Palladium complexes with meso-bioxazoline ligands for alternating styrene/CO copolymerisation: Counterion effect

Article abstract of DOI:10.1016/j.jorganchem.2005.01.063

Two sets of mono- and dicationic palladium complexes (8) and (10), having CF3SO3-,BF4- and PF6- as counterions, were synthesised. The interionic structure of the methyl-acetonitrile complexes [Pd((R,S)-Bn-Box)(CH₃) (NCCH₃)](X) (8) in

Full text of DOI:10.1016/j.jorganchem.2005.01.063

Journal of Organometallic Chemistry 690 (2005) 2254–2262
www.elsevier.com/locate/jorganchem
Palladium complexes with meso-bioxazoline ligands for
alternating styrene/CO copolymerisation: Counterion effect
a
a,
b
c
Doina Sirbu , Giambattista Consiglio *, Barbara Milani , P.G. Anil Kumar ,
c
Paul S. Pregosin , Sebastian Gischig
c
a
Eidgeno¨ssische Technische Hochschule, Institut fu¨r Chemie und Bioingenieurwissenschaften, Ho¨nggerberg, CH-8093 Zu¨rich, Switzerland
b
`
Dipartimento di Scienze Chimiche, Universita di Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy
c
Eidgeno¨ssische Technische Hochschule, Laboratorium fu¨r Anorganische Chemie, Ho¨nggerberg, CH-8093 Zu¨rich, Switzerland
Received 23 November 2004; revised 17 January 2005; accepted 17 January 2005
Available online 14 April 2005
Abstract
Two sets of mono- and dicationic palladium complexes (8) and (10), having CF3SOꢀ3 ; BF4ꢀ and PF6ꢀ as counterions, were syn-
thesised. The interionic structure of the methyl-acetonitrile complexes [Pd((R,S)-Bn-Box)(CH3)(NCCH3)](X) (8) in solution, was
investigated by pulsed-gradient spin-echo (PGSE) diffusion measurements and (1H, 19F)-HOESY NMR spectroscopy. A high degree
of ion-pairing was found in each complex. The HOESY spectra showed that the BFꢀ4 and PF6ꢀ anions take up selective positions, on
the side of the complex remote from the benzyl groups, but close to the acetonitrile ligand, while the triflate is, partially, occupying a
pseudo fifth coordination position on the side of the cation remote from the two benzyl-groups. The complexes 8 and 10 were used
as catalyst precursors for the copolymerisation of styrene with carbon monoxide, producing syndiotactic copolymers, with the
exception of complex 10a, that led to isotactic copolymers.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Palladium; Bioxazoline; Copolymerisation; Styrene; Carbon monoxide; Counterion effects
1. Introduction
The use of palladium complexes [Pd(N,N)(H2O)2]-
(X)2, where N,N = (R,R)- or (R,S)-4,40-dibenzyl-2,20-
bi-(2-oxazoline), as catalyst precursors, was reported
[4] to lead to poly[1-oxo-2-phenylpropane-1,3-diyl] hav-
ing all possible limiting steric structures (isotactic, atac-
tic, syndiotactic), depending on the copolymerisation
reaction conditions. Thus, the diaquapalladium catalyst
precursor, modified with both the chiral and the meso-
bioxazoline ligands, produces a styrene CO copolymer
with a prevailing isotactic structure, in methylene chlo-
ride as the solvent. When used in the presence of the free
ligand, the optically active catalyst gives an atactic
copolymer, whereas the meso-catalyst, remarkably,
leads to a prevailingly syndiotactic copolymer [4]. More-
over, the meso-catalyst produces also syndiotactic
copolymers when methanol is present in the solvent
The alternating copolymerisation of olefins with car-
bon monoxide has been investigated in the past both for
the practical application of the polyketone products ob-
tained and for the interest in the mechanism of the pro-
cess, and it is still the subject of extensive research [1].
Using styrene as the olefin, suitable catalysts are mainly
cationic Pd(II) complexes with nitrogen bidentate li-
gands and weakly coordinating anions [2]. Highly iso-
tactic optically active polyketones have been obtained
with bisoxazoline, bioxazoline, diketimine or diphos-
phine chiral ligands with C2 symmetry [3].
*
Corresponding author. Tel.: +41 1 63 23552; fax: +41 1 63 21162.
E-mail address: consiglio@chem.ethz.ch (G. Consiglio).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.063

D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
2255
mixture [4]. These results suggest that there are counter-
ion effects present.
literature procedure [6], involving the synthesis of the
crystalline [Pd((R,S)-Bn-Box)(CH3)Cl] complex (7), the
structure of which was investigated by X-ray analysis
(Fig. 1). The most interesting feature of this molecule
is the position of the benzyl groups, both pointing
downwards. A selection of characteristic bond lengths
and bond angles for this structure is given in Table 1.
The [Pd((R,S)-Bn-Box)(H2O)2] (X)2 complexes
(10a–c), bearing different counterions (X = CF3SO3,
BF4, PF6, respectively), were prepared by a two step
procedure, based on the synthesis of the neutral deriv-
ative [Pd((R,S)-Bn-Box)Cl2] (9) and followed by the
usual dehalogenation using the corresponding silver
salts [7].
Therefore, we decided to investigate the interionic
structure of the monocationic complexes [Pd((R,S)-
Bn-Box)(CH3)(NCCH3)](X), where X = CF3SO3, BF4
and PF6. The study of the anion–cation interactions in
solution could lead to a better understanding of the role
of the anion in the catalytic processes and to optimizing
the choice of the ‘‘cation–anion pair’’.
This study presents the synthesis of [Pd((R,S)-Bn-
Box)(CH3)(NCCH3)](X)
and
[Pd((R,S)-Bn-Box)-
(H2O)2](X)2 complexes, (where X = CF3SO3, BF4 and
PF6, respectively), and their catalytic activity toward
styrene/CO copolymerisation. The interionic structure
of the methyl–acetonitrile complexes in solution was
investigated by pulsed-gradient spin-echo (PGSE) diffu-
sion measurements and (1H, 19F)-HOESY NMR
spectroscopy.
