Syntheses of Molybdenum(VI) Imido Alkylidene Complexes That Contain a Bidentate Dithiolate Ligand

Article abstract of DOI:10.1021/acs.organomet.8b00614

Zn(DCTC) (DCTC = 3,6-dichlorodithiacatecholate) reacts with Mo(NAd)(CHCMe₂Ph)Cl₂(PPh₂Me) (Ad = 1-adamantyl) to give Mo(NAd)(CHCMe₂Ph)(DCTC)(PPh₂Me). The reactions between Zn(DCTC) and Mo(NAd)(CH-t-Bu)(OTf)₂(dme) or Mo(NAr)(CHCMe₂Ph)(OTf)₂(dme) (Ar = 2,6-i-Pr₂C₆H₃; OTf = triflate; dme = 1,2-dimethoxyethane) produce [Mo(NAd)(CH-t-Bu)(DCTC)]₂ and [Mo(NAr)(CHCMe₂Ph)(DCTC)]₂, respectively. Complexes that contain a 3,3′,5,5′-tetrasubstituted dithiabiphenolate were prepared in a reaction between Mo(NAr)(CHCMe₂Ph)(Me₂pyr)₂ (Me₂pyr = 2,5-dimethylpyrrolide) and the 3,3′,5,5′-tetrasubstituted dithiabiphenols, (3,3′,5,5′-tetrachlorodithiabiphenol (H₂Cl₄S₂), 3,3′,5,5′-tetrabromodithiabiphenol (H₂Br₄S₂), and 3,3′,5,5′-tetra-t-Bu-dithiabiphenol (H₂Bu₄S₂)). The isolated complexes include Mo(NAr)(CHCMe₂Ph)(Cl₄S₂)(pyridine), Mo(NAr)(CHCMe₂Ph)(Br₄S₂)(pyridine), Mo(NAr)(CHCMe₂Ph)(Bu₄S₂)(PMe₃), and [Mo(NAr)(CHCMe₂Ph)(Cl₄S₂)]₂. Only the dithiabiphenolate derivatives (in the presence of B(C₆F₅)₃) show activity for the metathesis of 1-decene, and although that reaction is limited by a sensitivity of the alkylidene complexes to ethylene, as suggested by the reaction between ethylene and Mo(NAr)(CHCMe₂Ph)(Bu₄S₂) to give the ethylene complex, Mo(NAr)(C₂H₄)(Bu₄S₂). Mo(NAr)(C₂H₄)(Bu₄S₂) was unstable with respect to loss of ethylene and formation of an ethylene-free dimer. Mo(NAd)(CHCMe₂Ph)(DCTC)(PPh₂Me), [Mo(NAr)(CHCMe₂Ph)(DCTC)]₂, and [Mo(NAr)(CHCMe₂Ph)(Cl₄S₂)]₂ were characterized crystallographically.

Full text of DOI:10.1021/acs.organomet.8b00614

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Syntheses of Molybdenum(VI) Imido Alkylidene Complexes That
Contain a Bidentate Dithiolate Ligand
̈
Hosein Tafazolian, Charlene Tsay, Richard R. Schrock,* and Peter Muller
Department of Chemistry 6-331, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
*
S Supporting Information
ABSTRACT: Zn(DCTC) (DCTC = 3,6-dichlorodithiacatecholate) reacts with
Mo(NAd)(CHCMe Ph)Cl (PPh Me) (Ad = 1-adamantyl) to give Mo(NAd)-
2
2
2
(
(
CHCMe Ph)(DCTC)(PPh Me). The reactions between Zn(DCTC) and Mo-
2 2
NAd)(CH-t-Bu)(OTf) (dme) or Mo(NAr)(CHCMe Ph)(OTf) (dme) (Ar = 2,6-
2
2
2
i-Pr C H ; OTf = triflate; dme = 1,2-dimethoxyethane) produce [Mo(NAd)(CH-t-
2
6
3
Bu)(DCTC)] and [Mo(NAr)(CHCMe Ph)(DCTC)] , respectively. Complexes
2
2
2
that contain a 3,3′,5,5′-tetrasubstituted dithiabiphenolate were prepared in a
reaction between Mo(NAr)(CHCMe Ph)(Me pyr) (Me pyr = 2,5-dimethylpyrro-
2
2
2
2
lide) and the 3,3′,5,5′-tetrasubstituted dithiabiphenols, (3,3′,5,5′-tetrachlorodithia-
biphenol (H Cl S ), 3,3′,5,5′-tetrabromodithiabiphenol (H Br S ), and 3,3′,5,5′-
2
4
2
2
4 2
tetra-t-Bu-dithiabiphenol (H Bu S )). The isolated complexes include Mo(NAr)-
2
4 2
(
(
CHCMe Ph)(Cl S )(pyridine), Mo(NAr)(CHCMe Ph)(Br S )(pyridine), Mo-
2 4 2 2 4 2
NAr)(CHCMe Ph)(Bu S )(PMe ), and [Mo(NAr)(CHCMe Ph)(Cl S )] . Only
2
4
2
3
2
4
2
2
the dithiabiphenolate derivatives (in the presence of B(C F ) ) show activity for the
6
5 3
metathesis of 1-decene, and although that reaction is limited by a sensitivity of the alkylidene complexes to ethylene, as
suggested by the reaction between ethylene and Mo(NAr)(CHCMe Ph)(Bu S ) to give the ethylene complex,
2
4 2
Mo(NAr)(C H )(Bu S ). Mo(NAr)(C H )(Bu S ) was unstable with respect to loss of ethylene and formation of an
2
4
4
2
2
4
4 2
ethylene-free dimer. Mo(NAd)(CHCMe Ph)(DCTC)(PPh Me), [Mo(NAr)(CHCMe Ph)(DCTC)] , and [Mo(NAr)-
2
2
2
2
(
CHCMe Ph)(Cl S )] were characterized crystallographically.
