 a monopalladated
product was isolated (9Ba), after refluxing for three days (see
Scheme 4). The 1H NMR spectrum for 9Ba exhibited the loss of
the aromatic proton between the two oxazoline moieties. In
addition, two sets of signals for oxazoline protons were
observed, showing a non-symmetrical structure in solution.
This behaviour showed that the formation of a terdentate com-
pound is favoured, although the activated position is ortho to
two electron-withdrawing groups. These results are consistent
with the formation of a terdentate complex with a meta-
bis(oxazoline) ligand, by an oxidative addition reaction.11
For C, a symmetrical bis-metallated compound was isolated
(11Ca) by reaction with Na2PdCl4 (see Scheme 4). When 9Ba
and 11Ca were treated with triphenylphosphine, mono- (10Ba)
and bi-metallic (12Ca) complexes were obtained, respectively.
The H NMR spectrum for 12Ca showed a symmetrical com-
pound, with one resonance for the aromatic protons of the
oxazoline groups (singlet at δ 9.00) and only one kind of oxazo-
line protons (see Table 3). The ratio between oxazoline and
phosphine signals is in agreement with one oxazoline group per
triphenylphosphine ligand.
For A no metallation was observed with Na2PdCl4 or
Pd(O2CMe)2. In both cases, only co-ordination products were
isolated.
Conclusion
A series of bis-oxazolines, based on the relative position of the
two oxazoline moieties on the phenyl group, allowed a study of
N,NЈ-co-ordination behaviour, as well as a study of Caryl–H
bond activation. The proximity of two nitrogen atoms when the
ortho-bis(oxazoline), A, interacts with a metal center facilitates
chelate co-ordination, while for meta- and para-bis(oxazoline)
ligands, B and C, only bridging co-ordination is observed. The
most interesting structural feature for A is the loss of C2 sym-
metry when it is co-ordinated in an N,NЈ-bidentate way. There-
fore, for complexes with A, two trans positions to nitrogen
atoms are non-equivalent, both in the solid state and in solu-
tion, and isomers can be distinguished in halogen substitution
processes, as in the formation of 2Aa and 2Ab. This co-
ordination behaviour explains the low asymmetric induction
observed with ortho-bis(oxazolinyl)aryl ligands in organic
transformations, such as Cu-catalysed cyclopropanations5 or
Pd-catalysed allylic substitutions.3 In the latter case the nucleo-
phile has different, but similar energetic positions to attack on
the substrate and hence more accessible transition states, and
thus low enantiomeric excesses are obtained. In addition,
cyclopalladation processes enable metallacycles to be obtained
with B and C. Ligand C stabilizes bis-metallated compounds by
two Caryl–H bond activations on the phenyl group, while for B a
terdentate complex is obtained due to selective activation of the
Caryl–H bond between two oxazoline substituents.
O
Et
N
O
O
O
N
N
N
Et
Et
Et
B
C
O
Et
Pd
N
O
O
N
N
N
Pd
Pd
Br
Experimental
General
Et
Et
Et
O
All compounds were prepared under a purified nitrogen atmos-
Scheme 3
O
O
O
i) Pd(O2CMe)2, HO2CMe
ii) LiBr, acetone
PPh3, acetone
O
O
N
Et
N
N
O
*
N
Pd
PPh3
N
Pd
Br
N
Et
Et
Et
Et
Br
Et
B
9Ba
10Ba
2
PPh3
Cl
N
Cl
Pd
O
Pd
Et
O
N
O
Et
N
Et
PPh3, acetone
Na2PdCl4, MeOH
O
Et
N
Et
N
O
O
N
Pd
Pd
Cl
Et
Ph3P
Cl
C
2
12Ca
11Ca
Scheme 4
J. Chem. Soc., Dalton Trans., 1998, 4229–4236
4233

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phere using standard Schlenk and vacuum-line techniques. The
solvents were purified by standard procedures24 and distilled
under nitrogen. -(-)-2-Aminobutanol (Janssen) was used with-
out previous purification, ZnCl2 (Merck) was purified by the
standard procedure24 and [{PdCl(η3-C3H5)(µ-Cl)}2],25 [PdCl2-
(cod)],26 and [PdCl(Me)(cod)]27 were prepared as described
previously. The NMR spectra were recorded on Varian XL-500
(1H, standard SiMe4), Gemini (13C, 50 MHz, standard SiMe4),
