Monocyclopentadienyl(niobium) compounds with imido and silsesquioxane ligands: Synthetic, structural and reactivity studies

Article abstract of DOI:10.1002/ejic.200900571

Anew half-sandwich imido compound, [Nb{η⁵-C ₅H₃(SiMe₃)₂}Cl₂(NrBu)] (1), was isolated by treatment of [Nb{η⁵C₅H ₃(SiMe₃)₂)Cl₄

Full text of DOI:10.1002/ejic.200900571

FULL PAPER
DOI: 10.1002/ejic.200900571
Monocyclopentadienyl(niobium) Compounds with Imido and Silsesquioxane
Ligands: Synthetic, Structural and Reactivity Studies
Carlos García,[a] Manuel Gómez,*[a] Pilar Gómez-Sal,[a] and José Manuel Hernández[a]
Keywords: Niobium / Silsesquioxane / Cyclopentadienyl ligands / Insertion / Structure–activity relationships
Anewhalf-sandwichimidocompound,[Nb{η5-C5H3(SiMe3)2}-
Cl2(NtBu)] (1), was isolated by treatment of [Nb{η5-
C5H3(SiMe3)2}Cl4] with 1 equiv. LiNHtBu in hexane. Alk-
ylimido derivatives [Nb{η5-C5H3(SiMe3)2}RRЈ(NtBu)] (R = Cl,
RЈ = Me 2; R = RЈ = Me 3, CH2SiMe3 4) can be prepared by
reaction of 1 with the appropriate alkylating reagent. Silses-
quioxane ligand [Si8O12Cl(iBu)7] (5a) can be obtained by
treatment of [Si7O9(OH)3(iBu)7] with 1 equiv. silicon tetra-
chloride in the presence of triethylamine. Ligand 5a reacts
with NH3 (g) at low temperatures to yield an amido deriva-
tive, [Si8O12(NH2)(iBu)7] (5b), whereas the reaction of the tri-
silanol with excess BuLi leads to the corresponding lithium
salt [Li3Si7O12(iBu)7] (5c). A dichlorido(silsesquioxanylimido)-
complex,
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}-
(NtBu)] (R = iBu 11), by reaction with LiNHtBu, whereas for X
= Me, a chlorido complex, [Nb{η5-C5H3(SiMe3)2}Cl(Si7O12R7-
κ3O,O,O)] (R = iBu 12), can be isolated. Alkylation of 10 and
12 leads to dimethyl, trimethylsilylmethylidene and methyl
derivatives 13, 14 and 15, respectively. Alkylimidoniobium
complexes 2–4 react with carbon monoxide or xylyl isocy-
anide at room temperature to give acylimidoniobium [Nb{η5-
C5H3(SiMe3)2}R(NtBu){C(RЈ)O-κ2C,O}] (R = Cl, RЈ = Me 16;
R = RЈ = Me 17, CH2SiMe3 18) and iminoacylimidoniobium
[Nb{η5-C5H3(SiMe3)2}R(NtBu){C(Me)NAr-κ2C,N}] (Ar = 2,6-
Me2C6H3; R = Cl 21, Me 22) compounds by simple insertion
reactions. However, compound 13 reacts with CO and 2,6-
Me2C6H3NC, leading to enediolato [Nb{η5-C5H3(SiMe3)-
niobium
compound
[Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl2-
{NSi8O12(iBu)7}] (X = Cl 6a, Me 6b) can be prepared by reac-
tion of 1 equiv. tetrachloridoniobium complex [Nb{η5-
C5H3(SiXMe2)(SiMe3)}Cl4] (X = Cl, Me) and amidosilses-
quioxane 5b. From 6b, three new alkyl derivatives, [Nb{η5-
C5H3(SiMe3)2}XY(NSi8O12R7)] (R = iBu, X = Cl, Y = Me 7; X
= Y = Me 8, CH2SiMe3 9), were isolated by usual alkylation
reactions. Alternatively, protonolysis reaction of trisilanol
[Si7O9R7(OH)3] with [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl4] (X =
Cl) in the presence of triethylamine produces a dichlorido
(Me2SiOSi7O11R7-κ2O,O)}{O(Me)C=C(Me)O-κ2O,O}] (R
=
iBu 19) and azaniobacyclopropane [Nb{η5-C5H3(SiMe3)-
(Me2SiOSi7O11R7-κ2O,O)}(CMe2NAr-κ2C,N)] (R = iBu, Ar =
2,6-Me2C6H3 20) derivatives through intermolecular cou-
pling between two acyl groups and by a double methyl mi-
gration processes, respectively. All new compounds have
been characterized by IR spectrophotometry, 1H, 13C{1H} and
29Si{1H} NMR spectroscopy and elemental analysis.
derivative,
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Cl2] (R = iBu 10), which can be transformed into an imido
idosilylcyclopentadienyl ligands with the M–Cl bond of
group 5 metal derivatives,[3] in which a series of methyl, di-
Introduction
Structural and reactivity aspects of early transition metal
cyclopentadienyl complexes have been extensively studied
because of their role in numerous applications, as reagents
in organic synthesis and also as soluble Ziegler–Natta cata-
lysts.[1] Although a vast series of derivatives with ancillary
cyclopentadienyl ligands has dominated this chemistry, the
presence of electron-withdrawing silyl substituents improves
catalytic activity, because steric and electronic properties
can be tailored particularly when such substituents contain
reactive functional groups.[2] We have recently reported a
study comparing the reactivity of the Si–Cl bond of chlor-
methyl, trimethyl and tetramethyl compounds [MCpCl4–x
-
Mex] {M = Nb, Ta; Cp = η5-C5H3(SiXMe2)(SiMe3); X =
Cl, Me; x = 1, 2, 3, 4} has been isolated in good yields.
Recent years have witnessed an extensive development of
imido group 5 metal chemistry[4] containing monofunc-
tional,[5] tetradentate triamidoamine[6] and Cp ligands in
mono-[7] and dicyclopentadienyl-type[8] complexes. Proton-
ated lithium amides[9] have been extensively used to gener-
ate the imido ligand, but other synthetic strategies have
been based on the deprotonation of cyclopentadiene by
metal amides,[10] β-hydrogen elimination of amides, amines
coordinated to metal(III) compounds[11] and oxidation of
metal(III) complexes with azides,[11b] as more relevant syn-
thetic processes. A lot of examples show that the develop-
ment of nonmetallocene chemistry[1,12] is an area of con-
stant activity. In this context, many neutral group 5 imido
[a] Departamento de Química Inorgánica, Universidad de Alcalá
de Henares,
Campus Universitario, 28871 Alcalá de Henares, Spain
Fax: +34-91-885-46-83
E-mail: manuel.gomez@uah.es
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C. García, M. Gómez, P. Gómez-Sal, J. M. Hernández
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compounds have been synthesized,[4,13] and their function- their geometric and electronic properties, they have been
alities were used as both ancillary ligands and reactive sites. extensively studied for a number of years, either as an excel-
As ancillary ligands, they have been compared electronically lent model system for heterogeneous and homogeneous sil-
with cyclopentadienide,[14] but at the same time several stoi- ica-supported catalysts,[20d,24] as building blocks for inor-
chiometric transformations, such as protonations of tanta- ganic and hybrid materials[25] or as ligand backbones for
lum amides,[15] additions of dihydrogen to tantalum–alkyl transition metal complexes.[20c,20e] In the literature, a large
groups[16] and insertions of unsaturated molecules (CO, number of complexes that contain silsesquioxane ligands
ArNC) into metal–alkyl bonds,[17] have been observed in with different condensation grades coordinated to metals
the presence of niobium and tantalum–imido groups. How- have been reported.[20h–20i,22j,26–29] With respect to the
ever, in contrast with these cases, imine and carbodiimide group 5 metals, the vanadium[30] complexes are the most
metatheses, imido-to-oxo ligand exchange and the acti- numerous, although in the last few years synthetic routes
vation of benzene C–H bonds have been observed with towards tantalum[28b,31] and niobium[32] derivatives have
Ta=NtBu bonds.[18]
been described.
On the other hand, many researchers[19] have focused
In this paper, we report the synthesis of several POSS
their attention on the chemistry of incompletely condensed ligands, their coordination to bis(silylcyclopentadienyl)ni-
polyhedral oligosilsesquioxanes (POSSs), as they are seen obium compounds and the comparative chemical behaviour
as attractive ligands with a sufficient degree of oligomeriza- between tert-butylimido and POSS derivatives in alkylation
tion so as to be relevant models for highly siliceous materi- and insertion processes.
als used to support heterogeneous catalysts. Furthermore,
they may retain reactive Si–OH functionalities, which allow
their use as ligands in a wide variety of main group and
Results and Discussion
transition metal compounds.[20–22] Silsesquioxane is a gene-
ral term for a type of spherosilicate with the general for-
A
pseudotetrahedral dichloridoimido compound,
mula [SiRO3/2] (R = H, organic group) and a random, lad- [Nb{η5-C5H3(SiMe3)2}Cl2(NtBu)] (1), can be synthesized
der, cage or partial cage structure. The most familiar struc- when hexane solutions of the starting material, [Nb{η5-
ture is that corresponding to the incompletely condensed C5H3(SiMe3)2}Cl4], are treated at room temperature with
POSS, which shows a hybrid organic–inorganic three-di- LiNHtBu. Reactions of 1 with stoichiometric amounts of
mensional geometry with three silanol groups. A POSS li- the alkylating reagent give solutions from which the alk-
gand dictates the coordination geometry of the metal com- ylimido complex, [Nb{η5-C5H3(SiMe3)2}RRЈ(NtBu)] (R =
plexes[20e] much more effectively, and 29Si NMR spec- Cl, RЈ = Me 2; R = RЈ = Me 3, CH2SiMe3 4), can be
troscopy[23] is an essential tool in the structural study of a isolated in good yields (Scheme 1). All of these complexes
broad variety of silsesquioxane derivatives. Further, due to are soluble in most organic solvents, including saturated hy-
Scheme 1.
