Carbosilane dendrimers containing peripheral cyclopentadienyl niobium- and tantalum-imido complexes

Article abstract of DOI:10.1016/j.jorganchem.2006.05.009

Anilines Gn-{(C₆H₄)N(SiMe₃)₂} _m, based on simple or dendritic carbosilanes, have been used to synthesized (imido)tantalum compounds Gn-{(C₆H₄)NTaCl₂Cp^*}

Full text of DOI:10.1016/j.jorganchem.2006.05.009

Journal of Organometallic Chemistry 691 (2006) 3602–3608
www.elsevier.com/locate/jorganchem
Carbosilane dendrimers containing peripheral
cyclopentadienyl niobium- and tantalum-imido complexes
*
*
´
´
Jose M. Benito, Ernesto de Jesus , F. Javier de la Mata, Juan C. Flores ,
´
´
Rafael Gomez, Pilar Gomez-Sal
Departamento de Quı´mica Inorga´nica, Universidad de Alcala´, Campus Universitario, 28871 Alcala´ de Henares, Madrid, Spain
Received 27 March 2006; received in revised form 5 May 2006; accepted 5 May 2006
Available online 19 May 2006
Abstract
Anilines Gn-{(C6H4)N(SiMe3)2}m, based on simple or dendritic carbosilanes, have been used to synthesized (imido)tantalum com-
pounds Gn-{(C6H4)NTaCl2Cp*}m (1, n = 0, m = 1; 2, n = 1, m = 4; Cp* = g5-C5Me5), by the reaction with [TaCl4Cp*] and elimination
of SiMe3Cl. (Imido)niobocene compounds of general formula Gn-fðC6H4ÞNNbClCp0 gm (3–5; n = 0,1,2; m = 1,4,8, respectively) have
2
been readily prepared from their corresponding half-sandwich complexes Gn-{(C6H4)NNbCl2Cp0}m by the reaction with m equiv. of
LiCp0 (Cp0 = g5-C5H4SiMe3). Compounds 1–5 are all found to be exceedingly moisture sensitive, and in the case of the (imido)niobocene
materials the hydrolytic reaction selectively leads to the formation of ½NbClðOÞCp02ꢀ (6). The molecular structure of 6 has been deter-
mined by X-ray diffraction studies.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Imido; Cyclopentadienyl; Dendrimers; Tantalum; Niobium; Metallocene
1. Introduction
evant dendritic effects on their polymerization catalyses [8],
and also explored the application of poly(pyrazolyl)meth-
ane ligands in the field of metallodendritic chemistry [7].
Imido ligands have led to a prominent family of com-
plexes in transition metal chemistry, being characterized
by their capability to stabilize high-valent metal complexes
due to their strong p-donor abilities [9,10], and with impor-
tant uses such as stable ancillary ligands at early transition
metal centers active in metathesis polymerization processes
[11]. In our search for useful anchoring functionalities, we
first identified the potential of terminal aniline groups to
support early transition metal compounds through imido
bonds on the periphery of carbosilane dendrimers [6a],
and later tuned this approach for the synthesis of
mono(cyclopentadienyl)niobium(V) carbosilane dendri-
mers with the metal complexes linked to the dendritic
framework through arylimidoAmetal bonds [6b]. These
previous results are used in this work for the synthesis of
new carbosilane dendrimers with imido-supported com-
plexes of niobium and tantalum at their periphery.
Metallodendrimer research has been steadily gaining
ground during the last few years, a considerable number
of dendritic macromolecules containing transition metals
at their core, branches, or periphery have been prepared
[1], and some of them studied in metal-based catalysis [2].
Much more limited is the number of examples describing
dendrimers containing early transition metals [3–7a]. We
have contributed with several works into the chemistry of
carbosilane dendrimers containing early transition-metal
complexes bonded to the dendritic periphery or focal point
[4], usually through O- [5], or N-donor anchoring ligands
[6]. Recently we have expanded the range of useful syn-
thetic routes available to attach metal complexes to dendri-
mers, by using pyridylimine ligands in the synthesis of
group 10 peripheral metallodendrimers, which showed rel-
*
Corresponding authors. Tel.: +34 91 885 46 07; fax: +34 91 885 46 83.
