Synthesis and structure of a series of new haloaryl imido complexes of molybdenum

Article abstract of DOI:10.1016/S0277-5387(00)00605-7

The synthesis of a series of mono- and bis-haloarylimido molybdenum(VI) complexes is described. Two methods of introducing the electron poor imido functionality are employed, first the condensation of substituted anilines with Na₂MoO₄ in the presence of Me₃SiCl/NEt₃, secondly the sulfinyl amine metathesis with [Mo(O)₂Cl₂(dme)] (1). The latter method works even in cases, when the first one does not work. Crystal structures of three complexes [Mo(NC₆F₅)(O)Cl₂(dme)] (2a), [Mo(N-2.6-Cl₂C₆H₃)₂Cl ₂(dme)] (3b) and [Mo(N-2.4,6-Br₃C₆H₂)₂Cl ₂(dme)] (4) are reported. The unusually small Mo-N-C(Ar) angle of 149.1(5)° has been found in the structure of 4.

Full text of DOI:10.1016/S0277-5387(00)00605-7

www.elsevier.nl/locate/poly
Polyhedron 20 (2001) 379–385
Synthesis and structure of a series of new haloaryl imido
complexes of molybdenum
Konstantin A. Rufanov b,*, Dmitry N. Zarubin a, Nikolai A. Ustynyuk a,
Dmitry N. Gourevitch a, Jo¨rg Sundermeyer b, Andrei V. Churakov c,1,
Judith A.K. Howard d
a A.N. Nesmeyano6 Institute of Organoelement Compounds, Russian Academy of Sciences, Va6ilo6 st., 28, 117813, Moscow, Russia
b Fachbereich Chemie der Philipps-Uni6ersitaet Marburg, Hans-Meerwein Strasse, D-35032 Marburg, Germany
c N.S. Kurnako6 Institute of Inorganic and General Chemistry, Russian Academy of Sciences, Leninski Prospekt, 31 Moscow, Russia
d Department of Chemistry, Uni6ersity of Durham, Science Laboratories, South Road, Durham DH1 3LE, UK
Received 2 August 2000; accepted 18 September 2000
Abstract
The synthesis of a series of mono- and bis-haloarylimido molybdenum(VI) complexes is described. Two methods of introducing
the electron poor imido functionality are employed, first the condensation of substituted anilines with Na2MoO4 in the presence
of Me3SiCl/NEt3, secondly the sulfinyl amine metathesis with [Mo(O)2Cl2(dme)] (1). The latter method works even in cases, when
the first one does not work. Crystal structures of three complexes [Mo(NC6F5)(O)Cl2(dme)] (2a), [Mo(N-2,6-Cl2C6H3)2Cl2(dme)]
(3b) and [Mo(N-2,4,6-Br3C6H2)2Cl2(dme)] (4) are reported. The unusually small MoꢀNꢀC(Ar) angle of 149.1(5)° has been found
in the structure of 4. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Molybdenum complexes; Imido complexes; Metathesis; Sulfinyl amines
Lewis acid catalysts for a number of organic transfor-
mations [2].
1. Introduction
Imido ligands employed before in this chemistry were
based on the sterically demanding hydrocarbons such
as t-BuN, AdN, 2,6-i-Pr2C6H3N, MesN etc. However
the area of complexes containing halocarbon type
imido ligands is still largely unexplored [3–6]. Few
haloalkylimido complexes of the type RꢀCCl2ꢀNꢁMCl4
(R=CCl3, Cl, Ph or CN; M=Mo, W, Re) were syn-
thesised by Fowels [7,8] and Dehnicke [9–12] using an
addition of transition metal chlorides to nitriles.
Among halocarbon arylimido ones only two examples
are known to date — [Mo(NAd)(NC6F5)Cl2(dme)] [3]
and [Mo(NC6F5)2Cl2(dme)] [4]. We expect that imido
complexes of such a type will reveal an enhanced
catalytic activity in olefin polymerisation because they
have an increased Lewis acidity of the metal centre. In
this paper we focused our attention on synthesis and
crystal structure studies of a series of haloarylimido
Mo(VI) complexes with different type and number of
halogen substituents at the phenyl rings.
