Synthesis of tungsten oxo alkylidene complexes

Article abstract of DOI:10.1021/om3008579

Reaction of W(O)₂(CH₂-t-Bu)₂(bipy) with a mixture of ZnCl₂(dioxane), PMe₂Ph, and trimethylsilyl chloride in toluene at 100 °C produced the known tungsten oxo alkylidene complex W(O)(CH-t-Bu)Cl₂

Full text of DOI:10.1021/om3008579

Article
pubs.acs.org/Organometallics
Synthesis of Tungsten Oxo Alkylidene Complexes
Dmitry V. Peryshkov and Richard R. Schrock*
Department of Chemistry 6-331, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
S
* Supporting Information
ABSTRACT: Reaction of W(O)2(CH2-t-Bu)2(bipy) with a mixture of
ZnCl2(dioxane), PMe2Ph, and trimethylsilyl chloride in toluene at 100 °C
produced the known tungsten oxo alkylidene complex W(O)(CH-t-Bu)-
Cl2(PMe2Ph)2 (1a) in 45% isolated yield. The neophylidene analogue
W(O)(CHCMe2Ph)Cl2(PMe2Ph)2 was prepared similarly in 39% yield. The
reaction between 1a and LiOR (LiOR = LiOHIPT, LiOHMT) in benzene at 22
°C led to formation of the off-white W(O)(CH-t-Bu)Cl(OR)(PMe2Ph)
complexes 4a (OR = OHMT = 2,6-dimesitylphenoxide) and 4b (OR = OHIPT = 2,6-(2,4,6-triisopropylphenyl)2phenoxide).
Compound 4a serves as a starting material for the synthesis of W(O)(CH-t-Bu)(OHMT)(2,6-diphenylpyrrolide) (6),
W(O)(CH-t-Bu)[N(C6F5)2](OHMT)(PMe2Ph) (7), W(O)(CH-t-Bu)[OSi(t-Bu)3](OHMT) (8), and W(O)(CH-t-Bu)-
(OHMT)2 (10). The reaction between 8 and ethylene was found to yield the square-pyramidal metallacyclobutane complex
W(O)(C3H6)[OSi(t-Bu)3](OHMT) (9), while the reaction between 10 and ethylene was found to yield the square-pyramidal
metallacyclobutane complex W(O)(C3H6)(OHMT)2 (11). Compound 11 loses ethylene to yield isolable W(O)(CH2)-
(OHMT)2 (12). X-ray structures were determined for 6, 7, 9, and 12.
Z-selective MAP catalysts have been O-2,6-(2,4,6-triisopropyl-
phenyl)2C6H3 (OHIPT)9 and O-2,6-Mesityl2C6H3 (OHMT).10
It has been proposed that the high steric demands of these
hexasubstituted 2,6-terphenoxide ligands force all substituents
on the metallacyclobutane ring to point away from the bulky
aryloxide ligand and therefore allow only Z products to form.
Since an oxo ligand is smaller than any NR ligand, we wanted
to know whether MAP versions of tungsten oxo alkylidene
complexes would be useful Z-selective catalysts, to what degree
the behavior of oxo alkylidene complexes as olefin metathesis
catalysts might differ from the behavior of imido alkylidene
complexes as olefin metathesis catalysts, and what ligands
would be required to stabilize oxo alkylidene complexes against
bimolecular decomposition reactions.
In 1996 we showed that W(O)(CH-t-Bu)L2Cl2 complexes
(L = PMe3 or other phosphines) would react with 2 equiv of
KO-2,6-Ph2C6H3 to yield W(O)(CH-t-Bu)(O-2,6-
Ph2C6H3)2(L) complexes, one of which was shown to be a
trigonal-bipyramidal complex containing an equatorial oxo, an
alkylidene, and one O-2,6-Ph2C6H3 ligand.6 More recently,11
we showed that a similar approach could be employed in order
to prepare W(O)(CH-t-Bu)(Cl)(OHIPT) and W(O)(CH-t-
Bu)(Cl)(OHMT)(PMe2Ph) and their 2,5-dimethylpyrrolide
derivatives W(O)(CH-t-Bu)(Me2Pyr)(OHIPT) and W(O)-
(CH-t-Bu)(Me2Pyr)(OHMT)(PMe2Ph). In line with the
theory of Z-selectivity described above, W(O)(CH-t-Bu)-
(Me2Pyr)(OHMT)(PMe2Ph) was shown to be a highly
effective catalyst for the Z-selective coupling of several terminal
olefins (at 0.2% loading) to give product in >75% yield with
>99% Z configuration. Addition of 2 equiv of B(C6F5)3 to
INTRODUCTION
■
Tungsten has figured prominently in the history of the olefin
metathesis reaction, which is the only way to prepare olefins
from olefins directly and catalytically.1,2 Oxo alkylidene
complexes were the first high-oxidation-state alkylidene
complexes containing tungsten to be identified as olefin
metathesis catalysts,3 but attention soon shifted to imido
alkylidene complexes of W, and ultimately Mo, in anticipation
of slowing bimolecular decomposition of 14-electron four-
coordinate M(NR)(CHR′)X2 catalysts, relative to hypothetical
M(O)(CHR′)X2 catalysts, for steric reasons.4 Unlike oxo
ligands, imido ligands, along with X ligands (e.g., alkoxides),
can be varied sterically and electronically and the chemistry of
Mo and W imido alkylidene complexes in olefin metathesis
reactions thereby controlled to a significant degree. For the last
25 years, imido alkylidene complexes have been the mainstay of
high-oxidation-state olefin metathesis catalysts. In contrast,
interest in oxo alkylidene complexes has been limited.5,6 Oxo
alkylidene complexes or oxo-free cationic complexes of the type
discovered by Osborn2 are likely to be the active catalysts in
many of the “classical” olefin metathesis systems. Therefore, we
thought it worthwhile to attempt to prepare oxo alkylidene
complexes using recently proven methods that have been
employed to slow bimolecular decomposition of imido
alkylidene complexes.
The most recent advance in Mo and W imido alkylidene
chemistry has been the discovery and development of
M(NR)(CHR′)(OR″)(Pyrrolide) (monoaryloxide pyrrolide
or MAP) complexes.7 One of the most interesting aspects of
MAP catalysts is that they can be designed to promote Z-
selective metathesis reactions as a consequence of the presence
of a relatively “large” aryloxide (OR″) in combination with a
“small” NR ligand.8 The most successful OR″ ligands so far in
Received: September 4, 2012
Published: October 2, 2012
© 2012 American Chemical Society
7278
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
W(O)(CH-t-Bu)(Me2Pyr)(OHMT)(PMe2Ph) led to forma-
tion of the adduct W[OB(C6F5)3](CH-t-Bu)(Me2Pyr)-
(OHMT), which was found to be highly active for olefin
metathesis, but gave the E:Z mixture expected from
thermodynamic control upon coupling terminal olefins. How
oxo alkylidene complexes behave in the presence of Lewis acids,
an issue that was explored by Osborn2 to some degree and that
remains unexplored as far as well-defined catalysts are
concerned, is an important goal that is relevant to “classical”
catalysts, as discussed above, and to new isolable oxo alkylidene
complexes.
aqueous workup in air of the crude product led to air-stable
W(O)2R2(bipy) complexes in good yields.
A starting material more convenient than W(O)2Br2 is
W(O)2Cl2, which can be prepared on a large scale in a reaction
between tungsten hexachloride and hexamethyldisiloxane in
dichloromethane.16 Pale yellow W(O)2Cl2(bipy) (2)16a,b can
be prepared on a large scale in essentially one step from WCl6
through addition of bipyridine to a dichloromethane solution of
W(O)2Cl2(DME) (DME = dimethoxyethane) (eq 2). Addition
A simpler synthesis of tungsten oxo alkylidene starting
materials would be beneficial to further studies of oxo
alkylidene chemistry. In this paper we report a simplified
synthesis of tungsten oxo alkylidene complexes that involves
formation of the neopentylidene ligand on tungsten through α
hydrogen atom abstraction in a dineopentyl precursor and
elaborate the syntheses of tungsten oxo alkylidene complexes
that are relevant to olefin metathesis. We also for the first time
prepare and characterize oxo metallacyclobutane and oxo
methylidene complexes.