E-mail address: juanc.flores@uah.es (J.C. Flores).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.009

J.M. Benito et al. / Journal of Organometallic Chemistry 691 (2006) 3602–3608
3603
2. Results and discussion
moisture sensitivity of polymetallic dendrimers in higher
generations. In fact, complexes 1 and 2 had to be prepared
in sealed tubes using strictly dry solvents, otherwise decom-
position was apparent by formation of some white-yellow-
ish precipitate. It is worth noting that compounds of
general formula [TaCl2Cp*(NAr)] containing sterically
demanding aryl-imido ligands, like ortho-disubstituted aryl
ring [9c], are fairly stable, whereas those with para-substi-
tuted or plain phenyl rings on the imido ligand are known
to be rather moisture-sensitive [10b,12]. Relative to the for-
mation of half-sandwich niobium-imido compounds, the
reactions leading to 1 and 2 required more severe condi-
tions, and in order to facilitate the formation of 2 by
removal of SiMe3Cl, vacuum was briefly applied several
times over the course reaction (see Section 4). Both com-
pounds are isolated as an orange solid, soluble in chlori-
nated and aromatic solvents, but not in saturated
hydrocarbons.
2.1. Synthesis of complexes
Preparative details and spectroscopic data for the new
compounds are given in Section 4. Only selected data will
be presented for this discussion. The cleavage of NASi
bonds has been previously employed as a route to form
transition metal imido bonds [9,10]. Thus, we have quanti-
tatively prepared new Ti and Nb imido complexes by reac-
tion of N,N-bis(trimethylsilyl)-anilines with metal chlorides
[6b]. Compared with other alternatives, such as amine
deprotonation or amine/imido exchange reactions, the pro-
cedure is selective and particularly straightforward since
the only by-product formed in the process is volatile
SiMe3Cl. These facts are essential because purification
methods are far more limited for the synthesis of metallo-
dendrimers than for simpler or smaller organometallic
compounds, and they become impracticable for highly
air-sensitive polymetallic dendritic species.
As previously reported the reaction of m equiv. of
[NbCl4Cp0] (Cp0 = g5-C5H4SiMe3) with polyanilines based
on carbosilane dendrimers up to the third generation Gn-
{(C6H4)N(SiMe3)2}m (n = 0,12,3; m = 1,4,8,16, respec-
tively) readily afforded half-sandwich niobium imido
dendrimers Gn-{(C6H4)NNbCl2Cp0}m (Scheme 1), which
were found to be stable solids under an inert atmosphere
[6b]. However, when [TaCl4Cp*] is used as the organome-
tallic precursor (Cp* = g5-C5Me5), only the monometallic
1 and the first generation dendrimer 2 have been success-
fully prepared (Scheme 1), probably due to an exceedingly
Complexes 1 and 2 were characterized by 1H, 13C NMR,
and IR spectroscopies. The [TaCl2(Cp*)(NC6H4-4)] moiety
1
is observed in the H NMR spectra as an intense singlet at
ca. 2.2 ppm due to the cyclopentadienyl ring, and an
AA0XX0 splitting pattern at lower field for the para-substi-
tuted aryl ring. The carbosilane part gives rise to a singlet
for 1 (ASiMe3), or a singlet and three multiplets
(ACH2CH2CH2SiMe2A) for 2, all in normal regions.
13C{1H} NMR data are consistent with their proposed
structures, and in the case of compound 2 are also in agree-
ment with the equivalence of the four metallic terminal
groups. The IR absorption due to the terminal imido
groups was observed at ca. 1320–1340 cmꢁ1
.
m
[TaCl4(
η
5–C5Me5)]
G
n
N(SiMe3)2
G
n
N=Ta
CH2Cl2
m
Cl
m
Cl
1
2
n
n
= 0,
= 1,
m
m
=1
=4
m
[NbCl4(
η
5–Cp')]
Cp' = C5H4SiMe3
Me3Si
N=Nb
Me3Si
N=Nb
Me3Si
H2O
LiCp'
toluene
Gn
G
n
O
Nb
Cl
Cl
Cl
m
m
Cl
Me3Si
Me3Si
3
4
5
n
n
n
= 0,
= 1,
= 2,
m
m
m
=1
=4
=8
6
Me
Si
Me
Si
G0 =
G1 =
G2 =
Si
Si
Me
Me3Si
Si
Me
Me
4
2
4
Scheme 1.