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Cyclopentadienyl(niobium) Complexes with Imido and Silsesquioxane Ligands
drocarbons. They are extremely air- and moisture-sensitive, shows four silicon resonances with relative intensities of
and rigorously dried solvents and handling under an argon 3:3:1:1; the first three signals can be assigned to the seven
atmosphere were found to be imperative for successful prep- silicon atoms of the Si7O12 moiety, and the fourth signal
arations.
can be assigned to the silicon atom directly bonded to the
Compounds 1–4 were characterized by analytic and spec- NH2 group. This NMR spectroscopic behaviour[20b,23] is
troscopic methods, and the data are in agreement with the also in agreement with that expected for totally condensed
proposed structures. The IR spectra of all complexes show and cap-cornered silsesquioxanes with the same substitu-
the characteristic absorptions for bis(trimethylsilyl)cyclo- ents (C3v symmetry group).
pentadienyl (ν
≈ 839 cm–1),[33,34] the trimethylsilyl sub-
Ligand 5c was synthesized as shown in Scheme 1 (see
˜
C–H
stituent [ν (CH ) ≈ 1250 cm–1][3,17d,35] and the Nb=N Experimental Section), and afterwards, the slow evapora-
˜
δs
3
stretching vibration (ν ≈ 1360 cm–1).[3a,17d] At room tem- tion of the reaction solvent (hexane) gave a small amount
˜
perature, chiral complex 2 shows the expected 1H NMR of crystals. The X-ray diffraction study of one of them
spectroscopic behaviour with three and two resonances for showed in an unambiguous way that a new species 5cЈ is
the protons of the disubstituted cyclopentadienyl ring and present, but the bad quality of the crystal hindered a good
the SiMe3 substituents, respectively, due to the absence of refinement. This new species is the tetrameric unit of 5c.
local symmetry in the C5H3(SiMe3)2 moiety. However, the The molecular structure and atom-labelling scheme of 5cЈ
NMR spectroscopic data for the complexes 1, 3 and 4 show are shown in Figure 2, and selected bond lengths and angles
an A2B spin system for the Cp ring protons, and consist- are given in the caption. Isobutyl groups are not shown for
ently, three ring carbon resonances appear in the 13C{1H} greater clarity. Compound 5cЈ consists of four incomplete
NMR spectra in agreement with the existence of a metal silsesquioxane cubes (Si7O12) bound through lithium–oxy-
centre in a characteristic three-legged piano-stool environ- gen and lithium–lithium interactions. The structure of the
ment (Cs symmetry).[3a,33,34]
core of the lithium atoms is a distorted icosahedron whose
Silsesquioxane ligands 5a–c were successively synthesized triangular faces are capped by oxygen atoms, and each lith-
from trisilanol Si7O9R7(OH)3 (R = iBu) by conventional ium atom is bonded to three oxygen atoms. Two oxygen
methods. The chloro derivative [Si8O12Cl(iBu)7] (5a) was atoms are provided by one Si7O12 unit and the other from
obtained in high yield by reaction of [Si7O9(OH)3(iBu)7] a different one, forming a core of O12Li12. Every silicon
with silicon tetrachloride in the presence of 3 equiv. triethyl- atom is bonded to an isobutyl group. To the best of our
amine. The ammonolysis of 5a in the presence of a large knowledge, only one similar dimeric compound has been
excess of NH3 (g) at –78 °C in dichloromethane led to the described[21d] in the literature with bond lengths and bond
expected amido derivative [Si8O12(NH2)(iBu)7] (5b), angles in the same range in both cases.
whereas at 0 °C the reaction of trisilanol with excess BuLi
The treatment of hexane solutions of [Nb{η5-
gave the corresponding lithium salt [Li3Si7O12(iBu)7] (5c) C5H3(SiXMe2)(SiMe3)}Cl4] (X = Cl, Me) with 1 equiv. sil-
(see Scheme 2). Compounds 5a–c were found not to be air- sesquioxane reagent 5b in the presence of triethylamine gave
and moisture-sensitive and are soluble in hexane, chlori- dichlorido(silsesquioxanylimido)
derivatives
[Nb{η5-
nated and aromatic solvents.
C5H3(SiXMe2)(SiMe3)}Cl2{NSi8O12(iBu)7}] (X = Cl 6a,
The IR and NMR (1H, 13C{1H}, 29Si{1H}) spectroscopic Me 6b) (Scheme 3) with a silsesquioxanylimido group. In
data are in agreement with the proposed structures. The addition, chloridomethyl-, dimethyl- and bis(trimethylsilyl-
29Si{1H} NMR spectrum of complex 5b (see Figure 1) methyl)silsesquioxanylimido
complexes
[Nb{η5-
Scheme 2.
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C. García, M. Gómez, P. Gómez-Sal, J. M. Hernández
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Figure 1. 29Si{1H} NMR spectrum of complex 5b ([D1]chloroform).
7.2 Hz can be assigned to the CH2 protons of such groups,
in agreement with the existence of
a
symmetric
C5H3(SiMe3)2 ring. On the other hand, chiral chloridome-
1
thyl complex 7 shows the expected H NMR spectroscopic
behaviour with both nonequivalent SiMe3 groups. All spec-
troscopic data for complexes 8 and 9 are in agreement with
a Cs symmetry and with a metal centre in a characteristic
three-legged piano-stool environment;[33] furthermore, com-
plex 9 shows an AB spin system for diastereotopic α-CH2
protons of trimethylsilylmethyl groups. Additionally, an IR
absorption band due to the Nb=N[3a,17d] stretching vi-
bration can be observed at ν ≈ 1350 cm–1.
˜
A series of chloridosilsesquioxanyl complexes was pre-
pared in good yields by different methods (Scheme 4).
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}Cl2] (R =
iBu 10) was synthesized by reaction of [Nb{η5-
C5H3(SiMe3)(SiClMe2)}Cl4] with 0.5 equiv. Si7O9(OH)3-
(iBu)7 in the presence of NEt3 or alternatively, by treat-
ment of the tetrachlorido compound with lithium salt 5c.
new imido derivative, [Nb{η5-C5H3(SiMe3)(Me2-
Figure 2. ORTEP view of 5cЈ. Isobutyl groups have been omitted
for clarity. Mean bond lengths [Å] and angles [°] are as follows.
Mean distances [Å]: Si–C 1.83(1), Si–O 1.631(13) and Li–O 1.91(2).
Mean angles [°]: Si–O–Si 145.3(9), O–Si–O 109.2(8).
A
SiOSi7O11R7-κ2O,O)}(NtBu)] (R = iBu 11), whose struc-
tural study shows an unaltered silsesquioxanyl moiety and
confirms that it is formed by the reaction of two Nb–Cl
bonds, can be isolated by reaction of 10 with 3 equiv.
LiNHtBu; in addition, 11 can be obtained by reaction be-
tween dichloridoimido derivative [Nb{η5-C5H3(SiClMe2)-
(SiMe3)}Cl2(NtBu)][3a] and trisilanol [Si7O9(iBu)7(OH)3] in
the presence of triethylamine. Further, a chloridosilses-
quioxanyl compound, [Nb{η5-C5H3(SiMe3)2}Cl(Si7O12R7-
κ3O,O,O)] (R = iBu 12), was prepared by reaction of tetra-
chlorido derivative [Nb{η5-C5H3(SiMe3)2}Cl4] with
Si7O9(OH)3(iBu)7 and NEt3.
C5H3(SiMe3)2}XY(NSi8O12R7)] (R = iBu; X = Cl, Y = Me
7; X = Y = Me 8, CH2SiMe3 9) can be prepared by treat-
ment of 6b with the appropriate alkylating reagent.
1
The complex 6a shows a H NMR spectrum in which
the resonances corresponding to the iBu substituents of the
silsesquioxanyl moiety appear as multiplets due to the pres-
ence of an asymmetric C5H3(SiClMe2)(SiMe3) ring, while
Silsesquioxane complexes were obtained as microcrystal-
in the spectrum of 6b, two doublets at δ = 0.59 and line solids soluble in most organic solvents, but repeated
0.52 ppm with observed vicinal (3JH,H) SSCC values of attempts under different conditions (solvent, temperature)
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Cyclopentadienyl(niobium) Complexes with Imido and Silsesquioxane Ligands
Scheme 3.
Scheme 4.
to prepare single crystals of adequate quality were unsuc- bonds react first, followed by the Si–Cl bond of the
cessful. However, the spectroscopic and analytical data are SiClMe2 substituent, to give the reported[3a] constrained-
in agreement with the proposed structures.
As illustrated in Scheme 5, we propose that the formation N)}Cl(NtBu)].
geometry complex [Nb{η5-C5H3(SiMe3)(SiMe2NtBu-κ
of compound 10 takes place by an alcoholysis process of
On the other hand, in agreement with the reported 29Si
three Nb–Cl (A) or two Nb–Cl and one Si–Cl (B) bonds. NMR spectroscopic studies,[23a,28a] in the spectrum of com-
Although the spectroscopic data does not permit us to plex 10 (see Figure 3) the resonance at δ = –3.57 ppm can
make a definitive structural assignment, we suggest struc- be assigned to the silicon atom of the SiMe2O moiety, and
ture B, because in the reaction of the original tetra- complexes 10 and 11 therefore present a structure in which
chloridoniobium compound with tBuNH2, the two Nb–Cl the cyclopentadienyl ring is bonded to the silsesquioxanyl
Eur. J. Inorg. Chem. 2009, 4401–4415
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At room temperature, the 1H NMR spectrum of complex
13 shows a broad signal for both methyl groups, probably
due to an intramolecular process that consists of the in-
terconversion between two four-legged piano-stool enantio-
meric ground states through a trigonal bipyramidal transi-
tion state, well known as Berry pseudorotation.[17b,17e,36b,38]
However, the resonances at δ = 0.35 and 0.28 ppm can be
assigned to the diastereotopic methyl groups of the SiMe2
substituent. On the other hand, for some reported coordi-
natively unsaturated alkylidene complexes,[37] the stretching
frequency corresponding to the C–H bond in the IR spec-
trum was assigned to absorption bands localized in the
2700–2350 cm–1 region, which are at a lower wavenumber
than those for normal C–H stretches, probably as a result
of the observed increase in the length of the C–H bond. In
the case of the compound 14, the absorption band localized
at ν 2717, 2625 cm–1 can be assigned to νC–H. A high degree
˜
of deshielding is observed for the alkylidene proton (δ =
9.68 ppm) and carbon (δ = 235.7 ppm) resonances, which
are comparable to other d0 terminal (alkylidene)niobium
and tantalum compounds.[37c,39,40]
Scheme 5.
ligand across a silicon atom of a silyl substituent, and the
observed IR absorption band at ν ≈ 635 cm–1 can be as-
signed to the νNb–O stretching vibration.[36]
The reactivity of the alkyl derivatives was studied in mi-
gratory insertion processes (Scheme 7). Chloridomethyl-,
dimethyl- and bis(trimethylsilylmethyl)imido complexes 2–
4 react with carbon monoxide (1 atm) at room temperature
in [D6]benzene (NMR spectroscopic scale, see Exp. Sect.) to
give chlorido-, methyl- and (trimethylsilylmethyl)imidoacyl
[Nb{η5-C5H3(SiMe3)2}R(NtBu){C(RЈ)O-κ2C,O}] (R = Cl,
RЈ = Me 16; R = RЈ = Me 17, CH2SiMe3 18) derivatives,
as result of simple migration of an alkyl group bonded to
the metal towards the electrophilic carbonyl atom of the
previously coordinated CO. The treatment of [D6]benzene
solutions of the alkylsilsesquioxanylimido complexes 7–9
with carbon monoxide leads to an unidentified product
mixture, but in the case of chloridomethyl compound 7, we
detected the formation of an unstable chloridoacyl deriva-
tive (1H NMR: δC(Me)O = 2.58 ppm) when the reaction was
followed by NMR spectroscopy. However, in contrast with
this result, an enediolato complex, [Nb{η5-C5H3(SiMe3)-
(Me2SiOSi7O11R7-κ2O,O)}{O(Me)C=C(Me)O-κ2O,O}] (R
Alkylation of 10 with 2 equiv. dimethylzinc at room tem-
perature in hexane yields the expected dimethyl derivative
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}Me2] (R =
iBu 13); however, treatment with 2 equiv. MgCl(CH2SiMe3)
under rigorously anhydrous conditions at room temperature
leads to the trimethylsilylmethylidene complex, [Nb{η5-
C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}(CHSiMe3)] (R =
iBu 14), by a spontaneous α-hydrogen-abstraction pro-
cess[37] with formation of an unstable dialkyl intermediate
and SiMe4 elimination (Scheme 6). In addition, a methyl
complex, [Nb{η5-C5H3(SiMe3)2}Me(Si7O12R7-κ3O,O,O)]
(R = iBu 15), was isolated by reaction of the chloridosilses-
quioxanyl complex 12 with excess (1 equiv.) ZnMe2 in tolu-
ene. The reaction of 12 with the stoichiometric amount of
ZnMe2 (2:1 molar ratio) leads to a mixture of 12 and 15,
probably because of the mild alkylating character of this
reagent.
