Assessing the scope of the introduction of Schiff bases as co-ligands for monometallic and homobimetallic ruthenium ring-opening metathesis polymerisation and ring-closing metathesis initiators

Article abstract of DOI:10.1002/1615-4169(200208)344:6/7<639::AID-ADSC639>3.0.CO;2-0

A new class of homobimetallic and mono-metallic Schiff base-substituted ruthenium olefin metathesis catalysts has been prepared, characterised and tested in ring-closing metathesis (RCM) and ring-opening metathesis polymerisation (ROMP) reactions. The results obtained point out that the synergy of Schiff base ligands with coordinatively labile ligands leads to bimetallic catalytic systems that combine very high activity with excellent stability. Furthermore, the catalytic activity of these catalysts is very dependent on the steric and electronic environment of the Schiff base. To conclude, a mechanism that explains the obtained data is postulated.

Full text of DOI:10.1002/1615-4169(200208)344:6/7<639::AID-ADSC639>3.0.CO;2-0

FULL PAPERS
Assessing the Scope of the Introduction of Schiff Bases as Co-
Ligands for Monometallic and Homobimetallic Ruthenium Ring-
Opening Metathesis Polymerisation and Ring-Closing Metathesis
Initiators
Bob De Clercq, Francis Verpoort*
Division of Organometallics and Catalysis, Department of Inorganic and Physical Chemistry, Ghent University,
Krijgslaan 281 (S-3), 9000 Ghent, Belgium
Fax.: ‡ (32)-9-264.49.83, e-mail: Francis.Verpoort@rug.ac.be
Received: January 9, 2002; Accepted: March 18, 2002
Abstract: A new class of homobimetallic and mono- Furthermore, the catalytic activity of these catalysts is
metallic Schiff base-substituted ruthenium olefin very dependent on the steric and electronic environ-
metathesis catalysts has been prepared, characterised ment of the Schiff base. To conclude, a mechanism
and tested in ring-closing metathesis (RCM) and ring- that explains the obtained data is postulated.
opening metathesis polymerisation (ROMP) reac-
tions. The results obtained point out that the synergy
of Schiff base ligands with coordinatively labile Keywords: bimetallic catalysts; homogeneous cataly-
ligands leads to bimetallic catalytic systems that sis; ring-closing metathesis; ring-opening metathesis
combine very high activity with excellent stability. polymerisation; ruthenium and compounds
Introduction
developed by Schrock and coworkers (complex A,
Figure 1) are significantly more reactive towards a
In the 34 years since the landmark report by Calderon broad range of substrates with many steric or electronic
and coworkers that both ring-opening polymerisation variations. Critical drawbacks of these Mo-based car-
and the disproportionation of acyclic olefins were the bene complexes are, however, their moderate to poor
[1]
same reaction, olefin metathesis has become one of the functional group tolerance, high sensitivity to air,
[
2]
most intensively investigated fields of research and moisture or even to trace impurities in solvents, thermal
this because of the central importance of carbon-carbon instability on storage and expense of preparation.[
bond formation in both organic synthesis and polymer In contrast to the early transition metal molybdenum
chemistry. Especially during the last decade the reaction catalysts, the ruthenium complexes developed by
has experienced a tremendous breakthrough due to the Grubbs and coworkers (complex B, Figure 1) possess
2h,3,5a,7]
[
3]
development of efficient molybdenum and rutheni- remarkable tolerance towards most functional groups
um[ catalysts having sufficiently well-balanced elec- and a diminished sensitivity to atmospheric oxygen and
tronic and coordinative unsaturation to allow conven- water. Moreover, they can be conveniently stored even
ient use and high turnover performance. These new under an air atmosphere without severe decomposition
4]
[
2h,5a,8]
generations of olefin polymerisation catalysts have for several weeks.
Recently, three groups almost
catapulted the polymer industry into a new area. Ring- simultaneously reported on the preparation and cata-
opening metathesis polymerisation (ROMP) has lytic properties of N-heterocyclic carbene ligand-con-
opened new synthetic routes to a variety of polymeric taining complexes (complex C, Figure 1) exhibiting
materials producing polymers with attractive mechan- metathesis activity comparable to that of the molybde-
[
5]
ical and electrical properties. There has also been a num complex A, yet having a remarkable air and water
rapid embrace of these catalysts as tools for organic fine stability similar to that of the parent benzylidene
[
9]
chemicals synthesis. Indeed, especially the broad scope complex B. In 1999 Herrmann and coworkers report-
and reliability of the ring-closing metathesis (RCM) ed on the synthesis and catalytic activity of the meta-
[
9g,9i]
reaction has greatly simplified the total synthesis of a thesis initiator D (Figure1).
wide variety of architecturally complex natural and This complex that combines an imidazolin-2-ylidene
[
6]
unnatural products. In comparison with the rutheni- ligand with a bimetallic catalyst system, is one of the
um-based catalytic systems, the molybdenum systems fastest metathesis initiators known so far. However, the
Adv. Synth. Catal. 2002, 344, No. 6+7
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1615-4150/02/3446+7-639 ± 648 $ 17.50+.50/0
639

FULL PAPERS
Bob De Clerq, Francis Verpoort
In a first set of experiments, the catalytic activity of the
Schiff base substituted ruthenium benzylidenes 2a ± f
and 3a ± f is checked for ROMP with some representa-
tive monomers. The yields [%] of the formed polymers
are depicted in Table 1.
It is obvious from Table 1 that both catalytic systems 2
and 3 succeed in performing ROMP reactions with the
monomers tested, although significant differences in
their behaviour were noticed. For the catalytic systems 2
the observed conversion sequence is 2b > 2a > 2d >
Figure 1.
2c > 2f > 2e whereas for the bimetallic initiators
corresponding propagating species of this system is too conversion sequence is reversed, 3e > 3f > 3c > 3d >
short-lived to take metathesis reactions of difficult 3a > 3b.
[
10]
substrates to completion.
These results show that for both the monometallic
In 1998 Grubbs et al. reported on the exceptional systems 2 as for the bimetallic systems 3 the bulkiness of
stability of Schiff base-substituted analogues of com- the Schiff base and the electron-withdrawing properties
plex B.[ As part of our systematic investigation on the of the Schiff base substituents exert a profound influ-
ruthenium(II)-Schiff base chemistry in various organic ence on the ROMP activity. For instance, phenylnor-
reactions[ and driven by the search for finding a well- bornene is converted in 98%, 80%, and 69% yield for 2a,
defined olefin metathesis initiator possessing the ideal 2c, and 2e, respectively, and in 19%, 61%, and 100%
balance between activity and stability, we came to the yield, respectively, for 3a, 3c, and 3e. These results also
idea of incorporating a Schiff base-substituted ruthe- show that the introduction of more bulkiness in the
nium centre in a bimetallic structure. Herein we report Schiff base is beneficial for the systems 3 but detrimental
that it is the combination of coordinatively more labile for systems 2. The influence of the electronic environ-
ligands with Schiff base ligands on the ruthenium centre ment of the Schiff base is best illustrated by comparing
that allows the class of bimetallic ruthenium catalysts to the catalytic performance of system 2a with that of 2b, 2c
11]
12]
develop their full commercial potential.
with 2d, 2e with 2f, 3a with 3b, 3c with 3d, and 3e with 3f.
