Subtle balance of steric and electronic effects for the synthesis of atactic polyketones catalyzed by Pd complexes with meta-substituted Aryl-BIAN ligands

Article abstract of DOI:10.1021/om7011858

Both symmetric and nonsymmetric bis(aryl)acenaphthenequinonediimine ligands, featured by substituents in meta-positions of the aryl rings, have been applied for the first time as ancillary ligands for the palladium-catalyzed CO/vinyl arene copolymerizatio

Full text of DOI:10.1021/om7011858

1486
Organometallics 2008, 27, 1486–1494
Subtle Balance of Steric and Electronic Effects for the Synthesis of
Atactic Polyketones Catalyzed by Pd Complexes with
Meta-Substituted Aryl-BIAN Ligands
,†
Alessandro Scarel,† M. Rosa Axet, Francesco Amoroso,† Fabio Ragaini,‡
Cornelis J. Elsevier,§ Alexandre Holuigue,§ Carla Carfagna,| Luca Mosca,| and
Barbara Milani*,†
Dipartimento di Scienze Chimiche, UniVersità di Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy,
Dipartimento di Chimica Inorganica, Metallorganica e Analitica, UniVersità di Milano, Via G. Venezian
21, 20133 Milano, Italy, Van’t Hoff Institute for Molecular Sciences, UniVersiteit Van Amsterdam, Nieuwe
Achtergracht 166, Amsterdam, The Netherlands, Istituto di Scienze Chimiche, UniVersità di Urbino, Piazza
Rinascimento 6, 61029 Urbino, Italy
ReceiVed NoVember 27, 2007
Both symmetric and nonsymmetric bis(aryl)acenaphthenequinonediimine ligands, featured by substituents
in meta-positions of the aryl rings, have been applied for the first time as ancillary ligands for the palladium-
catalyzed CO/vinyl arene copolymerization. The nature and the number of substituents affect both the
productivity and the molecular weight of the synthesized copolymers. Palladium complexes containing
the nonsymmetric ligands are the most efficient catalysts reported so far for the synthesis of atactic
polyketones.
of the synthesized macromolecules is a main target11 and in
Introduction
the case of vinyl arene comonomers a considerable number of
The discovery by Brookhart that late transition metal com-
plexes modified with R-diimine ligands, having a 1,4-diaza-
1,3-butadiene or an acenaphthene (Ar-BIAN) skeleton, are
extremely efficient catalysts for homopolymerization of alkenes
had a galvanizing effect for the research in this field, resulting
in the development of a huge number of bis(nitrogen) ligands
of this nature.1,2 All the Ar-BIAN ligands applied to the
polymerization reactions share the following common features:
(i) the two nitrogen atoms bear identical aryl rings; (ii) these
aryl rings are almost invariably substituted in the ortho and/or
para positions; and (iii) the nature and the number of substituents
affect the yield3 in the polymer, the selectivity1,4 in the product,
the microstructure of the polymer,4 and the relative amount5 of
the comonomers inserted into the polymer chain in R-olefins
copolymerization.
nitrogen-donor ligands have been applied to this reaction with
this aim.12 This collection of data allowed a relationship between
the symmetry of the ligand and the tacticity of the obtained
polyketones to be defined: generally, C2V symmetric ligands lead
to syndiotactic copolymers, while polyketones with isotactic
microstructure are obtained with ligands of C2 symmetry. Atactic
CO/styrene polyketones were obtained for the first time with
P-N ligands of C1 symmetry, under drastic reaction conditions
like a CO pressure of 320 bar, and reaching a productivity of
3.42 g CP/g Pd · h (g CP/g Pd · h ) grams of copolymer per
gram of palladium per hour).13,14 Also, Pd complexes containing
pyridine-imidazoline ligands led to atactic CO/4- tert-butylsty-
rene copolymers under mild reaction conditions. For this system,
both the productivity and the stereoregularity of the obtained
polyketones were affected by the electronic properties and the
stereochemistry of the ligand: (R,S)-pyridine-imidazolines yielded
the atactic polyketones with moderate productivities, while the
corresponding (R,R)-diastereoisomer generated very efficient
catalysts for the synthesis of the syndiotactic copolymer.15,16
During the last two decades considerable interest has been
given to the CO/alkene copolymerization reaction yielding
perfectly alternating polyketones.6–10 In particular, when prochiral
alkenes are the comonomers the control of the stereochemistry
* Corresponding author. Phone: +39 040 5583956. Fax: +39 040
5583903. E-mail: milaniba@units.it.
(8) Nakano, K.; Kosaka, N.; Hiyama, T.; Nozaki, K. Dalton Trans. 2003,
4039, 4050.
† Università di Trieste.
Current address: Laboratoire de Chimie de Coordination, 205, route
de Narbonne 31077, Toulouse cedex 04, France
‡ Università di Milano.
(9) Durand, J.; Milani, B. Coord. Chem. ReV. 2006, 250, 542–560.
(10) Suárez, E. J. G.; Godard, C.; Ruiz, A.; Claver, C. Eur. J. Inorg.
Chem. 2007, 2582, 2593.
§ Universiteit van Amsterdam.
(11) Nozaki, K. Synthesis of chiral, optically active copolymers. In
Catalytic synthesis of alkene-carbon monoxide copolymers and cooligo-
mers; Sen, A., Ed.; Kluwer Academic Publishers: Dordrecht, The Nether-
lands, 2003; pp 217–235..
| Università di Urbino.
(1) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc.
1998, 120, 4049–4050.
(2) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169–1203.
(12) Consiglio, G.; Milani, B. Stereochemical aspects of cooligomer-
ization and copolymerization. In Catalytic synthesis of alkene-carbon
monoxide copolymers and cooligomers; Sen, A., Ed.; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 2003; pp 189–215..
(13) Sperrle, M.; Aeby, A.; Consiglio, G.; Pfaltz, A. HelV. Chim. Acta
1996, 79, 1387–1392.
(3) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414–6415.
(4) Pappalardo, D.; Mazzeo, M.; Antinucci, S.; Pellecchia, C. Macro-
molecules 2000, 33, 9483–9487.
(5) Kiesewetter, J.; Kaminsky, W. Chem. Eur. J. 2003, 9, 1750–1758.
(6) Drent, E.; Budzelaar, P. H. M. Chem. ReV. 1996, 96, 663–681.
(7) Bianchini, C.; Meli, A. Coord. Chem. ReV. 2002, 225, 35–66.
(14) Sperrle, M. Ph. D., ETH, Zurich, 1996.
(15) Bastero, A.; Ruiz, A.; Claver, C.; Castillón, S. Eur. J. Inorg. Chem.
2001, 3009, 3011.
10.1021/om7011858 CCC: $40.75
2008 American Chemical Society
Publication on Web 03/13/2008

Synthesis of Atactic Polyketones
Organometallics, Vol. 27, No. 7, 2008 1487
Scheme 1. Synthetic Pathway for the Monocationic
Palladium Complexes 1b–8b and the Studied Ar-BIAN
Ligands
Here, we discuss the catalytic behavior of a series of Pd(II)
complexes, [Pd(CH3)(CH3CN)(N-N)][PF6] 1b–8b (N-N )
1–8), in the CO/vinyl arene copolymerization.
Results and Discussion
The new mixed ligand 8 was prepared by a transimination
reaction, in a way analogous to that already reported for 7 and
other mixed Ar′,Ar-BIAN ligands (Scheme 2),27 but an im-
proved chromatographic separation was employed. Quite sur-
prisingly, the symmetrical 3,4,5-(CH3O)3C6H3-BIAN (6) could
not be obtained by the direct reaction of the corresponding amine
with acenaphthenequinone in refluxing acetic acid. Apparently
the quinone is acting as an oxidant for trimethoxyaniline under
these conditions, highlighting the very electron-rich nature of
the latter. To the best of our knowledge, this is the first time
this synthetic strategy fails with an electron-rich aniline.24
Ligand 6 could be obtained without problems by transimination
from ligand 5 by the same procedure employed for ligand 8,
but employing a 3-fold molar excess of amine (Scheme 2).
