Synthesis and structural characterisation of new organo-diimido tantalum and niobium complexes

Article abstract of DOI:10.1039/b211126h

The organo-diimido tantalum complexes [{Ta(L₂)Cl ₃}₂(μ-1,n-NC₆H₄N)], L = MeCN (1) and 4-^tBupy (2), have been prepared by two alternative experimental methods: (1) the initial formation of the corresponding TaCl₅· adduct, L = 4-^tBupy or CH₃CN, followed by addition of the appropriate phenylenediamine, or (2) the initial formation of the corresponding organo-diimido species and subsequent addition of the ligand L. These complexes, as well as some related niobium complexes, were alkylated using the appropriate Grignard reagent to afford the alkyl-containing complexes [{M(L)R₃}₂(μ-1,n-NC₆H₄N)] (4, 5, 6, 7, 8, 9) (M = Nb, Ta; n = 3, 4; L = MeCN, R = CH₂SiMe₃, CH₂CMe₃, CH₂CMe₂Ph). These complexes can be prepared by treating the corresponding chloro-complexes with dialkyl-magnesium reagents MgR₂(THF)₂. Niobium complexes containing THF ligands, i.e. [{Nb(THF)R₃}₂(μ-1, 3-NC₆-H₄N)] (10, 11) (R = CH₂SiMe₃, CH₂CMe₃), were isolated by using THF as the solvent and also from the acetonitrilecontaining complexes 8b and 9b by simply adding THF. The complex [{Nb(CH₂CMe₂Ph)₃} ₂(μ-1,4-NC₆H₄N)] (12a) was prepared by addition of the corresponding Grignard reagent to a suspension of [{Nb(MeCN)₂Cl₃}2(μ-1,4-NC₆-H₄N)] in THF. The reaction of complexes [{M(MeCN)₂Cl₃} ₂(μ-1,n-NC₆H₄N)] (M = Ta, Nb; n= 3, 4) with Li[C₅H₄-SiMe₃] was carried out and afforded the tetrakis-cyclopentadienyl-diimido complexes [{M(??⁵-C ₅H₄SiMe₃)₂Cl}₂-(μ-1,n- NC₆H₄N)] [M = Ta, n= 4 (13a); M = Ta, n = 3 (13b); M = Nb, n = 4 (14a); M = Nb, n = 3 (14b)]. The structure of 13a has been solved by X-ray diffraction. Finally, we have performed the reactions between the diimido-containing compounds [{M(MeCN)₂Cl₃} ₂(μ-1,n-NC₆H₄N)] (M = Ta, Nb; n = 3,4) and the lithium benzamidinate Li[PhC-(NSiMe₃)₂] to afford the benzamidinate-containing complexes [{M[PhC(NSiMe₃)] ₂Cl}₂(μ-1,n-NC₆H₄N)] [M = Ta, n = 4 (15a); M = Ta, n= 3 (15b); M = Nb, n = 4(16a)]. The structures of the different families of compounds were determined by spectroscopic methods. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b211126h

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis and structural characterisation of new organo-diimido
tantalum and niobium complexes
Antonio Antiñolo,*a Iván Dorado,b Mariano Fajardo,b Andrés Garcés,b Marek M. Kubicki,c
Carmen López-Mardomingod and Antonio Oteroa
a Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Química,
Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain
b Departamento de Ciencias Experimentales e Ingeniería, E.S.C.E.T.,
Universidad Rey Juan Carlos, 28933 Móstoles, Madrid, Spain
c Laboratoire de Synthèse et d’Electrosynthèse Organometalliques, CNRS URA 1685,
Faculté des Sciences Gabriel, 6 Bd. Gabriel, 21000 Dijon, France
d Departamento de Química Orgánica, Campus Universitario, Universidad de Alcalá,
28871 Alcalá de Henares, Madrid, Spain
Received 11th November 2002, Accepted 14th January 2003
First published as an Advance Article on the web 4th February 2003
The organo-diimido tantalum complexes [{Ta(L2)Cl3}2(µ-1,n-NC6H4N)], L = MeCN (1) and 4-tBupy (2), have been
prepared by two alternative experimental methods: (1) the initial formation of the corresponding TaCl5ؒL adduct,
L = 4-tBupy or CH3CN, followed by addition of the appropriate phenylenediamine, or (2) the initial formation of the
corresponding organo-diimido species and subsequent addition of the ligand L. These complexes, as well as some
related niobium complexes, were alkylated using the appropriate Grignard reagent to afford the alkyl-containing
complexes [{M(L)R3}2(µ-1,n-NC6H4N)] (4, 5, 6, 7, 8, 9) (M = Nb, Ta; n = 3, 4; L = MeCN, R = CH2SiMe3, CH2CMe3,
CH2CMe2Ph). These complexes can be prepared by treating the corresponding chloro-complexes with dialkyl-
magnesium reagents MgR2(THF)2. Niobium complexes containing THF ligands, i.e. [{Nb(THF)R3}2(µ-1,3-NC6-
H4N)] (10, 11) (R = CH2SiMe3, CH2CMe3), were isolated by using THF as the solvent and also from the acetonitrile-
containing complexes 8b and 9b by simply adding THF. The complex [{Nb(CH2CMe2Ph)3}2(µ-1,4-NC6H4N)] (12a)
was prepared by addition of the corresponding Grignard reagent to a suspension of [{Nb(MeCN)2Cl3}2(µ-1,4-NC6-
H4N)] in THF. The reaction of complexes [{M(MeCN)2Cl3}2(µ-1,n-NC6H4N)] (M = Ta, Nb; n = 3, 4) with Li[C5H4-
SiMe3] was carried out and afforded the tetrakis-cyclopentadienyl-diimido complexes [{M(η5-C5H4SiMe3)2Cl}2-
(µ-1,n-NC6H4N)] [M = Ta, n = 4 (13a); M = Ta, n = 3 (13b); M = Nb, n = 4 (14a); M = Nb, n = 3 (14b)]. The structure
of 13a has been solved by X-ray diffraction. Finally, we have performed the reactions between the diimido-containing
compounds [{M(MeCN)2Cl3}2(µ-1,n-NC6H4N)] (M = Ta, Nb; n = 3, 4) and the lithium benzamidinate Li[PhC-
(NSiMe3)2] to afford the benzamidinate-containing complexes [{M[PhC(NSiMe3)2]2Cl}2(µ-1,n-NC6H4N)] [M = Ta,
n = 4 (15a); M = Ta, n = 3 (15b); M = Nb, n = 4 (16a)]. The structures of the different families of compounds were
determined by spectroscopic methods.
to give the corresponding alkyl complexes, namely [{NbLR3}2-
(µ-1,4-NC6H4N)] (L = THF, CH3CN and R = CH2SiMe3,
Introduction
Transition metal complexes in which the metal centres are
CH2CMe3). As a continuation of our research in this field we
linked by a bridging ligand that has a delocalized π-system are
report here the reactivity of TaCl5 towards different 1,n-phenyl-
well known and have been the subject of intense research due to
enediamines and the reactivity of both tantalum complexes and
their potential applications in the design of low-dimensional,
the previously prepared niobium complexes toward alkylating
polymeric materials with novel electrical and/or magnetic prop-
agents. The aim of this work was to synthesize new types of
erties.1 Several such complexes that incorporate aryldiimido
binuclear organo-diimido niobium and tantalum complexes in
which both metallic centres are linked by conjugated π-systems.
