((2-Hydroxynapthalen-1-yl)methylene)aniline derived Schiff base adducts of MTO: Synthesis and catalytic application

Article abstract of DOI:10.1016/j.jorganchem.2008.07.015

Equimolar reactions of the derivatives of ((2-hydroxynapthalen-1-yl)methylene)aniline with methyltrioxorhenium (MTO) lead to complexes 1-4, where MTO is coordinated via the oxygen of the former hydroxyl-group to MTO. The resulting complexes are very stabl

Full text of DOI:10.1016/j.jorganchem.2008.07.015

Journal of Organometallic Chemistry 693 (2008) 3240–3244
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
((2-Hydroxynapthalen-1-yl)methylene)aniline derived Schiff base adducts of
MTO: Synthesis and catalytic application
Alejandro Capapé a,1, Ming-Dong Zhou a,b,1,2, Shu-Liang Zang b,c,2, Fritz E. Kühn a, ,1
*
a Molecular Catalysis, Fakultät für Chemie der Technischen Universität München, Lichtenbergstrasse 4, D-85747 Garching bei München, Germany
b Department of Chemistry, Liaoning University, Chongshan Middle Road, No. 66, 110036 Shenyang, PR China
c Department of Petroleum and Chemical Technology, Liaoning Shihua University, Dandong Road, No. 1, 113001 Fushun, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2008
Received in revised form 4 July 2008
Accepted 14 July 2008
Available online 22 July 2008
Equimolar reactions of the derivatives of ((2-hydroxynapthalen-1-yl)methylene)aniline with methyltri-
oxorhenium (MTO) lead to complexes 1–4, where MTO is coordinated via the oxygen of the former
hydroxyl-group to MTO. The resulting complexes are very stable but not particularly catalytically active
if no electron acceptor resides on the Schiff base. The electron withdrawing groups placed on the Schiff
base ligand have the effect of increasing the catalytic activity but somewhat decrease the complex
stability.
Keywords:
Homogeneous catalysis
Ligand effects
Ó 2008 Published by Elsevier B.V.
Methyltrioxorhenium
Olefin epoxidation
Schiff bases
1. Introduction
1960s [3] and since then many research groups concentrated on
mechanistic aspects of these catalytic reactions and on finding im-
Epoxides (Oxiranes), particularly ethylene and propene oxide,
are key raw materials for a wide variety of chemicals such as gly-
cols, glycol ethers, alkanolamines, and polymers. The simplest oxi-
rane, ethylene oxide, is manufactured by vapor-phase oxidation of
ethylene by air or oxygen over a heterogeneously supported silver
catalyst at a multi million ton scale per year [1]. This method, how-
ever, is not applicable to propene, which gives low yields of pro-
pene oxide, owing to competing oxidation of allylic C–H bonds
and leading to a variety of by-products. A method that has been ap-
plied for a long time for the synthesis of propylene oxide is the
chlorhydrine route. This method, however, consumes a consider-
able amount of Cl2 and has a very negative environmental impact.
For the last decades significant research efforts both in industry
and at universities have been dedicated to finding more efficient
and less problematic synthetic pathways to propylene oxide and
other valuable epoxides [2]. ARCO and Halcon described a homoge-
neous catalytic process for the synthesis of epoxides in the late
proved catalysts [4–6]. Among the variety of efficient catalysts
known today for olefin epoxidation are several organometallic oxi-
des containing a metal in high oxidation state [7].
Well defined, highly active, inexpensive and stable catalysts,
operating under environmentally benign conditions at room tem-
perature and atmospheric pressure utilizing oxygen from air for
epoxide generation would be the ideal means for industrial appli-
cations of olefin epoxidation, particularly in the synthesis of inter-
mediates for high value added products such as pharmaceuticals.
Unfortunately, such a stage has not yet been reached. The main
obstacles in the way are currently a lack of mechanistic insight,
high catalyst prices and insufficient catalyst stability and recycla-
bility. However, several well-defined transition metal epoxidation
catalysts already operate at room temperature and atmospheric
pressure with impressively high turnover frequencies and good
stability against ‘‘green solvents” such as water. Most prominent
among them is methyltrioxorhenium (MTO) being available since
quite recently from non-toxic, low price starting materials [8,9]
and several organometallic and inorganic molybdenum and tung-
sten catalysts, employing comparatively cheap metals and being
able to provide chiral ligand environments for chiral epoxidation
[10,11] catalysis. The major drawback of most of these systems is
their inability to utilize oxygen as an oxidizing agent, and, in part,
the difficulty in immobilizing them on proper carrier materials or
matrices and to obtain high epoxide selectivities [12].
