Syndiotactic CO/styrene copolymerization catalyzed by α-diimine Pd(II) complexes: Regio- and stereochemical control

Article abstract of DOI:10.1021/om000971n

Using the catalytic system [(PrⁱDAB)Pd(Me)(NCMe)]⁺[{3,5-(CF₃)₂C ₆H₃} ₄B]^-, where PrⁱDAB = 1,4-diisopropyl-1,4-diaza-1,3-butadiene, it has been possible to obtain copolymers of styrene or p-methylstyrene with carbon monoxide, which have alternating, head-to-tail, syndiotactic structure and a stereochemical purity of 92%. To investigate the reaction mechanism, the first steps of the copolymerization were studied by isolating and characterizing the reaction intermediates. The reactivity of the catalyst toward carbon monoxide was studied, and the corresponding methyl carbonyl Pd initiator complex was isolated. The regiospecific 2,1-insertion of p-methylstyrene in the Pd-acyl bond was proved by NOE measurements performed on the first intermediate, a five-membered palladacycle, in which the acetylic oxygen is coordinated to the palladium. Moreover, the intermediate resulting after the second sequence of CO and styrene insertion unexpectedly showed a doubling of the signals, both in the proton and carbon-13 NMR spectra. This finding, attributed to the presence of two diastereoisomeric complexes, showed that the chain-end stereorchemical control is not fully effective during the initial steps of the copolymerization. Last, the fluxional character of some examined complexes was studied and the relative activation energies were determined.

Full text of DOI:10.1021/om000971n

Organometallics 2001, 20, 2175-2182
2175
Syn d iota ctic CO/Styr en e Cop olym er iza tion Ca ta lyzed by
r-Diim in e P d (II) Com p lexes: Regio- a n d Ster eoch em ica l
Con tr ol†
Carla Carfagna,*,‡ Giuseppe Gatti,‡ Domenico Martini,§ and Claudio Pettinari§
Istituto di Scienze Chimiche, Universita` degli Studi di Urbino, Piazza Rinascimento 6,
61029 Urbino, Italy, and Dipartimento di Scienze Chimiche, Universita` degli Studi
di Camerino, Via S. Agostino 1, 62032 Camerino, Italy
Received November 15, 2000
Using the catalytic system [(PriDAB)Pd(Me)(NCMe)]+[{3,5-(CF3)2C6H3}4B]-, where
PriDAB ) 1,4-diisopropyl-1,4-diaza-1,3-butadiene, it has been possible to obtain copolymers
of styrene or p-methylstyrene with carbon monoxide, which have alternating, head-to-tail,
syndiotactic structure and a stereochemical purity of 92%. To investigate the reaction
mechanism, the first steps of the copolymerization were studied by isolating and character-
izing the reaction intermediates. The reactivity of the catalyst toward carbon monoxide was
studied, and the corresponding methyl carbonyl Pd initiator complex was isolated. The
regiospecific 2,1-insertion of p-methylstyrene in the Pd-acyl bond was proved by NOE
measurements performed on the first intermediate, a five-membered palladacycle, in which
the acetylic oxygen is coordinated to the palladium. Moreover, the intermediate resulting
after the second sequence of CO and styrene insertion unexpectedly showed a doubling of
the signals, both in the proton and carbon-13 NMR spectra. This finding, attributed to the
presence of two diastereoisomeric complexes, showed that the chain-end stereochemical
control is not fully effective during the initial steps of the copolymerization. Last, the fluxional
character of some examined complexes was studied and the relative activation energies were
determined.
In tr od u ction
obtained are characterized by chemoregularity, i.e.
perfect alternation of the carbon monoxide and styrene
comonomers, and by regioregularity, i.e. head-to-tail
placement of the styrene monomeric units, the latter
being a consequence of the secondary migratory inser-
tion of the styrene units into the palladium-acyl bond
of the catalytic system, as shown by studies of low
molecular weight copolymers and oligomers4 and model
compounds.2b,5 In the case of syndiotactic-specific cata-
lysts, the stereochemical control of the copolymerization
has been ascribed to the chirality of the polymer chain
end,1c,2a,2l whereas in the case of isotactic-specific cata-
lysts, it has been ascribed to the chirality of the
ligands.3a,b,5a,6
Since the pioneering work of Drent,1 the copolymer-
ization of styrene or styrene analogues with carbon
monoxide, catalyzed by palladium complexes, has been
extensively investigated.2 Pd(II) complexes containing
nitrogen bidentate ligands and weakly coordinating
anions have been used as active precatalysts, high
values of CO pressure, fairly high temperature, and
methanol as solvent generally being the reaction condi-
tions. Copolymers have been produced at low pressure
of CO (1 or 4 bar)2b,3 only in a few cases. The copolymers
† This paper is dedicated to Professor Alfredo Musco.
* Corresponding author. Fax: +39-0722-2754. E-mail: schim@chim.
uniurb.it.
From recent reports in the literature1c it appears that
this field of polyketone chemistry is an opportunity for
testing new catalytic systems and checking mechanism
hypotheses. Prompted by this, we tried our approach:
‡ Universita` degli Studi di Urbino.
§ Universita` degli Studi di Camerino.
(1) (a) Drent, E. Eur. Pat. Appl. 1986, 229, 408; Chem. Abstr. 1988,
108, 6617. (b) Drent, E.; van Broekhoven, J . A. M.; Doyle, M. J . J .
Organomet. Chem. 1991, 417, 235. (c) Drent, E.; Budzelaar, P. H. M.
Chem. Rev. 1996, 96, 663.
(3) (a) Brookhart, M.; Wagner, M. I.; Balavoine, G. G. A.; Haddou,
H. A. J . Am. Chem. Soc. 1994, 116, 3641. (b) Bartolini, S.; Carfagna,
C.; Musco, A. Macromol. Rapid Commun. 1995, 16, 9. (c) Milani, B.;
Alessio, E.; Mestroni, G.; Zangrando, E.; Randaccio, L.; Consiglio, G.
J . Chem. Soc., Dalton Trans. 1996, 1021. (d) Macchioni, A.; Bella-
chioma, G.; Cardaci, G.; Travaglia, M.; Zuccaccia, C.; Milani, B.; Corso,
G.; Zangrando, E.; Mestroni, G.; Carfagna, C.; Formica, M. Organo-
metallics 1999, 18, 3061.
(4) Barsacchi, M.; Consiglio, G.; Medici, L.; Petrucci, G.; Suter, U.
