Synthesis and structure of a series of new d1-aryl imido-vanadium(IV) complexes stabilized by N-donor ligands

Article abstract of DOI:10.1021/ic020312y

A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are reported. Reaction of V(NMe₂)₄ with anilines ArNH₂, where Ar = 2,6-i-Pr₂-C₆H₃, 2,6-Me₂-C₆H₃, Ph, 2,6-Cl₂-C₆H₃, and C₆F₅, afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe₂)₂]₂ (1a-e). Chlorination of 1a-e with trimethylchlorosilane afforded complexes 2a-e formulated as [V(=NAr)Cl₂(NHMe₂)_x]_n. One-pot reaction of V(NMe₂)₄ with ArNH₂ in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(=NAr)-Cl₂(NHMe₂)₂] (3a-e). Reaction of 3a-e with pyridine, bipyridine (bipy), or N,N,N′,N′-tetramethylethylenediamine (tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(=NAr)Cl₂(Py)₃] (4a-e) or [V(=NAr)-Cl₂(Py)₂(NHMe₂)] (5a), bipyridine complexes [V(=NAr)Cl₂(bipy)(NHMe₂)] (5a-e) and [V(=NAr)Cl₂(bipy)(Py)] (9a), and tmeda adduct [V(=NAr)Cl₂(tmeda)(NHMe₂) (10a). Moreover, five-coordinate complexes free of NHMe₂ ligands, such as [V(=NAr)Cl₂(PY)₂] (5a), [V(=NAr)Cl₂(bipy)] (8a), and [V(=NAr)Cl₂(tmeda)] (11a), were directly prepared starting from precursors 2a-e. All compounds were totally characterized by spectroscopic methods (IR, ¹H NMR for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.

Full text of DOI:10.1021/ic020312y

Inorg. Chem. 2002, 41, 4217−4226
Synthesis and Structure of a Series of New d1-Aryl Imido−Vanadium(IV)
Complexes Stabilized by N-Donor Ligands
Christian Lorber,* Robert Choukroun, and Bruno Donnadieu
Laboratoire de Chimie de Coordination, CNRS UPR 8241, 205 route de Narbonne,
31077 Toulouse Cedex 04, France
Received May 3, 2002
A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are
reported. Reaction of V(NMe2)4 with anilines ArNH , where Ar ) 2,6-i-Pr2-C H , 2,6-Me2-C H , Ph, 2,6-Cl2-C H ,
2
6
3
6
3
6 3
and C F , afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe2)2]2 (1a−e). Chlorination of 1a−e with
6
5
trimethylchlorosilane afforded complexes 2a−e formulated as [V(dNAr)Cl2(NHMe2)x]n. One-pot reaction of V(NMe2)4
with ArNH in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(dNAr)-
2
Cl2(NHMe2)2] (3a−e). Reaction of 3a−e with pyridine, bipyridine (bipy), or N,N,N′,N′-tetramethylethylenediamine
(tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(dNAr)Cl2(Py)3] (4a−e) or [V(dNAr)-
Cl2(Py)2(NHMe2)] (5a), bipyridine complexes [V(dNAr)Cl2(bipy)(NHMe2)] (5a−e) and [V(dNAr)Cl2(bipy)(Py)] (9a),
and tmeda adduct [V(dNAr)Cl2(tmeda)(NHMe2)] (10a). Moreover, five-coordinate complexes free of NHMe2 ligands,
such as [V(dNAr)Cl2(Py)2] (5a), [V(dNAr)Cl2(bipy)] (8a), and [V(dNAr)Cl2(tmeda)] (11a), were directly prepared
starting from precursors 2a−e. All compounds were totally characterized by spectroscopic methods (IR, 1H NMR
for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-
crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.
Introduction
metathesis,8 oxo-imido exchange,9 C-H activation,10 reac-
tions with unsatured C-C11 or C-X bonds,12...
The last two decades have witnessed a strong interest in
the coordination chemistry of transition metal complexes
containing imido ligands [NR]2- (R ) alkyl or aryl).1,2 The
dianionic π-donor terminal imido functional group is in-
volved in a rich chemistry that can be subdivided into two
types: the first concerns reactions in which the imido group
acts as a spectator ligand,1,2 the [NR]2- moiety being isolobal
with [C5H5]- 3 (e.g. in alkene methathesis4 or olefin
polymerization5-7), but the MdNR linkage itself can also
be involved in a variety of transformations such as imine
As part of an ongoing study of vanadium alkoxide,13
diamide,14 poly-yne,15 or iminoacyl16 complexes, we recently
described the synthesis and molecular structure of the new
terminal imido complex [V(NdAr)Cl2(NHMe2)2] (Ar ) 2,6-
i-Pr2-C6H3),7 one of the very few Cp-free vanadium(IV)
(8) (a) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 974-985. (b) Meyer, T. Y.; Kantrell, G. K. Chem.
Commun. 1997, 1551-1552. (c) Meyer, T. Y.; Kantrell, G. K.
Organometallics 1997, 16, 5381-5883. (d) McInnes, J. M.; Mountford,
P. Chem. Commun. 1998, 1669-1670.
(9) Nugent, W. A. Inorg. Chem. 1983, 22, 955-969.
* E-mail: lorber@lcc-toulouse.fr.
(10) (a) Bennet, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1997, 119,
10696-10709. (b) Lee, S. Y.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 5877-5878.
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Interscience: New York, 1998.
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W.; Hockless, D. C. R.; O’Neil, P. A.; Gibson, V. C. J. Chem. Soc.,
Dalton Trans. 1992, 739-751.
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2000, 4497-4498.
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10.1021/ic020312y CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/16/2002
Inorganic Chemistry, Vol. 41, No. 16, 2002 4217

Lorber et al.
Chart 1. Designation of Vanadium-Imido Complexesa
terminal imido compounds that have been structurally
characterized.17-20
In this paper we report on the synthesis of a series of new
aryl imido derivatives of vanadium(IV) prepared by an
extremely convenient one-pot reaction, together with some
aspects of their coordination chemistry toward neutral
N-donor ligands: pyridine (Py), bipyridine (bipy), and
N,N,N′,N′-tetramethylethane-1,2-diamine (tmeda).
a Ar ) 2,6-i-Pr2-C6H3 (a), 2,6-Me2-C6H3 (b), Ph (c), 2,6-Cl2-C6H3 (d),
and C6F5 (e).
Experimental Section
blocks), 10a (red plates), and 11a (dark-green blocks). For the seven
structures data were collected at low temperature (T ) 180 K) on
a Stoe Imaging Plate Diffraction System (IPDS), equipped with an
Oxford Cryosystems Cryostream Cooler Device and graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å). Final unit cell
parameters were obtained by means of a least-squares refinement
of a set of 8000 well-measured reflections, and the crystal decay
was monitored during data collection by measuring 200 reflections
by image; no significant fluctuation of intensities has been observed.
Structures have been solved by means of Direct Methods with the
program SIR92,23 and subsequent difference Fourier maps and
models were refined by least-squares procedures on F2 by using
SHELXL-9724 integrated in the package WINGX version 1.64,25
and empirical absorption corrections were applied to the data.26
All hydrogen atoms have been located on differences Fourier maps
and introduced in the refinement in idealized positions by using
rigid groups with an isotropic thermal parameter fixed at 20% higher
than those of carbon atoms with which they are connected, except
for few specific hydrogen atoms which have been isotropically
refined (those on NHMe2 groups). For the seven structures all non-
hydrogen atoms were anisotropically refined: in the last cycles of
refinement a weighting scheme was used, where weights are
General Methods and Instrumentation. All manipulations were
carried out using standard Schlenk line or drybox techniques under
an atmosphere of argon. Solvents were refluxed and dried over
appropriate drying agents under an atmosphere of argon and
collected by distillation. NMR spectra were recorded on Bruker
AM200, AM250, and DPX300 spectrometers and referenced
internally to residual protio-solvent (1H) resonances and are reported
relative to tetramethylsilane (δ ) 0 ppm). 19F NMR (188 MHz)
spectra were recorded on a Brucker AM200 spectrometer (reference
CF3CO2H). Chemical shifts are quoted in δ (ppm). Infrared spectra
were prepared as KBr pelets under argon in a glovebox and were
recorded on a Perkin-Elmer Spectrum GX FT-IR spectrometer.
