First enantiopure phosphapalladacycle with a palladium bonded stereogenic carbon as the sole chirality source

Article abstract of DOI:10.1016/j.poly.2010.09.024

First enantiomerically pure phosphapalladacycle bearing an asymmetric carbon directly bonded to a palladium atom as a single chirality source was prepared by the resolution of racemic dimer {Pd(η²-L)(μ-Cl)} ₂ (1), where L=2-Bu2tPC6H4

Full text of DOI:10.1016/j.poly.2010.09.024

Polyhedron 30 (2011) 27–32
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
First enantiopure phosphapalladacycle with a palladium bonded stereogenic
carbon as the sole chirality source
b
a
a
b
Valery V. Dunina a, , Olga N. Gorunova , Michail V. Livantsov , Yuri K. Grishin , Konstantin A. Kochetkov ,
⇑
Andrey V. Churakov c, Lyudmila G. Kuz’mina c
a Department of Chemistry, M.V. Lomonosov Moscow State University, Lenin Hills, GSP-1, Moscow 119991, Russian Federation
b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciencies, Vavilova St. 28, Moscow 119991, Russian Federation
c N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciencies, Leninsky Prospect 31, Moscow 119991, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2010
Accepted 21 September 2010
Available online 29 September 2010
First enantiomerically pure phosphapalladacycle bearing an asymmetric carbon directly bonded to a
palladium atom as a single chirality source was prepared by the resolution of racemic dimer {Pd(g
2-L)
(l
-Cl)}2 (1), where L ¼ 2-But PC6H4CHMe, using (R,R)-stilbendiamine as an auxiliary ligand. Double
2
recrystallization of a 1:1 mixture of diastereomers (S,RR)-4a and (R,RR)-4b from MeCN affords one of
them, (S,RR)-4a, as a single isomer (>98% de, 31P{1H} NMR data). Another diastereomerically pure
complex, (R,SS)-4c, was isolated by the same method using (S,S)-stilbendiamine as a resolving agent. This
diastereomer (R,SS)-4c was converted into the enantiopure dimer (R,R)-1 (>98% ee, 31P{1H} NMR data) by
the diamine protonation with dilute acetic acid at ꢀ5 °C. Dimer (R,R)-1 is configurationally stable at high
temperatures up to at least 110 °C. The absolute configuration of the C*-stereocenter in dimer (S,S)-1 was
established by an X-ray diffraction study of its precursor (S,RR)-4a.
Keywords:
Phosphapalladacycle
Pd–C* bond
Enantiomer separation
X-ray study
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
chirality elements (I–IV) [6a–c], or configurational lability of the
carbon stereocenter (IV, R = Me, Ph or MeO) [6d].
Complexes containing an asymmetric carbon atom directly
bonded to a palladium(II) center represent excellent models to
investigate mechanistic aspects of various reactions promoted by
palladium [1], in general, and palladacycles, in particular [2]. There
are several known examples of cyclopalladated complexes (CPCs)
of C*N- [3], C*NO- [4], C*S- [5], and C*P-type [6], bearing Pd–C*
bond. Unfortunately, most of these CPCs are not appropriate for
mechanistic applications due to (i) their diastereomeric nature that
makes Pd–C* bond dependent on other chirality sources
[2a,2b,6,7], (ii) low configurational stability caused by tautomer-
ization or reversible b-H elimination [6a,d], (iii) low extent of their
enantiomeric enrichment [2b,c,3b,3d–f], or (iv) a non-reproducible
preparation method [3e,f]. Phoshapalladacycles with a Pd–C* bond
as the sole chirality source appear to be especially attractive mod-
els for mechanistic studies because of the possibility of using
31P{1H} NMR spectroscopy to probe stereochemical control (in di-
rect mode or after chiral derivatizing of the reaction product).
However, to the best of our knowledge, of the known optically
active C*P-palladacycles (I–IV, Fig. 1) none are suitable for such
studies due to either their Pd–C* bond combining with other
The aim of this work was to prepare an enantiopure phospha-
palladacycle with Pd atom directly bonded to a carbon stereogenic
center and without additional chirality elements in the structure.
The preliminary results of this research were reported recently [8].
