Arylimido niobium(V) complexes: Mononuclear and dendritic derivatives

Article abstract of DOI:10.1016/S0022-328X(02)02019-3

The compound 4-LiC₆H₄N(SiMe₃)₂ reacted in tetrahydrofuran with SiMe₃Cl or with silicon-chloride groups located at the periphery of carbosilane dendrimers of first, second, and third generation to afford (SiMe₃)₂)₂)₄ (7), and Si(CH₂CH₂CH₂SiMe(CH₂ CH₂CH₂SiMe (CH₂CH₂CH ₂SiMe₂C₆H₄N(SiMe ₃)₂)₂)₂)₄ (8). The N,N-bis(trimethylsilyl) aniline groups of 3 reacted with niobium pentachloride in acetonitrile or [NbCp′Cl4] (Cp′ = η⁵-C₅H₄SiMe₃) in dichloromethane to give imido mononuclear complexes [Nb(NC₆H₄SiMe₃-4)Cl₃ (CH₃CN)₂] (4) and [NbCp′(NC₆H₄SiMe₃-4)Cl ₂] (5), respectively. Reaction of dendrimers 6-8 and [NbCp′Cl₄] in CH₂Cl ₂ afforded metallodendrimers [Si(CH₂CH ₂CH₂SiMe₂C₆H₄N = NbCp′Cl₂)₄] (9), [Si(CH₂CH ₂CH₂SiMe(CH₂CH₂CH ₂SiMe₂C₆H₄N = NbCp′Cl₂)₂)₄] (10), and [Si(CH₂CH₂CH₂SiMe (CH₂CH₂CH₂SiMe(CH₂ CH₂-CH₂SiMe₂C₆ H₄N = NbCp′Cl₂)₂) ₂)₄] (11), in which the metal moieties are linked to the carbosilane framework through imidometal bonds. The structure of complexes 4 and 5 has been determined by X-ray diffraction methods.

Full text of DOI:10.1016/S0022-328X(02)02019-3

Journal of Organometallic Chemistry 664 (2002) 258Á267
/
www.elsevier.com/locate/jorganchem
Arylimido niobium(V) complexes: mononuclear and dendritic
derivatives
Jose´ M. Benito, Ernesto de Jesu´s ꢀ, F. Javier de la Mata, Juan C. Flores ꢀ,
Rafael Go´mez, Pilar Go´mez-Sal
´ ´ ´ ´
Departamento de Quımica Inorganica, Universidad de Alcala, Campus Universitario, E28871 Alcala de Henares (Madrid), Spain
Received 9 September 2002; received in revised form 8 October 2002; accepted 14 October 2002
Abstract
The compound 4-LiC6H4N(SiMe3)2 reacted in tetrahydrofuran with SiMe3Cl or with silicon-chloride groups located at the
periphery of carbosilane dendrimers of first, second, and third generation to afford 4-SiMe3C6H4N(SiMe3)2 (3) and functionalized
dendrimers Si(CH2CH2CH2SiMe2C6H4N(SiMe3)2)4 (6), Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4N(SiMe3)2)2)4 (7), and
Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4N(SiMe3)2)2)2)4 (8). The N,N-bis(trimethylsilyl)aniline groups
of 3 reacted with niobium pentachloride in acetonitrile or [NbCp?Cl4] (Cp?ꢁ
mononuclear complexes [Nb(NC6H4SiMe3-4)Cl3(CH3CN)2] (4) and [NbCp?(NC6H4SiMe3-4)Cl2] (5), respectively. Reaction of
dendrimers 6Á8 and [NbCp?Cl4] in CH2Cl2 afforded metallodendrimers [Si(CH2CH2CH2SiMe2C6H4NÄNbCp?Cl2)4] (9),
[Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe2C6H4NÄNbCp?Cl2)2)4] (10), and [Si(CH2CH2CH2SiMe(CH2CH2CH2SiMe(CH2CH2-
CH2SiMe2C6H4NÄNbCp?Cl2)2)2)4] (11), in which the metal moieties are linked to the carbosilane framework through imidoÃ
/
h5-C5H4SiMe3) in dichloromethane to give imido
/
/
/
/
/
metal bonds. The structure of complexes 4 and 5 has been determined by X-ray diffraction methods.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Cyclopentadienyl ligands; Dendrimers; Niobium; N Ligands
1. Introduction
[6]. Imido ligands are exceptionally suited for the
stabilization of high-valent metal complexes due to their
strong p-donor abilities [7].
An increasing number of reports have been published
on the incorporation of transition metals at the core,
branches, or periphery of dendrimers [1]. Applications
of these macromolecular systems in catalysis are being
widely studied [2]. However, little attention has been
paid to dendrimers containing early-transition metals
[3]. We have focused our research work on the synthesis
of dendrimers containing Group 4 complexes at their
periphery [4] or at their focal point [5]. Recently, we
have suggested that carbosilane dendrimers functiona-
lized with aniline groups might support early-transition
metal complexes at their periphery through imido bonds
In our previous report [6], the formation of metalÃ
/
imido bonds from metal halides was carried out on
mononuclear models or small dendritic molecules by
means of deprotonation of aniline end-groups [7] or
cleavage of nitrogenÃ/silicon bonds in their N,N-bis(tri-
methylsilyl) derivatives [8]. The ortho- or para-carbon
atoms of the aniline group were linked up with a
dendritic silicon atom through an oxo bridge. This fact
limited the scope of the reported procedures because of
side-reactions between the SiÃ
/
O bonds and the oxophi-
lic early-transition metals. Here, we present the synthesis
of new niobium(V) imido dendrimers obtained by
reaction of metal chlorides with the N,N-bis(trimethyl-
silyl)aniline end-groups of oxygen-free dendrimers. Syn-
thetic and structural studies on mononuclear models are
in addition presented.
ꢀ Corresponding authors. Tel.:
8854683
E-mail address: ernesto.dejesus@uah.es (E. de Jesu´s).
