Simple molybdenum(IV) olefin complexes of the type Mo(NR)(X)(Y)(olefin)

Article abstract of DOI:10.1021/om101003v

Exposure of heptane solutions of Mo(NAr)(CHCMe₂Ph)(Me ₂Pyr)(OAr) (1a; Ar = 2,6-diisopropylphenyl), Mo(NAr)(CHCMe ₃)(Me₂Pyr)[OCMe(CF₃)₂] (1b), and Mo(NAr)(CHCMe₂Ph)(Me₂Pyr)(OSiPh₃) (1c) to one atmosphere of ethylene for 12 h yields the ethylene complexes, Mo(NAr)(CH ₂CH₂)(Me₂Pyr)(OAr) (2a), Mo(NAr)(CH ₂CH₂)(Me₂Pyr)[OCMe(CF₃) ₂] (2b), and Mo(NAr)(CH₂CH₂)(Me ₂Pyr)(OSiPh₃) (2c). Addition of 1 equiv of triphenylsilanol to a solution of 2c gives Mo(NAr)(CH₂CH ₂)(OSiPh₃)₂ (3) readily. Mo(NAr)(CHCMe ₂Ph)(OTf)₂(dme) reacts slowly with ethylene (60 psi) in toluene at 80 °C to give cis and trans isomers of Mo(NAr)(CH ₂CH₂)(OTf)₂(dme) (4a) in the ratio of ～2(cis):1. Addition of lithium 2,5-dimethylpyrrolide to 4a under 1 atm of ethylene produces Mo(NAr)(CH₂CH₂)(η¹- Me₂Pyr)(η⁵-Me₂Pyr) (5a). Mo(NAr)(CHCMe ₂Ph)(η¹-MesPyr)₂ (MesPyr = 2-mesitylpyrrolide) reacts cleanly with ethylene in benzene at 60 °C over a period of four days to give exclusively Mo(NAr)(CH₂CH ₂)(MesPyr)₂ (5b). Treatment of 5b with 2 equiv of (CF ₃)₂CHOH in ether yields Mo(NAr)(CH₂CH ₂)[OCH(CF₃)₂]₂(Et₂O) (6). Neat styrene reacts with 2c and 3 to generate the styrene complexes, Mo(NAr)(CH₂CHPh)(Me₂Pyr)(OSiPh₃) (7) and Mo(NAr)(CH₂CHPh)(OSiPh₃)₂ (8), respectively. Similarly, the trans-3-hexene complex, Mo(NAr)(trans-3-hexene)(OSiPh ₃)₂ (9a), can be prepared from 3 and neat trans-3-hexene. When 3 is exposed to 1 atm of ethylene, the molybdacyclopentane species, Mo(NAr)(C₄H₈)(OSiPh₃)₂ (10), is generated. X-ray structural studies were carried out on 2c, 5a, 6, 8, 9a, and 10. All evidence suggests that alkene exchange at the Mo(IV) center is facile, followed by cis,trans isomerization and isomerization via double bond migration. In addition, trace amounts of alkylidene complexes are formed that result in slow metathesis reactions of free olefins to give (e.g.) a distribution of all possible linear olefins from an initial olefin and its double bond isomers.

Full text of DOI:10.1021/om101003v

6816 Organometallics 2010, 29, 6816–6828
DOI: 10.1021/om101003v
Simple Molybdenum(IV) Olefin Complexes of the Type
Mo(NR)(X)(Y)(olefin)
Smaranda C. Marinescu, Annie J. King, Richard R. Schrock,* Rojendra Singh,
€
Peter Muller, and Michael K. Takase
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,
United States
Received October 21, 2010
Exposure of heptane solutions of Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OAr) (1a; Ar=2,6-diisopropylphenyl),
Mo(NAr)(CHCMe3)(Me2Pyr)[OCMe(CF3)2] (1b), and Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OSiPh3)
(1c) to one atmosphere of ethylene for 12 h yields the ethylene complexes, Mo(NAr)(CH2CH2)-
(Me2Pyr)(OAr) (2a), Mo(NAr)(CH2CH2)(Me2Pyr)[OCMe(CF3)2] (2b), and Mo(NAr)(CH2CH2)-
(Me2Pyr)(OSiPh3) (2c). Addition of 1 equiv of triphenylsilanol to a solution of 2c gives
Mo(NAr)(CH2CH2)(OSiPh3)2 (3) readily. Mo(NAr)(CHCMe2Ph)(OTf)2(dme) reacts slowly with
ethylene (60 psi) in toluene at 80 °C to give cis and trans isomers of Mo(NAr)(CH2CH2)(OTf)2(dme)
(4a) in the ratio of ∼2(cis):1. Addition of lithium 2,5-dimethylpyrrolide to 4a under 1 atm of ethylene
produces Mo(NAr)(CH2CH2)(η1-Me2Pyr)(η5-Me2Pyr) (5a). Mo(NAr)(CHCMe2Ph)(η1-MesPyr)2
(MesPyr = 2-mesitylpyrrolide) reacts cleanly with ethylene in benzene at 60 °C over a period of four
days to give exclusively Mo(NAr)(CH2CH2)(MesPyr)2 (5b). Treatment of 5b with 2 equiv of
(CF3)2CHOH in ether yields Mo(NAr)(CH2CH2)[OCH(CF3)2]2(Et2O) (6). Neat styrene reacts with
2c and 3 to generate the styrene complexes, Mo(NAr)(CH2CHPh)(Me2Pyr)(OSiPh3) (7) and
Mo(NAr)(CH2CHPh)(OSiPh3)2 (8), respectively. Similarly, the trans-3-hexene complex, Mo(NAr)-
(trans-3-hexene)(OSiPh3)2 (9a), can be prepared from 3 and neat trans-3-hexene. When 3 is exposed
to 1 atm of ethylene, the molybdacyclopentane species, Mo(NAr)(C4H8)(OSiPh3)2 (10), is generated.
X-ray structural studies were carried out on 2c, 5a, 6, 8, 9a, and 10. All evidence suggests that alkene
exchange at the Mo(IV) center is facile, followed by cis,trans isomerization and isomerization via
double bond migration. In addition, trace amounts of alkylidene complexes are formed that result in
slow metathesis reactions of free olefins to give (e.g.) a distribution of all possible linear olefins from
an initial olefin and its double bond isomers.
Introduction
and tungsten biphenolate and binaphtholate catalysts have
been studied most thoroughly.2,3 (Fewer studies have been
reported for analogous Mo complexes.4) Among the species
observed in solution are an unsubstituted tungstacyclobu-
tane complex, an ethylene complex, an unsubstituted tung-
stacyclopentane complex, and a heterochiral dimeric methylidene
complex. Ethylene has also been employed in order to study
the mechanism of catalyst decomposition and formation of
bimetallic species. For example, the tungstacyclobutane
complex, W(NArCl)(Biphen)(C3H6) (ArCl = 2,6-Cl2C6H3;
Biphen = 6,60-dimethyl-3,30,5,50-tetra-t-butyl-1,10-biphe-
nyl-2,20-diolate), was found to decompose to yield (inter
alia) the dimeric, heterochiral methylidene complex,
[W(NArCl)(Biphen)(μ-CH2)]2, which decomposed further
to yield homochiral [W(NArCl)(Biphen)]2(μ-CH2CH2), which
in turn lost ethylene to yield [W(NArCl)(Biphen)]2.5 The ethylene
complexes that have been prepared in reactions between
Ethylene is a product of olefin metathesis reactions that
involve one or more terminal olefins. High oxidation state
molybdenum and tungsten imido alkylidene complexes1
react with ethylene to give methylidene complexes, which
are the least stable alkylidenes toward bimolecular decom-
position, and unsubstituted metallacyclobutane complexes,
which are the most stable metallacycles toward loss of an
olefin. Ethylene also has been proposed to promote rearran-
gement of an unsubstituted metallacyclobutane to an olefin
and thereby to lead to decomposition of high oxidation state
alkylidene catalysts.2
Perhaps the most informative studies concerning reactions
between alkylidene complexes and ethylene in solution have
employed 13C-labeled ethylene. Reactions between 13C2H4
*To whom correspondence should be addressed. Phone: 617-253-
1596. Fax: 617-253-7670. E-mail: rrs@mit.edu.
(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. (e) Poater, A.; Solans-Monfort, X.; Clot, E.;
(3) Tsang, W. C. P.; Hultzsch, K. C.; Alexander, J. B.; Bonitatebus,
P. J., Jr.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2003, 125,
2652.
(4) Tsang, W. C. P.; Jamieson, J. Y.; Aeilts, S. A.; Hultzsch, K. C.;
ꢀ
Coperet, C.; Eisenstein, O. J. Am. Chem. Soc. 2007, 129, 8207.
Schrock, R. R.; Hoveyda, A. H. Organometallics 2004, 23, 1997.
€
(2) Tsang, W. C. P.; Schrock, R. R.; Hoveyda, A. H. Organometallics
2001, 20, 5658.
(5) Arndt, S.; Schrock, R. R.; Muller, P. Organometallics 2007, 26,
1279.
r
2010 American Chemical Society
pubs.acs.org/Organometallics
Published on Web 12/02/2010

