A planar chiral non-metallocenic analogue of the most popular N,N-dimethylbenzylaminate palladacycle

Article abstract of DOI:10.1016/j.poly.2011.09.043

A racemic planar chiral tertiary amine pCp-CH₂NMe₂ (HL¹, pCp = [2.2]paracyclophane-4-yl) was prepared by aminomethylation of the bromide pCp-Br with Eschenmoser's salt. Direct cyclopalladation of this new ligand with palla

Full text of DOI:10.1016/j.poly.2011.09.043

Polyhedron 31 (2012) 413–421
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Polyhedron
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A planar chiral non-metallocenic analogue of the most popular
N,N-dimethylbenzylaminate palladacycle
a
b
a
Valery V. Dunina a, , Eugeniya I. Turubanova , Olga N. Gorunova , Michail V. Livantsov ,
⇑
Konstantin A. Lyssenko b, Dmitrii Yu. Antonov b, Yuri K. Grishin a
a Department of Chemistry, M.V. Lomonosov Moscow State University, Lenin Hills, 119991 Moscow, Russian Federation
b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova St. 28, 119991 Moscow, Russian Federation
a r t i c l e i n f o
a b s t r a c t
A racemic planar chiral tertiary amine pCp-CH2NMe2 (HL1, pCp = [2.2]paracyclophane-4-yl) was prepared
by aminomethylation of the bromide pCp-Br with Eschenmoser’s salt. Direct cyclopalladation of this new
ligand with palladium(II) acetate results in the formation of the racemic CN-dimer rac-3 in a moderate
yield of 64%. The enantiomerically pure dimer (Spl, Spl)-3 was obtained by the standard procedure of
racemic palladacycle resolution using (SC)-prolinate as a chiral derivatising agent. The ortho-palladated
structure, absolute configuration of the chiral plane and stereochemical peculiarities of the new CN-pal-
ladacycle were established by means of NMR spectroscopy and an X-ray diffraction study of its (SC)-pro-
linate derivative.
Article history:
Received 26 August 2011
Accepted 26 September 2011
Available online 8 October 2011
Keywords:
Planar chirality
Azapalladacycles
Enantiomer separation
Chirality transfer
X-ray study
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
their aromaticity, we might expect that (sp2)C–H bond activation
may present difficulties. Because of this, we have decided to intro-
Excellent efficiency of planar chiral coordination complexes in
general [1] and cyclopalladated compounds (CPCs) in particular
[2] in diverse processes of chiral recognition is widely recognised.
However these promising stereoselectors are mainly derived from
ligands with a metallocenic framework, possessing undesirable re-
dox-activity. This drawback has stimulated the development of
routes to enantiopure planar chiral CPCs of a non-metallocenic
nature, for example those based on [2.2]paracyclophane (pCp)
derived ligands. Until recently, the number of such structures
remained to be restricted to several examples of CN- and CP-palla-
dacycles bearing oxazoline (I, II [3]), imine (III [4]) or phosphinite
(IV [5]) donor groups (Fig. 1), including palladacycles of only planar
chirality (III, IV) and structures containing elements of planar and
central chirality (I, II).
duce optical activity at the last stages of the overall process using
the strategy of racemic palladacycle resolution.
The starting racemic N,N-dimethyl([2.2]paracyclophane-4-yl-
methyl)amine (rac-HL1) was prepared in moderate yield by ami-
nomethylation [7] of the known bromide 4-Br-pCp (rac-2) [8]
using dimethyl(methylene)ammonium iodide (Eschenmoser’s salt
[9]) as a reagent (Scheme 1).
In spite of a rather wide collection of chiral pCp derived ligands
being published [1f,g,j,10], including
a-branched 1-([2.2]paracy-
clophan-4-yl)alkylamines [11] with planar and central chirality,
the racemic tertiary amine HL1 has not been reported until now.
2.1. Cyclopalladation of the amine HL1
In this work we report the preparation of an enantiopure CN-
palladacycle (1) with a donor tertiary amino group and a [2.2]para-
cyclophane framework, which is a planar chiral analogue of the
most popular N,N-dimethylbenzylaminate CN-palladacycle.
All our experiments on the cyclopalladation of the tertiary
amine rac-HL1 illustrated the reduced ability of the phenylene ring
(sp2)C–H bonds to be activated, which is in drastic contrast with
the behaviour of its achiral analogue N,N-dimethylbenzylamine
(HL2). Thus, our initial attempts to use Li2PdCl4 as a palladation
agent for the amine rac-HL1 in the presence of sodium acetate as
2. Results and discussion
a base failed completely; the target dimer [{Pd(g l-Cl)}2]
2-L1)(
Taking into account that the boat-like deformation of phenylene
rings, typical for sterically compressed pCp-derivatives [6], reduces
(rac-3) was formed only in traces (Method 1). To compare, the
ortho-palladation of the achiral analogue HL2 with the same re-
agent and under milder conditions affords the required dimer
⇑
Corresponding author. Tel.: +7 495 939 53 76; fax: +7 495 932 88 46.
E-mail address: dunina@org.chem.msu.ru (V.V. Dunina).
[{Pd(g l-Cl)}2] in nearly quantitative yield (95%) [12].
2-L2)(
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.09.043

414
V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
But
Pd
O
N
Pd
But
N
O
But
N
Pd
(SCRpl)-I
O
(SplSC)-I
(SCSpl)-II
H
O
C
PPh2
Me2N
N
Pd
Pd
Pd
X
(Rpl)-III
(Rpl)-IV
(Spl)-1
Fig. 1. Reported palladacycles with non-metallocenic planar chirality (I–IV) and target pCp-derived aminate CN-palladacycle (Spl)-1 of the same structural and
stereochemical type.
2
1
Br
4
8
7
NMe2
NMe2
i)
ii)
13
15
16
iii)
5
Pd
9
2
X
10
rac-2
rac-HL1
rac-4
rac-3
iv)
v)
O
vi),
vii)
H
H9a
2
H9s
H
Pd
Cl
N
O
10
Pd
viii)
5
4
NMe2
Cl
NMe2
NMe2
16
15
Pd
PPh3
2
1
(Spl,Spl)-3
(Spl,SCSN)-6
rac-5
Scheme 1. Syntheses of the ligand HL1 and its cyclopalladated derivatives, and optical resolution of the dimer rac-3. Reagents and conditions: (i) BuLi, Et2O; [CH2@NMe2]+Iꢀ;
HCl, Et2O; (ii) NaOHaq; (iii) Pd(OAc)2, toluene, r.t., 9 days; (iv) LiCl, acetone, r.t., 12 h; (v) PPh3, toluene, 20 °C, 0.5 h; (vi) potassium (SC)-prolinate, MeOH, r.t.; (vii) twofold
crystallisation of the diastereomer mixture from methanol/diethyl ether; (viii) 0.5 M HClaq/dichloromethane, r.t.