* Corresponding author. Address: Molecular Catalysis, Fakultät für Chemie der
Technischen Universität München, Lichtenbergstrasse 4, D-85747 Garching bei
München, Germany.
E-mail addresses: slzang@lnu.edu.cn (S.-L. Zang), fritz.kuehn@ch.tum.de (F.E.
Kühn).
1
Fax: +49 089 289 13473.
Fax: +86 24 6220 2006.
2
0022-328X/$ - see front matter Ó 2008 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2008.07.015

A. Capapé et al. / Journal of Organometallic Chemistry 693 (2008) 3240–3244
3241
Selectivity was a major concern for the otherwise excellent
MTO/H2O2 catalyst system for a couple of years. Due to the high Le-
wis-acidity of MTO and formation of water as a by-product from
the oxidant hydrogen peroxide during the catalytic oxidation pro-
cess, epoxide ring opening under diol formation took place at pro-
longed reaction times, being an unwanted side reaction. Addition
of Lewis bases, such as triethylamine or quinuclidine did not lead
to more satisfying results, since the diol formation was largely pre-
vented at the expense of a great reduction of activity and catalyst
life time [13]. However, it was found out later that aromatic Lewis
base adducts of MTO show high activity in olefin epoxidation reac-
tions, particularly when using the Lewis base in ca. 10-fold excess.
Lower excesses usually reduce the activity or lead to more diol-
byproducts [13]. It was also noted that aliphatic Lewis bases
reduce the activity of MTO, regardless in which amount they are
applied [14].
Recently, stable Schiff base adducts of MTO have been synthe-
sized [15]. They show comparatively good catalytic activities in
cyclooctene epoxidation and above-average stability under cata-
lytic conditions. Moreover, an excess of ligand is not required
for these compounds to be utilized in catalysis. In this work,
((2-hydroxynapthalen-1-yl)methylene)aniline derivatives are ap-
plied as ligands for MTO and their catalytic activity is examined.
reacting MTO with the respective ligands, at room temperature
in diethyl ether. It has to be emphasized that at lower tempera-
tures than 0 °C no reaction takes place, whereas yields up to 80–
90% are obtained in all examined cases when the reaction is
executed at 20 °C. All products were re-crystallized from dichloro-
methane/n-hexane mixtures. Compounds 1–3 are stable and show
no signs of decomposition, either in the solid state or in solution.
They are stable in air and can be synthesized without further pre-
cautions. On the other hand, compound 4 is slightly moisture sen-
sitive and needs to be stored at low temperatures in order to avoid
decomposition.
The IR spectra of the compounds show some common features.
The stretching bands of the iminic bonds, located at ca. 1600–
1650 cmÀ1, are shifted to higher wave numbers when compared
to the free ligands in the case of the adducts due to electron delo-
calization. The geometry and coordination of the compounds can
be inferred qualitatively when looking at the characteristic Re@O
and Re–C stretching bands of the CH3ReO3 moiety (see Table 1).
On account of the expected complex symmetry (C3v), a splitting
of the asymmetric ReO3 stretching band can be expected. This is
seen in the case of compound 3, but for complexes 1, 2 and 4 only
one single broad peak without clear substructure is observed. As
the separation between the peaks is only ca. 10 cmÀ1 in the case
of compound 3, it is likely that the splitting is too small in these
compounds to be resolved properly. Due to the donor capability
of the ligands, which reduces somewhat the Re@O bond order,
average symmetric and asymmetric Re@O stretching vibrations
are red-shifted (20–30 cmÀ1) in comparison to non-coordinated
MTO. The same conclusion can be drawn from the observed blue
shift changes of the iminic stretching vibrations. The difference be-
tween the coordinated and non-coordinated ligands is only ca.
10 cmÀ1 for the compounds 1–4. As pointed out in our previous
work [15] this displacement of the C@N stretching band can be ex-
plained in part by the formation of an intra molecular H bond be-
tween the N atom and the phenolic proton, which – according to
the obtained IR data – seems to be quite weak in the case of ad-
ducts 1–4.
