Counterion effect on CO/styrene copolymerization catalyzed by cationic palladium(II) organometallic complexes: An interionic structural and dynamic investigation based on NMR spectroscopy

Article abstract of DOI:10.1021/om990372k

Complexes [Pd(η¹,η²-C₈H ₁₂OMe)bipy]⁺X^- (2a-f) (where X = BPh₄^- (a), CF₃SO₃^- (b), BF₄^- (c), PF₆^- (d), SbF₆^- (e), and B(3,5-(CF₃)₂C₆H₃)₄ ^- (f); bipy = 2,2′-bipyridine; C₈H₁₂OMe = cyclooctenylmethoxy group) were synthesized by the reaction of the dimer [Pd(η¹,η₂-C₈H₁₂-OMe)Cl] ₂ (1) with the bipy ligand in methanol containing Y⁺X^- salts. They were characterized in solution by multinuclear and multidimensional NMR spectroscopy. The solid-state structure of complex 2d was obtained by X-ray single-crystal investigation. The catalytic activity of complexes 2 toward CO/styrene copolymerization in methylene chloride was tested and related to the type of counterion. The order of the catalytic activity of complexes 2a-f is the following: BPh₄^- ? CF₃SO₃^- < BF₄^- < PF₆^- < SbF₆^- < B(3,5-(CF₃)₂C₆H₃)₄ ^-. If the copolymerization reactions are carried out in the presence of an excess of the bipy ligand, the anion effect is less important and the order is the following: BPh₄^- ? CF₃SO₃^- < BF₄^- ≈ B(3,5-(CF₃)₂C₆H₃)₄ ^- ≈ PF₆^- ≈ SbF₆^-. The interionic structure of all complexes was investigated in CD₂Cl₂ at room and low temperature by ¹⁹F{¹H} HOESY and ¹H NOESY NMR spectroscopies. In solution, the counterions are located above or below the bipy ligand shifted toward the pyridine ring trans to the Pd-C σ bond, while in the crystal structure of 2d, they are settled sideways to the cationic moiety. The best anion in catalysis is the least strong coordinating one that shows the weakest interionic contacts in the ¹⁹F-{¹H} HOESY or ¹H NOESY NMR spectra. The dynamic process that exchanges the two pyridyl rings was investigated by variable-temperature NMR spectroscopy in CD₂Cl₂. The activation parameters were determined. AG^?₂₉₈ values range from 54 to 58 kJ/mol. The negative values of ΔS^? (-58/-108 J K^-1 mol^-1), for all compounds, with the exception of 2f, suggest an associative mechanism.

Full text of DOI:10.1021/om990372k

Organometallics 1999, 18, 3061-3069
3061
Cou n ter ion Effect on CO/Styr en e Cop olym er iza tion
Ca ta lyzed by Ca tion ic P a lla d iu m (II) Or ga n om eta llic
Com p lexes: An In ter ion ic Str u ctu r a l a n d Dyn a m ic
In vestiga tion Ba sed on NMR Sp ectr oscop y§
Alceo Macchioni,* Gianfranco Bellachioma, Giuseppe Cardaci,
Monia Travaglia, and Cristiano Zuccaccia
Dipartimento di Chimica, Universita` di Perugia, Via Elce di Sotto, 8-06123 Perugia, Italy
Barbara Milani, Gianni Corso, Ennio Zangrando, and Giovanni Mestroni
Dipartimento di Scienze Chimiche, Universita` di Trieste, Via Licio Giorgieri,
1-34127 Trieste, Italy
Carla Carfagna and Mauro Formica
Istituto di Scienze Chimiche, Universita` di Urbino, Piazza Rinascimento,
6-61029 Urbino, Italy
Received May 18, 1999
-
Complexes [Pd(η1,η2-C8H12OMe)bipy]+X- (2a -f) (where X ) BPh4- (a ), CF3SO3- (b), BF4
-
-
-
(c), PF6 (d ), SbF6 (e), and B(3,5-(CF3)2C6H3)4 (f); bipy ) 2,2′-bipyridine; C8H12OMe )
cyclooctenylmethoxy group) were synthesized by the reaction of the dimer [Pd(η1,η2-C8H12-
OMe)Cl]2 (1) with the bipy ligand in methanol containing Y+X- salts. They were characterized
in solution by multinuclear and multidimensional NMR spectroscopy. The solid-state
structure of complex 2d was obtained by X-ray single-crystal investigation. The catalytic
activity of complexes 2 toward CO/styrene copolymerization in methylene chloride was tested
and related to the type of counterion. The order of the catalytic activity of complexes 2a -f
-
-
-
-
-
-
is the following: BPh4 , CF3SO3 < BF4 < PF6 < SbF6 < B(3,5-(CF3)2C6H3)4 . If the
copolymerization reactions are carried out in the presence of an excess of the bipy ligand,
-
the anion effect is less important and the order is the following: BPh4- , CF3SO3- < BF4
≈ B(3,5-(CF3)2C6H3)4 ≈ PF6 ≈ SbF6-. The interionic structure of all complexes was
-
-
investigated in CD2Cl2 at room and low temperature by 19F{1H} HOESY and H NOESY
1
NMR spectroscopies. In solution, the counterions are located above or below the bipy ligand
shifted toward the pyridine ring trans to the Pd-C σ bond, while in the crystal structure of
2d , they are settled sideways to the cationic moiety. The best anion in catalysis is the least
strong coordinating one that shows the weakest interionic contacts in the 19F{1H} HOESY
1
or H NOESY NMR spectra. The dynamic process that exchanges the two pyridyl rings was
investigated by variable-temperature NMR spectroscopy in CD2Cl2. The activation param-
eters were determined. ∆Gq values range from 54 to 58 kJ /mol. The negative values of
298
∆Sq (-58/-108 J K-1 mol-1), for all compounds, with the exception of 2f, suggest an
associative mechanism.
In tr od u ction
by detecting the interionic dipolar interaction between
the NMR-active nuclei of the organometallic fragment
and those belonging to its counterion. Our previous
studies on model compounds, based on NOESY and
HOESY NMR spectroscopies, have demonstrated that
in methylene chloride solution the counterion not only
prefers to stay in a specific position1,2 but also has a
preferential orientation when it is unsymmetric.3 This
During the past few years, some of us have been
involved in the investigation of the interionic solution
structure of charged organometallic complexes by NMR
spectroscopy.1 The principal aim of our studies has been
addressed to determine the relative cation-anion posi-
tion in solution and, in particular, in solvents where
intimate ion-pairs are mainly present. This can be done
§ Dedicated to the memory of Michelangelo Minciotti.
* To whom correspondence should be addressed.
(1) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G.;
Terenzi, S. Organometallics 1996, 15, 4349-4351. Macchioni, A.;
Bellachioma, G.; Cardaci, G.; Gramlich, V.; Ru¨egger, H.; Terenzi, S.;
Venanzi, L. M. Organometallics 1997, 16, 2139-2145.
(2) Macchioni, A.; Bellachioma, G.; Cardaci, G.; Cruciani, G.; Foresti,
E.; Sabatino, P.; Zuccaccia, C. Organometallics 1998, 17, 5549-5556.
Bellachioma, G.; Cardaci, G.; Gramlich, V.; Macchioni, A.; Valentini,
M.; Zuccaccia, C. Organometallics 1998, 17, 5025-5030.
(3) Zuccaccia, C.; Bellachioma, G.; Cardaci, G.; Macchioni, A. Or-
ganometallics 1999, 18, 1-3.
10.1021/om990372k CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/17/1999

3062 Organometallics, Vol. 18, No. 16, 1999
Macchioni et al.
Sch em e 1
makes possible the estimatation of the average inter-
ionic distances3 by measuring the kinetics of NOE
buildup.
To the best of our knowledge such information about
the structure of ion-pairs in solution is very difficult to
obtain by other methods. Furthermore, it is very im-
portant for homogeneous catalysis. It is in fact well-
known from the literature4 that several processes,
mediated by charged organometallic complexes, are
strongly dependent on the nature of the counterion. The
possibility of directly observing the anion-cation inter-
actions 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”.
