A new class of ruthenium complexes containing Schiff base ligands as promising catalysts for atom transfer radical polymerization and ring opening metathesis polymerization

Article abstract of DOI:10.1016/S1381-1169(01)00451-4

A novel series of Schiff base ruthenium complexes that are active catalysts in the field of atom transfer radical polymerization (ATRP), have been prepared. Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good cataly

Full text of DOI:10.1016/S1381-1169(01)00451-4

Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
A new class of ruthenium complexes containing Schiff base
ligands as promising catalysts for atom transfer radical
polymerization and ring opening metathesis polymerization
Bob De Clercq, Francis Verpoort∗
Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281 (S-3), 9000 Gent, Belgium
Received 15 August 2001; accepted 12 November 2001
Abstract
A novel series of Schiff base ruthenium complexes that are active catalysts in the field of atom transfer radical polymerization
(ATRP), have been prepared. Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good
catalytic activity in the ring opening metathesis polymerization (ROMP) of norbornene and cyclooctene. The activity for both
the ROMP and ATRP reaction is dependent on the steric bulk and electron donating ability of the Schiff base ligand. The
control over polymerization in ATRP was verified for the two substrates that exhibit the highest activity, namely MMA and
styrene. The results show that the optimal ATRP equilibrium leading to a controlled polymerization, can be established by
adjusting the steric and electronic properties of the Schiff base ligand. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Ring opening metathesis polymerization; Atom transfer radical polymerization; Ruthenium alkylidene; Schiff bases; Homogeneous
catalysis
1. Introduction
important commercial process leading to high molecu-
lar weight polymers. A large variety of monomers can
be polymerised and copolymerised radically under rel-
atively simple experimental conditions which require
the absence of oxygen but can be carried out in the
presence of water. However, free radical polymeriza-
tion processes often yield polymers with ill-controlled
molecular weights and high polydispersities. The idea
of combining the advantages of both living polymer-
ization and radical polymerization has attracted much
attention. Indeed, recent years have witnessed a rapid
progress in the development of controlled/“living”
radical polymerization. Among the newly introduced
controlled radical polymerization processes, atom
transfer radical polymerization (ATRP) is most suc-
cessful. The groups of Kato et al. [4], and Wang and
Matyjaszewski [5] reported in 1995 on this living
radical polymerization process. ATRP is based on a
Well-defined polymers with low polydispersities
(PDI) and complex architectures can be achieved
by living polymerization processes in which there
is neither chain transfer nor termination. Before the
mid 90’s, most of the living polymerization systems
were reported for anionic [1], cationic [2] or group
transfer polymerizations [3]. However, the industrial
applications of these techniques have been limited by
the need for high-purity monomers and solvents,
reactive initiators and anhydrous conditions. In con-
trast, free radical polymerization is probably the most
∗ Corresponding author. Tel.: +32-9-264-44-36;
fax: +32-9-264-49-83.
E-mail addresses: b.declercq@rug.ac.be (B. De Clercq),
francis.verpoort@rug.ac.be (F. Verpoort).
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(01)00451-4

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B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
Scheme 1. Atom transfer radical polymerization (ATRP) (M: monomer, Mt: metal).
Fig. 1. Catalyst that are efficient for both olefin metathesis and ATRP reactions.
dynamic equilibration between the propagating rad-
icals and the dormant species which is established
through the reversible transition metal-catalysed clea-
vage of the covalent carbon–halogen bond in the
dormant species (Scheme 1).
Polymerization systems utilising this concept have
been developed with complexes of Cu, Ru, Ni, Pd, Rh
and Fe to establish the ATRP equilibrium [6].
Recently, there have been some reports on the
ATRP activity of the complexes 1, 2, 3 and 4 (Fig. 1)
[7]. The complexes 1, 2 and 3 are also known to be
highly efficient for ring opening metathesis polymeri-
zation (ROMP) reactions [8] and when activated with
trimethylsilyldiazomethane (TMSD) also 4 shows
high activity for ROMP reactions [9].
in ethanol (p.a.) at 80 ◦C for 2 h. Upon cooling to
0 ◦C, a yellow solid precipitated from the reaction mix-
ture. The solid was filtered, washed with cold ethanol
and then dried in vacuo to afford the desired salicy-
laldimine ligand in excellent yields. The condensation
of salicylaldehyde with the aliphatic amine derivatives
was carried out with stirring in THF at reflux tem-
perature for 2 h. The reaction mixture changed from a
colourless to a yellow solution and was further used
without purification (Scheme 2).
2.1.2. General procedure for the preparation
of thallium salts 2-a, 2-b, 2-c
To a solution of Schiff bases 1-a, 1-b, 1-c in THF
(15 ml) was added drop-wise a solution of thalli-
umethoxide in THF (5 ml) at room temperature. Im-
mediately after the addition, a yellow solid formed
and the reaction mixture was stirred for 2 h at room
temperature. Filtration of the solid under a nitrogen
atmosphere gave the thallium salts 2-a, 2-b, 2-c in
quantitative yields. The salts were immediately used
in the next step without further purification.
The dual behaviour of these ruthenium catalysts
prompted us to explore the activity of some new homo-
geneous catalytic ruthenium-based systems in the field
of ATRP and ROMP.
2. Results and discussion
2.1. Synthesis
2.1.3. General procedure for the preparation
of Schiff base substituted Ru complexes 3-a, 3-b, 3-c
To a solution of [RuCl2(p-cymene)]2 in THF (5 ml)
was added a solution of the corresponding thallium
salts in THF (5 ml). The reaction mixture was stirred
at room temperature for 6 h. The thalliumchloride
2.1.1. General procedure for the preparation
of Schiff base ligands
The condensation of salicylaldehyde with the aro-
matic amine derivative was carried out with stirring