Transimination proceeds under much milder conditions and no
oxidant is present.
Palladium complexes of ortho-substituted Ar-BIAN were
introduced17 and used as model compounds for unraveling the
mechanism of the polymer chain growth during the CO/alkene
copolymerization.17–20 When monocationic Pd(II) complexes
with ortho-disubstituted Ar-BIAN ligands were tested as pre-
catalysts in the CO/4-Me-styrene copolymerization, low pro-
ductivity (15 g CP/g Pd corresponding to 0.3 g CP/g Pd · h) or
complete inactivity were observed depending on the nature of
the substituents.21–23 Moreover, these copolymers have a
prevailingly isotactic microstructure despite the C2V symmetry
of the Ar-BIAN ligand present in the catalyst.
So far, Ar-BIAN ligands with substituents in the meta position
have not been applied to CO/alkene copolymerizations, nor have
any nonsymmetric Ar′,Ar-BIAN ligands (Ar′ * Ar) been tested
in catalysis, in general. We envisaged that attenuation of steric
effectsscompared to the presence of ortho substituentssand/
or the creation of subtle electronic unbalance on the N-atoms
could be advantageous for the copolymerization reaction; hence,
we have now focused our attention on Ar-BIAN ligands
substituted in the meta position by methyl (2 and 4) or
trifluoromethyl (3 and 5) or methoxy (6) groups (Scheme 1).24–26
Moreover, the nonsymmetric Ar′,Ar-BIAN ligands (7 and 8)
are studied for the first time.27 Ligands 6 and 8 have not been
reported before and they have been synthesized for this purpose.
The new monocationic complexes 1b–8b were prepared
starting from the corresponding neutral derivatives 1a–8a,
following the well-established procedure reported in the litera-
ture (Scheme 1).28
Both neutral and monocationic complexes were characterized
by elemental analysis and 1H NMR spectroscopy recording the
spectra in CD2Cl2 solution, at room temperature. The 1H
assignments are based on the number of signals, on their
integration, on NOE, and on homonuclear COSY experiments.
From a general point of view, the spectra can be divided into
three regions, respectively those of the aromatic protons, of the
protons of the substituents of the aryl rings, and of the Pd-CH3
fragment. The signals that are more diagnostic for the coordina-
tion of ligand to palladium are those of H3 and H10 for the
acenaphthene skeleton and that due to the Pd-CH3 moiety (Chart
1, Table 1).
For complexes 1a–6a and 1b–6b, having the symmetric Ar-
BIAN ligands, the number of signals and their integration
confirm the coordination of the R-diimine to palladium in a
nonsymmetric environment. No signal due to the free ligand is
present (Table 1). The protons of the two halves of the ligand
were distinguished thanks to NOE experiments based on the
irradiation of the signal of H14′,18′ and resulting in the increase
in the intensity of the singlet due to the Pd-CH3 fragment and
of the doublet assigned to H10. In analogy, when the signal of
H14,18 was irradiated, an increase in the intensity of the doublet
assigned to H3 was observed, while no interaction with the Pd-
CH3 fragment was evidenced. In addition, both NOE experi-
ments highlighted the presence of an exchange equilibrium
between the two halves of the ligand. This equilibrium is slow
on the NMR time scale.
(16) Bastero, A.; Claver, C.; Ruiz, A.; Castillon, S.; Daura, E.; Bo, C.;
Zangrando, E. Chem. Eur. J. 2004, 10, 3747–3760.
(17) Van Asselt, R.; Elsevier, C. J. Organometallics 1992, 11, 1999–
2001.
(18) van Asselt, R.; Gielens, E. E. C. G.; Rülke, R. E.; Elsevier, C. J.
J. Chem. Soc., Chem. Commun. 1993, 1203, 1205.
(19) van Asselt, R.; Gielens, E. E. C. G.; Rülke, R. E.; Vrieze, K.;
Elsevier, C. J. J. Am. Chem. Soc. 1994, 116, 977–985.
(20) Groen, J. H.; Delis, J. G. P.; van Leeuwen, P. W. N. M.; Vrieze,
K. Organometallics 1997, 16, 68–77.
H3 and H10 protons were the most affected by the coordination
to palladium: they generated two well-separated doublets that
were at low frequency with respect to the signals of H5 and H8,
both in the free ligand and in the Pd complexes, due to the fact
that they fall in the shielding cone of the aryl rings. The
coordination to palladium shifted the signal of H3 to high
frequency, whereas that of H10 was shifted to low frequency
with respect to the same signals in the free ligand, confirming
(21) Bellachioma, G.; Binotti, B.; Cardaci, G.; Carfagna, C.; Macchioni,
A.; Sabatini, S.; Zuccaccia, C. Inorg. Chim. Acta 2002, 330, 44–51.
(22) Binotti, B.; Carfagna, C.; Zuccaccia, C.; Macchioni, A. Chem.
Commun. 2005, 92, 94.
(23) Binotti, B.; Bellachioma, G.; Cardaci, G.; Carfagna, C.; Zuccaccia,
C.; Macchioni, A. Chem. Eur. J. 2007, 13, 1570–1582.
(24) Gasperini, M.; Ragaini, F.; Cenini, S. Organometallics 2002, 21,
2950–2957.
(25) Gasperini, M.; Ragaini, F. Organometallics 2004, 23, 995–1001.
(26) Kluwer, A. M.; Koblenz, T. S.; Jonischkeit, T.; Woelk, K.; Elsevier,
C. J. J. Am. Chem. Soc. 2005, 127, 15470–15480.
(28) Durand, J.; Zangrando, E.; Stener, M.; Fronzoni, G.; Carfagna, C.;
Binotti, B.; Kamer, P. C. J.; Muller, C.; Caporali, M.; van Leeuwen,
P. W. N. M.; Vogt, D.; Milani, B. Chem. Eur. J. 2006, 12, 7639–7651.
(27) Gasperini, M.; Ragaini, F.; Gazzola, E.; Caselli, A.; Macchi, P.
Dalton Trans. 2004, 3376, 3382.

1488 Organometallics, Vol. 27, No. 7, 2008
Scheme 2. Synthetic Pathway for Ligands 6 and 8
Scarel et al.
the assignment that H3 is cis to the chloride.29 The Pd-CH3
fragment gave one singlet centered at 0.90 ppm in the neutral
derivatives, while it was shifted to low frequency by about 0.10
ppm in the cationic complexes. No effect of the nature of the
ligand on the chemical shift of this signal was observed (Table
1).
