New boron-containing molybdenum imido alkylidene complexes for linear olefin homometathesis

Article abstract of DOI:10.1021/om400577k

The new molybdenum imido alkylidene complex Mo(N(2,6-iPr₂C ₆H₃))(CHCMe₂Ph)(NC₄H ₂Me₂)(OB(Mes)₂) (1; Mes = 2,4,6-MePh) containing both boroxide and pyrrolide ligands is

Full text of DOI:10.1021/om400577k

Article
pubs.acs.org/Organometallics
New Boron-Containing Molybdenum Imido Alkylidene Complexes
for Linear Olefin Homometathesis
Alexandre Nasr,† Pierre-Alain R. Breuil,*,† Duarte C. Silva,† Mikael Berthod,† Nicolas Dellus,†
̈
Erwann Jeanneau,‡ Marc Lemaire,§ and Helene Olivier-Bourbigou*,†
́
̀
†IFP Energies nouvelles, Rond-point de l’ec
‡Centre de Diffractomet
rie Henri Longchambon, Universite
§Laboratoire de Catalyse et Synthes
e Organique (UMR 5246 CNRS), Universite
́
hangeur de Solaize, BP 3, 69360 Solaize, France
Claude Bernard (Lyon I), 5 rue de la Doua, 69100 Villeurbanne, France
Claude Bernard (Lyon I), 43 Boulevard du 11
́
́
̀
́
Novembre 1918, 69622 Villeurbanne Cedex, France
S
* Supporting Information
ABSTRACT: The new molybdenum imido alkylidene com-
plex Mo(N(2,6-iPr2C6H3))(CHCMe2Ph)(NC4H2Me2)(OB-
(Mes)2) (1; Mes = 2,4,6-MePh) containing both boroxide
and pyrrolide ligands is reported. Its formation results from the
reaction between bis(mesityl)borinic acid ((Mes)2BOH) and
the bis-pyrrolide Schrock-type precursor Mo(N-2,6-iPr2C6H3)-
(CHCMe2Ph)(NC4H2Me2)2. The complex was fully charac-
1
terized by H, 13C, 11B, and 95Mo NMR spectroscopy, X-ray
diffraction, and elemental analysis. Complex 1 proved to be
active for homometathesis reactions of 1- and 2-octene at 0.1
mol % loading. The synthesis of mixed pyrrolide boroxide
imido molybdenum alkylidene complexes was extended to
other borinic acids. The catalytic activity of these new
complexes was evaluated in the homometathesis of linear
olefins.
ell-defined high-oxidation-state molybdenum imido
alkylidene complexes were reported for the first time
(Mo).8 Later, Cole and co-workers reported X-ray diffraction of
molybdenum complexes with the formula Mo(NR)2(OB-
(Mes)2)2 (Mes = 2,4,6-MePh).9 Interestingly, we observed
that these compounds may display longer metal−oxygen bonds
and shorter imido bonds than those usually observed for MAP
complexes, suggesting that the boron atom significantly
influences the π-donating effect of the oxygen atom, lowering
the electronic density on the Mo. Such a parameter could
provide a more effective association between Mo complexes
and π-donor olefin substrates.2c
W
in 1987.1 Over the years,2 intensive research led to the
development of monoalkoxide/aryloxide pyrrolide (MAP)
complexes3 with the formula Mo(NR)(CHR′)(Pyr)(OR″),
where Pyr is a pyrrolide or substituted pyrrolide ligand and
OR″ is an alkoxide or an aryloxide. According to theoretical
studies,4 the introduction of non-identical ligands leading to
unsymmetrical catalysts of the type Mo(NR)(CHR′)(X)(Y) (X
≠ Y) results in dramatically different reactivities with respect to
catalytic olefin metathesis. Furthermore, MAP complexes
bearing sterically hindered alkoxides have proven to be highly
active for enantioselective or Z-selective olefin metathesis5 and
ethenolysis.6 An interesting way to induce an electron-
withdrawing effect on alkoxide type ligands is to incorporate
a substituent at the oxygen atom that has π-acceptor properties.