2. Results and discussion
As the strategy for the preparation of an enantiomerically pure
CPC of this kind, we have chosen resolution of the corresponding
racemic palladacycle, and as the target molecule – a cyclopalladat-
ed derivative of bulky prochiral di-tert-butyl-ortho-ethylphenyl-
phosphine (HL). Racemic cyclopalladated dimer (1) was prepared
many years ago using a two-step protocol through the formation
of the coordination complex trans-[PdCl2(HL)2] in a total yield of
78% [9]. We performed the cyclopalladation of phosphine HL using
palladium(II) acetate as a metallating agent. Steric promotion [10]
of the (sp3)C–H bond activation by bulky substituents at the phos-
phorus atom of ligand HL allowed us to isolate the target dimer
rac-1 in 92% yield. Complete insolubility of the racemic dimer 1
in common solvents forced us to elaborate a non-standard route
for its purification, including its conversion into the much more
soluble mononuclear pyridine derivative (2), its chromatographic
isolation on silica, followed by protolytic removal of the auxiliary
ligand. The structure of the CP-palladacycle 1 was confirmed by
⇑
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).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.09.024

28
V.V. Dunina et al. / Polyhedron 30 (2011) 27–32
Et
Et
Me
Cl
Pd
+
H
Cl
Cl
Ph
P
I
NMe2
Ph2P
P
Pd
2
O
Fe
Ph
Pd
C(O)R
H
+
Me
Et
Pd
N
P
Me
Ph2P
+
PPh2
Et
(S)-I
(S)-II
(RPSC)-III
(R,R)-IV
Fig. 1. Reported phosphapalladacycles with the Pd–C* bond.
spectral studies of its phosphine derivative rac-3 prepared by a
standard chloride bridge cleavage reaction between rac-1 and
PPh3 (Scheme 1).
The spectral characteristics of complex rac-3 confirm metalla-
tion at the a-carbon of the ortho-Et substituent. It is deduced from
(Stien), as chiral derivatizing reagents. Reaction of the dimer rac-
1 with diamine (R,R)-Stien afforded equimolar mixture of two
diastereomeric derivatives, (S,RR)-4a and (R,RR)-4b, in nearly
quantitative yield of 97%. After twofold recrystallization of this
mixture from acetonitrile containing a trace quantity of MeOH
the pure diastereomer (S,RR)-4a (>98% de, 31P{1H} NMR data) was
isolated in 56% yield with respect to the corresponding enantiomer
of the racemic dimer (R,S)-1 (Scheme 1). Unfortunately, all at-
tempts to isolate other diastereomer (R,RR)-4b from mother li-
quors were unsuccessful because of its high solubility in all
solvent systems used; the enrichment extent does not exceed
40–60% de.
This problem was solved using (S,S)-Stien as the resolving agent.
As the result, another enantiomer of the C*P-palladacycle was iso-
lated in the form of diastereomer (R,SS)-4c (>98% de, 31P{1H} NMR
data) by separation of the diastereomer mixture, (R,SS)-4c and
(S,SS)-4d, under similar conditions.
the presence in its 1H NMR spectrum of doublets for the two intact
PBut groups (d 1.47 and 1.65 ppm) and signals for CHMe and CHMe
at d 1.13 and 3.14, respectively, present as expected multiplets
(ddd and ddq, respectively). The 31P{1H} and 1H NMR spectra of
complex 3 contain only one signal or one set of signals, respec-
tively, which confirms regioselective coordination of the soft phos-
phorus donor atom of the auxiliary ligand; its trans(P,P)-geometry
2
is evident from the value of the spin-spin coupling constant JPP
353 Hz.
Initial attempts to separate enantiomers of the C*P-dimer 1
using (S)-a-methylbenzylamine or (S)-prolinate as chiral derivatiz-
ing agents were unsuccessful: (i) the first reagent forms dynami-
cally flexible mononuclear adducts; (ii) coordination with dimer
rac-1 of the second non-symmetric N,O-reagent bearing hard donor
atoms occurs with low regioselectivity, that is typical for phospha-
palladacycles [11].
