Synthesis and reactivity of monocyclopentadienyltantalum(V) siloxide complexes

Article abstract of DOI:10.1002/ejic.200800229

The new tantalum siloxide complex [TaCp*Me₃(OSiPh ₃)] (1; Cp* = η⁵-C₅Me₅) has been synthesized. The reaction of complex 1 with isocyanides yields the respective azatantalacyclopropanes [TaCp*(η²-Me ₂CNxylyl)Me(OSiPh₃)] (2; xylyl = 2,6-dimethylphenyl) and [TaCp*(η²-Me₂CNtBu)Me(OSiPh₃)] (3). The molecular structure of complex 2 has been established by X-ray diffraction. Complex 2 reacts with a second mol-equiv. of 2,6-xylyl isocyanide to yield [TaCp*(Nxylyl)-[N(xylyl)CMe=CMe₂)(OSiPh₃)] (4). The reaction of 1 with carbon monoxide gives [TaCp*(O)(OCMe=CMe ₂)(OSiPh₃)] (5), whereas 1 reacts with B(C ₆F₅)₃ to give the corresponding cationic compound [TaCp*Me₂(OSiPh₃)][MeB(C₆F ₅)₃] (6). Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800229

FULL PAPER
DOI: 10.1002/ejic.200800229
Synthesis and Reactivity of Monocyclopentadienyltantalum(V) Siloxide
Complexes
Ana Conde,[a] Rosa Fandos,*[a] Antonio Otero,*[b] Ana Rodríguez,[c] and Pilar Terreros[d]
Keywords: Cyclopentadienyl ligands / Tantalum / Silicon
The new tantalum siloxide complex [TaCp*Me3(OSiPh3)] (1;
mol-equiv. of 2,6-xylyl isocyanide to yield [TaCp*(Nxylyl)-
Cp* = η5-C5Me5) has been synthesized. The reaction of com- [N(xylyl)CMe=CMe2)(OSiPh3)] (4). The reaction of 1 with
plex 1 with isocyanides yields the respective azatantalacyclo-
propanes [TaCp*(η2-Me2CNxylyl)Me(OSiPh3)] (2; xylyl =
2,6-dimethylphenyl) and [TaCp*(η2-Me2CNtBu)Me(OSiPh3)]
(3). The molecular structure of complex 2 has been estab-
lished by X-ray diffraction. Complex 2 reacts with a second
carbon monoxide gives [TaCp*(O)(OCMe=CMe2)(OSiPh3)]
(5), whereas 1 reacts with B(C6F5)3 to give the corresponding
cationic compound [TaCp*Me2(OSiPh3)][MeB(C6F5)3] (6).
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
lum siloxide derivative [TaCp*Me3(OSiPh3)] and its
reactivity with unsaturated organic molecules and with
B(C6F5)3.
Introduction
Oxygen-donor Lewis bases such as alkoxides or aryl-
oxides have been extensively used as versatile ligands for
transition metals since the appropriate substitution patterns
allow for an important modification of the steric and elec-
tronic requirements. More recently, siloxide groups have
been widely used as ligands because well-defined and solu-
ble metallasiloxanes[1,2] are analogous to the active centers
in silica-grafted heterogeneous catalysts and therefore can
be used to facilitate the understanding of the situation in
solid materials or as precursors. These complexes are also
precursors to metal oxides and silicates in sol-gel and re-
lated processes,[3] and have applications as catalysts in olefin
polymerization[4] and olefin metathesis reactions,[5] amongst
others. The heterogenization of well-defined homogeneous
catalysts is a field of growing interest because it offers op-
portunities to combine the advantages of both supported
and homogeneous catalysts.[6]
Results and Discussion
The tantalum derivative [TaCp*Me4] reacts with 1 mol-
equiv. of triphenylsilanol in toluene at room temperature to
form the alkyltantalum siloxide complex 1 in a protonolysis
process (Scheme 1). Complex 1 is an air-sensitive yellow
solid that is soluble in the most commonly used aprotic or-
ganic solvents. It was characterized by the usual analytical
and spectroscopic techniques.