In the monometallic series, the complex bearing the
electron-withdrawing nitro substituent (2b, 2d, and 2f)
reaches substantially higher conversions whereas for the
bimetallic complexes the opposite is observed. Further-
Results and Discussion
The 12 different catalytic systems for which the catalytic more, it is clear that for both types of initiators the
performance in ROMP and RCM reactions was as- bulkiness of the Schiff base has a greater impact on
sessed, are depicted in Scheme 1. In the experimental catalytic performance in ROMP reactions than the
section the details of the synthesis are given.
electronic influence exerted by the Schiff base substitu-
Scheme 1. Synthesis route of the different catalytic systems.
640
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The Scope of the Introduction of Schiff Bases as Co-Ligands in ROMP and RCM
FULL PAPERS
Table 1. Yield (%) for ring-opening metathesis polymerisation of some representative monomers using catalytic systems 2a ± f
and 3a ± f (for details concerning the reaction conditions, see experimental section).
Catalytic system
Substrate
2a/3a
2b/3b
2c/3c
90/76
2d/3d
92/64
2e/3e
2f/3f
Cyclooctene
96/31
100/23
86/100
89/90
Norbornene derivatives (endo and exo)
R ˆ H
100/59
100/41
100/34
100/18
100/9
100/37
98/19
95/13
100/41
31/9
38/15
100/51
100/43
100/48
100/33
100/24
100/11
100/ < 5
100/26
100/15
100/12
100/36
38/ < 5
43/ < 5
100/36
100/29
100/87
100/79
95/70
92/55
88/34
84/72
80/61
77/55
95/76
11/27
19/39
98/85
92/71
100/78
100/66
98/61
97/49
93/20
91/63
88/50
85/46
96/67
17/19
23/28
100/67
97/58
100/100
100/100
91/100
89/100
81/100
76/100
69/100
66/100
79/100
< 5/66
12/74
100/96
100/91
93/84
92/73
87/56
81/94
77/86
73/81
88/83
8/43
R ˆ ethyl
R ˆ butyl
R ˆ hexyl
R ˆ decyl
R ˆ ethylidene
R ˆ phenyl
R ˆ cyclohexenyl
R ˆ ethylnorbornane
R ˆ cyano
R ˆ hydroxymethyl
R ˆ chloromethyl
R ˆ triethoxysilyl
17/51
87/97
82/89
81/100
77/100
Table 2. Properties of the polymers formed with the most performance initiators, 2b and I3e, of both types of catalysts 2 and I3.
b/3e
2
3
[a]
PDI[a]
sc[b]
fi[c]
Substrate
M ( Â 10 )
n
Cyclooctene
24/29
1.86/1.49
0.48/0.46
0.92/0.76
Norbornene derivatives
R ˆ H
84/95
1.51/1.37
1.63/1.35
1.55/1.31
1.62/1.37
1.58/1.29
1.70/1.39
1.68/1.36
1.62/1.41
1.66/1.39
1.52/1.27
1.57/1.33
1.71/1.40
1.58/1.36
0.25/0.22
0.22/0.21
0.24/0.29
0.22/0.18
0.26/0.25
0.19/0.21
0.29/0.27
0.27/0.27
0.18/0.23
0.22/0.18
0.26/0.24
0.24/0.29
0.27/0.31
0.90/0.79
0.88/0.71
0.87/0.66
0.81/0.69
0.84/0.73
0.86/0.70
0.80/0.66
0.83/0.74
0.81/0.67
0.55/0.51
0.58/0.48
0.84/0.72
0.87/0.74
R ˆ ethyl
111/138
138/183
176/207
223/257
112/137
170/206
168/188
186/225
66/123
R ˆ butyl
R ˆ hexyl
R ˆ decyl
R ˆ ethylidene
R ˆ phenyl
R ˆ cyclohexenyl
R ˆ ethylnorbornane
R ˆ cyano
R ˆ hydroxymethyl
R ˆ chloromethyl
R ˆ triethoxysilyl
74/153
136/158
236/277
[
[
[
a]
b]
c]
M and the polydispersities (PDI) are determined by size-exclusion chromatography (SEC) with polystyrene calibration.
Fraction of polymers with cis configuration.
n
fi ˆ initiation efficiency ˆ Mn, theor./Mn, exp. with Mn, theor. ˆ ([monomer] /[initiator] )  MW(monomer)  conversion.
0
0
ents. The properties of the polymers obtained with the obtained with the bimetallic complex 3e. This indicates
highest performing initiators for both classes of catalytic that in the latter case the polymerisations have a more
systems, namely 2b and 3e, are depicted in Table 2.
living character. It is also remarkable that the number
From Table 2 one observes that for system 2b the average molecular weights (M ) are much higher in the
n
polydispersity index (PDI) of the formed polymers is case of the bimetallic system, meaning that the initiation
much higher in comparison with the PDI of the polymers efficiencyis lower (Table 2). A trans configuration of the
Adv. Synth. Catal. 2002, 344, 639 ± 648
641

FULL PAPERS
Bob De Clerq, Francis Verpoort
Table 3. Yield (%) for RCM of some representative substrates using catalytic systems 2a ± f and 3a ± f.[a]
Entry
1
Substrate[b]
Product
2a/3a
2b/3b
2c/3c
2d/3d
2e/3e
2f/3f
100/100
100/100
100/100
100/100
100/100
100/100
2
3
4
< 5/13
< 5/6
< 5/ < 5
< 5/ < 5
100/100
< 5/58
< 5/41
100/100
9/44
6/29
18/83
11/62
21/72
17/49
100/100
100/100
100/100
100/100
5
6
100/100
40/40
100/100
44/31
100/100
47/71
100/100
59/67
100/100
68/96
100/100
76/89
7
12/32
13/25
18/69
25/66
41/87
56/74
[
[
a]
b]
For details concerning the reaction conditions see experimental section.
E ˆ COOEt.
polynorbornene derivatives and polycyclooctene is order of 2f > 2e > 2d > 2c > 2b > 2a. When
predominant, irrespective the catalytic system used. comparing the electronic influence for the same series of
This is in accordance with the general observation for catalysts, the same trend is observed as for ROMP.
ruthenium catalysts in ROMP reactions.
