Synthesis and reactivity of new mono- and dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [Ta(η5-C 5H4SiMe3)Cl2{NC6Me 4-4-(N(SiMe3)2</s

Article abstract of DOI:10.1016/j.jorganchem.2005.12.016

The reaction of [1,4-{SiMe₃(H)N}₂C₆Me ₄] (1) with 2 equivalents of LiBuⁿ followed by the addition of SiMe₃Cl gave the diamine compound [1,4-{(SiMe ₃)₂N}₂C

Full text of DOI:10.1016/j.jorganchem.2005.12.016

Journal of Organometallic Chemistry 691 (2006) 1361–1368
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of new mono- and dinuclear niobium
and tantalum imido complexes: X-ray crystal structure of
[Ta(g5-C5H4SiMe3)Cl2{@NC6Me4-4-(N(SiMe3)2)}]
a
b
c,
b
*
´
´
´
Antonio Antinolo , Ivan Dorado , Mariano Fajardo , Andres Garces ,
˜
d
e
a
a
´
Marek M. Kubicki , Carmen Lopez-Mardomingo , Antonio Otero , Sanjiv Prashar
a
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Facultad de Quı´mica, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain
b
Departamento de Quı´mica Inorga´nica, Campus Universitario, Universidad de Alcala´, 28871 Alcala´ de Henares, Madrid, Spain
Departamento de Ciencias Experimentales e Ingenierı´a, E.S.C.E.T., Universidad Rey Juan Carlos, 28933 Mo´stoles, Madrid, Spain
` `
´ ´ ´
Laboratoire de Synthese et d’Electrosynthese Organometalliques, CNRS URA 5188, Faculte des Sciences Mirande, Universite de Bourgogne,
c
d
6 Bd. Gabriel, 21000 Dijon, France
Departamento de Quı´mica Orga´nica, Campus Universitario, Universidad de Alcala´, 28871 Alcala´ de Henares, Madrid, Spain
e
Received 7 November 2005; received in revised form 7 December 2005; accepted 8 December 2005
Available online 19 January 2006
Abstract
The reaction of [1,4-{SiMe3(H)N}2C6Me4] (1) with 2 equivalents of LiBun followed by the addition of SiMe3Cl gave the diamine
compound [1,4-{(SiMe3)2N}2C6Me4] (2). [Ta(g5-C5H4SiMe3)Cl4] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture
of the dinuclear, [{Ta(g5-C5H4SiMe3)Cl2}2(l-1,4-NC6Me4N)] (3), and mononuclear, [Ta(g5-C5H4SiMe3)Cl2{@NC6Me4-4-
(N(SiMe3)2)}] (4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacu-
ation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated
from the reaction of [Ta(g5-C5H4SiMe3)Cl4] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-
ray diffraction studies. [TaCl3(CH3CN)2{@NC6Me4-4-(N(SiMe3)2)}] (5) has been prepared by the reaction of one molar equivalent
of TaCl5 with 2 in a CH3CN/CH2Cl2 solvent mixture. The synthesis of the niobium complexes, [{Nb(g5-C5H4SiMe3)Cl2}2(l-1,4-
NC6Me4N)] (6) and [Nb(g5-C5H4SiMe3)Cl2{@NC6Me4-4-(N(SiMe3)2)}] (7), was achieved in a similar manner to their tantalum
analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl
or lithium dimethylamide, has been studied and the following compounds prepared: [Nb(g5-C5H4SiMe3)RCl{@NC6Me4-4-
(N(SiMe3)2)}] (R = g5-C5H4SiMe3 (8), PhC(NSiMe3)2 (9), NMe2 (10)). In an attempt to form the hetero bimetallic com-
plex, [{Nb(g5-C5H4SiMe3)Cl2}(l-1,4-NC6Me4N){Ta(g5-C5H4SiMe3)Cl2}] (11), the reaction of 7 with [Ta(g5-C5H4SiMe3)Cl4] has
been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3
and 6.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Imido; Niobium; Tantalum
1. Introduction
In recent years, there has been a great interest in the syn-
thesis of homo- and hetero-dinuclear complexes in which
two transition metals are united by a p-conjugated organic
*
Corresponding author. Present address: Departamento de Tecnologia
Quimica y Ambiental, Universidad Rey Juan Carlos, C/ Tulipan s/n,
28933 Mostoles, Madrid, Spain. Tel.: +34916447444; fax: +34914888143.
ligand [1] due to the potential applications in the design of
E-mail address: mariano.fajardo@urjc.es (M. Fajardo).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.016

1362
A. Antin˜olo et al. / Journal of Organometallic Chemistry 691 (2006) 1361–1368
low-dimensional, polymeric materials with novel electrical
and/or magnetic properties [2].
readded and the reaction mixture heated. On repeating this
process two more times, 3 could be obtained in yields of ca.