2.2. NMR studies
All the complexes were characterised at room temper-
1
ature in dichloromethane by H, 13C, 19F, one dimen-
2. Results and discussions
sional spectra, plus 1H–1H COSY, 13C–1H one-bond
1
and long-range correlations, and H–1H NOESY mea-
2.1. Synthesis
surements. Fig. 2 depicts a section of the COSY in the
benzylic proton region for complex 8c. This figure al-
lows us to distinguish between the weakly coupled AB
spin system (d = 2.77 and 3.04) and a strongly coupled
The meso-bioxazoline ligand ((R,S)-Bn-Box) (6) was
prepared by a four step literature procedure [5], and sep-
arated from the racemic mixture by flash chromatogra-
phy, in 72% yield (Scheme 1).
The methyl–palladium complexes [Pd((R,S)-Bn-Box)
(CH3)(NCCH3)] (X) (8a–c), (where X = CF3SO3,
BF4, PF6, respectively), were prepared by a four step
1
AB spin system centered at d = 2.93. H–1H NOESY
measurements indicate that the weakly coupled benzylic
protons were close to the complexed methyl group and
those of strongly coupled spins close to the bound
acetonitrile.
HO
O
HO
O
NEt3
OEt
+
Cl
OEt
THF / DMF
Bn
N
H2N
Bn
O
H
O
1
(S)-2
3
HO
Toluene,
80 oC
H2N
Bn
(R)-2
HO
Bn
Cl
O
O
H
N
H
SOCl2
Bn
N
Bn
N
Bn
N
H
H
O
O
OH
Cl
5, 93%
4, 80%
84%
KOH
O
N
O
N
O
N
O
N
O
N
O
N
+
+
Bn
Bn
Bn
Bn
Bn
Bn
(R,S)-6
Scheme 1. Synthesis of (R,S)-4,40-dibenzyl-2,20-bi-(2-oxazoline) ligand (6).
(R,R)-6
(S,S)-6

2256
D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
The diffusion constants, D, from the PGSE measure-
ments in dichloromethane/methanol (9:1) solutions on
the complexes [Pd((R,S)-Bn-Box)(CH3)(NCCH3)](X),
8a–c, are presented in Table 2.
The Stokes–Einstein equation allows us to use mea-
sured D-values to estimate a hydrodynamic radius, rH.
kT
6pgrH
D ¼
;
where rH is the radius, g is the viscosity.
While the D-values for the three cations do not differ
much as a function of the anion, the rH values for the
anions suggest differing degrees of ion pairing. It is
known that dichloromethane solutions usually promote
ion-pairing in salts of various transition metals [9]. For
8a–c the highest degree of ion-pairing was found with
triflate as the counterion, although the differences are
not dramatic.
Fig. 1. ORTEP drawing of the complex [Pd((R,S)-Bn-Box)(CH3)Cl]
(7).
Table 1
˚
Relevant bond lengths (A) and angles (ꢁ) for complex 7
The effect of methanol as co-solvent was uncertain so
that we have measured D-values for a model complex,
11 (Fig. 3), which (1) was soluble in both dichlorometh-
ane and dichloromethane/methanol (9:1); (2) has the an-
ion of interest and (3) has an oxazoline ring bound to
palladium. These data (see Table 3) suggest that the
ca. 10% methanol has no effect, on the cation, and only
a small effect on the triflate.
Pd(1)–C(1)
Pd(1)–Cl(1)
2.025(5)
2.2758(17)
Pd(1)–N(1)
Pd(1)–N(2)
2.162(4)
2.066(4)
C(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–N(1)
C(1)–Pd(1)–N(1)
89.04(17)
78.19(17)
173.8(2)
C(1)–Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
96.7(2)
96.14(13)
174.00(13)
2.2.2. (1H, 19F)-HOESY NMR experiments
(1H, 19F)-HOESY methods provide useful structural
tools for salts with fluorine containing anions in that
they help to localise the position of the counter-ion with
Table 2
Diffusion coefficients measured for the complexes [Pd((R,S)-Bn-
Box)(CH3)(NCCH3)] (X) (8a–c) in CD2Cl2:CD3OD, 9:1
X
Diff. coeff (D)
Radiusa (rH)
CF3SO3 8a
Cation
Anion
8.71
11.01
6.1
4.9
BF4 8b
Cation
Anion
8.80
12.50
6.1
4.3
PF6 8c
Cation
Anion
8.54
11.60
6.3
4.6
Fig. 2. Benzyl section of 1H-1H COSY for [Pd((R,S)-Bn-Box)
(CH3)(NCCH3)] (PF6) (8c).
a
Using viscosity of CH2Cl2 = 0.410.
2.2.1. Pulsed-gradient spin-echo (PGSE) diffusion
measurements
-
CF3SO3
O
N
Pulsed-gradient spin-echo (PGSE) diffusion measure-
ments [8] provide information with respect to ion-
pairing in that the diffusion constants for the anions
decrease with increasing ion-pairing. Consequently, by
using a multinuclear NMR diffusion approach, e.g.,
1H for the cation and 19F for the anion, combined with
(1H, 19F)-HOESY data, it is possible to follow the inter-
actions between anions and cations.
Pri
Ph
Pd+
P
Ph2
Ph
Fig. 3. Model complex 11.

D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
2257
Table 3
Diffusion coefficients measured for the complex 11 in the following
solvents
Solvent
CD2Cl2
Diff. coeff (D)
Radius (rH)
Cation
Anion
8.02
12.67
6.7a
4.2a
CD3OD
Cation
Anion
5.92
12.89
7.0b
3.2b
CD2Cl2:CD3OD (9:1)
Cation
Anion
7.82
13.00
6.8c (6.7d)
4.1c(4.0d)
a
Viscosity of CH2Cl2 = 0.410.
Viscosity of CH3OH = 0.526.
