Molybdenum imido alkylidene complexes that contain a β-diketiminate ligand

Article abstract of DOI:10.1021/om7003207

The molybdenum β-diketiminate complexes Mo(NR)(CHCMe ₂R′)(Ar-nacnac)(OTf) (R = 2,6-diisopropylphenyl, 2,6-dimethylphenyl, 1-adamantyl, 2,6-dichlorophenyl, or 2-tert-butylphenyl; Ar = 2,6-dichlorophenyl, 2,6-dimethylphenyl, 3,5-dimethylphenyl, or 2,6-difluorophenyl; R′ = Me or Ph; Ar-nacnac = [ArNC(Me)J₂CH; OTf = trifluoromethanesulfonate) have been prepared from Mo(NR)(CHCMe ₂RO(OTf)₂(DME) by metathesis with the corresponding Li{Ar-nacnac} salt. Reaction of Mo-(NR)(CHCMe₂R′)(Ar-nacnac) (OTf) with NaBAr^f4 (Ar_f = 3,5-(CF₃) ₂C₆H₃) in the presence or absence of THF affords the cationic species {Mo(NR)(CHCMe₂R′)(Ar-nacnac)(THF) _n}{BAr_f4} (n = 0 or 1) depending on the nature of Ar. The reactivity of the cationic β-diketiminate (nacnac) complexes toward olefins has been examined, as has the thermal decomposition modes of the neutral and cationic nacnac complexes. Results demonstrate that the cationic species have short catalyst lifetimes and that decomposition modes dominate the chemistry of several of the nacnac complexes.

Full text of DOI:10.1021/om7003207

Organometallics 2007, 26, 3771-3783
3771
Molybdenum Imido Alkylidene Complexes that Contain a
â-Diketiminate Ligand
Zachary J. Tonzetich, Annie J. Jiang, Richard R. Schrock,* and Peter Mu¨ller
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
ReceiVed April 2, 2007
The molybdenum â-diketiminate complexes Mo(NR)(CHCMe2R′)(Ar-nacnac)(OTf) (R ) 2,6-
diisopropylphenyl, 2,6-dimethylphenyl, 1-adamantyl, 2,6-dichlorophenyl, or 2-tert-butylphenyl; Ar )
2,6-dichlorophenyl, 2,6-dimethylphenyl, 3,5-dimethylphenyl, or 2,6-difluorophenyl; R′ ) Me or Ph;
Ar-nacnac ) [ArNC(Me)]2CH; OTf ) trifluoromethanesulfonate) have been prepared from Mo(NR)-
(CHCMe2R′)(OTf)2(DME) by metathesis with the corresponding Li{Ar-nacnac} salt. Reaction of Mo-
(NR)(CHCMe2R′)(Ar-nacnac)(OTf) with NaBArf4 (Arf ) 3,5-(CF3)2C6H3) in the presence or absence of
THF affords the cationic species {Mo(NR)(CHCMe2R′)(Ar-nacnac)(THF)n}{BArf4} (n ) 0 or 1) depending
on the nature of Ar. The reactivity of the cationic â-diketiminate (nacnac) complexes toward olefins has
been examined, as has the thermal decomposition modes of the neutral and cationic nacnac complexes.
Results demonstrate that the cationic species have short catalyst lifetimes and that decomposition modes
dominate the chemistry of several of the nacnac complexes.
relatively poorly coordinating {B[3,5-(CF3)2C6H3]4}- ({BArf4}-)
anion.5 We showed that while complexes such as {Mo(N-2,6-
i-Pr2C6H3)(CHCMe2Ph)(TMHD)(THF)}{BArf4} (TMHD )
2,2,6,6-tetramethylheptane-3,5-dionato) could be prepared readily,
there was little evidence at that time, and little has been gathered
since then,6 that â-diketonate species are active metathesis
catalysts. For example, we noted that {Mo(N-2,6-i-Pr2C6H3)-
(CHCMe2Ph)(TMHD)(THF)}{BArf4} reacts with ethylene to
give cyclopropane, an unusual third pathway for decomposition
of early metal high oxidation state catalysts.7 In contrast, on
the basis of preliminary studies, â-diketiminate complexes
seemed more promising than â-diketonate complexes. Also,
â-diketiminates are now a well-established class of supporting
ligands in organotransition metal chemistry.8,9 Recent Ti and
V complexes in which a metal-carbon double or triple bond is
present are especially relevant.10 In this paper we report the
preparation of a variety of cationic molybdenum alkylidene
complexes that contain a â-diketiminate ligand. The molybde-
num compounds described here, which include those described
in our initial report, are some of the first examples of Mo nacnac
complexes.11
Introduction
The vast majority of high oxidation state Mo and W catalysts
that have been developed for the metathesis of alkenes have
been neutral species of the type M(NR)(CHR′)(OR′′)2 or
M(NR)(CHR′)(diolate) in which the initial alkylidene (e.g.,
neopentylidene), imido group (e.g., 2,6-diisopropylphenylimido),
and alkoxides or diolate (e.g., hexafluoro-tert-butoxide or 3,3′-
di-tert-Bu-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diolate, re-
spectively) are all relatively sterically demanding.1 In contrast,
cationic metathesis catalysts that contain tungsten2 or molyb-
denum3 are rare, especially those in which the anion is relatively
noncoordinating. In the case of ruthenium, several catalytically
active cationic alkylidene complexes have been published.4 One
might expect the metal center in high oxidation state cationic
imido alkylidene complexes to be more electrophilic, although
it is difficult to predict whether metathesis turnover would be
more or less competitive in cationic species relative to metal-
lacyclobutane rearrangement or bimolecular alkylidene decom-
position reactions.
Recently we reported in a preliminary fashion the preparation
of cationic imido alkylidene complexes in which a â-diketonate
or a â-diketiminate ligand is present and the anion is the
(5) Tonzetich, Z. J.; Jiang, A. J.; Schrock, R. R.; Mu¨ller, P. Organome-
tallics 2006, 25, 4725.
* Corresponding author. E-mail: rrs@mit.edu.
(1) (a) Schrock, R. R. Chem. ReV. 2002, 102, 145. (b) Schrock, R. R.
Chem. Commun. 2005, 2773.
(6) Tonzetich, Z. J. Ph.D. Thesis, MIT, 2007.
(7) Cyclopropane has only recently been detected as a product of
metallacyclobutane decomposition in a well-defined catalyst system; see:
Tsang, W. C. P.; Jamieson, J. Y.; Aeilts, S. A.; Hultzsch, K. C.; Schrock,
R. R.; Hoveyda, A. H. Organometallics 2004, 23, 1997.
(8) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031.
(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) (a) Furstner, A. Chem. Commun. 1998, 1315. (b) Sanford, M. S.;
Henling, L. M.; Grubbs, R. H. Organometallics 1998, 17, 5384. (c) Hansen,
S. M.; Volland, M. A. O.; Rominger, F.; Eisentrager, F.; Hofmann, P.
Angew. Chem., Int. Ed. 1999, 38, 1273. (d) Furstner, A.; Liebl, M.;
Lehmann, C. W.; Picquet, M.; Kunz, R.; Bruneau, C.; Touchard, D.;
Dixneuf, P. H. Chem.-Eur. J. 2000, 6, 1847. (e) Hofmann, P.; Volland,
M. A. O.; Hansen, S. M.; Eisentrager, F.; Gross, J. H.; Stengel, K. J.
Organomet. Chem. 2000, 606, 88. (f) Bassetti, M.; Centola, F.; Semeril,
D.; Bruneau, C.; Dixneuf, P. H. Organometallics 2003, 22, 4459.
(9) Mindiola, D. J. Acc. Chem. Res. 2006, 39, 813.
(10) (a) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. J. Am. Chem. Soc. 2003, 125, 6052. (b) Basuli, F.;
Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2003,
125, 10170. (c) Basuli, F.; Bailey, B. C.; Brown, D.; Tomaszewski, J.;
Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2004, 126,
10506. (d) Bailey, B. C.; Basuli, F.; Huffman, J. C.; Mindiola, D. J.
Organometallics 2006, 25, 3963. (e) Basuli, F.; Bailey, B. C.; Huffman, J.
C.; Mindiola, D. J. Organometallics 2005, 24, 3321.
(11) There are several reports of macrocyclic tetradentate â-diketiminate
complexes of Mo, but no examples with a bidentate nacnac ligand. For
example see: Giraudon, J.-M.; Mandon, D.; Sala-Pala, J.; Guerchais, J. E.;
Kerbaol, J.-M.; Le Mest, Y.; L’Haridon, P. Inorg. Chem. 1990, 29, 707,
and references therein.
10.1021/om7003207 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/22/2007

3772 Organometallics, Vol. 26, No. 15, 2007
Tonzetich et al.
Figure 1. Thermal ellipsoid drawing (35%) of la showing the syn (left) and anti (right) components of the disordered structure. Hydrogen
atoms, cocrystallized diethyl ether, and minor components of disordered atoms are omitted for clarity. The phenyl groups originating on
atoms C(41) and C(41A) have also been omitted for clarity. Selected bond distances (Å) and angles (deg): Mo(1)-C(1) ) 1.858(3);
Mo(1)-N(1) ) 2.1266(16); Mo(1)-N(2) ) 2.147(16); Mo(1)-N(3) ) 1.7356(16); Mo(1)-O(1) ) 2.5193 (14); Mo(1)-C(1)-C(2) )
152.6(3); N(3)-Mo(1)-C(1) ) 112.02(12); N(2)-Mo(1)-N(1) ) 83.91(6); Mo(1)-N(3)-C(31) ) 155.6(3); Mo(1)-C(1A) ) 2.002(8);
Mo(1)-C(1A)-C(2A) ) 128.5(7); N(3)-Mo(1)-C(1A) ) 93.9(3).
Table 1. Crystal Data and Structure Refinement for 1a, 4a, and 3a′′a
1a
4a
3a′′
Reciprocal net ident. code
empirical formula
fw
cryst syst
space group
06066
C42H47Cl4F3MoN3O3.5
976.63
monoclinic
P2(1)/n
06192
C80H76BCl2F24MoN3O
1729.09
triclinic
P1h
a ) 11.4290(4) Å
b ) 18.7038(7) Å
c ) 19.0217(7) Å
R ) 95.7510(10)°
â ) 94.0100(10)°
γ ) 101.9670(10)˚
3940.6(2) Å3
06187
C44H54F3MoN3O3S
857.90
monoclinic
P2(1)
S
unit cell dimens
a ) 11.0969(5) Å
b ) 17.9753(8) Å
c ) 21.9851(8) Å
R ) 90°
a ) 10.7550(5) Å
b ) 17.4054(9) Å
c ) 22.5561(12) Å
R ) 90°
â ) 92.2900(10)°
γ ) 90°
â ) 92.020(2)°
γ ) 90°
volume
Z
density (calcd)
absorp coeff
F(000)
cryst size
θ range for data collection
index ranges
4381.9(3) Å3
4
4219.8(4) Å3
4
2
1.480 g/cm3
0.647 mm-1
2004
1.457 g/cm3
1.350 g/cm3
0.338 mm-1
0.415 mm-1
1764
1792
0.25 × 0.20 × 0.15 mm3
0.35 × 0.25 × 0.10 mm3
1.65 to 29.57°
-15 e h e 15,
-25 e k e 25,
-26 e l e 26
88 758
0.30 × 0.10 × 0.08 mm3
1.48 to 29.13°
-14 e h e 14,
-23 e k e 23,
0 e l e 30
1.85 to 29.57°
-15 e h e 15,
-24 e k e 24,
-30 e l e 30
no. of reflns collected
no. of indep reflns
94 631
26 565
12 298 [R(int) ) 0.0629]
100.0%
22 050 [R(int) ) 0.0316]
99.7%
26 569b
completeness to θ ) 29.57°
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
99.5%
0.9092 and 0.8551
12 298/1468/874
1.086
R1 ) 0.0374, wR2 ) 0.0908
R1 ) 0.0452, wR2 ) 0.0947
0.847 and 0.489 e‚Å-3
0.9670 and 0.8909
22 050/2444/1192
1.025
R1 ) 0.0407, wR2 ) 0.1056
R1 ) 0.0471, wR2 ) 0.1099
1.103 and 0.589 e‚Å-3
0.9675 and 0.8855
26 569/986/1026
1.009
R1 ) 0.0389, wR2 ) 0.0765
R1 ) 0.0450, wR2 ) 0.0782
0.970 and 0.647 e‚Å-3
largest diff peak and hole
a Diffraction data was collected at 100(2) K using Mo KR radiation with a wavelength of 0.71073 Å. The absorption correction was semiempirical from
equivalents, and the refinement method used was full-matrix least-squares on F2. b Compound 3a′′ crystallized as a non-meriohedral twin; absolute structure
factor ) -0.017(15).
(NR)(CHCMe2R′)(ArCl-nacnac)(OTf) (eq 1, 1a; R ) 2,6-i-
Results
Pr2C6H3, R′ ) Ph, OTf ) OSO2CF3) was prepared by treating
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) with Li{ArCl-
Synthesis of Monotriflate and Cationic Nacnac Complexes.
The first nacnac ligand we chose to explore was one that
contains 2,6-dichlorophenyl substituents (ArCl-nacnac).12 Mo-
(12) Budzelaar, P. H. M.; Moonen, N. N. P.; De Gelder, R.; Smits, J.
M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2000 (4), 753.

Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 26, No. 15, 2007 3773
1
Figure 2. Variable-temperature 500 MHz H NMR spectrum of 4c in methylene chloride-d2.
nacnac} in diethyl ether and isolated as yellow crystals in 83%
yield. 1H NMR spectra in benzene-d6 at 20 °C indicate that 1a
The reaction between 1a and NaBArf4 generated the cationic
species, 2a (eq 2; R ) 2,6-i-Pr2C6H3, R′ ) Ph). 1H NMR spectra
in methylene chloride-d2 indicate that predominantly the syn
is a 1:4 mixture of anti (δHR ) 15.29 ppm) to syn (δHR
)
12.30 ppm) isomers. The syn resonance was assigned on the
basis of the observed JCH value of 116 Hz. A JCH value for the
anti species could not be determined due to its relatively low
concentration. However, chemical shift patterns for syn and anti
isomers follow a similar trend in all of the compounds discussed
herein, with anti alkylidene resonances being found 1.5-3 ppm
downfield of syn alkylidene resonances.
isomer is present (δHR ) 13.10 ppm, δCR ) 320.0 ppm, JCH )
116 Hz). Variable-temperature spectra from 20 to -90 °C show
that the methine protons of the aryl imido become magnetically
inequivalent near -40 °C, as do the nacnac methyl protons.
(See Supporting Information.) Such inequivalencies are con-
sistent with low-temperature binding of an ortho chlorine atom
in one of the two 2,6-dichlorophenyl groups to molybdenum,
as shown in eq 2.
The crystal structure of 1a (Figure 1 and Table 1) shows it
to be a distorted trigonal bipyramid in which the alkylidene
carbon, imido nitrogen, and one nacnac nitrogen atom lie
approximately in the equatorial plane. The structure shows
several disordered atoms, all of which were modeled satisfac-
torily. (See Supporting Information.) The most significant aspect
of the disorder is the presence of both syn (70%) and anti (30%)
alkylidene ligands (Figure 1 parts A and B, respectively). The
refined occupancies of the syn and anti components are very
similar to the ratios observed spectroscopically in solution. The
bond distances and angles are largely in the expected range,
with the Mo(1)-N(3)-C(31) angle (155.6(3)°), Mo(1)-C(1)-
C(2) angle (152.6(3)°), and Mo(1)-C(1) distance (1.858(3) Å)
being characteristic of a syn isomer. In contrast, Mo(1)-C(1A)
in the anti isomer is 2.002(8) Å and Mo(1)-C(1A)-C(2A) is
128.5(7)°. Other bond distances and angles, some of which can
be found in the caption to Figure 1, are unexceptional. It should
be noted that there is no Mo-Cl interaction in the solid state.
Analogous triflate complexes possessing â-diketonate ligands
demonstrated a tendency to form six-coordinate 18-electron
complexes.6 The nacnac ligand therefore appears better suited
to stabilize unsaturated complexes.
The structure of 2a, which has been reported previously, is
a distorted trigonal bipyramid in which the alkylidene has the
anti configuration.5 The main finding is that an ortho chlorine
atom is indeed coordinated to the metal in the solid state,
consistent with the spectroscopically observed lack of symmetry
in the low-temperature limit. We propose that compound 2a is
fluxional on the NMR time scale at higher temperatures as a
consequence of rapid dissociation and reassociation of chlorine
donors to give an averaged spectrum with apparent Cs symmetry.
Monotriflate species possessing imido groups other than 2,6-
diisopropylphenyl can be prepared in yields that range from 36
to 41% (1b-1d, eq 1). Subsequent treatment of monotriflates
1b-1d with NaBArf4 as shown in eq 2 yielded salts 2b-2d,
for which NMR spectra again suggest that an ortho chlorine
atom in one ArCl group weakly coordinates to the metal at low
temperatures. The 1H NMR spectrum of {Mo(N-2,6-
Me2C6H3)(CHCMe2Ph)(ArCl-nacnac)}{BArf4} (2b) at -60 °C
reveals a major (13.74 ppm 88%) and a minor alkylidene
resonance (13.04 ppm, 12%), both consistent with syn isomers.
The appearance of two isomers at lower temperatures is
consistent with formation of diastereomers as a consequence

3774 Organometallics, Vol. 26, No. 15, 2007
Tonzetich et al.
of coordination of the ortho chlorine atoms. Similar results were
also obtained with {Mo(N-1-adamantyl)(CHCMe2Ph)(ArCl-
nacnac)}{BArf4} (2d), which displayed two alkylidene proton
resonances at 0 °C at 13.40 and 13.12 ppm in a ratio of 3:5.
We next examined a nacnac ligand possessing 2,6-dimeth-
ylphenyl substituents (Ar′-nacnac).5 Reaction of Li{Ar′-nacnac}
with Mo(NR)(CHCMe2R′)(OTf)2(DME) in diethyl ether gives
the nacnac complexes shown in eq 3 in 71-79% yield.
Complexes 3a, 3c, and 3e are all pentane-insoluble microcrys-
talline powders that may be crystallized conveniently from
diethyl ether. Proton NMR spectra of all three compounds are
consistent with the structure depicted in eq 3. In samples of 3a
rotation about the N-aryl bond in the diketiminate is slow on
the NMR time scale, as judged by sharp singlet resonances for
each of the aryl methyl groups. Rotation of the imido aryl ring
in 3a is also hindered, as evidenced by inequivalent methine
resonances.
Figure 3. Thermal ellipsoid drawing (50%) of the cation of 4a.
Hydrogen atoms, the phenyl group of the neophylidene, and the
cocrystallized molecule of CH2Cl2 are omitted for clarity. Selected
bond distances (Å) and angles (deg): Mo(1)-C(1) ) 1.909(2); Mo-
(1)-N(1) ) 1.7460(16); Mo(1)-N(2) ) 2.1435(16); Mo(1)-N(3)
) 2.1220(16); Mo(1)-O(1T) ) 2.2417(13); Mo(1)-C(1)-C(2) )
155.26(17); Mo(1)-N(1)-C(11) ) 162.68(15); N(1)-Mo(1)-C(1)
) 110.49(9); N(2)-Mo(1)-N(3) ) 84.99(6).
Cations 4a and 4c were prepared in methylene chloride in
the presence of several equivalents of THF, as shown in eq 4;
isolated yields exceed 85%. Reactions in methylene chloride
in the absence of THF led only to unidentifiable decomposition
products, although peaks characteristic of CH activation of one
of the benzylic methyl groups were observable in several
instances (see later). In solution at 20 °C, coordinated THF is
observed to exchange rapidly with free THF according to proton
NMR spectra of both 4a and 4c in methylene chloride-d2. The
alkylidene in each case is the syn isomer, as judged by JCH
values near 115 Hz for each. Variable-temperature spectra down
to -80 °C are consistent with a slowing of various rotational
processes, including rotation of the THF ligand, on the NMR
time scale (Figure 2).
the Mo-Cl dative interaction of 2.581(5) Å observed in the
solid-state structure of 2a.5 The relatively large Mo(1)-C(1)-
C(2) and Mo(1)-N(1)-C(11) angles (155.26(17)° and 162.68-
(15)°, respectively) are characteristic of syn alkylidene com-
plexes of this general type.
Triflate abstraction from compound 3e was found to give an
orange crystalline solid after crystallization from methylene
chloride/pentane that is believed to be largely the cationic
species 4e (eq 5). However, 4e decomposes readily in a manner
described in a later section below and, therefore, cannot be
isolated in pure form.
Crystals of 4a suitable for X-ray diffraction were grown by
slow cooling of a saturated methylene chloride/pentane solution
at -25 °C. The solid-state structure is shown in Figure 3, and
refinement details are listed in Table 1. The structure of 4a is
consistent with the low-temperature spectral limit observed in
solution for both 4a and 4c. As in 2a, the alkylidene, imide,
and one nacnac nitrogen atom occupy the equatorial plane of a
trigonal bipyramid. The second nacnac nitrogen and the THF
molecule bind in axial positions, completing the coordination
sphere. All bond lengths and angles (Figure 3 caption) are
consistent with other five-coordinate solvent adducts13 of this
type. The Mo(1)-O(1T) bond length of 2.2417(13) Å is
consistent with a dative interaction and significantly shorter than
The 3,5-dimethylphenyl-substituted nacnac ligand (Ar′′-
nacnac)14 was examined next in order to compare it with the
Ar′-nacnac ligand. Reaction of Li{Ar′′-nacnac} with Mo(N-2,6-
i-Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) in diethyl ether afforded
complex 5a in 75% yield as an orange-red crystalline solid (eq
6). The 2,6-diisopropylphenyl ring in 5a rotates rapidly at room
temperature, while rotation of the 3,5-dimethylphenyl rings is
hindered, as judged by broadened resonances for the o-H
resonances of the 3,5-dimethylphenyl rings. Recrystallized
samples of 5a show predominantly the syn isomer (92%; δHR
) 12.12 ppm, JCH ) 116 Hz in benzene-d6).
Addition of NaB(C6F5)4‚THF to a methylene chloride-d2
solution of 5a produced what is tentatively assigned as the
(13) Schrock, R. R.; Crowe, W. E.; Bazan, G. C.; DiMare, M.; O’Regan,
M. B.; Schofield, M. H. Organometallics 1991, 10, 1832.
(14) Laitar, D. S.; Mathison, C. J. N.; Davis, W. M.; Sadighi, J. P. Inorg.
Chem. 2003, 42, 7354.

Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 26, No. 15, 2007 3775
about the Mo-O bond. Unlike compounds 4a and 4c, the
coordinated THF molecule in 8a does not appear to exchange
readily with free THF on the NMR time scale at 20 °C. The
alkylidene proton in the anti isomer (∼5%) shows a coupling
to fluorine of 3.5 Hz; no such coupling is apparent in the syn
isomer. Compound 8a has resisted attempts at recrystallization
and requires several days to precipitate from concentrated
solutions. These results cast some doubt on the proposed
structure of 8a since decomposition may have occurred in the
time required for crystallization. As a result of the difficulties
in preparing and handling 8a, no further reactivity was
examined.
cationic complex 6a (eq 7). Complex 6a exists as a single isomer
with an alkylidene resonance at 14.23 ppm. The chemical shift
of 6a is suggestive of an anti alkylidene isomer, although
definitive evidence (JCH value) could not be gathered. The
remainder of the spectrum is broad, and coordinated THF
appears to exchange readily with free THF. The 2,6-diisopro-
pylphenyl ring appears to rotate readily on the NMR time scale
at 20 °C. Attempts to isolate the BArf4 salt of the cation have
resulted in oily, intractable materials, and decomposition of 6a
cannot be ruled out.
Decomposition Reactions. The propensity for nacnac ligands
to undergo intramolecular transformations has been demon-
strated in a number of different systems across the transition
series. Several of the compounds that have been described above
decompose in relatively well-defined ways to yield new
organometallic species. Some of those decomposition pathways
are reported here.
At or above 60 °C, solutions of 3a, 3c, and 3e decompose to
yield molybdaziridine species (3a′′, 3c′′, and 3e′′) shown in eq
10. The nature of these compounds was determined by subject-
ing 3a′′ to an X-ray diffraction study. Compound 3a′′ crystallizes
from diethyl ether with two chemically identical but crystallo-
graphically independent molecules in the asymmetric unit. One
of the molecules is shown in Figure 4. Metric parameters appear
in the caption to Figure 4 and refinement details are listed in
Table 1. The most striking feature of 3a′′ is the presence of the
neophyl group attached to C(2), which is derived from the
original neophylidene ligand in 3a. One of the CH bonds of
the ortho-methyl groups has also been activated, resulting in a
new metal-carbon bond. The former nacnac ligand is now best
described as a chelating η1/η2-diimine ligand with an additional
bond from the benzylic methyl group. The diimine description
is borne out well in the bond lengths and angles (Figure 4
caption and Supporting Information).
In analogy with the ArCl-nacnac ligand, ArF-nacnac15 (ArF
) 2,6-difluorophenyl) was prepared and examined as a potential
ligand. In contrast to the nacnac ligands discussed above, salt
metathesis reactions similar to those in eq 2 with Li{ArF-nacnac}
did not afford the desired â-diketiminate complex; only starting
materials were recovered. However, the synthesis of 7a was
accomplished in toluene through use of the thallium complex,
Tl(ArF-nacnac)15 (eq 8). Compound 7a is similar to compounds
discussed above, and NMR spectra indicate the presence of both
syn and anti isomers in a 1:1.5 ratio, respectively. The alkylidene
proton resonance for the syn isomer appears at 12.42 ppm with
a JCH value of 116 Hz in benzene-d6. The alkylidene resonance
for the anti isomer appears at 14.90 ppm (JCH ) 145 Hz) and
shows a small coupling (J ) 1.2 Hz), presumably to fluorine.
This small coupling may be indicative of fluorine coordination
in the anti isomer. No coupling could be resolved for the syn
isomer.
Reaction of 7a with NaBArf4 in the absence of THF led only
to decomposition. We had expected that intramolecular fluorine
coordination would be sufficient to stabilize the cation. Either
that is not the case, or coordination of an ortho fluorine leads
to some further decomposition. However, in the presence of
THF, a cationic species may be isolated in moderate yield (8a,
eq 9). The spectroscopic features of 8a are consistent with the
structure shown in eq 9. The 2,6-diisopropylphenyl ring appears
to be rotating slowly at 20 °C, as evidenced by distinct
broadened methine resonances. The THF ligand displays two
multiplet resonances near 2.5 ppm, consistent with free rotation
The spectroscopic features of 3a′′ are in accord with the solid-
state structure. The proton attached to C(2) appears at 4.12 ppm
as a triplet with JHH ) 4.5 Hz in benzene-d6. The 13C NMR
was assigned with the help of HSQC and HMBC experiments,
which located carbon atoms C(1) and C(3) at 197.8 and 82.8
ppm, respectively in benzene-d6. Mindiola and others have
reported benzylic CH activation reactions of aryl-nacnac
ligands,16 but the decomposition mode shown in eq 3 to our
(16) Basuli, F.; Bailey, B. C.; Watson, L. A.; Tomaszewski, J.; Huffman,
J. C.; Mindiola, D. J. Organometallics 2005, 24, 1886.
(15) Dai, X, Ph.D. Thesis, Georgetown University, 2003.

3776 Organometallics, Vol. 26, No. 15, 2007
Tonzetich et al.
We were somewhat surprised to find that thermolysis of 5a
(lacking ortho methyl groups) in benzene-d6 at 60 °C for 24 h
1
led to decomposition, as judged by H NMR spectroscopy.
Unfortunately, the nature of the decomposition product is not
known at this time, although spectra are consistent with
destruction of the alkylidene ligand. Therefore, moving the
methyl groups from the 2 and 6 positions of the aryl ring to the
3 and 5 positions does not prevent facile thermal decomposi-
tions.
Unlike the monotriflate species possessing 2,6-dimethylphenyl
and 3,5-dimethylphenyl nacnac substituents, the complexes
bearing 2,6-dichlorophenyl or 2,6-difluorophenyl nacnac sub-
stituents appear to be quite stable at elevated temperatures. For
example, thermolysis at 70 °C of a benzene-d6 solution of 7a
for 12 h resulted in no noticeable change by NMR. Similar
results were found for 1a-1d.
Cationic species that contain the Ar′-nacnac ligand are also
prone to decomposition. For example, solutions of 4a stored at
or even below 20 °C decompose slowly to generate what we
propose is 4a′′ (eq 12). The intermediate is proposed to be a
dialkyl species, 4a′ (eq 13), analogous to 3a′ discussed above.
tert-Butylbenzene is observed in NMR spectra, consistent with
Figure 4. Thermal ellipsoid drawing (50%) of one of the two
independent molecules of 3a′′ in the asymmetric unit. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Mo(1)-N(1) ) 1.723(3); Mo(1)-N(2) ) 2.239(3); Mo-
(1)-N(3) ) 1.992(3); Mo(1)-C(37) ) 2.165(3); Mo(1)-C(3) )
2.207(3); Mo(1)-O(1) ) 2.127(2); C(3)-N(3) ) 1.380(4); C(1)-
N(2) ) 1.285(4); C(1)-C(2) ) 1.505(5); N(1)-Mo(1)-C(37) )
97.24(13); N(1)-Mo(1)-N(2) ) 136.09(10).
knowledge has not been reported before. The qualitative rate
of decomposition in compounds 3a, 3c, and 3e was observed
to roughly follow the order 3a ≈ 3e > 3c.
To further examine the thermal decomposition pathway of
3a, reaction kinetics were followed by 1H NMR. In toluene-d8,
3a decomposes in a smooth, first-order manner between 60 and
90 °C through several half-lives with no intermediates being
observed (see Supporting Information for kinetic plots). An
Eyring plot for the reaction is shown in Figure 5. We propose
a mechanism for the reaction that consists of rate-limiting
addition of a CH bond from an ortho methyl group across the
ModC bond of the alkylidene ligand. This proton transfer
generates a putative dialkyl intermediate of the type shown in
eq 11. The neophyl ligand then adds across a CdC bond of the
nacnac ligand generating 3a′′. The possibility that addition of
the neophyl ligand across the CdC bond of the nacnac ligand
occurs in a biomolecular fashion was ruled out by conducting
cross-over experiments with 3a and 3e. When a benzene-d6
solution of both compounds was heated to 70 °C, no scrambling
of the neophyl/neopentyl ligands between different imides was
observed. The only products were 3a′′ and 3e′′. Also note that
C(6) and the Mo atom are on the same side of the C(2)-C(3)
bond, consistent with cis addition across the C(2)dC(3) bond
shown in eq 11. It is likely that CH addition across the
alkylidene ligand is influenced by steric congestion about the
coordination sphere of the Mo atom. Not surprisingly, the
qualitative trend in decomposition rates observed for 3a, 3c,
and 3e roughly parallel the steric properties of the respective
imides.
protonation of the original neophylidene ligand. Decomposition
of 4a in methylene chloride-d2 at 40 °C was found to take place
in a first-order manner with k ) 3.23 × 10-4 M-1 s-1, as
determined through 1H NMR studies (see Supporting Informa-
tion). Unfortunately, 4a′′ has resisted attempts at isolation; only
oils have been obtained. Although the proposed intermediate,
4a′, is not observed, its intermediacy is consistent with observa-
tion of a related dialkyl species during decomposition of the
2-tert-butylphenylimido species described below.
It was noted above that compound 4e (eq 5) could not be
isolated cleanly, unlike its 2,6-diisopropylphenylimido analogue,
4a. Examination of the reaction in 1H NMR experiments
demonstrated that 4e is formed initially, but it decomposes
readily over a period of 2-3 h at room temperature to a new
complex, 4e′. The spectroscopic features of 4e′ are consistent
with a dialkyl complex on the basis of the appearance of doublet
1
resonances in the H NMR spectrum at 4.45 and 2.75 ppm

Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 26, No. 15, 2007 3777
Figure 5. Eyring plot for the thermal reaction of 3a in toluene-d8.
(methylene chloride-d2). One possible structure is shown in
eq 14.
Section.) This species is tentatively assigned as the cationic THF
adduct (3a′′′) shown in eq 16. The THF molecule is bound
strongly to Mo in 3a′′′, as evidenced by the absence of rapid
exchange with free THF. Compound 3a′′′ is quite stable, which
rules out the possibility of it being the “dialkyl” intermediate
that decomposes to 4a′′ (eq 12).
Four methylene proton doublets would be expected for a
compound with this structure, although the complexity of the
NMR spectrum and the presence of significant quantities of 4e
prevented assignment of all the resonances. Furthermore, 4e′
decomposes at 20 °C to a new alkylidene complex that we
propose is 4e′′ (eq 15), an analogue of compound 4a′′.
Reactions of nacnac Complexes with Olefins. Monotriflate
species such as Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(ArCl-nacnac)-
(OTf) (1a) in a solvent such as toluene do not react with 1 atm
of ethylene at room temperature over a period of 24 h. This
result is not surprising since the monotriflate species are
coordinatively saturated species. Only dissociation of the triflate
ion to yield a four-coordinate 14-electron cation would create
a pathway for facile reactions with olefins.
On the other hand, {Mo(NAr)(CHCMe2Ph)(ArCl-nacnac)}-
{BArf4} (2a) does react with ethylene to give 3-methyl-3-phenyl-
1-butene, the initial metathesis product. However, it was not
possible to identify any product in what appeared to be complex
mixtures. Similar results were obtained in reactions between
ethylene and 2b-d. All four cationic catalysts (2a-2d) po-
lymerized 44 equiv of norbornene over a period of ∼20 min,
affording polynorbornene with various cis/trans ratios, but no
resonances for alkylidene intermediates were observed.
When solutions of 2a, 2b, and 2c in methylene chloride-d2
were exposed to 19, 25, and 16 equiv of N,N-diallyltosylamine,
respectively, at room temperature for 20 min, 4 equiv of the
ring-closed metathesized product was observed. When com-
pound 2d was mixed with 19 equiv of N,N-diallyltosylamine
at room temperature for 20 min, all 19 equiv was converted to
product.
Compound 4e′ can be observed, unlike 4a′, since the 2-tert-
butylphenylimido group is less sterically demanding than the
2,6-diisopropylphenylimido group and the subsequent R-abstrac-
tion in 4e′ to yield 4e′′ is relatively slow. It is not known whether
THF is coordinated strongly to the metal in 4e′ or not, but it
should be noted that coordination of THF (and other donor
ligands) is known to accelerate R-abstraction reactions in
tantalum neopentyl species.17
Compound 3a′′ was allowed to react with NaB(C6F5)4‚THF
1
in methylene chloride-d2. Observation of the reaction by H
NMR revealed slow conversion (t1/2 ≈ 1 h) to a new species
with very similar spectral features to 3a′′. (See Experimental
(17) (a) Schrock, R. R. In Reactions of Coordinated Ligands; Braterman,
P. R., Ed.; Plenum: New York, 1986; Vol. 1, pp 221-283. (b) Rupprecht,
G. A.; Messerle, L. W.; Fellmann, J. D.; Schrock, R. R. J. Am. Chem. Soc.
1980, 102, 6236.
Compound 2a in methylene chloride-d2 was exposed to 3
equiv of allyltrimethylsilane for 20 min in the presence of
anthracene as the internal standard. A new alkylidene resonance