60%.
The presence of imido groups in the organometallic
chemistry of niobium and tantalum is well documented
[3] and our contribution to this field has recently been
published [4]. Part of our research work has been dedi-
cated to the use of metal centre bridging di-imido
ligands [5] and as a continuation of this, we now report
the synthesis, structural characterization and reactivity of
mono- and dinuclear niobium and tantalum imido
complexes.
2 [M(η5-C5H4SiMe3)Cl4]
+
Me
Me
Me3Si
Me3Si
SiMe3
SiMe3
N
N
Me
Me
2
2. Results and discussion
The preparation of N,N,N0,N0-tetrakis(trimethyl-
silyl)-2,3,5,6,-tetramethyl-1,4-phenylenediamine (2) was
achieved adapting the method previously described for
similar ligands [6]. The reaction of 2,3,5,6,-tetramethyl-
1,4-phenylenediamine with 2 molar equivalents of LiBun
in THF and the subsequent addition of SiMe3Cl gave
N,N0-bis(trimethylsilyl)-2,3,5,6,-tetramethyl-1,4-phenylene-
diamine (1). Repeating this procedure with 1 yielded the
desired compound 2 (Eq. (1)).
SiMe3
Cl
N
M
SiMe3
SiMe3
N
Cl
SiMe3
Cl
+
M = Ta (4), Nb (7)
Cl
M
N
Me
Me
Me
Me
N
Cl
Li
Li
M
2LiBun
Cl
H2N
NH2
HN
Me
NH
M = Ta (3), Nb (6)
Me3Si
Me
Me
Me
Me
ð2Þ
2SiMe3Cl
Me
3 was characterized by NMR spectroscopy. The 1H and
13C NMR spectra of 3 exhibit the characteristic signals for
both the cyclopentadienyl and phenylene groups. The sym-
metry of the molecule leads to the equivalency of the four
methyl groups of the phenylene moiety (one signal in the
1H and 13C NMR spectra). Two multiplets were observed
H
H
N
N
Me3Si
SiMe3
2LiBun
Me
Me
1
1
in the H NMR spectra corresponding to the cyclopenta-
Me
Me
Me
dienyl protons.
Li
Me3SiN
Li
NSiMe3
The synthesis of the mononuclear complex 4 was
achieved in a 54% yield by the reaction of a 1:1 molar
ratio of [Ta(g5-C5H4SiMe3)Cl4] with 2. The 1H NMR
spectra of 4 gave two singlets for the methyl protons of
the phenylene moiety. Two multiplets were observed for
the cyclopentadienyl ring protons. Suitable crystals for
X-ray diffraction studies were obtained on cooling
(ꢀ20 ꢁC) a concentrated solution of 4 in hexane. The
molecular structure of 4 and atomic numbering scheme
are shown in Fig. 1. Selected bond lengths and angles
are given in Table 1.
2SiMe3Cl
Me3Si
Me
Me
Me
Me
SiMe3
SiMe3
N
N
Me3Si
Me
2
ð1Þ
The reaction, in CH2Cl2, of 2 with 2 molar equivalents
of [Ta(g5-C5H4SiMe3)Cl4] (Eq. (2)) initially afforded a
mixture of the dinuclear, [{Ta(g5-C5H4SiMe3)Cl2}2(l-1,4-
NC6Me4N)] (3), and mononuclear, [Ta(g5-C5H4SiMe3)-
Cl2{@NC6Me4-4-(N(SiMe3)2)}] (4), imido complexes along
with 2. In order to favour the production of 3, the volatile
SiMe3Cl was removed from the medium by placing the
reaction mixture under reduced pressure. Solvent was then
In the molecular structure of 4 the tantalum atom is
bound to the cyclopentadienyl ring in a formally g5
mode, to two chlorine atoms and to the nitrogen of the
imido group in a three-legged piano-stool conformation
about the metal centre. The tantalum atom is out of the
plane defined by N(1), C(10), C(11) and C(6) by
˚
0.274(8) A.

A. Antin˜olo et al. / Journal of Organometallic Chemistry 691 (2006) 1361–1368
1363
Fig. 1. Molecular structure and atom-labelling scheme for [Ta(g5-C5H4SiMe3)Cl2{@NC6Me4-4-(N(SiMe3)2)}] (4), with thermal ellipsoids at 30%
probability.
Table 1
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for complex 4
Selected structural data of some group 5 metal imido complexes
˚
˚
Bond lengths (A)
M–N (A) M–N–C (ꢁ) Ref.