Using viscosity of CH2Cl2.
b
c
d
Viscosity of 90% CD2Cl2 + 10% CD3OD = 0.422.
respect to the cation. For the complex 8a (X = CF3SO3)
the (1H,19F)-HOESY spectrum shows a series of modest
strength cross-peaks connecting the fluorine spins of the
triflate to the protons of: (a) palladium methyl; (b) the
bound acetonitrile; (c) several oxazoline aliphatic pro-
tons and (d) an aromatic resonance (Fig. 4). The analo-
gous spectrum for 8b, (and also 8c, not shown) is
noteworthy in that the contact to the palladium methyl
is absent and the cross-peak to the acetonitrile is stron-
ger (see Figs. 4 and 5). Based on detailed proton assign-
ments for 8b,c, it would appear that the BFꢀ4 and
PFꢀ6 anions take up selective positions close to the ace-
tonitrile ligand and closer to one half of the bidentate
oxazoline ligand, i.e., the anion prefers to avoid the re-
gion of the negatively charged Pd–CH3 group. This type
of selective behavior for an anion is not unusual [10].
Based on all of the NMR data, it would seem that the
triflate anion is, partially, occupying a pseudo fifth posi-
tion on the side of the cation remote from the two ben-
zyl-groups. The ion-pairing is not 100%; however,
assuming that a hydrodynamic radius, rH of ca. 3.0–
Fig. 5. (1H, 19F)-HOESY spectra of complex [Pd((R,S)-Bn-Box)-
(CH3)(NCCH3)] (BF4) (8b).
˚
3.2 A would be a reasonable estimate for a methanol sol-
vated triflate [9], and that 100% ion-pairing would give
˚
an rH value of ca 6.1 A, then the observed value of
˚
4.9 A is suggestive of ca. 50–55% ion-pairing. Possibly,
the difference in size between OTfꢀ and e.g., BF4ꢀ, com-
bined with the differences in relative position and ion-
pairing could lead to some difference in reactivity for
the cation.
2.3. Styrene/CO copolymerisation reactions
The [Pd((R,S)-Bn-Box)(CH3)(NCCH3)](X) com-
plexes (8a–c) were used as catalyst precursors for the
copolymerisation reaction of styrene with carbon mon-
oxide [4]. The productivity of each reaction and the
molecular weight of the copolymers obtained are pre-
sented in Table 4. A characteristic of all copolymers
produced was the low molecular weight (2200–
1000 g Æ molꢀ1), with the number of copolymer chains
produced per mol of catalyst varying from 3 up to 11.
The gray color of the copolymers indicates that the ac-
tive species partially decomposed into palladium metal.
Table 4
Copolymerisation of styrene with CO using as catalyst precursor
[Pd((R,S)-Bn-Box)(CH3)(NCCH3)] (X)a
X
g CP/g Pd
Mn(g molꢀ1
)
ll
ul/lu
lu/ul
uu
CF3SO3 8a
BF4 8b
PF6 8c
59
85
2200
1100
1000
0
0
0
1
1
1
4
24
14
95
75
83
106
Triads distribution of the obtained polyketones (in %).
Reaction conditions: nPd = 0.15 mmol; nBQ = 2 mmol; styrene
30 ml; solvent: 1 ml MeOH, 9 ml CH2Cl2; T = 25 ꢁC; PCO = 1.5 bar.
Fig. 4. (1H, 19F)-HOESY spectra of complex [Pd((R,S)-Bn-
Box)(CH3)(NCCH3)](CF3SO3) (8a).
a

2258
D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
The stereochemistry of the polyketones obtained was
studied by 13C NMR spectroscopy, in CDCl3 solution.
The microtacticity was determined by integration of
the signals due to the ipso carbon atom.
The results of the copolymerisation reactions sug-
gest a unique behavior for the triflate anion, in agree-
ment with the results of the NMR studies. The
copolymerisation reactions with 8a show that this
complex has the lowest productivity, perhaps as a
consequence of the position of the anion. All three
catalyst precursors produce copolymers having a pre-
vailing syndiotactic structure, the content of uu triads
being presented in Table 4.
To study the influence of the charge, we prepared the
dicationic [Pd((R,S)-Bn-Box)(H2O)2] (X)2 complexes
(10a–c), and used them as catalyst precursors in the
copolymerisation reaction of styrene with carbon mon-
oxide. The reaction conditions were the same as for
the methyl–acetonitrile complexes and the productivity
of each reaction and the molecular weight of the copoly-
mers obtained are presented in Table 5.
3. Conclusions
We reported here the synthesis and the study of the
interionic structure of monocationic palladium com-
plexes 8a–c. The presence of the specific cation–anion
interactions was confirmed by the diffusion measure-
ments, while the specific position of the counterions
was determined by the (1H, 19F)-HOESY spectra. The
catalytic behavior of these complexes suggests that the
triflate anion plays a special role, in accordance with
the results of the NMR studies.
For the aqua-complexes, 10a–c, the interionic struc-
ture could not be determined by NMR. The results of
the copolymerisation reactions, however, showed that
the complex having the triflate as counterion led to iso-
tactic copolymers, while the other two complexes led to
syndiotactic copolymers. The nature of the catalytic spe-
cies formed from 10a, and responsible for the formation
of a single polymeric chain, remains unknown; however,
it must be different from that formed from the precursor
8a.
The molecular weight of the copolymers produced is
still low (2600–1200 g Æ molꢀ1), but the number of
copolymer chains produced per mol of catalyst de-
creases, being maximum 6. In fact, the catalyst 10a pro-
duced only one polymeric chain per mol catalyst. The
effect of the anion on the productivity was evident with
an increase of productivity being observed on going
from CF3SOꢀ3 to BF4ꢀ to PFꢀ6 .
The catalyst precursor 10a (X = CF3SO3) leads to the
formation of a copolymer with an isotactic structure
(99% ll triads), whereas the catalysts 10b and 10c lead
to copolymers with a prevailing syndiotactic structure
(the content of uu triads being 87% and 69%, respec-
tively). These results show that, under our reaction con-
ditions, the stereochemistry of the copolymers produced
is influenced by the nature of the counterion. Although
counterion effects were observed on single-site olefin
polymerisation reactions [11], no such phenomenon
was reported so far for the copolymerisation reactions
of olefins with carbon monoxide.
