Catalytic epoxidation of stilbenes with non-peripherally alkyl substituted carbonyl ruthenium phthalocyanine complexes

Article abstract of DOI:10.1142/S1088424612500459

A number of novel carbonyl(1,4,8,11,15,18,22,25-octaalkylphthalocyaninato)- ruthenium(II) complexes were prepared by metal insertion with Ru ₃(CO)₁₂. The new compounds have been characterized by ¹H NMR, ¹³C NMR, IR, UV-vis and mass spectroscopy. This study demonstrated that this type of complexes and specifically carbonyl(1,4,8,11,15,18,22,25-octahexylphthalo-cyaninato)ruthenium(II) and carbonyl[1,4,8,11,15,18,22,25-octa(2-cyclohexylethyl)phthalocyaninato] -ruthenium(II), exhibit high catalytic activity and stability in the epoxidation of stilbenes with 2,6-dichloropyridine N-oxide as oxidant.

Full text of DOI:10.1142/S1088424612500459

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 1–10
DOI: 10.1142/S1088424612500459
Published at http://www.worldscinet.com/jpp/
Catalytic epoxidation of stilbenes with non-peripherally alkyl
substituted carbonyl ruthenium phthalocyanine complexes
Charles A. Enow, Charlene Marais and Barend C.B. Bezuidenhoudt*◊
Department of Chemistry, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa
Received 8 September 2011
Accepted 29 February 2012
ABSTRACT:
A
number of novel carbonyl(1,4,8,11,15,18,22,25-octaalkylphthalocyaninato)-
ruthenium(II) complexes were prepared by metal insertion with Ru3(CO)12. The new compounds have
been characterized by 1H NMR, 13C NMR, IR, UV-vis and mass spectroscopy. This study demonstrated
that this type of complexes and specifically carbonyl(1,4,8,11,15,18,22,25-octahexylphthalo-
cyaninato)ruthenium(II) and carbonyl[1,4,8,11,15,18,22,25-octa(2-cyclohexylethyl)phthalocyaninato]-
ruthenium(II), exhibit high catalytic activity and stability in the epoxidation of stilbenes with
2,6-dichloropyridine N-oxide as oxidant.
KEYWORDS: non-peripherally alkyl substituted phthalocyanine, carbonyl, ruthenium, epoxidation,
stilbene, 2,6-dichloropyridine N-oxide.
structure with the consequence of reduced aggregation
INTRODUCTION
and enhanced solubility in organic solvents [11–13]. The
improved solubility and associated reduced deactivation
through aggregation served as impetus towards an
investigation into the application of ruthenium carbonyl
phthalocyanine complexes as catalysts in the epoxidation
of alkenes.
In recent years, numerous ruthenium-based catalytic
systems for epoxidation have been developed, a notable
example being the ‘Hirobe system’ which employs
mainly the carbonyl ruthenium porphyrins or the
dioxo ruthenium porphyrins with pyridine N-oxides as
oxidants [14–18]. Because of their structural similarity
to porphyrins, and the fact that Pcs are more resistant
to oxidative degradation, ruthenium phthalocyanines
are attractive as catalysts in epoxidation reactions. To
the best of our knowledge, the application of ruthenium
phthalocyanines in catalytic epoxidation has not been
reported before, though its applicability as catalyst for
the oxidation of alkenes and alkanes have received some
attention [4, 19, 20].
There are many domains in which phthalocyanine
(Pc) chemistry have found wide application including;
chemical sensing [1], the dye industry [2], catalysis [3,
4], nonlinear optics [5], medicine (mainly photodynamic
therapy)[4,6,7],dyesensitizedsolarcells[4,8]andoptical
limiting materials [9]. To a large extent, the applicability
of phthalocyanine molecules has corresponded with the
type of central metal ion and/or the substituents on the
Pc. Thus, to expand the applicability of phthalocyanines,
a variety of metals ions (> 70 elements) and substituents
have been introduced into the Pc structure.
While some Fe, Mn, and Co containing
phthalocyanines have been studied as epoxidation
catalysts [10], the poor solubility of these complexes in
common organic solvents due to aggregation, (which is
pronounced at high concentration) has limited success in
this area of research. Attachment of alkyl substituents to
the non-peripheral positions of Pc complexes, however,
resulted in those molecules adapting a “saddle shaped”
In view of utilizing the carbonyl ruthenium
phthalocyanines in epoxidation reactions, we undertook
the preparation of some alkyl substituted ruthenium
phthalocyanines thereby extending the work of
Cammidge et al. [21, 22].
SPP full member in good standing
*Correspondence to: Barend C.B. Bezuidenhoudt, email:
bezuidbc@ufs.ac.za, tel: +27 51-401-9021, fax: +27 51-444-
6384
Copyright © 2012 World Scientific Publishing Company

2
C.A. ENOW ET AL.
the catalyst in the ruthenium based porphyrin/N-oxide
system varied with the bulkiness of the substituents on
the ligand especially when applied to stilbene substrates
[23–25], we also synthesized the more bulky isopentyl
(1d) and cyclohexylethyl (1e) carbonyl ruthenium Pcs.
Our findings on the application of non-peripherally
substituted carbonyl ruthenium phthalocyanines and
R
R
R
R
R
N
N
N
N
Ru
N
OC
N
specifically
carbonyl(1,4,8,11,15,18,22,25-octahexyl-
N
N
R
phthalocyaninato)ruthenium(II) (1a) and carbonyl-
[1,4,8,11,15,18,22,25-octa(2-cyclohexylethyl)phthalo-
cyaninato]ruthenium(II) (1e) on the catalytic epoxidation
of stilbenes with 2,6-dichloropyridine N-oxide as oxygen
donor, are thus disclosed.