Figure 3. 29Si{1H} NMR spectrum of complex 10 ([D6]benzene).
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Cyclopentadienyl(niobium) Complexes with Imido and Silsesquioxane Ligands
Scheme 6.
Scheme 7.
= iBu 19), is easily obtained when the corresponding [D6]- gration of one methyl group to the electrophilic isocyanide
benzene solution of dimethylsilsesquioxanyl compound 13 carbon atom to give an iminoacyl intermediate, followed
reacts with carbon monoxide under the same conditions. by nucleophilic attack of the second methyl group to the
This reaction probably takes place by an intramolecular iminoacyl carbon atom to give an imine ligand. However,
coupling process[17c,41] between two electrophilic acyl car- the treatment of solutions of alkylimido complexes 2–3 with
bon atoms of the unstable bis(acyl) intermediate, which 1 equiv. xylyl isocyanide under the same conditions leads
could not be observed when the reaction was followed by to stable, 18-electron imidoiminoacyl compounds [Nb{η5-
1H NMR spectroscopy.
C5H3(SiMe3)2}R(NtBu){C(Me)NAr-κ2C,N}] (R = Cl 21,
On the other hand, when 1 equiv. 2,6-Me2C6H3NC is Me 22). In the case of dimethylimido complex 3, the mi-
added to a solution of 13, under rigorously anhydrous con- gration of the second methyl group observed for dimethyl-
ditions, an instantaneous reaction takes place, leading to silsesquioxanyl complex 13 and other dimethyl deriva-
an orange solution from which an azaniobacyclopropane tives[17e,42] does not take place, and the presence of excess
derivative, [Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}- isocyanide does not produce a second insertion reaction in
(CMe2NAr-κ2C,N] (R = iBu, Ar = 2,6-Me2C6H3 20), was the Nb–Me or Nb–Ciminoacyl bond. Alkyl derivatives 4, 7–9
recovered as an orange solid. Previously, we reported[17a,17e] and 15 also react with xylyl isocyanide, but insertion products
the synthesis and the crystal structure of similar azametalla- cannot be isolated or detected by NMR spectroscopy, and
cylopropane complexes, whose formation involves mi- the reaction leads to an unidentified mixture of products.
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Analytical and spectroscopic data for insertion com- tion processes. Although alkylimido compounds react with
plexes 16–22 are in agreement with the stoichiometry pro- carbon monoxide and xylyl isocyanide to give the expected
posed. IR spectra show characteristic absorptions for the acyl and iminoacyl derivatives, as a result of a simple inser-
trimethylsilylcyclopentadienyl ring (νC–H ≈ 839 cm–1)[33,34] tion process, alkylsilsesquioxanyl complexes lead to enediol-
and for the SiMe3 substituent [δas (CH3)
≈ 1253 ato and azaniobacyclopropane systems by coupling and
cm–1].[3,17d,35] The formulation of 19 as an enediolato com- double migration processes, respectively.
plex is supported by the IR spectra,which show νC=C, νC–O
and νNb–O absorptions at ν = 1466,[17c,17d,43] 1150[43] and
˜
900[36a,36c] cm–1, respectively. Their 1H NMR spectrum
shows two resonances at δ = 1.76 and 1.63 ppm, corre-
sponding to the nonequivalent methyl substituents of the
enediolato ligand, whereas the resonance assignable to the
sp2 C atoms appears at δ = 98.4 ppm. In addition, chiral
pseudo-square-pyramidal acylimido complexes 16–18 show
Experimental Section
General
All reactions and manipulations were carried out under a dry argon
atmosphere by using standard Schlenk tube and cannula tech-
niques or in a conventional argon-filled glove-box. The following
solvents were refluxed over an appropriate drying agent and dis-
tilled and degassed prior to use: [D6]benzene and hexane (Na/K
alloy), [D1]chloroform (NaH) and dicloromethane (P4O10). Starting
materials [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl4] (X = Cl,Me),[3a] [Nb-
the characteristic absorption for the acyl moiety [νC(Y)=O
]
at 1587 cm–1; such stretching vibrations in acyl derivatives
range from ν ≈ 1453 to 1625 cm–1, and the lowest fre-
˜
{η5-C5H3(SiClMe2)(SiMe3)}Cl2(NtBu)],[3a] [Si7O9(OH)3(iBu)7],[45]
quencies occur for high-valent transition metals, which in
our case can be attributed to the carbene character of the
acyl carbon atom.
LiNHtBu[46] and LiCH2SiMe3
were prepared as described pre-
[47]
viously. Reagent grade CO and NH3 (Air Líquide), BuLi (1.6  in
hexane), SiCl4, MgClMe (3  in thf), MgCl(CH2SiMe3) (1  in di-
ethyl ether) and ZnMe2 (2  in toluene) (Aldrich), NEt3 and 2,6-
Me2C6H3NC (Fluka) were purchased from commercial sources
and were used without further purification.
On the other hand, all structural data for iminoacyl com-
plexes 21–22 are in agreement with the expected pseudo-
square-pyramidal geometry found for similar chiral group
5 metal derivatives.[17d] The iminoacyl carbon resonance ap-
pears at δ = 228 ppm, and absorptions due to the C(R)=N–
Ar and Nb=N–tBu stretching vibrations are observed at
1645 and 1352 cm–1, respectively. At room temperature, the
1H and 13C NMR spectra of 20 show two equivalent methyl
groups and suggest an azaniobacyclopropane struc-
ture[17a,17b,17e] with the plane of the metallacycle perpendic-
ular to the Cp ring. The resonance located at δ = 74 ppm
in the 13C NMR spectrum can be assigned to the Cα of the
azaniobacyclopropane moiety, and the absorption band due
to the C–N stretching vibration[44] was observed at
1365 cm–1 in the IR spectrum.
Infrared spectra were recorded with a Perkin–Elmer Spectrum 2000
spectrophotometer (4000–300 cm–1) with samples as Nujol mulls
between CsI plates or in KBr pellets. 1H, 13C{1H} and 29Si{1H}
NMR spectra were recorded with Varian Unity 300 or Varian
Unity 500 Plus spectrometers; chemical shifts were referenced to
the 13C (δ = 128, 77 ppm) or residual 1H (δ = 7.15, 7.24 ppm) reso-
nances of the [D6]benzene or [D1]chloroform solvents, respectively,
and for the 29Si NMR spectra, they were referenced to the internal
TMS resonance. C, H and N analyses were carried out with a
LECO CHNS 932 microanalyzer.
[Nb{η5-C5H3(SiMe3)2}Cl2(NtBu)] (1):
A mixture of LiNHtBu
(0.20 g, 2.25 mmol) and Nb{η5-C5H3(SiMe3)2}Cl4 (1.00 g,
2.25 mmol) was dissolved in hexane (50 mL) under rigorously an-
hydrous conditions. The reaction mixture was stirred for 2 h at
room temperature, and then the resulting suspension was decanted
and filtered. The filtrate was concentrated to dryness, and the resi-
due was extracted with hexane (2ϫ15 mL). Concentration and
cooling of the filtrate produced 1 as an orange solid. Yield 0.80 g
Conclusions
This article presents advances related to the chemistry of
monocyclopentadienylniobium compounds. By conven-
tional methods, new alkylimido complexes [Nb{η5-
C5H3(SiMe3)2}RRЈ(NtBu)] (R = Cl, RЈ = Me; R = RЈ =
Me, CH2SiMe3) have been isolated and several silsesquiox-
ane ligands have been synthesized by treatment of trisilanol
[Si7O9(OH)3(iBu)7] with the appropriate reagents. Starting
from [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl4] (X = Cl, Me), by
reaction with amidosilsesquioxane [Si8O12(iBu)7(NH2)], a
(80%). IR (KBr): ν = 2957 (s), 1402 (m), 1375 (m), 1249 (vs), 1090
˜
(s), 840 (vs), 451 (m) cm–1. 1H NMR (300 MHz, [D1]chloroform,
25°C): δ = 6.93 (m, 1 H), 6.76 [m, 2 H, C5H3(SiMe3)2], 1.27 [s, 9
H, NbN(CMe3)], 0.29 [s, 18 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR
(75 MHz, [D1]chloroform, 25°C): δ = 129.6 (Ci), 127.0, 121.8
[C5H3(SiMe3)2], 70.1 [NbN(CMe3)], 30.4 [NbN(CMe3)], –0.12
[C5H3(SiMe3)2] ppm. C15H30Cl2NNbSi2 (444.394): calcd. C 40.54,
H 6.80, N 3.15; found C 40.65, H 6.85, N 3.09.
[Nb{η5-C5H3(SiMe3)2}Cl(Me)(NtBu)] (2): A hexane (50 mL) solu-
tion of 1 (0.80 g, 1.80 mmol) was treated at room temperature with
ZnMe2 (2  in toluene, 1.10 mL, 0.90 mmol). The reaction mixture
was stirred for 1 h, and the solvent was removed under reduced
pressure. The resulting brown residue was extracted with hexane
(2ϫ15 mL), the solution was concentrated and cooled to –20 °C
to give a brown microcrystalline solid, which was characterized as
dichlorido(silsesquioxanylimido)
compound,
[Nb{η5-
C5H3(SiXMe2)(SiMe3)}Cl2{NSi8O12(iBu)7}] (X = Cl, Me),
which reacts with alkylating reagents to yield the corre-
sponding alkyl derivatives, [Nb{η5-C5H3(SiMe3)2}XY-
(NSi8O12R7)] (R = iBu; X = Cl, Y = Me; X = Y = Me,
CH2SiMe3), can be prepared, while by protonolysis with
trisilanol, a new group of silsesquioxanyl complexes can be
isolated with a POSS ligand bonded to niobium atom in
a different coordination mode. The comparative chemical
2 (0.56 g, 74%). IR (KBr): ν = 2959 (s), 1406 (m), 1356 (m), 1251
˜
(vs), 1084 (vs), 840 (vs), 471 (m), 397 (s) cm–1. 1H NMR (300 MHz,
[D6]benzene, 25°C): δ = 6.55 (m, 1 H), 6.24 (br., 1 H), 6.17 [br., 1
behaviour of all alkyl derivatives was studied in the inser- H, C5H3(SiMe3)2], 1.26 [s, 9 H, NbN(CMe3)], 1.24 (s, 3 H, NbMe),
4408
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4401–4415

Cyclopentadienyl(niobium) Complexes with Imido and Silsesquioxane Ligands
0.26 (s, 9 H), 0.23 [s, 9 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR
NH3 (g). The solution was warmed to room temperature and stirred
(75 MHz, [D6]benzene, 25°C): δ = 123.6, 122.9 (Ci), 121.3 (Ci), vigorously for 15 h. After the ampoule was opened, the ammonium
118.7, 117.4 [C5H3(SiMe3)2], 70.5 [NbN(CMe3)], 67.42 (NbMe),
31.3 [NbN(CMe3)], 0.15, –0.06 [C5H3(SiMe3)2] ppm. trated to a volume of ca. 10 mL. Cooling at –40 °C led to the depo-
sition of a white microcrystalline solid identified as 5b. Yield 0.31 g
salt formed was removed by filtration, and the filtrate was concen-
C16H33ClNNbSi2 (423.976): calcd. C 45.33, H 7.85, N 3.30; found
C 45.46, H 7.94, N 3.29.
