Effect of 5-Me substituent(s) on the catalytic activity of palladium(II) 2,2′-bipyridine complexes in CO/4-tert-butylstyrene copolymerization

Article abstract of DOI:10.1016/j.jorganchem.2004.01.032

The coordination of two 5-substituted-2,2^′-bipyridines L (L¹=5-methyl-2,2^′-bipyridine, L²=5,5^′-dimethyl-2,2^′ -bipyridine) to palladium was studied. The neutral complexes [Pd(L)Cl₂] and [Pd(L)(Me)Cl], and the cationic complexes obtained after chlorine abstraction [Pd(L)₂] [BAr^′₄]₂ and [Pd(L)(Me)(NCMe)] [BAr^′₄] (Ar^′=3,5- (CF₃)₂-C₆H₃), respectively, were isolated and characterized by NMR and FAB mass spectroscopy. The complex [Pd(L²)(L³)][BAr^′ ₄]₂ (L³=2,2^′ -bipyridine) bearing different ligands, was prepared for comparison purposes. The activity of the monocationic and dicationic complexes as catalytic precursors in the CO/4- tert -butylstyrene copolymerization was compared with that of related well-known catalysts containing the unsubstituted 2,2^′-bipyridine as nitrogen ligand, to evaluate the influence of the substituents in 5- and 5,5^′-position. The presence of one or two substituents on the nitrogen ligand has a positive effect on productivity using both types of precursors. No influence was observed on the polymer properties in terms of molecular weight and tacticity. Analysis of the reactivity of the methyl-palladium complexes towards carbon monoxide shows further differences depending on the nitrogen ligand.

Full text of DOI:10.1016/j.jorganchem.2004.01.032

Journal of Organometallic Chemistry 689 (2004) 1521–1529
www.elsevier.com/locate/jorganchem
Effect of 5-Me substituent(s) on the catalytic activity
of palladium(II) 2,20-bipyridine complexes in
CO/4-tert-butylstyrene copolymerization
a
a,
a
a
Barbara Soro , Sergio Stoccoro *, Maria Agostina Cinellu , Giovanni Minghetti ,
a
Antonio Zucca , Amaia Bastero , Carmen Claver
b
b,
*
a
Dipartimento di Chimica di Sassari, Via Vienna 2, 07100 Sassari, Italy
Departament de Quimica Fꢀısica i Inorgꢁanica, Universitat Rovira i Virgili, Pl. Imperial Tꢁarraco 1, 43005 Tarragona, Spain
b
Received 8 November 2003; accepted 23 January 2004
Abstract
The coordination of two 5-substituted-2,20-bipyridines L (L1 ¼ 5-methyl-2,20-bipyridine, L2 ¼ 5,50-dimethyl-2,20-bipyridine) to
palladium was studied. The neutral complexes [Pd(L)Cl2] and [Pd(L)(Me)Cl], and the cationic complexes obtained after chlorine
abstraction [Pd(L)2][BAr0 ]2 and [Pd(L)(Me)(NCMe)][BAr0 ] (Ar0 ¼ 3,5-(CF3)2-C6H3), respectively, were isolated and characterized
4
4
by NMR and FAB mass spectroscopy. The complex [Pd(L2)(L3)][BAr40 ]2 (L3 ¼ 2,20-bipyridine) bearing different ligands, was pre-
pared for comparison purposes. The activity of the monocationic and dicationic complexes as catalytic precursors in the CO/4-tert-
butylstyrene copolymerization was compared with that of related well-known catalysts containing the unsubstituted 2,20-bipyridine
as nitrogen ligand, to evaluate the influence of the substituents in 5- and 5,50-position. The presence of one or two substituents on the
nitrogen ligand has a positive effect on productivity using both types of precursors. No influence was observed on the polymer
properties in terms of molecular weight and tacticity. Analysis of the reactivity of the methyl–palladium complexes towards carbon
monoxide shows further differences depending on the nitrogen ligand.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Catalysis; Copolymerization; 4-tert-Butylstyrene; Palladium complexes; Nitrogen ligands
1. Introduction
dium species which contain the unsubstituted 2-20-bi-
pyridine or 1,10-phenanthroline as N–N ligand as well
as other heterocyclic related N–N ligands as for instance
pyridine–pyrazole, pyridine–oxazoline and pyridine–
imidazoline [3]. Although recently the enhanced activity
shown by a substituted phenanthroline has been re-
ported [4], the effect of substituents on these heterocyclic
ligands has not been thoroughly investigated. In the case
of the bis-chelated derivatives [Pd(L)2]2þ, little attention
has been given to species having both unsubstituted and
substituted ligands [3d,3e,3p,4,5]. We have reported a
series of [Pd(bipyR)2]2þ and [Pd(bipy)(bipyR)]2þ com-
plexes, where bipyR is a 6-substituted-2-20-bipyridine
(R ¼ Me, Et, i-Pr): we studied their activity as catalytic
precursors in the CO/styrene and 4-tert-butylstyrene
copolymerization and observed that rather than an
electronic effect, the presence of the substituent in alpha
In the copolymerization of CO with aromatic olefins
using palladium catalysts [1], it has been shown that
while chelating diphosphines lead only to monocarb-
onylated products [2], bidentate N-donor ligands afford
polyketones with high selectivity [1e,1f]. This intriguing
effect exerted by the chelating ligands in the reactivity of
the palladium catalysts makes the synthesis of new
precatalysts and, in particular, the study of the influence
of different N–N ligands, very attractive.
Most of the reported precursors in the CO/styrene
copolymerization are monocationic or dicationic palla-
* Corresponding authors.