Ta(1)–N(1)
Ta(1)–Cl(1)
Ta(1)–Cl(2)
Ta(1)–Ct(1)
Ta(1)–C(1)
Ta(1)–C(2)
Ta(1)–C(3)
Ta(1)–C(4)
Ta(1)–C(5)
N(1)–C(11)
N(2)–C(8)
N(2)–Si(2)
N(2)–Si(3)
1.777(4)
2.329(2)
2.334(2)
2.114
2.386(5)
2.367(5)
2.415(7)
2.504(6)
2.472(1)
1.396(6)
1.452(6)
1.743(5)
1.741(5)
[{Nb(g5-C5H4SiMe3)(CH2Ph)2}2-
(l-1,4-NC6H4N)]
1.79(1),
1.75(1)
1.776(8)
159(1),
168(1)
160.9(7)
[5e]
[{Nb(g5-C5H4SiMe3)Cl2}2-
(l-1,4-NC6H4N)]
[5d]
[{Ta(g5-C5Me5)Cl2}2(l-1,4-NC6H4N)] 1.783(5)
166.4(5)
167.4(5)
[5d]
[5d]
[{Ta(g5-C5Me5)(CH2SiMe3)2}2-
(l-1,4-NC6H4N)]
1.794(5)
[Nb(g5-C5H5)(NHBut)Cl(@NAr)]a
[Nb(g5-C5H5)Cl2(@NAr)]a
[Nb(g5-C5H5)Cl2(@NAr)]b
[Nb(g5-C5H5)(g2-NHBut)-
(CH2But)H(@NAr)]a
1.793
1.761
1.763
1.787
168.5
165.6
166.6
174.6
[7c]
[7a]
[7d]
[7e]
[Ta(g5-C5Me5)Cl2(@NAr)]a
[Ta(g5-C5Me5)Cl2(@NAr)]b
[Ta(g5-C5Me5)(CO){Si(SiMe3)3}-
H(@NAr)]a
1.780
1.774
1.812
171.3
169.9
171.4
[7a]
[7b]
[7f]
Bond angles (ꢁ)
N(1)–Ta(1)–Cl(1)
N(1)–Ta(1)–Cl(2)
Cl(1)–Ta(1)–Cl(2)
Ct(1)–Ta(1)–Cl(1)
Ct(1)–Ta(1)–Cl(2)
Ct(1)–Ta(1)–N(1)
Ta(1)–N(1)–C(11)
C(8)–N(2)–Si(3)
C(8)–N(2)–Si(2)
Si(2)–N(2)–Si(3)
102.9(1)
101.9(1)
103.16(7)
113.5
112.0
121.3
169.3(3)
117.5(3)
116.5(3)
125.9(3)
[Ta(g5-C5H5)(PMe3)-
1.821
171.8
[7g]
(SiMe2Cl)H(@NAr)]a
[Ta(g5-C5H4SiMe3)Cl2-
{@NC6Me4-4-(N(SiMe3)2)}] (4)
1.777(4)
169.3(3)
This
work
a
Ar = 2,6-Pri2C6H3.
Ar = 2,6-Me2C6H3.
b
Ct(1) is the centroid of C(1)–C(5).
plex can vary up to 140ꢁ with little effect on the metal–
nitrogen bonding [8]. Therefore, we propose that in 4 that
the nitrogen atom is sp hybridized.
˚
The tantalum–nitrogen distance, 1.777(4) A, lies within
the range expected for a triple bond [7] although, the
The cyclopentadienyl group is in a typical [7a] eclipsed
fashion with respect to the imido group. There is slight
˚
˚
N(1)–C(11) bond distance of 1.397 A (compare with
N(2)–C(8) 1.452 A) indicates a degree of conjugation with
lengthening of the distances Ta(1)–C(4), 2.504(6) A, and
˚
˚
Ta(1)–C(5), 2.472(1) A, with respect to other Ta–C ring
the phenyl p-system. The Ta(1)–N(1)–C(11) angle of
169.3(3)ꢁ deviates slightly from linear. Such deviations
from linear are normally in the range 10–15ꢁ (see Table 2).
In the case of [Nb(g5-C5H4SiMe3)2Cl(@NPh)] extended-
distances. The g5–g3 slippage of the cyclopentadienyl ring
is most probably due to the electron repulsions between the
Ta–N triple bond and the C(2)–H bond. The N(1), Ta(1),
and C(2) atoms and the C5 centroid are roughly co-planar.
The reaction of the 2 with 2 molar equivalents of TaCl5
in a solvent mixture of CH3CN/CH2Cl2 has been studied.
Huckel molecular-orbital calculations established that the
¨
imido bond angles for ‘‘linear imide’’ in this class of com-

1364
A. Antin˜olo et al. / Journal of Organometallic Chemistry 691 (2006) 1361–1368
SiMe3
A mixture of products was obtained, consisting of
[TaCl5(CH3CN)], the mononuclear imido complex
[TaCl3(CH3CN)2{@NC6Me4-4-(N(SiMe3)2)}] (5) as the
major product and another compound tentatively
assigned to the corresponding diimido derivative. Unfor-
tunately, we were unable to isolate or characterize this
possible dinuclear complex.
