Studies of ligand and solvent effects in the alternating copolymerization of carbon monoxide and ethene by palladium-diphosphine catalysis

Article abstract of DOI:10.1021/om020461o

The ligand and solvent effects in the alternating copolymerization of carbon monoxide and ethene were studied by palladium-diphosphine catalysis. The methyl precursors exhibited comparable values of both intrinsic activity and energy barriers to migratory

Full text of DOI:10.1021/om020461o

Organometallics 2002, 21, 4965-4977
4965
Stu d ies of Liga n d a n d Solven t Effects in th e Alter n a tin g
Cop olym er iza tion of Ca r bon Mon oxid e a n d Eth en e by
P a lla d iu m -Dip h osp h in e Ca ta lysis
Claudio Bianchini,* Andrea Meli, Gaby Mu¨ller, Werner Oberhauser, and
Elisa Passaglia
Istituto di Chimica dei Composti Organometallici (ICCOM)-CNR,
Via J . Nardi 39, 50132 Firenze, Italy
Received J une 10, 2002
The Pd(II) methyl complexes [Pd(Me)(MeCN)(P-P)]PF6 are effective catalyst precursors
for the alternating copolymerization of carbon monoxide with ethene in CH2Cl2 (P-P ) 1,3-
bis(diphenylphosphino)propane (dppp), meso-2,4-bis(diphenylphosphino)pentane (meso-bdpp),
rac-2,4-bis(diphenylphosphino)pentane (rac-bdpp)). The productivity in high molecular weight
polyketones within 30 min follows the ligand order dppp > meso-bdpp > rac-bdpp. All the
methyl precursors exhibit comparable values of both intrinsic activity and energy barriers
to migratory insertions [Pd(Me)(CO), Pd(COMe)(C2H4)] as well as opening of â-chelates [Pd-
(CH2CH2C(O)Me)(P-P)]+ by CO. It is concluded that the presence and/or stereochemistry
of methyl groups in the 1,3-positions of dppp do not exert a significant influence on the
propagation rate of the copolymerization reaction in CH2Cl2. High-pressure NMR studies
under catalytic conditions show the occurrence of chain transfer by protonolysis with
adventitious water to give µ-hydroxo compounds [Pd(µ-OH)(P-P)]22+. With time, the bis-
chelates [Pd(P-P)2]2+ are the only species visible on the NMR time scale. Independent
copolymerization reactions in CH2Cl2 with either µ-OH or bis-chelate precursors show that
both resting states can reenter the catalysis cycle to give alternating polyketones with
2+
productivities increasing in the orders [Pd(µ-OH)(rac-bdpp)]22+ < [Pd(µ-OH)(meso-bdpp)]2
< [Pd(µ-OH)(dppp)]22+, and [Pd(rac-bdpp)2]2+ < [Pd(dppp)2]2+ < [Pd(meso-bdpp)2]2+. On the
basis of the batch reactions and in situ NMR experiments it is suggested that both µ-hydroxo
and bis-chelate compounds contribute appreciably to determine the overall productivity of
the methyl precursors [Pd(Me)(MeCN)(P-P)]+ in CH2Cl2. The bis-chelates are also active
catalysts for the CO/ethene copolymerization in MeOH with productivities that increase in
the ligand order dppp , rac-bdpp < meso-bdpp.
In tr od u ction
in the copolymerization of CO and ethene in MeOH
(P-P ) 1,3-bis(diphenylphosphino)propane (dppp), meso-
2,4-bis(diphenylphosphino)pentane (meso-bdpp), rac-2,4-
bis(diphenylphosphino)pentane (rac-bdpp); OTs ) p-tol-
uenesulfonate). The precursor with meso-bdpp proved
significantly more active than those containing dppp
and rac-bdpp, yet all catalysts gave perfectly alternating
polyketones (alt-E-CO) with relatively low molecular
weight (Mn ranging from 10 to 20 kg mol-1) (Scheme
1).3
In situ HPNMR studies of the three catalytic systems
showed neither deactivation by autoionization of the
precursors4,5 nor different resting states on the NMR
time scale. The greater productivity of the meso-bdpp
catalyst was not rationalized but empirically related to
two experimental observables: (i) Cyclic voltammetry
The alternating copolymerization of carbon monoxide
and ethene is a reaction of remarkable fundamental and
industrial relevance that Pd(II) compounds stabilized
by chelating diphosphine ligands catalyze in different
phase variation systems.1,2 Therefore, increasing re-
search efforts are being paid to both design more
efficient Pd-diphosphine catalysts and understand in
depth the mechanism(s) by which the copolymerization
proceeds.2
We have recently found that methyl substituents in
the 1,3-positions of the ligand backbone affect remark-
ably the catalytic activity of Pd(OTs)2(P-P) precursors
(1) (a) Drent, E. Eur. Pat. Appl. 121965A2, 1984; Chem. Abstr. 1985,
102, 46423. (b) Drent, E.; van Broekhoven, J . A. M.; Doyle, M. J .
Organomet. Chem. 1991, 417, 235. (c) Shell, Carilon Thermoplastic
Polymers, Information Sheet, 1994. (d) Eur. Plastics News 1995,
October, 57. (e) Ash, C. E. Int. J . Polym. Mater. 1995, 30, 1.
(2) (a) Sen, A. Acc. Chem. Res. 1993, 26, 303. (b) Drent, E.;
Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663. (c) Drent, E.; van
Broekhoven, J . A. M.; Budzelaar, P. H. M. In Applied Homogeneous
Catalysis with Organometallic Compounds; Cornils, B., Herrmann, W.
A., Eds.; VCH: Weinheim, 1996; Vol. 1, p 333. (d) Sommazzi, A.;
Garbassi, G. Prog. Polym. Sci. 1997, 22, 1547. (e) Nozaki, K.; Hijama,
T. J . Organomet. Chem. 1999, 576, 248. (f) Bianchini, C.; Meli, A.
Coord. Chem. Rev. 2002, 225, 35.
(3) (a) Bianchini, C.; Lee, H. M.; Meli, A.; Moneti, S.; Vizza, F.;
Fontani, M.; Zanello, P. Macromolecules 1999, 32, 4183. (b) Bianchini,
C.; Lee, H. M.; Barbaro, P.; Meli, A.; Moneti, S.; Vizza, F. New J . Chem.
1999, 23, 929.
(4) Bianchini, C.; Lee, H. M.; Meli, A.; Oberhauser, W.; Peruzzini,
M.; Vizza, F. Organometallics 2002, 21, 16.
(5) (a) J arrett, P. S.; Sadler, P. J . Inorg. Chem. 1991, 30, 2098. (b)
Angulo, I. M.; Bouwman, E.; Lutz, M.; Mul, W. P.; Spek, A. L. Inorg.
Chem. 2001, 40, 2073. (c) Angulo, I. M.; Bouwman, E.; Lok, S. M.; Lutz,
M.; Mul, W. P.; Spek, A. L. Eur. J . Inorg. Chem. 2001, 1465.
10.1021/om020461o CCC: $22.00 © 2002 American Chemical Society
Publication on Web 10/18/2002

4966 Organometallics, Vol. 21, No. 23, 2002
Bianchini et al.
Sch em e 1
was connected to a gas reservoir to maintain a constant
pressure over the catalytic reactions. Deuterated solvents for
routine NMR measurements were dried over molecular sieves.
1H, 13C{1H}, and 31P{1H} NMR spectra were obtained on either
a Bruker ACP 200 (200.13, 50.32, and 81.01 MHz, respectively)
or a Bruker DPX 300 spectrometer (300.13, 75.49, and 121.51
MHz, respectively). All chemical shifts are reported in ppm
(δ) relative to tetramethylsilane, referenced to the chemical
shifts of residual solvent resonances (1H, 13C) or 85% H3PO4
(31P). The 10 mm sapphire NMR tube was purchased from
Saphikon (Milford, NH), while the titanium high-pressure
charging head was constructed at the ISSECC-CNR (Firenze,
Italy).10 Caution: Since high gas pressures are involved, safety
precautions must be taken at all stages of studies involving
high-pressure NMR tubes. GC analyses of the solutions were
performed on a Shimadzu GC-14 A gas chromatograph equipped
with a flame ionization detector and a 30 m (0.25 mm i.d., 0.25
µm film thickness) SPB-1 Supelco fused silica capillary column.
GC/MS analyses were performed on a Shimadzu QP 5000
apparatus equipped with a SPB-1 Supelco fused silica capillary
column. Elemental analyses were performed using a Carlo
Erba Model 1106 elemental analyzer. Infrared spectra were
recorded on a Perkin-Elmer 1600 Series FT-IR spectropho-
tometer. Melting points were determined in glass capillaries
under air. The intrinsic viscosity (η) for selected polyketone
samples was obtained as the average value of Huggins and
Kraemer inherent viscosities in 1,1,1,3,3,3-hexafluoropropan-
2-ol (HFIP) at 25 °C using a standard capillary viscosity-
measuring device. Thermogravimetric analyses (TGA) of se-
lected polyketone samples were obtained with a Mettler Toledo
(STARe Thermal Analysis) apparatus (STARe software) coupled
to a TGA/SDTA 851e instrument. The analyses were run from
25 to 600 °C, with a scanning rate of 10 °C/min and a nitrogen
flow of 60 mL/min. Materials and apparatus for electrochem-
istry have been described elsewhere.11 Potential values are
referred to the saturated calomel electrode (SCE). Under the
present experimental conditions the one-electron oxidation of
ferrocene occurs at E°′ ) +0.39 V.
showed the meso-bdpp precursor to undergo a chemi-
cally reversible Pd(II)/Pd(I) one-electron reduction prior
to be reduced to Pd(0), whereas the dppp and rac-bdpp
complexes were irreversibly reduced. Therefore, it was
suggested that the oxidant cocatalyst 1,4-benzoquinone
(BQ), necessary to oxidize inactive Pd(0) to Pd(II) sites,2
could be more efficient for the meso precursor than for
the dppp and rac-bdpp ones.3a (ii) NMR spectroscopy
showed the meso-bdpp complex to adopt in solution a
chair conformation with the four phenyl groups spatially
disposed on either side of the PPdP coordination plane,
while the dppp and rac-bdpp complexes exhibited a
skewphos conformation with the phenyl groups diago-
nally positioned with respect to the same plane. Whether
and to what extent this different steric situation might
affect chain transfer and/or propagation was not clari-
fied, however.3a
In this paper are reported the results obtained from
an in-depth study of the catalytic performance of several
Pd(II) complexes stabilized by dppp, rac-bdpp, and meso-
bdpp. These include methyl precursors, resting states,
and byproducts derived from chain transfer. Moreover,
energy barriers associated with relevant propagation
steps in model copolymerization intermediates have
been determined. This study has allowed us to unravel
the role of various Pd(II)-diphosphine compounds that
may form during CO/ethene copolymerization reactions
in either CH2Cl2 or MeOH as well as make a step
forward in the design of more efficient catalysts.
Exp er im en ta l Section
All reactions and manipulations were carried out under an
atmosphere of nitrogen by using Schlenk-type techniques.
Diethyl ether and tetrahydrofuran (THF) were distilled from
LiAlH4. Reagent grade methanol or CH2Cl2 (CD2Cl2) freshly
distilled from CaH2 was used in the copolymerization reactions.
All the other reagents and solvents were used as purchased
from Aldrich, Fluka, or Strem. The ligand meso-bdpp3a and
the palladium complexes PdCl2(COD),6a PdCl(Me)(COD)6b
(COD ) cycloocta-1,5-diene), [PdCl(Me)(dppp)]7 (1), [Pd(Me)-
r a c-CH2(CH3CHOTs)2. A solution of p-toluenesulfonic acid
chloride (50 g, 262 mmol) in 80 mL of pyridine was slowly
added to a solution of 2,4-pentanediol (mixture of isomers) (10
g, 96 mmol) in 20 mL of pyridine, cooled to 0 °C. The reaction
mixture was stirred at 0 °C for 30 min and then at room
temperature overnight. The excess of p-toluenesulfonic acid
chloride was hydrolyzed by addition of 100 mL of water at 0
°C. A further 300 mL of CH2Cl2 and 200 mL of water were
added. The organic layer was separated and washed with
water, diluted hydrochloric acid and water, and dried over Na2-
SO4. The solvent was removed under reduced pressure to give
a 2:1 (meso:rac) mixture of the tosylates. The rac-isomer (3 g)
was obtained in >98% purity (1H NMR integration) by
treatment of the crude product with 4 × 20 mL of diethyl ether
and 3 × 10 mL of acetone. Anal. Calcd for C19H24O6S2: C,
55.35; H, 5.82. Found: C, 56.00; H, 5.90. 1H NMR (CDCl3):
8
(MeCN)(dppp)]BF48 (4BF 4), [Pd(CH2CH2C(O)Me)(dppp)]SbF6
(7SbF 6), and PdCl2(dppp) (10)9 were prepared following lit-
erature methods. All of the isolated solid samples were
collected on sintered-glass frits and washed with appropriate
solvents before being dried under
a stream of nitrogen.
Copolymerization reactions were performed with a 250 mL
stainless steel autoclave, constructed at the ICCOM-CNR
(Firenze, Italy), equipped with a magnetic drive stirrer and a
Parr 4842 temperature and pressure controller. The autoclave
(6) (a) Drew, D.; Doyle, J . R. Inorg. Synth. 1972, 13, 52. (b) Ru¨lke,
R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van Leeuwen, P. W.
N. M.; Vrieze, K. Inorg. Chem. 1993, 16 (9), 5972.
3
3
1.23 (d, J (HH) ) 6.3 Hz, 6H, CH3CH), 1.87 (t, J (HH) ) 6.0
(7) Dekker: G. P. C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M. Organometallics 1992, 11, 1598.
(8) Shultz, C. S.; Ledford, J .; DeSimone, J . M.; Brookhart, M. J . Am.
Chem. Soc. 2000, 122, 6351.
(10) Bianchini, C.; Meli, A.; Traversi, A. Ital. Pat. FI A000025, 1997.
(11) Fabrizi de Biani, F.; Laschi, F.; Zanello, P.; Ferguson, G.;
Trotter, J .; O’Riordan, G. M.; Spalding, T. R. J . Chem. Soc., Dalton
Trans. 2001, 1520.
(9) Sanger, A. R. J . Chem. Soc., Dalton Trans. 1979, 1971.

