New bis(silyl)cyclopentadienidoniobium and -tantalum complexes: X-ray crystal structures of [NbCp∧Cl4] and [NbCp∧Cl 4(CNAr)] [Cp∧ = η5-C5H 3(SiClMe2)(SiMe3); Ar = 2,6-Me 2</

Article abstract of DOI:10.1002/ejic.200600633

The [bis(silyl)cyclopentadienido]tetrachloroniobium and -tantalum complexes [MCp∧Cl₄] [Cp∧ = η⁵-C₅H ₃(SiClMe₂)(SiMe₃); M = Nb 3, Ta 4] were synthesized by reaction of the pentachlorides MCl

Full text of DOI:10.1002/ejic.200600633

FULL PAPER
DOI: 10.1002/ejic.200600633
New Bis(silyl)cyclopentadienidoniobium and -tantalum Complexes:
∧
∧
X-ray Crystal Structures of [NbCp Cl4] and [NbCp Cl4(CNAr)]
5
∧
[Cp = η -C5H3(SiClMe2)(SiMe3); Ar = 2,6-Me2C6H3]
Manuel Gómez,*[a] Pilar Gómez-Sal,[a] and José Manuel Hernández[a]
Keywords: Niobium / Tantalum / Cyclopentadienyl complexes
The [bis(silyl)cyclopentadienido]tetrachloroniobium and
[C5H3(SiMe2NHtBu)(SiMe3)2] (2) by elimination of 1. The tet-
∧
∧
-tantalum complexes [MCp Cl4] [Cp = η5-C5H3(SiClMe2)-
(SiMe3); M = Nb 3, Ta 4] were synthesized by reaction of the
pentachlorides MCl5 with C5H3(SiClMe2)(SiMe3)2 (1). Al-
though the Lewis acidity of tetrachloro complexes 3 and 4
is lower than that of the pentahalides, two adducts [M{η5-
C5H3(SiClMe2)(SiMe3)}Cl4(CNAr)] (Ar = 2,6-Me2C6H3; M =
Nb 5, Ta 6) have been isolated by reaction with ArNC. Com-
plexes 3 and 4 react with tert-butylamine or lithium amides
to afford the dichloroimido and amidochloroimido complexes
[M{η5-C5H3(SiClMe2)(SiMe3)}Cl2(NR)] (R = tBu, M = Nb 7,
Ta 8; R = Me, M = Nb 9) and [Ta{η5-C5H3(SiClMe2)(SiMe3)}-
Cl(NHtBu)(NtBu)] (10), respectively. In addition, 7 and 8 can
be prepared by treatment of the pentachlorides with
rachloro compound 3 reacts with four equivalents of tBuNH2
to give the constrained-geometry derivative [Nb{η5-C5H3(Si-
Me2NtBu-κN)(SiMe3)}Cl(NtBu)] (11), whereas the treatment
of toluene solutions of 3 and 4 with H2NCH2CH2NH2 in the
presence of triethylamine leads to the trichloro complexes
[M{η5-C5H3(SiMe2NCH2CH2NH2-κ2N,N)(SiMe3)}Cl3] (M
=
Nb 12, Ta 13). All the reported complexes were studied by
IR and NMR spectroscopy and the molecular structures of
complexes 3 and 5 were determined by X-ray diffraction
methods.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
with the cyclopentadienido moiety[5] and therefore provides
group 5 metal complexes that are isoelectronic with the
group 4 metallocenes that are extensively used as Ziegler–
Natta catalysts. Furthermore, the easy modification of the
steric and electronic properties of the imido ligand by vary-
ing its alkyl moiety make this type of compound very versa-
tile. For these reasons a rich chemistry of imido group 5
metal complexes has been reported in the last few years.[6]
As part our interest in the structure–reactivity relation-
ship analysis in group 5 metal monocyclopentadienido
compounds, we report here the synthesis of new bis(silyl)-
cyclopentadienidoniobium and -tantalum complexes and
the results obtained in the study of the simultaneous ami-
nolysis of Si–Cl and M–Cl bonds. In addition, the molecu-
lar structures of complexes 3 and 5, as determined by X-
ray diffraction methods, are reported.
Introduction
Mono- and bis(cyclopentadienido) complexes of early
transition metals with silyl-substituted cyclopentadienido
rings have been extensively used as reagents in organic syn-
thesis and also as precursors to prepare soluble Ziegler–
Natta-type olefin polymerization catalysts.[1] The presence
of different substituents in the cyclopentadienido moiety
modifies the steric and electronic requirements of the cen-
tral metal atom, particularly when such substituents con-
tain reactive functional groups. Thus, when chlorine is pres-
ent in these silyl groups the complex offers a new reactivity
center that allows their fixation on silica supports and the
cyclopentadienido ring loses its exclusive role as an ancil-
lary ligand. In the last few years various studies have been
published regarding the comparative reactivity between the
Si–Cl and M–Cl bonds of different chlorosilylcyclopen-
tadienido complexes[2] that have been used as versatile start-
ing compounds in significant synthetic strategies for con-
strained-geometry catalysts[2d,3] with bidentate η5-silylcy-
clopentadienido-η1-amido ligands.
Results and Discussion
The synthesis of C5H3(SiClMe2)(SiMe3)2 (1) was effected
by treatment of a tetrahydrofuran suspension of the lithium
salt [Li{C5H3(SiMe3)2}][7] with dichlorodimethylsilane at
–78 °C (Scheme 1). After work-up, 1 was obtained as a yel-
low oil which can be stored in the dark under an inert atmo-
sphere for several weeks (yield 85%) and was identified by
1H NMR spectroscopy (see Experimental Section) as an
equilibrium mixture of isomers in which 1-(chlorodimethyl-
The imido group is a strong π-donor ligand that is useful
for stabilizing high-valent metal complexes.[4] It is isolobal
[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
5106
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Bis(silyl)cyclopentadienidoniobium and Tantalum Complexes
FULL PAPER
Scheme 1.
silyl)-1,3-bis(trimethylsilyl)cyclopentadiene (I) and 1,1-bis- Cl4] (M = Nb 3, Ta, 4) with elimination of SiClMe3. The
(trimethylsilyl)-3-(chlorodimethylsilyl)cyclopentadiene (II) red (M = Nb) and green (M = Ta) compounds were isolated
are the major components in a 3:2 ratio, as usually occurs in 90 and 70% yield, respectively, upon cooling their solu-
in all cyclopentadienes of the type C5H3X2Y. [8]
tions to –20 °C. Both tetrachloro complexes 3 and 4 show
The precursor C5H3(SiMe2NHtBu)(SiMe3)2 (2) was pre- a Lewis acidic character and adducts [M{η5-C5H3(SiMe3)-
pared in good yields (90%) as an orange oil by treatment (SiClMe2)}Cl4(CNAr)] (Ar = 2,6-Me2C6H3; M = Nb 5, Ta,
of 1 with two equivalents of tert-butylamine in hexane at 6) can be isolated by addition of one equivalent of 2,6-
room temperature. Compound 2 was characterized by Me2C6H3NC to their toluene solutions.