bridges have been described previously.2
We reported the preparation of niobocene organo-diimido
complexes, namely [{Nb(η5-C5H4SiMe3)2Cl}2(µ-N2C6H4)], by
the reaction of [{Nb(η5-C5H4SiMe3)2Cl}2] with the appropriate
Results and discussion
amount of the corresponding aniline, 1,4- or 1,3-phenylene-
diamine.3 More recently, we described the preparation of
organo-diimido niobium and titanium complexes [{Nb(L2)-
Cl3}2(µ-1,n-NC6H4N)] (where L = CH3CN or 4-tBupy and n = 2,
3, 4) and [{Ti(L2)Cl2}2(µ-1,n-NC6H4N)] (where L = 4-tBupy or
L2 = TMEDA and n = 3, 4) by treating NbCl5 or TiCl4 in the
presence of L with the appropriate amount of the corre-
sponding aniline, 1,4-, 1,3- or 1,2-phenylenediamine. In addi-
tion, we reported the synthesis of organo-imido titanium com-
plexes [{Ti(L2)Cl2}(1,n-NC6H4N(SiMe3)2)] (where L = 4-tBupy
or L2 = TMEDA and n = 3, 4) by treatment of TiCl4 in the
presence of L with the appropriate amount of the corre-
sponding aniline, 1,4- or 1,3-phenylenediamine.4 Another
aspect of our studies concerned the reaction of [{Nb(CH3-
CN)2Cl3}2(µ-1,4-NC6H4N)] with appropriate alkylating agents
The preparation of organo-diimido tantalum complexes will
be considered first. In fact, TaCl5 reacts with the appropriate
N,N,NЈ,NЈ-tetrakis(trimethylsilyl)-1,4-, -1,3- or -1,2-phenylene-
diamine in CH2Cl2 in the presence of acetonitrile or 4-tBupy to
afford the corresponding organo-diimido tantalum complexes
[{Ta(L2)Cl3}2(µ-1,n-NC6H4N)] (1 and 2), eqn. (1). In these reac-
tions, which were carried out under mild conditions, a selective
elimination of SiMe3Cl takes place as a consequence of the
complete substitution of the four trimethylsilyl groups to give
the appropriate organo-diimido species in high yields.
The reactions were carried out by two alternative experi-
mental methods. The first involved the initial formation of the
corresponding TaCl5ؒL adduct, L = 4-tBupy or CH3CN, fol-
lowed by addition of the appropriate phenylenediamine. The
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
910

View Article Online
(1)
(2)
adduct TaCl5ؒ4-tBupy (3) was isolated and fully characterized.
The second method consisted of the initial formation of the
corresponding organo-diimido species and subsequent addition
of the ligand L. These two methods can be used in all cases
although the second one affords the final products more rapidly
than the first, probably due to the lower solubility of the start-
ing material TaCl5 in CH2Cl2. Alternatively, complexes contain-
ing 4-tBupy (i.e. 2) can be prepared from the corresponding
acetonitrile complexes 1 by simple addition of 4-tBupy on the
basis that this ligand displaces the more labile acetonitrile.
The method described above constitutes a very easy and
selective route for the preparation of imido complexes because
the formation of the volatile by-product SiMe3Cl facilitates the
isolation of the corresponding diimido complex. These organo-
diimido complexes, as well as the other complexes described in
alkylmagnesium reagents MgR2(THF)2 (see, as illustrative
examples, the preparation of 5a and 9b in the Experimental
section). Niobium complexes containing THF ligands, [{Nb-
(THF)R3}2(µ-1,3-NC6H4N)] (10, 11) (R = CH2SiMe3, CH2-
CMe3, respectively), were isolated when THF was employed as
the solvent because the acetonitrile was replaced by THF.
Moreover, these same complexes can be prepared from the
acetonitrile-containing complexes 8b and 9b by simply adding
THF, eqn. (3).
1
this work, were characterized by H, 13C NMR spectroscopy,
elemental analysis and IR spectroscopy (see Experimental).
The 1H NMR spectra of complexes 2 exhibit two resonances
t
for the two non-equivalent Bupy units around each tantalum
atom, while the analogous spectra for acetonitrile-containing
complexes 1 in CD3CN each show a single signal corresponding
to free CH3CN, which is removed from the metal by the deuter-
ated solvent. In order to confirm the presence of two coordin-
ated acetonitrile ligands for each metal centre in this type of
complex, the spectra were acquired in CD3NO2. In this case two
signals were observed at lower field than the corresponding
signals in acetonitrile and these are due to the two ligands in cis
positions. The 13C NMR spectra contain the signals of the
phenyl groups of the phenylene ligand at δ 152.4 (Cipso), 128.7
and 153.7 (Cipso) and 128.1, 125.1 and 122.4 for 1,4- and 1,3-
phenylene complexes, respectively (see Experimental). On the
basis of both the spectroscopic and analytical data, it can be
concluded that two acetonitrile or 4-tBupy ligands are present
in the proposed octahedral environment with a mer disposition
for the Cl ligands and cis dispositions for the ligands L (Fig. 1).
(3)
Finally, the complex [{Nb(CH2CMe2Ph)3}2(µ-1,4-NC6H4N)]
(12a) was prepared by addition of the corresponding Grignard
reagent to a suspension of [{Nb(MeCN)2Cl3}2(µ-1,4-NC6H4N)]
in THF and after removal of the solvent, the residue was
washed with cold hexane and extracted with hexane at room
temperature. The coordination of THF does not take place,
probably due to the more space required for the alkyl group
around the metal, eqn. (4).
Fig. 1 Structural disposition proposed around each tantalum atom for
complexes 1 and 2.
(4)
A similar structure was found in analogous organo-diimido
niobium complexes.3 In the structure of 1 and 2 a diimido-
phenylene group bridges two tantalum atoms, which are
probably located in the plane formed by this ligand.
In addition, we propose that both nitrogen atoms are sp
hybridized with the following two limiting descriptions,
Ϫ
ϩ
᎐
Ta ᎐N –R and Ta᎐N–R, which are an accurate representation
᎐
᎐
of the bonding situation.5
Complex 1 and some related niobium complexes3 were alkyl-
ated using the appropriate Grignard reagents in a 1 : 6 molar
ratio. The reactions afforded the corresponding alkyl-contain-
ing complexes [{M(L)R3}2(µ-1,n-NC6H4N)] (4, 5, 6, 7, 8, 9)
(M = Nb, Ta; n = 3, 4; L = MeCN, R = CH2SiMe3, CH2CMe3,
CH2CMe2Ph) in good yields (80–90%), eqn. (2).
The different alkyl complexes were isolated as air-sensitive
yellow crystalline solids after the appropriate work-up and all
are sparingly soluble in alkanes but soluble in Et2O and THF.
The structural characterization of the alkyl compounds was
1
Alternatively, these complexes can be prepared in similar
yields by treating the corresponding chloro-complexes with di-
carried out by spectroscopic studies. The H and 13C NMR
spectra for complexes 4–12 show the characteristic resonances
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
911

View Article Online
(5)
Table 1 Selected bond lengths (Å) and angles (Њ) for complex 13a
of alkyl groups bound to a metal atom (see Experimental).
When the coordinated acetonitrile was replaced by THF, i.e.
Ta–N
1.792(7)
2.430(3)
2.471(10)
2.431(10)
2.463(10)
2.579(10)
2.520(10)
1.381(11)
90.1(3)
Ta–C(6)
Ta–C(7)
Ta–C(8)
Ta–C(9)
Ta–C(10)
Ta–CT(1)
Ta–CT(2)
CT(1)–Ta–CT(2)
Ta–N–C(17)
2.497(10)
2.508(10)
2.546(10)
2.468(11)
2.429(10)
2.186
2.184
124.8
168.6(7)
1
complexes 10 and 11, the H and 13C resonances were shifted
Ta–Cl(1)
Ta–C(1)
Ta–C(2)
Ta–C(3)
Ta–C(4)
Ta–C(5)
N–C(17)
Cl–Ta–N
slightly with respect to the signals of the free ligand. The 13C
NMR spectra of these complexes exhibit a broad signal
between δ 61 and 93 for the methylene group resulting from
the niobium quadrupole, indicating its coordination with the
niobium atom.