R
R
1a R = n-C6H13
1b R = n-C8H17
1d R =
1c R = n-C12H25
RESULTS AND DISCUSSION
1e R =
1f R = n-C10H21
Phthalocyanines with alkyl substituents on the non-
peripheralpositions(1,4,8,11,15,18,22,25-octa-substituted)
are usually prepared by cyclotetramerization of the
appropriate 3,6-disubstituted phthalonitriles. The challenge
in the synthesis of this type of compound lies at the level
of obtaining the 3,6-disubstituted phthalonitrile precursor.
Starting with thiophene 7, the 3,6-phthalonitriles 3a–3e and
the corresponding metal free phthalocyanine complexes
2a–2e were synthesized as described in Scheme 2 [13].
1g R = H
Scheme 1. Carbonyl ruthenium phthalocyanines 1a–1g
Herein, we report on the synthesis and characterization
of a series of non-peripherally alkyl-substituted carbonyl
ruthenium phthalocyanines 1a–1e of which all but 1b
are novel (Scheme 1). Since selectivity and activity of
Li
R
R
O
CN
DMDO
NC
n-BuLi
RBr
S
S
S
S
,
24 h
24 h
160 ˚C, 16 h
O
Li
R
R
7
6
5
4
R
R
R
R
R
R
R
R
R
R
R
R
N
N
N
N
N
N
N
CN
CN
CO
Ru3(CO)12
Li
N
HN
Ru
NH
N
benzonitrile,
reflux
pentanol,
reflux
N
N
N
N
N
R
R
R
R
R
R
3
2
1
a
c
e
R = n-C6H13
R = n-C12H25
R =
b
d
R = n-C8H17
R =
Scheme 2. Synthetic pathway for carbonyl ruthenium phthalocyanines 1a–1e
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 2–10

CATALYTIC EPOXIDATION OF STILBENES WITH NON-PERIPHERALLY ALKYL
3
Fig. 1. UV-vis spectra of 1a–1e in petroleum ether
Utilization of the methodology developed by Cammidge
from the absence of any N–H stretching vibrations at
et al. [21, 22], previously employed in the synthesis of 1b
and RuPc-C10 (1f), i.e. refluxing the metal free Pc together
with Ru3(CO)12 in benzonitrile, led to the formation
of the desired ruthenium carbonyl phthalocyanines
1a–1e (Scheme 1). Precipitating the products out of the
benzonitrile solution by adding methanol proved to be a
rather tedious process, even when large amounts of the
methanol was added. So the pure products were obtained
in 65–86% yields by flash column chromatography
followed by recrystallization from a methanol-petroleum
ether mixture (1:1). UV-vis spectroscopy, MALDI-TOF
mass spectrometry, 1H NMR, 13C NMR, IR spectroscopy
and HRMS were used to characterize each of the four
new carbonyl phthalocyanine ruthenium complexes
1a–1e.
Since the Q-band in the UV-visible spectra of
metal substituted phthalocyanines represent one of the
characteristic properties of these compounds [11–13], the
prepared RuPcs 1a–1e were analyzed with this technique
first. The UV-vis spectra of compounds 1a–1e in THF
(Fig. 1) exhibited a single Q-band [1a = 660 nm (4.84),
1b = 670 nm (5.21), 1c = 685 nm (4.85), 1d = 675 nm
(4.70), 1e = 680 nm (4.40)] of high intensity together with
a blue shift (from ca. ~725 nm to 660–685 nm) indicative
of a metal complex having been formed [21, 22].
The presence of the shoulder at the slightly lower
energy side of the Q-band is probably explicable in terms
of some level of aggregation in the solution while the
spectra were being recorded. The fact that the intensity
of the shoulder increased at higher concentrations gave
additional credence to this suggestion.
ThepresenceofanaxialCOligandinalloftheprepared
RuPc complexes (1a–1e) was confirmed by a strong
absorption band at 1952–1965 cm-1 in the IR spectra of
these compounds. Further evidence as to the presence
of a metal inside the cavity of the phthalocyanine came
ca. 3300 in the IR spectra of all of the metal complexes.
1
The H NMR spectra of complexes 1a–1e displayed
all the expected proton signals and were almost
identical to those of the metal-free Pcs 2a–2e, the only
differences being the disappearance of the inner NH
resonances (at d = -0.29–0.32 ppm in the spectra of the
metal-free compounds) and a splitting of the benzylic
signals into two multiplets for 1a; 1b, 1d, and 1e [d =
4.65–4.62 and 4.59–4.55 for 1a; 4.65–4.60 and 4.57–
4.52 for 1b; 4.67–4.61 and 4.60–4.55 for 1d; 4.65–4.61
and 4.60–4.56 for 1e), indicating non-equivalence of
these protons and thus two possible orientations for the
alkyl substituents.
In the case of 1c, the resonance from the benzylic
protons appears as a very broad singlet (d = 5.05–4.70)
probably due to more than two orientations of the alkyl
groups originating from severe restricted rotation. The
pressence of the CO ligand in the complexes was further
confirmed by a CO resonance at d = 183.34, 180.25,
181.32, 174.77 and 183.32 for 1a, 1b, 1c, 1d, and 1e,
respectively in the 13C NMR spectra.
Contrary to the 13C NMR spectra of the metal free Pcs
(2a–2e) where all the aromatic carbons were equivalent,
these carbons in the ruthenium complexes 1a–1e were
visible as four separate signals at ca. d = 129–145 ppm.
The presence of ruthenium in the structures of complexes
1a–1e were also confirmed by the isotope pattern found in
the MALDI-TOF mass spectra (Fig. 2) where the spectra
of 1a, 1b, and 1c showed a signal cluster for both the [M]
and [M–CO] isotopes, whereas those of 1d and 1e were
represented by a cluster of isotope peaks at an m/z value
corresponding to [M–CO]. Further proof of the structures
of 1a, 1b, 1c, and 1d came from the high resolution mass
spectra (HRMS) of these compounds where [M+] (except
in the case of 1c) and [M+ + CH3OH] (except in the case
of 1d) ions were found at m/z = 1314.8062 and 1346.7935
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 3–10

4
C.A. ENOW ET AL.