RESULTS
■
New Synthesis of Oxo Alkylidene Complexes of
Tungsten. The original synthesis of W(O)(CH-t-Bu)-
Cl2(PMe2Ph)2 (1a) and related bis-phosphine complexes3
was based on synthesis of a tantalum neopentylidene complex
and transfer of the neopentylidene ligand from tantalum to
tungsten, as shown in eq 1. Ta(CH-t-Bu)Cl2(PMe2Ph)2 is
of 3.7 equiv of neopentylmagnesium chloride to a solution of 2
in THF results in the formation of dark red solutions. After
aqueous aerobic workup analogous to that reported by
Schrauzer,15 yellow W(O)2(CH2-t-Bu)2(bipy) (3a) can be
isolated in 70% yield. Similar reactions employing
PhMe2CH2MgCl led to W(O)2(CH2CMe2Ph)2(bipy) (3b) in
70% yield. Proton NMR spectra are consistent with 3a,b having
C2v symmetry with the two oxo ligands cis to each other and
trans to bipy. All structurally characterized M(O)2R2(bipy)
complexes (M = Mo, W) have this basic structure.15,17
Furstner showed that bipy can be removed from
̈
molybdenum imido alkylidene or alkylidyne complexes through
addition of zinc chloride and catalysts for olefin or acetylene
metathesis thereby generated in situ.18 Bipy complexes also can
be useful intermediates in synthesis, as we have shown recently
for some molybdenum-based MAP complexes.19 Treatment of
3a with a mixture containing 1 equiv of ZnCl2(dioxane),
slightly less than 2 equiv of of PMe2Ph, and 2 equiv of
trimethylsilyl chloride (TMSCl) in toluene at 100 °C for 2 h
led to the formation of the tungsten oxo alkylidene complex
W(O)(CH-t-Bu)Cl2(PMe2Ph)2 (1a), hexamethyldisiloxane,
neopentane, and ZnCl2(bipy) (eq 2). Double recrystallization
of the crude product from a mixture of diethyl ether and
tetrahydrofuran gave 1a in 45% isolated yield. The neo-
phylidene analogue W(O)(CHCMe2Ph)Cl2(PMe2Ph)2 (1b)
was prepared in a similar manner and isolated in 39% yield as a
yellow solid. Like 1a, 1b is a syn alkylidene on the basis of the
formed readily upon addition of PMe2Ph to a solution of
Ta(CH2-t-Bu)3Cl2 in pentane. The synthesis of Ta(CH2-t-
Bu)3Cl2 from TaCl5 and Zn(CH2-t-Bu)2 in pentane is also
straightforward, but Zn(CH2-t-Bu)2 must be prepared and
purified for this purpose. W(O)(O-t-Bu)4 can be synthesized in
modest yield in a reaction between W(O)Cl4 and LiO-t-Bu and
isolated through sublimation. Therefore, synthesis of W(O)-
(CH-t-Bu)Cl2L2 complexes (L = a phosphine) is somewhat
lengthy and “indirect”: i.e., the alkylidene is not prepared on
tungsten.
Alternative methods of forming tungsten oxo alkylidene
complexes have included oxidation of W(II) and W(IV)
complexes and hydrolysis of W(VI) alkylidynes.12,15 Although
it would be most desirable to prepare oxo alkylidenes through
alkylation of W(O)Cl4, direct alkylation of W(O)Cl4 with
lithium, magnesium, and zinc alkyls has been found to lead to
complex mixtures in which the oxo group has been removed
from the metal and/or the metal has been reduced.2,13 Several
tungsten d0 oxo alkyl complexes are known,2,14,15 but they
generally cannot be synthesized through direct alkylation for
the reasons just stated. What could be called exceptions are
reactions between W(O)2Br2(bipy) (bipy = 2,2′-bipyridine)
and Grignard reagents developed and explored by Schrauzer’s
group.15 Although alkylations of W(O)2Br2(bipy) with methyl,
ethyl, propyl, and neopentyl Grignard reagents led to dark
mixtures that probably contain reduced metal complexes,
JCH value for the alkylidene (126 Hz). The two phosphine
α
ligands are equivalent and remain bound to tungsten on the
NMR time scale at 22 °C with JPW = 333 Hz. The new
synthesis of W(O)(CHR)Cl2(PMe2Ph)2 complexes consists of
three relatively simple steps starting from tungsten hexa-
chloride, which is a significant improvement over the existing
method shown in eq 1.
The mechanism of formation of the alkylidene in 1a,b is
proposed to involve attack on one of the oxo ligands in
W(O)2(CH2R)2(bipy) (R = t-Bu, CMe2Ph) successively by 2
equiv of TMSCl to give TMS2O and a W(O)-
Cl2(CH2R)2(bipy) intermediate, from which CH3R is lost to
7279
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
give W(O)(CHR)Cl2(bipy). Intramolecular abstraction of an α
proton in the alkyl group becomes possible after one oxo ligand
is replaced by two chlorides,4 especially in the presence of a
ligand that could promote α abstraction in an 18-electron,
seven-coordinate intermediate. We cannot exclude the
possibility that α abstraction takes place in an intermediate
W(O)Cl(OSiMe3)(CH2R)2(bipy) species followed by replace-
ment of the trimethylsiloxide with chloride upon further
reaction with TMSCl. Although treatment of W(O)2(CH2-t-
Bu)2(bipy) with only 2 equiv of TMSCl leads to a product
mixture whose NMR spectra are consistent with the major
product being W(O)(CH-t-Bu)Cl2(bipy), we have not been
able to obtain this compound in pure form. The one-step
conversion of 3a,b to 1a,b is more convenient in any case.
Synthesis of Oxo Alkylidene Derivatives. The reaction
between 1a and LiOR (LiOR = LiOHIPT, LiOHMT) in
benzene at 22 °C led to formation of the off-white W(O)(CH-
t-Bu)Cl(OR)(PMe2Ph) complexes 4a (OR = OHMT) and 4b
(OR = OHIPT), each as a mixture of two syn alkylidene
isomers.11 The phosphine remains bound to tungsten on the
NMR time scale at 22 °C in both 4a and 4b. Addition of
LiMe2Pyr to 4a,b led to isolation of W(O)(CH-t-Bu)(η1-
Me2Pyr)(OHMT)(PMe2Ph) (5a) and W(O)(CH-t-Bu)(η1-
Me2Pyr)(OHIPT) (5b), both of which were characterized
through X-ray studies.11 Phosphine-free 5b is formed as a
consequence of the greater steric demand of the OHIPT versus
that of the OHMT ligand. The structure of 5a is a square
pyramid with a syn neopentylidene in the apical position and
the phosphine bound trans to the pyrrolide.11 The equilibrium
constant for phosphine dissociation in 5a was estimated to be
0.015 M at room temperature through NMR studies, a value
that corresponds to 57% dissociation of phosphine-free
W(O)(CH-t-Bu)(η1-Me2Pyr)(OHMT) being present in a 20
mM solution of 5a in C6D6. The steric demand of the OHIPT
ligand limits the reactivity of 5b versus that of 5a in the few
reactions that were explored.11
(cf. 9.14 ppm in 5a11) with JCH = 124 Hz, which is
characteristic of a syn orientation of the alkylidene. Although
the alkylidene resonance is broadened slightly, the 183W
satellites are discernible (JHW = 10 Hz). The resonances for
the two protons on the pyrrolide ring are broad at room
temperature, which suggests either hindered rotation of the
diphenylpyrrolide ligand or an equilibrium between η1 and η5
coordination modes. Compound 6 apparently is too crowded
to coordinate dimethylphenylphosphine to give an adduct
analogous to 5a.11
Single crystals of 6 were grown from toluene/pentane
solution at −30 °C. A thermal ellipsoid drawing of the structure
is shown in Figure 1. The WO distance (1.690(1) Å) is
Figure 1. Thermal ellipsoid plot (50% probability) of W(O)(CH-t-
Bu)(Ph2Pyr)(OHMT) (6). Hydrogen atoms have been omitted for
clarity. Selected bond distances (Å) and angles (deg): W1−C1 =
1.895(2), W1−O1 = 1.690(1), W1−O2 = 1.894(1), W1−N1 =
2.037(2); W1−C1−C2 = 141.1(1), W1−O2−C6 = 143.1(1).
