Organomolybdenum(VI) and lithium organomolybdate(VI) and -(V) complexes with C,N-chelating aminoaryl ligands

Article abstract of DOI:10.1021/om9900364

The synthesis and characterization of new, five-coordinate molybdenum bis(imidoaryl) complexes [Mo(NAr)₂(C-AT)X] (Ar = C₆H₃i-Pr₂-2,6; C-N= [C₆H₄(CH₂NMe₂)-2]^-; X = Cl (1), Me (2), Et (3), Bu (4), CH₂SiMe₃ (5), (p-tolyl) (6), (C-N) (7)) is reported. The solid-state structure of 2 has been elucidated by single-crystal X-ray analysis. Compounds 2, 3, 4, 5, and 6 react with alkyl- or aryllithium compounds to form lithium molybdate(VI) derivatives, of which [Li(DME)Mo(NAr)₂(C-N(Me)(p-tolyl)] (10), formed by the reaction of 2 with [Li-(p-tolyl)], has been structurally (X-ray) characterized. Thermal activation of these lithium molybdates leads to the formation of paramagnetic lithium molybdate(V) compounds instead of the anticipated molybdenum(VI) alkylidenes. The actual temperature (between -10 and 80 °C) at which paramagnetic Mo(V) radical anions are formed is dependent on both the type of alkyl or aryl substituent (introduced via LiR′) and the solvent. The synthesis of [LiMo-(NAr)₂(C-N)₂] (11) by reaction of 7 with n-BuLi is described. The initially formed lithium molybdate(VI) compound [Li(DME)_nMo(NAr)₂(C-N(n-Bu)] is not stable at room temperature and converts directly to the lithium molybdate(V) derivative 11. The solid-state structure of 11 has been elucidated by single-crystal X-ray analysis. None of the lithium molybdate(VI) nor -(V) derivatives described herein are active catalysts for ROMP, as thermal activation does not lead to the formation of a molybdenum alkylidene complex but to electron transfer and formation of a lithium molybdate(V) instead. However, upon treatment of a solution of any of the molybdate(V) derivatives with dry air, catalytic ROMP is observed.

Full text of DOI:10.1021/om9900364

Organometallics 1999, 18, 2633-2641
2633
Or ga n om olybd en u m (VI) a n d Lith iu m
Or ga n om olybd a te(VI) a n d -(V) Com p lexes w ith
C,N-Ch ela tin g Am in oa r yl Liga n d s
J im A. M. Brandts,† Marloes van Leur,† Robert A. Gossage,† J aap Boersma,†
Anthony L. Spek,‡,§ and Gerard van Koten*,†
Debye Institute, Department of Metal-Mediated Synthesis, Utrecht University, Padualaan 8,
3584 CH, Utrecht, The Netherlands, and Bijvoet Institute for Biomolecular Research,
Department of Crystal and Structural Chemistry, Utrecht University, Padualaan 8,
3584 CH, Utrecht, The Netherlands
Received J anuary 21, 1999
The synthesis and characterization of new, five-coordinate molybdenum bis(imidoaryl)
complexes [Mo(NAr)2(C-N)X] (Ar ) C6H3i-Pr2-2,6; C-N ) [C6H4(CH2NMe2)-2]-; X ) Cl (1),
Me (2), Et (3), Bu (4), CH2SiMe3 (5), (p-tolyl) (6), (C-N) (7)) is reported. The solid-state
structure of 2 has been elucidated by single-crystal X-ray analysis. Compounds 2, 3, 4, 5,
and 6 react with alkyl- or aryllithium compounds to form lithium molybdate(VI) derivatives,
of which [Li(DME)Mo(NAr)2(C-N)(Me)(p-tolyl)] (10), formed by the reaction of 2 with [Li-
(p-tolyl)], has been structurally (X-ray) characterized. Thermal activation of these lithium
molybdates leads to the formation of paramagnetic lithium molybdate(V) compounds instead
of the anticipated molybdenum(VI) alkylidenes. The actual temperature (between -10 and
80 °C) at which paramagnetic Mo(V) radical anions are formed is dependent on both the
type of alkyl or aryl substituent (introduced via LiR′) and the solvent. The synthesis of [LiMo-
(NAr)2(C-N)2] (11) by reaction of 7 with n-BuLi is described. The initially formed lithium
molybdate(VI) compound [Li(DME)nMo(NAr)2(C-N)2(n-Bu)] is not stable at room temper-
ature and converts directly to the lithium molybdate(V) derivative 11. The solid-state
structure of 11 has been elucidated by single-crystal X-ray analysis. None of the lithium
molybdate(VI) nor -(V) derivatives described herein are active catalysts for ROMP, as thermal
activation does not lead to the formation of a molybdenum alkylidene complex but to electron
transfer and formation of a lithium molybdate(V) instead. However, upon treatment of a
solution of any of the molybdate(V) derivatives with dry air, catalytic ROMP is observed.
In tr od u ction
produces more than 2 × 104 turnovers per hour at 70
°C in benzene.1a These so-called “latent” catalysts allow
the mixing of monomer and catalyst precursor in
advance without polymerization taking place. Only
when the reaction mixture is heated would initiation
and polymerization occur.
Tungsten(VI)1 and tantalum(V)2,3 alkylidenes con-
taining monoanionic C,N- (C-N ) C6H4(CH2NMe2)-2)
or O,N-chelating (O,N ) η2-OCPh2(2-py), η2-OCMe2(2-
py) or 8-quinolinolate) ligands reveal remarkable ther-
mal stability and reactivity toward olefins and strained
cyclic alkenes. Some of these tungsten(VI) alkylidenes
also show temperature-dependent ring-opening metath-
esis polymerization (ROMP) activity toward norbornene.2
For example, [W(dCHSiMe3)(CH2SiMe3){η2-OCPh2(2-
py)}(NPh)] is unreactive at room temperature but
We became interested in the synthesis of the analo-
gous compounds based on molybdenum primarily be-
cause of their expected higher stability. From a syn-
thetic point of view [Mo(NAr)2Cl2(DME)]4 (Ar ) C6H3(i-
Pr)2-2,6, DME ) 1,2-dimethoxyethane) is an attractive
starting material to synthesize monoanionic, C,N-
chelating aminoaryl ligands containing Mo(VI) com-
plexes, from which molybdenum alkylidene complexes
can be generated. At this point we have focused on the
synthesis of Mo(VI) compounds with the general formula
[Mo(NAr)2(C-N)(R)] (C-N ) C6H4(CH2NMe2)-2; R ) Cl
(1), Me (2), Et (3), n-Bu (4), CH2SiMe3 (5), p-tolyl (6),
(C-N) (7)) and studied the possible C-H activation
reactions that could lead to molybdenum alkylidene
complexes (Scheme 1).
* To whom correspondence should be addressed. Tel: +3130
2533120. Fax: +3130 2523615. E-mail: g.vankoten@chem.uu.nl.
† Debye Institute, Utrecht University.
‡ Bijvoet Institute for Biomolecular Research.
§ Address correspondence pertaining to crystallographic studies to
this author. E-mail: A.L.Spek@chem.uu.nl.
(1) (a) van der Schaaf, P. A.; Abbenhuis, R. A. T. M.; van der Noort,
W. P. A.; de Graaf, R.; Grove, D. M.; Smeets, W. J . J .; Spek, A. L.; van
Koten, G. Organometallics 1994, 13, 1433. (b) van der Schaaf, P. A.;
Grove, D. M.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. Organome-
tallics 1993, 12, 3955. (c) van der Schaaf, P. A.; Smeets, W. J . J .; Spek,
A. L.; van Koten, G. J . Chem. Soc., Chem. Commun. 1992, 717.
(2) Abbenhuis, H. C. L.; Rietveld, M. H. P.; Haarman, H. F.;
Hogerheide, M. P.; Spek, A. L.; van Koten, G. Organometallics 1994,
13, 3259-3268.
Examples of NMe2-group-assisted intramolecular
R-C-H activation reactions (route i) have been reported
(3) Rietveld, M. H. P.; Klumpers, E. G.; J astrzebski, J . T. B. H.;
Grove, D. M.; Veldman, N.; Spek, A. L.; van Koten, G. Organometallics
1997, 16, 4260.
(4) Fox, H. H.; Yap, K. B.; Robbins, J .; Cai, S.; Schrock, R. R. Inorg.
Chem. 1992, 31, 2287.
10.1021/om9900364 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/15/1999

2634 Organometallics, Vol. 18, No. 14, 1999
Brandts et al.