Article
Organometallics, Vol. 29, No. 24, 2010 6817
imido alkylidene complexes and ethylene and that have been
isolated and structurally characterized are the five-coordinate
species W(NArCl)(CH2CH2)(Biphen)(THF),5 Mo(NArCl)-
(CH2CH2)(Biphen)(Et2O),4 and{Mo(NAr)(CH2CH2)[OCMe-
(CF3)2](THF)3}B(3,5-(CF3)2C6H3)4.6
or η1-pyrrolide) are related to TaCp*Cl2(olefin) complexes,
which catalyze the dimerization of terminal olefins to tail-to-tail
or head-to-tail dimers via a metallacyclopentane “ring-
contraction” mechanism.13 Complexes that contain
Mo(NAr)(X)(Y) or W(NAr)(X)(Y) cores also will dimerize
ethylene slowly to 1-butene.3,4
There is some evidence that alkylidene complexes can be
formed in reactions between Mo(IV) or W(IV) imido bisalk-
oxide or biphenolate complexes and ethylene. For example,
vinyltributylstannane is homologated to allyltributylstan-
nane by Mo(IV) complexes in the presence of ethylene.7
Although Mo(NArCl)(CH2CH2)(rac-Biphen)(ether) is inactive
for ring-closing diallyl ether in 10 days at 22 °C, when 10 equiv
of norbornene were added to a benzene solution of 5 mol %
Mo(NArCl)(CH2CH2)(rac-Biphen)(ether) and diallyl ether,
a 56% yield of 2,4-dihydrofuran was obtained in 10 days.8
In the last several years, new types of Mo and W imido
alkylidene complexes that have the formula M(NR)(CHR0)-
(OR00)(Pyr), where Pyr is a pyrrolide or substituted pyrrolide
ligand and OR00 usually is an aryloxide, have been prepared
and explored.9 These monoalkoxidepyrrolide (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 new features of fundamental inter-
est, perhaps the most important of which is the presence of a
stereogenic metal center. MAP species have proven to be
extraordinarily reactive,9,10 as are isoelectronic rhenium
alkylidyne alkylidene species that contain a stereogenic
metal center.11 Under the right circumstances, many have
been found to be long-lived compared to first or second
generation catalysts. Initial studies of reactions between
MAP species and ethylene showed that when a sterically
relatively small set of ligands is present, ethylene complexes
are often formed in the presence of ethylene.12
In view of the isomeric relationship between olefin and
alkylidene complexes,14-16 as well as the roles olefins may
play in metathesis chemistry beyond the obvious role as
substrates, as has been outlined above, we decided to explore
routes to simple Mo(IV) ethylene complexes of the type
Mo(NAr)(X)(Y)(CH2CH2) and reactions between ethylene
complexes and olefins. The results of this investigation are
reported here.
Results
Exposure of heptane solutions of Mo(NAr)(CHCMe2Ph)-
(Me2Pyr)(OAr) (1a; Ar = 2,6-diisopropylphenyl, Me2Pyr =2,
5-dimethylpyrrolide) and Mo(NAr)(CHCMe3)(Me2Pyr)-
[OCMe(CF3)2] (1b) to one atmosphere of ethylene for 12 h
led to formation of the ethylene complexes, Mo(NAr)-
(CH2CH2)(Me2Pyr)(OAr) (2a) and Mo(NAr)(CH2CH2)-
(Me2Pyr)[OCMe(CF3)2] (2b) in isolated yields of 59% and
63%, respectively (eq 1). Proton NMR spectra in C6D6
revealed resonances for bound ethylene at 2.95 (2H), 2.60
(1H), and 1.95 (1H) ppm in 2a and 2.74 (2H), 2.45 (1H), 2.16
(1H) ppm in 2b. The presence of four ethylene resonances
(two overlapping) suggests that the ethylene does not rotate
rapidly on the NMR time scale. A similar reaction between
Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OSiPh3) (1c) and ethylene
led to formation of Mo(NAr)(CH2CH2)(Me2Pyr)(OSiPh3)
(2c) in 70% yield (ethylene resonances at 2.87 (1H), 2.70
(1H), and 2.20 (2H) ppm). Experiments employing 13C2H4
revealed ethylene carbon resonances at 56.3 and 60.2 ppm
with JCH = 155 Hz and JCC = 39 Hz for 2a and at 56.9 and
58.0 ppm with JCH = 153 Hz and JCC = 37 Hz for 2c. These
chemical shifts and JCH values are similar to those reported
in ethylene complexes noted earlier5,6 and others reported here.
It is interesting to note that olefin complexes of the type
M(NAr)(X)(Y)(olefin) (M = Mo or W; X or Y = alkoxide
€
(6) Jiang, A. J.; Schrock, R. R.; Muller, P. Organometallics 2008, 27,
4428.
(7) Schrock, R. R.; Duval-Lungulescu, M.; Tsang, W. C. P.; Hoveyda,
A. H. J. Am. Chem. Soc. 2004, 126, 1948.
(8) Schrock, R. R.; Lopez, L. P. H.; Hafer, J.; Singh, R.; Sinha, A.;
€
Muller, P. Organometallics 2005, 24, 5211.
€
(9) (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) Malcolmson, S. J.;
Meek, S. J.; Sattely, E. S.; Schrock, R. R.; Hoveyda, A. H. Nature 2008, 456,
933. (d) Sattely, E. S.; Meek, S. J.; Malcolmson, S. J.; Schrock, R. R.;
Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 943. (e) Schrock, R. R. Chem.
Rev. 2009, 109, 3211. (f) Ibrahem, I; Yu, M.; Schrock, R. R.; Hoveyda, A. H.
J. Am. Chem. Soc. 2009, 131, 3844. (g) Jiang, A. J.; Simpson, J. H.; M€uller,
P.; Schrock, R. R. J. Am. Chem. Soc. 2009, 131, 7770. (h) Meek, S. J.;
Malcolmson, S. J.; Li, B.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc.
2009, 131, 16407. (i) Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H.
J. Am. Chem. Soc. 2009, 131, 16630. (j) Flook, M. M.; Jiang, A. J.; Schrock,
R. R.; M€uller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 7962. (k)
Lee, Y.-J.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131,
10652. (l) Marinescu, S. C.; Schrock, R. R.; M€uller, P.; Hoveyda, A. H.
J. Am. Chem. Soc. 2009, 131, 10840.
The results of a single crystal X-ray structural study of 2c
˚
are shown in Figure 1. The C(1)-C(2) bond length is 1.420(3) A,
which should be compared to the ethylene C-C bond
lengths inMo(NAr )(CH2CH2)(Biphen)(Et2O) (1.400(13) A),
ꢀ
(10) Solans-Monfort, X.; Coperet, C.; Eisenstein, O. J. Am. Chem.
Cl
4
˚
Soc. 2010, 132, 7750.
(11) (a) Solans-Monfort, X.; Clot, E.; Coperet, C.; Eisenstein, O.
Cl
W(NAr )(CH2CH2)(Biphen)(THF) (1.452(3) A), and {Mo-
5
ꢀ
˚
J. Am. Chem. Soc. 2005, 127, 14015. (b) Chabanas, M.; Baudouin, A.;
6
(NAr)(CH2CH2)[OC(CF3)2Me](THF)3}þ (1.408(4) A). The
˚
ꢀ
Coperet, C.; Basset, J.-M. J. Am. Chem. Soc. 2001, 123, 2062.
(12) Singh, R.; , Ph.D. Thesis, Massachusetts Institute of Technol-
ogy, 2008.
(14) Miller, G. A.; Cooper, N. J. J. Am. Chem. Soc. 1985, 107, 709.
(15) Freundlich, J. S.; Schrock, R. R.; Davis, W. M. J. Am. Chem.
Soc. 1996, 118, 3643.
(16) Hirsekorn, K. F.; Veige, A. S.; Marshak, M. P.; Koldobskaya,
Y.; Wolczanski, P. T.; Cundari, T. R.; Lobkovsky, E. B. J. Am. Chem.
Soc. 2005, 127, 4809.
(13) (a) McLain, S. J.; Schrock, R. R. J. Am. Chem. Soc. 1978, 100,
1315. (b) McLain, S. J.; Sancho, J.; Schrock, R. R. J. Am. Chem. Soc. 1979,
101, 5451. (c) Schrock, R. R.; McLain, S. J.; Sancho, J. Pure Appl. Chem.
1980, 52, 729. (d) McLain, S. J.; Sancho, J.; Schrock, R. R. J. Am. Chem.
Soc. 1980, 102, 5610.

6818 Organometallics, Vol. 29, No. 24, 2010
Marinescu et al.
ethylene in mirror symmetric Mo(NAr)(CH2CH2)(OSiPh3)2
(3) (eq 2). Protonolysis of pyrrolide ligands in these
circumstances has been proposed to require coordination of
the alcohol oxygen to the metal before proton migration,9e
which in turn suggests that the 18e count in 2c is first reduced
to 14e through ready formation of intermediate Mo(NAr)-
(CH2CH2)(η1-Me2Pyr)(OSiPh3).
To prepare potentially a large variety of ethylene complexes,
we attempted to prepare an ethylene complex through a reaction
between Mo(NAr)(CHCMe2Ph)(OTf)2(dme) and ethylene.
Mo(NAr)(CHCMe2Ph)(OTf)2(dme) was found to react slowly
with ethylene (60 psi) in toluene at 80 °C. After two days, a red
ethylene complex can be isolated in 86% yield. The 1H NMR
spectrum revealed several multiplet resonances between 4 and
2.5 ppm that could be ascribed to an ethylene ligand, while
the 19F NMR spectrum showed three singlet resonances at
δ -78.26, -78.30, and -78.59 for triflate ligands in approxi-
mately a 1:1:1 ratio. All data are consistent with the reaction
between Mo(NAr)(CHCMe2Ph)(OTf)2(dme) and ethylene
giving cis and trans isomers of Mo(NAr)(CH2CH2)(OTf)2(dme)
(4a) in the ratio of 2:1, respectively (eq 3). The reaction between
Mo(NAr)(OTf)2(CHCMe2Ph)(dme) and ethylene most likely
proceeds through metathesis to yield Mo(NAr)(OTf)2(CH2)-
(dme), which then decomposes in the presence of ethylene to
give the observed product. To our knowledge, the reaction
shown in eq 3 is the only metathetical reaction of Mo(NAr)-
(OTf)2(CHCMe2Ph)(dme) to have been reported. Using a
similar procedure (1 atm ethylene; 60 °C, 6 h), Mo(NAd)-
(CH2CH2)(OTf)2(dme) (4b) can be obtained as approximately
a 2:1 mixture of cis and trans isomers, respectively.
Figure 1. POV-ray drawing of 2c. Thermal ellipsoids are dis-
played at 50% probability level. Hydrogen atoms are omitted.
Selected distances (A) and angles (deg): Mo(1)-C(1) = 2.190(2) A,
˚
˚
˚
˚
Mo(1)-C(2)=2.182(2) A, Mo(1)-N(1)=1.7353(18) A, Mo(1)-
˚
˚
O(1)=2.0080(15) A, C(1)-C(2)=1.420(3) A, Mo(1)-N(2)=
2.3588(18) A, Mo(1)-C(22) = 2.458(2) A, Mo(1)-C(23) =
˚
˚
˚
˚
2.506(2) A, Mo(1)-C(24) = 2.441(2) A, Mo(1)-C(25) =
˚
2.355(2) A, Mo(1)-N(1)-C(11) = 163.09(15)°, Mo(1)-
O(1)-Si(1)=149.06(9)°, N(1)-Mo(1)-C(1)=98.75(9)°, N(1)-
Mo(1)-C(2)=97.89(8)°.
imido ligand bends (Mo(1)-N(1)-C(11) = 163.09(15)°) in
response to some significant steric interaction between the
triphenylsiloxide and the 2,6-diisopropylphenylimido ligand.
The ethylene is oriented so that its C-C axis is essentially
perpendicular to the Mo(1)-N(1) axis (N(1)-Mo(1)-C(1) =
98.75(9)°, N(1)-Mo(1)-C(2) = 97.89(8)°).
A reaction between 1c and propylene in C6D6 led to
formation of the ethylidene complex Mo(NAr)(CHMe)-
(Me2Pyr)(OSiPh3) initially, as judged from appearance of
a new alkylidene quartet at 12.32 ppm, along with 2c and
other species, but after 1 day at room temperature, only
2c is observed along with propylene and expected me-
tathesis products (2-butenes, H2CdCHCMe2Ph, etc.).
Because ethylene is generated in the metathesis reaction
and because ethylene is the smallest and most reactive
olefin, the ultimate product or products are derived from
ethylene.
Addition of CD2CD2 (1 atm) to a C6H6 solution of 2c led
to immediate formation of Mo(NAr)(CD2CD2)(Me2Pyr)-
(OSiPh3), according to 2H NMR spectroscopy. This obser-
vation confirms that ethylene exchanges readily in 2c, either
through direct displacement of ethylene by CD2CD2 in a
five-coordinate intermediate or through rapid formation and
breakup of an intermediate five-coordinate molybdacyclo-
pentane (vide infra). Rapid exchange can also be observed
employing 13C NMR and 13C2H4.
Addition of 1 equiv of triphenylsilanol to a solution of 2c
led to an immediate color change from red to purple. A
proton NMR spectrum revealed two pseudo quartets at 2.74
and 1.99 ppm which integrate as two protons each for bound
Addition of lithium 2,5-dimethylpyrrolide to 4a under
1 atm of ethylene led to formation of Mo(NAr)(CH2CH2)(η1-
Me2Pyr)(η5-Me2Pyr) (5a) (eq 4). If the reaction is attempted in
the absence of ethylene, a significant amount of decomposition
is observed. Compound 5a could not be prepared through a
reaction between Mo(NAr)(CHCMe2Ph)(η1-Me2Pyr)(η5-
Me2Pyr) and ethylene (1 atm) at 80 °C. Two ethylene reso-
nances were found at 51.3 and 48.1 ppm. A single crystal X-ray
structural study of 5a (Figure 2) confirms that the pyrrolide

