Ligand effects in the non-alternating CO-ethylene copolymerization by palladium(ii) catalysis

Article abstract of DOI:10.1039/b711280g

In this paper we report on a comparative study of the non-alternating CO-C₂H₄ copolymerization catalyzed by neutral Pd ^II complexes with the phosphine-sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and b

Full text of DOI:10.1039/b711280g

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PAPER
www.rsc.org/dalton | Dalton Transactions
Ligand effects in the non-alternating CO–ethylene copolymerization by
palladium(II) catalysis†
Lorenzo Bettucci,a Claudio Bianchini,*a Carmen Claver,b Eduardo J. Garcia Suarez,b
Aurora Ruiz,b Andrea Melia and Werner Oberhauser*a
Received 24th July 2007, Accepted 2nd October 2007
First published as an Advance Article on the web 17th October 2007
DOI: 10.1039/b711280g
In this paper we report on a comparative study of the non-alternating CO–C2H4 copolymerization
catalyzed by neutral PdII complexes with the phosphine–sulfonate ligands bis(o-methoxyphenyl)-
phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former
ligand, featuring a lower skeletal flexibility, has been found to form more active catalysts as well as
produce polyketones with higher molecular weight and higher extra-ethylene incorporation. Operando
high-pressure NMR studies have allowed us to intercept, for the first time, PdII(phosphine–sulfonate)
b-chelates in the non-alternating copolymerization cycle, while model organometallic reactions have
contributed to demonstrate that PdII (phosphine–sulfonate) fragments do not form stable carbonyl
complexes. The opening of the b-chelates has been found to be a viable process by either comonomer,
which contrasts with the behaviour of PdII (chelating diphosphine) catalysts for the perfectly alternating
copolymerization.
Introduction
Copolymers of ethylene and carbon monoxide can exist either with
the non-alternating structure (Scheme 1a) or with the perfectly
alternating structure (Scheme 1b). Polyketones with the latter
structure are invariably produced by insertion polymerization pro-
cesses for which palladium(II) complexes supported by chelating
diphosphine ligands generate by far the most efficient catalytic
Scheme 2
systems.1 In contrast, non-alternating copolymers can be obtained
by either free radical2 or insertion polymerization reactions.3
of view, it is agreed that the non-alternation of co-monomers
is promoted by high temperatures (> 100 ◦C) and low partial
pressures of CO in the feed. Much less consensus has been reached
on the stereoelectronic factors that favour non-alternation over
perfect alternation. Some authors suggest that non-alternation
is a result of facile decarbonylation of Pd acyl species with no
intermediacy of b-chelates;3d,e other authors propose that multiple
ethylene insertion is just facilitated by the destabilization of neutral
b-chelates.3a–c
Scheme 1
The known catalysts for non-alternation by insertion polymer-
ization are based on palladium(II) salts modified with anionic
chelating ligands bearing phosphorus and oxygen donor atoms
(P ∼ O−). An example of these ligands, primarily described by
Drent,3a is shown in Scheme 2a.
Following Drent’s discovery, other authors have demonstrated
the effectiveness of such P ∼ O− ligands in the non-alternating CO–
C2H4 copolymerization and their studies, both experimental3a–c
and theoretical,3d,e have contributed to shed light onto the factors
responsible for the non-alternation. From an experimental point
At present, the catalysts producing non-alternating copolymers
are nearly two orders of magnitude less active than those
producing strictly alternating copolymers. New catalytic systems
should therefore be designed to increase the productivity, which is
still a relevant goal since non-alternating polyketones exhibit lower
melting points as compared to perfectly alternating materials.3a,b
In this paper we report on a study of the non-alternating
CO–C2H4 copolymerization by palladium(II) catalysis where the
catalytic activity promoted by the Drent’s bis(o-methoxyphenyl)-
phosphinophenylenesulfonate ligand (La−) is compared to that
of the recently synthesized bis(o-methoxyphenyl)phosphinoethyl-
enesulfonate ligand4 (Lb−) (Scheme 2b). For the first time, the non-
alternating CO–C2H4 copolymerization has been investigated by
means of batch catalytic reactions, operando high-pressure NMR
experiments and model organometallic reactions. We are confident
that the gathered structural and mechanistic information will
aIstituto di Chimica dei Composti Organometallici (ICCOM-CNR), Area di
Ricerca CNR di Firenze, via Madonna del Piano 10, 50019, Sesto Fiorentino,
Italy. E-mail: claudio.bianchini@iccom.cnr.it, werner.oberhauser@
iccom.cnr.it; Fax: +39 055 5225203
bDept. de Qu´ımica F´ısica i Inorganica, Facultat de Qu´ımica, Universitat
Rovira i Virgili, c/Marcel.li Domingo s/n, 43007, Tarragona, Spain
† CCDC reference number for 2b: 653758. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b711280g
5590 | Dalton Trans., 2007, 5590–5602
This journal is
The Royal Society of Chemistry 2007
©

Table 1 Crystallographic data for 2b
be useful in designing improved catalytic systems for the non-
alternating CO–C2H4 copolymerization.
Formula
M
C32H36O10P2PdS2
813.07
Monoclinic
P21
9.403(5)
19.844(5)
10.566(5)
90.0
114.647(5)
90.0
1791.9(14)
1.507
2
0.777
832
0.71073
Crystal system
Space group
Results and discussion
˚
a/A
˚
b/A
Synthesis and characterization of the catalyst precursors
˚
c/A
a/◦
b/◦
c /◦
Instead of using the in situ procedure reported by Drent to
generate the copolymerization catalyst, i.e., the addition of a
slight excess of ligand to a MeOH solution of Pd(OAc)2,3a we
decided to synthesize well-defined PdII alkyl precursors. Indeed,
only structurally defined precursors would have allowed us to
draw out reliable information from the model and operando
studies. One of the synthetic protocols adopted, primarily de-
scribed by Rieger,3b is shown in Scheme 3. The sodium salt
of the appropriate zwitterionic P ∼ O ligand, either 2-{bis(2-
methoxyphenyl)phosphonium}benezenesulfonate3a (HLa) or 2-
{bis(2-methoxyphenyl)phosphonium}ethylenesulfonate4 (HLb),
was reacted in CH2Cl2 at room temperature with the palladium
3
˚
V/A
Dc/Mg m−3
Z
l/mm−1
F(000)
˚
k/A
T/K
293(2)
2803
2765
428
Measured reflections
Unique reflections
Refined parameters
Final R indices [I > 2r(I)]
R indices (all data)
S on F2
R1 = 0.0299, wR1 = 0.0827
R1 = 0.0306, wR2 = 0.0832
1.081
1
2
Flack parameter
Dqmin/e A
˚
Dqmax/e A
0.01(3)
−0.417
0.086
complex [Pd(l-Cl)(g ,g -codyl*)]2 (codyl* = 2-methoxycyclooct-
−3
˚
−3
1
2
5-enyl).5 As a result, the neutral palladium complexes Pd(g ,g -
1
2
codyl*)(La) (1a) and Pd(g ,g -codyl*)(Lb)4 (1b) were obtained in
good yield and were characterized in solution by multinuclear
NMR spectroscopy and in the solid state by elemental analysis
(Scheme 3).