3778 Organometallics, Vol. 26, No. 15, 2007
Tonzetich et al.
Figure 6. 125 MHz 13C{1H} NMR spectrum of the reaction of 4a with 1 atm of ethylene-13C. The inset shows the region of the spectrum
1
near 70 ppm without H decoupling. s ) CD2Cl2; # ) 13CH2dCHCMe2Ph; * ) 13CH2d13CH13CH3.
was observed at 13.59 ppm, compared to the resonance for 2a
at 13.10 ppm; the ratio was ∼1:1. The broad alkylidene
resonance for the new species sharpens into a triplet at 13.86
ppm upon addition of THF to the sample. The new compound
decomposes over a period of 1-2 h; it could not be isolated
nor identified. Related experiments with vinyltrimethylsilane
were not successful.
â-hydrogen rearrangement of an intermediate unsubstituted
metallacyclobutane complex. Rearrangement of metallacycles
and formation of ethylene complexes have been observed before
in imido bisalkoxide systems, and two ethylene complexes that
result from reactions that involve ethylene have been isolated.7,18
Unfortunately, attempts to crystallize either 9a or 9b resulted
only in decomposition.
Reactions between compounds 4a and 4c and vinyltrimeth-
ylsilane, N,N-diallyltosylamine, and norbornene were explored.
Both 4a and 4c would polymerize 100 equiv of norbornene in
methylene chloride-d2 in seconds. Reaction of 4a with vinyl-
trimethylsilane was slow and no product could be identified.
In contrast, vinyltrimethylsilane reacted with 4c to yield a new
species with resonances that we ascribe to syn and anti isomers
of a ModCHSiMe3 species at 15.35 and 16.47 ppm, respec-
tively. The ModCHSiMe3 species appeared relatively stable
in solution at 20 °C, but no attempt was made to isolate it. Both
4a and 4c would ring-close N,N-diallyltosylamine in 10 min
(12% and 33%, respectively), but no additional conversion was
observed.
Conclusions
Experiments described in the preceding sections lead us to
conclude that cationic nacnac complexes can be relatively stable
if they contain a neopentylidene or a neophylidene ligand.
However, even these species can undergo reactions that involve
the nacnac backbone or CH activation in a nacnac nitrogen
substituent. Although the initial neopentylidene or neophylidene
species can react with olefins in a metathesis-like fashion, it
seems clear that several significant problems prevent metathesis
activity that we have come to expect from a relatively stable
catalyst. Unfortunately, we can only guess at the precise nature
of these problems and the reason for them. Certainly, the nacnac
ligand itself seems compromised. But whether any problems
can be traced to the relatively rigid nature of the nacnac ligand
or to its relatively restricted bite angle we cannot say. It is also
Solutions of 4a and 4c in methylene chloride-d2 were exposed
to 1 atm of ethylene gas. Both cations react rapidly to yield
what we propose to be ethylene complexes (9a and 9c, eq 17).
Resonances for 3-methyl-3-phenylbutene (the initial metathesis
product) and propylene are clearly evident in 1H NMR and 13
C
NMR spectra. Protons of the ethylene ligand appear as a set of
multiplets at 2.57 and 0.86 ppm (in methylene chloride-d2).
Reactions in methylene chloride-d2 that employ 13CH2d13CH2
lead to spectra such as that involving 4a shown in Figure 6, in
which both partially labeled 3-methyl-3-phenylbutene and
completely labeled propylene can be observed, along with a
carbon resonance for the labeled coordinated ethylene at 70.3
ppm (JCH ) 157 Hz). The molecule has mirror symmetry on
the NMR time scale. Formation of propylene is consistent with
(18) Arndt, S.; Schrock, R. R.; Mu¨ller, P. Organometallics 2007, 26,
1279.

Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 26, No. 15, 2007 3779
layered with 10 mL of pentane. The mixture was set aside at -25
°C for 18 h to afford 2.683 g (83%) of fine yellow crystals. The
compound was a 7:3 mixture of syn to anti isomers in solution:
1H NMR (300 MHz, C6D6) δ 15.29 (s, 1, anti MoCHR), 12.30 (s,
1, syn MoCHR), syn isomer only 7.13 (m, 14, Ar), 5.78 (s, 1, nacnac-
CH), 5.64 (sep, 1, CHMe2), 3.56 (sep, 1, CHMe2), 2.67 (s, 3,
nacnac-Me), 2.40 (s, 3, nacnac-Me), 2.31 (s, 3, CMe2Ph), 2.19 (d,
3, CHMe2), 2.03 (s, 3, CMe2Ph), 1.93 (d, 3, CHMe2), 1.87 (m, 6,
CHMe2); 13C NMR (125 MHz, CD2Cl2) both isomers δ 325.2 (anti
MoCR), 304.4 (syn MoCR), 167.5 (syn CdN), 169.3 (syn CdN),
169.0 (anti CdN), 167.0 (anti CdN), 155.0, 154.0, 151.9, 150.9,
150.8, 150.0, 149.7, 149.1, 148.6, 146.2, 145.1, 144.1, 133.9, 133.1,
132.9, 132.3, 131.9, 131.4, 130.3, 130.0, 129.7, 129.6, 129.4, 129.2,
129.1, 128.8, 128.7, 128.6, 128.5, 128.1, 128.0, 127.9, 127.0, 126.8,
126.5, 126.4, 126.3, 125.8, 123.5, 123.2, 122.9, 122.8, 119.5 (q,
JCF ) 319 Hz, CF3), 104.8 (anti nacnac-CH), 104.7 (syn nacnac-
CH), 57.5 (anti CMe2Ph), 56.9 (syn CMe2Ph), 34.4, 33.3, 32.2,
30.8, 28.7, 28.2, 26.7, 25.6, 25.5, 24.9, 24.6, 24.2, 24.0, 23.9, 22.6;
19F NMR (282 MHz) δ -76.6. Anal. Calcd for C40H42Cl4F3-
MoN3O3S: C, 51.13; H, 4.51; Cl, 15.07; N, 4.47. Found: C, 51.21;
H, 4.46; Cl, 15.14; N, 4.37.
Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(ArCl-nacnac)(OTf) (1b). To
a solution of 1.002 g (0.831 mmol) of Mo(N-2,6-Me2C6H3)(CHCMe2-
Ph)(OTf)2(DME) in 20 mL of diethyl ether was added 0.390 g
(0.831 mmol) of Li(Et2O){ArCl-nacnac} as a solid in one portion.
The reaction mixture became red and homogeneous after being
stirred at room temperature for 2 h. The solution was allowed to
stir at room temperature for a further 18 h. All volatiles were
removed in Vacuo, and the remaining red residue was extracted
into toluene. The extract was filtered through a bed of Celite, and
the volatiles were again removed from the filtrate in Vacuo. The
residue was dissolved in methylene chloride and layered with
pentane. The mixture was set aside at -25 °C for 3 days to afford
0.299 g (41%) of the product as orange blocks: 1H NMR (500
MHz, CD2Cl2) δ 12.40 (s, 1, syn MoCHR, JCH ) 117 Hz), 7.45 (d,
1, Ar), 7.40 (d, 1, Ar), 7.28 (m, 4, Ar), 7.17 (m, 2, Ar), 6.93 (t, 2,
Ar), 6.84 (br d, 2, Ar), 6.79 (br d, 1, Ar), 6.66 (t, 1, Ar), 5.96 (s,
1, nacnac-CH), 2.60 (s, 3, Me), 2.24 (s, 3, Me), 2.22 (s, 3, Me),
2.09 (s, 3, Me) 1.86 (s, 3, Me), 1.49 (s, 3, Me); 19F NMR (282
MHz) δ -77.4. Anal. Calcd for C36H34Cl4F3MoN3O3S: C, 48.94;
H, 3.88; Cl, 16.05; N, 4.76. Found: C, 48.78; H, 3.80; Cl, 16.00;
N, 4.67.
Mo(N-2,6-Cl2C6H3)(CH-t-Bu)(ArCl-nacnac)(OTf) (1c). To a
solution of 0.753 g (0.637 mmol) of Mo(N-2,6-Cl2C6H3)(CH-t-Bu)-
(OTf)2(DME) in 20 mL of diethyl ether was added 0.298 g (0.637
mmol) of Li(Et2O){ArCl-nacnac} as a solid in one portion. The
reaction mixture immediately became homogeneous and turned deep
red. After stirring the mixture for 7 h at room temperature, all
volatiles were removed in Vacuo. The red residue was extracted
into toluene, and the extract was filtered through a bed of Celite.
The volatiles were again removed from the filtrate in Vacuo, and
the residue was triturated with diethyl ether to give 0.218 g (40%)
of the product as a burnt orange powder: 1H NMR (300 MHz,
CD2Cl2) δ 12.66 (s, 1, MoCHR, JCH ) 116 Hz), 7.41 (d, 2, m-ArCl),
7.19 (m, 5, m-ArCl + p-ArCl), 7.28 (m, 4, m-ArCl), 6.95 (t, 1, p-ArCl),
6.85 (t, 1, p-ArCl), 5.94 (s, 1, nacnac-CH), 2.06 (s, 3, nacnac-Me),
1.93 (s, 3, nacnac-Me), 1.23 (s, 9, t-Bu); 19F NMR (282 MHz) δ
-77.9. Anal. Calcd for C29H26Cl6F3MoN3O3S: C, 40.40; H, 3.04;
Cl, 24.67; N, 4.87. Found: C, 40.26; H, 3.72; Cl, 24.36; N, 4.79.
Mo(N-1-adamantyl)(CHCMe2Ph)(ArCl-nacnac)(OTf) (1d). A
flask containing 0.702 g (0.917 mmol) of Mo(N-1-adamantyl)-
(CHCMe2Ph)(OTf)2(DME) and 8 mL of diethyl ether was chilled
at -25 °C for 1 h. To the solution was added 0.429 g (0.917 mmol)
of Li(Et2O){ArCl-nacnac} as a solid in one portion. After stirring
the mixture at room temperature for 2 h, the cloudy and colorless
reaction mixture changed to red and became homogeneous. The
reaction was allowed to stir for a further 18 h at room temperature.
All volatiles were removed in Vacuo, and the remaining red residue
much too early to conclude that the cationic nature of these
species itself leads to unstable products and side reactions. In
order to explore this issue, we hope to prepare and explore other
types of cations, including those that do not contain chelating
supporting ligands.
Experimental Section
General Comments. All manipulations were performed in oven-
dried (200 °C) glassware under an atmosphere of nitrogen on a
dual-manifold Schlenk line or in a Vacuum Atmospheres glovebox.
HPLC grade organic solvents were sparged with nitrogen, passed
through activated alumina, and stored over 4 Å Linde-type
molecular sieves prior to use. Benzene-d6 and toluene-d8 were dried
over sodium/benzophenone ketyl and vacuum distilled prior to use.
Methylene chloride-d2 and bromobenzene-d5 were dried over CaH2
and vacuum distilled prior to use. NMR spectra were recorded on
Varian Mercury and Varian INOVA spectrometers operating at 300
1
and 500 MHz (1H), respectively. Chemical shifts for H and 13C
1
spectra were referenced to the residual H/13C resonances of the
deuterated solvent (1H: C6D6, δ 7.16; C6D5CD3, δ 2.09; CD2Cl2,
δ 5.32; C6D5Br, δ 7.29; 13C: C6D6, δ 128.39; CD2Cl2, δ 54.00)
and are reported as parts per million relative to tetramethylsilane.
19F NMR spectra were referenced externally to fluorobenzene (δ
-113.15 ppm upfield of CFCl3). Elemental analyses were per-
formed by H. Kolbe Microanalytics Laboratory, Mu¨lheim an der
Ruhr, Germany.
Materials. Mo(NR)(CHCMe2R′)(OTf)2(DME) precursors, Na-
BArf4, Ar′-nacnac, ArF-nacnac, Ar′′-nacnac, and ArCl-nacnac were
prepared according to published procedures cited in the text. Lithium
salts of the various nacnac ligands were prepared through addition
of n-BuLi to a pentane solution of the corresponding diketimine.
NaB(C6F5)4‚THF was prepared through addition of NaH to a THF
solution of {HNMe2Ph}{B(C6F5)4} (Strem) followed by crystal-
lization from THF/pentane. TlOAc was purchased from commercial
vendors and used as received. All methathesis substrates were
prepared and purified according to published procedures. Experi-
mental procedures for compounds 1a, 2a, and 3a were com-
municated previously in a preliminary fashion5 and are repeated
below for convenience.
Crystallography. Low-temperature diffraction data were col-
lected 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
æ- and ω-scans. All structures were solved by direct methods using
SHELXS19 and refined against F2 on all data by full-matrix least-
squares with SHELXL-97.20 All non-hydrogen atoms were refined
anisotropically. Unless described otherwise, all hydrogen atoms
were included into 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).
See Supporting Information for a full discussion of each structure.
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(ArCl-nacnac)(OTf) (1a).
A
flask containing 2.714 g (3.43 mmol) of Mo(N-2,6-i-
Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) and 20 mL of diethyl ether was
chilled at -25 °C for 1 h. To the solution was added 1.351 g (3.43
mmol) of Li{ArCl-nacnac} as a solid in one portion. The color of
the reaction mixture changed from orange to dark red immediately
and the mixture was allowed to stir overnight at room temperature.
All volatiles were removed in Vacuo. The remaining red residue
was extracted into toluene, and the extract was filtered through a
bed of Celite. The volatiles were again removed from the filtrate
in Vacuo. The residue was dissolved in 5 mL of diethyl ether and
(19) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(20) Sheldrick, G. M. SHELXL 97; University of Go¨ttingen: Germany,
1997.