2. Results and discussion
2.1. Synthesis and spectroscopic characterisation
In our previous work on Schiff base adducts of MTO it was noted
that the electronic (and possibly the steric) constitution of the
Schiff bases have a considerable influence on both the stability
and the catalytic activity of the adducts [15]. However, stability
and catalytic activity trends are unfortunately not necessarily
going in the same direction. Another important issue is the acces-
sibility of the applied Schiff bases, since complicated, low yielding,
or expensive synthetic pathways are unwanted for almost any
application. In this work, we utilize well established ((2-Hydroxy-
napthalen-1-yl)methylene)aniline derived Schiff bases as ligands
for MTO [16]. Compounds 1–4 (Scheme 1) were synthesised by
The shift difference of 60–80 cmÀ1 between
a(Re@O) indicates a trigonal-bipyramidal coordination, in con-
ms(Re@O) and
m
trast to the tetrahedral structure of free MTO [5a] (see Tables 1
and 2).
CH3
A selection of the NMR data of complexes 1–4 is shown in Table
3. On the first glance the 1H NMR spectra show only slight changes
from the non-coordinated MTO to Schiff base coordinated MTO. It
should be noted, however, that in the p-CH3 derivative the Re
bound CH3 protons display the strongest electron shift (compared
to that of the protons of the Re–CH3 group in free MTO), whereas in
the case of the Cl-substituted Schiff base this shift is the weakest
observed for the studied compounds. The ((2-hydroxynapthalen-
1-yl)methylene)aniline derived Schiff base ligands are, as deduced
from the obtained NMR data, coordinated to a slightly stronger ex-
tent than the previously reported Schiff bases utilized for MTO ad-
ducts. Within the four compounds examined in this work,
compound 1 can be considered as a standard, non-substituted
+
N
+
N
H
H
O-
O-
O
O
O Re
O Re
O
O
H3C
1
H3C
2
CH3
CH3
+
N
H
+
N
H
Table 1
Characteristic vibrations of the MTO fragments (cmÀ1) in 1–4
Cl
MTO
1
2
3
4
Assignment
O-
O-
1368
1205
998
1355
1215
991
1366
1217
989
1355
1219
1006
940
931
558
959
71
1356
1217
992
CH3, asym.def.
CH3, sym.def.
ReO3 sym. str.
ReO3 asym.str.
O
O
O Re
O Re
O
O
965
930
926
925
H3C
4
H3C
3
567
981
33
566
961
61
567
958
63
553
959
67
ReC str.
ReO str. average
(ms–ma) ReO3
Scheme 1. Formulae of compounds 1–4.

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A. Capapé et al. / Journal of Organometallic Chemistry 693 (2008) 3240–3244
Table 2
Selected IR data (cmÀ1) for compounds 1–4
Compound
Imine group
Phenolic OH group and coupled ring vibrations
m(C@N)
b(OH)
m(CX)
m(CX)
m(CX)
c(OH)
C
1
C
2
C
3
C
4
17H13NO
18H15NO
19H17NO
17H12NClO
1621
1629
1620
1631
1619
1632
1622
1615
1331
1251
1138
821 s
750vs
742 m
747 m
752vs
1327
1339
1324
1251
1257
1257
1083
1108
1092
815 m
829 m
821 m
The respective vibrations of the non-coordinated, pure ligands are given for the sake of comparison.
Notation of vibrational modes: (C@N), C@N stretching; b(OH), hydrogen bonded OH in-plane deformation; m(CX) substituent sensitive aromatic ring stretchings; c(OH)
m
phenolic out-of-plane vibrations.
tions are in good accord with the previously mentioned stabilities
of the compounds, with complex 4 being the least stable. Similar
fragmentation patterns have been observed and noted for MTO
Lewis base adducts under the same conditions [13b,c].