Indeed, 2f has a higher activity than 2e, 2d has a higher
In a second set of experiments, the performance of the activity than 2c, and 2b has a higher activity than 2a.
two classes of catalytic systems was tested in RCM However, examining steric effects, a totally different
reactions. Table 3 summarises the RCM results obtained behaviour is observed. In this case, introduction of more
with some representative substrates.
steric bulk in the Schiff base ligand leads to an increase
First of all it needs to be mentioned that the difference in RCM activity. Indeed, catalytic performance increas-
in reaction temperature between the monometallic and es in the order of the series 2e, f > the series 2c, d > the
the bimetalllic systems is a result of the observation that series 2a, b.
for the bimetallic catalytic systems already very good
To explain the influence of steric bulk and electronic
conversions were obtained at a temperature of 55 8C, contribution of the Schiff base ligands and the difference
whereas preliminary tests pointed out that the mono- or analogy in reactivity between ROMP and RCM
metallic catalytic systems could only exploit their full reactions for both types of catalysts 2 and 3, the
potential at a temperature of 70 8C.
mechanism for metathesis reactions is depicted in
When analysing the results gathered in Table 3, one Scheme 2. In accordance with the proposed mechanism
observes the same order in catalyst performance for for ruthenium benzylidene complexes B, C, and D from
[
13]
RCM and ROMP reactions for the bimetallic catalytic Figure 1 , the mechanism of the ligand substitution for
complexes. For instance, the tetrasubstituted malonate both types of initiators 2 and 3 with olefinic substrate is
derivative (Entry 3, Table 3) is converted with 6%, proposed to take place in a dissociative fashion.
<
5%, 41%, 29%, 62%, and 49% with systems 3a, 3b, 3c,
The fundamental difference however, lies in the fact
3d, 3e, and 3f, respectively. The conclusions about the that for the monometallic complexes of class 2 it is
steric bulk of the Schiff base ligands and the electron- suggested that the mechanism involves the decoordina-
withdrawing properties of the Schiff base substituents tion and coordination of ™one-arm∫ of the bidentate
that were made for the ROMP reactions with this type of Schiff base ligand instead of the usual PCy dissociation
3
catalyst can also be drawn here. For the monometallic as for the systems B and C. This dissociation of the N-
catalysts, however, a totally different behaviour in bonded arm of the chelating salicylaldimine ligand is
ROMP and RCM reactions is observed. As opposed proposed for the following reasons: (1) addition of CuCl,
to ROMP, RCM activities generally decrease in the a well-known phosphine scavenger, to solutions of
642
Adv. Synth. Catal. 2002, 344, 639 ± 648

The Scope of the Introduction of Schiff Bases as Co-Ligands in ROMP and RCM
FULL PAPERS
Scheme 2. Mechanism for metathesis reactions with catalytic systems 2a ± f and 3a ± f.
several catalysts of type 2, in the presence of an olefin with P-donors.[20] (5) In general, [Mt]-N bonds are
substrate did not result in a noteworthy increase of mainly of the s-type and [Mt]-P bonds of s- and p-
[
15,17]
2
activity both in ROMP and RCM reactions. (2) When types.
nitrogen donors are used as co-ligands in combination dized nitrogen atoms, as is the case with Schiff base
with phosphorus as donors, the so-called trans effect
However, with ligands containing sp -hybri-
[
14]
ligands, p-interactions and thus p-back-bonding effects
must be taken into account. In a given complex one can can take place. Nevertheless, while their occurrence is
have a substitutionally inert, coordinated phosphane beyond dispute, the extent to which these p-effects
2
ligand and trans to this P-donor, a kinetically labile determine the binding properties between an sp -
ligand. For complexes combining a nitrogen and a hybridized N-ligand and the metal remain much smaller
phosphorus donor in their coordination sphere, this than the influence that these p-effects exert on the
trans effect will play a decisive role in the dissociation binding properties between P-containing ligands and
[
16]
behaviour of both ligands because the difference in metal centres. (6) The distinct influence of the steric
electron-donating properties of both ligands is bulk of the Schiff base ligands on catalytic performance
small.[
15,16]
One should not take into account a dissoci- of type 2 initiators is in line with the fact that the strength
ation of the O-bonded arm of the salicylaldimine ligand of [Mt]-N bonds is very much affected by steric
[
21]
because this O is not in a trans position to the effects. (7) Further evidence for the mechanism of
phosphorus and because in general, [Mt]-O bonds are dissociation for type 2 catalytic systems was provided by
[
17]
much stronger than [Mt]-N bonds. (3) The ™hard and transferring 0.5 mmol of the catalyst solution in C D Cl
6
5
soft acid-base theory∫ can also be used to explain a into a 15-mL vessel followed by the addition of
favourable dissociation of the nitrogen donor over the 1 equivalent of norbornene solution in C D Cl. The
6
5
phosphorus donor. The fairly soft late-transition metal reaction mixture was then heated at 70 8C. At regular
ruthenium will prefer to bond with the softer P-donor time periods, NMR samples were taken from the
[
18]
31
instead of with the harder N-donor. (4) In general, the reaction mixture and analysed via P NMR. Despite
most stable organometallic compounds are those in careful monitoring of the reaction mixture, no evidence
which all low-energy orbitals are involved in (prefera- was found for the dissociation of the PCy ligand.
3
bly) two-electron bonding. This implies an absence of
The proposed dissociative mechanism for the bimet-
unpaired electrons on the metal centre which is fulfilled allic type 3 initiators is in total agreement with the
when the metal centre has an even number of electrons findings of Herrmann et al. with analogous bimetallic
and when the complex is of the low-spin type, that is, one ruthenium complexes (e.g., complex D from Fig-
[
13 (b)]
where there is maximum pairing of all the available ure 1).
metal d electrons.
Indeed, also Herrmann postulates a two-
[
19]
It is a well-known fact that, in step dissociation mechanism with a sequential hetero-
general, nitrogen donors are not as effective in produc- lytic cleavage of the two chloro bridges and liberation of
ing low-spin complexes with the consequence that the the coordinatively labile ligand {(p-cymene)RuCl } as
2
species produced are less thermodynamically stable and the key step in the olefin metathesis reaction pathway
more kinetically labile than their low-spin analogues with first- and second-generation Grubbs-type bimetal-
Adv. Synth. Catal. 2002, 344, 639 ± 648
643

FULL PAPERS
Bob De Clerq, Francis Verpoort
lic ruthenium complexes. The trans effect of the chloro
bond on the stability of the [Mt]-N bond should not be
taken into account here because it is well-known that
chlorine atoms exhibit a very weak trans labilising
effect.[ Thus, because of the absence of a ligand with
strong labilising effect trans to the [Mt]-N bond, the
15]
lability of the {(p-cymene)RuCl } fragment and the
2
possibility that the dissociation of the {(p-cymene)RuCl2}
fragment is assisted by the exothermic dimerisation
Figure 2. Illustration of the detrimental influence of steric
Schiff bases on ROMP activity with catalytic systems 2.