In spite of the growing interest in the chemistry of metal
siloxide compounds only a few monocyclopentadienyl-
tantalum complexes with siloxide ligands have been re-
ported so far.[7] Herein we describe the synthesis of a tanta-
Scheme 1.
1
The H NMR spectrum of 1 shows two singlets at δ =
0.66 and 0.72 ppm, which were assigned to the two methyl
groups bonded to the tantalum center in the trans positions
and to the methyl group trans to the siloxide moiety, respec-
tively. The Cp* group gives rise to a singlet at δ = 1.61 ppm,
whereas the aromatic protons appear as multiplets at δ =
7.15 and 7.80 ppm. The 13C NMR spectrum indicates that
the three phenyl groups bonded to the silicon atom are in
the same chemical environment.
In order to test the reactivity of 1 we studied its behavior
toward several unsaturated organic molecules. Migratory
insertion of molecules such as carbon monoxide[8] or isocy-
anides[9] into alkyl–metal bonds, and the reactivity of the
resulting acyl–metal and iminoacyl–metal functions,[10] are
[a] Departamento de Química Inorgánica, Orgánica y Bioquímica,
Universidad de Castilla-La Mancha, Facultad de Ciencias del
Medio Ambiente,
Avda. Carlos III, s/n, 45071 Toledo, Spain
[b] Departamento de Química Inorgánica, Orgánica y Bioquímica,
Universidad de Castilla-La Mancha, Facultad de Químicas,
Campus de Ciudad Real,
Avda. Camilo José Cela, 10, 13071 Ciudad Real, Spain
[c] Departamento de Química Inorgánica, Orgánica y Bioquímica,
Universidad de Castilla-La Mancha, ETS Ingenieros Industria-
les, Campus de Ciudad Real,
Avda. Camilo José Cela, 3,13071 Ciudad Real, Spain
[d] Instituto de Catálisis y Petroleoquímica, CSIC,
Cantoblanco, 28049 Madrid, Spain
3062
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Monocyclopentadienyltantalum(V) Siloxide Complexes
among the most important organometallic reactions, with
A single-crystal X-ray diffraction study of complex 2 was
many synthetic applications because of the C–C bond for- carried out in order to accurately define the bonding char-
mation under mild reaction conditions. Complex 1 reacts acteristics of the η2-imine group. The molecular structure
readily with 1 equiv. of xylyl or tert-butyl isocyanide, at of complex 2 is depicted in Figure 1 and selected bond
room temperature, to yield the corresponding azatantalacy- lengths and angles are listed in Table 1.
clopropane complexes 2 and 3, respectively (Scheme 2).
Complex 2 was isolated as yellow crystals in 86% yield,
whereas compound 3 was isolated with a yield of 74% as an
orange microcrystalline compound. Both compounds were
characterized by the usual analytical and spectroscopic
techniques.
Scheme 2.
Figure 1. ORTEP diagram of [TaCp*(η2-Me2CNxylyl)Me(OSiPh3)]
(2).
The spectroscopic data indicate that the structure of both
derivatives is analogous. As an example, the 1H NMR spec-
Table 1. Bond lengths [Å] and angles [°] for 2.
trum of 3 shows singlets at δ = 0.82, 1.28, and 1.73 ppm
due to the methyl group bonded to the tantalum atom, to
the tert-butyl moiety, and to the Cp* ligand, respectively.
The inserted methyl groups give rise to two singlets at δ =
1.84 and 2.15 ppm, in agreement with their different chemi-
cal environments, whereas the aromatic proton signals ap-
pear at δ = 7.15 and 7.75 ppm. These data are in agreement
Ta(1)–O(1)
Ta(1)–N(1)
Ta(1)–C(1)
Ta(1)–C(2)
Ta(1)–C(31)
Ta(1)–C(32)
Ta(1)–C(33)
Ta(1)–C(34)
Ta(1)–C(35)
N(1)–C(5)
N(1)–C(2)
C(2)–C(4)
1.919(5)
1.938(7)
2.171(8)
2.206(8)
2.446(7)
2.455(8)
2.485(8)
2.540(8)
2.533(8)
1.42(1)
O(1)–Ta(1)–N(1)
O(1)–Ta(1)–C(1)
N(1)–Ta(1)–C(1)
O(1)–Ta(1)–C(2)
N(1)–Ta(1)–C(2)
C(1)–Ta(1)–C(2)
Si(1)–O(1)–Ta(1)
C(5)–N(1)–C(2)
C(5)–N(1)–Ta(1)
C(2)–N(1)–Ta(1)
N(1)–C(2)–C(4)
N(1)–C(2)–C(3)
C(4)–C(2)–C(3)
N(1)–C(2)–Ta(1)
C(4)–C(2)–Ta(1)
C(3)–C(2)–Ta(1)
117.9(3)
105.3(3)
105.5(3)
91.3(3)
40.7(3)
84.9(3)
169.8(3)
124.6(7)
155.4(6)
79.5(5)
115.9(8)
114.0(8)
109.8(8)
59.8(4)
with the coordination mode proposed in Scheme 2. The 13
C
NMR spectrum shows a signal at δ = 64.5 ppm which we
tentatively assign to the carbon atom of the imine ligand.
