(Alkyl)- and (alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum complexes

Article abstract of DOI:10.1002/ejic.200600173

Alkylation of [TaCp*Cl₄] (Cp* = η⁵- C₅Me₅) with 3 equiv. of MgCl(CH₂SiMe ₃) gives the chloridotris(trimethylsilylmethyl) complex [TaCp*Cl(CH₂SiMe₃)₃] (1). TaCp*Cl₂Me₂ reacts with 2 equiv. of LiR (R = CH ₂Ph, CH₂SiMe₃) to give the mixed alkyl derivatives [TaCp*Me₂R₂] (R = CH₂Ph, 2, CH₂SiMe₃, 3). The dimethyldineopentyl complex [TaCp*Me₂(CH₂-CMe₃)₂] (4) was obtained by reaction of TaCp*Cl₂-(CH₂CMe ₃)₂ with 2 equiv. of LiMe. The treatment of a toluene solution of TaCp*Cl₂Me₂ with 2 equiv. of neophyllithium in a standard vacuum line gave a mixture of three compounds, [{TaCp*Me₂(CH₂CMe₂Ph)} ₂(μ-O)] (5), [TaCp*Me₂(CH₂CMe ₂-o-C₆H₄-κ²C,C)] (6) and [TaCp*Me(CH₂CMe₂Ph)-(CH₂)] (7), which were identified by NMR spectroscopy. However, when the reaction was carried out under rigorously anhydrous conditions, only complexes 6 and 7 were isolated. A chlorido(trimethylsilylmethyl)(trimethylsilylmethylidene) complex [TaCp*Cl(CH₂SiMe₃)(CHSiMe₃)] (8) was prepared by heating 1 at 60°C, or by leaving it at room temperature for a long time. A 3:2 (9/10) mixture of [TaCp*MeR-(CHSiMe₃)] (R = CH₂SiMe₃, 9; Me, 10) was obtained by thermal treatment of 3, which was accompanied by the evolution of CH₄ and SiMe ₄. However, irradiation of a [D₆]benzene solution of 3 with a sun lamp gave a mixture of 9 and [TaCp*(CH₂SiMe ₃)R(CH₂)] (R = Me, 11; CH₂SiMe₃, 12) in a 2:1:1 (9/11/12) ratio. When a [D₆]benzene solution of 4 was heated at 60°C, a mixture of the (alkyl)(neopentylidene) derivatives [TaCp*MeR(CHCMe₃)] (R = Me, 13; CH₂CMe₃, 14) in a 4:1 (13/14) ratio was detected by NMR spectroscopy, while irradiation with a sun lamp produced a mixture of alkylidene complexes [TaCp*(CH ₂CMe₃)R(CH₂)] (R = Me, 15; CH ₂CMe₃, 16) in a 3:1 (15/16) ratio. On the other hand, the alkylation of TaCp*Cl₂(CH₂CMe₃) ₂ with 2 equiv. of LiCH₂SiMe₃ gave the (alkyl)(alkylidene) complex [TaCp*(CH₂CMe₃)(CH ₂SiMe₃)(CHCMe₃)] (17) with the elimination of SiMe₄, whereas the treatment of TaCp*Cl₂-(CH ₂SiMe₃)₂ with the appropriate reagent gave [TaCp*(CH₂R)(CH₂SiMe₃)(CHR′)] (R = R′ = Ph, 18; R = CMe₂Ph, R′ = SiMe₃, 19) with the elimination of SiMe₄ and CMe₃Ph, respectively. All compounds were studied by IR and NMR spectroscopy, and the molecular structures of complexes 1, 4 and 5 were determined by X-ray diffraction methods. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600173

FULL PAPER
DOI: 10.1002/ejic.200600173
(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum
Complexes
Mikhail V. Galakhov,[a] Manuel Gómez,*[b] Pilar Gómez-Sal,[b] and Patricia Velasco[b]
Dedicated to Prof. Victor Riera on the occasion of his 70th birthday
Keywords: Tantalum / Alkyl / Alkylidene / Cyclopentadienyl ligands
Alkylation of [TaCp*Cl4] (Cp* = η5-C5Me5) with 3 equiv. of
MgCl(CH2SiMe3) gives the chloridotris(trimethylsilylmethyl)
complex [TaCp*Cl(CH2SiMe3)3] (1). TaCp*Cl2Me2 reacts
with 2 equiv. of LiR (R = CH2Ph, CH2SiMe3) to give the mixed
alkyl derivatives [TaCp*Me2R2] (R = CH2Ph, 2; CH2SiMe3,
3). The dimethyldineopentyl complex [TaCp*Me2(CH2-
CMe3)2] (4) was obtained by reaction of TaCp*Cl2-
(CH2CMe3)2 with 2 equiv. of LiMe. The treatment of a tolu-
ene solution of TaCp*Cl2Me2 with 2 equiv. of neophyllithium
in a standard vacuum line gave a mixture of three com-
pounds, [{TaCp*Me2(CH2CMe2Ph)}2(µ-O)] (5), [TaCp*Me2-
(CH2CMe2–o-C6H4-κ2C,C)] (6) and [TaCp*Me(CH2CMe2Ph)-
(CH2)] (7), which were identified by NMR spectroscopy.
However, when the reaction was carried out under rigorously
anhydrous conditions, only complexes 6 and 7 were isolated.
solution of 3 with a sun lamp gave a mixture of 9 and
[TaCp*(CH2SiMe3)R(CH2)] (R = Me, 11; CH2SiMe3, 12) in a
2:1:1 (9/11/12) ratio. When a [D6]benzene solution of 4 was
heated at 60 °C, a mixture of the (alkyl)(neopentylidene) de-
rivatives [TaCp*MeR(CHCMe3)] (R = Me, 13; CH2CMe3, 14)
in a 4:1 (13/14) ratio was detected by NMR spectroscopy,
while irradiation with a sun lamp produced a mixture of
alkylidene complexes [TaCp*(CH2CMe3)R(CH2)] (R = Me,
15; CH2CMe3, 16) in a 3:1 (15/16) ratio. On the other hand,
the alkylation of TaCp*Cl2(CH2CMe3)2 with 2 equiv. of
LiCH2SiMe3
gave
the
(alkyl)(alkylidene)
complex
[TaCp*(CH2CMe3)(CH2SiMe3)(CHCMe3)] (17) with the eli-
mination of SiMe4, whereas the treatment of TaCp*Cl2-
(CH2SiMe3)2
with
the
appropriate
reagent
gave
[TaCp*(CH2R)(CH2SiMe3)(CHRЈ)] (R = RЈ = Ph, 18; R =
CMe2Ph, RЈ = SiMe3, 19) with the elimination of SiMe4 and
CMe3Ph, respectively. All compounds were studied by IR and
NMR spectroscopy, and the molecular structures of com-
plexes 1, 4 and 5 were determined by X-ray diffraction meth-
ods.
A
chlorido(trimethylsilylmethyl)(trimethylsilylmethylidene)
complex [TaCp*Cl(CH2SiMe3)(CHSiMe3)] (8) was prepared
by heating 1 at 60 °C, or by leaving it at room temperature
for
a long time. A 3:2 (9/10) mixture of [TaCp*MeR-
(CHSiMe3)] (R = CH2SiMe3, 9; Me, 10) was obtained by ther-
mal treatment of 3, which was accompanied by the evolution
of CH4 and SiMe4. However, irradiation of a [D6]benzene
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
they are able to catalyse.[3] Further, in combination with
stronger Lewis acids they form highly reactive species that
are important as catalysts in other processes involving ole-
fins.[3b,3c,4–6] Additionally, µ-alkylidene complexes have
been postulated as intermediates in Fischer–Tropsch, olefin
metathesis and Ziegler–Natta catalytic processes.[7]
Preliminary reports from our group have focused on the
ability of tetrachlorido(cyclopentadienyl)niobium and -tan-
talum compounds to coordinate with bulky alkyl substitu-
ents. Thus, the crowding of the coordination sphere of the
metal by the trimethylsilylmethyl group is the basis for the
formation of an alkylidene complex by a spontaneous α-
hydrogen-elimination process.[8] On the other hand, we re-
ported[9] that the use of the 2-[(dimethylamino)methyl]-
phenyl ligand leads to the synthesis of tantalum(V) com-
plexes that can be transformed into new cyclometalated
(alkylidene)tantalum derivatives by the activation of car-
bon–hydrogen bonds in one of the methylamino groups of
Introduction
The study of early-transition-metal compounds in high
oxidation states has been a topic of intense research because
of their applications in organic synthesis and in catalysis.[1]
In particular, metal alkyls and alkylidenes are among the
most studied derivatives. Alkyl derivatives have been exten-
sively used as catalysts for the polymerization of olefins,[1,2]
while the importance of alkylidenes is demonstrated by a
comprehensive study of the olefin metathesis reactions that
[a] Centro de Espectroscopia de RMN, Universidad de Alcalá de
Henares,
Campus Universitario, 28871 Alcalá de Henares, Spain
[b] 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
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Eur. J. Inorg. Chem. 2006, 4242–4253

(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes
FULL PAPER
Scheme 1.
the ligand. More recently, the µ-alkylidene complexes
[(TaCp*CpЈ)2(µ-CHR)2] (Cp* = η5-C5Me5, CpЈ = η5-
C5H4SiMe3, R = C6H5, SiMe3, CMe3) have been prepared
by treatment of the (mixed dicyclopentadienyl)tantalum
compound TaCp*CpЈCl2 with an appropriate amount of
the corresponding alkyllithium.[10]
In this article, we report the preparation of new (alkyl)-
and (alkyl)(alkylidene)mono(pentamethylcyclopentadienyl)-
tantalum(V) complexes. All compounds were studied by
spectroscopic methods. In addition, the molecular struc-
tures of complexes 1, 4 and 5 were determined by X-ray
diffraction.