Infrared data are quoted in wavenumber (cm-1). EPR spectra were
recorded on a Bruker ESP300E spectrometer. Elemental analyses
were performed at the Laboratoire de Chimie de Coordination
(Toulouse, France) (C, H, N) or by the Service Central de
Microanalyses du CNRS at Vernaison (France) (C, H, N, Cl).
Magnetic susceptibility data were collected on powdered samples
of the different compounds with use of a homemade Faraday-type
automatic magnetometer with mercury tetra(thiocyanato)cobaltate
(susceptibility at 20°, 16.44 × 10-6 cm3 mol-1). Diamagnetic
corrections were applied by using Pascal’s constants.21 Although
each compound was characterized by IR spectroscopy, only the
data corresponding to νNH are given in the experimental part; for
full IR spectroscopy data see the Supporting Information.
V(NMe2)4 was prepared by a modification of a literature
procedure.22 Liquid anilines ArNH2 (Ar ) 2,6-i-Pr2-C6H3, 2,6-Me2-
C6H3, Ph) were dried over KOH, refluxed, distilled, and stored over
4 Å molecular sieves under argon before use. Trimethylchlorosilane
was distilled and stored over 4 Å molecular sieves under argon
before use.
2
calculated from the following formula: w ) 1/[σ2(Fo ) + (aP)2 +
2
bP], where P ) (Fo + 2Fc2)/3.
Synthesis of Complexes [V(NAr)(NMe2)2]2 (1a-e): General
Procedure (See Supporting Information for Full Details). A
toluene solution (4 g) of 1.00 g of V(NMe2)4 (4.40 mmol) and
ArNH2 (4.40 mmol) was heated at 100 °C for 1 day giving a dark-
red solution. Removal of the volatiles under vacuum gave a purple
oil that was triturated several times with 5 mL of pentane and dried
under vacuum for a prolonged period of time to afford a sticky
solid. Analytically pure samples were obtained after two successive
recrystallizations in cold pentane.
Crystal Structure Determination of 1b, 3d, 4b, 4d, 7c, 10a,
and 11a. Reference is made to the numerical designation of
complexes in Chart 1. The structures of the seven compounds in
Table 1 were determined: crystals of 1b (dark-red blocks), 3d
(orange blocks), 4b (red blocks), 4d (dark-red blocks), 7c (red
(a) [V(N-2,6-C6H3iPr2)(NMe2)2]2 (1a): Yield 51% (red purple
solid). 1H NMR (C6D6) 7.28 (d, 2H, m-C6H3), 7.00 (t, 1H, p-C6H3),
4.35 (sept, 2H, CHMe2), 3.00 (s, 12H, NMe2), 1.24 (d, 12H,
CHMe2). µeff(20 °C) ) 0 µB. Anal. Calcd for C16H29N3V: C, 61.13;
H, 9.30; N, 13.37. Found: C, 60.91; H, 9.42; N, 13.62.
(b) [V(N-2,6-C6H3Me2)(NMe2)2]2 (1b): Yield 70% (red purple
solid). 1H NMR (C6D6) 7.19 (d, 2H, m-C6H3), 6.98 (t, 1H, p-C6H3),
2.99 (s, 12H, NMe2), 2.07 (s, 6H, MeAr). µeff ) 0 µB (300 K). Anal.
Calcd for C12H21N3V: C, 55.81; H, 8.20; N, 16.27. Found: C,
54.98; H, 8.29; N, 15.08.
(13) Lorber, C. Unpublished results.
(14) Lorber, C.; Donnadieu, B.; Choukroun, R. Organometallics 2000, 19,
1963-1966.
(15) (a) Choukroun, R.; Lorber, C.; Donnadieu, B.; Henner, B.; Frantz,
R.; Guerin C. Chem. Commun. 1999, 1099-1100. (b) Choukroun,
R.; Donnadieu, B.; Lorber, C.; Pellny, P.-M; Baumann, W.; Rosenthal,
U. Chem. Eur. J. 2000, 6, 4505-4509.
1
(16) Choukroun, R.; Donnadieu, B.; Lorber, C. Chem. Eur. J. 2002, 8,
2700-2704.
(c) [V(NPh)(NMe2)2]2 (1c): Yield 80% (dark-purple solid). H
NMR (C6D6) 7.51 (dd, 2H, m-C6H5), 7.41 (d, 2H, o-C6H5), 6.98 (t,
(17) Preuss, F.; Perner, J.; Frank, W.; Reiss, G. Z. Anorg. Allg. Chem. 1999,
625, 901-909.
(18) Davis, J. A.; Davie, C. P.; Sable, D. B.; Armstrong, W. H. Chem.
Commun. 1998, 1649-1650.
(23) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(24) SHELX97 [Includes SHELXS97, SHELXL97, CIFTAB], Programs
for Crystal Structure Analysis (Release 97-2); Sheldrick, G. M.;
Institu¨t fu¨r Anorganische Chemie der Universita¨t: Tammanstrasse 4,
D-3400 Go¨ttingen, Germany, 1998.
(19) Hagen, H.; Bezemer, C.; Boersma, J.; Kooijman, H.; Lutz, M.; Spek,
A. L.; van Koten, G. Inorg. Chem. 2000, 39, 3970-3977.
(20) Gade, L. H.; Mountford, P. Coord. Chem. ReV. 2001, 216-217, 65-
99.
(21) Pascal, P. Ann. Chim. Phys. 1910, 19, 5.
(22) Bradley, D. C.; Gitlitz, M. H. J. Chem. Soc. A 1969, 980.
(25) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(26) Walker, N.; Stuart, D. Acta Crystallogr. A 1983, 39, 158-166.
4218 Inorganic Chemistry, Vol. 41, No. 16, 2002

Synthesis of New d1-Aryl Imido-Vanadium(IV) Complexes
Table 1. Crystallographic Data, Data Collection, and Refinement Parameters for Compounds 1b, 3d, 4b, 4d, 7c, 10a, and 11a
1b
3d
4b
4d
7c
10a
11a
chem formula
fw
cryst system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C24H42N6V2
516.52
monoclinic
P21/n
10.2676(8)
14.6499(11
18.1559(14)
90.0
97.638(9)°
90.0
2706.8(4)
4
1.267
0.712
1096
C10H17Cl4N3V
372.01
triclinic
P1h
9.879(5)
10.247(5)
10.334(5)
109.261(5)
100.005(5)
117.271(5)
809.3(7)
2
C51H48Cl4N9V2
1030.66
monoclinic
C2/c
33.724(5)
9.941(5)
16.617(5)
90.0
102.497(5)
90.0
5439(3)
4
C21H18Cl4N4V
519.13
monoclinic
P21/c
10.355(2)
9.966(2)
22.725(5)
90.0
98.84(3)
90.0
2317.3(8)
4
1.488
0.905
1052
C19H22Cl4N4V
499.15
triclinic
P1h
9.916(5)
11.723(5)
12.082(5)
110.152(5)
112.847(5)
96.685(5)
1163.1(9)
2
C20H40Cl2N4V
458.40
monoclinic
I2/a
14.431(3)
13.298(3)
28.605(6)
90.0
94.40(3)
90.0
5473(2)
8
1.113
0.568
1960
C18H33Cl2N3V
413.31
monoclinic
P21/n
11.147(5)
19.357(5)
10.003(5)
90.0
94.763(5)
90.0
2150.9(15)
4
1.276
0.715
876
Z
D
calcd, g cm-3
1.527
1.259
378
1.259
0.581
2124
1.425
0.898
510
µ(Mo KR), mm-1
F(000)
2θ range (deg)
measured reflcns
unique reflcns/Rint
parameters/restraints
final R indices [I > σ2(I)]
R1
4.52-52.34
4.52-46.50
4.82-44.92
5.46-41.62
4.66-52.24
4.94-46.52
4.60-52.16
19956
5927
13448
3740
11148
14292
16529
5039/0.0518
301/0
2175/0.0578
173/1
3514/0.0325
162/365
1719/0.1560
272/0
4130/0.0364
259/0
3898/0.0421
262/25
4103/0.0481
225/0
0.0363
0.0813
0.0586
0.1504
0.0455
0.1214
0.1227
0.3470
0.0349,
0.0918
0.0403,
0.1052
0.0298
0.0781
wR2
final R indices all data
R1
wR2
goodness of fit
∆Fmax - ∆Fmin
0.0597
0.0901
0.970
0.329 and
-0.326
0.0683
0.1587
1.062
0.832 and
-0.511
0.0509
0.1269
1.045
1.076 and
-0.436
0.1384
0.3597
1.130
0.704 and
-0.775
0.0374
0.0938
1.043
0.597 and
-0.669
0.0504
0.1100
1.047
0.289 and
-0.315
0.0342
0.0807
1.039
0.387 and
-0.245
1H, p-C6H5), 3.04 (s, 12H, NMe2). µeff ) 0 µB (300 K). Anal. Calcd
for C10H17N3V: C, 52.17; H, 7.44; N, 18.25. Found: C, 51.33; H,
7.62; N, 17.27.
