Synthesis of palladium(II) complexes containing a new α-d- xylofuranose-modified diphosphine and their application as catalyst precursors in the co- and terpolymerization of CO-ethene and propene

Article abstract of DOI:10.1039/b719748a

The diphosphine 3,5-dideoxy-1,2-O-isopropylidene-3,5-bis(di(2- methoxyphenyl)phosphanyl)-α-d-xylofuranose (o-MeO-xylophos), which differs from the known 3,5-dideoxy-1,2-O-isopropylidene-3,5-bis(diphenylphosphanyl)- α-d-xylofuranose (xylophos) by the presence of 2-methoxy substituents on the P-aryl rings, has been synthesized and characterized. These two ligands have been employed to stabilize the Pd^II complexes [PdCl ₂(o-MeO-xylophos)] (1a), [PdCl₂(xylophos)] (2a), [PdClMe(o-MeO-xylophos)] (1b), [PdClMe(xylophos)] (2b), [Pd(OTs)(H ₂O)(o-MeO-xylophos)](OTs) (1c) and [Pd(OTs)(H₂O)(xylophos) ](OTs) (2c). All complexes have been characterized by multinuclear-NMR spectroscopy. The solid-state structure of 1a has been determined by a single crystal X-ray analysis. The Pd-aqua complexes 1c and 2c have been employed to catalyse the CO-ethene and CO-propene copolymerization as well as the CO-ethene-propene terpolymerization reaction in MeOH. The catalytic activity and the molecular weight of the polyketones have been compared to those of the products obtained with analogous catalysts, [Pd(H₂O) ₂(o-MeO-dppp)](OTs)₂ (3c) and [Pd(H₂O)(OTs) (dppp)](OTs) (4c), bearing the classical 1,3-bis(diphenylphoshino)propane ligand (dppp). Under comparable catalytic conditions, all catalysts produce structurally similar polymeric materials, with 1c yielding the largest propene incorporation as well as the highest productivity of low-molecular-weight terpolymers. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b719748a

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Synthesis of palladium(II) complexes containing a new a-D-xylofuranose-
modified diphosphine and their application as catalyst precursors in the
co- and terpolymerization of CO–ethene and propene†
Bianca K. Mun˜oz-Moreno,a Carmen Claver,*a Aurora Ruiz,a Claudio Bianchini,*b Andrea Melib and
Werner Oberhauser*b
Received 21st December 2007, Accepted 18th February 2008
First published as an Advance Article on the web 31st March 2008
DOI: 10.1039/b719748a
The diphosphine 3,5-dideoxy-1,2-O-isopropylidene-3,5-bis(di(2-methoxyphenyl)phosphanyl)-a-D-
xylofuranose (o-MeO-xylophos), which differs from the known 3,5-dideoxy-1,2-O-isopropylidene-3,5-
bis(diphenylphosphanyl)-a-D-xylofuranose (xylophos) by the presence of 2-methoxy substituents on the
P-aryl rings, has been synthesized and characterized. These two ligands have been employed to stabilize
the PdII complexes [PdCl2(o-MeO-xylophos)] (1a), [PdCl2(xylophos)] (2a), [PdClMe(o-MeO-xylophos)]
(1b), [PdClMe(xylophos)] (2b), [Pd(OTs)(H2O)(o-MeO-xylophos)](OTs) (1c) and
[Pd(OTs)(H2O)(xylophos)](OTs) (2c). All complexes have been characterized by multinuclear-NMR
spectroscopy. The solid-state structure of 1a has been determined by a single crystal X-ray analysis. The
Pd–aqua complexes 1c and 2c have been employed to catalyse the CO–ethene and CO–propene
copolymerization as well as the CO–ethene–propene terpolymerization reaction in MeOH. The
catalytic activity and the molecular weight of the polyketones have been compared to those of the
products obtained with analogous catalysts, [Pd(H2O)2(o-MeO-dppp)](OTs)2 (3c) and
[Pd(H2O)(OTs)(dppp)](OTs) (4c), bearing the classical 1,3-bis(diphenylphoshino)propane ligand
(dppp). Under comparable catalytic conditions, all catalysts produce structurally similar polymeric
materials, with 1c yielding the largest propene incorporation as well as the highest productivity of
low-molecular-weight terpolymers.
related to the ability of the methoxy oxygen atoms to interact with
Introduction
the metal centre, play a major role in driving the catalytic activity.7
The design of conformationally rigid polyphosphine ligands for
However, the overall effect on the catalytic activity induced by
the coordination of late transition metals is a subject of much
the combination of ligand conformation and the presence of
current interest in organometallic chemistry and homogeneous
specific aryl substituents is still rather obscure, especially by
catalysis, where the selectivity and activity can be significantly
varying the experimental conditions, as one may readily realize
influenced by the steric and conformational properties of the
metal–diphosphine precursor.1
Indeed, in the alternating CO–alkene copolymerization, an
from a perusal of Scheme 1 that shows the molecular structure of
some diphosphines together with the productivity (kg(polyketone)
(g(Pd) × h)−1) of the corresponding PdII catalysts in the CO–ethene
copolymerization.6 For catalytic systems based on unsubstituted-
phenyl diphosphines (Scheme 1a), the activity does increase with
chelating ligand rigidity, whereas no well-defined trend can be
drawn for the systems based on o-methoxy-substituted ligands
(Scheme 1b).
effective relation between ligand rigidity and catalytic productivity
has been often observed, especially for palladium complexes
bearing C2 and C3-carbon-bridged diphosphines.2–4 Besides ligand
conformation, an important role in determining both productivity
and polyketone molecular weight is also provided by the presence
of substituents on the P-aryl rings.5 In particular, the introduction
of one o-methoxy substituent on each phosphorus aryl ring of
the ligand has been found to greatly enhance the productivity as
compared to reactions promoted by catalysts with unsubstituted
diphosphines.6 A recent study has shown that electronic effects,
Herein, we report the synthesis and characterization of the
2-methoxy-modified, C3-bridged diphosphine 3,5-dideoxy-1,2-
O-isopropylidene-3,5-bis(di(2-methoxyphenyl)phosphanyl)-a-D-
xylofuranose (o-MeO-xylophos, 1) (Scheme 2). The preparation
of the phenyl derivative xylophos (2) has been reported elsewhere.8
The mono-cationic PdII–aqua complexes [Pd(OTs)(H2O)(P–
P)]OTs (P–P = o-MeO-xylophos, 1c; P–P = xylophos, 2c; OTs = p-
toluenesulfonate) have been synthesized and employed to catalyze
the formation of polyketones by CO–ethene or CO–propene
copolymerizations as well as by CO–ethene–propene terpoly-
merization in MeOH. For comparative purposes, the analogous
PdII–aqua complexes [Pd(H2O)2(o-MeO-dppp)](OTs)2 (3c, o-
MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane)6
aDept. de Qu´ımica F´ısica i Inorganica, Facultat de Qu´ımica, Universitat
Rovira i Virgili, c/Marcel.li Domingo s/n, 43007, Tarragona, Spain. E-mail:
carmen.claver@urv.cat; Fax: +34-977-559563
bIstituto di Chimica dei Composti Organometallici (ICCOM-CNR), Area
di Ricerca CNR di Firenze, via Madonna del Piano 10, 50019, Sesto Fioren-
tino, Italy. E-mail: claudio.bianchini@iccom.cnr.it; werner.oberhauser@
iccom.cnr.it; Fax: +39-055-5225203
† CCDC reference number 660552. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b719748a
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at −50.83 (P1) and −41.86 ppm (P2) (Scheme 3), showing a
4J(P,P) of 15.9 Hz, which is double the value observed for the
analogous phenyl-counterpart 3,5-dideoxy-1,2-O-isopropylidene-
3,5-bis(diphenylphosphanyl)-a-D-xylofuranose (2).8 The methoxy
protons gave rise to four 1H-NMR singlets, in the range from 3.62
to 3.83 ppm, which is accounted for by the presence of two different
phosphorus donor atoms, each of which bears one axially- and one
equatorially-oriented 2-methoxyphenyl unit.
