Molybdenum monoaryloxide pyrrolide alkylidene complexes that contain mono-ortho-substituted phenyl imido ligands

Article abstract of DOI:10.1021/om3000289

Monaryloxide pyrrolide (MAP) molybdenum imido alkylidene complexes of the type Mo(NAr^X)(CHCMe₂R)(Me₂Pyr)(OR′) (Me₂Pyr = 2,5-dimethylpyrrolide) have been prepared in which NAr ^X is an ortho-substituted phenylimido group (X = Cl (NAr ^Cl), CF₃ (NAr^CF3), i-Pr (NAr^iPr), t-Bu (NAr^tBu), mesityl (NAr^M), or TRIP (TRIP = triisopropylphenyl; NAr^T)) and OR′ = O-2,3,5,6-(C ₆H₅)₄C₆H (OTPP), O-2,6-(2,4,6-Me₃C₆H₂)₂C ₆H₃ (OHMT), or O-2,6-(2,4,6-i-Pr₃C ₆H₂)₂C₆H₃ (OHIPT). The object was to explore to what extent relatively "large" NAr ^M or NAr^T ligands would alter the performance of MAP catalysts in reactions that have been proposed to depend upon the relative size of the imido and OR′ groups. Preliminary studies employing the ring-opening metathesis polymerization of 5,6-dicarbomethoxynorbornadiene as a measure of selectivity suggest that a single phenylimido ortho substituent, even in an NAr^M or NAr^T group, does not produce any unique behavior and that the outcome of the ROMP reaction correlates with the overall relative size of the imido and OR′ group. Single-crystal X-ray structures of six species that contain the new NAr^M or NAr^T groups are reported.

Full text of DOI:10.1021/om3000289

Article
pubs.acs.org/Organometallics
Molybdenum Monoaryloxide Pyrrolide Alkylidene Complexes That
Contain Mono-ortho-substituted Phenyl Imido Ligands
Alejandro G. Lichtscheidl, Victor W. L. Ng, Peter Muller, Michael K. Takase, and Richard R. Schrock*
̈
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
S
* Supporting Information
ABSTRACT: Monaryloxide pyrrolide (MAP) molybdenum imido alkylidene
complexes of the type Mo(NArX)(CHCMe2R)(Me2Pyr)(OR′) (Me2Pyr = 2,5-
dimethylpyrrolide) have been prepared in which NArX is an ortho-substituted
phenylimido group (X = Cl (NArCl), CF3 (NArCF3), i-Pr (NAriPr), t-Bu (NArtBu),
mesityl (NArM), or TRIP (TRIP = triisopropylphenyl; NArT)) and OR′ = O-2,3,5,6-
(C6H5)4C6H (OTPP), O-2,6-(2,4,6-Me3C6H2)2C6H3 (OHMT), or O-2,6-(2,4,6-i-
Pr3C6H2)2C6H3 (OHIPT). The object was to explore to what extent relatively “large”
NArM or NArT ligands would alter the performance of MAP catalysts in reactions
that have been proposed to depend upon the relative size of the imido and OR′
groups. Preliminary studies employing the ring-opening metathesis polymerization of
5,6-dicarbomethoxynorbornadiene as a measure of selectivity suggest that a single
phenylimido ortho substituent, even in an NArM or NArT group, does not produce
any unique behavior and that the outcome of the ROMP reaction correlates with the
overall relative size of the imido and OR′ group. Single-crystal X-ray structures of six species that contain the new NArM or NArT
groups are reported.
bisalkoxide catalysts in many cases, and MAP species can be
engineered to be highly Z-selective for the coupling of terminal
olefins.7 MAP species also have been the subject of detailed
calculations.8
INTRODUCTION
■
High oxidation state molybdenum and tungsten imido
alkylidene complexes1 with the generic formula M(NR)-
(CHR′)(X)(Y) (where X and Y are monoanionic ligands,
initially both alkoxides) were first prepared approximately 25
years ago.2 Unlike an oxo ligand, which was present in the first
high oxidation state group 6 complexes to be discovered,3 the
isoelectronic imido ligand can retard bimolecular decomposi-
tion of alkylidenes for steric reasons. Imido ligands also are
available in many steric and electronic variations. Phenylimido
ligands have been popular, especially 2,6-disubstituted versions
(2,6-i-Pr2C6H3, 2,6-Me2C6H3, 2,6-Cl2C6H3, etc). 2-Substituted
imido ligands are less common,4 while those with no ortho
substituents are rare; one example is N-3,5-Me2C6H3.5
Complexes that contain phenylimido ligands with progressively
less steric protection in ortho positions are more difficult to
prepare, and the resulting imido alkylidene complexes appear to
be less stable toward what is presumed to be bimolecular
decomposition.