This chemical shift is in agreement with that expected for
an azametallacycle and is consistent with the values re-
ported for early-d-block η2-imine compounds.[11] These
data indicate the selective adoption of either of the two geo-
metries shown in Scheme 3.
1.46(1)
1.51(1)
1.52(1)
C(2)–C(3)
125.7(7)
121.1(7)
The molecular structure shows that complex 2 is a mono-
nuclear compound in which the tantalum center is coordi-
nated to the Cp* ligand, the siloxide moiety, a methyl
group, and to the η2-imine function, which is side-on
bonded to the tantalum atom. It can also be seen that the
CN vector of the imine group is oriented in such a way that
the nitrogen atom points toward the Cp* ligand. Hence,
isomer I (Scheme 3) is preferred in the solid state and, ac-
cording to the NOESY experiments, also in solution.
The Ta(1)–C(2) bond [2.206(8) Å] is slightly longer than
Scheme 3.
A NOESY experiment was carried out to determine the
1
orientation of the imine fragment. The response in the H the Ta(1)–C(1) bond [2.171(8) Å] and is comparable to
NOESY-1D experiment from the Cp* ligand upon irradiat- those found in [TaCp*Me2{η2-Me2CN(C6H3Me2)}]
ing the methyl groups of the xylyl or tert-butyl moieties [2.209(6) Å].[12] The value of the C(2)–N(1) bond length
indicates that orientation I is preferred in solution. The for- [1.463(10) Å] is within the range expected for a C–N single
mation of 2 and 3 presumably takes place by a pathway bond. The Ta(1)–O(1) distance [1.919(5) Å] is longer than
involving an initial insertion of isocyanide into one Me–Ta that found in other electronically more unsaturated
bond to give the corresponding mono(η2-iminoacyl) com- complexes such as [Ta{OSi(C6H4Me-2)3}C14·Et2O]
plex, followed by a second methyl migration to give an η2- [1.812(3) Å].[13] The Si(1)–O(1)–Ta(1) angle [169.8(3)°] is
imine derivative.[12]
somewhat smaller than that found in the above tantalum
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A. Conde, R. Fandos, A. Otero, A. Rodríguez, P. Terreros
FULL PAPER
derivative [172.1(2)°], where the near linearity of the Ta–O– agreement with the structure proposed in Scheme 5.[15]
Si chain has been related to the presence of a significant O– However, the IR spectrum of compound 5 does not show
Ta pπ-dπ interaction.
strong absorptions between 1000 and 700 cm–1 which could
Complex 2 reacts with a second mol-equiv. of 2,6-xylyl be assigned to a Ta=O stretching frequency, therefore 5 is
isocyanide to give the alkenylamido complex [TaCp*- not a discrete monomer but an oligomer containing Ta–O–
(Nxylyl){N(xylyl)CMe=CMe2}(OSiPh3)] (4), which was Ta bonds.
isolated in a 44% yield as a yellow microcrystalline solid
1
(Scheme 4). The H and 13C NMR spectra of this complex
indicate that seven different types of methyl groups are pres-
ent in the molecule. Furthermore, the 13C NMR spectrum
shows signals at δ = 115.1 and 133.8 ppm due to the olefinic
carbon atoms, in agreement with the formation of an alken-
ylamido moiety.[14]
Scheme 5.