B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
69
Table 1
Properties of the polyNBE formed with the catalytic systems 3-a,
3-b and 3-c when activated with a catalytic amount of TMSD
Mn
Mw
PDI
cis/trans
3-a
3-b
3-c
74000
78000
98000
471000
462000
682000
6.34
5.95
6.95
0.38
0.32
0.39
Table 2
Properties of the polycyclooctene formed with the catalytic systems
3-a, 3-b and 3-c when activated with a catalytic amount of TMSD
Mn
Mw
PDI
cis/trans
3-c
3-a
3-b
57000
55000
59000
262000
181000
196000
4.62
3.26
3.35
0.38
0.36
0.34
For both ROMP reactions of NBE and cyclooctene,
a linear increase of the conversion versus time is
observed within the time period of 80 min. After this
period, for all three systems the maximum conver-
sion for both NBE and cyclooctene polymerization
is reached. The catalytic system with the aromatic
substituted imine ligand (3-c) is clearly the most
active. The polydispersities are in all cases broad
which indicates that the polymerization is subjected
to backbiting and transfer reactions.
A trans configuration of the polyNBE and polycy-
clooctene is preferred. This is in accordance with the
general observation for ruthenium catalysts in ROMP
reactions [8].
Scheme 2. Reaction sequence for the synthesis of the three different
Schiff base substituted ruthenium catalysts (i) THF, ꢀ, 2 h for
H2NR1,2 and EtOH, 80 ◦C, 2 h for H2NR3; (ii) TlOEt, THF, RT,
2 h; (iii) [RuCl2(p-cymene)]2, THF, RT, 6 h.
When the polymerization of norbornene was tested
with pure TMSD (no addition of catalyst, 1 ml of
a 0.8410 M NBE solution in toluene and [NBE]/
[TMSD] = 800/2, tested at 85 and 40 ◦C, 6 h) no
polymerization was observed. However, when nor-
bornene was tested with the homogeneous catalyst 3-c
without activation with TMSD ([Ru]/[NBE] = 1/800,
1 ml toluene, 6 h), a conversion of 6% was observed.
Because there was no TMSD activation, the initiating
metal–carbene complex must result from a reaction
between the catalyst and the substrate olefin.
In order to elucidate the mechanism of carbene
formation, 0.5 mmol of the catalyst solution in C6D6
was transferred into a 15 ml vessel followed by the
addition of 1 equivalent of norbornene solution in
C6D6. The reaction mixture was then heated for 4 h
(the by-product of the reaction) was removed via fil-
tration. After evaporation of the solvent, the residue
was dissolved in a minimal amount of toluene and
cooled to 0 ◦C. The obtained crystals were then
washed with cold toluene (3 × 10 ml) and dried.
The Schiff base ruthenium complexes 3-a, 3-b, 3-c
appeared as red-brown solids.
The percentage conversion versus time plot for the
ROMP of norbornene and cyclooctene are depicted
in Figs. 2 and 3, respectively. The properties of the
polyNBE and polycyclooctene obtained with the dif-
ferent catalytic systems are summarised in Tables 1
and 2, respectively.

