Ruthenium catalyst with a chelating pyridinyl-alcoholato ligand for application in linear alkene metathesis

Article abstract of DOI:10.1002/adsc.200600474

The catalytic activity of ruthenium alkylidene complexes [RuCl(LX(ON)(=CHPh)] [L = H₂IMes and PCy₃, ON = 1-(2′-pyridinyl)cyclohexan-1-olate)], bearing a chelating pyridinyl-alcoholate ligand, was investigated for the metathesis of 1-octene in the absence of a solvent. Both systems were active for the metathesis of 1-octene yielding trans-7-tetradecene and ethene as the primary metathesis products. Although the activity of both systems increased with an increase in reaction temperature, the activity of [RuCl(H₂IMes)(ON)(=CHPh)] started to decrease at temperatures above 70°C, with a simultaneous exponential increase in the secondary metathesis products due to double-bond isomerisation of the substrate. Although the initiation rates for these systems are slower compared to Grubbs 1 and Grubbs 2 for the metathesis of 1-octene at 60°C, they have a higher activity and longer lifetime.

Full text of DOI:10.1002/adsc.200600474

FULL PAPERS
DOI: 10.1002/adsc.200600474
Ruthenium Catalyst with a Chelating Pyridinyl-Alcoholato
Ligand for Application in Linear Alkene Metathesis
a
a,
Margaritha Jordaan and H. C. Manie Vosloo *
a
SST Catalysis and Synthesis Research Group, School of Chemistry, North-West University, 2520 Potchefstroom, South
Africa
Fax : (+27)-18-299-2350; e-mail: manie.vosloo@nwu.ac.za
Received: September 15, 2006
Abstract: The catalytic activity of ruthenium alkyli- started to decrease at temperatures above 708C, with
_
dene complexes [RuCl(L)
A
T
E
N
(ON)
A
H
R
U
G
a simultaneous exponential increase in the secondary
metathesis products due to double-bond isomerisa-
_
[
L=H IMes and PCy , ON=1-(2’-pyridinyl)cyclo-
2 3
hexan-1-olate)], bearing a chelating pyridinyl-alco- tion of the substrate. Although the initiation rates
holate ligand, was investigated for the metathesis of for these systems are slower compared to Grubbs 1
1-octene in the absence of a solvent. Both systems and Grubbs 2 for the metathesis of 1-octene at 608C,
were active for the metathesis of 1-octene yielding they have a higher activity and longer lifetime.
trans-7-tetradecene and ethene as the primary meta-
thesis products. Although the activity of both sys-
tems increased with an increase in reaction tempera- Keywords: alkene metathesis; chelating ligands;
_
ture, the activity of [RuCl
A
H
R
U
G
A
H
R
N
(ON)
A
H
R
U
G
Grubbs-type precatalyst; 1-octene; ruthenium
2
[
6–8]
Introduction
reactivity to their metal complexes.
Hemilabile li-
gands, which are a class of chelating ligands, have the
The ruthenium carbene complexes developed by the ability to place two or more donor atoms with very
Grubbs group, RuCl LL’(=CHPh) [L, L’=PCy (1) different electronic properties close to the metal atom
AHCTREUNG
2
3
and L=PCy , L’=NHC (2)], are of interest because (Figure 1). The relevance of these ligands is increasing
3
of their high 1-alkene metathesis activity and toler-
Figure 1. Schematic representation of the concept of hemila-
bility.
[
1,2]
ance towards polar functional groups.
The lifetime
and reactivity of the metal carbene complex 1 have
been improved through the replacement of the phos- in coordination and organometallic chemistry, since
phine ligand by a more bulky and basic N-heterocy- they can reversibly create and/or occupy a vacant co-
[
3,4]
clic carbene ligand.
The higher activity of 2 can ordination site at the metal, with consequent stabilisa-
also be attributed to electronic and steric effects that tion of reactive intermediates or enhancement of re-
[
9,10]
influence the dissociation of the phosphine ligand as activity in catalytic reactions.
It is presumed that
well as the ratio of alkene to phosphine coordination these ligands act as chelating ligands at room temper-
[
5]
during the mechanistic cycle.
ature and at elevated temperatures will liberate one
The chemistry of transition metal complexes with coordination site ꢀon demandꢁ of a competing sub-
[
10,11]
chelating ligands containing mixed functionalities is strate, e.g., an alkene.
enjoying an increase in popularity, as the different A number of ruthenium carbene systems with hemi-
features associated with each donor atom give unique labile ligands for application in ring-opening meta-
184
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 184 – 192

Ruthenium Catalyst with a Chelating Pyridinyl-Alcoholato Ligand
FULL PAPERS
[10,12–16]
Figure 2. Chelating ruthenium catalysts for alkene metathesis.