Complexes 4 and 5 are probably formed through a
mechanism analogous to that proposed previously for
(alkenylamido)- or (alkenylalkoxido)tantalum deriva-
tives[14,15] (Scheme 6). Thus, insertion of a second mol-
equiv. of CO or isocyanide into either the Me–Ta bond or
the tantalacycle carbon bond of the (ketone)- or (imine)-
tantalum complex, respectively, would yield intermediates
A or B. Both intermediates would furnish intermediate C,
Scheme 4.
Complex 4 can also be obtained by treatment of 1 with which then forms derivatives 4 or 5.
2 mol-equiv. of 2,6-xylyl isocyanide (Scheme 4). In contrast
The synthesis of stable cationic alkyl complexes of the
to the reactivity observed for complex 2, complex 3 does early transition metals is an objective of prime importance
not react with an excess of tBuNC under the same experi- in organometallic chemistry as these compounds are active
mental conditions.
in many catalytic processes.[16] Thus, addition of 1 equiv. of
Complex 1 also reacts readily with an excess of CO at B(C6F5)3 to a toluene solution of compound 1 affords an
room temperature to give the (alkenylalkoxido)(oxido) com- insoluble brownish oil which was characterized as the
plex [TaCp*(O)(OCMe=CMe2)(OSiPh3)] (5; Scheme 5), ionic derivative [TaCp*Me2(OSiPh3)][MeB(C6F5)3] (6)
which was isolated in 51% yield as a yellow crystalline so- (Scheme 7). Compound 6 is soluble in dichloromethane and
1
lid. Its H NMR spectrum shows four singlets at δ = 1.52, CDCl3 and is highly unstable in the presence of traces of
1.60, 1.83, and 2.03 ppm, in a 1:1:1:5 ratio, which were as- water.
signed to the three different methyl groups of the coordi-
1
The H and 13C NMR spectra of compound 6 in CDCl3
nated alkenylalkoxido and to the Cp* ligand. The aromatic show one resonance for the two equivalent Me–Ta groups
proton signals of the siloxide group appear at δ = 7.35 and of a pseudo-tetrahedral cation. A broad signal for the
7.65 ppm. The 13C NMR spectrum of 5 shows signals at δ methyl group of the borate anion was also observed in the
= 107.5 and 146.5 ppm for the olefinic carbon atoms of 1H NMR spectrum. The resonances in the 19F NMR spec-
the OC(Me)=CMe2 group. These spectroscopic data are in trum are in agreement with the formation of the
Scheme 6.
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Eur. J. Inorg. Chem. 2008, 3062–3067

Monocyclopentadienyltantalum(V) Siloxide Complexes
Scheme 7.
1
700 (s), 591 (w), 512 (s) cm–1. H NMR (C6D6, room temp.): δ =
[MeB(C6F5)3] anion, the difference between the m- and p-
C6F5 values (∆δ = 2.5 ppm) being consistent with the pres-
ence of separate cationic and anionic [MeB(C6F5)3]– moie-
ties.[17]
0.96 (s, 3 H, Ta-Me), 1.49 (s, 3 H, CMe2), 1.61 (s, 15 H, Cp*), 1.98
(s, 6 H, 2,6-Me2C6H3), 2.07 (s, 3 H, CMe2), 6.86 (m, 3 H, Ar), 7.14
(m, 9 H, Ar), 7.80 (m, 6 H, Ar) ppm. 13C{1H} NMR: δ = 10.7
(Cp*), 20.9 (2,6-Me2C6H3), 27.6 (CMe2), 29.8 (CMe2), 39.4 (Ta-
Me), 78.6 (CMe2) 117.4 (Cp*), 124.0 (Ar), 127.9 (Ar), 128.6 (Ar),
129.9 (Ar), 134.3 (Aripso), 136.0 (Ar), 137.2 (Aripso), 151.3 (Aripso
ppm. C40H48NOSiTa (767.89): calcd. C 62.57, H 6.29, N 1.82;
found C 62.09, H 6.49, N 1.66.
)
Conclusions
We have reported the synthesis of several monocyclopen-
tadienyl complexes of tantalum containing a siloxide group
as an ancillary ligand and have studied their reactivity with
several unsaturated organic molecules such as isocyanides
or carbon monoxide. We have also explored the synthesis
of cationic alkyl derivatives.