Results and Discussion
[TaCp*Cl(CH2SiMe3)3] (1) was synthesized in good yield
by the reaction of [TaCp*Cl4] (Cp* = η5-C5Me5) with
Figure 1. ORTEP drawing of compound 1 with thermal ellipsoids
3 equiv. of MgCl(CH2SiMe3) (Scheme 1). In contrast, we
previously reported[8] the preparation of a dialkyl(alkylid-
ene) derivative [TaCp*(CH2SiMe3)2(CHSiMe3)] by the reac-
tion of the tetrachlorido complex with 4 equiv. of an alkyl-
ating reagent. Two absorptions bands were observed in the
at the 50% probability level.
Table 1. Selected bond lengths [Å] and angles [°] for compound 1.[a]
Ta1–Cl1
Ta1–C6
Ta1–C8
Ta1–C2
Ta1–C4
Si1–C6
Si3–C8
Cp1–Ta1–Cl1
Cp1–Ta1–C7
C6–Ta1–C8
C8–Ta1–C7
C7–Ta1–Cl1
Si1–C6–Ta1
Si3–C8–Ta1
2.481(5)
2.137(16)
2.156(16)
2.47(2)
Ta1–Cp1
Ta1–C7
Ta1–C1
Ta1–C3
Ta1–C5
Si2–C7
2.180
IR spectrum of 1 at ν = 1026 and 1243 cm–1, which can be
˜
2.188(14)
2.430(16)
2.52(2)
2.480(19)
1.888(15)
assigned to νC–C(Cp*)[11] and δas(CH3)(SiMe3),[11c] respec-
tively. The NMR spectra of this complex are in agreement
with a C3v local symmetry around the tantalum atom.
The crystal structure of complex 1 (Figure 1) shows a
tantalum atom in a distorted trigonal bipyramidal environ-
ment with the three alkyl groups occupying the equatorial
positions, and the centroid of the pentamethylcyclopen-
tadienyl ring and the chlorine atom at the apical sites. The
tantalum atom is displaced towards the Cp* ring by 0.46 Å
from the equatorial plane containing the three carbon
(alkyl) atoms.[12] The bond lengths for Ta–Cp*(centroid),
Ta–C (average), and Ta–Cl are 2.180, 2.160 and 2.481(1) Å,
respectively (Table 1). The Ta–C(alkyl) distance is in the
range corresponding to normal values for a Ta–C[11d,13,14]
2.49(2)
1.911(18)
1.924(15)
176.84
Cp1–Ta1–C6
Cp1–Ta1–C8
C6–Ta1–C7
C6–Ta1–Cl1
C8–Ta1–Cl1
Si2–C7–Ta1
103.17
103.25
114.4(6)
79.6(5)
76.9(5)
126.4(9)
100.89
111.7(6)
120.3(6)
76.5(4)
127.2(9)
126.9(9)
[a] Cp1 is the centroid of the C1–C5 ring.
The mixed alkyl complexes [TaCp*Me2R2] (R = CH2Ph,
single bond, whereas the Ta–Cl distance is shorter than that 2; CH2SiMe3, 3) were obtained (Scheme 2) at room tem-
for a bridging chlorine[15] and longer than that for a ter- perature by treatment of toluene solutions of TaCp*Cl2Me2
minal chlorine.[11d,14b,16] The angle Cp*–Ta–Cl is 176.84° with stoichiometric amounts of the alkyllithium, LiR, un-
and confirms the apical position of the chlorine atom. This der rigorously anhydrous conditions, while the dimethyldi-
pentacoordination is unusual, and to the best of our knowl- neopentyl complex [TaCp*Me2(CH2CMe3)2] (4) was syn-
edge, no other group 5 metal (alkyl)chlorido(cyclopentadi- thesized by alkylation, at –78 °C, of the dichloridodineop-
enyl) derivative has this trigonal bipyramidal configuration; entyl derivative with 2 equiv. of LiMe in a diethyl ether/
all other examples have a four-legged piano-stool arrange- hexane mixture.
ment.[11b–d,17,18] In this case, such an arrangement is very
unfavourable because of the important steric requirement moisture-sensitive, are soluble in most organic solvents and
The mixed alkyl complexes 2–4 are extremely air- and
of the trimethylsilylmethyl substituent.
were characterised by analytical and spectroscopic methods.
Eur. J. Inorg. Chem. 2006, 4242–4253
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M. V. Galakhov, M. Gómez, P. Gómez-Sal, P. Velasco
FULL PAPER
Scheme 2.
Further, the molecular structure of 4 was studied by X-ray Table 2. Selected bond lengths [Å] and angles [°] for compound 4.[a]
diffraction. A view of this molecule is shown in Figure 2,
which indicates the atom labelling scheme employed. Se-
lected bond lengths and angles are given in Table 2.
Molecule A
Molecule B
Cp1–Ta1
C1A–Ta1
C2A–Ta1
C3A–Ta1
C4A–Ta1
C5A–Ta1
C11A-Ta1
C12A-Ta1
2.175
2.49(2)
2.48(2)
2.50(2)
2.51(2)
2.46(2)
2.20(2)
2.27(2)
2.23(2)
2.245(19)
1.49(3)
1.52(3)
109.65
Cp2–Ta2
C1–Ta2
C2–Ta2
C3–Ta2
C4–Ta2
C5–Ta2
C11–Ta2
C12–Ta2
C13–Ta2
C14–Ta2
C12–C15
C14–C19
Cp2–Ta2–C11
Cp2–Ta2–C12
Cp2–Ta2–C13
Cp2–Ta2–C14
C11–Ta2–C13
C11–Ta2–C14
C14–Ta2–C13
C11–Ta2–C12
C13–Ta2–C12
C14–Ta2–C12
C15–C12–Ta2
C19–C14–Ta2
2.175
2.48(2)
2.48(2)
2.46(2)
2.48(2)
2.49(3)
2.19(2)
2.26(2)
2.22(2)
2.20(2)
1.56(4)
1.64(3)
111.00
108.17
108.87
111.17
140.1(10)
84.4(11)
81.7(10)
82.1(10)
85.4(10)
140.7(9)
132(2)
C13A-Ta1
C14A-Ta1
C12A-C15A
C14A-C19A
Cp1–Ta1–C11A
Cp1–Ta1–C12A
Cp1–Ta1–C13A
Cp1–Ta1–C14A
C11A–Ta1–C13A
C11A–Ta1–C14A
C13A–Ta1–C14A
C11A–Ta1–C12A
C13A–Ta1–C12A
C14A–Ta1–C12A
C15A-C12A-Ta1
C19A-C14A-Ta1
111.62
109.72
108.38
140.6(8)
83.4(9)
83.7(10)
83.3(9)
83.1(9)
140.0(8)
133.5(17)
128.5(16)
Figure 2. ORTEP drawing of compound 4 with thermal ellipsoids
at the 50% probability level.
135(2)
[a] Cp1 is the centroid of the C1A–C5A ring and Cp2 is the
centroid of the C1–C5 ring.
Complex 4 is a monomer, and if Cp* is considered as
occupying the apical coordination site, it has distorted
square pyramid geometry. Two independent molecules were tively. On the other hand, the minor component, detected
found in the asymmetric unit, and their geometrical param- in a NOESY1D spectra (Figure 3), shows an AB spin sys-
eters were essentially coincident. The tantalum atom devi- tem (2JH,H = 12.8 Hz) for the Ta–(CH2CMe3)2 dia-
ates towards the Cp* ring by 0.75 Å from a plane passing stereotopic protons.
through the atoms C11, C12, C13 and C14, and the two
In contrast to 4, the Ta–(CH2SiMe3)2 resonance appears
methyl groups and the two neopentyl groups are mutually as a broad signal (∆ν = 37 Hz) at δ = –0.25 ppm in the 1H
½
trans in order to separate the sterically demanding groups. NMR spectrum of 3 at 298 K, while the signal correspond-
This arrangement is usual in five-coordinate cyclopen- ing to Ta–(CH3)2 was observed as a quintuplet (4JH,H
tadienyl complexes.[11b,11c,11d,17,18] All the bond lengths and 1.31 Hz) at δ = 0.44 ppm.
=
angles are in the normal ranges.