(d) [V(N-2,6-C6H3Cl2)(NMe2)2]2 (1d): Yield 70% (brown solid).
1H NMR (C6D6) 6.80 (d, 2H, m-C6H3), 6.50 (t, 1H, p-C6H3), 3.25
(s, 12H, NMe2). µeff ) 0 µB (300 K). Anal. Calcd for C10H15-
Cl2N3V: C, 40.16; H, 5.05; N, 14.05. Found: C, 39.12; H, 4.36;
N, 11.25.
(e) [V(NC6F5)(NMe2)2]2 (1e): Yield 68% (dark red-purple solid).
1H NMR (C6D6) 3.08 (s, 12H, NMe2). 19F NMR (C6D6) -78.60
(d, 2F, o-C6F5), -89.80 (t, 2F, m-C6F5), -92.65 (t, 1F, o-C6F5).
µeff ) 0 µB (300 K). Anal. Calcd for C10H12F5N3V: C, 37.52; H,
3.78; N, 13.12. Found: C, 38.06; H, 3.72; N, 12.33.
EPR Monitoring of the Formation of 1a-e. A stock solution
of V(NMe2)4 (10-2 M) in toluene was prepared and used as
reference for EPR and to perform a calibration curve of the EPR
spectra at different concentrations. One equivalent of the anilines
ArNH2 was added to 1 mL of V(NMe2)4 solution and the evolution
of the reaction (formation of the bridged imido complex) was
monitored by EPR spectroscopy at room temperature and 100 °C.
The vanadium(IV) signal was integrated and compared to the signal
of the reference solution of V(NMe2)4 and its calibration curve. In
all cases, when present, the EPR signal observed after reaction with
the aniline integrated less than 5% of the initial integration of the
vanadium(IV) before adding the aniline.
Attemps to Prepare [V(NAr)Cl2]n: Synthesis of Compounds
2a-e. A toluene solution (2 g) of 250 mg of V(NMe2)4 (1.10 mmol)
and 1 equiv of aniline ArNH2 (1.10 mmol) was heated at 100 °C
for 1 day giving a dark-red solution. After removal of the volatiles,
toluene (2 g) and excess Me3SiCl (1.20 g) were added and the
solution was stirred for 2 days at 100 °C. Removal of the volatiles
under vaccum and washing with pentane afforded dark red-purple
(2a, 2c, 2e) or brown (2b, 2d) solids (240-300 mg). EPR (PhCH3,
20 °C): 2a, g ) 1.989, A(51V) ) 92.5 G; 2b, g ) 1.989, A(51V) )
93.1 G; 2d, g ) 1.988, A(51V) ) 90.5 G; 2e, g ) 1.989, A(51V) )
89.4 G. Satisfactory and reproducible elemental analyses (C, H,
N) have not been obtained for this series of compounds, with data
corresponding to compounds having analyses between those
expected for 2a-e and 3a-e (see Results and Discussion).
Synthesis of Complexes [V(dNAr)Cl2(NHMe2)2] (3a-e):
General Procedure (See Supporting Information for Full
Details). To a toluene solution (5 mL) of 1.00 g of V(NMe2)4 (4.40
mmol) was added the aniline ArNH2 (4.40 mmol) at room
temperature. Then, to this solution was slowly added 4.00 g of Me3-
SiCl at room temperature. The resulting solution was placed in a
25 mL screw cap vial and heated at 100 °C for 20 h. The volatiles
were pumped off, and the yellow-orange microcrystalline solid was
washed with pentane (2 × 10 mL) and dried under vacuum.
(a) [V(dN-2,6-C6H3iPr2)Cl2(NHMe2)2] (3a): Yield 88%. EPR
(PhCH3, 20 °C) g ) 1.990, A(51V) ) 92.3 G. IR 3274 (m, νNH),
3263 (m, νNH). µeff ) 1.80 µB (300 K). Anal. Calcd for C16H31-
Cl2N3V: C, 49.62; H, 8.07; N, 10.85; Cl, 18.31. Found: C, 49.34;
H, 8.00; N, 10.63; Cl, 18.25.
(b) [V(dN-2,6-C6H3Me2)Cl2(NHMe2)2] (3b): Yield 79%. EPR
(CH2Cl2, 20 °C) g ) 1.990, A(51V) ) 92.9 G. IR 3247 (s, νNH).
µeff ) 1.92 µB (300 K). Anal. Calcd for C12H23Cl2N3V: C, 43.52;
H, 7.00; N, 12.69. Found: C, 42.78; H, 6.96; N, 12.50.
(c) [V(dNPh)Cl2(NHMe2)2] (3c): Yield 80%. EPR (PhCH3, 20
°C) g ) 1.990, A(51V) ) 92.2 G. IR 3232 (s, νNH). µeff ) 1.90 µB
(300 K). Anal. Calcd for C10H19Cl2N3V: C, 39.62; H, 6.32; N,
13.86; Cl, 23.39. Found: C, 39.50; H, 6.21; N, 13.66; Cl, 22.72.
(d) [V(dN-2,6-C6H3Cl2)Cl2(NHMe2)2] (3d): Yield 96%. EPR
(PhCH3, 20 °C) g ) 1.988, A(51V) ) 92.4 G. IR 3255 (s, νNH).
Anal. Calcd for C10H17Cl4N3V: C, 32.29; H, 4.61; N, 11.30; Cl,
38.12. Found: C, 32.26; H, 4.73; N, 11.07; Cl, 37.53.
(e) [V(dNC6F5)Cl2(NHMe2)2] (3e): Yield 73%. EPR (PhCH3,
20 °C) g ) 1.992, A(51V) ) 87.7 G. IR 3252 (s, νNH). Anal. Calcd
for C10H14Cl2F5N3V: C, 30.56; H, 3.59; N, 10.69. Found: C, 30.05;
H, 3.75; N, 10.67.
Preparation of 2a from 3a. A 100-mg sample of orange
complex 3a was heated at 160 °C under a dynamic vacuum of
0.005-0.001 mbar for 2 h. The color of the solid turned red-purple.
Yield 70 mg. Analytically pure sample was obtained after extraction
with toluene (to remove trace of impurities due to decomposition).
Inorganic Chemistry, Vol. 41, No. 16, 2002 4219

Lorber et al.
EPR (CH2Cl2, 20 °C) g ) 1.990, A(51V) ) 92.9 G. Anal. Calcd
for C12H17Cl2NV: C, 48.51; H, 5.77; N, 4.71. Found: C; 48.35;
H, 5.95; N, 5.44.
Cl2N4V‚CH2Cl2: C, 51.48; H, 5.88; N, 9.60. Found: C, 51.56; H,
5.86; N, 9.98.
(b) [V(dN-2,6-C6H3Me2)Cl2(bipy)(NHMe2)] (7b): Yield 90%.