W. Angew. Chem., Int. Ed. Engl. 1991, 30, 989.
(5) (a) Aeby, A.; Bangerter, F.; Consiglio, G. Helv. Chim. Acta 1998,
81, 764. (b) Carfagna, C.; Formica, M.; Gatti, G.; Musco, A.; Pierleoni,
A. Chem. Commun. 1998, 1113.
(2) (a) Corradini, P.; De Rosa, C.; Panunzi, A.; Petrucci, G.; Pino, P.
Chimia 1990, 44, 52. (b) Brookhart, M.; Rix, F. C.; DeSimone, J . M.;
Barborak, J . C. J . Am. Chem. Soc. 1992, 114, 5894. (c) Sen, A.; J iang,
Z. Macromolecules 1993, 26, 911. (d) Busico, V.; Corradini, P.; Lan-
driani, L.; Trifuoggi, M. Makromol. Chem. Rapid. Commun. 1993, 14,
261. (e) J iang, Z.; Adams, S. E.; Sen, A. Macromolecules 1994, 27, 2694.
(f) Milani, B.; Alessio, E.; Mestroni, G.; Sommazzi, A.; Garbassi, F.;
Zangrando, E.; Bresciani-Pahor, N.; Randaccio, L. J . Chem. Soc.,
Dalton Trans. 1994, 1903. (g) Milani, B.; Anzilutti, A.; Vicentini, L.;
Sessanta o Santi, A.; Zangrando, E.; Geremia, S.; Mestroni, G.
Organometallics 1997, 16, 5064. (h) Nozaki, K.; Hiyama, T. J . Orga-
nomet. Chem. 1999, 576, 248. (i) Milani, B.; Corso, G.; Mestroni, G.;
Carfagna, C.; Formica, M.; Seraglia, R. Organometallics 2000, 19, 3435.
(j) Aeby, A.; Gsponer, A.; Sperrle, M.; Consiglio, G. J . Organomet.
Chem. 2000, 603, 122.
(6) (a) Sperrle, M.; Aeby, A.; Consiglio, G.; Pfaltz, A. Helv. Chim.
Acta 1996, 79, 1387. (b) Brookhart, M.; Wagner, M. I. J . Am. Chem.
Soc. 1996, 118, 7219.
10.1021/om000971n CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/04/2001

2176 Organometallics, Vol. 20, No. 11, 2001
Carfagna et al.
Sch em e 1
1
by using precatalysts of the type [(N-N)Pd(CH3)-
(NCCH3)]+[{3,5-(CF3)2C6H3}4B]- we devised catalytic
systems capable of producing both syndiotactic (in the
case in which N-N ) diazabutadienes)5b and isotactic
(in the case in which N-N ) bioxazolines)3b copolymers.
The reaction conditions in both cases are very mild (PCO
) 1 bar and T ) 0 °C, solvent ) dichloromethane).
An appropriate ligand choice (1,4-diisopropyl-1,4-
diazabuta-1,3-diene ) PriDAB) allowed us to monitor
the first steps of polymer chain growth. Thus, with the
aim of adding further knowledge to the syndiotactic
propagation, we decided to investigate the stereochem-
istry of the intermediate complexes.
In this paper we report the results of the copolymer-
ization reactions of styrene and p-methylstyrene with
CO, using the syndiospecific precatalyst [(PriDAB)Pd-
(CH3)(NCCH3)]+[{3,5-(CF3)2C6H3}4B]-, where PriDAB )
1,4-diisopropyl-1,4-diaza-1,3-butadiene. Moreover, we
describe the full details of the synthesis and spectro-
scopic characterization of the catalyst and precursors.
Last, but not least, we report on the reactivity of the
catalyst with the comonomers and on the isolation and
characterization of reaction intermediates, which was
in part the subject of a preliminary note.5b
by PriDAB within a few hours. The H NMR spectrum
(20 °C) of 1 shows two characteristic broad singlets for
the two nonequivalent imine (CHdN) protons, centered
at 8.13 and 8.00 ppm, respectively, and in the 13C NMR
spectra the corresponding diimine carbons are at 160.0
and 155.2 ppm. This indicates that, at this temperature,
the complex is in the regime of slow exchange on the
NMR time scale. Moreover, the two isopropyl groups are
not equivalent: the CH3 signals are two doublets (J )
6.5 Hz) and the CH signals are two double septets (J )
6.5 Hz, and 1.2 Hz), the small splitting being due to
long-range coupling with CHdN protons. Last, Pd-CH3
resonances are at δH 1.06 and at δC 0.1, the shielding
being due to the coordination of the metal. In the IR
spectrum of 1, in a film, two (CdN) stretching bands at
1637.3 and 1582.2 cm-1 are found, due to the difference
in trans effect exerted by the chlorine and the methyl
group.
From the reaction of complex 1 with Na+BAr′4 (Ar′
-
) 3,5-(CF3)2C6H3) at -40 °C in a CH2Cl2/CH3CN
(5:1 v/v) mixture, the cationic acetonitrile complex
[(PriDAB)Pd(CH3)(NCCH3)]+[{3,5-(CF3)2C6H3}4B]-, 2,
was formed in good yields (Scheme 1), which is ana-
logous to nitrile palladium adducts, containing R-di-
imine ligands with bulkier substituents, used by
Brookhart as catalysts for olefin polymerizations8a and
for the copolymerization of ethylene and R-olefins with
methyl acrylate.8b
Resu lts a n d Discu ssion
A. Syn th esis of Com p lexes 1 a n d 2. The complex
(PriDAB)Pd(CH3)(Cl), 1, was synthesized from the reac-
tion of (COD)Pd(CH3)(Cl) (COD ) 1,5-cyclooctadiene)
with the R-diimine ligand in dichloromethane at room
temperature;7 the diene was substituted quantitatively
Complex 2 was characterized by 1H and 13C NMR
spectra. It appears, from the H NMR spectral pattern,
1
(8) (a) Tempel, D. J .; J ohnson, L. K.; Huff, R. L.; White, P. S.;
Brookhart, M. J . Am. Chem. Soc. 2000, 122, 6686. (b) Mecking, S.;
J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120,
888.
(7) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

Syndiotactic CO/ Styrene Copolymerization
Organometallics, Vol. 20, No. 11, 2001 2177
similar to that of 1, that 2, at room temperature, is also
in the regime of slow exchange. Moreover, the methyl
resonance of the acetonitrile is shifted at δ 2.35, due to
the coordination to palladium.
methyl group (36.2 ppm) in the corresponding 13C
spectrum. The acetyl complex 5 is thermally stable as
a solid and also in solution if stored at - 20 °C and does
not show any tendency to decarbonylate. Indeed, if
nitrogen is bubbled through a chloroform solution of 5
up to complete evaporation of the solvent, 5 is recovered
unchanged.