2 4 2 2
INTRODUCTION
would not be productive. However, the relatively recent
■
discovery of active and Z-selective 14e catecholate ruthenium
The olefin metathesis chemistry of four-coordinate catalysts
with the formula M(NR)(CHR′)(X)(Y) (M = Mo or W) has
been dominated by compounds in which X and Y are
monoanionic and oxygen-based (alkoxides, aryloxides, biphe-
nolates, and binaphtholates) or those in which X is oxygen-
based and Y is a pyrrolide or (more recently ) a chloride.
9
catalysts raises the question as to whether any 14e Mo or W
complex that contains a catecholate or other bidentate
dithiolate ligand, of which we could find no examples in the
literature, might for some non-obvious reason be especially
metathesis active. In this paper, we prepare several examples of
Mo complexes that contain a bidentate dithiolate ligand and
provide some answers to this question.
1
2
Analogous M(O)(CHR′)(X)(Y) complexes have been studied
to a lesser degree because of synthetic challenges, but examples
3
4
are now known for W and even Mo. It is generally agreed
that high metathesis activity requires formation of a trigonal
bipyramidal metallacyclobutane intermediate in which the
RESULTS AND DISCUSSION
Zn(DCTC) reacts with Mo(NAd)(CHCMe Ph)Cl (PPh Me)
in dichloromethane to give 1a(PMePh ) (eq 1). NMR studies
■
2
2
2
1
,5
2
metallacycle occupies equatorial positions; square pyramidal
metallacycles must convert to a TBP in order to lose an olefin
readily. Metathesis activity has long been known to correlate
directly with the electrophilicity of the metal center. In
particular, the reduced metathesis activity of thiolate analogues
6
of bisalkoxides or aryloxides are relatively dramatic examples
of what has been attributed to the greater degree of electron
donation by a thiolate ligand to the metal relative to an
alkoxide or aryloxide analogue. Alkylidene thiolate complexes
7
8
suggested that 1a contains 1 equiv of coordinated PPh Me and
of tantalum and alkylidyne thiolate complexes of tungsten
2
an alkylidene in which the CMe Ph group points toward the
also show greatly reduced reactivity toward olefins or internal
acetylenes, respectively. This necessarily short history of
thiolate complexes would suggest that further attempts to
prepare metathesis-active thiolate complexes of Mo or W
2
Received: August 26, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00614
Organometallics XXXX, XXX, XXX−XXX

Organometallics
imido ligand (the syn isomer) on the basis of the value for J
Article
1
1c are both dimers in which one sulfur of one catecholate
ligand is bridging two Mo centers, whereas the other sulfur of
that DCTC ligand is bound to only one Mo, as shown in eqs 2
and 3.
CH
1
3
(
JCH = 118 Hz, J = 5.2 Hz).
An X-ray structural study (Figure 1) shows that the core
HP
geometry of 1a(PMePh ) is approximately halfway between a
2
An X-ray structural study of 1c confirmed the above
proposal (Figure 2). The overall structure at each Mo is closest
Figure 1. Thermal ellipsoid drawing of 1a(PMePh ). Hydrogen
2
atems have been omitted for clarity.
Figure 2. Thermal ellipsoid drawing of 1c (τ = 0.17).
trigonal bipyramid (TBP) and a square pyramid (SP)
10
according to the τ value (0.54). The metal−ligand bond
lengths (Table 1) are not unusual. The relatively long Mo1−
P1 bond suggests that the phosphine may be labile, but so far,
attempts to remove any dissociated phosphine through
addition of B(C F ) (in CH Cl or benzene) have led only
to a TBP (τ = 0.17), with the values for Mo1−S1 and Mo1−S3
being similar to the Mo−S values found in 1a(PMePh ),
2
6
5 3
2
2
whereas Mo1−S2 (2.366(6) Å) is understandably the shortest
of the three Mo−S distancs in 1c. Diffusion-ordered
spectroscopy (DOSY) showed that the diffusion coefficient
to complex mixtures instead of the expected phosphine-free
complex to be described immediately below.
−
10
2
Phosphine-free variations of 1a(PMePh ) were prepared in
obtained for 1a(PMePh ) (6.90 × 10 m /s) is larger than
2
10 2
2
−
reactions between Mo(NAd)(CH-t-Bu)(OTf) (dme) or Mo-
that of 1b (5.56 × 10 m /s), which supports the proposal
that 1b is a dimer rather than a monomer in solution. The
hydrodynamic molecular radii obtained from the Stokes−
Einstein equation for both complexes also were relatively close
to radii calculated from the X-ray data (see the Supporting
Information).
2
(
=
NAr)(CHCMe Ph)(OTf) (dme) (Ar = 2,6-i-Pr C H ; OTf
triflate; dme = 1,2-dimethoxyethane) and Zn(DCTC) (eqs 2
2 2 2 6 3
Dithiolate ligands derived from the three dithiols shown
below (H Cl S , H Br S , H Bu S ) are related to various
2
4
2
2
4
2
2
4 2
biphenolate and binaphtholate complexes that have been used
so successfully for ring-opening metathesis polymerization of
norbornenes and norbornadienes to yield cis,isotactic poly-
11
mers or (in enantiomerically pure form) for asymmetric
1a,12
metathesis reactions.