Table 3
Selected 1H and 13C NMR data (ppm) of MTO complexes in CDCl3
Compound
MTO–CH3
d(1H)
d(13C)
MTO
2.67
2.59
2.50
2.58
2.62
19.03
19.46
19.88
19.26
19.09
2.2. Application in epoxidation catalysis
1
2
3
4
Compounds 1–4 were examined as catalysts for the epoxidation
of cyclooctene, 1-octene and styrene with hydrogen peroxide. Fur-
ther details of the catalytic reactions are given in Section 4. In the
case of cyclooctene and 1-octene as substrates, no significant
amounts of epoxide are formed in the absence of catalyst, and no
by-products (such as diols) were detected during the course of
the reaction. The catalyst:substrate:oxidant ratio was 1:100:200
in all cases, using mesitylene as internal standard. The time-depen-
dent curves suggest first order kinetics.
compound; compounds 2 and 3, which have donor substituents,
lead in principle to a somewhat stronger coordination. Compound
4 bears an electron withdrawing ligand. The observed chemical
shifts match that ligand pattern very well. It was expected that
compound 4 would be both the least stable and most catalytically
active compound. Both expectations turned out to be correct (vide
supra for stability, vide infra for catalytic activity). In addition, the
expected behaviour for compound 2 (i.e., to be the most stable
and the least catalytically active amongst the examined com-
plexes) was also fulfilled, as reflected in the NMR data.
As mentioned in a previous paper [15], the trans or cis arrange-
ment of the Re bound CH3 group with respect to the co-ordinating
O-atom of the Schiff base ligand may be attributed to crystal pack-
ing effects in the solid state. Unfortunately, single crystal struc-
tures for complexes 1–4 could not be obtained. Nevertheless, 17O
NMR spectroscopy is a useful tool to examine the electron richness
of the (terminal) oxygen atoms in solution. Axially coordinated oxo
ligands are usually clearly distinguished by their chemical shift
from equatorial oxo ligands, but these differences can often be seen
only at low temperatures, since on the NMR time scale fast position
changes of the oxo ligands take place [14,17]. A number of 17O
NMR experiments were carried out at different temperatures,
using deuterated chloroform as solvent (see Table 4). The results
show only one single signal in all cases for compounds 1–4. Only
a broadening of the 17O signals at 223 K as it is usual at lower tem-
peratures is observed.
Compounds 1–3 show low catalytic activity achieving yields not
higher than 40% during the first 24 h with all examined substrates,
not even with cyclooctene, being the most easy to oxidize. In con-
trast, complex 4 affords a 70% yield within 4 h for cyclooctene
epoxide, more than 50% for styrene epoxide and 1-octene and
reaches 100% within 24 h in all three examined substrate cases
(Fig. 1). These results match well with the spectroscopic data of
the complexes presented above and show that the least electron
donating ligand (complex 4) leads to the weakest complex, but also
to the most active catalyst. Stronger donating ligands lead to more
stable catalysts (1–3), which are, however, less active. This can be
explained by the influence of the ligands on the Lewis acidity of the
Re atom and the adjacent terminal ligands. If the Lewis acidity of
the metal is reduced, the formation of catalytically active mono-
and bisperoxo complexes is hampered. Additionally, a decrease
in the electron deficiency of the peroxo-oxygen atoms makes the
catalyst less prone to a nucleophilic attack by an olefin [13b].
The steric bulk of the Schiff base ligand seems to be of minor
importance in comparison to the donor/acceptor capabilities.
Hence the Re–O (Schiff base) bond is strengthened, if the Schiff
base can donate more electron density and weakened, if it gives
little density. While complexes 1–4 are not as active as
non-coordinated MTO in epoxidation catalysis, they show an in-
creased selectivity towards epoxides. It should be pointed out that
The CI-MS spectra show, in all cases, the peaks of both MTO and
the intact ligands. In addition, the molecular peak of the complete
molecule can be seen in the case of complexes 1–3. These observa-
Table 4
Temperature-dependent 17O NMR spectroscopic data for complexes 1–4 in chloroform
Temperature (°C)
1
2
3
4
d (ppm)
D
m1/2 (Hz)
d (ppm)
D
m1/2 (Hz)
d (ppm)
D
m1/2 (Hz)
d (ppm)
Dm1/2 (Hz)
À50
À20
0
830
827
827
827
90
37
36
25
833
828
827
827
74
24
16
12
830
827
826
827
75
24
17
14
829
827
826
826
88
35
29
20
20

A. Capapé et al. / Journal of Organometallic Chemistry 693 (2008) 3240–3244
3243
ment equipped with a FID and a VF-5 ms column. The Schiff base
ligands were prepared as described previously [16].