Instead, bubbling nitrogen through a dichloromethane
solution of 4 at -15 °C resulted in the formation of 6,
upon releasing of one molecule of CO. Exposure of the
solution of 6 to CO atmosphere led to the regeneration
of 4. This observation shows that this carbonylation
reaction is reversible.
B. Cop olym er iza tion of Styr en e or p-Meth ylsty-
r en e w ith Ca r bon Mon oxid e. Styrene or p-methyl-
styrene was added to a dichloromethane solution of 2
presaturated with carbon monoxide (molar ratio olefin:
palladium 250:1) at low temperature (0 °C) (Scheme 1).
The solution was left for 24 h under CO atmosphere,
and the copolymers poly(1-oxo-2-phenyltrimethylene),
3a , or poly(1-oxo-2-(4-methyl)phenyltrimethylene), 3b,
were collected by precipitation with MeOH. Both co-
polymers were obtained in moderate yields: 98 g of
copolymer 3a /g Pd and 116 g of copolymer 3b/g Pd were
recovered. The molecular weight (Mw) was 8400 and
9200 amu, respectively, with a very low polydispersity
(Mw/Mn) of 1.2-1.3. The stereoregularity of the copoly-
mers was determined by 13C NMR spectrometry ((CF3)2-
CHOH/CDCl3 (50:50, v/v) at 45 °C): the carbons CO,
Finally the five-membered palladacycle 7 was syn-
thesized by reaction of 6 with p-methylstyrene in
CH2Cl2 as preliminarily reported5b(Scheme 2).
D. F lu xion a l Beh a vior . The 1H and 13C NMR
spectra of the complexes 1, 2, 4, 5, and 6 are tempera-
ture dependent. By lowering the temperature of the
samples, the resonances of the PriDAB ligand become
broad and then split in two different sets of chemical
shifts. This observation can be rationalized by assuming
a fluxional interconversion between two forms (as shown
in Scheme 3), which is fast at high temperature and
slow at low temperature. However, the temperature of
coalescence appears to be quite different in the series
of complexes. Moreover, measuring the spectrum of 2
upon addition of 1 equiv of CH3CN and, likewise,
measuring the spectrum of 4 and 5 under CO atmo-
sphere results in a considerable lowering of the coales-
cence temperature. To obtain a quantitative evaluation
of the process, the chemical shift difference, measured
in the slow interconversion regime, was used to estimate
the interconversion frequency with the relationship k
) π∆ν/x2. The Gibbs free energy of activation for the
process at the coalescence temperature was then cal-
culated using the Eyring equation. The results of this
analysis, performed on the proton signals of the frag-
ment -NdCH-CHdN-, are shown in Table 1. It
appears that the activation energy barrier depends
strongly on the substituent pattern of the Pd center.
Moreover the addition of free ligands such as CO and
CH3CN results in a lower energy barrier.
C
ipso, CH2, and CH show four strong signals, as well as
small signals due to stereoisomeric impurities. The
chemical shifts of the above carbons observed for 3a and
3b (see Experimental Section) correspond to the values
reported in the literature1,2,4,9 for the alternating head-
to-tail syndiotactic copolymer. The stereoisomeric purity
was estimated in the region of Cipso, where the ratio of
the uu triad to the ul and lu triads were 92% to 8% for
3a and 3b, while the ll triad was not detected.
C. Syn th eses of Com p lexes 4-7. The key steps of
the copolymerization process are the insertion reactions
of CO in the palladium-alkyl bond and of alkene in the
palladium-acyl bond.10 To investigate the mechanism
of the copolymerization promoted by our catalytic
system 2, we first studied the reaction of 2 toward
carbon monoxide under the same conditions used for the
synthesis of polyketones 3a and 3b (Scheme 1).
By exposure of 2 to CO atmosphere, the corresponding
acetyl carbonyl complex 4 was obtained. A convenient
alternative route to complex 4, acetonitrile free, was
realized by addition of Na+[{3,5-(CF3)2C6H3}4B]- to 1
at low temperature under CO atmosphere in dichlo-
romethane previously saturated with CO. The mixture
was slowly warmed to 0 °C, and after NaCl filtration,
followed by solvent evaporation, an oil was obtained;
washing with hexane produced a yellow powder corre-
sponding to complex 4.
E. Mech a n istic Stu d ies: Alk en e a n d CO In ser -
tion s. Several examples are described in the literature
of reactions resulting from the insertion of various
alkenes into metal acyl bonds, either preexistent or
formed after R-migration of the alkyl,11 but the olefin
employed is styrene or substituted styrenes in only a
few cases.2b,12 The chain propagation has been observed
by Brookhart, at low temperature, by using the 2,2′-
bipyridine ligand.2b
Complex 1 also turned out to be very reactive with
respect to carbon monoxide insertion. Indeed, by dis-
solving complex 1 in dichloromethane previously satu-
rated with CO at -20 °C and slowly warming the
solution to 20 °C, the pure acetylchloropalladium com-
plex 5 was obtained as an orange solid after filtration,
evaporation of the solvent, and washing with hexane.
The CO insertion into the Pd-Me bond was confirmed
from the spectroscopic data: high-frequency shift of the
We used complex 2 as the initiator of the syndiotactic
copolymerization but, by studying its evolution under
(11) (a) Brumbaugh, J . S.; Whittle, R. R.; Parvez, M.; Sen, A.
Organometallics 1990, 9, 1735. (b) Ozawa, F.; Hayashi, T.; Koide, H.;
Yamamoto, A. J . Chem. Soc., Chem. Commun. 1991, 1469. (c) Markies,
B. A.; Verkerk, K. A. N.; Rietveld, M. H. P.; Boersma, J .; Kooijman,
H.; Spek, A. L.; van Koten, G. J . Chem. Soc., Chem. Commun. 1993,
1317. (d) Sen, A. Acc. Chem. Res. 1993, 26, 303. (e) van Asselt, R.;
Gielsens, E. E. C. G.; Ru¨lke, R. E.; Vrieze, K.; Elsevie, C. J . J . Am.
Chem. Soc. 1994, 116, 977. (f) Ru¨lke, R. E.; Kaasjager, V. E.; Kliphuis,
D.; Elsevier, C. J .; van Leeuwen, P. W. N. M.; Vrieze, K. Organome-
tallics 1996, 15, 668. (g) Rix, F. C.; Brookhart, M.; White, P. S. J . Am.
Chem. Soc. 1996, 118, 4746.
1
methyl resonance in the H NMR spectrum from 1.06
to 2.62 ppm, the presence of the characteristic CO
stretching in the IR spectrum (1700 cm-1), and last, the
chemical shift values for the CO (229 ppm) and for the
(9) Barsacchi, M.; Batistini, A.; Consiglio, G.; Suter, U. W. Macro-
molecules 1992, 25, 3604.