In the last several years new types of Mo and W imido
alkylidene complexes that have the formula M(NR)(CHR′)-
(OR″)(Pyr), where Pyr is a pyrrolide or substituted pyrrolide
ligand and OR″ usually is an aryloxide, have been prepared and
explored.1a,6 These monoaryloxide pyrrolide (MAP) species
can be viewed as third-generation high oxidation state imido
alkylidene catalysts (after “first-generation” bisalkoxides and
“second-generation” biphenolates and binaphtholates1). MAP
species have many features of fundamental interest. MAP
species contain a stereogenic metal center, MAP species have
proven to be much more efficient (higher turnover) than
We have begun to explore the consequences of increasing the
size of imido groups in MAP complexes to the point that their
size approaches or exceeds that of sterically demanding O-2,6-
(2,4,6-Me3C6H2)2C6H3 (OHMT) or O-2,6-(2,4,6-i-
Pr3C6H2)2C6H3 (OHIPT) ligands that have been employed
in order to enforce Z-selective reactions.9,10 Phenylimido
ligands that are monosubstituted in the ortho position, N-2-
XC6H4 species, especially those in which X is mesityl (NArM)
or triisopropylphenyl (NArT), could prove to be interesting
variations of MAP catalysts. The syntheses of NArM and NArT
species and a comparison of them with NArCl, NArCF3, NAriPr,
and NArtBu species are the subject of this paper. The main
question we wanted to answer is in what way, if any, do
compounds that contain NArM or NArT ligands differ from
those that contain NArCl, NArCF3, NAriPr, or NArtBu ligands in
some test reactions that may be sensitive to the size of X in N-
2-XC6H4 MAP species.
RESULTS AND DISCUSSION
■
Anilines that contain either a Mes (2,4,6-trimethylphenyl) or a
TRIP (2,4,6-triisopropylphenyl) substituent were prepared as
shown in eq 1. Methods of preparing these crystalline anilines
Received: January 13, 2012
Published: March 5, 2012
© 2012 American Chemical Society
2388
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394

Organometallics
Article
are adapted from literature reports;11,12 no palladium-catalyzed
step is required.
Bisimido dichloride complexes in which the imido ligand is
NArCl, NArM, or NArT could be prepared by the standard
method shown in eq 2. When a mixture of two equivalents of
Figure 2. Solid-state structure of 3 (50% probability ellipsoids).
Selected bond lengths (Å) and angles (deg): Mo(1)−N(1) =
1.7522(12), Mo(1)−O(1) = 2.3381(11), Mo(1)−Cl(1) =
2.4023(4), N(1)−Mo(1)−N(2) = 101.44(8), C(11)−N(1)−Mo(1)
= 149.39(10), Cl(1)−Mo(1)−Cl(2) = 159.37(2).
1). The imido ligands in both 2 and 3 are bent at the imido
nitrogen; the smaller Mo−N−C angle in 3 (149.39(10)°)
versus 2 (160.05(19)° and 156.4(2)°) can be attributed to the
greater steric demand of the TRIP group in 3 compared to the
Mes group in 2. Other bond distances and angles are similar to
other complexes of this general type that have been
crystallographically characterized.1 A complete list of bond
distances and angles can be found in the Supporting
Information.
ArMNH2, Na2MoO4, NEt3, and TMSCl in DME is heated at 60
°C overnight, an orange product is formed, but the DME
adduct could not be isolated in crystalline form. However,
recrystallization of the crude DME adduct from a mixture of
pentane and THF led to red, crystalline 2 in 85% isolated yield.
A proton NMR spectrum of 2 shows that four equivalents of
THF are present, as confirmed through elemental analysis. We
propose that two equivalents of THF are present as solvent of
crystallization (vide infra) and that THF exchange is fast on the
NMR time scale at room temperature.