H Cl S and H Bu S are known,
2 4 2 2 4 2
whereas H Br S was synthesized in a manner that is nearly
2
4 2
identical to that used to make H Cl S . In the metal-free or
2
4 2
protonated forms, none of the four is likely to be resolvable
into enantiomerically pure forms as a consequence of facile
180° rotation about the Caryl−Caryl bond.
and 3, respectively). NMR spectra of 1b and 1c are consistent
with molecules that contain a syn-alkylidene but that do not
have mirror symmetry; that is, the catecholate protons on C4
and C5 are inequivalent. Therefore, we proposed that 1b and
Table 1. Selected Bond Lengths (Å) in 1a(L) (L = PMePh ) and 1c
2
Mo1−C1
Mo1−N1
Mo1−S1
Mo1−S2
Mo1−P1
Mo1−S3
1
1
a(L)
c
1.924(11)
1.936(2)
1.731(9)
1.730(19)
2.434(6)
2.522(5)
2.436(10)
2.366(6)
2.523(3)
na
na
2.488(5)
B
DOI: 10.1021/acs.organomet.8b00614
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
The tetrachloro- (H Cl S ) and tetrabromodithiols
H Br S ) react within 30 min in C D with Mo(NAr)-
2 4 2 6 6
2
4 2
(
(
CHCMe Ph)(Me pyr) in the presence of pyridine to yield
2
2
2
the five-coordinate complexes 2(py) and 3(py) (eqs 4 and 5).
Figure 3. Thermal ellipsoid drawing of 2.
Both 2(py) and 3(py) contain the anti isomer of the alkylidene
according to the JCH values (144 and 143 Hz). Proton NMR
spectra of both complexes show broad isopropyl methyl and
methine groups at room temperature. Pyridine that has been
added to proton NMR samples of 2(py) or 3(py) does not
exchange on the NMR time scale with coordinated pyridine, so
pyridine exchange cannot be part of the process that leads to
the broadening just described. Therefore, we attribute the
broadening to internal restricted motion.
When pyridine is omitted in the reaction shown in eq 4,
pyridine-free dimeric 2 is formed (eq 6). The proton NMR
Figure 4. 1H NMR spectra of (a) 2(py) and 2(py) + 1 equiv
B(C F ) after (b) 15 min, (c) 2 h, and (d) 12 h (C D , 400 MHz)
6
5
3
6
6
(
*initially formed dimeric product).
from 2(py) almost certainly is a slight variation of that
observed for 2, but we cannot say in detail what its structure is.
The reaction between Mo(NAr)(CHCMe Ph)(Me pyr)
2
spectrum of 2 contains contains two different syn-alkylidene
proton resonances of equal intensity at 14.35 ppm (JCH = 121
Hz) and 13.43 ppm (JCH = 120 Hz) in CD Cl (cf. 14.56 and
2
2
and H Bu S in benzene requires 2 days at 70 °C to go to
2
4 2
2
2
completion (eq 7). All volatiles were removed in vacuo to give
1
3.64 ppm in C D . An X-ray structural study of 2 (Figure 3)
6 6
showed that two thiolate sulfur atoms (S2 and S4) bridge
between two Mo centers, while two (S1 and S3) do not. One
of the chlorides in each dithiolate ligand could be said to be
weakly interacting with Mo (Mo1−Cl8 = 2.797 Å; Mo2−Cl4
=
2.839 Å). The arrangements of the “six” atoms in the primary
coordination spheres of each metal are different, which leads to
the two alkylidenes being inequivalent in the proton NMR
spectrum on the NMR time scale. It may be relevant (see
below) to note that the two dithiolate ligands have the same
a brittle red solid that is extremely soluble in pentane, a
property that suggests that it is a 14e monomer. No crystals or
precipitate could be obtained from even highly concentrated
solutions at −78 °C. However, a saturated solution of 4 in
acetonitrile resulted in the formation of a brown powder upon
standing the solution at −20 °C overnight. A H NMR
spectrum of the brown powder obtained upon filtration and
drying it in vacuo is identical to that of 4. Dissolution of 4 in 5
“
chirality” with respect to the relative orientation of the two
phenyl rings about the C−C bond connecting the two phenyl
rings. Compound 2 reacts with pyridine (1−3 equiv) to give
small amounts of 2(py) only very slowly (days) at 22 °C.
Compound 2 also can be prepared through addition of one
equivalent of B(C F ) to 2(py) followed by removal of
1
6
5 3
(
py)B(C F ) . As shown Figure 4, two alkylidene resonances
6 5 3
with equal area at 15.44 and 14.74 ppm grow in initially and
only after 12 h are replaced with the two alkylidene resonances
for 2. The complex formed initially upon removing pyridine
mL of pentane and addition of 2 equiv of PMe followed by
removal of all volatiles in vacuo gave orange crystals of the
3
adduct, 4(PMe ), which can be recrystallized from a saturated
3
C
DOI: 10.1021/acs.organomet.8b00614
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
pentane solution at −20 °C. Addition of 1 equiv of B(C F )
likely the reason why the metatheses of 1-decene noted earlier
do not proceed to completion.
6
5 3
to 4(PMe ) in C D led to a precipitate of (PMe )B(C F )
3
6
6
3
6 5 3
and a proton NMR spectrum identical to that of 4 described
above. The doublet syn-alkylidene α proton resonance for
CONCLUSIONS
■
3
1
4
(PMe ) at 11.79 ppm ( J = 3.8 Hz and J = 110 Hz)
We conclude that the molybdenum imido alkylidene thiolato
complexes we have prepared here are likely to be poor
metathesis catalysts because 14e core four-coordinate com-
plexes cannot be accessed readily; either a phosphine ligand is
not labile enough, or sulfur ultimately bridges too strongly to
give dimeric complexes that do not dissociate readily into 14e
monomers to any significant degree. The ultimate problem
continues to be bimolecular decomposition to give inactive
alkylidene-free complexes. Although in rare cases even
“alkylidene-free” complexes will metathesize some olefins
3
HP
CH
suggests that the phosphine is not dissociating from the metal
rapidly enough to be decoupled from the alkylidene proton.