3604
J.M. Benito et al. / Journal of Organometallic Chemistry 691 (2006) 3602–3608
A limited number of procedures for the synthesis of
synthesis of oxoniobocene compounds comprise the oxida-
tion of dichloro complexes [18], or olefin-hydride or alkyl-
and halo-carbonyl niobocenes in their reaction with O2
[15], or the decarbonylation of coordinated carbon dioxide
[19].
niobocene-imido complexes has been reported so far [13].
A straightforward method consists in the reaction of
niobium-imido halide precursors with alkali or alkaline
earth metal cyclopentadienides [14]. Thus, niobocene-
imido compounds up to the second generation
The [NbCl(Cp0)2(NC6H4-4)] moiety is observed in the
1H NMR spectra of compounds 3–5 as an ABCD spin sys-
tem for the cyclopentadienyl rings (d 5.5–6.5), together
with an AA0XX0 system for the aryl ring protons (d 6.3–
7.4), and an intense resonance at ca. 0.2 ppm for the Cp0
substituent (ASiMe3). When compared to the monocyclo-
pentadienyl precursors, the presence of the second five-
membered ring causes the lost of the symmetry plane that
splits the Cp0 ring, and as a result the four ring protons,
as well the five carbons, of each Cp0 group are now non-
equivalent. Besides, the additional shielding introduced
with the second ring makes the resonances for the N-ortho
phenyl protons, and the average corresponding to the C5H4
protons to shift to higher field (0.4–0.5 ppm). Similarly, rel-
evant shifts to higher field (up to 13 ppm) are noticeable in
Gn-fðC6H4ÞNNbClCp0 gm (n = 0,1,2; m = 1, 4,8; 3–5) were
2
prepared by the reaction of Gn-{(C6H4)NNbCl2Cp0}m with
m equiv. of LiCp0 in toluene (Scheme 1, Fig. 1). Compounds
3–5 were isolated as an orange to red solid, with yields
around 50% after work up as well as recrystallization, and
were found to be soluble in all common solvents including
alkanes.
The niobium compounds 3–5 are stable under inert
atmosphere, but they quickly decompose in the presence
of traces of water to give complex 6, an chloro(oxo)niobo-
cene previously synthesized by means of the oxidation of
½NbClCp0 ðCOÞꢀ with O2 [15a]. The moisture-sensitivity of
2
complexes 3–5 increases with the metallic load on the den-
dritic molecule (5 > 4 > 3). Even though mono- and di-
metallic chloro(arylimido)niobocene complexes closely
related to 3–5, have been reported to be air-stable as solid
materials [16], the formation of an oxoniobocene by selec-
tive hydrolysis of arylimidoANb bond has been prece-
dented [17]. Compound 6 can be quantitatively prepared
by dissolution of complex 3 in wet dichloromethane (or
CDCl3) giving free amine 4-Me3Si-C6H4-NH2 [6b] as single
by-product (1H NMR evidence). Other procedures for the
13
the C{1H} NMR data for the Cp0 and phenyl ring car-
bons. On the contrary, the carbosilane framework is insig-
nificantly affected by the formation of the niobocene
complexes at their periphery, and therefore the general
characteristics of their NMR spectra are almost identical
to those described for the dendritic monocyclopentadienyl
precursors [6b]. Thus, a singlet (3) for the SiMe3 group or
three sets of signals attributed to the methylene groups (4
SiMe3
Cl
Cl
Me3Si
Nb
Me3Si
SiMe3
Nb
N
N
SiMe3
Cl
Me
Me
Me3Si
Si
Me
Nb
Si
Me
N
Cl
Nb
N
Me
Si
Si
Si
Si
Me3Si
Me
Si
Me
Me
Me
SiMe3
Me
Me
Si
Si
Me
Me3Si
Si
Me
Me
Si
Me
Me
SiMe3
N
Nb
Cl
N
Me
Nb
Si
Me
Cl
Si
SiMe3
Me
Me
Me3Si
N
N
Nb
Cl
Me3Si
SiMe3
Nb
Cl
SiMe3
Me3Si
Fig. 1. (Imido)niobocene dendrimer 5.