Dichloride complexes 1, 2, and 3 were converted into
dineopentyl or dineophyl complexes 4, 5, and 6 in good yield
through standard procedures (eq 3). The alkyl ligand is chosen
The results of X-ray structural studies of 2 and 3 are shown
in Figures 1 and 2, respectively. As proposed, crystals of 2
contain two THF molecules of crystallization (shown in Figure
on the basis of the ease of isolating the dialkyl product.
Compounds 4, 5, and 6 were then treated with three
equivalents of triflic acid to yield 7, 8, and 9 (eq 4). We
found it difficult to separate 8 from the anilinium triflate
byproduct. So far, trituration with diethyl ether is the only way
to remove all anilinium triflate; the isolated yield of 8 (28%)
therefore suffers as a consequence of it being partially soluble in
ether. Although the reaction between 6 and triflic acid yields 9
smoothly, separation of 9 from the anilinium triflate is again
problematic; the isolated yield of 9 is only 47%. Bistriflate
complexes that contain NArCF3, NAriPr, and NArtBu imido
Figure 1. Solid-state structure of 2 (50% probability ellipsoids).
Selected bond lengths (Å) and angles (deg): Mo(1)−N(1) =
1.750(2), Mo(1)−N(2) = 1.7535(19), Mo(1)−O(1) = 2.3138(18),
Mo(1)−O(2) = 2.3394(6), Mo(1)−Cl(1) = 2.3863(9), Mo(1)−Cl(2)
= 2.4119(9), N(1)−Mo(1)−N(2) = 102.95(10), C(11)−N(1)−
Mo(1) = 160.05(19), C(31)−N(2)−Mo(1) = 156.4(2), Cl(1)−
Mo(1)−Cl(2) = 160.63(3).
2389
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394

Organometallics
Article
1
1
Figure 3. (a) The four alkylidene proton resonances in the H NMR spectrum of 9. (b) H (top) and 19F (bottom) NMR spectra of two of the
isomers of 9.
groups have been reported previously.4a Details can be found in
the Supporting Information.
respect to one another. Proton NMR data suggest that they are
syn isomers (JCH = 125 3 Hz), in which the alkylidene group
points toward the imido group, as shown in eq 4. In contrast,
1H NMR spectra (in C6D6) of both 8 and 9 each show more
than the expected two alkylidene resonances for cis and trans
Bistriflate complexes that contain NArCF3, NAriPr, NArtBu, and
NArCl groups all show resonances for two isomers in solution.
Fluorine NMR spectra suggest that these isomers contain
triflate ligands that are either cis, as shown in eq 4, or trans with
2390
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394

Organometallics
Article
isomers, and ratios of the alkylidene resonances vary from run
to run. The three most prominent resonances for 8 have JCH
values that range from 122 to 129 Hz; for 9 (Figure 3) they
range from 122 to 126 Hz. All JCH values that can be measured
are characteristic of syn species. Two isomers of compounds in
the mixture whose NMR spectrum is shown in Figure 3 are
isolated upon recrystallizing the compound from diethyl ether
at −35 °C. Proton and fluorine NMR spectra (Figure 3) are
consistent with these isomers of 9 being cis (84%) and trans
(16%) species. Cis and trans mixtures of bistriflate dimethoxy-
ethane complexes of this general type have been observed in
other circumstances;13 only two isomers are possible if the
alkylidene and imido ligands are required to be cis to one
another, which is what has been observed in all imido
alkylidene complexes to date. The observation of more than
two isomers suggests several possibilities. One or more of the
adducts loses DME in the solid state, one or more of the
isomers is actually not a solvent adduct, or the large mesityl and
TRIP substituents give rise to isomers in which the mesityl or
TRIP substituents limit free rotation of the imido phenyl group
about the MoN axis on the NMR time scale. Spectra in the
alkylidene region did not change significantly when several
equivalents of DME were added, and the amount of DME in a
complex mixture could not be measured accurately through
integration. Therefore, we cannot determine the exact reason
for isomer formation. Unfortunately, multiple elemental
analyses of 8 and 9 as mixtures of four isomers were variable,
as were elemental analyses of the mixture of cis and trans
isomers shown in Figure 3; the reasons are not known.
Figure 4. Solid-state structure of 14 (50% probability ellipsoids).