Article
Organometallics, Vol. 29, No. 24, 2010 6819
ligands are bound in an η1 and η5 manner. The C(1)-C(2)
˚
bond length is 1.404(4) A. The N(1)-Mo(1)-C(1) and N(1)-
Mo(1)-C(2) angles (87.32(8)° and 101.17(8)°, respectively)
suggest that ethylene is twisted a few degrees from being
perpendicular to the Mo-N(1) bond.
In contrast to the failure to prepare 5a through a reaction
between Mo(NAr)(CHCMe2Ph)(Me2Pyr)2 and ethylene, Mo-
6
(NAr)(CHCMe2Ph)(η1-MesPyr)2 (MesPyr =2-mesitylpyrrolide)
reacts cleanly with ethylene in benzene at 60 °C over a period of
four days to give Mo(NAr)(CH2CH2)(MesPyr)2 (5b) in 71%
isolated yield (eq 5). The higher reactivity
Figure 2. POV-ray drawing of 5a. Thermal ellipsoids are dis-
played at 50% probability level. Hydrogen atoms are omitted.
˚
˚
Selected distances (A) andangles(deg):Mo(1)-C(1) = 2.215(2) A,
˚
˚
Mo(1)-C(2)=2.199(2) A, Mo(1)-N(1)=1.7423(17) A, Mo(1)-
N(2)=2.3785(17) A, Mo(1)-N(3)=2.1444(17) A, C(1)-C(2)=
1.404(4) A,Mo(1)-C(31)=2.396(2) A,Mo(1)-C(32)=2.407(2) A,
Mo(1)-C(33)=2.420(2) A, Mo(1)-C(34)=2.396(2) A, Mo(1)-
N(1)-C(11)=174.88(14)°, N(1)-Mo(1)-C(1)=87.32(8)°, N(1)-
Mo(1)-C(2)=101.17(8)°.
˚
˚
˚
˚
˚
˚
˚
the ether oxygen as a consequence of the long Mo-Oether
˚
bond length (2.3071(14) A) relative to Mo-Cethylene bond
˚
lengths (2.181(2) and 2.178(2) A). The C(1)-C(2) distance is
1.409(3) A, which is characteristic of other ethylene com-
of Mo(NAr)(CHCMe2Ph)(η1-MesPyr)2 toward ethylene can
be ascribed to the fact that it is a 14-electron species, in
contrast to 5a. One ethylene carbon resonance was found at
54.2 ppm with JCH = 160 Hz. Proton NMR spectra reveal
multiplets at 2.45 and 1.96 ppm for the ethylene protons,
consistent with the 2-mesitylpyrrolide ligands in 5b being
bound in an η1 manner, as found in Mo(NAr)(CHCMe2Ph)-
(η1-MesPyr)2.6 As a demonstration that 5b can be employed
as a precursor to other bisalkoxide ethylene complexes, 5b
was treated with 2 equiv of HOCH(CF3)2 in ether to yield
Mo(NAr)(CH2CH2)[OCH(CF3)2]2(Et2O) (6) in 41% iso-
lated yield after recrystallization. As judged from the proton
NMR spectrum, 6 contains a mirror plane of symmetry on
the NMR time scale, the equivalent alkoxides each contain
two inequivalent CF3 groups, and two ethylene proton
resonances are observed at 2.64 ppm and 1.83 ppm. An ether
adduct of the bishexafluoroisopropoxide imido alkylidene
complex is formed as a consequence of the relatively small
size of the hexafluoroisopropoxide ligand.17,18
˚
plexes discussed here. The trans relationship of the ether and
ethylene might suggest that a five-coordinate intermediate in
which (especially large) imido and alkoxide ligands occupy
equatorialpositions is the mostfacile mechanism of displacing
one two electron ligand by another, including one olefin by
another (vide infra). It should be noted that the planar three-
coordinate monomeric species, W(N-t-Bu)[OSi(t-Bu)3]2, which
is analogous to the central core of 6, is known.19
When a sample of 6 in benzene-d6 was degassed and
exposed to 1 atm of 13C-ethylene, a 13C NMR spectrum
suggested that a metallacyclopentane complex is formed on the
basis of a CR resonance at 78.54 ppm (JCH = 134 Hz) and a Cβ
resonance at 39.21 ppm (JCH = 127 Hz). In a proton NMR
spectrum employing unlabeled ethylene at room temperature,
only broad resonances were observed for the metallacycle and
ethylene protons. When all volatile components were removed
from the sample the residue was found to consist of 6. An X-ray
structural study of an isolated molybdacyclopentane complex
is reported later in this paper.
In the interest of isolating other olefin complexes we
treated 2c with neat styrene. Dry styrene was vacuum
transferred to a Schlenk flask charged with solid Mo(NAr)-
(CH2CH2)(Me2Pyr)(OSiPh3) (2c). Removal of all volatiles in
The structure of Mo(NAr)(CH2CH2)(O-i-PrF6)2(Et2O) is
best described as a distorted trigonal bipyramid in which the
alkoxide and the imido ligands are in equatorial positions
(Figure 3). The sum of the angles between the equatorial
ligands is 351.6°, and they are all displaced slightly toward
(17) Schrock, R. R.; Luo, S.; Zanetti, N. C.; Fox, H. H. Organome-
tallics 1994, 12, 3396.
(18) Anders, U.; Nuyken, O.; Buchmeiser, M. R.; Wurst, K. Macro-
molecules 2002, 35, 9029.
(19) Eppley, D. F.; Wolczanski, P. T.; Vanduyne, G. D. Angew.
Chem., Int. Ed. 1991, 30, 584.

6820 Organometallics, Vol. 29, No. 24, 2010
Marinescu et al.
Compound 8 also can be prepared by treating Mo(NAr)-
(CH2CHPh)(Me2Pyr)(OSiPh3) (7) with 1 equiv of Ph3SiOH.
An X-ray structural study of a single crystal of 8 showed it
to be the isomer in which the phenyl ring points toward the
imido ligand (Figure 4). The styrene is oriented perpendicular
to the Mo(1)-N(1) axis (N(1)-Mo(1)-C(1) = 98.49(10)°
and N(1)-Mo(1)-C(2) = 98.76(10)°) with C(1)-C(2) =
˚
1.433(4) A.
A reaction between Mo(NAr)(CH2CH2)(OSiPh3)2 (3) and
neat trans-3-hexene immediately produced an indigo colored
hexene complex (eq 9) whose NMR spectrum in C6D6
revealed the presence of 2 isomers in the ratio of 4:1. The
major isomer displays two olefinic multiplets between 3.5
and 2 ppm, consistent with the formation of Mo(NAr)-
(OSiPh3)2(trans-3-hexene) (9a, eq 9). Crystals of 9a could
be obtained through recrystallization of crude 9. An X-ray
structural study of the major isomer reveals it to have the
expected structure (Figure 5).
Figure 3. POV-ray drawing of 6. Thermal ellipsoids are dis-
played at 50% probability level. Hydrogen atoms are omitted.
Selected distances (A) andangles(deg):Mo(1)-C(1) = 2.181(2) A,
˚
˚
˚
˚
Mo(1)-C(2) = 2.178(2) A, C(1)-C(2) = 1.409(3) A, Mo(1)-
˚
˚
O(1) = 1.9792(14) A, Mo(1)-O(2) = 1.9888(14) A, Mo(1)-O(3) =
˚
˚
2.3071(14) A, Mo(1)-N(1) = 1.7148(16) A, Mo(1)-N(1)-
C(11) = 178.18(14)°, Mo(1)-O(1)-C(23) = 138.89(13)°,Mo(1)-
O(2)-C(26) = 137.50(13)°, O(1)-Mo(1)-O(2) = 118.18(6)°,
O(1)-Mo(1)-N(1) = 117.77(7)°, N(1)-Mo(1)-O(2) =
115.60(7)°.
vacuo after 15 min gave a gray residue whose proton NMR
spectrum in C6D6 suggested that the product, Mo(NAr)-
(CH2CHPh)(Me2Pyr)(OSiPh3) (7), was a mixture of four
isomers. Four isomers of 7 can be rationalized in view of the
presence of a stereogenic metal center, enantiotopic styrene
faces, and no rotation of styrene on the NMR time scale. The
major isomer (∼30%) displays olefinic proton resonances at
4.23 (t, 1H), 3.08 (dd, 1H), and 2.40 (dd, 1H) ppm. We were
not able to obtain a crystalline sample of 7 suitable for an
X-ray study.
The most logical proposal is for the second isomer of 9 to
be Mo(NAr)(cis-3-hexene)(OSiPh3)2 (9b). Treatment of 3
with neat cis-3-hexene led to a 1:1 mixture of 9a and what we
propose to be Mo(NAr)(cis-3-hexene)(OSiPh3)2 (9b) on the
basis of its mirror symmetry. Over a period of 5 h, the
mixture evolved into approximately the same 4:1 mixture
of 9a and 9b formed upon treatment of 3 with trans-3-hexene.
Therefore, 9a and 9b are in slow equilibrium with the
position of that equilibrium being approximately what one
would predict on the basis of the relative energies of the free
1
olefins. After 12 h, the H NMR spectrum reveals other
olefinic resonances that correspond to the initial resonances
in the spectrum of Mo(NAr)(2-hexene)(OSiPh3)2, which is
prepared independently from 3 and neat trans-2-hexene.
Therefore, we propose that 9a and 9b slowly are converted
into a complex mixture that contain Mo(NAr)(trans-2-hexene)-
(OSiPh3)2 (9c) (2isomers) andMo(NAr)(cis-2-hexene)(OSiPh3)2
(9d) (2 isomers). An even more complex mixture (up to eight
isomers eventually) is formed when 3 is treated with neat
1-hexene; we propose that Mo(NAr)(1-hexene)(OSiPh3)2
forms initially and is then converted into isomers of Mo(NAr)-
(2-hexene)(OSiPh3)2 and Mo(NAr)(3-hexene)(OSiPh3)2.
When a sample of 3 in toluene-d8 was degassed and
exposed to 1 atm of ethylene, the color changed from purple
to red-orange. At 20 °C, two broad resonances were
observed at ∼3.1 and ∼2.5 ppm, which integrate to four
The reaction between purple Mo(NAr)(CH2CH2)(OSiPh3)2
(3) and neat, freshly dried styrene immediately yielded a green
solution from which a green product could be obtained upon
removal of all volatiles in vacuo. Recrystallization of the residue
from pentane yielded green crystals of Mo(NAr)(CH2CHPh)-
(OSiPh3)2 (8, eq 8), the proton NMR spectrum of which in
C6D6 showed two isomers to be present in the ratio of 2:1. The
major isomer displays olefinic proton resonances at 3.58 (t,
1H), 3.28 (dd, 1H), and 2.44 (dd, 1H) ppm for the bound
styrene, while olefinic proton resonances for the minor isomer
are found at 4.64 (t, 1H), 2.99 (dd, 1H), and 2.26 (dd, 1H) ppm.

