Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

Article abstract of DOI:10.1016/j.jorganchem.2008.11.047

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-me

Full text of DOI:10.1016/j.jorganchem.2008.11.047

Journal of Organometallic Chemistry 694 (2009) 649–654
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)
b
c
Ari Lehtonen a, , Hynek Balcar , Reijo Sillanpää
*
a Department of Chemistry, University of Turku, FIN-20014 Turku, Finland
b J. Heyrovsky´ Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 182 00 Prague 8, Czech Republic
c Department of Chemistry, University of Jyväskylä, FIN-40351 Jyväskylä, Finland
a r t i c l e i n f o
a b s t r a c t
The reactions of trans-[MoO(ONOMe)Cl2] 1 (ONOMe = methylamino-N,N-bis(2-methylene-4,6-dimethyl-
Article history:
Received 15 October 2008
Received in revised form 13 November 2008
Accepted 19 November 2008
Available online 30 November 2008
phenolate) dianion) and trans-[MoO(ONOtBu)Cl2]
2
(ONOtBu = methylamino-N,N-bis(2-methylene-4-
methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes
trans-[Mo(NPh)(ONOMe)Cl2] 3 and trans-[Mo(NPh)(ONOtBu)Cl2] 4, respectively. As analogous oxotungsten
starting materials did not show similar reactivity, corresponding imido tungsten complexes were pre-
pared by the reaction between [W(NPh)Cl4] with aminobis(phenol)s. These reactions yielded cis- and
trans-isomers of dichloro complexes [W(NPh)(ONOMe)Cl2] 5 and [W(NPh)(ONOtBu)Cl2] 6, respectively.
The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted
imido tungsten(VI) complex cis-[W(NPh)(ONOtBu)Me2] 7 was prepared by the transmetallation reaction
of 6 (either cis or trans isomer) with methyl magnesium iodide.
Keywords:
Tungsten
Molybdenum
Imido ligand
Aryloxide ligand
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
The corresponding molybdenum complex trans-[MoO(ONOMe)-
Cl2]
1
was prepared by reaching the starting material
The significance of transition metal imido complexes in organo-
metallic chemistry and catalytic applications has increased while
more pieces of information have gathered on their preparations,
reactivities and structures [1]. Especially, the spectator ligand ef-
fect of the imido group contributes to the high reactivity of several
active catalysts. For example, various molybdenum(VI) and tung-
sten(VI) compounds with such ligands have proven useful in a
number of catalytic processes, including olefin [2] and imine [3]
[MoO2Cl2(dmf)2] (dmf = dimethylformamide) with a stoichiome-
tric amount of H2ONOMe, which leads to the condensation reaction
of a Mo@O group with two phenol moieties of the ligand precursor
[10]. All these complexes can catalyse ring-opening metathesis
polymerization (ROMP) of norbornene derivatives when activated
by Et2AlCl co-catalyst. In present paper, we report seven new
molybdenum(VI) and tungsten(VI) complexes with aminobis(phe-
nolate) and imido ligands.
metathesis reactions. The p-donor property of the multiply bonded
imido ligand is beneficial to stabilize the high oxidation state of a
metal ion. Moreover, the electronic and steric effects of imido
groups can be tuned by altering the organic part of the ligand
[4]. On the synthetic point of view, the reaction of organic isocya-
nates with transition metal oxo compounds is frequently used to
produce corresponding metal imido complexes [5,6].