position of the Pd-CH3 fragment with respect to the two halves
of the ligand. For the sake of convenience, the isomer with the
Pd-CH3 moiety trans to the Pd-N bond with the iminic N-atom
having the aryl ring bearing the CF3 groups was conventionally
called trans (Chart 1). For all four complexes, NOE experiments,
performed upon irradiation of the Pd-CH3 signal, proved that
the major species was the trans isomer. For the neutral
complexes the ratio between the trans and cis isomers was 10:1
and 6:1 for 7a and 8a, respectively. In the case of the
monocationic derivatives, the trans-to-cis ratio was decreased
As far as 1H NMR spectra of Pd complexes with the
nonsymmetric Ar′,Ar-BIAN ligands are concerned (7a, 8a, 7b,
8b) the number of signals and their integration indicated the
presence in solution of two species, in different amounts, which
are due to the cis and trans isomers, that differ in the relative
Table 1. Selected 1H NMR Data for Complexes 1a–8a and 1b–8ba
N-N/complex
H3
H10
Pd-CH3
Chart 1. Numbering Scheme for Free and Coordinated
Ligands
1
6.84 (d)
7.16 (d)
7.30 (d)
6.86 (d)
7.01 (m)
7.03 (m)
6.86 (d)
7.16 (d)
7.25 (br)
6.92 (d)
7.16 (d)
7.32 (d)
6.89 (d)
7.21 (d)
7.26 (d)
7.12 (d)
7.47 (d)
7.44 (d)
6.81 (d)
7.11 (m)
7.22 (d)
6.82 (d)
7.15 (d)
7.24 (d)
6.84 (d)
6.54 (d)
6.54 (d)
6.86 (d)
6.58 (d)
6.57 (d)
6.86 (d)
6.56 (d)
6.51 (d)
6.92 (d)
6.62 (d)
6.61 (d)
6.89 (d)
6.63 (d)
6.57 (d)
7.12 (d)
6.81 (d)
6.82 (d)
7.01 (d)
6.67 (d)
6.60 (d)
7.20 (d)
6.88 (d)
6.85 (d)
1a
1b
2
2a
2b
3
3a
3b
4
4a
4b
5
5a
5b
6
6a
6b
7
7a
7b
8
8a
8b
0.91(s)
0.81(s)
0.91(s)
0.83(s)
0.90(s)
0.80(s)
0.91(s)
0.84(s)
0.77(s)
0.86(s)
0.87(s)
0.93(s)
1.01(s,trans),0.79(s,cis)
0.96(s,trans),0.71(s,cis)
0.95(s,trans),0.69(s,cis)
1.05(s,trans),0.74(s,cis)
a Recorded in CD2Cl2, at room temperature; s ) singlet, d ) doublet,
m ) multiplet, br ) broad; δ values are in ppm.

Synthesis of Atactic Polyketones
Organometallics, Vol. 27, No. 7, 2008 1489
Table 2. CO/Styrene Copolymerization: Effect of the Ligand and of
Table 3. CO/4-Me-Styrene Copolymerization: Effect of the Ligand
and of BQ (Catalyst Precursor: [Pd(CH3)(CH3CN)(N-N)][PF6]1b–
8b)a
BQ (Catalyst Precursor: [Pd(CH3)(CH3CN)(N-N)][PF6] 1b–8b)a
run
N-N
[BQ]/[Pd]
kg CP/g Pd
MW (Mw/Mn)
run
N-N
[BQ]/[Pd]
kg CP/g Pd
MW (Mw/Mn)
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
0
0
0
0
0
0
0
0
1.23
0.42
1.34
0.93
0.46
1.45
1.45
1.16
43000 (2.2)
37500 (2.2)
41000 (2.1)
33000 (2.1)
14000 (2.0)
20000 (2.9)
47000 (2.0)
20000 (3.3)
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
0
0
0
0
0
0
0
0
5
5
5
5
5
5
5
5
1.05
1.33
0.21b
1.32
0.78b
1.79
1.59
1.33
1.19
1.48
0.69b
1.58
1.35b
1.95
2.36
1.64
33000 (1.9)
30000 (1.9)
16000 (2.6)
38500 (2.0)
n.d.
23000 (1.7)
16000 (1.5)
11000 (1.7)
20500 (1.6)
26000 (1.8)
7000 (1.6)
29000 (1.7)
9000 (1.4)
7000 (1.5)
22000 (1.6)
6500 (1.5)
9
1
2
3
4
5
6
7
8
5
5
5
5
5
5
5
5
2.18
0.74
2.50
1.82
1.26
3.45
2.54
3.70
29000 (1.9)
20000 (1.9)
20500 (1.8)
22000 (1.9)
7000 (1.6)
7500 (1.7)
20500 (1.7)
22000 (1.7)
9
10
11
12
13
14
15
16
10
11
12
13
14
15
16
a Reaction conditions: nPd ) 1.27 × 10-5 mol; TFE V ) 20 mL;
styrene V ) 10 mL; [styrene]/[Pd] ) 6800; T ) 303 K; PCO ) 1 atm; t
) 24 h.
a Reaction conditions: nPd ) 1.27 × 10-5 mol; TFE V ) 20 mL;
4-Me-styrene V ) 10 mL; [4-Me-styrene]/[Pd] ) 5900; T ) 303 K; PCO
) 1 atm; t ) 24 h. b Productivity based on the amount of copolymer;
n.d. ) not determined.
to 3:1 for both 7b and 8b. These observations are in agreement
with the literature data, which indicate a preferential tendency
to coordinate the methyl group trans to less basic N atom for
Pd-methyl complexes with electronically nonequivalent N-
donor atoms.16,28,30,31
As observed for complexes 1a–6a and 1b–6b, even for 7a,b
and 8a,b in solution an exchange equilibrium was present, in
this case the equilibrium involves the two isomers. The rate of
this equilibrium was slow on the NMR time scale. The
mechanism of this equilibrium might occur via the cleavage of
one Pd-N bond, the rotation around the other Pd-N bond, and
the closure of the chemical bond, resulting in the exchange of
the two halves of the ligand with respect to the Pd-methyl
fragment. The lability of the Pd-N bond for the Ar-BIAN
ligands and their fluxional behavior in solution was already
reported.32
Copolymerization Reactions. Complexes 1b–8b were tested
as precatalysts in the CO/vinyl arene copolymerization in 2,2,2-
trifluoroethanol (TFE), at T ) 30 °C, under 1 atm of CO, in
the presence or absence of 1,4-benzoquinone (BQ) as oxidant.
All the complexes generated active species for the studied
reaction and the solids isolated at the end of the runs were
perfectly alternating polyketones.
In the case of CO/styrene copolymerization, regardless of the
presence of the oxidant in the reaction mixture, the substitution
of one of the two meta positions on the aryl rings with a methyl
group resulted in a remarkable decrease in the productivity with
respect to the data obtained with the nonsubstituted ligand 1
(Table 2, run 1 vs 2; run 9 vs 10). On the other hand, when a
CF3 group is introduced on one meta position a slight increase
in the productivity was observed (Table 2, run 1 vs 3; run 9 vs
11). This trend of productivity is in agreement with that showed
by analogous complexes with 4,7-disubstituted-1,10-phenan-
throlines, which evidenced an increase in the productivity on
decreasing the Lewis basicity of the N-N ligand.28 In that case
the complex with the 5,5,6,6-tetrafluoro-5,6-dihydro-1,10-
phenanthroline was found to be the best catalyst ever reported,
in terms of catalytic activity, productivity, molecular weight,
and stereoregularity, for the synthesis of CO/vinyl arene
polyketones with a syndiotactic microstructure.
When the aryl rings both have meta positions substituted by
CH3 or CF3 groups in a symmetrical way, a decrease in the
productivity was found with respect to data obtained with 1b
regardless of the substituents (Table 2, run 1 vs 4 and 5; run 9
vs 12 and 13), thus suggesting that steric hindrance is the
prevailing effect when all the meta positions bear substituents.
When 4-Me-styrene was the comonomer, the effect of the
ligand on the productivity was less pronounced and different
than that in the case of styrene (Table 3). The introduction of
one methyl group on one of the two meta positions resulted in
an increase in the productivity with respect to the values
obtained both with the reference ligand 1 and ligand 3 with
one CF3 on one meta position, regardless of the presence of
benzoquinone (Table 3, run 2 vs 1 and 3; run 10 vs 9 and 11).
Even catalyst 4b, containing the ligand with both meta positions
substituted with methyl groups, was found to be more productive
than 1b and 5b (Table 3, run 4 vs 1 and 5; run 12 vs 9 and 13).
These trends of productivity are the opposite of those observed
for styrene. In addition, with styrene no formation of inactive
palladium metal was observed, while with 4-Me-styrene cata-
lysts 3b and 5b decomposed to palladium metal and decomposi-
tion was more pronounced when benzoquinone was not present
in the reaction mixture. These results suggest that in the case
of 4-Me-styrene the trend of productivity is mainly affected by
the stability of the catalyst, which is higher for ligands having
a higher Lewis basicity, such as 2 and 4, which generate more
productive catalysts. The effect that the stability of the catalyst
conceals the effect of the ligand was also found by us in the
catalytic system based on the 4,7-disubstituted-1,10-phenan-
throlines.28
(29) Rülke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; Van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769–5778.