On the basis of these spectroscopic data and of those of the
molecular structure previously described for an analogous
niobium complex, namely [{Nb(MeCN)(CH2SiMe3)3}2(µ-1,4-
NC6H4N)],4 a trigonal bipyramidal geometry for each metal
centre can be proposed for the different metal-alkyl complexes
studied. The ligand L occupies therein a trans position with
respect to the imido ligand. This type of structure, where a
labile ligand like acetonitrile or pyridine is located in a coordin-
ation site trans to the imido ligand, has already been observed
in several imido-containing early transition metal complexes.6
A further alkylation reaction was also performed. We carried
out the reaction of complexes [{M(MeCN)2Cl3}2(µ-1,n-NC6-
H4N)] (M = Ta, Nb; n = 3, 4) with Li[C5H4SiMe3] in a 1 : 4
molar ratio. The reactions take place by substitution of the
chloride ligand and elimination of the labile acetonitrile mole-
cules to afford the tetrakis-cyclopentadienyl-diimido complexes
[{M(η5-C5H4SiMe3)2Cl}2(µ-1,n-NC6H4N)] [M = Ta, n = 4 (13a);
M = Ta, n = 3 (13b); M = Nb, n = 4 (14a); M = Nb, n = 3 (14b)],
eqn. (5).
CT(1) is a geometrical centre of C(1)–C(5) atoms, CT(2) is that of
C(6)–C(10) atoms.
Some of these complexes have been already prepared in our
group by the treatment of [{Nb(η5-C5H4SiMe3)2Cl}2] with the
appropriate amount of the corresponding aniline, 1,4- or 1,3-
phenylenediamine or, alternatively, by heating the corre-
sponding diisocyanate derivatives.3 These compounds were
cleanly isolated in good yields and were characterized by ele-
mental analysis and 1H and 13C NMR spectroscopy (see
Fig. 2 ORTEP drawing (30% probability level) for 13a.
1
Experimental). The H NMR spectra provide evidence for the
presence of an ABCD system for the cyclopentadienyl rings
and a singlet or an A2BC system for the phenylene ring in 1,4-
or 1,3-phenylene complexes, respectively. In order to confirm
unequivocally the proposed structure of these complexes, we
were able to obtain crystals suitable for a molecular structure
determination by X-ray diffraction in the case of compound
13a. An ORTEP drawing of this complex is depicted in Fig. 2
and selected bond lengths and angles are given in Table 1.
13a crystallizes in the P21/n space group with two molecules
per unit cell and, consequently, the dinuclear molecule lies over
a symmetry centre. The Ta(1) and Ta(1Ј) deviate by less than
0.3 Å from the plane formed by the bridging diimidophenylene
ligand. The cyclopentadienyl rings adopt an anti conformation.
The Ta–N bond length of 1.792(7) Å falls into the intermediate
range expected for a double and a triple Ta–N bond. The
Ta–N–C17 (ipso) angle [168.6(7)Њ] agrees with the values previ-
ously reported by us for other similar complexes.3 Con-
sequently, we propose that the nitrogen atom is sp hybridized
Ϫ
ϩ
᎐
with the two limiting structures, Ta ᎐N –R and Ta᎐N–R, in
᎐
᎐
which the nitrogen lone pair is involved in the delocalized con-
jugated Ta–bridging ligand bonding. Finally, the chlorine
atoms were found to be in a trans disposition with respect to the
Ta–Ta vector.
On the other hand, imidinate compounds have been pro-
posed as alternative ligands to the cyclopentadienyl rings.7,8 In
order to extend the study of the reactivity of our trichloro-
diimido complexes, an additional alkylation reaction was under-
taken. We carried out the reaction of the diimido-containing
compounds [{M(MeCN)2Cl3}2(µ-1,n-NC6H4N)] (M = Ta, Nb;
n = 3, 4) with the lithium benzamidinate Li[PhC(NSiMe3)2] in a
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
912

View Article Online
1 : 4 molar ratio. The process afforded the benzamidinate-
containing complexes [{M[PhC(NSiMe3)2]2Cl}2(µ-1,n-NC6-
H4N)] [M = Ta, n = 4 (15a); M = Ta, n = 3 (15b); M = Nb, n = 4
(16a)], eqn. (6).
behaviour even at Ϫ80 ЊC, although geometry A cannot be
ruled out.
Experimental
General methods and instrumentation
All manipulations were carried out under an argon atmosphere
using either standard Schlenk techniques or an MBraun glove-
box. Solvents were dried and distilled under argon: tetrahydro-
furan and diethyl ether from sodium benzophenone ketyl,
hexane and pentane from sodium and potassium alloy, CH2Cl2
from P2O5, acetonitrile and CDCl3 from finely ground calcium
hydride.
4-tert-Butylpyridine was dried under argon over activated 4A
molecular sieves and stored under argon. Other reagents were
obtained from commercial sources and used as received or
prepared as reported elsewhere: N,N,NЈ,NЈ-Tetrakis(trimethyl-
(6)
silyl)phenylendiamine,13
[{Nb(CH3CN)2Cl3}2(µ-1,4-NC6H4-
N)],4 [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)],4 Mg(Me3CCH2)2ؒ
2THF,14 Li[PhC(NSiMe3)2],7a Li[C5H4SiMe3].15
IR spectra were recorded in Nujol mulls between CsI pellets
over the range 4000–370 cmϪ1 on a Perkin-Elmer model 883
spectrophotometer and/or a Perkin-Elmer IR-FT Spectro-
photometer 2000. 1H and 13C NMR spectra were recorded on a
Gemini-200 and/or UNITY-300 (Varian) spectrometer. Chem-
ical shifts (δ ppm) were measured relative to residual 1H and 13
C
resonances for acetonitrile-d3, nitromethane-d3, chloroform-d1
and benzene-d6 as solvents. C, H and N analyses were carried
out with a Perkin-Elmer 240–13, Perkin-Elmer 240 C and/or
Heraeus-CHN-O-Rapid microanalyser.
The complexes were isolated as air-sensitive red solids and
are soluble in common organic solvents. These materials were
characterized by elemental analysis and 1H and 13C NMR and
IR spectroscopy (see Experimental). In each case the IR spec-
Preparations
1
trum shows the νN–C–N band at ca. 1522 cmϪ1. The H NMR
[{Ta(CH2CN)3Cl3}2(ꢀ-1,4-NC6H4N)] (1a) and [{Ta(CH3CN)2-
Cl3}2(ꢀ-1,3-NC6H4N)] (1b). To a solution of TaCl5 in aceto-
nitrile was added dropwise at room temperature over 45 min a
solution in CH2Cl2 of the corresponding N,N,NЈ,NЈ-tetra-
kis(trimethylsilyl)phenylendiamine in a 2 : 1 molar ratio. Vigor-
ous stirring was required during the addition. The initial yellow
solution changed to deep red for 1a and to orange for complex
1b. The mixture was vigorously stirred overnight at room tem-
perature. The solvent was removed in vacuo, the solids were
washed several times with hexane and identified as 1a or 1b,
respectively.
spectra of these complexes include a single signal for the eight
SiMe3 groups at ca. Ϫ0.07 ppm, even when the spectra were
acquired at Ϫ80 ЊC, and this fact could indicate a local sym-
metry around the metal centre with a trans disposition of the
imido and chloro-ligands in an octahedral environment (see
Fig. 3, situation A) or, alternatively, a cis disposition of these
ligands around the metal centre with a fluxional behaviour (see
Fig. 3, situation B) in an octahedral environment. In the case
where static behaviour is observed in situation B, one would
1
expect four signals in the H NMR spectrum for the SiMe3
groups.
Complex 1a: from TaCl5 (3.60 g, 10.00 mmol), 1,4-{(Me3Si)2-
N}2C6H4 (2.00 g, 5.02 mmol) and CH3CN (100 ml), (yield:
1
quantitative). NMR (CD3CN): H (300 MHz), δ 1.95 (s, 12H,
CH3CN), 6.92 (s, 4H, phenylene ring); (CD3NO2): 1H (300
MHz), δ 2.37 and 2.58 (s, br, 12H, CH3CN), 6.99 (s, 4H, phenyl-
ene ring); 13C-{1H} (75 MHz), δ 1.7 (CH3CN), 127.0 (phenylene
ring), 128.7 (CH3CN), 152.4 (Cipso of phenylene ring); (CD3-
NO2): 1H (300 MHz), δ 2.37 and 2.58 (s, br, 12H, CH3CN), 6.99
(s, 4H, phenylene ring). IR: 2318s, 2290s, 1489s, 1346s, 1095m,
847s, 522m and 318s cmϪ1. [Found (Calc. for Ta2Cl6N6C14H16):
C, 19.55 (19.95); H, 1.93 (1.91); N, 9.60 (9.97)%].