2. Results and discussion
2.1. Preparation of molybdenum complexes
The imido-for-oxo substitution reaction of transition metal
compounds is typically carried out in inert solvents using organic
isocyanates as imido sources. In order to prepare new molybde-
num imido complexes, we selected phenyl isocyanate and mono-
We are currently looking for new synthetic methods with the
aim of obtain air- and moisture-stable molybdenum(VI) and tung-
sten(VI) complexes as starting materials for catalytic applications
[7–10]. During these investigations, we have, for example, pre-
pared the cis and trans isomers of dichloro complexes [WO(ONOMe)-
oxo complexes
1 and 2 as starting materials. Molybdenum
precursors were heated with an excess of phenyl isocyanate in tol-
uene solution at a reflux temperature. In this kind of substitution,
the Mo@O fragment undergoes supposedly a [2+2] cycloaddition
reaction with the N@C bond of phenyl isocyanate, which reaction
is directly followed by an elimination of CO2 to give the final imido
complexes [3]. Under applied conditions, the reactions proceeded
smoothly to give imido derivatives 3 and 4 in synthetically useful
yields. Air-stable, deep blue complexes were isolated and purified
by a silica column chromatography and finally crystallised from
Cl2]
(ONOMe = methylamino-N,N-bis(2-methylene-4,6-dimethyl
phenolate) dianion) and [WO(ONOtBu)Cl2] (ONOtBu = methylamino-
N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) by
a reaction of WOCl4 with an appropriate aminobis(phenol) [7].
* Corresponding author. Tel.: +358 2 333 6733; fax: +358 2 333 6700.
E-mail address: Ari.Lehtonen@utu.fi (A. Lehtonen).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.11.047

650
A. Lehtonen et al. / Journal of Organometallic Chemistry 694 (2009) 649–654
acetonitrile. The 1H NMR spectra of 3 and 4 consist of sharp duplets
at ca. 5.2 and 3.1 ppm due to the AX system for the Ar–CH2–N
methylene units, which indicates that the trans configuration of
starting complexes has retained [10]. The molecular structure of
4 was verified also by XRD analysis (see below). Air-stable com-
plexes 3 and 4 are soluble in common organic solvents i.e. aromatic
hydrocarbons, chlorinated solvents and ethers, but they decom-
pose slowly in alcohol solutions.
It has been shown that amino(phenolate) complexes of Mo(VI)
and W(VI) when activated with organoaluminium compounds ex-
hibit high activity in ROMP of norbornene and its derivatives [10].
Especially, their stability on air represents an important advantage
in comparison with metathesis catalysts based on W and Mo chlo-
rides [11]. Therefore, dichloro complexes 3 and trans-6 and di-
methyl derivative 7 were tested as catalyst precursors for ROMP
of norbornene. When the experiments were run without any co-
catalyst, no activity was observed. This could be expected accord-
ing to the high stability of the studied complexes. However, when
the reaction mixtures in benzene were treated with a five-fold ex-
cess of organoaluminium reagent Et2AlCl, the monomer conver-
sions after 180 min reaction at room temperature were
quantitative for precursors 3 and trans-6 and 23% for 7. At 60 °C,
a system 7/Et2AlCl produced polynorbornene as an insoluble rub-
ber-like material in an 80% yield during one hour. When activated,
precursors 3 and 7 polymerised also 2-norbornen-5-yl acetate,
however, in low yields (about 5%). As a consequence, it seems that
the dichloro complexes can be activated by aluminium co-catalyst,
2.2. Preparation of tungsten complexes
In a preliminary experiment, we tried to carry out the imido-
for-oxo substitutions with oxotungsten complexes trans-[WO(O-
NOR)Cl2] in a similar manner as outlined for the reactions of
molybdenum analogues. However, although the attempted synthe-
ses were repeated in various solvents (toluene, chlorobenzene and
hexane) even with prolonged reaction time, no reactions were ob-
served. The tungsten imido complexes were finally prepared by the
alcoholysis reaction of [W(NPh)Cl4] with aminobis(phenol)s
H2ONOR in toluene solutions at reflux temperature. Under these
conditions, the reactions proceeded rapidly yielding the corre-
sponding imido dichloro complexes 5 and 6 in ca. 50–60% yields.