E-mail addresses: stoccoro@uniss.it (S. Stoccoro), claver@correu.
urv.es (C. Claver).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.01.032

1522
B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
position to the coordinating nitrogen accounted for a
steric effect [5d]. We decided it was worthwhile investi-
gating the behaviour of 2-20-bipyridines with substitu-
ents in 5- and 5,50- i.e., in positions not sterically
significant. Different palladium(II) complexes0 of for-
mula [Pd(L)2][BAr40 ]2, [Pd(L)(2,20-bipy)][BAr4]2 and
[Pd(Me)(L)(MeCN)][BAr04] (L ¼ 5-Me or 5,50-Me2-2,20-
bipyridine; Ar0 ¼ 3,5-(CF3)2C6H3) were prepared and
tested as catalysts in the CO/4-tert-butylstyrene copo-
lymerization. All catalysts showed activity comparable
to that of some of the most efficient systems reported up
to now [3k,3m]. The effect of the substitution of the
[BAr04]ꢀ anion for other poorly co-ordinating counteri-
ons is commented on. In all cases prevailing syndiotactic
copolymers were obtained.
CH3
CH3
CH3
N
N
N
N
L1
L2
N
N
L3
Scheme 1.
The second step of reaction (1) allowed us to syn-
thesize species with two different chelating L ligands,
such as complex 4, [Pd(L2)(L3)][BAr40 ]2, obtained from
[Pd(L2)Cl2] (2a), L3 and Na[BAr04]. Yields are fairly
good owing to the insolubility of NaCl in dichlorome-
thane which drives the reaction to completeness. As
expected for [BAr04] salts, complexes 1–4 are highly sol-
uble in most organic solvents. After filtration of NaCl,
evaporation of the solvent allows isolation of the cat-
ionic complexes, which are then washed with pentane or
hexane. The new complexes were completely character-
ized by elemental analyses, conductivity measurements,
1H NMR and FAB-MASS spectroscopy.
The reactivity of the monocationic complexes
[Pd(Me)(L)(MeCN)][BAr04] with carbon monoxide was
analysed by NMR.
2. Results and discussion
To analyze systematically the effect of a given sub-
stituent on the N–N ligand, we chose a monosubstituted
bipyridine (5-Me-2,20-bipyridine, L1), the disubstituted
(5,50-Me2-2,20-bipyridine, L2) and the unsubstituted 2,20-
bipyridine, L3 (Scheme 1).
The monosubstituted ligand L1, was obtained ac-
cording to a published method [6], whereas the disub-
stituted L2 and the nonsubstituted L3 are commercially
available. The cationic bis-chelated complexes
[Pd(L)2][BAr40 ]2, (1: L ¼ L1; 2, L ¼ L2; 3, L ¼ L3) were
synthesized by the following two-step reaction:
1
In particular, the H NMR spectra of complexes 1
and 4 deserve a few comments. For complex 1, owing to
the unsymmetrical nature of the ligand, two isomers are
1
possible. However the H NMR spectrum shows only
one species in solution. A NOE difference experiment
confirmed the presence of the transoid isomer as a single
1
isomer (Scheme 2). A H–1H COSY spectrum allowed
MeOH
[Pd(L)Cl2]+ 2 NaCl
Na2[PdCl4] + L
L1
L2
L3
1a
2a
3a
ð1Þ
CH2Cl2
[Pd(L)2][BAr'4]2 + 2 NaCl
[Pd(L)Cl2] + L + 2 Na[BAr'4]
L1
1a
2a
3a
2a
1
2
3
4
L2
L3
L3
The neutral complexes [Pd(L)Cl2] (L ¼ L1: 1a;
L ¼ L2: 2a; L ¼ L3: 3a), slightly soluble in several or-
ganic solvents, were prepared according to methods
described in the literature [7] and fully characterized
by 1H NMR and FAB mass spectroscopy (see
Section 5).
the complete assignment of the resonances. In particu-
lar, the assignment of the signals of H6 (at d 8.63) and
H60 (at d 8.73) is required for the right interpretation of
the NOE experiment (see Scheme 3 for numbering).
Comparison with the spectra of the symmetric com-
plexes 2 and 3 was used as confirmation.

B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
1523
Irradiation of the H6, H60 (L2) resonance gives en-
hancement of both the signals of the methyl groups in
5,50- and of H6, H60 (L3) protons, whereas by irradiating
the resonance of the latter protons, enhancement of the
signals of H6, H60 (L2) and H5, H50 (L3) is observed
(Scheme 3). It is worth noting that mixtures of species
have been previously observed in solution for bis-
chelated complexes having different N–N ligands such
2+
CH 3
N
N
N
N
Pd
[Pd(bipyR)(bipy)]2þ
(bipyR ¼ 6-substituted-2,20-
H3C
as
bipyridine)
[5d],
[Pd(bipy)(phen)]2þ
[5d],
and
[Pd(bipy)(tmphen)]2þ
1,10-phenanthroline) [8].
(tmphen ¼ 3,4,7,8-tetramethyl-
Scheme 2. Cation of complex 1.
In the FAB mass spectra (positive ions) the molecular
ions [M]þ at m=z 446, 474, 418 for 1, 2, 3, respectively,
provide evidence for the stability of these species even in
gas phase. In the case of complex 4, the FAB mass
spectrum shows the expected peak for [M]þ at m=z 446
(ca. 20%), flanked by less abundant peaks at m=z 474
(15%) and m=z 418 (10%) corresponding to the sym-
metric species [Pd(L2)2]þ and [Pd(L3)2]þ. In the frag-
mentation pattern, peaks due to [M–L]þ are observed in
all cases.
4'
3'
3
4
2+
5'
5
H3C
CH3
2'
2
2
N
N
6'
6
6
Pd
6'
N
N
2'
5'
5
Additionally,
a
second series of complexes,
[Pd(L)(Me)(MeCN)][BAr04], (8, L ¼ L1; 9, L ¼ L2; 10,
L ¼ L3 ¼ 2,20-bipyridine) was obtained by a two-step
reaction scheme:
3
4
3'
4'
Scheme 3. Cation of complex 4.