(90%). IR (KBr): ν = 3432 (m), 2956 (vs), 1467 (m), 1232 (s), 1100
˜
(vs), 911 (s), 839 (s), 743 (vs), 565 (s), 483 (vs), 432 (s) cm–1. 1H
NMR (300 MHz, [D1]chloroform, 25°C): δ = 1.83 [m, 7 H,
(Me2CHCH2)7Si8O12(NH2)], not observed [(Me2CHCH2)7Si8O12-
[Nb{η5-C5H3(SiMe3)2}Me2(NtBu)] (3): At room temperature,
MgClMe (3  in tetrahydrofuran, 1.20 mL, 3.60 mmol) was added
to a hexane (30 mL) solution of 1 (0.80 g, 1.80 mmol), and the
mixture was stirred for 1 h. The colour of the mixture changed
quickly from orange to red. The resulting suspension was decanted,
the MgCl2 formed was removed by filtration, and the filtrate was
concentrated to a volume of ca. 10 mL. Cooling to –40 °C over-
night led to the deposition of 3 as a red microcrystalline solid.
3
4
(NH2)], 0.94 [dd, JH,H = 6.6, JH,H = 1.8 Hz, 42 H, Me2CHCH27-
3
Si8O12(NH2)], 0.59 [t, JH,H = 6.6 Hz, 14 H, (Me2CHCH2)7-
Si8O12(NH2)] ppm. 13C{1H} NMR (75 MHz, [D1]chloroform,
25°C): δ = 25.7, 25.64, 25.63 [3:1:3, (Me2CHCH2)7Si8O12(NH2)],
23.82
[(Me2CHCH2)7Si8O12(NH2)],
22.47,
22.44,
22.40
[(Me2CHCH2)7Si8O12(NH2)] ppm. 29Si{1H} NMR (60 MHz, [D1]-
chloroform, 25°C): δ = –87.4 [1Si, Si7O12Si(NH2)(iBu)7], –67.45
(1Si), –67.42 (3Si), –67 [3Si, Si7O12Si(NH2)(iBu)7] ppm.
C28H65NO12Si8 (832.508): calcd. C 40.40, H 7.87, N 1.68; found C
40.25, H 7.81, N 1.67.
Yield 0.51 g (70%). IR (KBr): ν = 2964 (s), 1406 (m), 1354 (m),
˜
1251 (vs), 1084 (vs), 838 (vs), 545 (m), 486 (m) cm–1. 1H NMR
(300 MHz, [D6]benzene, 25°C): δ = 6.34 (s, 1 H), 6.17 [m, 2 H,
C5H3(SiMe3)2], 1.41 [s, 9 H, NbN(CMe3)], 0.60 (s, 6 H, NbMe2),
0.28 [s, 18 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz, [D6]-
benzene, 25°C): δ = 119.4 (Ci), 118.9, 116.3 [C5H3(SiMe3)2], 70.0
[NbN(CMe3)], 70.0 (NbMe2), 32.2 [NbN(CMe3)], 0.21
[C5H3(SiMe3)2] ppm. C17H36NNbSi2 (403.558): calcd. C 50.60, H
8.99, N 3.47; found C 50.45, H 8.85, N 3.45.
[Li3Si7O12(iBu)7] (5c): BuLi (1.6  in hexane, 0.82 mL, 1.32 mmol)
was added dropwise at 0 °C to a hexane (60 mL) solution of
Si7O9(iBu)7(OH)3 (0.35 g, 0.44 mmol). The reaction mixture was
then warmed to room temperature and stirred for 20 h. The LiCl
formed was filtered off, and the volatiles were partially removed at
reduced pressure to give 5c as a white microcrystalline solid. Yield
[Nb{η5-C5H3(SiMe3)2}(CH2SiMe3)2(NtBu)] (4): A hexane (40 mL)
solution of 1 (1.04 g, 2.40 mmol) was treated with a 1  solution
of MgCl(CH2SiMe3) in diethyl ether (0.48 mL, 4.80 mmol), and the
mixture was stirred for 2 h. The suspension was decanted, the
MgCl2 formed was filtered off, and the solution was concentrated
to dryness to give a yellow solid identified as 4. Yield 0.78 g (60%).
0.27 g (76%). IR (KBr): ν = 2955 (vs), 1467 (s), 1367 (m), 1332
˜
(m), 1230 (s), 1100 (vs), 971 (s), 836 (s), 739 (vs), 584 (s), 497 (s)
1
cm–1. H NMR (300 MHz, [D6]benzene, 25°C): δ = 2.21 [m, 7 H,
(Me2CHCH2Si)7O12Li3], 1.25 [m, 42 H, (Me2CHCH2Si)7O12Li3],
1.10 [m, 14 H, (Me2CHCH2Si)7O12Li3] ppm. 13C{1H} NMR
(75 MHz, [D6]benzene, 25°C): δ = 26.7–25.5 [(Me2CHCH2Si)7-
O12Li3], 24.7–24.5 [(Me2CHCH2Si)7O12Li3], 23.0 [(Me2CHCH2Si)7-
O12Li3] ppm. C28H63Li3O12Si7 (809.223): calcd. C 41.56, H 7.85;
found C 41.63, H 7.93.
[Nb{η5-C5H3(SiMe3)(SiXMe2)}Cl2{NSi8O12(iBu)7}] (X = Cl 6a, Me
6b): Under rigorously anhydrous conditions, a hexane (25 mL)
solution of [Nb{η5-C5H3(SiXMe2)(SiMe3)}Cl4] (1.00 mmol; X =
Cl, 0.465 g; X = Me, 0.444 g) was treated at room temperature with
a solution of Si8O12(iBu)7(NH2) (0.83 g, 1.00 mmol) and triethyl-
amine (0.20 g, 2.00 mmol) in hexane (15 mL) for 5 h. The suspen-
sion was decanted, and the ammonium salt was filtered off. After-
wards, the volatiles were removed under reduced pressure to give
6a/6b as microcrystalline yellow solids. Yields 6a (0.98 g, 80%) and
6b (1.08 g, 90%).
IR (KBr): ν = 2956 (s), 2360 (w), 1610 (m), 1407 (m), 1355 (m),
˜
1260 (vs), 1086 (vs), 838 (vs), 756 (s), 636 (m), 472 (m), 392 (s)
1
cm–1. H NMR (300 MHz, [D6]benzene, 25°C): δ = 6.64 (m, 1 H),
6.11 [m, 2 H, C5H3(SiMe3)2], 1.45 [s, 9 H, NbN(CMe3)], 0.96, 0.71
2
[AB, JH,H = 10 Hz, 4 H, Nb(CH2SiMe3)2], 0.27 [s, 18 H,
C5H3(SiMe3)2], 0.26 [s, 18 H, Nb(CH2SiMe3)2] ppm. 13C{1H}
NMR (75 MHz, [D6]benzene, 25°C): δ = 129.8, 122.3 (Ci), 112.2
[C5H3(SiMe3)2], 66.0 [NbN(CMe3)], 50.9 [Nb(CH2SiMe3)2], 33.0
[NbN(CMe3)], 3.2 [Nb(CH2SiMe3)2], 0.50 [C5H3(SiMe3)2] ppm.
C23H52NNbSi4 (547.922): calcd. C 50.42, H 9.57, N 2.56; found C
50.45, H 9.60, N 2.45.
[Si8O12(iBu)7Cl] (5a): A stirred solution of Si7O9(iBu)7(OH)3
(1.77 g, 2.24 mmol) and NEt3 (0.94 mL, 6.72 mmol) in hexane
(60 mL) was treated with SiCl4 (0.24 mL, 2.24 mmol) under rigor-
ously anhydrous conditions for 12 h. The suspension was decanted,
the ammonium salt [NHEt3]Cl formed was removed by filtration,
the filtrate was concentrated to ca. 5 mL and cooled to –20 °C to
give 5a as a white microcrystalline solid. Yield 1.62 g (85%). IR
6a: IR (CsI/Nujol mull): ν = 2954 (vs), 1466 (vs), 1332 (s), 1260
˜
1
(vs), 1076 (vs), 919 (s), 841 (vs), 737 (m), 568 (m), 507 (s) cm–1. H
NMR (300 MHz, [D1]chloroform, 25°C): δ = 7.17 (m, 1 H), 6.85
[m, 2 H, C5H3(SiClMe2)(SiMe3)], 1.81 [m, 7 H, NSi(Me2CHCH2Si)7-
O12], 0.93 [m, 42 H, NSi(Me2CHCH2Si)7O12], 0.62 [m, 14 H, NSi-
(Me2CHCH2Si)7O12], 0.294 [s, 9 H, C5H3(SiClMe2)(SiMe3)], 0.290
(s, 3 H), 0.03 [s, 3 H, C5H3(SiClMe2)(SiMe3)] ppm. 13C{1H} NMR
(75 MHz, [D1]chloroform, 25°C): δ = 131.1 (Ci), 127.1, 125.7 (Ci),
123.7, 123.6 [C5H3(SiClMe2)(SiMe3)], 25.7, 25.6 [NSi(Me2-
CHCH2Si)7O12], 23.67, 23.71 [NSi(Me2CHCH2Si)7O12], 22.3, 22.2
[NSi(Me2CHCH2Si)7O12], 3.0, 2.1, [C5H3(SiClMe2)(SiMe3)], –0.55
[C5H3(SiClMe2)(SiMe3)] ppm. 29Si{1H} NMR (60 MHz, [D6]ben-
(KBr): ν = 2956 (vs), 1467 (s), 1402 (m), 1368 (m), 1334 (m), 1232
˜
(s), 1107 (vs), 839 (s), 742 (s), 654 (s), 478 (s) cm–1. 1H NMR
(300 MHz, [D1]chloroform, 25°C): δ = 1.85 [m, 7 H, (Me2CHCH2)7-
Si8O12Cl], 0.96 [m, 42 H, (Me2CHCH2)7Si8O12Cl], 0.68 [m, 14 H,
(Me2CHCH2)7Si8O12Cl] ppm. 13C{1H} NMR (75 MHz, [D1]chlo-
roform, 25°C): δ = 25.8–25.6 [(Me2CHCH2)7Si8O12Cl], 23.9–23.7
[(Me2CHCH2)7Si8O12Cl], 23.1–22.0 [(Me2CHCH2)7Si8O12Cl] ppm.
