Nonclassical bonding in titanasilacyclohexadiene compounds resulting from highly methyl-substituted titanocene-bis(trimethylsilyl)ethyne complexes and bis((trimethylsilyl)ethynyl)silanes

Article abstract of DOI:10.1021/om058038d

Reactions at elevated temperatures (150°C) of titanocene-η2- bis(trimethylsiryl)ethyne (btmse) complexes [(η⁵-C ₅H_5-nMe_n)₂Ti(η²- btmse)] (n = 3-5; 1b-d) with bis((trimethylsilyl)-ethynyl)dimethylsilane (2a) afford the unusual 1,1-bis(η⁵-cyclopentadienyl)-4,4-dimethyl-3,5- bis(trimethylsilyl)-1-titana-4-silacyclohexa-2,5-diene complexes [(η5-C ₅H_5-nMe_n)₂Ti{C=C(SiMe ₃)}₂SiMe₂] (4b-d), whereas the nonmethylated precursor [(η-C₅H₅)₂Ti(η²- btmse)] (1a) gives under similar conditions the known dinuclear, acetylide-bridged complex [{(η⁵-C₅H₅) ₂-Ti(μ-η¹:η²-C≡CSiMe ₃)}₂] (3a). In contrast, analogous reactions with bis((trimethylsilyl)-ethynyl)diphenylsilane (2b) give the product of simple ligand exchange [(η-C₅Me₅)₂Ti(η ²-Me₃SiC≡CSiPh₂C≡CSiMe ₃)] (6d) from 1d and mixtures containing the similar complex [(η⁵-C₅HMe₄)₂Ti(η ²-Me₃SiC≡CSiPh₂C≡CSiMe ₃)] (6c) and the titanasilacyclohexadiene [Ti(η⁵- C₅HMe₄)₂Ti{C=C(SiMe₃)} ₂SiPh₂] (5c) from 1c. Hydrogenolysis of 5c (1 bar/3 h) affords 1,4-bis(trimethylsilyl)-5,5-diphenyl-5-silacyclopenta-1,3-diene (7). Compounds 4 and 5 possess a surplus of two bonding electrons at the titanium-bonded carbon atoms (C^α) with paired spins, whose presence is reflected by extremely short Ti-C^α bond lengths (1.981(4)-1.998(3) A) and C^α-C^α contacts (1.821(4)-1.933(2) A), the latter excluding the presence of a 3-silacyclopenta-1,4-diene moiety simply bonded to titanium via two a bonds. DFT calculations showed that the two singly occupied p orbitals at C ^α interact with the titanocene 1a₁ orbital, giving rise to a three-center-two-electron, Δ-shaped bond.

Full text of DOI:10.1021/om058038d

6094
Organometallics 2005, 24, 6094-6103
Nonclassical Bonding in Titanasilacyclohexadiene
Compounds Resulting from Highly Methyl-Substituted
Titanocene-Bis(trimethylsilyl)ethyne Complexes and
Bis((trimethylsilyl)ethynyl)silanes
Michal Hora´cˇek,† Petr Sˇteˇpnicˇka,‡ Ro´bert Gyepes,‡ Ivana C´ısarˇova´,‡
Jirˇ´ı Kubisˇta,† Lenka Lukesˇova´,† Philippe Meunier,§ and Karel Mach*,†
J. Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejsˇkova 3, 182 23 Prague 8, Czech Republic, Department of Inorganic Chemistry,
Faculty of Science, Charles University, Prague, Czech Republic, and Laboratoire de Synthe`se
et d’Electrosynthe`se Organome´talliques associe´ au CNRS (LSEO UMR 5632),
Universite´ de Bourgogne, Faculte´ des Sciences Gabriel, Dijon, France
Received June 30, 2005
Reactions at elevated temperatures (150 °C) of titanocene-η2-bis(trimethylsilyl)ethyne
(btmse) complexes [(η5-C5H5-nMen)2Ti(η2-btmse)] (n ) 3-5; 1b-d) with bis((trimethylsilyl)-
ethynyl)dimethylsilane (2a) afford the unusual 1,1-bis(η5-cyclopentadienyl)-4,4-dimethyl-
3,5-bis(trimethylsilyl)-1-titana-4-silacyclohexa-2,5-diene complexes [(η5-C5H5-nMen)2Ti{Cd
C(SiMe3)}2SiMe2] (4b-d), whereas the nonmethylated precursor [(η5-C5H5)2Ti(η2-btmse)] (1a)
gives under similar conditions the known dinuclear, acetylide-bridged complex [{(η5-C5H5)2-
Ti(µ-η1:η2-CtCSiMe3)}2] (3a). In contrast, analogous reactions with bis((trimethylsilyl)-
ethynyl)diphenylsilane (2b) give the product of simple ligand exchange [(η5-C5Me5)2Ti(η2-
Me3SiCtCSiPh2CtCSiMe3)] (6d) from 1d and mixtures containing the similar complex [(η5-
C5HMe4)2Ti(η2-Me3SiCtCSiPh2CtCSiMe3)] (6c) and the titanasilacyclohexadiene [Ti(η5-
C5HMe4)2Ti{CdC(SiMe3)}2SiPh2] (5c) from 1c. Hydrogenolysis of 5c (1 bar/3 h) affords 1,4-
bis(trimethylsilyl)-5,5-diphenyl-5-silacyclopenta-1,3-diene (7). Compounds 4 and 5 possess
a surplus of two bonding electrons at the titanium-bonded carbon atoms (CR) with paired
spins, whose presence is reflected by extremely short Ti-CR bond lengths (1.981(4)-
1.998(3) Å) and CR-CR contacts (1.821(4)-1.933(2) Å), the latter excluding the presence of
a 3-silacyclopenta-1,4-diene moiety simply bonded to titanium via two σ bonds. DFT
calculations showed that the two singly occupied p orbitals at CR interact with the titanocene
1a1 orbital, giving rise to a three-center-two-electron, ∆-shaped bond.
Introduction
because the active magnesium can activate other bonds
which can thus participate in the reaction with the
acetylenic reagent. Examples of such a behavior can be
sought in the magnesium reduction of [MCl2(η5-C5Me5)2]
(M ) Ti, Zr) in the presence of 1,4-disubstituted buta-
1,3-diynes where methyl groups at the pentamethylcy-
clopentadienyl ligands reacted with the diynes,2a,b yield-
ing products differing from those obtained from the
metallocene-btmse complexes.2c
Titanocene- and zirconocene-bis(trimethylsilyl)-
ethyne (btmse) complexes, [M(η5-C5H5-nMen)2(η2-btmse)]
(M ) Ti, Zr; n ) 0, 5), are known to react with a variety
of reagents by simple replacement of the btmse ligand.
In this way, a number of organometallic products arising
from reactions of otherwise highly unstable transient
titanocenes or zirconocenes, [M(η5-C5H5-nMen)2], were
obtained under relatively mild conditions.1 For the cases
where the reagent contains an acetylenic moiety, the
direct reduction of the metallocene dichlorides by mag-
nesium in the presence of the acetylenic reagent can
afford the same product as that arising from the btmse
replacement. However, the latter method is less specific,
Generally, the reaction pathway depends on the
nature of the metallocene and the substituents of both
the diynes and the η5-cyclopentadienyl rings in the
metallocene unit as well as on the metal-to-diyne ratio.1c
Nonconjugated diynes with single-atom spacers,
(R1CtC)2X, where X ) CH2, SiR2 , PR3, were shown to
2
react with zirconocene precursors in different ways,
depending on the nature of the spacer X: diynes
possessing the methylene group afford binuclear zir-
* To whom correspondence should be addressed. E-mail: mach@
jh-inst.cas.cz.
† Academy of Sciences of the Czech Republic.
‡ Charles University.
§ Universite´ de Bourgogne.
(2) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. J. Am. Chem. Soc. 1999, 121, 8313-
8323. (b) Hora´cˇek, M.; Sˇteˇpnicˇka, P.; Gyepes, R.; C´ısarˇova´, I.; Pola´sˇek,
M.; Mach, K.; Pellny, P.-M.; Burlakov, V. V.; Baumann, W.; Spannen-
berg, A.; Rosenthal, U. J. Am. Chem. Soc. 1999, 121, 10638-10639.
(c) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Chem. Eur. J. 2000, 6, 81-90.
(1) (a) Rosenthal, U.; Burlakov, V. V. In Titanium and Zirconium
in Organic Synthesis; Marek, I., Ed.; Wiley-VCH: Weinheim, Germany,
2002; p 355. (b) Rosenthal, U.; Burlakov, V. V.; Arndt, P.; Baumann,
W.; Spannenberg, A. Organometallics 2003, 22, 884-900. (c) Rosenthal,
U.; Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V. Acc. Chem. Res.