(10) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd. ed.;
Wiley: New York, 1992.
(12) (a) Dekker, G. P C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M.; Roobeek, C. F. J . Organomet. Chem. 1992, 430, 357. (b)
Aeby, A.; Consiglio, G. J . Chem. Soc., Dalton Trans. 1999, 655.

2178 Organometallics, Vol. 20, No. 11, 2001
Carfagna et al.
Sch em e 2
Sch em e 3
to -40 °C in an NMR tube and bubbling CO through
the solution for 4 min. The conversion to the acyl
carbonyl complex 8 was monitored by NMR, because it
is stable only in solution at low temperature. This CO
insertion is reversible, since by bubbling nitrogen
through the solution for 4 min, at -50 °C, complex 7
was regenerated quantitatively. Last, one molecule of
p-methylstyrene and one of carbon monoxide were
inserted in complex 8 in order to determine the stere-
ochemistry of complex 9, in which two styrene units are
present. Complex 9 can also be obtained directly from
complex 6, by adding 2 equiv of p-methylstyrene and
bubbling CO (Scheme 2).
Ta ble 1. Kin etic P a r a m eter s of F lu xion a lity
The structures of complex 7 and of the rather un-
stable species 8 and 9, prepared with the aim of
investigating the initial steps of the copolymerization
reaction, were determined by 13C, 1H NMR, and IR
spectroscopy. To allow comparison, the 13C chemical
shifts of Pd-(CO) and of the growing polymeric chain
are shown in Table 2.
2
4
5
1
2
+CH3CN
4
+CO
5
+CO
6
T
coalesc (K)
k (s-1
∆Gq ( 2
kJ mol-1
335 336
271
33
58
213 196 278 240 288
)
56
72
33
73
24
45
24
42
44
59
40
51
19
63
First of all, it appears that the spectral pattern of the
chelated complex 7 is considerably different from the
open chain complex 8. Thus the CO signal of 7 is found
at 224.9 ppm and is strongly deshielded when compared
with the acetyl signal of 8, which falls at 206.6 ppm,
while the CH2 signal of 7 appears, at 52 ppm, strongly
deshielded in relation to the 45.9 ppm of 8, which
conforms to the presence of a chelating acetyl group in
the cyclic structure 7. These observations also give
evidence in favor of the open chain structure of complex
8, which was previously postulated to be cyclic.5b This
assignment is further confirmed by the carbonyl signal
similar conditions used for the reaction, the real cata-
lytic species was identified in complex 6. It is isolable
and adequately stable and is a useful starting point to
follow the stoichiometric insertion of the unsaturated
molecules step by step. In fact, the catalytic site of the
metal center is easily obtainable by means of the alpha
migration of the methyl. While the alkene insertion in
complex 4 was very slow, the five-membered pallada-
cycle 7 was smoothly obtained from 6 in good yield
(Scheme 2).
The next step of the copolymerization reaction was
investigated by cooling a CDCl3 solution of complex 7

Syndiotactic CO/ Styrene Copolymerization
Organometallics, Vol. 20, No. 11, 2001 2179
Ta ble 2. Selected 13C Ch em ica l Sh ifts of th e F ir st In ter m ed ia tes of Cop olym er iza tion (p p m fr om TMS)
complex
Pd-(CO)
-CO-
-CH-
-CH2-
CH3
29.2
29.7
7
8
9
224.9
47.0
61.6
60.9; 52.5;
52.1
52.0
45.9
171.5
172.7; 171.9
211.2; 206.6
209.2; 208.6; 208.2;
207.9; 207.8; 207.6
46.8; 46.3; 44.7; 29.9; 29.6
44.3
Sch em e 4
at 171.5 ppm in the 13C spectrum of 8 and by the
presence in the IR spectrum of two bands at 2126 and
1718 cm-1, the former being typical of a CO ligand
bonded to a cationic palladium center. Moreover, in the
13C NMR spectrum, the CH signal of 8 shifts at 61.6
ppm compared to 47 ppm in 7, thereby proving the CO
insertion in 8. However, in the acetyl group, the chemi-
cal shift of methyl, is not strongly different between 7
and 8.
Both observations are in agreement with 2,1-insertion
of the styrene monomer unit.
The neat ABX pattern of the CH-CH2 present in the
spectrum of 8 has different spectral parameters than
that of 7. The observed deshielding of the CH is in
agreement with the vicinal CO insertion, while the
changes of the vicinal coupling constants are due to the
different conformation of the noncyclic form. The proton
signal for the CH3CO group, which is not bonded to the
Pd center, is found at 2.15 ppm.
As far as regards complex 9, in which two styrene
units are inserted, the number of resonances observed
in each spectral region described above indicates the
presence of two forms. In particular the resonance of
the Pd-CO is split into two signals (172.7 and 171.9
ppm), and the resonances for the other three acyl CO
groups are split into six signals (209.2, 208.6, 208.2,
207.9, 207.8, and 207.6 ppm), whereas three resonances
for CH (52.5, 52.1, and two overlapping at 60.9 ppm),
four resonances for CH2 (46.8, 46.3, 44.7, and 44.3 ppm),
and two for the terminal methyl group (29.9 and 29.6
ppm) were found. On the basis of the relatively small
shifts observed, we suggest that the two forms are the
two diastereoisomeric complexes 9a and 9b, as reported
in Scheme 4. From the relative intensity of the split
signals, it appears that the amount of one form is
approximately double of the other.
The above picture is confirmed by 1H NMR data. The
analysis of the ABX pattern due to the CH-CH2
fragment in the spectrum of 7 (previously reported)5b
is additional evidence of styrene insertion. Moreover,
the measurement of a strong NOE effect between the
CH3CO and the CH2 proves the proximity of these
groups and therefore the 2,1-regiochemistry of the
styrene insertion. The NOE effect measurements al-
lowed the assignment of regiochemistry; thus irradiation
of CH3CO resulted in enhancement of the CH2 signal
but not of the CH of the styrene unit. Furthermore,
irradiation of the ortho proton of the phenyl ring
resulted in enhancement of the proximal isopropyl CH.
1
The H spectrum of complex 9 contains a CH-CH2
pattern of signals, which overlap in a complicated
manner. However, in the CH region it is still possible
to identify four quartets (J vic ≈ 11 Hz, J vic ≈ 3 Hz), two
centered at 4.2, one at 4.1, and one at 4.05 ppm, while
in the CH2 region this distinction is not so easy. In any
case, the remaining J value of ca. -18 Hz can be
measured, which is diagnostic of geminal coupling of the
CH2 group linked to CO.