For this reason we decided to investigate the inter-
ionic structure of [Pd(η1,η2-C8H12OMe)bipy]+X- 5 orga-
nometallic complexes because (1) they are active cata-
lysts for CO/styrene copolymerization6 in methylene
chloride at room temperature and atmospheric pressure
and (2) while all the protons are unsymmetrically
distributed around palladium, their resonances are well
resolved in the 1H NMR spectrum, which allows the
eventual effects of the counterion interactions to be
clearly detected.
CF3SO3-, BF4-, PF6-, SbF6-, and B(3,5-(CF3)2C6H3)4-),
forming complexes 2a -f, which precipitate from solu-
tion. Compounds 2c-e are stable for several hours in
methylene chloride solution at room temperature (≈298
K) under inert atmosphere. Complexes 2b and 2f start
to transform into unidentified compounds within a few
minutes, while 2a decomposes into Pd metal within a
few minutes.
Ch a r a cter iza tion a n d Str u ctu r e. (a ) In tr a m o-
lecu la r Solu tion Str u ctu r e. Complexes 2a -f were
characterized in methylene chloride solution by 1H, 13C,
19F, and 31P NMR spectroscopies.
In this paper, we report the syntheses of complexes
-
[Pd(η1,η2-C8H12OMe)bipy]+X- (2a -f) (where X ) BPh4
-
-
-
-
(a ), CF3SO3 (b), BF4 (c), PF6 (d ), SbF6 (e), and
-
B(3,5-(CF3)2C6H3)4 (f); bipy ) 2,2′-bipyridine; C8H12
-
OMe ) cyclooctenylmethoxy group), their catalytic
activity toward the CO/styrene copolymerization, and
the crystal structure of complex 2d . We also describe
the determination of the interionic structure in solution
of the complexes by 19F{1H} HOESY and 1H NOESY
NMR spectroscopies. Finally, the activation parameters
of the dynamic process that averages the two pyridine
rings in the 1H NMR spectra as a function of the
counterion nature are presented.
The olefinic and aliphatic regions of the 1H NMR
spectra do not show any particular features, and the
complete assignment is reported in the Experimental
Section. On the other hand, the aromatic region of the
1H NMR spectra at room temperature (304 K) shows
only three resonances, and each of them integrates for
1
two protons (for an example see the H NMR spectrum
of complex 2c recorded at 302 K, reported in Figure 3).
The resonance relative to the 6-6′ couple is apparently
missing. A dynamic process that averages the two
pyridine rings is present (see below). This makes the
four proton pairs equivalent (6-6′, 5-5′, 4-4′, and 3-3′,
see numeration below). Due to this reason, the afore-
mentioned relative instability of complexes 2a , 2b, and
2f in solution at room temperature, and the need to
differentiate all the positions around palladium in order
to better localize the counterions (see below), we per-
formed low-temperature NMR experiments.
Resu lts a n d Discu ssion
Syn th esis. Organometallic complexes were synthe-
sized according to Scheme 1 as reported in the litera-
ture.5 The first step of the reaction involves a direct exo
attack7 of MeO- on the coordinated cyclooctadiene with
the formation of compound 1 as an air-stable, pale
yellow solid. Compound 1 reacts in methanol with 2,2′-
bipyridine in the presence of NH4X or NaX (X ) BPh4
-
,
(4) (a) Chen, Y.-X.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J . J .
Am. Chem. Soc. 1998, 120, 6287-6305. (b) Chen, Y.-X.; Stern, C. L.;
Marks, T. J . J . Am. Chem. Soc. 1997, 119, 2582-2583. (c) J ia, L.; Yang,
X.; Stern, C. L.; Marks, T. J . Organometallics 1997, 16, 842-857. (d)
Chen, Y.-X.; Stern, C. L.; Yang, X.; Marks, T. J . J . Am. Chem. Soc.
1996, 118, 12451-12452. (e) Yang, X.; Stern, C. L.; Marks, T. J . J .
Am. Chem. Soc. 1994, 116, 10015-10031. (f) J ohnson, L. K.; Mecking,
S.; Brookhart, M. J . Am. Chem. Soc. 1996, 118, 267-268. (g) Drent,
E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681. (h) Milani, B.;
Vicentini, L.; Sommazzi, A.; Garbassi, F.; Chiarparin, E.; Zangrando,
E.; Mestroni, G. J . Chem. Soc., Dalton Trans. 1996, 3139-3144. (i)
Lightfoot, A.; Schnider, O.; Pfaltz, A. Angew. Chem., Int. Ed. Engl.
1998, 37, 2897-2899.
(5) The synthesis of compounds with the 2,2′-bipyridyl- and 1,10-
phenanthroline ligand and with X- ) PF6 was previously reported:
-
Pietropaolo, G.; Cusmano, F.; Rotondo, E.; Spadaro, A. J . Organomet.
Chem. 1978, 155, 117-122.
At 217 K the two pyridine rings are no longer
equivalent in all the complexes, and consequently, eight
resonances are present in the aromatic region of the 1H
NMR spectra. In Table 1 we report the chemical shifts
of these resonances and those of the cyclooctenyl protons
that are more sensitive to counterion type at 217 K. A
(6) Milani, B.; Mestroni, G.; Sommazzi, A.; Garbassi, F. Italian
Patent N. MI 95/A 000337, 1995; European Patent N. 96101967.6-
2102, 1996.
(7) Hoel, G. R.; Stockland, R. A., J r.; Anderson, G. K.; Lapido, F. T.;
Braddock-Wilking, J .; Rath, N. P.; Mareque-Rivas, J . C. Organome-
tallics 1998, 17, 1155-1165.

Counterion Effect on CO/ Styrene Copolymerization
Organometallics, Vol. 18, No. 16, 1999 3063
F igu r e 1. Three sections of the 19F{1H} HOESY NMR spectra of complexes 2c and 2d recorded at 376 MHz in CD2Cl2 at
217 K showing that (a) the interionic contacts between the counterions and aromatic protons are stronger than those with
aliphatic protons and (b) the interionic contact between 6′ and the counterion is significantly weaker than the other aromatic
contacts.
F igu r e 2. Representation of the interionic structure in
solution deduced from interionic NMR investigations. The
counterion X- appear to be localized above or below the
bipyridine ligand but shifted toward the pyridine ring trans
to the Pd-C σ bond, as indicated by the gray cloud.
1
complete assignment of all the H and 13C resonances
has been done for complex 2d by recording the 1H
1
COSY, 1H NOESY, and H{13C} COSY (“standard” and
long-range) NMR spectra both at room (304 K) and low
(217 K) temperatures. In particular, it is possible to
distinguish the pyridine ring that is trans to the Pd-C
σ bond from that which is trans to the olefinic fragment
by detecting the intramolecular contacts between the 6
and 4′′-5′′ protons and between the 6′ protons and the
1
8′′ and OMe ones, in the H NOESY spectrum.
(b) Solu tion In ter ion ic Str u ctu r e. The interionic
F igu r e 3. Variable-temperature 1H NMR spectra of
complex 2c recorded at 400.13 MHz in CD2Cl2 showing the
structure has been investigated by recording (1) the
19F{1H} HOESY NMR spectra both at 304 K and at 217
passage from slow to fast exchange for 3-3′, 4-4′, and 5-5′
1
K for complexes 2b-d , (2) the H NOESY NMR spec-
trum of the 2a complex only at 217 K, (3) both the
protons. At 302 K the resonances of protons 6-6′ are so
broad that they are apparently missing.
1
19F{1H} HOESY and H NOESY NMR spectra at 217
K for 2f. Complex 2e could not be studied by 19F{1H}
HOESY NMR spectroscopy due to the presence of 121Sb
(I ) 5/2, natural abundance ) 57.25) and 123Sb (I ) 7/2,
natural abundance ) 42.75), which afford 14 broad
resonances in the fluorine NMR spectrum with eventual
interionic interactions that are too disperse to be
detected. All the measurements were carried out in CD2-
Cl2, the solvent used for copolymerization reactions.