4. Experimental
4.1. General data
All reactions were carried out under nitrogen atmo-
sphere by using Schlenk techniques. CP grade chemicals
were used as received. Solvents were dried by standard
methods and freshly distilled under nitrogen. Carbon
monoxide (CP grade, 99.5%) was supplied by AGA.
One and two-dimensional NMR spectra were measured
on Bruker AC 200, Bruker AVANCE 400 and Bruker
AMX 500, at ambient temperature. The MS spectra
were measured with MALDI-FT-ICR technique, in
the positive mode, on an IonSpec Ultima instrument.
The microanalytical laboratory in-house performed ele-
mental analyses. The molecular weights of copolymers
(Mw) were measured with MALDI TOF technique (Ma-
trix DCTB 0.1 M), in the positive mode, on a Bruker
Reflex instrument.
Unfortunately, NMR-studies similar to those re-
ported above for the complexes 8a–c, were hampered
by the low stability of the diaqua-palladium complexes.
4.2. Synthesis of N,N-bis[1-(hydroxymethyl)-2-
phenylethyl]ethanediamide (4)
(S)-(2-Phenyl-1-hydroxymethyl)ethylamino
ethyl
Table 5
Copolymerisation of styrene with CO using as catalyst precursor
oxalate (3)2 (5 g, 19.8 mmol) and (R)-phenylalanol
(3.29 g, 21.78 mmol) were dissolved in toluene (100 ml)
and heated to reflux for 3 h. During this time, fine white
crystals precipitated from solution. The mixture was
cooled to room temperature and hexane (100 ml) was
added. The product was collected by filtration, washed
with hexane (50 ml) and dried (100 ꢁC at 0.2 Torr) to af-
ford 5.7 g (80%) of the bisamide (4) as white crystals. 1H
NMR (200 MHz, DMSO-d6): d 2.68–2.88 (m, 4H,
a
[Pd((R,S)-Bn-Box)(H2O)2] (X)2
X
g CP/g Pd Mn (g molꢀ1
)
ll
ul/lu lu/ul uu
CF3SO3 10a 30
2600
2300
1200
99
0
1
4
4
0
9
0
87
69
BF4 10b
PF6 10c
61
69
0
27
Triads distribution of the obtained polyketones (in %).
a
Reaction conditions: nPd = 0.15 mmol; nBQ = 2 mmol; styrene
30 ml; solvent: 1 ml MeOH, 9 ml CH2Cl2; T = 25 ꢁC; PCO = 1.5 bar.

D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
2259
CH2Ph); 3.34–3.40 (m, 4H, CH2OH); 3.89–3.99 (m, 2H,
CH); 4.85 (t, J 5.6, 2H, CH2OH); 7.14–7.27 (m, 10H,
Ph); 8.31 (d, 2H, NH).
4.5. Synthesis of (R,S)-4,40-dibenzyl-2,20-bi-(2-
oxazoline-kN)chloro(methyl)palladium (7)
265 mg (0.828 mmol) (R,S)-4,40-dibenzyl-2,20-bi-(2-
oxazoline) (6) dissolved in 3 ml dichloromethane were
added via a syringe to a solution of (g2,g2-cycloocta-
1,5-dien)chloro(methyl)palladium ((COD)Pd(Me)Cl)7
(212 mg, 0.80 mmol) and 3 ml dichloromethane. The
mixture was stirred over night under argon, at ambient
temperature, then the solution was filtrated through Cel-
ite. Upon the evaporation of the solvent, a yellow oil
was obtained. This was washed with hexane (2 · 2 ml),
redissolved in dichloromethane and then cooled in liq.
N2. Upon addition of diethyl ether, a bright yellow com-
pound precipitated and it was isolated by filtration;
320 mg (81%) of pure compound were obtained. Single
crystals of complex 7 were obtained by slow evaporation
of a solution of 7 in a mixture of dichloromethane and
4.3. Synthesis of N,N-bis[1-(chloromethyl)-2-
phenylethyl]ethanediamide (5)
Thionyl chloride (0.78 ml, 14.7 mmol) was added
quickly to a suspension of the hydroxy-diamide 4
(1.75 g, 4.9 mmol) in toluene (35 ml) at 60 ꢁC. The reac-
tion mixture was maintained at 60–70 ꢁC for 1 h and
then heated to 90 ꢁC for 4 h. The mixture was cooled
to ambient temperature before it was poured into a cold
(0 ꢁC) solution of 20% aqueous KOH (100 ml) and ex-
tracted with dichloromethane (3 · 150 ml). The organic
extracts were washed with brine, dried (Na2SO4) and
then filtered through a pad of Celite. Evaporation of
the solvent under vacuum led to 1.8 g (93%) of product
1
hexane (10:1). H NMR (500 MHz, CD2Cl2): d 1.08 (s,
1
3H, PdCH3); 2.83 (dd, 2J 14.0, 3J 8.2, 1H, CH2Ph);
as white powder. H NMR (200 MHz, CDCl3): d 2.97
2
3
2
(d, J 7.1, 4H, CH2Ph); 3.47–3.65 (m, 4H, CH2Cl);
4.31–4.47 (m, 2H, CH); 7.22–7.36 (m, 10H, Ph); 7.69
(d, J 8.8, 2H, NH). 13C NMR: d 37.3 (CH2Ph); 45.5
(CH2Cl); 51.5 (CH); 127.1, 128.8, 129.2, 136.1 (Ph);
158.8 (CO).
3.25 (dd, J 14.0, J 7.7, 1H, CH2Ph); 3.2 (dd, J 14.1,
3J 3.5, 1H, CH2Ph); 3.42 (dd, 2J 13.8, 3J 3.3, 1H,
CH2Ph); 4.45 (t, J 7.0, 1H, CH); 4.54–4.60 (m, 1H,
CH); 4.63–4.68 (m, 4H, CH2O); 7.28–7.42 (m, 10H,
Ph). 13C NMR: d ꢀ7.5 (PdCH3); 39.3, 39.9 (CH2Ph);
64.1, 64.4 (CHN); 76.5, 76.7 (CH2O); 127.4, 127.8,
129.0, 129.3, 130.0, 130.2, 135.1, 136.2 (Ph); 157.9,
160.4 (C@N). MS m/z: 425 [M+ ꢀ Cl ꢀ CH3]. Anal.
