Bis[η 5-tetramethyl(trimethylsilyl)cyclopentadienyl]titanium(II) and its π-complexes with bis(trimethylsilyl)acetylene and ethylene

Article abstract of DOI:10.1021/om990286k

Thermally induced elimination of bis(trimethylsilyl)acetylene from its titanocene complex [{η⁵-C₅Me₄(SiMe₃)} ₂Ti(η²-Me₃SiC≡CSiMe₃)] (1) afforded the stable titanocene

Full text of DOI:10.1021/om990286k

3572
Organometallics 1999, 18, 3572-3578
Articles
Bis[η5-tetr a m eth yl(tr im eth ylsilyl)cyclop en ta d ien yl]tita n iu m (II)
a n d Its π-Com p lexes w ith Bis(tr im eth ylsilyl)a cetylen e
a n d Eth ylen e
Michal Hora´cˇek,† Volkmar Kupfer,‡ Ulf Thewalt,‡ Petr Sˇteˇpnicˇka,§
Miroslav Pola´sˇek,† and Karel Mach*,†
J . Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejsˇkova 3, 182 23 Prague 8, Czech Republic, Sektion fu¨r Ro¨ntgen- und Elektronenbeugung,
Universita¨t Ulm, 89069 Ulm, Germany, and Department of Inorganic Chemistry,
Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic
Received April 21, 1999
Thermally induced elimination of bis(trimethylsilyl)acetylene from its titanocene complex
[{η5-C5Me4(SiMe3)}2Ti(η2-Me3SiCtCSiMe3)] (1) afforded the stable titanocene [{η5-C5-
Me4(SiMe3)}2TiII] (2) in high yield under mild conditions. Compound 2 exhibits paramagnetic
1
line broadening of H NMR signals, although it is silent in EPR spectra down to -196 °C.
The solid-state structure determination revealed an exactly parallel arrangement of the
cyclopentadienyl rings in 2 due to crystallographically imposed symmetry. Complex 2
smoothly reacts with ethylene to give the yellow η2-ethylene complex [{η5-C5Me4(SiMe3)}2-
Ti(η2-CH2dCH2)] (3). The structures of 1 and 3, determined by single-crystal X-ray diffraction,
show the bent-titanocene moieties with the η2-coordinated Me3SiCtCSiMe3 and CH2dCH2
ligands, respectively.
In tr od u ction
(µ-H)2],3 or to titanocene complexes with electron donors
capable of π-back-bonding [(η5-C5H5)2TiL2], where L2 )
(PF3)2,4 (PMe3)2,5 (CO)2,6 Me2P(CH2)2PMe2,7 and R1Ct
CR2 (R1 ) R2 ) Ph;8a R1 ) Ph, R2 ) SiMe3;8b R1 ) R2 )
SiMe38c,d). Replacement of protons on the cyclopentadi-
enyl (Cp) rings by methyl groups stabilizes electron-
deficient metallocenes by steric shielding as well as by
increasing electron density on the metal due to the
increased electron-donating ability of the Cp ligand.
Indeed, permethyltitanocene, [(η5-C5Me5)2TiII], was first
obtained by elimination of nitrogen from the [{(η5-C5-
Me5)2Ti}2(µ-N2)] complex, although it was contaminated
by the hydride species [(η5-C5Me5)(η1:η5-C5Me4CH2)TiH],
Metallocenes [(η5-C5R5)2M] and their derivatives are
undoubtedly a milestone in the development of transi-
tion-metal organometallic chemistry, affording evidence
on the diverse properties of metal-cyclopentadienyl ring
bonds. In the class of electron-deficient early transition
metals (Ti, Zr, Hf; Nb, Ta; Mo, W), however, such data
are mostly available only indirectly from metallocene
derivatives. The respective metallocenes are highly
unstable, since they tend tenaciously to stabilize them-
selves by acquiring other ligands or by forming new
bonds through various rearrangements in order to
increase the number of valence electrons.1 Among these
metallocenes, much effort has been devoted to obtaining
titanocene, [(η5-C5H5)TiII], as it remains the last un-
known metallocene in the 3d series transition metals.
All attempts to reduce the starting material titanocene
dichloride have led in most cases to the bright green
dimeric titanocene [{(η5-C5H5)Ti}2(µ-η5:η5-C10H8)(µ-
H)2],2 to the dimeric hydride complex [{(η5-C5H5)2Ti}2-
(3) (a) Bercaw, J . E.; Brintzinger, H. H. J . Am. Chem. Soc. 1969,
91, 7301-7306. (b) Bercaw J . E.; Marvich, R. H.; Bell, L. G.; Brintz-
inger, H. H. J . Am. Chem. Soc. 1972, 94, 1219-1238.
(4) Sikora, D. J .; Rausch, M. D.; Rogers, R. D.; Atwood, J . L. J . Am.
Chem. Soc. 1981, 103, 1265-1267.
(5) Kool, L. B.; Rausch, M. D.; Alt, H. G.; Herberhold, M.; Thewalt,
U.; Honold, B. J . Organomet. Chem. 1986, 310, 27-34 and references
therein.
(6) Sikora, D. J .; Macomber, D. W.; Rausch, M. D. Adv. Organomet.
Chem. 1986, 25, 317-379.
* To whom correspondence should be addressed. E-mail: mach@
jh-inst.cas.cz.
(7) Girolami, G. S.; Wilkinson, G.; Thorntonpett, M.; Hursthouse,
M. B. J . Chem. Soc., Dalton Trans. 1984, 2347-2350.
(8) (a) Shur, V. B.; Burlakov, V. V.; Vol’pin, M. E. J . Organomet.
Chem. 1988, 347, 77-83. (b) Rosenthal, U.; Go¨rls, H.; Burlakov, V.