and Bruker DRX 250 (31P, 101 MHz, standard H3PO4)
spectrometers. Chemical shifts are reported downfield from
standards. The IR spectra were recorded on a Nicolet 520 FT-
IR spectrometer. The FAB mass chromatograms were obtained
on a Fisons V6-Quattro instrument. The GC analysis, for chiral
ligands, was performed on a Hewlett-Packard 5890 Series II gas
chromatograph [25 m FS-cyclodex-β-I/P column: heptakis-
(2,3,6-tri-O-methyl)-β-cyclodextrin–polysiloxane] with a flame
ionization detector. The GC-MS analysis was performed on
a Hewlett-Packard 5890 Series II gas chromatograph (50 m
Ultra 2 capillary column) interfaced to a Hewlett-Packard 5971
mass selective detector. Magnetic measurements were carried
out at variable temperature (300–4 K) on polycrystalline sam-
ples with a pendulum type magnetometer (Manics DSM8)
equipped with a Drusch EAF 16 UE electromagnet. The mag-
netic field was approximately 1.5 T. Diamagnetic corrections
were estimated from Pascal’s tables. Optical rotations were
measured on a Perkin-Elmer 241 MC spectropolarimeter. Con-
ductivities were obtained on a Radiometer CDM3 conducti-
meter. Elemental analyses were carried out by the Serveis
Cientifico-Tècnics de la Universitat de Barcelona in an Eager
1108 microanalyzer. The molecular mechanics calculations
were performed using the Spartan program, version 5.0 (Wave-
function Inc., Irvine, CA, USA, 1997).
5.50 mmol) and A (1.50 g, 5.50 mmol) were dissolved in 30 cm3
of dichloromethane at room temperature and stirred for 8 h
(the reaction was monitored by TLC until no free A was
observed). The reaction mixture was filtered over Celite, con-
centrated to ca. 15 cm3 under reduced pressure and hexane
added. A yellow solid separated, which was recrystallized from
dichloromethane and diethyl ether (1.94 g, 78%), mp
(decomp.) = 130 ЊC. (Found: C, 42.53; H, 4.66; N, 6.22. Calc.
for C16H20Cl2N2O2Pd: C, 42.74; H, 4.48; N, 6.23%). MS (FAB
positive): m/z 415 (M Ϫ Cl), 377 (M Ϫ 2 Cl), 272 (A).
{1,2-Bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene-N,NЈ}-
dichloronickel(II) 1Ab. The compound NiCl2ؒ6H2O (1.31 g,
5.50 mmol) and A (1.50 g, 5.5 mmol) were dissolved in 30 cm3
of absolute ethanol. The reaction mixture was warmed to 60 ЊC
for 24 h (the reaction was monitored by TLC until no free A was
observed), filtered, concentrated to ca. 15 cm3 under reduced
pressure, and hexane added. A blue solid was obtained after
cooling the solution in a refrigerator overnight. The product
was separated by filtration, washed with diethyl ether and dried
under reduced pressure (1.16 g, 54%), mp (decomp) = 70 ЊC
(Found: C, 47.31; H, 5.33; N, 7.08. Calc. for C16H20Cl2N2NiO2:
C, 47.81; H, 5.02; N, 6.97%). MS (FAB positive): m/z 366
(M Ϫ Cl), 330 (M Ϫ 2 Cl), 272 (A).
{1,2-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene-N,NЈ}-
bromo(2,4,6-trimethylphenyl)metal(II), 2Aa (M ؍ Pd) and 2Ab
(M ؍ Ni). A THF solution 16 cm3 (3.8 mmol) of the Grignard
compound, BrMg(Mes) (Mes = mesityl),† was added slowly
over a solution of the dichloro derivative (1Aa 0.85 g, 1.9
mmols; 1Ab, 0.5 g, 1.24 mmol) in 25 cm3 of THF. The reaction
mixture was stirred for 30 min at room temperature. Excess of
Grignard compound was eliminated by hydrolysis with distilled
water. The organic phase was dried over anhydrous Na2SO4,
filtered, concentrated to ca. 15 cm3 under reduced pressure, and
hexane added. A white solid was obtained after cooling the
solution in a refrigerator overnight. The product was separated
by filtration, washed with diethyl ether and dried under reduced
pressure (2Aa, 0.72 g, 66%; 2Ab, 0.66 g, 65%). For 2Aa: mp
(decomp) = 133 ЊC (Found: C, 56.17; H, 5.92; N, 4.83. Calc. for
C25H31BrN2O2Pd: C, 51.97; H, 5.41; N, 4.85%). MS (FAB posi-
tive) m/z 495 (M Ϫ Br), 377 (M Ϫ Br Ϫ Mes), 272 (A). For 2Ab:
mp (decomp) = 160 ЊC (Found: C, 56.34; H, 6.02; N, 5.66. Calc.