Calc. for C21H23ClN2O2Pd: C, 52.85; H, 4.86; N, 5.87.
Found: C, 52.72; H, 4.98; N, 5.79%.
4.4. Synthesis of (R,S)-4,40-bis(phenylmethyl)-2,20,5,50-
tetrahydro-2,20-bioxazole (6)
N,N-bis[1-(chloromethyl)-2-phenylethyl]ethanedia-
mide (5) (5 g, 12.7 mmol) and potassium hydroxide
(1.78 g, 31.8 mmol, 2.5 eqv.) were heated to reflux in
methanol (150 ml) for 3 h. As the reaction proceeded,
potassium chloride gradually precipitated from solution.
The reaction mixture was cooled to ambient tempera-
ture, poured into water (200 ml) and extracted with
dichloromethane (3 · 100 ml). The organic extracts were
washed with brine (1 · 150 ml), combined, dried
(Na2SO4) and then filtered through a pad of Celite.
Evaporation of the solvent under vacuum led to 3.41 g
(84%) of product 6, as a mixture of stereoisomers, the
ratio between the chiral stereoisomers and the meso-
form being 13:87 (GC). The meso-bioxazoline (R,S)-6
was separated from this mixture by flash chromatogra-
phy, using 3% Et3N in a mixture of hexane: EtOAc,
2:1. The Rf values for the diastereomers are:
Rf (R,R) = 0.2, Rf (R,S) = 0.13. 2.8 g (72%) of the meso-
ligand were obtained after the separation, their purity
being 99.3% (GC). 1H NMR (300 MHz, CDCl3): d
2.71 (dd, 2J 13.9, 3J 9.1, 2H, CH2Ph); 3.27 (dd, 2J
4.6. General procedure for preparation of [Pd(R,S)-
Bn-Box(CH3)(NCCH3)] (X) complexes 8a–c
In a two-neck 50 ml flask covered with aluminum
folia, 210 mg (0.44 mmol) (R,S)-4,40-dibenzyl-2,20-bi-
(2-oxazoline-kN)chloro(methyl)-palladium (7) were dis-
solved in 5 ml mixture of dichloromethane/acetonitrile
(5:1, v/v), under argon, and cooled to ꢀ40 ꢁC. The silver
salts (0.44 mmol) dissolved in 3 ml solution of dichloro-
methane/acetonitrile (5:1, v/v), were added to the mix-
ture via a dropping funnel. The reaction mixture was
stirred at ꢀ40 ꢁC for 1 h, then slowly warmed to 0 ꢁC
and kept at this temperature for another hour. Filtration
through Celite was used to remove the precipitated silver
chloride. The pale yellow filtrate was evaporated under
vacuum and an yellow oil was obtained; upon treatment
with hexane (3 · 3 ml) and drying under vacuum, the
complexes 8a–c were obtained as yellow powders in
84–97% yield.
3
4.6.1. (Acetonitril-kN){(R,S)-4,40-dibenzyl-2,20-bi-(2-
oxazoline-kN)}methylpalladium (+) trifluoromethane
sulphonate (8a)
270 mg (97%) product were obtained. 1H NMR
(500 MHz, CD2Cl2): d 1.08 (s, 3H, CH3); 2.34 (s, 3H,
13.9, J 5.0, 2H, CH2Ph); 4.15 (t, J 8.9, 2H, CH2O);
4.39 (t, J 8.9, 2H, CH2O); 4.56–4.67 (m, 2H, CH);
7.19–7.33 (m, 10H, Ph). 13C NMR: d 41.0 (CH2Ph);
69.1 (CH); 72.7 (CH2O); 126.7, 128.6, 129.0 (Ph);
155.0 (C@N).

2260
D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
2
3
NCCH3); 2.81 (dd, J 14.1, J 8.0, 1H, CH2Ph); 2.93-
3.01 (m, 2H, CH2Ph); 3.05 (dd, 2J 14.1, 3J 3.7, 1H,
CH2Ph); 4.22–4.32 (m, 1H, CH); 4.32–4.59 (m, 1H,
CH2O); 4.60–4.89 (m, 4H, CH and CH2O); 7.17–7.36
(m, 10H, Ph). 13C NMR: d ꢀ3.9 (PdCH3); 3.8
(PdNCCH3); 40.8, 40.6 (CH2Ph); 63.3, 65.3 (CHN);
77.0, 77.6 (CH2O); 121.6 (CNCH3); 129.7 (CF3); 127.4,
127.8, 128.8, 129.0, 129.1, 129.9, 134.1, 135.3 (Ph);
158.6, 161.6 (C@N). 19F NMR: d ꢀ79.03 (CF3). MS
m/z: 425 [M+ ꢀ NCCH3 ꢀ CH3]. Anal. Calc. for
C24H26F3N3O5PdS: C, 45.61; H, 4.15; N, 6.65. Found:
C, 45.57; H, 4.31; N, 6.42%.
at ambient temperature for 1.5 h. Hexane was then
added (40 ml) and the mixture was cooled to 0 ꢁC. The
product precipitated and it was collected by filtration;
386 mg (93%) of yellow powder were obtained. 1H
2
3
NMR (500 MHz, CDCl3): d 3.01 (dd, J 13.9, J 8.8,
2H, CH2Ph); 3.61 (dd, 2J 13.9, 3J 3.3, 2H, CH2Ph);
2
4.67 (dd, J 8.7, J 6.0, 2H, CH2O); 4.76–4.87 (m, 2H,
3
2
3
CH); 5.3 (dd, J 8.7, J 9.8, 2H, CH2O); 7.28–7.34 (m,
10H, Ph). Anal. Calc. for C20H20Cl2N2O2Pd: C, 48.26;
H, 4.05; N, 5.63. Found: C, 48.13; H, 4.22; N, 5.70%.