ꢂ
/
34-91-8854603; fax:
ꢂ/34-91-
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 2 0 1 9 - 3

J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á
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267
259
2. Results and discussion
Compounds 1Á
/
3 are liquids at room temperature and
have been found to undergo hydrolysis of their
nitrogenÃ
/
silicon bonds upon exposure to air. Their
1H-NMR spectra show downfield resonances for the
2.1. Synthesis and characterization of mononuclear
complexes
aromatic ring protons (AA?BB? spin systems), and a
broad singlet for the NÃ
/
H group in 1 (d 3.47). The
Preparative details and spectroscopic data for all the
new compounds are given in Section 4. Only selected
data will be presented for discussion. Nitrogen-silylation
in haloanilines is a typical reaction for the protection of
amino groups [9]. For the preparation of 4-iodo-N,N-
bis(trimethylsilyl)aniline (2, Scheme 1), we have fol-
lowed a stepwise route in which the monosilylated
compound 1 is synthesized as an intermediate. The
preparation of 1 has been carried out in a decagram
scale by the addition of SiMe3Cl to 4-iodoaniline
followed by dehydrohalogenation of the resulting am-
monium salt with triethylamine [10]. In our hands, the
alternative method [11], in which the aniline is deproto-
nated with one equivalent of n-BuLi and the amide
anion reacted with SiMe3Cl, was reliable for the
preparation of 1 in only a small scale. Slow addition
SiMe3 groups give one (for 1 and 2) or two (for 3)
1
singlets in H-, 13C{1H}-, and 29Si{1H}-NMR. The 13C
chemical shift for the ipso-carbon in 4-position gives a
spectroscopic handle to determine whether or not the
iodo substitution occurred. After silylation, this reso-
nance is shifted from higher (d 78.3 for 1 and 87.6 for 2)
to much lower fields (d 134.5 for 3).
As discussed above, N,N-bis(trimethylsilyl)-substi-
tuted anilines are suitable starting materials for the
synthesis of metal imido complexes from metal chlor-
ides. In our experience, this procedure, which only
produces volatile SiMe3Cl by-product, is in general
quantitative and cleaner than other alternatives em-
ployed for the formation of metalÃ
/imido bonds (e.g.
deprotonation or exchange reactions). Purification
methods are far more limited in dendrimers than in
other areas of chemistry, making selectivity an essential
question. Previously to the use of dendrimers, we have
prepared related mononuclear complexes to prove
selectivity and to determine optimal reaction conditions.
Aniline 3 reacts smoothly with NbCl5 in acetonitrile or
of one equivalent of n-BuLi to 1 in hexane at ꢃ
gives a white solid that reacts with SiMe3Cl in tetra-
hydrofuran (THF) at ꢃ78 8C to afford 2 in high yield
/
78 8C
/
(Scheme 1). In these conditions, only silylation at the
amino group has been observed, although the selectivity
of this route is highly sensitive to the experimental
conditions. Thus, when the addition of n-BuLi was
carried out in hexane at room temperature or in THF at
with [NbCp?Cl4] (Cp?ꢁ
h5-C5H4SiMe3) in dichloro-
/
methane affording imido complexes 4 and 5, respectively
(Scheme 1). Both reactions were quantitative (1H-NMR
evidence) although the final yield on 5 was reduced to
ꢃ78 8C, 2 was isolated with different amounts of
/
impurities mainly due to concurrent partial metallation
at the iodo position. Further reaction of 2 with one
equivalent of n-BuLi, now in pentane and at room
temperature, lead to the formation of 4-
LiC6H4N(SiMe3)2 as a white precipitate, which can be
isolated in ca. 80% yield and stored in a dry-box or
90% after recrystallization from pentane. H- and 13C-
1
NMR data show the presence of two equivalent CH3CN
ligands in 4 at room temperature. This behavior
contrasts with the solid-state structure determined by
X-ray (see below) in which one of the ligands is
coordinated trans to a chloride atom and the other to
the imido fragment. Therefore, it should be assumed the
directly reacted with SiMe3Cl in THF ꢃ
/
78 8C to give
the trisilylated compound 3 in quantitative yield [9].
Scheme 1.

260
J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á267
/
confirmed up to now by X-ray analysis correspond to
niobium and tantalum complexes [M(NC6Hi3Pr2-
2,6)X3L2] (Xꢁ
/
Cl, Br; L2ꢁdimethoxyethane or tetra-
/
methyletilendiamine) for which the bidentate L2 ligand
forces the cis arrangement [13].
Compound 5 has a three-legged piano stool geometry
with the phenyl ring of the imido ligand in a quasi
reflection plane which roughly bisects the cyclopenta-
dienyl ring and the ClÃ
/
NbÃ
/
Cl angle (Fig. 2). In other
structurally characterized derivatives, the cyclopentadie-
nyl ring is eclipsed with respect to the imido ligand
[8a,12,14]. Instead, an anti conformation is adopted by
the substituted Cp ring in 5 in such a way that C(1) is
located trans to the imido group, in a position occupied
Fig. 1. View of the molecular structure of 4 with the atom-numbering
scheme.
existence of either an isomerization or a rapid dynamical
behavior of 4 in solution. The second interpretation has
been confirmed by low-temperature 1H-NMR spectra in
which two resonances are observed at d 2.37 and 2.43
by a ring CÃ
/
C bond in closely related structures. This
arrangement directs the SiMe3 group away from the
arylimido ligand, avoiding unfavorable steric interac-
tions in the solid-state. On the other hand, the orienta-
tion of the aryl ring observed in comparable structures is
either aligned or perpendicular to the reflection plane.
The former is found in [Nb(h5-C5H5){N(C6H5t Bu-
2)}Cl2] [14b], and the latter in species of Nb and Ta
with 2,6-disubstituted aryl rings [12,14a]. In these
examples, the ring is arranged in order to minimize the
steric congestion between the cyclopentadienyl ring and
the aryl substituents in ortho. Interestingly, the ortho
non-substituted ring in compound 5 is accommodated
on the reflection plane of the molecule. By contrast, the
(Tcoal
ꢁ
/
276 K, DG%276
ꢁ
55 kJ molꢃ1). The cyclopenta-
/
dienyl ligand of complex 5 shows two sets of resonances
at d 6.75 and 6.98 (AA?BB? spin system) due to the ring
protons, and a singlet at d 0.28 corresponding to the
SiMe3 group. IR bands at 1333 for 4 and 1320 cmꢃ1 for
5 are within the characteristic range of terminal imido
ligands (1200Á
1350 cmꢃ1). The terminal coordination
/
mode of the ligand is a relevant point here, since imido
bridges [12] might lead to undesired cross-linking of
dendritic molecules.
dinuclear
analog
[{Nb(h5-C5H4SiMe3)Cl2}(m-p-
2.2. Crystal structures of 4 and 5
N2C6H4)}] [15] shows the perpendicular alignment of
aryl ring and the eclipsed conformation of the cyclo-
pentadienyl ligand. Clearly, it should be assumed that
crystal-packing forces have a significant effect on the
positioning of these groups in the solid-state structure of
compound 5.