However, PMe is lost readily on the chemical time scale and
3
therefore can be scavenged by B(C F ) .
6
5 3
All complexes were tested for metathesis of 1-decene. No
metathesis activity was observed in the presence of 1a-
(
PMePh ), 1b, or 1c. The most likely explanation, in our
2
opinion, is that 14e complexes simply are not formed in
solution in significant amounts; PMePh is bound too strongly
2
13,18
to the metal in 1a(PMePh ), and the bridging sulfurs are too
slowly through re-formation of an alkylidene,
activities so far are miniscule as a consequence of very little
alkylidene being re-formed. We had hoped that dimerization of
metathesis
2
strongly bound in 1b and 1c to allow them to break into 14e
monomeric fragments. Some metathesis of 1-decene was
4
through sulfur bridges would be limited because of the steric
observed in the presence of 5% 2(py), 3(py), or 4(PMe ) and
3
demands of the t-butyl groups in the 3 and 3′ positions of the
6
mol % of B(C F ) in C D in a J-Young NMR tube. A
6 5 3 6 6
2
−
[
t-Bu S ] ligand, but the relatively large size of sulfur and its
4 2
moderate conversion (20−33%) to 9-octadecenes and ethyl-
ene was observed within the first 30 min, but the catalytic
activity essentially stopped thereafter.
nucleophilic character continue to be damaging characteristics
if monomer Mo and W d alkylidene complexes are desired. In
0
contrast, M(NR)(CHR′)(X)(Y) (M = Mo or W) complexes
that contain two bulky alkoxides or one bulky 2,6-terphenoxide
are relatively stable toward bimolecular decompositions. It
should be pointed out that the imido groups in all complexes
prepared here are not comparable in steric demand to the
dimesityl NHC ligand found in monomeric ruthenium
We suspected that sensitivity of an alkylidene complex to
ethylene may be the reason why conversion of 1-decene to
product is limited. Therefore, we explored the reaction of
2
(py) and 4(PMe ) with ethylene in the presence B(C F ) . In
3 6 5 3
both reactions, 3-methyl-3-phenyl-1-butene (from the reaction
between the initial complex and ethylene) was observed along
with less than 1 equiv of propylene. (The exact amount of
propylene in solution could not be measured reliably in the
proton NMR spectrum due to some propylene residing in the
head space.) These data suggest that a methylene complex is
formed when 3-methyl-3-phenyl-1-butene is formed and part
or all of it reacts with ethylene to form an unsubstituted
metallacyclobutane complex, which then rearranges to
propylene; propylene then is displaced by ethylene.
9
catecholate complexes. Therefore, imido alkylidene catecho-
late complexes that contain 2,6-disubstituted phenylimido
1
9a
ligands (with the 2 and 6 substituents being 2,4,6-Me C H
3
6
2
19b
or 2,4,6-i-Pr C H
2
groups) could be relatively stable toward
3
6
bimolecular decomposition.
EXPERIMENTAL SECTION
■
General Procedures. All air- and moisture-sensitive compounds
were manipulated under a nitrogen atmosphere in a vacuum
atmosphere glovebox or on a Schlenk line. Glassware was oven-
dried prior to use. Solvents were degassed and dried by passing
through columns of activated alumina or 4 Å molecular sieves and
stored over activated molecular sieves. Pentane was shaken with
sulfuric acid and then water before use in the solvent purification
system. Benzene-d and toluene-d were dried over Na/benzophe-
The reaction of 4 with ethylene yields a single Mo product,
which appears to be an ethylene complex, Mo(NAr)(Bu S )-
4
2
(
C H ), on the basis of ethylene multiplets being observed at
2 4
2
.92, 2.80, 2.36, and 1.95 ppm in proton NMR spectra (see
Supporting Information Figure S33). Bisalkoxide Mo(IV)
13
imido olefin complexes are known, including monomeric
ethylene complexes, but in general, Mo(IV) olefin complexes
6
8
none, vacuum transferred onto molecular sieves, and stored in the
1
13
1
1
4
glovebox. H and C{ H} NMR spectra were referenced to the NMR
are relatively rare. However, attempted isolation of “Mo-
31
1
solvent residual peak, and P { H} spectra were referenced externally
to H PO in a D O standard. Pyridine was purchased from Alfa Aesar,
(
NAr)(Bu S )(C H )” led only to formation of a yellow
4
2
2
4
3
4
2
crystalline product that lacks ethylene proton resonances and
degassed under vacuum, and kept over molecular sieves before use.
B(C F ) was purchased from Strem and used as received. PMe and
does not react with ethylene to yield “Mo(NAr)(Bu S )-
4
2
6
5
3
3
(
C H )”. We propose that this final product is [Mo(NAr)-
PPh Me were purchased from Strem and degassed and stored over
2
2
4
sieves prior to use. Ultra-high-purity ethylene was purchased from
(
Bu S )] . Formations of a variety of metal−metal bonded
4
2
2
15
Airgas and used without further purification. H DCTC was purchased
2
complexes are known modes of decomposition of Mo-,
W-,
2
0
1
4c,16
17
from Sigma-Aldrich and used as received. Syntheses of Zn(DCTC),
H Cl S and H Bu S , Mo(NAd)(CHCMe Ph)Cl (PPh Me),
and Re-based alkylidene complexes, and stepwise
21
2b
2
4
2
2
4
2
2
2
2
loss of ethylene to form a dimeric tungsten product has been
22
Mo(NAd)(CHCMe )(OTf) DME,
Mo(NAr)(CHCMe Ph)-
2
23
3
2
1
4c
documented. We had no interest in decomposition products
that do not contain an alkylidene ligand and therefore did not
isolate and characterize “[Mo(NAr)(Bu S )] ”. Because
(
OTf) DME (NAr = 2,6-diisopropylphenylimido), and Mo(NAr)-
2
24
(CHCMe Ph)(Me Pyr) have been prepared as described in the
2
2
2
literature. Elemental analyses were performed at the Elemental
Analysis facility at the University of Rochester, New York, Midwest
Microlab, Indiana, and Atlantic Microlab, Georgia. In the descriptions
below, any dimeric compounds are shown as monomers for simplicity.
