Synthesis and ROMP chemistry of decafluoroterphenoxide molybdenum imido alkylidene and ethylene complexes

Article abstract of DOI:10.1021/om400199u

The bisDFTO alkylidene complexes of molybdenum Mo(NR)(CHCMe ₂Ph)(DFTO)₂ (R = 2,6-i-Pr₂C₆H ₃, 2,6-Me₂C₆H₃, C₆F ₅, 1-adamantyl; DFTO = 2,6-(C₆F₅) ₂C₆H₃O) and monoaryloxide monopyrrolide (MAP) complexes Mo(NR)(CHCMe₂Ph)(Me₂Pyr)(OAr) (Me₂Pyr = 2,5-dimethylpyrrolide; R = C₆F₅, OAr = DFTO, 2,6-dimesitylphenoxide (HMTO); R = 2,6-Me₂C₆H₃, OAr = DFTO) have been prepared in good yields. Addition of dicarbomethoxynorbornadiene (DCMNBD) to bisDFTO complexes yielded polymers that have a cis,isotactic structure. Polymerization of DCMNBD by Mo(NC ₆F₅)(CHCMe₂Ph)(Me₂Pyr)(HMTO) gives a polymer that contains the expected cis,syndiotactic structure, but polymerization of DCMNBD by Mo(NR)(CHCMe₂Ph)(Me₂Pyr)(DFTO) (R = C₆F₅, 2,6-Me₂C₆H₃) generates a polymer that has a cis,isotactic structure, the first observation of a cis,isotactic polymer prepared employing a MAP initiator. Norbornene is polymerized to give what is proposed to be highly tactic cis-polyNBE. Addition of ethylene to Mo(NC₆F₅)(CHCMe₂Ph)(DFTO) ₂ leads to formation of Mo(NC₆F₅)(CH ₂CH₂)(DFTO)₂, which also behaves as an initiator for polymerization of DCMNBD to cis,isotactic-polyDCMNBD and norbornene to cis highly tactic polyNBE. Mo(NC₆F₅)(CH ₂CH₂)(DFTO)₂ reacts with 3-methyl-3- phenylcyclopropene (MPCP) to give Mo(NC₆F₅)(CHCHCMePh) (DFTO)₂ in ～50% yield.

Full text of DOI:10.1021/om400199u

Article
pubs.acs.org/Organometallics
Synthesis and ROMP Chemistry of Decafluoroterphenoxide
Molybdenum Imido Alkylidene and Ethylene Complexes
Jian Yuan, Richard R. Schrock,* Laura C. H. Gerber, Peter Muller, and Stacey Smith
̈
Department of Chemistry 6-331, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
S
* Supporting Information
ABSTRACT: The bisDFTO alkylidene complexes of molybdenum
Mo(NR)(CHCMe2Ph)(DFTO)2 (R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3,
C6F5, 1-adamantyl; DFTO = 2,6-(C6F5)2C6H3O) and monoaryloxide
monopyrrolide (MAP) complexes Mo(NR)(CHCMe2Ph)(Me2Pyr)-
(OAr) (Me2Pyr = 2,5-dimethylpyrrolide; R = C6F5, OAr = DFTO, 2,6-
dimesitylphenoxide (HMTO); R = 2,6-Me2C6H3, OAr = DFTO) have
been prepared in good yields. Addition of dicarbomethoxynorbornadiene
(DCMNBD) to bisDFTO complexes yielded polymers that have a
cis,isotactic structure. Polymerization of DCMNBD by Mo(NC6F5)-
(CHCMe2Ph)(Me2Pyr)(HMTO) gives a polymer that contains the
expected cis,syndiotactic structure, but polymerization of DCMNBD by
Mo(NR)(CHCMe2Ph)(Me2Pyr)(DFTO) (R = C6F5, 2,6-Me2C6H3)
generates a polymer that has a cis,isotactic structure, the first observation
of a cis,isotactic polymer prepared employing a MAP initiator. Norbornene is polymerized to give what is proposed to be highly
tactic cis-polyNBE. Addition of ethylene to Mo(NC6F5)(CHCMe2Ph)(DFTO)2 leads to formation of Mo(NC6F5)(CH2CH2)-
(DFTO)2, which also behaves as an initiator for polymerization of DCMNBD to cis,isotactic-polyDCMNBD and norbornene to
cis highly tactic polyNBE. Mo(NC6F5)(CH2CH2)(DFTO)2 reacts with 3-methyl-3-phenylcyclopropene (MPCP) to give
Mo(NC6F5)(CHCHCMePh)(DFTO)2 in ∼50% yield.
bomethoxynorbornadiene (DCMNBD) to give poly-
(DCMNBD) with a structure that is >99% cis and isotactic, a
result that is not known for bisalkoxide or bisaryloxide imido
alkylidene complexes.4 In this paper we report the synthesis of
new MAP complexes that contain the DFTO ligand along with
a more thorough exploration of reactions of bisDFTO
complexes that are relevant to ROMP reactions. This
exploration includes the synthesis and chemistry of the ethylene
complex Mo(NC6F5)(CH2CH2)(DFTO)2 and a study of its
behavior as an initiator for ROMP.
INTRODUCTION
■
Olefin metathesis is of continuing importance to the synthesis
of organic molecules and polymers, both as a consequence of
its very nature, i.e., the synthesis of CC bonds catalytically
from CC bonds, and because of the control that can be
exercised through the use of well-defined Mo, W, and Ru
complexes as catalysts for that reaction.1 In the interest of
exploring variations of Mo and W olefin metathesis complexes
that contain an electron-withdrawing imido ligand, we recently
devised routes to pentafluorophenylimido alkylidene com-
plexes.2 We were especially interested in exploring high-
oxidation-state monoaryloxide pyrrolide (MAP) imido alkyli-
dene complexes of Mo and W for Z-selective olefin metathesis
reactions.3 In the process we introduced the 2,6-bis-
(pentafluorophenyl)phenoxide (decafluoroterphenoxide or
DFTO) ligand, a sterically demanding but more electron
withdrawing terphenoxide than either HMTO (O-2,6-(2,4,6-
Me3C6H3)2C6H3) or HIPTO (O-2,6-(2,4,6-i-Pr3C6H3)2C6H3),
and one that also is unlikely to be subject to any CH activation
within the ligand. We failed to make MAP complexes that
contain the DFTO ligand through protonation of bispyrrolide
precursors as a consequence of “overprotonation” to yield
M(NC6F5)(CHCMe2Ph)(DFTO)2 complexes. However, M-
(NC6F5)(CHCMe2Ph)(DFTO)2 complexes attracted our
attention because analogous bisHMTO or bisHIPTO com-
plexes have not been prepared and because M(NC6F5)-
(CHCMe2Ph)(DFTO)2 initiates polymerization of 2,3-dicar-
RESULTS AND DISCUSSION
■
Synthesis of BisDFTO Mo Complexes. Treatment of
Mo(NR)(CHCMe2Ph)(OTf)2(DME) complexes with 2 equiv
of DFTOLi (LiO-2,6-(C6F5)2C6H3) at −30 °C in toluene gave
the bisDFTO complexes Mo(NR)(CHCMe2Ph)(DFTO)2
(1a−d, R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3, C6F5, 1-adamantyl;
eq 1). These complexes also can be prepared through addition
of 2 equiv of DFTOH to Mo(NR)(CHCMe2Ph)(Me2Pyr)2 in
diethyl ether at room temperature. We attribute the failure to
prepare Mo(NR)(CHCMe2Ph)(OR)2 by either method when
OR is HIPTO or HMTO to a higher pKa for HIPTOH or
HMTOH and therefore slower protonation of pyrrolide ligands
or to side reactions that involve deprotonation of the
Received: March 11, 2013
Published: May 6, 2013
© 2013 American Chemical Society
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in 60% yield (eq 2). However, addition of 1 equiv of DFTOH
to Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2 at 22 or −30 °C in
alkylidene5 when Mo(NR)(CHCMe2Ph)(OTf)2(DME) is
treated with aryloxide salts.
toluene followed by warming the sample to 20 °C produced a
mixture of Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2, Mo(NC6F5)-
(CHCMe2Ph)(Me2Pyr)(DFTO) (2b), and Mo(NC6F5)-
(CHCMe2Ph)(DFTO)2 (1c) (∼1:1:1 through integration of
alkylidene resonances). In contrast, when reactions between
Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2 and DFTOH were car-
ried out in acetonitrile, Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)-
(DFTO)(MeCN) (2b′) could be isolated as an orange solid in
75% yield. Proton NMR studies suggest that the acetonitrile in
2b′ dissociates readily; indeed, it can be removed by dissolving
2b′ in toluene and removing the toluene and acetonitrile in
vacuo in several cycles. Compound 2b was obtained as a red-
orange solid that could be recrystallized from a mixture of
diethyl ether and pentane. We propose that in the reaction
between Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2 and DFTOH
acetonitrile is a good enough ligand to prevent over-
protonation, since the oxygen of DFTOH must bind to the
metal before the proton can transfer to the pyrrolide ligand.