J.M. Benito et al. / Journal of Organometallic Chemistry 691 (2006) 3602–3608
3605
˚
and 5) have been observed with the expected integration
ratio. For the SiCH2CH2CH2Si branches, the middle meth-
ylenes are located at ca. 1.25 ppm, and those directly
bonded to silicon atoms are centered at ca. 0.45 ppm,
except the outermost ones (CH2SiMe2Ph) that appear at
ca. 0.75 ppm. Methylene carbon resonances are situated
within the range 18–21 ppm. External SiMe2 protons/car-
bons are located at about 0.17/ꢁ3.0 ppm and the internal
SiMe groups in dendrimer 5 at ꢁ0.14/ꢁ5.0 ppm.
respectively), whilst the Nb@O (1.816(5) A) and NbACl
˚
(2.418(2) A) bond distances are somewhat longer and at
the lower limits, respectively, than those previously
reported (1.63–1.74 and 2.43–2.45 A, respectively). For
instance, in the closely related methyl-oxo compound
[NbMe(O)(C5H4SiMe3)2] [15a], the Nb@O bond distance
is 1.720(7) A. The p donor capability of the chloro ligand
˚
˚
in 6 must, in turn, weaken the p-bonding interaction with
the oxo ligand elongating the NbAO distance. The most
distinctive feature in the structure of compound 6 is the anti
positioning of the two C5H4SiMe3 rings, therefore, making
the niobium atom to be a stereogenic center in the solid
state. In fact, the two rac-enantiomers are present in the
unit cell (only one is depicted in Fig. 2). Compounds such
as [NbCl(O)(C5H4But)(C5H4Me)] and [NbCl(O)(C5H4-
Pri)2] [21], [NbMe(O)(C5H4SiMe3)2] [15a], or [NbY(O)-
(C5H4Me)2] (Y = Cl, CH2SiMe3) [19], all show crystal
structures with a syn-conformation of the monosubstituted
cyclopentadienyl ligands, where the rings are eclipsed or
staggered and their substituents are on the side of the oxy-
gen atom probably due to the presence of Oꢂ ꢂ ꢂH-bonding
type interactions. The different arrangement in 6 compare
to the methyl-oxo analogous [15a], must be caused by weak
stabilizing interactions in its crystal packing.
2.2. Structure of ½NbClðOÞCp02ꢀ ð6Þ
Spectroscopic characterization of compound 6 has been
reported elsewhere [15a]. Fig. 2 shows an ORTEP represen-
tation of the molecular structure found in the solid state by
single crystal X-ray diffraction studies for compound 6,
while relevant bond lengths and angles are tabulated in
Table 1. The crystal structure of 6 consists of a discrete mol-
ecule in a typical bent metallocene arrangement, where the
niobium atom shows a pseudo-tetrahedral geometry, and
binds to two Cp0 rings, an oxygen atom and a chloro ligand.
Comparison with the structural information found in
other oxoniobocene complexes [17,20,21], reveals the
ClANbAO (94.71(18)ꢁ) and Cp0ANbACp0 (126.31ꢁ) angles
in 6 to be at the lower limits (95.6–99.7ꢁ and 126.5–131.0ꢁ,
3. Conclusion
In summary, the synthetic strategy accounted in our pre-
vious report to synthesized (imido)niobium(V) carbosilane
dendrimers, has been now extended to the preparation of
related tantalum(V) compounds, as well as peripheral (ary-
limido)niobocene dendrimers. While half-sandwich com-
pounds Gn-{(C6H4)NNbCl2Cp0}m described earlier were
found to be easy-to-handle air-sensitive materials, the tan-
talum or biscyclopentadienyl derivatives of this work are
remarkably moisture sensitive. Therefore, these studies
demonstrate the efficiency of the procedures used for the
synthesis of group 5 metal-imido dendrimers, without
other limitation than the own stability of the final products.
Thus, the hydrolysis of metal-imido bonds has prevented
the preparation of higher generation metallodendrimers.