Article
Organometallics, Vol. 29, No. 24, 2010 6821
3 was exposed to 13C-ethylene (∼0.5 atm) at 20 °C, two
resonances are observed in the 13C NMR spectrum at 72.4
and 37.5 ppm that can be assigned to CR and Cβ, respectively,
along with a resonance for the 13C-labeled ethylene complex (at
55.2 ppm). Although ethylene exchange is facile on the chemical
time scale, this exchange is not rapid on the NMR time scale
because a small amount of 3 can be observed throughout the
temperature range shown in Figure 6. It appears that the
fluxional process shown in Figure 6 leads to equilibration of
the two types of CHR resonances (“upper” and “lower”) and
the two types of CHβ resonances (“upper” and “lower”) but not
to interconversion of CHR and CHβ resonances or equilibration
of 10 with 3on the NMR time scale. Compound 10 clearly must
Figure 4. POV-ray drawing of 8. Thermal ellipsoids are dis-
played at 50% probability level. Hydrogen atoms are omitted.
form from an intermediate bis ethylene complex in which the
ethylenes are approximately cis to one another, perhaps
through rearrangement of an initial species that has some
other structure, even an initial TBP species that contains
ethylenes trans to one another. The fluxional process ob-
served for 10 is proposed to consist of a five-coordinate
rearrangement of either the intact metallacyclopentane or a
Mo(VI) alkenyl hydride species formed from the metallacy-
clopentane through reversible β hydride elimination. The
fact that CHR and CHβ resonances do not exchange elim-
inates the possibility of formation of a bisethylene species in
which one or both ethylenes can rotate about the Mo-
(ethylene) bond axis. The fluxional process has been inves-
tigated by line-shape analyses of the β-protons (see Supporting
Information). The activation parameters for the exchange of
the β-protons were obtained from the Eyring plot: ΔHq =
18.0(0.3) kcal/mol and ΔSq= 15.6(1.2) eu. The large and
positive entropy of activation is consistent with significant
disorder in the transition state and therefore would favor
formation of an alkenyl hydride intermediate.
˚
˚
Selected distances (A) andangles(deg):Mo(1)-N(1) = 1.738(2) A,
˚
˚
Mo(1)-O(1)=1.9116(15) A,Mo(1)-O(2)=1.9176(16) A,Mo(1)-
C(1) = 2.121(3) A, Mo(1)-C(2) = 2.159(2) A, C(1)-C(2) =
1.433(4) A, Mo(1)-N(1)-C(11)=169.78(17)°, N(1)-Mo(1)-
˚
˚
˚
C(1)=98.49(10)°, N(1)-Mo(1)-C(2)=98.76(9)°.
X-ray quality crystals of 10 were grown from a pentane:
toluene (10:1) solution of 10 at -35 °C under 1 atm of
ethylene. A drawing of the structure of 10 is shown in Figure 7.
Complex 10 has an approximate square pyramidal coordina-
tion geometry, with the imido ligand occupying the apical
position. It is similar to the structure of a molybdacyclopentane
reported by Boncella.20 The Mo(1)-C(1) and Mo(1)-C(4)
˚
bonds (2.176(3) and 2.200(3) A) are typical of Mo-C single
Figure 5. POV-ray drawing of 9a. Thermal ellipsoids are dis-
played at 50% probability level. Hydrogen atoms are omitted.
Selected distances (A) and angles (deg): Mo(1)-N(1) =
bonds and the C(1)-C(2), C(2)-C(3), and C(3)-C(4) bond
lengths (1.513(5), 1.526(5), and 1.524(5) A, respectively) are
typical of C-C single bonds.
When a sample of Mo(NAr)(CHCMe2Ph)(OSiPh3)2 in
toluene-d8 was degassed and exposed to 1 atm of ethylene,
four broad peaks were observed at 3.38, 2.86, 2.23, and 1.24
ppm in the ratio of 1:1:2:2 (see Supporting Information),
consistent with the formation of the square pyramidal
˚
˚
˚
˚
1.7337(13) A, Mo(1)-O(1) = 1.9381(11) A, Mo(1)-O(2) =
21
˚
˚
1.9197(11) A, Mo(1)-C(3) = 2.1509(15) A, Mo(1)-C(4) =
˚
˚
2.1350(15) A, C(3)-C(4) = 1.440(2) A, Mo(1)-N(1)-C(11) =
174.15(11)°, N(1)-Mo(1)-C(3) = 98.17(6)°, N(1)-Mo(1)-
C(4) = 97.88(6)°.
protons each (Figure 6). At -20 °C, four resonances are
observed at 3.11, 3.06, 2.58, and 2.41 ppm integrating as two
protons each, consistent with formation of the metallacyclo-
pentane species, Mo(NAr)(C4H8)(OSiPh3)2 (10) (eq 10). When
(20) Ison, E. A.; Abboud, K. A.; Boncella, J. M. Organometallics
2006, 25, 1557.
(21) Wampler, K. M.; Schrock, R. R.; Hock, A. S. Organometallics
2007, 26, 6674.

6822 Organometallics, Vol. 29, No. 24, 2010
Marinescu et al.
Figure 6. Variable-temperature 1H NMR spectroscopic studies of Mo(NAr)(OSiPh3)2(C4H8) (10) in toluene-d8 under 1 atm
of ethylene.
respectively, in a square pyramidal metallacyclobutane
species.22 Although 11 can be isolated, after 1 day at room
temperature Mo(NAr)(CH2CH2)(OSiPh3)2 (3) and Mo-
(NAr)(C4H8)(OSiPh3)2 (10) are also found in a solution of
11 as a consequence of decomposition of unobserved Mo-
(NAr)(CH2)(OSiPh3)2.
Olefin exchange and double bond isomerization would
suggest that linear olefins can be isomerized catalytically. In
fact, treatment of 2c with 20 equiv of 1-decene in C6D6 (15
mM) at room temperature led to resonances near 5.5 ppm
characteristic of internal olefins. Upon heating the sample
for a period of two days at 85 °C, the 1-decene was converted
almost completely to internal olefins according to 1H NMR
spectroscopic studies shown in Figure 8.
When 6 was treated with 20 equiv of 1-hexene in C6D6,
trace amounts of internal olefins were observed after 20 min
at room temperature. After one day at 22 °C, the sample
contained 52% internal olefins. At 60 °C over a period of
Figure 7. POV-ray drawing of 10. Thermal ellipsoids are dis-
played at 50% probability level. Hydrogen atoms are omitted.
˚
˚
Selected distances (A) and angles (deg): Mo(1)-N(1)=1.719(2) A,
˚
˚
Mo(1)-O(1) =1.911(2) A, Mo(1)-O(2) =1.880(2) A, Mo(1)-
˚
˚
C(1)=2.176(3) A, Mo(1)-C(4)=2.200(3) A, C(1)-C(2)=1.513
(5) A, C(2)-C(3)=1.526(5) A, C(3)-C(4) = 1.524(5) A, Mo(1)-
N(1)-C(11)=175.2(2)°, C(1)-Mo(1)-C(4)=71.86(13)°.
˚
˚
˚
molybdacylobutane species, Mo(NAr)(C3H6)(OSiPh3)2(11)
(eq 11). When Mo(NAr)(CHCMe2Ph)(OSiPh3)2 was ex-
posed to 13C-ethylene (∼0.5 atm) at 20 °C, two doublet
resonances were observed in the 13C NMR spectrum at
37.6 ppm (JCC = 33 Hz, JCH = 138 Hz) and 27.8 ppm
(JCC = 33 Hz, JCH = 132 Hz), corresponding to CR and Cβ,
(22) (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. (d) Bazan, G. C.; Oskam, J. H.; Cho, H.-N.; Park, L. Y.;
Schrock, R. R. J. Am. Chem. Soc. 1991, 113, 6899.