[Pd(COD)(Me)Cl] + L
[Pd(L)(Me)Cl] + COD
L1
L2
L3
5
6
7
ð2aÞ
ð2bÞ
CH2Cl2/MeCN
[Pd(L)(Me)(MeCN)][BAr'4]
[Pd(L)(Me)Cl] + Na[BAr'4]
- NaCl
5
6
7
8
9
10
In the case of complex 4, the 1H NMR spectrum
shows only one set of signals, consistent with one species
having both ligands L2 and L3 co-ordinated to the pal-
ladium atom. The hypothesis of a mixture of two sym-
metric species [Pd(L2)2]2þ and [Pd(L3)2]2þ was also ruled
out by a NOE difference experiment.
The chloride intermediates, 5–7, (5, L ¼ L1; 6,
L ¼ L2; 7, L ¼ L3 ¼ 2,20-bipyridine) could be isolated
in good yields. The 1H NMR spectrum of complex
5, [Pd(L1)(Me)Cl], indicates the presence of the
two stereoisomers, 5a and 5b, in a ca. 1:1 ratio
(Scheme 4).

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B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
showed, in addition to the resonances at d 2.30 and 2.40
CH3
CH3
(corresponding to the methyl substituents) a doublet at d
2.54 [2J(1H–13C) ¼ 6.7 Hz] assignable to a Pd–C(O)Me
group. The presence in the 13C spectrum of a resonance
at d 224.9 confirmed the presence of 0 the insertion
product [Pd(L2)(13COMe)(MeCN)][BAr4] (9b). The
resonance of the coordinated MeCN, partially hidden in
the 1H spectrum at 0 °C, was well resolved at low
temperature (at )80 °C, d 2.41). It is worth noting that
the three complexes were observed on lowering the
temperature from 0 to )80 °C throughout the experi-
ment (ca. 1.5 h) indicating that the reactivity with car-
bon monoxide was not very high.
N
N
N
N
Pd
Pd
H3C
Cl
Cl
CH3
5a
5b
Scheme 4.
Very small differences, if any, are observed in the two
isomers as regards the methyl resonances, Pd–Me and 5-
Me. Nevertheless, assignment of the resonances to each
of the two isomers is possible by comparison with the
spectra of the symmetric species 2a and 3a and by taking
into account the strong deshielding effect exerted by the
chlorine atom, indicating proximity to H6 or H60 [9].
Assignment of the signals was confirmed by a NOE
difference experiment. Two isomers also are observed in
the case of the ionic complex 8, [Pd(L1)(Me) (MeCN)]-
[BAr04], (ca. 1:1 ratio) obtained through reaction (2b).
3.2. Complex 8
As previously discussed, complex 8 is a mixture of
two geometric isomers arising from the non-symmetric
nature of the ligand, therefore a more complex situation
may be expected after reaction with carbon monoxide.
In fact the NMR spectra gave evidence of a different
behaviour from that of complex 9 (Scheme 6). After
reacting 8 with 13CO at 0 °C for 5 min the 1H spectrum,
recorded at this temperature, showed only one set of
rather broad signals, suggesting a dynamic process. The
presence of a broad signal in the region typical for
Pd–C(O)Mecomplexes (d 2.77) and the lack ofresonances
in the Pd–Me region indicated that the 13CO insertion
into the Pd–Me bond was quite fast. On lowering the
temperature at )40 °C the presence of two species be-
came evident in a ratio of 8.6:1. The major species
1
The assignment of the H resonances was possible with
1
the help of a H NOESY spectrum.
3. CO insertion studies
For the complexes [Pd(L)(Me)(MeCN)][BAr04] (8
L ¼ L1; 9 L ¼ L2) the reactivity with labelled CO, was
studied by in situ H and 13C NMR experiments at low
temperature.
1
1
3.1. Complex 9
characterized in the H spectrum by a resonance at d
2.77 (d, 2J(1H–13C) ¼ 6.0 Hz) and in the 13C spectrum by
resonances at d 215.5 and d 172.5 was identified as the
carbonyl-acetyl species [Pd(L1)(13COMe)(13CO)][BAr40 ]
(8a). The minor species was characterized by a reso-
nance at d 2.56 in the 1H NMR spectrum and at d 226.2
in the 13C spectrum. The absence of other 13CO reso-
nances in the range d 170–180 and the chemical shift of
the new 13C(O)Me resonance, at low field, suggested
an acetonitrile solvato of the acetyl complex,
[Pd(L1)(13COMe)(MeCN)][BAr04] (8b). On further low-
ering the temperature down to )60 °C, in the 13C NMR
spectrum, both resonances corresponding to Pd–
13C(O)Me groups were split (d 216.6 and 216.4; d 227.5
and 227.8), possibly owing to a complicated set of
The spectrum recorded after reacting complex 9 with
13CO at 0 °C for 5 min showed, besides the signals
corresponding to the starting complex, the appearance
of two new species, molar ratio ca. 1:2. The minor of the
new species, which decreased with time, exhibited three
rather sharp resonances in the aliphatic region of the 1H
spectrum, d 1.36 (Pd–Me), d 2.30 and 2.42 (non-equiv-
alent methyl groups of the ligand); in the 13C spectrum a
resonance was observed at d 175.8, i.e. in the range
previously assigned to coordinated CO in analogous
species [3c,3q]. These data provided clear evidence for
the presence of complex [Pd(L2)(Me)(13CO)][BAr40 ]
1
(Scheme 5, 9a). The H spectrum of the major species
+
+
+
CH 3
CH3
CH3
CH3
CH3
CH3
N
N
*CO
N
N
+MeCN
N
N
Pd
Pd
Pd
- MeCN
MeCN
CH3
OC*
CH3
MeCN
*COCH3
9
9a
Scheme 5.
9b

B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
1525
+
+
+
+
CH3
CH3
CH3
CH 3
N
N
N
N
+
N
N
+
N
N
*CO
Pd
Pd
Pd
Pd
NCMe
*CO
H3 C
CH3OC*
MeCN
CH3
OC*
*COCH3
8a
8
- *CO
+ MeCN
+
+
CH3
CH3
N
N
N
N
+
Pd
Pd
CH3OC*
NCMe
MeCN
*COCH3
8b
Scheme 6.
Table 1
CO/4-tert-butylstyrene (TBS) copolymerization using dicationic 1–4
catalyst precursors
equilibria involving also geometrical isomers frozen
on the NMR time scale only at low temperature
(Scheme 6).