Palladium-Diphosphine Catalysis
Organometallics, Vol. 21, No. 23, 2002 4967
Hz, 2H, CH2), 2.45 (s, 6H, CH3-Ar), 4.70 (m, 2H, CHCH3),
7.34 (d, J (HH) ) 8.3 Hz, 4H, Ar), 7.80 (d, J (HH) ) 8.3 Hz,
4H, Ar).
40.8 (d, 2J (PP) ) 53.2 Hz), 8.0 (d). 1H NMR (CDCl3): δ 0.58
(dd, 3H, 3J (PH) ) 7.1 Hz, 3J (PH) ) 2.15 Hz, PdCH3), 1.09 (dd,
3H, 3J (PH) ) 12.2 Hz, 3J (HH) ) 7.1 Hz, CHCH3), 1.21 (dd,
3H, 3J (PH) ) 15.5 Hz, J (HH) ) 7.0 Hz, CHCH3), 1.91 (m, 2H,
CH2), 2.05 (s, 3H, MeCN), 2.73 (m, 1H, CHCH3), 2.88 (m, 1H,
CHCH3), 7.30-7.83 (m, 20H, Ar). IR (Nujol mull, KBr
plates): (MeCN) 2317, 2289 cm-1, (BF4) 1055 cm-1. Anal. Calcd
for C32H36BF4NP2Pd: C, 55.74; H, 5.22; N, 2.03. Found: C,
55.85; H, 5.32; N, 2.15. 6P F 6: 31P{1H} NMR (CD2Cl2): δ 40.8
3
3
r a c-2,4-Bis(d ip h en ylp h osp h in o)p en ta n e (r a c-bd p p ).3a
BuLi (7.80 mL, 12.5 mmol) was added to a solution of
diphenylphosphine (2.18 mL, 12.5 mmol) in 50 mL of THF,
cooled to 0 °C. The solution was stirred for 10 min, and then
a solution of the rac-tosylate (2.46 g, 6 mmol) in 20 mL of THF
was added and the reaction mixture was stirred at room
temperature for 2 h. Water (2 mL) was added, and the solvent
was removed under reduced pressure. CH2Cl2 and water were
added (100 mL each), and the organic layer was separated.
The water layer was extracted with 2 × 50 mL of CH2Cl2, and
the combined organic layers were dried over Na2SO4. Evapora-
2
1
(d, J (PP) ) 52.7 Hz), 8.0 (d). H NMR (CD2Cl2): δ 0.53 (dd,
3
3
3H, J (PH) ) 7.0 Hz, J (PH) ) 2.1 Hz PdCH3), 1.05 (dd, 3H,
3J (PH) ) 11.8 Hz, 3J (HH) ) 7.0 Hz, CHCH3), 1.18 (dd, 3H,
3J (PH) ) 15.7 Hz, 3J (HH) ) 7.1 Hz, CHCH3), 1.89 (m, 2H,
CH2), 1.92 (s, MeCN), 2.70 (m, 1H, CHCH3), 2.90 (m, 1H,
CHCH3), 7.33-7.80 (m, 20H, Ar). IR (Nujol mull, KBr
plates): (MeCN) 2317, 2289 cm-1, (PF6) 839 cm-1. Anal. Calcd
for C32H36F6NP3Pd: C, 51.41; H, 4.81; N, 1.87. Found: C,
51.54; H, 4.90; N, 1.95.
tion of the solvent left
a colorless oil, which contained
exclusively rac-bdpp and impurities of phosphine oxides.
Overall yield: 2.36 g (90%). All our attempts to crystallize the
diphosphine were unsuccessful.
[P d (CH2CH2C(O)Me)(m eso-bd p p )]BF 4 (8BF 4). A solution
of 5BF 4 (70 mg, 0.1 mmol) in 2 mL of CH2Cl2 was transferred
into a 10 mm o.d. sapphire tube which was pressurized to 20
bar of CO at room temperature. The gas was vented off, and
the reaction mixture was cooled to - 20 °C. Acetonitrile (20
µL) was added, and the residual CO was removed from the
solution by bubbling nitrogen for 2 min. The tube was
pressurized with ethene (20 bar) at -20 °C. The gaseous phase
was vented off, and the solution was transferred to a Schlenk
tube. The solvent was evaporated under reduced pressure at
-20 °C to leave a brownish oil. 31P{1H} NMR (CD2Cl2): δ 42.2
P d Cl(Me)(P -P ) (P -P ) m eso-bd p p , 2; r a c-bd p p , 3). To
a stirred solution of PdCl(Me)(COD) (0.13 g, 0.50 mmol) in CH2-
Cl2 (20 mL) was added 1 equiv of diphosphine (0.50 mmol) at
room temperature. After 2 h stirring, the solvent was reduced
to 5 mL under reduced pressure, and 15 mL of 1:1 diethyl
ether/petroleum ether was added to the reaction mixture to
complete the precipitation of the product, which was filtered
off, washed with petroleum ether, and dried in a nitrogen
stream. Yield: 80-90%. 2: 31P{1H} NMR (CD2Cl2): δ 42.0 (d,
J (PP) ) 47.0 Hz), 15.5 (d). 1H NMR (CD2Cl2): δ 0.41 (dd,
3J (PH) ) 3.5 Hz, 3J (PH) ) 7.7 Hz, 3H, PdCH3), 0.95 (dd,
3J (HH) ) 7.1 Hz, 3J (PH) ) 10.4 Hz, 3H, CHCH3), 1.05 (dd,
3J (HH) ) 7.3 Hz, 3J (PH) ) 12.6 Hz, 3H, CHCH3), 1.85 (m,
2H, CH2), 2.53 (m, 2H, CHCH3), 7.3-8.0 (m, 20H, aromatic
protons). Anal. Calcd for C30H33ClP2Pd: C, 60.34; H, 5.52.
Found: C, 60.60, 5.54. 3: 31P{1H} NMR (CD2Cl2): δ 39.6 (d,
2J (PP) ) 50.5 Hz), 7.1 (d).1H NMR (CD2Cl2): δ 0.47 (dd, 3H,
3J (PH) ) 7.8 Hz, 3J (PH) ) 3.4 Hz, PdCH3), 0.96 (dd, 3H,
3J (PH) ) 11.8 Hz, 3J (HH) ) 7.1 Hz, CHCH3), 1.12 (dd, 3H,
3J (PH) ) 14.3 Hz, 3J (HH) ) 7.2 Hz, CHCH3), 1.91 (m, 2H,
CH2), 2.64 (m, 1H, CHCH3), 2.87 (m, 1H, CHCH3), 7.25-7.94
(m, 20H, Ar). Anal. Calcd for C30H33ClP2Pd: C, 60.34; H, 5.52.
Found: C, 60.52; H, 5.70.
1
(d, J (PP) ) 52.2 Hz), 15.8 (d). H NMR (CD2Cl2): δ 1.05 (dd,
3
3
3H, J (HP) ) 12.07 Hz, J (HH) ) 7.06 Hz, CHCH3), 1.11 (dd,
3H, 3J (HP) ) 15.14 Hz, 3J (HH) ) 8.17 Hz, CHCH3), 1.34 (tdd,
2H, 3J (HP) ) 8.0 Hz, 3J (HP) ) 1.94 Hz, 3J (HH) ) 6.72 Hz,
PdCH2), 1.89 (m, 2H, CH2), 2.26 (s, 3H, CH3CO), 2.74 (m, 2H,
CHCH3), 3.08 (td, 2H, 3J (HH) ) 6.0 Hz, 4J (PH) ) 6.5 Hz, CH2-
CO), 7.37-7.93 (m, 20H, Ar). IR (Nujol mull, KBr plates): ν-
(CdO) 1626 cm-1. Anal. Calcd for C33H37BF4OP2Pd: C, 56.26;
H, 5.25. Found: C, 56.32; H, 5.30.
[P d (CH2CH2C(O)Me)(r a c-bd p p )]SbF 6 (9SbF 6). PdCl(M-
e)(rac-bdpp) (0.169 mmol) was dissolved in 2 mL of CH2Cl2
and transferred into a 10 mm sapphire tube, which was then
pressurized to 20 bar of CO. After 3 min the tube was
immersed into a cooling bath (at -20 °C) and the CO pressure
was released. The residual CO was removed from the solution
by bubbling a gentle stream of nitrogen through the solution
for 7 min. The solution was transferred into a Schlenk tube
cooled to -20 °C, and a stream of ethene was bubbled through
the solution for 5 min. The reaction mixture was maintained
at -20 °C while AgSbF6 (0.186 mmol) was added. The silver
chloride was separated by filtration through cotton wool.
Removal of the solvent under reduced pressure at -10 °C left
a brownish solid. 31P{1H} NMR (CD2Cl2): δ 39.6 (d, J (PP) )
[P d (Me)(MeCN)(P -P )]Y [P -P ) m eso-bd p p , Y ) BF 4
(5BF 4), P F 6 (5P F 6); P -P ) r a c-bd p p , Y ) BF 4 (6BF 4), P F 6
(6P F 6)]. A solid sample of either AgBF4 or AgPF6 (0.50 mmol)
was added to a magnetically stirred solution of the appropriate
PdCl(Me)(P-P) complex (0.45 mmol) in a 10:1 (v:v) mixture
of CH2Cl2/MeCN. After 1 h stirring at room temperature, AgCl
was removed by filtration on Celite. The resultant colorless
solution was concentrated to ca. 2 mL under reduced pressure.
Addition of a 1:10 (v:v) mixture of diethyl ether/n-hexane (20
mL) led to the precipitation of a brownish solid, which was
filtered off, washed with petroleum ether, and dried in a
nitrogen stream. Yield: 50-60%. 5BF 4: 31P{1H} NMR (CDCl3):
δ 41.2 (d, 2J (PP) ) 51.1 Hz), 15.5 (d). 1H NMR (CDCl3): δ 0.46
1
3
54.5 Hz), 8.3 (d). H NMR (CD2Cl2): δ 1.08 (dd, 3H, J (PH) )
15.2 Hz, 3J (HH) ) 7.2 Hz, CHCH3), 1.21 (dd, 3H, 3J (PH) )
7.6 Hz, 3J (HH) ) 3.6 Hz, CHCH3), 1.34 (tdd, 2H, 3J (HH) )
6.4 Hz, 3J (PH) ) 2.2 Hz, 3J (PH) ) 7.3 Hz, PdCH2), 1.8 (m,
2H, CH2), 2.33 (s, 3H, CH3CO), 2.90 (m, 2H, CHCH3), 3.12 (td,
2H, 3J (HH) ) 6.4 Hz, 4J (PH) ) 6.8 Hz, CH2CO), 7.11-8.10
3
3
(dd, 3H, J (PH) ) 2.3 Hz, J (PH) ) 7.2 Hz, PdCH3), 1.08 (dd,
3H, 3J (HH) ) 7.2 Hz, 3J (PH) ) 14.3 Hz, CHCH3), 1.10 (dd,
3H, 3J (HH) ) 7.2 Hz, 3J (PH) ) 11.8 Hz, CHCH3), 1.90 (m,
2H, CH2), 2.03 (s, 3H, MeCN), 2.70 (m, 1H, CHCH3), 2.87 (m,
1H, CHCH3), 7.3-7.9 (m, 20H, aromatic protons). IR (Nujol
(m, 20H, Ar). IR (Nujol mull, KBr plates): ν(CdO) 1632 cm-1
.
mull, KBr plates): (MeCN) 2318, 2290 cm-1, (BF4) 1060 cm-1
.
Anal. Calcd for C33H37F6OSbP2Pd: C, 46.44; H, 4.33. Found:
C, 46.52; H, 4.40.
Anal. Calcd for C32H36BF4NP2Pd: C, 55.75; H, 5.22; N, 2.03.
Found: C, 55.90; H, 5.30; N, 2.20. 5P F 6: 31P{1H} NMR (CD2-
P d Cl2(P -P ) (P -P ) m eso-bd p p , 11; r a c-bd p p , 12).
PdCl2(COD) (135 mg, 0.47 mmol) was added to a solution of
the chelating diphosphine (0.47 mmol) in 20 mL of CH2Cl2.
The solution was stirred at room temperature for 1 h and then
reduced to 2 mL in vacuo. A 1:1 (v:v) mixture of diethyl ether
and petroleum ether was added to the remaining solution,
which separated a pale yellow microcrystalline product. This
was filtered off, washed with a small amount of n-hexane, and
dried under a stream of dry nitrogen. Yields: 85-90%. 11: 31P-
2
1
Cl2): δ 41.7 (d, J (PP) ) 50.8 Hz), 15.6 (d). H NMR (CD2Cl2):
δ 0.46 (dd, 3H, 3J (PH) ) 2.2 Hz, 3J (HP) ) 7.1 Hz, PdCH3),
1.04 (dd, 3H, 3J (PH) ) 13.8 Hz, 3J (HH) ) 6.9 Hz, CHCH3),
1.10 (dd, 3H, 3J (PH) ) 12.0 Hz, 3J (HH) ) 7.1 Hz, CHCH3),
1.92 (s, 3H, MeCN), 1.85 (m, 2H, CH2), 2.63 (m, 1H, CHCH3),
2.78 (m, 1H, CHCH3), 7.31-7.87 (m, 20H, Ar). IR (Nujol mull,
KBr plates): (MeCN) 2317, 2290 cm-1, (PF6) 839 cm-1. Anal.
Calcd for C32H36F6NP3Pd: C, 51.41; H, 4.81; N, 1.87. Found:
C, 51.60; H, 4.95; N, 1.90. 6BF 4: 31P{1H} NMR (CDCl3): δ
1
{1H} NMR (CDCl3): δ 29.7 (s). H NMR (CDCl3): δ 1.04 (dd,