Our interest in the chemistry of transition metal
imido complexes is due to the known ability of p-basic
imido ligands to stabilise transition metal compounds
in high oxidation states. Variation of steric and elec-
tronic properties of N-substituents provides a handle to
tune the ligand cone angle, its p-basicity and therefore
indirectly the Lewis acidity of the metal centre. The
isolobal relationship between Cp2Zr and (RN)2Mo moi-
eties caused an enhanced attention to bis-imido com-
plexes of Group 6 transition metals. They are very
promising pre-catalysts for the Ziegler-Natta type olefin
polymerisation related to the known systems based on
the Group 4 metallocenes [1] and they are serving as
* Corresponding author. Tel.: +49-6421-28-25693; fax: 49-6421-
28-28917.
E-mail address: jsu@chemie.uni-marburg.de (K.A. Rufanov).
1 To whom crystallographic inquiries should be addressed.
0277-5387/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0277-5387(00)00605-7

380
K.A. Rufano6 et al. / Polyhedron 20 (2001) 379–385
2. Results and discussion
This method of preparation of 1 is obviously very
simple and convenient and therefore it is superior to
At the present time there is a number of synthetic
methods known for introducing the imido functionality
into coordination compounds [6]. In our work the
preparation of desired Mo(VI) imido complexes fol-
lowed the simple and efficient procedure worked out by
Schrock [4] and modified by Gibson [13] (Eq. (1)).
one, which has been applied before [14].
2.2. Synthesis of Mo(VI) imido complexes
We started with an re-investigation of the synthesis
of [Mo(NC6F5)2Cl2(dme)] (2b) [4] and found that con-
densation reaction of 2 equiv. of C6F5NH2 with
Na2MoO4, Me3SiCl and Et3N does not give pure 2b
even after 6 h in refluxing dme, but result in formation
of a mixture of 2b and [Mo(NC6F5)(O)Cl2(dme)] (2a),
in a ratio of approximately 1:1. The oxo-imido interme-
diate 2a was obtained in the reaction of Na2MoO4 with
just 1 equiv. of C6F5NH2 under analogous conditions
as an orange crystalline material in a 65% yield. It can
readily be separated from the reaction mixture by crys-
tallisation from the toluene. On the other hand, our
efforts to obtain 2b in more than 35% yield failed, even
after prolonged heating with 50% excess of C6F5NH2 (3
equiv.). We speculate that introduction of one per-
fluorophenyl imido ligand into the coordination sphere
of the Mo atom decreases the rate of the second
oxo/imido replacement step. Any attempts to get crys-
tals of 2b suitable for X-ray structure determination
were unsuccessful. However red crystals of 2a suitable
for X-ray analysis were obtained by a slow evaporation
of its saturated toluene solution at r.t. Scheme 1 sum-
marises the synthetic results.
(1)
The procedure consists in an interaction of sodium
molybdate with primary aryl amines in presence of
chlorotrimethylsilane and triethylamine using 1,2-
dimethoxyethane (dme) as a solvent. This reaction is a
multistep process. It involves an intermediate formation
of N-silylated arylamines (ArꢀNHꢀSiMe3) and the for-
mation of the dme adduct of dioxomolybdenum dichlo-
ride, [Mo(O)2Cl2(dme)], (1).
2.1. A preparation procedure for the [Mo(O)2Cl2(dme)]
(1)
Synthesis of 1 was developed in preparative manner.
This compound can easily be obtained in excellent yield
by interaction of Na2MoO4 with 4 equiv. of Me3SiCl in
DME (65°C, 12 h).
Furthermore we have studied a series of chloro- and
bromo-substituted anilines for preparation molybde-
num bis-imido complexes using the same synthetic
method. We found that in the reactions of Na2MoO4
with 2 equiv. of various polychlorinated anilines the
corresponding bis-imido Mo(VI) complexes are formed
in high to moderate yields (see Table 1).
(2)
Scheme 1.

K.A. Rufano6 et al. / Polyhedron 20 (2001) 379–385
381
Table 1
Red–orange needle type crystals of 3b suitable for an
X-ray study were grown from saturated DME solution
by its slow evaporation at r.t.