Precursor g (CP) g (CP)/g (Pd) Productivity
g (CP)/g (Pd) h
Mw ðMw=MnÞ
1
2
3
4
3.24
3.31
3.10
3.28
11289
11521
10608
11429
806
823
758
816
120300 (2.5)
166652 (3.2)
128903 (2.5)
n.d.
4. CO/4-tert-butylstyrene copolymerization experiments
Our previous investigations [5d] on the catalytic
activity of a series of [Pd(L)2]2þ and [Pd(L)(bipy)]2þ
complexes with L ¼ 6-substituded-2,20-bipyridine showed
that: (i) the 6-substituted ligands inhibit the activity and
(ii) increase of the CO pressure (from 10 to 40 bar) leads
to a decrease in productivity. Accordingly, at low pres-
sure (10 bar), the [Pd(bipy)2][BAr04]2 salt is one of the
best precatalysts. The same negative effect on the cata-
lytic activity of substituents close to the nitrogen donors
has been previously reported for the [Pd(2,9-R2-phen)-
(MeCN)2]2þ species (phen ¼ 1,10-phenanthroline) [3d].
In the case of the latter derivatives, substituents in other
positions have been shown to have modest positive
(5-methyl or 5-nitro) or negative (3,4,7,8-methyl) effects
[3d]. In contrast, quite recently, the dicationic bis-
chelated Pd(II) compound [Pd(3-R-phen)2][PF6]2 (R ¼
1,2,2-trimethylpropyl) was shown to provide very high
productivity in CO/styrene copolymerization, giving a
polymer with molecular weight values higher than
300,000 [4].
Here, we report the effects of 5-alkyl substituents in
the bis-chelated compounds [Pd(bipy)2]2þ on the CO/4-
tert-butylstyrene copolymerization. The tests were run
in 2,2,2-trifluroethanol, at 60 °C, under 40 bar of CO, in
presence of 1,4-benzoquinone. The results are shown in
Table 1.
Under these experimental conditions, the productiv-
ity of complexes 1, 2 and 4, containing at least one
substituted bipyridine, showed a ca. 10% increase com-
Reaction conditions: n(Pd) ¼ 2,7 ꢁ 10ꢀ3 mmol; n(BQ)/n(Pd) ¼ 64;
V(TBS) ¼ 24 mL (0.131 mmol); V(TFE) ¼ 10 mL; P(CO) ¼ 40 bar;
T ¼ 60 °C; t ¼ 14 h.
pared with that of [Pd(bipy)2][BAr0 ]2, 3. The Mw values
4
were in the range 120,000 (compound 1)–166,000
(compound 2). The absence of palladium black after 14
h of reaction accounts for the high stability of catalysts
1, 2 and 4.
A comparison of the activity of the [BAr04] salts with
the corresponding [PF6] compounds, under strictly
comparable conditions, confirms, even in this case, the
positive effect of the [BAr04] anion, as previously ob-
served in the CO/styrene copolymerization [5d]. Pro-
ductivities of 758 and 543 g(CP)/g(Pd) h were obtained
with 3 and with [Pd(bipy)2][PF6]2 [10], respectively.
The catalytic activity of the complexes [Pd(L1)(Me)
(MeCN)][BAr04], 8, and [Pd(L2)(Me)(MeCN)] [BAr04], 9,
was compared with that of the corresponding salt of the
unsubstituted 2,20-bipyridine (L3), 10. The results of our
tests and the details of the experimental conditions are
shown in Fig. 1 and 2.
Both increasing of productivity and molecular weight
are observed. After 48 h of reaction time the produc-
tivity of the catalysts 8 and 9 remains constant probably
due to the combined effects of partial decomposition of
the catalysts and increase of the concentration of the

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B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
The syndiotacticity of the polyketones obtained with
precursor 8
precursor 9
precursor 10
the complexes bearing substituted bipyridine ligands
was basically the same as that of the copolymer obtained
using bipy as ligand. In conclusion, it seems that the
productivity of both types of precursors is somewhat
favoured by an alkyl substituent(s) in 5.
600
500
400
300
200
100
0
5. Experimental
All reactions were carried out in a nitrogen atmo-
sphere at room temperature (r.t.) using standard
Schlenk techniques. Solvents for synthetic purposes
were distilled and purified prior to use unless otherwise
stated. Solvents for spectroscopy were used without
further purification. Carbon monoxide labelled (CP
grade 99%) was supplied by Aldrich. The bidentate ni-
trogen-donor chelating ligands L (5,50-Me2-2,20-bipyri-
dine, L2, and 2,20-bipyridine, L3) were purchased from
Aldrich and used as received, whereas the ligand L1 (5-
Me-2,20-bipyridine) was prepared according to methods
described in the literature. Na2[PdCl4] (29.15% Pd) was
obtained from Enghelard. The salt Na[BAr04] {sodium
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate} and the
compound [Pd(COD)(Me)Cl] were prepared by re-
ported methods [11,12].
0
10
20
30
40
50
60
70
80
time (h)
Fig. 1. CO/TBS copolymerization using catalyst precursors 8, 9 and 10:
effect of time on productivity. Reaction conditions: n(Pd) ¼ 5 ꢁ 10ꢀ2
mmol; TBS/Pd ¼ 310; V(TBS) ¼ 2.8 ml (15.5 mmol); V(C6H5Cl) ¼ 20
ml; P(CO) ¼ 1 bar; T ¼ 25 °C.
precursors 8
precursor 9
precursor 10
60000
50000
40000
30000
20000
10000
0
1H and 13C{1H} NMR spectra were recorded on a
1
Varian Gemini VXR 300 spectrometer with a H reso-
nance frequency of 300 MHz and a 13C frequency of
75.4 MHz; on a Varian Mercury VX spectrometer with
1
a H resonance frequency of 400 MHz and a 13C fre-
quency of 100.5 MHz. Chemical shifts are given in ppm
relative to internal TMS (1H, 13C). The NOE difference
experiments and two-dimensional 1H NOESY were
obtained by means of standard pulse sequences. The
mass spectrometric measurements were performed on a
VG7070EQ instrument, equipped with a PDP 11-250J
data system and operating under positive ion fast atom
bombardment (FAB) conditions with 3-nitrobenzyl al-
cohol as supporting matrix.