[
13b]
reaction to give [(p-cymene)RuCl ] ,
it is very
2
2
reasonable to state that the bimetallic type 3 catalysts
are able to populate the dissociative pathway just as
readily as D.
above-mentioned monomers. Moreover, the decrease
By accepting the mechanisms depicted in Scheme 2, is for both catalytic systems more or less the same
the observed activities of both type 2 and type 3 catalytic leading to the conclusion that the detrimental effect of
systems in ROMP and RCM can be explained. For the cyano or hydroxymethyl substituents is comparable for
bimetallic type 3 complexes, the increasing activity in both systems. The difference in yield must be sought in
ROMP and RCM metathesis reactions with increasing the activity of the catalysts. It seems that the turnover
±1
±1
bulk of the Schiff base ligand and the disadvantageous frequency for 3e (132 h and 148 h for, respectively,
effect of the electron-withdrawing nitro substituent on cyano- and hydroxymethylnorbornene) is substantially
the Schiff base makes perfect sense because, according higher in comparison with 2b (76 h± and 86 h for,
1
±1
to the proposed mechanism, the active intermediate respectively. cyano- and hydroxymethylnorbornene)
(
having a vacancy for olefin coordination) is stabilised as 3e reaches considerably higher conversions than 2b
or, respectively, destabilised when the steric and elec- with cyano- and hydroxymethylnorbornene within the
tronic parameters are altered in the above-mentioned same time period. These observations are in line with
way. For type 2 complexes, the profitable influence of the observations that catalysts of type C (Figure 1)
the electron-withdrawing nitro substituent on the Schiff have remarkable lower turnover frequencies than the
base for the activity of these complexes in RCM and analogous bimetallic complexes of type D (Fig-
ROMP reactions are in perfect agreement with the ure 1).
proposed mechanism. Indeed, by diminishing the elec- The outstandingstabilityof the initiators of type 2 have
[
10]
[
11]
tron density on the nitrogen atom, the ™one-arm∫ alreadybeendemonstratedbyGrubbs etal. Inorderto
decoordination of the chelating salicylaldimine ligand assess the stability of the bimetallic type 3 catalytic
is stimulated. The opposite influence of the steric bulk systems, these systems were stored for one week in the
on RCM and ROMP performance with this type of solid state under an air atmosphere after which we tested
initiators can be understood when one bears in mind that them in ROMP reactions with phenylnorbornene. The
in ROMP reactions the growing polymer remains results ofthese experiments indicated nonoteworthy loss
attached to the metal centre. It is clear, for a certain of performance. The same conclusion could be drawn
degree of polymerisation, that the incoming new when these complexes were transferred into a solution of
monomer will be severely hindered by this ™polymer- chlorobenzene under inert atmosphere. Again, after one
tail∫ when the Schiff base is too bulky (Figure 2).
In RCM reactions the incoming new olefin substrate is ments using phenylnorbornene as substrate.
never a problem because of the absence of such a Although we have purified the bimetallic catalytic
polymer-tail∫. On the contrary, the results gathered in systems (see experimental section), it should be men-
week, no loss of activity was revealed in ROMP experi-
™
Table 3 indicate that introduction of more bulkiness in tioned that the stoichiometrically generated piano-
the Schiff base ligand has a stabilising effect on the stool-type complexes {Ru(p-cymene)PCy Cl } (see
3
2
reactive intermediate (having the vacancy) and thus Scheme 1) do not affect catalyst activity and, in fact,
stimulates the ™one-arm∫ decoordination of the biden- do not need to be separated for routine usage.[
22]
tate salicylaldimine ligand.
Moreover, Demonceau et al. showed that these piano-
The results gathered in Tables 1 and 2 also reveal that stool-type complexes are extremely active in Atom
our mechanistic proposals are not affected by heter- Transfer Radical Polymerization (ATRP) reactions.[
oatoms in the ROMP-monomers. The difference in In addition, our laboratory succeeded in heterogenising
conversion for cyano- and hydroxymethylnorbornene these compounds on mesoporous and amorphous silica
with catalysts 2b and 3e (respectively, 38% and 43% for carriers leading to very active systems for ATRP.[ So
23]
24]
2b and 66% and 74% for 3e) can be explained by the by following this heterogenising methodology devel-
initiator efficiencies for 2b and 3e with these monomers. oped in our laboratory, it is now possible to come to a
Whereas for all monomers the initiator efficiencies vary highly active heterogeneous ATRP catalyst and a highly
between 0.7 and 0.8, they drop to 0.5 ± 0.6 for the two performing metathesis catalyst via one synthesis.
644
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The Scope of the Introduction of Schiff Bases as Co-Ligands in ROMP and RCM
FULL PAPERS
temperature for 2 hours. After cooling to room temperature,
the viscous yellow oily condensation products were purified by
silica gel chromatography (silica gel 60, 0.063 ± 0.200 mm,
Merck, a 5:1 benzene-tetrahydrofuran mixture was used as an
eluant) and the desired salicylaldimine ligands were obtained
in excellent yields. The condensations of salicylaldehydes with
aromatic amine derivatives were carried out with stirring in
ethanol at 80 8C for 2 hours. Upon cooling to 0 8C, a yellow
solid precipitated from the reaction mixture. The solids were
Conclusion
In conclusion, we have succeeded in synthesising and
characterising a new class of homobimetallic ruthenium
olefin metathesis catalysts exhibiting the best combina-
tion of stability and activity known so far for this type of
catalyst. Moreover, we also synthesised, characterised,
and tested the monometallic counterparts. In addition,
we postulate a reasonable mechanism that explains all filtered, washed with cold ethanol and then dried under
the observed results for both types of catalytic systems in vacuum to afford the desired salicylaldimine ligand in quanti-
ring-closing metathesis and ring-opening metathesis tative yields.
Schiff base 1a: Salicylaldehyde (0.24 g, 2 mmol), methyl-
polymerisation reactions.
amine (2.0 M solution in THF; 1 mL, 2 mmol) and THF
Further studies concerning the combination of
ROMP and ATRP methodologies to make new poly-
mers with interesting properties and further proof
concerning the postulated mechanism depicted in
Scheme 2, are currently under way.
1
(
(
1
15 mL) afforded the compound as a yellow liquid. H NMR
CDCl ): d ˆ 12.96 (s, 1H), 8.75 (s, 1H), 7.50 (d, 1H), 7.15 (d,
3
1
3
H), 7.27 (t, 1H), 6.78 (t, 1H), 3.30 (d, 3H); C NMR (CDCl ):
3
d ˆ 166.4, 161.7, 137.0, 133.8, 120.8, 119.9, 118.4, 45.9; IR: n ˆ
3
325 (n , br), 3061 (n , w), 2976 (n , w), 2845 ± 2910 (n
,
CH3
OH
CH
HCˆN
br), 1623 (n , s), 1573 [nCˆC(Ph), w], 1525 [nCˆC(Ph), w], 1497
CˆN
1
[
nCˆC(Ph), w], 1465 [nCˆC(Ph), w], 1125 cm± (nCO, br).
Schiff base 1b: 5-Nitrosalicylaldehyde (0.33 g, 2 mmol),
methylamine (2.0 M solution in THF; 1 mL, 2 mmol) and
Experimental Section
THF (15 mL) afforded the compound as a yellow liquid.
