Cationic molybdenum imido alkylidene complexes

Article abstract of DOI:10.1021/om800209b

Addition of 1 equiv of [HNMe₂Ph]BAr₄^F (Ar^F = 3,5-(CF₃)₂C₆H₃) to Mo(NAr)(CHCMe₂Ph)(Pyrrolide)₂ (Pyrrolide = parent pyrrolide (Pyr) or 2,5-dimethyl

Full text of DOI:10.1021/om800209b

4428
Organometallics 2008, 27, 4428–4438
Cationic Molybdenum Imido Alkylidene Complexes
Annie J. Jiang, Richard R. Schrock,* and Peter Mu¨ller
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
ReceiVed March 6, 2008
Addition of 1 equiv of [HNMe2Ph]BArF4 (ArF ) 3,5-(CF3)2C6H3) to Mo(NAr)(CHCMe2Ph)(Pyrrolide)2
(Pyrrolide ) parent pyrrolide (Pyr) or 2,5-dimethylpyrrolide (Me2Pyr)) species in THF produced
[Mo(NAr)(CHCMe2Ph)(Pyrrolide)(THF)x]BArF4 species (x ) 2 for Me2Pyr (1b) or 3 (1a) for Pyr; Ar )
2,6-diisopropylphenyl). [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(2,4-lutidine)]BArF (1c) was formed upon
4
addition of 2,4-lutidine to [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]BArF (1b). Addition of 1 equiv of
4
hexafluoro-tert-butanol to 1a produced {Mo(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)3}BArF4 (3a), while
{Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2](THF)2}BArF (3b) was obtained similarly through addition of
4
hexafluoro-tert-butanol to 1b. Similar reactions produced unstable [Mo(NAr)(CHCMe2Ph)(O-2,6-i-
Pr2C6H3)(THF)]BArF (3c) and [Mo(NAr)(CHCMe2Ph)(OAdamantyl)(THF)2]BArF (3d). Treatment of
4
4
1b with 2 equiv of 2,6-diisopropylphenol yielded [Mo(NAr)(CH2CMe2Ph)(O-2,6-i-Pr2C6H3)2]BArF4 (4).
Compound 3a reacts with ethylene to yield {Mo(NAr)(CH2CH2)[OC(CF3)2Me](THF)3}BArF (6). The
4
reaction between Mo(NAr)(CHCMe2Ph)(OTf)2(dme) and 2 equiv of Li(MesPyr) (MesPyr ) 2-mesi-
tylpyrrolide) gave Mo(NAr)(CHCMe2Ph)(MesPyr)2 (2), but no cationic species could be prepared that
contain 2-mesitylpyrrolide. Compounds 1a, 1c, 2, 3a, 4, and 6 were characterized crystallographically.
some cases could be ascribed to decomposition reactions that
involve the nacnac ligands. However, we also considered the
possibility that the chelating nature of the nacnac ligand might
restrict rearrangement of metalacyclobutane complexes that are
required for productive turnover. Therefore, we decided to
prepare cationic molybdenum complexes that do not contain a
chelating monoanionic ligand, an example being
Introduction
The vast majority of high oxidation state Mo and W catalysts
that have been developed for the metathesis of alkenes are
neutral species of the type M(NR)(CHR′)(OR′′)2 or
M(NR)(CHR′)(diolate).1 In contrast, cationic tungsten2 or
molybdenum3 imido alkylidene complexes are rare, especially
those in which the metal has an electron count of less than 18.
Since bimolecular coupling of alkylidenes is a major mode of
decomposition of neutral alkylidene complexes, especially
methylene complexes, we felt that bimolecular decomposition
might be slower in cationic species. Therefore, we have been
exploring the synthesis of some cationic high oxidation state
alkylidene species that contain bulky ligands.
[Mo(NAr)(CHR′)(OR′′)(S)n]BArF , where S is a solvent such
4
as THF or some other two-electron donor. That opportunity
presented itself as a consequence of the recent synthesis of
various bispyrrolide complexes with the empirical formula
Mo(NR)(CHR′)(pyrrolide)2.5 Many of these species react readily
with alcohols and therefore would be expected to react readily
with [BArF ]- acids. The results of these experiments are
4
reported here.
In a previous paper we chose to explore cationic molybdenum
ꢀ-diketiminate complexes prepared from complexes of the type
Mo(NR)(CHR′)(Ar-nacnac)(OTf) (Ar-nacnac
)
[ArNC-
Results and Discussion
(Me)]2CH, OTf ) trifluoromethanesulfonate, R′ ) CMe3 or
CMe2Ph).4 Reaction of Mo(NR)(CHR′)(Ar-nacnac)(OTf) with
NaBArF4 (ArF ) 3,5-(CF3)2C6H3) afforded the cationic species
Synthesis of Cationic Monopyrrolide Complexes. Addition
of 1 equiv of [HNMe2Ph]BArF to the bispyrrolide species5,6
4
{Mo(NR)(CHR′)(Ar-nacnac)(THF)n}BArF (n ) 0 or 1, de-
in tetrahydrofuran produced cationic 1a (eq 1) as a fine
crystalline powder in 81% yield. Compound 1a is an 18e species
if π donation from the imido ligand is included. In methylene
4
pending on the nature of Ar). These cationic species reacted
with olefins, but in general were poor metathesis catalysts with
short catalyst lifetimes. Instability of these cationic species in
1
chloride-d2, the H NMR spectrum of 1a at room temperature
revealed the alkylidene HR resonance at 13.93 ppm with a JCH
value of 119 Hz and the CR resonance at 322.2 ppm; the JCH
value is characteristic of a syn alkylidene isomer, as shown in
eq 1.
Crystals of 1a suitable for X-ray diffraction were isolated
from a mixture of diethyl ether and pentane (Table 1).
Compound 1a is a six-coordinate octahedral species with three
THF ligands in a fac arrangement trans to the imido, alkylidene,
* Corresponding author. E-mail: rrs@mit.edu.
(1) (a) Schrock, R. R. Chem. ReV. 2002, 102, 145. (b) Schrock, R. R.;
Hoveyda, A. H. Angew. Chem., Int. Ed. 2003, 42, 4592. (c) Schrock, R. R.;
Czekelius, C. C. AdV. Synth. Catal. 2007, 349, 55.
(2) (a) Schrock, R. R.; Rocklage, S. M.; Wengrovius, J. H.; Rupprecht,
G.; Fellmann, J. J. Mol. Catal. 1980, 8, 73. (b) Wengrovius, J. H.; Schrock,
R. R. Organometallics 1982, 1, 148. (c) Blosch, L. L.; Gamble, A. S.;
Abboud, K.; Boncella, J. M. Organometallics 1992, 11, 2342. (d) Kress,
J.; Osborn, J. A. J. Am. Chem. Soc. 1983, 105, 6346. (e) Kress, J.; Osborn,
J. A. Angew. Chem. 1992, 104, 1660.
(3) (a) Vaughan, W. M.; Abboud, K. A.; Boncella, J. M. Organometallics
1995, 14, 1567. (b) Vaughan, W. M.; Abboud, K. A.; Boncella, J. M. J.
Organomet. Chem. 1995, 485, 37.
(4) Tonzetich, Z. J.; Jiang, A. J.; Schrock, R. R.; Mu¨ller, P. Organo-
metallics 2006, 25, 4725.
(5) (a) Hock, A. S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc.
2006, 128, 16373. (b) Singh, R.; Czekelius, C.; Schrock, R. R.; Muller, P.
Organometallics 2007, 26, 2528.
(6) The reader should refer to ref 5 for details of the structure of the
bispyrrolide in eq 1.
10.1021/om800209b CCC: $40.75
2008 American Chemical Society
Publication on Web 08/06/2008

Cationic Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 27, No. 17, 2008 4429
2 (07178)
Table 1. Crystallographic Data for 1a, 1c, and 2a
1a (07011) 1c (07164)
C72H74BF24MoN2O3.50 C67H58BF24MoN3
empirical formula
fw
C48H57MoN3
771.91
1586.08
1467.91
temperature (K)
cryst syst
space group
100(2)
monoclinic
P2(1)/n
100(2)
monoclinic
P2(1)/n
203(2)
monoclinic
P2(1)/n
unit cell dimens (Å, deg)
a ) 18.4389(6)
b ) 21.1079(7)
c ) 18.8695(6)
ꢀ ) 95.3130(10)
7312.6(4)
a ) 24.9162(9)
b ) 18.8260(7)
c ) 28.0325(11)
ꢀ ) 93.7380(10)
13121.3(9)
8
1.486
0.311
5952
a ) 11.3790(6)
b ) 19.8001(10)
c ) 18.8237(10)
ꢀ ) 99.000(2)
4188.9(4)
4
1.224
0.348
1632
volume (Å3)
Z
4
density (calcd; Mg/m3)
1.441
0.288
3244
absorp coeff (mm-1
F(000)
)
cryst size (mm3)
θ range (deg)
index ranges
0.30 × 0.25 × 0.15
1.76 to 29.57
-25 e h e 25, -29 e k e 28,
-26 e l e 26
145 199
0.50 × 0.45 × 0.30
0.30 × 0.25 × 0.20
1.06 to 30.26
1.97 to 29.85
-35e<h)35, -26 e k e 26,
-39 e l e 39
355 073
38 819 [R(int) ) 0.0591]
99.1%
-15 e h e 15, -27 e k e 27,
-25 e l e 26
94 578
12 047[R(int) ) 0.0438]
100%
no. of reflns collected
no. of indep reflns
completeness to θ
20 491 [R(int) ) 0.0490]
99.9%
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
0.9580 and 0.9185
20 491/2908/1150
1.045
R1 ) 0.0409, wR2 ) 0.0927
R1 ) 0.0602, wR2 ) 0.1027
0.848 and -0.444
0.9124 and 0.8598
38 819/5039/1995
1.050
R1 ) 0.0476, wR2 ) 0.1068
R1 ) 0.0716, wR2 ) 0.1215
1.504 and -1.076
0.9336 and 0.9027
12 047/1/484
1.042
R1 ) 0.0316, wR2 ) 0.0769
R1 ) 0.0435, wR2 ) 0.0847
0.610 and -0.604
larg diff peak and hole (e Å-3
)
a All structures were determined with 0.71073 Å radiation. The absorption correction was semiempirical from equivalents, and the method of
refinement was full-matrix least-squares on F2.