Synthesis of [TaCp*(η2-Me2CNtBu)Me(OSiPh3)] (3): tBuNϵC
(54.88 µL, 0.485 mmol) was added to a solution of [TaCp*Me3-
(OSiPh3)] (0.309 g, 0.485 mmol) in toluene (15 mL). After 15 min
at room temperature, the solution became orange. The mixture was
filtered and the solvent evaporated to dryness. The residue was ex-
tracted with pentane and the solution cooled to –30 °C to give 3
as an orange microcrystalline solid (yield 0.259 g, 74%). IR (KBr):
ν = 1588 (w), 1428 (s), 1354 (m), 1249 (m), 1201 (m), 1113 (s), 1045
˜
Experimental Section
(w), 1030 (w), 957 (s), 940 (s), 709 (s), 535 (m), 508 (s), 411 (w)
cm–1. 1H NMR (C6D6, room temp.): δ = 0.82 (s, 3 H, Ta-Me), 1.28
(s, 9 H, NCMe3), 1.73 (s, 15 H, Cp*), 1.84 (s, 3 H, CMe2), 2.15 (s,
3 H, CMe2), 7.15 (m, 9 H, Ar), 7.75 (m, 6 H, Ar) ppm. 13C{1H}
NMR: δ = 11.7 (Cp*), 31.7 (CMe2), 32.3 (CMe2), 32.7 (NCMe3),
34.3 (Ta-Me), 61.9 (CMe2), 64.5 (NCMe3), 116.5 (Cp*), 127.8 (Ar),
129.9 (Ar), 135.9 (Ar), 136.9 (Aripso) ppm. C36H48NOSiTa (719.46):
calcd. C 60.07, H 6.71, N 1.94; found C 59.52, H 6.70, N 2.00.
General Procedures: The preparation and handling of the described
compounds was performed with rigorous exclusion of air and
moisture under nitrogen using standard vacuum-line and Schlenk
techniques. All solvents were dried and distilled under nitrogen.
The following reagents were prepared according to literature pro-
cedures: [TaCp*Cl4],[18] [TaCp*Me4].[19] The commercially available
compounds xylyl isocyanide and tert-butyl isocyanide were used as
received from Aldrich. 1H and 13C NMR spectra were recorded
with a 200 Mercury Varian Fourier Transform spectrometer. Trace
amounts of protonated solvents were used as reference, and chemi-
cal shifts are reported in units of ppm relative to SiMe4. IR spectra
were recorded in the region 4000–400 cm–1 with a Nicolet Magna-
IR 550 spectrophotometer as Nujol mulls using PET cells or KBr
pellets.
Synthesis of [TaCp*(Nxylyl){N(xylyl)CMe=CMe2}(OSiPh3)] (R =
2,6-Me2C6H3) (4): xylylNϵC (0.083 g, 0.634 mmol) was added to
a
toluene (15 mL) solution of [TaCp*Me3(OSiPh3)] (0.202 g,
0.32 mmol) and the solution stirred at room temperature for 1 h.