Molecular structures of imido complexes 4 and 5
based on X-ray structural analyses are given in Figs. 1
and 2. Selected bond distances and angles are listed in
Tables 1 and 2, respectively.
Compound 4 exhibits a cis Á
octahedral environment with three chloro atoms in the
plane perpendicular to the NbÃN axis and the acetoni-
trile ligands mutually cis (Fig. 1). This is the first
crystallographic evidence of cis Ámer geometry in Group
5 complexes of general formula [M(NAr)X3L2] with
Lꢁmonodentate ligand. Although this arrangement
/
mer stereochemistry in an
In both complexes, the niobiumÃ/nitrogen distance
/
lies within the range expected for a triple bond (1.754(4)
˚
for 4 and 1.740(9) A for 5) and the imido ligand is
/
approximately linear (NbÃ
169.0(7)8 for 5) [12Á14]. The trans influence of the imido
ligand in 4 is manifested by a NbÃCH3CN(cis) bond
distance ca. 0.15 A shorter than the NbÃCH3CN(trans)
one. In compound 5, the trans influence gives rise to a
/
NÃCipso: 167.6(4)8 for 4 and
/
/
/
/
˚
has previously been proposed for several complexes on
the basis of their NMR data, the only structures
/
Fig. 2. View of the molecular structure of 5 with the atom-numbering scheme.

J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á
/
267
261
Table 1
Table 2
˚
˚
Selected bond distances (A) and angles (8) for 4
Selected bond distances (A) and angles (8) for 5
Bond distances
Bond distances
Nb(1)ÃN(1)
Nb(1)ÃCl(1)
Nb(1)ÃCl(2)
Nb(1)ÃN(1)
Nb(1)ÃN(2)
Nb(1)ÃN(3)
Nb(1)ÃCl(1)
Nb(1)ÃCl(2)
Nb(1)ÃCl(3)
N(1)ÃC(1)
N(2)ÃC(7)
N(3)ÃC(9)
C(7)ÃC(8)
1.754(4)
1.740(9)
2.354(7)
2.323(6)
2.128
2.260(6)
2.412(6)
2.388(2)
2.370(2)
2.388(2)
1.395(7)
1.139(8)
1.129(8)
1.442(9)
1.449(9)
a
Nb(1)ÃCp(1)
Nb(1)ÃC(1)
Nb(1)ÃC(2)
Nb(1)ÃC(3)
Nb(1)ÃC(4)
Nb(1)ÃC(5)
N(1)ÃC(6)
Si(1)ÃC(1)
C(1)ÃC(5)
C(1)ÃC(2)
C(2)ÃC(3)
C(3)ÃC(4)
C(4)ÃC(5)
2.526(10)
2.442(19)
2.39(2)
2.35(2)
2.46(2)
1.418(13)
1.887(11)
1.35(2)
C(9)ÃC(10)
Bond angles
1.47(2)
1.43(2)
N(1)ÃNb(1)ÃCl(1)
N(1)ÃNb(1)ÃCl(2)
N(1)ÃNb(1)ÃCl(3)
N(1)ÃNb(1)ÃN(2)
N(1)ÃNb(1)ÃN(3)
N(2)ÃNb(1)ÃCl(1)
N(2)ÃNb(1)ÃCl(2)
N(2)ÃNb(1)ÃCl(3)
N(2)ÃNb(1)ÃN(3)
N(3)ÃNb(1)ÃCl(1)
N(3)ÃNb(1)ÃCl(2)
N(3)ÃNb(1)ÃCl(3)
Cl(1)ÃNb(1)ÃCl(2)
Cl(1)ÃNb(1)ÃCl(3)
Cl(2)ÃNb(1)ÃCl(3)
C(1)ÃN(1)ÃNb(1)
C(7)ÃN(2)ÃNb(1)
C(9)ÃN(3)ÃNb(1)
N(2)ÃC(7)ÃC(8)
N(3)ÃC(9)ÃC(10)
100.99(17)
99.07(17)
95.66(17)
91.9(2)
1.356(16)
1.40(3)
174.2(2)
82.98(14)
169.04(14)
82.36(14)
84.02(19)
82.69(15)
85.04(14)
79.69(15)
95.16(7)
158.11(7)
96.15(7)
167.6(4)
170.8(5)
170.9(6)
179.4(7)
177.8(8)
Bond angles
N(1)ÃNb(1)ÃCl(1)
N(1)ÃNb(1)ÃCl(2)
N(1)ÃNb(1)ÃCp(1)
Cl(1)ÃNb(1)ÃCl(2)
Cl(1)ÃNb(1)ÃCp(1)
Cl(2)ÃNb(1)ÃCp(1)
C(6)ÃN(1)ÃNb(1)
102.7(6)
101.4(6)
119.8
106.08(18)
107.8
117.3
a
a
169.0(7)
a
Cp(1) is the centroid of C(1)ÃC(5).
{(C6H4)NNbCp?Cl2}x (9Á
/
11, Scheme 2, Fig. 3) were
6
obtained in dichloromethane from
[NbCp?Cl4] in a quantitative reaction, as in the case of
the model compound 5. After crystallization, final yields
to 8 and
were in the range 50Á
Organic dendrimers 6Á
oils whereas niobium derivatives 9Á
lized as red solids. All the new dendrimers are moisture
sensitive. Niobium dendrimers are quite thermally stable
as shown by the fact that solutions of 9 in CDCl3
remained unchanged after 15 days at 70 8C in a PTFE-
/
73%.
8 were obtained as colorless
11 could be crystal-
/
distorted coordination of the cyclopentadienyl ring, with
carbon bond distances ranging from
/
the niobiumÃ
/
˚
2.526(10) A for C(1) to 2.39(2) and 2.35(2) A for C(3)
˚
and C(4), respectively.
valved NMR tube. NitrogenÃ
/
silicon bonds in 6Á8 are
/
2.3. Synthesis and characterization of dendrimers
easily hydrolyzed. However, attempts to prepare NH2-
terminated dendrimers by reaction with mild acids failed
to give pure products. This could be due to concurrent
The syntheses of dendrimers containing niobium
centers at their periphery have been studied. For this
purpose, chloro-terminated dendrimers of first, second,
and third generation (Scheme 2) were synthesized
according to previously reported methods [16]. These
partial breaking of siliconÃ
amounts of C6H5NH2 are detected by H-NMR in the
crude of reaction. Although it is well known that
/
phenyl bonds, since small
1
aminophenylÃ
/
silicon bonds are sensitive to protic acids
dendrimers containing peripheral SiÃ
converted into Gn Ã{(C6H4)N(SiMe3)2}x (nꢁ
(6); nꢁ2, xꢁ8 (7); nꢁ3, xꢁ16 (8)), which might be
considered polyaniline analogues of 3. These conver-
sions (85Á97% yield) were carried out by a parallel
/
Cl bonds were
[17], it is noteworthy that hydrolysis of 3 in the same
conditions produced its quantitative conversion into
Me3SiC6H4NH2 (1H-NMR evidence) [9a].