3780 Organometallics, Vol. 26, No. 15, 2007
Tonzetich et al.
was extracted into toluene. The extract was filtered through a bed
of Celite, and the volatiles were again removed from the filtrate in
Vacuo. The residue was dissolved in 2 mL of diethyl ether and
layered with 8 mL of pentane. The mixture was set aside at -25
°C for 2 days to afford 0.299 g (36%) of the product as yellow
blocks: 1H NMR (500 MHz, CD2Cl2) δ 12.95 (s, 1, syn MoCHR,
JCH ) 115 Hz), 7.27 (m, 11, Ar), 5.94 (s, 1, nacnac-CH), 1.91,
1.72, 1.48 (three overlapping broad singlets, 27, adamantyl, CMe2-
Ph + nacnac-Me); 19F NMR (282 MHz) δ -79.1. Anal. Calcd for
C38H40Cl4F3MoN3O3S: C, 49.96; H, 4.41; Cl, 15.52; N, 4.60.
Found: C, 50.08; H, 4.39; Cl, 15.39; N, 4.47.
{Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(ArCl-nacnac)}{BArf4} (2a).
A flask containing 2.033 g (2.16 mmol) of Mo(N-2,6-i-Pr2C6H3)-
(CHCMe2Ph)(ArCl-nacnac)(OTf) in 25 mL of methylene chloride
was chilled in the glovebox freezer to -25 °C for 1 h. To the cold
solution was added 1.915 g (2.16 mmol) of NaBArf4 as a solid.
The reaction mixture changed from light red to dark red rapidly.
After stirring the mixture for 3 h at room temperature it was filtered
through a bed of Celite, and the filtrate was concentrated in Vacuo
to give a red oil. Crystallization of the oil from a mixture of
methylene chloride and pentane afforded 2.689 g (61%) of the
product as red blocks. Crystals suitable for X-ray diffraction were
grown by vapor diffusion of pentane into a saturated methylene
chloride solution: 1H NMR (300 MHz, CD2Cl2) δ 13.11 (s, 1,
MoCHR, JCH ) 116 Hz), 7.74 (s, 8, o-Arf), 7.57 (s, 4, p-Arf), 7.51
(d, 2, Ar), 7.37 (d, 2, Ar), 7.22 (m, 8, Ar), 6.95 (d, 2, Ar), 6.17 (s,
1, nacnac-CH), 3.37 (br sep, 2, CHMe2), 2.19 (s, 6, nacnac-Me),
1.29 (s, 6, CMe2Ph), 1.20 (d, 12, CHMe2); 13C NMR (125 MHz,
CD2Cl2) δ 320.0 (MoCR), 169.4 (2, CdN), 162.4 (q, JCB ) 50 Hz,
ipso-Arf), 154.3, 147.4, 145.9, 145.5, 144.9, 135.5 (o-Arf), 132.8,
131.8, 131.5, 131.2, 130.5, 129.3 (q, JCF ) 32 Hz, m-Arf), 128.5,
128.0, 127.7, 126.5, 126.0, 125.5, 125.3 (q, JCF ) 272 Hz, CF3),
124.3, 118.1 (m, p-Arf), 109.9 (nacnac-CH), 57.3 (CMe2Ph), 31.2,
28.7, 24.4, 23.6; 19F NMR (282 MHz) δ -62.8. Anal. Calcd for
C71H54BCl4F24MoN3: C, 51.37; H, 3.29; Cl, 8.58; N, 2.54. Found:
C, 51.62; H, 3.19; Cl, 8.61; N, 2.47.
{Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(ArCl-nacnac)}{BArf4} (2b).
A solution of 1.205 g (1.26 mmol) of Mo(N-2,6-Me2C6H3)(CHCMe2-
Ph)(ArCl-nacnac)(OTf) in 20 mL of methylene chloride was chilled
at -25 °C for an hour, at which point 1.330 g (1.50 mmol) of
NaBArf4 was added as a solid in one portion. The reaction mixture
changed from yellow to deep orange and LiOTf precipitated
immediately. The mixture was stirred at room temperature for 18
h and filtered through a plug of Celite. All volatiles were removed
from the filtrate in Vacuo, and the resulting oil was triturated until
solid began to precipitate. The crude solid was purified by
precipitation from a mixture of methylene chloride and pentane to
afford 0.950 g (43%) of red-brown powder. The compound was a
3:1 mixture of syn to anti isomers: 1H NMR (300 MHz, CD2Cl2)
δ 14.85 (br s, 1, anti MoCHR), 13.03 (br s, 1, syn MoCHR), syn
isomer only 7.73 (s, 8, o-Arf), 7.56 (s, 4, p-Arf), 7.31 (m, 14, Ar),
6.07 (s, 1, nacnac-CH), 2.42 (br s, 6, Ar′-Me), 2.14 (s, 6, nacnac-
Me), 1.50 (br s, 6, CMe2Ph); 13C NMR (125 MHz, CD2Cl2) δ 322.8
(MoCR), 168.7 (2, CdN), 162.3 (q, JCB ) 49 Hz, ipso-Arf), 145.4,
144.8, 137.7, 135.4 (o-Arf), 130.7, 129.4 (qq, JCF ) 32 Hz, m-Arf),
128.9, 128.8, 128.4, 127.7, 126.6, 126.3, 124.1, 121.9, 118.1 (m,
p-Arf), 109.5 (nacnac-CH), 57.3, 29.2, 23.1, 20.8; 19F NMR (282
MHz) δ -62.8. Anal. Calcd for C67H46BCl4F24MoN3: C, 50.37;
H, 2.90; Cl, 8.88; N, 2.63. Found: C, 50.09; H, 2.96 Cl, 8.78; N,
2.48.
h, the mixture was filtered through a bed of Celite and all volatiles
were removed from the filtrate in Vacuo. The resulting oil was
triturated with pentane until solid appeared. Reprecipitation of the
resulting solid from a mixture of methylene chloride and pentane
gave 1.218 g (87%) of a red-brown powder: 1H NMR (300 MHz,
CD2Cl2) δ 15.75 (br s, anti MoCHR), 13.64 (br s, syn MoCHR),
syn isomer only 7.72 (s, 8, o-Arf), 7.55 (s, 4, p-Arf), 7.35 (d, 2,
m-ArCl), 7.43 (br m, 3, Ar), 7.25 (br m, 4, Ar), 6.29 (s, 1, nacnac-
CH), 2.16 (s, 6, nacnac-Me), 1.05 (s, 9, t-Bu); 13C NMR (125 MHz,
CD2Cl2) δ 335.2 (MoCR), 168.7 (2, CdN), 162.4 (q, JCB ) 50 Hz,
ipso-Arf), 151.6 (br), 144.4, 135.4 (o-Arf), 130.7 (br), 130.1, 129.5
(qq, JCF ) 32 Hz, m-Arf), 129.1, 128.7, 125.2 (q, JCF ) 272 Hz,
CF3), 118.1 (m, p-Arf), 110.7 (nacnac-CH), 51.6 (CMe2Ph), 29.9,
23.1 (CMe3); 19F NMR (282 MHz) δ -62.7. Anal. Calcd for C60H38-
BCl6F24MoN3: C, 45.72; H, 2.43; Cl, 13.49; N, 2.67. Found: C,
45.63; H, 2.40; Cl, 13.54; N, 2.56.
{Mo(N-1-adamantyl)(CHCMe2Ph)(ArCl-nacnac)}{BArf4} (2d).
A flask containing 0.299 g (0.327 mmol) of Mo(N-1-adamantyl)-
(CHCMe2Ph)(ArCl-nacnac)(OTf) and 6 mL of methylene chloride
was chilled at -25 °C for 1 h. To the cold solution was added
0.316 g (0.356 mmol) of NaBArf4 as a solid in one portion. The
reaction mixture changed from yellow to red after stirring at room
temperature for 2 h. The mixture was allowed to stir for an
additional 18 h at room temperature and filtered through a bed of
Celite. The filtrate was concentrated in Vacuo to give a foam.
Crystals were obtained from a mixture of methylene chloride and
pentane at -25 °C to afford 0.523 g (98%) of the product as a fine
yellow powder: 1H NMR (300 MHz, CD2Cl2) δ 13.32 (br s, 1,
MoCHR), 7.75 (s, 8, o-Arf), 7.58 (s, 4, p-Arf), 7.44 (m, 4, Ar), 7.21
(br m, 11, Ar), 6.07 (br s, 1, nacnac-CH), 2.14, 2.06, 1.61 (sharp
s overlapping with two br s, 27, adamantly + CMe2Ph + nacnac-
Me); 13C NMR (125 MHz, CD2Cl2) δ 324.8 (MoCR), 162.4 (q, JCB
) 50.0 Hz, ipso-Arf), 145.6 (br), 135.5 (o-Arf), 131.2 (v br), 129.5
(qq, JCF ) 32 Hz, m-Arf), 129.3, 128.9, 127.5, 126.5, 125.2 (q, JCF
) 272 Hz, CF3), 109.2 (br, nacnac-CH), 118.1 (m, p-Arf), 78.9
(br, adamantly-NC), 55.1 (CMe2Ph), 44.5 (br, adamantly-C), 35.8,
30.0, 29.5 (br, adamantly-C) 22.9; 19F NMR (282 MHz) δ -65.1.
Anal. Calcd for C69H52BCl4F24MoN3: C, 50.92; H, 3.22; Cl, 8.71;
N, 2.58. Found: C, 50.79; H, 3.29; Cl, 8.68; N, 2.48.
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(Ar′-nacnac)(OTf) (3a). A
flask was charged with 1.650 g (2.08 mmol) of Mo(N-2,6-i-
Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) and 40 mL of diethyl ether.
The mixture was chilled briefly at -25 °C before 0.656 g (2.10
mmol) of Li{Ar′-nacnac} was added as a solid in one portion. The
mixture was allowed to stir at room temperature for 20 h, during
which time it became homogeneous and turned orange-yellow. All
volatiles were removed in Vacuo, and the residue was extracted
with 30 mL of toluene. The extract was filtered through a plug of
Celite and evaporated to dryness. The residue was dissolved in a
minimal amount of diethyl ether and set aside at -25 °C overnight
to yield 1.413 g (79%) of orange needles: 1H NMR (500 MHz,
C6D6) δ 11.56 (s, 1, MoCHR, JCH ) 118 Hz), 7.25 (d, 2, o-CMe2Ph),
7.14 (t, 2, m-CMe2Ph), 7.12 (br t, 1, p-Ar′), 7.06 (t, 1, p-CMe2Ph),
7.04 (br d, 2, m-N-2,6-i-Pr2C6H3), 6.93 (br d, 1, m-Ar′), 6.82 (t, 1,
p-N-2,6-i-Pr2C6H3), 6.74 (br d, 1, m-Ar′), 6.61 (br d, 1 m-Ar′), 6.54
(br m, 2, m/p-Ar′), 5.39 (s, 1, nacnac-CH), 4.94 (sep, 1, CHMe2),
2.75 (sep, 1, CHMe2), 2.35 (s, 3, Me), 2.21 (s, 3, Me), 2.15 (s, 3,
Me), 1.81 (s, 3, Me), 1.77 (s, 3, Me), 1.65 (s, 3, Me), 1.60 (d, 3,
CHMe2), 1.59 (s, 3, Me), 1.34 (m, 6, Me + CHMe2), 1.20 (d, 3,
CHMe2), 1.14 (d, 3, CHMe2); 13C NMR (125 MHz, CD2Cl2) many
peaks broad δ 299.1 (MoCR), 167.7 (2, CdN), 153.5, 153.3, 149.9,
148.4, 147.8, 145.5, 133.6, 132.5, 131.9, 131.3, 129.6, 129.3, 128.9,
128.8 128.7, 126.7, 126.4, 126.3, 125.8, 123.5, 122.9, 119.5 (q,
JCF ) 319 Hz, CF3), 104.8 (nacnac-CH), 56.7 (CMe2Ph), 33.6, 32.1,
28.1, 26.4, 25.5, 25.3 (nacnac-Me), 24.3 (nacnac-Me), 23.9, 20.2,
19.2; 19F NMR (282 MHz) δ -76.1. Anal. Calcd for C44H54F3-
MoN3O3S: C, 61.60; H, 6.34; N, 4.90. Found: C, 61.72; H, 6.46;
N, 4.81.
{Mo(N-2,6-Cl2C6H3)(CH-t-Bu)(ArCl-nacnac)}{BArf4} (2c). A
solution of 0.767 g (0.889 mmol) of Mo(N-2,6-Cl2C6H3)(CH-t-Bu)-
(ArCl-nacnac)(OTf) (0.767 g, 0.889 mmol) in 20 mL of methylene
chloride was chilled at -25 °C for 1 h, at which point 0.788 g
(0.889 mmol) of NaBArf4 was added as a solid in one portion. The
reaction mixture changed from yellow to deep orange, and LiOTf
precipitated immediately. After stirring at room temperature for 24

Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 26, No. 15, 2007 3781
Mo(N-2,6-Cl2C6H3)(CH-t-Bu)(Ar′-nacnac)(OTf) (3c). A flask
was charged with 0.714 g (1.00 mmol) of Mo(N-2,6-Cl2C6H3)(CH-
t-Bu)(OTf)2(DME) and 20 mL of diethyl ether. Li{Ar′-nacnac}
(0.319 g, 1.02 mmol) was added to the solution as a solid in one
portion. The reaction was stirred at room temperature for 18 h. All
volatiles were removed in Vacuo, and the residue extracted into a
4:1 mixture of toluene and methylene chloride. The mixture was
filtered through a bed of Celite and the solution volume concentrated
to ∼3 mL in Vacuo. Several volumes of pentane were added until
a wine-red precipitate formed. The mixture was set aside at
-25 °C for 30 min. The solid was collected by filtration and washed
with pentane to yield 0.595 g (71%) of a deep red microcrystalline
p-Arf), 7.28 (d, 2 Ar), 7.19 (br m, 4 Ar), 7.03 (br d, 1 Ar), 5.91 (br
s, 1 nacnac-CH), 4.75 (br m, 1 CHMe2), 3.5 (v br, 4 OCH2), 2.71
(br m, 1 CHMe2), 2.33 (s, 3 Me), 2.13 (s, 3 Me), 1.95 (s, 3 Me),
1.89 (s, 3 Me), 1.82 (s, 3 Me), 1.73 (s, 3 Me), 1.52 (s, 3 Me), 1.44
(br s, 3 Me), 1.29 (br m, 12 CHMe2), 0.95 (s, 3 Me); 13C NMR
(238 K, 125 MHz, CD2Cl2) δ 317.6 (MoCR), 168.9 (CN), 167.4
(CN), 161.9 (q, JCB ) 49.6 Hz, ipso-Arf), 154.3, 153.9, 148.0, 147.1,
143.9, 143.1, 135.1, 134.9 (o-Arf), 132.7, 131.1, 131.0, 130.4, 129.7,
129.5, 129.4, 129.1, 128.9 (qq, JCF ) 31.3 Hz, m-Arf), 127.8, 127.4,
126.7, 125.9, 124.7 (q, JCF ) 272 Hz, CF3), 124.6, 124.5, 117.7
(m, p-Arf), 105.7 (nacnac-CH), 80.2 (OCH2), 79.3 (OCH2), 56.6
(CMe2Ph), 31.3, 29.7, 28.2, 27.3, 26.5, 25.5, 25.3, 25.2, 25.1, 25.0,
23.8, 19.6, 19.4, 19.3, 18.8; 19F NMR (293 K, 472 MHz) δ -62.4.
Anal. Calcd for C79H74BF24MoN3O: C, 57.71; H, 4.54; N, 2.53.
Found: C, 57.48; H, 4.68; N, 2.45.
powder: 1H NMR (500 MHz, C6D6) δ 11.93 (s, 1, MoCHR, JCH
)
115 Hz), 7.12 (d, 1, m-Ar′), 7.04 (t, 1, p-Ar′), 7.01 (d, 1, m-Ar′),
6.79 (d, 1, m-Ar′), 6.64 (t, 1, p-Ar′), 6.56 (m, 3, m-Ar′ + m-2,6-
Cl2C6H3), 6.10 (t, 1, p-2,6-Cl2C6H3), 5.47 (s, 1, nacnac-CH), 2.44
(s, 3, Me), 2.31 (s, 3, Me), 2.13 (s, 3, Me), 1.91 (s, 3, Me), 1.58 (s,
3, nacnac-Me), 1.51 (s, 9, t-Bu), 1.45 (s, 3, nacnac-Me); 13C NMR
(125 MHz, CD2Cl2) δ 311.9 (MoCR), 167.4 (CdN), 166.8 (CdN),
153.8, 149.6, 147.7, 140.0, 134.3, 131.8, 131.6, 130.1, 129.6, 128.9,
128.5, 128.4, 128.2, 126.9, 126.5, 125.7, 119.4 (q, JCF ) 319 Hz,
CF3), 104.6 (nacnac-CH), 50.4 (CMe3), 30.7 (CMe3), 25.8, 23.7,
21.5, 20.9, 19.6, 18.8; 19F NMR (282 MHz) δ -77.2. Anal. Calcd
for C33H38Cl2F3MoN3O3S: C, 50.78; H, 4.91; N, 5.38. Found: C,
52.06, 53.98; H, 5.10, 4.71; N, 5.15, 5.06. The variable and incorrect
analytical results are due to residual toluene (∼5% by NMR), which
could not be removed in Vacuo at room temperature, and higher
temperatures would risk decomposition.
{Mo(N-2,6-Cl2C6H3)(CHCMe3)(Ar′-nacnac)(THF)}{BArf4} (4c).
A flask was charged with 0.183 g (0.235 mmol) of Mo(N-2,6-
Cl2C6H3)(CH-t-Bu)(Ar′-nacnac)(OTf), 1 mL of THF, and 20 mL
of methylene chloride. The solution was cooled to -25 °C, and
NaBArf4 (0.255 g, 0.257 mmol) was added as a solid in one portion.
The mixture was allowed to stir at room temperature for 10 min.
All volatiles were removed in Vacuo. The residue was extracted
into methylene chloride, and the extract was filtered through Celite.
The solvent volume was reduced to ∼2 mL in Vacuo and layered
with several volumes of pentane. The mixture was set aside at
-25 °C for 2 days to afford 0.322 g (87%) of red crystals: 1H
NMR (300 MHz, CD2Cl2) δ 13.11 (s, 1, MoCHR, JCH ) 116 Hz),
7.72 (s, 8, o-Arf), 7.56 (s, 4, p-Arf), 7.41 (d, 2, m-ArCl), 7.16 (t, 1,
p-ArCl), 7.11 (br, 6, Ar′), 6.15 (s, 1, nacnac-CH), 3.1 (v br, 4, OCH2),
2.26 (br, 6, Me), 1.84 (br m, 12, Me), 1.62 (m, 4, OCH2CH2), 0.94
(s, 9, t-Bu); 13C NMR (125 MHz, CD2Cl2) δ 332.8 (MoCR), 168
(v br, CdN), 162.4 (q, JCB ) 49.9 Hz, ipso-Arf), 151.4 (ipso-ArCl),
135.4 (m-Arf), 130.3 (m-ArCl), 130.2 (o-ArCl), 130.1 (p-ArCl), 129.5
(q, JCF ) 32.5 Hz, m-Arf), 129.1 (br, Ar′), 128.0 (br, Ar′), 125.2
(q, JCF ) 271 Hz, CF3), 118.0 (sep, JCF ) 3.8 Hz, p-Arf), 106.9
(nacnac-CH), 80.6 (br, OCH2CH2), 51.8 (CMe3), 31.4 (CMe3), 26.1,
25.2, 19.5; 19F NMR (282 MHz) δ -63.3. Anal. Calcd for C68H58-
BCl2F24MoN3O: C, 52.13; H, 3.73; N, 2.68. Found: C, 52.19; H,
3.80; N, 2.64.
Mo(N-2-t-BuC6H4)(CH-t-Bu)(Ar′-nacnac)(OTf) (3e). A flask
was charged with 0.792 g (1.13 mmol) of Mo(N-2-t-BuC6H4)(CH-
t-Bu)(OTf)2(DME) and 35 mL of diethyl ether. To this stirring
solution was added 0.390 g (1.25 mmol) of Li{Ar′-nacnac} as a
solid in one portion. The mixture was stirred at room temperature
for 2 h, during which time it became homogeneous and turned
yellow-brown. All volatiles were removed in Vacuo, and the residue
was extracted into 30 mL of toluene. The solution was filtered
through Celite, and the solvents were removed in Vacuo. The residue
was dissolved in a minimal amount of diethyl ether and set aside
at -25 °C for 24 h, during which time the compound precipitated
as an orange, microcrystalline solid (0.693 g; 74%): 1H NMR (500
MHz, C6D6) δ 11.43 (s, 1, MoCHR, JCH ) 116 Hz), 8.18 (v br, 1,
o-2-t-BuC6H4), 7.09 (t, 1, Ar), 7.03 (m, 3, Ar), 6.90 (t, 1, Ar), 6.76
(t, 1, Ar), 6.65 (m, 3, Ar), 5.36 (s, 1, nacnac-CH), 2.39 (s, 3, Me),
2.18 (s, 6, Me), 1.58 (s, 3, Me), 1.42 (s, 3, Me), 1.37 (s, 9, t-Bu),
1.35 (s, 9, t-Bu); 13C NMR (125 MHz, CD2Cl2) many peaks broad
δ 310.3 (MoCR), 167.7 (CdN), 167.4 (CdN), 154.6, 154.2, 147.9,
132.9, 132.8, 132.5, 131.5, 129.5, 129.4, 129.3, 129.2, 129.1, 128.4,
128.3, 126.0, 125.7, 119.5 (q, JCF ) 319 Hz, CF3), 104.5 (nacnac-
CH), 51.3 (CMe3), 36.70, 32.70, 30.73, 25.49, 24.43, 20.79, 20.69,
20.05, 19.46; 19F NMR (282 MHz) δ -77.2. Anal. Calcd for
C37H48F3MoN3O3S: C, 57.88; H, 6.30; N, 5.47. Found: C, 57.89;
H, 6.39; N, 5.41.
{Mo(N-2-t-BuC6H4)(CH-t-Bu)(Ar′-nacnac)(THF)}{BArf4} (4e).
Compound 4e was prepared in analogous fashion to that used to
prepare 4a and 4c, starting from 0.155 g (0.20 mmol) of Mo(N-
2-t-BuC6H4)(CH-t-Bu)(Ar′-nacnac)(OTf) and 0.192 g (0.22 mmol)
of NaBArf4. Upon recrystallization from a mixture of methylene
chloride and pentane, 0.279 g of a bright orange powder was
obtained. NMR spectra showed the compound to be a mixture of
two compounds, 4e and 4e′, as well as a mixture of syn and anti
isomers of 4e: 1H NMR (500 MHz, CD2Cl2) δ 14.52 (s, anti
MoCHR), 11.85 (v br s, syn MoCHR), 11.08 (v br s, syn MoCHR),
7.75 (s, o-Arf), 7.60 (s, p-Arf), 7.2 (v br m, Ar), 6.15 (s, anti nacnac-
CH), 6.0 (v br s, syn nacnac-CH), 3.6 (v br m, THF), 2.60 (s, Me),
2.30 (br s, Me), 2.10 (br m, Me), 1.90 (s, t-Bu), 1.83 (br s, Me),
1.75 (br m, THF), 1.65 (s, t-Bu), 1.56 (s, t-Bu), 1.1 (br, Me).
{Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(Ar′-nacnac)(THF)}-
{BArf4} (4a). A flask was charged with 0.502 g (0.585 mmol) of
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(Ar′-nacnac)(OTf), 1 mL of THF,
and 25 mL of methylene chloride. The solution was cooled to
-25 °C, and 0.513 g (0.592 mmol) of solid NaBArf4 was added in
one portion. The mixture was stirred at room temperature for 5
min. All volatiles were removed in Vacuo. The residue was extracted
with methylene chloride, and the mixture was filtered through
Celite. The extract’s volume was reduced to ∼5 mL in Vacuo, and
the solution was layered with several volumes of pentane. The
product crystallized at -25 °C as an orange microcrystalline solid;
yield 0.887 g (92%). Crystals suitable for X-ray diffraction were
grown by slowly cooling a saturated solution of methylene chloride
and pentane at -25 °C: 1H NMR (238 K, 500 MHz, CD2Cl2) δ
12.18 (s, 1 MoCHR, JCH ) 116 Hz), 7.75 (s, 8, o-Arf), 7.58 (s, 4,
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(Ar′′-nacnac)(OTf) (5a). A
flask was charged with 1.190 g (1.50 mmol) of Mo(N-2,6-i-
Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) and 25 mL of diethyl ether.
The solution was chilled to -25 °C, and Li{Ar′′-nacnac} (0.473
g; 1.51 mmol) was added as a solid in one portion. The mixture
was allowed to stir at room temperature for 2 h, during which time
the color darkened from yellow to yellow-brown. All volatiles were
removed in Vacuo and the residue extracted into 20 mL of toluene.
The extract was filtered through Celite and evaporated to dryness
in Vacuo. The resulting solid was recrystallized from a minimal
amount of diethyl ether to yield an orange-red crystalline solid
(0.970 g, 75%). The compound was found to exist as a 15:1 mixture
of syn and anti isomers: 1H NMR (300 MHz, C6D6) δ 14.30 (s, 1,
anti MoCHR), 12.12 (s, 1, syn MoCHR, JCH ) 117 Hz), syn isomer