4968 Organometallics, Vol. 21, No. 23, 2002
Bianchini et al.
6H, 3J (PH) ) 14.1 Hz, 3J (HH) ) 7.0 Hz, CHCH3), 2.20 (m,
2H, CH2), 2.60 (m, 2H, CHCH3), 7.20-7.98 (m, 20H, Ar). Anal.
Calcd for C29H30Cl2P2Pd: C, 56.40; H, 4.85. Found: C, 56.52;
H, 4.80. 12: 31P{1H} NMR (CDCl3): 24.9 (s). 1H NMR
(CDCl3): 1.09 (dd, 6H, 3J (PH) ) 14.2 Hz, 3J (HH) ) 6.9 Hz,
CHCH3), 2.23 (m, 2H, CH2), 2.65 (m, 2H, CHCH3), 7.27-7.96
(m, 20H, Ar). Anal. Calcd for C29H30Cl2P2Pd: C, 56.40; H, 4.85.
Found: C, 56.50; H, 4.70.
bath. After the unreacted gases were released, the insoluble
copolymer was filtered off, washed with CH2Cl2, and dried in
a vacuum oven at 70 °C overnight. Anal. Calcd for (COCH2-
CH2)n: C, 64.3; H, 7.2. Found: C, 64.1; H, 7.1. IR (powder
sample in KBr pellet): 3391 (w), 2912 (m), 1694 (vs), 1408 (s),
1
1333 (s), 1259 (m), 1056 (s), 811 (m), 592 (m) cm-1. H NMR
(HFIP-d2): δ 2.85 (s, CH2C(O)CH2). 13C{1H} NMR (HFIP-d2):
δ 213.6 (CH2C(O)CH2), 36.0 (CH2C(O)CH2). Melting points:
260-263 °C (catalyst precursor 4P F 6), 262-264 °C with
decomposition (5P F 6), 258-260 °C (6P F 6). Intrinsic viscosity
values for samples obtained in 30 min: 25.7 dL g-1 (catalyst
precursor 4P F 6), 5.0 dL g-1 (5P F 6), 7.3 dL g-1 (6P F 6).
B. HP NMR Exp er im en ts. The reactions were followed by
variable-temperature 31P{1H} and 1H NMR spectroscopy.
Details of the procedure are exemplified for 4P F 6. A 10 mm
sapphire HPNMR tube was charged under nitrogen with a
solution of the methyl acetonitrile complex (1.77 × 10-2 mmol)
in CD2Cl2 (freshly distilled under nitrogen from CaH2, 2 mL)
and then placed into the NMR probe at room temperature.
After 31P{1H} and 1H NMR spectra were acquired, the tube
was pressurized with a 1:1 mixture of CO/ethene to 40 bar at
room temperature. NMR spectra were recorded at room
temperature, 50 °C, and 70 °C. After 1 h at 70 °C, the probe-
head was cooled to room temperature and the internal pres-
sure was released. A gray precipitate of Pd metal was found
in the NMR tube together with the copolymer. The solution
was shown to contain the bis-chelate complex 16 together with
traces of the binuclear µ-OH complex 13.
R ea ct ion of t h e â-Ch ela t es 7Sb F 6, 8BF 4, a n d 9Sb F 6
w ith Wa ter F ollow ed by Rea ction of th e F or m ed µ-OH
Com p lexes w ith CO/Eth en e. A 10 mm sapphire NMR tube
was charged with a solution of a â-chelate complex (0.01 mmol)
in 2 mL of CD2Cl2 under nitrogen. After the 31P{1H} NMR
spectrum was acquired at room temperature, the tube was
removed from the NMR probe and 20 µL of H2O was syringed
under nitrogen into it. The results of this investigation have
been discussed in a previous section.
Cop olym er iza t ion of E t h en e a n d Ca r bon Mon oxid e
Ca ta lyzed by th e µ-OH Com p lexes 13-15 a n d th e Bis-
ch ela te Com p lexes 16-18 in CH2Cl2 or MeOH. Au tocla ve
Exp er im en ts. The catalytic activity of the µ-OH binuclear
complexes was tested in 30 min experiments following a
procedure analogous to that employed for the methyl aceto-
nitrile complexes.
[P d (OH)(P -P )]2(P F 6)2 (P -P ) d p p p , 13; m eso-bd p p ,
cis-/tr a n s-14; r a c-bd p p , cis-/tr a n s-15). Solid AgPF6 (184.3
mg,0.729 mmol) was added to a CH2Cl2 (30 mL) solution of
the appropriate PdCl2(P-P) complex (0.33 mmol) at room
temperature. After AgCl was removed by filtration, KOBut
(40.5 mg, 0.33 mmol) dissolved in 1 mL of water was added
under vigorous stirring. After 30 min, the solvent was removed
under reduced pressure and the solid residue was treated with
20 mL of CH2Cl2. The CH2Cl2 phase was passed through Celite,
and the resulting clear yellow solution was concentrated to 5
mL under reduced pressure. Addition of a 1:1 mixture of
diethyl ether and n-hexane led to the precipitation of a
microcrystalline solid, which was filtered off, washed with
diethyl ether, and dried in a stream of nitrogen. Yield: 45-
1
50%. 13: 31P{1H} NMR (CDCl3): δ 15.2 (s). H NMR (CDCl3):
δ -2.42 (s, 2H, PdOH), 2.09 (m, 4H, CH2), 2.68 (m, 8H, CH2P),
7.33-7.50 (m, 40H, Ar). IR (Nujol mull, KBr plates): v(OH)
3587 cm-1. Anal. Calcd for C54H54F12O2P6Pd2: C, 47.65; H, 3.97.
Found: C, 47.72; H, 3.93. cis-/tr a n s-14: 31P{1H}NMR (CD2-
Cl2): δ 29.5 (s, 70%), 32.8 (s, 30%). 1H NMR (CD2Cl2): δ -2.52
(s, 2H, PdOH), -2.39 (s, 2H, PdOH), 1.11 (m, 12H, CH3), 2.05
(m, 4H, CH2), 2.84 (m, 4H, CHP), 7.11-7.68 (m, 40H, Ar). IR
(Nujol mull, KBr plates): ν(OH) 3597 cm-1. Anal. Calcd for
C
58H62F12O2P6Pd2: C, 49.16; H, 4.37. Found: C, 49.32; H, 4.44.
cis-/tr a n s-15: 31P{1H}NMR (CD2Cl2): δ 27.3 (s, 40%), 27.7
1
(s, 60%). H NMR (CD2Cl2): δ -2.46 (s, 2H, PdOH), -2.41 (s,
2H, PdOH), 1.19 (m, 12H, CH3), 2.06 (m, 4H, CH2), 2.77 (m,
4H, CHP), 7.24-7.66 (m, 40H, Ar). IR (Nujol mull, KBr
plates): ν(OH) 3599 cm-1. Anal. Calcd for C58H62F12O2P6Pd2:
C, 49.16; H, 4.37. Found: C, 49.09; H, 4.40.
[P d (P -P )2](P F 6)2 (P -P ) d p p p , 16; m eso-bd p p , cis-/
tr a n s-17; r a c-bd p p , cis-/tr a n s-18). PdCl2(P-P) (0.47 mmol)
in 30 mL of a 10:1 mixture of CH2Cl2/MeCN was reacted with
AgPF6 (0.94 mmol). The resulting mixture was stirred for 1 h,
then it was filtered through Celite. One equivalent of the
appropriate diphosphine ligand was added to this solution,
which was stirred at room temperature for 15 min. The solvent
was removed under reduced pressure, leaving a solid product.
This was recrystallized by CH2Cl2/n-hexane. Yields: 45-55%.
16: 31P{1H} NMR (CD2Cl2): δ -1.9 (s). Anal. Calcd for
In Situ Ca r bon yla tion of th e Meth yl Aceton itr ile
Com p lexes 4-6BF 4. HP NMR Exp er im en ts. In a typical
experiment, the methyl acetonitrile complex (0.035 mmol) was
dissolved in 2 mL of deoxygenated CD2Cl2, and the resulting
solution was then transferred into a 10 mm sapphire tube.
After 31P{1H} and 1H NMR spectra of this sample were
acquired at room temperature, the NMR probe-head was
C
54H52F12P6Pd: C, 53.13; H, 4.26. Found: C, 53.20; H, 4.30.
cis-/tr a n s-17: 31P{1H} NMR (CD2Cl2): δ 14.2 (s, 13%), 12.2
(s, 87%). Anal. Calcd for C58H60F12P6Pd: C, 54.56; H, 4.70.
Found: C, 54.50; H, 4.60. cis-/tr a n s-18: 31P{1H} NMR (CD2-
Cl2): δ 21.7 (s, 17%), 17.4 (s, 83%). Anal. Calcd for C58H60F12P6-
Pd: C, 54.56; H, 4.70. Found: C, 54.65; H, 4.55.
1
cooled to -80 °C. 31P{1H} and H NMR spectra were recorded
at this temperature. The sapphire tube was removed from the
spectrophotometer, immersed into an ethanol/liquid nitrogen
thermostat bath (-117 °C), and charged with 15 bar of CO.
After this procedure the tube was placed into the probe head
precooled to -80 °C. Irrespective of the diphosphine ligand,
the 31P{1H} and 1H NMR spectra showed the quantitative
conversion of the starting methyl acetonitrile complex into the
corresponding methyl carbonyl derivative [Pd(Me)(CO)(P-P)]-
Cop olym er iza t ion of E t h en e a n d Ca r b on Mon oxid e
Ca ta lyzed by th e Meth yl Aceton itr ile Com p lexes 4-6P F 6
in CH2Cl2. A. Au tocla ve Exp er im en ts. Typically, under a
nitrogen atmosphere, a 100 mL solution of CH2Cl2 (freshly
distilled under nitrogen from CaH2) containing the catalyst
precursor (0.01 mmol) was introduced into a 250 mL autoclave
equipped with a magnetic drive stirrer and a temperature and
pressure controller. The autoclave was charged with 20 bar of
CO and 20 bar of ethene. After the contents of the autoclave
had been brought to 70 °C, the pressure was maintained at
ca. 40 bar by continuous feeding of an equimolar mixture of
ethene and CO from a high-pressure gas reservoir connected
to the autoclave. A pressure gauge connected to the gas
reservoir was employed to determine the gas consumption
during the reactions. The reaction mixture was then stirred
(1400 rpm) for the desired time. The reaction was stopped by
cooling the autoclave to room temperature using an ice-water
1
BF4 (selected 31P{1H} and H NMR data of the methyl carbonyl
complexes 19-21 are reported in Tables 1 and 2, respectively).
Afterward the probe temperature was gradually increased and
1
31P{1H} and H NMR spectra were recorded at each intermedi-
ate temperature. Increasing the temperature converted each
methyl carbonyl complex into the corresponding carbonyl acyl
1
derivative [Pd(COMe)(CO)(P-P)]BF4 (selected 31P{1H} and H
NMR data of the carbonyl acyl complexes 22-24 are reported
in Tables 1 and 2, respectively). At the conversion temperature,
the decrease in concentration of the methyl carbonyl complex
was followed by 31P{1H} NMR spectroscopy. Spectra were