Further, the variable low temperature spectra of 3 indi-
1
The H NMR spectrum of 4 in [D2]dichloromethane at cate the occurrence of a typical spin exchange process be-
298 K shows two sets of signals in a ratio of 14:1. For the tween two very differently populated positions. The minor
major compound, a quintuplet (δ = 0.59 ppm) and a sep- position (10%) was detected by EXSY1D at 213 K and
4
tuplet (δ = 0.20 ppm, JH,H = 1.29 Hz) were observed for showed an AB spin system (2JH,H = 11.6 Hz) at δav = –0.01
the Ta–(CH3)2 and the Ta–(CH2CMe3)2 moieties, respec- for the Ta–(CH2SiMe3)2 resonance.
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Eur. J. Inorg. Chem. 2006, 4242–4253

(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes
FULL PAPER
idene)(neophyl) complex [TaCp*Me(CH2CMe2Ph)(CH2)]
(7), which were observed by NMR spectroscopy. Complexes
5–7 can be isolated as pure samples by successive recrystalli-
sations from hexane (see Experimental Section). However,
when the same reaction is carried out under rigorously an-
hydrous conditions (glove box) complex 5 is not formed.
We suggest, as a plausible pathway for this alkylation reac-
tion, the initial formation of a mixed alkyl complex
“[TaCp*Me2(CH2CMe2Ph)2]”, that, when followed by or-
thometalation[10,19] of the phenyl ring and by α-hydrogen
activation[7e,20] of a methyl group with the elimination of
CMe3Ph, produces complexes 6 and 7, respectively, while
the hydrolysis of this mixed alkyl complex produces the µ-
oxido complex 5.
Figure 3. The PFG WFG noesy 1d (mix = 500 ms) proton spectra
(spectrum phase = 180°) of complex 4 at 298 K [bottom: Ta–
(CH2CMe3)2; top: Ta–(CH3)2 resonances].
In the IR spectrum of complex 5 the absorption band
[15,21]
observed at 740 cm–1 could be assigned to νTa–O–Ta
,
while all the NMR spectroscopic data (see Experimental
Section) are in agreement with a structural formulation that
shows a trans arrangement of the methyl groups.
This spectral behaviour is in agreement with a trans ar-
rangement of the methyl and the alkyl groups (C2v local
The molecular structure of complex 5 (Figure 4) shows
symmetry) in the major component and a cis arrangement two TaCp*Me2(CH2CMe2Ph) fragments bonded through a
of the groups in the minor (Cs symmetry) isomers, which bridging oxygen atom, which acts as an inversion centre.
undergo the mutual spin-exchange process known as Berry The angle Ta1–O1–Ta2 is 180,° and the bond length Ta–O
pseudorotation.[14c,14d,16b,18] We hypothesise that in solution is 1.9227(6) Å (Table 3). This distance is very short and in
both isomers of the 2–4 mixed alkyl complexes exhibit agreement with the existence of a π-bonding interaction be-
pseudo-square-pyramidal geometry in the ground state and tween the oxygen and tantalum atoms.[14c] Each tantalum
a distorted trigonal bipyramidal environment, similar to atom exhibits the normal four-legged piano-stool geome-
that of 1, in the transition state. Moreover, the isomeriza- try[11,17,18] in which the pentamethylcyclopentadienyl ring
tion process in complex 3 is faster than that in 4, this is occupies the apical position and the metal centre is dis-
probably caused by the size of the alkyl group. The 13C placed towards the Cp* ring by 0.78 Å from a plane formed
NMR spectra of complexes 2–4 show all the expected reso- by the atoms C21, C6, C8 and O1. The bridging oxygen
nances (see Experimental Section).
atom is located in a trans position with respect to the bulky
The addition of 2 equiv. of LiCH2CMe2Ph to a toluene ligand. This fact, together with the inversion centre, elimin-
solution of TaCp*Cl2Me2 by using a standard vacuum line ates steric problems. The distance Ta–C21 [2.294(12) Å] is
(Scheme 3) gives a mixture of the dimethyl(neophyl)(µ-ox- significantly longer than the bonds between the metal and
ido) complex [{TaCp*Me2(CH2CMe2Ph)}2(µ-O)] (5), the the methyl groups[18] [Ta–C6 2.208(11) Å and Ta–C8
dimethyltantalabenzocyclopentene complex [TaCp*Me2- 2.194(12) Å], which is probably a result of the trans influ-
(CH2CMe2-o-C6H4-κ2C,C)] (6) and the (methyl)(methyl- ence.
Scheme 3.
Eur. J. Inorg. Chem. 2006, 4242–4253
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M. V. Galakhov, M. Gómez, P. Gómez-Sal, P. Velasco
FULL PAPER
1
The H NMR spectrum of complex 7 in [D2]dichloro-
methane at 298 K shows a singlet for the Cp* ring (δ =
1.95 ppm), three multiplets for the C6H5 group (δ = 7.4, 7.3,
7.13 ppm), two diastereotopic –CMe2– (δ = 1.46, 1.40 ppm)
groups and an ABC3 spin system at δ = 1.26, 0.04 (AB)
and –0.52 (d, 2JH,H = 14.8 Hz, 4JH,H = 1.1 Hz) ppm for the
Ta–CH2CMe2Ph and Ta–Me moieties, respectively. Al-
though 7 contains an asymmetric tantalum(V) central
atom, the Ta=CH2 resonance is observed as one singlet (1H
1
NMR, δ = 5.27 ppm; 13C NMR, δ = 205.9 ppm, JC,H
=
126.1 Hz), which is not like an AB spin system. In the vari-
1
able temperature H NMR study, the maximum broad line
(∆ν = 110 Hz) of the methylidene resonance was observed
½
at 173 K, although the multiplicity could not be resolved.
We believe that this experimental result could be due to the
fast rotation (∆G϶173 K Ͻ 32 kJmol–1) about the Ta–C vec-
tor that accompanies the heterolytic rupture of the double
bond, which is in accordance with the reactivity of these
complexes. This is known to occur in other methylidene
complexes,[18c,23] organic imines[24] and organometallic
complexes.[14c,18d]
Figure 4. ORTEP drawing of compound 5 with thermal ellipsoids
at the 50% probability level.
(Alkyl)(alkylidene)tantalum compounds were obtained
by the thermal or photochemical treatment of mixed alkyl
derivatives. So, when a toluene or [D6]benzene solution of 1
was heated at 60 °C for 48 h, the (alkyl)(alkylidene)chlorido
complex [TaCp*Cl(CH2SiMe3)(CHSiMe3)] (8) was formed
with the elimination of SiMe4 (Scheme 4). However, com-
plex 1 in [D2]dichloromethane slowly transforms into com-
plex 8 at room temperature.
Table 3. Selected bond lengths [Å] and angles [°] for compound 5.[a]
Ta1–O1
Ta1–Cp1
Ta1–C8
Ta1–C1
Ta1–C3
Ta1–C5
C22–C23
1.9227(6)
2.158
2.194(10)
2.502(12)
2.366(16)
2.533(11)
1.529(15)
O1–Ta1#1
Ta1–C6
Ta1–C21
Ta1–C2
Ta1–C4
C21–C22
1.9227(6)
2.208(11)
2.294(12)
2.416(14)
2.431(13)
1.538(17)
1
The H NMR spectrum of 8 (D = 13.0×10–10 m2 s–1)[22]
Ta1#1–O1–Ta1
Cp1–Ta1–C6
Cp1–Ta1–C21
C8–Ta1–C6
O1–Ta1–C8
C6–Ta1–C21
C22–C21–Ta1
180.00(16) Cp1–Ta1–O1
120.73
109.22
84.2(3)
135.9(3)
79.1(4)
112.9(9)
shows signals at δ = 5.54 (1 H) and 0.065 ppm (9 H) for
Ta=CHSiMe3 (29Si NMR, δ = –8.2 ppm), an AB spin sys-
tem at δ = 0.053 and 0.23 ppm (2JH,H = 12.65 Hz, 2 H) and
one singlet at δ = 0.12 ppm (9 H) for the Ta–CH2SiMe3
moiety, and also a resonance for the Cp* ring at δ =
2.15 ppm. Further, free SiMe4 (D = 24.5×10–10 m2 s–1) that
was eliminated from 1 during the reaction was also ob-
served in the solution. The assignment of the trimethylsilyl
resonances and the determination of the 29Si NMR chemi-
cal shifts were based on CIGAR data (Figure 5).
109.88
Cp1–Ta1–C8
O1–Ta1–C6
O1–Ta1–C21
C8–Ta1–C21
C23–C22–C21
103.36
139.2(5)
85.9(3)
80.9(4)
134.4(8)
[a] Cp1 is the centroid of the C1–C5 ring. Symmetry transforma-
tions used to generate equivalent atoms: #1 –x+1, –y+2, –z.