(30) Bastero, A.; Ruiz, A.; Claver, C.; Milani, B.; Zangrando, E.
Organometallics 2002, 21, 5820–5829.
It should be noted that, whereas in the CO/styrene copolym-
erization the selectivity of the reaction was always 100% in
the polyketone, in the CO/4-Me-styrene reaction when com-
plexes containing the symmetric Ar-BIAN ligands with CF3
substituents, 3b and 5b, were applied, the concomitant formation
of homopolymer was observed. The amount of poly-4-Me-
styrene was very low (4% and 7% for 3b and 5b, respectively)
(31) Scarel, A.; Durand, J.; Franchi, D.; Zangrando, E.; Mestroni, G.;
Milani, B.; Gladiali, S.; Carfagna, C.; Binotti, B.; Bronco, S.; Gragnoli, T.
J. Organomet. Chem. 2005, 690, 2106–2120.
(32) Groen, J. H.; de Jong, B. J.; Ernsting, J.-M.; van Leeuwen,
P. W. N. M.; Vrieze, K.; Smeets, W. J. J.; Spek, A. L. J. Organomet. Chem.
1999, 573, 3–13.

1490 Organometallics, Vol. 27, No. 7, 2008
Scarel et al.
Figure 1. 13C NMR spectra of polyketones synthesized with complex 6b: (a) the ipso carbon atom region of the CO/styrene copolymer and
(b) the methylenic carbon atom region of the CO/4-Me-styrene copolymer.
when benzoquinone was present in the reaction mixture, while
when the reaction was carried out in the absence of the oxidant
the amount of coproduced homopolymer was considerably
higher: 27% for 3b and 80% for 5b. With the aim to shed light
on the mechanism of the homopolymerization, three experiments
were performed at T ) 303 K and for 24 h as in the
copolymerization tests, but varying the components of the
system: (1) when 4-Me-styrene was treated in TFE with BQ,
without addition of CO, no polymerization was observed; (2)
the same happened when 4-Me-styrene was treated in TFE with
BQ, without addition of CO, in the presence of complex 5b;
(3) only traces of homopolymer were formed when 4-Me-styrene
was treated in TFE in the presence of 5b, but neither with BQ
nor with CO. These results are not an absolute proof that the
homopolymerization occurs via a radical rather than an insertion
mechanism. However, they suggest that the palladium complex
and CO are required to start the homopolymerization of 4-Me-
styrene, which might occur through the Pd-alkyl bond homoly-
sis. The propensity of neutral Pd-alkyl species to undergo Pd-C
bond homolysis has been recently reported.33 The nature of the
mechanism of the homopolymerization of alkenes catalyzed by
palladium complexes has been recently debated.34
CO/1-hexene copolymerizations catalyzed by Pd-diphosphine
systems based on ligands belonging to the Josiphos35,36 and to
the dppp families,37 respectively.
In contrast with the literature,38–41 where 4-Me-styrene was
claimed to be a more reactive alkene than styrene, we observed
that, in the present system, productivities in the CO/4-Me-styrene
copolymerization were similar or slightly lower compared to
those obtained in the CO/styrene reaction (Tables 2 and 3).
The effect of the nature of the ligand on the molecular weight
values was not very pronounced: the introduction of a group
on one or both meta positions generally led to polyketones with
lower molecular weight values than those prepared with complex
1b (Tables 2 and 3). The highest Mw value (Mw ) 47000) was
reached for the CO/styrene copolymer synthesized with 7b. In
agreement with the literature,42–44 the introduction of BQ into
the reaction mixture, even if it increased the productivity,
resulted in the synthesis of shorter polyketone chains, for both
alkenes (Tables 2 and 3).
The stereochemistry of these polyketones was studied by 13
C
NMR spectroscopy and the microtacticity was determined by
integration of the signal of the ipso carbon atom in the case of
styrene-containing copolymers, and of that of the methylenic
carbon in the case of CO/4-Me-styrene copolymers (Figure 1).
The 13C NMR spectra showed that atactic copolymers were
obtained in all cases, suggesting that all these ligands create an
active site with the same steric environment around palladium
regardless of the symmetry of the ligand itself, namely C2V for
1, 4, 5, and 6, Cs or C2 for 2 and 3, and Cs for 7 and 8.
A detailed mechanistic investigation on the CO/4-Me-styrene
copolymerization catalyzed by palladium complexes with aryl-
For both alkenes, the active species containing ligand 6
showed a productivity higher than that of 1 (Table 2, run 6 vs
1; run 14 vs 9; Table 3, run 6 vs 1; run 14 vs 9), regardless of
the presence of benzoquinone in the reaction mixture.
The highest values of productivity were reached with
complexes 7b or 8b, having the nonsymmetric Ar′,Ar-BIAN
(Tables 2 and 3). In particular, ligand 8b led to the most
productive catalyst among those tested, achieving the value of
3.70 kg CP/g Pd (corresponding to 154 g CP/g Pd · h) in the
CO/styrene copolymerization, while in the case of 4-Me-styrene
the highest value of productivity was reached with 7b. The
comparison of the productivity data of the Ar′,Ar-BIAN-
containing catalysts with those of the complexes having the
related symmetric ligands evidenced that, for both alkenes, 7b
showed a productivity remarkably higher than that of 4b and
5b. The same was observed for 8b in the CO/styrene copolym-
erization carried out in the presence of BQ, while in both CO/
4-Me-styrene and CO/styrene with no addition of BQ, 8b was
found less productive than 6b together with a slight formation
of palladium metal. In all cases, with catalysts containing the
nonsymmetric ligands the selectivity was 100% in the polyketone.
These data suggest that the unbalance of electron density on
the nitrogen-donor atoms of the ligand has a positive effect on
the catalyst performances. Moreover, in this case the favorable
electronic effect might be partially attenuated by the negative
effect of the steric hindrance created by substituents on all meta
positions. The effect of two electronically nonequivalent ligand
fragments was previously reported for the CO/propene and the
(33) Nagel, M.; Sen, A. Organometallics 2006, 25, 4722–4724.
(34) Sen, A.; Borkar, S. J. Organomet. Chem. 2007, 692, 3291–3299.
(35) Gambs, C.; Chaloupka, S.; Consiglio, G.; Togni, A. Angew. Chem.,
Int. Ed. 2000, 39, 2486–2488.
(36) Gambs, C.; Consiglio, G.; Togni, A. HelV. Chim. Acta 2001, 84,
3105–3126.
(37) Perez-Foullerat, D.; Meier, U. W.; Hild, S.; Rieger, B. Macromol.
Chem. Phys. 2004, 205, 2292–2302.
(38) Brookhart, M.; Wagner, M. I.; Balavoine, G. G. A.; Haddou, H. A.
J. Am. Chem. Soc. 1994, 116, 3641–3642.
(39) Bartolini, S.; Carfagna, C.; Musco, A. Macromol. Rapid Commun.
1995, 16, 9–14.
(40) Carfagna, C.; Gatti, G.; Martini, D.; Pettinari, C. Organometallics
2001, 20, 2175–2182.
(41) Scarel, A.; Milani, B.; Zangrando, E.; Stener, M.; Furlan, S.;
Fronzoni, G.; Mestroni, G.; Gladiali, S.; Carfagna, C.; Mosca, L. Organo-
metallics 2004, 23, 5593–5605.
(42) Barsacchi, M.; Consiglio, G.; Medici, L.; Petrucci, G.; Suter, U. W.
Angew. Chem., Int. Ed. Engl. 1991, 30, 989–991.