Synthesis and characterization of the palladium complexes with
o-MeO-xylophos and xylophos
The reaction of [PdCl2(COD)] with either 1 or 2 in dichloro-
methane yielded the neutral complexes [PdCl2(P–P)] (1a and
2a11) as pale yellow air-stable compounds in 74% and 80% yield,
respectively (Scheme 4).
Scheme 1
Scheme 4
Both complexes were characterized in solution by multinuclear
NMR spectroscopy and in the solid state by elemental analysis.
1
The 31P{ H} NMR spectra of 1a and 2a showed two broad
Scheme 2
singlets centred at 19.47 and 22.27 ppm and two doublets at
and
[Pd(OTs)(H2O)(dppp)]OTs
(4c,
dppp
=
1,3-
18.20 and 22.8 ppm (2J(P,P) = 7.4 Hz), respectively. The high-
bis(diphenylphosphino)propane)6 were tested under identical
experimental conditions as catalyst precursors for the same
reactions. As will be shown in this work, where the diphosphines
used are amongst the most skeletally rigid ever employed in
PdII-catalysed CO–alkene copolymerization, the presence of
o-methoxy substituents seems to prevail over any other structural
motif in controlling the productivity.
1
field 31P{ H} NMR signal of both complexes (19.47 (1a) and
18.20 (2a) ppm) has been assigned to the phosphorus atom P2
(Scheme 4) by means of 1H–31P correlation spectroscopy. Complex
1a showed two low-field shifted 1H multiplets, centred at 9.16 and
9.38 ppm, due to palladium–ortho-hydrogen atom interactions6,7,12
which persist also in the solid state, as confirmed by a single
crystal X-ray structure analysis. Indeed, crystals of 1a, suitable
for a single crystal X-ray diffraction analysis, were obtained by
slow evaporation of a 1 : 1 (v : v) CHCl3–1,4-dioxane solution of
1a at room temperature. It is worth mentioning that the ORTEP
plot shown in Fig. 1 describes the first crystal structure of a
transition metal complex bearing a modified a-D-xylofuranosyl
moiety. Selected bond distances and angles, as well as experimental
diffraction parameters for 1a are reported in Tables 1 and 3,
respectively.
Results and discussion
Synthesis and characterization of the ligand o-MeO-xylophos
The new chiral diphosphine ligand o-MeO-xylophos (1) was
synthesized by the reaction of the lithium-salt of bis-(2-
methoxyphenyl)phosphine9 with 1,2-O-isopropylidene-3,5-di-O-
trifluoromethanesulfonyl-a-D-ribofuranose10 in THF (Scheme 3).
The ligand was obtained in 65% yield as a white semi-crystalline
compound.
The crystal structure of 1a exhibits a typically square-planar
˚
coordinated palladium atom, which deviates by 0.0257(8) A in
the direction of C(29) from the least-squares coordination plane,
defined by the atoms Cl(1), Cl(2), P(1) and P(2), The Pd–P bond
˚
lengths of 2.269(1) and 2.246(1) A (Table 1) are significantly
◦
˚
Table 1 Selected bond length (A) and angles ( ) for 1a
Pd(1)–Cl(1)
Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(2)
P(1)–Pd(1)–P(2)
Intramolecular distances (A)
2.349(1)
2.362(1)
92.81(5)
91.27(5)
˚
Pd(1)–P(1)
Pd(1)–P(2)
Cl(1)–Pd(1)–P(1)
Cl(2)–Pd(1)–P(2)
2.269(1)
2.246(1)
174.71(6)
172.38(5)
Scheme 3
Ligand 1 was characterized in solution by multinuclear NMR
spectroscopy and in the solid state by elemental analysis. In
accordance with two non-equivalent phosphorus donor atoms,
Pd(1) · · · O(1)
Pd(1) · · · O(2)
Pd(1) · · · O(3)
3.673(4)
5.207(4)
5.171(4)
Pd(1) · · · O(4)
Pd(1) · · · H(9)
Pd(1) · · · H(16)
3.477(4)
2.756
2.894
1
the 31P{ H} NMR spectrum of 1 showed two doublets centred
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an envelope conformation. Like related ortho-methoxy-modified
PdII–diphosphine complexes,6,7 the relative spatial orientation of
the four 2-methoxyphenyl-groups leads to pair-wise short and
long intramolecular palladium–ortho-methoxy-oxygen distances,
˚
ranging from 3.477(4) to 5.207(4) A (Table 1).
In order to corroborate the different r-donor character of the
phosphorus atoms of ligands 1 and 2, the neutral complexes
[PdClMe(P–P)] (1b and 2b) were synthesized by reacting [Pd-
ClMe(COD)] with a stoichiometric amount of either 1 or 2
(Scheme 5).
Complexes 1b and 2b were isolated as white solids in 76 and 83%
yield, respectively. The NMR characterization of both compounds
in solution showed clearly the presence of geometrical isomers in
either case. The ratio between the two isomers A and B (Scheme 5)
was found to be 3 : 1 and 5 : 2 for 1b and 2b, respectively. The major
isomer A exhibited the methyl group coordinated to palladium in
a trans position with respect to the phosphorus atom P1, as shown
in Scheme 5. Since the methyl group exerts a higher trans influence
when compared to chloride, the phosphorus atom with the lower
r-donor capacity P1 is preferentially located trans to the methyl
group (Scheme 5), which is in line with the results of the single
crystal structure analysis (vide supra).
Fig. 1 ORTEP plot of 1a. The thermal ellipsoids are presented at a 30%
probability level and hydrogen atoms are omitted for clarity.