The NMR spectrum of 6, which is a monomer species [D
When a [D6]benzene solution of 3 was heated at 60 °C
= (11.7 0.2)×10–11 m2 s–1][22] in [D2]dichloromethane [D = for 20 h, a mixture of the dialkyl(alkylidene) compounds
(29.2 0.5) ×10–11 m2 s–1] at 298 K, exhibits an ABCD spin [TaCp*MeR(CHSiMe3)] (R = CH2SiMe3, 9; Me, 10) was
system at δ = 8.1, 7.3, 7.2 and 7.12 ppm corresponding to generated in a 3:2 ratio; this mixture was identified by
the C6H4 moiety, and four singlets for the η5-C5Me5 (δ = NMR spectroscopy. The reaction occurred with the elimi-
1.94 ppm, 15 H), Ta–CH2CMe2Ph (δ = 1.15 ppm, 6 H), Ta– nation of CH4 and SiMe4 (Scheme 5). On the other hand,
CH2CMe2Ph (δ = 0.88 ppm, 2 H, ∆ν = 8.7 Hz) and Ta– the irradiation of a [D6]benzene solution of 3 with a sun
½
Me2 (δ = 0.27 ppm, 6 H) proton resonances, which justifies lamp gave a mixture of 9 and [TaCp*(CH2SiMe3)R(CH2)]
the assignment of Cs symmetry to this complex. Unfortu- (R = Me, 11; CH2SiMe3, 12) in a 2:1:1 ratio. Both processes,
nately, the variable temperature spectra did not show any thermal and photochemical, take place by C–Hα activation
significant changes (∆ν
= 12.7 Hz) to enable the study of the CH2SiMe3 or Me groups. Complex 9 is the major
½max
of any possible fluxional behaviour. NOE data at 203 K product that results from the preferential elimination of
indicate short distances between the pentamethylcyclopen- CH4.
tadienyl ring and the –CMe2–, Ta–Me2 and Ta–CH2– moie-
In addition, [D6]benzene solutions of the mixed tet-
ties, and between Ta–Me2 and the phenyl (H2 proton) ring, raalkyl complex 4 slowly decomposed at room temperature
suggesting an axial position for the phenyl group in the dis- when exposed to a sun lamp, yielding a mixture of the alk-
torted trigonal bipyramidal structure of 6, as shown in ylidenes 13–16. When solutions of 4 were heated at 60 °C,
Scheme 3.
the decomposition was faster, and a mixture of (alkyl)(neo-
4246
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Eur. J. Inorg. Chem. 2006, 4242–4253

(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes
FULL PAPER
Scheme 4.
Figure 5. PFG Accord HMBC (CIGAR) 1H-{29Si} spectra of 8 acquired over a period of 20 minutes in a Mercury VX spectrometer
1
with PFG-Z VT 5 mm ATB NMR probe. All parameters were optimized for the H–29Si geminal spin coupling.
Scheme 5.
pentylidene) derivatives [TaCp*MeR(CHCMe3)] (R = Me, [TaCp*Cl2(CH2CMe3)2] with 2 equiv. of LiCH2SiMe3 gave
13; CH2CMe3, 14) in a 4:1 ratio was produced and iden- the (alkyl)(alkylidene) complex [TaCp*(CH2CMe3)(CH2Si-
tified by NMR spectroscopy. Further, a mixture of the (alk- Me3)(CHCMe3)] (17) with the selective elimination of
yl)(methylidene) complexes [TaCp*(CH2CMe3)R(CH2)] (R SiMe4 (Scheme 6). The use of neophyllithium or benzyl-
= Me, 15; CH2CMe3, 16) in a 3:1 ratio was obtained from magnesium chloride leads to an unidentified mixture of alk-
the irradiation of a [D6]benzene solution of 4 with a sun ylidene derivatives. However, new (alkyl)(alkylidene) deriva-
lamp. These results indicate that a C–Hα bond is activated tives [TaCp*(CH2R)(CH2SiMe3)(CHRЈ)] (R = RЈ = Ph, 18;
by thermal (–CH2CMe3) and photochemical (–CH3) pro- R = CMe2Ph, RЈ = SiMe3, 19) were prepared by treatment
cesses, but in both cases the elimination of neopentane is of [TaCp*Cl2(CH2SiMe3)2] with 2 equiv. of the appropriate
preferential. alkylating reagent; these reactions occur with the elimi-
A spontaneous α-hydrogen-abstraction process takes nation of SiMe4 and CMe3Ph, respectively.
place in unstable mixed tetraalkyl intermediates formed by
For some reported coordinatively unsaturated alkylidene
the reaction of complexes [TaCp*Cl2(CH2R)2] (R = CMe3, complexes,[8,25] the stretching frequency corresponding to
SiMe3) with an alkylating reagent. So, the reaction of the C–H bond in the IR spectrum was assigned to absorp-
Eur. J. Inorg. Chem. 2006, 4242–4253
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4247

M. V. Galakhov, M. Gómez, P. Gómez-Sal, P. Velasco
FULL PAPER
Scheme 6.
tion bands localized in the 2700–2350 cm–1 region, which tion of 3 gave a mixture of 9 and [TaCp*(CH2SiMe3)-
are at a lower wavenumber than those for normal C–H R(CH2)] (R = Me, 11; CH2SiMe3, 12). On the other hand,
stretches probably as a result of the observed increase in the [D6]benzene solutions of 4 slowly decompose at room
length of the C–H bond. In the case of (alkyl)(alkylidene) temperature,
compounds 7 and 17–19, the absorption band localized at [TaCp*MeR(CHCMe3)] (R = Me, 13; CH2CMe3, 14) and
= 2553 cm–1 can be assigned to νC–H
[TaCp*(CH2CMe3)R(CH2)] (R = Me, 15; CH2CMe3, 16),
In accordance with all the NMR spectroscopic data (see but the decomposition is faster when activated thermally or
giving
a
mixture
of
alkylidenes
ν
˜
.
average
Experimental Section) the alkylidene complexes 7–19 are photochemically, leading to a mixture of 13–14 and 15–16,
monomeric species with the expected three-legged piano- respectively. Finally, a spontaneous α-hydrogen-abstraction
stool geometry.[8,26,27]A large degree of deshielding is ob- process occurs during the alkylation reaction of
served for the alkylidene carbon resonances (δ Ͼ 200 ppm). TaCp*Cl2(CH2CMe3)2 with LiCH2SiMe3, which gives
The direct proton–carbon coupling constants for the [TaCp*(CH2CMe3)(CH2SiMe3)(CHCMe3)] (17) with selec-
Ta=CHR signals for complexes 7, 11, 12, 15 and 16 are tive elimination of SiMe4. However, new (alkyl)(alkylidene)
1
smaller than the JC,H values resulting from coupling in- complexes [TaCp*(CH2R)(CH2SiMe3)(CHRЈ)] (R = RЈ =
volving an sp3 carbon (Ta–CH2R groups) and are compar- Ph, 18; R = CMe2Ph, RЈ = SiMe3, 19) were obtained by
able to other d0 terminal (alkylidene)niobium and -tanta- treatment of TaCp*Cl2(CH2SiMe3)2 with 2 equiv. of the ap-
lum complexes.[26,27] For the rest of the complexes, we propriate alkylating reagent; these reactions occurred with
found similar values for the isostructural alkylmethylidene the elimination of SiMe4 and CMe3Ph, respectively.
moiety.
Experimental Section
Conclusions
All operations were carried out under a dry argon atmosphere, by
New trialkylchlorido and dialkyldimethyl(pentamethyl-
cyclopentadienyl)tantalum complexes [TaCp*ClxMeyRz] (x
= 1, y = 0, z = 3, R = CH2SiMe3, 1; x = 0, y = z = 2, R =
CH2Ph, 2; CH2SiMe3, 3; CH2CMe3, 4) have been prepared
by the direct reaction of tetrachlorido or dialkyldichlorido
derivatives [TaCp*Cl4–xRx] (x = 0; x = 2, R = Me,
CH2CMe3) with the appropriate alkylating reagent. How-
ever, when lithium neophyl is used as the reagent under
standard conditions, a different sequence of reactions takes
using standard Schlenk tube and cannula techniques, or in a con-
ventional argon-filled glove-box. Solvents were refluxed over an ap-
propriate drying agent, distilled and degassed prior to use: [D6]-
benzene and hexane (Na/K alloy), and toluene (Na). Starting mate-
rials Ta(η5-C5Me5)Cl4,[28] Ta(η5-C5Me5)Cl2Me2,[13] Ta(η5-C5Me5)-
[26a,29]
Cl2(CH2CMe3)2
and the alkylating reagents LiR (R =
CH2SiMe3, CH2CMe2Ph)[30] and Li(CH2C6H5)(tmeda)[31] were
prepared as previously described. Reagent grade LiMe (1.5  in
diethyl ether, Aldrich) and MgCl(CH2SiMe3) (1  in diethyl ether,
Aldrich) were purchased from commercial sources and were used
without further purification.
place, which leads to
[{TaCp*Me2(CH2CMe2Ph)}2(µ-O)]
(CH2CMe2–o-C6H4-κ2C,C)]
(6)
a
mixture from which
(5),
[TaCp*Me2-
[TaCp*Me-
Samples for infrared spectroscopy were prepared as KBr pellets or
as Nujol mulls between CsI plates, and the spectra were recorded
with a Perkin–Elmer Spectrum 2000 spectrophotometer (4000–
400 cm–1). The NMR spectra were recorded with Unity 300, Mer-
cury VX 300 and Unity Plus 500 (Varian NMR Systems) spectrome-
ters; chemical shifts were referenced to the 13C- and residual 1H
resonances of the deuterated solvents. Microanalyses (C, H) were
performed with a LECO CHNS 932 microanalyser.