Article
Organometallics, Vol. 29, No. 24, 2010 6823
Figure 8. 1H NMR spectroscopic studies to monitor the reaction between Mo(NAr)(CH2CH2)(Me2Pyr)(OSiPh3) (2c) (5 mol %)
and 1-decene.
24 h, the amount of internal olefins increased to 85% of the
mixture, according to NMR spectra similar to those shown
in Figure 8. A GC-mass spectrum of the reaction mixture
revealed the presence of C7H14, C8H16, C9H18, C10H20, C11H22,
and C12H24 species. The shorter chains (C7 and C8) clearly
consist of more than one isomer. When the reaction between 6
and 1-hexene was attempted in diethyl ether under similar
conditions, no internal olefins were found after one day. This
experiment suggests that diethyl ether blocks any reaction that
produces internal olefins. When 6 in C6D6 was treated with
trans-3-hexene under similar conditions to those employed for
1-hexene, 1H NMR and GCMS results were analogous to those
observed for reactions involving 1-hexene.
the molybdacylopentane species 10 was observed immedi-
ately, along with free trans-3-hexene. After 2 weeks at room
temperature, 1-butene was observed in the 1H NMR spectrum
of the reaction mixture. When 13C-ethylene was employed, a
singlet at 113.4 ppm for 13CH2dCHCH2CH3 was observed in
the 13C NMR spectrum of the reaction mixture, consistent with
its formation through a metathesis reaction of trans-3-hexene
with 13CH213CH2. After another week at room temperature,
13CH2dCHCH3 (115.9 ppm), 13CH3CHdCHCH3, and
13CH2dCH13CH3 (19.3 and 18.0 ppm) were observed in the
reaction mixture, all of which are consistent with isomerization
of 1-butene to 2-butene, followed by reaction of 2-butene with
13CH213CH2. All observations are consistent with very slow
metathesis of olefins over a period of weeks.
When 6 was treated with 20 equiv of 1-octene, conversion
to 90% internal olefins was observed after heating the
reaction mixture to 100 °C for 18 h. When a similar experi-
ment was carried out in ether, no internal olefins were
observed. A GC-mass spectrum of the internal olefins
(Figure 9a) revealed that olefins from C8H16 to C20H40 are
present, with C13 and C14 being the most abundant; chains
longer than C15 constitute a relatively small portion of the
mixture. Hydrogenation of the olefins in this mixture (Pd/C
catalyst; Figure 9b) converted all olefin isomers to a single
linear alkane, which suggests that all internal olefins are
linear. A GC-mass spectrum of a standard of linear alkanes
C8H18 to C14H30 matched the GC-mass spectrum obtained
for the hydrogenated mixture in retention time, peak shape,
and fragmentation patterns for each alkane.
A benzene solution of 6 was placed under 1 atm of
CD3CHdCH2, and the sample was heated to 60 °C for 1 day.
A 2H NMR spectrum (Figure 10) showed resonances at 4.8 and
5.8 ppm, consistent with scrambling of deuterium into all three
propylene sites through a process that must involve more than
reversible CH or CD activation of CD3CHdCH2 to give allyl
intermediates. (See Discussion Section.)
When 6 was treated with 100 equiv of cyclooctene in C6D6,
polycyclooctene was formed and could be isolated in 38%
yield after 24 h through precipitation with methanol. The
polycyclooctene sample contained 88% trans double bonds
according to 13C NMR spectra.
Discussion
Mixtures of linear olefins most likely form through me-
tathesis reactions. When 9 was treated with 1 atm of ethylene,
It is clear from the work reported here that molybdenum
ethylene complexes can be the product of “reduction” of the

6824 Organometallics, Vol. 29, No. 24, 2010
Marinescu et al.
Figure 9. Reaction of 20 equiv of 1-octene with Mo(NAr)(CH2CH2)[OCH(CF3)2]2(Et2O) after one day at 100 °C. (a) GC trace of the
reaction mixture prior to hydrogenation. (b) GC trace of the reaction mixture after hydrogenation.
metal upon exposure of MAP species, or bisalkoxides, to
ethylene. These results are similar to what has been observed
in solution in Mo or W biphenolate or binaphtholate
systems.3,4,5 The two most likely mechanisms for reduction
are rearrangement of a molybdacyclobutane complex to an
olefin (e.g., rearrangement of the unsubstituted metallacy-
clobutane to propylene) or bimolecular coupling of methyli-
dene species. Both experimental3 and theoretical evidence (for
oxidation state tungsten system,5 formation of the final
ethylene complex is likely to involve ethylene attack on the
bis-μ-ethylene
high oxidation state Re, Mo, and W systems on silica10,23
)
suggest that ethylene assists metallacycle rearrangement.
Calculations suggest that the mechanism consists of ethy-
lene accepting a β hydride from the metallacyclobutane ring
and donating it back to an R carbon of the allyl intermedi-
ate. Because bis-μ-methylidene species and a bis-μ-ethylene
species have been structurally characterized in one high
species to give 2 equiv of the ethylene species (eq 12) rather
than formation of 1 equiv of the ethylene species and a high
energy three-coordinate intermediate that is then captured
by ethylene. Restricting ethylene from the coordination
sphere at the point where it is required for the last step
(shown in eq 12) could be one of the reasons why MAP
methylidene species that contain relatively bulky aryloxides
are relatively stable toward decomposition reactions and
lead to long-lived methylidene complexes and long-lived
catalysts in the presence of ethylene.9g
(23) Leduc, A.-M.; Salameh, A.; Soulivong, D.; Chabanas, M.;
ꢀ
Basset, J.-M.; Coperet, C.; Solans-Monfort, X.; Clot, E.; Eisenstein,
O.; Boehm, V. P. W.; Roeper, M. J. Am. Chem. Soc. 2008, 130, 6288.

Article
Organometallics, Vol. 29, No. 24, 2010 6825
Figure 10. 2H NMR spectrum of Mo(NAr)(CH2CH2)[OCH(CF3)2]2(Et2O) in benzene under 1 atm of CD3CH(CH2). From left to
right: 7.16 (benzene), 5.69 (1 H), 5.45 (0.33 H), 5.35 (0.46 H), 5.23 (0.71 H), 4.99 (1.05 H), 4.93 (1.45 H), 1.47 (7.68 H), 1.43 (1.21 H), 0.85
(0.41 H).
Other important findings reported here include facile
catalytic isomerization of olefins. We propose that olefins
are isomerized via allylic CH activation to give an allyl
intermediate (σ or π). However, it is not necessarily true that
the H is transferred to the metal, as shown in eq 13. Another
possibility is for H to be transferred to the imido nitrogen to
yield an intermediate Mo(IV) allyl amido species. However,
for the purposes of discussion, we will choose the proposal
shown in eq 13. This oxidative addition mechanism of
isomerizing olefins is one of the classic methods that has
been documented for decades.24
are) responsible for formation of alkylidenes in the systems
reported here or confirming that they are imido alkylidenes.
An important question is how an alkylidene, albeit only
traces of it, is formed. Some of the leading candidates for
forming an alkylidene from an ordinary olefin at a single
metal center include addition of H from an external or
internal source (e.g., through CH activation in a ligand) to
the olefin to give an alkyl followed by R abstration of H from
the alkyl, e.g., as shown in eq 14.14-16 (For convenience, the
“þH” and “-H” nomenclature is meant to encompass
reactions that involve M-H species and other possible
mechanistic variations, e.g., transfer of H to and from
another ligand through CH activations, etc.) A second
possible general mechanism of forming an alkylidene is to
form an allyl hydride complex followed by a metallacyclo-
butane ring; an example is shown in eq 15. Formation of a
metallacyclobutane could be an alternative consequence of
formation of an olefin isomer from an allyl hydride inter-
mediate (eq 13). The third possibility is to form and contract
a metallacyclopentane ring to a metallacyclobutane ring and
then lose an olefin to form an alkylidene, e.g., as shown in
eq 16.25,26 Unfortunately, we have not been able to think of a
means of determining exactly which process is (or processes
The results presented here are related to others we have
uncovered in which Mo(IV) or W(IV) compounds slowly
catalyze typical metathesis reactions. As mentioned in the
Introduction, one is a homologation of a vinyl tin species to
an allyl tin species in the presence of ethylene and Mo(NAr)-
(CH2CH2)(Biphen)7 as a catalyst. A mechanism was proposed
that involved contraction of a “mixed” metallacyclopentane
ring containing ethylene and the vinyl tin species to a metalla-
cyclobutane ring. Complexes that contain an unsupported
MdM double bond (M = Mo or W) such as [Mo(NAr)-
(CH2-t-Bu)(OC6F5)]2 (Ar = 2,6-i-Pr2C6H3) or {W(NAr0)-
[OCMe2(CF3)]2}2 (Ar0 = 2,6-Me2C6H3) also will slowly cata-
lyze olefin metathesis reactions.8 However, it was estimated
that only a relatively small amount (∼2%) of the MdM species
was “activated” by the olefin. Finally, an ethylene complex
mentioned earlier in this paper, Mo(N-2,6-Cl2C6H3)-
(CH2CH2)(rac-Biphen)(ether), is inactive for ring-closing of
diallyl ether over a period of 10 days at 22 °C, but when 10 equiv
of norbornene were added to a benzene solution of 5 mol %
Mo(NArCl)(CH2CH2)(rac-Biphen)(ether) and diallyl ether, a
56% yield of 2,4-dihydrofuran was obtained in 10 days.
(24) Organotransition Metal Chemistry; From Bonding to Catalysis;
Hartwig, J., Ed.; University Science Books: Sausalito, CA, 2010.
(25) McLain, S. J.; Sancho, J.; Schrock, R. R. J. Am. Chem. Soc.
1979, 101, 5451.
(26) Yang, G. K.; Bergman, R. G. Organometallics 1985, 4, 129.