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B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
Fig. 2. Plot of the percentage conversion vs. time for the ROMP of norbornene using catalysts 3-a, 3-b and 3-c.
at 85 ◦C. After cooling to RT the reaction mixture
was quenched with 10 equivalents ethylvinylether.
1H-NMR of the reaction mixture revealed the presence
of a species containing the alkoxy substituted carbene
ligand [Ru] = CHOEt (compound 3, Scheme 3). The
proton of this species is absorbed at 14.95 ppm as a
singlet. After purification of the concentrated reaction
mixture by flash column chromatography using sil-
ica gel, the methylene–norbornane compound (com-
pound 4, Scheme 3) was unambiguously identified by
1H-NMR and 13C-NMR analysis. When a reaction
mixture of 0.5 mmol of the catalyst solution in C6D6
and 5 equivalents of norbornene solution in C6D6
was stirred for 4 h at 85 ◦C, the propagating carbene
proton of the polymer growing chain (compound
5, Scheme 3) appeared as a doublet at 18.85 ppm.
Despite careful NMR monitoring, no evidence was
found for a η4 or η2 ligation of the p-cymene ligand.
Moreover, the 1H-NMR measurements reveal that the
propagating ruthenium–carbene peak could be inte-
grated for about 2.5% of the total ruthenium in solu-
tion, in agreement with the amount of free p-cymene
released in the solution.
These results strongly support the assumption that
the homogeneous catalyst, which is an 18-electron
complex, catalyses the polymerization of norbornene,
through the loss of a p-cymene ligand followed by
coordination of the norbornene and rearrangement to
a ruthenium–carbene complex which then propagates
ROMP. Therefore, it is very reasonable to assume
that compound 2 from Scheme 3, produced by a
2,3 hydrogen shift in the ruthenium–olefin complex
Fig. 3. Plot of the percentage conversion vs. time for the ROMP of cyclooctene using catalysts 3-a, 3-b and 3-c.

B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
71
Scheme 3. Possible mechanism for the formation of the initial metal–carbene in the absence of TMSD.
(compound 1 from Scheme 3), is here the initiating
ruthenium–carbene complex.
catalytically active species in ROMP reactions with
3-a, 3-b and 3-c activated with TMSD.
When 2 equivalents TMSD were added to a solution
containing 0.5 mmol of catalytic system 3-c in C6D6,
evolution of nitrogen took place and a species con-
taining the trimethylsilyl-substituted carbene ligand,
In Table 3 polymer yields obtained with these cat-
alytic systems for ATRP reactions are summarised.
Here also catalyst 3-c gives the highest conversions.
For methylmethacrylate (entry 3) and styrene (entry 6)
almost quantitative conversions are obtained. Compar-
ing the catalytic activity of the different systems towa-
rds the polymerization of acrylates and methacrylates,
it is obvious that the methacrylates (entries 3 and 4)
are polymerised more easily than the acrylates (entries
1 and 2). For both the acrylates and methacrylates, the
conversion decreases when the substrate becomes too
bulky (compare entry 2 and 1 for the acrylates and en-
try 4 and 3 for the methacrylates). Unfortunately, the
catalysts were not able to polymerise acrylonitrile.
The properties of the polymers obtained with
styrene and methylmethacrylate (MMA), the two
substrates which give the highest conversions, are
depicted in Table 4. For the systems 3-a and 3-b the
quite broad polydispersities indicate a less controlled
polymerization.
1
[Ru] = CHSiMe3, was observed in H-NMR (in the
absence of olefin). The proton of this carbene species
absorbed at 23.66 ppm as a singlet and the methyl
groups of the carbene–trimethylsilyl moiety appeared
as a singlet at 0.46 ppm at room temperature. As soon
as norbornene (5 equivalents in C6D6) was added to
the reaction mixture, the species at 23.66 ppm van-
ished and was replaced by the propagating carbene
of the growing polymer chain at 18.85 ppm. Now,
the ruthenium–carbene peak could be integrated for
about 12% of the total ruthenium in solution, again
in agreement with the amount of free p-cymene re-
leased in solution after addition of TMSD. Again, no
η4 or η2 ligation of the arene ligand was observed
during 1H-NMR monitoring of the reaction mix-
ture. Moreover, studies by other teams dealing with
metathesis reactions mediated by ruthenium–arene
complexes have shown that the release of the arene
ligand is crucial and is responsible for the generation
of the catalytically active species [7,10,13]. Therefore,
it is plausible to state that the mechanism depicted
in Scheme 4 is responsible for the formation of the
However, for system 3-c, the good initiator efficien-
cies and the polydispersities obtained, indicate that the
polymerization proceeds in a more restrained fashion.
Moreover, the linear time dependence of ln ([M]0/
[M]t ) (Fig. 4) and the linear relationship between Mn
and the conversion (Fig. 5) for both styrene and MMA