The neutral complexes 1a and 2a were transformed into the
corresponding mono-cationic aqua complexes [Pd(OTs)(H2O)(P–
P)]OTs (1c and 2c) by the reaction with AgOTs in dichloromethane
(Scheme 6).
different from each other, due to the different r-donor properties
of the donor atoms, being greater for P(2) than for P(1). As a con-
sequence, the trans influence of P(2) is higher than that of P(1) and
˚
the Pd(1)–Cl(2) bond length of 2.362(1) A is significantly longer
˚
Complexes 1c and 2c were isolated as yellow amorphous
compounds in 61 and 64% yield, respectively. Conductivity
measurements on both complexes in nitroethane solution showed
both compounds to behave as 1 : 1 electrolytes, with one tosylate
anion coordinated to palladium.6,5,13 The fourth coordination site
at palladium is apparently occupied by a water molecule which is
in fast exchange with the coordinating tosylate anion as shown in
Scheme 6. Unlike 1c, complex 2c showed a 1H NMR broad singlet
at 5.90 ppm, which was assigned to a coordinated water molecule.
when compared to the Pd(1)–Cl(1) bond length of 2.349(1) A. The
two bridging carbon atoms C(29) and C(31), which are directly
attached to the phosphorus atoms P(1) and P(2), respectively, ex-
hibit an opposite, non-equidistant deviation from the least-squares
˚
coordination plane of −0.968(5) and 0.874(6) A, respectively. This
finding suggests a twist conformation of the six-membered ring,
which includes the palladium atom. A similar conformation of the
six-membered metallaring was predicted for a related Rh–COD
complex (COD = cycloocta-1,5-diene) of the type [Rh(COD)(P–
P)]BF4 (P–P = 2) by means of molecular mechanics calculations.8
The carbon atoms C(29) and C(30), which show S and R configu-
rations, respectively, share a six- and a five-membered heterocyclic
ring. The latter ring is further connected to a 1,3-dioxolane ring,
through the chiral carbon atoms C(32) and C(33), which exhibit
an R configuration. Both five-membered heterocyclic rings show
1
The 31P{ H} NMR spectra in CDCl3 showed a singlet at 25.76 ppm
for the former complex, while the latter complex exhibited an AB
pattern for the two non-equivalent phosphorus atoms, with two
doublets at 21.70 and 21.93 ppm featured by a J(P,P) constant of
17.2 Hz. This value is significantly larger than that reported for
the corresponding PdCl2-complex 2a11 (7.4 Hz), which seems to
Scheme 5
Scheme 6
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reflect the weaker trans influence of water and tosylate ligands as
compared to chloride. As a consequence, the Pd–P bond length
for the mono-cationic complex 2c is shorter than those in 2a
and, thus, it was not surprising to find an increased J(P,P) value
dioxolane ring of ligands 1 and 2 was observed. The results of this
catalytic study are presented in Table 2.
As a comparison, reactions under identical catalytic conditions
were carried out in the presence of the PdII complexes [Pd(H2O)2(o-
MeO-dppp)](OTs)2 (3c)6 and [Pd(H2O)(OTs)(dppp)]OTs (4c).6
A perusal of Table 2 for the CO–ethene copolymerization
reactions shows that, irrespective of the presence or absence of
p-benzoquinone (BQ), the catalytic productivity of the ortho-
methoxy modified PdII–aqua precatalysts follows an opposite
trend to that of the analogous phenyl-derivatives (Table 2, entries
7, 8 vs 1, 2 and 10, 11 vs 4, 5). Indeed, the methoxy-modified
dppp precatalyst 3c was more active than the o-MeO-xylophos
derivative 1c, which suggests that the concomitant presence
of ortho-methoxy substituents on the phenyl rings and of a
remarkable ligand rigidity exerts a negative effect on the catalytic
productivity. Whether this effect is originated by kinetic or stability
factors is hard to say at the present stage. Irrespective of the aryl
substituent, the skeletal rigidity reduces the molecular weight of
the polyketone products (Table 2, entries 1 and 4 vs 7 and 10) that
are featured by keto and esters end groups in a 1 : 1 ratio.14 The
lowest average-weight copolymers were actually produced with
precatalyst 2c (Table 2, entry 4). Previous studies have shown that
the alternating polyketone molecular weight is controlled by a
subtle web of factors.6,14 As a general trend, the molecular weight
decreases by decreasing the basicity of the metal centre (as the
termination rate by either methanolysis or protonolysis increases
with the electrophilicity of the metal center) as well as by increasing
1
for the former complex. A variable temperature 31P{ H} NMR
study of 1c in CDCl3 showed the coalescence temperature and the
slow exchange limit temperature for the water–tosylate exchange
process at palladium at −20 and −60 ◦C, respectively. Indeed,
the 31P{ H} NMR spectrum of the latter complex at −60 ◦C
1
showed two broad singlets at 25.94 and 26.92 ppm, which were
assigned to the atoms P1 and P2, while the 1H NMR spectrum at
the same temperature contained two unresolved multiplets centred
at 9.09 and 9.42 ppm for two ortho-hydrogen atoms belonging to
the axially oriented 2-methoxyphenyl units. The corresponding
1H NMR spectrum at room temperature exhibited a broad
unresolved hump centred at 9.05 ppm for the same hydrogen
atoms. Similar low-field shifts of the ortho-hydrogen atoms, due to
palladium–hydrogen interactions, have already been observed for
related neutral and cationic 2-methoxyphenyl-modified palladium
diphosphine complexes.6,7
Catalytic co-and terpolymerization of CO, ethene and propene
The mono-cationic PdII–aqua complexes 1c and 2c were employed
to catalyse the CO–ethene and CO–propene copolymerization
reactions as well as the CO–ethene–propene terpolymerization
reaction in methanol.14 It is important to emphasize that, under
the catalytic conditions applied, no hydrolysis reaction of the 1,3-
Table 2 Co- and terpolymerization reactions in methanol employing the cationic palladium–aqua-complexes 1c-4c
c
Mn
Head-to-tail
Entry
Pre-catalyst
t/h
p-Benzoquinone (equiv.)
Productivityb
[Mw/Mn]
Propene (%)
regio-selectivityd (%)
CO–ethene copolymerizationa
1e
2e
3e
4
1c
1c
1c
2c
2c
2c
3c
3c
3c
4c
4c
4c
1
1
3
1
1
3
1
1
3
1
1
3
—
80
—
—
80
—
—
80
—
—
80
—
8.4
14.8
5.6
9.0
10.0
8.4
13.6
18.1
13.2
3.5
4.1
2.5
10.5
3.8
5
6
7e
8e
9e
> 35.0
15.0
10
11
12
CO–propene copolymerizationf
13
14
15
16
1c
2c
3c
4c
3
3
3
3
80
80
80
80
1.8
0.7
1.1
1.2
1.0
0.5
0.8
0.5
48
57
57
66
CO–ethene–propene terpolymerizationf,g
17
18
19
20
1c
2c
3c
4c
3
3
3
3
80
80
80
80
3.7
1.0
2.5
2.4
3.7 [2.7]
58
49
53
43
0.8 [1.8]
3.1 [2.3]
1.0 [2.1]
a Catalytic conditions: catalytic precursor, 0.0048 mmol; MeOH, 100 mL; p(CO)/p(C2H4), 21/21 bar; temperature, 85 ◦C; stirring rate, 1200 rpm.