We have found 4a to be a suitable starting point for
formation of several other oxo alkylidene species, in addition to
5a, as shown in Scheme 1, most of which are obtained as 14e
comparable to the WO bond length in 5b (1.695(3) Å).11
The pyrrolide ligand is coordinated in η1 fashion with an
W−Npyr distance of 2.037(2) Å, versus the W−Npyr bond
length in 5b (2.001(2) Å). In Mo(NAr)(CH-t-Bu)(η1-2,5-
Ph2Pyr)(η5-2,5-Ph2Pyr),20 the Mo−Npyr bond length for the η1
pyrrolide is slightly longer (2.1145(10) Å) than in 5b, as one
might expect for an 18-electron complex. The W−NPyr vector
in 6 does not lie in the plane of the pyrrolide ligand: i.e., the
pyrrolide is tipped so that the angle between the W−NPyr
vector and the plane is 161.7°. This phenomenon has been
noticed in other high-oxidation-state pyrrolide complexes such
as trigonal-bipyramidal unsubstituted metallacyclobutane com-
plexes of Mo and W.21
Scheme 1
22
Treatment of 4a with LiN(C6F5)2 in CH2Cl2 led to
formation of W(O)(CH-t-Bu)[N(C6F5)2](OHMT)(PMe2Ph)
(7) in 60% isolated yield. The X-ray structure of 7 showed it to
be essentially a square pyramid with the syn alkylidene ligand in
the apical position and the phosphine ligand trans to the amide
(Figure 2). The amido nitrogen atom is not planar (the three
angles sum to 349.7(2)°), and one of the ortho fluorides (F1)
could be interacting weakly with the metal trans to the
alkylidene (W−F1 = 2.758(1) Å), which is not unusual in
compounds that contain the perfluorodiphenylamido ligand.22
(phosphine-free) species. Addition of 1 equiv of lithium 2,5-
diphenylpyrrolide to a toluene solution of W(O)(CH-t-
Bu)(OHMT)Cl(PMe2Ph) at room temperature led to the
formation of yellow W(O)(CH-t-Bu)(Ph2Pyr)(OHMT) (6) in
57% isolated yield. The α proton resonance for the alkylidene
resonance in the 1H NMR spectrum of 6 is found at 9.99 ppm
7280
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
ethylene in the WC3 ring on the NMR time scale. Only three
metallacycle resonances are observed for W(O)(C3H6)-
(OHMT)(Silox) in C6D6 (4.10, 2.54, and 1.93 ppm, 1:1:1
ratio); presumably three other resonances are obscured. Three
13C resonances can be attributed to the metallacycle at 43.8,
41.5, and 22.3 ppm. The range of chemical shifts of
metallacycle protons and carbons is indicative of square-
pyramidal (SP) coordination of the metal center found for
W(NAr)[CH2CH(t-Bu)CH2](O-t-Bu)2.23
Single crystals of 9 were grown from a mixture of toluene and
pentane at −30 °C. An X-ray structural study confirmed the
proposed SP configuration of 9, in which the oxo ligand is in
the apical position (Figure 3). To our knowledge, 9 is the first
Figure 2. Thermal ellipsoid plot (50% probability) of W(O)(CH-t-
Bu)[N(C6F5)2](OHMT)(PMe2Ph) (7). Hydrogen atoms have been
omitted for clarity. Selected bond distances (Å) and angles (deg):
W1−C1 = 1.898(2), W1−O1 = 1.710(2), W1−O2 = 1.965(1), W1−
N1 = 2.127(2), W1−P1 = 2.564(1); W1−C1−C2 = 141(2), W1−
O2−C6 = 154.0(1).
The amido ligand could also be said to be “tipped” out of
planarity, as found for the diphenylpyrrolide in 6. The broad
alkylidene resonance in 7 results from the phosphine
dissociating in solution at room temperature. A variable-
1
temperature H and 31P NMR study of a 74 mM solution of 7
in toluene-d8 showed that the phosphine is bound on the NMR
time scale below −20 °C (a sharp resonance is found at 2.69
ppm with JPW = 347 Hz), but in toluene at 22 °C Keq is ∼0.002
M, i.e., ∼50% of 7 is converted into W(O)(CH-t-Bu)[N-
(C6F5)2](OHMT) at 74 mM concentration. A Keq value of
0.002 should be compared with that for 5a (0.015 M) noted
earlier. At −20 °C, 10 broadened 19F resonances are observed
for 7, which suggests that the N(C6F5)2 ligand is not rotating
freely at −20 °C on the NMR time scale.
Figure 3. Thermal ellipsoid plot (50% probability) of square-
pyramidal W(O)(C3H6)(OHMT)(Silox) (9). Hydrogen atoms,
except for those on the metallacycle, have been omitted for clarity.
Only the major component of disorder is shown. Selected bond
distances (Å) and angles (deg): W1−C1 = 2.172(3), W1−C3 =
2.168(3), W1−O1 = 1.690(2), W1−O2 = 1.896(2), W1−O3 =
1.875(3), C1−C2 =1.527(4), C2−C3 = 1.522(4); W1−C1−C2 =
95.0(2), W1−C3−C2 = 95.4(2), C1−C2−C3 = 95.6(2), C1−W1−C3
= 62.7(1), O2−W1−O3 = 103.3(1), O1−W1−O2 = 113.6(1), O1−
W1−O3 = 113.4(1), W1−O2−C4 = 148.0(1), W1−O3−Si1 =
161.9(4).
Addition of 1 equiv of NaSilox to 4a at room temperature
resulted in formation of phosphine-free W(O)(CH-t-Bu)-
(OHMT)(Silox) (8) as essentially the only product, according
1
to H and 31P NMR data. However, 8 was too soluble in
structurally characterized metallacyclobutane derived from an
oxo alkylidene and the first unsubstituted high-oxidation-state
molybdacyclobutane or tungstacyclobutane that has a square-
pyramidal geometry. (All unsubstituted Mo or W imido
metallacyclobutane complexes have TBP geometries.23) The
bond lengths and bond angles in the WC3 ring in 9 are identical
with those in W(NAr)[CH2CH(t-Bu)CH2][OCMe2(CF3)]2
(within 3σ), as shown in Figure 4.23 The WC3 ring in 9 is
bent with a 33.8° dihedral angle between the C1−W−C3 and
C1−C2−C3 planes, in comparison to a 33.4° angle in
W(NAr)[CH2CH(t-Bu)CH2][OCMe2(CF3)]2.23 Relatively
long W−Cβ distances in SP metallacyclobutane complexes of
W (W···C2 = 2.762(3) Å in 9) have led to the proposal that SP
metallacyclobutane complexes are further from the transition
state for loss of olefin to give an alkylidene than are TBP
metallacycles.24
pentane to isolate on the small scale employed (150 mg).
Therefore, 8 was prepared from 250 mg of 4a and a solution of
it in pentane was exposed to 1 atm of ethylene; the
metallacyclobutane complex W(O)(CH2CH2CH2)(OHMT)-
(Silox) (9) crystallized out as light yellow crystals in 25%
isolated yield (eq 3). A 0.018 M solution of 9 in C6D6 under
dinitrogen was found to consist of 98% 9 and 2% of what is
proposed to be the methylidene complex W(O)(CH2)-
(OHMT)(Silox) (δ(CH2) at 7.77 and 8.93 ppm), formed
through loss of ethylene from 9. Heating a solution of 9 in
C6D6 to 70 °C led to broadening of the metallacycle proton
resonances and the appearance of free ethylene and broadened
methylidene resonances, consistent with facile exchange of
Addition of 1 equiv of LiOHMT to W(O)(CH-t-Bu)-
(OHMT)Cl(PMe2Ph) (100 °C, toluene) leads to formation of
W(O)(CH-t-Bu)(OHMT)2 (10) in good yield, but 10 is
prepared most conveniently in 41% isolated yield by treating
7281
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
Figure 4. Comparison of bond distances and angles in two SP
metallacyclobutane complexes.
W(O)(CH-t-Bu)Cl2(PMe2Ph)2 with 2 equiv of LiOHMT at
100 °C in toluene for 48 h. The resonance for the alkylidene
proton in the proton NMR spectrum of 10 is found at 7.34
1
2
ppm with JCH = 122 Hz and JHW = 14 Hz. Three mesityl
methyl resonances were observed for the OHMT ligands in the
proton NMR spectrum at 22 °C, consistent with the OHMT
ligands being equivalent, free rotation about the W−O bonds,
and (as one would expect) no rotation about the C−C bonds
to the central phenyl ring. The two sets of ortho mesityl methyl
groups arise from the fact that no symmetry plane bisects the
CWO angle in 10. Two other bis-2,6-terphenoxide
alkylidene complexes, M(NC6F5)(CHR)(ODFT)2 (M = Mo,
W; ODFT = O-2,6-(C6F5)2C6H3), have been reported in the
literature.25 The fluorine NMR spectra of M(NC6F5)(CHR)-
(ODFT)2 complexes show one para, two meta, and two ortho
fluorine resonances between 22 and 100 °C, which is consistent
with the proposals with respect to 10 discussed above.