/
/
1, xꢁ4
/
/
/
/
/
1H-, 13C{1H}-, and 29Si{1H}-NMR chemical shifts of
/
terminal PhN(SiMe3)2 groups for 6Á8 are comparable to
those found for 3. The replacement at the end of the
dendritic branches of the chloride atom in dendrimers
/
procedure to that described for model compound 3, in
which the appropriated chloro-terminated dendrimer
Gn Ã
/
Cl is used instead of SiMe3Cl. Dendrimers 6Á8 were
/
Gn Ã
/
Cl by PhN(SiMe3)2 groups in 6Á8 is confirmed,
/
used as supports for 4, 8, or 16 niobium centers that
were anchored to the dendritic framework through
within the NMR resolution, by the shift of the SiMe2
resonances from d 0.38 (1H) and 1.9 (13C) to 0.19 (1H)
imido bonds. Thus, niobium dendrimers Gn Ã
/

262
J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á267
/
Scheme 2.
to silicon atoms are centered at ca. d 0.50, except the
outermost ones (CH2SiMe2Ph) that appear at ca. d 0.75.
In the 13C-NMR spectra, the methylene carbon reso-
nances are situated within the range d 17Á21. For the
/
dendrimers of second and third generation, the three
peaks due to the outer branches can be unambiguously
assigned, although smaller signals, corresponding to the
inner shells, are also observed. The external SiMe2
protons are located at d 0.19 but the internal SiMe
groups are not observed probably because of over-
lapping with N(SiMe3)2 resonances.
Spectroscopic and analytical data for metallodendri-
mers 9Á11 are consistent with their proposed structures
/
shown in Scheme 2 and Fig. 3. IR spectra confirmed the
terminal nature of their imido ligands (bands at ca. 1320
cmꢃ1). The presence of niobium complexes at the end of
the dendritic branches was established by NMR. The
proton and carbon atoms of the Cp? ring appear at the
same positions that those in their mononuclear analog 5.
The carbosilane framework is insignificantly affected by
the presence of niobium complexes at their periphery
and therefore the general characteristics of the NMR
Fig. 3. Niobium dendrimer G3Ã{(C6H4)NNbCp?Cl2}16 (11).
/
spectra of dendrimers 9Á/11 are almost identical to that
1
and ꢃ
/
4.3 (13C). The H-NMR spectra of the carbosi-
described above for metal-free dendrimers 6Á
/8.
lane framework for dendrimers 6Á
/
8 show almost
identical shifts for analogous nuclei in different genera-
tions. The overlapping of groups situated at different
shells of a given dendrimer together with their restricted
mobility, explain the typical peak broadening and loss
of resolution observed in increasing the generation [18].
Three sets of signals attributed to the methylene groups
of the SiCH2CH2CH2Si branches have been observed
with the expected integration ratio. The middle methy-
lenes are located at ca. d 1.25, and those directly bonded
3. Conclusion
In summary, a synthetic strategy that allows the
anchoring of metal centers to the periphery of carbosi-
lane dendrimers through imido ligands has been devel-
oped and applied to the synthesis of the first examples of
niobium dendrimers. The formation of imido links is
carried out via elimination of SiMe3Cl from metal

J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á
/
267
263
halides and N,N-bis(trimethylsilyl)aniline-ended dendri-
mers. This procedure has been shown to be suitable for
the growing up to the third generation, although it could
be useful for higher generations and for other metal
complexes [19].
4.3. Preparation of 4-iodo-N,N-
bis(trimethylsilyl)aniline (2)
One equivalent of n-BuLi (14.5 ml, 1.6 M in hexanes,
23.2 mmol) was slowly added from a funnel, equipped
with a bubbler, to a solution of compound 1 (6.74 g,
23.1 mmol) in C6H14 (50 ml) at ꢃ78 8C. When the
/
addition was completed, the mixture was allowed to
warm up to r.t. and stirred overnight. Then, the
resulting white precipitate was separated from the
4. Experimental
4.1. Reagents and general techniques
solution by filtration, washed with C5H12 (2ꢄ
dried, dissolved in THF (50 ml), and reacted with
SiMe3Cl (3.0 ml, 23.7 mmol) at ꢃ78 8C. The reaction
/25 ml),
All operat ions were performed under an Ar atmo-
sphere using Schlenk or dry-box techniques. Unless
otherwise stated, reagents were obtained from commer-
cial sources and used as received. [NbCp?Cl4] [20], and
carbosilane dendrimers Gn Ã
prepared according to literature procedures; the purity
of dendrimers was checked by GPC analysis of the Gn Ã
(allyl) intermediates. Solvents were previously dried and
distilled under Ar as described elsewhere [21]. NMR
spectra were recorded on Varian Unity 300 or 500 Plus
spectrometers. Chemical shifts (d, ppm) are reported in
ppm referenced to SiMe4 for 1H, 13C and 29Si. IR
/
mixture was stirred for 2 h at r.t., the solvent was
removed under reduced pressure, and the oily residue
extracted with C5H12 (2ꢄ25 ml). Removal of the C5H12
/
/
Cl (nꢁ
/
1Á
/
3) [16] were
afforded spectroscopically pure 2 (7.23 g, 86%) as a pale-
yellow liquid, which could be distilled under vacuum
/
(70Á
73 8C, 10ꢃ3 mmHg). Anal. Calc. for C12H22INSi2:
/
C, 39.7; H, 6.1; N, 3.9. Found: C, 40.0; H, 6.1; N, 4.4%.