for C25H31BrN2NiO2: C, 56.64; H, 5.89; N, 5.29%). MS (FAB
positive) m/z 447 (M Ϫ Br), 330 (M Ϫ Br Ϫ Mes), 272 (A).
Syntheses
1,x-Bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene ligands:
A (x ؍ 2), B (x ؍ 3), and C (x ؍ 4). The oxazolines A, B and C
were synthesized following published procedures with minor
modifications.12,28 -(-)-2-Aminobutanol (6.63 g, 74.40 mmol),
1,x-bis(cyano)benzene (x = 2, 3 or 4; 2.5 g, 19.50 mmol), and
ZnCl2 (180 mg, 1.32 mmol) were dissolved in 25 cm3 of toluene
and refluxed under nitrogen for some hours (24 h, for A; 96 h,
for B; 72 h, for C), until no nitrile was observed (reaction moni-
tored by gas chromatography). The reaction mixture was fil-
tered, washed with water, and the organic phase dried over
anhydrous Na2SO4 and distilled under vacuum, affording a
yellow oil. The product was purified by SiO2 column chrom-
atography (ethyl acetate–hexane, 2:1 for A and B, 4:1 for C).
For A, a mixture of diastereoisomers was obtained, RR (80%)
and RS (20%). Yields: A 4.47 g, 84%; B 2.23 g, 50%; C 3.73 g,
70%. [α]D25 = ϩ100 (A); ϩ135.44 (B); ϩ120.05 deg cm3 gϪ1
dmϪ1 (C) (c 0.1 g per 100 cm3, CHCl3). 1H NMR data (CDCl3,
500 MHz): A, δ 0.99 (H5Ј, 3 H, t, J 7.2); 1.62 (H4Ј, 1 H, m); 1.73
(H4Ј, 1 H, m); 4.20 (H3Ј, 1 H, m); 3.98 (H2Ј, 1 H, t, J 8.0); 4.42
(H2Ј, 1 H, dd, J 9.0, 8.0 Hz); 7.73 (H2, 1 H, m); 7.44 (H3, 1 H,
m); B, δ 0.98 (H5Ј, 6 H, t, J 7.2); 1.59 (H4Ј, 2 H, m); 1.74 (H4Ј, 2
H, m); 4.23 (H3Ј, 2 H, m); 4.04 (H2Ј, 2 H, t, J 8.0); 4.46 (H2Ј, 2
H, dd, 9.0, J 8.0); 8.47 (H2, 1 H, t, J 1.5 Hz); 8.04 (H3, 2 H, dd,
8.0, J 1.5); 7.42 (H4, 1 H, t, J 8.0 Hz); C, δ 0.96 (H5Ј, 3 H, t,
J 7.2); 1.59 (H4Ј, 1 H, m); 1.75 (H4Ј, 1 H, m); 4.20 (H3Ј, 1 H,
m); 4.03 (H2Ј, 1 H, t, J 8.0); 4.46 (H2Ј, 1 H, dd, 9.0, J 8.0 Hz);
7.95 (H2, 2 H, s). 13C NMR data (CDCl3, 50 MHz): A, δ 9.1
(C5Ј); 27.4 (C4Ј); 67.3 (C3Ј); 71.6 (C2Ј); 127.5 (C1); 128.8, 128.4
(C2); 129.3 (C3), 162.7 (C1Ј); B, δ 9.9 (C5Ј); 28.6 (C4Ј); 68.0
(C3Ј); 72.2 (C2Ј); 128.2 (C1); 128.1, 128.4 (C2, C5); 130.8 (C4),
162.8 (C1Ј); C, δ 10.0 (C5Ј); 28.6 (C4Ј); 68.1 (C3Ј); 72.3 (C2Ј);
130.3 (C1); 128.1 (C2); 162.9 (C1Ј).