The above results suggest that the stereocontrol is not
yet fully effective during the second sequence of CO and
styrene insertion. To check this finding, we have exam-
ined the 13C resonance of the terminal methyl of the
copolymer by measuring long-term accumulations spec-
tra with high signal to-noise ratio: it was possible to
detect again two different resonances, at 29.6 and 30.3
ppm. The weakest signal at 29.6 was assigned to the
isotactic chain end by comparison with an authentic
sample of highly isotactic copolymer prepared with an
isospecific catalyst.3b The intensity ratio of the two
signals observed for the chain-end methyl groups of the
copolymers is the same of that already observed in the
complex 9; therefore, the syndiotactic terminal config-
uration is, in both cases, more abundant than the
isotactic configuration. All of this evidence suggests that
in the case of our catalytic system the mechanism of
chain-end stereocontrol is not fully working in the first
steps of the copolymerization. However, considering the
high stereoregularity of the obtained syndiotactic co-

2180 Organometallics, Vol. 20, No. 11, 2001
Carfagna et al.
pulse program, with irradiation times of 2-4 s and power on
the order of 32-36 dB (low scale). 13C NMR spectra were
measured at 50 MHz with a multinuclear 10 mm probehead.
1H and 13C NMR spectra chemical shifts are referred to the
residual proton or carbon resonance of the deuterated solvents
relative to TMS. Editing of 13C NMR was obtained from DEPT
spectra.
polymer together with the absence of ll triads, undoubt-
edly such a mechanism becomes more effective in the
next steps of the copolymerization. This might be
ascribed to the increased length of the polymer chain
on the last inserted chiral CH carbon, which enhances
the asymmetric induction.
The molecular weights (Mw) of copolymers and the molecular
weight distributions (Mw/Mn) were determined by gel perme-
ation chromatography versus polystyrene standards. The
analyses were recorded on a Bruker HPLC (model LC-22) with
an Alltech macrosphere GPC 60 Å column and chloroform as
solvent (flow rate 0.5 mL/min). The CO/styrene copolymer was
dissolved as follows: 3 mg of the sample was solubilized with
120 µL of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and chlo-
roform was added up to 10 mL, while the CO/p-methylstyrene
copolymer was directly soluble in chloroform. The statistical
calculations were performed using the Bruker Chromstar
software program.
Con clu sion s
The catalytic system based on R-diimine Pd(II) com-
plex 2, in dichloromethane, affords regio- and stereo-
regular alternating copolymers of carbon monoxide with
styrene or p-methylstyrene. The reaction can be carried
out at low temperature and 1 bar carbon monoxide. The
yield can be slightly enhanced by use of the p-methyl-
styrene comonomer. The structure of the copolymer
resulted from NMR to be more than 92% syndiotactic.
Starting from our catalytic system we were able to
identify the methyl carbonyl complex 6 as the active
species for the initial olefin insertion. Moreover, it was
possible to monitor the first steps of copolymerization
through stoichiometric reactions. Insertion of the first
olefin monomeric unit was observed by isolating a five-
membered palladacycle, of which the fully characterized
structure gave experimental support to the 2,1-mech-
anism of enchainment.
The intermediate 7 was proved, through spectroscopic
evidence, to be able to insert carbon monoxide and a
further olefin unit, thus resulting in the first dyad of
the growing chain. Multiplicity of the NMR spectra,
observed for complex 9, was attributed to the presence
of both u and l configurations. This unexpected finding
suggests that the chain-end stereocontrol mechanism
is not fully effective at this stage of the copolymerization
reaction. However, considering the high stereoregularity
of the syndiotactic copolymer, together with the absence
of the ll triad, undoubtedly such a mechanism becomes
effective in the next steps of copolymerization.
(i-C3H7-DAB)P d (CH3)Cl (1). To a solution of 0.348 g (2.49
mmol) of i-C3H7-DAB in 8 mL of dichloromethane was added
a solution of 0.600 g (2.26 mmol) of (COD)Pd(CH3)Cl in 6 mL
of the same solvent. The solution was stirred overnight at room
temperature. After filtration through Celite, the solution was
evaporated in a vacuum and the brownish oil was washed with
hexane, yielding 1 as a yellow powder (0.643 g, 2.16 mmol,
96%). IR (film, cm-1): 1637.3, 1582.2 (CdN). IR (CH2Cl2, cm-1):
1635.2, 1577.4 (CdN). 1H NMR (CDCl3): δ 8.13 (s br, 1H,
3
CHdN), 8.00 (s br, 1H, CHdN), 4.37 (dsept, J ) 6.5 Hz and
4J ) 1.2 Hz, 1H, CH(CH3)2), 4.26 (dsept, J ) 6.5 and 1.2 Hz,
1H, CH(CH3)2), 1.43 (d, J ) 6.5 Hz, 6H, CH(CH3)2), 1.37 (d, J
) 6.5 Hz, 6H, CH(CH3)2), 1.06 (s, 3H, Pd-CH3). 13C NMR
(CDCl3): δ 160.0, 155.2 (CdN); 59.1, 56.6 (CH(CH3)2); 22.7,
22.2 (CH(CH3)2), 0.1 (Pd-CH3). Anal. Calcd for C9H19ClN2Pd:
C, 36.38; H, 6.45; N, 9.43. Found: C, 36.37; H, 6.59; N, 9.44.
[(i-C3H7-DAB)P d (CH3)NCCH3]+[BAr ′4]- (2). To a solution
containing 0.247 g (0.83 mmol) of 1 in 7 mL of dichlo-
romethane/acetonitrile (5:1) cooled to -40 °C was added a
dichloromethane/acetonitrile (5:1) solution (7 mL) containing
[{3,5-(CF3)2C6H3}4B]-Na+ (0.738 g, 0.83 mmol). The reaction
mixture was slowly warmed to 0 °C, stirred for 15 min, and
filtered through Celite to remove NaCl. After evaporation in
a vacuum a dark oil was obtained, which upon treatment with
hexane (6 mL) at -80 °C gave 2 as a yellow powder (0.916 g,
0.79 mmol, 95%). IR (Nujol, cm-1): 2330.7, 2302.9 (CH3CN),
1610.1 (CdN). 1H NMR (CDCl3): δ 7.92 (s br, 1H, CHdN),
Last, all the examined complexes showed fluxional
behavior with different free energy barriers depending
on the pattern of the substituents. Moreover, in some
cases it was possible to observe a definite lowering of
the activation energy by addition of ligand excess to the
solution, such as acetonitrile and carbon monoxide.