Cyclopalladation of the amine rac-HL1 was realised only in its
reactions with the more electrophilic reagent Pd(OAc)2, following
anion metathesis of the intermediate acetate-bridged dimer
that we observed similar difficulties in the course of the cyclopal-
ladation of the pCp-derived phosphinite ligand [5].
[{Pd(g
2-L1)(
l-OAc)}2] (rac-4). Careful optimisation of the reaction
2.2. Spectral confirmation of the new CN-palladacycle structure
conditions offered the opportunity to increase the target dimer
rac-3 yield from the very low initial yield of 12% with slight heating
(50 °C, 1 h; Method 2) to 31% with an increased duration (45 °C, 5 h;
Method 3), and finally to 64% without heating and at a longer reac-
tion time (r.t., 9 days; Method 4; Scheme 1).
It is known that usually direct intramolecular activation of aro-
matic (sp2)C–H bonds with palladium(II) occurs much more effi-
ciently compared to that of aliphatic (sp3)C–H bonds; examples
of CN-palladacycles of the last type are rare [13]. As a consequence,
we can propose that some problems in the (sp2)C–H bond activa-
tion in the case of the amine HL1 may be caused by the decreased
aromaticity of the phenylene rings of the [2.2]paracyclophane
framework deformed in a boat-like manner. It is important to note
The structure of the amine HL1 provides two alternative sites
for cyclopalladation: (i) the aromatic (sp2)C–H bond of the trisub-
stituted phenylene ring, and (ii) the benzylic (sp3)C–H bond of
the neighbouring methylene group of the pCp-moiety. The sole
precedent of high yield isolation of both regioisomeric palladacy-
cles, (SCRpl)-I and (SCSpl)-II, was reported in the reactions of
2-oxazolinyl-pCp with the same palladation agent, Pd(OAc)2, un-
der comparable conditions [3]. Despite this fact, the first of the
two above-mentioned directions of the palladium(II) attack on
the pCp-derived ligands in general and on the tertiary amine
HL1 in particular can be considered as much more preferable
for the following reasons: (i) more efficient activation of the

V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
415
(sp2)C–H bonds with palladium(II) compared to that of the
(sp3)C–H bonds [13]; (ii) the first direction results in the forma-
tion of the more preferable five-membered palladacycle com-
pared to the six-membered one in the second case; (iii) the
nature of the palladium(II) acetate used as a metallation agent
provides optimal conditions for electrophilic aromatic
substitution.
Unfortunately, the dimeric complex rac-3 cannot be used for
any spectral studies due to its existence as a complicated mixture
of syn/anti and meso/dl isomers and their dynamic mobility. Be-
cause of this, for evaluation of the regiochemistry of the amine
rac-HL1 cyclopalladation, the dimer rac-3 was transformed into
its mononuclear derivative rac-5 via chloride bridge cleavage by
the auxiliary triphenylphosphine ligand (Scheme 1). Two main
advantages of using a phosphine derivative for this purpose in-
clude: (i) facilitation of 1H NMR spectra interpretation due to
spin-spin coupling of defined protons with the 31P nucleus, and
(ii) regioselective coordination of the auxiliary phosphine ligand
in a trans(P,N) configuration, evident from the presence of only
one signal in the 31P{1H} NMR spectrum of the adduct rac-5 at d
30.3 ppm.
ing its dipole–dipole interaction with the pseudo-geminal proton
H(8) (1.9%, Fig. 2a).
As a reference point for the assignment of the methylene pro-
tons of the pCp moiety we used the signal of the H(2a) proton, lo-
cated due to its dipole–dipole interaction with the aromatic H(8)
proton (3.1%), and the high-field position of this signal at d
1.90 ppm (ddd) caused by the anisotropy influence of the PPh3
ligand. It should be noted that the same effect was previously
observed for the PPh3 derivative of the imine CN-palladacycle
rac-III (d 1.93 ppm for the H(2a) proton) [4]. The signal at d
2.78 ppm (dddd) was identified as belonging to the H(2s) proton
due to detection of a coupling constant 5JHP ꢂ 1.1 Hz. A rather large
value of this constant is indicative of a significant contribution of
the through-space 1Hꢃꢃꢃ31P interaction of the proton H(2s) with
the auxiliary PPh3 ligand, and may be considered as unambiguous
confirmation of a trans(P,N) configuration of the phosphine adduct
rac-5.
The comparative analysis of the 1H NMR spectral data for the
triphenylphosphine derivative rac-5 and the corresponding deriva-
tives of other palladacycles bearing a pCp-framework (III [4] and IV
[5,14]), offers the opportunity to determine several trends, which
may be useful for signal assignment in the 1H NMR spectra of re-
lated structures:
The signal assignment in the 1H NMR spectrum of the adduct
rac-5 was performed using homo- and heteronuclear decoupling,
COSY and NOE experiments. These spectral data unambiguously
confirm the activation of the (sp2)C–H bond in the course of the li-
gand HL1 cyclopalladation: the 1H NMR spectrum of the phosphine
adduct rac-5 contains signals of only six aromatic protons of the
pCp-phenylene rings in the range d 5.46–6.55 ppm, well separated
from the signals of the PPh3 protons (d 7.25–7.62 ppm), and the
signals of all eight methylene protons of the pCp-framework (d
1.90–3.14 ppm).
(i) the signal of the methylene H(2a) proton may be identified
by its high-field position caused by influence of the auxiliary
ligand PPh3;
(ii) the signal of the methylene H(2s) proton may be located due
to the presence of the spin-spin coupling constant (5JHP 0.7–
2.1 Hz) with the phosphorus atom of the auxiliary ligand
PPh3, probably with a contribution of their interaction
through space;
(iii) the most low-field position is typical for the signal of the
methylene H(9s) proton, which is brought close to the palla-
dacycle side chain (CH2NMe2, CH = NAr or OPPh2);
(iv) the signals of the H(7) and H(8) aromatic protons of the met-
allated phenylene ring are high-field shifted compared to
those of other aromatic protons of the pCp-moiety.
As expected, the non-equivalence of the two diastereotopic
NMe groups is evident only in the spectrum of the ortho-palladated
complex rac-5 (
Dd = 0.17 ppm), while in the case of the flexible
free amine rac-HL1 they are formally equivalent. The difference
in the spin-spin coupling efficiency of the diastereotopic
a-CH2
protons and N-methyl groups with the 31P nuclei of the auxiliary
ligand PPh3 in the 1H NMR spectrum of the adduct rac-5 has pro-
4
vided a basis for their differentiation: (i) the constants JHP = 3.2
and 1.7 Hz were found for the equatorial (N-Meeq) and axial (N-
2.3. Preparation of enantiomerically pure CN-palladacycle (Spl)-1
Meax) N-methyl groups, respectively; (ii) of the two
a-methylene
proton signals, only one reveals a spin–spin coupling constant,
The resolution of the racemic dimeric complex rac-3 was per-
formed using the (SC)-prolinate ligand for its chiral derivatisation.