1H NMR spectra of isolated dark red materials indicated the pres-
ence of both cis and trans isomers in a ca. 1:4 ratio. Isomeric mix-
tures were separated by column chromatography to obtain
individual isomers as intense red crystalline solids. Molecular
structures of complexes 5 and 6 were characterised by 1H and
13C NMR data in addition to XRD determinations of cis and trans
isomers of 6 (see below). The 1H and 13C NMR spectra of complexes
5 and 6 showed expected resonances for phenyl imido groups as
well as for coordinated aminobis(phenolato) ligands. In the 1H
NMR spectra of cis isomers the Ar–CH2–N protons were seen as
broad overlapping signals at 3.6–3.2 ppm, which is typical for cis
configuration of aminobis(phenolato) ligands [7,9]. For compari-
son, trans isomers presented sharp doublets at 5.2–5.3 and
3.2 ppm for the same methylene protons. On the whole, trans iso-
mers have closely similar 1H and 13C NMR spectra than found for
structurally identical molybdenum complexes 3 and 4, although
the signals for ortho and para hydrogens of phenylimido ligands
were found to be shifted to down-field by 0.3 ppm compared to
corresponding molybdenum complexes.
probably due to Et for Cl exchange which is followed by an a-elim-
ination reaction to yield active carbene species [12]. Significantly
lower activity of dimethyl complex suggests another less efficient
process of activation, e.g. coordination of organoaluminium com-
pound as a Lewis acid [13] followed by primary carbene formation
from norbornene molecule. The quite low activities of studied
compounds in comparison with bidentate aminophenolate ligands
[10] are supposedly due to the rigid tridentate chelate ligands,
which may prevent the necessary reorganisation of the coordina-
tion sphere during the carbene formation and/or polymerization
process.
2.3. Structural studies
Crystals of 4, cis-6, trans-6 and 7 were grown from acetonitrile
solutions at 4 °C. All four complexes form mononuclear molecules,
in which the dianionic aminobis(phenolato) group is coordinated
to the metal ion as a tripodal O2N ligand (see Figs. 1–4 and Table
1). The weakly bonded nitrogen donor of the chelate backbone is
located trans to the imido ligand. The overall geometry and bond-
ing parameters of 4 and trans-6 are quite similar resembling those
structures reported earlier for aminobis(phenolate) complexes of
Complexes 5 and 6 are stable in air at room temperature and
are soluble in typical organic solvents, but they decompose
slowly in wet alcohol solutions. When trans-6 was dissolved in
anhydrous ether and treated with two equivalents of MeMgI,
the reaction mixture turned yellow. The stable, yellow solid
product was isolated by column chromatography and character-
ised by NMR spectroscopy to be cis-[W(NPh)(ONOtBu)Me2] 7.
The strong trans influence of methyl group appears to make cis
configuration thermodynamically more favoured, which leads to
the reorientation of aminobis(phenolato) ligand during the trans-
metallation. Similar rearrangement is earlier seen in the reaction
of trans-[WO(ONOtBu)Cl2] [9]. The synthesis of 7 was repeated
using cis-6 as a precursor, in which case the reaction yielded
an identical product. 1H NMR of 7 in CDCl3 showed a single res-
onance at 0.54 ppm for W–Me protons, whereas related signal in
13C NMR spectrum was seen at 38.88 ppm. All other alkylation
reactions of studied molybdenum and tungsten complexes with
Grignard reagents RMgX (R = Et, Ph, CH2CMe2Ph) failed leading
to the complex mixtures from which no single products could
be isolated. To observe whether dimethyl complex
7 could
decompose by -elimination to produce a corresponding methy-
a
lene complex, it was heated to 100 °C in a toluene solution, while
the reaction was monitored by 1H NMR. Although this complex
seems to decompose upon heating, no evidence on carbene for-
mation was observed.
Fig. 1. A diagram of the molecular structure of trans-[Mo(NPh)(ONOtBu)Cl2] 4.
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms have
been omitted for clarity.