6826 Organometallics, Vol. 29, No. 24, 2010
Marinescu et al.
The results reported here also suggest that formation of
Mo(IV) species as products of decomposition of metathesis
catalysts could lead to isomerization of double bonds in
metathesis substrates or products. Fortunately, metathesis
usually is several orders of magnitude faster than olefin
isomerization. Yet there may be some circumstances in
which “reformation” of alkylidenes from olefins contributes
to catalyst activity over the long-term, e.g., “alkane metathesis,”
which is usually carried out at temperatures of 125° or more.27
Eventually, however, decomposition processes that involve
destruction of the basic structure of an imido alkylidene catalyst
will lead to irreversible loss of metathesis activity.
the resonances at 60.24 ppm and 56.29 ppm to be those for ethylene
carbons (JCH = 155 Hz and JCC = 39 Hz). Anal. Calcd for
C32H46MoN2O: C, 67.35; H, 8.12; N, 4.91. Found: C, 67.56; H,
8.11; N, 4.97.
Mo(NAr)(CH2CH2)[OCCMe(CF3)2](2,5-Me2NC4H2) (2b).
Compound 2b was prepared in a manner analogous to 2a by
treating Mo(NAr)(CHCMe3)[OCMe(CF3)2](2,5-Me2NC4H2)
(235 mg, 0.347 mmol) with ethylene in heptane. The complex
was crystallized from pentane at -30 °C as dark-red crystals;
1
yield 123 mg, 57%. H NMR (300 MHz, C6D6) δ 6.19-6.81
(m, 3, Ar), 5.51 (br, 2, Pyr), 3.48 (sept, 2, CHMe2), 2.77 (m, 2,
ethylene), 2.45 (m, 1, ethylene), 2.16 (m, 1, ethylene), 2.10 (s, 6,
PyrMe), 1.65 (s, 3, OCMe) 1.10 (d, 6, CHMe2), 1.06 (d, 6,
CHMe2). 19F NMR (282 MHz, C6D6) δ - 75.20, - 77.80. 13
C
NMR (125 MHz, C6D6) δ 154.24, 145.74, 128.68, 128.27,
123.79, 110.15, 105.39, 56.34, 54.12, 28.09, 25.35, 23.62,
20.37, 16.26. Anal. Calcd for C24H32F6MoN2O: C, 50.18;
H, 5.61; N, 4.88. Found: C, 50.26; H, 5.31; N, 4.67.
Conclusions
All of our observations suggest that (i) olefin complexes of
the type M(NAr)(X)(Y)(olefin) can form readily, (ii) exchange
of olefins at Mo(IV) centers is facile, (iii) isomerization of
olefins at Mo(IV) centers is facile, and (iv) traces of metathesis
catalysts are formed. We propose that the metathesis catalysts
are of the type M(NAr)(X)(Y)(alkylidene) but that the
amounts present are in the undetectable range (<1%).
Mo(NAr)(CH2CH2)(2,5-Me2NC4H2)(OSiPh3)(2c).Compound
2c was prepared in a manner analogous to 2b by treating Mo-
(NAr)(CHCMe2Ph)(2,5-Me2NC4H2)(OSiPh3) (250 mg, 0.32
mmol) with ethylene in 5 mL of diethylether. The dark-red
precipitate was collected and recrystallized from diethylether; yield
150 mg, 70%. 1H NMR (500 MHz, C6D6) δ 7.89 (dd, 6H, Ar, J =
7.5 Hz, 2.0 Hz), 7.24-7.14 (m, 9H, Ar), 6.94-6.83 (m, 3H, Ar),
5.00-6.00 (br, 2H, NC4H2), 3.71 (sept, 2H, MeCHMe, J=6.5 Hz),
2.87 (m, 1H, C2H4), 2.70 (m, 1H, C2H4), 2.20 (m, 2H, C2H4), 2.11
(br s, 6H, CH3), 1.10 (d, 6H, MeCHMe, J = 7.0 Hz), 1.00 (d, 6H,
MeCHMe, J=7.0 Hz). 13C NMR (125 MHz, C6D6) δ153.8, 145.8,
141.3, 136.3, 135.9, 129.5, 128.7, 128.1, 127.9, 57.9, 56.8, 28.3, 25.6,
23.2, 17.0. Experiments employing 13C2H4 revealed ethylene car-
Experimental Section
General synthetic procedures can be found in earlier papers
that concern MAP catalysts.9 Compounds 1a and 1b were prepared
as described in the literature.9a
Mo(NAr)(CHCMe2Ph)(2,5-Me2NC4H2)(OSiPh3) (1c). A cold
solution of Ph3SiOH (149 mg, 0.54 mmol, 1 equiv) in 5 mL of
diethyl ether was added dropwise to a cold solution of Mo(NAr)-
(CHCMe2Ph)(2,5-Me2NC4H2)2 (319 mg, 0.54 mmol, 1 equiv) in
5 mL of diethyl ether. The reaction mixture was stirred at room
temperature for 30 min, and the volatile components were removed
in vacuo. The resulting orange solid was recrystallized from diethyl
ether to give 259 mg of orange crystals; yield 62%. 1H NMR (500
MHz, CD2Cl2) δ 11.85 (s, 1H, syn ModCH, JCH = 120.4 Hz),
7.54-7.08 (m, 23H, Ar), 5.79 (s, 2H, NC4H2), 3.72 (sept, 2H,
MeCHMe, J = 7.0 Hz), 2.11 (s, 6H, CH3), 1.62 (s, 3H, CH3), 1.52
(s, 3H, CH3), 1.06 (app d, 6H, MeCHMe), 0.96 (br, 6H,
MeCHMe). 13C NMR (125 MHz, CD2Cl2) δ 286.7, 153.4, 148.6,
147.5, 136.4, 135.7, 135.5, 130.6, 130.4, 128.6, 128.4, 126.5, 126.3,
123.5, 109.7, 108.9, 108.1, 54.9, 31.9, 30.6, 30.4, 29.1, 23.8 (br), 17.3
(br). Anal. Calcd for C46H52MoN2OSi: C, 71.48; H, 6.78; N, 3.62.
Found: C, 71.44; H, 6.69; N, 3.75.
Mo(NAr)(CH2CH2)(OAr)(2,5-Me2NC4H2) (2a). A Schlenk
flask was charged with Mo(NAr)(CHCMe2Ph)(OAr)(2,5-
Me2NC4H2) (60 mg, 0.090 mmol), a stir bar, and 2 mL of
heptane. The solution was degassed by freeze-pump-thawing
the solution (3 times), and 1 atm of ethylene was introduced. The
reaction was stirred at room temperature for 15 min and set
aside at -30 °C for 12 h. Removal of the volatiles in vacuo
followed by addition of pentane to the residue afforded a dark-
red precipitate of the product; yield 31 mg, 59%. 1H NMR (300
MHz, C6D6) δ 7.22 (d, 2, Ar), 7.02 (t, 1, Ar), 6.89 (s, 3, Ar), 5.78
(br, 2, Pyr), 3.57 (sept, 2, CHMe2), 3.25 (br, 2, CHMe2), 2.95 (m,
2, ethylene), 2.60 (m, 1, ethylene), 2.16 (s, 6, PyrMe), 1.95 (m, 1,
ethylene), 1.25-1.13 (m, 24, CHMe2). 13C NMR (125 MHz,
C6D6) δ 163.84, 155.02, 143.74, 139.41, 128.68, 128.40, 128.30,
127.22, 123.96, 123.75, 120.77, 107.65, 60.24, 56.29, 28.39, 25.97,
25.18, 24.70, 24.57, 16.02. Experiments employing 13C2H4 revealed
bon resonances at 56.8 and 57.9 ppm (JCH=153 Hz and JCC =
37 Hz). Anal. Calcd for C38H44MoN2OSi: C, 68.24; H, 6.63; N,
4.19. Found: C, 68.18; H, 6.60; N, 3.84.
Mo(NAr)(CH2CH2)(OSiPh3)2 (3). Mo(NAr)(CH2CH2)(2,5-
Me2NC4H2)(OSiPh3) (25.6 mg, 0.038 mmol, 1 equiv) and
Ph3SiOH (10.6 mg, 0.038, 1 equiv) were transferred to a 20 mL
vial equipped with a magnetic stir bar. Pentane (7 mL) and diethyl
ether (0.1 mL) were added. The color of the reaction mixture
changed from red to purple. The reaction mixture was stirred at
room temperature until triphenylsiloxide was completely consumed.
The reaction mixture was stored at -35 °C, and 20 mg of purple
crystals were obtained; yield = 61%. 1H NMR (500 MHz, C6D6) δ
7.77 (d, 12H, Ar), 7.20-7.10 (m, 18H, Ar), 6.98-6.89 (m, 3H, Ar),
3.69 (sept, 2H, MeCHMe, J = 6.9 Hz), 2.74 (app q, 2H, C2H4, J =
6.2Hz, 5.6Hz), 1.99(appq, 2H, C2H4, J=6.2Hz, 5.6Hz), 1.00(d,
12H, Me2CHMe2, J=7.0 Hz). 13C NMR (125 MHz, C6D6) δ154.6,
146.7, 137.6, 135.9, 130.3, 128.5, 123.4, 55.2, 29.7, 24.0. Experiments
employing 13C2H4 revealed the resonance at 55.2 ppm to be that for
ethylene carbons (JCH=155 Hz). Anal. Calcd for C50H51MoN2O-
Si2: C, 70.65; H, 6.05; N, 1.65. Found: C, 70.61; H, 6.14; N, 1.86.
Mo(NAr)(CH2CH2)(OTf)2(dme) (4a). Ethylene (60 psi) was
added to a solution of Mo(NAr)(CHCMe2Ph)(OTf)2(dme)
(0.800 g, 1.1 mmol) in 10 mL of toluene. The reaction mixture
was heated to 80 °C for two days under a 60 psi of ethylene. Red
crystals (0.646 g, yield = 86%) were isolated directly from the
reaction via filtration. The product is a mixture of cis and trans
isomers in the ratio of ∼2:1, as determined by 1H and 19F NMR
spectroscopy studies. 1H NMR (500 MHz, C6D6) cis-4 (selected
resonances) δ 3.93-3.84 (m, 1H), 3.82-3.73 (m, 1H), 3.53 (s,
3H, OMe),3.35(s,3H,OMe),1.15(d,6H,Me2CHMe2,J=7.0 Hz),
0.98 (d, 6H, Me2CHMe2, J=7.0 Hz). 1H NMR (500 MHz, C6D6)
trans-4 (selected resonances) δ 3.08 (s, 3H, OMe), 2.95 (s, 3H,
OMe),1.26(d,12H,Me2CHMe2,J=7.0 Hz). 13CNMR(125MHz,
C6D6) δ 151.0, 139.4, 124.7, 124.3, 77.4, 72.3, 70.7, 70.2, 69.2, 64.2,
63.1, 28.6, 25.4, 24.9, 23.7. 19F(282MHz,C6D6) δ-78.3, -78.3, -78.6.
Anal. Calcd for C20H31F6MoNO8S2: C, 34.94; H, 4.54; N, 2.04.
Found: C, 35.24; H, 4.58; N, 2.06.
(27) (a) Kundu, S.; Choliy, Y.; Zhuo, G.; Ahuja, R.; Emge, T. J.;
Warmuth, R.; Brookhart, M.; Krogh-Jespersen, K.; Goldman, A. S.
Organometallics 2009, 28, 5432. (b) Huang, Z. B., M.; Goldman, A. S.;
Kundu, S.; Ray, A.; Scott, S. L.; Vicentec, B. C. Adv. Synth. Catal. 2009,
351, 188. (c) Bailey, B. C.; Schrock, R. R.; Kundu, S.; Goldman, A. S.;
Huang, Z.; Brookhart, M. Organometallics 2009, 28, 355.
Mo(NAd)(CH2CH2)(OTf)2(dme) (4b). A 100 mL Schlenk
round-bottom flask equipped with a side arm and a magnetic stir