4.8. General procedure for preparation of
[Pd((R,S)-Bn-Box)(H2O)2] (X)2 complexes 10a–c
4.6.2. (Acetonitril-kN){(R,S)-4,40-dibenzyl-2,20-bi-
(2-oxazoline-kN)}methylpalladium (+)
tetrafluoroborate (8b)
215 mg (0.43 mmol) [Pd((R,S)-Bn-Box)Cl2] complex
(9) were dissolved in dichloromethane (20 ml), under ar-
gon, in a flask covered with aluminum folia. The corre-
sponding silver salts (0.95 mmol), dissolved also in
dichloromethane (10 ml), were added slowly via a drop-
ping funnel to the solution. The resulting mixture was
stirred at ambient temperature for 2 h and then filtered
through Celite under argon. The solvent was evaporated
to dryness under vacuum, under argon, and a brown oil
was obtained. The products were precipitated by various
techniques and dried for several hours under high vac-
uum, leading to the moisture sensitive complexes 10a–
c in 41–58% yield.
210 mg (84%) product were obtained. 1H NMR
(500 MHz, CD2Cl2): d 1.15 (s, 3H, PdCH3); 2.30 (s,
2
3
3H, NCCH3); 2.84 (dd, J 14.2, J 8.0, 1H, CH2Ph);
2
3
3.0 (dd, J 6.73, J 3.3, 2H, CH2Ph); 3.11 (dd,2J 14.1,
3J 3.8, 1H, CH2Ph); 4.52–4.57 (m, 1H, CH); 4.57 (dd,
2J 9.0, 3J 6.7, 1H, CH2O); 4.67–4.75 (m, 1H, CH);
4.75–4.85 (m, 3H, CH2O); 7.25–7.45 (m, 10H, Ph). 13C
NMR: d ꢀ3.6 (PdCH3); 3.5 (NCCH3); 39.5, 40.6
(CH2Ph); 63.3, 65.3 (CHN); 77.0, 77.6 (CH2O); 121.6
(CNCH3); 127.4, 127.8, 128.8, 129.0, 129.1, 129.7,
129.9, 134.1, 135.3 (Ph); 158.6, 161.6 (C@N). 19F
NMR:
[M+ ꢀ NCCH3 ꢀ CH3].
d
ꢀ153.1 (d, BF4). MS m/z: 425
Anal.
Calc.
for
4.8.1. (R,S)-4,40-dibenzyl-2,20-bi-(2-oxazoline-kN)
diaqua palladium (2+) ditrifluoromethanesulphonate
(10a)
C23H26BF4N3O2Pd: C, 48.49; H, 4.60; N, 7.38. Found:
C, 48.68; H, 4.85; N, 7.20%.
The resulting brown oil was washed with small por-
tions (3–4 ml) of n-pentane, which was then removed
via a cannula. The resulting foam was dried for several
hours under high vacuum, leading to 190 mg (58% yield)
of a brown-green powder. 1H NMR (500 MHz, 10%
THF-d8 in CD2Cl2): d 2.5–3.5 (br m, 4H, CH2Ph);
4.1–4.95 (br m, 6H, 2H CH and 4H CH2O); 7.0–7.7
(m, 10H, Ph). 13C NMR: d 38.8 (CH2Ph); 64.3 (CH);
78.9 (CH2O); 129.3 (CF3); 127.9, 129.6, 130.4, 137.4
(Ph); 163.5 (C@N). 19F NMR (400 MHz, CD2Cl2/
4.6.3. (Acetonitril-kN){(R,S)-4,40-dibenzyl-2,20-bi-
(2-oxazoline-kN)}methylpalladium (+)
hexafluorophosphate (8c)
255 mg (92%) product were obtained. 1H NMR
(500 MHz, CD2Cl2): d 1.17 (s, 3H, PdCH3); 2.29 (s,
3H, NCCH3); 2.84 (dd, J 14.2, J 8.0, 1H, CH2Ph);
2
3
2
3
2
3.0 (dd, J 6.7, J 3.3, 2H, CH2Ph); 3.11 (dd, J 14.1,
3J 3.8, 1H, CH2Ph); 4.52–4.57 (m, 1H, CH); 4.57 (dd,
2J 9.0, 3J 6.7, 1H, CH2O); 4.67–4.75 (m, 1H, CH);
4.75–4.85 (m, 3H, CH2O); 7.25–7.45 (m, 10H, Ph). 13C
NMR: d ꢀ3.6 (PdCH3); 3.5 (NCCH3); 39.5, 40.6
(CH2Ph); 63.3, 65.3 (CHN); 77.0, 77.6 (CH2O); 121.6
(CNCH3); 127.4, 127.8, 128.8, 129.0, 129.1, 129.7,
129.9, 134.1, 135.3 (Ph); 158.6, 161.6 (C@N). 19F
MeOD, 9:1):
d
C22H24F6N2O10PdS2: C, 35.71; H, 3.18; N, 3.68. Found:
ꢀ79.38 (CF3). Anal. Calc. for
C, 35.60; H, 3.45; N, 3.48%.
4.8.2. (R,S)-4,40-dibenzyl-2,20-bi-(2-oxazoline-
NMR:
[M+ ꢀ NCCH3 ꢀ CH3]. HRMS: Calc. for C20H19-
d
ꢀ72.4, ꢀ74.3 (PF6). MS m/z: 425
kN)diaqua palladium (2+) ditetrafluoroborate (10b)
The brown oil obtained was redissolved in dichloro-
methane (5 ml), cooled (ꢀ78 ꢁC) and the product precip-
itated by adding diethyl ether dropwise. While the
mixture was still very cold, the product was quickly fil-
trated, affording 117 mg (42% yield) of yellow solid.