Cl
Nb
N
SiMe3
SiMe3
N
SiMe3
8
Complex 5 can, however, be directly prepared by
the reaction of two molar equivalents of 2 with one
molar equivalent of TaCl5 (Eq. (3)). After successive
recrystallizations from CH2Cl2, 5 was obtained in a yield
of 30%.
SiMe3
Cl
Li(C5H4SiMe3)
Nb
N
SiMe3
SiMe3
N
Cl
ð4Þ
Li(NMe2)
SiMe3
Me3Si
Me3Si
SiMe3
SiMe3
N
N
TaCl5
+
Li{PhC(NSiMe3)2
2
Cl
Nb
N
SiMe3
SiMe3
N
Me2N
ð3Þ
10
SiMe3
Cl
NCCH3
Cl
Me3Si
Ph
Nb
Cl
Cl
Ta
N
N
N
SiMe3
SiMe3
SiMe3
N
N
N
NCCH3
SiMe3
SiMe3
9
5
1
With the aim of forming the hetero bimetallic
The H NMR spectrum of 5 showed a singlet for the
trimethylsilyl moieties, two singlets for the methyl groups
of the phenylene fragment and a broad signal correspond-
ing to the protons of the acetonitrile ligand.
complex, [{Nb(g5-C5H4SiMe3)Cl2}(l-1,4-NC6Me4N){Ta-
(g5-C5H4SiMe3)Cl2}] (11), the reaction of
7
with
[Ta(g5-C5H4SiMe3)Cl4] has been studied (Eq. (5)).
The preparation of [{Nb(g5-C5H4SiMe3)Cl2{@NC6-
Me4-4-(N(SiMe3)2)}] (7) was achieved by the reaction of 2
with [Nb(g5-C5H4SiMe3)Cl4] in a 1:1 stoichiometric ratio.
However, in order to obtain a reasonable yield the reaction
mixture was submitted to three repeated cycles of volatile
removal by reduced pressure followed by addition of sol-
vent and subsequent heating. Finally, 7 was isolated by
recrystallization from hexane although in lower yields
(45%) than those obtained, employing a simpler reaction
work up, for its tantalum analogue 4 (54%).
SiMe3
Cl
Nb
N
SiMe3
N
Cl
SiMe3
[Ta(η5-C5H4SiMe3)Cl4]
SiMe3
Cl
ð5Þ
The preparation of [{Nb(g5-C5H4SiMe3)Cl2}2(l-1,4-
NC6Me4N)] (6) (Eq. (2)) required 17 repeated cycles of vol-
atile removal, solvent addition and heating in order to
obtain a reasonable yield. The final product was washed
with hexane and recrystallized from CH2Cl2.
Nb
N
Cl
N
Cl
Ta
Cl
The reactivity of 7 towards nucleophilic reagents has
been studied. The metathesis reaction of 7 with lithium
benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or
lithium dimethylamide gave the following compounds:
[Nb(g5-C5H4SiMe3)RCl{@NC6Me4-4-(N(SiMe3)2)}] (R =
g5-C5H4SiMe3 (8), PhC(NSiMe3)2 (9), NMe2 (10)), respec-
tively (Eq. (4)). 8–10 were isolated in good yields and high
purity. The H NMR spectra of 8–10 provide evidence of
an ABCD system for the cyclopentadienyl rings, and two
signals for the methyl groups of the phenylene ring.
Me3Si
11
1
Analysis of the reaction products, by H NMR spectros-
copy, showed the presence of the homo bimetallic com-
plexes 3 and 6 along with a third compound, in minor
quantities, that logically can be assumed to be 11. The for-
mation of 3 and 6 can be explained by the initial synthesis
of 11 which undergoes an imido exchange reaction to give a
1

A. Antin˜olo et al. / Journal of Organometallic Chemistry 691 (2006) 1361–1368
1365
Cp'
Cp'
vacuo and the residue extracted with hexane (3 · 50 ml).
Evaporation of hexane gave the title compound as a white
solid (8.52 g, 91%). 1H NMR (300 MHz, CDCl3): d 0.09 (s,
18H, SiMe3), 2.20 (s, 12H, C6Me4), 3.35 (br, 2H, NH).
13C{1H} NMR (75 MHz, CDCl3): d 0.9 (SiMe3), 16.6
(C6Me4), 129.7, 137.4 (CN) (C6Me4). Anal. Calc. for
C16H32N2Si2: C, 62.27; H, 10.45; N, 9.08. Found: C,
62.26; H, 10.76; N, 9.05%.