Fig. 2. MALDI-TOF mass spectrum of 1d
for 1a, 1539.0474 and 1572.0377 for 1b, 2020.5658 for
1c and 1202.6756 for 1d.
at 30 °C in dichloromethane with 0.1 mol% of catalyst
1d (catalyst/substrate/oxidant molar ratio 1:1000:1500).
Under these conditions, poor conversion and epoxide
yield (<6%) were obtained for trans-stilbene 8, even
after extended reaction times (2 days). When the reaction
temperature was increased to 45 °C, 26% conversion and
a 13% yield of 9 could be obtained after 48 h (Table 2,
entry 1). Changing the solvent to toluene, the replacement
for carcinogenic benzene, led to 22% conversion and a
12% yield of 9 (Table 2, entry 2).
As almost similar yields were obtained in
dichloromethane and toluene and considering that
Berkessel and co-workers [17] found conversion rates,
yields and turnover frequencies (TOF) to be promoted by
higher reaction temperatures in a ruthenium porphyrin/
N-oxide system, the higher boiling solvent, toluene,
was selected for further investigations. An increase
With the series of carbonyl ruthenium phthalocyanines
(1a–1e) in hand, the catalytic activity thereof towards the
epoxidation of alkenes could be investigated (Scheme 3).
Although some metal-containing phthalocyanines have
been employed in the catalytic epoxidation of alkenes,
yields and selectivities towards the epoxide were
generally poor [26–29]. Attention was thus shifted to
Ru-based systems and since pyridine N-oxides, and
especially 2,6-dichloropyridine N-oxide (2,6-DCPNO),
are commonly employed as oxidants in ruthenium
porphyrin catalyzed epoxidations, 2,6-DCPNO was
also selected as oxidant in the current investigations.
As Hirobe et al. [14–16] performed Ru porphyrin
epoxidations in either dichloromethane or benzene at
room temperature or 30 °C, our investigation was started
2,6-DCPNO
RuPc-catalyst
O
9
8
O
2,6-DCPNO
RuPc-catalyst
CHO
+
+
O
11
10
9
12
Scheme 3. RuPc catalyzed epoxidation of stilbenes 8 and 10 by 2,6-DCPNO
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 4–10

CATALYTIC EPOXIDATION OF STILBENES WITH NON-PERIPHERALLY ALKYL
5
Table 1. Catalytic epoxidation of trans-stilbene (8) by 2,6-DCPNO with Ru(II)–Pc complexes (0.1 mol%)a
Entry
Catalyst
T, °C
t, h
Conversion, %c
Product (% yield)
Selectivity, %
TOF, h-1
1b
2
3
4
5
6
1d
1d
1d
1d
1a
1a
45
45
48
48
48
8
26
22
13
12
56
61
21
82
50
55
77
74
91
82
90
73
104
174
30
115
60
83
48
48
23
90
>99
120
a Reaction conditions: unless specified otherwise, toluene was used as solvent (2 mL); catalyst/substrate/oxidant
molar ratio 1:1000:1500; b CH2Cl2; c Conversions were determined by GC using dodecane as internal standard.
Table 2. Epoxidation of stilbenes 8 and 10 with 2,6-DCPNO catalyzed by ruthenium phthalocyanines
1a–1e and 1g
Entry
Substrate
Catalyst
Cat., mol%
Conversion, %b
Yield, %
Selectivity, %
1
2
8
8
1a
1a
1a
1b
1c
1d
1e
1g
1a
1e
0.1
68
>95
100
100
100
100
95
57
92
84
97
95
99
100
75
88
67
84
79
0.23
0.45
0.45
0.45
0.45
0.45
0.45
0.45
3
8
95
4
8
99
5
8
100
75
6
8
7
8
84
8
8
27
18
9
10
10
100
76
84c
60c
10
0.45
b
aReaction conditions: Toluene, 90 °C, 24 h; Conversions were determined by GC using dodecane as
internal standard; cSmall amounts of trans-stilbene oxide (9) formed together with the cis-isomer (11).
in temperature from 45 to 90 °C facilitated a drastic
increase in substrate conversion (73% vs. 2%) and
epoxide 9 yield (56% vs. 12%, Table 1, entries 2 and 3).
A further increase in temperature to 115 °C drastically
reduced the required reaction time to only 8 h and
increased both conversion (83% vs. 73%) and yield
(61% vs. 56%) with a slightly lower selectivity (74% vs.
77%) towards the epoxide (Table 1, entries 3 and 4). The
sterically more demanding catalyst 1d was less reactive
than 1a, resulting in only 73% conversion of 8 and 56%
yield of 9 at 90 °C compared to the > 99% conversion and
82% yield obtained with 1a (Table 1, entries 3 and 6). As
expected, an increase in temperature from 60 to 90 °C
in the presence of RuPc 1a also promoted conversion
(>99% vs. 23%) and yields (82% vs. 21%) (Table 1,
entries 5 and 6), though, as was encountered with 1d,
selectivity towards the epoxide decreased (82% vs. 91%)
with increase in temperature. In addition, though the
epoxide formed faster at higher temperatures as is also
evident from the turnover frequencies (TOF) (Table 1,
entries 3 and 4; entries 5 and 6), catalyst decomposition
was also enhanced at increased temperatures as was
evident from the rapid color change of the reaction
mixture from blue to brown.