1
b Productivity expressed as kg(polyketone) (g(Pd) × h)−1
85 ◦C. g p(C2H4), 7 bar at 20 ◦C.
.
c Mn expressed as kg mol−1
.
d (h–t) Regioselectivity given in %, based on 13C{ H} NMR
integration. e Catalytic precursor, 0.0024 mmol. f Catalytic precursor, 0.0048 mmol; MeOH, 100 mL; propene, 30 g and constant CO pressure, 42 bar at
2744 | Dalton Trans., 2008, 2741–2750
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the steric hindrance at the metal centre (as it negatively affects
the propagation rate). The effect of the ligand-backbone strain
on the basicity of the palladium centre has been estimated by
IR spectroscopy analysing the IR m(CO) of the Rh–dicarbonyl
complexes [Rh(CO)2(P–P)]PF6 (P–P = o-MeO-xylophos and o-
MeO-dppp) in CH2Cl2. The observed values of 2094, 2047 cm−1
and 2088, 2038 cm−1, respectively, are consistent with a lower r-
donor ability of o-MeO-xylophos as compared to its more flexible
counterpart o-MeO-dppp.
derivative 2c shows the lowest catalytic productivity (Table 2,
entry 14).
As for the regioselectivity of the propene enchainment (i.e., 1,2
or 2,1 insertion), all the catalysts gave a lower selectivity than
that of dppp (Table 2, entries 13–16). The regioselectivity of the
propene insertion into the growing polymer chain was determined
1
by 13C{ H} NMR spectroscopy, integrating the 13C CO signals,
deriving from tail to tail (t–t), head to tail (h–t) and head to head
(h–h) regioisomers. (Scheme 9).17
Accordingly, it is possible that the low molecular weights of the
polyketones produced with 2c are due to the synergistic effect of
ligand strain and phenyl substituents on the phosphorus donor
atoms as the –PPh2 moiety is less basic than the –P(o-MeO-
Ar)2 one.6 Similar effects on the metal nucleophilicity have been
reported for other mononuclear Pd complexes containing (P–P)
ligands.4
Scheme 9
In parallel to the CO–ethene copolymerization reactions, CO–
propene copolymerizations in MeOH in the presence of BQ were
carried out, employing the same precatalysts in the presence
of a fixed amount of propene (30 g) and a constant CO feed
It is well known, that Pd precatalysts bearing dppp as ligand lead
to the only formation of regioirregular copolymers, evidencing
thus, that both 1,2- and 2,1-propene insertion into the growing
polymer chain occurs with comparable probability.14,16 Indeed,
much higher regioselectivities were obtained with symmetrically
substituted C3-bridged diphosphines bearing either alkyl sub-
stituents at the phosphorus donor atoms (Scheme 10a)16b or two
electronically different phosphorus atoms in combination with a
Josiphos-type carbon skeleton (> 99% head-to-tail enchainment)
(Scheme 10b).17
1
(Table 2, entries 13–16). 1H and 13C{ H} NMR spectra of the CO–
propene products in CDCl3 clearly showed the exclusive forma-
tion of poly(1-oxo-2-methyltrimethylene) materials (Scheme 7a)
with no trace of poly[spiro-2,5-(3-methyltetrahydrofuran)] product
(Scheme 7b).15 Irrespective of the precatalyst, the polyketones
contained, ester (E) (Scheme 8a), ketone (K) (Scheme 8b) and vinyl
(V) end groups (Scheme 8c), as a consequence of chain-transfer
by methanolysis, protonolysis and Pd–b-hydride elimination,
respectively.14,16
In the present case, neither the substitution of the phenyl groups
by the more electron-donating 2-methoxyphenyl group nor the
introduction of the chiral a-D-xylofuranose back-bone improved
the regioselectivity of the propene enchainment (Table 2).
All four precatalysts (1c–4c) were used to catalyse the ter-
polymerization reaction of CO–ethene and propene in MeOH,
employing a fixed amount of propene (30 g) and ethene (7 bar
at 20 ◦C) (Table 2, entries 17–20). Under these conditions, highly
viscous low-molecular weight terpolymers (Table 2, entries 17–
20) were obtained.14,18 The new PdII–aqua complex 1c showed
the highest propene incorporation and led thus to the highest
catalytic productivity within the precatalysts investigated (Table 2,
Scheme 7
1
entry 17). The 1H and 13C{ H} NMR spectra of the terpolymers in
CDCl3 solutions showed the occurrence of the same type of end-
groups and approximately the same vinyl–ester end-group ratios
as observed for the CO–propene cooligomers.18
Conclusions
The new methoxy modified diphosphine o-MeO-xylophos (1) and
several neutral and cationic PdII complexes stabilized by 1 or by
its phenyl counterpart xylophos (2) were synthesized and charac-
terized. PdII–aqua complexes of the formula [Pd(OTs)(H2O)(P–
P)]OTs (P–P = 1 or 2) were employed to catalyse the CO–
ethene and CO–propene copolymerization as well as the CO–
ethene–propene terpolymerization reaction, and their catalytic
performance was compared to those of analogous PdII–aqua
complexes bearing the less structurally rigid o-MeO-dppp and
dppp ligands.
Scheme 8
1
Due to the partial overlapping of the H NMR signals of the
methyl groups from the ketone-end groups and from the repeating
propyl unit, only 1H NMR-based integral ratios between vinyl (V)
and ester (E) end groups can be reported: 1.2 : 3.0 (1c), 1.3 : 3.0 (2c),
1.0 : 3.0 (3c), 1.6 : 3.0 (4c). The highest catalytic productivity was
observed for 1c (Table 2, entry 13), while the analogous phenyl
From this comparative catalytic screening, it turned out that:
(i) The concomitant presence of ortho-methoxy substituents on
the P-phenyl rings and of a high conformational rigidity of
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Scheme 10
the diphosphine ligand exert a negative effect on the catalytic
productivity as compared to the ortho-methoxy-dppp-based PdII
precatalyst. (ii) In CO–ethene copolymerization the molecular
weight of the polyketones decreases by decreasing the basicity
of the chelating diphosphine and increases by decreasing the
skeletal rigidity. (iii) Neither the substitution of phenyl with
2-methoxyphenyl nor the introduction of an a-D-xylofuranosyl
carbon backbone increases the low regioselectivity of propene
insertion as compared to the dppp-based PdII precatalysts.16 (iv)
The PdII–aqua complex 1c with o-MeO-xylophos promotes the
largest propene incorporation as well as the highest productivity of
low-molecular-weight terpolymers. In particular, the productivity
with 1c is comparable to that obtained with the industrial catalytic
system comprising an in situ generated precatalyst from Pd(OAc)2
and o-MeO-dppp and, as solvent, a complex mixture of protic
solvents (MeOH–H2O–HOAc–MeOAc) at a much higher total
gas pressure (72 bar).18
DRX-400 spectrometer (400.13, 100.62, 161.98 MHz). Chemical
shifts are reported in ppm (d) relative to TMS, referenced to
the chemical shifts of residual solvent resonances (1H and
1
1
13C{ H} NMR) or 85% H3PO4 (31P{ H} NMR). All 2D NMR
1
1
1
spectra (i.e. H COSY, H–13C and H–31P correlation spectra)
were recorded on a Bruker Avance DRX-400 instrument, using
deareated non-spinning samples. All NMR spectra were recorded
at room temperature, unless stated otherwise. The conductivity
measurements of ionic compounds were carried out with an
Orion model 990101 conductance cell connected to a model
101 conductivity meter. The conductivity data were obtained
at a sample concentration of 10−3 M in nitroethane solutions.20
GPC-analyses were performed in THF (HPLC grade) on a
SEC-MALLS system equipped with a WATERS 510 GPC pump,
three-serial linear columns (Shodex K80M, Plgel 5 l Mixed-D
Plgel 3 l Mixed-E), a precolumn (Shodex K800P), two serial
detectors, a laser light scattering detector (miniDAWN from
Wyatt Technology Corp.) and a refractive index detector (RID-6A
from Shimadzu). The data were analysed with ASTRette 1.2
software for Macintosh from Wyatt Technology.