29Si{1H} NMR (60 MHz, [D1]chloroform, 25°C): δ = –90.2 [1Si,
Si7O12Si(Cl)(iBu)7], –67.8 (1Si), –66.8 (3Si), –66.7 [3Si, Si7O12Si-
(Cl)(iBu)7] ppm. C28H63ClO12Si8 (851.938): calcd. C 39.48, H 7.45;
found C 39.83, H 7.25.
zene, 25°C):
δ
=
15.52 [C5H3(SiClMe2)(SiMe3)], –5.12
[C5H3(SiClMe2)(SiMe3)], –66.86, –66.88, –66.95, –67.82, –67.84,
–67.86, –67.88 [NSi(Me2CHCH2Si)7O12], not observed [NSi-
(Me2CHCH2Si)7O12] ppm. C38H81Cl3NNbO12Si10 (1224.176):
calcd. C 37.28, H 6.67, N 1.14; found C 37.48, H 6.65, N 1.20.
[Si8O12(iBu)7(NH2)] (5b): A solution of Si8O12(iBu)7Cl (0.34 g,
0.40 mmol) in dichloromethane (50 mL) was placed in an ampoule
under rigorously anhydrous conditions. The ampoule was cooled
to –78 °C, and then the inert atmosphere was replaced with
6b: IR (CsI/Nujol mull): ν = 2952 (vs), 1464 (vs), 1332 (s), 1255
˜
1
(vs), 1176 (vs), 919 (vs), 846 (s), 739 (s), 567 (m), 499 (s) cm–1. H
Eur. J. Inorg. Chem. 2009, 4401–4415
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4409

C. García, M. Gómez, P. Gómez-Sal, J. M. Hernández
FULL PAPER
NMR (300 MHz, [D1]chloroform, 25°C): δ = 7.03 (m, 1 H), 6.77
was decanted, filtered, and the solvent was removed under reduced
[m, 2 H, C5H3(SiMe3)2], 1.80 [m, 7 H, NSi(Me2CHCH2Si)7O12], pressure. The residue was extracted with hexane (2ϫ10 mL), and
2
0.90 [m, 42 H, NSi(Me2CHCH2Si)7O12], 0.59 (d, JH,H = 7.5 Hz, 7 the solution was concentrated to ca. 5 mL and cooled overnight to
2
H), 0.52 [d, JH,H = 7.5 Hz, 7 H, NSi(Me2CHCH2Si)7O12], 0.25 [s, –40°C, giving 9 as a microcrystalline yellow solid. Yield 0.22 g
18 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz, [D1]chloro-
(70%). IR (CsI/Nujol mull): ν = 2954 (vs), 1466 (s), 1333 (m), 1261
˜
form, 25°C): δ = 131.0, 125.8, 123.7 [C5H3(SiMe3)2], 25.3, 25.1 (s), 1111 (vs), 920 (s), 839 (vs), 742 (s), 484 (s) cm–1. 1H NMR
[NSi(Me2CHCH2Si)7O12], 23.3 [NSi(Me2CHCH2Si)7O12], 22.0, (300 MHz, [D6]benzene, 25°C): δ = 6.62 (br., 1 H), 6.35 [br., 2 H,
21.9 [NSi(Me2CHCH2Si)7O12], –0.89 [C5H3(SiMe3)2] ppm. C5H3(SiMe3)2], 2.13 [m, 7 H, NSi(Me2CHCH2Si)7O12], 1.15 [m, 42
C39H84Cl2NNbO12Si10 (1203.758): calcd. C 38.91, H 7.03, N 1.16;
found C 39.17, H 7.13, N 1.12.
H, NSi(Me2CHCH2Si)7O12], 0.86 [m, 14 H, NSi(Me2CHCH2Si)7-
O12], 1.26, 0.58 [AB, JH,H = 11 Hz, 4 H, Nb(CH2SiMe3)2], 0.36 [s,
2
18 H, C5H3(SiMe3)2], 0.31 [s, 18 H, Nb(CH2SiMe3)2] ppm. 13C{1H}
NMR (75 MHz, [D6]benzene, 25°C): δ = 124.0, 114.5, 110.4 (Ci,
C5H3(SiMe3)2], 56.4 [Nb(CH2SiMe3)2], 26.2, 26.0, 25.9 [NSi-
(Me2CHCH2Si)7O12], 24.5, 24.4 [NSi(Me2CHCH2Si)7O12], 23.5,
23.0 [NSi(Me2CHCH2Si)7O12], 2.5 [Nb(CH2SiMe3)2], 0.1
[C5H3(SiMe3)2] ppm. C47H106NNbO12Si12 (1307.286): calcd. C
43.18, H 8.17, N 1.07; found C 43.01, H 8.08, N 1.00.
[Nb{η5-C5H3(SiMe3)2}X(Me)(NSi8O12R7)] (R = iBu, X = Cl 7, Me
8)
7: In a sealed NMR tube and under rigorously anhydrous condi-
tions, [D6]benzene (0.70 mL) was added to a mixture of complex
6b (0.060 g, 0.050 mmol) and ZnMe2 (2  in toluene, 0.050 mL,
0.100 mmol). The colour of the mixture changed quickly from yel-
low to brown. The reaction was monitored by 1H NMR spec-
troscopy, and after 1 h, the spectrum showed the total conversion
of 6 into chloridomethyl derivative 7 in quantitative yield. The sus-
pension was decanted and filtered. The filtrate was concentrated to
dryness, and the residue was extracted with hexane (2ϫ5 mL). The
resulting solution was concentrated to ca. 1 mL and cooled to
–40°C to give 7 as a microcrystalline brown solid. Yield 0.047 g
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}Cl2] (R = iBu 10):
The synthesis of complex 10 was carried out by two different meth-
ods.
Method A: [Nb{η5-C5H3(SiClMe2)(SiMe3)}Cl4] (0.40 g, 0.86
mmol) was added to a hexane (50 mL) solution of Si7O9(iBu)7-
(OH)3 (0.34 g, 0.42 mmol) and triethylamine (0.26 g, 2.58 mmol).
The mixture was stirred for 4 h, and the suspension was then de-
canted. The ammonium salt formed was filtered off, and the solu-
tion was concentrated to ca. 10 mL. Cooling of the solution to
–40 °C gave 10 as a microcrystalline yellow solid. Yield 0.88 g
(90%).
(80%). IR (CsI/Nujol mull): ν = 2950 (vs), 1463 (s), 1365 (m), 1335
˜
(m), 1245 (vs), 1109 (vs), 925 (s), 839 (s), 747 (m), 577 (m), 480 (m)
1
cm–1. H NMR (300 MHz, [D6]benzene, 25°C): δ = 6.70 (m, 1 H),
6.43 (m, 1 H), 6.33 [m, 1 H, C5H3(SiMe3)2], 2.14 [m, 7 H, NSi-
(Me2CHCH2Si)7O12], 1.47 (s, 3 H, NbMe), 1.12 [m, 42 H, NSi-
(Me2CHCH2Si)7O12], 0.85 [m, 14 H, NSi(Me2CHCH2Si)7O12], 0.32
(s, 9 H), 0.29 [s, 9 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz,
[D6]benzene, 25°C): δ = 129.3 (Ci), 124.3 (Ci), 122.9, 120.6, 119.8
[C5H3(SiMe3)2], 48.2 (NbMe), 26.1, 25.9 [NSi(Me2CHCH2Si)7O12],
24.4 [NSi(Me2CHCH2Si)7O12], 23.1, 23.0 [NSi(Me2CHCH2Si)7-
O12], –0.1, –0.2 [C5H3(SiMe3)2] ppm. C40H87ClNNbO12Si10
(1183.34): calcd. C 40.60, H 7.41, N 1.18; found C 40.80, H 7.64,
N 1.93.
Method B: In a standard experiment, a solution in [D6]benzene
(0.70 mL) of [Nb{η5-C5H3(SiClMe2)(SiMe3)}Cl4] (0.25 g, 0.54
mmol) and [Li3Si7O12(iBu)7] (0.45 g, 0.57 mmol) was transferred to
a valved NMR tube. The colour of the mixture changed quickly
from dark red to yellow, and the reaction was monitored for 30 min
1
by H NMR spectroscopy until quantitative conversion of the ni-
obium starting complex to 10 was observed. The solvent was re-
moved in vacuo, and the residue was extracted into hexane
(2ϫ10 mL). The hexane solution was concentrated to ca. 5 mL
and cooled to –40°C to give 10 as a microcrystalline yellow solid.
8: At room temperature, a tetrahydrofuran solution of MgClMe
(3 , 0.33 mL, 1.00 mmol) was added to a hexane (40 mL) solution
of 6b (0.60 g, 0.50 mmol). After 1 h, the resulting brown suspension
was decanted, and the MgCl2 formed was separated by filtration.
The volatiles were removed under reduced pressure, and the residue
was extracted with hexane (2ϫ10 mL). The solution was filtered,
concentrated to ca. 5 mL and cooled to –40°C to give 8 as a micro-
Yield 0.46 g (75%). IR (CsI/Nujol mull): ν = 2961 (vs), 1465 (vs),
˜
1401 (vs), 1366 (vs), 1332 (vs), 1260 (vs), 1233 (s), 1095 (s), 967 (s),
739 (s), 634 (m), 584 (m), 471 (vs) cm–1. 1H NMR (300 MHz, [D1]-
chloroform, 25°C): δ = 7.05 (br., 2 H), 6.83 [m, 1 H, C5H3(SiMe3)-
(Me2SiOSi7O11R7)], 1.84 [m, 7 H, C5H3(SiMe3){Me2SiO(Me2-
CHCH2Si)7O11}], 0.94 [m, 42 H, C5H3(SiMe3){Me2SiO(Me2-
CHCH2Si)7O11}], 0.58 [m, 14 H, C5H3(SiMe3){Me2SiO(Me2-
CHCH2Si)7O11}], 0.43 (s, 3 H), 0.28 [s, 3 H, C5H3(SiMe3)(Me2-
SiOSi7O11R7)], 0.38 [s, 9 H, C5H3(SiMe3)(Me2SiOSi7O11R7)] ppm.