thesis polymerisation (ROMP) and ring-closing meta- version of diethyl diallylmalonate to diethyl 3-cyclo-
[
11–16]
thesis (RCM) has been published (Figure 2).
pentenecarboxylate after 30 min at 808C. The 2-pyri-
[12]
[13,14]
Grubbs
and later Verpoort
introduced biden- dinylcarbinol-containing ruthenium carbene catalysts
tate O,N-chelated Schiff-base ligands on 1 and 2 to are therefore very active for metathesis reactions. To
give 3a and 3b, respectively. The thermal stability and our knowledge the catalytic activity of these types of
activity of these complexes towards ROMP and RCM systems towards the self-metathesis of linear alkenes
were increased through the combination of the Schiff- has not been previously investigated or reported.
[
11,14,17]
base ligand with an NHC ligand (3b).
2-Pyridi-
In this study we report on the synthesis and catalyt-
_
nylcarbinol (L1) is another type of O,N-chelated ic activity of the precatalysts [RuCl(L)
A
H
R
U
G
A
T
E
N
(=CHPh)]
_
[
2
3
clohexan-1-olate] for the metathesis of 1-octene at
elevated temperatures. The formation and interaction
of the carbene active species are illustrated with the
1
use of H NMR spectroscopy.
Results and Discussion
ligand, which has been well established in tungsten Synthesis of Complexes 4a and 7
[
18]
(
VI) catalyst precursors for ROMP reactions. Sev-
eral groups incorporated this type of ligand into the Precatalysts 4a and 7 were prepared by stirring 1 and
first-and second g- eneration Grubbs systems to give
2, respectively, with the lithium salt (L2) of 2-pyridi-
complexes 4 to 6, which were shown to be active for
[
11,15,16]
[11]
RCM and/or ROMP.
Although Denk et al.
have synthesised 4a, they did not report on its meta-
thesis activity. Complex 4a was only used as an inter-
mediate in the synthesis of 5a and 5b, which catalysed
the ROMP of norbornene and cyclooctene, respec-
tively, in 78 and 98% yield within 60 min. This type of
ligand has also found application in the design of pe-
riphery-functionalised dendritic catalysts (6) for RCM
[16]
[16]
reactions. Van Koten et al. reported a 100% con-
Adv. Synth. Catal. 2007, 349, 184 – 192
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
185

Margaritha Jordaan and H. C. Manie Vosloo
FULL PAPERS
Scheme 1. Schematic representation of the synthesis of cata-
lysts 4a and 7.
nylcarbinol (L1), which was obtained through reac-
[
11,19]
tion of L1 with butyllithium (Scheme 1).
The re-
action mixture was stirred for 2 days in tetrahydrofur-
an (THF) at room temperature for 4a and at 358C for
7
. Although within 120 min a dark green solution was
Figure 3. GC/FID chromatogram of the reaction mixture of
obtained for 7 and a brown solution for 4a, TLC indi-
cated that substrate was still present, and therefore
the mixture was stirred for a longer period than what
1
-octene in the presence of 4a at 608C after 60 min.
[
11]
was reported by Denk et al. The formation of LiCl
drives the reaction and its high solubility in THF may identified, i.e., primary metathesis products (PMP),
be the reason why these reactions took so long. The isomerisation products (IP) and secondary metathesis
LiCl was removed through the extraction of the prod- products (SMP).
uct with toluene. The free phosphine was removed by
It has been reported that the phosphine-based
sonification (10 min) of the product in pentane with ruthenium carbene systems with an O,N-chelating
subsequent removal of the pentane by syringe. The ligand are not very active for RCM and ROMP reac-
[
11,12,15]
complexes were finally obtained in moderate yields as tions at room temperature.
Therefore, experi-
microcrystalline powders through recrystallisation ments were carried out at reaction temperatures rang-
from THF/pentane.
ing from 35–808C to determine the effect of tempera-
ture on the metathesis activity and selectivity of 4a
and 7 at a 1-octene/Ru molar ratio of 9000. Samples
(0.3 mL) were withdrawn by syringe at regular time
intervals and quenched with a solution of toluene
Metathesis of 1-Octene using 4a and 7
A mixture of products can form during the metathesis (0.3 mL) and tert-butyl hydrogen peroxide (2 drops).
of 1-octene due to alkene isomerisation and the meta- The reaction was monitored by GC/FID to determine
thesis reactions (self-and cross m- etathesis) that can
the different products that form during the metathesis
occur simultaneously as the reaction proceeds of 1-octene; these products were identified by GC/
[20]
(
Table 1). As a result of double-bond isomerisation MSD. The self-metathesis of 1-octene typically leads
occurring during the metathesis reaction secondary to the formation of two isomers (Figure 3), cis-and
cross-metathesis between the various alkenes can take trans-7-tetradecene, which combined with ethene (not
place yielding a range of C –C alkene products. observed by GC) represent the PMP of the reac-
2
14
Therefore three major groups of products can be tion.