◦
˚
Table 2 Selected bond distances (A) and angles ( ) for 2b
Pd(1)–P(1)
Pd(1)–P(2)
Pd(1)–O(5)
Pd(1)–O(8)
2.241(1)
2.340(1)
2.105(4)
2.103(4)
Compounds 1a and 1b are soluble in polar organic solvents
(MeOH, CH2Cl2, THF) where they are moderately stable at room
temperature. Above 40◦C, both complexes start decomposing with
formation of palladium black and a palladium complex analysed
as Pd(La)2 (2a) or Pd(Lb)2 (2b). However, while 2a persisted
as the major product in solution for several hours, 2b rapidly
disappeared. Unfortunately, the latter complex is insoluble in
common organic solvents and its crystal dimensions were too small
for reliable X-ray data collection. Therefore, the identification of 2b
was achieved indirectly by reacting Pd(OAc)2 with two equivalents
of Lb in CH2Cl2 mixture. The single crystals obtained could be
studied by X-ray diffraction methods showing the complex to
contain a palladium(II) centre coordinated by two ligands (vide
infra). Since the elemental analysis data and IR spectra of the
independently prepared complex are identical to those of 2b, one
may safely conclude that 1b decomposes in solution yielding the
PdII bis-chelate Pd(Lb)2 (Scheme 3). The same considerations
can be made for 2a whose X-ray structure has been published
elsewhere.3b
P(1)–Pd(1)–P(2)
O(5)–Pd(1)–O(8)
P(1)–Pd(1)–O(5)
P(2)–Pd(1)–O(8)
102.97(6)
87.29(17)
85.30(12)
84.44(13)
˚
Intramolecular distances/A
Pd(1) · · · O(1)
Pd(1) · · · O(2)
Pd(1) · · · O(3)
Pd(1) · · · O(4)
Pd(1) · · · H(9)
Pd(1) · · · H(25)
5.083(5)
3.679(4)
3.783(5)
5.018(4)
2.720
2.756
The metal center in 2b is square-planar coordinated by two
cis phosphorus and sulfonato oxygen atoms belonging to two
different P ∼ O ligands.3b,6 Notably, a similar structure has been
reported for the analogous La derivative, Pd(La)2 (2a).3b
The palladium atom in 2b shows no significant deviation from
the best coordination plane defined by the atoms P(1), P(2), O(5)
and O(8). The molecule is C2-symmetric with the C2 axis bisecting
Experimental X-ray diffraction parameters and selected bond
length and distances for 2b are reported in Tables 1 and 2,
respectively, while an ORTEP drawing of the structure is shown in
Fig. 1.
Scheme 3
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Dalton Trans., 2007, 5590–5602 | 5591
©

troscopy and elemental analysis. Compounds 3a and 3b were
transformed into the neutral derivatives Pd(H2O)Me(La) (4a) and
Pd(H2O)Me(Lb) (4b), respectively, on treatment with AgOTs in
CH2Cl2, followed by extraction of the (NHEt3)OTs by-product
with water. The identification of 4a, 4b was achieved in situ
1
by 1H and 31P{ H} NMR spectroscopy. No evidence for an
intermolecular agostic Pd–methyl-hydrogen interaction resulted
from 1H NMR spectra. Upon solvent elimination under reduced
pressure, 4a and 4b were transformed into two different species,
insoluble in CH2Cl2, for which we propose the binuclear structures
[PdMe(La)]2 (5a) and [PdMe(Lb)]2 (5b) where two Pd(P ∼
O) units are kept together by Pd–O bonds as shown in Scheme 4.
Apparently, the water molecule in 4a and 4b is weakly bound to
palladium so as to be easily removed under reduced pressure.
In this eventuality, the unsaturated PdMe(P ∼ O) fragment
has no other choice than dimerization to get stabilized. It is
noteworthy to recall that a quite similar binuclear structure
has been reported for neutral [NiPh(P ∼ O)]2 complexes where
P ∼ O is a chelating phosphanylenolato ligand.9 Interestingly,
the dissolution of 5a and 5b in MeOH gave the mononuclear
methylpalladium complexes Pd(S)Me(La) (4aꢀ) and Pd(S)Me(Lb)
(4bꢀ) where S may be either MeOH or adventitious H2O, the latter
being preferred for its greater binding affinity to PdII centers.10
Since the NMR spectra of 4aꢀ and 4bꢀ have been acquired in
MeOH-d4, a fast exchange between a possibly coordinated solvent
molecule and the bulk solvent, would not allow for the observation
of a coordinated solvent by 1H spectroscopy. Compounds 5a
and 5b dissolve also in CH2Cl2 containing nucleophiles such as
pyridine or triphenylphosphine to give complexes with the formula
Pd(Lꢀ)Me(L) (L = La, Lb; Lꢀ = Py, PPh3).3c One may therefore
conclude that the intramolecular Pd–O interaction that bridges
the PdMe(P ∼ O) moieties in 5a and 5b is very weak and can be
broken up by any sort of nucleophile.
Fig. 1 ORTEP drawing of 2b. Hydrogen atoms are omitted for clarity
and thermal ellipsoids are drawn at a 30% probability level.
the P(1)–Pd(1)–P(2) angle of 102.97(6)◦. The bite angles of each
ligand are only slightly different from each other (85.30(12)◦
(P(1)–Pd(1)–O(5)) and 84.44(13)◦ (P(2)–Pd(1)–O(8)), and both
˚
Pd–O bonds are almost identical (2.105(4) A for Pd(1)–O(5) and
˚
2.103(4) A for (Pd(1)–O(8)). In contrast, the Pd–P bond lengths are
˚
significantly different from each other (2.241(1) A for Pd(1)–P(1))
˚
and 2.340(1) A for Pd(1)–P(2)), which may be due to the steric
congestion exerted by the two equatorial 2-methoxyphenyl units.
The distances between Pd and the o-methoxy oxygen atoms
˚
˚
range from 3.679(4) A to 5.083(5) A and are thus far from
being considered bonding interactions.7 In contrast, the Pd center
˚
˚
exhibits distances of 2.720 A (Pd(1)–H(9)) and 2.756 A (Pd(1)–
H(25)) from the ortho hydrogen atom belonging to the axial 2-
methoxyphenyl units of each P ∼ O ligand.
The anionic methylpalladium(II) complexes [PdClMe(La)]-
(NHEt3)8 (3a) and [PdClMe(Lb)](NHEt3) (3b) were prepared by
the reaction of the triethylammonium salt of HLa and HLb with
PdClMe(cod). The overall synthetic procedure is summarized in
Scheme 4.
Catalytic copolymerization of CO and ethylene
The neutral PdII alkyl complexes 1a, 1b, 5a and 5b have been
tested as catalyst precursors for the CO–C2H4 copolymerization
either in MeOH or in TFE. The reaction temperatures of 120 ◦C
(1a/5a) and 110 ◦C for (1b/5b) correspond to the maximum of
Both complexes were isolated as off-white microcrystals and
were satisfactorily characterized by multinuclear NMR spec-
Scheme 4
5592 | Dalton Trans., 2007, 5590–5602
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©

Table 3 Non-perfectly alternating copolymerization of CO and ethylene catalyzed by 1a and 5aa
Entry Precat. t/h T/◦C C2H4/CO pressure/bar
C2H4/CO ratio TsOH/BQ amount (equiv.)
Prod.b
Extra C2H4 (%)c
Mp
240
230
225
1
2d
1a
1a
1a
5a
1a
1a
5a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
120
120
110
120
120
120
120
120
120
120
120
120
120
120
120
120
28.0/28.0
28.0/28.0
42.0/14.0
42.0/14.0
42.0/14.0
42.0/14.0
42.0/14.0
42.0/14.0
42.0/14.0
42.0/14.0
48.0/8.0
48.0/8.0
53.3/2.7
53.3/2.7
53.3/2.7
53.3/2.7
1
1
3
254
490
153
170
175
90
101
337
337
607
125
205
41
1.5
1.1
3.2
5.6
6.0
5.8
5.9
4.4
3.4
2.9
9.9
8.5
27.8
23.6
23.8
20.2
0/80
3
4
3
5
6
3
3
3
3
20/0
20/0
0/80
7
8d
228
235
9d,e
10d,e
11
12d
13
14d
15d,e
16d,e
3
3
6
6
20
20
20
20
0/80
0/80
0/80
0/80
220
218
193
195
93
77
130
196
a Catalytic conditions: palladium, 0.012 mmol; P(total) at reaction temp., 56.0 bar; MeOH, 50 mL; stirring rate, 1300 rpm. b Productivity expressed as
1
g(polyketone) (mmol(Pd) × h)−1
.
c Total mol% of C2H4 involved in non-alternation, calculated from 13C{ H} NMR spectra. d Palladium, 0.003 mmol.
e TFE, 50 mL.
the catalytic productivity for each precursor. Different partial
pressures of CO and C2H4 as well as the addition of co-reagents
have been investigated. The results of this study are reported in
Tables 3 and 4
Indeed, 1b has been found to oligomerize ethylene to butenes and
traces of hexenes.
Notably, we have observed by 13C NMR spectroscopy that 1a
was capable of promoting the triple ethylene insertion,3a whereas
only double ethylene insertion was found in the materials obtained
with 1b.