Slow diffusion of pentane into the toluene solution yielded 4 as a
yellow microcrystalline solid (yield 0.124 g, 44%). IR (KBr): ν =
˜
1670 (w), 1589 (w), 1456 (m), 1427 (s), 1376 (w), 1308 (s), 1254 (w),
1188 (w), 1168 (w), 1138 (m), 1004 (s), 929 (s), 919 (s), 868 (m),
Synthesis of [TaCp*Me3(OSiPh3)] (1): Toluene (10 mL) was added
to a mixture of [TaCp*Me4] (0.753 g, 2.0 mmol) and HOSiPh3
(0.553 g, 2.0 mmol) and the mixture stirred at room temperature
for 3 h. The solution was then filtered and the solvent evaporated
under vacuum. The residue was washed with cool pentane to afford
1
762 (m), 743 (m), 703 (s), 531 (w), 514 (s), 500 (s) cm–1. H NMR
(C6D6, room temp.): δ = 1.65 [s, 3 H, C(Me)=CMe2], 1.69 [s, 3 H,
C(Me)=CMe2], 1.81 (s, 15 H, Cp*), 1.96 [s, 3 H, C(Me)=CMe2],
2.13 (s, 9 H, 2,6-Me2C6H3), 2.36 (s, 3 H, 2,6-Me2C6H3), 6.57 (m, 6
H, Ar), 7.13 (m, 9 H, Ar), 7.79 (m, 6 H, Ar) ppm. 13C{1H} NMR:
δ = 12.1 (Cp*), 20.4 (2,6-Me2C6H3), 21.4 (2,6-Me2C6H3), 21.7 (2,6-
Me2C6H3), 22.2 [C(Me)=CMe2], 22.9 [C(Me)=CMe2], 23.8
[C(Me)=CMe2], 115.1 [C(Me)=CMe2], 120.1 (Cp*), 122.4 (Ar),
123.6 (Ar), 125.6 (Ar), 127.2 (Ar), 127.7 (Ar), 129.2 (Ar), 129.6
(Ar), 133.8 [C(Me)=CMe2],134.6 (Aripso), 135.0 (Aripso), 136.6 (Ar),
138.2 (Aripso), 152.7 (Aripso), 155.6 (Aripso) ppm. C49H57N2OSiTa
(899.07): calcd. C 65.46, H 6.38, N 3.11; found C 65.26, H 6.34, N
3.20.
1 as a yellow solid (yield 1.02 g, 80%). IR (Nujol/PET): ν = 1589
˜
(w), 1428 (s), 1113 (s), 1001 (m), 952 (s), 931 (s), 705 (s), 651 (w),
1
584 (w), 513 (m) cm–1. H NMR (C6D6, room temp.): δ = 0.66 (s,
6 H, Ta-Me), 0.72 (s, 3 H, Ta-Me), 1.61 (s, 15 H, Cp*), 7.15 (m, 9
H, Ar), 7.80 (m, 6 H, Ar) ppm. 13C{1H} NMR: δ = 11.0 (Cp*),
55.1 (Ta-Me), 56.5 (Ta-Me), 116.8 (Cp*), 128.1 (Ph), 130.1 (Ph),
135.8 (Ph), 136.2 (Phipso) ppm. C31H39OSiTa (636.71): calcd. C
58.48, H 6.16; found C 58.00, H 6.07.
Synthesis of [TaCp*(η2-Me2CNxylyl)Me(OSiPh3)] (2): Toluene
(15 mL) was added to a mixture of [TaCp*Me3(OSiPh3)] (0.290 g,
0.455 mmol) and xylylNϵC (0.059 g, 0.455 mmol) and the solution
stirred at room temperature for 15 min. The solvent was then evap-
orated under vacuum and the residue extracted with pentane. The
solution was cooled to –30 °C to yield 2 as yellow crystals (yield
Synthesis of [TaCp*(O)(OCMe=CMe2)(OSiPh3)] (5): A toluene
(15 mL) solution of [TaCp*Me3(OSiPh3)] (0.189 g, 0.296 mmol)
was placed in a Schlenk tube under CO. The reaction mixture was
left at room temperature for 24 h to yield yellow crystals of com-
plex 5 (yield 0.140 g, 51%). IR (Nujol/PET): ν = 1658 (m), 1261
˜
0.301 g, 86%). IR (KBr): ν = 1589 (w), 1465 (m), 1428 (s), 1374 (m), 1200 (s), 1112 (m), 1001 (w), 937 (s), 651 (m), 584 (m), 517 (s)
˜
(w), 1115 (s), 1004 (m), 991 (m), 945 (s), 920 (s), 865 (m), 763 (m),
cm–1. 1H NMR (CDCl3, room temp.):
δ
=
1.52 [s,
3
H,
Eur. J. Inorg. Chem. 2008, 3062–3067
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. Conde, R. Fandos, A. Otero, A. Rodríguez, P. Terreros
FULL PAPER
OC(Me)=CMe2], 1.60 [s, 3 H, OC(Me)=CMe2], 1.83 [s, 3 H, OC-
charge from The Cambridge Crystallographic Data Center via
(Me)=CMe2], 2.03 (s, 15 H, Cp*), 7.35 (m, 9 H, Ar), 7.65 (m, 6 H, www.ccdc.cam.ac.uk/data_request/cif.