Yields of haloarylimido molybdenum complexes obtained via the
Schrock method (Eq. (2))
Finally we have tried the synthesis of the 2,4,6-tri-
bromo-analogue of the 3a. Surprisingly under the same
conditions but after 30 h heating we failed to obtain a
corresponding bis-imido Mo(VI) complex. The major
product of the reaction was identified as monosilylated
aniline 2,4,6-Br3C6H3NHꢀSiMe3. We believe that in the
case of such bulky N-silylanilines a considerable steric
effect paired with their low nucleophilicity prevents
formation of imido complexes via the condensation
route outlined by Schrock.
Complexes
Yield (%)
[Mo(NC6F5)(O)Cl2(dme)] (2a)
[Mo(NC6F5)2Cl2(dme)] (2b)
[Mo(N-2,4,6-Cl3C6H2)2Cl2(dme)] (3a)
[Mo(N-2,6-Cl2C6H3)2Cl2(dme)] (3b)
[Mo(N-2,5-Cl2C6H3)2Cl2(dme)] (3c)
66
35
75
90
95
In order to overcome this problem we decided to use
another synthetic method, the sulfinylamine metathesis,
that has been systematically investigated by us [15]. The
interaction of transition metal oxo-halides with N-aryl-
sulfinyl amines leads smoothly to the corresponding
imido complexes and sulfur dioxide.
This method seems to be the best and most simple
one for the synthesis of imido complexes with electron
withdrawing and sterically demanding N-substituents.
Reaction of 1 with 2 equiv. of 2,4,6-Br3C6H2NSO in
toluene under reflux for 5 h readily affords the desired
bis-imido complex [Mo(N-2,4,6-Br3C6H2)2Cl2(dme)] (4)
in nearly quantitative yield (Eq. (3)).
Fig. 1. Molecular structure of [Mo(NC6F5)(O)Cl2(dme)] (2a).
Na2MoO4+Me3SiClꢀꢀDꢀꢀMꢀEꢀꢂ MoO2Cl2*DME+2(Me3Si)2O
−2NaCl
(3)
Analytically pure 4 immediately precipitates in the
form of dark red crystals after cooling the reaction
down to r.t. This reaction requires relatively high tem-
peratures and does not proceed in lower boiling sol-
vents like DME or benzene. Plate-like crystals of 4
suitable for X-ray study were obtained by slow diffu-
sion of pentane into chloroform solution of 4 at r.t.
2.3. Molecular structures of 3b, 4, 2a
Figs. 1–3 present the results of the single-crystal
X-ray diffraction studies. Selected bond lengths and
angles for these compounds are given in Table 2.
In the structures of 3b and 4, the coordination sphere
of the central metal atom is best described as a dis-
torted octahedron, with cis imido groups and trans
arrangement of the chloro ligands. For both structures,
the displacement of the molybdenum atom from the
least-squares plane defined by the O(1), O(2) (dme) and
Fig. 2. Molecular structure of [Mo(N-2,4,6-Br3C6H2)2Cl2(dme)] (4).
It should be noted that the best yield in the series of
bis-imido Mo(VI) complexes synthesised by the conden-
sation method was achieved in the case of the most
nucleophilic and the sterically less demanding 2,5-
dichloroaniline. It is obvious that a decrease of aniline
nucleophilicity that is controlled by electronic effect of
the halogen-substituents leads to a decrease in the
yields of the target complexes.
,
N(1), N(2) (imido) atoms is rather small (0.02 A).
However, due to electronic repulsions of the halogen
lone pairs and the electron density of the imido p-bonds
the chlorine atoms are noticeably bent away from the
imido ligands. In general, the core geometry in 3b and
4 is very similar to that one previously found for closely

382
K.A. Rufano6 et al. / Polyhedron 20 (2001) 379–385
CH2ꢀC6H4ꢀ (5c), 2,2%-C6H4ꢀC2H4ꢀC6H4ꢀ (5d), 4,4%-(2,6-
i-Pr2C6H2)ꢀCH2ꢀ(2,6-i-Pr2C6H2)ꢀ (5e) [17]; 2,6-i-
Pr2C6H3 (5f) [18]).
related bis-arylimido complexes [Mo(NR)(NR%)Cl2-
(dme)] (where R, R%=(2-CN)ꢀC6H4ꢀ (5a) [16]; R=
Adꢀ, R%=C6F5ꢀ (5b) [3]; R, R%=2,2%-C6H4ꢀ
Thus, the values of NꢀMoꢀN and OꢀMoꢀO angles as
well as MoꢀCl distances for 3b and for 4 (see Table 2)
lie within the ranges observed for 5a–f (100.8(5)–
107.13(7)°, 69.29(5)–71.0(3)° and 2.3841(12)–2.4145(5)
,
A, respectively). In the structure of 4 the ClꢀMoꢀCl
angle is not significantly reduced to 156.01(6)°, while
being the smallest one among those observed in 5a–f
complexes (157.01(9)–160.97(12)°).