Fortunately, acetonitrile is also a poor enough ligand in this
situation to be removed from 2b′ in vacuo.
In 19F NMR spectra of 1a−d at 20 °C, one para, two meta,
and two ortho fluorine DFTO resonances are observed (Figure
1). The presence of two meta and two ortho resonances is
An X-ray study of 2b′ revealed it to have a square-pyramidal
structure (τ = 0.067; τ = 0 for a perfect square pyramid6) with
the alkylidene in the apical position and acetonitrile bound
trans to the dimethylpyrrolide (Figure 2). The Mo(1)−N(1)
(1.751(1) Å) and the Mo(1)−C(1) (1.889(1) Å) distances are
similar to those found in other square-pyramidal MAP adducts
that contain PMe3 or THF.7 The alkylidene is found in the
apical position of the square pyramid in all crystallographically
characterized MAP adducts so far.
Synthesis of a Molybdenum Ethylene Complex.
Reaction of a new alkylidene complex with ethylene is a
relatively routine means of exploring the ease of formation and
stability of methylidene and unsubstituted metallacyclobutane
complexes.
Figure 1. Variable-temperature 19F NMR spectra of 1c (in toluene-d8).
consistent with hindered rotation of the C6F5 ring about the
C−C connection between C6F5 rings and the central phenyl
ring but free rotation about the Mo−O bonds on the NMR
time scale. The 19F NMR spectrum of 1c at −80 °C reveals
resonances (some overlapping) for eight DFTO ortho fluorines,
eight meta fluorines, and four para fluorines, consistent with no
molecular symmetry for 1c on the NMR time scale at that
temperature. An X-ray structure2 revealed that the two DFTO
ligands are oriented approximately perpendicular to each other
to give an enantiomorphic atropisomer in the solid state. The
DFTO ligands in the atropisomer resemble the halves of a
baseball cover with the basic C2 symmetry being reduced to Cs
as a consequence of the presence of the imido and alkylidene
ligands. We propose that the atropisomeric form leads to the
inequivalence of all 20 DFTO fluorines on the NMR time scale.
Rotation of the two DFTO ligands past one another and past
the imido and alkylidene ligands creates a mirror plane on the
NMR time scale at higher temperatures that coincides with the
Nimido−Mo−C plane.
Exposure of a diethyl ether solution of Mo(NC6F5)-
(CHCMe2Ph)(DFTO)2 (1c) to 1 atm of ethylene at room
temperature led to a color change from orange to deep purple
over a period of 16 h and formation of the ethylene complex
Mo(NC6F5)(CH2CH2)(DFTO)2 (3; eq 3), in 76% yield. At
Synthesis of MAP Complexes. Treatment of Mo-
(NC6F5)(CHCMe2Ph)(Me2Pyr)2 with 1 equiv of 2,6-dimesi-
tylphenol (HMTOH) at 70 °C for 16 h led to formation of the
MAP complex Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(HMTO)
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Figure 4. Thermal ellipsoid plot of 3. Hydrogen atoms have been
omitted for clarity. Selected bond distances (Å) and angles (deg):
Mo(1)−N(1) = 1.720(3), Mo(1)−O(2) = 1.935(3), Mo(1)−O(1) =
1.946(3), Mo(1)−C(2) = 2.140(4), Mo(1)−C(1) = 2.153(4), C(1)−
C(2) = 1.415(6); N(1)−Mo(1)−O(2) = 121.37(14), N(1)−Mo(1)−
O(1) = 114.79(14), O(2)−Mo(1)−O(1) = 108.45(11), C(2)−
Mo(1)−C(1) = 38.49(15), C(2)−C(1)−Mo(1) = 70.3(2), C(1)−
C(2)−Mo(1) = 71.2(2).
Figure 2. Thermal ellipsoid plot of the structure of 2b′. Hydrogen
atoms have been omitted for clarity. Selected bond distances (Å) and
angles (deg): Mo(1)−N(1) = 1.751(1), Mo(1)−C(1) = 1.889(1),
Mo(1)−O(1) = 1.995(1), Mo(1)−N(2) = 2.084(1), Mo(1)−N(3) =
2.190(1), C(11)−N(1) = 1.378(1), O(1)−C(31) = 1.336(1); N(1)−
Mo(1)−O(1) = 154.35(4), N(2)−Mo(1)−N(3) = 158.37(4).
1
room temperature the H NMR spectrum for 3 in tol-d8
showed two ethylene proton resonances at 1.33 and 2.48
ppm (Figure 3). At −80 °C these two resonances split into four
bond (2.153(4) Å). The C1−C2 bond distance is 1.415(6) Å,
and the C1−Mo1−C2 angle is 38.49(15)°. The C1−C2 bond
is essentially perpendicular to the Mo1−N1 bond (N1−Mo1−
C1 = 97.00(15)°; N1−Mo1−C2 = 96.00(16)°). These
structural features are similar to those observed for the four
other Mo imido ethylene complexes in the literature.8
13
When 1c was treated with 13CH2 CH2 in C6D6 and the
reaction followed by 13C NMR, 1c was fully converted into a
mixture of a TBP metallacyclobutane complex, Mo(NC6F5)-
(13CH213CH213CH2)(DFTO)2 (4*), and 13CH2CHCMe2Ph
in 5 min. After 15 min, resonances for Mo(NC6F5)-
13
(13CH213CH2)(DFTO)2 (3*) and 13CH2 CH13CH3 could
be observed; after 24 h conversion to 3* and
13
13CH2 CH13CH3 was complete. According to proton
NMR spectra the amount of propylene was less than 1 equiv,
as a consequence of some being lost into the head space. A 13
C
NMR spectrum of isolated 3* under ∼0.5 atm of 13CH213CH2
at room temperature showed that two carbon resonances were
present at δ 82.9 and 39.9 ppm (with a second-order coupling
pattern), consistent with formation of a small amount of the
m e t a l l a c y c l o p e n t a n e c o m p l e x M o ( N C 6 F 5 ) -
(13CH213CH213CH213CH2)(DFTO)2 (∼2%; Figure 5).9 We
propose that Mo(NC6F5)(13CH213CH213CH2)(DFTO)2 rear-
1
Figure 3. Variable-temperature H NMR spectra of 3 (tol-d8).
at δ 0.81, 1.85, 2.19, and 2.60 ppm. The 19F NMR spectrum of
3 at −80 °C reveals resonances for eight ortho fluorines, eight
meta fluorines, and four para fluorines for the two DFTO
ligands, as found for 1c (Figure 1). All data are consistent with
3 having no symmetry at −80 °C on the NMR time scale, as
found for 1c.
The structure of 3 as determined through a single-crystal X-
ray diffraction study is shown in Figure 4. The Mo1−C2 bond
length (2.140(4) Å) is essentially the same as the Mo1−C1
ranges to Mo(NC6F5)(13CH2 CH13CH3)(DFTO)2 and that
13
propylene is then displaced (most likely) by ethylene to give
Mo(NC6F5)(13CH213CH2)(DFTO)2 and free propylene. The
mechanism of rearrangement is proposed to consist of β
hydride elimination in the metallacyclobutane complex to give
an intermediate allyl hydride followed by reductive elimination.