V.; Shur, V. B.; Vol′pin, M. E. J . Organomet. Chem. 1992, 426, C53-
C57. (c) Burlakov, V. V.; Rosenthal, U.; Petrovskii, P. V.; Shur, V. B.;
Vol’pin, M. E. Metalloorg. Khim. 1988, 1, 953-954. (d) Burlakov, V.
V.; Polyakov, A. V.; Yanovsky, A. I.; Struchkov, Yu. T.; Shur, V. B.;
Vol’pin, M. E.; Rosenthal, U.; Go¨rls, H. J . Organomet. Chem. 1994,
476, 197-205.
† Academy of Sciences of the Czech Republic.
‡ Universita¨t Ulm.
§ Charles University.
(1) (a) Long, N. J . Metallocenes; Blackwell Science: Oxford, U.K.,
1998. (b) Beckhaus, R. In Metallocenes; Togni, A., Halterman, R. L.,
Eds.; Wiley-VCH: Weinheim, Germany, 1998; Chapter 4, pp 153-239.
(2) (a) Brintzinger, H. H.; Bercaw, J . E. J . Am. Chem. Soc. 1970,
92, 6182-6185. (b) Troyanov, S. I.; Antropiusova´, H.; Mach, K. J .
Organomet. Chem. 1992, 427, 49-55 and references therein.
10.1021/om990286k CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/08/1999

Bis(cyclopentadienyl)titanium(II) Complexes
Organometallics, Vol. 18, No. 18, 1999 3573
Sch em e 1
F igu r e 1. ORTEP drawing of 1 with 30% probability
thermal ellipsoids and the atom-numbering scheme. For
clarity, all hydrogen atoms are omitted.
Sch em e 2
an inherent product of rearrangement.9 Octamethylti-
tanocene prepared in an analogous way decomposes
rapidly by a hydrogen elimination, affording the dimeric
complex [{(η5-C5HMe4)Ti(µ-η5:η1-C5Me4)}2].10 Neither of
the aforementioned titanocenes was obtained in a
crystalline form.
A successful synthesis of a crystalline titanocene was
reported very recently: bis[η5-(tert-butyldimethylsilyl)-
tetramethylcyclopentadienyl]titanium(II) was obtained
from the reduction of [{η5-C5Me4(SiMe2-t-Bu)}2TiCl] by
sodium amalgam in toluene.11 Independently, we have
developed an efficient alternative method for the syn-
thesis of analogous titanocenes and applied it toward
the synthesis of the trimethylsilyl derivative.12 Here we
describe the synthesis, spectral characterization, and
crystal structures of [{η5-C5Me4(SiMe3)}2TiII] (2), its
precursor [{η5-C5Me4(SiMe3)}2Ti(η2-Me3SiCtCSiMe3)]
(1), and its complex with ethylene [{η5-C5Me4(SiMe3)]2-
Ti(η2-CH2dCH2)] (3).
[{η5:η1-C5Me4(SiMe2CH2)}{η5-C5Me4(SiMe3)}TiIII] (4) and
[{{η5-C5Me4SiMe2(µ-CH2(Mg,Mg))}{η5-C5Me4(SiMe3)}-
TiIII(µ-H)2Mg(THF)}2] (5) are obtained instead as the
major and the minor products, respectively.15 To avoid
the formation of these and some other byproducts,
complex 1, resulting in the form of a THF/BTMSA
solution by the low-temperature reduction, has to be
separated from excess magnesium at low temperature,
as well. Subsequent evaporation of the solvent under
vacuum, extraction of the residue by hexane, and
crystallization at low temperature affords yellow crys-
talline 1 in good yield. The compound shows spectro-
scopic features typical of titanocene-BTMSA complexes,
e.g., a large downfield shift of NMR signals due to the
coordinated triple bond (δC 246.4 ppm), a shift of ν(Ct
C) wavenumber to 1600 cm-1, and an electronic absorp-
tion band at 980 nm.14,16 The molecular structure of 1
was verified by single-crystal X-ray diffraction (Figure
1), and its gross features differ only marginally from
that of [(η5-C5Me5)2Ti(η2-BTMSA)] (see below). This
contrasts with a remarkably lower thermal stability of
1 compared to that of the latter complex. Whereas [(η5-
C5Me5)2Ti(η2-BTMSA)] thermolyzes at 130 °C,14 crystal-
Resu lts a n d Discu ssion
The starting complex 1 was obtained by the reduction
of the titanocene dichloride [{η5-C5Me4(SiMe3)}2TiCl2]13
with activated magnesium in THF in the presence of a
large excess of bis(trimethylsilyl)acetylene (BTMSA) at
-18 °C (Scheme 1). At elevated temperature (60 °C),
which is commonly used in the synthesis of the nonsi-
lylated analogues of 1, [(η5-C5H5-nMen)2Ti(η2-Me3SiCt
CSiMe3)] (n ) 0-5),8d,14 the paramagnetic complexes
(9) (a) Bercaw, J . E.; Brintzinger, H. H. J . Am. Chem. Soc. 1971,
93, 2045-2046. (b) Bercaw, J . E. J . Am. Chem. Soc. 1974, 96, 5087-
5095.
(10) De Wolf, J . M.; Blaauw, R.; Meetsma, A.; Teuben, J . H.; Gyepes,
R.; Varga, V.; Mach, K.; Veldman, N.; Spek, A. L. Organometallics
1996, 15, 4977-4983.
(11) Hitchcock, P. B.; Kerton, F. M.; Lawless, G. A. J . Am. Chem.
Soc. 1998, 120, 10264-10265.