Irrespective of the experimental conditions, the pre-catalysts
with ligand La were much more active than those with the more
flexible ligand Lb and also gave much higher molecular weight
copolymers (Mw > 30 kg mol−1)3a (Tables 3–4). Likewise, irrespec-
tive of the pre-catalyst, the presence of an organic oxidant such as
BQ had a beneficial effect on the productivity. Indeed, a drawback
of any PdII-based catalyst for the CO–C2H4 copolymerization
is its tendency to undergo irreversible reduction to Pd-species,
precursor to palladium black. This degradation path is apparently
more effective for 1b than for 1a (vide infra).
Besides adding an oxidant, the stability of catalysts in the
CO–C2H4 alternating copolymerization can be increased by the
co-presence of protic acids, generally TsOH, in the catalytic
mixtures.1 In the case of non-alternating processes, the role of
the protic acid might be even more complex as it may protonate
the sulfonato group, leading to the disruption of the chelating
structure with consequent formation of less stable monodentate
[HSO3 ∼ P(aryl)2]PdII complexes. This negative action of the protic
acid may account for the decreased productivity of the reactions
catalyzed by 1a and 5a (entries 6 and 7, Table 3), whereas a
positive effect seems to still prevail for the reactions catalyzed
by 1b (Table 4). In the latter case, the loss of stability due to the
disruption of the chelate metalla-ring by the protic acid might be
compensated by the positive action on the metal oxidation state.
The productivity decreased for all catalysts by decreasing the
partial pressure of CO, which is in line with perfectly alternating
CO–C2H4 copolymerizations by chelating diphosphine-PdII catal-
ysis, except for those reactions where the catalysts are stabilized by
chelating diphosphine bearing o-methoxy substituted aryl groups
(zero-order dependence on CO pressure).7b,11
As for the degree of ethylene extra-insertion, the catalysts
containing the ligand La gave higher olefin incorporation than
those with Lb under comparable experimental conditions. The
degree of extra-insertion into the growing polyketone chain
is controlled by several factors.3d,e In agreement with previous
reports, we have found that higher temperatures and lower partial
pressures of CO, at constant total pressure, favour the extra
enchainment of ethylene. The presence of BQ did not appreciably
affect the degree of extra-insertion, while an increase of the latter
was observed by adding TsOH to the reactions catalyzed by 1b.
As expected, the melting point of the polyketones decreased on
increasing the amount of extra-ethylene insertion, for example
from 230 ◦C with 3.2% extra-insertion (entry 3, Table 3) to 193 ◦C
with 27.8% extra-insertion (entry 13, Table 3).
An end-group analysis was carried out on the polyketones
obtained with 1b as their molecular weight was sufficiently low to
allow for a reliable 1H NMR investigation in a 1 : 3 (v : v) mixture
of HFIP-d2 and C6D6. In the absence of added protic acid, three
types of end-groups, namely ester (E), ketone (K) and vinyl (V),
were observed in a 10 : 10 : 1 ratio, respectively, which means that
chain transfer may occur by protonolysis, methanolysis or both
of them. On the other hand, the observed keto-ester ratio and
the results of the model studies in MeOH (vide infra, Scheme 5)
suggest that the chain transfer occurs prevalently by methanolysis.
The small but appreciable amount of vinyl end groups shows that
also b-H elimination is a possible termination path. In the presence
of acid, only ketone end groups were observed.1
Replacing MeOH with TFE as reaction solvent increased the
productivity, especially for the catalysts with the more rigid ligand
La (entries 9 and 10 and 15 and 16, Table 3; entry 9, Table 4).7a,12
The beneficial effect of TFE on the catalytic activity is typical for
CO–C2H4 copolymerization reactions due to the good solubility
Irrespective of the precatalyst as well as catalytic conditions,
all non-alternating polyketones exhibit a linear polymeric chain
1
(13C{ H}NMR evidence) with no evidence of incorporation of
ethylene oligomers that may form by ethylene oligomerisation.3a
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Dalton Trans., 2007, 5590–5602 | 5593
©

of polyketones in fluorinated solvents, which improves the mass
transfer.13
Model organometallic study
In an attempt to identify the organometallic species, which might
form during the CO–C2H4 copolymerization reactions catalyzed
by the present PdII(P ∼ O) complexes in MeOH, the methyl
derivatives 4aꢀ and 4bꢀ were employed as model compounds to
study in situ the stepwise uptake of CO and ethylene. The results
of this study are summarized in Scheme 5.
Bubbling CO into a NMR tube containing a MeOH-d4 solution
of either 4aꢀ or 4bꢀ at room temperature converted the latter
compounds into the corresponding PdII acetyl complexes 6a or
6b (Scheme 5a). However, while the selective formation of 6a
occurred in 10 min, the complete disappearance of 4bꢀ required
40 min and, in addition to the acetyl complex 6b, the two CO-
bridged PdI dimers (l-CO)[Pd(Lb)]2 (9b) and [Pd(l-CO)(Lb)]2
(10b) were formed, showing a 6b : 9b : 10b ratio of 2 : 1 : 1.
The concomitant production of CH3C(O)OCD3 indicates that
the formation of 9b and 10b proceeds via methanolysis of 6b
(Scheme 5b).14 The structure of the Pd(I) complexes 9b and 10b
as shown in Scheme 5b have been assigned on the basis of the
following considerations: (i) Both complexes are formed by the
reaction of 6b with methanol in the presence of CO. Therefore the
formation of CO bridged Pd(I) complexes would be quite likely.
(ii) The corresponding 1H NMR spectrum exhibited no evidence
for the formation of dimer PdI(l-H)(l-CO).15 (iii) The shift of the
31P NMR signal, from 23.66 ppm (6b) to 8.09 (9b) and 8.55 (10b) is
characteristic for the formation of PdI species.15 (iv) Furthermore
performing the methanolysis reaction of 6b in the presence of p-
benzoquinone (BQ) did not lead to the formation of 9b and 10b.
The assignment of the 31P and 13C (carbonyl) NMR signals of both
latter compounds was performed following the inter-conversion of
compound 9b into 10b by bubbling CO through the corresponding
MeOH-d4 solution (Scheme 5b), while bubbling nitrogen through
the same solution led to the conversion of 10b into 9b.
Unlike 6b, the methanolysis reaction of 6a required a much
higher temperature to occur. Indeed, the process initiated at 90 ◦C
yielding CH3C(O)OCD3, the deuterated free ligand DLa and
palladium black (Scheme 5c).
1
The acetyl complexes 6a and 6b were characterized by 31P{ H}
1
and 13C{ H} NMR spectroscopy. In either complex, the palla-
dium(II) centre is square-planar coordinated by cis acetyl and
phosphine groups with the fourth site presumably occupied by
CD3OD or adventitious water. In principle, one cannot disregard
the existence of a fast exchange involving solvent molecules and
1
1
CO, yet there is no proof for that. Indeed, the 31P{ H} and 13C{ H}
NMR spectra of 6a, 6b are identical with those of the compounds
obtained by removing CO from the reaction mixture. Moreover,
the carbonylation of 4aꢀ–4bꢀ with a (1 : 9) 13CO/12CO mixture
1
(14.0 bar) showed no additional C–P coupling in the 13C{ H}
1
and 31P{ H} NMR spectra as compared to those acquired under
standard CO. The fact that CO forms stable species with PdI(P
∼ O) fragments (compounds 9b and 10b, Scheme 5b) but not
with PdII(P ∼ O) fragments suggests that the PdII centre in the
latter species is not sufficiently electron-rich for effective p-back
bonding.
5594 | Dalton Trans., 2007, 5590–5602
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The Royal Society of Chemistry 2007
©

Scheme 5
Scheme 6
Bubbling ethylene into a MeOH-d4 solution of 6a for 2 min at
is CO, CD3OD, or adventitious H2O, eventually in fast exchange
with each other. Indeed, replacing CO with N2 for enough time to
get rid of all dissolved CO gave a product (8aꢀ) spectroscopically
indistinguishable from 8a, which confirms that the coordination
of CO to PdII(P ∼ O), if any, is dramatically weak (Scheme 6). As
room temperature led to the selective formation of the b-chelate
7a (Scheme 5a). A longer ethylene bubbling time (20 min) was
required to obtain the analogous complex 7b from a 1 : 1 mixture
of 6b and 9b. Under this condition the latter compound was stable.