From the literature, it is known that in this solvent
analogous complexes are mainly present as intimate
ion-pairs.8
The 19F{1H} HOESY NMR spectra recorded at 304 K
for complexes 2b-d show strong interionic interactions
(8) Romeo, R.; Arena, G.; Monsu` Scolaro, L.; Plutino, M. R. Inorg.
Chim. Acta 1995, 240, 81-92.

3064 Organometallics, Vol. 18, No. 16, 1999
Macchioni et al.
Ta ble 1. Selected 1H NMR Ch em ica l Sh ift Va lu es
Obta in ed in CD2Cl2 a t 217 K for Com p ou n d s 2a -f
Ta ble 2. Activa tion En er gy Da ta for Com p lexes
2a -f in CD2Cl2
2a
2b
2c
2d
2e
2f
∆Hq (kJ /mol)
∆Sq (J /(mol K))
∆Gq (kJ /mol)
298
3
3′
4
4′
5
5′
6
6′
1′′
4′′
5′′
8′′
OMe
7.67
7.72
7.87
7.96
7.40
7.61
7.62
8.52
2.92
5.79
5.69
3.66
3.41
8.45
8.52
8.21
8.34
7.73
7.83
8.11
8.62
2.96
6.12
5.92
3.68
3.40
8.38
8.46
8.21
8.33
7.72
7.82
8.09
8.61
2.97
6.11
5.91
3.67
3.40
8.32
8.40
8.20
8.32
7.72
7.82
8.06
8.60
2.96
6.09
5.91
3.67
3.40
8.31
8.39
8.20
8.32
7.72
7.83
8.07
8.62
2.97
6.09
5.91
3.68
3.40
8.12
8.19
8.07
8.18
7.61
7.75
7.99
8.61
2.97
6.05
5.87
3.66
3.39
2a
2b
2c
2d
2e
2f
26 ( 1
38 ( 2
36 ( 1
33 ( 1
35 ( 1
61 ( 3
-108 ( 5
-58 ( 8
-59 ( 4
-86 ( 3
-83 ( 4
13 ( 10
58 ( 3
55 ( 5
54 ( 2
59 ( 2
60 ( 2
57 ( 6
The effect is more marked for compound 2a because of
a higher electron density on the aromatic rings. Indeed
the protons that exhibit the strongest interionic contacts
are those that are more shielded with respect to the
same protons of complex 2b (∆δ up to 0.80 ppm for 3
and 3′). The different behavior of protons 6 and 6′ that
are shielded by 0.49 and 0.10 ppm, respectively, is
significant and in perfect agreement with the findings
of the interionic structure that indicate a shift of the
counterion toward the pyridine ring that is trans to the
Pd-C single bond.
between the fluorine atoms of the counterion and all
the aromatic protons. Whereas there are weak contacts
with protons that are close to palladium (4′′, 5′′, 1′′, 8′′,
and OMe), are no interactions with the other protons
of the η1,η2-C8H12OMe ligand (2′′, 3′′, 6′′, and 7′′). The
above observations indicate that the counterion is
localized above or below the coordination plane in all
three complexes and is shifted toward the bipyridine
ligand. The strength of the contacts follow the order 2c
The 1H NOESY NMR spectrum for complex 2f re-
corded at 217 K does not show any interionic contact,
while the 19F{1H} HOESY NMR spectrum shows only
a weak contact between the fluorine atoms of the
counterion and the bipy proton in position 4. This is not
-
> 2d > 2b, but it must be considered that, while BF4
and PF6 have the fluorine atoms homogeneously
-
-
surprising because B(3,5-(CF3)2C6H3)4 is such a weak
distributed around the negative charge, in CF3SO3-, the
fluorines point away from it. This means that the
distance between the fluorine atoms and the protons of
the charged organometallic moiety is structurally longer
and, consequently, the interionic contacts are weaker
coordinating anion11 that its salts can give nonintimate
ion pairs even in methylene chloride.12 In any case, it
is interesting to note that the only weak interionic
contact that we observe in the 19F{1H} HOESY NMR
spectrum is with an aromatic proton. This means that
the interionic structure of the few intimate ion pairs of
complex 2f is probably the same as that of the other
complexes.
-
-
than those for BF4 and PF6
.
The 19F{1H} HOESY and 1H NOESY NMR spectra
recorded at 217 K for complexes 2b-d and 2a , respec-
tively, again show strong interionic contacts between
the atoms of the counterions and the aromatic protons
and weak contacts with protons 4′′, 5′′, 1′′, 8′′, and OMe.
At this temperature, it is possible to distinguish the
protons belonging to the two different pyridine rings,
and it is interesting to note that the counterion interacts
preferentially with the ring that is trans to the η1-arm
of the cyclooctenyl derived ligand (see Figure 1) in
complexes 2b-d . Therefore the low-temperature experi-
ments not only confirm that the counterion is localized
both above and below the bipyridine ligand but also
indicate that it is shifted toward the pyridine ring that
is trans to the Pd-C single bond (see Figure 2). It is
impossible to understand if this is also true for complex
2a because, in this case, the dynamic process that
exchanges the two pyridine rings is fast on the longi-
tudinal relaxation time scale and the cross-peaks be-
tween the protons of the counterion and those of a
proton pair that are exchanging have the same inten-
sity.9
(c) Dyn a m ic Beh a vior of Com p lexes 2a -f. The
aforementioned dynamic process that equilibrates the
environment of the two pyridine rings was investigated
in the temperature range 204-304 K in CD2Cl2. The
aromatic section of 1H NMR spectra clearly exhibits the
passage from slow to fast exchange (see Figure 3) for
all but the 6-6′ proton pairs. The rate constants of
exchange for complexes 2a -f at different temperatures
were determined by a full line shape analysis. The
thermodynamic parameters of activation for the ex-
change process were derived from Eyring plots and are
collected in Table 2. The ∆Gq298 values agree with those
reported in the literature for similar processes13 and are
not significantly affected by the nature of the counterion.
The activation entropies are negative for all the com-
plexes except 2f. For complex 2f ∆Sq is slightly posi-
-
tive. This means that B(3,5-(CF3)2C6H3)4 in both the
ground state and the transition state that attend to the
dynamic process does not afford association with the
cationic fragment. Complex 2a is the only one where
the entropic contribution (T∆Sq
) - 32 kJ /mol) is
298
Confirmation of the interionic structure depicted in
Figure 2 has been derived from the analysis of the
chemical shifts of the aromatic protons reported in Table
1. The shifts related to complexes 2a and 2f are
particularly indicative because the proximity of the
aromatic rings of the counterion to the protons of the
cationic fragment are indicated by a shielding effect.10
(10) Haigh, C. W.; Mallion, R. B. Prog. NMR Spectrosc. 1980, 13,
303-344.
(11) Strauss S. H. Chem. Rev. 1993, 93, 927-942.
(12) NOESY and HOESY NMR spectroscopies can detect only
interionic dipolar interactions that are closer than 4.5-5 Å (ref 9) and
are useful only when intimate ion-pairs are substantially present.
(13) (a) Gogol, A.; Ornebro, J .; Grennberg, H.; Ba¨ckvall J .-E. J . Am.
Chem. Soc. 1994, 116, 3631-3632. (b) Stockland, R. A. J r.; Anderson,
G. K. Organometallics 1998, 17, 4694-4699. (c) Groen, J . H.; Van
Leeuwen, P. W. N. M.; Vrieze, K. J . Chem. Soc., Dalton Trans. 1998,
113-117. (d) Gelling, A.; Orrell, K. G.; Osborne, A. G.; Sik, V. J . Chem.
Soc., Dalton Trans. 1998, 937-945.
(9) Neuhaus, D.; Williamson, M. The Nuclear Overhauser Effect in
Structural and Conformational Analysis; VCH Publishers: New York,
1989; pp 141-181.