Cl
N
Cl
N
Nb
Ta
Ta
Cl
Cl
N
N
Cl
Cl
Ta
Ta
Cl
Cl
Cp'
Cp'
Cp'
Cp'
Cl
N
Cl
N
Nb
Cl
Cl
N
Cl
N
Cl
4.3. Synthesis of [1,4-{(SiMe3)2N}2C6Me4] (2)
Nb
Nb
Cl
Cl
Cp'
Cp'
To a solution of 1 (8.50 g, 27.54 mmol) in THF (75 ml)
was added dropwise, at ꢀ78 ꢁC, LiBun (1.6 M in hexane)
(34.4 mL, 55.04 mmol). The mixture was stirred for 6 h at
room temperature giving a yellow suspension. SiMe3Cl
(7.0 ml, 55.22 mmol) was added at 0 ꢁC and subsequently
stirred 18 h at room temperature. The solvent was removed
in vacuo and the residue extracted with hexane (3 · 50 ml).
The resulting yellow solution was concentrated to the half
its initial volume and cooled to ꢀ40 ꢁC to yield the title
Fig. 2. Possible imido exchange mechanism.
mixture the homo bimetallic complexes of niobium and
tantalum (Fig. 2). This type of imido exchange reaction
has previously been reported by Gibson and coworkers
[9]. Similar results were obtained when the reaction of 4
with [Nb(g5-C5H4SiMe3)Cl4] was carried out.
1
3. Conclusions
compound as a white crystalline solid (9.50 g, 76%). H
NMR (300 MHz, CDCl3): d 0.08 (s, 36H, SiMe3), 2.18 (s,
12H, C6Me4). 13C{1H} NMR (75 MHz, CDCl3): d 2.0
(SiMe3), 17.9 (C6Me4), 132.7, 140.6 (CN) (C6Me4). Anal.
Calc. for C22H48N2Si4: C, 58.33; H, 10.68; N, 6.18. Found:
C, 58.07; H, 10.67; N, 6.41%.
In this paper, we report the synthesis and characteriza-
tion of new mono- and dinuclear imido complexes of nio-
bium and tantalum. We have also studied their reactivity
towards nucleophilic reagents. In our attempt to form het-
ero bimetallic niobium/tantalum complexes, we observed
an imido exchange reaction which yielded the homo bime-
tallic derivatives.
4.4. Synthesis of [{Ta(g5-C5H4SiMe3)Cl2}2(l-1,4-
NC6Me4N)] (3)
CH2Cl2 (40 ml) was added to a mixture of [Ta(g5-C5H4Si-
Me3)Cl4] (0.50 g, 1.09 mmol) and 2 (0.25 g, 0.55 mmol) in a
Teflon valve ampoule. The ampoule was placed in an oil bath
and heated at 90 ꢁC during 48 h. The resulting deep red solu-
tion was allowed to cool down to room temperature and vol-
atiles were removed by applying reduced pressure. CH2Cl2
(20 ml) was then added to the ampoule and the reaction mix-
ture at 90 ꢁC during 16 h. This process (removal of volatiles,
solvent addition and heating) was repeated two more times.
Finally, solvent was removed in vacuo to give a red solid
which was washed with hexane (3 · 15 ml). Recrystallization
from CH2Cl2 gave the title complex (0.48 g, 94%). 1H NMR
(300 MHz, CDCl3): d 0.27 (s, 18H, SiMe3), 2.28 (s, 12H,
C6Me4) 6.51 (4H), 6.63 (4H) (m, C5H4). 13C{1H} NMR
(75 MHz, CDCl3): d ꢀ0.6 (SiMe3), 15.4 (C6Me4), 113.1,
121.2, 124.7 (C5H4), 130.3, 149.9 (CN) (C6Me4). Anal. Calc.
for C26H38Cl4N2Si2Ta2: C, 33.28; H, 4.08; N, 2.97. Found:
C, 33.49; H, 4.08; N, 3.36%.
4. Experimental
4.1. Materials and procedures
All reactions were performed using standard Schlenk
tube techniques in an atmosphere of dry nitrogen. Solvents
were distilled from appropriate drying agents and degassed
before use. Li{PhC(NSiMe3)2} [10], Li(C5H4SiMe3) [11],
[Ta(g5-C5H4SiMe3)Cl4] [12] and [Nb(g5-C5H4SiMe3)Cl4]
[13] were prepared as described earlier. LiNMe2 and
2,3,5,6-tetramethyl-1,4-phenylenediamine were purchased
from Aldrich and used without further purification. 1H
and 13C{1H} spectra were recorded on Gemini-200, Varian
UNITY-300 and Varian Mercury FT-400 spectrometers
and referenced to the residual deuteriated solvent. Micro-
analyses were carried out with a Heraeus-CHN-O-Rapid
microanalyser.