Selected bond lengths (Å) and angles (deg): Mo(1)−N(1) =
1.7340(16), Mo(1)−C(1) = 1.940(2), Mo(1)−N(2) = 2.4117(17),
Mo(1)−N(3) = 2.1134(17), Mo(1)−C(32) = 2.391(2), Mo(1)−
C(33) = 2.376(2), Mo(1)−C(34) = 2.458(2), Mo(1)−C(35) =
2.458(2), C(11)−N(1)−Mo(1) = 175.40(15), C(2)−C(1)−Mo(1) =
139.84(15).
bisphenoxide species (16) could be prepared (in 55% yield)
from the bistriflate as shown in eq 6. Since 16 would appear to
Treatment of the bistriflate complexes with two equivalents
of Li-2,5-Me2C4H2N led to bispyrrolide compounds in yields
ranging from 36% to 85% (eq 5). The neophylidene analogue
be a relatively crowded species, an X-ray structural determi-
nation (Figure 5) was carried out. Compound 16 is a distorted
tetrahedron with the smallest and largest angles being
99.29(12)o (N(1)−Mo(1)−C(1)) and 120.85(9)o (N(1)−
Mo(1)−O(2)). The Mo(1)−O(1)−C(31)and Mo(1)−O(2)−
of 11 has been reported previously.4d The low isolated yield of
15 we propose is the result of its poor crystallinity. Proton
NMR spectra of complexes 10−13 exhibit a single alkylidene
peak and broad peaks corresponding to fluxional pyrrolide
ligands, behavior which is analogous to other bispyrrolide
compounds of this general type.14 An X-ray structural study of
14 shows it to contain both η1 and η5 pyrrolide ligands and a
syn alkylidene, as expected (Figure 4).
Addition of t-BuOH, (CF3)2MeCOH, or Ph3SiOH to
complexes 10−15 led to formation of bisalkoxide complexes
as the only observable product, instead of the desired MAP
species. Since N-2,6-i-Pr2C6H3 (NAr) MAP species that contain
tert-butoxide, hexafluoro-tert-butoxide, or triphenylsiloxide can
be obtained in good yields in similar reactions,6a these findings
suggest that NArM and NArT ligands offer less steric protection
toward rapid protonation of the second pyrrolide than
bispyrrolides that contain the NAr ligand.
Figure 5. Solid-state structure of 16 (50% probability ellipsoids).
Selected bond lengths (Å) and angles (deg): Mo(1)−N(1) =
1.732(2), Mo(1)−C(1) = 1.880(3), Mo(1)−O(1) = 1.9402(18),
Mo(1)−O(2) = 1.9303(17), Mes-TPP = 4.343, C(11)−N(1)−Mo(1)
= 173.13(19), C(2)−C(1)−Mo(1) = 141.8(2), C(31)−O(1)−Mo(1)
= 147.00(17), C(61)−O(2)−Mo(1) = 148.18(16).
Addition of one equivalent of 2,3,5,6-tetraphenylphenol
(TPPOH) to 14 led to a mixture that contains 25% 14, 50%
of a MAP product, and 25% of the bisphenoxide. The
2391
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394

Organometallics
Article
C(61) bond angles (147.00(17)o and 148.18(16)o, respec-
tively) are relatively large, as might be expected as a
consequence of steric crowding. The Mo(1)−N(1)−C(11)
bond angle is close to 180° (173.13(19)o). The ready formation
of 16 confirms that 2,3,5,6-tetraphenoxide ligands are opera-
tionally not as large as one might think, as has been found in
other circumstances.5 In contrast, the reaction between 15 and
one equivalent of TPPOH yields only Mo(NArT)(CH-t-
Bu)(Me2Pyr)(OTPP) (17; eq 7); that is, increasing the bulk
The structures of 22 and 24 are shown in Figures 6 and 7,
respectively. Both are distorted tetrahedra, with angles at the
of the imido group (from ArM to ArT) decreases the rate of
formation of the bisphenoxide and, therefore, allows the
synthesis of the MAP species.
2,6-Dimesitylphenol (HMTOH) reacts readily at 22 °C with
10−13 to generate MAP products in modest to good yields (eq
8). However, reactions of HMTOH or hexaisopropylterphenol
Figure 6. Solid-state structure of 22 (50% probability ellipsoids).
Selected bond lengths (Å) and angles (deg): Mo(1)−C(1) =
1.8752(13), Mo(1)−N(1) = 2.0230(11), Mo(1)−N(2) =
1.7302(11), Mo(1)−O(1) = 1.8997(9), Mes−Pyr = 3.837, C(21)−
N(2)−Mo(1) = 175.50(10), C(2)−C(1)−Mo(1) = 146.02(10),
C(41)−O(1)−Mo(1) = 158.89(9).