NMR spectroscopy as essentially the only product of the
The molecular structure and atom-labeling scheme of 3
reaction.
are shown in Figure 1, while the most relevant geometrical
Compound 1 reacts with one equivalent of the penta- parameters are summarized in Table 1. In the solid state,
chlorides MCl5 (M = Nb, Ta) in toluene (M = Nb) or this complex presents a dimeric structure with the two half
dichloromethane (M = Ta) at 0 °C (M = Nb) or room tem- moieties related by a symmetric center and the niobium
perature (M = Ta) to give the corresponding monocyclo- atoms bonded through two asymmetrically bridging chlo-
pentadienido complexes [M{η5-C5H3(SiClMe2)(SiMe3)}- rine atoms. The coordination sphere of the niobium atom
Figure 1. ORTEP drawing of compound 3 with thermal ellipsoids at the 50% probability level.
Eur. J. Inorg. Chem. 2006, 5106–5114
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Table 1. Selected bond lengths [Å] and angles [°] for compound 3.[a]
Nb(1)–Cl(1)
Nb(1)–Cl(3)
Nb(1)–Cl(4)#1
Nb(1)–C(1)
Nb(1)–C(3)
Nb(1)–C(5)
Si(2)–C(3)
Si(2)–C(8)
Si(2)–C(9)
2.380(2)
2.401(2)
2.764(2)
2.443(7)
2.480(8)
2.426(8)
1.894(8)
1.869(8)
1.922(7)
1.848(9)
102.99
Nb(1)–Cl(2)
Nb(1)–Cl(4)
Cl(4)–Nb(1)#1
Nb(1)–C(2)
Nb(1)–C(4)
Nb(1)–Cp(1)
Si(1)–C(1)
Cl(5)–Si(1)
Si(1)–C(6)
2.3765(19)
2.4808(18)
2.764(2)
2.422(8)
2.457(8)
1.235
1.885(8)
2.072(3)
1.832(9)
1.847(9)
108.17
Si(2)–C(10)
Si(1)–C(7)
Cp(1)–Nb(1)–Cl(1)
Cp(1)–Nb(1)–Cl(3)
Cl(2)–Nb(1)–Cl(1)
Cl(1)–Nb(1)–Cl(3)
Cl(2)–Nb(1)–Cl(4)
Cl(4)–Nb(1)–Cl(4)#1
C(6)–Si(1)–Cl(5)
Cp(1)–Nb(1)–Cl(4)#1
Cp(1)–Nb(1)–Cl(2)
Cp(1)–Nb(1)–Cl(4)
Cl(2)–Nb(1)–Cl(3)
Cl(1)–Nb(1)–Cl(4)
Cl(3)–Nb(1)–Cl(4)
Nb(1)–Cl(4)–Nb(1)#1
C(1)–Si(1)–Cl(5)
103.39
103.17
87.23(8)
153.54(7)
148.61(7)
71.90(6)
108.6(4)
175.03
86.43(8)
86.65(7)
85.50(7)
108.10(6)
99.7(3)
[a] Cp(1) is the centroid of C(1)–C(5); symmetry operation #1: –x + 2, –y + 1, –z.
can be described as elongated octahedral, with the cyclo- 2.442(3) Å. Complex 5 is pseudo-octahedral if the centroid
∧
pentadienido ring and a chlorine atom in the apical posi- of the Cp ring is considered as occupying a coordination
tions and with four chlorine atoms in the equatorial plane. site, although the niobium atom is displaced by 0.60 Å from
The niobium atom is located 0.6 Å above the equatorial the mean equatorial plane passing through the four chlorine
plane.[6d,6f,9,10] The Nb–Clequatorial bond lengths range from atoms toward the cyclopentadienido ring.
2.375(2) to 2.482(2) Å, with the largest distance corre-
sponding to the chlorine atom implicated in the bridging
system that is also bonded at the apical position of the sym-
metry-related niobium atom, although in this case with a
larger distance of 2.763(2) Å. The Cp–Nb–Cl(4)apical angle
and the Nb–Cp distance are 175.03° and 1.235 Å, respec-
tively, both of which are in the normal range. A similar
asymmetric bridge has been described for the complexes
[{(NbCl2)2(µ-O)(µ-Cl)2}{(η5-C5H4)2(Me2SiOSiMe2)}][6c]
and [{Nb(η5-C5H4SiMe3)Cl2}2(µ-O)(µ-Cl)2],[11] although in
these cases a bridging oxygen atom is also present.
The two silicon atoms of the substituents in the cyclopen-
tadienido ring [Si(1) and Si(2)] are located above the Cp
plane by 0.37 and 0.39 Å, respectively, and the chlorine
atom is perpendicular to this plane. This position for the
chlorine atom has been described in other complexes con-
taining a C5H4(SiClMe2) ring.[12] It is relevant to note that
no other similar structures with a disubstituted Cp ring
have been described.