1H NMR (500 MHz, 10% THF-d8 in CD2Cl2): d 2.75–
3.65 (br m, 4H, CH2Ph); 4.5–5.04 (br m, 6H, 2H CH
and 4H CH2O); 6.87–7.71 (m, 10H, Ph). 19F NMR
O2N2Pd, 425.0475. Found: 425.0482%
4.7. Synthesis of (R,S)-4,40-dibenzyl-2,20-bi-
(2-oxazoline-kN)dichloropalladium (9)
320 mg (0.83 mmol) [PdCl2(PhCN)2] and 267 mg
(0.83 mmol) meso-bioxazoline (R,S)-6 were dissolved in
20 ml dry dichloromethane, under argon, and stirred
(400 MHz, CD2Cl2/MeOD, 9:1):
d
ꢀ150.9 (BF4).

D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
2261
Table 6
Crystal data and structure refinement for [Pd((R,S)-Bn-Box)(CH3)Cl]
HRMS: Calc. for C20H24O4N2B2F8Pd, 636.4302.
Found: 636.4309%.
Color, shape
Yellow, brick
C21H23ClN2O2Pd
477.29
4.8.3. (R,S)-4,40-dibenzyl-2,20-bi-(2-oxazoline-
Empirical formula
Formula weight
Temperature (K)
kN)diaqua palladium (2+) dihexafluorophosphate (10c)
After filtration through a pad of Celite, the resulting
yellow filtrate was concentrated (15 ml), cooled
(ꢀ78 ꢁC) and diethyl ether was added dropwise, when
a beige precipitate started to appear. More diethyl ether
was added until the precipitation was complete, then the
product was quickly filtrated and dried under vacuum.
120 mg (41% yield) of beige solid were obtained. 1H
NMR (500 MHz, 10% THF-d8 in CD2Cl2): d 2.65–3.84
(br m, 4H, CH2Ph); 4.26–4.94 (br m, 6H, 2H CH and
4H CH2O); 6.77–7.51 (m, 10H, Ph). 13C NMR: d 38.4
(CH2Ph); 63.4 (CH); 77.9 (CH2O); 129.3 (CF3); 127.3,
128.5, 128.9, 129.1, 129.3, 129.6, 134.9, (Ph); 161.7
(C@N). 19F NMR: d ꢀ70.4, ꢀ74.2 (PF6). 31P NMR: d
ꢀ143.56 (PF6). HRMS: Calc. for C20H24O4N2F12P2Pd,
752.0049. Found: 752.0057%.
293
0.71073
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
Monoclinic
C2/c
˚
a (A)
21.057(4)
10.0434(18)
˚
b (A)
˚
c (A)
19.148(3)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
91.940(4)
90
4047.3(12)
3
˚
V (A )
Z
8
1.567
1.067
Dcalc (g cmꢀ3
)
Abs. coeff. (mmꢀ1
Crystal size (mm)
)
0.30 · 0.16 · 0.13
20179, 5089
0.0282
Full-matrix least-squares on F2
5089, 0, 244
1.328
Reflections collected, unique
Rint
Refinemet method
Data, restraints, parameters
4.9. Structure determination
GOF
R, Rw
0.0717, 0.1526
1.134/ꢀ0.948
ꢀ3
˚
Minimum/maximum resd (e A
)
X-ray structural measurements for the complex
[Pd((R,S)-Bn-Box)(CH3)Cl] were carried out on a Bru-
ker CCD diffractometer (Bruker SMART PLAT-
FORM, with CCD detector, graphite monochromator,
Mo Ka radiation). The program SMART served for data
collection. Integration was performed with SAINT. The
structure solution (Patterson method) and refinement
on F2 were accomplished with SHELXTL 97. Model plots
were made with ORTEP32. All non-hydrogen atoms were
refined freely with anisotropic displacement parameters.
The hydrogen atoms were refined at calculated positions
riding on their carrier atoms. Weights were optimised in
the final refinement cycles. Crystallographic data are gi-
ven in Table 6.
The (1H, 19F)-HOESY NMR measurements were
carried out with a doubly tuned TXI probe. A mixing
time of 600 ms was used and 32 scans for each of the
1024 T1 increments were recorded. 10 mM or higher
concentration solutions were used to measure the
correlation.
4.11. General procedure for the copolymerisation
reactions
All copolymerisation reactions were performed in the
same conditions, in a 150 ml autoclave, using 0.15 mmol
palladium catalyst and 2 mmol benzoquinone, which
were set in the autoclave as solids. A mixture of dichlo-
romethane (9 ml), methanol (1 ml) and styrene (30 ml)
were then added under nitrogen, and the autoclave
was connected to a CO source through a Buchi-bpc
gas-flow controller, which maintained a constant pres-
sure of CO of 1.5 bar. The reaction time of 48 h was kept
constant for all reactions. For isolation of the obtained
copolymers, the reaction mixture was poured in cold
methanol (0 ꢁC) where the copolymers precipitated
and were isolated by filtration. Usually, gray copolymers
were obtained, and they were purified further by dissolv-
ing them in a mixture of chloroform and HFIP (10:1),
followed by filtration through Celite and reprecipitation
with methanol. The filtration afforded a white copoly-
mer, which was then used for analysis. The stereochem-
istry of the polyketones was studied by 13C NMR
spectroscopy, the spectra being recorded in CDCl3.
4.10. Experimental conditions used for the NMR
measurements
All PGSE diffusion measurements were performed on
Bruker AVANCE spectrometer (400 MHz) equipped
with a microprocessor controlled gradient unit and a
multinuclear probe (normal or inverse) with an actively
shielded Z-gradient coil. The shape of the gradient pulse
was rectangular, their length 1.75 ms and its strength
varied automatically in the course of the experiment.
The time between mid points of the gradients (D) was
chosen as 167.75 ms. The measurements were carried
out without sample spinning and in the absence of exter-
nal airflow. The T1 were measured for all the nuclei and
the relaxation delay was set to 5T1 accordingly. The con-
centration used for the measurements was 2 mM.
The error coefficients for the D-values based on our
experience is 0.06.

2262
D. Sirbu et al. / Journal of Organometallic Chemistry 690 (2005) 2254–2262
(j) A. Macchioni, G. Bellachioma, G. Cardaci, M. Travaglia,
C. Zuccaccia, B. Milani, G. Corso, E. Zangrando, G.
Mestroni, C. Carfagna, M. Formica, Organometallics 18
(1999) 3061;
The microtacticity was determined by integration of the
signals due to the ipso carbon atom.