EPR (CH2Cl2, 20 °C) g ) 1.993, A(51V) ) 91.5 G. IR 3279 (w,
Synthesis of Complexes [V(dNAr)Cl2(Py)3] (4a-e): General
Procedure (See Supporting Information for Full Details). (a)
[V(dN-2,6-C6H3iPr2)Cl2(Py)3] (4a): A 250-mg sample (0.6465
mM) of 3a were dissolved in 2 mL of pyridine. The resulting red
solution was stirred overnight. Volatiles were removed under
vacuum to afford a red solid that was washed with pentane (yield
330 mg, 95%). EPR (PhCH3, 20 °C) g ) 1.990, A(51V) ) 92.9 G.
µeff ) 1.90 µB (300 K). Anal. Calcd for C27H32Cl2N4V: C, 60.68;
H, 6.04; N, 10.48. Found: C, 60.16; H, 6.13; N, 10.55. Alterna-
tively, 4a was prepared by the same procedure but starting with 2a
(instead of 3a), giving 4a in quantitative yield.
νNH). Anal. Calcd for C20H24Cl2N4V: C, 54.31; H, 5.47; N, 12.67.
Found: C, 53.97; H, 5.42; N, 12.36.
(c) [V(dNPh)Cl2(bipy)(NHMe2)] (7c): Yield 73%. This com-
pound crystallized with one molecule of dichloromethane as shown
by an X-ray analysis (vide infra). EPR (CH2Cl2, 20 °C) g ) 1.991,
A(51V) ) 92.8 G. IR 3220 (m, νNH). Anal. Calcd for C18H20-
Cl2N4V.CH2Cl2: C, 45.72; H, 4.44; N, 11.22. Found: C, 45.70;
H, 4.48; N, 11.20.
(d) [V(dN-2,6-C6H3Cl2)Cl2(bipy)(NHMe2)] (7d): Yield 80%.
EPR (CH2Cl2, 20 °C) g ) 1.990, A(51V) ) 90.8 G. IR 3250 (m,
(b) [V(dN-2,6-C6H3Me2)Cl2(Py)3] (4b): Compound 4b crystal-
lized as a pyridine solvate. Yield 36%. EPR (PhCH3, 20 °C) g )
1.991, A(51V) ) 93.5 G. µeff ) 1.84 µB (300 K). Anal. Calcd for
C23H24Cl2N4V.C5H5N: C, 60.63; H, 5.24; N, 12.56. Found: C,
59.94; H, 5.30; N, 12.36.
(c) [V(dNPh)Cl2(Py)3] (4c): Yield 86%. EPR (PhCH3, 20 °C)
g ) 1.993, A(51V) ) 92.1 G. µeff ) 1.98 µB (300 K). Anal. Calcd
for C21H20Cl2N4V: C, 56.02; H, 4.48; N, 12.44. Found: C, 55.94;
H, 4.98; N, 12.19.
(d) [V(dN-2,6-C6H3Cl2)Cl2(Py)3] (4d): Yield 83%. EPR (py-
ridine, 20 °C) g ) 1.991, A(51V) ) 91.5 G. µeff ) 1.82 µB (300 K).
Anal. Calcd for C21H18Cl4N4V: C, 48.58; H, 3.49; N, 10.79.
Found: C, 48.41; H, 3.45; N, 10.69.
(e) [V(dNC6F5)Cl2(Py)3] (4e): Yield 90%. EPR (CH2Cl2, 20
°C) g ) 1.992, A(51V) ) 92.1 G. Anal. Calcd for C21H15-
Cl2F5N4V: C, 46.69; H, 2.80; N, 10.37. Found: C, 47.00; H, 3.45;
N, 10.17.
Preparation of [V(dN-2,6-C6H3iPr2)Cl2(Py)2] (5a). Method
1: A 100-mg sample of complex 4a was heated at 105 °C for 1 h
under a dynamic vacuum (0.005-0.001 mbar) giving 5a as a
brown-red powder (80 mg). Anal. Calcd for C22H27Cl2N3V: C,
58.03; H, 5.98; N, 9.23. Found: C, 56.84; H, 5.73; N, 8.87.
Method 2: An 80-mg sample of pyridine (1.001 mM) was added
to a dichloromethane solution (2 mL) of compound 2a (150 mg,
0.5049 mM). The resulting red solution was layered with pentane
giving red crystals of 5a (110 mg, 55%). EPR (PhCH3, 20 °C) g )
1.993, A(51V) ) 91.4 G. Anal. Calcd for C22H27Cl2N3V: C, 58.03;
H, 5.98; N, 9.23. Found: C, 58.69; H, 5.72; N, 10.07.
Synthesis of [V(dN-2,6-C6H3iPr2)Cl2(NHMe2)(Py)2] (6a). A
55-mg sample of pyridine (0.6939 mM) was added to a toluene
solution (3 mL) of 3a (125 mg, 0.3304 mM) with stirring for 7 h.
The solution was filtered through a bed of Celite, and the solvent
of the filtrate was removed under vacuum to afford an orange solid
(110 mg, 67%). EPR (PhCH3, 20 °C) g ) 1.990, A(51V) ) 93.6 G.
IR 3274 (νNH, w), 3266 (νNH, w). Anal. Calcd for C24H34Cl2N4V:
C, 57.61; H, 6.85; N, 11.20. Found: C, 57.00; H, 6.67; N, 10.63.
Synthesis of Complexes [V(dNAr)Cl2(bipy)(NHMe2)] (7a-
e): General Procedure (See Supporting Information for Full
Details). (a) [V(dN-2,6-C6H3iPr2)Cl2(bipy)(NHMe2)] (7a): To
a dichloromethane solution (2 mL) of complex 3a (125 mg, 0.3304
mM) was added by portions 1 equiv of bipyridine (50 mg). The
resulting red-orange solution was left at room temperature without
stirring for 1 day, and then pentane (4 mL) was carefully layered
on this solution and the system was allowed to equilibrate for 3
days. The solvent was decanted, and the deep red crystals of 7a
were collected, washed with pentane, and vaccum dried (150 mg,
78%). 7a crystallized with one molecule of dichloromethane. EPR
(CH2Cl2, 20 °C) g ) 1.992, A(51V) ) 90.5 G. IR 3290 (m, νNH),
3270(m, νNH). µeff ) 1.94 µB (300 K). Anal. Calcd for C24H32-
ν
NH). Anal. Calcd for C18H18Cl4N4V: C, 44.75; H, 3.76; N, 11.60.
Found: C, 43.80; H, 3.77; N, 10.97.
(e) [V(dNC6F5)Cl2(bipy)(NHMe2)] (7e): Yield, 75%. EPR
(CH2Cl2, 20 °C) g ) 1.991, A(51V) ) 89.2 G. IR 3245 (m, νNH).
Anal. Calcd for C18H15Cl2F5N4V: C, 42.88; H, 3.00; N, 11.11.
Found: C, 42.84; H, 3.32; N, 11.40.
Synthesis of [V(dN-2,6-C6H3iPr2)Cl2(bipy)] (8a). Method 1:
A 79-mg sample of bipyridine was added to a dichloromethane (4
mL) of compound 2a (150 mg, 0.5049 mM). After a few hours,
crystallization started to occur, and pentane was slowly layered to
the dark red solution. Red crystals were collected by decantation
and dried under vacuum (190 mg, 83%). EPR (CH2Cl2, 20 °C) g
) 1.993, A(51V) ) 88.7 G. Anal. Calcd for C22H25Cl2N3V: C,
58.29; H, 5.56; N, 9.27. Found: C, 57.84; H, 5.03; N, 9.58.
Method 2: A 74-mg sample of compound 7a was heated at 140
°C under a dynamic vacuum of 0.05 mbar for 1 h (60 mg, 63%).
Anal. Calcd for C22H25Cl2N3V: C, 58.29; H, 5.56; N, 9.27.
Found: C, 56.70; H, 5.18; N, 9.20.