Boroxide −OBR2 and siloxide −OSiMe3 ligands, which
respectively bear 2p and 3d empty orbitals, fit this criterion.
The π-acceptor effect should be more effective for boroxide
ligands than siloxide, since donation of the oxygen lone pairs to
the empty 2p orbital is probably energetically favored toward
the silicium 3d orbital. Moreover, the higher electronegativity of
boron (2.0) in comparison to that of silicium (1.8) could
induce a decrease of the electronic density on the oxygen and,
thus, on the Mo. Pioneering work on the coordination of
boroxide ligands was reported by Power (Co)7 and Gibson
Here we report a facile synthesis route to the first imido
alkylidene complex bearing a boroxide ligand,10 active for the
homometathesis of linear α and internal olefins. This air- and
1
moisture-sensitive complex was characterized by H, 13C, 11B
and 95Mo NMR and elemental analysis, and crystals suitable for
an X-ray diffraction study were obtained. More complexes of
the same type were prepared in situ using different arylborinic
acids. The activity of these catalysts toward 1-octene and 2-
octene homometathesis has also been investigated. All complex
syntheses and catalytic tests were performed in a glovebox.
Received: June 19, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om400577k | Organometallics XXXX, XXX, XXX−XXX

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ISOLATED MBP CATALYST
■
The first Mo-based monoboroxy pyrrolide (MBP) complex,
Mo(N(2,6-iPr2C6H3))(CHCMe2Ph)(NC4H2Me2)(OB(Mes)2)
(1), was obtained in 64% isolated yield as an orange powder by
addition under argon of 1.1 equiv of bis(mesityl)borinic acid to
a solution of the bis(pyrrolide) precursor Mo(N(2,6-
11
iPr2C6H3))(CHCMe2Ph)(NC4H2Me2)2 in diethyl ether at
−35 °C (Scheme 1). Using 2 equiv of borinic acid did not yield
Scheme 1. Synthesis of Monoboroxy Pyrrolide Complex 1
Figure 1. ORTEP of Mo(N(2,6-iPr2C6H3))(CHCMe2Ph)-
̈
(NC4H2Me2)(OB(Mes)2) (1). The displacement ellipsoids are
the corresponding bis(boroxy) imido alkylidene complex,
probably due to bis(mesityl)borinic acid steric hindrance and
lack of acidity required to protonate the second pyrrolide
ligand.12
shown at the 30% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths (Å): Mo1−N22 = 1.726(2), Mo1−N35
= 2.024(2), Mo1−C42 = 1.875(2), Mo1−O2 = 1.956(2), O2−B3 =
1.361(3). Selected bond angles (deg): Mo1−C42−C43 = 145.1(2),
Mo1−N22−C23 = 176.6(2), Mo1−O2−B3 = 131.4(1), O2−Mo1−
N35 = 120.64(7), O2−Mo1−C42 = 110.07(8), N35−Mo1−C42 =
104.37(8), N22−Mo1−C42 = 101.64(9), N22−Mo1−N35 =
104.87(8), O2−Mo1−N22 = 113.28(7).
Complex 1 was fully characterized by 1H, 13C, 11B, and 95Mo
1
NMR. A clear shift for the carbenic signal is observed by H
NMR from 13.30 ppm (bis-pyrrolide precursor carbene) to
11.56 ppm, consistent with a new carbene and confirmed by
13C NMR spectroscopy (signal at 289.22 ppm).3,5 The
1
measured JCH value (121 Hz) for this complex is typical of
corresponding MAP complex (1.9145(10) Å),3a suggesting
the delocalization of the oxygen lone pairs on the boron center.
Furthermore, the distance reported between Mo and B atoms
(3.033 Å), due to a short Mo1−O2−B3 angle (131.4(1)°),
allowed us to suppose that boron could influence the Mo
coordination sphere (sum of van der Waals radii 3.80 Å)16 and
have an effect on metathesis activity.
syn alkylidene protons (Hα pointing in the opposite direction of
the imido ligand), known to be stabilized through an agostic
interaction with Mo (σC−H → σ*Mo−N).2c,13 This sensitive
complex undergoes partial degradation after 2 h 30 min in
C6D6, leading to a new carbenic signal (Hα at 11.68 ppm,
∼8%). All attempts to isolate and characterize the correspond-
ing product ended with complete degradation of the mixture.