(43) Pisano, C.; Nefkens, S. C. A.; Consiglio, G. Organometallics 1992,
11, 1975–1978.
(44) Scarel, A.; Durand, J.; Franchi, D.; Zangrando, E.; Mestroni, G.;
Carfagna, C.; Mosca, L.; Seraglia, R.; Consiglio, G.; Milani, B. Chem. Eur.
J. 2005, 11, 6014–6023.

Synthesis of Atactic Polyketones
Organometallics, Vol. 27, No. 7, 2008 1491
R-diimmine ligands, having the 1,4-diaza-1,3-butadiene skeleton
and aryl rings substituted in the ortho or in the para position
has been reported. The latter leads to copolymers with an atactic
microstructure.45 The intermediates involved in the insertion of
the first molecules of comonomers on the palladium complexes
were detected and characterized by multinuclear NMR. These
species are open-chain intermediates and the formation of the
six-membered metallacycle, up to now considered responsible
for the stereochemical control in the catalytic systems based
on N-donor complexes, was not observed. In the case of the
more flexible para-substituted diimmine ligands the oscillation
of the aryl rings around the N-Cipso bond23 was proposed as
responsible for a statistical insertion of the styrene enantiotopic
faces leading to the formation of atactic copolymers. It is
reasonable to speculate that analogous intermediates and an
analogous mechanism might be present in the catalytic system
under investigation based on aryl-R-diimmine ligands substituted
in the meta position.
of substituents on the ortho positions of the aryl rings of
R-diimines was a crucial requirements for directing the selectiv-
ity of the homopolymerization of alkenes from oligomers to
polymers. In the present system, the introduction of substituents
on ortho positions had a negative effect on the productivity and
on the molecular weight; thus to obtain very efficient catalysts,
aryl-R-diimines substituted in the meta position were required.
In addition, among the ligands tested, the nonsymmetric
Ar′,Ar-BIAN generated the most active catalysts providing the
atactic CO/vinyl arene copolymers in very high yield, thus
pointing out the importance of the electronic unbalance on the
two donor atoms of the ligand and, at the same time, opening
the possibility to study their chemical, physical, and mechanical
properties for evaluating their potential applications.
Experimental Section
The productivity value of 1.23 kg CP/g Pd obtained with
complex 1b, having the nonsubstituted Ar-BIAN ligand, in the
CO/styrene copolymerization with no addition of BQ, can be
compared with the value of 0.68 kg CP/g Pd obtained with
complex [Pd(CH3)(CH3CN)(phen)][PF6], highlighting the higher
activity of the present complex with respect to the catalyst with
the simple phen. However, it should be evidenced that the phen
catalyst led to the syndiotactic copolymer.
To confirm the positive effect of the substituents in the meta
position, the Ar-BIAN ligand with all the ortho positions
substituted by methyl groups, namely (2,6-(CH3)2C6H3)2-BIAN
(9), was prepared and used to synthesize the corresponding
palladium-monocationic complex 9b, which was tested as a
precatalyst in the studied copolymerizations under the same
reaction conditions of complexes 1b–8b. 9b yielded, working
with [BQ]/[Pd] ) 5, the CO/styrene and CO/4-Me-styrene
polyketones with productivity values of 0.31 and 0.13 kg CP/g
Pd, respectively. These values are remarkably lower than those
obtained with 4b (Tables 2 and 3, run 12). Even the molecular
weight values (16000 (1.3) for the CO/styrene and 10000 (1.3)
for the CO/4-Me-styrene polyketones) are lower than those of
the polymers synthesized with 4b. In agreement with the
literature,22 the stereochemistry of the polyketones synthesized
with 9b differs from that of the copolymers obtained with
ligands substituted in the meta position, being mainly isotactic
with a content of 70% of the ll triad and 30% of the heterotactic
triads.
General Considerations. [Pd(OAc)2] was a loan from Engelhard
Italia and was used as received. The Ar-BIAN ligands 1–5 and 7
were prepared according to the procedures reported in the
literature.24–27,46 For ligands 2 and 4 a simplified procedure with
respect to that published was applied. 2,2,2-Trifluoroethanol (TFE)
(Aldrich) and the analytical grade solvents (Fluka) were used
without further purification for synthetic, spectroscopic, and catalytic
purposes. Dichloromethane used for the synthesis of complexes was
purified through distillation over CaH2 under inert atmosphere and
was used freshly distilled. THF used for the synthesis of 2 and 4
was distilled over sodium, under inert atmosphere. Carbon mon-
1
oxide (CP grade 99.9%) was supplied by SIAD. H NMR spectra
were recorded at 400 MHz on a JEOL EX 400; the resonances
were referenced to the solvent peak versus TMS (CDCl3 at δ 7.26
and CD2Cl2 at δ 5.32) 13C NMR of polyketones were recorded in
1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) with a small amount of
CDCl3 for locking purposes at 100.5 MHz and referenced at δ 77.0.
Caution: HFIP is a very volatile and highly toxic solvent, so proper
protection should be used when it is handled.
Synthesis of Ligands 2 and 4. Acenaphthenequinone (2 mmol)
was dissolved in distilled THF (40 mL). To this solution was added
anhydrous Na2SO4, followed by the addition of the proper aniline
(9 mmol), which was 3-methylaniline for ligand 2 or 3,5-
dimethylaniline for ligand 4. The suspension was kept at 50 °C for
1 h or until the complete dissolution of the solid. Then the solution
was kept under reflux. The reaction was monitored by TLC. The
reaction went to completion in 1 week. The solution was concen-
trated almost to dryness and then was used, as it was, to charge a
chromatography column. The product was separated from the excess
of aniline and from the monoketoimine by chromatography on silica
gel (230–400 mesh) with a mixture of CH2Cl2 (50%), n-hexane
(44%), diethyl ether (5%), and triethylamine (1%) as eluent.
Average yield: 70%. Elemental analysis: 2 calcd for C26H20N2: C,
86.64; H, 5.59, N, 7.77. Found: C, 86.90; H, 5.42; N, 7.40. 4 calcd
for C28H24N2: C, 86.56; H, 6.23, N, 7.21. Found: C, 86.40; H, 6.40;
N, 7.10.
Conclusions
In this paper we have applied, for the first time, palladium
complexes with both symmetric and nonsymmetric Ar-BIAN
ligands substituted in the meta position to the CO/vinyl arene
copolymerization reaction. These palladium complexes generate
very efficient catalysts, under atmospheric CO pressure, for the
synthesis of regioregular, atactic polyketones. Both productivity
and molecular weight are affected by the nature and the number
of meta substitutents, which is equally unprecedented.
As we envisaged at the beginning, moving the substituents
on the aryl rings from ortho to meta positions resulted in a
remarkable increase in the productivity (from 0.3 g CP/g Pd · h
to 5 g CP/g Pd · h). This trend together with the molecular weight
values point out an important difference between this catalytic
system and the Brookhart’s system. In that case the introduction
1H NMR (400 MHz, CDCl3, 298 K): 2, δ 7.88 (d, 2H, H5,8),
7.38 (t, 2H, H4,9), 7.35 (t, 2H, H15,15′), 7.07 (d, 2H, H14,14′), 6.95
(s, 2H, H18,18′), 6.92 (d, 2H, H16,16′), 6.86 (d, 2H, H3,10), 2.39 (s,
6H, CH3); 4, δ 7.90 (d, 2H, H5,8), 7.40 (t, 2H, H4,9), 6.92 (d, 2H,
H3,10), 6.90 (d, 2H, H16,16′), 6.75 (d, 4H, H14,14′,18,18′), 2.38 (s,
12H, CH3).
(45) Carfagna, C.; Gatti, G.; Mosca, L.; Passeri, A.; Paoli, P.; Guerri,
A. Chem. Commun. 2007, 4540-4542.
(46) Van Asselt, R.; Elsevier, C. J.; Smeets, W. J. J.; Spek, A. L.;
Benedix, R. Recl. TraV. Chim. Pays-Bas 1994, 113, 88–98.