Article
Organometallics, Vol. 29, No. 24, 2010 6827
bar was charged with solid Mo(NAd)(OTf)2(CH2CH2)(dme) (354
mg) and 10 mL of benzene. The reaction mixture was degassed
(3ꢀ) and then exposed to 1 atm of ethylene. The reaction mixture
was heated at 60 °C for 6 h. The volatiles were removed under
vacuum, and the yellow solid generated was washed with diethyl
ether; 155.4 mg of yellow solid were obtained (yield = 71%). The
product obtained is a mixture of cis and trans isomers in the ratio of
∼2: 1, as determined by 1H and 19F NMR spectroscopy studies. 1H
NMR (500 MHz, C6D6) 3.95-3.80 (m), 3.51 (s, OMe), 3.47 (s,
OMe), 3.45-3.40 (m), 3.33 (s, OMe), 3.14 (s, OMe), 2.95-2.65
(m), 2.58-2.45 (m), 2.26-2.17 (m), 2.11 (br), 1.77 (br), 1.31 (br).
13C NMR (125 MHz, C6D6) δ 78.3, 77.4, 72.9, 72.6, 71.7, 69.9,
69.8, 67.6, 65.8, 64.2, 63.0, 60.9, 41.9, 41.1, 35.8, 35.7, 29.4, 29.3. 19F
(282 MHz, C6D6) δ -77.5, -77.8, -78.3. Anal. Calcd for
C18H29F6MoNO8S2: C, 32.68; H, 4.42; N, 2.12. Found: C, 33.26;
H, 4.44; N, 2.00.
C2H4), 1.83 (m, 2, C2H4), 1.13 (d, 12, CHMe2, JHH = 7 Hz), 0.88
(t, 6, Et2O). 13C NMR (125 MHz, C6D6) δ 155.05, 148.33, 129.96,
128.58, 124.00, 78.75 (CF3),66.09(O((CH2)Me)2),63.17(CH2CH2),
29.14 (CHMe2), 24.44 (CHMe2), 14.26 (O((CH2)Me)2). 19F NMR
(282 MHz, C6D6) δ -75.56, -75.88. Anal. Calcd for C24H33-
F12MoNO3: C, 40.75; H, 4.70; N, 1.98. Found: C, 40.91; H, 4.67;
N, 2.40.
Mo(NAr)(CH2CHPh)(2,5-Me2NC4H2)(OSiPh3) (7). A 25 mL
Schlenk round-bottom flask equipped with a side arm and a
magnetic stir bar was charged with solid Mo(NAr)(CH2CH2)-
(2,5-Me2NC4H2)(OSiPh3) (306 mg, 0.458 mmol). Styrene, freshly
dried over CaH2, was vacuum transferred into the Schlenk flask.
The reaction mixture was allowed to stir at room temperature for
15 min. The volatiles were removed in vacuo. Pentane (5 mL) was
added, and the reaction mixture was placed at -35 °C; 252 mg of
gray solid product was isolated (yield 74%). 1H NMR (500 MHz,
C7D8) (four isomers; selected peaks) δ 4.23 (t, 1H, CH2dCHPh,
J = 11.5 Hz), 4.16 (t, 1H, CH2dCHPh, J = 11.5 Hz), 3.80 (br),
3.74-3.20 (m), 3.08 (dd, 1H, CH2dCHPh, J = 11.5, 6.5 Hz), 2.97
(dd, 1H, CH2dCHPh, J = 11.5, 6.0 Hz), 2.87-2.79 (m), 2.72 (dd,
1H, CH2dCHPh, J = 12.2, 6.0 Hz), 2.63-2.56 (m), 2.40 (dd, 1H,
CH2dCHPh, J = 11.5, 6.5 Hz), 2.22 (s, Me), 2.09 (s, Me), 1.94 (s,
Me), 1.89 (br), 1.83 (s, Me), 1.33 (d, 6H, MeCHMe, J = 6.5 Hz),
1.17 (d, 6H, MeCHMe, J = 6.5 Hz), 1.12 (d, 6H, MeCHMe, J =
6.5 Hz), 0.95 (d, 6H, MeCHMe, J = 6.5 Hz), 0.83 (d, 6H,
MeCHMe, J = 6.5 Hz). 13C NMR (125 MHz, C7D8) δ 154.6,
154.0, 151.8, 147.0, 146.7, 146.5, 146.1, 146.0, 141.5, 141.0, 139.8,
138.4, 136.4, 136.3, 130.0, 129.8, 128.9, 128.3, 128.0, 127.0, 126.2,
124.0, 123.8, 123.6, 113.9, 109.2 (br), 104.1, 76.8, 73.7, 66.8, 60.0,
57.9, 57.7, 56.7, 54.6, 29.1, 28.7, 28.6, 26.2, 25.6, 25.3, 24.1, 23.6,
23.4, 17.4. Anal. Calcd for C44H48MoN2OSi: C, 70.94; H, 6.49; N,
3.76. Found: C, 70.62; H, 6.67; N, 3.75.
Mo(NAr)(CH2CH2)(η1-2,5-Me2NC4H2)(η5-2,5-Me2NC4H2)
(5a). A 25 mL Schlenk round-bottom flask equipped with a side
arm and a magnetic stir bar was charged with solid Mo(NAr)-
(OTf)2(CH2CH2)(dme) (156 mg, 0.23 mmol, 1 equiv) and lithium
2,5-dimethylpyrrolide (46 mg, 0.46 mmol, 2 equiv). The flask was
degassed, and 5 mL of diethyl ether were vacuum transferred into
it. The reaction mixture was allowed to warm up to room
temperature and then immediately exposed to 1 atm of ethylene.
The mixture was allowed to stir at room temperature for 3 h. The
volatile materials were removed under vacuum. Benzene was
added, and the reaction mixture was filtered through Celite. The
volatile materials were removed, and the residue was recrystallized
1
from pentane to give 58.3 mg of red crystals; yield = 52%. H
NMR (500 MHz, C6D6) δ 6.90-6.78 (m, 3H, Ar), 6.51 (s, 2H,
NC4H2), 5.76 (s, 1H, NC4H2), 5.27 (s, 1H, NC4H2), 3.34 (sept, 2H,
MeCHMe, J = 6.8 Hz), 3.06-2.96 (m, 1H, C2H4), 2.78-2.68 (m,
1H, C2H4), 2.66-2.56 (m, 1H, C2H4), 2.33-2.23 (m, 1H, C2H4),
2.52 (s, 3H, CH3), 2.44 (s, 3H, CH3), 1.88 (s, 3H, CH3), 1.65 (s, 3H,
CH3), 1.05 (d, 6H, MeCHMe, J = 6.8 Hz), 1.00 (d, 6H, MeCHMe,
J = 6.8 Hz). 13C NMR (125 MHz, C6D6) δ 152.0, 151.6, 147.9,
139.8, 139.1, 139.6, 123.9, 112.3, 110.9, 103.7, 100.7, 99.4, 51.3,
48.1, 28.0, 25.5, 23.3, 21.0, 20.1, 17.2, 14.6. Experiments employing
13C2H4 revealed the resonances at 51.3 ppm and 48.1 ppm to be
those for ethylene carbons (JCH = 157 Hz for each). Anal. Calcd
for C26H37MoN3: C, 64.05; H, 7.65; N, 8.62. Found: C, 63.47; H,
7.52; N, 8.44.
Mo(NAr)(CH2CHPh)(OSiPh3)2 (8). Method A. A 25 mL
Schlenk round-bottom flask equipped with a side arm and a
magnetic stir bar was charged with solid Mo(NAr)(CH2-
CH2)(OSiPh3)2 (60 mg, 0.0706 mmol). Styrene, freshly dried
over CaH2, was vacuum transferred to the Schlenk flask. The
reaction mixture changed immediately from purple to green. The
volatiles were then removed in vacuo and after recrystallization
from pentane, 64 mg of green crystals were generated (yield =
98%).
Method B. Mo(NAr)(CH2CHPh)(2,5-Me2NC4H2)(OSiPh3)
(41.5 mg, 0.056 mmol, 1 equiv) and Ph3SiOH (15.4 mg, 0.056,
1 equiv) were transferred to a 20 mL vial equipped with a
magnetic stir bar. Pentane (5 mL) and 0.1 mL of diethyl ether
were added. The color of the reaction mixture changed from red
to green. The reaction mixture was stirred at room temperature
until the starting material was completely consumed. The reac-
tion mixture was placed at -35 °C, and 44.1 mg of green crystals
were obtained (yield 85%). 1H NMR (500 MHz, C6D6) (major
isomer (67%)) δ 7.79 (d, 6H, Ar, J = 6.5 Hz), 7.73 (d, 6H, Ar,
J = 6.5 Hz), 7.30-6.60 (m, 26H, Ar), 3.58 (t, 1H, CH2dCHPh,
J = 12.3 Hz), 3.41 (sept, 2H, MeCHMe, J = 6.8 Hz), 3.28 (dd,
1H, CH2dCHPh, J = 12.3, 6.4 Hz), 2.44 (dd, 1H, CH2dCHPh,
J = 12.3, 6.4 Hz), 0.98 (d, 6H, MeCHMe, J = 6.8 Hz), 0.75 (d,
6H, MeCHMe, J = 6.8 Hz); (minor isomer (33%)) δ 7.75 (d, 6H,
Ar, J = 6.5 Hz), 7.47 (d, 6H, Ar, J = 6.5 Hz), 7.30-6.60 (m,
26H, Ar), 4.64 (t, 1H, CH2dCHPh, J = 10.9 Hz), 3.72 (sept, 2H,
MeCHMe, J = 6.8 Hz), 2.99 (dd, 1H, CH2dCHPh, J = 10.9,
6.7 Hz), 2.26 (dd, 1H, CH2dCHPh, J = 10.9, 6.7 Hz), 1.02 (d,
6H, MeCHMe, J = 6.8 Hz), 0.96 (d, 6H, MeCHMe, J = 6.8 Hz).
13C NMR (125 MHz, C6D6) (major and minor isomers) δ 154.8,
154.0, 148.1, 147.1, 145.6, 144.7, 137.7, 137.5, 137.5, 137.2, 136.2,
136.1, 136.0, 135.9, 130.5, 130.4, 130.3, 130.0, 129.0, 128.7, 128.6,
128.5, 128.3, 128.0, 126.8, 126.2, 125.9, 125.7, 123.5, 123.3, 77.0,
73.0, 54.3, 52.1, 29.7, 29.4, 25.1, 24.7, 23.7, 23.0. Anal. Calcd for
C56H55MoO2Si2: C, 72.62; H, 5.99; N, 1.51. Found: C, 72.71; H,
6.01; N, 1.47.
Mo(NAr)(CH2CH2)(2-MesitylNC4H3)2 (5b). Benzene (10 mL)
was added to a 25 mL Schlenk flask charged with a stir bar and
Mo(NAr)(CHCMe2Ph)(MesPyr)2 (0.9243 g, 1.302 mmol). The
solution was degassed via three freeze-pump-thaw cycles and
then exposed to 1 atm of ethylene. The closed flask was heated at
60 °C for 4 days. The volatiles were removed in vacuo to give a
brown residue. Pentane (∼5 mL) and Et2O (∼1 mL) were added to
the residue. The brown solids were collected and dried in vacuo for
1 h; yield 0.620 g (71%). 1H NMR (500 MHz, C6D6) δ 6.88 (m, 3,
Ar-H, Pyr-H), 6.82 (s, 1, Ar-H), 6.81 (s, 1, Ar-H), 6.77 (s, 4, Ar-H),
6.53 (m, 2, Pyr-H), 6.24 (m, 2, Pyr-H), 3.43 (sept, 2, CHMe2), 2.65
(m, 2, C2H4), 2.16 (s, 6, Pyr-Me), 2.11 (s, 12, Pyr-Me), 1.96 (m, 2,
C2H4), 1.00 (d, 12, CHMe2, JHH = 7 Hz). 13C NMR (125 MHz,
C6D6) δ 154.71, 147.80, 140.50, 139.23, 138.28, 132.46, 129.39,
129.15, 128.96, 123.64 (NC4H3Mes), 111.92 (NC4H3Mes), 110.30
(NC4H3Mes), 54.22 (CH2CH2), 28.70, 24.45, 21.95, 21.52. Experi-
ments employing 13C2H4 revealed that the 54.22 resonance is due
to ethylene (JCH = 160 Hz). Anal. Calcd for C40H49MoN3: C,
71.94; H, 7.20; N, 6.29. Found: C, 72.24; H, 7.29; N, 6.05.
Mo(NAr)(CH2CH2)[OCH(CF3)2]2(Et2O) (6). Mo(NAr)-
(CH2CH2)(MesPyr)2 (0.201 g, 0.301 mmol) and 5 mL of diethyl
ether were added to a 20 mL scintillation vial. Hexafluoroisopro-
panol (74 μL, 0.7.03 mmol, 2.33 equiv) was added in portions. The
mixture was stirred for 30 min and filtered through glass wool. The
filtrate was concentrated in vacuo to ∼1 mL. After standing the
solution at -27 °C for 1 day, red crystals were isolated; yield 0.088 g
(41%). 1H NMR (500 MHz, C6D6) δ 6.92 (m, 3, Ar-H), 4.68 (s, 2,
OCH(CF3)2), 3.64 (q, 4, Et2O), 3.54 (sept, 2, CHMe2), 2.64 (m, 2,
Mo(NAr)(trans-3-hexene)(OSiPh3)2 (9). A 1 dram vial was
charged with solid Mo(NAr) (CH2CH2) (OSiPh3)2 (96 mg,