The coordination of the boron ligand induces a shift in 11B
NMR from 50.4 ppm for the borinic acid to 53.1 ppm for
complex 1. We have then carried out a 95Mo NMR study in
saturated CD2Cl2 solution in order to analyze the influence of
the boroxide on Mo electronic density. Complex 1 displays a
Mo chemical shift at 374.5 ppm in comparison to −247.1 ppm
for the bis-pyrrolide complex.14 This is consistent with the fact
that π-electron density of the oxygen is lowered by the
influence of the boron p orbital, reducing the electron density at
the molybdenum. Similar behavior involving Mo complexes
bearing phosphorus ligands has previously been described.15
An X-ray study of 1 (Figure 1) revealed a distorted-
tetrahedral structure for this complex. The values for the Mo1−
N35 bond length (2.024 Å) and Mo1−N22−C23 angle
(176.6(2)°) are typical of MAP complexes. The alkylidene
fragment presents, as expected by NMR, a syn orientation and a
very opened Mo1−C42−C43 angle (145.1(2)°) in comparison
to other MAP complexes (139.5(9)−146.4(3)°).3a−d Most
likely due to steric hindrance induced by the boroxide ligand,
an η1-2,5-dimethylpyrrolyl ligand is observed, comparable to
complexes bearing a bulky alkoxy ligand.3a Interestingly, while
the B−O length does not vary significantly in comparison to
that of the borinic acid (1.367 Å),9 complex 1 displays a Mo−O
(1.956(2) Å) bond longer than Mo−O bonds reported by Cole
and co-workers (1.870(5)−1.9089(16) Å)9 or in the
Additional experiments showed that MBP complex 1 does
not react with 2,2′-bipyridine or 1,10-phenanthroline to afford a
stable 18-electron species such as those recently described by
Furstner and Schrock;17 only recovery of the starting material
̈
was observed, probably for steric reasons.
We then evaluated the catalytic performance of 1 for
homometathesis reactions (Table 1). Catalytic tests were
performed under argon in the presence of dodecane as internal
standard. Experiments involving 1-octene and 2-octene were
carried out in a glovebox with needle-pierced septa to promote
evacuation of lightweight compounds such as ethylene. These
conditions favor higher yields and minimization of the catalyst
decomposition which could occur through methylidene
formation.5i The different products were analyzed and
quantified by gas chromatography techniques after quenching
the reaction with n-butyl vinyl ether, dilution in n-heptane, and
filtration on a plug of silica. Molybdenum catalysts may lead to
different product distributions, due to homometathesis or
cross-metathesis reactions. We therefore describe the molar
distribution in the different tables as follows: the remaining C8
substrate (1-octene or 2-octene), the primary homometathesis
products (PHP) corresponding to 7-tetradecene and ethylene
for 1-octene transformation and to 6-dodecene and 2-butene
for 2-octene transformation, and the secondary metathesis
products (SMP), such as tridecene, propylene, nonene, and
heptene, mainly formed from cross-metathesis of 1-octene and
B
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a
Table 1. Evaluation of Complex 1 toward 1-Octene and 2-Octene Metathesis
b
bc
,
b
b
d
e
entry
cat. loading (mol %)
T (°C)
conversn (%)
C8
C8 isomers
PHP
SMP
PHP selectivity (% E)
1-Octene
94.6
1
2
3
4
5
0.01
0.05
0.1
0.5
1
25
25
25
25
25
25
40
70
4
68
76
79
79
73
82
84
1.6
1.9
1.2
1.3
2.3
0.8
1.5
1.7
3.8
67.9
75.1
78.3
78.5
72.2
81.9
83.1
−
70.4 (58)
97.1 (72)
97.8 (84)
97.7 (85)
96.5 (87)
98.2 (83)
97.6 (82)
97.4 (80)
30.1
<0.1
<0.5
<0.5
<0.5
<0.5
<0.5
<0.5
23.2
19.9
18.7
f
6
0.1
0.1
0.1
26.5
7
8
16.1
14.7
2-Octene
−
59.8
9
0.01
0.05
0.1
0.5
1
25
25
25
25
25
40
70
<1
40
56
55
59
65
68
−
−
−
−
10
11
12
13
14
15
<0.1
<0.1
<0.1
<0.5
<0.1
<0.1
39.6
55.5
55.0
58.2
64.2
67.6
<0.5
<0.5
<0.5
<0.5
<0.5
<0.5
98.5
98.9
98.9
98.3
99.0
43.9
44.4
42.7
0.1
0.1
35.2
31.8
99.1
a
b
Experimental conditions: dodecane (internal standard), 0.5 mL of dry toluene, atmospheric pressure, 2 h, n(olefin) = 13 mmol. Amounts given in
c
mol %, determined by GC analysis and calculations (see the Supporting Information for details). For 1-C8: % C8 isomers represents 2-octenes. For
2-octenes: % C8 isomers represents 3-octenes after 2 h. See the text and the Supporting Information for contents of isomers in the substrates.