A high efficiency of this amino acidate for enantiomer separation
of CN- [15] and CP-palladacycles [16] is well documented.
Treatment of the racemic dimer rac-3 with potassium (SC)-
prolinate in a 1:2 ratio affords an equimolar mixture of diastereo-
meric derivatives, (Spl,SCSN)-6 and (Rpl,SCSN)-6. After its twofold
slow crystallisation by the vapour diffusion method using diethyl
4JHP = 5.1 Hz, which is indicative of its equatorial orientation (
a-
CHeq).
As a starting point, in the assignment of the aromatic protons of
the pCp moiety we used the signal of the H(8) proton of the
metallated phenylene ring, which appears as a doublet with a cou-
5
pling constant JHP ꢁ 0.6 Hz. Proton H(15) of the non-palladated
C6H4 ring was identified on the basis of a NOE experiment, reveal-
H1s
H
H1a
H2a
H
N
3.1%
H2s
2.8%
PPh3
O
H15
H13
Cl
H15
H16
H13
O
N
Pd
H8
Pd
H8
4.0%
1.9%
Meeq
Meax
Me
H12
N
H16
H12
3.1%
1.2%
H7
H7
Me
Heq
1.2% H10a
ax
Heq
ax
H10a
2.6%
H
3.0%
H
4.2%
H10s
3.0%
H10s
H9s
H9a
H9s
H9a
(a)
(b)
Fig. 2. Numbering schemes and NOE-basis for the assignments of resonances of aromatic and methylene protons of the pCp moiety in the 1H NMR spectra of the phosphine
adduct rac-5 (a) and prolinate diastereomer (Spl,SCSN)-6 (b).

416
V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
ether and methanol, the less soluble diastereomer (Spl,SCSN)-6 was
isolated in a diastereomerically pure state (>99% de, 1H NMR data)
2.5. X-ray diffraction study of the (SC)-prolinate diastereomer
(Spl,SCSN)-6
in
a moderate yield of 38% (Scheme 1). Unfortunately, the
extremely high solubility of the second diastereomer (Rpl,SCSN)-6
in all solvents tested has prevented its isolation in the individual
state.
The enantiopure dimeric complex (Spl,Spl)-3 was obtained with a
yield of 86% with [a]D +360° (c 0.12, CH2Cl2) using a standard pro-
The ortho-palladated structure and the absolute configuration
of the new planar chiral CN-palladacycle (Spl)-1 and the
trans(N,N)-geometry of its (SC)-prolinate derivative (Spl,SCSN)-6
were established unambiguously by an X-ray diffraction study of
the latter complex. The molecular structure of complex (Spl,SCSN)-
6, the numbering scheme and selected bond lengths and angles
are presented in Fig. 3.
tocol of auxiliary ligand removal by its protonation with dilute HCl
in a two-phase solvent system.
The (Spl)-configuration of the 4,5-disubstituted [2.2]paracyclo-
phane derivative (Spl,SCSN)-6 is confirmed independently using
the coordinated (SCSN)-prolinate ligand as a reference point and
on the basis of the anomalous X-ray scattering method with the
Flack parameter 0.000(17). Taking into account that complex
(Spl,SCSN)-6 is a derivative of the first amine CN-palladacycle (Spl)-
1 with non-metallocenic planar chirality, it was necessary to
compare its structural parameters with those of the known achiral
N,N-dimethylbenzylaminate analogues to estimate the influence of
the phenylene ring replacement by a pCp-moiety. The set of achiral
analogues includes the dimeric compounds V and VI, and the
mononuclear phosphine adducts VII, containing a total of 14
non-equivalent palladacycles (Fig. 4).
2.4. Spectral study of the prolinate derivative (Spl,SCSN)-6
The structure of the diastereomer (Spl,SCSN)-6 in solution was
confirmed by 1H NMR spectroscopy. Despite rather strong signal
overlapping in the high field region, we were able to identify the
main signals of the CN-palladacycle using homonuclear decou-
pling, NOE (Fig. 2b) and COSY techniques; in some instances inter-
atomic distances in the crystal structure of the complex (Spl,SCSN)-6
(see Section 2.5) were used for confirmation of the signal assign-
ments. The signal assignments in the spectrum of the prolinate
complex (Spl,SCSN)-6 were based on the following arguments:
(i) In the NOE experiment we observed a dipole–dipole interac-
The Pd–C bond in complex (Spl,SCSN)-6, lying on the diagonal
C–Pd–O, is slightly elongated (2.016 Å) compared to the Pd–C
bonds in the corresponding achiral compounds, namely, dimers
Vb–e (1.961–1.987 Å) and the phosphine adducts VIIb, c (1.972–
2.012 Å), where it lies on the diagonal C–Pd–Cl. What is more, this
bond length also exceeds the Pd–C bond lengths in the complexes
tion (3.1%) between one of the a-methylene protons (repre-
sented by the doublet at d 3.91 ppm) and one of the aromatic
protons of the non-metallated phenylene ring (lowfield dd at
d 6.73 ppm), which allows us to identify these signals as
belonging to an axial
a-methylene proton (a
-CHax) and an
aromatic proton H(12), respectively. This assignment may
be confirmed additionally by the minimum distance
between these protons in the crystal structure (2.505 Å).
(ii) The signals of protons H(13) and H(16) were located using
homonuclear 1H{1H} decoupling of proton H(12), which
results in the removal of the spin–spin coupling constants
4
3JHH and JHH, respectively.
(iii) The assignment of high-field signals at d 6.07 and 6.11 ppm
to protons H(7) and H(8) is evident from their doublet
nature; their differentiation was based on the dipole-dipole
interaction (1.2%) of the first of these protons with proton
H(16).
(iv) Identification of the singlet signals of the diastereotopic N-
methyl groups, NMeax and NMeeq
,
was based on the
differences in their dipole–dipole interactions with the axial
-methylene proton, viz., NOE 3.0% and 1.2%, respectively.
a
This difference is in accordance with the differences
between the averaged values of the distances
a
-CHeqꢃꢃꢃH
(Meax) and
a
-CHeqꢃꢃꢃH(Meeq) found in the crystal structure
of the prolinate complex (Spl,SCSN)-6 (2.834 and 3.111 Å,
respectively).