A view of the molecular structure of complex 5 is shown
in Figure 2 together with the atom-numbering scheme. Se-
lected bond lengths and angles are given in Table 2. The
∧
Figure 2. ORTEP drawing of compound 5 with thermal ellipsoids
Cp ring is bound to the niobium atom in a nearly symmet-
at the 50% probability level.
ric η5-fashion with the distance between the metal and the
centroid of the ring being 2.137 Å and with the two silicon
atoms of the substituents Si(6) and Si(7) located 0.31 Å
The comparative reactivity of the two different types of
above the ring plane. The isocyanide ligand is linearly Si–Cl and M–Cl bonds present in the starting tetrachloro
bound to the niobium atom, the values of the Nb–C(6) complexes 3 and 4 was studied in reactions with amines and
bond length and of the Nb–C(6)–N(1) and C(6)–N(1)–C(7) amides. Related studies with chlorocyclopentadienidotitani-
angles being 2.215(13) Å and 176.3(11)° and 175.2(13)°, um[3g,3h,14] and -niobium[2d] derivatives led to the formation
respectively; the length of the N(1)–C(6) bond [1.192(15) Å] of constrained monomeric cyclic species containing the
is in agreement with a triple bond.[6,13] The coordination pendant amido group of the cyclopentadienido ligand coor-
around the niobium atom is completed by four chlorine dinated to the metal center. The dichloroimido complexes
atoms with Nb–Cl bond lengths ranging from 2.412(3) to [MCp Cl2(NR)] [Cp = η5-C5H3(SiClMe2)(SiMe3); R =
∧
∧
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Table 2. Selected bond lengths [Å] and angles [°] for compound 5.[a]
Nb(1)–Cl(1)
Nb(1)–Cl(3)
Nb(1)–C(6)
Nb(1)–C(2)
Nb(1)–C(4)
Si(6)–C(3)
Si(6)–C(17)
Si(6)–C(18)
2.412(3)
2.442(3)
2.215(13)
2.431(11)
2.475(11)
1.894(12)
1.861(13)
1.852(13)
1.955(10)
2.137
76.2(3)
75.2(3)
87.31(12)
151.39(12)
84.74(11)
178.56
Nb(1)–Cl(2)
Nb(1)–Cl(4)
Nb(1)–C(1)
Nb(1)–C(3)
Nb(1)–C(5)
Si(7)–C(1)
Si(7)–Cl(5)
Si(7)–C(15)
2.418(3)
2.430(3)
2.458(10)
2.485(11)
2.444(12)
1.897(11)
2.064(6)
1.809(13)
1.897(11)
1.192(15)
74.5(4)
Si(6)–C(19)
Cp(1)–Nb(1)
Si(7)–C(16)
C(6)–N(1)
C(6)–Nb(1)–Cl(1)
C(6)–Nb(1)–Cl(3)
Cl(1)–Nb(1)–Cl(2)
Cl(1)–Nb(1)–Cl(3)
Cl(2)–Nb(1)–Cl(3)
Cp(1)–Nb(1)–N(1)
Cp(1)–Nb(1)–Cl(2)
Cp(1)–Nb(1)–Cl(14)
C(6)–N(1)–C(7)
C(6)–Nb(1)–Cl(2)
C(6)–Nb(1)–Cl(4)
Cl(1)–Nb(1)–Cl(4)
Cl(2)–Nb(1)–Cl(4)
Cl(4)–Nb(1)–Cl(3)
Cp(1)–Nb(1)–Cl(1)
Cp(1)–Nb(1)–Cl(3)
Nb(1)–C(1)–N(1)
76.2(4)
86.93(12)
150.68(11)
86.74(11)
104.44
104.11
176.3(11)
104.33
105.03
175.2(13)
[a] Cp is the centroid of C(1)–C(5).
tBu, M = Nb 7, Ta, 8; R = Me, M = Nb 9] were isolated
Alternatively, the reaction of 2 with niobium and tanta-
in good yields upon treatment of 3 and 4 with one equiva- lum pentachlorides in a 1:1 ratio leads to the dichloroimido
lent of the appropriate lithium amide (see Scheme 2). Com- compounds 7 and 8, respectively, by elimination of HCl,
plex 7 also can be prepared with two equivalents of tert- cyclopentadiene 1, and a mixture of other, unidentified
butylamine, whereas the treatment of 4 with 1.5 equivalents products.
of LiNHtBu leads to the amidochloroimido complex
Partial substitution of the chloride moieties occurs upon
[Ta{η5-C5H3(SiMe3)(SiClMe2)}Cl(NHtBu)(NtBu)]
(10). treatment of a hexane solution of 3 with four equivalents of
The formation of the imido complexes 7–10 takes place tBuNH2 (Scheme 3) and leads to the constrained-geometry
with elimination of LiCl and HCl but the Si–Cl bond of complex [Nb{η5-C5H3(SiMe3)(SiMe2NtBu-κN)}Cl(NtBu)]
the cyclopentadienido ring remaining unaltered.
(11) with evolution of HCl. Furthermore, the addition of
Scheme 2.
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M. Gómez, P. Gómez-Sal, J. M. Hernández
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Scheme 3.
one equivalent of ethylenediamine and two equivalents of three and five resonances for the C5H3(SiClMe2)(SiMe3)
NEt3 to toluene solutions of the tetrachloro complexes 3 ring protons and carbons are observed, respectively.
and 4 gives, after separation of the ammonium salt formed,
Although the structures of complexes 7–10 in the solid
the pseudo-octahedral trichloro species [M{η5-C5H3- state have not been determined, we assume them to be
(SiMe3)[SiMe2N(CH2)2NH2-κ2N,N]}Cl3] (M = Nb 12, Ta monomers that are pseudo-tetrahedral and isostructural
13). However, a mixture of complexes 7 and 11 was ob- with other half-sandwich imido group 5 metal deriva-
tained upon treatment of 3 with two equivalents of tives.[6b,6d,6e] Their formulation as dichloroimido complexes
LiNHtBu.
is supported by analytical and spectroscopic data (see Ex-
Complexes 3–13 are soluble in most organic solvents, in- perimental Section) according to the behavior expected for
cluding saturated hydrocarbons. They are extremely air- three-legged piano-stool species.
and moisture-sensitive, so rigorously dried solvents and
Complex 11 is a disymmetric molecule due to the
handling under dry inert atmosphere were found to be im- enantiotopic faces of the cyclopentadienido ring and the
1
perative for successful preparations. Their spectroscopic niobium atom. Its H NMR spectrum shows a singlet for
data (see Experimental Section) are in agreement with the the equivalent methyl protons of the SiMe3 substituent, two
proposed structures. The IR spectra show the characteristic singlets for the inequivalent methyl groups bonded to the
absorptions for
a
cyclopentadienido ring (νC–H
≈
silicon in the SiClMe2 moiety, and three low-field multiplets
839 cm–1)[15] and the trimethylsilyl substituent [δs(CH3) ≈ for the ring protons due to the presence of the chiral ni-
[6a,13]
1254 cm–1].[6f,15] Complexes 5 and 6 show νCϵN
at obium center. In addition, three methylsilyl resonances, two
around 2221 cm–1, whereas the imido complexes show the NtBu signals, and five ring carbon resonances appear in the
[6,15,16]
νM=N
IR absorption at about 1348 cm–1. The M–C, 13C{1H} NMR spectrum.