and pyrrolide ligands, as shown in Figure 1. The Mo-O bond
lengths for the THF ligands trans to the imido and alkylidene
ligands are 2.3101(12) and 2.3612(13) Å, respectively, while
Figure 1. Thermal ellipsoid (50%) rendering of {Mo(NAr)-
the Mo-O bond length trans to the pyrrolide is 2.1945(13) Å.
(CHCMe2Ph)(NC4H4)(THF)3}BArF4 (1a). Hydrogen atoms, a minor
The ModC and ModN bond lengths are unexceptional. The
disorder, solvent molecules, and the anion are not shown for clarity.
alkylidene is in the syn orientation with Mo-C(1)-C(2) )
Selected bond distances (Å) and angles (deg): Mo1-C1 )
143.13(14)°, a typical Mo-C(1)-C(2) angle for a syn alkylidene
1.9209(19); Mo1-N1 ) 1.7329(15); Mo1-N2 ) 2.0810(15);
in a high oxidation state Mo species.
Mo1-O2 ) 2.1945(13); Mo1-O3 ) 2.3101(12); Mo1-O4 )
Upon treating Mo(NAr)(CHCMe2Ph)(Me2Pyr)2 (Me2Pyr )
2.3612(13);Mo1-C1-C2)143.13(14);N1-Mo1-O3)170.11(6);
O4-Mo1-C1)168.85(6);N2-Mo1-O2)159.11(6);Mo1-N1-C11
) 177.06(13).
2,5-Me2NC4H2)5b with [HNMe2Ph]BArF in THF, [Mo(NAr)-
4
(CHCMe2Ph)(Me2Pyr)(THF)2]BArF4 (1b) was isolated in 71%
yield as a burnt orange crystalline powder. The additional steric
hindrance presented by the 2,5-dimethylpyrrolide ligand appar-
ently limits coordination of only two THF ligands to the metal
center, according to solution proton NMR studies. The exact
coordination geometry of the molecule in solution is unclear
because the THF proton resonances are broad. At room
temperature, the 1H NMR spectrum of the sample in methylene
chloride displays four THF resonances at 3.84, 3.70, 2.02, and
1.83 ppm in the ratios 2:6:4:4. The syn alkylidene proton
resonance is found at 14.26 ppm (JCH ) 128 Hz). Upon cooling
the solution to -80 °C, two alkylidene proton resonances are
observed at 14.17 and 13.77 ppm. Therefore at least two isomers
must be present at -80 °C, and some equilibration process is
rapid on the NMR time scale at room temperature. Upon treating
1b with 1 equiv of 2,4-lutidine in dichloromethane, [Mo(NAr)-
(CHCMe2Ph)(Me2Pyr)(2,4-Lut)]BArF4 (1c) could be isolated as
a yellow powder in 99% yield (eq 2). Proton NMR studies
suggest that this is a syn species and that THF is not present.
Asymmetry at the metal center is suggested by the presence of
two singlet resonances for the backbone protons of the pyrrolide
and a total of six singlets for the methyl groups on the lutidine,
pyrrolide, and alkylidene ligands.
An X-ray structure of 1c (Table 1) reveals it to contain one
bound 2,4-lutidine and an η5-dimethylpyrrolide in a pseudot-
etrahedral arrangement around the metal (Figure 2). The metal
therefore has an 18e count. The Mo-pyrrolide centroid distance
is 2.10 Å, the Mo-N5 distance is 2.411(2) Å, and two of the

4430 Organometallics, Vol. 27, No. 17, 2008
Jiang et al.
reaction between Mo(NAr)(CHCMe2Ph)(OTf)2(dme) and 2
equiv of Li(MesPyr) gave Mo(NAr)(CHCMe2Ph)(MesPyr)2 (2)
(eq 3), which was isolated as orange blocks in 54% yield.
According to proton NMR studies, 2 has a mirror plane on the
NMR time scale that relates the two pyrrolides and a syn
alkylidene with δHR ) 11.56 ppm and JCH ) 120 Hz.
Figure 2. Thermal ellipsoid (50%) rendering of one of the two
crystallographically independent molecules in the structure of
[Mo(NAr)(CHCMe2Ph)(Me2Pyr)(2,4-Me2NC5H3)]BArF4 (1c). Hy-
drogen atoms, the anion, and the second molecule of the asymmetric
unit are not shown. Selected bond distances (Å) and angles (deg):
Mo2-C110 ) 1.937(2); Mo2-N4 ) 1.7396(18); Mo2-N5 )
2.4114(19); Mo2-N6 ) 2.1908(18); Mo2-C51 ) 2.343(2);
Mo2-C53 ) 2.359(2); Mo2-C54 ) 2.459(2); Mo2-C55 )
2.479(2); Mo2-Centroid of pyrrolide ) 2.096; Mo2-C110-C111
) 139.94(16); Mo2-N4-C41 ) 170.24(15).
An X-ray study reveals that 2 has a pseudotetrahedral
structure in which the two MesPyr ligands are both bound in
an η1 fashion (Table 1, Figure 3). The perpendicular orientation
of the mesityl ring with respect to the pyrrolide ring and the
overall steric demands of the MesPyr ligand evidently prevent
η5 coordination of one of the pyrrolides, as found in Mo(NAd)-
(CHCMe3)(η5-Me2Pyr)(η1-Me2Pyr)9andW(NAr)(CHCMe2Ph)(η5-
Me2Pyr)(η1-Me2Pyr).7 Therefore 2 is a 14-electron species if
no possible π bonding from the pyrrolide nitrogen to the metal
is included. Metal-ligand bond lengths in general are slightly
shorter in 2 than in 1a or 1c as a consequence of its lower
electron count and coordination number (e.g., ModC )
1.8660(16) Å in 2 and 1.932(2) Å in 1c).
Unfortunately, addition of [HNMe2Ph]BArF to 2 in THF
4
yielded only an oily mixture of unidentified materials. An oily
mixture of unidentified products also was formed when
[HNMe2Ph]BArF was added to 2 in dichloromethane in the
4
presence of excess 2,4-lutidine.
Synthesis of Cationic Monoalkoxides. Addition of 1 equiv of
hexafluoro-tert-butanol to 1a produced {Mo(NAr)(CHCMe2Ph)-
[OC(CF3)2Me](THF)3}BArF (3a), which was isolated in 82%
4
yield as a yellow powder (eq 4). The analogous compound,
{Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2](THF)2}BArF4 (3b), was
obtained in 91% yield similarly through addition of hexafluoro-
Mo-C single bond lengths (2.460(3) and 2.479(2) Å) are longer
than the other two Mo-C bonds (2.344(2) and 2.360(2) Å).
This Mo-pyrrolide centroid distance is comparable to the
W-centroid distance (2.08 Å) in the 2,5-dimethylpyrrolenine
tert-butanol to {Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2}BArF .
4
The low values for JCH (∼119 Hz) suggest that a syn alkylidene
is present in 3a and 3b.
species
{W(N-2,6-Cl2C6H3)(CHCMe3)(Me2Pyr)(2,5-
An X-ray study of 3a (Table 2) revealed it to have a pseudo-
octahedral structure with the hexafluoro-tert-butoxide trans to
the imido ligand (Figure 4). The THF trans to the alkylidene is
weakly bound (Mo-O(2) ) 2.4398(13) Å) compared to the
mutually trans THF ligands (Mo-O ) 2.1495(11) Å and
2.1527(11) Å). Therefore it is not surprising that 16e 3b can be
isolated, in which only two THF ligands are present.
Treating the cationic pyrrolide complexes with other mono-
dentate alcohols produced monoalkoxide complexes similar to
3a. For example, [Mo(NAr)(CHCMe2Ph)(O-2,6-i-Pr2C6H3)-
(THF)]BArF4 (3c, δHR ) 14.73 ppm) was isolated in 90% crude
yield upon treating [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]-
Me2NC4H3)}BArF .7 The Mo-N6 distance (2.1908(18) Å) is
4
typical for a 2e donor bound to Mo. The alkylidene is in the
syn orientation. All other bond distances and angles are
unexceptional.