Mo(NAd)(CHCMe Ph)(Cl S )(PPh Me) (1a(PMePh )). Mo(NAd)-
4
2
2
2
−
monomeric complexes that contain the [Bu S ] ligand are
4
2
the least likely to dimerize from a steric point of view, yet do
ultimately, we did not investigate any other reactions of
complexes reported here with ethylene. In view of formation of
dimers through bimolecular coupling in Mo, W, and Re
chemistry noted above, and the reaction of 4 with ethylene just
described, we think that formation of bimolecular complexes is
2
2
2
2
2
(
CHCMe Ph)Cl (PPh Me) (400 mg, 0.617 mmol, 1 equiv) and
2 2 2
Zn(DCTC) (186 mg, 0.678 mmol, 1.1 equiv) were placed in separate
vials, and 5 and 10 mL of CH Cl was added, respectively, to each.
2
2
The solution of Mo(NAd)(CHCMe Ph)Cl (PPh Me) was trans-
2
2
2
D
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Organometallics
Article
3
ferred to the slurry of Zn(DCTC), while the mixture was stirred. The
vial was washed with another 5 mL of CH Cl and transferred to the
1H), 3.60 (septet, 3JHH = 6.7 Hz, 1H), 3.26 (septet, J = 6.7 Hz,
HH
3
1H), 1.69 (s, 3H), 1.43 (s, 3H), 1.40 (s, 3H), 1.28 (d, J = 6.7 Hz,
2
2
HH
3
3
reaction mixture. The vial was capped, and the mixture was stirred for
3H), 1.23 (d, J = 6.7 Hz, 3H), 1.18 (d, J = 6.7 Hz, 3H), 1.11
(d, J = 6.7 Hz, 3H), 0.66 (d, J = 6.7 Hz, 3H), 0.60 (s, 3H),
HH HH
0.57 (d, J = 6.7 Hz, 3H), 0.42 (d, J = 6.7 Hz, 3H), 0.32 (d,
JHH = 6.7 Hz, 3H); C{ H} (CD Cl , 100.6 MHz) δ 329, 318, 154,
153, 151, 149.9, 149.6, 148.9, 148.8, 148.6, 148.2, 147.72, 147.68,
43, 140.69, 140.67, 139.8, 139.6, 139.4, 135.8, 135.7, 133.1, 132.8,
HH HH
1
3
3
4
h. (Completion of the reaction was confirmed by H NMR
3
3
analysis.) The mixture was filtered through a frit and the filtrate
reduced to a yellow-green residue in vacuo. This residue was stirred in
pentane until it became a yellow powder. The yellow powder was
HH HH
3
13
1
2
2
filtered off, and all solvent was removed in vacuo; yield 404 mg
1
1
(
1
69%). Two isomers were found (83% syn with J = 118 Hz and
CH
132.6, 132.3, 130, 129.4, 129.3, 129.2, 128.8, 128.5, 128.3, 128.0,
127.1, 127.0, 126.7, 126.5, 126.1, 125, 124.3, 124.1, 123.8, 58.6, 58.4,
32, 31, 30.4, 30.0, 28.9, 28.82, 28.80, 27.8, 27.6, 26, 25, 24.8, 24.7,
24.5, 23.8, 23.0. Anal. Calcd for C H Cl Mo N S ·0.3Et O: C,
1
1
7% anti with J = 137 Hz): H NMR (syn isomer, CD Cl , 400
C
H
2
2
3
1
MHz) δ 12.09 (d, J = 5.2 Hz, J = 118 Hz, 1H), 7.50−7.44 (m,
HP
CH
3
9
1
1
H), 7.20−6.99 (m, 8H), 2.12 (d, J = 8.8 Hz, 3H), 2.03 (m, 3H),
HP
6
8
66
8
2
2
4
2
.94 (m, 1H), 1.91 (m, 3H), 1.87 (m, 2H), 1.86 (s, 3H), 1.84 (m,
5
4.07%; H, 4.52%; N, 1.82%. Found: C, 54.53%; H, 4.49%; N, 1.96%.
1
3
1
H), 1.67 (s, 3H), 1.56 (m, 5H); C{ H} (CD Cl , 100.6 MHz,
1
2
2
(On the basis of the intensity of the ether resonances in the H NMR
spectrum of the analyzed sample, 0.3 equiv of diethyl was included in
the calculated values.)
Mo(NAr)(CHCMe Ph)(Cl S )(py) (2(py)). A solution of H DCTC
(1 equiv, 0.339 mmol) and pyridine (4 equiv, 1.36 mmol) in benzene
(5 mL) was added dropwise to a solution of Mo(NAr)(CHCMe Ph)-
(Me pyr) in 10 mL of benzene. The solution was stirred for 4 h, and
the solvent was removed in vacuo. The residue was washed twice with
cold pentane, and the pentane wash was discarded. The resulting
yellow solid was dried in vacuo; yield 189 mg (67%): H NMR
synisomer) δ 323 (d, JCP = 21.3 Hz), 147 (d, JCP = 2.1 Hz), 133.7,
33.6, 133.19 (d, JCP = 11.2 Hz), 133.14 (d, JCP = 11.5 Hz), 132.0 (d,
JCP = 19.9 Hz), 131.3 (d, JCP = 2.5 Hz), 131.2 (d, JCP = 2.4 Hz), 129.1
d, JCP = 10.4 Hz), 129.03 (d, JCP = 10.3 Hz), 129.02 (d, JCP = 10.3
1
2
4
2
2
(
Hz), 128.7, 128.6, 126.6, 126.5, 126.4, 125, 123, 73, 54, 45 (d, JCP
=
2
0
(
.8 Hz), 44 (d, JCP = 1.3 Hz), 36, 31 (d, J = 2.3 Hz), 30.1, 30.0, 19
CP
2
2
d, JCP = 30.0 Hz); 31P{ H} NMR (CD Cl , 162.0 MHz) δ 25.3. Anal.