A serious problem arose during conversion of the diamine ad-
ducts (S,RR)-4a and (R,SS)-4c conversion to the corresponding
enantiopure dimers (S,S)-1 and (R,R)-1. The commonly used ap-
proach of protonation of the auxiliary ligand with a strong acid
such as HCl typically results in partial racemization [3b] or epimer-
ization [2a] of CPCs containing a Pd–C* bond. This is presumably
This problem was solved using both enantiomers of C2-sym-
metric ligand, (R,R)- and (S,S)-1,2-diphenylethane-1,2-diamine
But
tBu
But
Pd
tBu
PBut2
P
P
(iii)
Cl
(i), (ii)
Cl
Py
Pd
H
C
H
2
H
Me
Me
H
Me
HL
rac-1 (crude)
rac-1 (pure)
rac-2
(iv), (v)
But
But
1
P
(vi)
Cl
tBu
P
But
Pd
+
Pd
H2
N
Ph
2PPh3
(vii)
Cl-
H
Me
N
rac-3
Ph
H
H2
Me
(R,RR)-4b
tBu
But
Pd
+
+
tBu
H2
P
Ph
Cl-
Ph
N
But
H2
N
+
(viii)
P
Ph
N
H
H2
Pd
Cl-
Ph
Me
N
(S,RR)-4a
>98% de (31P NMR data)
H
H2
Me
(S,RR)-4a
Scheme 1. Synthesis and resolution of the cyclopalladated dimer 1. Reagents and conditions: (i) Pd(OAc)2, PhMe, 50 °C, 1 h. (ii) LiCl, MeOH, rt. (iii) Py, PhH, rt, 0.5 h. (iv) SiO2.
(v) 1M HClaq, CH2Cl2, rt. (vi) PPh3, PhH, 55 °C, ꢀ7 min; rt, 40 min. (vii) (R,R)-Stien, MeOH, rt, 1 h. (viii) MeCN/MeOH (ꢀ100:1), ꢁ18 °C, double recrystallization.

V.V. Dunina et al. / Polyhedron 30 (2011) 27–32
29
But
Cl
tBu
H
But
Cl
tBu
H
tBu
But
Pd
+
-
H2
N
P
P
Ph
P
1M HClaq
1M AcOHaq
Pd
Pd
Cl
Ph
2
2
Method 1
Method 2
N
H
H2
Me
Me
Me
(R,R)-1, 70% ee
(R,SS)-4c, >98% de
(R,R)-1, >98% ee
Scheme 2. Auxiliary ligand removing. Reagents and conditions. Method 1: 1M HClaq/CH2Cl2, ꢀ5 °C, ꢀ1 min; Method 2: 1M AcOHaq/CH2Cl2, ꢀ5 °C, ꢀ2 min.
the reason for the absence of any data regarding removal of the
auxiliary ligand from CPCs of this kind; the procedure is usually
ineffective on such non-reactive phosphine [3a,3e,f] or pyridine
stabilised forms of the palladacycle [4].
Taking into account an expected high sensitivity of the Pd–C*
bond to acids, we have modified the standard conditions of protoly-
sis with 1M HCl [12] by using a low-temperature regime (ca. 5 °C).
However, protolytic removal of the auxiliary diamine Stien from dia-
stereomerically pure (>98% de) complex (R,SS)-4c under these con-
ditions (see Experimental, Method 1) resulted in a considerable
decrease of enantiopurity (ca 70% ee, 31P{1H} NMR data)1 of the pal-
ladacycle in dimer (R,R)-1. The enantiomerically pure dimer (R,R)-1
was obtained only after replacing the strong acid HCl with the weak
acid CH3CO2H and performing the reaction as fast as possible under
a low-temperature regime (ca. 5 °C, Method 2, Scheme 2).
The enantiomeric dimer (S,S)-1 may be isolated in a similar
manner from its diastereomerically pure diamine derivative
(S,RR)-4d.
This success was achieved due to a combination of three fac-
tors: (i) using a weak acid, CH3CO2H, (ii) performing the protolysis
at a lower temperature, and (iii) minimising the contact time
between the palladacycle and the acid. By comparison, removal
of the amino acidate ligand by protolysis with AcOH but at room
temperature and a longer contact time of ca. 12 h resulted in de-
crease of enantiomeric purity from 33% to 28% ee [3b].
Fig. 2. Molecular structure and numbering scheme for the diastereomer (S,RR)-4a;
hydrogen atoms (except for NH2) and solvent MeCN molecule are omitted for
clarity. Selected bond lengths (Å): Pd(1)–C(7) 2.078(7), Pd(1)–P(1) 2.238(2), Pd(1)–
N(1) 2.186(6), Pd(1)–N(2) 2.137(6); P(1)–C(1) 1.823(9), P(1)–C(31) 1.863(10),
P(1)–C(35) 1.880(8); N(1)–C(11) 1.498(9), N(2)–C(21) 1.486(9). Selected angles
(°): C(6)–C(7)–Pd(1) 117.6(6), C(7)–Pd(1)–P(1) 84.5(2), C(1)–P(1)–Pd(1) 104.2(3),
C(6)–C(1)–P(1) 113.2(6), C(7)–C(6)–C(1) 120.5(7); N(2)–Pd(1)–N(1) 79.4(2), Pd(1)–
N(1)–C(11) 110.7(4), N(1)–C(11)–C(21) 110.3(6), C(11)–C(21)–N(2) 107,5(6),
C(21)–N(2)–Pd(1) 109.7(4); N(1)–Pd(1)–P(1) 104.61(17), C(7)–Pd(1)–N(2) 91.7(3),
C(7)–Pd(1)–N(1) 169.9(3), N(2)–Pd(1)–P(1) 175.57(19); C(31)–P(1)–Pd(1) 113.1(3),
C(35)–P(1)–Pd(1) 112.3(3).