Experimental
Materials and physical measurements
Preparations
All reactions and manipulations were carried out under a nitrogen
atmosphere by using Schlenk-type techniques. The reagents were
used as purchased from Aldrich or Fluka. 1,2-o-Isopro-
pylidene-3,5-di-trifluoromethansulfonyl-a-D-ribofuranose,10 di(2-
methoxyphenyl)phosphine,9 3,5-dideoxy-1,2-O-isopropylidene-
3,5-bis-(diphenylphosphanyl)-a-D-xylofuranose, xylophos (2),8
[PdCl2(COD)] (COD = 1,5-cyclooctadiene),19a PdClMe(COD),19b
[PdCl2(xylophos)] (2a),11 [Pd(H2O)2(o-MeO-dppp)](OTs)2 (3c),6
[Pd(OTs)(H2O)(dppp)]OTs (4c)6 were prepared according to
literature methods. Catalytic reactions were performed using a
320 mL stainless steel autoclave equipped with a mechanical
stirrer and a Parr 4842 temperature and pressure controller. All
catalytic reactions were carried out at a constant total gas pressure
by connecting the autoclave to a gas reservoir. GC/MS analysis of
the catalysis solutions were performed on a Shimadzu QP2010S
apparatus equipped with a SPB-1 Supelco fused silica capillary
column (30 m, 0.25 nm i.d., 0.25 lm film thickness). Deuterated
solvents for routine NMR measurements were dried over
3,5-Dideoxy-1,2-O-isopropylidene-3,5-bis(di(2-methoxyphenyl)-
phosphanyl)-a-D-xylofuranose (1). To a deareated solution of
di(2-methoxyphenyl)phosphine (1.14 g, 4.60 mmol) in THF
(30 mL), which was cooled to −10 ◦C by means of an ice–
acetone bath, was slowly added butyllithium (4.31 mL (1.6 M),
6.90 mmol). After the complete addition of the latter reagent,
the suspension was allowed to stir at room temperature for 1 h,
followed by the addition of a solution of 1,2-O-isopropylidene-
3,5-di-O-trifluoromethansulfonyl-a-D-ribofuranose
(1.00
g,
2.20 mmol) in THF (20 mL). The reaction mixture was stirred for
3 h at this temperature, followed by the evaporation of the solvent
to dryness and redissolving the residue in dichloromethane. The
organic phase was washed with water, separated and dried over
magnesium sulfate. Then, the solvent was removed completely
yielding the compound as a brownish foamy product, which was
recrystallized from toluene and ethanol to give the diphosphine as
a white semi-crystalline solid. Yield: 65.8% (0.96 g, 1.49 mmol).
C36H40O7P2 (646.27): calc. C 67.90, H 6.19; found C 67.80, H
6.12%. 1H NMR (CDCl3, 400.13 MHz, ppm): d 1.17 (s, 3H, CH3),
1.34 (s, 3H, CH3), 2.67 (dd, 2J(H5,H5ꢀ ) 13.4 Hz, 3J(H5,H4) 6.7 Hz,
1
1
1
molecular sieves. H, 13C{ H}, and 31P{ H} NMR spectra were
obtained on either a Bruker Avance II DRX 300 spectrometer
(300.13, 75.49, 121.49 MHz, respectively) or a Bruker Avance
2746 | Dalton Trans., 2008, 2741–2750
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1H, H5), 2.94 (m, 1H, H5ꢀ ), 3.10 (m, 1H, H3), 3.62 (s, 3H, OCH3),
3.70 (s, 3H, OCH3), 3.78 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 4.55
(m, 1H, H2), 4.59 (m, 1H, H4), 4.75 (d, 3J(H1,H2) 3.6 Hz, 1H, H1),
2J(C,P1) 105.7 Hz, Pd-CH3(A)), 10.68 (d, J(C,P2) 81.2 Hz, Pd-
CH3(B)), 26.09 + 26.19 + 26.25 (s, CH3(A + B)), 26.84 (dd,
1J(C5,P2) 33.2 Hz, 3J(C5,P1) 20.2 Hz, C5(A + B), 43.73 (br s,
2
6.77–7.57 (m, 16H, Ar–H). 13C{ H}NMR (CDCl3, 100.62 MHz,
C3(A)), 46.03 (dd, J(C3,P1) 21.5 Hz, J(C3,P2) 11.2 Hz, C3(B)),
54.52 + 55.67 + 55.73 + 56.21 (s, OCH3(A)), 54.62 + 55.56 +
55.74 + 55.98 (s, OCH3(B)), 74.36 (s, C4(A + B)), 84.07 (s, C2(B)),
84.15 (s, C2(A)), 104.19 (s, C1(A)), 104.26 (s, C1(B)), 110.88 +
1
1
3
ppm): d 26.39 (s, CH3), 26.57 (s, CH3), 26.91 (br s, C5), 44.65 (d,
1J(C3,P1) 19.1 Hz, C3), 55.43 (s, OCH3), 55.52 (s, OCH3), 77.00
2
(d, J(C4,P1) 30.4 Hz, C4), 84.47 (s, C2), 104.21 (s, C1), 109.87 (s,
1
1
C6), 110.23–161.93 (Ar–C). 31P{ H} NMR (CDCl3, 161.98 MHz,
111.07 (s, C6(A + B), 110.06–161.62 (m, Ar-C(A + B)). 31P{ H}
4
4
ppm): d −50.83 (d, J(P1,P2) 15.9 Hz, P1), −41.86 (d, J(P1,P2)
NMR (CDCl3, 161.98 MHz, ppm): d 1.38 (d, 2J(P1,P2) + 4J(P1,P2)
15.9 Hz, P2).
48.7 Hz, P2(B)), 5.22 (d, J(P1,P2) + J(P1,P2) 46.9 Hz, P1(A)),
26.19 (d, 2J(P1,P2) + 4J(P1,P2) 46.9 Hz, P2(A)), 31.10 (d, 2J(P1,P2)
+ 4J(P1,P2) 48.7 Hz P1(B)).