Compounds 7a and 7b showed NMR and the IR data (mCO at
1641 cm−1), which are in line with trans P and Oketo donor atoms.
Complex 7a was converted into the second-generation acyl
complex Pd(Lꢀ)COCH2CH2COMe(La) (8a) by bubbling CO into
a matter of fact, the 13C{ H} and 31P{ H} of 8a obtained using a
1 : 9 mixture of 13CO/12CO were identical to those acquired under
non isotopically enriched CO.
1
1
In conclusion, this study has shown that neutral Pd(P ∼ O)
1
1
a MeOH-d4 solution of 7a at room temperature. A 13C{ H}NMR
fragments are able to stabiliseg -acyl as well asb-chelate complexes
spectrum acquired in MeOH-d4 at room temperature under CO,
under copolymerization conditions. Though no evidence of the
formation of c-chelates16 was obtained on the NMR timescale, the
presence of such species in the catalysis cycle cannot be ruled out.
In an independent experiment, a HP NMR tube containing a
MeOH-d4 solution of 7a was pressurized with 42.0 bar of ethylene.
2
showed a doublet at d 221.44 with a JPC of 7.5 Hz and a singlet
at 210.18, which can be assigned to the acyl group bonded to
palladium and to the free COMe, respectively.7b On the other
hand, the NMR spectra did not allow us to determine whether Lꢀ
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Dalton Trans., 2007, 5590–5602 | 5595
©

Upon heating to 110 ◦C, linear polyethylene was formed, while the
palladium precursor was most likely converted into a new species
completely converted into the acyl complex Pd(Lꢀ)(COMe)(La)
(6aꢀꢀ Lꢀ = CO, TFE or adventitious H2O) (singlet at d 0.20; Fig. 2,
trace b). Replacing CO with a (1 : 9) 13CO/12CO mixture gave the
1
(31P{ H}NMR d 25.8) that we suggest to be an alkyl derivative
1
1
(Scheme 7).
same 13C{ H} and 31P{ H} NMR spectra with no evidence of CO
coordination to palladium.
1
It is worth noticing that both the 31P{ H} NMR chemical shift
of 6aꢀꢀ and the signal for the COCH3 carbon atom (d 211.49,
1
2JPC 3.9 Hz) in the 13C{ H} NMR spectrum of 6aꢀꢀ are shifted
in TFE/C6D6 as compared to the corresponding signals of 6a
1
1
in MeOH-d4 (31P{ H}NMR d 13.60 (s); 13C{ H}NMR d 222.58,
2JPC 8.0 Hz). We are inclined to attribute this difference just to
the presence of TFE that can form a network of hydrogen bonds
involving oxygen atoms from metal complexes.7a,13 As a matter of
fact, the addition of TFE to a MeOH-d4 solution of 6a, prepared as
described above, caused a similar high field shift of the resonances.
Once compound 6aꢀꢀ was formed, the sapphire tube was
pressurized with 600 psi of ethylene at room temperature. As a
result, the acyl complex was completely transformed into the b-
chelate species 7aM, which is most likely a mixture of different
generations of such compounds due to subsequent insertions of
Scheme 7
Operando HP-NMR study
The model organometallic study described in the previous section
has shown the formation and reactivity of several species that
might be involved in the real catalytic cycle of the non-alternating
CO–C2H4 copolymerization assisted by the present Pd(P ∼ O)
systems. In an attempt of discriminating purely model compounds
from truly catalytic intermediates, at least those visible on the
NMR timescale, operando HP-NMR experiments have been
carried out with 5a and 5b at an overall 800 psi pressure using
a 1 : 3 CO–C2H4 blend.
1
CO and C2H4. These b-chelates are featured by a 31P{ H}NMR
singlet at d 21.50 (Fig. 2, trace c), almost in the same position of
the first generation b-chelate 7a (d 21.73). Apparently, the steric
congestion caused by the growing polyketone chain does not allow
TFE to affect significantly the environment of the P–Pd moiety.
Heating the NMR tube to 110 ◦C (Fig. 2, trace d) and then cooling
it down to room temperature (Fig. 2, trace e) did not form other
NMR-detectable species than the b-chelates 7aM. The broader
NMR signal observed after catalysis is attributed to the formation
of further generations of b-chelates with different propagating
tails (Scheme 8a). Consistently, non-alternating polyketones were
collected from the NMR tube after this was heated for 1 h at
110 ◦C.
Since 5a produces high molecular weight polyketones, the HP-
NMR study with this precatalyst was performed in a 3 : 1 (v : v)
mixture of TFE and C6D6 to favour as much homogeneous as
possible conditions. The HP-NMR reaction catalyzed by 5b was
carried out in MeOH-d4. A sequence of selected 31P{ H} NMR
1
spectra are shown in Fig. 2 and 3.
Scheme 8
The fact that the copolymerization catalyzed by 5a initiates
already at room temperature is remarkable as it has allowed
us to collect enough material to establish its prevalent perfectly
alternating structure (< 1.0% of extra-ethylene inserted) (separate
experiment lasting 12 h) (Scheme 8b).
An analogous variable-temperature HP-NMR experiment was
carried out using pre-catalyst 5b in MeOH-d4 (Fig. 3). At room
temperature, the spectrum showed a singlet at d 38.00 due to 4bꢀ
(Fig. 3, trace a). On pressurizing the tube with 14.0 bar of CO, 4bꢀ
was immediately converted into a mixture of the acyl 6b (largely
prevailing) and of the binuclear PdI complex 10b, formed by
methanolysis of 6b (Scheme 5). The addition of 600 psi of ethylene
converted 6b into the b-chelates 7bM already at room temperature.
1
Fig.
2
Variable-temperature 31P{ H} NMR study (sapphire tube,
TFE/C6D6 (v : v) (3 : 1), 81.01 MHz) of the non-alternating CO–ethylene
copolymerization reaction catalyzed by pre-catalyst 5a: (a) 4aꢀꢀ obtained
from 5a under nitrogen at 22 ◦C; (b) under CO (200 psi) at 22 ◦C; (c) under
CO–C2H4 (1 : 3) (800 psi) at 22 ◦C; (d) after 10 min at 110 ◦C; (e) after
cooling to 22 ◦C.
◦
On dissolution in a 3 : 1 mixture of TFE/C6D6, 5a converted
immediately at room temperature into Pd(S)Me(La) (4aꢀꢀ; S = TFE
Upon heating the tube to 110 C, the complete conversion of 6b
and 10b into 7bM occurred within a few minutes (Fig. 3, trace
d), which means that the l-CO PdI dimer is not a dead end for
the CO–C2H4 copolymerization reaction.14b The b-chelates 7bM
were the only phosphorus-containing compounds also at room
or adventitious H2O; Scheme 4) whose 31P{ H} NMR spectrum
1
consists of a singlet at d 27.9 (Fig. 2, trace a). On pressurizing the
sapphire tube with CO (14.0 bar) at room temperature, 4aꢀꢀ was
5596 | Dalton Trans., 2007, 5590–5602
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©

to elucidate the intrinsic factors that, in a broader sense, favour
non-alternation over perfect alternation.
Two clear facts have emerged from the carbonylation of PdII(P ∼
O)alkyl precursors: (i) The formation of acyl complexes (migratory
insertion of Pd(alkyl)CO) is much faster for the species supported
by La (Scheme 5), but neither system forms stable CO adducts
(Schemes 5 and 6). The latter evidence contrasts remarkably with
the behaviour of PdII(diphosphine) catalysts for the perfect CO–
C2H4 alternation that invariably form detectable Pd(acyl)CO or
Pd(alkyl)CO intermediates with relevance in the rate-determining
step.1,7b,16c As suggested in a previous section, the low propensity
to bind strongly CO, as a crucial factor for favouring multiple
ethylene insertions,3d,e may be due to the scarce basicity of the
PdII centres modified with P ∼ O− ligands. (ii) Once formed,
the acyl complexes exhibit different reactivity with methanol: the
complex with La is stable at room temperature and undergoes
methanolysis only at 90 ◦C; in contrast, the acyl complex with
ligand Lb reacts with MeOH already at room temperature. Since
methanolysis is an effective chain transfer mechanism in the
present copolymerization reactions, this evidence may account for
the lower activity and smaller molecular weight materials obtained
with 1b.