d
e
f
Selectivity in primary homometathesis products. Could not be calculated for C12 products due to overlapping of Z/E isomers. Reaction performed
in neat 1-octene.
2-octene or of pentene and undecene, nonene, and heptene
from cross-metathesis of 2-octene and 3-octene (Scheme 2).
the metathesis reactions described with respect to the
conversion and selectivity.
While low conversion was observed at 0.01 mol % of 1 for 1-
octene metathesis, 68% of 1-octene was converted at a 0.05 mol
% catalyst loading (Table 1, entries 1 and 2). Increasing the
catalyst loading up to 0.5 mol % led to an increase of
conversion, up to 79% along with formation of C9−13 SMP
(<0.5%) (Table 1, entries 3 and 4). Surprisingly, using 1 mol %
of catalyst did not improve 1-octene conversion (79%), which
suggests that bimolecular degradation2e of the catalyst is
favored at high concentration (Table 1, entry 5). The highest
selectivity in homometathesis products (97.8%) was reached
using 0.1 mol % of 1 (Table 1, entry 3). Moreover, using 0.1
mol % of 1 in neat 1-octene afforded similar results (73%
conversion, 98.2% selectivity and 83% E product) for the
metathesis reaction (Table 1, entry 6). At 40 °C complex 1 led
to 82% conversion of 1-octene with 97.6% selectivity (Table 1,
entry 7). Raising the reaction temperature to 70 °C did not
significantly improve 1-octene conversion (84%) and led to
comparable selectivity (97.4%, Table 1, entry 8).
Scheme 2. General Procedure for Evaluation of Complex 1
for Homometathesis of 1-Octene and 2-Octene
For catalyst loading over 0.1 mol %, the Z/E isomers in C14
olefins are in an average 15/85 ratio. This ratio tends in favor of
the Z isomers at lower conversion (and catalyst loading). We
also noticed by sampling at different conversions that the
formation of E isomer increases: i.e., for 0.1 mol % at 41%
conversion (t = 5 min), Z/E isomers are observed in a 53/47
ratio, while at 76% conversion (t = 2 h), this ratio is 16/84.
Evolution of the Z/E ratio most often results from the
homometathesis/ethenolysis thermodynamic equilibrium.
However, the use of needle-pierced septa promotes the
evacuation of ethylene, limiting the ethenolysis reaction.
These ratio are consistent with the formation of the
thermodynamically stable E olefin as the major product along
the reaction. However, at any catalyst loading, the conversion
reaches a maximum after 1 h (i.e., for 0.1 mol %, Figure 2),
suggesting a deactivation of the catalyst; in the meantime, a
longer reaction time did not influence the excellent selectivity
The starting 1-octene and 2-octene were analyzed by GC prior
to use to check their purity. It should be noted that 1-octene
contains around 2.0% of 2-octene and 2-octene contains
around 0.5% of 1-octene. This may lead to SMP formation such
as tridecene, nonene, and heptene. The selectivity in PHP
products represents the catalyst’s ability to perform the
homometathesis of the chosen substrate over the secondary
metathesis reactions described above. The C14 Z/E ratio was
deduced by GC data analysis, whereas C12 Z/E isomers were
not distinguishable.18,19 Sampling allowed kinetic monitoring of
C
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Figure 2. Kinetic study of 1-octene metathesis with 0.1 mol % isolated
MBP complex 1.