The optically active C*P-palladacycle 1 with the (sp3)C*–Pd
bond is configurationally stable at high temperature: after reflux-
ing of the scalemic (70% ee) dimer (R,R)-1 in toluene (110 °C, 3 h)
its enantiomeric composition remained the same (31P{1H} NMR
data). This fact seemed to be rather surprising taking into account
the presence of several b-H atoms quite suitable for the b-hydride
elimination (cf. [2a]). As a probable reason for such reluctance to
undergo b-H elimination one can suggest that conformation of
the palladacycle imposes some steric restrictions on this process.
As indirect evidence in favor of the C*P-palladacycle conformation
The geometric parameters of the C*P-palladacycle and N,N-che-
lated diamine ring in complex (S,RR)-4a are in the range of the val-
ues found for the known derivatives Va–c [13a–c], VIa,b [13d,e]
and (SP,SCSN)-VII [14] of related cyclopalladated phosphines
oTol2PR (R = ortho-Tol, tert-Bu), and a known adduct of CN-pallada-
cycle with diamine (S,S)-Stien, (SCRN,SCSC)-VIII [12a,b], respectively
(Fig. 3).
The Pd–P bond lengths in the structures of our adduct (S,RR)-4a
and its analog (SP, SCSN)-VII are very similar (2.238 c.f. 2.240 Å,
respectively), and this is quite expected taking into account the
close Structural Trans-Influences (STI) of trans-disposed amino
groups of prolinate and diamine ligands and similarity of electronic
and stereochemical characteristics of P-donor groups in these com-
with quasi-axial orientation of the
a-methyl group (preventing
b-H elimination) we could mention spectral data in support of qua-
si-equatorial position of the a
-CH proton: in the 1H NMR spectrum
of the phosphine adduct rac-3 the coupling constant 3JHP2 for
a-CH
proton has a rather large value equal to 13.1 Hz.
The absolute configuration of the palladium bonded carbon ste-
reocenter in dimers (S,S)-1 and (R,R)-1 was determined by an X-ray
diffraction study of diamine precursor (S,RR)-4a (which was crys-
tallized as mono-acetonitrile solvate). The molecular structure of
this diastereomer with the numbering scheme and selected bond
lengths and angles are presented in Fig. 2. The (S)-configuration
of the palladium bonded C*-atom is established independently
using diamine (R,R)-Stien as a reference point and based on the
anomalous X-ray scattering method with the Flack parameter of
0.01(5). The metallation at the (sp3)C–H bond of the ortho-Et sub-
stituent was also confirmed unambiguously.
plexes (Tolman angles h for PBut2 and PToloBut are equal to 121°
2
3
and 126°, respectively) [15]. The length of the Pd–C(sp3) bond in
the complex (S,RR)-4a (2.078 Å) is within the range of literature
values (2.010–2.091 Å) for cyclopalladated derivatives V–VII of
di- and tri-ortho-tolylphosphines.
The lengths of Pd NH2 bond in diamine adduct (S,RR)-4a and
Pd NH bond in prolinate derivative (SP,SCSN)-VII lying on the diag-
onal N–Pd–P are also similar (2.137 cf. 2.119 Å, respectively) due to
close levels of STI for these P-donor groups [11]. To compare, the
Pd NH2 bond trans-disposed to amino group in structure of
CN-analog (SCRN,SCSC)-VIII is markedly stronger (2.058 Å) in accor-
dance with the less pronounced STI of N-donor atom of the palla-
dacycle. Some weakening of the Pd NH2 bond in the structure
of our complex (S,RR)-4a compared with that in its ortho-palladat-
ed CN-analog (SCRN,SCSC)-VIII (2.186 and 2.152 Å, respectively)
1
Here and later on, enantiomeric purity of all samples of the dimer
1 was
determined by 31P{1H} NMR spectroscopy after its chiral derivatization with diamine
(S,S)- or (R,R)-Stien in situ.