1H-NMR (CDCl3): d 0.04 (s, 18H, SiMe3), 6.63 (AA?
part of an AA?BB? spin system, 2H, C6H4), 7.48 (BB?
part of an AA?BB? spin system, 2H, C6H4). 13C{1H}-
NMR (CDCl3): d 2.0 (SiMe3), 87.6 (ipso IÃ
(C6H4), 137.5 (C6H4), 148.1 (ipso NÃ
C6H4). 29Si{1H}-
NMR (CDCl3): d 5.3 (SiMe3).
/C6H4), 132.3
spectra were recorded in Nujol mulls on a PerkinÁElmer
/
/
FT-IR Spectrum-2000 spectrophotometer. Elemental
analyses were performed by Microanalytical Labora-
tories of the University of Alcala´ on a Heraeus CHN-O-
Rapid mycroanalyzer.
4.4. Preparation of 4-trimethylsilyl-N,N-
bis(trimethylsilyl)aniline (3)
4.2. Preparation of 4-iodo-N-trimethylsilylaniline (1)
n-BuLi (7.2 ml, 1.6 M in hexanes, 11.5 mmol) was
added from a syringe to a solution of compound 2 (4.16
g, 11.4 mmol) in C5H12 (10 ml) at r.t. The solution
turned slowly to a suspension of white solid. The
mixture was stirred overnight and then filtered to
separate the n-BuI by-product from the white precipi-
This compound was synthesized by adapting a
literature procedure relating the monosilylation reaction
of aromatic amines [10b]. A solution of 4-IC6H4NH2
(29.40 g, 134.2 mmol) in Et2O (250 ml) was treated with
an excess of SiMe3Cl (25.5 ml, 201 mmol) at 0 8C. The
resulting suspension of white precipitate was stirred for
30 min and Et3N (28.1 ml, 201 mmol) was slowly added
also at 0 8C. The reaction mixture was allowed to warm
up to room temperature (r.t.) and was stirred for 5 h.
After filtration of the solution, the remaining solid was
tate that was washed with C5H12 (2ꢄ15 ml) and dried
/
under vacuum. The lithiated compound 4-
LiC6H4N(SiMe3)2 thus obtained, which can be stored
in a dry-box, was subsequently treated with SiMe3Cl
(1.50 ml, 11.8 mmol) in THF (15 ml) at ꢃ78 8C. The
reaction mixture was stirred for 4 h at r.t., the solvent
was removed under reduced pressure, and the residue
/
washed with C5H12 (2ꢄ
combined and the volatiles removed in vacuo to give
crude 1 as a yellowÁbrownish sticky liquid. The mono-
silylated aniline was purified by crystallization in C5H12
(ca. 70 ml) at ꢃ78 8C, leading to 1 as a white solid
(32.80 g, 84%) which melts back at r.t. Anal. Calc. for
C9H14INSi: C, 37.1; H, 4.8; N, 4.8. Found: C, 36.9; H,
1
4.8; N, 5.3%. H-NMR (CDCl3): d 0.28 (s, 9H, SiMe3),
/
50 ml). The filtrates were
/
extracted with C5H12 (2ꢄ25 ml). Removal of the
/
solvent in vacuo gave 3 as a pale-yellow liquid (2.59 g,
73%). Anal. Calc. for C15H31NSi3: C, 58.2; H, 10.1; N,
4.5. Found: C, 58.3; H, 10.2; N, 5.5%. 1H-NMR
/
(CDCl3): d 0.06 (s, 18H, NÃ
/
SiMe3), 0.24 (s, 9H, PhÃ
/
SiMe3), 6.86 (AA? part of an AA?BB? spin system, 2H,
C6H4), 7.32 (BB? part of an AA?BB? spin system, 2H,
3.47 (broad s, 1H, NH), 6.45 (AA? part of an AA?BB?
spin system, 2H, C6H4), 7.38 (BB? part of an AA?BB?
spin system, 2H, C6H4). 13C{1H}-NMR (CDCl3): d
C6H4). 13C{1H}-NMR (CDCl3): d ꢃ
/
0.9 (PhÃ
SiMe3), 129.5 (C6H4), 133.5 (C6H4), 134.5 (ipso
C6H4), 148.5 (ipso NÃ
C6H4). 29Si{1H}-NMR
(CDCl3): d ꢃ4.4 (PhÃSiMe3), 4.7 (NÃSiMe3).
/
SiMe3),
2.1 (NÃ
/
ꢃ
/
0.1 (SiMe3), 78.3 (ipso IÃ
(C6H4), 147.1 (ipso NÃ
C6H4). 29Si{1H}-NMR (CDCl3):
d 3.3 (SiMe3).
/
C6H4), 118.4 (C6H4), 137.8
/
SiÃ
/
/
/
/
/

264
J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á267
/
4.5. Preparation of bis(acetonitrile)trichloro(4-
trimethylsilylphenylimido)niobium(V) (4)
Calc. for C68H136N4Si13: C, 59.4; H, 10.0; N, 4.1.
1
Found: C, 59.2; H, 10.3; N, 4.2%. H-NMR (CDCl3):
d 0.03 (s, 18H, SiMe3), 0.19 (s, 6H, SiMe2), 0.50 (m, 2H,
SiCH2), 0.76 (m, 2H, CH2SiMe2), 1.28 (m, 2H,
CH2CH2CH2), 6.83 (AA? part of an AA?BB? spin
system, 2H, C6H4), 7.27 (BB? part of an AA?BB? spin
A solution of 3 (2.09 g, 6.75 mmol) in MeCN (25 ml)
was added to NbCl5 (1.824 g, 6.75 mmol) in MeCN (25
ml) at r.t. The solution turned quickly from clear-yellow
to red. The stirring was kept for 90 min. Solvent
system, 2H, C6H4). 13C{1H}-NMR (CDCl3): d ꢃ
/2.7
evaporation afforded a foamy purpleÁ
was treated with C5H12 (2ꢄ40 ml) and dried in vacuo to
give pure 4 (2.88 g, 96%) as a purpleÁred powder. Anal.
Calc. for C13H19Cl3N3NbSi: C, 35.1; H, 4.3; N, 9.4.
1
Found: C, 34.8; H, 4.3; N, 9.1%. H-NMR (CDCl3): d
/
red solid which
(SiMe2), 2.2 (SiMe3), 17.3 (CH2), 18.6 (CH2), 20.9
/
(CH2), 129.5 (C6H4), 133.7 (C6H4), 134.8 (ipso SiÃ
/
/
C6H4), 148.5 (ipso NÃ
/
C6H4). 29Si{1H}-NMR (CDCl3):
d ꢃ4.4 (SiMe2), 0.8 (central Si), 4.4 (SiMe3).