The structures of 1a and 1c suggest that more sterically
demanding pyrrolides might be desirable in order to avoid 18e
counts at the metal and, in particular, pyrrolides that are unlikely
to be able to bind to the metal in an η5 fashion. Therefore we
explored the synthesis of compounds that contain the 2-mesi-
tylpyrrolide ligand (MesPyr). Treatment of 2-mesitylpyrrole8
with n-butyllithium in diethyl ether produced Li(MesPyr). The
BArF with 2,6-diisopropylphenol, and [Mo(NAr)(CHCMe2-
4
Ph)(OAd)(THF)2]BArF (3d, δHR ) 15.07 ppm) was isolated
(7) Kreickmann, T.; Arndt, S.; Schrock, R. R.; Mueller, P. Organome-
tallics 2007, 26, 5702.
4
(8) Reith, R. D.; Mankad, N. P.; Calimano, E.; Sadighi, J. P. Org. Lett.
2004, 6, 3981.
(9) Singh, R. Ph.D. thesis, Massachusetts Institute of Technology, 2008.

Cationic Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 27, No. 17, 2008 4431
6 (07029)
Table 2. Crystallographic Data for 3a, 4, and 6a
3a (07005)
C70H68BF30MoNO4
1664
4 (07170)
empirical formula
fw
C78H76BF24MoNO2
1622.15
C60H60BCl2F30MoNO4
1606.74
temperature (K)
cryst syst
space group
100(2)
monoclinic
P2(1)/n
100(2)
monoclinic
P2(1)/m
100(2)
triclinic
j
P1
unit cell dimens (Å, deg)
a ) 16.200(2)
b ) 22.500(3)
c ) 20.048(3)
R ) 90
ꢀ ) 96.045(2)
γ ) 90
7266.6(18)
a ) 13.3339(5)
b ) 56.707(2)
c ) 15.0088(5)
R ) 90
ꢀ ) 90.2990(10)
γ ) 90
11348.4(7)
a ) 12.9370(4)
b ) 12.9705(4)
c ) 22.1851(7)
R ) 89.3430(10)
ꢀ ) 75.4770(10)
γ ) 85.3940(10)
3591.91(19)
volume (Å3)
Z
4
6
2
density (calcd; Mg/m3)
1.521
0.305
3376
1.424
0.279
4980
1.486
0.378
1620
absorp coeff (mm-1
F(000)
)
cryst size (mm3)
θ range (deg)
index ranges
0.30 × 0.25 × 0.20
1.71 to 29.57
-22 e h e 22, -31 e k e 31,
-26 e l e 27
158 588
0.20 × 0.20 × 0.07
0.72 to 28.28
-17 e h e 17, -75 e k e 75,
-19 e l e 20
279 787
0.30 × 0.25 × 0.20
0.95 to 29.57
-17 e h e 17, -18 e k e 18,
-30 e l e 30
80 936
20 089 [R(int) ) 0.0313]
99.7%
no. of reflns collected
no. of indep reflns
completeness to θ
20 382 [R(int) ) 0.0672]
100.0%
28 423 [R(int) ) 0.0830]
100.0%
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
0.9414 and 0.9139
20 382/2009 /1177
1.032
R1 ) 0.0354, wR2 ) 0.0874
R1 ) 0.0482, wR2 ) 0.0970
0.948 and -0.598
0.9808 and 0.9464
28 423/6579/2360
1.054
R1 ) 0.0913, wR2 ) 0.2251
R1 ) 0.1187, wR2 ) 0.2463
2.157 and -1.719
0.9283 and 0.8951
20 089/2831/1194
1.060
R1 ) 0.0525, wR2 ) 0.1489
R1 ) 0.0625, wR2 ) 0.1575
3.141 and -1.343
larg diff peak and hole (e Å-3
)
a All structures were determined with 0.71073 Å radiation. The absorption correction was semiempirical from equivalents, and the method of
refinement was full-matrix least-squares on F2.
Figure 3. Thermal ellipsoid (50%) rendering of Mo(NAr)-
(CHCMe2Ph)(MesPyr)2 (2). Hydrogen atoms are removed for
clarity. Selected bond distances (Å) and angles (deg): Mo1-C1 )
Figure 4. Thermal ellipsoid (50%) rendering of {Mo(NAr)-
1.8660(16); Mo1-N1 ) 1.7361(13); Mo1-N2 ) 2.0200(13);
(CHCMe2Ph)[OCMe(CF3)2](THF)3}BArF4 (3a). Hydrogen atoms,
Mo1-N3)2.0430(13);Mo1-C1-C2)146.75(12);Mo1-N1-C11
a minor disorder, and the anion are removed for clarity. Selected
) 172.45(11).
bond distances (Å) and angles (deg): Mo1-C1 ) 1.9227(16);
Mo1-N1 ) 1.7514(14); Mo1-O1 ) 2.0218(11); Mo1-O2 )
in 88% crude yield upon treating [Mo(NAr)(CHCMe2Ph)(Pyr)-
2.4398(13); Mo1-O3 ) 2.1495(11); Mo1-O4 ) 2.1527(11);
(THF)3]BArF4 with 1-adamantanol. However, during recrystal-
Mo1-C1-C2)143.66(12);N1-Mo1-O1)166.31(6);O3-Mo1-O4
lization attempts to purify both 3c and 3d in a mixture of diethyl
) 165.75(4); C1-Mo1-O2 ) 176.84(6); Mo1-N1-C11 )
ether and pentane, they decomposed over a period of several
days; therefore elemental analyses on recrystallized material
could not be obtained. However, elemental analysis of crude
3d was successful. Attempts to recrystallize about 50 mg of 3c
via vapor diffusion of pentane into a diethyl ether solution of
thecompoundproducedatraceamountof[Mo(NAr)(CH2CMe2Ph)(O-
176.30(12).
2 equiv of 2,6-diisopropylphenol (eq 5, DIPP ) 2,6-diisopro-
1
pylphenoxide). The H NMR spectrum of 4 indicates that it
has a mirror plane which renders the HR protons equivalent (at
δ 4.06 ppm in methylene chloride-d2) and ꢀ methyl groups in
the alkyl equivalent. Treatment of 1a with 3,3′-di-tert-butyl-
5,5′,6,6′-tetramethylbiphenyl-2,2′-diol (rac-BIPHENH2) also
produced an alkyl complex (5) in 80% yield, whose proton NMR
2,6-i-Pr2C6H3)2]BArF (4).
4
Compound 4 could be prepared and isolated in 29% yield
by treating [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]BArF4 with

4432 Organometallics, Vol. 27, No. 17, 2008
Jiang et al.
Figure 5. Thermal ellipsoid (50%) rendering of the well-behaved
molecule of the structure of [Mo(NAr)(CH2CMe2Ph)(O-2,6-i-
Pr2C6H3)2]BArF (4). Hydrogen atoms (except for the alkyl’s R
4
protons) and the anion are removed for clarity. Selected bond
distances (Å) and angles (deg): Mo1-C1 ) 2.113(4); Mo1-N1 )
1.699(3); Mo1-O1 ) 1.840(3); Mo1-O2 ) 1.843(3); Mo1-C1-C2
) 110.1(3), Mo1-N1-C11 ) 170.6(3); Mo1-O1-C21 ) 145.1(3);
Mo1-O2-C31 ) 139.4(3).
spectrum is characteristic of a chiral species; for example, the
HR protons in the neophyl ligand have chemical shifts of 4.95
and 2.39 ppm with a JHH of 12 Hz.
An X-ray structure of 4 (Table 2, Figure 5) revealed it to be
the expected pseudotetrahedral cationic alkyl complex with a
Mo-CR bond length of 2.113(4) Å and a ModN bond length
of 1.699(3) Å. Other bond lengths and various bond angles are
unexceptional. Compounds 4 and 5 are unusual in that they are
pseudotetrahedral, electron-deficient, cationic alkyls of Mo(VI).
So far we have found no other examples in the literature.
Reactions of Cationic Complexes with Olefins. Complexes
1a-c did not react with ethylene in THF. Compound 1a
decomposed when it was exposed to 1 atm of ethylene in
CD2Cl2, while 1c in CD2Cl2 did not react with ethylene (1 atm)
in 7 days.
The reaction between 3a and ethylene in CD2Cl2 over a period
of 2 h yielded 6, which was isolated in 91% yield (eq 6). In
1
solution the H NMR spectrum (CD2Cl2, 20 °C) of 6 showed
broad resonances for the three THF ligands. At -70 °C each
broad resonance separated into two THF resonances in the ratio
of 2:1. At room temperature sharp multiplets were found for
the ethylene protons at 3.08 and 2.62 ppm and the ethylene
carbon resonance was found at 63.47 ppm in bromobenzene-d5
(JCH ) 152 Hz).
An X-ray structure study of 6 (Table 2, Figure 6) revealed
that its structure is overall similar to that of 3a, with the ethylene
ligand in place of the alkylidene ligand. The Mo-C(1) bond
length is 2.213(2) Å, Mo-C(2) ) 2.220(2) Å, and C(1)-C(2)
) 1.408(4) Å, similar to other known ethylene complexes of
this general type.10,11 The ethylene is oriented along the
O(3)-Mo-O(4) axis, as expected, in order to employ the d
Figure 6.