1
H NMR (CDCl ): d ˆ 13.18 (s, 1H), 8.98 (s, 1H), 8.10 (d, 1H),
General
3
1
3
8
1
(
.03 (d, 1H), 7.67 (d, 1H), 3.41 (d, 3H); C NMR (CDCl ): d ˆ
3
All reactions and manipulations were performed under an
argon atmosphere by using conventional Schlenck-tube tech-
68.2, 164.3, 143.4, 137.9, 134.7, 123.1, 120.8, 49.4; IR: n ˆ 3329
n
, br), 3067 (n , w), 2986 (n
, w), 2840 ± 2912 (n , br),
HCˆN CH3
OH
CH
niques. Argon gas was dried by passage through P O (Aldrich
2
5
1618 (n , s), 1570 (nNO2, s), 1546 [n
1
br).
, w], 1524 [n
, w],
CˆN
CˆC(Ph)
CˆC(Ph)
1
9
7%). H NMR (500 MHz) spectra were recorded on a Bruker
±1
492 [nCˆC(Ph), w], 1465 [nCˆC(Ph), w], 1329 (nNO2, s), 1133 cm (n
,
CO
1
3
31
AM spectrometer. C NMR (75.41 MHz) and P NMR
121.40 MHz) spectra were recorded on a Varian Unity 300
(
Schiff base 1c: Salicylaldehyde (0.24 g, 2 mmol), 4-bromo-
spectrometer. Chemical shifts are reported in ppm downfield
from tetramethylsilane (TMS) with TMS employed as the
internal solvent for proton spectra and 85% phosphoric acid
employed as the external solvent. IR spectra were taken with a
Mattson 5000 FTIR spectrometer. The number and weight
average molecular weights (M and M ) and polydispersity
2
,6-dimethylaniline (0.4 g, 2 mmol) and ethanol (15 mL)
1
afforded the compound as a yellow solid. H NMR (CDCl ):
3
d ˆ 12.85 (s, 1H), 8.32 (s, 1H), 7.93 (t, 1H), 7.56 (t, 1H), 7.28 (d,
13
1
H), 7.22 (s, 2H), 7.05 (d, 1H), 2.21 (s, 6H); C NMR (CDCl ):
3
d ˆ 164.0, 160.9, 138.0, 132.4, 130.1, 129.8, 127.6, 127.1, 117.6,
n
w
117.3, 116.4, 18.2; IR: n ˆ 3342 (n , br), 3065 (n , w), 3031
OH
CH
(
M /M ) of the polymers were determined by gel permeation
w n
(n , w), 2850 ± 2925 (n , br), 1620 (n , s), 1569 [n
CˆC(Ph)
, w],
, w], 1467 [n , w], 1093 cm
CˆC(Ph)
CH
CH3
CˆN
chromatography (GPC) (CHCl , 25 8C) using polystyrene
±1
3
1523 [n
, w], 1491 [n
CˆC(Ph)
CˆC(Ph)
standards. The GPC instrument used is a Waters Maxima 820
system equipped with a PL gel column. Elemental analyses
were performed with Carlo Erba EA 1110 equipment.
(
nCO, br).
Schiff base 1d: 5-Nitrosalicylaldehyde (0.33 g, 2 mmol), 4-
bromo-2,6-dimethylaniline (0.4 g, 2 mmol) and ethanol
The ruthenium dimer [RuCl (p-cymene)] was prepared
1
2
2
(15 mL) afforded the compound as a yellow solid. H NMR
[
25]
according to literature procedures and the structure and
purity were checked with IR and H NMR and C NMR
(
1
CDCl ): d ˆ 13.94 (s, 1H), 8.43 (s, 1H), 8.35 (d, 1H), 8.31 (d,
3
1
13
13
H), 7.26 (s, 2H), 7.12 (d, 1H), 2.20 (s, 6H); C NMR (CDCl ):
3
spectroscopy. Cyclooctene and norbornene were purchased
d ˆ 166.2, 165.3, 145.5, 139.9, 131.2, 130.2, 128.7, 128.5, 118.5,
from Aldrich and distilled from CaH under nitrogen prior to
2
118.0, 117.4, 18.1; IR: n ˆ 3337 (n , br), 3068 (n , w), 3036
OH
CH
use. The other norbornene derivatives were purchased from
INEOS and used as received. Commercial grade solvents were
dried and deoxygenated for at least 24 h over appropriate
drying agents under nitrogen atmosphere and distilled prior to
use. Unless otherwise noted, all other compounds were
purchased from Aldrich Chemical Co., and used as received.
(
n , w), 2848 ± 2922 (n , br), 1626 (n , s), 1567(nNO2, s), 1548
CH CH3 CˆN
[nCˆC(Ph), w], 1527 [nCˆC(Ph), w], 1494 [nCˆC(Ph), w], 1467 [nCˆC(Ph),
±1
w], 1334 (nNO2, s), 1096 cm (nCO, br).
The spectroscopic properties of Schiff bases 1e and 1f have
[11]
been reported.
General Procedure for Preparation of the Schiff Base General Procedure for the Preparation of Schiff Base-
Ligands 1a ± f
Substituted Ruthenium Complexes 2a ± f
The Schiff base ligands 1a ± f were prepared and purified using
well-established procedures.[
The Schiff base-substituted ruthenium complexes 2a ± f were
prepared and purified using well-established procedures.
11]
[11]
The condensations of salicylaldehydes with aliphatic amine
derivatives were carried out with stirring in THF at reflux
To a solution of the appropriate Schiff base (1a ± f) in THF
(10 mL), a solution of thallium ethoxide in THF (5 mL) was
Adv. Synth. Catal. 2002, 344, 639 ± 648
645

FULL PAPERS
Bob De Clerq, Francis Verpoort
added dropwise at room temperature. Immediately after the
addition, a pale yellow solid formed and the reaction mixture
was stirred for 2 hours at room temperature. Filtration of the
solid under an argon atmosphere gave the respective thallium
salt in quantitative yield. The salt was immediately used in the
next step without further purification. A solution of the
appropriate thallium salt in THF (5 mL) was added to a
solution of the first generation Grubbs catalyst
1H), 7.97 (d, 2H), 7.54 (t, 1H), 7.26 (t, 2H), 7.14 (s, 1H), 7.09 (s,
1H), 7.03 (d, 1H), 2.49 (q, 3H), 2.40 (s, 3H), 1.84 (d, 3H), 1.15 ±
3
1
1.83 (m, 30 H); P NMR (CDCl ): d ˆ 50.66; IR: n ˆ 3048 (nCH,
3
w), 3035 (n , w), 2846 ± 2957 (n
, br), 1598 (n , s), 1577
CˆN
CH
CH3, CH2
[nCˆC(Ph), w], 1544 (nNO2, s), 1521 [nCˆC(Ph), w], 1462 [nCˆC(Ph), w],
1441 [nCˆC(Ph), w], 1326 (nNO2, s), 1048 (nRu-O-Ph, w), 1001 (nskel.PCy3
w), 797 (gCH, w), 783 (g , w), 690 (nC-Br, s), 664 (nRu-N, w), 546
,
Ph
±1
(nRu-O-Ph, w), 518 (nRu-Cl, w), 432 cm (nRu-P, w); anal. calcd. (%)
[
RuCl (PCy ) ˆCHPh] in THF (5 mL). The reaction mixture
for RuC H O N ClBrP (855.18): C 56.18, H 6.01, N 3.28;
2
3
2
40 51
3
2
was stirred at room temperature for 4 hours. After evaporation
of the solvent, the residuewas dissolved in aminimal amount of
benzene and cooled to 0 8C. The thallium chloride was
removed by filtration. After evaporation of the solvent, the
solid residue was recrystallised from pentane ( ± 70 8C) to give
the respective Schiff base-substituted ruthenium complex
found: C 56.27, H 6.07, N 3.25.