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B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
Scheme 4. Possible mechanism for the formation of the catalytically active species in ROMP reactions.
Table 3
ATRP results of representative substrates (T = 85 ◦C except for styrene 110 ◦C and acrylonitrile 65 ◦C, solvent: toluene, [substrate]/
[catalyst]/[initiator] = 800/1/2, NR: no reaction)
Entry
1
Substrate
Initiator
Time (min)
3-a (%)
3-b (%)
3-c (%)
60
480
1020
60
480
1020
6
35
34
6
16
19
7
45
46
10
22
24
11
52
54
9
34
35
2
3
60
480
1020
19
66
66
26
77
76
22
84
84
4
5
60
480
1020
60
7
35
34
8
38
39
13
58
62
=
H2C CHCN
H3C–CH(Cl)CN
480
NR
NR
NR
1020
6
60
19
36
48
480
1020
69
74
75
77
93
95
Table 4
Properties of the polymers formed via ATRP
Styrene/methylmethacrylatea
b
b
Mn
Mw
PDIb
fic
3-a
3-b
3-c
40000/34000
38000/39000
54000/48000
84000/67000
74000/79000
98000/84000
2.10/1.97
1.94/2.01
1.81/1.75
0.70/0.64
0.61/0.63
0.70/0.71
a Properties determined of polymers obtained after 8 h of reaction.
b GPC versus polystyrene standards.
c fi = initiator efficiency = Mn(theor.)/Mn(exp.) with Mn(theor.) = ([monomer]0/[initiator]0) × MWmonomer × conversion.

B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
73
Fig. 4. Plot of ln ([M]0/[M]t ) vs. time (h) for MMA and styrene polymerization mediated by complex 3-c at 85 and 110 ◦C, respectively.
[M]0 and [M]t are the monomer concentrations at times 0 and t, respectively.
with catalyst 3-c is also in agreement with a con-
trolled process with a constant number of growing
chains. Also, the observation that the polydispersities
decrease with increasing conversion is in agreement
with a controlled polymerization following the ATRP
concept (Fig. 6).
The reason for the difference in control over poly-
merization must be sought in the lability of the
X–Mt bond in the deactivator [11] which increases in
the order of 3-a < 3-b < 3-c. To get an idea of the
lability of the Mt–X bond, the atomic charge on the
nitrogen atom of the Schiff base ligands was deducted
by modelling these compounds via a semi-empirical
molecular orbital method [12]. The atomic charges
were −0.099718, −0.172322 and −0.511666 e (with
1 e = 1.6021 × 10−19 C) for compounds 3-a, 3-b and
3-c, respectively. It is obvious that the more electron
donating the N of the Schiff base becomes, the more
the lability of the Mt–X bond increases.
These results support the idea that control over poly-
merization in ATRP with catalysts 3-a, 3-b and 3-c
can easily be improved by fine-tuning the Schiff base
ligands in order to find the ideal Mt–X bond strength
leading to the optimal ATRP equilibrium.
Fig. 5. Plot of Mn vs. the percentage conversion for MMA and styrene polymerization mediated by complex 3-c at 85 and 110 ◦C,
respectively.