1492 Organometallics, Vol. 27, No. 7, 2008
Synthesis of Ligands and 8. (3,4,5-(CH3O)3C6H2)
Scarel et al.
6
Synthesis of Complexes. All manipulations were carried out
under argon atmosphere with Schlenk technique and at room
temperature.
(3,5-(CF3)2C6H3)-BIAN (8). To a 100 mL Schlenk flask under N2
and with magnetic stirring were added at room temperature (3,5-
(CF3)2C6H3-BIAN)ZnCl2 (460 mg, 0.63 mmol),24 3,4,5-
(CH3O)3C6H2NH2 (120 mg, 0.66 mmol), and methanol (20 mL).
The complex completely dissolved. The reaction was monitored
by TLC (alumina, CH2Cl2). To do so, a 0.5 mL aliquot of the
solution was withdrawn and coordinated ZnCl2 was eliminated by
the method detailed below for the final product. The reaction
terminated after 2 h, during which time the solution turned from
orange to red. At this stage, a precipitate had formed, but the
solution still contained appreciable amounts of the product, so the
suspension was evaporated in vacuo and the solid washed with a
1:1 hexane/toluene mixture (10 mL) to remove the free anilines.
To eliminate the coordinated ZnCl2, the solid was dissolved in
CH2Cl2 (25 mL) in a separating funnel and shaken with a saturated
K2C2O4 aqueous solution (10 mL) for 10 min. The organic phase
was separated, washed with water (3 × 10 mL), dried with Na2SO4,
and evaporated in vacuo. The obtained solid was purified by column
chromatography on silica, using 10:0.5 hexane/triethylamine as
eluent. Ligand 8 was eluted first (85 mg, 24% yield), followed by
a small amount of 6. However, the latter compound is better
prepared as described in the next paragraph. Anal. Calcd for
C29H20F6N2O3: C, 62.37, H, 3.61, N, 5.02. Found: C, 61.99, H,
3.50, N, 5.10.
Synthesis of Neutral Complexes [Pd(CH3)(Cl)(N-N)] (1a–
8a). All the complexes were prepared starting from [Pd(Cl)2(cod)],
following the procedure reported in the literature.29,47 In particular,
1.1 equiv of N-N ligand was added to 0.40 mmol of
[Pd(CH3)(Cl)(cod)], dissolved in dichloromethane, at room tem-
perature. After 1 h, diethyl ether was added and the product
precipitated as a red-orange solid. Average yield: 94%.
[Pd(CH3)(Cl)(1)] (1a). Elemental Anal. Calcd for C25H19ClN2Pd:
1
C, 61.37; H, 3.91, N, 5.73. Found: C, 61.11; H, 3.78; N, 5.67. H
NMR (400 MHz, CD2Cl2, 298 K): δ 8.04 (dd, 2H, H5,8), 7.61 (t,
2H, H15′,17′), 7.55 (t, 2H, H15,17), 7.51–7.40 (m, 4H, H4,9 and
H16,16′), 7.38 (d, 2H, H14,18), 7.23 (d, 2H, H14′,18′), 7.16 (d, 1H,
H3), 6.54 (d, 1H, H10), 0.91 (s, 3H, CH3-Pd).
[Pd(CH3)(Cl)(2)] (2a). Elemental Anal. Calcd for C27H23ClN2Pd:
1
C, 62.68; H, 4.48, N, 5.41. Found: C, 62.40; H, 4.30; N, 4.97. H
NMR (400 MHz, CD2Cl2, 298 K): δ 8.04 (dd, 2H, H5,8), 7.50–7.41
(m, 4H, H4,9 and H17,17′), 7.29–7.14 (m, 5H, H16,18,16′,18′ e H14),
7.01 (m, 2H, H14′ and H3), 6.58 (d, 1H, H10), 2.47 (s, 3H, CH3-
Ph), 2.44 (s, 3H, CH3-Ph), 0.91 (s, 3H, CH3-Pd).
[Pd(CH3)(Cl)(3)] (3a). Elemental Anal. Calcd for
C27H17ClF6N2Pd: C, 51.86; H, 2.74, N, 4.48. Found: C, 52.06; H,
1
2.65; N, 4.60. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.16 (dd,
2H, H5,8), 7.80–7.46 (m, 6H, H16,17,18,16′,17′,18′), 7.64 (s, 2H,
H14,14′), 7.53–7.46 (m, H4,9), 7.16 (d, 1H, H3), 6.56 (d, 1H, H10),
0.90 (s, 3H, CH3-Pd).
As for all other known asymmetric Ar′,Ar-BIAN compounds,
the free ligand is present in solution as a mixture of the anti-anti
and syn-anti isomers, with the former prevailing.27
[Pd(CH3)(Cl)(4)] (4a). Elemental Anal. Calcd for C29H27ClN2Pd:
1
C, 63.86; H, 4.99, N, 5.14. Found: C, 63.70; H, 4.66; N, 5.12. H
NMR (400 MHz, CD2Cl2, 298 K): δ 8.03 (dd, 2H, H5,8), 7.45 (dt,
2H, H4,9), 7.16 (d, 1H, H3), 7.08 (s, 1H, H16′), 7.02 (s, 1H, H16),
6.95 (s, 2H, H14,18), 6.81 (s, 2H, H14′,18′), 6.62 (d, 1H, H10), 2.41
(s, 6H, 15′,17′-(CH3)2-Ph), 2.39 (s, 6H, 15,17-(CH3)2-Ph), 0.91 (s,
3H, CH3-Pd).
[Pd(CH3)(Cl)(5)] (5a). Elemental Anal. Calcd for
C29H15ClF12N2Pd: C, 45.75; H, 1.99, N, 3.68. Found: C, 45.50; H,
1
The ratio between the two isomers calculated from both the 1H
and the 19F NMR is 8:1, which is comparable to that found for
other ligands of the same class.27 For the minor isomer, only some
signals could be clearly assigned in the 1H NMR spectrum and are
reported below.
1.96; N, 3.92. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.22 (dd,
2H, H5,8), 8.09 (s, 1H, H16′), 8.01 (s, 1H, H16), 7.92 (s, 2H, H14,18),
7.83 (s, 2H, H14′,18′), 7.58 (dt, 2H, H4,9), 7.21 (d, 1H, H3), 6.63 (d,
1H, H10), 0.77 (s, 3H, CH3-Pd).
[Pd(CH3)(Cl)(6)] (6a). Elemental Anal. Calcd for
C31H31ClO6N2Pd: C, 55.62; H, 4.67; N, 4.18. Found: C, 55.35; H,
Major isomer (anti-anti). 1H NMR (CDCl3, 298 K) δ 8.00 (d,
J ) 7.6 Hz, 1H, H5), 7.96 (d, J ) 7.63 Hz, 1H, H8), 7.80 (s, 1H,
H16), 7.62 (s, 2H, H14, H18), 7.52 (pst, H9), 7.47 (pst, H4), 7.20 (d,
J ) 7.2 Hz, 1H, H10), 6.82 (d, J ) 7.2 Hz, 1H, H3), 6.40 (s, 2H,
H14′, H18′), 3.96 (s, 3H, p-OCH3), 3.86 (s, 6H, m-OCH3). 19F NMR
(CDCl3, 298 K) δ -63.2 (s, CF3).
1
4.55; N, 4.00. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.11 (dd,
2H, H5,8), 7.55 (dd, 2H, H4,9), 7.44 (d, 1H, H3), 6.81 (d, 1H, H10),
6.66 (s, 2H, Hortho cis to Pd-Cl), 6.48 (s, 2H, Hortho cis to Pd-
CH3), 3.90 (s, 6H, OCH3 para), 3.86 (s, 6H, OCH3 meta), 3.84 (s,
6H, OCH3 meta), 0.87 (s, 3H, CH3-Pd).