Thermal ellipsoid (50%) rendering of
{Mo(NAr)(C2H4)[OCMe(CF3)2](THF)3}BArF (6). Hydrogen at-
4
oms, a minor disorder, a disordered pentane, and the anion are
removed for clarity. Selected bond distances (Å) and angles (deg):
Mo1-C1 ) 2.213(2); Mo1-C2 ) 2.220(2); Mo1-N1 ) 1.7558(19);
Mo1-O1 ) 2.0196(17); Mo1-O2 ) 2.2499(16); Mo1-O3 )
2.2013(17);Mo1-O4)2.2051(17);C1-C2)1.408(4);Mo1-C1-C2
) 71.76(14); Mo1-C2-C1 ) 71.20(14); Mo1-N1-C11 )
178.17(16); Mo1-O1-C3 ) 157.7(2); N1-Mo1-O1 ) 175.71(8).
orbital in the O(2)-O(3)-Mo-O(4) plane for back-bonding
(the same orbital that is employed to form the ModC bond in
3a).
When a degassed, frozen solution of 3a (∼40 mg) in CD2Cl2
(10) Tsang, W. C. P.; Jamieson, J. Y.; Aeilts, S. L.; Hultzsch, K. S.;
Schrock, R. R.; Hoveyda, A. H. Organometallics 2004, 23, 1997.
(11) Arndt, S.; Schrock, R. R.; Mueller, P. Organometallics 2007, 26,
1279.
(∼0.6 mL) in an NMR tube was exposed to ∼300 mmHg of
1
13C ethylene, the H NMR spectrum of the solution ∼15 min
after being thawed showed that a methylidene complex had been

Cationic Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 27, No. 17, 2008 4433
1
Figure 7. H NMR spectrum of the reaction of 3a in CD2Cl2 and
13C ethylene after approximately 15 min of reaction time at room
temperature. Only the alkylidene region is depicted.
formed (Figure 7) whose proton resonances are found at 14.77
and 13.68 ppm (JHH ) 5 Hz, JCH ) 140 and 166 Hz,
respectively); the JHH ) 5 Hz and JCH ) 140 and 166 Hz values
are comparable to those found for other (rare) high oxidation
state methylene complexes.7,12 The 13C NMR spectrum of this
mixture shows a CR resonance at 302.30 ppm. A small amount
of a metallacyclopentane complex (doublet resonances at 121.52
and 18.31 ppm, JCC ) 43 Hz) is present along with 3-methyl-
3-phenyl-1-butene (singlet resonance at 110.95 ppm) and the
ethylene complex (resonance at 63.40 ppm). No resonance for
free ethylene was observed. In an analogous sample that
contained 30 mg of 3a, the metallacyclopentane complex and
propylene (dd, 134.34 ppm, JCC ) 70 and 42 Hz; d, 115.81
ppm, JCC ) 70 Hz; d, 19.63, JCC ) 42 Hz) could be observed
clearly (Figure 8). After 15 min the 13C NMR spectrum showed
a decrease in free ethylene and formation of 1-butene (Figure
9; dd at 141.21 ppm with JCC ) 70 and 42 Hz; d at 113.38
ppm with JCC ) 70 Hz; dd at 27.25 ppm with JCC ) 42 and 35
Hz; d at 13.46 ppm with JCC ) 35 Hz). We conclude that the
metallacyclopentane complex rearranges to 1-butene via ꢀ-hy-
dride elimination. When isolated 6 was exposed to 1 atm of
ethylene, ethylene was dimerized catalytically to 1-butene.
The mechanism (Scheme 1) that explains how the products
mentioned above are formed has precedent in the literature.10,13
Upon exposure to ethylene, a solution of 3a first forms an
unobservable substituted metallacyclobutane complex. The
metallacycle releases 3-methyl-3-phenyl-1-butene to form a
molybdenum methylidene complex, which reacts with another
ethylene to yield an unsubstituted metallacyclobutane (also not
observed in this case, but see below). The unsubstituted
metallacyclobutane complex rearranges to form propylene, a
rearrangement that may be promoted by ethylene.10 Propylene
is displaced by ethylene to form the ethylene complex (6), and
6 then reacts with ethylene to yield the metallacyclopentane,
which is an intermediate in the catalytic formation of 1-butene.
It should be noted that the particular species that are observed
in any given experiment may depend greatly upon the conditions
of that experiment.
Figure 8. 13C NMR after exposing 3a (CD2Cl2) to ∼300 mmHg
of 13C-ethylene at room temperature for approximately 5 min.
A degassed sample of complex 3c (∼30 mg in ∼0.6 mL of
CD2Cl2) was treated with 1 atm of ethylene at room temperature
to give ∼5% of a methylidene complex with HR resonances at
δ 14.93 and 13.72 ppm (JHH ) 4.5 Hz) after 15 min. Similarly,
Figure 9. 13C NMR after exposing 3a (CD2Cl2) to ∼300 mmHg
of 13C-ethylene at room temperature for 15 min.
a frozen and degassed sample of complex 3c (∼30 mg in ∼0.6
mL of CD2Cl2) was treated with ∼300 mmHg of 13C-ethylene.
After 30 min, 13C NMR spectra showed evidence of an ethylene
complex (carbon resonance at 57.62 ppm), in addition to
3-methyl-3-phenyl-1-butene and ethylene. After 3 h, the ethylene
(12) Fox, H. H.; Lee, K.-K.; Park, L. Y.; Schrock, R. R. Organometallics
1993, 12, 759.
(13) Tsang, W. C. P.; Hultzsch, K. S.; Alexander, J. B.; Peter, J.;
Bonitatebus, J.; Schrock, R. R.; Hoveyda, A. H J. Am. Chem. Soc. 2003,
125, 2653.

4434 Organometallics, Vol. 27, No. 17, 2008
Jiang et al.
Scheme 1
resonance had disappeared and trans-2-butene (dd, 126.32 ppm,
JCC ) 28 and 16 Hz; dd, 18.18 ppm, JCC ) 28 and 16 Hz) and
cis-2-butene (dd, 125.06 ppm, JCC ) 27 and 16 Hz; dd, 12.66
ppm, JCC ) 27 and 16 Hz) were observed. 2-Butene is believed
to be formed through catalytic metathesis of 1-propene.
When a degassed sample of complex 3d (∼30 mg in ∼0.6
mL of CD2Cl2) was treated with 1 atm of ethylene at room
temperature, no methylidene complex was observed after 15
min. A frozen and degassed sample of complex 3d (∼30 mg in
∼0.6 mL of CD2Cl2) was treated with ∼300 mmHg of 13C-
ethylene. After 30 min, 13C NMR spectra showed the sample
to contain 3-methyl-3-phenyl-1-butene, ethylene, and a metal-
lacyclobutane complex (doublet at 104.00 ppm with JCC ) 13
Hz and a triplet at -0.19 ppm with JCC ) 13 Hz). After 5 h,
the metallacyclobutane complex had disappeared. After 24 h,
cis and trans 2-butene were present in addition to ethylene,
3-methyl-3-phenyl-1-butene, and 1-butene. No ethylene complex
was observed in this case.
Table 3. Ring-Closing Reactions with 3b in CD2Cl2
The monoalkoxide species 3a, 3c, and 3d (5 mol %) catalyze
the conversion of 1-hexene to 5-decene in 1 h at 22 °C (90%,
90%, and 45%, respectively) and the ring-closure diallytosy-
lamine to give the expected cyclopentene product after 24 h at
60 °C in 90%, 60%, and 20% yields, respectively. Attmpted
ring-closing reactions on selected substrates in CD2Cl2 (shown
in Table 3) generally were inefficient and low yielding, with
the maximum product yield being 88%. Finally, 3b was found
to initiate ROMP polymerization of 2,3-dicarbomethoxynor-
bornadiene (100 equiv) in 30 min at 22 °C in mixtures of
dichloromethane and toluene. The polymer was isolated in 87%
yield. Carbon NMR studies indicated that the polymer is ∼95%
cis but not highly tactic.14
metathesis catalysts. However, at least with the catalysts and
substrates that we have examined so far, cationic species do
not appear to have any significant advantages over neutral
species. In fact it appears that cationic alkylidenes are less stable
than neutral species. However it is not yet known whether a
lower stability can be ascribed to a bimolecular coupling of
alkylidenes, especially methylenes, rearrangement of metala-
cyclobutanes to olefins, or other decomposition pathways.
Conclusions
(14) (a) McConville, D. H.; Wolf, J. R.; Schrock, R. R. J. Am. Chem.
Soc. 1993, 115, 4413. (b) Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast,
W. J.; Gibson, V. C.; O’Regan, M. B.; Thomas, J. K.; Davis, W. M. J. Am.
Chem. Soc. 1990, 112, 8378.