Convincing evidence has been accumulated showing b-chelates
to be key intermediates in the non-alternating copolymerization
(Figs. 2 and 3) as hypothesized by Drent.3a In particular, the for-
mation of both b-chelates (migratory insertion of Pd(acyl)C2H4) is
much faster for the species supported by La (Scheme 5a). Unlike
the b-chelates supported by diphosphine ligands and selective for
perfect alternation, however, the b-chelates supported by the P
∼ O− ligands are opened to the alkyl form both by CO and by
ethylene (Schemes 6 and 7), which contrasts with the behaviour of
PdII(diphoshine) analogues opened exclusively by CO.16b
1
Fig.
3
Variable-temperature 31P{ H} NMR study (sapphire tube,
MeOH-d4, 81.01 MHz) of the non-alternating CO–ethylene copolymeriza-
tion reaction catalyzed by pre-catalyst 5b: (a) 4bꢀ obtained from 5b under
nitrogen at 22 ◦C; (b) under CO (200 psi) at 22 ◦C; (c) under CO–C2H4 (1 :
3) (800 psi) at 22 ◦C; (d) after 10 min at 110 ◦C; (e) after cooling to 22 ◦C.
temperature (Fig. 3, trace e). Again, the broadness of the resonance
is attributed to the formation of several generations of b-chelates.
The 31P{ H} HPNMR experiment illustrated in Fig. 3 was
1
repeated in the presence of TsOH (20 equiv.) added just after
dissolving 5b in MeOH-d4. Since the NMR picture was fully
comparable to that shown in Fig. 2, one may conclude that also in
effective copolymerization conditions (Table 4), the b-chelates are
key intermediates in the catalysis cycle.
Mechanistic considerations
The model organometallic and operando studies have shown
that the two PdII(P ∼ O) systems under investigation catalyze
the non-alternating CO–C2H4 copolymerization via quite similar
mechanisms. For catalytic systems exhibiting both a similar
mechanism and a comparable chemical stability, a dramatically
different activity, as it has been observed for 1a and 1b, would
be interpreted in terms of different rates of relevant steps in the
catalytic cycle. Unfortunately, both precursors and intermediates
supported by Lb are much less stable than analogous derivatives
supported by La. Therefore, it is very likely that the main reason
for the much lower productivity of the reactions catalyzed by
1b is just the faster degradation of catalytically active species
into inactive ones. Since La and Lb differ only for the backbone
Theoretical studies of the non-alternating CO–ethylene copoly-
merization catalyzed by neutral Pd(P ∼ O) complexes suggest that
the rate determining step for the extra-ethylene insertion is the
migratory insertion of Pd(alkyl)(C2H4) (intermediate C) shown
in Scheme 9.3d,e This scheme has been supplemented with the
introduction of a b-chelate intermediate.
Therefore, the experimental conditions that favour the accumu-
lation of intermediate C at the expense of the concentration of
intermediate E would favour the extra-ethylene insertion into the
growing polymeric chain.3d,e Indeed, the extra-ethylene insertion
increases by increasing the partial pressure of ethylene and the
reaction temperature.3 Furthermore the increasing amount of
Brønsted acid in combination with the more flexible precatalysts
1b/5b may favour the unfastening of the sulfonate unit from
the palladium atom thus favouring the isomerization reaction of
the Pd(alkyl)(C2H4) species B into C. Indeed, from theoretical
calculations emerged, that the latter species inserts ethylene much
more rapidly than the former one does, due to the fact, that the
phosphorus atom in species C exerts a higher trans influence on the
migrating alkyl group as compared to the oxygen atom in species
B.3d,e
−
rigidity of the spacer between the P(aryl)2 and SO3 groups, one
may suggest that the more flexible ligand Lb, having a higher
degree of freedom, does not chelate the metal centre as strongly
as La, leading to less stable monodentate complexes, which may
be favoured on increasing the amount of Brønsted-acid. The
positive effect of ligand rigidity in catalysis has innumerable
precedents in the literature, including several examples of CO–
olefin copolymerization.17
Keeping in mind that the lower productivity of the reactions
assisted by 1b and related species is mainly due to the lower catalyst
stability, let us proceed to analyze the results obtained in the course
of the model and operando studies. Indeed, we feel that some of
these results are very useful to better comprehend the different
activity of the catalysts investigated, while others may contribute
Conclusions
A comparative study of the non-alternating CO–C2H4 copoly-
merization reaction catalyzed by neutral PdII complexes modified
with phosphine–sulfonate ligands has shown that the higher the
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Dalton Trans., 2007, 5590–5602 | 5597
©

Scheme 9
backbone rigidity of the P ∼ O ligand, the higher the catalytic
Bruker ACP 200 (200.13, 50.32 and 81.01 MHz, respectively)
or a Bruker Avance DRX-400 spectrometer (400.13, 100.62
and 161.98 MHz), respectively. Chemical shifts are reported in
ppm (d) relative to TMS, referenced to the chemical shifts of
residual solvents resonances (1H and 13C NMR) or 85% H3PO4
(31P NMR). High-pressure NMR (HP-NMR) experiments were
carried out on a Bruker ACP 200 using a 10 mm HP-NMR tube
(Saphikon sapphire tube purchased from Milford, NH; titanium
high-pressure charging head constructed at the ICCOM-CNR).19
Elemental analyses were performed using a Carlo Erba Model
1106 elemental analyzer. Infrared spectra were recorded on a FT-
IR Spectrum GX instrument (Perkin Elmer). Polyketone products
activity, the molecular weight and the extra-ethylene contents of
the polyketones.
Operando HP-NMR studies have allowed us to intercept for
the first time PdII (phosphine–sulfonate) b-chelates in the catalysis
cycle, while model organometallic reactions have contributed to
demonstrate that PdII(P ∼ O) fragments do not form stable
carbonyl complexes. Notably, the opening of PdII(P ∼ O) b-
chelates is a viable process by either comonomer, which con-
trasts with the behaviour of PdII(diphosphine) catalysts for the
perfectly alternating copolymerization. This finding may be the
clue to rationalize the mechanism of the non-alternating CO–C2H4
copolymerization as well as design improved catalytic systems for
such a process.
1
1
were analysed by IR, H, and 13C{ H} NMR spectroscopy. The
NMR measurements were performed in a solvent mixture of
1,1,1,3,3,3-hexafluoroisopropanol-d2 (HFIP-d2)/C6D6 (1 : 3, v/v).
1
1
The assignment of H9 and 13C{ H} NMR3a chemical shifts was
made on the basis of reports in the literature. The number-average
molecular weight (Mn) of the low-molecular weight copolymers
was determined by 1H NMR spectroscopy. The extra C2H4
Experimental
Materials and physical measurements
1
All reactions and manipulations were carried out under a nitrogen
atmosphere by using Schlenk-type techniques. The solvents were
generally distilled over dehydrating reagents and were deoxy-
genated before use. The reagents were used as purchased from
Aldrich or Fluka, unless stated otherwise. (2-MeO-C6H4)2P-
insertion (%) was calculated from 13C{ H} NMR spectra. Melting
points were recorded on a Stuart Scientific SMP3 apparatus.
Preparations
3a
4
1
(H)C6H4SO3
(HLa), (2-MeO-C6H4)2P(H)C2H4SO3 (HLb),
Pd(g1,g2-codyl*)(La) (1a). A solution of [Pd(l-Cl)(g ,g2-
PdCl(Me)(cod) (cod = 1,5-cyclooctadiene),18 [Pd(l-Cl)(g ,g -
codyl*)]2 (103.4 mg, 0.184 mmol) in CH2Cl2 (2 mL) was added
to a solution of the sodium salt of the ligand previously prepared
in situ by reaction of NaH (14.7 mg, 0.368 mmol) with HLa
(148.2 mg, 0.368 mmol) in CH2Cl2 (5 mL) for 30 min at room
temperature. After 1 h stirring at room temperature, the resulting
solution was concentrated to 2 mL. Addition of n-pentane (10 mL)
led to the precipitation of a yellow microcrystalline product, which
was filtered off and washed with n-pentane. Yield 67% (160 mg).