The effect of catalyst concentration on the epoxidation
rate was subsequently investigated at concentrations of
1a ranging from 0.1 to 0.45 mol% over a 24 h period
at 90 °C (Table 2). Though the epoxidation rate is
clearly higher at higher catalyst concentrations (68, 95,
and 100% respectively for 0.1, 0.23, 0.45 mol%), the
overall epoxide yields obtained with 0.23 and 0.45 mol%
catalyst (Table 2, entries 2 and 3) are so close that it
can be concluded that once a certain threshold catalyst
concentration is attained, the epoxidation rate remains
unaffected by further increases in catalyst concentration.
With the reaction conditions optimized (0.45 mol%
catalyst at 90 °C), the activities of the different RuPc
complexes (1a–1f) towards the epoxidation of trans-
stilbene (8) with 2,6-DCPNO were thus investigated
in a comparative study. With the exception of the
1g-catalyzed epoxidation (Table 2, entry 8), excellent
conversions (> 95%), high yields (> 75%) and excellent
selectivities (>75%) were obtained (Table 2). These
results furthermore undoubtedly prove that the attachment
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 5–10

6
C.A. ENOW ET AL.
of substituents to the non-peripheral positions increases
the catalytic activity of the ruthenium phthalocyanines,
most probably due to reduced levels of aggregation in
solution due to the acquired “saddle shape” [11–13].
It was further evident that activities and selectivities
obtained with the linear alkyl catalysts 1a, 1b, and 1c
were the same within experimental error (Table 2, entries
3–5) and that these catalysts were more active than the
bulkier isopentyl-(1d) and cyclohexyl-substituted (1e)
complexes (Table 2, entries 6 and 7). Optimum yields
were obtained within 10 to 12 h with 1a and 1e, where
after epoxide decomposition resulted in a drop in yield.
Both catalysts 1a and 1b were more active towards the
catalyticepoxidationoftrans-stilbene(8)thancis-stilbene
(10) (Table 2, entries 3 and 9 for 1a and entries 7 and
10 for 1e). These results greatly contrast those obtained
in the homogeneous and heterogeneous epoxidation of
trans-stilbene (8) by the ruthenium porphyrin/N-oxide
system as reported by Hirobe [31], Gross [33], Berkessel
[17], and Zhang [30]. These workers reported poor or no
epoxidation of this substrate even with highly electron
deficient ruthenium porphyrin complexes.
trans-stilbene (8) with homogeneous chiral ruthenium
porphyrins were reported to be ca. 21% and 270 (after
16 h) [33, 30], respectively, while heterogeneous
polymer-supported ruthenium porphyrin catalysts gave
88% conversion and TON of 870 after 24 h [35].
In order to determine if some of the catalyst might
have been deactivated by aggregation and to see if
differences in catalyst activity could be accentuated, the
catalyst concentration was reduced even further to 0.02
mol% (catalyst:alkene:2,6-DCPNO = 1:5000:5000) and
the reactions repeated. Although yields and conversions
dropped quite dramatically when compared to the
reactions performed with 0.1 mole% catalyst (Table 3,
entry 3 vs. 2 for 1a and entry 6 vs. 5 for 1b), the increase
in turnover numbers indicated that the catalysts were still
active up to the end of the reactions as in the previous
runs at the higher concentrations.
EXPERIMENTAL
Techniques
The activity and stability of catalysts 1a and 1e during
the epoxidation of both trans- (8) and cis-stilbene (10) was
further evaluated through the determination of turnover
number (TON) and frequency (TOF) (Table 3, entries 1
and 4). In this case, the catalyst (0.1 mol%) was reacted
with 1000 equiv. of substrate and 1500 equiv. oxidant at
90 °C for 48 h. Since catalyst concentrations were lower,
reaction rates also dropped with the consequence of
increased decomposition of epoxide 11 and thus lower
epoxide yields and selectivities. A relatively high TON
of 520 after 48 h at a TOF of 41 h-1 were obtained for the
epoxidation of cis-stilbene (10) catalyzed by ruthenium
phthallocyanine 1a (Table 3, entry 1), whereas the bulkier
1e was less active with a TON of 340 after 48 h at a TOF
of 25 h-1 (Table 3, entry 4).
All reagents and solvents were of reagent-grade quality
purchasedfromSigma-Aldrichandwereusedassupplied.
Infrared spectra (thin films between NaCl plates of either
pure liquids or Nujol mulls of solids) were recorded
on a Hitachi model 270–50 spectrophotometer. UV-vis
spectra were recorded on a Varian Cary 50 UV/vis dual
beam spectrophotometer at 25 °C. 1H NMR and 13C NMR
spectra were recorded on a Bruker AM 300 or a Bruker
600 FT-spectrometer at 296 K with tetramethylsilane
(TMS) as internal standard. Mass spectrometry was
performed by means of electron impact (EI) ionization
through direct injection onto the mass spectrometer of
a Shimadzu GC-MS Qp-2010 gas chromatograph-mass
spectrometer. MALDI-TOF spectra were collected by a
Bruker Microflex LRF20 in the positive mode with the
minimum laser power required to observe signals. High
resolution MS (ES-MS, +ve) was performed by either
PMBMS, University of KwaZulu-Natal, or Cambridge
University Chemical Laboratory. Melting points were
recorded on a Barloworld Scientific Stuart Melting
Both catalysts 1a and 1e once again proved to be more
reactive towards trans-stilbene (8) than cis-stilbene (10)
(Table 3, entry 2 vs. 1 and entry 5 vs. 4), with turnovers
of up to 820 being obtained with complex 1a after 48 h.