and
(CH2CMe2Ph)(CH2)] (7) were isolated and identified by
NMR spectroscopy. Thermal treatment of toluene or [D6]-
benzene solutions of 1 leads to an intramolecular C–Hα
bond activation in an alkyl group, giving the (alkyl)(alkylid-
ene)chlorido complex [TaCp*Cl(CH2SiMe3)(CHSiMe3)] (8)
with the evolution of SiMe4. A mixture of dialkyl(alkylid-
ene) derivatives [TaCp*MeR(CHSiMe3)] (R = CH2SiMe3,
9; Me, 10) was produced when 3 was heated at 60 °C in
[D6]benzene; the mixture was identified by NMR measure-
[TaCp*Cl(CH2SiMe3)3] (1):
A solution of MgCl(CH2SiMe3)
[6.90 mL, 1 , 6.60 mmol] in diethyl ether was added, at room tem-
perature, to a suspension of TaCp*Cl4 (1.00 g, 2.20 mmol) in hex-
ments. Further, the direct irradiation of a [D6]benzene solu- ane (25 mL), and the mixture was stirred for 12 h. The resulting
4248 Eur. J. Inorg. Chem. 2006, 4242–4253
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(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes
FULL PAPER
suspension was filtered through Celite and then concentrated to ca.
10 mL, the solution was cooled to –20 °C to give 1 as a yellow benzene, 25 °C): δ = 118.6 (C5Me5), 111.2 (Ta–CH2CMe3), 76.6
microcrystalline solid. Yield 0.90 g (68%). IR (KBr): ν = 2917 (vs), (Ta–Me2), not detected (Ta–CH2CMe3), 36.3 (Ta–CH2CMe3), 11.7
1494 (m), 1441 (m), 1380 (s), 1243 (vs), 1105 (s), 1026 (s), 845 (vs), (C5Me5) ppm. C22H43Ta (488.53): calcd. C 54.09, H 8.87; found C
1.3 Hz, 4 H, Ta–CH2CMe3) ppm. 13C{1H} NMR (75 MHz, [D6]-
˜
1
749 (s), 678 (s), 470 (m), 407 (m) cm–1. H NMR (300 MHz, [D6]-
benzene, 25 °C): δ = 1.78 (s, 15 H, C5Me5), 0.65 (s, 6 H,
CH2SiMe3), 0.35 (s, 27 H, CH2SiMe3) ppm. 13C{1H} NMR (75
MHz, [D6]benzene, 25 °C): δ = 121.5 (C5Me5), 88.0 (CH2SiMe3),
12.8 (C5Me5), 4.2 (CH2SiMe3) ppm. C22H48ClSi3Ta (613.28): calcd.
C 43.08, H 7.89; found C 43.31, H 7.78.
53.95, H 8.72.
[{TaCp*Me2(CH2CMe2Ph)}2(µ-O)] (5): Complex 5 was isolated to-
gether with complexes 6 and 7 by using a standard vacuum line
and Schlenk techniques. A mixture of TaCp*Cl2Me2 (0.50 g,
1.20 mmol) and LiCH2CMe2Ph (0.34 g, 2.40 mmol) was stirred in
toluene (30 mL) at room temperature for 15 h. LiCl was filtered
off, and the resulting solution was concentrated to dryness. The
brown residue was extracted with hexane (3×10 mL), concentrated
to ca. 10 mL, and then cooled to –40 °C to give 5. The filtrate was
cooled to –78 °C to give 6 as a yellow microcrystalline solid, and
the final solution was concentrated to dryness to give 7 as a brown
[TaCp*Me2(CH2C6H5)2] (2): This reaction was carried out in a dry
box by using darkened glassware designed for photosensitive mate-
rials. A solution of Li(CH2Ph)(tmeda) (0.31 g, 1.44 mmol) in tolu-
ene (20 mL) was added to a solution of TaCp*Cl2Me2 (0.30 g,
0.72 mmol) in toluene (30 mL) at room temperature, and the mix-
ture was stirred for 10 h. The suspension was concentrated to dry-
ness and the residue extracted with hexane (3×20 mL). The solu-
tion was filtered, concentrated to ca. 10 mL, and cooled to give 2
oil. IR (KBr): ν = 2912 (s), 1599 (w), 1491 (m), 1436 (s), 1378 (s),
˜
1203 (w), 1157 (m), 1027 (m), 740 (vs), 709 (s), 650 (m), 555 (w),
466 (m) cm–1. H NMR (300 MHz, [D6]benzene, 25 °C): δ = 7.62
1
as a red microcrystalline solid. Yield 0.29 g (80%). IR (KBr): ν =
˜
(m, 4 H), 7.33 (m, 4 H), 7.12 (m, 2 H, H5C6Me2C–CH2–Ta), 1.79
(s, 12 H, Ta–CH2CMe2Ph), 1.68 (s, 30 H, C5Me5), 1.04 (s, 4 H, Ta–
CH2CMe2Ph), 0.68 (s, 12 H, Ta–Me2) ppm. 13C{1H} NMR (75
MHz, [D6]benzene, 25 °C): δ = 157.3 (Ci), 127.9, 126.3, 124.8
(H5C6Me2C–CH2), 117.8 (C5Me5), 88.3 (Ta–CH2CMe2Ph), 61.4
(Ta–Me2), 43.7 (Ta–CH2CMe2Ph), 35.2 (Ta–CH2CMe2Ph), 11.4
(C5Me5) ppm.
2916 (s), 1591 (m), 1484 (vs), 1450 (m), 1379 (s), 1203 (s), 1150 (m),
1062 (s), 1025 (s), 807 (m), 750 (vs), 698 (vs), 601 (m), 529 (m), 443
1
(w) cm–1. H NMR (300 MHz, [D6]benzene, 25 °C): δ = 7.21 (m,
2 H), 7.11 (m, 2 H), 6.85 (m, 1 H, H5C6CH2–Ta), 1.67 (br., 4 H,
Ta–CH2Ph), 1.60 (s, 15 H, C5Me5), 0.86 (br., 6 H, Ta–Me2) ppm.
13C{1H} NMR (75 MHz, [D6]benzene, 25 °C): δ = not detected
(Ci), 127.9 (Cm), 127.3 (Co), 123.2 (Cp, C6H5CH2–Ta), 119.5
(C5Me5), 94.8 (Ta–CH2C6H5), 81.3 (Ta–Me2), 11.4 (C5Me5) ppm.
C26H35Ta (528.51): calcd. C 59.08, H 6.67; found C 58.98, H 6.70.
[TaCp*Me2(CH2CMe2–o-C6H4-κ2C,C)] (6) and [TaCp*Me-
(CH2CMe2Ph)(CH2)] (7): Under rigorously anhydrous conditions
(glove box), a solution of TaCp*Cl2Me2 (0.50 g, 1.20 mmol) in tol-
uene (30 mL) was treated with a solution of LiCH2CMe2Ph (0.34 g,
2.40 mmol) in toluene (10 mL), and the mixture was stirred at room
temperature for 15 h. The resulting suspension was concentrated to
dryness, and the residue extracted with hexane (2×15 mL). The
solution was filtered, concentrated to ca. 10 mL and cooled to
–78 °C over a period of several minutes to give a pale brown micro-
crystalline solid identified as 6. Compound 6 was then filtered off,
and the solution was concentrated to dryness to give 7 as a sticky
brown solid.
[TaCp*Me2(CH2SiMe3)2] (3):
A
stirred suspension of
TaCp*Cl2Me2 (0.50 g, 1.20 mmol) in toluene (30 mL) was treated
with a solution of LiCH2SiMe3 (0.23 g, 2.40 mmol) in toluene
(20 mL). The reaction mixture was stirred for 10 h at room tem-
perature, and the resulting suspension was decanted and filtered.
The solution was concentrated to dryness and the residue extracted
with hexane (3×15 mL). The solution was filtered, concentrated to
ca. 10 mL, and cooled to –40 °C to give 3 as a yellow microcrystal-
line solid. Yield 0.35 g (74%). IR (KBr): ν = 2947 (vs), 1490 (m),
˜
1432 (s), 1380 (m), 1295 (w), 1241 (s), 1160 (m), 1026 (m), 947 (s),
856 (vs), 823 (vs), 744 (m), 718 (s), 676 (m), 612 (m), 521 (w), 442
(m) cm–1. 1H NMR (500 MHz, [D2]dichloromethane, 25 °C): δ =
Data for 6: Yield 0.18 g (32%). IR (KBr): ν = 2909 (vs), 1654 (w),
˜
1574 (w), 1492 (m), 1438 (s), 1377 (s), 1238 (m), 1102 (m), 1024
(m), 762 (s), 731 (vs), 560 (m), 460 (m), 411 (m) cm–1. 1H NMR
(500 MHz, [D2]dichloromethane, –40 °C): δ = 8.05 (m, 1 H, H4C6–
o-CMe2–CH2–Ta), 7.27 (m, 1 H, H4C6–o-CMe2–CH2–Ta), 7.20 (m,
1 H, H4C6–o-CMe2–CH2–Ta), 7.10 (m, 1 H, H4C6–o-CMe2–CH2–
Ta), 1.89 (s, 15 H, C5Me5), 1.07 (s, 6 H, H4C6–o-CMe2–CH2–Ta),
0.77 (s, 2 H, H4C6–o-CMe2–CH2–Ta), 0.18 (s, 6 H, Ta–Me2) ppm.