C29H33O6PPdS (647.03): calc. C 53.83, H 5.14; found C 53.42, H
1
2
1
2
codyl*)]2 (codyl*
=
2-methoxycyclooct-5-enyl),5 Pd(g ,g -
codyl*)(Lb)4 (1b), and [PdClMe(La)](NHEt3)8 (3a) were prepared
according to literature methods. All the isolated solid samples
were collected on sintered-glass frits and washed with appropriate
solvents before being dried under a stream of nitrogen. Copoly-
merization reactions were performed with a 200 mL stainless steel
autoclave constructed at the ICCOM-CNR, equipped with a mag-
netic drive stirrer and a temperature and pressure controller. The
autoclave was connected to a gas reservoir to maintain a constant
pressure during the catalytic reactions. GC-MS analyses of the
solutions were performed on a Shimadzu QP2010S apparatus
equipped with a SPB-1 Supelco fused silica capillary column (30
m, 0.25 mm i.d., 0.25 lm film thickness). Deuterated solvents for
routine NMR measurements were dried over molecular sieves.
1
5.01%. H NMR (CDCl3, 400.13 MHz): d 1.70–2.72 (m, 10H,
codyl-H), 2.42 (s, 3H, codyl-OMe), 3.59 (s, 3H, Ar-OMe), 3.65
(s, 3H, Ar-OMe), 6.04 (m, 1H, codyl-H), 6.72 (m, 1H, codyl-H),
3
6.92–7.51 (m, 10H, Ar-H/Anisyl-H), 8.07 (dd, J(HP) 20.0 Hz,
3
3
3J(HH) 8.0 Hz, 1H, Ar-Ho), 8.16 (dd, J(HP) 12.4 Hz, J(HH)
10.0 Hz, 1H, Anisyl-Ho). 13C{ H} NMR (CDCl3, 100.62 MHz):
1
1
1
1H, 13C{ H}, 31P{ H} NMR spectra were obtained on either a
d 25.37 (s, codyl-C), 28.62 (s, codyl-C), 30.72 (s, codyl-C), 35.26
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1
(s, codyl-C), 40.72 (s, codyl-C), 54.82 (s, OMe), 55.27 (s, OMe),
55.54 (s, OMe), 81.55 (s, codyl-C), 111.24 (s, Ar–C), 114.70 (d,
Ar–CHm), 111.59 (d, J(CP) 53.7 Hz, 2C, Ar-Cipso), 120.55 (d,
3J(CP) 11.2 Hz, 2C, Ar–CHm), 133.25 (s, 2C, Ar–CHo), 135.81 (s,
1J(CP) 52.0 Hz, Ar-Cipso), 115.37 (d, J(CP) 52.0 Hz, Ar-Cipso),
2C, Ar-CHp), 160.62 (s, 2C, Ar–Co). 31P{ H} NMR (MeOH-d4,
1
1
117.08 (d, 3J(CP) 9.2 Hz, CH), 120.85 (d, 3J(CP) 9.4 Hz, Ar–C),
161.98 MHz): d 31.44 (s).
121.14 (d, 3J(CP) Ar–C), 121.42 (d, 2J(CP) 12.1 Hz, CH), 127.10
Reaction of [PdClMe(L)](NHEt3) (L = La (3a), Lb (3b)) with
AgOTs: in situ synthesis of neutral complexes of the type
Pd(solvent)Me(L). The appropriate chloro-methylpalladium
complex (0.12 mmol) was added to a Schlenk flask contain-
ing a solution of AgOTs (OTs = p-toluenesulfonate, 33.5 mg,
0.12 mmol) in CD2Cl2 (2 mL) at room temperature. After 20 min
stirring, the solution was carefully filtered and introduced by a
syringe into a NMR tube. Multinuclear NMR analysis showed the
formation of (NHEt3)OTs together with a new methylpalladium
complex of the formula Pd(S)Me(L) (S = CD2Cl2 or adventitious
water).10 Spectroscopic data of Pd(S)Me(La). 1H NMR (CD2Cl2,
400.13 MHz): d 0.16 (s, 3H, PdMe), 3.69 (s, 6H, OMe), 7.05–
1
2
(d, J(CP) 51.5 Hz, Ar-Cipso), 127.85 (d, J(CP) 7.5 Hz, Ar–C),
128.45 (d, 2J(CP) 6.8 Hz, Ar–C), 130.27 (s, Ar–C), 132.93 (s, Ar–
C), 134.27 (s, Ar–C), 134.90 (s, Ar–C), 134.93 (d, 3J(CP) 5.2 Hz,
Ar–C), 140.47 (d, 2J(CP) 27.8 Hz, Ar–C), 147.90 (s, Ar–C), 160.04
1
(s, Ar–C), 161.06 (s, Ar–C). 31P{ H} NMR (CDCl3, 161.98 MHz):
d 8.20 (s).
Thermal reaction of 1a in MeOH: synthesis of Pd(La)2 (2a).
Compound 1a (84.1 mg, 0.13 mmol) was dissolved in MeOH
(3 mL) under nitrogen and heated to 90 ◦C for 2 h. During
this time yellow microcrystals of 2a precipitated along with
palladium black. The solution was allowed to cool slowly to room
temperature. The product was decanted, filtered and washed with
n-pentane (3 mL). The product was insoluble in common organic
solvents including DMF and DMSO. Yield: 40% (23.6 mg).
C40H36O10P2PdS2 (908.83): calc. C 52.86, H 3.96; found C 52.99,
H 4.52%.
3
4
7.61 (m, 11H, Ar-H), 8.04 (dd, J(HH) 7.5 Hz, J(HP) 4.6 Hz,
1H, Ar–Ho). 31P{ H} NMR (CD2Cl2, 161.98 MHz): d 26.90
1
(s). Spectroscopic data of Pd(S)Me(Lb). 1H NMR (CD2Cl2,
400.13 MHz): d 0.31 (s, 3H, PdMe), 3.1–3.3 (m, 4H, CH2CH2), 3.91
(s, 6H, OMe), 7.0–7.8 (m, 8H, Ar–H). 31P{ H} NMR (CD2Cl2,
1
161.98 MHz): d 37.61 (s). After the extraction of (NHEt3)OTs with
D2O, the NMR spectra of the residual CD2Cl2 solution showed
no significant change, which is consistent with the presence of
the same methylpalladium complex, most likely as a D2O adduct
(vide infra, 4a,4b). Evaporation under reduced pressure of this
CD2Cl2 solution led to an off-white solid residue (5a,5b, vide
infra) that, once formed, was completely insoluble in CD2Cl2,
whereas it dissolved readily in MeOH-d4. The NMR spectra of
these solutions were practically identical to those of the solvated
methylpalladium complexes reported above. Accordingly, we think
that the coordinated solvent is either MeOH-d4 or water (vide infra,
4aꢀ–4bꢀ) with a preference for the latter as reported in the literature
for PdII complexes with chelating ligands.10
Thermal reaction of 1b in MeOH: synthesis of Pd(Lb)2 (2b).
Compound 1b (80.0 mg, 0.13 mmol) was dissolved in MeOH
(3 mL) under nitrogen and heated to 60 ◦C for 30 min. During
this time yellow microcrystals of 2b precipitated along with
palladium black. The solution was allowed to cool slowly to room
temperature. The product was decanted, filtered and washed with
n-pentane (3 mL). The product was insoluble in common organic
solvents including DMF and DMSO. Yield: 36% (19.0 mg).
C32H36O10P2PdS2 (813.12): calc. C 47.27, H 4.46; found C 47.01,
H 4.38%.
Alternative synthesis of 2b. A solid sample of the ligand HLb
(38.5 mg, 0.109 mmol) was added to a solution of Pd(OAc)2
(12.2 mg, 0.054 mmol) in CH2Cl2 (2 mL). The resulting solution
was allowed to stand for 3 h at room temperature. During this time
the product precipitated as yellow crystals, which were filtered
off and washed with diethyl ether (5 mL). Yield: 65% (28 mg).
C32H36O10P2PdS2 (813.12): calc. C 47.27, H 4.46; found C 46.95,
H 4.45%.