Sch em e 1: P ossible Alk ylid en e F or m a tion via
C-H Activa tion Rea ction s of [Mo(NAr )2(C-N)R]
Com p lexes Ba sed on Exa m p les fr om Ta ,2,6,7 W,8
a n d Zr 5 Ch em istr y
Sch em e 2a
a
i: 1/2 [Zn(C-N)2], Et2O/benzene, -DME, -ZnCl2, >95%
for Ta alkylidene complexes.3 Many examples of C-H
activation reactions of a NMe2 moiety (route ii) have
been reported for Zr,5 Ta,6,7 and W8 complexes. After a
second R-C-H activation reaction the azamolybdena-
cyclopropane ring could be converted to a molybdenum
alkylidene compound as shown for analogous tantalum7
and tungsten8 complexes. A new approach, explored in
the present study, is the introduction of additional, R-H
hydrogen-containing alkyl groups (or alkyl/aryl groups
that can easily abstract an R-H) on the molybdenum
center via formation of the corresponding lithium mo-
lybdates (route iii).
yield. ii: LiR (R ) n-Bu, CH2SiMe3, p-tolyl, Et2O, -LiCl or
RMgCl (R ) Et), THF, -MgCl2, >90% yield. iii: MeMgCl,
THF, -MgCl2, 96% yield. iv: R′Li (R′ ) Me, n-Bu, p-tolyl),
THF/DME, -78 °C, >70% yield. v: 1/2 [Li2(C-N)2], Et2O, -LiCl,
91% yield. vi: n-BuLi, toluene. vii: Thermal activation reaction
strongly depending on the solvent, temperature, and R′.
Resu lts a n d Discu ssion
Syn th esis of Am in oa r yl Molybd en u m (VI) Com -
p lexes. The novel molybdenum(VI) compound [Mo-
(NAr)2(C-N)Cl] (1) was obtained as a yellow solid in
almost quantitative yield by treatment of [Mo(NAr)2-
Cl2(DME)]4 (Ar ) C6H3(i-Pr)2-2,6), DME ) 1,2-dimethoxy-
ethane) with 0.5 equiv of [Zn(C-N)2]9 (C-N ) [C6H4-
(CH2NMe2)-2]-). The methyl-containing derivative
[Mo(NAr)2(C-N)(Me)] (2) was synthesized via trans-
metalation of compound 1 using MeMgCl. The molyb-
denum(VI) complexes [Mo(NAr)2(C-N)(Et)] (3), [Mo-
(NAr)2(C-N)(n-Bu)] (4), [Mo(NAr)2(C-N)(CH2SiMe3)]
(5), and [Mo(NAr)2(C-N)(p-tolyl)] (6) were obtained
using a similar synthetic route (Scheme 2).
Herein we report the synthesis, reactivity, and struc-
tural aspects of the Mo(VI) bis(imidoaryl) compounds
1-7, the organolithium molybdate(VI) compounds [Li-
(DME)Mo(NAr)2(C-N)(Me)(R′)] (R′ ) Me (8), n-Bu (9),
p-tolyl (10)), and a study of the possible C-H activation
reactions mentioned in Scheme 1. Unexpectedly odd-
electron organolithium molybdate(V) anions were formed
during the thermal activation of 8-10. The structure
in the solid state of one example, [LiMo(NAr)2(C-N)2]
(11), has been characterized by X-ray diffraction tech-
niques. Surprisingly, some of these odd-electron molyb-
date(V) compounds showed ROMP of norbornene after
dry air activation.
Compounds 1-6 are yellow solids that melt or de-
compose above 125 °C in an inert atmosphere. In air 1
(Cl) decomposes within several hours (similar to that
found for [Mo(NAr)2(η2-C,N-NCN)Cl]10a with NCN )
[C6H3(CH2NMe2)2-2,6]-), while 2, 3, 4, and 6 are more
stable and decompose within several days. Compound
5 is stable in air for weeks. These materials are soluble
in the common polar and aromatic solvents, but 1 and
2 have limited solubility in pentane or hexanes.
(5) Bertuleit, A.; Fritze, C.; Erker, G.; Fro¨hlich, R. Organometallics
1997, 16, 2891-2899.
(6) Abbenhuis, H. C. L.; van Belzen, R.; Grove, D. M.; Klomp, A. J .
A.; van Mier, G. P. M.; Spek, A. L.; van Koten, G. Organometallics
1993, 12, 210.
(7) de Castro, I.; Galakhov, M. V.; Gomez, M.; Gomez-Sal, P.; Royo,
P. Organometallics 1996, 15, 1362-1368.
(8) Brandts, J . A. M.; Kruiswijk, E.; Boersma, J .; Spek, A. L.; van
Koten, G. To be published.
1
The H NMR spectra of 1-6 (C6D6) show for the i-Pr
ortho-substituents of the NAr ligands one septet and two
(9) Osman, A.; Steevensz, R. G.; Tuck, D. G.; Meinema, H. A.; Noltes,
J . G. Can. J . Chem. 1984, 62, 1698.

Organomolybdenum(VI) Complexes
Organometallics, Vol. 18, No. 14, 1999 2635
doublet resonances. In the 13C{1H} NMR spectra these
i-Pr groups appear as three separate resonances, indi-
cating that all four i-Pr groups are equivalent (isochro-
nous) but that the CMe2 groupings are diastereotopic.
These results show that these molecules lack an appar-
ent molecular symmetry plane containing the prochiral
(Me2)C centers. It is therefore significant that both the
benzylic and the dimethylamino groups of the ortho-
CH2NMe2 substituent appear as singlets over the whole
temperature range (220-330 K) studied. This can only
be rationalized either by a structure with Mo-N coor-
dination in which the prochiral benzylic C and (Me2)N
centers are residing in an apparent molecular symmetry
plane or when the C,N-ligand is η1-C-coordinated and
the NMe2 substituent undergoes rapid pyramidal inver-
sion at the N center as well as rotation around the C-N
1
bond (extensive discussions of the detection by H and
13C NMR of the various bonding possibilities of C,N- and
N,C,N-ligands have been reported).11
F igu r e 1. Thermal motion ellipsoid plot (ORTEP, at 50%
probability level) of the molecular structure of 2, together
with the adopted numbering scheme. Hydrogen atoms have
been omitted for clarity.
In the 1H NMR spectra of 2, 3, 4, and 5 the R-H
protons all appear between 0.95 and 1.76 ppm (1H NMR)
and 22.6 and 30 ppm (13C NMR), indicating that agostic
R-H- - -Mo interactions in the Mo-CH2R grouping are
absent.12 As compounds 1-6 have similar NMR fea-
tures, it can be assumed that these compounds have the
same structural characteristics.
Ta ble 1. Selected Geom etr ica l Deta ils for
[Mo(NAr )2(C-N)(Me)] (2)a a n d
[Li(DME)Mo(NAr )2(C-N)(Me)(p-tolyl)] (10)a
2
10
To get further insight in the molecular geometry of
1-6, a single-crystal X-ray structure determination of
one of them was carried out. Crystals were obtained for
2, and its molecular structure, with the adopted num-
bering scheme, is depicted in Figure 1, while selected
bond distances and angles are given in Table 1.
Compound 2 has the ligands arrayed in a distorted
square pyramidal geometry around the metal center
(73.1% along the Berry-pseudorotation coordinate from
trigonal bipyramid to square pyramid). One imido
ligand occupies the apical position N(3), while the N
atom N(2) of the second imido group resides in the basal
plane. The metal lies slightly above the basal plane
defined by C(101), N(1), N(2), and the methyl group
C(4). The Mo-C(4) distance is rather large (this bond
in other molybdenum alkyl complexes lies in the range
2.08-2.20 Å).10 The (dimethylamino)methyl substituent
is indeed coordinating to the molybdenum center.
Although the solid-state structure of 2 shows η2-C,N-
coordination to the molybdenum center, the NMR data
suggest fluxional behavior in solution.
Bond Lengths (Å)
2.176(2)
Mo-C(101)
Mo-C(4)
2.239(4)
2.177(2)
Mo-C(401)
Mo-C(5)
2.216(4)
2.195(6)
Mo-N(1)
2.383(2)
1.7495(13)
1.773(2)
1.386(3)
1.401(4)
Mo-N(2)
1.770(4)
1.772(4)
1.382(6)
1.397(6)
2.012(10)
1.993(9)
2.074(10)
Mo-N(3)
C(201)-N(2)
C(301)-N(3)
Li(1)-O(1)
Li(1)-O(2)
Li(1)-N(1)
Bond Angles (deg)
136.61(12)
C(4)-Mo-C(101)
N(2)-Mo-N(3)
C(201)-N(2)-Mo
C(301)-N(3)-Mo
C(4)-Mo-N(1)
C(401)-Mo(1)-C(5)
C(5)-Mo(1)-C(101)
111.56(10)
176.58(17)
150.37(16)
82.12(10)
156.7(4)
174.1(3)
148.47(16)
79.07(15)
a
The estimated standard deviations of the last significant digits
are shown in parentheses.