Table 1. Possible reactions of 1-octene in the presence of metathesis catalysts.
[a]
[a]
Reaction
Substrate
Products
Primary metathesis
[
b]
-
-
Self -m etathesis
Isomerisation
C =C7
C =C7
C=C+C =C
A
C
H
T
R
E
U
N
G
(PMP)
7
7
[
c]
C =C +C =C +C =C
4
(IP)
(SMP)
2
6
3
5
4
Secondary metathesis
[d]
-
-
Cross-metathesis
Self-metathesis
C=C +C =C
C =C +C=C +C=C +C =C
7
ACHTREUNG
7
2
6
2
7
6
2
6
C =C
2
C =C +C =C
2 2 6 6
6
[
[
[
[
a]
Hydrogens are omitted and geometrical isomers not shown for simplicity.
Primary metathesis products (PMP) refers to the homometathesis products of 1-octene, i.e., C =C and C=C.
Isomerisation products (IP) refers to the double bond isomerisation reaction of terminal to internal alkenes.
Secondary metathesis products (SMP) refers to the metathesis of the isomerisation products of 1-octene.
b]
c]
d]
7
7
186
www.asc.wiley-vch.de
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 184 – 192

Ruthenium Catalyst with a Chelating Pyridinyl-Alcoholato Ligand
FULL PAPERS
Table 2. Catalytic activity and selectivity of 4a and 7 towards the metathesis of 1-octene at 35 to 808C (1-octene/Ru=9000,
no solvent) after 420 min.
[a]
À1
Catalyst
T [8C]
PMP [%]
SMP [%]
IP [%]
% S
kinit [mol s ]
TON
À8
À6
À6
À6
À8
À6
À5
À5
4
a
35
10.2
53.2
59.6
90.3
3.3
81.1
91.8
59.9
0.1
0.4
1.2
8.1
0.0
0.5
1.5
2.2
0.0
0.0
0.0
0.3
98.67
98.34
95.97
89.80
85.40
86.28
77.83
50.46
5.48”10
2.06”10
5.55”10
6.39”10
6.00”10
5.19”10
1.35”10
2.82”10
1143
5907
6652
10119
379
9214
10428
6811
6
7
8
0
0
0
7
35
0.6
6
7
8
0
0
0
12.9
26.1
58.5
[
a]
Selectivity towards PMP
Table 2 summarises the catalytic activity and selec- Table 3. Catalytic activity and selectivity of 4a towards the
tivity of 4a and 7 towards the metathesis of 1-octene metathesis of 1-octene at 608C at different 1-octene/Ru
molar ratio (no solvent) after 420 min.
over a temperature range of 35 to 808C. Both 4a and
7
showed rather low activity for the metathesis of 1-
1
-Octene/Ru
PMP SMP IP
[%] [%] [%]
%
S
k
s ]
[mol TON
init
À1
octene at 358C, i.e., approximately 10% and 3%
PMP after 420 min, respectively. Although a linear in-
crease in the activity of 4a towards the formation of
PMP was observed with an increase in temperature,
exponential increases in IP and SMP were noted. In
contrast, 7 shows a sharp increase in PMP formation
up to 708C with an even sharper decrease in activity
when the temperature increases above 708C with an
exponential increase in SMP. It was also noted that in
[a]
molar ratio
À6
À6
À7
2
9
1
000
000
00 000
68.0 1.5
53.2 0.4
32.0 0.2
0.9 96.59 2.65”10 1728
0.5 98.34 2.06”10 5907
0.5 97.86 5.52”10 3569
[a]
Selectivity towards PMP
the presence of 7 the mol% IP increases to a maxi- exponentially for 7 with an increase in temperature
mum within the first 10 min followed by a sharp de- (Figure 4). Although a steady increase in the turnover
crease to 0% within 30 min as the reaction proceeds, number (TON) was observed for both 4a and 7 at ele-
most probably due to cross-metathesis of the IPs to vated temperatures, a sharp reduction in the selectivi-
form SMPs.
ty and TON was noted for 7 at temperatures above
À1
The initiation rate constants (kinit [mol s ]) for 708C (Table 2). The optimum reaction temperature
both 4a and 7 were determined as a function of the where both catalytic systems gave high activity while
mol 7-tetradecene formed over time. A linear in- retaining a high degree of selectivity towards PMP
crease in kinit for the formation of 7-tetradecene was with a limited amount of SMP and IP formation was
observed in the presence of 4a, while kinit increased found to be 608C. All reactions were further per-
formed at 608C.