30
V.V. Dunina et al. / Polyhedron 30 (2011) 27–32
H
Me
N
Tol o
X
Tol o
o
R
Tol o
But
Pri
H
Tol
P
P
X
P
Pd
Pd
Pd
H
2
Pd
Cl-
Q
O
H2N
NH2
N
Va-c
R = But, X = AcO (a);
R = Tolo: X = AcO (b), I (c). X Q = pz3BH (b).
VIa,b
X =AcO, Q = Et3N (a);
H
Ph
(SCRN,SCSC)-VIII
O
Ph
(SP,SCSN)-VII
Fig. 3. Reported CPCs of CP-type with the Pd–C(sp3) bond (V-VII) and adduct of CN-palladacycle with diamine Stien (VIII).
illustrates greater STI of the carbanionic aliphatic (sp3)C– atom
compared to aromatic (sp2)C–.
analyses were performed with automatic analyzer VarioMicroC-
OBE of firm Elementar.
The palladium coordination environment in diastereomers
(S,RR)-4a and (SP,SCSN)-VII reveals very slight tetrahedral distortion
with interplanar angles {N–Pd–E}/{P–Pd–C}, equal to 5.24° and
3.5°, respectively. As for unusual peculiarity of the adduct (S,RR)-
4a we can mention near-ideal planar structure of its phosphapalla-
All reactions were conducted under argon using TLC control on
Silufol. All manipulations with free phosphine were carried out un-
der dry purified argon in carefully dezoxygenated and dried sol-
vents using Schlenk technique. The purification of the
compounds was performed by means of short dry column [16] or
flash-chromatography on silica gel (60, Fluka).
ꢀ
dacycle with averaged intrachelate torsion angle (xav) equal to
2.64°, that is in drastic contrast with very significant palladacycle
twisting in the structures of its analogs V–VII (xav 11.5–29.2°).
As one may expect, N,N-chelated diamine ring in C*P-adduct
(S,RR)-4a and in its CN-analog (SCRN,SCSC)-VIII reveals the pro-
Benzene, toluene and hexane were dried with the appropriate
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 methox-
ide for 3 h and then distilled; AcOH was freshly freezed out; CD2Cl2
and CDCl3 (from Aldrich) were distilled from CaH2 just before
using; acetonitrile was distilled under argon from P2O5 and then
from K2CO3.
ꢀ
ꢀ
nounced distortion in the form of envelope with xav values equal
to 30.8° and 32.2°, respectively.
3. Conclusions
The first representative of enantiopure C*P-palladacycles with
the Pd atom directly bonded to a carbon stereocenter that is the
only chirality element present, has been prepared via resolution
of the corresponding racemic dimer using both enantiomers of
C2-symmetric diamine Stien as chiral derivatizing agent. The proce-
dure for removal of the auxiliary diamine ligand from the interme-
diate mononuclear diastereomerically pure diamine derivative has
been refined so that it proceeds without any loss in the palladacy-
cle enantiopurity. The absolute (S)-configuration of the carbon ste-
reocenters in the enantiopure dimer 1 was determined by X-ray
diffraction study of its diamine precursor (S,RR)-4a. It was estab-
lished that dimer (R,R)-1 was configurationally stable at tempera-
tures up to 110 °C.
4.2. Reagents and starting compounds
Palladium(II) acetate, (R,R)-(+)- and (S,S)-(–)-1,2-diphenylethy-
lenediamines (from Aldrich) were used as received; pyridine
was dried with 4 Å molecular sieves and distilled from KOH;
triphenylphosphine (from Chemapol) was purified by twofold
recrystallization from a benzene/hexane mixture. Di-tert-butyl-
ortho-ethylphenylphosphine (HL) was synthesized by known
method [7] in the yield of 71%: bp (0.5 torr) 85–87°C, 31P{1H}
NMR (CDCl3, d, ppm): 13.9 (s).
4.3. Syntheses of cyclopalladated complexes
Currently, we are studying stoichiometric and catalytic reac-
tions with participation of C*P-dimer 1 and other optically active
cyclopalladated derivatives of prochiral ligands in order to obtain
some mechanistic information regarding these processes.