The work described here confirms that cationic imido
alkylidene species can be prepared and that they are viable

Cationic Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 27, No. 17, 2008 4435
CHMe2); 13C NMR (125 MHz, CD2Cl2) δ 325.36 (MoCR), 162.35
(q, 1JC ) 50 Hz, ipso-C of BArF ), 152.32, 147.45, 145.46,
Experimental Section
11B
4
135.39, 130.70, 129.52, 129.51 (qq, 2JCF ) 31 Hz, 3JC B ) 3 Hz,
General Comments. Glassware was oven-dried at 175 °C and
purged with nitrogen on a dual-manifold Schlenk line or cooled in
the evacuated antechamber of a nitrogen-filled glovebox. Experi-
ments were conducted either in a nitrogen drybox or a dual-manifold
Schlenk line under dinitrogen. HPLC grade diethyl ether, toluene,
pentane, tetrahydrofuran, and methylene chloride were sparged with
nitrogen and passed through activated alumina; in addition, benzene
was passed through a copper catalyst; organic solvents were then
stored over activated 4 Å Linde-type molecular sieves. Methylene
chloride-d2 and benzene-d6 were sparged with nitrogen and stored
over activated 4 Å Linde-type molecular sieves prior to use. NMR
spectra were obtained on Varian 300 or 500 MHz spectrometers,
reported in δ (parts per million) relative to tetramethylsilane, and
referenced to the residual 1H/13C signals of the deuterated solvent
(1H (δ): benzene 7.16, methylene chloride 5.32; 13C (δ): benzene
128.39, methylene chloride 54.00). 19F NMR spectra were refer-
enced to an external sample of neat fluorobenzene at δ -113.15
ppm relative to CFCl3. H. Kolbe Microanalytics Laboratory
(Mu¨lheim an der Ruhr, Germany) provided the elemental analyses
results. [HNMe2Ph]BArF4 was obtained by treating NaBArF4 with
[HNMe2Ph]Cl in diethyl ether or dichloromethane. All other
reagents were used without further purification unless noted
otherwise. Mo(NR)(CHCMe2Ph)(NC4H4)2 and Mo(NR)(CHCMe2Ph)-
(2,5-Me2NC4H2)2 were prepared as described in the literature.5
[Mo(NAr)(CHCMe2Ph)(NC4H4)(THF)3]BArF4 (1a). Mo(NAr)-
(CHCMe2Ph)(Pyr)2 (0.506 g, 0.945 mmol) was dissolved in 10 mL
of THF to give a dark yellow solution, and to this solution was
11
m-Ar of BArF ), 127.90, 126.60, 125.55 (q, JCF ) 272 Hz, CF3 of
4
BArF ), 124.81, 118.07 (m, p-Ar of BArF ), 107.94, 103.8, 86.08,
4
4
68.92, 30.13, 29.93, 28.99, 27.98, 26.10, 25.02, 24.57, 24.19, 18.46,
16.91; 19F NMR (282 MHz, CD2Cl2) δ -62.78. Anal. Calcd for
C68H65BF24MoN2O2: C, 54.27; H, 4.35; N, 1.86. Found: C, 54.36;
H, 4.39; N, 1.84.
[Mo(NAr)(CHCMe2Ph)(Me2Pyr)(2,4-Me2NC5H3)]BArF (1c).
4
[Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]BArF (0.406 g, 0.270
4
mmol) was dissolved in CH2Cl2 (∼2 mL) to give an orange solution.
2,4-Dimethylpyridine (37 µL, 0.319 mmol, 1.18 equiv) was added
via syringe to the orange solution. The mixture was stirred at room
temperature for ∼10 min. Volatiles were removed in Vacuo to yield
a yellow foam. Pentane (∼3 mL) was added to the foam, and the
mixture was stirred for 10 min. Vacuum was applied to remove
the volatiles, leaving behind a yellow powder. The solid was dried
in Vacuo for 2 h; yield 0.371 g (99%): 1H NMR (500 MHz, CD2Cl2)
δ 13.91 (s, 1, MoCHR), 7.73 (br s, 8, o-H of BArF ), 7.57 (s, 4,
4
p-H of BArF ), 7.30 (m, 11, Ar-H), 6.30 (d, 1, NC4H2Me2), 5.92
4
(d, 1, NC4H2Me2), 3.10 (sept, 2, CHMe2), 2.50 (s, 3, Me), 2.43 (s,
3, Me), 2.33 (s, 3, Me), 1.76 (s, 3, Me), 1.71 (s, 3, Me), 1.57 (s, 3,
Me), 1.22 (d, 12, CHMe2); 13C NMR (125 MHz, CD2Cl2) δ 333.68
(MoCR), 162.01 (q, 1JC ) 50 Hz, ipso-C of BArF ), 160.99,
11B
4
158.47, 157.45, 156.97, 155.37, 152.29, 151.99, 149.52, 147.19,
145.17, 142.82, 135.37, 130.37, 129.95, 129.56 (qq, 2JCF ) 31 Hz,
3JC ) 3 Hz, m-Ar of BArF ), 129.42, 127.74, 126.84, 126.74,
11B
4
125.41, 125.16 (q, JCF ) 272 Hz, CF3 of BArF ), 124.96, 118.06
added [HNMe2Ph]BArF (0.931 g, 0.945 mmol) as a solid in one
4
4
(m, p-Ar of BArF ), 106.30, 105.97, 61.66, 30.04, 29.77, 28.91,
4
portion. The reaction mixture became light yellow immediately and
was stirred at room temperature for 45 min. All volatiles were then
removed, leaving behind an oil. Pentane was added to the oil, and
all volatiles were removed in Vacuo. This was repeated three more
times to yield a yellow solid. The solid was redissolved in a
minimum amount of diethyl ether, and pentane (∼5 mL) was
layered on top of this solution. A fine yellow crystalline powder
was isolated after 24 h at -27 °C; yield ) 1.188 g (81%): 1H NMR
28.81, 26.49, 24.99, 24.23, 21.66, 18.85, 15.18; 19F NMR (282
MHz, CD2Cl2) δ -62.81. Anal. Calcd for C67H58BF24MoN3: C,
54.82; H, 3.98; N, 2.86. Found: C, 54.76; H, 3.88; N, 2.82.
Mo(NAr)(CHCMe2Ph)(MesPyr)2 (2). Mo(NAr)(CHCMe2Ph)-
(OTf)2(DME) (0.314 g, 0.397 mmol) and Li(MesPyr)(THF) (0.209
g, 0.794 mmol) were mixed as solids. Diethyl ether (∼4 mL) was
added to the mixture of solids, and the resulting red-orange mixture
was stirred at room temperature for 2 h. The volatiles were then
removed in Vacuo. Toluene was added to the residue, and the
mixture was filtered through Celite in order to remove LiOTf. The
filtrate was dried in Vacuo to give a red oil. The oil was dissolved
in a minimum amount of a 1:1 mixture of diethyl either and pentane.
The solution was stored at -27 °C overnight, and red-orange blocks
were filtered off; yield 0.164 g (54%): 1H NMR (500 MHz, C6D6)
δ 11.56 (s, 1, MoCHR, JCH ) 119.6 Hz), 7.11 (m, 4, Ar-H), 6.98
(m, 4, Ar-H), 6.81 (s, 2, mesityl-H), 6.72 (s, 2, mesityl-H), 6.64
(br s, 2, NC4H3Mes), 6.30 (t, 2, NC4H3Mes, JHH ) 2.8 Hz), 6.22
(dd, 2, NC4H3Mes, JHH ) 2.8 Hz), 3.54 (sept, 2, CHMe2), 2.26 (s,
6, Me), 2.22 (s, 6, Me), 2.05 (s, 6, Me), 1.22 (s, 6, Me), 1.22 (d,
12, CHMe2); 13C NMR (125 MHz, C6D6) δ 287.54 (MoCR), 154.18,
148.23, 147.73, 140.74, 140.23, 139.43, 138.04, 134.25, 129.61,
129.26, 128.75, 128.69, 126.80, 126.44, 123.91, 112.10, 110.99,
66.48, 55.64, 31.28 (CHCMe2Ph), 28.26 (CHMe2), 24.90 (CHMe2),
22.11 (para-mesityl Me), 21.58 (ortho-mesityl Me), 21.21 (ortho-
mesityl Me), 15.95 (CHCMe2Ph). Anal. Calcd for C48H57MoN3:
C, 74.69; H, 7.44; 5.44. Found: C, 74.78; H, 7.41; N, 5.38.
1
(500 MHz, CD2Cl2) δ 13.93 (s, 1, syn MoCHR, JCH ) 119 Hz),
7.72 (s, 8, o-H of BArF ), 7.56 (s, 4, p-H of BArF ), 7.30 (m, 8,
4
4
Ar-H), 6.42 (br s, 2, NC4H4), 6.12 (t, 2, NC4H4), 3.76 (br s, 12,
THF-H), 3.44 (q, 2, Et2O), 3.10 (m, 2, CHMe2), 1.98 (br s, 12,
THF-H), 1.85 (s, 3, CHCMe2Ph), 1.67 (s, 3, CHCMe2Ph), 1.16 (t,
3, Et2O), 1.13 (d, 6, CHMe2), 1.10 (d, 6, CHMe2); 13C NMR (125
MHz, CD2Cl2) δ 322.15 (MoCR), 162.41 (q, 1JC B ) 50 Hz, ipso-C
11
of BArF ), 152.29, 151.61, 147.59, 135.46, 130.92, 129.58, 129.54
4
(qq, 2JCF ) 31 Hz, 3JC B ) 3 Hz, m-Ar of BArF ), 127.74, 126.16,
11
4
125.3 (q, JCF ) 272 Hz, BArF ),125.12, 124.17, 122.01, 118.14
4
(m, p-Ar of BArF ), 110.72, 58.93, 32.06, 30.00, 27.94, 26.20,
4
25.94, 24.60; 19F NMR (282 MHz, CD2Cl2) δ -62.77.