Counterion Effect on CO/ Styrene Copolymerization
Organometallics, Vol. 18, No. 16, 1999 3065
Sch em e 2
F igu r e 4. Molecular structure and atom-labeling scheme
of the [Pd(η1,η2-C8H12OMe)bipy]+cation. Thermal ellipsoids
are drawn at the 40% probability level.
nate complex, analogous to that derived from the
association of 2 with the counterion, can be isolated and
characterized when X- ) Cl-.
In the case of complex 2f, the equilibrium of step (a)
is shifted toward the free ions, as indicated by the high
values of ∆Hq ()61 kJ /mol) and ∆Sq ()13 J /mol K); the
mechanism could also be dissociative, involving a T-
shaped 14-electron three-coordinate molecular frag-
ment.18
higher, in absolute value, than the enthalpic one (∆Hq
) 26 kJ /mol). This is in agreement with the tendency
of BPh4- to associate with the electrophilic fragment,14
which, in some cases, activates a phenyl group.
In the case of complex 2d , the process that equili-
brates the two pyridyl rings was investigated in the
presence of excess amounts of free bipy (up to 1:4) and
counterion (up to 1:8). The addition of free bipy in-
creased the process rate, and there was also a slight
increase in the process rate when an excess of counter-
ion was added. This increase was less marked than that
caused by the addition of free N,N-ligand and can be
reasonably attributed to a further shift of the ion-pair
dissociation equilibrium toward the intimate ion-pairs.
The two experiments carried out in the presence of a 4-
and 8-fold excess of counterion afforded the same rate
constants, which indicates that, in both cases, the
solution is made up of nearly 100% intimate ion-pairs.
The reaction mechanism that we consider more prob-
able for the exchange of the two pyridyl rings in
complexes 2a -e involves (see Scheme 2) (a) the associa-
tion of the counterion with the palladium, which leads
to a five-coordinate intermediate, (b) the dissociation of
an N-arm that can afford two different complexes where
the bipy is η1-coordinated, (c) the re-entry of the free
N-arm, and (d) the dissociation of the anion X-. How-
ever, the rearrangement of the five-coordinated inter-
mediate via Berry pseudorotation15 or “turnstile”16
mechanisms cannot be excluded.
The results of the experiments carried out in the
presence of an excess of free bipy could also be explained
with the proposed mechanism. In fact, free bipy can
compete with X- on attacking the apical position in (a).
The second N-arm of bipy can substitute an N-arm of
the coordinated bipy, giving an intermediate that is
analogous to the one coming from process (b) where,
instead of X, there is another η1-coordinated bipy. A
19F{1H} HOESY spectrum was recorded for complex 2d
at 217 K in the presence of an excess (2:1) of free bipy.
Unfortunately, due to the exchange processes within the
coordinated bipy and between the free and coordinated
bipy, no useful information was obtained. The spectrum
shows the same interionic contacts with the same
intensities as that recorded without the excess of free
bipy. There are also contacts with all the protons of the
free bipy.
(d ) Solid Sta te: X-r a y Str u ctu r e of 2d . A perspec-
tive drawing of the molecule with the atom-numbering
scheme is shown in Figure 4; a selection of bond lengths
and angles is reported in Table 3.
The environment of the palladium atom is essentially
square planar (Figure 4) with the bipy molecule acting
as bidentate ligand (planar within (0.043(4) Å), and the
organic octa-membered ring is linked through a σ-bond-
ed carbon atom (C(1)) and a π-olefinic bond (C(4)-C(5)).
The molecular structure of the cation shows an exo
orientation of the methoxy group, which was also as
detected in solution. Inspection of the data of Table 3
shows that the Pd-N(1) bond distance (2.154(3) Å) is
about 0.05 Å longer than the Pd-N(2) one (2.105(3) Å),
because of the influence exerted by the σ-bonded C(1)
atom in the trans position. On the other hand, the Pd-
The associative nature of the process is supported by
the negative values of the entropy of activation. Fur-
thermore, previous studies17 showed that a five-coordi-
(14) Fachinetti, G.; Funaioli, T.; Zanazzi, P. F. J . Chem. Soc., Chem.
Commun. 1988, 1100-1101. J ordan, R. F. Adv. Organomet. Chem.
1991, 32, 325-387. Horton, A. D.; Frijns, J . H. G. Angew. Chem., Int.
Ed. Engl. 1991, 30, 1152-1154. Bochmann, M.; J aggar, A. J .; Nicholls,
J . C. Angew. Chem., Int. Ed. Engl. 1990, 29, 780-782. Hlatky, G. G.;
Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc. 1989, 111, 2728-
2729. Taube, R.; Krukowka, L. J . Organomet. Chem. 1988, 347, C9-
C12. Turner, H. W.; European Patent Appl. 277004 (assigned to
Exxon), 1988. Lin, Z.; Lo Marechall, J .-F.; Sabat, M.; Marks, T. J . J .
Am. Chem. Soc. 1987, 109, 4127-4129. J ordan, R. F.; Bajgur, C. S.;
Willett, R.; Scott, B. J . Am. Chem. Soc. 1986, 108, 7410-7411.
(15) Cesares, J . A.; Espinet, P. Inorg. Chem. 1997, 36, 5428.
(16) Ugi, I.; Marquarding, D.; Klusacek, H.; Gillespie, P. Acc. Chem.
Res. 1971, 4, 288.
(17) Albano, V. G.; Castellari, C.; Morelli, G.; Vitagliano, A. Gazz.
Chim. Ital. 1989, 119, 235-239. For a review on five-coordinated
alkene complexes of Pd(II) and Pt(II) see: Albano, V. G.; Natile, G.;
Panunzi, A. Coord. Chem. Rev. 1994, 133, 67-114.
(18) Romeo, R.; Monsu` Scolaro, L.; Nastasi, N.; Arena, G. Inorg.
Chem. 1996, 35, 5087-5096, and references therein.

3066 Organometallics, Vol. 18, No. 16, 1999
Macchioni et al.
Ta ble 3. Releva n t Bon d Len gth s [Å] a n d An gles
[d eg] for 2d
Ta ble 4. CO/Styr en e Cop olym er iza tion : Effect of
bip y Ad d ed to th e Rea ction Mixtu r ea
Pd-C(1)
Pd-N(1)
Pd-N(2)
2.040(3)
2.154(3)
2.105(3)
Pd-C(5)
Pd-C(4)
C(5)-C(4)
2.175(3)
2.190(4)
1.367(6)
run
[bipy]/[Pd]b
g CPc
g CP/g Pd
Mw (Mw/Mn)d
1
2
3
4
1
1.05 (g)
0.89 (w)
0.84 (y)
0.75 (y)
395
335
316
281
27200 (2.3)
23000 (2.3)
22000 (3.0)
20200 (2.3)
1.25
1.5
2
C(1)-Pd-N(1)
C(1)-Pd-N(2)
C(1)-Pd-C(4)
C(1)-Pd-C(5)
N(2)-Pd-N(1)
N(1)-Pd-C(4)
N(1)-Pd-C(5)
174.57(12)
97.79(12)
80.03(14)
88.9(2)
77.72(10)
104.09(13)
96.52(12)
N(2)-Pd-C(5)
N(2)-Pd-C(4)
C(5)-Pd-C(4)
C(8)-C(1)-Pd
C(2)-C(1)-Pd
C(4)-C(5)-Pd
150.18(14)
173.28(13)
36.5(2)
110.1(3)
109.5(2)
72.3(2)
Catalyst precursor: [Pd(η1,η2-C8H12OMe)bipy]+PF6-. Reaction
a
conditions: nPd ) 2.5 × 10-5 mol; styrene V ) 20 mL; solvent
b
CH2Cl2 V ) 20 mL; T ) 30 °C; PCO ) 1 atm; t ) 4 h. In runs 2-4
free bipy added at the reaction mixture. c Color of the copolymer:
d
g ) gray, w ) white, y ) yellow. Determined by GPC vs poly-
styrene standards.
complex. Moreover, no interaction between the metal
and the counterion is evidenced, which means that
packing forces in the solid state are predominant over
Pd‚‚‚F interactions. The interionic structure in solution
deduced from the 1H-19F dipolar interactions is re-
ported in Figure 2. It may be due (1) to two types of
ion-pairs which have the counterion above or below the
coordination plane and shifted toward the pyridine ring
trans to the Pd-C single bond or (2) to several types of
ion-pairs, with each one contributing one or two inter-
ionic contacts where the counterion is located sideways
to the “Pd-moiety”, as in the solid state. We believe that
hypothesis (1) is more probable because the packing
forces are absent in solution and the “natural” position
to maximize electrostatic interactions is either above or
below the coordination plane.