[Pd(CH3)(Cl)(7)] (7a). Elemental Anal. Calcd for
C29H15ClF6N2Pd: C, 53.31; H, 3.24, N, 4.29. Found: C, 53.50; H,
1
Minor isomer (syn-anti. H NMR (CDCl3, 298 K) δ 6.00 (s,
2H, H14′, H18′), 3.86 (s, 3H, p-OCH3), 3.74 (s, 6H, m-OCH3). 19F
NMR (CDCl3, 298 K) δ -63.07 (s, CF3).
1
2.96; N, 3.92. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.12 (dd,
2H, H5,8), 7.93 (s, 1H, H16), 7.89 (s, 2H, H14,18), 7.52 (dt, 2H,
H4,9), 7.11 (m, 2H, H16′ and H3), 6.81 (s, 2H, H14′,18′), 6.67 (d,
1H, H10), 2.43 (s, 6H, 15′,17′-(CH3)2-Ph), 1.01 (s, 3H, CH3-Pd
major isomer, it is trans to the aryl ring substituted with CF3), 0.79
(s, 3H, CH3-Pd minor isomer, it is trans to the aryl ring substituted
with CH3), in the aromatic region also the signals due to the minor
isomer are visible, with the ratio between the two isomers 10/1.
[Pd(CH3)(Cl)(8)] (8a). Elemental Anal. Calcd for
C30H23ClF6N2O3Pd: C, 50.37; H, 3.24, N, 3.91. Found: C, 40.95;
H, 3.06; N, 3.92. 1H NMR (400 MHz, CD2Cl2, 298 K): δ 8.16 (d,
2H, H5,8), 7.80 (s, 1H, H16), 7.90 (s, 2H, H14,18), 7.55 (m, 2H,
H4,9), 7.15 (d, 1H, H3), 6.88 (d, 1H, H10), 6.49 (s, 2H, H14′,18′),
3.90 (s, 3H, OCH3 para), 3.88 (s, OCH3 meta, minor isomer), 3.85
(s, 6H, OCH3 meta, major isomer), 0.95 (s, 3H, CH3-Pd major
(3,4,5-(CH3O)3C6H2)2-BIAN (6). To a 100 mL Schlenk flask
under N2 and with magnetic stirring were added at room temperature
(3,5-(CF3)2C6H3-BIAN)ZnCl2 (305.5 mg, 0.412 mmol), 3,4,5-
(CH3O)3C6H2NH2 (227.3 mg, 1.241 mmol), and methanol (20 mL).
The complex completely dissolved. The reaction was stirred at room
temperature overnight, during which time the solution turned from
orange to red and a red precipitate formed. The solid was collected
by filtration and washed with hexane (3 × 10 mL) to remove any
free amine. The free ligand was obtained by the same procedure
described for 8, but in this case no chromatographic purification
was necessary and the ligand is obtained analytically pure (126.7
mg, 60.0% yield). Anal. Calcd for C30H28N2O6: C, 70.30, H, 5.51,
N, 5.47. Found: C, 70.01, H, 5.80, N, 5.12.
1H NMR (CDCl3, 298 K) δ 7.97 (d, J ) 8.3 Hz, 2H, H5), 7.47
(pst, J ) 7.9 Hz, 2H, H4), 7.12 (d, J ) 7.2 Hz, 2H, H3), 6.40 (s,
4H, H14,18), 3.96, (s, 2H, p-OCH3), 3.85 (s, 4H, m-OCH3).
(47) Milani, B.; Marson, A.; Zangrando, E.; Mestroni, G.; Ernsting, J. M.;
Elsevier, C. J. Inorg. Chim. Acta 2002, 327, 188–201.

Synthesis of Atactic Polyketones
Organometallics, Vol. 27, No. 7, 2008 1493
isomer, it is trans to the aryl ring substituted with CF3), 0.69 (s,
3H, CH3-Pd minor isomer, it is trans to the aryl ring substituted
with CH3), in the aromatic region also the signals due to the minor
isomer are visible, with the ratio between the two isomers 6/1.
substituted with CH3), in the aromatic region also the signals due
to the minor isomer are visible, with the ratio between the two
isomers 3/1.
[Pd(CH3)(CH3CN)(8)][PF6] (8b). Elemental Anal. Calcd for
C32H26F12N3O3PPd: C, 44.39; H, 3.03, N, 4.85. Found: C, 44.47;
Synthesis of Cationic Complexes [Pd(CH3)(CH3CN)
(N-N)][PF6] (1b–8b). All the complexes were obtained starting
from the corresponding neutral derivatives upon addition of AgPF6
in a mixture of CH2Cl2 and CH3CN. [Pd(CH3)(Cl)(N-N)] (1a–8a)
(0.40 mmol) was dissolved in the minimal amount of CH2Cl2 under
Ar. To the obtained solution was added a solution of AgPF6 in
CH3CN (1.1 equiv in 6 mL), leading to the precipitation of AgCl.
After 30 min, the solution was filtered over Celite and concentrated
to half-volume under vacuum. Upon addition of diethyl ether the
product precipitated as a yellow solid. Average yield: 90%.
[Pd(CH3)(CH3CN)(1)][PF6] (1b). Elemental Anal. Calcd for
C27H22F6N3PPd: C, 50.68; H, 3.46, N, 6.57. Found: C, 50.90; H,
1
H, 3.28; N, 4.82. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.23 (t,
2H, H5,8), 8.07 (s, 1H, H16), 7.98 (s, 2H, H14,18), 7.61 (m, 2H,
H4,9), 7.24 (d, 1H, H3), 6.85 (d, 1H, H10), 6.50 (s, 2H, H14′,18′),
3.90 (s, 6H, OCH3 meta), 3.86 (s, 3H, OCH3 para), 2.16 (s, 3H,
CH3CN major isomer), 2.12 (s, 3H, CH3CN, minor isomer),1.05
(s, 3H, CH3-Pd major isomer, it is trans to the aryl ring substituted
with CF3), 0.74 (s, 3H, CH3-Pd minor isomer, it is trans to the aryl
ring substituted with CH3), in the aromatic region also the signals
due to the minor isomer are visible, with the ratio between the two
isomers 3/1.
General Procedure for Copolymerization Reactions. All
copolymerization experiments were carried out in a three-necked,
thermostated, 75 mL glass reactor equipped with a magnetic stirrer
and connected to a temperature controller. After establishment of
the reaction temperature (30 °C), the precatalyst, 1,4-benzoquinone
(when required), the vinyl arene, and TFE were placed inside. CO
was bubbled through the solution for 10 min; afterward a 4 L
balloon filled with CO was connected to the reactor. The system
was stirred at the same temperature for 24 h to give a cloudy white
suspension. The reaction mixture was then poured into methanol
(100 mL) and stirred for 1 h at room temperature, causing the
precipitation of the polymer, which was filtered, washed with
methanol, and dried under vacuum until constant weight was
reached.
1H NMR (400 MHz, CDCl3, 298 K): CO/styrene: δ 6.69–7.41
(aromatic protons), 3.90–4.04 (broad, CH), 3.14 (broad, CH2), 2.59
(broad, CH2). 13C NMR (100.5 MHz, HFIP + CDCl3, 298 K) δC
209.5–210.4 (broad, CO), 136.5, 136.1, 135.8, 135.3 (Cipso), 129.4,
128.3, 128.0 (Carom), 53.5 (CH), 42.3–44.5 (broad, CH2).
1H NMR (400 MHz, CDCl3, 298 K): CO/4-Me-styrene: δ
6.55–7.33 (aromatic protons), 3.84–3.95 (broad, CH), 3.10 (broad,
CH2), 2.54 (broad, CH2), 2.24 (broad, CH3). 13C NMR (100.5 MHz,
HFIP + CDCl3, 298 K) δC 210.1–210.9 (broad, CO), 133.4, 133.0,
132.5, 131.9 (Cipso), 129.9–130.1, 128.0 (Carom), 52.6–53.4 (broad,
CH), 42.6–44.8 (broad, CH2), 20.4 (s, CH3).