(12) The synthesis and structure of 2 has already been com-
municated: Mach, K.; Hora´cˇek, M.; Kupfer, V.; Thewalt, U. XXIth
Polish-German Colloquy on Organometallic Chemistry; Hotel Star-
Dadaj, Poland, September 1998; Book of Abstracts, p 2.
(13) Hora´cˇek, M.; Gyepes, R.; C´ısarˇova´, I.; Pola´sˇek, M.; Varga, V.;
Mach, K. Collect. Czech. Chem. Commun. 1996, 61, 1307-1320.
(14) Varga, V.; Mach, K.; Pola´sˇek, M.; Sedmera, P.; Hiller, J .;
Thewalt, U.; Troyanov, S. I. J . Organomet. Chem. 1996, 506, 241-
251.
(15) Hora´cˇek, M.; Hiller. J .; Thewalt, U.; Pola´sˇek, M.; Mach, K.
Organometallics 1997, 16, 4185-4191.
(16) Varga, V.; Hiller, J .; Pola´sˇek, M.; Sedmera, P.; Thewalt, U.;
Mach, K. J . Organomet. Chem. 1997, 538, 63-74.

3574 Organometallics, Vol. 18, No. 18, 1999
Hora´cˇek et al.
Ta ble 1. Selected Bon d Dista n ces (Å), Bon d An gles
(d eg), a n d Dih ed r a l An gles (d eg) for 1-3,
1*, a n d 3*
line 1 liberates BTMSA upon warming to 70 °C under
high vacuum, leaving 2 as a pale green liquid which
solidifies upon cooling to room temperature (Scheme 2).
The complete removal of BTMSA from 1 can be achieved
even at room temperature by repeated dissolving of the
solid 1 in hexane and subsequent evaporation of all
volatiles under high vacuum. This points to a dissocia-
tion equilibrium (eq 1) taking place in solution. Accord-
1
1*
2
3
3*
Ti-Cav
2.45(3)
2.43(2)
2.35(3)
2.45(5)
2.41(4)
Ti-CEa
Ti-C13
Ti-C14
C13-C14
2.137(4)b 2.114(4)b 2.020(2) 2.129(3) 2.092(5)
2.125(3)
2.144(3)
1.313(4)
2.122(3)
2.126(3)
1.309(4)
2.167(4) 2.160(4)
1.442(9)c 1.438(5)c
CE-Ti-CE′ 142.2(1)
φd
41.4(1)
138.6(1)
41.1(1)
180
0
147.0(1) 143.6(4)
39.7(1)
40.6(4)
1 a 2 + BTMSA
(1)
a
b
CE denotes the centroid of the corresponding Cp ring. Av-
erage value. c C13-C13′. Dihedral angle between the least-
squares planes of the Cp rings.
d
ingly, the presence of a small amount of noncoordinated
BTMSA was detected by NMR spectroscopy in a C6D6
solution prepared from crystalline 1. On the other hand,
crystalline 1 is stable under a dynamic vacuum of 10-2
Torr at ambient temperature but its EI-MS spectrum
shows fragmentation patterns attributable to titanocene
2 and to free BTMSA. The absence of the molecular peak
1•+ in the spectrum indicates that 1 dissociates either
upon evaporation in the probe or after the electron
impact.
ethylene, changing its pale green color to intense yellow.
The product of the reaction, [{η5-C5Me4(SiMe3)}2Ti(η2-
CH2dCH2)] (3), crystallizes from hexane solution as
yellow prisms, and its structure was confirmed by X-ray
diffraction analysis (see below). The NMR spectra of 3
exhibit features due to the C5Me4(SiMe3) ligand similar
to those of 1 and also the resonances of an η2-
coordinated ethylene molecule (δH 2.34, δC 104.3), which
compare well to those reported for [(η5-C5Me5)2Ti(η2-
CH2dCH2)] (δH 2.02, δC 105.1).18 The electronic absorp-
tion spectrum of 3 is nearly identical with the spectrum
of 1, proving that both BTMSA and ethylene ligands
are involved in the bonding by one pair of multiple-bond
π-electrons, whereas titanium d2 electrons are donated
into the empty π* orbitals of the ligands.19
Cr ysta l Str u ctu r es of Com p ou n d s 1-3. The crys-
tal structures of compounds 1-3 do not represent new
structural types, since the structures of [(η5-C5Me5)2Ti-
(η2-BTMSA)] (1*)8d and [(η5-C5Me5)2Ti(η2-CH2dCH2)]
(3*),18 the permethylated analogues of 1 and 3, are
known. Moreover, the structure of 2 is very similar to
that of [{η5-C5Me4(SiMe2-t-Bu)}2Ti] (2′). Nevertheless,
structural data for complexes 1-3 and 1* and 3* (Table
1) allow us to compare molecular geometry of the parent
titanocene with those of its η2-complexes and to ratio-
nalize the significantly higher thermal stability of the
silylated titanocenes 2 and 2′ with respect to that of [(η5-
C5Me5)2Ti].
Crude compound 2 obtained by the thermolysis or
solvolysis of 1 requires a recrystallization from hexane
to remove a more soluble blue paramagnetic impurity.17
The fact that approximately the same content of the
impurity was detected in compound 2 obtained by
repeated evaporation of a solution of 1 in hexane at room
temperature or by thermolysis of crystalline 1 at 70 °C
indicates a good thermal stability of 2. However, all
attempts to purify crude 2 by high-vacuum sublimation
at 110 °C failed, affording a product containing a
considerably increased amount of the impurity.17 After
crystallization from hexane, pure 2 was obtained as
large brown-pink plates which are highly soluble in
hexane, benzene-d6, or toluene to dichroic solutions (the
solutions are pale green in incident but red in transmit-
ted light). The electronic absorption spectrum of 2 shows
an intense band at 570 nm with a low-intensity shoulder
extending to 900 nm. The titanium(II) complex 2 is
paramagnetic. Its 1H NMR spectrum consists of two
broad signals whose chemical shifts are temperature-
dependent, obeying the Curie law in the range observed
(0-60 °C). A very similar behavior was reported for the
signal of methyl groups in [(η2-C5Me5)2Ti].9 However,
the presence of the spin-unpaired d2 electrons was not
observed in the ESR spectra in the temperature range
-196 to +25 °C, probably due to short relaxation times
of the spin states. The infrared spectrum of 2 in a KBr
pellet shows the bands typical of the C5Me4(SiMe3)
ligand, virtually independent of the presence of other
coordinated ligands such as (σ-Cl)2, σ-Cl,13 η2-C2H4, and
η2-BTMSA (see Experimental Section).