The spectroscopic properties of ruthenium Schiff base
complexes 2e and 2f have been reported.[
11]
(
2a ± f) in good yield as a brown solid.
General Procedure for the Preparation of Schiff Base-
Ruthenium Schiff base complex 2a: Ruthenium complex Substituted Bimetallic Ruthenium Complexes 3a ± f
[
RuCl (PCy ) ˆCHPh] (1.20 g, 1.50 mmol), the thallium salt of
2
3 2
To a solution of the Schiff base-substituted ruthenium complex
2a ±f) in benzene (25 mL) was added a solution of Ru-dimer
RuCl (p-cymene)] in benzene (25 mL). The solution was
stirred for 4 h at room temperature during which time a solid
precipitate formed from the solution. The solid was isolated by
filtration under inert atmosphere and washed with benzene
ligand 1a (0.51 g, 1.50 mmol) and THF (20 mL) afforded the
complex 2a as a brown solid; yield: 0.85 g (88%). H NMR
(
[
1
2
2
(
(
(
CDCl ): d ˆ 19.95 (d, 1H), 8.98 (d, 1H), 7.58 (t, 1H), 7.05 ± 7.39
3
br m, 7H), 6.86 (t, 1H), 3.57 (q, 3H), 3.27 (d, 3H), 1.28 ± 1.86
m, 30H); 31P NMR (CDCl ): d ˆ 52.44; IR: n ˆ 3063 (nCH, w),
3
3
055 (nCH, w), 2840 ± 2905 (n , br), 2810 (n , w), 1618 (n
,
CˆN
CH3
CH2
(
3 Â30 mL) to remove the [(p-cymene)RuCl PCy ] byproduct
2
3
s), 1607 [nCˆC(Ph), w], 1584 [nCˆC(Ph), w], 1506 [nCˆC(Ph), w], 1458
nCH2, w), 1451 [nCˆC(Ph), w], 1107 (nRu-O-Ph, w), 1005 (nskel.PCy3, w),
68 (nRu-O-Ph, w), 545 (nRu-O-Ph, w), 512 (nRu-Cl, w), 448 (nRu-N, w),
42 cm±1 (nRu-P, w); anal. calcd. (%) for RuC H ONClP
641.19): C 61.81, H 7.39, N 2.18; found: C 61.86, H 7.42, N 2.17.
and any unreacted starting materials. After recrystallisation
(
5
4
(
from chlorobenzene/pentane and additional washing with 2 Â
1
0 mL of pentane to remove the residual chlorobenzene, the
33
47
productwasdriedunder vacuum,affordingthebimetallicSchiff
base substituted ruthenium complexes 3a ±f in good yields.
Bimetallic Schiff base-substituted ruthenium complex 3.a:
Ruthenium complex 2a (0.64 g, 1 mmol) and the dimer
Ruthenium Schiff base complex 2b: Ruthenium complex
[
RuCl (PCy ) ˆCHPh] (1.20 g, 1.50 mmol), the thallium salt of
2
3 2
ligand 1b (0.58 g, 1.50 mmol) and THF (20 mL) afforded the
[
3
RuCl (p-cymene)] (0.61 g, 1 mmol) afforded the complex
a as an orange-green powder; yield: 0.419 g (63%). H NMR
2
2
1
complex 2b as a brown solid; yield: 0.81 g (79%). H NMR
1
(
1
1
CDCl ): d ˆ 19.99 (d, 1H), 9.05 (d, 1H), 8.27 (d, 1H), 8.14 (d,
3
(
CDCl ): d ˆ 19.97 (d, 1H), 9.03 (d, 1H), 7.64 (t, 1H), 7.09 ± 7.44
3
H), 7.10 ± 7.42 (m, 5H), 7.08 (d, 1H), 3.32 (d, 3H), 2.63 (q, 3H),
(
br m, 7H), 7.01 (t, 1H), 5.58 (d, 1H), 5.46 (d, 1H), 5.29 (d, 1H),
3
1
.31 ± 1.88 (m, 30H); P NMR (CDCl ): d ˆ 52.47; IR: n ˆ 3056
3
5
3
2
1
.15 (d, 1H), 3.31 (d, 3H), 2.92 (septet, 1H), 2.19 (s, 3H), 1.35 (d,
(
n , w), 3050 (n , w), 2838 ± 2900 (n , br), 2806 (n , w),
CH CH CH3 CH2
H), 1.32 (d, 3H); IR: n ˆ 3060 (nCH, w), 3054 (nCH, w), 2838 ±
1
1
1
616 (n , s), 1603 [nCˆC(Ph), w], 1580 [nCˆC(Ph), w], 1552 (nNO2, s),
501 [nCˆC(Ph), w], 1451 (nCH2, w), 1443 [nCˆC(Ph), w], 1335 (nNO2, s),
102 (n
w), 440 cm (nRu-P, w); anal. calcd. (%) for RuC H O N ClP
686.17): C 57.76, H 6.76, N 4.08; found: C 57.82, H 6.84, N 4.06.