We also investigated the influence of the 1-octene/
Ru molar ratio on the performance of 4a to deter-
mine if the catalyst will be active at lower catalyst
concentrations. Table 3 summarises the catalytic activ-
ity and selectivity of 4a towards the metathesis of 1-
octene at 608C varying the 1-octene/Ru molar ratio
from 2000 to 100,000. The activity of 4a towards the
formation of PMP increases with a decrease in the 1-
octene/Ru molar ratio as illustrated in Figure 5, with
a simultaneous increase in both the SMP and IP
(
Table 3). Although the initiation rate of 4a increased
with an increase in the catalyst concentration, a sharp
decrease in the TON was observed after reaching a
maximum at a 1-octene/Ru molar ratio of 9000.
Therefore, in order to have a high activity and selec-
tivity of 4a towards PMP with limited SMP and IP
Figure 4. Initiation rate (kinit) as a function of temperature formation, an 1-octene/Ru molar ratio=9000 was
[
&
4a, * 7]
used for further investigations.
Adv. Synth. Catal. 2007, 349, 184 – 192
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
187

Margaritha Jordaan and H. C. Manie Vosloo
FULL PAPERS
Figure 5. Influence of 1-octene/Ru molar ratio on the self-
Figure 6. Self-metathesis of 1-octene to 7-tetradecene and
ethene (PMP) in the presence of precatalysts 1, 2, 4a and 7
at 608C (1-octene/Ru=9000) [&
2, * 1, ^ 7, ~ 4a].
metathesis of 1-octene to 7-tetradecene and ethene (PMP)
in the presence of catalyst 4a at 608C [^ 2000,
&
9000, *
100,000].
Subsequently a comparative study on the activity while 1 (21% PMP) and 2 (63% PMP) are inactive.
and selectivity of 1, 2, 4a and 7 was performed at a 1- Although the initiation rates of 4a and 7 are slower
octene/Ru molar ratio of 9000. Table 4 summarises compared to those of 1 and 2, the TON, selectivity
the catalytic activity and selectivity of the various cat- and lifetime of the precatalysts are improved. This in-
alysts towards the metathesis of 1-octene at 608C. 1- dicates that the incorporation of a hemilabile ligand
Octene was converted to approximately 15% trans- into the Grubbs systems improves the lifetime, activi-
and 12% cis-7-tetradecene (approximately 53% ty and selectivity of the catalysts towards 1-alkene
[11]
PMP) in the presence of 4a as compared to 6% trans- metathesis at higher temperatures. Denk et al. and
[
16]
and 5% cis-7-tetradecene (approximately 21% PMP) van Koten et al. have also shown that the incorpo-
for 1 after 420 in (Figure 6). In the presence of 7 1- ration of a hemilabile ligand into the Grubbs system
octene was converted to approximately 36% trans- improves the activity of the catalyst for ROMP and
and 7% cis-7-tetradecene (approximately 81% PMP) RCM reactions.
as compared to 27% trans-and 6% cis-7-tetradecene
In addition we investigated the metathesis of 1-
1
(
approximately 63% PMP) for 2 after 420 min octene in the presence of 4a and 7 with H NMR at
(
Figure 6). SMP formation due to the double-bond 508C in CDCl , to gain some insight into the reaction
3
isomerisation of 1-octene to mainly 2-octene and the mechanism.
subsequent metathesis reactions remained below 2%
for both 1 and 4a while 13% and 36% SMP are ob-
served in the presence of 7 and 2, respectively. The se- NMR Investigation: Metathesis with 4a
lectivity towards the formation of PMP increase with
2
0–35% in the presence of 4a and 7 compared to 1 The carbene a-H (denoted H* in the structures)
and 2. After 18 h both 4a and 7 still show activity, i.e., signal of the coordinated benzylidene 4a appears at
approximately 69% and 81% PMP, respectively, d=17.85 ppm, that of the heptylidene [RuCl(PCy )-
ACHTREUNG
3
_
(
ON)
methylidene [RuCl(PCy )(ON)(=CH )] (4ac) at
3 2
A
H
R
U
G
Table 4. Catalytic activity and selectivity of catalysts 1, 2, 4a d=16.19 ppm. The shift of the carbene a-H peak of
and 7 towards the metathesis of 1-octene at 608C (1-octene/
Ru=9000, no solvent) after 420 min.
the benzylidene to lower field to produce a triplet
and doublet is due to the change in the electronic en-
vironment of the ligand attached to the carbene
carbon. A shift in the pyridine a-H (denoted H in
Catalyst PMP
%]
SMP
[%]
IP
[%]
%
S
kinit
TON
†
[
a]
À1
[
[mol s ]
the structures) signal was also observed during the
course of the reaction, indicating that the electronic
environment of the ligand is changing, most probably
due to the coordination and decoordination of the N-
donor atom as the reaction continues. The pyridine a-
H signal of the coordinated benzylidene 4a appears at
À5
À4
1
2
4
7
21.1
63.4
53.2
81.1
0.2
35.8
0.4
4.8
0.4
0.5
0.0
81.16 3.78”10 2175
63.73 1.36”10 6750
À6
a
98.34 2.06”10 5907
À6
12.9
86.28 5.19”10 9214
[
a]
Selectivity towards PMP.