100
90
80
70
60
50
40
30
20
10
0
Compounds 1–4 were prepared as follows: A solution of
[(CH3)ReO3] (0.15 g, 0.6 mmol) in diethyl ether (5 mL) was added
drop wise to an equally concentrated solution of ligand (0.6 mmol)
in diethyl ether (5 mL) whilst stirring at room temperature. After
20–30 min the yellow-orange solution-mixture was dried under
oil pump vacuum and the orange precipitate recrystallized under
CH2Cl2/hexane.
1: Yield: 82%. 1H NMR (400 MHz, CDCl3, rt, ppm): d = 15.46 (d,
3
3J(H–H) = 3.2, 1H, C–N+–H), 9.31 (d, J(H–H) = 3.7, 1H, CH@N), 8.1–
7.1 (m, 11H, aryl), 2.59 (s, 3H, CH3–MTO); 13C NMR (100.28 MHz,
CDCl3, rt, ppm): d = 171.26 (C–OÀ), 154.13 (CH@N), 144.61,
136.90, 129.71, 128.14, 126.56, 123.55, 122.51, 120.12, 118.74,
Time
(2h, 4h, 24h)
m
[cmÀ1]): see Tables
1
108.70 (aryl-C), 19.46 (CH3–MTO); IR (KBr,
2
1 and 2; CI-MS (70 eV) m/z: 497.06 [M+], 250.9 [M+-MTO], 248.9
[M+-L]; Anal. Calc. for C18H16NO4Re: C, 43.54; H, 3.25; N, 2.82.
Found: C, 43.84; H, 3.24; N, 2.81%.
3
Compound
4
Fig. 1. Yield of cyclooctene epoxidation after 2 h, (yellow bars) 4 h (red bars), and
after 24 h (blue bars) in the presence of catalytic amounts of the complexes 1–4.
(For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
2: Yield: 80%. 1H NMR (400 MHz, CDCl3, rt, ppm): d = 15.49 (d,
3
3J(H–H) = 4.2, 1H, C–N+–H), 9.23 (d, J(H–H) = 4.2, 1H, CH@N), 8.1–
7.0 (m, 10H, H-aryl), 2.50 (s, 3H, CH3–MTO), 2.38 (s, 1H, Ph–
CH3); 13C NMR (100.28 MHz, CDCl3, rt, ppm): 171.87 (C–OÀ),
153.72 (CH@N), 141.33, 137.19, 136.66, 133.31, 130.29, 129.37,
128.10, 127.06, 123.43, 122.69, 119.77, 118.62 (aryl-C), 70.57,
excess of Schiff base ligand leads to catalyst decomposition and
loss of catalytic activity. This is in contrast to the behaviour of Le-
wis base adducts of MTO, where pyridine based ligands signifi-
cantly accelerate the catalytic reactions when applied in larger
excess [13].
26.48, 20.99 (CH3–Ph), 19.88 (CH3–MTO); IR (KBr,
m
[cmÀ1]): see
Tables 1 and 2; CI-MS (70 eV) m/z: 513.1 [M+], 262.1 [M+-MTO],
251.0 [M+-L]; Anal. Calc. for C19H18NO4Re: C, 44.70; H, 3.55; N,
2.74. Found: C, 45.07; H, 3.53; N, 2.69%.
3: Yield: 94%. 1H NMR (270 MHz, CDCl3, rt, ppm): d = 15.72 (d,
3
3J(H–H) = 5.6, 1H, C–N+–H), 9.26 (d, J(H–H) = 5.8, 1H, CH@N), 8.1–
3. Conclusions
7.0 (m, 9H, H-aryl), 2.58 (s, 1H, CH3–MTO), 2.45–2.42 (s, 2H, Ph–
CH3); 13C NMR (100.28 MHz, CDCl3, rt, ppm): d = 172.51 (C–OÀ),
153.13 (CH@N), 137.15, 130.96, 129.39, 128.11, 127.24, 123.44,
122.98, 118.66, 117.72, 108.71 (aryl-C), 21.15, 17.70 (CH3–Ph),
Selected ((2-hydroxynapthalen-1-yl)methylene)aniline derived
Schiff base ligands react with MTO, yielding 1:1 adducts. The ob-
tained complexes resemble in principle the previously described
(salicylidene)aniline Schiff base ligands but are in general more
stable (also under CI-MS conditions) and can be handled in air
for hours without problem, with the exception of the compound
bearing a chloro substituent in ortho position. Despite being the
least stable of the examined compounds, the latter complex dis-
plays the highest catalytic activity in olefin epoxidation. The elec-
tron donor capability of the Schiff base ligands is also reflected in
the NMR spectra of the MTO moiety. Despite the seemingly weak
coordination of the Schiff base ligand, the latter has a quite signif-
icant influence on both the stability and the catalytic performance
of the resulting complex. More work, whether this observation can
be regarded as a general rule for MTO Schiff base complexes is un-
der work in our laboratories.