In the case of the niobium compounds the hydrolytic reac-
tion leads selectively to a structurally characterized
chloro(oxo)niobocene compound.
Fig. 2. ORTEP diagram of compound 6 with the atomic numbering
scheme.
4. Experimental
Table 1
4.1. Reagents and general techniques
a
˚
Selected bond lengths [A], and angles [ꢁ] for compound 6
Nb(1)AO(1)
Nb(1)ACl(1)
Nb(1)ACp(1)
Nb(1)ACp(2)
Nb(1)AC(Cp(1))b
Nb(1)AC(Cp(2))b
a
1.816(5)
2.418(2)
2.186
2.186
2.491(7)
2.491(7)
Cp(1)ANb(1)ACp(2)
O(1)ANb(1)ACp(1)
O(2)ANb(1)ACp(2)
Cl(1)ANb(1)ACp(1)
Cl(1)ANb(1)ACp(2)
Cl(1)ANb(1)AO(1)
126.31
110.98
109.00
104.87
105.98
94.71(18)
All operations were performed under an argon atmo-
sphere using Schlenk or dry-box techniques. Unless other-
wise stated, reagents were obtained from commercial
sources and used as received. LiCp0 (Cp0 = g5-C5H4SiMe3)
[22], [TaCl4Cp*] (Cp* = g5-C5Me5) [23], silylated anilines
Gn-{(C6H4)N(SiMe3)2}m, and niobium derivatives Gn-
{(C6H4)NNbCl2Cp0}m (n = 0,1,2; m = 1,4,8, respectively)
[6b] were prepared according to the literature procedures.
Cp(1) and Cp(2) denote the cyclopentadienyl-centroid of C1AC5 and
C6AC10 rings, respectively.
b
Average value.

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J.M. Benito et al. / Journal of Organometallic Chemistry 691 (2006) 3602–3608
Solvents were previously dried and distilled under argon as
described elsewhere [24]. NMR spectra were recorded on
Varian Unity 500+, Varian Unity VR-300 or Varian Unity
200 NMR spectrometers. Chemical shifts (d) are reported
in ppm referenced to SiMe4 for 1H and 13C. 1H NMR inte-
grated values for dendritic compounds are given relative to
one of the four arms of the molecule. Elemental analyses
were performed by Microanalytical Laboratories of the
4.4. Preparation of G0-fðC6H4ÞNNbCp0 Clg, chloro(bis-g5-
2
trimethylsilylcyclopentadienyl)(4-trimethylsilylphenylimido)-
niobium(V) (3)
Solid compounds [(4-Me3Si-C6H4)NNbCl2Cp0] (0.50 g,
1.07 mmol) and LiCp0 (158 mg, 1.09 mmol) were weighed
and introduced into a Schlenk tube, toluene (35 mL) was
added and the mixture stirred 18 h at room temperature.
Then the solvent was removed in vacuo and the residue
extracted with pentane (2 · 15 mL). After elimination of
the solvent, complex 3 is obtained as an orange solid that
could be recrystallized from pentane solutions (0.32 g,
53%). Anal. Calcd. for C25H39NSi3ClNb (566.21): C,
53.03; H, 6.94; N, 2.47. Found: C, 52.76; H, 7.19; N,
´
University of Alcala on a Heraeus CHN-O-Rapid and Per-
kin–Elmer 2400 Series II C, H, N, S/O microanalyzers.
4.2. Preparation of G0-{(C6H4)NTaCl2Cp*}, dichloro(g5-
pentamethylcyclopentadienyl)(4-trimethylsilylphenylimido)-
tantalum(V) (1)
1
2.22%. H NMR (CDCl3): d 0.22 (s, 9H, Ph-Si Me3), 0.27
A solution of 4-trimethylsilyl-N,N-bis(trimethylsilyl)ani-
line (0.83 g, 2.68 mmol) in dichloromethane (30 mL),
together with another solution of [TaCl4Cp*] (1.22 g,
2.68 mmol) in toluene (30 mL) were introduced in an
ampoule tube equipped with a PTFE valve. The tube was
sealed and the mixture warmed up to 75 ꢁC during 48 h.