According to their composition and structural fea-
tures, it was unlikely that 1-6 as such can be active as
ring-opening polymerization (ROMP) catalysts. At best
they can be seen as latent catalysts that need thermal
activation to create the active metal alkylidene moiety
via one of the routes shown in Scheme 1. Indeed 1-6
were inactive at room temperature, but from the fact
that also at higher temperatures no ROMP activity was
observed it has to be concluded that compounds 1-6
have a surprising thermal stability.
(10) (a) Brandts, J . A. M.; Gossage, R. A.; Boersma, J .; Spek, A. L.;
van Koten, G. To be published. (b) Casty, G. L.; Don Tilley, T.; Yap, G.
P. A.; Rheingold, A. L. Organometallics 1997, 16, 4746. (c) Bell, A.;
Clegg, W.; Dyer, P. W.; Elsegood, M. R. J .; Gibson, V. C.; Marshall, E.
L. J . Chem. Soc., Chem. Commun. 1994, 2547. (d) Bell, A.; Clegg, W.;
Dyer, P. W.; Elsegood, M. R. J .; Gibson, V. C.; Marshall, E. L. Ibid.
1994, 2247. (e) Vaughan, W. M.; Abboud, K. A.; Boncella, J . M. J .
Organomet. Chem. 1995, 485, 37. (f) Green, G. C.; Green, M. L. H.;
J ames, J . T.; Konidaris, P. C.; Maunder, G. H.; Mountford, P. J . Chem.
Soc., Chem Commun. 1992, 1361.
(11) (a) van Koten, G. Pure Appl. Chem. 1989, 61, 1681. (b) Rietveld,
M. H. P.; Grove, D. M.; van Koten, G. New J . Chem. 1997, 21, 751.
(12) Examples of related complexes showing R-H agostic interactions
are: (a) Poole, A. D.; Williams, D. N.; Kenwright, A. M.; Gibson, V. C.;
Clegg, W.; Hockless, D. C. R.; O’Neil, P. A. Organometallics 1993, 12,
2549. (b) Bell, A.; Clegg, W.; Dyer, P. W.; Elsegood, M. R. J .; Gibson,
V. C.; Marshall, E. L. J . Chem. Soc., Chem. Commun. 1994, 2547. (c)
Coles, M. P.; Gibson, V. C.; Clegg, W.; Elsegood, M. R. J .; Porrelli, P.
A. J . Chem. Soc., Chem. Commun. 1996, 1963.
F or m a tion of Molybd en u m (VI) An ion s. The in-
troduction of more R-H-containing (and bulkier) sub-
stituents on the molybdenum center might force R-H
elimination to occur with formation of the corresponding
molybdenum alkylidenes. To this end the various alkyl
derivatives were reacted with different alkyl- or aryl-
lithium reagents. For example, when 2 was treated with
equimolar amounts of an alkyl- or aryllithium reagent
in the presence of DME, bright yellow and very air-
sensitive compounds could be isolated (Scheme 2).

2636 Organometallics, Vol. 18, No. 14, 1999
Brandts et al.
The 1H and 13C{1H} NMR spectra and elemental
analysis of the products pointed to the selective forma-
tion of new compounds that contained in all cases the
organic groups originally present in the starting com-
pounds, as well as the new alkyl or aryl group (intro-
duced via LiR′). Moreover, DME quantities were in-
cluded that varied between 1 and 4 equiv per (C-N)
ligand.13 From these data it was concluded that rather
than molybdenum alkylidenes, new lithium molybdate-
(VI) compounds were synthesized and isolated as pure
compounds.
The dimethylmolybdate(VI) 8, its (methyl)(butyl)
analogue 9, and the (methyl)(p-tolyl) derivative 10 are
very soluble in polar solvents such as Et2O, THF, and
DME. As solids they all slowly decompose at room
temperature. Compound 8 is insoluble in benzene and
toluene, whereas 9 is slightly soluble in these solvents,
but decomposes in these solvents within 5 min. Al-
though 10 is stable for several hours in a benzene
solution at room temperature, it decomposes within half
an hour at 50 °C. During the decomposition reaction of
10 in a benzene solution a mixture of products is
formed.14 However, no toluene or C6H5CH2NMe2 could
be detected (NMR or GC-MS), which indicates that R-
or NMe2 C-H activation reactions (cf. routes i and ii in
Scheme 1) are not taking place.
F igu r e 2. Thermal motion ellipsoid plot (ORTEP, at 50%
probability level) of the molecular structure of 10, together
with the adopted numbering scheme. Hydrogen atoms and
a C6D6 solvent molecule have been omitted for clarity.
resonances, indicating the presence of inequivalent
1
imidoaryl ligands. The H NMR chemical shift values
of compound 10 are also strongly dependent upon the
amount of DME in the sample. From these NMR data
we were unable to establish the site of attack of the R′-
nucleophile, i.e. whether a new Mo-R′ bond had been
formed. Neither was it possible to clarify the position
of the lithium cation and the overall structure in
general. Fortunately, X-ray quality single crystals could
be obtained from the reaction mixture, and the molec-
ular structure of the (methyl)(p-tolyl)molybdate(VI)
derivative 10 (see Figure 2) in the solid state could be
elucidated. Important bond distances and angles are
given in Table 1.
The X-ray structure study shows that the (methyl)-
(p-tolyl)molybdenum(VI) compound 10 is a lithium
molybdate(VI) complex in which all of the introduced
organic and inorganic groups are bonded to the molyb-
denum(VI) center. The latter center is pentacoordinated
(54.9% along the Berry-pseudorotation coordinate from
trigonal bipyramid to square pyramid) and formally
carries a negative charge with a lithium positive coun-
terion. The lithium cation is bonded to the 2-(dimeth-
ylamino)methyl nitrogen atom N(1) and η6 to the p-tolyl
ligand, a phenomenon also observed for Lewis-base free,
σ-bonded lithium aryls with very bulky ortho-substitu-
ents.15 One chelate bonded DME molecule completes the
tetrahedral coordination sphere of the lithium atom. The
total amount of DME present in solid 10 is dependent
on the synthetic procedure followed. In general DME
amounts varying between 2 and 4 were observed (1H
NMR). Apparently, DME is incorporated differently in
the crystal lattice and the powder. The p-tolyl ligand
and methyl groups are virtually positioned trans with
respect to each other. The molybdenum alkyl and aryl
bond distances are slightly elongated compared to the
distances in the neutral compound 2, most likely
because of the influence of the trans ligands. Although
both molybdenum compounds 2 and 10 are formally 14-
electron species (the (NAr) ligands are counted as 4 e
donor ligands), the Mo(VI) center in 10 contains more
The 1H and 13C{1H} NMR spectra of 8 in THF-d8 show
singlet resonances at 294 K for the benzylic, NMe2, and
Mo-Me resonances (200-294 K), and as in the case of
the alkyl(C-N)Mo(VI) compounds, no conclusion about
the actual binding mode of the C,N-ligand in the
molybdate complexes could be drawn. At room temper-
ature the same spectral characteristics are found for the
(methyl)(butyl) derivative 9 in THF-d8. However, on
cooling the solution to 230 K, the benzylic protons start
to decoalesce, whereas the other resonances remain
unchanged. The 1H and 13C{1H} NMR spectra of the
p-tolyllithium adduct 10 in THF-d8 show singlet reso-
nances at 294 K for the benzylic, NMe2, and Mo-Me
resonances (200-294 K). No kinetic parameters for the
dynamic solvent- and temperature-dependent NMR
behavior of 10 were collected. However, the 1H NMR
spectra of 10 in toluene-d8 show a clear AB pattern for
the benzylic protons and a broad singlet resonance for
the (dimethylamino)methyl substituent of the (C-N)
ligand. This resonance further decoalesced, yielding two
separate singlet resonances upon cooling the sample
(-10 °C) in toluene-d8; that is, as a result of solvent-
solute interactions in toluene-d8, the η2-C,N-bonding of
the C,N-ligand became detectable. The diastereotopicity
of the protons of the CH2 group indicated already that
10 lacks a molecular symmetry plane containing both
the (H2)C and (Me2)N centers. The fact that also the
NMe2 grouping becomes diastereotopic at temperatures
below -10 °C is proof for M-N coordination (M ) Mo
or Li). Moreover, the 1H NMR shows two separate septet
(13) The amount of DME found in the lithium molybdates was
strongly dependent upon the source of lithium reagent and workup
procedure and could only partly be removed by evaporation.