Complex 1b: from TaCl5 (0.90 g, 2.52 mmol), 1,3-{(Me3Si)2-
N}2C6H4 (0.50 g, 1.26 mmol) and CH3CN (30 ml), (yield: quan-
titative). NMR (CD3CN): 1H (300 MHz), δ 1.99 (s, 12H,
CH3CN), 6.44 (part A2 of an A2BC spin system, 2H, phenylene
ring), 6.47 (part B of an A2BC spin system, 1H, phenylene
ring), 7.31 (part C of an A2BC, 1H, phenylene ring); 13C-{1H}
(75 MHz), δ 1.7 (CH3CN), 122.4, 125.1, 128.1 (phenylene ring),
128.3 (CH3CN), 153.7 (Cipso of phenylene ring). IR: 2316s,
2288s, 1571vs, 1331s, 1031m, 874m and 789m cmϪ1. [Found
(Calc. for Ta2Cl6N6C14H16): C, 20.32 (19.95); H, 2.02 (1.91); N,
9.74 (9.97)%].
Fig. 3
For the complexes [V(=N-4-C6H4Me){PhC(NSiMe3)2}2Cl]9
and [Nb(O){4-C6H4Me)C(NSiMe3)2}2Cl],10 situation B was
proposed on the basis of crystallographic and NMR data.
VTNMR experiments carried out for these species indicate
a fluxional behaviour even at low temperatures. The 1H
i
NMR spectrum of the complex [Ta(᎐N-2,6-C H Pr ){PhC-
᎐
6
3
2
(NSiMe3)2}2Cl]11 shows only one signal for the SiMe3 groups
i
and two signals for the Pr groups – a result of restricted
rotation around the N–C bond in the imido ligand. Likewise, it
is common in benzamidinate complexes to observe the type of
fluxional behaviour proposed in our complexes.9,10,12
On the basis of the data outlined above we propose geometry
B as the more probable for our complexes with a fluxional
[{Ta(CH3CN)2Cl3}2(ꢀ-1,2-NC6H4N)] (1c). To a vigorously
stirred suspension of TaCl5 (1.80 g, 5.02 mmol) in CH2Cl2 (50
ml) was added dropwise a solution of 1,2-{(Me3Si)2N}2C6H4
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
913

View Article Online
1
(1.00 g, 2.51 mmol) in CH2Cl2 (25 ml). The initial yellow sus-
pension changed to a brown suspension. The mixture was
stirred during 6 d and during this time the suspension changed
to a deeper red solution. The solvent was removed in vacuo and
CH3CN (15 ml) was added. The mixture was stirred for 15 min
and the solvent was evaporated to dryness to give 1.74 g of
complex 1c as a brown solid, which was washed with hexane
(3 × 15 ml) and dried in vacuo (yield: 82%). NMR (CD3CN): 1H
(300 MHz), δ 1.95 (s, 12H, CH3CN), 6.90 (part AAЈ of an
AAЈBBЈ spin system, 2H, phenylene ring), 7.18 (part BBЈ of an
AAЈBBЈ spin system, 2H, phenylene ring); 13C-{1H} (75 MHz),
δ 1.7 (CH3CN), 125.9, 130.4 (phenylene ring), 129.1 (CH3CN),
149.7 (Cipso of phenylene ring). IR: 2315s, 2287s, 1441s, 1354s,
1027m, 847s and 759m cmϪ1. [Found (Calc. for Ta2Cl6N6-
C14H16): C, 20.15 (19.95); H, 1.94 (1.91); N, 10.08 (9.97)%].
in vacuo and identified as 3. (yield: 92%). NMR (CDCl3): H
(300 MHz), δ 1.37 (s, 9H, CMe3) 7.55 (AAЈ part of an AAЈBBЈ
spin system, 2H, m-H of NC5H4But), 9.30 (BBЈ part of an
AAЈBBЈ spin system, 2H, o-H of NC5H4But); 13C-{1H} (75
MHz), δ 30.1 [NC5H4C(CH3)3], 35.8 [NC5H4C(CH3)3], 122.3
(m-NC5H4But), 152.6 (o-NC5H4But), 166.9 (Cipso of NC5H4But).
IR: 1620s, 1273m, 1237m, 1064m, 1024s, 831s, 730m and 392s
cmϪ1. [Found (Calc. for TaCl5C9H13N): C, 22.46 (21.91); H, 2.85
(2.66); N, 2.81 (2.84)%].
[{Ta(CH3CN)(CH2SiMe3)3}2(ꢀ-1,4-NC6H4N)](4a),[{Ta(CH3-
CN)(CH2CMe3)3}2(ꢀ-1,4-NC6H4N)] (5a) and [{Ta(CH3CN)-
(CH2CPhMe2)3}2(ꢀ-1,4-NC6H4N)] (6a). To a suspension of
complex 1a in Et2O (25 ml) was added dropwise, at Ϫ78 ЊC, a
solution of the corresponding Grignard reagent diluted in Et2O
(25 ml). The mixture was stirred overnight at room temper-
ature. During this time the initial red suspension became a
yellow solution. The solution was filtered and the residue
was extracted with Et2O (3 × 15 ml). The solvent was removed
in vacuo and a yellow solid (oil for complex 6a) was obtained
and identified as complex 4a, 5a or 6a.
Complex 4a: from 1a (0.50 g, 0.59 mmol) and Me3SiCH2-
MgCl (3.50 mmol). 0.48 g of a yellow solid was obtained (yield:
76%). NMR (C6D6): H (300 MHz), δ 0.26 [s, 54H, Si(CH3)3],
0.58 (br, s, 6H, CH3CN), 0.64 (s, 12H, CH2), 7.59 (s, 4H, phenyl-
ene ring); 13C-{1H} (75 MHz), δ 1.4 (CH3CN), 3.2 [Si(CH3)3],
74.4 (Ta–CH2), 121.4 (CH3CN), 125.7 (phenylene ring) and
154.5 (Cipso of phenylene ring). IR: 2309m, 2282m, 1494vs,
1341vs, 1244vs, 908vs, 847vs, 743s, 702s and 485w cmϪ1. [Found
(Calc. for Ta2N4C34H76Si6): C, 38.00 (38.12); H, 7.27 (7.15); N,
4.94 (5.23)%].
[{Ta(tBupy)2Cl3}2(ꢀ-1,4-NC6H4N)] (2a) and [{Ta(tBupy)2Cl3}2-
(ꢀ-1,3-NC6H4N)] (2b). To a vigorously stirred suspension of
TaCl5 in CH2Cl2 (25 ml) was added tBupy in a 1 : 2 molar ratio.
The initial suspension changed to a colourless solution. To
this solution was added dropwise over 45 min a solution of
the corresponding N,N,NЈ,NЈ-tetrakis(trimethylsilyl)phenylen-
diamine in CH2Cl2 (25 ml) at room temperature. The mixture
was vigorously stirred during 18 h at room temperature. The
solvent was removed in vacuo and the solids obtained were
washed with hexane (3 × 15 ml) and identified as 2a or 2b.
Complex 2a: from TaCl5 (0.45 g, 1.26 mmol), 1,4-{(Me3Si)2-
N}2C6H4 (0.25 g, 0.63 mmol) and 4-tert-butylpyridine (0.4 ml,
2.70 mmol). This compound was recrystallized from CH2Cl2–
hexane (1 : 1) and 0.65 g of an orange microcrystalline solid was
obtained (yield: 84%). NMR (CDCl3): 1H (300 MHz), δ 1.31 (s,
18H, trans-CMe3), 1.35 (s, 18H, cis-CMe3), 7.07 (s, 4H, phenyl-
ene ring), 7.35 (AAЈ part of an AAЈBBЈ spin system, 4H, trans
m-NC5H4But), 7.42 (AAЈ part of an AAЈBBЈ spin system, 4H,
cis m-NC5H4But), 8.65 (BBЈ part of an AAЈBBЈ spin system,
4H, trans o-NC5H4But), 9.01 (BBЈ part of an AAЈBBЈ spin
system, 4H, cis o-NC5H4But); 13C-{1H} (50 MHz), δ 30.1
(trans-CMe3), 30.3 (cis-CMe3), 35.2 (trans-CMe3), 35.6 (cis-
CMe3), 121.5 (trans m-NC5H4But), 122.0 (cis m-NC5H4-
But), 126.6 (phenylene ring), 151.4 (trans o-NC5H4But), 151.5
(cis o-NC5H4But), 151.9 (Cipso of phenylene ring), 163.6
(trans p-NC5H4But), 165.3 (cis p-NC5H4But). IR: 1618vs,
1421m, 1343s, 1275m, 1067s, 831vs and 572s cmϪ1. [Found
(Calc. for Ta2Cl6C42H56N6): C, 41.18 (41.36); H, 4.93 (4.63); N,
7.44 (6.89)%].