188
www.asc.wiley-vch.de
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 184 – 192

Ruthenium Catalyst with a Chelating Pyridinyl-Alcoholato Ligand
FULL PAPERS
1
Figure 8. The H NMR peak integration values (normalized)
of the carbenes involved in the metathesis reaction of 1-
octene in the presence of 4a [
7.00 ppm, ~ d=16.17 ppm].
&
d=17.85 ppm, * d=
1
of the benzylidene to the heptylidene and methyli-
dene; after 200 min all of 4a has been converted. The
heptylidene and methylidene signals increase to a
maximum followed by a gradual decrease to a mini-
mum as the reaction proceeds. The simultaneous de-
1
Figure 7. H NMR spectra of the carbene proton region at
different time intervals of a 1-octene/4a reaction mixture in
CDCl at 508C.
3
d=9.04 ppm, but the other signals cannot be assigned composition of the benzylidene to some other species
with certainty to the other intermediates. cannot be ruled out. In the presence of 1-octene it
Only three carbene species were observed during seems as if the benzylidene is simultaneously convert-
the metathesis of 1-octene in the presence of 4a ed to the heptylidene and the methylidene as the re-
(
Figure 7). Theoretically six carbenes should be in- action proceeds.
volved, but neither of the carbene a-H signals for the
uncoordinated intermediates (4a-open, 4ab-open and
4
ac-open) was observed. This may be due to the fast NMR Investigation: Metathesis with 7
rate of the reaction, and the fact that approximately
3 min were needed for each NMR spectrum to be re- We also investigated the metathesis of 1-octene in the
1
1
corded over a period of 5 h. The reaction may there- presence of 7 with H NMR at 508C in CDCl . In con-
3
fore proceed at such a fast rate that some of the car- trast to 4a, five carbene species were observed during
bene signals are not observed within the time scale of the metathesis of 1-octene in the presence of 7, which
the NMR.
might relate to the open and coordinated intermedi-
Figure 8 illustrates the change in the peak integra- ates as illustrated in Figure 9. The carbene a-H signal
tion values of the individual carbene species as a func- of the uncoordinated heptylidene intermediate (7b-
tion of time. The methylidene intermediate seems to open) was not observed.
follow a different pattern than what was reported for
The carbene a-H signal of the coordinated benzyli-
[20]
1
in which it seems the signal increases to a maxi- dene 7 appears at d=18.05 ppm, that of the heptyli-
_
mum with a gradual decrease without it being deplet- dene [RuCl
A
H
R
U
G
A
T
E
N
2
ed in the 5 h the reaction proceeds. The benzylidene 16.71 ppm and the methylidene [RuCl(H IMes)-
2
_
signal gradually decreases suggesting the conversion (ON)(=CH )] (7c) at d=16.08 ppm. The shift of the
A
H
R
U
G
2
Adv. Synth. Catal. 2007, 349, 184 – 192
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
189

Margaritha Jordaan and H. C. Manie Vosloo
FULL PAPERS
1
Figure 9. H NMR spectra of the carbene proton region at different time intervals of a 1-octene/7 reaction mixture in CDCl3
at 508C.
carbene a-H peak of the benzylidene to lower field to
produce a doublet and singlet is due to the change in
the electronic environment of the ligand attached to
the carbene carbon. The appearance of singlets at d=
19.48 ppm and d=19.76 ppm can be attributed to the
decoordination of the N-donor to produce the open
benzylidene (7-open) and methylidene (7c-open) in-
termediates. The downfield shift of the carbene sig-
nals is due to the decrease in electron density around
the Ru=C moiety and therefore the carbene a-H be-
comes less shielded. A shift in the pyridine a-H signal
was also observed during the course of the reaction,
indicating that the electronic environment of the
ligand is changing, most probably due to the coordi-
nation and decoordination of the N-donor atom as
the reaction continues. The pyridine a-H signal of the
coordinated benzylidene 7 appears at d=9.48 ppm,
but the other signals cannot be assigned with certainty
1
Figure 10. The H NMR peak integration values (normal-
ised) of the carbenes involved in the metathesis reaction of
-octene in the presence of 7 [! d=19.76 ppm, ^ d=
1
to the coordinated and uncoordinated heptylidene 19.48 ppm,
and methylidene intermediates nor the uncoordinated 16.08 ppm].
benzylidene.