For a homogeneous catalytic system, these results are
quite pleasing as the best conversion and turnover for
Table 3. Catalytic epoxidation of stilbenes 8 and 10 by 2,6-DCPNO with RuPc complexes 1a and 1e
Entry
Alkene
Catalyst
Cat., mol%
Conversion, %
Product (% yield, % selectivity)
TONa (TOFb (h-1))
1
2
3
4
5
6
10
8
1a
1a
1a
1e
1e
1e
0.1
64
100
22
11 (40, 63)
9 (82, 82)
9 (22, 100)
11 (26, 57)
9 (59, 87)
9 (20, 100)
520 (41)
820
0.1
8
0.02
0.1
1085 (151)
340 (25)
590
10
8
46
0.1
68
8
0.02
20
1002 (93)
aDetermined after 48 h; bDetermined after 1 h.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 6–10

CATALYTIC EPOXIDATION OF STILBENES WITH NON-PERIPHERALLY ALKYL
7
Point (SMP3) apparatus. GC analyses were performed
solution of 2,5-dialkylthiophene (5) (0.015 mol) in
dichloromethane (270 cm3) in a 3 litre 2-necked flask
equipped with an efficient stirrer and a large CO2-
acetone condenser. The resulting heterogeneous mixture
was cooled in an ice bath before solid oxone (300 g,
1.97 mol, 131.4 equiv.) was carefully added over 30
minutes with efficient stirring. Stirring continued for a
further 16 h at room temperature before water (1,500
cm3) was added to dissolve most inorganics. The
decanted aqueous layer, and all remaining solids were
extracted into dichloromethane (750 cm3), the combined
organic phases washed with water (1,500 cm3) and dried
over magnesium sulfate before solvent removal and
re-crystallization of the residue from ethanol gave the
2,5-dialkylthiophene-1,1-dioxides.
on a Shimadzu GC-2010 fitted with a PONA column
(50.0 m × 0.20 mm × 0.50) and FID detector. The N2/
Air (carrier gas) linear velocity was 1.07 mL/min and the
injector and detector temperatures 200 °C and 290 °C,
respectively. Injections were made in the split mode.
The initial column temperature of 60 °C was kept for
5 min, whereafter it was increased to 250 °C at 5 °C/min
and kept at this temperature for the rest of the analysis.
Retention times were compared to those of commercially
available samples. Products were identified by GC-MS
analyses on a Shimadzu GC-MS Qp-2010 fitted with a
similar column and operated under conditions similar to
that of the GC with helium as carrier gas.
2,5-di(2-cyclohexylethyl)thiophene 1,1-dioxide (4e).
Using general procedure B: 2,5-di(2-cyclohexylethyl)-
thiophene (5e) (4.57 g, 0.015 mol), DCM (270 cm3),
H2O (330 cm3), acetone (240 cm3), NaHCO3 (180 g,
2.14 mol), oxone (300 g, 1.97 mol, 131.4 equiv.) gave
2,5-di(2-cyclohexylethyl)thiophene 1,1-dioxide (4e) (3.5
Ligand synthesis
By varying the alkyl groups (-R) on the thiophene,
phthalonitriles with carbon side chains of different
lengths were synthesized. From these the corresponding
metal free and ruthenium complexed phthalocyanines
were prepared.
1
g, 69.5%) as off white needles: mp 111 °C. H NMR
General procedure
A
[13]. Preparation of
(600 MHz, C6D6): dH, ppm 5.58 (2H, s), 2.44 (4H, t,
J = 7.95), 1.72–1.62 (10H, m), 1.24–1.11 (8H, m), 0.85–
0.79 (4H, m). 13C NMR (150.9 MHz, CDCl3): dC, ppm
144.32, 121.47, 37.20, 33.95, 33.00, 26.51, 26.19, 21.69.
IR (neat): lmax, cm-1 2957, 2918, 2850, 1469, 1445, 1385,
1367, 1277 (–SO2), 1139 (–SO2), 1118, 1097, 841, 627,
610, 558. MS (EI): m/z 336.30 ([M]+, 33.42%), 185.15
(100%). HRMS (ES-MS, +ve): m/z C20H32O2SNa+ [M +
Na+] requires 359.2021, found 359.2196.
General procedure C [13]. Preparation of 3,6-dialkyl-
phthalonitriles (3a–3e). In a typical experiment, 2,5-
dialkylthiophene-1,1-dioxide (4) (0.015 mol) and fuma-
ronitrile (1.14 g, 0.015 mol, 1 equiv.) in chloroform
(1 cm3) were heated in a sealed tube at 150 °C for 18 h.
The contents of the tube were dissolved in chloroform
and the solvent removed under reduced pressure at 90 °C
until the residue stopped liberating bubbles. The dark
residue was then purified by column chromatography
over silica gel with toluene as eluent to give the
3,6-dialkylphthalonitrile.
3,6-di(2-cyclohexylethyl)phthalonitrile (3e). Using
general procedure C: 2,5-di(2-cyclohexylethyl)thio-
phene-1,1-dioxide (4e) (5.0 g, 0.015 mol), fumaronitrile
(1.14 g, 0.015 mol, 1 equiv.), in chloroform (1 cm3) gave
3,6-di(2-cyclohexylethyl)phthalonitrile (3e) (2 g, 40%)
as off white needles: mp 147.5 °C. 1H NMR (300 MHz,
C6D6): dH, ppm 6.75 (2H, s), 2.60 (4H, t, J = 8.27), 1.75
(10H, m), 1.41–1.34 (2H, m), 1.26–1.15 (8H, m), 0.99–
0.88 (4H, m). 13C NMR (150.9 MHz, CDCl3): dC, ppm
146.56, 133.37, 115.59, 115.09, 38.51, 37.40, 33.06,
31.92, 26.49, 26.18. IR (neat): lmax, cm-1 2919, 2855,
2845, 2226 (C≡N), 2147, 1556, 1486, 1236, 1187, 882,
841, 660, 595, 557. MS (EI): m/z 348.30 ([M]+, 100%).
HRMS (ES-MS, +ve): m/z C24H32N2Na+ [M + Na]+
requires 371.2463, found 371.2455.