13C{1H} NMR (75 MHz, [D1]chloroform, 25°C): δ = 142.7 (Ci),
135.5 (Ci), 132.1, 129.7, 127.0 [C5H3(SiMe3)(Me2SiOSi7O11R7)],
26.6–25.6 [C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 24.1, 24.0,
23.9, 23.8 [C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 23.21,
22.9, 22.3, 22.2, 22.1 [C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}],
2.5, 0.6 [C5H3(SiMe3)(Me2SiOSi7O11R7)], –0.5 [C5H3(SiMe3)(Me2-
SiOSi7O11R7)] ppm. 29Si{1H} NMR (60 MHz, [D6]benzene, 25°C):
δ = –69.2, –68.1, –67.7, –66.3, –66.21, –66.16, –63.7 [C5H3(SiMe3)-
(Me2SiOSi7O11R7)], –4.91 [C5H3(SiMe3)(Me2SiOSi7O11R7)], –3.57
crystalline brown solid. Yield 0.29 g (50%). IR (CsI/Nujol mull): ν
˜
= 2955 (vs), 1466 (s), 1367 (m), 1333 (m), 1261 (s), 1111 (vs), 920
(s), 839 (vs), 742 (s), 567 (m), 484 (s) cm–1. 1H NMR (300 MHz,
[D6]benzene, 25°C): δ = 6.46 (m, 1 H), 6.27 [m, 2 H, C5H3-
(SiMe3)2], 2.10 [m, 7 H, NSi(Me2CHCH2Si)7O12], 1.10 [m, 42 H,
NSi(Me2CHCH2Si)7O12], 0.88 [m, 14 H, NSi(Me2CHCH2Si)7O12],
0.80 (s, 6 H, NbMe2), 0.26 [s, 18 H, C5H3(SiMe3)2] ppm. 13C{1H}
NMR (75 MHz, [D6]benzene, 25°C): δ = 125.4 (Ci), 119.7, 117.3
[C5H3(SiMe3)2], 38.6 (NbMe2), 26.10, 25.94, 25.90 [NSi(Me2-
CHCH2Si)7O12], 24.43, 24.40 [NSi(Me2CHCH2Si)7O12], 23.3, 23.0
[NSi(Me2CHCH2Si)7O12],
–0.06
[C5H3(SiMe3)2]
ppm.
C41H90NNbO12Si10 (1162.922): calcd. C 42.35, H 7.80, N 1.20;
found C 42.25, H 7.69, N 1.27.
[C5H3(SiMe3)(Me2SiOSi7O11R7)]
ppm.
C38H81Cl2NbO12Si9
[Nb{η5-C5H3(SiMe3)2}(CH2SiMe3)2{NSi8O12(iBu)7}] (9): In
a
(1146.542): calcd. C 39.81, H 7.11; found C 39.90, H 7.18.
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}(NtBu)] (R = iBu
11): Complex 11 was prepared by two different methods.
valved NMR tube, a [D6]benzene (0.70 mL) solution of 6b (0.30 g,
0.25 mmol) was treated with a slight excess of LiCH2SiMe3 (0.52 g,
1
0.55 mmol). The reaction was checked by H NMR spectroscopy.
After 2 h the spectrum showed the transformation of 6b into di-
alkyl compound 9 with a nearly quantitative yield. The suspension
Method A: LiNHtBu (0.10 g, 1.50 mmol) was added at room tem-
perature to a hexane (20 mL) solution of 10 (0.57 g, 0.50 mmol),
4410
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4401–4415

Cyclopentadienyl(niobium) Complexes with Imido and Silsesquioxane Ligands
and the mixture was stirred for 12 h. The LiCl formed was removed
by filtration, and the filtrate was concentrated to a volume of ca.
5 mL. Cooling at –40 °C overnight led to the deposition of a micro-
crystalline yellow solid identified as 11. Yield 0.46 g (80%).
(Me2CHCH2Si)7O11}], 0.22 (s, 6 H, NbMe2), 0.35 (s, 3 H), 0.28 [s,
3 H, C5H3(SiMe3)(Me2SiOSi7O11R7)], 0.27 [s, 9 H, C5H3(SiMe3)-
(Me2SiOSi7O11R7)] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25°C): δ = 132.6 (Ci), 126.4, 123.6 (Ci), 121.3, 119.8 [C5H3(SiMe3)-
(Me2SiOSi7O11R7)], 53.5, 53 (NbMe2), 26.4–25.9 [C5H3(SiMe3)
{Me2SiO(Me2CHCH2Si)7O11}], 24.8–24.5 [C5H3(SiMe3){Me2SiO-
(Me2CHCH2Si)7O11}], 24.0, 23.8, 23.1, 23.0 [C5H3(SiMe3){Me2-
SiO(Me2CHCH2Si)7O11}], 2.7, 0.9 [C5H3(SiMe3)(Me2SiOSi7-
O11R7)], –0.4 [C5H3(SiMe3)(Me2SiOSi7O11R7)] ppm. C40H87Nb-
O12Si9 (1105.795): calcd. C 43.45, H 7.93; found C 43.33, H 7.65.
Method B: Hexane (60 mL) was added to a mixture of [Nb{η5-
C5H3(SiClMe2)(SiMe3)}Cl2(NtBu)](0.24 g,0.51 mmol),Si7O9(iBu)7-
(OH)3 (0.41 g, 0.51 mmol) and NEt3 (0.27 mL, 1.24 mmol), and the
mixture was stirred for 4 h. The resulting suspension was decanted
and filtered. The solution was concentrated to ca. 5 mL and cooled
to –40 °C to give 11 as a microcrystalline yellow solid. Yield 0.50 g
(85%). IR (CsI/Nujol mull): ν = 2954 (vs), 1465 (vs), 1366 (s), 1331 [Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}(CHSiMe3)] (R =
˜
(s), 1251 (vs), 1228 (vs), 1103 (vs), 978 (vs), 919 (vs), 839 (s), 740
(s), 609 (s), 536 (m), 478 (s) cm–1. 1H NMR (300 MHz, [D6]ben- treated with a 1  solution of MgCl(CH2SiMe3) in diethyl ether
zene, 25°C): δ = 7.20 (m, 1 H), 7.00 (m, 1 H), 6.20 [m, 1 H, C5H3(Si- (1.00 mL, 1.00 mmol), and the colour of the mixture changed
iBu 14): A hexane (25 mL) solution of 10 (0.57 g, 0.50 mmol) was
Me3)(Me2SiOSi7O11R7)], 2.14 [m, 7 H, C5H3(SiMe3){Me2SiO- quickly from yellow to dark orange. The resulting suspension was
(Me2CHCH2Si)7O11}], 1.26 (s, 9 H, NbNCMe3), 1.12 [m, 42 H, stirred for 1 h, the magnesium chloride formed was then removed
C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 0.85 [m, 14 H, by filtration, and the filtrate was concentrated to a volume of ca.
C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 0.62 (s, 3 H), 0.27 [s, 5 mL. Cooling at –40 °C yielded 14 as a microcrystalline orange
3 H, C5H3(SiMe3)(Me2SiOSi7O11R7)], 0.30 [s, 9 H, C5H3(SiMe3)- solid. Yield 0.44 g (77%). IR (KBr): ν = 2954 (vs), 2717 (w), 2625
˜
(Me2SiOSi7O11R7)] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25°C): δ = 132.0 (Ci), 131.8, 123.9 (Ci), 115.5, 113.73 [C5H3(SiMe3)-
(w), 1465 (s), 1365 (m), 1331 (m), 1252 (vs), 1228 (s), 1115 (vs), 983
(s), 839 (vs), 740 (s), 686 (m), 631 (m), 477 (s) cm–1. 1H NMR
(Me2SiOSi7O11R7)], 66.8 (NbNCMe3), 32.2 (NbNCMe3), 26.5– (300 MHz, [D6]benzene, 25°C): δ = 9.68 (s, 1 H, NbCHSiMe3), 8.06
26.2 [C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 25.0–24.5 [C5H3- (m, 1 H), 6.65 (m, 1 H), 6.38 [m, 1 H, C5H3(SiMe3)(Me2-
(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 24.0–23.0 [C5H3(SiMe3)- SiOSi7O11R7)], 2.07 [m, 7 H, C5H3(SiMe3) {Me2SiO(Me2CH-
{Me2SiO(Me2CHCH2Si)7O11}], 3.63, –0.63 [C5H3(SiMe3)(Me2- CH2Si)7O11}], 1.11 [m, 42 H, C5H3(SiMe3) {Me2SiO(Me2-
SiOSi7O11R7)], –0.27 [C5H3(SiMe3)(Me2SiOSi7O11R7)] ppm.
C42H90NNbO12Si9 (1146.848): calcd. C 43.99, H 7.91, N 1.22;
found C 43.82, H 7.74, N 1.09.
CHCH2Si)7O11}], 0.88 [m, 14 H, C5H3(SiMe3){Me2SiO-
(Me2CHCH2Si)7O11}], 0.385 (s, 3 H), 0.381 [s, 3 H, C5H3(SiMe3)-
(Me2SiOSi7O11R7)], 0.25 [s, 9 H, C5H3(SiMe3)(Me2SiOSi7O11R7)],
0.21 (s, 9 H, NbCHSiMe3) ppm. 13C{1H} NMR (75 MHz, [D6]-
benzene, 25°C): δ = 235.73 (NbCHSiMe3), 129.6 (Ci), 124.5 (Ci),
120.3, 119.2, 112.43 [C5H3(SiMe3)(Me2SiOSi7O11R7)], 26.4–25.9
[C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 24.9–24.1 [C5H3(Si-
Me3){Me2SiO(Me2CHCH2Si)7O11}], 23.6, 23.3, 23.0 [C5H3-
(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 3.7, 3.3 [C5H3(SiMe3)-
(Me2SiOSi7O11R7)], 2.36 (NbCHSiMe3), –0.5 [C5H3(SiMe3)(Me2-
SiOSi7O11R7)] ppm. C42H89NbO12Si10 (1159.918): calcd. C 43.49,
H 7.73; found C 43.38, H 7.78.
[Nb{η5-C5H3(SiMe3)2}Cl(Si7O12R7-κ3O,O,O)] (R = iBu 12): A
solution of [Nb{η5-C5H3(SiMe3)2}Cl4] (0.33 g, 0.75 mmol) in hex-
ane (20 mL) was added to a solution of Si7O9(OH)3(iBu)7 (0.30 g,
0.37 mmol) and triethylamine (0.23 g, 2.25 mmol) in hexane
(10 mL) at room temperature. The reaction mixture was stirred for
4 h. The supernatant solution was separated from the solid by fil-
tration, and the filtrate was concentrated to dryness. The residue
was extracted with cool hexane (2ϫ10 mL). The resulting solution
was filtered, and the solvent was partially removed under reduced
pressure to give a microcrystalline yellow solid identified as 12.