2000, 33, 119-129.
10.1021/om058038d CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/25/2005

Titanasilacyclohexadiene Compounds
Organometallics, Vol. 24, No. 25, 2005 6095
Chart 1
Scheme 1
conacyclopentadiene complexes (Chart 1, A; R1 ) SiMe3),3
those with bis(organyl)silylene bridge give rise to an-
nelated zirconacyclobutene-silacyclobutene compounds
(Chart 1, B; R1 ) Me, Et, Ph; R2 ) Ph, p-tolyl),4 and
the dialkynylphosphanes (PhCtC)2PR3 (R3 ) substi-
tuted aryl, CMe3, N(iPr)2) react to give zirconacyclo-
pentadiene-phosphiranes (Chart 1, C).5 In all cases, a
divalent zirconium intermediate undergoes oxidative
cycloaddition to provide ZrIV complexes; only the rigid
two-carbon o-phenylene spacer allows the zirconium
atom to remain divalent, π-coordinating both triple
bonds (Chart 1, D).6
Results and Discussion
The reaction of equimolar amounts of [Ti(η2-Me3Si-
CtCSiMe3)(η5-C5H5-nMen)2] (1; n ) 0 (a), 3 (b), 4 (c), 5
(d)) and Me2Si(CtCSiMe3)2 (2a) at 150 °C led to
different products for n ) 3-5 and for n ) 0 (Scheme
1). For n ) 0, the main reaction pathway was a scission
of 2a, affording the thermodynamically stable dimeric
acetylide complex 3a. The molecular structure of 3a was
virtually identical with those published by Wood et al.9a
and by Rosenthal and Go¨rls,9b although the unit cells
differ crystallographically in all cases.10 On the other
hand, for n ) 3-5, the above reaction yielded exclusively
the highly unusual 1-titana-4,4-dimethyl-4-sila-3,5-bis-
(trimethylsilyl)cyclohexa-2,5-diene complexes 4b-d
(Scheme 1).
Reactions between titanocene precursors and spaced
diynes have been extensively studied by Rosenthal et
al.1c It was shown that tetraalkynylsilanes react with
titanocene- or zirconocene-btmse complexes to give
dinuclear spirocyclic complexes in which the planar
zirconacyclobutene-silacyclobutene moieties (type B)
share a tetrahedral silicon atom.7 We have found that
compounds of type B (Chart 1) are accessible in high
yields from [Ti(η2-btmse)(η5-C5H5-nMen)2] (n ) 0, 4, 5)
The molecular structures of 4b-d have been estab-
lished by X-ray single-crystal diffraction analysis (see
1
below) and further corroborated by H and 13C NMR
spectra. The spectra confirmed the presence of C2- and/
or mirror-symmetric (η5-C5H5-nMen)2Ti units and two
chemically different methylsilyl groups in the intensity
ratio 2:1. In addition, the 13C NMR spectra show very
characteristic signals due to CR and Câ at δC 335-338
and ca. 133, respectively. The proton-coupled 13C NMR
spectra clearly exclude the presence of hydrogen atoms
and R2 Si(CtCR1)2 for R1/R2 ) Ph/Ph and Ph/Me, while
2
for R1/R2 ) t-Bu/Me the same reaction proceeds satis-
factorily only with titanocene precursors having less
sterically demanding cyclopentadienyl ligands such as
C5H5 or 1,3-C5H3Me2. The bulkier titanocene complex
[Ti(η5-C5HMe4)2(η2-btmse)] reacted sluggishly with Me2-
Si{CtC(t-Bu)}2 even at 150 °C/8 h, giving intractable
product mixtures, whereas [Ti(η5-C5Me5)2(η2-btmse)]
underwent thermolysis at 130 °C to give the doubly
tucked-in complex [Ti(η5-C5Me5){η3:η4-C5Me3(CH2)2}].8
In this contribution, we report on the reactions of
other bulky dialkynylsilanes, (Me3SiCtC)2SiMe2 and
(Me3SiCtC)2SiPh2, with a series of titanocene-btmse
complexes [Ti(η5-C5H5-nMen)2(η2-btmse)] (n ) 0, 3, 4, 5)
and on the unprecedented bonding mode occurring in
their products.
at CR and Câ, showing the expected JCH coupling
constants for the rest of the molecules.
1
IR spectra of complexes 4b-d and 5c showed a strong
and broad absorption band attributable to a ν(CRdCâ)
stretching vibration, whose position shifts from 1544
cm-1 for 4b to 1528 cm-1 for 4d, following the increasing
electron density at the titanium atom. In EI-MS spectra,
the compounds displayed only low-intensity peaks for
the molecular ions, whose intensities were lower as the
temperature of evaporation became higher. In addition,
the spectra displayed titanocene ions as the base peaks,
ions of the diynes, and fragments of the latter.
(3) Du, B.; Farona, M. F.; McConnville, D. B.; Youngs, W. J.
Tetrahedron 1995, 51, 4359-4370.
(4) Takahashi, H.; Xi, Z.; Obora, Y.; Suzuki, N. J. Am. Chem. Soc.
1995, 117, 2665-2666. (b) Xi, Z.; Fischer, R.; Hara, R.; Sun, W.-H.;
Obora, Y.; Suzuki, N.; Nakajima, K.; Takahashi, H. J. Am. Chem. Soc.
1997, 119, 12842-12848.
(5) Mathieu, A.; Miquel, Y.; Igau, A.; Donnadieu, B.; Majoral, J.-P.
Organometallics 1997, 16, 3086-3088.
(6) Warner, B. P.; Davis, W. M.; Buchwald, S. L. J. Am. Chem. Soc.
1994, 116, 5471-5472.
(7) Pellny, P.-M.; Peulecke, N.; Burlakov, V. V.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Organometallics 1996, 15, 1198-1200.
(8) Hora´cˇek, M.; Bazyakina, N.; Sˇteˇpnicˇka, P.; Gyepes, R.; C´ısa-
rˇova´,I.; Bredeau, S.; Meunier, Ph.; Kubisˇta, J.; Mach, K. J. Organomet.
Chem. 2001, 628, 30-38.
In subsequent work, the diyne component was modi-
fied at the bridging silicon atom by replacing the
methyls with phenyl groups. However, this change
(9) (a) Wood, G. L.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1989, 28, 382-384. (b) Rosenthal, U.; Go¨rls, H. J. Organomet. Chem.
1992, 426, C53-C59.
(10) Crystallographic data for C30H38Si2Ti2: monoclinic crystal
system, space group P21/n (No. 14), a ) 11.3200(4) Å, b ) 14.9700(5)
Å, c ) 16.6930 Å; â ) 96.216(2)°; V ) 2812.17(15) Å3, Z ) 4, F ) 1.300
g cm-3, CCDC deposition number CCDC-275739.

6096 Organometallics, Vol. 24, No. 25, 2005
Hora´cˇek et al.
Scheme 2
Figure 1. View of molecule 1 of compound 4d. Thermal
ellipsoids are drawn at the 30% probability level; hydrogen
atoms are omitted for clarity.
resulted in a remarkable change of the diyne reactiv-
ity: the decamethyltitanocene complex 1d reacted with
bis((trimethylsilyl)ethynyl)diphenylsilane (2b) with ligand
exchange to give [(η5-C5Me5)2Ti(η2-Me3SiCtCSiPh2-
CtCSiMe3)] (6d), while the less electron-saturated and
less sterically congested titanocene-btmse complex 1c
afforded under identical conditions a mixture of [(η5-
C5HMe4)2Ti(η2-Me3SiCtCSiMe2CtCSiPh3)] (6c) and
1,1-bis(η5-tetramethylcyclopentadienyl)-4,4-diphenyl-
3,5-bis(trimethylsilyl)-1-titana-4-silacyclohexa-2,5-di-
ene (5c) (Scheme 2). Neither prolonged heating of the
1d-2b mixture to 130 °C nor heating to a higher
temperature led to a titanasilacyclohexadiene complex.
Instead, compound 6d dissociated at 150 °C with a
concurrent hydrogen transfer from two vicinal methyl
groups of one cyclopentadienyl ligand onto the leaving
silyldiyne to give the allyl-diene derivative [Ti(η5-C5-
Me5){η3:η4-C5Me3(CH2)2}].11 It is noteworthy that this
compound results directly from thermolysis of 1d (at 130
°C).12 The reaction of 2b with 1a gave an intractable
material, though the NMR signals at δC 234.3 and 248.5
clearly indicate the presence of a 6-type product; at-
tempts to isolate pure product, however, failed. The
molecular structures of 6d and 5c were established by
X-ray diffraction analysis and NMR and IR spectra.