2,5-dialkylthiophenes compounds (5a–5e). In a typical
experiment, thiophene (7) (9 g, 0.107 mol) in dry THF
(50 cm3) was treated with n-butyllithium in hexane
(2.5 M, 107 cm3, 0.267 mol, 2.5 equiv.) at -78 °C under
an argon atmosphere. The solution was allowed to
warm to room temperature and stirred for 24 h, before
it was cooled again to -78 °C and the alkylhalide (2.5
equiv.) added drop wise over 30 min. The mixture was
then poured into iced water (500 cm3) and extracted into
diethyl ether (3 × 150 cm3). The combined organic layers
were washed with brine (100 cm3), dried over magnesium
sulfate, filtered, and concentrated under reduced pressure
to give the 2,5-dialkylthiophene as a pale yellow oil,
which was used without further purification.
2,5-di(2-cyclohexylethyl)thiophene (5e). Using
general procedure A, thiophene (7) (9 g, 0.107 mol) in
dry THF (50 cm3) was treated with n-butyllithium (2.5 M
in hexane, 107 cm3, 0.267 mol, 2.5 equiv.) followed by
2-cyclohexylethylbromide (51 g, 0.267 mol, 2.5 equiv.)
to give 2,5-di(2-cyclohexylethyl)thiophene (5e) (22.5 g,
69%) as a pale yellow oil. 1H NMR (600 MHz, C6D6): dH,
ppm 6.69 (2H, s), 2.81 (4H, t, J = 7.94), 1.74–1.69 (10H,
m), 1.67–1.63 (4H, m), 1.27–1.19 (8H, m) 0.95–0.88
(4H, m). 13C NMR (150.9 MHz, CDCl3): dC, ppm 143.44,
123.30, 39.68, 37.38, 33.46–33.44, 27.78, 26.95, 26.93,
26.58. IR (neat): lmax, cm-1 2910, 2850 (CH), 1447, 1346,
1261, 1078, 1025, 962, 889, 843, 797, 689 (CH3). MS
(EI): m/z 304 ([M]+, 65%), 126 (C9H18, 100%). HRMS
(ES-MS, +ve): m/z C20H33S+ [M + H]+ requires 305.2303,
found 305.2307.
General procedure
B
[13]. Preparation of
2,5-dialkylthiophene-1,1-dioxides (4a–4e). In a typical
experiment, a mixture of H2O (330 cm3), acetone (240
cm3) and NaHCO3 (180 g, 2.14 mol) was added to a
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 7–10

8
C.A. ENOW ET AL.
General procedure
D
[13]. Preparation of
(0.3 g, 0.47 mmol, 2 equiv.), benzonitrile (10 cm3), gave
carbonyl(1,4,8,11,15,18,22,25-octahexylphthalocy-
aninato)ruthenium(II) (1a) (0.25 g, 80%) as a dark blue
amorphous solid. 1H NMR (600 MHz, CDCl3): dH, ppm
7.87 (8H, s), 4.65–4.62 (8H, m), 4.59–4.55 (8H, m),
2.30–2.22 (16H, m), 1.75–1.68 (16H, m), 1.46–1.39
(16H, m), 1.38–1.34 (16H, m), 0.89 (24H, t, J = 7.2).
13C NMR (150.9 MHz, CDCl3): dC, ppm 183.34, 145.17,
137.95, 136.57, 129.79, 32.68, 32.31, 30.88, 29.10,
22.76, 14.15. UV-vis (petroleum ether): l, nm (log
e) 660 (4.84). IR (neat): lmax, cm-1 2953, 2925, 2855,
1958 (Ru-C=O), 1600, 1573, 1468, 1433, 1329, 1261,
1167, 1108, 1017, 911, 801, 726.1936. MS (MALDI-
TOF): m/z 1313.688 [M], 1295 [M - CO]. HRMS (ES-
MS, +ve): m/z C81H112N8ORu requires 1314.7997 found
1314.8062.
1,4,8,11,15,18,22,25-octaalkyl-phthalocyanines (2a–2e).
In a typical experiment, 3,6-dialkylphthalonitrile (3)
(0.001 mol) was dissolved in warm (80 °C) pentanol
(10 cm3). An excess of clean lithium metal (0.35 g, 0.05
mol, 30–40 equiv.) was added in small portions at 110 °C
and the mixture refluxed for 16 h. The cooled (rt) deep
green coloured suspension was stirred with acetone
(50 cm3), the solution filtered, and the solids washed
with acetone (50 cm3) before the combined acetone
solutions were concentrated in vacuo to ca. 25 cm3.
Acetic acid (50 cm3) was added, the heterogeneous
mixture stirred for 30 min, and the precipitate collected
to afford, after recrystallization from THF-methanol, the
1,4,8,11,15,18,22,25-octaalkyl-phthalocyanine.
1,4,8,11,15,18,22,25-octa(2-cyclohexylethyl)phth-
alocyanine (2e). Using general procedure D: 3,6-di(2-
cyclohexylethyl)phthalonitrile (3e) (0.35 g, 0.001
mol), warm pentanol (10 cm3), and clean lithium metal
(0.35 g, 0.05 mol) gave 1,4,8,11,15,18,22,25-octa(2-
cyclohexylethyl)phthalocyanine (2e) (0.19 g, 14%) as a
Carbonyl(1,4,8,11,15,18,22,25-octaoctylph-
thalocyaninato)ruthenium(II) (1b) [21]. Using general
procedure E: 1,4,8,11,15,18,22,25-octaoctylphthalo-
cyanine [11] (2b) (0.33 g, 0.23 mmol), triruthenium
dodecacarbonyl (0.3 g, 0.47 mmol, 2 equiv.), benzonitrile
(10 cm3) gave carbonyl(1,4,8,11,15,18,22,25-octaoctyl-
phthalocyaninato)ruthenium(II) [16] (1b) (0.3 g, 86%)
1
green solid. H NMR (600 MHz, CDCl3): dH, ppm 7.88
(8H, s), 4.48 (16H, t, J = 7.7), 1.95–1.90 (32H, m), 1.69–
1.64 (24H, m), 1.27–1.18 (32H, m), 1.04–0.98 (16H, m).