CO/Styr en e Cop olym er iza tion . The monochelated
monocationic compounds 2, tested in the CO/styrene
copolymerization, yielded perfectly alternating poly-
ketones, whose characterization (elemental analyses, IR,
1H and 13C NMR spectra) is in agreement with the
literature data.23,24 Some preliminary results have
evidenced that these compounds are active catalyst
precursors in nonalcoholic medium without any acid
cocatalyst or any oxidant.6 Moreover, the 2,2′-bipyridine
was the most active ligand tested.6
The copolymerization reactions were carried out in a
thermostated glass reactor under a continuous flow of
CO. When the hexafluorophosphate derivative was used
as catalyst precursor, almost 400 g CP/g Pd (g CP/g Pd
) grams of copolymer per gram of palladium) was
obtained after 4 h; the CO/styrene polyketone has a
molecular weight of 27200 amu (Table 4, run 1).
However, the gray color of the copolymer indicates that
the active species partially decomposed into palladium
metal.
The catalytic system was optimized toward the stabil-
ity of the active species by adding different amounts of
free bipyridine to the reaction mixture. The addition of
small amounts with respect to palladium decreased
productivity of the system, which corresponded to a
slight decrease in the molecular weight of the copoly-
mers (Table 4, runs 2-4). It can be noted that as soon
as a small amount of free bipy was added, the copolymer
was white, indicating a negligible decomposition to
metal; yellow copolymers were obtained when increased
amounts of bipy were added. The filtered yellow poly-
F igu r e 5. Crystal structure as viewed along the crystal-
lographic axis a.
C(1) bond distance (2.040(3) Å) is comparable to those
found for other sp3 carbons which are trans to a bipy
nitrogen atom (2.023(4) Å19 and 2.036(6) Å20).
As far as the Pd-olefin interaction is concerned, the
structural data for some cycloocta- and cyclononadienes
show that the square-planar coordination of the metal
is defined by the midpoint of the carbon-carbon bond.21
In the present compound, atoms C(1), C(4), N(1), and
N(2) settle a plane with max deviations of (0.031(2) Å,
and therefore the Pd-C(5) and Pd-C(4) distances are
slightly different (Table 3). The CdC bond distance of
1.367(6) Å is longer than the mean value of 1.318 Å
reported for a cis-C-CHdCH-C group22 and indicates
a π-back-donation of the filled metal d orbitals to the
empty π ligand. However the olefin carbons maintain
their sp2 character, as attested by the coplanarity of the
C(3), C(4), C(5), and C(6) atoms, whose mean plane
defines a dihedral angle of 77.48(16)° with the coordina-
tion plane.
(e) Solid ver su s Solu tion In ter ion ic Str u ctu r e.
An interesting feature of the crystal structure is the
pairs of complexes arranged about the crystallographic
-
symmetry centers, while the PF6 anions are located
sideways running along the b axis (Figure 5). The
shortest contacts between the fluorine and the complex
hydrogen atoms are about 2.5 Å, and there is no
preferential location of the anions with respect to the
(19) Markies, A. B.; Rietveld, M. H. P.; Boersma, J .; Spek, A. L.;
van Koten, G. J . Organomet. Chem. 1992, 424, C12-C16.
(20) Byers, P. K.; Canty, A. J .; Skelton, B. W.; White, A. H. J .
Organomet. Chem. 1987, 336, C55-C60.
(21) Retting, M. F.; Wing, R. M.; Wiger G. R. J . Am. Chem. Soc.
1981, 103, 2980-2986.
(22) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. Typical interatomic distances: organic compounds.
In International Tables for Crystallography; Wilson, A. J . C., Ed.;
Kuwler Academic Publishers: Dordrecht, Boston, London, 1992; Vol
C.
(23) Milani, B.; Alessio, E.; Mestroni, G.; Sommazzi, A.; Garbassi,
F.; Zangrando, E.; Bresciani-Pahor, N.; Randaccio, L. J . Chem. Soc.,
Dalton Trans. 1994, 1903-1911.
(24) Barsacchi, M.; Consiglio, G.; Medici, L.; Petrucci, G.; Suter, U.
W. Angew. Chem., Int. Ed. Engl., 1991, 30, 989-991.

Counterion Effect on CO/ Styrene Copolymerization
Organometallics, Vol. 18, No. 16, 1999 3067
Ta ble 5. CO/Styr en e Cop olym er iza tion : Effect of
th e An ion a
favors the dissociation of one N-arm of the bipy molecule
and, therefore, the decomposition of the active species
to metal.
runb
X
g CP
g CP/g Pd Mw(Mw/Mn)c
-
In agreement with the above observation, when the
copolymerization reactions were carried out in the
presence of an excess of bipy with respect to palladium,
the active species was stable and no significant effect
of the anion was found.
1
2
3
4
5
6
7
8
9
B(3,5-(CF3)2C6H3)4
1.45 (lg)d
1.14 (g)
1.05 (g)
0.74 (g)
0.20 (g)
0.80 (y)
0.75 (y)
0.72 (w)
0.69 (y)
0.18 (y)
545
429
395
278
75
301
281
271
259
68
24000 (2.3)
27000 (2.3)
27200 (2.3)
26600 (2.2)
9200 (1.5)
22600 (2.2)
20200 (2.3)
18800 (2.6)
20700 (2.2)
9700 (1.6)
-
SbF6
-
PF6-
BF4
CF3SO3
-
-
SbF6
-
PF6
-
B(3,5-(CF3)2C6H3)4
Con clu sion s
-
BF4
-
10
CF3SO3
We have shown that monochelated monocationic
Pd(II) complexes of the type [Pd(η1,η2-C8H12OMe)-
bipy]+X- are among the most active catalysts for the
CO/styrene copolymerization carried out at room tem-
perature and atmospheric pressure. The polyketones
formed under such mild conditions have some of the
highest molecular weights. Their activity decreases as
the counterion becomes more coordinating. Further-
more, if the copolymerizations are carried out in the
presence of an excess of free bipy, the catalytic activity
decreases and the effect of the counterion is flattened.
Catalyst precursor: [Pd(η1,η2-C8H12OMe)bipy]+X-. Reaction
a
conditions: nPd ) 2.5 × 10-5 mol; styrene V ) 20 mL; solvent
b
CH2Cl2 V ) 20 mL; T ) 30 °C; PCO ) 1 atm; t ) 4 h. Runs 6-10
free bipy added: [bipy]/[Pd] ) 2. c Determined by GPC vs poly-
d
styrene standards. Color of the copolymer: lg ) light gray.
ketones which were stirred in methanol, at room tem-
perature, turned to gray after 30 s. This observation
suggests that the polymeric chains are bonded to
palladium and the treatment with methanol causes the
alcoholysis of the Pd-C bond with the formation of
palladium metal. A similar behavior has recently been
reported for living CO/olefin alternating copolymeriza-
tion promoted by [iodo(endo-6-phenyl-2-norbornene-
endo-5σ,2π)(PPh3)Pd(II)].25
1
Using H NOESY and 19F{1H} HOESY NMR spec-
troscopies, we have directly localized the counterion in
methylene chloride solution with respect to the “Pd-
moiety”. Regardless of the type of counterion, it is
located above or below the coordination plane shifted
toward the bipy ring trans to the σ-bond of the η1,η2-
cyclooctenyl ligand. This position differs from that
observed in the solid state for complex 2d , where the
packing forces between different “Pd-moieties” predomi-
nate over the Pd...F interionic interactions, and conse-
quently, the counterion lies on the side of the coordi-
nation plane.