(14) When the lithium molybdates 8-10 were thermally activated,
NMR and ESR of the resulting reaction mixtures always showed the
presence of Mo(V) complexes and a number of [Mo(NAr)2(C-N)R]
compounds resulting from ligand exchange reactions. When 8 was
heated, always small amounts of 2 were found. When 9 was heated,
always small amounts of 2 and 4 were found and small amounts of
1-butene were detected as a result of â-H elimination reacions. When
10 was heated, always small amounts of 2 and 6 were found.
(15) Wehmschulte, R. J .; Power, P. P. J . Am. Chem. Soc. 1997, 119,
2847-2852, and references therein.

Organomolybdenum(VI) Complexes
Organometallics, Vol. 18, No. 14, 1999 2637
Ta ble 2. Th er m a l Activa tion of Lith iu m
Molybd a tes Dep en d in g on Solven t a n d
Tem p er a tu r ea
compound
R′
Me
solvent
T (°C)a
8
THF
50
toluene
THF
insol.
80
9
n-Bu
toluene
THF
<25
80
10
p-tolyl
toluene
50
a
Temperature required to decompose half of the amount of the
lithium molybdate in 1 h.
anionic ligands. As a result, the Mo(VI) center in 10 is
much less electrophilic than in 2. Another rare example
of an “ate” structure ([Li(DME)Mo(NAr)(dCHCMe2Ph)-
(OCMe(CF3)2)(OTf)2]) has recently been reported by
Schrock and co-workers.16 Finally it is noteworthy that
compound 10 can also be made by reacting compound
6 with MeLi under similar conditions.
For m ation of P ar am agn etic Molybden u m (V) An -
ion s. Lithium molybdate compounds 8-10 are stable
as solids at temperatures below 0 °C and do not undergo
R-H elimination reactions to give Mo(VI) alkylidene
species upon heating the samples in different solvents.
Instead, thermal activation of 8-10 generates para-
magnetic molybdenum(V) species (see vii, Scheme 2) at
different temperatures, while the onset of this conver-
sion is strongly solvent dependent; see Table 2.
At the onset temperature the solution of the com-
plexes changes in color from yellow/orange to dark
brown. Spectroscopic characterization of these clear
brown solutions by NMR showed only very broad peaks,
pointing to the presence in solution of DME, diamag-
netic molybdenum(VI) compounds,14 and paramagnetic
species. This conclusion was corroborated by the EPR
measurements of solutions of these compounds, which
revealed the presence of paramagnetic molybdenum
species with splitting patterns and g-values character-
istic for molybdenum(V) compounds.17
All the products obtained from the thermal activation
reactions (Table 2) are brown, air-sensitive oils. There-
fore, we have investigated the synthesis of molybdenum
bis(imidoaryl) compounds that contain additional donor
ligands in an attempt to structurally stabilize the
paramagnetic product. The synthesis of [Mo(NAr)2(C-
N)2] (7) can be performed by treatment of 1 with 0.5
equiv of [(Li2(C-N)2] or by reacting [Mo(NAr)2Cl2(DME)]
with 1 equiv of [(Li2(C-N)2] (see Scheme 2). The
resulting red crystalline solid (7) is thermally (>200 °C)
and air stable and can be obtained in almost quantita-
tive yield from both reactions. When this bis(aryl)-
molybdenum(VI) compound 7 is reacted with 1 equiv of
n-BuLi in toluene at room temperature, crystals suitable
for single-crystal X-ray analysis of a reaction product
(11) can be obtained (32% yield). The crystal structure
contains two independent molecules in the unit cell (Z
) 4). Both molecules have the ligands arrayed very
similarly. Although the bond distances and angles are
F igu r e 3. Thermal motion ellipsoid plot (ORTEP, at 50%
probability level) of one of the two independent molecular
structures of 11, together with the adopted numbering
scheme. Hydrogen atoms have been omitted for clarity.
different (listed in Table 3), only one (molecule 1) is
depicted in Figure 3.
The solid-state structure of the lithium diarylmolyb-
date(V) (11) compounds comprises two (C-N) ligands,
which each bridge via Cipso of the C-N ligand between
the molybdenum and the lithium center. Both Mo and
Li have a distorted tetrahedral coordination. The Li-N
coordination of the two nitrogen atoms of the (C-N)
ligands renders the lithium four-coordinate and thereby
probably helps to stabilize the complex. Possibly crystal-
packing forces can explain the formation of two inde-
pendent molecules. A similar type of bridging mode of
a (C-N) ligand has been observed in related lithium-
zincates18a and tantalum(V)-zinc18b complexes. Com-
pound 11, being an 13-electron molybdate(V) species,
can be considered as a persistent organometallic radical.
It is very reactive toward electrophiles, e.g., O2, but is
unreactive with linear alkenes.
During the reaction of 7 with n-BuLi the formation
of amounts of 1-butene, which must result from â-H
elimination reactions, was detected. This indicates that
at least some of the n-butyl nucleophiles were bonded
to the Mo center. Because the amounts of 1-butene
found were not quantitative, it cannot be ruled out that
this â-H elimination, which will give Mo-H19 complexes,
is the only pathway leading to the formation of 11.
Alternative routes involve direct butyl radical forma-
tion20 after Mo-C bond cleavage or innersphere single
electron transfer between 7 and n-BuLi clusters.21
(18) (a) Rijnberg, E.; J astrzebski, J . T. B. H.; Boersma, J .; Kooijman,
H.; Veldman, N.; Spek, A. L.; van Koten, G. Organometallics 1997,
16, 2239. (b) Rietveld, M. H. P.; Lohner, P.; Nijkamp, M. G.; Grove, D.
M.; Veldman, N.; Spek, A. L.; Pfeffer, M.; van Koten, G. Chem. Eur. J .
1997, 3, 817.
(19) We were unable to detect traces of “Mo-H” species during the
process of â-H elimination (monitored by NMR), probably due to the
instability of the Mo-H bond.
(20) After the reaction all volatiles were collected in a cold trap, and
the mixture was analyzed by NMR and GC-MS. We were unable to
detect any products arising from butyl radicals, even when the reaction
was carried out in the presence of a radical trap like TEMPO.
(21) (a) Tamura, M.; Kochi, J . K. J . Am. Chem. Soc. 1971, 93, 1487.
(b) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th
ed., 1988; pp 1306-1315.
(16) Schrock, R. R.; Luo, S.; Lee, J . C.; Zanetti, N. C.; Davis, W. M.
J . Am. Chem. Soc. 1996, 118, 3883.
(17) (a) Balagopalakrishna, C.; Kimbrough, J . T.; Westmoreland, T.
D. Inorg. Chem. 1996, 35, 7758. (b) Legzdins, P.; Sayers, S. F.
Organometallics 1996, 15, 3907. (c) Barnard, K. R.; Bruck, M.; Huber,
S.; Grittini, Enemark, J . H.; Gable, R. W.; Wedd, A. G. Inorg. Chem.
1997, 36, 637.

2638 Organometallics, Vol. 18, No. 14, 1999
Ta ble 3. Selected Geom etr ica l Deta ils for [LiMo(NAr )2(C-N)2] (11)a
molecule 1 molecule 2
Brandts et al.
Bond Lengths (Å)
Mo(1)-C(101)
Li(2)-C(101)
Li(2)-N(1)
Mo(1)-N(3)
N(3)-C(301)
2.159(5)
2.361(11)
2.002(7)
1.770(5)
1.375(7)
Mo(2)-C(201)
Li(1)-C(201)
Li(1)-N(2)
Mo(2)-N(4)
N(4)-C(401)
2.129(6)
2.401(12)
1.996(7)
1.772(4)
1.396(6)
Bond Angles (deg)
Mo(1)-C(101)-Li(2)
N(1)-Li(2)-N(1a)
C(101)-Li(2)-C(101a)
C(101)-Mo(1)-C(101a)
Mo(1)-N(3)-C(301)
79.3(3)
143.4(8)
94.5(5)
106.84(19)
162.3(4)
Mo(2)-C(201)-Li(1)
N(2)-Li(1)-N(2b)
C(201)-Li(1)-C(201b)
C(201)-Mo(2)-C(201b)
Mo(2)-N(4)-C(401)
80.9(3)
142.2(9)
91.1(6)
107.2(2)
165.1(4)
a
Comparable bonds lengths and angles in molecules 1 and 2 are combined on one line. The estimated standard deviations of the last
significant digits are shown in parentheses.