0
10
20
30
40
50
60
70
80
time (h)
Fig. 2. CO/TBS copolymerization using catalyst precursors 8, 9 and 10:
effect of timeonmolecularweight. Forthe reaction conditions, see Fig. 1.
copolymer in solution hindering the access of the
monomer to the catalyst. In our study, working under
[3c] conditions (Fig.1), a moderate but significant in-
crease in the activity was observed when the ligand was a
modified bypiridine, particularly in the case of the 5,50-
substituted-2,20-bipyridine (L2). A comparable effect
was observed also under the same conditions of [3o]
(Table 2).
Elemental analyses (C, H, N) were performed with a
Perkin–Elmer elemental analyzer 240B, by Mr. A. Canu
(Dipartimento di Chimica, Universita degli Studi di
ꢁ
Sassari). Conductivities were measured with a Philips
PW 9505 conductimeter. The molecular weight of the
copolymers and molecular weight distributions were
determined by gel permeation chromatography mea-
surements made in THF on a Waters 515-GPC device
using a linear Waters Untrastyragel column with a
Waters 2410 refractive index detector using polystyrene
standards.
Table 2
Precursor g (CP) g (CP)/g (Pd) g (CP)/g (Pd) h Mw ðMw=MnÞ
8
1.43
1.53
1.33
360.5
386.1
334.5
15.02
16.10
13.94
32500 (1.6)
18500 (1.5)
16800 (1.5)
9
10
5.1. [Pd(L)Cl2] [L ¼ L1 1a, L ¼ L2 2a, L ¼ L3 3a]
Reactions condition: n(Pd) ¼ 3.74 ꢁ 10ꢀ2 mmol; TBS/Pd ¼ 250;
V(TBS) ¼ 1.7 ml (9.34 mmol); V(CH2Cl2) ¼ 15 ml; P(CO) ¼ 1 bar;
t ¼ 24 h; T ¼ 0 °C for 30 min and room temperature for 24 h.
To a solution of Na2[PdCl4] (308.8 mg, 1.00 mmol) in
CH3OH (10 mL) were added 1.09 mmol of L (185.6,

B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
1527
200.8, and 170.2 mg for L1, L2 and L3, respectively). In a
few minutes the product began to precipitate. The
mixture was stirred at room temperature for 1 h. The
precipitate formed was filtered off and washed with
water, ethanol and diethyl ether to obtain the analytical
sample as a yellow solid.
3. Yield: 74%, mp: 138–140 °C. Found: C, 46.90; H,
2.13; N 2.34 (Calcd for C84H40B2F48N4Pd: C, 47.03; H,
1
1.88; N, 2.61). H NMR (300 MHz, CD3OD): d 7.59 s
[24H] [BAr04]ꢀ (Ar0 ¼ 3,5-(CF3)2-C6H3); 7.97 t [4H], H5,
H50; 8.52 t [4H], H4, H40; 8.66 d [4H] H3,H30; 8.84 d
[4H], H6, H60. FAB mass spectrum, m=z: 418 [M]þ; 262
[M–L3]þ.
1a. Yield: 98%, mp: stable up to 290 °C. Found: C,
37.52; H, 2.61; N 7.79 (Calcd for C11H10N2Cl2Pd: C,
37.98; H, 2.88; N, 8.05). H NMR (300 MHz, DMSO-
5.3. [Pd(L2)(L3)][BAr40 ]2, 4
1
d6): d 2.45 s [3H], 5-Me; 8.90 s [1H], H6; 9.08 d [1H],
H60; 7.70–8.53 [5H] other aromatics. FAB mass spec-
trum, m=z: 311 [M–Cl]þ; 276 [M–2Cl]þ.
To a solution of Na[BAr40 ] (483.8 mg, 0.55 mmol) and
L3 (42.8 mg, 0.27 mmol) in 20 mL of CH2Cl2, was added
slowly, under stirring at room temperature, a solution of
[Pd(L2)Cl2] (98.7 mg, 0.27 mmol, in 40 mL of CH2Cl2).
The solution was left to react for 1 h. After filtration of
NaCl, the solution was evaporated to dryness in vacuo.
The crude product, as pale-yellow foam, was converted
to a solid by triturating with pentane or hexane. The
analytical sample was obtained by repeated washings of
the solid with the same solvents and drying for 24 h in
vacuo.
2a. Yield: 92%, mp: stable up to 290 °C. Found: C,
39.58; H, 2.91; N 7.45 (Calcd for C12H12N2Cl2Pd: C,
1
39.83; H, 3.32; N, 7.74). H NMR (300 MHz, DMSO-
d6): d 2.44 s [6H], 5,50-Me2; 8.89 s [2H], H6, H60; 8.17–
8.42 [4H] other aromatics. FAB mass spectrum, m=z:
325 [M–Cl]þ; 290 [M–2Cl]þ.
3a. Yield: 98%, mp: stable up to 290 °C. Found: C,
36.11; H, 2.53; N 8.18 (Calcd for C10H8N2Cl2Pd: C,
1
35.98; H, 2.40; N, 8.39). H NMR (300 MHz, DMSO-
d6): d 9.13 d [2H], H6, H60; 7.81–8.58 [6H] other aro-
matics.