Synthesis of [PdMe(L)]2 (L = La (5a), Lb (5b)). The appropri-
ate chloro-methylpalladium complex 3a,3b (0.20 mmol) was added
to a Schlenk flask containing a solution of AgOTs (0.21 mmol) in
CD2Cl2 (5 mL) at room temperature. The suspension was stirred
for 30 min and then filtered through a Celite column. The CH2Cl2
solution was extracted with water (3 × 5 mL). Solvent evaporation
under reduced pressure led to an off-white solid residue of the
dinuclear complex 5a,5b in rather low yield: 5a, 36.0 mg (35%);
5b, 38.0 mg (40%). C42H42O10Pd2P2S2 (1045.70) (5a): calc. C 48.24,
H 4.05; found C 48.15, H 3.90%. C34H42O10Pd2P2S2 (949.61)
(5b): C 43.00, H 4.46; found C 42.91, H, 4.37%. Both dinuclear
complexes were not soluble in CH2Cl2 but very soluble in MeOH
(or MeOH-d4) where they regenerated the mononuclear complexes
Pd(S)Me(L) (L = La (4aꢀ), Lb (4bꢀ); S = MeOH/MeOH-d4
[PdClMe(Lb)](NHEt3)
(3b). Triethylamine
(97.6
lL,
0.70 mmol) was syringed into a solution of ligand HLb
(49.6 mg, 0.14 mmol) in CH2Cl2 (10 mL). After 15 min stirring
at room temperature, solid PdClMe(cod) (37.1 mg, 0.14 mmol)
was added. The resulting solution was stirred for 1 h at room
temperature and then filtered through a Celite column. Addition
of n-hexane (20 mL) caused the precipitation of the product as
off-white microcrystals, which were filtered off and washed with
n-hexane. Yield: 73% (62 mg). C23H37ClNO5PdPS (612.46): calc.
1
and/or adventitious H2O). Spectroscopic data for 4aꢀ. H NMR
1
3
C 45.11, H 6.09; found C 45.01, H 5.97%. H NMR (MeOH-d4,
(MeOH-d4, 400.13 MHz): d 0.18 (d, J(HP) 0.8 Hz, 3H, PdMe),
3
400.13 MHz): d 0.37 (s, 3H, PdMe), 1.33 (t, 3J(HH) 7.2 Hz, 9H,
CH2CH3), 3.02 (m, 2H, CH2S), 3.12 (m, 2H, CH2P), 3.22 (q,
3J(HH) 7.2 Hz, 6H, NCH2), 3.91 (s, 6H, OMe), 7.05 (m, 2H,
Ar-H), 7.15 (m, 2H, Ar-H), 7.57 (m, 2H, Ar–H), 7.68 (m, 2H,
3.69 (s, 6H, OMe), 7.05–7.61 (m, 11H, Ar–H), 8.02 (dd, J(HH)
4
1
7.6 Hz, J(HP) 4.8 Hz, 1H, Ar–Ho). 13C{ H}NMR (MeOH-d4,
100.62 MHz): d −0.63 (s, PdMe), 54.31 (s, OMe), 111.33 (d, 3J(CP)
4.3 Hz, Ar–CHm), 115.37 (d, 1J(CP) 61.4 Hz, Ar-Cipso), 120.20 (d,
Ar–H). 13C{ H} NMR (MeOH-d4, 100.62 MHz): d −0.20 (s,
3J(CP) 12.5 Hz, Ar-CHm), 126.80 (d, J(CP) 8.3 Hz, Ar–CH),
127.84 (d, J(CP) 53.0 Hz, Ar-Cipso), 128.74 (d, J(CP) 8.2 Hz,
Ar–CH), 129.99 (s, 2C, Ar–CH), 133.56 (s, Ar–CHo), 134.92 (s,
Ar–CH), 137.40 (s, Ar-CHp), 146.87 (d, 2J(CP) 14.0 Hz, Ar-
1
3
1
3
1C, PdMe), 7.87 (s, 3C, CH2CH3), 22.32 (d, 1J(CP) 33.7 Hz,
1C, CH2P), 46.48 (s, 3C, CH2CH3), 47.60 (overlapped signal,
3
1C, CH2S), 55.12 (s, 2C, OMe), 111.31 (d, J(CP) 4.3 Hz, 2C,
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Dalton Trans., 2007, 5590–5602 | 5599
©

1
1
C), 160.44 (s, Ar-Co). 31P{ H} NMR (MeOH-d4, 161.98 MHz):
d4, 100.62 MHz): d 227.60 (s, CO). 31P{ H} NMR (MeOH-
d 26.98 (s). Spectroscopic data for 4bꢀ. 1H NMR (MeOH-d4,
d4, 161.98 MHz): d 8.09 (s). Selected spectroscopic data for
3
1
400.13 MHz): d 0.11 (d, J(HP) 1.2 Hz, 3H, PdMe), 3.06 (m,
10b. 13C{ H} NMR (MeOH-d4, 100.62 MHz): d 225.36 (s, CO).
1
2H, CH2S), 3.12 (m, 2H, CH2P), 3.90 (s, 6H, OMe), 7.04–7.65 (m,
31P{ H} NMR (MeOH-d4, 161.98 MHz): d 8.55 (s).
8H, Ar-H). 13C{ H} NMR (MeOH-d4, 100.62 MHz): d −2.22 (s,
1
Reaction of 6a,6b with C2H4: in situ synthesis of PdCH2CH2-
COMe(L) (L = La, 7a; Lb, 7b). A MeOH-d4 solution of 6a,6b
(9b/10b) prepared as reported above at room temperature was
treated with nitrogen for 2 min to eliminate the excess CO. During
this procedure 10b converted into 9b. Bubbling ethylene at
room temperature for 2 and 20 min, respectively, led to the
complete transformation of 6a,6b into 7a,7b. IR spectroscopic
data in CH2Cl2 for 7a and 7b were obtained by evaporating both
MeOH-d4 solutions to dryness and re-dissolving the residue in
1
PdMe), 22.99 (d, J(CP) 35.2 Hz, CH2P), 46.84(s, CH2S), 54.78
3
1
(s, OMe), 111.31 (d, J(CP) 4.3 Hz, Ar-CHm), 115.32 (d, J(CP)
3
53.7 Hz, Ar-Cipso), 120.55 (d, J(CP) 11.2 Hz, Ar-CHm), 133.25
(s, Ar-CHo), 136.91 (s, Ar-CHp); 160.36 (s, Ar-Co). 31P{ H} NMR
1
(MeOH-d4, 161.98 MHz): d 37.67 (s). The low yields of 5a and
5b were simply due to the extraction procedure adopted. Indeed,
on concentrating the water phases to dryness, a solid residue was
obtained, which was dissolved in MeOH-d4 and authenticated by
NMR spectroscopy as a mixture of (NHEt3)OTs and either 4aꢀ or
4bꢀ.
1
CH2Cl2. Selected spectroscopic data for 7a. H NMR (MeOH-
d4, 400.13 MHz): d 1.33 (td, 3J(HH) 6.2 Hz, 3J(HP) 2.6 Hz,
3
2H, PdCH2), 2.36 (s, 3H, COMe), 2.84 (t, J(HH) 6.2 Hz, 2H,
Reaction of 4aꢀ–4bꢀ with CO: in situ synthesis of Pd(Lꢀ)-
(COMe)(L) (L = La (6a), Lb (6b); Lꢀ = CO, CD3OD, H2O).
A sample of 5a,5b (0.05 mmol) was dissolved in MeOH-d4
(1.5 mL) and the solution was transferred into a 5 mm NMR
tube. The NMR spectra of this solution showed the presence
of the mononuclear methylpalladium complex 4aꢀ,4bꢀ. Bubbling
CO through a solution of 4bꢀ at room temperature converted the
latter compound into a 2 : 1 : 1 mixture of 6b and the CO-
bridged PdI dimers (l-CO)[Pd(Lb)]2 (9b) and [Pd( l-CO)(Lb)]2
(10b) in 40 min. The formation of the latter two complexes was
preceded by the methanolysis of 6b as indicated by the production
of CH3C(O)OCD3 (1H NMR and GC/MS analysis). Bubbling
nitrogen through the final reaction mixture converted 10b into 9b,
which accounted for the assigned structures. In contrast, bubbling
CO through the solution of 4aꢀ at room temperature produced
quantitatively the acetyl complex 6a in only 10 min. To verify an
eventual methanolysis reaction of 6a, the corresponding MeOH-
d4 solution contained in a 10 mm HPNMR tube was progressively
heated under CO (14.0 bar). At 90 ◦C, the methanolysis reaction
occurred yielding CH3C(O)OCD3 and the deuterated free ligand
DLa in its zwitterionic form. Selected spectroscopic data for DLa.