4.3.1. Preparation of racemic di-l-chlorobis[1-{2-(di-tert-butyl-
phosphino)phenyl}ethyl-C1,P] dipalladium(II) (rac-1)
A solution of Pd(OAc)2 (0.6277 g, 2.796 mmol) and phosphine
HL (0.700 g, 2.796 mmol) in toluene (15 mL) was stirred for 1 h
at 50 °C, then the solvent was evaporated and the residue was trea-
ted with a solution of LiCl (0.2371 g, 5.592 mmol) in methanol
(15 mL). The precipitate formed was filtered and washed with
methanol (5 mL). The crude dimer was treated with pyridine
(3.398 mmol) in benzene (10 mL) at r.t., after 30 min of stirring
the solvent was evaporated. The crude mononuclear pyridine
derivative rac-2 (31P{1H} NMR: d 93.25 (s) in CDCl3) was purified
using dry column chromatography (h = 1 cm, d = 4 cm; eluent:
CHCl3). The solution of adduct rac-2 in CH2Cl2 (20 mL) was treated
with solution of 1N HClaq (2 ꢂ 10 mL), organic layer was washed
with water, dried over Na2SO4 and evaporated to give dimer rac-
1 as a light-yellow amorphous powder insoluble in common or-
ganic solvents. Yield: 92% (1.0087 g, 1.289 mmol). M.p. (dec.)
303–306 °C; Rf 0.85 (benzene). Anal. Calc. for C32H52P2Pd2Cl2 re-
quires: C, 49.12; H, 6.70; P, 7.92. Found: C, 49.30; H, 6.68; P,
7.80%. 31P{1H} NMR (CDCl3): d 95.39 (br. s).
4. Experimental section
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 (unless otherwise indicated). The proton chemical shifts
are reported in parts per million relative to TMS as internal stan-
dard; the 31P chemical shifts are given relative to H3PO4 as an
external reference. The assignment of signals was based on the
homo- and heteronuclear decoupling and NOE experiments. Opti-
cal rotations were measured with VNIEKI-Prodmush AI-EPO in
1.2 dm cells at 25 °C. Melting points were measured with Electro-
thermal IA 9000 series device in a sealed capillary. Elemental

V.V. Dunina et al. / Polyhedron 30 (2011) 27–32
31
4.3.2. Preparation of racemic chloro[1-{2-(di-tert-butylphosphino)
phenyl}ethyl-C1,P](triphenylphosphine-P) palladium(II) (rac-3)
A suspension of dimer rac-1 (0.0300 g, 0.0383 mmol) and slight
excess of PPh3 (0.0221 g, 0.084 mmol) in benzene (2 mL) was
stirred at r.t. for 40 min and then at 55 °C, for 7 min. It was evap-
orated in vacuo to dryness, and the crude product was purified
using dry column chromatography (h = 5 cm, d = 4 cm; eluents:
hexane and then hexane/benzene, 1:1) to afford the adduct 3 as
colorless crystalline solid. Yield: 86% (0.0431 g, 0.0659 mmol).
M.p 208–210 °C; Rf 0.34 (benzene). Anal. Calc. for C34H41P2PdCl re-
quires: C, 62.49; H, 6.32. Found: C, 62.84; H, 6.29%. 31P{1H} NMR
(CDCl3, d, ppm, J, Hz): d = 24.00 [d, P2, 2J(P2P1) = 352.7], 83.01 [d,
P1, 2J(P1P2) = 352.7]. 1H NMR (CDCl3, d, ppm, J, Hz): d = 1.13 [ddd,
3J(HH) = 7.4, 4J(HP1) = 2.8, 4J(HP2) = 6.0, 3H, CHMe], 1.47 [d,
d = 3.69 (br. s. 1H), 4.10–4.69 (a group of br. s., 4H), 4.72 (br. s.,
1H). Anal. Calc. for C30H42N2PClPd requires: C, 59.70; H, 7.01; N,
4.64. Found: C, 59.62; H, 7.11; N, 4.71%. 31P{1H} NMR (CDCl3): d
92.94 (s).
4.5. Removal of the auxiliary diamine ligand
4.5.1. (R,R)-Di–chlorobis[1-{2-(di-tert-butylphosphino)phenyl}ethyl-
C1,P]dipalladium(II) ((R,R)-1)
Two methods of isolation of optically active dimer (R,R)-1 were
employed and both included using cold solvents, acid solution and
precooled glassware (ca. 5 °C), at minimal duration of CPC contact
with acid.
Method 1. The solution of individual diastereomer (R,SS)-4c
(0.0470 g, 0.0778 mmol) in dichloromethane (5 mL) was treated
with aqueous 1M HCl (2 ꢂ 5 mL) under vigorous shaking during
ca. 1 min. Then combined organic layers were washed with water
(3 ꢂ 5 mL), dried over MgSO4, and concentrated in vacuo to dry-
ness. The residue was dried in vacuo (7 mm Hg) over CaCl2/paraf-
fine to obtain dimer (R,R)-1 as amorphous light-yellow powder.