3782 Organometallics, Vol. 26, No. 15, 2007
Tonzetich et al.
only 7.35 (d, 2, o-CMe2Ph), 7.17 (t, 2, m-CMe2Ph), 7.05 (t, 1,
p-CMe2Ph), 6.94 (br s, 2, o-Ar′′), 6.81 (m, 3, m/p-N-2,6-i-Pr2C6H3),
6.74 (s, 1, p-Ar′′), 6.26 (s, 1, p-Ar′′), 5.91 (br s, 2, o-Ar′′), 5.28 (s,
1, nacnac-CH), 3.56 (sep, 2, CHMe2), 2.30 (s, 3, Me), 2.27 (s, 6,
Ar′′-Me), 1.87 (br s, 6, Ar′′-Me), 1.77 (s, 3, Me), 1.70 (s, 3, Me),
1.47 (s, 3, Me), 1.34 (d, 6, CHMe2), 1.04 (d, 6, CHMe2); 13C NMR
(125 MHz, C6D6) δ 297.8 (MoCR), 167.1 (CdN), 165.4 (CdN),
154.5, 152.2, 149.4, 149.0, 147.6 (br), 138.6 (br), 129.1, 128.9,
127.3, 126.9, 126.6, 126.1 (br), 123.0, 122.2 (br), 120.7 (q, CF3,
JCF ) 319 Hz), 104.8 (nacnac-CH), 55.3 (CMe2Ph), 32.6 (br), 31.0,
27.9, 24.7 (br m), 24.1, 21.6 (br); 19F NMR (282 MHz) δ -76.7.
Anal. Calcd for C44H54F3MoN3O3S: C, 61.60; H, 6.34; N, 4.90.
Found: C, 61.54; H, 6.31; N, 4.86.
Tl(ArF-nacnac). A flask was charged with 0.519 g (1.58 mmol)
of Li{ArF-nacnac} and 25 mL of tetrahydrofuran. To the solution
was added 0.415 g (1.58 mmol) of Tl(OAc) as a solid in one portion.
The mixture was allowed to stir in the dark for 24 h at room
temperature. All volatiles were removed in Vacuo, and the residue
was extracted into diethyl ether. The solution was filtered through
Celite, and the solvent volume was reduced to ∼7 mL in Vacuo.
The solution was set aside at -25 °C for several days to afford the
product as a yellow solid, which was isolated by filtration and dried
in Vacuo; yield 0.515 g (62%): 1H NMR (300 MHz, C6D6) δ 6.67
(m, 4, m-ArF), 6.49 (m, 2, o-ArF), 4.92 (br s, 1, nacnac-CH), 1.90
(s, 6, Me); 19F NMR (282 MHz) δ 121.3 (d, JTlF ) 753 Hz, ArF).
Spectroscopic features were consistent with previously reported
values.15
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(ArF-nacnac)(OTf) (7a). A
flask was charged with 0.724 g (0.913 mmol) of Mo(N-2,6-i-
Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) and 25 mL of toluene. To the
solution was added 0.482 g (0.916 mmol) of solid Tl(ArF-nacnac)
in one portion. The mixture was allowed to stir at room temperature
for 40 h in the dark. All volatiles were removed in Vacuo, and the
residue was extracted into 25 mL of toluene. The extract was filtered
through a pad of Celite and evaporated to dryness. The residue
was then dissolved in a minimal amount of diethyl ether and set
aside at -25 °C. The product precipitated in two crops of yellow
microcrystals that exist as a 1:1.5 mixture of syn to anti isomers in
solution; yield 0.630 g (79%): 1H NMR (300 MHz, C6D6) δ 14.90
p-Arf), 7.4 - 6.9 (m, 9, Ar), 5.94 (s, 1, nacnac-CH), 3.7 (v br m,
1, CHMe2), 2.84 (m, 2, OCH2), 2.45 (m, 2, OCH2), 2.17 (s, 3, CMe2-
Ph), 1.94 (s, 3, CMe2Ph), 1.57 (s, 3, nacnac-Me), 1.36 (m, 4,
OCH2CH2), 1.28 (br, 6, CHMe2), 1.22 (d, 6, CHMe2), 1.10 (s, 3,
nacnac-Me); 19F NMR (470 MHz) δ -62.5 (Arf), -115.4 (ArF),
-115.7 (ArF), -117.2 (ArF), -119.5 (ArF). Anal. Calcd for C75H62-
BF28MoN3O: C, 54.27; H, 3.76; N, 2.53. Found: C, 54.33; H, 3.68;
N, 2.46.
Decomposition of 3a to Give 3a′′. A flask was charged with
0.103 g (0.119 mmol) of Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(Ar′-
nacnac)(OTf) and 10 mL of toluene. The orange solution was heated
to 90 °C for 45 min. All volatiles were removed in Vacuo, and the
residue was crystallized from a minimal amount of diethyl ether at
-25 °C to give 0.090 g (89%) of an orange-yellow crystalline solid.
Crystals suitable for X-ray diffraction were grown by slow cooling
of a saturated diethyl ether solution at 23 °C. NMR assignments
1
are based on H, 13C, HSQC, and HMBC experiments: 1H NMR
(300 MHz, C6D6) δ 7.11 (m, 2, Ar), 6.97 (m, 6, Ar), 6.79 (m, 4,
Ar), 5.38 (d, JHH ) 14 Hz, 1, C37H2), 4.14 (m, 1, CHMe2), 4.12 (t,
JHH ) 4.5 Hz, 1, C2H), 3.70 (d, JHH ) 14 Hz, 1, C37H2), 2.63 (dd,
JHH ) 15 Hz, 4.5 Hz, 1, C6H2), 2.59 (m, 1, CHMe2), 2.19 (s, 3,
Me), 2.02 (s, 3, Me), 1.77 (dd, JHH ) 15 Hz, 4.5 Hz, 1 C6H2), 1.61
(d, 3, CHMe2), 1.57 (s, 3, Me), 1.41 (d, 3, CHMe2), 1.34 (d, 3,
CHMe2), 1.23 (s, 3, Me), 1.21 (s, 3, Me), 1.09 (s, 3, Me), 0.65 (d,
3, CHMe2), 0.57 (s, 3, Me); 13C NMR (125 MHz, C6D6) δ 197.80
(C1), 158.03, 153.78, 150.22, 147.89, 146.67, 145.36, 143.92,
129.90, 129.54, 129.50, 129.33, 128.53, 128.52, 128.03, 127.51,
127.31, 126.86, 125.84, 123.68, 123.63, 123.31, 123.05, 120.52 (q,
JCF ) 319 Hz, CF3), 82.83 (C3), 66.76 (C37), 59.61 (C2), 46.60
(C6), 38.61 (C7), 31.12, 30.70, 28.63, 27.75, 25.88, 25.73, 24.15,
22.20 (C5), 21.84, 19.84 (C4), 18.77 (C38), 18.21, 18.18. 19F NMR
(282 MHz) δ -77.3 (CF3). Anal. Calcd for C44H54F3MoN3O3S:
C, 61.60; H, 6.34; N, 4.90. Found: C, 61.78; H, 6.42; N, 4.81.
(s, 1, anti MoCHR, JCH ) 145 Hz), 12.42 (s, 1, syn MoCHR, JCH
)
117 Hz), 7.42 (d, 2, anti o-CMe2Ph), 7.35 (d, 2, syn o-CMe2Ph),
7.18 (t, 2, anti m-CMe2Ph), 7.16 (t, 2, syn m-CMe2Ph), 7.07 (t, 1,
syn p-CMe2Ph), 7.05 (t, 1, p-CMe2Ph), 6.91 - 6.58 (m, 13, syn/
anti ArF + m/p-2,6-i-Pr2C6H3), 6.26 (m, 2, syn ArF), 6.00 (m, 3,
anti ArF), 5.15 (s, 1, syn nacnac-CH), 5.14 (s, 1, anti nacnac-CH),
4.08 (br m, 1, anti CHMe2), 3.81 (sep, 2, syn CHMe2), 3.37 (br m,
1, anti CHMe2), 2.12 (s, 3, anti Me), 2.01 (s, 3, syn Me), 1.90 (s,
3, syn Me), 1.88 (s, 3, anti Me), 1.70 (br, 3, anti CHMe2), 1.64 (s,
3, anti Me), 1.42 (d, 6, syn CHMe2), 1.41 (s, 3, syn Me), 1.40 (br,
3, anti CHMe2), 1.39 (s, 3, anti Me), 1.34 (d, 6, syn CHMe2), 1.21
(br, 6, anti CHMe2); 13C NMR (125 MHz, C6D6) selected peaks
only δ 322.8 (anti MoCR), 303.1 (syn MoCR), 169.8 (syn CdN),
169.5 (anti CdN), 169.0 (syn CdN), 167.2 (anti CdN), 104.7 (syn
nacnac-CH), 103.7 (anti nacnac-CH), 56.8 (syn CMe2Ph), 54.9 (anti
CMe2Ph); 19F NMR (282 MHz) δ -76.7 (CF3), -114.3 (anti ArF),
-114.5 (syn ArF), -116.2 (anti ArF), -117.5 (2, syn ArF), -118.4
(syn ArF), -119.7 (anti ArF), -120.1 (anti ArF). Anal. Calcd for
C40H42F7MoN3O3S: C, 54.98; H, 4.84; N, 4.81. Found: C, 55.05;
H, 4.88; N, 4.70.
{Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(ArF-nacnac)(THF)}-
{BArf4} (8a). This compound was prepared in fashion analogous
to that employed to prepare 4a starting from 0.327 g (0.374 mmol)
of 7a and 0.330 g (0.381 mmol) of NaBArf4. The complex was
observed to form an oil upon attempts at crystallization and was
finally precipitated as 0.421 g (68%) of a yellow-brown powder:
1H NMR (300 MHz, CD2Cl2) δ 14.86 (d, JHF ) 3.5 Hz, anti
MoCHR), 12.75 (s, 1, syn MoCHR), 7.75 (s, 8, o-Arf), 6.58 (s, 4,
Compound 3a′′′. This species was observed spectroscopically
by mixing equimolar amounts of 3a′′ and NaB(C6F5)4‚THF in
methylene chloride-d2 at 23 °C: 1H NMR (300 MHz) δ 7.49 (d, 2,
Ar), 7.35 (t, 2, Ar), 7.22 (t, 1, Ar), 7.16 (m, 4, Ar), 7.08 (d, 1, Ar),
7.07 (t, 1, Ar), 6.95 (d, 1, Ar), 6.89 (m, 2, Ar), 4.54 (d, JHH ) 12.9
Hz, CH2), 4.50 (t, JHH ) 3.0 Hz, CH), 3.93 (m, 3, CHMe2 + THF),
3.52 (m, 2, THF), 3.01 (d, JHH ) 12.9 Hz, 1, CH2), 2.79 (dd, JHH
) 15.6 Hz, JHH ) 3.0 Hz, 1, CH2), 2.31 (s, 1, Me), 2.15 (sep, 1,
CHMe2), 2.14 (s, 3, Me), 1.97 (dd, JHH ) 15.6 Hz, JHH ) 3.0 Hz,
1, CH2), 1.86 (s, 3, Me), 1.82 (m, 4, THF), 1.63 (s, 3, Me), 1.60 (s,
3, Me), 1.51 (d, 3, CHMe2), 1.33 (d, 3, CHMe2), 1.17 (s, 3, Me),
1.04 (s, 3, Me), 1.03 (d, 3, CHMe2), 0.44 (d, 3, CHMe2).
Compound 4a′′. This species was observed spectroscopically
upon thermolysis of a 15 mM solution of 4a in methylene chloride-
d2 at 40 °C for 3 h: 1H NMR (500 MHz) δ including tert-
butylbenzene δ 14.28 (br s, 1, MoCH), 8.26 (s, 8, o-Arf), 7.64 (s,
4, p-Arf), 7.34 (d, 2, Ar), 7.27 (t, 1, Ar), 7.22 (d, 1, Ar), 7.14 (m,