COCH2). 13C{ H} NMR (MeOH-d4, 100.62 MHz): d 20.63 (s,
1
PdCH2), 26.34 (s, COMe), 49.80 (s, COCH2), 231.59 (s, COMe).
31P{ H} NMR (MeOH-d4, 161.98 MHz) d 21.73 (s). IR (CH2Cl2):
1
m(CO) 1641 cm−1. Selected spectroscopic data for 7b. H NMR
1
(MeOH-d4, 400.13 MHz): d 1.21 (td, 3J(HH) 6.2 Hz, 3J(HP)
2.4 Hz, 2H, PdCH2), 2.30 (s, 3H, COMe), 2.81 (t, 3J(HH) 6.2 Hz,
2H, COCH2); 13C{ H} NMR (MeOH-d4, 100.62 MHz): d 19.80 (s,
1
PdCH2), 26.02 (s, COMe), 49.47 (s, COCH2), 230.86 (s, COMe);
31P{ H} NMR (MeOH-d4, 161.98 MHz): d 32.80 (s). IR (CH2Cl2):
1
m(CO) 1641 cm−1.
Reaction of 7a with CO: in situ synthesis of Pd(Lꢀ)COCH2-
CH2COMe(La) (8a; Lꢀ = CO, CD3OD, H2O). A MeOH-d4
solution of 7a prepared as reported above at room temperature
was treated with nitrogen for 2 min to eliminate the excess ethylene.
Bubbling CO at room temperature for 10 min led to the complete
transformation of 7a into 8a. Bubbling nitrogen through the
solution of 8a caused no change in the 13C{ H} and 31P{ H}
NMR spectra. To verify the eventual coordination of CO in 8a, the
reaction was carried out also under a (1 : 9) 13CO/12CO mixture
1
1
(14.0 bar): no additional C–P coupling was detected in the 13C{ H}
1
31P{ H} NMR (MeOH-d4, 90 ◦C, 81.01 MHz): d −9.20 (br.
1
and 31P{ H} NMR spectra, which confirmed that the fourth
1
s). 31P{ H} NMR (CD2Cl2, 90 ◦C, 81.01 MHz): d −10.80 (1 :
1
position in the palladium coordination sphere was occupied by CO
and solvent molecules in rapid exchange. Selected spectroscopic
1
1 : 1 triplet, J(PD) 92.0 Hz). When the solutions of 6a or 6b
(9b/10b) were treated with nitrogen to eliminate the excess of
1
data for 8a. H NMR (MeOH-d4, 400.13 MHz): d 2.02 (s, 3H,
CO, no change in their 13C{ H} and 31P{ H} NMR spectra of
6a,6b was observed. The carbonylation reactions of 4aꢀ,4bꢀ were
carried out also under a (1 : 9) 13CO/12CO mixture (14.0 bar): no
1
1
3
3
COMe), 2.18 (t, J(HH) 6.6 Hz, 2H, CH2CO), 2.61 (t, J(HH)
6.6 Hz, 2H, PdCOCH2). 13C{ H} NMR (MeOH-d4, 100.62 MHz):
1
3
d 28.28 (s, COMe), 36.97 (s, CH2CO), 39.92 (d, J(CP) 26.3 Hz,
additional C–P coupling was detected in the 13C{ H} and 31P{ H}
NMR spectra as compared to those acquired under standard
CO. These additional experimental evidences indicated that, under
CO atmosphere, the fourth position in the palladium coordination
sphere of both acetyl complexes was occupied by CO and solvent
molecules in rapid exchange. Selected spectroscopic data for 6a.
1
1
PdCOCH2), 210.18 (s, COMe), 221.44 (d, 2J(CP) 7.5 Hz, COCH2).
31P{ H} NMR (MeOH-d4, 161.98 MHz): d 14.53 (s).
1
Reaction of 7a with C2H4 in 2,2,2-trifluoroethanol (TFE).
A
solution of 7a (0.03 mmol) in a 3 : 1 (v/v) mixture of TFE/C6D6
was prepared following a procedure analogous to that reported
above in MeOH-d4. The solution was then transferred into a HP-
NMR tube and pressurized with ethylene to 42.0 bar at room
1H NMR (MeOH-d4, 400.13 MHz): d 1.85 (d, J(HP) 0.4 Hz,
4
3H, COMe). 13C{ H} NMR (MeOH-d4, 100.62 MHz): d 34.24
1
3
2
1
(d, J(CP) 29.2 Hz, COMe), 222.58 (d, J(CP) 8.0 Hz, COMe).
temperature (31P{ H} NMR singlet at d 21.50). The tube was
31P{ H} NMR (MeOH-d4, 161.98 MHz): d 13.60 (s). Selected
gradually heated (10 ◦C steps) and 31P{ H} NMR spectra were
1
1
acquired at all temperatures. At 110 ◦C, 7a started to convert most
1
spectroscopic data for 6b. H NMR (MeOH-d4, 400.13 MHz):
d 1.84 (d, J(HP) 0.4 Hz, 3H, COMe). 13C{ H} NMR (MeOH-
likely into a new alkyl species (31P{ H} NMR singlet at d 24.20).
4
1
1
3
d4, 100.62 MHz): d 32.38 (d, J(CP) 28.1 Hz, COMe), 223.34
After 20 min, the HP-NMR tube was cooled to room temperature.
(s, COMe). 31P{ H} NMR (MeOH-d4, 161.98 MHz): d 23.66
The 31P{ H} spectrum showed a ca. 50% conversion of 7a into the
1
1
(s). Selected spectroscopic data for 9b. 13C{ H} NMR (MeOH-
new compound (d 25.80). After removal of the tube from the
1
5600 | Dalton Trans., 2007, 5590–5602
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©

NMR probe, a thin layer of linear polyethylene located at the
solid–gas interphase was visible in the tube. A GC-MS analysis of
the solution showed no formation of oligomers.
An experimental absorption correction (psi-scan) was performed.
All structure determination calculations were performed with the
WINGX package20a with SIR-9720b SHELXL-9720c and ORTEP-
3 programs.20d 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 respective
carbon atoms. Crystallographic data of 2b are reported in Table 1.
CCDC reference number for 2b: 653758.
Catalytic copolymerisation of CO and ethylene
Autoclave experiments in MeOH or TFE with 1a, 1b, 5a and
5b as catalyst precursors. Typically, MeOH (50 mL) or TFE
(50 mL), was introduced by suction into an autoclave (200 mL),
previously evacuated by a vacuum pump, containing the catalyst
precursor (0.012 mmol palladium). When the catalytic reaction
was performed in the presence of 1,4-benzoquinone (BQ) or p-
toluenesulfonic acid monohydrate (TsOH), these compounds and
the catalytic precursor were added together in the autoclave. The
autoclave was then charged with the desired CO–C2H4 mixture to
42.0 bar at room temperature followed by heating to the desired
temperature. Once the desired temperature was reached the total
pressure of the gas mixture was equilibrated to 56.0 bar and
stirring (1300 rpm) was started. After the desired reaction time,
the autoclave was cooled by means of an ice–water bath and the
gases released. Due to the much higher solubilizing capacity of
TFE13 for the copolymer as compared to MeOH, two different
procedures were employed to collect the copolymer products. For
the experiments in MeOH, the insoluble copolymer was filtered
off, washed with MeOH, and dried under vacuum at 60 ◦C to
constant weight. For the experiments in TFE, the catalysis mixture
was poured into MeOH (100 mL), followed by stirring for 30 min
before filtering the solid product.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b711280g
Acknowledgements
Thanks are due to the European Commission (STREP contract
no. NMP3-CT-2005–516972-NANOHYBRID) and Ministero
dell’Istruzione, dell’Universita` e della Ricerca (FIRB contract
n. RBNE03R78E-NANOPACK and FISR project “Nanosistemi
inorganici ed ibridi per lo sviluppo e l’innovazione di celle a
combustibile”) for financial support.
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