Yield: 89% (0.0272 g, 0.0347 mmol) and of optical purity 70% ee
t
t
3J(HP1) = 13.7, 9H, Bu], 1.65 [d, 3J(HP1) = 14.1, 9H, Bu], 3.14 [ddq,
3J(HP1) = 3.6, 3J(HP2) = 13.1, 1H, -CH], 6.88 [d, 3J(H3H4) = 7.9, 1H,
a
H3), 7.16 (m, 1H, H5), 7.20 (m, 1H, H4) 7.37–7.42 (m, 9H, ortho-
and meta-PPh), 7.65 [dd, 3J(H6H5) = 7.5, 3J(HP1) = 5.8, 1H, H6].
4.4. Separation of the enantiomers of racemic dimer 1
4.4.1. Preparation of diastereomeric mixture (S,RR)/(R,RR)-[1-{2-(di-
tert-butylphosphino)phenyl}ethyl-C1,P](1,2-diphenylethane-1,2-di-
amine-N,N)palladium(II) chloride ((S,RR)-4a/(R,RR)-4b)
(
31P{1H} NMR data).
Method 2. solution of the pure diastereomer (R,SS)-4c
A
(0.0233 mmol) in CH2Cl2 (5 mL) was treated with 1M aqueous
AcOH (2 ꢂ 5 mL) under vigorous shaking during ca. 2 min. The
combined organic layers were washed with water (3 ꢂ 5 mL), satu-
rated aqueous NaHCO3 solution (2 ꢂ 5 mL) and water (3 ꢂ 5 mL),
dried over Na2SO4, and evaporated. A solution of the residue in
CH2Cl2 was eluted through a short SiO2 column (h = 0.5 cm,
d = 2.5 cm; eluent: CH2Cl2). After drying in vacuo, the enantiopure
dimer (R,R)-1 (>98% ee, 31P{1H} NMR data) was isolated as an amor-
A suspension of dimer rac-1 (0.932 g, 1.19 mmol) and diamine
(R,R)-Stien (0.5057 g, 2.38 mmol) in anhydrous MeOH (20 mL)
was stirred for 1 h at r.t., the solution was filtered and evaporated
to dryness to give the diastereomer mixture (S,RR)-4a/(R,RR)-4b as
a colorless amorphous powder. Yield: 97% (1.4008 g, 2.321 mmol).
½
a 2D5
+ 20.0° (c 0.25, CHCl3). Anal. Calc. for C30H42N2PClPd requires:
C, 59.70; H, 7.01; N, 4.64. Found: C, 59.65; H, 7.05; N, 4.55%.
ꢃ
31P{1H} NMR (CDCl3): d 92.98 (s), 93.22 (s).
phous light-yellow powder. Yield: 87% (0.0131 g, 0.0167 mmol).
20
589
Mp 238–240 °C; Rf 0.75 (benzene/acetone 15:1). ½
aꢃ
ꢁ43.3° (c
4.4.2. Isolation of diastereomer (S,RR)-[1-{2-(di-tert-butylphosphino)
phenyl}ethyl-C1,P](1,2-diphenylethane-1,2-diamine-N,N)palladium(II)
chloride ((S,RR)-4a)
0.3, CH2Cl2). Anal. Calc. for C32H52P2Pd2Cl2 requires: C, 49.12; H,
6.70; P, 7.92. Found: C, 49.27; H, 6.62; P, 7.98%. 31P{1H} NMR
(CDCl3): d 95.35 (br.s). 1H NMR (CDCl3, d, ppm, J, Hz): d = 1.45 [d,
3J(HP) = 14.3, 9H, But], 1.51 [d, 3J(HP) = 14.5, 9H, But], 1.56 (br. m,
A first low-temperature crystallization of this mixture from ace-
tonitrile-MeOH ꢀ100:1 mixture affords the less soluble diastereo-
mer (S,RR)-4a enriched to 80% de (31P{1H} NMR data) and more
soluble diastereomer (R,RR)-4a (isolated from mother liquor) of
only 40% de. After a second crystallization of the diastereomer
(S,RR)-4a under the same conditions, and thoroughly drying in
vacuo (1 mm Hg), the diastereomer (S,RR)-4a (>98% de, 31P NMR
data) was isolated as colorless crystals. Yield: 56% (0.3921 g,
0.6496 mmol) with respect to the corresponding enantiomer of
3H,
a-Me), 4.23 (br. m, 1H, a-CH), 7.19 (m, 1H, H6), 7.28–7.39
(m, 2H, H4, H5), 7.55 (m, 1H, H3).