13C NMR (150.9 MHz, CDCl3): dC, ppm 139.14, 130.57,
77.21, 77.00, 76.79, 38.28, 37.26, 33.71, 29.89, 29.69,
26.73, 26.42. UV-vis (petroleum ether): l, nm (log e)
734 (0.91), 695 (0.79), 674 (0.26), 639 (0.10), 364 (0.30).
IR (neat): lmax, cm-1 3300 [N–H], 3302, 2910, 2848,
1596, 1508, 1425, 1313, 1032, 882, 816, 762, 716. MS
(MALDI-TOF): m/z 1396.04 [M].
1
as a dark blue amorphous solid. H NMR (600 MHz,
CDCl3): dH, ppm 7.86 (8H, s), 4.65–4.60 (8H, m), 4.57–
4.52 (8H, m), 2.27–2.22 (16H, m), 1.72–1.67 (16H, m),
1.46–1.39 (16H, m), 1.35–1.29 (16H, m), 1.27–1.23
(32H, m), 0.84 (24H, t, J = 6.9). 13C NMR (150.9 MHz,
CDCl3): dC, ppm 180.25, 145.16, 137.93, 136.57, 129.72,
32.62, 31.91, 30.89, 30.01, 29.40, 29.36, 22.62, 14.02.
UV-vis (petroleum ether): l, nm (log e) 670 (5.21). IR
(neat): lmax, cm-1 2954, 2922, 2852, 1963 (Ru-C=O),
1502, 1466, 1328, 1167, 1112, 913, 721. MS (MALDI-
TOF): m/z 1539.777 [M], 1511.85 [M–CO]. HRMS (ES-
MS, +ve): m/z C97H144N8ORu requires 1539.0501, found
1539.0474.
Synthesis of the carbonylphthalocyanine ruthenium
complexes
General procedure E. Preparation of ruthenium(II)
carbonyl(1,4,8,11,15,18,22,25-octaalkylphthalocyanines
(1a–1e) [21]. To a flame dried flask under an argon
atmosphere was added 1,4,8,11,15,18,22,25-octaalkyl-
phthalocyanine (2) (0.23 mmol) and triruthenium
dodecacarbonyl (0.3 g, 0.47 mmol, 2 equiv.). Benzonitrile
(10 cm3) was added and the reaction mixture was heated
at reflux for 100 min. The cooled reaction mixture
was poured into cold methanol (400 cm3) causing
the formation of some crystals. After cooling to 5 °C
for a further 72 h, the excess solvent was decanted.
The crude product was purified by flash column
chromatography (eluting with methanol to remove
benzonitrile and then with petroleum ether 40–60 °C).
Reprecipitation (petroleum ether-methanol) gave the
1,4,8,11,15,18,22,25-octaalkylphthalocyaninatoru-
theniums.
Carbonyl(1,4,8,11,15,18,22,25-octadodecylph-
thalocyaninato)ruthenium(II) (1c). Using general
procedure E: 1,4,8,11,15,18,22,25-octadodecylphthalo-
cyanine [13] (2c) (0.43 g, 0.23 mmol), triruthenium
dodecacarbonyl (0.3 g, 0.47 mmol, 2 equiv.), and
benzonitrile(10cm3)gavecarbonyl(1,4,8,11,15,18,22,25-
octadodecylphthalocyaninato)-ruthenium(II)(1c)(0.32g,
1
70%) as a dark blue amorphous solid. H NMR (600
MHz, C6D6 with a drop of pyridine): dH, ppm 7.95 (8H,
d, J = 22.9 Hz), 5.05–4.70 (16H, m), 2.49–2.41 (16H, m),
1.89–1.84 (17H, m), 1.57–1.37 (128H, m), 0.95 (24H,
13
t, J = 6.7 Hz). C NMR (150.9 MHz, C6D6 + pyridine):
dC, ppm 181.24, 145.37, 138.13, 137.40, 130.08, 32.84,
32.36, 32.02, 31.14, 30.29, 29.91, 29.84, 29.59, 29.51,
29.15, 22.81, 14.07. UV-vis (petroleum ether): l, nm
(log e) 685 (4.85). IR (neat): lmax, cm-1 2921, 2852, 1967
(Ru-C=O), 1456, 1328, 1172, 1111, 1021, 803, 720.
MS (MALDI-TOF): m/z 1988.324 [M], 1960.862 [M–
CO]; C129H208N8ORu.CH3OH requires 2020.5810, found
2020.5658.
Carbonyl(1,4,8,11,15,18,22,25-octahexylphtha-
locyaninato)ruthenium(II)(1a).Usinggeneralprocedure
E: 1,4,8,11,15,18,22,25-octahexylphthalocyanine [11]
(2a) (0.28 g, 0.23 mmol), triruthenium dodecacarbonyl
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 8–10

CATALYTIC EPOXIDATION OF STILBENES WITH NON-PERIPHERALLY ALKYL
9
Table 4. Reagent ratios
Catalyst (mole%)
Stilbene
Dodecane
2,6-DNPNO
0.45
0.1
110 μmol, 220 equiv.
500 μmol, 1000 equiv.
2500 μmol, 5000 equiv.
25 μl, 110 μmol, 220 equiv.
114 μl, 500 μmol, 1000 equiv.
570 μl, 2500 μmol, 5000 equiv.
27 mg, 165 μmol, 330 equiv.
122 mg, 750 μmol, 1500 equiv.
615 mg, 3750 μmol, 7500 equiv.