Formation of an alkyl intermediate through CH activation in
either the DFTO or the NC6F5 ligand is not possible. However,
migration of the β hydride in the metallacyclobutane to the
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Table 2. GPC Studies of Poly(DCMNBD) Prepared with 1c
a
as the Initiator
n
conversion (%)
Mn
PDI
50
100
200
800
>98
>98
>98
>98
7000
13000
24000
88000
1.19
1.17
1.15
1.10
a
Mn in CHCl3 vs polystyrene; n = equivalents of monomer added.
measured in CHCl3 versus polystyrene standards is linear
with an R2 value of 0.9999 (Figure S1 in the Supporting
Information).
13
Figure 5. 13C NMR spectrum of Mo(NC6F5)(13CH2 CH2)-
Polymerization of DCMNBD by bisDFTO initiators 1b,c to
yield cis,isotactic-poly(DCMNBD) would seem to require that
the monomer attack the same side of a MC bond in each
step. We tentatively suggest that cis,isotactic-poly(DCMNBD)
forms through a type of chain end control where one
diastereomer is created through interlocking of the terphen-
oxide ligands in combination with the chirality of the last
inserted monomer; reaction of the other diastereomer is not
competitive. The failure of 1d to yield cis,isotactic-poly-
(DCMNBD) suggests that the nature of the imido group is a
significant part of the puzzle that is not yet understood.
Polymerization of DCMNBD Initiated by 2a−c.
Addition of 100 equiv of DCMNBD to 2a led to consumption
of the monomer and formation of polymer within 30 min. The
polymer is >98% cis,syndiotactic (Table 3), as is the poly-
(DFTO)2 and 13CH2 CH2 in C6D6 at room temperature ([Mo]
13
= Mo(NC6F5)(DFTO)2).
imido nitrogen to give an intermediate Mo(IV) complex,
Mo(NHC6F5)(13CH213CH13CH2)(DFTO)2, cannot be ruled
out.
Polymerization of DCMNBD Initiated by 1. We often
employ polymerization of 2,3-dicarbomethoxynorbornadiene
(DCMNBD) as a means of assessing the potential stereo-
selectivity of a given initiator. We noted in a communication
that DCMNBD was polymerized by initiator 1c to give
cis,isotactic polymer.2 Addition of 100 equiv of DCMNBD to
1a,b,d also led to the formation of poly(DCMNBD). As shown
in Table 1, only initiators 1b,c produce a polymer with a highly
Table 1. Poly(DCMNBD) Formed Employing
Mo(NR)(CHCMe2Ph)(DFTO)2 Initiators
Table 3. Poly(DCMNBD) Formed with Initiators
Mo(NR)(CHCMe2Ph)(Me2Pyr)(OAr) (2a−c)
compd
R
cis (%)
tacticity (%)
initiator
R
ArO
cis (%)
tacticity (%)
1a
1b
1c
1d
2,6-i-Pr2C6H3
2,6-Me2C6H3
C6F5
89
>98
>98
72 iso
2a
C6F5
C6F5
C6F5
HMTO
DFTO
DFTO
DFTO
>98
92
>98 syndio
atactic
>98 iso
>98 iso
atactic
2b′
2b
2c
95
91 iso
adamantyl
2,6-Me2C6H3
>98
96 iso
regular >98% cis, >98% isotactic structure, on the basis of the
chemical shift of the methylene carbon (C(7)) at 38.7 ppm in
CDCl3;10 this contrasts with a chemical shift for C(7) of 38.0
ppm in cis,syndiotactic-poly(DCMNBD).3b Formation of
cis,isotactic-poly(DCMNBD) employing an imido alkylidene
bisalkoxide initiator is not known.4 However, polymerization of
DCMNBD initiated by W(CH-t-Bu)(O)(O-2,6-
Ph2C6H3)2(PPh2Me) has been reported to produce >95% cis,
>95% isotactic poly(DCMNBD).11 Initiators that contain chiral
biphenolate and binaphtholate ligands produce cis,isotactic-
poly(DCMNBD) through enantiomorphic site control.4 Only
atactic polymer was formed employing initiator 1d, either
isolated or prepared in situ. The lower efficiency of forming a
cis,isotactic polymer with initiator 1a is likely to be a
consequence of too much steric hindrance.
GPC analyses of cis,isotactic-poly(DCMNBD) made from 50,
100, 200, and 800 equiv of DCMNBD in CHCl3 at room
temperature with initiator 1c (Table 2) showed that the
polydispersity of each sample is relatively low and decreases as
the polymer length increases, both of which suggest that the
polymerization is relatively well-behaved. (For a neophylidene
initiator kp often is greater than ki and PDI values therefore are
higher than when kp and ki are comparable.) The relationship
between the number of equivalents of monomer employed and
the number average molecular weight of the polymers
(DCMNBD) produced employing Mo(NAd)(CHCMe2Ph)-
(Pyr)(OHIPT)3b as an initiator. The polymer obtained with
2b′ is largely cis but relatively atactic, presumably solely as a
consequence of the presence of 1 equiv of acetonitrile. To our
surprise, treatment of 2b with 100 equiv of DCMNBD led to
the formation of a new polymer that has a 95% cis and 91%
isotactic structure, while poly(DCMNBD) prepared with 2c as
the initiator was found to contain ∼98% cis and 96% isotactic
dyads. Formation of cis,isotactic polymer with a MAP initiator
has never been observed, although formation of trans,isotactic-
poly[(+)-2,3-dicarbomethoxynorbornene] employing a MAP
initiator has been reported recently.3l The change in tacticity
upon changing from HMTO (in 2a) to DFTO (in 2b) is
striking, as is the disruption of the tacticity of the poly-
(DCMNBD) in the presence of 1 equiv of acetonitrile (in 2b′).
Poly(DCMNBD) made from 50, 100, and 200 equiv of
monomer in CHCl3 with initiator 2b was analyzed by GPC
(Table 4). In comparison to the polymer produced by initiator
1c (Table 2), the polydispersities of each of the samples are
relatively high and increase as the polymer length increases.
The relationship between the number of equivalents of
monomer employed and the number average molecular weight
of the polymers measured in CHCl3 versus polystyrene
standards is also linear, with an R2 value of 0.99 (Figure S2
in the Supporting Information). The molecular weights of these
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Table 4. GPC Studies of Poly(DCMNBD) Samples Using 2b
a
as an Initiator
n
conversion (%)
Mn
PDI
n′
n/n′
50
100
200
>99
>99
>99
28000
55000
90000
1.19
1.20
1.26
242
490
817
0.21
0.20
0.24
a
Mn in CHCl3 vs polystyrene; n = equivalents of monomer added; n′ =
the required equivalents of monomer to produce the same Mn with
initiator 1c.
polymers are about 5 times what they are when 1c is employed
as the initiator, as can be seen from the data in Table 2; the
ratio n/n′ is ∼0.2, where n′ would be the required number of
equivalents to produce an observed Mn employing initiator 1c.
Formation of largely cis,isotactic-poly(DCMNBD) by 2b,c
contrasts dramatically with the cis,syndiotactic-poly(DCMNBD)
formed when 2a is employed as an initiator. In fact, we can
explain formation of cis,isotactic-poly(DCMNBD) only if the
“rule” concerning approach of the monomer trans to a pyrrolide
ligand does not hold in this situation or if we invoke a turnstile
rotation of a metallacyclobutane intermediate followed by a
rotation of the alkylidene ligand, as shown in Scheme 1. We
have entertained the possibility that a propagating species
generated from 2b disproportionates to yield bispyrrolide and
bisDFTO complexes and that the cis,isotactic structure arises
through selective polymerization of DCMNBD by the
bisDFTO complex so formed. However, a mixture of 1c and
Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2 (1:1) in C6D6 did not
give any 2b at room temperature or upon heating to 50 °C for
16 h. Also, the data in Table 4 would suggest that the amount
of disproportionation would have to be ∼20%. It should be
noted that Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OC6F5) has been
found to yield a mixture of Mo(NAr)(CHCMe2Ph)(Me2Pyr)2
plus Mo(NAr)(CHCMe2Ph)(OC6F5)2 in solution.12 We
conclude that disproportionation of a propagating species
generated from 2b cannot be rejected out of hand, but it
seems unlikely at this stage.