The resulting orange solution was filtered to a Schlenk
tube, the solvent was removed in vacuo and the residue
washed with pentane to give 1 as an orange solid (1.30 g,
88%). Anal. Calcd. for C19H28NSiCl2Ta (550.38): C,
41.46; H, 5.13; N, 2.55. Found: C, 41.20; H, 5.27; N,
(s, 18H, Cp-Si Me3), 5.52 (m, ABCD spin system, 2H,
C5H4), 5.99 (m, ABCD spin system, 2H, C5H4), 6.25 (m,
ABCD spin system, 2H, C5H4), 6.38 (m, ABCD spin system,
2H, C5H4), 6.58 (m, AA0 part of an AA0XX0 spin system, 2H,
C6H4), 7.43 (m, XX0 part of an AA0XX0 spin system, 2H,
C6H4). 13C{1H} NMR (CDCl3): d ꢁ0.9 (Ph-Si Me3), 0.1
(Cp-Si Me3), 111.2 (C5H4), 110.5 (C6H4), 116.9 (C5H4),
119.2 (ipso C5H4), 120.9 (C6H4), 126.3 (C5H4), 133.2
(C5H4, and ipso Si-C6H4 overlapping), 159.9 (ipso N-
C6H4). IR (KBr): m 1329 cmꢁ1 (NbN).
1
2.33%. H NMR (CDCl3): d 0.21 (s, 9H, Si Me3), 2.19 (s,
4.5. Preparation of G1-fðC6H4ÞNNbClCp02g4 ð4Þ
15H, C5 Me5), 6.73 (m, AA0 part of an AA0XX0 spin sys-
tem, 2H, C6H4), 7.35 (m, XX0 part of an AA0XX0 spin sys-
tem, 2H, C6H4). 13C{1H} NMR (CDCl3): d ꢁ0.8 (Si Me3),
11.6 (C5 Me5), 121.8 (C5Me5), 125.2 (C6H4), 132.9 (C6H4),
135.5 (ipso Si-C6H4), 154.4 (ipso N-C6H4). IR (KBr): m
1321 cmꢁ1 (s, TaN), 1032 cmꢁ1 (s, Cp*).
Solid LiCp0 (144 mg, 1.00 mmol) and G1–{(C6H4)N-
NbCl2Cp0}4 (0.50 g, 0.25 mmol) were placed into a Schlenk
tube together with toluene as a solvent (25 mL). The red-
dish solution was stirred over a 48 h period, observing
the formation of white precipitate. The LiCl by-product
was eliminated by filtration, and the solvent under reduced
pressure, affording compound 4 as a red solid. The niobo-
dendrimer was recrystallized from toluene solutions by
cooling at ꢁ20 ꢁC during several days (0.30 g, 50%). Anal.
Calcd. for C108H168N4Si13Cl4Nb4 (2401.10): C, 54.02; H,
7.05; N, 2.33. Found: C, 54.42; H, 6.91; N, 2.70%. 1H
NMR (CDCl3): d 0.17 (s, 6H, Si Me2), 0.19 (s, 18H, Cp-
Si Me3), 0.42 (m, 2H, SiCH2), 0.75 (m, 2H, CH2SiMe2),
1.24 (m, 2H, CH2CH2CH2), 6.00 (m, ABCD spin system,
2H, C5H4), 6.34 (m, AA0 part of an AA0XX0 spin system,
2H, C6H4), 6.39 (m, ABCD spin system, 2H, C5H4), 6.44
(m, ABCD spin system, 2H, C5H4), 6.47 (m, ABCD spin
system, 2H, C5H4), 7.24 (m, XX0 part of an AA0XX0 spin
system, 2H, C6H4). 13C{1H} NMR (CDCl3): d ꢁ2.7 (Si
Me2), 0.0 (Si Me3), 17.8 (CH2), 18.5 (CH2), 20.9 (CH2),
110.4 (C6H4), 111.2 (C5H4), 116.9 (C5H4), 119.1 (ipso
C5H4), 120.7 (C6H4), 126.3 (C5H4), 133.3 (C5H4), 133.6
(ipso Si-C6H4), 159.8 (ipso N-C6H4).