The structure of the bent-titanocene complex 1 is
asymmetrical (Figure 1), although 1* exhibits only
marginal asymmetry8d and the titanium atom of [(η5-
C5HMe4)2Ti(η2-BTMSA)] resides on a crystallographic
2-fold axis.14 In 1, a substantial difference in the Ti-
Calkyne bond lengths (0.02 Å) is noticeable (Table 1).
However, it may originate from solid-state effects and
be of no relevance to an intramolecular congestion. The
SiMe3 groups on the Cp rings are situated in side
positions and do not affect the hindrance between Cp
ligands at their hinge position. Consequently, the
dihedral angles between the Cp-ring least-squares
planes (φ) in 1 and 1* are virtually the same (41.4(1)°
vs 41.1(1)°). The presence of the SiMe3 groups has a
noticeable effect on the Ti-C(Cp) bond lengths. The
average Ti-CE distance is longer by 0.02 Å, and this
also accounts for a larger CE-Ti-CE′ angle (142.2(1)°
in 1 vs 138.6(1)° in 1*). The average Ti-Calkyne distance
Compound 2 in hexane solution does not visually
react with gaseous nitrogen at atmospheric pressure in
the temperature range -196 to +25 °C. This is at
variance with the behavior of [(η5-C5Me5)2Ti]9 and [(η5-
C5HMe4)2Ti]],10 which react reversibly with N2 to give
[{(η5-C5Me5)2Ti}2(µ-N2)] and [{(η5-C5HMe4)2Ti}2(µ-N2)],
respectively, both displaying an intense blue color.
Nevertheless, titanocene 2 reacts smoothly with gaseous
is longer only slightly (by 0.01 Å) in 1, and the Calkyne
-
(17) The impurity is identical with the paramagnetic blue waxy solid
which is obtained by repeated sublimation of 1-3 under vacuum. EPR
(toluene, 23 °C): g ) 1.9767, ∆H ) 3.0 G, aTi ) 7.6 G. EPR (toluene,
-140 °C): g1 ) 1.999, g2 ) 1.980, g3 ) 1.953, gav) 1.977. UV-near-IR
(hexane, 23 °C, nm): 585.
(18) Cohen, S. A.; Auburn, P. R.; Bercaw, J . E. J . Am. Chem. Soc.
1983, 105, 1136-1143.
(19) Stockis, A.; Hoffmann, R. J . Am. Chem. Soc. 1980, 102, 2952-
2962.

Bis(cyclopentadienyl)titanium(II) Complexes
Organometallics, Vol. 18, No. 18, 1999 3575
F igu r e 2. Molecular structure of 2 showing the atom-
labeling scheme. Thermal ellipsoids are drawn at the 50%
probability level; all hydrogen atoms are omitted for clarity.
The nonlabeled atoms are generated by the following
symmetry operations: -x, -y, -z; x, -y, -z; -x, y, z.
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 2a
F igu r e 3. Molecular structure of 3 showing the atom-
numbering scheme. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms are omitted,
except those of the ethylene ligand. The nonlabeled atoms
are generated by the following symmetry operation: -x,
y, -z + 2.
Ti(1)-C(1)
Ti(1)-C(2)
Ti(1)-C(3)
C(1)-C(2)
C(1)-Si(1)
C(2)-C(3)
2.322(4)
2.334(3)
2.386(3)
1.427(4)
1.875(4)
1.416(4)
C(2)-C(4)
C(3)-C(3)i
C(3)-C(5)
Si(1)-C(6)
Si(1)-C(7)
Ti(1)-CE(1)
1.506(4)
1.399(5)
1.501(4)
1.848(4)
1.854(6)
2.020(2)
CE(1)-Ti-CE(2)
C(3)i-C(3)-C(2)
aSymmetry transformation: (i) -x, y, z.
180.0
107.97(16)
C(3)-C(2)-C(1)
C(2)-C(1)-C(2)i
109.3(2)
105.6(3)
frame by the SiMe3 group induces a considerable exten-
sion of the Ti-C(Cp) bonds and in the case of 1 also an
extension of Ti-Calkyne bond length (average 0.01 Å).
The ease of liberation of BTMSA from 1 (70 °C), 1* (130
°C), and [(C5HMe4)2Ti(BTMSA)] (200 °C) may be rel-
evant to the Ti-Calkyne bond lengths (average 2.134,
average 2.124, and 2.106 Å, respectively).14 The elonga-
tion of Ti-C(Cp) is accompanied by a distortion of the
Cp rings that was described in detail for 2, where no
steric congestion, inherent in the bent arrangement,
may interfere. Regardless of the stereoelectronic reasons
for these effects, the bond extension implies that the
hydrogen abstraction by the central titanium atom from
the C5Me4(SiMe3) ligands requires a higher activation
energy than the hydrogen abstraction from a more
closely located C5Me5 ligand. In other words, the Ti-C
bond extension accounts for a higher stability of 2 and
2′ toward hydride abstraction reactions, yielding, e.g.,
η3:η4-allyldiene20 or η1:η5-fulvene complexes9a,21 from
[(η5-C5Me5)2Ti]. A significantly shorter Ti-CE distance
in 2 in comparison to those in 1 and 3 is apparently
brought about by a lower coordination number of the
central atom. Provided the extension of Ti-C bonds as
found for pairs 1, 1* and 3, 3* applies to 2 and [(η5-C5-
Me5)2Ti], the Ti-CE distance in the latter compound
should be very close to 2.00 Å. The reason for the
parallel arrangement of the Cp rings in 2 (and 2′) is to
be sought in the crystal-packing effects and a possible
small gain of electronic energy in the pseudo D5d
configuration of 2.22 The interpretation of the parallel
structure due to intramolecular crowding of the methyl
groups of one ring and the methyl groups of the SiMe2-
(t-Bu) group of the other Cp ring11 does not seem to be
Calkyne bond lengths are equal within the precision of
the measurements.