Scheme 3
with excess methanol to 90 °C for 3 h afforded 1,4-bis-
(trimethylsilyl)-5,5-dimethyl-5-silacyclopenta-1,3-
diene (8; Scheme 3), according to GC-MS analysis. Other
products of the methanolysis were pentamethylcyclo-
pentadiene (IR spectrum) and [(η5-C5Me5)Ti(OMe)-
(µ-OMe)]2,13 identified by its IR spectrum and X-ray
crystal structure analysis.
Structural Data. The molecular structures of com-
plexes 4b-d and 5c combine titanocene moieties with
the unprecedented titanasilacyclohexadiene moieties,
whose geometric parameters provide essential informa-
tion for the discussion of the bonding situation. Molec-
ular structures of complexes 4d and 5c as determined
by single-crystal X-ray diffraction are presented in
Figures 1 and 2, respectively, and the selected geometric
parameters for 4b-d and 5c are listed in Table 1.
The arrangement of the bent-titanocene moiety is
known to vary with the number of the ring methyl
substituents.14 In the compounds studied, the cyclopen-
tadienyl ligands are staggered, and when they contain
at least one hydrogen substituent on each cyclopenta-
dienyl ligand, these protons occupy the hinge positions.
In the permethylated complex 4d, the sterically strained
methyl groups in the hinge positions are responsible for
a remarkably smaller dihedral angle between the cy-
clopentadienyl ring least-squares planes (38.3(2) vs
45.3(1)° for 4c).
Attempts to prepare the titanocene complexes with
η2-coordinated 2b by reduction of the appropriate ti-
tanocene dichlorides with magnesium in the presence
of 1 molar equiv of the diyne met with no success except
for [TiCl2(η5-C5Me5)2], which afforded 6d in a high yield.
The analogous products 6a and 6c are likely formed as
well, but the reluctance of the crude reaction mixtures
to crystallize did not allow for isolation of pure products.
To support the formulation and bonding (see below)
of 4 and 5 type complexes, we attempted hydrogenolysis
or methanolysis of each representative type. Thus,
exposure of hexane solution of 5c to hydrogen (1 bar/3
h) resulted in liberation of 1,4-bis(trimethylsilyl)-5,5-
diphenyl-5-silacyclopenta-1,3-diene (7; Scheme 3), which
1
was identified by means H and 13C NMR and EI-MS
spectra. Likewise, heating of a hexane solution of 4d
(11) 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.
(12) Varga, V.; Mach, K.; Pola´sˇek, M.; Sedmera, P.; Hiller, J.;
Thewalt, U.; Troyanov, S. I. J. Organomet. Chem. 1996, 506, 241-
251.
(13) Mach, K.; Kubisˇta, J.; C´ısarˇova´, I.; Sˇteˇpnicˇka, P. Inorg. Chem.
Commun. 2003, 6, 974-977.
(14) Varga, V.; Hiller, J.; Gyepes, R.; Pola´sˇek, M.; Sedmera, P.;
Thewalt, U.; Mach, K. J. Organomet. Chem. 1997, 538, 63-74.

Titanasilacyclohexadiene Compounds
Organometallics, Vol. 24, No. 25, 2005 6097
Figure 3. Perspective view of the molecular structure of
6d with the atom-labeling scheme (30% probability).
Figure 2. Perspective view of the molecular structure of
5c, showing the atom-labeling scheme (30% probability).
Table 2. Selected Bond Lengths (Å) and Bond
Angles (deg) for 6d
Table 1. Selected Bond Lengths (Å) and Bond
Angles (deg) for 4b-d and 5c
Ti-Cg(1)a
2.1174(12)
2.130(2)
1.313(3)
1.868(2)
1.839(3)
1.877(2)
Ti-Cg(2)a
2.1235(12)
2.128(2)
1.210(3)
1.846(2)
1.847(3)
1.883(2)
4b
4c
4d
5c
Ti-C(21)
Ti-C(22)
C(21)-C(22)
C(21)-Si(1)
Si(2)-C(23)
Si(2)-C(25)
C(23)-C(24)
C(22)-Si(2)
Si(3)-C(24)
Si(2)-C(31)
Bond Lengths
Ti-Cg(1)a
2.068(1)
2.067(1)
1.996(2)
1.985(2)
1.326(3)
1.324(3)
1.882(2)
1.882(2)
1.870(2)
1.871(2)
1.924(3)
2.0717(7) 2.099(2)
2.0764(7) 2.099(2)
1.9894(14) 1.981(4)
1.9916(15) 1.996(4)
1.326(2)
1.328(2)
2.0722(17)
2.0837(17)
1.998(3)
1.992(3)
1.348(4)
1.333(4)
1.870(3)
1.869(3)
1.869(3)
1.858(3)
1.821(4)
Ti-Cg(2)a
Ti-C(R1)
Ti-C(R2)
Cg(1)-Ti-Cg(2)a
Cg(1)-Ti-C(22)
Cg(2)-Ti-C(22)
Ti-C(21)-C(22)
138.69(5) Cg(1)-Ti-C(21)
109.43(7) Cg(2)-Ti-C(21)
110.37(7) C(21)-Ti-C(22)
71.97(14) Ti-C(22)-C(21)
108.99(8)
109.55(7)
35.93(9)
C(R1)-C(â1)
C(R2)-C(â2)
Si-C(â1)
1.333(6)
1.338(6)
1.8780(15) 1.878(5)
1.8791(15) 1.881(4)
1.8665(15) 1.862(4)
1.8691(15) 1.859(4)
Si-C(â2)
72.10(14)
C(â1)-Si(â1)
C(â2)-Si(â2)
C(R1)-C(R2)b
Si(1)-C(21)-C(22) 136.27(19) Si(2)-C(22)-C(21) 135.15(19)
C(22)-Si(2)-C(23) 109.44(11) Si(2)-C(23)-C(24) 175.3(2)
æb
40.84(7)
19.66(12)
1.933(2)
1.902(6)
Si(3)-C(24)-C(23) 176.8(2)
τc 21.35(12) τd
Bond Angles
Cg(1)-Ti-Cg(2)a
Cg(1)-Ti-C(R1)
Cg(1)-Ti-C(R2)
Cg(2)-Ti-C(R1)
Cg(2)-Ti-C(R2)
C(R1)-Ti-C(R2)
Ti-C(R1)-C(â1)
Ti-C(R2)-C(â2)
Si-C(â1)-C(R1)
Si-C(â2)-C(R2)
C(â1)-Si-C(â2)
137.98(4) 139.12(3) 142.81(9) 140.13(7)
107.38(7) 107.96(5) 105.86(14) 107.87(11)
107.14(7) 108.25(5) 106.01(14) 107.54(11)
109.44(7) 107.65(5) 106.51(14) 107.93(11)
109.20(7) 107.24(5) 106.66(14) 107.29(11)
a Cg(1) and Cg(2) are centroids of the C(1-5) and C(11-15)
cyclopentadienyl rings, respectively. b æ is the dihedral angle
between the least-squares cyclopentadienyl planes. c τ is the
dihedral angle between the plane defined by Ti, C(21), and C(22)
and the least-squares plane of the cyclopentadienyl plane of Cg(1).
d τ is the dihedral angle between the plane defined by Ti, C(21),
and C(22) and the least-squares plane of the cyclopentadienyl
plane of Cg(2).
57.81(9)
58.09(6)
57.16(17) 54.32(13)
171.05(18) 171.3(1)
172.18(18) 171.0(1)
110.13(16) 110.3(1)
109.89(16) 110.4(1)
98.65(10) 98.62(6)
173.0(4)
171.2(3)
109.6(3)
110.0(3)
98.5(2)
174.4(3)
174.8(3)
108.4(2)
108.8(2)
98.45(14)
123.2(2)
122.1(3)
41.49(15)
23.20(21)
18.29(25)
between the CR carbon atoms attached to titanium are
within 1.821(4) Å (5c) and 1.933(2) Å (4c). The C-Si
bonds within the rings (average 1.879(2) Å) are slightly
longer than the C-Si bonds to outer trimethylsilyl
groups (average 1.868(2) Å). The in-ring angles at the
silicon atoms are much larger (average 98.65(7)°) than
the analogous angles at the titanium atoms (average
58.05(6)°) and, correspondingly, the angles at the double
bonds to Ti (average 171.2(1)°) are much larger than to
ring Si atoms (110.2(1)°). Accordingly, the angles at the
double bonds involving the outer Si atoms are larger
than expected for the ideal sp2 hybridization (average
124.3(1)°). The structure of 5c with a bridging diphe-
nylsilyl group differed from the 4b-d structures in a
considerably shorter CR-CR distance of 1.821(4) Å, a
smaller CR-Ti-CR angle at the Ti atom (54.3(1)°), and
a more linear arrangement of Ti-CR-Câ bonds (average
Ti-CR-Câ ) 174.6(3)°) (see Table 1).