Palladium-Diphosphine Catalysis
Organometallics, Vol. 21, No. 23, 2002 4969
Ta ble 1. 31P {1H} NMR Ch em ica l Sh ifts (p p m ), (Mu ltip licity), a n d [P P Cou p lin g Con sta n ts] (Hz) for th e
P a lla d iu m Com p lexes [P d (X)(Y)(P -P )]0/+ in CD2Cl2 Solu tion s a t {T} in °C
X )Me
X ) COMe
Y ) CO
X ) COMe
Y ) Cl
X ) CO(CH2)2COMe
Y ) CO
P-P
dppp
Y ) CO
17.0 (d) [61.0]
-7.2 (d) {-80}
32.2 (d) [56.2]
12.1 (d) {-80}
30.0 (d) [58.0]
4.2 (d) {-80}
4.5 (d) [82.3]
-6.2 (d) {22}
24.0 (d) [78.3]
11.5 (d) {22}
19.0 (d) [78.1]
6.2 (d) {22}
12.0 (d) [72.2]
-9.0 (d) {22}
30.5 (d) [69.0]
12.4 (d) {22}
25.5 (d) [70.4]
4.4 (d) {22}
2.0 (d) [86.0]
-9.0 (d) {-70}
23.0 (d) [82.0]
7.8 (d) {-70}
18.0 (d) [74.5]
6.0 (d) {22}
meso-bdpp
rac-bdpp
Ta ble 2. 1H NMR Ch em ica l Sh ifts (p p m ) a n d Mu ltip licity for Selected Reson a n ces of th e P a lla d iu m
Com p lexes [P d (X)(Y)(P -P )]0/+ in CD2Cl2 Solu tion s a t {T} in °C
X )Me
X ) COMe
Y ) CO
X ) COMe
Y ) NCMe
X ) COMe
Y ) Cl
X ) (CO)(CH2)2COMe
Y ) CO
P-P
dppp
Y ) CO
0.48 (br s) Me
{-80}
1.95 (s) COMe
{22}
1.97 (s) COMe
{22}
1.85 (s) COMe
{22}
1.97 (s) COMe
2.14 (m) CH2CO
2.56 (m) Pd(CO)CH2
{-70}
1.97 (s) COMe
2.40 (m) CH2CO
2.99 (m) Pd(CO)CH2
{22}
1.97 (s) COMe
2.60 (m) CH2CO
2.91 (m) Pd(CO)CH2
{22}
meso-bdpp
rac-bdpp
0.50 (br s) Me
{-80}
1.98 (s) COMe
{22}
2.03 (s) COMe
{22}
1.65 (s) COMe
{-30}
0.60 (br s) Me
{-80}
2.00 (s) COMe
{0}
1.97 (s) COMe
{0}
1.81 (s) COMe
{22}
1
taken at intervals of 5-10 min, depending on conditions. The
reaction was followed for 2-3 half-lives. The experiment was
repeated with varying pressures of CO (5-25) to determine
the dependence of the reaction rate on the CO concentration.
The results indicated that the rate of the reaction is indepen-
dent of CO. According to first-order kinetics, the free energy
of activation was calculated as follows: ∆Gq ) RT(ln kr - ln
CH2C(O)Me)(CO)(P-P)]SbF6 to occur (selected 31P{1H} and H
NMR data of the carbonyl acyl complexes 28-30 are reported
in Tables 1 and 2, respectively). At the conversion temperature
the decrease in concentration of the methyl carbonyl complex
was followed by 31P{1H} NMR spectroscopy. Spectra were
taken at intervals of 5-10 min, depending on conditions. The
reaction was followed for 2-3 half-lives.
kT/h) with kr ) ln 2/t1/2
.
[P d (CH2CH2C(O)Me)(P -P )]SbF 6/[P d (COCH2CH2C(O)-
Me)(CO)(P -P )]SbF 6 Equ ilibr ia . Solutions of the carbonyl
acyl complexes 28-30, prepared as reported above in HPNMR
tubes, were immersed in a thermostat bath at -20 °C. CO was
released, and then couples of vacuum-nitrogen cycles were
applied. 31P{1H} and 1H NMR spectra of these samples
acquired at -20 °C allowed us to follow the transformation of
the carbonyl acyl complexes into the corresponding â-chelates
7-9SbF 6.
Attem p ted Deter m in a tion of th e Migr a tor y In ser tion
Ba r r ier s of [P d (COMe)(C2H4)(P -P )]SbF 6. Solid samples of
the chloride acyl complexes 25-27 (0.035 mmol) were prepared
by a procedure analogous to that reported above in an HPNMR
tube followed by evaporation of the solvent under vacuum.
AgSbF6 and CDCl2F/CD2Cl2 (1:1) were added to the tube cooled
to -130 °C under N2, immediately followed by pressurization
with ethene (15 bar) again at -130 °C. The tube was
introduced into a precooled NMR probe-head. Only the â-che-
lates 7-9SbF 6 were seen in the first NMR spectrum at -117
°C.
Gen er a tion a n d Ca r bon yla tion of th e â-Ch ela te Com -
p lexes 7-9SbF 6. HP NMR Exp er im en ts. In a typical experi-
ment, the chloride methyl complex PdCl(Me)(P-P) (0.035
mmol) was dissolved in 2 mL of deoxygenated CD2Cl2, and the
resulting solution was first transferred into a 10 mm sapphire
tube and then pressurized to 20 bar of CO at room tempera-
ture. Irrespective of the diphosphine, the quantitative forma-
tion of the corresponding chloride acyl complex PdCl(COMe)-
((P-P) occurred at room temperature (selected 31P{1H} and
1H NMR data of the chloride acyl complexes 25-27 are
reported in Tables 1 and 2, respectively). Once the chloride
acyl complex was obtained, the tube was removed from the
spectrometer and the excess CO was released. The tube was
then immersed into a thermostat bath at -20 °C, and nitrogen
was bubbled through the solution for 15 min to eliminate any
trace of CO. Ethene was bubbled through the solution main-
tained at -20 °C for 5 min, and then a solid sample of AgSbF6
(0.04 mmol) was added to the solution. The immediately
formed AgCl settled on the bottom of the tube. Irrespective of
the diphosphine ligand, the 31P{1H} and 1H NMR spectra of
this sample showed the quantitative conversion of the chloride
acyl complex into the corresponding â-chelate complex. After-
ward, the NMR probe-head was cooled to -90 °C, and 31P-
Resu lts
1
{1H} and H NMR spectra were recorded at this temperature.
Syn th esis of th e Meth yl Aceton itr ile Com p lexes
[P d (Me)(MeCN)(P -P )]Y [P -P ) d p p p , Y ) BF 4
(4BF 4), P F 6 (4P F 6); P -P ) m eso-bd p p , Y ) BF 4
(5BF 4), P F 6 (5P F 6); P -P ) r a c-bd p p , Y ) BF 4
(6BF 4), P F 6 (6P F 6)]. Methyl acetonitrile palladium
complexes with meso-bdpp and rac-bdpp were synthe-
sized following a procedure analogous to that previously
reported for the dppp derivatives.7 This involves the
treatment of the neutral complexes PdCl(Me)(meso-
bdpp) (2) and PdCl(Me)(rac-bdpp) (3) dissolved in a CH2-
Cl2/MeCN solution (10:1, v:v) with either AgBF4 or
AgPF6 as chloride scavenger. Concentration under
The sapphire tube was removed from the probe, and nitrogen
was bubbled through the solution at room temperature to
eliminate any trace of ethene. The sapphire tube was im-
mersed into an ethanol/liquid nitrogen thermostat bath (-117
°C) and charged with 20 bar of CO. After this procedure the
tube was placed into the probe-head precooled to -90 °C. 31P-
{1H} and 1H NMR spectra showed that the â-chelate complexes
were still present. Afterward the probe temperature was
gradually increased, and 31P{1H} and 1H NMR spectra were
recorded at each intermediate temperature. Increasing the
temperature caused the conversion of the â-chelate complex
into the corresponding carbonyl acyl derivative [Pd(COCH2-