Figure 6. Consumption of DCMNBD in CDCl3 by 3 at 50 °C. Blue
diamonds imply 2% catalyst loading, green triangles imply 1% catalyst
loading, and red squares and purple crosses are 1% catalyst loading
with 3 that had been exposed to ethylene to remove any alkylidene
impurities.
polymer is >99% cis and isotactic. The same phenomenon was
observed when 1% catalyst was employed, even when samples
of 3 were exposed multiple times to ethylene and recovered.
Therefore, the evidence argues against the possibility that the
polymerization can be ascribed to a trace of residual alkylidene
complex. Since cis,isotactic-poly(DCMNBD) is formed employ-
ing Mo(NC6F5)(CHCMe2Ph)(DFTO)2 as an initiator, it
seems highly likely that the initiator for the polymerization is
a bisDFTO complex and that the initiator is generated from
DCMNBD itself.
Addition of 1 equiv of DCMNBD to Mo(NC6F5)-
(CH2CH2)(DFTO)2 led to formation of a red-orange
crystalline product in 57% yield with the apparent composition
Mo(NC6F5)(CH2CH2)(DCMNBD)(DFTO)2 (5).
The 1H NMR spectrum showed four triplet of doublet
resonances (12, 4 Hz) at δ 1.43, 1.77, 2.72, and 3.07 ppm for
the ethylene protons, which is indicative of a product with no
symmetry. An X-ray diffraction study showed that the
DCMNBD has bonded to Mo through the carbonyl groups
in the two esters (O1 and O3, Figure 7), rather than forming a
“mixed” metallacyclopentane from DCMNBD and ethylene.
One ester is trans to the ethylene ligand, while the other is trans
to the imido group. The two DFTO ligands are trans to each
other. The bond lengths and angles are unsurprising. The
Mo1−C1 distance (2.187(1) Å) is slightly shorter than the
Mo1−C2 distance (2.195(1) Å), and the C1−C2 distance is
1.416(2) Å.
ROMP Initiated by Mo(NC6F5)(CH2CH2)(DFTO)2 (3).
When Mo(NC6F5)(CH2CH2)(DFTO)2 was treated with 50
equiv of DCMNBD in CDCl3 in a J. Young tube, a trace
amount of polymer was observed after 16 h at room
temperature. When the reaction mixture was heated for 4 h
at 50 °C, 48% of the monomer was consumed. The reaction
was monitored by 1H NMR, and conversion vs time is shown in
Figure 6. All monomer was consumed after 16 h at 50 °C in a
Schlenk flask when ethylene was removed in a flow of nitrogen
gas. 13C NMR analysis of the poly(DCMNBD) showed that the
The synthesis of six-coordinate 5 suggests that the steric
limits associated with, or imposed by, two terphenoxide ligands
Scheme 1. A Mechanism That Leads to cis,isotactic-Poly(DCMNBD)
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initiators 1c and 2a were identical with those prepared with
initiator 3. The widths of the resonances at half height are ∼9
Hz at 125 MHz, which are unusually narrow. It seems unlikely,
but not impossible, that the samples made with 1c and 2a are
each highly tactic but have different tacticities (expected to be
iso and syndio, respectively), since at least one additional
resonance in a 125 MHz 13C NMR experiment, most likely
near that at 38.72 ppm, should be present if polymers with two
different tacticities are formed. In early work on poly(NBE) 13
C
NMR spectra,13 Ivin and co-workers decided that fine structure
due to tacticity differences, at least in the relatively low
frequency 13C NMR experiments at that time, could not be
detected. However, a second explanation of the result obtained
here is that the cis highly tactic poly(NBE) samples produced
with initiators 1c and 2a are both isotactic. This possibility
would require that the “rule” concerning formation of
syndiotactic polymers with HMTO MAP species breaks
down for norbornene, just as it did when cis,isotactic-
poly(DCMNBD) was formed with initiators 2b,c. Whether
the tacticity of poly(NBE) is iso or syndio cannot be determined
through NMR studies, since no chiral element is present in the
polymer.4 As far as we are aware, this is the first time that pure
>98% cis and (we propose) highly (>98%) tactic poly-
(norbornene) has been prepared.
Addition of 1 equiv of norbornene to Mo(NC6F5)-
(13CH213CH2)(DFTO)2 at −78 °C in toluene-d8 showed
that, after 1 h at −70 °C, 69% of the ethylene complex was
converted to the “mixed” metallacyclopentane complex 6 (eq
4). The 13CH2 resonances in the metallacycle were observed as
Figure 7. Thermal ellipsoid plot of 5. Hydrogen atoms have been
omitted for clarity. Selected bond distances (Å) and angles (deg):
C(1)−C(2) = 1.416(2), Mo(1)−C(1) = 2.187(1), Mo(1)−C(2) =
2.195(1), Mo(1)−N(1) = 1.7290(9), Mo(1)−O(1) = 2.1983(8),
Mo(1)−O(3) = 2.2198(8), Mo(1)−O(5) = 2.0664(7), Mo(1)−O(6)
= 2.1041(7); N(1)−Mo(1)−O(3) = 178.92(4), O(5)−Mo(1)−O(6)
= 148.94(3), C(1)−Mo(1)−C(2) = 37.70(4).
are difficult to predict, although the electron-withdrawing
DFTO ligands should encourage adduct formation. It also
should be noted that bisaryloxide catalysts have been employed
in macrocyclizations that give trisubstituted double bonds,3k
which suggests that crowded bisaryloxide catalysts may turn out
to have some special properties in metathesis reactions that
have been overlooked. In any case, coordination of the esters in
DCMNBD to the metal almost certainly impedes formation of
an initiator from DCMNBD.
first-order doublets at δ 84.7 and 46.6 ppm (1JCC = 37 Hz) in
the 13C NMR spectrum at −70 °C, consistent with one isomer
of 6 being formed. When the temperature was raised to −50
°C, the concentration of 6 decreased while the concentrations
of 3 and poly(norbornene) increased. After 1 h at −50 °C, all
the norbornene had been consumed and the ethylene complex
3 was observed as the only Mo species to contain a 13C label:
Addition of 100 equiv of DCMNBD to Mo(NC6F5)-
(13CH213CH2)(DFTO)2 led to the formation of ∼50% yield
of polymer in 8 h at 50 °C in CDCl3. The 13C NMR spectra
exhibit one 13C resonance at δ 116.1 ppm along with others
expected for naturally abundant 13C in the polymer. A 2D
13C−1H HMBC experiment (Figure S3, Supporting Informa-
tion) confirmed that the 13C resonance at 116.1 ppm is that in a
13
i.e., no PCH CH2 group was detected in this experiment. As
13
PCH CH2 group (P = polymer) at one end of the
in reactions between 3 and DCMNBD, ethylene does not
appear to be involved in formation of the initiator.
poly(DCMNBD); the magnitudes of the coupling of the two
protons in the 13CH2 group to a third olefinic proton were
found to be 17 Hz (Jtrans) and 7 Hz (Jcis). We propose, in part
on the basis of results to be described later, that the
Treatment of 3 with 1 equiv of a mixture of labeled and
unlabeled 3-methyl-3-phenylcyclopropene (MPCP; two parts
of unlabeled MCPC to one part in which one CH is 13C
labeled) at −78 °C led to an immediate color change from
purple to orange and formation of Mo(NC6F5)(CHCH
CMePh)(DFTO)2 (7; eq 5) upon warming the sample to room
temperature. Since one-third of the MPCP was monolabeled
with 13C in an olefinic position, the alkylidene proton
13
PCH CH2 group results from a back reaction between
liberated 13CH213CH2 and a growing polymer chain, not
through formation of Mo(NC6F5)(13CH2)(DFTO)2 as the
initiator.