F igu r e 4. ROMP activity measured on varying [O2].
Attempts to isolate the precursor of 11, i.e., the
lithium molybdate(VI) complex [Li(DME)nMo(NAr)2(C-
N)2(n-Bu)] by reaction of 7 with n-BuLi in THF/DME
or DME solutions, failed because n-BuLi reacts with
these solvents before the target product is formed.
Likewise, the use of other strongly coordinating mol-
ecules such as tetramethylethylenediamine was unsuc-
cessful.
Dr y Air Activa tion . As no evidence was found for
direct alkylidene formation, i.e., R-H elimination does
not take place (cf. route iii in Scheme 1), it was
surprising to find ROMP activity when the in situ
prepared Mo(V) compounds were activated by bubbling
dry air (air passed over a NaOH(s) column) through the
solution in the presence of norbornene or norbornene
derivatives. No ROMP activity was found when nor-
bornene was mixed with 2, the lithium molybdate(VI)
compounds derived from it, or the corresponding lithium
molybdate(V) derivatives without dry air activation. The
addition of 3 equiv of O2 (∼21% v/v of the dry air used
is O2)22 resulted in the highest ROMP activity (see
Figure 4). The polymerization of norbornene was fol-
lowed in time employing the in situ prepared catalyst
system (2 with 1 equiv of n-BuLi in toluene) by GC (see
F igu r e 5. Concentration of free norbornene as measured
over time by GC.
Figure 5), and the resulting polynorbornene was char-
acterized by gel permeation chromatography (GPC) and
1H NMR.
After the addition of the catalyst solution was com-
plete, slow polymerization was observed initially, but
this activity ceased after approximately 10 min. How-
ever, most noteworthy is the dramatic effect of the
addition of dry air to the reaction mixture. The addition
of 3 equiv of O2 (from dry air) caused rapid polymeri-
zation, and within 20 min stirring problems occurred
because of the greatly increased viscosity of the solution.
The polymerization reaction was stopped by the addition
of methanol, and the polymer was subsequently isolated.
Analysis showed high molecular weight polynorbornene
with a high polydispersity (MW ) 953 000 g/mol, PDI
) 2.63, and 91% cis-double bonds in polynorbornene).
Although O2 activation has been reported earlier in
the literature for tungsten and molybdenum complexes23
(often in combination with aluminum compounds), its
role in the catalytic system employed here is still
unclear. As indicated by the high molecular weight of
the polynorbornene thus produced, only a small per-
centage of the catalyst actually participates in the
polymerization. We believe that the very high propaga-
(22) CRC Handbook of Chemistry and Physics, 76th ed.; Lide, D.
R., Ed.; CRC Press, Inc.: Boca Raton, FL, 1995; pp 14-14.

Organomolybdenum(VI) Complexes
Organometallics, Vol. 18, No. 14, 1999 2639
of a yellow product (pure by NMR and elemental analysis).
The complex can be recrystallized by cooling a Et2O solution
of 2 to -30 °C. H NMR (δ): 7.98 (d, 1, o-aryl-H), 7.06 (m, 8,
tion rate with respect to initiation rate using norbornene
derivatives is a contributing factor to the small number
of catalytic particles that are active in the polymeriza-
tion reaction.
1
NAr-H + ArH), 6.88 (t, 1, p-aryl-H), 3.84 (s, 2, CH2), 3.79
(sept, 4, CHMe2), 2.30 (s, 6, NMe2), 1.13 (d, 12, CHMe2), 1.12
(d, 12, CHMe2), 1.12 (s, 3, Mo-Me). 13C NMR (δ): 179.8 (Cipso),
152.5 (Cipso NAr), 147.3, 144.5, 143.1, 143.4, 126.5, 125.9, 123.0,
122.8 (aryl-C), 74.0 (CH2), 48.9 (NMe2), 28.4 (CHMe2), 24.2
(CHMe2), 23.4 (CHMe2), 23.4 (Mo-Me).27 Tmelt >188 °C.
Elemental Anal. (Calcd) for C34H49MoN3: C, 68.57 (68.55); H,
8.21 (8.29); N, 6.79 (7.05).
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were carried out under
an atmosphere of dry and deoxygenated dinitrogen using
standard Schlenk techniques unless otherwise stated. All
solvents were carefully dried and distilled from sodium under
nitrogen, prior to use, except CH2Cl2, which was distilled from
[Mo(NAr )2(C-N)(Et)] (3). To a clear yellow solution of 1
(0.71 g, 1,15 mmol) in 60 mL of THF was added 0.39 mL of a
freshly prepared THF solution of EtMgBr (0.39 mL, 1.5 M,
0.58 mmol) at 0 °C. The reaction mixture was allowed to warm
to room temperature. After 17 h the reaction was complete.
All volatiles were removed in vacuo. The residual yellow solids
was extracted with pentane (3 × 50 mL). The collected pentane
fraction were concentrated to 20 mL. After several days at -30
°C, 0.31 g (0.51 mmol) of yellow crystals of compound 3 could
1
CaH2. The H (300 MHz) and 13C{1H} (75 MHz) NMR spectra
were recorded in benzene-d6 at room temperature unless
otherwise indicated. Chemical shifts (in ppm) are referenced
to Me4Si. GC measurements were performed on a Philips PU
4600 gas chromatograph with a J . & W. Scientific 30 m × 0.320
mm, 0.25 µm film thickness and liquid-phase DB-5 column.
GPC measurements were taken on a J ordi-Gel DVB mixed bed,
300 mm and i.d. 7.8 mm column, using a Thermo Separation
Products P200 pump and UV2000 and Shodex RI-71 detectors.
EPR spectra were recorded in toluene at room temperature
on a Varian E-9 EPR spectrometer. Elemental analyses were
carried out by Dornis und Kolbe, Mikroanalytisches Labora-
torium, Mu¨lheim a.d. Ruhr, Germany. Commercially available
reagents were distilled prior to use. [Mo(NAr)2Cl2(DME)],4 [Zn-
(C-N)2],9 [Li(p-tolyl)],24 [LiCH2SiMe3],25 and [Li2(C-N)2]26 were
synthesized according to literature procedures. Elemental
analyses were carried out by Dornis und Kolbe, Mikroana-
lytisches Laboratorium, Mu¨lheim a.d. Ruhr, Germany.
[Mo(NAr )2(C-N)Cl] (1). To an Et2O/benzene (70 mL/30
mL) solution of [Mo(NAr)2Cl2(DME)] (1.92 g, 3.16 mmol) was
added a solution of [Zn(C-N)2] (0.53 g, 1.60 mmol) in Et2O
(20 mL) at ambient temperature. After the addition was
complete, the mixture was stirred overnight. After 17 h, all
volatiles were removed in vacuo (3 h; 60 °C). The residual
orange solids were extracted with benzene (2 × 80 mL), and
after centrifugation the benzene layers were collected. All
volatiles were removed in vacuo, leaving behind 1.85 g (95%)
of a yellow product (compound 1) which was pure by NMR and
elemental analysis. The complex can be recrystallized by
1
be isolated from the solution (2 crops). Yield: 88%. H NMR
(330 K) (δ): 7.98 (d, 1, o-aryl-H), 7.10-6.98 (m, 8, NAr-H +
ArH), 6.92 (t, 1, p-aryl-H), 3.87 (sept, 4, CHMe2), 3.82 (s, 2,
CH2), 2.32 (s, 6, NMe2), 1.97 (t, 3, CH2CH3), 1.76 (q, 2, CH2-
CH3), 1.14 (d, 12, CHMe2), 1.10 (d, 12, CHMe2). 13C NMR (300
K) (δ): 180.3 (Cipso), 152.1 (Cipso NAr), 147.3, 144.7 (broad),
144.0, 126.3, 125.8, 123.0, 122.8 (aryl-C), 74.0 (CH2N), 49.0
(NMe2), 45.7 (Mo-CH2CH3), 28.3 (CHMe2), 24.0 (CHMe2), 20.7
(Mo-CH2CH3). Tdecomp ) 162 °C. Elemental Anal. (Calcd) for
C
35H51MoN3. Found: C, 68.86 (68.94); H, 8.48 (8.43); N, 6.77
(6.89).