Ar) ppm. 13C{1H} NMR: δ = 10.8 (Cp*), 16.6 [OC(Me)=CMe2],
17.3 [OC(Me)=CMe2], 19.2 [OC(Me)=CMe2], 107.5 [OC(Me)=
CMe2], 119.7 (Cp*), 127.9 (Ar), 129.9 (Ar), 135.4 (Ar), 136.5
(Aripso), 146.5 [OC(Me)=CMe2] ppm. C33H39O3SiTa·0.7C7H8
Acknowledgments
(757.23): calcd. C 60.12, H 5.93; found C 60.24, H 5.84.
We gratefully acknowledge financial support from the Dirección
General de Investigación (MEC), Spain (project CTQ2005-08123-
C02-01/BQU) and the Junta de Comunidades de Castilla-La Man-
cha, Spain (project PBI05-023).
Synthesis of [TaCp*Me2(OSiPh3)][MeB(C6F5)3] (6): A solution of
B(C6F5)3 (0.075g, 0.147 mmol) in toluene (10 mL) was added to
a solution of [TaCp*Me3(OSiPh3)] (0.94g, 0.147 mmol) in toluene
(15 mL) at room temperature. The oil formed after 5 min was sepa-
rated from the solution and characterized as complex 6 (yield
0.112 g, 67%). 1H NMR (CDCl3, room temp.): δ = 0.34 (br. s, 3
H, MeB), 0.90 (s, 6 H, Ta-Me), 1.89 (s, 15 H, Cp*), 7.43 (m, 15 H,
Ar) ppm. 13C{1H} NMR: δ = 11.7 (B-Me), 11.82 (Cp*), 77.7 (Ta-
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Me), 126.8 (Cp*), 129.6 (Ar), 131.4 (Ar), 132.8 (Ar), 135.5 (Aripso
)
ppm. 19F NMR: δ = –132.6 (m, 6 F), –164.8 (m, 3 F), –167.3 (m,
6 F) ppm.
X-ray Structure Determination for 2: Crystals of 2 were obtained
from pentane. Data were collected with a Bruker X8 APEX II
CCD-based diffractometer equipped with a graphite-monochro-
mated Mo-Kα radiation source (λ = 0.71073 Å). The crystal data,
data collection, structural solution, and refinement parameters are
summarized in Table 2. Data were integrated using SAINT[20] and
an absorption correction was performed with the program SAD-
ABS.[21] The structure was solved by direct methods using
SHELXTL,[22] and refined by full-matrix least-squares methods
based on F2. All non-hydrogen atoms were refined with anisotropic
thermal parameters. Hydrogen atoms were placed using a “riding
model” and included in the refinement at calculated positions. The
large residual electron density is probably due to the poor quality
of the crystals. CCDC-673906 contains the supplementary crystal-
lographic data for this paper. These data can be obtained free of
Table 2. Crystal data and structure refinement for 2.
Empirical formula
Formula mass
C40H48NOSiTa
767.83
Temperature [K]
Wavelength [Å]
180(2)
0.71073
Crystal system
Space group
triclinic
P1
¯
a [Å]
b [Å]
c [Å]
α [°]
9.6650(5)
12.8440(7)
16.5020(9)
67.348(3)
β [°]
86.194(3)
68.956(3)
1758.2(2)
γ [°]
Volume [Å3]
Z
2
Density (calculated) [gcm–3]
Absorption coefficient [mm–1]
F(000)
1.450
3.191
780
Crystal size [mm]
θ range for data collection [°]
Index ranges
0.14ϫ0.11ϫ0.09
1.34–26.45
–12ՅhՅ11
–16ՅkՅ16
–20ՅlՅ20
23496
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
Largest diff. peak/hole
7212 [R(int) = 0.1092]
7212/0/407
0.963
R1 = 0.0579, wR2 = 0.1107
2.149/–1.234
3066
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Eur. J. Inorg. Chem. 2008, 3062–3067

Monocyclopentadienyltantalum(V) Siloxide Complexes
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Published Online: May 20, 2008
Eur. J. Inorg. Chem. 2008, 3062–3067
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3067