A. Lehtonen et al. / Journal of Organometallic Chemistry 694 (2009) 649–654
651
Fig. 2. A diagram of the molecular structure of cis-[W(NPh)(ONOtBu)Cl2] cis-6.
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms have
been omitted for clarity.
Fig. 4. A diagram of the molecular structure of cis-[W(NPh)(ONOtBu)Me2] 7.
Thermal ellipsoids are drawn at the 30% probability level..
plexes with a six-coordination. For both compounds, the coordina-
tion around the tungsten atom is similar than found for cis dichloro
or dimethyl complexes of oxotungsten(VI) with related amin-
obis(phenolate)s. In all studied complexes, the M–Nimido–C bond
angles are nearly linear, which suggest that the imido nitrogen is
sp-hybridised. Accordingly, the M„N bond order is three, which
makes the imido ligand as a six-electron donor. The strong trans
influence of the imido group is seen in the distortion of equatorial
ligands, since the Nimido–M–O angles are in the range 95.16(8)–
99.15(8) and the Nimido–M–Cl angles vary between 91.64(7) and
96.53(7). In all compounds, the M–N8 distances are ca. 0.1 Å short-
Table 1
Crystallographic data for trans-[Mo(NPh)(ONOtBu)Cl2] 4, trans-[W(NPh)(ONOtBu)Cl2]
trans-6, cis-[W(NPh)(ONOtBu)Cl2] cis-6 and cis-[W(NPh)(ONOtBu)Me2] 7.
4
trans-6
cis-6
7
Formula C31H40Cl2MoN2O2 C31H40Cl2N2O2W C31H40Cl2N2O2W C33H46
N2O2W
Fig. 3. A diagram of the molecular structure of trans-[W(NPh)(ONOtBu)Cl2] trans-6.
Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms have
been omitted for clarity.
Mr
639.49
system
727.4
727.4
686.57
Crystal
Triclinic
Monoclinic
Monoclinic
Monoclinic
group
ꢀ
Space
P21/c
Z
P1
P21/n
P21/c
oxomolybdenum(VI) and oxotungsten(VI) with a trans dichloro
moiety [7,8]. Although the molecular structures of these two com-
plexes are closely similar, they are not crystallographically identi-
2
4
4
4
a (Å)
b (Å)
c (Å)
9.3686(2)
10.2573(2)
16.3306(3)
97.0420(10)
93.3910(10)
101.4940(10)
1520.60(5)
9.56030(10)
23.5055(4)
14.0927(2)
90
105.7630(10)
90
10.70850(10)
16.3339(2)
17.3987(2)
90
90.0500(10)
90
9.9696(2)
24.3566(6)
13.3218(2)
90
99.9140(10)
90
cal, i.e.
4 crystallises in a triclinic system, whereas trans-6
a
(°)
crystallises in a monoclinic space group. They show also some
noticeable differences in their bonding parameters. In particular,
the M–Nimido distances are 1.732(2) Å for 4 and 1.751(3) Å for
trans-6, whereas related M–N–C angles are 171.5(2)° and
176.9(3)°, respectively. As expected according to the spectral char-
acterizations, complex cis-6 is formed of molecular units in which
two cis-aryloxide moieties and two cis-chlorides occupy the equa-
torial plane. The overall geometry of 7 is comparable to that found
for cis-6. The W–C(methyl) bond lengths are 2.172(3) and
2.206(4) Å, which are typical values for tungsten(VI) alkyl com-
b (°)
c
(°)
V (Å3)
l
3047.81(7)
6.37
3043.23(6)
3.995
3186.57(11)
4.001
(cmÀ1
)
3.654
Dcalc
1.431
2h
2.07–
R1, wR2
(g cmÀ3
)
1.397
1.585
1.588
Range (°)
28.00
0.0627, 0.0845
2.23–28.3
0.052, 0.0561
2.29–28.27
0.033, 0.044
1.71–28.25
0.034,
0.0694

652
A. Lehtonen et al. / Journal of Organometallic Chemistry 694 (2009) 649–654
Table 2
for C25H28Cl2MoN2O2: C, 54.07; H, 5.08; N, 5.04. Found: C, 53.78; H,
5.24; N, 5.05%.