4.2. Synthesis of [1,4-(SiMe3HN)2C6Me4] (1)
4.5. Synthesis of [Ta(g5-C5H4SiMe3)Cl2{@NC6Me4-4-
(N(SiMe3)2)}] (4)
To a solution of 2,3,5,6-tetramethyl-1,4-phenylenedi-
amine (5.00 g, 30.44 mmol) in THF (75 ml) was added
dropwise, at ꢀ78 ꢁC, LiBun (1.6 M in hexane) (39.0 ml,
62.40 mmol). The mixture was stirred for 16 h at room tem-
perature to give a white suspension. SiMe3Cl (8.0 ml,
63.11 mmol) was added at 0 ꢁC the reaction mixture stirred
for 12 h at room temperature. Solvent was removed in
CH2Cl2 (40 ml) was added to a mixture of [Ta(g5-
C5H4SiMe3)Cl4] (0.27 g, 0.59 mmol) and
2
(0.40 g,
0.88 mmol) in a Teflon valve ampoule. The ampoule was
placed in an oil bath and heated at 90 ꢁC during 60 h.
The resulting deep red solution was allowed to cool down

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A. Antin˜olo et al. / Journal of Organometallic Chemistry 691 (2006) 1361–1368
to room temperature and volatiles were removed by apply-
ing reduced pressure. The resulting red solid was extracted
with hexane (3 · 15 ml). Recrystallization from hexane
5.43 mmol) in a Teflon valve ampoule. The ampoule was
placed in an oil bath and heated at 90 ꢁC during 48 h.
CH2Cl2 (20 ml) was then added to the ampoule and the
reaction mixture at 90 ꢁC during 16 h. This process
(removal of volatiles, solvent addition and heating) was
repeated two more times. Finally, solvent was removed in
vacuo and the residue was extracted with hexane
(3 · 15 ml). Recrystallization from hexane gave the title
complex as a purple solid (1.50 g, 45%). 1H NMR
(400 MHz, CDCl3): d 0.04 (s, 18H, NSiMe3), 0.25 (s, 9H,
C5H4SiMe3), 2.09 (6H), 2.34 (6H) (s, C6Me4), 6.55 (2H),
6.69 (2H) (m, C5H4). 13C{1H} NMR (100 MHz, CDCl3):
d ꢀ0.5 (C5H4SiMe3), 2.3 (NSiMe3), 16.4, 17.5 (C6Me4),
114.6, 122.1, 125.2 (C5H4), 130.9, 132.6, 143.7 (CN),
150.3 (CN) (C6Me4). Anal. Calc. for C24H43Cl2N2NbSi3:
C, 47.44; H, 7.13; N, 4.61. Found: C, 47.55; H, 7.25; N,
4.72%.
1
gave the title complex (0.22 g, 54%). H NMR (300 MHz,
CDCl3): d 0.01 (s, 18H, NSiMe3), 0.21 (s, 9H, C5H4SiMe3),
2.04 (6H), 2.35 (6H) (s, C6Me4) 6.58 (2H), 6.64 (2H) (m,
C5H4). 13C{1H} NMR (75 MHz, CDCl3):
d
ꢀ0.7
(C5H4SiMe3), 2.17 (NSiMe3), 15.8, 17.5 (C6Me4), 114.4,
120.8, 123.1 (C5H4), 131.4, 131.9, 142.9 (CN), 148.4 (CN)
(C6Me4). Anal. Calc. for C24H43Cl2N2Si3Ta: C, 41.43; H,
6.23; N, 4.03. Found: C, 41.72; H, 6.35; N, 4.24%.
4.6. Synthesis of [TaCl3(CH3CN)2{@NC6Me4-4-
(N(SiMe3)2)}] (5)
To a solution of 2(1.00 g, 2.20 mmol) in CH2Cl2 (25 ml)
was added, at ꢀ40 ꢁC, to a solution of TaCl5 (0.40 g,
1.12 mmol) in CH3CN (30 ml). The mixture was stirred,
at room temperature, for 18 h. Solvent was removed by
applying reduced pressure to give a yellow solid, which
was washed with hexane (3 · 15 ml) and recrystallized from
CH2Cl2 (40 ml) (0.23 g, 30%) 1H NMR (300 MHz, CDCl3):
d 0.03 (s, 18H, NSiMe3), 2.23 (6H), 2.35 (6H) (s, C6Me4)
2.52 (br, 6H, CH3CN). 13C{1H} NMR (75 MHz, CDCl3):
d 2.15 (NSiMe3), 3.79 (CH3CN), 15.5, 17.6 (C6Me4),
126.9, 136.2, 140.0 (CN), 148.5 (CN) (C6Me4), 130.7
(CH3CN). Anal. Calc. for C20H36Cl3N4Si2Ta: C, 35.53;
H, 5.37; N, 8.29. Found: C, 35.72; H, 5.51; N, 8.41%.