The geometric parameters of arylimido ligands in 3b
and 4 are of particular interest. Both MoꢀN and NꢀC
distances fall into the range for complexes 5a–f
(MoꢀN: 1.725(7)–1.775(3) and MoꢀC: 1.373(4)–
,
1.406(7) A, respectively). The MoꢀNꢀC angles 165.8(2)
and 166.0(2)° in 3b are typical for close to linear imido
ligands (160–180°) [17]. For compound 4, the
MoꢀN(2)ꢀC(11) angle (149.1°) is extremely small, how-
ever this bending does not influence seriously on the
MoꢀN(2) and N(2)ꢀC(11) bond lengths. Nevertheless,
the MoꢀO(1) bond lying trans to the more bent imido
Fig. 3. Molecular structure of [Mo(N-2,6-Cl2C6H4)2Cl2(dme)] (3b).
Table 2
,
ligand is significantly longer (2.378(5) A) than the
,
Selected bond lengths (A) and angles (°) for 3b, 4 and 2a
,
MoꢀO(2) bond (2.311(5) A). This may be taken as
3b
4
2a
indication for a weaker thermodynamic trans effect of
the considerably more bend imido functionality.
In the structures of 3b and 4, all of the phenyl rings
adopt an out-of-plane arrangement with respect to the
least-squares planes defined by the two oxygen and the
two nitrogen atoms (dihedral angles lie within the range
36.9–55.5°). This conformation minimizes two kinds of
the possible non-valent interactions: first between chlo-
rine atoms attached to Mo and ortho-halogen sub-
stituents at phenyl rings and second between
ortho-halogen substituents at neighbouring phenyl
rings.
In the structure of 2a, the central Mo atom has a
distorted octahedral coordination sphere with cis orien-
tated arylimido- and oxo- ligands, trans chloro ligands,
and with the oxygen atoms of dme occupying trans
positions to the oxo- and imido- ligands. The main
geometric parameters of complex 2a (see Table 2) are
very close (differences lie within 3|s) to those reported
for the similar oxoimido complex [Mo(NC6H2Ph3)-
(O)Cl2(dme)] [19].
In all three structures five-membered metallacycle
containing dme molecule adopts a twist conformation,
with C(2) and C(3) atoms occupying the flap sites. The
methyl substituents C(1) and C(4) are in the equatorial
positions.
Table 2 contains the information about halogen-
C(Ar) bond lengths in 3b, 4 and 2a. It is of interest,
that CꢀHal bonds in ortho-positions to NꢀC(Ar) are
slightly, but systematically longer than those ones in
para-positions.
MoꢀN(1)
MoꢀN(2)
MoꢀO(3)
MoꢀCl(1)
MoꢀCl(2)
MoꢀO(1)
MoꢀO(2)
N(1)ꢀC(5)
N(2)ꢀC(11)
1.747(3)
1.750(3)
1.742(5)
1.767(6)
1.749(3)
1.695(2)
2.3770(9)
2.3876(9)
2.286(2)
2.318(2)
1.377(4)
2.4037(9)
2.3958(9)
2.331(3)
2.354(2)
1.377(4)
1.369(4)
2.391(2)
2.393(2)
2.378(5)
2.311(5)
1.377(8)
1.382(9)
N(1)ꢀMoꢀN(2)
NꢀMoꢀO(3)
Cl(1)ꢀMoꢀCl(2)
O(1)ꢀMoꢀO(2)
C(5)ꢀN(1)ꢀMo
C(11)ꢀN(2)ꢀMo
104.88(13)
103.0(3)