[Nb{η5-C5H3(SiMe3)2}Me(Si7O12R7-κ3O,O,O)] (R = iBu 15): Un-
der rigorously anhydrous conditions, a toluene (20 mL) solution of
12 (0.84 g, 0.75 mmol) was treated with excess ZnMe2 (2  in tolu-
ene, 0.37 mL, 0.75 mmol), and the mixture was stirred at room tem-
perature for 12 h. The resulting suspension was decanted and fil-
Yield 0.71 g (85%). IR (KBr): ν = 2954 (vs), 1465 (m), 1251 (s),
˜
1228 (s), 1099 (vs), 998 (vs), 842 (vs), 756 (m), 634 (w), 464 (m),
1
391 (s) cm–1. H NMR (300 MHz, [D1]chloroform, 25°C): δ = 6.92
(br.,
2 H), 6.83 [br., 1 H, C5H3(SiMe3)2], 1.78 [m, 7 H,
(Me2CHCH2Si)7O12], 0.87 [m, 42 H, (Me2CHCH2Si)7O12], 0.52 [m, tered. The solution was concentrated to ca. 5 mL and cooled to
14 H, (Me2CHCH2Si)7O12], 0.29 [s, 18 H, C5H3(SiMe3)2] ppm.
–40°C to give 15 as a microcrystalline brown solid. Yield 0.58 g
13C{1H} NMR (75 MHz, [D1]chloroform, 25°C): δ = 135.6, 133.9 (70%). IR (KBr): ν = 2954 (vs), 1466 (s), 1402 (m), 1332 (m), 1252
˜
(Ci), 129.4 [C5H3(SiMe3)2], 25.6, 25.5, 25.4 [(Me2CHCH2Si)7O12], (s), 1229 (s), 1097 (vs), 997 (s), 838 (vs), 741 (s), 634 (m), 467 (s),
23.6, 23.5 [(Me2CHCH2Si)7O12], 23 [(Me2CHCH2Si)7O12], –1.1 388 (m) cm–1. 1H NMR (300 MHz, [D6]benzene, 25°C): δ = 6.91
[C5H3(SiMe3)2] ppm. C39H84ClNbO12Si9 (1126.213): calcd.
C
(br., 1 H), 6.63 [br., 2 H, C5H3(SiMe3)2], 2.13 [m, 7 H,
41.59, H 7.52; found C 41.82, H 7.53.
(Me2CHCH2Si)7O12], 1.52 (br., 3 H, NbMe), 1.10 [m, 42 H,
(Me2CHCH2Si)7O12], 0.85 [m, 14 H, (Me2CHCH2Si)7O12], 0.28 [s,
18 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25°C): δ = 133.0, 132.1, 127.1, 125.1, 123.5 [C5H3(SiMe3)2], 52.2
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}Me2] (R = iBu 13):
At room temperature, a stirred hexane (30 mL) solution of 10
(0.92 g, 0.80 mmol) was treated with a 2  toluene solution of
ZnMe2 (0.80 mL, 1.60 mmol). After 12 h, the resulting suspension
was decanted, and the ZnCl2 formed was separated by filtration.
The volatiles were removed under reduced pressure to give 13 as a
[NbMe],
26.1–25.9
[(Me2CHCH2Si)7O12],
24.5,
24.4
[(Me2CHCH2Si)7O12], 23.5, 23.1 [(Me2CHCH2Si)7O12], –0.1
[C5H3(SiMe3)2] ppm. C40H87NbO12Si9 (1105.795): calcd. C 43.45,
H 7.93; found C 43.57, H 8.02.
microcrystalline brown solid. Yield 0.62 g (70%). IR (KBr): ν =
˜
2954 (vs), 1465 (s), 1402 (m), 1331 (m), 1259 (vs), 1228 (s), 1099 [Nb{η5-C5H3(SiMe3)2}R(NtBu){C(Me)O-κ2C,O}] (R = Cl 16, Me
(vs), 990 (vs), 839 (vs), 741 (s), 479 (s), 392 (m) cm–1. 1H NMR 17): A [D6]benzene (0.70 mL) solution of 2 (0.21 g, 0.50 mmol) or
(300 MHz, [D6]benzene, 25°C): δ = 6.55 (m, 1 H), 6.33 [m, 2 H,
C5H3(SiMe3)(Me2SiOSi7O11R7)], 2.14 [m, H, C5H3(SiMe3)-
{Me2SiO(Me2CHCH2Si)7O11}], 1.13 [m, 42 H, C5H3(SiMe3) {Me2-
3 (0.20 g, 0.50 mmol) was placed in a valved NMR tube, and the
argon atmosphere was replaced by carbon monoxide (1 atm). The
solution was shaken until it was homogeneous, and the colour of
7
SiO(Me2CHCH2Si)7O11}], 0.86 [m, 14 H, C5H3(SiMe3) {Me2SiO- the mixture changed from dark brown to orange. The reaction was
Eur. J. Inorg. Chem. 2009, 4401–4415
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4411

C. García, M. Gómez, P. Gómez-Sal, J. M. Hernández
FULL PAPER
monitored by 1H NMR spectroscopy, and after 30 min the com-
plete conversion of the starting niobium complex into the acyl de-
(vs), 741 (s), 478 (s) cm–1. 1H NMR (300 MHz, [D6]benzene, 25°C):
δ = 7.24 (m, 1 H), 7.09 (m, 1 H), 5.15 [m, 1 H, C5H3(SiMe3)(Me2-
rivative was confirmed. The resulting solution was then concen- SiOSi7O11R7)], 2.12 [m, 7 H, C5H3(SiMe3) {Me2SiO(Me2CH-
trated to dryness to give an orange microcrystalline solid identified
as 16 (R = Cl) or 17 (R = Me).
CH2Si)7O11}], 1.76 (s, 3 H), 1.63 [s, 3 H, O(Me)C=C(Me)O], 1.13
[m, 42 H, C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}], 0.81 [m, 14
H, C5H3(SiMe3) {Me2SiO(Me2CHCH2Si)7O11}], 0.53 (s, 3 H), 0.41
[s, 3 H, C5H3(SiMe3) {Me2SiO(Me2CHCH2Si)7O11}], 0.24 [s, 9 H,
C5H3(SiMe3){Me2SiO(Me2CHCH2Si)7O11}] ppm. 13C{1H} NMR
(75 MHz, [D6]benzene, 25°C): δ = 134.2 (Ci), 130.8 (Ci), 126.7,
122.4, 111.8 [C5H3(SiMe3)(Me2SiOSi7O11R7)], 98.4 [O(Me)C=C-
(Me)O], 31.1, 30.8 [O(Me)C=C(Me)O], 26.5–25.8 [C5H3(SiMe3)-
{Me2SiO(Me2CHCH2Si)7O11}], 24.8–24.4 [C5H3(SiMe3){Me2SiO-
(Me2CHCH2Si)7O11}]. 23.9–23.0 [C5H3(SiMe3){Me2SiO(Me2-
CHCH2Si)7O11}], –0.3 [C5H3(SiMe3)(Me2SiOSi7O11R7)], –0.5, –4.1
[C5H3(SiMe3)(Me2SiOSi7O11R7)] ppm. C42H87NbO14Si9
(1161.815): calcd. C 43.42, H 7.55; found C 43.51, H 7.63.
16: IR (KBr): ν = 2966 (vs), 1577 (s), 1356 (s), 1248 (s), 1083 (s),
˜
920 (s), 838 (vs), 756 (s), 635 (m), 546 (m), 473 (m) cm–1. 1H NMR
(300 MHz, [D6]benzene, 25°C): δ = 6.81 (m, 1 H), 6.21 [m, 2 H,
C5H3(SiMe3)2], 2.47 [s, 3 H, NbC(Me)O], 0.97 (s, 9 H, NbCMe3),
0.44 (s, 9 H), 0.01 [s, 9 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR
(75 MHz, [D6]benzene, 25°C): δ = 295.2 [C(Me)O], 122.3 (Ci),
122.0 (Ci), 116.5, 110.9, 110.7 [C5H3(SiMe3)2], 65.8 (NbNCMe3),
32.4 (NbNCMe3), 29.5 [C(Me)O], –0.15, –0.19 [C5H3(SiMe3)2]
ppm. C17H33ClNNbOSi2 (451.986): calcd. C 45.17, H 7.36, N 3.10;
found C 44.92, H 7.30, N 3.25.
17: IR (KBr): ν = 2960 (vs), 1697 (s), 1405 (s), 1367 (m), 1261 (vs),
˜
1086 (vs), 918 (s), 838 (vs), 694 (s), 634 (s) cm–1. 1H NMR
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}(CMe2NAr-
(300 MHz, [D6]benzene, 25°C): δ = 6.40 (m, 1 H), 6.22 (m, 1 H), κ2C,N)] (R = iBu, Ar = 2,6-Me2C6H3 20): Under rigorously anhy-
6.12 [m, 1 H, C5H3(SiMe3)2], 2.54 [s, 3 H, NbC(Me)O], 1.19 (s, 3
drous conditions, 2,6-Me2C6H3NC (0.065 g, 0.50 mmol) was added
H, NbMe), 1.08 (s, 9 H, NbCMe3), 0.23 (s, 9 H), 0.14 [s, 9 H, at room temperature to a hexane (30 mL) solution of 13 (0.55 g,
C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25°C): 0.50 mmol). The reaction mixture was stirred vigorously for 30 min
δ = 300.5 [C(Me)O], 122.7 (Ci), 122.5 (Ci), 117.3, 114.9, 112.7
[C5H3(SiMe3)2], 67.8 (NbNCMe3), 32.2 (NbNCMe3), 31.5
(NbMe), 30.5 [C(Me)O], –0.18, –0.21 [C5H3(SiMe3)2] ppm.
and then filtered. The filtrate was concentrated to ca. 5 mL and
cooled to –40 °C to give 20 as a dark orange microcrystalline solid.