Yield: 93%, mp: 191–193 °C. Found: C, 47.70; H,
1.75; N 2.61 (Calcd for C86H44B2F48N4Pd: C, 47.53; H,
1
2.04; N, 2.58). H NMR (300 MHz, CD3OD): d 2.61 s
5.2. [Pd(L)2][BAr04]2 [L ¼ L1 1, L ¼ L2 2, L ¼ L3 3]
[6H], 5,50-Me2; 7.59 s [24H] [BAr0 ]ꢀ (Ar0 ¼ 3,5-(CF3)2-
4
C6H3); 7.99 t [2H] H5, H50 (L3); 8,31 d [2H] H4, H40
(L2); 8,46 d [2H] H3, H30 (L2); 8,52 t [2H] H4, H40 (L3);
8.61 s [2H], H6, H60 (L2); 8,66 d [2H] H3, H30 (L3); 8.86
d [2H], H6, H60 (L3). KM (5 ꢁ 10ꢀ4 M, acetone): 151
Xꢀ1 cm2 molꢀ1. FAB mass spectrum, m=z: 446 [M]þ of
[Pd(L2)(L3)]2þ; 474 [M]þof [Pd(L2)2]2þ; 418 [M]þ of
To a solution of Na[BAr40 ] (291.0 mg, 0.33 mmol) and
L (0.17 mmol, 29.1, 31.3 and 26.5 mg for L1, L2 and L3,
respectively) in 20 mL of CH2Cl2, was added slowly,
under stirring at room temperature, a solution of
[Pd(L)Cl2] (0.16 mmol, 56.4, 57.8 and 53.4 mg, for L1,
L2 and L3, respectively) in 40 mL of CH2Cl2. The so-
lution was left to react for 1 h. After filtration of NaCl,
the solution was evaporated to dryness in vacuo. The
crude product, as pale-yellow foam, was converted to a
solid by triturating with pentane or hexane. The ana-
lytical sample was obtained by repeated washings of
the solid with the same solvents and drying for 24 h in
vacuo.
[Pd(L3)2]2þ
.
5.4. [Pd(L)(Me)Cl] [L ¼ L1 5, L ¼ L2 6, L ¼ L3 7]
To a solution of [Pd(COD)(Me)Cl] (235.9 mg, 0.89
mmol) in benzene (20 mL) was added under stirring at
room temperature 1.14 mmol of L(194.7, 210.0, 178.1
mg for L1, L2 and L3, respectively) in 20 mL of diethyl
ether. In a few minutes the product began to precipitate
as a yellow solid that after 1 h was filtered off, washed
with Et2O to obtain, after drying in vacuo, the analytical
sample as a yellow solid. In the case of L1, the product
was obtained as a mixture of two geometrical isomers
(5a/5b ca. 1:1; NMR criterion).
1. Yield: 94%, mp: 125–127 °C. Found: C, 47.98; H,
2.23; N 2.83 (Calcd for C86H44B2F48N4Pd: C, 47.53; H,
1
2.04; N, 2.58). H NMR (300 MHz, CD3OD): d 2.54 s
[6H], 5-Me; 7.59 s [24H] [BAr04]ꢀ (Ar0 ¼ 3,5-(CF3)2-
C6H3); 7.76 m [2H], H50; 8.20 d [2H], H4; 8.33 t [2H],
H40; 8.41 d [2H], H3; 8.48 d [2H], H30; 8.63 s [2H], H6;
8.73 d [2H], H60. KM (5 ꢁ 10ꢀ4 M, acetone): 126
Xꢀ1 cm2 molꢀ1. FAB mass spectrum, m=z: 446 [M]þ;
276 [M–L1]þ.
5. Yield: 91%, mp: 225 °C (dec). Found: C, 44.19; H,
4.28; N 8.34 (Calcd for C12H13ClN2Pd: C, 44.02; H,
1
3.97; N, 8.56). H NMR (300 MHz, CDCl3): d 1.00 s
2. Yield: 90%, mp: 215–217 °C. Found: C, 47.91; H,
2.01; N 2.68 (Calcd for C88H48B2F48N4Pd: C, 48.01; H,
[3H+3H], Pd–Me (5a, 5b, overlapping signals); 2.44 s
[3H], 5-Me (5a); 2.49 s [3H], 5-Me(5b); 8.43 s [1H], H6
(5b); 8.63 d [1H], H60, (5a); 8.97 s [1H], H6 (5a); 9.15 d
[1H], H60 (5b); 7.27–8.09 [5H+5H] other aromatics.
FAB mass spectrum, m=z: 311 [M–Me]þ; 291 [M–Cl]þ;
276 [M–Me–Cl]þ.
1
2.20; N, 2.55). H NMR (300 MHz, CD3OD): d 2.61 s
[12H], 5,50-Me2; 7.59 s [24H] [BAr0 ]ꢀ (Ar0 ¼ 3,5-(CF3)2-
4
C6H3); 8.31 d [4H] H4,H40; 8.46 d [4H] H3,H30; 8.62 s
[4H], H6, H60. KM (5 ꢁ 10ꢀ4 M, acetone): 148
Xꢀ1 cm2 molꢀ1. FAB mass spectrum, m=z: 474 [Mþ],
290 [M–L2]þ.
6. Yield: 95%, mp 235 °C. Found: C, 45.18; H, 4.01;
N 8.44 (Calcd for C13H15ClN2Pd: C, 45.77; H, 4.43; N,

1528
B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
8.21). 1H NMR (300 MHz, CDCl3; in the structure
formula N1 trans Me and N10 trans Cl): d 0.98 s [3H],
Pd–Me; 2.42 s [3H], 5-Me; 2.47 s [3H], 50-Me; 8.40 s
[1H], H60; 8.95 s [1H], H6; 7.74-7.95 [4H] other aro-
matics. FAB mass spectrum, m=z: 325 [M–Me]þ; 305
[M–Cl]þ; 290 [M–Me–Cl]þ.
7. Yield: 98%, mp: 216 °C (dec). Found: C, 42.62; H,
3.40; N 8.81 (Calcd for C11H11ClN2Pd: C, 42.16; H,
3.51; N, 8.94). 1H NMR (300 MHz, CDCl3, in the
structure formula N1 trans Me and N10 trans Cl): d 1.05
s [3H], Pd–Me; 8.68 s [1H], H60; 9.21 s [1H], H6; 7.51-
8.14 [6H] other aromatics. FAB mass spectrum, m=z:
297 [M–Me]þ; 277 [M–Cl]þ; 262 [M–Me–Cl]þ.