104.57(13)
159.37(3)
70.46(8)
158.95(3)
70.46(11)
165.8(2)
166.0(2)
156.01(6)
70.9(2)
170.5(5)
149.1(5)
172.0(3)
C-halogen bonds
ortho-
C(6)ꢀCl(3)
C(10)ꢀCl(4)
C(12)ꢀCl(5)
C(16)ꢀCl(6)
C(6)ꢀBr(1)
C(10)ꢀBr(3)
C(12)ꢀBr(4)
C(16)ꢀBr(6)
C(6)ꢀF(1)
C(10)ꢀF(5)
meta-
C(7)ꢀF(2)
C(9)ꢀF(4)
para-
C(8)ꢀBr(2)
C(14)ꢀBr(5)
C(8)ꢀF(3)
1.734(3)
1.740(3)
1.739(4)
1.734(3)
1.876(7)
1.880(7)
1.887(7)
1.889(8)
1.335(4)
1.336(4)
1.342(4)
1.348(4)
1.911(7)
1.901(7)
1.343(4)

K.A. Rufano6 et al. / Polyhedron 20 (2001) 379–385
383
Table 3
Crystal data, data collection, structure solution and refinement parameters for 3b, 4 and 2a
Empirical formula
Formula weight
Colour, habit
Crystal size (mm)
Crystal system
C16H16Cl6Mo1N2O2 (3b)
576.95
red block
0.24×0.06×0.04
monoclinic
P21/c
C
912.59
red block
0.48×0.32×0.16
monoclinic
P21/c
16H14Br6Cl2Mo1N2O2 (4)
C10H10Cl2F5Mo1N1O3 (2a)
454.03
orange block
0.20×0.10×0.10
monoclinic
Space group
P21/n
Unit cell dimensions
,
a (A)
8.2069(1)
16.1053(1)
16.4984(1)
94.844(1)
2172.88(3)
4
1.764
1.356
7.9559(1)
8.5914(1)
35.5411(2)
94.887(1)
2420.49(4)
4
2.504
10.684
1704
7.2461(1)
18.5672(1)
11.6387(1)
100.766(1)
1538.31(2)
4
1.960
1.262
888
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
Absorption coefficient (mm−1
F(000)
)
1144
Diffractometer
Temperature (K)
Siemens SMART CCD [21]
150.0(2)
150.0(2)
150.0(2)
,
Radiation (u/A)
Scan mode
graphite-monochromated Mo Ka (0.71073)
ꢀ
ꢀ
ꢀ
Scan step (in ꢀ) (°)
Time per step (s)
? range (°)
0.3
30
0.3
10
0.3
30
1.77–27.49
−105h510
−205k520
−105l521
1.15–27.48
−105h510
−115k510
−465l541
16717
2.09–27.49
−95h59
−245k516
−145l515
11173
Index ranges
Reflections collected
Independent reflections
Data reduction
Absorbtion correction
Minimum and maximum transmission
Solution method
13076
4794 [Rint=0.0497]
Siemens SAINT [22]
From real crystal shape [23]
0.7272 and 0.9581
Direct methods (SHELX-86) [24]
Full-matrix least-squares on F2
4765/0/309
5520 [Rint=0.0696]
3535 [Rint=0.0456]
Empirical [23]
0.2048 and 0.7828
0.7021 and 0.8234
Refinement method
(
SHELXL-93) [25]
5487/0/265
Data/restraints/parameters
Reflections with I\2|(I)
Weighting scheme w−1
3518/0/240
3973
4539
2976
|2(F2)+(0.0071P)2+4.8918P
|2(F2)+(0.0284P)2
|2(F2)+(0.0278P)2+3.0675P
+27.333P
where P=(2F2c+Fo2)/3
1.160
Goodness-of-fit on F2
1.142
1.088
Final R indices [I\2|(I)]
R1=0.0367
wR2=0.0689
R1=0.0527
wR2=0.0824
0.0008(2)
R1=0.0482
wR2=0.1027
R1=0.0653
wR2=0.1191
0.00051(9)
R1=0.0336
wR2=0.0713
R1=0.0487
wR2=0.0835
0.0014(3)
R indices (all data)
Extinction coefficient
Largest diff. peak/hole (e A
−3
,
)
0.441/−0.578
1.010/−1.274
0.452/−0.585
3. Experimental
Br3C6H2NSO was performed by a literature known
procedure [20].