When a pentane solution of 10 was placed under 1 atm of
ethylene, a yellow precipitate can be isolated whose proton
NMR spectrum in C6D6 shows that a mixture of W(O)-
(C3H6)(OHMT)2 (11) and W(O)(CH2)(OHMT)2 (12) in a
3:1 ratio is present. We propose that the precipitate is pure 11,
but upon dissolution in benzene some ethylene is lost from 11
to give the mixture of 11 and 12 in solution. Theoretical values
for % C and % H are too similar for 11 (68.00 and 6.27) and 12
(67.43 and 6.01) to confirm that the precipitate is pure 11
(found: C, 67.82; H, 6.29) through elemental analysis;
therefore, we have to rely on the fact that only 11 is sufficiently
insoluble to precipitate in the manner described. Compound 12
can be isolated in pure form through repeated dissolution of
mixtures of 11 and 12 in toluene followed by slow removal of
the solvent in vacuo (eq 4). Two methylidene doublet
Figure 5. Thermal ellipsoid plot (50% probability) of tetrahedral
W(O)(CH2)(OHMT)2 (12). Hydrogen atoms, except for those on
the methylidene, have been omitted for clarity. Only the major
component of disorder is shown. Selected bond distances (Å) and
angles (deg): W1−C1 = 1.895(8), W1−O1 = 1.694(5), W1−O2 =
1.881(2), W1−O3 = 1.917(2); W1−C1−H1A = 109(3), W1−C1−
H1B = 127(3), H1A−C1−H1B = 123(4), O1−W1−C1 = 103.1(3),
W1−O2−C2 = 136.3(2), W1−O3−C26 = 138.6(2).
methylidene ligands were found to be mutually disordered in
a ratio of 71:29. The disorder could be resolved and the
methylidene protons located in the major component; they
were refined semifreely with appropriate bond length restraints
(see the Supporting Information). The WC bond length
(1.895(8) Å) is similar to the MC distances in two
structurally characterized 14e imido methylidene MAP
complexes of Mo (1.892(5) Å) and W (1.908(4) Å).26 The
CH2 plane is tipped ∼9° relative to the OWC plane, as is
also found in the two Mo and W imido methylidene complexes
(by 8°). The WC1−H1a (Hanti) angle (109(3)°) is smaller
than the WC1−H1b (Hsyn) angle (127(3)°), consistent with
an agostic interaction between the CHanti bond and the metal
center and with the lower 2JCH values relative to 2JCH values.
anti
syn
The WO bond length (1.694(5) Å) is comparable to that in
W(O)(CH-t-Bu)(Me2Pyr)(HIPTO) (1.695(3) Å).11 The
planes of two phenolate rings of the terphenoxides intersect
at an angle of 81.5° with respect to each other. This nearly
“perpendicular” relationship of the two OHMT ligands
resembles a baseball cover and must hinder formation of the
bis-μ-methylidene intermediate required for bimolecular
decomposition yet not block access of ethylene to the metal
and formation of the square-pyramidal metallacyclobutane
complex 11.
1
DISCUSSION
resonances are observed in H NMR spectra of 12 in C6D6
■
at 8.90 ppm (Hsyn, 1JCH = 160 Hz, 2JHH = 10 Hz) and 7.85 ppm
The most interesting synthetic aspect of this work is the
preparation of relatively stable 14e or 16e tungsten oxo
alkylidene complexes with some variety. Bimolecular decom-
position must be discouraged primarily by the two anionic
ligands present, where at least one is a 2,6-terphenoxide
(OHMT in this work). Dimethylphenylphosphine is sometimes
retained in the product (as in 7) but is partially dissociated in
solution. All 14e tungsten oxo neopentylidene complexes have
been found to be the syn isomer, which is not surprising from a
steric point of view. It is interesting to note that reactions of the
type shown in Scheme 1 do not appear to suffer from
(Hanti,
1JCH = 140 Hz). The lower JCH value for Hanti is
consistent with a C−Hanti agostic interaction with the metal
center. Three mesityl methyl resonances are found in the
proton NMR spectrum at 22 °C, as noted above for 10.
Compound 12 was found to be stable in solution for at least 24
h at room temperature at a concentration of ∼20 mM.
An X-ray structural determination of 12 confirms that it is a
monomeric tetrahedral 14-electron species in the solid state
(Figure 5). To our knowledge, this is the first X-ray structural
study of an oxo methylidene complex. The oxo and
7282
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
of the mixture through Celite. A solution of 2,2′-bipyridine (10.33 g,
66.1 mmol, 1.05 equiv) in 30 mL of dichloromethane was added, and
the mixture was stirred for 30 min. The precipitate was isolated by
filtration, washed twice with 50 mL of dichloromethane, and dried
under vacuum. The pale yellow powder was collected (25.83 g, 58.3
mmol, 92% yield). Anal. Calcd for C10H8Cl2N2O2W: C, 27.10; H,
1.82; N, 6.32. Found: C, 26.27; H, 1.86; N, 5.97.
competitive deprotonation of the alkylidene ligand by the
added nucleophile, a problem that has been encountered in the
synthesis of certain stereogenic-at-metal imido alkylidene
complexes of molybdenum recently that contain sterically
demanding ligands.27
Another interesting feature of this work is that we have seen
no evidence for intermediate trigonal-bipyramidal metal-
lacyclobutane complexes, even unsubstituted metallacycles.
Therefore, it appears that square-pyramidal oxo metal-
lacyclobutane complexes are significantly more stable than the
TBP versions, in contrast to the case for many tungsten imido
analogues. This fact could have major implications in terms of
the ease of turnover in metathesis reactions, since SP
metallacycles are further from the transition state for loss of
olefin than TBP metallacycles, as noted earlier. Extensive
calculations on oxo alkylidene and metallacyclobutane com-
plexes have been reported recently.34
There are many aspects of oxo alkylidene chemistry that will
be explored in due course. One of the most interesting is the
role of Lewis acids in oxo alkylidene chemistry. In the
preliminary communication11 it was noted that W[OB-
(C6F5)3](CH-t-Bu)(Me2Pyr)(OHMT), which is in equilibrium
with W(O)(CH-t-Bu)(Me2Pyr)(OHMT) and B(C6F5)3 in
solution, could be structurally characterized and that it was
highly active for olefin metathesis. Therefore, we now have an
opportunity to move toward an understanding of the
consequence of Lewis acids being present in oxo alkylidene
systems. We anticipate being able to determine (inter alia)
whether the general intolerance of classical catalysts, which are
often prepared in the presence of Lewis acids, toward organic
electron donor functionalities is a consequence of basic
functionalities competing for the Lewis acid and thereby
deactivating the catalyst. Studies concerned with the role of
Lewis acids in oxo alkylidene chemistry are in progress.
Synthesis of W(O)2(CH2-t-Bu)2(bipy) (3a). Compound 3a was
prepared in a manner similar to the published procedure15 using
W(O)2Cl2(bipy) instead of W(O)2Br2(bipy) as a starting material. A
cold (−30 °C) solution of t-BuCH2MgCl in ether (40 mL, 1.66 M, 3.7
equiv) was added to a cold (−30 °C) suspension of W(O)2Cl2(bipy)
(8.00 g, 18.06 mmol) in 150 mL of THF. The reaction mixture was
stirred at room temperature for 1 h. Volatiles were removed under
vacuum, leaving a dark red residue. After addition of water (300 mL)
the mixture was periodically shaken with CH2Cl2 (200 mL) in air. The
organic fraction gradually changed color from green to yellow to
orange. The mixture was filtered through Celite. The aqueous layer
was separated and discarded. The organic layer was washed five times
with portions of water (150 mL), dried with anhydrous MgSO4, and
concentrated to 20 mL volume, causing formation of a yellow solid. A
portion of hexane (200 mL) was added, and the mixture was filtered.
The precipitate was recrystallized from dichloromethane/hexane. The
solid product was isolated by filtration and dried under vacuum (6.47
g, 12.57 mmol, 70% yield): 1H NMR (CD2Cl2) δ 9.55 (m, 2, bipy H),
8.39 (m, 2, bipy H), 8.15 (m, 2, bipy H), 7.58 (m, 2, bipy H), 0.94 (s,
18, CH2CMe3), 0.81 (s, 4, CH2CMe3, JWH = 8 Hz); 13C NMR
(CD2Cl2) δ 196.3, 152.0, 150.4, 139.2, 125.8, 123.6, 68.1, 34.9, 33.5.
Anal. Calcd for C20H30N2O2W: C, 46.71; H, 5.88; N, 5.45. Found: C,
46.79; H, 5.91; N, 5.47.