/
0.21 (s, 9H, PhÃ/SiMe3), 2.31 (s broad, 6H, MeCN), 7.27
4.8. Preparation of G2Ã
/
{(C6H4)N(SiMe3)2}8 (7)
(AA? part of an AA?BB? spin system, 2H, C6H4), 7.44
(BB? part of an AA?BB? spin system, 2H, C6H4).
4-LiC6H4N(SiMe3)2 (1.16 g, 4.8 mmol) and G2Ã
/
Cl
13C{1H}-NMR (CDCl3): d
ꢃ
/
1.2 (SiMe3), 3.2 (s,
MeCN), 120.1 (s very broad, MeCN), 124.5 (C6H4),
133.1 (C6H4), 140.2 (ipso SiÃC6H4), 154.6 (ipso NÃ
3.7 (SiMe3). IR
(0.87 g, 0.60 mmol) were reacted in THF as described
above for 6 to give 7 as a colorless oil (1.78 g, 97%).
Anal. Calc. for C152H308N8Si29: C, 59.6; H, 10.1; N, 3.7.
/
/
C6H4). 29Si{1H}-NMR (CDCl3): d ꢃ
/
Found: C, 58.8; H, 9.9; N, 4.0%. H-NMR (CDCl3): d
1
(Nujol, CsI): n 1333 cmꢃ1 (NbN).
ꢃ0.19 (s, 3H, SiMe), 0.02 (s, 36H, SiMe3), 0.19 (s, 12H,
/
SiMe2), 0.48 (m, 8H, SiCH2), 0.73 (m, 4H, CH2SiMe2),
1.25 (m, 6H, CH2CH2CH2), 6.81 (AA? part of an
AA?BB? spin system, 4H, C6H4), 7.27 (BB? part of an
AA?BB? spin system, 4H, C6H4). 13C{1H}-NMR
4.6. Preparation of dichloro(h5-
trimethylsilylcyclopentadienyl)(4-
trimethylsilylphenylimido)niobium(V) (5)
(CDCl3): d ꢃ
18.5 (CH2), 18.6 (CH2), 20.7 (CH2), 129.4 (C6H4), 133.7
(C6H4), 134.7 (ipso SiÃC6H4), 148.4 (ipso NÃC6H4).
29Si{1H}-NMR (CDCl3): d ꢃ
4.3 (SiMe2), 1.0 (SiMe),
4.4 (SiMe3), central Si not observed.
/
5.1 (SiMe), ꢃ2.7 (SiMe2), 2.1 (SiMe3),
/
A solution of [NbCp?Cl4] (1.60 g, 4.30 mmol) in
CH2Cl2 (40 ml) was added to a solution of compound 3
(1.33 g, 4.30 mmol) in CH2Cl2 (40 ml) at r.t. The
solution was stirred overnight, and the solvent was
removed in vacuo. The residue was dissolved in C5H12
(ca. 40 ml), and the solution was concentrated and
/
/
/
4.9. Preparation of G3Ã
/
{(C6H4)N(SiMe3)2}16 (8)
stored at ꢃ20 8C overnight. Complex 5 precipitated as a
/
microcrystalline orange solid that was filtered and dried
in vacuo (1.80 g, 90%). Anal. Calc. for
C17H26Cl2NNbSi2: C, 44.0; H, 5.6; N, 3.0. Found: C,
43.9; H, 5.8; N, 2.7%. 1H-NMR (CDCl3): d 0.22 (s, 9H,
4-LiC6H4N(SiMe3)2 (3.32 g, 13.6 mmol) and G3Ã
/
Cl
(2.74 g, 0.85 mmol) were reacted in THF as described
above for 6 to give 8 as a colorless oil (4.85 g, 89%).
Anal. Calc. for C320H652N16Si61: C, 59.7; H, 10.2; N, 3.5.
Found: C, 59.1; H, 10.0; N, 3.7%. 1H-NMR (CDCl3): d
PhÃ
/
SiMe3), 0.28 (s, 9H, CpÃSiMe3), 6.62 (AA? part of
/
an AA?BB? spin system, 2H, C5H4), 6.75 (BB? part of an
AA?BB? spin system, 2H, C5H4), 6.98 (AA? part of an
AA?BB? spin system, 2H, C6H4), 7.39 (BB? part of an
AA?BB? spin system, 2H, C6H4). 13C{1H}-NMR
ꢃ0.19 (s, 9H, SiMe), 0.02 (s, 72H, SiMe3), 0.19 (s, 24H,
/
SiMe2), 0.50 (m, 20H, SiCH2), 0.73 (m, 8H, CH2SiMe2),
1.26 (m, 14H, CH2CH2CH2), 6.82 (AA? part of an
AA?BB? spin system, 8H, C6H4), 7.27 (BB? part of an
AA?BB? spin system, 8H, C6H4). 13C{1H}-NMR
(C6D6): d ꢃ
(C5H4), 122.0 (C5H4), 123.7 (C6H4), 125.5 (ipso C5H4),
133.80 (C6H4), 138.5 (ipso SiÃC6H4), 156.4 (ipso NÃ
C6H4). 29Si{1H}-NMR (C6D6): d ꢃ
5.2 (C5H4SiMe3),
4.1 (PhSiMe3). IR (Nujol, CsI): n 1321 cmꢃ1 (NbN).
/
1.1 (PhÃ
/
SiMe3), ꢃ
/
0.6 (CpÃ/SiMe3), 114.2
(CDCl3): d
distinguished), ꢃ
18.6 (CH2), 20.8 (CH2), 129.5 (C6H4), 133.7 (C6H4),
134.8 (ipso SiÃC6H4), 148.5 (ipso NÃ
C6H4). 29Si{1H}-
NMR (CDCl3): d ꢃ4.3 (SiMe2), 1.1 (G2ÃSiMe), 4.4
(SiMe3), G1ÃSiMe and central Si not observed.
ꢃ
/
5.1 (SiMe, only one peak can be
/
/
/2.7 (SiMe2), 2.1 (SiMe3), 18.5 (CH2),
/
ꢃ
/
/
/
/
/
4.7. Preparation of G1Ã
/
{(C6H4)N(SiMe3)2}4 (6)
/
A solution of 4-LiC6H4N(SiMe3)2 (1.12 g, 4.60 mmol)
in THF (30 ml), prepared as for 3, was added to G1ÃCl
(0.66 g, 1.15 mmol) at ꢃ78 8C. The solution was
allowed to reach r.t., stirred overnight, and evaporated
to dryness. The residue was extracted with C5H12 (30 ml)
and filtered. The colorless oil obtained after solvent
evaporation was characterized as 6 (1.34 g, 85%). Anal.