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B. De Clercq, F. Verpoort / Journal of Molecular Catalysis A: Chemical 180 (2002) 67–76
Fig. 6. Evolution of polydispersities with percentage conversion for MMA and styrene polymerization mediated by complex 3-c.
The observation that the activity of our systems
the structure and purity was checked with IR and
1H-NMR spectroscopy. Cyclooctene and norbornene
were purchased from Aldrich and distilled from CaH2
under nitrogen prior to use. Commercial grade sol-
vents were dried and deoxygenated for at least 24 h
over appropriate drying agents under nitrogen atmo-
sphere and distilled prior to use. Unless otherwise
noted, all other compounds were purchased from
Aldrich, and used as received.
In a typical ROMP experiment 0.005 mmol of the
catalyst solution in toluene was transferred into a
15 ml vessel followed by the addition of a catalytic
amount (2 equivalents) of TMSD diluted in 1 ml
toluene via a precision syringe over 0.5 h to allow
the formation of the initiating metal–carbene species.
Then, the right amount of monomer solution in toluene
(800 equivalents for norbornene, 200 equivalents for
cyclooctene) was added and the reaction mixture was
then kept stirring at 85 ◦C for different time periods.
To stop the polymerization reaction, 2–3 ml of an
ethylvinylether/BHT solution is added and the solu-
tion is stirred till the deactivation of the active species
is completed. The solution is poured into 50 ml
methanol (containing 0.1% BHT) and the polymers
are precipitated and dried in vacuum overnight.
improve with increasing bulkiness of the Schiff base
ligand (compare the results of catalysts 3-a and 3-b)
and increasing negative atomic charge on the N atom
of the Schiff base ligand, follows the same trend
that Demonceau and coworkers found with their
RuPR3Cl2(p-cymene) systems where an increased
activity towards ATRP and ROMP reactions was
witnessed as the bulkiness and the basicity of the
phosphine ligands increased [9,14].
3. Experimental section
3.1. General
All reactions and manipulations were performed
under an argon atmosphere by using conventional
Schlenck-tube techniques. Argon gas was dried by
passage through P2O5 (Aldrich 97%). 1H-NMR
(500 MHz) and 13C-NMR (126 MHz) spectra were
recorded on a Bruker AM spectrometer. IR spectra
were taken with a Mattson 5000 FTIR spectrometer.
The number and weight average molecular weights
(Mn and Mw) and polydispersity (Mw/Mn) of the poly-
mers were determined by gel permeation chromatog-
raphy (CHCl3, 25 ◦C) using polystyrene standards.
The GPC instrument used is a Waters Maxima 820
system equipped with a PL gel column.
In a typical ATRP experiment 0.0117 mmol of cat-
alyst was placed in a glass tube (in which the air was
expelled by three vacuum–nitrogen cycles) containing
a magnet barr and capped by a three-way stopcock.
Then, the monomer and initiator were added so that
the molar ratios [catalyst]/[initiator]/[monomer] were
The ruthenium dimer [RuCl2(p-cymene)]2 was
prepared according to literature procedures [15] and