Figure 3. Kinetic study of 2-octene metathesis with 0.1 mol % isolated
MBP complex 1.
obtained in primary homometathesis products and Z/E ratios
measured. Addition of 1-octene after 2 h to the reaction did not
induce further transformation.
reaction conditions only yielded full recovery of the starting
materials.
While no conversion of 2-octene was observed at 0.01 mol %
of catalyst, complex 1 converted 2-octene (40%) at a 0.05 mol
% catalyst loading (Table 1, entries 9 and 10). Increasing the
catalyst concentration up to 0.5 mol % of 1 raised the
conversion up to 56% with up to 98.9% selectivity in
homometathesis products (Table 1, entries 10−12). Finally,
using up to 1 mol % catalyst raised the conversion to 59% with
only slight 2-octene isomerization into 3-octene (<0.5%)
(Table 1, entry 13). According to GC data analysis, 3-octene
did not undergo any metathesis reaction, probably for
concentration reasons. The highest selectivity in homometa-
thesis product (98.9%) with maximization of the conversion
(56%) was reached using 0.1 mol % of 1 (Table 1, entry 11).
Carrying out the experiment at 40 °C with 0.1 mol % catalyst
raised the 2-octene conversion to 65% with 99.0% selectivity
(Table 1, entry 14). In the same way, working at 70 °C afforded
68% conversion of 2-octene with 99.1% selectivity (Table 1,
entry 15).
IN SITU GENERATION OF MBP CATALYSTS
■
We then extended the synthesis of the mixed pyrrolide
boroxide alkylidene molybdenum complexes to other borinic
acids. The molybdenum bis-pyrrolide complex Mo(N(2,6-
iPr2C6H3))(CHCMe2Ph)(NC4H2Me2)2 was dissolved in C6D6
and cooled to −35 °C. Several diarylborinic acids were then
added to the mixture, leading to the corresponding
monoboroxy pyrrolide complexes 1−4. Reaction progress was
followed by the proton shift of the alkylidene group (Table 2).
1
Analysis of H NMR spectra showed that reactions were no
longer evolving after 24 h. Not surprisingly, addition of the
bis(mesityl)borinic acid afforded complex 1 with complete
Table 2. Synthesis of Monoboroxy Pyrrolide (MBP)
a
Complexes using Diarylborinic Acids
Even if no Z/E isomers for C12 can be distinguished, we
observed an interesting evolution of the Z/E ratio of the
starting 2-octene (75/25). At any catalyst loading, it tends in
favor of the E isomer. Sampling at different conversions showed
that, i.e. for 0.1 mol % at 18% conversion (t = 5 min), Z/E
isomers are observed in a 68/32 ratio, while at 56% conversion
(t = 2 h), this ratio is 20/80 (Table 1, entry 11). This suggests a
higher reactivity of the (Z)-2-octene for homometathesis in
comparison to (E)-2-octene, probably due to steric consid-
erations, along with slight isomerization from (Z)- to (E)-
octene, leading to an inversion of the Z/E ratio in favor of the E
product. Up to 82% of (E)-2-octene Z/E ratio was observed
through catalyst loading screening (0.01−1 mol %) after 2 h.
Such evolution of the Z/E linear olefin ratio has already been
observed in the presence of ethylene pressure (Z-selective
ethenolysis).6b Stable and excellent selectivity in the homo-
metathesis reaction of 2-octene was observed over time, and the
maximum conversion was reached after 1 h of stirring at room
temperature (i.e., for 0.1 mol %, Figure 3). Furthermore, the
conversion and Z/E ratio of the starting material did not evolve
any further after 2 h; therefore, we supposed that deactivation
of the catalyst occurred. In the course of our investigations we
also evaluated the reactivity of 1 toward terminal disubstituted
(2-methyl-1-butene) and trisubstituted (2-methyl-2-pentene)
olefins; using 0.1 mol % catalyst at 25 °C under the same
a
Experimental conditions: bis(pyrrolide) precursor 5 in C6D6 (42
mM), 1.1 equiv of diarylborinic acid added at −35 °C, 24 h of stirring
at room temperature. Transformation of the bis-pyrrolide Mo
complex was followed by H NMR.