M–N, and N–H stretching vibrations are observed at ν ≈
The trichloro complexes 12 and 13 show a similar NMR
behavior to that discussed above for 11, and all these ansa
˜
469,[6a,17] 594,[6d] and 3248 cm–1,[6a,18] respectively.
1
The H NMR spectra of complexes 3 and 4 show the compounds exhibit a characteristic 13C signal due to the
expected resonances for the methyl groups bonded to sili- ring carbon C1–SiClMe2 [δ = 110 (11), 106 (12), 105.2 ppm
con. Three broad multiplets corresponding to an ABC spin (13)], which is shifted upfield with respect to the other ring
system are observed for the cyclopentadienido ring protons. carbon resonances.[3h,19]
These assignments were confirmed by the 13C{1H} NMR
spectra. The NMR spectroscopic data of adducts 5 and 6
are in agreement with the expected behavior for pseudo-
Conclusions
octahedral compounds[6a,13] with the cyclopentadienido
ring and the isocyanide ligand mutually trans. The o-meth-
The tetrachlorobis(silyl)cyclopentadienidoniobium and
ylphenyl isocyanide groups are equivalent and, in addition, -tantalum complexes [M{η5-C5H3(SiClMe2)(SiMe3)}Cl4]
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SiClMe2), –0.04 ppm (s, 18 H, SiMe3). 13C{1H} NMR ([D6]ben-
zene, 25 °C): I (major): δ = 147.3 (C3), 143.2, 136.7, 135.2, 71.5 (br.,
C1 of C5 ring), 1.8, 1.4 (SiClMe2), –0.77 (SiMe3), –0.83 ppm
(SiMe3); II (minor): δ = 147.1 (C3), 137.5, 135.3, 133.6, 71.5 (br.,
C1 of C5 ring), 2.7 (SiClMe2), –0.7 ppm (SiMe3). 29Si NMR ([D6]-
benzene, 25 °C): I (major): δ = 19.7 (SiClMe2), –1.0 (SiMe3),
–10.4 ppm (SiMe3); II (minor): δ = 14.4 (SiClMe2), –1.9 ppm
(SiMe3).
(M = Nb 3, Ta 4) have been prepared by a conventional
reaction between MCl5 and C5H3(SiClMe2)(SiMe3)2 (1). Its
Lewis acid character has been established by reaction with
isocyanides to give [M{η5-C5H3(SiClMe2)(SiMe3)}Cl4L]
(M = Nb 5, Ta 6; L = 2,6-Me2C6H3NC), while in the pres-
ence of stoichiometric amounts of amines or lithium amides
the dichloroimido and amidochloroimido complexes
[M{η5-C5H3(SiClMe2)(SiMe3)}Cl2(NR)] (R = tBu, M =
Nb 7, Ta 8; R = Me, M = Nb 9) and [Ta{η5-C5H3-
(SiClMe2)(SiMe3)}Cl(NHtBu)(NtBu)] (10), respectively, are
isolated. In addition, the constrained-geometry niobium de-
rivative [Nb{η5-C5H3(SiMe2NtBu-κN)(SiMe3)}Cl(NtBu)]
(11) can be prepared by treatment of the tetrachloro com-
pound with four equivlents of tBuNH2, whereas with ethyl-
enediamine the pseudo-octahedral trichloro complexes
[M{η5-C5H3(SiMe2NCH2CH2NH2-κ2N,N)(SiMe3)}Cl3] (M
= Nb 12, Ta 13) were obtained.
[C5H3(SiMe2NHtBu)(SiMe3)2] (2):
A solution of 1 (10.00 g,
33.00 mmol) in hexane (150 mL) was treated with tert-butylamine
(4.83 g, 66.00 mmol) at room temperature. The reaction mixture
was stirred for 20 h and then the resulting suspension was filtered.
The solvent was evaporated to dryness to give an orange oil, which
was identified as compound 2. Yield: 7.95 g (90%). 1H NMR ([D6]-
benzene, 25 °C): δ = 7.00 (m, 1 H, C5H3), 6.85 (m, 1 H, C5H3),
6.51 (m, 1 H, C5H3), 1.17 (s, 9 H, tBu), 0.36 (s, 6 H, Si-
Me2NHtBu), –0.02 ppm (s, 18 H, SiMe3); NH signal not detected.
13C{1H} NMR ([D6]benzene, 25 °C): δ = 146.7 (C3), 145.3, 136.2,
135.3, 60 (C1 of C5 ring), 49.6 (CMe3), 33.9 (CMe3), 2.0 (SiMe2),
–0.5 ppm (SiMe3).
[Nb{η5-C5H3(SiClMe2)(SiMe3)}Cl4] (3): Compound
7.40 mmol) was added to suspension of NbCl5 (2.00 g,
1 (2.24 g,
Experimental Section
a
7.40 mmol) in toluene (150 mL) at 0 °C. The reaction was slowly
warmed at room temperature and stirred for 20 h. After filtration,
the resulting solution was concentrated to about 25 mL and cooled
to –20 °C to give a dark red microcrystalline solid which was char-
General: All reactions and manipulations were carried out under
argon using standard Schlenk-tube and globe-box techniques. Sol-
vents were refluxed in the presence of an appropriate drying agent
and distilled and degassed prior use: [D6]benzene and hexane (Na/
K alloy), [D]chloroform (NaH), tetrahydrofuran (Na/benzophe-
none), dichloromethane (P2O5), and toluene (Na). Bis(trimethylsi-
lyl)cyclopentadienide[7d] was synthesized as described previously,
while LiNHtBu was prepared by treatment of tBuNH2 with LinBu.