Yield 0.49 g (80%). IR (KBr): ν = 2953 (vs), 2118 (s), 1466 (s),
˜
C18H36NNbOSi2 (431.568): calcd. C 50.10, H 8.41, N 3.25; found 1365 (w), 1253 (s), 1107 (vs), 921 (s), 838 (vs), 740 (s), 484 (m)
1
C 49.59, H 8.35, N 3.18.
cm–1. H NMR (300 MHz, [D6]benzene, 25°C): δ = 7.02 (m, 3 H,
Me2C6H3), 7.43 (m, 1 H), 7.33 (m, 1 H), 5.65 [m, 1 H, C5H3-
[Nb{η5-C5H3(SiMe3)2}R(NtBu){C(R)O-κ2C,O}] (R = CH2SiMe3
18): A yellow solution of 4 (0.15 g, 0.27 mmol) in [D6]benzene
(0.8 mL) was placed into a valved NMR tube, and the argon atmo-
sphere was replaced by carbon monoxide (1 atm). The reaction was
monitored by 1H NMR spectroscopy at room temperature. After
30 min, the formation of alkyl acyl complex 18 with a nearly quan-
titative yield was confirmed by 1H and 13C NMR spectra. The solu-
tion was concentrated to dryness, giving 18 as a dark orange micro-
(SiMe3)(Me2SiOSi7O11R7)], 2.12 [m,
7 H, C5H3(SiMe3){Me2-
SiO(Me2CHCH2Si)7O11}], 1.73 (s, 3 H), 1.69 (s, 3 H, Me2C6H3),
not observed (CMe2NAr), 1.12 [m, 42 H, C5H3(SiMe3){Me2-
SiO(Me2CHCH2Si)7O11}], 0.82 [m, 14 H, C5H3(SiMe3){Me2SiO-
(Me2CHCH2Si)7O11}], 0.48 (s, 3 H), 0.39 [s, 3 H, C5H3(SiMe3)-
(Me2SiOSi7O11R7)], 0.34 [s, 9 H, C5H3(SiMe3)(Me2SiOSi7O11R7)]
ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25°C): δ = 151.83
(Ci), 135.0, 131.6, 129.2 (several phenyl, Me2C6H3), 131.6 (Ci),
125.5, 125.2, 123.6 (Ci), 111.2 [C5H3(SiMe3)(Me2SiOSi7O11R7)],
74.0 (CMe2NAr), 30.3, 28.7 (CMe2NAr), 26.9–25.9 [C5H3(SiMe3)-
{Me2SiO(Me2CHCH2Si)7O11}], 24.9–24.4 [C5H3(SiMe3){Me2SiO-
(Me2CHCH2Si)7O11}], 24.0–22.0 [C5H3(SiMe3){Me2SiO(Me2-
CHCH2Si)7O11}], not observed (Me2C6H3), 4.5, –0.2 [C5H3-
(SiMe3)(Me2SiOSi7O11R7)], 0.05 [C5H3(SiMe3)(Me2SiOSi7O11R7)]
ppm. C49H96NNbO12Si9 (1236.973): calcd. C 47.58, H 7.82, N 1.13;
found C 47.44, H 7.92, N 1.17.
crystalline compound. Yield 0.135 g (85%). IR (KBr): ν = 2956
˜
(vs), 1577 (s), 1450 (s), 1357 (m), 1249 (s), 1084 (s), 840 (vs), 755 (s),
1
635 (m), 470 (m) cm–1. H NMR (300 MHz, [D6]benzene, 25°C): δ
= 6.35 (m, 2 H), 6.24 [m, 1 H, C5H3(SiMe3)2], 3.45, 2.73 [AB, 2JH,H
= 10 Hz, 2 H, C(CH2SiMe3)O], 1.20 [s, 9 H, NbN(CMe3)], 0.97,
2
0.78 (AB, JH,H = 10 Hz, 2 H, NbCH2SiMe3), 0.53 [s, 9 H,
C(CH2SiMe3)O], 0.10 (s, 9 H, NbCH2SiMe3), 0.31 (s, 9 H), 0.13 [s,
9 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25°C): δ = 298.0 [C(CH2SiMe3)O], 122.1 (Ci), 121.9 (Ci), 117.4,
111.7, 110.9 [C5H3(SiMe3)2], 65.6 [NbN(CMe3)], 42.3
[C(CH2SiMe3)O], 33.1 [NbN(CMe3)], 29.6 (NbCH2SiMe3), 4.0
[C(CH2SiMe3)O], 0.64 (NbCH2SiMe3), –0.1, –0.2 [C5H3(SiMe3)2]
ppm. C24H52NNbOSi4 (575.932): calcd. C 50.05, H 9.10, N 2.43;
found C 49.87, H 8.96, N 2.37.
[Nb{η5-C5H3(SiMe3)2}Cl(NtBu){C(Me)NAr-κ2C,N}] (Ar
Me2C6H3 21): A hexane (40 mL) solution of 2 (0.11 g, 0.26 mmol)
was treated with solution of 2,6-Me2C6H3NC (0.034 g,
= 2,6-
a
0.26 mmol) in hexane (5 mL). The reaction mixture was stirred vig-
orously for 1 h, and then the solution was filtered. The volatiles
were removed by vacuum, and the brown residue was extracted
with hexane (2ϫ10 mL). The solution was concentrated to ca.
[Nb{η5-C5H3(SiMe3)(Me2SiOSi7O11R7-κ2O,O)}{O(Me)C=C(Me)-
O-κ2O,O}] (R = iBu 19): In a standard experiment, a sample of 13
(0.55 g, 0.50 mmol) was placed in a valved NMR tube, and [D6]- 5 mL and cooled to –40 °C to give 21 (0.10 g, 69%) as a brown
benzene was (0.70 mL) added. Subsequently, the inert atmosphere
was replaced by carbon monoxide, and the colour of the mixture
changed from gold-plated to yellow. The reaction was monitored
by 1H NMR spectroscopy until total conversion of the starting
niobium complex was achieved. After 2 h, the formation of 19 in
quantitative yield was confirmed by its 1H NMR spectrum. The
[D6]benzene solution was concentrated to dryness, and the yellow
oily residue was extracted with hexane (2ϫ10 mL). The solution
was filtered, concentrated to ca. 5 mL and cooled to –40°C to give
19 as a microcrystalline yellow solid. Yield 0.46 g (80%). IR (KBr):
microcrystalline solid. IR (KBr): ν = 2967 (vs), 2111 (s), 1650 (s),
˜
1474 (s), 1427 (s), 1353 (m), 1249 (s), 1080 (s), 920 (s), 837 (vs),
762 (s), 637 (m), 541 (m), 499 (m) cm–1. 1H NMR (300 MHz, [D6]-
benzene, 25°C): δ = 6.90 (m, 3 H, Me2C6H3), 6.67 (m, 1 H), 6.25
(m, 1 H), 6.02 [m, 1 H, C5H3(SiMe3)2], 2.14 [s, 3 H, C(Me)NAr],
2.12 (s, 3 H), 1.77 (s, 3 H, Me2C6H3), 1.18 [s, 9 H, NbN(CMe3)],
0.52 (s, 9 H), 0.32 [s, 9 H, C5H3(SiMe3)2] ppm. 13C{1H} NMR
(75 MHz, [D6]benzene, 25°C): δ = 227.3 [C(Me)NAr], 140.4 (Ci),
135.4 (Ci), 131.2, 129.8, 128.7, 126.4 (Me2C6H3), 122.7 (Ci), 119.3,
119.2, 119.1, 117.3 (Ci, C5H3(SiMe3)2], 67.1 [NbN(CMe3)], 31.5
[NbN(CMe3)], 23.9 [C(Me)NAr], 18.7, 18.4 (Me2C6H3), 0.95, –0.88
ν = 2954 (vs), 1466 (s), 1400 (s), 1253 (s), 1115 (vs), 1099 (vs), 839
˜
4412
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4401–4415

Cyclopentadienyl(niobium) Complexes with Imido and Silsesquioxane Ligands
[C5H3(SiMe3)2] ppm. C25H42ClN2NbSi2 (555.154): calcd. C 54.09,
H 7.63, N 5.05; found C 53.85, H 7.54, N 4.88.
[Nb{η5-C5H3(SiMe3)2}Me(NtBu){C(Me)NAr-κ2C,N}] (Ar = 2,6- [1] V. C. Gibson, S. K. Spitzmeseer, Chem. Rev. 2003, 103, 283–
315.
Me2C6H3 22): In a standard experiment, 3 (0.15 g, 0.372 mmol),
2,6-Me2C6H3NC (0.049 g, 0.372 mmol) and [D6]benzene (0.8 mL)
were placed in a valved NMR tube. The reaction was monitored
by 1H NMR spectroscopy until the starting material was totally
transformed and no further change was observed. The formation
of iminoacyl compound 22 was confirmed by its 1H NMR spec-
trum. When the solvent was removed by vacuum, 22 was isolated
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as a brown microcrystalline solid. Yield 0.17 g (86%). IR (KBr): ν
˜
= 2961 (vs), 1634 (s), 1442 (s), 1351 (m), 1250 (vs), 1080 (vs), 921
1
(vs), 836 (vs), 757 (s), 640 (m), 539 (m) cm–1. H NMR (300 MHz,
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[D6]benzene, 25°C): δ = 6.91 (m, 3 H, Me2C6H3), 6.31 (m, 1 H),
6.00 (m, 1 H), 5.59 [m, 1 H, C5H3(SiMe3)2], 2.18 [s, 3 H, C(Me)-
NAr], 1.96 (s, 3 H), 1.67 (s, 3 H, Me2C6H3), 1.20 [s, 9 H,
NbN(CMe3)], 0.67 (s, 3 H, NbMe), 0.26 (s, 9 H), 0.11 [s, 9 H,
C5H3(SiMe3)2] ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25°C):
δ = 230.1 [C(Me)NAr], 141.7 (Ci), 134.2 (Ci), 130.47, 129.8, 125.9
(several phenyl, Me2C6H3), 122.8 (Ci), 119.0 (Ci), 117.2, 115.9,
113.7 [C5H3(SiMe3)2], 69.9 [NbN(CMe3)], 64.62 (NbMe), 32.4
[NbN(CMe3)], 23.9 [C(Me)NAr], 18.2, 18.1 (Me2C6H3), 1.08, –0.93
[C5H3(SiMe3)2] ppm. C26H45N2NbSi2 (534.736): calcd. C 58.40, H
8.48, N 5.24; found C 58.25, H 8.35, N 5.18.
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A crystal of 5cЈ suitable for X-ray analysis was obtained by the
slow concentration of a hexane solution of 5c. The crystal was then
covered with mineral oil and mounted in the N2 stream of a
Bruker-Nonius Kappa CCD diffractometer. Data was collected by
using graphite monochromated Mo-Kα radiation (λ = 0.71073 Å).
Data collection was performed at 150 K with an exposure time of
76 s per frame (11 sets, 1021 frames). Raw data was corrected for
Lorentz and polarization effects.
The structure was solved by direct methods, completed by subse-
quent difference Fourier techniques and refined by full-matrix le-
ast-squares on F2 (SHEXL-97).[48] Due to the bad quality of the
crystal, only some of the atoms could be refined anisotropically;
most of them were refined with isotropic thermal parameters, and
in some cases it was necessary to fix them. Hydrogen atoms were
included in geometrical calculations and refined by using a riding
model. Some other different space groups were checked, but the
results were not satisfactory. All the calculations were performed
with the WINGX system.[49]
Crystal data: C112H252Li12O48Si28; Mw = 3236.89; orthorhombic;
space group Pna21; a = 28.260(6) Å, b = 21.764(6) Å, c =
31.558(9) Å; V = 19410(9) Å3; 124325 reflections collected, 22506
unique reflections (Rint = 0.1834), final R1 = 0.2185 [I Ͼ 2σ(l)].
CCDC-683456 contains the supplementary crystallographic data
(excluding structure factors) for 5cЈ. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
We thank the Ministerio de Ciencia e Innovación (project CTQ
2006-04540/BQU), Factoría de Cristalización Consolider 2010 and
Comunidad de Madrid (project S-0505/PPQ/0328-02) for their fin-
ancial support of this research. J. M. H. and C. G. are grateful to
Ministerio de Ciencia e Innovación and Universidad de Alcalá,
respectively, for a fellowship.
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68.
Eur. J. Inorg. Chem. 2009, 4401–4415
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4413

C. García, M. Gómez, P. Gómez-Sal, J. M. Hernández
FULL PAPER
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Received: June 22, 2009
Published Online: September 2, 2009
Eur. J. Inorg. Chem. 2009, 4401–4415
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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