[Mo(NAr )2(C-N)(n -Bu )] (4). A synthetic procedure similar
to that described for 3 was used. Only n-BuLi was used and
1
was added to 1 at -78 °C in Et2O. Yield: 57% yield. H NMR
(320 K) (δ): 7.99 (d, 1, o-aryl-H), 7.10-6.99 (m, 8, NAr-H +
ArH), 6.90 (t, 1, p-aryl-H), 3.87 (sept, 4, CHMe2), 3.82 (s, 2,
CH2), 2.33 (s, 6, NMe2), 2.22 (m, 2, CH2CH2CH2CH3), 1.74 (m,
2, CH2CH2CH2CH3), 1.47 (sextet, 2, CH2CH2CH2CH3), 1.15 (d,
12, CHMe2), 1.11 (d, 12, CHMe2), 0.96 (t, 3, CH2CH2CH2CH3).
13C NMR (320 K) (δ): 180.3 (Cipso), 152.2 (Cipso NAr), 147.2,
144.7 (broad), 143.8, 126.3, 125.9, 123.0, 122.8 (aryl-C), 74.1
(CH2N), 52.6 (CH2CH2CH2CH3), 49.1 (NMe2), 38.3 (CH2CH2-
CH2CH3), 29.9 (CH2CH2CH2CH3), 28.2 (CHMe2), 23.9 (CHMe2),
13.7 (CH2CH2CH2CH3). Tdecomp ) 125 °C. Elemental Anal.
(Calcd) for C37H55MoN3: C, 69.68 (69.76); H, 8.69 (8.61); N,
6.59 (6.51).
1
cooling an Et2O solution of 1 to -30 °C. H NMR (δ): 7.83 (d,
1, o-aryl-H), 7.03 (m, 8, NAr-H + ArH), 6.80 (t, 1, p-aryl-
H), 3.85 (s, 2, CH2), 3.78 (sept, 4, CHMe2), 2.61 (s, 6, NMe2),
1.12 (d, 12, CHMe2), 1.10 (d, 12, CHMe2). 13C NMR (δ): 176.9
(Cipso), 152.5 (Cipso NAr), 147.2, 145.2, 143.1, 142.5, 129.3, 127.0,
123.5, 122.9 (aryl-C), 72.1 (CH2), 48.7 (NMe2), 28.7 (CHMe2),
24.2 (CHMe2), 23.5 (CHMe2). Tmelt > 200 °C. Elemental Anal.
(Calcd) for C33H46ClMoN3: C, 64.41 (64.33); H, 7.50 (7.53); N,
6.75 (6.82).
[Mo(NAr )2(C-N)(CH2Si(CH3)3)] (5). A synthetic proce-
dure similar to that described for 3 was used. Only LiCH2Si-
(CH3)3 (0.11 g, 1.15 mmol) was used and was added to 1 at
1
-78 °C in Et2O. Yield: 80%. H NMR (δ): 8.04 (d, 1, o-aryl-
H), 7.04 (m, 8, NAr-H + ArH), 6.92 (t, 1, p-aryl-H), 3.82 (sept,
4, CHMe2), 3.75 (s, 2, CH2), 2.34 (s, 6, NMe2), 1.15 (d, 12,
CHMe2), 1.07 (d, 12, CHMe2), 0.95 (s, 2, Mo-CH2), 0.24 (s, 9,
Si(CH3)3). 13C NMR (δ): 179.7 (Cipso), 152.5 (Cipso NAr), 147.6,
144.7, 143.7, 126.3, 126.2, 123.4, 123.0 (aryl-C), 73.2 (CH2),
49.5 (NMe2), 39.0 (CHMe2), 28.0 (CHMe2), 24.3 (CHMe2), 22.6
(MoCH2), 3.4 (Si(CH3)3). Tmelt > 200 °C. Elemental Anal.
(Calcd) for C37H57MoN3Si: C, 66.65 (66.54); H, 8.67(8.60); N,
6.21 (6.29).
[Mo(NAr )2(C-N)(Me)] (2). To a solution of 1 (0.85 g, 1.38
mmol) in THF was carefully added 0.48 mL (1.44 mmol) of a
3 M solution of MeMgCl (THF) at -30 °C. After the addition
was complete, the reaction mixture was warmed to room
temperature. After 4 h, all volatiles were removed in vacuo (3
h; 60 °C). The residual orange solids were extracted with Et2O
(2 × 80 mL), and the Et2O layers were collected following
centrifugation. The Et2O was evaporated, yielding 1.86 g (96%)
[Mo(NAr )2(C-N)(p-tolyl)] (6). To a solution of 1 (2.21 g,
3.59 mmol) in 50 mL of Et2O and 50 mL of benzene was added
dropwise 0.35 g (3.59 mmol) of [Li(p-tolyl)] in Et2O at -78 °C.
After the addition was complete, the mixture was warmed to
room temperature. After 4 h the precipitate was separated
from the clear solution by centrifugation. The residual pre-
cipitate was washed with Et2O (20 mL), and the Et2O/benzene
layers were combined. The volatiles were removed in vacuo,
(23) (a) Bilhou, J . L.; Mutin, R.; Leconte, M.; Basset, J . M. Recl.
Trav. Chim. Pays-Bas 1977, 96, M5. (b) Bilhou, J . L.; Basset, J .
M.Mutin, R.; Graydon, W. F. J . Am. Chem. Soc. 1977, 99, 4083. (c)
Vanderyse, L. M., Verdonck, L.; Bossuyt, A. R.; Van Wijnsberghe, F.
M. G.; van der Kelen, G. P. Bull. Soc. Chim. Belg. 1988, 97, 317. (d)
Vanderyse, L. M.; Haemers, T.; Bossuyt, A. R.; Verdonck, L.; van der
Kelen, G. P. Ibid. 1988, 97, 723. (e) van Ruyskensvelde, S.; Bossuyt,
A. R.; Haemers, T.; Verdonck, L. Ibid. 1988, 104, 401.
(24) [Li(p-tolyl)] was synthesized from [C6H4I-4] and n-BuLi in
toluene.
(25) Sommer, L. H.; Mitch, F. A.; Goldberg, G. M. J . Am. Chem.
Soc. 1949, 71, 2746.
(26) J astrzebski, J . T. B. H.; van Koten, G. Inorg. Synth. 1989, 26,
152.
(27) The 13C{1H} NMR Mo-Me resonance in compound 2 (C6D6) is
exactly situated under a CHMe2 peak (23.4 ppm), which was proven
by 1H-13C 2D heteronuclear NMR measurements.

2640 Organometallics, Vol. 18, No. 14, 1999
Brandts et al.
leaving a yellow crystalline material that was washed with
40 mL of pentane. The pentane solution was removed, and
the residual yellow precipitate was dried in vacuo. This
afforded 1.74 g (2.59 mmol, 72% yield) of a yellow microcrys-
talline material, which was pure by NMR and elemental
analysis. The pentane layer afforded another 0.22 g of crystal-
line compound 6. Total yield: 81%. 1H NMR (δ): 8.24 (d, 1,
o-aryl-H), 7.96 (d, 2, o-tolyl-H), 7.05 (m, 11, NAr-H + ArH
+ m-tolyl-H),), 4.03 (sept, 4, CHMe2), 3.83 (s, 2, CH2), 2.19
(s, 3, tolyl-Me), 2.10 (s, 6, NMe2), 1.14 (d, 12, CHMe2), 1.06
(d, 12, CHMe2). 13C NMR (δ): 180.1 (Cipso), 176.9 (Cipso-tolyl),
153.1 (Cipso NAr), 148.5, 144.7, 144.6, 143.4, 135.6, 135.5, 128.4,
128.1, 126.4, 126.2, 123.6, 123.1 (aryl-C), 72.9 (CH2), 49.6
(NMe2), 28.2 (CHMe2), 24.6 (CHMe2), 24.2 (CHMe2), 21.4
(tolyl-CH3). Tdecomp ) 192 °C. Elemental Anal. (Calcd) for
solution was concentrated to a volume of 10 mL. To the reddish
oil, 50 mL of cold pentane was added, the mixture was stirred
vigorously, and a yellow precipitate appeared. The yellow
solution was decanted from the yellow precipitate, and the
precipitate was washed with cold pentane (3 × 50 mL). The
precipitate was dried in vacuo, and the residue was extracted
with cold Et2O (2 × 30 mL). The Et2O layers were collected
and concentrated to a volume of 50 mL. After 3 days yellow
air-sensitive crystals (0.74 g, 0.88 mmol, 71% yield) could be
isolated at -30 °C. 1H NMR (δ in THF-d8, 294 K): 7.52 (dd, 1,
o-aryl-H), 7.22 (dd, 1, m-aryl-H), 6.79 (m, 4, NAr-H + ArH),
6.60 (m, 4, NAr-H + ArH), 4.07 (sept, 2, CH(CH3)2), 4.06 (sept,
2, CH(CH3)2), 3.57 (s, 2, CH2), 3.41 (s, 8, CH2O), 3.25 (s, 12,
OCH3), 2.17 (s, 6, N(CH3)2), 1.94 (m, 2, MoCH2CH2CH2CH3),
1.71 (m, 2, MoCH2CH2CH2CH3), 1.46 (m, 2, MoCH2CH2CH2-
CH3), 1.07 (4 × d, 4 × 6, CH(CH3)2), 0.71 (s, 3, Mo-CH3) 0.63
(t, 3, MoCH2CH2CH2CH3). 13C NMR (δ in THF-d8, 294 K):
202.8 (Cipso C-N), 154.1 (Cipso NAr), 153.3 (Cipso NAr), 141.6,
140.0, 137.0, 133.0, 123.5, 121.8, 120.2, 120.1, 120.0, 118.8,
117.7 (C-Ar), 70.9 (OCH3), 67.3 (CH2), 57.0 (CH2O), 44.5
(N(CH3)2), 41.5 (MoCH2CH2CH2CH3), 35.9 (MoCH2CH2CH2-
CH3), 28.4 (MoCH2CH2CH2CH3), 26.2, 26.0 (CH(CH3)2), 23.2,
23.0, 22.7, 22.7, (CH(CH3)2), 20.7 (Mo-CH3), 12.6 (MoCH2CH2-
C
40H53MoN3: C, 71.62 (71.51); H, 7.99 (7.95); N, 6.18 (6.25).