Addition of 100 equiv of norbornene to 3 at room
temperature led to formation of poly(norbornene) in seconds.
The 13C NMR spectrum of the polymer in CDCl3 showed only
four sharp resonances (at 134.00, 42.83, 38.72, and 33.34 ppm),
characteristic of pure cis poly(NBE).13 Samples prepared with
3
resonance consists of a doublet at δ 12.10 ppm (d, JHH = 9
Hz) along with two 13C satellites (1JCH = 130 Hz, 3JHH = 9 Hz)
in a ratio of 1:4:1 (Figure 8), consistent with 7 being a mixture
13
of [Mo] CHCHC(Me)Ph, [Mo]CH13CHC(Me)-
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electron-withdrawing ability of the DFTO ligand in combina-
tion with dramatic steric bulk. However, formation of
cis,isotactic-poly(DCMNBD) from both MAP initiators 2b,c,
as well as apparently identical cis and highly tactic poly-
(norbornene) samples employing initiators 1c and 2a, suggest
that the “rule” concerning formation of syndiotactic polymers
from MAP initiators requires rethinking and testing. Finally,
ROMP polymerization initiated by the ethylene complex 3
appears to proceed via an alkylidene formed from the monomer
itself.
Ph, and [Mo]CHCHC(Me)Ph in one isomeric form
(where [M] = Mo(NC6F5)(DFTO)2). (The isomer shown in
eq 5 is arbitrary.) A similar coupling pattern was observed for
3
the β-hydrogen at δ 8.33 ppm (1JCH = 159 Hz, JHH = 9 Hz).
The origin of the minor resonances at 12.20, 8.65, and 8.15
ppm (inter alia) has not been identified. In the 13C NMR
spectrum, the alkylidene carbon resonance was found at δ 264.5
ppm and the β-carbon resonance was found at δ 136.0 ppm.
The vinyl alkylidene 7 rapidly initiates ROMP of MPCP at −78
°C or room temperature to yield atactic poly(MPCP).3d We
propose that MPCP replaces ethylene in 3 to give a MPCP
complex that then rearranges to form the vinyl alkylidene
complex 7. A single experiment employing 3, unlabeled
ethylene, and trimethoxybenzene as an internal standard
showed that Mo(NC6F5)(CHCHCMePh)(DFTO)2 was
formed in 50% yield. We propose that some MPCP is
polymerized in the process. Ready conversion of 3 into an
alkylidene is analogous to the results of reactions between 3,3-
diphenylcyclopropene and complexes that contain Ti(II) and
Zr(II),14 W(IV),15 and Ru(II).16
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were conducted
under a nitrogen atmosphere in a glovebox under nitrogen or through
Schlenk techniques. All glassware was dried in an oven prior to use.
Ether, pentane, toluene, dichloromethane, toluene, and benzene were
degassed with dinitrogen and passed through activated alumina
columns under nitrogen. All dried and deoxygenated solvents were
stored over molecular sieves in a nitrogen- or argon-filled glovebox.
NMR spectra were recorded on a 500 MHz spectrometer. Chemical
1
1
shifts for H spectra were referenced to the residual H resonances of
the deuterated solvent (1H NMR C6D6 δ 7.16 ppm, CDCl3 δ 7.26
ppm, toluene-d8 7.09, 7.01, 6.97, 2.08 ppm; 13C NMR C6D6 δ 128.06
ppm, CDCl3 δ 77.16 ppm, toluene-d8 20.43 ppm) and are reported as
parts per million relative to tetramethylsilane. Midwest Microlab,
Indianapolis, IN, provided elemental analyses. The following
abbreviations refer to the multiplicity: s = singlet, d = doublet, t =
triplet, m = multiplet, br = broad. Other abbreviations include Ar′ =
2,6-Me2C6H3, Ad = 1-adamantyl, and Ar = 2,6-i-Pr2C6H3. Mo-
(NC6F5)(CHCMe2Ph)(OTf)2(DME),2 Mo(NC6F5)(CHCMe2Ph)-
(Me2Pyr)2,2 Mo(NAr′)(CHCMe2Ph)(OTf)2(DME),3c Mo(NAr′)-
(CHCMe2Ph)(Me2Pyr)2,2 Mo(NC6F5)(CHCMe2Ph)(DFTO)2,2 Mo-
(NAd)(CHCMe2Ph)(Me2Pyr)2,7a and DFTOH2 were prepared as
described in the literature. All the other reagents were used as received
unless noted otherwise.
Mo(NAr)(CHCMe2Ph)(DFTO)2 (1a). Mo(NAr)(CHCMe2Ph)-
(Me2Pyr)2 (100 mg, 0.159 mmol) was dissolved in benzene (5 mL).
DFTOH (136 mg, 0.320 mmol) was added at room temperature, and
the mixture was heated at 100 °C for 16 h. The solvent was removed
to give an orange oily product. The residue was recrystallized from a
mixture of diethyl ether and pentane to give a yellow solid (174 mg,
87%): 1H NMR (500 MHz, C6D6, 20 °C) δ 11.69 (s, 1H, MoCH),
6.97 (m, 3H), 6.84 (d, 8 Hz, 5H), 6.76 (d, 3JHH = 8 Hz, 2H), 6.68 (m,
4H), 1.90 (sept, JHH = 7 Hz, 2H), 1.36 (s, JHH = 6 Hz), 0.84 (s,
12H); 19F NMR (282 MHz, C6D6, 20 °C) δ −137.8 (m, 4F), −139.2
(m, 4F), −154.6 (m, 4F), −161.2 (m, 4F), −161.7 (m, 4F); 13C{1H}
NMR (125 MHz, C6D6, 20 °C) δ 288.7 (s, 1C, MoC), 164.5, 147.6,
14.7 (d, 1JCF = 252 Hz), 141.4 (d, 1JCF = 250 Hz), 138.3 (d, 1JCF = 254
Hz), 134.8, 133.5, 125.6 (d, 50 Hz), 124.3 (d, 52 Hz), 122.5, 121.2,
118.3, 113.0, 56.8, 29.3, 28.3. Anal. Calcd for C58H30F20MoNO2: C,
55.65; H, 2.81; N, 1.12. Found: C, 55.39; H, 2.93; N, 1.14.
1
Figure 8. H NMR spectrum of 7 in C6D6.
The ROMP of DCMNBD with 3 to give cis,isotactic-
poly(DCMNBD), strongly suggests that some Mo(NC6F5)-
(ODFT)2(CRR′) initiator is formed from DCMNBD. The
ROMP of norbornene by 3 also suggests that some initiator
forms from norbornene. These results can be added to others
in the last several years that employ Mo(IV) or W(IV)
initiators for metathesis reactions.17 Evidence in the literature
that stretches over several decades suggests that a norborny-
lidene complex can form from a norbornene via a 1,2-shift of an
olefinic hydrogen.18 However, to our knowledge no pure
norbornylidene complex has ever been prepared. The closest is
formation of a mixture of (Silox)3M(norbornene) (Silox = t-
Bu3SiO; M = Nb, Ta) and (Silox)3M(norbornylidene) as part
of a study of isomerization of (Silox)3M(alkene) complexes to
(Silox)3M(alkylidene) complexes via formation of intermediate
alkyl complexes through CH activation in a Silox ligand.19
3
3
Mo(NAr′)(CHCMe2Ph)(DFTO)2 (1b). Mo(NAr′)(CHCMe2Ph)-
(OTf)2(DME) (Ar′ = 2,6-Me2C6H3; 100 mg, 0.121 mmol) was
suspended in toluene (5 mL), and the mixture was cooled to −30 °C.
DFTOLi (110.4 mg, 0.255 mmol) was added at −30 °C, and the
temperature was allowed to rise to 22 °C. After 1 h, the solvent was
removed in vacuo, the dark oily residue was extracted with CH2Cl2,
and the solvent was removed again in vacuo. Pentane (2 mL) was
added and the mixture was stirred for 30 min. The resulting yellow
precipitate was filtered off and dried in vacuo; yield 115 mg (79%) of a
yellow solid; 1H NMR (500 MHz, C6D6, 20 °C) δ 11.39 (s, 1H, Mo
CONCLUSIONS
■
3
3
CH), 6.91 (d, JHH = 7.5 Hz, 4H), 6.83 (d, JHH = 7.5 Hz, 2H), 6.75
(d, 3JHH = 7.5 Hz, 2H), 6.72 (m, 3H), 6.54 (t, 3JHH = 7.5 Hz, 2H), 6.43
This first exploration of DFTO alkylidene complexes suggests
that they can behave quite differently from complexes that
contain superficially similar terphenoxides such as HMTO.