4970 Organometallics, Vol. 21, No. 23, 2002
Bianchini et al.
A series of catalytic experiments lasting 30 min were
carried out using “wet” CH2Cl2 obtained by adding a
controlled amount of water (1%) to freshly distilled
solvent. The productivity trend was the same as in the
reactions performed in distilled CH2Cl2: dppp (2.6 kg
(g of Pd)-1) > meso-bdpp (2.4) . rac-bdpp (1.4); yet a
significant decrease in catalytic activity was observed
for the rac complex.
Irrespective of the ligand, the molecular weights of
the copolymers produced by the methyl acetonitrile
precursors in CH2Cl2 were much larger than those
obtained in MeOH with the bis-p-toluenesulfonate
precursors Pd(OTs)2(P-P) (Scheme 1).3a Indeed, we
could not determine the nature of the end groups by 1H
NMR spectroscopy in HFIP-d2.2,4,12 It is very likely that
all copolymers contain vinyl and ketone end groups due
to by â-H chain transfer and Pd-H initiation, respec-
tively,2,4,12 yet other end groups produced by adventi-
tious water (e.g., -COOH) might be present.2 Unlike
the polyketones obtained in MeOH (Scheme 1),3 the
materials produced in CH2Cl2 were significantly differ-
ent from each other, as indicated by their intrinsic
viscosities (η) of 25.7 (dppp), 5.0 (meso-bdpp), and 7.3
(rac-bdpp) dL g-1, respectively.2,12 Due to the limitations
of our GPC instrumentation, we were unable to deter-
mine the molecular weights of these copolymers. These
should have much longer polymer chains than those
produced in MeOH (Mn ) 10-20 kg mol-1), which were
F igu r e 1. Productivity expressed as kg of polyketone (g
of Pd)-1 vs chelating diphosphine ligand for the series of
precursors [Pd(Me)(MeCN)(P-P)]PF6 (P-P ) dppp, meso-
bdpp, rac-bdpp).
F igu r e 2. Plot of gas uptake vs time for copolymerization
reactions catalyzed by 4P F 6, 5P F 6, and 6P F 6.
reduced pressure and addition of diethyl ether/n-hexane
gave analytically pure samples of [Pd(Me)(MeCN)(P-
P)]Y (Y ) BF4, PF6), whose unambiguous identification
was achieved by both 31P{1H} (AM patterns) and 1H
NMR spectroscopy.7
featured by η values in the range 0.5-0.8 dL g-1 3a
.
The polyketone samples subjected to viscosity mea-
surements were also studied by thermogravimetric
analysis (TGA) under inert atmosphere. All samples
showed one degradation step with inflection points that,
although very similar, increased in the ligand order
meso-bdpp (389.9 °C) < rac-bdpp (400.6 °C) < dppp
(402.2 °C). The amount of residue recovered at 600 °C
was rather large for all samples (26% in weight for the
dppp and rac catalysts and 38% for the meso catalyst),
which reflects the occurrence of copolymer cross-linking
via radical pathways promoted by residual palladi-
um.12a,13
In Situ HP NMR Stu d y of th e Alter n a tin g Cop o-
lym er iza tion of Eth en e a n d Ca r bon Mon oxid e
Ca ta lyzed by [P d (Me)(MeCN)(P -P )]P F 6 P r ecu r -
sor s in CD2Cl2. The CO/ethene copolymerization reac-
tions catalyzed by 4P F 6, 5P F 6, and 6P F 6 were studied
in situ by means of HPNMR spectroscopy in 10 mm o.d.
sapphire tubes under experimental conditions compa-
rable to those of the batch reactions. In the NMR
experiments was employed a palladium concentration
higher than that in the batch reactions (ca. 10-2 vs 10-4
M) in order to acquire well-resolved NMR spectra in a
short residence time.3,4,14 The much higher concentra-
tion of Pd(II) precursor in the HPNMR studies as
compared to the batch reactions may have relevant
A cyclic voltammetry study was carried out on CH2-
Cl2 solutions of 4P F 6, 5P F 6, and 6P F 6 using [NBu4]PF6
as supporting electrolyte. Both 4P F 6 and 6P F 6 under-
went an irreversible two-electron reduction at Ep
)
-1.21 and -1.01 V, respectively. In contrast, the meso
complex 5P F 6 showed two separate, irreversible reduc-
tion processes at Ep ) -1.15 and -1.39 V.
Alter n a tin g Cop olym er iza tion of Eth en e a n d
Ca r bon Mon oxid e Ca ta lyzed by [P d (Me)(MeCN)-
(P -P )]P F 6 P r ecu r sor s in CH2Cl2. Complexes 4P F 6,
5P F 6, and 6P F 6 were employed as catalyst precursors
for the copolymerization of CO and ethene in freshly
distilled CH2Cl2 at 70 °C under a constant CO/ethene
pressure of 40 bar. The results of reactions lasting 30
min and 3 h are reported in Figure 1. The initial
copolymerization rates were estimated over three runs
measuring the gas uptake within the first 10 min
(Figure 2).
As illustrated in Figure 2, the initial rates were rather
similar for the three catalysts with a prevalence for the
dppp system; however, after only 6 min, the activity of
the meso catalyst surpassed that of the rac catalyst and
approached that of the dppp catalyst. Consistently, the
productivities (kg of polyketone (g of Pd)-1) of batch
reactions lasting 30 min were in the order dppp (2.8) >
meso-bdpp (2.5) > rac-bdpp (2.0), while after 3 h the
dppp and meso-bdpp catalysts were equally active and
(12) (a) Valli, V. L. K.; Alper, H. J . Polym. Sci., Part A: Polym. Chem.
1995, 33, 1715. (b) Koide, Y.; Bott, S. G.; Barron, A. R. Organometalllics
1996, 15, 2213. (c) Koide, Y.; Barron, A. R. Macromolecules 1996, 29,
1110. (d) Keim, W.; Maas, H. J . Organomet. Chem. 1996, 514, 271. (e)
Reddy, K. R.; Chen, C.-L.; Hung Liu, Y.-H.; Peng, S.-M.; Chen, J .-T.;
Liu, S.-T. Organometalllics 1999, 18, 2574. (f) Schwarz, J .; Herdtweck,
E.; Herrmann, W. A. Organometalllics 2000, 19, 3154. (g) Barlow, G.
K.; Boyle, J . D.; Cooley, N. A.; Ghaffar, T.; Wass, D. F. Organometalllics
2000, 19, 1470. (h) Braunstein, P., Fryzuk, M. D.; Le Dall, M.; Naud,
F.; Rettig, S.; Speiser, F. J . Chem. Soc., Dalton Trans. 2000, 1067.
(13) DeVito, S.; Bronco, S. Polym. Degrad. Stab. 1999, 63, 399.
produced much more polyketone (7.9-8.0 kg (g of Pd)-1
)
than the rac complex (5.1) (Figure 1). A comparison of
the productivities obtained after 30 min and 3 h showed
that all catalytic systems underwent deactivation with
time, yet the meso-bdpp catalyst proved to be the most
robust, as in 3 h its productivity was slightly better than
that of the dppp system.