Synthesis of [V(dN-2,6-C6H3iPr2)Cl2(bipy)(Py)] (9a). To a
dichloromethane solution (2 mL) of complex 3a (125 mg, 0.3304
mM) was added in portions 1 equiv of bipyridine (50 mg). The
resulting red-orange solution was left at room temperature with
stirring for 2 h, and then 118 mg of pyridine was added. After 16
h, pentane was slowly added on the top of this solution. The red-
orange solid was collected after decantation of the solution and
dried under vacuum (170 mg, 96%). EPR (CH2Cl2, 20 °C) g )
1.992, A(51V) ) 92.1 G. Anal. Calcd for C27H30Cl2N4V: C, 60.91;
H, 5.68; N, 10.52. Found: C, 59.50; H, 5.78; N, 10.55.
Synthesis of [V(dN-2,6-C6H3iPr2)Cl2(tmeda)(NHMe2)] (10a).
A 355-mg sample of tmeda was added with stirring to a toluene
solution (3 mL) of complex 3a (0.6455 mM). After 18 h, the
volatiles were removed under vacuum, to give 290 mg of orange
crystals (yield 97%). EPR (CH2Cl2, 20 °C) g ) 1.990, A(51V) )
92.9 G. IR 3282 (w, νNH). µeff ) 1.80 µB (300 K). Anal. Calcd for
C20H40Cl2N4V: C, 52.40; H, 8.80; N, 12.22. Found: C, 52.35; H,
9.03; N, 11.37.
Synthesis of [V(dN-2,6-C6H3iPr2)Cl2(tmeda)] (11a). Complex
11a was prepared according to the same preparation as for complex
10a, but starting with 250 mg of 2a (yield 160 mg, 46%). EPR
(PhCH3, 20 °C) g ) 1.990, A(51V) ) 92.5 G. µeff ) 1.76 µB (300
K). Anal. Calcd for C18H33Cl2N3V: C, 52.31; H, 8.05; N, 10.17.
Found: C, 51.99; H, 8.32; N, 11.09.
Results and Discussion
This work constitutes the first systematic investigation of
the synthetic and structural chemistry of aryl imido-
vanadium(IV) complexes of any type. The synthesis and
proposed structures of the new aryl imido complexes of
4220 Inorganic Chemistry, Vol. 41, No. 16, 2002

Synthesis of New d1-Aryl Imido-Vanadium(IV) Complexes
vanadium(IV) are summarized in Schemes 1-3. Structures
of eight complexes are set out in Figures 1-8; selected metric
data are collected in Table 2.
1. Synthesis of the Imido Precursors. In our preliminary
paper,7 we described the synthesis of [V(dN-2,6-i-Pr2-C6H3)-
Cl2(NHMe2)2], in a two-step synthesis: reaction of the aniline
2,6-i-Pr2-C6H3-NH2 with V(NMe2)4 in toluene at 100 °C for
1 day afforded a dark red arylimido complex A that we
initially formulated as being “[V(dNAr)(NMe2)2(NHMe2)2]”.
A subsequent reaction with an excess of trimethylchlorosilane
at room temperature in toluene for 2 days afforded a purple
solid from which we could crystallized a complex formulated
as [V(dNAr)Cl2(NHMe2)2] based on its X-ray determination.
Keeping in mind that we are dealing with d1-V(IV) para-
magnetic species, and despite an elementary analysis for A
in accordance with a dimethylamine-free compound of the
type [V(dNAr)(NMe2)2], we concluded there must be a bis-
dimethylamine adduct A to explain the presence of two
NHMe2 in 3a (revealed by the crystal structure determination
of 3a).
Figure 1. Molecular structure of 1b with selected bond distances (Å) and
angles (deg), showing 50% probability ellipsoids and partial atom-labeling
schemes. Hydrogen atoms are omitted for clarity. V1‚‚‚V2 2.4955(6), V1-
N1 1.864(2), V1-N2 1.873(2), V1-N3 1.862(2), V1-N4 1.864(2), V2-
N1 1.877(2), V2-N2 1.878(2), V2-N5 1.866(2), V2-N6 1.842(2), N1-
C9 1.408(3), N2-C17 1.408(3); V1-N1-V2 83.70(8), V1-N2-V2
83.40(8), N1-V1-N2 95.73(9), N1-V2-N2 95.11(9).
Since then, we reexamined the first step of the reaction
between V(NMe2)4 and different anilines ArNH2 (Ar ) 2,6-
i-Pr2-C6H3, 2,6-Me2-C6H3, Ph, 2,6-Cl2-C6H3, C6F5), in both
pentane and toluene as solvent, in particular by following
the course of the reaction by EPR spectroscopy. In toluene,
at room temperature and 100 °C, the EPR spectra of a
solution containing an equimolar amount of V(NMe2)4 and
ArNH2 show the disappearance of more than 95% of the
strong eight-line characteristic signal of paramagnetic d1-
V(IV) species (due to hyperfine interaction between the
vanadium nucleus (I ) 7/2) and the unpaired electron), which
suggest the formation of diamagnetic compounds. From the
reaction of V(NMe2)4 and ArNH2 in toluene at 100 °C, we
isolated dark red to brown often sticky solids (Scheme 1),
but fortunately we were able to obtain crystals of one of
these complexes with Ar ) 2,6-Me2-C6H3 by cooling a
saturated pentane solution of 1b to -20 °C, which allowed
us to determine its molecular structure.
tion geometry of vanadium is distorted tetrahedral. The V2N2
core is almost planar (torsion angle V1-N1-V2-N2 )
10.93(8)°) and is characterized by a short V‚‚‚V distance
[V1‚‚‚V2 ) 2.4955(6) Å]; although this is one of the shortest
distances ever found among dinuclear complexes of vana-
dium, such a short V‚‚‚V distance is not unusual.27 The angle
formed by the bridging nitrogen atoms with the two
vanadium atoms [V1-N1-V2 ) 83.70(8)°] deviates sig-
nificantly from that expected for an sp2 nitrogen atom. The
V-Nimido distances being comprised between 1.864 and 1.878
Å are longer by ca. 0.2 Å than in terminal imido complexes
(vide infra). The (Me2N)2V moiety is normal14 with the
expected V-N bond distances and angles [V-Namido ranging
from 1.842 to 1.866 Å].
Diamagnetic complexes 1a-e could later be characterized
1
by their H NMR spectroscopy (the sharpness of the peaks
The molecular structure of 1b is shown in Figure 1, with
selected bond distances and angles: the complex is a
dimer [V(N-2,6-Me2-C6H3)(NMe2)2]2 with two imido ligands
bridging two (Me2N)2V moieties. The molecule is a cen-
trosymmetric dimer (monoclinic, P21/n), and the coordina-
of the well-solved 1H NMR spectrum of 1a-e indicate that
the dinuclear structure is retained in C6D6 solution), elemental
analysis, and the absence of magnetic moment. The diamag-
netism of 1a-e indicates a strong electronic coupling
between the two metal centers, either through the nitrogen
Scheme 1. Synthesis of Aryl Imido-Vanadium(IV) Complexes 1-3
Inorganic Chemistry, Vol. 41, No. 16, 2002 4221

Lorber et al.
Table 2. Comparison of Average Interatomic Distances (Å) and Angles (deg)
1b
3aa
3d
4b
4d
7c
10a
11a
V-Nimido
imido-Cipso
V-Nimido-Cipso
V-Cl1
V-Cl2
Cl1-V-Cl2
V-NNHMe2
V-NPy(trans)
V-NPy(cis)
V-Nbipy
1.872(3)b
1.483(3)b
1.654(3)
1.380(5)
178.4(3)
2.3199(14)
2.3268(12)
136.48(5)
2.095(5)b
1.656(4)
1.388(6)
176.0(3)
2.3216(18)
2.3185(16)
135.69(6)
2.148(4)b
1.709(3)
1.395(4)
171.4(2)
2.4724(10)
2.4676(9)
168.44(3)
1.671(14)
1.38(2)
170.0(14)
2.390(6)
2.394(5)
168.0(2)
1.6754(16)
1.373(2)
171.74(14)
2.3866(12)
2.4075(10)
93.73(3)
1.676(2)
1.389(4)
1.6674(13)
1.3936(18)
164.48(10)
2.3078(8)
2.3231(8)
91.06(3)
N
177.59(19)
2.3573(10)
2.3748(11)
154.67(3)
2.16(3)
2.1947(19)
2.363(3)
2.298(14)
2.161(16)b
2.208(3)b
cis 2.1255(17)
trans 2.2363(16)
V-Ntmeda
cis 2.224(2)
trans 2.820(3)
2.199(2)b
a See ref 7. b Mean distance.
atoms of the imido bridges or resulting from the short V-V
distance. In pentane, the room temperature reactions between
V(NMe2)4 and ArNH2 give less clear-cut observations, since
mixtures of two or three compounds are often formed and
will not be discussed further here.
an oligomeric structure such as that in [Ti(Nt-Bu)(NH2t-
Bu)2]3,29a [(Me3SiN)TiCl2]8,29b or [t-BuNH3]2[V7(t-BuN)7(µ-
Cl)14Cl2]17 but with additional Me2NH co-ligands.