b
1
D
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a
Table 3. In Situ Homocoupling of 1-Octene and 2-Octene with Monoboroxy Pyrrolide Complexes 1−4
b
c
cd
,
c
c
e
f
entry
catalyst
cat. loading (mol %)
conversn (%)
C8
C8 isomers
PHP
SMP
PHP selectivity (% E)
1-Octene
21.5
1
2
3
4
5
1
2
3
4
0.1
77
52
1.5
2.1
1.8
1.8
−
76.5
51.8
26.3
12.5
−
<0.5
<0.1
<0.1
<0.1
−
97.5 (84)
95.9 (63)
93.2 (58)
86.8 (57)
−
0.095
0.06
0.05
0.1
46.0
26
71.8
13
85.6
g
ref
<0.5
−
2-Octene
6
1
2
3
4
0.1
56
57
43.9
<0.1
<0.1
<0.1
<0.1
−
55.5
56.0
44.2
50.3
−
<0.5
<0.5
<0.5
<0.5
−
98.9
98.9
98.7
98.8
7
0.095
0.06
0.05
0.1
43.4
8
45
55.2
9
51
49.1
g
10
ref
<0.5
−
−
a
b
Experimental conditions: dodecane (internal standard), 0.5 mL of dry toluene, atmospheric pressure, 2 h, n(olefin) = 13 mmol. Concentration in
c
active catalyst (estimated by analysis of 1H NMR spectra), 25 °C. Amounts given in mol %, determined by GC data analysis and calculations (see
d
the Supporting Information for details). For 1-C8: % C8 isomers represents 2-octenes. For 2-octenes: % C8 isomers represents 3-octenes after 2 h.
See the text and the Supporting Information for contents of isomers in the substrates. Selectivity in primary homometathesis products. Could not
be calculated for C12 products due to overlapping of Z/E isomers. Bis-pyrrolide precursor Mo(N(2,6-iPr2C6H3))(CHCMe2Ph)(NC4H2Me2)2 used
e
f
g
as reference.
conversion of the starting material (Table 2, entry 1). Traces of
bis-pyrrolide precursor (singlet at 13.30 ppm on H NMR
As previously reported for 1-octene metathesis, in situ
generated 1 showed results for 2-octene conversion (56%) and
selectivity (98.9%) similar to those observed using isolated
catalyst 1 (56% conversion, 98.9% selectivity) (Table 3, entry 6,
and Table 1, entry 11). In spite of their structural differences,
complexes 2−4 exhibited similar behavior for 2-octene
metathesis. Indeed, similar values for conversion (45−57%)
and selectivity of around 98.8% were obtained (Table 3, entries
7−9). As previously observed, evolution of the Z/E ratio of the
starting material (75/25) tends in favor of the E isomer for
complexes 1−4, which is in line with the higher reactivity of
(Z)-2-octene with MBP complexes in comparison to (E)-2-
octene described above. Interestingly, in situ generated
complexes 2−4 are more efficient in the homometathesis of
2-octene than in the homometathesis of 1-octene in terms of
conversion (see Table 3). It seems that the introduction of
boroxide ligands induced very interesting effects on Mo
alkylidene complexes which deserve to be specifically
investigated.
In conclusion, we prepared a novel molybdenum complex
based on monoboroxy pyrrolide (MBP) mixed ligands. To the
best of our knowledge, this is the first synthesis of an imido
alkylidene molybdenum complex containing boron. This
complex was fully characterized by NMR spectroscopy. X-ray
diffraction showed a long Mo−O bond, corresponding to
delocalization of the oxygen lone pairs on the boron center.
Furthermore, it exhibited high activity for linear olefin (1-
octene and 2-octene) homometathesis at low catalyst loadings.
More MBP complexes containing various boroxide ligands were
also generated in situ and tested for 1-octene and 2-octene
metathesis, exhibiting an interesting potential for homometa-
thesis reactions.