The signals of the methylene bridges of the pCp moiety are
represented by a group of complicated overlapping multiplets with
seven of eight signals located in the rather narrow range d 2.83–
3.17 ppm. Nevertheless, several signals were identified using the
NOE technique due to the following dipole–dipole interactions
Fig. 3. Molecular structure and numbering scheme for the diastereomer (Spl,SCSN)-6
with thermal ellipsoids at 50%; hydrogen atoms are omitted for clarity. Selected
bond lengths (Å): Pd(1)–C(4) 2.016(2), Pd(1)–N(1) 2.0599(17), Pd(1)–O(1)
2.1096(15), Pd(1)–N(2) 2.0809(17), N(1)–C(17) 1.485(3), N(1)–C(19) 1.480(3),
N(1)–C(18) 1.487(3), N(2)–C(21) 1.500(2), N(2)–C(24) 1.504(3), O(1)–C(20)
1.277(2), O(2)–C(20) 1.237(2), C(4)–C(5) 1.421(3), C(5)–C(6) 1.408(3), C(3)–C(4)
1.405(3); selected bond angles (°): C(4)–Pd(1)–N(1) 82.73(8), C(4)–Pd(1)–N(2)
105.76(7), N(1)–Pd(1)–N(2) 168.35(7), C(4)–Pd(1)–O(1) 173.95(7), N(1)–Pd(1)–
O(1) 91.72(6), N(2)–Pd(1)–O(1) 79.40(6), C(20)–O(1)–Pd(1) 113.91(12), C(17)–
(Fig. 2b):
a
-CHeq ? H(9s) (4.2%), H(12) ? H(10s) (2.6%),
H(16) ? H(10a) (3.0%) and H(13) ? H(1s) (2.8%).
Signals of the protons of the auxiliary prolinate ligand were
separated from all the other signals using the COSY technique.
Unfortunately, we were only able to perform unambiguous assign-
N(1)–Pd(1)
113.87(13), C(17)–N(1)–C(18) 109.73(17), C(19)–N(1)–C(17) 109.90(16), C(19)–
N(1)–C(18) 109.00(17), C(21)–N(2)–Pd(1) 104.86(11), C(24)–N(2)–Pd(1)
108.71(12),
C(18)–N(1)–Pd(1)
105.51(13),
C(19)–N(1)–Pd(1)
ment for the multiplet of the a
-C⁄H proton at the carbon stereocen-
119.87(13), C(3)–C(4)–Pd(1) 130.29(15), C(5)–C(4)–Pd(1) 112.30(15), N(1)–C(17)–
C(5) 108.17(16), C(21)–N(2)–C(24) 105.26(15), N(2)–C(21)–C(22) 104.28(15), N(2)–
tre based on its high-field position (at d 4.15 ppm). Despite using
all possible NMR techniques (including temperature variation),
our attempts to identify other prolinate proton signals failed due
to their complicated form and very strong overlapping.
C(21)–C(20)
109.65(15),
O(2)–C(20)–O(1)
125.35(19),
O(1)–C(20)–C(21)
115.95(16), O(2)–C(20)–C(21) 118.60(17), C(4)–C(5)–C(17) 115.83(17), C(6)–C(5)–
C(17) 121.09(18).

V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
417
gen [22]. The intrachelate angle \CPdN in the structure of the com-
plex (Spl,SCSN)-6 (82.73°) falls within the range typical for all its
achiral analogues V–VII (81.44–82.94°).
NMe2
Rn
Pd
Pd
To follow the chirality transfer in CPCs bearing a pCp-frame-
work, the structure of the complex (Spl,SCSN)-6 was compared with
those of a few known analogues based on the pCp-derived N- and
P-donor ligands. The set of such planar chiral non-metallocenic
complexes is restricted to triphenylphosphine derivatives of CN-
palladacycles with an oxazolinyl donor group (diastereomers
(RplSC)-Ia and (SplSC)-Ia [3]) or an imine donor ((Spl)⁄-IIIa [4]), and
a (SC)-prolinate derivative (Spl,SCSN)-IVa of the phosphinite CP-pal-
ladacycle (Spl)-IV [5] (Fig. 5 and Table 1).
The coordination environment of the palladium atom in the
complex (Spl,SCSN)-6 reveals two kinds of deviations from an ideal
square-planar configuration. First, a slight pyramidal distortion
with the metal atom in the top position was observed, which devi-
ates from the mean coordination plane {PdC4N1O1N2} by +0.076 Å
in the direction of the non-metallated phenylene ring of the
paracyclophane framework. Such a pyramidal distortion of the
coordination sphere has to be recognised as typical for achiral
N,N-dimethylbenzylaminate CPCs V–VII since it was found for 12
of the 14 palladacycles of this kind. Second, the palladium coordi-
nation environment in the complex (Spl,SCSN)-6 reveals a marked
tetrahedral distortion with an interplanar angle {C4PdN1}{N2PdO1}
(bPd) equal to 7.90°; this value is close to the lower end of this
parameter range for all pCp-derived complexes (7.30–30.84°,
Table 1), but exceeds the averaged value of this parameter for ben-
zylaminate CPCs V–VII (5.63°).
Cl
H
O
NMe2
NMe2
X
Pd
2
Pd
NMe2
X
R3P
VII
V
VI
Fig. 4. Structures of achiral N,N-dimethylbenzylaminate CN-palladacycles charac-
terised by the X-ray diffraction method: for V Rn = H, X = Tfa (Va) [17], Cl (Vb) [18];
X = Cl, Rn = 3-MeO (Vc) [19], 4-MeO (Vd) [19], 5-MeO (Ve) [19]; VI [20]; for VII
X = Tfa, R = 4-CF3C6H4 (VIIa) [21], X = Cl, R = Ph (VIIb) [18,21], Cy (VIIc) [17].
PPh3
O
Cl
Pd
But
But
N
N
Pd
Cl
O
PPh3
(RplSC)-Ia
(SplSC)-Ia
H
O
O
H
PPh3
Cl
N
Pd
Pd
Me
According to the ‘‘skew-line convention’’ [23] the absolute con-
figuration (AC) of the pseudo-tetrahedral coordination environ-
ment of the metal in the complex (Spl,SCSN)-6 may be defined as
N
PPh2
O
Me
H
D
(Spl) on the basis of the negative value of the pseudo-torsion angle
\C4N1O1N2 connecting the four palladium-bonded atoms (
Pd),
(Spl) ste-
s
(Spl)*-IIIa
S ,S
( S
pl
C
N
)-IVa
which is equal to ꢀ4.00°. It is important that the same
D
Fig. 5. Planar chiral CN- and CP-palladacycles based on [2.2]paracyclophane-
derived ligands and characterised by the X-ray diffraction method.
reochemistry was found for the palladium environment in the
complexes (SplSC)-Ia and (Spl)⁄-IIIa, that may be deduced from
the negative sign of the corresponding angles, equal to ꢀ12.35
and ꢀ16.48°, respectively. In contrast, the direction of tetrahedral
Va and VIIa where the bonds lies on the same diagonal, C–Pd–O
(1.954–1.999 Å). Such weakening of the Pd–C bond in the complex
(Spl,SCSN)-6 may be explained by the repulsive interaction between
the pyrrolidine ring of the auxiliary prolinate ligand and the pCp-
moiety.
The Pd–N(1) bond length in the complex (Spl,SCSN)-6 (2.060 Å) is
close to the lower end of this parameter range for the dimers Va–e,
VI (2.060–2.094 Å), but is less than the values found for the phos-
phine adducts VIIa–c (2.106–2.159 Å). The last effect is a quite
expectable consequence of the much greater Structural Trans-
Influence (STI) of the phosphorus atom compared to that of nitro-
distortion is inverted to the
K(Rpl) configuration in the case of
the diastereomer (RplSC)-Ia of the opposite planar chirality (the an-
gle sPd is equal to +29.02°, see Table 1).