13C NMR[32] (125 MHz, [D2]dichloromethane, 25 °C): δ = 219.1
(Ci–Ta), 137.1, 124.0, 123.8, 123.2, 160.3 ppm (H4C6–o-CMe2–
CH2–Ta), 115.9 (C5Me5), 112.4 (H4C6–o-CMe2–CH2–Ta), 67.4
(Ta–Me2), 49.5 (H4C6–o-CMe2–CH2–Ta), 34.0 (H4C6–o-CMe2–
CH2–Ta), 10.2 (C5Me5) ppm. C22H33Ta (478.45): calcd. C 55.23, H
6.95; found C 55.10, H 6.75.
4
2.00 (s, 15 H, C5Me5), 0.40 (quint, JH,H = 1.1 Hz, 6 H, Ta–Me2),
0.06 (s, 18 H, Ta–CH2SiMe3), –0.30 (m, 4 H, Ta–CH2SiMe3) ppm.
13C{1H} NMR (75 MHz, [D6]benzene, 25 °C): δ = 118.9 (C5Me5),
83.6 (Ta–CH2SiMe3), 71.7 (Ta–Me2), 11.7 (C5Me5), 3.8
(CH2SiMe3) ppm. 13C{1H} NMR (125 MHz, [D2]dichloromethane,
25 °C): δ = 118.9 (C5Me5), 83.2 (Ta–CH2SiMe3), 70.7 (Ta–Me2),
11.1 (C5Me5), 3.5 (CH2SiMe3) ppm. C20H43Si2Ta (520.68): calcd.
C 46.12, H 8.32; found C 45.90, H 8.02.
[TaCp*Me2(CH2CMe3)2] (4): A solution of LiMe in diethyl ether
(1.30 mL, 1.5 , 1.95 mmol) was added to
a solution of
TaCp*Cl2(CH2CMe3)2 (0.40 g, 0.75 mmol) in hexane (40 mL) at
–78 °C, and the mixture was stirred for 5 h. The suspension was
then warmed to room temperature and LiCl filtered off. The solu-
tion was concentrated to ca. 10 mL and cooled to –40 °C to give a
yellow microcrystalline solid identified as 4. Yield 0.30 g (81%). IR
1
Data for 7: Yield 0.32 g (56%). H NMR (500 MHz, [D2]dichloro-
methane, 25 °C): δ = 7.41, 7.28, 7.13 (H5C6Me2C–CH2–Ta), 5.27
(s, 2 H, Ta=CH2), 1.95 (s, 15 H, C5Me5), 1.46 (s, 3 H), 1.40 (s, 3
2
(KBr): ν = 2940 (vs), 1431 (m), 1379 (s), 1205 (s), 1157 (m), 1023 H, H5C6Me2C–CH2–Ta), 1.26 (d), 0.04 (q, AB, JH,H = 14.8 Hz, 2
˜
1
4
(m), 804 (w), 746 (m), 601 (m), 522 (m), 455 (m) cm–1. H NMR H, H5C6Me2C–CH2–Ta), –0.52 (d, JH,H = 1.1 Hz, 3 H, Ta–Me)
(300 MHz, [D6]benzene, 25 °C): δ = 1.66 (s, 15 H, C5Me5), 1.40 (s,
18 H, Ta–CH2CMe3), 0.92 (6 H, Ta–Me2), 0.34 (4 H, Ta–
ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25 °C): δ = 205.9 (t,
1JC,H = 126.1 Hz, Ta=CH2), 153.5–125.4 (H5C6Me2C–CH2–Ta),
CH2CMe3) ppm. 1H NMR (500 MHz, [D2]dichloromethane, 113.6 (C5Me5), 94.8 (t, JC,H = 105.6 Hz, H5C6Me2C–CH2–Ta), 44
1
25 °C): δ = 1.96 (s, 15 H, C5Me5), 1.07 (s, 18 H, Ta–CH2CMe3), (Ta–Me), 40 (H5C6Me2C–CH2–Ta), 31.4, 32 (H5C6Me2C–CH2–
4
4
0.59 (quint, JH,H = 1.3 Hz, 6 H, Ta–Me2), 0.20 (sept, JH,H
=
Ta), 11.3 (C5Me5) ppm.
Eur. J. Inorg. Chem. 2006, 4242–4253
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4249

M. V. Galakhov, M. Gómez, P. Gómez-Sal, P. Velasco
FULL PAPER
[TaCp*Cl(CH2SiMe3)(CHSiMe3)] (8): A solution of 1 (0.15 g,
0.24 mmol) in toluene (20 mL) was placed in an ampoule under
rigorously anhydrous conditions and then sealed. The solution was
heated to 60 °C for 2 days. After the ampoule was opened, the
solution was concentrated to dryness, and the brown oil residue
a sealed NMR tube and then heated to 60 °C for 4 h. The reaction
was monitored by NMR, and a mixture of (alkyl)(alkylidene) com-
pounds 13 and 14, in a 4:1 ratio, together with the organic elimi-
nation products CMe4 (δ = 0.9 ppm) and CH4 (δ = 0.15 ppm), was
identified by NMR spectroscopy.
was identified as 8. Yield 0.10 g (80%). IR (KBr): ν = 2913 (s),
Data for 13: 1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 3.38 (s,
1 H, Ta=CHCMe3), 1.84 (s, 15 H, C5Me5), 1.30 (s, 9 H,
Ta=CHCMe3), 0.07 (s, 6 H, Ta–Me2) ppm. 13C{1H} NMR (75
˜
2578 (w), 1584 (m), 1488 (m), 1432 (m), 1378 (m), 1244 (vs), 1097
(m), 1026 (s), 941 (s), 841 (vs), 750 (s), 682 (s), 483 (m), 437 (w)
1
cm–1. H NMR (500 MHz, [D2]dichloromethane, 25 °C): δ = 5.54
MHz, [D6]benzene, 25 °C):
Ta=CHCMe3), 114.3 (C5Me5),
δ
=
224.2 (d,1JC,H
40.9 (Ta–Me2),
=
80.3 Hz,
34.9
2
(s, 1 H, Ta=CHSiMe3), 2.15 (s, 15 H, C5Me5), 0.23 (AB, JH,H
=
12.7 Hz, 1 H, Ta–CHHSiMe3), 0.12 (s, 9 H, Ta–CH2SiMe3), 0.07
(Ta=CHCMe3), 33.9 (Ta=CHCMe3), 11.3 (C5Me5) ppm.
2
(s, 9 H, Ta=CHSiMe3), 0.053 (AB, JH,H = 12.7 Hz, 1 H, Ta–
1
Data for 14: H NMR (300 MHz, [D6]benzene, 25 °C): δ = 3.26 (s,
CHHSiMe3) ppm. 13C{1H} NMR (125 MHz, [D6]benzene, 25 °C):
1 H, Ta=CHCMe3), 1.83 (s, 15 H, C5Me5), 1.34 (s, 9 H,
1
δ = 231.5 (d, JC,H = 89.0 Hz, Ta=CHSiMe3), 116.5 (C5Me5), 50.6
2
Ta=CHCMe3), 1.34 (s, 9 H, Ta–CH2CMe3), 1.08 (AB, JH,H
=
(Ta–CH2SiMe3), 11.9 (C5Me5), 3.4 (Ta–CH2SiMe3), 2.5 (Ta=CHSi-
Me3) ppm. C18H36ClSi2Ta (524.879): calcd. C 41.15, H 6.91; found
C 41.18, H 6.81.
14.2 Hz, 1 H, Ta–CHHCMe3), –0.07 (s, 3 H, Ta–Me), –0.71 (AB,
2JH,H = 14.2 Hz, 1 H, Ta–CHHCMe3) ppm. 13C{1H} NMR (75
1
MHz, [D6]benzene, 25 °C): δ = 226.1 (d, JC,H = 78.1 Hz,
1
[TaCp*MeR(CHSiMe3)] (R = CH2SiMe3, 9; Me, 10): A solution
of 3 (0.07 g, 0.13 mmol) in [D6]benzene (0.70 mL) was placed into
an NMR tube with a valve, and this tube was heated to 60 °C. The
reaction was monitored by NMR spectroscopy, and after 20 h the
formation of a mixture of the (alkyl)(alkylidene) derivatives 9 and
10 in a 3:2 ratio was confirmed.
Ta=CHCMe3), 113.9 (C5Me5), 94.2 (t, JC,H = 102.1 Hz, Ta–
CH2CMe3), 47.1, 37 (Ta–Me), 35.2, 34.0 (Ta=CHCMe3, Ta–
CH2CMe3), 33.7 (Ta=CHCMe3, Ta–CH2CMe3), 11.6 (C5Me5)
ppm.