0.02
Carbonyl(1,4,8,11,15,18,22,25-octaisopentylphtha-
locyaninato)ruthenium(II) (1d). Using general proce-
dure E: 1,4,8,11,15,18,22,25-octaisopentylphthalocyanine
[11] (2d) (0.25 g, 0.23 mmol), triruthenium dodeca-
carbonyl (0.3 g, 0.47 mmol, 2 equiv.), and benzonitrile
(10 cm3) gave carbonyl(1,4,8,11,15,18,22,25-octaisopen-
tylphthalocyaninato)-ruthenium(II) (1d) (0.18 g, 65%)
CONCLUSION
Sterically hindered RuPc complexes with non-
peripheral hexyl- (1a), octyl- (1b), dodecyl- (1c),
isopentyl- (1d) and 2-cyclohexylethylsubstituents (1e),
have been synthesized and characterized by NMR,
IR, UV-vis, MS and elemental analysis. Compound
1b had been previously reported in literature [10,
16], while compounds 1a, 1c, 1d, and 1e prepared by
extending the procedure for 1b to a range of ligands,
are new compounds. The formation of a huge amount of
by-product alongside the metal-free Pcs (2a–2e) during
cyclisation of the phthalonitriles (3a–3e) in refluxing
pentanol largely account for the poor yields observed in
this step. Improving on the yield of this step would be
critical if these compounds are to be used as catalysts
and this aspect will receive attention in a follow-up
study.
In this study it was also demonstrated for the first
time that ruthenium phthalocyanines can be used in
the epoxidation of alkenes and that non-peripherally
alkyl substituted ruthenium phthalocyanines in
particular are highly active catalysts with true catalytic
activities at very low concentrations (< 0.45 mol%).
Complete conversion and high turnovers (> 800 in 48
h for 0.1% catalyst load), comparable to or better than
those published for other catalytic systems, could be
obtained for trans-stilbene (8). At low catalyst loading
(0.02 mole%), TONs above 1000 in 48 h and TOFs
above 90 h-1 could be obtained for trans-stilbene
(8). The epoxidation of trans-stilbene (8) proceeded
unexpectedly facile, whereas results for cis-stilbene
(10) were comparable to those reported for other
catalytic systems (vide supra).
1
as a dark blue amorphous solid. H NMR (600 MHz,
CDCl3): dH, ppm 7.86–7.81 (8H, d, J = 13), 4.67–4.61
(8H, m), 4.60–4.55 (8H, m), 2.12–2.08 (16H, m), 1.97–
1.93 (8H, m, H-3’), 1.09 (48H, d, J = 6.5). 13C NMR
(150.9 MHz, CDCl3): dC, ppm 174.77, 145.03, 138.05,
136.62, 129.62, 40.29, 30.23, 27.13, 23.12. UV-vis
(petroleum ether): l, nm (log e) 675 (4.70). IR (neat):
l
max, cm-1 2952, 2929, 2866, 1958 (Ru-C=O), 1601,
1502, 1449, 1329, 1180, 1104, 1025, 917, 794, 759. MS
(MALDI-TOF): m/z 1174.681 [M–CO]. HRMS (ES-
MS, +ve): m/z C73H96N8ORu requires 1202.6751, found
1202.6756.
Carbonyl[1,4,8,11,15,18,22,25-octa(2-cyclohexyle-
thylphthalocyaninato]ruthenium(II) (1e). Using
general procedure E: 1,4,8,11,15,18,22,25-octa(2-
cyclohexylethyl)phthalocyanine (2e) (0.33 g, 0.23
mmol), triruthenium dodecacarbonyl (0.3 g, 0.47 mmol,
2 equiv.), and benzonitrile (10 cm3) gave cabonyl-
[1,4,8,11,15,18,22,25-octa(2-cyclohexylethyl)-phthalo-
cyaninato]-ruthenium(II) (1e) (0.25 g, 70%) as a dark
1
blue amorphous solid. H NMR (600 MHz, CDCl3): dH,
ppm 7.84 (8H, s), 4.65–4.61 (8H, m), 4.60–4.56 (8H,
m), 2.10 (16H, dd, J = 14.4, 7.4), 2.02 (16H, s, br), 1.76
(16H, d, J = 12.3), 1.73–1.65 (16H, m), 1.34–1.21 (24H,
m), 1.09 (16 H, dd, J = 24.0, 12.0). 13C NMR (150.9
MHz, CDCl3): dC, ppm 183.32, 145.13, 138.20, 136.56,
129.58, 38.70, 36.85, 33.88, 29.59, 26.82, 26.50. UV-vis
(petroleum ether): l, nm (log e) 680 (4.40). IR (neat):
All substituted ruthenium phthalocyanines (1a–1e)
performed markedly better as epoxidation catalysts
than the unsubstituted equivalent (1g), most probably
because of reduced levels of aggregation in solution due
to the acquired “saddle shape” of substituted ruthenium
phthalocyanines with non-peripheral substituents.
Increasing the steric bulk of substituents attached to the
phthalocyanine lowered the catalytic activity to some
extent.
l
max, cm-1 2920, 2854, 2227, 1972 (Ru-C=O), 1456,
1326, 1077, 1035, 881, 796. MS (MALDI-TOF): m/z
1494.863 [M–CO].
Catalysis
A 15 mL Schlenk flask was charged with catalyst 1a
(0.7 mg, 0.5 μmol, 1 equiv.) or 1e (0.8 mg, 0.5 μmol,
1 equiv.), stilbene, dodecane (internal standard) and dry
toluene (2 mL) under an argon atmosphere (Table 4).
2,6-Dichloropyridine-N-oxide (2,6-DNPNO) was added
and the solution stirred at 90 °C. Reactions were followed
by gas chromatography.
Acknowledgements
Financial support by SASOL is gratefully
acknowledged.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 9–10

10
C.A. ENOW ET AL.
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