4.6. X-ray crystallographic data for diastereomer (S,RR)-4a
Crystals of complex (S,RR)-4a (C32H47ClN3OPPd, FW = 662,55)
are orthorhombic, space group P212121 at 120(2) K, a = 8.0701(3),
b = 11.9266(5), c = 34.1120(14) Å, V = 3283.2(2) Å3, Z = 4, dcalc
=
the racemic dimer (R,S)-1. mp 205–206 °C; ½a D25
ꢃ
+ 8.9° (c 0.25,
1.340 gcm-3, (MoK
tions were measured on a Bruker SMART 6K diffractometer
(k(MoK ) = 0.71073 Å, h < 26.00°) and 6416 independent reflec-
a
) = 0.723 mmꢁ1. Intensities of 12891 reflec-
CHCl3). Anal. Calc. for C30H42N2PClPd requires: C, 59.70; H, 7.01;
N, 4.64. Found C, 59.98; H, 7.15; N, 4.87%. 31P{1H} NMR (CDCl3):
d 92.94 (s).
a
tions (Rint = 0.0686) were used in further refinement. The structure
was solved by direct methods and refined by the full-matrix least-
squares on F2 with anisotropic thermal parameters for all non-
hydrogen atoms except solvent MeCN molecule. Acetonitrile atoms
N3, C9 and C10 were refined in an isotropic approximation. All
hydrogen atoms (except water) were placed in calculated positions
and refined using a riding model. Both water H atoms were found
from difference Fourier synthesis and also refined using a riding
model. The refinement converged to R1 = 0.0608 for 4652 reflec-
tions with I > 2(I) and wR2 = 0.1418 for all data. Flack parameter re-
sulted in 0.01(5). All calculations were performed using SHELXTL
software.
4.4.3. Isolation of diastereomer (R,SS)-[1-{2-(di-tert-butylphosphino)
phenyl}ethyl-C1,P](1,2-diphenylethane-1,2-diamine-N,N)palladium(II)
chloride ((R,SS)-4c)
In a similar manner the diastereomer mixture (R,SS)-4c/(S,SS)-
4d was obtained using diamine (S,S)-Stien as chiral derivatizing
agent in the yield of 98% (0.5204 g, 0.8622 mmol). Its double
low-temperature crystallization from acetonitrile affords diaste-
reomer (R,SS)-4c (>98% de, 31P NMR data) as colorless crystals.
Yield: 37% (0.0961 g, 0.159 mmol). M.p 204–206 °C. ½a 20
ꢃ
589–9.2 (c
0.25, CHCl3). 31P{1H} NMR (CDCl3): d 92.98 (s). 1H NMR (CD2Cl2,
at 8 °C, d, ppm, J, Hz): palladacycle signals: d = 1.34 [d,
3J(HP) = 14.2, 9H, But], 1.42 [d, 3J(HP) = 14.1, 9H, But], 1.45 [dd,
Acknowledgments
4J(HP) = 2.7, 2J(HH) = 7.3, 3H,
a
-Me], 3.91 [dq, 2J(HH) = 7.3,
3J(HP) = 4.0, 1H,
a-CH]; aromatic protons of palladacycle:
This study was supported partly by the Russian Academy of
Sciences, grant OXNM-01. The authors thank Dr. I.P. Smoliakova
for valuable discussion.
d = 7.20–7.27 (m, 7H), 7.34–7.41 (m, 6H), 7.57 [t, 3J(HP) = 6.8,
2J(HH) = 7.9, 1H, H6]; (S,S)-Stien ligand CH and NH signals:

32
V.V. Dunina et al. / Polyhedron 30 (2011) 27–32
Chem. 54 (1984) 2290 (Engl. Transl. is available);
A. Supplementary data
(c) V.V. Dunina, O.A. Zalevskaya, I.P. Smoliakova, V.M. Potapov, Dokl. Akad.
Nauk SSSR 278 (1984) 628 (Engl. Transl. is available).
CCDC 763106 contains the supplementary crystallographic data
for complex (S,RR)-4a acetonitrile mono-solvate. 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.
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Rheingold, Organometallics 23 (2004) 2228;
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ˇ
´
ˇ
ˇ
ˇ
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