In compound 6d, the permethyltitanocene moiety
binds one triple bond in a π-bonding mode, as in the
parent complex 1d (Figure 3). The molecular geometry
of the titanocene-acetylenic moiety (Table 2) is very
close to that of 1d (n.b.: the triple bond is substituted
by similar silyl groups).1b,15 The angles at the coordi-
nated triple bond, Si1-C21-C22 ) 136.3(2)° and Si2-
C22-C21 ) 135.2(2)°, and at the free triple bond, Si2-
Si(â1)-C(â1)-C(R1) 123.51(17) 123.97(11) 124.3(4)
Si(â2)-C(â2)-C(R2) 122.89(17) 124.75(11) 124.4(3)
æc
τd
τe
48.18(10) 45.3(1)
23.33(14) 23.0(1)
24.85(14) 22.3(1)
38.3(2)
19.3(2)
19.0(2)
a Cg(1) and Cg(2) are centroids of the cyclopentadienyl rings
denoted by lower and higher numbers of carbon atoms, respec-
tively. b Nonbonding distance. c æ is the dihedral angle between
the least-squares cyclopentadienyl planes. d τ is the dihedral angle
between the least-squares plane defined by Ti, C(R1), C(â1), C(R2),
C(â2), and Si and the least-squares plane of the cyclopentadienyl
ring of Cg(1). e τ is the dihedral angle between the least-squares
plane defined by Ti, C(R1), C(â1), C(R2), C(â2), and Si and the
least-squares plane of the cyclopentadienyl ring of Cg(2).
In all the structures, the 1-titana-4-silacyclohexa-2,5-
diene moiety is planar, with both terminal trimethylsilyl
groups attached to Câ carbon atoms with respect to the
titanium center. This is at variance with structure B
(Chart 1), where the shift of only one terminal silyl
group allows for cross-linking via carbon atoms with the
formation of a fused titanacyclobutene-silacyclobutene
system.8 There is no doubt about the position of the
double bonds; their lengths range from 1.326(2) to
1.348(4) Å. The Ti-CR bonds (1.985(2)-1.998(3) Å) are
shorter by ca. 0.2 Å than in the corresponding deriva-
tives possessing B-type structures,8 and the distances

6098 Organometallics, Vol. 24, No. 25, 2005
Hora´cˇek et al.
Scheme 4
C23-C24 ) 175.3(2)° and Si3-C24-C23 ) 176.8(2)°,
differ negligibly in the pairs, and the bond lengths C21-
C22 ) 1.313(3) Å and C23-C24 ) 1.210(3) Å fall into
the range of distances known thus far.1c The angle
subtended by the cyclopentadienyl least-squares planes,
40.8(1)°, is nearly regularly bisected by the Ti,C21,C22
plane (21.3(1) and 19.6(1)°). A similar permethyl-
titanocene-1,4-bis(trimethylsilyl)buta-1,3-diyne π-co-
ordinated by one triple bond showed a remarkable
difference between the angles of the coordinated triple
bond with the SiMe3 group (130.0(2)°) and with the
carbon atom of the noncoordinated triple bond
(141.9(3)°).2a
Figure 4. Graphical representation of the Ψ1 molecular
orbital (∆ bond).
action is extended even to the metallic center. The
respective molecular orbital is generated from the empty
a1 orbital at the titanium atom, which being in proper
orientation for good overlap with the singly occupied
carbon p orbitals (Scheme 4b), causes the carbon p lobes
to become more elongated and generate a long-range
CR-CR bond (Figure 4). Although this bond is formally
of σ type (the wave function having no node in the
CR-CR interconnection), it can be described more prop-
erly as a three-center-two-electron (3c-2e) C-Ti-C
bond both for its shape and for the involvement of the
metallic center. To justify the correctness of the 3c-2e
bond formalism, a natural bonding analysis (NBA) was
carried out against several possible Lewis representa-
tions and the best fit to the molecular wave function
was obtained under the assumption of a 3c-2e bonding
interaction while retaining the “regular” Ti-CR σ bonds.
In our further discussion, this 3c-2e bond will be
referred to as a ∆ bond because of its unique shape.
The above molecular wave function was also utilized
to obtain the NMR shifts for individual atoms in 4c. The
excellent correlation between GIAO parameters and
observed 13C NMR shifts confirmed the correctness of
the wave function.
The genesis of the ∆ bond is similar to that of other
3c-2e bonds. Its best theoretical description lies in the
extension of the MO LCAO scheme to three interacting
atoms, producing three MO’s (one bonding, one practi-
cally nonbonding, and one antibonding) from three AO’s.
It is important to realize at this point that any potential
ligand orbital going into interaction with the titanocene
a1 orbital must transform according to the same ir-
reducible representation. In our case, however, neither
of the carbon p orbitals obeys this criterion. Neverthe-
less, the hybrid orbital resulting from the linear com-
bination æ1 + æ2 meets this requirement (Scheme 5).
Interaction of this hybrid orbital with the metallic a1
orbital gives rise to one bonding (Ψ1, the ∆ bond) and
one nonbonding MO (Ψ2). The third MO (Ψ3), resulting
from the antibonding interaction æ1 - æ2, has b2
symmetry and will have an interaction with the ap-
propriate frontier titanocene orbital.
Ab Initio Study. A CR-CR distance larger than 1.82
Å is not compatible with a σ bond, as drawn in a
silacyclopentadiene-titanacyclopropane representation
of compounds 4 and 5. Simultaneously, the diamagne-
tism of these compounds corroborates that that the
compounds are not true biradicals (Scheme 4a). On the
other hand, the shortness of the Ti-CR bonds can be
accounted for by the contribution of multiple bonding
(see discussion of the crystal structures above). Since
there is no pairing electron available at the titanium
atom, whose valency cannot be formally higher than 4,
one has to assume that one valence electron resides
predominantly on each of the CR carbon atoms, resulting
not only in an increase of the Ti-C bond order but also
leading to some CR-CR interactions that are reflected
in contacts significantly shorter than the sum of van
der Waals radii.
For a proper understanding of the rather peculiar
bonding scheme, the molecule of 4c has been subjected
to DFT studies. In agreement with chemical intuition,
calculational results confirmed the presence of σ bonds
between CR carbon atoms and the central titanium
atom. These σ bonds are the result of the Cp2Ti
fragment b2 frontier orbital16 interacting with the ap-
propriately oriented carbon p orbitals. As further ex-
pected, the second set of p orbitals generates the π bonds
between CR and Câ atoms.
Examination of the highest occupied molecular orbital
(HOMO) revealed the nature of the seemingly missing
CR-CR bond. The spatial shape of the HOMO indicates
that CR carbon atoms undergo a bonding interaction,
despite their large interatomic distance, and this inter-
(15) Burlakov, V. V.; Rosenthal, U.; Beckhaus, R.; Struchkov, Yu.
T.; Oehme, G.; Shur, V. B.; Vol’pin, M. E. Organomet. Chem. USSR
1990, 3, 237-238. (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.
(16) Orbitals are labeled according to: Lauher, J. W.; Hoffmann,
R. J. Am. Chem. Soc. 1976, 98, 1729-1741.
Comments on the Tentative Reaction Mecha-
nism. As for the formation of zirconocene B-type

Titanasilacyclohexadiene Compounds
Organometallics, Vol. 24, No. 25, 2005 6099
Scheme 5
B-type complex was recently explained by Negishi to
proceed via formation of zirconate-carbocationic di-
poles.19
The formation of thermodynamically stable com-
pounds 4 and 5, different from those of type B, is
apparently controlled by electronic and steric effects of
terminal trimethylsilyl groups. These are in “allylic”
positions with respect to the bridging dimethylsilylene
group, which leads to the induction of a positive charge
on all silicon atoms and, hence, to their mutual de-
stabilization. This effect has recently been demonstrated
for the first stable vinyl cation stabilized by the presence
of two silyl groups in positions â to the carbocation.20
The same effect is apparently responsible for an easy
scission of 1,4-bis(trimethylsilyl)buta-1,3-diyne at low-
valent titanocene species, affording dimeric titanocene-
(III) acetylides,21a methyl-substituted titanocene(III)
diacetylide tweezer complexes,21b or butenyne deriva-
tives,22 as well as for an easy silicon migration over
cyclopentadiene systems.23
Scheme 6
When the above-mentioned insertion mechanism4b,20
(Scheme 6) is considered, the silicon â-effect of bridging
silylene could also facilitate the 1,2-shift of SiMe3 groups
following the subsequent scission of the silirane and
silacyclobutene rings. In the particular case of dialky-
nylsilanes 2a,b, however, the two terminal trimethyl-
silyl groups in â-positions should also facilitate the
liberation of silylene. Since compounds 4 and 5 are
formed at temperatures where the titanocene-btmse
complexes lose btmse while generating titanocene in-
termediates,12 one can expect the Ti d2 atom to compete
with the silylene to give titanocene diacetylide, which
is subsequently stabilized by addition of the evolved
silylene to give thermodynamically stable structures 4
or 5 (Scheme 6). The process, for simplicity depicted as
a concerted one, is apparently a complex sequence of
steps which may contain, e.g., an oxidative addition of
the tC-SiMe2Ct bond to Ti(II) followed by liberation
of SiMe2, which brings about the formation of 3a in case
of more acidic and less sterically shielded [Ti(η5-C5H5)2]
species.24 For highly methyl-substituted titanocenes the
homolysis of the Ti-SiMe2(C2SiMe3) bond should lead
to the intermediate depicted in Scheme 6. In the absence
of direct experimental evidence, however, no preference
can be given to either mechanism. A somewhat similar
process resulting in a formal shift of phenyl groups was
observed during coupling of phenylacetylide groups in
zirconocene diacetylide induced by vanadocene.25
complexes, a vinylidene mechanism and an insertion
mechanism were considered, both suggesting the initial
coordination of the dialkynylsilane by one triple bond
to the titanium atom (Scheme 6).4b The vinylidene
mechanism should plausibly give the B-type product;
however, the titanocene-vinylidene species are known
to be highly unstable,17 and their presence is not
considered to take part in catalytic conversions medi-
ated by early-transition-metal complexes.18 On the other
hand, the insertion mechanism required the transient
formation of a fused zirconacyclopentadiene-silirane
intermediate.4b The rearrangement of the latter to the
(19) Negishi, E. Dalton Trans. 2005, 827-848.