&
d=18.05 ppm,
*
d=16.71 ppm,
~
d=
Figure 10 illustrates the change in the peak integra-
tion values of the individual carbene species as a func- the methylidene signal gradually increases to a maxi-
tion of time. The individual species seems to follow a mum within 3 h. This is followed by a slow decrease
similar pattern as was reported for 1 in which it has possibly due to catalyst decomposition or formation
been shown that the heptylidene is thermodynamical- of the uncoordinated methylidene intermediate,
ly and kinetically favoured above the methylidene which may be correlated to the gradual formation of
[20]
species.
The sharp decrease of the benzylidene the carbene a-H signal at d=19.76 ppm. The form of
signal suggests a fast conversion of the benzylidene to the graph for signals d=19.48 ppm and d=16.71 ppm
either the uncoordinated benzylidene intermediate (7- follows the same pattern, which suggests that these
open) or the heptylidene and methylidene; after signals might be connected to each other in the form
50 min all of 7 has been converted. The simultaneous of the uncoordinated and coordinated heptylidene
decomposition of the benzylidene to some other spe- species, respectively. In the presence of 1-octene it
cies cannot be ruled out. The increase of the heptyli- seems as if the benzylidene is rapidly converted to the
dene signal to a maximum within 26 min is followed heptylidene while the formation of the methylidene
by a gradual decrease as the reaction proceeds while proceeds at a much slower rate.
190
www.asc.wiley-vch.de
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 184 – 192

Ruthenium Catalyst with a Chelating Pyridinyl-Alcoholato Ligand
FULL PAPERS
Conclusions
autosampler, HP-5 MS capillary column (30 m”320 mm”
.25 mm) and an Agilent 5973 mass selective detector
MSD). The same oven program was used as before with a
0
(
Complexes 4a and 7 have been shown to be active for
the self-metathesis of 1-octene. As expected, these
systems show low reactivity at room temperature due
to the additional stabilization of the chelating ligand.
At elevated temperatures these systems show higher
À1
6
min solvent delay and He as carrier gas with a 1 mLmin
flow rate at 208C.
1
The H NMR investigations of the 1-octene metathesis re-
actions were performed in an NMR tube with 1-octene
0.05 mL, 0.32 mmol) mixed with a solution of the catalyst
(
activity and stability towards the formation of PMP
(
0.032 mmol) in CDCl (0.75 mL) at 508C. Spectra were re-
3
relative to 1 and 2, since after 18 h 4a and 7 still show corded at approximately 13 min intervals.
activity for the metathesis of 1-octene. The SMP for
both catalyst systems increases exponentially at tem-
peratures above 708C with a slight decrease in the se-
lectivity of 4a, while a sharp decrease in selectivity
and TON is observed for 7 at temperatures above
Complex 4a
A solution of lithium alcoholate (0.650 mmol, 0.120 g) in
THF (5 mL) was added dropwise to a solution of 1
(
0.580 mmol, 0.479 g) in THF (5–10 mL). The reaction mix-
708C. This indicates that 60–708C is the optimum
ture was stirred at room temperature for 60 min with a
colour change of dark purple to brown. The progress of the
reaction was monitored by TLC to determine if the starting
temperature for both 4a and 7 to maintain high selec-
tivity towards PMP and limit the formation of SMP
and IP during the metathesis of 1-octene. The incor- complex was being consumed. The reaction mixture was stir-
poration of a hemilabile ligand into the Grubbs sys- red until the TLC indicated that the starting complex was
tems therefore decreased the degree of SMP and IP not present any more. After evaporation of the solvent, the
residue was dissolved in a minimal amount of toluene. The
formation and increased the activity and selectivity of
lithium chloride was then removed by filtration via a syringe
filter and the volume of the filtrate reduced to ca. 0 mL.
THF (1 mL) was added to the residue and after layering 10–
1
and 2.
The NMR results indicate that the heptylidene is
the catalytically active species that preferentially
forms in the 1-octene metathesis reaction with 7 at
5
1
5 mL cold pentane onto the THF, it was placed in the re-
frigerator awaiting precipitation of the desired complex.
After removal of the pentane via syringe, the desired com-
plex was washed with cold pentane and sonificated for
08C in CDCl . In contrast, both the heptylidene and
3
methylidene species forms simultaneously during the
1
-octene metathesis reaction with 4a. Investigations 10 min. The solid thus obtained was filtered and then dried
are currently underway to verify the intermediate spe- under vacuum to afford 4a as a dark brown microcrystalline
cies formed during the reaction.