(k) C.R. Baar, M.C. Jennings, R.J. Puddephatt, Organo-
metallics 20 (2001) 3459;
5. Supplementary material
(l) A. Bastero, A. Ruiz, C. Claver, S. Castillon, Eur. J.
Inorg. Chem. (2001) 3009;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 247718. These data can be ob-
tained free of charge via www.ccdc.cam.ac.uk/data_re-
quest/cif,by emailing data_request@ccdc.cam.ac.uk, or
by contacting The Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
(m) G. Bellachioma, B. Binotti, C. Carfagna, A. Macchioni,
S. Sabatini, C. Zuccaccia, Inorg. Chim. Acta 330 (2002) 44;
(n) B. Binotti, C. Carfagna, G. Gatti, D. Martini, L.
Mosca, C. Pettinari, Organometallics 22 (2003) 1115.
[3] (a) M. Brookhart, M.I. Wagner, G.G.A. Balavoine, H.A. Had-
dou, J. Am. Chem. Soc. 116 (1994) 3641;
(b) S. Bartolini, C. Carfagna, A. Musco, Makromol. Chem.
Rapid Commun. 16 (1995) 9;
(c) M.T. Reetz, G. Haderlein, K. Angermund, J. Am. Chem. Soc.
122 (2000) 996;
(d) J.C. Yuan, S.J. Lu, Organometallics 20 (2001) 2697.
[4] A. Gsponer, B. Milani, G. Consiglio, Helv. Chim. Acta. 85 (2002)
4074.
Acknowledgements
[5] (a) D.C. Horwell, R.A. Lewthwaite, M.C. Pritchard, J.S. Ratcliffe,
J.R. Rubin, Tetrahedron 54 (1998) 4591;
Financial support from European Network Palla-
dium 15th Framework Programm, contract No
HPRN-CT-2002-00196 and Swiss Research Council
(BBW) is gratefully acknowledged. We also thank Mr.
Eric Meister for the viscosity measurements.
(b) R.A. Stavenger, A.M. Faucher, J.P. Edwards, J. Org. Chem.
62 (1997) 3375.
[6] R.E. Rulke, J.M. Ernsting, A.L. Spek, C.J. Elsevier, P.W.N.M.
van Leeuwen, K. Vrieze, Inorg. Chem. 32 (1993) 5769.
[7] M. Sperrle, G. Consiglio, J. Am. Chem. Soc. 117 (1995) 12130.
[8] M. Valentini, H. Ruegger, P.S. Pregosin, Helv. Chim. Acta. 84
(2001) 2833.
References
[9] (a) M. Valentini, P.S. Pregosin, H. Ruegger, Organometallics 19
¨
(2000) 2551;
(b) E. Martinez-Viviente, H. Ruegger, P.S. Pregosin, J. Lopez-
Serrano, Organometallics 21 (2002) 5841;
(c) P.G.A. Kumar, P.S. Pregosin, J.M. Goicoechea, M.K.
Whittlesey, Organometallics 22 (2003) 2956;
(d) P.S. Pregosin, E. Martinez-Viviente, P.G.A. Kumar, Dalton
Trans. 21 (2003) 4007;
[1] (a) E. Drent, P.H.M. Budzelaar, Chem. Rev. 96 (1996) 663;
(b) K. Nozaki, T. Hiyama, J. Organomet. Chem. 576 (1999) 248;
(c) C. Bianchini, A. Meli, Coord. Chem. Rev. 225 (2002) 35.
[2] (a) E. Drent, Eur. Pat. Appl. 229 (1986) 408;
Chem. Abstr. 108 (1988) 6617;
(b) P. Corradini, C. De Rosa, A. Panuzi, G. Petrucci, P. Pino,
Chimia 44 (1990) 52;
(e) E. Martinez-Viviente, P.S. Pregosin, Inorg. Chem. 42 (2003)
2209.
(c) M. Barsacchi, G. Consiglio, L. Medici, G. Petrucci, U.W.
Suter, Angew. Chem., Int. Ed. Engl. 30 (1991) 989;
(d) M. Brookhart, F.C. Rix, J.M. DeSimone, J.C. Barborak, J.
Am. Chem. Soc. 114 (1992) 5894;
[10] (a) D. Drago, P.S. Pregosin, A. Pfaltz, Chem. Commun. 3 (2002)
286;
(b) E. Martinez-Viviente, P.S. Pregosin, Inorg. Chem.42 (2003)
2209;
(e) A. Sen, Z. Jiang, Macromolecules 26 (1993) 911;
(f) V. Busico, P. Corradini, L. Landriani, M. Trifuoggi, Makro-
mol. Chem. Rapid Commun. 14 (1993) 261;
(c) A. Macchioni, C. Zuccaccia, E. Clot, K. Gruet, R.H. Crabtree,
Organometallics 20 (2001) 2367;
(d) P.G.A. Kumar, P.S. Pregosin, T. Schmid, G. Consiglio,
Magn. Reson. Chem. 42 (2004) 795;
(g) B. Milani, E. Alessio, G. Mestroni, A. Sommazzi, F. Garbassi,
E. Zangrando, N. Bresciani-Pahor, L. Randaccio, J. Chem. Soc.
Dalton Trans. (1994) 1903;
(e) P.G.A. Kumar, P.S. Pregosin, M. Vallet, G. Bernardinelli,
R.F. Jazzar, F. Viton, E.P. Kuendig, Organometallics 23 (2004)
5410.
(h) Z. Jiang, S.E. Adams, A. Sen, Macromolecules 27 (1994)
2694;
[11] M.C. Chen, J.A.S. Roberts, T.J. Marks, J. Am. Chem. Soc. 126
(2004) 4605.
(i) B. Milani, E. Alessio, G. Mestroni, E. Zangrando, L. Randac-
cio, G. Consiglio, J. Chem. Soc. Dalton Trans. (1996) 1021;