2
4
PdCl2(o-MeO-xylophos) (1a). To a deareated solution of
ligand 1 (0.22 g, 0.34 mmol) in dichloromethane (10 mL) was
added a deareated solution of PdCl2(COD) (0.09 g, 0.32 mmol)
in dichloromethane (10 mL) under nitrogen. The solution was
allowed to stir at room temperature for 1 h, followed by its
concentration to half of the original volume (10 mL). On the
addition of diethyl ether (25 mL) the product precipitated as a
yellow semi-crystalline compound, which was filtered off, washed
with diethyl ether (15 mL) and dried in a stream of nitrogen.
Yield: 73.5% (0.21 g, 0.25 mmol). C36H40Cl2O7P2Pd (823.58): calc.
[Pd(OTs)(H2O)(o-MeO-xylophos)]OTs (1c). To a deareated
solution of compound 1a (0.10 g, 0.13 mmol) in dichloromethane
(20 mL) was added AgOTs (0.07 g, 0.27 mmol). The suspension
was allowed to stir at room temperature, in the absence of day-
light, for 2 h, followed by filtration through Celite in order to
remove AgCl. The clear solution was concentrated to half of its
original volume (10 mL) and then diethyl ether (25 mL) was added
to precipitate the product as a yellow solid, which was filtered off,
washed with diethyl ether (5 mL) and dried in a stream of nitrogen.
Yield: 61.5% (0.09 g, 0.08 mmol). C50H56O14P2S2Pd (1112.90): calc.
1
C 52.50, H 4.85; found C 52.10, H 4.72%. H NMR (CDCl3,
ꢀ
400.13 MHz, ppm): d 1.14 (s, 6H, CH3), 2.77 (ddd, J(H5,H5 )
13.4 Hz, ꢀ3J(H4,H5) 12.2 Hz, 2J(H5,P2) 7.2 Hz, 1H, H5), 3.15 (ddd,
2
1
C 53.96, H 5.03; found C 53.71, H 5.06%. H NMR (CDCl3,
400.13 MHz, ppm): d 1.15 (s, 3H, CH3), 1.18 (s, 3H, CH3), 2.36
(s, 6H, Ar-CH3), 2.76 (m, 1H, H5), 3.18 (m, 1H, H5ꢀ ), 3.59 (m, 1H,
H3), 3.78 (s, 6H, OCH3), 3.96 (s, 3H, OCH3), 4.13 (s, 3H, OCH3),
4.33 (m, 1H, H4), 4.76 (br s, 1H, H2), 5.61 (s, 1H, H1), 6.50–7.90
(m, 22H, Ar-H), 8.90–9.20 (br m, 2H, o-Ar-H). 1H NMR (CDCl3,
400.13 MHz, −60 ◦C, ppm): d 1.11 (s, 3H, CH3), 1.16 (s, 3H,
CH3), 2.12 (s, 6H, Ar-CH3), 2.80 (m, 1H, H5), 3.28 (m, 1H, H5ꢀ ),
3.41 (m, 1H, H3), 3.77 (s, 6H, OCH3), 4.04 (s, 3H, OCH3), 4.14
(s, 3H, OCH3), 4.28 (br m, 1H, H4), 4.80 (s, 1H, H2), 5.58 (s, 1H,
H1), 6.55–7.90 (m, 22H, Ar-H), 9.09 (m, 1H, o-Ar-H(P2)), 9.42 (m,
ꢀ
ꢀ
3
2
2J(H5,H5 ) 13.4 Hz, J(H4,H5 ) 6.4 Hz, J(H5 ,P2) 10.4 Hz, 1H,
H5ꢀ ), 3.55 (dd, 3J(H3,H4) 6.2 Hz, 2J(H3,P1) 6.9 Hz 1H, H3), 3.73 (s,
3H, OCH3), 3.75 (s, 3H OCH3), 3.91 (s, 3H, OCH3), 4.04 (s, 3H,
OCH3), 4.20 (m, 1H, H4), 4.72 (dd, J(H1,H2) 3.9 Hz, J(H2,P1)
3
3
7.6 Hz, 1H, H2), 5.56 (d, J(H1,H2) 3.9 Hz, 1H, H1), 6.70–7.80
3
(m, 26H, Ar-H), 9.16 (m, 1H, o-Ar-H(P2)), 9.38 (m, 1H, o-Ar-
H(P1)). 13C{ H} NMR (CDCl3, 100.62 MHz, ppm): d 24.81 (dd,
1
1J(C5,P2) 33.6 Hz, J(C5,P1) 19.9 Hz, C5), 26.34 (s, CH3), 26.54
3
(s, CH3), 44.39 (dd, J(C3,P1) 25.0 Hz, J(C3,P2) 11.9 Hz, C3),
54.87 (s, OCH3), 55.88 (s, OCH3), 56.60 (s, OCH3), 73.61 (s, C4),
83.47 (s, C2), 104.21 (s, C1), 110.68 (s, C6), 110.90–161.66 (Ar-C).
1
3
1
1H, o-Ar-H(P1)). 13C{ H} NMR (CDCl3, 100.62 MHz, ppm): d
21.04 (s, Ar-CH3), 24.08 (dd, 1J(C5,P2) 38.9 Hz, 3J (C5,P1) 18.4 Hz,
31P{ H} NMR (CDCl3, 161.98 MHz, ppm): d 22.27 (br s, P1), 19.47
1
1
C5), 26.09 (s, CH3), 26.23 (s, CH3), 43.80 (d, J(C3,P1) 32.5 Hz,
(br s, P2).
C3), 55.52 (s, OCH3), 56.08 (s, OCH3), 56.25 (s, OCH3), 56.64
(s, OCH3), 73.31 (s, C4), 82.51 (s, C2), 104.35 (s, C1), 110.81 (s,
PdClMe(o-MeO-xylophos) (1b). To a deareated solution of
ligand 1 (0.12 g, 0.18 mmol) in dichloromethane (5 mL) was added
a deareated solution of PdClMe(COD) (0.05 g, 0.15 mmol) in
dichloromethane (5 mL). The clear solution was stirred for 0.5 h
at room temperature, followed by concentration to half of the
original volume (5 mL). Then diethyl ether (20 mL) was added
to yield an off-white solid, which was filtered off, washed with
diethyl ether (8 mL) and dried in a stream of nitrogen. Yield: 77.7%
(0.11 g, 0.14 mmol). C37H43ClO7P2Pd (803.10): calc. C 54.33, H
5.35; found C 54.22, H 5.15%. Compound 1b was obtained as
a 3 : 1 mixture of the geometric isomers A and B as shown in
Scheme 5. Integrals of 1H NMR signals are not reported, due to
the partial overlapping of signals, stemming from both isomers. 1H
NMR (CDCl3, 400.13 MHz, ppm): d 0.28 (dd 3J(H,P)trans 7.1 Hz,
3J(H,P)cis 3.8 Hz, Pd-CH3(A + B)), 1.14 + 1.15 (s, CH3), 2.51 (m,
H5(B)), 2.80 (m, H5(A)), 3.08 (m, H5ꢀ (B)), 3.18 (m, H5ꢀ (A)), 3.31
1
C6), 111.20–161.25 (Ar-C). 31P{ H} NMR (CDCl3, 161.98 MHz,
◦
1
ppm): d 25.76 (br s). 31P{ H} NMR (CDCl3, 161.98 MHz, −60 C,
ppm): d 25.94 (br s, P2), 26.92 (br s, P1). KM (nitroethane, 28 ◦C):