Bis{1,2-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene-
N,NЈ}palladium(II) hexafluorophosphate 3Aa. To a solution of
Pd(O2CMe)2 (0.50 g, 2.23 mmol) in 25 cm3 of CH2Cl2 was
added NH4PF6 (1.0 g, 4.46 mmol). Then, the ligand A (1.20 g,
4.41 mmol) was added and the reaction mixture stirred at room
temperature for 24 h, yielding a white solid. The product was
filtered off and washed with distilled water several times until
ammonium salts were removed. The solid was then washed with
diethyl ether and dried under reduced pressure (1.80 g, 86%),
mp (decomp.) = 281 ЊC. (Found: C, 40.50; H, 4.13; N, 6.00.
Calc. for C32H40F6N4O4PPd: C, 40.84; H, 4.28; N, 5.95%). MS
(FAB positive) m/z 795 (M2ϩ ϩ PF6), 650 (M2ϩ), 377
(M2ϩ Ϫ A).
Bis{1,2-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene-
N,NЈ}nickel(II) perchlorate 3Ab. The salt Ni(ClO4)2ؒxH2O (0.50
g, 1.94 mmol) and A (1.06 g, 3.88 mmol) were dissolved in 30
cm3 of absolute ethanol. The reaction mixture was stirred at
room temperature for 30 min, yielding a pale yellow solid. The
† Prepared by reaction of magnesium metal (0.5 g, 20 mmol) with
bromomesitylene (1.51 cm3, 10 mmol) in 20 cm3 of THF, at 40 ЊC for
1 h. The reaction was monitored by GC.
{1,2-Bis[(4R)-(4-ethyl-3,4-dihydrooxazol-2-yl]benzene-N,NЈ}-
dichloropalladium(II) 1Aa. The compound [PdCl2(cod)] (1.57,
4234
J. Chem. Soc., Dalton Trans., 1998, 4229–4236

View Article Online
product was separated by filtration, washed with diethyl ether
and dried under reduced pressure (1.39 g, 89%), mp (decomp.) =
195 ЊC (Found: C, 47.54; H, 5.26; N, 7.01. Calc. for C32H40-
Cl2N4NiO12: C, 47.90; H, 5.03; N, 6.98%). MS (FAB positive)
m/z 602 (M2ϩ), 330 (M2ϩ Ϫ A).
N2O2Pd: C, 41.98; H, 4.15; N, 6.12%). MS (FAB positive):
m/z 377 (M Ϫ Br).
{2,6-Bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl)]phenyl-C,N}-
bromo(triphenylphosphine)palladium(II) 10Ba. Complex 9Ba
(0.25 g, 0.27 mmol) and triphenylphosphine (0.14 g, 0.54 mmol)
were dissolved in 10 cm3 of dichloromethane. The reaction mix-
ture was refluxed for 3 h (the reaction was monitored by 31P
NMR until no free phosphine was observed), then filtered over
Celite and the solvent removed under reduced pressure, afford-
ing a brown solid. The product was separated by filtration and
recrystallized from dichloromethane and hexane (0.09 g, 50%),
mp (decomp.) = 165 ЊC (Found: C, 56.40; H, 4.68; N, 3.96. Calc.
for C34H34BrN2O2PPd: C, 56.72; H, 4.76; N, 3.89%). MS (FAB
positive): m/z 639 (M Ϫ Br).
Deco-ordination of complex 3Ab. To complex 3Ab (1.0 g, 1.25
mmol) and potassium cyanide (0.52 g, 8 mmol) 20 cm3 of etha-
nol were added. The reaction mixture was stirred at room tem-
perature until a colorless solution was obtained. The solvent
was then removed under reduced pressure, and 25 cm3 of
dichloromethane was added. The mixture was washed with
water until no free cyanide was observed in the aqueous phase.
The organic phase was dried over anhydrous Na2SO4, filtered
off, and the solvent removed under reduced pressure, affording
a white oil.