1
Complex 5a: from 1a (0.36 g, 0.43 mmol) and (Me3CCH2)2-
Mgؒ2THF (0.4 g, 1.29 mmol). 0.34 g of a pale-yellow solid was
obtained (yield: 81%). NMR (C6D6): 1H (300 MHz), δ 0.48 (br,
s, 6H, CH3CN), 0.94 (s, 12H, CH2), 1.24 [s, 54H, C(CH3)3], 7.71
(s, 4H, phenylene ring); 13C-{1H} (50 MHz), δ 1.4 (CH3CN),
35.1 [C(CH3)3], 36.2 (CMe3), 107.5 (Ta–CH2), 118.6 (CH3CN),
126.3 (phenylene ring) and 154.6 (Cipso of phenylene ring). IR:
2302m, 2275m, 1484vs, 1332vs, 1230s, 1025s and 571w cmϪ1
[Found (Calc. for Ta2N4C40H76): C, 49.54 (49.28); H, 7.90
(7.86); N, 5.36 (5.75)%].
.
Complex 6a: from 1a (0.50 g, 0.59 mmol) and Me2PhCCH2-
MgCl (3.50 mmol). 0.61 g of yellow oil was obtained (yield:
77%). NMR (C6D6): 1H (300 MHz), δ 0.43 (br, s, 6H, CH3CN),
0.97 (s, 12H, CH2), 1.52 [s, 36H, C(CH3)2], 7.08, 7.23 and 7.40
(m, 30H, C–C6H5), 7.35 (s, 4H, phenylene ring); 13C-{1H}
(75 MHz), δ 0.2 (CH3CN), 34.0 [C(CH3)2], 42.2 (CMe2Ph),
106.9 (Ta–CH2), 118.6 (CH3CN), 125.7, 125.8 and 128.6
(C6H5), 126.0 (phenylene ring) 154.1 (Cipso of C6H5) and 154.3
(Cipso of phenylene ring). IR: 2311m, 2276m, 1494vs, 1339vs,
Complex 2b: from TaCl5 (0.90 g, 2.52 mmol), 1,3-{(Me3Si)2-
N}2C6H4 (0.50 g, 1.26 mmol) and 4-tert-butylpyridine (0.8 ml,
5.40 mmol). This compound was recrystallized from toluene–
hexane (1 : 1) to give 1.20 g of a yellow microcrystalline solid
1
(yield: 78%). NMR (CDCl3): H (300 MHz), δ 1.30 (s, 18H,
trans-CMe3), 1.34 (s, 18H, cis-CMe3), 6.68, 6.70 and 7.31 (m,
4H, phenylene ring), 7.41 (AAЈ part of an AAЈBBЈ spin system,
4H, trans m-NC5H4But), 7.44 (AAЈ part of an AAЈBBЈ spin
system, 4H, cis m-NC5H4But), 8.70 (BBЈ part of an AAЈBBЈ
spin system, 4H, trans o-NC5H4But), 9.02 (BBЈ part of an
AAЈBBЈ spin system, 4H, cis o-NC5H4But); 13C-{1H} (75 MHz),
δ 30.1 (trans-CMe3), 30.2 (cis-CMe3), 35.2 (trans-CMe3), 35.5
(cis-CMe3), 121.5 (trans m-NC5H4But), 122.0 (cis m-NC5H4-
But), 124.7, 125.5 and 126.7 (phenylene ring), 151.5 (trans
o-NC5H4But), 151.7 (cis o-NC5H4But), 152.8 (Cipso of phenylene
ring), 163.5 (trans p-NC5H4But), 165.3 (cis p-NC5H4But). IR:
764f, 698f and 553w cmϪ1
.
[{Nb(CH3CN)(CH2PhMe2)3}2(ꢀ-1,4-NC6H4N)] (7a). To
a
suspension of complex [{Nb(CH3CN)2Cl3}2(µ-1,4-NC6H4N)]
(0.66 g, 0.98 mmol) in Et2O (40 ml) was added dropwise, at Ϫ78
ЊC, a solution of Me2PhCCH2MgCl (11.80 ml, 5.90 mmol)
diluted in Et2O (40 ml) and the mixture was stirred overnight
at room temperature. The initial green suspension became a
yellow solution. The solution was filtered and the residue
was extracted with Et2O (4 × 20 ml). The solvent was removed
in vacuo to give 0.9 g of a yellow oil, which was identified as
1617vs, 1570s, 1343s, 1233s, 1067s, 831vs and 571s cmϪ1
.
complex 7a (yield: 79%). NMR (C6D6): H (300 MHz), δ 0.46
1
[Found (Calc. for Ta2Cl6C42H56N6): C, 41.87 (41.36); H, 4.81
(4.63); N, 6.72 (6.89)%].
(br, s, 6H, CH3CN), 1.30 (s, 12H, CH2), 1.48 [s, 36H, C(CH3)2],
7.06–7.41 (m, 34H, C–C6H5 and phenylene ring); 13C-{1H}
(75 MHz), δ 0.2 (CH3CN), 33.5 [C(CH3)2], 41.9 (CMe2Ph), 90.7
(br, Nb–CH2), 119.8 (CH3CN), 125.5 (phenylene ring), 125.9,
128.6 and another signal hidden by the solvent (C6H5), 153.9
(Cipso of C6H5) and 154.1 (Cipso of phenylene ring). IR: 2316w,
2288w, 1599w 1487m, 1318m, 1262w, 1179w, 1082w, 1030w,
[Ta(tBupy)Cl5] (3). To a suspension of TaCl5 (0.47 g 1.31
mmol) in CH2Cl2 (25 ml) was added 4-tert-butylpyridine
(0.2 ml, 1.35 mmol). The solution formed was stirred for 30 min
and filtered. The solvent was evaporated to dryness and the
white solid obtained was washed with hexane (3 × 15 ml), dried
834w, 802w, 763m, 699s, 583w and 549w cmϪ1
.
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
914

View Article Online
[{Ta(CH3CN)(CH2SiMe3)3}2(ꢀ-1,3-NC6H4N)] (4b). To a sus-
pension of complex 1b (0.5 g, 0.59 mmol) in Et2O (25 ml) was
added dropwise, at Ϫ78 ЊC, a solution of Me3SiCH2MgCl
(3.50 mmol) diluted in Et2O (25 ml). The mixture was stirred
overnight at room temperature. The initial red suspension
became a yellow solution. The solution was filtered and the
residue was extracted with Et2O (3 × 15 ml). The solvent was
removed in vacuo to give 0.46 g of a yellow solid and this was
Complex 10b: from [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)]
(0.84 g, 1.27 mmol) and Me3SiCH2MgCl (7.60 ml, 7.60 mmol).
0.95 g of a yellow solid was obtained (yield: 78%). Complex
11b: from [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)] (0.57 g, 0.85
mmol) and (Me3CCH2)2Mgؒ2THF (0.79 g, 2.55 mmol). 0.64 g
of a pale yellow solid was obtained (yield: 83%).
Method B. To the complex 8b or 9b was added THF (20 ml)
and the mixture was stirred for 1 h. The solvent was removed in
vacuo and hexane (15 ml) was added. The solvent was removed
in vacuo in order to remove excess THF. A yellow solid was
obtained and identified as 10b or 11b.