Selected distances (Å) and angles (°) for trans-[Mo(NPh)(ONOtBu)Cl2] 4, trans-
[W(NPh)(ONOtBu)Cl2] trans-6, cis-[W(NPh)(ONOtBu)Cl2] cis-6 and cis-[W(NPh)-
(ONOtBu)Me2] 7.
3.4. trans-[Mo(NPh)(ONOtBu)Cl2]
4
trans-6
cis-6
cis-7
335 mg (55%). 1H NMR (CDCl3): d 7.80 (d, J = 7.5 Hz, 2H, NAr-
Hortho), 7.53 (t, J = 7.9 Hz, 2H, NArHmeta), 7.34 (t, J = 7.5 Hz, 1H,
NArHpara), 7.19 (s, 2H, OArH), 6.93 (s, 2H, OArH), 5.16 (d,
J = 12.9 Hz, 2H, N-CH2), 3.13 (d, J = 12.9 Hz, 2H, N-CH2), 2.39 (s,
6H, Ar-CH3), 2.22 (s, 3H, NCH3) 1.53 (18 H, s, C(CH3)3) ppm. 13C
NMR (CDCl3): d 160.66, 155.39, 139.03, 135.29, 131.50, 129.21,
129.14, 128.61, 127.66, 126.89, 63.59, 46.88, 35.41, 30.76,
21.39 ppm. Anal. Calc. for C31H40Cl2MoN2O2: C, 58.22; H, 6.30; N,
4.38. Found: C, 58.27; H, 6.48; N, 4.05%.
M–N1
M–Cl1
M–Cl2
M–O2
M–O3
M–N8
M–N1–C27
Cl1–M–Cl2
O2–M–O3
N1–M–N8
1.732(2)
1.751(3)
2.3752(9)
2.4025(9)
1.907(2)
1.905(2)
2.399(3)
176.9(3)
172.00(3)
163.25(9)
178.95(11)
1.738(2)
1.734(3)
2.206(4)a
2.172(3)a
1.922(3)
1.954(2)
2.471(3)
174.0(2)
79.60(15)
99.94(10)
176.98(10)
2.3956(7)
2.4245(7)
1.9134(17)
1.9033(17)
2.3943(19)
171.5(2)
171.88(2)
164.43(7)
176.73(9)
2.3715(6)
2.3682(6)
1.8991(16)
1.9246(16)
2.417(2)
171.93(18)
85.34(2)
93.80(7)
174.62(8)
a
W–C(33) and W–C(34) distances, C(33)–W–C(34) angle.
3.5. Preparation of W–imido complexes. General procedure
er and M–OAr distances are slightly longer than in corresponding
oxo complexes [7–9] (see Table 2).
0.50 mmol (210 mg) of [W(NPh)Cl4] was suspended in 10 ml of
toluene and subsequently treated with 0.50 mmol of H2ONOR. The
dark mixture that formed was then stirred for 3 h at reflux temper-
ature. The mixtures of cis- and trans-isomers of [W(NPh)Cl2(LR)]
thus obtained were separated by silica column chromatography
using a hexane–toluene mixture (1:1) as an eluent.
3. Experimental section
Starting compounds [W(NPh)Cl4] and H2ONOR were prepared
according published procedures [14,15]. trans-[MoO(ONOMe)Cl2]
was synthesised as described earlier by us [10], while trans-
[MoO(ONOtBu)Cl2] was prepared using analogous procedure. Other
chemicals were from commercial sources and were used as pur-
chased. Toluene and diethyl ether were distilled over CaH2; other
solvents were of HPLC grade. All syntheses and manipulations
were performed under ambient laboratory atmosphere if not
otherwise stated. The purity of isolated complexes as well as the
progress of the reactions was monitored by thin-layer chromatog-
raphy. 1H NMR (500 MHz) and 13C NMR spectra (200 MHz) were
recorded at 20 °C using Bruker AV 500 spectrometer in CDCl3 solu-
tions and were referenced internally to SiMe4. Elemental analyses
were obtained using a Perkin–Elmer CHNS-Analyzer 2400. Cata-
lytic tests were run similarly as presented in Ref. [10].