Synthesis of W(O)2(CH2CMe2Ph)2(bipy) (3b). The compound
was prepared in a manner analogous to that employed to prepare 3a. A
cold (−30 °C) solution of (CH3)2PhCCH2MgCl in ether (100 mL,
0.5 M, 3.7 equiv) was added to a cold (−30 °C) suspension of
W(O)2Cl2(bipy) (6.000 g, 13.55 mmol) in 80 mL of THF. The
reaction mixture was stirred at room temperature for 1 h. Volatiles
were removed under vacuum, leaving a dark red residue. After addition
of water (300 mL) the mixture was periodically shaken with CH2Cl2
(200 mL) in air. The organic fraction gradually changed color from
green to yellow. The mixture was filtered through Celite. The aqueous
layer was separated and discarded. The organic layer was washed five
times with portions of water (150 mL), dried with anhydrous MgSO4,
and concentrated to 20 mL volume, causing formation of a pale yellow
solid. A portion of hexane (150 mL) was added, and the mixture was
filtered. The precipitate was recrystallized from chloroform/hexane.
The solid product was isolated by filtration and dried under vacuum
(5.85 g, 9.16 mmol, 67% yield): 1H NMR (CD2Cl2) δ 8.95 (m, 2, bipy
H), 8.24 (m, 2, bipy H), 8.03 (m, 2, bipy H), 7.35 (m, 2, bipy H), 7.05
(m, 10, CH2CMe2Ph), 1.38 (s, 12, CH2CMe2Ph), 1.06 (s, 4,
CH2CMe2Ph, JWH = 8 Hz); 13C NMR (CD2Cl2) δ 154.1, 152.0,
149.9, 138.9, 127.7, 126.0, 125.8, 124.8, 123.6, 68.2, 41.3, 32.2. Anal.
Calcd for C30H34N2O2W: C, 56.44; H, 5.37; N, 4.39. Found: C, 56.42;
H, 5.44; N, 4.35.
EXPERIMENTAL SECTION
■
General Comments. All manipulations were done either in a
nitrogen-filled drybox or on an air-free dual-manifold Schlenk line. The
solvents were sparged with nitrogen, passed through activated alumina,
and stored over activated 4 Å Linde-type molecular sieves. Methylene
chloride-d2, benzene-d6, and toluene-d8 were distilled from calcium
hydride (CD2Cl2) or sodium ketyl (C6D6, C7D8) and stored over
activated 4 Å Linde-type molecular sieves. NMR spectra were recorded
using Varian spectrometers at 500 (1H), 125 (13C), and 121 (31P)
MHz, reported in δ (parts per million) relative to tetramethylsilane
(1H, 13C) or 85% phosphoric acid (31P), and referenced to the residual
1H/13C resonances of the deuterated solvent (1H (δ), benzene 7.16,
methylene chloride 5.32, chloroform 7.26, toluene 7.09, 7.01, 6.97,
2.08; 13C (δ), benzene 128.06, methylene chloride 53.84, chloroform
77.16, toluene 20.43) or external 85% phosphoric acid standard (31P
(δ), 0) and hexafluorobenzene (19F (δ), −164.9). Midwest Microlab,
Indianapolis, IN, provided the elemental analysis results.
Synthesis of W(O)(CH-t-Bu)Cl2(PMe2Ph)2 (1a). Compound 3a
(3.80 g, 7.39 mmol) was mixed with ZnCl2(dioxane) (1.74 g, 7.76
mmol, 1.05 equiv) and PMe2Ph (1.94 g, 14.04 mmol, 1.9 equiv) in 40
mL of toluene. The mixture was cooled to −30 °C, and TMSCl (1.77
g, 16.26 mmol, 2.2 equiv) was added. The mixture was stirred at room
temperature for 30 min and then heated to 100 °C for 2 h, during
which time the color darkened and a precipitate formed. All the
volatiles were removed under vacuum at 50 °C. Benzene (40 mL) was
added to the dark residue, and the mixture was filtered through Celite.
Solvent was evaporated from the filtrate in vacuo, leaving a yellow
solid and a brown oil. The residue was stirred with 40 mL of ether for
3 h, during which time the oil disappeared and a yellow solid
remained. The solid was recrystallized twice from a mixture of ether
and tetrahydrofuran at −30 °C to produce a yellow crystalline solid
(2.03 g, 45% yield). The 1H NMR spectrum of the product is identical
W(O)(CH-t-Bu)Cl(HMTO)(PMe2Ph),11 2,5-diphenylpyrrolide,28
29
and NH(C6F5)2 were prepared according to reported procedures.
H(Silox) was received as a generous gift from Professor Pete
Wolczanski. NaSilox was prepared in the reaction of H(Silox) and
NaH in THF. All other reagents were used as received unless noted
otherwise.
Synthesis of W(O)2Cl2(bipy) (2). Compound 2 was prepared by a
modification of the published procedure.16 A solution of hexame-
thyldisiloxane (21.49 g, 132 mmol, 2.1 equiv) was added dropwise to
the solution of tungsten hexachloride (25.00 g, 63.0 mmol) in 250 mL
of dichloromethane. A solution of dimethoxyethane (13.06 g, 145
mmol, 2.3 equiv) was added. The mixture was stirred for 2 h at room
temperature, during which time it became dark blue and contained a
suspended precipitate. A pale blue solution was obtained after filtration
with that reported: 1H NMR (C6D6) δ 12.10 (t, 1, WCHCMe3, 1JCH
=
125 Hz, 3JPH = 4 Hz), 7.65 (m, 4), 6.97 (m, 6), 1.92 (m, 12, PMe2Ph),
7283
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
0.82 (s, 9, WCHCMe3). Anal. Calcd for C21H32Cl2OP2W: C, 40.87; H,
5.23. Found: C, 40.90; H, 5.12.
Synthesis of W(O)(C3H6)(OHMT)(Silox) (9). A cold (−30 °C)
solution of W(O)(CH-t-Bu)(OHMT)Cl(PMe2Ph) (250 mg, 0.323
mmol) in 10 mL of toluene was added to a portion of solid NaSilox
(85 mg, 0.357 mmol, 1.1 equiv). The brown reaction mixture was
stirred at room temperature for 3 h. The solvent was removed in vacuo
to give a brown oil. The product was extracted to toluene (5 mL), and
the mixture was filtered through a bed of Celite. Toluene was removed
in vacuo to produce a brown oil. Pentane (3 mL) was added to the oil.
The solution was degassed by three successive freeze−pump−thaw
cycles, and 1 atm of ethylene was added. The mixture was stirred at 0
°C for 1 h, during which time a yellow crystalline precipitate formed.
The precipitate was filtered off, washed with 0.5 mL of cold pentane,
and collected: yield 64 mg, 25%. A 0.018 M solution in C6D6
contained 98% of 4 and 2% of the corresponding methylidene along
with the equivalent amount of ethylene: 1H NMR (C6D6) δ 7.02−6.90
(m, 7, Ar H), 4.10 (m, 1, WC3H6), 2.54 (m, 1, WC3H6), 2.26 (br s, 12,
Ar Me), 2.20 (s, 6, Ar Me), 1.93 (m, 1, WC3H6), 1.05 (s, 27, SiCMe3);
13C NMR (C6D6) δ 156.6, 136.8 (br), 136.4 (br), 135.0 (br), 134.4
(br), 130.6, 129.2, 128.7, 124.0, 43.8 (WC3H6), 41.4 (WC3H6), 30.0
(SiCMe3), 23.9 (SiCMe3), 22.3 (WC3H6), 21.4 (br, Ar Me), 21.2 (Ar
Me). Anal. Calcd for C39H58O3SiW: C, 59.42; H, 7.43. Found: C,
59.20; H, 7.11.
Synthesis of W(O)(CH-t-Bu)(OHMT)2 (10). A solution of
W(O)(CH-t-Bu)Cl2(PMe2Ph) (200 mg, 0.324 mmol) in 10 mL of
toluene was added to a solution of LiOHMT (262 mg, 0.778 mmol,
2.4 equiv). The reaction mixture was stirred at 100 °C for 48 h, and
the volatiles were removed in vacuo to give a brown oil. The product
was extracted into toluene (5 mL), and the mixture was filtered
through a bed of Celite. The toluene was removed in vacuo to give a
brown oil. Addition of 4 mL of pentane caused a yellow solid to
precipitate. The solid was filtered off and washed with 3 mL of cold
pentane: yield 124 mg, 41%; 1H NMR (C6D6) δ 7.34 (s, 1, WCH-t-Bu,
1JCH = 122 Hz, 2JWH = 14 Hz), 6.90 (br s, 4, Ar H), 6.87−6.85 (m, 8,
Ar H), 6.83−6.80 (m, 2, Ar H), 2.26 (s, 12, Ar Me), 2.08 (s, 12, Ar
Me), 2.03 (s, 12, Ar Me), 0.92 (s, 9, WCH-t-Bu); 13C NMR (C6D6) δ
253.6 (WCH-t-Bu), 158.5, 137.0, 136.7, 136.5, 134.9, 131.7, 130.7,
128.9, 128.8, 123.0, 41.1, 33.2, 21.6, 21.3, 20.8. Anal. Calcd for
C53H60O3W: C, 68.53; H, 6.51. Found: C, 68.22; H, 6.53.