79 X−1 cm2 mol−1.
PdClMe(xylophos) (2b). To a deareated solution of ligand
2 (0.16 g, 0.31 mmol) in dichloromethane (5 mL) was added
a deareated solution of PdClMe(COD) (0.08 g, 0.31 mmol)
in dichloromethane (5 mL). The clear solution was stirred for
0.5 h at room temperature, followed by its concentration to half
of the original volume (5 mL) and on the addition of diethyl
ether (20 mL) an off-white solid precipitated, which was filtered
off, washed with diethyl ether (8 mL) and dried in a stream
of nitrogen. Yield: 83.0% (0.17 g, 0.30 mmol). C33H35ClO3P2Pd
(683.14): calc. C 58.02, H 5.12; found C 58.17, H 5.22%. The
product was obtained as a 5 : 2 mixture of the geometric-isomers
3
3
1
(d, J(H3,H4) 6.0 Hz, H3(A)), 3.50 (d, J(H3,H4) 5.5 Hz, H3(B)),
3.72 + 3.75 + 3. 98 (s, OCH3(A + B)), 4.14 (m, H4(A)), 4.21
(m, H4(B)), 4.71 (br s, H2(B)), 4.80 (br s, H2(A)), 5.50 (s, H1(A)),
5.53 (s, H1(B)), 6.68–7.82 (m, Ar-H), 8.72 (m, o-Ar-H), 9.10 (m,
A and B as shown in Scheme 5. Integrals of H NMR signals
are not reported, due to overlapping of signals, stemming from
1
both isomers. H NMR (CDCl3, 400.13 MHz, ppm): d 0.45 dd,
2J(H,P2) 8.4 Hz, 2J(H,P1) 4.4 Hz Pd-CH3(B)), 0.58 (dd, 2J(H,P1)
o-Ar-H). 13C{ H} NMR (CDCl3, 100.62 MHz, ppm): d 9.25 (d,
8.0 Hz, J(H,P2) 4.0 Hz Pd-CH3(A)), 1.16 (s, CH3(A)), 1.18 (s,
1
2
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CH3(B)), 1.27 (s, CH3(A)), 1.29 (s, CH3(B)), 2.17 (ddd, 2J(H5,H5ꢀ )
13.9 Hz, 3ꢀ J(H4,H5ꢀ ) 10.6 Hz, ꢀ2J(H5ꢀ ,P2) 1.8 Hz, H5ꢀ (B)), 2.65 ꢀ(ddd,
2J(H5,H5 ) 14.6 Hz, 3J(H4,H5 ) 10.1 Hz, 2J(H5ꢀ ,P2) 2.9 Hz, H5 (A)),
2.71 (dd,ꢀ 3J(H3,H4) 6.7 Hz, 3J(H2,H3) 2.6 Hz, H3(A)), 2.84 (ddd,
Table 3 Experimental X-ray diffraction parameters and crystal data for
1a
Empirical formula
M
C36H40Cl2O7P2Pd
823.92
Orthorhombic
P212121
11.395(5)
17.986(5)
20.001(5)
90.0
90.0
90.0
4099(2)
1.335
3
2
2J(H5,H5 ) 13.9 Hz, J(H4,H5) 6.5 Hz, J(H5,P2) 3.3 Hz, H5(B)),
2.98 (ddd, 2J(H5,H5ꢀ ) 14.6 Hz, 3J(H4,H5) 5.8 Hz, 2J(H5,P2) 5.6 Hz,
H5(A)), 3.11 (dd, 2J(H3,P1) 6.4 Hz, 3J(H3,H4) 6.5 Hz, H3(B)), 4.56
Crystal system
Space group
˚
a/A
˚
b/A
3
3
(m, H4(A + B)), 4.79 (dd, J(H1,H2) 3.9 Hz, J(H2,P1) 4.9 Hz,
˚
c/A
H2(A)), 4.82 (dd, J(H1,H2) 4.1 Hz, 3J(H2,P1) 7.1 Hz, H2(B)),
3
a/◦
b/◦
c /◦
5.47 (d, 3J(H1,H2) 4.0 Hz, H1(A)), 5.67 (d, 3J(H1,H2) 4.0 Hz,
H1(B)), 7.40–8.10 (m, Ar-H(A + B)). 13C{ H} NMR (CDCl3,
1
3
˚
Unit cell volume/A
100.62 MHz, ppm): d 11.86 (d, J(C,P1) 102.4 Hz, Pd-CH3(A)),
2
D
calcd/g cm−3
14.09 (d, 2J(C,P2) 104.0 Hz, Pd-CH3(B)), 26.03 (s, CH3(A)) 26.08
(s, CH3(B)), 26.17 (s, CH3(B)), 26.20 (s, CH3(A)), 26.29 (m, C5(B),
29.60 (dd, 1J(C5,P2) 30.3 Hz, 3J(C5,P1) 20.2 Hz, C5(A)), 43.97 (dd,
Z
4
l(Mo-Ka)/mm−1
F(000)
5.936
1688
T/◦C
−103(2)
1J(C3,P1) 10.6 Hz, J(C3,P2) 5.4 Hz, C3(A)), 47.30 (dd, J(C3,P1)
22.3 Hz, 3J(C3,P2) 11.7 Hz, C3(B)), 74.41 (s, C4(A)), 74.54 (s,
C4(B)), 82.96 (d, 2J(C2,P1) 2.9 Hz, C2(A)), 83.22 (s, C2(B)), 103.63
(s, C1(A)), 103.74 (s, C1(B)), 111.28 (s, C6(A + B)), 127.02–135.07
3
1
˚
k/A
1.54184
Absorption correction
Refinement method
SADABS
Full-matrix least-squares on F2
5206/0/439
Data/restraints/parameter
Final R indices
[I > 2r(I)] R1 = 0.0415, wR2 = 0.0900
R1 = 0.0574, wR2 = 0.0954
0.967
(Ar-C). 31P{ H} NMR (CDCl3, 161.98 MHz, ppm): d −4.43 (d,
1
R indices (all data)
2J(P1,P2) + 4J(P1,P2) 48.6 Hz, P2(B)), 1.18 (d, 2J(P1,P2) + 4J(P1,P2)
Goodness-of- fit on F2
Absolute structure parameter
46.8 Hz, P1(A)), 25.70 (d, J(P1,P2) + J(P1,P2) 46.8 Hz, P2(A)),
2
4
−0.016(8)
3
˚
31.20 (d, 2J(P1,P2) + 4J(P1,P2) 48.6 Hz, P1(B)).