3.6. cis-[W(NPh)(ONOMe)Cl2]
42 mg (13%). 1H NMR (CDCl3): d 7.60 (t, 2H, J = 7.6 Hz, NArHmeta),
7.36 (d, J = 7.4 Hz, 2H, NArHortho), 7.10 (s, 2H, OArH), 7.08 (t,
J = 7.6 Hz, 1H, NArHpara), 6.86 (s, 2H, OArH), 4.17 (br, 2H, N-CH2),
3.71 (br, 2H, N-CH2), 2.70 (s, 3H, N-CH3), 2.40 (s, 6H, Ar-CH3),
2.39 (s, 6H, Ar-CH3) ppm. 13C NMR (CDCl3): d 155.46, 133.46,
131.39, 129.74, 128.64, 128.43, 127.75, 127.67, 125.29, 111.08,
61.73, 48.97, 20.73, 16.15 ppm. Anal. Calc. for C25H28Cl2N2O2W:
C, 46.68; H, 4.39; N, 4.35. Found: C, 46.80; H, 4.27; N, 4.11%.
3.7. trans-[W(NPh)(ONOMe)Cl2]
3.1. trans-[MoO(ONOtBu)Cl2]
135 mg (42%). 1H NMR (CDCl3): d 7.60 (t, J = 7.9 Hz, 2H,
NarHmeta), 7.34 (d, J = 7.5 Hz, 2H, NarHortho), 7.11 (t, J = 7.4 Hz, 1H,
NArHpara), 7.10 (s, 2H, OArH), 6.85 (s, 2H, OArH), 5.31 (d,
J = 12.9 Hz, 2H, N-CH2), 3.20 (d, J = 12.9 Hz, 2H, N-CH2), 2.43
(s, 6H, Ar-CH3), 2.41 (s, 6H, Ar-CH3) 2.22 (s, 3H, N-CH3) ppm. 13C
NMR (CDCl3): d 155.45, 152.83, 133.98, 131.41, 130.70, 129.49,
128.10, 127.98, 127.70, 125.36, 62.91, 46.80, 20.75, 16.08 ppm.
Anal. Calc. for C25H28Cl2N2O2W: C, 46.68; H, 4.39; N, 4.35. Found:
C, 46.88; H, 4.64; N, 4.25%.
520 mg (92%). 1H NMR (CDCl3): d 7.25 (s, 2H, Ar), 6.96 (s, 2H,
Ar), 4.80 (d, J = 13 Hz, 2H , N-CH2), 3.09 (d, J = 13 Hz, 2H, N-CH2),
2.49 (s, 6H, Ar-CH3), 1.99 (s, 3H, N-CH3), 1.59 (s, 18H, C(CH3)3).
13C NMR (CDCl3):
d 161.19, 140.76, 138.67, 130.75, 129.71,
127.60, 63.42, 47.21, 35.59, 30.85, 21.62. Anal. Calc. for
C25H35Cl2MoNO3: C, 53.20; H, 6.25; N, 2.48. Found: C, 53.08; H,
6.12; N, 2.30%.