Taking into account this fact, we discovered a much more
convenient path to complexes of the type [V(dNAr)Cl2-
(NHMe2)2], 3a-e. When a toluene solution of V(NMe2)4 is
reacted in a one-pot reaction with 1 equiv of ArNH2 and an
excess of trimethylchlorosilane in a screw-cap vial at 100
°C overnight, yellow-orange 3a-e compounds are formed
exclusively and often separate by crystallization on cooling
to room temperature as large yellow-orange needles or
crystals with good yields (73-96%) (see Scheme 1). 3a-e
have been characterized by their infrared spectrum (with
strong νNH absorptions around 3250 cm-1 consistent with
NH‚‚‚Cl-V intermolecular hydrogen bonding weak interac-
tions), room temperature EPR spectrum (A(51V) ca. 88-93
G and g ) 1.990), elemental analysis, and magnetism studies
in agreement with d1-paramagnetic species (µeff ) ca. 1.7-
1.9 µB).
Single crystals of two of these complexes, 3a and 3d,
suitable for X-ray diffraction studies were obtained from cold
toluene-pentane (3a)30 or toluene (3d) solutions. A thermal
ellipsoid plot is presented in Figures 2 and 3 along with
selected bond lengths and angles, and Table 2 shows a
comparison of their structural parameters. Both molecular
structures are best described as distorted square-pyramid with
an axial aryl imido that exhibits a short vanadium-nitrogen
distance of 1.654(3) Å for 3a and 1.656(4) Å for 3d. The
imido linkage being almost linear [V1-N1-C1 angle )
178.4(3)° in 3a and 176.0(3)° in 3d] is consistent with the
lone pair on nitrogen being donated to an acceptor orbital
on vanadium. Hence the imido V-N bond can be considered
as a triple bond. The two chlorine atoms are mutually trans
with a Cl1-V-Cl2 angle of 136.48(5)° (3a) and 135.69(6)
Å (3d). V-Cl bonds are normal with mean V-Cl 2.323 Å
(3a) and 2.320 Å (3d). The two trans dimethylamino ligands
In a second step (Scheme 1), when 1a-e is reacted with
an excess of Me3SiCl in toluene at 100 °C,28 dimethylamido
ligands are exchanged for chlorine atoms, giving red-purple
or brown compounds 2a-e. We believe these compounds
have a general formula of variable composition [V(NAr)-
Cl2(NHMe2)x]n, x being between 0 and 2, based on three
pieces of evidence: (1) the color of 2a-e differs from
yellow-orange [V(dNAr)Cl2(NHMe2)2] (3a-e) (fully char-
acterized, vide infra), (2) very weak νNH bands may be
observed in the 3250 cm-1 region in 2a-e infrared spectra,
and (3) the elemental analysis of 2a-e is consistent with
such formulation for 2 (presence of NHMe2). The amount
of coordinated dimethylamine present in these materials is
probably dependent on the aryl group and on the length of
time complexes 1a-e were dried under vacuum in the
preceding step. The presence of NHMe2 in compounds 2a-e
may arise from the difficulty of removing it totally from oily
or sticky 1a-e, and may explain why we originally crystal-
lized a bis-amino adduct 3a from these red-purple or brown
solutions. The paramagnetic properties of these materials
precluded further spectroscopic investigations, and com-
pounds 2a-e rather could imply a mixture of compounds
in solution. While the available experimental data do not
establish a solution structure, we propose 2a-e consist of
an equilibrium mixture of oligomeric [V(NAr)Cl2]n, Me2-
NH, and the monomeric imido complex 3a-e. A similar
equilibrium has already been suggested in titanium imido
chemistry.29a In the solid state, compounds 2a-e may have
(27) (a) Solan, G. A.; Cozzi, P. G.; Floriani, C.; Chiesi-Villa, A.
Organometallics 1994, 13, 2572-2574. (b) Ruiz, J.; Vivanco, M.;
Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1993, 12,
1811-1822. (c) Preuss, F.; Becker, H.; Wieland, T. Z. Naturforsh. B
1988, 43B, 1195-1200. (d) Minhas, R. K.; Edema, J. J. H.;
Gambarotta, S.; Meetsma, A. J. Am. Chem. Soc. 1993, 115, 6710-
6717. (e) Edema, J. J. H.; Meetsma, A. J.; van Bolhris, F.; Gambarotta,
S. Inorg. Chem. 1991, 30, 2056-2061. (f) Dorfman, J. R.; Holm, R.
H. Inorg. Chem. 1983, 22, 3179-3181. (g) Buijink, J.-K. F.; Meetsma,
A.; Teuben, J. H.; Kooijman, H.; Spek, A. L. J. Organomet. Chem.
1995, 497, 161-170.
(29) (a) Lewkebandara, T. S.; Sheridan, P. H.; Heeg, M. J.; Rheingold, A.
L.; Winter, C. H. Inorg. Chem. 1994, 33, 5879-5889. (b) Betten-
hausen, R.; Milius, W.; Schnick, W. Chem. Eur. J. 1997, 3, 1337-
1341.
(30) The molecular structure of 3a was presented in a preliminary
communication (see ref 7). This complex was recently crystallized
(pentane, -20 °C) in a different crystallographic group: orthorhombic
Pbnm, a ) 10.4066(9) Å, b ) 16.6909(11) Å, c ) 10.7051(7) Å, V
) 2193.6(3) Å3.
(28) Although generally sufficient, it is nevertheless necessary in some cases
to perform the reaction at 100 °C to afford total and/or rapid
chlorination of the two dimethylamido ligands.
4222 Inorganic Chemistry, Vol. 41, No. 16, 2002

Synthesis of New d1-Aryl Imido-Vanadium(IV) Complexes
(in comparison to the strong νNH in 3a) suggests the loss of
NHMe2 ligands, with formation of a complex that may
certainly be similar to that of 2a.
Terminal imido compounds 3a-e obviously may be key
starting materials in a whole new coordination chemistry of
vanadium, and we have started to explore this new chemistry.
2. Reactivity toward Pyridine. When dissolved in pyri-
dine, complexes 3a-e (and 2a-e) instantly give dark red
solutions at room temperature. Slow addition of toluene
followed by layering these solutions with pentane affords
red crystals characterized as being the tris-pyridine adduct
trans,mer-[V(dNAr)Cl2(Py)3], 4a-e. Compounds 4a-e are
formed from 3a-e by an amine elimination reaction with
good yields (83-95%) (Scheme 2). Crystals suitable for an
X-ray analysis have been obtained for complexes 4b and
4d and an ORTEP view is presented in Figures 4 and 5.32
Compound 4b crystallizes with one molecule of pyridine.
Both complexes have a pseudooctahedral geometry with
mutually trans chloride and pyridine ligands, the third
pyridine ligand being trans to the imido group. The aryl rings
are rotated out of the VCl(1)Cl(2)NimidoNPy-trans plane by ca.