Mo(NR)(CHCMe2Ph)(DFTO)2 complexes have no HMTO
or HIPTO analogues and behave in a ROMP reaction as if the
metal were chiral. Some observations can be ascribed to the
(d, JHH = 7.5 Hz, 2H), 1.49 (s, 6H), 1.02 (s, 6H); 19F NMR (282
3
MHz, C6D6, 20 °C) δ −138.9 (d, 3JFF = 23 Hz, 4F), −139.7 (d, 3JFF
=
23 Hz, 4F), −154.7 (t, 3JFF = 23 Hz, 4F), −161.7 (m, 4F), −162.0 (m,
4F); 13C{1H} NMR (125 MHz, C6D6, 20 °C) δ 286.0 (s, 1C, Mo
C), 164.7, 156.3, 147.3, 144.7 (dm, 1JCF = 249 Hz), 141.5 (dm, 1JCF
=
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3
252 Hz), 138.3 (dm, 1JCF = 252 Hz), 135.9, 125.5, 121.7, 117.8, 112.7
(m), 55.2, 29.5, 17.5. Anal. Calcd for C54H27F20MoNO2: C, 54.15; H,
2.27; N, 1.17. Found: C, 53.83; H, 1.96; N, 0.99.
MHz, C6D6, 20 °C) δ 12.13 (br, 1H, MoCH), 7.08 (d, JHH = 7.5
Hz, 2H), 7.01 (d, 3JHH = 7.5 Hz, 2H), 6.83 (t, 3JHH = 7.5 Hz, 3H), 6.67
(brt, 3JHH = 7 Hz, 1H), 5.83 (br, 2H), 3.25 (q,, 3JHH = 7 Hz, 2H), 2.06
3
(br, 6H), 1.30 (s, 3H), 1.19 (s, 3H), 1.12 (t, JHH = 7 Hz, 3H), 0.62
Mo(NAd)(CHCMe2Ph)(DFTO)2 (1d). Mo(NAd)(CHCMe2Ph)-
(Me2Pyr)2 (100 mg, 0.177 mmol) was suspended in diethyl ether (5
mL). DFTOH (151 mg, 0.354 mmol) was added at room temperature.
After 1 h, the solvent was removed to give a yellow oil. Pentane (1
mL) was added, and the mixture was stirred for 30 min. The yellow
precipitate was filtered off and dried in vacuo to give a yellow solid
(br, 3H); 19F NMR (282 MHz, C6D6, 20 °C) δ −140.3 (br, 4F),
−147.9 (d, 3JFF = 20 Hz, 2F), −154.9 (br, 2F), −156.1 (t, 3JFF = 20 Hz,
1F), −162.1 (br, 2F), −162.7 (br, 2F), −163.7 (m, 2F). Anal. Calcd
for C44H31F15MoN3O1.5: C, 52.50; H, 3.10; N, 4.17. Found: C, 52.82;
H, 3.29; N, 4.04.
1
Mo(NAr′)(CHCMe2Ph)(Me2Pyr)(DFTO) (2c). Mo(NAr′)-
(CHCMe2Ph)(Me2Pyr)2 (130 mg, 0.242 mmol) was suspended in
toluene (5 mL). The suspension was cooled to −30 °C, and DFTOH
(103 mg, 0.242 mmol) was added at −30 °C. The mixture was
warmed to room temperature. After 1 h, the solvent was removed in
vacuo to give a dark red oily product. Pentane (2 mL) was added, the
mixture was stirred for 30 min to give a homogeneous reddish
solution, and MeCN (3 drops) was added. The brownish precipitate
was recrystallized from a mixture of ether and pentane to give 2c as a
yellow solid; yield 162 mg (76%): 1H NMR (500 MHz, C6D6, 20 °C)
(190 mg, 88%): H NMR (500 MHz, C6D6, 20 °C) δ 11.08 (s, 1H,
3
3
MoCH), 7.02 (m, 6H), 6.92 (t, JHH = 12 Hz, 1H), 6.77 (t, JHH
=
3
12 Hz, 2H), 6.58 (d, JHH = 12 Hz, 2H), 1.57 (s, 2H), 1.14 (s, 6H),
1.08 (s, 6H), 0.97 (s, 6H); 19F NMR (282 MHz, C6D6, 20 °C) δ
−139.6 (m, 4F), −140.1 (m, 4F), −155.1 (t, 3JFF = 21 Hz, 4F), −162.1
(m, 4F), −162.5 (m, 4F); 13C{1H} NMR (125 MHz, C6D6, 20 °C) δ
280.0 (s, 1C, MoC), 162.967, 149.5, 144.7 (d, 1JCF = 247 Hz), 141.4
(d, 1JCF = 254 Hz), 138.2 (d, 1JCF = 247 Hz), 133.7 (m), 126.5, 121.6,
117.8, 115.0, 112.7, 78.8, 53.1, 50.1, 43.6 (m), 35.1 (m), 31.6, 29.7
(m). Anal. Calcd for C56H33F20MoNO2: C, 54.78; H, 2.71; N, 1.14.
Found: C, 54.82; H, 2.61; N, 1.20.
δ 12.08 (s, 1H, MoCH), 7.13 (d, 3JHH = 7.5 Hz, 2H), 6.99 (d, JHH
3
3
3
= 7.5 Hz, 2H), 6.91 (d, JHH = 7.5 Hz, 2H), 6.88 (d, JHH = 7.5 Hz,
1H), 6.82 (d, 3JHH = 7.5 Hz, 1H), 6.61 (d, 3JHH = 7.5 Hz, 1H), 6.53 (d,
3JHH = 7.5 Hz, 2H), 5.85 (br, 2H), 1.93 (br, 6H), 1.69 (br, 6H), 1.30
(s, 3H), 1.24 (s, 3H); 19F NMR (282 MHz, C6D6, 20 °C) δ −139.8
(dm, 3JFF = 23 Hz, 2F), −140.6 (dm, 3JFF = 23 Hz, 2F), −153.9 (t, 3JFF
Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(HMTO) (2a). Mo(NC6F5)-
(CHCMe2Ph)(Me2Pyr)2 (300 mg, 0.502 mmol) was dissolved in
benzene (5 mL). HMTOH (183 mg, 0.557 mmol) was added, and the
mixture was heated to 70 °C. After 16 h, the solvent was removed in
vacuo to give a dark oily product. The residue was recrystallized from a
mixture of pentane and diethyl ether to give an orange solid; yield 259
= 23 Hz, 2F), −161.7 (m, 4F); 13C{1H} NMR (125 MHz, C6D6, 20
1
1
°C) δ 294.6 (s, 1C, MoC), 164.9, 155.8, 147.2, 144.7 (dm, JCF
=
mg (60%): H NMR (500 Hz, C6D6, 20 °C) δ 11.08 (s, 1H, Mo
242 Hz), 141.2 (dm, 1JCF = 252 Hz), 138.2(dm, 1JCF = 247 Hz), 133.7
(d, JCF = 22 Hz), 121.8, 117.6, 115.9, 112.5, 109.9 (br), 100.9, 55.2,
30.6, 17.6, 14.2. Crystals of 2c′, the MeCN adduct, were obtained from
a mixture of diethyl ether and MeCN. Anal. Calcd for
C42H32F10MoN2O: C, 58.22; H, 3.89; N, 4.64. Found: C, 58.51; H,
4.19; N, 4.26.