19.26 (CH3–MTO); IR (KBr,
m
[cmÀ1]): see Tables 1 and 2; CI-MS
(70 eV) m/z: 527.1 [M+] 276.1 [M+ÀMTO], 250.9 [M+ÀL]; Anal. Calc.
for C20H20NO4Re: C, 45.79; H, 3.84; N, 2.67. Found: C, 45.69; H,
3.76; N, 2.63%.
4: Yield: 80%. 1H NMR (400 MHz, CDCl3, rt, ppm): d = 15.40 (d,
3
3J(H–H) = 3.2, 1H, C–N+–H), 9.39 (d, J(H–H) = 3.2, 1H, CH@N), 8.1–
7.1 (m, 10H, H-aryl), 2.62 (s, 1H, CH3–MTO); 13C NMR
(100.28 MHz, CDCl3, rt, ppm): 168.97 (C–OÀ), 155.60 (CH@N),
143.23, 136.83, 133.09, 130.38, 129.43, 128.16, 127.88, 127.50,
127.14, 123.73, 121.71, 118.96, 118.67, 109.22 (C-aryl), 19.09
(CH3–MTO); IR (KBr,
m
[cmÀ1]): see Tables 1 and 2; CI-MS (70 eV)
m/z: 282.0 [M+ÀMTO], 250.9 [M+ÀL]; Anal. Calc. for
C18H15ClNO4Re: C, 40.72; H, 2.85; N, 2.64; Cl, 6.68. Found: C,
40.53; H, 2.84; N, 2.44; Cl, 6.78%.
4. Experimental
4.2. Catalytic reactions
4.1. Synthesis and characterisation
cis-Cyclooctene (800 mg, 7.3 mmol), 1.00 g of mesitylene (inter-
nal standard), H2O2 (30% aqueous solution; 1.62 ml, 14.6 mmol)
All preparations and manipulations were performed using stan-
dard Schlenk techniques under an argon atmosphere. However, in
the case of 1–3 the synthesis can be carried out under air without
problems. Solvents were dried by standard procedures (n-hexane
and Et2O over Na/benzophenone; CH2Cl2 over CaH2), distilled un-
der argon and kept over molecular sieves. Elemental analyses were
performed with a Flash EA 1112 series elemental analyser. 1H, 13C
NMR and 17O NMR were measured in CDCl3 with a Varian 270 and
400 or a 400 MHz Bruker Avance DPX-400 spectrometer. IR spectra
were recorded with a Perkin–Elmer FT-IR spectrometer using KBr
pellets as the IR matrix. CI mass spectra (isobutene as CI gas) were
obtained with a Finnigan MAT 90 mass spectrometer. Catalytic
runs were monitored by GC methods on a Varian CP-3800 instru-
and 1 mol% (73 lmol) of compounds 1–4 were mixed, diluted in
30 ml of CH2Cl2, added to the reaction vessel under air at room
temperature and the reaction was started by adding H2O2. The
course of the reactions was monitored by quantitative GC analysis.
Samples were taken at regular time intervals and treated with a
catalytic amount of MgSO4 and MnO2 to remove water and to
destroy the unreacted peroxide. The resulting slurry was filtered
and the filtrate injected onto a GC column. The conversion of
cyclooctene and the formation of cyclooctene oxide were calcu-
lated from calibration curves (r2 = 0.999) recorded prior to the
reaction.
The reactions with 1-octene and styrene were performed in the
same way.

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A. Capapé et al. / Journal of Organometallic Chemistry 693 (2008) 3240–3244
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