3.1. General methods
All synthetic procedures were performed under atmo-
sphere of purified argon using standard Schlenk tech-
nique. Solvents were distilled over appropriate drying
agent and degassed prior to use. The NMR-spectra on
1H, 13C, 19F nuclei were obtained on a Varian VXR-400
spectrometer. Mass-spectra analyses were performed on
Varian CH-7a MAT device using electron-impact tech-
nique. Na2MoO4, Me3SiCl and Et3N were used as
supplied (Merck, Aldrich). The synthesis of 2,4,6-
3.2. X-ray crystallography
Crystal data, data collection, structure solution and
refinement parameters for compounds 3b, 4 and 2a are
listed in the Table 3. In the structures of 2a and 3b all
hydrogen atoms were found from difference Fourier
synthesis and refined in isotropic approximation. For
the structure of 4, all hydrogen atoms were placed in
calculated positions and refined using a riding model.

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K.A. Rufano6 et al. / Polyhedron 20 (2001) 379–385
3.3. Synthesis of [Mo(O)2Cl2(dme)] (1)
3.6. Synthesis of [Mo(N-2,6-Cl2C6H4)2Cl2(dme)] (3b)
To a stirred suspension of Na2MoO4 (20.6 g, 100
mmol) in dme (200 ml) Me3SiCl (50.76 ml, 400 mmol)
was added in one portion. The obtained mixture was
heated under reflux for approximately 12 h. The solu-
tion was cooled to r.t. The obtained precipitate of NaCl
was filtered off, the solution was then evaporated giving
pale-blue crystalline solid. The compound was washed
by hexane (50 ml) and dried in vacuo. The yield is 26.3
g (91%). 1H NMR (CDCl3): l (ppm) 3.95 (s, 4H,
CH2Oꢀ) and 4.00 (s, 6H, ꢀOCH3). MS (EI, 70 eV): 200
(M+-dme), 165 (M+-dme-Cl), 90 (dme).
To the stirred suspension of Na2MoO4 (2.06 g, 10
mmol) in dme (100 ml) 2,6-dichloroaniline (3.24 g, 20
mmol) and Et3N (5.58ml, 40 mmol) each in dme (20 ml)
were added. Then Me3SiCl (10.15 ml, 80 mmol) was
added dropwise. The suspension was stirred under gen-
tle reflux for 18 h to afford dark red mixture. The
solution was allowed to achieve r.t. and was filtered
from the ammonium salt precipitated. The precipitate
was washed by dme (2×30 ml) and the extract was
combined with the initial mother solution. The filtrate
was partially evaporated and cooled to 0°C to give
analytically pure red needles in a yield of 5.20 g (90%).
1H NMR (CDCl3): l (ppm) 7.26 (Hm, d, 4H); 6.93(Hp,
t, 2H); 4.0 (dme, br.s, 10H). MS (EI, 70 eV): 488
(M+-dme). Anal. Calc. for C16H16Cl6MoN2O2: C,
33.30; H, 2.79; N, 4.86; Mo, 16.6. Found: C, 32.95; H,
2.72; N, 4.69; Mo, 15.4%.
3.4. Synthesis of [Mo(NC6F5)(O)Cl2(dme)] (2a)
To a stirred suspension of Na2MoO4 (1.03 g, 5
mmol) in dme (70 ml) C6F5NH2 (0.95 g, 5 mmol), Et3N
(1.38 ml, 10 mmol), and Me3SiCl (3.8 ml, 30 mmol)
each in 10 ml dme are added. The reaction mixture was
stirred for 1h at room temperature and then for addi-
tional 6 h at 68°C. The red solution was allowed to cool
to r.t. and was filtered from the precipitate formed. The
volatile components were removed in vacuum to give a
red oily product. The latter was dissolved with hexane
(30 ml) and left in the freezer overnight. The orange
precipitate obtained was collected by filtration, washed
by pre-cooled pentane (20 ml) and dried in vacuum;
yield 1.48 g (65%). Analytical pure orange crystals were
3.7. Synthesis of [Mo(N-2,4,6-Cl3C6H2)2Cl2(dme)] (3a)
The complex 3a was prepared analogously to the
synthesis of 3b starting from 2,4,6-trichloroaniline (3.91
g, 20 mmol). The yield is 5.60 g (75%). 1H NMR
(CDCl3): l (ppm) 7.56 (Hm, d, 4H); 3.8 (dme, br, s,
10H). MS (EI, 70 eV): 523 (M+-dme). Anal. Calc. for
C16H14Cl8MoN2O2: C, 29.75; H, 2.18; N, 4.34; Mo,
14.9. Found: C, 30.05; H, 2.01; N, 4.33; Mo, 15.1%.
1
obtained by re-crystallisation from toluene. H NMR
3.8. Synthesis of [Mo(N-2,5-Cl2C6H4)2Cl2(dme)] (3c)
(CDCl3): l (ppm) 3.6 (s, 4H, CH2Oꢀ) and 3.4 (s, 6H,
ꢀOCH3). MS (EI, 70 eV): 365 (M+-dme), 420 (M+ꢀCl).