4.10. Preparation of G1Ã{(C6H4)NNbCp?Cl2}4 (9)
/
/
/
A solution of [NbCp?Cl4] (1.04 g, 2.80 mmol) in
CH2Cl2 (30 ml) was added to 6 (0.96 g, 0.70 mmol), and
stirred for 12 h. Then, the solvent was removed in vacuo
to dryness. The red oil thus obtained was crystallized by
washing twice with cold C5H12 (2ꢄ15 ml) to give
/

J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á
/
267
265
dendrimer 9 as a red solid that was filtered and dried in
vacuo (0.70 g, 50%). Anal. Calc. for
C76H116Cl8N4Nb4Si9: C, 45.8; H, 5.9; N, 2.8. Found:
(CH2), 18.7 (CH2), 20.5 (CH2), 114.0 (C5H4), 122.2
(C5H4), 123.2 (C6H4), 126.1 (ipso C5H4), 133.6 (C6H4),
138.0 (ipso SiÃ
/
C6H4), 156.3 (ipso NÃ
/
C6H4). 29Si{1H}-
3.9 (SiMe2), 1.2
1
C, 44.4; H, 5.9; N, 2.7%. H-NMR (CDCl3): d 0.20 (s,
NMR (CDCl3): d ꢃ
/
5.5 (SiMe3), ꢃ
/
6H, SiMe2), 0.28 (s, 9H, SiMe3), 0.48 (m, 2H, SiCH2),
0.75 (m, 2H, CH2SiMe2), 1.26 (m, 2H, CH2CH2CH2),
6.60 (AA? part of an AA?BB? spin system, 2H, C5H4),
6.75 (BB? part of an AA?BB? spin system, 2H, C5H4),
6.97 (AA? part of an AA?BB? spin system, 2H, C6H4),
7.36 (BB? part of an AA?BB? spin system, 2H, C6H4).
(G2Ã
/
SiMe), G1Ã
/
SiMe and central Si not assigned. IR
(Nujol, CsI): n 1321 cmꢃ1 (NbN).
4.13. Crystal structure determinations
13C{1H}-NMR (CDCl3):
d
(SiMe3), 17.4 (CH2), 18.5 (CH2), 20.6 (CH2), 113.9
ꢃ
/
2.9 (SiMe2),
ꢃ0.5
/
Purple crystals of compound 4 were obtained by
cooling a concentrated solution in MeCN at ꢃ20 8C.
/
Orange crystals of 5 were obtained by slow concentra-
tion of a C6H14 solution. Suitable sized crystals were
sealed under Ar in a Lindemann tube and mounted in an
(C5H4), 122.1 (C5H4), 123.2 (C6H4), 126.1 (ipso C5H4),
133.6 (C6H4), 138.0 (ipso SiÃ
C6H4). 29Si{1H}-NMR (CDCl3): d
4.6 (SiMe2), central Si not observed. IR (Nujol,
CsI): n 1320 cmꢃ1 (NbN).
/
C6H4), 156.3 (ipso NÃ
/
ꢃ
/
4.8 (SiMe3),
EnrafÁ
/
Nonius CAD 4 automatic four-circle diffract-
Ka radia-
ꢃ
/
ometer with graphite monochromated MoÁ
/
Table 3
Crystallographic details for 4 and 5
4.11. Preparation of G2Ã{(C6H4)NNbCp?Cl2}8 (10)
/
[NbCp?Cl4] (1.02 g, 2.74 mmol) and 7 (1.05 g, 0.34
mmol) were reacted in CH2Cl2 as described above for 9
to give 10 as a red solid (0.98 g, 67%). Anal. Calc. for
4
5
Chemical formula
Habit
Formula weight
C13H19Cl3N3NbSi
Prismatic
444.66
C17H26Cl2NNbSi2
Prismatic
464.38
C
168H268Cl16N8Nb8Si21: C, 46.9; H, 6.3; N, 2.6. Found:
0.14 (s,
C, 47.0; H, 6.5; N, 2.7%. 1H-NMR (CDCl3): d ꢃ
/
Temperature (K)
˚
293(2)
0.71069
293(2)
0.71073
3H, SiMe), 0.19 (s, 12H, SiMe2), 0.27 (s, 18H, SiMe3),
0.51 (m, 8H, SiCH2), 0.74 (m, 4H, CH2SiMe2), 1.29 (m,
6H, CH2CH2CH2), 6.60 (AA? part of an AA?BB? spin
system, 4H, C5H4), 6,74 (BB? part of an AA?BB? spin
system, 4H, C5H4), 6.95 (AA? part of an AA?BB? spin
system, 4H, C6H4), 7.35 (BB? part of an AA?BB? spin
l (MoÁ/Ka) (A)
Crystal system
Space group
Triclinic
¯
Orthorhombic
Pna21
/
P1/
˚
a (A)
7.173(5)
9.874(5)
14.665(5)
74.230(5)
86.600(5)
86.650(5)
996.8(9)
2
24.389(3)
8.848(1)
10.502(1)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
system, 4H, C6H4). 13C{1H}-NMR (CDCl3): d ꢃ
/
5.0
0.5 (SiMe3), 18.4 (CH2), 18.7
(CH2), 20.4 (CH2), 113.9 (C5H4), 122.1 (C5H4), 123.2
(C6H4), 126.1 (ipso C5H4), 133.6 (C6H4), 138.0 (ipso SiÃ
C6H4), 156.3 (ipso NÃ
C6H4). 29Si{1H}-NMR (C6D6): d
5.0 (SiMe3), ꢃ3.8 (SiMe2), 1.0 (SiMe), central Si not
observed. IR (Nujol, CsI): n 1321 cmꢃ1 (NbN).