53.8(1)° and 61.5(4)° respectively for 4b and 4d, and so may
interact to some extent with both of the imido nitrogen pπ
orbitals (although the presence of o-aryl substituents may
contribute to that feature). Bond lengths and angles are
unexceptional, and are very similar to those of titanium
analogues:33 the vanadium-nitrogen bond distances of the
imido fragments were 1.709(2) and 1.700(14) Å respectively
for 4b and 4d, V-Nimido-Cipso of 171.4(2)° and 170.0(14)°
respectively for 4b and 4d, and average V-Cl of 2.470(10)
and 2.392(6) Å respectively for 4b and 4d. The trans
V-N(Py) of 2.363(3) and 2.398(14) Å respectively for 4b
and 4d are significantly longer than average cis V-N(Py)
bond distances of 2.208(3) and 2.161(16) Å respectively for
4b and 4d, suggesting that the trans-pyridine ligand is less
tighly bound then those bonded cis reflecting the trans-
labilizing ability of the imido ligand. Indeed, heating a
sample of 5a at 105 °C under a dynamic vacuum (0.005-
0.001 mbar) gave almost quantitative conversion to the
corresponding five-coordinate bis-pyridine complex [V(d
NAr)Cl2Py2] (5a: Ar ) 2,6-iPr2-C6H3), as a brownish
powder, reflecting the trans-labilizing ability of the imido
group in 5a.
Figure 2. Molecular structure of 3a with selected bond distances (Å) and
angles (deg), showing 50% probability ellipsoids and partial atom-labeling
schemes. Hydrogen atoms are omitted for clarity, except those on nitrogen
amino groups. V1-N1 1.654(3), V1-N2 2.018(5), V1-N3 2.171(4), V1-
Cl1 2.3202(14), V1-Cl2 2.3257(12), N1-C1 1.388(5); C1-N1-V1 178.4-
(3), Cl1-V1-Cl2 136.48(5), N2-V1-N3 165.23(16).
Figure 3. Molecular structure of 3d with selected bond distances (Å) and
angles (deg), showing 50% probability ellipsoids and partial atom-labeling
schemes. Hydrogen atoms are omitted for clarity, except those on nitrogen
amino groups. V1-N1 1.656(4), V1-N2 2.151(4), V1-N3 2.146(4), V1-
Cl1 2.3216(18), V1-Cl2 2.3185(16), N1-C1 1.388(6), N2-HN2 0.69(5),
N3-HN3 0.69(5); C1-N1-V1 176.0(3), Cl1-V1-Cl2 135.69(6), N2-
V1-N3 163.96(17).
form the base of the square pyramid with the two chlorine
5a could also be prepared by addition of only 2 equiv of
pyridine to complex 2a, affording a crystalline sample of
5a. Although we do not have a crystal structure of this
compound, we suggest it has a similar structure to that of
the titanium analogue,33 with the pyridine ligands trans of
the base of a square pyramid.
However, when the tris-amino complex 3a was reacted
with only 2 equiv of pyridine in toluene, an orange complex
6a was obtained (Scheme 2). This compound possesses two
atoms, and have V-Namine bonds of 2.018(5) and 2.171(4)
Å in 3a and 2.151(4) and 2.146(4) Å in 3d, with an Namine
-
V-Namine angle of 165.23(16)° in 3a and 163.96(17)° in 3d.
The hydrogen bonds between the N-H groups of NHMe2
ligands and V-Cl on neighboring vanadium complexes may
be considered as “intermediate” according to Brammer and
Orpen’s classification31 with V-Cl‚‚‚H-N contacts of 2.987
(3a) and 2.848 Å (3d) with associated angles of 127.9° and
154.6°, respectively.
Heating yellow-orange 3a at 160 °C for 2 h under vacuum
(0.001 mbar) gives a red-purple solid with little decomposi-
tion. This compound having almost no νNH in its IR spectrum
νNH bands in its infrared spectrum and its elemental analysis
(32) A crystal structure for complex 4a was also determined but will not
be discussed here. Monoclinic P21/n, a ) 18.6863(19) Å, b ) 17.8866-
(18) Å, c ) 18.7909(18) Å, â ) 119.447(10)°, V ) 5469.2(1) Å3.
(33) Collier, P. E.; Dunn, S. C.; Mountford, P.; Shishkin, O. V.; Swallow,
D. J. Chem. Soc., Dalton Trans. 1995, 3743-3745.
(31) Aullon, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.; Orpen, A. G.
Chem. Commun. 1998, 653-654.
Inorganic Chemistry, Vol. 41, No. 16, 2002 4223

Lorber et al.
Scheme 2. Synthesis of Aryl Imido-Vanadium(IV) Complexes 4-6
is consistent with a dimethylamino-bis-pyridine adduct
[V(dNAr)Cl2(NHMe2)Py2] (Ar ) 2,6-i-Pr-C6H3). At this
point we cannot exclude that 6a is a mixture of isomers,
i.e., the ligand trans to the imido group could either be the
NHMe2 group or one pyridine ligand.
3. Reaction with Bipyridine. Complexes 3a-e were also
reacted with 1 equiv of bipyridine at room temperature in
dichloromethane (Scheme 3). The solution rapidly turned
dark red, and slow addition of pentane caused the crystal-
lization of red crystals of complexes 7a-e. The structure
was assigned as being [V(NAr)Cl2(bipy)(NHMe2)] based on
spectral and analytical data, and from an X-ray crystal-
lographic structure determination. The infrared spectra of
7a-e show the characteristic band for νNH around 3250 cm-1.
A crystal structure for one of these new derivatives (7c) has
been obtained and is presented in Figure 6. The solid-state
structure of 7c confirms the presence of one NHMe2 ligand
with coordination of one bipy ligand and the pseudoocta-
hedral nature of the complex with the imido in the axial
Figure 4. Molecular structure of 4b with selected bond distances (Å) and
angles (deg), showing 50% probability ellipsoids and partial atom-labeling
schemes. Hydrogen atoms are omitted for clarity. V1-N1 1.709(3), V1-
N2 2.215(3), V1-N3 2.201(3), V1-N4 2.363(3), V1-Cl1 2.4724(10), V1-
Cl2 2.4676(9), N1-C1 1.395(4), C1-N1-V1 171.4(2); Cl1-V1-Cl2
168.44(3), N1-V1-N4 174.03(10), N1-V1-N2 94.33(10), N1-V1-N3
99.35(11), N3-V1-N2 166.25(9).
position [V-Nimido ) 1.6754(16) Å, V-Nimido-Cipso
)
171.74(14)°]. The chlorine atoms are mutually cis [V-Cl1
) 2.3866(12) Å and V-Cl2 ) 2.4075(10) Å], the NHMe2
ligand is trans to one chloride and cis to the other
[V-N(NHMe2) ) 2.195(2) Å], and the bipy ligand is trans
to the imido group and to one chloride atom, with the
nitrogen atom trans to the imido being significantly longer
by ca. 0.11 Å [trans V-Nbipy ) 2.2363(16) Å, cis V-Nbipy
) 2.1255(17) Å].
The hydrogen bonds between the N-H group of the
NHMe2 ligand and V-Cl on neighboring vanadium com-
plexes are now shorter with V-Cl‚‚‚H-N contacts of 2.58
Å and an associated angle of 148.0°.
the absence of the νNH band in the infrared spectrum of 8a
prepared in this way).
Seeking a complex containing both pyridine and bipyridine
ligands, we first reacted complex 3a with 1 equiv of
bipyridine (with in-situ formation of 7a) and 2 h later with
4 equiv of pyridine. Slow addition of pentane afforded
crystalline red-orange complex [V(NAr)Cl2(bipy)(Py)], 9a
(Ar ) 2,6-i-Pr-C6H3). Although we do not have a crystal
structure of this compound yet, we propose its structure is
similar to that of 7a with one pyridine ligand instead of the
dimethylamino group, but other isomers cannot be excluded
(Scheme 3).