Reagent-grade chemicals were purchased from commercial sources
and used without further purification: SiClMe3, SiCl2Me2,
tBuNH2, TaCl5, LinBu (1.6  in hexanes), LiNMe2, NEt3, and
H2N–(CH2)2–NH2 from Aldrich, and NbCl5 from Fluka. Infrared
spectra were recorded with a Perkin–Elmer Spectrum 2000 spectro-
acterized as 3. Yield: 3.10 g (90%). IR (KBr): ν = 3091 cm–1 w,
˜
1397 m, 1262 vs, 1089 m, 839 vs, 488 vs, 455 s. 1H NMR ([D1]chlo-
roform, 25 °C): δ = 7.49 (br., 1 H, C5H3), 7.41 (br., 1 H, C5H3),
7.20 (br., 1 H, C5H3), 0.92 (s, 6 H, SiClMe2), 0.43 ppm (s, 9 H,
SiMe3). 13C{1H} NMR ([D1]chloroform, 25 °C): δ = 146.6 (C1),
139.7 (C3), 134, 133.6, 133.2 (C5H3), 1.9 (SiClMe2), –0.6 ppm
(SiMe3). C10H18Cl5NbSi2 (464.60): calcd. C 25.85, H 3.90; found
C 25.78, H 3.63.
[Ta{η5-C5H3(SiClMe2)(SiMe3)}Cl4] (4): A mixture of equimolar
amounts of 1 (2.53 g, 8.36 mmol) and freshly sublimed TaCl5
(3.00 g, 8.36 mmol) in dichloromethane (200 mL) was stirred at
room temperature for 36 h in a sealed ampoule. After the ampoule
was opened, the suspension was filtered and the resulting green
solution was concentrated to about 25 mL and cooled to –20 °C to
give 4 as a green microcrystalline solid. Yield: 3.23 g (70%). IR
1
photometer (4000–400 cm–1) with samples as KBr pellets. H and
13C{1H} NMR spectra were recorded with a “Unity 300” or a
“Mercury VX 300” (Varian NMR Systems) spectrometer; chemical
1
shifts are referenced to the H (δ = 7.15 and 7.24 ppm) and 13C (δ
= 128 and 77 ppm) residual resonances of [D6]benzene and [D1]-
chloroform, respectively. Microanalyses (C,H,N) were performed
with a LECO CHNS 932 microanalyzer.
(KBr): ν = 3093 cm–1 w, 1393 m, 1252 vs, 1093 s, 831 vs, 497 vs, 455
˜
s. 1H NMR ([D1]chloroform, 25 °C): δ = 7.32 (m, 1 H, C5H3), 7.23
(m, 1 H, C5H3), 7.00 (m, 1 H, C5H3), 0.91 (s, 6 H, SiClMe2),
0.42 ppm (s, 9 H, SiMe3). 13C{1H} NMR ([D1]chloroform, 25 °C):
δ = 142.5 (C1), 131.6 (C3), 131.1, 130.9, 130.8 (C5H3), 2.0
(SiClMe2), –0.5 ppm (SiMe3). C10H18Cl5Si2Ta (552.64): calcd. C
21.73, H 3.28; found C 21.65, H 3.13.
[M{η5-C5H3(SiClMe2)(SiMe3)}Cl4(CNAr)] [Ar = 2,6-Me2C6H3; M
= Nb (5), Ta (6)]: 2,6-Me2C6H3NC (0.17 g, 1.30 mmol) was added
to a toluene (70 mL) solution of 3 (0.60 g, 1.30 mmol) or 4 (0.72 g,
1.30 mmol) under rigorously anhydrous conditions. The mixture
was stirred for 4 h and then filtered. Concentration and cooling of
the filtrate gave 5 and 6 as rose (5) and green (6) microcrystalline
solids.
[C5H3(SiClMe2)(SiMe3)2] (1): A 1.6  hexane solution of LinBu
(62.5 mL, 100 mmol) was added dropwise at 0 °C to a solution of
freshly distilled C5H4(SiMe3)2 (21.02 g, 100 mmol) in hexane
(400 mL). The reaction mixture was slowly warmed to room tem-
perature and stirred for 20 h to afford a white precipitate, which,
after filtration, was washed with hexane (2ϫ100 mL), dried under
vacuum, and identified as LiC5H3(SiMe3)2 (19.45 g, 90.00 mmol,
90%).
A suspension of LiC5H3(SiMe3)2 (19.45 g, 90.00 mmol) in tetra-
hydrofuran (300 mL) was treated with SiCl2Me2 (10.92 mL,
90.00 mmol) at –78 °C. The reaction mixture was then warmed to
room temperature and stirred for 20 h. After filtration, the solvent
was removed by evaporation under vacuum and the residue ex-
tracted with hexane (2ϫ100 mL). The solvent was again removed
to give a yellow oil, which was characterized as compound 1
(23.18 g, 80.00 mmol, 85%). 1H NMR ([D6]benzene, 25 °C): I
5: Yield: 0.70 g (90%). IR (KBr): ν = 3100 cm–1 w, 2957 m, 2218 s,
˜
1
1625 m, 1473 m, 1401 m, 1255 vs, 1089 s, 842 vs, 484 vs, 455 vs. H
3
NMR ([D1]chloroform, 25 °C): δ = 7.52 (t, JH,H = 2.1 Hz, 1 H,
(major): δ = 6.85 (m, 1 H, C5H3), 6.81 (m, 1 H, C5H3), 6.49 (m, 1 C5H3), 7.41 (t, 3JH,H = 2.1 Hz, 1 H, C5H3), 7.21 (t, 3JH,H = 2.1 Hz,
3
3
H, C5H3), 0.24 (s, 9 H, SiMe3), 0.19 (s, 3 H, SiClMe2), 0.16 (s, 3
H, SiClMe2), 0.07 ppm (s, 9 H, SiMe3); II (minor): δ = 6.95 (m, 1
1 H, C5H3), 7.25 (t, JH,H = 7.8 Hz, 1 H, p-C6H3), 7.11 (d, JH,H
= 7.8 Hz, 2 H, m-C6H3), 2.54 (s, 6 H, C6H3Me2NC), 0.95 (s, 3 H,
H, C5H3), 6.90 (m, 1 H, C5H3), 6.46 (m, 1 H, C5H3), 0.54 (s, 6 H, SiClMe2), 0.88 (s, 3 H, SiClMe2), 0.41 ppm (s, 9 H, SiMe3).