3
CH), 7.24 (d, J = 8 Hz, 2H), 6.94 (m, 3H), 6.88(m, 2H), 6.79 (s,
2H), 6.73 (s, 2H), 6.69 (m, 1H), 6.07 (s, 2H), 2.05 (d, J = 10.5 Hz,
12H), 1.98 (br, 12H), 1.36 (d, J = 11.3 Hz, 6H); 19F NMR (282 Hz,
3
3
C6D6, 20 °C) δ −145.7 (d, 2F, J = 23 Hz, o-Ar), −159.4 (t, 1F, J =
24 Hz, p-Ar), −165.0 (t, 2F, J = 23 Hz, m-Ar); 13C{1H} NMR (125
3
MHz, C6D6, 20 °C) δ 295.3 (s, 1C, MoC), 157.9, 148.4, 143.0(d,
1JCF = 245 Hz), 139.4(d, 1JCF = 260 Hz), 136.9, 136.8, 136.4, 135.5 (d,
1JCF = 235 Hz), 135.2, 134.7, 131.9, 129.8, 129.1, 127.3, 126.0, 123.4,
109.7, 155.5, 34.4, 32.5, 28.6, 22.7, 21.1, 19.9, 16.8, 14.4. Anal. Calcd
for C46H45F5MoN2O2: C, 66.34; H, 5.45; N, 3.36. Found: C, 66.27; H,
5.49; N, 3.33.
Mo(NC6F5)(CH2CH2)(DFTO)2 (3). Mo(NC6F5)(CHCMe2Ph)-
(DFTO)2 (138 mg, 0.119 mmol) was dissolved in ether (10 mL).
The Schlenk bomb was freeze−pump−thawed three times. Ethylene
(1 atm) was added. After the mixture was stirred at room temperature
for 16 h, the orange solution turned dark purple. The solvent was
removed, and pentane (1 mL) was added. The mixture was stirred to
30 min to give a purple solid, cooled to −30 °C overnight, and filtered.
The purple solid was washed with cold pentane and dried in vacuo;
yield 105 mg (76%): 1H NMR (500 MHz, tol-d8, 20 °C) δ 6.95 (d, 3J
= 8 Hz, 4H), 6.78 (t, 3J = 8 Hz, 2H), 2.48 (dt, J = 8 Hz, J = 5 Hz, 2H,
CH2CH2), 1.33 (dt, J = 8 Hz, J = 5 Hz, 2H, CH2CH2); 19F NMR
(282 MHz, tol-d8, 20 °C) δ −140.7 (d, 3JFF = 22 Hz, 8F, o-F), −150.7
Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(DFTO) (2b). Mo(NC6F5)-
(CHCMe2Ph)(Me2Pyr)2 (300 mg, 0.491 mmol) was dissolved in
MeCN (10 mL), and DFTOH (209 mg, 0.491 mmol) was added as a
solid at room temperature. After 16 h, the solvent was removed in
vacuo to give an orange oily product. Diethyl ether (1 mL) was added,
and the mixture was stirred for 30 min to give an orange solid of
Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(DFTO)(MeCN) (356 mg,
75%). The solid was dissolved in toluene, and the solvent was
removed in vacuo. This step was repeated 10 times to remove MeCN
3
(d, JFF = 25 Hz, 2F, o-F of NC6F5), −154.8 (m, 5F), −162.3 (m,
10F); 13C{1H} NMR (125 MHz, tol-d8, 20 °C) δ 161.5, 144.4 (dm,
1JCF = 246 Hz, 8C, DFTO), 142.9 (dm, JCF =253 Hz, 2C, NC6F5),
1
1
and give 2b as a red foam (341 mg): H NMR (500 MHz, C6D6, 20
141.2 (dm, 1JCF = 255 Hz, 4C, DFTO), 140.5 (dm, 1JCF = 255 Hz, 1C,
NC6F5), 138.2 (dm, 1JCF = 253 Hz, 8C, DFTO), 137.3 (dm, 1JCF = 255
Hz, 2C, NC6F5), 133.8 (m), 122.5 (m), 118.2, 112.3 (td, 9 Hz, 4 Hz),
°C) δ 11.64 (br, 1H, MoCH), 7.13 (d, 3JHH = 7.5 Hz, 2H), 6.99 (d,
3JHH = 7.5 Hz, 2H), 6.88 (t, 3JHH = 7.5 Hz, 1H), 6.79 (brt, 3JHH = 7 Hz,
3
1
2H), 6.60 (brt, JHH = 7 Hz, 1H), 5.68 (br, 2H), 2.01 (br, 6H), 1.29
61.1 (CH2CH2); H NMR (500 MHz, tol-d8, −80 °C) δ 7.05 (br,
(br, 3H), 1.05 (s, 3H); 19F NMR (282 MHz, C6D6, 20 °C) δ −140.0
4H), 6.81 (br, 2H), 2.60 (br, 1H), 2.19 (br, 1H), 1.85 (br, 1H), 0.81
(br, 1H); 19F NMR (282 MHz, tol-d8, −80 °C) δ −140.0 (1F),
−141.2 (1F), −142.1 (1F), −142.3 (1F), −143.3 (4F), −151.5 (1F),
−152.0 (2F), −154.5 (2F), −154.8 (2F), −159.7 (1F), −161.4 (1),
−162.4 (5F), −163.5 (2F), −164.2 (1F). Anal. Calcd for
C44H10F25MoNO2: C, 45.74; H, 0.87; N, 1.21. Found: C, 45.79; H,
1.06; N, 1.26.
3
(br, 2F), −140.4 (br, 2F), −148.0 (d, JFF = 20 Hz, 2F), −154.7 (br,
3
2F), −156.5 (t, JFF = 20 Hz, 1F), −162.1 (br, 2F), −162.8 (br, 2F),
−163.8 (m, 2F); 13C{1H} NMR (125 MHz, C6D6, 20 °C) δ 298.8 (br,
1
1
MoC), 165.3, 147.6, 144.6 (dm, JCF = 246 Hz), 142.8 (dm, JCF
=
241 Hz), 141.4 (dm, 1JCF = 246 Hz), 140.5 (dm, 1JCF = 246 Hz), 138.4
(dm, JCF = 249 Hz), 137.4 (dm, JCF = 251 Hz), 133.9, 133.6, 131.3
1
1
(t, 15 Hz), 126.7, 126.4, 122.1, 117.7, 112.3, 110.2, 55.7, 29.1, 15.7
Mo(NC6F5)(CH2CH2)(DCMNBD)(DFTO)2 (5). Mo(NC6F5)-
(CH2CH2)(DFTO)2 (40 mg, 0.0341 mmol) was dissolved in
C6D6 (0.5 mL). DCMNBD (7.1 mg, 0.0341 mol) was added as a
solution in C6D6 (0.071 mL, 100 mg/mL). After 16 h, reddish orange
1
(br); H NMR (500 MHz, CDCl3, 20 °C) δ 11.59 (br, 1H, Mo
3
3
CH), 7.37 (d, JHH = 7 Hz, 2H), 7.19 (t, JHH = 8 Hz, 1H), 7.12 (d,
3JHH = 7.5 Hz, 2H), 7.06 (t, 3JHH = 7.5 Hz, 2H), 6.93 (t, 3JHH = 7.5 Hz,
1H), 5.73 (br, 2H), 2.00 (br, 6H), 1.41 (s, 3H), 1.25 (s, 3H); 19F
NMR (282 MHz, CDCl3, 20 °C) δ −139.4 (br, 2F), −140.1 (br, 2F),
−147.2 (d, 3JFF = 20 Hz, 2F), −154.4 (br, 2F), −155.8 (t, 3JFF = 20 Hz,
1F), −161.9 (br, 2F), −162.5 (br, 2F), −163.3 (m, 2F). The foamlike
solid was recrystallized from a mixture of acetonitrile, diethyl ether,
and pentane to give analytically pure orange crystals of Mo(NC6F5)-
(CHCMe2Ph)(Me2Pyr)(DFTO)(MeCN)(Et2O)0.5: 1H NMR (500
1
crystals were formed (27 mg, 57%): H NMR (500 MHz, C6D6, 20
°C) δ 7.16 (d, J = 8 Hz, 2H), 7.10 (br, 2H), 6.89 (br, 2H), 6.79 (br,
1H), 6.72 (t, J = 8 Hz, 1H), 3.91 (s, 1H), 3.85 (s, 1H), 3.73 (s, 3H),
3.07 (td, J = 12 Hz, J = 4 Hz, 1H, CH2CH2), 2.72 (td, J = 12 Hz, J =
4 Hz, 1H, CH2CH2), 2.39 (s, 3H, OMe), 2.45 (d, 8 Hz, 1H), 1.94
(d, 8 Hz, 1H), 1.77 (td, J = 12 Hz, J = 4 Hz, 1H, CH2CH2), 1.43
(td, J = 12 Hz, J = 4 Hz, 1H, CH2CH2); 19F NMR (282 MHz, C6D6,
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dx.doi.org/10.1021/om400199u | Organometallics 2013, 32, 2983−2992

Organometallics
Article
20 °C) δ −133.3 (br, 1F), −137.3 (br, 1F), −140.9 (s, 2F), −145.3
(br, 1F), −150.5 (s, 1F), −151.5 (s, 1F), −152.0 (s, 1F), 154.6 (s, 1F),
−156.2 (s, 1F), −157.0 (m, 2F), −158.9 (br, 2F), −162.3 (bs, 4F),
−163.9 (m, 4F). Compound 5 slowly decomposes in the solid state at
room temperature and therefore could not be analyzed.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Observation of Mo(NC6F5)(13CH213CH213CH2)(DFTO)2 (4*).