1
2 2
Calcd for C H Cl MoNPS ·0.2CH Cl : C, 58.58%; H, 5.32%; N,
39
42
2
2
2
2
1
.74%. Found: C, 58.42%; H, 5.48%; N, 1.86%.
1
Mo(NAd)(CHCMe )(Cl S ) (1b). A mixture of Mo(NAd)-
1
3
2
2
(CD Cl , 400 MHz, anti isomer) δ 14.55 (s, J = 144 Hz, 2H), 9.13
(dt, J = 5.0 Hz, J = 1.5 Hz, 2H), 7.84 (tt, J = 7.6 Hz, J
2
2
CH
(
CHCMe )(OTf) DME (200 mg, 0.284 mmol, 1 equiv) and
3
4
3
4
3
2
=
HH
HH
HH
HH
Zn(DCTC) (117 mg, 0.426 mmol, 1.5 equiv) in 10 mL of benzene
was stirred for 2 h. The solvent was removed in vacuo to give a yellow
solid. The solid was suspended in 4 mL of acetonitrile; the mixture
was stirred for a few minutes, and the acetonitrile washed supernatant
was discarded. This step was repeated a second time. The obtained
yellow precipitate was dissolved in benzene; the solution was filtered
through a frit, and the solvent was removed from the filtrate in vacuo
to produce 1b as a yellow powder; yield 73 mg (49%). Crystals of this
complex can be obtained from a cold benzene/acetonitrile (or
4
1
7
1
6
.5 Hz, 1H), 7.47 (d, J = 2.4 Hz, 1H), 7.40−7.36 (m, 2H), 7.22−
HH
4
4
.05 (m, 6H), 7.16 (d, J = 2.4 Hz, 1H), 7.08 (d, J = 2.4 Hz,
HH
HH
4
4
H), 7.08 (d, J = 0.9 Hz, 1H), 7.06 (d, J = 0.9 Hz, 1H), 6.90−
.87 (m, 2H), 3.75 (broad s, 2H), 1.60 (s, 3H), 1.59 (s, 3H), 1.16
broad s, 12H); C{ H} (CD Cl , 100.6 MHz) δ 327, 156, 154,
49.1, 148.7, 147.9, 146.6, 144, 139.6, 139.4, 138.7, 131.7, 131.6,
28.7, 128.6, 128.3, 127.9, 127.8, 126.5, 126.0, 125.6, 123 (broad), 53,
0 (broad), 27, 24, 23 (broad). Anal. Calcd for C H Cl MoN S : C,
5.99%; H, 4.58%; N, 3.35%. Found: C, 56.01%; H, 4.58%; N, 3.18%.
,3′,5,5′-Tetrabromo-[1,1′-biphenyl]-2,2′-dithiol. H Br S was
synthesized using the reported procedure described for H Cl S
HH
HH
13
1
(
2 2
1
1
3
5
3
9
37
4
2 4
1
toluene/acetonitrile) solution: H NMR (CD Cl , 400 MHz, syn
2
2
3
1
3
2
4 2
isomer) δ 12.62 (s, J = 109.5 Hz, 2H), 7.21 (d, J = 8.3 Hz,
H), 7.11 (d, J = 8.3 Hz, 2H), 2.06−1.97 (m, 20H), 1.61 (m,
0H), 0.94 (s, 18H); C{ H} (CD Cl , 100.6 MHz) δ 331, 152,
20
CH
HH
3
2
4 2
2
1
1
HH
and crystallized from hot ethanol as a white solid; yield 950 mg (12%)
13 1
2
2
from 2.7 g of 2,2′-biphenol. 3,3′,5,5′-Tetrabromo-[1,1′-biphenyl]-
44.5, 134, 133, 129, 125, 76, 48, 45, 36, 30.3, 30.0. Anal. Calcd for
2
,2′-diol can be prepared in large scale through addition of slight
C H Cl Mo N S : C, 48.10%; H, 5.19%; N, 2.67%. Found: C,
42
54
4
2
2 4
excess neat bromine to a methanol solution of 2,2′-biphenol. After the
reaction was stirred for 2 h, the white precipitate was collected on a
frit and washed with cold methanol and finally dried in vacuo. This
compound was converted to the dithiol as it was described for
4
7.84%; H, 5.19%; N, 2.64%.