(20) Mu¨ller, T.; Juhasz, M.; Reed, C. A. Angew. Chem., Int. Ed. 2004,
43, 1543-1546.
(21) (a) Rosenthal, U.; Go¨rls, H. J. Organomet. Chem. 1992, 439,
C36-C41. (b) Troyanov, S. I.; Varga, V.; Mach, K. Organometallics
1993, 12, 2820-2824.
(22) (a) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Spannen-
berg, A.; Mach, K.; Rosenthal, U. Chem. Commun. 1999, 2505-2506.
(b) Hora´cˇek, M.; C´ısarˇova´, I.; Kubisˇta, J.; Spannenberg, A.; Rosenthal,
U.; Mach, K. J. Organomet. Chem. 2004, 689, 4592-4600.
(23) (a) Jutzi, P. Chem. Rev. 1986, 86, 983-996. (b) Pinkas, J.;
Kubisˇta, J.; Gyepes, R.; Cˇ ejka, J.; Meunier, P.; Mach, K. J. Organomet.
Chem. 2005, 690, 731-741.
(17) (a) Beckhaus, R.; Oster, J.; Wang, R.; Bo¨hme, U. Organo-
metallics 1998, 17, 2215-2221. (b) Beckhaus, R.; Sang, J.; Wagner,
T.; Ganter, B. Organometallics 1996, 15, 1176. (c) Beckhaus, R. In
Metallocenes; Togni, A., Haltermann, R. L., Eds.; Wiley-VCH: Wein-
heim, Germany, 1998; Vol. 1, Chapter 4.4, pp 175-210.
(18) (a) Beckhaus, R.; Wagner, M.; Burlakov, V. V.; Baumann, W.;
Peulecke, N.; Spannenberg, A.; Kempe, R.; Rosenthal, U. Z. Anorg.
Allg. Chem. 1998, 624, 129-134. (b) Sˇteˇpnicˇka, P.; Gyepes, R.;
C´ısarˇova´, I.; Hora´cˇek, M.; Kubisˇta, J.; Mach, K. Organometallics 1999,
18, 4869-4880.
(24) Oxidative addition of Me3SnCtCSnMe3 to {(η5-C5H5-nMen)2-
Ti} species afforded analogues of 3a, [{(η5-C5H5-nMen)2Ti(µ-η2:η1-
CtCSnMe3}2] (n ) 0, 2), and hexamethyldisilane under mild condi-
tions: Varga, V.; Mach, K.; Hiller, J.; Thewalt, U.; Sedmera, P.;
Pola´sˇek, M. Organometallics 1995, 14, 1410-1416.

6100 Organometallics, Vol. 24, No. 25, 2005
Hora´cˇek et al.
mL). After the mixture was stirred for 2 h, about half of the
solvent was distilled off under vacuum. The residue was cooled
to dry-ice temperature, dichlorodimethylsilane (6.0 mL, 50
mmol) was added dropwise, and the mixture was warmed to
ambient temperature with stirring and then refluxed for 6 h.
Subsequently, most of the volatiles were distilled off, and the
residue was purified by chromatography on alumina using
hexane as the eluent. The pure product was obtained as a
colorless oil, which crystallized in a refrigerator. Yield: 10.3
g (68% on Me3SiCtCH).
Conclusions
The interaction of siladiyne 2a with the highly me-
thylated titanocene equivalents 1b,c results in complete
isomerization of the siladiyne, yielding the uprecedented
titanasilacyclohexadiene complexes 4b-d. In contrast,
the nonmethylated titanocene precursor 1a gives under
similar conditions the known complex 3a, whereas
siladiyne 2b reacts to give the η2 complexes 6c,d and
titanasilacyclohexadiene 5c, depending on the ti-
tanocene component. As indicated by theoretical calcu-
lations, the titanasilacyclohexadiene complexes feature
unusual triangular 2e-3c bonds involving the titanium
and both CR atoms. The reasons for the 2-fold migration
of the trimethylsilyl groups in diynes 2 can be sought
in their steric interactions with the bulky methyl-
substituted cyclopentadienyl ligands and their electronic
interaction with the silylene group. In consideration of
the reaction course, one has to bear in mind that the
reaction requires temperatures around 150 °C to pro-
ceed, which allows the products to acquire the thermo-
dynamically most stable structure.
1H NMR (C6D6): δ 0.08 (s, 9 H, SiMe3), 0.34 (s, 3 H, SiMe2).
13C{1H} NMR (C6D6): δ -0.4 (SiMe3), 0.5 (SiMe2), 110.2 and
115.6 (CtC). IR (neat, cm-1): 2948 (s), 2895 (m), 2850 (sh,
w), 2780 (vw), 2100 (w), 1940 (vw), 1863 (vw), 1450 (w), 1405
(m), 1315 (w), 1248 (s), 1116 (w), 1040 (w, b), 832 (vs, b), 753
(s), 697 (m), 664 (w), 625 (vw), 614 (vw), 440 (w).
Preparation of Bis((trimethylsilyl)ethynyl)diphen-
ylsilane [(Me3SiCtC)2SiPh2] (2b). The above procedure for
obtaining 2a was followed using the same molar ratios of LiBu,
HCtCSiMe3, and SiCl2Ph2. Column chromatography as above
afforded pure crystalline 2b. Yield: 17.5 g, 83%.
1H NMR (C6D6): δ 0.00 (s, 9 H, SiMe3), 7.04-7.98 (m, 5 H,
Ph). 13C{1H} NMR (C6D6): δ -0.5 (SiMe3), 107.2, 119.1
(CtC), 128.4, 130.5, 133.1, and 135.2 (Ph). EI-MS (50 °C; m/z
(relative abundance, %)): 378 (12), 377 (25), 376 (M•+; 57), 375
(23), 362 (16), 361 ([M - Me]+; 37), 336 (12), 303 ([M - SiMe3]+;
22), 281 (12), 280 (27), 279 ([M - C2SiMe3]+; 84), 226 (13), 221
(27), 217 (20), 202 ([M - C2SiMe3 - Ph]+; 16), 197 (19), 173
(21), 159 (36), 145 (17), 136 (15), 135 (87), 129 (21), 105 (40),
73 ([SiMe3]+; 100). IR (KBr; cm-1): 3068 (m), 3051 (m), 3023
(w), 2961 (s), 2107 (w), 1589 (w), 1570 (vw), 1484 (w), 1429
(m), 1251 (s), 1188 (w), 1114 (s), 1029 (vw), 998 (vw), 847 (vs,
b), 768 (vs, b), 741 (m), 711 (m), 698 (s), 501 (s).
Experimental Section
General Considerations. Reactions of titanocene-btmse
complexes with 2a,b were carried out under vacuum conditions
in sealed glass ampules equipped with breakable glass seals.
Sample tubes for NMR measurements were also sealed to glass
devices at the vacuum line, filled with C6D6 solutions under
vacuum, and sealed off. Crystalline samples for EI-MS and
IR spectra, melting points, and X-ray diffraction measure-
ments were handled in a Labmaster 130 glovebox (mBraun)
under purified nitrogen.