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75
1/2/800. All liquids were handled under argon with
dried syringes. The reaction mixture was then heated
for different time periods at the reaction temperature
which was 85 ◦C for the acrylates and methacrylates,
110 ◦C for styrene and 65 ◦C for acrylonitrile. After
cooling, it was diluted in THF and poured in 50 ml
n-heptane (for the acrylates, methacrylates and acry-
lonitrile) or 50 ml methanol (for styrene) under vig-
orous stirring. The precipitated polymer was filtered
with succion and dried in vacuum overnight.
1H-NMR (CDCl3) aldimine ligand δ (ppm) 9.95 (s,
1H), 6.85–7.20 (m, 4H), 3.12 (s, 3H), p-cymene δ
(ppm) 5.47 (d, 2H), 5.34 (d, 2H), 2.92 (sp, 1H), 2.17
(s, 3H), 1.25 (d, 6H); IR (cm−1) 3050, 3032, 2956,
2923, 2853, 1920, 1672, 1594, 1536, 1467, 1447,
1376, 1347, 757; elemental analysis calculated (%)
for RuC18H22ONCl (404.90): C 53.40, H 5.48, N
3.46; found: C 53.34, H 5.44, N 3.44.
3.2.5. Complex 3-b
Ru dimer [RuCl2(p-cymene)]2 (0.49 g, 0.8 mmol),
thallium salt 2-b (0.61 g, 1.60 mmol), and THF
(20 ml) afforded the complex 3-b as a red-brown
solid: 1H-NMR (CDCl3) aldimine ligand δ (ppm)
8.25 (s, 1H), 6.85–7.00 (m, 4H), 7.26 (s, 2H) 2.54
(s, 6H), p-cymene δ 5.46 (d, 2H), 5.32 (d, 2H), 2.75
(sp, 1H), 2.24 (s, 3H), 1.25 (d, 6H); IR (cm−1) 3052,
2962, 2918, 2851, 1933, 1732, 1606, 1528, 1462,
1443, 1379, 1361, 1261, 801; elemental analysis cal-
culated (%) for RuC21H28ONCl (446.98): C 56.43, H
6.31, N 3.13; found: C 56.38, H 6.33, N 3.16.
3.2. Characterisation
3.2.1. Schiff base ligand 1-a
Salicylaldehyde (0.24 g, 2 mmol), methylamine
2.0 M solution in THF (1 ml, 2 mmol) and THF
(15 ml) afforded the compound as a yellow liquid:
1H-NMR (CDCl3) δ (ppm) 3.30 (s, 3H), 6.75–7.50
(m, 4H), 9.75 (s, 1H), 12.96 (s, 1H) ); 13C-NMR
(CDCl3) δ (ppm) 166.4, 161.7, 137.0, 133.8, 120.8,
119.9, 118.4, 45.9; IR (cm−1) 3061, 2976, 2860,
2845–2910, 1623, 1573, 1525, 1497, 1465, 1125.
3.2.6. Complex 3-c
3.2.2. Schiff base ligand 1-b
Ru dimer [RuCl2(p-cymene)]2 (0.49 g, 0.8 mmol),
thallium salt 2-c (0.81 g, 1.60 mmol), and THF (20 ml)
afforded the complex 3-c as a red-brown solid.
1H-NMR (CDCl3) aldimine ligand δ (ppm) 9.85 (s,
1H), 6.83–7.10 (m, 4H), 1.35 (s, 9H), p-cymene δ
(ppm) 5.48 (d, 2H), 5.36 (d, 2H), 2.90 (sp, 1H),
2.16 (s, 3H), 1.26 (d, 6H); IR (cm−1) 3053, 2958,
2923, 2853, 1920, 1671, 1598, 1567, 1516, 1462,
1447, 1374, 757, elemental analysis calculated (%)
for RuC25H27ONClBr (573.92): C 52.32, H 4.74, N
2.44; found: C 52.22, H 4.78, N 2.41.
Salicylaldehyde (0.24 g, 2 mmol), t-butylamine
(0.210 ml, 2 mmol) and THF (15 ml) afforded the
compound as a yellow liquid: 1H-NMR (CDCl3) δ
(ppm) 1.26 (s, 9H), 6.75–7.35 (m, 4H), 8.34 (s, 1H),
12.86 (s, 1H) ); 13C-NMR (CDCl3) δ (ppm) 162.1,
159.6, 132.0, 131.3, 118.9, 118.1, 117.3, 56.9, 29.5;
IR (cm−1) 3031, 3061, 1626, 1572, 1522, 1497, 1464,
2840–2920, 1120.
3.2.3. Schiff base ligand 1-c
Salicylaldehyde (0.24 g, 2 mmol), 4-bromo-2,6-di-
methylaniline (0.4 g, 2 mmol) and ethanol (15 ml)
afforded the compound as a yellow solid: H-NMR
1
4. Conclusion
(CDCl3) δ (ppm) 2.21 (s, 6H), 7.15–7.30 (m, 6H),
8.32 (s, 1H), 12.85 (s, 1H); 13C-NMR (CDCl3) δ
(ppm) 167.01, 160.92, 148.33, 138.99 133.35, 132.14,
130.79, 130.31, 118.97, 117.56, 117.22, 18.18; IR
(cm−1) 3031, 3065, 2850–2925, 1620, 1569, 1523,
1491, 1467, 1113.
In conclusion, we succeeded in synthesising a new
class of ruthenium-based catalysts which exhibit good
activity in ATRP reactions. The ROMP activity of our
systems for norbornene is poor but increases dramat-
ically when TMSD is added to activate the catalytic
systems. With the activated catalysts even the less
strained cyclooctene can be converted smoothly. The
results show that the control over polymerization is
very dependent on the electronic and steric properties
of the Schiff base ligands. So, by further fine-tuning
3.2.4. Complex 3-a
Ru dimer [RuCl2(p-cymene)]2 (0.49 g, 0.8 mmol),
thallium salt 2-a (0.54 g, 1.60 mmol), and THF (20 ml)
afforded the complex 3-a as a red-brown solid:

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the Schiff base ligands, the potential of these catalytic
systems in the field of ROMP and ATRP can be much
improved. Furthermore, the fact that these catalysts
exhibit good activities in both ROMP and ATRP
reactions allows them to combine the ROMP and
the ATRP methodologies to make block copolymers
with interesting properties by using new monomer
combinations.
[5] (a) J.S. Wang, K. Matyjaszewski, J. Am. Chem. Soc. 117
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Acknowledgements
B.D.C. is indebted to the IWT (Vlaams instituut
voor de bevordering van het wetenschappelijk-techno-
logisch onderzoek in de industrie) for a research
grant. F.V. is indebted to the Fund for Scientific
Research-Flanders (Fonds voor Wetenschappelijk
Onderzoek-Vlaanderen) and to the Research Council
of Ghent University (Bijzonder Onderzoeksfonds) for
financial support. M. Vandriessche (Texaco Research
Centre, Ghent, Belgium) is gratefully acknowledged
for the elemental analysis.
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