Bis{ì-1,4-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene-
N,NЈ}tetrabromodipalladium(II) 6Ca. The compound Pd(O2-
CMe)2 (1.23 g, 5.50 mmol) and C (1.50 g, 5.50 mmol) were
dissolved in 20 cm3 of chloroform. The reaction mixture was
warmed at 40 ЊC for 24 h (the reaction was monitored by TLC
until no free C was observed), then filtered over Celite and the
solvent removed under reduced pressure, affording a dark
brown oil which was dissolved in 10 cm3 of CH2Cl2. Lithium
bromide (0.54 g, 6.18 mmol) was then added and the reaction
mixture stirred at room temperature for 1 h. The mixture was
again filtered over Celite and 10 cm3 of diethyl ether were
added. A brown solid was obtained after cooling the solution in
a refrigerator overnight. It was filtered off and recrystallized
from dichloromethane and diethyl ether, affording a dark red
solid (0.99 g, 50%), mp (decomp.) = 170 ЊC (Found: C, 35.56; H,
5.18; N, 3.72. Calc. for C16H20Br2N2O2Pd: C, 35.65; H, 5.10; N,
3.74%). MS (FAB positive): m/z 916 (M Ϫ 2 Br), 837 (M Ϫ 3
Br), 728 (M Ϫ 4 Br Ϫ C2H5).
(ç3-Allyl){1,2-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]-
benzene-N,NЈ}palladium(II) hexafluorophosphate 4Aa. To a
solution of di-µ-chloro-bis[(η3-allyl)palladium] (0.34 g, 0.75
mmol) in 20 cm3 of absolute ethanol were added NH4PF6 (0.24
g, 1.5 mmol) and A (0.41 g, 1.5 mmol). The reaction mixture
was stirred at room temperature for 3 h (the reaction was moni-
tored by TLC until no free A was observed), then concentrated
to ca. 10 cm3 under reduced pressure and hexane added, pro-
ducing a white solid. The product was filtered off, washed with
diethyl ether and dried under reduced pressure (0.28 g, 76%),
mp (decomp.) = 140 ЊC (Found: C, 40.51; H, 4.62; N, 5.15. Calc.
for C19H25F6N2O2PPd: C, 40.41; H, 4.46; N, 4.96%). MS (FAB
positive) m/z 421 (Mϩ), 650 (M2ϩ), 377 (Mϩ Ϫ A), 272 (A).
Bis{ì-1,3-bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]benzene-
N,NЈ}tetrachlorodipalladium(II) 5Ba. The complex [PdCl2(cod)]
(0.40 g, 1.40 mmol) and B (0.38 g, 1.40 mmol) were dissolved in
30 cm3 of dichloromethane. The reaction mixture was stirred at
room temperature for 5 h (the reaction was monitored by TLC
until no free B was observed), then concentrated to ca. 15 cm3
under reduced pressure and hexane added. A yellow solid was
obtained after cooling the solution in a refrigerator overnight.
The product was separated by filtration and recrystallized from
dichloromethane and diethyl ether, producing an orange solid
(0.30 g, 60%), mp (decomp.) = 200 ЊC (Found: C, 42.65; H,
4.45; N, 3.23. Calc. for C16H20Cl2N2O2Pd: C, 42.70; H, 4.48; N,
3.13%). MS (FAB positive): m/z 828 (Mϩ Ϫ 2Cl).
Bis{ì-1,4-bis[(4R)-(4-ethyl-3,4-dihydrooxazol-2-yl]benzene-
N,NЈ}dichlorodimethyldipalladium(II) 7Ca. The complex [PdCl-
(Me)(cod)] (0.10 g, 0.38 mmol) and C (0.103 g, 0.38 mmol) were
dissolved in 20 cm3 of dichloromethane. The reaction mixture
was stirred at room temperature for 4 h (the reaction was moni-
tored by TLC until no free C was observed). The solvent was
removed under reduced pressure, and diethyl ether then added.
A white solid was obtained after cooling the solution in a
refrigerator overnight. The product was separated by filtration
and recrystallized from dichloromethane and diethyl ether (0.16
g, 50%), mp (decomp.) = 185 ЊC (Found: C, 47.48; H, 5.42;
N, 6.88. Calc. for C17H23ClN2O2Pd: C, 47.57; H, 5.40; N,
6.53%). MS (FAB positive): m/z 828 (M Ϫ Cl), 757 (M Ϫ 2
Cl Ϫ 2 Me).