NMR spectra were recorded on a Varian UNITY Inova 400
spectrometer (1H, 399.95 MHz; 13C, 100.58 MHz) in C6D6
solutions at 25 °C. Chemical shifts (δ/ppm) are referenced to
the residual solvent signal (δH 7.15) and to the solvent
resonance (δC 128.0). EI-MS spectra were measured on a VG-
7070E mass spectrometer at 70 eV. The crystalline samples
in sealed capillaries were opened and inserted into a direct
inlet probe under argon. IR spectra were measured in an air-
protecting cuvette on a Nicolet Avatar FT IR spectrometer in
the range 400-4000 cm-1. KBr pellets were prepared in the
glovebox.
Preparation of [{(η5-C5H5)2Ti(µ-η1:η2-CtCSiMe3)}2] (3a).
A mixture of 1a (0.35 g, 1.0 mmol) and 2a (0.25 g, 1.0 mmol)
in toluene (10 mL) was heated to 150 °C for 5 h in a sealed
ampule. After the mixture was cooled, all volatiles were
removed under vacuum, and the residue was extracted with
hexane. Cooling of a concentrated solution in the refrigerator
gave orange-red crystals, which were identified by X-ray
single-crystal analysis to be another crystallographic modifica-
tion of 3a.8,9 Yield: 0.18 g (65%). (Note: NMR analysis of the
crude reaction mixture revealed minor signals attributable to
a titanasilahexadiyne product, particularly the signal at δC
343.2.)
EI-MS (direct inlet, 70 eV, 160 °C; m/z (relative abundance)
550 (M•+; 7), 276 (11), 275 ([M/2]+; 36), 274 (7), 260 (9), 202
(8), 180 (10), 179 (21), 178 ([(C5H5)2Ti]+; 100), 177 (12), 176
(12), 113 (14), 83 (12), 71 (11), 69 (9), 57 (18), 55 (11), 43 (17).
IR (KBr; cm-1): 3090 (w, b), 2945 (s), 2889 (m), 2847 (w), 1788
(s), 1560 (m), 1503 (w), 1443 (m), 1404 (m), 1365 (w), 1297
(vw), 1246 (s), 1128 (vw), 1066 (w), 1016 (s), 905 (m), 835 (vs,
b), 753 (s), 723 (m), 687 (s), 640 (m), 593 (m), 506 (vw), 482
(w), 442 (w). UV-vis (hexane; nm): 370 (sh) > 450 . 830 >
1050 (sh).
Preparation of 4,4-Dimethyl-3,5-bis(trimethylsilyl)-1-
titana-4-silacyclohexa-2,5-dienes (4). Solutions of the [Ti-
(η5-C5H5-nMen)2(η2-Me3SiCtCSiMe3)] complexes (1b-d; 2.0
mmol) in m-xylene (10 mL) were mixed with 2a (0.6 mL, 2.3
mmol), and the mixture was heated to 150 °C for 8 h (1b,c) or
5 h (1d) in an ampule with attached quartz cell (d ) 0.2 cm).
The conversion of the btmse complexes to titanasilacyclohexa-
diene compounds was followed by diminution of absorption
band intensity due to the starting btmse complex (1b at 915
nm, 1c at 920 nm, and 1d at 915 nm). When the reaction was
complete, the ampule was cooled to ambient temperature and
all volatiles were distilled off under vacuum at 100 °C. The
residue was extracted with hexane. Concentrated solutions
were cooled by dry ice for crystallization. The crystals were
recrystallized from a minimum amount of hexane in a freezer
(-18 °C).
Chemicals. The solvents THF, hexane, and toluene were
dried by refluxing over LiAlH4 and stored as solutions of
dimeric titanocene [(µ-η5:η5-C5H4C5H4)(µ-H)2{Ti(η5-C5H5)}2].26
Butyllithium in hexanes, dimethyldichlorosilane, diphenyldi-
chlorosilane, and (trimethylsilyl)ethyne (all Aldrich) were
transferred by syringe under argon. Bis((trimethylsilyl)eth-
ynyl)dimethylsilane
and
bis((trimethylsilyl)ethynyl)-
diphenylsilane were synthesized as reported.27 Complexes
1a-e were obtained in nearly quantitative yields from the
reduction of the respective bis(η5-cyclopentadienyl)dichloro-
titanium(IV) complexes with magnesium in THF in the pres-
ence of excess btmse, as reported earlier.12
Preparation of Bis((trimethylsilyl)ethynyl)dimeth-
ylsilane [(Me3SiCtC)2SiMe2] (2a). LiBu (2.5 M in hexanes,
46.0 mL, 0.115 mol) was added to a stirred solution of
(trimethylsilyl)ethyne (17.0 mL, 0.120 mmol) in hexane (50
(25) (a) Choukroun, R.; Donnadieu, B.; Zhao, J.-S.; Cassoux, P.;
Lepetit, C.; Silvi, B. Organometallics 2000, 19, 1901-1911. (b) Danjoy,
C.; Zhao, J.-S.; Donnadieu, B.; Legros, J.-P.; Valade, L.; Choukroun,
R.; Zwick, A.; Cassoux, P. Chem. Eur. J. 1998, 4, 1100-1105.
(26) Antropiusova´, H.; Dosedlova´, A.; Hanusˇ, V.; Mach, K. Transition
Met. Chem. 1981, 6, 90-93.
(27) Ibekwe, S. D.; Newlands, M. J. J. Chem. Soc. 1965, 4608-4610.

Titanasilacyclohexadiene Compounds
Organometallics, Vol. 24, No. 25, 2005 6101
cyclo-[(η5-1,2,3-C5H2Me3)2Ti{CdC(SiMe3)}2SiMe2] (4b).
Red crystals. Yield: 0.71 g (69%). Mp: 95 °C. 1H NMR (C6D6):
δ 0.19 (s, 9 H, SiMe3), 0.47 (s, 3 H, SiMe2), 1.73 (s, 3 H, C5Me),
1.78 (s, 6 H, C5Me2), 5.00 (s, 2 H, C5H2). 13C{1H} NMR (C6D6):
δ 1.5 (SiMe3), 3.4 (SiMe2), 12.3 and 14.8 (2 C) (C5Me3), 101.0
(CH of C5Me3H2), 115.6 (2 C), 116.3 (CMe of C5Me3H2); 133.4
(s, Cipso), 338.0 (s, Cipso). EI-MS (110 °C; m/z (relative abun-
dance, %)): 515 (10), 514 (M•+; 16), 264 (9), 263 (25), 262 ([Cp′2-
Ti]+; 100), 261 (19), 260 (15), 252 ([2a]+; 16), 238 (10), 237 ([2a
- Me]+; 35), 155 ([Cp′Ti]+; 7), 141 (9), 73 ([SiMe3]+; 59). IR
(KBr; cm-1): 3083 (vw), 2949 (vs), 2905 (s), 2854 (m), 1544
(vs), 1445 (vw), 1430 (vw), 1392 (w), 1377 (m), 1245 (vs), 1010
(m), 899 (s), 852 (vs), 836 (vs), 801 (s), 766 (s), 684 (m), 635
(vw, 611 (w), 588 (vw), 487 (m), 431 (m). Anal. Calcd for C28H46-
Si3Ti (514.81): C, 65.33; H, 9.01. Found: C, 65.38; H, 8.97.
137.38 (Cipso of Ph), 227.21 and 254.78 (η2-CtC). UV-vis
(hexane; nm): 920.
Preparation of [Ti(η5-C5Me5)2(η2-Me3SiCtCSiPh2-
CtCSiMe3)] (6d). A solution of [Ti(η5-C5Me5)2(η2-Me3Si-
CtCSiMe3)] in toluene (2.0 mmol in 10 mL) was mixed with
solid 2b (0.752 g, 2.0 mmol), and the mixture was heated to
130 °C for 8 h. After the mixture was cooled, all volatiles were
evaporated under vacuum at 100 °C, and the dark solid was
extracted by hexane. Slow cooling of the concentrated solution
in a freezer induced crystallization of blue crystals of [Ti(η5-
C5Me5){η3:η4-C5Me3(CH2)2}].11 These were removed, and the
yellow solution was further cooled to -18 °C for crystallization.
Yellow crystals were obtained from the mother liquor after 3
days. The mother liquor afforded an additional crop of crystals.
Total yield of 6d: 1.08 g (78%).