Palladium-Diphosphine Catalysis
Organometallics, Vol. 21, No. 23, 2002 4971
pressurizing the tube to 40 bar with a 1:1 CO/ethene
mixture at room temperature, polyketone formation
occurred, while the methyl complex was converted first
to the known8,15 â-chelate [Pd(CH2CH2C(O)Me)(dppp)]+
(see below) and then to higher homologues [Pd(CH2-
CH2C(O)-chain)(dppp)]+, where “chain” is the propagat-
1
ing copolymer (trace b). By H NMR integration on a
spectrum acquired after 10 min, the average repeating
units of the chain have been estimated to be 11.2,4,8,15-17
1H NMR spectroscopy was also useful to confirm the
formation of the â-chelates, as all the methyl Pd(II)
precursors and the â-chelates are featured by a fortu-
itous coincidence of the 31P{1H} chemical shifts, with
different J (PP) values, however.
The â-chelates were the only phosphorus-containing
compounds visible on the NMR time scale up to 40 °C.
A new resonance (singlet at δ 15.3) appeared only at
50 °C in fact (trace c, recorded after 15 min at 50 °C).
An independent study showed this new signal to be due
to the µ-hydroxo complex [Pd(µ-OH)(dppp)]2(PF6)2 (13)
apparently formed by chain transfer with adventitious
water (see below).18a,b Increasing the temperature to 70
°C accelerated the formation of this complex, which was
the only species visible on the NMR time scale after 10
min (trace d). With time, however, the µ-hydroxo
complex decomposed to give the bis-chelate complex [Pd-
(dppp)2](PF6)2 (16) (singlet at δ -0.9, trace e) and
palladium metal.4,19,20 After 1 h at 70 °C, the bis-chelate
was the largely predominant species. This complex was
stable at room temperature (trace f) even after depres-
surizing the tube. Besides polyketone, some black pal-
ladium metal was recovered in the tube.
F igu r e 3. Variable-temperature 31P{1H} NMR study
(sapphire tube, CD2Cl2, 81.01 MHz) of CO/ethene copoly-
merization assisted by 4P F 6: (a) dissolving 4P F 6 in CD2-
Cl2 under nitrogen at room temperature; (b) after the tube
was pressurized with 40 bar of CO/ethene (1:1) at room
temperature; (c) after 15 min at 50 °C; (d) after 10 min at
70 °C; (e) after 60 min at 70 °C; (f) after the tube was
depressurized at room temperature.
The copolymerization reactions catalyzed by 5P F 6 and
6P F 6 (Figure 4) gave a NMR picture qualitatively
similar to that of 4P F 6; yet an important difference was
noticed in the higher stability to carbonylation of the
rac-bdpp µ-hydroxo complex [Pd(µ-OH)(rac-bdpp)]2+
.
The 31P{1H} NMR spectrum at room temperature
under nitrogen of 6P F 6 (AM pattern with δ 40.8 and
8.0, J (PP) ) 52.7 Hz) is shown in trace a. Pressurizing
the tube to 40 bar with a 1:1 mixture of carbon
monoxide/ethene at room temperature transformed the
methyl precursor into the â-chelate complexes [Pd(CH2-
CH2C(O)-chain)(rac-bdpp)]+ (AM pattern, δ 39.6, 8.3 and
J (PP) ) 54.5 Hz, number of average repeating units
after 10 min ) 7) and also gave the µ-hydroxo complex
[Pd(µ-OH)(rac-bdpp)]2(PF6)2 (cis-/tr a n s-15) as mixture
of cis and trans stereoisomers (broad resonance at δ 27.5
due to overlapping of two singlets, see below) (trace b).4
F igu r e 4. Variable-temperature 31P{1H} NMR study
(sapphire tube, CD2Cl2, 81.01 MHz) of CO/ethene copoly-
merization assisted by 6P F 6: (a) dissolving 6P F 6 in CD2-
Cl2 under nitrogen at room temperature; (b) after the tube
was pressurized with 40 bar of CO/ethene (1:1) at room
temperature; (c) after 10 min at 50 °C; (d) after 10 min at
70 °C; (e) after 60 min at 70 °C; (f) after the tube was
depressurized at room temperature.
effects in the kinetics of formation of some palladium
species during the catalysis (i.e., resting states and
degradation products).14 Nevertheless, the information
obtained in the HPNMR studies is generally valuable
for series of homologous compounds such as the present
Pd-methyl complexes.
(15) Zuideveld, M. A.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.;
Klusener, P. A. A.; Stil, H. A.; Roobeek, C. F. J . Am. Chem. Soc. 1998,
120, 7977.
(16) (a) Ozawa, F.; Hayashi, T.; Koide, H.; Yamamoto, A. J . Chem.
Soc., Chem. Commun. 1991, 1469. (b) Reddy, K. R.; Surekha, K.; Lee,
G.-H.; Peng, S.-M.; Chen, J .-T.; Liu, S.-T. Organometalllics 2001, 20,
1292.
(17) 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.
(18) (a) Pisano, C.; Consiglio, G.; Sironi, A.; Moret, M. J . Chem. Soc.,
Chem. Commun. 1991, 421. (b) Pisano, C.; Consiglio, G. Gazz. Chim.
It. 1994, 124, 393. (c) Longato, B.; Pilloni, G.; Valle, G.; Corain, B.
Inorg. Chem. 1988, 27, 956. (d) Bushnell, G. W.; Dixon, K. R.; Hunter,
R. G.; McFarland, J . J . Can. J . Chem. 1972, 50, 3694. (e) Cataldo, M.;
Nieddu, E.; Gavagnin, R.; Pinna, F.; Strukul, G. J . Mol. Catal. A:
Chem. 1999, 142, 305.
(19) Bianchini, C.; Mantovani, G.; Meli, A.; Oberhauser, W.;
Bru¨ggeller, P.; Stampfl, T. J . Chem. Soc., Dalton Trans. 2001, 690.
(20) Luo, H.-K.; Kou, Y.; Wang, X.-W.; Li, D.-G. J . Mol. Catal. 2000,
151, 91.
Selected 31P{1H} NMR spectra relative to the reac-
tions catalyzed by 4P F 6 and 6P F 6 are reported in
Figures 3 and 4.
The 31P{1H} NMR spectrum of 4P F 6 at room temper-
ature is shown in Figure 3 (trace a). Immediately after
(14) (a) Bianchini, C.; Herrera, V.; J ime´nez, M. V.; Meli, A.; Sa´nchez-
Delgado, R. A.; Vizza, F. J . Am. Chem. Soc. 1995, 117, 8567. (b)
Bianchini, C.; Fabbri, D.; Gladiali, S.; Meli, A.; Pohl, W.; Vizza, F.
Organometallics 1996, 15, 4604. (c) Bianchini, C.; J ime´nez, M. V.; Meli,
A.; Moneti, S.; Patinec, V.; Vizza, F. Organometallics 1997, 16, 5696.
(d) Bianchini, C.; Meli, A.; Patinec, V.; Sernau, V.; Vizza, F. J . Am.
Chem. Soc. 1997, 119, 4945. (e) Bianchini, C.; Meli, A.; Moneti, S.;
Oberhauser, W.; Vizza, F.; Herrera, V.; Fuentes, A.; Sa´nchez-Delgado,
R. A. J . Am. Chem. Soc. 1999, 121, 7071. (f) Bianchini, C.; Lee, H. M.;
Meli, A.; Vizza, F. Organometallics 2000, 19, 849.

4972 Organometallics, Vol. 21, No. 23, 2002
Bianchini et al.
appropriate chelating diphosphine.9,21a Then, the de-
sired µ-hydroxo complexes [Pd(µ-OH)(P-P)]2(PF6)2 (P-P
) dppp, 13; meso-bdpp, 14; rac-bdpp, 15) were obtained
as off-white crystals by treatment of the bis-chlorides
in CH2Cl2 with AgPF6, followed by reaction with an
aqueous solution of KOBut.18 In turn, the bis-chelates
[Pd(P-P)2](PF6)2 (P-P ) dppp, 16; meso-bdpp, 17; rac-
bdpp, 18) were prepared by reacting the bis-chlorides
10-12 with 2 equiv of AgPF6 in a CH2Cl2/MeCN
mixture, followed by addition of 1 equiv of the appropri-
ate diphosphine.4,19,20 As previously observed for analo-
gous meso- and rac-dppb compounds,4 both the µ-hy-
droxo and bis-chelate Pd(II) complexes with meso- and
rac-bdpp were formed as a mixture of stereoisomers
differing from each other by the orientation of the
methyl substituents in the ligand backbone (Scheme 3).
Unambiguous characterization of all new complexes
was achieved by multinuclear NMR spectroscopy as well
as comparisons with literature data on structurally
related compounds.4,7-9,15-21
Sch em e 2
The appearance of the â-chelates at room temperature
coincided with the formation of the copolymer product.
As the temperature was increased to 50 °C, the intensity
of the â-chelate signal decreased remarkably with
concomitant increase of the concentration of the µ-hy-
droxo complexes (trace c). The latter species were
apparently stable even at 70 °C (trace d). Only after 30
min at 70 °C did the formation of the bis-chelate
complexes cis/trans-[Pd(rac-bdpp)2](PF6)2 (cis-/tr a n s-
18) become appreciable (singlet at δ 17.5; the other
singlet is not observable due to the high noise/signal
ratio) and was accompanied by the formation of pal-
ladium metal. After 1 h at 70 °C, both the bis-chelate
and µ-hydroxo complexes were present in comparable
amounts (trace e), showing that the rac-bdpp catalytic
system diverges significantly from the dppp-based
system for the stability of the µ-hydroxo complexes
under copolymerization conditions.
Palladium â-chelate complexes have several impor-
tant roles in Pd(II)-assisted CO/ethene copolymeriza-
tions in either solutions or slurries of aprotic solvents.
Indeed, besides controlling the perfect alternating inser-
tion of the two comonomers,2 they have been shown to
be crucial compounds in the chain transfer by proto-
nolysis.15 Scheme 4 shows the role played by â-chelates
in this chain-transfer process and indirectly in the
formation of two resting states of palladium(II) during
the copolymerization, namely, the µ-hydroxo binuclear
complexes [Pd(µ-OH)(P-P)]22+ and the mononuclear bis-
chelates [Pd(P-P)2]2+ 4,15
In situ NMR experiments
.
proved the present â-chelates 7-9 to undergo the
reaction sequence illustrated in Scheme 4 upon heating
in either freshly distilled or “wet” CD2Cl2. The experi-
ments were carried out in high-pressure sapphire tubes
in order to study the further reactivity of the chain-
transfer µ-hydroxo products with CO/ethene.
Independent NMR experiments with isolated [Pd(µ-
OH)(P-P)]2(PF6)2 (13-15) showed these complexes to
decompose in CH2Cl2 to [Pd(P-P)2](PF6)2 (16-18) and
palladium metal when treated with 40 bar CO/ethene
at 70 °C (see below).
A 10 mm sapphire HPNMR tube was therefore
charged with a solution of a â-chelate complex in CD2-
Cl2 under nitrogen. The 31P{1H} NMR spectra recorded
at room temperature showed in all cases the exclusive
presence of the â-chelates. With time the â-chelates
disappeared with formation of several palladium prod-
ucts including the bis-chelates, the µ-hydroxo complexes,
and traces of palladium metal. After 15 h, GC/MS
analysis of the solution showed the presence of a ca. 4:1
mixture of methyl vinyl ketone and methyl ethyl ketone.
The formation of the latter product was ascribed to
traces of water in the solvent.4,15 Increasing the tem-
perature to 70 °C had the effect of only accelerating this
degradation process.
Syn th esis a n d Rea ctivity of P a lla d iu m (II) Com -
pou n ds Relevan t to P r opagation an d Ch ain Tr an s-
fer a n d th eir Use in HP NMR Ca ta lytic Exp er i-
m en ts. Several model compounds with relevance to
intermediate species in CO/ethene copolymerization
were synthesized in an attempt to rationalize the
catalytic performance of the dppp, meso-bdpp, and rac-
bdpp catalysts in CH2Cl2 as well as to elucidate the
results of in situ HPNMR studies.
Scheme 2 shows the two routes employed to isolate
the â-chelates [Pd(CH2CH2C(O)Me)(P-P)]+ as either
BF4- or SbF6- salts (P-P ) dppp, 7; meso-bdpp, 8; rac-
bdpp, 9). The procedure involving the removal of chlo-
ride from Pd(acyl)(chloride) compounds by AgSbF6 has
been developed by Brookhart and co-workers8 to syn-
thesize [Pd(CH2CH2C(O)Me)(dppp)]SbF6 (7SbF 6), while
the method involving Pd(acyl)(MeCN) intermediates to
synthesize 8BF 4 was designed by us to prepare the
â-chelates [Pd(CH2CH2C(O)Me)(P-P)]BF4 (P-P ) meso-
dppb, rac-dppb).4
When 20 µL of H2O was syringed under nitrogen into
the CD2Cl2 solutions of the â-chelates, 31P{1H} NMR
spectra showed the selective formation of the binuclear
2+
µ-OH species [Pd(µ-OH)(P-P)]2 in ca. 4 h at room
temperature and in ca. 10 min at 70 °C.
NMR tubes containing these solutions of µ-hydroxo
complexes were pressurized with ethene to 20 bar at
room temperature. No reaction was observed at 70 °C.
Then, the tubes were pressurized with 20 bar CO at
The bis-chloride complexes PdCl2(P-P) (P-P ) dppp,
10; meso-bdpp, 11; rac-bdpp, 12) were conveniently
prepared by the plain reaction of PdCl2(COD)6a with the
(21) (a) To´th, I.; Elsevier, C. J . Organometallics 1994, 13, 2118. (b)
To´th, I.; Elsevier: C. J . J . Am. Chem. Soc. 1993, 115, 10388. (c) To´th,
I.; Elsevier, C. J . J . Chem. Soc., Chem. Commun. 1993, 529.