7.85 (s br, 1H, CHdN), 7.70 (double q of q, 4J HH ) 2.5 Hz 4J HCF
3
6
) 2.5 J HCF ) 0.6, 8H, Ar-H0), 7.55 (m br, 4H, Ar-Hp), 4.07
3
(sept, J ) 6.6 and 1.2 Hz, 1H, CH(CH3)2), 3.78 (sept, J ) 6.6
and 1.2 Hz, 1H, CH(CH3)2), 2.35 (s, 3H, CH3CN); 1.29 (d, J )
6.5 Hz, 6H, CH(CH3)2), 1.21 (d, J ) 6.5 Hz, 6H, CH(CH3)2),
1.05 (s, 3H, Pd-CH3). 13C NMR (CDCl3, -10 °C): δ 163.1, 157.0
Exp er im en ta l Section
All manipulations were carried out under a nitrogen atmo-
sphere and using Schlenk techniques. CP grade chemicals
were used as received unless otherwise stated. Solvents were
dried by standard methods and freshly distilled under nitro-
gen. CDCl3 was degassed and stored over 3 Å molecular sieves.
1,4-Diisopropyl-1,4-diazabuta-1,3-diene13 and [{3,5-(CF3)2-
C6H3}4B]-Na+ 14 were synthesized as previously reported in
the literature. Carbon monoxide (Cp grade 99.99%) was
supplied by Air Liquide.
Elemental analyses (C, H, N) were carried out with a Fisons
Instruments 1108 CHNS-O elemental analyzer. Infrared
spectra were measured as Nujols mulls between KBr disks or
as films or in dichloromethane solution in the range 4000-
600 cm-1 on a Bruker IFS-48 FT-IR spectrometer. 1H NMR
spectra were measured on a Bruker AC200 spectrometer
operating at 200.13 MHz with a selective 5 mm probehead.
NOE measurements were performed using a Bruker noemult
1
(CdN), 161.6 (q, J CB ) 49.9 Hz, Ar-Ci), 134.8 (Ar-Co); 128.8
2
4
(double q, J CF ) 31.4 Hz, J CF ) 2.8 Hz, Ar-Cm), 124.5 (q,
1J CF ) 272.5 Hz, CF3), 122.6 (CH3CN), 117.6 (Ar-Cp), 62.0, 57.4
(CH(CH3)2), 22.2, 21.8 (CH(CH3)2), 5.0 (Pd-CH3); 3.3 (CH3CN).
Anal. Calcd for C43H34BF24N3Pd: C, 44.30; H, 2.94; N, 3.60.
Found: C, 44.19; H, 3.03; N, 3.54.
P oly(1-oxo-2-p h en yltr im eth ylen e) (3a ). The copolymer-
ization reaction was carried out in a thermostated Schlenk
flask equipped with a carbon monoxide gas line and a tank
for the CO. The complex 2 (0.195 g, 0.167 mmol) was dissolved
at 0 °C in dichloromethane saturated with CO, and it was
allowed to react for 30 min. The color of the solution changed
from pale yellow to orange-yellow, then styrene (4.8 mL, 41.7
mmol) was added (olefin/palladium molar ratio 250:1); the
solution was kept under CO at 0 °C. Within 6 h the solution
started to darken slightly; after 24 h the resulting gray
polymer was precipitated by adding methanol (30 mL) and
washed with methanol. To remove metallic palladium traces,
it was redissolved in 1,1,1,3,3,3,-hexafluoro-2-propanol, diluted
(13) Kliegman, J . M.; Barnes, R. K. Tetrahedron 1970, 26, 2555.
(14) (a) Bahr, S. R.; Boudjouk, P. J . Org. Chem. 1992, 57, 5545. (b)
Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992, 11, 3920.

Syndiotactic CO/ Styrene Copolymerization
Organometallics, Vol. 20, No. 11, 2001 2181
with dichloromethane, and filtered through Celite. After
precipitation with methanol, washing with methanol and
ether, and drying under vacuum, 1.75 g of copolymer (98 g of
polymer/g Pd) was collected. This copolymerization reaction
can also be carried out at room temperature (18 °C), but in
this case the polymer yield decreases. IR (film, cm-1): 1695
(7 mL) of 4 (0.240 g, 0.20 mmol). After filtration through Celite
and evaporation of the solvent at -15 °C in a vacuum a yellow
solid was obtained, which was dissolved in dichloromethane,
reprecipitated, and washed with hexane at -15 °C to yield 6
as a white powder (0.210 g, 0.18 mmol, 90%). IR (Nujol, cm-1):
2130 (Pd-CO), 1610 (CdN). 1H NMR (CDCl3, -20 °C): δ 7.96
(s, 1H, CHdN), 7.92 (s, 1H, CHdN), 7.69 (s, 8H, Ar′-Ho); 7.54
(s, 4H, Ar′-Hp), 4.13 (sept, 1H, CH(CH3)2), 3.77 (sept, 1H,
CH(CH3)2), 1.36 (s, 3H, Pd-CH3), 1.25 (d, J ) 6.7 Hz, 12H,
CH(CH3)2). 13C NMR (CD2Cl2, 0 °C): δ 174.8 (Pd-CO), 165.8,
1
(CO). H NMR (CDCl3, 17 °C): δ 7.20-6.60 (m, 5H, Ph), 4.09
(t, J ) 6.8 Hz, 1H, CH-CH2); 3.08 (dd, J ) 17.8 Hz e 7.3 Hz,
1H, CH-CH2), 2.65 (dd, J ) 17.8 Hz e 6.8 Hz, 1H,CH-CH2).
13C NMR (CDCl3/(CF3)2CHOH, 50:50) 45 °C: δ 210.7 (CO);
136.2 (Ph-Cipso); 129.9, 128.9, 128.5 (Ph-Co,m,p); 54.6 (CH-CH2);
43.5 (CH-CH2). Anal. Calcd for (C9H8O)n: C, 81.79; H, 6.10.
Found: C, 81.51; H, 6.06.
1
160.1 (CdN), 161.5 (q, J CB ) 49.6 Hz, Ar′-Ci), 134.6 (Ar′-Co),
2
1
128.7 (q, J CF ) 30.0 Hz, Ar′-Cm), 124.3 (q, J CF ) 272.5 Hz,
CF3); 117.5 (Ar′-Cp); 63.4, 56.3 (CH(CH3)2), 22.7, 21.8 (CH-
(CH3)2), 5.7 (Pd-CH3). Anal. Calcd for C42H31BF24N2OPd: C,
43.76; H, 2.71; N, 2.43. Found: C, 43.74; H, 2.62; N, 2.53.