Eur. J. Inorg. Chem. 2006, 5106–5114
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5111

M. Gómez, P. Gómez-Sal, J. M. Hernández
13C{1H} NMR ([D1]chloroform, 25 °C ): δ = 195 (CN), 142.4, tracted with hexane (2ϫ10 mL). Concentration and cooling of the
FULL PAPER
139.2, 139, 138.4, 136.8 (C5H3), 130.5 (C2,6), 129 (C1), 128.1 (C3,5),
125.3 (C4, C6H3Me2NC), 18.4 (C6H3Me2NC), 3.02, 2.97
(SiClMe2), 0.03 ppm (SiMe3). C19H27Cl5NNbSi2 (595.775): calcd.
C 38.30, H 4.57, N 2.35; found C 38.49, H 4.65, N 2.30.
filtrate produced 9 as a brown solid. Yield: 0.10 g (37%). 1H NMR
([D6]benzene, 25 °C): δ = 6.85 (m, 1 H, C5H3), 6.34 (m, 1 H, C5H3),
6.27 (m, 1 H, C5H3), 3.31(s, 3 H, NMe), 0.55 (s, 3 H, SiClMe2),
0.53 (s, 3 H, SiClMe2), 0.17 ppm (s, 9 H, SiMe3). 13C{1H} NMR
([D6]benzene, 25 °C):
δ = 129.5, 122.7, 122.5, 122.1, 121.6
6: Yield: 0.62 g (70%). IR (KBr): ν = 3098 cm–1 w, 2954 m, 2223 s,
˜
(C5H3), 54.3 (NMe), 3.2, 2.7 (SiClMe2), –0.3 ppm (SiMe3).
C11H21Cl3NSi2Ta (422.733): calcd. C 31.25, H 5.01, N 3.31; found
C 31.12, H 4.94, N 3.25.
1629 s, 1474 m, 1403 m, 1252 vs, 1091 s, 840 vs, 490 vs, 457 s. 1H
NMR ([D1]chloroform, 25 °C): δ = 7.23 (t, 1 H), 7.20 (t, 1 H), 6.88
(t, 3JH,H = 2.1 Hz, 1 H, C5H3), 7.10 (m, 3 H, C6H3Me2NC), 2.52 (s,
6 H, C6H3Me2NC), 0.99 (s, 3 H, SiClMe2), 0.88 (s, 3 H, SiClMe2),
0.41 ppm (s, 9 H, SiMe3). C19H27Cl5NSi2Ta (683.817): calcd. C
33.37, H 3.98, N 2.05; found C 33.17, H 3.83, N 2.00.
[Ta{η5-C5H3(SiClMe2)(SiMe3)}Cl(NHtBu)(NtBu)] (10): A toluene
(15 mL) solution of LiNHtBu (0.06 g, 0.81 mmol) was slowly
added to a solution of 4 (0.30 g, 0.54 mmol) in toluene (60 mL)
and the reaction mixture was stirred overnight. The resulting sus-
pension was filtered and the solvent evaporated to dryness. The
residue was extracted with hexane (2ϫ10 mL) and the solution was
concentrated and cooled to –20 °C to give an oily yellow product
[Nb{η5-C5H3(SiClMe2)(SiMe3)}Cl2(NtBu)] (7): Complex 7 can be
prepared by two synthetic methods.
Method A: tBuNH2 (0.07 g, 0.96 mmol) was added under rigor-
ously anhydrous conditions to a solution of 3 (0.22 g, 0.48 mmol)
in hexane (50 mL) and the reaction mixture was stirred for 15 h.
The solution was filtered and the solvent reduced to dryness to give
an orange oil which was identified as 7.
which was characterized as 10. Yield: 0.09 g (30%). IR (KBr): ν =
˜
3083 cm–1 w, 1403 m, 1358 s, 1261 vs, 1085 vs, 840 vs, 633 m, 504 s,
548 m. 1H NMR ([D1]chloroform, 25 °C): δ = 8.09 (br., 1 H,
NHtBu), 7.05 (m, 1 H, C5H3), 6.79 (m, 2 H, C5H3), 1.24 (s, 18 H,
NHtBu + NtBu), 0.74 (s, 3 H, SiClMe2), 0.72 (s, 3 H, SiClMe2),
0.31 ppm (s, 9 H, SiMe3). 13C{1H} NMR ([D1]chloroform, 25 °C):
δ = 134.8, 127.8, 127.3, 121.6, 121.2 (C5H3), 66.6 (NCMe3), 53.2
Method B: A solution of LiNHtBu (0.04 g, 0.48 mmol) in hexane
(15 mL) was added to a solution of 3 (0.22 g, 0.48 mmol) in hexane
(50 mL) at room temperature. The reaction mixture was stirred for
15 h. Filtration of the supernatant solution from the solid, followed
by concentration to dryness, produced 7 as an orange oil. Yield:
(NHCMe3), 32.1 (NHCMe3
(SiClMe2), –0.1 ppm (SiMe3). C18H37Cl2N2Si2Ta (589.53): calcd. C
36.67, H 6.33, N 4.75; found C 36.47, H 6.43, N 4.57.
+ NCMe3), 3.4 (SiClMe2), 2.9
0.16 g (70%). IR (KBr): ν = 3190 cm–1 w, 2973 m, 1404 m, 1359 m,
˜
1254 vs, 1084 vs, 840 vs, 503 vs, 459 m. 1H NMR ([D6]benzene,
25 °C): δ = 7.04 (m, 1 H, C5H3), 6.49 (m, 1 H, C5H3), 6.45 (m, 1
H, C5H3), 1.13(s, 9 H, NtBu), 0.59 (s, 6 H, SiClMe2), 0.21 ppm (s,
9 H, SiMe3). 13C{1H} NMR ([D6]benzene, 25 °C ): δ = 130 (C1),
129.3 (C3), 124.4, 122.1, 121.6 (C5H3), 70.2 [N(CMe3)], 30.5
[Nb{η5-C5H3(SiMe2NtBu-κN)(SiMe3)}Cl(NtBu)] (11): A solution
of 3 (0.22 g, 0.48 mmol) in hexane (50 mL) was treated with
tBuNH2 (0.14 g, 1.92 mmol). The mixture was stirred at room tem-
perature for 15 h and then filtered. Solvent was removed from the
resulting solution to give 11 as a yellow oil. Yield: 0.14 g (60%).