Palladium-Diphosphine Catalysis
Organometallics, Vol. 21, No. 23, 2002 4973
Sch em e 3
Sch em e 4
room temperature. Only when the temperature was
increased to 70 °C did the µ-hydroxo compounds start
to transform into the corresponding bis-chelate com-
plexes. Notably, the dppp and meso-bdpp µ-hydroxo
complexes converted almost completely to the bis-
chelates in ca. 1 h at 70 °C, while ca. 50% conversion
was observed for the rac complex. At this point the
temperature was decreased to 20 °C, and the tubes were
removed from the spectrometer. The formation of polyke-
tone as a fluffy solid had occurred, while GC/MS
analysis of the filtrate revealed the presence of methyl
ethyl ketone.
F igu r e 5. Productivity expressed as kg of polyketone (g
of Pd)-1 vs chelating diphosphine ligand for the series of
precursors (a) [Pd(µ-OH)(P-P)]2(PF6)2; (b) [Pd(P-P)2](PF6)2
(P-P ) dppp, meso-bdpp, rac-bdpp). Reaction conditions:
solvent, CH2Cl2; time, 30 min.
The next step was to look at the bis-chelates 16-18
as potential catalyst precursors for the CO/ethylene
copolymerization in CH2Cl2. Indeed, we were aware of
a previous report showing that [Pd(dppp)2](TFA)2 (TFA
) trifluoroacetate) was active in MeOH.22 Therefore,
batch reactions were performed with the bis-chelates
16-18. Polyketone was obtained in all cases, albeit in
low yield, as the meso derivative gave 350 g of polyke-
tone (g of Pd)-1, while the rac complex was the least
efficient with 140 g (g of Pd)-1 (Figure 5b).
The mechanism through which Pd(II) µ-hydroxo rest-
ing states can re-enter the copolymerization catalytic
cycle has already been discussed.2,4 Active Pd-H moi-
eties have been proposed to form by the stepwise process
shown in Scheme 5a, which involves the cleavage of the
binuclear structure by CO, followed by CO insertion to
give Pd-COOH, and finally by CO2 elimination.
In contrast, there is no mechanism that may allow
the bis-chelates to generate catalytically active Pd(II)
in copolymerization reactions performed in anhydrous
CH2Cl2. Some water is needed to convert the bis-
chelates to Pd-COOH via either Pd-OH or Pd-CO in
Alter n a tin g Cop olym er iza tion of Eth en e a n d
Ca r bon Mon oxid e Ca ta lyzed by [P d (µ-OH)(P -P )]2-
(P F 6)2 a n d [P d (P -P )2](P F 6)2 P r ecu r sor s in CH2Cl2.
It has been recently shown that Pd(II) µ-hydroxo
precursors with dppe and meso/rac-dppb ligands cata-
lyze the CO/ethene copolymerization in CH2Cl2.4 Our
first evidence that also the µ-hydroxo complexes with
dppp, meso-bdpp, and rac-bdpp do not represent a dead
end to copolymerization was actually provided by the
HPNMR experiments described above. Confirmatory
evidence was obtained from the results of batch reac-
tions in which 13-15 were used as precursors (Figure
5a). Interestingly, the productivity was found to de-
crease in the ligand order dppp (1.8 kg of polyketone (g
of Pd)-1) > meso-bdpp (1.5) . rac-bdpp (0.5), which
resembles the order of stability of the µ-hydroxo com-
plexes in catalytic conditions (see Figures 3 and 4 and
relative comments).
(22) Belov, G. P.; Golodkov, O. N.; Dzhabieva, Z. M. Macromol.
Symp. 1995, 89, 455.

4974 Organometallics, Vol. 21, No. 23, 2002
Bianchini et al.
Sch em e 5
fact (Scheme 5b). Therefore, the catalytic activity of the
bis-chelates under the conditions of Figure 5b confirms
once more that the presence of water in batch copoly-
merization reactions is virtually unavoidable (traces of
water may be delivered by the two gases or may be
present on the reactor walls or in the solvent).
Alter n a tin g Cop olym er iza tion of Eth en e a n d
Ca r bon Mon oxid e Ca ta lyzed by [P d (µ-OH)(P -P )]2-
(P F 6)2 a n d [P d (P -P )2](P F 6)2 P r ecu r sor s in MeOH.
The presence of some water is not a problem at all in
copolymerization reactions catalyzed by Pd(II)-diphos-
phine systems in MeOH, as these reactions are com-
monly carried out in the presence of a strong protic acid
such as TsOH that converts eventual Pd-OH to Pd-
OTs.2 The initiation proceeds via Pd-OMe and Pd-H
species.2 As in CH2Cl2, however, catalyst deactivation
is rather fast in MeOH due to the inherent propensity
of [PdH(P-P)]+ species to form Pd0, H+, and free P-P
ligand.2 The latter can form bis-chelates [Pd(P-
P)2]2+ by reaction with monochelate [Pd(P-P)]2+ moie-
ties.2,4,19-21 In light of the results reported in Figure 5b,
we decided to carry out CO/ethene copolymerization
reactions in MeOH in the presence of the bis-chelates
16-18. The results of this study are reported in Figure
6a, while Figure 6b reports productivity data obtained
with Pd(OTs)2((P-P) precursors in MeOH under com-
parable experimental conditions.3b It turned out that the
productivity decreases in the ligand order meso-bdpp >
rac-bdpp . dppp.
F igu r e 6. Productivities expressed as kg of polyketone (g
of Pd)-1 for the copolymerization reactions (precursor, 0.01
mmol; MeOH; 100 mL; BQ, 80 equiv; p-TsOH, 20 equiv)
with (a) [Pd(P-P)2](PF6)2 (time, 30 min); (b) Pd(TFA)2(P-
P) (time, 3 h).
Sch em e 6
Gen er a tion a n d Migr a tor y In ser tion Ba r r ier s of
[P d (Me)(CO)(P -P )]BF 4. Migratory insertion barriers
relative to reactions that occur during the propagation
of the alternating copolymerization catalyzed by the
Pd(II) methyl complexes 4-6BF 4 were estimated by
NMR spectroscopy for various model intermediates.4
The methyl carbonyl complexes [Pd(Me)(CO)(P-P)]-
BF4 (P-P ) dppp, 19; meso-bdpp, 20; rac-bdpp, 21) were
generated in HPNMR tubes by pressurizing CD2Cl2
solutions of the corresponding methyl acetonitrile com-
pounds (4-6BF 4) with CO (15 bar) at -117 °C. The
quantitative formation of the methyl carbonyl complexes
occurred already at -80 °C. Upon slow heating of the
NMR probe-head, the methyl carbonyl complexes trans-
formed selectively into the corresponding carbonyl acyl
derivatives [Pd(COMe)(CO)(P-P)]BF4 (P-P ) dppp, 22;
meso-bdpp, 23; rac-bdpp, 24) (Scheme 6).
1
identified by 31P{1H} and H NMR spectroscopy (Tables
1 and 2). Comparisons with the spectra of similar or
related complexes described in the literature have
substantially contributed to validate our structural
assignments.4,7,8,15,17,21
Kinetics of transformation of the methyl carbonyl
complexes into the corresponding acyl carbonyl products
were studied by 31P{1H} NMR spectroscopy at -60 °C
(dppp complex 22), -70 °C (meso-bdpp complex 23), and
-80 °C (rac-bdpp complex 24), where the reactions were
sufficiently fast to allow for a reliable determination of
the half-life times (t1/2). As previously observed by
Brookhart and co-workers8 for [Pd(Me)(CO)(dppp)]BAr′4
and by us for the series [Pd(Me)(CO)(P-P)](PF6) (P-P
) dppe, meso-dppb, rac-dppb),4 the rate of conversion
of the methyl carbonyl complexes is independent of the
CO pressure (5-25 bar) and follows first-order kinetics.
The observed rate constants are therefore the true rate
This transformation started to occur at -70 °C for 19
and at -80 °C for 20 and 21. Both the methyl carbonyl
and acyl carbonyl compounds were straightforwardly