Polyketone Recrystallization. The copolymers (100 mg) were
dissolved in chloroform (100 mL). The solution was filtered over
Celite, which was then washed with chloroform. The solution
was concentrated under vacuum to initiate precipitation of the
polymer that was completed upon addition of ethanol. The white
polymer was filtered, washed with methanol, and dried under
vacuum.
Homopolymer/Copolymer Separation. The solids that are a
mixture of homopolymer and copolymer are treated according to
the following procedures to separate the two polymers. (a) If the
amount of homopolymer is higher than 50%, the solid is dissolved
in the minimum volume of CH2Cl2. The solution is added dropwise
to diethyl ether (the volume of diethyl ether is three times the
volume of CH2Cl2). The copolymer immediately precipitates. The
suspension is stirred overnight at room temperature, filtrated under
vacuum, washed with diethyl ether and vaccuum dried. (b) If the
solid contains less than 50% of homopolymer, the procedure is the
same, but after the precipitation with diethyl ether the suspension
is stirred at room temperature for 2 h only before filtering the
copolymer.
1
3.78; N, 6.59. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.12 (pst,
2H, H5,8), 7.68 (t, 2H, H15′,17′), 7.65 (t, 2H, H15,17), 7.57–7.45 (m,
4H, H4,9 and H16,16′), 7.43 (d, 2H, H14,18), 7.30 (d, 1H, H3), 7.25
(d, 2H, H14′,18′), 6.54 (d, 1H, H10), 2.14 (s, 3H, CH3CN), 0.81 (s,
3H, CH3-Pd).
[Pd(CH3)(CH3CN)(2)][PF6] (2b). Elemental Anal. Calcd for
C29H26F6N3PPd: C, 52.15; H, 3.92, N, 6.29. Found: C, 52.50; H,
1
3.72; N, 6.30. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.12 (pst,
2H, H5,8), 7.58–7.47 (m, 4H, H4,9 and H17,17′), 7.34–7.21 (m, 5H,
H16,18,16′,18′ and H14), 7.03 (m, 2H, H14′ and H3), 6.57 (d, 1H, H10),
2.49 (s, 6H, 15,15′-(CH3)2-Ph), 2.16 (s, 3H, CH3CN), 0.83 (s, 3H,
CH3-Pd).
[Pd(CH3)(CH3CN)(3)][PF6] (3b). Elemental Anal. Calcd for
C29H20F12N3PPd: C, 44.89; H, 2.60, N, 5.42. Found: C, 44.70; H,
1
2.70; N, 5.62. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.15 (pst,
2H, H5,8), 7.91–7.48 (m, 8H, H16,17,18,16′,17′,18′ and H14,14′),
7.63–7.48 (m, 2H, H4,9), 7.25 (br, 1H, H3), 6.51 (d, 1H, H10), 2.14
(s, 3H, CH3CN), 0.80 (s, 3H, CH3-Pd).
[Pd(CH3)(CH3CN)(4)][PF6] (4b). Elemental Anal. Calcd for
C31H30F6N3PPd: C, 53.50; H, 4.34, N, 6.04. Found: C, 53.20; H,
1
4.28; N, 6.10. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.12 (pst,
2H, H5,8), 7.57 (pst, 1H, H4), 7.50 (pst, 1H, H9), 7.32 (d, 1H, H3),
7.14 (s, 1H, H16′), 7.13 (s, 2H, H16), 6.98 (s, 2H, H14,18), 6.81 (s,
2H, H14′,18′), 6.61 (d, 1H, H10), 2.45 (s, 6H, 15′,17′-(CH3)2-Ph),
2.44 (s, 6H, 15,17-(CH3)2-Ph), 2.17 (s, 3H, CH3CN), 0.84 (s, 3H,
CH3-Pd).
[Pd(CH3)(CH3CN)(5)][PF6] (5b). Elemental Anal. Calcd for
C31H18F18N3PPd: C, 40.83; H, 1.99, N, 4.61. Found: C, 40.70; H,
1
1.68; N, 4.65. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.27 (dd,
2H, H5,8), 8.13 (s, 1H, H16′), 8.09 (s, 1H, H16), 8.02 (s, 2H, H14,18),
7.88 (s, 2H, H14′,18′), 7.63 (dt, 2H, H4,9), 7.26 (d, 1H, H3), 6.57 (d,
1H, H10), 2.17 (s, 3H, CH3CN), 0.86 (s, 3H, CH3-Pd).
[Pd(CH3)(CH3CN)(6)][PF6] (6b). Elemental Anal. Calcd for
C33H34F6N3O6PPd: C, 48.33; H, 4.18, N, 5.12. Found: C, 48.07;
1
H, 4.28; N, 5.28. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.18 (t,
2H, H5,8), 7.67–7.55 (dt, 2H, H4,9), 7.44 (d, 1H, H3), 6.82 (d, 1H,
H10), 6.62 (s, 2H, H14,18), 6.45 (s, 2H, H14′,18′), 3.90, 3.88, 3.85
(3s, 18H, OCH3 para and meta), 2.17 (s, 3H, CH3CN), 0.93 (s, 3H,
CH3-Pd).
[Pd(CH3)(CH3CN)(7)][PF6] (7b). Elemental Anal. Calcd for
C31H24F12N3PPd: C, 46.31; H, 3.01, N, 5.23. Found: C, 46.47; H,
1
3.28; N, 5.28. H NMR (400 MHz, CD2Cl2, 298 K): δ 8.14 (dd,
2H, H5,8), 8.04 (s, 2H, H14,18), 8.00 (s, 1H, H16), 7.54 (dt, 2H,
H4,9), 7.22 (d, 1H, H3), 7.14 (br, 1H, H16′), 6.87 (s, 2H, H14′,18′),
6.60 (d, 1H, H10), 2.45 (s, 6H, 15′,17′-(CH3)2-Ph minor isomer),
2.43 (s, 6H, 15′,17′-(CH3)2-Ph major isomer), 2.17 (s, 3H, CH3CN
major isomer), 2.14 (s, 3H, CH3CN, minor isomer), 0.96 (s, 3H,
CH3-Pd, major isomer, it is trans to the aryl ring substituted with
CF3), 0.71 (s, 3H, CH3-Pd, minor isomer, it is trans to the aryl ring
Molecular Weight Measurements. The molecular weights
(MW) of copolymers and molecular weight distributions (Mw/Mn)
were determined by gel permeation chromatography versus poly-
styrene standards. The analyses were recorded on a Kanuer HPLC
(K-501 Pump, K-2501 UV detector) with a Plgel 5 µm 104 Å GPC
column and chloroform as solvent (flow rate 0.6 mL min-1). CO/
styrene samples were prepared as follows: 2 mg of the copolymer

1494 Organometallics, Vol. 27, No. 7, 2008
Scarel et al.
was solubilized with 120 µL of 1,1,1,3,3,3-hexafluoro-2-propanol
(HFIP) and chloroform was added up to 10 mL; instead, CO/4-
Me-styrene copolymers were directly soluble in chloroform. The
statistical calculations were performed with the Bruker Chromstar
software program.
2005035123 and no. 2006031888). Engelhard Italia is
gratefully acknowledged for a generous gift of [Pd(OAc)2].
We thank R. Lariccia for preparing ligand 7 and A. Schira
and M. Hagar for preparing ligand 8.
Supporting Information Available: 13C NMR of the two
polyketones. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. This work was supported by the
European Network “PALLADIUM” (5th Framework Pro-
gram, contract no. HPRN-CT-2002-00196) and by Ministero
dell’Università e della Ricerca (MUR-Rome; PRIN no.
OM7011858