[N(CMe3)],
3.6,
3.1
(SiClMe2),
0.02 ppm
(SiMe3).
IR (KBr): ν = 3196 cm–1 w, 1448 m, 1359 s, 1250 vs, 1081 vs, 841 vs,
˜
C14H27Cl3NNbSi2 (464.814): calcd. C 36.18, H 5.85, N 3.01; found
C 35.93, H 5.96, N 2.90.
633 m, 499 m. 1H NMR ([D6]benzene, 25 °C): δ = 7.09 (m, 1 H,
C5H3), 6.64 (m, 1 H, C5H3), 6.50 (m, 1 H, C5H3), 1.19 (s, 9 H,
tBu), 1.03 (s, 9 H, tBu), 0.48 (s, 3 H, SiMe2), 0.42 (s, 3 H, SiMe2),
0.27 ppm (s, 9 H, SiMe3). 13C{1H} NMR ([D6]benzene, 25 °C): δ
= 137.3 (C1), 123.1, 122.2, 122.1, 110 (C3, C5H3), 49.9, 48.5
(NCMe3), 33.8, 30.6 (NCMe3), 2.9, 2.7 (SiMe2), 0.15 ppm (SiMe3).
C18H36ClN2NbSi2 (465.03): calcd. C 46.49, H 7.80, N 6.02; found
C 46.38, H 7.69, N 5.92.
[Ta{η5-C5H3(SiClMe2)(SiMe3)}Cl2(NtBu)] (8): LiNHtBu (0.003 g,
0.040 mmol) was added to a solution of 4 (0.20 g, 0.40 mmol) in
[D6]benzene (0.7 mL) in a valved NMR tube under rigorously an-
hydrous conditions. The reaction was monitored by 1H NMR spec-
troscopy until no further changes were observed. The final spec-
trum was indicative of complete transformation of the starting
material and confirmed the formation of 8 in quantitative yield.
Evaporation of the solvent gave 8 as a yellow oil. Yield: 0.17 g
(75%). 1H NMR ([D6]benzene, 25 °C): δ = 7.03 (m, 1 H, C5H3),
6.42 (m, 2 H, C5H3), 1.20 (s, 9 H, NtBu), 0.58 (s, 3 H, SiClMe2),
0.56 (s, 3 H, SiClMe2), 0.2 ppm (s, 9 H, SiMe3). 13C{1H} NMR
([D6]benzene, 25 °C): δ = 127 (C1), 127.3, 122.3, 121.6, 121.2
(C5H3), 66.6 [N(CMe3)], 32.1 [N(CMe3)], 3.4, 3.0 (SiClMe2),
–0.1 ppm (SiMe3). C14H27Cl3NNbSi2 (552.86): calcd. C 30.42, H
4.92, N 2.53; found C 30.44, H 4.71, N 2.37.
Reaction of [Nb{η5-C5H3(SiClMe2)(SiMe3)}Cl4] (3) with LiNHtBu:
LiNHtBu (0.07 g, 0.86 mmol) was added to a solution of 3 (0.20 g,
0.43 mmol) in hexane (30 mL). The reaction mixture was stirred
for 20 h and the solvent was then completely removed under vac-
uum. The resulting oily brown product was characterized as a mix-
1
ture of complexes 7 and 11 by H NMR spectroscopy.
[Nb{η5-C5H3(SiMe2NCH2CH2NH2-κ2N,N)(SiMe3)}Cl3] (12):
A
solution of 3 (1.40 g, 3.00 mmol) in toluene (150 mL) was treated
at room temperature with a solution of ethylenediamine (0.18 g,
3.00 mmol) and triethylamine (0.61 g, 6.00 mmol) in toluene
(20 mL). The reaction mixture was stirred for 48 h and the solvent
was evaporated to dryness. The resulting yellow residue was washed
with cool hexane (2ϫ5 mL) and the solid was dried in vacuo and
identified as 12. The result was similar when 3 was treated with
Reaction of C5H3(SiMe2NHtBu)(SiMe2) (2) with MCl5 (M = Nb,
Ta): C5H3(SiMe2NHtBu)(SiMe2) (0.63 g, 1.85 mmol) was added to
a suspension of NbCl5 (0.50 g, 1.85 mmol) in dichloromethane
(80 mL) and the reaction mixture stirred for 15 h. After filtration,
the volatiles were removed under vacuum to give a yellow oil, which
1
was identified as a mixture of 1 and 7 by H NMR spectroscopy.
2 equiv. of ethylenediamine. Yield: 1.00 g (75%). IR (KBr): ν =
˜
1
With TaCl5 a mixture of 1 and 8 was identified by H NMR spec-
3249 cm–1 m, 3072 w, 1448 w, 1259 vs, 1248 vs, 1089 s, 836 vs, 553 s,
493 m. 1H NMR ([D6]benzene, 25 °C): δ = 6.94 (m, 1 H, C5H3),
6.86 (m, 2 H, C5H3), 4.60 (br, 2 H, CH2CH2NH2), 3.27 (m, 2 H,
NCH2CH2), 2.68 (m, 2 H, NCH2CH2), 0.51 (s, 9 H, SiMe3), 0.08
(s, 3 H, SiMe2), 0.05 ppm (s, 3 H, SiMe2). 13C{1H} NMR ([D6]-
benzene, 25 °C): δ = 140.8 (C1), 133.4, 130.1, 130, 106 [C3, C5H3(Si-
Me2NCH2CH2NH2)(SiMe3)], 59.7 (NCH2CH2), 45.4 (NCH2CH2),
troscopy.