Synthesis of W(O)(CHCMe2Ph)Cl2(PMe2Ph)2 (1b). The com-
pound was prepared in a manner analogous to that described for 1a.
Compound 3b (2.99 g, 4.68 mmol) was mixed with ZnCl2(dioxane)
(1.10 g, 4.91 mmol, 1.05 equiv) and PMe2Ph (1.22 g, 8.85 mmol, 1.8
equiv) in 40 mL of toluene. The mixture was cooled to −30 °C, and
TMSCl (1.17 g, 10.76 mmol, 2.3 equiv) was added. The mixture was
stirred at room temperature for 30 min and was heated at 100 °C for 2
h, during which time the color darkened and a precipitate formed. The
solvent volume was reduced to approximately 30 mL in vacuo, and 10
mL of pentane was added. The solution was filtered through Celite,
and the volatiles were removed in vacuo, leaving a brown oil. The
residue was recrystallized twice from a mixture of ether and
tetrahydrofuran at −30 °C to give a yellow crystalline solid (1.24 g,
39% yield): 1H NMR (C6D6) δ 12.01 (t, 1, WCHCMe2Ph, 1JCH = 126
3
Hz, JPH = 4 Hz), 7.68 (m, 4), 7.03 (m, 8), 6.96 (m, 3), 1.94 (t, 6,
PMe2Ph), 1.58 (t, 6, PMe2Ph), 1.27 (s, 6, WCHCMe2Ph); 13C NMR
(C6D6) δ 315.8 (t, WCHCMe2Ph, JPC = 11 Hz), 150.6, 135.1 (t),
131.4 (t), 130.6, 128.75, 128.70, 128.65, 126.8, 126.1, 51.9, 30.9, 14.7
(td); 31P NMR (C6D6) δ 4.02 (JPW = 333 Hz). Anal. Calcd for
C26H34Cl2OP2W: C, 45.97; H, 5.05. Found: C, 46.23; H, 4.99.
Synthesis of W(O)(CH-t-Bu)(Ph2Pyr)(OHMT) (6). A solution of
W(O)(CH-t-Bu)Cl(OHMT)(PMe2Ph) (300 mg, 0.388 mmol) in 10
mL of benzene was added to a portion of solid Li(Ph2Pyr) (105 mg,
0.466 mmol, 1.2 equiv). The cloudy reaction mixture was stirred at
room temperature for 24 h. The solvent was removed in vacuo to give
a brown oil. The product was extracted into toluene (5 mL), and the
solution was filtered through a bed of Celite. Toluene was removed in
vacuo to produce a brown oil. Yellow solid precipitated upon addition
of pentane (4 mL), and the resulting suspension was filtered and
washed with 5 mL of pentane. The yellow product was recrystallized
from a mixture of toluene and pentane at −30 °C: yield 182 mg, 57%;
1
2
1H NMR (C6D6) δ 9.99 (s, 1, WCH-t-Bu, JCH = 124 Hz, JWH = 11
Hz), 7.24−6.94 (m, 12), 6.89 (s, 2), 6.65 (s, 2), 6.61 (d, 1), 6.46−6.14
(br., 2), 2.22 (s, 6, Ar Me), 2.18 (s, 6, Ar Me), 2.04 (s, 6, Ar Me), 0.71
(s, 9, WCH-t-Bu); 13C NMR (C6D6) δ 279.7 (WCH-t-Bu, 1JCW = 201
Hz), 157.4, 137.8, 137.5, 137.3, 136.2, 133.8, 133.5, 133.1, 131.5,
130.7, 129.4, 129.2, 129.1, 127.1, 126.4, 124.3, 123.1, 113.1, 111.4,
108.6, 42.9, 32.1, 21.4, 21.2, 21.1. Anal. Calcd for C45H47NO2W: C,
66.10; H, 5.79; N, 1.71. Found: C, 65.93; H, 5.90; N, 1.76.
Synthesis of W(O)(C3H6)(OHMT)2 (11). A degassed solution of
10 (324 mg, 0.348 mmol) in 8 mL of pentane was exposed to 1 atm of
ethylene at 0 °C for 2 h. The yellow precipitate that formed was
filtered off and washed with 0.5 mL of cold pentane: yield 150 mg,
Synthesis of W(O)(CH-t-Bu)[N(C6F5)2](OHMT)(PMe2Ph) (7). A
solution of W(O)(CH-t-Bu)Cl(OHMT)(PMe2Ph) (252 mg, 0.326
mmol) in 10 mL of dichloromethane was added to a portion of solid
LiN(C6F5)2 (127 mg, 0.358 mmol, 1.1 equiv). The reaction mixture
was stirred at room temperature for 8 h, during which time a white
precipitate formed. The solvent was removed in vacuo to give a brown
oil. The product was extracted into toluene (5 mL), and the solvent
was filtered through a bed of Celite. Toluene was removed in vacuo to
produce a yellow oil. The oil was dissolved in a 1/4 mixture of ether
and pentane and cooled to −30 °C. The product was collected as an
off-white solid: yield 230 mg, 65%; 1H NMR (74 mM in C6D5CD3, 22
°C) δ 10.21 (br, 1, WCH-t-Bu), 7.25 (m, 2), 7.00 (m, 3), 6.82 (m, 6),
6.64 (br, 2), 2.23 (br, 6, Ar Me), 2.10 (br, 6, Ar Me), 2.04 (br, 6, Ar
Me), 1.20 (br, 6, PMe2Ph) 0.60 (br, 9, WCH-t-Bu); 31P NMR (74 mM
in C6D5CD3, 22 °C) δ 2.44 (br); 1H NMR (74 mM in C6D5CD3, −20
°C) δ 10.37 (br, 1, WCH-t-Bu), 7.20 (m, 2), 6.95 (m, 3), 6.81 (m, 6),
6.72 (br, 1), 6.54 (br, 1), 2.35 (br, 3, Ar Me), 2.22 (br, 3, Ar Me), 2.17
(br, 6, Ar Me) 2.03 (br, 3, Ar Me), 2.00 (br, 3, Ar Me), 1.17 (d, 6,
PMe2Ph) 0.52 (br, 9, WCH-t-Bu); 13C NMR (74 mM in C6D5CD3,
−20 °C, C−F are expected to be weak) δ 297.3 (WCH-t-Bu), 160.1,
139.1, 138.5, 138.0, 137.6, 137.1, 136.8, 136.5, 135.0, 134.7, 133.8,
133.4, 133.0, 132.7, 131.9, 130.9, 130.8, 130.6, 129.7, 128.5, 128.4,
128.2, 120.9, 44.3, 29.8, 22.1, 21.8, 21.4, 21.1, 21.0, 20.9, 14.3 (d), 11.4
(d); 31P NMR (74 mM in C6D5CD3, −20 °C) δ 2.69 (s, JPW = 347
Hz); 19F NMR (74 mM in C6D5CD3, −20 °C) δ −146.18 (br, 1),
−146.62 (br, 1), −152.04 (br, 1), −160.78 (br, 1), −165.66 (br, 1),
−167.58 (br, 2), −168.91 (br, 1), −169.09 (br, 1), −174.82 (br, 1).
Anal. Calcd for C49H46F10NO2PW: C, 54.21; H, 4.27; N, 1.29. Found:
C, 54.50; H, 4.32; N, 1.59.
1
0.167 mmol, 48%. An H NMR spectrum of 11 in C6D6 shows it to
contain ∼25% of 12 (vide infra): 1H NMR (C6D6) δ 6.89 (br s, 14, Ar
H), 3.72 (m, 1, WCH2CH2CH2), 2.28 (s, 12, Ar Me), 2.08 (s, 12, Ar
Me), 2.05 (s, 12, Ar Me), 1.73 (m, 2, WCH2CH2CH2), 0.54 (m, 2,
WCH2CH2CH2) (one of the metallacycle resonances is obscured by
two Ar Me peaks at 2.08 and 2.05 ppm); 13C NMR (C6D6) δ 156.7,
137.0, 136.8, 136.7, 135.0, 131.0, 130.0, 128.9, 128.8, 123.8, 42.4
(WCH2CH2CH2, JCH = 135 Hz), 22.2 (WCH2CH2CH2, JCH = 132
Hz), 21.5, 21.0, 20.8. Anal. Calcd for C51H56O3W: C, 68.00; H, 6.27.
Found: C, 67.82; H, 6.29.