The conformation of the CN-palladacycle in the complex
(Spl,SCSN)-6 may be described as a distorted envelope with the
nitrogen atom in the top position, which deviates from the plane
of four remaining atoms by 0.542 Å. Such a conformation is typical
for achiral N,N-dimethylbenzylaminate CPCs, since it was found for
13 of the 14 palladacycles in complexes V–VII. The palladacycle
non-planarity in complex (Spl,SCSN)-6 is rather high, with the
Table 1
Stereochemical characteristics of CN- and CP-palladacycles with a pCp-framework from X-ray data for complexes of the general type trans(E,E0)-[{g2-Cð4Þ\E)Pd(E0)X].
Complex
Palladacycle conformation
Palladium environment
pCp-frameworka
b
d
e
f
g
xav (°)
\E-Y-C5-C4 c (°)
bPd (°)
sPd (°)/AC
ꢀ4.00/
ꢀ12.35/
+29.02/
ꢀ16.48/
ꢀ4.81/
bAr (°)
sAr (°)/AC
(Spl,SCSN)-6
(Spl,SC)-Ia
23.03
16.21
4.44
6.19
9.41
ꢀ31.8 (k)
+10(3) (d)
+6.0(8) (d)
+1.80(3)
+2.1(5)
7.90
16.02
30.84
16.9
D
D
K
D
14.11–15.45
13.77–16.12
14.26–16.19
13.18–16.56
12.97–14.30
ꢀ1.7/r
ꢀ3.08/
r
q
r
(Rpl,SC)-Ia
+6.52/
(Spl)⁄-IIIa
ꢀ3.01/
(Spl,SCSN)-IVa
7.30
D
ꢀ3.9/r
a
b
c
d
e
f
Parameter xav denotes the average intrachelate torsion angle.
There are only parameters of the metallated phenylene ring of pCp moiety presented.
Here E is the palladium-bonded heterodonor atom, and Y is the adjacent
Parameter bPd denotes the interplanar angle {C4PdE}{E0PdX}.
Parameter sPd denotes the pseudo-torsion angle \C4ꢃꢃꢃEꢃꢃꢃXꢃꢃꢃE0.
a-disposed atom of the palladacycle.
Parameter bAr denotes the averaged value of the two dihedral angles between the mean plane of four central atoms of the metallated phenylene ring {C4C5C7C8}, forming
the ‘‘boat basis’’, and the planes including the methylene-bonded ipso-carbon atoms, viz., {C3C4C8} and {C5C6C7}.
g
Parameter sAr denotes the pseudo-torsion angle between the four central atoms of the metallated phenylene ring, forming the ‘‘boat basis’’, viz., \C4–C5ꢃꢃꢃC7–C8.

418
V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
average magnitude of the absolute values of intrachelate torsion
angles ( av) equal to 23.03°. This parameter falls within the range
of values 19.89–25.39° found for all its achiral -non-substituted
analogues V–VII. In addition, the CN-palladacycle in the prolinate
derivative (Spl,SCSN)-6 reveals a pronounced twisting, with the tor-
sion angle \N1–C17–C5–C4 equal to ꢀ31.8(2)°. The absolute value
of this parameter also falls in the range of values 23.66–37.90°,
of the tetrasubstituted phenylene ring of the pCp moiety cannot
be considered as a fortuitous phenomenon.
The geometric parameters of the prolinate moiety of the diaste-
reomer (Spl,SCSN)-6 are mainly in the range of values typical for the
other known (SCSN)-prolinate derivatives of CN- [15b–d,16a,25]
and CP-palladacycles [15a,16b,c] of a trans(O,C)-configuration.
x
a
found for the achiral
a-non-substituted analogues V–VII, and its
sign is indicative of a CN-palladacycle k(Spl) conformation (Fig. 6).
The torsion angles, related to \N1–C17–C5–C4 in the structure of
complex (Spl,SCSN)-6, are positive in the case of both diastereomers
of Bolm’s complex of opposite planar chirality, (SplSC)-Ia and
(RplSC)-Ia (see Table 1), which is indicative of the dependence of
these palladacycle conformations upon the oxazoline carbon (SC)-
stereocentre rather than upon the chiral plane of the pCp-moiety.
Unfortunately, the twisting extent of two other palladacycles in
the complexes (Spl)⁄-IIIa and (Spl,SCSN)-IVa is too low (with torsion
angles of ca. 2°) for any discussion of their stereochemistry.
It is known [6,24] that the phenylene rings of the pCp-moiety
adopt a boat-like form due to steric compression. Their non-pla-
narity extent may be characterised by angles between the plane
of four central atoms (forming the ‘‘boat basis’’) and planes includ-
ing the methylene-bonded ipso-carbon atoms (bAr). In the case of
complex (Spl,SCSN)-6, this parameter varies in the range 14.11–
15.45° for the metallated phenylene ring, which is comparable
with this parameter range found for other CPCs with a pCp-back-
bone (12.97–16.56°, see Table 1). In all the pCp-derived CPCs, this
kind of deformation is more pronounced for the palladated pheny-
lene ring. More importantly, the latter possesses an additional
puckering: the ‘‘boat base’’ of this phenylene ring is twisted
according to the torsion angles \C4–C5ꢃꢃꢃC7–C8 equal to ꢀ1.70°
for complex (Spl,SCSN)-6, and varying from ꢀ3.01° to ꢀ3.9° for com-
plexes (Spl,SC)-Ia, (Spl)⁄-IIIa and (Spl,SCSN)-IVa, but inverting to
+6.52° for complex (Rpl,SC)-Ia. The signs of these angles are indica-
tive of the dependence of this twist direction upon the configura-
3. Conclusions
We have synthesised the previously unknown tertiary amine
pCp-CH2NMe2 with a [2.2]paracyclophane framework as a race-
mate. Its direct cyclopalladation was possible only with palla-
dium(II) acetate due to the decreased (sp2)-character of the
deformed phenylene rings of the pCp-moiety; it occurs in a regio-
selective mode with the formation of an (sp2)C–Pd bond. Enantio-
merically pure dimer (Spl,Spl)-3 was obtained by the standard
procedure of racemic palladacycle resolution using (SC)-prolinate
as the chiral derivatising agent. The ortho-palladated structure of
the new CN-dimer rac-3 and the absolute configuration of the chi-
ral plane in enantiopure dimer (Spl,Spl)-3 were established by
means of spectral studies of their mononuclear phosphine (rac-5)
or (SC)-prolinate derivative ((Spl,SCSN)-6), respectively, and an X-
ray diffraction study of the latter.