The crystal structure of 2 is of a higher symmetry
(orthorhombic, Cmca) than that of 2′ (monoclinic, P21/
n).11 The titanium atom sits on an inversion center; a
mirror plane contains the Ti atom, Si atoms, four carbon
atoms, and two hydrogen atoms, and a 2-fold axis
perpendicular to the plane passes the Ti atom. The
imposed symmetry implies that the Cp rings are exactly
planar and parallel, and the normal to these planes
contains the Ti atom and both centroids (Figure 2). An
inspection of bond distances and bond angles (Table 2)
shows that the Cp ring is distorted by the presence of
the trimethylsilyl substituent: the C-C bonds involving
C(1), the SiMe3-substituted carbon atom, are the longest
within the ring C-C bonds, and the C-C-C angle at
this carbon atom is the smallest among the ring internal
angles. This silicon-induced distortion of the ring also
results in different Ti-C(Cp) distances. The carbon
atoms of the Cp methyl groups and the Si atom are bent
from the ring plane out from the metal center by 0.07
and 0.31 Å, respectively. The molecular parameters of
2 and 2′ are equal to each other within the precision of
the measurement, and the reported comparison of Ti-
CE distances for 2′ and representative titanocene
complexes11 is fully applicable to 2.
The molecular structure of 3 (Figure 3) exhibits gross
features similar to 1 and closely resembles that of 3*.
The comparison of molecular parameters of 3 and 3*
(Table 1) shows that the dihedral angles φ are virtually
equal in both cases, whereas the Ti-C bond lengths are
longer, and consequently, the CE-Ti-CE′ angle is
larger in 3. The C-C bond lengths in π-coordinated
ethylene in both 3 and 3* do not differ.
(20) Pattiasina, J . W.; Hissink, C. E.; de Boer, J . L.; Meetsma, A.;
Teuben, J . H.; Spek, A. L. J . Am. Chem. Soc. 1985, 107, 7758-7759.
(21) Fischer, J . M.; Piers, W. E.; Young, V. G. Organometallics 1996,
15, 2410-2412.
(22) Theoretical calculations for early-transition-metal metallocenes
by extended Hu¨ckel22a and ADF methods22b assume a negligible energy
difference in parallel and bent structures: (a) Lauher, J . W.; Hoffmann,
R. J . Am. Chem. Soc. 1976, 98, 1729-1741. (b) Green, J . C. Chem.
Soc. Rev. 1998, 263-271.
The comparison of molecular parameters in pairs of
compounds 1, 1* and 3, 3* indicates that the replace-
ment of one methyl group in the permethyltitanocene

3576 Organometallics, Vol. 18, No. 18, 1999
Hora´cˇek et al.
opened and inserted into the direct inlet under argon. GC-MS
analyses were performed on a Hewlett-Packard gas chromato-
graph (5890 series II) equipped with an SPB-1 capillary
column (length 30 m; Supelco) and a mass spectrometric
detector (5971 A). EPR spectra were obtained on an ERS-220
spectrometer (Center for Production of Scientific Instruments,
Academy of Sciences of GDR, Berlin, Germany) operated by a
CU-1 unit (Magnettech, Berlin, Germany) in the X-band. g
values were determined by using an Mn2+ standard at g )
1.9860 (MI ) -1/2 line). A variable-temperature unit (STT-3)
was used for measurements in the range -196 to +25 °C. UV-
near-IR spectra in the range 280-2000 nm were measured
on a Varian Cary 17D spectrometer in all-sealed quartz
cuvettes (Hellma). KBr pellets were prepared in a Labmaster
130 glovebox (mBraun) under purified nitrogen. IR spectra
were measured in an air-protecting cuvette on a Specord IR-
75 (Carl Zeiss, J ena, Germany) infrared spectrometer.
Ch em ica ls. The solvents THF, hexane, and toluene were
dried by refluxing over LiAlH4 and stored as solutions of the
dimeric titanocene [{(η5-C5H5)Ti}2(µ-η5:η5-C10H8)(µ-H)2].28 Bis-
(trimethylsilyl)acetylene (BTMSA, Fluka) was degassed, stored
as a solution of dimeric titanocene for 4 h, and distilled into
ampules on a vacuum line. Magnesium turnings (Fluka,
purum for Grignard reactions) were first used in large excess
for the preparation of [(η5-C5Me5)2Ti(η2-BTMSA)].14 Then,
activated magnesium was separated from the reaction mix-
ture, washed thoroughly with THF, and stored in ampules
equipped with breakable seals. Ethylene (polymerization
grade; Polymer Institute Brno, Brno, Czech Republic) was
condensed at liquid-nitrogen temperature, degassed under
high vacuum, and expanded to a reservoir under ambient
pressure. The synthesis of [{η5-C5Me4(SiMe3)}2TiCl2] was
carried out as recently reported.13
justified in view of solid-state structures of 1 and 3,
which show the bending in the direction perpendicular
to the Si-Si line with the Si atoms deviated from the
least-squares Cp planes by as much as 0.69 and 0.82 Å
in 1 and as little as 0.17 Å in 3.