[TaCp*(CH2CMe3)R(CH2)] (R = Me, 15; CH2CMe3, 16): In a typi-
cal experiment, a yellow solution of 4 (0.04 g, 0.08 mmol) in [D6]-
benzene (0.60 mL) was transferred to a valved NMR tube and then
irradiated with a sun lamp for 3 h. The (alkyl)(alkylidene) com-
plexes 15 and 16, in a ratio of 3:1, and the organic elimination
products CMe4 and CH4 were identified in the NMR spectrum.
1
Data for 9: H NMR (300 MHz, [D6]benzene, 25 °C): δ = 4.80 (s,
1 H, Ta=CHSiMe3), 1.82 (s, 15 H, C5Me5), 0.32 (s, 9 H, Ta–
CH2SiMe3), 0.28 (s, 9 H, Ta=CHSiMe3), 0.06 (s, 3 H, Ta–Me),
2
–0.06 (AB, JH,H = 12.4 Hz, 1 H, Ta–CHHSiMe3), –0.93 (AB,
2JH,H = 12.4 Hz, 1 H, Ta–CHHSiMe3) ppm. 13C{1H} NMR (75
MHz, [D6]benzene, 25 °C): δ = 223.3 (d, 1JC,H = 76.9 Hz, Ta=CHSi-
Data for 15: 1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 5.92 (s,
2 H, Ta=CH2), 1.75 (s, 15 H, C5Me5), 1.28 (s, 9 H, Ta–CH2CMe3),
1
Me3), 114.8 (C5Me5), 59.9 (t, JC,H = 105.3 Hz, Ta–CH2SiMe3),
2
1.06 (AB, JH,H = 14.4 Hz, 1 H, Ta–CHHCMe3), 0.032 (s, 3 H,
42.2 (Ta–Me), 11.8 (C5Me5), 3.7 (Ta–CH2SiMe3), 2.8 (Ta=CHSi-
Me3) ppm.
2
Ta–Me), –0.30 (AB, JH,H = 14.4 Hz, 1 H, Ta–CHHCMe3) ppm.
13C{1H} NMR (75 MHz, [D6]benzene, 25 °C): δ = 205.5 (t,
Data for 10: 1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 5.81 (s,
1 H, Ta=CHSiMe3), 1.79 (s, 15 H, C5Me5), 0.37 (s, 9 H, Ta=CHSi-
Me3), 0.13 (s, 6 H, Ta–Me2) ppm. 13C{1H} NMR (75 MHz, [D6]-
Ta=CH2, JC,H = 125.3 Hz), 113.2 (C5Me5), 96 (t, Ta–CH2CMe3,
1
1JC,H = 117.2 Hz), 42.9 (Ta–Me), 34.8 (Ta–CH2CMe3), 32.8 (Ta–
CH2CMe3), 11.2 (C5Me5).
1
benzene, 25 °C): δ = 222.8 (d, JC,H = 75.7 Hz, Ta=CHSiMe3),
Data for 16: 1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 5.80 (s,
2 H, Ta=CH2), 1.77 (s, 15 H, C5Me5), 1.34 (s, 18 H, Ta–CH2CMe3),
114.7 (C5Me5), 47.9 (Ta–Me2), 11.6 (C5Me5), 3.9 (Ta=CHSiMe3)
ppm.
2
1.20 (AB, 2JH,H = 13.0 Hz, 1 H, Ta–CHHCMe3), –0.40 (AB, JH,H
= 13.0 Hz, 1 H, Ta–CHHCMe3) ppm. 13C{1H} NMR (75 MHz,
[D6]benzene, 25 °C): δ = 209.4 (t, 1JC,H = 126.1 Hz, Ta=CH2), 112.8
[TaCp*(CH2SiMe3)R(CH2)] (R = Me, 11; CH2SiMe3, 12): In a
standard experiment, a solution of 3 (0.07 g, 0.13 mmol) in [D6]-
benzene (0.60 mL) was transferred to a valved NMR tube and then
irradiated with a sun lamp for 2 h. A mixture of the (alkyl)(alkylid-
ene) compounds 9, 11 and 12, in a ratio 2:1:1, together with the
elimination products CH4 and SiMe4, was identified in the NMR
spectrum of the resulting solution.
1
(C5Me5), 92.4 (t, JC,H = 110.9 Hz, Ta–CH2CMe3), 35 (Ta–
CH2CMe3), 34 (Ta–CH2CMe3), 11.6 (C5Me5) ppm.
[TaCp*(CH2CMe3)(CH2SiMe3)(CHCMe3)]
(17):
TaCp*Cl2-
(CH2CMe3)2 (0.70 g, 1.30 mmol) and LiCH2SiMe3 (0.25 g,
2.60 mmol) were stirred in hexane (45 mL) at room temperature for
10 h. The resulting suspension was filtered and concentrated to ca.
5 mL and cooled overnight to –40 °C to give 17 as an orange micro-
1
Data for 11: H NMR (300 MHz, [D6]benzene, 25 °C): δ = 6.06 (s,
2 H, Ta=CH2), 1.77 (s, 15 H, C5Me5), 0.34 (s, 9 H, Ta–CH2SiMe3),
2
crystalline solid. Yield 0.44 (61%). IR (CsI): ν = 2940 (vs), 2430
˜
0.11 (s, 3 H, Ta–Me), –0.14 (AB, JH,H = 12.5 Hz, 1 H, Ta–
2
(m), 1459 (s), 1434 (m), 1353 (s), 1243 (vs), 1024 (m), 950 (s), 853
(vs), 827 (s), 744 (m), 720 (m), 684 (m), 573 (w), 508 (m), 417 (m)
CHHSiMe3), –0.69 (AB, JH,H = 12.5 Hz, 1 H, Ta–CHHSiMe3)
ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25 °C): δ = 207.0 (t,
1JC,H = 125.8 Hz, Ta=CH2), 113.3 (C5Me5), 60 (Ta–CH2SiMe3),
43.1 (Ta–Me), 11.3 (C5Me5), 2.5 (Ta–CH2SiMe3) ppm.
1
cm–1. H NMR (500 MHz, [D6]benzene, 25 °C): δ = 3.10 (s, 1 H,
Ta=CHCMe3), 1.84 (s, 15 H, C5Me5), 1.38 (s, 9 H) and 1.35 (s, 9
2
H) (Ta=CHCMe3 and Ta–CH2CMe3), 1.03 (AB, JH,H = 13.8 Hz,
Data for 12: 1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 5.89 (s,
2 H, Ta=CH2), 1.79 (s, 15 H, C5Me5), 0.31 (s, 18 H, Ta–
1 H, Ta–CHHCMe3), 0.32 (s, 9 H, Ta–CH2SiMe3), 0.11 (AB, 2JH,H
= 12.0 Hz, 1 H, Ta–CHHSiMe3), –0.38 (AB, 2JH,H = 13.8 Hz, 1 H,
Ta–CHHCMe3), –1.44 (AB, 2JH,H = 12.0 Hz, 1 H, Ta–CHHSiMe3)
ppm. 13C{1H} NMR (125 MHz, [D6]benzene, 25 °C): δ = 226.4 (d,
2
CH2SiMe3), 0.06 (AB, JH,H = 11.9 Hz, 1 H, Ta–CHHSiMe3),
2
–1.05 (AB, JH,H = 11.9 Hz, 1 H, Ta–CHHSiMe3) ppm. 13C{1H}
1
NMR (75 MHz, [D6]benzene, 25 °C): δ = 205.5 (t, JC,H
=
1JC,H
= 77.4 Hz, Ta=CHSiMe3), 114 (C5Me5), 88.7 (Ta–
126.6 Hz, Ta=CH2), 113.2 (C5Me5), 56.8 (Ta–CH2SiMe3), 11.5
(C5Me5), 2.6 (Ta–CH2SiMe3) ppm.
CH2CMe3), 53.7 (Ta–CH2SiMe3), 47.6, 35.4, 34.2 (Ta–CH2CMe3,
Ta=CHCMe3), 34.1 (Ta–CH2CMe3, Ta=CHCMe3), 12.0 (C5Me5),
[TaCp*MeR(CHCMe3)] (R = Me, 13; CH2CMe3, 14): A solution 3.2 (Ta–CH2SiMe3) ppm. C24H47SiTa (544.663): calcd. C 52.92, H
of 4 (0.04 g, 0.08 mmol) in [D6]benzene (0.60 mL) was placed into 8.69; found C 52.67, H 8.97.