4.3. Preparation of G1-{(C6H4)NTaCl2Cp*}4 (2)
Using a dry-box, a solution of [TaCl4Cp*] (0.86 g,
1.88 mmol)
and
G1-{(C6H4)N(SiMe3)2}4
(0.65 g,
0.47 mmol) in a dichloromethane/toluene solvent mixture
(1:1, 60 mL) was poured and sealed into an ampoule-tube
like that described above. Again warming was kept 48 h,
and now vacuum was periodically applied briefly through
the PTFE valve. After filtration of the solution and
removal of the volatiles, the resulting residue was washed
in portions with pentane to give an orange solid character-
ized as compound 2 (0.70 g, 64%). Anal. Calcd. for
C84H126N4Si5Cl8Ta4 (2339.79): C, 43.12; H, 5.43; N, 2.39.
1
Found: C, 41.93; H, 5.35; N, 1.96%. H NMR (CDCl3):
d 0.18 (s, 6H, Si Me2), 0,48 (m, 2H, SiCH2), 0,74 (m, 2H,
CH2SiMe2), 1.30 (m, 2H, CH2CH2CH2), 2.18 (s, 15H, C5
Me5), 6.70 (m, AA0 part of an AA0XX0 spin system, 2H,
C6H4), 7.34 (m, XX0 part of an AA0XX0 spin system, 2H,
C6H4). 13C{1H} NMR (CDCl3): d ꢁ2.7 (Si Me3), 11.6
(C5 Me5), 17.4 (CH2), 18.6 (CH2), 20.9 (CH2), 121.7
(C5Me5), 125.1 (C6H4), 133.1 (C6H4), 134.8 (ipso Si-
C6H4), 154.3 (ipso N-C6H4). IR (KBr): m 1341 cmꢁ1 (s,
TaN), 1030 cmꢁ1 (s, Cp*).
4.6. Preparation of G2-fðC6H4ÞNNbCp02Clg8 ð5Þ
Dendritic compound 5 was synthesized as described
above for
(0.55 g, 0.13 mmol) and LiCp0 (150 mg, 1.04 mmol) in
4
starting from G2-{(C6H4)NNbCl2Cp0}8

J.M. Benito et al. / Journal of Organometallic Chemistry 691 (2006) 3602–3608
3607
Table 2
toluene (25 mL). Compound 5 was isolated as a oily red
Crystal data and structure refinement for compound 6
solid that solidified by repeating freezing/vacuum opera-
tions, and was recrystallized from cold toluene (0.33 g,
50%). Anal. Calcd. for C232H372N8Si29Cl8Nb8 (5114.91):
C, 54.47; H, 7.33; N, 2.19. Found: C, 54.40; H, 7.94; N,
Empirical formula
Formula weight
Color
C16H26ClNbOSi2
418.91
Orange
293.0(2)
0.71073
Temperature (K)
1
2.35%. H NMR (CDCl3): d ꢁ0.14 (s, 3H, Si Me), 0.17
˚
Wavelength (A)
ꢀ
(s, 12H, Si Me2), 0.19 (s, 36H, Cp-Si Me3), 0.51 (m, 8H,
SiCH2), 0.76 (m, 4H, CH2SiMe2), 1.30 (m, 6H,
CH2CH2CH2), 6.00 (m, ABCD spin system, 4H, C5H4),
6.34 (m, AA0 part of an AA0XX0 spin system, 4H, C6H4),
6.39 (m, ABCD spin system, 4H, C5H4), 6.44 (m, ABCD
spin system, 4H, C5H4), 6.47 (m, ABCD spin system, 4H,
C5H4), 7.24 (m, XX0 part of an AA0XX0 spin system, 4H,
C6H4). 13C{1H} NMR (CDCl3): d ꢁ5.4 (Si Me), ꢁ3.1 (Si
Me2), 0.4 (Si Me3), 18.1 (CH2), 18.3 (CH2), 20.2 (CH2),
20.3 (CH2), 110.1 (C6H4), 110.8 (C5H4), 116.5 (C5H4),
118.7 (ipso C5H4), 120.3 (C6H4), 125.9 (C5H4), 132.9
(C5H4), 134.3 (ipso Si-C6H4), 159.4 (ipso N-C6H4).