Con clu d in g Rem a r k s
The preparation of titanocene 2 by thermally induced
elimination of the BTMSA ligand from the bent-ti-
tanocene complex 1 represents a novel approach toward
synthesis of titanocenes, offering an alternative to
generally used reduction methods.23 It also exemplifies
the primary step of a dissociative mechanism which has
been proposed for various reactions of titanocene-
BTMSA complexes with σ-electron donors or acetylenes
on the basis of reaction intermediates or products.24 In
contrast, zirconocene-BTMSA complexes react cur-
rently by an associative mechanism, probably due to a
larger atom diameter and a higher electropositivity of
zirconium.25 On the other hand, these properties may
make the preparation and isolation of zirconocene yet
more difficult. In the case of 2, its good thermal stability
and inertness toward nitrogen are induced by the SiMe3
substituent at the methylated cyclopentadienyl ligands.
The comparison of molecular parameters of a series of
compounds related to 2 showed that this can be hardly
accounted for by only the steric effects of a bulky silyl
group. Subtle electronic effects of the trimethylsilyl
group on energies of d-based frontier orbitals are not
well understood, although a huge amount of experimen-
tal material on the transition-metal silyl compounds is
available26 and theoretical approaches are currently
being developed.27
P r ep a r a tion of [{η5-C5Me4(SiMe3)}2Ti(η2-Me3SiCtCSi-
Me3)] (1). The complex [{η5-C5Me4(SiMe3)}2TiCl2] (1.0 g, 2.0
mmol) was degassed and rapidly mixed with activated mag-
nesium (ca. 0.5 g, 20 mmol), BTMSA (3.0 mL, 13.4 mmol), and
THF (40 mL). The mixture was cooled to -18 °C in a freezer
before the solution turned blue, to avoid byproduct formation
due to a rapid reduction of [{η5-C5Me4(SiMe3)}2TiCl]. After 40
h at -18 °C with occasional shaking, the resulting yellow
solution was rapidly separated from unreacted magnesium
while the temperature was kept below -5 °C. THF and
BTMSA were distilled off under vacuum, and the residue was
extracted by hexane. The yellow hexane solution was allowed
to stand overnight at -5 °C, whereupon a white powder (likely
MgCl2) separated from a clear yellow solution. The solution
was concentrated and cooled to -18 °C overnight to give a crop
of 1 as yellow crystals, which were separated from the mother
liquor at -5 °C. Yield 1.0 g (80%). The crystals were directly
used for X-ray diffraction analysis and all spectroscopic
measurements. Recrystallization of this material from hexane
afforded a crystalline mixture of 1 and 2. Data for 1 are as
follows. 1H NMR (C6D6): δ -0.07, 0.08 (2 × s, 18H, Me3Si);
1.89, 2.04 (2 × s, 12H, C5(CH3)4(Me3Si)). 13C{1H} NMR
(C6D6): δ 3.5, 4.8 (Me3Si); 14.6, 17.5 ((CH3)4(Me3Si)C5); 118.7
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations, including
spectroscopic measurements, were performed under vacuum
using all-sealed glass devices equipped with breakable seals.
1H (399.95 MHz), 13C{1H} (100.58 MHz), and 29Si (79.46 MHz)
NMR spectra were recorded on a Varian UNITY Inova 400
spectrometer in C6D6 solutions at 25 °C. 29Si NMR spectra were
measured by the DEPT pulse sequence. Chemical shifts (δ/
ppm) are given relative to the solvent signal (δH 7.15, δC 128.0)
and to external tetramethylsilane in C6D6 (δSi 0). EI-MS
spectra were obtained on a VG-7070E mass spectrometer at
70 eV. The crystalline samples in sealed capillaries were
(23) Compound 2 can be obtained by the reduction of [{η5-C5-
Me4(SiMe3)}2TiCl2] by active Mg in THF at room temperature, however,
it is strongly contaminated by the impurity described in ref 17, by the
hydride 5,15 or by [{η5-C5Me4(SiMe3)}2TiCl].13
(24) (a) Burlakov, V. V.; Dolgushin, F. M.; Yanovsky, A. I.; Struch-
kov, Yu. T.; Shur, V. B.; Rosenthal, U.; Thewalt, U. J . Organomet.
Chem. 1996, 522, 241-247. (b) Burlakov, V. V.; Polyakov, A. V.;
Yanovsky, A. I.; Struchkov, Yu. T.; Shur, V. B.; Vol’pin, M. E.;
Rosenthal, U.; Go¨rls, H. J . Organomet. Chem. 1994, 476, 197-206. (c)
Ohff, A.; Zippel, T.; Arndt, P.; Spannenberg, A.; Kempe, R.; Rosenthal,
U. Organometallics 1998, 17, 4429-4437. (d) Witte, P. T., Klein, R.;
Kooijman, H.; Spek, A. L.; Pola´sˇek, M.; Varga, V. Mach, K. J .
Organomet. Chem. 1996, 519, 195-204.
(C(Cp)-SiMe3); 129.8, 130.1 (C(Cp)-Me); 246.4 (η2-CtC). 29
-
Si NMR (C6D6): δ -16.1 (η2-(Me3Si)2C2), -7.5 ((CH3)4(Me3Si)-
C5). The sample contained a small amount of free BTMSA. IR
(KBr, cm-1): 2946 (s), 2887 (s), 1620 (sh), 1595 (s), 1560 (sh),
1453 (m), 1403 (w), 1373 (m), 1333 (w), 1317 (s), 1242 (vs),
1124 (m), 1015 (m), 840 (vs), 752 (s), 677 (m), 652 (w), 633
(m), 618 (w), 447 (m). UV-near-IR (hexane, 22 °C, nm): 980.