[Nb{η5-C5H3(SiClMe2)(SiMe3)}Cl2(NMe)] (9): A mixture of 3
(0.30 g, 0.64 mmol) and LiNMe2 (0.03 g, 0.64 mmol) was dissolved
in hexane (50 mL) under rigorously anhydrous conditions. The re-
action mixture was stirred for 20 h at room temperature and then
filtered. The filtrate was evaporated to dryness and the residue ex-
5112
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 5106–5114

Bis(silyl)cyclopentadienidoniobium and Tantalum Complexes
FULL PAPER
Table 3. Crystal data and structure refinement for 3 and 5.[a]
3
5
Formula
Fw
C10H18Cl5NbSi2
464.58
C19H27Cl5NNbSi2
595.76
T [K]
λ (Mo-Kα) [Å]
170(2)
0.71073
200(2)
0.71073
Crystal system, space group
a [Å]
b [Å]
c [Å]
monoclinic, P21/n
7.0559(8)
12.0123(13)
20.8380(15)
92.751(6)
1764.1(3)
4
1.749
1.557
928
monoclinic, P21/a
12.936(2)
10.1328(8)
20.959(3)
106.01(1)
2640.8(6)
4
1.498
1.060
β [°]
V [Å3]
Z
ρcalcd [gcm–3]
µ [mm–1]
F(000)
1208
Crystal size [mm]
θ range [deg]
Index ranges
0.4ϫ0.4ϫ0.3
5.05 to 27.50
–9 Յ h Յ 9
–15 Յ k Յ 15
25 Յ l Յ 27
21029
0.43ϫ0.23ϫ0.2
3.03 to 26.02
–15 Յ h Յ 15
–11 Յ k Յ 12
–25 Յ l Յ 25
14858
No. of data collected
No. of unique data [I Ͼ 2σ(I)]
Absorption correction
Max. and min. transmission
Parameters refined
3914 [R(int) = 0.2754]
none
5147 [R(int) = 0.2309]
semiempirical from equivalents
1.446 and 0.774
248
158
1.133
Goodness-of-fit on F2
1.086
Final R indices [I Ͼ 2σ(I)]
R1 = 0.0827
wR2 = 0.1986
R1 = 0.0990
wR2 = 0.2072
1.602 and –2.254
R1 = 0.0924
wR2 = 0.1997
R1 = 0.2300
wR2 = 0.2798
1.544 and –1.364
R indices (all data)
Largest diff. peak and hole [eÅ–3]
[a] R1 = Σ||Fo| – |Fc||/[Σ|Fo|]; wR2 = {[Σw(Fo – Fc)2]/[Σw(Fo2)2]}1/2
.
2
0.05 (SiMe3), –3.9 (SiMe2), –5.4 ppm (SiMe2). 29Si NMR ([D6]- compound 3 with an exposure time of 8 s per frame (5 sets; 391
benzene, 25 °C): –3.9 (SiMe3), –12.3 ppm (SiMe2). frames) and for compound 5 with an exposure time of 36 s per
δ
=
C12H24Cl3N2NbSi2 (451.78): calcd. C 31.90, H 5.35, N 6.20; found
C 32.00, H 5.32, N 5.73.
frame (5 sets; 240 frames). Raw data were corrected for Lorenz and
polarization effects.
Both structures were solved by direct methods, completed by the
subsequent difference Fourier techniques, and refined by full-ma-
trix least-squares on F2 with SHELXL-97.[20] Anisotropic thermal
parameters were used in the last cycles of refinement for the non
hydrogen atoms. The hydrogen atoms were included from geometri-
cal calculations and refined using a riding model. All the calcula-
tions were made using the WINGX system.[21]
[Ta{η5-C5H3(SiMe2NCH2CH2NH2-κ2N,N)(SiMe3)}Cl3] (13):
A
solution of ethylenediamine (0.039 g, 0.65 mmol) and triethylamine
(0.13 g, 1.30 mmol) in toluene (10 mL) was slowly added to a solu-
tion of 4 (0.36 g, 0.65 mmol) in toluene (50 mL) at –78 °C. The
reaction mixture was warmed to room temperature and stirred for
16 h. The volatiles were removed in vacuo and the residue was ex-
tracted with hexane (2ϫ10 mL). The resulting solution was concen-
trated and cooled to –20 °C to afford 11 as a pale-yellow crystalline
CCDC-613239 (for 3) and -613240 (for 5) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
solid. Yield: 0.15 g (40%). IR (KBr): ν = 3247 cm–1 br. s, 3073 w,
˜
1443 w, 1248 vs, 1089 s, 847 vs, 556 s, 492 m. 1H NMR ([D6]ben- tained free of charge from The Cambridge Crystallographic Data
zene, 25 °C): δ = 6.79 (d, 3JH,H = 2.1 Hz, 1 H, C5H3), 6.67 (d, 3JH,H Centre via www.ccdc.cam.ac.uk/data_request/cif.
= 2.1 Hz, 2 H, C5H3), 4.28 (br, 2 H, CH2CH2NH2), 3.54 (m, 2 H,
CH2CH2NH2), 2.63 (m, 2 H, CH2CH2NH2), 0.51 (s, 9 H, SiMe3),
Acknowledgments
0.12 (s, 3 H, SiMe2), 0.09 ppm (s, 3 H, SiMe2). 13C{1H} NMR
([D6]benzene, 25 °C): δ = 131.3 (C1), 129.3, 126.4, 125.6, 105.2 (C3,
C5H3), 55.4, 45.3 (CH2CH2NH2), 1.4 (SiMe3), 0.4 (SiMe2), 0.2 ppm
(SiMe2). 29Si NMR ([D6]benzene, 25 °C): δ = –4.5 (SiMe3),
–13.2 ppm (SiMe2). C12H24Cl3N2Si2Ta (539.82): calcd. C 26.70, H
4.48, N 5.19; found C 26.55, H 4.33, N 5.25.
We thank the MEC (project CTQ 2006-04540/BQU), the CAM
(project S-0505/PPQ/0328-02), and the Universidad de Alcalá (pro-
ject GC 2005/94) for their financial support of this research.
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perimental details of the crystal structure determinations are given
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were performed at low temperature (see Table 3), in the case of
Eur. J. Inorg. Chem. 2006, 5106–5114
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5113

M. Gómez, P. Gómez-Sal, J. M. Hernández
FULL PAPER
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Received: July 4, 2006
Published Online: October 27, 2006
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