3.8. cis-[W(NPh)(ONOtBu)Cl2]
3.2. Preparation of Mo–imido complexes. General procedure
1.00 mmol of starting compound (480 mg of trans-[MoO(ONOMe
)
55 mg (15%). 1H NMR (CDCl3): d 7.58 (t, J = 8.2 Hz, 2H, NArHmeta),
7.39 (d, J = 7.3 Hz, 2H, NArHortho), 7.21 (s, 2H, OArH), 7.06 (t,
J = 7.5 Hz, 1H, NArHpara), 6.91 (s, 2H, OArH), 4.22 (s, br, 2H, N-
CH2), 3.65 (s, br, 2H, N-CH2), 2.85 (s, 3H, NCH3), 2.42 (s, 6H, Ar-
CH3), 1.43 (s, 18H, C(CH3)3) ppm. 13C NMR (CDCl3): d 156.91,
152.07, 140.28, 133.16, 129.49, 128.67, 128.25, 127.76, 127.62,
126.82, 61.21, 49.26, 40.85, 34.91, 30.26, 21.07 ppm. Anal. Calc.
for C31H40Cl2N2O2W: C, 51.23; H, 5.55; N, 3.86. Found: C, 51.60;
H, 5.24; N, 4.00%.
Cl2] or 564 mg of trans-[MoO(ONOtBu)Cl2]) was dissolved in 10 ml
of toluene. An excess of phenyl isocyanate (0.20 ml, 1.6 mmol)
was added and the blue solutions were stirred at reflux tempera-
ture for 2 h. The products were column chromatographed over sil-
ica gel using a hexane–toluene mixture (1:1) as an eluent. The
intense blue solid products were crystallised from hot acetonitrile.
3.3. trans-[Mo(NPh)(ONOMe)Cl2]
400 mg (72%). 1H NMR (CDCl3): d 7.74 (d, J = 7.5 Hz, 2H, NAr-
Hortho), 7.57 (t, J = 7.7 Hz, 2H, NArHmeta), 7.39 (t, J = 7.5 Hz, 1H,
NArHpara), 7.06 (s, 2H, OArH), 6.89 (s, 2H, OArH), 5.20 (d,
J = 12.9 Hz, 2H, N-CH2), 3.13 (d, J = 12.9 Hz, 2H, N-CH2), 2.42 (s,
6H, Ar-CH3), 2.39 (s, 6H, Ar-CH3) 2.09 (s, 3H, NCH3) ppm. 13C
NMR (CDCl3): d 160.02, 155.52, 135.46, 132.11, 128.82, 128.74,
128.63, 127.07, 126.42, 63.16, 46.48, 21.05, 16.51 ppm. Anal. Calc.
3.9. trans-[W(NPh)(ONOtBu)Cl2]
170 mg (55%). 1H NMR (CDCl3): d 7.57 (t, J = 8.0 Hz, 2H,
NArHmeta), 7.40 (d, J = 7.9 Hz, 2H, NArHortho), 7.24 (s, 2H, OArH),
7.06 (t, J = 7.5 Hz, 1H, NArHpara), 6.90 (s, 2H, OArH), 5.2 (d, 2H,
J = 12.9 Hz, N-CH2), 3.20 (d, J = 12.9 Hz, 2H, N-CH2), 2.37 (s, 6H,
Ar-CH3), 2.02 (s, 3H, NCH3) 1.51 (18 H, s, C(CH3)3) ppm. 13C NMR

A. Lehtonen et al. / Journal of Organometallic Chemistry 694 (2009) 649–654
653
Scheme 1. Preparation of trans-[Mo(NPh)(ONOR)Cl2].
(CDCl3): d 156.10, 152.80, 139.99, 133.80, 130.08, 129.68, 128.68,
4. X-ray crystallography
127.92, 127.62, 126.51, 63.34, 47.33, 35.12, 30.58, 21.09 ppm. Anal.
Calc. for C31H40Cl2N2O2W: C, 51.23; H, 5.55; N, 3.86. Found: C,
50.98; H, 5.44; N, 4.01%.