In solution all complexes show a dynamic process that
exchanges the two pyridyl rings. A variable-temperature
NMR investigation showed that this process is affected
little by the nature of counterion, even if it is favored
by more coordinating counterions. The activation en-
tropies are negative for all but 2f complexes, suggesting
an associative mechanism for the process. An excess of
free bipy accelerates the process. An excess of counterion
slightly favors the process, but the effect is less marked
and can be reasonably attributed to a shift of the ion-
pair dissociation equilibrium toward the intimate ion-
pairs.
The effect of the anion was investigated in both the
presence and absence of free bipy, added to the reaction
mixture. In its absence productivity decreased from
B(3,5-(CF3)2C6H3)4 to CF3SO3-, the complex with the
-
B(3,5-(CF3)2C6H3)4- anion being the most active (Table
5, runs 1-5). The anion had no effect on the molecular
weight except for the triflate derivative (Table 5, run
5), which is also much less active than the other
complexes.
When the same analysis was repeated by adding free
bipy in a 1:1 ratio with respect to palladium, the
compound with the B(3, 5-(CF3)2C6H3)4 anion had a
productivity slightly lower than that of the SbF6 and
PF6 derivatives. Due to the addition of the free bipy,
-
-
-
the nature of the anion does not influence the catalytic
activity of the system, with the exception of triflate
(Table 5, runs 6-10). As expected, the polyketones
obtained have very similar molecular weights. The
complex with the BPh4- anion was completely inactive
with the active species decomposing very quickly to
metal either in the absence or presence of excess bipy.
A similar behavior has been reported for the compound
[Pd(bipy)2](BPh4)2 when used as a catalyst precursor for
the reductive carbonylation of nitroaromatic compounds
into urethanes and was explained by assuming a phenyl
group transfer from the anion to Pd(II).26
On the basis of the interionic structure, evidenced in
solution, the effect of the anion on the catalytic activity
of the system, in the absence of added bipy, may be
related to the strength of interionic interactions. Pro-
ductivity increases as the interionic interactions de-
Exp er im en ta l Section
Gen er a l Da ta . Reactions were carried out in a dried
apparatus under a dry inert atmosphere of nitrogen using
standard Schlenk techniques. Solvents were purified prior to
use by conventional methods.27 The methylene chloride (Baker)
was used without further purification for the copolymerization
reactions. Carbon monoxide (CP grade, 99.9%) was supplied
by SIAD.
IR spectra were taken on a 1725 X FTIR Perkin-Elmer
spectrophotometer. One- and two-dimensional 1H, 13C, 19F, and
31P NMR spectra were measured on Bruker DPX 200 and DRX
400 spectrometers. Referencing is relative to TMS (1H and 13C),
CCl3F (19F), and 85% H3PO4 (31P). NMR samples were prepared
dissolving about 20 mg of compound in 0.5 mL of CD2Cl2. An
appropriate quantity of NBu4PF6 was added for the experi-
ments carried out for complex 2d in the presence of an excess
-
crease. It is the highest for the B(3,5-(CF3)2C6H3)4
derivative, which affords very little concentration of
intimate ion-pairs. Indeed, the position of the anion
(25) Safir, A. L.; Novak, B. M. J . Am. Chem. Soc. 1998, 120, 643-
650.
(26) Bontempi, A.; Alessio, E.; Chanos, G.; Mestroni, G. J . Mol.
Catal. 1987, 42, 67-80.
(27) Weissberger, A.; Proskauer, E. S. Technique of Organic Chem-
istry; Interscience: New York, 1955; Vol. VII.

3068 Organometallics, Vol. 18, No. 16, 1999
Macchioni et al.
(5.25). H NMR (in CD2Cl2, 217 K, J values in Hz): δ 8.62 (d,
of counterion. Two-dimensional 1H NOESY and 19F{1H}
1
3
3
HOESY spectra were obtained with a mixing time of 500-
3J 6′,5′ ) 4.5, 6′); 8.52 (d, J 3′,4′ ) 7.8, 3′); 8.45 (d, J 3,4 ) 8.2, 3);
800 ms. Complex 128 and B(3,5-(CF3)2C6H3)4
were synthe-
8.34 (td, J 4′,5′ ) J 4′,3′ ) 7.8, J 4′,6′ ) 1.4, 4′); 8.21 (td, J 4,5 )
4 3
- 29
3
3
4
3
sized as previously reported in the literature.
3J 4,3 ) 7.9, J 4,6 ) 1.5, 4); 8.11 (d, J 6,5 ) 5.2, 6); 7.83 (ddd,
3 4 3
Syn th esis of Com p lexes 2a , 2d , a n d 2e. The ligand bipy
(170 mg, 1.10 mmol) was added to a suspension of complex 1
(250 mg, 0.44 mmol) in methanol (10 mL) at room temperature.
After that, the suspension became a yellow solution, the salt
NaBPh4 (2a ), NH4PF6 (2d ), or NaSbF6 (2e) (1.80 mmol)
previously dissolved in methanol was added, and a solid
precipitated that was filtered off and washed with ethyl ether
and dried under vacuum.
3J 5′,4′ ) 7.5, J 5′,6′ ) 5.5, J 5′,3′ ) 1.1, 5′); 7.73 (dd, J 5,4 ) 7.7,
3J 5,6 ) 5.3, 5); 6.12 (m, 3J 4′′,5′′ ) 9.0, 3J 4′′,3′′a ) 6.7, 4′′); 5.92 (ddd,
3J 5′′,4′′ ) 9.3, 3J 5′′,6′′a ) 5.2, 3J 5′′,6′′b ) 1.9, 5′′); 3.68 (ddd, 3J 8′′,1′′
)
3.3, 3J 8′′,7′′a ) 6.6, 3J 8′′,7′′b ) 6.1, 8′′); 3.40 (s, OMe); 2.96 (m, 1′′);
2
2.87 (d, J 6′′a,6′′b ) 18.2, 6′′a); 2.67 (m, 6′′b); 2.39 (m, 2′′a and
3′′); 2.14 (m, 7′′); 1.76 (m, 2′′b). 19F NMR (in CD2Cl2, 304 K, J
values in Hz): δ -79.3 (s).