[Mo(NAr)(CHCMe2Ph)(Me2NC4H2)(THF)2]BArF (1b). Mo)-
4
(NAr(CHCMe2Ph)(Me2Pyr)2 (1.667 g, 2.817 mmol) was dissolved
in ∼20 mL of THF, and to the red solution was added
[HNMe2Ph][BArF ] (3.053 g, 3.098 mmol) in one portion as a solid.
4
The resulting mixture darkened immediately and was stirred for
30 min at room temperature. All volatiles were then removed in
Vacuo to yield an oil. Pentane was added to the oil, the mixture
was stirred for ∼5 min, and the volatiles were removed in Vacuo.
This was repeated once more to yield a red solid, which was then
redissolved in a minimum amount of a 1:1 mixture of ether and
pentane (∼10 mL). The solution was allowed to stand at -27 °C
overnight. A burnt orange crystalline solid was isolated; yield 2.682
g (71%): 1H NMR (500 MHz, CD2Cl2) δ 14.23 (s, 1, MoCHR,
1JCH ) 128 Hz), 7.72 (s, 8, o-H of BArF ), 7.56 (s, 4, p-H of BArF ),
{Mo(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)3}BArF
(3a).
4
Hexafluoro-tert-butanol (134 µL, 1.088 mmol) was added to
{Mo(NAr)(CHCMe2Ph)(Pyr)(THF)3}BArF4 (1.285 g, 0.830 mmol)
in ∼10 mL of CH2Cl2. The reaction mixture was stirred at room
temperature for 20 min. All volatiles were removed in Vacuo to
give an oil. To the oil was added ∼7 mL of pentane. The resulting
mixture was stirred for 5 min, and vacuum was applied to remove
all volatiles. This procedure was repeated once more to give a
yellow solid, which was washed with pentane and then dried in
Vacuo for 30 min. The yellow solid was dissolved in a minimum
amount of a 1:1 mixture of diethyl ether and pentane (∼8 mL) and
4
4
7.32 (m, 8, Ar-H), 6.31 (br s, 1, NC4H2Me2), 5.91 (br s, 1,
NC4H2Me2), 3.84 (m, 2, THF-H), 3.70 (m, 6, THF-H), 3.20 (sept,
2, CHMe2), 2.42 (s, 3, Me), 2.36 (s, 3, Me), 2.02 (m, 6, THF-H),
1.83 (m, 2, THF-H), 1.81 (s, 3, Me), 1.68 (s, 3, Me), 1.31 (d, 12,

4436 Organometallics, Vol. 27, No. 17, 2008
Jiang et al.
stored at -27 °C overnight. A light yellow powder was isolated
analyses of crude 3c were not satisfactory since it could not be
1
and dried in Vacuo for 1 h; yield 1.139 g (82%): H NMR (500
purified by recrystallization without decomposing.
[Mo(NAr)(CHCMe2Ph)(OAd)(THF)2]BArF (3d). The same
1
MHz, CD2Cl2) δ 14.20 (s, 1, syn MoCHR, JCH ) 119 Hz), 7.79
4
(s, 8, o-H of BArF ), 7.62 (s, 4, p-H of BArF ), 7.37 (m, 8, Ar-H),
procedure employed for the synthesis of {Mo(NAr)(CHCMe2Ph)-
4
4
[OC(CF3)2Me](THF)3}BArF was employed starting with
3.92 (m, 4, THF-H and CHMe2), 3.71 (m, 10, THF-H and CHMe2),
1.96 (s, 6, CHCMe2Ph), 1.85 (br s, 12, THF-H), 1.76 (s, 3,
OC(CF3)2Me), 1.32 (d, 12, CHMe2); 13C NMR (125 MHz, CD2Cl2)
4
[Mo(NAr)(CHCMe2Ph)(Pyr)(THF)3]BArF . The crude yield was
4
88% (theory ) 0.275 g): 1H NMR (500 MHz, CD2Cl2) δ 15.07 (s,
0.3, MoCHR), 14.52 (s, 0.7, MoCHR), 7.72 (br s, 8, o-H of BArF ),
1
δ 314.68 (MoCR), 162.48 (q, JC ) 50 Hz, ipso-C of BArF ),
11B
4
4
7.56 (s, 4, p-H of BArF ), 7.35 (m, 8, Ar-H), 3.75 (m, 10, CHMe2
2
152.05, 147.17, 146.48, 135.51, 131.72, 129.93, 129.61 (qq, JCF
4
) 31 Hz, JC ) 3 Hz, m-Ar of BArF ), 128.33, 126.26, 125.30
3
11
and THF), 2.26 (s, 3, Me), 1.82 (m, 25, adamantyl and THF), 1.34
(d, 6, CHMe2, JHH ) 6.9 Hz), 1.29 (d, 6, JHH ) 6.9 Hz); 13C NMR
(125 MHz, CD2Cl2) δ 328.02 (MoCR), minor MoCR could not be
B
4
(q, JCF ) 272 Hz,), 125.15, 124.34, 118.15 (m, p-Ar of BArF ),
4
80.84, 69.25, 66.32, 56.58, 31.09, 25.97, 24.76, 19.64, 15.70; 19F
NMR (282 MHz, CD2Cl2) δ -61.84, -77.10. Anal. Calcd for
C70H68BF30MoN2O4: C, 50.53; H, 4.12; N, 0.84. Found: C, 50.42;
H, 4.17; N, 0.81.
detected, 162.43 (q, 1JC ) 50 Hz, ipso-C of BArF ), 148.34,
11B
4
2
3
11B
146.88, 135.38, 133.36, 130.12, 129.55 (qq, JCF ) 31 Hz, JC
) 3 Hz, m-Ar of BArF ), 128.56, 128.35, 126.63, 125.18 (q, JCF
)
4
272 Hz, CF3 of BArF ), 124.74, 118.07 (m, p-Ar of BArF ), 98.99,
{Mo(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)2}BArF
(3b).
4
4
4
87.16, 79.51, 46.23, 35.51, 32.40, 32.11, 29.83, 25.97, 24.59, 23.76;
19F NMR (282 MHz, CD2Cl2) δ -62.80. Compound 3d decom-
posed to a significant degree upon attempted recrystallization.
However, a sample of the crude material (before recrystallization)
did survive in the solid state and analyzed satisfactorily. Anal. Calcd
for C72H72BF24MoNO3: C, 55.36; H, 4.65; N, 0.90. Found: C, 55.08;
H, 5.13; N, 1.12.
Hexafluoro-tert-butanol (38 µL, 0.310 mmol, 1.2 equiv) was added
to {Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2}{BArF } (0.389 g, 0.259
4
mmol) in ∼10 mL of CH2Cl2. The reaction mixture was stirred at
room temperature for 20 min. All volatiles were removed in Vacuo,
leaving behind a foam. To the foam was added ∼7 mL of pentane.
The resulting mixture was stirred for 5 min, and all volatiles were
then removed in Vacuo. This procedure was repeated once more to
give a yellow solid. The yellow solid was washed with pentane
and dried in Vacuo for 1 h, affording 0.374 g (91%): 1H NMR
(500 MHz, CD2Cl2) δ 14.05 (s, 1, MoCHR), 7.72 (s, 8, o-H of
BArF ), 7.56 (s, 4, p-H of BArF ), 7.31 (m, 8, Ar-H), 3.90 (m, 4,
[Mo(NAr)(CH2CMe2Ph)(O-2,6-i-Pr2C6H3)2]BArF (4). [Mo-
4
(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]BArF4 (0.477 g, 0.317 mmol)
was dissolved in 2 mL of CH2Cl2 to give a red solution.
2,6-Diisopropylphenol (123 µL, 0.666 mmol) was added via syringe
to the solution in one portion at room temperature, and the mixture
was stirred at room temperature overnight. Removal of all volatiles
from the mixture in Vacuo gave a red oil. A proton NMR spectrum
of the oil showed it to be largely 4. Methylene chloride (∼1 mL)
and a few drops of benzene were added to the oil. The mixture
was allowed to sit at -27 °C. Over the course of 2 weeks, three
crops of red crystals were collected, affording a total yield of 0.152
4
4
THF-H), 3.65 (m, 6, THF-H and CHMe2), 1.94 (s, 6, CHCMe2Ph),
1.82 (m, 8, THF-H), 1.72 (s, 3, OC(CF3)2Me), 1.30 (d, 12, CHMe2).