[Mo(NAr )2(C-N)2] (7). To a clear red solution of [Mo-
(NAr)2Cl2(DME)] (1.70 g, 2.80 mmol) in 80 mL of Et2O was
added [Li2(C-N)2] (0.79 g, 2.80 mmol) as a solid at room
temperture. After 18 h the reaction was complete. All volatiles
were removed in vacuo (3 h, 50 °C). The residual precipitate
was extracted with Et2O (30 mL) and separated from the solids
by centrifugation. The residual solids were extracted with CH2-
Cl2 (80 mL), and the CH2Cl2 layer was collected after centrifu-
gation. All volatiles were removed in vacuo, leaving a red
crystalline solid (1.83 g, compound 7: 91% yield) which was
pure by NMR and elemental analysis. 1H NMR (δ): 8.39 (d,
2, o-aryl-H), 7.04 (m, 12, NAr-H + ArH), 4.27 (sept, 4,
CHMe2), 3.62 (d, 2, 2J H )13.8 Hz, CHaHbN), 3.34 (d, 2, 2J H
CH2CH3). Tdecomp < 20 °C. Elemental Anal. (Calcd) for C46H78
-
LiMoN3O4: C, 65.65 (65.77); H, 9.42 (9.36); N, 4.87 (5.00).
[Li(DME)nMo(NAr )2(C-N)(p-tolyl)] (10). To a DME/THF
(30 mL/50 mL) solution of 2 (0.88 g, 1.48 mmol) was added a
THF solution (20 mL) of 0.15 g of [Li(p-tolyl)] (1.53 mmol) at
-78 °C. The mixture was allowed to warm to room tempera-
ture. After 12 h the reaction was complete, and the clear yellow
solution was concentrated to a volume of 10 mL. To the reddish
oil, 50 mL of pentane was added, the mixture was stirred
vigorously, and a yellow precipitate appeared. The yellow
solution was decanted from the yellow precipitate, and the
residual precipitate was washed with cold pentane (3 × 50
mL). The precipitate was dried in vacuo, leaving an air-
sensitive, yellow powder (1.00 g, 1.27 mmol, 86% yield) that
was pure by NMR and elemental analysis. Crystals suitable
for X-ray analysis were grown in a saturated C6D6 solution at
15 °C within 24 h. 1H NMR (δ in toluene-d8): 8.52 (d, 1, o-aryl-
H), 8.05 (d, 2, o-tolyl-H), 7.04 (m, 9, NAr-H + ArH), 6.67 (d,
H
H
b
a
b
a
)13.8 Hz, CHaHbN), 2.11 (s, 12, NMe2), 1.14 (d, 12, CHMe2),
1.04 (d, 12, CHMe2). 13C NMR (δ): 181.3 (Cipso), 153.4 (Cipso
NAr), 147.9, 143.1, 142.9, 126.6, 125.4, 125.2, 124.8, 123.7
(aryl-C), 70.2 (CH2), 50.7 (NMe2), 27.5 (CHMe2), 26.6 (CHMe2),
24.1 (CHMe2). Tmelt > 200 °C. Elemental Anal. (Calcd) for
C
42H58MoN4: C, 70.64 (70.56); H, 8.21 (8.18); N, 7.80 (7.84).
[Li(DME)2Mo(NAr )2(C-N)(Me)2] (8). Never let the tem-
perature exceed 0 °C during the synthesis of 8! To a DME/
THF (30 mL/50 mL) solution of 2 (0.83 g, 1.39 mmol) was
added 0.97 mL (1.55 mmol) of a 1.6 M solution of MeLi (Et2O)
at -78 °C. The mixture was allowed to warm to 0 °C. After 2
h, the reaction was complete, and the clear yellow solution was
concentrated to a volume of 10 mL. To the reddish oil was
added 50 mL of cold pentane, the mixture was stirred vigor-
ously, and a yellow, sticky precipitate appeared. The yellow
solution was decanted from the yellow precipitate, and the
residual precipitate was washed with cold pentane (3 × 50
mL). The precipitate was dried in vacuo, and the residue was
extracted with cold Et2O (2 × 30 mL). The Et2O layers were
collected and concentrated to a volume of 15 mL. A yellow/
brown oil precipitated from the solution and was isolated by
decantation of the upper layer. All volatiles were removed in
vacuo, leaving an air-sensitive, yellow powder (0.88 g, 1.10
mmol, 79% yield) that was pure by NMR and elemental
2, m-tolyl-H), 4.31 (sept, 2, CHMe2), 4.21 (d, 1, 2J H b)12.0
H
a
Hz, CHaHbN) 3.88 (sept, 2, CHMe2),3.08 (d, 1, 2J H
) 12.0
H
a
b
Hz, CHaHbN), 2.59 (s, 14, CH2O), 2.45 (s, 21, CH3O), 1.92 (s,
3, p-tolyl-CH3), 1.76 (s, 6, NMe2), 1.36 (d, 6, CHMe2), 1.31 (d,
6, CHMe2), 1.30 (s, 3, Mo-CH3), 1.16 (d, 6, CHMe2), 1.12 (d,
6, CHMe2). 1H NMR (δ in THF-d8, 294 K): 7.94 (dd, 1, o-aryl-
H), 7.23 (d, 2, o-(p-tolyl)-H), 7.05 (dd, 1, m-aryl-H), 6.80 (m,
4, NAr-H + ArH), 6.61 (m, 2, NAr-H + ArH), 6.51 (m, 4,
NAr-H + ArH),4.00 (sept, 4, CH(CH3)2), 3.56 (s, 2, CH2), 3.40
(s, 14, CH2O), 3.24 (s, 21, OCH3), 1.82 (s, 6, N(CH3)2), 1.04 (d,
12, (CH(CH3)2), 0.91 (s, 3, Mo-CH3), 0.89 (d, 12, CH(CH3)2).
13C NMR (δ in THF-d8, 294 K): 190.4 (Cipso C-N), 185.2
(Cipso p-tolyl), 153.3 (Cipso NAr), 144.2, 142.2, 141.2, 141.0,
135.1, 125.4, 124.1, 123.5, 121.9 120.2, 119.2 (C-Ar), 70.8
(OCH3), 66.0 (CH2), 57.1 (CH2O), 44.2 (N(CH3)2), 44.1 (p-tolyl-
CH3), 26.4 (CH(CH3)2), 26.3, 23.2 (CH(CH3)2), 19.7 (Mo-CH3).
Tdecomp < 20 °C. Elemental Anal. (Calcd) for C41H56LiMoN3-
(DME)3.5: C, 65.26 (65.46); H, 8.89 (9.09); N, 4.40 (4.16). 1H
NMR confirmed the presence of 3.5 equiv of DME.
[LiMo(NAr )2(C-N)2] (11). To a clear red solution of 6 (0.86
g, 1.21 mmol) in 50 mL of toluene was added 0.76 mL of n-BuLi
(1.6 M solution in pentane) at -78 °C. The reaction mixture
was allowed to warm to room temperature, and after 18 h all
volatiles were removed in vacuo. The sticky brown residue was
suspended in benzene (30 mL) and was filtered over Celite.