Crystal system, space group
Triclinic, P1
Unit cell dimensions
˚
a (A)
6.550(5)
12.955(5)
˚
b (A)
˚
c (A)
13.315(5)
a (ꢁ)
b (ꢁ)
c (ꢁ)
64.281(5)
83.774(5)
76.888(5)
991.3(9)
2, 1.403
0.860
432
3
˚
Volume (A )
Z, Calculated density (g/cm3)
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm)
h Ranges (ꢁ)
0.22 · 0.20 · 0.18
1.70–22.97
ꢁ7 6 h 6 7, ꢁ14 6 k 6 0,
ꢁ14 6 l 6 13
2967/2753 [0.0312]
1960 [I > 2r(I)]
Limiting indices
4.7. Preparation of ½NbClðOÞCp02ꢀ, chloro(oxo)(bis-g5-
trimethylsilyl-cyclopentadienyl)niobium(V) (6)
Reflections collected/unique [R(int)]
Reflections observed
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final Ra indices [I > 2r(I)]
R indices (all data)
Full-matrix least-squares on F2
2753/0/190
This compound was prepared by treatment of imido
complex 3 (0.20 g, 0.35 mmol) with wet dichloromethane
(10 lL/100 mL) over night. After evaporation of the sol-
vent and washing with pentane (10 mL), complex 6 is iso-
lated as yellow-orange microcrystalline solid in
quantitative yield (147 mg). Anal. Calcd. for C16H26Si2-
ClONb (418.91): C, 45.87; H, 6.26. Found: C, 45.70; H,
1.044
R1 = 0.0501, wR2 = 0.1119
R1 = 0.0993, wR2 = 0.1278
1.130 and ꢁ0.377
Largest difference in peak and
3
˚
hole (e/A )
P
P
P
P
2
1=2
a
R1 = iFo| ꢁ |Fci/ |Fo|; wR2 ¼ f½ xðF 2o ꢁ F c2Þꢀ=½ xðF o2Þ ꢀg
.
1
tions and refined using a riding model. All the calculations
were made using the WINGX system [26].
6.45%. H NMR (CDCl3): d 0.26 (s, 18H, Cp–Si Me3),
6.14 (m, ABCD spin system, 2H, C5H4), 6.38 (m, ABCD
spin system, 2H, C5H4), 6.50 (m, ABCD spin system, 2H,
C5H4), 6.59 (m, ABCD spin system, 2H, C5H4). 13C{1H}
NMR (CDCl3): d 0.2 (Cp-Si Me3), 115.1 (C5H4), 115.7
(C5H4), 120.3 (C5H4), 125.2 (ipso C5H4), 126.9 (C5H4).
IR (KBr): m 920 cmꢁ1 (NbO).
Acknowledgements
We gratefully acknowledge financial support from the
´
Spanish Ministerio de Educacion y Ciencia (Project
CTQ2005-00795/BQU) and Comunidad de Madrid (Pro-
ject S-0505/PPQ/0328-03).
4.8. X-ray crystallographic studies
Appendix A. Supplementary data
Suitable monocrystals of 6 were obtained by slow diffu-
sion of a pentane layer into a dichloromethane solution of
the niobium complex at room temperature. A summary of
crystal data, data collection, and refinement parameters for
the structural analysis is given in Table 2.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 602652 for compound 6. Copies of this
information can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK.
Fax: (int. code) +44 1223 336 033; or e-mail: depos-
it@ccdc.cam.ac.uk; or www.cccd.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2006.05.009.
An orange suitable sized crystal were sealed under argon
in a Lindemann capillary tube and mounted in an Enraf
Nonius CAD 4 automatic four-circle diffractometer with
graphite-monochromated Mo Ka radiation (k =
˚
0.71073 A). Intensities were collected at room temperature
and were corrected for Lorenz and polarization effects in
the usual manner. No extinction or absorption correction
were made. Structure was solved by direct methods, com-
pleted by the subsequent difference Fourier techniques
and refined by full-matrix least squares on F2 (SHELXL-97)
[25]. Anisotropic thermal parameters were used in the last
cycles of refinement for the non hydrogen atoms. The
hydrogen atoms were included from geometrical calcula-
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