Synthesis of W(O)(CH2)(OHMT)2 (12). A sample of 11 (60 mg,
0.067 mmol) was dissolved in 1 mL of toluene, and the solvent was
removed in vacuo at room temperature. After two additional
dissolution/evacuation cycles, a brown oil was obtained. Toluene
(0.1−0.2 mL) and pentane (0.3−0.5 mL) were added, and the sample
was placed in a freezer at −30 °C for 2 days. Yellow crystals formed
and were separated from the brown mother liquor by decantation:
1
2
yield 32 mg, 55%; H NMR (C6D6) δ 8.90 (d, 1, WCHsyn, JHH = 10
1
2
1
Hz, JCH = 160 Hz), 7.85 (d, 1, WCHanti, JHH = 10 Hz, JCH = 140
Hz), 6.90 (br s, 4, Ar H), 6.89−6.85 (m, 8, Ar H), 6.84−6.80 (m, 2, Ar
H), 2.22 (s, 12, Ar Me), 2.00 (s, 12, Ar Me), 1.96 (s, 12, Ar Me); 13C
NMR (C6D6) δ 225.8 (WCH2), 158.1, 137.2, 136.9, 136.7, 134.4,
131.5, 130.0, 128.3, 123.4, 123.0, 21.3, 20.9, 20.8. Anal. Calcd for
C49H52O3W: C, 67.43; H, 6.01. Found: C, 67.74; H, 6.12.
X-ray Crystal Structure Determination Details. Low-temper-
ature diffraction data (φ and ω scans) were collected on a Bruker-AXS
X8 Kappa Duo diffractometer coupled to a Smart APEX 2 CCD
detector with Mo Kα radiation (λ = 0.710 73 Å) from an IμS
7284
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
microsource. Absorption and other corrections were applied using
SADABS.30 All structures were solved by direct methods using
SHELXS31 and refined against F2 on all data by full-matrix least
squares with SHELXL-9732 using established refinement approaches.33
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were included in the models at geometrically calculated positions and
refined using a riding model, except for alkylidene, metallacycle, and
methylidene protons. Coordinates for these hydrogen atoms were
taken from the difference Fourier synthesis, and the hydrogen atoms
were subsequently refined semifreely with the help of distance
restraints. The isotropic displacement parameters of all hydrogen
atoms were fixed to 1.2 times the Ueq value of the atoms they are
linked to (1.5 times for methyl groups). All disordered atoms were
refined with the help of similarity restraints on the 1,2- and 1,3-
distances and displacement parameters as well as rigid bond restraints
for anisotropic displacement parameters.
Soc. 1968, 90, 4133. (c) Basset, J. M.; Coudurier, G.; Praliaud, H. J.
Catal. 1974, 34, 152. (d) Mocella, M. T.; Rovner, R.; Muetterties, E. L.
J. Am. Chem. Soc. 1976, 98, 4689. (e) Burwell, R. L., Jr.; Brenner, A. J.
Mol. Catal. 1976, 1, 77. (f) Muetterties, E. L.; Band, E. J. Am. Chem.
Soc. 1980, 102, 6572.
(2) (a) Kress, J. R. M.; Russell, M. J. M.; Wesolek, M. G.; Osborn, J.
A. J. Chem. Soc., Chem. Commun. 1980, 431. (b) Kress, J. R. M.;
Wesolek, M. G.; Le Ny, J.-P.; Osborn, J. A. J. Chem. Soc., Chem.
Commun. 1981, 1039. (c) Kress, J. R. M.; Wesolek, M. G.; Osborn, J.
A. J. Chem. Soc., Chem. Commun. 1982, 514.
(3) (a) Schrock, R. R.; Rocklage, S. M.; Wengrovius, J. H.;
Rupprecht, G.; Fellmann, J. J. Mol. Catal. 1980, 8, 73. (b) Churchill,
M. R.; Rheingold, A. L.; Youngs, W. J.; Schrock, R. R.; Wengrovius, J.
H. J. Organomet. Chem. 1981, 204, C17. (c) Wengrovius, J. H.;
Schrock, R. R. Organometallics 1982, 1, 148. (d) Wengrovius, J. H.;
Schrock, R. R.; Churchill, M. R.; Missert, J. R.; Youngs, W. J. J. Am.
Chem. Soc. 1980, 102, 4515.
(4) (a) Schrock, R. R. In Reactions of Coordinated Ligands; Braterman,
P. R., Ed.; Plenum: New York, 1986; p 221. (b) (b) Schrock, R. R.
Chem. Rev. 2002, 102, 145. (c) Schrock, R. R. In Handbook of
Metathesis,; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, Germany,
2003; Vol. 1.
(5) (a) Bryan, J. C.; Mayer, J. C. J. Am. Chem. Soc. 1990, 112, 2298.
(b) Blosch, L. L.; Abboud, K.; Boncella, J. M. J. Am. Chem. Soc. 1991,
113, 7066. (c) Ahn, S.; Mayr, A. J. Am. Chem. Soc. 1996, 118, 7408.
(d) De la Mata, F. J.; Grubbs, R. H. Organometallics 1996, 15, 577.
(e) Crane, T. W.; White, P. S.; Templeton, J. L. Organometallics 1999,
18, 1897.
(6) O’Donoghue, M. B.; Schrock, R. R.; LaPointe, A. M.; Davis., W.
M. Organometallics 1996, 15, 1334.
(7) Schrock, R. R. Chem. Rev. 2009, 109, 3211.
(8) (a) Ibrahem, I.; Yu, M.; Schrock, R. R.; Hoveyda, A. H. J. Am.
W(O)(CH-t-Bu)(Ph2Pyr)(OHMT) (6) crystallizes in the triclinic
space group P1 with one molecule in the asymmetric unit. Coordinates
̅
for the hydrogen atom bound to C1 were taken from the difference
Fourier synthesis as noted above.
W(O)(CH-t-Bu)(N(C6F5)2)(OHMT)(PMe2Ph) (7) crystallizes in
monoclinic space group P21/c with one molecule in the asymmetric
unit. Coordinates for the hydrogen atom bound to C1 were taken
from the difference Fourier synthesis as noted above.
W(O)(C3H6)(OHMT)(Silox) (9) crystallizes in the triclinic space
group P1 with one molecule in the asymmetric unit. The tungsten
̅
atom and oxo ligand were modeled as a two-component disorder, and
the ratio of the occupancies was refined to 0.9687(6):0.0313(6). The
Silox ligand was also found to be disordered over two positions, and
the ratio of occupancies was refined to 0.521(8):0.479(8). The
anisotropic displacement parameters for silicon and carbon atoms of
the Silox group were constrained to be equivalent, pairwise.
W(O)(CH2)(OHMT)2 (12) crystallizes in the monoclinic space
group P21/n with one molecule in the asymmetric unit. The tungsten
atom, oxo, and methylidene ligand were modeled as a two-component
disorder, and the ratio of the occupancies was refined to
0.711(1):0.289(1). The anisotropic displacement parameters for the
tungsten (W1, W1A), oxo, and chloride ligands (C1, O1A and C1A,
O1) were constrained to be equivalent, pairwise. Coordinates of the
hydrogen atoms bound to C1 were taken from the difference Fourier
synthesis as noted above. The hydrogen atoms bound to C1A, the
minor component of the disorder, could not be found in the difference
Fourier synthesis and were not included in the model.
Chem. Soc. 2009, 131, 3844. (b) Flook, M. M.; Jiang, A. J.; Schrock, R.
R.; Muller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 7962.
̈
(c) Flook, M. M.; Gerber, L. C. H.; Debelouchina, G. T.; Schrock, R.
R. Macromolecules 2010, 43, 7515. (d) Flook, M. M.; Ng, V. W. L.;
Schrock, R. R. J. Am. Chem. Soc. 2011, 133, 1784. (e) Jiang, A. J.; Zhao,
Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 16630.
(f) Marinescu, S. C; Schrock, R. R.; Muller, P.; Takase, M. K.;
̈
Hoveyda, A. H. Organometallics 2011, 30, 1780. (g) Marinescu, S. C.;
Levine, D. S.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem.
Soc. 2011, 133, 11512. (h) Malcolmson, S. J.; Meek, S. J.; Sattely, E. S.;
Schrock, R. R.; Hoveyda, A. H. Nature 2008, 456, 933. (i) Meek, S. J.;
O’Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H. Nature
2011, 471, 461. (j) Yu, M.; Wang, C.; Kyle, A. F.; Jakubec, P.; Dixon,
D. J.; Schrock, R. R.; Hoveyda, A. H. Nature 2011, 479, 88.
(9) Stanciu, C.; Olmstead, M. M.; Phillips, A. D.; Stender, M.; Power,
P. P. Eur. J. Inorg. Chem. 2003, 3495.
ASSOCIATED CONTENT
* Supporting Information
■
S
Tables and CIF files giving crystallographic details and data.