(HIPTOH) with 14 and 15 are slow. Therefore, their
preparation must be carried out at high temperatures in
toluene for hours to days, depending on the phenol. The
reactions at 110 °C between 14 or 15 and one equivalent of
HMTOH to give 22 and 24, respectively, required 18 h, while
that between 14 and one equivalent of HIPTOH to give 23
required 5 days. Reaction between 15 and HIPTOH required
14 days at 80 °C to give 97% of the desired product. These data
show that reactions between HMTOH and 14 or 15 clearly
take place more readily. It is noteworthy that the MAP products
do not decompose under the relatively harsh conditions
required to prepare 22−25. The isolated yields of 22−24 are
modest (35−57%), the lowest being that for 23 as a
consequence of its high solubility in solvents such as pentane
or tetramethylsilane. Complexes 22 and 24 are more crystalline
than 23 and, therefore, can be isolated in higher yields. Due to
the long times required for reactions between 25 and HIPTOH
and possible complications during purification, 25 could be
prepared only in situ. All reactions benefit from being run under
more concentrated conditions, but a large excess of HMTOH
or HIPTOH cannot be employed without creating problems
with isolation of the desired pure product in the presence of the
phenol.
Figure 7. Solid-state structure of 24 (50% probability ellipsoids).
Selected bond lengths (Å) and angles (deg): Mo(1)−C(1) =
1.862(3), Mo(1)−N(1) = 1.736(2), Mo(1)−N(2) = 2.037(2),
Mo(1)−O(1) = 1.9103(19), C(11)−N(1)−Mo(1) = 170.9(2),
C(2)−C(1)−Mo(1) = 147.5(2), C(51)−O(1)−Mo(1) = 147.32(19).
metal ranging from 102.97(5)° to 117.48(5)° and 101.41(12)o
to 116.40(10)o, respectively. The Mo−N−C(imido) and the
Mo(1)−C(1)−C(2) angles are similar in the two complexes
and to analogous angles in other complexes of this general type.
On the other hand, the Mo(1)−O(1)−C(41) angle of 22 is
158.89(9)o, which is 10° larger than the Mo−O−C angle in
either 24 or 16; large M−O−C angles are not uncommon
among MAP complexes containing HMTO or HIPTO. In both
22 and 24 the Mes and Trip groups point away from the
alkylidene and therefore would not seem to block an olefin
from binding to the metal trans to the pyrrolide. In 22 an
additional feature worth mentioning is a possible π-stacking
interaction between the mesityl ring of the NArM ligand and the
pyrrolide ring beneath it. However, this interaction is weak due
2392
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394

Organometallics
Article
to the distance between the rings (3.837 Å from the centroid of
the mesityl ring to the centroid of the pyrrolide ring).15
Compounds 22−25 show different numbers of isomers in
solution, as evidenced by their respective 1H NMR spectrum. A
trend is clearly observed between the overall steric hindrance at
the metal center and the number of isomers observed in
solution; the greater the steric hindrance, the higher the
number of isomers present. Thus, 22, which has the smallest
combination of imido and aryloxide ligands (among these four
catalysts), has only one isomer, while 24, which contains the
slightly larger NArT imido group, has two isomers. In the case
where the aryloxide is HIPTO there are four isomers present in
both NArM and NArT imido complexes. These findings can be
rationalized in terms of steric crowding overall. As steric
crowding around the metal increases, restricted rotation results
in locking of the ligands on the NMR time scale in various
positions that give rise to more than the expected number of
isomers. On this basis we can propose that complex 16 (two
observable isomers) is less crowded than 24 or 25 but more
crowded than 22.
The ROMP of 2,3-dicarbomethoxynorbornadiene
(DCMNBD) has been employed as a means of judging the
stereospecificity (cis/trans selectivity and tacticity) of a MAP
metathesis catalyst.16 Therefore, all MAP catalysts (17−24 plus
25 prepared in situ) were treated with 25−100 equivalents of
monomer in toluene at 22 °C. The polymerization was
complete after one hour, and the resulting polymers were
isolated and analyzed by NMR methods. The results are
summarized in Table 1. All ROMP reactions are relatively fast.