Palladium-Diphosphine Catalysis
Organometallics, Vol. 21, No. 23, 2002 4975
Ta ble 3. Exp er im en ta l Activa tion Ba r r ier s a n d Tem p er a tu r es for Migr a tor y In ser tion s
[Pd(Me)(CO)(P-P)]+
t1/2 (min)
[Pd(CH2CH2C(O)Me)(P-P)]+
P-P
dppp
meso-bdpp
rac-bdpp
∆Gq (kcal/mol)
T (°C)
T (°C)
t1/2 (min)
p(CO) (bar)
15.2(1)
14.6(1)
14.2(1)
10
13
31
-60
-70
-80
-70
-70
-70
84
200
13
20
20
20
Sch em e 7
Sch em e 8
constants, and the ∆Gq values associated with the
migratory insertion of the methyl carbonyl complexes
could be straightforwardly calculated from the t1/2 values
using the equation ∆Gq ) RT(ln kr - ln kT/h) with kr )
ln 2/t1/2.8 The energy barriers were found to increase in
the ligand order rac-bdpp < meso-bdpp < dppp (Table
3). Notably, the activation barriers for insertion calcu-
lated in this work nicely fit previous data for [Pd(Me)-
(CO)(dppp)]BAr′4 (14.8(1) kcal mol-1 at -81.7 °C)8 and
[Pd(Me)(CO){(S,S)-bdpp}]BF4 (14.5 kcal mol-1 at -80
°C).21b
Gen er a tion a n d Ca r bon yla tion of â-Ch ela tes
[P d (CH2CH2C(O)Me)(P -P )]SbF 6. The â-chelates [Pd-
(CH2CH2C(O)Me)(P-P)]SbF6 (7-9SbF 6) were prepared
in situ following the procedures described in Scheme 2.8
HPNMR tubes containing CD2Cl2 solutions of these
complexes under Ar at room temperature were cooled
to ca. -117 °C, pressurized with 20 bar CO, and then
inserted into the NMR probe-head precooled at -90 °C.
The conversion of the â-chelates to the carbonyl acyl
complexes [Pd(CO)(COCH2CH2C(O)Me)(P-P)]SbF6 (P-P
) dppp, 28; meso-bdpp, 29; rac-bdpp, 30) was followed
by variable-temperature 31P{1H} NMR spectroscopy
(Scheme 7). The transformation of all â-chelate com-
plexes occurred already at -80 °C.
reported for the carbonylation of the â-chelates [Pd(CH2-
CH2C(O)Me)(P-P)]+ containing the latter diphosphine
ligands contrast those observed for the present com-
pounds; that is, the opening of the â-chelate by CO was
much easier for the meso-dppb (t1/2 ) 97 min at -40
°C) and rac-dppb (t1/2 ) 480 min at -40 °C) derivatives
than for the dppe one (t1/2 ) 15 min at 20 °C). The
different behavior of the dppe and dppp systems con-
firms the importance of the chelating diphosphine
structure in determining the intrinsic activity of the
corresponding Pd(II) catalysts in the CO/ethene copo-
lymerization.2,4
Attem p ted Deter m in a tion of th e Migr a tor y In -
ser tion Ba r r ier s of [P d (COMe)(C2H4)(P -P )]BF 4. In
an attempt to determine the activation barriers to the
migratory insertion of acyl ethylene intermediates [Pd-
(COMe)(C2H4)(P-P)]+,4,8 the chloride ligand was re-
moved from the acyl chloride derivatives 25-27 with
AgSbF6 in the presence of ethene (15 bar) at -120 °C
(Scheme 9). Only the â-chelates were seen already in
the first NMR spectrum at -117 °C, which is consistent
with an activation barrier lower than 12 kcal mol-1 for
all reactions. A ∆Gq value of 12.3(1) kcal mol-1 has been
reported by Brookhart and co-workers for [Pd(COMe)-
(C2H4)(P-P)]SbF6 in an experiment performed at -135
°C.8
Like all the other new products obtained in situ,
unambiguous characterization of the carbonyl acyl
complexes 28-30 was achieved by NMR spectroscopy
as well as comparisons with literature data (Tables 1
and 2).4,8,15,21
The rates of conversion of the â-chelates to carbonyl
acyl complexes were evaluated as half-life times ob-
tained from the decay (and increase) of the phosphorus
resonances at -70 °C (Table 3). The activation barriers
for the processes could not be calculated straightfor-
wardly from the t1/2 values, as the reaction rates proved
to be dependent on the CO pressure in the range
investigated (15-25 bar). The t1/2 values decrease in the
order meso-bdpp > dppp > rac-bdpp, yet the difference
is not very significant. In line with previous observa-
tions,4 the opening of the metallacycle by CO (steps a,
b) is rate limiting in the stepwise process illustrated in
Scheme 8 since the following migratory insertion of the
alkyl carbonyl complex (step c) is independent of the
CO pressure. The opening of the â-chelates by CO is
most probably the rate-limiting step of the overall
copolymerization reaction in CH2Cl2, as previously
reported for the reactions catalyzed by [Pd(Me)(MeCN)-
(P-P)]+ precursors (P-P ) dppe, meso-dppb, rac-dppb).4
Interestingly, the kinetic and thermodynamic trends
Discu ssion
The perfect alternation of the comonomers in the CO/
ethene copolymerization by Pd(II)-chelating diphosphine
catalysis is thermodynamically and kinetically driven.
In particular, misinsertions do not occur, as the migra-
tory insertions of Pd(COR)(CO) and Pd(CH2CH2C(O)R)-
(C2H4) are thermodynamically and kinetically disfa-
vored, respectively.2,8,23 This strict control changes
neither with the solvent nor with the diphosphine ligand
provided the latter is appropriate for CO/ethene copo-
lymerization;2 yet solvent and ligand are of utmost
importance in determining the catalytic productivity as
well as many copolymer properties such as the molec-
ular weight, morphology, and nature of the end groups
of the polyketone product.2 Ultimately, the solvent rules
(23) (a) Chen, J .-T.; Sen, A. J . Am. Chem. Soc. 1984, 106, 1506. (b)
Sen, A.; Chen, J .-T.; Vetter, W. M.; Whittle, R. J . Am. Chem. Soc. 1987,
109, 148.

4976 Organometallics, Vol. 21, No. 23, 2002
Bianchini et al.
Sch em e 9
Sch em e 10
the kinetics of propagation and the mechanisms of
initiation and chain transfer.2,22,24
(Figure 5b), we propose that both the faster chain-
transfer rate by protonolysis with adventitious water and
the greater stability of the µ-OH resting state are
responsible for the lower activity of the rac-bdpp methyl
precursor 6P F 6 in CH2Cl2 as compared to 4P F 6 and
5P F6.
Pd-alkyl complexes, either preformed or generated in
situ with alkylating agents,12b,c are required to initiate
the copolymerization in CH2Cl2, whose relevant steps
are illustrated in Scheme 10 together with paths leading
to the formation of µ-hydroxo and bis-chelate resting
states.2
Our results confirm the importance of the solvent/
ligand assembly in determining the performance of
Pd(II)-diphosphine catalysts in CO/ethene copolymeri-
zation and also highlight the complexity and variety of
the reactions involved in this process.
No contribution of µ-hydroxo complexes to the pro-
ductivity of Pd(OTs)2(P-P) precursors in CO/ethene
copolymerization in MeOH can be envisaged for the
simple reason that these compounds do not form as the
reactions are carried out in the presence of a strong
protic acid (TsOH).2,3 On the other hand, all Pd(II)-
diphosphine catalysts degrade in MeOH with time to
palladium metal and free ligand, following the mecha-
nism detailed in the upper part of Scheme 10, once the
organic oxidant and the protic acid are consumed.2,19,22
Evidence of the formation of Pd(II) bis-chelates upon
disappearance of BQ and H+ in the catalytic mixtures
has been provided for ethene and styrene carbonylation
in MeOH.19,22 It is therefore reasonable to conclude that
the bis-chelate complexes are likely resting states of
copolymerization reactions, able to re-enter the catalysis
through the sequence of reactions shown in Scheme 5b
using MeOH instead of H2O.20 In this eventuality, the
amount of polyketone produced by the bis-chelates [Pd-
(P-P)2]2+ (meso-bdpp > rac-bdpp . dppp) (Figure 6a)
might make the difference and hence contribute to
determine the overall productivity of the Pd(OTs)2(P-
P) precursors (Figure 6b). On the other hand, the overall
productivity of CO/olefin copolymerizations is controlled
by a complex web of factors, including the fact that the
reactions become heterogeneous after the polymer chain
is long enough to make the propagating species in-
soluble in MeOH.25 Therefore, one may not rule out that
other factors, for example the morphology of the pro-
The first and perhaps most important conclusion that
can be reached on the basis of our study is that the
presence and/ or stereochemistry of methyl groups in the
1,3-positions of the dppp backbone do not apparently
exert a significant influence on the propagation rate of
the copolymerization in CH2Cl2. Nevertheless, the ligands
dppp and meso-bdpp give rise to more productive
catalysts than rac-bdpp (Figure 1). An explanation for
this experimental observable has been provided by in
situ NMR experiments under catalytic conditions which
have shown that both the rate of formation and stability
of the rac-bdpp µ-OH complex are appreciably higher
than those of the dppp and meso-bdpp analogues
(Figures 3 and 4). Accordingly, a larger number of
palladium active sites would be subtracted to catalyze
the reaction assisted by the rac-bdpp precursor, which
is consistent with the results of the batch copolymeri-
zation reactions catalyzed by either [Pd(Me)(MeCN)(P-
P)]+ (Figure 1) or isolated [Pd(µ-OH)(P-P)]2 (Figure
2+
5a). Since the contribution of the bis-chelates [Pd(P-
P)2]2+ to the overall productivity is almost negligible and
comparable for all precursors within experimental error
(24) Toniolo, L.; Kulkarni, S. M.; Fatutto, D.; Chaudari, R. V. Ind.
Eng. Chem. Res. 2001, 40, 2037.
(25) Mul, W. P.; Drent, E.; J ansens, P. J .; Kramer, A. H.; Sonne-
mans, M. H. W. J . Am. Chem. Soc. 2001, 123, 5350.

Palladium-Diphosphine Catalysis
Organometallics, Vol. 21, No. 23, 2002 4977
duced polymer, contribute to determine the different
productivity of the dppp, meso-bdpp, and rac-bdpp
catalysts. In contrast, the intrinsic activity in CH2Cl2,
being determined at the very early stages of the reac-
tion, allows for more reliable comparisons.
states under catalytic conditions. This control should
be essentially steric in nature and related to the
different conformations and rigidity of the Pd(dppp)
(fluxional skew), Pd(meso-bdpp) (chair), and Pd(rac-
bdpp) (rigid δ-skew) moieties in solution.3a,4
In conclusion, our studies demonstrate that methyl
substituents in the 1,3-positions of the dppp backbone
do not have any significant influence on the propagation
rate of CO/ethene copolymerization in aprotic solvents,
yet they may affect the chain-transfer rate by proto-
nolysis with adventitious water. In contrast, these
methyl groups might influence the productivity by
controlling the stability of µ-OH or bis-chelate resting
Ack n ow led gm en t. The European Commission (con-
tracts no. HPRN-CT-2000-00010 and RTN2-2001-00127)
and the COST Action D17 (WG 0007/2000) are grate-
fully acknowledged for financial support. Thanks are
due to Prof. Piero Zanello for carrying out the CV study.
OM020461O