EI-MS (direct inlet, 70 eV, 60-80 °C): cluster of peaks with
the most abundant m/z 434 ([M - BTMSA]+) and peaks arising
from BTMSA at m/z 170, 155, and 73 in relative abundances
corresponding well to those of free BTMSA. Intensities of the
peaks due to BTMSA decreased with respect to those of (M -
(25) (a) Mansel, S.; Thomas, D.; Lefeber, C.; Heller, D.; Kempe, R.;
Baumann, W.; Rosenthal, U. Organometallics 1997, 16, 2886-2890.
(b) Thomas, D.; Arndt, P.; Peulecke, N.; Spannenberg, A.; Kempe, R.;
Rosenthal, U. Eur. J . Inorg. Chem. 1998, 1351-1357. (c) Zippel, T.;
Arndt, P.; Ohff, A.; Spannenberg, A.; Kempe, R.; Rosenthal, U.
Organometallics 1998, 17, 4429-4437.
(26) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175-
292.
(27) Yoshida, J .; Nishiwaki, K. J . Chem. Soc., Dalton Trans. 1998,
2589-2596.
(28) Antropiusova´, H.; Dosedlova´, A.; Hanusˇ, V.; Mach, K. Transition
Met. Chem. 1981, 6, 90-93.

Bis(cyclopentadienyl)titanium(II) Complexes
Organometallics, Vol. 18, No. 18, 1999 3577
Ta ble 3. Cr ysta llogr a p h ic Da ta a n d Deta ils of th e Da ta Collection a n d Str u ctu r e Refin em en t for 1-3a
1
2
3
formula
Mr
cryst syst
space group
a (Å)
b (Å)
c (Å)
C
32H60Si4Ti
C24H42Si2Ti
434.66
orthorhombic
Cmca (No. 64)
14.087(3)
11.574(2)
16.137(3)
C26H46Si2Ti
462.71
monoclinic
C2/c (No. 15)
17.241(5)
8.309(2)
18.878(5)
98.65(2)
2673.6(12); 4
1.150
605.06
monoclinic
I2/a (No. 15)
18.807(2)
18.927(2)
21.214(2)
97.180(16)
7492.1(15); 8
1.073
â (deg)
V (Å3); Z
Dcalcd (g cm-3
2631.1(8); 4
1.097
0.423
brown-pink, prism
0.2 × 0.3 × 0.4
8010
)
µ (mm-1
)
0.374
0.420
color, habit
yellow, prism
0.3 × 0.3 × 0.5
13 477
yellow, prism
0.2 × 0.3 × 0.3
7847
cryst dimens (mm3)
no. of diffractions collected
2θ range (deg)
4.30-52.08
5.04-48.2
2.39-24.07
hkl range
no. of unique diffractions
-22 to +18; -19 to +23; -18 to +26 -16 to +16; -13 to +13; -18 to +18 -19 to +18; -9 to +8; -21 to +21
7125
1085
2084
no. of obsd diffractions, I > 2σ(I) 3059
925
944
1452
1008
F(000)
2640
no. of params
R(F); Rw(F2) (%)
GOF (F2), all data
R(F); Rw(F2) (I > 2σ(I))
R(σ) (%)
334
11.43; 10.63
0.730
4.72; 9.24
13.98
0.232; -0.273
68
140
7.80; 13.09
1.172
5.42; 12.29
5.66
0.595; -0.645
5.62; 15.23
1.084
4.91; 14.70
2.64
∆F (e Å-3
)
0.353; -0.272
R(F) ) ∑||Fo| - |Fc||/∑|Fo|, Rw(F2) ) [∑(w(Fo - Fc2)2)/(∑w(Fo2)2)]1/2, GOF ) [∑(w(Fo - Fc2)2)/(Ndiffrns - Nparams)]1/2, and R(σ) ) ∑σ(Fo2)/
a
2
2
2
∑Fo
.
BTMSA) during the course of measurement. Anal. Calcd for
dissolved in hexane. Crystallization from a concentrated
C
32H60Si4Ti: C, 63.52; H, 9.99. Found: C, 63.56; H, 10.04.
P r ep a r a tion of [{η5-C5Me4(SiMe3)}2Ti] (2). Crystalline
solution at -18 °C afforded 3 as greenish yellow crystals. Yield
0.2 g (86%). H NMR (C6D6): δ -0.08 (s, 9H, Me3Si); 1.33 (s,
1
1 (0.5 g, 0.8 mmol) was heated to 70 °C in a water bath under
a vacuum of 10-4 Torr while volatiles were collected in a trap
cooled by liquid nitrogen. After about 2 h, a pale green liquid
remained in the ampule, which solidified upon standing at
ambient temperature. GC-MS analysis of the volatiles revealed
BTMSA to be the sole component. The solid was dissolved by
condensing hexane vapor and crystallized from a minimum
amount of hexane at -18 °C to afford 2 as brown-pink platelike
crystals. The solutions of 2 in hexane, toluene, or C6D6 were
pale green.
6H, (CH3)4(Me3Si)C5); 2.09 (s, 6H, (CH3)4(Me3Si)C5); 2.34 (s,
2H, dCH2). 13C{1H} NMR (C6D6): δ 2.0 (Me3Si); 11.9, 15.6
((CH3)4(Me3Si)C5); 104.3 (dCH2); 121.0, 123.8, 130.1 (C(Cp)).