Bis(ç3-allyl)-ì-{1,3-bis(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]-
benzene-N,NЈ}dibromo-dipalladium(II) 8Ba. Di-(µ-bromo)-bis-
[(η3-allyl)palladium] (1.36 g, 3.0 mmol) and B (0.40 g, 1.50
mmol) were dissolved in 20 cm3 of CH2Cl2. The reaction mix-
ture was stirred under reflux for 3 h (the reaction was monitored
by TLC until no free B was observed), then concentrated to ca.
10 cm3 under reduced pressure and hexane added. A yellow
solid was obtained after cooling the solution in a refrigerator
overnight. The product was separated by filtration and
recrystallized from dichloromethane and hexane (0.96 g, 93%),
mp (decomp.) = 200 ЊC (Found: C, 35.92; H, 4.21; N, 3.81. Calc.
for C11H15BrNOPd: C, 36.34; H, 4.16; N, 3.85%). MS (FAB
positive): m/z 645 (M Ϫ Br), 564 (M Ϫ 2 allyl Ϫ Br).
{2,5-Bis[(4R)-(4-ethyl-3,4-dihydrooxazol-2Ј-yl]phenyl-C,N}-
dichlorobis(triphenylphosphine)dipalladium(II) 12Ca. The com-
pound PdCl2 (0.18 g, 1.0 mmol) and LiCl (0.085 g, 2 mmol)
were dissolved in 10 cm3 of methanol and 3 cm3 of water. The
mixture was warmed to 40 ЊC and stirred for 6 h until the
palladium chloride dissolved. Ligand C (0.14 g, 0.5 mmol)
dissolved in 8 cm3 of methanol was then added. The reaction
mixture was refluxed for 1 d. The yellow solid (11Ca) obtained
was separated by filtration and washed with diethyl ether. This
residue (0.30 g) was treated with triphenylphosphine (0.18 g,
0.66 mmol) in 10 cm3 of chloroform. The reaction mixture was
refluxed for 2 h (the reaction was monitored by 31P NMR until
no free phosphine was observed). The solvent was removed
until ca. 5 cm3 and diethyl ether added. A yellow solid was
obtained after cooling the solution in a refrigerator overnight.
The product was separated by filtration, washed with diethyl
ether and dried under reduced pressure (0.27 g, 60%). The
product was purified by column chromatography (SiO2) with
diethyl ether and ethyl acetate (1:1) as an eluent, mp
(decomp.) = 215 ЊC (Found: C, 56.48; H, 4.28; N, 2.35. Calc. for
{2,6-Bis[(4R)-4-ethyl-3,4-dihydrooxazol-2-yl]phenyl-C,N,NЈ}-
bromopalladium(II) 9Ba. The compound Pd(O2CMe)2 (0.23 g,
1.0 mmol) and B (0.14 g, 0.50 mmol) were dissolved in 10 cm3
of chloroform. The reaction mixture was refluxed for 3 d (the
reaction was monitored by TLC until no free B was observed).
Lithium bromide (0.09 g, 1 mmol) was then added and the
mixture refluxed for 2 h, filtered over Celite and the solvent
removed under reduced pressure. After addition of diethyl ether
a yellow solid was obtained, which was recrystallized from
dichloromethane and hexane (0.78 g, 45%), mp (decomp.) =
180 ЊC (Found: C, 41.00: H, 4.10; N, 6.30. Calc. for C16H19Br-
J. Chem. Soc., Dalton Trans., 1998, 4229–4236
4235

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Table 4 Crystal data for complex 1Aa
2 J. M. Takacs, D. A. Quincy, W. Shay, B. E. Jones and C. R.
Ross, Tetrahedron: Asymmetry, 1997, 8, 3079; S. Kanemasa,
Y. Oderaotoshi and D. P. Curran, J. Org. Chem., 1997, 62, 6454.
3 G. Chelucci, Tetrahedron: Asymmetry, 1997, 8, 2667.
4 S.-G. Lee, C. W. Lim, C. E. Song, I. O. Kim and C.-H. Jun,
Tetrahedron: Asymmetry, 1997, 8, 2927.
5 A. V. Bedekar, E. B. Koroleva and P. G. Andersson, J. Org. Chem.,
1997, 62, 2518.