[(i-C3H7DAB)P d CH(p -CH 3-P h )CH 2C(O)CH 3]+[BAr ′4]-
(7). To a solution of 6 (0.166 g, 0.144 mmol) in 2 mL of
dichloromethane, cooled to -15 °C, was added p-methylstyrene
(0.018 g, 0.151 mmol); the orange solution formed was slowly
warmed at 25 °C and then 5 mL of n-hexane was added. The
resulting oil was washed with n-hexane and then dried in a
vacuum to yield 7 as a red powder (0.176 g, 0.138 mmol, 96%).
IR (Nujol, cm-1): 1721 (CO-CH3), 1610 (CdN). 1H NMR
(CDCl3, -3 °C): δ 7.80 (s, 1H, CHdN), 7.78 (s, 1H, CHdN),
7.71 (s, 8H, Ar′-Ho), 7.54 (s, 4H, Ar′-Hp), 7.2 (d, J ) 7.9 Hz,
2H, Ph-Ho, Ph-Hm), 7.0 (d, J ) 7.9 Hz, 2H, Ph-Ho, Ph-Hm), 3.88
(sept, 1H, CH(CH3)2), 3.68 (sept, 1H, CH(CH3)2), 3.76 (dd, J )
8.3 and 3.5 Hz, 1H, CH-CH2), 3.04 (dd, J ) 19.5 and 8.3 Hz,
1H, CH-CH2), 2.70 (dd, J ) 19.5 and 3.5 Hz, 1H, CH-CH2),
2.39 (s, 3H, CO-CH3), 2.19 (s, 3H, Ph-CH3), 1.29, 1.17, 1.09
(3d, J ) 6.4 Hz, 12H, CH(CH3)2). 13C NMR (CDCl3, -20 °C): δ
P oly(1-oxo-2-(4-m eth yl)p h en yltr im eth ylen e) (3b). The
copolymer 3b was obtained according to the procedure de-
scribed above. To a solution of 2 (0.176 g, 0.151 mmol) in 15
mL of dichloromethane saturated with CO, kept for 30 min at
0 °C, was added p-methylstyrene (5 mL, 38 mmol). The
polymerization was carried out for 24 h. The resulting copoly-
mer was precipitated by adding methanol (30 mL) and then
washed with methanol. To remove Pd traces, the copolymer
was redissolved in chloroform, filtered through Celite, pre-
cipitated with methanol, washed with methanol and ether, and
dried under vacuum to yield 1.87 g of copolymer (116 g of
polymer/g Pd). IR (film, cm-1): 1707 (CO). 1H NMR (CDCl3,
17 °C): δ 6.75 (d, J ) 7.9 Hz, 2H, Ph), 6.55 (d, J ) 7.9 Hz, 4H,
Ph), 4.05 (t, J ) 6.8 Hz, 1H, CH-CH2), 3.02 (dd, J ) 17.6 Hz
e 6.8 Hz, 1H, CH-CH2), 2.60 (dd, J ) 17.6 Hz e 6.8 Hz, 1H,
CH-CH2), 2.20 (s, 3H, Ph-CH3). 13C NMR (CDCl3/(CF3)2CHOH,
50:50) 45 °C: δ 210.9 (CO), 138.5 (Ph-Cp), 133.0 (Ph-Cipso),
130.4, 128.7 (Ph-Co,m), 54.3 (CH-CH2), 43.4 (CH-CH2), 20.9
(Ph-CH3). Anal. Calcd for (C10H10O)n: C, 82.16; H, 6.89.
Found: C, 82.46; H, 7.02.
1
224.9 (COCH3), 161.7 (q, J CB ) 49.2 Hz, Ar′-Ci), 161.2, 157.1
(CdN), 139.9 (Ph-Ci), 134.8 (Ar′-Co), 132.1 (Ph-Co), 130.8
(Ph-Cp), 128.8 (q, 2J CF ) 31.5 Hz, Ar′-Cm), 124.5 (q, 1J CF ) 272.4
Hz, CF3), 119.9 (Ph-Cm), 117.6 (Ar′-Cp), 62.1, 59.5 (CH(CH3)2),
52.0 (CH-CH2), 47.0 (CH-CH2), 29.2 (COCH3), 22.8, 22.0, 21.4,
21.3 (CH(CH3)2), 21.9 (Ph-CH3). Anal. Calcd for C51H41BF24N2-
OPd: C, 48.19; H, 3.25; N, 2.20. Found: C, 48.01; H, 3.22; N,
2.14.
[(i-C3H7-DAB)P d (COCH3)CO]+[BAr ′4]- (4). A 0.159 g
(0.54 mmol) sample of 1 and 0.475 g (0.54 mmol) of [{3,5-
(CF3)2C6H3}4B]-Na+ were suspended at -40 °C under CO
atmosphere in 8 mL of dichloromethane previously saturated
with CO. The reaction mixture was slowly warmed at 0 °C,
stirred for 1 h, and filtered through Celite to remove NaCl.
After evaporation of the solvent by bubbling CO, an oil was
obtained, which, upon treatment with hexane saturated with
CO, gave 4 as a yellow powder (0.578 g, 0.49 mmol, 92%). IR
[(i-C3H 7-DAB)P d (COCH (p -CH 3-P h )CH 2COCH 3)CO]+-
[BAr ′4]- (8). To a CDCl3 solution (0.6 mL) of 6 (38 mg, 0.03296
× 10-3 mol), at -40 °C, was added 4.8 µL (0.03626 × 10-3 mol)
of p-methylstyrene. After a few minutes, the solution was
warmed to 0 °C, whereupon it changed color from yellow to
red. Bubbling of CO at -40 °C for 4 min finally resulted in
the yellow solution of 8. Complex 8 was stable only in solution
and for a few hours, which precludes elemental analysis. IR
(CDCl3, cm-1): 2126 (Pd-CO); 1718.7 br (CO), 1610 (CdN). 1H
NMR (CDCl3, -20 °C): δ 7.71 (s, 2H, CHdN), 7.63 (s, 8H, Ar′-
Ho), 7.47 (s, 4H, Ar′-Hp), 7.10 (s, 4H, Ph-Ho, Ph-Hm), 4.54 (dd,
J ) 10.7 and 2.4 Hz, 1H, CH-CH2), 3.67 (br s, 2H, CH(CH3)2),
3.50 (dd, J ) 18.6 and 10.7 Hz, 1H, CH-CH2), 2.67 (dd, J )
18.6 and 2.4 Hz, 1H, CH-CH2), 2.19 (s, 3H, Ph-CH3), 2.15 (s,
3H, CO-CH3), 0.97 (d, J ) 6.4 Hz, 12H, CH(CH3)2). 13C NMR
(CDCl3, -48 °C): δ 211.2, 206.6 (CO-CH3, CO-CH), 171.5
1
(Nujol, cm-1): 2137 (Pd-CO), 1750 (COCH3), 1611 (CdN). H
NMR (CD2Cl2, -75 °C): δ 7.98 (s, 1H, CHdN), 7.92 (s, 1H,
CHdN), 7.65 (s, 8H, Ar′-Ho), 7.47 (s, 4H, Ar′-Hp), 3.72 (m br,
2H, CH(CH3)2), 2.67 (s, 3H, COCH3), 1.10 (d, J ) 6.1 Hz, 12H,
CH(CH3)2). 13C NMR (CD2Cl2, -75 °C): δ 214.5 (COCH3), 172.9
1
(Pd-CO), 164.1, 160.5 (CdN), 162.1 (q, J CB ) 49.4 Hz, Ar′-
2
Ci), 134.9 (Ar′-Co), 128.9 (q, J CF ) 31.4 Hz, Ar′-Cm), 124.7 (q,
1J CF ) 272.6 Hz, CF3), 117.9 (Ar′-Cp), 63.8, 59.5 (CH(CH3)2),
41.6 (COCH3), 23.2, 22.0 (CH(CH3)2). Anal. Calcd for C43H31
-
BF24N2O2Pd: C, 43.73; H, 2.65; N, 2.37. Found: C, 43.54; H,
2.77; N, 2.23.