(SiMe), ꢃ
/
2.8 (SiMe2), ꢃ
/
3
˚
V (A )
Z
2266.2(4)
4
1.361
Dcalc (g cmꢃ3
)
1.481
10.62
/
m (cmꢃ1
)
8.71
0.35ꢄ0.27ꢄ0.20
2.45Á24.99
0Bh B28,
0Bk B10,
ꢃ12Bl B0
2312
/
Crystal size (mm)
u Limits (8)
Limiting indices
0.30ꢄ0.27ꢄ0.27
1.44Á
ꢃ7Bh B7,
ꢃ10Bh B10,
0Bk Bꢃ16
2962
ꢃ
/
/
/
22.97
/
4.12. Preparation of G3Ã{(C6H4)NNbCp?Cl2}16 (11)
/
Reflections col-
lected
[NbCp?Cl4] (0.59 g, 1.59 mmol) and 8 (0.64 g, 0.10
mmol) were reacted in CH2Cl2 as described above for 9
to give 11 as a red solid (0.65 g, 73%). Anal. Calc. for
Reflections unique 2762 [Rintꢁ0.04]
2108
1294
Reflections ob-
served [I ꢀ2s(I)]
Data/restraints/
parameters
2095
C
352H572Cl32N16Nb16Si45: C, 47.4; H, 6.5; N, 2.5.
1
2762/0 /230
0.0439; 0.1038
2108/0 /121
0.0534; 0.1163
1.014
Found: C, 46.7; H, 6.7; N, 2.4%. H-NMR (CDCl3): d
0.14 (s broad, 9H, SiMe, only one peak can be
R [(I ꢀ2s(I)];
wR2 a
ꢃ
/
distinguished), 0.19 (s, 24H, SiMe2), 0.27 (s, 36H,
SiMe3), 0.51 (m, 20H, SiCH2), 0.73 (m, 8H, CH2SiMe2),
1.28 (m, 14H, CH2CH2CH2), 6.59 (AA? part of an
AA?BB? spin system, 8H, C5H4), 6.74 (BB? part of an
AA?BB? spin system, 8H, C5H4), 6.96 (AA? part of an
AA?BB? spin system, 8H, C6H4), 7.36 (BB? part of an
AA?BB? spin system, 8H, C6H4). 13C{1H}-NMR
Goodness-of-fit in- 1.031
dicator
Max peak in final
difference map (e
0.661
0.815
ꢃ3
˚
A
)
Min peak in final
difference map (e
ꢃ0.501
ꢃ0.399
ꢃ3
˚
A
)
(CDCl3): d
distinguished),
ꢃ
/
4.9 (SiMe, only one peak can be
Rꢁa jjFojꢃjFcjj/a jFoj]; wR2ꢁ
/
[a w(Fo2 ꢃFc2)2=a w(Fo2)2]1=2
:/
a
ꢃ
/
2.8 (SiMe2), 0.5 (SiMe3), 18.5
ꢃ
/

266
J.M. Benito et al. / Journal of Organometallic Chemistry 664 (2002) 258Á267
/
[3] (a) D. Seyferth, R. Wryrwa, U.W. Franz, S. Becke, PCT Int.
Appl. WO 97/32908, 1997; Chem Abstr. 127 (1997) 263179;
tion. Crystallographic and experimental details are
summarized in Table 3. Data were collected at r.t.
Intensities were corrected for Lp effects in the usual
manner. No absorption or extinction corrections were
made. The structure was solved by direct methods
(b) K. Bruning, H. Lang, J. Organomet. Chem. 575 (1999) 153;
¨
(c) V. Cadierno, A. Igau, B. Donnadieu, A.M. Caminade, J.P.
Majoral, Organometallics 18 (1999) 1580;
(d) V. Cadierno, M. Zablocka, B. Donnadieu, A. Igau, J.P.
Majoral, A. Skowronska, Chem. Eur. J. 7 (2001) 221;
(e) D. Seebach, R.E. Marti, T. Hintermann, Helv. Chim. Acta 79
(1996) 1710;
(
SHELXL-90) [22] and refined by least-squares against
(
F2
SHELXL-97) [23]. All non hydrogen atoms were
refined anisotropically, and the hydrogen atoms were
introduced from geometrical calculations and refined
using a riding model. Compound 5 could be solved in
the centersymmetric Pnma group with a crystallo-
graphic symmetry plane. In that case the whole molecule
is well defined but the SiMe3 group bonded to the Cp
group, and two phenyl carbon atoms appear seriously
disordered.
(f) P.B. Rheiner, H. Sellner, D. Seebach, Helv. Chim. Acta 80
(1997) 2027;
(g) H. Sellner, D. Seebach, Angew. Chem. 111 (1999) 2039;
(h) P.B. Rheiner, D. Seebach, Chem. Eur. J. 5 (1999) 3221.
[4] (a) S. Are´valo, J.M. Benito, E. de Jesu´s, F.J. de la Mata, J.C.
Flores, R. Go´mez, J. Organomet. Chem. 602 (2000) 208;
(b) S. Are´valo, E. de Jesu´s, F.J. de la Mata, J.C. Flores, R.
Go´mez, Organometallics 20 (2001) 2583.
[5] R. Andre´s, E. de Jesu´s, F.J. de la Mata, J.C. Flores, R. Go´mez,
Eur. J. Inorg. Chem. (2002) 2281.
[6] J.M. Benito, S. Are´valo, E. de Jesu´s, F.J. de la Mata, J.C. Flores,
R. Go´mez, J. Organomet. Chem. 610 (2000) 42.
[7] (a) D.E. Wigley, Prog. Inorg. Chem. 42 (1994) 239;
(b) W.A. Nugent, B.L. Haymore, Coord. Chem. Rev. 31 (1980)
123.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 188939Á188940 for com-
pounds 4 and 5. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
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We gratefully acknowledge financial support from the
DGESIC-Ministerio de Educacio´n y Cultura (project
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[19] For example, the first generation analogue of 4, G1Ã
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{(C6H4)NNbCl3(CH3CN)2}4, has been prepared by a similar
procedure to that described for the mononuclear complex. 1H-
NMR (CD3CN): d 0.16 (s, 6H, SiMe2), 0.39 (m, 2H, SiCH2), 0.72
(m, 2H, CH2SiMe2), 1.21 (m, 2H, CH2CH2CH2), 7.15 (AA? part
of an AA?BB? spin system, 2H, C6H4), 7.46 (BB? part of an
AA?BB? spin system, 2H, C6H4). 13C{1H}-NMR (CD3CN): d
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ꢃ
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2.7 (SiMe2), 17.8 (CH2), 19.3 (CH2), 20.9 (CH2), 124.7 (C6H4),
[23] G.M. Sheldrick, SHELXL-97, University of Gottingen, Gottingen,
¨ ¨
Germany, 1997.
134.5 (C6H4), 140.2 (ipso SiÃC6H4), 155.1 (ipso NÃC6H4).
/
/