Important conclusions regarding chirality transfer in CPCs with
a [2.2]paracyclophane framework were deduced from a compari-
son of the stereochemical peculiarity of the new CN-palladacycle
in the (SC)-prolinate complex (Spl,SCSN)-6 with those of phosphine
or (SC)-prolinate derivatives of known structurally characterised
CN- (I, III) and CP-palladacycles (IV). First, the configuration of
the chiral plane determines the twist direction of the metallated
phenylene ring of the pCp-framework, namely it becomes
twisted in the complexes with an (Spl)-configuration, but it reveals
-twist in the case of the complex with an (Rpl)-configuration.
r-
a
q
Second, the tetrahedral distortion of the metal coordination envi-
ronment in pCp-derived CPCs also reveals a clear dependence upon
the absolute configuration of the chiral plane: a quasi-tetrahedron
tion of the chiral plane: it may be described as an
r(Spl)-twist for
the complexes with an (Spl)-configuration, but as an
q(Rpl)-twist
for the complex with an (Rpl)-configuration.
of
D
-configuration was found in structures of all known complexes
-quasi-tetrahedron in
The analysis of CCDC data has shown that a similar dependence
is also applicable for more general cases of organic 4-X-5-Y-disub-
stituted derivatives of [2.2]paracyclophane: all the compounds
with an (Spl)-configuration are characterised by a negative torsion
of the (Spl) chiral plane, in contrast with the
K
the case of a sole complex containing a chiral plane of the (Rpl)-
configuration. The routes of chirality transfer for all pCp-derived
CPCs may be represented as following:
angle \C4–C5ꢃꢃꢃC7–C8 corresponding to
r(Spl)-twist, while the posi-
tive angles are typical for compounds with an (Rpl)-configuration,
(Spl)-chiral plane ?
(Rpl)-chiral plane ?
r
-pCp-twist ? -tetrahedron, or
-pCp-twist ? K-tetrahedron.
D
which is indicative of
q
(Rpl)-twist [4,14]. Thus, the directed twist
q
The chirality transfer from the pCp-framework to the palladacy-
cle conformation is not so universal. In the case of the amine-de-
rived complex (Spl,SCSN)-6, the (Spl) chiral plane induces a twist of
the strongly puckered palladacycle in the k conformation. In this
case the total scheme of the chirality transfer may be presented
as follows:
C5
Y
C4
C4
Pd
Pd
E
E
C5
Y
(a)
(b)
(Spl)-chiral plane ?
? k-conformation.
r-pCp-twist ? D-tetrahedron
C5
E
E
Y
C5
In contrast, in the complexes of mixed stereochemistry, (RplSC)-
Ia and (SplSC)-Ia, the (SC)-carbon stereocentre in the side chain dic-
tates the opposite d conformation of the palladacycles in both
these diastereomers:
Y
(_) tors. angle
(+) tors. angle
λ
δ
(c)
(d)
(SCSpl)-configuration ?
d-conformation.
r-pCp-twist ? D-tetrahedron ?
Fig. 6. Chiral k (a) and d (b) conformations of five-membered palladacycles and
Newmen’s projections along the bond Y–C4 (c and d), illustrating the correlation
between the sign of the torsion angle \E–Y–C5–C4 and the palladacycle
conformation.
The extent of the versatility of these conclusions may be esti-
mated only after further investigation of other pCp-derived CPCs

V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
419
bearing diverse donor atoms and belonging to diverse stereochem-
a
-CH), 4.24 (d, 2J(HH) = 13.0, 1H,
a-CH), 6.36–6.69 (m, 7H, aromatic
ical types.
protons), 10.6 (br s, 1H, NH).
4.3.2. Isolation of free racemic N,N-dimethyl([2.2]paracyclophane-4-
yl)methylamine (rac-HL1)
4. Experimental
A suspension of the ammonium salt rac-HLꢃHCl (0.3890 g,
1.290 mmol) in toluene (15 mL) was treated with an excess of a
1 M aqueous solution of NaOH (0.150 g, 3.75 mmol) and stirred
at r.t. for 2 h. The organic phase was washed with water
(5 ꢄ 10 mL) up to pH 7, dried over Na2SO4, evaporated to dryness
and the residue was dried in vacuo (1 mm Hg) over paraffin and
CaCl2. The amine rac-HL1 was obtained in a yield of 90.3%
(0.3157 g, 1.189 mmol) as a colourless oil which became solid after
cooling. M.p. 52 °C, Rf 0.48 (toluene/acetone, 10:1). 1H NMR (CDCl3;
d, ppm, J, Hz): 2.24 (c, 6H, NMe2), 2.90 (ddd, 2J(HH) = 13.1,
3J(HH) = 10.7, 3J(HH) = 5.8, 1H, CHH–CH2), 3.02–3.23 (m, 6H, CH2–
4.1. General remarks
1H and 31P{1H} NMR spectra were recorded with Varian VXR-
400 and Bruker DPX-400 spectrometers operating at the frequen-
cies 400 and 161.9 MHz for 1H and 31P nuclei, respectively. The
measurements were carried out at ambient temperature in CDCl3
solutions. The proton chemical shifts are reported in parts per mil-
lion relative to TMS as an internal standard; the 31P chemical shifts
are given relative to H3PO4 as an external reference. The assign-
ment of the signals was based on the homo- and heteronuclear
decoupling – 1H{1H} and 1H{31P}, COSY and NOE experiments.
Optical rotations were measured with a VNIEKI-Prodmush AI-
EPO at 25 °C. Melting points were measured with an Electrother-
mal IA 9000 series device in a sealed capillary. Elemental analyses
were performed with an automatic analyser VarioMicroCOBE of
the firm Elementar.
All reactions were conducted under argon using TLC control on
Silufol UV-254. The purification of the compounds was performed
by means of short dry column [26] or flash-chromatography on
Silica Gel 60 (from Fluka).
Benzene, toluene, hexane and ether were dried with the appro-
priate drying agents and then distilled from sodium; CH2Cl2 and
CHCl3 were purified chromatographically on a column of Al2O3
and then distilled from CaH2; MeOH was refluxed over magnesium
methoxide for 3 h and then distilled; CDCl3 (from Aldrich) was dis-
tilled from CaH2 just before use. Acetone of high purity (from Rea-
chim) was used without additional purification.
CH2), 3.05 (d, 2J(HH) = 12.6, 1H,
a
-CH), 3.55 (d, 2J(HH) = 12.6, 1H,
a
-CH), 3.56 (m, 1H, H(2s)), 6.35 (br s, 1H, H(5)), 6.54 (br d,
3J(HH) = 7.7, 1H, H(7)), 6.51 (d, 3J(HH) = 7.7, 1H, H(8)), 6.47 (d,
3J(HH) = 7.9, 1H, H(12) or H(13)), 6.69 (d, 3J(HH) = 7.9, 1H, H(13)
or H(12)), 6.56 (d, 3J(HH) = 7.9, 1H, H(15) or H(16)), 6.62 (d,
3J(HH) = 7.9, 1H, H(16) or H(15)).