[(i-C3H7-DAB)P d (COCH3)Cl] (5). A 0.201 g (0.68 mmol)
sample of 1 was dissolved at -20 °C under CO atmosphere in
3 mL of dichloromethane previously saturated with CO. The
solution was slowly warmed to 20 °C, stirred for 15 min, and
then filtered through Celite to remove metallic Pd traces. After
evaporation of solvent by bubbling CO at 0 °C, an orange solid
was obtained, which was washed with hexane and dried and
shown to be compound 5 (0.216 g, 0.66 mmol, 98%). IR (Nujol,
cm-1): 1700 (Pd-COCH3). 1H NMR (CDCl3, -30 °C): δ 8.05
(s, 1H, CHdN), 7.95 (s, 1H, CHdN), 4.04 (sept, J ) 6.4 Hz,
2H, CH(CH3)2), 2.62 (s, 3H, COCH3), 1.38 (d, J ) 6.4 Hz, 6H,
CH(CH3)2), 1.29 (d, J ) 6.4 Hz, 6H, CH(CH3)2). 13C NMR
(CDCl3, -28 °C): δ 229.0 (COCH3), 158.8, 155.9 (CdN), 60.5,
59.4 (CH(CH3)2), 36.2 (COCH3), 22.1 (CH(CH3)2). Anal. Calcd
for C10H19ClN2OPd: C, 36.94; H, 5.89; N, 8.62. Found: C,
37.05; H, 6.08; N, 8.65.
1
(Pd-CO), 163.2, 159.2 (CdN), 161.7 (q, J CB ) 49.5 Hz, Ar′-
Ci), 140.4 (Ph-Cp), 134.4 (Ar′-Co), 130.9, 129.5 (Ph-Co,m), 128.8
2
1
(q, J CF ) 31.1 Hz, Ar′-Cm), 124.2 (q, J CF ) 272.8 Hz, CF3),
117.7 (Ar′-Cp), 62.9, 59.8 (CH(CH3)2), 61.6 (CH-CH2), 45.9
(CH-CH2), 29.7 (CO-CH3), 22.1 (CH(CH3)2), 21.3 (Ph-CH3).
+
3
[(i-C H7-DAB)P d ((COCH(p-CH3-P h )CH2)2COCH3)CO] -
[BAr ′4]- (9). To a CDCl3 solution (0.8 mL) of 6, [(i-C3H7DAB)-
Pd(CH3)CO]+[BAr′4]- (84.2 mg, 0.0730959 × 10-3 mol), at -20
°C, was added 10.0 µL of p-methylstyrene (0.07675 × 10-3 mol).
After bubbling CO and subsequent addition of p-methylstyrene
(9.6 µL, 0.0730959 × 10-3 mol), and bubbling CO at -40 °C,
the solution was left 16 h at -14 °C to yield compound 9, which
is stable only in solution. IR (CDCl3, cm-1): 2126 (Pd-CO), 1716
(br, CO), 1610 (CdN). 1H NMR (CD2Cl2, -25 °C): δ 7.89 (s,
1H, CHdN), 7.82 (s, 1H, CHdN), 7.68 (s, 8H, Ar′-Ho), 7.50 (s,
4H, Ar′-Hp), 7.27-6.40 (m, 8H, Ph-Ho, Ph-Hm); 4.20 (dd, J ≈
[(i-C3H7DAB)P d (CH3)CO]+[BAr ′4]- (6). Nitrogen gas was
bubbled at -15 °C for 10 min in a dichloromethane solution

2182 Organometallics, Vol. 20, No. 11, 2001
Carfagna et al.
11 and 3 Hz, 1H, CH-CH2), 4.10, 4.05 (2 dd, J ≈ 11 and 3 Hz,
1H, CH-CH2), 3.85 (br, 2H, CH(CH3)2), 3.72-3.25 (m, 2H,
CH-CH2), 2.80-2.50 (m, 2H, CH-CH2), 2.31, 2.25, 2.18, 2.10,
2.07 (5s, 9H, Ph-CH3 and CO-CH3), 1.30-0.99 (m, 12H,
CH(CH3)2). 13C NMR (CDCl3, -20 °C): δ 209.2, 208.6, 208.2,
207.9, 207.8, 207.6 (CO-CH3, CO-CH), 172.7, 171.9 (Pd-CO),
29.6 (CO-CH3), 22.7, 22.1, 22.0, 21.6 (Ph-CH3), 20.9 br
(CH(CH3)2).
Ack n ow led gm en t. This work was supported by the
Ministero dell’Universita` e della Ricerca Scientifica
(MURST-Rome) grant no. 9803026360 and grant no.
MM03027791. We would like to thank Ms. Anna Rita
Pierleoni for her technical assistance.
1
157.4, 156.8 (CdN), 161.4 (q, J CB ) 49.6 Hz, Ar′-Ci); 140.1,
140.0, 139.8, 139.7 (Ph-Cp), 134.5 (Ar′-Co), 130.6-129.5
2
1
(Ph-Co,m,i), 128.6 (q, J CF ) 32.6 Hz, Ar′-Cm), 124.3 (q, J CF
)
272.9 Hz, CF3), 117.4 (Ar′-Cp), 61.7, 59.8 (CH(CH3)2), 60.9,
52.5, 52.1 (CH-CH2), 46.8, 46.3, 44.7, 44.3 (CH-CH2), 29.9,
OM000971N