6 B. M. Trost and D. L. van Vranken, Chem. Rev., 1996, 96, 395 and
references therein.
7 S.-B. Park, N. Sakata and H. Nishiyama, Chem. Eur. J., 1996, 2, 303.
8 T. Ye and A. Mckervey, Chem. Rev., 1994, 94, 1091.
9 J. D. Oslob, B. Åkermark, P. Helquist and P.-O. Norrby,
Organometallics, 1997, 16, 3015.
10 H. Nishiyama, Y. Itoh, H. Matsumoto, S.-B. Park and K. Itoh,
J. Am. Chem. Soc., 1994, 116, 2223; H. Nishiyama, Y. Itoh,
Y. Sugawara, H. Matsumoto, K. Aoki and K. Itoh, Bull. Chem. Soc.
Jpn., 1995, 68, 1247.
Formula
M
Crystal dimensions/mm
T/K
Crystal system
Space group
a/Å
b/Å
C16H20Cl2N2O2Pd
449.64
0.1 × 0.1 × 0.2
293
Orthorhombic
P212121
10.498(4)
11.953(9)
14.112(2)
1771(2)
c/Å
V/Å3
Z
4
Dc/g cmϪ3
1.687
Final R1, wR2 [I > 2σ(I)]
(all data)
Goodness of fit
0.0422, 0.0948
0.0513, 0.1385
1.057
11 S. E. Denmark, R. A. Stavenger, A.-M. Faucher and J. P. Edwards,
J. Org. Chem., 1997, 62, 3375; Y. Motoyama, N. Makihara,
Y. Mikami, K. Aoki and H. Nishiyama, Chem. Lett., 1997, 951.
12 C. Bolm, K. Weickhardt, M. Zehnder and T. Ranff, Chem. Ber.,
1991, 124, 1173.
13 R. S. Cahn, C. Ingold and V. Prelog, Angew. Chem., Int. Ed. Engl.,
1966, 5, 385.
C26H24ClNOPPd: C, 57.91; H, 4.48; N, 2.60%). MS (FAB posi-
tive): m/z 1042 (M Ϫ Cl), 1007 (M Ϫ 2 Cl).
Crystallography
The crystallographic data for complex 1Aa are summarized in
Table 4. Crystals were obtained by slow diffusion of diethyl
ether over a dichloromethane solution of the complex.
The crystal data were measured on an Enraf-Nonius CAD4
four circle diffractometer. Unit-cell parameters were deter-
mined from automatic centering of 25 reflections (12 < θ < 21Њ)
and refined by the least-squares method. Intensities were col-
lected with graphite monochromatized Mo-Kα radiation
(λ = 0.71069 Å), using the ω–2θ scan technique. 2626 Reflec-
tions were measured in the range 2.23 < θ < 29.95Њ, 2603 of
which were non-equivalent by symmetry [Rint (on I) = 0.017].
2404 Reflections were assumed observed [I > 2θ(I)]. Three
reflections were measured every 2 h as orientation and intensity
controls, and significant intensity decay was not observed.
Lorentz-polarization but not absorption corrections were
made.
The structure was solved by direct methods, using the
SHELXS computer program28 and was refined by the full-
matrix least-squares method with the SHELXL 93 computer
program,29 using 2553 reflections (very negative intensities were
ignored). The function minimized was Σw |Fo|2 Ϫ Fc|2|2, where
w = [σ2(I) ϩ (0.0610 P)2]Ϫ1, and P = (|Fo|2 ϩ 2|Fc|2)/3 values of f,
f Ј and f Љ were taken from ref. 30. The extinction coefficient was
0.0000(8). The chirality of the structure was defined from the
Flack coefficient,31 0.03(6). Nine H atoms were located by a
difference synthesis and refined with an overall isotropic ther-
mal parameter and 10 H atoms were computed and refined
with an overall isotropic thermal parameter using a riding
model. The final R (on F) factor was 0.042, wR (on |F |2) = 0.095
and goodness of fit = 1.057 for all observed reflections. The
number of refined parameters was 234. The maximum and
minimum peaks in the final difference synthesis were 0.954 and
Ϫ0.445 e ÅϪ3, respectively.
14 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
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Acknowledgements
We thank the Generalitat de Catalunya (grant number QFN95-
4708 and SGR 00199) for financial support.
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