4.4. Syntheses of the cyclopalladated complexes
4.4.1. Preparation of racemic dimer di-l-chlorobis{5-(N,N-
dimethylaminomethyl)[2.2]paracyclophane-4-yl-C,N}dipalladium(II)
(rac-3)
Method 1. A solution of a mixture of the ammonium salt rac-
HL1ꢃHCl (0.1222 g, 0.4053 mmol), Li2PdCl4 (0.1063 g, 0.4053 mmol)
and sodium acetate (0.0997 g, 1.216 mmol) in methanol (10 mL)
was stirred at 50 °C for 1 h. Intensive formation of palladium black
prevented the isolation of the target dimer 3, which was detected
in only trace quantities (TLC data).
Method 2. A solution of Pd(OAc)2 (0.0457 g, 0.2037 mmol) and
amine rac-HL1 (0.0541 g, 0.2038 mmol) in toluene (10 mL) was
stirred for 1 h at 50 °C, then the solvent was evaporated and the
4.2. Reagents and starting compounds
Palladium(II) chloride and acetate, BuLi (from Aldrich) and (S)-
proline (high purity grade) were used as received; triphenylphos-
phine (from Chemapol) was purified by twofold recrystallization
from a benzene/hexane mixture. Racemic 4-bromo[2.2]paracyclo-
phane [8] and dimethyl(methylene)ammonium iodide
(Eschenmoser’s salt) [9] were synthesized by known methods.
Potassium (S)-prolinate was prepared by treatment of (S)-proline
with an equimolar amount of KOH in methanol at r.t.; after re-
moval of the solvent, the residue was thoroughly dried in vacuo.
residue was treated with
a
solution of LiCl (0.01730 g,
0.4081 mmol) in acetone (10 mL). The reaction mixture was stirred
for 1 h at r.t., treated with water (15 mL) and additionally stirred
for 1 h. The precipitate formed was filtered, washed with water
and dried in vacuo (1 mm Hg). After purification using dry column
chromatography (h = 6 cm, d = 3.7 cm; eluents: toluene/acetone
mixtures in ratios from 50:1 to 20:1), the target dimer was crystal-
lized from a dichloromethane/hexane mixture, washed with hex-
ane and dried in vacuo (1 mm Hg) over paraffin and CaCl2 to
afford the target dimer rac-3 as a yellow amorphous powder. Yield:
12% (0.0108 g, 0.0132 mmol). M.p. (dec.) 222–223 °C; Rf 0.66 (ben-
zene/acetone, 10:1). Anal. Calc. for C38H44Cl2N2Pd2: C, 56.17; H,
5.34; N, 3.45. Found: C, 56.40; H, 5.34; N, 3.32%.
4.3. Synthesis of the racemic amine HL1
4.3.1. Preparation of racemic N,N-dimethyl([2.2]paracyclophane-4-yl-
methyl)ammonium chloride (rac-HL1HCl)
A 2.5 M solution of nBuLi in hexane (14 mL, 34.8 mmol) was
added drop-by-drop to a solution of 4-bromo[2.2]paracyclophane
(5.00 g, 17.4 mmol) in ether (200 mL) under argon, with stirring.
The reaction mixture was stirred at r.t. for 2 h, Eschenmoser’s salt
(6.50 g, 35.1 mmol) was added and stirring was continued for addi-
tional 1 h. After washing with water (200 mL) and drying over
Na2SO4, the organic solvents were removed in vacuo, and the
residue was dissolved in ether (50 mL) and ammonium salt was
treated with a saturated solution of HCl gas in ether. The precipi-
tate formed was filtered, washed by ether and thoroughly dried
in vacuo (1 mm Hg). After its precipitation from chloroform
(50 mL) by benzene, the salt rac-HL1ꢃHCl was isolated in 55% yield
(2.95 g, 9.78 mmol). M.p. 244.5–246 °C. Anal. Calc. for C19H24NCl: C,
75.45; H. 8.15; N, 4.61. Found: C, 75.60; H, 8.01; N, 4.64%. 1H NMR
(d6-DMSO; d, ppm, J, Hz): 2.57 (br s, 6H, NMe2), 2.78–3.18 (m, 7H,
CH2–CH2), 3.48–3.62 (m, 1H, CHH–CH2), 3.99 (d, 2J(HH) = 13.0, 1H,
Method 3. The reaction of Pd(OAc)2 (0.0489 g, 0.2177 mmol)
with the amine rac-HL1 (0.0578 g, 0.2177 mmol) in toluene
(10 mL) was conducted in a similar manner, but in the more mild
temperature regime: for 3 h at 34 °C, then 5 h at 45 °C, and finally
for 16 h at r.t. After purification using flash-column chromatogra-
phy (h = 14 cm, d = 2.5 cm; eluents: benzene/acetone mixtures in
ratios from 80:1 to 30:1) and crystallization, the dimer rac-3 was
obtained in a 31% yield (0.0276 g, 0.0339 mmol).
Method 4. The same reaction of Pd(OAc)2 (0.1488 g,
0.6627 mmol) with the amine rac-HL1 (0.1759 g, 0.6627 mmol)
was conducted in toluene (15 mL) at r.t. for 9 days. After purifica-
tion using flash-column chromatography (h = 14.5 cm, d = 1.5 cm;
eluents: toluene, then toluene/acetone mixtures in ratios from
80:1 to 30:1) and crystallization from a toluene/hexane mixture,
dimer rac-3 was obtained in
a yield of 64% (0.1713 g,
0.2108 mmol).

420
V.V. Dunina et al. / Polyhedron 31 (2012) 413–421
4.4.2. Preparation of the racemic mononuclear adduct chloro{5-(N,N-
dimethylaminomethyl)[2.2]paracyclophane-4-yl-
C,N}(triphenylphosphine-P)palladium(II) (rac-5)
ous 0.5 M HCl (2 ꢄ 5 mL). Then the combined organic layers were
washed with water (3 ꢄ 5 mL), dried over Na2SO4, evaporated to
dryness and precipitated from toluene by hexane to obtain the di-
mer (Spl,Spl)-3 as a yellow amorphous powder. Yield: 86% (0.0080 g,
0.0984 mmol). M.p. (dec.) 178–180 °C, Rf 0.66 (benzene/acetone,
A solution of the dimer rac-3 (0.0210 g, 0.0258 mmol) and a
slight excess of PPh3 (0.0149 g, 0.0570 mmol) in toluene (15 mL)
was stirred for 30 min at r.t. Then the reaction mixture was con-
centrated and treated with hexane. The precipitate formed was
washed with hexane and dried in vacuo (1 mm Hg) over paraffin
and CaCl2 to afford the target adduct rac-5 as a light-yellow amor-
phous powder. Yield: 92% (0.0317 g, 0.0474 mmol). M.p. (dec.)