1
cyclo-[(η5-C5HMe4)2Ti{CdC(SiMe3)}2SiMe2] (4c). Orange-
brown crystals. Yield: 0.91 g (84%). Mp: 160 °C. 1H NMR
(C6D6): δ 0.21 (s, 9 H, SiMe3), 0.49 (s, 3 H, SiMe2), 1.73 and
1.75 (2 × s, 6 H, C5Me4H), 5.01 (s, 1 H, C5Me4H). 13C NMR
(C6D6): δ 1.8 (q, 1JCH ) 118 Hz, SiMe3), 3.4 (q, 1JCH ) 119 Hz,
Mp: 182 °C. H NMR (C6D6): δ 0.06 and 0.22 (2 × s, 9 H,
SiMe3), 1.80 (s, 30 H, C5Me5), 7.08-7.37 (m, 10 H, Ph). 13C-
{1H} NMR (C6D6): δ -0.19 and 4.42 (SiMe3), 13.14 (Me of C5-
Me5), 115.26 and 117.60 (CtC), 122.94 (Cipsoof C5Me5), 127.50
(CH of Ph), 129.35 (CH of Ph), 136.35 (CH of Ph), 137.63 (Cipso
of Ph), 228.52 and 255.09 (η2-CtC). EI-MS (direct inlet, 70
eV, 230 °C; m/z (relative abundance)): 694 (M•+; not observed),
377 (16), 376 ([2b]+; 41), 375 (15), 362 (9), 361 ([2b - Me]+;
1
SiMe2), 12.9 and 14.0 (2 × q, JCH ) 126 Hz, C5Me4H), 105.2
(d, 1JCH ) 167 Hz, C5Me4H, CH), 111.6 and 116.1 (s, C5Me4H,
CMe), 132.8 (s, Cipso), 337.6 (s, Cipso). EI-MS (130 °C; m/z
(relative abundance, %)): 542 (M•+; 0.4), 292 (10), 291 (28),
290 ([(C5HMe4)2Ti]+; (100), 289 (17), 288 (15), 252 ([2a]+; 5),
238 (7), 237 ([2a - Me]+; 24), 111 (5), 73 ([SiMe3]+; 11). IR
(KBr; cm-1): 3060 (vw), 2949 (s), 2906 (s), 2856 (m), 1541 (vs,
b), 1434 (w), 1380 (m), 1368 (m), 1245 (s), 1149 (vw), 1022 (w,
b), 897 (s), 850 (vs), 835 (vs), 766 (m), 683 (m), 644 (vw), 613
(w), 486 (w), 435 (m). Anal. Calcd for C30H50Si3Ti (542.87): C,
66.37; H, 9.28. Found: C, 66.39; H, 9.26.
24), 320 (12), 319 (29), 318 ([Cp* Ti]+; 100), 317 (23), 316 (18),
2
303 ([2b - SiMe3]+; 16), 299 ([2b - Ph]+; 7), 279 ([2b - C2-
SiMe3]+; 10), 221 ([2b - Ph - HPh]+; 17), 217 (13), 202 (11),
181 (10), 178 (10), 173 (43), 159 (24), 135 (43), 105 (16), 73
(31). IR (KBr; cm-1): 3068 (w), 3051 (w), 2957 (m), 2900 (s),
2859 (m), 1613 (w), 1556 (m), 1485 (w), 1445 (m), 1428 (s),
1377 (m), 1250 (s), 1241 (s), 1192 (vw), 1107 (m), 1022 (w),
847 (vs, b), 796 (m), 764 (vs), 739 (s), 702 (s), 651 (w), 586 (w),
517 (vs), 479 (w), 438 (m). UV-vis (hexane; nm): 900. Anal.
Calcd for C42H58Si3Ti (695.06): C, 72.58; H, 8.41. Found: C,
72.61; H, 8.38.
cyclo-[(η5-C5Me5)2Ti{CdC(SiMe3)}2SiMe2] (4d). Orange-
brown crystals. Yield: 0.89 g (78%). Mp: 219 °C. 1H NMR
(C6D6): δ 0.25 (s, 3 H, SiMe3), 0.53 (s, 1 H, SiMe2), 1.73 (s, 5
H, C5Me5). 13C NMR (C6D6; only 1JCH are given): δ 1.9 (q, 1JCH
Alternative Preparations of 6d. (A) A mixture of 1d (0.49
g, 1.0 mmol) and 2b (0.38 g, 1.0 mmol) in toluene (10 mL) was
heated to 150 °C for 5 h in a sealed ampule. After workup as
above pure crystalline yellow 6d (0.30 g, 43%) and blue [Ti-
(η5-C5Me5){η3:η4-C5Me3(CH2)2}] (0.066 g, 21%) were separated.
(B) [TiCl2(η5-C5Me5)2] (0.388 g, 1.0 mmol), magnesium (0.12
g, 5 mmol), and 2b (0.376 g, 1.0 mmol) were degassed, and
THF (20 mL) was added. This mixture was heated to 60 °C in
a sealed ampule until its color changed to yellow (5 h). Then,
all volatiles were evaporated under vacuum, and the residue
was extracted with hexane. Cooling to -18 °C of the concen-
trated hexane solution afforded yellow crystals of 6d: 0.60 g
(86%).
1
1
) 118 Hz, SiMe3), 3.6 (q, JCH ) 119 Hz, SiMe2), 12.3 (q, JCH
) 126 Hz, C5Me5), 113.1 (s, C5Me5), 132.0 (s, Cipso), 335.5 (s,
C
ipso). EI-MS (180 °C; m/z (relative abundance, %)): 570 (M•+
;
1), 320 (18), 319 (46), 318 ([Cp*2Ti]+; 100), 317 (26), 316 (22),
252 ([2a]+; 3), 237 ([2a - Me]+; 8), 181 ([(C5Me5)Ti - 2H]+; 6),
178 (4), 159 (11), 73 ([SiMe3]+; 6). IR (KBr; cm-1): 2978 (sh),
2953 (vs), 2903 (vs), 2867 (sh), 1528 (s, b), 1435 (m), 1375 (s),
1253 (sh), 1246 (vs), 1021 (m), 902 (s), 844 (vs), 835 (vs), 769
(m), 684 (m), 643 (vw), 615 (w), 485 (m), 432 (m). Anal. Calcd
for C32H54Si3Ti (570.92): C, 67.32; H, 9.53. Found: C, 67.37;
H, 9.49.
Reaction of 1c with 2b. A reaction as above of 1c with 2b
in toluene at 150 °C for 8 h gave a mixture of the η2-alkyne
complex 6c, the titanasilahexadiene complex 5c, and an
unknown titanocene compound. Whereas pure 5c partly
crystallized from the mixture, 6c and the unknown component
could not be separated due to similar solubilities. Nevertheless,
data for 6d allowed us to analyze NMR data for the mixture
(5c, δC 336.32 (Cipso); unknown byproduct, δC 179.1 (CH) and
246.8 (Cipso)).
Data for 5c are as follows. Mp: 175 °C. EI-MS (direct inlet,
70 eV, 220 °C; m/z (relative abundance)): 666 (M•+; 1), 376
([2b]+; 19), 361 ([2b - Me]+; 9), 292 (15), 291 (38), 290 ([Cp′2-
Ti]+; 100), 289 (29), 288 (23), 135 (32), 91 (9), 73 (29). IR (KBr;
cm-1): 3083 (vw), 3067 (w), 3045 (vw), 2949 (s), 2903 (s), 2861
(sh), 1514 (s, b), 1429 (m), 1379 (w), 1328 (vw), 1240 (s), 1181
(vw), 1101 (m, b), 1021 (w), 908 (m), 835 (vs), 756 (m), 736
(m), 701 (s), 648 (vw), 614 (vw), 523 (m), 504 (m), 455 (w).
Data for 6c are as follows. 1H NMR (C6D6): δ -0.02 and
0.23 (2 × s, 9 H, SiMe3), 1.36, 1.56, 1.97, and 2.04 (4 × s, 6 H,
C5HMe4), 5.85 (s, 2 H, C5HMe4), 7.06-7.47 (m, 10 H, Ph). 13C-
{1H} NMR (C6D6): δ -0.13 and 3.13 (SiMe3), 13.19, 13.27,
13.60, and 14.30 (Me of C5HMe4), 113.64 (CH of C5HMe5),
114.31 and 117.47 (CtC), 122.65, 123.16, 124.74, and 125.52
(Cipso of C5HMe5), 127.64, 129.36, and 135.84 (3 × CH of Ph),
Hydrogenolysis of 5c. A solution of 5c (ca. 0.2 g) in hexane
(8 mL) was exposed to hydrogen (1 bar) for 3 h while being
stirred with a magnetic stirrer. The volatiles were evaporated
under vacuum, the residue was dissolved in C6D6, and the
solution was analyzed by NMR spectra. Then, the tube was
opened to air and the solution purified by chromatography on
a silica gel column using diethyl ether-hexane (1:5) as the
eluent. The first band was collected and evaporated to give a
yellowish oily residue, which was analyzed by NMR spectros-
copy. The spectra recorded for the crude and purified samples
were practically identical, showing 1,4-bis(trimethylsilyl)-5,5-
diphenyl-5-silacyclopenta-1,3-diene (7) as the major compo-
nent. The yield was not determined.