1
identified as complex 4b (Yield: 73%). NMR (C6D6): H (300
MHz), δ 0.29 [s, 54H, Si(CH3)3], 0.58 (br, s, 6H, CH3CN), 0.64
(s, 12H, CH2), 7.13, 7.34 and 7.42 (m, 4H, phenylene ring);
13C-{1H} (75 MHz), δ 1.4 (CH3CN), 3.1 [Si(CH3)3], 77.0 (Ta–
CH2), 121.5 (CH3CN), 120.6, 122.8 and 128.5 (phenylene ring)
and 158.9 (Cipso of phenylene ring). IR: 2301m, 2275m, 1566vs,
1324vs, 1242vs, 908vs, 847vs, 743s, 696s and 490m cmϪ1. [Found
(Calc. for Ta2N4C34H76Si6): C, 37.89 (38.12); H, 7.27 (7.15); N,
5.56 (5.23)%].
Complex 10b: from complex 8b (0.38 g, 0.43 mmol). 0.41 g of
1
a yellow solid was obtained (yield: 100%). NMR (C6D6): H
(300 MHz), δ 0.27 [s, 54H, Si(CH3)3], 0.98 (s, 12H, CH2), 1.39
(m, 8H, C4H8O), 3.70 (m, 8H, C4H8O), 7.27 (B part of an A2BC
spin system, JAB = 7.8 Hz, 1H, phenylene ring), 7.36 (A2 part of
an A2BC spin system, JAB = 7.8 Hz, JAC = 1.8 Hz, 2H, phenylene
ring) and 7.77 (C part of an A2BC spin system, JAC = 1.8 Hz,
1H, phenylene ring); 13C-{1H} (75 MHz), δ 3.1 [Si(CH3)3], 25.6
(C4H8O), 61.9 (br, Nb–CH2), 70.0 (C4H8O), 120.9, 121.6 and
128.4 (phenylene ring) and 158.1 (Cipso of phenylene ring).
IR: 1567m, 1549w, 1414w, 1347m, 1306m, 1287m, 1256m,
1244s, 1150w, 1075w, 1026m, 918w, 892s, 846vs, 828s, 777w,
745m, 697m, 611w, 564w and 479w cmϪ1. [Found (Calc. for
Nb2N2C38H86Si6O2): C, 48.32 (47.67); H, 8.96 (9.05); N, 3.26
(2.93)%].
[{Nb(CH3CN)(CH2SiMe3)3}2(ꢀ-1,3-NC6H4N)] (8b) and [{Nb-
(CH3CN)(CH2CMe3)3}2(ꢀ-1,3-NC6H4N)] (9b). To a suspension
of [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)] in hexane (20 ml) was
added Et2O (30 ml). A solution of the corresponding Grignard
reagent diluted in Et2O (40 ml) was then added dropwise at
Ϫ78 ЊC and the mixture was stirred overnight at room temper-
ature. The initial pink suspension became a yellow solution.
The solution was filtered and the residue was extracted with
Et2O (4 × 20 ml). The solvent was removed in vacuo to give a
yellow solid, which was identified as complex 8b or 9b.
Complex 11b: from complex 9b (0.37 g, 0.46 mmol). 0.42 g of
1
a yellow solid was obtained (yield: 100%). NMR (C6D6): H
Complex 8b: from [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)]
(0.76 g, 1.13 mmol) and Me3SiCH2MgCl (6.80 ml, 6.80 mmol).
0.8 g of a yellow solid was obtained (yield: 79%). NMR (C6D6):
1H (300 MHz), δ 0.34 [s, 54H, Si(CH3)3], 0.63 (s, 6H, CH3CN),
(300 MHz), δ 1.22 (s, 12H, CH2), 1.30 [s, 54H, C(CH3)3], 1.37
(m, 8H, C4H8O), 3.80 (m, 8H, C4H8O), 7.26 (B part of an A2BC
spin system, 3JAB = 7.8 Hz, 1H, phenylene ring), 7.53 (A2 part of
an A2BC spin system, 2H, phenylene ring) and 8.07 (C part
4
1.27 (s, 12H, CH2), 7.32 (B part of an A2BC spin system, 3JAB
=
of an A2BC spin system, JAC = 1.8 Hz, 1H, phenylene ring);
7.8 Hz, 1H, phenylene ring), 7.46 (A2 part of an A2BC spin
system, 2H, phenylene ring), 7.95 (C part of an A2BC spin
system, 4JAC = 1.8 Hz, 1H, phenylene ring); 13C-{1H} (75 MHz),
δ 0.3 (CH3CN), 3.1 [Si(CH3)3], 62.1 (br, Nb–CH2), 121.7
(CH3CN), 120.7, 121.7 and 128.4 (phenylene ring) and 158.0
(Cipso of phenylene ring). IR: 2302w, 2275w, 1564m, 1548m,
1413m, 1348m, 1308m, 1282m, 1241s, 1152w, 1020w, 899s,
13C-{1H} (75 MHz), δ 25.6 (C4H8O), 34.6 [C(CH3)3], 35.9
(CMe3), 69.8 (C4H8O), 91.7 (br, Nb–CH2), 121.5, 124.1, 128.5
(phenylene ring) and 158.5 (Cipso of phenylene ring). IR: 1568s,
1549m, 1407m, 1357s, 1341s, 1304s, 1286s, 1261m, 1232s,
1154w, 1097m, 1028s, 930w, 867m, 803w, 781m, 750w, 686w,
595w, 554w and 488w cmϪ1. [Found (Calc. for Nb2N2C44H86O2):
C, 60.12 (61.38); H, 9.95 (10.07); N, 3.22 (3.25)%].
870m, 846vs, 780w, 743m, 695m, 609w, 574w and 497w cmϪ1
.
[Found (Calc. for Nb2N4C34H76Si6): C, 44.91 (45.61); H, 8.51
(8.56); N, 5.80 (6.26)%]
[{Nb(CH2PhMe2)3}2(ꢀ-1,4-NC6H4N)] (12a). To a suspension
of [{Nb(CH3CN)2Cl3}2(µ-1,4-NC6H4N)] (0.54 g, 0.81 mmol)
in THF (40 ml) was added dropwise, at Ϫ78 ЊC, a solution
of Me2PhCCH2MgCl (9.70 ml, 4.86 mmol) diluted in THF
(40 ml). The mixture was stirred overnight at room temperature.
The initial green suspension became a yellow solution. The
solution was filtered and the solvent was removed in vacuo. The
residue was washed with cold hexane (4 × 20 ml) and extracted
with hexane at room temperature (5 × 30 ml). The solvent was
removed in vacuo to give 0.5 g of a yellow oil, which was identi-
fied as complex 12a (yield: 61%). NMR (C6D6): 1H (300 MHz),
δ 1.14 (s, 12H, CH2), 1.39 [s, 36H, C(CH3)2], 7.06–7.37 (m, 34H,
C–C6H5 and phenylene ring); 13C-{1H} (75 MHz), δ 33.3
[C(CH3)2], 41.3 (CMe2Ph), 92.5 (br, Nb–CH2), 125.1 (phenyl-
ene ring), 125.7, 126.0 and 129.1 (C6H5), 152.9 (Cipso of C6H5)
and 155.0 (Cipso of phenylene ring). IR: 1599w 1495m, 1319m,
1261m, 1082m, 1030m, 836w, 802m, 763m, 699s and 668w
Complex 9b: from [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)]
(0.59 g, 0.88 mmol) and (Me3CCH2)2Mgؒ2THF (0.82 g, 2.65
mmol). 0.55 g of a pale yellow solid was obtained (yield: 78%).