CˆN
901 (n , br), 2806 (n , w), 1617 (n , s), 1605 [nCˆC(Ph), w],
CH3
CH2
CˆN
583 [nCˆC(Ph), w], 1506 [nCˆC(Ph), w], 1455 [nCˆC(Ph), w], 1449 (nCH2
,
, w), 1000 (nskel.PCy3, w), 507 (nRu-Cl, w), 443 (nRu-N,
Ru-O-Ph
w), 1382 (skel.i-Pr, m), 1361 (skel.i-Pr, m), 1106 (nRu-O-Ph, w), 1003
±
1
33
46
3
2
(
(
nskel.PCy3, w), 773 (gCH, w), 564 (nRu-O-Ph, w), 544 (nRu-O-Ph, w), 512
(
±1
nRu-Cl
,
w), 440 cm
(nRu-N, w); anal. calcd. (%) for
Ruthenium Schiff base complex 2c: Ruthenium complex
Ru C H ONCl (666.96): C 45.02, H 4.23, N 2.10; found: C
2
25 28
3
[
RuCl (PCy ) ˆCHPh] (1.20 g, 1.50 mmol), the thallium salt of
2
3
2
45.10, H 4.25, N 2.11.
ligand 1c (0.76 g, 1.50 mmol) and THF (20 mL) afforded the
Bimetallic Schiff base-substituted ruthenium complex 3b:
1
complex 2c as a brown solid; yield: 0.91 g (75%). H NMR
Ruthenium complex 2b (0.69 g, 1 mmol) and the dimer [RuCl (p-
2
(
CDCl ): d ˆ 19.45 (d, 1H), 8.19 (d, 1H), 7.99 (d, 1H), 7.95 (d,
3
cymene)] (0.61 g, 1 mmol) afforded the complex 3b as an
2
2
1
3
3
H), 6.95 (d, 1H), 7.56 (t, 1H), 7.34 (t, 1H), 7.24 (t, 2H), 7.05 (t,
1
orange-green powder; yield: 0.476 g (67%). H NMR (CDCl ):
3
H), 7.01 (s, 1H), 6.98 (s, 1H), 2.45 (q, 3H), 2.33 (s, 3H), 1.78 (d,
d ˆ 20.02 (d, 1H), 9.08 (d, 1H), 8.34 (d, 1H), 8.19 (d, 1H), 7.53
(d, 2H), 7.45 (t, 1H), 7.38 (t, 2H), 7.16 (d, 1H), 5.64 (d, 1H), 5.52
(d, 1H), 5.33 (d, 1H), 5.19 (d, 1H), 3.36 (d, 3H), 2.96 (septet,
1H), 2.21 (s, 3H), 1.40 (d, 3H), 1.37 (d, 3H); IR: n ˆ 3054 (nCH,
w), 3047 (n , w), 2835 ± 2898 (n , br), 2802 (n , w), 1615
3
1
H), 1.14 ± 1.71 (m, 30H); P NMR (CDCl ): d ˆ 50.56; IR: n ˆ
3
053 (n , w), 3038 (n , w), 2850 ± 2961 (n , br), 1603
CH3, CH2
CH
CH
(
n
, s), 1582 [nCˆC(Ph), w], 1524 [nCˆC(Ph), w], 1469 [nCˆC(Ph), w],
443 [nCˆC(Ph), w], 1065 (nRu-O-Ph, w), 1004 (nskel.PCy3, w), 801 (gCH
,
w), 787 (g , w), 694 (nC-Br, s), 670 (nRu-N, w), 558 (nRu-O-Ph, w), 532
nRu-O-Ph, w), 498 (nRu-Cl, w), 439 (nRu-P, w); anal. calcd. (%) for
RuC H ONClBrP (810.20): C 59.29, H 6.47, N 1.73; found: C
9.33, H 6.51, N 1.70.
CˆN
1
CH
CH3
CH2
Ph
(n , s), 1600 [nCˆC(Ph), w], 1577 [nCˆC(Ph), w], 1550 (nNO2, s), 1500
CˆN
(
[nCˆC(Ph), w], 1447 [nCˆC(Ph), w], 1441 (nCH2, w), 1382 (skel.i-Pr, m),
4
0
52
1363 (skel.i-Pr, m), 1332 (nNO2, s), 1098 (nRu-O-Ph, w), 997 (nskel.PCy3
,
,
5
w), 768 (g , w), 558 (nRu-O-Ph, w), 540 (nRu-O-Ph, w), 503 (nRu-Cl
CH
±1
Ruthenium Schiff base complex 2d: Ruthenium complex
w), 437 cm ) (n , w); anal. calcd. (%) for Ru C H O N Cl
Ru-N 2 25 27 3 2
3
[
RuCl (PCy ) ˆCHPh] (1.20 g, 1.50 mmol), the thallium salt of
(711.94): C 42.17, H 3.82, N 3.93; found: C 42.24, H 3.84, N 3.91.
Bimetallic Schiff base-substituted ruthenium complex 3c:
Ruthenium complex 2c (0.81 g, 1 mmol) and the dimer
[RuCl (p-cymene)] (0.61 g, 1 mmol) afforded the complex
2
3 2
ligand 1d (0.83 g, 1.50 mmol) and THF (20 mL) afforded the
1
complex 2.d as a brown solid; yield: 0.93 g (72%). H NMR
(
CDCl ): d ˆ 19.49 (d, 1H), 8.24 (d, 1H), 8.06 (d, 1H), 8.05 (d,
3
2
2
646
Adv. Synth. Catal. 2002, 344, 639 ± 648

The Scope of the Introduction of Schiff Bases as Co-Ligands in ROMP and RCM
FULL PAPERS
3
c as an orange powder; yield: 0.511 g (61%). 1H NMR General Procedure for Ring-Opening Metathesis
(
CDCl ): d ˆ 19.48 (d, 1H), 8.21 (d, 1H), 8.12 (d, 1H),
3
Polymerisations (ROMP)
8
7
5
2
.06 (d, 2H), 7.72 (t, 1H), 7.44 (t, 2H), 7.38 (t, 1H), 7.12 (t, 1H),
.09 (s, 1H), 7.06 (d, 1H), 7.02 (s, 1H), 5.45 (d, 1H), 5.30 (d, 1H),
.17 (d, 1H), 5.06 (d, 1H), 2.84 (septet, 1H), 2.06 (s, 3H),
.03 (s, 3H), 1.89 (d, 3H), 1.28 (d, 3H), 1.24 (d, 3H); IR:
In a typical ROMP experiment 0.005 mmol of the catalyst as a
solution in chlorobenzene (0.1004 M) was transferred into a
1
5-mL vessel followed by the addition the appropriate amount
of monomer solution (200 equivalents for cyclooctene and
00 equivalents for the norbornene derivatives) in chloroben-
zene. The reaction mixture was then kept stirring at 70 8C for
hours. To stop the polymerisation reaction, 2 ± 3 mL of an
n ˆ 3052 (nCH, w), 3038 (nCH, w), 2848 ± 2968 (nCH3, br), 1601
8
(
1
n
CˆN
, s), 1579 [nCˆC(Ph), w], 1523 [nCˆC(Ph), w], 1466 [nCˆC(Ph), w],
443 [nCˆC(Ph), w], 1385 (skel.i-Pr, m), 1367 (skel.i-Pr, m), 1062
4
(
(
nRu-O-Ph, w), 1003 (nskel.PCy3, w), 801 (gCH, w), 784 (gCH, w), 692
nC-Br, s), 666 (nRu-N, w), 554 (nRu-O-Ph, w), 527 (nRu-O-Ph, w),
ethyl vinyl ether/BHT solution was added and the solution was
stirred for 0.5 hour to make sure that the deactivation of the
active species was completed. The solution was poured into
methanol (50 mL containing 0.1% BHT) and the polymers
were precipitated and dried under vacuum overnight.