13C NMR (125 MHz, CD2Cl2) δ 313.24 (MoCR), 162.36 (q, 1JC
11B
) 50 Hz, ipso-C of BArF ), 151.94, 146.84, 146.37, 135.40, 131.75,
4
129.89, 129.55 (qq, 2JCF ) 31 Hz, 3JC B ) 3 Hz, m-Ar of BArF ),
11
4
128.28, 126.28, 125.20 (q, JCF ) 272 Hz, CF3 of BArF ), 125.05,
4
118.09 (m, p-Ar of BArF ), 80.77, 56.25, 31.07, 30.87, 25.89, 24.70,
4
1
g (29%): H NMR (500 MHz, CD2Cl2) δ 7.80 (d, 2, Ar-H), 7.75
19.54; 19F NMR (282 MHz, CD2Cl2) δ -62.82, -78.19. Anal.
Calcd for C66H60F30MoNO3: C, 49.80; H, 3.80; N, 0.88. Found: C,
50.02; H, 4.37; N, 1.44.
(br s, 8, o-H of BArF ), 7.57 (br s, 4, p-H of BArF ), 7.54 (t, 2,
4
4
Ar-H), 7.42 (t, 1, Ar-H), 7.16 (m, 9, Ar-H), 4.06 (s, 2, CH2CMe2Ph),
2.98 (sept, 4, CHMe2), 2.86 (sept, 2, CHMe2), 1.77 (s, 6,
CH2CMe2Ph), 1.26 (d, 12, CHMe2, JHH ) 6.5 Hz), 1.07 (d, 12,
[Mo(NAr)(CHCMe2Ph)(O-2,6-i-Pr2C6H3)(THF)]BArF (3c).
4
CHMe2, JHH ) 6.5 Hz), 0.95 (d, 12, CHMe2, JHH ) 6.5 Hz); 13C
The same procedure employed for the synthesis of
{Mo(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)3}BArF was em-
1
4
11
NMR (125 MHz, CD2Cl2) δ 162.48 (q, JC ) 50 Hz, ipso-C of
B
BArF ), 161.93, 155.33, 148.55, 144.73, 138.06, 135.38 (br s, o-Ar
ployed for 3c starting with [Mo(NAr)(CHCMe2Ph)(Me2-
4
Pyr)(THF)2]BArF . After letting the reaction mixture stir for 20 min
of BArF ), 134.07, 131.42, 130.45, 129.45 (qq, 2JCF ) 31 Hz, 3JC
4
4
11B
) 3 Hz, m-Ar of BArF ), 129.23, 126.83, 125.18 (q, JCF ) 272
at room temperature, all volatiles were removed in Vacuo to yield
a red oil. To the red oil was added ∼5 mL of pentane. The mixture
was stirred for 5 min, and all volatiles were removed in Vacuo.
The procedure was repeated once more to give a red solid. The
red solid was added to ∼5 mL of pentane. The product was filtered
off and dried in Vacuo for 30 min; crude yield 90% (on a scale
with a theoretical yield of 0.188 g): 1H NMR (500 MHz, CD2Cl2)
4
Hz, BArF -CF3), 125.17, 124.62, 118.06 (m, p-Ar of BArF ), 95.76
4
4
(s, MoCR), 41.47 (CH2CMe2Ph), 31.35 (CHMe2), 31.20
(CH2CMe2Ph), 28.17 (CHMe2), 24.42 (CHMe2), 24.08 (CHMe2),
23.48 (CHMe2); 19F NMR (282 MHz, CD2Cl2) δ -62.80. Anal.
Calcd for C78H76BF24MoNO2: C, 57.75; H, 4.72; N, 0.86. Found:
C, 57.84; H, 4.67; N, 0.87.
δ 14.73 (s, 1, MoCHR), 7.72 (br s, 8, o-H of BArF ), 7.56 (s, 4,
[Mo(NAr)(CH2CMe2Ph)(rac-BIPHEN)]BArF4 (5). {Mo(NAr)-
4
p-H of BArF ), 7.31 (m, 11, Ar-H), 3.77 (m, 8, CHMe2 and THF),
(CHCMe2Ph)(Pyr)(THF)3}BArF (0.191 g, 0.124 mmol) and rac-
4
4
1.96 (s, 3, Me), 1.82 (m, 7, Me and THF), 1.31 (br d, 24, CHMe2);
BIPHEN-H2 (3,3′-di-tert-butyl-5,5′,6,6′-tetramethylbiphenyl-2,2′-
diol) (0.044 g, 0.124 mmol) were mixed together as solids.
Dichloromethane (5 mL) was added at room temperature, and the
red mixture was stirred overnight. The mixture was concentrated
in Vacuo, and pentane was added to the residue. The mixture was
stored at -27 °C for one week. Red needle-like crystals were
isolated; yield 0.160 g (80%): 1H NMR (300 MHz, CD2Cl2) δ 7.76
(s, 8, o-H of BArF ), 7.57 (s, 4, p-H of BArF ), 7.24 (m, 10, Ar-H),
13C NMR (125 MHz, CD2Cl2) δ 312.74 (MoCR), 162.45 (q, 1JC
11B
) 50 Hz, ipso-C of BArF ), 158.78, 151.58, 147.27, 146.92, 141.40,
4
138.05, 137.28, 135.45 (br s, o-Ar of BArF ), 132.10, 130.65,
4
129.78, 129.52 (qq, 2JCF ) 31 Hz, 3JC B ) 3 Hz, m-Ar of BArF ),
11
4
128.19, 126.09, 125.23 (q, JCF ) 272 Hz, BArF -CF3), 125.22,
4
124.87, 124.73, 123.15, 119.88, 118.15 (m, p-Ar of BArF ), 79.66,
4
66.62, 56.46, 48.29, 34.76, 31.18, 30.06, 28.24, 25.93, 25.05, 24.45,
24.27, 24.10, 23.54, 22.97, 15.49, 14.42; 19F NMR (282 MHz,
CD2Cl2) δ -62.78. When ∼50 mg of the red powder was dissolved
in minimum amount of diethyl ether and pentane was vapor diffused
into the ether solution at -27 °C for one week, a few flakes of
crystalline material (less than 10% of the mixture) in the oily
mixture was characterized by single-crystal X-ray crystallography
4
4
2
4.95 (d, 1, CH2CMe2Ph, JHH ) 12 Hz), 2.92 (sept, 2, CHMe2),
2.53 (s, 3, Me), 2.39 (d, 1, CH2CMe2Ph, 2JHH ) 12 Hz), 2.22 (s, 3,
Me), 1.69 (s, 3, Me), 1.49 (s, 3, Me), 1.46 (s, 9, CMe3), 1.41 (s, 3,
Me), 1.22 (s, 3, Me), 1.17 (d, 6, CHMe2), 1.13 (s, 9, CMe3), 1.06
1
(d, 6, CHMe2); 13C NMR (125 MHz, CD2Cl2) δ 162.32 (q, JC
11B
) 49 Hz, ipso-C of BArF ), 155.82, 152.58, 149.29, 145.86, 144.70,
4
to be {Mo(NAr)(CH2CMe2Ph)(O-2,6-i-Pr2C6H3)2}BArF . Elemental
142.60, 140.07, 139.29, 138.91, 138.22, 135.72, 135.37, 133.99,
4

Cationic Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 27, No. 17, 2008 4437
133.26, 130.44, 129.52 (qq, 2JCF ) 31 Hz, 3JC B ) 3 Hz, m-Ar of
transferred to the J-Young tube. Spectra were immediately recorded
(10-15 min after addition of olefin) at ∼20 °C, but additional
spectra were collected over time as needed.
11
BArF ), 128.51, 125.82, 125.24 (q, JCF ) 272 Hz, CF3 of BArF ),
4
4
125.04, 124.48, 118.05 (m, p-Ar of BArF ), 101.25, 66.41, 43.99,
4
Crystallographic Details. Low-temperature diffraction data were
collected on a Siemens Platform three-circle diffractometer coupled
to a Bruker-AXS Smart Apex CCD detector with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å), performing
- and ω-scans. All structures were solved by direct methods using
SHELXS and refined against F2 on all data by full-matrix least-
squares with SHELXL-97. All non-hydrogen atoms were refined
anisotropically. Coordinates for the hydrogen atoms on CR of the
alkylidene or alkyl groups were taken from the difference Fourier
synthesis and subsequently refined semifreely with the help of
distance restraints. All other hydrogen atoms were included in the
model at geometrically calculated positions and refined using a
riding model. The isotropic displacement parameters of all hydrogen
atoms were fixed to 1.2 times the U value of the atoms they are
linked to (1.5 times for methyl groups).
36.32, 35.40, 32.24, 30.63, 30.57, 30.56, 24.58, 24.54, 22.93, 21.14,
20.86, 17.27, 16.09, 15.52, 14.40; 19F NMR (282 MHz, CD2Cl2) δ
-62.79. Anal. Calcd for C78H74BF24MoNO2: C, 57.82; H, 4.60;
N, 0.86. Found: C, 57.91; H, 4.68; N, 0.90.
{Mo(NAr)(C2H4)[OC(CF3)2Me](THF)3}BArF4 (6). {Mo(NAr)-
(CHCMe2Ph)[OC(CF3)2Me](THF)3}BArF4 (0.232 g, 0.139 mmol)
was dissolved in ∼10 mL of CH2Cl2 in a 25 mL Schlenk flask.