1
NMR (C6D6): H (300 MHz), δ 0.50 (s, 6H, CH3CN), 1.35 [s,
54H, C(CH3)3], 1.41 (s, 12H, CH2), 7.29 (B part of an A2BC
spin system, 3JAB = 7.8 Hz, 1H, phenylene ring), 7.58 (A2 part of
an A2BC spin system, 2H, phenylene ring) and 8.14 (C part of
an A2BC spin system, 4JAC = 1.8 Hz, 1H, phenylene ring); 13C-
{1H} (75 MHz), δ 1.3 (CH3CN), 34.7 [C(CH3)3], 35.9 (CMe3),
91.0 (br, Nb–CH2), 119.4 (CH3CN), 121.4, 124.0, 128.5
(phenylene ring) and 158.5 (Cipso of phenylene ring). IR: 2303w,
2277w, 1567m, 1408m, 1355s, 1342s, 1303s, 1286s, 1261m,
1232s, 1154w, 1095w, 1027m, 933w, 875w, 802w, 779w, 690w,
590w, 556w and 494w cmϪ1. [Found (Calc. for Nb2N4C40H76):
C, 60.38 (60.14); H, 9.22 (9.59); N, 7.42 (7.01)%].
cmϪ1
.
[{Nb(THF)(CH2SiMe3)3}2(ꢀ-1,3-NC6H4N)]
(10b)
and
[{Nb(THF)(CH2CMe3)3}2(ꢀ-1,3-NC6H4N)] (11b). Method A. To
a suspension of [{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)] in hex-
ane (20 ml) was added THF (30 ml). A solution of the corre-
sponding Grignard reagent diluted in THF (40 ml) was then
added dropwise at Ϫ78 ЊC and the mixture was stirred over-
night at room temperature. The initial pink suspension became
a yellow solution. The solution was filtered and the solvent was
removed in vacuo. The residue was extracted with Et2O (4 ×
20 ml). The solvent was removed and a yellow solid was
obtained and identified as complex 10b or 11b.
[{Ta(ꢁ5-C5H4SiMe3)2Cl}2(ꢀ-1,4-NC6H4N)] (13a). Toluene (40
ml) was added to a mixture of complex 1a (0.43 g, 0.51 mmol)
and Li[C5H4SiMe3] (0.30 g, 2.08 mmol) in a Teflon-valve
ampoule. The ampoule was placed in an oil bath and heated to
100 ЊC for 16 h. The resulting solution was allowed to cool to
room temperature and was filtered. The solvent removed under
reduced pressure to give 0.43 g of 13a as a red solid (yield:
78%). Samples prepared in this way are sufficiently pure (1H
NMR spectroscopy) to use in further studies. An analytically
pure, X-ray-quality sample was obtained from a saturated
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
915

View Article Online
1
hexane–toluene (50%) solution at Ϫ40 ЊC. NMR (C6D6): H
128.9 (phenylene ring), 126.3, 128.1 and 129.0 (C6H5), 140.7
(Cipso of C6H5), 155.5 (Cipso of phenylene ring), 178.1 [PhC(NSi-
Me3)2]. IR: 1571vs, 1527s, 1323vs, 1248vs, 1005s, 988vs, 840vs,
762s, 705s and 503m cmϪ1. [Found (Calc. for Ta2N10C58H96-
Cl2Si8): C, 43.02 (43.79); H, 5.90 (6.08); N, 8.90 (8.80)%].
(300 MHz), δ 0.29 [s, 36H, Si(CH3)3], 5.57, 5.93, 6.29 and 6.37
(m, 4 × 4H, C5H4), 6.47 (s, 4H, phenylene ring); 13C-{1H}
(75 MHz), δ 0.39 [Si(CH3)3], 109.8, 111.0, 118.4 and 126.1
(C5H4), 116.2 (C5H4 Cipso), 119.7 (phenylene ring), 154.6 (Cipso of
phenylene ring). IR: 1331s, 1246vs, 1176s, 1034s, 978s, 836vs,
630s and 409s cmϪ1. [Found (Calc. for Ta2N2C38H56Cl2Si4): C,
42.07 (42.03); H, 5.14 (5.20); N, 2.90 (2.58)%].
[{Nb[PhC(NSiMe3)2]2Cl}2(ꢀ-1,4-NC6H4N)] (16a). Et2O (60
ml) was added to a mixture of [{Nb(CH3CN)2Cl3}2(µ-1,4-
NC6H4N)] (0.65 g, 0.97 mmol) and Li[PhC(NSiMe3)2] (1.05 g,
3.89 mmol). The suspension was stirred for 12 h. The initial
green suspension became a red solution. The solution was fil-
[{Ta(ꢁ5-C5H4SiMe3)2Cl}2(ꢀ-1,3-NC6H4N)] (13b). The syn-
thesis of 13b was carried out in an identical manner to 13a
using 1b (0.38 g, 0.45 mmol) and Li[C5H4SiMe3] (0.26 g, 1.80
mmol). 0.40 g of 13b was obtained as a red solid (yield: 83%).
tered and the residue was extracted with Et2
O (2 × 20 ml). The
solvent was removed in vacuo to give 1.22 g of a brown solid,
which was identified as 16a (yield: 89%). NMR (C6D6): 1H (300
MHz), δ 0.16 [s, 72H, Si(CH3)3], 6.97 (m, 12H, C6H5), 7.28 (m,
8H, C6H5) and 7.62 (s, 4H, phenylene ring); 13C-{1H} (CDCl3,
75 MHz), δ 2.1 [Si(CH3)3], 125.8 (phenylene ring), 126.3, 128.1
and 129.0 (C6H ), 140.3 (C of C6H5), 151.9 (Cipso of phenyl-
1
NMR (C6D6): H (300 MHz), δ 0.34 [s, 36H, Si(CH3)3], 5.49,
4
5.94, 6.29 and 6.46 (m, 4 × 4H, C5H4), 5.52 (t, JAC = 1.8 Hz,
1H, C part of an A2BC spin system, phenylene ring), 5.85 (dd,
2H, A2 part of an A2BC spin system, phenylene ring), 6.36 (t,
3JAB = 7.5 Hz, 1H, B part of an A2BC spin system, phenylene
ring); 13C-{1H} (75 MHz), δ 0.43 [Si(CH3)3], 109.3, 109.9 118.4
and 126.6 (C5H4), 117.4 (C5H4 Cipso), 109.7, 112.9 and 127.2
(phenylene ring), 159.6 (Cipso of phenylene ring). IR: 1560s,
5
ipso
ene ring) and 178.7 [PhC(NSiMe3)2]. IR: 1588w, 1570w, 1522m,
1325m, 1248m, 1169w, 1092w, 1002w, 979m, 841s, 762m,
743m, 703m, 506w, 378w and 321w cm
Ϫ1. [Found (Calc. for
1322s, 1247s, 1174m, 1035m, 905s, 838vs, 632s and 411s cmϪ1
.
Nb2N10C58H96Cl2Si8): C, 50.17 (49.24); H, 7.00 (6.84); N, 9.67
(9.90)%].
[Found (Calc. for Ta2N2C38H56Cl2Si4): C, 42.03 (42.03); H, 5.18
(5.20); N, 2.95 (2.58)%].