Anal. Calc. for C10H10Cl2F5MoNO3: C, 26.40; H, 2.20;
N, 3.08. Found: C, 27.10; H, 2.35; N, 3.10%.
The complex 3c was prepared analogously to the
synthesis of 3b starting with 2,5-dichloroaniline (20
mmol, 3.24 g). The yield is 5.49 g (95%). 1H NMR
(CDCl3): l (ppm) 8.10 (Ho, d, 2H); 7.53 (Hm,p, m, 4H);
3.8 (dme, br, s, 10H). MS (EI, 70 eV): 488 (M+-dme).
Anal. Calc. for C16H16Cl6MoN2O2: C, 33.30; H, 2.79;
N, 4.86; Mo, 16.6. Found: C, 33.05; H, 2.61; N, 4.98;
Mo, 16.4%.
3.5. Synthesis of [Mo(NC6F5)2Cl2(dme)] (2b)
Na2MoO4 (1.03 g, 5 mmol), C6F5NH2 (1.83 g, 10
mmol), Et3N (2.79 ml, 20 mmol) and Me3SiCl (5.1 ml,
40 mmol) were sequentially mixed in dme (100 ml). The
reaction mixture was stirred under reflux for 18 h. The
mixture was cooled at r.t. and treated as described
above for 2a. The oily residue was diluted by pentane
(40 ml), all insoluble admixtures were then filtered off
and the mother liquid was cooled on dry ice for 24 h
3.9. Synthesis of [Mo(N-2,4,6-Br3C6H2)2Cl2(dme)] (4)
A mixture of 1 (1.45 g, 5 mmol) and N-sulfinyl-2,4,6-
tribromoaniline (3.75 g, 10 mmol) was refluxed in tolu-
ene (70 ml) for 6 h. After cooling the solution to r.t.,
the dark red crystalline product immediately separated.
The crystals were collected, washed by Et2O (20 ml)
1
giving red needles of 2b in a yield of 1.08 g (35%). H
1
NMR (CDCl3): l (ppm) 4.05 (s, 4H, CH2Oꢀ); 4.0 (s,
6H, ꢀOCH3). 19F NMR (CDCl3): l (ppm) −145.0
(o-F, d, 4F); −152.2 (p-F, t, 2F); −161.4 (m-F, dd,
4F). MS (EI, 70 eV): 620 (M+), 570 (M+−CH3Cl),
530 (M+-dme). Anal. Calc. for C16H10Cl2F10MoN2O2:
C, 31.04; H, 1.63; N, 4.52. Found: C, 30.72; H, 1.65; N,
4.50%.
and dried under vacuum. The yield is 4.4 g (97%). H
NMR (CDCl3): l (ppm) 7.94 (sym-Hm, s, 2H); 7.45,
7.53 (assym-Hm, s, s, 1H, 1H); 3.9 (dme, br, s, 10H).
MS (EI, 70 eV): 863 (M+ꢀCH3Cl), 823 (M+-dme).
Anal. Calc. for C16H14Br6Cl2MoN2O2: C, 21.09; H,
1.54; N, 3.07; Mo, 10.5. Found: C, 21.34; H, 1.53; N,
3.02; Mo, 10.1%.

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4. Supplementary data
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 136118 for compound 3b,
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may be obtained free of charge from The Director, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
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http://www.ccdc.cam.ac.uk).
Acknowledgements
This work was supported by Russian Foundation for
Basic Research (grant No 98-03-33142). Finacial sup-
port of INTAS 96-1185 and SFB-260 is greatfully
acknowledged. Special thanks must be expressed to
Prof. Ludmila Kuz’mina (N.S. Kurnakov Institute,
Moscow) for fruitful discussions on the X-ray structure
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