IR (KBr, cm-1): 2966 (sh), 2948 (vs), 2896 (vs), 2860 (sh), 1650
(w, b), 1476 (m), 1445 (m), 1431 (m), 1372 (m), 1345 (w), 1329
(s), 1244 (vs), 1121 (m), 1080 (w), 1017 (s), 837 (vs), 785 (m),
752 (s), 683 (m), 666 (w), 631 (m), 614 (w), 573 (m), 566 (sh),
553 (sh), 468 (m), 416 (s). UV-near-IR (hexane, nm, 22 °C):
340(sh) . 990 nm. EI-MS (direct inlet, 70 eV, 50-70 °C); m/z
(relative abundance)): a cluster of peaks with the highest
abundance of m/z 433 ([M - C2H5]+, 11), 194 (13), 177 (14),
120 (20), 73 (100). Anal. Calcd for C26H46Si2Ti: C, 67.49; H,
10.02. Found: C, 67.46; H, 9.99.
Alternatively, crystalline 1 was dissolved in fresh hexane,
the solution was evaporated under vacuum, and the residue
was kept at ambient temperature under dynamic vacuum
overnight. Crystallization of the greenish residue from its
hexane solution gave the same product as the above procedure.
The conversions of 1 to 2 were virtually quantitative. Yields
of pure crystals were in both cases ca. 0.2 g (50-60%). The
only observable byproduct was an unidentified blue paramag-
netic compound.17 Larger concentrations of this impurity were
detected in the mother liquors from the crystallizations. Data
for 2 are as follows. 1H NMR (C6D6, 25 °C): δ 6.95 (Me3Si,
∆ν1/2 ≈ 40 Hz), 26.25 ((CH3)4(Me3Si)C5), ∆ν1/2 ≈ 110 Hz).
Chemical shifts follow the Curie law in the range 0-60 °C as
proved by numeric regression in the form δ ) a + bT-1. IR
(KBr, cm-1): 2940 (vs), 2888 (vs), 2850 (vs), 2719 (w), 1473
(m), 1440 (m), 1402 (w), 1372 (m), 1341 (sh), 1327 (s), 1315
(sh), 1241 (vs), 1120 (m), 1080 (w), 1017 (s), 942 (w), 835 (vs),
750 (s), 681 (s), 644 (sh), 629 (s), 613 (m), 573 (s), 555 (sh),
416 (s). UV-near-IR (hexane, 22 °C, nm): 300 > 340 (sh) >
370 (sh) . 570 . 950 (sh). EI-MS (direct inlet, 70 eV, 50-70
Attem p ted Rea ction of 2 w ith Din itr ogen . An evacuated
ampule (500 mL) equipped with a glass stopcock and a
breakable seal was filled by purified nitrogen to atmospheric
pressure in a glovebox and closed. The stopcock was sealed
off, and the ampule was attached to another one containing
the solution of 2 in hexane. The solution was poured from one
ampule to the other with shaking and finally transferred into
a device with quartz cuvettes. Neither a visual color change
upon cooling the solution to liquid-nitrogen temperature nor
any change in its UV-near-IR spectrum on cooling to -15 °C
were observed.
X-r a y Cr ysta l Deter m in a tion . Selected crystals of 1-3
were mounted in Lindenmann glass capillaries under nitrogen
in a glovebox (Labmaster 130, mBraun), and the capillaries
were closed with sealing wax. The X-ray measurements were
carried out at room temperature on a STOE IPDS imaging
plate diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å). The diffraction data were corrected
for Lorentz and polarization effects. Since the absorption
coefficients were low, no absorption correction was applied.
Structures 1 and 3 were solved by direct methods;29 structure
2 was solved by the heavy-atom (Patterson) method.30 The
refinement was carried out by full-matrix least squares on F2
°C; m/z (relative abundance)): 436 (13), 435 (27), 434 (M•+
,
61), 433 (32), 432 (16), 361 ([M - SiMe3]+, 10), 177 (10), 120
(9), 73 (100). Anal. Calcd for C24H42Si2Ti: C, 66.32; H, 9.74.
Found: C, 66.27; H, 9.71.
P r epar ation of [{η5-C5Me4(SiMe3)}2Ti(η2-CH2dCH2)] (3).
On a vacuum line, ethylene at a pressure of 600 Torr was
admitted to a solution of 2 (0.2 g, 0.5 mmol) in hexane. The
solution was cooled by liquid nitrogen and warmed to room
temperature. This cycle was repeated for the second time,
although even after the first cycle the pale green solution
turned an intense yellow. Ethylene and hexane were evapo-
rated under vacuum, and a yellow crystalline residue was
(29) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473.
(30) Sheldrick, G. M.; Dauter, Z.; Wilson, K. S.; Hope, H.; Sieker,
L. C. Acta Crystallogr. 1993, D49, 18-23.

3578 Organometallics, Vol. 18, No. 18, 1999
Hora´cˇek et al.
using a variance-based weighting scheme in the final stages.31
All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were included in their calculated positions and
readjusted after each refinement cycle. In structure 2, the
hydrogen atoms bonded to C(7) (one H atom by space group
symmetry) were identified in a difference Fourier map and
then readjusted into their idealized positions. In the structure
of 3, the two hydrogen atoms at C(13) were found on a
difference Fourier map and refined isotropically. The relevant
crystal data and details on the data collection and the structure
refinement for 1-3 are given in Table 3.
Ack n ow led gm en t. This research was supported by
the Grant Agency of the Academy of Sciences of the
Czech Republic (Grant No. A4040711) and by the
Volkswagen Stiftung. The Grant Agency of the Czech
Republic sponsored access to the Cambridge Structure
Database (Grant No. 203/99/0067).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, atomic coordinates, thermal parameters, in-
tramolecular distances and angles, and dihedral angles of
least-squares planes and packing diagrams for 1-3. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(31) Sheldrick, G. M. SHELXL97: Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1997.
OM990286K