X-Ray structure analysis of 13a
[{Nb(ꢁ5-C5H4SiMe3)2Cl}2(ꢀ-1,4-NC6H4N)] (14a). Toluene
(60 ml) was added to a mixture of [{Nb(CH3CN)2Cl3}2(µ-1,4-
NC6H4N)] (0.85 g, 1.27 mmol) and Li[C5H4SiMe3] (0.77 g,
5.35 mmol) in a Teflon-valve ampoule. The ampoule was placed
in an oil bath and heated at 100 ЊC for 24 h. The resulting
solution was allowed to cool to room temperature and the
resulting red solution was filtered. The solvent was removed
under reduced pressure to give 0.95 g (yield: 82%) of a red solid,
which was identified as 14a by comparison of its 1H NMR data
with the literature values.3
An irregularly shaped red crystal for X-ray measurements has
been cut off from a larger twinned sample of crystallization and
mounted on a Nonius KappaCCD diffractometer. Crystallo-
graphic data: C38H56Cl2N2Si4Ta2, M = 1086.01, monoclinic, P21/
n, a = 6.9570(4), b = 26.464(2), c = 11.6880(7) Å, β = 97.408(3)Њ,
V = 2133.9(3) Å3, Z = 2, dcalc = 1.690 g cmϪ3, µ = 5.39 mmϪ1
,
F(000) = 1068, T = 110(2) K. Collected intensities have been
further treated with DENZO/Scalpack routines.16 The model
structure has been found by direct methods implemented in
SHELXS97 and refined with SHELXL97.17 All non hydrogen
atoms were refined with anisotropic thermal parameters,
whereas the hydrogen atoms were included in calculated posi-
tions and refined in a riding isotropic model. The final R and Rw
(on F 2) discrepancy factors calculated with 4378 observed
reflections with I>2σ(I ) for 217 parameters are equal to 0.069
and 0.1762, respectively. Because of the rather low quality of
the crystal some high residual electron density (ρmax = 4.06 e
[{Nb(ꢁ5-C5H4SiMe3)2Cl}2(ꢀ-1,3-NC6H4N)] (14b). The syn-
thesis of 14b was carried out in an identical manner to 14a from
[{Nb(CH3CN)2Cl3}2(µ-1,3-NC6H4N)] (1.03 g, 1.54 mmol) and
Li(C5H4SiMe3) (0.94 g, 6.49 mmol). 1.15 g of a red solid (yield:
82%) was obtained and identified as 14b by comparison of its
1H NMR data with the literature values.3
Å
Ϫ3) has been found around the Ta atom (<1 Å). No presence
[{Ta[PhC(NSiMe3)2]2Cl}2(ꢀ-1,4-NC6H4N)] (15a). Complex
1a (0.40 g, 0.47 mmol) and Li[PhC(NSiMe3)2] (0.52 g, 1.92
mmol) were placed in a Teflon-valve ampoule along with tolu-
ene (35 ml). The ampoule was placed in an oil bath and heated
at 100 ЊC for 14 h. The resulting solution was allowed to cool to
room temperature and filtered. The solvent was removed under
reduced pressure to give 0.57 g of 15a as a red solid (yield:
76%). NMR (CDCl3): 1H (300 MHz), δ Ϫ0.08 [s, 72H,
Si(CH3)3], 6.91 (s, 4H, phenylene ring), 7.28, 7.36 and 7.38
(m, 20H, C6H5); 13C-{1H} (75 MHz), δ 2.0 [Si(CH3)3], 126.6
(phenylene ring), 126.2, 128.1 and 129.0 (C6H5), 140.7 (Cipso of
C6H5), 151.7 (Cipso of phenylene ring) 178.0 [PhC(NSiMe3)2].
IR: 1522s, 1496vs, 1482vs, 1338vs, 1248vs, 1003s, 988vs, 920s,
840vs, 786s, 761s, 704vs and 504m cmϪ1. [Found (Calc. for
Ta2N10C58H96Cl2Si8): C, 44.29 (43.79); H, 6.17 (6.08); N, 8.91
(8.80)%].
of solvent molecules has been detected.
CCDC reference number 197351.
See http://www.rsc.org/suppdata/dt/b2/b211126h/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
The authors gratefully acknowledge financial support from
Dirección General de Enseñanza Superior y de Investigación
Científica y Técnica (grant no. PB98-0159-C02-01-02 and grant
no. BQU2000-0463) and Dirección General de Investigación de
la Consejería de Educación de la Comunidad Autónoma de
Madrid (grant no. 07N-0036/98).
References
1 (a) C. Creutz, Prog. Inorg. Chem., 1983, 30, 1; (b) C. Creutz and
H. Taube, J. Am. Chem. Soc., 1969, 91, 3988; (c) A. Haim,
Prog. Inorg. Chem., 1983, 30, 273; (d ) T. J. Meyer, Prog. Inorg.
Chem., 1983, 30, 389; (e) T. J. Meyer in Mixed-Valence
compounds, ed. D. B. Brown, Reidel, Dordrecht, The Netherlands,
1980, 75; ( f ) J. E. Miller, Adv. Chem. Ser., 1976, 150, 18.
2 (a) E. A. Maatta and D. D. Devore, Angew. Chem., Int. Ed. Engl.,
1988, 27, 569; (b) E. A. Maatta and C. Kim, Inorg. Chem., 1989, 28,
624; (c) R. K. Rosen, R. A. Anderson and N. M. Edelstein, J. Am.
Chem. Soc., 1990, 112, 4588; (d ) W. Clegg, R. J. Errington, D. C. R.
Hockless, J. M. Kirck and C. Redshaw, Polyhedron, 1992, 11, 381; (e)
C. Redshaw, G. Wilkinson, B. Hussain-Bates and M. B. Hursthouse,
[{Ta[PhC(NSiMe3)2]2Cl}2(ꢀ-1,3-NC6H4N)] (15b). The syn-
thesis of 15b was carried out in an identical manner to 15a from
1b (0.8 g, 0.95 mmol) and Li[PhC(NSiMe3)2] (1.04 g, 3.84
mmol). 1.1 g of 15b was obtained as an orange solid (yield:
73%). NMR (CDCl3): 1H (300 MHz), δ Ϫ0.06 [s, 72H,
Si(CH3)3], 6.50 (dd, 2H, A2 part of an A2BX spin system,
phenylene ring), 6.77 (t, 4JAC = 1.8 Hz, 1H, C part of an A2BC
spin system, phenylene ring), 7.14 (t, 3JAB = 7.8 Hz, 1H, B part
of an A2BC spin system, phenylene ring), 7.26–7.39 (m, 20H,
C6H5); 13C-{1H} (75 MHz), δ 2.1 [Si(CH3)3], 122.6, 128.6 and
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
916

View Article Online
J. Chem. Soc., Dalton Trans., 1992, 555; ( f ) G. Hogart, R. L.
Mallors and T. J. Norman, J. Chem. Soc., Chem. Commun., 1993,
1721.
3 A. Antiñolo, F. Carrillo-Hermosilla, A. Otero, M. Fajardo,
A. Garcés, P. Gómez-Sal, C. López-Mardomingo, A. Martín and
C. Miranda, J. Chem. Soc., Dalton Trans., 1998, 59.
4 I. Dorado, A. Garcés, C. López-Mardomingo, M. Fajardo,
A. Rodríguez, A. Antiñolo and A. Otero, J. Chem. Soc., Dalton
Trans., 2000, 2375.
8 R. Duchateau, C. T. Van Wee, A. Meetsma, P. T. Van Duijnen and
J. H. Teuben, Organometallics, 1996, 15, 2279.
9 (a) F. T. Edelman, Coord. Chem. Rev., 1994, 137, 403; (b) A. L. Spek,
Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 2001, 57,
147.
10 P. J. Steward, A. J. Blake and P. Mountford, Inorg. Chem., 1997, 36,
1982.
11 D. Y. Dawson and J. Arnold, Organometallics, 1997, 16, 1111.
12 C. T. Chen, L. H. Doerrer, V. C. Williams and M. L. H. Green,
J. Chem. Soc., Dalton Trans., 2000, 967.
13 H. Bock, J. Meuret, C. Näther and U. Krynitz, Chem. Ber., 1994,
127, 55.
5 G. Parkin, A. Van Asselt, D. J. L. Leahy, R. N. Whinnery, N. G.
Hua, R. W. Quan, L. M. Henling, W. P. Schaefer, B. D. Santarsiero
and J. E. Bercaw, Inorg. Chem., 1992, 31, 82.
6 See for example: A. J. Blake, P. E. Collier, S. D. Dunn, W. S. Li,
P. Mountford and O. V. Shishkin, J. Chem. Soc., Dalton Trans., 1997,
1549.
7 (a) M. Wedler, F. Knösel, M. Noltenmeyer and F. T. Edelman,
J. Organomet. Chem., 1990, 388, 21; (b) F. T. Edelman, J. Organomet.
Chem., 1992, 426, 295.
14 R. R. Schrock, J. Organomet. Chem., 1976, 122, 209.
15 P. Jutzi and R. Sauer, J. Organomet. Chem., 1973, 50, C29.
16 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307.
17 G. M. Sheldrick, SHELXS97 and SHELXL97 programs for
structure solution and refinement, University of Göttingen,
Germany, 1997.
D a l t o n T r a n s . , 2 0 0 3 , 9 1 0 – 9 1 7
917