2.20; N, 3.55). 1H NMR (300 MHz, CDCl3, in the
structure formula N1 trans Me and N10 trans MeCN): d
1.04 s [3H], Pd–Me; 2.38 s [3H], Pd-NCMe; 7.50 s [4H]
Hp[BAr04]ꢀ (Ar0 ¼ 3,5-(CF3)2-C6H3); 7.70 s [8H] Ho
[BAr04]ꢀ (Ar0 ¼ 3,5-(CF3)2-C6H3); 8.35 d [1H], H6; 8.50
d [1H], H60; 7.37–8.02 [8H] other aromatics. KM
(5 ꢁ 10ꢀ4 M, acetone): 99 Xꢀ1 cm2 molꢀ1. FAB mass
spectrum, m=z: 318 [M]þ; 277 [M–MeCN]þ; 262 [M–
MeCN–Me]þ.
5.5.1. Copolymerization reactions – general procedure
4-tert-Butylstyrene, TBS (passed through a small
column of basic Al2O3 prior to use), 2,2,2-trifluoretha-
nol, TFE (dried on anhydrous CaSO4 prior to use), 1,4-
benzoquinone (BQ used as received) and chlorobenzene
(used as received) were purchased from Aldrich.
The reactions (with precursors 1, 2, 3, 4) were carried
out in a stainless steel autoclave (150 mL), equipped
with a magnetic stirrer and a temperature regulator. The
precursor, 4-tert-butyl-styrene, 1,4-benzoquinone, and
the alcohol were placed in the autoclave, which was
purged then pressurized with CO and heated. After
cooling and releasing the residual gas, the solution was
poured dropwise into 200 mL of methanol under stir-
ring. The white precipitate was collected by filtration,
washed with methanol and dried in a vacuum oven at 70
°C overnight.
In a typical procedure the cationic precursor 8, 9 or
10 was dissolved in chlorobenzene (or dichloromethane)
in a previously flushed Schlenk flask and the N2 atmo-
sphere replaced with CO. 4-tert-Butylstyrene was then
introduced and the reaction was allowed to take place at
r.t. (or initially at 0 °C in dichloromethane) and 1bar of
CO. Reaction time varied from 24 to 72 h. Work-up
included filtration of the reaction mixture through
Kieselghur and precipitation of the polymeric material
by pouring the reaction solution dropwise into 200 ml of
methanol under stirring. The off-white precipitate was
collected by filtration, washed with methanol and dried
in a vacuum oven at 70 °C overnight. Percentage con-
versions were calculated from the weight of the isolated
polymeric material. The polymer was purified by rep-
recipitation and then polymer weights were measured.
The copolymers were dissolved in the minimum amount
of THF, the solution was filtered through a 0.22 lm
filter and added dropwise to methanol under stirring.
The solid was then filtered and dried as previously
stated.
5.5. [Pd(L)(Me)(MeCN)][BAr04] [L ¼ L1 8, L ¼ L2 9,
L ¼ L3 10]
To a solution of Na[BAr04] (338.1 mg, 0.38 mmol) in
1.20 mL of MeCN, were added under stirring at room
temperature 0.38 mmol of [Pd(L)(Me)Cl] (118.7, 124.3,
118.9 mg for L1, L2 and L3, respectively) in 20 mL of
CH2Cl2. The yellow solution immediately faded and a
NaCl precipitate was formed. The mixture was stirred
for 1 h. The NaCl precipitate was filtered through fine
paper and the yellow solution obtained was evaporated
to dryness. The crude product was crystallized from
CH2Cl2/pentane to give 8, 9 and 10. In the case of L1,
the product was obtained as a mixture of two geomet-
rical isomers as compound 5 (8a/8b, ca. 1:1, NMR cri-
terion).
8. Yield: 87%, mp: 53–55 °C. Found: C, 46.66; H,
2.65; N 3.39 (Calcd for C46H28BF24N3Pd: C, 46.16; H,
1
2.34; N, 3.51). H NMR (300 MHz, CDCl3): d 1.02 s
[3H], Pd–Me (8a); 1.04 s [3H], Pd–Me (8b); 2.35 s [3H],
5-Me (8a); 2.38 s [3H], Pd-NCMe; 2.39 s [3H], Pd-
NCMe; 2.44 s [3H], 5-Me (8b); 7.50 s [4H] Hp [BAr04]ꢀ
(Ar0 ¼ 3,5-(CF3)2-C6H3); 7.70
s
[8H] Ho [BAr04]ꢀ
(Ar0 ¼ 3,5-(CF3)2-C6H3); 8.17 s [1H], H6, (8a); 8.30 s
[1H], H6, (8b); 8.32 d [1H], H60 (8b); 8.44 d [1H], H60
(8a); 7.32–7.99 [5H+5H] other aromatics. KM (5 ꢁ 10ꢀ4
M, acetone): 56 Xꢀ1 cm2 molꢀ1. FAB mass spectrum,
m=z: 332 [Mþ], 291 [M–MeCN]þ, 276 [M–MeCN–
Me]þ.
9. Yield: 83%, mp: 56–58 °C. Found: C, 46.84; H,
2.37; N 3.36 (Calcd for C47H30BF24N3Pd: C, 46.61; H,
2.48; N, 3.47). 1H NMR (300 MHz, CDCl3, in the
structure formula N1 trans Me and N10 trans MeCN): d
1.03 s [3H], Pd–Me; 2.33 s [3H], 5-Me; 2.40 s [3H], Pd-
NCMe; 2.44 s [3H], 50-Me; 7.50 s [4H] Hp[BAr04]ꢀ
(Ar0 ¼ 3,5-(CF3)2-C6H3); 7.70
s
[8H] Ho[BAr04]ꢀ
(Ar0 ¼ 3,5-(CF3)2-C6H3); 8.13 s [1H], H6; 8.28 s [1H],
H60; 7.72-7.80 [4H] other aromatics. KM (5 ꢁ 10ꢀ4 M,
acetone): 56 Xꢀ1 cm2 molꢀ1. FAB mass spectrum, m=z:
346 [Mþ], 305 [M–MeCN]þ, 290 [M–MeCN–Me]þ.