4. Reaction with tmeda. We also investigated the
coordination chemistry of our imido complexes toward tmeda
(Scheme 3). Addition of 6 equiv of tmeda to a toluene
solution of 3a leads to complex 10a with 97% yield,34 fully
characterized including by an X-ray structure such as [V(d
NAr)Cl2(tmeda)(NHMe2)] (Ar ) 2,6-i-Pr-C6H3). Again, the
infrared spectrum shows the characteristic bands for the
NHMe2 ligand at 3281 cm-1. The molecular structure (Figure
Compound 2a possesses similar reactivity to that of 3a,
with the exception that complexes free of NHMe2 are now
accessible: 2a was reacted with 1 equiv of bipyridine in
dichloromethane. Dark red crystals of [V(NAr)Cl2(bipy)],
8a (Ar ) 2,6-i-Pr-C6H3), were obtained by carefully layering
pentane into this solution (Scheme 3). This compound was
also prepared by heating a sample of 7a at 140 °C under a
dynamic vacuum (0.05 mbar) for a prolonged time, which
released the coordinated NHMe2 ligand in 7a (confirmed by
4224 Inorganic Chemistry, Vol. 41, No. 16, 2002

Synthesis of New d1-Aryl Imido-Vanadium(IV) Complexes
Figure 6. Molecular structure of 7c with selected bond distances (Å) and
angles (deg), showing 50% probability ellipsoids and partial atom-labeling
schemes. Dichloromethane solvent and hydrogen atoms are omitted for
clarity, except the one on the nitrogen amino group. V1-N1 1.6754(16),
V1-N2 2.2363(16), V1-N3 2.1255(17), V1-N4 2.1947(19), N1-C1
1.373(2), V1-Cl1 2.3866(12), V1-Cl2 2.4075(10), V-H(4N) 0.88(3); V1-
N1-C1 171.74(14), Cl1-V1-Cl2 93.73(3), N1-V1-N2 169.40(7), N1-
V1-N3 95.71(7), N2-V1-N3 73.79(6).
Figure 5. Molecular structure of 4d with selected bond distances (Å) and
angles (deg), showing 50% probability ellipsoids and partial atom-labeling
schemes. Pyridine solvent and hydrogen atoms are omitted for clarity. V1-
N1 1.671(14), V1-N2 2.154(15), V1-N3 2.168(16), V1-N4 2.298(14),
V1-Cl1 2.390(6), V1-Cl2 2.394(5), N1-C1 1.38(2); C1-N1-V1 170.0-
(14), Cl1-V1-Cl2 168.44(3), N1-V1-N4, N1-V1-N2 96.9(6), N1-
V1-N397.0(7), N3-V1-N2 166.1(6).
Scheme 3. Synthesis of Aryl Imido-Vanadium(IV) Complexes 7-11
V-Nimido-Cipso angle of 177.59(19)°. Mutually trans chlorine
atoms are cis to the imido group [V-Cl1 ) 2.3773(10) and
V-Cl2 ) 2.3448 (11) Å], and the NHMe2 ligand is cis to
both chlorine atoms and trans to one nitrogen atom of the
tmeda ligand [V-N(NHMe2) ) 2.167(3) Å]. The tmeda
ligand, which is located trans to the imido group and to the
NHMe2 ligand, has a surprising coordination mode: the
nitrogen atom trans to the imido is longer by ca. 0.60 Å as
compared to the one in the basal plane [trans V-Ntmeda
)
2.820(3) Å, cis V-Nbipy ) 2.224(2) Å]. This very long
V-Ntmeda bond may arise from the trans influence of the
imido group. In that way, complex 10a may be regarded as
a 5-coordinate square-pyramidal complex (as in the bis-amino
complexes 3a-e) but with a very weak extra-coordination
to the tmeda nitrogen trans to the imido moiety. This point
may explain why the chlorine atoms are mutually trans in
tmeda complex 10a whereas they are cis in bipyridine
complex 7a.
Addition of tmeda to a toluene solution of 2a afforded
the NHMe2-free complex [V(dNAr)Cl2(tmeda)] (11a) (Ar
) 2,6-i-Pr-C6H3), in a similar way as we already observed
with bipy (complex 8a) or with 2 equiv of pyridine (complex
6a) (Scheme 3). The molecular structure (Figure 8) is best
described as a distorted square pyramid as in compound 3a
with an axial aryl imido that exhibits a V-N distance of
1.6674(13) Å, the imido linkage being somewhat less linear
than in 3a [V1-Nimido-Cipso angle ) 164.48(10)°]. Com-
pared to 3a, the major difference comes from the tmeda
ligand that forces the two chlorine atoms to be cis with a
Cl1-V-Cl2 angle of 91.06(3)° [V-Cl1 ) 2.3078(8) Å and
V-Cl2 ) 2.3231(8) Å]. The two cis nitrogen atoms of the
tmeda ligand form the base of the square pyramid with the
7) confirms the presence of one NHMe2 and one tmeda
ligand, with a pseudooctahedral geometry around the vana-
dium center. The imido fragment sits in the axial position
with a vanadium-nitrogen distance of 1.676(2) Å and a
(34) For unknown reasons, complex 3d does not react with an excess of
tmeda with replacement of the NHMe2 ligands.
Inorganic Chemistry, Vol. 41, No. 16, 2002 4225

Lorber et al.
Figure 8. Molecular structure of 11a with selected bond distances (Å)
and angles (deg), showing 50% probability ellipsoids and partial atom-
labeling schemes. Hydrogen atoms are omitted for clarity. V1-N1 1.6674-
(13), V1-N2 2.1774(15), V1-N3 2.2196(14), N1-C1 1.3936(18), V1-
Cl1 2.3078(8), V1-Cl2 2.3231(8), V1-N1-C1 164.48(10), Cl1-V1-Cl2
91.06(3), N2-V1-N3 79.39(5), N1-V1-N2 100.81(5), N1-V1-N3
108.24(6).
Figure 7. Molecular structure of 10a with selected bond distances (Å)
and angles (deg), showing 50% probability ellipsoids and partial atom-
labeling schemes. Hydrogen atoms are omitted for clarity, except the one
on the nitrogen amino group. V1-N1 1.676(2), V1-N2 2.224(2), V1-N3
2.820(3), V1-N4 2.167(3), N1-C1 1.389(4), V1-Cl1 2.3748(11), V1-
Cl2 2.3573(11); V1-N1-C1 177.59(19), Cl1-V1-Cl2 154.67(3), N1-
V1-N3 166.37(9), N1-V1-N2 92.28(9), N2-V1-N3 74.45(10).
or tmeda adducts. We are exploring the chemistry of imido
vanadium(IV) complexes with other imido groups (in
particular alkyl groups) and other donor ligands (with O or
P ligation) and their use in homogeneous catalysis. These
results will appear in future publications.
chlorine atoms, and have V-Ntmeda bonds of 2.1774(15) and
2.2196(14) Å, with a Ntmeda-V-Ntmeda angle of 79.39(5)°.
Conclusions
We have described simple routes to paramagnetic N-
containing ligands supported aryl imido-vanadium(IV)
dichloride complexes that demonstrate that such terminal
imido vanadium(IV) species are now accessible. The bis-
(dimethylamido) aryl imido complexes 1a-e have been
shown to be diamagnetic dimers that can be transformed by
chlorination into complexes 2a-e. Although the structure
of these materials was not conclusively established and
remains unclear, we showed that they represent precursors
for the synthesis of monomeric terminal imido complexes,
free of dimethylamine co-ligands. The bis(dimethylamino)
aryl imido dichloride derivatives 3a-e are stable and readily
obtained in a synthetically useful way, and give easy access
to the corresponding complexes with pyridine, bipyridine,
Acknowledgment. We are grateful to the CNRS for
financial support and to Prof. Michel Etienne (LCC-
Toulouse) for helpful discussions.
Supporting Information Available: Full details for experi-
mental procedures for complexes 1a-e, 3a-e, 4a-e, and 7a-e
and the complete IR spectroscopic data for all complexes; crystal-
lographic data for compounds 1b, 3d, 4b, 4d, 7c, 10a, and 11a,
including ORTEP diagrams, tables of crystal data and data
collection parameters, atomic coordinates, anisotropic displacement
parameters, and all bond lengths and bond angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC020312Y
4226 Inorganic Chemistry, Vol. 41, No. 16, 2002