The clear benzene solution was concentrated to a volume of
10 mL. After 2 weeks dark crystals were growing in two crops
(0.28 g, 32%). The crystals showed no clear NMR spectrum
and are extremely sensitive toward air. EPR: concentration
) 8 mM, giso ) 1.974, Aiso ) 35 G (3420 G, 9.449 MHz, 1 G )
1
analysis. H NMR (δ in THF-d8, 294 K): 7.49 (dd, 1, o-aryl-
H), 7.23 (dd, 1, m-aryl-H), 6.81 (m, 4, NAr-H + ArH), 6.59
(m, 4, NAr-H + ArH), 4.04 (sept, 4, CH(CH3)2), 3.48 (s, 2,
CH2), 3.41 (s, 8, CH2O), 3.24 (s, 12, OCH3), 2.16 (s, 6, N(CH3)2),
1.10 (d, 12, (CH(CH3)2), 1.08 (d, 12, CH(CH3)2), 0.79 (s, 6, Mo-
CH3). 13C NMR (δ in THF-d8, 294 K): 203.3 (Cipso C-N), 154.1
(Cipso NAr), 153.7 (Cipso NAr), 141.0, 139.8, 136.4, 132.6, 124.0,
122.3, 120.1, 120.0, 118.7, 117.8, 117.7 (C-Ar), 70.8 (OCH3),
67.5 (CH2), 57.1 (CH2O), 44.5 (N(CH3)2), 26.4, 26.3 (CH(CH3)2),
23.0, 22.6, 22.4, 20.1 (CH(CH3)2), 13.9 (Mo-CH3). Tdecomp < 20
°C. Elemental Anal. (Calcd) for C43H72LiMoN3O4: C, 64.54
(64.73); H, 9.18 (9.10); N, 5.09 (5.27).
[Li(DME)2Mo(NAr )2(C-N)(n -Bu )] (9). Never let the tem-
perature exceed 0 °C during the synthesis of 9! To a DME/
THF (30 mL/50 mL) solution of 2 (0.74 g, 1.24 mmol) was
added 1.02 mL of a 1.21 M solution of n-BuLi (1.26 mmol) in
pentane at -78 °C. The mixture was allowed to warm to 0 °C.
After 2 h the reaction was complete, and the clear orange

Organomolybdenum(VI) Complexes
Organometallics, Vol. 18, No. 14, 1999 2641
Ta ble 4. Exp er im en ta l Da ta for th e X-r a y Diffr a ction Stu d ies of 2, 10, a n d 11
2
10
11
formula
fw
temp, K
cryst syst
space group
a (Å)
C
34H49MoN3
C45H66LiMoN3O2 (C6D6)
868.07
150
monoclinic
Cc
18.856(2)
C42H58LiMoN4
721.80
150
monoclinic
P2/c
19.594(3)
10.996(2)
23.335(7)
126.37(2)
3517.9(5)
595.70
150
monoclinic
P21/c
10.9411(6)
29.098(2)
11.700(2)
122.243(4)
3150.5(6)
4
b (Å)
c (Å)
13.751(3)
19.4151(14)
100.064(6)
4956.7(13)
4
â (deg)
volume (Å3)
Z
4
dcalcd (g cm-3
)
1.256
1.155
1.184
F(000) (electrons)
1264
0.4
0.33 × 0.35 × 0.35
Mo KR (0.71073)a
1.4, 27.5
1840
3.0
0.5 × 0.20 × 0.20
Mo KR (0.71073)a
1.8, 27.5
1532
0.4
0.05 × 0.50 × 0.50
Mo KR (0.71073)a
1.3, 23.0
µ(Mo KR) (cm-1
)
crystal size (mm)
radiation (Å)
θ
min,θmax(deg)
scan (ω-mode) (deg)
h; k; l (min, max)
total/unique reflns
obsd reflns
0.65 + 0.35 tan(θ)
-9,14; -37,37; -15,12
17516, 7235
5644 (I > 2.0σ(I))
7235, 354
0.0352; 0.0788; 1.04
σ2(Fo2) + (0.0308P)2 + 1.4579P
-0.50, 0.57
0.79 + 0.35 tan(θ)
-15,24; -14,17; -25,24
12075, 8350
6588 (I > 2.0σ(I))
8350, 537
0.0520; 0.0997; 1.02
σ2(Fo2) + (0.0349P)2
-0.71, 0.47
1.00 + 0.35 tan(θ)
-20,21; -12,12; -20,25
11224, 5637
3638 (I > 2.0σ(I))
5637, 444
0.0522; 0.1019; 1.01
σ2(Fo2) + (0.0257P)2
-0.41, 0.31
N
ref, Npar
R; wR; Sb
weight (w-1
)
c
min, max resd dens (e/Å3)
Graphite monochromated. R ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
c P ) (max(Fo2, 0) + 2Fc2)/3.
a
b
2
10-4 T). No nitrogen or lithium couplings were detected. No
satisfactory elemental analysis was obtained probably due to
partial oxidation caused by air leakage.
techniques (SHELXL93)31 using no observance criterion. Hy-
drogen atoms were included on calculated positions, riding on
their carrier atoms. All non-hydrogen atoms were refined with
anisotropic atomic displacement parameters. All hydrogen
atoms were refined with a fixed isotropic atomic displacement
parameter related to the value of the equivalent isotropic
atomic displacement parameter of their carrier atom. Weights
were optimized in the final refinement cycles. Neutral atom
scattering factors and anomalous dispersion corrections were
taken from the International Tables for Crystallography.32
Geometrical calculations and illustrations were performed with
PLATON.29 All calculations were performed on a DECstation
5000 cluster. Crystal data and numerical details of the
structure determinations and refinements are collected in
Table 4. Selected geometrical details of the structures of 2 and
10 are listed in Table 1 and for 11 in Table 3.
Gen er a l P olym er iza tion P r oced u r e. The catalyst system
was prepared in situ by dissolving 0.30 g of 2 (0.5 mmol) in
toluene (20 mL), to which 0.8 mL of a 1.6 M solution of n-BuLi
(0.5 mmol) was added at -30 °C. The reaction mixture was
allowed to warm to room temperature, was stirred overnight,
and was used as such. In a Schlenk vessel 13.4 mL of a 3.72
M norbornene solution in toluene (50 mmol) was brought
together with 3.61 g of mesitylene (30 mmol) and 63 mL of
toluene. The catalyst solution was added to this mixture
quickly, and the polymerization reaction was followed from
this point on. Samples of 1 mL were taken from the reaction
mixture and were mixed with 10 mL of methanol. The white
precipitate was removed by filtration, and the clear solution
was measured by GC. When the reaction was complete, the
solution was quenched with methanol, and the polymer was
precipitated from methanol, dried in vacuo, and analyzed by
NMR and GPC.
Str u ctu r e Deter m in a tion a n d Refin em en t of 2, 10, a n d
11. X-ray data were collected on an Enraf-Nonius CAD4-T
rotating anode diffractometer for a transparent, yellowish (2
and 10) or dark brown (11) crystal glued on top of a glass fiber.
Accurate unit-cell parameters and an orientation matrix were
determined by least-squares refinement of the setting angles
of a set of 25 well-centered reflections (SET4).28 The unit-cell
parameters were checked for the presence of higher lattice
symmetry. Data were corrected for Lorentz polarization effects.
An empirical absorption correction was applied (PLATON/
DELABS).29 The structures were solved by Direct methods and
subsequent difference Fourier techniques (SHELXS86).30 Re-
finement on F2 was carried out by full-matrix least-squares
Ack n ow led gm en t. J .A.M.B., J .B., and G.v.K. grate-
fully thank Dr. G. J . M. Gruter (DSM Research), Dr. J .
A. M. van Beek, Dr. F. H. van der Steen (Shell,
Amsterdam), and Dr. A. A. van der Huizen (Shell) for
the fruitful discussions. Financial support was granted
by the Dutch Technology Foundation (STW) with finan-
cial aid from the Council for Chemical Science of The
Netherlands/Organization for Scientific Research (NWO/
CW).
Su p p or tin g In for m a tion Ava ila ble: Tables of the struc-
ture determination, atomic coordinates, bond lengths and
angles, and thermal parameters for 2, 10, and 11. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM9900364
(28) Boer, J . L.; Duisenberg, A. J . M. Acta Crystallogr. 1984, A40,
C-410.
(29) Spek, A. L. Acta Crystallogr. 1990, A46, C-34.
(30) Sheldrick, G. M. SHELXS86. Program for crystal structure
determination; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(31) Sheldrick, G. M. SHELXL93. Program for crystal structure
refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(32) Wilson, A. J . C., Ed. International Tables for Crystallography;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C.