Com p lex 2c: pale yellow solid, yield 83%. Anal. Calcd
(found) for C19H23N2OBF4Pd: C 41.70 (42.10); H 4.70 (4.50);
Com p lex 2a : white solid, yield 84%. Anal. Calcd (found)
for C43H43N2OBPd: C 71.54 (71.60); H 5.97 (6.03); N 3.89
1
N 5.73 (5.55). H NMR (in CD2Cl2, 217 K, J values in Hz): δ
1
(3.95). H NMR (in CD2Cl2, 217 K, J values in Hz): δ 8.52 (d,
8.61 (dd, 3J 6′,5′ ) 5.5, 3J 6′,4′ )1.6, 6′); 8.46 (dd, 3J 3′,4′ ) 7.7, 3J 3′,5′
3
3
4
3
4
3
3J 6′,5′ ) 4.7, 6′); 7.96 (td, J 4′,5′ ) J 4′,3′ ) 7.9, J 4′,6′ ) 1.2, 4′);
) 1.3, 3′); 8.38 (dd, J 3,4 ) 7.7, J 3,5 ) 1.2, 3); 8.33 (td, J 4′,5′
)
)
7.87 (td, J 4,5 ) 3J 4,3 ) 7.9, J 4,6 ) 1.4, 4); 7.72 (d, J 3′,4′ ) 7.6,
3J 4′,3′ ) 7.6, J 4′,6′ ) 1.6, 4′); 8.21 (td, J 4,5 ) 3J 4,3 ) 7.7, J 4,6
3
4
3
4
3
4
3′); 7.67 (d, 3J 3,4 ) 8.1, 3); 7.62 (d, 3J 6,5 ≈ 5.4, 6); 7.61 (dd, mixed
1.6, 4); 8.09 (ddd, J 6,5 ) 5.3, J 6,4 ) 1.7, J 6,3 ) 0.7, 6); 7.82
3 4 5
3
3
with 6, 5′); 7.40 (dd, J 5,4 ) 6.8, J 5,6 ) 5.4, 5); 7.36 (m, o-H);
7.02 (t, 3J m,o ) 3J m,p ) 7.4, m-H); 6.87 (t, 3J p,m ) 7.2, p-H); 5.79
(ddd, 3J 5′,4′ ) 7.6, 3J 5′,6′ ) 5.5, 4J 5′,3′ ) 1.3, 5′); 7.72 (ddd, 3J 5,4
)
)
3
4
3
3
7.6, J 5,6 ) 5.3, J 5,3 ) 1.2, 5); 6.11 (ddd, J 4′′,5′′ ) 9.4, J 4′′,3′′a
3
3
4
(m, J 4′′,5′′ ) 8.2, 4′′); 5.69 (dd, J 5′′,4′′ ) 9.3, J 5′′,3′′ ) 3.5, 5′′);
3.66 (m, 8′′); 3.41 (s, OMe); 2.92 (br, 1′′); 2.82 (br d, J 6′′a,6′′b
6.9, 3J 4′′,3′′b ) 3.3, 4′′); 5.91 (ddd, 3J 5′′,4′′ ) 9.2, 3J 5′′,6′′a ) 5.2, 3J 5′′,6′′b
2
3
3
3
)
) 2.4, 5′′); 3.67 (ddd, J 8′′,1′′ ) 3.6, J 8′′,7′′a ) 5.1, J 8′′,7′′b ) 6.1,
2
17.6, 6′′a); 2.61 (m, 6′′b); 2.36 (m, 2′′a and 3′′); 2.12 (m, 7′′);
1.77 (m, 2′′b).
Com p lex 2d : white solid, yield 84%. Anal. Calcd (found)
for C19H23N2OF6PPd: C 41.68 (41.34); H 4.21 (4.48); N 5.13
(4.91).1H NMR (in CD2Cl2, 217 K, J values in Hz): δ 8.60 (dd,
8′′); 3.40 (s, OMe); 2.97 (m, 1′′); 2.86 (d, J 6′′a,6′′b ) 16.9, 6′′a);
2.69 (m, 6′′b); 2.38 (m, 2′′a and 3′′); 2.12 (m, 7′′); 1.75 (m, 2′′b).
19F NMR (in CD2Cl2, 304 K, J values in Hz): δ - 150.00 (br,
10BF4-); - 150.06 (q, J FB )1, 11BF4-).
1
Syn th esis of Com p lexes 2f. The ligand bipy (68 mg, 0.44
mmol) was added to a suspension of complex 1 (100 mg, 0.18
mmol) in methanol (8 mL) at room temperature. After the
suspension became a yellow solution, an excess of the salt
Na+(3,5-(CF3)2C6H3)4B)-, previously dissolved in methanol, was
added and a solid precipitated that was washed with ethyl
ether and dried under vacuum.
3
3
3
3J 6′,5′ ) 5.8, J 6′,4′ )1.2, 6′); 8.40 (dd, J 3′,4′ ) 8.3, J 3′,5′ ) 1.3,
3
3
4
3
3′); 8.32 (td, J 4′,5′ ) J 4′,3′ ) 8.0, J 4′,6′ ) 1.5, 4′); 8.32 (d, J 3,4
3
3
4
) 8.2, 3); 8.20 (td, J 4,5 ) J 4,3 ) 7.8, J 4,6 ) 1.6, 4); 8.06 (dd,
3J 6,5 ) 5.3, J 6,4 ) 1.2, 6); 7.82 (ddd, J 5′,4′ ) 7.5, J 5′,6′ ) 5.4,
4
3
3
4J 5′,3′ ) 1.3, 5′); 7.72 (ddd, 3J 5,4 ) 7.6, 3J 5,6 ) 5.3, 4J 5,3 ) 1.1, 5);
3
3
3
6.09 (ddd, J 4′′,5′′ ) 9.4, J 4′′,3′′a ) 6.9, J 4′′,3′′b ) 3.3, 4′′); 5.91
3
3
3
(ddd, J 5′′,4′′ ) 9.2, J 5′′,6′′a ) 5.2, J 5′′,6′′b ) 2.4, 5′′); 3.67 (ddd,
3J 8′′,1′′ ) 3.7, 3J 8′′,7′′a ) 8.6, 3J 8′′,7′′b ) 5.0, 8′′); 3.40 (s, OMe); 2.96
(ddd, 3J 1′′,8′′ ) 3.6, 3J 1′′,2′′a ) 5.9, 3J 1′′,2′′b ) 2.3, 1′′); 2.87 (d, 2J 6′′a,6′′b
Com p lex 2f: white solid, yield 38%. Anal. Calcd (found)
for C51H35N2F24BOPd: C 48.37 (48.55); H 2.77 (3.04); N 2.21
1
(2.43). H NMR (in CD2Cl2, 217 K, J values in Hz): δ 8.61 (d,
3
3
3
3
) 16.6, 6′′a); 2.67 (ddd, J 6′′b,5′′ ) 5.3, 6′′b); 2.38 (m, 2′′a and
3J 6′,5′ ) 5.5, 6′); 8.19 (d, J 3′,4′ ) 8.0, 3′); 8.18 (td, J 4′,5′ ) J 4′,3′
3′′); 2.12 (m, 7′′); 1.75 (m, 2”b). 13C NMR (in CD2Cl2, 217 K):
δ 156.1 (s, 2′ or 2); 153.1 (s, 2 or 2′); 148.7 (s, 6′); 148.0 (s, 6);
142.5 (s, 4′); 141.4 (s, 4); 128.4 (s, 5); 128.2 (s, 5′); 124.5 (s, 3′);
123.8 (s, 3); 107.5 (s, 5′′); 106.6 (s, 4′′); 82.5 (s, 8′′); 56.9 (s,
OMe); 53.5 (s, 1′′); 33.8 (s, 2′′); 30.7 (s, 7′′); 29.5 (s, 6′′); 26.5 (s,
3′′). 31P NMR (in CD2Cl2, 304 K, J values in Hz): δ -141.3
) 8.2, J 4′,6′ ) 1.3, 4′); 8.12 (d, J 3,4 ) 7.9, 3); 8.07 (td, J 4,5 )
4 3
4
3
3
3J 4,3 ) 7.5, J 4,6 ) 1.6, 4); 7.97 (ddd, J 6,5 ) 5.0, 6); 7.76 (q,
3J H11B ) 1.7, o-H); 7.75 (ddd, partially buried under o-H, 5′);
3
3
4
7.61 (ddd, J 5,4 ) 7.6, J 5,6 ) 5.2, J 5,3 ) 1.3, 5); 7.57 (s, p-H);
6.05 (m, 4”); 5.87 (ddd, 3J 5′′,4′′ ) 9.3, 3J 5′′,6′′a ) 5.3, 3J 5′′,6′′b ) 2.0,
5′′); 3.66 (ddd, 3J 8′′,1′′ ) 3.4, 3J 8′′,7′′a ) 5.1, 3J 8′′,7′′b ) 6.1, 8′′); 3.39
(sept. J PF ) 711.0). 19F NMR (in CD2Cl2, 304 K, J values in
(s, OMe); 2.97 (m, 1′′); 2.85 (d, J 6′′a,6′′b ) 18.3, 6′′a); 2.68 (m,
1
2
1
Hz): δ -71.6 (d, J FP ) 711.0).