CONCLUSION
■
We have found that MAP catalysts that contain NArM and
NArT ligands can be prepared through traditional synthetic
routes analogous to those employed to prepare catalysts that
contain NArCl, NArCF3, NAriPr, and NArtBu imido groups.
However, no imido ligands investigated in this report have
properties that lead to unusual results for ROMP polymer-
ization of DCMNBD. We conclude that a single ortho
substituent in the 2-substituted imido groups explored here
can point away from the C−M−Nimido face where the olefin is
proposed to bind, thereby minimizing interaction with the
approaching olefin. Complexes that contain a 2-substituted
imido ligand behave like much smaller imido groups in
reactions that have been explored so far. The results reported
here seem to imply that any attempt to employ a highly
sterically demanding phenyl imido group will lead to unique
metathesis behavior only if that catalyst contains a 2,6-
disubstituted phenylimido ligand such as 2,6-dimesitylphenyl
imido.10 Therefore we are now exploring the synthesis and
reactions of catalysts that contain a 2,6-dimesitylphenylimido
ligand.9
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis and characterization details for all complexes.
Crystallographic details, fully labeled thermal ellipsoid diagrams
for all crystallographically characterized species, and crystallo-
graphic information files in CIF format. This information 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.
Table 1. ROMP of DCMNBD with MAP Initiators 17−25 in
Toluene at 22 °C
AUTHOR INFORMATION
Corresponding Author
*E-mail: rrs@mit.edu.
Notes
catalyst
[catalyst] (mM)
DCMNBD equivalents
polymer structure
■
17
18
19
20
21
22
23
24
25
12
1.9
5.5
1.9
5.8
13
48
13
62
50
100
50
50% cis
>98% cis, syndio
>98% cis, syndio
>98% cis, syndio
76% cis
100
50
The authors declare no competing financial interest.
25
69% cis
ACKNOWLEDGMENTS
■
25
∼93% cis, syndio
77% cis
R.R.S. thanks the National Science Foundation (CHE-0841187
and CHE-1111133) for research support and for support for
departmental X-ray diffraction instrumentation (CHE-
0946721). V.W.L.N. thanks the Agency for Science, Technol-
ogy and Research (Singapore) for an A*STAR International
Fellowship.
25
25
83% cis
Compound 17 fails to initiate formation of a highly structured
polymer, presumably as a consequence of the imido group
being too large relative to the aryloxide (OTPP). There is a
drop in cis-selectivity from >98% to ∼70% in MAP species 21
and 22 when the imido ligand is larger than NAriPr. However,
increasing the size of the phenoxide from HMTO to HIPTO
(with initiator 23) again leads to a polymer that is >93%
cis,syndiotactic. Initiators 24 and 25 are unsuccessful, presum-
ably because NArT is too large in combination with OHMT or
OHIPT aryloxides. A lower cis-selectivity also has been
observed when Mo(NAr)(CHCMe2Ph)(Pyr)(OHIPT) is
employed as an initiator in place of Mo(NAd)(CHCMe2Ph)-
(Pyr)(OHIPT) (Ad = adamantyl and Ar = 2,6-i-Pr2C6H3).6h
The fact that 23 is almost as Z-selective as Mo(NAd)-
(CHCMe2Ph)(Pyr)(OHIPT) and 22−25 is surprising since it
REFERENCES
■
(1) (a) Schrock, R. R. Chem. Rev. 2009, 109, 3211. (b) Schrock, R. R.
Chem. Rev. 2002, 102, 145. (c) Schrock, R. R.; Hoveyda, A. H. Angew.
Chem., Int. Ed. 2003, 42, 4592. (d) Schrock, R. R.; Czekelius, C. C.
Adv. Syn. Catal. 2007, 349, 55.
(2) Schaverien, C. J.; Dewan, J. C.; Schrock, R. R. J. Am. Chem. Soc.
1986, 108, 2771.
(3) (a) Wengrovius, J. H.; Schrock, R. R.; Churchill, M. R.; Missert, J.
R.; Youngs, W. J. J. Am. Chem. Soc. 1980, 102, 4515. (b) Schrock, R.
R.; Rocklage, S. M.; Wengrovius, J. H.; Rupprecht, G.; Fellmann, J. J.
Mol. Catal. 1980, 8, 73. (c) Wengrovius, J. H.; Schrock, R. R.
Organometallics 1982, 1, 148.
(4) (a) Oskam, J. H.; Fox, H. H.; Yap, K. B.; McConville, D. H.;
O’Dell, R.; Lichtenstein, B. J.; Schrock, R. R. J. Organomet. Chem.