4250
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4242–4253

(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes
FULL PAPER
[TaCp*(CH2Ph)(CH2SiMe3)(CHPh)] (18): This reaction was car-
ried out in a glove box in darkened glassware designed for photo-
sensitive materials. A 1  solution of MgCl(CH2Ph) in diethyl ether
tion was filtered and concentrated to dryness to give 19 as a pale
brown oil. Yield 0.26 g (81%). IR (CsI): ν = 2910 (vs), 2564 (w),
˜
1599 (w), 1492 (m), 1442 (s), 1379 (s), 1242 (vs), 1169 (m), 1028
(1.50 mL, 1.45 mmol) was added to a solution of TaCp*Cl2- (m), 945 (vs), 847 (vs), 762 (s), 702 (s), 626 (w), 552 (m), 434 (m)
1
(CH2SiMe3)2 (0.40 g, 1.71 mmol) in hexane (30 mL), and the mix-
ture was stirred for 14 h. The resulting suspension was decanted
and filtered through Celite. The red solution was concentrated to
ca. 5 mL and cooled to –40 °C overnight to give 18 as a red micro-
cm–1. H NMR (300 MHz, [D6]benzene, 25 °C): δ = 7.44 (m, 2 H,
H5C6Me2CCH2–Ta), 7.26 (m, 2 H, H5C6Me2CCH2–Ta), 7.09 (m,
1 H, H5C6Me2CCH2–Ta), 4.17(s, 1 H, Ta=CHSiMe3), 1.79 (s, 15
H, C5Me5), 1.70 (s, 3 H), 1.57 (s, 3 H, Ta–CH2CMe2Ph), 1.01 (AB,
2
crystalline solid. Yield 0.27 g (65%). IR (CsI): ν = 2914 (vs), 2494
2JH,H = 14.4 Hz, 1 H), not detected (AB, JH,H = 14.4 Hz, 1 H),
0.40 (AB, JH,H
˜
2
(w), 1856 (w), 1592 (m), 1485 (vs), 1449 (s), 1378 (m), 1242 (s),
=
11.7 Hz,
2
H, Ta–CHHCMe2Ph, Ta–
1199 (m), 1054 (m), 1027 (s), 950 (m), 850 (vs), 750 (vs), 695 (s), CHHSiMe3), 0.28 (s, 9 H), 0.14 (s, 9 H, Ta–CH2SiMe3, Ta=CHSi-
1
2
536 (m), 438 (w) cm–1. H NMR (300 MHz, [D6]benzene, 25 °C):
Me3), –2.05 (AB, JH,H = 11.7 Hz, 2 H, Ta–CHHCMe2Ph, Ta–
δ = 7.29–6.86 (several phenyl, H5C6CH2–Ta, H5C6CH=Ta), 5.45 CHHSiMe3) ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25 °C):
(s, 1 H, Ta=CHPh), 1.79 (s, 15 H, C5Me5), 1.68 (AB, JH,H
12.3 Hz, 1 H, Ta–CHHPh), 1.61 (AB, JH,H = 12.3 Hz, 1 H, Ta– (Co), 126.4 (Cm), 125.5 (Cp, H5C6Me2CCH2–Ta), 114.4 (C5Me5),
CHHPh), 0.88 (AB, JH,H = 12.1 Hz, 2 H, Ta–CHHPh , Ta–
2
1
=
δ = 226.8 (d, JC,H = 76.6 Hz, Ta=CHSiMe3), 153.6 (Ci), 128.5
2
2
1
1
86.7 (t, JC,H = 109.5 Hz, Ta–CH2CMe2Ph), 64.0 (t, JC,H =
103.4 Hz Ta–CH2SiMe3), 40.1 (Ta–CH2CMe2Ph), 36.9, 31.9 (Ta–
2
CHHSiMe3), 0.09 (s, 9 H, Ta–CH2SiMe3), –1.29 (AB, JH,H
=
12.1 Hz, 2 H, Ta–CHHPh, Ta–CHHSiMe3) ppm. 13C{1H} NMR CH2CMe2Ph), 11.9 (C5Me5), 3.6, 2.8 (Ta–CH2SiMe3, TaCHSi-
1
(75 MHz, [D6]benzene, 25 °C): δ = 216.7 (d, JC,H = 82.6 Hz,
Me3).
Ta=CHPh),
151.1–122.9
(several phenyl,
H5C6CH2–Ta,
Crystal Structure Determination for Compounds 1, 4 and 5: Crystal-
lographic and experimental details of the crystal structure determi-
nations are given in Table 4. Suitably sized crystals were sealed un-
der argon in a Lindemann capillary tube and mounted on an Enraf
Nonius CAD 4 automatic four circle diffractometer with graphite
1
H5C6CH=Ta), 114.5 (C5Me5), 69.1 (t, JC,H = 119.4 Hz, Ta–
CH2Ph), 64.1 (t, JC,H = 104.2 Hz, Ta–CH2SiMe3), 11.3 (C5Me5),
2.7 (Ta–CH2SiMe3) ppm. C28H39SiTa (584.65): calcd. C 57.52, H
6.72; found C 57.48, H 6.75.
1
[TaCp*(CH2CMe2Ph)(CH2SiMe3)(CHSiMe3)] (19): TaCp*Cl2- monochromated Mo-Kα radiation (λ = 0.71073 Å). Intensities were
(CH2SiMe3)2 (0.30 g, 0.53 mmol) and Li(CH2CMe2Ph) (0.16 g, collected at room temperature and corrected for Lorenz and polar-
1.20 mmol) were stirred in toluene (40 mL) at room temperature ization effects in the usual manner. No extinction corrections were
for 15 h. The volatiles were removed under reduced pressure, and
made. Empirical absorption corrections (DIFABS)[33] were made
the residual solid was extracted with hexane (2×15 mL). The solu-
to the data for 1 and 4, and the data for 5 were corrected with ψ
Table 4. Crystal data and structure refinement details for 1, 4 and 5.[a]
1
4
5
Chemical formula
Formula weight
T [K]
λ (Mo-Kα) [Å]
Crystal system, space group
a [Å]; α [°]
C22H48ClSi3Ta
613.27
293(2)
C22H43Ta
488.529
293(2)
C44H68OTa2
974.8
293(2)
0.71073
0.71073
0.71073
Triclinic, P1
¯
Monoclinic, P21/n
15.401(1); 90.00
10.945(1); 91.09(2)
17.721(1); 90.00
2986.6(4)
Monoclinic, P21/c
9.230(1); 90.00
31.913(1); 99.06(5)
16.087(1); 90.00
4679.4(6)
8.639(2); 101.7(2)
10.278(2); 98.77(2)
12.159(4); 100.71(2)
1018.3(5)
b [Å]; β [°]
c [Å]; γ [°]
V [Å]3
Z
4
8
1
ρcalcd [gcm–3]
1.364
3.896
1.3804
4.698
1.590
5.399
µ [mm–1]
F(000)
1248
1984
486
Crystal size [mm3]
θ range [°]
0.27×0.30×0.33
1.32 to 22.97
–16 ՅhՅ 16
–12 ՅkՅ 0
0 ՅlՅ 19
0.35×0.30×0.20
1.28 to 22.93
–9 ՅhՅ 0
–34 ՅkՅ 0
–16 ՅlՅ 16
6144
0.35×0.35×0.10
2.08 to 25.11
–10 ՅhՅ 0
–12 ՅkՅ 12
–14 ՅlՅ 14
3873
Index ranges
Number of data collected
Number of unique data
Number of observed reflections
[IϾ2σ(I)]
4366
4134 [R(int) = 0.0661]
1669
5711 [R(int) = 0.1381]
2531
3612 [R(int) = 0.0172]
3368
Absorption correction
Max. and min. transmission
Number of refined parameters
Goodness-of-fit on F2
Empirical (DIFABS)
0.702, 0.243
244
Empirical (DIFABS)
0.638, 0.166
390
ψ-scan
0.5815, 0.0942
214
0.926
0.951
1.105
Final R indices [IϾ2σ(I)]
R1 = 0.0628
wR2 = 0.1079
R1 = 0.2540
wR2 = 0.1469
R1 = 0.0677
wR2 = 0.1421
R1 = 0.2431
wR2 = 0.1870
0.917 and –1.605
R1 = 0.0710
wR2 = 0.1764
R1 = 0.0744
wR2 = 0.1802
5.664 and –5.187 (near Ta)
R indices (all data)
Largest diff. peak and hole [eÅ–3] 0.857 and –1.422
[a] R1 = Σ||Fo|–|Fc||/[Σ|Fo|]; wR2 = {[Σw(Fo2 –Fc)2]/[Σw(Fo2)2]}1/2
.
Eur. J. Inorg. Chem. 2006, 4242–4253
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4251

M. V. Galakhov, M. Gómez, P. Gómez-Sal, P. Velasco
FULL PAPER
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scan methods. Structures were initially solved by direct methods,
completed by the subsequent difference Fourier techniques and re-
fined by full-matrix least-squares on F2 (SHELXL-97).[34] Aniso-
tropic thermal parameters were included in the last cycles of refine-
ment for the non-hydrogen atoms, except for five carbon atoms in
compound 5 that remained isotropic. The hydrogen atoms were
included from geometrical calculations and refined by using a ri-
ding model. All the calculations were performed with the WINGX
system.[35]
[12]
[13]
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CCDC-299683(1), 299684(4) and 299685(5) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
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Supporting Information (see footnote on the first page of this arti-
1
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We thank the MCYT (Project BQU 2002–03754) and Universidad
de Alcalá (Project GC 2005/94) for their financial support for this
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(Alkyl)- and (Alkyl)(alkylidene)(pentamethylcyclopentadienyl)tantalum Complexes
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Received: February 27, 2006
Published Online: September 14, 2006
Eur. J. Inorg. Chem. 2006, 4242–4253
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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