Mo(NAr)(CHCMe Ph)(Cl S ) (1c). A mixture of Mo(NAr)-
2
2 2
(
CHCMe Ph)(OTf) DME (200 mg, 0.253 mmol, 1 equiv) and
2 2
Zn(DCTC) (83 mg, 0.303 mmol, 1.2 equiv) was stirred in 10 mL of a
mixture of toluene and acetonitrile (9:1) for 30 min. The reaction
mixture was then filtered through a glass frit, and all volatiles were
removed from the filtrate in vacuo. The residue was washed with
acetonitrile (2×, 2 mL each) and dried in vacuo to give a yellow solid;
1
H Cl S , and intermediate compounds were only characterized by H
2
4 2
NMR spectroscopy due to similarity to the tetrachloro analogue. It is
noteworthy to say that although the Miyazaki−Newman−Kwart
rearrangement step does not proceed well, the crude messy mixture
can be reduced by LiAlH (without further purification) and the
desired product will crystallize upon cooling a hot ethanol solution:
4
yield 107 mg (69%). Crystals of this complex can be obtained from a
1
cold benzene/acetonitrile (or toluene/acetonitrile) solution:
H
1
4
1
H NMR (CDCl
3
, 400 MHz) δ 7.78 (d, JHH = 2.1 Hz, 2H), 7.25 (d,
= 2.1 Hz, 2H), 3.94 (s, 2H); C{ H} (CDCl , 100.6 MHz) δ
NMR (CD Cl , 400 MHz, syn isomer) δ 13.26 (s, J = 122.8 Hz,
H), 7.21−7.01 (m, 20H), 3.94 (septet, J = 6.7 Hz, 4H), 1.59 (s,
H), 1.25 (d, J = 6.7 Hz, 12H), 1.22 (s, 6H), 0.93 (d, J = 6.7
2
2
CH
4J
13
1
3
2
6
HH
3
HH
3
3
140, 136, 134, 132, 123, 119. Anal. Calcd for C H Br S : C, 27.00%;
12 6 4 2
HH
HH
1
3
1
H, 1.13%. Found: C, 27.38%; H, 1.10%.
Mo(NAr)(CHCMe Ph)(Br S )(py) (3(py)). Complex 3(py) was
synthesized in a manner analogous to that used to prepare 2(py);
Hz, 12H); C{ H} (CD Cl , 100.6 MHz) δ 332, 153, 152, 147.1,
2
2
1
2
5
46.7, 145, 134, 133, 130, 129, 128, 127, 126.6, 126.5, 123, 59, 31, 29,
2
4 2
7, 24, 23. Anal. Calcd for C H Cl Mo N S ·C H : C, 57.14%; H,
5
6
62
4
2
2
4
6
6
1
yield 138 mg (81%): H NMR (CD Cl , 400 MHz, anti isomer) δ
.26%; N, 2.15%. Found: C, 56.95%; H, 5.56%; N, 2.15%.
2
2
1
3
1
7
6
3
4.60 (s, J = 14 Hz), 9.2 (d, J = 5.3 Hz, 2H), 7.9−7.7 (m, 1H),
Mo(NAr)(CHCMe Ph)(Cl S ) (2). A solution of H DCTC (1 equiv,
CH
HH
2
4
2
2
4
4
3
.6 (d, J = 2.2 Hz, 1H), 7.5 (d, J = 2.2 Hz, 1H), 7.4 (t, J =
0
.169 mmol) in benzene (5 mL) was added dropwise to a solution of
HH
HH
HH
.0 Hz, 2H), 7.3−7.1 (m, 6H), 7.0−6.9 (m, 2H), 4.3 (broad s, 1H),
.2 (broad s, 1H), 1.7 (s, 3H), 1.6 (s, 3H), 1.5 (broad s, 12H);
, 100.6 MHz) δ 326, 155, 153, 152, 150, 149, 148.1,
147.7, 146, 139, 134, 133, 131.3, 130.9, 130.6, 130.3, 128.3, 128.2,
126.1, 125.8, 125.5, 125.2, 123, 119.2, 119.0, 53, 29 (broad), 26, 24
(broad), 22, 14. Anal. Calcd for C39H37Br MoN S : C, 46.22%; H,
3.68%; N, 2.76%. Found: C, 46.36%; H, 3.52%; N, 2.65%.
Mo(NAr)(CHCMe Ph)(Bu S )(PMe ) (4(PMe )). Mo(NAr)-
Mo(NAr)(CHCMe Ph)(Me pyr) in benzene (3 mL), and the
2
2
2
mixture was stirred for 6 h. All volatiles were removed in vacuo,
and the residue was washed with cold pentane (2×, 4 mL each). The
resulting orange solid was washed with 4 mL of acetonitrile and dried
in vacuo; yield 103 mg (80%). Crystals of 2 were grown from an
1
3
1
C{ H} (CD
Cl
2
2
1
diethyl ether/acetonitrile solution at −20 °C: H NMR (CD Cl , 400
4 2 2
2
2
1
1
MHz) δ 14.35 (s, J = 121 Hz, 1H), 13.43 (s, J = 120 Hz, 1H),
CH
CH
4
4
7
.62 (d, J = 2.3 Hz, 1H), 7.48 (d, J = 2.3 Hz, 1H), 7.40−7.39
HH
HH
2
4
2
3
3
4
(
(
1
m, 2H), 7.25 (d, JHH = 2.3 Hz, 1H), 7.20−7.18 (m, 3H), 7.16−7.10
(CHCMe Ph)(Me pyr) (1 equiv 0.338 mmol) and H Bu S (tetra-
2 2 2 2 4 2
m, 5H), 7.07−6.99 (m, 9H), 6.77−6.74 (m, 2H), 6.62−6.60 (m,
t-butyldithiophenol, 1 equiv, 0.338 mmol) were dissolved in 15 mL of
benzene, and the reaction mixture was stirred at 70 °C for 2 days. All
3
3
H), 4.5 (septet, J = 6.7 Hz, 1H), 3.68 (septet, J = 6.7 Hz,
HH
HH
E
DOI: 10.1021/acs.organomet.8b00614
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
volatiles were removed in vacuo with gentle heating (40 °C). The
resulting red brittle solid was redissolved in pentane, and solvent was
removed in vacuo at 40 °C. The obtained red solid was dissolved in
ACKNOWLEDGMENTS
■
We are grateful for financial support from the National Science
Foundation (CHE-1463707).