1993, 459, 185. (b) Fox, H. H.; Yap, K. B.; Robbins, J.; Cai, S.;
Schrock, R. R. Inorg. Chem. 1992, 31, 2287. (c) Alexander, J. B.;
Schrock, R. R.; Davis, W. M.; Hultzsch, K. C.; Hoveyda, A. H.; Houser,
suggests that NArM is in the same category as NArCl, NArCF3
,
and NAriPr imido ligands as far as producing polymers that have
a high cis,syndiotactic content; that is, NArM is operationally
relatively “small”.
2393
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394

Organometallics
Article
J. H. Organometallics 2000, 19, 3700. (d) Singh, R.; Czekelius, C.;
Schrock, R. R.; Muller, P.; Hoveyda, A. H. Organometallics 2007, 26,
̈
2528.
(5) Marinescu, S. C.; Schrock, R. R.; Muller, P.; Takase, M. K.;
̈
Hoveyda, A. H. Organometallics 2011, 30, 1780.
(6) (a) Singh, R.; Schrock, R. R.; Muller, P.; Hoveyda, A. H. J. Am.
̈
Chem. Soc. 2007, 129, 12654. (b) Marinescu, S. C.; Schrock, R. R.; Li,
B.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 58. (c) Sattely, E. S.;
Meek, S. J.; Malcolmson, S. J.; Schrock, R. R.; Hoveyda, A. H. J. Am.
Chem. Soc. 2009, 131, 943. (d) Ibrahem, I; Yu, M.; Schrock, R. R.;
Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 3844. (e) Jiang, A. J.;
Simpson, J. H.; Muller, P.; Schrock, R. R. J. Am. Chem. Soc. 2009, 131,
̈
7770. (f) Meek, S. J.; Malcolmson, S. J.; Li, B.; Schrock, R. R.;
Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 16407. (g) Jiang, A. J.;
Zhao, Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131,
16630. (h) Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Muller, P.;
̈
Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 7962. (i) Lee, Y.-J.;
Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 10652.
(j) Marinescu, S. C.; Schrock, R. R.; Muller, P.; Hoveyda, A. H. J. Am.
̈
Chem. Soc. 2009, 131, 10840.
(7) (a) Malcolmson, S. J.; Meek, S. J.; Sattely, E. S.; Schrock, R. R.;
Hoveyda, A. H. Nature 2008, 456, 933. (b) Meek, S. J.; O’Brien, R. V.;
Llaveria, J.; Schrock, R. R.; Hoveyda, A. H. Nature 2011, 471, 461.
(c) Yu, M.; Wang, C.; Kyle, A. F.; Jakubec, P.; Dixon, D. J.; Schrock, R.
R.; Hoveyda, A. H. Nature 2011, 479, 88.
(8) Solans-Monfort, X.; Coper
2010, 132, 7750.
́
et, C.; Eisenstein, O. J. Am. Chem. Soc.
(9) Gerber, L. C. H.; Schrock, R. R.; Muller, P.; Takase, M. K. J. Am.
̈
Chem. Soc. 2011, 133, 18142.
(10) (a) Gavenonis, J.; Tilley, T. D. Organometallics 2002, 21, 5549.
(b) Gavenonis, J.; Tilley, T. D. Organometallics 2004, 23, 31.
(11) Huang, X.; Anderson, K. W.; Zim, D.; Jiang, L.; Klapars, A.;
Buchwald, S. L. J. Am. Chem. Soc. 2003, 125, 6653.
(12) Hartmann, N.; Niemeyer, M. Synth. Commun. 2001, 31, 3839.
(13) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.;
DiMare, M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875.
(14) Marinescu, S. C.; Singh, R.; Hock, A. S.; Wampler, K. M.;
Schrock, R. R.; Muller, P. Organometallics 2008, 27, 6570.
̈
(15) (a) Sinnokrot, M. O.; Valeev, E. F.; Sherrill, C. D. J. Am. Chem.
Soc. 2002, 124, 10887. (b) Hunter, C. A.; Sanders, J. K. M. J. Am.
Chem. Soc. 1990, 112, 5525.
(16) Schrock, R. R. Dalton Trans. 2011, 40, 7484.
2394
dx.doi.org/10.1021/om3000289 | Organometallics 2012, 31, 2388−2394