6′′b); 2.38 (m, 2′′a and 3′′); 2.13 (m, 7′′); 1.76 (m, 2′′b). 19F NMR
(in CD2Cl2, 304 K, J values in Hz): δ - 63.0 (s).
Com p lex 2e: yellow solid, yield 70%. Anal. Calcd (found)
for C19H23N2OF6PdSb: C 35.74 (36.02); H 3.61 (3.70); N 4.39
(4.30). 1H NMR (in CD2Cl2, 217 K, J values in Hz): δ 8.62
Va r ia ble-Tem p er a tu r e NMR Exp er im en ts. In a typical
experiment, approximately 20 mg of complex was dissolved
3
3
3
3
1
(dd, J 6′,5′ ) 5.5, J 6′,4′ )1.5, 6′); 8.39 (dd, J 3′,4′ ) 8.2, J 3′,5′
)
in 0.6 mL of CD2Cl2. The H NMR spectra were recorded over
3
3
4
1.4, 3′); 8.32 (td, J 4′,5′ ) J 4′,3′ ) 7.8, J 4′,6′ ) 1.5, 4′); 8.31 (dd,
the temperature range 204-304 K. The spectra were simu-
lated using the program DNMR3.30 The exchange constants,
obtained from the simulations, were used to determine ∆Hq,
3J 3,4 ) 8.1, J 3,5 ) 1.1, 3); 8.20 (td, J 4,5 ) J 4,3 ) 7.7, J 4,6
)
)
)
4
3
3
4
3
4
3
1.6, 4); 8.07 (dd, J 6,5 ) 5.3, J 6,4 ) 1.6, 6); 7.83 (ddd, J 5′,4′
3
4
3
3
7.5, J 5′,6′ ) 5.5, J 5′,3′ ) 1.4, 5′); 7.72 (ddd, J 5,4 ) 7.6, J 5,6
∆Sq, and ∆Gq from the Eyring equation k ) (kB/h)T exp-
298
4
3
3
5.2, J 5,3 ) 1.2, 5); 6.09 (m, J 4′′,5′′ ) 9.5, J 4′′,3′′a ) 6.5, 4”); 5.91
(-∆Hq/RT) exp(∆Sq/R), where kB is Boltzmann’s constant, h
is Planck’s constant, and R is the ideal gas constant.
Ca ta lysis. CO/Styr en e Cop olym er iza tion Rea ction s.
These reactions were carried out in a thermostated glass
reactor (100 mL), equipped with a magnetic stirrer and a
carbon monoxide gas line. After introducing the solvent,
styrene, and catalyst precursor, carbon monoxide was continu-
ously bubbled into the reaction mixture and heated to 30 °C.
After 4 h the carbon monoxide flow was stopped and the
reaction mixture was put into methanol (200 mL). The
copolymer was filtered off, washed with methanol, and dried
under vacuum.
3
3
3
(ddd, J 5′′,4′′ ) 9.3, J 5′′,6′′a ) 5.2, J 5′′,6′′b ) 1.7, 5′′); 3.68 (ddd,
3J 8′′,1′′ ) 3.4, J 8′′,7′′a ) 10.1, J 8′′,7′′b ) 6.1, 8′′); 3.40 (s, OMe);
3
3
2
3
2.97 (m, 1”); 2.88 (d, J 6′′a,6′′b ) 18.4, 6′′a); 2.67 (m, J 6′′b,5′′
)
5.6, 6′′b); 2.38 (m, 2′′a and 3′′); 2.14 (m, 7′′); 1.75 (m, 2′′b). 19F
NMR (in CD2Cl2, 304 K, J values in Hz): δ -124.3 (superposi-
tion of a sextet due to 121SbF6 and an octet due to 123SbF6
,
-
-
1
1J F
) 1946 Hz, J F
) 1069).
121
123
Sb
Sb
Syn th esis of Com p lexes 2b a n d 2c. The procedure is
similar to that reported above, but the precipitation following
the addition of the salts (NaBF4 or NaCF3SO3) is more difficult.
For this reason the reactions were carried out in 10 mL of
methanol and complexes 2b and 2c were precipitated by
adding ethyl ether.
Molecu la r Weigh t Mea su r em en t. The molecular weights
(Mw) of the copolymers and the molecular weight distributions
Com p lex 2b: white solid, yield 40%. Anal. Calcd (found)
for C20H23N2O4F3PdS: C 43.54 (43.23); H 4.17 (4.25); N 5.08
(29) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
(30) Kleier, D. A.; Binsch, G. DNMR3 Program 165, Quantum
Chemistry Program Exchange, Indiana University, IN, 1970.
(28) Chatt, J .; Vallarino, L. M.; Venanzi, L. M. J . Chem. Soc. 1957,
3413-3416.

Counterion Effect on CO/ Styrene Copolymerization
Organometallics, Vol. 18, No. 16, 1999 3069
(Mw/Mn) were determined by gel permeation chromatography
versus polystyrene standards. The analysis were recorded on
a Bruker HPLC (model LC-22) with an Alltech macrosphere
GPC 60 E column and chloroform as solvent (flow rate 0.5 mL/
min).
The CO/styrene copolymers were dissolved as follows: 3 mg
of each sample was solubilized with 120 µL of 1,1,1,3,3,3-
hexafluoro-2-propanol (HFIP), and chloroform was then added
up to 10 mL.
final cycle of refinement, with the contribution of hydrogen
atoms at fixed calculated positions, was based on 3486
observed reflections with I > 2σ(I) and 272 parameters and
converged with R(F), wR(F2), and S (goodness-of-fit) to 0.0351,
0.0844, and 1.056, respectively. The largest residuals in the
∆F map were +1.07 and -0.95 e Å-3
.
Ack n ow led gm en t. This work was supported by
grants from the Ministero dell’Universita` e della Ricerca
Scientifica e Tecnologica (MURST, Rome, Italy). Pro-
gramma di Rilevante Interesse Nazionale, Cofinanzia-
mento 1998-1999.
The statistical calculations were performed by using the
Bruker Chromstar software program.
X-r a y An a lysis. X-r a y Str u ctu r e Deter m in a tion of 2d .
C
19H23PdPF6ON2, M ) 546.76, monoclinic, space group P21/n
(alternative setting of no. 14), a ) 10.820(2)Å, b ) 10.161-
(1)Å, c )19.220(2) Å, â ) 95.89(6)°, V ) 2101.9(5) Å3, Z ) 4,
Dc ) 1.728 Mg/m3, µ(Mo KR) ) 1.025 mm-1, F(000) ) 1096.
Diffraction measurements were carried out, at room temper-
ature, on an Enraf-Nonius CAD4 diffractometer equipped with
graphite monochromator and Mo KR radiation (λ ) 0.71073
Å, θ range 2.07-26.97°, index ranges -13 e h e 13, 0 e k e
12, 0 e l e 24). A total of 4970 reflections were collected, of
which 4565 were independent [R(int) ) 0.0282]. The unit cell
dimensions were refined by least-squares treatment of 25
reflections in the range θ 14-17°. The intensities of three
standard reflections, measured at regular intervals throughout
the data collection, showed no noticeable decay. All data were
corrected for Lorentz-polarization effects and absorption
(empirical ψ scan method), and the structure was solved by
conventional Patterson31 and Fourier techniques and refined32
by the full-matrix anisotropic least-squares method on F2. The
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement (Table 1S), atomic coordinates
and equivalent isotropic displacement parameters (Table 2S),
bond lengths and angles (Table 3S), anisotropic displacement
parameters (Table 4S), and hydrogen coordinates and isotropic
displacement parameters (Table 5S) for 2d . Kinetic rate
constants for the process that equilibrates the two pirydine
rings (Table 6S) for the complexes 2a -f. This material is
available free of charge via the Internet at http://pubs.acs.org.
An X-ray crystallographic file is available in CIF format.
OM990372K
(31) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, A46, 467-
4730.
(32) Sheldrick, G. M. SHELXL-97, Program for crystal structure
refinement; University of Go¨ttingen: Germany, 1997.