1
0 mL of pentane, and PMe (2 equiv, 0.676 mmol) was added as a
3
solution in 5 mL of pentane. The mixture was stirred for 10 min, and
all volatiles were then removed in vacuo. Orange crystals of 4(PMe3)
can be obtained after a few hours from a saturated pentane solution at
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(
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Hosein Tafazolian: 0000-0002-4311-1013
Richard R. Schrock: 0000-0001-5827-3552
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F
DOI: 10.1021/acs.organomet.8b00614
Organometallics XXXX, XXX, XXX−XXX

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1
15, 4413−4414. (b) Schrock, R. R. Synthesis of stereoregular ROMP
(23) Oskam, H. J.; Fox, H. H.; Yap, B. K.; McConville, H. D.;
polymers using molybdenum and tungsten imido alkylidene initiators.
Dalton Trans 2011, 40, 7484−7495. (c) Schrock, R. R. Synthesis of
Stereoregular Polymers through Ring-Opening Metathesis Polymer-
ization. Acc. Chem. Res. 2014, 47, 2457−2466.
O'Dell, R.; Lichtenstein, J. B.; Schrock, R. R. Ligand Variation in
Alkylidene Complexes of the Type Mo(CHR)(NR’)(OR″) . J.
2
Organomet. Chem. 1993, 459, 185−198.
(
24) Singh, R.; Czekelius, C.; Schrock, R. R.; Muller, P.; Hoveyda, A.
̈
(
12) (a) Ogasawara, M.; Tseng, Y.; Uryu, M.; Ohya, N.; Chang, N.;
H. Molybdenum Imido Alkylidene Metathesis Catalysts that Contain
Ishimoto, H.; Arae, S.; Takahashi, T.; Kamikawa, K. Molybdenum-
5
Electron Withdrawing Biphenoxides or Biphenolates. Organometallics
Catalyzed Enantioselective Synthesis of Planar-Chiral (η -
2007, 26, 2528−2539.
Phosphacyclopentadienyl)manganese(I) Complexes and Application
in Asymmetric Catalysis. Organometallics 2017, 36, 4061−4069.
(
b) Ogasawara, M.; Tseng, Y.; Liu, Q.; Chang, N.; Yang, X.;
5
Takahashi, T.; Kamikawa, K. Kinetic Resolution of Planar-Chiral (η -
Bromocyclopentadienyl)manganese(I) Complexes by Molybdenum-
Catalyzed Asymmetric Ring-Closing Metathesis. Organometallics
2
017, 36, 1430−1435. (c) Ogasawara, M.; Arae, S.; Watanabe, S.;
Nakajima, K.; Takahashi, T. Kinetic Resolution of Planar-Chiral
Ferrocenylphosphine Derivatives by Molybdenum-Catalyzed Asym-
metric Ring-Closing Metathesis and Their Application in Asymmetric
Catalysis. ACS Catal. 2016, 6, 1308−1315.
(
13) Marinescu, S. C.; King, A. J.; Schrock, R. R.; Singh, R.; Muller,
̈
P.; Takase, M. K. Simple Molybdenum(IV) Olefin Complexes of the
Type Mo(NR)(X)(Y)(olefin). Organometallics 2010, 29, 6816−6828.
(
14) (a) Sues, P. E.; John, J. M.; Bukhryakov, K. V.; Schrock, R. R.;
̈
ller, P. Molybdenum and Tungsten Alkylidene Complexes That
Mu
Contain a 2-Pyridyl-Substituted Phenoxide Ligand. Organometallics
016, 35, 3587−3593. (b) Tsang, W. C. P.; Jamieson, J. Y.; Aeilts, S.
2
A.; Hultzsch, K. C.; Schrock, R. R.; Hoveyda, A. H. Investigations of
Reactions Between Enantiomerically Pure Molybdenum Imido
Alkylidene Complexes and Ethylene: Observation of Unsolvated
Base-free Methylene Complexes, Metalacyclobutane and Metal-
acyclopentane Complexes, and Molybdenum (IV) Olefin Complexes.
Organometallics 2004, 23, 1997−2007. (c) Arndt, S.; Schrock, R. R.;
Mu
that Contain the 2,6-Dichlorophenylimido Ligand. Organometallics
007, 26, 1279−1290. (d) Jiang, A. J.; Schrock, R. R.; Muller, P.
Cationic Molybdenum Imido Alkylidene Complexes. Organometallics
008, 27, 4428−4438.
15) Robbins, J.; Bazan, G. C.; Murdzek, J. S.; O’Regan, M. B.;
̈
ller, P. Synthesis and Reactions of Tungsten Alkylidene Complexes
2
̈
2
(
Schrock, R. R. Reduction of Molybdenum Imido-Alkylidene
Complexes in the Presence of Olefins to Give Molybdenum(IV)
Complexes. Organometallics 1991, 10, 2902−2907.
(
16) (a) Lopez, L. P. H.; Schrock, R. R. Formation of Dimers That
Contain Unbridged W(IV)/W(IV) Double Bonds. J. Am. Chem. Soc.
ller, P.
2
004, 126, 9526−9527. (b) Lopez, L. P. H.; Schrock, R. R.; Mu
̈
Dimers that Contain Unbridged W(IV)/W(IV) Double Bonds.
Organometallics 2006, 25, 1978−1986.
(
17) Toreki, R.; Schrock, R. R.; Vale, M. G. Two Rhenium
Complexes That Contain an Unsupported Metal-Metal Double Bond
in the Presence of Potentially Bridging Ligands. J. Am. Chem. Soc.
1991, 113, 3610−3611.
G
DOI: 10.1021/acs.organomet.8b00614
Organometallics XXXX, XXX, XXX−XXX