3
1
1
powder; yield: 317.5 mg (85%). P( H) NMR (121 MHz,
1
CDCl ): d=41.5 (s); H NMR (300 MHz, CDCl ): d=17.85
3
3
(
d, 1H, Ru=CHPh), 7.09 (d, 2H, ortho H of C H ), 7.38 (t,
6 5
1
H, para H of C H ), 6.97 (dd, 2H, meta H of C H ), 8.95
6 5 6 5
Experimental Section
(bs, 1H, ortho H of C
5 4
H N), 6.97 (dd, 1H, para H of
C H N), 6.90 (dd, 1H, meta H of C H N), 7.03 (dd, 1H,
5
4
5
4
meta H of C H N), 0.85–2.45 (m, 43H, CH of PCy and
General Procedures
5
4
2
3
À1
C H ); anal. calcd. for C H ClNOPRu (683.76 gmol ): C
6
10
36 53
Manipulations of organometallic compounds were per-
formed using standard Schlenk techniques under an atmos-
phere of dry argon. All reactions were performed in oven-
dried (1008C) glassware. 1-Octene (Aldrich) was passed
through a column of basic alumina and stored on molecular
sieves (4 Š) under nitrogen. Solvents were dried by standard
methods and distilled over 4 Š molecular sieves under nitro-
6
3.24, H 7.81, N 2.05; found: C 62.82, H 8.05, N 1.77.
Complex 7
A solution of lithium alcoholate (0.650 mmol, 0.120 g) in
THF (5 mL) was added dropwise to a solution of 2
(0.620 mmol, 0.527 g) in THF (5–10 mL). The reaction mix-
ture was stirred at 30–408C for 1 h with a colour change of
brown to dark green. The progress of the reaction was moni-
tored by TLC to determine if the starting complex was
being consumed. The reaction mixture was stirred until the
TLC indicated that the starting complex was not present
any more. After removing the solvent under vacuum the res-
idue was dissolved in a minimal amount of toluene. The lith-
ium chloride was then removed by filtration via a syringe
filter and the toluene removed under vacuum. THF (1 mL)
was added to the residue. The product was precipitated by
layering 10–15 mL cold pentane onto the THF and placing it
in a refrigerator for 8 h. After removal of the pentane via
syringe, the desired complex was washed with cold pentane
and sonificated for 10 min. The solid thus obtained was fil-
tered and then dried under vacuum to afford 7 as a forest
green microcrystalline powder; yield: 370 mg (84%).
gen. RuCl
A
C
H
T
R
E
U
N
G
(PCy )L(=CHPh) [L=PCy (1) or H Imes (2)]
A
C
H
T
R
E
U
N
G
2
3
3 2
(
Fluka) were used as received. The synthesis of ruthenium
[11]
complexes 4a and 7 was adapted from literature.
The
1
H NMR spectra were recorded on a Varian Gemini 300
Broadband NMR spectrometer at 300 MHz in deuterated
chloroform. Gas chromatographic analyses were performed
on an Agilent 6890 gas chromatograph equipped with an
Agilent 7683 autoinjector, HP-5 capillary column (30 m”
320 mm”0.25 mm) and a flame ionisation detector (FID).
The following instrumental conditions were used: inlet tem-
perature of 2008C, oven programmed from 60 to 1308C
(
2
hold time 16 min) and 130 to 2908C (hold time 5 min) at
À1
À1
58C min , N carrier gas with a flow rate of 2 mLmin at
2
208C and FID temperature of 2508C. For product identifica-
tion the reaction mixtures were also analysed using an Agi-
lent 6890 gas chromatograph equipped with an Agilent 7683
Adv. Synth. Catal. 2007, 349, 184 – 192
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
191

Margaritha Jordaan and H. C. Manie Vosloo
FULL PAPERS
1
H NMR (300 MHz, CDCl ): d=17.96 (s, 1H, Ru=CHPh),
[2] M. B. Dinger, J. C. Mol, Adv. Synth. Catal. 2002, 344,
671.
3
7
.25 (d, 2H, ortho H of C H ), 7.05–7.15 (m, 1H, para H of
6 5
C H ), 6.88 (dd, 2H, meta H of C H ), 9.55 (d, 1H, ortho H
[3] J. Huang, H.-J. Schanz, E. D. Stevens, S. P. Nolan, Orga-
nometallics 1999, 18, 5375.
[4] T. Weskamp, F. J. Kohl, W. Hieringer, D. Gleich, W. A.
Herrmann, Angew. Chem. Int. Ed. 1999, 38, 2416.
[5] M. S. Sanford, J. A. Love, R. H. Grubbs, J. Am. Chem.