Mo(NC6F5)(CHCMe2Ph)(DFTO)2 (10 mg) was dissolved in C6D6
(0.5 mL) in a J. Young NMR tube. The solution was freeze−pump−
R.R.S. thanks the National Science Foundation (CHE-
1111133) and the Department of Energy (DE-FG02-
86ER13564) for supporting this research. The Department of
Chemistry thanks the NSF (CHE-9808061) for funds to
purchase a 500 MHz NMR instrument and an X-ray
diffractometer (CHE-0946721).
13
thawed three times. 13CH2 CH2 (<1 atm) was added. After 5 min,
all of the starting material was consumed and 4* was formed in
addition to Mo(NC6F5)(13CH213CH213CH2)(DFTO)2: 1H NMR (500
MHz, C6D6, 20 °C) δ 3.67 (brd, JCH = 165 Hz, 2H, α-H), 3.55 (brd,
JCH = 155 Hz, 2H, α-H), −0.72 (brd, JCH = 154 Hz, 1H, β-H), −1.33
(brd, JCH = 154 Hz, 1H, β-H); 13C{1H} NMR (125 MHz, C6D6, 20
°C) δ 102.5 (Cα), −3.1 (Cβ).
REFERENCES
■
Mo(NC6F5)(13CH213CH213CH213CH2)(DFTO)2 (Observation).
Mo(NC6F5)(13CH213CH2)(DFTO)2 (10 mg, 0.00852 mmol) was
dissolved in C6D6 (0.5 mL) in a J. Young NMR tube. The solution was
(1) (a) Schrock, R. R. Angew. Chem., Int. Ed. 2006, 45, 3748.
(b) Grubbs, R. H. Angew. Chem., Int. Ed. 2006, 45, 3760. (c)
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Germany, 2003; Vols. 1−3. (d) Schrock, R. R. Chem. Rev. 2009, 109,
3211.
13
freeze−pump−thawed three times. 13CH2 CH2 was added through
vacuum transfer. After 2 days, about 1% 13C-labelled Mo(NC6F5)-
(CH2CH2CH2CH2)(DFTO)2 was formed: 13C{1H} NMR (125 MHz,
C6D6, 20 °C) δ 82.9 (m, AA′BB′, Cα), 39.9 (m, AA′BB′, Cβ).
Mo(NC6F5)(13CH213CH2-norbornene)(DFTO)2 (Observation).
Mo(NC6F5)(13CH213CH2)(DFTO)2 (10 mg, 0.00852 mmol) was
dissolved in toluene-d8 (0.5 mL) in a septum-capped tube and cooled
to −78 °C. Norbornene (0.8 mg, 0.00852 mmol) was added as a
solution in toluene-d8 (0.5 mL) drop by drop. The NMR tube was
inserted into a −70 °C NMR. After 1 h, 69% of the product was
formed: 13C{1H} NMR (125 MHz, C6D6, 20 °C) δ 84.7 (d, 1JCC = 37
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(c) Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem.
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1
Hz, MoCα), 46.6 ppm (d, JCC = 37 Hz, Cβ).
Mo(NC6F5)(CHCHCMePh)(DFTO)2 (Observation). Mo(NC6F5)-
(CH2CH2)(DFTO)2 (10 mg, 0.00853 mmol) was dissolved in toluene
(4 mL), and the solution was cooled to −78 °C. MPCP (1.11 mg,
0.00853 mmol) was added dropwise as a solution in toluene (1 mL).
The purple color changed to orange immediately. After 1 h, the
mixture was warmed to room temperature and the solvent removed to
R. R.; Muller, P.; Takase, M. K.; Hoveyda, A. H. Organometallics 2011,
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30, 1780. (h) Yu, M.; Ibrahem, I.; Hasegawa, M.; Schrock, R. R.;
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1
give an oily orange product (12 mg): H NMR (500 MHz, C6D6, 20
°C) δ 12.10 (dd, 1JCH = 130 Hz, 3JHH = 9 Hz, MoCH), 8.33 (dd, 1JCH
3
̈
= 159 Hz, JHH = 9 Hz, β-H), the other resonances overlap with
polymer resonances; 13C{1H} NMR (125 MHz, C6D6, 20 °C) δ 264.5
(s, Cα), 136.0 (s, Cβ).
Procedure for ROMP of DCMNBD. The initiator (1 mg) was
dissolved in CDCl3 (0.5 mL). DCMNBD (100 equiv) was added as a
solution in CDCl3 (0.5 mL). After 30 min, benzaldehyde (0.1 mL) was
added to the mixture. The reaction mixture became deep green within
5 min and was stirred for 1 h. The entire mixture was added dropwise
to 100 mL of vigorously stirred methanol. A fine white solid formed
immediately. After 2 h the polymer was filtered off, rinsed with MeOH,
and dried in vacuo.
̈
Schrock, R. R.; Muller, P. Organometallics 2008, 27, 6570. (b) Jiang, A.
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J. Am. Chem. Soc. 2009, 131, 58.
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Measurement of Conversion of DCMNBD by 3. DCMNBD
̈
(50 mg, 0.240 mmol) and an internal standard of anthracene were
1
27, 4428. (b) Marinescu, S. C.; King, A. J.; Schrock, R. R.; Singh, R.;
dissolved in CDCl3 in a J. Young NMR tube. A H NMR spectrum
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̈
was obtained. A 12.0 mM solution of 3 was prepared, and 0.2 mL (2.4
μmol) was added to the NMR tube. The tube was inverted to mix, and
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Hoveyda, A. H. Organometallics 2004, 23, 1997.
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1
the tube was then heated to 50 °C. H NMR spectra were obtained
over 120 h. Conversion was measured by integration of the olefinic
resonance of DCMNBD against the anthracene internal standard.
ASSOCIATED CONTENT
■
(11) O’Donoghue, M. B.; Schrock, R. R.; LaPointe, A. M.; Davis, W.
M. Organometallics 1996, 15, 1334.
(12) Singh, R. Ph.D. thesis, Massachusetts Institute of Technology,
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S
* Supporting Information
Figures S1−S3 and text, tables, and CIF files giving
crystallographic details and data for 2b′, 3, and 5. This material
is available free of charge via the Internet at http://pubs.acs.org.
(14) Binger, P.; Muller, P.; Benn, R.; Mynott, R. Angew. Chem., Int.
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Ed. Engl. 1989, 28, 610.
AUTHOR INFORMATION
■
(15) (a) De la Mata, F. J.; Grubbs, R. H. Organometallics 1996, 15,
577. (b) Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc.
1993, 115, 8130.
Corresponding Author
*E-mail for R.R.S.: rrs@mit.edu.
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