166–167 °C; Rf 0.68 (toluene/acetone, 3:1). Anal. Calc. for
10:1), [a]
25 +360° (c 0.12, CH2Cl2). Anal. Calc. for C38H44Cl2N2Pd2:
D
C, 56.17; H, 5.34; N, 3.45. Found: C, 56.40; H, 5.34; N, 3.32%. 1H
NMR (CDCl3; d, ppm, J, Hz; two sets of signals of anti- and syn-iso-
mers in ca. 4:3 ratio): 2.56, 2.63 (s, 3H, NMe), 2.89, 3.01 (s, 3H,
NMe), 3.65, 3.67 (d, 2J(HH) = 13.4, 1H,
a
-CH), 4.12, 4.17 (d,
2J(HH) = 13.4, 1H,
a-CH), 3.84–3.96 (m, 1H, H(2s)), 2.75–3.22
C
37H37ClNPPd: C, 66.47; H, 5.58; N, 2.10. Found: C, 66.45; H,
(group of m, 7H, CH2CH2), aromatic protons: 6.0–6.10 (m, 2H),
6.51, 6.52 (d, 3J(HH) = 7.7, 1H, H(7) or H(8)), 6.07, 6.08 (d,
3J(HH) = 7.7, 1H, H(8) or H(7)), 6.61–6.67 (m, 1H), 6.82 (br t,
3J(HH) = 7.8, 1H, H(12)), 6.91 (br t, 3J(HH) = 7.8, 1H, H(13)).
5.36; N, 1.97%.
31P{1H} NMR (CDCl3; d, ppm): 30.31 (s). 1H NMR (CDCl3; d, ppm,
J, Hz): palladacycle signals: 1.90 (ddd, 2J(HH) = 13.2, 3J(HH) = 10.6,
3J(HH) = 3.3, 1H, H(2a)), 2.68 (ddd, 2J(HH) = 13.3, 3J(HH) = 10.6,
3J(HH) = 4.7, 1H, H(1a)), 2.78 (dddd, 2J(HH) = 13.2, 3J(HH) = 10.3,
3J(HH) = 4.7, 5J(HP) = 1.1, 1H, H(2s)), 2.89–2.97 (m, 3H, H(9a),
H(10s), H(10a)), 3.04 (ddd, 2J(HH) = 13.3, 3J(HH) = 10.3,
3J(HH) = 3.3, 1H, H(1s)), 3.10 (d, 4J(HP) = 3.2, 3H, NMeeq), 3.14 (m,
1H, H(9s)), 3.27 (d, 4J(HP) = 1.7, 3H, NMea[), 3.83 (dd,
4.6. X-ray crystallographic data for the diastereomer {(Spl)-5-(N,N-
dimethylaminomethyl)[2.2]paracyclophane-4-yl-C,N}{(SCSN)-
prolinate-N,O}palladium(II) ((Spl,SCSN)-6)
Crystals of complex 6 (C24H30N2O2Pd, FW = 484.90) are ortho-
rhombic, space group P212121 at 100 K, a = 10.3221(4),
b = 12.1660(4), c = 16.5131(6) Å, V = 2073.7(1) Å3, Z = 4 (Z0 = 1),
2J(HH) = 15.4, 4J(HP) = 5.1, 1H,
a
-CHeq), 4.34 (d, 2J(HH) = 15.4, 1H,
a
-CHa[), 5.46 (dd, 3J(HH) = 7.5, 5J(HP) = 0.6, 1H, H(8)), 5.83 (d,
3J(HH) = 7.5, 1H, H(7)), 6.47 (br s, 2H, H(12), H(13)), 6.54 (dd,
3J(HH) = 7.7, 4J(HH) = 1.5, 1H, H(16)), 6.55 (dd, 3J(HH) = 7.7,
4J(HH) = 1.5, 1H, H(15)); PPh3 ligand signals: 7.25–7.30 (m, 6H,
meta-H), 7.36–7.40 (m, 3H, para-H), 7.62 (ddd, 4J(HH) = 1.3,
3J(HH) = 7.7, 3J(HP) = 11.1, 6H, ortho-H).
Dcalc = 1.553 g cmꢀ3
,
l
(Mo K
ties of 26399 reflections were measured with a Bruker APEX II CCD
diffractometer [k(Mo K ) = 0.71072 Å, -scans, 2h < 58°] and 5773
a
) = 9.18 cmꢀ1, F(000) = 1000. Intensi-
a
x
independent reflections [Rint = 0.0423] were used in further refine-
ment. The structure was solved by the direct method and refined
by the full-matrix least-squares technique against F2 in the aniso-
tropic-isotropic approximation. The absolute configuration was
additionally proved by Flack parameter whose value in the case
of the (Spl,SCSN) configuration was equal to 0.000(17). Hydrogen
atoms were located from the Fourier synthesis of the electron den-
sity and refined in the riding model. The refinement converged to
wR2 = 0.0533 and GOF = 1.017 for all the independent reflections
(R1 = 0.0223 was calculated against F for 5561 observed reflections
4.5. Optical resolution of the racemic dimer rac-3
4.5.1. Preparation of the diastereomer {(Spl)-5-(N,N-
dimethylaminomethyl)[2.2]paracyclophane-4-yl-C,N}{(SCSN)-
prolinate-N,O}palladium(II) ((Spl,SCSN)-6)
A suspension of the dimer rac-3 (0.1513 g, 0.1862 mmol) and
potassium (SC)-prolinate (0.0571 g, 0.3729 mmol) in methanol
(15 mL) was stirred at r.t. for 9 h, and evaporated to dryness. The
residue was dissolved in dichloromethane, washed with water
(3 ꢄ 15 mL), dried over Na2SO4 and evaporated to dryness. After
twofold recrystallization from methanol/ether (under conditions
of ether diffusion into a concentrated solution of the complex in
MeOH), washing with ether and drying in vacuo (1 mm Hg) over
paraffin and CaCl2, the diastereomer (Spl,SCSN)-6 was obtained in
with I > 2r(I)). All calculations were performed using SHELXTL
PLUS 5.0 software.
Appendix A. Supplementary data
CCDC 838753 contains the supplementary crystallographic data
for the complex (Spl,SCSN)-6. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
a yield of 38% (0.0342 g, 0.0705 mmol) as a light-yellow crystalline
solid. M.p. (dec.) 184–185 °C, Rf 0.35 (CH2Cl2/MeOH, 10:1), [a]
25
D
+244.6° (c 0.39, CH2Cl2). Anal. Calc. for C24H30N2O2Pd: C, 59.44;
H, 6.24; N, 5.78. Found: C, 59.46; H, 6.25; N, 5.71%. 1H NMR (CDCl3;
d, ppm, J, Hz): palladacycle signals: 2.53–2.63 (m, 1H, CHHCH2),
2.64 (s, 3H, NMeax), 2.83–2.89 (m, 2H, CHHCHH), 2.85 (m, 1H,
H(9s)), 2.93 (m, 1H, H(10s)), 3.03 (s, 3H, NMeeq), 3.06 (m, 1H,
H(1s)), 3.07 (m, 1H, H(10a)), 3.10–3.17 (m, 1H, CHHCH2), 3.72 (d,
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