Molybdenum Imido Alkylidene Complexes
Organometallics, Vol. 26, No. 15, 2007 3783
3, Ar), 6.99 (d, 1, Ar), 6.83 (t, 1, Ar), 6.69 (d, 2, Ar), 6.53 (d, 1,
Ar), 4.85 (br s, 1, nacnac-CH), 3.32 (sep, 2, CHMe2), 3.28 (m, 2,
THF), 2.98 (m, 2, THF), 2.29 (s, 3, Me), 2.10 (br s, 3, Me), 1.87
(s, 3, Me), 1.65 (s, 3, Me), 1.4 - 1.1 (br m, 19, THF + CHMe2 +
Me), 0.74 (br s, 6, CHMe2); 13C NMR (258 K, 125 MHz) δ 299.5
(MoCR), 166.2 (CN), 162.1 (q, JCB ) 49.7 Hz, ipso-Arf), 152.5,
151.4, 150.7, 147.0, 146.7 (v br), 143.2, 135.1 (o-Arf), 133.0, 131.5,
129.9, 129.2, 129.1, 129.1 (qq, JCF ) 31.3 Hz, m-Arf), 129.0, 127.9,
126.1, 124.9 (q, JCF ) 272 Hz, CF3), 124.6, 123.8, 119.4, 81.5,
75.8, 28.7, 26.7, 25.4 (br), 24.1, 23.5, 22.1, 19.3, 17.7, 17.5.
Compound 4e′′. This species was observed spectroscopically
upon thermolysis of a mixture of 4e and 4e′ at 40 °C for 3 h in
methylene chloride-d2: 1H NMR (300 MHz) δ 14.13 (s, 1, MoCH),
7.73 (s, 8, o-Arf), 7.56 (s, 4, p-Arf), 7.40 (d, 1, Ar), 7.15 (m, 3,
Ar), 6.98 (t, 1, Ar), 6.90 (t, 1, Ar), 6.81 (t, 1, Ar), 6.74 (d, 1 Ar),
6.65 (d, 1, Ar) 5.89 (d, 1, Ar), 5.35 (s, 1, nacnac-CH), 3.78 (m, 2,
THF), 3.41 (m, 4, THF), 2.57 (s, 3, Me), 2.48 (s, 3, Me), 2.06 (s,
3, Me), 1.97 (s, 3, Me), 1.85 (m, 4, THF), 1.58 (s, 9, t-Bu), 1.17
(s, 3, Me).
Me), 1.80 (br s, 4, THF), 1.77 (s, 6, Me), 1.16 (d, 12, CHMe2),
0.86 (m, 2, CH2CH2); 13C NMR (125 MHz) δ 70.3 (CH2, JCH
)
157 Hz).
1
Kinetic Experiments. Kinetic data were obtained by H NMR
at 500 MHz using temperature values that were calibrated with
ethylene glycol. Experiments were performed in either toluene-d8
(for 3a) or methylene chloride-d2 (for 4a) at concentrations of 18.0
and 19.5 mM, respectively.
Acknowledgment. R.R.S. thanks the National Science
Foundation (CHE-0138495) for supporting this research. Z.J.T.
thanks the Alan Davison Fellowship Fund for one semester of
support.
1
Supporting Information Available: Variable-temperature H
NMR spectra of 2a, 4a, and 4a′′. Kinetic plots for thermal
degradation of compounds 3a and 4a. Labeled thermal ellipsoid
drawings, crystal data and structure refinement, atomic coordinates
and equivalent isotropic displacement parameters, bond lengths and
angles, and anisotropic displacement parameters for all crystallo-
graphically characterized compounds. Crystallographic information
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
(06066), 4a, (06192), and 3a′′ (06187) are also available to the
public at http://reciprocal.mit.edu.
{Mo(N-2,6-i-Pr2C6H3)(CH2CH2)(Ar′-nacnac)(THF)}-
{BArf4} (9a). This species was observed spectroscopically by
exposing a solution of 4a to 1 atm of ethylene or ethylene-13C at
23 °C in methylene chloride-d2: 1H NMR (300 MHz) δ 7.73 (s, 8,
o-Arf), 7.56 (s, 4, p-Arf), 7.40 (t, 2, Ar), 7.36-7.26 (m, 5, Ar),
7.15 (d, 2 Ar), 6.46 (s, 1, nacnac-CH), 3.65 (br s, 4, THF), 2.85
(sep, 2, CHMe2), 2.57 (m, 2, CH2CH2), 2.33 (s, 6, Me), 1.93 (s, 6,
OM7003207