Largest diff. peak and hole/e A
1.045/−0.684
with the Oxford diffraction software and SADABS, respectively.21a
All structure determination calculations were performed with the
WINGX package,21b with SIR-97,21c SHELXL-9721d and ORTEP-
3 programs.21e The structure was solved by direct methods and
refined by full-matrix F2 refinement. Final refinements based on
F2 were carried out with anisotropic thermal parameters for all
non-hydrogen atoms, which were included using a riding model
with isotropic U values 20% larger than those of the adjacent
carbon atoms. Crystallographic data for 1a are reported in Table 3.
CCDC reference number for 1a: 660552.
[Pd(OTs)(H2O)(xylophos)]OTs (2c). To a deareated solution
of compound 2a (0.08 g, 0.11 mmol) in dichloromethane (8 mL)
was added AgOTs (0.07 g, 0.24 mmol). The yellow suspension
was stirred at room temperature, in the absence of day-light, for
2 h, followed by its filtration through Celite in order to remove
AgCl. The clear solution was concentrated to half of its original
volume (4 mL) and on addition of diethyl ether (20 mL) the
product precipitated from the solution as a yellow solid, which was
filtered off, washed with diethyl ether (8 mL) and dried in a stream
of nitrogen. Yield: 63.6% (0.07 g, 0.07 mmol). C46H48O10P2S2Pd
(992.90): calc. C 56.64, H 4.83; found C 56.74, H 4.95%. 1H NMR
(CDCl3, 400.13 MHz, ppm): d 1.25 (s, 3H, CH3), 1.40 (s, 3H,
CH3), 2.33 (s, 6H, Ar-CH3), 2.73 (m, 2H, H5 + H5ꢀ ), 3.24 (dd,
Catalytic co- and terpolymerization reactions
3
3J(H3,H4) 7.2 Hz, J(H3,P1) 8.0 Hz, 1H, H3), 4.88 (m, 1H, H4),
CO–ethene copolymerization reactions in MeOH with 1c–4c as
catalyst precursors. In a typical experiment, a MeOH (100 mL)
solution containing the catalyst precursor (0.0048 mmol), was
introduced by suction into the autoclave (320 mL), previously
evacuated using a vacuum pump. When the catalytic reactions were
performed in the presence of 1,4-benzoquinone (BQ), this reagent
was dissolved in MeOH. The autoclave was charged with a 1 : 1
CO–C2H4 mixture to 21 bar at room temperature and then heated
to 85 ◦C, where the pressure was adjusted to 42 bar and the reaction
conducted under stirring (1200 rpm) at constant pressure, feeding
the autoclave with a 1 : 1 CO–ethene gas-mixture. After the desired
reaction time, the autoclave was cooled to room temperature by
means of an ice–water bath and the unreacted gases were released.
The insoluble copolymer was filtered off, washed with methanol,
and dried under vacuum at 50 ◦C to constant weight.
3
3
5.08 (d, J(H2,H1) 2.8 Hz, 1H, H2), 5.90 (br s + d, J(H1,H2)
2.8 Hz, 3H, H2O + H1), 6.97–8.02 (m, 28H, Ar-H). 13C{ H}
1
NMR (CDCl3, 100.62 MHz, ppm): d 21.02 (s, Ar-CH3), 25.44
(dd, 1J(C5,P2) 36.6 Hz, 3J (C5,P1) 17.9 Hz, C5), 26.1 (s, CH3), 26.3
(s, CH3), 42.30 (dd, 1J(C3,P1) 29.8 Hz, 3J(C3,P2) 11.0 Hz, C3), 73.91
(s, C4), 82.19 (s, C2), 104.40 (s, C1), 112.19 (s, C6), 123.48–141.50
(Ar-C). 31P{ H} NMR (CDCl3, 161.98 MHz, ppm): d 21.70 (d,
1
2J(P1,P2) + J(P1,P2) 17.2 Hz, P2), 21.93 (d, J(P1,P2) + J(P1,P2)
4
2
4
17.2 Hz, P1). KM (nitroethane, 28 ◦C): 65 X−1 cm2 mol−1.
X-Ray crystallographic data collection and refinement of the
structure of 1a
Crystals, suitable for a single crystal X-ray structure analysis were
obtained by slow evaporation of a 1 : 1 (v : v) CHCl3–1,4-dioxane
solution of compound 1a at room temperature. Diffraction inten-
sity data were collected at −103 ◦C on an Oxford Diffraction CCD
diffractometer, operating with graphite-monochromated Cu–Ka
CO–propene copolymerization in MeOH with 1c–4c as cata-
lyst precursors. In a typical experiment, a MeOH (100 mL)
solution containing the catalyst precursor (0.0048 mmol) and
BQ (0.0384 mmol) was introduced by suction into the autoclave
(320 mL), previously evacuated using a vacuum pump. The
˚
radiation (k = 1.54184 A) and using x-scans. Cell refinement, data
reduction, and empirical absorption correction were carried out
2748 | Dalton Trans., 2008, 2741–2750
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autoclave was cooled to 0 ◦C, followed by charging it with propene
(30 g). Then the autoclave was warmed to 20 ◦C and charged with
CO (7 bar), followed by heating at 85 ◦C. At this temperature
stirring (1200 rpm) was started and the total pressure was adjusted
with CO to 42 bar. The reaction was performed at constant
pressure upon feeding the autoclave with CO. After a reaction
time of 3 h, the autoclave was cooled to room temperature by
means of an ice–water bath and the unreacted gases were released.
The MeOH solution of the oligomeric material was evaporated at
room temperature by means of a vacuum pump to reach constant
weight of the cooligomers.
(PALLADIUM network, contract no. HPRN-CT-2002-00196),
the Generalitat de Catalunya (2005SGR007777 and Distinction
for Research Promotion, 2003 C.C.) for financial support and for
awarding a research grant to B. K. Mun˜oz-Moreno.
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(w), 2934 (w), 2901 (w), 2879 (w), 1701 (s), 1459 (m), 1388 (m),
1376 (m) and 1023 (m) cm−1. The most significant IR values for the
CO–ethene–propene terpolymers are: 2967 (w), 2935 (w), 2904 (w),
1701 (s), 1458 (w), 1394 (m), 1379 (m), 1360 (m) and 1085 (m) cm−1.
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We thank the Spanish Government (CTQ2004-04412/BQU, Con-
solider Ingenio 2010, CSD2006-0003), the European Community
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The Royal Society of Chemistry 2008
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2750 | Dalton Trans., 2008, 2741–2750
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The Royal Society of Chemistry 2008
©