Soc. 2001, 123, 6543.
6
5
6
5
of C H N), 7.05–7.15 (m, 1H, para H of C H N), 6.78 (dd,
5
4
5
4
1
H, meta H of C H N), 6.60 (d, 1H, meta H of C H N), 6.66
5
4
5
4
and 6.88 (bs, 4H, meta H mesityl), 3.85 (m, 4H, CH of
2
NHC), 2.15, 2.40 and 2.55 (s, CH mesityl), 1.25–1.65 (m,
3
1
0H, CH2 of C H ); anal. calcd. for C H ClNOPRu
6 10 39 47
À1
(
683.76 gmol ): C 65.94, H 6.67, N 5.92; found: C 66.45, H
.58, N 5.29.
[
[
6] J. A. Davies, F. R. Hartley, Chem. Rev. 1981, 81, 79.
7] E. Lindner, M. Haustein, H. A. Mayer, K. Gierling, R.
Fawzi, M. Steimann, Organometallics 1995, 14, 2246–
2252.
6
General Experimental Procedure for Self-Metathesis
Experiments
[8] T. B. Higgins, C. A. Mirkin, Inorg. Chim. Acta 1995,
40, 347–353.
2
The metathesis reactions were carried out in a 100-mL
three-necked round-bottom flask fitted with a reflux con-
denser, thermometer and septum. 1-Octene (20 mL,
[
9] M. Esterhuysen, R. Brꢃll, H. Raubenheimer, C. Ester-
huysen, G. Kruger, J. Organomet. Chem. 2001, 619, 164.
10] W. H. Meyer, R. Brull, H. G. Raubenheimer, C.
[
0.127 mmol) and nonane (1 mL) were transferred to the
Thompson, G. J. Kruger, J. Organomet. Chem. 1998,
flask after flushing it for 5 min with a steady stream of Ar.
Nonane served as internal standard for quantification. The
solution was heated to 608C, and the catalyst (0.015 mmol)
was added to the flask, and the reaction mixture stirred for
5
53, 83.
[
[
[
[
11] K. Denk, J. Fridgen, W. A. Herrmann, Adv. Synth.
Catal. 2002, 344, 666–670.
12] S. Chang, L. Jones II, C. Wang, L. M. Henling, R. H.
Grubbs, Organometallics 1998, 17, 3460.
7
h. Samples (0.3 mL) were withdrawn by syringe at regular
time intervals, quenched with a solution of toluene (0.3 mL)
and tert-butyl hydrogen peroxide (2 drops) and then ana-
lysed by GC/FID. The sample collected after 3 h was also
analysed by GC/MSD to characterise the mixture. Conver-
sions are reported as the molar% 1-octene that was convert-
ed to the desired 7-tetradecene product.
13] B. de Clercq, F. Verpoort, J. Mol. Catal. A: Chem. 2002,
1
80, 67.
14] B. de Clercq, F. Verpoort, Adv. Synth. Catal. 2002, 344,
39.
6
[15] P. A. van der Schaaf, A. Muhlbach, A. Hafner, R.
Kolly, World Patent WO 99/29701, 1999.
[
16] P. Wijkens, J. T. B. H. Jastrzebski, P. A. van der Schaaf,
R. Kolly, A. Hafner, G. van Koten, Org. Lett. 2000, 2,
1
621.
Acknowledgements
[
17] B. de Clercq, F. Verpoort, Tetrahedron Lett. 2002, 43,
We would like to express our gratitude to Andre Joubert for
acquiring the NMR data and Dr. Wolfgang H. Meyer (Sasol
Technology R&D) for stimulating discussions. Sasol Technol-
ogy R&D and the THRIP programme (grant # 2789) of the
National Research Foundation of South Africa are acknowl-
edged for their financial contribution towards the studies of
M. J.
9101.
[18] P. A. van der Schaaf, R. A. T. M. Abbenhuis, W. P. A.
van der Noort, R. de Graaf, D. M. Grove, W. J. J.
Smeets, A. L. Spek, G. van Koten, Organometallics
1994, 13, 1433.
[19] W. A. Herrmann, G. M. Lobmaier, T. Priermeier, M. R.
Mattner, B. Scharbert, J. Mol. Catal. A: Chem. 1997,
1
17, 455–469.
[
20] M. Jordaan, P. van Helden, C. G. C. E. van Sittert,
References
H. C. M. Vosloo, J. Mol. Catal. A: Chem. 2006, 254,
1
45.
[1] C. van Schalkwyk, H. C. M. Vosloo, J. A. K. du Plessis,
Adv. Synth. Catal. 2002, 344, 781–788.
192
www.asc.wiley-vch.de
ꢂ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2007, 349, 184 – 192