After three freeze/pump/thaw cycles the reaction mixture was
exposed to 1 atm of ethylene at room temperature. The mixture
darkened slightly. The mixture was then stirred for 3 h at room
temperature. The volume was reduced to ∼5 mL in Vacuo. Pentane
(∼7 mL) was layered on top of the mixture, and the reaction was
stored for 2 days at -27 °C. The yellow crystals were isolated by
removing the supernatant and drying the crystals in Vacuo for 2 h;
1
yield 0.198 g (91%): H NMR (500 MHz, CD2Cl2) δ 7.75 (s, 8,
o-H of BArF ), 7.59 (s, 4, p-H of BArF ), 7.23 (m, 3, Ar-H), 4.05
Compound 1a crystallizes in the monoclinic space group P21/n
with one molecule of 1a, one [B(ArF)4]- counterion, and half a
molecule of diethyl ether per asymmetric unit. Most of the CF3
groups in the anion were disordered; five of these disorders could
be resolved. The solvent molecule is disordered over four positions,
two of which are generated from the other two by the crystal-
lographic inversion center. This disorder results in a noninteger
value for oxygen in the empirical formula.
4
4
(br s, 12, THF-H), 3.24 (sept, 2, CHMe2), 3.08 (m, 2, C2H4), 2.62
(m, 2, C2H4), 2.00 (br s, 12, THF-H), 1.64 (s, 3, OC(CF3)2Me),
1.27 (d, 12, CHMe2); 13C NMR (125 MHz, CD2Cl2) δ 162.36 (q,
1JC B ) 50 Hz, ipso-C of BArF ), 152.93, 148.28, 135.40, 130.83,
11
4
131.72, 129.47 (qq, 2JCF ) 29 Hz, m-Ar of BArF ), 125.20 (q, JCF
4
) 272 Hz, CF3 of BArF ), 125.00, 124.04 (q, JCF ) 289 Hz, CF3
4
of OCMe(CF3)2), 118.08 (m, p-Ar of BArF ), 77.20 (OCH4CH4,
4
THF), 63.24 (MoC2H2), 30.17 (OCH4CH4, THF), 25.87 (CHMe2),
24.71 (CHMe2), 19.34 (OCMe(CF3)2); 13C NMR (125 MHz,
BrC6D5) showed the MoC2H4 at 63.47 with JCH ) 152 Hz; 19F
NMR (282 MHz, CD2Cl2) δ -62.81, -78.18. Anal. Calcd for
C62H60BF30MoNO4: C, 47.74; H, 3.88; N, 0.90. Found: C, 47.64;
H, 3.85; N, 0.88.
Compound 1d crystallizes in the monoclinic space group P21/n
with two molecules of 1d and two [B(ArF)4]- counterions per
asymmetric unit. Most of the CF3 groups in the [B(ArF)4]- ions
are disordered; nine of these disorders could be resolved.
Compound 3a crystallizes in the monoclinic space group P21/n
with one molecule of 3a and one [B(ArF)4]- counterion per
asymmetric unit. The OCMe(CF3)2 ligand shows 2-fold disorder
corresponding to a rotation about the O-C bond. In addition, two
of the THF molecules show well-behaved disorder of two of their
carbon positions, and most of the CF3 groups in the [B(ArF)4]-
ion are disordered; three of these CF3 disorders could be re-
solved.
Polymerization of 2,3-Dicarbomethoxynorbornadiene. {Mo-
(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)2}BArF (3b) (0.033 g,
4
0.020 mmol) was dissolved in ∼0.5 mL of CH2Cl2. The substrate
(0.429 g, 2.060 mmol) in 5 mL of toluene was added dropwise to
a stirred solution of metal complex at room temperature. The vial
was rinsed with toluene (5 mL), and the contents were added to
the mixture. The mixture was stirred for 30 min. Benzaldehyde
(25 µL) was added to the mixture, which was then stirred for 30
min. The mixture was added dropwise to 75 mL of hexane while
stirring the solvent vigorously. A white, gooey material was isolated,
and the yellow solvent was discarded. The white material was
dissolved in hot THF, and the mixture was added dropwise to
another 75 mL of stirred hexane. White, fluffy material precipitated
out and was filtered off and dried in Vacuo for 3 h; yield 0.374 g
Compound 4 crystallizes in the monoclinic space group P21/m
with 1.5 molecules of 4 and 1.5 [B(ArF)4]- counterions per
asymmetric unit. The refinement of this structure was particularly
challenging, and the quality of the model is not as good as that of
the other structures (for refinement and data quality statistics see
Tables 1 and 2). One of the two crystallographically independent
molecules of each species found in the structure is comparatively
well behaved, while the other one is strongly affected by uncom-
monly complicated disorders. The complete second molecule of 4
is spread over four positions (all atoms), two of which are generated
from the other two by the crystallographic mirror, while all atoms
of the disordered [B(ArF)4]- ion are disordered over two positions,
also involving the crystallographic mirror. The close proximity of
the two heavily disordered molecules to crystallographic symmetry
elements results in an effective occupancy of 50% in the asymmetric
unit for those atoms, and the second halves of the molecules are
generated by the respective symmetry operator. Another conse-
quence of this arrangement is the rather unusual value of Z ) 6
for this space group. Parametrization of additionally disordered CF3
groups in the otherwise well-behaved [B(ArF)4]- ion were trivial
when compared to the refinement of the two half-occupied
molecules. The quality of the data set on which the structure of
compound 4 is based is altogether only mediocre, and it was not
possible to locate the two hydrogen atoms on the CR of either the
Mo-alkyl groups in the difference Fourier synthesis. The Mo-CR
as well as the CR-Cꢀ bond lengths, however, allow us to infer that
the CR must carry two hydrogen atoms. Thus the hydrogen atoms
were included at their calculated positions for all three crystallo-
graphically independent CR and refined using a riding model. Bond
1
(87%): H NMR (500 MHz, CDCl3) δ 5.41 (br, dCH), 3.95 (br,
methine), 3.75 (s, CO2Me), 2.52 (br, CHH), 1.44 (br, (br, CHH));
13C NMR (125 MHz, CDCl3) δ 165.41 (CO2Me), 142.43
(dCCO2Me), 131.61 (CH), 52.25 (CO2Me), 44.37 (dCH), 38.89
(CH2).
General Procedure for Reactions Involving Olefins. About
20 to 30 µmol of alkylidene complex was added to a J-Young NMR
tube along with ∼0.6 mL of CD2Cl2. In the case of 1-hexene, the
substrate was then added to the solution via microsyringe. In the
case of ethylene, the solution of the alkylidene complex was
degassed by three successive freeze-pump-thaw cycles and then
exposed to 1 atm of the gas. In the case of 13C-ethylene, the solution
of the alkylidene complex was degassed by three successive
freeze-pump-thaw cycles and then the frozen solution was
exposed to ∼300 mmHg of the gas. In the case of 1-hexene,
diallyltosylamine, and the substrates in Table 3, the substrates were
weighed out in a 2 mL vial and CD2Cl2 (∼0.4 mL) was added.
Then the catalyst was added to the vial in one portion as a solid.
The contents were then mixed by slurping the mixture with a pipet
and then transferred to a Teflon capped J-Young tube. The vial
was then rinsed with ∼0.3 mL of CD2Cl2, and the rinse was

4438 Organometallics, Vol. 27, No. 17, 2008
Jiang et al.
lengths and angles between atoms of the heavily disordered
molecules are significantly less well determined than those between
the corresponding atoms of the well-behaved ones. Therefore,
whenever in this paper bond distances and angles are quoted for
the structure of compound 4, those of the well-behaved molecules
are used.
Compound 6 crystallizes in the triclinic space group P with one
molecule of 7, one [B(ArF)4]- counterion, and one 3-fold disordered
molecule of pentane per asymmetric unit. Disorders of both CF3
groups in the molecule of 6 and six of the eight CF3 groups in the
[B(ArF)4]- ion could be resolved.
of perfect hexagons and planarity restraints were applied to all
aromatic systems in the disordered molecules. In addition, the
anisotropic displacement ellipsoids of all fluorine atoms in the
heavily disordered molecule of compound 4 were restrained to
assume approximately spherical shape within a standard uncertainty
of 0.2 Å2 (applied to the Uij terms of the anisotropic displacement
tensor).
Acknowledgment. R.R.S. thanks the National Science
Foundation (CHE-0554734) for supporting this research.
All disorders were refined with the help of similarity restraints
on 1-2 and 1-3 distances and displacement parameters as well as
rigid bond restraints for anisotropic displacement parameters.
Occupancy ratios were refined freely, while constraining the sum
of occupancies of all components of any given disorder to unity.
In the case of the disorders in the structure of compound 4, some
of the disordered phenyl rings were constrained to assume the shape
Supporting Information Available: Crystallographic informa-
tion files in cif format. This material is available free of charge via
the Internet at http://pubs.acs.org. X-ray crystallographic data for
1a (07011), 1c (07164), 2 (07178), 3a (07005), 4 (07170), and 6
(07029) are also available to the public at http://reciprocal.mit.edu.
OM800209B