1
spectra) were detected during the synthesis of 2 with
bis(naphthyl)borinic acid, even with higher reaction time or
heating the solution to 50 °C (Table 2, entry 2). Reaction of
the bis-pyrrolide precursor with bis(3,5-di-tert-butylphenyl)-
and bis(p-tert-butylphenyl)borinic acid afforded the expected
complexes 3 and 4 with 60% and 50% conversion, respectively
1
(Table 2, entries 3 and 4). Analysis of in situ H NMR spectra
showed new signals at 11.71, 12.41, and 12.29 ppm for air- and
moisture-sensitive complexes 2−4, respectively. Such chemical
shifts are consistent with the formation of new MBP carbenic
complexes. Due to the similar properties of the bis-pyrrolide
precursor and complexes 2−4, all our attempts to isolate or
further characterize these complexes ended with full degrada-
tion of the mixture.
In situ generated MBP imido alkylidene molybdenum
catalysts were then screened for linear olefin metathesis
without isolating the complexes (Table 3). Considering that
(i) no activity for homometathesis of 1-octene or 2-octene has
been observed using pure bis-pyrrolide precursor (Table 3,
entries 5 and 10) and (ii) free pyrrolide, which is generated
during the complex synthesis, does not influence the metathesis
reaction, this approach was adapted to study the activity of
complexes 1−4 toward 1-octene and 2-octene metathesis. The
catalyst loading for in situ generated 1−4 was estimated by
1
analysis of the corresponding H NMR spectra. We observed
that in situ generated 1 and isolated 1 exhibited similar results
for conversion (77% versus 76%, respectively) and selectivity
(97.5% versus 97.8%, respectively) (Table 3, entry 1, and Table
1, entry 3). Catalysts 2−4 showed low to moderate 1-octene
conversion (between 13% and 52%) with up to 95.9%
selectivity (Table 3, entries 2−4). We noticed an increase of
the C14 Z/E ratio at lower conversion. The highest Z/E ratio in
C14 (42/58) with maximization of 1-octene conversion (26%)
was reached using complex 3 (Table 3, entry 3). With the
exception of 1, all Z/E ratios were found to be constant along
the reaction. Considering these results, we suppose that tert-
butyl groups are bulky enough to stimulate (Z)-C14
production.5b−d,g−i
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, tables, and a CIF file giving general procedures,
NMR spectra for isolated and in situ generated complexes,
calculation details for amounts of metathesis products, results
for metathesis kinetic studies, and X-ray crystallographic data
for complex 1. This material is available free of charge via the
Internet at http://pubs.acs.org.
E
dx.doi.org/10.1021/om400577k | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(13) Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem.
1988, 36, 1−124.
AUTHOR INFORMATION
Corresponding Authors
*E-mail for P.-A.R.B.: pierre-alain.breuil@ifpen.fr.
*E-mail for H.O.-B.: helene.olivier-bourbigou@ifpen.fr.
■
(14) 95Mo NMR spectra are available in the Supporting Information.
(15) Gray, G. M.; Kraihanzel, C. S. Inorg. Chem. 1983, 22, 2959−
2961.
(16) Batsanov, S. S. Inorg. Mater. 2001, 37, 871−885.
Notes
(17) (a) Heppekausen, J.; Furstner, A. Angew. Chem., Int. Ed. 2011,
̈
The authors declare no competing financial interest.
50, 7829−7832. (b) Lichtscheidl, A. G.; Ng, V. W. L.; Muller, P.;
̈
Takase, M. K.; Schrock, R. R. Organometallics 2012, 31, 4558−4564.
(18) (a) Kovats, E. Helv. Chim. Acta 1958, 41, 1915. (b) Van Den
Dool, H.; Kratz, P. D. J. Chromatogr. 1963, 11, 463−471.
(19) For (Z/E)-6-dodecene Kovats RI values, see the NIST
(National Institute of Standards and Technology) gas chromatography
database and references therein.
ACKNOWLEDGMENTS
■
We thank IFP Energies nouvelles for the permission to publish
these results and financial support. We thank David Proriol for
assistance with NMR experiments.
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