10. Yield: 92%, mp: 85–87 °C. Found: C, 45.82; H,
2.02; N 3.54 (Calcd for C45H26BF24N3Pd: C, 45.72; H,
5.5.2. Copolymer CO/4-tert-butylstyrene characterization
3
1H NMR (300 MHz, CDCl3, r.t.): d 7.0 (d J ¼ 8.1
3
Hz), 2H Hb or Hc; 6.6 (d J ¼ 8.1 Hz), 2H Hc or Hb;
4.11 (t 3J ¼ 7.1 Hz), 1H CH; 3.0 (dd 2J ¼ 18.1 Hz,
3J ¼ 6.8 Hz), 1H CH2; 2.6 (dd 2J ¼ 18.1 Hz, 3J ¼ 6.8 Hz),
1H CH2; 1.23 (s, 9H, C(CH3)3).

B. Soro et al. / Journal of Organometallic Chemistry 689 (2004) 1521–1529
1529
13C NMR (75.4 MHz, CDCl3, r.t.): d 206.7 (-C(O)-);
149.6 (Cd); 134.0 (Ca); 128.0 (Cc); 125.4 (Cb); 52.6 (CH);
43.0(CH2); 34.3 (C(CH3)3); 31.3 (C(CH3)3).
[2] For the only example where the use of diphosphines leads to
formation of polyketones: J.C. Yuan, S.J. Lu, Organometallics 20
(2001) 2697.
[3] (a) C. Pisano, S.C.A. Nefkens, G. Consiglio, Organometallics 11
(1992) 1975;
(b) C. Pisano, C. Mezzetti, G. Consiglio, Organometallics 11
(1992) 20;
O
(c) M. Brookhart, F. Rix, J.M. De Simone, J.C. Barborak, J. Am.
Chem. Soc. 114 (1992) 5894;
(d) A. Sen, Z. Jiang, Macromolecules 26 (1993) 911;
(e) J. Zhaozhong, S.E. Adam, A. Sen, Macromolecules 27 (1994)
2694;
n
α
(f) C. Pisano, G. Consiglio, Gazz. Chim. It. 124 (1994) 393;
(g) M. Brookhart, M.I. Wagner, G.G.A. Balavoine, H.A. Had-
dou, J. Am. Chem. Soc. 116 (1994) 3641;
β
γ
(h) B. Milani, E. Alessio, G. Mestroni, A. Sommazzi, F. Garbassi,
E. Zangrando, N. Bresciani-Pahor, L. Randaccio, J. Chem. Soc.,
Dalton Trans. 13 (1994) 1903;
δ
(i) S. Bartolini, C. Carfagna, A. Musco, Macromol. Chem.,
Rapid. Commun. 16 (1995) 9;
(j) M. Brookhart, M.I. Wagner, J. Am. Chem. Soc. 118 (1996)
7219;
(k) B. Milani, A. Anzilutti, L. Vicentini, A. Sessanta o Santi, E.
Zangrando, S. Geremia, G. Mestroni, Organometallics 16 (1997)
5064;
5.5.3. 13CO NMR study
(l) A. Aeby, G. Consiglio, Inorg. Chim. Acta 45 (1999) 296;
(m) B. Milani, G. Corso, G. Mestroni, C. Carfagna, M. Formica,
R. Seraglia, Organometallics 19 (2000) 3435;
(n) M.T. Reetz, G. Haderlein, K. Angermund, J. Am. Chem. Soc.
122 (2000) 996;
The reactivity of the complexes 8 and 9 with carbon
monoxide was studied in situ by 1H and 13C NMR
spectroscopy. CD2Cl2 (0.7 mL) was added to a 5 mm
NMR tube charged with the complex (7 ꢁ 10ꢀ3 mmol).
After cooling the solution to 0 °C, 13CO was bubbled for
5 min via a needle into the NMR tube. The sample was
placed in a precooled NMR probe and 1H and 13C
NMR spectra were recorded after 15 min. The spectra
were recorded at 0; )20; )60 and )80 °C.
(o) C. Carfagna, G. Gatti, D. Martini, C. Pettinari, Organomet-
allics 20 (2001) 2175;
(p) A. Bastero, A. Ruiz, J.A. Reina, C. Claver, A.M. Guerrero,
ꢀ
F.A. Jalon, B.R. Manzano, J. Organomet. Chem. 619 (2001) 287;
(q) A. Bastero, A. Ruiz, C. Claver, B. Milani, E. Zangrando,
Organometallics 21 (2002) 5820;
(r) B. Binotti, C. Carfagna, G. Gatti, D. Martini, L. Mosca, C.
Pettinari, Organometallics 22 (2003) 1115.
[4] B. Milani, A. Scarel, G. Mestroni, S. Gladiali, R. Taras, C.
Carfagna, L. Mosca, Organometallics 21 (2002) 1323.
[5] (a) B. Milani, E. Alessio, G. Mestroni, E. Zangrando, L.
Randaccio, G. Consiglio, J. Chem. Soc., Dalton Trans. (1996)
1021;
Acknowledgements
ꢁ
We thank the Universita di Sassari and the Spanish
Ministerio de Education, Cultura y Deporte (BQU-
2001-0656 and RTN2-2001-00127) for financial support;
(b) R. Santi, A.M. Romano, R. Garrone, L. Abbondanza, M.
Scalabrini, G. Bacchilega, Macromol. Chem. Phys. 200 (1999) 25;
ꢀ
the Ministerio de Ciencia y Tecnologıa for awarding a
research grant (to A. Bastero).
ꢀ
(c) A. Bastero, A. Ruiz, C. Claver, S. Castillon, Eur. J. Inorg.
Chem. 12 (2001) 3009;
(d) S. Stoccoro, G. Alesso, M.A. Cinellu, G. Minghetti, A. Zucca,
A. Bastero, C. Claver, M. Manassero, J. Organomet. Chem. 664
(2002) 77.
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