4.9. Synthesis of [Nb(g5-C5H4SiMe3)2Cl{@NC6Me4-4-
(N(SiMe3)2)}] (8)
A suspension of Li(C5H4SiMe3) (0.09 g, 0.63 mmol) in
hexane (30 ml) was added, at ꢀ78 ꢁC, to a solution of 6
(0.35 g, 0.57 mmol) in hexane (30 ml). The mixture was
allowed to warm to room temperature and stirred for
12 h. The suspension was filtered and solvent removed in
vacuo to yield the title compound as a red solid (0.39 g,
96%). 1H NMR (400 MHz, C6D6): d 0.16 (s, 18H,
NSiMe3), 0.28 (s, 18H, C5H4SiMe3), 2.19 (6H), 2.34 (6H)
(s, C6Me4) 5.48 (2H), 6.14 (2H), 6.22 (2H), 6.31 (2H) (m,
C5H4). 13C{1H} NMR (100 MHz, C6D6): d 0.2 (C5H4-
SiMe3), 2.6 (NSiMe3), 17.0, 18.0 (C6Me4), 108.6, 113.3,
120.6, 121.4, 129.0 (C5H4), 130.6, 132.4, 139.9 (CN),
154.1 (CN) (C6Me4). Anal. Calc. for C32H56ClN2NbSi4:
C, 54.17; H, 7.96; N, 3.95. Found: C, 54.48; H, 8.21; N,
4.15%.
4.7. Synthesis of [{Nb(g5-C5H4SiMe3)Cl2}2(l-1,4-
NC6Me4N)] (6)
CH2Cl2 (40 ml) was added to a mixture of [Nb(g5-
C5H4SiMe3)Cl4] (1.02 g, 2.75 mmol) and 2(0.62 g,
1.37 mmol) in a Teflon valve ampoule. The ampoule was
placed in an oil bath and heated at 90 ꢁC during 48 h.
The resulting deep brown solution was allowed to cool
down to room temperature and volatiles were removed
by applying reduced pressure. CH2Cl2 (20 ml) was then
added to the ampoule and the reaction mixture at 90 ꢁC
during 16 h. This process (removal of volatiles, solvent
addition and heating) was repeated 17 more times. Finally,
solvent was removed in vacuo to give a green solid which
was washed with hexane (3 · 15 ml). Recrystallization from
CH2Cl2 gave the title complex (0.58 g, 56%). 1H NMR
(400 MHz, CDCl3): d 0.30 (s, 18H, SiMe3), 2.28 (s, 12H,
C6Me4) 6.49 (4H), 6.68 (4H) (m, C5H4). 13C{1H} NMR
(100 MHz, CDCl3): d ꢀ0.5 (SiMe3), 15.7 (C6Me4), 113.4,
122.7, 126.8 (C5H4), 130.5, 151.8 (CN) (C6Me4). Anal.
Calc. for C26H38Cl4N2Nb2Si2: C, 40.96; H, 5.02; N, 3.67.
Found: C, 41.12; H, 5.09; N, 3.78%.
4.10. Synthesis of [Nb(g5-C5H4SiMe3){PhC(NSiMe3)2}-
Cl{@NC6Me4-4-(N(SiMe3)2)}] (9)
A
suspension of Li{PhC(NSiMe3)2} (0.193 g,
0.71 mmol) in hexane (30 ml) was added, at ꢀ78 ꢁC, to a
solution of 6 (0.43 g, 0.71 mmol) in hexane (30 ml). The
mixture was allowed to warm to room temperature and
stirred for 12 h. The suspension was filtered and solvent
removed in vacuo to yield the title compound as a yellow
1
solid (0.52 g, 88%). H NMR (400 MHz, C6D6): d ꢀ0.16
(9H), 0.48 (9H) (s, PhC(NSiMe3)2), 0.11 (s, 18H, SiN-
SiMe3), 0.26 (s, 9H, C5H4SiMe3), 2.16 (6H), 2.70 (6H) (s,
C6Me4) 6.42 (1H), 6.52 (1H), 6.66 (1H), 6.78 (1H) (m,
C5H4), 6.99 (m, 5H, Ph). 13C{1H} NMR (100 MHz,
C6D6):
d 0.9 (C5H4SiMe3), 2.6 (NSiMe3), 2.7, 3.9
4.8. Synthesis of [Nb(g5-C5H4SiMe3)Cl2{@NC6Me4-4-
(N(SiMe3)2)}] (7)
(PhC(NSiMe3)2) 17.5, 18.0 (C6Me4), 112.8, 114.4, 117.5,
117.7, 128.0 (C5H4), 131.6, 132.5, 140.8 (CN), 152.0 (CN)
(C6Me4), 128.8, 129.4, 131.9, 142.4 (Ph), 179.8
(PhC(NSiMe3)2). Anal. Calc. for C37H66ClN4NbSi5: C,
53.17; H, 7.96; N, 6.70. Found: C, 53.40; H, 8.18; N, 6.85%.