92 cm±1 (nRu-Cl, w); anal. calcd. (%) for Ru C H ONCl Br
4
2 32 33 3
(
835.97): C 45.97, H 3.98, N 1.68; found: C 46.03, H 4.01, N 1.65.
Bimetallic Schiff base-substituted ruthenium complex 3d:
Ruthenium complex 2d (0.86 g, 1 mmol) and the dimer
[
3
RuCl (p-cymene)] (0.61 g, 1 mmol) afforded the complex
d as a dark orange powder; yield: 0.602 g (68%). H NMR
2
2
1
(
8
CDCl ): d ˆ 19.50 (d, 1H), 8.36 (d, 1H), 8.31 (d, 1H), General Procedure for Ring-Closing Metathesis
3
.10 (d, 2H), 7.76 (t, 1H), 7.71 (d, 1H), 7.43 (t, 2H), 7.15 Reactions (RCM)
(
d, 1H), 7.11 (s, 1H), 7.07 (s, 1H), 5.49 (d, 1H), 5.36 (d, 1H),
All reactions were performed on the benchtop in air by
weighing 5 mol % of the catalyst into a dry NMR tube and
dissolving the solid in 1 mL of C D Cl. A solution of the
5
2
.21 (d, 1H), 5.11 (d, 1H), 2.86 (septet, 1H), 2.09 (s, 3H),
.06 (s, 3H), 1.96 (d, 3H), 1.31 (d, 3H), 1.29 (d, 3H); IR:
6
5
n ˆ 3045 (nCH, w), 3031 (nCH, w), 2844 ± 2963 (nCH3, br), 1597
appropriate substrate (0.1 mmol) in C D Cl (1 mL) was added.
6
5
(
1
(
7
n
CˆN
, s), 1576 [nCˆC(Ph), w], 1541 (nNO2, s), 1517 [nCˆC(Ph), w],
The tube was then capped, wrapped with parafilm, and shaken
for 4 hours at 55 8C for catalytic systems 2 and at 70 8C for
catalytic systems 3. Product formation (all reaction products
were unambiguously identified previously[ ) and diene
disappearance were monitored by integrating the allylic
methylene peaks.
458 [nCˆC(Ph), w], 1440 [nCˆC(Ph), w], 1389 (skel.i-Pr, m), 1369
skel.i-Pr, m), 1322 (nNO2, s), 1044 (nRu-O-Ph, w), 995 (nskel.PCy3, w),
93 (gCH, w), 779 (gCH, w), 683 (n , s), 659 (nRu-N, w), 541
C-Br
±1
12b]
(
(
nRu-O-Ph, w), 514 (nRu-O-Ph, w), 482 cm (nRu-Cl, w); anal. calcd.
%) for Ru C H O N Cl Br (880.95): C 43.63, H 3.66, N 3.18;
2
32 32
3
2
3
found: C 43.71, H 3.70, N 3.17.
Bimetallic Schiff base-substituted ruthenium complex 3e:
Ruthenium complex 2e (0.79 g, 1 mmol) and the dimer
[
3
RuCl (p-cymene)] (0.61 g, 1 mmol) afforded the complex
e as a yellow-green powder; yield: 0.597 g (73%). H NMR
2
2
Acknowledgements
1
(
CDCl ): d ˆ 19.71 (d, 1H), 8.12 (d, 1H), 7.96 (d, 2H), 7.55 (t,
3
B.D.C. is indebted to the IWT (Vlaams instituut voor de
bevordering van het wetenschappelijk-technologisch onderzoek
in de industrie) for a research grant. F.V. is indebted to the FWO
1
1
1
1
3
H), 7.11-7.44 (br m, 8 H), 6.66 (t, 1H), 5.42 (d, 1H), 5.27 (d,
H), 5.12 (d, 1H), 5.01 (d, 1H), 3.41 (septet, 1H), 2.81 (septet,
H), 2.25 (septet, 1H), 2.01 (s, 3H), 1.67 (d, 3H), 1.29 (d, 3H),
.26 (d, 3H), 1.21 (d, 3H), 0.82 (dd, 6H); IR: n ˆ 3059 (nCH, w),
(
Fonds voor Wetenschappelijk Onderzoek-Vlaanderen) and to
the Research Funds of Ghent University for financial support.
040 (n , w), 2857±2961 (n , br), 1607 (n , s), 1586 [nCˆC(Ph)
,
CH
CH3
CˆN
w], 1527 [nCˆC(Ph), w], 1469 [nCˆC(Ph), w], 1445 [nCˆC(Ph), w], 1383
skel.i-Pr, m), 1364 (skel.i-Pr, m), 1070 (nRu-O-Ph, w), 1009 (nskel.PCy3
w), 806 (gCH, w), 794 (gCH, w), 688 (nRu-N, w), 564 (nRu-O-Ph, w),
(
,
References
±1
537 (nRu-O-Ph, w), 508 cm (nRu-Cl, w); anal. calcd. (%) for
[
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Ru C H ONCl (813.18): C 53.17, H 5.21, N 1.72; found: C
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36 42
3
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Bimetallic Schiff base-substituted ruthenium complex 3f:
Ruthenium complex 2f (0.83 g, 1 mmol) and the dimer
RuCl (p-cymene)] (0.61 g, 1 mmol) afforded the complex 3f
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[
2
2
1
as an orange powder; yield: 0.587 g (68%). H NMR (CDCl ):
3
d ˆ 19.81 (d, 1H), 8.32 (d, 1H), 8.22 (d, 1H), 8.16 (d, 1H), 7.34 ±
7
1
.98 (br m, 8H), 7.06 (d, 1H), 5.39 (d, 1H), 5.25 (d, 1H), 5.08 (d,
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1
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3
(
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septet, 1H), 1.98 (s, 3H), 1.74 (d, 3H), 1.34 (d, 3H), 1.20 (d,
H), 1.16 (d, 3H), 0.88 (dd, 6H); IR: n ˆ 3054 (nCH, w), 3037
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n
CH
CH3
CˆN
550 (nNO2, s), 1528 [nCˆC(Ph), w], 1464[nCˆC(Ph), w], 1444 [nCˆC(Ph), w],
1387 (skel.i-Pr, m), 1366 (skel.i-Pr, m), 1331 (nNO2, s), 1100
(
(
nRu-O-Ph, w), 1057 (nskel.PCy3, w), 798 (gCH, w), 785 (gCH, w), 678
nRu-N, w), 557 (nRu-O-Ph, w), 529 (nRu-O-Ph, w), 496 cm (nRu-Cl, w);
1
2
999, 3, 211; d) A. F¸rstner, Angew. Chem. Int. Ed. Engl.
000, 39, 3012.
±1
anal. calcd. (%) for Ru C H O N Cl (858.16): C 50.38, H
2
36 41
3
2
3
[
3] R. R. Schrock, J. S. Murdzek, G. C. Bozan, J. Robbins, M.
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