1H NMR (C6D6): δ 0.04 (s, 9 H, SiMe3), 7.12-7.82 (m, 5 H,
1
SiPh), 7.33 (s, 1 H, dCH). 13C NMR (C6D6): δ -0.13 (q, JCH
) 118 Hz, SiMe3), 130.17 (dt, 1JCH )160 Hz, CH of Ph), 132.62
1
(br s, Cipso of Ph), 135.88 (d of m, JCH ca. 160 Hz, CH of Ph),
1
2
149.15 (s, dCSiMe3), 156.33 (dd, JCH ) 157, JCH ) 8.5 Hz,
dCH); one CH resonance of the phenyl group is probably
obscured by the solvent signal. GC-MS (m/z (relative abun-
dance)): 380 (12), 379 (29), 378 (M•+; 71), 364 (19), 363 ([M -
Me]+; 46), 306 (21), 305 ([M - SiMe3]+; 69), 291 (13), 290 ([M
- Me - SiMe3]+; 40), 283 (19), 245 (12), 244 (13), 243 (51),
228 (16), 227 (11), 197 (26), 145 (20), 135 (100), 105 ([PhSi]+;

6102 Organometallics, Vol. 24, No. 25, 2005
Hora´cˇek et al.
Table 3. Crystallographic Data and Data Collection and Structure Refinement Details for Compounds
4b-d, 5c, and 6da
4b
4c
4d
5c
6d
formula
mol wt
cryst syst
space group
a (Å)
C
28H46Si3Ti
C30H50Si3Ti
542.87
C32H54Si3Ti
570.92
C40H54Si3Ti
667.00
C42H58Si3Ti
695.05
514.82
monoclinic
P21/n (No. 14)
9.9510(2)
17.5260(3)
16.9310(3)
90
triclinic
P1h (No. 2)
9.9650(1)
18.2720(2)
18.8890(3)
106.5850(7)
104.7610(7)
90.6820(8)
3174.13(7)
150(2)
monoclinic
C2/c (No. 15)
35.9376(3)
20.8789(2)
36.4854(3)
90
monoclinic
P21/c (No. 14)
10.0360(3)
17.3500(9)
23.2160(11)
90
monoclinic
P21/c (No.14)
15.1670(4)
11.3270(2)
23.4860(6)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
91.4700(10)
90
96.6974(4)
90
111.992(3)
90
95.5150(10)
90
2951.82(9)
150(2)
27189.5(4)
150(2)
3748.3(3)
150(2)
4016.14(16)
150(2)
T (K)
Z
4
4
32
4
4
Dcalcd (g cm-3
)
1.158
1.136
1.116
1.182
1.150
µ (mm-1
)
0.426
0.399
0.376
0.350
0.330
cryst color
red
red
deep red
0.5 × 0.42 × 0.25
25.04
red
orange
cryst size (mm3)
θmax (deg)
0.6 × 0.45 × 0.35
0.7 × 0.45 × 0.45
0.28 × 0.18 × 0.10
0.40 × 0.15 × 0.10
27.47
27.55
25.01
25.05
no. of rflns collected
no. og unique rflns
no. of params
6747
14 247
23 910
6575
7097
5629
12 188
18 254
3891
5327
303
645
1369
411
431
R; Rw (all data)a
R (obsd data)b
5.56; 10.41
4.35
4.34; 8.95
3.39
11.91; 16.08
8.47
11.86; 11.43
5.23
6.75; 10.56
4.20
∆F (e Å-3
)
0.64; -0.41
0.31;-0.32
0.68; -0.41
0.24; -0.25
0.28; -0.29
2
2
a Definitions: R(F) ) ∑||Fo| - |Fc||/∑|Fo|, Rw(F2) ) [∑(w(Fo - Fc )2)/(∑w(Fo2)2)]1/2
.
b Reflections with I > 2σ(I).
26), 73 ([Me3Si]+; 49). HR-MS: calcd for C22H30Si3, 378.1655;
found, 378.1663.
unit cell parameters were determined with precision compa-
rable to that for 4c (see Table 3) the precision in determination
of molecular parameters for molecules of 4d is considerably
lower.
Computational Details. DFT calculations, including NBA
and GIAO analyses, have been performed at the Supercom-
puter Centre of Charles University using Gaussian 98, Revi-
sion A.7.31 The applied density functional combined the Becke
exchange32 and the Perdew-Wang 91 correlation functional.33
The 6-311G(2d) basis set was employed for all atoms. The
input geometry was that obtained from X-ray diffraction data
for 4c at ambient temperature using the coordinates of one of
the two symmetrically independent molecules. Due to the size
of the problem, no geometry optimization was carried out.
Although the molecule should apparently possess a C2v
symmetry in solution, symmetrization of the solid-state struc-
ture was not carried out, as this would have led to some rather
significant changes in atomic positions. For this reason, DFT
calculations were performed in point group C1; however,
irreducible representations for orbitals are given assuming C2v
symmetry.
Natural bonding analysis was performed by the NBO 3.134
program integrated in Gaussian as link 607; contours of the
∆ bond appearing in Figure 4 were obtained using Molden.35
Methanolysis of 4d. Compound 4d (0.32 g, 0.56 mmol) in
hexane (3 mL) was reacted with anhydrous MeOH (0.5 mL,
12 mmol) at 80 °C for 5 h, whereupon the color changed from
intense brown-red to brown. All volatiles were distilled under
high vacuum into a trap cooled by liquid nitrogen, and the
residue was dissolved in a minimum amount of hexane and
crystallized by cooling to -18 °C. The volatiles were separated
by column chromatography on silica gel. Elution with hexane
gave the first fraction, containing 1,4-bis(trimethylsilyl)-5,5-
dimethyl-5-silacyclopenta-1,3-diene (8) according to GC-MS
analysis. The following band eluted with hexane gave, after
evaporation, an oily residue whose IR spectrum indicated an
overwhelming presence of pentamethylcyclopentadiene. Brown
crystals obtained from the solid residue exhibited unit cell
parameters identical with those of [(η5-C5Me5)Ti(OMe)(µ-
OMe)]2.13
Data for 8 are as follows. GC-MS: 255 (25), 254 (M•+; 58),
241 (17), 240 (42), 239 ([M - Me]+; 91), 238 (13), 182 (28), 181
([M - SiMe3]+; 77), 180 (11), 166 ([M - Me - SiMe3]+; 17),
141 ([M - C3H4 - SiMe3]+; 20), 83 (13), 73 ([SiMe3]+; (100).
X-ray Crystallography. The diffraction data for complexes
4b-d, 5c, and 6d were collected on a Nonius KappaCCD
image plate diffractometer (Mo KR radiation, λ ) 0.710 73 Å)
and analyzed by the HKL program package.28 In all cases, the
structures were solved by direct methods (SIR97),29 followed
by consecutive Fourier syntheses and refined by full-matrix
least squares on F2 (SHELX97).30 All non-hydrogen atoms were
refined anisotropically; hydrogen atoms were included in ideal
positions and refined isotropically using the riding model.
Compound 4d crystallizes in monoclinic space group C2/c
in an extremely large unit cell containing four symmetrically
independent molecules in the asymmetric unit. Although the
(31) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.,
Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J. A. Gaussian 98, revision A.7; Gaussian, Inc.: Pittsburgh, PA,
1998.
(28) Otwinowski, Z.; Minor, W. HKL Denzo and Scalepack Program
Package; Nonius BV, Delft, The Netherlands, 1997. For a reference
see: Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307-
326.
(29) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27,
435-436.
(30) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement from Diffraction Data; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
(32) Perdew, J. P.; Chevary, J. A.; Vosko, S. H.; Jackson, K. A.;
Pederson, M. R.; Singh, D. J.; Fiolhais, C. Phys. Rev. B 1992, 46, 6671-
6687.
(33) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3100.
(34) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F.
Theoretical Chemistry Institute and Department of Chemistry, Uni-
versity of Wisconsin, Madison, WI 53706.

Titanasilacyclohexadiene Compounds
Organometallics, Vol. 24, No. 25, 2005 6103
Supporting Information Available: CIF files for the
structures of 4b-d, 5c, and 6d, Platon drawings of structures
4b-d, 5c, and 6d at the 30% probability level, Lewis repre-
sentations of examined bonding modes in 4c, and GIAO
parameters and their correlation with experimental 13C NMR
shifts. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. This research was supported by
the Grant Agency of the Czech Republic (Grant No. 104/
05/0474). The suggestions of Prof. U. Rosenthal (Uni-
versita¨t Rostock) on the reaction mechanism are highly
appreciated.
(35) Schaftenaar G.; Noordik, J. H. Molden: a pre- and postpro-
cessing program for molecular and electronic structures. J. Comput.-
Aided Mol. Design 2000, 14, 123-134.
OM058038D