Crystals of 4, cis-6 and trans-6 were grown from concentrated
acetonitrile solutions upon slow cooling to 4 °C. The crystal data
for the compounds are summarized in Table 1. The crystallographic
data were collected at 173 K on an Enraf Nonius Kappa CCD area-
3.10. Preparation of cis-[W(NPh)(ONOtBu)Me2]
detector diffractometer using graphite monochromatised Mo K
radiation (k = 0.71073 Å). Data collection was performed using /
and scans and the data were processed using DENZO-SMN
v0.93.0 [16]. SADABS [17] absorption correction was applied to the
data of all compounds. The structures were solved by direct
methods using the SHELXS-97 program and full-matrix least-squares
refinements on F2 were performed using the SHELXL-97
program [18]. Structure figures were drawn using Ortep-3 for Win-
dows [19].
a
3.10.1. From trans-[W(NPh)(ONOtBu)Cl2]
0.20 mmol (146 mg) of trans-[W(NPh)(ONOtBu)Cl2] was dis-
solved in 10 ml of anhydrous diethyl ether under N2 atmosphere.
The red solution was treated with freshly prepared MeMgI (ca.
0.6 mmol) in diethyl ether (0.6 ml) while the reaction mixture
turned rapidly yellow. The yellow solution was then stirred for
an hour at room temperature. The solvent was evaporated and
the yellow-orange solid product was isolated by a silica column
chromatography using a hexane-toluene mixture (1:1) as an
eluent. 95 mg (69%). 1H NMR (CDCl3): d 7.46 (2H, t, J = 7.8 Hz,
NArHmeta), 7.32 (2H, d, J = 7.4 Hz, NArHortho), 7.17 (2H, s, OArH),
7.11 (1H, t, J = 7.4 Hz, NArHpara), 6.85 (2H, s, OArH), 3.6–4.0 (4H,
br, N-CH2), 2.45 (3H, s, NCH3), 2.36 (6H, s, Ar-CH3), 1.42 (18H, s,
C(CH3)3), 0.54 (6H, s, W-CH3). 13C NMR (CDCl3) d: 155.25, 154.03,
140.75, 130.39, 128.46, 128.04, 127.50, 126.54, 125.96, 125.68,
61.68, 47.57, 38.88, 34.86, 29.87, 21.09. Anal. Calc. for
C33H46N2O2W: C, 57.73; H, 6.75; N, 4.08. Found: C, 57.78; H,
6.91; N, 4.04%.
x
5. Conclusions
In conclusion, we have found that the aminobis(phenolato)
complexes trans-[MoO(ONOR)Cl2] can react with PhNCO to yield
air-stable imido molybdenum complexes trans-[Mo(NPh)(O-
NOR)Cl2]. Regardless their structural similarities, analogous oxo-
tungsten complexes do not show the same reactivity, but
corresponding imido tungsten complexes can be prepared by the
reaction of [W(NPh)Cl4] with aminobis(phenol)s. These reactions
yield cis- and trans-isomers of dichloro complexes [W(NPh)(O-
NOR)Cl2] in a ca. 1:4 ratio. Moreover, cis and trans isomers of tung-
sten complex [W(NPh)(ONOtBu)Cl2] react with methyl Grignard
reagent to yield corresponding dimethyl complex cis-[W(NPh)(O-
NOtBu)(Me)2] (see Schemes 1 and 2).
3.10.2. From cis-[WO(ONOtBu)Cl2]
The reaction was carried out using 0.10 mmol (73 mg) of cis-
[W(NPh)(ONOtBu)Cl2] and 0.3 mmol of MeMgI in diethyl ether to
yield 52 mg (75%) of a yellow product. The 1H and 13C NMR spectra
of the product were identical with those described above.
Acknowledgement
The Academy of Sciences of the Czech Republic (KAN100400701)
is acknowledged for the financial support (for H.B.).
Appendix A. Supplementary material
CCDC 699861–699864 (for 4, trans-6, cis-6 and cis-7, respec-
tively) contain the supplementary crystallographic data for this pa-
per. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.2008.
11.047.
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654
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