6828 Organometallics, Vol. 29, No. 24, 2010
Marinescu et al.
0.113 mmol). Addition of neat trans-3-hexene (100 μL) led to a
color change from purple to indigo. Pentane (0.1 mL) was added,
and indigo crystals formed and were filtered off. The crystals were
washed with pentane and dried in vacuo; yield 69 mg (67%). 1H
NMR (500 MHz, C6D6) (major isomer 9a (80%) selected peaks) δ
7.79 (t, 12H, Ar, J = 6.7 Hz), 7.26-7.04 (m, 18H, Ar), 7.00-6.88
(m, 3H, Ar), 3.82 (sept, 2H, MeCHMe, J = 6.8 Hz), 3.49-3.32 (m,
1H), 2.42-2.30 (m, 1H), 2.20-2.03 (m, 1H), 2.03-1.91 (m, 1H),
1.75-1.62 (m, 1H), 1.42-1.32 (m, 1H), 1.11 (d, 6H, MeCHMe,
J = 6.8 Hz), 0.97 (d, 6H, MeCHMe, J = 6.8 Hz), 0.94 (t, 3H,
MeCH2CH=, J = 7.3 Hz), 0.89 (t, 3H, MeCH2CH=, J = 7.3
Hz); (minor isomer 9b (20%) selected peaks) δ 3.75 (sept, 2H,
MeCHMe, J = 6.8 Hz), 2.68 (m, 2H, MeCH2CHd), 1.00 (d, 12H,
MeCHMe, J = 6.8 Hz). 13C NMR (125 MHz, C6D6) (major and
minor isomers) δ 153.6, 147.3, 138.3, 137.4, 136.1, 136.0, 135.8,
130.4, 130.1, 128.7, 128.4, 128.3, 123.5, 78.1, 77.3, 33.8, 29.8, 28.4,
25.4, 23.0, 20.0, 18.6. Anal. Calcd for C54H59MoO2Si2: C, 71.57; H,
6.56; N, 1.55. Found: C, 71.67; H, 6.65; N, 1.59.
placed at -35 °C. Red crystals (5.3 mg) were generated (yield =
65%). 1H NMR (500 MHz, C7D8) (selected peaks) δ 3.73 (sept,
2H, MeCHMe, J = 6.8 Hz), 3.38 (br, 1H, MoCH), 2.86 (br, 1H,
MoCH), 2.23 (br, 2H, MoCH2), 1.24 (br, 2H, MoCH2CH2), 1.00
(d, 12H, MeCHMe, J = 6.8 Hz). When 13C2H4 (∼0.5 atm) was
used, the following peaks were observed corresponding to the
square-pyramidal molybdacyclobutane carbons. 13C NMR (125
MHz, C7D8) δ 37.6 (d, JCC = 33 Hz, JCH = 138 Hz, MoCR), 27.8
(d, JCC = 33 Hz, JCH = 132 Hz, MoCRCβ). Anal. Calcd for
C51H53MoO2Si2: C, 70.89; H, 6.18; N, 1.62. Found: C, 71.30; H,
6.48; N, 1.40.
Reaction Involving Cyclooctene. To a benzene-d6 (0.6 mL)
solution of Mo(NAr)(CH2CH2)(O-i-PrF6)2(Et2O) (0.014 g,
0.0198 mmol) was added (260 μL, 1.98 mmol) of cyclooctene
via syringe. After 24 h at 23 °C, the mixture was dissolved in
methylene chloride, and the solution was then added dropwise
to methanol with vigorous stirring. A white precipitate of
polycyclooctene was filtered off from the methanol solution;
yield 0.082 g (38%). Both trans (88%) and cis (12%) CHdCH
bonds were observed. 1H NMR (500 MHz, CDCl3) δ 5.38 (m, 1,
trans-CH), 5.36 (m, 1, cis-CH), 2.01 (m, 2, trans-CH2), 1.97 (m,
Mo(NAr)(C4H8)(OSiPh3)2 (10). A J-Young NMR tube was
charged with a solution of Mo(NAr) (CH2CH2)(OSiPh3)2 (15
mg) in 0.6 mL of pentane and 0.1 mL of diethyl ether. The NMR
tube was degassed three times and filled with 1 atm of ethylene.
After 10 min at room temperature, the reaction mixture had
changed from purple to red-orange. The NMR tube was stored
at -35 °C to give orange crystals; 5.0 mg, 32% yield. X-ray
quality crystals of 10 were grown from a pentane:toluene
2, cis-CH2), 1.31 (br m, 4, trans-CH2), 1.29 (m, 2, cis-CH2). 13
C
NMR (125 MHz, CDCl3) δ 130.54 (m, trans-CH), 130.08 (m,
cis-CH), 32.83 (has a shoulder, trans- and cis-CH2), 29.96 (cis-
CH2), 29.85 (trans-CH2), 29.40 (cis-CH2), 29.26 (trans-CH2).
Crystal Structure Determinations. All structures were solved
by direct methods using SHELXS28 and refined against F2 on
all data by full-matrix least-squares with SHELXL-9729 using
established refinement techniques.30 For details, see Supporting
Information.
1
solution (10:1) of 10 at -35 °C under 1 atm of ethylene. H
NMR (500 MHz, C7D8, -20 °C) δ 7.72 (d, 12H, Ar, J = 7.3 Hz),
7.16 (t, 6H, Ar, J = 7.3 Hz), 7.07 (t, 12H, Ar, J = 7.3 Hz),
7.02-6.91 (m, 3H, Ar), 3.85 (sept, 2H, MeCHMe, J = 7.0 Hz),
3.11 (br, 2H, MoCH2), 3.06 (br, 2H, MoCH2), 2.58 (br, 2H,
MoCH2CH2), 2.41 (br, 2H, MoCH2CH2), 1.04 (d, 12H,
MeCHMe, J = 7.0 Hz). Anal. Calcd for C52H55MoO2Si2: C,
71.12; H, 6.31; N, 1.60. Found: C, 71.50; H, 6.48; N, 1.40.
When 13C2H4 (∼0.5 atm) was used, the following resonances
were observed for the metallacyclopentane carbons. 13C NMR
(125 MHz, C7D8, -20 °C) δ 72.4 (MoCR), 37.5 (MoCRCβ).
Mo(NAr)(C3H6)(OSiPh3)2 (11). A J-Young NMR tube was
charged with a suspension of Mo(NAr)(OSiPh3)2(CHCMe2Ph)21
(9 mg) in 0.6 mL of pentane. The suspension was degassed (3ꢀ)
and then exposed to 1 atm of ethylene. The reaction mixture was
Acknowledgment. We thank the National Science
Foundation for research support (CHE-0841187 to R.R.S.)
and for departmental X-ray diffraction instrumentation
(CHE-0946721).
Supporting Information Available: Experimental details for all
NMR experiments and X-ray structural studies. This material is
available free of charge via the Internet at http://pubs.acs.org.
(29) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112.
(28) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
1990, 46, 467.
€
(30) Muller, P. Crystallogr. Rev. 2009, 15, 57.