This material is available free of charge via the Internet at
http://pubs.acs.org. Data for the X-ray structures are also
available to the public at http://www.reciprocalnet.org.
(10) Dickie, D. A.; MacIntosh, I. S.; Ino, D. D.; He, Q.; Labeodan, O.
A; Jennings, M. C.; Schatte, G.; Walsby, C. J.; Clyburne, J. A. C. Can. J.
Chem. 2008, 86, 20.
(11) Peryshkov, D. V.; Schrock, R. R.; Takase, M. K.; Muller, P.;
Hoveyda, A. H. J. Am. Chem. Soc. 2011, 133, 20754.
(12) Rocklage, S. M.; Schrock, R. R.; Churchill, M. R.; Wasserman,
H. J. Organometallics 1982, 1, 1332.
(13) Stavropoulos, P.; Wilkinson, G.; Motevalli, M.; Hursthouse, M.
AUTHOR INFORMATION
Corresponding Author
*E-mail: rrs@mit.edu.
Notes
̈
■
The authors declare no competing financial interest.
B. Polyhedron 1987, 6, 1081.
(14) (a) Feinstein-Jaffe, I.; Pedersen, S. F.; Schrock, R. R. J. Am.
Chem. Soc. 1983, 105, 7176. (b) Feinstein-Jaffe, I.; Gibson, D.;
Lippard, S. J.; Schrock, R. R.; Spool, A. J. Am. Chem. Soc. 1984, 106,
6305. (c) Rosenfeld, D. C.; Kuiper, D. S.; Lobkovsky, E. B.;
Wolczanski, P. T. Polyhedron 2006, 25, 251. (d) Lehtonen, A.;
Sillanpaa, R. Organometallics 2005, 24, 2795.
(15) Zhang, C.; Schlemper, E. O.; Schrauzer, G. N. Organometallics
1990, 9, 1016.
(16) (a) Gibson, V. C.; Kee, T. P.; Shaw., A. Polyhedron 1988, 7, 579.
(b) Herrman, W. A.; Theil, W. R.; Herdweck, E. Chem. Ber. 1990, 123,
271. (c) Kuhn, F. E.; Xue, W.-M.; Al-Ajlouni, A.; Santos, A. M.; Zang,
ACKNOWLEDGMENTS
■
R.R.S. thanks the National Science Foundation (CHE-
1111133) for research support. The Department of Chemistry
thanks the NSF (CHE-9808061) for funds to purchase a Varian
500 NMR instrument.
REFERENCES
■
(1) (a) Ivin, K. J.; Mol, J. C., Olefin Metathesis and Metathesis
Polymerization; Academic Press: San Diego, CA, 1997. (b) Calderon,
N.; Ofstead, E. A.; Ward, J. P.; Judy, W. A.; Scott, K. W. J. Am. Chem.
S.; Romao, C. C.; Eickerling, G.; Herdtweck, E. Inorg. Chem. 2002, 41,
̃
7285
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286

Organometallics
Article
4468. (d) Dreisch, K.; Andersson, C.; Stalhandske, C. Polyhedron
1991, 10, 2417.
(17) (a) Schrauzer, G. N.; Hughes, L. A.; Strampach, N.; Robinson,
P. R.; Schlemper, E. O. Organometallics 1982, 1, 44. (b) Schrauzer, G.
N.; Hughes, L. A.; Therien, M. J.; Schlemper, E. O.; Ross, F.; Ross, D.
Organometallics 1983, 2, 1163. (c) Schrauzer, G. N.; Hughes, L. A.;
Strampach, N.; Ross, F.; Ross, D.; Schlemper, E. O. Organometallics
1983, 2, 481. (d) Schrauzer, G. N.; Schlemper, E. O.; Hui, L. N.;
Rubin, K.; Zhang, X.; Long, X.; Chin, C. S. Organometallics 1986, 5,
2452. (e) Schrauzer, G. N.; Zhang, X.; Liu, N.; Schlemper, E. O.
Organometallics 1988, 7, 279. (f) Zhang, C.; Zhang, X.; Liu, N. H.;
Schrauzer, G. N.; Schlemper, E. O. Organometallics 1990, 9, 1307.
(18) (a) Heppekausen, J.; Furstner, A. Angew. Chem., Int. Ed. 2011,
̈
50, 7829. (b) Heppekausen, J.; Stade, R.; Goddard, A.; Furstner, A. J.
̈
Am. Chem. Soc. 2010, 132, 11045.
(19) Lichtscheidl, A. G.; Ng, V. W. L.; Muller, P.; Takase, K.;
̈
Schrock, R. R.; Malcolmson, S. J.; Meek, S. J.; Li, B.; Kiesewetter, E. T.;
Hoveyda, A. H. Organometallics 2012, 31, 4558.
(20) Marinescu, S. C.; Singh, R.; Hock, A. S.; Wampler, K. M.;
Schrock, R. R.; Muller, P. Organometallics 2008, 27, 6570.
̈
(21) (a) Jiang, A. J.; Simpson, J. H.; Muller, P.; Schrock, R. R. J. Am.
̈
Chem. Soc. 2009, 131, 7770. (b) Marinescu, S. C.; Schrock, R. R.;
Muller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 10840.
̈
(22) (a) Cornelissen, C.; Chan, G.; Masuda, J. D.; Stephan, D. W.
Can. J. Chem. 2007, 85, 135. (b) Click, D. R.; Scott, B. L.; Watkin, J. G.
Chem. Commun. 1999, 633. (c) Shutov, P. L.; Karlov, S. S.; Harms, K.;
Sundermeyer, J.; Lorberth, J.; Zaitseva, G. S. J. Fluor. Chem. 2009, 130,
1017. (d) Yao, S.; Zhang, X.; Xiong, Y.; Schwarz, H.; Driess, M.
Organometallics 2010, 29, 5353. (e) Khvorost, A.; Shutov, P. L.;
Harms, K.; Lorberth, J.; Sundermeyer, J.; Karlov, S. S.; Zaitseva, G. S.
Z. Anorg. Allg. Chem. 2004, 630, 885. (f) Giesbrecht, G. R.; Gordon, J.
C.; Clark, D. L.; Hijar, C. A.; Scott, B. L.; Watkin, J. G. Polyhedron
2003, 22, 153. (g) Weber, K.; Korn, K.; Schorm, A.; Kipke, J.; Lemke,
M.; Khvorost, A.; Harms, K.; Sundermeyer, J. Z. Anorg. Allg. Chem.
2003, 629, 744.
(23) (a) Feldman, J.; Davis, W. M.; Schrock, R. R. Organometallics
1989, 8, 2266. (b) Feldman, J.; Davis, W. M.; Thomas, J. K.; Schrock,
R. R. Organometallics 1990, 9, 2535. (c) Feldman, J.; Schrock, R. R.
Prog. Inorg. Chem. 1991, 39, 1.
(24) (a) Poater, A.; Solans-Monfort, X.; Clot, E.; Coper
Eisenstein, O. J. Am. Chem. Soc. 2007, 129, 8207. (b) Solans-Monfort,
X.; Coperet, C.; Eisenstein, O. J. Am. Chem. Soc. 2010, 132, 7750.
́
et, C.;
́
(25) Yuan, J.; Schrock, R. R.; Muller, P.; Axtell, J. C.; Dobereiner, G.
̈
E. Organometallics 2012, 31, 4650.
(26) Schrock, R. R.; King, A. J.; Marinescu, S. C.; Simpson, J. H.;
Muller, P. Organometallics 2010, 29, 5241.
̈
(27) Marinescu, S. C.; Ng, V. W. L.; Lichtscheidl, A. G.; Schrock, R.
R.; Muller, P.; Takase, M. K. Organometallics 2012, 31, 6336.
̈
(28) Patterson, J. M.; Soedigdo, S. J. Org. Chem. 1968, 33, 2057.
(29) Koppang, R. Acta Chem. Scand. 1971, 25, 3067.
(30) Sheldrick, G. M. SADABS, v. 2.10-A program for area detector
absorption corrections; Bruker AXS, Madison, WI, 2003.
(31) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(32) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(33) Muller, P. Crystallogr. Rev. 2009, 15, 57.
̈
́
(34) Solans-Monfort, X.; Coperet, C.; Eisensein, O. Organometallics,
published online September 26, 2012 http://dx.doi.org/10.1021/
om300576r.
7286
dx.doi.org/10.1021/om3008579 | Organometallics 2012, 31, 7278−7286