CH2Cl2 (40 ml) was added to a mixture of [Nb(g5-
C5H4SiMe3)Cl4] (2.02 g, 5.43 mmol) and
2
(2.46 g,

A. Antin˜olo et al. / Journal of Organometallic Chemistry 691 (2006) 1361–1368
1367
4.11. Synthesis of [Nb(g5-C5H4SiMe3)(NMe2)Cl-
{@NC6Me4-4-(N(SiMe3)2)}] (10)
4.13. X-ray structure determination of [Ta(g5-C5H4-
SiMe3)Cl2{@NC6Me4-4-(N(SiMe3)2)}] (4)
A suspension of Li(NMe2) (0.036 g, 0.71 mmol) in Et2O
(30 ml) was added, at ꢀ78 ꢁC, to a solution of 6 (0.43 g,
0.71 mmol) in Et2O (30 ml). The mixture was allowed to
warm to room temperature and stirred for 12 h. The sus-
pension was filtered and solvent removed in vacuo to yield
the title compound as a brown solid (0.39 g, 89%). 1H
NMR (400 MHz, C6D6): d 0.14 (s, 18H, NSiMe3), 0.18
(s, 9H, C5H4SiMe3), 2.17 (6H), 2.54 (6H) (s, C6Me4), 2.88
(3H), 3.60 (3H) (br, NMe2), 5.93 (1H), 5.96 (1H), 6.13
(1H), 6.53 (1H) (m, C5H4). 13C{1H} NMR (100 MHz,
C6D6): d ꢀ0.1 (C5H4SiMe3), 2.6 (NSiMe3), 2.7, 3.9
(PhC(NSiMe3)2) 17.0, 18.0 (C6Me4), 50.1, 59.5 (NMe2),
111.4, 112.1, 112.3, 120.0, 124.0 (C5H4), 130.9, 132.8,
141.9 (CN), 153.0 (CN) (C6Me4). Anal. Calc. for
C26H49ClN3NbSi3: C, 50.67; H, 8.01; N, 6.82. Found: C,
50.82; H, 8.14; N, 6.91%.
A red irregularly shaped (0.4 · 0.2 · 0.1 mm) crystal of 4
has been mounted on Nonius KappaCCD diffractometer.
Unit cell and intensity measurements have been carried
˚
out with Mo Ka (k = 0.71073 A) at 115(2) K. No absorp-
tion correction was applied. Intensity data were reduced
with DENZO and SCALEPACK programs [14]. The structure
was solved using the SHELXTL structure determination pack-
age [15] by direct methods and refined by full-matrix least-
squares based on F2. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were included in calcu-
lated positions, and refined in a riding model. Crystallo-
graphic data are given in Table 3.
Acknowledgements
The authors gratefully acknowledge financial support
´
from Direccion General de Ensenanza Superior y de
˜
4.12. Attempted synthesis of [{Nb(g5-C5H4SiMe3)Cl2}-
(l-1,4-NC6Me4N){Ta(g5-C5H4SiMe3)Cl2}] (11)
´
´
´
Investigacion Cientıfica y Tecnica (Grants PB98-0159-
C02-01-02 and BQU2000-0463) and Direccion General
´
´
´
´
de Investigacion de la Consejerıa de Educacion de
CH2Cl2 (40 ml) was added to a mixture of [Ta(g5-
C5H4SiMe3)Cl4] (1.13 g, 2.47 mmol) and 7(1.50 g,
2.47 mmol) in a Teflon valve ampoule. The ampoule was
placed in an oil bath and heated at 90 ꢁC during 60 h.
The resulting deep red solution was allowed to cool down
to room temperature and volatiles were removed by apply-
ing reduced pressure. The solid was washed with hexane
´
la Comunidad Autonoma de Madrid (Grant 07N-0036/
98).
Appendix A. Supplementary data
Crystallographic data for the structural analysis of 4
have been deposited with the Cambridge Crystallographic
Data Centre, CCDC 288820. Copies of this information
may be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223
336 033; e-mail: deposit@ccdc.cam.ac.uk or http//
www.ccdc.cam.ac.uk). Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2005.12.016.
1
(3 · 15 ml) and identified by H NMR spectroscopy as a
mixture of 3 and 6 along with a third complex.
Table 3
Crystal data and structure refinement details for 4
Formula
C24H43Cl2N2Si3Ta
Formula weight
T (K)
695.72
115
References
Crystal system
Space group
Monoclinic
P21/a (No. 14)
14.3882(3)
14.5795(4)
16.4813(4)
109.7049(11)
3254.87(14)
4
1.420
3.666
1400
2.05–27.50
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